🎥Patterning
For a description of what the team at CMU is working on in Spring 2025, check out this document!
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
Developed Resolution
describe out standardized test: darkfield/brightfield, developed with AZ400K for 80s, measured pitch distance, used airforce test pattern
Value:
Tools Required for Verification:
Method of Verification:
Possible Variation: Error during development (see Patterning SOP)
References: pics/videos
Automation Capabilities / Throughput
what human actions are required: manual loading/unloading, choose the pattern, align manually or automatically with software
approximate area exposed per second
how much time to do one exposure, how much of that is active work vs. waiting around
Patterning Machine Specifications:
Optical Resolution
Tools Required for Verification: Microscope + Calibrated Camera to convert pixels to μm
Method of Verification: make another page for optical resolution test?
Possible Variation: misalignment of optics during assembly
References: pics/videos
Developed Resolution
Tools Required for Verification:
Method of Verification:
Possible Variation: Error during development (see Patterning SOP)
References: pics/videos
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