Edge finding in wafers
First Claim
1. A method of locating the peripheral flat edge of a wafer comprising,(a) placing a wafer onto a wafer chuck rotatable about an axis,(b) spinning said wafer about said axis for one 360 degree rotation,(c) determining the orientation of said chuck with respect to an initial orientation,(d) sampling the position of said edge of said wafer for a plurality of chuck orientations to obtain a set of data points, each data point consisting of an orientation angle and a corresponding edge position,(e) fitting a cosine curve to said set of data points,(f) subtracting said cosine curve at each of said orientation angles from said corresponding edge positions to obtain a second set of points representing the deviation of said data points from said cosine curve, and(g) finding the angle of maximum deviation of said data points from said cosine curve, said angle being an estimate of a flat edge angle indicating the location of said flat edge of said wafer with respect to said axis of rotation.
1 Assignment
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Accused Products
Abstract
A system for finding the orientation of a substantially circular disk shaped wafer with at least one flat region on an edge thereof, in which the wafer is spun one 360 degree turn on a chuck and the edge position is measured by a linear array to obtain a set of data points at various wafer orientations. The rotation axis may differ from the wafer center by an unknown eccentricity. The flat angle is found by fitting a cosine curve to the data, subtracting the expected data derived from the cosine curve from the actual data to obtain a deviation. The angle of maximum deviation of the data from the cosine curve is a first estimate of the flat angle. The estimate may be corrected for errors due to a finite number of data points and wafer eccentricity by calculating an adjustment angle from data points on the wafer flat. After determining the flat angle, the wafer is spun to the desired orientation. The wafer eccentricity may be calculated from four of the data points located away from the flat edge region, and the wafer is then centered.
60 Citations
15 Claims
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1. A method of locating the peripheral flat edge of a wafer comprising,
(a) placing a wafer onto a wafer chuck rotatable about an axis, (b) spinning said wafer about said axis for one 360 degree rotation, (c) determining the orientation of said chuck with respect to an initial orientation, (d) sampling the position of said edge of said wafer for a plurality of chuck orientations to obtain a set of data points, each data point consisting of an orientation angle and a corresponding edge position, (e) fitting a cosine curve to said set of data points, (f) subtracting said cosine curve at each of said orientation angles from said corresponding edge positions to obtain a second set of points representing the deviation of said data points from said cosine curve, and (g) finding the angle of maximum deviation of said data points from said cosine curve, said angle being an estimate of a flat edge angle indicating the location of said flat edge of said wafer with respect to said axis of rotation.
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8. A method of locating the peripheral flat edge of a wafer comprising,
(a) placing a wafer onto a wafer chuck rotatable about a rotation axis, (b) spinning said wafer about said axis for one 360 degree rotation, (c) determining the orientation of said chuck with respect to an initial orientation, (d) sampling the position of said edge of said wafer relative to said rotation axis for a plurality of chuck orientations to obtain a set of N data points, each data point i consisting of an orientation angle θ -
i and a corresponding edge position Pi,
(e) calculating from said set of data points a mean r, and cosine and sine components, e cos φ and
e sin φ
respectively, of a cosine curve representing expected values Pi of said data points,(f) subtracting said expected Pi at each of said orientation angles θ
i from said corresponding edge positions Pi to obtain a second set of points Δ
i representing the deviation of said data points from said cosine curve, and(g) finding an orientation θ
j such that Δ
j is the minimum in the second set of points, said angle θ
j being an estimate of a flat edge angle indicating the location of the flat edge of said wafer with respect to said rotation axis. - View Dependent Claims (9, 10, 11, 12)
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i and a corresponding edge position Pi,
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13. A wafer orientation determining apparatus comprising,
a wafer chuck for engaging a wafer, said chuck being rotatable about an axis, means for rotating said chuck, means for determining the orientation of said chuck with respect to an initial orientation and producing a first electrical signal representing an orientation angle of said chuck, means for detecting the position of an edge of said wafer with respect to said axis and producing a second electrical signal representing said wafer edge position, means in electrical communication to receive said first and second electrical signals for producing a plurality of data points therefrom for a plurality of chuck orientations, each data point consisting of an orientation angle and a corresponding edge position, said sampling means producing data signals representing said data points, and computer means connected to said sampling means to operatively receive said data signals for: -
(a) fitting a cosine curve to said data points, (b) subtracting said cosine curve at each of said orientation angles from said corresponding edge position to obtain a deviation, and (c) determining the orientation angle where said deviation is greatest, said angle representing the location of flat edge of said wafer with respect to said axis of rotation. - View Dependent Claims (14, 15)
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Specification