Substrate pre-alignment method

Abstract

A method for pre-aligning a substrate includes the steps of: 1) providing a substrate having a plurality of marks are arranged circumferentially on a surface thereof, wherein each of the plurality of marks consists of at least one first stripe extending in a first direction and at least one second stripe extending in a first direction; 2) aligning a center of the substrate with a given point on a substrate carrier stage; 3) illuminating a mark selected from the plurality of marks on the surface of the substrate with light and obtaining an image of the selected mark; 4) processing the image to obtain first projection data corresponding to the first direction and second projection data corresponding to the second direction; 5) identifying a set of first peak values corresponding to the at least one first stripe of the selected mark from the first projection data and a set of second peak values corresponding to the at least one second stripe of the selected mark from the second projection data; 6) selecting first peak values and second peak values that a) correspond to numbers of the at least one first stripe and the at least one second stripe and b) are deemed authentic, from the set of first peak values and the set of second peak values identified in step 5) and proceeding to step 7); otherwise selecting a next mark as the selected mark and returning to step 4); 7) calculating a current position of the selected mark relative to the substrate carrier stage based on the first and second peak values selected in step 6); and 8) rotating the substrate, according to the current position of the selected mark relative to the substrate carrier stage calculated in step 7), a relative position of the selected mark on the substrate and a desired rotation angle of the substrate relative to the substrate carrier stage, until the substrate is oriented at the desired rotation angle.