JP2014041030A - Impurity analysis method of semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an impurity analysis method of a semiconductor substrate, which is capable of analyzing impurities existing in a depth direction from a surface of a semiconductor substrate and of specifying in-plane positions of the impurities.SOLUTION: First, vapor of a mixture of hydrofluoric acid and nitric acid is generated (S11). A silicon substrate is placed in a reaction chamber, and the vapor of the mixture is introduced to the reaction chamber to etch (decompose) a surface layer part of the silicon substrate by the vapor of the mixture (S12). Supply of the vapor of the mixture to the reaction chamber is stopped, and only N2 gas is supplied to the reaction chamber. The surface (decomposed surface) of the silicon substrate after decomposition is blown with the N2 gas for a prescribed time to remove silicon reaction residues from reaction residues remaining on the decomposed surface (S13). Thereafter, impurities on the decomposed surface are measured by a total reflection fluorescent X-ray analysis method (S14). In addition, a distribution in a depth direction of impurities can be evaluated by repeating the steps S12 to S14.

Description

  The present invention relates to a method for analyzing impurities present in a semiconductor substrate such as a silicon substrate.

  With the high integration of the silicon substrate device process, metal contamination control and management of the silicon substrate has become important. Conventionally, as a method for analyzing metal impurities on the surface or surface layer of a semiconductor substrate such as a silicon substrate, an ICP-MS analysis method using a vapor phase decomposition method (VPD) (hereinafter referred to as a VPD-ICP-MS method) or total reflection Fluorescence X-ray analysis (TXRF: Total Reflection X-Ray Fluorescence) is performed (see, for example, Patent Documents 1 and 2).

JP 2001-153768 A JP 2001-242052 A

  In the VPD-ICP-MS method, for example, an oxide film on the surface of a semiconductor substrate is decomposed with hydrofluoric acid (HF) vapor, the decomposition residue is recovered, and the decomposition residue is analyzed by ICP-MS (inductively coupled plasma mass spectrometer). However, since the decomposition residue is collected and collected, there is a problem that the in-plane position of the impurity with respect to the semiconductor substrate cannot be specified.

  In this respect, the total reflection X-ray fluorescence analysis (TXRF) has a problem that although the in-plane position of the impurity relative to the semiconductor substrate can be specified, only the impurity analysis on the surface of the semiconductor substrate can be performed.

  The present invention has been made in view of the above problems, and provides an impurity analysis method for a semiconductor substrate which can analyze impurities existing in the depth direction from the surface of the semiconductor substrate and can identify the in-plane position of the impurities. This is the issue.

In order to solve the above problems, the present invention is a method for analyzing impurities present in a surface layer of a semiconductor substrate,
A decomposition step of decomposing a surface layer of the semiconductor substrate by reacting a decomposition substance on the surface of the semiconductor substrate;
A measurement step of measuring impurities on the post-decomposition surface while leaving the reaction residue of the surface layer decomposed in the decomposition step on the post-decomposition surface that is the surface of the semiconductor substrate after the decomposition step;
It is characterized by including.

  According to the present invention, first, in the decomposition step, the surface of the semiconductor substrate is decomposed by causing a decomposition substance to react with the surface of the semiconductor substrate. On the surface of the semiconductor substrate after decomposition (surface after decomposition), a reaction residue on the surface layer of the decomposed semiconductor substrate remains. The reaction residue includes decomposed surface layer components (components constituting the semiconductor substrate (a silicon reaction residue when the semiconductor substrate is a silicon substrate) and impurities contained in the surface layer). Next, while the reaction residue is left on the surface after decomposition, the impurities on the surface after decomposition are measured (measurement step). Thus, impurities in the reaction residue remaining on the surface after decomposition, that is, impurities in the decomposed surface layer (layer from the surface to a certain depth) can be analyzed. Further, since the measurement is performed without recovering the reaction residue and remaining on the surface after decomposition, the in-plane position of the measured impurity can be specified.

  Further, in the present invention, the method includes a removal step of removing a residue component formed by a reaction between the semiconductor substrate other than impurities and the substance for decomposition from the reaction residue between the decomposition step and the measurement step. preferable. According to this, since impurities in the reaction residue can be revealed, impurities can be measured well in the measurement process.

  In the present invention, the decomposition step, the removal step, and the measurement step may be repeated. Thereby, the depth direction distribution of impurities in the semiconductor substrate can be evaluated.

  In the present invention, the semiconductor substrate may be a silicon substrate, and the decomposition substance may be a mixed vapor of hydrofluoric acid and nitric acid. Thus, when the semiconductor substrate is a silicon substrate, the surface layer of the silicon substrate can be decomposed by employing a mixed vapor of hydrofluoric acid and nitric acid as a decomposition substance. Further, the amount of impurities contained in the solution (chemical solution) brought into the reaction phase can be reduced as compared with the case where a substance for decomposing the solution is employed. As a result, the background of the impurity concentration in the silicon substrate is lowered, and the lower detection limit can be improved.

  In this case, it is preferable to react the mixed vapor on the surface of the semiconductor substrate for 3 to 60 minutes in the decomposition step. The present inventor has obtained the knowledge that when a mixed vapor of hydrofluoric acid and nitric acid is reacted on the surface of a silicon substrate as a semiconductor substrate for 3 to 60 minutes, the surface layer of the silicon substrate is decomposed between about 0.5 μm and about 5 μm. ing. Therefore, by adjusting the reaction time with the mixed vapor between 3 and 60 minutes, impurities in the surface layer having a depth of about 0.5 μm to about 5 μm can be analyzed.

  Moreover, in this invention, it is preferable to measure an impurity by the total reflection X-ray fluorescence analysis method in the said measurement process. Thereby, the kind and density | concentration of the impurity in the reaction residue which remain | survives on the surface after decomposition | disassembly can be measured.

FIG. 3 is a schematic diagram of a decomposition gas generation unit 10 and a surface layer etching unit 20. 3 is a schematic diagram of a measuring device 7. FIG. It is a flowchart of the analysis process of the metal impurity which exists in the surface layer of a silicon substrate. It is the figure which showed the state of the silicon substrate 5 in each process of FIG. It is a flowchart of the analysis process of the metal impurity in an Example. It is the figure which showed the impurity concentration which exists in the surface layer of the depth from a sample surface to 2 micrometers. It is the figure which showed the depth direction distribution of Fe. It is the figure which showed the depth direction distribution of Cr. It is the figure which showed the depth direction distribution of Ni. It is the figure which showed the relationship between the reaction time with the mixed vapor | steam of a hydrofluoric acid and nitric acid, and etching depth. It is a result when impurities are measured by a conventional method, and is a diagram showing impurity concentration at a site of intentional contamination on a sample surface.

  Embodiments of a semiconductor substrate impurity analysis method according to the present invention will be described below with reference to the drawings. FIG. 1 and FIG. 2 are schematic views of each device used in the impurity analysis method of this embodiment. Specifically, FIG. 1 shows a decomposition gas generating unit 10 that generates a decomposition gas (decomposition substance) for etching (decomposing) the surface layer of the semiconductor substrate 5, and the surface layer of the semiconductor substrate 5 with the decomposition gas. The schematic diagram with the surface layer etching part 20 for performing etching (decomposition | disassembly) is shown. FIG. 2 is a schematic diagram of a measuring apparatus 7 that measures the type and concentration of impurities with respect to the surface 51 of the semiconductor substrate using total reflection X-ray fluorescence analysis.

  A gas generation chamber 1 is provided in the decomposition gas generation section 10 of FIG. A container 12 containing a mixed solution 13 of hydrofluoric acid and nitric acid is placed in the gas generating chamber 1. The cracking gas generator 10 is provided with a heater 15 for heating the container 12. The gas generation chamber 1 is connected to an N2 gas supply port 11 for supplying N2 gas into the gas generation chamber 1 so that the N2 gas is bubbled into the container 12. The gas generation chamber 1 is connected to a mixed vapor supply port 3 for supplying a mixed vapor 14 of hydrofluoric acid and nitric acid as a decomposition gas generated from the mixed solution 13 to the reaction chamber 2 described later. .

  A reaction chamber 2 is provided in the surface layer etching unit 20. The reaction chamber 2 is provided with a mounting table 21 on which a silicon substrate 5 as a semiconductor substrate is mounted. In addition, a mixed vapor supply port 3 is connected to the reaction chamber 2. Further, an N 2 gas supply port 16 for supplying N 2 gas into the reaction chamber 2 is connected to the reaction chamber 2 on the same side as the mixed vapor supply port 3. Further, an exhaust port 4 for exhausting the gas in the reaction chamber 2 is connected to the reaction chamber 2 on the side opposite to the side where the mixed vapor supply port 3 and the N2 gas supply port 16 are connected. The surface etching unit 20 is provided with a heater 6 that heats the reaction chamber 2 and a portion 32 of the mixed vapor supply port 3 near the reaction chamber 2.

  The measuring apparatus 7 of FIG. 2 includes an X-ray generator 71, a fluorescent X-ray detector 72, and an analyzer 73. The X-ray generator 71 generates X-rays and causes the generated X-rays 81 (incident X-rays) to enter the surface 51 of the silicon substrate 5. At this time, the X-ray generator 71 controls the incident angle of the incident X-ray 81 so that the incident angle of the incident X-ray 81 with respect to the surface 51 becomes a critical angle at which the incident X-ray 81 is totally reflected. FIG. 2 also shows reflected X-rays 82. The X-ray generator 71 also controls the incident position of the X-ray 81 on the surface 51. FIG. 2 shows an example in which the X-ray 81 is incident on the central portion 51 a of the surface 51.

  The X-ray fluorescence detector 72 detects X-ray fluorescence 83 emitted from an element (metal impurity element) present on the surface 51 excited by the X-ray 81 from the X-ray generator 71. The analyzer 73 analyzes the wavelength and peak intensity of the fluorescent X-ray 83 detected by the fluorescent X-ray detector 72 and identifies the type and concentration of the metal impurity present on the surface 51. In FIG. 2, the type and concentration of the metal impurity present in the central portion 51a of the surface 51 are measured.

  Next, a process for analyzing metal impurities present on the surface layer of the silicon substrate will be described using each apparatus shown in FIGS. FIG. 3 is a flowchart showing the process. 3 will be described with reference to FIGS. 1 and 2. First, the decomposition gas generation unit 10 generates a mixed vapor 14 of hydrofluoric acid and nitric acid (S11). Specifically, a mixed solution 13 of hydrofluoric acid and nitric acid is prepared, and the container 12 containing the mixed solution 13 is placed in the gas generation chamber 1. Next, while the container 12 is heated to a predetermined temperature by the heater 15, N2 gas is blown into the container 12 in the gas generation chamber 1 from the N2 gas supply port 11, and the mixed solution 13 is bubbled by the blowing. As a result, a mixed vapor 14 of hydrofluoric acid and nitric acid is generated. The generated mixed vapor 14 is supplied to the reaction chamber 2 through the mixed vapor supply port 3 using N2 gas as a carrier gas.

  Next, the mixed vapor 14 is reacted with the surface 51 of the silicon substrate 5 for a predetermined time to etch (decompose) the surface layer of the silicon substrate 5 (S12). Specifically, the silicon substrate 5 is mounted on the mounting table 21 of the reaction chamber 2. In consideration of the reactivity between the mixed steam 14 and the surface 51, the mixed steam 14 is exhausted from the exhaust port 4 so that a certain amount of the mixed steam 14 is always supplied to the surface 51. Further, the heater 6 heats the reaction chamber 2 and the portion 32 of the mixed vapor supply port 3 near the reaction chamber 2 to a predetermined temperature to prevent condensation of the mixed vapor 14. The step S12 corresponds to the “decomposition step” of the present invention.

As a result, as shown in FIG. 4A, the surface 510 (initial surface) of the silicon substrate 5 and the mixed vapor 14 react as shown in the following formulas 1 to 5, for example, in accordance with the reaction time. The depth surface layer 520 is etched (decomposed). In addition, Formula 1-Formula 3 have shown the gas phase reaction, Formula 4 and Formula 5 have shown the liquid phase reaction.
Gas phase reaction:
4Si + 10HNO ₃ = 4Si (NO ₃ ) ₂ + No ₃ ⁻ + NH ₄ ⁺ + 3H ₂ O (Formula 1)
Si (NO ₃ ) ₂ + 6HF = H ₂ SiF ₆ + 2NO ₂ + 2H ₂ O (Formula 2)
H ₂ SiF ₆ + 2NH ₄ ⁺ = (NH ₄ ) ₂ SiF ₆ + 2H ⁺ (formula 3)
Liquid phase reaction:
Si + 4HNO ₃ = SiO ₂ + 4NO ₂ + 2H ₂ O (Formula 4)
SiO ₂ + 6HF = H ₂ SiF ₆ + 2H ₂ O (Formula 5)

FIG. 4B shows a schematic diagram of the silicon substrate 5 after performing S12. As shown in FIG. 4B, on the surface 511 (surface corresponding to the broken line 511 in FIG. 4A, the surface after decomposition) of the silicon substrate 5 after performing S12, the surface layer portion 520 and the mixed vapor 14 The reaction residue 530 remains. The reaction residue 530 was included in the silicon reaction residue (Si, H ₂ SiF ₆ , SiO ₂ , (NH ₄ ) ₂ SiF _6, etc.) generated by the reactions of the above formulas 1 to 5 and the surface layer portion 520. It consists of metal impurities.

  Next, the silicon reaction residue in the reaction residue 530 of FIG. 4B is removed (S13). Specifically, for example, the N2 gas supply from the N2 gas supply port 11 to the container 12 in the gas generating chamber 1 is stopped, and only the N2 gas from the N2 gas supply port 16 is supplied to the reaction chamber 2. Then, the surface 511 is blown for a predetermined time with the N 2 gas, and the silicon reaction residue is sublimated from the reaction residue 530. As a result, the silicon reaction residue can be removed from the reaction residue 530 by the amount corresponding to the blow time. As a result, the metal impurities in the reaction residue 530 can be revealed, and the irregular reflection of the incident X-ray 81 can be prevented when the measurement is performed by the measuring device 7 of FIG. In addition, the process of S13 corresponds to the “removal process” of the present invention.

  Next, the silicon substrate 5 of FIG. 4B after performing S13 is set in the measurement apparatus 7 of FIG. 2, and the measurement apparatus 7 performs impurity measurement on the surface 511 (S14). Thus, the type and concentration of the reaction residue 530 remaining on the surface 511, that is, the metal impurity existing in the surface layer portion 520 in FIG. 4A can be analyzed. Further, when the X-ray 81 is incident on, for example, the central portion 511a (see FIG. 4B) of the surface 511, the metal impurities at the central portion 511a (the central portion of the surface layer portion 520) can be analyzed. Further, when the X-ray 81 is incident on, for example, the outer peripheral portion 511b (see FIG. 4B) of the surface 511, the metal impurities at the outer peripheral portion 511b (the outer peripheral portion of the surface layer portion 520) can be analyzed. That is, the in-plane position information of the analyzed metal impurity can be acquired. In addition, the process of S14 corresponds to the “measurement process” of the present invention.

  The above-described steps S12 to S14 are repeated as appropriate. When the steps S12 to S14 are performed again on the silicon substrate 5 of FIG. 4B, the silicon substrate 5 is set in the reaction chamber 2 again. FIG. 4C shows a schematic diagram of the silicon substrate 5 set in the reaction chamber 2. Then, the mixed vapor 14 is reacted with the new surface 511 of the silicon substrate 5 to etch (decompose) the surface layer portion 521 in FIG. 4C (S12).

  FIG. 4D is a schematic diagram of the silicon substrate 5 after S12 is performed on the silicon substrate 5 of FIG. As shown in FIG. 4D, the reaction residue 531 of the surface layer portion 521 in FIG. 4C remains on the surface 512 of the silicon substrate 5 (corresponding to the broken line 512 in FIG. 4C). Next, the silicon reaction residue is removed from the reaction residue 531 (S13), and metal impurities are analyzed on the removed silicon substrate 5 (S14). Thereby, the type, concentration, and in-plane position information of the metal impurities present in the reaction residue 531 (the surface layer portion 521 in FIG. 4C) can be obtained.

  Thus, the depth direction distribution of the metal impurity existing in the silicon substrate can be evaluated by repeating the steps S12 to S14.

Example 1
In order to confirm the effect of the present invention, a sample of a silicon substrate was prepared, and the sample was intentionally contaminated with Fe, Cr, and Ni as metal impurities, and an experiment was conducted to measure the Fe, Cr, and Ni. . The prepared sample is a silicon substrate having a diameter of 200 mmφ, CZ-PW (manufactured by the CZ method, with mirror polishing), a conductivity type of P type, a surface orientation of <100>, and a resistivity of 8 to 12 Ωcm. FIG. 5 is a flowchart of this experimental process.

  First, as a solution for intentional contamination, a standard solution for atomic absorption analysis of Fe, Cr and Ni (1000 ppm) was diluted and mixed to prepare a 5% nitric acid base mixed solution having a concentration of 10 ppb for each of Fe, Cr and Ni. (S21). Next, 500 μl of the Fe, Cr, Ni mixed solution prepared in S21 was dispensed with a micropipette and dropped onto a part of the sample (in this example, the center of the sample) (S22). Next, the solution dropped in S22 was dried (S23). After the drying of S23, in order to diffuse each impurity (Fe, Cr, Ni) from the sample surface, the sample was heat-treated in an N2 atmosphere at 650 ° C. for 30 minutes (S24). By S21 to S24, the sample (in this example, the sample center) was intentionally contaminated with Fe, Cr, and Ni.

  In order to evaluate impurities in the surface layer in a sample that was intentionally contaminated, a PFA container containing a 1: 1 mixed solution (200 ml) of hydrofluoric acid (50%) and nitric acid (61%) was heated at 85 ° C. Bubbling was performed with N2 gas at a flow rate of 1 liter per minute to generate a hydrofluoric acid / nitric acid mixed vapor (S25, corresponding to S11 in FIG. 3).

  Next, the sample was placed in a reaction chamber made of PTFE, and a mixed vapor of hydrofluoric acid / nitric acid was introduced into the reaction chamber (S26). In consideration of the reactivity with the mixed steam, the steam was extracted from the exhaust port so that a constant amount of steam was always supplied (S26). The reaction chamber and the inlet side of the mixed steam were heated at 85 ° C. to prevent condensation of the steam (S26). Then, the mixed vapor was reacted for about 20 minutes on the sample surface in the reaction chamber (S26). At this time, the sample surface was etched by about 2 μm. The step S26 corresponds to the step S12 in FIG.

  In this state, since a large amount of reaction residue (particularly silicon reaction residue) remains on the sample surface, the supply to the reaction chamber is switched from the mixed vapor to only N2 gas and blown for 30 minutes to sublimate the silicon reaction residue. (S27, corresponding to S13 in FIG. 3).

  Next, total reflection X-ray fluorescence analysis was performed on the sample surface (S28, corresponding to S14 in FIG. 3). The result is shown in FIG. FIG. 6 shows the concentration of impurities present in the surface layer at a depth of 2 μm from the sample surface. FIG. 6 shows the concentration of impurities present at the site (center of the sample) where the solution for intentional contamination is dropped, and the region not affected by the intentional contamination of metal impurities (30 mm inside from the outer periphery of the sample). The concentration of the impurity is shown. In FIG. 6, the concentration of impurities at the center of the sample is illustrated as “intentional contamination site”, and the concentration of impurities in the region not affected by intentional contamination is illustrated as “unintentional contamination site”. As shown in FIG. 6, both intentional contamination sites and unintentional contamination sites can detect metallic impurities such as Fe, Cr, and Ni, and it is possible to obtain an in-plane distribution of metal impurities existing on the sample surface layer. It was done. In addition, it was shown that Fe, Cr, and Ni could be detected better in the intentionally contaminated site than in the unintentionally contaminated site.

Moreover, in this experiment, the process of S26-S28 was repeated 3 times. That is, the depth direction distribution of impurities up to 6 μm was evaluated every 2 μm. The results at this time are shown in FIG. 7, FIG. 8, and FIG. FIG. 7 shows the depth direction distribution of Fe, FIG. 8 shows the depth direction distribution of Cr, and FIG. 9 shows the depth direction of Ni. As shown in FIGS. 7 to 9, all of Fe, Cr and Ni have good impurity concentration at a depth of 0 to 2 μm, impurity concentration at a depth of 2 μm to 4 μm, and impurity concentration at a depth of 4 μm to 6 μm. It was shown that it was detected. Specifically, the Fe concentration at the site of intentional contamination in FIG. 7 is 1.2 × 10 ¹³ (atoms / cm ² ) at a depth of 0 to ² μm, and 5.2 × 10 ¹² (atoms at a depth of ² to 4 μm. / ^cm 2), it has become the depth ^{4~6μm 2.3 × 10 11 (atoms /} cm 2). The Cr concentration at the site of intentional contamination in FIG. 8 is 1.1 × 10 ¹³ (atoms / cm ² ) at a depth of 0 to ² μm, 4.3 × 10 ¹² (atoms / cm ² ) at a depth of ² to 4 μm, It became 4.3 * 10 < ¹¹ > (atoms / cm < ² >) in the depth of 4-6 micrometers. The Ni concentration at the site of intentional contamination in FIG. 9 is 6.3 × 10 ¹¹ (atoms / cm ² ) at a depth of 0 to ² μm, 2.1 × 10 ¹¹ (atoms / cm ² ) at a depth of ² to 4 μm, The depth was 2.3 × 10 ¹¹ (atoms / cm ² ) at a depth of 4 to 6 μm. The impurity concentration at the unintentional contamination site was 5.0 × 10 ⁹ (atoms / cm ² ) in all cases.

(Example 2)
The relationship between the reaction time of the hydrofluoric acid and nitric acid mixed vapor and the etching depth of the silicon substrate was investigated. The mixed steam at this time is the same as the mixed steam generated in S25 of Example 1. The silicon substrate is the same as the sample prepared in Example 1 (200 mmφ, CZ-PW, P-type <100>, 8-12 Ωcm sample). This time, the etching depth was measured when the reaction time between the mixed vapor and the silicon substrate surface was changed between 3 minutes and 60 minutes. The result is shown in FIG. As shown in FIG. 10, when the reaction time is between 3 minutes and 60 minutes, the reaction time and the etching depth are substantially proportional. It has been shown that the etch depth varies between about 0.5 μm and about 5 μm as the reaction time varies between 3 minutes and 60 minutes. Therefore, by reacting the mixed vapor with a reaction time of 3 minutes to 60 minutes, impurities can be analyzed at a depth of about 0.5 μm to about 5 μm from the surface. At this time, the reaction time of the mixed vapor corresponding to the target etching depth can be easily determined by referring to the relationship of FIG. The reaction time of the mixed vapor may be other than 3 minutes to 60 minutes. For example, if the reaction time is 3 minutes or less, impurity analysis at a depth of 0.5 μm or less from the surface can be performed. Further, for example, if the reaction time is 60 minutes or more, impurity analysis at a depth of 5 μm or more from the surface can be performed.

(Comparative example)
As a comparative example, FIG. 11 shows the results of evaluation of a sample prepared in the example (sample with intentional contamination at the center of the sample) by a conventional method (evaluation of impurities on the surface of the sample electrode by the TXRF method). In other words, FIG. 11 shows the results when the TXRF measurement of S28 is directly performed on the sample in which the sample center is intentionally contaminated in the steps S21 to S24 of FIG. 5 while omitting the steps S25, S26, and S27. Show. In addition, in FIG. 11, the impurity concentration of the unintentional contamination site | part (30 mm inside from the outer periphery of a sample) is also illustrated similarly to FIG. The Fe concentration in FIG. 11 is 1.4 × 10 ¹³ (atoms / cm ² ), the Cr concentration is 1.3 × 10 ¹³ (atoms / cm ² ), and the Ni concentration is 8.7 × 10 ¹¹ (atoms). / Cm ² ). As shown in FIG. 11, in the conventional method, the positional information of impurities in the sample surface and the surface impurity concentration can be evaluated, but the impurity distribution in the depth direction from the surface is completely unknown.

  As described above, in this embodiment, since the surface layer of the silicon substrate is decomposed and TXRF measurement is performed on the surface of the silicon substrate after decomposition, the metal impurities existing in the decomposed surface layer can be evaluated. That is, metal impurities existing in the depth direction from the surface can be evaluated. Moreover, since TXRF measurement is performed without collecting the reaction residue, the in-plane distribution of metal impurities can be evaluated. Moreover, since the decomposition of the surface layer and the TXRF measurement are repeatedly performed, the depth direction distribution of metal impurities can also be evaluated.

  The above-described embodiment is an exemplification, and the embodiment having substantially the same configuration as the technical idea described in the claims of the present invention and having the same function and effect is any type. Are also included in the technical scope of the present invention. For example, in the above embodiment, a mixed vapor of hydrofluoric acid and nitric acid is used as a decomposition material for decomposing the surface layer of the silicon substrate. However, the oxidizing agent that can decompose the surface layer is a side reaction product (other than the silicon reaction residue). Any substance may be employed as a decomposition substance as long as it does not produce a reaction product. For example, ozone may be used as the decomposition material. Moreover, although the said embodiment demonstrated the example of the impurity analysis with respect to the silicon substrate manufactured by CZ method as an example, this invention is applicable also to a silicon epitaxial wafer. Further, the present invention may be applied to impurity analysis for semiconductor substrates other than silicon substrates (for example, GaAs substrates and GaP substrates).

DESCRIPTION OF SYMBOLS 5 Silicon substrate 7 Measuring apparatus 10 Decomposition gas generation part 14 Mixed vapor | steam of hydrofluoric acid and nitric acid 20 Surface layer etching part 510 Surface of silicon substrate 511, 512 Surface after decomposition of silicon substrate 520, 521 Surface layer part of silicon substrate 530, 531 Reaction Residue

Claims (6)

A method for analyzing impurities present in a surface layer of a semiconductor substrate,
A decomposition step of decomposing a surface layer of the semiconductor substrate by reacting a decomposition substance on the surface of the semiconductor substrate;
A measurement step of measuring impurities on the post-decomposition surface while leaving the reaction residue of the surface layer decomposed in the decomposition step on the post-decomposition surface that is the surface of the semiconductor substrate after the decomposition step;
And a method for analyzing impurities in a semiconductor substrate.   2. A removal step of removing a residue component formed by a reaction between the semiconductor substrate other than impurities and the decomposition substance from the reaction residue between the decomposition step and the measurement step. The impurity analysis method of the semiconductor substrate as described in 2.   3. The method for analyzing impurities in a semiconductor substrate according to claim 2, wherein the decomposition step, the removal step, and the measurement step are repeated. The semiconductor substrate is a silicon substrate;
The impurity analysis method for a semiconductor substrate according to claim 1, wherein the decomposition substance is a mixed vapor of hydrofluoric acid and nitric acid.   5. The impurity analysis method for a semiconductor substrate according to claim 4, wherein in the decomposition step, the mixed vapor is allowed to react for 3 to 60 minutes on the surface of the semiconductor substrate. 6. The impurity analysis method for a semiconductor substrate according to claim 1, wherein in the measurement step, impurities are measured by a total reflection fluorescent X-ray analysis method.

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