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

Wright State University

David C Look

Dennis C Walters

Millard G Mier

John R Sizelove

Eileen Pimentel

James S Sewell

Scott C Dudley

Philip D Mumford

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 non-destructive measurement system for producing whole wafer maps of sheet Hall concentration and Hall mobility in a GaAs wafer. The wafer need only have van der Pauw patterns available for the wafer measurements to be made. The measurement system includes an automatic test prober apparatus modified to incorporate a powerful permanent magnet providing a magnetic field to produce a Hall effect in the GaAs wafer. A parametric measurement system coupled through test probes to the van der Pauw patterns is programmed to measure sheet resistivity, Hall voltage and magnetic field strength, from which are derived values of sheet Hall concentration and mobility that are stored and mapped.

On-wafer Hall-effect measurement system

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##

Method and system for automated measurement of whole-wafer etch pit

An apparatus for measuring the average characteristics of a semiconductor wafer. The apparatus comprises four electrical contacts removably connected to the wafer at generally equidistant positions on the periphery of the wafer and a flat permanent magnet positioned, adjacent the wafer for applying a substantially uniform magnetic field to one surface of the wafer. The apparatus further comprises control apparatus, connected to each of the electrical contacts for applying current successively to each of four sets of adjacent electrical contacts and measuring the voltage across the opposing set of adjacent electrical contacts in response to each application of current and to each of two sets of opposing electrical contacts and measuring the voltage across the other set of opposing electrical contacts in response to each application of current. As a result, the average dark resistivity, the average dark carrier mobility, and the average dark carrier concentration of the wafer are determined. The apparatus may also be adapted to measure the average light characteristics of a photoconductive semiconductor wafer, wherein the apparatus further comprises a light source for directing light of substantially uniform intensity toward the other surface of the wafer, whereby the average light resistivity, the average light carrier mobility and the average light carrier concentration of the wafer are determined.

Method and apparatus for measuring average resistivity and hall-effect

A method and apparatus for measuring the characteristics of a photoconductive semiconductor wafer. The apparatus comprises a light source for directing light of substantially uniform intensity toward one surface of the wafer. The apparatus further comprises masking apparatus, interposed between the wafer and light source, for transmitting the light to the wafer in the shape of a cross formed by a pixel of light at the intersection of the cross and four paths extending outwardly from the pixel to the periphery of the wafer. The apparatus also comprises a first set of contacts for providing an electrical contact with the paths of light. The apparatus further comprises control apparatus connected to each of the contacts of the first set, for applying current successively to each of four sets of adjacent paths of light and measuring the voltage across the opposing set of adjacent paths in response to each application of current. As a result, the resistivity of a first portion of the wafer illuminated by the projection of the pixel of light through the wafer is determined. The apparatus may also comprise a magnet for applying a substantially uniform magnetic field to the other surface of the wafer. As a result, the carrier mobility and carrier concentration of the first portion of the wafer illuminated by the projection of the pixel light are determined.

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Dayton, OH, United States of America

David C Look