Clustering of plasma nitridation and post anneal steps to improve threshold voltage repeatability

The incorporation of nitrogen into gate dielectrics produces a shift in the threshold voltage, V_t, and its concentration must be precisely controlled to maintain the V_t within a specified range. The V_t sensitivity to nitrogen concentration is presented to define control limits for its incorporation. The nitrogen loss as a function of time between processing steps is determined to assess the risk in a manufacturing environment. A typical foundry fab is then modeled to determine the range and distribution of possible delay times and its impact on lot to lot variation in V_t. This variability can then be removed by clustering the nitridation and post anneal steps.