Hello Venu,

The undercutting you are seeing is due to the fact that both your material and
your etch process are
isotropic. To obtain straight sidewalls in polysilicon, you will need to use a
physical etch (such as a
sputter etch), or a physical-chemical etch (such as a reactive ion etch).

Best Wishes,

Craig McGray
6211 Sudikoff Laboratory
Dartmouth College
Hanover, NH 03755



[email protected] wrote:

> Date: Wed, 1 Dec 1999 02:05:12 +0530 (IST)
> From: "Venubabu.U" 
> Subject: [mems-talk] polycrystalline silicon etchant
>
>   Hi,all:
>       Can someone tell me the polysilicon wet etchant having good
>       selectivity with Positive PR and less undercutting.
>       Presently iam using HNA etchant(HF:HNO3:WATER :: 6:100:40).
>       Iam realising some cantilevers with this etchant,iam getting the
>       width of beam at the top is less compare to the bottom.
>       I want uniform width from top to bottom.
>
>       Any information is gratefully appreciated.
>                                                          venu babu,
>                                                          Research scholar,
>                                                          IIT MADRAS, INDIA.