Surface inspection method and apparatus

• US 5,694,214 A
• Filed: 12/18/1996
• Issued: 12/02/1997
• Est. Priority Date: 01/08/1996
• Status: Expired due to Term

• Current Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi High-Tech Electronics Engineering Co., Ltd. (Hitachi, Ltd.)
• Inventors: Watanabe, Tetsuya, Morishige, Yoshio, Nakamura, Hisato
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Ratliff, Reginald A.
• Application Number:
  US08/768,553
• Time in Patent Office: 349 Days
• Field of Search: 356/237, 356/247, 356/253, 356/252, 356/399, 356/124
• US Class Current: 356/237.2
• CPC Class Codes: G01N 21/8851 Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges G01N21/8806 and G01N21/93 - G01N21/95692 take precedence; optical measurement of dimensions G01B11/00; optical scanning G02B26/10; image transformation G06T3/00; computerised image enhancement G06T5/00; image processing per se for flaw detection G06T7/0002

Abstract

A surface inspection apparatus of the present invention comprises an optical sensor having a plurality of detecting portions arranged in a sub-scan direction, the detecting portions being responsive to the scattering light for producing the detection signals correspondingly to respective pixels, a detection optical system including an objective lens and disposed between the optical sensor and the thing to be inspected, a projection optical system for irradiating the thing to be inspected with the laser beam having a cross sectional area large enough to cover the scattering light to be received by the plurality of the detecting portions through the detection optical system and an inspection device responsive to the detection signals for inspecting the surface of the thing to be inspected, wherein one of the detection optical system lens and the optical sensor is mounted such that a setting axis thereof is aligned in a plane perpendicular to an optical axis of the detection optical system lens with a light receiving direction which makes an angle with respect to the sub scan direction and in which shading is minimum.

Claims

1. A surface inspection apparatus in which a surface condition of a thing to be inspected is inspected on the basis of detection signals each corresponding to intensity of scattering light obtained by X-Y scanning the thing to be inspected with a laser beam making a predetermined angle with respect to a surface of the thing in one of X and Y direction as a main scan direction and the other as a sub-scan direction, said surface inspection apparatus comprising:

an optical sensor having a plurality of detecting portions arranged in the sub-scan direction, said detecting portions being responsive to the scattering light for producing the detection signals correspondingly to respective pixels;

a detection optical system including an objective lens and disposed between said optical sensor and the thing to be inspected;

a projection optical system for irradiating the thing to be inspected with the laser beam having a cross sectional area large enough to cover the scattering light to be received by the plurality of said detecting portions through said detection optical system; and

an inspection device responsive to the detection signals for inspecting the surface of the thing to be inspected, wherein one of said detection optical system lens and said optical sensor is mounted such that a setting axis thereof is aligned in a plane perpendicular to an optical axis of said detection optical system lens with a light receiving direction which makes an angle with respect to the sub scan direction and in which shading is minimum.

2. A surface inspection apparatus as claimed in claim 1, wherein said optical sensor is rotated by the predetermined angle and mounted, a width of the irradiating laser beam in the main scan direction is set in at least an area in which said optical sensor can receive light by the rotation thereof by the predetermined angle.

3. A surface inspection apparatus as claimed in claim 2, wherein said optical sensor comprises a line sensor and the predetermined angle is determined according to data of attenuation of a transmission light amount of said detection optical system lens measured by two dimensional scan along the optical axis of said detection optical system lens and one of X and Y setting axes.

4. A surface inspection apparatus as claimed in claim 3, wherein the attenuation is displayed as a contour map corresponding to the two dimensional scan and the predetermined angle is an angle between a direction corresponding to a major axis of an ellipse of said map and the one setting axis.

5. A surface inspection apparatus as claimed in claim 4, wherein said line sensor comprises a CCD sensor and said detection optical system lens comprises a telecentric lens unit including telecentrically arranged objective lens and having a front focal point set in a focusing position of said wafer and a back focal point coincident with a light receiving plane of said CCD sensor.

6. A surface inspection apparatus as claimed in claim 5, wherein the thing to be inspected is a wafer, the inspection of surface condition is to detect extraneous substance on a surface of said wafer, said map is obtained by a measuring device comprising a light source optical system for focusing an image of a point-source light in a focal point of said detection optical system lens unit, a light receiving unit, a measuring optical system including said detection optical system lens unit detachably coupled thereto with an optical axis of the measuring optical system is aligned with an optical axis of said detection optical system lens unit, for focusing the image of the point-source of light from said detection optical system lens unit in a light receiving surface of said light receiving unit, a first moving means for moving the measuring optical system along said optical axis of said measuring optical system, a second moving means for linearly moving said measuring optical system in a direction perpendicular to the optical axis of said measuring optical system and a mathematical operation processor for obtaining a level of the image of said point-source light obtained from said light receiving unit together with 2-dimensional coordinates of respective measuring points by 2-dimensionally moving said measuring optical system by said first and second moving means and for outputting data of levels of light from the respective measuring points, which are the same as the level of the image of said point-source light.

7. A surface inspection apparatus as claimed in claim 6, wherein the image of said point-source of light is formed by a pin-hole and said light receiving unit comprises a CCD camera.

8. A method of inspecting a surface of a thing, in which a surface condition of a thing to be inspected is inspected on the basis of detection signals from an optical sensor having a plurality of detecting portions arranged in the sub-scan direction, each of said detection signals corresponding to intensity of scattering light obtained by X-Y scanning the thing to be inspected with a laser beam making a predetermined angle with respect to a surface of the thing in one of X and Y direction as a main scan direction and the other as a sub-scan direction, said surface inspection method comprising:

a map acquisition step of obtaining a map of levels equal to a level of the image of the point-source light by using a measuring device comprising a light source optical system for focusing an image of a point-source light in a focal point of a detection optical system lens unit, a light receiving unit, a measuring optical system including said detection optical system lens unit detachably coupled thereto with an optical axis of the measuring optical system is aligned with an optical axis of said detection optical system lens unit, for focusing the image of the point-source of light from said detection optical system lens unit in a light receiving surface of said light receiving unit, a first moving means for moving the measuring optical system along said optical axis of said measuring optical system, a second moving means for linearly moving said measuring optical system in a direction perpendicular to the optical axis of said measuring optical system and a mathematical operation processor for obtaining a level of the image of said point-source light obtained from said light receiving unit together with 2-dimensional coordinates of respective measuring points by 2-dimensionally moving said measuring optical system by said first and second moving means and for outputting data of levels of light from the respective measuring points, which are the same as the level of the image of said point-source light;

an angle acquisition step of obtaining an angle of the light receiving direction in which the shading effect of the lens of the detection optical system in the plane perpendicular to the optical axis of the measuring optical system is minimum from the map; and

a step of making a relation between the detection optical system lens and the optical sensor a state where they are rotated by a setting angle in a light receiving direction in which shading is minimum, wherein the surface condition is inspected on the basis of the level of the detection signal.

9. A method as claimed in claim 8, wherein the image of the point-source of light is formed by a pin hole, the detection optical system lens is a telecentric lens unit, the light receiving unit is a CCD camera, the mathematical operation processor includes a micro processor and a memory and is adapted to receive a signal obtained by A/D converting the detection signal from the optical sensor and obtain the light receiving levels of the respective measuring points and the map displays the attenuation of transmission light amount of the detection optical system lens as contour lines.