Browse Prior Art Database

Spatial Frequency Filtering for Chips and Masks

IP.com Disclosure Number: IPCOM000074269D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Pennington, KS: AUTHOR [+2]

Abstract

This is a method for detection of defects in semiconductor wafers by spatial frequency filtering without the necessity of filter alignment. The method is applicable to wafer structures having periodic images. There is shown an optical system for detecting defects in wafer 10 which has a dense highly periodic image. A collimated beam is imposed upon the wafer 10 by means of an argon laser 12 which passes a beam of coherent light through pin hole 14. The front surface reflected beam is positioned so that a Fourier transform lens 16 creates a Fourier plane at surface P2 which is recorded on a spectroscopic plate 18. The plate 18 is then developed and returned to exact x, y, and theta coordinates used in the exposure or, as shown, developed in situ.

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Spatial Frequency Filtering for Chips and Masks

This is a method for detection of defects in semiconductor wafers by spatial frequency filtering without the necessity of filter alignment. The method is applicable to wafer structures having periodic images. There is shown an optical system for detecting defects in wafer 10 which has a dense highly periodic image. A collimated beam is imposed upon the wafer 10 by means of an argon laser 12 which passes a beam of coherent light through pin hole 14. The front surface reflected beam is positioned so that a Fourier transform lens 16 creates a Fourier plane at surface P2 which is recorded on a spectroscopic plate 18. The plate 18 is then developed and returned to exact x, y, and theta coordinates used in the exposure or, as shown, developed in situ.

The developed plate 18 acts as a filter for the pattern which is displayed onto an output plane 20 by means of the inverse Fourier transform lens 22. Defects appear in the output after convolution with the point spread function for the reconstructed lens.

The system enhances defects in the highly repetitive pattern on the wafer 10 by parallel optical processing. This enhancement is accomplished without prealignment. It is noted, that the performance of the system is directly proportional to the pattern repetition. The output plane is subject to visual inspection for detection of wafer defects.

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