A surprisingly small Windows desktop, about 10mm by 8mm, projected through the prototype lithography optics.

Photolithography on a budget

(2019, Age 13-14)

Inspired by Sam Zeloof, I decided that I should try my hand at the garage fab, specifically the most interesting and accessible section; lithography.

Although it may not seem very accessible, I correctly assumed that it would be easier than wrangling HV power supplies, tube furnaces, or HF. Furthermore, I conjectured that it could be done mostly using COTS parts.

Wielding a 70-200 f/2.8 camera lens, a tripod, and a DLP projector, I sent the light from the projector through the objective optic of the camera lens to reduce it down to the size of the image sensor on the camera, much like a camera lens normally does. Surprisingly, this worked fairly well, producing an image around the size of a Micro-SD card, with an acceptable resolution for patterning. A kinematic mirror mount was placed atop the objective optic of the lens with a first-surface mirror, as well as a 3D-printed aperture to reduce unwanted aberrations outside of the exposure area.

Unfortunately enough for me, the harder part of the process was the supposedly easy part; coating the wafers with photoresist using a spin coater. I acquired the wafers (50.8mm test grade) from University Wafer, the photoresist (KL5305) from Kemlab¹, and made the ill-fated decision to build the spin coater myself.

As it turns out, spinning a thin wafer of silicon at somewhat absurd speeds — while it is covered in viscous formaldehyde-scented liquids — is not the wisest idea, and I decided against continuing after a wafer rapidly transformed into a fine mist on the spin coater.

Given this, I still have reason to believe that there was some exposure, as I had earlier observed the photoresist experiencing what would be best described as pre-development — and I again observed this. I ran out of budget around this time, and decided to move on to different endeavors — but I have always wanted to revisit this. I would do it very differently now, but I cannot deny that my prior approach was also valid.

Let this be a lesson to balance your spin coater.

¹Thank you to Karen from Kemlab for representing the only supplier of photoresists in the entire world who did not immediately laugh me out of the email chain, but still have the gall to sign me up for their marketing emails. That happened twice. I sometimes wonder whether my antics are the reason for their new online store, an industry first as far as I know.