Taku Ninomiya

Focusing and leveling based on wafer surface profile detection with interferometry for optical lithography

A new concept of shot-by-shot leveling for high resolution stepper systems, profile-based- leveling, is presented. This detects the wafer surface profile using laser interferometry. From the detected profile, this system determines where on the LSI chip to focus, and controls the wafer stage for focusing and leveling. With an experimental setup, a profile detection repeatability of +/- 0.02 micrometers , a tilt measurement repeatability of +/- 0.24 (mu) rad and a tilt measurement linearity of +/- 1.4 (mu) rad were obtained.

Shot leveling and focusing with interferometry for optical lithography of sub-half-micron LSI

This paper presents a shot-by-shot leveling applied to an i-line stepper system. This shot leveler utilizes laser interferometry with a laser beam that has S-polarization and a large incident angle to the exposure surface of the LSI wafer. Thereby leveling and focusing accuracy is preserved regardless of the wafer surface condition under the photoresist. This system acquires interference fringe data with charge-coupled device (CCD) line image detector, and extracts the fringe frequency and phase information with a fast-Fourier-transformation (FFT). These correspond to the tilt and height information of the photoresist surface. The performance was evaluated with 4M-DRAM process wafers. Tilt and height measurement linearity was proved to be ±2 µrad and ±0.3 µm respectively, and total leveling control accuracy was proved to be better than ±7 µrad.