Method of providing images of surfaces with a correlation microscope by transforming interference signals

• US 5,194,918 A
• Filed: 05/14/1991
• Issued: 03/16/1993
• Est. Priority Date: 05/14/1991
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: Chim, Stanley S. C., Kino, Gordon S.
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): KEESEE, LACHARLES
• Application Number:
  US07/700,525
• Time in Patent Office: 672 Days
• Field of Search: 356/359, 356/360, 356/124, 356/125, 356/351, 356/356, 382/43
• US Class Current: 356/497
• CPC Class Codes: G01B 11/2441 using interferometry
• CPC Class Codes: G01B 9/02057 by using common path configuration, i.e. reference and object path almost entirely overlapping
• CPC Class Codes: G01B 9/02084 Processing in the Fourier or frequency domain when not imaged in the frequency domain
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers

Abstract

A method of processing the interference signals form a correlation microscope to provide images of a surface being examined. The interference signals for a plurality of x,y locations at a plurality of z positions are transformed to provide an intensity envelope of the signals along the z axis for each x,y location. The intensity envelope can then be processed to provide desired images.

Claims

1. The method of providing images of a surface of a sample using a correlation microscope comprising the steps of

at each of a plurality of x,y locations of said sample, focusing an illumination beam at a multiplicity of distinct z positions ranging from a position above the sample to a position below the sample;

generating interference signals for each x,y,z location at which said illumination beam is focused by said focusing step;

storing the interference signals for each of said x,y,z locations as the object is moved in the z plane, and

transforming the stored interference signals at each x,y location in the z direction to obtain an intensity envelope of interfering signals in the z direction for each x,y location.

2. The method as in claim 1 wherein said step of transforming the signals at each location comprises a Fourier transform.

3. The method as in claim 1 wherein the step of transforming the signals at each location comprises a Hilbert transform.

4. The method as in claims 1, 2 or 3 in which the transformed signals include phase information for use in surface profiling, edge detection and feature recognition.

5. The method of providing images of a surface of a sample using a correlation microscope comprising the steps of

at each of a plurality of x,y locations of said sample, focusing an illumination beam at a multiplicity of distinct z positions ranging from a position above the sample to a position below the sample;

generating at an image plane interference signals for each x,y,z location at which said illumination beam is focused by said focusing step;

digitizing the signals at each of said x,y,z locations and storing the digital signals,

transforming the digital signals at each x,y location in the z direction to obtain an intensity envelope of the interfering signals in the z direction for each x,y location, and

processing said intensity envelopes to provide a selected image of the surface.

6. The method of claim 5 in which the signals are sequentially transformed for each x,y location.

7. The method as in claim 6 in which the signals are transformed by a Fourier transform in the z direction, digital filtering in the z spatial domain and inverse transforming along the z direction.

8. The method as in claim 5 in which the signals for all x,y locations are transformed in parallel.

9. The method as in claim 8 in which the transform is a Hilbert transform.