epitaxial silicon wafer

Abstract

To provide a silicon wafer with extremely low resistance by containing boron at an extremely high concentration, which has high gettering ability due to the ability to form high concentration oxygen precipitates, and can suppress epitaxial defects originating from the oxygen precipitates when forming an epitaxial layer.SOLUTION: A silicon wafer contains boron as a dopant, has a resistivity of 1 mΩ cm or more and 10 mΩ cm or less, an oxygen concentration of 14.5×1017 atoms / cm3 or more and 16×1017 atoms / cm3 or less, and a carbon concentration of 2×1016 atoms / cm3 or more and 5×1017 atoms / cm3 or less. The silicon wafer is made of single-crystal silicon that is free of COPs and dislocation clusters.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silicon wafer (so-called p++ silicon wafer) that has an extremely low resistance due to the inclusion of an ultra-high concentration of boron, and an epitaxial silicon wafer using the same. [Background technology]

[0002] Epitaxial silicon wafers, which have an epitaxial layer of single-crystal silicon formed on a silicon wafer, are used as substrates for fabricating various semiconductor devices. Heavy metal impurities in epitaxial silicon wafers can cause semiconductor device performance defects, so they must be minimized. One technique for reducing these heavy metal impurities is gettering. One known gettering technique is intrinsic gettering (IG), which forms oxygen precipitates (BMD: Bulk Micro Defects) within the silicon wafer and traps heavy metal impurities there. Recent trends toward lower device heat treatment temperatures (heat treatments performed during semiconductor device fabrication) have led to a demand for epitaxial silicon wafers with higher BMD density to further enhance gettering capabilities.

[0003] Furthermore, when an integrated circuit of a semiconductor device operates, the floating charge that occurs causes an unintended parasitic transistor to operate, resulting in a phenomenon known as latch-up. When latch-up occurs, the semiconductor device will no longer function properly, and in order to restore it to a normal state, trouble will arise in which the power supply must be turned off. For this reason, as a countermeasure against latch-up, 18 atoms / cm 3An epitaxial silicon wafer (so-called p / p+ epitaxial silicon wafer) is used, in which an epitaxial layer with a higher resistivity than the silicon wafer is formed on the surface of a 300mm diameter p+ silicon wafer with a resistivity of about 20mΩ·cm and doped with about 100mΩ·cm of boron. This p / p+ epitaxial wafer utilizes the gettering effect of silicon wafers (p+ silicon wafers) containing a high concentration of boron, and in addition to preventing the latch-up phenomenon mentioned above, it can also improve device functionality by preventing the expansion of the depletion layer that occurs when voltage is applied around the trench when a trench-structured capacitor is used.

[0004] Regarding p / p+ epitaxial silicon wafers, Patent Document 1 describes that boron is added so that the resistivity is 30 mΩ·cm or less, and the oxygen concentration is 8×10 17 ~16×10 17 atoms / cm 3 and the nitrogen concentration is 1×10 13 ~1×10 15 atoms / cm 3 and the carbon concentration is 5×10 15 ~5×10 17 atoms / cm 3 and an epitaxial silicon wafer having an epitaxial layer formed on the silicon wafer. Patent Document 1 describes that adding carbon increases the BMD density and improves the gettering ability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-252920 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a demand for p / p++ epitaxial silicon wafers, which have a lower resistance by further increasing the boron concentration in the silicon wafer, rather than p / p+ epitaxial wafers. Also, as mentioned above, with the recent trend toward lower temperatures in device heat treatment, epitaxial wafers with a high BMD density are required to provide even greater gettering capability. Specifically, the density of BMDs formed inside the wafer needs to be reduced to 1x10 9 pieces / cm 3 It is required to do more than this.

[0007] It is known that the BMD density can be increased by increasing the oxygen concentration in the silicon wafer. As a result of extensive research by the present inventors, it was found that the oxygen concentration in the silicon wafer can be increased to 14.5 × 10 in p / p++ epitaxial silicon wafers. 17 atoms / cm 3 By setting it to 1×10 or more, 9 pieces / cm 3 It was found that a high BMD density could be obtained.

[0008] However, 1×10 9 pieces / cm 3 In order to ensure a BMD density of 14.5×10 or more, the oxygen concentration in the silicon wafer was set to 14.5×10 17 atoms / cm 3 In the above cases, it was found that during the epitaxial growth process, a large number of stacking faults (SFs) are generated in the epitaxial layer, originating from BMDs present in the surface layer of the silicon wafer, resulting in an increased SF density observed on the surface of the epitaxial layer. In this specification, stacking faults generated in the epitaxial layer are also referred to as "epitaxial defects."

[0009] In view of the above problems, an object of the present invention is to provide a silicon wafer that has an extremely low resistance due to an ultra-high concentration of boron contained therein, that has a high gettering ability due to the ability to form high-concentration oxygen precipitates, and that can suppress epitaxial defects originating from the oxygen precipitates when an epitaxial layer is formed.

[0010] Another object of the present invention is to provide an epitaxial silicon wafer including a silicon wafer that has been made to have an extremely low resistance by containing boron at an ultra-high concentration, wherein high-concentration oxygen precipitates can be formed in the silicon wafer, thereby providing a high gettering capability and suppressing epitaxial defects originating from the oxygen precipitates. [Means for solving the problem]

[0011] In order to solve the above problem, the present inventors have conducted extensive research and have found that in p / p++ epitaxial silicon wafers, the oxygen concentration in the silicon wafer can be reduced to 14.5 × 10 17 atoms / cm 3 The occurrence of epitaxial defects, which becomes significant when the carbon concentration in the silicon wafer is set to a predetermined threshold value or higher, specifically, 2×10 16 atoms / cm 3 It has been found that the occurrence of epitaxial defects, a side effect of high oxygen concentration, can be sufficiently suppressed by setting the carbon concentration in the silicon wafer at a predetermined threshold or higher. Conventionally, adding carbon to silicon wafers has been recognized as increasing BMD density and improving gettering capability. However, according to experiments conducted by the present inventors, it has been found that the occurrence of epitaxial defects, a side effect of high oxygen concentration, can be suppressed in p / p++ epitaxial silicon wafers by setting the carbon concentration in the silicon wafer at a predetermined threshold or higher.

[0012] The gist and configuration of the present invention, which has been completed based on the above findings, is as follows. [1] Contains boron as a dopant, has a resistivity of 1 mΩ cm or more and 10 mΩ cm or less, and an oxygen concentration of 14.5 × 10 17 atoms / cm3 Over 16 x 10 17 atoms / cm 3 The carbon concentration is 2×10 16 atoms / cm 3 5x10 or more 17 atoms / cm 3 A silicon wafer made of single crystal silicon having a crystallinity of 0.1 to 1.0 times or less, and having no COPs and no dislocation clusters.

[0013] [2] An epitaxial silicon wafer comprising the silicon wafer according to [1] above and an epitaxial layer formed on a surface of the silicon wafer.

[0014] [3] The epitaxial silicon wafer according to [2] above, wherein the density of LPDs of 0.09 μm or larger observed on the surface of the epitaxial layer is 5 or less per wafer, and the wafer has a diameter of 300 mm.

[0015] [4] Oxygen Precipitation Evaluation When heat treatment is performed, the density of oxygen precipitates formed inside the silicon wafer is 1 × 10 9 pieces / cm 3 The epitaxial silicon wafer according to the above [2] or [3]. [Effects of the Invention]

[0016] The silicon wafer of the present invention has an extremely low resistance due to the ultra-high boron content, and has a high gettering ability due to the ability to form high-concentration oxygen precipitates. Furthermore, when an epitaxial layer is formed, epitaxial defects originating from the oxygen precipitates can be suppressed.

[0017] The epitaxial silicon wafer of the present invention includes a silicon wafer having an extremely low resistivity due to the inclusion of an ultra-high concentration of boron, and has a high gettering ability due to the ability to form high-concentration oxygen precipitates in the silicon wafer, and epitaxial defects originating from the oxygen precipitates are suppressed. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view of a silicon wafer 100 according to an embodiment of the present invention. [Figure 2] 1 is a schematic cross-sectional view of an epitaxial silicon wafer 200 according to an embodiment of the present invention. [Figure 3] 1 is a graph showing the relationship between resistivity and BMD density when the oxygen concentration and carbon concentration in a silicon wafer are adjusted. [Figure 4] 1 is a graph showing the relationship between resistivity and the number of SFs when the oxygen concentration and carbon concentration in a silicon wafer are adjusted. [Figure 5] 5 is a graph showing the relationship between the carbon concentration in a silicon wafer and the number of SFs in the experiment shown in FIG. 4. [Figure 6] 1 is a schematic diagram showing the relationship between the ratio V / G of the pulling rate V to the temperature gradient G at the solid-liquid interface and the crystalline region in a single crystal silicon ingot. DETAILED DESCRIPTION OF THE INVENTION

[0019] (silicon wafer) Referring to FIG. 1, a silicon wafer 100 according to an embodiment of the present invention contains boron as a dopant, has a resistivity of 1 mΩ·cm or more and 10 mΩ·cm or less, and an oxygen concentration of 14.5×10 17 atoms / cm 3 Over 16 x 10 17 atoms / cm 3 The carbon concentration is 2×10 16 atoms / cm 3 5x10 or more 17 atoms / cm 3 and is characterized by being made of single crystal silicon that is free of COPs and dislocation clusters.

[0020] The silicon wafer 100 is a so-called p++ silicon wafer that contains boron as a dopant and has an ultra-low resistivity of 1 mΩ·cm or more and 10 mΩ·cm or less. A resistivity of 10 mΩ·cm or less results in a high boron concentration in the silicon wafer, which enhances the boron gettering ability and increases the density of BMDs formed inside the silicon wafer. In this specification, the resistivity of the silicon wafer is a value measured on the backside of the silicon wafer using the four-point probe method.

[0021] The boron concentration of the silicon wafer 100 to achieve the above resistivity range is 8.5×10 18 atoms / cm 3 Over 1.2 x 10 20 atoms / cm 3 The boron concentration is 8.5×10 18 atoms / cm 3 If the boron concentration is 1.2×10 or more, the resistivity can be reduced to 10 mΩ cm or less. 20 atoms / cm 3 If the resistivity is less than 1 mΩ cm, the resistivity can be made 1 mΩ cm or more. In this specification, the boron concentration of a silicon wafer is defined as the value measured by secondary ion mass spectrometry (SIMS) at the center of the thickness and the center of the surface of the silicon wafer after thinning the silicon wafer by polishing.

[0022] The oxygen concentration of silicon wafer 100 is 14.5 x 10 17 atoms / cm 3 Over 16 x 10 17 atoms / cm 3 It is important that the oxygen concentration of the silicon wafer is 14.5 × 10 or less. The oxygen concentration of the silicon wafer has a significant effect on the density of BMDs formed inside the wafer. Specifically, the higher the oxygen concentration, the higher the BMD density. 17 atoms / cm 3By setting the resistivity at 1 mΩ cm or more and 10 mΩ cm or less, the density of BMD formed inside the wafer can be reduced to 1×10 9 pieces / cm 3 However, although the gettering effect increases as the BMD density increases, an excessive increase in the BMD density causes an increase in epitaxial defects (SFs). Therefore, the oxygen concentration of the silicon wafer 100 is set to 16×10 17 atoms / cm 3 The oxygen concentration in a silicon wafer is defined as the value measured by SIMS at the center of the thickness and the center of the surface of the silicon wafer after the silicon wafer is thinned by polishing. Since the surface layer of a silicon wafer contains a large amount of noise, it is difficult to measure the oxygen concentration accurately. Therefore, accurate measurement of the oxygen concentration is possible if the measurement is performed at a depth of 1 μm or more from the wafer surface, excluding the surface layer. In this specification, the measurement value at the center of the thickness of the silicon wafer is used to obtain a more accurate value.

[0023] The carbon concentration of silicon wafer 100 is 2 x 10 16 atoms / cm 3 5x10 or more 17 atoms / cm 3 It is important that the oxygen concentration of silicon wafer 100 is 14.5 × 10 17 atoms / cm 3 By setting the carbon concentration of the silicon wafer 100 to 2×10 or more, it is possible to increase the BMD density, but on the other hand, a problem arises in that a large number of epitaxial defects originating from the BMDs occur when an epitaxial layer is formed. 16 atoms / cm 3 By setting the carbon concentration at or above 2×10, epitaxial defects originating from BMD can be sufficiently suppressed. 16 atoms / cm 3 It is important that the density is at least 3 x 10. 16 atoms / cm 3That's all. The reason why such an effect is obtained is probably because the carbon in the silicon wafer 100 has the effect of alleviating the strain generated around the BMD. However, if the carbon concentration is too high, dislocations will occur during the growth of the single crystal ingot by the CZ method, making it difficult to grow a dislocation-free single crystal ingot. Therefore, the carbon concentration of the silicon wafer 100 is set to 5×10 17 atoms / cm 3 The carbon concentration of a silicon wafer is defined as follows. In this specification, the carbon concentration of a silicon wafer is defined as a value obtained by thinning the silicon wafer by polishing, and measuring the carbon concentration at the center of the thickness and the center of the surface of the silicon wafer by SIMS. Since the surface layer of a silicon wafer contains a lot of noise components, it is difficult to measure the carbon concentration accurately. Therefore, accurate measurement of the carbon concentration is possible if the measurement is made at a depth of 1 μm or more from the wafer surface, excluding the surface layer. In this specification, the measurement value at the center of the silicon wafer thickness is used to obtain a more accurate value.

[0024] Nitrogen is not actively added to the silicon wafer 100. That is, the nitrogen concentration of the silicon wafer 100 is below the detection limit in SIMS measurement. If nitrogen is added to the silicon wafer, the nitrogen acts to emphasize minute distortions caused by the agglomeration of BMDs, which increases epitaxial defects in p++ silicon wafers.

[0025] The silicon wafer 100 is made of single crystal silicon that is free of COPs and dislocation clusters. A detailed description will be given with reference to FIG. 6. A typical method for manufacturing a single crystal silicon ingot is the Czochralski method (CZ method). It is known that single crystal silicon ingots grown by the CZ method develop various grown-in defects that can cause problems in device fabrication processes, depending on the ratio V / G of the pulling rate V to the temperature gradient G at the solid-liquid interface.

[0026] Referring to FIG. 6, under conditions where V / G is large, the single crystal silicon ingot is dominated by a COP generation region 11, which is a crystalline region where COPs (crystal originated particles) are detected. This COP generation region 11 is a region where vacancies are dominant and is also referred to as a V region. That is, COPs are microvoid defects that are aggregates of vacancies. Under conditions where V / G is large, the COP generation region 11 exists throughout the entire radial region of the ingot, but as V / G becomes smaller, it becomes narrower toward the central axis of the ingot.

[0027] Under conditions where V / G is small, the single crystal silicon ingot is dominated by a dislocation cluster region 15, which is a crystalline region where dislocation clusters are detected. This dislocation cluster region 15 is a region where interstitial silicon is dominant and is also called an I region. In other words, dislocation clusters are defects (dislocation loops) formed as agglomerates of excess interstitial silicon.

[0028] Between the V and I regions is a crystalline region where no COPs are detected and no dislocation clusters are present, and which is generally considered to be defect-free. However, in descending order of V / G, this region is classified into an OSF region 12, an oxygen precipitation promotion region (Pv region) 13, and an oxygen precipitation inhibition region (Pi region) 14.

[0029] The OSF region 12 contains nuclei of oxidation-induced stacking faults (OSFs) in the as-grown state, and is a region where the OSF nuclei become apparent when thermal oxidation is performed at a high temperature of 1000° C. Due to the shape of the COP generation region 11, the OSF region 12 located outside of it is distributed in a ring shape on the wafer surface when the ingot is processed into wafers.

[0030] Between the OSF region 12 and the dislocation cluster region 15, no COPs are detected and neither dislocation clusters nor OSFs exist, making this a defect-free region, also referred to as a P (Perfect) region or an N (Neutral) region. However, the P region (N region) can be divided into an oxygen precipitation promotion region 13 (also referred to as a Pv region or an Nv region) with a relatively large number of vacancies, oxygen precipitation nuclei present in the as-grown state, and oxygen precipitation prone to occur when heat treatment is performed, and an oxygen precipitation suppression region 14 (also referred to as a Pi region or an Ni region) with a relatively large number of interstitial silicon, almost no oxygen precipitation nuclei present in the as-grown state, and oxygen precipitation unlikely to occur even when heat treatment is performed.

[0031] Generally, when a single crystal silicon wafer sliced ​​from a single crystal silicon ingot contains a COP generation region 11, the oxide film breakdown voltage characteristics of the single crystal silicon wafer are not good. Also, when a single crystal silicon wafer contains a dislocation cluster region 15, league defects occur in semiconductor device products. Therefore, it is known that a single crystal silicon wafer containing only a P region (N region) is desirable from the viewpoint of oxide film breakdown voltage characteristics and prevention of leakage defects in semiconductor device products.

[0032] Here, when growing a single crystal silicon ingot using the CZ method, as the boron concentration increases, the ring-shaped OSF region 12 shrinks toward the center of the crystal. Therefore, when the ultra-high concentration of boron required to obtain a p++ silicon wafer is added, a single crystal silicon ingot is grown that consists of a crystal region in which the OSF region 12 disappears at the center of the crystal, i.e., a defect-free region (P region). Therefore, the p++ silicon wafer sliced ​​from this single crystal silicon ingot is a single crystal silicon wafer that does not contain COPs and dislocation clusters.

[0033] Here, in this specification, "no COPs are present" means that no COPs are detected by the observation and evaluation described below. Specifically, first, a silicon wafer cut from a single crystal silicon ingot grown by the CZ method is subjected to SC-1 cleaning (i.e., cleaning with a mixture of ammonia water, hydrogen peroxide solution, and ultrapure water in a ratio of 1:1:15). The surface of the silicon wafer after cleaning is observed and evaluated using a KLA-Tencor Surfscan SP-2 surface defect inspection system to identify light point defects (LPDs) estimated to be surface pits. The observation mode is oblique mode (oblique incidence mode), and the surface pits are estimated based on the detection size ratio of the wide / narrow channel. The LPDs thus identified are evaluated for their presence or absence of COPs using an atomic force microscope (AFM). Silicon wafers in which no COPs are observed by this observation and evaluation are defined as "silicon wafers without COPs present."

[0034] In this specification, "no dislocation clusters are present" means that no dislocation clusters are detected by the observation evaluation described below. That is, first, the surface of a silicon wafer cut from a single crystal silicon ingot grown by the CZ method is observed by X-ray topography, and a silicon wafer in which no dislocation defects are observed in the photographed image is defined as a "silicon wafer free of dislocation clusters."

[0035] Note that the addition of ultra-high concentration boron causes the ring-shaped OSF region 12 to shrink toward the crystal center, resulting in a crystal region where the OSF region disappears at the crystal center. In other words, the silicon wafer 100 becomes a wafer without an OSF region. The OSF region can be visualized and evaluated by subjecting the silicon wafer to heat treatment in an oxygen atmosphere at a temperature of 1000 to 1200°C. For example, a silicon wafer can be subjected to an oxidation heat treatment in a dry oxygen atmosphere at 1100°C for 2 hours, followed by selective etching in which the wafer surface is etched by 2 μm using a light etching solution. The presence or absence of an OSF region can be determined by evaluating the wafer surface after the etching process using an atomic force microscope (AFM).

[0036] There are no particular limitations on the thickness and diameter of the silicon wafer 100. The thickness can be within a range of, for example, 720 to 780 μm. The diameter can be within a range of, for example, 200 to 300 mm, with 300 mm being particularly preferred.

[0037] (epitaxial silicon wafer) Referring to FIG. 2, an epitaxial silicon wafer 200 according to one embodiment of the present invention includes the above-described silicon wafer 100 and an epitaxial layer 110 formed on the surface of the silicon wafer 100.

[0038] The epitaxial silicon wafer 200 includes the silicon wafer 100 that has been made extremely low resistive by containing an ultra-high concentration of boron, and has the effect of having a high gettering ability due to the ability to form high-concentration oxygen precipitates in the silicon wafer 100, and also suppressing epitaxial defects originating from the oxygen precipitates.

[0039] The epitaxial layer 110 is a layer made of single-crystal silicon formed by epitaxial growth. The thickness of the epitaxial layer 110 is not particularly limited and may be appropriately set depending on the type of semiconductor device to be fabricated therein, and may be within the range of 2 to 10 μm, for example.

[0040] The resistivity of the epitaxial layer 110 is preferably 1 Ωcm or more and 10 Ωcm or less. As dopant species to be added to the epitaxial layer, boron can be used as a p-type dopant, and phosphorus, arsenic, antimony, etc. can be used as an n-type dopant. In particular, the boron concentration is set to 1.3×10 15 atoms / cm 3 Over 1.5 x 10 16 atoms / cm 3 It is desirable to provide a p / p++ epitaxial silicon wafer having an epitaxial layer formed thereon, which satisfies the following criteria: In this specification, the resistivity of the epitaxial layer is a value measured using a four-point probe method.

[0041] When the epitaxial silicon wafer 200 is subjected to the heat treatment for evaluating oxygen precipitates, the density of the oxygen precipitates (BMD) formed inside the silicon wafer 100 is 1×10 9 pieces / cm 3 Although the upper limit of the BMD density is not particularly limited, in this embodiment it is approximately 1×10 11 pieces / cm 3 The following is the result.

[0042] The BMD density of an epitaxial silicon wafer can be confirmed by growing BMD nuclei through an evaluation heat treatment (oxygen precipitate evaluation heat treatment) that simulates a device process. The "BMD density" in this specification refers to a BMD density per unit volume determined by performing an oxygen precipitate evaluation heat treatment on an epitaxial silicon wafer in an oxygen gas atmosphere at 800°C for 3 hours and then at 1000°C for 16 hours, cleaving the epitaxial silicon wafer in the thickness direction so as to include the in-plane center position, and selectively etching the cleaved cross section to a depth of 2 μm using a Wright Etching solution. The cleaved cross section at the center of the silicon wafer's thickness (three locations in the radial direction: the wafer center, the R / 2 position (R; wafer radius), and 10 mm from the outer periphery) was then observed with an optical microscope, and the BMD density per unit volume was determined from the average etch pit density within a 100 μm × 100 μm square area.

[0043] In the epitaxial silicon wafer 200, the density of LPDs of 0.09 μm or larger observed on the surface of the epitaxial layer 110 is preferably 5 or less (0 or more) per wafer. In this specification, "LPD density" refers to the number of light point defects (LPDs) of 0.09 μm or larger detected when the epitaxial layer surface (excluding a circular region within 3 mm radially from the outermost periphery) is observed in DCN mode (Dark Field Composite Normal mode) using a surface defect inspection device, Surfscan SP-1, manufactured by KLA-Tencor Corporation. The detected LPD sites of 0.09 μm or larger were observed and evaluated using an atomic force microscope (AFM) to determine whether the LPDs were stacking faults (SFs).

[0044] The diameter of the epitaxial silicon wafer 200 is the same as that of the silicon wafer 100, and is not particularly limited, but can be, for example, within the range of 200 to 300 mm, and is particularly preferably 300 mm.

[0045] (Silicon wafer manufacturing method) A suitable method for manufacturing a silicon wafer 100 according to one embodiment of the present invention includes the steps of: preparing a single crystal silicon ingot by the Czochralski method (CZ method); slicing a plurality of wafers from the body of the single crystal silicon ingot perpendicular to the pulling direction; and subjecting the sliced ​​wafers to various processes such as grinding, polishing, and cleaning to obtain silicon wafers.

[0046] The oxygen concentration of a single crystal silicon ingot is 14.5 x 10 17 atoms / cm 3 Over 16 x 10 17 atoms / cm 3The oxygen concentration in the crystal can be controlled by various conditions such as the rotation speed of the crucible, the center position of the applied magnetic field, the magnetic field strength, the Ar gas flow rate, the furnace pressure, and the heater power.

[0047] Boron is added as a dopant to the single crystal silicon ingot so that the resistivity is in the range of 1 mΩ·cm to 10 mΩ·cm. To achieve the above resistivity range, the boron concentration added to the single crystal silicon ingot is 8.5×10 18 atoms / cm 3 Over 1.2 x 10 20 atoms / cm 3 In addition, since boron segregation occurs during the process of pulling up the single crystal silicon ingot, the boron concentration increases and the resistivity decreases from the top side of the straight body part of the single crystal silicon ingot to the tail side. Therefore, the resistivity at the top of the straight body part is set to 10 mΩ·cm or less, that is, the boron concentration at the top of the straight body part is set to 8.5×10 18 atoms / cm 3 It is preferable to add boron so that the above ranges of resistivity and boron concentration are satisfied throughout the entire body portion.

[0048] The carbon concentration in the single crystal silicon ingot is 2×10 16 atoms / cm 3 5x10 or more 17 atoms / cm 3 Carbon is added so that the carbon concentration becomes as follows. Note that, since carbon segregation occurs during the process of pulling the single crystal silicon ingot, the carbon concentration increases from the top side of the straight body part of the single crystal silicon ingot toward the tail side. Therefore, if the carbon concentration at the top of the straight body part is 2×10 16 atoms / cm 3 It is preferable to add carbon so that the carbon concentration satisfies the above range throughout the entire straight body portion.

[0049] Nitrogen is not actively added to the single crystal silicon ingot.

[0050] Although there are no particular limitations on the pulling speed of the single crystal silicon ingot, it is preferable to set it appropriately so as to grow a single crystal silicon ingot consisting of a crystal region in which the OSF region 12 shown in Fig. 6 has disappeared at the center of the crystal, i.e., a defect-free region (P region). As a result, p++ silicon wafers sliced ​​from the grown single crystal silicon ingot are single crystal silicon wafers that are free of COPs and dislocation clusters.

[0051] (Method for manufacturing epitaxial silicon wafers) A suitable method for manufacturing an epitaxial silicon wafer 200 according to one embodiment of the present invention includes a step of forming an epitaxial layer 110 on the surface of the silicon wafer 100. The epitaxial layer 110 formed in this step may be a silicon epitaxial layer, which can be formed under typical conditions. For example, hydrogen is used as a carrier gas and a source gas such as dichlorosilane or trichlorosilane is introduced into a chamber. While the growth temperature varies depending on the source gas used, epitaxial growth can be performed on the silicon wafer 100 by a CVD method at a temperature generally in the range of 1000 to 1200°C. The thickness of the epitaxial layer 110 can be, for example, within the range of 2 to 10 μm. [Example]

[0052] A single crystal silicon ingot was grown by the Czochralski method (CZ method). At that time, the target resistivity at the top of the straight body was set to 10 mΩ cm, that is, the boron concentration at the top of the straight body was set to 8.5 × 10 18 atoms / cm 3 Boron was added so that the resistivity of the single crystal ingot in the rear half of the straight body was 5.5 mΩcm due to boron segregation. The oxygen concentration in the single crystal silicon ingot was 11.0 to 12.5 × 10 17 atoms / cm 3(Comparative Example 1), 12.5 to 14.0 × 10 17 atoms / cm 3 (Comparative Example 2), 14.5 to 16.0 × 10 17 atoms / cm 3 Growth conditions such as the crucible rotation speed and furnace pressure were controlled to fall within the ranges of Comparative Example 3, Example 1, and Example 2. The pulling rate was set so as to grow a single crystal silicon ingot consisting of a defect-free region (P region).

[0053] In Comparative Examples 1 to 3, carbon was not intentionally added to the single crystal silicon ingot. In Examples 1 and 2, the carbon concentration at the top of the straight body portion was 1.00×10 16 atoms / cm 3 (Example 1) and 2.00 × 10 16 atoms / cm 3 Carbon was added to the single crystal silicon ingot so that the resistivity became 5.5 mΩcm in the straight body portion due to carbon segregation. 16 atoms / cm 3 (Example 1) and 24.50 × 10 16 atoms / cm 3 (Example 2).

[0054] In Comparative Examples 1 to 3 and Examples 1 and 2, nitrogen was not intentionally added to the single crystal silicon ingot.

[0055] A plurality of wafers were cut from the single crystal silicon ingots grown in Comparative Examples 1 to 3 and Examples 1 and 2, and were subjected to various processes such as grinding, polishing, and cleaning to produce silicon wafers with a diameter of 300 mm. The obtained silicon wafers were single crystal silicon wafers that were free of COPs and dislocation clusters.

[0056] An epitaxial layer made of single crystal silicon was formed on the surface of silicon wafers obtained from parts of the straight body at various distances from the top of the body, and epitaxial silicon wafers with a diameter of 300 mm were fabricated. 16 atoms / cm 3 It is a p-type silicon epitaxial layer containing 1.0 Ω·cm of boron, with a thickness of 3 μm.

[0057] The resistivity, boron concentration, oxygen concentration, and carbon concentration of the produced epitaxial silicon wafer were measured by the methods described above.

[0058] [BMD density evaluation] For Comparative Examples 1 to 3 and Example 1, the BMD density was measured by the method described above, and the results are shown in Figure 3. In all examples, a tendency was observed in which the resistivity decreased as the distance from the top increased, and the BMD density increased as the resistivity decreased, due to boron segregation. Furthermore, with reference to Comparative Examples 1 to 3, it was confirmed that the BMD density also depends greatly on the oxygen concentration in the silicon wafer, and that the higher the oxygen concentration, the higher the BMD density when compared at the same resistivity. In particular, when the oxygen concentration of the silicon wafer was increased to 14.5 x 10 17 atoms / cm 3 By setting the resistivity at 1 mΩ cm or more and 10 mΩ cm or less, the density of BMD formed inside the wafer can be reduced to 1×10 9 pieces / cm 3 Furthermore, with reference to Comparative Example 3 and Example 1, it was confirmed that in p++ silicon wafers in which the oxygen concentration was set high, the BMD density did not increase significantly even when carbon was added.

[0059] [SF number evaluation] For Comparative Examples 1 to 3 and Examples 1 and 2, the number of LPDs (number of SFs) was measured by the method already described, and the results are shown in Figures 4 and 5. With reference to Comparative Examples 1 to 3, when the oxygen concentration was 11.0 to 12.5 × 10 17 atoms / cm 3Comparative Example 1, and the oxygen concentration is 12.5 to 14.0 × 10 17 atoms / cm 3 In Comparative Example 2, the number of SFs was 5 or less, and the problem of epitaxial defects was not apparent. However, the oxygen concentration was 14.5 to 16.0 × 10 17 atoms / cm 3 In Comparative Example 3, the number of SFs was 65 to 114, revealing the problem of epitaxial defects. This is thought to be because a large number of stacking faults (SFs) were generated in the epitaxial layer during the epitaxial growth process, originating from BMDs present in the surface layer of the silicon wafer.

[0060] Furthermore, referring to Comparative Example 3, Example 1, and Example 2, in the p++ silicon wafer, the carbon concentration was 2×10 16 atoms / cm 3 It was found that the SF density observed on the epitaxial layer surface can be significantly reduced by setting the above values. Specifically, in Example 1, at a point where the resistivity was 8.5 mΩ cm, the number of SFs was 73 / wafer, and no SF reduction effect was observed. The carbon concentration at this time was 1.99 × 10 16 atoms / cm 3 At the point of 8 mΩ cm, the number of SFs was 33 / wafer, and an SF reduction effect was observed. The carbon concentration at this point was 2.58 × 10 16 atoms / cm 3 In Example 2, the number of SFs was 5 or less per wafer at the 10 mΩ cm point, and the number of SFs was 5 or less per wafer at each measurement point up to the 5.5 mΩ cm point. The carbon concentration at the 5.5 mΩ cm point was 24.50 × 10 16 atoms / cm 3 It was. [Industrial Applicability]

[0061] An epitaxial silicon wafer using the silicon wafer of the present invention, and the epitaxial silicon wafer of the present invention have a high gettering ability due to a high concentration of oxygen precipitates and a high-quality epitaxial layer in which epitaxial defects originating from oxygen precipitates are suppressed, and are useful as substrates for producing semiconductor devices. [Explanation of symbols]

[0062] 100 silicon wafers 110 epitaxial layer 200 epitaxial silicon wafers 11 COP generation region (V region) 12 OSF area 13 Oxygen precipitation promotion region (Pv region) 14 Oxygen precipitation suppression region (Pi region) 15. Dislocation cluster region (I region)

Claims

1. containing boron as a dopant and having a resistivity of 1 mΩ cm or more and 10 mΩ cm or less; Oxygen concentration is 14.5 x 10 １７ atoms / cm ３ 16 x 10 or more １７ atoms / cm ３ is as follows: Carbon concentration is 3 x 10 １６ atoms / cm ３ 5x10 or more １７ atoms / cm ３ is as follows: a silicon wafer made of single crystal silicon that is free of COPs and dislocation clusters; an epitaxial layer formed on the surface of the silicon wafer; and wherein the density of LPDs of 0.09 μm or larger in size observed on the surface of the epitaxial layer is 5 or less per wafer.

2. An epitaxial silicon wafer as described in claim 1, having a diameter of 300 mm.

3. When the silicon wafer is subjected to an oxygen precipitate evaluation heat treatment, the density of oxygen precipitates formed inside the silicon wafer is 1×10 ９ pieces / cm ３ 3. The epitaxial silicon wafer according to claim 1 or 2.

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