JP6971622B2 - Manufacturing method of semiconductor wafer and semiconductor wafer - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor wafer and a semiconductor wafer.

In the manufacture of semiconductor wafers, heat treatment is performed for the purpose of reducing crystal defects, for example, void defects in the device forming region of the semiconductor wafer. A void defect is a cavity-like defect formed by a collection of pores, and is a defect in which the wall surface surrounding the cavity is covered with an oxide film _{made of silicon oxide (SiO 2).} It is known that the presence of void defects in the device forming region of a semiconductor wafer affects the characteristics of the semiconductor device.

Further, the heat treatment of the semiconductor wafer is also performed for the purpose of growing the BMD (Bulk Micro Defect). Since BMD acts as a gettering site for metal impurities in the device manufacturing process, the growth of BMD is indispensable for obtaining high quality semiconductor devices.

Such heat treatment is performed, for example, using a vertical heat treatment furnace in an argon (Ar) atmosphere, a hydrogen atmosphere, or a mixed atmosphere thereof. In this heat treatment, as a jig for supporting the semiconductor wafer to be processed, a jig whose base material is made of a material having excellent heat resistance such as silicon carbide (SiC) can be used. In this case, the heat treatment is generally performed in an Ar atmosphere.

Patent Document 1 describes a SiC jig in a heat treatment process and a technique for preventing carbon contamination of a silicon wafer from the environment. Specifically, after the heat treatment in the Ar atmosphere and prior to taking out the silicon wafer from the quartz tube of the heat treatment furnace, the atmosphere in the furnace is switched from the Ar atmosphere to the oxygen atmosphere, and the atmosphere in the furnace is changed to the oxygen atmosphere. It is described that an oxide film is formed on the surface of a SiC jig.

In Patent Document 2, in a solid-state image sensor composed of a photoconductive layer containing silicon and a pair of electrodes, a solid-state image sensor in which a semiconductor layer containing at least silicon and carbon is provided between the photoconductive layer and the electrodes. Is described. A solid-state image sensor having such a structure achieves a small dark current and excellent optical sensitivity because the carbon contained in the semiconductor layer suppresses carrier injection from the electrode.

Non-Patent Document 1 describes that carbon in a silicon substrate has an effect of suppressing the formation of oxygen donors generated during heat treatment.

Japanese Unexamined Patent Publication No. 2015-41738 Japanese Unexamined Patent Publication No. 60-24795

Tadahiro Ohmi, supervised by Yuhisa Nitta, "Science of Silicon", Realize Publishing Co., Ltd., 1996, p. 542

In the process of manufacturing a semiconductor wafer, it is inevitable that impurities such as carbon are mixed in during the growth of the single crystal. In particular, the single crystal ingot grown by the Czochralski method may have a relatively large variation in the concentration of impurities such as carbon in the axial direction. Therefore, in order to reduce the variation in the performance of the device obtained by using the semiconductor wafer sliced from the ingot, the process conditions for device manufacturing are set according to the position of the ingot corresponding to the semiconductor wafer used for the manufacturing. Needed to change.

The method described in Patent Document 1 includes forming an oxide film on the surface of a SiC jig in a heat treatment step of a silicon wafer. This makes it possible to reduce the amount of carbon contamination from the SiC jig to the silicon wafer due to repeated use of the SiC jig. However, the reduction of the amount of carbon contamination in the heat treatment step cannot have the effect of reducing the variation in the carbon concentration mixed during crystal growth. Therefore, in this method, it is necessary to change the process conditions for manufacturing the device according to the position of the ingot corresponding to the silicon wafer used for the manufacturing, which may complicate the manufacturing of the device.

Patent Document 2 and Non-Patent Document 1 show improvement in performance by including carbon in a silicon substrate. However, it is not described to reduce the variation in carbon concentration.

Therefore, in view of the above situation, it is an object of the present invention to enable the production of a semiconductor wafer having excellent carbon concentration uniformity.

According to the first aspect of the present invention, the semiconductor wafer is heat-treated in an atmosphere containing a carbon-containing gas so that the carbon concentration reaches saturation at any position where the distance from the surface in the depth direction is 5 μm or less. The semiconductor wafer is heat-treated in an inert atmosphere or a reducing atmosphere prior to the heat treatment in the atmosphere containing the carbon-containing gas, and the heat treatment is performed in the atmosphere containing the carbon-containing gas. heat treatment are performed by the temperature in the range of 1080 to 1220 ° C., wherein the heat treatment in an inert atmosphere or the reducing atmosphere, maintaining the 60 to 120 minutes to a temperature in the range of the semiconductor wafer 1130 to 1220 ° C. A method for manufacturing a semiconductor wafer including the above is provided.

According to the second aspect of the present invention, the LSTD density is 0.1 pieces / cm ² or less at a position where the distance from the surface in the depth direction is 5 μm, and the carbon concentration at any position where the distance is smaller than 2 μm. 1 × 10 ¹⁶ atoms / cm ³ or more and the carbon concentration at any position within the range of 2 to 30 μm is 2 × 10 ¹⁶ atoms / cm ³ or more and the distance is greater than 30 μm. A semiconductor wafer having a carbon concentration in the range of 1 × 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ at that position is provided.

According to the third aspect of the present invention, the carbon concentration in the surface region is ^{less than 1 × 10 15} atoms / cm ³ , and the carbon at any position within the depth range of 2 to 30 μm from the surface. The concentration is 2 × 10 ¹⁶ atoms / cm ³ or more, and the carbon concentration at any position where the distance is greater than 30 μm is in the range of 1 × 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3. A semiconductor wafer is provided.

According to the present invention, it is possible to manufacture a semiconductor wafer having excellent carbon concentration uniformity.

The cross-sectional view schematically showing the heat treatment apparatus which can be used in the manufacturing method which concerns on one Embodiment of this invention. FIG. 6 is a perspective view schematically showing a boat included in the heat treatment apparatus of FIG. The graph which shows an example of the heat treatment sequence which can be adopted in the 1st and 2nd heat treatment steps performed in the manufacturing method of the semiconductor wafer which concerns on 1 Embodiment. The graph which shows an example of the heat treatment sequence which can be adopted in the 1st to 3rd heat treatment steps performed in the manufacturing method of the semiconductor wafer which concerns on 1 Embodiment. The graph which shows the measurement result of the carbon concentration of the semiconductor wafer obtained in Example 1. A graph showing the measurement results of the carbon concentration of the semiconductor wafer obtained in Comparative Example 1. The graph which shows the variation of the carbon concentration which occurs in the semiconductor wafer which concerns on Example 1 and Comparative Example 1. The graph which shows the simulation result of the carbon concentration of the semiconductor wafer obtained in the test example 3. The graph which shows the distribution of the carbon concentration of the semiconductor wafer ion-implanted with carbon.

Hereinafter, embodiments of the present invention will be described in detail, but the following description is not intended to limit the present invention.

<Heat treatment equipment>
A heat treatment apparatus that can be used in the production method according to the embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a cross-sectional view schematically showing a heat treatment apparatus that can be used in the manufacturing method according to the embodiment of the present invention. FIG. 2 is a perspective view schematically showing a boat included in the heat treatment apparatus shown in FIG.

The heat treatment apparatus 1 shown in FIG. 1 includes an apparatus main body 10, a boat 20, an exhaust apparatus 30, a gas supply apparatus 40, and a transfer apparatus (not shown).

The apparatus main body 10 includes a quartz furnace core tube 11, a SiC soaking tube 12, a heating device 13, a heat tube 14, a heat shield plate 15, a sealing member 16, a lid 17, a heat retaining device 18, and a support. Includes 19 and.

The quartz furnace core tube 11 includes a quartz furnace core tube main body 111 and a flange portion 112.
The quartz furnace core tube main body 111 has a tubular shape in which one opening is closed and the other opening faces downward. The wall at the top of the quartz furnace core tube main body 111 is provided with a through hole into which the gas supply tube 41 described later is inserted.

The flange portion 112 is a plate provided with a circular through hole 113 in the center. The flange portion 112 is joined to the quartz furnace core tube main body 111 at an opening below the flange portion 112.

The SiC heat soaking tube 12 has a tubular shape in which one opening is closed and the other opening faces downward. The SiC heat equalizing tube 12 is installed so as to surround the quartz furnace core tube main body 111. The SiC soaking tube 12 has a structure in which a SiC layer is provided on the surface of a main body made of a material capable of induction heating such as graphite.

The heating device 13 includes a coil installed so as to surround the SiC heat equalizing tube 12 and a power supply device for passing a high frequency current through the coil. The heating device 13 generates an eddy current in the main body of the SiC soaking tube 12, thereby heating the inside thereof.

The heat tube 14 has a tubular shape in which one opening is closed and the other opening faces downward. The heat tube 14 is installed so as to surround the SiC heat equalizing tube 12 and the coil. The side wall of the heat tube 14 is reduced in diameter in the vicinity of the lower opening. The heat tube 14 prevents electromagnetic waves and heat from leaking to the outside of the apparatus main body 10.

The heat shield plate 15 is installed below the SiC heat equalizing tube 12 and the heat tube 14. The heat shield plate 15 has a through hole, and the quartz furnace core tube main body 111 is inserted through the through hole. The heat shield plate 15 protects the elements installed below the heat shield plate 15 from heat.

The sealing member 16 is installed below the quartz furnace core tube 11. The seal member 16 includes a main body 161 and O-rings 162 and 163.

The main body 161 is a plate-shaped body having a recess having a diameter substantially equal to the outer diameter of the flange portion 112 on one main surface. A groove is provided in an annular shape at the bottom of the recess, and an O-ring 162 is installed in the groove. The main body 161 is installed so that the main surface provided with the recess faces upward, and the flange portion 112 is fitted in the recess. The O-ring 162 prevents gas from flowing through the gap between the main body 161 and the flange portion 112.

The main body 161 has a through hole 164 having a diameter substantially equal to that of the through hole 113 in the center of the recess. The through hole 164, together with the through hole 113, constitutes an carry-in / out port used for carrying in the quartz furnace core tube 11 such as a boat 20 and carrying out from the quartz furnace core tube 11. Further, the main body 161 is provided with a through hole leading from the outer peripheral surface thereof to the through hole 113.

An annular groove is provided on the other main surface of the main body 161 so as to surround the opening of the through hole 164, and the O-ring 163 is installed in this groove. The O-ring 163 prevents gas from flowing through the gap between the main body 161 and the lid 17 when the lid 17 comes into contact with the lower surface of the main body 161.

The lid 17 is installed below the seal member 16. The lid 17 is a plate-like body having a diameter larger than the outer diameter of the O-ring 163. The lid 17 is movable in the vertical direction by a transport device (not shown).

The heat insulating device 18 includes a support 181 and a plurality of quartz reflectors 182. The support 181 supports the quartz reflectors 182 so that their main surfaces are horizontal and are arranged vertically apart from each other. The heat retaining device 18 suppresses the leakage of heat downward from the quartz furnace core tube 11 by the quartz reflecting plate 182 reflecting the heat in the quartz furnace core tube main body 111. The heat insulating device 18 is movable in the vertical direction integrally with the lid 17 by a transport device (not shown).

The support 19 is installed above the heat insulating device 18. The support 19 supports the boat 20 in a detachable manner. The support 19 is movable in the vertical direction integrally with the lid 17 and the heat retaining device 18 by a transport device (not shown). The support 19 may include a rotation mechanism that rotates the boat 20 around an axis parallel to the height direction thereof.

The boat 20 supports a large number of semiconductor wafers 50 so that their main surfaces are horizontal and vertically spaced apart from each other. As the boat 20, for example, a boat made of SiC or Si can be used. Hereinafter, as an example, a boat made of SiC and having a silicon oxide film on the surface will be used.

Here, as shown in FIG. 2, the boat 20 includes a base 21, four columns 22, a top plate 23, and a plurality of holding portions 24.

The base 21 and the top plate 23 are disk-shaped. The base 21 and the top plate 23 face their main surfaces.

One end of each of the columns 22 is fixed to the base 21, and the other end of each is fixed to the top plate 23. The length direction of these columns 22 is perpendicular to the main surface of the base 21 and the top plate 23. Further, the orthographic projections of the columns 22 with respect to the main surface of the base 21 or the top plate 23 are arranged at substantially equal intervals on an arc of a substantially semicircle.

The holding portion 24 has a rod shape. One end of each holding portion 24 is supported by any of the columns 22. The holding portions 24 are arranged on each column 22 at substantially equal intervals in the vertical direction. The length direction of the holding portion 24 is substantially perpendicular to the length direction of the support column 22. The holding portion 24 extends inward from each column 22. The holding portion 24 may have a curved portion or a bent portion.

The boat 20 holds the semiconductor wafer 50 by placing the individual semiconductor wafers 50 on the four holding portions 24 extending from the four columns 22 respectively. As shown in FIG. 1, the boat 20 is detachably supported by a support 19 so that the base 21 is located below and the top plate 23 is located above.

The exhaust device 30 includes one or more vacuum pumps and a pressure regulating valve. One end of the gas discharge pipe 31 is connected to the exhaust device 30. The other end of the gas discharge pipe 31 is inserted into a through hole leading from the outer peripheral surface of the main body 161 to the through hole 113. The exhaust device 30 exhausts the gas in the quartz furnace core tube 11.

The gas supply device 40 includes a tank containing a gas such as an inert gas, a carbon-containing gas, a hydrogen gas, and an oxygen gas, a valve for switching the discharged gas, and a gas flow rate adjusting device for adjusting the gas flow rate. I'm out. One end of the gas supply pipe 41 is connected to the gas supply device 40. The other end of the gas supply pipe 41 is inserted into a through hole provided in the wall at the top of the quartz furnace core tube main body 111. The gas supply device 40 supplies an inert gas, a carbon-containing gas, a hydrogen gas, an oxygen gas, or a mixed gas obtained by diluting them with an inert gas into the quartz furnace core tube 11 at a desired flow rate.

A transport device (not shown) is installed below the lid 17. The transport device integrally moves the lid 17, the heat insulating device 18, the support 19, and the boat 20 up and down. As a result, the transport device enables the boat 20 to be attached to and detached from the support 19, and also allows the quartz furnace core tube 11 to be sealed and opened by the lid 17 and the sealing member 16.

<Manufacturing method of semiconductor wafer>
A method for manufacturing a semiconductor wafer according to an embodiment of the present invention will be described. Here, as an example, the heat treatment apparatus 1 described with reference to FIGS. 1 and 2 will be used.

(Preparation of semiconductor wafer before heat treatment)
First, the semiconductor wafer 50 before heat treatment is prepared. As the semiconductor wafer 50, for example, a wafer cut out from a silicon single crystal ingot manufactured by the Czochralski method is used. The semiconductor wafer 50 thus obtained usually has a void defect in the device forming region. The "device forming region" is, for example, a surface region of the semiconductor wafer 50 in which the distance from one of the main surfaces is within the range of 0 μm to 10 μm.

Next, these semiconductor wafers 50 are supported by the boat 20 and supported by the support 19 shown in FIG. Subsequently, a transfer device (not shown) is driven to transfer the boat 20 to the inside of the quartz furnace core tube 11 together with the support 19 and the heat retaining device 18, and the lid 17 is applied to the lower surface of the main body 161 of the seal member 16. The quartz furnace core tube 11 is sealed by being brought into contact with each other.

(First heat treatment step)
Next, the semiconductor wafer 50 is heat-treated in an inert atmosphere or a reducing atmosphere (first heat treatment step). Here, as an example, the first heat treatment step is performed according to the heat treatment sequence shown in FIG.

FIG. 3 is a graph showing an example of a heat treatment sequence that can be adopted in the first and second heat treatment steps performed in the method for manufacturing a semiconductor wafer according to an embodiment. In FIG. 3, the vertical axis shows the temperature of the semiconductor wafer 50, and the horizontal axis shows the time.

The heat treatment sequence shown in FIG. 3 includes a first period S1, a second period S2, a third period S3, a fourth period S4, a fifth period S5, a sixth period S6, and a seventh period S7. Includes. In the first period S1 to the third period S3, the first heat treatment step is performed. Further, in the 4th period S4 to the 7th period S7, the second heat treatment step described later is performed.

In the preliminary operation period prior to the first period S1, the exhaust device 30 is driven to remove the gas in the internal space of the quartz furnace core tube 11. At the same time, the gas supply device 40 is driven to introduce the inert gas or the reducing gas into the quartz furnace core tube 11. The preparatory operation period ends when the gas in the internal space of the quartz furnace core tube 11 is replaced with the inert gas or the reducing gas.

As the inert gas, for example, Ar gas can be used. Further, as the reducing gas, for example, hydrogen gas or a mixed gas obtained by diluting the hydrogen gas with an inert gas can be used. In particular, when a SiC boat is used as the boat 20, it is preferable to use Ar gas.

The inert gas or reducing gas is preferably introduced into the quartz furnace core tube 11 so that the flow velocity above the top plate 23 of the boat 20 is 33.5 m / s or less, for example. If this flow velocity is too large, the etching of the oxide film provided on the surface of the boat 20 by the gas becomes remarkable.

In the first period S1 following the preliminary operation period, the heating device 13 is driven to raise the temperature of the semiconductor wafer 50. This heating is performed by applying high frequency power (for example, 10 to 100 kHz, 10 to 200 kW) to the magnetic field coil, generating an eddy current in the SiC soaking tube 12, and utilizing the Joule heat generated thereby. The first period S1 ends when the temperature of the semiconductor wafer 50 reaches a predetermined temperature, specifically, a temperature within the range maintained in the second period S2.

In the second period S2 following the first period S1, the temperature of the semiconductor wafer 50 is maintained within a predetermined range. In the second period S2, the semiconductor wafer 50 is preferably heated so as to be maintained at a temperature in the range of 1130 to 1220 ° C., and is heated so as to be maintained at a temperature in the range of 1150 to 1200 ° C. Is more preferable. If this temperature is too low, a long heat treatment time is required, and production efficiency may deteriorate. Further, if this temperature is too high, contamination of the semiconductor wafer 50 and slip dislocations may easily occur.

In the second period S2, the temperature of the semiconductor wafer 50 is maintained at a temperature within the above range, for example, for 60 to 120 minutes. If the heat treatment time is too short, the elimination of void defects may be insufficient. Further, if the heat treatment time is too long, slip dislocations may easily occur on the semiconductor wafer 50.

In the third period S3 following the second period S2, the temperature of the semiconductor wafer 50 is lowered. In the third period S3, it is preferable to lower the temperature of the semiconductor wafer 50 to a temperature within the range of 700 to 850 ° C. while maintaining the atmosphere inside the quartz furnace core tube 11 in an inert atmosphere or a reducing atmosphere, preferably 700 to 850 ° C. It is more preferable to lower the temperature to a temperature within the range of 800 ° C. It is also possible to omit the third period S3 to the fifth period S5 and continue the sixth period S6 to the second period S2. However, by lowering the temperature to the above temperature, it is possible to prevent the surface of the semiconductor wafer 50 from being roughened.

The above-mentioned first heat treatment step can be omitted. However, by performing this first heat treatment step, void defects in the device forming region can be reduced.

(Second heat treatment step)
In the second heat treatment step, as described below, the carbon concentration of the semiconductor wafer 50 is saturated at any position where the distance from the surface to the depth direction of the semiconductor wafer 50 is 5 μm or less in an atmosphere containing carbon-containing gas. Heat treat to reach.

First, in the fourth period S4 following the third period S3, the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 while continuing the exhaust inside the quartz furnace core tube 11 is an inert gas. Alternatively, the reducing gas is switched to a carbon-containing gas or a mixed gas obtained by diluting the same with an inert gas. As a result, the atmosphere surrounding the semiconductor wafer 50 is switched from the inert atmosphere or the reducing atmosphere to the atmosphere containing the carbon-containing gas.

The carbon-containing gas is, for example, a gas containing at least one of carbon monoxide, carbon dioxide, and a hydrocarbon. The carbon-containing gas preferably contains at least one of carbon monoxide and carbon dioxide. When a hydrocarbon is used alone as the carbon-containing gas, it is preferable to carry out the third heat treatment step described later.

The carbon-containing gas is preferably introduced into the quartz furnace core tube 11 as a mixed gas diluted with an inert gas, for example. As the inert gas, for example, Ar gas can be used.

The ratio of the carbon-containing gas to the mixed gas is preferably in the range of 1 to 20% by volume, and more preferably in the range of 1 to 15% by volume. If this ratio is too small, the carbon concentration introduced into the semiconductor wafer 50 may not reach the saturation concentration. Further, if this ratio is too large, the SiOC film may be formed on the surface of the semiconductor wafer 50 and the carbon concentration may not reach the saturation concentration, and the SiOC film may be removed by washing after the heat treatment. It can be difficult and complicate the manufacturing process.

The mixed gas or the carbon-containing gas is preferably introduced into the quartz furnace core tube 11 so that the flow velocity above the top plate 23 of the boat 20 is 2.2 m / s or more, for example. If the flow velocity is too small, the gas tends to stagnate in the internal space of the quartz furnace core tube 11, and the uniformity of the carbon concentration introduced into the semiconductor wafer 50 may decrease.

Further, the introduction of the mixed gas or the carbon-containing gas into the inside of the quartz furnace core tube 11 by the gas supply device 40 and the exhaust inside the quartz furnace core tube 11 by the exhaust device 30 contain carbon inside the quartz furnace core tube 11. It is preferable that the partial pressure of the gas is, for example, in ^{the range of 1.0 × 10 3 to} 2.0 × 10 ⁴ Pa, and preferably in the range of ^{1.0 × 10 3 to} 1.5 × 10 ^{4 Pa.} It is more preferable to do it so that it is inside. If this partial pressure is too low, the carbon concentration may not reach the saturation concentration. If the partial pressure is too high, the SiOC film may not reach the saturation concentration due to the formation of the SiOC film on the surface of the semiconductor wafer 50, and it becomes difficult to remove the SiOC film by washing after the heat treatment. , The manufacturing process can be complicated.

In the fifth period S5 following the fourth period S4, the heating device 13 is driven to raise the temperature of the semiconductor wafer 50. This heating is performed by applying high frequency power (for example, 10 to 100 kHz, 10 to 200 kW) to the magnetic field coil, generating an eddy current in the SiC soaking tube 12, and utilizing the Joule heat generated thereby. The fifth period S5 ends when the temperature of the semiconductor wafer 50 reaches a predetermined temperature, specifically, a temperature within the range maintained in the sixth period S6.

In the sixth period S6 following the fifth period S5, the temperature of the semiconductor wafer 50 is maintained within a predetermined range. In the sixth period S6, the temperature of the semiconductor wafer 50 is set to a temperature within the range of 1080 to 1220 ° C. so that the carbon concentration at any position of the semiconductor wafer 50 at a distance of 5 μm or less reaches saturation. , Preferably heated to a temperature in the range of 1100 to 1200 ° C. If the temperature is too low, the saturation concentration of carbon becomes low due to the above-mentioned reason, and the uniformity of the carbon concentration may become low. Further, if the temperature is too high, contamination of the semiconductor wafer 50 and slip dislocations may easily occur.

Whether or not the carbon concentration at any position where the distance from the surface of the semiconductor wafer in the thickness direction is 5 μm or less has reached saturation at the heat treatment temperature can be confirmed by, for example, the following method. First, the carbon concentration of the semiconductor wafer obtained by the heat treatment is measured by the secondary ion mass spectrometry (SIMS) method to obtain the carbon concentration distribution in the thickness direction of the semiconductor wafer. Next, a simulation is performed based on the result, and the carbon concentration distribution in the heat treatment (when the maximum temperature is reached) in the atmosphere containing the carbon-containing gas is estimated. Then, by comparing the known saturation concentration of carbon at the maximum temperature with the carbon concentration distribution obtained by the simulation, it is confirmed whether or not the carbon concentration has reached the saturation at the heat treatment temperature.
The known saturation concentration of carbon at the maximum temperature varies depending on the type of material constituting the semiconductor wafer 50 and the heating temperature. For example, when a semiconductor wafer 50 made of silicon is heated at 1100 ° C, 1150 ° C, and 1200 ° C, the carbon saturation concentrations are 4 × 10 ¹⁶ atoms / cm ³ , 7 × 10 ¹⁶ atoms / cm ³ , and, respectively. It is 11 × 10 ¹⁶ atoms / cm ³ .

In the sixth period S6, the temperature of the semiconductor wafer 50 is maintained at a temperature within the above range, for example, for 10 to 120 minutes. If the heat treatment time is too short, the carbon concentration may not reach the saturation concentration. Further, if the heat treatment time is too long, slip dislocations may easily occur on the semiconductor wafer 50.

In the seventh period S7 following the sixth period S6, the temperature of the semiconductor wafer 50 is lowered. The temperature lowering rate of the semiconductor wafer 50 in the seventh period S7 is, for example, 4 ° C./min.

In the seventh period S7, the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 may be a carbon-containing gas or a mixed gas obtained by diluting the gas with an inert gas, and may be left as an inert gas. It may be switched, or it may be switched to an oxygen gas or a mixed gas obtained by diluting the oxygen gas with an inert gas. However, especially when the boat 20 is made of SiC, the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 is oxygen gas or a mixed gas obtained by diluting this with an inert gas. Is preferable.

The film thickness of the oxide film provided on the surface of the boat 20 is reduced by going through the first and second heat treatment steps and the like. In particular, in the SiC boat 20 having an oxide film on the surface, the etching reaction shown below occurs at the contact portion with the semiconductor wafer 50 made of silicon, so that the thickness of the contact portion decreases rapidly.

Si (S) + SiO ₂ (S) → 2SiO (V)
When the film thickness of the oxide film provided on the surface of the SiC boat 20 is reduced, the carbon contained in the boat 20 may contaminate the semiconductor wafer 50 and reduce the uniformity of the carbon concentration in the semiconductor wafer 50. .. Further, if the film thickness of the oxide film provided on the surface of the SiC boat 20 decreases, the carbon contained in the boat 20 may diffuse into the atmosphere, and the carbon concentration in the atmosphere may become excessively high. ..

When the temperature of the semiconductor wafer 50 is lowered in an atmosphere containing oxygen, the film thickness of the oxide film provided on the surface of the boat 20 increases, and as a result, the decrease can be suppressed. For example, in the seventh period S7, by increasing the film thickness of the oxide film by 10 nm or more, it is possible to prevent the film thickness from decreasing. Therefore, the above problem can be avoided.

In the seventh period S7, the ratio of oxygen gas to the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 is preferably 50% by volume or more, more preferably 100% by volume. When the oxygen gas is diluted with an inert gas, for example, Ar gas can be used as the inert gas. If this ratio is too small, it is difficult to sufficiently suppress the decrease in the film thickness of the oxide film provided on the surface of the boat 20.

Oxygen gas by the gas supply device 40 or a mixed gas obtained by diluting the gas with an inert gas is introduced into the inside of the quartz furnace core tube 11 and exhausted inside the quartz furnace core tube 11 by the exhaust device 30 is the quartz furnace core tube. It is preferable that the partial pressure of the oxygen gas inside the 11 is, for example, in ^{the range of 5.0 × 10 4 to} 1.0 × 10 ^{5 Pa.}

Mixing of the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 from a carbon-containing gas or a mixed gas obtained by diluting the carbon-containing gas with an inert gas to oxygen gas or a mixed gas obtained by diluting the gas with an inert gas. It is preferable to switch to the gas after the temperature of the semiconductor wafer 50 reaches less than 1100 ° C. If the temperature is too high, the surface of the semiconductor wafer 50 may be roughened. Further, it is preferable to perform this switching before the temperature in the furnace becomes 1000 ° C. or lower. If this temperature is too low, it is difficult to increase the film thickness of the oxide film provided on the surface of the boat 20. The introduction of the oxygen gas or the mixed gas obtained by diluting the oxygen gas or the mixed gas obtained by diluting the oxygen gas into the quartz furnace core tube 11 is preferably continued until the temperature in the furnace drops to 800 ° C. or lower.

After the temperature of the semiconductor wafer 50 is sufficiently lowered, the operations of the exhaust device 30 and the gas supply device 40 are stopped. After that, a transfer device (not shown) is driven to move the boat 20 downward together with the support 19 and the heat insulating device 18 to carry it out of the quartz furnace core tube 11. Further, the boat 20 is removed from the support 19, and each semiconductor wafer 50 is recovered from the boat 20. As described above, the production of the semiconductor wafer is completed.

<Semiconductor wafer>
The semiconductor wafer 50 subjected to the above heat treatment has the following characteristics. That is, the semiconductor wafer 50 has an LSTD (Laser Scattering Tomography Defect) density of 0.1 pieces / cm ² or less at a position where the distance D in the depth direction from the surface is 5 μm. Here, the LSTD is a void defect observed by an infrared scattering tomograph (LST: Laser Scattering Tomography) in which an infrared laser beam is incident from the surface of the semiconductor wafer 50 and the scattered light is detected. For the detection of LSTD, for example, an LSTD scanner (MO601 manufactured by RAYTEX Corporation) can be used.
When the first heat treatment step is omitted, the LSTD density at the position where the distance D from the surface in the depth direction is 5 μm usually exceeds the above-mentioned upper limit value.

Further, the semiconductor wafer 50 subjected to the above heat treatment has a BMD density of 1 × 10 ⁹ pieces / cm ³ or more. Here, for the measurement of the BMD density, for example, IR tomography (MO-441 manufactured by RAYTEX Corporation) can be used.
When the first heat treatment step is omitted, the BMD density is usually lower than the above-mentioned lower limit value.

Further, the semiconductor wafer 50 subjected to the above heat treatment has the characteristics described below regarding the distribution of the carbon concentration in the thickness direction. That is, the semiconductor wafer 50 subjected to the above heat treatment has an LSTD density of 0.1 pieces / cm ² or less at a position where the distance D from the surface in the depth direction is 5 μm, and the distance D is smaller than 2 μm. The carbon concentration at the position is 1 × 10 ¹⁶ atoms / cm ³ or more, the carbon concentration at any position within the range of 2 to 30 μm is 2 × 10 ¹⁶ atoms / cm ³ or more, and the distance D is. The carbon concentration at any position greater than 30 μm is in the range of 1 × 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ .

According to one example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship becomes an upwardly convex curve. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 30 μm, and the maximum value of the carbon concentration is in the range of 2 × 10 ^{16 to} 5 × 10 ¹⁶ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 1 × 10 ^{16 to} 4 × 10 ¹⁶ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant or monotonously decreasing within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

According to another example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship is an upwardly convex curve. Become. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 30 μm, and the maximum value of the carbon concentration is in the range of 2 × 10 ^{16 to} 8 × 10 ¹⁶ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 1 × 10 ^{16 to} 5 × 10 ¹⁶ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

According to yet another example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship is an upwardly convex curve. Will be. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 30 μm, and the maximum value of the carbon concentration is in the range of 4 × 10 ^{16 to} 9 × 10 ¹⁶ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 2 × 10 ^{16 to} 7 × 10 ¹⁶ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant or monotonously decreasing within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

According to yet another example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship is an upwardly convex curve. Will be. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 30 μm, and the maximum value of the carbon concentration is in the range of 4 × 10 ^{16 to} 10 × 10 ¹⁶ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 2 × 10 ^{16 to} 8 × 10 ¹⁶ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

<Effect>
In the above-mentioned manufacturing method, in the second heat treatment step, carbon is introduced into the device forming region of the semiconductor wafer 50 until its saturation concentration is reached. Therefore, even if the carbon concentration in the semiconductor wafer 50 before the heat treatment varies in the plane or between the wafers, the variation can be canceled by the second heat treatment step. Therefore, according to this method, for example, it is possible to manufacture a semiconductor wafer in which the variation in carbon concentration in the in-plane direction is small and the variation in carbon concentration distribution in the thickness direction in the device forming region is small among wafers. That is, according to this method, it is possible to manufacture a semiconductor wafer having excellent carbon concentration uniformity.

Further, in the above-mentioned manufacturing method, in the seventh period S7 in which the temperature of the semiconductor wafer 50 is lowered, oxygen gas or a mixed gas obtained by diluting the oxygen gas with an inert gas is introduced into the quartz furnace core tube 11, and the product is made of SiC. It is possible to prevent the thickness of the oxide film provided on the surface of the boat 20 from becoming insufficient. In this case, for example, it is possible to prevent local contamination of the semiconductor wafer 50 by carbon contained in the boat 20. Further, in this case, the influence of the carbon contained in the boat 20 on the carbon concentration in the atmosphere can be reduced or eliminated. Therefore, in this case, it becomes possible to manufacture an excellent semiconductor wafer due to the uniformity of the carbon concentration.

The effect of preventing the film thickness of the oxide film from decreasing can also be achieved by taking out the semiconductor wafer 50 from the boat 20 and then carrying the boat 20 into a heat treatment furnace and performing heat treatment in an atmosphere containing oxygen. Will be done. However, it is effective to perform the oxide film forming step when the temperature of the semiconductor wafer is lowered in order to improve the manufacturing efficiency.
Further, when a Si boat is used as the boat 20, carbon contamination from the boat surface does not occur, so that the oxide film forming step is unnecessary.

As described above, according to this manufacturing method, a semiconductor wafer having excellent carbon concentration uniformity can be manufactured. That is, it is possible to introduce carbon into the device forming region of the semiconductor wafer at a controlled concentration. Therefore, it is possible to prevent device malfunctions such as Vth (threshold voltage) shift of semiconductor devices from occurring due to variations in carbon concentration.

Further, in this manufacturing method, heat treatment is performed in an inert atmosphere in the first heat treatment step. Therefore, it is possible to obtain a semiconductor wafer in which void defects are reduced and the BMD is sufficiently grown.

<Modification example of manufacturing method>
The method described above can be modified in various ways.
For example, in the above-mentioned manufacturing method, the vertical heat treatment apparatus 1 shown in FIG. 1 is used, but the technique described here can be applied to short-time high-temperature heat treatment such as RTP (Rapid Thermal Process). be.
Further, the above-mentioned production method may further include a third heat treatment step described below.

(Third heat treatment step)
In the third heat treatment step, the semiconductor wafer 50 is heat-treated in a reducing atmosphere containing hydrogen gas, as described below. By performing the third heat treatment step, carbon existing in the surface region of the semiconductor wafer 50 can be diffused to the outside of the semiconductor wafer 50, that is, diffused outward. The third heat treatment step can be omitted. However, in applications where it is desired that the carbon concentration in the device forming region of the semiconductor wafer 50 is low, it is advantageous to perform the third heat treatment step.

FIG. 4 is a graph showing an example of a heat treatment sequence that can be adopted in the first to third heat treatment steps performed in the method for manufacturing a semiconductor wafer according to an embodiment. In FIG. 4, the vertical axis shows the temperature of the semiconductor wafer 50, and the horizontal axis shows the time.

The heat treatment sequence shown in FIG. 4 includes a first period S1, a second period S2, a third period S3, a fourth period S4, a fifth period S5, a sixth period S6, and a seventh period S7. The eighth period S8, the ninth period S9, the tenth period S10, and the eleventh period S11 are included. In the first period S1 to the third period S3, the above-mentioned first heat treatment step is performed, and in the fourth period S4 to the seventh period S7, the above-mentioned second heat treatment step is performed. Further, in the 8th period S8 to the 11th period S11, the third heat treatment step described in detail below is performed.

First, in the eighth period S8 following the seventh period S7, the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 while continuing the exhaust inside the quartz furnace core tube 11 is a carbon-containing gas. Alternatively, the mixed gas obtained by diluting this with an inert gas is switched to hydrogen gas or a mixed gas obtained by diluting this with an inert gas. As a result, the atmosphere surrounding the semiconductor wafer 50 is switched from an atmosphere containing carbon-containing gas to a reducing atmosphere containing hydrogen gas.

In the eighth period S8, the ratio of hydrogen gas to the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 is preferably 20% by volume or more, more preferably 100% by volume. When the hydrogen gas is diluted with an inert gas, for example, Ar gas can be used as the inert gas. If this ratio is too small, it is difficult to sufficiently diffuse carbon from the surface of the semiconductor wafer 50.

The introduction of hydrogen gas by the gas supply device 40 or a mixed gas obtained by diluting the hydrogen gas with an inert gas into the inside of the quartz furnace core tube 11 and the exhaust of the inside of the quartz furnace core tube 11 by the exhaust device 30 are carried out by the quartz furnace core tube 11. It is preferable that the partial pressure of the hydrogen gas inside the 11 is in ^{the range of 2.0 × 10 4 to} 1.0 × 10 ^{5 Pa.}

Mixing of the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 from a carbon-containing gas or a mixed gas obtained by diluting the carbon-containing gas with an inert gas to hydrogen gas or a mixed gas obtained by diluting the same with an inert gas. The switch to gas is preferably performed at a temperature within the range of 700 to 850 ° C. for the semiconductor wafer 50, or at a temperature lower than that. By performing the above switching at such a temperature, it is possible to prevent the surface of the semiconductor wafer 50 from being roughened.

In the ninth period S9 following the eighth period S8, the heating device 13 is driven to raise the temperature of the semiconductor wafer. This heating is performed in the same manner as the heating in the fifth period S5 described above, for example.

In the tenth period S10 following the ninth period S9, the temperature of the semiconductor wafer 50 is maintained within a predetermined range. In the tenth period S10, the temperature of the semiconductor wafer 50 is maintained preferably in the range of 1080 to 1220 ° C, more preferably in the range of 1100 to 1200 ° C. If the temperature is too low, it is difficult to sufficiently diffuse carbon from the surface of the semiconductor wafer 50. If the temperature is too high, contamination of the semiconductor wafer 50 and slip dislocations may easily occur.

In the tenth period S10, the temperature of the semiconductor wafer 50 is maintained at a temperature within the above range, for example, for 1 minute to 2 hours. If the heat treatment time is too short, it may be difficult to sufficiently diffuse the carbon present on the surface of the semiconductor wafer 50 to the outside. Further, if the heat treatment time is too long, the carbon supplied in the second heat treatment step may diffuse outward more than necessary, and the influence of the variation in carbon concentration between wafers may reappear. ..

In the eleventh period following the tenth period S10, the temperature of the semiconductor wafer is lowered. The temperature lowering rate of the semiconductor wafer 50 in the eleventh period S11 is, for example, 4 ° C./min.

In the eleventh period S11, the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 may be hydrogen gas or a mixed gas obtained by diluting the gas with an inert gas, and may be switched to an inert gas. Alternatively, it may be switched to an oxygen gas or a mixed gas obtained by diluting the oxygen gas with an inert gas. However, especially when the boat 20 is made of SiC, the gas introduced into the inside of the quartz furnace core tube 11 by the gas supply device 40 is oxygen gas or a mixed gas obtained by diluting this with an inert gas. Is preferable. As the oxygen gas or the mixed gas obtained by diluting the oxygen gas with an inert gas, the gas described with reference to S7 in the 7th period can be used.

<Modification example of semiconductor wafer>
The heat-treated semiconductor wafer 50 described with reference to FIG. 4 has the characteristics described below regarding the distribution of carbon concentration in the thickness direction. That is, the semiconductor wafer 50 has a carbon concentration in the surface region of ^{less than 1 × 10 15} atoms / cm ³ , and the carbon concentration at any position where the distance D from the surface in the depth direction is within the range of 2 to 30 μm. Is 2 × 10 ¹⁶ atoms / cm ³ or more, and the carbon concentration at any position where the distance D is greater than 30 μm is in the range of 1 × 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ .

According to one example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship becomes an upwardly convex curve. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 30 μm, and the maximum value of the carbon concentration is in the range of 2 × 10 ^{16 to} 2 × 10 ¹⁷ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 1 × 10 ^{14 to} 1 × 10 ¹⁵ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant or monotonously decreasing within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

According to another example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship is an upwardly convex curve. Become. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 30 μm, and the maximum value of the carbon concentration is in the range of 2 × 10 ^{16 to} 2 × 10 ¹⁷ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 1 × 10 ^{14 to} 1 × 10 ¹⁵ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

According to yet another example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship is an upwardly convex curve. Will be. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 15 μm, and the maximum value of the carbon concentration is in the range of 4 × 10 ^{16 to} 2 × 10 ¹⁷ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 3 × 10 ^{14 to} 1 × 10 ¹⁵ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant or monotonously decreasing within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

According to yet another example, when the relationship between the distance D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship is an upwardly convex curve. Will be. In this case, for example, the distance D at which the carbon concentration is maximum is in the range of 2 to 15 μm, and the maximum value of the carbon concentration is in the range of 4 × 10 ^{16 to} 2 × 10 ¹⁷ atoms / cm ³ . Further, in this case, for example, when the distance D is zero, the carbon concentration is in the range of 3 × 10 ^{14 to} 1 × 10 ¹⁵ atoms / cm ³ , and when the distance D is in the range of more than 30 μm, the carbon concentration is 1 ×. It is almost constant within the range of 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ^3.

The semiconductor wafer 50 subjected to the above heat treatment has carbon in the above-mentioned distribution. That is, according to the above-mentioned method, in the second heat treatment step, carbon is introduced into the device forming region of the semiconductor wafer 50 until its saturation concentration is reached, and in the third heat treatment step, carbon is outwardly removed from the surface of the semiconductor wafer 50. Since it is diffused, it is possible to obtain a semiconductor wafer in which the carbon concentration contained in the surface of the semiconductor wafer 50 is uniform and not excessively high.

When the semiconductor wafer 50 according to the modified example is further subjected to the first heat treatment, the LSTD density and the BMD density are within the above-mentioned ranges.

<Effect of modified example>
According to the method according to the modified example, the same effect as the method described with reference to FIGS. 1 to 3 can be obtained. In addition, in this method, since the third heat treatment step is performed, the carbon concentration in the device forming region can be reduced. Therefore, the semiconductor wafer obtained by this method is suitable for applications in which a low carbon concentration in the device forming region is desired.

Next, a specific example of the present invention will be described.
<< Test Example 1 >>
(Example 1)
<Preparation of semiconductor wafer>
From a silicon single crystal ingot of φ300 mm manufactured by the Czochralski method, two sets of wafers were prepared, each consisting of a plurality of semiconductor wafers having the same carbon concentration and having different carbon concentrations from each other. The carbon concentration was measured by the SIMS method.

Specifically, from a first wafer group consisting of 20 semiconductor wafers having a carbon concentration of 5 × 10 ¹⁵ atoms / cm ³ and 20 semiconductor wafers having a carbon concentration of 1 × 10 ¹⁶ atoms / cm ^3. A second wafer group was prepared.

<Heat treatment of semiconductor wafer>
Ten semiconductor wafers were extracted from each of the first wafer group and the second wafer group and placed on the boat 20 shown in FIG. Here, as the boat 20, a SiC boat having an oxide film having a thickness of 50 nm on the surface was used. This boat 20 was conveyed to the inside of the quartz furnace core tube 11 of the heat treatment apparatus 1 shown in FIG. 1 and the second heat treatment step described above was performed.

Specifically, the temperature of the semiconductor wafer was raised to 1200 ° C. in an atmosphere containing a carbon-containing gas, and the temperature was maintained at this temperature for 60 minutes. _{Here, CO 2} was used as the carbon-containing gas, and this was diluted with Ar gas. The CO ₂ content in this atmosphere was 1% by volume.

Then, the temperature of the semiconductor wafer was lowered to 600 ° C., and they were taken out to the outside of the heat treatment apparatus 1. The obtained semiconductor wafer was used as the first lot.

The same heat treatment was performed on the remaining 10 semiconductor wafers of each of the first and second wafer groups. The obtained semiconductor wafer was used as the second lot.

(Example 2)
The heat treatment was carried out in the same manner as in Example 1 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 10% by volume.

(Example 3)
The heat treatment was carried out in the same manner as in Example 1 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 20% by volume.

(Example 4)
The heat treatment was performed in the same manner as in Example 1 except that the heat treatment temperature in the second heat treatment step was changed from 1200 ° C. to 1100 ° C.

(Example 5)
The heat treatment was performed in the same manner as in Example 2 except that the heat treatment temperature in the second heat treatment step was changed from 1200 ° C. to 1100 ° C.

(Example 6)
The heat treatment was performed in the same manner as in Example 3 except that the heat treatment temperature in the second heat treatment step was changed from 1200 ° C. to 1100 ° C.

(Comparative Example 1)
The heat treatment was carried out in the same manner as in Example 1 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 0% by volume.

(Comparative Example 2)
The heat treatment was carried out in the same manner as in Example 1 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 0.5% by volume.

(Comparative Example 3)
The heat treatment was carried out in the same manner as in Example 1 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 30% by volume.

(Comparative Example 4)
The heat treatment was carried out in the same manner as in Example 1 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 100% by volume.

(Comparative Example 5)
The heat treatment was carried out in the same manner as in Example 4 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 0.5% by volume.

(Comparative Example 6)
The heat treatment was carried out in the same manner as in Example 4 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 30% by volume.

(Comparative Example 7)
The heat treatment was carried out in the same manner as in Example 4 except that _{the CO 2} content in the atmosphere was changed from 1% by volume to 100% by volume.

(Comparative Example 8)
The heat treatment was performed in the same manner as in Example 2 except that the heat treatment temperature in the second heat treatment step was changed from 1200 ° C. to 1250 ° C.

(Comparative Example 9)
The heat treatment was performed in the same manner as in Example 2 except that the heat treatment temperature in the second heat treatment step was changed from 1200 ° C. to 1050 ° C.

<Evaluation>
The carbon concentration of the semiconductor wafers obtained in Examples 1 to 6 and Comparative Examples 1 to 9 was measured, and slip dislocations were confirmed. The results are shown in Table 1.

(Measurement and evaluation of carbon concentration)
The carbon concentration was measured by measuring the carbon concentration at each position where the distance D in the depth direction from the surface of the semiconductor wafer was 15 μm or less by the SIMS method. Then, these measurement results were averaged for each wafer group. The measurement results of the first lot and the second lot were averaged together. The measurement results of the carbon concentration of the semiconductor wafer are shown in FIGS. 5 and 6.

FIG. 5 is a graph showing the measurement results of the carbon concentration of the semiconductor wafer obtained in Example 1. FIG. 6 is a graph showing the measurement results of the carbon concentration of the semiconductor wafer obtained in Comparative Example 1.

In the graphs shown in FIGS. 5 and 6, the vertical axis indicates the carbon concentration, and the horizontal axis indicates the distance D from the surface of the semiconductor wafer in the depth direction. Further, each plot represents the average value of the carbon concentration at a specific distance D of the semiconductor wafers included in each wafer group.

Based on this result, whether or not the carbon reached the saturation concentration at the heat treatment temperature was evaluated by the following method. First, the carbon concentration of the semiconductor wafer obtained by the heat treatment was measured by the SIMS method to obtain the carbon concentration distribution in the thickness direction of the semiconductor wafer. Next, a simulation was performed based on the results, and the carbon concentration distribution during heat treatment (when the maximum temperature was reached) in an atmosphere containing carbon-containing gas was estimated. Then, by comparing the known saturation concentration of carbon at the maximum temperature with the carbon concentration distribution obtained by simulation, the distance from the surface of the semiconductor wafer in the thickness direction is at any position of 5 μm or less. It was evaluated whether the carbon concentration had reached saturation. In Table 1, the heat treatment conditions for obtaining the semiconductor wafer having reached the saturation concentration are represented by “◯”, and the heat treatment conditions for obtaining the semiconductor wafer having reached the saturation concentration are represented by “x”. The carbon saturation concentration is, for example, 11 × 10 ¹⁶ atoms / cm ^{3 when the silicon wafer is heated at 1200 ° C.} Further, the saturation concentration of carbon when the silicon wafer is heated at 1100 ° C. is 4 × 10 ¹⁶ atoms / cm ³ .

As is clear from FIG. 6, in the semiconductor wafer according to Comparative Example 1, the difference in carbon concentration that occurred between the first wafer group and the second wafer group before the heat treatment, that is, the variation in carbon concentration is the distance. It happens no matter what D is. On the other hand, as is clear from FIG. 5, in the semiconductor wafer according to Example 1, almost variation in carbon concentration is observed between the first wafer group and the second wafer group within the range of the distance D of 5 μm or less. No.

Therefore, when the distance D is 5 μm, the variation in carbon concentration between the first wafer group and the second wafer group is obtained as a coefficient of variation. Here, it was calculated from the following equation.
Coefficient of variation = standard deviation / average value As shown in Table 1, the coefficient of variation of the semiconductor wafer obtained under heating conditions where carbon does not reach the saturation concentration is 0.5 or more, whereas carbon reaches the saturation concentration. The coefficient of variation of the semiconductor wafer obtained under the heating conditions was less than 0.5. That is, it was shown that the variation in carbon concentration that had existed before the heat treatment was eliminated.

The semiconductor wafer according to Comparative Example 9 showed a relatively large coefficient of variation even though the carbon reached the saturation concentration. It is considered that this is because the heating temperature in the second heat treatment step was too low. That is, it is considered that the variation was not eliminated because the carbon concentration contained in the semiconductor wafer before the heat treatment was higher than the carbon concentration introduced by the heat treatment.

In FIG. 7, the variation in carbon concentration generated in the semiconductor wafer obtained in Example 1 and the variation in carbon concentration generated in the semiconductor wafer obtained in Comparative Example 1 are calculated at a distance D within a range of 15 μm or less. The results of the comparison are shown.

FIG. 7 is a graph showing variations in carbon concentration occurring in the semiconductor wafers according to Example 1 and Comparative Example 1. In the graph shown in FIG. 7, the vertical axis shows the variation (coefficient of variation) in carbon concentration between the first wafer group and the second wafer group, and the horizontal axis shows the distance D.

As shown in FIG. 7, the semiconductor wafer according to Example 1 has a small coefficient of variation within a range of a distance D of 5 μm or less. On the other hand, the semiconductor wafer according to Comparative Example 1 shows a relatively large coefficient of variation regardless of the distance D.

(Confirmation and evaluation of slip dislocations)
The surface of the semiconductor wafer was irradiated with laser light, image data was created from the intensity of the reflected light, and the length of slip dislocations was measured. In Table 1, among the semiconductor wafers obtained under each heating condition, the heating conditions including the semiconductor wafers in which slip dislocations having a length of 10 mm or more were detected were “yes”, and the heating conditions not detected were “yes”. -”Is represented.

As shown in Table 1, slip dislocations having a length of 10 mm or more were detected only in the semiconductor wafer according to Comparative Example 8. This is considered to be due to the heating temperature being too high.

From the above results, it was shown that the semiconductor wafers obtained by the manufacturing methods of Examples 1 to 6 have particularly excellent carbon concentration uniformity in the device forming region.

<< Test Example 2 >>
The semiconductor wafer prepared by the same method as in Test Example 1 was subjected to the first and second heat treatment steps. Specifically, the procedure was as follows.

(Example 7)
The heat treatment was performed in the same manner as in Example 3 except for the following. That is, the first heat treatment step was performed prior to the second heat treatment step. In the first heat treatment step, specifically, the semiconductor wafer was heated to 1200 ° C. in an inert atmosphere and maintained at this temperature for 60 minutes. Here, Ar gas was used as the inert gas. After that, the temperature of the semiconductor wafer was lowered to 800 ° C., and in this state, the atmosphere surrounding the semiconductor wafer was switched from the inert atmosphere to the atmosphere containing carbon-containing gas.

(Example 8)
The heat treatment was performed in the same manner as in Example 7 except that the atmosphere for lowering the temperature after the second heat treatment step was changed from a carbon-containing gas atmosphere to an atmosphere containing oxygen gas. The oxygen content in the atmosphere was 100% by volume.

(Example 9)
A semiconductor wafer was prepared by the same method as in Test Example 1, and heat treatment was performed by the same method as in Example 6 except for the following. That is, the first heat treatment step was performed prior to the second heat treatment step. In the first heat treatment step, specifically, the semiconductor wafer was heated to 1200 ° C. in an inert atmosphere and maintained at this temperature for 60 minutes. Here, Ar gas was used as the inert gas. After that, the temperature of the semiconductor wafer was lowered to 800 ° C., and in this state, the atmosphere surrounding the semiconductor wafer was switched from the inert atmosphere to the atmosphere containing carbon-containing gas.

(Example 10)
The heat treatment was performed in the same manner as in Example 9 except that the atmosphere for lowering the temperature after the second heat treatment step was changed from a carbon-containing gas atmosphere to an atmosphere containing oxygen gas. The content of oxygen gas in the atmosphere was 100% by volume.

<Evaluation>
(Measurement of crystal defect density)
For the semiconductor wafers obtained in Examples 7 to 10, the LSTD density was measured when the distance D was 5 μm. Here, an LSTD scanner (MO601 manufactured by RAYTEX Corporation) was used for measuring the LSTD density. As a result, the LSTD densities of the semiconductor wafers obtained in Examples 7 to 10 were 0.1 pieces / cm ² or less.

(Measurement of BMD density)
Further, the BMD density of the semiconductor wafers obtained in Examples 7 to 10 was measured. Here, IR tomography (MO-441 manufactured by RAYTEX Corporation) was used for measuring the BMD density. As a result, the BMD densities of the semiconductor wafers obtained in Examples 7 to 10 were 1 × 10 ⁹ pieces / cm ³ or more.

From these results, it was shown that the reduction of void defects and the growth of BMD in the device forming region of the semiconductor wafer can be achieved by performing the first heat treatment prior to the implementation of the second heat treatment step.

(Confirmation of the effect of the atmosphere at the time of temperature decrease on quality)
The heat treatment was repeated using the same heat treatment apparatus under the same conditions as in Examples 7 to 10 above. Then, after the first heat treatment, the thickness of the oxide film of each boat was measured. Specifically, the film thickness of the oxide film on the surface of the holding portion in contact with the semiconductor wafer was measured. The results are shown in Table 2. The film thickness of the oxide film before the first heat treatment was 50 nm.

As shown in Table 2, the oxide film of the boat used in Examples 8 and 10 maintained a thickness of 10 nm or more. On the other hand, the oxide film of the boat used in Examples 7 and 9 was significantly reduced as compared with that before the heat treatment. The film thickness of the oxide film after the second and subsequent heat treatments was about the same as the film thickness of the oxide film after the first heat treatment.
Further, with respect to the semiconductor wafers contained in the lots subjected to the second heat treatment, it was confirmed by the same method as in Test Example 1 whether or not their carbons had reached the saturation concentration. Then, the heat treatment conditions with carbon contamination from the surface of the SiC boat were evaluated as "yes", and the heat treatment conditions without carbon contamination were evaluated as "-".

When the heat treatment was repeated under the same conditions as in Examples 7 and 9, the carbon concentration of the semiconductor wafer did not reach saturation, and the carbon concentration was compared with the case where the heat treatment was repeated under the same conditions as in Examples 8 and 10. The uniformity was low. This is considered to be due to the following reasons.
That is, under the same conditions as in Examples 7 and 9, the thickness of the oxide film covering the SiC boat remains thin and does not recover by undergoing the first and second heat treatment steps. Therefore, in the second and subsequent heat treatments, as shown in Table 2, carbon contamination from the surface of the SiC boat occurs. That is, the carbon contained in the boat diffuses into the gas phase, and the carbon concentration in the atmosphere increases. As a result, a SiOC film is formed on the surface of the semiconductor wafer. This SiOC film prevents the diffusion of carbon into the semiconductor wafer. Therefore, under the same conditions as in Examples 7 and 9, the carbon concentration of the semiconductor wafer does not reach saturation when the heat treatment is repeated.

On the other hand, under the same conditions as in Example 8, the oxide film covering the SiC boat is thicker at the time when the second heat treatment is completed than at the time before the first heat treatment is started. It has become. Further, under the same conditions as in Example 10, the oxide film covering the SiC boat maintains a film thickness of 10 nm or more even after the second heat treatment is completed. Therefore, the diffusion of carbon contained in the boat into the gas phase is suppressed, and the carbon concentration in the atmosphere does not increase. As a result, the SiOC film is not formed on the surface of the semiconductor wafer even when the heat treatment is repeated. Therefore, no matter how many times the heat treatment is repeated, the carbon concentration of the semiconductor wafer reaches saturation and the uniformity of the carbon concentration does not decrease.

From the above results, it is possible to reduce void defects and achieve BMD growth by performing the first heat treatment prior to the implementation of the second heat treatment step, and further, the temperature is lowered after the second heat treatment in an oxygen-containing atmosphere. By doing so, it was shown that the production of a semiconductor wafer having more excellent uniformity can be achieved.

<< Test Example 3 >>
<Preparation of semiconductor wafer>
(Example 11)
Simulations were performed for semiconductor wafers prepared by the same method as in Test Example 1 except for the following, when the second and third heat treatment steps were performed.

Here, four sets of wafers having different carbon concentrations were prepared. Specifically, the first wafer group has a carbon concentration of 5 × 10 ¹⁵ atoms / cm ³ , the second wafer group ^{has a carbon concentration of 1 × 10 16} atoms / cm ³ , and 1 × 10 ¹⁵ atoms / cm ³ . A third wafer group and a fourth wafer group having 5 × 10 ¹⁶ atoms / cm ³ were prepared.
The first to fourth wafer groups were heat-treated under the following conditions.

<Heat treatment of semiconductor wafer>
The heat treatment was performed in the same manner as in Example 1 except for the following. That is, the carbon-containing gas was changed from CO _{2 to CO.} Then, the temperature of the semiconductor wafer was lowered to 800 ° C., and in this state, the atmosphere was switched to a reducing atmosphere containing hydrogen gas, and then the third heat treatment step was carried out.

As the third heat treatment, specifically, the temperature of the semiconductor wafer was raised to 1200 ° C. in a reducing atmosphere containing hydrogen gas, and the temperature was maintained at this temperature for 60 minutes. Then, the temperature of the semiconductor wafer was lowered to 600 ° C., and they were taken out to the outside of the heat treatment apparatus 1. The hydrogen content in the atmosphere was 100% by volume.

<Evaluation>
FIG. 8 shows the simulation results of calculating the distribution of carbon concentration in the semiconductor wafer subjected to the above heat treatment.

FIG. 8 is a graph showing the simulation results of the carbon concentration of the semiconductor wafer obtained in Test Example 3. In the graph shown in FIG. 8, the vertical axis shows the carbon concentration and the horizontal axis shows the distance D. Further, each plot represents the average value of the carbon concentration at a specific distance D of the semiconductor wafers included in each wafer group.

As shown in FIG. 8, in the semiconductor wafer obtained by heat treatment in a reducing atmosphere containing hydrogen gas, the carbon concentration in the surface region of the semiconductor wafer is reduced. According to this simulation, the carbon concentration in the surface region of the obtained semiconductor wafer is less than ^{1 × 10 15} atoms / cm ^3. In addition, the carbon concentration at positions where the distance D is within the range of 2 to 30 μm is 2 × 10 ¹⁶ atoms / cm ³ or more, and the carbon concentration at any position where the distance D is greater than 30 μm is 1 × 10 ¹⁴ atoms. / cm ³ or in the range of ^{2 × 10 16 atoms / cm 3} .

<< Distribution of carbon concentration in semiconductor wafers >>
The characteristics of the semiconductor wafer obtained by the above method and the characteristics of the semiconductor wafer obtained by the other method will be described with reference to Table 3. Here, the semiconductor wafers A to C are semiconductor wafers having a carbon concentration of 1 × 10 ¹⁶ atoms / cm ³ subjected to the above-mentioned heat treatment, and the semiconductor wafer D has a carbon concentration of 2 × 10 ¹⁶ atoms / cm. Carbon is implanted into the semiconductor wafer of No. ^{3 by ion implantation.}

The semiconductor wafer A is a semiconductor wafer that has been subjected to only the second heat treatment step. As shown in Table 3, the semiconductor wafer A has the following characteristics. ^{That is, the semiconductor wafer A has a carbon concentration of 1 × 10 16} atoms / cm ³ or more at any position where the distance D is smaller than 2 μm, and a carbon concentration at any position where the distance D is within the range of 2 to 30 μm. Was 2 × 10 ¹⁶ atoms / cm ³ or more, and the carbon concentration at a position where the distance D was larger than 30 μm was in the range of 1 × 10 ¹⁴ atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ .

As a result of drawing the relationship between the distance D in the depth direction from the surface of the semiconductor wafer A and the carbon concentration in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line showing this relationship is on the top. It became a convex curve. The carbon concentration in 0 ≦ D <2 increased monotonically with the increase of the distance D. The carbon concentration in 2 ≦ D ≦ 30 increased monotonically with the increase of the distance D, and decreased monotonically after reaching the maximum value. Further, the carbon concentration at 30 <D maintained a substantially constant value as the distance D increased. The carbon concentration at 30 <D was smaller than the carbon concentration at 0 ≦ D <2.

Further, as described with reference to FIG. 5, the semiconductor wafer A is introduced into the semiconductor wafer until the carbon reaches the saturation concentration in the second heat treatment step, so that the distance D is 5 μm or less. The variation in carbon concentration was eliminated.

The semiconductor wafer B is a semiconductor wafer that has undergone a third heat treatment after the second heat treatment step. The semiconductor wafer B has the following characteristics. That is, the semiconductor wafer B has a carbon concentration of ^{less than 1 × 10 15} atoms / cm ³ in the surface region, and the carbon concentration at any position within the range where the distance D in the depth direction from the surface is 2 to 30 μm. The carbon concentration was in the range of 1 × 10 ^{14 to} 2 × 10 ¹⁶ atoms / cm ^{3 at} a position of 2 × 10 ¹⁶ atoms / cm ^{3 or more and a distance D greater than 30 μm.}

As a result of drawing the relationship between the distance D in the depth direction from the surface of the semiconductor wafer B and the carbon concentration in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration, the line representing this relationship is D =. At 0, it became an upwardly convex curve showing a minimum value. The carbon concentration in 0 ≦ D <2 decreased sharply as the distance D decreased. Then, the carbon concentration in 2 ≦ D ≦ 30 monotonically increased to the maximum value with the increase of the distance D, and then monotonically decreased. Further, the carbon concentration at 30 <D maintained a substantially constant value as the distance D increased. The carbon concentration at 30 <D was higher than the carbon concentration at D = 0 and lower than the carbon concentration at 2 ≦ D ≦ 30.

The semiconductor wafers A and B having the above-mentioned characteristics are different from the semiconductor wafers C and D obtained by other methods in the following points.

The semiconductor wafer C is a semiconductor wafer that has been subjected to only the first heat treatment step. The carbon concentration of the semiconductor wafer C at 0 ≦ D <2 decreased monotonically with the decrease of the distance D, and converged to ^{about 1 × 10 15} atoms / cm ^3. The carbon concentration at 2 ≦ D ≦ 30 and 30 <D maintained a substantially constant value.

The semiconductor wafer D is a semiconductor wafer to which carbon ions have been implanted. The distribution of the carbon concentration of the semiconductor wafer D is shown in FIG. FIG. 9 is a graph showing the distribution of carbon concentration in a semiconductor wafer to which carbon ions have been implanted. As shown in FIG. 9, the relationship between the distance D in the depth direction from the surface of the semiconductor wafer D and the carbon concentration is drawn in Cartesian coordinates with the horizontal axis as the distance D and the vertical axis as the carbon concentration. The line representing the relationship was a curve that was steeply convex upward within the range of 0 ≦ D ≦ 0.35. Specifically, the carbon concentration in 0 ≦ D <2 monotonically increased to the maximum value with the increase of the distance D, and then monotonically decreased. The carbon concentration in 2 ≦ D <30 and 30 ≦ D maintained a substantially constant value. The carbon concentration in 2 ≦ D <30 and 30 ≦ D was smaller than the carbon concentration in D = 0.

The present invention is not limited to the above embodiment, and can be variously modified at the implementation stage without departing from the gist thereof. In addition, each embodiment may be carried out in combination as appropriate, in which case the combined effect can be obtained. Further, the above-described embodiment includes various inventions, and various inventions can be extracted by a combination selected from a plurality of disclosed constituent requirements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, if the problem can be solved and the effect is obtained, the configuration in which the constituent elements are deleted can be extracted as an invention.
The inventions described in the original claims are described below.
[1]
It involves heat treating the semiconductor wafer in an atmosphere containing carbon-containing gas so that the carbon concentration reaches saturation at any position where the distance from the surface in the depth direction is 5 μm or less.
A method for manufacturing a semiconductor wafer, wherein the heat treatment in an atmosphere containing a carbon-containing gas is performed at a temperature in the range of 1080 to 1220 ° C.
[2]
Item 2. The production method according to Item 1, wherein the content of the carbon-containing gas in the atmosphere containing the carbon-containing gas is in the range of 1 to 20% by volume.
[3]
Item 2. The production method according to Item 1 or 2, wherein the carbon-containing gas contains at least any one of carbon monoxide, carbon dioxide and a hydrocarbon.
[4]
The heat treatment in the atmosphere containing the carbon-containing gas is performed in a state where the semiconductor wafer is supported by a SiC boat on which a silicon oxide film is formed, and after the heat treatment in the atmosphere containing the carbon-containing gas, the heat treatment is performed. The atmosphere surrounding the semiconductor wafer and the SiC boat that supports it is changed from the carbon-containing gas-containing atmosphere to the oxygen gas-containing atmosphere so as to maintain the silicon oxide film on the surface of the SiC boat. The manufacturing method according to any one of Items 1 to 3, further comprising switching.
[5]
Item 6. The production method according to any one of Items 1 to 4, further comprising heat-treating the semiconductor wafer in an inert atmosphere or a reducing atmosphere prior to the heat treatment in the atmosphere containing the carbon-containing gas.
[6]
Item 5. The production method according to Item 5, wherein the heat treatment in the inert atmosphere or the reducing atmosphere is performed at a temperature in the range of 1130 to 1220 ° C.
[7]
Item 6. The production method according to any one of Items 1 to 6, further comprising heat-treating the semiconductor wafer in a reducing atmosphere containing hydrogen gas after the heat treatment in the atmosphere containing carbon-containing gas. ..
[8]
The LSTD density at a position where the distance from the surface in the depth direction is 5 μm is 0.1 pieces / cm ² or less.
The carbon concentration at any position where the distance is smaller than 2 μm is 1 × 10 ¹⁶ atoms / cm ³ or more.
The carbon concentration at any position within the range of 2 to 30 μm is 2 × 10 ¹⁶ atoms / cm ³ or more.
A semiconductor wafer having a ^{carbon concentration in the range of 1 × 10 14} atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ at any position where the distance is greater than 30 μm.
[9]
The carbon concentration in the surface region is less than ^{1 × 10 15} atoms / cm ^{3 and}
The carbon concentration at any position within the range of 2 to 30 μm from the surface in the depth direction is 2 × 10 ¹⁶ atoms / cm ³ or more.
A semiconductor wafer having a ^{carbon concentration in the range of 1 × 10 14} atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ at any position where the distance is greater than 30 μm.

1 ... heat treatment device, 10 ... device body, 11 ... quartz furnace core tube, 12 ... SiC soaking tube, 13 ... heating device, 14 ... heat tube, 15 ... heat shield plate, 16 ... seal member, 17 ... lid, 18 ... Heat insulation device, 19 ... support, 20 ... boat, 21 ... base, 22 ... support, 23 ... top plate, 24 ... holding part, 30 ... exhaust device, 31 ... gas discharge pipe, 40 ... gas supply device, 41 ... gas Supply pipe, 111 ... Quartz furnace core tube main body, 112 ... Flange part, 113 ... Through hole, 161 ... Main body, 162 ... O ring, 163 ... O ring, 164 ... Through hole, 181 ... Support, 182 ... Quartz reflector ..

Claims (7)

The semiconductor wafer is heat-treated in an atmosphere containing a carbon-containing gas so that the carbon concentration reaches saturation at any position where the distance from the surface in the depth direction is 5 μm or less .
The semiconductor wafer is heat-treated in an inert atmosphere or a reducing atmosphere prior to the heat treatment in the atmosphere containing the carbon-containing gas .
Are performed by the temperature in the range of heat treatment is 1080 to 1220 ° C. in an atmosphere containing the carbon-containing gas,
A method for producing a semiconductor wafer, wherein the heat treatment in the inert atmosphere or the reducing atmosphere comprises maintaining the semiconductor wafer at a temperature in the range of 1130 to 1220 ° C. for 60 to 120 minutes. The production method according to claim 1, wherein the content of the carbon-containing gas in the atmosphere containing the carbon-containing gas is in the range of 1 to 20% by volume. The production method according to claim 1 or 2, wherein the carbon-containing gas contains at least any one of carbon monoxide, carbon dioxide and a hydrocarbon. The heat treatment in the atmosphere containing the carbon-containing gas is performed in a state where the semiconductor wafer is supported by a SiC boat on which a silicon oxide film is formed, and after the heat treatment in the atmosphere containing the carbon-containing gas, the heat treatment is performed. The atmosphere surrounding the semiconductor wafer and the SiC boat that supports it is changed from the carbon-containing gas-containing atmosphere to the oxygen gas-containing atmosphere so as to maintain the silicon oxide film on the surface of the SiC boat. The manufacturing method according to any one of claims 1 to 3, further comprising switching. The production according to any one of claims 1 to 4 , further comprising heat-treating the semiconductor wafer in a reducing atmosphere containing hydrogen gas after the heat treatment in the atmosphere containing carbon-containing gas. Method. The LSTD density at a position where the distance from the surface in the depth direction is 5 μm is 0.1 pieces / cm ² or less.
The carbon concentration at any position where the distance is smaller than 2 μm is 1 × 10 ¹⁶ atoms / cm ³ or more.
The carbon concentration at any position within the range of 2 to 30 μm is 2 × 10 ¹⁶ atoms / cm ³ or more.
A semiconductor wafer having a ^{carbon concentration in the range of 1 × 10 14} atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ at any position where the distance is greater than 30 μm. The carbon concentration in the surface region is less than ^{1 × 10 15} atoms / cm ^{3 and}
The carbon concentration at any position within the range of 2 to 30 μm from the surface in the depth direction is 2 × 10 ¹⁶ atoms / cm ³ or more.
A semiconductor wafer having a ^{carbon concentration in the range of 1 × 10 14} atoms / cm ^{3 to} 2 × 10 ¹⁶ atoms / cm ³ at any position where the distance is greater than 30 μm.

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