JP3498003B2 - Method for analyzing surface impurities of polysilicon and sample processing container for etching polysilicon - Google Patents

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 the 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 portion of polysilicon which enables a 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 the higher integration of devices, there is a demand for reduction of metal impurities in silicon wafers. Therefore, it is inevitably necessary to reduce impurities also in the case of polysilicon, which is a raw material of silicon wafers, and along with this, establish a highly sensitive analysis technique for evaluating the impurity content of polysilicon. Is desired.

The conventional method of analyzing impurities in the surface layer of polysilicon is such that a polysilicon sample and the sample are sufficiently immersed in a sample processing container for etching the polysilicon.
An etching solution typified by mixed acid is added to etch polysilicon, the obtained etching solution is concentrated and dried to perform sample treatment, and the treated sample is subjected to inductively coupled plasma mass spectrometry (ICP-MS) or It was analyzed using flameless atomic absorption spectrometry (FL-AAS) or the like.

However, in the conventional sample processing, since a relatively large amount of etching solution for sufficiently immersing the polysilicon sample is used, it is possible to concentrate the analysis in order to increase the sensitivity of the analysis. Was needed. Normal,
An evaporating and concentrating instrument made of high-purity platinum having a purity of about 99.999% is used for the concentration, and the amount of metal impurities originally contained in the etching solution is amplified by the concentration to obtain a sample for analysis. As they exist inside,
A large amount of metal impurities were eluted from the evaporation / concentration instrument, and the detection limit in an analytical instrument was increased due to contamination of the analytical sample, resulting in a decrease in the sensitivity of analysis.

It is also conceivable to use an evaporative concentration device made of a fluororesin to prevent contamination during the concentration, but such an evaporation concentration device requires a great amount of time to evaporate the liquid amount. Have a problem.

[0006]

Therefore, there is a demand for a method for analyzing impurities in the surface layer portion of polysilicon which can suppress contamination of a sample during analysis and can rapidly perform a highly sensitive analysis. It was made in consideration of the circumstances
An object of the present invention is to provide a method for analyzing impurities in the surface layer portion of polysilicon, which enables high-sensitivity analysis without contamination of the sample during analysis, and a sample processing container used for the analysis.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted research to achieve such an object, and as a result, in a process of etching a polysilicon sample, a sample processing container containing the polysilicon sample is given a rotational motion . As a result, even if the amount of the etching solution to be stored together with the sample is much smaller than the conventional amount, the surface can be uniformly etched, and even if the etching solution is subsequently concentrated as necessary, the sample It is possible to significantly reduce the amount of impurities derived from the etching solution in the treatment, and by adopting a fluororesin as the material of the sample processing container, it is possible to prevent the elution of impurities from the container during etching, and it is extremely sensitive. They found that the analysis was feasible and completed the present invention.

That is, according to the present invention, a bulk polysilicon sample and a small amount of etching solution are stored in a sample processing container made of fluororesin, and then the sample processing container is moved to the sample processing container (hereinafter,
(Meaning "rotational motion") is applied to bring the etching solution into contact with the surface of the polysilicon sample, the etching solution is then recovered from the sample processing container, and the recovered etching solution is analyzed. This is a method of analyzing impurities in the surface layer of silicon.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The size of a polysilicon sample to be analyzed in the present invention may be such that it can be accommodated 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 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 can be used without particular limitation. Generally, a composition capable of etching the oxide film existing on the surface of the polysilicon sample or the oxide film and the surface layer portion is used. Specifically, hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid,
Acetic acid, hydrobromic acid, hydrogen peroxide solution, ammonia water, etc. 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.
Further, as the etching liquid for the oxide film and the surface layer portion, a combination that exhibits the action of an acid and an oxidizing agent is preferable. For example, a mixed acid of hydrofluoric acid and nitric acid is suitable. In this case, hydrofluoric acid is 10 to 20% by weight, nitric acid is 30 to 50%.
More preferably, it is used in a weight percentage.

The higher the purity of the etching solution, the more preferable it is to improve the sensitivity of the analysis. Generally, it is 20 pp.
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 suppress the elution amount of the metal due to the contact with the etching solution to be extremely small and to perform a highly sensitive analysis. As the fluororesin, known ones may be used without particular limitation. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride,
Examples thereof include tetrafluoroethylene-hexafluoropropylene copolymer and tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA).
Among them, PFA is preferably used because it has excellent characteristics such as moldability for forming a processing container described later. Also, P
Since FA is semi-transparent, it has a feature that the etching state of polysilicon can be grasped from outside the sample processing container.

In the present invention, a bulk polysilicon sample and a small amount of etching liquid are stored in the fluororesin sample processing container, and then the sample processing container is rotatably transported.
It is important to bring the etching liquid into contact with the surface of the polysilicon sample by giving a motion to uniformly etch the surface of the polysilicon sample with a small amount of the etching liquid.

That is, according to the present invention, like the conventional processing method,
In a sample processing container, rather than immersing almost all of the polysilicon sample in the etching solution, use a small amount of etching solution that allows the polysilicon sample to be partly immersed, and move the sample processing container. By uniformly contacting the etching solution with the polysilicon sample, the amount of impurities derived from the etching solution, which is amplified by the concentration of the etching solution described later and affects the high-sensitivity analysis, is attempted to be reduced.

In order to sufficiently bring out the above effects, the amount of the polysilicon sample to be 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 silicon sample used and / or the size of the container. That is, when the amount of the polysilicon sample is less than 5% by volume, the effect of reducing the amount of the etching solution with respect to the sample generally decreases, and
If the amount of the polysilicon sample is more than 30% by volume, it becomes difficult to perform uniform etching.

The amount of the polysilicon sample is selected within the above range and does not substantially overlap the polysilicon samples in the container during etching, and the distance between the adjacent polysilicon samples is not too wide. It is desirable to do.

Further, the use ratio of the etching solution to the polysilicon sample varies depending on the shape of the sample processing container, the size of the polysilicon sample, etc. and cannot be unconditionally limited, but generally, per 100 g of the polysilicon sample, 5 to 30 cc, preferably 5 to 20 cc are suitable.

In the present invention, by giving a movement to the sample processing container, the surface of the polysilicon sample which does not come into contact with the etching solution in a stationary state can be brought into uniform contact with the etching solution.

The above-described movement may damage the polysilicon sample if the sample processing container is subjected to too violent movement. Therefore, it is desirable that the polysilicon sample be rotated in the container as gently as possible.

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

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 not damaged and is efficiently etched. A liquid can be contacted, which is preferable.

In the analysis method of the present invention, the etching treatment amount of the polysilicon sample in the sample processing container is appropriately adjusted according to the thickness of the target surface layer portion. In addition, examples of the adjustment method include a mode in which adjustment is performed according to the processing time, and a mode in which the effective amount of the activity of the etching solution is adjusted by appropriately adjusting the amount, concentration, composition, etc. of the etching solution.

In the case of analyzing the surface oxide film of the polysilicon sample and the surface layer part including the polysilicon of the surface layer part,
It is preferable to adjust the treatment amount of the polysilicon sample to be 0.2 to 2% by weight, preferably 0.5 to 1.5% by weight of the polysilicon sample.

In the present invention, the amount of the etching solution recovered from the sample processing container is extremely small compared to the conventional method, and therefore the high-sensitivity analysis method may be used depending on the type of the etching solution. It is also possible to use it.

However, in order to improve the sensitivity of the analysis by increasing the concentration of impurities in the sample for analysis, or when an etching solution that cannot be directly used for high sensitivity analysis is used, the etching solution is concentrated (concentrated). -Including dryness) to prepare an analytical sample and analyze the analytical sample. When the etching solution is concentrated, a polyhydric alcohol such as glycerin or adonit may be added to the etching solution.
l), mannitol, dulcito and sorbito
It is preferable to add l) or the like. By adding these polyhydric alcohols, it is possible to extremely effectively prevent the loss of elements due to the evaporation and concentration of the etching solution, and to perform accurate quantitative analysis.

For the above-mentioned concentration, a known evaporation / concentration device can be used without particular limitation, but in particular, in order to avoid mixing of impurities, an evaporation / concentration device made of a fluororesin is preferable. Conventionally, such an evaporative concentration tool made of a fluororesin has a thermal conductivity, and its use has been difficult to carry out because it leads to an increase in analysis time. Since the amount can be suppressed to an extremely small amount, it can be used, and the elution amount of impurities at the time of evaporation of the etching solution can be significantly reduced,
Most effective in improving the sensitivity of analysis.

In the present invention, as a method for concentrating the recovered etching solution and using it as a sample for analysis, known methods can be adopted without any particular limitation depending on the type of the analysis method described below. For example, the etching solution is directly used as a sample for analysis in an appropriate concentration ratio, for example, in a state of being concentrated to about 1/5 to 1/100 of the original solution. There is an embodiment in which a solution, for example, a dilute acid solution, is redissolved to an arbitrary concentration and then subjected to high-sensitivity analysis. Further, 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, 1/5 to 1/10 of the original solution is used.
It is desirable to adjust the amount of liquid used so that the amount of liquid used is approximately zero.

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

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

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

First, FIG. 1 shows the structure of a sample processing container 1 preferably 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 which serves as an inlet / outlet for a polysilicon sample, and the main body 2
Has a lid body 3 made of a fluororesin which is detachably provided in the opening 2a of the main body 2 and the main body 2 or an etching liquid inlet / outlet 5 in the lid body 3 and is brought into contact with a rotating roller to form the main body 2
Is provided with an outer surface structure capable of rotating in at least one direction, for example, flat knurls 4 and 6. It should be noted that the rotation by contact with the flat knurled roller is performed more efficiently, and when the container has a cylindrical shape, the flat knurls 4 and 6 are omitted, and the function of the outer surface structure also depends on the outer circumference of the container. Can be demonstrated.

The main body 2 preferably has a tubular shape that can easily rotate in a certain direction by contact with a rotating roller in a roller shaker or the like, and particularly a cylindrical or polygonal bottomed cylindrical body is preferable. The opening 2a of the main body 2 which serves as the entrance and exit of the polysilicon sample has a lid 3 which is detachably provided by means such as screwing.

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

Next, a method of processing a polysilicon sample using the sample processing container 1 for the surface layer impurity analysis sample of polysilicon will be described.

The lid 3 of the processing container 1 which has been washed thoroughly is removed, and the polysilicon for analysis sample is put in the main body 2. After that, the lid 3 is screwed onto the main body 2, and then the etching liquid is injected from the etching liquid inlet / outlet 5.

As shown in FIG. 2, the sample processing container 1 containing the polysilicon sample and the etching solution is placed between the rotationally driven roller R1 and the driven roller R2 of the commonly used roller shaker S, and is flattened. The rotation is given through the knurls 4 and 6.

The polysilicon sample is rotated in the container by the rotation of the sample processing container 1, and the entire surface layer is uniformly etched by the etching solution.

After the etching is completed, as shown in FIG. 3, an evaporation / concentration device 7 made of a fluororesin, for example, PFA, which is well washed with the etching liquid obtained by etching the polysilicon with the mixed acid from the etching liquid inlet / outlet 5 of the lid 3. Transfer.

As described above, in the mode in which the etching solution is transferred from the etching solution inlet / outlet 5 provided on the top of the conical lid 3 to the evaporative concentration container, the etching solution or the polysilicon sample may be dropped on the workbench. No, again lid 3
Since it is not necessary to remove it, the operation is easy, and the contamination of the sample (etching solution) due to the operation can be eliminated, which is preferable.

The sample obtained as described above is transferred to the evaporative concentration tool 7, concentrated and dried in a usual manner 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 highly sensitive analysis method such as inductively coupled plasma mass spectrometry, a sample solution as a sample for analysis is gasified or aerosolized by a neprizer, and the ICP made of quartz glass is used. It is introduced into the argon plasma of a plasma generator consisting of a torch. Alternatively, by using an electric heating device, a sample solution concentrated to a high magnification of about 50 μl (about 20 times that of a sprayer) can be introduced into an ICP torch from an electric graphite furnace. Furthermore, the sample is 600 in atmospheric pressure plasma.
When heated to 0 to 7,000 K, each element is atomized and further ionized. Ionized ions pass through a skimmer (interface), energy is converged by an ion lens unit, and finally, they are guided to a quadrupole mass spectrometer unit evacuated to a high vacuum and analyzed.

Also, by using flameless atomic absorption spectrometry as a highly sensitive analytical method, highly sensitive analysis of surface layer impurities of polysilicon can be performed. The content of impurities in the silicon-based analysis sample can be analyzed with high accuracy.

By analyzing the surface layer impurities of the polysilicon according to the present invention, the method of treating the sample, and the sample treated using the treatment container,
Impurity concentration can be measured in an extremely small amount range of 0.1 ppt order.

[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 (amount of impurities: 5
(10 ppt or less), and then concentrated and dried with a PFA evaporative concentrator, and the resulting dry solid is treated with a 0.2% aqueous sulfuric acid solution (impurity amount of 5 ppt or less). It was dissolved in 0.25 cc and diluted. This was electrically heated and vaporized and analyzed by the ICP-MS method. The results are shown in Table 1. As can be understood from the table below, it was confirmed that the added impurities can obtain a recovery rate close to 100% without volatilization of the target element during evaporation and concentration.

[0046]

[Table 1]

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

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

In the conventional method, the above 100 cc etching solution is evaporated to dryness by an evaporation concentrating device made of platinum having a purity of 99.999%. In the present invention, 10 cc is used.
After the etching solution of 1. was evaporated to dryness by a PFA evaporation concentrator, the obtained dried solids were dissolved and diluted to 0.25 cc with a 0.2% aqueous sulfuric acid solution (impurity amount of 5 ppt or less), A sample for analysis was prepared. This sample for analysis was introduced by electric heating vaporization and analyzed by the ICP-MS method.

The blank test was performed 5 times, and the lower limit of quantification was determined by converting the measured value of 3σ into concentration.

The results are shown in Table 2. As is clear from this result, according to the present invention, the lower limit of quantification on the order of 0.1 pptw was obtained, and the sensitivity was increased by 1 to 2 digits as compared with the conventional method. Further, the lower limit of the measurement was similarly performed for other typical etching solutions, but the method of the present invention hardly changed, and a low value of 0.1 ppttw order could be uniformly obtained.

[0052]

[Table 2]

Example 1 The surface layer impurities of a polysilicon sample were analyzed by the following method.

A sample treatment container 1 made of PFA and having a structure as shown in FIG. 1 which was washed with ultrapure water and dried in a clean room (main body: inner diameter 52 mm, length 150 mm, internal capacity: 340 cc) After accommodating 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 etching solution inlet / outlet (impurity amount: 5 pp
An etching solution of 15 cc) was supplied.

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

Next, the etching solution is transferred from the etching solution inlet / outlet port 3 of the sample processing container 1 to a PFA evaporative concentration tool, concentrated and dried, and the resulting dry solid is a 0.2% aqueous sulfuric acid solution (impurities). A sample for analysis was prepared by dissolving it in 0.25 cc in an amount of 5 ppt or less) and diluting it. This sample for analysis was introduced by electric heating vaporization and analyzed by the ICP-MS method. The results are shown in Table 3.

Comparative Example 1 In Example 1, a polysilicon sample was etched by the following method. That is, a bottomed cylindrical PFA container (inner diameter 54 mm) was used as a sample processing container, and 100 g of the same polysilicon sample as in Example 1 and the amount of liquid required to immerse the entire polysilicon sample therein. (1
Etching solution having the same composition as in Example 1 (00 cc) was housed and left standing until the etching amount was the same as in Example 1 for etching.

The above etching solution was transferred to a platinum evaporation / concentration instrument, concentrated and dried to dryness, and the obtained dried solid was dissolved in 0.25 cc of 0.2% sulfuric acid aqueous solution (impurity amount of 5 ppt or less). It diluted and produced the sample for analysis. This sample for analysis was introduced by electric heating vaporization and analyzed by the ICP-MS method. The results are shown in Table 3.

[0059]

[Table 3]

[0060]

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

That is, since the sample processing container made of fluororesin is used, the metal elution amount becomes extremely small,
The metal contamination of the etching liquid used as the analysis sample is extremely small.

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

Further, since the analysis of the recovered etching solution is carried out by concentrating it with a fluororesin evaporation concentrator, the analysis sensitivity can be further increased.

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

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

[Brief description of 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 process using the sample processing container according to the present invention.

FIG. 3 is an explanatory diagram showing an etching liquid recovery process using the sample processing container according to the present invention.

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

[Explanation of symbols]

1 Fluororesin sample storage container 2 body 2a opening 3 lid 4 flat knurl 5 Etching liquid inlet / outlet 6 flat knurls R1 and R2 rollers S roller shaker

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Murota 7-24 Harumi-cho, Tokuyama City, Yamaguchi Prefecture Tokuyama Co., Ltd. (56) References JP-A-8-233709 (JP, A) JP-A-8-139145 (JP, A) JP 5-288743 (JP, A) JP 11-37911 (JP, A) JP 10-332554 (JP, A) JP 10-253511 (JP, A) Kaihei 10-242228 (JP, A) Actually open 62-37743 (JP, U) Actually open 61-206845 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 1 / 00-1/44 G01N 31/00-31/22 H01L 21/00-21/98 JISST file (JOIS)

Claims (3)

(57) [Claims] 1. A sample processing container made of fluororesin, in which lumps are formed.
After containing the polysilicon sample and a small amount of etching solution, contact the etching solution to the surface of the polysilicon sample by giving a rotational motion to the sample processing container, then recover the etching solution from the sample processing container, A method for analyzing impurities in a surface layer portion of polysilicon, which comprises analyzing the collected etching solution. 2. The analysis of the recovered etching solution,
The method for analyzing impurities in a surface layer portion of polysilicon according to claim 1, wherein the method is performed by concentrating with an evaporative concentrator made of a fluororesin. 3. A main body made of a fluororesin container having an opening serving as an inlet / outlet of a bulk polysilicon sample, a fluororesin lid detachably provided in the opening of the main body, the main body or A sample processing container for etching polysilicon, which has an outer surface structure capable of rotating the main body in at least one direction by contacting a rotating roller and an etching solution inlet / outlet port formed on the lid.