Hughes Aircraft Company

Ipec Precision Inc.

Anthony M Ledger

George J Gardopee

Michael P Power

Alexander A Gomez

A method and apparatus for moving an article relative to and between a pair of distance sensing probes of a thickness measuring apparatus which are spaced apart a known distance D is described. In the method, the article is moved relative to and between the pair of probes in at least one direction in a plane normal to a common measurement axis A,between the probes. A distance a along the common measurement axis A,between the first probe and a point on the surface of the article nearest to the first probe of the pair that intersects the common measurement axis A,is measured. A similar distance b between the second probe and the article is measured. From the measured distance a, the article is moved relative to the probes along the common measurement axis A,so as to minimize any difference between the measured distance a and a desired distance a,along the common measurement axis A,between the first probe and a point on the surface of the article nearest to the first probe that intersects the common measurement axis. The measured distances a and b and the position of the article relative to the probes in at least one direction are recorded at predetermined time intervals to develop a thickness map of the article. In a thickness computation, all of the measured distances a for each recorded position of the article are substantially the same.

Method and apparatus for moving an article relative to and between a pair of thickness measuring probes to develop a thickness map for the article

A transparent chuck is used to force a semiconductor wafer to take a prescribed shape. Any gap which is formed between the chuck and the wafer can be imaged through the transparent chuck. An interferometer is used to illuminate the gap with a narrow band illumination to create interference fringes in the gap. The fringes can be electronically imaged to create a digital input to a computer. Merit functions corresponding to the total volume of fringes in the gap or to the summation of nearest neighbor slopes of such fringes provide a measure of the thickness of such gap.

Transparent optical chuck incorporating optical monitoring

An oblique incidence multispectral interferometric apparatus and the process of using it for measuring gross surface height errors of for measuring the total thickness of a substrate such as a semiconductor wafer or a photo mask. The instrumentation can be configured to either measure the air film between a reference flat and the substrate, or it can measure the air film on both sides of a substrate placed between reference flats. If the substrate is a flexible silicon wafer then it can be held against a known reference flat using a vacuum or other suitable means or the wafer surface can be measured from both sides in a free standing mode. In all cases the thickness map of the air space or spaces between the substrate surface or surfaces and a corresponding calibrated reference surface is measured using multispectral pattern matching.

Substrate thickness measurement using oblique incidence multispectral

Systems for making thickness measurements in a thin film structure using an incoherently or coherently coupled structured surface. A system is used to measure the thickness of a thin film layer of a thin film structure in which polished and structured surfaces are coherently coupled together. Visible light used to measure the thickness of thin bonded wafers that have a ground upper surface, or infrared light is used to measure the thickness of thick silicon wafers where one surface is ground, and the other is polished. Other systems use a structured surface that is incoherently coupled to a thin film structure in order to illuminate the thin film structure at many angles. The systems produce interference fringes that are detected and recorded, and multispectral pattern matching is used in a computer to compute film thickness based on scattering characteristics included in a library f stored interference patterns.

Film thickness measurement of structures containing a scattering surface

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.

Cofocal optical system for thickness measurements of patterned wafers

The thickness of the entire surface of a thick semiconductor (94) layer on an insulator is determined all at once by dividing the surface into a plurality of pixels, by varying the length of a variable length optical path (110) in a Michelson interferometer (66) having an infrared source (62), illuminating the entire surface of the layer with an image of the IR source during the length variation operation, and by detecting (64) the product of the intensity (I.sub.s (z)) from the Michelson interferometer and the reflectivity R(t) of the layer as the path length is varied, such being indicative of the thickness of the layer, and by determining, for each pixel, which one of a plurality of groups of stored reflectance values, for a corresponding plurality of thicknesses, best matches the detected values, thereby providing a thickness map of the semiconductor layer.

Apparatus and method for thick wafer measurement

A measurement instrument which detects the thickness of the outer layer of a wafer 24, includes a filtered white light source forming an aperture image. The white light source includes a halogen lamp 10, a condensing lens 12, a circular aperture 14, a collimator lens 16, a narrow band filter wheel 18, and a second collimator lens 20. A monochromatic beam generated by this filtered white light source illuminates the entire surface of the wafer 24 with collimated light that has passed through a third collimator lens 22. The light reflected off the wafer 24 returns through the third collimator lens 22 and forms an aperture image upon an optical device which redirects this image to a charge coupled device (CCD) camera 30. The image is converted to a map of measured reflectance data by a digitizing circuit 34 and a computer 36. This map of measured reflectance data is then self-normalized and compared to reference reflectance data to generate a map of the outer layer thickness profile of the wafer 24.

Apparatus and method for measuring the thickness of thin films

A measurement instrument which detects the thickness of the outer layer of a wafer 24, includes a filtered white light source forming an aperture image. The white light source includes a halogen lamp 10, a condensing lens 12, a circular aperture 14, a collimator lens 16, a narrow band filter wheel 18, and a second collimator lens 20. A monochromatic beam generated by this filtered white light source illuminates the entire surface of the wafer 24 with collimated light that has passed through a third collimator lens 22. The light reflected off the wafer 24 returns through the third collimator lens 22 and forms an aperture image upon an optical device which redirects this image to a charge coupled device (CCD) camera 30. The image is converted to a map of measured reflectance data by a digitizing circuit 34 and a computer 36. This map of measured reflectance data is then compared to reference reflectance data to generate a map of the outer layer thickness profile of the wafer 24.

Apparatus and method for interferometrically measuring the thickness of

An apparatus (1) that measures the thickness of a thin film layer of a wafer (24), includes a filtered white light source that forms a monochromatic light beam. The white light source includes a halogen lamp (10), a condensing lens (12), a circular aperture (14), a collimator lens (16), a narrow band filter wheel (18), and a second collimator lens (20). The monochromatic light beam generated by this filtered white light source illuminates an entire surface of the wafer (24). Prior to illumination, the wafer (24) is deformed into a reflective condenser. Thus, the monochromatic light beam that illuminates the wafer (24) is reflected off the wafer (24) and collected by an optical scheme that redirects the beam to a detector array (31) of a charge coupled device (CCD) camera (30). The monochromatic light beam incident upon the CCD camera detector array (31) contains an image of an interference fringe pattern that is formed by coherent interactions in the monochromatic light beam as it is reflected within the wafer structure (24). The interference fringe pattern image is displayed on the CCD camera detector array (31) and captured by the CCD camera (30). The captured image is then converted to a map of measured reflectance data by a digitizing circuit (34) and a computer (36). This map of measured reflectance data is then compared to reference reflectance data to generate a map of the thin film layer thickness over a full aperture of the wafer (24).

Apparatus and method for performing thin film layer thickness metrology

An apparatus (1) that measures the thickness of a thin film layer of a wafer (24), includes an extended light source that forms a diffuse polychromatic light beam. The extended light source includes a halogen lamp (10), a fiber optic light guide (12), a ground glass screen (19), and a condenser lens (16). The diffuse polychromatic light beam generated by this extended light source illuminates an entire surface of the wafer (24). The diffuse polychromatic light beam is reflected off the wafer (24) and passed through a spatial filter (26, 28) and a spectral filter (37, 38) so as to form a monochromatic light beam that is projected onto a detector array (31) of a charge coupled device (CCD) camera (30). The monochromatic light beam displays an interference fringe pattern image on the CCD camera detector array (31) which is the result of coherent interactions in the diffuse polychromatic light beam as it is reflected within the wafer structure (24). The interference fringe pattern image displayed on the CCD camera detector array (31) is captured by the CCD camera (30). The captured image is then converted to a map of measured reflectance data by a digitizing circuit (34) and a computer (36). This map of measured reflectance data is then compared to reference reflectance data to generate a map of the thin film layer thickness over a full aperture of the wafer (24).

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New Fairfield, CT, United States of America

Anthony M Ledger