METHOD FOR EVALUATING AND PRODUCING SILICON WAFERS

Abstract

A method for evaluating a silicon wafer cut from a silicon single crystal ingot grown by a CZ method, comprising Measuring a generation rate of thermal donors generated when a thermal donor generation heat treatment is applied to the silicon wafer, and Determining the presence / absence of a crystal defect region or the type of a crystal defect based on the measured generation rate of thermal donors, wherein measuring a generation rate of thermal donors includes: Calculating a first thermal donor generation rate, which is the generation rate of the thermal donors generated at a first measurement point on a first silicon wafer cut from the silicon single-crystal ingot when the thermal donor generation heat treatment is applied in a state where the first silicon wafer contains oxygen clusters, Calculating a second generation rate of thermal donors, which is the generation rate of the thermal donors generated at a second measurement point on a second silicon wafer different from the first silicon wafer cut from the silicon single crystal ingot when a donor removal treatment and the thermal donor generation heat treatment are applied sequentially, and wherein Determining the presence / absence of a crystal defect region or the type of crystal defect includes: Determining, based on a thermal donor generation rate ratio, which is a ratio of the first thermal donor generation rate to the second thermal donor generation rate, which region, selected from a region with OSF nuclei, a region with vacancy defects, and a defect-free region, the first measurement point corresponds to.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for evaluating and manufacturing silicon wafers, and more particularly to an evaluation method for a crystal defect region of a silicon wafer manufactured by a Czochralski method (hereinafter referred to as "CZ method"). TECHNICAL BACKGROUND

[0002] There are various methods for producing a silicon single crystal used as a semiconductor material. Generally, a CZ (Czochralski) method or an FZ (Floating Zone) method is used. In the CZ method, a polycrystalline raw material filled in a quartz crucible is heated and melted by a heater. A seed crystal is immersed in the resulting melt and then pulled up while rotating, thereby growing a single crystal. In the FZ method, a portion of a polycrystalline raw material rod is heated and melted by high frequency to form a melt zone, and a single crystal is grown while the melt zone is agitated. The CZ method facilitates the formation of a larger-diameter crystal, so a wafer sliced ​​from a silicon single crystal produced by the CZ method is used as a high-density semiconductor device substrate.

[0003] In a silicon wafer produced by the CZ process, oxidation-induced stacking faults appearing in a ring shape (hereinafter referred to as an "OSF" ring) may be generated when the silicon wafer is subjected to thermal oxidation treatment for 1 to 10 hours in an acid atmosphere of 1000°C to 1200°C. In addition, several types of minute defects (hereinafter referred to as "ingrown defects") may be formed.

[0004] A location where the OSF ring appears in the crystal is determined by a ratio V / G between the pulling rate (pulling speed) V of the silicon single crystal and an intra-crystal temperature gradient G in a pulling axis direction within a temperature range from the melting point of a silicon single crystal to be grown up to 1300°C. When V / G exceeds a critical value at which the OSF ring is eliminated in a crystal center portion, vacancy clustering occurs, and octahedral vacancy defects of about 0.1 µm are formed. These vacancy defects can reduce the voltage withstandable by a gate oxide film or can cause an insulation failure in a device isolation region when fabricating a MOS-type LSI. Furthermore, these vacancy defects can cause a characteristic defect such as capacitor breakdown when using trench capacitors.On the other hand, if V / G is below the critical value, interstitial silicon accumulation occurs and dislocation clusters are formed, which may lead to a characteristic defect such as a PN junction leakage.

[0005] To address such problems, various methods have been proposed. For example, Positions proposes a method that controls the ratio V / G between the pulling rate V during single-crystal growth and the intra-crystal temperature gradient G to grow a region (hereinafter referred to as the "defect-free region") where neither an in-growth defect nor an OSF ring is found.

[0006] For example, as an evaluation method for the grown-in defect or the OSF ring, a method that detects the vacancy defects by infrared light scattering tomography, a method that observes the OSF ring updated by etching after the thermal oxidation treatment at 1000°C to 1200°C using a microscope, and the like are known.

[0007] JP H10-227729 A and JP 2001-81000 A describe a method for analyzing and evaluating crystal defects of a silicon wafer using a so-called copper decoration method. For example, the analysis method described in JP H10-227729 A includes a step of forming a thermal oxidation layer with a predetermined thickness on the surface of a bare wafer, a step of etching the backside of the bare wafer, a step of decorating the defect region of the bare wafer with copper, and a step of analyzing the defect region of the copper-decorated wafer after the copper decoration step. In the analysis step, the distribution and density of the defect area of ​​the copper-decorated wafer are analyzed with the naked eye, and the morphology of the defect area of ​​the copper-decorated wafer is analyzed by transmission electron microscopy (TEM) or scanning electron microscopy (SEM).

[0008] JP 2001-81000 A describes a method for analyzing crystal defects in a silicon single crystal produced by the CZ process using a copper decoration method that involves heat-treating a copper-contaminated sample and then rapidly cooling the sample. In this evaluation method, the copper decoration method is applied to a silicon single crystal with a low oxygen concentration, where the interstitial oxygen concentration in the crystal is less than or equal to 10×10 17 atoms / cm 3 (ASTM'79) to detect an area where the OSF or nuclei that will become the OSF exist with high sensitivity.

[0009] JP H09 - 82 768 A describes a method for evaluating a wafer structure with respect to oxygen concentration distribution, such as the layer thickness of an epitaxial layer in an epitaxial wafer or a DZ layer, by measuring the wafer resistivity caused by thermal donors generated from interstitial oxygen when a silicon wafer is annealed at a low temperature of about 450°C. SUMMARY OF THE INVENTION [Problem to be solved by the invention]

[0010] However, the conventional general evaluation method for the crystal defects of the silicon wafer involves multiple heat treatment processes and etching processes according to the type of crystal defect, which requires a lot of time and cost for the evaluation.

[0011] Although the evaluation method for the crystal defects of the silicon wafer using the copper decoration method can evaluate the presence / absence of the grown-in defect region and the OSF ring region at the same time, it still requires a heat treatment process that takes several dozen hours for the copper decoration, which disadvantageously lacks simplicity.

[0012] The object of the present invention is therefore to provide a method for evaluating and manufacturing a silicon wafer capable of evaluating the presence / absence and types of crystal defect regions with a simple method while saving time and cost. [Means of solving the problem]

[0013] To solve the above problems, a method for evaluating a silicon wafer according to the present invention is an evaluation method for a silicon wafer cut from a silicon single crystal ingot grown by a CZ method, the method including: measuring a generation rate of thermal donors generated when a heat treatment for generating thermal donors is applied to the silicon wafer, and determining the presence / absence of a crystal defect region or the type of a crystal defect based on the measured generation rate of thermal donors, wherein measuring a generation rate of thermal donors includes: Calculating a first thermal donor generation rate, which is the generation rate of the thermal donors generated at a first measurement point on a first silicon wafer cut from the silicon single-crystal ingot when the thermal donor generation heat treatment is applied in a state where the first silicon wafer contains oxygen clusters, Calculating a second generation rate of thermal donors, which is the generation rate of the thermal donors generated at a second measurement point on a second silicon wafer different from the first silicon wafer cut from the silicon single crystal ingot when a donor removal treatment and the thermal donor generation heat treatment are applied sequentially, and wherein Determining the presence / absence of a crystal defect region or the type of crystal defect includes: Determining, based on a thermal donor generation rate ratio, which is a ratio of the first thermal donor generation rate to the second thermal donor generation rate, which region, selected from a region with OSF nuclei, a region with vacancy defects, and a defect-free region, the first measurement point corresponds to.

[0014] According to the present invention, by measuring the generation rate of thermal donors based on a change in resistivity caused by heat treatment applied to the silicon wafer sliced ​​from the silicon single crystal ingot grown by the CZ method while controlling V / G, the presence / absence of the crystal defect region and the type of the crystal defect can be easily evaluated.

[0015] The state in which the silicon wafer contains oxygen clusters refers to a state before the donor removal treatment is applied to a silicon wafer in an as-grown state. The defect-free region refers to a region that does not contain a grown-in defect and where no OSF ring is generated after an evaluation heat treatment. As described above, according to the present invention, the presence / absence of the crystal defect region or the type of the crystal defect can be easily evaluated based on the first and second thermal donor generation rates, which are respectively calculated from the two wafers, one of which is subjected to the donor removal treatment and the other of which is not.

[0016] Preferably, the silicon wafer evaluation method according to the present invention determines that the first measurement point on the first silicon wafer corresponds to the defect-free region when the generation rate ratio of thermal donors falls within a first rate range, determines that the first measurement point corresponds to the region with the vacancy defects when the generation rate ratio of thermal donors falls within a second rate range that is higher than the first rate range, and determines that the first measurement point corresponds to the region with the OSF nuclei when the generation rate ratio of thermal donors falls within a third rate range that is higher than the second rate range. This allows the OSF ring region, the region with the vacancy defects, and the defect-free region to be easily determined.

[0017] In the present invention, the heat treatment for generating thermal donors is preferably applied for two to four hours at a temperature in the range of 430°C to 480°C, and more preferably for four hours at 450°C. Under this heat treatment condition, the oxygen clusters can be activated to allow the presence / absence of the crystal defect region or the type of crystal defect to be evaluated based on the generation rate of thermal donors.

[0018] The silicon wafer evaluation method according to the present invention preferably determines that the first measurement point on the silicon wafer corresponds to the defect-free region when the heat treatment for generating thermal donors is applied at 450°C for four hours and the generation rate ratio of thermal donors is greater than or equal to 1.3 and less than 1.7; determines that the first measurement point corresponds to the region having the vacancy defect when the heat treatment for generating thermal donors is applied at 450°C for four hours and the generation rate ratio of thermal donors is greater than or equal to 1.7 and less than 1.9; and determines that the first measurement point corresponds to the region having the OSF core when the heat treatment for generating thermal donors is applied at 450°C for four hours and the generation rate ratio of thermal donors is greater than or equal to 1.9 and less than 2.3.This allows the OSF ring region, the vacancy defect region, and the defect-free region to be easily determined.

[0019] The silicon wafer evaluation method according to the present invention preferably creates a crystal defect map of the silicon wafer in the radial direction thereof by measuring the generation rate of thermal donors at a plurality of measuring points set in the radial direction of the silicon wafer.

[0020] Preferably, in the silicon wafer evaluation method according to the present invention, it is preferable that the resistivities of the silicon wafer are measured, a carrier concentration is calculated from an Irvin curve based on the resistivities, a thermal donor generation rate is calculated based on the carrier concentration before and after the thermal donor generation heat treatment, and the thermal donor generation rate is calculated from the relationship between the time required for the thermal donor generation heat treatment and the thermal donor generation rate. In this case, the resistivities of the silicon wafer are preferably measured by a four-probe method.

[0021] A silicon wafer manufacturing method according to the present invention includes: growing a first silicon single crystal ingot by the CZ method, measuring a generation rate of thermal donors generated when the heat treatment for generating thermal donors is applied to a silicon wafer for evaluation cut out of the first silicon single crystal ingot, determining the presence / absence of the crystal defect region or the type of the crystal defect in the silicon wafer for evaluation based on a result of measuring the generation rate of thermal donors, Adjusting a growth condition for a second silicon single crystal ingot based on a growth condition for the first silicon single crystal ingot and a result of the determination on the presence / absence of the crystal defect region or the type of the crystal defect in the silicon wafer for evaluation, and cutting out silicon wafers for product from the second silicon single crystal ingot, wherein measuring a generation rate of thermal donors includes: Calculating a first thermal donor generation rate, which is the generation rate of the thermal donors generated at a first measurement point on a first silicon wafer cut from the first silicon single-crystal ingot when the thermal donor generation heat treatment is applied in a state where the first silicon wafer contains oxygen clusters, Calculating a second generation rate of thermal donors, which is the generation rate of the thermal donors generated at a second measurement point on a second silicon wafer different from the first silicon wafer cut from the first silicon single crystal ingot when a donor removal treatment and the thermal donor generation heat treatment are applied sequentially, and wherein Determining the presence / absence of a crystal defect region or the type of crystal defect includes: Determining, based on a thermal donor generation rate ratio, which is a ratio of the first thermal donor generation rate to the second thermal donor generation rate, which region, selected from a region with OSF nuclei, a region with vacancy defects, and a defect-free region, the first measurement point corresponds to.

[0022] The silicon wafer manufacturing method according to the present invention can grow the second silicon single crystal ingot having a defect-free region, the second silicon single crystal ingot having a region with vacancy defects, or the second silicon single crystal ingot having a region with OSF nuclei, by adjusting the growth condition for the second silicon single crystal ingot. Furthermore, in the present invention, a pulling speed of the second silicon single crystal ingot is preferably adjusted as the growth condition for the second silicon single crystal ingot. Thus, various types of silicon wafers can be obtained using evaluation results based on the generation rate of thermal donors.

[0023] In the present invention, a donor removal treatment is preferably applied to the silicon wafers for product production. This allows for the provision of silicon wafer products that are unaffected by thermal donors. [Advantageous effects of the invention]

[0024] According to the present invention, there can be provided a silicon wafer evaluation method and a silicon wafer manufacturing method that can evaluate the presence / absence of a crystal defect region and the type of a crystal defect using a simple method without reducing cost and time. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flowchart for explaining a silicon wafer manufacturing method according to an embodiment of the present invention; Fig. Figure 2 is a view showing the typical relationship between V / G and the type and distribution of crystal defects; Fig. Figure 3 is a flowchart illustrating the step of measuring thermal donor generation rates; Fig. 4 is a flowchart illustrating the step of determining the presence / absence of the crystal defect region and the type of the crystal defect in the wafer; Fig. 5 is a graph showing the relationship between the generation rate of thermal donors in each of the wafer samples A1 to A3 and B1 to B3 and the heat treatment time for generating thermal donors; Fig. 6 is a graph showing the relationship between the generation rate of thermal donors and oxygen concentration in each of the OSF ring generation region, the vacancy defect region, and the defect-free region when the thermal donor generation treatment is applied at 450°C for four hours; and Fig. 7 is a graph showing the generation rate of thermal donors at each measurement point of the wafer not subjected to the donor removal treatment normalized by the generation rate of thermal donors at the same measurement point of the wafer subjected to the donor removal treatment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] Preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0026] Fig. 1 is a flowchart for explaining a silicon wafer manufacturing method according to an embodiment of the present invention.

[0027] As in Fig. 1, a silicon single crystal manufacturing method according to the present embodiment includes a crystal growth step (S11) of growing a silicon single crystal ingot by the CZ method, a cutting step (S12) of cutting out silicon wafers from the silicon single crystal ingot, a thermal donor generation rate measurement step (S13J, S14) performed when evaluation of the crystal defect region of the silicon wafer is necessary, a determination step (S15) of determining the presence / absence of the crystal defect region and the type of the crystal defect based on a measurement result of the thermal donor generation rate, and an adjusting step (S16J, S17) of adjusting a growth condition for subsequent silicon single crystal ingots based on a result of the determination of the presence / absence of the crystal defect region and the type of the crystal defect.

[0028] The silicon single crystal manufacturing method according to the present invention further includes a donor removal treatment step (S18) performed when evaluation of the silicon wafer is unnecessary, and a product processing step (S19) including mirror surface polishing, etc., applied to the silicon wafer that has been subjected to the donor removal treatment.

[0029] The type and distribution of crystal defects contained in the silicon single crystal grown by the CZ method depend on a ratio V / G between a silicon single crystal pulling speed V and an intra-crystal temperature gradient G in a pulling axis direction. Therefore, to control the crystal quality in the silicon single crystal, it is necessary to precisely control V / G. However, whether a silicon single crystal ingot (first silicon single crystal ingot) grown under a certain condition possesses a desired crystal quality or not can be determined only when the crystal quality is actually evaluated.

[0030] Thus, in the present embodiment, the presence / absence of the crystal defect region and the type of the crystal defect are evaluated in the wafer cut from the silicon single-crystal ingot. If the desired crystal quality is insufficient as a result of the evaluation of the presence / absence of the crystal defect region and the type of the crystal defect, the evaluation result is returned to the growth step for a subsequent silicon single-crystal ingot (second silicon single-crystal ingot), and a crystal growth condition such as the crystal pulling speed V is adjusted to obtain the desired crystal quality.

[0031] Fig. Figure 2 is a view showing the typical relationship between V / G and the type and distribution of crystal defects.

[0032] As in Fig. As shown in Figure 2, when V / G is large, vacancies are excessively generated, producing vacancy defects, which are clusters of vacancies. The vacancy defect is a crystal defect generally referred to as COP (Crystal Originated Particle). On the other hand, when V / G is small, interstitial silicon atoms are excessively generated, producing dislocation clusters, which are clusters of interstitial silicon. Therefore, to produce a single crystal containing neither COP nor dislocation clusters, it is necessary to control V / G in both the radial direction and the length direction (crystal growth direction) of the single crystal.

[0033] The crystal pulling rate V is constant at any position in the radial direction of the single crystal, so in order to make the intra-crystal temperature gradient G in the radial direction fall within a predetermined range, it is necessary to form a sufficiently high-temperature region (hot zone) in a chamber. The intra-crystal temperature gradient G in the radial direction is controlled by a heat-shielding body provided over a silicon melt, whereby an adequate hot zone can be formed near a solid-liquid interface. On the other hand, the intra-crystal temperature gradient G in the length direction depends not only on the structure of the hot zone but also on the crystal pulling rate V, so the single-crystal pulling rate V needs to be adjusted.Currently, a silicon single crystal with a diameter of 300 mm, free of COP and dislocation clusters, is produced under strict control of the crystal pulling rate V.

[0034] However, the COP-free and dislocation cluster-free silicon wafer grown by controlling V / G is not homogeneous over the entire surface, but contains multiple regions exhibiting different behaviors after heat treatment. For example, an OSF region, a Pv region, and a Pi region exist between a region where COPs are generated and a region where dislocation clusters are generated, in descending order of V / G.

[0035] The OSF region is a region containing plate-like oxygen precipitates (OSF nuclei) in an as-grown state (a state where no heat treatment is performed after the single crystal is grown), and in which OSFs are generated when oxidation heat treatment is performed at a temperature of up to 1000°C to 1200°C. The Pv region contains oxygen precipitate nuclei in the as-grown state, and in which oxygen precipitates are easily generated when two-step heat treatments of low temperature and high temperature (e.g., 800°C and 1000°C) are applied. The Pi region rarely contains oxygen precipitates in the as-grown state, and in which oxygen precipitates are hardly generated even though heat treatment is applied.

[0036] As described above, V / G is mainly controlled by adjusting the pulling speed V. For example, when a wafer containing many vacancy defect regions or OSF ring regions is produced, although a wafer mainly containing the defect-free region is desired, V / G is determined to be too large, and the crystal pulling speed V is reduced. Conversely, when a wafer containing many defect-free regions is produced, although a wafer mainly containing the OSF ring region is desired, V / G is determined to be too small, and the crystal pulling speed V is increased. By adjusting the crystal pulling speed V, a silicon single-crystal ingot with the desired crystal quality can be produced.

[0037] In the present embodiment, in order to determine whether the manufactured silicon single crystal ingot satisfies a desired crystal quality or not, a temporal change of thermal donors in the silicon wafer cut from the ingot is measured.

[0038] In the CZ process, a polycrystalline silicon raw material filled in a quartz crucible is melted, and the silicon single crystal is grown from the resulting melt. Thus, the silicon single crystal contains oxygen, which is extracted from the quartz crucible at a concentration of approximately 10×10 17 atoms / cm 3(according to the standard test method ASTM F-121, 1979, specified by ASTM International). This oxygen causes complex effects: It can cause the crystal defects in the wafer to produce a device-specific defect, while contributing to an increase in wafer thickness in the device manufacturing process to suppress deformation or the formation of oxygen precipitates with a gettering effect that traps heavy metals, causing device malfunction within the wafer.

[0039] Generally, oxygen atoms in silicon are electrically neutral and do not affect the electrical resistance of silicon. However, it is known that the silicon single crystal produced by the CZ method is grown using a quartz crucible, so supersaturated oxygen is contained in the crystal. When the silicon single crystal is subjected to heat treatment at a temperature as low as about 450°C, several oxygen atoms combine to form an oxygen cluster, which serves as a donor that emits electrons.

[0040] The thermal donors formed by the heat treatment at approximately 450°C are influenced by point defects, and the generation rate of thermal donors differs due to a difference in the concentration of point defects between a defect-dominant region (COP region, OSF ring region) and the defect-free region. Thus, in the present embodiment, the presence / absence of the crystal defect region and the type of crystal defect in the silicon wafer are determined based on the generation rate of the thermal donors generated in the silicon wafer.

[0041] In the thermal donor generation rate measurement step (S14), two silicon wafers for evaluation, which were successively cut out from the ingot in the cutting step (S12), are prepared. The two wafers for evaluation are preferably cut out from the ingot by a wire saw and are preferably subjected to rough polishing. Then, one (first wafer) of the two wafers is subjected to a thermal donor generation heat treatment without previously undergoing the donor removal treatment, and the other (second wafer) thereof is subjected to the thermal donor generation heat treatment after previously undergoing the donor removal treatment. Then, the thermal donor generation rate is calculated from a change in the resistivity of each of the first and second wafers before and after the thermal donor generation heat treatment.

[0042] Fig. Figure 3 is a flowchart illustrating the measurement step for thermal donor generation rates.

[0043] As in Fig. 3, the thermal donor generation rate measuring step (S14) includes a preparation step (S20) of preparing the first and second wafers in the as-grown state, a resistivity measuring step (S21) of measuring the resistivity of the first wafer, a thermal donor generation heat treatment step (S22) of applying the thermal donor generation heat treatment to the first wafer after measuring the resistivity, a resistivity measuring step (S23) of measuring the resistivity of the first wafer after the thermal donor generation heat treatment, and a step (S24) of calculating a first thermal donor generation rate from the two resistivity measurement values ​​obtained before and after the thermal donor generation heat treatment.

[0044] The thermal donor generation rate measuring step (S14) further includes a step (S25) of applying the donor removal treatment to the second wafer, a resistance measuring step (S26) of measuring the resistivity of the second wafer after the donor removal treatment, a thermal donor generation heat treatment step (S27) of applying, to the second wafer after resistivity measurement, the same thermal donor generation heat treatment as that for the first wafer, a resistivity measuring step (S28) of measuring the resistivity of the second wafer after the thermal donor generation heat treatment, and a step (S29) of calculating a second thermal donor generation rate from the two resistivity measurement values ​​obtained before and after the thermal donor generation heat treatment.

[0045] The temperature of the heat treatment for generating thermal donors is preferably set in a range of 430°C to 480°C, and more preferably set at 450°C. The time for the heat treatment for generating thermal donors is preferably set in a range of one to four hours, and more preferably set in a range of two to four hours. The donor removal treatment is a short-term heat treatment applied under an inert gas atmosphere of, for example, 600°C to 700°C, and the heat treatment time is set to, for example, about 15 minutes.

[0046] The in-plane resistivity of a silicon wafer can be measured using a so-called four-probe method. Based on the measured resistivity, a carrier concentration is calculated from an Irvin curve. The amount of thermal donor generation is calculated based on the carrier concentration before and after the thermal donor generation heat treatment. The thermal donor generation rate can be calculated based on the relationship between the time required for the thermal donor generation heat treatment and the amount of thermal donor generation.

[0047] In the present embodiment, it is preferable that multiple measurement points are set along the radial direction of the silicon wafer, resistance measurements are performed at each measurement point, and the generation rate of thermal donors is calculated from the measurement results. By thus evaluating the presence / absence of the crystal defect region and the type of crystal defect for each measurement point, a defect map of the silicon wafer in the radial direction can be created.

[0048] Fig. 4 is a flowchart illustrating the step of determining the presence / absence of the crystal defect region and the type of the crystal defect in the wafer.

[0049] As in Fig. As shown in Figure 4, in the determination step (S15) of the presence / absence of the crystal defect region in the wafer and the type of the crystal defect, a ratio of the first generation rate of thermal donors to the second generation rate of thermal donors is calculated (S30). If the calculated ratio is greater than or equal to 1.3 and less than 1.7, the relevant measurement point is determined as a defect-free region (S31J, S34); if the calculated ratio is greater than or equal to 1.7 and less than 1.9, the relevant measurement point is determined as a region with vacancy defects (S31N, S32J, S35); and if the calculated ratio is greater than or equal to 1.9 and less than 2.3, the relevant measurement point is determined as a region with OSF nuclei (S31N, S32N, S33J, S36). Furthermore, if the calculated ratio does not fall within any of the above ranges, the relevant measurement point is determined as indeterminable (S31N, S32N, S33N, S37).

[0050] As described above, in the silicon wafer evaluation method according to the present embodiment, the silicon wafer is cut from the silicon single-crystal ingot grown by the CZ method. Then, the generation rate of thermal donors generated when the thermal donor generation heat treatment is applied to the silicon wafer, and the presence / absence of the crystal defect region and the type of crystal defect are determined based on the thermal donor generation rate. This allows an OSF nuclei region, a vacancy defect region, or the defect-free region to be easily determined in a short time. Furthermore, the evaluation can be achieved by a comparatively short-time low-temperature heat treatment, for example, without requiring the copper decoration step used in the conventional evaluation method.That is, it is possible to evaluate the presence / absence of the crystal defect region in the silicon wafer and the type of crystal defect using a simple method with time and cost reduction.

[0051] Furthermore, in the silicon wafer manufacturing method according to the present embodiment, the generation rate of thermal donors of the silicon wafer for evaluation cut from a previous silicon single crystal ingot is measured, the presence / absence of the crystal defect region or the type of the crystal defect in the silicon wafer for evaluation is determined based on a result of the measurement of the generation rate of thermal donors, and a growth condition for subsequent silicon single crystal ingots is adjusted based on a result of the determination, so that the crystal growth condition can be easily optimized.

[0052] Although the preferred embodiment of the present invention has been described, the present invention is not limited to the above embodiment, and various modifications may be made within the scope of the present invention. Accordingly, all such modifications are included in the present invention.

[0053] For example, in the above embodiment, the first and second silicon wafers cut from the silicon single-crystal ingot are prepared in the thermal donor generation rate measurement step (S14), and the thermal donor generation heat treatment (S27) is applied to the second wafer after the donor removal treatment (S25) to calculate the second thermal donor generation rate. However, the above second thermal donor generation rate calculation step may be omitted in the present invention. That is, the second thermal donor generation rate is previously calculated by applying the donor removal treatment and the thermal donor generation heat treatment to a silicon wafer similar to the second silicon wafer, and stored as a database.Then, the presence / absence of the crystal defect region and the type of the crystal defect are evaluated only by measuring the first generation rate of thermal donors and reading the second generation rate of thermal donors from the database.

[0054] The influence of the type of crystal defect on the generation rate of thermal donors was evaluated. In this evaluation test, 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. At this time, the silicon single-crystal ingot was grown under V / G control such that an OSF ring generation region was included in the silicon single-crystal ingot. The oxygen concentration of the silicon single-crystal ingot was 5×10 17 up to 20×10 17 atoms / cm 3(ASTM F-121, 1979). By cutting the silicon single-crystal ingot, two silicon wafer samples, A1 and B1, were obtained, each with an OSF generation region. The OSF ring generation region refers to the region where the OSF ring is generated after evaluation heat treatment, i.e., a region with the OSF nuclei in the as-grown state.

[0055] Furthermore, another silicon single crystal ingot was grown under the same conditions as those for samples A1 and B1 except that V / G was controlled such that a region having the vacancy defects was included in the silicon single crystal ingot, and the obtained silicon single crystal ingot was sliced ​​to obtain two silicon wafer samples A2 and B2 each having the region having the vacancy defects.

[0056] Furthermore, another silicon single crystal ingot was grown under the same conditions as those for samples A1 and B1 except that V / G was controlled such that the silicon single crystal ingot consisted of the defect-free region, and the obtained silicon single crystal ingot was sliced ​​to obtain two silicon wafer samples A3 and B3, each consisting of the defect-free region.

[0057] Thereafter, the donor removal treatment was applied for 15 minutes under a nitride atmosphere of 700°C to eliminate thermal donors generated during crystal growth in each of the silicon wafer samples B1, B2 and B3.

[0058] The heat treatment for generating thermal donors was applied to the silicon wafer samples A1 to A3 (Examples 1 to 3) prepared by a process not including the donor removal treatment and the silicon wafer samples B1 to B3 (Comparative Examples 1 to 3) prepared by a process including the donor removal treatment under a nitride atmosphere of 450°C to generate the thermal donors.

[0059] The resistivity of each of the silicon wafer samples A1 to A3 and B1 to B3 was measured using a resistivity measurement method according to a four-probe method specified by Japanese Industrial Standard (JIS) H 0602:1995, and a carrier concentration was calculated using an Irvin curve. Furthermore, a thermal donor generation rate was calculated based on the carrier concentration before and after the thermal donor generation heat treatment, and the thermal donor generation rate was calculated based on the relationship between the heat treatment time and the thermal donor generation rate.

[0060] Fig. Figure 5 is a graph showing the relationship between the generation rate of thermal donors in each of the wafer samples A1 to A3 and B1 to B3 and the heat treatment time for thermal donor generation. The horizontal axis indicates the heat treatment time (h), and the vertical axis indicates the generation rate of thermal donors (cm -3 / h). This graphical representation only refers to wafers with an oxygen concentration of 11×10 17 atoms / cm 3 is enough.

[0061] If, as in Fig. As shown in Figure 5, when the heat treatment time is less than 4 hours, the generation rate of thermal donors in the samples (samples A1, A2, and A3) that were not subjected to the donor removal treatment was higher than in the samples (samples B1, B2, and B3) that were subjected to the donor removal treatment in any of the OSF ring generation region, the vacancy defect region, and the defect-free region. Furthermore, the generation rate of thermal donors was the same among the above regions in the samples subjected to the donor removal treatment, while the generation rate of thermal donors became higher in the order of the OSF ring generation region, the vacancy defect region, and the defect-free region in the samples that were not subjected to the donor removal treatment.When the heat treatment time exceeded four hours, the generation rate of thermal donors increased once and then decreased in the samples not subjected to donor removal treatment. On the other hand, in the samples subjected to donor removal treatment, the generation rate of thermal donors decreased when the heat treatment time exceeded four hours and remained the same in all conditions after 16 hours.

[0062] Fig. Figure 6 is a graph showing the relationship between the generation rate of thermal donors and oxygen concentration in each of the OSF ring generation region, the vacancy defect region, and the defect-free region when the thermal donor generation heat treatment is applied at 450°C for four hours. The horizontal axis indicates the oxygen concentration (× 10 17 atoms / cm 3), and the vertical axis indicates the generation rate of thermal donors (cm -3 / h).

[0063] As in Fig. 6, as in the case of Fig. 1, the generation rate of thermal donors was higher in the samples (samples A1, A2, and A3) that were not subjected to donor removal treatment than in the samples (samples B1, B2, and B3) that were subjected to donor removal treatment at each oxygen concentration. Furthermore, the generation rate of thermal donors was the same among the above regions in the samples subjected to donor removal treatment, while the generation rate of thermal donors became higher in the order of OSF ring generation region, vacancy defect region, and defect-free region in the samples not subjected to donor removal treatment.

[0064] Fig. Figure 7 is a graph showing the thermal donor generation rate at each measurement point of the wafer not subjected to the donor removal treatment, normalized by the thermal donor generation rate at the same measurement point of the wafer subjected to the donor removal treatment. The horizontal axis indicates the oxygen concentration (× 10 17 atoms / cm 3 ), and the vertical axis indicates the generation rate of thermal donors (normalized value).

[0065] As in Fig.As shown in Figure 7, the generation rate of thermal donors in the defect-free region of the wafer that was not subjected to the donor removal treatment is 1.3 times or more and less than 1.7 times the generation rate of thermal donors in the wafer that was subjected to the donor removal treatment. Furthermore, the generation rate of thermal donors in the vacancy defect region of the wafer that was not subjected to the donor removal treatment is 1.7 times or more and less than 1.9 times the generation rate of thermal donors in the wafer that was subjected to the donor removal treatment.Furthermore, the generation rate of thermal donors in the OSF generation region of the wafer not subjected to the donor removal treatment is 1.9 times or more and less than 2.3 times the generation rate of thermal donors in the wafer subjected to the donor removal treatment. [List of reference symbols] S11 Crystal growth step S12 Cutting step S13, S14 Measurement step for the generation rates of thermal donors S15 Determination step S16, 17 Crystal growth condition adjustment step S20 Wafer preparation step S21 Specific resistance measurement step for the first wafer S22 Heat treatment step to produce thermal donors for the first wafer S23 Specific resistance measurement step for the first wafer S24 first calculation step for the generation rates of thermal donors S25 Donor removal treatment step for the second wafer S26 Specific resistance measurement step for the second wafer S27 Heat treatment step for generating thermal donors for the second wafer S28 Specific resistance measurement step for the second wafer S29 second calculation step for the generation rates of thermal donors

Claims

[1] A method for evaluating a silicon wafer cut from a silicon single crystal ingot grown by a CZ method, comprising Measuring a generation rate of thermal donors generated when a thermal donor generation heat treatment is applied to the silicon wafer, and Determining the presence / absence of a crystal defect region or the type of a crystal defect based on the measured generation rate of thermal donors, wherein measuring a generation rate of thermal donors includes: Calculating a first thermal donor generation rate, which is the generation rate of the thermal donors generated at a first measurement point on a first silicon wafer cut from the silicon single-crystal ingot when the thermal donor generation heat treatment is applied in a state where the first silicon wafer contains oxygen clusters, Calculating a second generation rate of thermal donors, which is the generation rate of the thermal donors generated at a second measurement point on a second silicon wafer different from the first silicon wafer cut from the silicon single crystal ingot when a donor removal treatment and the thermal donor generation heat treatment are applied sequentially, and wherein Determining the presence / absence of a crystal defect region or the type of crystal defect includes: Determining, based on a thermal donor generation rate ratio, which is a ratio of the first thermal donor generation rate to the second thermal donor generation rate, which region, selected from a region with OSF nuclei, a region with vacancy defects, and a defect-free region, the first measurement point corresponds to. [2] A method for evaluating a silicon wafer according to claim 1, wherein it is determined that the first measuring point on the first silicon wafer corresponds to the defect-free area when the generation rate ratio of thermal donors falls within a first rate range, it is determined that the first measurement point corresponds to the area with the vacancy defects if the generation rate ratio of thermal donors falls within a second rate range which is higher than the first rate range, and it is determined that the first measurement point corresponds to the area with the OSF nuclei if the generation rate ratio of thermal donors falls into a third rate range that is higher than the second rate range. [3] A method for evaluating a silicon wafer according to any one of claims 1 to 2, wherein the heat treatment for generating thermal donors is applied for two to four hours at a temperature in the range of 430°C to 480°C. [4] The method for evaluating a silicon wafer according to claim 1, wherein it is determined that the first measurement point on the first silicon wafer corresponds to the defect-free region when the heat treatment for generating thermal donors is applied at 450°C for four hours and the generation rate ratio of thermal donors is greater than or equal to 1.3 and less than 1.

7. [5] The method for evaluating a silicon wafer according to claim 1 or 4, wherein it is determined that the first measurement point corresponds to the region having the vacancy defect when the heat treatment for generating thermal donors is applied at 450°C for four hours and the generation rate ratio of thermal donors is greater than or equal to 1.7 and less than 1.

9. [6] The method for evaluating a silicon wafer according to claim 1, 4 or 5, wherein the first measurement point is determined to correspond to the region having the OSF core when the heat treatment for generating thermal donors is applied at 450°C for four hours and the generation rate ratio of thermal donors is greater than or equal to 1.9 and less than 2.

3. [7] A method for evaluating a silicon wafer according to any one of claims 1 to 6, further comprising preparing a crystal defect map of the silicon wafer in the radial direction thereof by measuring the generation rate of thermal donors at a plurality of measuring points set in the radial direction of the silicon wafer. [8] A method for evaluating a silicon wafer according to claim 1, wherein specific resistances of the silicon wafer are measured, a carrier concentration is calculated using an Irvin curve based on the specific resistances, an extent of thermal donor generation is calculated based on the carrier concentration before and after the heat treatment to generate thermal donors, and the generation rate of thermal donors is calculated from the relationship between the time required for heat treatment to generate thermal donors and the extent of thermal donor generation. [9] A method for producing silicon wafers, comprising Growing a first silicon single crystal ingot using the CZ process, Measuring a generation rate of thermal donors generated when the thermal donor generation heat treatment is applied to a silicon wafer for evaluation cut from the first silicon single crystal ingot, Determining the presence / absence of a crystal defect region or the type of a crystal defect in the silicon wafer for evaluation based on a result of measuring the generation rate of thermal donors, Adjusting a growth condition for a second silicon single crystal ingot based on a growth condition for the first silicon single crystal ingot and a result of the determination of the presence / absence of the crystal defect region or the type of the crystal defect in the silicon wafer for evaluation, and Cutting silicon wafers for product from the second silicon single crystal ingot, wherein measuring a generation rate of thermal donors includes: Calculating a first thermal donor generation rate, which is the generation rate of the thermal donors generated at a first measurement point on a first silicon wafer cut from the first silicon single-crystal ingot when the thermal donor generation heat treatment is applied in a state where the first silicon wafer contains oxygen clusters, Calculating a second generation rate of thermal donors, which is the generation rate of the thermal donors generated at a second measurement point on a second silicon wafer different from the first silicon wafer cut from the first silicon single crystal ingot when a donor removal treatment and the thermal donor generation heat treatment are applied sequentially, and wherein Determining the presence / absence of a crystal defect region or the type of crystal defect includes: Determining, based on a thermal donor generation rate ratio, which is a ratio of the first thermal donor generation rate to the second thermal donor generation rate, which region, selected from a region with OSF nuclei, a region with vacancy defects, and a defect-free region, the first measurement point corresponds to. [10] A method of manufacturing silicon wafers according to claim 9, including growing the second silicon single crystal ingot having a defect-free region by adjusting the growth condition for the second silicon single crystal ingot. [11] A method of manufacturing silicon wafers according to claim 9, comprising growing the second silicon single crystal ingot having a region with vacancy defects by adjusting the growth condition for the second silicon single crystal ingot. [12] A method of manufacturing silicon wafers according to claim 9, comprising growing the second silicon single crystal ingot having a region with OSF nuclei by adjusting the growth condition for the second silicon single crystal ingot. [13] A method for producing silicon wafers according to claims 9 to 12, including adjusting a pulling speed of the second silicon single crystal ingot as the growth condition for the second silicon single crystal ingot. [14] A method of manufacturing silicon wafers according to any one of claims 9 to 13, wherein a donor removal treatment is applied to the silicon wafers for product.

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