Camera and illumination matching for inspection system

• US 7,589,783 B2
• Filed: 07/14/2004
• Issued: 09/15/2009
• Est. Priority Date: 07/14/2003
• Status: Active Grant

• Current Assignee: Onto Innovation Inc.
• Original Assignee: Rudolph Technologies Incorporated (Onto Innovation Inc.)
• Inventors: Watkins, Cory, Simpkins, Patrick
• Primary Examiner(s): Henn; Timothy J
• Application Number:
  US10/890,862
• Publication Number:
  US 20050052530A1
• Time in Patent Office: 1,889 Days
• Field of Search: 348/86, 348/87, 348 91- 93, 348/125, 348/126, 348/129, 348/130, 348/132, 348/370, 348/371, 348/131, 348/255
• US Class Current: 348/370
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: H04N 7/188 Capturing isolated or intermittent images triggered by the occurrence of a predetermined event, e.g. an object reaching a predetermined position signal generation from motion picture films H04N5/253

Abstract

An inspection tool includes a camera having a gain value and an offset value set to provide a first camera output indicating a first desired average gray value when the camera is illuminated with a precision light source set at a first light level. The inspection tool includes an inspection light source configured to be set at a second light level such that when the inspection light source illuminates a known target, the camera provides a second output indicating a second desired average gray value.

Claims

1. An inspection system comprising:

a first inspection tool comprising a first camera, the first camera having a gain value and an offset value set such that the first inspection tool provides an output indicating a first desired average gray value when the first camera is illuminated with a precision light source set at a first light level; and

a second inspection tool comprising a second camera matched to the first camera,

wherein the first inspection tool comprises a first controller, the first controller configured to;

step a light level setting of the precision light source through a plurality of light levels;

illuminate a sensor array of the first camera with the precision light source at each of the plurality of light levels;

determine an average gray value for the sensor array at each of the plurality of light levels;

fit the plurality of light levels and the average gray value at each of the plurality of light levels to a line;

compare a slope and an intercept of the line to desired values; and

adjust the gain and the offset of the first camera based on the comparison.

2. The inspection system of claim 1, wherein the second camera is configured to be matched to the first camera by adjusting the gain and the offset of the first camera and a gain and an offset of the second camera such that an output of the second camera when focused on a target is substantially equal to an output of the first camera when focused on the target.

3. The inspection system of claim 2, wherein the line is in the form y=m*x +b, wherein y is an average gray value, x

is a light level, m is the slope of the line, and b is the intercept of the line.

4. The inspection system of claim 3, wherein the second inspection tool comprises a second controller, the second controller configured to adjust the gain and the offset of the second camera in substantially the same manner as the first controller is configured to adjust the first camera.

5. The inspection system of claim 1, wherein the precision light source is National Institute of Standards and Technology (NIST) traceable.

6. The inspection system of claim 1, wherein the first inspection tool comprises a first inspection light source and the second inspection tool comprises a second inspection light source, and wherein the first inspection tool is illumination matched to the second inspection tool.

7. The inspection system of claim 6, wherein the first controller is configured to:

illuminate a target of known reflectance with the first inspection light source;

step the first inspection light source through a plurality of light level settings; and

adjust a first inspection light level at each of the plurality of light level settings until an average gray value of a sensor array of the first camera focused on the target is within a desired range at each of the plurality of light level settings.

8. The inspection system of claim 7, wherein the second controller is configured to:

illuminate the target with the second inspection light source;

step the second inspection light source through the plurality of light level settings; and

adjust a second light level at each of the plurality of light level settings until an average gray value of a sensor array of the second camera focused on the target is within the desired range at each of the plurality of light level settings.

9. An inspection system comprising:

a first inspection tool comprising a first camera, the first camera having a gain value and an offset value set such that the first inspection tool provides an output indicating a first desired average gray value when the first camera is illuminated with a light source providing a first light level; and

a second inspection tool comprising a second camera, the second camera having a gain value and an offset value set such that the second inspection tool provides an output indicating the first desired average gray value when the second camera is illuminated with a light source providing the first light level,

wherein the first inspection tool comprises a first controller, the first controller configured to;

step a light level setting of the light source through a plurality of light levels;

illuminate a sensor array of the first camera with the light source at each of the plurality of light levels;

determine an average gray value for the sensor array at each of the plurality of light level;

fit the plurality of light levels and the average gray value at each of the plurality of light levels to a line;

compare a slope and an intercept of the line to desired values; and

adjust the gain and the offset of the first camera based on the comparison.

10. The inspection system of claim 9, wherein the first camera has a gain value and an offset value for each individual pixel of the first camera such that the first inspection tool provides an output for each pixel of the first camera indicating the first desired gray value when the first camera is illuminated with a light source providing the first light level;

and

wherein the second camera has a gain value and an offset value for each individual pixel of the second camera such that the second inspection tool provides an output for each pixel of the second camera indicating the first desired gray value when the second camera is illuminated with a light source providing the first light level.

11. The inspection system of claim 9, wherein the first inspection tool comprises a first inspection light source configured to be set at a second light level such that when the first inspection light source illuminates a known target, the first inspection system provides an output indicating a second desired average gray value;

and

wherein the second inspection tool comprises a second inspection light source configured to be set at the second light level such that when the second inspection light source illuminates the known target, the second inspection system provides an output indicating the second desired average gray value.

12. An inspection system comprising:

a first inspection tool comprising a first camera and a first inspection light source, the first camera having a gain value and an offset value set such that the first inspection tool provides an output indicating a first desired average gray value when the first camera is illuminated with a precision light source providing a first light level; and

a second inspection tool comprising a second camera and a second inspection light source, the second camera having a gain value and an offset value set such that the second inspection tool provides an output indicating the first desired average gray value when the second camera is illuminated with the precision light source providing the first light level,

wherein the first inspection light source is illumination matched to the second inspection light source, and

wherein the first inspection tool comprises a first controller, the first controller configured to;

step a light level setting of the precision light source through a plurality of light levels;

illuminate a sensor array of the first camera with the precision light source at each of the plurality of light levels;

determine an average gray value for the sensor array at each of the plurality of light levels;

fit the plurality of light levels and the average gray value at each of the plurality of light levels to a line;

compare a slope and an intercept of the line to desired values; and

adjust the gain and the offset of the first camera based on the comparison.

13. The inspection system of claim 12, wherein the precision light source is National Institute of Standards and Technology (NIST) traceable.