JPH0886724A - Impurity analyzer - Google Patents

Abstract

PURPOSE: To provide an impurity analyzer by which impurity can be speedily and easily analyzed while having accurate quantitative performance and high detecting sensitivity. CONSTITUTION: An impurity analyzer is provided with selective etching means 1a, 5 and 6 to deposit and enrich impurity in a sample 2 on a surface of the sample by selectively etching a main component of the sample 2 and irradiation detecting means 1b, 12 and 9 to detect intensity of fluorescence X-rays generated by the irradiation of the exciting light at a critical angle or less of total reflection to the surface of the sample 2 on which etching is performed by these selective etching means 1a, 5 and 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impurity analyzer for analyzing impurities in a solid, and more particularly to an impurity analyzer using a total reflection X-ray fluorescence analysis technique.

[0002]

2. Description of the Related Art In recent years, in the analysis of impurities in solids, it is possible to perform quick and easy measurement with accurate quantification and high detection sensitivity, and to analyze the distribution of impurities in the depth direction. A device is highly desired. For example, in a silicon wafer, which is the most basic material in manufacturing a semiconductor device such as an LSI, the impurity concentration in the raw material is the most important factor that determines its electrical characteristics.
Further, in particular, when the wafer is subjected to treatments such as ion implantation and thermal diffusion, it is required to analyze the concentration of impurities introduced by these treatments in the depth direction with good quantitativeness.

Conventionally, as one of the methods for measuring the average impurity concentration of a solid sample, impurities are concentrated and collected by various pretreatments such as melting the whole sample, and this is collected by an inductively coupled plasma mass spectrometer (ICP- There is a method of analysis by MS). This method is widely used because it has high detection sensitivity and good quantitativeness. However, in this method, since the sample concentrated by the pretreatment contains a solvent, impurities originally present in the solvent or impurities mixed in from the pretreatment device become a background, which substantially lowers the detection sensitivity. was there. Further, since the pretreatment device and the analysis device are separate, there are problems that the operation becomes complicated and the analysis time becomes long. In addition, this method basically does not analyze impurities in the depth direction.

On the other hand, a secondary ion mass spectrometer (SIMS)
It is known that the analysis method using is capable of analyzing impurities in the depth direction and has high sensitivity. However, this method has the drawback of lacking in quantitativeness. Further, the surface of the sample is uniformly removed by ion sputtering, and the impurity concentration on the surface of the sample thus obtained is analyzed by a surface analysis method such as Auger electron spectroscopy (AES) or X-ray photoelectron spectroscopy (XPS). The analysis method is also widely used as an analysis method capable of analyzing impurities in the depth direction. But,
This method has a problem that the sensitivity is insufficient. In order to improve the sensitivity of such a method, the surface obtained by uniformly removing the sample surface portion by ion sputtering as described above is used as a total reflection fluorescent X-ray with a strong synchroton radiation as an excitation light source. A method of evaluating with an analyzer has been proposed (JP-A-63-177047). However, in this method, there is a problem that the apparatus is large-scale because synchrotron radiation is used, the measurement is not easy, and the analysis time including measurement preparation and the like is long.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, and provides an impurity analyzer capable of rapid and easy impurity analysis while having accurate quantitativeness and high detection sensitivity. The purpose is to provide.

[0006]

In order to achieve the above object, an impurity analyzer according to the present invention selectively etches a main component of a sample to precipitate and concentrate impurities of the sample on the surface of the sample. A selective etching unit; and an irradiation detecting unit for detecting the intensity of fluorescent X-rays generated by irradiating the surface of the sample etched by the selective etching unit with excitation light at a critical angle of total reflection or less. Is characterized by. The etching performed by the selective etching means means the removal of the main component, and
It is used in a meaning different from the selective etching performed using a mask for performing pattern processing in the SI process or the like.

[0007]

In the above structure, the selective etching means is capable of selectively etching, that is, removing only the main component of the sample to be analyzed, or only the main component of the sample and a part of the impurities. By removing only the main component of the sample from one surface of the sample by such a selective etching means, some or all of the impurities contained in the film thickness portion removed by etching are deposited on the surface of the sample. It is then concentrated.

Therefore, the selective etching means allows only the main components of the sample to have a desired film thickness or time,
Excitation light of impurities measured by etching and precipitating and concentrating impurities in the sample on the surface of the sample, and measuring at or below the critical angle of total reflection on the surface of the sample etched by the selective etching means by the irradiation detecting means. Fluorescence X-ray intensity generated by irradiating the
The average impurity concentration in the etched portion of the sample can be determined from the line intensity.

In such an analysis, the impurities precipitated and concentrated on the surface of the sample by etching can be analyzed as they are. Therefore, it is not necessary to use a solvent or the like to collect a part of the sample, and therefore, it exists in the solvent. It is not affected by the background due to impurities, and the labor required for measurement can be reduced. further,
In the present invention, fluorescent X-ray analysis is performed in a total reflection mode in which excitation light is incident at a critical angle of total reflection or less on the surface of a sample on which impurities are deposited by etching. The ground can be suppressed.

Here, etching of a desired film thickness (time) is intermittently performed by the above-mentioned selective etching means (step etching), and the fluorescent X-ray intensity is detected and detected by the irradiation detecting means for each etching. By obtaining the difference in the intensity of the fluorescent X-rays obtained and calculating the average impurity concentration in the film thickness portion corresponding to one etching from this difference, the impurity distribution in the depth direction of the sample can be obtained with good quantitativeness. .

Therefore, according to the present invention, the average impurity concentration of the etched portion of the sample (impurity concentration concentrated on the sample surface) and the impurity distribution in the depth direction of the sample can be detected accurately, with high accuracy. It is sensitive and can be measured quickly and easily.

Further, when the impurity concentration in the SIMS is below the lower limit of detection, no evaluation can be made at all. However, in the present invention, the film thickness or time of the step etching is set large and the impurities are integrated, so that the resolution in the depth direction is increased. However, the lower limit of detection can be lowered. That is, it is possible to give priority to the resolution of the distribution measurement in the depth direction when the impurity concentration is high, and to give priority to the detection sensitivity when the impurity concentration is low.

It should be noted that, for example, a space for performing the etching by the selective etching means and a space for irradiating the excitation light by the irradiation detecting means and detecting the fluorescent X-ray intensity generated by this irradiation are adjacent to each other, or By setting the same space, it becomes easy to shift to the detection of the fluorescent X-ray intensity after etching, or the fluorescent X-ray intensity can be detected while etching, which greatly simplifies and facilitates the analysis. To be done.

In particular, when the etching space and the detection space are adjacent to each other, the sample can be freely moved between the two spaces by a communication hole or the like that connects the two spaces. The labor of transportation is further improved.

When the space for performing the etching and the space for performing the detection are set to the same space and the fluorescent X-ray intensity is detected while performing the etching, the analysis time is obtained by obtaining the time derivative of the fluorescent X-ray intensity. It can be greatly shortened.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the impurity analyzer according to the present invention will be described below with reference to FIGS.

First, a first embodiment will be described with reference to FIGS. 1 and 2.

FIG. 1 is a sectional view schematically showing the chamber 13. As shown in FIG. 1, the chamber 13 includes an etching chamber 1a in which selective etching is performed in the sample 2, irradiation of excitation light to the surface of the sample 2, and detection of the intensity of fluorescent X-rays generated. The measuring chamber 1b is provided.

A window 7 is provided in the etching chamber 1a so that the etching state of the sample 2 can be visually confirmed. This window 7 is not always necessary, and is not necessary, for example, when the etching amount is controlled based on only time. Further, when it is desired to control the etching amount by the film thickness, various etching monitoring methods, for example, an etching monitor utilizing change in interference intensity of monochromatic light (Japanese Patent Laid-Open No. 2-90644) may be used in combination.

On the other hand, in the measurement chamber 1b, an X-ray source 9 for irradiating the surface of the sample 2 with excitation light at a critical angle of total reflection or less, and the intensity of fluorescent X-rays generated by this irradiation are detected. X-ray detectors 12 are attached via windows 10 and 11, respectively. The X-ray source 9 and the X-ray detector 12 are not particularly limited, and appropriate ones may be combined according to the element to be detected. For example, when detecting a transition metal, the characteristic X-ray of tungsten may be selected as the light source, and the generated fluorescent X-ray may be detected by the semiconductor detector. Here, as the material of the window 10 and the window 11,
It goes without saying that it is preferable to select an element that does not include the element to be detected and the one close to the absorption edge so as not to absorb the characteristic X-ray used and the fluorescent X-ray of interest.

The etching chamber 1a and the measuring chamber 1b are adjacent to each other with a partition 4 interposed between them.
Communication hole 4a for communicating between the etching chamber 1a and the measurement chamber 1b
Is provided. A sample stage 3 for mounting the sample 2 is provided in both the etching chamber 1a and the measurement chamber 1b.

The sample stage 3 has a disc shape, and a central portion 3b thereof is rotatably fixed on a horizontal plane by an axis passing through the inside of the partition 4 while being interposed in the communication hole 4a. The chamber 13 is provided with a stage drive mechanism 8 that is controlled by a control unit 16 (FIG. 2) described below to drive the rotation of the sample stage 3. By the rotational movement of the sample stage 3 provided by the stage driving mechanism 8, the sample 2 placed on the sample stage 3 can move and reciprocate between the etching chamber 1a and the measurement chamber 1b. However, this stage drive mechanism 8
Not only is it automatically activated as described above,
A rotation screw provided at the upper end of the shaft passing through the inside of the partition 4 may be used to manually operate the rotation of the sample stage 3.

On the upper surface of the sample stage 3, two recesses 3a having the same shape are provided so as to face each other on a horizontal plane. In order to prevent contamination of the sample 2 from the sample stage 3, the recess 3a is set to have a size and shape so that the inner wall surface of the recess 3a does not come into contact with the back surface of the sample 2 placed on the sample stage 3 as much as possible. To be done. Also, the recess 3a
Is formed so that the inner diameter thereof matches the outer diameter of the sample 2 in order to prevent the etching atmosphere from wrapping around around the back surface of the sample 2 placed on the sample stage 3 and causing the etching from the back surface of the sample 2. Has been done. For example, the inner surface of each of the recesses 3a may be inclined such that the inner diameter becomes smaller as the depth of the recess becomes deeper, and the inner diameter of the recess 3 in the middle of this inclination coincides with the outer diameter of the sample 2. it can.
However, the depth, shape, etc. of the concave portion 3a can take various structures according to the shape of the sample 2, and are not particularly limited.

By the way, as the etching method,
In order to precipitate and concentrate the impurities in the sample 2 on the surface of the sample 2, a method capable of selectively removing from the surface of the sample 2 only a main component of the sample 2 and a part of the impurities, most preferably the main component is selected. To be done. In other words, the etching method is not particularly limited as long as it can deposit or concentrate some or all of the impurities contained in the film thickness portion removed by etching on the surface obtained by etching. The etching method is selected according to the material of the sample 2 to be etched.

As such an etching method, in the present embodiment, an acid vapor decomposition etching method (for example, JP-A-61-61) is used.
(Disclosed in Japanese Patent Laid-Open No. 38547).

Since this acid vapor decomposition etching method is used, the acid solution 5 is injected into the etching chamber 1a, and a heater 6 for heating the acid solution 5 is provided in the lower portion outside the etching chamber 1a. .

The structure and material of the etching chamber 1a are basically set in accordance with the etching method selected as described above. Take a structure that can prevent it. And
In this embodiment, since the acid vapor decomposition etching method is adopted, the material of the etching chamber 1a is heat resistant enough to withstand the heating required to generate acid vapor without being eroded by various acid vapors used. The one that has a small amount of impurities and is eluted is used. For example, when the sample is a semiconductor crystal, hydrofluoric acid or the like is used as the acid solution 5, but since the acid solution 5 is heated to about 200 ° C. by the heater 6 to generate acid vapor, the etching chamber 1a is It is preferably composed of Teflon. The material of the window 7 provided in the etching chamber 1a is preferably such that it is not corroded by acid vapor and the amount of impurities eluted is small, and for example, calcium fluoride is suitable.

There is a slight gap between the sample stage 3 and the partition 4, and when the sample 2 is moved between the etching chamber 1a and the measuring chamber 1b, the etching atmosphere flows into the measuring chamber 1b. For measurement, measurement room 1b and window 1
The materials 0 and 11 are selected so as not to be corroded by the etching atmosphere. The material of the sample stage 3 is preferably such that it is not corroded by the etching atmosphere and the amount of impurities eluted is small. However, it is not always necessary that all of them are made of a material resistant to etching, and for example, only the surface thereof may be covered with a material resistant to etching.
If the impurities to be detected are light elements, the measurement chamber 1b
In order to avoid the absorption of X-rays by the gas in the measurement chamber 1b
It is necessary to attach a pump for exhaust to.

FIG. 2 is a block diagram showing the overall structure of the impurity analyzer according to the first embodiment. This FIG. 2 is shown in FIG.
The operation of the first embodiment will be described below with reference to FIG.

First, the sample 2 is placed on the concave portion 3a of the sample stage 3 in the etching chamber 1a with the surface to be etched up. Then, while the operation of the heater 6 is controlled by the etching control unit 14, the main component of the sample 2 is etched and impurities are deposited on the surface of the sample 2. In the etching timer 15, the etching time per time is set based on the etching rate. When the set etching time has elapsed and etching has been performed to a desired film thickness, the stage drive mechanism 8 is actuated by the instruction from the control unit 16 to rotate the sample stage 3 to remove the etched sample 2. It is moved to the measurement chamber 1b. In the measurement chamber 1b, X-rays are incident on the surface of the sample 2 from the X-ray source 9 at a critical angle of total reflection or less, and the fluorescent X-ray intensity of impurities generated in the total reflection mode is detected by the X-ray detector 12. .

The fluorescent X-ray intensity obtained by this detection is processed by the signal processing section 20, and the average impurity concentration in the etched film thickness is obtained. The obtained average impurity concentration is sequentially sent to the display unit 21 and the recording unit 22 for display and recording.

At this time, if the fluorescent X-ray intensity obtained by the above-mentioned measurement is below the detection limit of the X-ray detector 12, only the etching is repeated a preset number of times according to the instruction of the control unit 16, and then the fluorescent light is again emitted. Try X-ray analysis. That is, only etching is repeated a preset number of times (two times or more, etc.) to deposit impurities to a detectable amount, and then the signal processing unit 20 processes the signal to determine the detected fluorescent X-ray intensity. Then, the average impurity concentration of the film thickness portion etched by a plurality of times of etching is obtained, and displayed and recorded on the display unit 21 and the recording unit 22. As a result, although the resolution in the depth direction is lowered, it is possible to evaluate even a low-concentration impurity distribution.

Further, in the above-mentioned operation, after etching a desired film thickness of the sample 2, the sample 2 is moved to the measuring chamber 1b side to detect the fluorescent X-ray intensity, and the etching chamber 1a is again detected.
By repeating the procedure of performing etching after returning to step 1, the difference in the detected fluorescent X-ray intensity for each etching is obtained, and the average impurity concentration of the film thickness portion corresponding to one etching is calculated from this difference, Impurity analysis in the depth direction of the sample 2 can be easily performed.

The etching is controlled by checking the etching rate in advance and measuring the etching time as described above. In addition, for example, the material of the film thickness portion of interest in Sample 2 and the material below it are used. Alternatively, an etching agent having a large etching selection ratio can be used.

As described above, in the present embodiment, the impurities concentrated on the surface of the sample 2 by the etching removal of the main component of the sample 2 can be evaluated without collecting with a solvent, so that the impurities are not included in the solvent. It is possible to reduce the influence of impurities and the labor required for measurement, and to obtain the average impurity concentration of the part removed by etching with high sensitivity and good quantification,
Also, it can be quickly and easily obtained.

Further, in this embodiment, the etching chamber 1a and the measurement chamber 1b are adjacent to each other, and the sample 2 placed on the sample stage 3 is rotated by the rotational movement of the sample stage 3 given by the stage drive mechanism 8. The chambers 1a and 1b are configured to be freely movable. For this reason, the labor of sample transportation is greatly improved, and the transition to the fluorescent X-ray intensity detection after etching becomes very easy. Therefore, not only is it easy to analyze the average impurity concentration,
The impurity distribution in the depth direction can also be obtained very easily. Further, with the above configuration, the sample 2 having impurities deposited on the surface in the etching chamber 1a can be transported to the measurement chamber 1b without being exposed to the outside air that causes contamination.
Sensitivity can be increased and analysis can be performed with higher quantitativeness.

Further, in the above embodiment, since the sample stage 3 is provided with the two recesses 3a so that the two samples 2 can be installed, during the etching of one sample 2,
The other sample 2 can be subjected to total reflection fluorescent X-ray analysis, and the measurement time can be greatly shortened especially when measuring a plurality of samples. Needless to say, when measuring a larger number of samples, it is possible to provide a sample stage on which two or more samples can be simultaneously placed.

Next, a second embodiment according to the present invention will be described with reference to FIG. In FIG. 3, the same or equivalent members as those shown in FIG. 1 are designated by the same reference numerals as those used in FIG. In the second embodiment, the etching chamber 1 in the first embodiment is used.
a and the measurement chamber 1b are provided in the same space, and an etching measurement chamber 1c is formed. Therefore, the fluorescent X-ray intensity can be detected while performing the etching, and the analysis time of the impurity concentration distribution in the depth direction can be significantly shortened by obtaining the time derivative of the fluorescent X-ray intensity.

[0039]

As described above, according to the present invention, the impurities concentrated on the surface of the sample due to the removal of the main components of the sample by etching can be analyzed without using a solvent. It is possible to reduce the influence of impurities contained and the labor required for measurement, and it is possible to quickly and easily obtain the average impurity concentration of the portion removed by etching with high detection sensitivity and high quantitativeness.

Further, the impurity concentration distribution in the depth direction can be obtained with good quantitativeness by performing the above-mentioned impurity analysis every time etching is performed for a desired film thickness or time.
Further, by controlling the film thickness or the time in one etching, it is possible to perform the measurement in which the depth direction resolution is prioritized when the impurity concentration is high and the detection sensitivity is prioritized when the impurity concentration is low.

Further, by performing the above-mentioned impurity analysis while etching, the distribution of the impurity concentration in the depth direction can be obtained quickly with good quantitativeness.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a part of an impurity analyzer according to a first embodiment of the present invention.

FIG. 2 is an overall schematic diagram of an impurity analyzer according to the first embodiment of the present invention.

FIG. 3 is a schematic sectional view of a part of an impurity analyzer according to a second embodiment of the present invention.

[Explanation of symbols]

 1a Etching chamber 1b Measurement chamber 2 Sample 3 Sample stage 5 Acid solution 6 Heater 9 X-ray source 8 Stage drive mechanism 12 X-ray detector 14 Etching control unit 15 Etching timer 16 Control unit 20 Signal processing unit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Miyuki Takenaka 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Toshiba Research & Development Center

Claims (1)

[Claims] 1. A selective etching means for selectively etching a main component of a sample to deposit and concentrate impurities of the sample on the surface of the sample, and a total of the surface of the sample etched by the selective etching means. An irradiation analyzer for detecting the intensity of fluorescent X-rays generated by irradiating excitation light at a critical angle of reflection or less, and an impurity analyzer.