Browse Prior Art Database

Laser-Scanning Exposure System With Active Focus Control

IP.com Disclosure Number: IPCOM000041565D
Original Publication Date: 1984-Feb-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR

Abstract

The small depth-of-focus in laser-scanning systems for photolithographic exposure with very high resolution is overcome by an active focus control allowing a rapid change of the focal plane in accordance with height data stored as design parameters for the pattern to be generated. High-precision laser scanners with ultraviolet light have lateral resolutions of the order of 1 micron and a depth-of-focus of the same order. During the manufacture of integrated circuits, height steps of this order are generated in the patterns (e.g., by etching), even if the wafer as a whole is perfectly flat. Conventional autofocus feedback loops are too slow to compensate for such height steps which generally extend only over short distances.

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Laser-Scanning Exposure System With Active Focus Control

The small depth-of-focus in laser-scanning systems for photolithographic exposure with very high resolution is overcome by an active focus control allowing a rapid change of the focal plane in accordance with height data stored as design parameters for the pattern to be generated. High-precision laser scanners with ultraviolet light have lateral resolutions of the order of 1 micron and a depth-of-focus of the same order. During the manufacture of integrated circuits, height steps of this order are generated in the patterns (e.g., by etching), even if the wafer as a whole is perfectly flat. Conventional autofocus feedback loops are too slow to compensate for such height steps which generally extend only over short distances. Therefore, it is proposed to provide a laser scanner with a fast active focus control, the input of which are the design data on the height of the individual points in the pattern. This height profile depends on the circuit structure in the local environment of the respective location and on the respective step of the manufacturing process, so that it can be calculated from the design data. In Fig. 1, the beam 2 of laser 1 passes an electronic shutter 3 and is filtered by a mode filter 5 onto which it is focussed by a lens 4. The diverging beam then traverses an autofocus device 6 which compensates for slowly varying height changes of the wafer in a conventional feedback loop. A second autofocus arrangement 7 corrects the rapidly changing height variations inherent in the circuit structure to be generated. A collimating lens 8 then directs the beam to a scanning u...