TEOS is back
Last week, JP and I resurrected using TEOS as the backside pattern and experimented with using a thermal oxide as the first protective oxide layer (instead of a sputtered oxide). The idea was to see how the reduced stress in the pattern (TEOS) would affect film morphology. The thermal oxide on the frontside was an attempt to reduce pinholes by using a denser film. We can’t call this a true experiment since we varied two things (TEOS backside and thermal ox frontside), but it does give an indication that these two changes DOES affect pore morphology.
There was a clear difference in porosity from inside to outside. JP says that the thermal oxide has a linear gradient in thickness, so perhaps this difference manifests itself as a non-uniformity in porosity. The last image in the panel is a comparison with our “standard” membrane (1000 RTP outside susceptor 100 C/s).
From these results, it seems that lower stress in the pattern yields smaller pores and lower porosity. The next step is to isolate the effects of TEOS and a thermal oxide protective layer. I did not see a reduction in pinhole density, unfortunately.