[labnetwork] Deep anisotropic etching of SiO2

[Andrei Alamariu]

Hello,
I am thinking if it would be possible to try to cast the thick  SiO2 layer, using the Spin On Glass (SOG) material  and a metal mold.
It would require a lot of auxiliary processing steps.
First choosing the metal - substrate assembly.
The low doped Si wafers (> 10 Ohm-cm) are transparent to NIR; but will alloy/ sinter with Aluminum, complicating the process. So you could use Si & Ti or Quartz & Al, etc.
What is the layout shape of the device and and of the substrate? 
Then machine the molds with very smooth and clean interior surfaces, and allow some process tolerances.
Then prepare the stable siting setting of the molds on the substrate surface using the first photo- etch procedure.
Then pour the SOG on the whole wafer surface, very slowly at the beginning.
Then gently reflow the SOG and anneal it, the higher the temperature the better, but for industrial machined Al no more than 525C.
Then  CMP the top surface! The unknown, the hardest and critical step. Using Ti molds would be easier.
Then use the second mask to cover the device area and a little over the metal mold too, and BOE etch the surrounding SiO2. (it will stop at the Si substrate surface, but not at Quartz surface!), then continue and etch the metal molds.
Then cut the Si substrate to the desired size and shape using the dice saw or photo and STS machine.
Thanks, Andrei




Sent from my iPad

> On Jan 18, 2023, at 4:52 PM, Ningzhi Xie <nzxie at uw.edu> wrote:
> 
> 
>  Dear college,
> 
> We want to perform a highly anisotropic, very deep (~500um) etching of SiO2 with a vertical side wall. On top of the SiO2 is nanostructures protected by photoresist. The etch depth needs to be controlled with a precision of 20% (we are thinking of using another  material as the substrate underneath the SiO2 layer, which acts as an etch-stopper). The structure and dimensions are shown in the attached image. It would be very helpful if anyone has any idea of this kind of etching (either dry and wet chemical etch is fine).
> 
> Thank you very much.
> 
> Best regards,
> Ningzhi Xie
> Department of Electrical and Computer Engineering
> University of Washington
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