US 5,204,734 A · Rough surface profiler and method

Abstract

A method of profiling a rough surface of an object includes moving the object along a z axis so that a highest point of the rough surface is optically aligned with and outside of the focus range of a solid-state imaging array. An interferogram of the rough surface then is produced by means of a two beam interferometer. The solid-state imaging array is operated to scan the rough surface along x and y axes to produce intensity data for each pixel of the solid-state imaging array for a plurality of frames each shifted from the other by a preselected phase difference. The modulation for each pixel is computed from the intensity data. The most recently computed modulation of each pixel is compared with a stored prior value of modulation of that pixel. The prior value is replaced with the most recently computed value if the most recently computed value is greater. The object is incrementally moved a selected distance along the z axis, and the foregoing procedure is repeated until maximum values of modulation and corresponding relative height of the rough surface are obtained and stored for each pixel.

Claims11

Dependent claims

A method of profiling a rough surface of an object, comprising the steps of:

(a) positioning the object along an optical axis so that a predetermined feature of the rough surface is optically aligned with an imaging device;
(b) producing an interference pattern of the rough surface by means of an interferometer;
(c) varying an optical path difference between the object and a reference surface of the interferometer;
(d) operating an imaging device to scan the rough surface to produce intensity data for each pixel of an image of the rough surface for a plurality of frames each shifted from the other by a preselected phase difference;
(e) extracting a modulation envelope from the intensity data for each pixel;
(f) locating a preselected characteristic of the modulation envelope for each pixel;
(g) correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface for each pixel,
wherein step (e) includes
(1) eliminates a constant or slow-charging component from the intensity data, as the optical path difference is varied, to produce a first digital signal;
(2) rectifying the first digital signal to produce a second digital signal;
and
(3) separating the modulation envelope from the second digital signal, the fist and second digital signals and the modulation envelope being successive values of digital words.

9 more elements

A method of profiling a surface of an object, comprising the steps of:

(a) moving the object along an optical axis so that a predetermined feature of the surface is optically aligned with an imaging device;
(b) producing an interference pattern of the surface by means of an interferometer;
(c) varying an optical path difference between the object and a reference surface at the interferometer;
(d) operating an imaging device of the interferometer to scan the surface to produce intensity data for each pixel of an image of the surface for a plurality of frames each shifted from the other by a preselected phase difference;
(e) computing phase information from the intensity data for each pixel;
(f) determining a relative height corresponding to the phase information for each pixel, and using the relative heights as the profile of the surface if the surface is of a predetermined smoothness;
(g) extracting a modulation envelope from the intensity data for each pixel;
(h) locating a preselected characteristic of the modulation envelope for each pixel;
(i) correlating the preselected characteristic of the modulation envelope to a relative height of the rough surface for each pixel, and using the relative heights as the profile of the surface if the surface is of roughness greater than a predetermined high roughness;
and
(j) combining the phase information with the relative height of the peak to obtain a relative height of improved accuracy for the surface at each pixel, and using the relative heights as the profile of the surface if the surface is of a predetermined intermediate roughness,
wherein step (g) includes
(1) eliminating a slow-charging component from the intensity data as the optical path difference is varied to produce a first digital signal;
(2) rectifying the first digital signal to produce a second digital signal;
and
(3) separating the modulation envelope from the second digital signal, the first and second digital signals and the modulation envelope being successive values of digital words.

13 more elements

Dependencies are inferred from the claim text.

Rough surface profiler and method

Life of this patent

Rough surface profiler and method

Life of this patent

Abstract

Claims11