Determination of best focus for step and repeat projection align

Details Determination of best focus for step and repeat projection align Determination of best focus for step and repeat projection align

1986-11-10

1988-07-26

Wan, Gene

Optics: measuring and testing

Lens or reflective image former testing

For optical transfer function

356125, G01B 900

Patent

active

047596260

ABSTRACT:
A reticle design is provided for step and repeat projection aligners which, when patterned on a wafer (10), allows quick macroscopic evaluation of best focus for used in fabricating integrated circuits. The reticle pattern consists of opaque lines and spaces of widths slightly above the resolution limit of the resist/aligner system. The macroscopic determination of best focus, being macroscopically visible, eliminates the need for microscopic determination, thereby providing a quick and easy method. The best focus determination is made by forming an array (22) of resist fields (14') on the wafer, subjecting each field to a different focus and exposure. Upon development, those fields away from the best focus and at the larger exposure doses will be removed, leaving a parabola (24) of fields whose apex (26) is at high exposure. Best focus is the focus setting used to print the row of fields (B) containing the apex. The procedure may be used at different lens locations and reticle orientations to quantify lens aberrations and field tilt. The method of the invention is also suitably used to qualitatively and quantitatively diagnose and characterize the lens, by printing full fields (34) with varying focus. In this manner, lens astigmatism and curvature and field tilt can be mapped, measured, and understood.

REFERENCES:
patent: 4585342 (1986-04-01), Lin et al.

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