Improved resist profiles and CD control through optimized thin dielectric stacks

摘要

Abstract: LOCOS processes use nitride layers in the range of 1000 - 2000 angstrom for oxidation barriers. The thicknesses are optimized for the stiffness needed to control the `bird's beak' and for stress which effects the subsequent gate oxide quality. We have found that CD control is generally poor on the active mask and that the resist profile is prone to `footing.' Simulation and experiments have shown that resist footing is dependent on the exposure dose at the resistitride interface. This, in turn, depends on the nitride thickness. This resist foot is not reproducible because of normal variations in the nitride thickness and it introduces CD variation. In addition the foot may produce problems with the nitride etch and contributes to the resist to final etched CD bias. Here we report on studies of the effect of nitride thickness on active masking. Optimizing the LOCOS film stack results in improved resist profiles and CD control. !4