Effect of degas before metal gate deposition on the threshold voltage

Abstract

The interaction between the dielectric and the metal gates is crucial for effective workfunction and V T. In this work, we investigate the effect of a degas step just before the metal gate deposition. The purpose of this step is to remove the water adsorbed at the surface of the dielectric by heating it under vacuum. Removing the water also means the suppression of an O source during following processing steps of the device. This leads to lower oxygen vacancies passivation. When the maximum of water is removed from the surface, NMOS long channel V T is decreased and PMOS long channel absolute V T is increased. From the dielectric point of view, degassing leads to lower intrinsic quality as measured by gate leakage increase as a function of the temperature.