SILICON WAFERS AND MANUFACTURING PROCESSES FOR THEM

Abstract

[Problem] To provide a silicon wafer with small variations in specific resistance after heat treatment of the device and high mechanical strength, and a method for producing the same. [Solution] A silicon wafer 1 according to the present invention has a resistivity of 1000 Ω·cm or more, an interstitial oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3 and a decrease in oxygen concentration of no more than 0.5 × 10 17 cm -3 at three or more points on the wafer surface after a heat treatment for oxygen excretion assessment, which is carried out at 780 °C for 3 hours and at 1000 °C for 1 hour.

Description

TECHNICAL AREA

[0001] The present invention relates to a silicon wafer and a method for producing the same. STATE OF THE ART

[0002] Recently, the demand for high-frequency devices has increased with the widespread use of short-range radio communication technologies. Using high-frequency devices as power amplifiers leads to reduced power consumption and thus contributes to improved energy efficiency.

[0003] Compound semiconductors such as GaAs are frequently used as materials for high-frequency devices. GaN, in particular, has excellent physical properties, such as high electron mobility and a wide bandgap, and is therefore expected to be suitable for high-voltage, high-frequency devices. However, GaN substrates are very expensive, and thus substrates obtained by heteroepitaxial growth of GaN on a sapphire, GaAs, or SiC substrate are generally used; nevertheless, these substrates are still expensive compared to silicon wafers. Heteroepitaxial growth of GaN on a silicon wafer presents several challenges, and the development of a buffer layer to be grown between the silicon wafer and the GaN is underway.

[0004] For GaN heteroepitaxy on silicon, silicon wafers with high resistivity are used to suppress the reduction in electron mobility in GaN due to the parasitic capacitance of the silicon substrate. However, the CZ process for fabricating single-crystal silicon uses a quartz crucible, and therefore oxygen dissolved from the quartz crucible is present in the single-crystal silicon in a supersaturated state. This oxygen forms oxygen donors (heat donors) during the heat treatment process for device circuit formation, causing a problem where the wafer resistivity varies on the device manufacturer's side.

[0005] The oxygen donors present in silicon wafers therefore influence the wafer's resistivity. In commonly used wafers with low resistivity, which are doped to control the resistivity, the oxygen donors have only a minor effect on the wafer's resistivity, causing no problem in actual operation. On the other hand, in wafers with high resistivity and low dopant concentrations, the resistivity of n-type wafers decreases significantly with an increase in oxygen donors. In p-type wafers, although the resistivity initially increases significantly with increasing oxygen donor concentration, the conductivity type changes from p-type to n-type after a further increase in oxygen donors, resulting in a significant decrease in resistivity.

[0006] Patent literature 1 discloses, in order to suppress significant fluctuations in specific resistance caused by an increase in oxygen donors, a silicon wafer with high specific resistance, having a specific resistance of 100 Ω·cm or more, and an interstitial oxygen concentration of no more than 8 × 10 17 atoms / cm² 3 (ASTM F121-1979) and a bulk microdefect (BMD) density of 5 × 10 7 / cm 3 or less. This high resistivity silicon wafer exhibits an oxygen concentration of 8 × 10 17 atoms / cm² 3or less limited (ASTM F121-1979), thereby suppressing the formation of oxygen donors during heat treatment for circuit formation carried out on the device manufacturer's side, which in turn suppresses variations in resistivity caused by an increase in oxygen donors. Furthermore, the bulk microdefect (BMD) density is reduced to 5 × 10 7 / cm 3 or less limited, making it possible to reduce defects due to the presence of oxygen on the wafer surface.

[0007] Furthermore, patent literature 2 discloses a method for producing a single-crystal silicon wafer for an IGBT. In this method, single-crystal silicon with an interstitial oxygen concentration of 5 × 10⁻⁶ is used. 17 atoms / cm² 3 or more and not more than 8.5 × 10 17 atoms / cm² 3The silicon wafer is grown using the CZ process with a pull rate that allows for the growth of embedded, defect-free single-crystal silicon. A silicon wafer obtained from the resulting single-crystal silicon undergoes RTA treatment at a temperature in the range of 100 to 1200 °C for one minute or longer in a nitrogen-free atmosphere. This eliminates oxygen precipitation nuclei or OSF nuclei, enabling the suppression of oxygen precipitation even after heat treatment in an IGBT device fabrication process.

[0008] Patent literature 3 discloses that an initial silicon wafer with a specific resistance of 100 Ω·cm, an oxygen concentration of 14 × 10 17 atoms / cm² 3 or more (ASTM F121, 1979) and a density of ingrown defects of 1 × 10 3 cm -3or less, as demonstrated by secco etching, is subjected to a heat treatment to form oxygen precipitation nuclei at a temperature of 500 to 900 °C for 5 hours or longer in a non-oxidative gas atmosphere, followed by a heat treatment to grow oxygen precipitates at a temperature of 950 to 1050 °C for 10 hours or longer, thereby reducing the residual oxygen concentration in the wafer to 12 × 10 17 atoms / cm² 3 or is less controlled. LITERATURE ON THE STATE OF TECHNOLOGY PATENT LITERATURE Patent literature 1: Japanese patent disclosure publication no. 2005-145744 Patent literature 2: International publication no. WO2009 / 025342 brochure Patent Literature 3: Japanese Patent Publication No. 2007-235153 SUMMARY OF THE INVENTIONAL TASK THAT THE INVENTION IS INTENDED TO SOLVE

[0009] However, the conventional high resistivity silicon wafer disclosed in patent literature 1 has an oxygen concentration as low as 8 × 10 17 atoms / cm² 3 or lower, resulting in low mechanical strength of the wafer, causing problems such as slip generation at boot-wafer contact sections during heat treatment and increased wafer distortion during heat treatment to form a circuit due to the stress of a film formed on the wafer.

[0010] Furthermore, the single-crystal silicon wafer for an IGBT, disclosed in patent literature 2, is intended to suppress oxygen precipitation during heat treatment in an IGBT device manufacturing process by applying an RTA treatment to a wafer with low oxygen content and therefore has an oxygen concentration as low as 8.5 × 10 17 atoms / cm²3 or lower, which leads to a low mechanical strength of the wafer, as described in patent literature 1.

[0011] The conventional technology disclosed in patent literature 3 can promote oxygen precipitation by heat treatment to form oxygen precipitation nuclei and heat treatment to grow oxygen precipitates, thereby reducing the residual oxygen concentration in the wafer and suppressing the formation of oxygen donors. However, if high-density oxygen precipitates are formed in the wafer, the wafer's mechanical strength deteriorates due to the decrease in residual oxygen concentration, which can frequently cause slippage during a fixture manufacturing process. Furthermore, the aforementioned heat treatment requires a long treatment time of 15 hours or more, resulting in increased wafer manufacturing costs.

[0012] Therefore, it is an object of the present invention to provide a silicon wafer with small variations in specific resistance after heat treatment of the device and high mechanical strength, and a method for producing the same. MEANS TO SOLVENT THE PROBLEMS

[0013] The present invention was made based on the new knowledge that the amount of donor formation increases when the oxygen concentration decreases after heat treatment. A silicon wafer according to the present invention has a resistivity of 1000 Ω·cm or more and an interstitial oxygen concentration of more than 8.5 × 10⁻⁶. 17 cm -3 (ASTM F121-1979; the same applies below to the oxygen concentration) and not more than 17 × 10 17 cm -3 and a decrease in oxygen concentration of no more than 0.5 × 10 17 cm -3at three or more points on the wafer surface after a heat treatment for oxygen excretion assessment, which is carried out at 780 °C for 3 hours and at 1000 °C for 1 hour.

[0014] According to the present invention, the decrease in oxygen concentration after heat treatment of the device is small on the part of the device manufacturer, so that the amount of donor formation can be reduced, thereby making it possible to suppress a change in specific resistance due to an increase in the amount of donor formation. Since the interstitial oxygen concentration is more than 8.5 × 10 17 cm -3 Furthermore, if the oxygen concentration is low, a deterioration of the wafer's mechanical strength due to a low oxygen concentration can be prevented.

[0015] In the present invention, the specific resistance is preferably 3000 Ω·cm or more, and more preferably 5000 Ω·cm or more. Such a high specific resistance of the wafer enables the production of a high-quality and highly reliable high-frequency device.

[0016] The silicon wafer according to the present invention preferably has a reduction in oxygen concentration of no more than 0.5 × 10 17 cm -3 Oxygen deposition is assessed at ten or more points on the wafer surface after heat treatment. This can improve the manufacturing yield of high-frequency devices.

[0017] A method for producing a silicon wafer according to the present invention comprises the steps of: growing a single-crystal silicon ingot with a resistivity of 1000 Ω·cm or more and an interstitial oxygen concentration of more than 8.5 × 10 17cm -3 and no more than 17 × 10 17 cm -3 by the CZ process; producing an initial silicon wafer by processing the single-crystal silicon ingot; and applying an RTA treatment to the initial silicon wafer.

[0018] According to the present invention, it is possible to produce a silicon wafer with high specific resistance with a small decrease in the interstitial oxygen concentration even after heat treatment of the device.

[0019] In the present invention, the step of applying the RTA treatment preferably heats the initial silicon wafer in an argon gas atmosphere at a temperature in the range of 1100 to 1250 °C for 5 to 30 seconds. This makes it possible to produce a silicon wafer with high resistivity and a small decrease in interstitial oxygen concentration even after the heat treatment of the device.

[0020] A method for producing a silicon wafer according to the present invention comprises the steps of: growing a single-crystal silicon ingot with a resistivity of 1000 Ω·cm or more and an interstitial oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3 by the CZ process; and fabrication of an initial silicon wafer by processing the single-crystal silicon ingot, wherein the step of fabricating the single-crystal silicon ingot by the CZ process sets the crystal growth conditions such that a Pi region (interstitial silicon region of predominantly defect-free type) is wider than a Pv region (vacancy region of predominantly defect-free type) in a cross-section perpendicular to the crystal growth direction.

[0021] According to the present invention, it is possible to produce a silicon wafer with high specific resistance with a small decrease in the interstitial oxygen concentration even after heat treatment of the device.

[0022] In the present invention, the crystal growth conditions preferably include the crystal pulling rate. This makes it possible to produce a silicon wafer with high resistivity with a small decrease in the interstitial oxygen concentration even after heat treatment of the device. EFFECTS OF THE INVENTION

[0023] The present invention provides a silicon wafer with small variations in specific resistance after heat treatment of the device and high mechanical strength, and a manufacturing method for such a silicon wafer. BRIEF DESCRIPTION OF THE DRAWINGS Fig.Figure 1 is a schematic perspective view showing a configuration of a silicon wafer according to an embodiment of the present invention. Fig. Figure 2 is a flowchart illustrating a silicon wafer manufacturing process according to a first embodiment of the present invention. Fig. Figure 3 is a flowchart illustrating a silicon wafer manufacturing process according to a second embodiment of the present invention. Fig. Figure 4 is a schematic view illustrating the relationship between a crystal growing rate and a crystal defect distribution. Fig. Figure 5 is a graph showing measurement results of oxygen concentration distributions of the silicon wafers according to examples 1 to 10 and comparison examples 1 to 5 before heat treatment for oxygen precipitation evaluation. Fig.Figure 6 is a graph showing measurement results of the decrease in oxygen concentration after heat treatment for the purpose of evaluating oxygen excretion. Fig. Figure 7 is a graph showing measurement results of the specific resistance after heat treatment for oxygen excretion evaluation, arranged by manufacturing conditions. Fig. Figure 8 is a graph showing measurement results of the specific resistance after heat treatment for oxygen excretion evaluation, arranged by specific resistance levels. Fig. Figure 9 is a graph that represents the relationship between a decrease in oxygen concentration and a quantity of oxygen donor production. MODE FOR EXECUTING THE INVENTION

[0024] Preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0025] Fig. Figure 1 is a schematic perspective view showing a configuration of a silicon wafer according to an embodiment of the present invention.

[0026] As in Fig.As shown in Figure 1, a silicon wafer 1 is a substantially circular substrate made of single-crystal silicon and has a front surface 1a, a rear surface 1b, and an outer peripheral surface 1c. The size (diameter R) of the silicon wafer 1 is not particularly limited, but is preferably 200 mm or more and more preferably 300 mm or more. This is because, as the wafer size increases, the problem of in-plane resistivity variation after heat treatment of the device becomes more severe. Although the thickness T of the silicon wafer 1 is not particularly limited, the thickness of a 200 mm wafer is, for example, 725 µm and the thickness of a 300 mm wafer is, for example, 775 µm.As shown, preferably a notch 1d is formed in the outer peripheral section (outer peripheral surface 1c) of the silicon wafer 1 to clearly indicate the crystal orientation of the single-crystal silicon; alternatively, an orientation plane can be formed.

[0027] The silicon wafer 1 preferably has a (111) plane orientation. A silicon wafer with a (111) plane orientation is suitably used as a substrate material for high-frequency devices using compound semiconductors such as GaN.

[0028] The silicon wafer 1 according to the present embodiment is a silicon wafer with high resistivity, exhibiting a resistivity of 1000 Ω·cm or more. The resistivity of the silicon wafer 1 is preferably 3000 Ω·cm or more and more preferably 5000 Ω·cm or more. This is because, as described above, a silicon wafer with high resistivity is suitable as a substrate material for high-frequency devices. To control the resistivity, the silicon wafer 1 is doped with a p-type dopant, such as boron, or an n-type dopant, such as phosphorus.

[0029] The silicon wafer 1 according to the present embodiment is characterized by a suppressed decrease in oxygen concentration when subjected to a heat treatment of the device or a predetermined heat treatment for oxygen precipitation evaluation, which simulates the heat treatment of the device, even if the interstitial oxygen concentration is relatively high. In particular, the decrease in oxygen concentration of the silicon wafer after the heat treatment for oxygen precipitation evaluation, which is carried out at 780 °C for 3 hours and at 1000 °C for 1 hour, is 0.5 × 10 17 cm -3 or less. As a result of the suppressed decrease in oxygen concentration, the amount of donor formation can be reduced. This makes it possible to suppress changes in the resistivity of a silicon wafer with high resistivity due to an increase in the amount of donor formation.

[0030] In the CZ process, single-crystal silicon is grown from a melt obtained by melting a polycrystalline silicon material loaded into a quartz crucible, and therefore contains oxygen, which is released from the quartz crucible at a concentration of approximately 10 × 10 17 atoms / cm² 3 This oxygen exerts complex effects, including adverse effects such as inducing crystal defects in the wafer, which cause failures in the device properties, and beneficial effects such as improving the mechanical strength of the wafer during a semiconductor device manufacturing process to suppress wafer deformation and forming oxygen precipitates that have a getter effect of trapping heavy metals that can cause operational defects in the semiconductor device.

[0031] Oxygen atoms in silicon are generally electrically neutral and do not affect the resistivity. However, a quartz crucible is used to grow single-crystal silicon by the CZ process, and therefore the single-crystal silicon contains oxygen in a supersaturated state. It is known that when heat treatment is performed at a low temperature of about 450 °C, a large number of oxygen atoms aggregate to form oxygen clusters, which constitute an oxygen donor that releases electrons. In the present embodiment, the reliability of the high-resistivity silicon wafer can be increased by suppressing changes in the wafer's resistivity due to an increase in such oxygen donors.

[0032] A process for manufacturing the silicon wafer 1 is described in detail below.

[0033] Fig.Figure 2 is a flowchart illustrating a silicon wafer manufacturing process according to a first embodiment of the present invention.

[0034] As in Fig. Figure 2 shows that in the production of a silicon wafer according to the present embodiment, a single-crystal silicon ingot with a resistivity of 1000 Ω·cm or more and an oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3 Bred using the CZ method (step S11).

[0035] The single-crystal silicon ingot is then processed to obtain an initial silicon wafer (step S12). The initial silicon wafer is generally formed by successively applying external peripheral grinding, cutting, lapping, etching, double-sided polishing, single-sided polishing, cleaning, and the like to the single-crystal silicon ingot.

[0036] The initial silicon wafer is then subjected to RTA treatment (step S13). RTA (Rapid Thermal Annealing) is a short-term heat treatment in which wafers are heated individually using an infrared lamp and is performed using a single-wafer heat treatment device. RTA is preferably carried out in an argon gas atmosphere at a temperature in the range of 1100 to 1250 °C for 5 to 30 seconds. This RTA treatment eliminates oxygen precipitation nuclei and OSF nuclei in the wafer, thereby suppressing a decrease in oxygen concentration after heat treatment by the device or after heat treatment for oxygen precipitation evaluation, which simulates heat treatment by the device.

[0037] The preceding steps complete the silicon wafer 1 according to the present embodiment.

[0038] In the silicon wafer fabrication process according to the present embodiment, single-crystal silicon grown by the CZ process is processed to obtain a silicon wafer with high resistivity. An RTA treatment is then applied to the resulting wafer, thereby pre-eliminating oxygen precipitation nuclei and OSF nuclei within the wafer and suppressing oxygen precipitation after heat treatment. Consequently, a decrease in oxygen concentration after heat treatment is suppressed, and the amount of donor formation is not significantly increased. This, in turn, prevents changes in the resistivity of the high-resistivity silicon wafer. As a result, variations in resistivity across the plane can be reduced.Since the interstitial oxygen concentration in the wafer is relatively high, the mechanical strength of the silicon wafer can also be improved, thereby preventing the occurrence of slippage and an increase in distortion.

[0039] Fig. Figure 3 is a flowchart illustrating a silicon wafer manufacturing process according to a second embodiment of the present invention.

[0040] As in Fig. Figure 3 shows that in the production of a silicon wafer with high resistivity according to the present embodiment, a single-crystal silicon ingot with a resistivity of 1000 Ω·cm or more and an oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3grown using the CZ process (step S21). In this stage, the crystal growth conditions, such as the crystal pull rate, are adjusted so that a Pi region (interstitial silicon region of predominantly defect-free type) is wider than a Pv region (vacancy region of predominantly defect-free type) in a cross-section perpendicular to the crystal growth direction.

[0041] It is known that the type and distribution of crystal defects contained in single-crystal silicon grown by the CZ process depends on a ratio V / G of a growth rate (crystal pulling rate) V of the single-crystal silicon to a temperature gradient G in the crystal in the pulling axis direction in a temperature range from the melting point to 1300 °C.

[0042] Fig. Figure 4 is a schematic view illustrating the relationship between a crystal growing rate and a crystal defect distribution.

[0043] As in Fig. As shown in Figure 4, when V / G is large, vacancies become excessive, leading to the formation of cavity defects, which are aggregates of vacancies. These cavity defects are crystal defects generally referred to as COPs (Crystal Originated Particles). Conversely, when V / G is small, interstitial silicon atoms become excessive, leading to the formation of dislocation clusters, which are aggregates of interstitial silicon atoms. Therefore, to produce a single crystal free of COPs and dislocation clusters, V / G must be tightly controlled.

[0044] Even a silicon wafer free of COPs and dislocation clusters, cut from single-crystal silicon grown under controlled V / G conditions, is not always homogeneous across its entire surface. Instead, it comprises a variety of regions that exhibit different behaviors after heat treatment. For example, between a region where COPs are generated and a region where dislocation clusters are generated, there are three regions: an OSF region, a Pv region, and a Pi region, in descending order of V / G.

[0045] The OSF range refers to a range containing OSF cores in the as-grown state, where OSFs (oxidation-induced stacking faults) are generated by thermal oxidation at a temperature of 1000 to 1200 °C for 1 to 10 hours. The Pv range refers to a range containing oxygen precipitation cores in the as-grown state, where oxygen precipitates are readily formed by a two-stage heat treatment involving a high-temperature step and a low-temperature step. The Pi range refers to a range containing very few oxygen precipitation cores in the as-grown state, where oxygen precipitates are unlikely to form even through heat treatment.

[0046] For single-crystal silicon to be defined as a defect-free crystal, it is necessary that the entire cross-section of the single-crystal silicon perpendicular to the drawing axis is a defect-free region. Here, the term "defect-free region" refers to a region that contains no embedded defects such as COPs or dislocation clusters, and in which no OSF ring is generated after the evaluation heat treatment; this is the Pv region or the Pi region.

[0047] To grow a defect-free crystal consisting of a Pv region or a Pi region with high yield while controlling the crystal growth rate V, the Pv-Pi span is preferably as wide as possible. In a broad sense, the term "Pv-Pi span" refers to an allowable range of the crystal growth rate V within which a specific region in single-crystal silicon can be made into a Pv region or a Pi region, while in a narrow sense, the term refers to a minimum value (Pv-Pi span in the plane) in the cross-section of the single-crystal silicon perpendicular to the growth axis. Since the temperature gradient G in the crystal is generally constant, the Pv-Pi span has a magnitude corresponding to a width of V / G from the Pv-OSF boundary to the Pi dislocation cluster boundary. Fig. 4 corresponds to.

[0048] In general, when controlling the growth of single-crystal silicon, the crystal growth rate is set within the Pv-Pi range, and in most cases, the Pv range is wider than the Pi range. However, in the present embodiment, the crystal growth rate V is set such that the Pi range is wider than the Pv range, and preferably the entire surface becomes a Pi range, thereby suppressing oxygen precipitation after heat treatment of the device. The crystal growth rate V thus set is preferably 0.94 to 0.98 times a median value of the Pv-Pi range.

[0049] The single-crystal silicon ingot is then processed to obtain a silicon wafer (step S22). As described above, the silicon wafer is formed by successively applying external peripheral grinding, cutting, lapping, etching, double-sided polishing, single-sided polishing, cleaning, and the like to the single-crystal silicon ingot. The preceding steps complete the silicon wafer 1 according to the present embodiment.

[0050] Although the silicon wafer fabrication process according to the present embodiment does not include RTA treatment applied to an initial silicon wafer in the first embodiment, the number of vacancies in the single-crystal silicon that can cause oxygen donors is reduced to a maximum during the crystal growth process. Thus, oxygen precipitation after heat treatment of the device can be suppressed without performing RTA treatment. Therefore, a decrease in oxygen concentration after heat treatment is suppressed, and the amount of donor formation is not significantly increased. This, in turn, can prevent changes in the resistivity of the high-resistivity silicon wafer. As a result, variations in resistivity across the plane can be reduced.Since the interstitial oxygen concentration in the wafer is relatively high, the mechanical strength of the silicon wafer can also be improved, thereby preventing the occurrence of slippage and an increase in distortion.

[0051] As described above, the silicon wafer according to the present embodiment has a specific resistance of 1000 Ω·cm or more, an interstitial oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3 Furthermore, the decrease in oxygen concentration of the silicon wafer after heat treatment for oxygen precipitation assessment, which is carried out at 780 °C for 3 hours and at 1000 °C for 1 hour, is 0.5 × 10 17 cm -3 or less. Thus, variations in the specific resistance of the wafer can be suppressed on the part of the device manufacturer.

[0052] Although the preferred embodiments of the present invention have been described, the present invention is not limited to the foregoing embodiments and various modifications may be made within the scope of protection of the present invention, and all such modifications are included in the present invention. [Examples]

[0053] A single-crystal silicon ingot with a diameter of approximately 300 mm, to which boron (p-type) or phosphorus (n-type) was added, was grown using the CZ process. The single-crystal silicon ingot was then processed to obtain a silicon wafer with a (111) plane orientation.

[0054] The resistivity of the silicon wafer was set to five levels: 100 Ω·cm, 1000 Ω·cm, 3000 Ω·cm, 5000 Ω·cm, and 10000 Ω·cm. Although the resistivity of the silicon wafer depends on the amount of dopant added and the cutting position of a single-crystal silicon ingot, the single-crystal silicon ingot was grown to obtain these resistivity values. Silicon wafers were then cut from the desired sections of the ingot. [Table 1] Samples Dosing agent specific resistance (Ω·cm) Manufacturing conditions Example 1 boron 100 Suppressed draw rate Example 2 boron 1000 Suppressed draw rate Example 3 boron 5000 Suppressed draw rate Example 4 boron 10000 Suppressed draw rate Example 5 phosphorus 3000 Suppressed draw rate Example 6 boron 100 RTA applied Example 7 boron 1000 RTA applied Example 8 boron 5000 RTA applied Example 9 boron 10000 RTA applied Example 10 phosphorus 3000 RTA applied See example 1 boron 100 - See example 2 boron 1000 - See example 3 boron 5000 - See example 4. boron 10000 - See example 5 phosphorus 3000 -

[0055] Examples 1 to 5 were silicon wafers with the five resistivity levels listed above, for which no measures were taken to reduce oxygen precipitation. Examples 1 to 5 were silicon wafers with the five resistivity levels listed above, cut from a single-crystal silicon ingot different from that used for Examples 1 to 5, for which the pull rate during crystal growth was reduced to 0.96 times that of Examples 1 to 5 to reduce oxygen precipitation. Examples 6 to 10 were silicon wafers obtained by applying an RTA treatment to silicon wafers cut from the same single-crystal silicon ingot as that used for Examples 1 to 5, in an argon atmosphere at 1100 °C for 30 seconds to reduce oxygen precipitation.

[0056] Oxygen concentration distributions of the silicon wafers were then measured according to Examples 1 to 10 and Comparison Examples 1 to 5 using FT-IR (QS-1200HP, manufactured by Nanometrix Inc.). Specifically, the oxygen concentration was measured at 15 points spaced 10 mm apart in a radial direction from the wafer center. The oxygen concentration measurement using FT-IR was performed according to SEMI MF1188-1107.

[0057] Fig. Figure 5 is a graph showing measurement results of oxygen concentration distributions of the silicon wafers according to examples 1 to 10 and comparison examples 1 to 5 before heat treatment for oxygen precipitation evaluation.

[0058] As in Fig.As shown in Figure 5, oxygen concentrations in the plane of the silicon wafers according to Examples 1 to 10 and Comparison Examples 1 to 5 were all uniform, and initial oxygen concentrations of these were approximately 13 × 10 17 cm -3 .

[0059] To clarify the relationship between a decrease in oxygen concentration and the amount of oxygen donor formation in the silicon wafers according to Examples 1 to 10 and Comparative Examples 1 to 5, a heat treatment for oxygen precipitation evaluation was performed at 780 °C for 3 hours and at 1000 °C for 1 hour to intentionally cause oxygen precipitation. Subsequently, a heat treatment for oxygen donor formation was performed at 400 °C for 20 minutes. Afterward, the oxygen concentration was measured at 15 points spaced 10 mm apart in a radial direction from the wafer center using FT-IR, and the difference between the oxygen concentration after and before the heat treatment was calculated to determine the decrease ΔOi in oxygen concentration at each measurement point.

[0060] Furthermore, the resistivity was measured at 15 points spaced 10 mm apart in a radial direction from the wafer center according to the four-probe method specified in JIS H 0602:1995. The amount of donor formation was then calculated from an Irvin curve based on post-heat treatment resistivity measurements for oxygen deposition evaluation and pre-heat treatment resistivity measurements, shown in Table 1.

[0061] Fig. Figure 6 is a graph showing measurement results of the decrease in oxygen concentration after heat treatment for the purpose of evaluating oxygen excretion.

[0062] As in Fig.As shown in Figure 6, in the wafers according to Comparative Examples 1 to 5, the decrease in oxygen concentration increased in the central and outer peripheral sections of the wafer, whereas in the wafers according to Examples 1 to 5 and 6 to 10, the decrease in oxygen concentration was suppressed compared to that in Comparative Examples 1 to 5. In particular, the decrease in oxygen concentration in the wafers according to Examples 6 to 10, to which the RTA treatment was applied, was very small and uniform across the wafer surface. That is, in the wafers according to Examples 6 to 10, the residual oxygen concentration after heat treatment for the oxygen precipitation assessment was approximately 13 × 10⁻⁶. 17 cm -3 .

[0063] Fig. 7 and Fig. Figure 8 shows graphs representing measurement results of the specific resistance after heat treatment for oxygen precipitation evaluation. The graph of Fig.7 is arranged by manufacturing conditions, and the graph of Fig. 8 is arranged by specific resistance levels.

[0064] As in Fig. 7 and Fig. As shown in Figure 8, the resistivity of the p-type silicon wafer according to Examples 1 and 6 and Comparative Example 1 after heat treatment for oxygen precipitation evaluation was 100 Ω·cm, which was the same as the resistivity before heat treatment for oxygen precipitation evaluation (initial resistivity). That is, there was no change in resistivity before and after heat treatment for oxygen precipitation evaluation, and no variation in resistivity in the plane was observed.

[0065] The resistivity of the p-type silicon wafers according to Examples 2 and 7 and Comparative Example 2 after heat treatment for oxygen precipitation evaluation was 1000 to 2000 Ω·cm (the initial resistivity before heat treatment was 1000 Ω·cm). In Comparative Example 2, an increase in resistivity was observed at the central and outer peripheral sections of the wafer, whereas in Examples 2 and 7, no such increase in resistivity was observed, and the resistivity was uniform across the wafer surface. That is, in Examples 2 and 7, an effect of suppressing a change in resistivity was confirmed.

[0066] The resistivity of the p-type silicon wafers according to Examples 3 and 8 and Comparative Example 3 after heat treatment for oxygen precipitation evaluation was approximately 5000 Ω·cm (the initial resistivity before heat treatment was 5000 Ω·cm). In Comparative Example 3, in-plane variations in resistivity were significantly large (minimum value: approximately 800 Ω·cm; maximum value: approximately 10000 Ω·cm). On the other hand, in Examples 3 and 8, in-plane variations in resistivity were small (within a range of 2000 to 6000 Ω·cm).

[0067] The resistivity of the p-type silicon wafers according to Examples 4 and 9 and Comparison Example 4 after heat treatment for oxygen precipitation evaluation was approximately 2000 Ω·cm (the initial resistivity before heat treatment was 10000 Ω·cm). A significant change in resistivity was observed in Comparison Example 4, as well as in Examples 4 and 9. It is assumed that the conductivity type of the silicon was inverted from p-type to n-type due to an increase in oxygen donors after heat treatment, resulting in a significant reduction in resistivity to approximately 2000 Ω·cm.

[0068] The resistivity of the n-type silicon wafers according to Examples 5 and 10 and Comparative Example 5 after heat treatment for oxygen precipitation evaluation was approximately 900 Ω·cm (the initial resistivity before heat treatment was 3000 Ω·cm). In Comparative Example 5, a decrease in resistivity was observed at the central and outer peripheral sections of the wafer, whereas in Examples 5 and 10, no such decrease in resistivity was observed, and the resistivity was uniform across the wafer surface. That is, even in Examples 5 and 10, which were n-type silicon wafers, an effect of suppressing a change in resistivity was confirmed.

[0069] Fig.Figure 9 is a graph representing results obtained by calculating the amount of donor formation from measurement results of the specific resistance and plotting, for each measurement point on the wafer surface, the decrease in oxygen concentration and the amount of oxygen donor formation.

[0070] As in Fig. As shown in Figure 9, in comparison examples 1 to 5, the decrease in oxygen concentration was 0.5 × 10 17 cm -3 The amount of donor production exceeded the limit due to the influence of oxygen excretion. The amount of donor production when the decrease in oxygen concentration is 0.5 × 10 17 cm -3 or less, is estimated to correspond to the amount of oxygen donors formed by a heat treatment for oxygen donor formation carried out at 400 °C for 20 minutes.

[0071] In examples 1 to 5, the decrease in oxygen concentration was reduced to 0.5 × 10 by the effect of decreasing oxygen excretion, which is obtained by suppressing the crystal growth rate. 17 cm -3 or less reduced, and an effect of suppressing an increase in the amount of donor formation due to oxygen excretion was confirmed at all measurement points on the wafer surface.

[0072] In examples 6 to 10, the decrease in oxygen concentration due to the reduction in oxygen excretion achieved by performing RTA treatment was reduced to 0.5 × 10 17 cm -3 or less reduced, and an effect of suppressing an increase in the amount of donor formation due to oxygen excretion was confirmed at all measurement points on the wafer surface. DESCRIPTION OF REFERENCE MARKS 1 silicon wafer 1a Front surface of the silicon wafer 1b rear surface of the silicon wafer 1c outer peripheral surface of the silicon wafer 1d notch QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2009 / 025342

[0008]

Claims

[1] Silicon wafers with a resistivity of 1000 Ω·cm or more, an interstitial oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3 and a decrease in oxygen concentration of no more than 0.5 × 10 17 cm -3 at three or more points on the wafer surface after a heat treatment for oxygen excretion assessment, which is carried out at 780 °C for 3 hours and at 1000 °C for 1 hour. [2] Silicon wafer according to claim 1, wherein the resistivity is 3000 Ω·cm or more. [3] Silicon wafer according to claim 1, wherein the resistivity is 5000 Ω·cm or more. [4] Silicon wafer according to claim 1, wherein the decrease in oxygen concentration is not more than 0.5 × 10 17 cm -3at ten or more points on the wafer surface after heat treatment for oxygen excretion assessment. [5] Method for producing a silicon wafer according to any one of claims 1 to 4, comprising the steps: Growing a single-crystal silicon ingot with a resistivity of 1000 Ω·cm or more and an interstitial oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3 through the CZ procedure; Production of an initial silicon wafer by processing the single-crystal silicon ingot; and Applying an RTA treatment to the initial silicon wafer. [6] Method for producing the silicon wafer according to claim 5, wherein the step of applying the RTA treatment heats the initial silicon wafer in an argon gas atmosphere at a temperature in the range of 1100 °C to 1250 °C for 5 seconds to 30 seconds. [7] Method for producing the silicon wafer according to any one of claims 1 to 4, comprising the steps: Growing a single-crystal silicon ingot with a resistivity of 1000 Ω·cm or more and an interstitial oxygen concentration of more than 8.5 × 10 17 cm -3 and no more than 17 × 10 17 cm -3 through the CZ procedure; and Production of an initial silicon wafer by processing the single-crystal silicon ingot, wherein The step of growing the single-crystal silicon ingot adjusts the crystal growth conditions such that a Pi region (interstitial silicon region of predominantly defect-free type) is wider than a Pv region (vacancy region of predominantly defect-free type) in a cross-section perpendicular to the crystal growth direction. [8] Method for producing the silicon wafer according to claim 7, wherein the crystal growth conditions include the crystal pulling rate.

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