Electronic Variable Wafer Plane
Original Publication Date: 1985-Sep-01
Included in the Prior Art Database: 2005-Feb-19
Increased control of the resolution in a photolithographic process employed in semiconductor manufacturing requires that the mask-to-wafer relationship be accurately controlled and easily moved for any one of the many different process levels within the projection mask alignment and exposure equipment. This is necessary so that the image of the mask coincides with the wafer in a projection printing system. Inability to easily change the mask to wafer relationship compromises other process steps required in the manufacture of high density integrated circuits. This article concerns a technique and apparatus for precisely locating the exact mask image anywhere on the wafer surface, e.g., the front surface of the photoresist or any other plane either positive or negative in direction from the limit bisect [*], e.g.