Dave,

Some how SiO2 was stuck in my mind so I suggested diluted HF such as 10:1 very
strong or 500:1 very diluted.

In case Si only, here is best mixture of chemical that you can etch Si with best
uniformity: 69%HNO3+49%HF+CH3COOH
When you use HNO3+HF then etch rate is very fast that means the uniformity might
not be good such as you described. The CH3COOH acts as a buffer agent so it
makes slow decomposition of HNO3 that you can control the etch rate.
Good luck,

Mehmet Delikanlioglu


----- Original Message -----
From: 
To: "General MEMS discussion" 
Sent: Wednesday, December 19, 2007 7:42 PM
Subject: Re: [mems-talk] How to uniformly etch ~0.05 - 0.3um off a 3" Si wafer?


> Dave,
>
> Use premixed diluted HF and overflow DI rinse.
>
> Mehmet Delikanlioglu
>
> ----- Original Message -----
> From: "Dave Goldstein" 
> To: 
> Sent: Tuesday, December 18, 2007 8:09 PM
> Subject: [mems-talk] How to uniformly etch ~0.05 - 0.3um off a 3" Si wafer?
>
>
>>I need to uniformly remove a thin layer of Si off a 3" Si wafer. No
>> structures, just the same material. No RIE. How to do it?
>>
>> I've tried the HNA solution but it doesn't look very uniform and some
>> white-ish looking cloud was left on the wafer.
>>
>> I have also tried using NaOH but it looked very bad after dipping the
>> wafer
>> in there for couple of minutes. And doesn't look very uniform.
>>
>> Right now I am trying using Piranha (H2SO4:H2O2=3:1) to chemically grow a
>> thin oxide and then etch off in Si. I am thinking that each cycle should
>> consume 2nm of Si then if I am doing this 30 times then I am removing 60nm
>> of material. But I have no way to verify this.
>>
>> What do you suggest to use to remove a thin layer off a Si wafer in a
>> uniform fashion?
>>
>> Dave
>>