Precision Position Detecting Technique for Alignment Mark Applied in a Step-and-Repeat Projection Aligners (1st Report)

Interference Cancellation within Resist using 4-wavelength Light Illumination

Abstract

Alignment accuracy is one of the most important factors in step-and-repeat projection aligners used for VLSI lithography. An illumination technique is described in which the interference fringes caused by the resist thickness asymmetry on the alignment mark are reduced, thus achieving high alignment accuracy. Using this technique, the following results are obtained : (1) Using 4-wavelength simultaneous illumination where wavelengths differ by increments of 27 nm, the variation of the reflected light intensity becomes less than 27% in the range of 0.5-2.3 μm of resist thickness. (2) Ideal laser wavelengths are 458, 488, 515 and 543 nm. (3) Experimental results, determined using the illumination technique on an alignment mark coated with a resist having asymmetric thickness, give an alignment accuracy of ± 0.04 μm (3σ).