Automated re-focusing of interferometric reference mirror

Patent metadata

Field	Value
Publication number	US-9664501-B2
Application number	US-201614991939-A
Country	US
Kind code	B2
Filing date	Jan 9, 2016
Priority date	Jun 24, 2013
Publication date	May 30, 2017
Grant date	May 30, 2017

Abstract

A reference surface is used to develop an empirical plot between a parameter of interest, such as roughness or modulation, and the position of the reference mirror in an interferometer by repeating measurements of the reference surface at different positions of the reference mirror so as to identify the in-focus position of the reference mirror. Serial quality-control measurements of samples of interest are carried out with the reference mirror in such in-focus position until a predetermined quality-control event triggers an automated system re-calibration by re-measuring the reference surface and, if the result does not correspond to the in-focus position of the reference mirror according to the plot, by finding a new in-focus position for the reference mirror using the same plot or, alternatively, a new similarly produced plot. Sample measurements are then resumed with the mirror placed at that new position.

First claim

We claim:

1. An interferometer comprising:
a light source;
a beam splitter optically coupled to the light source to produce a reference beam directed to a reference mirror and a test beam directed to a sample surface through an objective;
a scanning mechanism adapted to scan the objective relative to the sample surface;
a translating mechanism coupled to the reference mirror;
a motor driving the translating mechanism so as to enable focusing of the reference mirror;
a counter configured to monitor an occurrence of a predetermined event;
an automated controller connected to the motor; and
a processor configured to drive the controller;
wherein the processor is programmed to drive the controller so as to
a) measure a parameter of interest in a reference surface to develop an empirical relationship between positions of said reference mirror and values of a parameter of interest, wherein said relationship identifies an in-focus position of the reference mirror as a function of the parameter of interest;
b) place the reference mirror in said in-focus position;
c) perform measurements on a plurality of samples sequentially until the occurrence of said predetermined event; and
d) repeat steps a) and b) to recalibrate said in-focus position after the occurrence of the predetermined event.

2. The interferometer of claim 1 , wherein the processor is further programmed to drive the controller, prior to said step d), so as to re-measure the parameter of interest in the reference surface upon said occurrence of the predetermined event; and
if, based on said empirical relationship, the value so measured corresponds to the in-focus position of the reference mirror, resume measurement of said plurality of samples; or
if, based on the empirical relationship, the value so measured corresponds to an out-of-focus position of the reference mirror, go to step d).

3. The interferometer of claim 1 , wherein said predetermined event includes a measurement of said parameter of interest that produces a result outside an acceptable range; and wherein the processor is further programmed to drive the controller, prior to said step d), so as to re-measure the parameter of interest in the reference surface upon said occurrence of the predetermined event; and
if, based on said empirical relationship, the value so measured corresponds to the in-focus position of the reference mirror, resume measurement of said plurality of samples; or
if, based on the empirical relationship the value so measured corresponds to an out-of-focus position of the reference mirror, reposition the reference mirror to a new in-focus position based on said empirical relationship between positions of the reference mirror and values of the parameter of interest.

4. An interferometer comprising:
a light source;
a beam splitter optically coupled to the light source to produce a reference beam directed to a reference mirror and a test beam directed to a sample surface through an objective;
a scanning mechanism adapted to scan the objective relative to the sample surface;
a translating mechanism coupled to the reference mirror;
a motor driving the translating mechanism so as to enable focusing of the reference mirror;
a sensor configured to monitor an occurrence of a predetermined event;
an automated controller connected to the motor; and
a processor configured to drive the controller;
wherein the processor is programmed to drive the controller so as to
a) measure a parameter of interest in a reference surface to develop an empirical relationship between positions of said reference mirror and values of a parameter of interest, wherein said relationship identifies an in-focus position of the reference mirror as a function of the parameter of interest;
b) place the reference mirror in said in-focus position;
c) perform measurements on a plurality of samples sequentially until the occurrence of said predetermined event; and
d) repeat steps a) and b) to recalibrate said in-focus position after the occurrence of the predetermined event.

5. The interferometer of claim 4 , wherein the processor is further programmed to drive the controller, prior to said step d), so as to re-measure the parameter of interest in the reference surface upon said occurrence of the predetermined event; and
if, based on said empirical relationship, the value so measured corresponds to the in-focus position of the reference mirror, resume measurement of said plurality of samples; or
if, based on the empirical relationship, the value so measured corresponds to an out-of-focus position of the reference mirror, go to step d).

6. The interferometer of claim 4 , wherein said predetermined event includes a measurement of said parameter of interest that produces a result outside an acceptable range; and wherein the processor is further programmed to drive the controller, prior to said step d), so as to re-measure the parameter of interest in the reference surface upon said occurrence of the predetermined event; and
if, based on said empirical relationship, the value so measured corresponds to the in-focus position of the reference mirror, resume measurement of said plurality of samples; or
if, based on the empirical relationship the value so measured corresponds to an out-of-focus position of the reference mirror, reposition the reference mirror to a new in-focus position based on said empirical relationship between positions of the reference mirror and values of the parameter of interest.

7. An interferometer comprising:
a light source;
a beam splitter optically coupled to the light source to produce a reference beam directed to a reference mirror and a test beam directed to a sample surface through an objective;
a scanning mechanism adapted to scan the objective relative to the sample surface;
a translating mechanism coupled to the reference mirror;
a motor driving the translating mechanism so as to enable focusing of the reference mirror;
a gauge configured to monitor an occurrence of a predetermined event;
an automated controller connected to the motor; and
a processor configured to drive the controller;
wherein the processor is programmed to drive the controller so as to
a) measure a parameter of interest in a reference surface to develop an empirical relationship between positions of said reference mirror and values of a parameter of interest, wherein said relationship identifies an in-focus position of the reference mirror as a function of the parameter of interest;
b) place the reference mirror in said in-focus position;
c) perform measurements on a plurality of samples sequentially until the occurrence of said predetermined event; and
d) repeat steps a) and b) to recalibrate said in-focus position after the occurrence of the predetermined event.

8. The interferometer of claim 7 , wherein the processor is further programmed to drive the controller, prior to said step d), so as to re-measure the parameter of interest in the reference surface upon said occurrence of the predetermined event; and
if, based on said empirical relationship, the value so measured corresponds to the in-focus position of the reference mirror, resume measurement of said plurality of samples; or
if, based on the empirical relationship, the value so measured corresponds to an out-of-focus position of the reference mirror, go to step d).

9. The interferometer of claim 7 , wherein said predetermined event includes a measurement of said parameter of interest that produces a result outside an acceptable range; and wherein the processor is further programmed to drive the controller, prior to said step d), so as to re-measure the parameter of interest in the reference surface upon said occurrenc

Assignees

• Bruke Nano Inc
• Bruker Nano Inc

Inventors

• Novak Erik
• Farrell Colin
• Guenther Bryan

Classifications

• G01B9/02063 Primary

  by particular alignment of focus position, e.g. dynamic focussing in optical coherence tomography · CPC title

• G01M11/02

  Testing optical properties · CPC title

• G01B9/02072

  by calibration or testing of interferometer · CPC title

• G01B9/02067

  by electronic control systems, i.e. using feedback acting on optics or light · CPC title