Recently, I was told n-epi (silicon) could be used as the etch stop.  That
is, the P substrate is etched away and the n-epi is left

This is contrary to my understanding.  I thought P+ silicon was the only
silicon etch stop.

Thanks in advance,

Roger Brennan
1620 Legacy Village Road
Reno, NV 89521-6164
Home: rogerbr@earthlink.net
Home: 775-852-4240

Applications Director
Solecon Labs
770 Trademark Drive
Reno, NV 89521-5926
Work: roger@Solecon.com
Work: 775-853-5900 ext 108