Ade Corporation

Jaydeep K Sinha

Christopher Gaal

Noel S Poduje

Peter A Harvey

William Drohan

Alexander Belyaev

Domenico Tortola

William Goldfarb

An apparatus for measuring semiconductor wafer shape that minimizes wafer distortion. The apparatus includes a plurality of wafer gripping fingers for holding a wafer in a predetermined position during wafer measurement. Each finger includes a groove that contacts the edge of the wafer. The groove and the wafer edge have respective radii of curvature, in which the radius of curvature of the groove is greater than that of the wafer edge. Each finger includes a rigid member having a recess formed in a central location at one end thereof, and a compliant material such as PEEK disposed in the recess in which the groove is formed. The compliant material extends a first distance beyond the rigid member at the central groove location and a second shorter distance beyond the rigid member on each side of the central location. Because the groove areas on each side of the central area are more rigid than the central groove area, the fingers can hold the wafer with a high degree of accuracy while reducing wafer distortion.

Wafer gripping fingers to minimize distortion

This method removes high frequency noise from shape data, significantly improves metrology system () performance and provides very compact representation of the shape. This model-based method for wafer shape reconstruction from data measured by a dimensional metrology system () is best accomplished using the set of Zernike polynomials (matrix L). The method is based on decomposition of the wafer shape over the complete set of the spatial function. A weighted least squares fit is used to provide the best linear estimates of the decomposition coefficients (Bnk). The method is operable with data that is not taken at regular data points and generates a reduced data field of Zernike coefficients compared to the large size of the original data field.

Specimen topography reconstruction

A ring chuck that holds a wafer with a vacuum uses a vacuum trough that contacts the entire outer edge of the wafer. The chuck has a base having a top surface equal to or slightly smaller than a water to be tested with vacuum channels in the base. The base provides the mechanism to connect the chuck to a measurement instrument and a vacuum source. An annulus of non-contaminant material that has concentric rings extending upward from its outer edge is fixed to the base top surface with the trough between the concentric rings connected to the vacuum channels. The vacuum trough holds the wafer securely to the chuck and minimizes vibrations when the wafer is rotated.

Ring chuck to hold 200 and 300 mm wafer

A method to determine the systematic error of an instrument that measures features of a semiconductor wafer includes the following sequential steps. Collecting sensor data from measurement runs on front and back surfaces of a wafer while the wafer is oriented at different angles to the instrument for each run, yielding a front data set and a back data set for each angle. Then organizing the data in each set into a wafer-fixed coordinate frame. Reflecting all back surface data about a diameter of the wafer creates a reflected back data set. Subtracting the reflected back data from the front data for each wafer angle, and dividing the result by two, yields an averaged wafer shape for each load angle. Adding the reflected back data to the front data and dividing the result by two, yields an instrument signature for each load angle. The symmetric corrector is calculated by taking the average over all instrument signatures at each load angle. The symmetric corrector is successively rotated to the same angle as a front shape measurement and subtracted, yielding a calibrated wafer data set. A wafer mean is computed by averaging these calibrated wafer shape measurements. When the wafer mean is subtracted from the individual front side corrected shape measurements, a set of shape residual maps for each load angle results. The average of the aligned residuals is the asymmetric error. The systematic error is the sum of the symmetric and asymmetric errors.

Wafer shape accuracy using symmetric and asymmetric instrument error signatures

A ring chuck that holds a wafer with a vacuum uses a vacuum trough that contacts the entire outer edge of the wafer. The chuck has a base having a top surface equal to or slightly smaller than a wafer to be tested with vacuum channels in the base. The base provides the mechanism to connect the chuck to a measurement instrument and a vacuum source. An annulus of non-contaminant material that has a plurality of concentric rings extending upward from its outer edge is fixed to the base top surface with the trough between the concentric rings connected to the vacuum channels. The vacuum trough holds the wafer securely to the chuck and minimizes vibrations when the wafer is rotated. When the plurality of concentric rings are contained within the wafer exclusion band, the print through onto the tested area is minimized. The tops of the concentric rings are minimally elevated from the top surface of the base and form a sealed volume that supports the interior portion of the wafer. The tops are also made very narrow to allow small deformations, minimize contamination of the wafer and restrict the transfer of particles between the chuck and the wafer. In addition, the narrow rings limit the number of particles already on the backside of the wafer that are forced onto the wafer. The consistent support provided by the ring chuck simplifies modeling of the chuck/wafer system under rotation, improving the ability to remove the instrument signature from measurements.

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Norwood, MA, United States of America

Jaydeep K Sinha