Inline composition and thickness control of SiON, HfSiON gate films using VUV capable spectroscopic ellipsometer

The area of gate metrology in the semiconductor fabrication process is being challenged with stringent thickness and composition control requirements. Control of component thicknesses and compositions of nitrided gate oxides and complex Hi-K film stacks has become a critical requirement for process development and control. Implementation of lab based techniques like XPS, XRF, XRR, SIMS, EXES etc. in the automated semiconductor fab environment is relatively novel and primarily in the development phase. Optical ellipsometry has typically been used for thickness control and rarely for estimation of volume fractions in composite films. This paper discusses the implementation of an extended UV (155 nm - 800 nm) spectroscopic ellipsometer for inline monitoring of various gate dielectric films viz. SiON and HfSiON. Results demonstrate the sensitivity of the technique to process variations, short term precision and long term stability that enable its implementation in an high volume automated fab for routine process monitoring. Some hardware enhancements required to make such measurements viable is also discussed. Efficient implementation of acquisition routines enables this enhanced composition metrology capability at higher throughput compared to typical X-ray based techniques that are naturally slower. The superior optics and sensors also provide enhanced long term stability.