Long-range gap detection with interferometric sensitivity...

Details Long-range gap detection with interferometric sensitivity... Long-range gap detection with interferometric sensitivity...

2007-07-24

2007-07-24

Lee, John R. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

C250S548000, C250S559300, C356S505000, C356S509000

Reexamination Certificate

active

11432574

ABSTRACT:
An apparatus and method measures the gap between one substantially planar object, such as a mask, and a second planar object, such as a substrate. A gapping mark is used for measuring a gap between the first and second plates. The gapping mark includes a first grating on a first surface of a first plate, the first grating having a first uniform period in a first direction. A second grating is located on the first surface of the first plate, the second grating being adjacent to the first grating in the first direction, the second grating having a second uniform period in the first direction. The gapping mark also includes a third grating on the first surface of the first plate, the third grating being adjacent to the first grating in a second direction, the second direction being substantially orthogonal to the first direction, the third grating having the second uniform period in the first direction. A fourth grating is located on the first surface of the first plate, the fourth grating being adjacent to the third grating in the first direction.

REFERENCES:
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patent: 5414514 (1995-05-01), Smith et al.
patent: 5808742 (1998-09-01), Everett et al.
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patent: 6522411 (2003-02-01), Moon et al.
patent: 6855464 (2005-02-01), Niu et al.
patent: 7181057 (2007-02-01), Adel et al.

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