During the development of a 0.5 μm, n‐type poly, complementary metal–oxide–semiconductor (MOS) process the influence of different process steps on the PMOS gate doping level was investigated. The application of spreading resistance measurements and secondary ion microscopy analysis for determination of the polysilicon dopant profile allowed us to define critical process conditions within which the process could be optimized using short loop tests. The influence of the polysilicon thickness and phosphorus doping level, of the p+ source/drain implantation dose, of the subsequent temperature steps, and of the silicidation were all investigated. It was concluded that a combination of certain process conditions, such as a polysilicon implant dose of 4.0×1015 combined with a p‐plus dose of 3.0×1015, does lead to unacceptably low active carrier concentrations, which are proven to result in gate depletion. Furthermore, it was noted that in case of low net impurity concentrations the modification of any of the processing conditions has a large influence on the final polysilicon spreading resistance probe profile. A detailed discussion of the different parameters and the resulting doping profiles are given in the article. Based on the results of the short loop tests the p‐plus implant dose was fixed at 2.0×1015. A full transistor lot was processed in which the remaining parameter, i.e., the polysilicon implantation dose, was varied. The device characteristics determined on this lot are in agreement with predictions, based on the results of the experiment.

This content is only available via PDF.
You do not currently have access to this content.