Ashok M. Khathuria

Advanced process control for poly-Si gate etching using integrated CD metrology

Advanced integrated metrology capability is actively being pursued in several process areas, including etch, to shorten process cycle times, enable wafer-level advanced process control (APC), and improve productivity. In this study, KLA-Tencors scatterometry-based iSpectra Spectroscopic CD was integrated on a Lam 2300 Versys Star silicon etch system. Feed-forward control techniques were used to reduce critical dimension (CD) variation. Pre-etch CD measurements were sent to the etch system to modify the trim time and achieve targeted CDs. CDs were brought to within 1 nm from a starting CD spread of 25 nm, showing the effectiveness of this process control approach together with the advantages of spectroscopic CD metrology over conventional CD measurement techniques.

Study of the influence of substrate topography on the focusing performance of advanced lithography scanners

A Phase-Grating Focus Monitor (PGFM) is used to assess the focus control of a state-of-the-art lithography scanner (TWINSCAN AT:1100) over substrate topography. The starting wafer flatness quality is found to be critical in minimizing the overall defocus distribution. In fact, on nearly all wafers, the most significant contributor to defocus across the wafer was the small-scale topography. Results obtained over programmed topography, created by etching various patterns into silicon, are found to agree well with the simulated defocus behavior based on the measurement of the wafer surface obtained on the scanner metrology stage. Finally, we report on preliminary focus control results over realistic device-type substrate topography, involving thin-film and polish effects.