JP7361061B2 - silicon wafer - Google Patents

Description

The present invention relates to silicon wafers, and particularly relates to silicon wafers in which crystal defects have been eliminated and BMD (Bulk Micro Defects made of oxygen precipitates in the bulk) are formed inside the wafer.

Silicon wafers, which are commonly used as semiconductor substrates, are generally formed from single-crystal silicon grown by the Czochralski method (CZ method), and crystal defects exist on the surface and surface layer of this semiconductor substrate.
Conventionally, heat treatment at 1000° C. to 1300° C. has been used as a method to eliminate these crystal defects. This heat treatment not only eliminates crystal defects in the device forming region, but also has the great advantage of forming the above-mentioned BMD. Note that this BMD is generally known to act as a gettering site for impurities.

This heat treatment is performed by mounting the silicon wafers on a wafer boat, placing them in a vertical heat treatment furnace, and raising the temperature of the inside of the heat treatment furnace to 1000° C. to 1300° C. in an Ar atmosphere. At that time, a wafer boat made of SiC with high heat resistance is used as the wafer boat.

By the way, when a SiC wafer boat is used in an Ar atmosphere, there is a problem in that free carbon contained in the SiC wafer boat contaminates the silicon wafers during heat treatment.
In order to solve this problem from the silicon wafer side, a silicon wafer manufacturing method described in Patent Document 1 has been proposed.
This silicon wafer manufacturing method includes a step of heat treatment in a non-oxidizing atmosphere at a temperature that can remove vacancy defects near the surface of the silicon wafer, and following this step, oxygen is added to the non-oxidizing atmosphere. By forming an oxide layer with a thickness of 0.01 to 0.1 μm on the surface of the silicon wafer, the surface of the silicon wafer is covered with an oxide film, and the formed oxide film prevents contamination. This is to suppress carbon pollution (free carbon pollution).

Furthermore, in order to solve the above problem from the SiC wafer boat side, the amount of carbon contamination of silicon wafers during heat treatment is reduced by using a SiC boat on which an oxide film is formed.
However, when a silicon wafer is heat-treated in an Ar atmosphere using a SiC wafer boat on which an oxide film has been formed, the oxide film formed on the surface of the wafer boat is gradually etched away during the heat treatment, resulting in a thicker oxide film. is decreasing.
As a result, when the heat treatment process is repeated continuously, the thickness of the oxide film decreases, and the release of free carbon can hardly be suppressed, causing defects and contamination on the silicon wafer surface to occur again. there were.

In order to solve the problem of free carbon release due to the decrease in the thickness of the oxide film on the SiC wafer boat, various methods have been proposed to restore the thickness of the oxide film on the SiC wafer boat that was etched during heat treatment. Suggestions have been made.
For example, in Patent Document 2, in the cooling process of the silicon wafer at 1000° C. or lower, which is performed after heat treating the silicon wafer at 1000 to 1300° C. in an inert gas atmosphere, silicon is placed on the SiC wafer boat. A heat treatment method has been proposed in which oxidation treatment is performed while the wafer is placed.

Further, Patent Document 3 describes a step of placing a silicon wafer on a SiC jig and putting it into a heat treatment furnace, and a step of heat-treating the silicon wafer in a first non-oxidizing atmosphere in the heat treatment furnace. The process includes a step of lowering the temperature of the silicon wafer to a temperature at which it can be carried out from inside the heat treatment furnace, and a step of carrying out the silicon wafer from the heat treatment furnace, and in the temperature lowering step, after the temperature has been lowered to a temperature at which it can be carried out, a first Switch the oxidizing atmosphere to an oxygen-containing atmosphere, form an oxide film with a thickness of 1 to 10 nm on the surface of the SiC jig under the oxygen-containing atmosphere, and then switch the oxygen-containing atmosphere to a second non-oxidizing atmosphere. A method of heat treating a wafer is shown.

Japanese Patent Application Publication No. 2010-177442 Japanese Patent Application Publication No. 2004-214492 JP2015-41738A

As described above, the heat treatment methods shown in Patent Document 2 and Patent Document 3 are intended to prevent contamination of silicon wafers by free carbon by recovering the oxide film on the surface of the SiC boat.
However, in Patent Document 2, the oxidation treatment is performed during the cooling process of the silicon wafer at 1000°C or less, and in Patent Document 3, the temperature of the silicon wafer is lowered to a temperature at which it can be taken out from the heat treatment furnace. After that, oxidation treatment is performed.

Therefore, in both the heat treatment methods of Patent Document 2 and Patent Document 3, the oxidation treatment is performed at a temperature of 1000°C or less, so the oxidation rate is low and an oxide film of sufficient thickness is formed on the surface of the SiC wafer boat. There was a technical problem in that forming it required a long heat treatment time. Further, there is a technical problem in that heat treating a silicon wafer for a long time at a temperature of 1000° C. or lower may affect the BMD density.
Further, as shown in Patent Document 3, if a SiC jig with an oxide film having a thickness of 1 to 10 nm is used again, the base material of the SiC jig will be exposed, and there is a fear that release of free carbon may not be suppressed.
Furthermore, since the oxidation rates of silicon wafers and SiC wafer boats are different, if the heat treatment time is prolonged, an oxide film layer that is more than necessary will be formed on the surface of the silicon wafer, making it difficult to perform the process for removing the oxide film layer. There was a technical issue.

In solving the problem of free carbon contained in SiC wafer boats contaminating silicon wafers during heat treatment, the present inventors studied both the silicon wafer side and the SiC wafer boat side, and completed the present invention. I ended up doing it.

The purpose of the present invention is to be able to form a sufficiently thick oxide film on the surface of a SiC wafer boat in a shorter time, to suppress the influence on the BMD density of the silicon wafer, and to An object of the present invention is to provide a silicon wafer with specific properties, which is formed by performing a silicon wafer heat treatment method in which an oxide film layer is not formed more than necessary.

The heat treatment method for silicon wafers, which has been made to achieve the above object, includes the steps of loading the silicon wafers onto a SiC wafer boat on which an oxide film of at least 50 nm is formed on the surface, and placing the silicon wafers into a heat treatment furnace; A first heat treatment step in which the silicon wafer is heat treated in an inert gas atmosphere at 1150 to 1200° C. for 30 to 120 minutes, and after the first heat treatment step, oxidizing After the replacing step with a gas atmosphere, the silicon wafer is heat-treated in an oxidizing gas atmosphere at 1100 to 1200° C. to form an oxide film of 500 nm or less on the surface of the silicon wafer and to form a SiC wafer. a second heat treatment step of forming an oxide film of at least 50 nm on the surface of the boat, and a step of lowering the temperature of the silicon wafer to a temperature at which it can be carried out from the heat treatment furnace after the second heat treatment step. It is characterized by

In this way, after the first heat treatment step, the inert gas atmosphere is replaced with an oxidizing gas atmosphere, and the second heat treatment is performed in the oxidizing gas atmosphere at 1100 to 1200°C. At the same time, an oxide film is formed on the surface of the SiC wafer boat.
At this time, since the heat treatment temperature is 1100 to 1200°C, the oxidation rate is higher than the conventional oxide film formation at 1000°C or lower, and it is possible to quickly form an oxide film on the surface of the SiC wafer boat. can.

On the other hand, an oxide film is also formed on the surface of the silicon wafer, but if more oxide film layer than necessary is formed, there is a possibility that the process for removing the oxide film layer will be difficult.
Therefore, the processing time of the second heat treatment step is set to be the time required to form an oxide film of 500 nm or less on the surface of the silicon wafer and to form an oxide film of at least 50 nm on the surface of the SiC wafer boat.

The reason why the thickness of the oxide film formed on the surface of the silicon wafer is set to 500 nm or less is that if the thickness of the oxide film exceeds 500 nm, the process for removing the oxide film layer may become difficult. Further, the reason why the thickness of the oxide film formed on the surface of the SiC wafer boat is set to at least 50 nm is to form the oxide film to a thickness exceeding the thickness of the oxide film that will be consumed in the first heat treatment step.
That is, by forming an oxide film of 500 nm or less on the surface of the silicon wafer and at least 50 nm of oxide film on the surface of the SiC wafer boat, the oxide film on the surface of the SiC boat can be quickly recovered, and the silicon Formation of an oxide film layer of a predetermined thickness or more on the wafer surface can be suppressed.

As a result, contamination of the silicon wafer by free carbon can be prevented, and the oxide film layer formed on the silicon wafer can be easily removed.

Here, the step of substituting an inert gas atmosphere with an oxidizing gas atmosphere is performed after the first heat treatment step and after the temperature inside the heat treatment furnace is lowered to 700 to 850° C., and the second heat treatment step is performed after the inert gas atmosphere is replaced with an oxidizing gas atmosphere. This may be performed after the step of replacing the gas atmosphere with an oxidizing gas atmosphere and after raising the temperature in the heat treatment furnace to 1100 to 1200°C.
In this manner, after the temperature inside the heat treatment furnace is lowered to 700 to 850° C., the temperature inside the heat treatment furnace may be raised again to 1100 to 1200° C. to perform the second heat treatment step.

Further, after the replacement step, it is preferable that a second heat treatment step is performed on the silicon wafer in an oxidizing gas atmosphere at 1100 to 1200° C. for at least 5 minutes.
In the second heat treatment step carried out in an oxidizing gas atmosphere at 1100 to 1200°C, an oxide film of 500 nm or less is formed on the surface of the silicon wafer, and an oxide film of at least 50 nm is formed on the surface of the SiC wafer boat. requires a heat treatment time of at least 5 minutes.

Furthermore, it is desirable that the thickness of the oxide film of the SiC wafer boat in the step of charging the silicon wafers into the heat treatment furnace is 50 nm or more and less than 400 nm.
In the first heat treatment step, the oxide film on the surface of the SiC wafer boat is consumed by 10 nm or more. For example, when processed for 30 to 120 minutes in an inert gas atmosphere at 1150° C. to 1200° C., a maximum of about 48 nm is consumed.
Therefore, it is necessary to form an oxide film with a thickness of 50 nm or more on the surface of the SiC wafer boat in consideration of wear and tear. It should be noted that if the thickness of the oxide film of the SiC wafer boat exceeds 400 nm, the oxide film layer may peel off and adhere to the silicon wafer, causing LPD (Light Point Defects) defects, which is not preferable.

Further, after the second heat treatment step, the thickness of the oxide film on the SiC wafer boat is 50 nm or more and 400 nm or less, and the thickness of the oxide film on the surface of the silicon wafer is 100 nm or more and 500 nm or less. is desirable.
In this way, since the thickness of the oxide film of the SiC wafer boat is 50 nm or more and 400 nm or less, the SiC wafer boat can be used again.
Further, since the oxide film on the surface of the silicon wafer is formed to a thickness of 100 nm or more, metal impurities introduced into the wafer can be incorporated into the oxide film by the second heat treatment step. By removing this oxide film in a later step, metal impurity contamination can be reduced.

Further, in the first heat treatment step, the flow velocity of the inert gas supplied to the plate on the gas supply side of the SiC wafer boat (flow velocity on the plate) is 2.2 m/s or more and 33.5 m/s or less. In the second heat treatment step, the flow velocity of the oxidizing gas supplied to the plate on the gas supply side of the SiC wafer boat (flow velocity on the plate) is 2.2 m/s or more and 33.5 m/s or less. is desirable.
The amount of reduction in the surface oxide film thickness of the SiC wafer boat is influenced by the gas flow rate supplied to the SiC wafer boat. In particular, the plate of the SiC wafer boat, which is directly exposed to the gas introduced into the processing chamber, has a large reduction in oxide film thickness, and because it is placed upstream of the gas flow, it has no effect on contamination of the silicon wafer. big.

As described above, by setting the flow velocity of the inert gas supplied to the plate on the gas supply side in the first heat treatment step (flow velocity on the plate) to 2.2 m/s or more and 33.5 m/s or less, The amount of decrease in the oxide film thickness of the plate can be suppressed.
In addition, by setting the flow velocity of the oxidizing gas supplied to the plate on the gas supply side in the second heat treatment step (flow velocity on the plate) to be 2.2 m/s or more and 33.5 m/s or less, the oxide film on the plate can be reduced. can be quickly recovered.

A silicon wafer heat-treated by the above silicon wafer heat treatment method has an oxide film on the surface of the silicon wafer with a thickness of 100 nm or more and 500 nm or less, and a carbon concentration of 5×10 ¹⁵ /cm in the 10 μm surface layer from which the oxide layer is removed. ³ or less, the LSTD density in the surface layer of 5 μm is 0.1 pieces/cm ² or less, and the average BMD density in the depth direction is 1×10 ⁹ pieces/cm ³ or more.
In this way, the carbon concentration is 5×10 ¹⁵ /cm ³ or less, which means less carbon contamination, the LSTD density is 0.1 pieces/cm ² or less, which means fewer crystal defects, and the average BMD density in the depth direction is 1×10 ⁹ Silicon wafers with a high BMD of 3 pieces/cm ³ or more can be obtained.

According to the present invention, it is possible to form a sufficiently thick oxide film on the surface of a SiC wafer boat in a shorter time, and the influence on the BMD density of the silicon wafer is minimized. A silicon wafer with specific properties can be obtained by performing a silicon wafer heat treatment method that does not form an oxide film layer more than necessary.

FIG. 1 is a diagram showing the relationship between the oxide film thickness on the SiC surface and the heat treatment temperature (oxidation temperature) when heat treated for one hour in an oxygen gas atmosphere. FIG. 2 is a diagram for explaining the silicon wafer heat treatment method according to the present invention. FIG. 3 is a diagram showing the relationship between the depth from the silicon wafer surface and the oxygen concentration in a silicon wafer when heat treated in an oxygen gas atmosphere. FIG. 4 is a diagram for explaining a first modification of the silicon wafer heat treatment method according to the present invention. FIG. 5 is a diagram for explaining a second modification of the silicon wafer heat treatment method according to the present invention.

The silicon wafer heat treatment method according to the present invention will be explained based on FIG. 1.
First, as the SiC wafer boat used for this heat treatment, although not shown, a known vertical SiC wafer boat can be used.
This vertical wafer boat includes a bottom plate, a top plate, and a support that connects the bottom plate and the top plate. Further, a plurality of shelf portions are formed in the vertical direction of the support column, and a silicon wafer is mounted on the shelf portions.

An oxide film of at least 50 nm is previously formed on the surface of the SiC wafer boat. Preferably, the thickness of the oxide film of the SiC wafer boat is 50 nm or more and less than 400 nm. In the first heat treatment step described below, the oxide film on the surface of the SiC wafer boat is consumed by 10 nm or more. For example, when processed for 30 to 120 minutes in an inert gas atmosphere at 1150° C. to 1200° C., a maximum of about 48 nm is consumed.
Therefore, it is necessary to form an oxide film with a thickness of 50 nm or more on the surface of the SiC wafer boat in consideration of wear and tear.
It should be noted that if the thickness of the oxide film of the SiC wafer boat exceeds 400 nm, the oxide film layer may peel off and adhere to the silicon wafer, which may cause LPD defects, which is not preferable.

This oxide film can be formed by placing a SiC wafer boat in a heat treatment furnace and heat-treating it at a predetermined temperature in an oxidizing gas atmosphere. For example, as shown in FIG. 1, an approximately 10 nm thick oxide film can be formed on the surface by heat treatment in an oxygen atmosphere at 1000° C. for one hour or more.
FIG. 1 is a diagram showing the relationship between the oxide film thickness on the SiC surface and the heat treatment temperature (oxidation temperature) when heat treated for one hour in an oxygen gas atmosphere. Since the oxidation rate increases as the temperature increases, the heat treatment time is shortened.

The reason why an oxide film with a thickness of at least 50 nm was formed on the surface in advance was to take into consideration the consumption of the oxide film during the heat treatment step performed in an inert gas atmosphere, as described above.
That is, in order to eliminate crystal defects in the silicon wafer and form BMD, the silicon wafer is heat treated in an inert gas atmosphere at 1150 to 1200° C. for 30 to 120 minutes (first heat treatment step). By this heat treatment, the oxide film on the surface of the SiC wafer boat is consumed by about 48 nm at most. Therefore, it is necessary to prevent exposure of the base material (SiC) by using a SiC wafer boat on which an oxide film of at least 50 nm is formed in advance, and to suppress contamination of the silicon wafer by free carbon.

Then, the silicon wafer is mounted on a SiC wafer boat on which an oxide film of at least 50 nm is formed, and the boat is placed in a heat treatment furnace.
As this heat treatment furnace, for example, a general annealing furnace that can accommodate the above-described vertical wafer boat can be used.

After loading a silicon wafer on a SiC wafer boat and putting it into a heat treatment furnace, as shown in FIG. Heat treatment is performed (first heat treatment step).
The temperature is raised to this heat treatment temperature at a rate of 5° C./min or less, and the temperature is maintained at 1150 to 1200° C. for 30 to 120 minutes.

If the heat treatment temperature is less than 1150° C., crystal defects on the surface and surface layer of the silicon wafer will not disappear, or even if the crystal defects disappear, it will take a long time for the heat treatment to eliminate them, which is not preferable.
When the heat treatment temperature exceeds 1200° C., slip is introduced into the wafer, which is not preferable.

Further, as described above, the heat treatment temperature is maintained in the range of 1150 to 1200° C. for 30 to 120 minutes.
If the treatment time is less than 30 minutes, it is not preferable because it becomes difficult to eliminate crystal defects on the surface and surface layer of the silicon wafer. Moreover, if the treatment time exceeds 120 minutes, it is not preferable because there is a possibility that slip may be introduced.

Furthermore, the flow velocity of the inert gas on the plate on the gas supply side is preferably set to 2.2 m/s to 33.5 m/s.
By setting the flow rate of the inert gas supplied to the plate on the gas supply side in this first heat treatment step to 33.5 m/s or less, the amount of decrease in the oxide film thickness of the upper plate can be suppressed.
Furthermore, if the flow rate of the inert gas is less than 2.2 m/s, it is not preferable because the replacement efficiency of the gas in the furnace may deteriorate and the silicon wafer may be locally contaminated. Further, as the inert gas, Ar gas, He gas, etc. are used.

Furthermore, after a first heat treatment step in which the silicon wafer is heat treated in an inert gas atmosphere at 1150 to 1200° C. for 30 to 120 minutes in the heat treatment furnace, the inert gas atmosphere is replaced with an oxidizing gas atmosphere. O ₂ gas is used as the oxidizing gas.

After the replacement step, the silicon wafer is heat-treated in an oxidizing gas atmosphere at 1100 to 1200°C to form an oxide film of 500 nm or less on the surface of the silicon wafer, and at least a first film on the surface of the SiC wafer boat. A second heat treatment step is performed to form an oxide film having a thickness equal to or greater than that reduced by the heat treatment.
By this second heat treatment, an oxide film is formed on the surface of the silicon wafer, and an oxide film is also formed on the surface of the SiC wafer boat.

In particular, since the heat treatment temperature in this second heat treatment step is performed at 1100 to 1200°C, the oxidation rate (for example, As shown in No. 1, 0.16 nm/min at 1000° C. and 1.83 nm/min at 1150° C.) is large, and an oxide film can be quickly formed on the surface of a SiC wafer boat.
Here, the reason why the thickness of the oxide film formed on the surface of the silicon wafer is set to 500 nm or less is that if the thickness exceeds 500 nm, there is a possibility that the process for removing the oxide film layer will be difficult.
On the other hand, the reason why an oxide film of at least 50 nm is formed on the surface of the SiC wafer boat is to restore the thickness of the oxide film that was consumed in the first heat treatment step.

In addition, as shown in Figure 3, by setting the heat treatment temperature to 1100 to 1200°C, there is an advantage that the oxygen concentration in the surface layer of the wafer (up to a depth of 10 μm) can be improved, which improves the mechanical strength of the silicon wafer. It is valid.
On the other hand, when the oxidation temperature is 1000°C, the improvement in surface layer oxygen concentration is smaller than when the oxidation temperature is 1100°C, and this advantage cannot be obtained.
Therefore, it is necessary to form an oxide film of 50 nm or more on the surface of the SiC wafer boat at a heat treatment temperature of 1100° C. to 1200° C.
In addition, FIG. 3 shows the results of heat treatment at 1200°C for 1 hour in an Ar gas atmosphere, 6 minutes at 1150°C in an oxygen gas atmosphere, and 1 hour heat treatment at 1200°C in an Ar gas atmosphere, then under an oxygen gas atmosphere. , heat treated at 1100°C for 12 minutes, then at 1200°C for 1 hour under an Ar gas atmosphere, then heat treated at 1000°C for 60 minutes under an oxygen gas atmosphere, and for 1 hour at 1200°C under an Ar gas atmosphere. FIG. 3 is a diagram showing the relationship between the depth from the silicon wafer surface and the oxygen concentration in a silicon wafer.
As can be seen from FIG. 3, as the heat treatment temperature becomes higher, the surface oxygen concentration can be improved in a shorter time.

Through the second heat treatment step, the thickness of the oxide film on the SiC wafer boat is 50 nm or more and 400 nm or less, and the thickness of the oxide film on the surface of the silicon wafer is 100 nm or more and 500 nm or less.
If the thickness of the oxide film on the SiC wafer boat exceeds 400 nm, there is a risk that the oxide film will peel off, and if the thickness of the oxide film on the surface of the silicon wafer is less than 100 nm, it will be susceptible to metal contamination. , undesirable.

The processing time of this second heat treatment step is set to a processing time that forms an oxide film of 500 nm or less on the surface of the silicon wafer and forms an oxide film of at least 50 nm on the surface of the SiC wafer boat.
The processing time varies depending on the processing temperature, concentration of oxidizing gas, etc., but it is necessary to form an oxide film of 500 nm or less on the surface of the silicon wafer and at least 50 nm on the surface of the SiC wafer boat. , a heat treatment of at least 5 minutes is required.

In addition, in the second heat treatment step, the flow velocity of the oxidizing gas supplied to the plate on the gas supply side of the SiC wafer boat (flow velocity on the plate) is set to 2.2 m/s or more and 33.5 m/s or less. be done.
By setting the flow velocity of the oxidizing gas supplied to the plate on the gas supply side in the second heat treatment step (flow velocity on the plate) to be 2.2 m/s or more and 33.5 m/s or less, the gas of the SiC wafer boat The oxide film on the supply side plate (upper plate) can be quickly recovered.

Further, as shown in FIG. 4, this second heat treatment step may be performed by lowering the temperature in the heat treatment furnace to 1100° C. in the step of replacing the inert gas atmosphere with an oxidizing gas atmosphere.
Further, as shown in FIG. 5, the step of replacing the inert gas atmosphere with an oxidizing gas atmosphere is performed after the first heat treatment step and after the temperature inside the heat treatment furnace is lowered to 700 to 850°C, and the second The heat treatment step may be performed after the step of replacing the inert gas atmosphere with an oxidizing gas atmosphere and after raising the temperature in the heat treatment furnace to 1100 to 1200°C.

After the second heat treatment step, the silicon wafer heat treatment method is completed through a step of lowering the temperature of the silicon wafer to a temperature at which it can be taken out from the heat treatment furnace.

A silicon wafer heat-treated by the above silicon wafer heat treatment method has an oxide film on the surface of the silicon wafer with a thickness of 100 nm or more and 500 nm or less, and a carbon concentration of 5×10 ¹⁵ / cm ³ or less, the LSTD density in the surface layer 5 μm is 0.1 pieces/cm ² or less, and the BMD density is 1×10 ⁹ pieces/cm ³ or more.
The carbon concentration in the 10 μm surface layer of the silicon wafer is 5×10 ¹⁵ /cm ³ or less, and carbon contamination can be stably suppressed. In addition, the LSTD density in the surface layer of 5 μm is 0.1 pieces/cm ² or less, which can reduce crystal defects, and the BMD density is 1 × 10 ⁹ pieces/cm ³ or more, which has high impurity gettering properties. Silicon wafers can be obtained.

EXAMPLES Hereinafter, the present invention will be explained in more detail based on Examples and Comparative Examples, but the present invention is not limited by these Examples.

(Example 1)
A wafer made from a Si single crystal with a diameter of 300 mm is mounted on a SiC wafer boat on which a 50 nm oxide film has been previously formed on the surface, and the silicon wafer is placed into a heat treatment furnace. The wafer is heat-treated at 1150° C. in an inert gas atmosphere for 60 minutes. Note that the flow velocity of the inert gas on the plate on the gas supply side was 15 m/s.
Then, the inert gas atmosphere is replaced with an oxidizing gas atmosphere, and the silicon wafer is heat-treated in an oxidizing gas atmosphere at 1100°C to form a 150 nm oxide film on the surface of the silicon wafer, and a SiC wafer boat. A new 40 nm oxide film was formed on the surface (the total oxide film thickness including the previously formed oxide film was 90 nm). Note that the flow rate of the oxidizing gas on the plate on the gas supply side was 15 m/s.
The oxide film on the surface of the heat-treated silicon wafer was removed using a dilute HF solution, and the carbon concentration at a depth of 10 μm from the surface layer was measured by secondary ion mass spectrometry (SIMS). As a result, the carbon concentration was 5×10 ¹⁵ /cm ³ or less.
Further, the LSTD density at a depth of 5 μm from the surface layer was measured using an LSTD scanner (MO601 manufactured by Raytex). As a result, the LSTD density was 0.1 pieces/cm ² or less.
Furthermore, the BMD density was measured by IR tomography (MO-441 manufactured by Raytex). As a result, the BMD density was 1×10 ⁹ pieces/cm ³ or more.

(Examples 2 to 16, Comparative Examples 1 to 10)
The various conditions in Example 1 were changed as shown in Table 1, and the carbon concentration, LSTD density, and BMD density were measured. The results are shown in Table 1.
Further, as a comparative example, various conditions in Example 1 were changed as shown in Table 2, and carbon concentration, LSTD density, and BMD density were measured. The results are shown in Table 2.

In Examples 1 to 16 in Table 1 above, the carbon concentration in the 10 μm surface layer from which the oxidized layer of the silicon wafer has been removed is 5×10 ¹⁵ /cm ³ or less, and the LSTD density in the 5 μm surface layer is 0.1 pieces/cm ² Hereinafter, a silicon wafer having a BMD density of 1×10 ⁹ pieces/cm ³ or more can be obtained.

Claims (1)

A silicon wafer heat-treated using a SiC wafer boat on which an oxide film is formed ,
The thickness of the oxide film on the surface of the silicon wafer is 105 nm or more and 300 nm or less, the carbon concentration in the 10 μm surface layer from which the oxide layer is removed is 5×10 ¹⁵ /cm ³ or less, and the LSTD density in the 5 μm surface layer is 0.1. /cm ² or less, and a BMD density of 1×10 ⁹ pieces/cm ³ or more.

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