Silicon wafer and manufacturing method thereof

Abstract

The present invention addresses the problem of providing a silicon wafer in which oxygen evolution in a surface layer portion can be reduced as much as possible and thermally stable oxygen evolution nuclei that are not subjected to heat treatment by a customer can be generated at a high density in a main body portion. The solution is that the density of oxygen deposits (BMD) generated in a surface layer portion (53) up to a depth of 30 [mu] m from a surface (50a) is 1 * 107 to 1 * 108 cm <-3 > after a silicon wafer (50) is subjected to a heat treatment at 780 DEG C for 3 hours and then subjected to a first evaluation heat treatment of a visual heat treatment at 950 to 1000 DEG C for 16 hours, and the density of BMD generated in a main body portion (54) deeper than the surface layer portion (53) by the first evaluation heat treatment is 1 * 109 to 7 * 109 cm <-3 >. When a first bulk density (d1) is the average density of BMD generated in the main body section (54) by the first evaluation heat treatment, and a second bulk density (d2) is the average density of BMD generated in the main body section (54) by a second evaluation heat treatment in which visual heat treatment is performed after heat treatment at 1150 DEG C for 2 minutes, d2 / d1 is 0.74-1.02.

Description

Technical Field

[0001] The present invention relates to a silicon wafer and a method for producing the same, and more particularly to a method for heat treating a silicon wafer produced by slicing a single crystal silicon ingot produced by a CZ method. The present invention also relates to a silicon wafer heat treated by such a heat treatment method. Background Art

[0002] Most silicon wafers used as substrate materials for semiconductor devices are manufactured using single crystal silicon ingots manufactured using the CZ method. The CZ method is a method of growing a single crystal larger than the seed crystal by slowly pulling up the seed crystal in contact with the silicon melt in a quartz crucible while rotating it relatively. The CZ method can improve the manufacturing yield of large-diameter single crystal silicon.

[0003] It is known that when single crystal silicon is grown by the CZ method, oxygen dissolved from the surface of the quartz crucible is incorporated into the silicon melt. The oxygen in the silicon melt becomes supersaturated during the cooling process of the single crystal silicon, and oxygen condenses to form oxygen precipitation nuclei.

[0004] The density of oxygen precipitates in a block silicon wafer just cut out from a single crystal silicon ingot is very low, and low-density oxygen precipitates have little effect on the characteristics of semiconductor devices. However, various heat treatments are repeatedly applied in the process of manufacturing semiconductor devices, which sometimes causes high-density oxygen precipitates. The oxygen precipitates present in the surface portion of the silicon wafer, which is the active region of the device, become the cause of the deterioration of device characteristics such as bonding cracks. On the other hand, the oxygen precipitates present in the main body outside the active region of the device effectively function as gettering sites that capture metal impurities that deteriorate device characteristics. Therefore, it is desirable to make the oxygen precipitates in the surface portion of the silicon wafer low-density and the oxygen precipitates in the region deeper than the surface portion (inside the wafer) high-density.

[0005] In order to obtain such a silicon wafer, for example, Patent Document 1 describes a method for manufacturing a silicon wafer, which includes: a first heat treatment step, heating the silicon wafer at 1100-1200°C for 1 to 30 seconds in a furnace in a non-oxidizing atmosphere; a second heat treatment step, heating the silicon wafer at 800-975°C for 2 to 10 minutes after the first heat treatment step; and a third heat treatment step, heating the silicon wafer at 1000-1200°C for 1 to 10 minutes after the second heat treatment step.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2021-168382 Summary of the invention

[0009] Problems to be solved by the invention

[0010] In recent years, the BCD (Bipolar-CMOS-DMOS) process, which forms bipolar, CMOS and DMOS on the same substrate, has attracted attention as a manufacturing process for power management semiconductor devices. The BCD process is accompanied by high-temperature heat treatment, so slip dislocations are easily generated on the wafer. In order to improve not only the impurity absorption ability of the silicon wafer but also the slip resistance, it is necessary to increase the density of oxygen precipitates. Furthermore, a deep DZ (Denuded Zone) of about tens of μm is required in the BCD process, so there is also a case where an epitaxial film is pre-formed on the surface of the silicon wafer. However, in the epitaxial film formation process, in addition to the slip problem accompanied by high-temperature heat treatment, the oxygen precipitates are easy to disappear, and the thermal stability of the oxygen precipitates is also questioned. As such, for silicon wafers used in the BCD process, the high density and stabilization of oxygen precipitates are one of the important issues.

[0011] However, in the method for manufacturing a silicon wafer described in Patent Document 1, for example, using 8×10 17 atoms / cm 3 In the case of a bulk silicon wafer with a low oxygen concentration of about 1000 μg / cm2 (ASTM F-121, 1979, the same applies to oxygen concentration below), the oxygen precipitation nuclei cannot be fully grown in the first to third heat treatment steps, and the oxygen precipitation nuclei disappear in the subsequent heat treatment of the customer, making it difficult to increase the oxygen precipitate density in the main body. On the other hand, when using 11×10 17 atoms / cm 3 In the case of a bulk silicon wafer having a high oxygen concentration of about 200 Å, oxygen precipitates are easily generated not only in the main body of the wafer but also in the surface layer, and therefore there is a possibility that it may not be compatible with future BCD devices.

[0012] Therefore, an object of the present invention is to provide a silicon wafer and a method for manufacturing the same, which can minimize oxygen precipitation in the surface layer and generate thermally stable oxygen precipitation nuclei in the main body at a high density regardless of the customer's heat treatment.

[0013] Solutions to Solve Problems

[0014] In order to solve the above-mentioned problems, the silicon wafer of the present invention is characterized in that it has: a surface layer portion from the surface to a depth of 30 μm, and a main body portion deeper than the surface layer portion, and the density of the oxygen precipitates generated in the surface layer portion by the first evaluation heat treatment is 1.0×10 7 ~1.0×10 8 cm -3 The density of the oxygen precipitates generated in the main body by the first evaluation heat treatment is 1.0×10 9 ~7.0×10 9 cm -3, when the average density of oxygen precipitates produced in the main body by the first evaluation heat treatment is set to the first main body density d1, and the average density of oxygen precipitates produced in the main body by the second evaluation heat treatment is set to the second main body density d2, the ratio of the second main body density d2 to the first main body density d1 (d2 / d1) is in the range of 0.74 to 1.02, the first evaluation heat treatment is a two-stage heat treatment of a visualized heat treatment after a heat treatment at 780°C for 3 hours, the second evaluation heat treatment is a two-stage heat treatment of a visualized heat treatment after a heat treatment at 1150°C for 2 minutes, and the visualized heat treatment is a heat treatment at 950 to 1000°C for 16 hours.

[0015] According to the present invention, it is possible to provide an evaluation method for the oxygen precipitate density of the surface layer after heat treatment to be as low as 1.0×10 8 cm -3 The silicon wafer has a thermally stable structure and a density of oxygen precipitates in the main body of the silicon wafer being 10 times higher than that in the surface layer. Therefore, the yield and reliability of semiconductor devices such as BCD manufactured using the silicon wafer can be improved.

[0016] In the present invention, it is preferred that the maximum value d of the density of the oxygen precipitates generated in the main body by the first evaluation heat treatment is max Relative to the minimum value d min The ratio (d max / d min ) and the maximum value d of the density of the oxygen precipitates generated in the main body by the second evaluation heat treatment max Relative to the minimum value d min The ratio (d max / d min ) are all less than 2. In this case, it is further preferred that the maximum value d of the density of the oxygen precipitates generated in the main body by the first evaluation heat treatment is max Relative to the minimum value d min The ratio (d max / d min ) is less than 1.30. In addition, it is further preferred that the maximum value d of the density of the oxygen precipitates generated in the main body by the second evaluation heat treatment is max Relative to the minimum value d min The ratio (d max / d min ) is 1.32 or less. Thus, thermally stable oxygen precipitates that are not affected by the heat treatment of the customer can be generated in the main body at a high density and uniformly.

[0017] In the present invention, it is preferred that the average density of the oxygen precipitates generated in the surface layer portion by the first evaluation heat treatment and the average density of the oxygen precipitates generated in the surface layer portion by the second evaluation heat treatment are both 2.1×10 7 cm -3 As a result, it is possible to provide a silicon wafer in which the density of oxygen precipitates in the surface layer portion is sufficiently reduced regardless of the heat treatment performed by the customer.

[0018] In addition, the silicon wafer of the present invention is characterized in that it comprises: a silicon substrate, and an epitaxial silicon film formed on a surface of the silicon substrate, wherein the silicon substrate has a surface layer portion from the surface to a depth of 30 μm, and a main body portion deeper than the surface layer portion, and the density of oxygen precipitates generated in the surface layer portion by the first evaluation heat treatment is 1.0×10 7 ~1.0×10 8 cm -3 The density of the oxygen precipitates generated in the main body by the first evaluation heat treatment is 1.0×10 9 ~7.0×10 9 cm -3 , when the average density of oxygen precipitates produced in the main body by the first evaluation heat treatment is set as the first main body density, and the average density of oxygen precipitates produced in the main body by the second evaluation heat treatment is set as the second main body density, the ratio of the second main body density to the first main body density is in the range of 0.98 to 1.02, the first evaluation heat treatment is a two-stage heat treatment of heat treatment at 780°C for 3 hours and then a visualized heat treatment is performed, the second evaluation heat treatment is the visualized heat treatment, and the visualized heat treatment is a heat treatment at 950 to 1000°C for 16 hours.

[0019] According to the present invention, it is possible to provide an evaluation method for the oxygen precipitate density of the surface layer after heat treatment to be as low as 1.0×10 8 cm -3 The present invention provides a thermally stable epitaxial silicon wafer having a density of oxygen precipitates in the main body at least 10 times higher than that in the surface layer. Therefore, the yield and reliability of semiconductor devices such as BCD manufactured using the epitaxial silicon wafer can be improved.

[0020] In the present invention, it is preferred that the maximum value d of the density of the oxygen precipitates generated in the main body by the first evaluation heat treatment is max Relative to the minimum value d min The ratio (d max / d min ) and the maximum value d of the density of the oxygen precipitates generated in the main body by the second evaluation heat treatment max Relative to the minimum value d min The ratio (d max / dmin ) are all less than 2. In this case, it is further preferred that the maximum value d of the density of the oxygen precipitates generated in the main body by the first evaluation heat treatment is max Relative to the minimum value d min The ratio (d max / d min ) is 1.29 or less. In addition, it is further preferred that the maximum value d of the density of the oxygen precipitates generated in the main body by the second evaluation heat treatment is max Relative to the minimum value d min The ratio (d max / d min ) is 1.35 or less. Thus, thermally stable oxygen precipitates that are not affected by the heat treatment of the customer can be generated in the main body at a high density and uniformly.

[0021] Furthermore, the method for manufacturing a silicon wafer of the present invention is characterized in that it comprises: a first heat treatment step of heating the silicon wafer to a temperature of 7×10 17 ~10×10 17 atoms / cm 3 (ASTM F-121, 1979); a second heat treatment step, after the aforementioned first heat treatment step, heating the aforementioned silicon wafer at a second temperature lower than the aforementioned first temperature; and a third heat treatment step, after the aforementioned second heat treatment step, heating the aforementioned silicon wafer at a third temperature higher than the aforementioned second temperature, the aforementioned first temperature is 1210-1250°C, the holding time of the aforementioned first temperature is 10-60 seconds, the aforementioned second temperature is 800-975°C, the holding time of the aforementioned second temperature is 2-10 minutes, and the aforementioned third temperature is 1150-1250°C, and the holding time of the aforementioned third temperature is 5-15 minutes.

[0022] According to the present invention, a first heat treatment step of a relatively short time and high temperature, a second heat treatment step of a relatively long time and low temperature, and then a third heat treatment step of a higher temperature than the second heat treatment step, thermally stable oxygen precipitation nuclei are generated at a high density inside the silicon wafer, and on the other hand, the oxygen precipitation nuclei can be reduced in the surface layer of the wafer. Therefore, a silicon wafer having a high density of thermally stable oxygen precipitation nuclei in the main body that is not affected by the heat treatment of the customer and a low density of oxygen precipitation nuclei in the device formation region can be manufactured.

[0023] Preferably, the first heat treatment step is performed in a non-oxidizing atmosphere containing ammonia or nitrogen, and the second heat treatment step and the third heat treatment step are performed in a non-oxidizing atmosphere not containing ammonia or nitrogen. By performing the first heat treatment step in a non-oxidizing atmosphere containing ammonia or nitrogen, a nitride film is formed on the surface of the wafer, and vacancies can be introduced into the interior of the wafer through the nitride film, thereby increasing the density of oxygen precipitation nuclei inside the wafer.

[0024] In the present invention, the heating rate to the first temperature and the heating rate from the second temperature to the third temperature are preferably 10 to 50°C / second. In addition, the cooling rate from the first temperature to the second temperature is preferably 20 to 120°C / second. Thus, thermally stable oxygen precipitation nuclei can be generated at a high density.

[0025] In the present invention, the silicon wafer before the heat treatment in the first heat treatment step is preferably a silicon wafer cut from a defect-free region of a single crystal silicon ingot without agglomerates of intercrystalline silicon type point defects and agglomerates of vacancy type point defects. Thus, a silicon wafer having a low density of oxygen precipitation nuclei in the surface layer and a high density of oxygen precipitation nuclei in the main body and being thermally stable can be manufactured. Therefore, the yield and reliability of semiconductor devices such as BCD manufactured using the silicon wafer can be improved.

[0026] Effects of the Invention

[0027] According to the present invention, it is possible to provide a silicon wafer and a method for manufacturing the same, which can minimize oxygen precipitation in the surface layer and generate thermally stable oxygen precipitation nuclei in the main body at a high density regardless of the customer's heat treatment.

[0028] Brief description of the attached figure

[0029] Figure 1 The flowchart schematically shows a method for manufacturing a silicon single crystal according to an embodiment of the present invention.

[0030] Figure 2 A flow chart illustrating the process of heat treating a silicon wafer.

[0031] Figure 3 This is a graph showing temperature changes during heat treatment, where the horizontal axis represents time and the vertical axis represents heating temperature.

[0032] Figure 4 (A) to (I) are schematic diagrams showing changes in the silicon wafer during the first to third thermal treatments.

[0033] Figure 5 A schematic diagram illustrating a method for determining the density of oxygen precipitates in a silicon wafer using light scattering tomography.

[0034] Figure 6 A schematic diagram of the evaluation steps used to determine the stability and uniformity of manufactured silicon wafers. DETAILED DESCRIPTION

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[0036] Figure 1The flowchart schematically shows a method for manufacturing a silicon single crystal according to an embodiment of the present invention.

[0037] like Figure 1 As shown, the method for manufacturing a silicon wafer of the present embodiment includes a step S11 of manufacturing a single crystal silicon ingot by a CZ method, a step S12 of processing the single crystal silicon ingot to produce a silicon wafer, and a step S13 of heat treating the silicon wafer.

[0038] In step S11 of manufacturing a single crystal silicon ingot, polycrystalline silicon filled in a quartz crucible is heated in a CZ furnace to generate silicon melt. Then, a seed crystal is brought into contact with the silicon melt, and the seed crystal and the quartz crucible are rotated while the seed crystal is slowly pulled up, thereby growing a large single crystal at the lower end of the seed crystal.

[0039] Next, in the step S12 of making silicon wafers, the single crystal silicon ingot is sliced ​​by a wire saw or the like, and then ground, etched, mirror-polished, cleaned, etc., to complete a bulk silicon wafer (polished wafer) as an intermediate product. The oxygen concentration of the CZ silicon wafer made in this way is preferably 7×10 17 ~10×10 17 atoms / cm 3 (ASTM F-121,1979). 17 atoms / cm 3 In the case of , stable oxygen precipitates cannot be generated at a high density in the main body. 17 atoms / cm 3 In the case of , the oxygen precipitates in the surface layer cannot be sufficiently reduced.

[0040] Here, it is desired that the silicon wafer is a so-called COP-free wafer that does not substantially contain crystal native particle (COP) defects. That is, the silicon wafer is preferably a silicon wafer cut from a defect-free region of a single crystal silicon ingot in which there are no agglomerates of intercrystalline silicon type point defects and agglomerates of vacancy type point defects. COP (Crystal Originated Particle) is a completely oriented octahedral cavity in crystallography, and its inner wall is usually covered with an oxide film 1 to 4 nm thick. Crystal defects related to vacancies such as COP defects have the possibility of causing problems for semiconductor devices, just like oxygen precipitates in the surface layer. Examples of device problems include reduced gate oxide integrity (GOI) and current leakage in PN junctions. In order to solve these problems, in some device applications, a low-defect crystal growth method can be applied to reduce the number of vacancy defects in the device area close to the surface. If the pulling speed of the crystal and the cooling speed of the crystal are changed, there is a possibility that the vacancy defect level will become lower. As a result, the recombination of vacancies with intercrystalline silicon atoms, the agglomeration of vacancies and the control of oxygen concentration become possible, and surface defects are reduced. In the COP-free wafer, “substantially free of COP” means that the density of COPs formed by aggregates of vacancy type point defects is 1×10 5 cm -3 the following.

[0041] In the step S13 of heat treating the silicon wafer, the wafer is heat treated in a three-stage temperature range in a rapid thermal annealing (RTA) furnace to generate thermally stable oxygen precipitation nuclei at a high density. Here, the expression "thermally stable" means that the wafer has a sufficient density for maintaining the gettering of metal impurities and the strength of the wafer in the state of wafer shipment, and the density is not affected by the subsequent heat treatment of the device by the customer. In addition, "high density" means at least 1×10 9 / cm 3 More than, preferably about 5×10 9 / cm 3 Density above.

[0042] Figure 2 This is a flow chart for explaining step S13 of heat treating the silicon wafer. Figure 3 This is a graph showing temperature changes during heat treatment, where the horizontal axis represents time and the vertical axis represents heating temperature.

[0043] like Figure 2 and Figure 3As shown, the heat treatment method of the silicon wafer of the embodiment of the present invention includes: a first heat treatment step S21, heating the silicon wafer at a first temperature T1 in the RTA furnace; a second heat treatment step S22, heating the silicon wafer at a second temperature T2 lower than the first temperature T1 after the first heat treatment step S21; and a third heat treatment step S23, heating the silicon wafer at a third temperature T3 higher than the second temperature T2 after the second heat treatment step S22. In this embodiment, the first to third heat treatment steps S21 to S23 are preferably implemented continuously in the same RTA furnace. However, it is also possible to perform the first heat treatment step S21 in the RTA furnace, take out the wafer from the RTA furnace, and perform the second heat treatment step S22 and the third heat treatment step S23 in another heat treatment device.

[0044] The first heat treatment step S21 is a rapid heat treatment performed in an RTA furnace in a non-oxidizing atmosphere. The non-oxidizing atmosphere is preferably an inert gas containing ammonia or nitrogen, and the inert gas is preferably argon. In the high-temperature heat treatment in a non-oxidizing atmosphere, a large amount of vacancies can be introduced into the interior of the wafer, thereby increasing the density of oxygen precipitation nuclei inside the wafer. Furthermore, by using argon gas containing ammonia or nitrogen, a nitride film is formed on the surface of the wafer, and vacancies can be introduced into the interior of the wafer through the nitride film, thereby increasing the density of oxygen precipitation nuclei inside the wafer. In addition, there are tiny oxygen precipitation nuclei generated during crystal growth in the silicon wafer, but by rapid heat treatment as described above, the oxygen precipitation nuclei on the surface of the wafer can be reduced.

[0045] The first temperature T1 in the first heat treatment step S21 is preferably about 1210°C to 1250°C. This is because when the first temperature T1 is lower than about 1180°C, the oxygen precipitation nuclei in the surface layer cannot be sufficiently reduced, and when the first temperature T1 is higher than about 1250°C, the probability of slip dislocation occurring in the silicon wafer increases. The heating rate (32) when switching from the standby temperature T0 (30) such as room temperature to the first temperature T1 is preferably about 10°C / sec to 50°C / sec.

[0046] The holding time H1 of the first temperature T1 in the first heat treatment step S21 is preferably about 10 to 60 seconds. This is because when the holding time H1 of the first temperature T1 is shorter than about 10 seconds, the density of oxygen precipitation nuclei in the surface layer cannot be sufficiently reduced, and even if the holding time H1 exceeds about 60 seconds, the increase in the number of vacancies cannot be observed. Not only that, the probability of slip dislocations also increases. Through the first heat treatment step S21, the oxygen precipitation nuclei in the surface layer can be eliminated, and a large number of vacancies can be introduced into the interior of the silicon wafer.

[0047] The second heat treatment step S22 is to heat treat the silicon wafer heat treated in the first heat treatment step S21 at a second temperature T2 lower than the first temperature T1. The second heat treatment step S22 is different from the first heat treatment step S21 and is preferably performed in a non-oxidizing atmosphere that does not contain ammonia or nitrogen. Therefore, the atmosphere gas in the RTA furnace is replaced after the first heat treatment step S21 is completed.

[0048] The second temperature T2 in the second heat treatment step S22 is preferably about 800° C. to 975° C. This is because when the second temperature T2 is less than about 800° C., thermally stable oxygen precipitation nuclei cannot be generated, and when the second temperature T2 exceeds about 975° C., oxygen precipitation nuclei cannot be generated at a high density. The cooling rate (34) when switching from the first temperature T1 to the second temperature T2 is preferably about 20 to 120° C. / sec.

[0049] The holding time H2 of the second temperature T2 in the second heat treatment step S22 is preferably about 2 to 10 minutes. This is because when the holding time H2 of the second temperature T2 is shorter than about 2 minutes, the oxygen precipitation nuclei cannot be generated at a high density, and even if the holding time H2 exceeds about 10 minutes, the oxygen precipitation nuclei density will not increase but only increase the cost. Through the second heat treatment step S22, the oxygen precipitation nuclei can be stably and densely generated inside the silicon wafer.

[0050] The third heat treatment step S23 is to heat treat the silicon wafer heat treated in the second heat treatment step S22 at a third temperature T3 higher than the second temperature T2. The third heat treatment step S23 is preferably performed in a non-oxidizing atmosphere containing no ammonia or nitrogen, similarly to the second heat treatment step S22.

[0051] The third temperature T3 in the third heat treatment step S23 is preferably about 1150°C to 1250°C. This is because when the third temperature T3 is lower than about 1150°C, the oxygen precipitation nucleus cannot be made thermally stable, and when the third temperature T3 is higher than about 1250°C, the probability of slip dislocation increases. The heating rate (36) when switching from the second temperature T2 to the third temperature T3 is preferably about 10 to 50°C / sec. Thus, the density of the oxygen precipitation nucleus can be increased, and the nucleus can be made more thermally stable.

[0052] The holding time H3 of the third temperature T3 in the third heat treatment step S23 is preferably about 5 to 15 minutes. This is because when the holding time H3 of the third temperature T3 is shorter than about 5 minutes, the high-density oxygen precipitation nuclei cannot be fixed, and even if the holding time H3 exceeds about 15 minutes, the effect of stabilizing the oxygen precipitation nuclei will not be particularly increased, but only the cost will be increased.

[0053] The third heat treatment step S23 stabilizes the oxygen precipitation nuclei formed in the silicon wafer and diffuses the excess vacancies inside the wafer outward, thereby suppressing the generation of excess oxygen precipitations during the subsequent heat treatment by the customer. Furthermore, the oxygen precipitation nuclei newly formed on the surface of the wafer in the second heat treatment step S22 are eliminated, and the density of oxygen precipitations generated on the surface of the wafer from the surface to 30 μm can be reduced to less than 1 / 100 of that on the main body.

[0054] Figure 4 (A)~ Figure 4 (I) is a schematic diagram showing changes in the silicon wafer 40 that occur during the first to third heat treatment steps S21 to S23. Figure 4 As shown in (A), there are a plurality of tiny oxygen precipitation nuclei 41 generated during crystal growth in the silicon wafer 40. Figure 4 As shown in (B), it can be understood that during the holding time H1 of the first heat treatment step S21, the tiny oxygen precipitation nuclei 41 disappear, and at the same time, the vacancies 44 and the Frenkel pairs 42 of the silicon atoms 45 between the lattices are generated. The additional vacancies 44 move from the interface between the Si3N4 layer 43 and the silicon wafer 40 to the inside of the silicon wafer 40. Through this heat treatment, the oxygen precipitation nuclei 41 generated during the crystal growth disappear, thereby making it possible to sufficiently reduce the oxygen precipitation nuclei in the DZ46 formed in the subsequent process.

[0055] Then, if Figure 4 As shown in FIG. 5C , during the cooling period between time t3 and time t4, the intercrystalline silicon atoms 45 and a portion of the vacancies 44a diffuse outward, and a portion of the vacancies 44b moves from the upper region 40a to the lower region 40b of the wafer, as shown in FIG. Figure 4 As shown in (D), DZ46 with a low oxygen precipitation nucleus density is formed.

[0056] Then, if Figure 4 As shown in (E), during the holding time H2 of the second heat treatment step S22, oxygen precipitation nuclei 47 and 47a are formed by the combination of vacancies 44, and the nuclei reach a sufficiently large size for stabilization. However, several vacancies 44 remain. Figure 4 As shown in (F), during the holding time H3 of the third heat treatment step S23, the remaining vacancies 44 are further recombined with the small oxygen precipitation nuclei 47a to form larger and more stable oxygen precipitation nuclei 47. Figure 4 As shown in (G), a large and stable oxygen precipitation nucleus 47 is formed and a DZ46 with a preferred width is formed, thereby ultimately reducing the density of oxygen precipitation from the wafer surface to the surface layer within 30 μm, and allowing stable oxygen precipitation to be generated at a high density in the main body deeper than 30 μm. Figure 4In (H), the Si3N4 layer 43 is removed by etching or grinding, showing the final formation of DZ46. Figure 4 As shown in (I), even if the wafer is processed to have an epitaxial layer 48, the DZ 46 can be maintained and the density of the oxygen precipitation nuclei 47 does not decrease.

[0057] Figure 5 A schematic diagram illustrating a method for determining the density of oxygen precipitates in a silicon wafer using light scattering tomography.

[0058] like Figure 5 As shown, oxygen precipitates of silicon wafer 50 can be observed as BMD (bulk micro defect). Silicon wafer 50 is cleaved, infrared laser 51 is incident from its surface (main surface) 50a, and infrared laser 51 is moved along cleavage plane 50b, thereby scanning BMD in the cleavage direction. The material to be inspected is mainly silicon, so Rayleigh scattered light can be collected by converging appropriate infrared laser on the sample. The micro dots appearing in the photographic image of the cleavage plane 50b of the wafer are equivalent to BMD 52. By counting the number of BMD 52 in a predetermined depth area, the BMD density in the depth area can be calculated. The wafer surface 50a is regarded as zero depth, and the BMD density in the surface layer 53 from the wafer surface 50a to 30μm is evaluated as the surface BMD density, and the BMD density in the main body 54 deeper than 30μm, for example, from the wafer surface to 50 to 300mm, is evaluated as the main body BMD density.

[0059] The density of BMD 52 is calculated by dividing the number of BMD 52 contained in a rectangular parallelepiped formed by a scanning width (standard condition 125 μm) corresponding to the width of the imaging screen of the cleavage plane 50 b, a depth (standard condition 8 μm) corresponding to the spot diameter of the infrared laser, and an arbitrary depth direction distance by the volume of the rectangular parallelepiped, which is equivalent to the density per unit volume (cm 3 ) of the BMD52. By extending the scan width to, for example, 398 μm, the accuracy of BMD density measurement can be improved. In the measurement of BMD density, the wafer is split and broken, so the characteristics related to the test of a certain wafer from a certain wafer batch can be regarded as suitable for the characteristics of the entire wafer batch.

[0060] The silicon wafer heat-treated as described above is taken out of the RTA furnace and put on the market as a so-called annealed silicon wafer. The density of the oxygen precipitates generated in the surface layer from the surface to 30 μm of the silicon wafer of this embodiment is 1.0×10 7 ~1.0×10 8 cm -3Such a low density. In addition, the BMD layer, which refers to the layer of oxygen precipitates, is strong. The strength here takes into account the change in the density of oxygen precipitates (BMD) in the heat treatment range in the manufacturing process of semiconductor integrated circuits, that is, from a lower heat treatment of less than about 1000°C to a higher heat treatment of more than about 1000°C. That is, the ratio (d2 / d1) of the average density of oxygen precipitates generated in the main body by high-temperature heat treatment (second main density d2) to the average density of oxygen precipitates generated in the main body by low-temperature heat treatment (first main density d1) is 0.74 to 1.02, and the change in the density of oxygen precipitates caused by heat treatment is within 30%. Even after the silicon wafer is subjected to the desired heat treatment in the manufacturing process of the semiconductor device, the average density of oxygen precipitates in the wafer is about 4×10 8 ~1×10 10 / cm 3 The variation rate of the range is limited to ±30%, more preferably limited to ±15%, further more preferably limited to ±10%, and further more preferably limited to ±5%. In this way, the silicon wafer of this embodiment includes thermally stable oxygen precipitation nuclei that are not affected by the customer's heat treatment at a high density, so the quality and reliability of semiconductor devices such as BCD devices can be improved.

[0061] An epitaxial silicon film can also be formed on the surface of the silicon wafer that has been subjected to the first to third heat treatment steps S21 to S23. In the case of forming an epitaxial silicon film, the silicon wafer (silicon substrate) is exposed to a high temperature of 1150°C. Therefore, if the oxygen precipitation nuclei in the silicon wafer are thermally unstable, the oxygen precipitation nuclei disappear after the device heat treatment, and there is a concern that the density of oxygen precipitates will drop significantly. However, according to this embodiment, since the oxygen precipitation nuclei are thermally stable, the decrease in the density of oxygen precipitates can be suppressed, and the decrease in the impurity absorption ability and the wafer strength can be prevented.

[0062] Silicon wafers used in the manufacture of power semiconductor devices such as BCD devices require both gettering ability and slip resistance. In order to satisfy such wafer characteristics, it is believed that at least about 4×10 8 / cm 3 , preferably about 1×10 9 / cm 3 For example, if the conventional annealed silicon wafer is manufactured by the technology of Japanese Patent Publication No. 2001-168382, even if there is a high temperature heat treatment such as an epitaxial growth process at the initial stage of the device process, it can ensure about 4×10 8 / cm 3 However, the more the device formation area can be fully secured, the more difficult it is to reduce the oxygen precipitate density in the surface layer.

[0063] However, the manufacturing method of the silicon wafer of the present embodiment utilizes rapid heating and rapid cooling at about 1210-1250°C to eliminate the oxygen precipitation nuclei (as grown nuclei) grown during crystal growth, and through continuous heat treatment at about 800-975°C for about 2-10 minutes for a relatively long time, tiny oxygen precipitation nuclei can be regenerated and grown inside the wafer. The oxygen precipitation nuclei generated / grown inside the wafer are thermally stable, and when subjected to heat treatment by the customer, high-density oxygen precipitates can be generated regardless of the heat treatment. Furthermore, by continuously performing high-temperature heat treatment at about 1150-1250°C for about 5-15 minutes, the tiny oxygen precipitation nuclei are further stabilized, and the excess vacancies inside the wafer are diffused outward, so that both the further stabilization of the oxygen precipitation nuclei density and the reduction of the oxygen precipitation nuclei density on the surface can be achieved.

[0064] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. It goes without saying that these modifications are also included in the scope of the present invention.

[0065] Example

[0066] <Forecast for three-stage heat treatment>

[0067] A p-type single crystal silicon ingot with a diameter of 300 mm and a plane orientation of (100) was grown by the CZ method. The single crystal silicon ingot was sliced ​​to produce a CZ silicon wafer. Next, the CZ silicon wafer was heat treated to produce two samples of annealed silicon wafers according to Example A1 and Comparative Examples A1 to A3.

[0068] In the preparation of the annealed silicon wafer according to Example A1, an oxygen concentration of 8×10 17 atoms / cm 3 The silicon wafer (CZ silicon wafer) of (ASTM F-121, 1979) was subjected to a three-stage heat treatment step in the order of the first heat treatment step (high temperature 1) → the second heat treatment step (low temperature) → the third heat treatment step (high temperature 2) using an RTA device. Specifically, the following steps were performed: room temperature input → heating at 50°C / second → holding at 1250°C for 10 seconds → cooling at 70°C / second → holding at 900°C for 5 minutes → heating at 50°C / second → holding at 1200°C for 5 minutes → cooling at 10°C / second → taking out at room temperature. The atmosphere gas in the first heat treatment step used argon gas containing ammonia, and the atmosphere gas in the second heat treatment step and the third heat treatment step used argon gas not containing ammonia. In this way, a sample of the annealed silicon wafer according to Example A1 was obtained.

[0069] In the preparation of the annealed silicon wafer according to Comparative Example A1, the heat treatment was performed under the same conditions as in Example A1 except that the temperature of the first heat treatment step was set to 1150° C. Thus, a sample of the annealed silicon wafer according to Comparative Example A1 was obtained.

[0070] In the preparation of the annealed silicon wafer according to Comparative Example A2, the heat treatment was performed under the same conditions as in Example A1 except that the temperature in the third heat treatment step was set to 1000° C. and the holding time was set to 1 minute.

[0071] In the preparation of the annealed silicon wafer according to Comparative Example A3, an oxygen concentration of 11×10 17 atoms / cm 3 The heat treatment was performed under the same conditions as in Example A1 except that the temperature of the first heat treatment step was set to 1150°C, the temperature of the third heat treatment step was set to 1000°C, and the holding time was set to 1 minute.

[0072] Table 1 summarizes the heat treatment conditions of Example A1 and Comparative Examples A1 to A3.

[0073] [Table 1]

[0074]

[0075] Next, one of the two samples of each annealed silicon wafer was subjected to a combination of a heat treatment that assumes the thermal history of the initial stage of the device process and a heat treatment that makes the oxygen precipitation nuclei visible (the first evaluation heat treatment), and the other sample was subjected to a combination of a heat treatment that simulates the epitaxial film formation process and a heat treatment that makes the oxygen precipitation nuclei visible (the second evaluation heat treatment). The first evaluation heat treatment was set as a two-stage heat treatment of a low-temperature heat treatment at 780°C for 3 hours and a visualized heat treatment at 950°C for 16 hours. In addition, the second evaluation heat treatment was set as a two-stage heat treatment of a high-temperature heat treatment at 1150°C for 2 minutes and a visualized heat treatment at 1000°C for 16 hours.

[0076] Figure 6 A schematic diagram of the evaluation steps used to determine the stability and uniformity of manufactured silicon wafers.

[0077] like Figure 6As shown, the silicon wafer 71 to be evaluated is split and divided into two parts. The A part 72 is sequentially subjected to a low temperature heat treatment 74 and a precipitate visualization heat treatment 76, while the B part 73 is sequentially subjected to a high temperature heat treatment 75 and a precipitate visualization heat treatment 76. Alternatively, two wafers from a prepared wafer batch can be used as wafers in which two wafers represent characteristics related to the entire batch. Next, each wafer part is subjected to an HF treatment 77 to remove the oxide film from the surface, and then the distribution of their oxygen precipitate density is determined using light scattering tomography 78. In this way, by evaluating the oxygen precipitates in each of the two parts, the stability of the wafer, that is, the ratio of the BMD density generated as a result of each part being subjected to the evaluation heat treatment at different temperatures and different holding times can be determined. The above evaluation steps are destructive, so it is not a problem to treat the characteristics related to the test of a certain wafer from a certain wafer batch as the characteristics attributed to the entire wafer batch.

[0078] Next, for each sample after the evaluation heat treatment, the BMD density of the surface part within 30 μm from the surface of the chip and the BMD density of the main part deeper than the surface part were measured by an infrared light scattering tomography device at intervals of about 5 mm (30 measurement points) in any radial direction from the center to the edge of the chip, and the average value was obtained. The diameter of the infrared laser of the infrared light scattering tomography device is 8 mm under standard conditions, and the measurement range (scan width) of each measurement point is set to 398 μm wider than the standard conditions in order to measure the surface BMD density as accurately as possible. In addition, as an indicator of stability, the ratio of the main body BMD density (second main body density d2) after the second evaluation heat treatment to the main body BMD density (first main body density d1) after the first evaluation heat treatment (BMD density ratio d2 / d1) was obtained. Furthermore, as an indicator of uniformity, the maximum value d of the main body BMD density measured at 30 points in the radial direction was used. max Relative to the minimum value d min The ratio d max / d min The evaluation results are shown in Table 2.

[0079] [Table 2]

[0080]

[0081] (Example A1)

[0082] In Example A1, the main BMD density after the first evaluation heat treatment was 6.6×10 9 cm -3 The second evaluation of the main body BMD density after heat treatment is 6.5×10 9 cm -3, the main BMD density ratio became 0.98. There was almost no difference in the main BMD density after the two evaluation heat treatments, which was confirmed to be very stable. In addition, the surface BMD density after the first evaluation heat treatment became 2.1×10 7 cm -3 The surface BMD density after the second evaluation heat treatment also became 2.1×10 7 cm -3 , which is confirmed to be more than two orders of magnitude lower than the bulk BMD density. For the uniformity of BMD density, the maximum value of BMD density in the radial direction of the wafer is d max Relative to the minimum value d min The ratio (d max / d min ) is also almost 1 (less than 2), which is confirmed to be good.

[0083] (Comparative Example A1)

[0084] In Comparative Example A1, the BMD density after the first evaluation heat treatment was 9.3×10 8 cm - 3 The BMD density after the second evaluation heat treatment also became 9.3×10 8 cm -3 , the main BMD density ratio becomes 1.00. In this way, it is confirmed that the main BMD density after the evaluation heat treatment is very stable. In addition, for the uniformity of BMD density, the maximum value d of the BMD density in the radial direction of the wafer is max Relative to the minimum value d min The ratio (d max / d min ) was almost 1 (less than 2), which was confirmed to be good. However, regarding the surface BMD density, the surface BMD density after the first evaluation heat treatment was 6.1×10 8 cm -3 The surface BMD density after the second evaluation heat treatment is 5.8×10 8 cm - 3 , an increase in the surface BMD density can be seen. This is considered to be because the temperature of the first heat treatment was low, so the oxygen precipitates generated in the crystal growth stage were not sufficiently eliminated.

[0085] (Comparative Example A2)

[0086] In Comparative Example A2, the BMD density after the first evaluation heat treatment was 6.5×10 9 cm -3 The BMD density after the second evaluation heat treatment is 2.1×10 8 cm -3, the main BMD density ratio becomes 0.03. In this way, when the temperature of the third heat treatment is low and the time is short, the oxygen precipitation nuclei are not sufficiently combined, so it is confirmed that the BMD density after the second evaluation heat treatment including a high-temperature heat treatment at 1150°C for 2 minutes that simulates the epitaxial film formation process decreases. In addition, along with the decrease in BMD density after the second evaluation heat treatment, the uniformity of BMD density also deteriorates. For the surface BMD density, the surface BMD density after the first evaluation heat treatment and the surface BMD density after the second evaluation heat treatment are both 2.1×10 7 cm -3 , becomes 10 7 cm -3 Horizontal low density.

[0087] (Comparative Example A3)

[0088] In Comparative Example A3, since the oxygen concentration is high, a stable and uniform bulk BMD density can be ensured. On the other hand, the surface BMD density after the first evaluation heat treatment is 7.0×10 8 cm- 3 The second evaluation of the surface BMD density after heat treatment is 6.5×10 8 cm- 3 , we can see the increase of surface BMD density.

[0089] <Evaluation of the first heat treatment step>

[0090] The influence of different heating conditions in the first heat treatment step on the stability and uniformity of the BMD density of the silicon wafer after the heat treatment was evaluated. The oxygen concentration of the silicon wafer used was set to 8×10 17 atoms / cm 3 The second heat treatment step and the third heat treatment step are set to common conditions. Specifically, the second heat treatment step is set to be carried out in an Ar atmosphere at a low temperature of 900°C for 5 minutes. The third heat treatment step is set to be carried out in an Ar atmosphere at a high temperature of 1200°C for 5 minutes.

[0091] In Examples B1, B2 and Comparative Example B1, the temperature of the first heat treatment step was set to 1210°C, and the holding time was set to 20 seconds, 60 seconds, and 10 seconds, respectively. In Examples B3 and B4, the temperature of the first heat treatment step was set to 1250°C, and the holding time was set to 10 seconds and 60 seconds, respectively. The heat treatment conditions according to Examples B1 to B4 and Comparative Example B1 are summarized in Table 3. In addition, the evaluation results are shown in Table 4.

[0092] [Table 3]

[0093]

[0094] [Table 4]

[0095]

[0096] As shown in Table 4, regarding the stability of the bulk BMD density, in Examples B1 to B4 and Comparative Example B1, the bulk BMD density after the first and second evaluation heat treatments was 10 9 cm- 3 The BMD density ratio was also within the range of 0.90 to 1.02. That is, it was confirmed that the main BMD density was stable regardless of the difference between the subsequent first and second evaluation heat treatments.

[0097] On the other hand, regarding the surface layer BMD density, in Examples B1 to B4, the surface layer BMD density after the first and second evaluation heat treatments was 10 7 cm- 3 However, in Comparative Example B1, the surface BMD density after the first and second evaluation heat treatments was 10 8 cm- 3 That is, it was confirmed that when the first heat treatment conditions were insufficient, the outward diffusion effect of the surface layer was insufficient and the surface BMD density was not sufficiently reduced.

[0098] Regarding the uniformity of the bulk BMD density, for any of Examples B1 to B4 and Comparative Example B1, the maximum bulk BMD density d in the wafer radial direction is max Relative to the minimum value d min The ratio (d max / d min ) are all less than 2, and no deterioration in the in-plane uniformity of the bulk BMD density is observed.

[0099] <Evaluation of the Second Heat Treatment Step>

[0100] The influence of different heating conditions in the second heat treatment step on the stability and uniformity of the BMD density of the silicon wafer after the heat treatment was evaluated. The oxygen concentration of the silicon wafer used was set to 8×10 17 atoms / cm 3 The first heat treatment step and the third heat treatment step are set to common conditions. Specifically, the first heat treatment step is set to high temperature RTA at 1250°C for 10 seconds in an Ar atmosphere containing NH3. The third heat treatment step is set to high temperature retention at 1200°C for 5 minutes in an Ar atmosphere.

[0101] In Examples C1, C2 and Comparative Example C5, the temperature of the second heat treatment step is set to 800°C, and the holding time is set to 2 minutes, 10 minutes and 1 minute, respectively. In Examples C3, C4 and Comparative Example C6, the temperature of the second heat treatment step is set to 900°C, and the holding time is set to 2 minutes, 10 minutes and 1 minute, respectively. In Examples C5 and C6, the temperature of the second heat treatment step is set to 975°C, and the holding time is set to 5 minutes and 10 minutes, respectively. In Comparative Examples C1 and C2, the temperature of the second heat treatment step is set to 775°C, and the holding time is set to 2 minutes and 10 minutes, respectively. In Comparative Examples C3 and C4, the temperature of the second heat treatment step is set to 775°C, and the holding time is set to 2 minutes and 10 minutes, respectively. The heat treatment conditions according to Examples C1 to C6 and Comparative Examples C1 to C6 are summarized in Table 5. The evaluation results are also shown in Table 6.

[0102] [Table 5]

[0103]

[0104] [Table 6]

[0105]

[0106] As shown in Table 6, regarding the stability of the bulk BMD density, in Examples C1 to C6, the bulk BMD density after the first and second evaluation heat treatments was 10 9 cm -3 The BMD density ratio was also within the range of 0.74 to 0.95. That is, it was confirmed that the main BMD density was substantially stable regardless of the difference in the subsequent evaluation heat treatment.

[0107] In contrast, in Comparative Examples C1 to C6, the main BMD density after the second evaluation heat treatment becomes smaller than the main BMD density after the first evaluation heat treatment, resulting in a main BMD density ratio of less than 0.5. It is believed that when the temperature of the second heat treatment is too low or too high, the BMD nuclei of the main body do not grow and disappear by receiving the second evaluation heat treatment. In addition, it is believed that even if the temperature of the second heat treatment is appropriate but the holding time is too short, the BMD nuclei of the main body still do not grow and disappear by receiving the second evaluation heat treatment including a heat treatment simulating the epitaxial film formation process.

[0108] Regarding the surface layer BMD density, for any of Examples C1 to C6 and Comparative Examples C1 to C6, the surface layer BMD density after the first and second evaluation heat treatments was 10 7 cm -3 That is, it was confirmed that the surface layer BMD density was low and stable regardless of the difference in the subsequent heat treatment conditions.

[0109] As for the uniformity of the bulk BMD density, similar to the evaluation of the stability of the bulk BMD density, Examples C1 to C6 showed good results, but Comparative Examples C1 to C6 showed a maximum value d of the bulk BMD density of 1.3447 W / cm2. max Relative to the minimum value d min The ratio (d max / d min ) becomes larger than 2, and degradation of uniformity of bulk BMD density is observed. It is considered that the oxygen precipitation nuclei are not sufficiently stabilized.

[0110] <Evaluation of the third heat treatment step>

[0111] The influence of the heating conditions in the third heat treatment step on the stability and uniformity of the BMD density of the silicon wafer after the heat treatment was evaluated. The oxygen concentration of the silicon wafer used was set to 8×10 17 atoms / cm 3 The first heat treatment step and the second heat treatment step are set to common conditions. Specifically, the first heat treatment step is set to high temperature RTA at 1250°C for 10 seconds in an Ar atmosphere containing NH3. The second heat treatment step is set to low temperature holding at 900°C for 5 minutes in an Ar atmosphere.

[0112] In Examples D1, D2, and D3, the temperature of the third heat treatment step is set to 1150°C, and the holding time is set to 5 minutes, 10 minutes, and 15 minutes, respectively. In Examples D4, D5, and D6, the temperature of the third heat treatment step is set to 1200°C, and the holding time is set to 5 minutes, 10 minutes, and 15 minutes, respectively. In Examples D7, D8, and D9, the temperature of the third heat treatment step is set to 1250°C, and the holding time is set to 5 minutes, 10 minutes, and 15 minutes, respectively. In Comparative Examples D1, D2, and D3, the temperature of the third heat treatment step is set to 1140°C, and the holding time is set to 5 minutes, 10 minutes, and 15 minutes, respectively. The heat treatment conditions according to Examples D1 to D6 and Comparative Examples D1 to D6 are summarized in Table 7. In addition, the evaluation results are shown in Table 8.

[0113] [Table 7]

[0114]

[0115] [Table 8]

[0116]

[0117] As shown in Table 8, regarding the stability of the bulk BMD density, in Examples D1 to D9, the bulk BMD density after the first and second evaluation heat treatments was 109 cm- 3 The BMD density ratio was also within the range of 0.94 to 1.00. That is, it was confirmed that the main BMD density was stable regardless of the difference between the subsequent first and second evaluation heat treatments.

[0118] In contrast, in Comparative Examples D1 to D3, the bulk BMD density after the second evaluation heat treatment was smaller than the bulk BMD density after the first evaluation heat treatment, resulting in a bulk BMD density ratio significantly lower than 0.5. It is believed that when the temperature of the third heat treatment was too low, the BMD nuclei in the bulk portion did not grow, but disappeared by the second evaluation heat treatment including the heat treatment simulating the epitaxial film formation process.

[0119] Regarding the surface layer BMD density, for any of Examples D1 to D9 and Comparative Examples D1 to D3, the surface layer BMD density after the first and second evaluation heat treatments was 10 7 cm- 3 Horizontal low density.

[0120] Regarding the uniformity of the bulk BMD density, unlike the evaluation of the stability of the bulk BMD density, good results were obtained not only for Examples D1 to D9 but also for Comparative Examples D1 to D3. max Relative to the minimum value d min The ratio (d max / d min ) are all less than 2, and the in-plane uniformity of the main BMD density is good.

[0121] <Evaluation of oxygen concentration in silicon wafer>

[0122] The influence of different oxygen concentrations of silicon wafers on the three-stage heat treatment and the stability and uniformity of the BMD density of the silicon wafers after the heat treatment was evaluated. In Example E1, an oxygen concentration of 7×10 17 atoms / cm 3 In Example E2, a low-oxygen bulk silicon wafer with an oxygen concentration of 10×10 17 atoms / cm 3 In Comparative Example E1, a silicon wafer with an oxygen concentration of 11×10 17 atoms / cm 3 In Comparative Example E2, a silicon wafer with an oxygen concentration of 6×10 17 atoms / cm 3In the three-stage heat treatment, for each block silicon wafer, the first heat treatment step was performed at 1250°C for 10 seconds, the second heat treatment step was performed at 900°C for 5 minutes, and the third heat treatment step was performed at 1200°C for 5 minutes. The differences in oxygen concentration according to Examples E1 and E2 and Comparative Examples E1 and E2 are summarized in Table 9. In addition, the evaluation results are shown in Table 10.

[0123] [Table 9]

[0124]

[0125] [Table 10]

[0126]

[0127] As shown in Table 10, in Examples E1 and E2, the bulk BMD density and the surface layer BMD density were good.

[0128] On the other hand, when the oxygen concentration was 11×10 17 atoms / cm 3 In Comparative Example E1 of the bulk silicon wafer, the bulk BMD density is good, but the surface BMD density is high. The in-plane uniformity of the bulk BMD density is good.

[0129] When using an oxygen concentration of 6×10 17 atoms / cm 3 In Comparative Example E2 of the silicon wafer of , the bulk BMD density after the second evaluation heat treatment is smaller than the bulk BMD density after the first evaluation heat treatment, resulting in a bulk BMD density ratio of less than 0.5. Regarding the uniformity of the bulk BMD density, the maximum value d of the bulk BMD density after the second evaluation heat treatment is max Relative to the minimum value d min The ratio (d max / d min ) became 13.3. As in the evaluation of the stability of the main BMD density, a significant deterioration in the in-plane uniformity of the main BMD density after the second evaluation heat treatment was observed. The in-plane uniformity of the main BMD density after the first evaluation heat treatment was good. Regarding the surface BMD density, an extremely good result was achieved in which no BMD was observed in the surface portion after the first and second evaluation heat treatments.

[0130] <Evaluation of the influence of epitaxial growth>

[0131] An epitaxial film was formed on a wafer manufactured by a three-stage heat treatment, and the stability of the BMD density after epitaxial growth was confirmed. As shown in Table 11, the growth temperature of Examples F1, F2, and F3 was set to 1050°C, and the holding time was set to 1 minute, 2 minutes, and 5 minutes, respectively. The growth temperature of Examples F4, F5, and F6 was set to 1150°C, and the holding time was set to 1 minute, 2 minutes, and 5 minutes, respectively. The thickness of the obtained epitaxial film was 2μm in Examples F1 and F4, 4μm in Examples F2 and F5, and 10μm in Examples F3 and F6.

[0132] In the evaluation heat treatment after epitaxial growth, the first evaluation heat treatment was set as a two-stage heat treatment of low temperature heat treatment at 780°C for 3 hours and visual heat treatment at 950°C for 16 hours. The second evaluation heat treatment omitted the high temperature heat treatment at 1150°C for 2 minutes that simulated the epitaxial film formation process, and was set only as a visual heat treatment at 1000°C for 16 hours. The evaluation results are shown in Table 12.

[0133] [Table 11]

[0134]

[0135] [Table 12]

[0136]

[0137] As shown in Table 12, it is confirmed that under any epitaxial growth conditions, the stability and uniformity of the main BMD density and the uniformity of the surface BMD density are good, and the main BMD density does not decrease even when epitaxial growth is performed on silicon wafers manufactured by three-stage heat treatment.

[0138] Explanation of symbols

[0139] S11 Process of manufacturing single crystal silicon ingots

[0140] S12 Silicon wafer manufacturing process

[0141] S13 Process of heat treating silicon wafers

[0142] S21 First heat treatment step

[0143] S22 Second heat treatment step

[0144] S23 Third heat treatment step

[0145] 30 Standby temperature

[0146] 32 Heating

[0147] 34 Cooling

[0148] 36 Heating

[0149] 40 Wafer

[0150] 40a Upper Zone

[0151] 40b Lower area

[0152] 41 Tiny oxygen precipitation nuclei (generated during crystal growth)

[0153] 42 Frenkel vs.

[0154] 43 Si3N4 layer

[0155] 44,44a,44b vacant

[0156] 45 Silicon atoms between lattices

[0157] 46 DZ

[0158] 47 Oxygen precipitation nucleus

[0159] 47a Small oxygen evolution nucleus

[0160] 48 epitaxial layer

[0161] 50 Wafer

[0162] 50a Wafer surface (main surface)

[0163] 50b Split face

[0164] 51 Infrared laser

[0165] 52 BMD (oxygen precipitates)

[0166] 53 Surface

[0167] 54 Main body

[0168] 71 Silicon Wafer

[0169] 72 Wafer A section

[0170] 73 Wafer B

[0171] 74 Low temperature heat treatment

[0172] 75 High temperature heat treatment

[0173] 76 Precipitate Visualization Heat Treatment

[0174] 77 HF treatment

[0175] 78 Light Scattering Tomography

Claims

1. A silicon wafer, characterized in that: have: The surface layer from the surface to a depth of 30 μm, and a main body portion deeper than the surface portion, The density of the oxygen precipitates generated in the surface layer portion by the first evaluation heat treatment was 1.0×10 7 ~1.0×10 8 cm- 3 , The density of the oxygen precipitates generated in the main body by the first evaluation heat treatment was 1.0×10 9 ~7.0×10 9 cm- 3 , When the average density of oxygen precipitates generated in the main body by the first evaluation heat treatment is set as a first main body density, and the average density of oxygen precipitates generated in the main body by the second evaluation heat treatment is set as a second main body density, the ratio of the second main body density to the first main body density is in the range of 0.74 to 1.02, The first evaluation heat treatment is a two-stage heat treatment of heat treatment at 780° C. for 3 hours followed by visualization heat treatment. The second evaluation heat treatment is a two-step heat treatment of performing the visualization heat treatment after heat treatment at 1150° C. for 2 minutes. The visualized heat treatment is a heat treatment performed at 950-1000° C. for 16 hours.

2. The silicon wafer according to claim 1, wherein a ratio of a maximum value to a minimum value of the density of oxygen precipitates produced in the main body by the first evaluation heat treatment and a ratio of a maximum value to a minimum value of the density of oxygen precipitates produced in the main body by the second evaluation heat treatment are both less than 2.

3. The silicon wafer according to claim 1, wherein the ratio of the maximum value to the minimum value of the density of oxygen precipitates produced in the main body by the first evaluation heat treatment is less than 1.30, and the ratio of the maximum value to the minimum value of the density of oxygen precipitates produced in the main body by the second evaluation heat treatment is less than 1.

32.

4. The silicon wafer according to any one of claims 1 to 3, wherein the average density of the oxygen precipitates generated in the surface layer portion by the first evaluation heat treatment and the average density of the oxygen precipitates generated in the surface layer portion by the second evaluation heat treatment are both 2.1×10 7 cm- 3 the following.

5. A silicon wafer, characterized in that: have: Silicon substrate, and an epitaxial silicon film formed on the surface of the silicon substrate, The silicon substrate has a surface layer portion extending from the surface to a depth of 30 μm and a main body portion deeper than the surface layer portion. The density of the oxygen precipitates generated in the surface layer portion by the first evaluation heat treatment was 1.0×10 7 ~1.0×10 8 cm- 3 , The density of the oxygen precipitates generated in the main body by the first evaluation heat treatment was 1.0×10 9 ~7.0×10 9 cm- 3 , When the average density of oxygen precipitates generated in the main body by the first evaluation heat treatment is set as a first main body density, and the average density of oxygen precipitates generated in the main body by the second evaluation heat treatment is set as a second main body density, a ratio of the second main body density to the first main body density is in the range of 0.98 to 1.02, The first evaluation heat treatment is a two-stage heat treatment of heat treatment at 780° C. for 3 hours followed by visualization heat treatment. The second evaluation heat treatment is the visualization heat treatment, The visualized heat treatment is a heat treatment performed at 950-1000° C. for 16 hours.

6. The silicon wafer according to claim 5, wherein a ratio of a maximum value to a minimum value of the density of oxygen precipitates generated in the main body by the first evaluation heat treatment and a ratio of a maximum value to a minimum value of the density of oxygen precipitates generated in the main body by the second evaluation heat treatment are both less than 2.

7. The silicon wafer according to claim 6, wherein the ratio of the maximum value to the minimum value of the density of oxygen precipitates produced in the main body by the first evaluation heat treatment is less than 1.29, and the ratio of the maximum value to the minimum value of the density of oxygen precipitates produced in the main body by the second evaluation heat treatment is less than 1.

35.

8. A method for manufacturing a silicon wafer, characterized in that: Include: In the first heat treatment step, the oxygen concentration is 7×10 17 ~10×10 17 atoms / cm 3 (ASTM F-121, 1979) silicon wafer heating, a second heat treatment step, after the first heat treatment step, heating the silicon wafer at a second temperature lower than the first temperature, and a third heat treatment step, after the second heat treatment step, heating the silicon wafer at a third temperature higher than the second temperature, The first temperature is 1210-1250° C., and the first temperature is maintained for 10-60 seconds. The second temperature is 800-975° C., and the second temperature is maintained for 2-10 minutes. The third temperature is 1150-1250° C., and the third temperature is maintained for 5-15 minutes.

9. The method for manufacturing a silicon wafer according to claim 8, wherein: The first heat treatment step is performed in a non-oxidizing atmosphere containing ammonia or nitrogen, The second heat treatment step and the third heat treatment step are performed in a non-oxidizing atmosphere not containing ammonia or nitrogen.

10. The method for manufacturing a silicon wafer according to claim 8 or 9, wherein: The heating rate to the first temperature and the heating rate from the second temperature to the third temperature are 10 to 50° C. / sec. 11 . The method for manufacturing a silicon wafer according to claim 8 , wherein a cooling rate from the first temperature to the second temperature is 20 to 120° C. / second.

12. The method for manufacturing a silicon wafer according to claim 8 or 9, wherein: The silicon wafer before the heat treatment in the first heat treatment step is a silicon wafer cut out from a defect-free region of a single crystal silicon ingot in which aggregates of intercrystalline silicon type point defects and aggregates of vacancy type point defects do not exist.

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