Buried etch stops

[tnoradam]

Hi Mattias,

I deposited an oxide/nitride/oxide stack, and then attempted to only WET-etch oxide via etch(x,y,[], :mode => :round). On some portions of the layout I have shapes that completely etch this stack (not included here), but this problem also occurs if the stack is not patterned.

Something is not right with the etch method. When I supply only 1 material (the top oxide), it of course only removes the top oxide, no matter how deep I tell it to etch.

However, when I tell it to etch the two oxides that sandwich the nitride, it proceeds as if the nitride wasnt there at all. It lets the etch method proceed below the nitride, even though it would actually block it.

Am I doing something wrong here ? Maybe I am missing a setting ?

Attached are pictures that show before and after etch, and below is the snippet (even though I had modified the output function).

Thanks.

Thomas.

mat_SP_OX1 = deposit(t_SP_OX1, t_SP_OX1, :mode => :round)
mat_SP_NIT = deposit(t_SP_NIT, t_SP_NIT, :mode => :round)
mat_SP_OX2 = deposit(t_SP_OX2, t_SP_OX2, :mode => :round)
output(     mat_SP_OX1,  8, 1000,   "SP_OX1", 0,      cOx,                      )
output(     mat_SP_NIT,  8, 1001,   "SP_NIT", 0,     cNit,                      )
output(     mat_SP_OX2,  8, 1002,   "SP_OX2", 0,      cOx,              "SP_DEP")

etch(  t_SP_OX2 + t_SP_NIT + t_SP_OX1/2, t_SP_OX2 + t_SP_NIT + t_SP_OX1/2, :into =>  [mat_SP_OX2, mat_SP_OX1] , :mode => :round)

output(     mat_SP_OX1,  8, 1000,   "SP_OX1", 0,      cOx,                      )
output(     mat_SP_NIT,  8, 1001,   "SP_NIT", 0,     cNit,                      )
output(     mat_SP_OX2,  8, 1002,   "SP_OX2", 0,      cOx,              "SP_DEP")