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Dynamic Focusing Technique for Photolithographic Tools

IP.com Disclosure Number: IPCOM000059703D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Latta, MR: AUTHOR [+2]

Abstract

All current techniques for focus optimization of photolithographic tools depend upon the use of the tool, the exposure and development of a suitable pattern onto a photoresist-coated wafer and the subsequent reading of this patterned wafer. Focus information is then entered into the tool microprocessor and adjustments made (if necessary). A new technique is now available to provide an active optical feedback system so that focus correction can be accomplished without the need for exposing, developing and reading a patterned wafer. A laser is used as the light source, preferably one which has a wavelength within the high reflectance bandpass of the mirror coatings but outside the sensitivity range of the photoresist used in the tool so that active focus monitoring and tool exposure can occur simultaneously.

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Dynamic Focusing Technique for Photolithographic Tools

All current techniques for focus optimization of photolithographic tools depend upon the use of the tool, the exposure and development of a suitable pattern onto a photoresist-coated wafer and the subsequent reading of this patterned wafer. Focus information is then entered into the tool microprocessor and adjustments made (if necessary). A new technique is now available to provide an active optical feedback system so that focus correction can be accomplished without the need for exposing, developing and reading a patterned wafer. A laser is used as the light source, preferably one which has a wavelength within the high reflectance bandpass of the mirror coatings but outside the sensitivity range of the photoresist used in the tool so that active focus monitoring and tool exposure can occur simultaneously. This input laser beam is focused to a point P1 which is conjugate to the intermediate image plane and then beam split into the system. The rays emanating from P1 then follow a reverse path to the normal direction and are focused onto the mask. After reflection from the mask, they trace the path including reflections from beam splitters BS1 and BS2 to form a point image at P2. A knife edge is located at P2 and a split-field photodetector PD1 is positioned behind that plane. Adjustment of the input focusing lens L1 will then insure that the monitor beam is properly in focus on the mask plane. The second porti...