We make microstructures out of 15 mill single crystal silicon substrates.
Using 110 oriented silicon and masking along the right 111 plane we can etch
vertically or almost completely anisotropically.  A recent application required
etching 60 mill silicon substrates.   The degree of anisotropy we can achieve
during etching is inconsistent.  We can rarely get vertical sidewalls while
etching.  I am told that this is because of "swirl" in the silicon substrates.
It is my understanding that swirl is a type of "crooked" growth defect during
LEC crystal growth processing.


 Can anyone verify that the poor anisotropic etching is due to "swirl"?  Is this
a common problem when performing bulk anisotropic etching of silicon substrates
that are > 45 mills thick?  Does anyone know where I can get single crystal 110
silicon substrates (~ 0.060 ") with minimal swirl?  Is there another way to get
excellent wet chemistry anisotropic etching without having to worry about swirl?

Any information I can get would be helpful.

Thank you,

Andrew J. Nielson
Graduate Student, Mechanical Engineering
Brigham Young University
Mems Group
email: nielsona@et.byu.edu
http://www.et.byu.edu:80/~nielsona