Equipment for optically measuring the height of step

• US 4,770,532 A
• Filed: 02/24/1987
• Issued: 09/13/1988
• Est. Priority Date: 03/13/1986
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Ito, Yoshitoshi
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Cooper, Crystal
• Application Number:
  US07/017,610
• Time in Patent Office: 567 Days
• Field of Search: 356/376, 356/372, 250/201 AF
• US Class Current: 356/625
• CPC Class Codes: G01B 11/0608 Height gauges

Abstract

An equipment for optically measuring the height of step according to the present invention is characterized in that a linearly polarized laser beam from a laser source is guided onto the side of an object through an optical fiber transferring said beam in the state that the plane of polarization thereof is maintained, the beam emitted from the optical fiber is applied onto the spots in proximity to each other on the surface of the object through the intermediary of an optical system separating said beam into two component beams having planes of polarization perpendicular to each other, the beams reflected from the surface of the object are made to go back through the aforesaid optical system so that two optical paths overlap each other, and are passed in the reverse direction through the aforesaid optical fiber and guided onto the side of the laser source, the optical power of the component parallel to the plane of polarization of the incident beam and the component perpendicular thereto out of the reflected beams emitted from the optical fiber are detected by photo detectors respectively, and the height of step in the object is determined from the ratio between these optical powers.

Claims

1. An equipment for optically measuring the height of a step, comprising:

a laser source for generating a linearly polarized laser beam having a plane of polarization;

a light transfer means for transferring said linearly polarized laser beam from one end to another end and for maintaining the plane of polarization of said beam;

an optical system including means for separating the laser beam emitted from the another end of said light transfer means into two optical paths formed of component beams having planes of polarization perpendicular to each other and for making said component beams fall on spots in proximity of each other on a surfce of an object, and for making the beams reflected from said object go back so that they overlap each other in one optical path and to focus the reflected beams thus overlapping on the another end of the light transfer means;

a light detecting means for detecting an optical power of a component parallel to the plane of polarization of the linearly polarized laser beam and an optical power of a component perpendicular thereto, from the reflected beams emitted from the one end of the light transfer means and for providing outputs indicative thereof; and

means for determining the height of a step on the surface of the object from a ratio between the outputs from said light detecting means indicative of the optical powers respectively.

2. An equipment for optically measuring the height of a step according to claim 1, the aforesaid light transfer means is a polarization-maintaining fiber.

3. An equipment for optically measuring the height of a step according to claim 1, wherein the laser source includes a semiconductor laser.

4. An equipment for optically measuring the height of step according to claim 1, wherein the optical system includes a Wollaston prism.

5. An equipment for optically measuring the height of a step according to claim 1, wherein the light detecting means includes a beam splitter, a polarizing beam splitter and photo detectors connected to the beam splitter and polarizing beam splitter respectively.

6. Equipment for optically measuring the height of a step, comprising:

laser source means for generating a linearly polarized laser beam;

light transfer means for transferring the laser beam from one end to another end thereof without varying a plane of polarization of the laser beam;

an optical system including means for separating the laser beam emitted from the another end of the light transfer means into two optical paths formed of component beams having planes of polarization perpendicular to each other and for making the component beams fall on spots in proximity to each other on a surface of an object, and for receiving an overlapping the beams reflected from the object in one optical path and focusing the reflected beams on the another end of the light trasfer means;

light detecting means responsive to the reflected beams emitted from the one end of the light transfer means for detecting an optical power of a component parallel to the plane of polarization of the linearly polarized laser beam and an optical power of a component perpendicular thereto and for providing outputs indicative of the respective detected optical powers; and

means for determining the height of a step on the surface of the object from a ratio between the outputs from the light detecting means indicative of the respective optical powers.

7. Equipment according to claim 6, wherein the light transfer means comprises a polarization-maintaining fiber.

8. Equipment according to claim 6, wherein the laser source means comprises a semiconductor laser.

9. Equipment according to claim 6, wherein the optical system includes a Wollaston prism.

10. Equipment according to claim 6, wherein the light detecting means comprises a first beam splitter, a second polarizing beam splitter, and first and second photodetectors connected respectively to the first and second beam splitters.