Methods for assessing purity, methods for determining the purity level and methods for producing silicon wafers

Abstract

Method for evaluating the purity of a component having a silicon carbide surface, comprising the following steps: - contacting the silicon carbide surface with a mixture of hydrofluoric acid, hydrochloric acid and nitric acid; - Concentrating the acid mixture that was brought into contact with the silicon carbide surface by heating; - Subjecting a sample solution obtained by diluting a concentrated liquid obtained by concentration to a quantitative analysis of metal components by inductively coupled plasma mass spectrometry; and - Evaluating the purity of the component, which has a silicon carbide surface, based on a quantitative finding obtained through the quantitative analysis of metal components.

Description

Technical field

[0001] The present invention relates to a method for evaluating purity, a method for determining the state of cleanliness, and a method for producing silicon wafers. Specifically, the present invention relates to a method for evaluating the purity of a component with a silicon carbide surface, a method for determining the state of cleanliness of a component with a silicon carbide surface, and a method for producing a silicon wafer. State of the art

[0002] Silicon carbide (SiC) is generally considered a material with excellent heat resistance, chemical resistance, and other properties. Accordingly, silicon carbide is widely used to form various components in diverse technical fields. For example, in the production of silicon wafers (hereinafter also referred to as "wafers"), it is used to coat the surface of an internal component (such as a heat-shielding component) of a lifting machine for use in the production of a single-crystal silicon ingot, which is then sliced ​​into wafers to form a silicon wafer or a surface of a component for placing a silicon wafer onto it during heat treatment (such as a susceptor or wafer boat); to form the entire component from silicon carbide; and so on.In the following, a component whose surface is at least partially made of silicon carbide, that is, a component that has at least a partial silicon carbide surface (SiC surface), is described as a "silicon carbide-based component".

[0003] With regard to a silicon carbide-based device, a silicon carbide-based device is cleaned to reduce the metal contamination of the silicon carbide-based device (see, for example, JP 2010-4073 A and JP 2000-169233 A).

[0004] Document JP H08-288 248 A discloses a method for evaluating the purity of a component having a silicon carbide surface. Claim 1 of the document relates to a method for determining the purity of a component having a silicon carbide surface. Claim 1 includes, among other things, the following steps: - Contacting the silicon carbide surface with an acid mixture of hydrofluoric acid, hydrochloric acid and nitric acid; - Concentrating the acid mixture by heating and obtaining a concentrated solution; - Dilution of a sample of this solution followed by mass spectrometric analysis. Summary of the invention

[0005] For example, with regard to silicon wafers, it is necessary to reduce the metal contamination of a silicon wafer, as this contamination affects the properties of any device being manufactured that uses the wafer. Causes of metal contamination of a silicon wafer include the fact that, as a result of metal contamination of a component that comes into contact with a wafer during the manufacturing process of a single-crystal silicon ingot or a silicon wafer, the metallic element diffuses from the component into the atmosphere and is absorbed by the single-crystal silicon ingot or the silicon wafer, or that a silicon wafer itself is contaminated with metal as a result of contact between the wafer and the component.Accordingly, in a silicon wafer manufacturing process, including one that uses a silicon carbide-based device, it is desirable to purify the silicon carbide-based device and thereby reduce its metal contamination. Furthermore, it is desirable to assess the purity of the silicon carbide-based device to determine whether it has been sufficiently reduced and purified, and to verify any changes in its purity if it is insufficient. A method for assessing the purity of a silicon carbide-based device therefore requires the ability to evaluate its metal contamination with high accuracy.

[0006] One aspect of the present invention provides a means for highly accurate evaluation of the metal contamination of a silicon carbide-based component.

[0007] One aspect of the present invention relates to a method for evaluating the purity of a component (silicon carbide-based component) having a silicon carbide surface, comprising the following steps: the contact of the silicon carbide surface with an acid mixture of hydrofluoric acid, hydrochloric acid and nitric acid; Concentrating the acid mixture that has been brought into contact with the silicon carbide surface by heating; Subjecting a sample solution obtained by diluting a concentrated liquid obtained by concentration to a quantitative analysis of metal components by inductively coupled plasma mass spectrometry (ICP-MS); and Evaluating the purity of the component, which has a silicon carbide surface, based on a quantitative finding obtained through the quantitative analysis of metal components.

[0008] In one embodiment, the acid mixture contains a concentration of hydrofluoric acid in the range of 5 to 15 wt%, a concentration of hydrochloric acid in the range of 5 to 15 wt%, and a concentration of nitric acid in the range of 5 to 15 wt%.

[0009] In one embodiment, the sample solution is prepared by diluting the concentrated liquid, which was obtained by concentration, by adding hydrofluoric acid and hydrogen peroxide.

[0010] In one embodiment, the component which has a silicon carbide surface is a component for the production of a silicon wafer.

[0011] In one embodiment, the component for manufacturing a silicon wafer is a susceptor.

[0012] Another aspect of the present invention relates to a method for determining the cleanliness state of a component having a silicon carbide surface, comprising the following steps: Cleaning a silicon carbide surface of a component that has a silicon carbide surface to a clean condition; Evaluation of the cleanliness of the component, which has a silicon carbide surface, after cleaning using the above method; and Determination of the state of purity under which the purity was determined in such a way that, as a result of the evaluation, it is within an acceptable level, as the state of purity of a component having a silicon carbide surface, in an actual manufacturing process of a silicon wafer, wherein the manufacturing process of the silicon wafer comprises: Cleaning a component for the production of a silicon wafer, which has a silicon carbide surface, to the specified state of cleanliness; and Manufacturing of a silicon wafer by a manufacturing process, including a process which uses the purified component to manufacture a silicon wafer.

[0013] Another aspect of the present invention relates to a method for producing a silicon wafer, which comprises: Evaluating the purity of a component for the production of a silicon wafer, having a silicon carbide surface, by the above purity evaluation method; and Production of a silicon wafer by a manufacturing process which includes a process which uses a component for the production of a silicon wafer whose purity has been determined such that, as a result of the evaluation, it is within an acceptable level.

[0014] According to one aspect of the present invention, it becomes possible to evaluate the metal contamination of a component with a silicon carbide surface (silicon carbide-based component) with high accuracy. Description of embodiments; methods for evaluating purity

[0015] One aspect of the present invention relates to a method for evaluating the purity of a component with a silicon carbide surface (silicon carbide-based component), wherein the method includes: contacting the silicon carbide surface with an acid mixture of hydrofluoric acid, hydrochloric acid, and nitric acid; concentrating the acid mixture that has been contacted with the silicon carbide surface by heating; subjecting a sample solution obtained by diluting a concentrated liquid obtained by concentration to a quantitative analysis of metal components by inductively coupled plasma mass spectrometry (ICP-MS);as well as the evaluation of the purity of the component, which has a silicon carbide surface, based on a quantitative finding of metal components obtained through quantitative analysis (hereinafter the above procedure is also simply referred to as a "method for evaluating purity").

[0016] In the present invention and description, “purity” means a degree of metal contamination. The method for evaluating purity according to one aspect of the present invention makes it possible to assess the purity of a silicon carbide-based device with high accuracy. The presenting inventors suggest that: the fact that the acid mixture can recover metal components from a silicon carbide-based surface in high yield; that the acid mixture, which has recovered metal components from the silicon carbide-based surface with high yield, is concentrated by heating; and that the quantitative analysis is carried out using ICP-MS, which is a highly sensitive analytical device, This contributes to the reason why a highly accurate assessment becomes possible. However, the above is a conjecture and does not limit the present invention in any way.

[0017] The procedure for assessing purity is described in more detail below. Target component for evaluation

[0018] One evaluation objective of the purity assessment procedure is a component with a silicon carbide surface (silicon carbide-based component). The silicon carbide surface refers to a surface formed from silicon carbide. In a component with a silicon carbide surface, the entire surface or a portion of the surface of the component is a silicon carbide surface. In one embodiment, the component with a silicon carbide surface is a component whose surface is at least partially, that is, partially or completely, covered with silicon carbide; in another embodiment, a component that is entirely made of silicon carbide; and furthermore, in other embodiments, a component that is partially made of silicon carbide, and the portion composed of silicon carbide is exposed to a portion of the component's surface.In a silicon carbide-based component with silicon carbide as a coating layer covering at least part of the component, the thickness of the coating layer is not specifically limited. Furthermore, the size and shape of a silicon carbide-based component that is an evaluation objective are also not specifically limited.

[0019] Taking, for example, a silicon wafer manufacturing process, a silicon carbide-based component is widely used as a component for silicon wafer production. Examples of silicon carbide-based components for silicon wafer production may include: an internal component (such as a heat-shielding component) of a lifting machine for use in the production of a single-crystal silicon ingot; a susceptor (a component for placing a wafer); a lifting pin of a susceptor; a boat in a heat treatment furnace or a CVD (chemical vapor deposition) furnace; and the like. The purity of these various components can be evaluated by the purity evaluation method according to an aspect of the present invention.However, the target components for evaluation in the purity assessment method according to one aspect of the present invention are not limited to components for the production of silicon wafers. If the components have a silicon carbide surface (silicon carbide-based components), it is possible to define silicon carbide-based components as the evaluation targets, which are not only usable in the production of silicon wafers but also in other areas.

[0020] According to the presenting inventors' review, the recovery of metal components from a silicon carbide surface is more difficult than the recovery of metal components from a silicon wafer surface. Regarding the reason for this, although the following is only a conjecture, the presenting inventors suggest that one cause is the rougher surface of the silicon carbide compared to the surface of a silicon wafer. For example, the SRc (mean peak height of the roughness of a curved surface) of a silicon carbide surface may be equal to or greater than 1.00 µm (for example, approximately 1.00 to 10.00 µm), and the SPc (mean peak height of the cross-section of a curved surface) of the same may be equal to or greater than 1.00 µm (for example, approximately 1.00 to 10.00 µm).Here, SRc is a value to be measured according to the procedure specified in JIS B 0601-2001, and SPC is a value to be measured according to the procedure specified in ISO 25178. Acid mixture

[0021] In the purity evaluation process, the silicon carbide surface of a silicon carbide-based component, which is the target for evaluation, is brought into contact with an acid mixture of hydrofluoric acid (HF), hydrochloric acid (HCl), and nitric acid (HNO3). This acid mixture is hereinafter also referred to as the "recovery liquid." The recovery liquid, containing the aforementioned three types of acid, can recover metal constituents adhering to a silicon carbide surface; that is, it can absorb these constituents into the recovery liquid with a high recovery yield. This feature was discovered as a result of intensive investigations by the presenting inventors.

[0022] Regarding the concentrations of the three acids contained in the acid mixture, the concentration of hydrofluoric acid is preferably in the range of 5 to 15 wt% and more preferably in the range of 5 to 10 wt%, the concentration of hydrochloric acid is preferably in the range of 5 to 15 wt% and more preferably in the range of 10 to 15 wt%, and the concentration of nitric acid is preferably in the range of 5 to 15 wt% and more preferably in the range of 10 to 15 wt%. The acid mixture can preferably be an aqueous solution of the above three acids.

[0023] Contact between the acid mixture and a silicon carbide surface can be achieved using a known contact method, such as immersing a component with a silicon carbide surface (a silicon carbide-based component) into the acid mixture, applying the acid mixture to the silicon carbide surface, or the like. The quantity of the acid mixture used is not specifically limited, and any acid mixture sufficient for the contact method can be used. Furthermore, contact between the acid mixture and a silicon carbide surface can be achieved, for example, at atmospheric pressure and room temperature (e.g., approximately 15 to 25 °C), and the acid mixture can be used without temperature control (heating or cooling). Preparation of the sample solution

[0024] As a result of contacting a silicon carbide surface with the acid mixture, as described above, metal components adhering to the silicon carbide surface can be recovered into the acid mixture. However, it is assumed that if the acid mixture containing the recovered metal components is introduced directly into the ICP-MS, interference with a mass number of a target metal will be induced, causing a decrease in quantitative accuracy, a reduction in sensitivity, damage to the instrument, and the like. Accordingly, in the purity assessment procedure described above, a sample solution prepared as follows is subjected to quantitative analysis of a metal component by ICP-MS. The presenting inventors believe that this also contributes to enabling a highly accurate assessment. Concentration through heating

[0025] To prepare a sample solution, the acid mixture, which has been brought into contact with a silicon carbide surface, is first heated for concentration. This heating can be carried out using a known method for concentrating solutions by heating, for example, by heating the mixture on a hot plate or in a vessel (such as a beaker) containing the acid mixture. Concentration by heating is preferably performed to allow the liquid to remain without completely drying and solidifying. The amount of liquid allowed to remain can be set, for example, at approximately 10 to 50 µl.Among the metallic components, there is one that evaporates upon complete drying and solidification. Therefore, it is preferred that some liquid be allowed to remain without complete drying and solidification to enable the quantitative determination of such metallic components. For example, the liquid quantity of the acid mixture (amount of acid mixture) before concentration is approximately 5,000 to 1,000 µl. However, as described above, the quantity of acid mixture that comes into contact with a silicon carbide surface is not specifically limited. Therefore, the quantity may be larger or smaller than the range mentioned above. dilution

[0026] A concentrated liquid obtained through concentration is then diluted to produce a sample solution for ICP-MS. Various types of dilute acids, known as dilute acids suitable for ICP-MS, can be used for dilution. Here, "dilute acid" refers to an acid solution (e.g., an aqueous solution) in which the concentration of any single acid (or, if multiple acids are present, the concentration of each) is less than 3% by mass. Examples of suitable dilute acids include a mixture of hydrochloric acid and hydrogen peroxide (HCl / H₂O₂), dilute nitric acid (dilute HNO₃), and similar solutions. The concentration of each acid in these solutions may be approximately 1 to 3% by mass.A dilution ratio can be appropriately determined by the amount of concentrated liquid before dilution. For example, on a volume basis, the dilution ratio can be set at approximately 20 to 100 times, relative to the amount of concentrated liquid before dilution. Here, the dilution ratio means, for instance, that a dilution ratio of 20 times is when the amount of liquid obtained by dilution is 20 times the amount of concentrated liquid before dilution, based on volume. Quantitative analysis

[0027] The sample solution, obtained as described above, is subjected to quantitative analysis of its metal components by ICP-MS. ICP-MS is an analytical technique capable of analyzing metal components with high sensitivity. It allows for highly accurate purity assessment by subjecting the sample solution to quantitative analysis by ICP-MS. Typically, in ICP-MS, a sample solution is converted into a gaseous state or into an aerosol using an atomizer. This aerosol is then introduced into an argon plasma generated by radio frequency energy applied via an inductively coupled coil. The sample is heated to approximately 6000 to 7000 K in a plasma at atmospheric pressure, and each element is atomized and further ionized with an efficiency typically equal to or greater than 90%.Ions pass through a skimmer (interface), are then energy-concentrated by an ion lens section and subsequently introduced into a mass spectrometer, maintaining a high vacuum condition, for example < 10. -6 Pa, in order to be subjected to mass analysis. Accordingly, metal components in the sample solution can be quantified. A quantitative analysis of metal components by ICP-MS can be performed using a commercially available ICP-MS or an ICP-MS with a known setup. ICP-MS can quantitatively analyze various metal components. Specific examples of metal components (metallic elements) that can be quantitatively analyzed include: Na, Al, Cr, Fe, Ni, Cu, Mo, W, Ti, Nb, Ta, K, Ca, Zn, Co, Mg, Mn, Li, Sr, Ag, Pb, V, Ba, and the like.

[0028] The higher quantity of metal components present in the sample solution indicates that the silicon carbide surface, which was a target for evaluation, was more heavily contaminated with these metal components, or more precisely, exhibited lower purity. Accordingly, the purity of a silicon carbide surface, which is a target for evaluation, can be assessed quantitatively by ICP-MS. The purity assessment can be expressed as the degree of contamination by a given metal component, or it can be expressed as the sum of the contamination levels by two or more types of metal components. Methods for determining the cleaning status

[0029] The method for evaluating purity, as described above, can be used, in one embodiment, to determine the cleanliness status of a component with a silicon carbide surface.

[0030] This means that one aspect of the present invention relates to a method for determining a cleaning state of a component with a silicon carbide surface, wherein the method includes: Cleaning a silicon carbide surface of a component having a silicon carbide surface, under a candidate for a cleaning condition; Evaluation of the purity of the component, having a silicon carbide surface, after cleaning by the above method for evaluating purity; and Determination of a candidate for a purity state under which the purity has been determined in such a way that, as a result of the evaluation, it is within an acceptable level, as a purity state of a component with a silicon carbide surface in a real manufacturing process for a silicon wafer.

[0031] According to the above purity assessment method, the purity of a device with a silicon carbide surface (silicon carbide-based device) can be assessed with high accuracy. The above method for determining a purity state makes it possible to use a silicon carbide-based device, which is expected to achieve high purity in a real-world manufacturing process, by determining, based on the assessment results, whether (or not) a candidate for a purity state is suitable in a real-world manufacturing process. Consequently, the metal contamination of a silicon wafer by a silicon carbide-based device can be suppressed in the real-world manufacturing process.

[0032] Examples of cleaning states for a silicon carbide-based device may include: the composition of a cleaning fluid, cleaning duration, number of cleaning cycles, and the like. In a case where an evaluation finding (purity) obtained by evaluating a silicon carbide-based device cleaned to a specific candidate cleaning state using the above purity evaluation procedure is within an acceptable level, the candidate cleaning state can be defined as a cleaning state for a silicon carbide-based device in a real-world silicon wafer manufacturing process. The acceptable level is not specifically limited here and can be determined based on the purity required for a silicon wafer, considering its intended use or similar factors.On the other hand, if an evaluation finding (purity) obtained by evaluating a silicon carbide-based device, cleaned under a specific candidate cleaning state using the above purity evaluation procedure, exceeds an acceptable level, the cleaning state may be determined to be unsuitable for a cleaning state in a real-world manufacturing process. In this case, it is also possible to modify the cleaning state, determine a new candidate cleaning state, and perform an evaluation with respect to this candidate cleaning state. Furthermore, it is also possible to determine a suitable cleaning state for a silicon carbide-based device in a real-world silicon wafer manufacturing process by repeatedly determining and evaluating such a new candidate cleaning state.

[0033] Examples of silicon carbide-based devices that represent purification targets can include various devices listed above as examples for manufacturing silicon wafers. Furthermore, examples of silicon wafers intended for real-world fabrication processes can include, in addition to a so-called bare wafer, various silicon wafer types such as an epitaxial silicon wafer with an epitaxial layer on a silicon substrate and a silicon wafer with a thermal oxide film as the outermost layer. Fabrication processes for these silicon wafers are known. Method for producing a silicon wafer

[0034] Another aspect of the present invention relates to a method for producing a silicon wafer, including: Determination of a cleaning state by the above procedure for determining a cleaning state; Cleaning a component for the production of a silicon wafer, which has a silicon carbide surface, under the previously determined cleaning condition; and Production of a silicon wafer by a manufacturing process that includes a process which uses the purified device to produce a silicon wafer. (Hereinafter, the above process is referred to as "Manufacturing Process 1".)

[0035] Another aspect of the present invention relates to a method for producing a silicon wafer, including: Evaluation of the purity of a component for the production of a silicon wafer having a silicon carbide surface, using the above purity evaluation method; and Production of a silicon wafer by a manufacturing process that includes a process which uses a component for the production of a silicon wafer whose purity has been determined such that, as a result of evaluation, it is within an acceptable level. (Hereinafter, the above process is referred to as "Manufacturing Process 2".)

[0036] According to manufacturing process 1, it is possible to produce a silicon wafer using a silicon carbide-based component (the component for producing a silicon wafer) purified to a state of purity determined by the above procedure for determining a state of purity. The state of purity determined by the above procedure for determining a state of purity is a state of purity under which the ability to provide a silicon carbide-based component with high purity has been confirmed. As a result of using a silicon carbide-based component purified to this state of purity, it becomes possible to produce a silicon wafer with reduced metal contamination.

[0037] According to manufacturing process 2, it is possible to produce a silicon wafer using a silicon carbide-based device (device for manufacturing a silicon wafer) whose purity has been confirmed as high by the purity assessment procedure described above. Accordingly, it becomes possible to produce a silicon wafer with reduced metal contamination. Furthermore, the permissible level is not specifically limited in manufacturing process 2 and can be determined based on the purity required for a silicon wafer with regard to its intended use.

[0038] Examples of components for manufacturing a silicon wafer in manufacturing processes 1 and 2 can include various components, which were listed above as examples of silicon wafer manufacturing components. Examples of processes that use the component can include various heat treatments, such as heat treatment to form an epitaxial layer (epitaxial growth by vapor deposition). During the heat treatment, a silicon wafer is placed on, for example, a silicon wafer manufacturing component (such as a susceptor and various types of boats, as described above), and at this point, the silicon wafer comes into contact with the silicon wafer manufacturing component.Additionally, a lifting pin of a susceptor comes into contact with the surface of a silicon wafer when it lifts the silicon wafer placed on the susceptor. If the device used to manufacture the silicon wafer is contaminated with metal, the metal component adheres to the silicon wafer, thus contaminating it. Furthermore, the silicon wafer can also become contaminated with metal as a result of diffusion of an adhering metal component into the interior of the silicon wafer due to heat treatment. In manufacturing processes 1 and 2, for example, it is possible to reduce the metal contamination of a silicon wafer produced in this way. As described above, a manufacturing process for a silicon wafer is known. In manufacturing processes 1 and 2, a silicon wafer can be produced using this known manufacturing process. Examples

[0039] The present invention is further explained below by means of examples. However, the present invention is not limited to embodiments cited in the examples. The “%” mentioned below means “mass %”. The following processes and evaluations were carried out at atmospheric pressure and room temperature (approximately 15 to 25 °C), and the acid mixture was used without temperature control (heating or cooling), unless otherwise specified. 1. Contamination of a silicon carbide-based component with metal of a known concentration

[0040] A susceptor of a commercially available gas-phase epitaxy device was subjected to contamination treatment with a metal of known concentration. The susceptor consists of a carbon-based material with a silicon carbide coating covering its entire surface. The metal contamination treatment was performed by dripping a liquid containing a metal component of known concentration onto the surface of the susceptor, followed by drying of the liquid.

[0041] For the purposes of the following evaluations, several susceptors that were to undergo contamination treatment were prepared in the same manner with a metal having a known concentration. 2. Recovery of metal components by contact of a silicon carbide surface with an acid mixture

[0042] Following scanning (contacting) a silicon wafer placement surface (silicon carbide surface) of the susceptor, which was to undergo contamination treatment with a metal of known concentration, with approximately 5,000 to 10,000 µl of various acid mixtures, a metal component adhering to the placement surface was recovered using an acid mixture. The acid mixtures used (recovery liquids) were as follows: Acid mixture of hydrofluoric acid and nitric acid (HF (2%) / HNO3 (2%)) [Comparison example] Acid mixture of hydrofluoric acid, hydrochloric acid and hydrogen peroxide (HF (4%) / HCl (3%) / H2O2 (3%)) [Comparison example] Acid mixture of hydrofluoric acid, hydrochloric acid and nitric acid (HF (8%) / HCl (12%) / HNO3 (14%)) [Example].

[0043] Each of these acid mixtures is an aqueous solution containing the acids as acidic components and containing the respective acid in the respective concentration. 3. Concentration by heating and diluting the recovered liquid

[0044] The acid mixture (the recovery liquid), which was brought into contact with the silicon wafer placement surface (silicon carbide surface) of the susceptor (step 2), was placed in a beaker and then heated on a hot plate (set temperature: 300 °C) to concentrate it to a volume of approximately 30 µl. An acid mixture of hydrofluoric acid and hydrogen peroxide (aqueous solution of 2% hydrofluoric acid and 2% hydrogen peroxide) was placed in a beaker containing the concentrated liquid obtained by concentration, and the volume of the resulting dilute liquid was 1000 µl. 4. Quantitative analysis of metal components by ICP-MS (1)

[0045] A sample solution obtained by dilution in 3 was introduced into an inductively coupled plasma mass spectrometer (ICP-MS), and a quantitative analysis of metal components was performed.

[0046] The contamination level of a known concentration below 1 was set to 100%, and the respective amount of a metal component, quantitatively determined by ICP-MS relative to the contamination level of a known concentration, was calculated as the recovery yield.

[0047] Table 1 below shows the results of the quantitative analysis (recovery yields, average recovery yields, and variation) obtained by applying procedures 2 to 4 twice to the susceptor, which had been treated in procedure 1 by metal contamination with a known concentration of the respective metal component. The variation was obtained as variation = {(maximum value - minimum value) / average value} × 100 / 2. The variations listed in Tables 2 and 3 are also values ​​calculated in the same way. Table 1 Acid mixture Metal for quantitative analysis N / a Al Cr Fe Ni Cu Mon W Ti Note Ta comparative example HF / HNO3 Recovery yield (1) / % 72 78 71 74 73 70 56 42 73 63 57 Recovery yield (2) / % 91 93 86 87 87 86 65 50 99 80 78 Average recovery yield / % 82 86 79 81 80 78 61 46 86 72 68 variation 11,656442 8,771930 9,554140 8,074534 8,750000 10,256410 7,438017 8,695652 15,116279 11,888112 15,555556 comparative example HF / HCl / H2O2 Recovery yield (1) / % 100 96 96 99 92 94 83 71 93 89 82 Recovery yield (2) / % 90 85 80 82 84 83 81 70 91 92 86 Average recovery yield / % 95 85 80 82 84 83 81 70 91 92 86 variation 5,263158 6,077348 9,090909 9,392265 4,545455 6,214689 1,219512 0,709220 1,086957 1,657459 2,380952 Example HF / HCl / HNO3 Recovery yield (1) / % 97 95 91 98 97 98 93 80 96 96 90 Recovery yield (2) / % 95 93 93 95 96 96 100 81 96 93 99 Average recovery yield / % 96 94 92 97 97 97 97 81 96 95 95 variation 1,041667 1,063830 1,086957 1,554404 0,518135 1,030928 3,626943 0,621118 0,000000 1,587302 4,761905 5. Quantitative analysis of metal components by ICP-MS (2)

[0048] Tables 2 and 3 below present the results of the quantitative analysis (recovery yields, average recovery yields, and variation) obtained by repeated execution, the number of each execution given in Tables 2 and 3 below, of a process of subjecting the susceptor treated by metal contamination with a known concentration in the same manner as in 1, the processes in 2 to 4 with respect to various metal constituents, which are given in Tables 2 and 3 below, by using different types of acid mixtures, which are given in Tables 2 and 3 below. The acid mixtures given in Tables 2 and 3 below are aqueous solutions containing acids, which are listed in the tables as acidic components and contain the respective acid in the respective concentrations as given in the tables. Table 2 Recovery fluid Number of performances Recovery yield N / a Al Cr Fe Ni Cu Mon W Ti Note Ta HF:H2O2 = 2%:2% (comparative example) 1 91 % 87 % 88 % 87 % 91 % 95 % 69 % 52 % 93 % 74 % 95 % 2 96 % 98 % 88 % 94 % 99 % 91 % 76 % 48 % 98 % 74 % 98 % 3 96 % 92 % 89 % 85 % 89 % 92 % 60 % 40 % 92 % 72 % 83 % 4 98 % 97 % 99 % 96 % 99 % 92 % 69 % 37 % 97 % 67 % 86 % 5 90 % 85 % 86 % 81 % 85 % 86 % 59 % 39 % 94 % 71 % 87 % 6 90 % 92 % 80 % 87 % 87 % 72 % 64 % 34 % 98 % 80 % 71 % 7 92 % 89 % 87 % 89 % 92 % 93 % 53 % 35 % 90 % 63 % 86 % 8 78 % 87 % 75 % 86 % 78 % 83 % 71 % 42 % 89 % 69 % 91 % 9 100 % 96 % 98 % 97 % 96 % 98 % 61 % 41 % 96 % 75 % 93 % 10 96 % 94 % 85 % 88 % 94 % 91 % 65 % 47 % 98 % 61 % 83 % mean 93 % 92 % 88 % 89 % 91 % 89 % 65 % 42 % 94 % 71 % 87 % variation 11,81025 7,523192 13,43561 9,212123 11,79414 14,65606 17,92586 21,62347 4,503831 13,48665 15,4867 HF:H2O2 = 18%:18% (comparative example) 1 91 % 95 % 93 % 95 % 87 % 97 % 94 % 76 % 99 % 95 % 93 % 2 99 % 95 % 90 % 91 % 92 % 92 % 85 % 61 % 95 % 87 % 95 % 3 94 % 100 % 91 % 85 % 87 % 86 % 77 % 67 % 99 % 80 % 92 % 4 93 % 99 % 91 % 87 % 92 % 84 % 84 % 69 % 96 % 91 % 96 % mean 94 % 97 % 91 % 89 % 89 % 90 % 85 % 69 % 97 % 88 % 94 % variation 4,230685 2,386234 1,817159 5,558101 2,974665 7,018923 10,42471 11,02422 2,185086 8,171128 1,62415 HCl:H2O2 = 2%:2% (comparative example) 1 73 % 68 % 63 % 64 % 70 % 64 % 52 % 25 % 83 % 64 % 44 % 2 90 % 89 % 83 % 76 % 84 % 86 % 50 % 25 % 85 % 62 % 43 % mean 81 % 79 % 73 % 70 % 77 % 75 % 51 % 25 % 84 % 63 % 43 % variation 10,70643 13,37999 13,53577 9,206073 9,408594 14,8169 1,804632 0,19425 1,331291 2,139104 1,322807 HF:HNO3 = 2%:2% (comparative example) 1 72 % 78 % 71 % 74 % 73 % 70 % 56 % 42 % 73 % 63 % 57 % 2 91 % 93 % 86 % 87 % 87 % 86 % 65 % 50 % 99 % 80 % 78 % mean 82 % 86 % 79 % 80 % 80 % 78 % 61 % 46 % 86 % 72 % 67 % variation 11,85557 8,317268 9,536486 8,099624 8,590793 10,31672 7,393014 8,732303 15,37552 11,40898 15,42041 HF:HNO3 = 2%:63% (comparative example) 1 97 % 97 % 93 % 94 % 89 % 87 % 76 % 57 % 93 % 83 % 90 % 2 95 % 73 % 91 % 92 % 83 % 64 % 87 % 65 % 94 % 93 % 90 % 3 72 % 72 % 69 % 76 % 68 % 58 % 72 % 57 % 80 % 75 % 89 % 4 89 % 77 % 91 % 90 % 83 % 57 % 81 % 61 % 98 % 93 % 93 % mean 88 % 80 % 86 % 88 % 81 % 66 % 79 % 60 % 91 % 86 % 91 % variation 14,43056 15,86977 13,96839 9,845738 13,03433 22,52942 8,913299 6,491822 9,760876 10,52831 2,478012 HCl:HNO3 = 15%:17% (comparative example) 1 88 % 96 % 89 % 92 % 90 % 74 % 70 % 49 % 29 % 29 % 42 % 2 83 % 100 % 86 % 87 % 92 % 87 % 55 % 43 % 20 % 20 % 46 % mean 86 % 98 % 87 % 90 % 91 % 81 % 62 % 46 % 24 % 24 % 44 % variation 2,783534 2,162472 1,668322 2,50828 1,231021 8,365455 11,84759 6,957114 19,04637 19,02423 3,910303 HCl:HNO3 = 5%:51% (comparative example) 1 67 % 75 % 70 % 68 % 44 % 74 % 61 % 38 % 29 % 28 % 27 % 2 86 % 95 % 85 % 81 % 57 % 93 % 72 % 52 % 23 % 25 % 32 % mean 76 % 85 % 77 % 75 % 51 % 83 % 67 % 45 % 26 % 27 % 30 % variation 12,87928 11,91481 9,661576 8,57539 11,91922 11,63275 8,664072 15,01884 11,82173 6,452176 7,511449 HF:HCl:H2O2 = 4% / 3% / 3% (comparative example) 1 99 % 83 % 94 % 99 % 99 % 98 % 84 % 70 % 93 % 89 % 93 % 2 99 % 88 % 96 % 99 % 92 % 94 % 73 % 76 % 93 % 74 % 82 % 3 98 % 85 % 81 % 92 % 96 % 94 % 88 % 69 % 94 % 92 % 83 % 4 90 % 85 % 80 % 82 % 84 % 83 % 61 % 60 % 81 % 72 % 86 % mean 97 % 85 % 88 % 93 % 93 % 92 % 77 % 69 % 90 % 81 % 86 % variation 4,843423 2,607979 9,477608 9,237332 8,028521 8,296885 17,31926 11,6246 7,422523 12,15215 6,368361 Table 3 Recovery fluid Number of executions Recovery yield N / a Al Cr Fe Ni Cu Mon W Ti Note Ta HF:HCl:HNO3 = 8% / 12% / 14% 1 95 % 91 % 99 % 93 % 99 % 97 % 95 % 84 % 93 % 94 % 100 % 2 98 % 94 % 99 % 99 % 99 % 92 % 89 % 80 % 91 % 83 % 92 % 3 95 % 100 % 95 % 96 % 96 % 91 % 83 % 73 % 95 % 87 % 91 % 4 99 % 93 % 98 % 98 % 93 % 91 % 87 % 78 % 94 % 90 % 97 % 5 97 % 90 % 91 % 98 % 90 % 91 % 93 % 80 % 90 % 86 % 90 % 6 92 % 91 % 96 % 99 % 97 % 95 % 94 % 84 % 91 % 99 % 96 % 7 93 % 94 % 99 % 94 % 98 % 92 % 83 % 75 % 99 % 84 % 98 % 8 99 % 99 % 98 % 93 % 91 % 96 % 85 % 77 % 97 % 97 % 92 % 9 95 % 93 % 93 % 95 % 92 % 91 % 89 % 78 % 98 % 93 % 99 % 10 99 % 100 % 95 % 96 % 91 % 92 % 93 % 76 % 96 % 94 % 96 % mean 96 % 94 % 96 % 96 % 95 % 93 % 89 % 78 % 94 % 91 % 95 % variation 3,738757 4,984849 4,094723 3,11877 4,647783 3,209129 6,955777 7,181595 5,022953 8,640351 4,794561 Recovery fluid Number of executions Recovery yield N / a Al Cr Fe Ni Cu Mon W Ti Note Ta HF:HCl:HNO3 = 8% / 12% / 14% 1 92 % 96 % 94 % 95 % 109 % 96 % 95 % 92 % 94 % 98 % 98 % 2 89 % 94 % 88 % 100 % 99 % 93 % 93 % 91 % 94 % 96 % 98 % 3 88 % 93 % 89 % 95 % 99 % 94 % 95 % 93 % 95 % 93 % 100 % 4 87 % 91 % 87 % 97 % 93 % 92 % 93 % 93 % 93 % 95 % 98 % 5 97 % 98 % 95 % 99 % 97 % 98 % 97 % 80 % 92 % 94 % 94 % 6 95 % 98 % 97 % 93 % 92 % 100 % 99 % 78 % 90 % 91 % 90 % 7 94 % 100 % 93 % 85 % 98 % 99 % 94 % 90 % 91 % 98 % 94 % 8 97 % 96 % 97 % 86 % 99 % 100 % 94 % 91 % 91 % 96 % 92 % 9 99 % 91 % 94 % 93 % 100 % 95 % 100 % 95 % 95 % 95 % 97 % 10 99 % 95 % 96 % 94 % 99 % 95 % 97 % 91 % 94 % 100 % 96 % mean 94 % 95 % 93 % 93 % 99 % 96 % 96 % 89 % 93 % 96 % 96 % variation 6,682799 4,522123 5,368057 7,763752 8,806553 3,823727 3,6461 9,552607 2,703794 4,56831 4,956766

[0049] From the comparison between the examples and the comparison examples listed in Tables 1 to 3, it can be confirmed that in the examples, various metals can be recovered with a higher recovery yield (various metals can be recovered with a recovery yield exceeding 75%) and the variation of the measurement results is smaller (variation less than 10% with respect to different metals) through the use of an acid mixture of hydrofluoric acid, hydrochloric acid and nitric acid as the recovery liquid than in the comparison examples.

[0050] Additionally, ICP-MS, which was used in the quantitative analysis examples, is a device capable of performing highly sensitive quantitative analysis. Even weak metal contamination can be detected and quantitatively analyzed using ICP-MS.

[0051] The results above confirm that the purity of a silicon carbide-based component could be analyzed with high accuracy in the examples.

[0052] The SRc (mean peak height of the roughness of a curved surface) and the SPc (mean peak height of the cross-sectional area of ​​a curved surface) of the silicon wafer placement area of ​​the susceptor, for which the evaluation was performed, were measured at four locations. The measurement results are shown in Table 4 below. Table 4 SRc (µm) SPc (µm) Measuring position 1 1,73 1,73 Measuring position 2 6,71 6,71 Measuring position 3 1,85 1,85 Measuring position 4 2,74 2,74

[0053] One aspect of the present invention is applicable in the field of silicon wafer production.

Claims

[1] Method for evaluating the purity of a component having a silicon carbide surface, comprising the following steps: - contacting the silicon carbide surface with a mixture of hydrofluoric acid, hydrochloric acid and nitric acid; - Concentrating the acid mixture that was brought into contact with the silicon carbide surface by heating; - Subjecting a sample solution obtained by diluting a concentrated liquid obtained by concentration to a quantitative analysis of metal components by inductively coupled plasma mass spectrometry; and - Evaluating the purity of the component, which has a silicon carbide surface, based on a quantitative finding obtained through the quantitative analysis of metal components. [2] Method for evaluating the purity according to claim 1, wherein the acid mixture contains a concentration of hydrofluoric acid in the range of 5 to 15 wt%, a concentration of hydrochloric acid in the range of 5 to 15 wt% and a concentration of nitric acid in the range of 5 to 15 wt%. [3] Method for evaluating the purity according to claim 1 or 2, wherein the sample solution is prepared by diluting the concentrated liquid obtained by concentration by adding hydrofluoric acid and hydrogen peroxide. [4] Method for evaluating purity according to any one of claims 1 to 3, wherein the component having a silicon carbide surface is a component for producing a silicon wafer. [5] Method for evaluating the purity according to claim 4, wherein the component for producing a silicon wafer is a susceptor. [6] Method for determining the cleanliness of a component having a silicon carbide surface, comprising the following steps: - Cleaning a silicon carbide surface of a component that has a silicon carbide surface to a clean condition; - Evaluation of the cleanliness of the component having a silicon carbide surface after cleaning by means of the method according to one of claims 1 to 5; and - Determination of the state of purity under which the purity has been determined in such a way that, as a result of the evaluation, it is within an acceptable level, as the state of purity of a component having a silicon carbide surface, in an actual manufacturing process of a silicon wafer, wherein the manufacturing process of the silicon wafer comprises: - Cleaning a component for the production of a silicon wafer, which has a silicon carbide surface, to the specified state of cleanliness; and - Production of a silicon wafer by a manufacturing process, including a process which uses the purified component to produce a silicon wafer. [7] Method for producing a silicon wafer, comprising: - Evaluating the purity of a component for the production of a silicon wafer, comprising a silicon carbide surface, by the method according to any one of claims 1 to 5; and - Production of a silicon wafer by a manufacturing process which includes a process which uses a component for the production of a silicon wafer whose purity has been determined such that, as a result of the evaluation, it is within an acceptable level.