Abstract

State-of-the-art microlithographic optical systems are normally evaluated by measuring developed photoresist patterns. Unfortunately, the highly nonlinear and variable resist characteristics complicate the quantitative evaluation of imagery with such techniques. A new approach for directly obtaining the image profile uses 0.4-µm wide slits of fluorescent material on a silicon wafer.¹ These slits are accurately scanned by the interferometrically controlled stage of a step-and-repeat system as fluorescence intensity is monitored. This paper presents image profiles of 1.2- and 0.8-µm objects at various field positions and focus parameters. Lens distortion data, relative to the laser stage grid, are shown. Atmospheric pressure variations were found to cause observable changes in the best focus parameter (0.17 µm/Torr) and in the lens reduction error (1 ppm/Torr). Finally, the relative vibration between image and wafer has been measured as position vs time, in contrast to normal accelerometer techniques which lose sensitivity at low frequencies.

© 1986 Optical Society of America