Method and apparatus for finding wafer index marks and centers
AssigneeAnn F. Koo
InventorDavid Cheng
Life of this patent
Estimating the term…
Abstract
A method and apparatus for finding wafer index marks and centers. A wafer having a flat or notch along its edge is placed on a rotatable platform so that a portion of the wafer's edge is positioned within a sensor assembly. The wafer is rotated, and the sensor reads the distance from the center of rotation to the edge of the wafer. This distance is measured at several angles of the wafer and the data is stored in a digital computer as a series of datapoints including an angle and a distance. A computer-implemented process calculates various geometries concerning the wafer including the location of the index mark and the center of the wafer.
Claims20
A method for finding an index mark on a wafer edge comprising steps of:
- (a) positioning a wafer having an index mark along an edge thereof on a rotatable platform;
- (b) rotating the platform and the wafer to a known angular position;
- (c) measuring a distance at said known angular position between an edge point of said wafer and a reference point to develop a datapoint comprising an angle of said known angular position and said distance;
- (d) repeating steps (b) and (c) to develop a series of datapoints;
- and
- (e) calculating a derivative of said series of datapoints;
- (f) finding a deviation in said derivative which corresponds to said index mark and performing deviation analysis on datapoints in said deviation to find an angular position of said index mark, wherein said angular position is a center of said index mark, and wherein said step of performing said deviation analysis includes calculating a least square line fit between maximum and minimum points of said deviation of said derivative;
- and
- (g) orienting and removing said wafer from said rotatable platform without translating said platform.
A wafer index mark and center finder comprising:
- a turntable operative to support and rotate a wafer around a center of rotation;
- a sensor device positioned such that an edge point of said wafer positioned on said turntable can be sensed by said sensor device, said sensor device being operative to measure a distance from said edge of said wafer to a known reference point;
- means for storing a plurality of datapoints, each of said plurality of datapoints including said measured distance and an angle of rotation at which said distance was measured, said plurality of datapoints being used to calculate a center of said wafer;
- means for calculating a derivative of said plurality of datapoints, where said derivative is used to find a position of an index mark of said wafer by finding a deviation in said derivative and performing deviation analysis on said derivative;
- and
- means for orienting said wafer and removing said wafer from said turntable without translating said turntable.
A method for finding a center point of a wafer comprising steps of:
- measuring a distance between a plurality of edge points of said wafer and a reference point to develop a plurality of datapoints comprising an angle and a distance;
- determining a first set of datapoints of said plurality of datapoints which describe all index marks positioned on the edge of said wafer by calculating a derivative of said datapoints;
- and
- calculating said center point of said wafer using a second set of datapoints of said plurality of datapoints which do not describe said index marks.
A method for finding an index mark on a wafer edge comprising steps of:
- (a) positioning a wafer having an index mark along an edge thereof on a rotatable platform;
- (b) rotating the platform and the wafer to a known angular position;
- (c) measuring a distance at said known angular position between an edge point of said wafer and a reference point to develop a datapoint comprising an angle of said known angular position and said distance;
- (d) repeating steps (b) and (c) to develop a series of datapoints;
- and
- (e) calculating a derivative of said series of datapoints;
- (f) finding a deviation in said derivative which corresponds to said index mark and performing deviation analysis on datapoints in said deviation to find an angular position of said index mark, wherein said step of performing deviation analysis includes determining if said index mark in said wafer is a flat or a notch, wherein said index mark is determined to be a notch when said datapoints in said deviation are under a threshold percentage of said plurality of datapoints;
- and
- (g) orienting and removing said wafer from said rotatable platform without translating said platform.
Dependencies are inferred from the claim text.