IMPORTANCE OF DETERMINING THE POLYSILICON DOPANT PROFILE DURING PROCESS-DEVELOPMENT

During the development of a 0.5 mu m, 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 anal ysis 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 thi ckness and phosphorus doping level, of the p(+) source/drain implantat ion 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 x 10(15 ) combined with a p-plus dose of 3.0 x 10(15), does lead to unacceptab ly low active carrier concentrations, which are proven to result in ga te depletion. Furthermore, it was noted that in case of low net impuri ty concentrations the modification of any of the processing conditions has a large influence on the final polysilicon spreading resistance p robe profile. A detailed discussion of the different parameters and th e resulting doping profiles are given in the article. Based on the res ults of the short loop tests the p-plus implant dose was fixed at 2.0 x 10(15). A full transistor lot was processed in which the remaining p arameter, i.e., the polysilicon implantation dose, was varied. The dev ice characteristics determined on this lot are in agreement with predi ctions, based on the results of the experiment. (C) 1996 American Vacu um Society.