Is it possible to get a vertical wall in wet etching of silicon?

Is it possible to thin a Si wafer with SF6 DRIE or KOH and then do lithography on that surface? If it is possible, could you please provide some suggestions regarding the thinning process?

Thanks a lot for your help!!

(I know that CMP is one of the standard thinning technology, but it seems not avaliable for small samples. In addition, my sample has a functional thin film in one side, which is a bit fragile.

I did SiO2 dry etching using CHF3 (100 W RIE power, 10 mT pressure, 20 sccm CHF3 flow) at 20C. After the etch process, I noticed cracks/peeling off in multiple places of my sample (image attached). The sample has GaSb on top and AlInAsSb and AlInSb on subsequent layers with varying percentage of Aluminum. If anybody experienced this or have some idea why this might happen, I will appreciate. Thanks

I have use some organic solvents like chloroform, toluene but doesn't work.

I have a 3D printed mold that I am using for transferring microfluidic features onto a thin PDMS membrane (~200 um). During the peeling-off process, either the features deform or the membrane breaks. Does anyone have any guides on how to prevent these issues?

I am using Sylgard 184 silicone elastomer kit (20 : 1 part A : B).

I want to create a hard etch mask for etching Si anisotropically using KOH. The etched structures need to be quite deep, several 100 um.

I understand that the two common hard etch mask materials are Si3N4 and SiO2. Currently I have access to RIE, but only Ar and O2 gas tanks, so I can't dry etch the silicon nitride, which seems to be the most common method. We've tried sputtered Cr as a mask, but the adhesion to Si is less than ideal. The best success we've had is a complicated process: sputter Cr onto Si3N4 coated Si, create a photoresist mask, etch the Cr, strip the resist, etch the Si3N4 with BOE, strip the Cr and finally etch the Si with KOH. I'm looking for something simpler ideally.

We are having trouble sourcing a reliable supply of HSQ. Can anyone recommend a supplier in Europe?

I know the issue is probably a fundamental one with the Dow Corning supply chain & production priorities, and not with our local Ellsworth office.

Assume we're starting with the <100> face up, so when the KOH starts the etch, it's the <111> faces that provide the sloped side walls.

But why does it always only ever slope *inward* from the edges of the exposed region from the mask?

Say you're looking at a cross-section of the area being etched, from the side...

On the 'left' side of the open part of the mask, the <111> face follows 'down and to the right'...and on the 'right' side of the open part of the mask, the <111> face follows 'down and to the left'.

BUT.

The <111> face that starts at the 'top left corner' of the open part of the mask and goes 'down and to the left', on the *left* side of the etched region is exactly the same as the <111> face that forms the 'down and to the left' slope side wall on the *right* side of the etched region.

So why does the 'left' side of the etched region only ever slope 'down and to the right' and the 'right' side of the etched region only ever slope 'down and to the left'...if both sets of <111> planes, at both orthogonal orientations, on *both* sides of the etched region...are the same?

I attached a simple illustration of our question. Thanks!

I am looking for a protocol since the lack of negative staining in compromising most of my recent TEM pictures.

I am trying to use TMAH to under-etch single crystalline Si to form released amorphous Si structures. The width of the under-etch is approximately 10 um. However, as far as I know, TMAH also attacks some metals like Al. Since I want the metal remains on my samples after the wet etching process to make electrical contacts, do you know what types of metals (namely gold, nickel, etc...) I can use?

Thank you.