KR20170037800A - Method and system for detecting nano-scale defects on transparent objects - Google Patents

Abstract

A method and system for detecting a fine defect in a transparent medium according to an embodiment of the present invention proposes a dual image removal method using a half-object light source based on a modified shear interferometer and a half-based reference light source, It is possible to acquire real information without DC bias and virtual image information without loss of shape information, and thus it is possible to quantitatively calculate minute defects of the transparent medium using real image information. These techniques can be used to determine whether a transparent medium, which can not be distinguished by the naked eye, is defective.

Description

METHOD AND SYSTEM FOR DETECTING NANO-SCALE DEFECTS ON TRANSPARENT OBJECTS < RTI ID = 0.0 >

The present invention relates to a microscopic defect detection method and system for quantitatively detecting a shape of a transparent medium, and more particularly, to a microscopic defect detection method and system for quantitatively detecting an object shape of a nanometer accuracy using a path difference of light passing through a transparent object It's about how you can.

The digital holography microscope is a technique capable of quantitatively measuring thickness information of an object to be measured by using hologram phase information formed by interference of a highly coherent light source. Unlike the conventional hologram recording method in which a digital holography microscope is recorded using a film, hologram pattern information is acquired using a CCD sensor, and numerical calculation of object thickness information can be performed using a calculator .

Generally, a digital holography microscopic system forms a holographic pattern using an optical interferometer. The optical interferometer used in the digital holography microscopy system separates the light stem obtained from the light source into an object light source and a reference light source by using a light separator and forms an interference pattern by contacting the two light sources. Michelson interferometers and Mach-Zehnder interferometers are widely used, and some shear interferometers use two object light sources without a reference light source. In the case of forming an interference pattern using the interferometers mentioned above, the pattern includes DC bias and virtual image information in addition to the real image. When the 3D image is numerically reconstructed, the DC bias and the virtual image are not only unnecessary information, but also can interfere with the reconstruction of real image information. In order to solve such a problem, methods for removing unnecessary information from hologram pattern information through a low-frequency filtering process in the frequency domain have been proposed.

In the case of a shear interferometer, unlike conventional Michelson interferometers and Mach-Zehnder interferometers, dual image due to interference of two object light sources occurs. In the dual image, the same object information is recorded in a redundant manner in the hologram pattern to form an interference, so that the representation of the thickness information about the object to be measured is limited when restoring the three-dimensional image. For this reason, the shear interferometer is simpler and more robust than the conventional Michelson interferometer and the Mach-Zehnder interferometer, but is not applicable to the industrial field because the error of the thickness information of the object to be measured is large in the 3D image reconstruction.

An embodiment of the present invention not only eliminates the DC bias and virtual image information that have been a problem in the existing Michelson interferometer and Mach-Zehnder interferometer but also eliminates the dual image problem caused by the two object light sources generated in the conventional shearing interferometer The present invention provides a method and system for detecting fine defects in a transparent medium which can obtain a simple and robust result than conventional interferometers.

According to an embodiment of the present invention, a defect detection method performed by a fine defect detection system of a transparent medium includes the steps of: (a) using a modified shearing interferometer including a transparent medium, Forming a reference light source that does not include an object light source and an object; (b) acquiring a hologram image using the half object light source and the half half reference light source; (c) acquiring real image information on the object by removing DC bias and virtual image information of the hologram image information; (d) extracting phase information of an object using the real-world information; And (e) quantitatively calculating defects of the transparent medium using phase information of the object to detect the presence or absence of defects in the transparent medium.

The step (a) includes the steps of: reflecting light emitted from the light source 111 to the optical mirror 112 to transmit a defective portion of the transparent medium 113a; Exposing a light source, which has passed through a transparent medium, by an objective lens 114; Forming an enlarged object light source with parallel light using an adjusting lens 115; Dividing the parallel light source into two object light sources by the front and back surfaces of the optical glass 117 to form half of the object light source and half of the reference light source; And acquiring the hologram image with the CCD camera 118 using half of the object light source and half of the reference light source. The numerical control unit 116 is used to precisely adjust the holder 113b for holding the transparent medium, the objective lens 114, the adjusting lens 115, and the CCD camera 118. [

The step (b) may include acquiring an object hologram image including information on an object and a reference hologram image not including information on the object, depending on the presence or absence of an object.

In the step (c), the DC bias and the virtual image information are removed using the low frequency region filtering method for the object hologram image and the reference hologram image to obtain real image information about the object. In the step (c), the low frequency region filtering method includes applying low frequency elimination filtering to the information obtained in the frequency domain, and removing noise included in the object hologram image and the reference hologram image.

In the step (d), the phase information of the object is obtained by using the real part and the imaginary part of the real part information.

The step (e) includes the steps of: extracting defect information on an object from the phase information of the object in the step (d); And calculating the defect of the transparent medium using the phase information of the step (d), the wavelength information of the light source emitted from the light source, and the refractive index information of the transparent medium.

According to another embodiment of the present invention, there is provided a system for detecting a micro defect in a transparent medium, comprising: an object hologram for obtaining a half-object light source and a half of the reference light source using a modified shear interferometer including a transparent medium; An image acquisition unit; A reference hologram image acquiring unit for acquiring a half of the object light source that does not include the information of the object in the object light source and a half of the hologram image of the reference light source; A real image information obtaining unit for obtaining real image information on the object by removing noise included in the object hologram image and the reference hologram image; An object phase information extraction unit for extracting phase information of an object using the real image information; And a fine defect detecting unit for quantitatively calculating the degree of defect of the transparent medium by using the phase information of the object and detecting whether or not the defect is defective.

In addition, the noise is DC bias and false image information included in the object hologram image and the reference hologram image.

The hologram image acquiring unit may include a light source; A transparent medium through which the light emitted from the light source is reflected and transmitted by the optical mirror; An objective lens for magnifying an object light source transmitted through the transparent medium; An adjusting lens for forming the enlarged object light source in parallel with the same size; An object light source division unit for forming the parallel object light source by half of the object light source and the half of the reference light source by using the optical glass; And a hologram image generating unit for generating a hologram image using the half of the object light source and the half of the reference light source.

The object light source division unit is formed of a transparent optical glass. The object light source reflected from the front and back surfaces of the optical glass interfere with each other to form a hologram image.

Also, the hologram image generating unit interferes with half of the object light sources reflected from the front surface of the optical glass and half of the reference light sources reflected from the back surface of the optical glass among the object light sources reflected from the front and back surfaces of the optical glass, .

The real image information obtaining unit may include a noise removing unit for removing DC bias and virtual image information using the low frequency filtering method for the object hologram and the reference hologram to obtain real image information about the object.

The noise eliminator may convert the object hologram image and the reference hologram image and perform low frequency elimination filtering in the frequency domain to remove DC bias and false image information included in the object hologram image and the reference hologram image, And a Fourier transform, a cosine transform, and the like for transforming the hologram image.

The object phase information extracting unit may acquire the phase information of the object using the imaginary part and real part of the real image information of the object hologram image and the reference hologram image.

Also, the micro defect detector may extract thickness information on the object from the phase information of the object, and calculate the micro defect amount using the phase information of the object, the wavelength of the light source emitted from the light source, and the refractive index of the transparent medium. Is calculated quantitatively.

The method and system for detecting a deficiency of a transparent medium according to an embodiment of the present invention proposes a method using a half-object light source and a half of a reference light source based on a modified shear interferometer, thereby reducing DC bias and real- And the degree of fine defects of the transparent medium included in the modified shear interferometer can be quantitatively calculated using the acquired real image information. The defect of the transparent medium can be judged based on the degree of fine defects quantitatively measured.

1 is a block diagram of an internal configuration of a fine defect detection system for a transparent medium according to an embodiment of the present invention.
2 is a structural diagram of an internal configuration of a hologram image acquiring unit according to an embodiment of the present invention.
FIG. 3 is a conceptual diagram illustrating a principle of generating a half-object light source and a half of a hologram image generated through a reference light source according to an embodiment of the present invention.
4 is a structural diagram for explaining the principle of an object image segmentation unit according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, if a part also includes a constituent element, it means that it can include other constituent elements, not excluding other constituent elements unless specifically stated otherwise.

Hereinafter, with reference to FIG. 1, a detailed description will be made of a fine defect detection system 100 for a transparent medium according to an embodiment of the present invention.

The microscopic defect detection system 100 for a transparent medium according to an exemplary embodiment of the present invention includes a half of an object light source and a half of a reference light source forming unit 110, a hologram image obtaining unit 120, a real image information obtaining unit 130, An object phase information extracting unit 140, and a fine defect detecting unit 150.

The half of the object light source and the half of the reference light source forming unit 110 form the object light source including the information of the object and the reference light source not including the information of the object through the front and back surfaces of the optical glass, 2, a half of the object light source reflected by the front surface of the optical glass and including information on the object is referred to as a half of the object light source O ₁ , and the information of the object reflected by the rear surface of the optical glass Half of the object light source that does not include the reference light source R is referred to as half of the reference light source R ₂ . At this time, the hologram interference pattern formed by using half of the object light source and half of the reference light source does not include the double image problem which was a problem in the conventional shearing interferometer.

The hologram image acquisition unit 120 proceeds to acquire an object hologram image and a reference hologram image. Here, the hologram image acquisition unit 120 is configured based on a modified front end interferometer. A modified shear interferometer is an interferometer in which an object light source containing information of an object is reflected at the front and back sides of the optical glass, and the two object light sources interfere with each other halfway. Further, the object hologram and the reference hologram are acquired in accordance with the presence or absence of the object.

Hereinafter, the configuration of the hologram image obtaining unit 120 will be described with reference to FIG. The hologram image acquiring unit 120 is a modified front end interferometer based transmission type digital holographic microscope and includes a light source 111, an optical mirror 112, a transparent medium holder 113b, a transparent medium 113a, an objective lens 114, An adjustment lens 115, an optical glass 117, a CCD camera 118, and a computer control unit 116.

First, the light source 111 emits light, and the emitted light is reflected by the optical mirror 112 and is transmitted through the transparent medium 113a. The light source that has transmitted the transparent medium 113a proceeds to the objective lens 114. [ The enlarged light source passing through the objective lens 114 forms collimated light by the adjustment lens 115 and enters the object light source division unit 117.

The object light source division unit 117 is composed of optical glass, and serves to generate interference by dividing the object light source passed through the adjustment lens into two object light sources. That is, half of the object light source and half of the reference light source formed on the front and back surfaces of the optical glass proceed to the CCD camera 118 through the adjustment lens.

At this time, an optimal lateral shearing interferometer should be formed in order to interfere half of the object light source area and half of the reference light source area. 4, when a parallel incident light source is incident on the optical glass as? _I , the incident light source is reflected in the air at an angle of? _I at the front of the optical glass, and the refractive index of the air and the optical glass because of the difference is a transmission angle θ _f. Further, the transmitted light source is reflected at an angle of? _F at the rear surface of the optical glass, and is transmitted to the air at the same angle of incidence angle? _I at the front surface of the optical glass. At this time, the half of the object light source reflected from the front surface of the optical glass and the half of the reference light source reflected from the back surface of the optical glass should form an optimal lateral shear distance d.

At this time, the optimal lateral shear distance is expressed by Equation (1).

Here, t is the thickness of the optical glass, θ _i is a mean angle of incidence of the object and the light source, and n ₁ and n ₂ denotes the refractive index of the refractive index of the optical glass of the air. The optimal lateral shear distance for forming half of the object light source and half of the reference light source is determined by considering the size of the object light source, the thickness of the optical glass, the refractive index, and the incident angle of the object light source.

The half-object light source and the half-half reference light source formed through the above process interfere with each other, and the object hologram image and the reference hologram image, from which the dual image has been removed, are recorded using the CCD camera 118.

The actual information obtaining unit 130 includes a process of removing the DC bias and the virtual image from the object hologram image and the reference hologram image acquired through the process. The acquired object hologram (U ₁ ) and reference hologram (U ₂ ) can be expressed by Equation ( ₂ ) as a complex conjugate hologram.

Here, U ₁ (x, y, 0) denotes the three-dimensional spatial coordinate of the object hologram interfered with the half-object light source and the half-light source including information on the object, U ₂ (x, , y, 0) denotes a three-dimensional spatial coordinate of a reference hologram interfered with a half of the object light source and half of the reference light source that do not include the object information. Then, the computer acquires only the DC bias of the object to be measured and the real image information from which the virtual image is removed through the two-dimensional Fourier transform and filtering using the object hologram image and the reference hologram image. In this case, the two-dimensional Fourier transform can be expressed by Equation (3), and the filtering process can be expressed by Equation (4).

Further, in order to recover the real image information of the object, the final complex hologram is obtained by the respective spectral method and two-dimensional inverse Fourier transform as shown in Equations (5) and (6).

The object phase information extraction unit 140 extracts the phase information of the object using the obtained conjugate hologram image and the complex conjugate hologram of the reference hologram image. This can be expressed by Equation (7).

Here, φ ₁ (x, y) and φ ₂ (x, y) represent the phase information of the object hologram image and the reference hologram image, respectively. In _{addition, Re [U 1 (x,} y, d)] and _{Im [U 1 (x, y} , d)] means the object hologram real part and an imaginary part, Re [U _2, and (x, y, d) ] and _{Im [U 2 (x, y} , d)] means the imaginary part and the real part of the reference holograms. And obtains phase difference information of only the object using the extracted object phase information and reference phase information. This is expressed by Equation (8).

Here, the phase difference information is used to compensate for distorted phase information by applying a phase spreading algorithm, and converts the compensated phase information into thickness information of an object to be measured. The converted thickness information can be expressed by Equation (9).

Here,? L (x, y, d) denotes thickness information of an object. λ denotes the wavelength of the light source, and Δn (x, y, d) denotes the refractive index difference of the medium surrounding the object and the object.

Then, the computation control unit 116 restores the three-dimensional shape of the object using the measured thickness information of the object, and simultaneously obtains the quantitative size information of the object. In addition, the degree of defect of an object is quantitatively confirmed and detected using quantitative size information of the object.

The method of an embodiment of the present invention may also be embodied in the form of a recording medium including instructions executable by a computer, such as program modules, being executed by a computer. Computer readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. In addition, the computer-readable medium may include both computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically includes any information delivery media, including computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave, or other transport mechanism.

The method according to an embodiment of the present invention may also be implemented as a computer program (or a computer program product) including instructions executable by a computer. A computer program includes programmable machine instructions that are processed by a processor and can be implemented in a high-level programming language, an object-oriented programming language, an assembly language, or a machine language . The computer program may also be recorded on a computer readable recording medium of a type (e.g., memory, hard disk, magnetic / optical medium or solid-state drive).

Thus, a method according to an embodiment of the present invention may be implemented by a computer program as described above being executed by a computing device. The computing device may include a processor, a memory, a storage device, a high-speed interface connected to the memory and a high-speed expansion port, and a low-speed interface connected to the low-speed bus and the storage device. Each of these components is connected to each other using a variety of buses and can be mounted on a common motherboard or mounted in any other suitable manner.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the embodiments described above are illustrative and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

100: Micro defect detection system of transparent medium
110: half of the object light source and half of the reference light source forming unit
111: Light source
112: Optical mirror
113a: transparent medium
113b: Transparent media holder
114: objective lens
115: Adjustable lens
116:
117: Optical glass
118: CCD camera
120: a hologram image acquiring unit
130: actual information acquisition unit
140: Object phase information extracting unit
150: micro defect detector

Claims (17)

A method for detecting a fine defect in a transparent medium,
(a) forming a reference light source that does not include an object light source and a half-object light source including an object to be measured using a modified shearing interferometer including a transparent medium;
(b) acquiring a hologram image using the half object light source and the half half reference light source;
(c) acquiring real image information on the object by removing DC bias and virtual image information of the hologram image information; And
(d) extracting phase information of an object using the real-world information;
(e) quantitatively calculating defects of the transparent medium by using the phase information of the object to detect presence or absence of defects in the transparent medium,
A method for detecting a fine defect in a transparent medium using a phase difference between the object hologram image and a reference hologram image. The method according to claim 1,
Wherein the noise is DC bias and virtual image information included in each object hologram image. The method according to claim 1,
The step (a)
Transmitting light emitted from the light source to a defective portion of the transparent medium; The light source having passed through the transparent medium is enlarged by the objective lens; Forming parallel light using an enlarged object light source using an adjusting lens; Dividing the parallel light source into two object light sources by the front and back surfaces of the optical glass to form half of the object light source and half of the reference light source; Acquiring a hologram image with a CCD camera using half of the object light source and half of the reference light source;
And detecting the fine defect in the transparent medium. The method according to claim 1,
The step (a)
Precisely adjusting the holder, the objective lens, the adjusting lens, and the CCD camera, which hold the transparent medium, using the computerized control unit;
And detecting the fine defect in the transparent medium. The method according to claim 1,
The step (b)
Obtaining an object hologram image including information of an object and a reference hologram image not including information of an object according to presence or absence of an object;
And detecting the fine defect in the transparent medium. The method according to claim 1,
The step (c)
Removing the DC bias and virtual image information using the low frequency region removal filtering method for the object hologram image and the reference hologram image to obtain real image information about the object; And performing filtering on low frequency domain information in the frequency domain;
And detecting the fine defect in the transparent medium. The method according to claim 1,
The step (d)
Obtaining phase information of the transparent medium by using the real part and the imaginary part of the real information of step (c);
And detecting the fine defect in the transparent medium. The method according to claim 1,
The step (e)
Extracting defect information on an object from phase information of the object; Calculating a defect of the transparent medium using the phase information, the wavelength information of the light source emitted from the light source, and the refractive index of the transparent medium;
And detecting the fine defect in the transparent medium. An object hologram image acquisition unit acquiring a hologram image with respect to half of the object light source and half of the reference light source using the modified shearing interferometer;
A reference hologram image acquiring unit for acquiring a half-object light source that does not include information of an object in the object light source and a hologram image of a half of the reference light source;
A real image information obtaining unit for obtaining real image information on the object by removing noise included in the object hologram image and the reference hologram image;
An object phase information extraction unit for extracting phase information of an object using the real image information; And
A detector for calculating the degree of defect of the transparent medium using the phase information of the object and detecting a defect;
Wherein the transparent medium is a transparent substrate. 10. The method of claim 9,
Wherein the noise is DC bias and virtual image information included in the object hologram image and the reference hologram image, and the transparent medium is a microscopic defect detection system. 10. The method of claim 9,
Wherein the hologram image acquiring unit comprises:
Light source;
A transparent medium through which the light emitted from the light source is reflected and transmitted by the optical mirror;
An objective lens for magnifying an object light source transmitted through the transparent medium;
An adjusting lens for forming the enlarged object light source in parallel with the same size;
An object light source division unit for forming the parallel object light source by half of the object light source and the half of the reference light source by using the optical glass;
A hologram image generation unit for generating a hologram image using the half object light source and the half half reference light source;
Wherein the transparent medium is a transparent substrate. 12. The method of claim 11,
The object light source division unit is composed of a transparent optical glass, and the object light sources reflected from the front and back surfaces of the optical glass interfere with each other to form a hologram image;
Wherein the transparent substrate is a transparent substrate. 12. The method of claim 11,
The hologram image generating unit acquires hologram image information by interfering with half of the object light sources reflected from the front surface of the optical glass and half of the reference light sources reflected from the back surface of the optical glass among the object light sources reflected from the front and back surfaces of the optical glass that;
Wherein the transparent substrate is a transparent substrate. 10. The method of claim 9,
Wherein the real image information obtaining unit includes a noise removing unit for removing DC bias and virtual image information using the low frequency elimination filtering method for the object hologram and the reference hologram to obtain real image information about the object;
Wherein the transparent substrate is a transparent substrate. 15. The method of claim 14,
Wherein the noise removing unit removes DC bias and virtual image information included in the object hologram image and the reference hologram image by filtering the low frequency region in the frequency domain by Fourier transforming the object hologram image and the reference hologram image, Obtaining only actual information;
Wherein the transparent substrate is a transparent substrate. 10. The method of claim 9,
Wherein the object phase information extraction unit obtains phase information of the object using an imaginary part and a real part of the real image information of the object hologram image and the reference hologram image,
Wherein the transparent substrate is a transparent substrate. 10. The method of claim 9,
Wherein the micro defect detection unit extracts thickness information on an object from the phase information of the object and quantifies the micro defect amount quantitatively using the phase information of the object, the wavelength of the light source emitted from the light source, and the refractive index of the transparent medium To calculate;
Wherein the transparent substrate is a transparent substrate.

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