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Measurement of Axial Resistivity of a Crystal

IP.com Disclosure Number: IPCOM000048959D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Ghosh, HN: AUTHOR [+3]

Abstract

By applying a voltage pulse of very short duration by means of a coaxial probe to successive locations along an element of a cylindrical semiconductor crystal, the reflection coefficient can be correlated with the resistivity of the crystal to delineate the volume of the crystal from which semiconductor wafers, having the necessary resistivity, should be sliced.

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Measurement of Axial Resistivity of a Crystal

By applying a voltage pulse of very short duration by means of a coaxial probe to successive locations along an element of a cylindrical semiconductor crystal, the reflection coefficient can be correlated with the resistivity of the crystal to delineate the volume of the crystal from which semiconductor wafers, having the necessary resistivity, should be sliced.

The prior method of determining where in the crystalline volume to slice the wafers was to cut successive slugs and measure the resistivity of the surfaces with a four-point probe until the resistivity was within specification. The instant method facilitates the selection of the crystal volume for slicing and eliminates the need for cutting slugs until a suitable resistivity is found.

This apparatus exploints and extrapolates the TDR (Time Domain Reflectometer) technology used for finding faults in cables, wherein the absorption of the energy of a short duration pulse is an indication of the cable fault.

In the drawing, a pulse generator (not shown) produces a pulse, having a duration of 28 picoseconds or less, which is sampled by a storage oscilloscope 10 which retains a measure of its amplitude, while at the same time coupling the pulse to a coaxial probe having an outside diameter of 0.85 inch. This probe couples the pulse energy to the surface of the crystal 11 which absorbs and reflects the energy as a function of the crystal resistivity. The ratio of the...