Effect of post-nitride-passivation processing on the long-term stability of polysilicon integrated circuit resistors

Results from 24 h experiments show that heat treatments of nitride-passivat ed polysilicon resistors at temperatures below that of the contact anneal, 450 degrees C, have a decisive influence on the stability of the resistors. In stress tests at 150 degrees C, it is shown that for heat treatments at 230 degrees C, the amount of loosely bound hydrogen in the grain boundaries and, consequently, the resistance drift is reduced by more than a factor o f 2. For heat treatments above 270 degrees C, the drift is larger due to a reoccupation of released dangling-bond sites in the temperature range 230-2 70 degrees C during cool down. This is also the temperature range in which the largest reduction in the resistance drift is found. The heat treatments did not affect the mechanisms involved in the drift. There are no indicati ons that hydrogen is released from the nitride at the highest temperatures, the reoccupation being independent of temperature. Possible mechanisms are discussed and the results are evaluated in terms of a previously introduce d model for the time-dependent loss of loosely bound hydrogen. (C) 2000 Ame rican Vacuum Society. [S0734-211X(00)08002-1].