Dark field alignment and alignment mark systems

Photocopying – Projection printing and copying cameras – Identifying – composing – or selecting

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Details

355 45, 355 53, G03B 2752, G03B 2770

Patent

active

047040270

ABSTRACT:
A dark field alignment system is provided wherein a bifurcated light source, including a secondary channel having spot sources of light located in a plane conjugate to the object plane of a reduction lens and directed through a peripheral ring of a plane conjugate to the apertgure plane of the reduction lens, illuminates the object plane of the reduction lens. Reflected and defracted light from an alignment mark of a semiconductive wafer in the image plane of the reduction lens is captured by a mirror located near the aperture plane of the reduction lens. This light is refocused to another plane conjugate to the object plane of the reduction lens and imaged onto detector arrays to provide alignment information. Also provided is an alignment mark system wherein the relative positions of alignment windows in an array of alignment windows, and alignment patterns in a corresponding array of alignment patterns are selected such that an image of an edge of each reticle alignment window illuminates a first edge of a counterpart alignment mark without illuminating any other edges of the alignment marks when the marks and windows are properly aligned.

REFERENCES:
patent: 3853398 (1974-12-01), Kano
patent: 4367046 (1983-01-01), Lacombat
patent: 4395117 (1983-07-01), Suzuki
patent: 4422755 (1983-12-01), Phillips
patent: 4452526 (1984-06-01), Johannsmeier et al.

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