Surface displacement sensor with opening angle control

• US 4,748,333 A
• Filed: 03/25/1987
• Issued: 05/31/1988
• Est. Priority Date: 03/31/1986
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nippon Kogaku K. K. (Nikon Corporation)
• Inventors: Ishizaka, Shoji, Mizutani, Hideo, Suto, Takeshi
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Ruoff, Jessica L.
• Application Number:
  US07/030,076
• Time in Patent Office: 433 Days
• Field of Search: 250/560, 250/561, 356/381, 356/376, 356/1, 356/4
• US Class Current: 250/559.07
• CPC Class Codes: G01D 5/30 the beams of light being detected by photocells
• CPC Class Codes: G01S 17/46 Indirect determination of position data
• CPC Class Codes: G03F 9/7026 Focusing

Abstract

A surface displacement sensor is so designed that a stop or aperture for controlling an angle of opening is disposed at the position of a pupil of a detection optical system in which a slit image is focused on the surface to be detected and the light rays reflected from the surface to be detected are collected to re-focus the slit image on the light receiving surface of the sensor. When the height position of the surface to be detected is detected by such stop for controlling the angle of opening, the deviation of the distribution of intensity of light which tends to occur in the widthwise direction of the slit through which passes the light beam which in turn focuses a slit image, can be positively decreased by limiting the angle of opening N.A. in the widthwise direction of the slit for passing the light beam to focus a slit image to be narrow and consequently the degree of detection accuracy can be improved. The stop for controlling the angle of opening is so designed and constructed that in the case of detecting operation of the sensor, the angle of opening N.A. in the widthwise direction of the slit image is limited so that the slit image having a sufficiently narrow angle of opening can be obtained. Furthermore, in the case of the focal point adjustment of the optical system, the stop is so switched that a slit image having a sufficiently wide angle of opening N.A. in the widthwise direction thereof can be focused on a receiving slit. The focal point adjustment is further facilitated in the surface displacement sensor.

Claims

1. A surface displacement sensor of the type in which a light image having a predetermined pattern is projected on a surface to be detected having an optically transparent thin film and a deviation of the position of the light image re-focused by the reflected light beam from said surface to be detected is optoelectrically detected, thereby detecting the displacement of said surface to be detected, comprising:

a radiation source capable of generating radiation rays;

a member which has a predetermined-shaped opening and which is illuminated by the radiation beam from said radiation source;

a radiation projection system which projects the radiation beam emitted from said radiation source and passed through said opening on said surface to be detected, thereby forming a first radiation image similar to said opening on said surface to be detected;

a radiation receiving system for causing the reflected radiation beam reflected from said surface to be detected to re-focus a second radiation image;

detection means for optoelectrically detecting the center of gravity of the amount of said second radiation image re-focused by said radiation receiving system; and

means for controlling the angle of opening which is inserted in the path of said detection radiation beam so as to control the angle of opening of at least one radiation beam focusing said radiation image in a plane of incidence including a normal line perpendicular to said surface to be detected.

2. A surface displacement sensor as set forth in claim 1, wherein said means for controlling the angle of opening comprises stop means having a rectangular opening for passing the radiation beam and is located at the position of a pupil of a radiation detection system including said radiation projection system and said radiation or at its conjugate position.

3. A surface displacement sensor as set forth in claim 1, wherein said means for controlling the angle of opening comprises stop means which has a rectangular opening for passing the radiation beam and which is rotatable about the radiation axis, whereby in the case of the detection of the displacement of said surface to be detected, the widthwise direction perpendicular to the longitudinal direction of said opening becomes in parallel with said plane of incidence while in the case of the adjustment of the focal point in said radiation projection system and in said radiation receiving system, the widthwise direction of said opening becomes perpendicular to said plane of incidence.

4. A surface displacement sensor as set forth in claim 1, wherein said radiation source is a multicolor light source capable of generating light rays each having a different wavelength so that interference between reflected light rays reflected from said optically transparent thin film will not adversely affect the photoelectric detection of said detection means.

5. A surface displacement sensor of the type in which a light image having a predetermined pattern is projected on a surface to be detected having an optically transparent thin film and a deviation of the position of the light image re-focused by the reflected light beam from said surface to be detected is optoelectrically detected, thereby detecting the displacement of said surface to be detected, comprising:

a multicolor light source capable of producing a detection light beam consisting of multicolor light rays each having a different wavelength;

a member which has a predetermined-shaped opening and which is illuminated by said detection light beam from said multicolor light source;

a projection optical system which projects the detection light beam emitted from said multicolor light source and passed through said opening on the surface to be detected, thereby forming a first light image similar to said opening thereon;

a light receiving optical system which causes the light beam reflected from said surface to be detected to re-focus a second light image; and

detection means for detecting the position of the center of gravity of the amount of light of said second light image re-focused by said light-receiving optical system.

6. A surface displacement sensor as set forth in claim 5, wherein said optical projection system and said light-receiving optical system are composed of a common single objective lens optical system;

said multicolor light source is located at a position conjugate with the position of a pupil of said common single objective lens optical system; and

said detection means comprises a pupil splitting prism which is located at a position conjugate with the position of a pupil of said common single objective lens optical system and a relay lens for causing the reflected light rays from said surface to be detected and splitted by said pupil splitting prism to re-focus images, respectively.