Dear MEMS research, when TMAH or EDP used as an etchant, and SOI 40 um wafer was used, I figured out that the etch stop and it didn't hit the buried Silicon dioxide and a layer with thickness based up on SEM photo ~10-15um, do you have any idea about this issue , if so would you please tell me what this layer is, and how can we get rid of it, and really I appreciate if you tell me about the reason that causes this layer. thanks a lot. BigBangwidth the exabit netOpticalTM company Abdullah Tashtoush MEMS Process Engineer Tel: (780) 490-4800 Ext. (227) Cell:(780) 953-0702 Fax: (780) 430-8545 atashtoush@BigBangwidth.com www.BigBangwidth.com