| 摘要 |
PURPOSE:To simultaneously control accurately an alignment control with a gap from the variation in the added intensity by including the light directly reflected and diffracted on the installing surface of the first diffraction grating of the first article and adding the intensity of the diffracted light of all degrees diffracted symmetrically to the incident light. CONSTITUTION:Only the lights of +1 and -1 order of the diffracted lights of diffraction gratings 12, 14 of a wafer 11 and a mask 13 are photoelectrically converted by converters 16, 17, and the intensities I+1, I-1 are added by an adder 18. When a signal of a pitch lambda/2 produced by the reflection on the back surface of the mask 13 is integrated, an envelope which exhibits a peak at the pitch P<2>/lambda is obtained, thereby attaining a signal of the ideal conditions of the zero reflection of the back surface. When an interval Z is regulated to the maximum peak value, it can be set to P<2>/lambda, 2P<2>/lambda,.... The maximum point is obtained with the signal (a) having a peak at every P<2>/lambda as roughly regulated signal. Further, a signal (b) of a period lambda/2 is used as an ultrafinely regulated signal to finely regulate in a region G. With this configuration, the position and the gap can be set in the order of 100Angstrom with the simple grating mark. |
