Browse Prior Art Database

Direct-Viewing Alignment Scheme for Projection Lithography

IP.com Disclosure Number: IPCOM000047966D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Lin, BJ: AUTHOR

Abstract

In a projection lithography system, wafer alignment is generally accomplished by inserting some alignment optics so that the images of the alignment marks on the mask and the wafer are superimposed through the imaging lens. This leads to complicated optical design, source of alignment errors, low resolving power, and limitation of signal-to-noise ratio. In this publication, a direct viewing scheme is proposed for a class of aligners in which the mask and the wafer can be moved together without changing their relative position. For example, one type of scanning projection aligner mounts the mask and the wafer on a surface of a scanning block, as shown in Fig. 1. Another aligner mounts the mask and the wafer at the opposite sides of the scanning block, as shown in Fig. 2. They are both suitable for direct viewing alignment.

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Direct-Viewing Alignment Scheme for Projection Lithography

In a projection lithography system, wafer alignment is generally accomplished by inserting some alignment optics so that the images of the alignment marks on the mask and the wafer are superimposed through the imaging lens. This leads to complicated optical design, source of alignment errors, low resolving power, and limitation of signal-to-noise ratio. In this publication, a direct viewing scheme is proposed for a class of aligners in which the mask and the wafer can be moved together without changing their relative position. For example, one type of scanning projection aligner mounts the mask and the wafer on a surface of a scanning block, as shown in Fig. 1. Another aligner mounts the mask and the wafer at the opposite sides of the scanning block, as shown in Fig. 2. They are both suitable for direct viewing alignment. In Figs. 1 and 2, the l+ marks are possible block alignment marks and the 2+ marks are possible locations of mask alignment marks. Four high numerical aperture (N.A.) microscopes are used. Two are used for wafer viewing, and the remaining two are used to view two fixed marks either on the mask/wafer mounting block or on the mask. A cross- hair type of centering aid is built in each microscope. These microscopes can be moved with respect to each other and can be locked rigidly after an initial calibration. To calibrate, the mask and the wafer are mechanically coarse aligned and locked in position. They are scanned to expose the wafer which is subsequently developed on the wafer-holding chuck so that the position of the developed alignment marks is unchanged with respect to the scanning block. The alignment marks on the scanning block are centered to the block alignment microscopes by moving the block to the desired position. The wafer-alignment microscopes can then be moved to the positions of the developed alignment marks and locked in place. Now, the aligner is calibrated for aligned exposure. Each wafer can be aligned to the wafer alignment microscopes without further calibration until the mask is changed....