Browse Prior Art Database

Improved Photo Alignment Using Trench Proximity

IP.com Disclosure Number: IPCOM000034951D
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Cronin, JE: AUTHOR [+3]

Abstract

Through the placement of a deep trench adjacent to wafer alignment markers, precise photo mask alignment is achieved. Typical photo alignment schemes optically align a mask to a wafer. As shown in Fig. 1, the aligner looks through the photoresist-coated wafer to see the wafer alignment aids. Different photo levels utilize different types and thickness of resist, and some techniques utilize multi-level resist (MLR) patterns. In all of these schemes, the resist is planarized over the wafer surface and over alignment aids as well, adding to the complexity of mask/wafer alignment. The inherent error introduced by looking through the various types of resist schemes to see the alignment aids can be eliminated by exposing the alignment aids.

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Improved Photo Alignment Using Trench Proximity

Through the placement of a deep trench adjacent to wafer alignment markers, precise photo mask alignment is achieved. Typical photo alignment schemes optically align a mask to a wafer. As shown in Fig. 1, the aligner looks through the photoresist-coated wafer to see the wafer alignment aids. Different photo levels utilize different types and thickness of resist, and some techniques utilize multi-level resist (MLR) patterns. In all of these schemes, the resist is planarized over the wafer surface and over alignment aids as well, adding to the complexity of mask/wafer alignment. The inherent error introduced by looking through the various types of resist schemes to see the alignment aids can be eliminated by exposing the alignment aids. By designing an over minimum size trench 10 microns wide, 10 microns long and 7 microns deep adjacent to the first set of alignment aids on a wafer, as shown in Fig. 2, any photoresist applied to the wafer tends to puddle in the trench during resist application. Local puddling pulls resist mass into the trench and leaves the wafer devoid of resist locally around the trench, exposing the alignment aids. This allows the aligner to see the alignment aids directly, without resist interference, and makes mask-to-wafer alignment easier and more accurate than the conventional method. When the wafer and mask are aligned, an image is exposed in a second alignment area that does not have trenche...