Method and its apparatus for measuring displacement of a specimen

• US 20090073457A1
• Filed: 05/15/2008
• Published: 03/19/2009
• Est. Priority Date: 05/15/2007
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Watanabe, Masahiro, Nakata, Toshihiko
• Granted Patent: US 8,860,946 B2
• Time in Patent Office: Days
• US Class Current: 356/498
• CPC Class Codes: G01B 2290/30 Grating as beam-splitter
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02018 Multipass interferometers, e.g. double-pass
• CPC Class Codes: G01B 9/02081 simultaneous quadrature detection, e.g. by spatial phase shifting

Abstract

In measuring the displacement of an object using the phase-shifting light interference, since three beam splitters were used for generating the four phase-shifting optical paths, an interferometer was increased in size, whereby the application objects were limited. Also, to solve an essential problem that if there is a disturbance such as a temperature distribution, a humidity distribution, an air pressure distribution, a density distribution or an air flow change on the phase-shifting optical paths, a measurement error occurs, the four phase-shifting optical paths are produced spatially in parallel by combining a four division prism with a photonic crystal λ/4 element and a photonic crystal polarizing element arranged like an array, constructing a small light interference displacement sensor in the invention, whereby the application objects are expanded, and the microscopic displacement or surface roughness of the object can be measured at a resolution of sub nanometer or less and with high reproducibility without influence of the disturbance.

Claims

1. A method for measuring the displacement of a specimen, including the steps of:

separating a light beam from a light source into a first light and a second light;

applying said first light to a movable object;

generating a plurality of interference lights by causing interference between the reflected light from said object and said second light with plural light phase differences on the same plane; and

detecting the movement amount of said object from said plurality of interference lights.

2. The method for measuring the displacement of the specimen according to claim 1, wherein the step of generating said interference lights includes generating the plurality of interference lights by causing interference between the reflected light from said object and said second light with plural light phase differences on the same plane using a polarizing element array.

3. The method for measuring the displacement of the specimen according to claim 2, wherein said polarizing element array is a photonic crystal array.

4. The method for measuring the displacement of the specimen according to claim 1, wherein said separating step includes separating the light beam from said light source into the first light and the second light using a wire-grid polarizing element.

5. The method for measuring the displacement of the specimen according to claim 1, wherein said separating step includes separating the light beam from said light source into the first light and the second light using a photonic crystal.

6. An apparatus for measuring the displacement of a specimen, comprising:

a light source;

means for separating a light beam from said light source into a first light and a second light;

irradiation means for applying said first light to a movable object;

interference means for generating a plurality of interference lights by causing interference between the reflected light from said object and said second light with plural light phase differences on the same plane; and

movement amount detection means for detecting the movement amount of said object from said plurality of interference lights.

7. The apparatus for measuring the displacement of the specimen according to claim 6, wherein said interference means is a polarizing element array.

8. The apparatus for measuring the displacement of the specimen according to claim 7, wherein said polarizing element array is a photonic crystal array.

9. The apparatus for measuring the displacement of the specimen according to claim 6, wherein said separating means is a wire-grid polarizing element.

10. The apparatus for measuring the displacement of the specimen according to claim 6, wherein said separating means is a photonic crystal.