Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-01-12
2001-06-05
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S662000
Reexamination Certificate
active
06242926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the measuring of various parameters of thin materials. More particularly, the present invention relates to a method and apparatus for moving an article relative to and between a pair of non-contact thickness measuring probes for the purpose of collecting data about the article which is moved in relation to the probes so that the thickness, bow and warp parameters of the article may be determined.
2. Description of the Prior Art
ASTM F1530 describes a standard test method for measuring flatness, thickness and thickness variations of semiconductor wafers by noncontact scanning. According to the ASTM test standard, the knowledge of flatness, thickness and thickness variations of semiconductor wafers is useful to both producer and consumer of such wafers to determine if the dimensional characteristics of a given wafer satisfy certain specified geometrical requirements.
Under the standard's test method, the above characteristics are measured by placing the wafer between two probes and measuring the distance between the surfaces of the wafer and the respective adjacent probes. More specifically, the wafer, supported by a chuck, is scanned along a prescribed pattern between both members of an opposed pair of probes to generate an array of displacement values. From knowledge of the array of displacement values, thickness, flatness and thickness variations can be determined. The method described in ASTM F1530 presumes that the wafer is held by a chuck having a face that is perpendicular to a measurement axis that is drawn between the two probes and that is ideally flat and clean.
U.S. Pat. No. 4,750,141 discloses a dual probe wafer thickness measurement gauge using capacitive sensors. The gauge uses a chuck to hold the wafer. The wafer is rotated and translated between the dual probes to develop an array of data. The gauge has a means for aligning the wafer so that the data points can be repeated whenever the wafer is turned over, as required to scan the entire wafer surface. Due to the method for holding and scanning the wafer, the wafer must be chucked in at least two non-overlapping portions of the wafer. The wafer measurements is repeated and the two maps stitched together. The repositioning of the wafer and the stitching of the maps increases the time required to characterize a wafer.
All dual probe measurement gauges experience distance dynamic range non-linearities that cause thickness errors as either or all wafer warp, wafer tilt in mount and mount distortions move the wafer nearer or farther from the probes during the scanning of the wafer between the probes. To overcome the non-linearity related errors, extensive calibration of the gauge prior to measurement is required and as well as the application of that calibration to each wafer computationally during a measurement of the wafer. The calibration and application thereof increases the time required to characterize a wafer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for measuring the thickness of semiconductor wafers.
It is another object of the present invention to provide a method and apparatus to move an article relative to and between a pair of distance measuring probes so as to reduce non-linearity related errors without the use of extensive calibrations.
It is another object of the present invention to provide a method and apparatus for measuring the thickness of semiconductor wafers with reduced non-linearity related errors without the use of extensive calibrations.
The aforementioned objects are accomplished, at least in part, by a method for moving an article relative to and between a pair of distance sensing probes of a thickness measuring apparatus which are spaced apart a known distance D, wherein a line between the probes defines a common measurement axis A
c
and wherein the apparatus has means to move the article relative to and between the pair of probes in a plane normal to the common measurement axis A
c
and to move the article relative to the probes along the common measurement axis A
c
. The method comprises the steps of: providing an article having a surface; moving the article relative to and between the pair of probes in at least one direction in the plane normal to the common measurement axis A
c
; measuring a distance a along the common measurement axis A
c
between the first probe of the pair and a point on the surface of the article nearest to the first probe that intersects the common measurement axis A
c
and measuring a distance b along the common measurement axis A
c
between the second probe and a point on the surface of the article nearest to the second probe that intersects the common measurement axis A
c
; and from the measured distance a, moving the article relative to the probes along the common measurement axis A
c
so as to minimize any difference between the measured distance a and a desired distance a
d
between the first probe and a point on the surface of the article nearest to the first probe that intersects the common measurement axis A
c
. The measured distance a, the measured distance b and the position of the article relative to the probes are recorded at predetermined time intervals to develop at least a thickness map of the article. An apparatus for carrying out the method is disclosed.
Other objects and advantages of the present invention will become apparent and the invention will be more fully understood when reference is made to the following detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4692700 (1987-09-01), Nix
patent: 4715007 (1987-12-01), Fujita et al.
patent: 4750141 (1988-06-01), Judell et al.
patent: 4860229 (1989-08-01), Abbe et al.
patent: 4910453 (1990-03-01), Abbe et al.
patent: 4920319 (1990-04-01), Viertl
patent: 4931962 (1990-06-01), Palleiko
patent: 4958129 (1990-09-01), Poduje et al.
patent: 5642298 (1997-06-01), Mallory et al.
Acuflat Wafer Thickness Mapper User Manualby IPEC Precision, Inc., dated Oct. 21, 1997.
Gardopee George J.
Gomez Alexander A.
Ledger Anthony M.
IPEC Precision Inc.
Metjahic Safet
Nguyen Vincent Q.
Snell & Wilmer L.L.P.
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