Browse Prior Art Database

Diffuse Surface Height Measurement

IP.com Disclosure Number: IPCOM000044177D
Original Publication Date: 1984-Nov-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Strope, DH: AUTHOR

Abstract

A diffuse surface height measurement is a system for detecting defects on diffuse surfaces using a laser light source and a microscope lens light collector. This system is a technique that can be used to measure height variation on a diffuse surface. A 1 mm beam of light 11 (6328 ˜) from a 1 mw helium neon laser 12 is passed (off center) through a 10x microscope eyepiece and focused (5-mil spot) on the surface 13 under study. If the surface is mirrored (specular), all of the light will be reflected in a small beam back through the objective 14 and measured by a photodiode 15 (Fig. 1). A diffuse surface, on the other hand, will cause scattering of the laser beam. In this technique the collected radiation is reflective scattering as opposed to the more commonly used forward scattering.

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Diffuse Surface Height Measurement

A diffuse surface height measurement is a system for detecting defects on diffuse surfaces using a laser light source and a microscope lens light collector. This system is a technique that can be used to measure height variation on a diffuse surface. A 1 mm beam of light 11 (6328 ~) from a 1 mw helium neon laser 12 is passed (off center) through a 10x microscope eyepiece and focused (5-mil spot) on the surface 13 under study. If the surface is mirrored (specular), all of the light will be reflected in a small beam back through the objective 14 and measured by a photodiode 15 (Fig. 1). A diffuse surface, on the other hand, will cause scattering of the laser beam. In this technique the collected radiation is reflective scattering as opposed to the more commonly used forward scattering. The microscope objective 14 acts as the collector window for this scattered light (Fig. 2). A nearly uniform diffuse surface will produce a reference light scatter level from the photodiode. The introduction of a height variation which is smaller than the laser spot diameter will cause a dramatic change in the scattering and the resulting diode light level due to the following changes: 1. Change in distance from the collector to the test surface (beam focus). 2. Change of angle of incidence (sidewalls of defect). 3. Change in surface roughness. The sensitivity of the measurement to a given size defect can be varied by changing the spot size that is...