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Four Field Stitching without Center Registration Marks

IP.com Disclosure Number: IPCOM000040897D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Ho, CT: AUTHOR

Abstract

Four deflection fields in an electron beam wafer writer can be stitched without using a center registration mark on the semiconductor chip being processed. A relatively large number of registration marks, which are needed to achieve the required overlay, may be scanned using this method with only a slight increase in the number of table (stage) moves.

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Four Field Stitching without Center Registration Marks

Four deflection fields in an electron beam wafer writer can be stitched without using a center registration mark on the semiconductor chip being processed. A relatively large number of registration marks, which are needed to achieve the required overlay, may be scanned using this method with only a slight increase in the number of table (stage) moves.

In processing semiconductor devices registration marks in the center of chips are undesirable because they add to the complexity of the design. When it is necessary to expose wafers with chip sizes greater than the deflection field of an E-beam wafer writer, one approach is to stitch together four smaller fields to cover the area to be exposed. With registration marks available in each of the four quadrants accurate stitching may be achieved. The object is to determine where the center registration mark would be if it had existed and to use that theoretical point to stitch the four fields together.

In the present method a six-point registration is performed prior to wafer writing. The figure shows four fields I-IV to be stitched. The three registration marks 1 in field I are scanned first. The table is then moved to the diagonally opposite field III and its three registration marks 2 are scanned. With these six registration marks located the center point 3 on diagonal 4 can be determined to a high degree of accuracy by linear interpolation. Once the center has b...