Thickness measuring apparatus and thickness measuring method

Patent metadata

Field	Value
Publication number	US-9927224-B2
Application number	US-201614988332-A
Country	US
Kind code	B2
Filing date	Jan 5, 2016
Priority date	Jan 12, 2015
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

A thickness measuring apparatus and a thickness measuring method. The thickness measuring apparatus includes a light source outputting an extended monochromatic light with coherence; a collimating lens converting output light of the light source into incident beam of parallel ray; a beam splitter reflecting and providing the incident beam to a measurement target and transmitting first reflection light reflected on a top surface of the measurement target and second reflection light reflected on a bottom surface of the measurement target; an imaging lens disposed between the measurement target and the beam splitter with a predetermined focal distance to receive and provide the incident beam to a measurement position of the measurement target disposed on the focal distance; a camera photographing an interference fringe formed by the first and second reflection lights and outputting an interference fringe image; and a processing part.

First claim

What is claimed is:

1. A thickness measuring apparatus comprising:
a light source for outputting an extended monochromatic light with coherence;
a collimating lens for converting output light of the light source into an incident beam of parallel ray;
a beam splitter for reflecting and providing the incident beam to a measurement target and transmitting first reflection light reflected on a top surface of the measurement target and second reflection light reflected on a bottom surface of the measurement target;
an imaging lens disposed between the measurement target and the beam splitter with a predetermined focal distance to receive and provide the incident beam to a measurement position of the measurement target disposed on the focal distance;
a camera for photographing an interference fringe formed by the first and second reflection lights and for outputting an interference fringe image; and
a processing part for generating a curve-fitted phase shift curve using phases and incidence angles, respectively corresponding to a plurality of valleys and a plurality of peaks, and for calculating thickness of the measurement target using the phase shift curve, the processing part comprising:
an image grabber for storing the interference fringe image;
a coarse thickness calculator for receiving the interference fringe image stored by the image grabber to calculate coarse thickness information between the top surface and the bottom surface of the measurement target using information of two points among peaks and valleys in the interference fringe image;
a phase shift curve generator for generating a curve-fitted phase shift curve using phases and incidence angles, respectively corresponding to a plurality of peaks and a plurality of valleys in the interference fringe image, and for extracting a center phase corresponding to a center point of the interference fringe using the curve-fitted phase shift curve;
an interference signal order extractor for extracting an interference signal order of the center point of the interference fringe image using the coarse thickness information and the center phase; and
a fine thickness calculator for calculating a fine thickness between the top surface and the bottom surface of the measurement target using the interference signal order of the center point of the interference fringe image and the center phase corresponding to the center point of the interference fringe.

2. The thickness measuring apparatus of claim 1 , wherein the light source comprises:
a laser diode configured to oscillate at a predetermined wavelength;
a speckle reducer for receiving output light of the laser diode to suppress a speckle; and
a multi-mode optical fiber for transferring light passing through the speckle reducer.

3. The thickness measuring apparatus of claim 1 , further comprising a relay optical part disposed between the beam splitter and the camera to adjust a magnification of the interference fringe.

4. The thickness measuring apparatus of claim 1 , further comprising a moving stage for moving the measurement target.

5. The thickness measuring apparatus of claim 1 , wherein the imaging lens is a cylindrical lens.

6. A thickness measuring method comprising:
providing extended monochromatic light with coherence in a form of parallel light;
receiving the parallel light using an imaging lens and illuminating the received parallel light to a measurement position of a measurement target disposed in a focal point of the imaging lens according to an incidence angle;
forming an interference fringe using first reflection light and second reflection light respectively reflected on a top surface and a bottom surface of the measurement target disposed in the focal point of the imaging lens;
photographing the interference fringe to form an interference fringe image;
forming a curve-fitted phase shift curve using phases and incidence angles, respectively corresponding to a plurality of peaks and a plurality of valleys in the interference fringe image; and
calculating a thickness of the measurement target using the phase shift curve, comprising steps of:
calculating coarse thickness information between the top surface and the bottom surface of the measurement target using information of two points among the peaks and the valleys in the interference fringe image;
extracting a center phase corresponding to a center point of the interference fringe using the curve-fitted phase shift curve;
extracting an interference signal order of the center point of the interference fringe image using the coarse thickness information and the center phase; and
calculating fine thickness between the top surface and the bottom surface of the measurement target using the interference signal order of the center point of the interference fringe image and the center phase corresponding to the center point of the interference fringe.

7. The thickness measuring method of claim 6 , wherein calculating the thickness of the measurement target using the phase shift curve comprises:
extracting a correction phase corresponding to a specific position of the interference fringe using the curve-fitted phase shift curve; and
calculating improved thickness information between the top surface and the bottom surface of the measurement target using the information of the two points among the peaks and the valleys in the interference fringe image.

8. The thickness measuring method of claim 6 , further comprising providing the parallel light to the imaging lens through a beam splitter.

9. The thickness measuring method of claim 8 , wherein forming the interference fringe using the imaging lens further comprises:
transferring the first reflection light and the second reflection light passing through the imaging lens and the beam splitter to a relay optical part having a predetermined magnification.

10. The thickness measuring method of claim 6 , wherein the imaging lens is a cylindrical lens, and a thickness of the measurement target is calculated at each position depending on an extending direction of the cylindrical lens.

11. A thickness measuring apparatus comprising:
an interferometer for forming an interference fringe concerning a measurement point of a measurement target using extended monochromatic light having coherence;
a camera for photographing the interference fringe to output an interference fringe image; and
a processing part for generating a curve-fitted phase shift curve using phases and incidence angles, respectively corresponding to a plurality of peaks and a plurality of valleys in the interference fringe image, and for calculating a thickness of the measurement target using the phase shift curve,
wherein the processing part comprises:
an image grabber for storing the interference fringe image;
a coarse thickness calculator for receiving the stored interference fringe image to calculate coarse thickness information between a top surface and a bottom surface of the measurement target using information of two points among peaks and valleys in the interference fringe image;
a phase shift curve generator for generating a curve-fitted phase shift curve using phases and incidence angles, respectively corresponding to a plurality of peaks and a plurality of valleys in the interference fringe image, and for extracting a center phase corresponding to a center point of the interference fringe using the curve-fitted phase shift curve;
an interference signal order extractor for extracting an interference signal order of the center point of the interference fringe image using the coarse thickness information or improved thickness and the center phase; and
a fine thickness calculator for calculatin

Assignees

• Korea Res Inst Standards & Sci

Inventors

• Kim Jong-Ahn
• Kim Jae-Wan
• Lee Jae-Yong
• Woo Jae-Heun

Classifications

• G01B11/0675 Primary

  using interferometry · CPC title

• G01B9/02097

  Self-interferometers · CPC title

• G01B9/02041 Primary

  characterised by particular imaging or detection techniques · CPC title

• G01B9/02038

  Shaping the wavefront, e.g. generating a spherical wavefront · CPC title

• H04N7/18

  Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast · CPC title