KR20140144673A - Method and apparatus for detecting defects - Google Patents

Abstract

The present invention provides a method for detecting microdefects which comprises the steps of: irradiating a pump laser beam with a constant frequency upon a sample; changing periodic reflection intensity as the temperature of a surface of a defect is changed due to a photo-thermal effect of the defect in an area upon which the pump laser beam is irradiated; and measuring a change of the reflection intensity by irradiating a probe beam upon the sample.

Description

[0001] The present invention relates to a method and apparatus for detecting micro-

More particularly, the present invention relates to a technique for detecting fine defects by irradiating a sample with a pump laser beam to induce a change in periodic reflection intensity due to the photothermal effect of a defect existing in an irradiation area, To a method and apparatus capable of detecting a minute defect in a sample by measuring a change in reflection intensity by irradiating a beam.

In the manufacture of thin films for active / passive devices such as semiconductor devices, for example transistors, solar cells, semiconductor lasers, cracks, scratches, structural defects, contaminants ) May occur in various kinds of thin films. It is very important to detect the defects of the thin film or to identify the cause of the defects in the manufacture of the semiconductor device because these defects act as a main cause of deteriorating the performance of the thin film device or shortening the lifetime.

For example, in the case of an optical thin film deposited for the purpose of controlling the optical performance (reflection, transmission, absorption, etc.) of a photoelectric device such as a semiconductor laser, a photodetector, or an optical amplifier, The difference in the thermal expansion coefficient and the thermal expansion coefficient of the thin film can cause a thermal stress and cause a laser induced damage of the thin film due to the thermal stress. damage threshold, LIDT). Ultimately, the lowering of the threshold value of the laser damage caused by the exposure of the laser ultimately leads to the damage of the thin film and the permanent destruction, thereby deteriorating the performance of the photoelectric device and shortening the lifetime of the device.

Therefore, there is a continuing need to detect fine defects in thin films in order to prevent damage to the thin films and ensure high quality optical characteristics.

Conventional techniques for this are described below. Photothermal microscopy (PTM) [B. Bertussi et al. , "High-resolution photothermal microscope: a sensitive tool for the detection of absorbing defects in optical coatings," Appl. As one of the most widely used thin film defect detection techniques, a pump beam is used as a pump beam, This method estimates the defect position by checking the refractive index change (thermal lens effect) around the defect due to stimulation as the deflection / refraction degree of the probe beam.

However, since this method acquires the defect distribution by the raster scanning method using the sample stage, the data acquisition time is long (more than several tens of minutes), and when the pump beam size is larger than the measurement defect, So that the accuracy of the detection is deteriorated.

In addition, since the photothermal signal is very sensitive to the relative positions of the probe beam and the pump beam, it is difficult to precisely adjust the angle of the probe beam every time the sample is measured, so that there is a problem in that it is limited to practical applications.

On the other hand, this problem has been explained by taking the case of a thin film as an example. However, even in the case of a bulk material, a wafer, etc., there is the same problem when detecting a micro defect.

Under these circumstances, it is an object of the present invention to provide a new technique using a reflection mode photothermal reflection microscope technique for measuring a defect position through a degree of change in reflectance instead of a change in refractive index due to a photothermal effect.

In order to achieve the above-mentioned object, a first aspect of the present invention provides a method for manufacturing a semiconductor device, comprising: irradiating a sample with a pump laser beam at a constant frequency f; Changing a periodic reflection intensity by changing a defect surface temperature due to a photothermal effect of a defect in a region irradiated with the pump laser beam; And irradiating the sample with a probe beam to measure a change in the reflection intensity.

The sample for detecting fine defects is not particularly limited, and various types of thin films, thick films, wafers, and bulk materials are possible.

Preferably, the method further comprises measuring from the reflectance variation of the sample by phase locked thermal cycling and converting it to thermal distribution. The detecting unit may further include a step of triggering the sample at a plurality of times of the frequency at which temperature-modulation is performed.

Meanwhile, the light source for generating the pump laser beam may be configured by using a wavelength tunable laser diode and a wavelength selection filter (not shown) so as to irradiate beams of various wavelengths.

The pump laser beam is preferably irradiated with a planar light source, but may be implemented by being modified to be irradiated in the form of a linear light source.

When the pump laser beam is irradiated with a surface light source, the probe beam imaging plane can be moved into the sample through the up and down movement of the sample stage, so that the 3D defect information of the sample can be implemented through the stage Z axis scan.

According to another aspect of the present invention, there is provided a sample mounting apparatus comprising: a sample mounting section for mounting a sample; A pump light source for irradiating the sample with a pump laser beam of a constant frequency (f); A probe light source for irradiating the sample with visible light; A detector for detecting light reflected by the probe light source and reflected from a surface of the sample; And a control unit and an image processing unit at a plurality of times of a period in which the sample is temperature-modulated by irradiation of the pump laser beam.

Preferably, the optical splitter further includes an optical splitter, and transmits the beam emitted from the probe light source to the sample and transmits the beam transmitted from the sample to the detector.

According to the invention as described above, since the system implementation is comparatively simple and relatively fast in a wide area, compared to the conventional defect detection method, it is possible to provide a quick and efficient defect inspection environment at the time of field application It is effective.

Further, according to the present invention, by using a two-dimensional array sensor as a signal detector, the probe beam irradiation area can be acquired at a time without any additional scanning, so that the imaging time can be greatly shortened (several tens of seconds) It is not required to provide a high degree of optical alignment between the defects.

1 is a flowchart illustrating a method for detecting a micro defect according to an embodiment of the present invention.
Figure 2 is a schematic block diagram of a system for implementing a method for detecting micro-defects of the present invention.
3 is a view for explaining a method of irradiating a sample with a pump light source according to the present invention.
4 is a photograph showing an example of detecting an impurity in a uniform medium using a method of detecting a micro defect according to an embodiment of the present invention.
FIG. 5 is a photograph showing the result of confirming the micro defect in the uniform PDMS manufactured by the system through the system.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

1 is a flowchart illustrating a method for detecting a micro defect according to an embodiment of the present invention.

Referring to FIG. 1, the method includes a step (S101) of irradiating a sample with a pump laser beam having a frequency (f) (S101) and a periodic change in refractive index due to a change in temperature around a defect (S103) in which the intensity of the reflected light is periodically changed (S103), and measuring a change in the reflection intensity by irradiating the probe beam onto the sample (S105).

More specifically, when a sample is irradiated with a pump beam of frequency (f), the defect in the sample absorbs the pump beam, and the absorbed light energy is converted into heat energy and transmitted around the defect. This thermal energy increases the temperature around the defect, which leads to a change in refractive index (thermal lens effect). Consequently, a change in the refractive index results in a change in the light reflection intensity. The relationship between the relative change in light reflection intensity and the temperature change can be expressed as follows.

, ΔT 는 각각 광 반사세기의 변화도, background 반사세기, 열반사 보정 계수, 그리고 샘플 표면의 온도변화를 나타내고 있다. 본 발명의 하나의 특징은 결함 위치 판별에 있으므로 상대적인 반사율 변화량 (ΔR/R)을 결함 위치 측정을 위한 파라미터로 사용할 수 있다.Here,? R, R,

, And ΔT are the changes in the light reflection intensity, the background reflection intensity, the thermal reflection correction coefficient, and the temperature change of the sample surface, respectively. Since one feature of the present invention is the defect position discrimination, the relative reflectance change amount DELTA R / R can be used as a parameter for defect position measurement.

When a thermo-optic action causes a periodic reflection intensity change of a micro defect, a probe beam can be used to measure it. Preferably, after the probe beam is uniformly incident on the sample through the microscope objective with a long working distance, the sample reflected light may be refocused by the objective lens and detected by a CCD camera operating at frequency 4f.

Figure 2 is a schematic block diagram of a system for implementing a method for detecting micro-defects of the present invention.

Referring to FIG. 2, there are two off-axis beams (pump beam 120 and probe beam 100) and a CCD-based thermoreflectance microscopy (TRM). A thermo-reflective microscope is an optical technique for measuring the distribution of micro-thermal changes in optoelectronic circuits. The actual temperature can be calculated by measuring the change in the relative reflection intensity of the sample caused by the temperature change. On the other hand, it is also possible to install the band-pass filter 270 in front of the CCD camera in order to block pump beam reflected light by the sample. The intensity of the reflected light recorded in any CCD pixel (x, y) can be expressed as follows.

는 샘플의 반사세기이며,

는 펌프 빔 여기에 의한 샘플의 상대적인 반사 세기 변화를 나타내고, f와

는 각각 반사빔의 변조 주파수와 광열변조에 기인된 위상 지연값을 나타내고 있다. CCD 카메라는 펌프 빔과 동기화 되어 있어 저주파 대역의 신호 복조 기법으로 잘 알려진 호모다인 위상장금검출법(homodyne lock-in detection)을 이용하여 CCD 카메라에 기록된 반사광 세기로부터 상대적인 반사율 변화량만을 추출할 수 있게 된다.
here,

Is the reflection intensity of the sample,

Represents the relative intensity variation of the sample by the pump beam excitation, f

Respectively represent the modulation frequency of the reflected beam and the phase delay value due to photothermal modulation. Since the CCD camera is synchronized with the pump beam, homodyne lock-in detection, which is well known as a low-frequency signal demodulation technique, can be used to extract only the relative reflectance variation from the reflected light intensity recorded in the CCD camera .

2, the system of the present invention includes a probe light source 100, a pump light source 120, a detection unit 300, a control unit and an image processing unit 400, and further includes an optical distributor 250, A beam emitted from the sample 100 may be transmitted to the sample and a beam transmitted from the sample may be transmitted to the detector 300. On the other hand, various lenses (C, L) may be disposed at the front end of the light source or the detection unit to assist focusing of the light.

The probe light source 100 is a light source that provides light in which light rays having a plurality of wavelengths are mixed in a visible light wavelength region. As the type thereof, a wavelength filter (not shown) for selecting only a certain wavelength and a light source capable of obtaining a wide wavelength line width, such as a white light having a wide wavelength line width, an LED, a solid light source, An LED having a specific wavelength band or the like can be used.

The pump light source 120 is for irradiating the sample with a beam of frequency f, and can be irradiated using a laser diode of 808 nm. It is needless to say that a multimode optical fiber or an optical fiber bundle may be used to guide the pump light source 120 to the sample.

In addition, the pump light source 120 may be configured by using a wavelength tunable laser diode and a wavelength selection filter (not shown) so as to irradiate beams of various wavelengths. That is, by irradiating beams of various wavelengths, wavelengths having good transmittance and light absorption are selected, and more effective defect imaging can be realized by using a wavelength selection filter.

On the other hand, since the pump laser beam is irradiated with the surface light source and the image plane of the probe beam can be moved into the sample through the up and down movement of the sample stage (the focal plane position moves into the sample) Dimensional defect information of the sample can be implemented. In the case of a large-area sample, this process is accompanied by a transverse scan of the sample stage to obtain three-dimensional defect information for the entire sample area. In the case of a large area, it is also possible to stitch the sample stage one step at a time and to obtain three-dimensional defect information on the entire area of the sample.

In addition, the beam irradiated from the pump light source 120 to the surface light source can intensively acquire information on a certain depth in the depth direction of a sample (for example, a thin film), and when the depth is outside the depth, . Therefore, it is also possible to scan in the depth direction in such a manner that the depth of the pump light source 120 irradiated in the sample is controlled. More specifically, by adjusting the distance between the pump light source 120, the condenser lens 295, and the sample 500, the focal plane in which the beam irradiated from the pump light source 120 is mainly focused is defined as a depth Direction. According to another method, it is possible to secure an internal defect as a three-dimensional image by using the fact that the wavelength of the pump light source 120 is changed to change the depth to be irradiated intensively in the sample. However, if the wavelength of the pump light source is changed, there is an effect of changing the image plane depending on the wavelength when using the lens, but it is difficult to obtain the same defect information because the light absorption of the defect changes depending on the wavelength.

The detector 300 may include a plurality of optical signal detectors including a charged coupled device (CCD), a photodetector, an avalanche photo diode (APD), and a photomultiplier tube (PMT).

The system control unit and the image processing unit 400 are constituted by hardware and software for generating signals for synchronizing the pump light source 120 and the detection unit 300 and for processing the measured image information.

According to this embodiment, the optical signal as the sample is applied, and at the same time, the visible light illumination is irradiated to the object through the optical microscope, and the distribution of the reflected light is detected, for example, by the CCD camera, The heat distribution of the object is measured.

More specifically, the sample is temperature-modulated by a pump beam at a particular frequency (f), where heating and cooling are repeated periodically. Such periodic heating and cooling drive signals cause periodic temperature changes around the defects in the sample. In this case, the CCD that is the detection unit 300 can detect the light reflected from the sample. The CCD, which is the detection unit 300, triggers a plurality of times (for example, four times) the frequency at which the sample is temperature-modulated, thereby generating a series of images (for example, four times) within one cycle of the temperature modulation of the sample . The data secured through the CCD is transmitted to the control unit and the image processing unit 400 and processed.

3 is a view for explaining a method of irradiating a sample with a pump light source according to the present invention. FIG. 3A shows a case where the pump light source is irradiated in an off-axis manner, FIG. 3B shows a case where the pump light source is irradiated in a collinear manner, and FIG. 3C shows a case where the pump light source is irradiated in an inverted manner.

4 is a photograph showing an example of detecting an impurity in a uniform medium using a method of detecting a micro defect according to an embodiment of the present invention. As an imaging sample, a PDMS (polydimethylsiloxane) mixture containing microparticles was prepared. Fig. 4 (a) is an image of microparticles located at a depth of 50 탆 from the PDMS surface, Fig. 4 (b) is a photo-thermal reflection image when the pump beam is in operation, Respectively. The image acquisition time was about 50 seconds after 50 averaging processes, and the acquired image size was 200 μm (X) × 148 μm (Y).

4 (b), only the change in the reflectance of the beads is mapped as shown in FIG. 4 (b) due to the photothermal effect of polystyrene beads, whereas when the pump beam is turned off , The photothermal effect of the bead is stopped and the overall reflectance change is not seen as shown in Fig. 4 (c).

FIG. 5 is a photograph showing the result of confirming the micro defect in the uniform PDMS manufactured by the system through the system. (B), (d), (d) and (c) show the results of micro-defect detection in the PDMS by depth, )to be. Submicron impurities are displayed more clearly in the expanded square box.

That is, FIGS. 5 (a) and 5 (c) are optical microscope images at the depths of 15 .mu.m and 20 .mu.m respectively from the surface of the PDMS, and as shown in the figure, there appear to be no defects in the naked eye. However, upon pump beam actuation, locally located submicron impurities (shown in an enlarged box) were found at each location as in Figures 5 (b) and 5 (d).

As described above, the present invention relates to a method and apparatus for detecting sub-micron micro-defects in a sample, by measuring a change in reflectance due to the photothermal effect of impurities by applying a heat reflection microscope technique based on a two- Can be imaged.

The present invention can perform defect inspection more quickly because the image acquisition time is several tens times faster than the conventional detection system for defect measurement and no separate optical alignment process is required. In particular, it can be said that the 3D defect inspection can be performed much faster than the conventional inspection equipment of the scan driving method in the multi-layer thin film composed of several layers, so that it is worth the industrial application in addition to the technical advantages.

Although the preferred embodiments of the method for analyzing defects according to the present invention have been described, the present invention is not limited thereto, and various modifications may be made within the scope of the claims, And this also belongs to the present invention.

Claims (11)

Irradiating a sample with a pump laser beam at a constant frequency (f);
Changing a periodic reflection intensity by changing a temperature around a defect due to a photothermal effect of a defect in a region irradiated with the pump laser beam; And
And irradiating the sample with a probe beam to measure a change in the reflection intensity.
The method according to claim 1,
Further comprising the step of measuring from the reflectance change of the sample by phase lock thermal cycling and converting it to a temperature distribution.
The method according to claim 1,
Wherein the pump laser beam is generated by using a tunable laser diode and a wavelength selection filter so that a beam of various wavelengths can be emitted.
The method according to claim 1,
Wherein the pump laser beam is irradiated in the form of a surface light source.
5. The method of claim 4,
When the pump laser beam is irradiated with a surface light source, the probe beam imaging plane can be moved into the sample through the up-and-down movement of the sample stage, so that the microscopic defect securing the three-dimensional defect information of the sample through this stage Z- / RTI >
A sample mounting part for mounting the sample;
A pump light source for irradiating the sample with a pump laser beam of a constant frequency (f);
A probe light source for irradiating the sample with visible light;
A detector that detects the light irradiated by the probe light source and reflected from the sample; And
Wherein the sample comprises a control part and an image processing part at a plurality of times of frequency which is temperature-modulated by irradiation of the pump laser beam.
The method according to claim 6,
Wherein the control unit and the image processing unit are configured to measure the phase change from the reflectance change by the phase lock thermal cycling method and to convert the measurement result into thermal distribution.
The method according to claim 6,
Wherein the pump light source is configured using a tunable laser diode and a wavelength selection filter so as to irradiate a beam of various wavelengths.
The method according to claim 6,
Wherein the pump laser beam is irradiated in the form of a surface light source.
The method according to claim 6,
When the pump light source is irradiated in an off-axis manner, when the pump light source is irradiated in a collinear manner, a method of detecting a microscopic defect irradiated in an inverted manner, .
The method according to claim 6,
Further comprising an optical splitter,
And transmits the beam emitted from the probe light source to the sample and transmits the beam transmitted from the sample to the detection unit.

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