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Scattered Light Feedback Detector for Automatic Wafer Alignment

IP.com Disclosure Number: IPCOM000083718D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Khoury, HA: AUTHOR

Abstract

This scattered light feedback detector uses a binocular optical system with photodetectors as the alignment datum (reference). Wafer alignment is in three directions: X, Y and theta with an accuracy of + or - 0.001 inch.

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Scattered Light Feedback Detector for Automatic Wafer Alignment

This scattered light feedback detector uses a binocular optical system with photodetectors as the alignment datum (reference). Wafer alignment is in three directions: X, Y and theta with an accuracy of + or - 0.001 inch.

Radial alignment marks are placed on the wafer at its "A" level, which are used in conjunction with two 0.002 inch diameter beams of dark field illumination, to provide a signal to the detectors when the alignment marks are in the optics field of view.

During alignment, the wafers are held by a wafer chuck, which is not discussed here. The wafer has a Vee (instead of the usual U) groove to engage the chuck fixed pin. A motor driven yoke-and-roller assembly, opposite the Vee groove, holds the wafer in the chuck and provides the theta wafer rotation during alignment. The entire assembly is mounted on a motor driven X-Y stage for coordinate alignment.

During alignment, when the target stripes fall outside of the detection optics, the wafer stage is driven in a raster scan (X and Y) until the alignment marks are detected.

Fig. 1 shows the light source 1, which illuminates the five micron etched target 2 on the wafer 3. The light is reduced to a spot through lens 4. A conical light shield 5 enables the use of the detector 6 at subdued ambient light levels. The light source 1 is at a 30 degree incidence angle and the detector 6 is aligned to the wafer surface. Detection is determined by the nonspecular light 7, which is scattered by the etched alignment target 2. Two sets of light sources 1 and detectors 6 form respective detector assemblies 15 and 16.

The targets 2 are etched on the wafer in a prelevel A pattern exposure or by laser writin...