The isotropic etchant attacks the Si surface
very strongly and non-uniformly, and the reaction
rate is very
sensitive to localized temperature changes due
to the exothermic nature of the reaction. As a
result, this etching process leads to varying, and
sometimes excessive, surface roughness--which is
what you observe.
The acetic acid enables a more controlled
reaction and minimizes localized overetching.

Hope this helps.


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| Shuvo Roy                                                     |
| Research Assistant, Microelectromechanical Systems Group      |
|                                                               |
|Office: Rm. 811 Glennan Bldg.                                  |
|        Department of Electrical Engineering & Applied Physics |
|        Case Western Reserve University                        |
|        Cleveland, Ohio 44106                                  |
|        USA                                                    |
|                                                               |
|Telephone: 216-368-3051        Fax: 216-368-2668               |
|                                                               |
|E-mail:  roy@mems4.eeap.edu            sxr37@po.cwru.edu       |
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|WWW: http://mems.cwru.edu/roy                                  |
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