Phase-sensitive interferometric mask-wafer alignment

Details Phase-sensitive interferometric mask-wafer alignment Phase-sensitive interferometric mask-wafer alignment

1988-06-17

1990-01-23

Willis, Davis L.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356363, G01B 902

Patent

active

048954470

ABSTRACT:
In an alignment method for lithographic devices of the proximity printing type two light beams (9a,d;9b,c) are made to impinge symmetrically on gratings (3) associated to each alignment direction on mask (1) and wafer (2) such that diffracted beams return along the optical axis of the alignment system. The relative phase of the diffracted beams is measured with a phase compensation technique using an electro-optic modulator (15). The alignment method is performed in two steps, the first being a normalizing step where a smooth portion of the wafer is brought under the alignment grating in the fixed mask (2) and a measuring step yielding the phase difference as a position control signal when the alignment grating on the wafer has been brought under the alignment grating of the mask. The four partial beams required for alignment in two orthogonal directions are generated from a single laser beam (15) in a compact set (14) of birefringent crystals or Wollaston plates and half-wave retarders.

REFERENCES:
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Makosch, G. et al., "Phase-Locked Interferometry for Automatic Mask Alignment in Projection Printers", "Applied Optics", vol. 26, No. 14, Jul. 15, 1987, pp. 2823-2835.
Makosch G. et al., "Interferometric Method for Checking the Mask Alignment Precision in the Lithographic Process", "Applied Optics", vol. 23, No. 4, Feb. 15, 1984, pp. 628-632.
Itoh, J. et al., "A New Interferometeric Displacement-Detection Method for Mask to Wafer . . .", Jap. Journ. of Appl. Phys., vol. 25, No. 6, Jun. 1986, pp. L487-L489.
Makosch, G. et al., "Surface Profiling by Electro-Optical Phase Measurements", Spie, vol. 316 High Resolution Soft X-Ray Optics (1981), pp. 42-53.
Une, A. et al., "A Highly Accurate Alignment Technique Using a Dual Grating", Bull. Japan Soc. of Prec. Eng., vol. 19, No. 1 (Mar. 1985), pp. 71-72.

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