[labnetwork] Crygenic Plasma Etching of Black Silicon

[Robert Vandusen]

Hi Kevin.
In the past on our old ECR etcher we had some success using double sided carbon tape to adhere onto a backing wafer. The tape comes in sheets from SEM supply stores.  It was important to trim the tape to ~ 1mm smaller than the sample so it was not exposed to the plasma.
For removal we heated the backing wafer on a hotplate up to ~ 75 Deg C as I recall then gently peeled up the sample piece.  I know it could could get messy if the sample doesn't some off right away, but acetone would usually clean it up.
We were able to get black silicon at temperatures up to -25 deg C.

Rob

-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu <labnetwork-bounces at mtl.mit.edu> On Behalf Of Kevin M McPeak
Sent: September 20, 2020 11:22 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Crygenic Plasma Etching of Black Silicon

[External Email]

Dear Colleagues,

We have a user at the LSU Nanofab that has developed a recipe for etching black Si into 4" Si wafers at cryogenic temperatures  (-130 C) using our Oxford ICP100 tool. The user also wants to produce Black Si on small pieces, e.g. 1" x 1" Si pieces which are attached to an Al masked Si carrier wafer. He is currently using Fomblin oil as a heat transfer agent between the Si chip and the carrier wafer (3 - 4 drops). Unfortunately, the small chips are giving him patchy black Si, whereas the whole 4" wafers are very uniform.

I suspect this issue is related to heat transfer across the Fomblin layer. He is currently waiting 2 minutes after loading the carrier + Si chip before striking the plasma. 3 - 4 drops of Fomblin between the carrier and 1" x 1" chip.

Does anyone have experience with cryogenic etching of Black Si on chips? If so, I would very much appreciate your thoughts on best practices for achieving good heat transfer to the chips. Thanks in advance.

Regards,
Kevin

--
Kevin M. McPeak
Assistant Professor | LSU Dept. of Chemical Engineering
225-578-0058 | mcpeaklab.com | lsu.edu/nanofabrication


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