Here's the all answers I received about KOH etching techniques.
Thank all who helped me!
                                                 zhengwei
Dear colleagues,

Now I am working on etching silicon wafer with KOH. I want to reduce the

thickness of silicon wafer to about 100 microns. But I found, after that

process
the surface of silicon became so worse that I could not continue my
work.

 Anyone can help me on  KOH etching techniques?
Thank you very much!

                                                              zhengwei

Hi!
I'm not sure if this helps.. but my colleague Jun Li

observed that if we start KOH etching from a polished face.. the surface

quality of the etched surface remains good for etches upto 200 micon
deep!
In short the end surface quality is dependant, inter alia, on the
starting
quality of that face.
Hope this helps.
Nilesh

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Nilesh D. Mankame

Dept of Mech Engg. & App. Mechanics. |297, Towne Bldg, 220 S.33rd
street,
School of Engg. & App. Science.      |Philadelphia, PA 19104-6315. USA.
University of Pennsylvania.          |Tel:(215) 898-4825
Fax:(215)573-6334.
Office : 327 Towne Bldg              |Manufacturing Tech lab, T168-B
______________________________________________________________________________



There is evidence in the literature (J. Micormech Microeng. Vol 5 1995
209-218 S.A. Campbell et at.  "Inhibition of pyramid formation in the
etching of Si p<100> in aqueous potassium hydroxide-isopropanol") that
addition of IPA and saturation of oxygen allows etching with nm type RMS

surface roughness.

Do you need to use KOH?  Can you use an etch which is isotropic?  There
is
some evidence (specifically by Zarowin and the CMP process) that an
isotropic etch actually can improve the polish.  Try a mixture of nitric

acid, water, and buffered hydrofluoric acid.  I use 250:100:25 and get
about 0.5 microns per minute at room temperature.  The biggest "problem"
is
bubble formation.  If the etch is too fast (too much HF in my
configuration), bubbles mask the etch.



                                                                Justin.

Justin Mansell          |       "Only a risk tests the reality of a
belief"
Ginzton Laboratory      |                       - C. S. Lewis
445 Via Palou St.       |
Stanford, CA 94305      |       (650) 723-2666 (fax)    (650) 725-2284
(office)


Hello Zhengwei,
If your intention is to reduce the thickness of Si wafers, you could (1)
use a mixture of HF + HNO3 + DIW, (2)
back-grind / CMP your wafers.

Jaideep

KOH tends to produce surface that is very rough. A company named SEZ
located
in Arizona has a tool for thinning wafers with a smooth surface.  They
use HF
and have a special way to wet process the backside of the wafer while
protecting the front side. They may have ability to provide you with
finished
wafers. I know of a company in San Jose that can do the same thing using
a
special lapping process if you are interested.  Bob Henderson
bobhendu@aol.com

Hi Zhengwei,

In order to prevent roughening of the Si surface during KOH etching add
to
KOH solution Isopropyl alcohol - IPA (if the volume of solution is 2l,
500ml of IPA will do)  which is the wetting etchant and removes the
bubbles from the wafer
surface during etching. You can also use megasonic sound or mechanical
stirring toremove the bubbles from the surface.

Regards,

Andrew Prochaska

Dear zhengwei,
After etching the silicon, VSI has found that a touch polishing for a
short amount of time works really well.
Ronnie Phelix
Sales & Marketing
Virginia Semiconductor
Phone : 540-373-2900
Fax : 540-371-0371

Try a little IPA added to solution as surfactant
  Brian P. Czimback
     (607) 974-1879
     CzimbackBP@corning.com

Zhengwei,

It is not a good idea to thin Si wafers with KOH due to its anisotropic
etch
of Si.  I am afraid that I can not provide any help on KOH etching.
However, I know of  one method of thinning wafers, that is, mechanical
grinding.  There are several commercial services in the United States
such
as Virginia semiconductor and Spin Technologies.  Yield is an issue
however
since 100 micron thick Si wafers are very fragile.

Good Luck,


Hi,zhengwei
   one of my co-worker forward your question about KOH to me.I do found
the starting surface affect the end result when i did KOH from polish
side of wafer. what is your test result? by the way. what kind of
research you are doing?
take care.
Jun

Hi,
Our laboratory is familiar with etching silicon wafer with KOH. We often
etch a single
crystal silicon to about 20~30um. The surface of silicon is very good
after etching.
The roughness is about 350A. The etching temperature is about 78C, and
the
concentration of KOH is about 40%. You may try it.


            xingyie@21cn.com