Resist Process Information
HSQ
HSQ, short for Hydrogen Silsesquioxane, is a negative-acting material that works well as an e-beam resist. It’s not a conventional resist, in that it’s not an organic polymer, it’s a spin-on-glass material that actually leaves behind an SiO2 material in exposed areas after development.
It is sometimes known as the old trade name FOX (which was short for Flowable Oxide), but perhaps due to lots of legal wrangling about patent rights, Dow doesn’t use the FOX name any more for this product. It is sold now as XR-1541.
It is very high resolution, but requires a high dose, so it’s slower to expose.
Right now, I have two dilutions:
XR-1541-002, a 2% dilution, listed as providing 30-60 nm thickness,
and
XR-1541-006, a 6% dilution, listed as providing 85-180 nm thickness.
In practice, I’ve found the 6% dilution generally gives a film in the 150 nm to 250 nm thickness range, but (and this is also somewhat unlike most organic photoresists), the film thickness seems to depend heavily on acceleration rate as well as spin speed. My guess is that the solvent evaporates pretty quickly, so the thickness is getting set during the acceleration phase.
There’s a huge range of suggested process parameters out there on the web, but here’s the main process I have used for quite a bit of work.
1) Preclean substrate, dehydration bake 110C hotplate, 5 min
2) Spin HSQ. Use EXTREMELY sparingly. This stuff is very expensive!
3) Bake, 80C hotplate, 4 minutes
4) Expose. I’m using a base dose of 2800 uC/cm2
5) Develop 25% TMAH, 4 minutes. {Keep the sample wet at all times until IPA rinse is complete!}
6) Rinse vigorously in spray DI water, 60 seconds. I’ve read this is very important to avoid streaks and spots
7) Rinse with IPA
8) Dry with N2
Here’s a data sheet from Dow-Corning, although it doesn’t provide a huge amount of information:
11-1547e-01