Method and apparatus for mapping surface topography of a substrate

(54) METHOD AND APPARATUS FOR MAPPING SURFACE TOPOGRAPHY OF A SUBSTRATE

(75) Inventors: James David Hunt, Charlotte, NC (US); Lee Dante Clementi, Lake Wylie, SC (US); Charles A. Monjak,

Clover, SC (US)

(73) Assignee: ADE Corporation, Westwood, MA (US)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days.

(21) Appl. No.: 09/418,722

(22) Filed: Oct. 15, 1999

Related U.S. Application Data

(60) Provisional application No. 60/104,490, filed on Oct. 16, 1998.

(51) Int. CI.7 G01B 11/24

(52) U.S. CI 356/601

(58) Field of Search 356/601-609,

356/237.1-237.5; 250/559.22, 559.4

Full surface maps of slope and height are determined for the surface of a highly smooth surface such as a silicon wafer, by an apparatus which includes a light source for creating a light beam and scanning and wafer transport systems which cause the incident beam to be scanned over the full surface of the wafer. A quad cell light detector is positioned to receive the beam specularly reflected from the wafer surface, the quad cell detector having four cells arranged in quadrants with each cell providing an electrical signal indicative of the amount of light received by the cell. A processor is programmed to calculate changes in spot location on the detector based on the signals from the cells, and to calculate changes in surface slopes based on the changes in spot location. Full maps of X- and Y-slope are produced, and a line integration algorithm is used for calculating full surface height maps. Regions of surface height gradient exceeding a threshold are flagged as defects by the processor.

18 Claims, 8 Drawing Sheets