Semiconductor wafer impurity measurement method and impurity measurement jig

Abstract

To provide a semiconductor wafer impurity measurement method and an impurity measurement jig that can accurately measure the impurity concentration of a semiconductor wafer in analyzing impurities contained in the semiconductor wafer.SOLUTION: A semiconductor wafer impurity measurement method includes the steps of: creating a first test piece SL1 from which a main surface of a semiconductor wafer W is not removed and a second test piece SL2 from which a part of the main surface of the semiconductor wafer W is removed to a predetermined depth in a thickness direction; performing gas phase decomposition on the first test piece and the second test piece in a closed space; dissolving the first test piece and the second test piece that have been subjected to gas phase decomposition to form respective liquid samples; performing mass spectrometry on each of the two liquid samples; and measuring the impurity concentration from a difference between the mass spectrometry results for the two liquid samples.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor wafer impurity measurement method and an impurity measurement tool for measuring the concentration of metal impurities contained in a semiconductor wafer such as a silicon wafer. [Background technology]

[0002] Conventionally, in the quality control of silicon wafers and crystals, metal impurities contained in silicon wafers have been measured and analyzed using an atomic absorption spectrometer, an ICP optical emission spectrometer, or an ICP mass spectrometer. For example, when evaluating the depth direction of metal impurities contained in a silicon wafer, the surface layer is removed by etching, and the metal impurities contained in that portion are measured.

[0003] Patent Document 1 (JP Patent Publication No. 7-333121A) describes a method in which an analytical sample container (evaporating dish) containing a silicon-based analytical sample (silicon wafer sample) and a sample decomposition solution (mixed acid of hydrofluoric acid and nitric acid) are stored in an airtight container constituting an airtight space system in an isolated state without contacting each other, and then the airtight container is heated to decompose and sublimate (vapor-phase decomposition) the silicon-based analytical sample, and the residue in the analytical sample container is recovered and analyzed.

[0004] Furthermore, Patent Document 2 (JP 2007-208198 A) discloses an impurity analysis method having a first step of masking the main surface of a semiconductor substrate with a protective plate having an opening, filling the opening of the protective plate with an etching solution, and etching the surface layer of the semiconductor substrate, and a second step of recovering the etching solution (liquid-phase decomposition) and analyzing the impurities in the surface layer of the semiconductor substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-333121 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-208198 Summary of the Invention [Problem to be solved by the invention]

[0006] As disclosed in Patent Document 1, when gas-phase decomposition of a sample is performed in a sealed container using a sample decomposition solution (a mixed acid of hydrofluoric acid and nitric acid), decomposition residues of the sample are unlikely to remain. However, if decomposition residues remain, there is a problem in that detection sensitivity decreases. Furthermore, when liquid-phase decomposition is performed using an etching solution as disclosed in Patent Document 2, there is a problem in that metal impurities contained in the acid chemical solution remain in the sample solution, which deteriorates the detection accuracy.

[0007] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a semiconductor wafer impurity measurement method and an impurity measurement tool that can accurately measure the impurity concentration of a semiconductor wafer in the analysis of impurities contained in the semiconductor wafer. [Means for solving the problem]

[0008] The semiconductor wafer impurity measuring method according to the present invention, which has been made to solve the above-mentioned problems, includes the steps of: sandwiching a semiconductor wafer between an upper jig having a plurality of first openings formed with the same area in the surface direction and penetrating in the thickness direction; and a lower jig having a plurality of second openings formed to match the positions of the first openings and penetrating in the thickness direction; pouring an etching solution into one of the plurality of first openings to remove a portion of the main surface of the semiconductor wafer facing the first opening in the thickness direction; placing the lower jig on an evaporating dish having a plurality of bottomed holes so that the positions of the plurality of second openings are aligned; the lower jig together with the evaporating dish in a sealed container, pouring a sample decomposition solution into the bottom of the sealed container, and heating the sealed container to vapor-phase decompose the semiconductor wafer facing the first opening; performing mass spectrometry measurements on a first liquid sample formed from the sample recovered in the evaporating dish by the vapor-phase decomposition, the first liquid sample having an unetched main surface of the semiconductor wafer, and a second liquid sample formed from the semiconductor wafer having a portion of the main surface etched away; and calculating the impurity concentration of the surface layer of the semiconductor wafer removed by etching based on the difference between the measurement results of the first and second liquid samples.

[0009] Alternatively, a method for measuring impurities in a semiconductor wafer according to the present invention, which has been made to solve the above-mentioned problems, includes the steps of: clamping a semiconductor wafer between an upper jig having a plurality of first openings formed with the same area in the surface direction and penetrating in the thickness direction; and a lower jig having a plurality of second openings formed to match the positions of the first openings and penetrating in the thickness direction; pouring an etching solution into one of the plurality of first openings and removing a portion of the main surface of the semiconductor wafer facing the first opening by a first depth in the thickness direction; pouring an etching solution into another one of the plurality of first openings and removing a portion of the main surface of the semiconductor wafer facing the first opening by a second depth in the thickness direction; and placing an etching solution in one of the plurality of second openings on an evaporating dish having a plurality of bottomed holes. the steps of placing the lower jig in position; placing the upper jig and the lower jig, with the semiconductor wafer sandwiched between them, together with the evaporating dish in a sealed container, pouring a sample decomposition solution into the bottom of the sealed container, and heating the sealed container to vapor-phase decompose the semiconductor wafer facing the first opening; performing mass spectrometry measurements on a first liquid sample formed from the sample recovered in the evaporating dish by the vapor-phase decomposition, in which a portion of the main surface of the semiconductor wafer has been removed by a first depth, and a second liquid sample formed from the main surface of the semiconductor wafer has been removed by a second depth; and calculating the impurity concentration in the surface layer of the semiconductor wafer based on the difference between the measurement results of the first and second liquid samples.

[0010] According to this method, it is not necessary to cleave the semiconductor wafer, and therefore metal impurities can be easily measured. Furthermore, because the semiconductor wafer is subjected to vapor-phase decomposition, it is not affected by impurities contained in the chemical solution, and detection sensitivity can be improved compared to analytical methods using liquid-phase decomposition. Furthermore, because vapor-phase decomposition is performed in an enclosed space, decomposition residues are less likely to remain, and because vapor-phase decomposition is performed on two samples obtained from the same semiconductor wafer in the same processing space and under the same conditions, highly accurate measurement results can be obtained. Furthermore, the measurement depth can be set as desired by adjusting the amount of material removed by etching.

[0011] The impurity measurement jig according to the present invention, which has been made to solve the above-mentioned problems, is used in the semiconductor wafer impurity measurement method, is placed in a sealed container having a sample decomposition solution placed at the bottom, and is used for vapor-phase decomposition of a semiconductor wafer, and comprises an upper jig having a plurality of first openings formed with the same area in the plane direction and penetrating in the thickness direction, a lower jig having a plurality of second openings formed to match the positions of the plurality of first openings and penetrating in the thickness direction, and which sandwiches the semiconductor wafer between itself and the upper jig, and an evaporating dish having a plurality of bottomed holes formed to match the positions of the second openings, and is characterized in that the first openings of the upper jig are used to form a sample by etching the semiconductor wafer to a desired depth, and are also used for vapor-phase decomposition of the semiconductor wafer facing the first openings by volatilization of the sample decomposition solution, and the vapor-phase decomposed sample is recovered in the bottomed holes of the evaporating dish.

[0012] Alternatively, a semiconductor wafer impurity measurement method according to the present invention, which has been made to solve the above-mentioned problems, is a semiconductor wafer impurity measurement method for analyzing impurities contained in a semiconductor wafer, and is characterized by comprising the steps of: preparing a first test piece from which the main surface of the semiconductor wafer has not been removed, and a second test piece having the same area as the first test piece and in which a portion of the main surface of the semiconductor wafer has been removed to a predetermined depth in the thickness direction; performing vapor-phase decomposition on the first test piece and the second test piece in an enclosed space; forming liquid samples from the vapor-decomposed first test piece and the second test piece; performing mass spectrometry on each of the two liquid samples; and measuring the impurity concentration from the difference in the results of mass spectrometry on the two liquid samples.

[0013] This method involves vapor-phase decomposition of the test piece, which is not affected by impurities contained in the chemical solution, and can improve detection sensitivity compared to analytical methods using liquid-phase decomposition. Furthermore, because the vapor-phase decomposition of the test piece is performed in an enclosed space, decomposition residues are less likely to remain, and because vapor-phase decomposition is performed on two samples obtained from the same semiconductor wafer in the same processing space and under the same conditions, highly accurate measurement results can be obtained. Furthermore, the measurement depth can be freely set by adjusting the amount of material removed by etching.

[0014] Alternatively, a semiconductor wafer impurity measurement method according to the present invention, which has been made to solve the above-mentioned problems, is a semiconductor wafer impurity measurement method for analyzing impurities contained in a semiconductor wafer, and is characterized by comprising the steps of: preparing a first test piece by removing a portion of a main surface of the semiconductor wafer to a first depth in the thickness direction; and preparing a second test piece having the same area as the first test piece by removing a portion of the main surface of the semiconductor wafer to a second depth in the thickness direction; performing vapor-phase decomposition on the first test piece and the second test piece in an enclosed space; dissolving the vapor-phase decomposed first test piece and the second test piece into liquid samples, respectively; performing mass spectrometry on the two liquid samples, respectively; and measuring the impurity concentration from the difference in the results of mass spectrometry on the two liquid samples.

[0015] According to this method, the concentration of metal impurities can be measured in any depth range by etching the two samples to different depths. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a semiconductor wafer impurity measurement method and an impurity measurement tool that can accurately measure the impurity concentration of a semiconductor wafer in the analysis of impurities contained in the semiconductor wafer. [Brief explanation of the drawings]

[0017] [Figure 1]FIG. 1 is a schematic cross-sectional view of a processing vessel used in a first embodiment of a method for measuring impurities in a semiconductor wafer according to the present invention. [Figure 2] FIG. 2 is a flow chart showing the flow of the first embodiment of the semiconductor wafer impurity measuring method of the present invention. [Figure 3] FIG. 3 is a flow chart showing the flow of a second embodiment of the semiconductor wafer impurity measuring method of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view of a semiconductor wafer for explaining a second embodiment of the semiconductor wafer impurity measuring method of the present invention. [Figure 5] FIG. 5 is a schematic cross-sectional view of a processing vessel used for vapor-phase decomposition of a sample in a second embodiment of the semiconductor wafer impurity measuring method of the present invention. [Figure 6] FIG. 6 is a flow chart showing the flow of the third embodiment of the semiconductor wafer impurity measuring method of the present invention. [Figure 7] FIG. 7 is a schematic cross-sectional view of a semiconductor wafer for explaining a third embodiment of the semiconductor wafer impurity measuring method of the present invention. [Figure 8] FIG. 8 is a bar graph showing the results of the example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a semiconductor wafer impurity measurement method and an impurity measurement jig according to the present invention will be described with reference to the drawings. However, this embodiment will be described as an example of the present invention, and the present invention is not limited thereto. Furthermore, in this embodiment, a silicon wafer will be used for the description, but the present invention is not limited to silicon wafers and may be a semiconductor wafer such as a SiC wafer or a GaN wafer. The semiconductor wafer impurity measurement method described below analyzes metal impurities contained in the surface layer of a silicon wafer.

[0019] First, a first embodiment of a semiconductor wafer impurity measurement method according to the present invention will be described. In the first embodiment of the semiconductor wafer impurity measurement method according to the present invention, a processing vessel 20 shown in FIG. 1 is used. 1 includes a lower outer cylindrical tube 21 having an internal space and opening at the top, and an upper outer cylindrical tube 22 that is open at the bottom and has an inner peripheral portion at its lower end that is fitted, for example, by screwing, to the outer peripheral portion at the upper end of the lower outer cylindrical tube 21. A mounting table 21a is disposed at the center of the bottom of the lower outer cylindrical tube 21. An evaporation dish 23 having a plurality of bottomed holes 23a is placed on the mounting table 21a, and a wafer jig 30 is configured to be placed on this evaporation dish 23 (the evaporation dish 23 and the wafer jig 30 constitute the impurity measuring jig of the present invention).

[0020] The wafer jig 30 is composed of a lower jig 31 and an upper jig 32, and is configured to sandwich the silicon wafer W therebetween. The lower jig 31 and the upper jig 32 are each formed with a plurality of openings 31a (first openings) and 32a (second openings) that penetrate vertically and have the same area, in alignment with the positions of the bottomed holes 23a of the evaporating dish 23.

[0021] FIG. 2 is a flow chart showing the flow of a first embodiment of a semiconductor wafer impurity measuring method according to the present invention. First, a silicon wafer W is sandwiched between wafer jigs 30, and etching is performed by dripping a mixed acid of hydrofluoric acid and nitric acid through a plurality of openings 32a in the upper jig 32. At this time, the mixed acid of hydrofluoric acid and nitric acid is poured (dropped) through, for example, two openings 32a, and the etching depths in the regions corresponding to the two openings 32a are set to arbitrary depths that are different from each other (step St1 in FIG. 2).

[0022] 1, the wafer jig 30 holding the silicon wafer W therebetween is placed on the evaporation dish 23 in the processing vessel 20 (step St2 in FIG. 2). At this time, the openings 31a and 32a of the wafer jig 30 are aligned with the bottomed hole 23a of the evaporation dish 23. A mixed solution 2 of hydrofluoric acid and nitric acid (sample decomposition solution) is placed at the bottom of the lower outer tube 21, and the processing vessel 20 is heated, for example, on a hot plate 10 at 150°C for 48 hours to perform a vapor-phase decomposition process (step St3 in FIG. 2). Specifically, the mixed solution 2 of hydrofluoric acid and nitric acid (HF+HNO) volatilizes, and the vaporized HF+HNO contacts the top surface of the silicon wafer W through the opening 32a of the wafer jig 30. Silicon (Si) in the silicon wafer W sublimes as hydrofluorosilicic acid (H2SiF6) and silicon tetrafluoride (SiF4). The sublimated hydrofluorosilicic acid (H2SiF6) and silicon tetrafluoride (SiF4) are absorbed by the mixed solution 2 of hydrofluoric acid and nitric acid (HF+HNO3), and metal impurities remain in each of the multiple bottomed holes 23a of the evaporating dish 23.

[0023] Next, the evaporating dish 23 is taken out and heated on a hot plate at 150° C. until it is dried, and 1 ml of 1% nitric acid is poured into each bottomed hole 23a to make the volume constant (step St4 in FIG. 2). Then, the constant volume solutions (first liquid sample, second liquid sample) in each bottomed hole 23a are measured using ICP-MS or the like, and the metal impurity concentration in the wafer surface layer corresponding to the etching difference is evaluated from the difference in the measured values ​​of the constant volume solutions in, for example, any two bottomed holes 23a (step St5 in Figure 2).

[0024] As described above, according to the first embodiment of the present invention, since there is no need to cleave the silicon wafer W, metal impurities can be easily measured. Furthermore, since the silicon wafer is partially vapor-phase decomposed, there is no influence of impurities contained in the chemical solution, and detection sensitivity can be improved compared to analysis methods using liquid-phase decomposition. Furthermore, the measurement depth can be set arbitrarily by adjusting the amount of material removed by etching.

[0025] In the first embodiment, vapor phase decomposition is performed on regions with different etching depths, and the metal impurity concentration is calculated from the difference in the measured values ​​of the two samples. However, the present invention is not limited to this form. For example, vapor phase decomposition may be performed on an unetched region and an etched region, and the metal impurity concentration may be determined from the difference in the measured values ​​of the two samples.

[0026] Next, a second embodiment of the semiconductor wafer impurity measuring method according to the present invention will be described. Fig. 3 is a flow chart showing the procedure of a second embodiment of the semiconductor wafer impurity measurement method of the present invention. Fig. 4 is a schematic cross-sectional view of a semiconductor wafer for explaining the second embodiment of the semiconductor wafer impurity measurement method of the present invention.

[0027] First, a partial region Ar1 is formed to an arbitrary depth y1 by etching as shown in Fig. 4(b) on the main surface W1 of a silicon wafer W having a thickness T shown in Fig. 4(a) (step S1 in Fig. 3). For etching, for example, a mixed acid of hydrofluoric acid and nitric acid is used. Next, the silicon wafer W is cleaved as shown in Fig. 4(c) to produce an unetched test piece SL1 (first test piece) and an etched test piece SL2 (second test piece) as shown in Fig. 4(d) (step S2 in Fig. 3). The test pieces SL1 and SL2 have the same area in the wafer surface direction.

[0028] The order of steps S1 and S2 may be reversed. That is, before performing the etching in step S1, the silicon wafer W may be cleaved to extract the test pieces SL1 and SL2, and the main surface W1 side of the test piece SL2 may be etched with, for example, a mixed acid of hydrofluoric acid and nitric acid to remove a portion to a desired depth. In this manner, it is possible to prepare the test piece SL2 from which the portion to be measured has been removed and the test piece SL1 from which the portion has not been removed.

[0029] Next, the two test pieces SL1 and SL2 are placed in the evaporating dishes 5 shown in FIG. 5, and these evaporating dishes 5 are placed in the processing vessel 1 (step S3 in FIG. 3). A mixed solution 2 of hydrofluoric acid and nitric acid is placed in the bottom of the processing vessel 1, and the processing vessel 1 is heated, for example, on a hot plate 10 at 150°C for 48 hours (step S4 in FIG. 3). This causes the test pieces SL1 and SL2 to undergo vapor-phase decomposition. That is, the mixed solution 2 of hydrofluoric acid and nitric acid (HF + HNO3) volatilizes, and the vaporized HF + HNO3 gas comes into contact with the silicon wafer test pieces SL1 and SL2. The silicon (Si) components of the test pieces SL1 and SL2 sublimate as hydrosilicofluoroacid (H2SiF6) and silicon tetrafluoride (SiF4). The sublimated hydrosilicofluoric acid (H2SiF6) and silicon tetrafluoride (SiF4) are absorbed into the mixture 2 of hydrofluoric acid and nitric acid (HF+HNO3), and metal impurities remain in the evaporating dish 5.

[0030] Next, the evaporating dish 5 is heated on a hot plate at 150° C. until it is dry, and 1 ml of 1% nitric acid is added to make the volume constant (step S5 in FIG. 3). Then, the constant volume solutions of the test pieces SL1 and SL2 are subjected to mass analysis using ICP-MS or the like, and the metal impurity concentration of the surface layer that has been removed by etching is evaluated from the difference in the measured values ​​of the test pieces SL1 and SL2 (step S6 in Figure 3).

[0031] As described above, according to the second embodiment of the present invention, the test pieces SL1 and SL2 are subjected to vapor-phase decomposition, which is not affected by impurities contained in the chemical solution and improves detection sensitivity compared to analysis methods using liquid-phase decomposition. Furthermore, because the vapor-phase decomposition of the test pieces SL1 and SL2 is performed in an enclosed space, decomposition residues are less likely to remain. Since the vapor-phase decomposition of the samples SL1 and SL2 obtained from the same silicon wafer W is performed in the same processing space and under the same conditions, highly accurate measurement results can be obtained. Furthermore, the measurement depth can be set arbitrarily by adjusting the amount removed by etching.

[0032] In the above-described impurity measurement method, both surfaces of the test pieces SL1 and SL2 may be etched to the same extent with a mixed acid of hydrofluoric acid and nitric acid after cleavage in order to remove contamination caused by the cleavage process.

[0033] Next, a third embodiment of the semiconductor wafer impurity measuring method according to the present invention will be described. Fig. 6 is a flow chart showing the procedure of a third embodiment of the semiconductor wafer impurity measurement method of the present invention. Fig. 7 is a schematic cross-sectional view of a semiconductor wafer for explaining the third embodiment of the semiconductor wafer impurity measurement method of the present invention.

[0034] First, on the main surface W1 of a silicon wafer W having a thickness T shown in Fig. 7(a), a partial region Ar2 is formed to an arbitrary depth y3 by etching as shown in Fig. 7(b), and a region Ar3 different from the region Ar2 is formed to a depth y4 deeper than the depth y3 by etching (step Sp1 in Fig. 6). For example, a mixed acid of hydrofluoric acid and nitric acid is used for etching. Next, the silicon wafer W is cleaved as shown in Fig. 7(c), and a test piece SL3 (first test piece) is etched to a depth y3 as shown in Fig. 7(d), and a test piece SL4 (second test piece) is etched to a depth y4 as shown in Fig. 6(step Sp2). The test pieces SL1 and SL2 have the same area in the wafer surface direction.

[0035] The order of steps Sp1 and Sp2 may be reversed. That is, before performing the etching in step Sp1, the silicon wafer W may be cleaved to extract the test pieces SL3 and SL4, and the main surface W1 side of the test piece SL3 may be etched to a depth y1, and the main surface W1 side of the test piece SL4 may be etched to a depth y4. In this manner, the test pieces SL3 and SL4 from which the portions to the depth to be measured have been removed may be prepared.

[0036] Next, as in the first embodiment, the two test pieces SL3 and SL4 are placed in the evaporating dishes 5 shown in FIG. 5, and these evaporating dishes 5 are placed in the processing vessel 1 (step Sp3 in FIG. 6). A mixed solution 2 of hydrofluoric acid and nitric acid is placed in the bottom of the processing vessel 1, and the processing vessel 1 is heated, for example, on a hot plate 10 at 150°C for 48 hours (step Sp4 in FIG. 6). This causes the test pieces SL3 and SL4 to undergo vapor-phase decomposition. That is, the mixed solution 2 of hydrofluoric acid and nitric acid (HF+HNO3) volatilizes, and the vaporized HF+HNO3 gas comes into contact with the silicon wafer test pieces SL3 and SL4. The silicon (Si) components of the test pieces SL3 and SL4 sublimate as hydrosilicofluoroacid (H2SiF6) and silicon tetrafluoride (SiF4). The sublimated hydrosilicofluoric acid (H2SiF6) and silicon tetrafluoride (SiF4) are absorbed into the mixture 2 of hydrofluoric acid and nitric acid (HF+HNO3), and metal impurities remain in the evaporating dish 5.

[0037] Next, the evaporating dish 5 is heated on a hot plate at 150° C. until it is dry, and 1 ml of 1% nitric acid is added to make the volume constant (step Sp5 in FIG. 6). Then, the constant volume solutions of test pieces SL3 and SL4 are subjected to mass analysis using ICP-MS or the like, and the metal impurity concentration of the surface layer that has been removed by etching is evaluated from the difference in the measured values ​​of test pieces SL3 and SL4 (step Sp6 in Figure 6).

[0038] As described above, according to the third embodiment of the present invention, the etching depth of the samples SL3 and SL4 can be set to any different positions, thereby making it possible to measure the concentration of metal impurities in any depth range. As in the second embodiment, the test pieces SL3 and SL4 are subjected to vapor-phase decomposition, which is not affected by impurities contained in the chemical solution, and thus detection sensitivity can be improved compared to analysis methods using liquid-phase decomposition. Furthermore, the test pieces SL3 and SL4 are subjected to vapor-phase decomposition in an enclosed space, which makes it difficult for decomposition residues to remain, and the samples SL3 and SL4 obtained from the same silicon wafer W are subjected to vapor-phase decomposition in the same processing space and under the same conditions, so highly accurate measurement results can be obtained. [Example]

[0039] The semiconductor wafer impurity measurement method and impurity measurement jig according to the present invention will be further described based on examples.

[0040] Example 1 In Example 1, 3 ml of a solution made by mixing 38% hydrofluoric acid and 68% nitric acid in a volume ratio of 1:4 was dropped onto a part of the main surface of a sample silicon wafer, and the wafer surface layer was etched for 2 minutes (this was carried out twice in total). Thereafter, the silicon wafer was cleaved to prepare test pieces of approximately 1 g each of the etched portion (thickness: 505 μm) and the unetched portion (thickness: 775 μm). Both test pieces were placed in the evaporating dishes 5 of the processing vessel 1 shown in FIG. 5, and a mixed solution consisting of 150 ml of 38% hydrofluoric acid and 50 ml of 68% nitric acid was placed in the bottom of the processing vessel 1. Next, the processing vessel 1 was heated on a hot plate 10 at 150° C. for 48 hours to carry out vapor phase decomposition. Thereafter, the evaporating dish 5 was removed, heated on a hot plate at 150°C until it was dry, and 1 ml of 1% nitric acid was added to make the solution constant. The solution was measured for metal impurities by ICP-MS. The results of Example 1 are shown in Table 1. Table 1 shows the measurement results for Fe, Na, and Mg.

[0041] [Table 1]

[0042] As shown in Table 1, the etched specimen showed 5.8E11 atoms / cm for Fe, 9.0E10 atoms / cm for Na, and 1.6E12 atoms / cm for Mg. 3 The unetched specimen showed 5.2E11 Fe, 2.4E11 Na, and 2.9E12 Mg atoms / cm 3 Detected. The metal impurity concentration of the part removed by etching was calculated from the metal impurity concentration and thickness of each test piece using the following formula 1. The metal impurity concentration of Fe was 3.9E11 atoms / cm 3And Na is 5.4E11atoms / cm 3 , Mg is 5.2E12 atoms / cm 3 It was.

[0043] (Formula 1) Metal impurity concentration in the etched area = ((Concentration of metal impurities in test piece A) × (Thickness of test piece A) – (Concentration of metal impurities in test piece B) × (Thickness of test piece B)) / ((Thickness of test piece A) – (Thickness of test piece B))

[0044] Example 2 In Example 2, a sample silicon wafer was clamped between the wafer jig 30 shown in FIG. 1, and 3 ml of a solution prepared by mixing 38% hydrofluoric acid and 68% nitric acid at a volume ratio of 1:4 was dropped into each through-hole 32a of the upper jig 32, and the surface layer of the wafer was etched for 2 minutes (this was carried out twice in total). Thereafter, a mixture of 150 ml of 38% hydrofluoric acid and 50 ml of 68% nitric acid was poured into the bottom of the lower outer tube 21, and the evaporation dish 23 and wafer jig 30 were placed so as not to come into contact with the mixture. Next, the processing vessel 20 was heated on a hot plate 10 at 150° C. for 48 hours to carry out vapor phase decomposition. Thereafter, the evaporating dish 23 was removed, heated on a hot plate at 150° C. until it was dry, and 1 ml of 1% nitric acid was added to make the solution constant. The solution thus made constant was measured for metal impurities by ICP-MS. The results of Example 2 are shown in Table 2. Table 2 shows the measurement results for Fe, Na, and Mg.

[0045] [Table 2]

[0046] As shown in Table 2, the etched specimen showed 5.8E11 Fe, 9.0E10 Na, and 4.0E10 Mg atoms / cm 3 The unetched specimen showed 5.2E11 Fe, 9.0E10 Na, and 4.0E10 Mg atoms / cm 3 Detected. The metal impurity concentration of the portion removed by etching was calculated from the metal impurity concentration and thickness of each test piece using the above formula 1. The metal impurity concentration of Fe was 3.9E11 atoms / cm 3 And Na is 9.0E10 atoms / cm 3 , Mg is 4.0E10 atoms / cm 3 It was.

[0047] (Comparative Example 1) In Comparative Example 1, 3 ml of a solution made by mixing 38% hydrofluoric acid and 68% nitric acid in a volume ratio of 1:4 was dropped onto a sample silicon wafer, and the surface layer of the wafer was etched for 2 minutes (this was carried out twice in total). The etching solution was collected, and 5 ml of 20% hydrochloric acid was added to it, and the mixture was placed in an evaporating dish. The evaporating dish was then heated on a hot plate at 150°C until it was dry, and 1 ml of 1% nitric acid was added to make the volume constant. The metal impurity concentrations of the solution were measured by ICP-MS. The results of Comparative Example 1 were: Fe: 1.0E13, Na: 1.0E13, Mg: 1.0E13 atoms / cm 3 Detected.

[0048] The results of Examples 1 and 2 and Comparative Example 1 are shown in the bar graph of FIG. As shown in Figure 8, the metal impurity concentration in Comparative Example 1 was significantly higher than in Examples 1 and 2. This is thought to be due to the measurement of metal impurities contained in the chemical solution. Therefore, it was confirmed that the present invention makes it possible to measure impurity concentrations with high accuracy. [Explanation of symbols]

[0049] 20 Processing container 21 Lower outer tube 22 Upper outer tube 23 Evaporation dish (tool for measuring impurities) 23a Bottomed hole 30 Wafer jig (impurity measurement jig) 31 Upper jig 31a aperture 32 Lower jig 32a aperture SL1 specimen SL2 specimen SL3 specimen SL4 specimen W Silicon wafer (semiconductor wafer)

Claims

1. a step of sandwiching the semiconductor wafer between an upper jig having a plurality of first openings formed with the same area in a surface direction and penetrating in a thickness direction, and a lower jig having a plurality of second openings formed in accordance with the positions of the first openings and penetrating in a thickness direction; pouring an etching solution into one of the plurality of first openings to remove a portion of the main surface of the semiconductor wafer facing the first opening in a thickness direction; placing the lower jig on an evaporating dish having a plurality of bottomed holes, with the positions of the plurality of second openings aligned; placing the upper jig and the lower jig, with the semiconductor wafer sandwiched therebetween, together with the evaporating dish, in a sealed container, pouring a sample decomposition solution into the bottom of the sealed container, and heating the sealed container to vapor-phase decompose the semiconductor wafer facing the first opening; performing mass spectrometry measurements on a first liquid sample formed from the sample recovered in the evaporating dish by the vapor-phase decomposition, the first liquid sample having the main surface of the semiconductor wafer unetched, and a second liquid sample formed from the main surface of the semiconductor wafer having a portion thereof removed by etching; calculating the impurity concentration of the surface layer of the semiconductor wafer removed by etching based on the difference between the measurement results of the first and second liquid samples; A method for measuring impurities in a semiconductor wafer, comprising:

2. a step of sandwiching the semiconductor wafer between an upper jig having a plurality of first openings formed with the same area in a surface direction and penetrating in a thickness direction, and a lower jig having a plurality of second openings formed in accordance with the positions of the first openings and penetrating in a thickness direction; pouring an etching solution into one of the plurality of first openings and removing a portion of the main surface of the semiconductor wafer facing the first opening by a first depth in a thickness direction; pouring an etching solution into another one of the plurality of first openings and removing a portion of the main surface of the semiconductor wafer facing the first opening by a second depth in the thickness direction; placing the lower jig on an evaporating dish having a plurality of bottomed holes, with the positions of the plurality of second openings aligned; placing the upper jig and the lower jig, with the semiconductor wafer sandwiched therebetween, together with the evaporating dish, in a sealed container, pouring a sample decomposition solution into the bottom of the sealed container, and heating the sealed container to vapor-phase decompose the semiconductor wafer facing the first opening; performing mass spectrometry measurements on a first liquid sample formed from the sample recovered in the evaporating dish by the vapor-phase decomposition, the first liquid sample being obtained by removing a portion of the main surface of the semiconductor wafer by a first depth, and a second liquid sample being obtained by removing a portion of the main surface of the semiconductor wafer by a second depth; calculating an impurity concentration in the surface layer of the semiconductor wafer based on a difference between the measurement results of the first and second liquid samples; A method for measuring impurities in a semiconductor wafer, comprising:

3. 3. An impurity measurement tool used in the semiconductor wafer impurity measurement method according to claim 1 or 2, the tool being placed in a sealed container having a sample decomposition solution placed at the bottom thereof and used for vapor-phase decomposition of a semiconductor wafer, an upper jig having a plurality of first openings formed with the same area in a surface direction and penetrating in a thickness direction; a lower jig having a plurality of second openings formed in accordance with the positions of the plurality of first openings and penetrating in a thickness direction, the lower jig sandwiching the semiconductor wafer between itself and the upper jig; an evaporating dish having a plurality of bottomed holes formed in accordance with the positions of the second openings, The first opening of the upper jig is used to form a sample by etching the semiconductor wafer to a desired depth, and is also used for vapor-phase decomposition of the semiconductor wafer facing the first opening by volatilization of the sample decomposition solution, and the vapor-phase decomposed sample is recovered in the bottomed hole of the evaporating dish.

4. A semiconductor wafer impurity measurement method for analyzing impurities contained in a semiconductor wafer, comprising: creating a first test piece in which the main surface of the semiconductor wafer is not removed, and a second test piece having the same area as the first test piece and in which a portion of the main surface of the semiconductor wafer is removed to a predetermined depth in the thickness direction; performing vapor-phase decomposition on the first test piece and the second test piece in a sealed space; forming a liquid sample by dissolving the vapor-phase decomposed first test piece and the vapor-phase decomposed second test piece into a solution; performing mass spectrometry on each of the two liquid samples; measuring the impurity concentration from the difference between the results of mass spectrometry for the two liquid samples; A method for measuring impurities in a semiconductor wafer, comprising:

5. A semiconductor wafer impurity measurement method for analyzing impurities contained in a semiconductor wafer, comprising: creating a first test piece by removing a portion of the main surface of the semiconductor wafer by a first depth in the thickness direction, and a second test piece having the same area as the first test piece by removing a portion of the main surface of the semiconductor wafer by a second depth in the thickness direction; performing vapor-phase decomposition on the first test piece and the second test piece in a sealed space; a step of converting the vapor-phase decomposed first test piece and second test piece into solutions to prepare liquid samples; performing mass spectrometry on each of the two liquid samples; measuring the impurity concentration from the difference between the results of mass spectrometry for the two liquid samples; A method for measuring impurities in a semiconductor wafer, comprising:

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