US 4,302,721 AGranted

Non-contacting resistivity instrument with structurally related conductance and distance measuring transducers

AssigneeTencor Instruments

InventorsKarel Urbanek, George J. Kren, William R. Wheeler

Life of this patent

Estimating the term…

Loading patent…

Abstract

An instrument for computing resistivity based upon measurements of thickness and conductance. A conductance transducer is a solenoid in an annular ferrite cup connected to a tank circuit for an eddy current measurement of conductance. Within the center of the annular ferrite cup concentric acoustic wave sending and receiving channels are disposed for making an acoustic pressure wave measurement which is used for a thickness measurement using two gauge heads, spaced on opposite sides of an article to be measured. Each gauge head contains identical conductance and thickness transducers. The thickness measurement is divided by the conductance measurement to derive resistivity.

Claims29

Dependent claims

A non-contacting resistivity gauge for magnetically susceptible sheet material comprising,

first and second gauge heads mutually spaced a distance relative to the opposite sides of a magnetically susceptible sheet material whose resistivity is to be measured, each gauge head having acoustic pressure means including a speaker and a microphone disposed in the portion of the gauge head facing the sheet material and having an acoustic pressure communication zone therebetween for producing a first electrical signal, the first electrical signals from the first and second gauge heads electrically combined to be representative of the thickness of said sheet material, each gauge head further having solenoid means generating an axial magnetic field zone which is generally perpendicular to said sheet material and in magnetic induction relation therewith for producing a second electrical signal, the second electrical signals from the first and second gauge heads electrically combined to be representative of the conductance of said sheet material, said solenoid means surrounding at least a portion of said acoustic pressure means, with said acoustic pressure communication zone coinciding with the axial magnetic field zone, such that the areas over which said conductivity and thickness measurements are made are the same, and
electrical circuit means for combining said first and second electrical signals yielding a third electrical signal representative of resistivity of said sheet material.

A method for measuring resistivity of magnetically susceptible sheet-like articles, such as semiconductor wafers and the like, of unknown thickness comprising,

(i) measuring the thicknes of a magnetically susceptible sheet-like article, by the steps comprising,
(a) directing acoustic energy at opposed sides of a sheet-like article of known thickness from aligned sources on opposite sides of said article, each of said sources having a surface proximate to the article defining a gap therebetween,
(b) simultaneously detecting said acoustic energy in the gap on each side of the article and producing a pair of first electrical signals in response thereto,
(c) generating a second pair of electrical signals representing acoustic energy output from said sources,
(d) combining respective first and second electrical signals of each pair of signals with a respective reference signal in accord with a known relation to yield first and second output signals respresenting gaps on each side of said article,
(e) repeating steps (a)-(d) for a sheet-like article of unknown thickness, and
(f) adding the first and second output signals representing the gaps on each side of said article of known thickness with a signal representing the thickness of said article of known thickness and subtracting therefrom first and second output signals representing the gaps on each side of said article of unknown thickness, the remainder converted to an output signal representing the unknown thickness of said sheet-like article,
(ii) measuring the conductance of said sheet-like article by generating axial solenoidal magnetic fields generally perpendicular to the sheet material and on opposed sides of the article, the zones of the magnetic fields and the acoustic energy mutually coinciding, such that the areas over which said conductivity and thickness measurements are made are the same, and producing an electrical signal representing said conductance,
(iii) dividing said thickness signal by said conductance signal to yield a signal representing the resistivity of said sheet-like article.

6 more elements

Dependencies are inferred from the claim text.

Facts

Application: 06/039,303Filed 15 May 1979 · continuation in part
Priority: 8 May 1978
Granted: 24 Nov 1981
Term ends: Not estimatedThe source records don’t support an estimate.

Classification10 codes

G01N 27/023
By investigating impedance: where the material is placed in the field of a coil
G01R 31/2648
Testing of individual semiconductor devices: characterising semiconductor materials
G01R 31/265
Testing of individual semiconductor devices: contactless testing
G01R 31/2831
Testing of electronic circuits specially adapted for particular applications not provided for elsewhere: testing of materials or semi-finished…