High Reliability Dynamic Auto-Focus System
Original Publication Date: 1988-Sep-01
Included in the Prior Art Database: 2005-Feb-15
This article describes an auto-focus system which performs dynamic auto-focusing over a substrate with different surface material and feature height. Redundant light paths and signal channels give high reliability to the system. The auto-focus system disclosed herein is generally based on the light section microscope principle. This system is intended to be used as an adjunct to a substrate inspection machine. While this is an established technique, there are additional functions in this disclosure. These are: 1) Accommodating a substrate on which a nominally uniform, patterned, thick metal has been deposited, and 2) Reliability improvements by use of a dual channel system and signal discrimination. The overall system is illustrated in Fig. 1.