Patent ID: 6859260
Filing Date: 2005-02-22
Classification: D21H,G03F,H04N

Abstract:
1. A method for improving focus accuracy in a lithography system including an exposing area for exposing images onto top surfaces of substrates, comprising the steps of: a. determining a proper focus distance for a specific region on a top surface of a substrate, the proper focus distance determined using a calibration sensor when the specific region is not positioned under the exposing area; b. producing a first measurement relating to the specific region at the proper focus distance, the first measurement produced using a secondary control sensor when the specific region is not positioned under the exposing area; c. producing a second measurement relating to the specific region, the second measurement produced using a primary control sensor while the specific region is positioned under the exposing area; and d. adjusting an actual focus distance based on the first and second measurements while the specific region is positioned under the exposing area, wherein the calibration sensor has a higher focus accuracy than each of the secondary control sensor and the primary control sensor.