| 摘要 |
PURPOSE:To measure the gap dimension between two bodies by converting the diffracted lights, which have been produced at the diffraction grating of the first body and the reflecting plane of the corresponding second body, to a gap detecting signal. CONSTITUTION:A linearly-polarized coherent light, emitted from a laser light source, is incident upon a diffraction grating mark 24 for gap detection, and splits into three components: the diffracted and reflected lights, 1, 1' at the back surface of the mark 24 in the symmetrical directions about the incident light; the lights 2, 2' reflected on the surface of the wafer 26 after having undergone diffraction and transmission; and the lights 3, 3' diffracted and transmitted at the mark 24 after having undergone transmission through the mark 24 and reflection on the surface of the wafer 26. Of these diffracted lights, the plus first-order diffraction light intensity I+1 is used as a gap detection signal, which is the superposed signal of the interference wave (a) and the envelope wave (b) produced by interference of the lights 1, 2, 3. As the maximum value (M) of the peaks (A-C) of the waves (b) and the gap dimension (Z) between the mark 24 and the wafer 26 are related in the following equation: M=lambdaZ/P<2>, Z can be derived from M. |
