Submicron linewidth measurement using an interferometric optical profiler

摘要

Optical instruments for submicron linewidth measurement are limited by the resolution associated with the wavelength of light. By measuring phase, rather than intensity, the lateral resolution of the system can be improved. This paper describes a system based upon an interferometric optical profiler using a Linnik interferometer and narrow-band illumination. The system measures surface height directly using phase-measurement interferometry techniques. Three-dimensional maps of surface structure over 1024 $MUL 1024 pixels are produced. The system includes an 80486-based AT-compatible computer and a Videk Megaplus camera. The Videk Megaplus camera has 1320 $MUL 1030 active square pixels spaced at 6.8 $mu@m intervals. It outputs an 8-bit digital signal which is interfaced to a framegrabber, and intensity is displayed live on a high resolution monitor. The incoherent optical resolution of the system is 0.34 $mu@m, and the detector samples the surface every 0.034 $mu@m. It has been found that features as small as 0.5 $mu@m can easily be measured. Two calibration standards traceable to NIST with feature sizes on the order of 1 $mu@m have been used to calibrate the lateral dimensions of the system. Results of measurements of photoresist lines on silicon with 0.5 $mu@m lines are presented.