Contact Printing
In contact printing, the resist-coated silicon wafer is bring into physical contact with the glass photo mask. The wafer is held on a vacuum chuck, and the entire assembly rises until the wafer and mask contact each other. The photoresist is exposed with UV light while the wafer is in contact position with the mask. Because of the contact among the resist and mask, very high resolution is possible in contact printing (e.g. 1-micron features in 0.5 microns of positive resist). The problem with contact printing is that debris, trapped among the resist and the mask, can damage the mask and cause defects in the pattern.