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Littrow interferometer

An interferometer and beam technology, applied in the field of Littrow interferometer, can solve the problem that the homodyne encoder is easily affected by low-frequency noise, etc.

Inactive Publication Date: 2007-06-27
AGILENT TECH INC
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

As in the case of interferometers, homodyne encoders are susceptible to low frequency noise

Method used

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[0018] Known encoder-based displacement measurement systems do not take full advantage of the fact that encoders require only a small air gap. The present invention takes advantage of this property to benefit from high precision metrology. The use of heterodyning techniques in conjunction with encoders, according to the teachings of the present invention, clearly has further benefits. Referring specifically to FIG. 1 , there is shown a first embodiment according to the invention, wherein a first light source 101 directs a light beam 102 towards an interferometer core 103 . In one particular embodiment, the interferometer core 103 includes a polarizing beam splitter in combination with other optics for receiving and directing a beam of light. Beam 102 may be a homodyne or heterodyne beam. In one heterodyne embodiment in accordance with the present invention, light beam 102 includes light of two different frequencies, each having orthogonal polarization components referred to ...

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Abstract

An apparatus and method for measuring displacement includes a light beam directed to an interferometer core that splits the light beam into first and second component beams. The first component beam is directed to a diffraction grating at approximately a Littrow angle. A diffraction is received by the interferometer core and is combined with the second component beam. The combination of the first and second component beams is measured to determine displacement of the diffraction grating.

Description

technical field [0001] The present invention relates to Littrow interferometers. Background technique [0002] Optical interferometry techniques can be used to make precise measurements in a variety of situations. For example, laser interferometry is currently used in semiconductor photolithography processing to make nanometer-accurate measurements of small displacements and precisely positioned stages. As semiconductor structures become smaller, more precise displacement measurements are required. With the known mirror-based laser interferometry technique, part of the measuring beam travels through air. If the refractive index of the air in the beam path changes, even if only locally, it will manifest itself as a significant displacement. This apparent displacement causes measurement errors, which can get worse the longer the path through air. Various methods are known to control, reduce or measure the change in the refractive index of the air through which light travel...

Claims

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Application Information

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IPC IPC(8): G01B9/02
CPCG01D5/38G01D5/266G01D5/344
Inventor 威廉·R·小图特纳杰阿英特·欧文艾伦·B·雷詹姆斯·普林斯埃里克·斯蒂芬·约翰斯通朱淼来纳德·S·卡特勒
Owner AGILENT TECH INC