Thermally activated ageing of polysilicon

Thermally induced resistance changes and long term stability of polysilicon resistors were characterized for temperatures up to 1400 K. For this purpose, a new test microstructure was developed which is based on a micro hotplate with a central polysilicon resistor as the material under test and two polysilicon heaters for temperature cycling of the membrane. This test system allows the separate measurement of thermally and electronically activated ageing processes. After thermal cycling, relative resistance changes at room temperature between 7% and 48% with respect to the resistance as fabricated were observed The changes strongly depend on the cooling rate /spl tau//sub c/. Additionally, it is possible to reversibly switch between different room temperature resistances by applying appropriate cooling rates. A relaxation of the resistance value during cycles with heating and cooling steps was observed. This relaxation is temperature dependent and related to the thermal history of the resistor. The test structure withstood 60 heating cycles up to temperatures of 1300 K.