KR100752161B1 - Method for Analysis using Auger Electron Spectroscope - Google Patents

Abstract

In the AES analysis method according to the present invention, the intensity of the secondary electrons at the elastic peak measured after adjusting the Z axis value of the sample and the intensity of the secondary electrons actually measured are measured. The sample is quantitatively analyzed by comparing normalized intensity values obtained by using ratios of values.

And the standardized intensity value is calculated by the following equation,

In = C × Ir / Iz

Here, In is a normalized intensity value, Iz is an intensity value of secondary electrons at an elastic peak after Z-axis adjustment, and Ir is an intensity value of actually measured secondary electrons ( intensity) value, and C represents an arbitrary constant.

According to the present invention, the ability of quantitative analysis by AES can be improved by normalizing the size of an elastic peak through Z-axis control. In addition, by greatly increasing the reproducibility of the data according to the AES quantitative analysis, it is possible to perform the surface analysis of the more reliable AES equipment.

AES, Z-axis, Auger Electronics, Normalization

Description

Method for Analysis using Auger Electron Spectroscope

1 is a schematic diagram illustrating the general principle of AES.

FIG. 2 is a graph of a universal curve showing the mean free path of particles. FIG.

3 is a schematic diagram illustrating an X-ray emission process by AES.

4 is a schematic diagram illustrating an Auger electron emission process by AES.

5 is a graph showing the type of elements depending on the energy of the Auger electrons.

6 is a graph showing the energy distribution of secondary electrons by AES.

7 is a schematic diagram showing the X, Y, Z axis and rotation, tilt axis of the sample stage in the AES chamber.

8 is a graph showing the spectrum of Auger electrons by adjusting the Z axis value of the actual AES.

9 is a graph schematically illustrating the spectrum of FIG. 8.

FIG. 10 is a graph showing a spectrum of Auger electrons normalizing intensity at the elastic peak position. FIG.

11 is a graph showing the spectrum of actual measured Auger electrons of a sample measured after Z-axis adjustment.

FIG. 12 is a graph showing a standardized spectrum of the data of FIG. 11; FIG.

The present invention relates to an Auger Electron Spectroscope (AES) analysis method, and more particularly to an AES analysis method that can increase the reliability of quantitative analysis by AES.

In general, semiconductor devices include various products such as memory and LCDs, and some of these semiconductor devices are manufactured as samples to be analyzed in various ways to improve yield and product performance. The AES device is for analysis of contamination or composition ratio of the composition.

The AES device is used for qualitative and quantitative analysis of the elements constituting the sample surface by measuring the kinetic energy of the auger electrons emitted by injecting an electron beam focused at several hundreds of microns onto the sample surface. Its excellent ability to analyze small areas is mainly used for particle analysis, damage area analysis and composition ratio analysis of thin films (Si ₃ N ₄ , WSi ₂ , TiN, PSG, BPSG…). As it is a device used, it has a very high resolution. Therefore, AES device is the most widely used surface analysis device among Auger Electron Spectroscope (AES), Secondary Ion Mass Spectrometry (SIMS), and X-ray Photoelectron Spectroscope (XPS), which are called three major types of surface analysis. In addition, it occupies a very important position in the research of materials fields such as advanced materials that are becoming more versatile.

Auger electrons, on the other hand, are emitted when the X-rays or electron beams are incident on the sample in the UHV chamber of the AES device, which is generally electron beams because the flux is small and difficult to focus. Use In addition, the size of the primary electron beam incident on the sample greatly affects the resolution and resolution of the sample. The use of the electron beam not only reduces the beam size to several hundred microseconds, but also uses scanning (electron optics) Since scanning can be performed, auger electrons are mainly generated by using an electron beam. Therefore, AES can observe the SE image of the sample by scanning the secondary electrons generated by the primary electron beam scanned in the sample, and can easily find the analysis position.

The electrons incident on the surface of the sample read and stop the energy while ionizing and exciting the atoms constituting the sample. The excitation volume formed in this process is 1 to 3 μm as shown in FIG. 1. To reach. In addition, secondary electrons, including auger electrons, and X-rays are generated in the excitation volume.

In this case, X-rays having a long inelastic mean free path may come out of the surface without losing their initial energy even if they occur deep below the surface, but have a kinetic energy of 3000 eV or less. In the case of auger electrons, if they occur deep within the surface, it is difficult to escape from the surface. As shown in FIG. 2, when looking at a universal curve showing a mean free path according to energy of a particle, an inelastic mean free path for an Auger electron having an energy of 3000 eV or less ( Because the inelastic mean free path is about 10 atomic layers, only the auger electrons that are generated near the surface can come out of the surface, which is the surface selectivity of AES. According to the universal curve shown in FIG. 2, the escape depth in the energy band of the Auger electrons is in the range of several hundred to fifty microns. It can be defined as the analytical depth that can be obtained.

On the other hand, the generation principle of the Auger electron is as follows.

When electrons in the bottom are excited by the primary electron beam incident on the sample, and a hole is formed in the inside angle (for example, K-angle), the bottom state is returned by two processes. As shown in FIG. 3, the electrons of the upper energy level are transferred to the cabinet to emit light (X-ray fluorescence), or as shown in FIG. 4, energy is transferred to surrounding electrons without emitting light and thus secondary. Electron electron emission. At this time, the secondary electrons generated by being transferred to the surrounding electrons are called Auger electrons, and the energy of the Auger electrons is determined by the energy of the level to which each electron belongs regardless of the incident electron beam energy. Is determined. At this time, since the composition of the energy level for each element, the binding energy and the like are different, the energy of the Auger electrons generated for each element also differs from element to element, and has a unique value.

As shown in the X-ray fluorescence and auger electron emission process, the L1 electrons are X-ray emission for the core hole in the K-angle. X-ray fluorescence and auger electron emission are competitive, and the probabilities of both processes add up to one. However, since the probability of auger electron emission varies depending on the atomic number, competition with X-ray fluorescence can be avoided.

The kinetic energy of these auger electrons is given by the binding energies of the electron angles involved in the transition:

E _XYZ = E _X -E _Y -E _Z -Φ

Where E _XYZ is the kinetic energy of the Auger electrons generated by the transition, and E _X , E _Y and E _Z are the binding energies of the X, Y and Z shells, respectively. energy, and Φ means the work function of the spectrometer. As described above, since the energy of the Auger electrons determined by the binding energy is unique for each element as shown in FIG. 5, the components of the sample can be distinguished using the characteristics of the Auger electrons. Can be.

FIG. 6 shows a curve showing the energy distribution of secondary electrons according to the relationship between N (E) and KE and between dN (E) / dE and KE.

As shown in the lower part of FIG. 6, the Auger peak is very weak due to the high background of the secondary electrons, which is difficult to identify. Therefore, as shown in the upper part of FIG. 6, the spectrum obtained by differentiating N (E) with respect to energy is mainly observed and analyzed.

As mentioned earlier, all elements have inherent auger energy, which allows for qualitative analysis through AES, with a limit of 0.1 to 1 atomic%.

On the other hand, among the methods generally used for quantitative analysis, there is a method using the "peak-to-peak height ratio" of the Auger peak obtained from the differential spectrum (spectrum). This method determines the concentration of an element by comparing it with a signal of a pure standard element, or calculates the concentration with its relative sensitivity by comparing it with a signal of pure silver (Ag). In this case, the sensitivity of the AES is determined by the possibility of an Auger transition, the dose of the incident beam, and the efficiency of the analyzer.

However, in the case of quantitative analysis using the "peak-to-peak height ratio", it is impossible to analyze the sample without the standard sample. However, it can be said that it is almost impossible to have all the standard samples of samples with tens of thousands of elemental combinations. In addition, in the case of AES analysis, since the reproducibility is greatly reduced even for the same sample under the same analysis conditions, it is difficult to make a comparative comparison with existing data. For some of these reasons, AES is mainly used for qualitative analysis, but relative quantitative analysis is performed by comparing samples loaded at the same time.

An object of the present invention is to increase the reliability of data according to quantitative analysis by AES and to greatly increase the reproducibility of the data.

 Another object of the present invention is to enable quantitative analysis by reliable AES without using a standard sample.

In the AES analysis method according to the present invention, the intensity of the secondary electrons at the elastic peak measured after adjusting the Z axis value of the sample and the intensity of the secondary electrons actually measured are measured. The sample is quantitatively analyzed by comparing normalized intensity values obtained by using ratios of values.

The normalized intensity value is calculated by the following equation,

In = C × Ir / Iz

Here, In is a normalized intensity value, Iz is an intensity value of secondary electrons at an elastic peak after Z-axis adjustment, and Ir is an intensity value of actually measured secondary electrons ( intensity) value, and C represents an arbitrary constant.

Embodiment

Embodiments of the present invention will be described below with reference to the drawings.

In general, the AES device is a device for detecting the characteristics of the sample by detecting the Auger electrons among the various particles generated after injecting the primary electron beam to the sample loaded in the UHV chamber. Among the particles generated in the sample, SE images can be observed by scanning secondary electrons in a secondary electron detector (SED), and multi-channels of auger electrons separated through a CMA (Clindlindrical Mirror Analyzer) The surface characteristics of the sample can be analyzed by detecting it with a multi-channel detector.

As shown in FIG. 7, the sample loaded in the sample stage in the AES chamber may be moved by X-axis, Y-axis, Z-axis movement, rotation, and tilt. The values of the X-axis, Y-axis, and rotation axis during the movement of the sample in this AES chamber do not significantly affect the analysis data of the sample. The position of the AES electron guns, detectors and analyzers is fixed, so it only changes the analysis position of the sample.

However, the position of the Z-axis and the value of the tilt-axis are one of the important analysis condition factors because they affect the data. If the value of the tilt axis of the sample is changed, the angle of the primary electron beam incident on the sample is also changed, the excitation volume of the sample is changed, and also affects the analysis area. This will affect the analytical data. In particular, AES has a greater impact because it is a device that analyzes information on the surface of the pole.

Z-axis values also have a significant effect on the sample data by AES analysis. Because AES needs to measure the kinetic energy of the Auger electrons, because the Z-axis value can change the position of the kinetic energy where elastic collision occurs for each AES device. In addition, since the electrons are not detected at the correct position unless the Z-axis value is corrected before the AES analysis, the position of the elastic peak must always be corrected through the adjustment of the Z axis before the AES analysis.

For this reason, Z-axis alignment should be performed before starting the AES analysis and after changing the values of the X, Y, rotation, and tilt axes of the sample. This is because the distance between the sample and the detector is slightly different depending on the position, the thickness of the sample, and the like.

On the other hand, the primary electron beam used for AES analysis uses an acceleration voltage of 1 keV to 20 keV and a current of 1 nA to 20 nA. At this time, proper combination of acceleration voltage and current is important. Conventional AES analysis uses a primary electron beam with a 10keV acceleration voltage and 10nA current.

The higher the acceleration voltage, the smaller the beam size, and the higher the resolution. However, the excitation volume of the sample becomes too large, and the electron beam damage is caused to the sample. The smaller the current of the electron beam is, the smaller the beam size is, and thus the resolution can be increased. However, since the intensity of the generated auger electrons is reduced, the noise of the data is reduced. Will be higher. For these reasons, the appropriate values of 10keV acceleration voltage and 10nA current are used for conventional AES analysis.

When the AES analyzer is not used or is in the air, the primary electron beam normally waits under 1 keV acceleration voltage and 0.5 nA current or less. The energy and current values of electron beams under these conditions are used in atmospheric conditions because they have too little energy to generate particles in the sample or equipment, and also minimize the damage to the sample.

Even if particles are generated, the detection limit of AES is about 0.1 to 1 at% (slightly different depending on the elements), so it is almost auger except for the background level secondary electrons and backscattered electrons. ) The former is not detected. However, at this time, many secondary electrons are generated at a position similar to the acceleration voltage due to the elastic collision of the primary electron beam. However, almost no particles are generated except the secondary electrons caused by the elastic collision of the primary electron beam.

This principle is used to adjust the Z axis value of the sample.

Before the AES analysis, the Z-axis value is always adjusted so that a kind of calibration is performed to form a peak at the correct position. At this time, even if an electron beam having a 1000 eV edge is incident due to various causes, an elastic collision does not occur at the 1000 eV position. This may be due to the error of the primary electron beam energy, the electron beam may lose some energy while coming to the sample, and the AES analysis data is analyzed using differential energy values.

For these reasons, the position of the kinetic energy where the elastic collision occurs for each AES device may be slightly different, but the Z-axis value is adjusted to generate the most secondary electrons. If the Z-axis value is not adjusted, the intensity of the AES analysis data is greatly reduced, resulting in relatively high background and noise. Also, first of all, since the auger electrons are not detected at the correct position, the correct analysis data cannot be obtained.

FIG. 8 shows the spectrum of Auger electrons formed when the Z-axis value of an AES device is adjusted. 9 is a diagram schematically illustrating the spectrum of FIG. 8.

At this time, in the AES device, the kinetic energy of the Auger electrons (represented by the X-axis value in the graph of FIG. 9) and the intensity of the secondary electrons (represented by the Y-axis value in the graph of FIG. 9) are functional relationships. Appears. At this time, the position of the elastic peak (elastic peak) is adjusted by adjusting the Z-axis value. In this case, the intensity of the secondary electrons at the elastic peak position generated by the elastic collision between the primary electrons and the sample is different depending on the state and position of the sample. Intensity in the conductor sample is higher than that of the insulation sample, and even in the case of a sample of the same material, a difference in intensity occurs according to the value of the tilt axis.

For these reasons, when quantitative analysis of AES is carried out, there is a limit in comparing and quantitating data if the sample elements are different. In addition, since the reproducibility of the AES analysis data is not good, there is a difference in intensity even with the same sample. In order to prevent this, when performing AES analysis, all samples are analyzed after obtaining a spectrum of Auger electrons as shown in FIG. 9 to control the Z-axis value. At this time, if the intensity value of the spectrum of the Auger electrons is equally standardized to an arbitrary constant called C for all data, the following proportional expression is established.

Iz: Ir = C: In

The above expression can be expressed as

In = C × Ir / Iz

Here, In is a normalized intensity value, Iz is an intensity value of secondary electrons at an elastic peak after Z-axis adjustment, and Ir is an intensity value of actually measured secondary electrons ( intensity), and C represents an arbitrary constant. That is, the data obtained by normalizing the ratio of the Iz value obtained by adjusting the Z axis of the AES device and the Ir value obtained by measuring the actual sample are obtained, and comparing the normalized data of each sample. In this way, quantitative analysis by AES is possible.

FIG. 10 illustrates a spectrum of an Auger electron normalizing the intensity at an elastic peak position, in which case the normalized In value is a constant C. FIG. do.

Meanwhile, FIGS. 11 and 12 show spectrums of auger electrons according to another embodiment of the AES analysis method according to the present invention. FIG. 11 illustrates actual data Ir values of samples measured after Z-axis adjustment, and FIG. 12 illustrates In values in which the data of FIG. 11 is normalized.

The present invention having such a configuration can be obtained by normalizing the AES analysis data every time the Z-axis value is adjusted using an appropriate method, for example, a method of adding a normalization program and a function in the equipment. Even if the measurement time is different or the analysis position of the sample is different, since the intensity of the secondary electrons is normalized, it will be possible to compare and analyze the data for different kinds of samples. That is, although the actual intensity value measured for each sample is different due to the experimentally demanding process conditions, the data of each sample is compared by comparing the intensity value obtained by standardizing the intensity value Ir. It can be compared quantitatively. In addition, even when performing AES analysis with a time difference, although the data reproducibility of the AES device itself is inferior, it is possible to compare and analyze the data through normalization of the intensity of the elastic peak. Can increase

Although specific embodiments of the present invention have been described with reference to the drawings, this is intended to be easily understood by those skilled in the art and is not intended to limit the technical scope of the present invention. Therefore, the technical scope of the present invention is determined by the matters described in the claims, and the embodiments described with reference to the drawings may be modified or modified as much as possible within the technical spirit and scope of the present invention.

According to the present invention, the ability of quantitative analysis by AES can be improved by normalizing the size of an elastic peak through Z-axis control.

In addition, the present invention increases the reliability of the data according to the AES quantitative analysis and greatly increases the reproducibility of the data, it is possible to perform a surface analysis of the AES equipment with a higher reliability.

Claims (2)

A method of analyzing the surface of a sample using an AES device, Adjusting the longitudinal (Z) axis of the sample to generate the most secondary electrons; Measuring an intensity value of secondary electrons at an elastic peak after adjusting the longitudinal axis value; Measuring the intensity value of the actual secondary electrons; Obtaining a normalized intensity value using the ratio of the two intensity values; And comparing the normalized intensity values to quantitatively analyze the sample. The method of claim 1, The normalized intensity value is calculated by the following equation, In = C × Ir / Iz Where In is the normalized intensity value, Iz is the intensity value of the secondary electron at the elastic peak after the longitudinal axis Z adjustment, Ir is the intensity value of the secondary electron actually measured, and C is an arbitrary constant. Surface analysis method of the sample, characterized in that.

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