JP2005326219A - Analysis sample preparing apparatus, analysis sample preparing method and semiconductor sample analysis method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analysis sample preparing apparatus capable of simply reducing silicon fluoride in an analysis sample when the analysis sample for analyzing metal impurities present in a semiconductor sample such as a silicon wafer or the like is prepared and capable of stably preparing the analysis sample suitable for analyzing metal impurities, and an analysis sample preparing method. <P>SOLUTION: The analysis sample preparing apparatus is constituted so as to prepare the analysis sample by decomposing the semiconductor sample and equipped with at least a hermetically closed container for receiving the semiconductor sample to decompose the same, a boat on which the semiconductor sample installed in the hermetically closed container is placed, a gas introducing pipe for introducing a decomposing gas for decomposing the semiconductor sample into the hermetically closed container, a pressure regulating valve for regulating the pressure of the decomposing gas introduced into the hermetically closed container, an exhaust means for evacuating the hermetically closed container to reduce the pressure in the container and a heating means for heating the semiconductor sample in the hermetically closed container. An analysis sample evaluating method is also disclosed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention performs an analysis sample adjustment apparatus, an analysis sample adjustment method, and an impurity analysis of a semiconductor sample for decomposing the semiconductor sample and adjusting the analysis sample when performing impurity analysis of the semiconductor sample. It relates to the analysis method.

  In recent years, as semiconductors are highly integrated, the degree of cleanliness required for the manufacturing process has become stricter. In particular, heavy metals such as Fe, Ni, and Cr have a great influence on the characteristics of semiconductors and cause defects such as leakage of pn junctions. In order not to deteriorate the electrical characteristics of semiconductor elements, these metal contamination In addition, it is important to control the metal impurities, and a technique for accurately analyzing and evaluating metal impurities present in the semiconductor wafer has been required.

  For example, as a method of analyzing metal impurities present in semiconductor wafers, after the semiconductor wafer surface is decomposed by vapor phase decomposition, the decomposition residue after decomposition is recovered in a recovery solution, and then the recovery solution is analyzed by atomic absorption spectrometry. There are known methods for analysis by a method (AAS: Atomic Absorption Spectroscopy) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS: Inductively Coupled Plasma Mass Spectrometry).

For example, when performing impurity analysis of a silicon wafer, first, an oxide is formed on the wafer surface by the reaction of the silicon wafer and the HNO ₃ gas by a vapor phase decomposition method using HF gas and HNO ₃ gas. Vapor phase decomposition of silicon wafer is performed by exposure to gas and decomposition. Next, the decomposition residue obtained by vapor phase decomposition of the silicon wafer is recovered with a recovery liquid such as pure water or dilute hydrogen fluoride water, and then the recovery liquid is analyzed by the ICP-MS method or the AAS method. The metal impurities present in the silicon wafer can be analyzed (see, for example, Patent Document 1).

  However, normally, when performing impurity analysis of a silicon wafer as described above, the decomposition residue obtained after vapor phase decomposition of the wafer contains silicon fluoride as a reaction product in addition to the metal impurity to be analyzed. ing. And after recovering such a decomposition residue containing silicon fluoride with a recovery liquid, when the recovery liquid is directly analyzed by an ICP-MS method or the like, the target element is affected by the influence of Si in the recovery liquid. There is a problem that a ghost peak due to a silicon complex molecule appears at a peak position at which sapphire should appear, or noise is generated, leading to deterioration of analytical sensitivity and making it very difficult to perform accurate analysis.

  Therefore, in order to solve the above problems, in Patent Document 2, a silicon decomposition product is generated on the surface of the silicon wafer by exposing the silicon wafer to a vapor of a decomposition solution containing hydrofluoric acid and nitric acid. And recovering the silicon decomposition product with a recovery solution containing hydrofluoric acid and hydrogen peroxide water to produce a silicon decomposition product-containing recovery solution, and the silicon decomposition product-containing recovery solution and hydrofluoric acid. And the desorption solution containing nitric acid are placed in the same sealed container, and each solution is heated for a predetermined time to desorb silicon in the silicon decomposition product-containing recovery solution and to contain the siliconized silicon decomposition product-containing recovery solution. The recovery solution containing the desiliconized silicon decomposition product is evaporated to dryness, the obtained residue is dissolved in dilute hydrofluoric acid to prepare a sample solution, and the sample solution is analyzed. It discloses the impurity analysis methods Doha.

  Thus, after recovering the decomposition residue remaining after the vapor phase decomposition of the silicon wafer with the recovery liquid, the silicon-containing recovery liquid (silicon decomposition product-containing recovery solution), hydrofluoric acid and nitric acid are contained. If the silicon in the silicon-containing solution is desorbed by placing the desorbed solution in the same sealed container and heating each solution for a predetermined time, the solution is then evaporated to dryness and diluted with hydrofluoric acid. When analyzing the sample solution obtained by dissolution by the ICP-MS method or the like, the analysis sensitivity is improved and the impurity analysis can be performed stably.

  However, in the method as disclosed in Patent Document 2, after the silicon is desorbed, it is necessary to separately collect residues such as evaporation to dryness and dissolution in dilute hydrofluoric acid as described above. The work is extremely complicated and the burden on the worker is increased, and since there are many processing steps, there is a possibility that problems such as contamination from the atmosphere and a decrease in analysis sensitivity due to metal impurities contained in the chemical may occur.

  In Patent Document 2, for example, vapor phase decomposition of a silicon wafer is performed by exposing a vapor of a decomposition solution containing hydrofluoric acid and nitric acid to the silicon wafer. However, such vapor phase decomposition of silicon wafers cannot uniformly control the surface of the silicon wafer because the amount of decomposition solution vapor and the ratio of hydrofluoric acid and nitric acid in the vapor cannot be controlled. There is a problem that the decomposition residue cannot be completely recovered even if the wafer surface is scanned with the recovery liquid after that. Furthermore, according to Patent Document 2, since it is possible to analyze metal impurities existing in the region of the wafer surface layer of 1 to 10 μm, there is a disadvantage that it cannot be applied to, for example, analysis of metal impurities in the wafer bulk portion. there were.

  On the other hand, Patent Document 3 discloses hydrofluoric acid as a method for analyzing impurities with a uniform etching amount in the etched surface, less contamination during concentration of the recovered solution, and capable of highly accurate and sensitive analysis. A gas containing hydrofluoric acid and nitric acid vapor generated by bubbling a carrier gas in a mixed solution containing nitric acid is introduced into a container having the gas introduction and exhaust system, and held in the container. And an etching step of condensing the surface of the cooled silicon wafer to etch the surface, a recovery step of recovering the decomposition residue by scanning the entire surface of the etched wafer surface with a mixed solution of hydrofluoric acid and hydrogen peroxide solution, A silicon wafer impurity analysis method including an analysis step of concentrating a collected solution and analyzing a metal impurity in the solution is disclosed.

  However, the impurity analysis method of Patent Document 3 also has a defect that the range that can be analyzed is 0.02 to 10.0 μm from the wafer surface, and it is difficult to analyze metal impurities in the wafer bulk portion. .

JP 7-333121 A JP 2002-368052 A JP 2003-13381 A

  Therefore, the present invention has been made in view of the above-mentioned problems, and the object of the present invention is to perform analysis when preparing an analysis sample for analyzing metal impurities present in a semiconductor sample such as a silicon wafer. To provide an analytical sample adjustment apparatus and adjustment method capable of easily reducing silicon fluoride in a sample and stably adjusting an analytical sample suitable for analyzing metal impurities. In addition, when analyzing metal impurities present in a semiconductor sample, there is little external contamination and the impurity analysis can be performed with high sensitivity, and the metal impurities in the wafer bulk part can be easily analyzed. It is an object of the present invention to provide a method for analyzing a semiconductor sample that enables the above.

  In order to achieve the above object, according to the present invention, there is provided an adjustment device for decomposing a semiconductor sample to prepare a sample for analysis, comprising at least a sealed container for introducing the semiconductor sample for decomposition, and the sealed A boat for placing the semiconductor sample installed in a container, a gas introduction pipe for introducing a decomposition gas for decomposing the semiconductor sample into the sealed container, and a gas for decomposition introduced into the sealed container An analytical sample adjustment apparatus comprising: a pressure adjustment valve for adjusting pressure; an exhaust means for exhausting and depressurizing the inside of the sealed container; and a heating means for heating the semiconductor sample in the sealed container. Is provided (claim 1).

  With the analytical sample preparation apparatus having such a configuration, when the analysis sample is prepared by disassembling the semiconductor sample, after placing the semiconductor sample on the boat, the semiconductor sample is heated and the inside of the sealed container is Thus, an apparatus capable of easily performing a pressurizing step of introducing and depressurizing a gas for decomposition and a depressurizing step of evacuating and depressurizing the inside of the sealed container after the pressurizing step. Therefore, the semiconductor sample and the decomposition gas are reacted in the pressurization process to decompose the semiconductor sample with sufficient decomposition capacity, and then the silicon fluoride generated in the pressurization process is volatilized and removed in the decompression process to analyze the sample. It is possible to easily reduce the silicon fluoride in the inside, and it is possible to provide an analytical sample adjustment device that can stably adjust an analytical sample suitable for analyzing metal impurities.

At this time, it is preferable that the inner wall of the sealed container is coated with fluororesin or fluororesin (Claim 2).
If the inner wall of the sealed container is coated with fluororesin or fluororesin in this way, it is excellent in chemical resistance and cleanliness, so it becomes a device that can withstand long-term use. It is possible to prevent the analysis sample from being contaminated from the inner wall of the sealed container.

The boat is preferably made of platinum (Claim 3).
In this way, if the boat is made of platinum, after preparing the analysis sample, a solution for dissolving the analysis sample is directly added to the boat, and the analysis sample is prepared for each boat by the ICP-MS method or the like. Analysis can be performed, the work is simplified, and contamination of the analysis sample can be reliably prevented. For example, the purity of platinum is more preferably 4N (99.99%) or more.

Further, the exhaust means is preferably a dry pump (Claim 4), and the heating means is preferably a heater or a hot plate (Claim 5).
If the evacuation means is a dry pump, the apparatus can reliably evacuate and depressurize the inside of the sealed container. Further, if the heating means is a heater or a hot plate, the apparatus can easily and stably heat the semiconductor sample placed in the sealed container.

  According to the present invention, in the method of preparing a sample for analysis by decomposing a semiconductor sample, the semiconductor sample is placed on a boat installed in a sealed container, and then the semiconductor sample is heated and the sealed A sample for analysis is prepared by performing a pressurizing step of introducing a gas for decomposition into a container and pressurizing and holding it, and a depressurizing step of exhausting and depressurizing the inside of the sealed container after the pressurizing step. A method for preparing an analytical sample is provided (claim 6).

  Thus, after placing the semiconductor sample on the boat installed in the hermetic container, the semiconductor sample is heated and the decomposition gas is introduced into the hermetic container to pressurize and hold, After the pressurization step, the semiconductor sample can be decomposed with sufficient decomposition capability by reacting the semiconductor sample and the decomposition gas in the pressurization step by evacuating the inside of the sealed container and reducing the pressure. Then, since the silicon fluoride produced in the pressurization step can be efficiently volatilized and removed in the decompression step, it is possible to easily reduce the silicon fluoride in the analysis sample and analyze the metal impurities. Therefore, it is possible to stably prepare an analytical sample that is very suitable for the above.

  At this time, in the pressurization step, pressurization is performed by adjusting the pressure of the decomposition gas introduced into the closed vessel without exhausting the closed vessel, and in the depressurization step, the decomposition gas is supplied. It is preferable to reduce the pressure by stopping the introduction of the gas and exhausting the sealed container using an exhaust means.

  Thus, the reaction between the semiconductor sample and the decomposition gas is promoted by adjusting the pressure of the decomposition gas introduced into the closed container without exhausting the closed container in the pressurization step. The semiconductor sample can be efficiently decomposed in a short time. In addition, the introduction of the decomposition gas is stopped in the decompression step, and the sealed container is exhausted by the exhaust means to reduce the pressure, thereby effectively removing and volatilizing the silicon fluoride produced in the pressurization step. be able to.

Further, in the pressurizing step, it is preferable to pressurize the inside of the sealed container to be higher than 1.0 × 10 ⁵ Pa and lower than 5.0 × 10 ⁵ Pa (Claim 8), while in the depressurizing step, The inside of the sealed container is preferably decompressed to 5.0 × 10 ² Pa or more and less than 1.0 × 10 ⁵ Pa (claim 9).

In the method for preparing an analytical sample of the present invention, the pressure in the sealed container is higher than 1.0 × 10 ⁵ Pa and lower than 5.0 × 10 ⁵ Pa, particularly 1.5 × 10 ⁵ Pa or higher in the pressurizing step. By pressurizing to 0 × 10 ⁵ Pa or less, the semiconductor sample can be decomposed very efficiently, and the pressure in the sealed container is set to 5.0 × 10 ² Pa or more and 1.0 × 10 6 in the decompression step. By reducing the pressure to less than ⁵ Pa, especially 1.0 × 10 ³ Pa or more and 5.0 × 10 ³ Pa or less, volatilization removal of silicon fluoride can be performed very efficiently. The sample can be adjusted stably in a short time.

Furthermore, after placing the semiconductor sample on a boat in an airtight container, it is preferable that the pressurizing step and the depressurizing step are alternately repeated a plurality of times (claim 10).
As described above, the semiconductor sample can be easily decomposed to a desired amount (weight) by alternately repeating the pressurizing step and the depressurizing step a plurality of times. Therefore, for example, when analyzing metal impurities in a semiconductor wafer, analysis in the bulk portion of the wafer, which has been difficult in the past, can be easily performed.

In the method for preparing an analytical sample of the present invention, the semiconductor sample can be made of silicon (claim 11). At this time, the silicon concentration in the adjusted analytical sample is 10 ppb or less. (Claim 12).
The analytical sample preparation method of the present invention can be particularly suitably used when a semiconductor sample made of silicon is decomposed to prepare an analytical sample. Thus, by decomposing a semiconductor sample made of silicon and adjusting an analysis sample according to the present invention, the silicon concentration in the adjusted analysis sample can be easily reduced to 10 ppb or less.

Furthermore, it is preferable that the decomposition gas is composed of HF gas and HNO ₃ gas.
If the decomposition gas is made of HF gas and HNO ₃ gas in this way, an oxide is formed on the sample surface by the reaction of the semiconductor sample and HNO ₃ gas, and then the oxide is exposed to HF gas. Since it can be easily decomposed, the semiconductor sample can be decomposed smoothly and stably.

  Further, according to the present invention, after the analysis sample is prepared from the semiconductor sample by the analysis sample preparation method of the present invention, the analysis of the semiconductor sample is performed by analyzing the analysis sample. A characteristic semiconductor sample analysis method can be provided (claim 14).

  According to the semiconductor sample analysis method of the present invention, impurities can be analyzed using an analysis sample in which silicon fluoride in the sample is reduced and secondary contamination from the outside is suppressed. Therefore, the metal impurities present in the semiconductor sample can be analyzed with high sensitivity and high accuracy. Furthermore, since the semiconductor sample analysis method of the present invention can decompose the semiconductor sample with sufficient decomposition capability, for example, it is possible to easily analyze metal impurities in the wafer bulk portion, which has been difficult in the past. It becomes possible.

At this time, when analyzing the analysis sample, it is preferable to analyze the analysis sample together with the boat after adding a solution for dissolving the analysis sample to the boat.
When analyzing the analysis sample in this way, after adding a solution for dissolving the analysis sample to the boat on which the prepared analysis sample is placed, the analysis sample is analyzed together with this boat. By doing so, for example, it is possible to analyze the sample for analysis by omitting the collection work with the collected liquid as conventionally performed, so that the work can be simplified and the burden on the worker can be reduced. Contamination that occurs after the preparation of the sample for use can be effectively prevented, so that the semiconductor sample can be analyzed with higher accuracy.

Further, according to the present invention, the analysis of the semiconductor sample can be performed by analyzing the sample for analysis by an ICP-MS method.
As described above, if the analysis sample is analyzed by the ICP-MS method, particularly the electrothermal vaporization (ETV) -ICP-MS method, the impurity analysis of the semiconductor sample can be performed with high accuracy and stability. it can.

  According to the present invention, the semiconductor sample can be decomposed with sufficient decomposition capability by reacting the semiconductor sample with the decomposition gas in the pressurizing step, and then the fluorination generated in the pressurizing step in the depressurizing step. Since silicon can be volatilized and removed efficiently, it is possible to easily reduce silicon fluoride in analysis samples, and stable preparation of analytical samples that are very suitable for analyzing metal impurities can do. Then, after the analysis sample is prepared in this way, the analysis sample is analyzed and the impurity analysis of the semiconductor sample is performed, so that silicon fluoride is reduced and contamination from the outside is also suppressed. Since the sample can be analyzed, the metal impurities present in the semiconductor sample can be analyzed with high sensitivity and high accuracy. Furthermore, according to the semiconductor sample analysis method of the present invention, it is possible to easily analyze metal impurities in the wafer bulk portion.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to these.
First, an analytical sample preparation apparatus according to the present invention will be described with reference to the drawings, but the present invention is not limited to this. FIG. 1 is a schematic configuration diagram showing an example of an analytical sample preparation apparatus of the present invention.

  The analytical sample preparation apparatus 1 of the present invention includes a sealed container 2 for introducing a semiconductor sample for decomposition, a boat 3 for placing the semiconductor sample installed in the sealed container 2, and a semiconductor in the sealed container 2. A gas introduction pipe 4 for introducing a decomposition gas for decomposing the sample, a pressure adjusting valve 5 for adjusting the pressure of the decomposition gas introduced into the sealed container 2, and an exhaust for exhausting the inside of the sealed container 2 to reduce the pressure. Means 6 and heating means 7 for heating the semiconductor sample in the sealed container 2 are provided.

  The airtight container 2 can be composed of, for example, an airtight container body 2a and a removable airtight container lid 2b, and it is easy to input a semiconductor sample into the airtight container 2 and take out the adjusted analytical sample. Can be done. The shape and size of the sealed container 2 are not particularly limited, and can be appropriately selected according to the shape, size, material, and the like of the semiconductor sample to be decomposed.

  At this time, the airtight container body 2a and the airtight container lid 2b can be screwed together by the screwing portion 8, and the airtight container main body 2a and the airtight container lid 2b are screwed in this manner, thereby sealing the airtight container. The sealing property of the container 2 can be improved. Furthermore, by installing an O-ring 9 made of a fluororesin such as PTFE (polytetrafluoroethylene) between the sealed container body 2a and the sealed container lid 2b, the sealing performance of the sealed container is further enhanced. Can do.

  Further, the inner wall of the sealed container 2 is preferably coated with a fluororesin such as PTFE or a fluororesin, so that the sealed container 2 has excellent chemical resistance and cleanliness, Furthermore, since it can endure long-term use, it is possible to prevent the analysis sample from being contaminated when the analysis sample is prepared.

  Moreover, the boat 3 installed in the hermetic container 2 is not particularly limited, but may be composed of, for example, a boat support 10 made of a fluororesin and a boat main body 11 on which a semiconductor sample is placed. it can. In particular, as shown in FIG. 1, since the boat body 11 is held so that the boat body 11 is levitated, retention of the reaction gas can be prevented, so that the sample placed on the boat body 11 is heated. In this case, the temperature of the sample can be controlled with high accuracy.

  At this time, it is preferable that the boat body 11 on which the semiconductor sample is placed is made of platinum. Thus, if the boat body 11 is made of platinum, for example, after the semiconductor sample is decomposed to prepare the analysis sample, the analysis sample is dissolved in the boat body 11 when analyzed by the ICP-MS method or the like. After the solution is directly added to dissolve the analysis sample, the boat body 11 can be attached to the analyzer for analysis.

Furthermore, a gas introduction pipe 4 for introducing a decomposition gas is attached to the sealed container 2. For example, when HF gas and HNO ₃ gas are used as decomposition gases for decomposing the semiconductor sample, HF gas and HNO ₃ gas can be separately introduced into the sealed container 2 as shown in FIG. Two gas introduction pipes, a gas introduction pipe 4a for gas and a gas introduction pipe 4b for HNO ₃ gas, can be attached.

At this time, the gas generator 12 for generating HF gas and the carrier gas cylinder 13 are connected to the gas inlet pipe 4a for HF gas, and the gas flow rate is adjusted between the gas inlet pipe 4a and the gas generator 12. A flow rate adjusting valve 14 is installed, and a pressure adjusting valve 5 for adjusting the gas pressure is installed between the gas introduction pipe 4 and the carrier gas cylinder 13. Similarly, to HNO ₃ gas gas introduction pipe 4b, together with the gas generator 12 for generating a HNO ₃ gas is connected via a flow control valve 14, the carrier gas cylinder 13 through a pressure regulating valve 5 It is connected. As the gas generator 12, for example, a device in which a hydrofluoric acid 16 or nitric acid 17 is sealed in a fluororesin container 15 and heated by solution heating means 18 such as a heater or a hot plate to generate steam is used. it can.

  In the sample preparation apparatus for analysis according to the present invention, a dry pump is installed in the exhaust pipe 19 as the exhaust means 6 so that the inside of the sealed container 2 can be exhausted and depressurized. Further, an exhaust side pressure adjusting valve 20 can be installed in the exhaust pipe 19 so that the pressure in the sealed container 2 can be adjusted.

  Further, a heating means 7 for heating the semiconductor sample is installed outside the sealed container 2. As the heating means 7, a heater (resistance heating or the like) or a hot plate can be used, and the semiconductor sample placed on the boat 3 can be easily and stably heated. The heating means 7 can be installed inside the sealed container 2 or embedded in the sealed container 2 as necessary.

Next, the method for preparing an analytical sample of the present invention will be described.
The method for preparing an analysis sample according to the present invention is a method of disassembling a semiconductor sample to prepare an analysis sample. The semiconductor sample is placed on a boat installed in a sealed container, and then the semiconductor sample is heated. In addition, a sample for analysis is prepared by performing a pressurizing step for introducing and depressurizing a decomposition gas into the sealed container, and a depressurizing step for exhausting and depressurizing the sealed container after the pressurizing step. It has a special feature.

  Hereinafter, with respect to the method for preparing an analytical sample of the present invention, an example in which an analytical sample is prepared using a silicon single crystal piece as a semiconductor sample by the analytical sample adjusting apparatus 1 will be described with reference to the drawings. While explaining. FIG. 2 is a flow chart showing an example of the analysis sample preparation method of the present invention and an example of the semiconductor sample analysis method of the present invention described later.

  First, after placing a silicon single crystal piece (semiconductor sample) to be analyzed for impurity analysis on the boat body 11, by screwing the sealed container lid 2b to the sealed container body 2a via the O-ring 9, The silicon single crystal piece is set in an analytical sample preparation device (step A in FIG. 2).

Next, the silicon single crystal piece set in the sealed container 2 is heated, and a pressurizing process is performed in which a decomposition gas is introduced into the sealed container and pressurized and held (process B in FIG. 2).
In this pressurizing step, first, the inside of the sealed container 2 is once depressurized to about 4.0 × 10 ³ Pa with the dry pump 6, then the exhaust side pressure adjustment valve 20 is closed and the dry pump 6 is stopped, and then the gas is discharged. A gas for decomposition is introduced from the introduction pipe 4 and pressurized until a predetermined pressure is reached, and the silicon single crystal piece is heated to 50 ° C. or higher and 200 ° C. or lower, preferably 60 ° C. or higher and 80 ° C. or lower by the heating means 10. Hold for about 20 minutes.

At this time, as the gas for decomposition introduced into the sealed container 2 in the pressurization step, a gas composed of HF gas and HNO ₃ gas can be used. For example, using the two gas generators 12 shown in FIG. 1, 38 to 50% by mass of hydrofluoric acid and 61 to 70% by mass of nitric acid are separately sealed in the containers 15 of the respective gas generators 12. HF gas and HNO ₃ gas are introduced into the sealed container 2 by heating and evaporating each of them by heating means 18 to 80 to 200 ° C. and flowing a carrier gas such as air, nitrogen or argon from the carrier gas cylinder 13. be able to. At this time, by adjusting the pressure of the carrier gas with the pressure control valve 5, the pressure of the decomposition gas introduced into the sealed container 2 can be adjusted to easily control the pressurization of the sealed container 2, The inside of the sealed container 2 can be stably pressurized up to a predetermined pressure.

Thus, by introducing HF gas and HNO ₃ gas into the sealed container 2 and performing a pressurizing step, an oxide is formed by the reaction between the silicon single crystal piece and the HNO ₃ gas, and this oxide is converted into HF gas. Since the decomposition reaction of the silicon single crystal piece by the decomposition gas, which is decomposed by exposure to hydrogen, can be promoted, the silicon single crystal piece can be efficiently decomposed with sufficient decomposition ability. In this pressurization step, silicon fluoride is simultaneously formed as a reaction product due to the reaction between the oxide and HF gas. If this silicon fluoride is contained in the sample for analysis, as described above, the analysis sensitivity is deteriorated when the analysis is performed by the ICP-MS method or the like.

In this pressurization process, if the pressure in the sealed container 2 is too small, the effect of promoting the reaction between the silicon single crystal piece and the decomposition gas is small, and it takes a long time to decompose the silicon single crystal piece. On the other hand, even if the pressure in the sealed container 2 is increased by a certain level or more, the effect of further promoting the reaction between the silicon single crystal piece and the decomposition gas is reduced. Therefore, in the pressurizing step, the inside of the sealed container 2 is pressurized to higher than 1.0 × 10 ⁵ Pa and lower than 5.0 × 10 ⁵ Pa, particularly 1.5 × 10 ⁵ Pa to 3.0 × 10 ⁵ Pa. It is preferable that the silicon single crystal piece can be decomposed very efficiently and stably.

In the present invention, since the HF gas and the HNO ₃ gas are separately introduced into the sealed container 2 as described above, for example, by adjusting the flow rate adjusting valve 14 attached to each gas generator 12. The flow rate of each gas can be arbitrarily controlled. Thereby, the gas ratio of HF gas and HNO ₃ gas introduced into the hermetic container 2 can be appropriately adjusted according to the material of the semiconductor sample to be decomposed, and the decomposition of various semiconductor samples is very effective. Can be done.

Then, after performing a pressurization process as mentioned above, the decompression process which exhausts the inside of the airtight container 2 and depressurizes is performed (process C of FIG. 2).
In this decompression step, for example, after the introduction of the decomposition gas is stopped, the inside of the sealed container 2 can be decompressed by opening the exhaust side pressure regulating valve 20 and exhausting the sealed container 2 using the dry pump 6. . By performing the depressurization step in this manner, the silicon fluoride generated in the pressurization step can be volatilized and removed, so that the silicon fluoride in the analysis sample can be easily reduced. In the present invention, it is not always necessary to stop the introduction of the gas into the sealed container 2 as described above in the decompression step. For example, the decompression step can be performed while flowing a small amount of carrier gas or the like as necessary.

At this time, in the decompression step, the inside of the sealed container 2 is decompressed to 5.0 × 10 ² Pa or more and less than 1.0 × 10 ⁵ Pa, particularly 1.0 × 10 ³ Pa or more and 5.0 × 10 ³ Pa or less. Is preferred. Thus, by reducing the pressure in the sealed container 2 to less than 1.0 × 10 ⁵ Pa, particularly 1.0 × 10 ³ Pa or more and 5.0 × 10 ³ Pa or less, the volatilization removal of the silicon fluoride is greatly reduced. Therefore, silicon fluoride in the analysis sample can be sufficiently reduced. On the other hand, even if the pressure in the sealed container 2 is reduced so as to be smaller than 5.0 × 10 ² Pa, the effect of further enhancing the volatilization removing effect of silicon fluoride is reduced. Therefore, by reducing the pressure in the sealed container 2 within the above-described range in the pressure reducing step, it becomes possible to perform the volatilization removal of the silicon fluoride very efficiently, and the analysis sample can be adjusted in a short time. Can be done.

  As described above, the semiconductor sample and the decomposing gas are reacted in the pressurizing step by decomposing the semiconductor sample such as a silicon single crystal piece and adjusting the analytical sample by the method for preparing the analytical sample of the present invention. The semiconductor sample can be decomposed with sufficient decomposition capability, and the silicon fluoride generated in the pressurization step can be efficiently volatilized and removed in the depressurization step. It is possible to reduce silicon, and it is possible to stably prepare an analytical sample that is very suitable for analyzing metal impurities.

  In particular, according to the present invention, since a semiconductor sample made of silicon such as the above-mentioned silicon single crystal piece can be decomposed with sufficient decomposition capability, an analytical sample can be prepared. The silicon concentration can be easily reduced to 10 ppb or less.

  Furthermore, in the method for preparing an analytical sample of the present invention, the semiconductor sample is placed on a boat in an airtight container and the sample is set (step A in FIG. 2). Accordingly, the pressurization step (step B in FIG. 2) and the pressure reduction step (step C in FIG. 2) can be alternately repeated a plurality of times.

  In this way, by repeatedly performing the pressurizing step and the depressurizing step a plurality of times, for example, about 2 to 10 times, the semiconductor sample can be easily decomposed to a desired amount (weight). Therefore, for example, even when an analytical sample is prepared from a relatively large semiconductor sample, the semiconductor sample can be completely decomposed. For example, metal impurities in the bulk portion of a wafer, which has been conventionally difficult, can be obtained. Analysis can be easily performed.

  Furthermore, when adjusting the sample for analysis by alternately repeating the pressurization step and the depressurization step multiple times, not only can the silicon fluoride be volatilized and removed in the depressurization step, but also between the semiconductor sample and the decomposition gas in the pressurization step. Water generated by the reaction can be removed. Normally, when the reaction between the sample and the gas for decomposition proceeds in the decomposition of the semiconductor sample, moisture is generated. If this moisture aggregates in the boat on which the sample is placed, the decomposition reaction of the semiconductor sample is suppressed. There was a problem. However, in the present invention, by repeating the pressurization step and the depressurization step a plurality of times alternately as described above, moisture generated by the reaction of the pressurization step is removed by exhausting the sealed container in the depressurization step. Therefore, the semiconductor sample can be efficiently and effectively decomposed without suppressing the reaction between the semiconductor sample and the decomposition gas due to moisture aggregation.

  In the present invention, there is provided a semiconductor sample analysis method for analyzing an impurity of a semiconductor sample by adjusting the analysis sample from the semiconductor sample by the analysis sample preparation method of the present invention and then analyzing the analysis sample. Can be provided.

Hereinafter, the semiconductor sample analysis method of the present invention will be described in detail with reference to the flowchart of FIG.
In the semiconductor sample analysis method of the present invention, for example, when impurity analysis of a silicon single crystal piece is performed, first, the above-described set of semiconductor samples (step A in FIG. 2), pressurization step (step B in FIG. 2), The depressurization step (step C in FIG. 2) is sequentially performed to prepare the analysis sample from the semiconductor sample. When analyzing such a silicon single crystal piece, it is preferable to visually check, for example, whether or not the silicon single crystal piece placed on the boat is completely decomposed.

  After the silicon single crystal piece is completely decomposed to prepare the analysis sample, the analysis sample is dissolved by adding the solution directly to the boat without collecting the analysis sample from the boat (step D in FIG. 2). . At this time, for example, 2 to 5% by mass of nitric acid or a mixed solution of hydrofluoric acid, nitric acid, and water can be used as the dissolving solution, and an appropriate amount of such a dissolving solution can be used according to the weight of the sample and the sensitivity of the analyzer. Although it adds, for example, the sample for analysis can be melt | dissolved by adding about 50-200 microliters to a boat.

Then, the analytical sample dissolved in this way is set in the analyzer together with the boat, and analyzed by the ICP-MS method, particularly the ETV-ICP-MS method (step E in FIG. 2).
By analyzing the sample for analysis in this way, heavy metals such as Fe, Ni, and Cr contained in the sample can be detected with high accuracy and stability.

  As described above, according to the method for analyzing a semiconductor sample of the present invention, an analysis sample in which silicon fluoride in the sample is reduced and contamination from the outside is suppressed can be analyzed. Metal impurities can be analyzed with high sensitivity and high accuracy.

  In particular, in the present invention, when analyzing an analysis sample, the dissolved analysis sample is set together with the boat in the analyzer to analyze the analysis sample. For example, a conventional decomposition sample is used. The analysis sample can be analyzed by omitting the recovery operation of dissolving and recovering in the recovery liquid. Therefore, the burden on the operator can be greatly reduced as compared with the conventional case, and the risk of external contamination that occurs after adjustment of the analysis sample can be reduced because the analysis process is simplified. Impurity analysis can be performed with higher accuracy.

  In the present invention, it is not always necessary to analyze the sample for analysis for each boat after the dissolution solution is directly added to the boat as described above. For example, according to the shape and size of the semiconductor sample to be analyzed. Then, after the analysis sample is recovered from the boat using the recovery solution, the impurity analysis can be performed using the recovered analysis sample.

  Furthermore, according to the method for analyzing a semiconductor sample of the present invention, when the sample for analysis is prepared, as described above, the pressurizing step and the depressurizing step are alternately repeated a plurality of times, so that the semiconductor sample is reduced to a desired amount. Since it can be easily decomposed, for example, analysis of metal impurities in the bulk portion of the wafer, which has been difficult in the past, can be easily performed.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example)
In order to investigate the decomposition ability of the semiconductor sample in the analytical sample preparation method of the present invention, the following experiment was conducted using the analytical sample preparation apparatus 1 shown in FIG. In this analytical sample preparation apparatus 1, a cylindrical container having a diameter of 230 mm × a height of 250 mm and a thickness of about 10 mm, which can be separated into a sealed container body 2 a and a sealed container lid 2 b as a sealed container 2, was used. Moreover, 50 mass% hydrofluoric acid and 70 mass% nitric acid were enclosed in the two gas generators 12, respectively.

In this experiment, five types of silicon single crystal pieces having a weight of 0.3 g, 0.5 g, 1.0 g, 1.5 g, and 2.0 g were prepared as semiconductor samples.
First, in order to disassemble a silicon single crystal piece having a weight of 0.3 g and prepare a sample for analysis, the silicon single crystal piece is placed on the boat body 11, and then a sealed container lid through an O-ring 9. The silicon single crystal piece was set in the sample preparation apparatus 1 for analysis by screwing 2b into the sealed container body 2a.

Next, after the inside of the sealed container 2 is once depressurized to 4.0 × 10 ³ Pa with the dry pump 6, a decomposition gas composed of HF gas and HNO ₃ gas is introduced from the gas introduction pipe 4 to 2.0 × 10 6. ^While pressurizing to ⁵ Pa, the pressing step was performed by heating the silicon single crystal piece to 80 ° C. with the heating means 7 and holding it for 20 minutes. Thereafter, the introduction of the decomposition gas was stopped, and the pressure reducing step was performed by reducing the pressure in the sealed container 2 to 4.0 × 10 ³ Pa using the exhaust means 6.

  And after performing a pressurization process and a pressure reduction process once each as mentioned above, the obtained sample for analysis was mixed with hydrofluoric acid, nitric acid, and pure water (3.8 mass% hydrofluoric acid: 6.8). (Mix% of nitric acid: pure water = 1: 1: 3), and the concentration of Si present in the sample for analysis was measured by ICP emission analysis.

  For silicon single crystal pieces having a weight of 0.5 g, 1.0 g, 1.5 g, and 2.0 g, the silicon single crystal pieces are set in the analytical sample adjusting device 1 and then subjected to the same conditions as above. The sample for analysis was prepared by repeating the pressurizing step and the depressurizing step three times, five times, seven times, and ten times, respectively. Then, each of the obtained samples for analysis was mixed with hydrofluoric acid, nitric acid and pure water (3.8 mass% hydrofluoric acid: 6.8 mass% nitric acid: pure water = 1: 1: 3 mixing ratio). Then, the concentration of Si present in the sample for analysis was measured by ICP emission spectrometry.

  As a result, it was found that the concentration of Si present in the analytical sample prepared from the above-mentioned five types of silicon single crystal pieces with different weights was less than 10 ppb (0.01 ppm), which is the lower limit of detection. Table 1 below shows the weight of the silicon single crystal piece and the number of times that the pressurizing step and the depressurizing step were repeated in order to decompose the single crystal piece. Furthermore, in order to confirm reproducibility, the same experiment as described above was performed a plurality of times, and the concentration of Si present in the analytical sample was measured. As a result, the concentration of Si present in the analytical sample was all zero. It was confirmed to be less than 0.01 ppm.

  Next, for each analytical sample prepared in the same manner as described above, about 50 μl each of 5% by mass of nitric acid was directly added to the boat as a solution, and this was analyzed by ICP-MS method to analyze impurities of silicon single crystal pieces. Analysis was carried out. As a result, no noise due to silicon fluoride was observed in any sample, and high-precision analysis of heavy metals was possible. In addition, it was found that 2 g crystal pieces can be easily analyzed, and according to the semiconductor sample analysis method of the present invention, the crystal bulk portion can be easily analyzed with high accuracy.

(Comparative example)
As in the above example, five types of silicon single crystal pieces having a weight of 0.3 g, 0.5 g, 1.0 g, 1.5 g, and 2.0 g were prepared as semiconductor samples.
These five types of silicon single crystal pieces were decomposed using a conventionally used adjusting device 31 as shown in FIG. 3 to prepare a sample for analysis. The conventional adjustment device 31 includes a sealed container 32 including a sealed container body 32a and a sealed container lid 32b, a sample placement unit 34 for placing a semiconductor sample 33, and a heating unit 36 for heating the sealed container 32. It comprises.

First, a sample decomposition solution 35 made of a mixture of hydrofluoric acid and nitric acid is stored and held in the sealed container main body 32a, and a silicon single crystal piece is placed in the sample mounting portion 34 installed above the sample decomposition solution 35. After placing 33, the sealed container lid 32b was screwed into the closed container body 32a. Next, the sealed container 32 was heated to 150 ° C. by the heating means 36 and held for 20 hours. By heating the sealed container 32, the silicon by vaporizing sample digestion solution 35 is convection HF-HNO ₃ vapor in the internal space of the sealed container, contacting the HF-HNO ₃ vapor and silicon single-crystal piece 33 The single crystal piece 33 was decomposed to prepare a sample for analysis.

  Then, the analytical sample thus prepared was mixed with hydrofluoric acid, nitric acid and pure water (3.8% by mass hydrofluoric acid: 6.8% by mass nitric acid: pure water) in the same manner as in the above example. = 1: 1: 3), and the concentration of Si present in the sample for analysis was measured by ICP emission spectrometry.

FIG. 4 shows the average of the results of measuring the Si concentration in each analytical sample prepared in the comparative example by performing the above experiment a plurality of times together with the measurement results of the Si concentration measured in the above example.
As shown in FIG. 4, the Si concentration in the analytical sample prepared according to the present invention was less than 10 ppb (0.01 ppm), which is the lower limit of detection as described above. From this result, according to the present invention, the silicon single crystal piece can be completely decomposed with sufficient decomposition ability by changing the number of times of repeating the pressurizing step and the decompression step according to the weight of the silicon single crystal piece. I understand that I can do it. On the other hand, in the case of the comparative example, as the weight of the silicon single crystal piece increases, the Si concentration remaining in the sample for analysis increases and it can be seen that the decomposition of Si could not be performed completely. .

The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
For example, in the above description, the case where a silicon single crystal piece is mainly used as a semiconductor sample is described as an example. However, the present invention is not limited to this. For example, a silicon polycrystalline piece, a silicon single crystal wafer, a compound semiconductor The same applies to the case of using a wafer or the like.

It is a schematic block diagram which shows roughly the structure of the preparation apparatus of the sample for analysis of this invention. It is a flowchart which shows an example of the adjustment method of the sample for analysis in this invention, and the analysis method of a semiconductor sample. It is a schematic block diagram which shows schematically the structure of the conventional adjustment apparatus. It is a graph which shows the result of having measured Si concentration in a sample for analysis in an example and a comparative example.

Explanation of symbols

1 ... Analytical sample preparation device, 2 ... Sealed container,
2a: closed container body, 2b: closed container lid,
3 ... boat, 4 ... gas inlet pipe,
4a ... Gas introduction pipe for HF gas, 4b ... Gas introduction pipe for HNO ₃ gas, 5 ... Pressure control valve, 6 ... Exhaust means (dry pump),
7 ... heating means, 8 ... screwing part, 9 ... O-ring,
10 ... boat support, 11 ... boat body, 12 ... gas generator,
13 ... Carrier gas cylinder, 14 ... Flow control valve, 15 ... Fluororesin container,
16 ... hydrofluoric acid, 17 ... nitric acid, 18 ... solution heating means, 19 ... exhaust pipe,
20: Exhaust side pressure adjustment valve,
31 ... adjustment device, 32 ... sealed container,
32a ... Sealed container body, 32b ... Sealed container lid,
33 ... Semiconductor sample (silicon single crystal piece), 34 ... Sample mounting part,
35 ... Sample decomposition solution, 36 ... Heating means.

Claims (16)

  An adjustment device for disassembling a semiconductor sample to adjust an analysis sample, at least a sealed container in which the semiconductor sample is charged and decomposed, and a boat on which the semiconductor sample installed in the sealed container is placed A gas introduction pipe for introducing a decomposition gas for decomposing the semiconductor sample into the sealed container, a pressure control valve for adjusting the pressure of the decomposition gas introduced into the sealed container, and the inside of the sealed container An apparatus for adjusting an analytical sample, comprising: exhaust means for exhausting and depressurizing; and heating means for heating the semiconductor sample in the sealed container.   2. The analytical sample preparation apparatus according to claim 1, wherein an inner wall of the sealed container is coated with fluororesin or fluororesin.   3. The analytical sample preparation apparatus according to claim 1, wherein the boat is made of platinum.   4. The analytical sample preparation apparatus according to claim 1, wherein the exhaust means is a dry pump.   The analytical sample preparation apparatus according to any one of claims 1 to 4, wherein the heating means is a heater or a hot plate.   In a method of preparing a sample for analysis by decomposing a semiconductor sample, the semiconductor sample is placed on a boat installed in a sealed container, and then the semiconductor sample is heated and a decomposition gas is introduced into the sealed container And adjusting the analytical sample by performing a pressurizing step for pressurizing and holding, and a depressurizing step for evacuating and depressurizing the inside of the sealed container after the pressurizing step. .   In the pressurizing step, pressurization is performed by adjusting the pressure of the decomposition gas introduced into the closed vessel without exhausting the closed vessel, and in the depressurizing step, introduction of the decomposition gas is performed. The method for preparing an analytical sample according to claim 6, wherein decompression is performed by stopping and exhausting the sealed container using an exhaust means. 8. The analytical sample according to claim 6, wherein in the pressurizing step, the inside of the sealed container is pressurized to higher than 1.0 × 10 ⁵ Pa and lower than 5.0 × 10 ⁵ Pa. 9. Adjustment method. The analysis according to any one of claims 6 to 8, wherein, in the decompression step, the inside of the sealed container is decompressed to 5.0 x 10 ² Pa or more and less than 1.0 x 10 ⁵ Pa. Method for preparing a sample.   10. The method according to claim 6, wherein after the semiconductor sample is placed on a boat in an airtight container, the pressurization step and the depressurization step are alternately repeated a plurality of times. Preparation method of sample for analysis.   11. The analytical sample preparation method according to claim 6, wherein the semiconductor sample is made of silicon.   12. The method for preparing an analytical sample according to claim 11, wherein the silicon concentration in the adjusted analytical sample is 10 ppb or less. The method for preparing an analytical sample according to any one of claims 6 to 12, wherein the decomposition gas is composed of HF gas and HNO ₃ gas.   The sample for analysis is adjusted from the semiconductor sample by the method for preparing the sample for analysis according to any one of claims 6 to 13, and then the impurity analysis of the semiconductor sample is performed by analyzing the sample for analysis. A method for analyzing a semiconductor sample, comprising:   15. The semiconductor according to claim 14, wherein when analyzing the analysis sample, the analysis sample is analyzed together with the boat after adding a solution for dissolving the analysis sample to the boat. Sample analysis method.   16. The method for analyzing a semiconductor sample according to claim 14, wherein the analysis of the sample for analysis is performed by an ICP-MS method to perform impurity analysis of the semiconductor sample.

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