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Technique for Editing Electron Beam Backscatter Signal for Distortion

IP.com Disclosure Number: IPCOM000052517D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Ainsworth, RA: AUTHOR [+3]

Abstract

In the process for exposing patterns using electron beam lithography it is necessary to perform periodic deflection calibrations so as to eliminate field distortions and to maintain pattern writing quality. This is normally done by collecting backscatter signal information while scanning a calibrated target and then processing the information to generate deflection corrections.

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Technique for Editing Electron Beam Backscatter Signal for Distortion

In the process for exposing patterns using electron beam lithography it is necessary to perform periodic deflection calibrations so as to eliminate field distortions and to maintain pattern writing quality. This is normally done by collecting backscatter signal information while scanning a calibrated target and then processing the information to generate deflection corrections.

When the electron beam crosses a marked edge on the calibration grid, a backscatter signal excursion is caused. The average digitized data from several scans is compared to two or more clip levels. When clip level crossings are detected, their corresponding relative displacements are noted and are averaged to determine the overall center displacement of the mark from nominal.

In addition to the determination of the nominal displacement of the mark center, the hardware also includes checking techniques for reading certain abnormal signal conditions. The width of the marked signal is checked to be within tolerance limits. The number of clip level crossings is also tested for confirmation of a fixed number based on the number of clip levels used. The actual mark displacement result is also checked to be within tolerance limits. Finally, during averaging, a comparison between incoming samples and the current average of preceding scans is made in order to detect large variations which might be caused by noise. Any of these checks may indicate an abnormal signal condition and thus indicate an error for a particular mark. When an error is noted, it is encoded and included in the normal displacement result data stream as a replacement for the displacement result that would occur if the particular error condition were to go unnoticed. The encoded error occupies the same fixed length workspace as the displacement result so that it has no effect on data volume. The error codes cannot occur within the valid range of the displacement result data, and, therefore, they are always distinguishable from the data.

The editing of the data is achieved utilizing digital circuits. The function of the digital circuits is as follows: For a given window which is made up of six bidirectional scans, a digital difference signal is generated for each incoming...