I would like to know whether it is possible to get vertical side walls in etching of either or silicon wafers using TMAH/KOH based wet etching processes. In general, if I etch silicon using TMAH, I get inclined walls (typically 50 deg with top surface), but I need vertical walls for my application. Though DRIE is an alternative, it rather costs a lot. Can anyone suggest an alternative?
Wet chemical etching is inherently more isotropic. There are some solutions that have a preferential etch rate for one crystal face like KOH, however it's just never going to be as anisotropic as DRIE. For vertical walls you'll have to use plasma etching.
You can obtain vertical walls (Si(111)) if etching Si(110) (with a certain masking layer) by KOH .
This can be seen in the following lecture from University of Pittsburgh:
http://www.pitt.edu/~qiw4/Academic/ME2080/lecture8.pdf
metal-assisted chemical etching (MaCE) will allow you to obtain vertical etching for a reference you can see the work of L. Li ; Materials Science and Engineering, Georgia Institute of Technology
Metal Assisted Chemical Etching. Huang, Z., Geyer, N., Werner, P., De Boor, J., & Gösele, U. (2011). Metal-assisted chemical etching of silicon: A review. Advanced Materials. doi:10.1002/adma.201001784
If you are interested in Metal-assisted chemical etching and sidewall control, check my work on producing straight and tapered structures (i.e. wires or holes):
Silicon nanowires with controlled sidewall profile and roughness fabricated by thin-film dewetting and metal-assisted chemical etching
Article in Nanotechnology 24(22):225305 · May 2013
DOI: 10.1088/0957-4484/24/22/225305
I think it's not possible to get perfectly vertical sidewall with wet chemical etching. You should consider some dry etching techniques such as reactive ion etching.
Yes, the sidewall control can be achieved during growth of silicon nanowires using simple metal-assisted chemical etching method.
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