intro.

Our Goals:

1. Make integrated circuit prototyping as fast as 3D printing

2. Make DIY version of every nanofabrication tool

3. Get there with collaborative open source hardware

Right now we use factories and tools that are optimized to manufacture at scale to do our integrated circuit prototyping. There does not exist a set of machines that enable rapid tape-out of semiconductor devices on a budget, nor are there sufficient resources to make/modify fab tools from the ground up.

The use of low-cost, abundant, and fast-turn-around hardware serves a larger purpose than making the fab cheaper. These design constraints are what enable others to recreate, modify, and contribute to our work. The simpler the better.

working on the hacker fab.

You don't need prior nanofabrication experience to create meaningful contributions.

this website.

This page is a home for all shared documentation. There are enough resources here to turn an empty room into one that fabricates simple IC's in a matter of months.

Many pages are works-in-progress. It is natural for individual contributors' work-in-progress notes to exist on google drive, notion, etc. Links to these exist at the top of each page, however these notes move to Gitbook as soon as possible.

Any contributor can submit change requests with a free Gitbook account. All of this is on Github, but formatted nicely here on Gitbook. You can contribute directly through Github as well.

fab toolkit.

Here is a list of all the tools built or bought necessary to make our devices.

Every build contains:

• BOM

• Links to Design Files

• Links to Code

• First Principles Understanding of Machine Design (WIP)

fabrication tools.

verification / metrology tools.

chemicals.

background and licensing.

The Hacker Fab was started by Elio Bourcart, Alexander Hakim, and Sam Zeloof.

The Hacker Fab is run entirely by independent contributors.

Link to General Lab Equipment BOM

BOM of each machine is included in separate build documents.

The Way we Source Parts

Organized List of Sellers

The goal function of the Hacker Fab is to never debug the same thing twice.

We operate under different constraints from the semiconductor fab industry. This allows us to curb a lot of complexity.

Goals:

1. Low cost

2. Create the simplest designs possible

   1. Increase reliability

   2. Reduce manufacturing complexity

3. Minimal danger

4. Small size

5. No cleanroom

6. Highly sourcable materials

7. High literacy in understanding working principles of tools and processes

8. End-to-end custom - from sand to NAND

   1. Make the wafers

   2. Design the tools

   3. Design the processes

   4. Design the IC

   5. Package the chip

Non-Goals:

1. Reuse of existing fab equipment

The 1970s vs. Now

On Open-Source Hardware

Who we are looking for, how we grow, how to get support

Design Constraints

On Improvement

Central to the Hacker Fab is fast turnaround hardware development - it’s in the name. This means extremely fast hardware prototyping, and with that comes the need for iteration. The careful design constraints placed on all projects and focus on documentation enables someone else to iterate on anything developed in the Hacker Fab. Improvement to a V1, V2, Vn of a design means

1. Directly improving upon a tool’s functionality

   1. Precision

   2. Reliability

   3. Throughput

   4. New features

   5. Safety

But there are other equally important ways to improve a design. Every tool version should try to be:

1. Easier to manufacture than the last

   1. Reduce number of tools required to manufacture

   2. Reduce # of vendors, lead time, BOM length

2. Better documented than the last

   1. Tool specs as close to first principles as possible

   2. Every tool spec should have a standardized test for others to verify performance

   3. Explain working principles to the detail of variables we can control (no more, no less). Referenced sources.

3. More “closed-loop” than the last

   1. In-situ sensors

   2. Calibration software should be more generalizable (“now you can use any camera…any piezo with draw distance in range X to Y…”)

On Cleanliness

On Process Node

On Education

Where to Start

TBD

Introduction

The SW needed for this project can be broken down into the following subsections.

Pattern Capture

KLayout

OpenROAD

CAM Translator

Computer-Aided Manufacturing software translates a 3D design into G-code instructions that a CNC machine (in this case laser burner) can understand, essentially "slicing" the design into smaller, machinable steps.

This SW takes a file with the desired mask (Pattern Capture Output) as an input and translates it into a set of machine instructions.

Burner Firmware

This software runs on the micro-controller that drives all the HW. It is responsible for taking sensor inputs and driving all output motors and lasers. This device also has an interface which can transmit all the data to/from the user.

Device Driver

This software is responsible for general control of the laser burner from the PC side.

Graphical User Interface

This SW is responsible for the user facing interface which gives the user full control of the burner.

Simplified View of Process

See Fabublox for Interactive View

Alternatively: See Google Sheets for Comprehensive Example with all Parameter Values (Chip 336 Shown Below)

Goals of this page:

• Not to try and cover theory or industry standard, but to break the problem into first principles just enough to give context to the quantifiable parameters

• Also an opportunity to frame the problem wide enough to set the tone of thinking of these machines from the ground up (aligned with goal, don't think of industry as immutable)

• Exhaustive list of industry methods and examples

• Quantifiable end user parameters with descriptions + standardized tests

Background

Overview

A photolithography stepper is a machine that exposes a pattern of light onto a layer of photoresist chemical on the wafer, then ‘steps’ over to the next pattern. Before each exposure, it must align with previous patterns on the wafer so that each layer of the device is in the correct position relative to the previous. The accuracy with which it can do this is called “alignment accuracy”. Alignment accuracy and optical resolution are the two most important metrics of a stepper’s performance.

There are 2 main components of our stepper: the light source and optics, and then the mechanical micropositioning stage that moves the chip itself. Alignment accuracy is a function of both the mechanical micropositioning stage and the reliability of the projector’s optomechanical components.

Masked vs. Maskless Lithography Systems

Commercial lithography machines use photomasks to create the image, typically made of chrome on glass. Instead, our Maskless Photolithography Stepper uses a DLP projector to create a pattern. This allows us to change patterns instantly, opening the option up for advanced techniques like tiling (making a circuit larger than one exposure field).

Quantifiable Parameters

Functional Specifications: The End Product

Patterning Machine Specifications:

• Rotate the optics so that the objective points downward instead of sideways

  • This allows using the much-improved X and Y axes of the stage, instead of X and Z, which permits higher movement resolution and repeatability

  • This also means that we no longer need the vacuum chuck, which means reduced vibration (and less complexity)

  • Unlike Stepper V1, which was cantilevered, V2.1 is supported on all sides by rigid optical mounting posts, which should avoid V1's vibration issues

• Mount the optics and projector much more rigidly, using a plate offset by posts to secure the optics directly, rather than relying on the projector's case and rubber feet

  • This further reduces relative vibrations between the optics and stage

  • This also makes the DLP DMD plane and the chip plane more parallel == more consistent focus both across a single exposure and between exposures

  • This also decouples the structure of the stepper from the mechanical design of the projector (as Stepper V2 relies on the actual shape of the projector to work) which will allow us to change to a different projector in the future

• Switch from a FLIR Blackfly camera to a Basler Ace camera, and reduce the sensor size from 1" to 1/1.2"

  • Not only is the Basler less expensive for an equivalent sensor, it also has a much, much nicer software suite that is distributable (a particular pain point with FLIR's)

  • Smaller sensor size means we're paying for less unused sensor (since any sensor area outside of the size of the projector's DMD is not used)

As a whole, these changes should improve the results we get out of Stepper V2.1 compared to Stepper V2, and the mechanical changes will set the stage for further patterning capabilities such as reliable automatic alignment. Furthermore, the decoupling of the projector from the rest of the design will in the future allow us to use different projector for further improvements.

Specifications

These remaining specs are from Stepper V2's documentation and have not been verified. The optical performance of both systems should be the same.

Bill of Materials

Total cost as currently specified: $3,012.13

(Not included in BOM: misc. bolts)

Design Files

Several parts from Stepper V2's CAD are used on 2.1:

Build Instructions

Tools required

• 3D Printer

• SMD soldering tools (solder paste, reflow oven, tweezers)

• Calipers

• Metric and imperial allen wrench sets

Fabricate the mechanical parts

There are several mechanical parts that will need to be fabricated:

• for builds that are not making use of an existing optical table: bottom plate. laser cut or machined, 1 inch grid of ¼ inch holes at least 6x6 inches

UV LED PCB Assembly

Projector Modification

These steps are heavily based on the steps done for V2, but some have changed.

1. Test the projector before we completely take it apart :)

1. Unplug all the connectors and remove the top PCB by unscrewing the standoffs.

1. Remove the side PCB.

1. Unscrew and remove the shroud by sliding it away from the rest of the optics.

1. NEW FOR 2.1: Remove the bolts and standoffs that hold the main projector assembly to the bottom plate. This should free the bottom assembly.

1. Unscrew and remove the heatsink for the front-most LED, which should be the blue one.

1. Disconnect the LED PCB from the cable. Heat it slightly on a hot plate or with a hot air gun to soften the adhesive and remove the black plastic housing.

2. Glue the black plastic piece to the DIY UV LED PCB, connect it to the blue cable, and reattach it to the optics housing. Put the heatsink back as well.

1. Unscrew the projection lens. That one makes things bigger, but we're trying to make things smaller. It's got to go.

1. Screw on the adapter plate with four countersunk M2 screws.

1. Use four M2.5 screws to screw on the Thorlabs SM1A53 adapter flange

2. NEW FOR 2.1: Do not reassemble the projector case - we will use it as-is.

Optics + Mechanics Assembly

These steps are heavily based on the same steps for V2, but slightly modified.

1. Start with the beamsplitter cube. Unscrew the set screws, remove the holder, and clip in the beamsplitter. The text ("Thorlabs") should be facing the microscope objective and camera when the holder is reinserted. Keep track of this during assembly and fix it later if necessary.

1. Assemble the DLP tube. From left to right, the parts in the first picture are 0.3" lens tube (SM1L03), 0.5" lens tube coupler (SM1CPL05), 0.5" adjustable lens tube (SM1V05), and 0.5" lens tube (SM1L05). You may want to remove any internal lens rings. The adjustable lens tube allows axial length adjustment and the coupler allows rotation about the optical axis.

1. Screw the DLP tube into the beamsplitter cube. The correct orientation is shown above, and the arrow points to the side of the beamsplitter with the text (and optical coating).

2. Assemble the camera tube, which similarly constructed. The parts are 1" lens tube (SM1L10), 1" lens tube coupler (SM1CPL10), 1" adjustable lens tube (SM1V10), another 1" lens tube (SM1L10), and C-mount SM1 adapter (SM1A9) (last two shown below).

1. Screw on the C-mount SM1 adapter (SM1A9) to the camera and the 1" lens tube. Adjust the lens tube coupler to align the camera with the beamsplitter cube.

1. Assemble the objective tube, which consists of a 0.3" lens tube (SM1L03), an SM1 to RMS adapter (SM1A3), and the microscope objective.

1. Use four #4-32 bolts to mount the beamsplitter cube to the top plate.

1. Mount the top plate to either your optical table (if you have one) or the bottom plate. First, mount the posts to the bottom plate/table using four 1/4-20 bolts (if you're using a bottom plate) or four 1/4-20 grub screws (if you're using the table). Then, mount the top plate on top with four #8-32 bolts.

1. Temporarily loosen the top lens tube coupler in order to screw that tube into the projector, and finally tighten it again with the projector mounted.

1. Mount the main PCB with the power connector facing downward using the 3D printed PCB holder part. Reconnect the ribbon cables and LED power cables.

Motion Stage Assembly

Print all of the parts in the table below. Any PLA is fine. You may need to re-orient them so they print well. The stepper mounts will all need small supports in the motor flange. The X and Y axes need other supports as well.

The video below describes the necessary components and the assembly process.

Electrical Assembly

To test the proximity switches, connect them to a 12V supply. The sensor output can be left unconnected. The red LED on the back of the switches should illuminate when the front of the sensor is held within ~4mm of a metal part of the stage, which will also pull the sensor output to ground.

Note: the limit switch pin block on the CNC shield has two rows of pins. One of the rows is connected only to ground; do not connect your limit switches to that row.

The sensors should be connected through a pull-up resistor to the Arduino's 5V supply. 12V should be supplied externally.

TODO: Add picture of CNC shield!

Software Setup

The video below descries the basic electronics setup and how to install GRBL and integrate the two. Make sure to cross reference this with the stepper instructions above.

Final Focusing

Once the software is set up, the final focus alignment can be done. These steps will align the two focus planes within the stepper (the projector and the camera) to ensure that images that appear in focus on the camera are actually in focus on the surface of the chip. This is done by adjusting the tube length between the projector housing and the beamsplitter cube (the length in the image below) such that both the projected image and the chip's surface are in focus in the camera view.

1. Load a chip with recognizable features into the stepper (a dirty chip is a good option).

2. Project a red-focus pattern with recognizable features that can be used to determine projector focus.

3. Adjust the Z position to focus onto the surface of the chip. This means that you should ensure that the features of the chip (the dirt, most likely) is sharp, but the projected focus pattern most likely is not.

4. Loosen the clamp that connects the two parts of the DLP-beamsplitter tube so that they freely rotate. (the bottom circle in the image)

5. Loosen the locking ring on the adjustable lens tube. (the top circle in the image)

6. Screw the adjustable lens tube in/out while periodically checking to see if the projected image gets more or less in focus. You may need to push the optics into the coupler to ensure that the surfaces of the lens tubes are coplanar.

7. Once both images are in focus at the same time, tighten the locking ring on the adjustable lens tune as well as the coupler.

Characterization

One of the core goals of Stepper V2.1 as compared to Stepper V2 is reduction of vibration through a more rigid frame. In order to test this, we characterized the amount of vibration that affects V2.1 using the following procedure:

1. Load a chip with recognizable features into the stepper and focus on it (in our testing, we just used a dirty chip)

2. Using the Basler Pylon Viewer software, collect a 10 second video clip of the surface of the chip. Pylon Viewer gives the video clip as a collection of .tiff frame images. Here is an example of a single frame:

1. Use ImageMagick to threshold the frames: magick '*.tiff' -channel G -threshold 75% -separate threshold.png (this is a bulk operation on all frames). Here is an example of a single frame:

1. Using an image editor, find a specific feature on the chip to focus on, and crop all of the frames to it: magick 'threshold*.png' -crop 300x300+1000+800 crop.png Here is an example of a single frame, plus a GIF of the frames playing in real time:

1. Multiply the thresholded frames together to produce a footprint of where the feature moved throughout the duration: magick 'crop*.png' -compose multiply -layers merge product.png

1. Subtract a frame from the footprint to produce an image that shows how much the feature meandered from its starting point: magick product.png crop-0.png -compose subtract -composite diff.png

In this final image, all of the white pixels are deviations from the starting image. This allows us to count a maximum deviation: in this image (which is from when we were testing the effect of someone resting their hands on the table) there is a maximum 3 pixel deviation.

From this, we can calculate the maximum peak-to-peak vibration amplitude: each pixel on the camera sensor is 5.86 μm square, which after the 10x reduction of our objective, means each pixel in this image is 586 nm on the chip. 3 pixels then is 3 * 586nm = 1.8 µm.

We also ran another test of "ideal" conditions, in which there was no external vibration added to the stepper table, which had 2px deviation. This leads to the result being 1.2 µm.

Assessment and Future Work

This section is a reflection by me, Sky.

The core design goal of V2.1 was pretty much a mixture of "make it less susceptible to vibration" and "make it less janky". I think I mostly succeeded in this department: although I lack proper numbers on V2's vibration issues, I am confident in asserting that V2.1 fixes them (mainly because you could visually see the vibration occurring on V2's camera, and you can't anymore on V2.1), and now that we have a rigidly mounted frame, the slop from the projector moving around on the table is gone.

However, there's still definitely some improvements to be made. For one, I think that the projector should probably be more directly supported - I didn't end up adding a direct support for the projector this semester because it didn't appear to be necessary, but I think this could further reduce vibration issues. This shouldn't be particularly hard because the disassembled projector has very convenient standoff mounting points directly on it.

Another improvement to make is to fix up the centering of the image on the camera: currently, the hole on the adapter plate is perfectly centered to the part's center, but it appears that the projector's actual image is slightly off to one side. This wasn't really an issue when the camera had a larger sensor, but now that it's smaller it very slightly cuts off part of the image. This only require a small change to the adapter plate to correct.

Background

Hardware Specs

Related Links

Litho Stepper Software

Tools Required for Manufacturing

• Water jet capable of cutting ¼” aluminum plate

• Manual milling machine and small end mill

• Drill

• Screwdriver and metric allen key sets

• Glass scribe (tungsten carbide or diamond)

• 3+ large C clamps or similar.

Bill of Materials

Total Cost: $5,820.10

Design File Summary

Most of the water jet components can be cut from a single 12” square aluminum plate. Water jet layout.SLDASM provides the pattern for this. The base needs a separate 18”x6” plate.

Build Instructions

The following steps do not need to be completed in order, except for the last three sections (assembling the structure, stepper, and alignment).

Fabricate the structural parts

1. Export “Water jet layout.sldasm” and “base.sldprt” to the appropriate 2D vector format for your water jet (likely .DXF).

2. Water jet these two files, following the instructions for your specific machine. A CNC router may also work.

3. 1. Be aware that the “base” part takes up the full 6”x18” plate, so no need to cut the outside edges. You may need to adjust the kerf settings so your water jet cuts on the inside of each hole.

4. Countersink all the holes on the bottom of the base plate.

6. Cut the angle iron into three 80 mm long pieces and one 60 mm long piece using a saw.

7. Cut the slot in the adjustable bracket using a 4mm or slightly larger endmill (3/16” works). None of the dimensions of the slot need to be precise. The holes in all the brackets will be drilled during the assembly process.

Assemble the optics

3. Bolt the two filter holders together using four M3x20 or similar screws and washers.

2. Screw together the rest of the optics, paying attention to the direction of the tube lenses.

Prepare the projector

1. Unscrew all available philips screws in the projector.

2. Use a small flathead screwdriver to pry open and remove the top projector housing. This takes some rough handling.

3. Remove the front foot by removing the metal pin as shown below, then unscrewing the foot out while pushing the tabs in.

1. Unscrew the three screws that hold the stock lens assembly to the projector and remove the lens.

1. Remove the plastic half-lens cover and cut the top housing as shown above.

1. Unscrew and detach the lamp assembly (screw circled).

1. 1. Use a scribe to mark the correct width on both sides of the UV-pass hot mirror.

   2. Use a straightedge to scribe a deep groove in the hot mirror. Use a lot of force and several passes.

   3. Apply bending pressure to the hot mirror with the groove facing away from you until it breaks.

Assemble the structure

The following steps will benefit from having two or more helpers. In the images below, the red arrows indicate applied pressure for ensuring parts are correctly mated. Green arrows indicate clamps. Yellow dots indicate tightened fasteners. For all drilling steps use the largest drill bit available that freely fits inside the holes for the brackets.

1. Put the projector back plate and triangle bracket into their slots in the base. Apply pressure as shown so that both parts are flat against the base and in the corner of their grooves.

1. While maintaining pressure, place one 80mm bracket between the triangle and the back plate and clamp it to the triangle.

1. With the clamp still attached, drill through the bracket using the holes in the triangle for alignment. Use M5 nuts and bolts to fasten the two parts together. Put the nuts on the outside to avoid interference with the projector.

1. Return the parts to their previous position, apply pressure, and clamp the bracket to the back plate.

1. With the parts still clamped, drill two holes and fasten. Depending on the size of your drill, it may be necessary to unbolt the triangle first.

1. Clamp the other 80 mm bracket to the back plate. Clamp the 60 mm bracket to the triangle. Ensure the brackets lay flush on the base.

1. Drill into the brackets using the holes in the back plate and triangle for alignment. Fasten with any protruding screws on the outside to avoid interfering with the projector.

1. Place the assembly back into the grooves on the base, again pushing them into the corner. Clamp both brackets to the base.

1. Flip the base upside down and use the holes on the bottom to drill into the brackets.

1. Attach all three brackets and plates.

1. Use three M4 screws to attach the support arm. Use a straightedge to ensure that the top edges of the support arm and back plate are parallel.

1. Clamp and drill holes in the adjustable bracket. Make sure the top surface of the bracket is flush with the support arm.

1. Structure is complete and ready for further assembly.

Assemble the stepper

2. Push the optics onto the projector coupler. You may need to temporarily detach the vertical parts of the optics assembly. This part was designed iteratively and may not fit perfectly because the true position of the DLP chip inside the projector is unknown. In that case, it can be modified or removed as needed.

1. Screw the camera onto the C-mount threads at the top of the optics.

Alignment

2. Connect the camera to your computer with a USB 3.0 cable.

3. Connect the projector to your computing using an HDMI cable.

4. Put in the UV filter. Remove the red filter.

5. Turn on the projector.

6. Open AmScope. Select the camera in “camera list”. If everything is working an image should appear (might be black).

7. Place a flat mirror-like object on the stage. This can be a bare silicon chip.

8. Adjust the height of the microscope objective to approximately 16 mm.

Default configuration Without objective

1. Unscrew and remove the microscope objective. You may still see an image. This is because if the two tube lenses are in the correct positions they will perfectly focus the collimated light between them. We will use this to our advantage by translating the entire optical assembly towards/away from the projector until the image is focused. When this step is complete, we know that the first tube lens is 151.8 mm from the DLP chip.

1. We can also use the no-objective configuration to check the stage’s orthogonality relative to the vertical axis of the optics. When aligned, the image will be centered in the camera frame. Any offset (shown below) can be fixed by adjusting the structure in the angles labeled A and B above. This correction fixes the planarity of the focal plane, visible in the images below. Rotation in A moves the image vertically and rotation in B moves the image horizontally in the camera frame.

To add: details about how to mechanically execute alignment, including shims.

No objective, before alignment

With objective, before alignment. Non-uniform focus is apparent in the top left corner.

No objective, after alignment. The projected image (purple) is centered in the camera frame.

With objective, after alignment. Focus is much more uniform.

Validation and Characterization

Demonstrate the operation of the hardware and characterize its performance for a specific application.

• Highlight a relevant use case.

• If possible, characterize performance of the hardware over operational parameters.

• Create a bulleted list describing the capabilities (and limitations) of the hardware. For example, load and operation time, spin speed, coefficient of variation, accuracy, precision, etc

Safety

Appendix

1. Download Klayout from their websites and follow the instructions to install the software

2. After it is successfully installed, open the Klayout editor

1. To create a new layout File>>New Layout

1. Set the initial layer(s) that you need. The current hacker fab process would require 5 layers which are substrate, poly, active, contact, and aluminum. This is just for getting started, you can always add new layers later if you need to do so.

The layers will be shown in the upper right corner.

1. Go to View>>Layer Toolbox to open the layer toolbox so that you can adjust the order of the layers and the texture of the layers based on your preference.

Double-click the layer to hide it. If you are drawing on a hidden layer, the following tip will show up.

1. To create a new layer, go to Edit>>Layer>>New Layer

1. Scroll your mouse to adjust the size of the grid

The grid can also be hidden through View>>Show Grid. When you need to export the masks as screenshots, the mask needs to be hidden.

1. Klayout has the following tools to draw the shapes. Press “shift” to draw straight lines.

1. Draw the rough shape of an object then adjust it to be the exact size by pressing “Q” to edit its property.

1. Mask Exporting (method 1):

   1. Go to Display>>Zoom Fit to maximize the size of the mask on the screenshot

1. Rename and sort the order of the layers according to the order of the fabrication steps. In this case, the easiest way is to sort them by name (0:substrate, 1:poly gate, 2:active layer, 3:contact hole, 4:aluminum)

1. To make the masks compatible with the lithography stepper, adjust the size of the substrate layer (layer 0 in this case) to be proportional to its resolution (3840x2160). In this set of masks, the size of the substrate layer is set to be 384x216. Under this setting, the actual size of the pattern coming from the stepper is 2.5 times the designed size.

2. Adjust the color and texture of the mask to be blue/red/black accordingly to make them compatible with the red focusing and UV focusing.

1. Hide or show certain layers based on the property of the mask and take screenshots via File>>Screenshot and save the mask.

2. Corp the screenshots since the exported screenshot would normally have white sides.

1. Mask Exporting (method 2):

   1. Set up steps are the same as Step 10 a. to c. steps.

   2. Go to Macros>>Macro Development to write Maros in Klayout

1. Select “Python” and change the Macro Template to “Plain Python file”

1. Paste the following code into the Python file you just created. 1

lv = pya.LayoutView.current()
ly = pya.CellView.active().layout()


# top cell bounding box in micrometer units
bbox = ly.top_cell().dbbox()


# compute an image size having the same aspect ratio than 
# the bounding box
w = 3840
h = int(0.5 + w * bbox.height() / bbox.width())


lv.save_image_with_options('/your_directory/your_picture_name.png', w, h, 0, 0, 0, bbox, True)

1. Change the path to the folder where you want your images to be saved. Note that if the name of your folder or file starts with a number, it will give you the following error message.

1. The .png file of your mask will be saved in black and white. Be sure to adjust the color and texture of the mask to be blue/red/black accordingly to make them compatible with the red focusing and UV focusing.

Reference:

Appendix 1. Klayout user guides

Klayout user manual from their websites:

Shorter one for getting started with basic functions:

Appendix 2. Masks for an NMOS enhancement load inverter

This page documents the current work being done on patterning systems and the goals of that work. If you want to start a new project or research related to patterning, add it here so we can keep track of what's being done!

Backlash Improvements

The current design for stepper v2 involves having the micrometer-motor couplers slide along the shaft of the motor. This leads to wear in the 3D print and prevents the use of a rigid connection, leading to the coupler eventually becoming loose. This can cause ~30º of backlash in the rotation, which corresponds to about 15 microns.

Mounting the motors on the stage that they move, rather than on a (relatively) fixed stage allows for using a rigid coupling without significant modification to other parts of the design. These fixes should be applicable to any fab with an existing v2 stage. This is a major enabler for Absolute Positioning.

This may require redesigning the stage to be mounted upright, or the stage to be turned sideways.

Absolute Positioning

In order to enable many features like automated or computer-assisted patterning, it must be possible to consistently refer to positions on a die. This requires being able to determine the absolute position of the stage.

There has been some experimentation with using inductive sensors for determining the stage position, though calibrating and mounting the sensors is difficult. The accuracy for a properly calibrated and mounted sensor may be sufficient, though. (TODO: Link inductive sensor notes once those get merged)

Currently, a design using simple limit switches is being developed (though blocked on Backlash Improvements).

Cost Reductions

The current optics system is not physically capable of handling the projector's resolution, i.e. some amount of detail is wasted in the optics system. This means that we can use a lower resolution (read: cheaper) projector.

Lastly, there are other components in the optics system itself that we believe can be modified/replaced to further reduce the cost. The ThorLabs components cost at least $700, but many of those parts such as tubes and flanges could be replaced by 3D-printed parts. We will have to test to see if heat generated by the stepper becomes an issue, but this would provide a significant reduction in cost.

Altogether, we believe that we can bring the cost of the stepper below $2000 - perhaps even $1500.

Introduction

The Lithography Spinner V1 plans to use the Blu-Ray disc assembly from a Play Station 5 (KEM-497AAA) to drive the whole system. They are readily available and can be found for $30-$70 in most places.

Typically a single IC is used to drive these modules but most vendors wont sell chips to individuals. So the plan is to design a discrete controller board to manage all the HW and write our own controller SW.

Introduction

This is the project page for a lithography system based on repurposing Blu-Ray drives. The initial goal is to reach a feature size of at least 500nm (2x the Blu-ray laser spot size). As a stretch goal, we would like to also use the sled and spindle motors as high speed nano-positioners and to spin coat and cure photo-resin.

Safety

✓ Safety goggles/glasses are absolutely necessary. A laser dot contains a large amount of energy in such a small space, in the form of light. Your eyes are extremely sensitive to light, and a direct exposure to this very dense energy light for less than a second will blind you for life. We can prevent this by wearing a special type of light filtering glasses, somewhat like the way sunglasses work. But, sunglasses will not work as laser safety glasses. These glasses need to be coated for the correct wavelength. Do not purchase any laser safety glasses under $30, buy from an authorized and reputable seller such as survival lasers. $5 lenses from China will not be sufficient, and have been proven unsafe.

Source: laserpointerforums.com

Project Status

Right now, the first project for this technology (Lithography Spinner V1) is in the research/idea stage. See work in progress page for details on upcoming tasks if you want to contribute.

Want to work on something? Plan a task add your name next to it!

Datasheets Used in the OPU Driver PCB

ECP5 Files

Power Supply

Introduction

In order to develop the SW for Texas Instruments TPIC2050 and test a good bit of the system, the BU40N blu-ray module was chosen for early development. Although available online, this module may not be available for long which is what disqualifies it from general use. Removing the MT1950 chip allows access to a lot of the pins of interest. Powering it is also relatively simple as it should only need 5V.

Introduction

The HW needed to drive the OPU can be broken into 3 sections:

1. Motors

2. PMIC

3. Laser Diode

Preliminary PCB

OPU_Driver_rev0p1 PCB CAD capture has been completed and is up for review on github here:

The board has been roughly quoted on JLCPCB:

• PCB= ~$35.00 / Ea

• Components = ~ $110.00 / Ea

3x Assembled PCBs = $550

At this time no orders are planned until firmware is far enough along to confirm pin out and FPGA logic size.

• uniformity

• deposition rate

• deposition precision (between runs)

• etch rate

• selectivity

• uniformity

• anisotropy

• effect on photoresist?

Links and Videos

• Nearly identical to what we do

• What our work was based on

• Electrons, bandgap, etc.

• Then we moved to silicon

• Extremely well told story of the man who figured out how to manufacture blue LEDs

• We are not the first people to claim that innovation in the semiconductor industry requires intimate knowledge of the fabrication tools

• A fantastic tool being developed by friends at MIT. Overview of many processes, with each being a linear recipe

• Make an account, and go to “fabubase” in menu

• Check out our Hacker fab process, as well as others

• Go through and try to recreate our process from scratch without cheating. See how far you get, and write down things that don’t make sense (1 hour)

How do these things even make computers?

• Application Specific Integrated Circuits

Not all transistors are created equal

Below: ideal transistor IV curve vs. our first curves.

These both exhibit transistor-like characteristics. Looking back at the Veritasium video about how the first computers were made with lightbulbs - a transistor really boils down to a repeatable switching action. When we look at our curve on the right, we see multiple issues:

• The curves don’t go through the origin, they start with a voltage offset

  • This means that when we apply a voltage to the gate (open the valve to allow current through), current doesn’t run through the drain to the source until we apply ~3V to the drain/source connection.

• The lines are all squiggly?

In reality here is what it is saying:

Put simply, we just directly connected an electrical characteristic (IV curve) to a physical process parameter. We now have an exact experiment to try over the next week:

• Less metal annealing

• More Si02 etch before metal deposition (to ensure metal contacts Si instead of SiO2)

Right now it takes about 8 hours of work + waiting overnight to turn a blank wafer into one with NMOS transistors on it. Then we go to the probe station, test it, organize the data, look at the graphs, and think. That’s how long it takes to verify each new experiment. With each machine, script, or management tool we create, we push to significantly decrease this iteration cycle.

Each unique device can also use different materials entirely, which requires different machines.

• What metal are we depositing?

• What does the doping profile look like?

• etc.

• Collect all necessary measurements of the current spin-coater to create the new 3D mode.

• Finalize an updated 3D model that includes the servo mount and any necessary adjustments to the lid design.

• Order required components, including a servo motor, necessary mounting brackets, and plastic material for a redesigned lid.

• Cut and prepare the new lid, ensuring proper fit and clearance for rotation

• Assemble all components and build the initial prototype.

• Conduct preliminary functionality tests, focusing on servo movement and integration with the claw mechanism.

• Optimize servo rotation angles and positioning to maximize clearance while minimizing occupied space.

• Conduct final system tests to verify smooth automation and reliable lid operation.

• Implement necessary refinements and finalize the design for long-term use.

1. Only requires a 3D printer (no machining)

2. Only requires vacuum pump 1/5th the size

3. 1/2 the height

4. Easier to assemble

5. More reliable excess liquid collection

   1. Easier cleaning

   2. Less motor stalling from dried residue

   3. Less residue on window for better visibility

6. Better user interface

   1. Replace touchscreen with potentiometers

   2. Put power button on top so entire operation with 1 hand is possible

   3. Top swinging window becomes flush with side wall and snaps into place

Working Docs

Links to work in progress notes from individual contributors - add your link here with a pull request

Hardware Specs

Hardware Description

Stepper version 2 has greatly improved optical and mechanical performance over V1 while using the same DLP chip from Texas Instruments. Several factors led to this improvement:

2. By swapping to a finite conjugate microscope objective, the optical path length is reduced from ~250 to 160 mm. This reduces the moment of inertia of the optics subassembly, therefore also reducing vibration.

4. Mounting the projector horizontally means less structure is needed.

Tools Required

• M3 and M4 taps

• 3D printer

• Solder paste (preferably a syringe)

• Tweezers or pick and place machine

• Reflow oven

• Calipers

Bill of Materials

Total Cost: $3,015.44 or** $3106.44 (excluding computer & peripherals) (last updated March 16, 2025)

*Upload this CSV file to Thorlabs for all the optomechanical parts + beamsplitter.

**The Basler camera and FLIR camera are mechanically interchangeable, but our software implementation for the Basler camera is more reliable and freely accessible (FLIR code distribution is restricted). For software installation simplicity, we recommend using the Basler camera.

Design File Summary

Note: the OnShape folder is organized poorly because it was our first time using it. Won't happen again, we promise!

Build Instructions

Building the Stepper V2 requires some simple CNC machining, PCB soldering, 3D printing, and other assembly steps, followed by software installation.

Get the Metal Parts Made

Option 1: Water Jet

The Base Plate is 15" long, so double check that your water jet is large enough.

When downloading the Adapter Plate DXF for water jetting, go to Config > Water jet to get the hole sizes right for tapping. The 2.2mm holes are clearance for M2, and the 2.5mm holes are M3 tapped and countersunk.

Option 2: CNC Shop

Option 3: Manual Machining

Adapter plate: This should be manually machinable but we haven't tried.

Solder the UV LED PCB

We used 410 nm UV LEDs on this PCB. We found that two LEDs in series is sufficient to produce enough UV light for patterning. We also found connectors that are compatible with the cable in the TI DLP dev kit.

When assembling the UV LED PCB, it is easiest to use a solder syringe to carefully deposit the paste onto the LED pads and connector pads. If you try to use a stencil mask, it is very easy to smear the paste, so this is not recommended.

Once the paste is applied, align the components with their pads (i.e. using tweezers or a pick and place machine). Keep in mind that you need to use a nozzle that is small enough to pick up the LEDs. Finally, you can put the PCB into a reflow oven to solder the components to the board.

You can test by applying 6V (limit to 1A) across the LED leads, but be sure to wear UV-protective glasses, as the LEDs will be bright! Once you are confident that the PCB works, you can now replace the blue LED PCB in the TI DLP dev kit with our new UV LED PCB. To see the UV light, simply look at the leds through your phone's camera, as the sensors see it as purple light.

Disassemble the TI DLP dev kit

Taking pictures after every step is key to ensuring you can put it back together properly.

1. Test the projector before we completely take it apart :)

1. Unplug all the connectors and remove the top PCB by unscrewing the standoffs.

1. Remove the side PCB.

1. Unscrew and remove the shroud by sliding it away from the rest of the optics.

1. Unscrew and remove the heatsink for the front-most LED, which should be the blue one.

1. Disconnect the LED PCB from the cable. Heat it slightly on a hot plate or with a hot air gun to soften the adhesive and remove the black plastic housing.

2. Glue the black plastic piece to the DIY UV LED PCB, connect it to the blue cable, and reattach it to the optics housing. Put the heatsink back as well.

1. Unscrew the projection lens. That one makes things bigger, but we're trying to make things smaller. It's got to go.

1. Screw on the adapter plate with four countersunk M2 screws.

1. Reassemble the rest of the projector, including the shroud and the PCBs.

Assemble the Optics

1. Start with the beamsplitter cube. Unscrew the set screws, remove the holder, and clip in the beamsplitter. The text ("Thorlabs") should be facing the microscope objective and camera when the holder is reinserted. Keep track of this during assembly and fix it later if necessary.

1. Assemble the DLP tube. From left to right, the parts in the first picture are 0.3" lens tube (SM1L03), 0.5" lens tube coupler (SM1CPL05), 0.5" adjustable lens tube (SM1V05), and 0.5" lens tube (SM1L05). You may want to remove any internal lens rings. The adjustable lens tube allows axial length adjustment and the coupler allows rotation about the optical axis.

1. Screw the DLP tube into the beamsplitter cube. The correct orientation is shown above, and the arrow points to the side of the beamsplitter with the text (and optical coating).

2. Assemble the camera tube, which similarly constructed. The parts are 1" lens tube (SM1L10), 1" lens tube coupler (SM1CPL10), 1" adjustable lens tube (SM1V10), another 1" lens tube (SM1L10), and C-mount SM1 adapter (SM1A9) (last two shown below).

1. Screw on the C-mount SM1 adapter (SM1A9) to the camera and the 1" lens tube. Adjust the lens tube coupler to align the camera with the beamsplitter cube.

1. Assemble the objective tube, which consists of a 0.5" lens tube (SM1L05), a 0.3" lens tube (SM1L03) an SM1 to RMS adapter (SM1A3), and the microscope objective.

1. Temporarily loosen the top lens tube coupler in order to finally screw the entire assembly into the projector.

3D Print and Assemble the Stage

Print all of the parts in the table below. Black PLA is fine. You may need to re-orient them so they print well. The stepper mounts will all need small supports in the motor flange. The X and Y axes need other supports as well.

1. Unscrew all the, micrometers, L-stops and stage locks from the micrometer stage. Separate the X, Y and Z axes. Throughout the assembly process we will be replacing the stock screws with ~4mm longer ones as we reattach the various components to the stage. All 3d printed mounts are 4mm thick at the screw holes. Have your M2.5 screw kit handy!

1. Press fit the three sliding shaft couplers onto the three micrometer handles until the knurled surface is fully covered. They should fit with significant force and maybe gentle hammering. Be careful - the micrometer handles may have different diameters so you may need to modify the CAD and reprint to get a correct fit.

1. The shaft couplers should slide on the motor shafts with zero slop. Modify dimensions and re-print if this is not the case. Graphite lubricant may help decrease sliding friction, and the fit will get looser after repeated axial movement as the steel deforms and smooths the plastic.

1. Screw the motor, coupler, and micrometer into the X axis motor mount as shown. Doing this step before attaching to the rest of the stage takes advantage of the slop in the micrometer mounting screws and aids alignment.

1. Slide the Y axis motor mount onto the Y axis. You will need to remove some screws and push the stage to allow it to slide on.

1. Attach the motor. Don't screw down the micrometer mount yet.

1. While pushing the stage so the micrometer isn't touching the stop, fasten the micrometer mount. This avoids preloading the micrometer/motor assembly and improves shaft alignment.

1. Reattach the X axis micrometer stop as well. You may need to adjust the screw length to get it to fit.

1. Insert the Z axis motor mount to the Z axis. The easiest way to do this is to insert it upside down from the opposite side, then flip it while pushing the stage up, then slide it back so the holes line up. Basically it takes some fiddling.

1. As with the other stages, attach the motor first, then secure the mounts. Tighten the set screw at the green arrow. Make sure the micrometer is flush with the mount at the yellow arrow. Again pushing upwards at the red arrow eliminates prelaod from the spring inside the stage and helps alignment.

1. Tighten down the Z axis mount.

1. Attach the X axis motor mount to the stage with the screws at the red arrows.

1. Add additional screws on the X and Y axes to make sure the mounts are solidly attached. Ignore the spring in the above image.

1. Attach the right angle bracket to the theta stage and the top of the Z stage.

1. Screw the chip vacuum chuck onto the theta stage. The stage is finished.

Mechanical Integration

1. Bolt the XYZ stage to the base plate using short screws so they don't protrude out the bottom. Ensure the stage is aligned with the tapped holes by pushing it forward while screwing it down.

2. Screw in the four alignment screws for the projector. They don't need to go in all the way.

1. Push the projector and optics against the four screws to ensure alignment.

1. Plug in everything: power for the projector, locking USB cable for the camera, USB cable for the stage, power for the stage, HDMI for the projector, power for the pump, and vacuum tube for the chuck. Do not power the stage arduino shield without the motors connected, or you will burn out the drivers.

Install Software and Flash Firmware (WIP)

To install and run the software, you will need a Windows system that has two USB ports. The rest of this section describes how to install the following dependencies:

1. Arduino GRBL firmware

2. Python version 3.10 and Python libraries

3. Basler camera or FLIR Blackfly S Camera Drivers & Viewer

After these are installed, you may clone and instantiate the stepper repository on your device. Our GUI supports a live camera preview of the stage when using the Basler camera. Optionally, you can develop your own driver for using the FLIR camera instead. Instructions for such are included below as well.

Arduino GRBL Installation

1. Install Arduino IDE.

1. To test that the installation was successful, open Arduino IDE and open the serial monitor. You should see text indicating that a version of GRBL is running on your Arduino.

Python Version 3.10 (if using FLIR camera)

If you are using the FLIR camera, you must install Python version 3.10. This is because at the time of development, the latest Python version the Flir Spinnaker SDK supports is version 3.10. As such, you must install libraries and run the software for/from this version. If you are using the Basler camera, later versions of Python should be compatible with the GUI software.

Basler Camera Drivers & Viewer Installation (WIP)

If you are using the Basler camera, install its necessary drivers and its GUI for live camera output.

FLIR Blackfly S Drivers & Viewer Installation (WIP)

Stepper GUI Installation

Follow the steps outlined in the linked repository (recommended). Alternatively, follow the steps below.

1. pen git terminal to the location where you want the Stepper GUI software to be downloaded. Then, run the following commands:

• git clone https://github.com/hacker-fab/stepper .

• cd stepper

1. Install software dependencies listed in the requirements.txt file

2. If you are using the FLIR camera and have access to the private FLIR camera submodule repository, then also enter the following commands:

• git submodule init

• git submodule update

  Otherwise, go to the stepper/config.toml file and toggle the necessary flags to select your camera (or disable it).

1. Configure config.toml with the settings most appropriate for your Stepper build and camera configuration.

2. Run gui.py with Python 3.10:

   • py -3.10 ./src/gui.py

Optional: FLIR Spinnaker SDK (for software developers)

The Stepper V2 build uses a Teledyne Flir camera and custom software written for it. The Stepper software uses the Flir Spinnaker SDK to integrate a live camera preview of the stepper's stage. Since the SDK and its derivative software are closed-source components, we currently do not possess the legal authority to grant access to our custom Flir camera driver to third parties. The following steps describe how to install the Flir Spinnaker SDK and how to develop your own driver. Please carefully review all terms, agreements, and licensing requirements. Follow the steps below.

3. Decompress your download if necessary. Open the README.txt file in the (decompressed) download and follow the installation instructions inside.

4. Test that the installation was successful by running an example program. To do this, first make sure your Flir camera is connected. Then, open git terminal in the "Examples" folder. Then, choose any example .py script and run it by entering py -3.10 NameOfYourScript.py. Ensure that the program output reports connection and communication with your FLIR camera.

5. • def __init__(self)

   • def setStreamCaptureCallback(self, callback)

   • def streamImageReady(self); returns True if live image is available

   • def getStreamCaptureImage(self); returns a tuple of (numpy ND image array, shape of that array, and an image format string ("rgb888" or "mono8")), or False if the image is invalid

   • def isOpen(self); returns True if the camera is active

   • def open(self); returns True on success

   • def close(self); returns True on success

   • def startStreamCapture(self); returns True on success

   • def stopStreamCapture(self); returns True on success

   • a Flir image event handler

   We also suggest optimizing live preview performance by selecting a low-overhead color processing scheme and by displaying only the most recently acquired image (i.e. newest first). The Flir SDK code examples show how you might do this.

6. In config.toml, select the FLIR camera. to an instance of your FlirCamera class.

Final Alignment (WIP)

Once the stepper is connected to a computer and the live camera feed is visible, proceed with final alignment. The goal is to adjust the tube length between the DLP housing and the beamsplitter cube such that both the projected image and the chip are in focus.

1. Place a chip with a visible pattern on it. Cracked glass or extremely dirty chips are good options.

2. Project a mostly red image with some fine marks for determining focus.

3. Using the Z axis (focus) of the stage, focus onto the chip surface. Disregard the projected pattern for now.

1. Loosen the clamp that connects the two parts of the DLP-beamsplitter tube so that they freely rotate. (update picture)

2. Loosen the locking ring on the adjustable lens tube.

3. Screw the adjustable lens tube in/out while periodically checking to see if the projected image gets more or less in focus. You may need to push the optics into the coupler to ensure planarity.

4. Once both images are in focus at the same time, tighten the locking ring on the adjustable lens tune as well as the coupler. (insert image)

Safety

Appendix

Project Specification

Datasheets

Vacuum Chamber Assembly

1. Assemble the chamber frame and plates

(i) Wrap an O-ring around each plate to ensure the chamber has a tight vacuum seal.

(ii) Screw in each plate with 8 bolts into the frame as shown in the following image.

Note: Plan where you want each plate to be (i.e. top, bottom, side) depending on your setup

2. Attach feedthroughs and/or blank flanges

Each opening must be covered and sealed for the vacuum to exist. Therefore, each opening needs a feedthrough in it or a blank flange to cover it. Ensure that each part has the correct dimension to properly fit in its corresponding port.

(i) Pair up the feedthrough/flange with its matching O-ring and clamp.

(ii) Layer the parts in the following order. Starting from the bottom closest to the plate place the O-ring, flange/feedthrough, and clamp. Then attach all necessary screws tightly. Repeat this process for all openings.

3. Turn a face into a door and attach feet

(i) Screw in the hinge into two adjacent plates where you want the door to be.

(ii) Attach knobs on opposite side of hinge to open and close the door securely.

(iii) Attach feet to the bottom of the chamber to minimize vibration.

Final product

Pumping down the Vacuum Chamber

1. Attach the turbo pump to the chamber

Connect the turbo pump (Hi-Cube 80) to the KF-40 plate using the corresponding KF-40 flange and O-ring. Since the turbo pump has a lip that makes it difficult to tighten the screws, we recommend using hex shaped 10-32 x 5/8" screws and tightening with a wrench.

2. Connect the pressure gauge

The Pfeiffer MPT 200 Gauge has a KF-25 connection port. To optimize the 6 plates we chose, an adapter from KF-25 to KF-16 is needed to connect the pressure gauge to the vacuum chamber. Attach using a KF-16 flange to the plate and a KF-25 clamp to connect the adapter to the pressure gauge.

Implement Heating Parts

Heating the vacuum chamber is necessary for two reasons. First, high temperatures of approximately 1200˚C are needed to evaporate the aluminum and perform the thermal evaporation process. Second, heating the chamber allows it to bakeout, meaning that the water trapped inside evaporates allowing the vacuum to achieve a lower pressure.

Our setup consists of two parts: the crucible and the substrate heater.

Crucible Set-Up

The crucible is comprised of the following parts:

Next, connect a power supply to the external end of the power feedthroughs to heat up the crucible.

Finally, attach the thermal breakout board and arduino to the thermocouple to read the temperature values.

Bill of Materials

Introduction

We are building a low cost Atomic Layer Deposition machine for the Hacker Fab to achieve improved gate dielectrics, which will help us achieve our goal of a 10 micron CMOS process as well as improve our capability in performing thin-film research. Our design work on it will be all open source, and we hope other labs can use our work to make their own ALDs at a fraction of the cost of commercial alternatives. We are building our ALD to fit 4" wafers so that it can be brought into the nanofab, which will help us lower the barrier to entry for researching thin film deposition and new materials. Although 4" is much larger than anything we are currently using in the Hacker Fab at CMU, this larger size will make it useful to a larger audience.

This document will present the current proposed machine design plan and the work completed to date for our vertically aligned, cold-walled reaction chamber ALD machine for the Hacker Fab.

Precursor Selection

Oxide of interest

For the current system we aim to deposit Indium-Tin Oxide. Indium Tin Oxide (ITO) is a versatile material widely recognized for its excellent electrical conductivity and optical transparency. These properties make ITO a promising candidate for advanced applications, particularly as a channel material in thin-film transistors (TFTs). Its high carrier mobility and tunable electrical characteristics offer significant potential for improving TFT performance in display technologies and flexible electronics. Additionally, ITO thin films are of great interest in materials and thin-film research due to their unique combination of metallic and semiconducting properties. This makes them an ideal system for exploring novel deposition techniques, optimizing film uniformity, and investigating structure-property relationships.

The precursors for the metals were chosen based on their feasibility to react with water vapor as the oxidizer. The precursors chosen are Trimethyl Indium (TMIn) for Indium and Tetrakis(dimethylamino) Tin (TDMASn) for Tin with Nitrogen carrier gas. They have been shown to be used for ALD and CVD processes with water as the oxidizer in literature. As a starting point our aim would be to reproduce the results achieved in [Zhang et al.]. The process parameters highlighted in the paper are as follows (substrate temperature: -225C):

Safety Considerations

Most precursors and specifically metal organic precursors used for CVD and ALD processes tend to be pyrophoric (i.e. thermally unstable and spontaneously ignite on exposure to air) thus necessitating safety measures.

Material Considerations

Compatibility with the precursors and byproducts produced during reaction are important to consider when selecting components for the delivery system. For our given precursors the chemical groups for which we checked compatibility are: 1) ability to handle pyrophoric materials, 2) ability to resist corrosion due to water vapor, 3) compatibility with methane (by product of TMIn reaction with water) and dimethylamine gas (by product of TDMASn reaction with water)

Specific choices:

• Stainless Steel Tubing

• Aflas O-rings - conventionally used Viton O-rings are incompatible with dimethylamine

• Aluminum vacuum chamber

• Stainless steel bellow hose

• Vacuum pump - Although the vacuum pump manufacturer warns against using the pump with pyrophoric gases, this caution can be safely disregarded in our case. Since we will be working with extremely dilute concentrations of these gases, the risk of combustion or hazardous reactions is significantly minimized. The low concentration ensures that the gases remain well within safe limits, allowing for the pump's use without compromising safety or performance.

Sourcing Precursors

DIY Substrate Heater

The goal of the DIY substrate heater is to develop a cost-effective, replicable ALD wafer heater to support thin-film deposition processes for materials research. Commercial solutions for wafer heating are often prohibitively expensive, making this tool an accessible alternative for Hacker Fab and other researchers. Existing solutions do not meet specific size, temperature, or vacuum compatibility requirements at an affordable price. By designing this tool, we contribute an open-source option tailored for ALD processes. This supports the open-source nature of Hacker Fab by enabling other researchers or users to replicate and build their own wafer heaters. It allows for a more cost-effective approach to ALD, contributing to the open-source knowledge base by providing detailed, replicable build instruction.

Heating Element Setup

• Use 22-gauge nichrome wire to create a heating coil.

• Arrange the wire in a zigzag pattern to cover the area of the heating plate (approximately 4.5-inch diameter).

• Place the nichrome wire between two boron nitride plates (each 0.1-inch thick). Boron nitride provides electrical insulation while allowing efficient heat transfer.

Construction of Heating Plate

• Mount the heating element (nichrome wire and boron nitride assembly) onto an aluminum disk (4.5-inch diameter, 0.1-inch thick). The aluminum disk acts as a heat spreader, ensuring uniform heat distribution to the wafer.

• Secure the boron nitride plates with aluminum bolts to ensure tight contact and structural integrity.

• Ensure that the wire ends extend outside the assembly for electrical connections.

Assembly and Connections

• Position the aluminum plate so that it faces upward, serving as the surface for the wafer.

• Connect the nichrome wire ends to a DC power supply. This power supply should allow adjustable voltage (up to 30V), which will control the current and regulate the temperature of the nichrome wire.

• Attach a thermocouple to the aluminum plate for temperature monitoring. This will help ensure the wafer reaches and maintains the target temperature (300°C).

Operation

• Gradually increase the voltage on the DC power supply to heat the nichrome wire. Use the thermocouple reading to fine-tune the voltage for achieving the desired temperature.

Specifications

• Temperature Range: 300°C to 500°C

• Material Compatibility: The heating element is designed to be compatible with a 4-inch wafer and is placed between aluminum and Boron Nitride plates.

• Voltage: The heater operates with a maximum input voltage of 30V.

• Power Requirements: The heater needs a stable DC power source capable of delivering sufficient current to reach the target temperature.

• Thermal Uniformity: The temperature should be uniformly distributed across the wafer, verified using a laser thermometer to ensure consistent heat application during ALD processes.

• Size: The heating element is sized to fit a 4-inch wafer, ensuring full coverage.

Voltage and temperature data

Select Vacuum-Compatible Feedthroughs

Feedthroughs are specialized components designed to pass electrical, thermal, or other signals through a vacuum boundary. For your heater, an electrical feedthrough is required.

Key Features:

• Vacuum Compatibility: Ensure it is leak-tight, rated for the vacuum level (e.g., high vacuum or ultra-high vacuum).

• Temperature Compatibility: The feedthrough must withstand high temperatures near the heater.

• Electrical Capacity: Rated for the current and voltage requirements of the nichrome wire.

Common Materials:

• Metal-to-ceramic seal feedthroughs: These use materials like stainless steel and alumina ceramics for high durability and vacuum compatibility.

• Glass-to-metal seals: Suitable for lower voltage and current applications.

Vendors:

Feedthroughs are available from companies such as:

• MDC Vacuum

• Kurt J. Lesker

• Conax Technologies

• Allectra

Mounting the Feedthrough:

• Install the feedthrough into a flange on the vacuum chamber (e.g., CF, KF, or ISO flange systems).

• Use O-ring seals (Viton or Buna-N) for lower vacuum applications or indium gaskets for ultra-high vacuum.

Wire Connections

• Inside the Chamber:

  • Connect the nichrome wire to the internal terminals of the feedthrough using vacuum-compatible connectors (e.g., nickel or stainless steel).

  • Ensure insulation with high-temperature, vacuum-compatible materials such as ceramic or polyimide.

• Outside the Chamber:

  • Connect the power supply to the external terminals of the feedthrough.

  • Use shielded cables if electromagnetic interference is a concern.

Detailed Instructions for Assembling the Substrate Heater Component

Materials Required

• Nichrome wire (22-gauge)

• Boron nitride plates (2, 4-inch diameter, 0.1-inch thick)

• Aluminum disk (1, 4-inch diameter, 0.1-inch thick)

• Thermocouple

• Bolts and nuts (compatible with boron nitride and aluminum plates)

• Insulating washers (if needed, for vacuum compatibility)

• DC power supply

• Wire connectors

• Heat-resistant adhesive (optional for securing wires)

Assembly Steps

Step 1: Preparation

• Cut the wire to the appropriate length (as per your design, typically around 14 inches).

Step 2: Setting up the Heating Element

• Wire Arrangement:

  • Lay one boron nitride plate flat on a stable surface.

  • Arrange the nichrome wire in a zigzag pattern across the surface, ensuring even coverage. Leave wire ends long enough to extend outside the assembly for electrical connections.

• Layering:

  • Place the second boron nitride plate on top of the first, sandwiching the nichrome wire between them. Ensure the plates align perfectly.

Step 3: Mounting onto Aluminum Plate

• Place the boron nitride and nichrome assembly onto the aluminum disk.

• Align the pre-drilled bolt holes in all three layers (aluminum, boron nitride plates).

• Insert bolts through the assembly, using insulating washers if needed to maintain electrical isolation.

• Secure the bolts with nuts, tightening evenly to ensure good thermal contact without over

Step 4: Electrical Connections

• Attach the thermocouple to the aluminum plate using thermal paste or tape for accurate temperature monitoring.

• Use a multimeter to check for electrical continuity and verify there are no short circuits.

• Attach the nichrome wire ends to the wire connectors and connect them to the DC

Step 5: Final Assembly

• Seal the feedthroughs to maintain vacuum integrity.

• Route wires for the power supply and thermocouple through vacuum chamber feedthroughs.

• Use vacuum-compatible connectors.

• Position the entire assembly inside the vacuum chamber

Future Testing Tasks

• Initial Power Testing:

  • Gradually increase the voltage while monitoring the temperature using the thermocouple.

  • Record the time required to reach target temperatures (e.g., 400°C, 500°C).

• Thermal Uniformity Testing:

  • Use a thermocouples to verify uniform heat distribution across the aluminum plate.

• Vacuum Compatibility:

  • Test the system under vacuum conditions to ensure no leaks in the feedthroughs and proper operation of the heater.

• Optimization of Wire Length and Voltage:

  • Experiment with different lengths of nichrome wire to find the optimal balance between power efficiency and heating uniformity.

• Long-Term Durability Testing:

  • Run the heater for extended periods to evaluate its stability and reliability.

• Temperature Controller Integration:

  • Test the system with a PID temperature controller to automate heating and maintain stable temperatures during operation.

• Documentation of Results:

  • Plot temperature vs. time, power vs. temperature, and voltage vs. temperature graphs based on experimental data.

  • Note any issues or observations to refine the design.

Challenges

• Wire Placement: Achieving uniform heating is dependent on precise placement of the nichrome wire.

• Vacuum Constraints: The vacuum environment imposes limitations on assembly and temperature uniformity

• Optimization of Power and Heating Time: There is a need to balance the wire length for optimal performance. A longer wire enhances heating uniformity but consumes more power and increases the time required to reach the target temperature.

Future Improvements

• Alternative Materials: Testing circular mica heaters or other heating elements for improved thermal response times.

• Optimization Studies: Verifying whether the aluminum disk is essential. Direct placement of the wafer on boron nitride could simplify the design without compromising functionality.

• Enhanced Efficiency: Refining nichrome wire routing to minimize heat loss and enhance system efficiency.

• Parameter Tuning: Finding the sweet spot between nichrome wire length and power consumption to maximize performance while minimizing energy usage and heating time.

Delivery System

System Design

For the delivery system we chose VCR connections for the gas lines in our vacuum system to ensure a reliable, leak-tight seal, essential for maintaining system integrity. These metal-to-metal sealing connections are ideal for ultra-high vacuum (UHV) and high-purity gas applications, reducing the risk of leaks, outgassing, and contamination. Their robust design and reusability also made them a practical choice for our setup, where frequent assembly and disassembly are required. We use a two-stage regulator at the carrier gas cylinder as it ensures consistent and precise pressure control, reducing the high-pressure gas from the source to a stable, manageable level for downstream components. This stability is essential for maintaining uniform gas flow in the system. The gas at the correct pressure is then delivered through a mass flow controller that regulates the flow rate of gases entering the system, providing precise control to meet process requirements. It ensures accurate delivery of gases to the precursor manifold. We are receiving a precursor manifold having three Swagelok ALD3 valves donated by the Claire & John Bertucci Nanotechnology Laboratory at CMU. The precursor manifold serves as a distribution hub, directing gases to valves. It includes multiple inlets for the precursor bubblers and an outlet to lead to the chamber, enabling the mixing or isolation of various precursors before delivery to the reaction chamber. The ALD valves in the manifold are high-speed, precise valves that control the pulsed delivery of precursors into the vacuum chamber. These valves are critical for achieving the sequential gas flows required in ALD processes. The line finally leads to the vacuum chamber designed to be a cross-flow reactor.

Components requiring connection for delivery line:

• Chamber precursor inlet: KF25 flange fitting

• Precursor Manifold:

  • Inlet: ¼” female VCR

  • Outlet: ¼” male VCR connector

• MFC inlet and outlet: ⅛” NPT female connectors

• Dual stage regulator: reduces cylinder pressure (~2000 psi) to operating pressure for Mass Flow Controller (<70 psi)

Control Systems

Components/Hardware Requiring Control

Parts to be controlled:

1. Mass Flow Controller - Controls the amount of carrier gas flowing through the tubing per time. Requires an analog signal 0-10Vdc and power supply of 12-24 Vdc, 250mA

2. ALD valves - Controls the duration for which precursors are open to the carrier gas line. Works on a pneumatic valve that is actuated by solenoids. Requires N2 gas input for pneumatic actuation and square wave signal of 24 Vdc with wave width equal to valve open time.

1. Delivery line and substrate heaters - Controls the temperature of the gas lines and substrate holder surface. Requires control of voltage and current being delivered to the heating element to modulate based on reading from the thermocouple.

2. Throttle Valve - Controls the pressure of the vacuum chamber by modulating the evacuation rate of the pump based on current pressure.

Outline of controls

Control parts using LabVIEW and RaspberryPi (given the number of different signals and components we decided to use a Pi instead of using an Arduino)

RaspberryPi is great for handling low-level hardware tasks, such as controlling valves, relays, and sensors. It can read analog or digital signals, control actuators (e.g., motors or heating elements), and interact with sensors that LabVIEW can’t interface with directly.

Progress

The ALD valves are controlled based on their status in a truth table, where each row corresponds to a specific step of the ALD cycle. The truth table defines the ON/OFF state of each valve, with True indicating the valve is ON and False indicating it is OFF. The appropriate row of the table is accessed dynamically, depending on the current step of the cycle.

To implement this control, a relay board is used to interface the ALD valves with a 24V DC wall adapter. The relay board switches the power supply to the valves according to the truth table commands, ensuring precise timing and coordination for each step of the ALD process. For depositing Indium Tin Oxide (ITO), which requires two metal precursors, the ALD valve operation is determined by the desired ratio of the two precursors. To achieve this, a sequential block is used to calculate the current cycle number in the ALD process. Based on the cycle number and the specified precursor ratio, the sequential logic selects which metal precursor valve to open. This setup allows for reliable and automated control of the gas delivery system during operation.

To control the heating elements, temperature data is collected from thermocouples at a specified sampling rate and frequency using a DAQ (Data Acquisition) system. The measured temperature readings are averaged to calculate a mean temperature, which provides a stable input for feedback control. The mean measured temperature and the target temperature are then fed into a PID (Proportional-Integral-Derivative) controller. The PID computes the required voltage adjustment to maintain the target temperature by supplying the appropriate voltage to the resistive heating elements. This feedback loop ensures precise temperature control, critical for maintaining process stability and uniformity during operation.

We are still in the process of testing this and are currently figuring out how to use DAQ hats on Raspberry Pi to collect the data at a given frequency.