Long-term stability and thermal cycling of thermocouple contacts to Si up to 350°C

We report on the long-term stability and thermal cycling of thermocouple contacts to silicon up to 350°C. Such contacts call be used as a lead for electric signals while at the same time measuring the temperature immediately at the semiconductor surface. Contacts were fabricated using Au based solders at temperatures between 600 and 850°C in vacuum. Different types of thermocouple materials have been tested with good results for a type E thermocouple. The characterisation of the contacts comprises electrical measurements (I-V characteristics) and determination of elemental and phase composition by EDX mapping in the contact region. The long-term stability of the contacts has been investigated during heat treatment up to 400 h at 300°C. Thermal cycling tests were performed between ~200°C and 350°C, continuously measuring the contact resistance. The tests showed a good mechanical and electrical stability of the contacts. For application temperature above 350°C, metallic diffusion barriers or layer stacking together with special high temperature solders can be used to form electrically stable thermocouple contacts to Si