Summary for adhesion of vacuum evaporated sn Discussion
The focus keyphrase here is adhesion of vacuum evaporated Sn on Ti, and the problem is that a 50 nm tin film on a 50 nm titanium adhesion layer over silicon can be wiped off by finger even though the Ti sticks well to the wafer. Tatsuo Nakato reports vacuum evaporation at about 1 Å/sec, base pressure around 1E-7 that rises to 1E-6 during Sn deposition, and substrate heating to 120 °C before and during deposition, but none of that improved the tin adhesion. The thread excerpt provided does not include any replies or alternate solutions, so there is no documented answer in the source beyond the problem statement itself. The practical takeaway is that the Ti underlayer alone was not enough to make the evaporated Sn mechanically durable under these conditions, and further process changes would be needed.
February 10, 2016
Q. I am trying to deposit 50nm thick Sn layer on Silicon wafer using Vacuum evaporation (1A/sec of deposition rate) using 50nm thick Ti layer underneath as an adhesion layer. Ti layer adheres well to Silicon, but Sn layer can be wiped off by finger easily. Vacuum pressure before Sn deposition is 1E-7 but it will degrade to 1E-6 level. I tried heating Silicon wafer up to 120 °C before Ti deposition as well as during Sn deposition. This didn’t help adhesion of Sn. Sn layer doesn’t de-laminate, just be wiped out by finger.
Any brilliant suggestion?
Tatsuo Nakato