A new technique for detecting with high accuracy the position of alignment patterns on both the wafer and the photomask has been developed. The technique which could be applied in an automatic projection mask aligner for LSI fabrication.
Interference fringes, which are caused by monochromatic illumination (g-line) on the surface of the photoresist layer coated over the alignment pattern on the wafer, are projected against a moving slit through the projection lens. The detected signal is generated by the slit movement on the magnified image of the alignment pattern on the wafer.
In order to detect the center of the interference fringes, which is considered to be coincident with the center of the alignment pattern on the wafer, a pattern matching method is applied on the detected signal. The detecting resolution is 0.04μm and the detecting repeatability is 0.074μ (3σ). The accuracy of detecting the relative displacement between the alignment pattern on the wafer and that on the photomask is 0.19μm (3σ).
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