Patterning SOP- Stepper V2 (UWaterloo)

Purpose

To transfer photomask patterns onto photoresist-coated wafers using the HackerFab custom DLP UV lithography system controlled via Raspberry Pi.

This SOP supports fabrication of microstructures targeting <10 µm feature sizes, as demonstrated in recent HackerFab calibration experiments.

Scope

Applies to:

• Photoresist-coated wafers

• DLP projector lithography system

• Raspberry Pi lithography controller

Used before:

• Development

• Etching

• Lift-off

Equipment & Materials

Equipment

• HackerFab DLP UV lithography system

• Raspberry Pi lithography controller

• Alignment stage + optics

• Computer terminal

• HDMI monitor (for troubleshooting)

• UV safety goggles

Materials

• Photoresist-coated wafer

• Pattern image file (.bmp)

• Developer solution

Safety Precautions

• Wear UV safety goggles.

• Avoid direct exposure to UV light.

• Handle wafers with tweezers.

• Follow the photoresist chemical SOP during development.

Process Parameters

Parameter	Typical Value
Exposure Time	10s
Focus Distance	Calibrated optics alignment
Feature Size Target	<10 µm
Image Format	.bmp

Procedure

1

Prepare Pattern File

1. Save pattern as .bmp image.

2. Place file on Desktop.

2

Upload Pattern to Raspberry Pi

Open terminal and run:

ls

ls ~/Desktop

scp ~/Desktop/[image_name.bmp] hackerfab@10.37.69.0:~

ssh hackerfab@10.37.69.0

3

Run Lithography Program

After logging into the Pi:

cd elegoo-mars-4-dlp-controller/src/

python3 litho_cli.py ../../[image_name.bmp] [exposure_time_in_seconds]

Example:

python3 litho_cli.py ../../hacker_fab_logo.bmp 8

This command projects the pattern onto the wafer.

4

Exposure

1. Place the photoresist-coated wafer on the lithography stage.

2. Secure the wafer holder.

3. Use the alignment camera to center the wafer and pattern area.

4. Run the test pattern focus_nologoa.bmp for ~30 seconds.

5. Adjust the stage height until the projected image appears sharp and well-defined.

6. This step sets the correct wafer holder height for proper focus.

7. Upload and select the desired pattern image file.

8. Execute the lithography command with the chosen exposure time.

9. Wait until exposure completes.

10. Do not move the stage during exposure.

5

Post-Exposure

1. Remove wafer.

2. Proceed to the development SOP.

3. Inspect the pattern under the microscope.

Troubleshooting

Problem	Cause	Fix
Cannot SSH into Pi	Pi IP changed	Connect Pi to monitor via HDMI to find new IP
No projection	File path wrong	Check bmp location
Blurry pattern	Misalignment	Refocus optics
Under/over exposure	Wrong dose	Adjust exposure time

Important Network Note

If the terminal does not connect or respond:

The Raspberry Pi IP address may have changed.

To find the new IP:

1. Connect Pi to a monitor using HDMI.

2. Boot the Pi.

3. The IP address will be displayed on screen.

4. Use the new IP in the SCP and SSH commands.

Expected Results

• Sharp patterned resist.

• Consistent exposure.

• Achievable <10 µm features with calibrated optics and spin-coated wafers.