I’m working in a cleanroom environment with 2-inch silicon wafers, and I’m encountering cloudy surface appearance on plain, unmasked Si wafers after a DRIE etch (~1 um deep). The surface appears glossy under most light, but under certain angled illumination, a cloudy, diffuse scatter is visible, indicating possible micro-roughness or contamination.

Here is my cleaning and etching process, step by step:

• Use a TRION DRIE etcher to etch ~1 um into the bare silicon.
• No photoresist is involved in these wafers (for now) — this test is to assess Si surface behavior.
• Etch depth is consistent, but post-etch surface appears cloudy (non-glossy) under certain lighting conditions. Afm imaging also shows rough surface

My initial goal was to pattern these wafers with Mir 701 14cps positive photoresist and etch into the silicon 1um deep and then deposit 200nm of silicon nitride. I was able to achieve a uniform deposition of silicon nitride the first time I ran this process but every following attempt I was met with ashy and nonuniform (rough) SiN. Ive been able to trace the problem to the etcher but I haven't found any good work arounds for solving the issue. I cant use a hard mask and I dont want to etch, strip the photoresist and clean the wafer and then realign and pattern. No matter how hard I try I know my alignment will never be the same. Ive attached pictures of my DRIE process. My etch is 560s long