Silicon Wafer and Method for Manufacturing the Same

Abstract

To provide a silicon wafer that can generate, at high density in a bulk section thereof, thermally stable oxygen precipitate nuclei that are not influenced by a customer's thermal treatment, while minimizing oxygen precipitate on a surface layer section of the silicon wafer.SOLUTION: A silicon wafer 50 has: an oxygen precipitate (BMD) density of 1×107-1×108 cm-3, in a surface layer section 53, from a surface 50a to a depth of 30 μm, the density occurring as a result of a first evaluation heat treatment in which, after a heat treatment at 780°C for 3 hours, a visualization heat treatment is carried out at 950-1,000°C for 16 hours; and a BMD density of 1×109-7×109 cm-3 in a bulk section 54, which is at a deeper location than the surface layer section 53, the density occurring as a result of the first evaluation heat treatment. When the BMD average density occurring in the bulk section 54 as a result of the first evaluation heat treatment is noted as a first bulk density d1 and the BMD average density occurring in the bulk section 54 as a result of a second evaluation heat treatment in which, after a heat treatment at 1,150°C for 2 minutes, a visualization heat treatment is carried out, is noted as a second bulk density d2, d2 / d1 is 0.74-1.02.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a silicon wafer and a method for manufacturing the same, and more particularly to a heat treatment method for a silicon wafer produced by slicing a silicon single crystal ingot manufactured by the Czochralski method (CZ method). The present invention also relates to a silicon wafer heat-treated by such a heat treatment method.

Background Art

[0002] Many of the silicon wafers that are substrate materials for semiconductor devices are manufactured using silicon single crystal ingots manufactured by the CZ method. The CZ method is a method of growing a single crystal larger than a seed crystal by gradually pulling up a seed crystal brought into contact with a silicon melt in a quartz crucible while relatively rotating it. According to the CZ method, the manufacturing yield of large-diameter silicon single crystals can be increased.

[0003] When growing a silicon single crystal by the CZ method, it is known that oxygen dissolved from the surface of the quartz crucible is taken into the silicon melt. Oxygen in the silicon melt becomes supersaturated in the process of cooling the silicon single crystal, and oxygen aggregates to form oxygen precipitation nuclei.

[0004] The oxygen precipitate density of a bulk silicon wafer immediately after being cut from a silicon single crystal ingot is very low, and the influence of low-density oxygen precipitates on the characteristics of semiconductor devices is small. However, various heat treatments are repeatedly performed in the process of manufacturing semiconductor devices, and this may cause the oxygen precipitates to become denser. Oxygen precipitates present in the surface layer portion of the silicon wafer, which is the device active region, cause deterioration of device characteristics such as junction leakage. On the other hand, oxygen precipitates present in the bulk portion other than the device active region 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 layer portion of the silicon wafer have a low density and make the oxygen precipitates in a region deeper than the surface layer portion (inside the wafer) have a high density.

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

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In recent years, as a manufacturing process for power management semiconductor devices, a BCD (Bipolar-CMOS-DMOS) process for forming bipolar, CMOS, and DMOS on the same substrate has attracted attention. Since the BCD process involves high-temperature heat treatment, slip dislocations are likely to occur in the wafer. In order to improve not only the gettering ability of the silicon wafer but also its slip resistance, it is necessary to increase the oxygen precipitate density. Furthermore, in the BCD process, a DZ (Denuded Zone) about several tens of μm deep is required. In some cases, an epitaxial film is formed on the surface of the silicon wafer in advance. However, in the epitaxial film formation process, in addition to the problem of slip associated with high-temperature heat treatment, oxygen precipitates are likely to disappear, and the thermal stability of oxygen precipitates is also questioned. Thus, for a silicon wafer used in the BCD process, increasing the density and stability of oxygen precipitates is one of the important issues.

[0008] However, in the method for manufacturing a silicon wafer described in Patent Document 1, for example, 8 × 10 17 atoms / cm 3(The same applies hereinafter to the oxygen concentration in ASTM F-121, 1979.) When using a bulk silicon wafer with a relatively low oxygen concentration, oxygen precipitation nuclei cannot be sufficiently grown by the first to third heat treatment steps, and the oxygen precipitation nuclei disappear during subsequent customer heat treatment, making it difficult to increase the oxygen precipitate density in the bulk portion. On the other hand, when using a bulk silicon wafer with an oxygen concentration of about 11×10 17 atoms / cm 3 which is relatively high, oxygen precipitates are likely to occur not only in the bulk portion of the wafer but also in the surface layer portion, so there is a possibility that it may not be compatible with future BCD devices.

[0009] Therefore, an object of the present invention is to provide a silicon wafer and a method for manufacturing the same that can generate oxygen precipitation nuclei that are thermally stable and not affected by customer heat treatment at a high density in the bulk portion while minimizing oxygen precipitation in the surface layer portion.

Means for Solving the Problem

[0010] To solve the above problems, the silicon wafer according to the present invention has a surface layer portion with a depth of up to 30 μm from the surface and a bulk 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 and the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is 1.0×10 9 ~7.0×10 9 cm -3wherein the average density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is defined as the first bulk density d1, and the average density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment is defined as the second bulk density d2, the ratio (d2 / d1) of the second bulk density d2 to the first bulk density d1 is in the range of 0.74 to 1.02, the first evaluation heat treatment is a two-step heat treatment in which visualization heat treatment is performed after heat treatment at 780°C for 3 hours, the second evaluation heat treatment is a two-step heat treatment in which the visualization heat treatment is performed after heat treatment at 1150°C for 2 minutes, and the visualization heat treatment is heat treatment at 950 to 1000°C for 16 hours.

[0011] According to the present invention, it is possible to provide a silicon wafer in which the density of oxygen precipitates in the surface layer portion after the evaluation heat treatment is as low as 1.0×10 8 cm -3 or less, and further, the density of oxygen precipitates in the bulk portion is 10 times or more higher than that in the surface layer portion and thermally stable. Therefore, the yield and reliability of semiconductor devices such as BCD manufactured using the silicon wafer can be improved.

[0012] In the present invention, the ratio (d min / d max ) of the minimum value d max to the maximum value d min of the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment and the ratio (d min / d max ) of the minimum value d max to the maximum value d min of the density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment are both preferably 2 or less. In this case, the ratio (d min / d max ) of the minimum value d max to the maximum value d min of the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is more preferably 1.30 or less. Further, the ratio (d min / d max ) of the minimum value d max / d min ) is more preferably 1.32 or less. This allows thermally stable oxygen precipitates that are not affected by the heat treatment of the customer to be generated uniformly and at a high density in the bulk portion.

[0013] In the present invention, the average density of the oxygen precipitates formed in the surface layer portion by the first evaluation heat treatment and the average density of the oxygen precipitates formed in the surface layer portion by the second evaluation heat treatment are both 2.1×10 7 cm -3 This makes it possible to provide silicon wafers in which the density of oxygen precipitates in the surface layer is sufficiently reduced without depending on the customer's heat treatment.

[0014] A silicon wafer according to the present invention includes a silicon substrate and an epitaxial silicon film formed on a surface of the silicon substrate, the silicon substrate having a surface layer portion extending from the surface to a depth of 30 μm and a bulk portion deeper than the surface layer portion, and a density of oxygen precipitates generated in the surface layer portion by a first evaluation heat treatment is 1.0×10 7 ~1.0×10 8 cm -3 and the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is 1.0×10 9 ~7.0×10 9 cm -3 wherein, when an average density of oxygen precipitates produced in the bulk portion by the first evaluation heat treatment is defined as a first bulk density and an average density of oxygen precipitates produced in the bulk portion by the second evaluation heat treatment is defined as a second bulk density, a ratio of the second bulk density to the first bulk density is within a range of 0.98 to 1.02, the first evaluation heat treatment is a two-stage heat treatment in which a heat treatment is performed at 780°C for 3 hours followed by a visualization heat treatment, and the second evaluation heat treatment is the visualization heat treatment, which is a heat treatment at 950 to 1000°C for 16 hours.

[0015] According to the present invention, the density of oxygen precipitates in the surface layer after the evaluation heat treatment is 1.0×10 8 cm -3It is possible to provide an epitaxial silicon wafer having a low oxygen precipitation density of 10 times or less than that of the surface layer, and having thermal stability. Therefore, it is possible to improve the yield and reliability of semiconductor devices such as BCD manufactured using the epitaxial silicon wafer.

[0016] In the present invention, the minimum density d of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment min Maximum value d for max The ratio (d max / d min ) and the minimum density d of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment min Maximum value d for max The ratio (d max / d min ) are preferably equal to or less than 2. In this case, the minimum density d min Maximum value d for max The ratio (d max / d min ) is more preferably 1.29 or less. In addition, the minimum density d min Maximum value d for max The ratio (d max / d min ) is more preferably 1.35 or less. This allows thermally stable oxygen precipitates that are not affected by the heat treatment of the customer to be generated uniformly and at a high density in the bulk portion.

[0017] Furthermore, in the method for producing a silicon wafer according to the present invention, the oxygen concentration is 7×10 17 ~10×10 17 atoms / cm 3A first heat treatment step of heating a silicon wafer, which is (ASTM F-121, 1979), at a first temperature, a second heat treatment step of heating the silicon wafer at a second temperature lower than the first temperature after the first heat treatment step, and a third heat treatment step of heating the silicon wafer at a third temperature higher than the second temperature after the second heat treatment step, wherein the first temperature is 1210 - 1250 °C, the holding time at the first temperature is 10 - 60 seconds, the second temperature is 800 - 975 °C, the holding time at the second temperature is 2 - 10 minutes, the third temperature is 1150 - 1250 °C, and the holding time at the third temperature is 5 - 15 minutes.

[0018] According to the present invention, by means of a first heat treatment step at a high temperature for a relatively short time, a second heat treatment step at a low temperature for a relatively long time, and a third heat treatment step at a higher temperature than the second heat treatment step, thermally stable oxygen precipitation nuclei can be generated at a high density inside the silicon wafer, while the oxygen precipitation nuclei can be reduced in the surface layer part of the wafer. Therefore, it is possible to manufacture a silicon wafer having thermally stable high-density oxygen precipitation nuclei in the bulk part that are not affected by the customer's heat treatment, and having low-density oxygen precipitation nuclei in the device formation region.

[0019] The first heat treatment step is preferably carried out in a non-oxidizing atmosphere containing ammonia or nitrogen, and the second and third heat treatment steps are preferably carried out in a non-oxidizing atmosphere not containing ammonia or nitrogen. By carrying out the first heat treatment step in a non-oxidizing atmosphere containing ammonia or nitrogen, a nitride film can be formed on the wafer surface, and pores can be introduced into the wafer through the nitride film, thereby increasing the density of oxygen precipitation nuclei inside the wafer.

[0020] 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 - 50 °C / second. Also, the cooling rate from the first temperature to the second temperature is preferably 20 - 120 °C / second. Thereby, thermally stable oxygen precipitation nuclei can be generated at a high density.

[0021] In the present invention, it is preferable that the silicon wafer before being heat-treated in the first heat treatment step is cut out from a defect-free region of a silicon single crystal ingot in which aggregates of interstitial silicon-type point defects and aggregates of vacancy-type point defects do not exist. Thereby, it is possible to manufacture a silicon wafer having a low density of oxygen precipitation nuclei in the surface layer portion, a high density of oxygen precipitation nuclei in the bulk portion, and being thermally stable. Therefore, the yield and reliability of semiconductor devices such as BCD manufactured using the silicon wafer can be improved.

Advantages of the Invention

[0022] According to the present invention, it is possible to provide a silicon wafer and a method for manufacturing the same, which can generate thermally stable oxygen precipitates with a high density in the bulk portion while minimizing oxygen precipitation in the surface layer portion and being independent of the customer's heat treatment.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0025] FIG. 1 is a flowchart schematically showing a method for manufacturing a silicon single crystal according to an embodiment of the present invention.

[0026] As shown in FIG. 1, the method for manufacturing a silicon wafer according to the present embodiment includes a step S11 of manufacturing a silicon single crystal ingot by the Czochralski (CZ) method, a step S12 of processing the silicon single crystal ingot to produce a silicon wafer, and a step S13 of heat-treating the silicon wafer.

[0027] In step S11 of manufacturing a silicon single crystal ingot, polycrystalline silicon filled in a quartz crucible is heated in a CZ furnace to generate a silicon melt. Next, a seed crystal is brought into contact with the silicon melt, and while rotating the seed crystal and the quartz crucible, the seed crystal is gradually pulled up to grow a large single crystal at the lower end of the seed crystal.

[0028] Next, in step S12 of producing a silicon wafer, the silicon single crystal ingot is sliced by a wire saw or the like, and then lapping, etching, mirror polishing, cleaning, etc. are performed to complete a bulk silicon wafer (polished wafer) as an intermediate product. The oxygen concentration of the CZ silicon wafer thus produced is preferably 7×10 17 ~10×10 17 atoms / cm 3 (ASTM F-121, 1979). When the concentration is lower than 7×10 17 atoms / cm 3 , stable oxygen precipitates cannot be generated at a high density in the bulk portion. When the concentration is higher than 10×10 17 atoms / cm 3 , oxygen precipitates in the surface layer portion cannot be sufficiently reduced.

[0029] Here, it is desirable that the silicon wafer is a so-called COP-free wafer that substantially does not contain crystal-originated particle (COP) defects. That is, it is preferable that the silicon wafer is cut from a defect-free region of a silicon single crystal ingot in which aggregates of interstitial silicon-type point defects and aggregates of vacancy-type point defects do not exist. COP (Crystal Originated Particle) is a crystallographically perfectly oriented octahedral cavity, and its inner wall is usually covered with an oxide film having a thickness of 1 to 4 nm. Crystal defects related to vacancies such as COP defects, like oxygen precipitates in the surface layer, may cause problems in semiconductor devices. Examples of device problems include a decrease in the gate oxide integrity (GOI) and current leakage at the PN junction. To address 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 region near the surface. By changing the crystal pulling speed and the crystal cooling speed, the vacancy defect level may be lowered. This enables the recombination of vacancies and interstitial silicon atoms, the aggregation of vacancies, and the control of oxygen concentration, resulting in a reduction in surface defects. In a COP-free wafer, "substantially free of COP" means that the density of COP consisting of aggregates of vacancy-type point defects is 1×10 5 cm -3 or less.

[0030] In the step S13 of heat-treating the silicon wafer, the wafer is heat-treated in a rapid thermal annealing (RTA) furnace in three temperature ranges to generate a high density of thermally stable oxygen precipitation nuclei. Here, the expression "thermally stable" means having a density sufficient to maintain metal impurity gettering and wafer strength in the wafer shipment state and the density is not affected by subsequent heat treatment in the customer's device. Also, "high density" means at least 1×10 9 / cm 3 or more, preferably about 5×10 9 / cm 3 or more.

[0031] FIG. 2 is a flowchart for explaining a step S13 of heat-treating a silicon wafer. FIG. 3 is a graph showing temperature changes during heat treatment, where the horizontal axis represents time and the vertical axis represents heating temperature, respectively.

[0032] As shown in FIGS. 2 and 3, the heat treatment method of a silicon wafer according to an embodiment of the present invention includes a first heat treatment S21 of heating the silicon wafer at a first temperature T1 in an RTA furnace, a second heat treatment S22 of heating the silicon wafer at a second temperature T2 lower than the first temperature T1 after the first heat treatment S21, and a third heat treatment S23 of heating the silicon wafer at a third temperature T3 higher than the second temperature T2 after the second heat treatment S22. In the present embodiment, it is preferable that the first to third heat treatments S21 to S23 are continuously performed in the same RTA furnace. However, after performing the first heat treatment S21 in the RTA furnace, the wafer may be taken out of the RTA furnace and the second heat treatment S22 and the third heat treatment S23 may be performed in another heat treatment apparatus.

[0033] The first heat treatment 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 Ar gas. In high-temperature heat treatment in a non-oxidizing atmosphere, a large number of pores can be introduced into the wafer, thereby increasing the density of oxygen precipitation nuclei inside the wafer. Furthermore, by using Ar gas containing ammonia or nitrogen, a nitride film can be formed on the wafer surface, and pores can be introduced into the wafer through the nitride film, thereby increasing the density of oxygen precipitation nuclei inside the wafer. Also, although there are minute oxygen precipitation nuclei generated during crystal growth in the silicon wafer, the oxygen precipitation nuclei in the surface layer portion of the wafer can be reduced by the rapid heat treatment as described above.

[0034] The first temperature T1 in the first heat treatment S21 is preferably about 1210°C to 1250°C. This is because if the first temperature T1 is lower than about 1180°C, the oxygen precipitation nuclei in the surface layer cannot be sufficiently reduced, and if the first temperature T1 is higher than about 1250°C, the probability of slip dislocations 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.

[0035] The holding time H1 of the first temperature T1 in the first heat treatment S21 is preferably about 10 to 60 seconds. If the holding time H1 of the first temperature T1 is shorter than about 10 seconds, the density of the oxygen precipitation nuclei in the surface layer cannot be sufficiently reduced. Also, if the holding time H1 exceeds about 60 seconds, not only can no increase in the number of vacancies be observed, but the probability of slip dislocations occurring increases. By the first heat treatment S21, while eliminating the oxygen precipitation nuclei in the surface layer, a large number of vacancies can be introduced into the interior of the silicon wafer.

[0036] The second heat treatment S22 heat-treats the silicon wafer heat-treated in the first heat treatment S21 at a second temperature T2 lower than the first temperature T1. The second heat treatment S22 is preferably performed in a non-oxidizing atmosphere that does not contain ammonia or nitrogen, unlike the first heat treatment S21. Therefore, after the completion of the first heat treatment S21, the atmosphere gas in the RTA furnace is replaced.

[0037] The second temperature T2 in the second heat treatment S22 is preferably about 800°C to 975°C. This is because if the second temperature T2 is less than about 800°C, thermally stable oxygen precipitation nuclei cannot be generated, and if 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°C / sec to 120°C / sec.

[0038] The holding time H2 of the second temperature T2 in the second heat treatment S22 is preferably about 2 to 10 minutes. When the holding time H2 of the second temperature T2 is shorter than about 2 minutes, oxygen precipitation nuclei cannot be generated at a high density, and even when the holding time H2 exceeds about 10 minutes, the oxygen precipitation nucleus density does not increase and only the cost increases. By the second heat treatment S22, oxygen precipitation nuclei can be stably and highly densely generated inside the silicon wafer.

[0039] In the third heat treatment S23, the silicon wafer heat-treated in the second heat treatment S22 is heat-treated at a third temperature T3 higher than the second temperature T2. The third heat treatment S23 is preferably performed in a non-oxidizing atmosphere containing no ammonia or nitrogen, similar to the second heat treatment S22.

[0040] The third temperature T3 in the third heat treatment S23 is preferably about 1150°C to 1250°C. When the third temperature T3 is lower than about 1150°C, the oxygen precipitation nuclei cannot be thermally stabilized. When the third temperature T3 is higher than about 1250°C, the probability of slip dislocation occurring increases. The heating rate (36) when switching from the second temperature T2 to the third temperature T3 is preferably about 10°C / sec to 50°C / sec. Thereby, the density of the oxygen precipitation nuclei can be increased, and the nuclei can be made more thermally stable.

[0041] The holding time H3 of the third temperature T3 in the third heat treatment S23 is preferably about 5 to 15 minutes. When the holding time H3 of the third temperature T3 is shorter than about 5 minutes, high-density oxygen precipitation nuclei cannot be fixed, and even when the holding time H3 exceeds about 15 minutes, the effect of stabilizing the oxygen precipitation nuclei does not particularly increase and only the cost increases.

[0042] By the third heat treatment S23, the oxygen precipitation nuclei formed in the silicon wafer are stabilized, and the excess vacancies inside the wafer are diffused outward, suppressing the generation of excess oxygen precipitates in the subsequent heat treatment by the customer. Furthermore, the oxygen precipitation nuclei in the newly formed wafer surface layer part in the second heat treatment are eliminated, and the density of oxygen precipitates generated in the surface layer part from the surface of the wafer to 30 μm can be reduced to 1 / 100 or less of that in the bulk part.

[0043] Figures 4(A) to 4(I) are schematic diagrams showing changes in the silicon wafer 40 that occur during the first to third heat treatments S21 to S23. As shown in Figure 4(A), a large number of minute oxygen precipitation nuclei 41 generated during crystal growth exist in the silicon wafer 40. As shown in Figure 4(B), during the holding time H1 of the first heat treatment S21, it is understood that the minute oxygen precipitation nuclei 41 disappear, and at the same time, the generation of Frenkel pairs 42 of vacancies 44 and interstitial silicon atoms 45 occurs. The additional vacancies 44 move from the interface between the Si3N4 layer 43 and the silicon wafer 40 into the silicon wafer 40. By this heat treatment, the oxygen precipitation nuclei 41 generated during crystal growth disappear, so that the oxygen precipitation nuclei in the DZ46 formed in the subsequent process can be sufficiently reduced.

[0044] Subsequently, as shown in Figure 4(C), during the temperature drop period between times t3 and t4, the outward diffusion of interstitial silicon atoms 45 and a part 44a of the vacancies, and the movement of a part 44b of the vacancies from the upper zone 40a to the lower zone 40b of the wafer occur, and a DZ46 with a low oxygen precipitation nucleus density is formed as shown in Figure 4(D).

[0045] Next, as shown in FIG. 4(E), during the holding time H2 of the second heat treatment S22, oxygen precipitation nuclei 47, 47a are formed from the combination of vacancies 44, and the nuclei reach a sufficiently large size for stabilization. However, some vacancies 44 remain. As shown in FIG. 4(F), during the holding time H3 of the third heat treatment S23, the remaining vacancies 44 and the small oxygen precipitation nuclei 47a further recombine to form larger and more stable oxygen precipitation nuclei 47. As shown in FIG. 4(G), by forming large and stable oxygen precipitation nuclei 47 and forming DZ46 having a preferable width, finally, the oxygen precipitate density in the surface layer portion within 30 μm from the wafer surface can be reduced, and stable oxygen precipitates can be generated at a high density in the bulk portion deeper than 30 μm. In FIG. 4(H), the Si3N4 layer 43 has been removed by etching or polishing, and the final formation of DZ46 is shown. As shown in FIG. 4(I), even if the wafer is processed to have an epitaxial layer 48, DZ46 is maintained and the density of the oxygen precipitation nuclei 47 does not decrease.

[0046] FIG. 5 is a schematic diagram illustrating a method of measuring the oxygen precipitate density of a silicon wafer using light scattering tomography.

[0047] As shown in FIG. 5, oxygen precipitates in the silicon wafer 50 can be observed as BMD (Bulk Micro defect). The silicon wafer 50 is cleaved, and an infrared laser beam 51 is incident from its surface (main surface) 50a. By moving the infrared laser beam 51 along the cleavage plane 50b, the BMD 510 is scanned in the cleavage direction. Since the material to be inspected is mainly silicon, Rayleigh scattered light can be collected by focusing an appropriate infrared laser beam on the sample. The minute points appearing in the captured image of the cleavage plane 50b of the wafer correspond to the BMD 52. By counting the number of BMD 52 within a predetermined depth region, the BMD density within the said depth region can be calculated. The wafer surface 50a is regarded as having a depth of zero. The BMD density in the surface layer portion 53 within 30 μm from the wafer surface 50a is evaluated as the surface layer BMD density, and the BMD density in the bulk portion 54 deeper than 30 μm, for example, from 50 to 300 mm from the wafer surface, is evaluated as the bulk BMD density.

[0048] The density of the BMD 52 is calculated by dividing the number of BMD 52 contained in a rectangular parallelepiped formed by the scan width (standard condition: 125 μm) corresponding to the lateral width of the captured image of the cleavage plane 50b, the depth corresponding to the spot diameter of the infrared laser beam (standard condition: 8 μm), and an arbitrary depth direction distance, by the volume of the rectangular parallelepiped, and corresponds to the number of BMD 52 per unit volume (cm 3 ). By widening the scan width to, for example, 398 μm, the measurement accuracy of the BMD density can be improved. Since the wafer is cleaved and destroyed in the measurement of the BMD density, the characteristics related to the test of a certain wafer from a certain wafer batch are regarded as applicable to the entire said wafer batch.

[0049] The silicon wafer heat-treated as described above is taken out from the RTA furnace and put on the market as a so-called annealed silicon wafer. The density of oxygen precipitates generated in the surface layer portion up to 30 μm from the surface of the silicon wafer according to the present embodiment is 1.0×10 7 ~1.0×10 8 cm -3and is low density. Also, the BMD layer, which refers to the layer of oxygen precipitates, is robust. The robustness here takes into account the change in the density of oxygen precipitates (BMD) from lower heat treatments of less than about 1000 °C to higher heat treatments of 1000 °C or more, which is the range of heat treatment in the manufacturing process of semiconductor integrated circuits. That is, the ratio (d2 / d1) of the average density of oxygen precipitates (second bulk density d2) generated in the bulk part by high-temperature heat treatment to the average density of oxygen precipitates (first bulk density d1) generated in the bulk part by low-temperature heat treatment is 0.74 to 1.02, and the change in the density of oxygen precipitates due to heat treatment is within 30%. Even after the silicon wafer has received the desired heat treatment in the manufacturing process of semiconductor devices, the average density of oxygen precipitates in the wafer is about 4×10 8 ~1×10 10 / cm 3 within the range, and the rate of variation within this range remains within ±30%, more preferably ±15%, even more preferably within the range of ±10%, and even more preferably within the range of ±5%. In this way, the silicon wafer according to this embodiment contains a high density of thermally stable oxygen precipitation nuclei that are not affected by the customer's heat treatment, and thus can improve the quality and reliability of semiconductor devices such as BCD devices.

[0050] An epitaxial silicon film may be formed on the surface of the silicon wafer that has received the first to third heat treatments S21 to S23. When forming an epitaxial silicon film, since the silicon wafer (silicon substrate) is exposed to a high temperature of about 1150 °C, if the oxygen precipitation nuclei in the silicon wafer are thermally unstable, the oxygen precipitation nuclei may disappear after device heat treatment, and the oxygen precipitate density may decrease significantly. However, according to this embodiment, since the oxygen precipitation nuclei are thermally stable, a decrease in the oxygen precipitate density can be suppressed, and a decrease in gettering ability and wafer strength can be prevented.

[0051] Both gettering ability and slip resistance are required for silicon wafers used in the manufacture of power semiconductor devices such as BCD devices. To satisfy such wafer characteristics, at least about 4×10 8 / cm 3, preferably about 1×10 9 / cm 3 of oxygen precipitates are considered necessary in the silicon wafer after device heat treatment. For example, in the case of a conventional annealed silicon wafer manufactured by the technique of Japanese Patent Application Laid-Open No. 2021-168382, even if there is a high-temperature heat treatment such as an epitaxial growth process in the first stage of the device process, about 4×10 8 / cm 3 or more oxygen precipitate density can be ensured. However, as long as a sufficient device formation region can be secured, the oxygen precipitate density in the surface layer portion could not be reduced.

[0052] However, in the method for manufacturing a silicon wafer according to the present embodiment, oxygen precipitate nuclei (as grown nuclei) grown during crystal growth are eliminated by rapid heating and cooling at about 1210 to 1250°C, and new minute oxygen precipitate nuclei inside the wafer can be generated and grown by heat treatment at about 800 to 975°C for a relatively long time of about 2 to 10 minutes continuously. The oxygen precipitate nuclei generated and grown inside the wafer become thermally stable, and regardless of what heat treatment the customer receives, high-density oxygen precipitates can be generated. Furthermore, by continuously performing a high-temperature heat treatment at about 1150 to 1250°C for about 5 to 15 minutes, the minute oxygen precipitate nuclei can be further stabilized, and extra vacancies inside the wafer can be diffused outward to achieve both further stabilization of the oxygen precipitate nucleus density and reduction of the oxygen precipitate nucleus density in the surface layer.

[0053] As described above, the preferred embodiments of the present invention have been described. However, 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, and it goes without saying that those are also included in the scope of the present invention.

Examples

[0054] <Preview of three-stage heat treatment> A p-type silicon single crystal ingot with a diameter of 300 mm and a plane orientation of (100) was grown by the CZ method. A CZ silicon wafer was fabricated by slicing the silicon single crystal ingot. Subsequently, the CZ silicon wafer was heat-treated to prepare two samples of annealed silicon wafers according to Example A1 and Comparative Examples A1 to A3.

[0055] In the preparation of the annealed silicon wafer according to Example A1, a silicon wafer (CZ silicon wafer) with an oxygen concentration of 8×10 17 atom / cm 3 (ASTM F-121, 1979) was used, and a three-step heat treatment process of performing the first heat treatment (high temperature 1) → the second heat treatment (low temperature) → the third heat treatment (high temperature 2) in sequence was carried out using an RTA apparatus. Specifically, room temperature input → heating at 50°C / sec → holding at 1250°C for 10 seconds → cooling at 70°C / sec → holding at 900°C for 5 minutes → heating at 50°C / sec → holding at 1200°C for 5 minutes → cooling at 10°C / sec → taking out at room temperature were performed. For the atmosphere gas during the first heat treatment, Ar gas containing ammonia was used, and for the atmosphere gases during the second and third heat treatments, Ar gas without ammonia was used. Thus, a sample of the annealed silicon wafer according to Example A1 was obtained.

[0056] In the preparation of the annealed silicon wafer according to Comparative Example A1, heat treatment was carried out under the same conditions as in Example A1 except that the temperature of the first heat treatment was 1150°C. Thus, a sample of the annealed silicon wafer according to Comparative Example A1 was obtained.

[0057] In the preparation of the annealed silicon wafer according to Comparative Example A2, heat treatment was carried out under the same conditions as in Example A1 except that the temperature of the third heat treatment was 1000°C and its holding time was 1 minute.

[0058] In the preparation of the annealed silicon wafer according to Comparative Example A3, the oxygen concentration was 11×10 17 atom / cm 3Using the silicon wafers of (ASTM F-121, 1979), heat treatment was carried out under the same conditions as in Example A1, except that the temperature of the first heat treatment was 1150 °C, the temperature of the third heat treatment was 1000 °C, and the holding time was 1 minute.

[0059] Table 1 shows a summary of the heat treatment conditions of Example A1 and Comparative Examples A1 to A3.

[0060]

Table 1

[0061] Next, one of the two samples of each annealed silicon wafer was subjected to a combination of heat treatment assuming the initial heat history of the device process and heat treatment to manifest oxygen precipitation nuclei (first evaluation heat treatment), and the other sample was subjected to a combination of heat treatment simulating the epitaxial film formation process and heat treatment to manifest oxygen precipitation nuclei (second evaluation heat treatment). The first evaluation heat treatment was a two-step heat treatment in which a low-temperature heat treatment at 780 °C for 3 hours and a visualization heat treatment at 950 °C for 16 hours were performed in sequence. Also, the second evaluation heat treatment was a two-step heat treatment in which a high-temperature heat treatment at 1150 °C for 2 minutes and a visualization heat treatment at 1000 °C for 16 hours were performed in sequence.

[0062] Figure 6 is a schematic diagram of an evaluation procedure for determining the stability and uniformity of the manufactured silicon wafers.

[0063] As shown in FIG. 6, the silicon wafer 71 to be evaluated is cleaved and divided into two parts. The A part 72 is subjected to a low-temperature heat treatment 74 and a precipitate visualization heat treatment 76 in sequence, and the B part 73 is subjected to a high-temperature heat treatment 75 and a precipitate visualization heat treatment 76 in sequence. Alternatively, two wafers from the prepared wafer batch may be used as representing the characteristics related to the entire batch. Next, each of the wafer parts is subjected to an HF treatment 77 to remove the oxide film from the surface, and then optical scattering tomography 78 is used to determine the oxygen precipitate density distribution thereof. In this way, the oxygen precipitates in each of the two parts are evaluated, and the stability of the wafer, that is, the ratio of the BMD density resulting from the results of each part subjected to the evaluation heat treatment at different temperatures and different holding times, can be determined. Since the above evaluation procedure is destructive, the characteristics related to the test of a wafer from a certain wafer batch may be attributed to the entire wafer batch without problem.

[0064] Next, for each sample after the evaluation heat treatment, at an interval of about 5 mm (30 measurement points) in an arbitrary radial direction from the center to the edge of the wafer, the BMD density of the surface layer 30 μm and the BMD density of the bulk part deeper than 30 μm from the surface layer were measured by an infrared scattering tomography apparatus, respectively, and the average value was obtained. The diameter of the infrared laser light of the infrared scattering tomography apparatus was 8 mm under standard conditions, and the measurement range (scan width) per measurement point was 398 μm, which is wider than the standard conditions, in order to measure the BMD density of the surface layer as accurately as possible. Also, as an index of stability, the ratio (BMD density ratio d2 / d1) of the bulk BMD density (second bulk density d2) after the second evaluation heat treatment to the bulk BMD density (first bulk density d1) after the first evaluation heat treatment was obtained. Furthermore, as an index of uniformity, the ratio d min of the minimum value d max to the maximum value d max / d min of the 30-point bulk BMD density measured in the radial direction was used. The evaluation results are shown in Table 2.

[0065]

Table 2

[0066] (Example A1) In Example A1, the bulk BMD density after the first evaluation heat treatment was 6.6×10 9 cm -3 , and the bulk BMD density after the second evaluation heat treatment was 6.5×10 9 cm -3 , resulting in a bulk BMD density ratio of 0.98. It was confirmed that there was almost no difference in the bulk BMD density after the two evaluation heat treatments and that it was very stable. Also, the surface layer BMD density after the first evaluation heat treatment was 2.1×10 7 cm -3 , and the surface layer BMD density after the second evaluation heat treatment was also 2.1×10 7 cm -3 , confirming that the BMD density was more than two orders of magnitude lower compared to the bulk BMD density. Regarding the uniformity of the BMD density, the ratio of the maximum value d min to the minimum value d max of the BMD density in the wafer diameter direction (d max / d min ) was almost 1 (2 or less), confirming that it was good.

[0067] (Comparative Example A1) In Comparative Example A1, the BMD density after the first evaluation heat treatment was 9.3×10 8 cm -3 , and the BMD density after the second evaluation heat treatment was also 9.3×10 8 cm -3 , resulting in a bulk BMD density ratio of 1.00. Thus, it was confirmed that the bulk BMD density after the evaluation heat treatment was very stable. Also, regarding the uniformity of the BMD density, the ratio of the maximum value d min to the minimum value d max of the BMD density in the wafer diameter direction (d max / d min ) was almost 1 (2 or less), confirming that it was good. However, regarding the surface layer BMD density, the surface layer BMD density after the first evaluation heat treatment was 6.1×10 8 cm -3 , and the surface layer BMD density after the second evaluation heat treatment was 5.8×10 8 cm -3As a result, an increase in the surface BMD density was observed. This is presumably because the temperature of the first heat treatment was low, and the effect of eliminating oxygen precipitates generated during the crystal growth stage was not sufficiently obtained.

[0068] (Comparative Example A2) In Comparative Example A2, the BMD density after the first evaluation heat treatment was 6.5×10 9 cm -3 and the BMD density after the second evaluation heat treatment was 2.1×10 8 cm -3 resulting in a bulk BMD density ratio of 0.03. Thus, when the temperature of the third heat treatment was low and the time was short, due to insufficient bonding of oxygen precipitation nuclei, it was confirmed that the BMD density decreased after the second evaluation heat treatment including a high-temperature heat treatment at 1150°C for 2 minutes simulating the epitaxial film formation process. Also, with the decrease in the BMD density after the second evaluation heat treatment, the uniformity of the BMD density also deteriorated. Regarding the surface BMD density, both the surface BMD density after the first evaluation heat treatment and the surface BMD density after the second evaluation heat treatment were 2.1×10 7 cm -3 resulting in a density as low as the 10 7 cm -3 level.

[0069] (Comparative Example A3) In Comparative Example A3, since the oxygen concentration was high, a stable and uniform bulk BMD density could be ensured. On the other hand, the surface BMD density after the first evaluation heat treatment was 7.0×10 8 cm -3 and the surface BMD density after the second evaluation heat treatment was 6.5×10 8 cm -3 resulting in an increase in the surface BMD density.

[0070] (Evaluation of the First Heat Treatment Step) The effect of differences in heating conditions in the first heat treatment step on the stability and uniformity of the BMD density of the silicon wafer after the evaluation heat treatment was evaluated. The oxygen concentration of the silicon wafer used was 8×10 17 atoms / cm 3The second heat treatment and the third heat treatment were set under common conditions. Specifically, the second heat treatment was a low-temperature holding at 900°C for 5 minutes performed in an Ar atmosphere. The third heat treatment was a high-temperature holding at 1200°C for 5 minutes performed in an Ar atmosphere.

[0071] In Examples B1, B2, and Comparative Example B1, the temperature of the first heat treatment was all set to 1210°C, and the holding times were 20 seconds, 60 seconds, and 10 seconds, respectively. In Examples B3 and B4, the temperature of the first heat treatment was all set to 1250°C, and the holding times were 10 seconds and 60 seconds, respectively. Table 3 shows a summary of the heat treatment conditions for Examples B1 to B4 and Comparative Example B1. Table 4 shows the evaluation results.

[0072]

Table 3

[0073]

Table 4

[0074] 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 at the 10 9 cm -3 level, and the BMD density ratio was also within the range of 0.90 to 1.02. That is, it was confirmed that the bulk BMD density was stable regardless of the difference in the subsequent first and second evaluation heat treatments.

[0075] 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 at a low density level of 10 7 cm -3 level, but in Comparative Example B1, the surface layer BMD density after the first and second evaluation heat treatments was at a high density level of 10 8 cm -3 level. 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 layer BMD density did not decrease sufficiently.

[0076] Regarding the uniformity of the bulk BMD density, in any of Examples B1 to B4 and Comparative Example B1, the minimum value d of the bulk BMD density in the wafer radial direction min with respect to the maximum value d max of the ratio (d max / d min ) was less than 2, and no deterioration in the in-plane uniformity of the bulk BMD density was observed.

[0077] <Evaluation of the Second Heat Treatment Step> The influence of the differences in heating conditions in the second heat treatment step on the stability and uniformity of the BMD density of the silicon wafer after the evaluation heat treatment was evaluated. The oxygen concentration of the bulk silicon wafer used was 8×10 17 atoms / cm 3 , and the first heat treatment and the third heat treatment were set to common conditions. Specifically, the first heat treatment was a high-temperature RTA at 1250°C for 10 seconds performed in an Ar atmosphere containing NH3. The third heat treatment was a high-temperature holding at 1200°C for 5 minutes performed in an Ar atmosphere.

[0078] In Examples C1, C2, and Comparative Example C5, the temperature of the second heat treatment was all set to 800°C, and the holding times were 2 minutes, 10 minutes, and 1 minute, respectively. In Examples C3, C4, and Comparative Example C6, the temperature of the second heat treatment was all set to 900°C, and the holding times were 2 minutes, 10 minutes, and 1 minute, respectively. In Examples C5, C6, the temperature of the second heat treatment was all set to 975°C, and the holding times were 5 minutes and 10 minutes, respectively. In Comparative Examples C1, C2, the temperature of the second heat treatment was all set to 775°C, and the holding times were 2 minutes and 10 minutes, respectively. In Comparative Examples C3, C4, the temperature of the second heat treatment was all set to 775°C, and the holding times were 2 minutes and 10 minutes, respectively. Table 5 shows a summary of the heat treatment conditions according to Examples C1 to C6 and Comparative Examples C1 to C6. Table 6 shows the evaluation results.

[0079]

Table 5

[0080]

Table 6

[0081] 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 level, and the BMD density ratio was also in the range of 0.74 to 0.95. That is, regardless of the difference in the subsequent evaluation heat treatment conditions, it was confirmed that the bulk BMD density was generally stable.

[0082] On the other hand, in Comparative Examples C1 to C6, the bulk BMD density after the second evaluation heat treatment became smaller than the bulk BMD density after the first evaluation heat treatment, and the bulk BMD density ratio was less than 0.5. When the temperature of the second heat treatment was too low or too high, it is considered that the BMD nuclei in the bulk did not grow and disappeared by receiving the second evaluation heat treatment. Also, even if the temperature of the second heat treatment was appropriate, if the holding time was too short, it is considered that the BMD nuclei in the bulk did not grow and disappeared by receiving the second evaluation heat treatment including the heat treatment simulating the epitaxial film formation process.

[0083] Regarding the surface layer BMD density, in both 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 level of low density. That is, regardless of the difference in the heat treatment conditions received later, it was confirmed that the surface layer BMD density was stable at a low density.

[0084] Regarding the uniformity of the bulk BMD density, similar to the evaluation of the stability of the bulk BMD density, good results were obtained for Examples C1 to C6. However, for Comparative Examples C1 to C6, the ratio of the maximum value d min to the minimum value d max of the bulk BMD density (d max / d min) became larger than 2, and deterioration of the uniformity of the bulk BMD density was observed. It is considered that the oxygen precipitation nuclei were not sufficiently stabilized.

[0085] <Evaluation of the Third Heat Treatment Step> The influence of differences in heating conditions in the third heat treatment step on the stability and uniformity of the BMD density of the silicon wafer after the evaluation heat treatment was evaluated. The oxygen concentration of the silicon wafer used was 8×10 17 atoms / cm 3 and the first and second heat treatments were under common conditions. Specifically, the first heat treatment was a high-temperature RTA at 1250°C for 10 seconds in an Ar atmosphere containing NH3. The second heat treatment was a low-temperature holding at 900°C for 5 minutes in an Ar atmosphere.

[0086] In Examples D1, D2, and D3, the temperature of the third heat treatment was all 1150°C, and the holding times were 5 minutes, 10 minutes, and 15 minutes, respectively. In Examples D4, D5, and D6, the temperature of the third heat treatment was all 1200°C, and the holding times were 5 minutes, 10 minutes, and 15 minutes, respectively. In Examples D7, D8, and D9, the temperature of the third heat treatment was all 1250°C, and the holding times were 5 minutes, 10 minutes, and 15 minutes, respectively. In Comparative Examples D1, D2, and D3, the temperature of the third heat treatment was all 1140°C, and the holding times were 5 minutes, 10 minutes, and 15 minutes, respectively. Table 7 shows a summary of the heat treatment conditions for Examples D1 to D6 and Comparative Examples D1 to D6. The evaluation results are shown in Table 8.

[0087]

Table 7

[0088]

Table 8

[0089] 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 10 9 cm-3 It became the level, and the BMD density ratio was also within the range of 0.94 to 1.00. That is, regardless of the difference in the subsequent first and second evaluation heat treatments, it was confirmed that the bulk BMD density was stable.

[0090] On the other hand, in Comparative Examples D1 to D3, the bulk BMD density after the second evaluation heat treatment became smaller than the bulk BMD density after the first evaluation heat treatment, and the bulk BMD density ratio was significantly less than 0.5. When the temperature of the third heat treatment was too low, it is considered that the BMD nuclei in the bulk portion did not grow and disappeared by receiving the second evaluation heat treatment including the heat treatment simulating the epitaxial film formation process.

[0091] Regarding the surface layer BMD density, in all 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 and had a low density level.

[0092] Regarding the uniformity of the bulk BMD density, different from the evaluation of the stability of the bulk BMD density, not only in Examples D1 to D9 but also in Comparative Examples D1 to D3, good results were obtained. That is, the ratio (d min ) of the maximum value d max to the minimum value d max / d min ) of the bulk BMD density was 2 or less, and the in-plane uniformity of the bulk BMD density was good.

[0093] <Evaluation of Oxygen Concentration of Silicon Wafer> It was evaluated how the difference in the oxygen concentration of the silicon wafer affects the stability and uniformity of the BMD density of the silicon wafer after the three-step heat treatment and the evaluation heat treatment. In Example E1, a low-oxygen bulk silicon wafer with an oxygen concentration of 7×10 17 atoms / cm 3 was used. In Example E2, a bulk silicon wafer with an oxygen concentration of 10×10 17 atoms / cm 3 was used. In Comparative Example E1, the oxygen concentration was 11×10 17atoms / cm 3 A bulk silicon wafer was used. In Comparative Example E2, the oxygen concentration was 6 × 10 17 atoms / cm 3 of a low-oxygen bulk silicon wafer was used. In the three-step heat treatment, for each bulk silicon wafer, the first heat treatment was performed at 1250°C for 10 seconds, the second heat treatment was performed at 900°C for 5 minutes, and the third heat treatment was performed at 1200°C for 5 minutes. Table 9 shows a summary of the differences in oxygen concentration among Examples E1 and E2 and Comparative Examples E1 and E2. Table 10 shows the evaluation results.

[0094]

Table 9

[0095]

Table 10

[0096] As shown in Table 10, in Examples E1 and E2, the bulk BMD density and the surface layer BMD density were good.

[0097] On the other hand, in Comparative Example E1 using a bulk silicon wafer with an oxygen concentration of 11 × 10 17 atoms / cm 3 the bulk BMD density was good, but the surface layer BMD density became high. The in-plane uniformity of the bulk BMD density was good.

[0098] In Comparative Example E2 using a silicon wafer with an oxygen concentration of 6 × 10 17 atoms / cm 3 the bulk BMD density after the second evaluation heat treatment became smaller than the bulk BMD density after the first evaluation heat treatment, and the bulk BMD density ratio was less than 0.5. Regarding the uniformity of the bulk BMD density, the ratio of the maximum value d min to the minimum value d max of the bulk BMD density after the second evaluation heat treatment (d max / d min) became 13.3, and similar to the evaluation of the stability of the bulk BMD density, a significant deterioration in the in-plane uniformity of the bulk BMD density was observed after the second evaluation heat treatment. The in-plane uniformity of the bulk BMD density after the first evaluation heat treatment was good. Regarding the surface layer BMD density, extremely good results were obtained where no BMD was observed in the surface layer after the first and second evaluation heat treatments.

[0099] <Evaluation of the Influence by Epitaxial Growth> An epitaxial film was formed on a wafer manufactured by performing three-stage heat treatment, and the stability of the BMD density after epitaxial growth was confirmed. As shown in Table 11, in Examples F1, F2, and F3, the growth temperature was all 1050°C, and the holding times were 1 minute, 2 minutes, and 5 minutes respectively. In Examples F4, F5, and F6, the growth temperature was all 1150°C, and the holding times were 1 minute, 2 minutes, and 5 minutes respectively. The thickness of the obtained epitaxial films was 2 μm in Examples F1 and F4, 4 μm in Examples F2 and F5, and 10 μm in Examples F3 and F6.

[0100] Among the evaluation heat treatments after epitaxial growth, the first evaluation heat treatment was a two-stage heat treatment that sequentially performed a low-temperature heat treatment at 780°C for 3 hours and a visualization heat treatment at 950°C for 16 hours. The second evaluation heat treatment was only a visualization heat treatment at 1000°C for 16 hours, omitting the high-temperature heat treatment at 1150°C for 2 minutes that simulated the epitaxial film formation process. The evaluation results are shown in Table 12.

[0101]

Table 11

[0102]

Table 12

[0103] As shown in Table 12, under any epitaxial growth conditions, the stability and uniformity of the bulk BMD density and the uniformity of the surface layer BMD density are good, and it was confirmed that the bulk BMD density does not decrease even when epitaxial growth is performed on a silicon wafer manufactured by three-step heat treatment.

Explanation of symbols

[0104] S11 Process of manufacturing a silicon single crystal ingot S12 Process of fabricating a silicon wafer S13 Process of heat-treating a silicon wafer S21 First heat treatment step S22 Second heat treatment step S23 Third heat treatment step 30 Standby temperature 32 Temperature increase 34 Temperature decrease 36 Temperature increase 40 Silicon wafer 40a Upper zone 40b Lower zone 41 Tiny oxygen precipitation nuclei (generated during crystal growth) 42 Frenkel pairs 43 Si3N4 layer 44, 44a, 44b Vacancies 45 Interstitial silicon atoms 46 DZ 47 Oxygen precipitation nuclei 47a Small oxygen precipitation nuclei 48 Epitaxial layer 50 Silicon wafer 50a Wafer surface (main surface) 50b Cleavage plane 51 Infrared laser light 52 BMD (oxygen precipitates) 53 Surface layer part 54 Bulk part 71 Silicon wafer 72 Part A of the wafer 73 Part B of the wafer 74 Low-temperature heat treatment 75 High-temperature heat treatment 76 Precipitate visualization heat treatment 77 HF treatment 78 Light scattering tomography

Claims

1. It has a surface layer portion from the surface to a depth of 30 μm and a bulk portion deeper than the surface layer portion, the density of oxygen precipitates generated in the surface layer portion by the first evaluation heat treatment is 1.0×10 ７ to 1.0×10 ８ cm －３ and the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is 1.0×10 ９ to 7.0×10 ９ cm －３ and when the average density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is defined as the first bulk density and the average density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment is defined as the second bulk density, the ratio of the second bulk density to the first bulk density is in the range of 0.74 to 1.02, the first evaluation heat treatment is a two-step heat treatment in which a visualization heat treatment is performed after heat treatment at 780°C for 3 hours, the second evaluation heat treatment is a two-step heat treatment in which the visualization heat treatment is performed after heat treatment at 1150°C for 2 minutes, and the visualization heat treatment is a heat treatment at 950 to 1000°C for 16 hours. A silicon wafer characterized by this.

2. The silicon wafer according to claim 1, wherein both the ratio of the maximum value to the minimum value of the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment and the ratio of the maximum value to the minimum value of the density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment are 2 or less.

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 generated in the bulk portion by the first evaluation heat treatment is 1.30 or less, and the ratio of the maximum value to the minimum value of the density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment is 1.32 or less.

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

5. A silicon substrate, An epitaxial silicon film formed on the surface of the silicon substrate, The silicon substrate has a surface layer portion with a depth of 30 μm from the surface and a bulk portion deeper than the surface layer portion, The density of oxygen precipitates generated in the surface layer by the first evaluation heat treatment is 1.0×10 ７ ~ 1.0×10 ８ cm －３ and The density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is 1.0×10 ９ ~ 7.0×10 ９ cm －３ and When the average density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is defined as the first bulk density and the average density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment is defined as the second bulk density, the ratio of the second bulk density to the first bulk density is within the range of 0.98 to 1.02, The first evaluation heat treatment is a two-step heat treatment in which a visualization heat treatment is performed after a heat treatment at 780°C for 3 hours, The second evaluation heat treatment is the visualization heat treatment, The visualization heat treatment is a heat treatment at 950 to 1000°C for 16 hours. A silicon wafer characterized by this.

6. The ratio of the maximum value to the minimum value of the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment and the ratio of the maximum value to the minimum value of the density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment are both 2 or less. The silicon wafer according to claim 5.

7. The ratio of the maximum value to the minimum value of the density of oxygen precipitates generated in the bulk portion by the first evaluation heat treatment is 1.29 or less, and the ratio of the maximum value to the minimum value of the density of oxygen precipitates generated in the bulk portion by the second evaluation heat treatment is 1.35 or less. The silicon wafer according to claim 6.

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

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

10. The rate of temperature increase to the first temperature and the rate of temperature increase from the second temperature to the third temperature are 10 to 50°C / second. The method for manufacturing a silicon wafer according to claim 8 or 9.

11. The rate of temperature decrease from the first temperature to the second temperature is 20 to 120°C / second. The method for manufacturing a silicon wafer according to claim 8 or 9.

12. The silicon wafer before being heat-treated in the first heat treatment step is cut out from a defect-free region of a silicon single crystal ingot in which there are no aggregates of interstitial silicon-type point defects and aggregates of vacancy-type point defects, the method for manufacturing a silicon wafer according to claim 8 or 9.

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