JP2008311597A - Method for analyzing impurity in depth direction of silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for analyzing metal impurities of a silicon wafer, analyzing impurities in the silicon wafer of one sheet, without any introduction of contamination from the outside with excellently high sensitivity and in a short time, which is a pre-treatment method for measuring metal impurities at an arbitrary depth at an arbitrary place of the silicon wafer surface of one sheet. <P>SOLUTION: In the method for analyzing impurities, the impurities are analyzed by measuring a volume of sucked recovered solution with a hydrofluoric acid applied from pores of the silicon wafer of one sheet treated by a pre-treatment technology in which homogeneous pores are formed to the depth direction of the silicon wafer by using a wet chemical etching solution method called as an electroless deposition method, and by analyzing by an inductive coupled plasma mass spectrometry or an ICP mass spectrometry. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for analyzing a surface layer of a silicon wafer. In particular, the present invention relates to a method for measuring the impurity concentration distribution of a silicon wafer suitable for measuring the concentration distribution of trace impurities in the depth direction at a silicon wafer surface and at any point on the surface.

As semiconductor devices have been highly integrated, reduction of metal impurities in silicon wafers has become an even more important issue.
This is because the metal impurity contamination of the silicon wafer adversely affects junction leakage, oxidation-induced stacking faults, oxide dielectric breakdown voltage, and the like, and is a major factor in yield reduction in the semiconductor device manufacturing process.
Along with this, it is said that progress in the measurement method of metal impurities in silicon wafers is indispensable for improving the yield in these manufacturing processes.

As a surface analysis method of a silicon wafer, methods called a surface analysis method, a bulk analysis method, and a depth direction analysis method for analyzing the impurity element concentration in the depth direction of the silicon wafer are known. In the surface analysis method, a mixed acid of nitric acid and hydrofluoric acid, called a droplet decomposition method, is used as an etching solution, the surface of the silicon wafer is directly dissolved, and metal impurities contained in the etching solution are measured. A method is known in which the surface of a silicon wafer is etched using a vapor of hydrofluoric acid and nitric acid, which is called a method, and metal impurities in the liquid condensed on the surface are measured.
For bulk analysis, a beaker in which a decomposition solution of nitric acid and hydrofluoric acid, called acid vapor decomposition, is placed in the lower part of a Teflon container and a silicon wafer sample is placed in ultrapure water on top of it. Set and seal. The container is heated on a hot plate to generate vapors of nitric acid and hydrofluoric acid, the vapor is absorbed in ultrapure water in a beaker, the sample is decomposed, and the target metal impurity is measured by atomic absorption spectrometry. This method consists of a measurement method that can reduce the contamination of impurities from the reagent, and a pretreatment technique called vapor phase sublimation method that simultaneously purifies the reagent by heating distillation of nitric acid and hydrofluoric acid and sublimation decomposition of the silicon wafer sample. It is used in combination with a mass spectrometer.
Furthermore, along with the progress of integration of semiconductor devices, analysis methods and analyzers in the depth direction of silicon wafers have been reported. In a measurement method called a step etching method, a Teflon jig for a silicon wafer is attached, dissolved repeatedly from the surface of the wafer with an etching solution, and metal impurities are measured by an atomic absorption method. Since this method can be etched in several minutes, data in the depth direction in the polishing process and heat treatment can be obtained quickly. In a measurement method called a vapor phase etching method, an etching solution of nitric acid and hydrofluoric acid is placed at the bottom of a Teflon container, and an analysis surface of the wafer and the etching solution are placed facing each other. Then, heating is performed from above the wafer by a heater to generate vapors of nitric acid and hydrofluoric acid, and after repeated gas phase etching from the surface of the wafer, metal impurities are measured by ICP mass spectrometry. In this method, since the wafer is heated, it is reported that condensation of the decomposition solution and contamination from the reagent are prevented, and advanced depth analysis can be performed.
However, even in this vapor phase etching method, the average amount of metal impurities at an arbitrary depth of the wafer is only measured.
In one silicon wafer, it is said that the metal impurities on the surface layer of the silicon wafer are increased as it goes to the outer periphery of the silicon wafer even in the conventional analysis method, and it is said that the outer peripheral portion is contaminated. Moreover, it is said that the yield in a manufacturing process is bad as the outer peripheral part.
As a pretreatment method for that purpose, a teflon sheet with fine pores is attached to the surface of a silicon wafer, and etching in the depth direction with an etch solution of nitric acid and hydrofluoric acid has been attempted. There is a problem with accurate measurement. Furthermore, attempts have been made to form pores by applying the above-described vapor phase etching method, but the same problems as those caused by the etch solution have been pointed out.
In this way, in order to improve the yield in the manufacturing process of a semiconductor device having a high degree of device integration, a new measurement method of metal impurities in the depth direction at any position of the silicon wafer, that is, the so-called depth. A local analysis method in the direction is required. That is, a three-dimensional map of metal impurities is required.

  The present invention relates to a method for analyzing metal impurities in a silicon wafer, which can analyze impurities in a single silicon wafer with extremely high sensitivity and in a short time without causing external contamination. The main object is to provide a pretreatment method for measuring metal impurities at an arbitrary depth at an arbitrary position on the wafer surface.

  The present inventor has been engaged in research and development of a method for measuring metal impurities on the surface layer of a silicon wafer for many years. As a result, a new impurity analysis method at an arbitrary position in the depth direction at an arbitrary position on the surface of the silicon wafer. A silicon wafer is wet-chemically etched using a noble metal such as silver or platinum as a catalyst to make a fine cylindrical hole vertically in the silicon wafer, and at any local location on the silicon wafer. It is characterized by impurity analysis at depth.

  In the impurity analysis method in the depth direction of a single silicon wafer, a liquid mixture containing hydrogen peroxide, hydrofluoric acid, a noble metal-containing aqueous solution, etc. is dropped or immersed on the surface of a cleaned silicon wafer only at an arbitrary measurement location. A pretreatment process comprising a wet chemical etching / dissolution process for precipitating a noble metal in the pores, and a solution recovery process for sucking and collecting from the pores while adding hydrofluoric acid to the solution; It is characterized in that the liquid is fixed and analyzed by inductively coupled plasma mass spectrometry or ICP mass spectrometry.

  In the silicon wafer pretreatment step, the wet chemical etching / dissolution step includes adding a noble metal salt such as silver nitrate, chloroplatinic acid, palladium nitrate, and chloroauric acid to hydrogen peroxide and hydrofluoric acid, and the dissolution. A pre-treatment step consisting of a solution recovery step of sucking and collecting from the pores while adding hydrofluoric acid to the solution, and measuring the recovered solution by inductively coupled plasma mass spectrometry or ICP mass spectrometry It is characterized by.

  In the silicon wafer pretreatment step, the etching solution in the wet chemical etching / dissolution step is hydrogen particles, hydrofluoric acid, silver particles, platinum particles, palladium particles, gold particles having a particle diameter of 100 to 0.1 microns. A pretreatment step comprising adding a noble metal particle-containing solution and a solution recovery step of sucking and recovering from the pores while adding hydrofluoric acid to the solution, and inductively coupled plasma with a constant volume of the recovered solution Analysis is performed by mass spectrometry or ICP mass spectrometry.

  In the silicon wafer pretreatment step, in the wet chemical etching / dissolution step, after masking and concealing other than the dissolution portion, the dissolution portion is treated, and the recovered solution is made constant and inductively coupled plasma is obtained. Analysis is performed by mass spectrometry or ICP mass spectrometry.

  Before adding hydrofluoric acid to the solution and sucking and recovering it from the pores, after dissolving the fine columnar silicon in the pores with a mixture of hydrofluoric acid and nitric acid, add hydrofluoric acid. A pretreatment process comprising a lysate recovery process for suction and recovery, and a volume of the recovered lysate is analyzed and analyzed by inductively coupled plasma mass spectrometry or ICP mass spectrometry.

  The pre-treatment process of the present invention can reduce the cost because the hole forming method, which has been the mainstream of the conventional dry etching method, can be processed by wet chemical etching, and is perpendicular to the silicon wafer that could not be obtained by the conventional dry etching method. The micromachining technology that does not increase the hole diameter is also applied and developed to the microhole machining technology for light metals such as aluminum other than silicon wafers.

In the present invention, noble metal fine particles are densely deposited on a part of a silicon surface, and pores are formed by a wet chemical etching method using the same as a catalyst. The relationship between the etching time at that time and the depth of the hole formed by the etching is obtained, and the correlation is obtained so that the depth of the hole at an arbitrary position on the surface of the silicon wafer can be measured by the etching time.
The types of silicon wafers used are:
P-Type Si (100) wafer (B-doped, resistivity 7-13 Ωcm, thickness 625 mm μm): Abbreviation P-Type
S-Type Si (100) wafer (P-doped, resistivity 8-12 Ωcm, thickness 625 mm μm): abbreviation S-Type
The above two types of silicon wafers were used.

The two types of silicon wafers are cut out to about 10 × 10 mm ^{2 □} , and the entire surface is attached with masking tape. The surface is shown in FIG. As shown in Fig. 5, a 5mmφ (diameter) hole is made in the masking tape and pasted. This hole portion was exposed, and this portion was subjected to wet chemical etching by a dipping method. As a work procedure,
(1) Silicon wafer sample cleaning process:
-Immerse in hydrogen peroxide solution (30%) / concentrated sulfuric acid (96%) = 1/4 (volume ratio) for 10 minutes.
・ Immerse in ultrapure water (specific resistance value: 15 MΩ · cm or more) for 10 minutes.
・ Immerse in 1% hydrofluoric acid for 1 minute.
・ Immerse in ultrapure water for 10 minutes.
(2) Silver particle deposition process on the exposed part (electroless plating process):
-Immerse in an aqueous solution containing 4.6M hydrofluoric acid and 0.01M silver nitrate for 3 minutes.
・ Immerse in ultrapure water for 10 minutes.
(3) Melting process (etching process) of the exposed part:
・ Immerse in an aqueous solution containing 5.3M hydrofluoric acid and 0.18M hydrogen peroxide.
-Immersion time shall be 5 minutes, 10 minutes, 20 minutes, 60 minutes, 120 minutes, 240 minutes, 360 minutes.
(4) Cleaning / drying process:
・ Immerse in ultrapure water for 10 seconds.
・ Immerse in ethanol for 3 minutes.
・ Immerse in pentane for 3 minutes and take it as a sample for inspection.

  Here, (2) Silver particle deposition process (electroless plating process) on the exposed portion: (4) Cleaning and drying process of the processed sample, and silver particle deposition using a scanning electron microscope The condition was observed. FIG. 2 is a photograph of the Si surface on which silver is deposited (a) p-type and (b) n-type. As a result, it was found that silver was deposited more densely in P-Type than in N-Type.

Next, the sample prepared in the above procedure was broken and the cross section was observed with a scanning electron microscope. As typical examples, photographs of holes formed by etching of FIG. 3 P-Type and FIG. 4 N-Type are shown as cross-sectional photographs of etching times of 20 minutes and 240 minutes. In any case, as shown in FIG. 2, it is shown that the deposited silver particles eroded and etched the silicon wafer with time to form pores as columnar holes. The relationship between the etching time and the etching depth is shown in Table 1 and FIG.
From these results, it was found that the etching time and the etching depth are substantially proportional.

Next, P-Type and N-Type 300 mmφ are prepared, and a Teflon masking tape is applied to the entire back surface. A hole of 5 mmφ (diameter) is pasted on the center (0 mmφ), 120 mmφ circumference, and 270 mmφ circumference of the Teflon masking tape stretched on the surface. This hole portion was exposed, and this portion was subjected to wet chemical etching by a dipping method.
As a work procedure,
(1) Silicon wafer sample cleaning process:
-Immerse in hydrogen peroxide solution (30%) / concentrated sulfuric acid (96%) = 1/4 (volume ratio) for 10 minutes.
・ Immerse in ultrapure water for 10 minutes.
・ Immerse in 1% hydrofluoric acid for 1 minute.
・ Immerse in ultrapure water for 10 minutes.
(2) Silver particle deposition process on the exposed part (electroless plating process):
-Immerse in an aqueous solution containing 4.6M hydrofluoric acid and 0.01M silver nitrate for 3 minutes.
・ Immerse in ultrapure water for 10 minutes.
(3) Melting process (etching process) of the exposed part:
・ Immerse in an aqueous solution containing 5.3M hydrofluoric acid and 0.18M hydrogen peroxide.
-Immersion time shall be 5 minutes, 10 minutes, 20 minutes, 60 minutes, 120 minutes, 240 minutes, 360 minutes.
(4) Recovery solution sampling process for analysis:
・ Constant volume of 5.3M hydrofluoric acid and drop it into the pores (5mmφ).
-Collect 10 μL of sample with a micropipette from the pore (5 mmφ).
The collected sample is analyzed for the amount of impurities using an ICP mass spectrometer. Table 2 shows the results of investigating the limit of quantification of the impurity analysis method according to this method, Table 3 shows the measurement number, hole (5 mmφ) position, and etching immersion time. Each measurement result was shown.

  Thus, it became possible to know the increase or decrease in the total amount of impurities at any point in the depth direction at any point on the surface of the silicon wafer.

The concentration of hydrofluoric acid (HF), hydrogen peroxide (H ₂ O ₂ ), silver nitrate (AgNO ₃ ), etc. used in this example is not limited to this value, and ( ₂ ) silver on exposed portions In the particle deposition process (electroless plating process), instead of silver nitrate (AgNO ₃ ), chloroplatinic acid (H ₂ PtCl ₆ ), chloroauric acid (H ₂ AuCl ₆ ), palladium nitrate (Pd (NO ₃ ) ₂ ) Equivalent deposition / etching was confirmed using noble metal salts such as silver particles, platinum particles, gold particles, and palladium particles.

  As a sample preparation method in the impurity analysis method in the depth direction of the silicon wafer, a pretreatment process as a measurement recovery solution by dropping a solution used as an etching solution onto the silicon wafer surface will be described.

Next, 300 mmφ of P-Type and N-Type were prepared and processed according to the following work procedure.
(1) Silicon wafer sample cleaning process:
-Immerse in hydrogen peroxide solution (30%) / concentrated sulfuric acid (96%) = 1/4 (volume ratio) for 10 minutes.
・ Immerse in ultrapure water for 10 minutes.
・ Immerse in 1% hydrofluoric acid for 1 minute.
・ Immerse in ultrapure water for 10 minutes.
・ Naturally dry in the clean booth.
(2) Silver particle deposition process (electroless plating process):
3 μL of the prepared aqueous solution containing 4.6 M hydrofluoric acid and 0.01 M silver nitrate is collected with a micropipette on the cleaned and dried silicon wafer, and dropped onto a predetermined position of the silicon wafer.
(3) Dissolution process (etching process):
3 μL of an aqueous solution containing 5.3 M hydrofluoric acid and 0.18 M hydrogen peroxide is sampled and dropped at the dropping position of the silicon wafer. The dissolution time is 5 minutes, 10 minutes, 20 minutes, 60 minutes, 120 minutes, 240 minutes, and 360 minutes.
(4) Recovery solution sampling process for analysis:
At the dropping position of the silicon wafer, 10 μL of 5.3 M hydrofluoric acid is collected with a micro pipette and dropped. 10 μL of sample is collected from each dropping position with a micropipette.
The collected sample is analyzed for the amount of impurities using an ICP mass spectrometer.
Table 5 shows the measurement number, the dropping position, and the etching immersion time. Each measurement result was shown.

  As in Example 1, the increase / decrease in the total amount of impurities at any point in the depth direction at any point on the surface of the silicon wafer can be known.

  In addition, 10 μL of a mixed solution in which 5.3 M hydrofluoric acid and 5.3 M nitric acid were mixed at a ratio of 1: 3 was sampled with a micropipette at the dropping position of the silicon wafer in the recovery solution sampling step (4). After dropping, the sample is allowed to stand for 3 minutes, and 10 μL of sample is collected from each dropping position with a micropipette. The result of analyzing the amount of impurities for the collected sample using an ICP mass spectrometer was also similar to the analysis result described in Table 6 above.

The concentration of hydrofluoric acid (HF), hydrogen peroxide (H ₂ O ₂ ), silver nitrate (AgNO ₃ ), etc. used in this example is not limited to this value, and ( ₂ ) silver on exposed portions In the particle deposition step (electroless plating step), noble metal salts such as chloroplatinic acid (H ₂ PtCl ₆ ), chloroauric acid (H ₂ AuCl ₆ ), palladium nitrate (PdNO ₃ ) and silver particles instead of silver nitrate, The same deposition / etching was confirmed even when noble metal fine particles such as platinum particles, gold particles, and palladium particles were used.

It is a figure which shows the exposed part which processed the silicon wafer with the masking tape. This is a photo of the silicon wafer surface on which silver particles are deposited. (A) P-Type (b) N-Type This is a photo of the hole formed by etching. (P-Type silicon wafer) (a) and (b) are cross-sectional photographs of an etching time of 20 minutes. (B) is a photograph of a part of (a) enlarged. (C) (d) is a cross-sectional photograph of an etching time of 240 minutes. (D) is a photograph of a part of (c) enlarged. This is a photo of the hole formed by etching. (N-Type silicon wafer) (a) and (b) are cross-sectional photographs of an etching time of 20 minutes. (B) is a photograph of a part of (a) enlarged. (C) (d) is a cross-sectional photograph of an etching time of 240 minutes. (D) is a photograph of a part of (c) enlarged. This figure shows the relationship between etching time and etching depth.

Claims (5)

In the impurity analysis method in the depth direction of one silicon wafer,
Wet chemical etching / dissolution process in which noble metal is deposited on the pores by dripping or immersing a mixture containing hydrogen peroxide, hydrofluoric acid and a noble metal-containing aqueous solution on the surface of a cleaned silicon wafer. When,
A pretreatment step consisting of a solution recovery step of sucking and collecting from the pores while adding hydrofluoric acid to the solution,
A method for analyzing impurities in a depth direction of a silicon wafer, wherein the volume of the recovered lysate is measured by inductively coupled plasma mass spectrometry or ICP mass spectrometry. In the silicon wafer pretreatment step,
Etching solution in wet chemical etching / dissolution process adds noble metal salts such as silver nitrate, chloroplatinic acid, palladium nitrate, chloroauric acid to hydrogen peroxide and hydrofluoric acid,
A pretreatment step consisting of a solution recovery step of sucking and collecting from the pores while adding hydrofluoric acid to the solution,
2. The method for analyzing impurities in a depth direction of a silicon wafer according to claim 1, wherein the volume of the recovered solution is measured by inductively coupled plasma mass spectrometry or ICP mass spectrometry. In the silicon wafer pretreatment step,
Adding a solution containing noble metal particles such as silver particles, platinum particles, palladium particles, and gold particles having a particle diameter of 100 to 0.1 microns to hydrogen peroxide and hydrofluoric acid as an etchant in the wet chemical etching / dissolution process;
A pretreatment step comprising a solution recovery step of sucking and collecting from the pores while adding hydrofluoric acid to the solution,
2. The method for analyzing impurities in a depth direction of a silicon wafer according to claim 1, wherein the volume of the recovered solution is measured by inductively coupled plasma mass spectrometry or ICP mass spectrometry. In the silicon wafer pretreatment step,
In the wet chemical etching / dissolution step, after masking and concealing other than the dissolution location, processing the dissolution location;
The method for analyzing impurities in the depth direction of a silicon wafer according to claim 1, 2 or 3, wherein the volume of the recovered solution is measured by inductively coupled plasma mass spectrometry or ICP mass spectrometry.   Before adding hydrofluoric acid to the solution and sucking and recovering it from the pores, after dissolving the fine columnar silicon in the pores with a mixture of hydrofluoric acid and nitric acid, add hydrofluoric acid. The pretreatment step comprising a lysate recovery step that is suction-recovered while collecting, and the recovered lysate is measured at a constant volume and analyzed by inductively coupled plasma mass spectrometry or ICP mass spectrometry. Impurity analysis method in the depth direction of silicon wafer.