JPH0499929A - Highly sensitive raman spectroscope, adjusting method and measuring method - Google Patents

Abstract

PURPOSE:To realize high detecting efficiency by forming each minute area on the photodetecting surface of a position detecting type photomultiplier in a manner corresponding to a signal of each wavelength so as to simultaneously measure the Raman spectrum at the low noise level near to a limit. CONSTITUTION:A standard sample for adjustment use having a grid pattern is provided at the position of a sample. At this time, it should be confirmed that the whole area of the pattern of a spot illuminated by a laser is observed without distortion at the position of an incident slit 12. Then, a switching mirror 17A of a single spectroscope 17 is switched to the adjusting side, and a focal length of a telescope 20 for adjusting an astigmatism correction optical system 3 is adjusted. The grid pattern is confirmed with use of a mercury lamp or the like. The optical system 3 is finely adjusted by a fine adjustment mechanism 14. When a laser light 7 is condensed into a circle on a sample 10, an image on the slit 12 is confirmed. Then, the mirror 17 is switched and the image of the spectrum on the detector of a position detecting type photomultiplier 18 is measured. The position of the detector at this time is adjusted by a fine adjustment mechanism 19.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for measuring Raman scattering of semiconductors, metals, inorganic materials, organic materials, living organisms, etc., and particularly relates to ultra-thin films of semiconductors and organic materials, or The present invention relates to a high-sensitivity Raman spectrometer, a Raman spectrometer adjustment method, and a measurement method suitable for detecting and evaluating weak Raman signals from trace amounts of atoms and molecules on surfaces and interfaces.

[Prior Art] Raman spectroscopy is a powerful method for providing a wealth of information regarding the microstructure and electronic state of substances, and its use has become increasingly popular in recent years. However, its biggest weakness is that the signal strength is very weak, and for this reason, the measurement targets have been limited to those with relatively strong signals and those with little laser damage. If Raman spectroscopy were to be able to measure ultrathin films, trace impurities, and trace molecules on surfaces and interfaces, which are difficult to measure with current technology, the impact would be immeasurable. In other words, it will be possible to obtain information about microscopic bonding states at the atomic or molecular level that cannot be obtained using techniques such as electron spectroscopy, ion scattering, and scanning tunneling microscopy. The device, its adjustment method, and measurement method presented here are the first to make the above-mentioned measurements possible, which until now were only a pipe dream. Here, we will first describe the principles of conventional measurement methods and the limitations of device performance, and then describe how the present invention overcomes these limitations.

In a Raman spectrometer, it is necessary to effectively separate the Raman scattered light to be analyzed from laser light and Rayleigh scattered light, and to detect weak signal light with sufficient resolution. Raman signal light from semiconductors etc. mainly appears at a position approximately 10-10-1000' away from the laser light, but in such a region, a single spectrometer using a single grating cannot completely remove Rayleigh scattered light. Therefore, double spectrometers are often used. However, although the double spectrometer is suitable for single-channel measurements by photon counting using a photomultiplier tube, it is not suitable for the multiple detectors that have been advanced in recent years. The reason for this is that in order to perform multiple detection, the intermediate slit must be sufficiently spaced, but this will significantly reduce the ability of the double spectrometer to remove stray light, and the scattered light will become strong (unable to be used too much). For this reason, a triple polychromator (spectrograph), which connects a differential dispersion type double spectrometer and a single spectrometer, came to be used. Install and -
This is an optical arrangement that converts the previously separated light back into white light, and because it only transmits light that falls within the width of the intermediate slit, it becomes a type of band pass filter. By making the width of the intermediate slit correspond to the width of the multiplex detector installed at the exit of the single spectrometer, the Raman signal from which Rayleigh light has been removed can be efficiently detected. This combination of triple spectrometers and multiple detectors has made it possible to detect weak signals that were impossible to measure with conventional double spectrometers and photomultiplier tubes for photon counting.

That is, in photon counting, the noise level of the detector is 1-20 volts/second, so signals with lower intensity cannot be detected, but if multiple detection is performed, the spectrometer will stop. This makes it possible to efficiently remove noise through integration, and it is possible to use photodiode arrays with cooled image intensifiers (hereinafter abbreviated as II-PDA), charge-coupled device detectors (hereinafter abbreviated as COD), and position detection types. If a photomultiplier tube is used, it is currently possible to detect a signal of about 0.1 force count/second in terms of a normal photomultiplier tube.

Systems such as those described above have enabled Raman detection of various thin films. For example, there are reports on signal detection from a 1 molar layer of a Langmuir-Prodgett film using a triple spectrometer and II-PDA, or a triple spectrometer and a cooled charge-coupled device detector (hereinafter abbreviated as COD).

In addition, Raman signal detection from several molar layers of germanium is performed using a triple spectrometer and a position-detecting photomultiplier tube.

In this way, compared to the traditional method using a double spectrometer and a photomultiplier tube for photon counting, triple
By using a polychromator and multiple detectors such as any PDA, CCD, or position-detecting photomultiplier tube, the power output is about 0.1 nt/sec in terms of photomultiplier tube, which is 2-3 orders of magnitude weaker than conventional ones. It has become possible to detect signals such as

[Problems to be Solved by the Invention] However, although the above measurement examples are highly sensitive, the signal strength is in the region of 0.1 force/count/second. In addition, in previous measurements, signal detection has been successful by carefully selecting systems with relatively strong signals that are easy to measure, and it has been difficult to detect systems with signals of less than 0.1 force count/second. . In order to detect Raman signals from ultra-thin films of various materials with weaker signal strength, such as molya or sub-molya, or from a small number of molecules adsorbed on the surface, signal detection in an even weaker region, that is, 0.01 force und. It is essential to be able to perform measurements at speeds of 1/sec or even lower.

Therefore, the purpose of the present invention is to improve Raman spectroscopy using a triple spectrometer and multiple detectors by carefully examining the characteristics of the position-detecting photomultiplier tube and the additional optical system. - It is an object of the present invention to provide a highly accurate and sensitive Raman spectroscopic device and measurement method with ultra-high sensitivity of three orders of magnitude or more, that is, at the level of 0.001 force units/second or 0.0001 force units/second. Another object of the present invention is to enable ultra-high sensitivity Raman spectroscopy with two-dimensional data, and to enable high-speed measurements and highly accurate differential Raman spectroscopy that are impossible with ordinary Raman spectroscopy using one-dimensional data. It's about doing.

[Means for Solving the Problems] In order to achieve such an object, the device of the present invention is a Raman spectrometer that detects a Raman signal by irradiating a sample with excitation light. A condensing optical system that condenses light, and a condensing optical system that receives output light from the condensing optical system through an entrance slit, and has a relatively low wave number with a Raman shift of 10 to 100100 O' for the received light. Even in the spectral domain, the triple spectrometer has a differential dispersion type double spectrometer for filtering and a single spectrometer placed next to the double spectrometer, which can sufficiently remove stray light due to Rayleigh scattering and measure good spectra.・Equipped with a spectroscopic optical system in the form of a polychromator, a micro channel plate, and a two-dimensional position detection mechanism in the subsequent stage,
A low-noise photomultiplier tube for photon counting that is not affected by pulse noise caused by high-energy particle beams, etc., which receives and amplifies the output light from the spectroscopic optical system by the micro-channel plate. ,
The amplified output signal is guided to a two-dimensional position detection mechanism, and the image is detected as a two-dimensional array of minute regions, thereby suppressing dark noise in each minute region to an extremely low level. Signal light of each wavelength from the upper minute irradiation area is placed in one-to-one correspondence on each minute area on the light-receiving surface of the position-detecting photomultiplier tube without image blurring due to aberrations of the spectroscope. an astigmatism correcting optical system having a cylindrical lens that allows the astigmatism to be transferred, and a switching mirror used to finely adjust the astigmatism correcting optical system to a position equivalent to the light receiving surface of the position detection type photomultiplier tube. and a fine adjustment mechanism that finely adjusts the position and orientation so that the light receiving surface of the position detection photomultiplier tube is accurately positioned at the focal plane of the spectrometer, The Raman spectrum is simultaneously measured at an extremely low noise level, with each micro region on the light receiving surface of the position detection photomultiplier tube corresponding to a signal of each wavelength. .

In the Raman spectrometer adjustment method of the present invention for adjusting the Raman spectrometer, the excitation light is correctly focused on the sample while monitoring the image of the sample with a telescope that looks directly at the entrance slit, Confirm that the scattered light is accurately transferred onto the incident slit, and then set up a standard sample for adjustment with a grid pattern at the position of the sample, and measure the entire area of the pattern at the position of the incident slit. is observed without distortion, the switching mirror disposed at the exit of the single spectrometer is switched to the adjustment side, and the focal length of the astigmatism correction optical system adjustment telescope is adjusted, The grid pattern is confirmed, and the astigmatism correction optical system is finely adjusted so that the vertical and horizontal patterns of the grid pattern are uniformly transferred over the entire area on the entrance slit without image blurring. , confirm again at the position of the entrance slit that the excitation light is correctly focused as a minute circular spot on the sample, and compare the spectrum of the Raman signal and plasma emission caused by this excitation light with the incident light as background light. The line emission uniformly incident on the entire slit is simultaneously measured by the position detection type photomultiplier tube, and the position detection type photomultiplier tube is positioned so that both spectra form an orthogonal pattern without distortion. The axis of the position-sensing photomultiplier tube is moved back and forth, tilted, and adjusted so that the light-receiving surface of the position-sensing photomultiplier tube is at a position equivalent to the focal plane adjusted in advance by the telescope. The present invention is characterized in that the fine adjustment of the rotation in the direction is sequentially and alternately performed, and the adjustment is finally made so that the spread of the signal on the light receiving surface is minimized and the spectral resolution is also in the best condition.

In the Raman spectroscopy method of the present invention, after adjusting the Raman spectrometer as described above, a sample is irradiated with the excitation light, a position-specific data signal is extracted from the position-detecting photomultiplier tube, and the signal processing device The method is characterized in that the Raman spectroscopic measurement results for the sample are obtained based on the accumulated signals.

Another form of the Raman spectroscopy method of the present invention uses a one-dimensional line-shaped laser beam as the excitation light, focuses the laser beam on the sample in a one-dimensional line shape, and excites the -dimensional line-shaped laser beam. The light is transferred onto the light receiving surface of the position-detecting photomultiplier tube while maintaining the spatial resolution, and the position-resolved spectrum is extracted as a two-dimensional image data signal and stored in a signal processing device. The method is characterized in that a differential process regarding one-dimensional position is performed on the sample to detect minute changes in the Raman spectrum due to the one-dimensional position on the sample.

[Function] II-PDA which is an analog detector among multiple detectors
CCDs and CCDs respond to strong pulse noise in proportion to its energy, so normally, while integrating weak signals over a long period of time, pulse noise appears all over the spectrum and becomes a non-negligible number. turn into. Empirically, this is 0.00000000000000000000000000000000,000,000,000,000,000,000,000,000,00,000,000,000,000,000,000,000,000, in terms of photomultiplier tubes per channel.
This results in a noise of 0.001-0.01 force-counts/sec. These are mainly caused by high-energy particle beams from space, so it is difficult to avoid them. One solution is to repeat the measurement several times and remove peaks that do not recur, using software, but this is not a fundamental solution as it may damage the signal itself. In contrast, in digital detectors such as position-sensitive photomultiplier tubes, the signals are constantly counted one by one by photon counting, and a pulse-height discriminator is usually used to distinguish high- or low-energy noise from true signals. This is the most suitable method for detecting ultra-weak signals because even if cosmic ray noise is counted, it only counts as one count, unlike analog detectors.

However, in the past, the characteristics of this position detection type photomultiplier tube have not been sufficiently examined, and for this reason, its maximum performance has been considered to be on the same level as II-PDA and CCD. Here, we returned to the principles of position-detecting photomultiplier tubes and discovered that it is possible to construct an ultra-low-noise Raman spectrometer that enables ultra-high sensitivity Raman spectroscopy, thereby completing the present invention.

In position-sensitive photomultiplier tubes, the noise level, like in regular photomultiplier tubes, is primarily due to some optical or electronic noise near the photocathode, which is at least 10-20 volts/sec. That's about it. It has been known that it is technically difficult to further reduce noise. Therefore, if we identify the pixel locations in a two-dimensional array of 1024 x 1024 pixels, the noise there will be 1-2 x 10-5 forces/sec per vixel.

Now, in Raman spectroscopy using multiple detection, a position-detecting photomultiplier tube has been used as a simple one-dimensional multiple detector. If we take the direction of the spectrum as the X-axis and the direction perpendicular to it as the Y-axis on the light-receiving surface of a position-detecting photomultiplier tube, we get
In a normal spectrometer, the spectrum is divided into two parts in the Y-axis direction at each wavelength.
It is spread by 00 to 400 pixels, and these are added together to form one-dimensional data. Total 1024 in Y-axis direction
If you add up the pixels, the noise in each channel will be 1-2 x 10-2 counts/second, and even if you add only the central 200-400 pixels where the signal exists, it will be 2-8 x 10-'' counts/second. Such noise levels are not much different from those of II-PDAs or high-sensitivity CCDs, and until now it was not thought that position-sensing photomultiplier tubes were especially ultra-sensitive compared to others. That makes sense.

However, if the spread of the spectrum in the Y-axis direction could be extremely narrowed, the noise per channel should be significantly reduced. For example, if the spread in the Y-axis direction can be reduced to 5 pixels or less, the noise level can be 5-10XIO-5 force counts/second per channel, which is 0,001-0. Since there is no pulse noise on the order of 0.01 ton/sec, high-sensitivity Raman spectroscopy of extremely weak light is possible.

In order to suppress such spread in the Y-axis direction, it is sufficient to create a spectroscope without astigmatism. Astigmatism occurs because the optical components that make up the spectrometer are not transmission type, such as lenses, but instead are reflective type, such as mirrors and gratings.For this reason, all optical components are arranged on the same optical axis. If a fully symmetrical optical component such as a spherical mirror is used, the vertical and horizontal focal lengths will be different.Place the detector's light-receiving surface at the focal position in the X-axis direction, where the spectral resolution is highest. When observed, Y
In the axial direction, this position is not the focal point, so the image spreads out. The theoretically best way to correct such astigmatism is to use an optical system using an ellipsoidal mirror, but this is extremely expensive, difficult to adjust, easily goes awry, and is not easy to modify or correct. For this reason, it is particularly unrealistic as a triple polychromator, and there has never been one manufactured so far, and it will never be possible in the future. The next possible method is to add a correction optical system such as a cylindrical lens that focuses light in only one direction to the outside of the optical system that has astigmatism, without affecting the X-axis direction at all. , a method is known in which the focal length in the Y-axis direction is corrected to match the focal length in the X-axis direction. Although this method is often used for single spectrometers, it is thought that it is possible in principle to perform correction using the same method for triple spectrometers as well.

Therefore, in order to achieve the above object, the high-sensitivity Raman measuring device of the present invention has a Raman beam focused between the focusing optical system and the input slit of the triple polychromator in the direction of the axis along the groove of the slit. Cylindrical material that can emit light
An astigmatism correction optical system equipped with a lens is arranged, and this cylindrical lens can be moved slightly along its optical axis.
Fine adjustment of the astigmatism correction optical system can be performed using a telescope equipped with a CCD camera placed at a position equivalent to the detector light-receiving surface by means of a switching mirror. This completely corrects the spread of the image on the light-receiving surface of the detector of the position-detecting photomultiplier tube at the exit of the polychromator due to astigmatism caused by the concave mirror of the spectrometer, and normally forms a band-shaped image. The spectrum is a spectrum on a thin straight line, and it is equipped with a fine movement mechanism that allows fine adjustment of the six degrees of freedom of the front, back, top, bottom, left and right positions of the detector relative to the spectrometer, as well as the rotation around the optical axis. The entire spectrum can be made to lie exactly on the acceptance plane of the detector, and a linear spectrum can be observed exactly in the X direction of the two-dimensional array of pixels that constitute the image of the position-detecting photomultiplier tube. Then, the entire image or the necessary parts are imported into the computer's memory as a two-dimensional image, that is, two-dimensional data with spectral information in the X direction and spatial distribution information in the Y direction, and then stored for a long time. By making the above-mentioned appropriate adjustments and using an appropriate measurement method, the object of the present invention can be completely achieved.

In addition, in the present invention, as an advantage of Raman spectroscopy,
Measurement targets include solids, liquids, gases, and semiconductors.

The present invention may be applied to metals, inorganic substances, organic substances, living organisms, plants, minerals, fossils, etc., but below we will mainly discuss examples targeting semiconductors, where the amount of industrial application seems to have a large influence.

[Example] Hereinafter, the present invention will be described in more detail with reference to the drawings and the like.

(Example 1) FIG. 1 is a configuration diagram of an ultra-high sensitivity Raman spectrometer to which an example of the present invention is applied.

This Raman spectrometer includes an irradiation optical system 1 that extends from a monochromatic laser 7 through a condensing lens 8 and a small mirror (or small prism) 9 for beam incidence to a sample 10, and a condensing lens for transmitting signal light scattered from the sample 10. A condensing optical system 2 that guides a condensing optical system 11 to an entrance slit 12, a cylindrical lens 13 for astigmatism correction installed in the middle of the condensing optical system 2, and a fine movement that adjusts its rotation, translation, and tilt with good reproducibility. Spectroscopy of a triple polychromator in which a single spectrometer 17 is connected to a differential dispersion type double spectrometer 16 having an astigmatism correction optical system 3 consisting of a mechanism 14 and a telescope 15 equipped with a CCD camera that looks directly at the entrance slit. Optical system 4 and position detection photomultiplier tube (PS-PMT) detector 18
A fine adjustment mechanism 19 that adjusts and fixes the rotation, parallel movement, and tilt of the lens and a telescope with a CCD fine adjustment mechanism that adjusts the astigmatism correction optical system to minimize astigmatism at the detector position. It consists of a detection system 5 consisting of a scope 20, and a signal processing circuit system 6 extending from a signal processing device 21 that receives signals from the detector 18 and stores them as position specific data signals to a two-dimensional data analysis computer 22.

Figure 2 shows a position detection photomultiplier tube (PSP M T,
) is a schematic diagram showing an example of a detector 18. 12 to 2
Photons incident on the 5 mm diameter light receiving surface 23 are converted into photoelectrons, multistage amplified while maintaining positional information by 3-5 micro channel plates 24, and finally resistive division generated in the resistive anode 25. It is detected by photon counting while calculating the arrival position of the electron from the ratio.

Position detection by resistive anode is 12 to 25
512 x 5 in 25 micron units for a mm square
Although the coordinates are determined as 12 to 1024 x 1024 pixels, the positional resolution is mainly determined by the thickness of the microchannel, which is about 40-70 microns. Usually, measurement is performed with an entrance slit width of 100 microns or more, and the resolution of the detector is sufficient.

In the following, for simplicity, the focal length of the double spectrometer 16 and the single spectrometer 17 will be described as 50 cm, and the imaging unit of the detector of the position detection photomultiplier tube 18 will be described as 25 microns square, 1024 pixels x 1024 pixels. .

(Example 2) In addition to the adjustment as a normal Raman device, this measurement device
An adjustment as described in claim 2 is necessary.

First, while monitoring the image of the sample 10 with a telescope 20 that looks directly into the entrance slit 12, check that the laser beam 7 is correctly focused on the sample and that its scattered light is correctly transferred onto the slit 12. Check. The same applies when using a microscope focusing optical system.

A standard sample for adjustment with a grid pattern is installed at this sample position, and the entire area of the pattern of the laser irradiation spot 12A is observed without distortion at the position of the entrance slit 12, as shown in FIG. 3(a). Check. This is a task to confirm that there is no distortion due to various aberrations in the condensing optical system 2.

Next, switch the switching mirror 17A at the exit of the final stage single spectrometer to the adjustment side, adjust the focal length of the telescope 20 with a CCD fine adjustment mechanism for adjusting the astigmatism correction optical system 3, and Check the grid pattern using monochromatic light such as a lamp for illumination. If the astigmatism correction optical system 3 is not used, the pattern is observed only in the direction of the slit groove, as shown in Figure 3(b), and the pattern in the direction perpendicular to the groove is completely blurred. .

This is because the focal length of the spectrometer differs in the vertical and horizontal directions due to astigmatism in the optical system that makes up the entire spectrometer. If the cylindrical lens 13 of the astigmatism correction optical system 3 has an appropriate focal length for the spectrometer aberration and is installed in the correct position and orientation, a pattern as shown in FIG. 3(C) will be formed. is observed as a two-dimensional image. Here, fine adjustment of tilting and parallel movement of the astigmatism correcting optical system 3 is performed by the fine movement mechanism 14 so that all the vertical and horizontal patterns are reliably transferred over the entire area on the slit. Thereby, a state without astigmatism can be created at the position of the detector light-receiving surface with an accuracy of 10 microns or less.

As shown in FIG. 4(a), the laser beam 7 is focused circularly on the sample 10, and this is confirmed by the image on the entrance slit 12.
When we switch the mirrors and look at the image of the spectrum on the detector of the position-detecting photomultiplier tube 18, when the astigmatism correction optical system 3 is not used, the result is as shown in Fig. 4(b). become. Here, each line is a Raman scattered light from a sample or a plasma emission line from a laser.

Since astigmatism has not been corrected, the image is spread out by 200 pixels in the Y-axis direction. If the same measurement is performed with the astigmatism correcting optical system 3 installed, the result will be as shown in FIG. 4(C). At this time, if we simultaneously measure the line emission from a mercury lamp, neon lamp, argon lamp, etc. that is uniformly incident on the entire slit as background light as shown in Figure 5(a), the result will be as shown in Figure 5(b). become. By using such two types of light emission, the position of the detector 5 can be adjusted accurately over a wide range of the light receiving surface. The position of the detector is slightly moved by the fine movement mechanism 19 so that the two spectra form orthogonal patterns without distortion.
The light receiving surface of the detector 5 is adjusted so that it is at a position equivalent to the focal plane adjusted in 0. At this time, in order for the entire light-receiving surface to be in the correct position, it is important not only to move the detector back and forth but also to tilt it. Further, for later data processing, it is necessary that the axial direction of two-dimensional position detection corresponds to the spectral direction, so fine adjustment of rotation is also important. Note that when image distortion occurs in the detector itself, it is necessary to minimize this by adjusting the circuit of the position detection mechanism. By sequentially and alternately performing these fine adjustments, it is possible to finally obtain the minimum signal spread and the best spectral resolution on the detector light-receiving surface.

Below, an example of measurement using a device adjusted in this manner will be described.

The spot of laser light irradiated onto the sample 10 by the irradiation optical system 1 is made into a minute circle. A diameter of about 10 to 100 microns can be used in the macro condensing system 2, and a diameter of about 1 to 10 microns can be used in the condensing system 2 using a microscope. For simplicity, consider the case where a microscope with a 100x objective lens is used, so that a 1 micron laser spot on the sample can be transferred onto a spectrometer entrance slit with a width of 100 microns and a diameter of 100 microns.

If the astigmatism correction optical system 3 is properly adjusted, this 100 micron diameter spot will be transferred onto the imaging detector as an approximately 100 micron diameter image if this light is monochromatic. At this time, even considering the positional resolution of 40-70 microns determined by the photoelectron multiplication process of the detector 5, the signals are concentrated in a range of 5-8 pixels in units of 25 microns. If the adjustment is done correctly, the signals of each wavelength will be aligned horizontally at each spectral position with a spread of 5 to 8 pixels.

Therefore, if one-dimensional data is obtained by adding up these 5 to 8 pixels in the vertical direction, it becomes Raman data.

Here, the dark noise of the position-detecting photomultiplier tube 18 is about 1-2 x 10-' counts/sec per pixel, so the number of dark noises per channel of Raman data is about 5-
15 x 10-5 force-counts/sec. Thus 0.00
If the signal is about 1 ton/sec, the signal to noise ratio is more than one digit.
Furthermore, even a signal of 0,0001 force/count/second can be detected satisfactorily.

Figures 6 and 7 show 520cm-
This is an example in which the peak near ' is measured while decreasing the intensity of the laser incident on the sample 10 one order at a time and increasing the measurement time ten times at the same time. In this way, a very weak Raman signal can be quantitatively generated with good reproducibility, making it possible to quantitatively evaluate the device. Here, the measurement was performed using the microscope focusing optical system 2 with the beam diameter narrowed down to 1 micron on the sample 10. FIG. 6 shows an example of measurement using the apparatus of the present invention, and FIG. 7 shows an example of measurement using II-PDA connected to the same spectroscopic system for comparison. In the measurement by II-PDA, pulse noise becomes impossible to ignore at 10 μW, and measurement becomes impossible at 1 μW due to this noise. These correspond to signal intensities of 0.1 force-count/second and 0.01 force-count/second, respectively, in terms of photomultiplier tubes. On the other hand, according to the device of the present invention, 100
At nW, a good spectrum with a high SN ratio was obtained, and even at 10 nW, a signal was detected with a sufficient SN ratio. These are respectively 0.001 force und/sec and 0
．． This corresponds to a signal strength of 0,001 volts/sec. Such measurements are impossible to achieve except with the device of the present invention, and are groundbreaking results that were previously only a pipe dream.

Furthermore, as a specific example of application to ultra-thin films, FIG. 8 shows a Raman spectrum from 3 molia of aluminum arsenide grown on a gallium arsenide single crystal, measured using this apparatus. A signal peak from aluminum arsenide is clearly observed above the strong spectrum of gallium arsenide.

Estimating from the peak intensity, it is not only estimated that a signal from 1 molar aluminum arsenide can be detected even in this state, but also Raman signal detection from sub-molar It is presumed that this is also possible.

Note that with analog detectors such as II-PDA and CCD, it is essentially impossible to avoid pulse noise, which is thought to be mainly caused by cosmic rays, as seen in Figure 7. This cannot be erased except by performing post-processing using software, such as repeating the process to remove peaks that do not recur.However, when using the position-detecting photomultiplier tube 18 as in the present invention, photon counting is performed. Therefore, even high-energy noise such as cosmic rays is not counted as more than 1 force count, making ultra-high sensitivity measurements possible. However, if this position-sensitive photomultiplier tube detector 18 is used as a multiplex detector like a normal II-PDA, 200-400 pixels per channel will be added vertically. , and a noise of 2-8 x 10-3 force/sec is unavoidable. That is, the SNNiO is about 250 for a signal of 0.1 force/count/second, which is not much different from that of II-PDA or CCD detectors.

As described above, in the conventional method of using the PS-PMT as a -dimensional detector for Raman spectroscopy, the original performance of the PS-PMT as an ultra-high sensitivity two-dimensional detector is not utilized.

In the present invention, in order to bring out the highest performance of this position detection type photomultiplier tube 18, a fine adjustment mechanism 19 of the detector 5, an optical system 3 for astigmatism correction, a fine adjustment mechanism 14 of the optical system, and two-dimensional data analysis are provided. The present invention is characterized by the use of appropriate combinations of devices 22 and the like, which makes it possible to detect signals that are two to three orders of magnitude weaker than conventional methods. These 2-3 digits are very important in practical applications, and for the first time, it has become possible to detect weak Raman signals from ultra-thin films on the sub-molecular level.

(Example 3) Next, in the case of the measurement method described in claim 4, in addition to the above adjustment, the following adjustment is further performed.

First, a cylindrical lens is used as the condensing lens 8 for making the laser beam 7 incident on the sample 10, and the sample is irradiated in a line shape. With the telescope 20 that looks directly at the entrance slit 12, this line is correctly aligned with the slit 12.
Make sure it is transferred above. Moreover, it is important here that the laser beam is uniformly irradiated onto the sample 10 in the dimensional direction.

Confirm that the two-dimensional image on the detector 5 is obtained using plasma emission from a laser.The cause of the distortion is that the light-receiving surface of the detector 5 is located at the focal plane of the spectrometer. There are two cases: the image is distorted when the detector 5 itself is tilted, and the image is distorted when detecting the position of the detector 5 itself.Adjust so that both are minimized. It is necessary to carry out the adjustment more strictly than in the case of the measurement according to claim 3.

FIG. 9 shows an example in which a region of a silicon single crystal is damaged by ion beam irradiation, and the amorphous region and the original single crystal region are simultaneously measured. Figure 9 (a,) is a schematic diagram of the sample and the irradiation area, with a length of about 1 mm perpendicular to the amorphous area with a thickness of 200 LLm.
The laser beam irradiation area was set. The results of the imaging measurement are shown in FIG. 9(b). The spectrum is given in the X direction, and the spatial distribution on the sample is measured in the Y direction. Non-irradiated area (■) and irradiated area II in FIG. 9(a).

The non-irradiated areas III are respectively shown in FIG. 9(b),
Compatible with III. FIG. 10 shows Raman spectra in the non-irradiated area (2) and the irradiated area (II), respectively. Although a 520 cm-' phonon peak from crystalline silicon is observed above and below the ion irradiation region, this peak disappears in the ion irradiation region, indicating that the region has become almost amorphous. In this example, the difference between the two is too clear, but if the difference spectrum between ■ and II is taken, it can be detected even if the difference between the two is very small. Since measurements are taken at different sites at the same time, not only is the measurement time shortened, but the measurement conditions are strictly the same, making it possible to evaluate differential Raman spectra with high precision.

[Effect of the Invention] As explained above, according to the present invention, the weakest signal measurable with the conventional world's highest performance device is 2-
Can detect signals that are three orders of magnitude weaker or more. In the present invention, the irradiation optical system, the condensing optical system, the astigmatism correction optical system, the spectroscopic optical system, the detection system, and the signal processing circuit system are appropriately combined and adjusted as described above. The significantly higher detection capability of the invention is realized. Normally, for this type of device, an improvement of 20%, 50%, or even double the detection capability is often considered a significant advance, which shows how revolutionary an improvement of 2-3 orders of magnitude is. It is obvious.

It is also possible to measure one-dimensional distribution images of Raman spectra with this same precision, allowing you to measure the location dependence of a sample at once, measure two or more samples simultaneously and directly compare them, and even use difference spectra. can be used to extract slight spectral differences.

As described above, according to the present invention, it is possible for the first time to perform Raman spectroscopy using ultra-thin films, etc., which overcomes the weak signal strength, which is a major drawback of Raman spectroscopy, and provides information at the atomic and molecular level. It is expected that this work will make a significant contribution to greatly expanding the applicability of Raman spectroscopy not only in the field of semiconductor evaluation but also in a variety of other fields. That is, the present invention provides monolayer or submolayer level semiconductors,
It is extremely effective for evaluating the physical properties of ultra-thin films of metals, organic substances, etc., molecules and atoms adsorbed on the surfaces of metals, semiconductors, etc., and minute amounts of impurities contained in semiconductors, ceramics, etc. using Raman scattering spectra.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the Raman spectrometer of the present invention. FIG. 2 is a principle diagram of an example of a position detection type photomultiplier tube used in the present invention. FIG. 3 is an explanatory diagram of the transferred image of the grid pattern used when adjusting the astigmatism correction optical system, and FIG. 3(a) shows the image confirmed by the entrance slit, Figure 3 (b) shows the image observed with the adjustment telescope placed at the same position as the detector when astigmatism correction is not being performed, and Figure 3 (c) shows the image observed when astigmatism correction is being adjusted. This shows the expected image when the process is completed. FIGS. 4(a), (b), and (c) are explanatory diagrams of spectra obtained with a position-detecting photomultiplier tube, and FIG. 4(a)
Figure 4(b) shows the spot of the laser beam when viewing the image of the sample on the entrance slit, and Figure 4(b) shows the image of the detector obtained when the astigmatism correction optical system is not used. Figure (c) shows an image of the detector when using an optical system for correcting astigmatism. FIGS. 5(a) and 5(b) show the adjustment method according to claim 2,
An image of the detector when simultaneously measuring the Raman signal from the laser irradiated as a circular spot on the sample, the plasma light emitting beam, and the emission line II from a mercury lamp, neon lamp, argon lamp, etc. that uniformly irradiates the entire slit area. FIG. 6 and 7 show Raman spectra of silicon single crystals, and FIG. 6 shows an example of measurement using the apparatus of the present invention.
Figure 7 shows an example of measurement with a II-PDA detector installed in the same optical system. While keeping the total signal amount constant by increasing the
This is an example of quantitatively investigating the detection limit of weak signals. Figure 8 is a Raman spectrum from aluminum arsenide grown on a gallium arsenide single crystal of 3 molia measured using this device. signal peaks are observed. FIGS. 9(a) and 9(b) are explanatory diagrams of an example in which one-dimensional spatial distribution images of the Raman spectrum of a silicon single crystal partially made amorphous by ion irradiation were measured. ) is the sample and irradiation area, Figure 9(b)
is a two-dimensional image of a position-sensitive photomultiplier tube. Figure 10 shows the non-irradiation area work and the irradiation area I in Figure 9(b).
1 is a diagram of a Raman spectrum obtained by processing data of I. 1... Irradiation optical system, 2... Condensing optical system, 3... Astigmatism correction optical system, 4... Spectroscopic optical system, 5... Detection system, 6... Signal processing Circuit system. Designated agent: Director, Electronics Research Institute, Agency of Industrial Science and Technology (b) (C) Figure 3: Entrance slit 12 Irradiation spot 12A Raman spectrum direction Figure 4: Raman shift (cm”) Figure 6: Raman shift (cm-) 1) Various P-to-Route Procedures?j-1'j Orthographic (Method) Heisei''/Fu. Person 4゜Designated agent (shipping port) Drawing subject to amendment 7゜Contents of amendment Drawing 9 (b) will be amended as shown in the attached drawing. I”d

Claims (1)

[Claims] 1) A Raman spectrometer that detects a Raman signal by irradiating a sample with excitation light, comprising: a condensing optical system that condenses scattered light from the sample; The output light is received through the entrance slit, and the Raman shift of the received light is 10.
A differential dispersion type double spectrometer for filters that can sufficiently remove stray light due to Rayleigh scattering and measure good spectra even in a relatively low wavenumber spectral region of ~1000 cm^-^1, and the double spectrometer It has a spectroscopic optical system in the form of a triple polychromator with a single spectrometer placed next to it, a micro channel plate, and a two-dimensional position detection mechanism in the subsequent stage. A low-noise photomultiplier tube for photon counting that is not affected by noise,
The channel plate receives and amplifies the output light from the spectroscopic optical system, guides the amplified output signal to a two-dimensional position detection mechanism, detects an image as a two-dimensional array of micro regions, and detects the image in each micro region. A position-detecting photomultiplier tube with extremely low dark noise and signal light of each wavelength from a minute irradiation area on the sample are transmitted to the position-detecting type photomultiplier tube without image blurring due to aberrations of the spectroscope. an astigmatism correcting optical system having a cylindrical lens that allows electrons to be transferred onto each minute area on a light receiving surface of a photomultiplier tube in a one-to-one correspondence; and when performing fine adjustment of the astigmatism correcting optical system. an adjustment telescope placed at a position equivalent to the light-receiving surface of the position-detecting photomultiplier tube using a switching mirror; and a fine adjustment mechanism for finely adjusting the position and orientation so that each micro region on the light receiving surface of the position detection type photomultiplier tube corresponds to a signal of each wavelength, and has an extremely low A highly sensitive Raman spectrometer characterized by simultaneous measurement of Raman spectra at noise levels. 2) A method for adjusting a Raman spectrometer for performing high-sensitivity Raman spectrometry using the Raman spectrometer according to claim 1, the method comprising: monitoring an image of the sample with a telescope that directly views the entrance slit; , confirm that the excitation light is correctly focused on the sample, and that the scattered light is accurately transferred onto the entrance slit, and place a standard sample for adjustment with a grid pattern at the position of the sample. and confirm that the entire pattern area can be observed without distortion at the position of the entrance slit, and switch the switching mirror placed at the exit of the single spectrometer to the adjustment side to correct the astigmatism. Adjust the focal length of the optical system adjustment telescope to check the grid pattern, and make sure that the vertical and horizontal patterns of the grid pattern are uniformly transferred over the entire area on the entrance slit without image blurring. Then, fine-tune the astigmatism correction optical system, reconfirm at the entrance slit position that the excitation light is correctly focused on the sample as a minute circular spot, and confirm that the Raman light generated by this excitation light is The spectra of signals, plasma emission, etc. and the line emission uniformly incident on the entire entrance slit as background light are simultaneously measured with the position detection type photomultiplier tube, and a pattern in which the two spectra are perpendicular to each other without distortion is obtained. The position of the position detection type photomultiplier tube is slightly moved so that the light receiving surface of the position detection type photomultiplier tube is at a position equivalent to the focal plane adjusted in advance by the telescope. By sequentially and alternately fine-tuning the movement, tilting, and axial rotation of the position-detecting photomultiplier tube, the final result is that the signal spread on the light-receiving surface is minimized and the spectral resolution is the best. A method for adjusting a Raman spectrometer, the method comprising adjusting the Raman spectrometer so that 3) When measuring Raman spectroscopy using the Raman spectrometer according to claim 1, the Raman spectrometer is adjusted by the method according to claim 2, and then the sample is irradiated with the excitation light, and the position detection type A high-sensitivity Raman spectroscopy method, characterized in that a position specific data signal is extracted from a photomultiplier tube, stored in a signal processing device, and a Raman spectroscopic measurement result for the sample is obtained based on the stored signal. 4) When measuring Raman spectroscopy using the Raman spectrometer according to claim 1, adjusting the Raman spectrometer according to the method according to claim 2, and using a one-dimensional line-shaped laser beam as the excitation light, The laser beam is focused onto the sample in a one-dimensional line, and the one-dimensional linear excitation light is transferred onto the light-receiving surface of the position-detecting photomultiplier tube while maintaining the spatial resolution. The spectrum is extracted as a two-dimensional image data signal and accumulated in a signal processing device, and the accumulated signal is subjected to differential processing regarding the one-dimensional position to detect minute changes in the Raman spectrum due to the one-dimensional position on the sample. A highly sensitive Raman spectroscopy method that detects