Wafer/mask alignment system using diffraction gratings

Details Wafer/mask alignment system using diffraction gratings Wafer/mask alignment system using diffraction gratings

1983-12-19

1986-12-23

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250237G, 356356, 356400, G01B 902, G01B 1127

Patent

active

046314164

ABSTRACT:
An alignment method in which light is diffracted from a mask grating to a wafer grating and back through the mask grating to produce a set of output diffraction orders. The intensity of the zeroth output order is monitored and the mask is translated and rotated within the plane containing the mask to align the mask with the wafer. Alignment occurs when the intensity of the zeroth output order is at an extremum. The distance between the mask and wafer is also adjusted to extremize the intensity of the zeroth output order to make the wafer lie within the focal plane of the exposure optics. The wafer mask is preferrably a holographic phase grating to simplify production of the grating and to eliminate resist related interference. Two dimensional gratings can be used to achieve alignment with only one grating on each wafer.

REFERENCES:
patent: 4200395 (1980-04-01), Smith et al.
patent: 4211489 (1980-07-01), Kleinknecht et al.
patent: 4265542 (1981-05-01), Snow
patent: 4332473 (1982-06-01), Ono
patent: 4340305 (1982-07-01), Smith et al.

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