Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Traffic analysis or control of aircraft
Reexamination Certificate
1999-05-27
2001-08-14
Shah, Kamini (Department: 2857)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Traffic analysis or control of aircraft
C702S159000
Reexamination Certificate
active
06275770
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the measurement of semiconductor wafers and, more specifically, to a pattern recognition methodology implemented in a semiconductor wafer measurement station for removing station induced error from measured object characteristics.
2. Background of the Invention
During the many phases of the integrated circuit fabrication process, it is useful to know the surface characteristics of the semiconductor wafers, especially the bow and warp of the wafers. One of the most difficult aspect of the measurement is the separation of the station or fixture-induced errors from the measurement data. As disclosed in U.S. Pat. No. 4,750,141 (Judell et al.), fixture-induced errors can be removed by performing Fourier Transform on the measurements of a wafers at different orientations. The major disadvantages of the measurement method as disclosed in Judell et al are as follows:
1. Even with the use of the Fast Fourier-Transform (FFT) technique, FT is, nonetheless, a procedure that requires either computing trigonometric functions for each act of the calculation of the FT, or storing the computed Fourier basis in the memory, resulting in a larger flop count or larger memory requirements.
2. The noise reduction through computing a weighted average of two solutions requires taking additional measurement of the rotated wafer, and.
3. It does not provide means to compensate for the tilt that may occur because the wafer surface touching the chuck is not flat.
It is, therefore, desirable to provide a method for measuring the surface characteristics of a semiconductor wafer and removing the fixture, or station-induced errors from the measurement without using the Fourier-Transform methodology and taking additional measurement of the rotated wafer for noise reduction.
SUMMARY OF THE INVENTION
The present invention provides a method of measuring the surface profile of an object to develop a surface profile map for the object's surface without station-induced errors, the method comprises the steps of:
1) providing an object having a surface whose profile is to be measured;
2) providing a measurement device having an object holder, a first distance sensor and a second distance sensor spaced apart from the first distance sensor by a known distance;
3) holding the object with the object holder in a first orientation with respect to the object holder;
4) disposing the object in the first orientation with respect to the object holder between the first and second distance sensors so that the object's surface is facing the first distance sensor;
5) measuring the distance between the first distance sensor and the object's surface in the first orientation with respect to the object holder for a plurality of points over the object's surface in a first coordinate pattern of known orientation with respect to the object holder to obtain a first matrix of measurement points;
6) rotating the object about a first axis which is substantially normal to the object's surface so as to hold the object with the object holder in a second orientation with respect to the object holder, wherein said rotation is represented by a rotation matrix;
7) disposing the object in the second orientation with respect to the object holder between the first and second distance sensors so that the object's surface is facing the first distance sensor;
8) measuring the distance between the first distance sensor and the object's surface in the second orientation with respect to the object holder for a plurality of points over the object's surface in second coordinate pattern of known orientation with respect to the object holder to obtain a second matrix of measurement points;
9) obtaining a difference matrix by subtracting the first matrix from the second matrix;
10) removing the rotation matrix by applying an inverse matrix to the difference matrix, wherein the inverse matrix is the inverse of difference between the rotation matrix and an identity matrix;
11) flipping the object about a second axis which is substantially perpendicular to the first axis so as to hold the object with the object holder in a third orientation with respect to the object holder;
12) disposing the object in the third orientation with respect to the object holder between the first and second distance sensors so that object's surface is facing the second distance sensor;
13) measuring the distance between the second distance sensor and the object's surface in the third orientation with respect to the object holder for a plurality of points over the object's surface in third coordinate pattern of known orientation with respect to the object holder to obtain a third matrix of measurement points; and
14) obtaining the surface map of the object's surface by applying selected measurement points of the third matrix to the difference matrix as processed in step 10.
The present invention will become apparent upon reading the drawings and the accompanying description.
REFERENCES:
patent: 4748335 (1988-05-01), Lindow et al.
patent: 4750141 (1988-06-01), Judell et al.
patent: 4805123 (1989-02-01), Specht et al.
patent: 4860229 (1989-08-01), Abbe et al.
patent: 4931962 (1990-06-01), Palleiko
patent: 5481483 (1996-01-01), Ebenstein
patent: 5546179 (1996-08-01), Cheng
patent: 5642298 (1997-06-01), Mallory et al.
patent: 5864394 (1999-01-01), Jordon, III et al.
patent: 09260252 (1997-03-01), None
IPEC PrecisionAcuflat Wafer Thickness Mapper User Manualrev. Oct. 21, 1997.
Standard Test Method for Measuring Flatness, Thickness, and Thickness Variation on Silicon Wafers by Automated Noncontact Scanning, ASTM Designation F 1530-94, 1994, pp. 610-615.
IPEC Precision Inc.
Miller Craig
Shah Kamini
Snell & Wilmer L.L.P.
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