Wafer Stepper Calibration Method for a New Mask Set
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
A technique is presented for determining the correct wafer stepper (x,y) table offset adjustments for each new mask set. When a new mask set is introduced into a wafer fabrication line, the wafer stepper (x,y) table control software must be calibrated with the new set to accommodate different mask level overlay errors. The present calibration method utilizes a test wafer which is coated with a photoresist patterned using the first and second masks from the new mask set. The test wafer is translated under a global alignment system until the stepper marks for the first mask level are located on the alignment display screen. The x,y coordinates of a corner of the stepping marks, as shown in the figure, are determined by a laser count displayed on the stepper alignment screen. These (x1, y1) coordinates are then recorded.