Cofocal optical system for thickness measurements of patterned w

Details Cofocal optical system for thickness measurements of patterned w Cofocal optical system for thickness measurements of patterned w

1993-10-12

1995-07-25

Rosenberger, Richard A.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356381, 356382, G01B 1102

Patent

active

054367255

ABSTRACT:
An optical system for providing low and high resolution images of a patterned wafer to provide for film thickness measurements thereof. The optical system comprises a spectrally filtered light source for providing light to illuminate the wafer. A low resolution imaging system is provided for imaging the wafer at a relatively low resolution. A high resolution imaging system is provided for imaging a subarea of the wafer at a relatively high resolution to create an enlarged image in the same object plane as the wafer. An image producing system is provided for producing a visual image of the wafer derived from the low and high resolution images. The high resolution imaging system uses subaperture optical elements, comprising either a small scanning lens or a sparse array of lenses, to image small areas of the wafer at higher resolution, and the subaperture optical elements create an enlarged image in the same object plane as the actual wafer. Both areas are then imaged onto the image producing system such as a CCD array of a CCD camera, by the low resolution imaging system (a lens or reflector) to provide a common or cofocal feature of the present invention. This arrangement avoids frequent refocussing to make thickness measurements on different parts of the wafer. The present invention allows the determination of thin film thicknesses of patterned wafers, planar wafers, and silicon-on-insulator (SOI) wafers, even though the spatial frequencies of the patterns are radically different in all these cases. The present invention provides the ability to make thickness maps of magnified regions within a semiconductor chip as well as test pads located in scribe alleys thereon. The use of high resolution multispectral subimages significantly increases the speed at which thickness maps of these patterned regions are generated. The invention may also be used to measure the that also allows determination of position and orientation of the wafer since the wafer edges are in focus.

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