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Mask to Wafer Alignment

IP.com Disclosure Number: IPCOM000086902D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Wetz, H: AUTHOR

Abstract

A wafer (substrate) cannot be aligned to a mask at mu m accuracy without special auxiliary means. In photolithographic processes such alignment problems are frequently encountered. Particularly troublesome are the preparation and the alignment of the first mask pattern, since the fiducial points necessary for the subsequent steps are applied in the first mask step. Therefore, it is desirable to facilitate the first alignment process.

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Mask to Wafer Alignment

A wafer (substrate) cannot be aligned to a mask at mu m accuracy without special auxiliary means. In photolithographic processes such alignment problems are frequently encountered. Particularly troublesome are the preparation and the alignment of the first mask pattern, since the fiducial points necessary for the subsequent steps are applied in the first mask step. Therefore, it is desirable to facilitate the first alignment process.

For this purpose stops in the form of edges or points, which are accurately dimensioned in relation to the pattern, are provided on the mask. The substrates to be exposed are guided towards these stops, and thus positioned.

The drawing shows the wafer/substrate held by conventional means, for example, a chuck. The wafer/substrate is moved from below by suitable manipulators (not shown) towards mask 2 held in mask holder 1. Mask 2 is, for example, a conventional glass or metal mask with a pattern, designated 3. It is essential that accurately dimensioned stops 4, in the form of edges, faces or points, are directly provided on the mask. Such stops are connected (for example, glued) to the mask and can be made of glass, plastics, metal, etc. It is particularly advantageous to use stop 4 with commercially available compressed- air pilot tubes 5, permitting an accurately adjustable distance control. This is because of the contact-free alignment of the substrate and the low sensitivity to small irregularities (e.g.,...