TEOS film stress
Kelly & I deposited 100 & 300 nm thick SiO2 films on bare wafers with the P5000 PE-CVD tool at RIT last week. The wafers were then annealed according to JP’s recipe overnight to stabilize the TEOS layer film stress. The stress was measured using the Tencor P2 profilometer by scanning across it before depositing the SiO2 layer (baseline) and after the anneal. The stress is calculated using net deflection of the wafer based on Stoney’s equation for thin films, which requires the wafer thickness and the film thickness but ignores other properties of the film . The results for measurements taken last Friday (morning following anneal) and this morning (four days later are shown below:
SiO2 thickness Stress, MPa, Tensile
5/16 5/20
100 nm 226 200
300 nm 158 129
I’m not sure what values JP has obtained with different TEOS thicknesses, so I don’t know if the difference I’m seeing is significant. It seems that the tensile stress is fairly stable – provided it doesn’t continue to drop over time.