United States of America As Represented by the Secretary of the Air Force

Millard G Mier

David C Look

Dennis C Walters

John R Sizelove

James S Sewell

Scott C Dudley

A method for nondestructively measuring dislocation density in a GaAs wafer is disclosed in which an unetched GaAs wafer is tested for fractional transmission (T) of light at a plurality of points over its surface. A light beam from a suitable source such as a tungsten-halogen lamp is passed through a monochromator and focused by a lens on the wafer. The fractional transmission (T) of light through the wafer is detected and the absorption coefficient (.alpha.) is calculated at each of the points from the detected values of the fractional transmission. Regions of dislocation density in the wafer are determined nondestructively from the absorption data by dividing the values of .alpha. into equal segments bounded by the minimum and the maximum calculated values. A histogram is plotted of the number of values of .alpha. in each segment versus the value of .alpha. at the midpoint of the segment. A reference .alpha. point is selected from the histogram coinciding with the point approximately at which the first minimum value of .alpha. occurs following the first maximum value of .alpha.. A map of the coordinate positions of all the values of .alpha. that are less than or equal to the reference .alpha. has been found to correspond substantially identically to the regions of dislocation density in the wafer as confirmed later by measurements on an etched wafer. The regions of dislocation density become readily discernible and are in marked contrast to the undislocated regions when the .alpha. is calculated from the fractional transmission at a wavelength (.lambda.) of 0.90.+-.0.03 .mu.m.

Method for nondestructive measurement of dislocation density in GaAs

A method and system for measuring whole-wafer etch pit density (.rho..sub.D) is disclosed in which an etch GaAs wafer is tested for fractional transmission at a plurality of points over its surface. The fractional transmission (T) of light through the wafer is detected, amplified and fed to a computer where at least two points of transmission measurement are selected for calibration. From these measurements, together with an estimate of the average etch pit size (area), the values for fractional transmission in regions of low etch pit density T.sub.O and high etch pit density T.sub.E may be calculated, and used to convert transmission data directly to etch pit density (.rho..sub.D) according to the equation ##EQU1##

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Yellow Springs, OH, United States of America

Millard G Mier