JP2000266650A - Method for analyzing surface-layer impurity of polysilicon, and sample-treating container for etching polysilicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the contamination of a sample in analysis for making a high- sensitivity analysis performable by housing a polysilicon sample and an etching liquid in a sample treatment container, then moving the treatment container for bringing the etching liquid into contact with the surface of the polysilicon sample, and collecting the etching liquid. SOLUTION: The sample treatment container 1 is provided with a container body 2 made of a fluororesin having an opening 2a of polysilicon sample inlet/outlet, a lid body 3 made of a fluororesin being provided at the opening 2a of the body 2 detachably and the body 2, and an etching liquid inlet/outlet 5 at the lid body 3. The container 1 is also provided with knurls 4 and 6 at the both end that can rotate the body 2 in one direction while being in contact with a rotary roller. In this configuration, the sample treatment container 1 accommodating the polysilicon sample and the etching liquid is mounted between a rotary-driving roller and a follower roller of a roller shaker for rotating via the knurls 4 and 6. After the etching is completed, the etching liquid is transferred to a washed evaporation condensation tool from the etching liquid inlet/outlet 5 of the lid body 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for analyzing impurities in a surface layer of polysilicon and a sample processing container used for the analysis. The present invention relates to a method for analyzing impurities in a surface layer of polysilicon capable of small and highly sensitive analysis and a sample processing container used for the analysis.

[0002]

2. Description of the Related Art With the increase in diameter of silicon wafers and high integration of devices, reduction of metal impurities in silicon wafers is required. For this reason, it is inevitable to reduce the impurities of polysilicon, which is a raw material for silicon wafers, and accordingly, a highly sensitive analytical technique for evaluating the impurity content of polysilicon must be established. Is desired.

A conventional method for analyzing the impurity in the surface portion of polysilicon is such that a polysilicon sample and a sample are sufficiently immersed in a sample processing vessel for etching polysilicon.
A polysilicon is etched by adding an etchant typified by a mixed acid, and the obtained etchant is concentrated and dried to perform sample processing. The processed sample is subjected to inductively coupled plasma mass spectrometry (ICP-MS) or the like. The analysis was performed using flameless atomic absorption analysis (FL-AAS) or the like.

However, the conventional sample processing uses a relatively large amount of an etching solution to sufficiently immerse the polysilicon sample, and therefore, it is necessary to concentrate the sample to perform the analysis in order to increase the sensitivity of the analysis. Was needed. Normal,
An evaporating and concentrating device made of high-purity platinum having a purity of about 99.999% is used for the concentration, but the amount of metal impurities originally contained in the etching solution is amplified by the concentration and the sample is analyzed. As well as being inside
A large amount of metal impurities are eluted from the evaporating and concentrating instrument, and the detection limit in an analytical instrument is increased due to contamination of the sample for analysis. As a result, the sensitivity of the analysis is reduced.

It is also conceivable to use a fluororesin evaporative concentrator in order to prevent contamination during the above concentration. However, such an evaporative concentrator requires a large amount of time to evaporate the liquid amount. Have a problem.

[0006]

Therefore, there is a need for a method of analyzing impurities in a surface layer of polysilicon which can suppress contamination of a sample during analysis and can quickly perform high-sensitivity analysis. Was made in consideration of the circumstances
An object of the present invention is to provide a method for analyzing impurities in a surface portion of polysilicon, which can perform high-sensitivity analysis without analyzing sample contamination during analysis and can perform analysis in a short time, and a sample processing container used for the analysis.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted studies to achieve the above object, and as a result, have found that, in a process of etching a polysilicon sample, a process is applied to a sample processing container containing a polysilicon sample. This makes it possible to uniformly etch the surface of the sample even when the amount of the etchant stored together with the sample is much smaller than the conventional amount. That the amount of impurities derived from the etching solution can be significantly reduced, and by adopting a fluororesin material as the material of the sample processing container,
The elution of impurities from the vessel during etching can be prevented, and it has been found that analysis with extremely high sensitivity can be realized. Thus, the present invention has been completed.

That is, according to the present invention, after a polysilicon sample and an etching solution are stored in a sample processing container made of fluororesin, the etching solution is brought into contact with the surface of the polysilicon sample by giving a motion to the sample processing container. A method for analyzing impurities in a surface layer of polysilicon, comprising collecting an etchant from a sample processing container and performing high-sensitivity analysis on the collected etchant.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The size of a polysilicon sample to be analyzed in the present invention may be any size as long as it can be stored in a sample processing container. The length of the long side is 2 to 100 mm, especially 10
It is preferable to provide for analysis as a lump having a size of about 50 mm.

As the etching solution used in the present invention, a known etching solution used for surface analysis of a polysilicon sample is used without any particular limitation. Generally, an oxide film existing on the surface of the polysilicon sample or a composition capable of etching the oxide film and the surface layer is used. Specifically, hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid,
Acetic acid, hydrobromic acid, aqueous hydrogen peroxide, aqueous ammonia or the like can be used alone or in combination depending on the intended etching location. For example, examples of the etchant for the oxide film of the polysilicon sample include hydrofluoric acid, a combination of hydrofluoric acid and ammonia, and the like.
As the etchant for the oxide film and the surface layer, a combination exhibiting the action of an acid and an oxidizing agent is preferable. For example, a mixed acid of hydrofluoric acid and nitric acid is preferable. In this case, 10 to 20% by weight of hydrofluoric acid and 30 to 50% of nitric acid are used.
More preferably, it is used in a proportion of% by weight.

[0011] The purity of the etching solution is preferably higher as the purity of the etching solution is improved.
Those having an impurity amount of t or less, preferably 10 ppt or less can be suitably used.

In the present invention, it is important to use a fluororesin as the material of the sample processing container in order to minimize the amount of metal elution due to contact with the etching solution and to perform highly sensitive analysis. As the fluororesin, a known resin is used without any particular limitation. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride,
Examples thereof include a tetrafluoroethylene-hexafluoropropylene copolymer and a tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA).
Among them, PFA is preferably used because it has excellent properties such as processability into a processing container described later. Also, P
Since the FA is translucent, it also has a feature that the etching state of polysilicon can be grasped from outside the sample processing container.

In the present invention, after the polysilicon sample and the etching solution are stored in the sample processing container made of fluororesin, the etching solution is brought into contact with the surface of the polysilicon sample by giving a movement to the sample processing container. It is important that the surface of the polysilicon sample be uniformly etched with a small amount of etching solution.

That is, according to the present invention, as in the conventional processing method,
In the sample processing container, rather than immersing almost all of the polysilicon sample in the etchant, use a small amount of the etchant so that the polysilicon sample is partially immersed in the sample processing container to give a motion to the sample processing container. By bringing the etchant into uniform contact with the polysilicon sample, the concentration of the etchant, which is amplified by the concentration of the etchant described later and affects the high-sensitivity analysis, is to be reduced.

In order to sufficiently exhibit the above-mentioned effects, the amount of the polysilicon sample stored in the sample processing container is 5 to 30% by volume, preferably 8 to 20% by volume of the volume of the container. It is preferable to adjust the amount of the silicon sample used and / or the size of the container. That is, when the amount of the polysilicon sample is smaller than 5% by volume, the effect of reducing the amount of the etchant on the sample generally decreases, and
When the amount of the polysilicon sample is more than 30% by volume, it is difficult to perform uniform etching.

The amount of the above-mentioned polysilicon sample is selected within the above-mentioned range, and an amount in which the polysilicon sample does not substantially overlap in the container during etching and the interval between adjacent polysilicon samples is not too large. It is desirable to do.

The ratio of the etching solution to the polysilicon sample depends on the shape of the sample processing container, the size of the polysilicon sample, and the like, and cannot be unconditionally limited. 5-30 cc, preferably 5-20 cc is suitable.

In the present invention, by imparting movement to the sample processing container, the surface of the polysilicon sample which does not come into contact with the etchant in a stationary state can be uniformly contacted with the etchant.

The above-mentioned movement may damage the polysilicon sample if the sample processing container is given too much movement. Therefore, it is desirable that the polysilicon sample be rotated in the container with a mild movement as much as possible.

A preferred mode of the movement given to the sample processing container is a mode of giving a rotational movement to the sample processing container. That is, by rotating the sample processing container at an appropriate rotation speed, it is possible to bring the entire surface into contact with the etching solution while rotating the polysilicon sample in the container,
Enables uniform etching.

[0021] A suitable rotation speed for rotating the sample processing container is 25 rpm or less, preferably 5 to 25 rpm, and more preferably 10 to 20 rpm, so that the polysilicon sample is free from damage and efficiently etched. Liquids can be brought into contact, which is preferable.

In the analysis method of the present invention, the etching amount of the polysilicon sample in the sample processing container is appropriately adjusted according to the thickness of the target surface layer. In addition, examples of the adjustment method include an embodiment in which the adjustment is performed according to the processing time, and an embodiment in which the amount, concentration, composition, and the like of the etching solution are appropriately adjusted so that the adjustment is performed according to the effective amount of the activity of the etching solution.

When analyzing the surface oxide film of the polysilicon sample and the surface layer containing the polysilicon of the surface layer, respectively,
The processing amount of the polysilicon sample is preferably adjusted to be 0.2 to 2% by weight of the polysilicon sample, preferably 0.5 to 1.5% by weight.

In the present invention, the amount of the etching solution recovered from the sample processing container is very small relative to the polysilicon sample as compared with the conventional method. It is also possible to provide.

However, in order to improve the sensitivity of the analysis by increasing the concentration of impurities in the sample for analysis, or when using an etching solution that cannot be directly used for high-sensitivity analysis, the etching solution is concentrated (concentrated). (Including dryness) to prepare a sample for analysis, and analyze the sample for analysis. When the etching solution is concentrated, a polyhydric alcohol such as glycerin, adonito is added to the etching solution.
1), mannitol, dulcito and sorbito
It is preferable to add l) and the like. By the addition of these polyhydric alcohols, loss of elements due to evaporation and concentration of the etching solution can be prevented very effectively, and accurate quantitative analysis can be performed.

For the concentration, a known evaporating and concentrating apparatus can be used without any particular limitation. In particular, in order to avoid mixing of impurities, an evaporating and concentrating apparatus made of fluororesin is preferable. Conventionally, such a fluororesin evaporating and concentrating apparatus is difficult to perform due to its thermal conductivity, and its use causes an increase in analysis time, but in the present invention, the recovered etching solution is Since the amount can be suppressed to a very small amount, it can be used, and the elution amount of impurities during the evaporation of the etching solution can be significantly reduced.
It is most effective in improving the sensitivity of the analysis.

In the present invention, as a method of concentrating the collected etching solution and using it as an analysis sample, a known method is employed without particular limitation according to the type of analysis method described later. For example, a mode in which the etching solution is directly used as an analysis sample in a state where the etching solution is concentrated to a suitable concentration ratio, for example, about 1/5 to 1/100 of the original solution. There is an embodiment in which the solution is redissolved to an arbitrary concentration with a dissolving solution, for example, a dilute acid solution, and is subjected to high-sensitivity analysis. In the case of diluting with the above-mentioned solution, in order to further improve the sensitivity of analysis by increasing the concentration of impurities in the sample for analysis, it is necessary to use 1/5 to 1/10 of the original solution.
It is desirable to adjust the amount of liquid used so that the amount of liquid is about 0.

In the present invention, known high-sensitivity analysis methods such as inductively coupled plasma mass spectrometry, atomic absorption spectrometry, MIP-MS, and ICP-AES are preferably used as the method for high-sensitivity analysis of a sample for analysis. .

Thus, according to the present invention, since the amount of impurities mixed in the process of preparing the sample for analysis is extremely small,
It is possible to perform an analysis making full use of the sensitivity of the high sensitivity analysis method, and it is possible to analyze the surface layer impurities of a polysilicon sample with extremely high accuracy.

An embodiment of a method for analyzing impurities in a surface layer of polysilicon and a sample processing container used in the method according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the structure of a sample processing container 1 suitably used in the present invention. That is, the sample processing container 1 includes a main body 2 made of a fluororesin container having an opening 2a serving as an entrance and exit of a polysilicon sample,
A lid 3 made of a fluororesin, which is detachably provided in the opening 2a of the main body 2; and the main body 2 or the etching liquid inlet / outlet 5 in the lid 3, and the main body 2 is brought into contact with a rotating roller.
Is characterized in that it has an outer surface structure that can rotate in at least one direction, for example, flat knurls 4 and 6. When the container has a cylindrical shape, the flat knurls 4 and 6 are omitted, and the function of the outer surface structure can be reduced by the outer periphery of the container. Can be demonstrated.

The main body 2 preferably has a cylindrical shape that is easily rotated in a fixed direction by contact with a rotating roller of a roller shaker or the like, and is particularly preferably a cylindrical or polygonal cylindrical body with a bottom. In addition, an opening 2a of the main body 2 serving as an entrance and exit of the polysilicon sample has a lid 3 that is detachably provided by means such as screwing.

The lid 3 has a conical shape, and an etching solution inlet / outlet 5 is provided at the top of the cone, and the diameter of the etching solution inlet / outlet 5 is set to a size such that a contained polysilicon sample cannot pass therethrough. However, it is preferable that after etching is completed, only the etching solution can be easily collected from the container while filtering out the polysilicon.

Next, a description will be given of a method of processing a polysilicon sample using the sample processing container 1 for a sample for analyzing impurities in the surface portion of polysilicon.

The lid 3 of the processing container 1 that has been cleaned is removed, and the analysis sample polysilicon is put into the main body 2. Thereafter, after the cover 3 is screwed onto the main body 2, an etching solution is injected from the etching solution inlet / outlet 5.

As shown in FIG. 2, the sample processing container 1 containing the polysilicon sample and the etching solution is placed between a driven roller R1 and a driven roller R2 of a generally used roller shaker S, and the flat plate The rotation is given via knurls 4 and 6.

The rotation of the sample processing container 1 causes the polysilicon sample to rotate in the container, and the entire surface layer is uniformly etched by the etchant.

After completion of the etching, as shown in FIG. 3, the etching solution obtained by etching the polysilicon with a mixed acid from the etching solution inlet / outlet 5 of the lid 3 is transferred to a well-cleaned evaporating and concentrating device 7 made of fluororesin, for example, PFA. Move.

As described above, in the mode in which the etching solution is transferred to the evaporating and concentrating container from the etching solution inlet / outlet port 5 provided on the top of the conical lid 3, the etching solution or the polysilicon sample may be dropped on the work table. No, and lid 3
The operation is easy because it is not necessary to remove the sample, and the contamination of the sample (etching solution) due to the operation is preferably eliminated.

The sample obtained as described above is transferred to the evaporating and concentrating apparatus 7, and concentrated and dried by a usual method to prepare a sample for analysis.

Next, an analysis method for the above analysis sample will be described.

As shown in FIG. 4, according to a high-sensitivity analysis method, for example, inductively coupled plasma mass spectrometry, a sample solution as a sample for analysis is gasified or aerosolized by a nebulizer, and the quartz glass ICP is used. It is introduced into the argon plasma of a torch plasma generator. Alternatively, a sample solution concentrated at a high magnification of about 50 μl (about 20 times that of a nebulizer) by using an electric heating device can be introduced from an electric graphite furnace into an ICP torch. In addition, the sample was placed in an atmospheric pressure plasma at 600
Heated to 0 to 7000K, each element is atomized and further ionized. After passing through a skimmer (interface), the ionized ions are converged in energy in an ion lens section, and finally guided to a quadrupole mass spectrometer which is evacuated to a high vacuum and analyzed.

Further, even if flameless atomic absorption spectrometry is used as a high sensitivity analysis method, high sensitivity analysis of surface layer impurities of polysilicon can be performed. The content of impurities in the silicon analysis sample can be analyzed with high accuracy.

The method for analyzing impurities in the surface layer portion of polysilicon according to the present invention, the method for treating the sample, and the sample treated by using the treatment vessel are analyzed.
Impurity concentration can be measured in a very small area of the order of 0.1 ppt.

[0045]

EXAMPLES (1) Recovery rate of metal impurities A solution containing a known amount (1 ng) of a metal element was treated with hydrogen fluoride 1
A mixed acid aqueous solution containing 9% by weight and 34% by weight of nitric acid (impurity amount 5
(ppt or less), and then concentrated and dried with a PFA evaporating and concentrating apparatus. The obtained dried product was dissolved in a 0.2% sulfuric acid aqueous solution (impurity amount 5 ppt or less). It was dissolved in 0.25 cc and diluted. This was introduced by electric heating vaporization and analyzed by ICP-MS. Table 1 shows the results. As can be understood from the table below, it was confirmed that the added impurities did not volatilize during vaporization and concentration of the target element, and a recovery rate close to 100% was obtained.

[0046]

[Table 1]

(2) Confirmation of lower limit of quantification of analysis In order to obtain the lower limit of quantification of the conventional analysis method and the analysis method of the present invention, a blank test was performed in which each analysis method was performed without etching the polysilicon sample. .

That is, as a conventional method, an etching solution amount of 100 cc necessary to immerse the entire polysilicon sample was used, and as a method of the present invention, a typical etching solution amount of 10 cc was used.

In the conventional method, the above-mentioned 100 cc of the etching solution is evaporated to dryness using a platinum evaporating and concentrating apparatus having a purity of 99.999%.
Was evaporated to dryness using a PFA evaporating and concentrating device, and the obtained dried product was dissolved in 0.25 cc of a 0.2% aqueous sulfuric acid solution (impurity amount: 5 ppt or less) to dilute it. A sample for analysis was prepared. This sample for analysis was introduced by electric heating vaporization and analyzed by an ICP-MS method.

The blank test was performed five times, and the lower limit of quantification was determined by converting the measured value of 3σ into a concentration.

Table 2 shows the results. As is clear from these results, according to the present invention, a lower limit of quantification of the order of 0.1 pptw was obtained, and the sensitivity was increased by one to two digits compared to the conventional method. The lower limit of the measurement was carried out in the same manner for other typical etching liquids. However, in the method of the present invention, there was almost no change, and a low value of the order of 0.1 pptw could be uniformly obtained.

[0052]

[Table 2]

Example 1 A polysilicon sample was analyzed for impurities in the surface layer by the following method.

In a clean room, a sample processing container 1 made of PFA (main body: inner diameter 52 mm, length 150 mm, internal capacity: 340 cc) having a structure as shown in FIG. 1 was washed with ultrapure water and dried. After storing 100 g of a polysilicon sample having an average side length of 34 mm and attaching the lid 3 by screwing, a mixed acid aqueous solution containing 19% by weight of hydrogen fluoride and 34% by weight of nitric acid from the inlet / outlet of the etching solution (impurity amount 5 pp)
t or less) was supplied.

Then, immediately, the sample processing container 1 is placed on the rollers R1 and R2 of the roller shaker S sideways, and the sample processing container is rotated at a speed of 15 rpm by the contact between the flat knurls 4 and 6 and the rotor. I was sorry. The rotation is stopped when the etching amount of the polysilicon sample obtained in advance becomes 0.75% by weight, and as a result of visually observing the etching state of the polysilicon sample, the surface of the polysilicon sample is uniformly etched. Was confirmed.

Next, the above-mentioned etching solution was transferred from the etching solution inlet / outlet 3 of the sample processing container 1 to an evaporating and concentrating device made of PFA, concentrated and dried, and the obtained dried product was subjected to a 0.2% sulfuric acid aqueous solution (impurity (5 ppt or less), dissolved in 0.25 cc and diluted to prepare a sample for analysis. This sample for analysis was introduced by electric heating vaporization and analyzed by an ICP-MS method. Table 3 shows the results.

Comparative Example 1 In Example 1, the polysilicon sample was etched by the following method. That is, a cylindrical container with a bottomed PFA (inner diameter: 54 mm) was used as a sample processing container, and the amount of liquid necessary for immersing 100 g of the same polysilicon sample as in Example 1 and the entirety of the polysilicon sample in this container. (1
(00 cc) and an etching solution having the same composition as in Example 1 was stored, and was left standing until the etching amount was the same as that in Example 1 to perform etching.

The above-mentioned etching solution was transferred to a platinum evaporating and concentrating apparatus and concentrated and dried. The obtained dried product was dissolved in 0.25 cc of a 0.2% aqueous sulfuric acid solution (impurity amount 5 ppt or less). After dilution, a sample for analysis was prepared. This sample for analysis was introduced by electric heating vaporization and analyzed by an ICP-MS method. Table 3 shows the results.

[0059]

[Table 3]

[0060]

According to the method for analyzing the impurity in the surface layer of polysilicon according to the present invention, the impurity in the surface layer of polysilicon can be analyzed with high sensitivity.

That is, since the sample processing container made of a fluororesin is used, the amount of metal elution is extremely small.
Very little metal contamination of the etchant used as the analysis sample.

In addition, in the etching of polysilicon using a sample processing container, by imparting a movement to the container, uniform etching can be performed with a small amount of etching solution (the amount of etching solution used can be reduced to 1/5 or less of the conventional etching solution). This makes it possible to prepare an analytical sample in which the amount of impurities mixed is significantly reduced, and it is possible to analyze the surface layer impurities of a polysilicon sample with high sensitivity.

Further, since the analysis of the collected etching solution is performed by concentrating it using an evaporating and concentrating device made of fluororesin, the analysis sensitivity can be further increased.

When this is concentrated and subjected to analysis by a high-sensitivity analysis method, contamination by impurities due to concentration can be suppressed to an extremely small amount.

With the above combination, it becomes possible to prepare an analysis sample in which the amount of impurities mixed is significantly reduced, and it becomes possible to analyze the surface layer impurities of a polysilicon sample with extremely high sensitivity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a sample processing container according to the present invention.

FIG. 2 is an explanatory view showing an etching step using a sample processing container according to the present invention.

FIG. 3 is an explanatory view showing an etching solution collecting step using a sample processing container according to the present invention.

FIG. 4 is a conceptual diagram of an inductively coupled plasma mass spectrometry used in a method of analyzing a surface layer impurity of a polysilicon sample.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fluororesin sample storage container 2 Main body 2a Opening 3 Lid 4 Flat knurl 5 Etching liquid inlet / outlet 6 Flat knurl R1, R2 Roller S Roller shaker

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Fumio Tokutake 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. (72) Inventor Hitoshi Murota 7-24 Harumi-cho, Tokuyama-shi, Yamaguchi Kuyama

Claims (4)

[Claims] After a polysilicon sample and an etching solution are accommodated in a sample processing container made of a fluororesin, the etching solution is brought into contact with the surface of the polysilicon sample by giving a motion to the sample processing container. A method for analyzing impurities in a surface layer portion of polysilicon, wherein an etching solution is collected from a sample processing container and the collected etching solution is analyzed. 2. The method according to claim 1, wherein the movement given to the sample processing container is a rotational movement. 3. The analysis of the collected etching solution is performed as follows:
2. The method for analyzing impurities in a surface layer of polysilicon according to claim 1, wherein the analysis is performed by concentrating using a fluororesin evaporation concentrator. 4. A body made of a fluororesin container having an opening serving as an entrance and exit for a polysilicon sample, a fluororesin lid detachably provided in the opening of the main body, and the main body or the lid. A sample processing container for etching polysilicon, having an outer surface structure capable of rotating the main body in at least one direction in contact with a formed etching solution inlet / outlet and a rotating roller.