Alignment technique using wafer rear surface

Abstract

A new wafer Rear Surface Alignment (RSA) technique for wafer stepper is proposed. Lithography systems such as wafer steppers are necessary to improve the overlay accuracy corresponding to resolution. For 0.1 ?m lithography, 0.03 ?m (3?) overlay accuracy is required. The RSA has the potential to obtain an overlay accuracy of more than 0.03 ?m (3?), because it is not affected in theory by resist film and asymmetric profile of patterns deformed by various device manufacturing processes. The RSA system, however, is affected by the thickness and tilt of a wafer; the process has been expanded to include the patterning of target marks on the wafer rear surface. These problems arise because the RSA system has not been widely applied to lithography systems. The new RSA called RECT alignment (using REar surface and Canceling Tilt effect) is independent of wafer tilt and dose not require any optics to detect wafer tilt or numerical compensator. The purpose of this paper is to propose the above RSA technique and to validate the RECT alignment optics. Experimental results are as follow: detecting error caused by wafer tilt of 50 ?rad is approximately less than 0.010 ?m. When the conventional sensor is used, on the other hand, the detecting error caused by wafer tilt is more than 0.03 ?m