Validation of correction method for gap shape measurement by vertical-objective-type ellipsometric microscopy with rotating-compensator ellipsometry

Abstract

Correction method for improving the accuracy of gap shape measurement using vertical-objective-type ellipsometric microscopy (VEM) was investigated. This method can provide observation with 0.1-μm-order lateral resolution. Since VEM-based measurement uses an optical microscope with high lateral resolution, the measured ellipsometric signal includes polarization change and incident angle unevenness when applying rotating compensator ellipsometry (RCE) to gap shape measurement. The effect of the variations of the ellipsometric signals on the gap measurement accuracy had been theoretically investigated and these could cause errors of more than 10 nm in gap measurements with RCE. Corrections of these errors were necessary for gap shape measurements with nm-accuracy. The proposed method enabled to correct the polarization change and the incident angle distribution due to using optical devices. Evaluation using gaps filled with air or lubricant (poly-α-olefin) demonstrated gap measurement accuracy of about 1 nm. The VEM gap shape measurement using the correction method showed the highest sensitivity for gaps around the contact region, and enabled observation of the differences in the contact state, which depended on small variations in surface roughness of less than 1 nm. This method also achieved to observe confined lubricant film of less than 1 nm in the contact area, which is possible to reduce the contact points between surfaces.

Keywords

• nanometer gap
• film thickness measurement
• ellipsometry
• tribology
• contact mechanics