The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 30, 1996
Filed:
Mar. 06, 1995
David C Look, Dayton, OH (US);
Millard G Mier, Yellow Springs, OH (US);
John R Sizelove, Dayton, OH (US);
Dennis C Walters, Fairborn, OH (US);
Abstract
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.