JP2007322411A - Measuring method and analytical method of energy level - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of obtaining impurity level and defect level accurately. <P>SOLUTION: The level of capture center is revealed by measuring the peak of intensity and wavelength of emitting light, because if ion beam 21 is irradiated on sample 15, the light of wavelength accoding to the difference of energy level of valence band and capture center is emitted, when holes excited by ion irradiation move to the capture center. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for measuring band gap energy of oxides, semiconductors, metals, etc. and energy levels of impurities.

  A cathode luminescence method is known as a method for measuring a defect level existing in a band gap of an insulator material. This method irradiates an insulator material with a high-speed electron beam and spectroscopically measures the light (photon) generated from the insulator material at that time, from the peak wavelength of the spectrum to the defect level from the bottom of the conductor. It is a technology to analyze the energy of. The spectrum measured by this method is not the ground state of the crystal defect, but the electronic state after electrons are emitted from the defect by electron beam irradiation and the crystal arrangement around the defect is changed. Therefore, it is impossible to measure the defect level itself in the ground state. Furthermore, since the cathode luminescence measurement uses electrons in the excited state rather than the defect level and impurity level, the energy such as the defect level can be determined only by the energy difference measured from the lower end of the conduction band. There was a problem. As another method for measuring the band gap energy, photoelectron spectroscopy is known.

In photoelectron spectroscopy, the energy from the electron level to the electron emission level is obtained by measuring photoelectrons emitted from the surface of the sample while sweeping light applied to the sample.
Since the electron emission level is a value obtained by combining the vacuum level and the work function, there is a problem in that the impurity level cannot be determined directly.
JP-A-2005-71858 JP 2005-353455 A JP-A-2005-71858 Yasushi, Motoyama, et.al., J. Appl.Phys., 95, 8424 (2004) Yoichi Koshi, et al., “Spectroscopy of ion excitation and its application”, p71-89, Academic Publishing Center, 1987

  An object of the present invention is to provide a technique capable of accurately measuring the size of a band gap and the energy level of a trap center such as a defect level and an impurity level.

In order to solve the above-described problem, the present invention irradiates a sample made of a measurement target substance having a band gap with charged particles, and detects emitted light emitted from the sample irradiated with the charged particles. Measurement of the energy level from the wavelength of the light contained in the emitted light to obtain the value of the energy level that is between the valence band and the conduction band of the sample and generated the light contained in the emitted light Is the method.
The present invention is also a method for measuring an energy level, wherein the charged particles are atomic ions or molecular ions.
Further, the present invention is a method for measuring an energy level in which the charged particles are accelerated at a voltage of 200 V or less and irradiated on the sample.
In the present invention, the content of the capture center contained in the measurement target substance having a band gap and the wavelength of the light generated by the capture center are previously measured and related, and the measurement target substance is configured. Irradiating the sample with charged particles, detecting emitted light emitted from the charged particle irradiated portion of the sample, and detecting the wavelength of the light contained in the emitted light and the association to determine the capture center of the sample. It is an analysis method that identifies the contents.
The present invention also provides an analysis method using atomic ions or molecular ions for the charged particles.
Further, the present invention is an analysis method in which the charged particles are accelerated at a voltage of 200 V or less and irradiated on the sample.

  When the inventors of the present invention irradiate a sample with a low-energy ion beam that does not cause sputtering, light of a wavelength corresponding to the difference in energy level between the sample's valence band and the capture center such as a defect is emitted from the sample. I found it released.

By analyzing the energy distribution of the light emitted from the sample, the energy level of the trap center can be found. In addition, it is possible to specify a trace substance contained in a sample from the relationship between the content of the capture center measured in advance and the energy level.
In either case, the acceleration voltage of the ion beam is desirably 200 V or less.

  By defining the energy of the trap centers such as multiple defect levels and impurity levels existing in the band gap by the energy difference from the reference energy point near the lower end of the conduction band and the upper end of the valence band, respectively. The gap energy, the defect level existing in the band gap, the impurity level, the energy level of the electron trap, and the impurity level can be determined with high accuracy.

First, the basic principle of the present invention will be described.
When the sample to be analyzed is irradiated with a beam of charged particles (hereinafter referred to as “ion”), electrons are emitted from the sample by a so-called Auger process. It was discovered that when an ion beam is irradiated, light is also emitted from the sample along with electron emission.

  This light was expected to be due to holes and electrons generated by ion beam irradiation, but when the intensity of the emitted light was measured using a substance with a known impurity level, the acceleration voltage of the irradiated ions was When it was small, it was found that the observed light had the energy of the difference between the impurity level and the valence band.

This is because light was emitted when holes generated by ion irradiation transitioned from the valence band to the level of the trap center (the level located between the conduction band and the valence band). It is thought that it shows.
Therefore, when the energy of the emitted light, that is, the wavelength of the emitted light is measured, it becomes possible to measure the capture center level of the sample.
When the sample is irradiated with ions, the current component caused by the generated holes can be extracted from the current flowing in the sample, and the number of generated holes can be known.

FIG. 3 is a graph showing the relationship between the acceleration voltage of ions and the yield of emitted electrons, and FIG. 4 is a graph showing the relationship between the acceleration voltage of ions and the intensity of emitted light. The horizontal axis represents the ion acceleration voltage, and the vertical axis represents the electron yield or emitted light intensity per hole.
When the acceleration voltage is 200 V or less, the yield of emitted electrons per hole and the intensity of emitted light are constant, but when the acceleration voltage is greater than 200 V, the positive voltage increases in proportion to the acceleration voltage. The yield per hole and the light intensity are increased.

  The energy at which ions in an ion beam generate holes and electrons is expected to be the sum of the ionization potential and kinetic energy of charged particles. Therefore, when the secondary electron emission efficiency by ion irradiation is measured, when the kinetic energy of the irradiation ions is large, that is, when the acceleration voltage is large, there is an acceleration voltage threshold at which the secondary electron emission efficiency starts to increase. When light emission due to ion irradiation is measured, a phenomenon is observed in which light emission starts to increase from an acceleration voltage substantially corresponding to this threshold value. This suggests that in the light emission measurement, light emission components due to atoms and molecules sputtered from the sample surface by the irradiated ions are superimposed. Therefore, in the case of light emission measurement, it is necessary to control the acceleration voltage of irradiated ions in order to exclude the light emission component caused by sputtering. In the present invention, an acceleration voltage of 200 V or less is desirable.

  When the measurement principle of the present invention is compared with the prior art, the cathode luminescence method that measures the defect level by electron irradiation as in the prior art injects excessively high energy electrons into the sample. There is concern about the crystallinity change. The most important thing to note is that the cathodoluminescence method measures the defect level after electrons are emitted from the defect, so the energy level in the ground state of the defect and its existence probability cannot be determined. .

  On the other hand, according to the present invention, electrons and holes are generated gently in the Auger neutralization reaction, so that the holes once remain in the initial state with a narrow energy width, and then the defect level, impurity level and Interact. Therefore, in the present invention, the energy width and intensity of the generated light are determined by the product of the initial state, that is, the energy width of the holes, the energy width of the defect level, and the impurity level. Is possible.

  When comparing the detection limit concentration of defect level and impurity level, the present invention can define the energy level of holes before interacting with the defect level and impurity level to a very narrow energy width. The photons emitted as a result of the interaction with the level and impurity level are excellent in monochromaticity and have a very large number of photons. Therefore, it is possible to detect a defect level and impurity concentration on the order of 1 ppb.

  In addition, since the density of the capture center is proportional to the light intensity of the light contained in the emitted light, it can be obtained by measuring a sample whose concentration of the capture center is known in advance and irradiating an ion beam of the same type and intensity. The approximate defect density of the sample can also be obtained by comparing the light intensity peaks of the spectroscopic analysis results.

  For the ion species, Auger neutralization reaction proceeds if the ionization potential of the irradiated ion is larger than the upper energy of the valence band, that is, the HOMO (Highest Occupied Molecular Orbital) level. Therefore, the ion species suitable for measurement is determined by the valence band structure of the sample to be measured.

  For example, when the sample is magnesium oxide (MgO), the band gap energy is 7.5 eV to 7.8 eV, and since the energy from the lower end of the conduction band to the vacuum level is about 1 eV, ions of about 9 eV or more are used. If there is potential, Auger neutralization reaction occurs, so it is sufficient to irradiate ion species that meet this condition.

  When an Auger neutralization reaction occurs at a deep level in the valence band, the electron may not be excited to the conduction band, but interacts with the defect level and impurity level only with holes, so the valence electron There is an advantage that the energy level measured from the upper end of the band can be obtained.

  Some ions, such as alkali metal ions, may be chemisorbed on the sample surface. In order to avoid chemical adsorption, rare gas ions or nitrogen (N) ions may be irradiated. Even when boron (B), phosphorus (P), or the like is ion-implanted into a semiconductor material, in-situ observation of the band gap, impurity level, and defect level according to the principle of the present invention is possible. For example, when doping an n-type element into a silicon material, the process of forming impurity levels formed in the band gap of silicon, which is a semiconductor, and the analysis of impurity concentration can be performed simultaneously with ion implantation, so that the ion implantation process can be optimized. There is an effect that can be used.

The starting point of the present invention is the generation of electrons and holes by Auger neutralization reaction. Therefore, in principle, the kinetic energy of ions irradiated on the sample surface may be zero, but it is necessary to irradiate the surface with positive ions against charge-up on the surface, so the kinetic energy for that is is necessary. In addition, even when ions are irradiated at an acceleration voltage higher than the kinetic energy necessary to resist charge-up, hole injection by positive ions is promoted, so the frequency of interaction between holes, defect levels, and impurity levels. Increases the emission intensity.
When the band gap energy is 10 eV, it is sufficient in the present invention to perform spectroscopic measurement at a wavelength longer than 124 nm.

Next, the measuring method of the present invention will be described together with the measuring device.
Referring to FIG. 1, reference numeral 1 is an example of a measuring apparatus that can carry out the measuring method of the present invention, and has a vacuum chamber 11. An evacuation system 28 is connected to the vacuum chamber 11, and the inside of the vacuum chamber 11 is evacuated by the evacuation system 28.
A sample mounting table 12 is disposed inside the vacuum chamber 11. Reference numeral 15 in FIG. 1 denotes a sample placed on the sample mounting table 12.

  An ion source 16 is disposed in the vacuum chamber 11. A gas introduction system 14 is connected to the ion source 16, and the irradiation gas introduced from the gas introduction system 14 is ionized inside the ion source 16, accelerated by an acceleration voltage, and irradiated to the sample 15 as an ion beam 21. It is configured as follows.

The irradiation gas used is a substance whose ionization energy is larger than the energy of the valence band of the sample 15, and when the sample beam 15 is irradiated with the ion beam 21 in a vacuum atmosphere of about 10 ⁻⁶ Pa in the vacuum chamber 11, Irradiated ions undergo an Auger neutralization reaction with atoms on the surface of the sample 15 to generate electron-hole pairs. The ionization energy is 25 eV for He, 21 eV for Ne, and 12 eV for Xe.
When the generated holes transit to the energy level of the capture center, electrons and emission light 22 are emitted from the portion of the sample 15 irradiated with the ion beam 21.

Inside the vacuum chamber 11, a light receiving device 17 for detecting emitted light 22 emitted from a portion irradiated with the ion beam 21 is disposed.
A spectroscopic analyzer 18 that measures the wavelength and light intensity (light quantity) of the emitted light 22 detected by the light receiving device 17 is disposed outside the vacuum chamber 11.

The light receiving device 17 is a device that measures the wavelength of light contained in the incident emitted light 22 and the intensity of light of that wavelength. Here, a device that can measure light having a wavelength in the range of 350 nm to 650 nm is used. ing.
The spectroscopic analyzer 18 detects a wavelength having a relative intensity equal to or greater than a predetermined value from the relationship between the measured wavelength of the emitted light 22 and the light intensity. When the composition of the sample 15 is known, since the energy level of the valence band is known, the impurity level can be determined from the wavelength of the detection light.

5 to 8 are graphs showing measurement results of the MgO thin film or the mixture of MgO and CeO, and show curves connecting the light intensities of 400 nm, 450 nm, 500 nm, 550 nm, and 600 nm. Peaks are observed around 450 nm and 550 nm, respectively. These are lights emitted by holes, and the level of the capture center of the sample 15 is determined from the wavelength.
When the component of the trace substance contained in the sample 15 is unknown, the unknown unknown substance can be identified by comparing the wavelength of the emitted light with the database.

This measuring apparatus 1 has an analysis device 19 and a storage device 20.
The wavelength of light emitted when ions are irradiated to a trace substance that may be contained is measured in advance, stored in the storage device 20, and ions are added to a sample containing an unknown substance. When irradiated, the wavelength of light contained in the emitted light is detected and compared with the stored content of the storage device 20 by the analysis device 19, the trace substance contained in the sample 15 can be identified.
When the sample 15 is irradiated with ions and light is emitted, electrons are emitted together with the light due to Auger transition.

  In the measurement apparatus 1 of FIG. 1, an electron multiplier tube 26 that multiplies an incident electron signal and a spectroscopic analyzer 27 that measures an energy distribution are arranged, and an electron emitted from a sample 15 together with light is arranged. The energy distribution is measured, and the element on the surface of the sample 15 (depth of about several nm) can be identified and quantified.

Next, FIG. 2 is another example of a measuring apparatus that can implement the method of the present invention.
In this measuring device 2 and the measuring device 1 of FIG. 1, common members are denoted by the same reference numerals and description thereof is omitted.
The measuring device 2 includes an optical filter 31 and a photomultiplier tube 33 in place of the light receiving device 17 and the spectroscopic analyzer 18.

The optical filter 31 is a band-pass filter that passes light of a specific wavelength and does not pass light of other wavelengths, and allows the wavelength of light originating from the capture center of the sample 13 that has been known in advance to pass. ing.
The light that has passed through the optical filter 31 enters the photomultiplier tube 33, a large amount of electrons are generated, and the light intensity of the transmitted light is amplified and detected by the analysis device 19. When the light intensity before multiplication is calculated from the multiplication curve of the photomultiplier tube 33, the light intensity of the wavelength that the optical filter 31 passes among the light emitted from the sample 15 can be obtained.

  If the optical filter 31 is replaced and light of different wavelengths is allowed to pass, the intensity of light of a plurality of wavelengths can be detected. FIGS. 5 to 8 show the results of measuring the light intensity of five types of wavelengths (400 nm, 450 nm, 500 nm, 550 nm, and 600 nm) by exchanging five filters.

This measuring device 2 may also be provided with an electron multiplier 26 and a spectroscopic analyzer 27 to detect emitted electrons and measure the energy distribution of the electrons.
When the measurement target substance is MgO, the energy of the band gap is 7.5 eV to 7.8 eV, and if the wavelength of 160 nm or more can be measured, all the light emitted from MgO can be measured. However, it may be practically possible to measure in the wavelength range of 250 nm to 700 nm.

In addition, the sample 15 that can be measured by the present invention is not limited to a single crystal or a thin film, but may be any material that has a band gap such as an insulator or a semiconductor in a portion irradiated with ions.
Further, ions of the ion beam that can be applied to the sample 15 include hydrogen (H), oxygen (O), nitrogen (N), boron (B), phosphorus, as well as rare gases such as He, Ne, Ar, Xe, and Kr. Ions such as (P), arsenic (As), gallium (Ga), and alkali metals can be used.
Any one of them may be irradiated alone, or ions of two or more elements may be mixed and irradiated.

  Although the case where atomic ions are irradiated to the sample or substrate to be measured has been described above, the charged particles of the present invention include elementary particles and molecular ions having charges such as electrons and protons. For example, in Auger analysis in which a substance is irradiated with electrons and the secondary electrons are observed, instead of measuring the secondary electrons, or in addition to measuring the secondary electrons, the light generated by the electron irradiation is detected and the light intensity is detected. An analysis method and a measurement method for measuring the wavelength are also included in the present invention.

An example of a measuring apparatus that can implement the method of the present invention Other examples of measuring apparatus that can implement the method of the present invention Graph showing the relationship between the acceleration voltage of the ion beam and the yield of electrons emitted from the sample Graph showing the relationship between the acceleration voltage of the ion beam and the intensity of light emitted from the sample Graph showing an analysis example according to the present invention (MgO: Xe) Graph showing an analysis example according to the present invention (MgO + CeO: Xe) Graph showing an analysis example according to the present invention (MgO: Ne) Graph showing an analysis example according to the present invention (MgO: He)

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Vacuum chamber 15 ... Sample 17 ... Light receiving device 18 ... Spectroscopic analysis device 19 ... Analysis device 20 ... Memory | storage device 21 ... Ion beam 22 ... Emission light

Claims (6)

A charged particle is irradiated to a sample composed of a measurement target substance having a band gap,
Detecting the emitted light emitted from the place where the charged particles of the sample are irradiated;
Energy level measurement method for obtaining a value of an energy level existing between a valence band and a conduction band of the sample and generating light contained in the emitted light from a wavelength of light contained in the emitted light .   The energy level measurement method according to claim 1, wherein the charged particles are atomic ions or molecular ions.   The energy level measuring method according to claim 1, wherein the charged particles are accelerated at a voltage of 200 V or less and irradiated on the sample. The content of the capture center contained in the measurement target substance having a band gap and the wavelength of the light generated by the capture center are measured and associated in advance,
Irradiating charged particles to a sample composed of the measurement target substance,
Detecting the emitted light emitted from the place where the charged particles of the sample are irradiated;
An analysis method for identifying the content of the capture center of the sample from the wavelength of light contained in the emitted light and the association.   The analysis method according to claim 4, wherein the charged particles are atomic ions or molecular ions.   The analysis method according to claim 4, wherein the charged particles are accelerated at a voltage of 200 V or less, and the sample is irradiated.

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