Effects of contact hole filling and multilevel metallization on gate oxide integrity and transistor performance

Effects of tungsten and polysilicon contact hole fillings as well as multilevel metallization on gate oxide integrity and transistor performance are evaluated. The data indicate that back-end processing may deteriorate gate oxide quality and hence degrade transistor performance. Monitoring gate oxide damage as a function of metallization process steps revealed severe oxide damage which is mainly generated by reactive ion etching and metal sputtering. However, subsequent processing at elevated temperatures (e.g. oxide or polysilicon deposition) efficiently reduced gate oxide damage prior to the final forming gas anneal. In the case of polysilicon contact hole filling this results in extremely low interface trap densities on fully processed wafers and excellent device characteristics. In contrast, severe degradation of transistor performance was found in the case of tungsten contact hole filling