KR20120001286A - Polarization diversity interferometer, and microscope using this - Google Patents

Abstract

PURPOSE: A polarization diversity interferometer and a microscope using the same, which can detect polarization changing by the polarization diversity, is provided to perform the analysis about the inside structure, material, and surface of a piece by simultaneously measuring the phase and amplitude change of a signal light. CONSTITUTION: A polarization diversity interferometer comprises a light source, a beam splitter(PBS), a polarizing beam splitter and an optical detector. The beam splitter separates the light of the light source. The optical detector detects the separated light by using the multiple optical detectors. If at least one optical detector has the polarization diversity of the light reflected and transmitted from a sample, the polarized light change detector detects the polarization change.

Description

Polarization diversity interferometer, and microscope using this

The present invention relates to an optical interferometer and a microscope using the same, and more particularly, to a polarization diversity optical interferometer and a microscope using the same that can detect a polarization change due to polarization diversity (polarization diversity).

Interferometric measuring device combines probe beam and reference beam using beamsplitter (BS) and measures the intensity of light from two output stages with separate photodetectors. to be. In this case, the electrical signal output from each photodetector is called an optical signal, and when the frequency of the detection light and the reference light are the same, it is called a homodyne interferometer, and when the frequencies are different, it is called a heterodyne interferometer.

In the case of a homodyne interferometer, the intensity of light from the two outputs of the BS changes according to the phase difference between the detection light and the reference light.If the light from one output is augmented, the light from the other output is extinguished. Causes That is, the interference signal of the light output to each output stage has a 180 degree phase difference. Therefore, by subtracting two optical signals with a differential amplifier, the correlated niose contained in each optical signal is eliminated and the optical signal is doubled to increase the signal-to-noise ratio. It is called a method. The signal output from the differential amplifier is represented by [Equation 1].

Where I _S and I _LO represent the intensity of the detection light and reference light, respectively, and φ _m and φ _o are respectively detected by the interferometer except phase values induced by the detection light due to the local structure or optical characteristics of the sample to be measured. Phase difference due to the optical path difference between light and reference light.

A scanning microscope is a device that optimally measures changes in local optical characteristics resulting from structural changes in a sample during the scanning process and restores the surface or internal structure shape of the sample from them. Therefore, φ _m is measured while scanning a sample or detection light. It should be measured optimally. In most cases, the size of φ _m is very small, so if using a feedback device, φ _o is always π (2n +1) / 2, n = 0, 1, 2,. If the path difference between the detection light and the reference light is adjusted so that [Equation 1] can be written as [Equation 2].

Therefore, the magnitude of the interference signal is proportional to φ _m so that the local phase change of the sample can be mapped by scanning. However, when the intensity and the phase of the detection light are changed at the same time, that is, for example, when the surface geometry and the material are changed at the same time, there is a disadvantage that they cannot be seen separately. Complex microscopic analysis has limitations.

In the case of the heterodyne interferometer, since the frequencies of the detection light and the reference light are different, the optical signal detected at each output terminal is given by Equation 3 below.

Here, Δω represents the frequency difference between the detection light and the reference light. That is, the interference signal is a beat signal in the RF or microwave region corresponding to the difference frequency of the two lights, and typical signal processing techniques used in RF can be used to measure the phase change or amplitude change induced by the surface by the detection light. have.

Research on the interferometer that can measure the phase and amplitude change induced by the detection light in the interferometer has been conducted by the inventor group of the present invention. In the case of homodyne I / Q-interferometer, the two interferometers have the same detection light and reference light paths by using the polarization state of the detection light and the reference light, but they have a phase difference of 90 degrees between the interference signals. Therefore, the signal of one interferometer appears as shown in [Equation 4].

The signal of another interferometer may be expressed by Equation 5 to perform I / Q demodulation of the optical signal. That is, the phase induced by the detection light can be obtained from [Equation 6], and the magnitude of the detection light is given by [Equation 7].

Therefore, in case of using I / Q-interferometer, the phase change induced by the detection light and the size change can be measured at the same time.

For more details on these interferometers and the results of surface microscopy, see Heise Jeong, Jong-Hoi Kim, Kyuma nn Cho, "Complete mapping of complex reflection coefficient of a surface using ascanning homodyne mu lport interferometer.", Optics communication, Vol. 204, pp. 45-52 (2002)).

Here, the surface analysis is a reflection type, which focuses the detection light at a point on the surface, and then scans the sample in the x and y-axis directions, mapping the change in local phase and magnitude of the detection light. The structural and material properties could be analyzed. Such a microscope greatly improved the function of a microscope using a conventional interferometer, and the inventors of the present invention showed that the reference material can find material damage that could not be distinguished from a conventional microscope by using such a microscope.

As can be seen from the above results, the homodyne interferometer consists of three PBSs and four photodetectors. Therefore, interferometers require a very difficult and specialized alignment process to function properly. The inventor group of the present invention has the same function, but can effectively measure the phase induced by the detection light, and consists of only two photo diodes (PD) in one detection light measurement, in addition to the simple optical system configuration, that is, the balanced detection method. A heterodyne interferometer technology was developed using a high-pass or band-pass filter in front of the Q demodulator.

As shown in FIG. 1, when the detection light and the reference light having different frequencies are interfered with each other using a BS and converted into an electrical signal using a photodetector, information on the amplitude and phase change of the detection light is expressed as shown in Equation 3 below. Since it is down converted to the RF or microwave band, the I / Q- demodulation method can easily measure the phase and magnitude change induced by the detection light. In the inventor group of the present invention, the I / Q-demodulator (demodulator) was used to measure a phase signal and apply it to a high-sensitivity displacement sensor, and the result is described in Reference 2 (Reference, "Heterodyne I / Q interferometer using a hybrid displacement sensor ", Sogang University (2003)).

As such, scanning microscopes using an I / Q interferometer can simultaneously distinguish and image phase changes and size changes induced in the detection light reflected or transmitted from the surface or inside of the sample, but according to the characteristics of the sample, birefringence and If the incident light is reflected or transmitted through the sample due to characteristics such as optical activity, the polarization change cannot be detected by the above-described configuration when the polarized light is changed due to polarization diversity. There is this.

In addition, the polarization change characteristics of these samples are used for observing, studying, or applying optical properties according to the change of magnetism in the case of birefringent material, optical activity, or magnetization element in a material such as superconductor. It is a very important problem, but there is no device that can combine the optical measurement.

In addition, scanning microscopes using an I / Q interferometer can simultaneously image the phase change and the size change induced in the detection light reflected or transmitted from the surface or inside of the sample. However, these microscopes also have a number of factors that can cause a phase change and a size change at the same time, and current scanning methods have limitations in accurately identifying the surface or internal structure of a sample accurately.

For example, in the microscopic analysis of the surface of a sample having a structure having a change in depth, if the focus of the detection light is focused on the area 1 even if the material does not change partially, the area 2 is moved to the area 2 during the scanning process. Since the position of the surface is changed, the amplitude of the detection light is changed by the depth change, so that the phase and the amplitude can be changed simultaneously. Therefore, even a scanning microscope using an I / Q interferometer has a limit in analyzing a sample.

The problem to be solved by the present invention for solving the above problems is to detect the polarization change according to the sample, can be applied to a variety of analysis equipment or a variety of equipment for the relevant research, as well as more precisely the optical characteristics of the sample To measure. In addition, it is to facilitate the analysis of the structure and material of the surface and the inside of the sample in a variety of ways.

A first aspect of the present invention for solving the above problems is a laser light source; A beam separator for separating light generated from the laser light source; A polarization separator that separates the laser light into light perpendicular to each other; And a plurality of photo detectors for detecting the separated light, wherein at least one of the photo detectors has polarization diversity according to polarization change of light reflected or transmitted through a sample. In this case, the polarization change detector capable of detecting the change in polarization.

The optical interferometer is a polarization diversity optical interferometer, characterized in that the homodyne or heterodyne interferometer.

The heterodyne interferometer may further include a heterodyne laser light source, first light detecting means PD1 for detecting reference light generated by the laser light source, and a polarized first light signal of the signal light generated and separated by the laser light source. When the second light detecting means PD2 scanning the frequency signal light by scanning the sample and the first frequency signal light scanned by the sample have polarization diversity, the polarization change is performed by polarization separation. It includes a third light detecting means (PD3) for detecting, it is detected by the first light detecting means (PD1) and the second light detecting means (PD2) without scanning the second frequency signal light to the sample.

In addition, a second aspect of the present invention is an optical interferometer, comprising: a heterodyne laser light source; First light detecting means (PD1) for detecting the reference light generated by the laser light source and separated; Second light detecting means (PD2) for scanning by scanning a polarized first frequency signal light of the signal light generated and separated by the laser light source to the sample; A polarization rotator for rotating the polarized light of the first frequency signal light scanned from the sample at a predetermined angle; And a third light detecting means PD3 for detecting the polarization change by polarizing the signal light polarized by the polarization rotator and scanning the first light detecting means without scanning the second frequency signal light on the sample. It detects by PD1) and 2nd light detection means PD2.

Here, in order to transmit the reference light, the first frequency signal light and the second frequency signal light to each light detecting means, it is preferable to include at least one beam splitter, a polarizing beam splitter (PBS) and a polarizing plate (HWP) The heterodyne laser light source is preferably a dual mode laser light source.

And as a third aspect of the invention, a scanning microscope comprises: said polarization diversity optical interferometer; An XY scanner having a sample stage on which sample stages are disposed, which moves the sample stage in two directions perpendicular to the traveling direction of the signal light; A scanner driver for controlling movement of the XY scanner; A condensing / collimating device for condensing the signal light provided from the optical interferometer to the surface of the sample or collimating the light from the sample; And extracting information on a surface of a sample by receiving an I-signal and a Q-signal output from the polarization diversity optical interferometer, or transmitting a movement control signal for controlling movement of an XY scanner to the scanner driver. It includes a computer.

Here, preferably, the polarization diversity optical interferometer of the scanning microscope may be a method in which signal light is reflected or transmitted from the surface of the sample, and the polarization diversity optical interferometer is I / Q. Equipped with a demodulator, the I / Q demodulator is an electrical signal for the reference light and the electrical signal for the signal light reflected or transmitted by the sample is input, I-signal and Q-signal for these may be output have.

In a fourth aspect of the present invention, the multifunction microscope preferably uses a balanced detection method for the polarization diversity optical interferometer, and the polarization diver according to any one of claims 1 to 3. Polarization diversity optical interferometer; An XY scanner having a sample stage on which a sample stage is arranged, and moving the sample stage in two directions perpendicular to the traveling direction of the signal light; A scanner driver for controlling movement of the XY scanner; A vertical movement mechanism for moving the sample stage in the same direction as the traveling direction of the detection light; Fine distance control device for controlling the movement of the vertical movement mechanism; A condensing / collimating device for condensing the signal light provided from the optical interferometer to the surface of the sample or collimating the light from the sample; And a movement control signal for controlling the movement of the XY scanner to the scanner driving device, or a signal for controlling the movement of the vertical movement mechanism to the fine distance adjusting device, and the I-scene provided from the I / Q interferometer. It includes a computer that receives call and Q-signals and extracts information about the surface or interior of the sample.

Here, the computer fixes the vertical movement mechanism at an arbitrary position, and then drives an XY scanner to scan the first tomographic layer of the sample, and then drives the vertical movement mechanism to move the sample stage, and then the XY scanner. It is preferable to drive to scan the second tomography of the sample, and repeat this process to perform a multi-layer scanning of the sample.

Further, the computer sets a reference phase by focusing the detection light at a specific position of the sample, and then adjusts a feedback distance error signal to prevent the reference phase from changing when the sample is scanned in the XY direction. It is provided to, and adjusts the distance between the focusing / collimating device and the sample according to the feedback control error signal, it is preferable to measure the height of the surface of the sample using the feedback control error signal according to the XY position.

In addition, the computer preferably finds the point where the amplitude signal is largest in the scanning result and connects the points having the same phase as the point where the amplitude signal is largest to obtain a contour line or contour surface for the surface shape.

By detecting the polarization change according to the sample, which could not be calculated and analyzed in the conventional general optical interferometer, it is not only applicable to various analysis equipment or various equipment for related research, but also to the optical characteristics of the sample. Precise measurement is possible.

In addition, since the phase and amplitude changes induced in the signal light transmitted or reflected from the sample are simultaneously measured, it is easy to analyze the structure and material of the surface and the inside of the sample.

In addition, the multi-layered and constant-phase scanning method was applied to the microscope to greatly improve the analysis ability of the surface or internal structure of the sample. In the multi-layer scanning method, the focusing position or the sample position of the light collecting device is moved in the x-axis direction at each interval while moving in the optical axis (z-axis) direction at regular intervals, that is, the sample is scanned layer by layer for each layer. It is a technique that can image local phase and amplitude change and analyze it more precisely and complexly by analyzing the surface or internal structure of the sample. The constant phase scanning method uses the feedback position control device to obtain the phase change signal from the interferometer. It is a technology that maintains a constant value during scanning so that the focus of the condenser is always located on the surface of the specimen so that the three-dimensional structure of the surface can be known from the error signal necessary for positioning. The change in the material of the surface can be seen from.

In the present invention, in order to further expand the functions of the multi-function microscope apparatus using the scanning polarization diversity optical interferometer, the multi-layer scanning and the constant phase scanning method are applied. In the multi-layer scanning, a constant step in the optical axis (z-axis) direction is performed. It is a technology that can get more accurate information about the geometry and material of the sample by scanning in the xy direction for each step while moving to. In case of the constant phase scanning method, the phase value obtained from the I / Q-interferometer is always constant. It is a scanning technology that adjusts the distance between the sample surface and the light collecting device by using a feedback positioning device to maintain the value. The former can be applied to both reflection and transmission modes, while the latter can mainly be applied to reflection modes.

1 is a view illustrating a balanced detection method using two conventional optical detection means and a differential amplifier,
2 is a diagram showing the configuration of a polarization diversity homodyne optical interferometer according to an embodiment of the present invention;
3 is a view showing the configuration of another example of a polarization diversity homodyne optical interferometer as another embodiment according to the present invention;
4 is a diagram illustrating a configuration of a polarization diversity heterodyne optical interferometer as an embodiment according to the present invention;
5 is a diagram illustrating the configuration of a polarization diversity heterodyne optical interferometer according to another embodiment of the present invention;
Figure 6 is a schematic diagram showing the path and the polarization state when the laser light is incident on the sample plane in the polarization change optical interferometer according to the present invention,
7 is a schematic diagram showing a path and a polarization state in which laser light is transmitted from a sample to a light detecting means in a polarization change optical interferometer according to the present invention;
8 is a view illustrating a configuration of a scanning microscope using a polarization diversity heterodyne optical interferometer according to the present invention;
9 is a view illustrating the configuration of a composite function microscope using a polarization diversity heterodyne optical interferometer as another embodiment according to the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram showing the configuration of a polarization diversity homodyne optical interferometer according to an embodiment of the present invention. As described above, the present invention provides a light source; A beam separator for separating light generated from the light source; A polarization separator that separates the light into light perpendicular to each other; And a plurality of photo detectors for detecting the separated light, wherein at least one of the photo detectors has polarization diversity when the light reflected or transmitted through the sample has polarization diversity. And a polarization change detector capable of detecting the change.

Here, the light source is preferably a laser light source, of course, various other light sources can be applied. In the embodiments described below, a laser light source will be described. In addition, the optical interferometer is a homodyne or a heterodyne interferometer.

That is, in the present invention, when there is a polarization change in the sample plane, the signal light reflected by the polarization state of the signal light is rotated or changed into an elliptical polarization state in the TM polarization due to interaction with the sample. PBS) is divided into TM (P wave) and TE (S wave) polarization components, each of which is incident on the light detection means to generate an interference signal. At this time, the component generated by any one of the light detecting means records only the change due to polarization diversity, so that it is possible to detect the polarization change according to the sample, which could not be calculated and analyzed by the conventional general optical interferometer.

FIG. 2 is a diagram illustrating a configuration of a homodyne optical interferometer capable of detecting a change in polarization, in which light generated from a laser light source is separated from each other in a vertically polarized state through a polarization separator, and separated Any one of the light is incident on the sample, and the other light is transmitted to the photo detector without incident on the sample. Here, the light incident on the sample is transmitted from the light reflected or transmitted through the sample to the TM-wave detector along the path II when there is a polarization change according to the sample, and the other beam is not incident on the sample. When the light is transmitted to the TM-wave detector again, the polarization change due to the polarization diversity of the sample can be detected through the interference signal of the two optical signals.

In addition, in the case of the homodyne interferometer as described above, the intensity of the light emitted from the two output terminals of the BS is changed according to the phase difference, and if the light emitted from one output stage is subjected to augmented interference, the light emitted from the other output stage is extinguished. Causes

That is, since the interference signal of the light from each output stage has a 180 degree phase difference, by subtracting the two optical signals into the differential amplifier, the correlated noise contained in each optical signal is removed and the optical signal Is an interferometer that can be doubled to increase the signal-to-noise ratio. This measurement method is called a balanced detection method.

3 is a view showing the configuration of another example of a polarization diversity homodyne optical interferometer as another embodiment according to the present invention. Unlike the embodiment of FIG. 2, not an interference signal through two photo detectors, but an apparatus for detecting and analyzing the interference signal through four detectors PD. That is, the signals obtained from the four photodetectors PD obtain 1,2, 3, and 4 differentially balanced signals or a combination of four signals to obtain optical I and Q signals.

As described above, the present invention is not limited to the embodiments illustrated in FIGS. 2 and 3, and the interference signal may be detected and analyzed through the arrangement of various optical elements having the characteristics of homodyne as an optical interferometer. In addition, the present invention has a key feature of using any one of the detectors as a detector capable of detecting a change in polarization due to polarization diversity according to a sample.

4 is a diagram illustrating a configuration of a polarization diversity heterodyne optical interferometer as an embodiment according to the present invention. As shown in FIG. 4, the optical interferometer of the present invention includes a heterodyne laser light source, first light detecting means PD1 for detecting reference light generated by the laser light source, and separated from the laser light source. The second light detecting means PD2 for scanning the polarized first frequency signal light among the detected signal lights by scanning the sample and the first frequency W1 signal light scanned by the sample are polarization diversity. ), A third optical detection means (PD3) for detecting the change in polarization by polarization separation, the first light detection means without scanning the second frequency (W2) signal light to the sample ( PD1) and the second optical detection means PD2.

More specifically, as shown in FIG. 4, light having two frequencies is incident from the laser light source, and is passed through an optical isolator to prevent the reflection of the reflected light into the light source. It is separated into light and signal light.

The reference light detects the light polarized by the polarizer (Pol) in the first light detecting means PD1, and the signal light passes through the half-wave plate (HWP) to change the polarization direction by 180 degrees, and the polarization beam separator The signal light having the first frequency W1 is transmitted through the PBS, and the signal light having the second frequency W2 is vertically reflected and separated.

First, the first frequency signal light goes straight to the reverberation of the sample, and the light from which the first frequency signal light is transmitted or reflected through the sample is reflected by the polarization beam splitter PBS to be second light detecting means ( PD2).

In addition, the first frequency signal light transmitted or reflected from a sample having birefringence characteristics and optical activity, which corresponds to the characteristics of the present invention, does not follow the path of 'path I', as shown in FIG. The light beam passes through the beam splitter PBS and is reflected by the polarization beam splitter PBS to be detected by the third light detecting means PD3.

Here, the first frequency signal light along the 'path II' path is rotated by 45 degrees by a polarization rotor (PR) between the polarization beam splitters (PBS) to be transmitted to the third light detecting means (PD3). This is to adjust the polarization direction for signal analysis relative to the second frequency signal light when the polarization change is caused by the sample.

That is, in the initial state, all of the signal light enters and interferes only with the direction of the second light detection means PD2, and the polarization change occurs in the sample in the direction of the third light detection means PD3. In this case, the signal is incident only when the P wave component is generated to generate an interference signal.

When the polarization change characteristics of the sample are divided and examined, when there is no polarization change on the sample surface, the first frequency signal light transmitted through the polarization beam splitter (PBS) immediately after the objective lens is in the state of TM polarization (P wave). Reflects all light from the second light detecting means PD2 along path I to generate an interference signal.

In addition, when there is a polarization change in the sample plane, due to interaction with the sample, the polarized state of the first frequency signal light is rotated in the TM polarized light or the polarized angle is changed to an elliptical polarized state so that the reflected signal light is polarized beam splitter ( PBS is divided into a TM (P wave) and a TE (S wave) polarization component to enter the second light detecting means PD2 and the third light detecting means PD3, respectively, to generate an interference signal. At this time, the component generated in the third light detecting means PD3 records only the change due to polarization diversity.

As such, in the present invention, it is possible to detect a polarization change due to polarization diversity according to a sample, which could not be calculated and analyzed in a conventional heterodyne optical interferometer, and thus, various analysis equipment for related research. Not only can be applied to, but also has the advantage that can be applied to a variety of equipment.

In general, the element that causes the change of polarization in the sample is due to the circular birefringence of the material. When the linearly polarized light is incident, the angle of the incident linearly polarized light is changed due to the difference in refractive index in the CW and CCW directions. In the present invention, it is possible to additionally detect the polarization change of such a sample in a conventional heterodyne interferometer.

FIG. 5 is a diagram illustrating the configuration of a polarization diversity heterodyne optical interferometer as another embodiment according to the present invention. As shown in Fig. 5, the optical interferometer of the present invention comprises a heterodyne laser light source; First light detecting means (PD1) for detecting the reference light generated by the laser light source and separated; Second light detecting means (PD2) for scanning by scanning a polarized first frequency signal light of the signal light generated and separated by the laser light source to the sample; A polarization rotator (PR) for rotating the polarization of the first frequency signal light scanned from the sample at a predetermined angle; And third light detecting means PD3 for detecting the polarization change by polarizing and separating the signal light polarized and rotated by the polarization rotator PR, wherein the first light does not scan the second frequency signal light on the sample. Detection is performed by the detection means PD1 and the second light detection means PD2.

As shown in FIG. 3, light having two frequencies is incident from the laser light source, and passes through a optical isolator to prevent the reflection of the reflected light into the light source. It is separated by signal light.

The reference light detects the light polarized by the polarizer in the first light detecting means PD1, and the signal light passes through the half-wave plate HWP to change the polarization direction by 180 degrees, and the polarization beam splitter PBS. The signal light having the first frequency is transmitted through Rx and the signal light having the second frequency is vertically reflected to be separated.

First, the first frequency signal light goes straight in the direction of the sample, and the light from which the first frequency signal light is transmitted or reflected through the sample is again reflected by the polarization beam splitter PBS and thus the second light detection means ( PD2).

And, corresponding to the features of the present invention, the first frequency signal light reflected or transmitted from the sample by converting the polarization angle at a predetermined angle through the polarization rotator (PR), and converts the converted first frequency signal light again The polarization beam splitter PBS separates the P-wave S wave into the second light detecting means PD2 and the third light detecting means PD3 so that the polarization change can be effectively detected.

Compared to the embodiment illustrated in FIG. 4, the second and third light detecting means PD2 and PD3 are provided by placing a polarization rotator (PR) positioned in front of the objective lens regardless of the change in the polarization state of the light in the sample. It sends light in half and half direction.

In the embodiment of FIG. 2, when there is no change in the polarization of light on the sample surface, light is not incident on one side of the light detecting means, thereby measuring only a noise image. The polarization change optical interferometer of the embodiment of FIG. Two images can be obtained with or without changes, and if the polarization change occurs in the sample plane, the two images measured are subtracted programmatically so that the remaining image can be directly observed only in the part with the polarization change in the sample plane. do. That is, it is possible to more clearly identify the point where the polarization changed, and its size also facilitates comparative analysis.

Figure 6 is a schematic diagram showing the path and polarization state when the laser light is incident on the sample plane in the polarization change optical interferometer according to the present invention. As shown in FIG. 6, the heterodyne laser light source is incident to the reference light and the signal light through an optical insulator through an optical insulator. The reference light is transmitted to the first light detecting means PD1, and the signal light is incident in the direction of the sample.

The signal light separates the first frequency signal light and the second frequency signal light through the polarization beam splitter PBS, and the signal light passing through the half-wave plate HWP is divided into horizontal and vertical polarization states and the first frequency signal. It is separated into light and the second frequency signal light.

Here, the first frequency signal light maintains the polarization state without changing the polarization until it is scanned on the sample, and the second frequency signal light is transmitted through the beam splitter to detect the relative intensity together with the first frequency signal light. The PD2 and the third light detecting means PD3 are directly transmitted without scanning the sample.

Figure 7 is a schematic diagram showing the path and polarization state that the laser light is transmitted from the sample to the light detection means in the polarization change optical interferometer according to the present invention. As shown in FIG. 7, when the first frequency signal light reflected or transmitted from the sample passes through the polarization rotator PR positioned between the objective lens and the polarization beam splitter PBS, when the polarization direction is rotated by 45 degrees, The polarization component in one direction is converted into two polarization components, and the S wave is separated and transmitted to the second optical detection means PD2 and the P wave is transmitted to the third optical detection means PD3 through the polarization beam splitter PBS. do.

In addition, the polarization beam splitter PBS or the half-wave plate is applied to the second light detecting means PD2 and the third light detecting means PD3 to have the same polarization direction of the first frequency signal light and the second frequency signal light. (HWP) will be placed in the proper position. This is to compare relative frequency optical signals, which are characteristics of heterodyne interferometer, to detect relative signal strength and phase.

As described above, the polarization change heterodyne optical interferometer according to the present invention can detect the polarization change according to a sample, which cannot be calculated and analyzed in the conventional general heterodyne optical interferometer, and thus, various analysis equipment for related research or Not only can it be applied to various equipments, it can also measure the optical characteristics of a sample more precisely.

8 is a diagram illustrating a configuration of a scanning microscope using a polarization diversity heterodyne optical interferometer according to the present invention. As shown in Fig. 8, the scanning microscope of the present invention comprises a polarization diversity heterodyne optical interferometer 10 exemplified above; An XY scanner (60) having a sample (50) on which a sample stage is disposed, which moves the sample stage in two directions perpendicular to the traveling direction of the signal light; A scanner driver 40 for controlling the movement of the XY scanner; A condensing / collimating device 20 for condensing the signal light provided from the heterodyne optical interferometer to the surface of the sample or collimating light from the sample; And a control signal for extracting information on a surface of a sample by receiving an I-signal and a Q-signal output from the polarization diversity heterodyne optical interferometer, or controlling the movement of the XY scanner by the scanner driving device. It characterized in that it comprises a computer 30 for transmitting.

That is, referring to FIG. 8, the scanning microscope according to the present invention includes a polarization diversity heterodyne optical interferometer 10, a light collecting / collimating device 20, an XY scanner 60, an A / D converter 15, a computer ( 30) and a scanner driver 40. The scanning microscope according to the present invention having such a configuration combines a polarization diversity heterodyne optical interferometer and a scanning microscope, thereby providing local optical characteristics, particularly polarization diversity, on the surface or inside of a sample that cannot be obtained with a conventional microscope. diversity can be analyzed to obtain structural and material information about the sample.

Hereinafter, the components constituting the scanning microscope according to the present invention will be described in detail.

Here, the polarization diversity heterodyne optical interferometer is as exemplified in FIGS. 4 and 5, and the light collecting / collimating device 20 condenses the signal light and collimates the signal light reflected or transmitted from the sample. Say the device. That is, the signal light emitted from the polarization diversity heterodyne optical interferometer 10 is focused on the surface of the sample 50 disposed on the scanner 60, and the light reflected from the surface or the inside of the sample 50 is returned. Collimation through the same optical system returns to the polarization diversity heterodyne optical interferometer 10.

Looking at the operation in detail, the two-mode, two polarized laser light output from the above-described polarization diversity heterodyne optical interferometer 10 is divided into two different paths using a beam splitter (BS), one of these Combines the two polarization components perpendicular to each other using a polarizer aligned at 45 degrees to the polarization direction, and uses the plurality of photodetectors (PD) to transmit the beat signal between two different frequencies. This is used as a local oscillator (LO) signal for I / Q recovery.

Each polarization component is divided by the beam splitter (BS) to form a modified Michelson interferometer, which is widely used in interferometric measurements using one as reference light and the other as signal light.

In this manner, the beat light signal can be obtained by interfering the signal light detected by the second light detecting means PD2 and the third light detecting means PD3 with the reference light detected by the first light detecting means PD1 (FIG. 2). And 3) balanced detection may be performed using three photodetectors PD and a differential amplifier. In addition, when the DC component is removed from the beat signal output from the light detecting means by using a high pass filter or a band pass filter, a beat signal such as [Equation 3] can be obtained. The beat signal obtained in this way is input to the RF input terminal of the I / Q demodulator to obtain the I and Q signals given in the equations (4) and (5), which are digitized by an A / D converter to the computer. By inputting and performing calculations such as [Equation 6] and [Equation 7], the phase and amplitude signals induced in the signal light can be simultaneously measured and measured, as well as polarization diversity (which has not been detected before). polarization change due to polarization diversity) can be detected.

In addition, an XY scanner 60, which is a transfer device capable of moving on the XY axis, is used to measure the surface of the sample, which is moved by the computer 30 and the scanner driver 40 at regular intervals. Therefore, as the sample moves to XY, the surface information is expressed as a phase shift value of light collected by the lens.

In addition, the detection method using the polarization change heterodyne optical interferometer according to the present invention is preferably to use a balanced detection method, which is the intensity of the two light output through the two output stages, namely reflection and transmission It changes according to the phase difference of the signal light, and if the light coming out of one output stage has augmentation interference, the light coming out of the other output stage causes extinction interference.

That is, the interference signal of the light output to each output stage has a 180 degree phase difference. Therefore, by subtracting two optical signals with a differential amplifier, the correlated noise contained in each optical signal is eliminated, and the optical signal is doubled to increase the signal-to-noise ratio. It is called a method. The electrical signal detected in this way is used as the RF signal of the I / Q demodulator. The demodulated I and Q signals through the I / Q demodulator are converted to digital signals by the A / D converter and sent to the computer. The computer uses this digital signal to perform calculations to obtain information about the surface of the specimen through phase and intensity values.

9 is a view illustrating the configuration of a composite function microscope using a polarization diversity heterodyne optical interferometer as another embodiment according to the present invention. As shown in Fig. 9, the multifunction microscope of the present invention comprises the above-mentioned polarization diversity heterodyne optical interferometer 10; An XY scanner (60) having a sample stage on which the sample (50) is disposed, and moving the sample stage in two directions perpendicular to the traveling direction of the signal light; A scanner driver 40 for controlling movement of the XY scanner; Vertical movement mechanism (55) for moving the sample stage in the same direction as the traveling direction of the detection light; Fine distance control device 35 for controlling the movement of the vertical movement mechanism (55); A condensing / collimating device (20) for condensing the signal light provided from the heterodyne optical interferometer (10) to the surface of the sample (50) or for collimating the light from the sample; And a movement control signal for controlling the movement of the XY scanner 60 to the scanner driving device, or a signal for controlling the movement of the vertical movement mechanism 55 to the fine distance adjusting device 35. It characterized in that it comprises a computer 30 for receiving the I-signal and Q-signal provided from the I / Q interferometer to extract information on the surface or inside of the sample 50.

Referring to FIG. 9, the composite function microscope according to the present invention includes a polarization diversity heterodyne optical interferometer 10, a detection light input / output device 13, a light collecting / collimating device 20, a vertical movement mechanism 55, and XY. The scanner 60, the computer 30, the scanner driver 40, and the fine distance adjusting device 35 are provided. Such a combined function microscope of the present invention combines a polarization diversity heterodyne optical interferometer 10 and a multi-layer scanning method, so that local optical characteristics, particularly polarization change, on the surface or inside of a sample that cannot be obtained with a conventional microscope. By analyzing such properties, structural and material information about the sample can be obtained. Hereinafter, description of the polarization diversity heterodyne optical interferometer 10 is omitted because it is the same as described above.

As such, the polarization diversity heterodyne optical interferometer 10 provides detection light or signal light and the detection light is focused and collimated on the sample 50 to include surface information of the sample 50 and again include I / Q. After input to the interferometer, it is converted into an I-signal and a Q-signal and provided to the computer 30.

Here, the computer 30 transmits a movement control signal to the scanner driver 40 that controls the movement of the XY scanner 60 that moves the sample stage on which the sample is placed, and the scanner driver 40 transmits the transferred movement. The movement of the XY scanner 60 is controlled in accordance with a control signal. The XY scanner 60 is configured to move the sample stage in two directions perpendicular to the traveling direction of the detection light. In addition, the computer 30 transmits a position adjustment error signal to the fine distance adjusting device 35 that controls the vertical movement distance of the vertical movement mechanism 55 on the sample stage on which the sample 50 is placed, and the fine distance The adjusting device 35 controls the vertical movement of the vertical movement mechanism 55 according to the position adjustment error signal. The vertical movement mechanism 55 is configured to move the sample stage in the same direction as the traveling direction of the detection light, and the PZT transfer apparatus or step motor transfer apparatus capable of precise transfer of the sample stage in the optical axis (z-axis) direction. This can be used.

Then, by scanning the region of interest while precisely changing the position by the XY scanner 60 connected to the computer, it is possible to obtain a phase and amplitude change map for the region, through which the surface or the inside of the sample is obtained. Complex microscope diagnosis of the structure and material of the

In the multi-layer scanning process according to the present embodiment, first, the sample (X) is placed on the sample stage, and then the sample stage is fixed to one position on the optical axis (z-axis) by using the vertical movement mechanism 55, and then the XY scanner. Scanning in the xy-direction using (60), the phase and amplitude values varying with the (x, y) position are measured from the polarization diversity optical interferometer 10 and stored in the computer 30. Next, the vertical movement mechanism 55 is moved one step in the optical axis (z-axis) to change the position on the optical axis (z-axis) and then scanned in the xy-direction to obtain data on phase and amplitude changes. (Not shown)

As described above, after the transfer in the optical axis (z-axis) direction, phase and amplitude change information is repeatedly obtained through the xy-direction scanning to scan the various tomography layers. At this time, the transfer step interval and the number of transfers in the optical axis (z-axis) direction can be set manually according to the sample, and the automatic setting function can be applied through software while comparing the scanning results for each tomography.

The computer 30 scans a sample for each tomography and stores a phase and amplitude change signal induced by the detection light from the polarization diversity optical interferometer 10 and stores the local to the corresponding tomography from the stored scanning results for each tomography. A map of phase change and amplitude change can be obtained, and the results of the scanning of several tomograms can be synthesized to quantitatively analyze the three-dimensional geometry and material distribution of the sample (X).

By applying multi-layer scanning technology, complex analysis of the structure of the sample surface at the same height as the focal point for each tomography is possible, and quantitative information about the three-dimensional structure and material of the sample by combining the analysis results obtained from each tomography. Can be obtained. In this case, the distance between the faults and the faults and the number of faults are determined manually by considering the characteristics of the sample and the depth of focus of the light collecting device, or automatically by comparing the changes between the faults and the faults using software. You can also determine the number of gaps and faults.

In case of surface diagnosis using multi-layer tomography, first find the point of the amplitude signal in the tomographic scanning result by using the point that the amplitude signal is the largest when the focal point is accurately positioned on the surface. Next, the contours or contours of the surface topography can be obtained by connecting the points with the same phase with the largest amplitude signal, and the contours or faces From the amplitude signal, information on the reflectance change due to the surface heterogeneity or the like can be obtained. In addition, since the points are always in focus, the sample can be analyzed with the optimal resolution of the light collecting device at that point.

Although a microscope or a composite function microscope has been described using a heterodyne interferometer among the optical interferometers according to the present invention, it is also possible to use a homodyne optical interferometer capable of detecting a change in polarization due to polarization diversity.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Anyone with it will know easily.

Claims (13)

Light source; A beam separator for separating light generated from the light source; A polarization separator that separates the light into light perpendicular to each other; And an optical interferometer for detecting the separated light,
At least one of the photo detectors is a polarization diversity detector, which is a polarization change detector capable of detecting the change in polarization when the light reflected or transmitted through the sample has polarization diversity. ) Optical interferometer.
The method of claim 1,
The optical interferometer is a polarization diversity optical interferometer, characterized in that the homodyne or heterodyne interferometer.
The method of claim 2,
The heterodyne interferometer,
Heterodyne light sources;
First light detecting means (PD1) for detecting the reference light generated by the light source and separated;
Second optical detection means (PD2) for scanning by scanning a polarized first frequency signal light of the signal light generated by the laser light source separated from the laser light source;
In the case where the first frequency signal light scanned by the sample has polarization diversity, the first frequency signal light includes a third light detecting means PD3 for separating the polarization to detect the change in polarization.
A polarization diversity optical interferometer characterized in that the first light detecting means (PD1) and the second light detecting means (PD2) detect the second frequency signal light without scanning the sample.
The method of claim 2,
The heterodyne interferometer,
Heterodyne light source,
First light detecting means PD1 for detecting the reference light generated by the light source and separated;
Second light detecting means (PD2) for scanning by scanning a polarized first frequency signal light of the signal light generated and separated by the laser light source to the sample;
A polarization rotator (PR) for rotating the polarization of the first frequency signal light scanned from the sample at a predetermined angle;
It includes a third light detection means PD3 for detecting the polarization change by polarized separation of the signal light polarized by the polarization rotating machine PR,
A polarization diversity optical interferometer, wherein the first light detecting means (PD1) and the second light detecting means (PD2) detect a second frequency signal light without scanning the sample.
The method according to claim 3 or 4,
Polarization diversity, characterized in that it comprises at least one beam splitter, a polarizing beam splitter (PBS) and a polarizing plate to transmit the reference light, the first frequency signal light and the second frequency signal light to each photodetecting means. diversity) optical interferometer.
A polarization diversity optical interferometer according to any one of claims 1 to 4;
An XY scanner having a sample stage on which a sample stage is arranged, and moving the sample stage in two directions perpendicular to the traveling direction of the signal light;
A scanner driver for controlling movement of the XY scanner;
A condensing / collimating device for condensing the signal light provided from the optical interferometer to the surface of the sample or collimating the light from the sample; And
Receiving I- and Q-signals output from the polarization diversity optical interferometer, extracting information on the surface of the sample, or transmitting a movement control signal for controlling movement of the XY scanner to the scanner driver A scanning microscope using a polarization diversity optical interferometer comprising a computer.
The method of claim 6,
The polarization diversity optical interferometer of the scanning microscope is a method of reflecting or transmitting the signal light on the surface of the sample, the scanning microscope using a polarization diversity optical interferometer.
The method of claim 6,
The polarization diversity optical interferometer includes an I / Q demodulator, and the I / Q demodulator receives an electrical signal for reference light and an electrical signal for signal light reflected or transmitted by a sample. A scanning microscope using a polarization diversity optical interferometer, characterized in that for outputting the I-signal and Q-signal.
The method of claim 6,
The polarization diversity optical interferometer is a scanning microscope using a polarization diversity optical interferometer, characterized in that using a balanced detection (Balanced Detection) method.
A polarization diversity optical interferometer according to any one of claims 1 to 4;
An XY scanner having a sample stage on which sample stages are disposed, which moves the sample stage in two directions perpendicular to the traveling direction of the signal light;
A scanner driver for controlling movement of the XY scanner;
A vertical movement mechanism for moving the sample stage in the same direction as the traveling direction of the detection light;
Fine distance control device for controlling the movement of the vertical movement mechanism;
A condensing / collimating device for condensing the signal light provided from the heterodyne optical interferometer to the surface of the sample or for collimating light from the sample; And
Transmitting a movement control signal for controlling the movement of the XY scanner to the scanner driving device, or a signal for controlling the movement of the vertical movement mechanism to the fine distance adjusting device, the I-signal provided from the I / Q interferometer, and A compound function microscope using a polarization diversity optical interferometer, comprising a computer receiving a Q-signal and extracting information on the surface or inside of a sample.
The method of claim 10,
The computer fixes the vertical movement mechanism at an arbitrary position and then drives an XY scanner to scan the first tomographic layer of the sample, and then drives the vertical movement mechanism to move the sample stage and drives the XY scanner. And scanning the second monolayer of the sample, and repeating this process to perform the multi-layer scanning of the sample, wherein the multifunction microscope uses a polarization diversity optical interferometer.
The method of claim 10,
The computer sets a reference phase by focusing the detection light at a specific position of the sample, and then provides a feedback control error signal to the micro-distance control device so that the reference phase does not change when the sample is scanned in the XY direction. Polarization diversity is characterized in that the distance between the condensing / collimating device and the sample is adjusted according to the feedback control error signal, and the height of the surface of the sample is measured using the feedback signal for error adjustment according to the XY position. diversity) Combined function microscope using optical interferometer.
The method of claim 10,
The computer finds the point where the amplitude signal is the largest in the scanning result, and connects the points having the same phase as the point where the amplitude signal is the largest to obtain contour lines or contour planes for the surface shape. diversity) Combined function microscope using optical interferometer.

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