Dear all,

when I was using TMAH to etch silicon, I noticed a notch under the mask(~2
nm). roughly like below
       _______________________________
              >                                  <
             /                                      \
            /                                        \
           /                                          \


does anybody know why it happens? is there any way to avoid this?
mask is SiN, TMAH(25%) 50 oC. I only etched 2.5 min as I do not want to much
undercut.

any information are welcome.

sincerely

Yu CHEN