Mask and wafer diffraction grating alignment system wherein the

Details Mask and wafer diffraction grating alignment system wherein the Mask and wafer diffraction grating alignment system wherein the

1995-01-20

1996-09-24

Turner, Samuel A.

Optics: measuring and testing

By polarized light examination

With birefringent element

356349, 250548, G01B 902

Patent

active

055596010

ABSTRACT:
The present invention provides a grating-grating interferometric wafer alignment system, sensor and method for microlithography. It includes: (1) an electromagnetic radiation source with collimating optics delivering a collimated beam of a coherent single or multiple discrete wavelengths or in some cases broadband electromagnetic radiation; (2) a detector of the intensity of the collimated return electromagnetic radiation; (3) x- and y-oriented independent linear gratings for the mask-mark; (3) a "checkerboard pattern" grating for the wafer-mark; and (4) software including an algorithm for determining alignment from the return electromagnetic radiation intensity measured as a function of the relative position of the wafer and mask grating, and a means such as a Fourier transform determining phase and amplitude of a known frequency component of the intensity. In one embodiment a laser diode is used and the backscatter from the mask and wafer gratings is returned to the laser diode creating a beat signal used to determine alignment of the mask and wafer. Alignment accuracy is increased and made more tolerant of processing variables such as wafer topography and coatings.

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