Linear Relationship Study between SiO_2 and Poly Silicon Polish Rate

摘要

In this paper, linear relationship between SiO_2 and poly silicon polish rate for two kinds of Rohm and Hass slurries had been studied. One of the slurry is originally chosen for SiO_2 polish, the other is chosen for Si polish. Poly silicon here actually is epitaxial growing very thick silicon on the top of poly. Before the study, the recipe was optimized and three factors were considered. One is the CMP head down force, which are indicated by the inner ring and membrane pressure. The second is the difference between inner ring and membrane pressure and the retain ring pressure. The third is the difference between CMP head and the platen pad rotation speed. It was found that for the poly silicon wafers, there have a limit for the down force increase, the membrane of the header will be raped out when down force reach this limit. To get it work at high down force limit, a down force ramp up recipe had been tested successfully. 6 PSI difference between inner ring and membrane pressure and the retain ring pressure was found to give the best uniformity results. If the platen pad rotation speed fixed at 80 RPM, it was found that 88 RPM head rotation speed will give the better uniformity results. With the optimized recipe, the strict linear relationship between SiO_2 and poly silicon polish rate was found for both kinds of slurries. Our experiment results show that either slurry can be chosen for both SiO_2 and poly silicon polish.