OCD Sensitivity Study and Parameter Optimization for Oxide-Nitride Spacer Etched Poly

Abstract

Optical critical dimension (OCD) measurement has been widely demonstrated as an essential metrology method for advanced IC process monitoring at 90 nm node and beyond. However, aggressive IC industry scaling requirements and sharply increased process control complexity motivated the development of metrology tools. Oxide - Nitride spacer etched poly, abbreviated as ON-spacer-etch, correlated tightly with channel drive current and leakage control. In this work, the spectroscopic ellipsometry diffraction on ON-spacer-etch gratings was simulated by rigorous coupled wave algorithm (RCWA) method. The sensitivity analysis provided optimal light incident direction and step size for the selected geometric parameters to be used in the practical measurement and spectral library generation. The after-etching inspection (AEI) measurement on ON-spacer-etch targets was taken. The dynamic repeatability and long-term stability tests were conducted to make an evaluation on the tool, while the correlation with reference data and machine noise was discussed in detail. CD extraction demonstrated in this work will help for ramping up yield and controlling cost in high volume manufacturing (HVM).