Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1990-06-13
1992-03-31
Turner, Samuel
Optics: measuring and testing
By particle light scattering
With photocell detection
356363, 356356, G01B 902
Patent
active
051002345
ABSTRACT:
A first diffraction grating is formed on a mask, and a second diffraction grating is formed on a wafer. Two light beams having slightly different frequencies interfere with each other and are diffracted as they travel through the first diffraction grating, are reflected by the second diffraction grating, and again pass through the first diffraction grating. As a result, they change into thrice diffracted light beams. The diffracted light beams are combined into a detection light beam which has a phase shift .phi..sub.A representing the displacement between the wafer and the mask, or a phase shift .phi..sub.G representing the gap between the wafer and the mask. The detection light beam is converted into a detection signal. The phase difference between the detection signal and a reference signal having no phase shifts are calculated, thus determining phase shift .phi..sub.A or .phi..sub.G. The displacement or the gap is determined from the phase shift. In accordance with the displacement or the gap, the wafer and the mask are aligned to each other, or the gap between them is adjusted to a desired value. Since the detection signal is generated from diffracted light beams, its S/N ratio is sufficiently great. Therefore, the displacement or the gap is determined with high precision. In addition, it is possible with the invention to perform the aligning of the wafer and the mask and the adjusting of the gap therebetween, simultaneously. Further, the incident light may be either circularly polarized light or non-polarized light.
REFERENCES:
patent: 4693605 (1987-09-01), Sommargren
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patent: 4815850 (1989-03-01), Kanayama et al.
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patent: 4988197 (1991-01-01), Ishibashi et al.
Hirano Ryoichi
Ishibashi Yoriyuki
Yamashita Kyoji
Kabushiki Kaisha Toshiba
Turner Samuel
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