JP2020043232A - Manufacturing method of epitaxial silicon wafer and epitaxial silicon wafer - Google Patents

Abstract

To provide a method capable of manufacturing an epitaxial silicon wafer having high gettering ability while suppressing formation of epitaxial defects, and the epitaxial silicon wafer.SOLUTION: The manufacturing method includes: a first step of heat-treating a silicon wafer having a front surface, a back surface, and an edge region at a temperature of 800°C or more and 980°C or less under a carbon-containing gas atmosphere to form a carbon diffusion layer at least on a surface layer part on the front surface side of the silicon wafer; and a second step of forming a silicon epitaxial layer at a temperature of 900°C or more and 1000°C or less on the carbon diffusion layer formed on the surface layer part on the front surface side of the silicon wafer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing an epitaxial silicon wafer and an epitaxial silicon wafer.

  Conventionally, silicon wafers have been widely used as substrates for semiconductor devices. However, if heavy metals are mixed into silicon wafers, device characteristics such as a pause time defect, a retention defect, a junction leak defect, and a dielectric breakdown of an oxide film are significantly adversely affected. . Therefore, by forming a gettering layer for capturing the heavy metal inside the wafer, the diffusion of the heavy metal into the device formation region is suppressed. Here, it is important to form a gettering layer immediately below the device formation region so that heavy metals such as titanium and molybdenum with a low diffusion rate can be captured.

  In recent years, it has been required that no crystal defects exist in the device formation region, and an epitaxial silicon wafer having a silicon epitaxial layer formed on a silicon wafer has been used as a substrate. In an epitaxial silicon wafer, for example, after a gettering layer is formed on a surface layer portion of a silicon wafer, a silicon epitaxial layer is formed on the gettering layer by a CVD method or the like.

  One of the methods for forming the gettering layer is an ion implantation method. For example, in Patent Document 1, carbon ions are implanted into the surface of a silicon wafer to form a gettering layer containing high-concentration carbon on the surface layer of the wafer, and a silicon epitaxial layer is formed on the formed gettering layer. A method is described.

  In order to form the gettering layer directly below the silicon epitaxial layer by the ion implantation method, it is necessary to implant ions into a shallower position from the surface of the silicon wafer. However, when ions are implanted at a position shallow from the wafer surface, implantation defects are formed on the wafer surface, and a large number of epitaxial defects are formed on the epitaxial layer formed thereon.

  As another method of forming a gettering layer, heat treatment is performed on a silicon wafer in a carbon-containing gas atmosphere to diffuse carbon into the inside of the silicon wafer, and the formed carbon diffusion layer is used as a gettering layer. A way to do that has been proposed. For example, Patent Document 2 discloses that a gas containing carbon is supplied to a silicon wafer at a temperature of 1000 ° C. or more and 1200 ° C. or less to form a layer of a gas containing pyrolyzed carbon, and an epitaxial layer is formed thereon. A method for manufacturing an epitaxial wafer having a gettering layer immediately below the epitaxial layer by forming the epitaxial wafer is described.

  Further, in Patent Document 3, a carbon-containing film is formed by immersing a silicon wafer in a solution containing carbon to form a carbon-containing film on the surface of the silicon wafer, and then heat-treating the silicon wafer at a temperature of 500 ° C. to 750 ° C. It describes a method of manufacturing an epitaxial wafer in which carbon inside is thermally diffused to a surface layer portion of a silicon wafer, and then an epitaxial layer is formed on the formed carbon diffusion layer.

Patent No. 3384506 JP 2013-51348 A JP 2010-34330 A

  However, it was found that many epitaxial defects were also formed in the epitaxial wafer manufactured by the method described in Patent Document 2. Further, it was found that the gettering ability of the epitaxial wafer manufactured by the method described in Patent Document 3 was insufficient.

  Therefore, an object of the present invention is to provide a method and an epitaxial silicon wafer capable of manufacturing an epitaxial silicon wafer having high gettering ability while suppressing formation of epitaxial defects.

The present invention for solving the above problems is as follows.
[1] A silicon wafer having a front surface, a back surface, and an edge region is subjected to a heat treatment at a temperature of 800 ° C. or more and 980 ° C. or less in a carbon-containing gas atmosphere, and at least the front surface side of the silicon wafer. A first step of forming a carbon diffusion layer on the surface layer portion of
A second step of forming a silicon epitaxial layer at a temperature of 900 ° C. or more and 1000 ° C. or less on the carbon diffusion layer formed on the surface layer on the front surface side of the silicon wafer;
A method for producing an epitaxial silicon wafer, comprising:

[2] The method for manufacturing an epitaxial silicon wafer according to [1], wherein, in the first step, the carbon diffusion layer is formed only on a surface layer on the front surface side of the silicon wafer.

[3] The method further includes a third step of forming a protective film on the back surface of the silicon wafer before the first step, and a fourth step of removing the protective film before or after the second step. The method for manufacturing an epitaxial silicon wafer according to the above [2].

[4] In the first step, the carbon diffusion layer is formed on both the front surface side and the rear surface side of the silicon wafer,
The method for producing an epitaxial silicon wafer according to [2], further comprising: a fifth step of removing the carbon diffusion layer formed in the surface layer portion on the back surface side before or after the second step.

[5] In the first step, the carbon diffusion layer is formed on at least the front surface side of each of the two silicon wafers with respect to the two silicon wafers whose back surfaces are overlapped with each other. ,
The method of manufacturing an epitaxial silicon wafer according to [2], further comprising: a sixth step of separating the two silicon wafers after the first step.

[6] The method according to any of [1] to [1], further including: a seventh step of removing the carbon diffusion layer formed on a surface portion of the edge region of the silicon wafer after the first step and before the second step. The method for producing an epitaxial silicon wafer according to any one of [5].

[7] The method for manufacturing an epitaxial silicon wafer according to any one of [1] to [6], wherein the first step is performed in an epitaxial growth furnace in which the second step is performed.

[8] The first step is to introduce the silicon wafer into a heat treatment apparatus capable of introducing the carbon-containing gas, and the second step is to introduce the silicon wafer after the heat treatment into an epitaxial growth furnace. The method for producing an epitaxial silicon wafer according to any one of the above [1] to [6].

[9] In the first step, heat treatment is performed so that a carbon peak concentration in the carbon diffusion layer is 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less.
In the second step, the epitaxial growth treatment is performed so that the hydrogen peak concentration in the carbon diffusion layer is 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. The method for producing an epitaxial silicon wafer according to any one of the preceding claims.

[10] a carbon diffusion layer formed at least on the front surface side of a silicon wafer having a front surface, a back surface, and an edge region;
A silicon epitaxial layer formed on the carbon diffusion layer in the surface layer on the front side,
Has,
The carbon diffusion layer has a carbon peak concentration of 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less;
An epitaxial silicon wafer, wherein the carbon diffusion layer has a hydrogen peak concentration of 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less.

[11] The epitaxial silicon wafer according to [10], wherein the carbon diffusion layer has a thickness of 200 nm or less.

[12] The epitaxial silicon wafer according to the above [10] or [11], wherein the carbon diffusion layer is formed only in the surface layer on the front surface side.

[13] The epitaxial silicon wafer according to any one of [10] to [12], wherein the carbon diffusion layer is not formed on a surface portion of the edge region.

  According to the present invention, it is possible to manufacture an epitaxial silicon wafer having high gettering ability while suppressing formation of epitaxial defects.

FIG. 4 is a diagram showing a flow of a method for manufacturing an epitaxial silicon wafer according to the present invention. FIG. 3 is a diagram showing an epitaxial silicon wafer having a carbon diffusion layer on both the front surface and the back surface. FIG. 3 is a diagram showing an example of a susceptor for preventing a carbon diffusion layer from being formed on the back surface of a silicon wafer. FIG. 3 is a view showing a silicon wafer having a protective film for preventing a carbon diffusion layer from being formed on the back surface. It is a figure which shows two silicon wafers with which the back surfaces were overlapped. FIG. 9 is a view showing a concentration profile of carbon and hydrogen in an epitaxial silicon wafer of Inventive Example 2.

(Method of manufacturing epitaxial silicon wafer)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a flow of a method for manufacturing an epitaxial silicon wafer according to the present invention. In the method for producing an epitaxial silicon wafer according to the present invention, the silicon wafer 11 having the front surface 11a, the back surface 11b, and the edge region 11c is subjected to a heat treatment at a temperature of 800 ° C. or more and 980 ° C. or less in a carbon-containing gas atmosphere. A first step of forming a carbon diffusion layer 12 on at least a surface portion of the silicon wafer 11 on the front surface 11a side, and a step of forming a carbon diffusion layer 12 on the surface layer portion of the silicon wafer 11 on the front surface 11a side. A second step of forming the silicon epitaxial layer 13 at a temperature of 900 ° C. or more and 1000 ° C. or less.

  As described above, Patent Documents 2 and 3 propose a technique in which carbon is diffused into a silicon wafer and the formed carbon diffusion layer is used as a gettering layer. However, a large number of epitaxial defects are formed in the epitaxial wafer manufactured by the method of Patent Document 2, and the gettering ability of the epitaxial wafer manufactured by the method of Patent Document 3 is insufficient.

  The present inventors have investigated the cause of the above problem in detail. As a result, the gettering ability of the epitaxial wafer obtained by the method of Patent Document 3 was insufficient because the heat treatment temperature was as low as 500 ° C. to 750 ° C., so that carbon in the carbon-containing film was in the wafer. It turned out that this was not due to sufficient diffusion.

  On the other hand, the cause of the formation of a large number of epitaxial defects in the epitaxial wafer obtained by the method of Patent Document 2 is that although the carbon diffusion layer is formed on the surface layer of the silicon wafer by the heat treatment, the heat treatment temperature is 1000 ° C. to 1200 ° C. It was found that the silicon structure constituting the carbon diffusion layer was sublimated due to the high carbon content, and the remaining carbon was bonded and precipitated, and the crystal structure of the wafer surface layer was disturbed.

  According to the above study, by performing the heat treatment at a temperature between the temperature described in Patent Document 3 and the temperature described in Patent Document 2, it is possible to suppress the formation of epitaxial defects and to improve the gettering ability. It is expected that a high epitaxial wafer can be manufactured.

  However, when the inventor manufactured an epitaxial silicon wafer by performing heat treatment in the above temperature range, it was found that many epitaxial defects were still formed. Then, the present inventors investigated the cause. As a result, the general formation temperature of the silicon epitaxial layer formed on the carbon diffusion layer is about 1150 ° C., but since this formation temperature is high, silicon in the carbon diffusion layer sublimates as described above, and carbon is reduced. It was found that this was due to precipitation.

  From the above study, the present inventors have found that in order to manufacture an epitaxial silicon wafer having a high gettering ability while suppressing the formation of epitaxial defects, carbon is sufficiently diffused into the inside of the silicon wafer in a carbon-containing gas atmosphere. While performing at a temperature at which silicon of the formed carbon diffusion layer sublimates and does not precipitate carbon, and also at a low temperature at which silicon of the formed carbon diffusion layer sublimates and does not precipitate carbon. We concluded that we needed to do it.

  As a result of the inventor's intensive study on specific temperature conditions, heat treatment of a silicon wafer in a carbon-containing gas atmosphere was performed at a temperature of 800 ° C. or more and 980 or less, and formation of a silicon epitaxial layer was performed at 900 ° C. or more. It has been found that by performing the treatment at a temperature of 1000 ° C. or less, an epitaxial silicon wafer having high gettering ability can be obtained while suppressing the formation of epitaxial defects, thereby completing the present invention. Hereinafter, each step will be described.

<First step>
First, the silicon wafer 11 having the front surface 11a, the back surface 11b, and the edge region 11c is subjected to a heat treatment at a temperature of 800 ° C. or more and 980 ° C. or less in a carbon-containing gas atmosphere. The carbon diffusion layer 12 is formed on the surface layer on the surface 11a side.

  As the silicon wafer 11, a wafer obtained by subjecting a single crystal silicon ingot grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method) to wafer processing can be used. . Carbon and / or nitrogen may be added to the silicon wafer 11 to obtain higher gettering ability. Further, n-type or p-type may be obtained by adding any appropriate impurity. The diameter of the silicon wafer 11 can be, for example, 200 mm, 300 mm, or 450 mm. The resistivity can also be set appropriately according to the design.

  In the present invention, "carbon-containing gas atmosphere" means an atmosphere composed of a gas containing carbon. Examples of the gas containing carbon include methane gas, ethane gas, and propane gas. Among them, it is preferable to use propane gas or ethane gas from the viewpoint of improving the reaction efficiency of carbon to the silicon wafer 11.

Further, the oxygen concentration of the silicon wafer 11 is preferably 1 × 10 ¹⁷ atom / cm ³ or more and 1 × 10 ¹⁸ atom / cm ³ or less. This makes it possible to suppress the formation of epitaxial defects due to oxygen precipitation while suppressing the occurrence of slip.

  As described above, in the present invention, it is important that the heat treatment temperature in a carbon-containing gas atmosphere be 800 ° C. or more and 980 ° C. or less. If the heat treatment temperature is lower than 800 ° C., a gas containing carbon, such as methane gas, constituting the carbon-containing gas atmosphere cannot be decomposed, and carbon cannot be diffused from the surface of the silicon wafer 11 into the wafer.

  On the other hand, when the heat treatment temperature exceeds 980 ° C., silicon in the formed carbon diffusion layer 12 is sublimated due to high thermal energy. As a result, the carbon remaining in the carbon diffusion layer 12 is bonded and deposited, the crystal structure of silicon is disturbed, and many epitaxial defects are formed in the silicon epitaxial layer 13 formed on the carbon diffusion layer 12. Therefore, the heat treatment temperature is set to 800 ° C. or more and 980 ° C. or less. More preferably, the heat treatment temperature is set to 800 ° C. or more and 950 ° C. or less.

By performing the heat treatment at a temperature within the above range, the carbon diffusion layer 12 can be formed by diffusing carbon into the inside of the silicon wafer 11 without disturbing the crystal structure of the surface layer. The concentration of carbon contained in the carbon diffusion layer 12 is 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less, and the carbon diffusion layer 12 contains sufficient concentration of carbon for heavy metal gettering. Can be. The carbon concentration is the maximum concentration in the inside of the silicon wafer 11, and the carbon concentration becomes maximum (peak) at the interface between the silicon wafer 11 and the silicon epitaxial layer 13.

  Further, the heat treatment time is preferably from 1 minute to 40 minutes. By setting the heat treatment time to 1 minute or more, carbon in the carbon-containing gas atmosphere is sufficiently diffused from the surface of the silicon wafer 11, and the carbon diffusion layer 12 containing high-concentration carbon is formed on the surface layer of the silicon wafer 11. can do. By setting the heat treatment time to 1 minute or more, the thickness of the carbon diffusion layer 12 becomes 20 nm or more. Even if the heat treatment time is longer than 40 minutes, the diffusion of carbon into the inside of the wafer is saturated. Therefore, the upper limit of the heat treatment time is preferably set to 40 minutes or less. The upper limit of the thickness of the formed carbon diffusion layer 12 is approximately 200 nm.

  As shown in FIG. 2, the carbon diffusion layer 12 is formed not only on the surface layer on the front surface 11a side of the silicon wafer 11 but also on the surface layer on the back surface 11b side, and the formed surface layer on the back surface 11b side is formed. The gettering ability can be further enhanced by using the part of the carbon diffusion layer 12 as a gettering layer.

  Further, the carbon diffusion layer 12 may be formed only on the surface layer on the front surface 11a side of the silicon wafer 11. Thereby, contamination by carbon can be suppressed. Note that the carbon diffusion layer 12 may be formed in the edge region 11c.

  The formation of the carbon diffusion layer 12 only on the surface layer portion on the front surface 11a side of the silicon wafer 11 is not a susceptor of a type that supports the edge region 11c of the silicon wafer 11 by line contact, for example, as shown in FIG. This can be done using a susceptor. That is, the susceptor 20 shown in FIG. 3 has the concave portion 21 defined by the side wall 21a and the bottom surface 21b, and the bottom surface 21b has a larger diameter than the silicon wafer 11. By arranging the silicon wafer 11 on the bottom surface 21b of the susceptor 20 and performing heat treatment with the back surface 11b in contact with the bottom surface 21b, the carbon diffusion layer 12 is formed only on the surface layer on the front surface 11a side. Can be formed.

  As shown in FIG. 4, a protective film 14 is formed on the back surface 11b of the silicon wafer 11 (third step), and the above-described heat treatment is performed in a state where the protective film 14 is formed, so that the carbon diffusion layer 12 is formed. Can be formed only on the surface layer on the front surface 11a side of the silicon wafer 11. The formed protective film 14 can be removed, for example, by polishing before or after a second step described later (fourth step). The protective film 14 may be any film as long as it can prevent the diffusion of carbon, and may be an oxide film, a nitride film, or the like.

  Furthermore, after once forming the carbon diffusion layer 12 on both the front surface 11a side and the back surface 11b side of the silicon wafer 11, the carbon diffusion layer 12 formed on the back surface 11b side is removed. Thus, the carbon diffusion layer 12 can be formed only on the surface layer on the front surface 11a side. The removal of the carbon diffusion layer 12 formed on the surface layer portion on the back surface 11b side can be performed by polishing, for example, before or after a second step described later (fifth step).

  Furthermore, in order to form the carbon diffusion layer 12 only on the surface layer on the front surface 11a side of the silicon wafer 11, two silicon wafers 11 with the back surfaces 11b overlapped with each other were prepared as shown in FIG. Then, in the first step, the carbon diffusion layer 12 may be formed on the front surface portion of each of the two silicon wafers 11 on the front surface 11a side. In this case, the two silicon wafers are separated from each other after the first step (sixth step), and in the second step, a silicon epitaxial layer is formed on the carbon diffusion layer 12 formed on the surface layer on the front surface 11a side. The layer 13 is formed.

  Note that, as described above, when the carbon diffusion layer 12 is formed only on the surface layer on the front surface 11a side of the silicon wafer 11, the outer peripheral portion of the wafer 11 is also rounded on the surface layer of the edge region 11c. A carbon diffusion layer 12 is formed. The carbon of the carbon diffusion layer 12 formed in the edge region 11c is diffused out of the wafer by being subjected to a heat treatment performed in a subsequent device process, and is diffused to the silicon epitaxial layer (device formation region) 13. There is a risk that carbon will be taken in. Therefore, it is preferable to remove the carbon diffusion layer 12 formed in the surface layer portion of the edge region 11c before the second step described later (seventh step). The carbon diffusion layer 12 formed on the surface of the edge region 11c can be removed by polishing.

  The first step can be performed in an epitaxial growth furnace for performing a second step described later. Specifically, first, the silicon wafer 11 is introduced into the epitaxial growth furnace, hydrogen gas is introduced into the furnace, the temperature is raised to 1100 ° C. to 1150 ° C., and hydrogen baking is performed to remove the natural oxide film on the surface of the silicon wafer 11. Remove. Next, the temperature in the furnace is lowered to a temperature of 800 to 980 ° C., and a carbon-containing gas such as methane gas is introduced into the furnace together with hydrogen gas (carrier gas), and the temperature is maintained, for example, for 1 minute. Thereby, carbon can be diffused from the surface of the silicon wafer 11 into the inside of the wafer, and the carbon diffusion layer 12 can be formed at least on the front surface 11a. Subsequently, the formation of the silicon epitaxial layer 13 in the second step can be performed.

  In the first step, the silicon wafer 11 as the substrate was introduced into a dedicated heat treatment apparatus capable of introducing a carbon-containing gas, and then the carbon-containing gas was introduced into the furnace to make the furnace a carbon-containing gas atmosphere. Thereafter, the heating can be performed by raising the temperature to a predetermined heat treatment temperature. The heat treatment apparatus is not particularly limited, and a vertical type or a horizontal type can be used. Further, an apparatus that processes one wafer, such as an RTA apparatus, may be used. However, it is preferable to use a batch-type heat treatment apparatus that can simultaneously heat many wafers. In this case, the second step can be performed by introducing the silicon wafer 11 after the heat treatment into the epitaxial growth furnace.

<Second step>
Next, a silicon epitaxial layer 13 is formed at a temperature of 900 ° C. or more and 1000 ° C. or less on the carbon diffusion layer 12 formed in the surface layer on the front surface 11a side in the first step. This can be performed by a vapor phase growth method such as a CVD method.

Specifically, the silicon wafer 11 on which the carbon diffusion layer 12 is formed in the first step is introduced into an epitaxial growth furnace, hydrogen gas is introduced into the furnace, the temperature is raised to about 1100 to 1150 ° C., and hydrogen baking is performed. Then, the natural oxide film on the surface of the silicon wafer 11 is removed. Next, for example, a hydrogen gas is used as a carrier gas, and a silane-based gas, such as a monosilane gas (SiH ₄ ) or a dichlorosilane gas (SiH ₂ Cl ₂ ), which is decomposed at 900 ° C. to 1000 ° C., is introduced into the furnace as a source gas. Thus, the silicon epitaxial layer 13 can be formed on the carbon diffusion layer 12. From the viewpoint of increasing the hydrogen concentration in the carbon diffusion layer 12, it is desirable to use monosilane gas (SiH ₄ ) having many hydrogen bonds.

  The thickness of the silicon epitaxial layer 13 can be appropriately set according to the design, but can be, for example, in the range of 1 to 15 μm. Also, the resistivity of the silicon epitaxial layer 13 can be appropriately set according to the design.

  If the formation temperature of the silicon epitaxial layer 13 is lower than 900 ° C., the silane-based gas as the source gas cannot be decomposed satisfactorily. When the formation temperature of the silicon epitaxial layer 13 is higher than 1000 ° C., silicon in the carbon diffusion layer 12 formed in the first step is sublimated and carbon is bonded and deposited. As a result, the crystal structure of silicon is disturbed, and a number of epitaxial defects are formed in the silicon epitaxial layer 13 formed on the carbon diffusion layer 12. Therefore, the formation temperature of the silicon epitaxial layer 13 is set to 900 ° C. or more and 1000 ° C. or less.

  Thus, the epitaxial silicon wafer 1 according to the present invention can be manufactured. The formed carbon diffusion layer 12 captures hydrogen contained in the source gas and hydrogen of the hydrogen gas as the carrier gas. The hydrogen trapped in the carbon diffusion layer 12 diffuses into the silicon epitaxial layer 13 during heat treatment in a device forming step, and has a function of passivating defects in the silicon epitaxial layer 13. In the present invention, the formation of the silicon epitaxial layer 13 is performed at a relatively low temperature of 900 ° C. or more and 1000 ° C. or less. Therefore, compared with the case where the silicon epitaxial layer 13 is formed at a high temperature of about 1150 ° C., a higher concentration of hydrogen can be captured by the carbon diffusion layer 12, and the effect of passivating defects can be enhanced.

Here, the peak concentration of hydrogen captured by the carbon diffusion layer 12 is 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. The hydrogen concentration is the maximum concentration inside the silicon wafer 11, and the hydrogen concentration is the maximum (peak) in the carbon diffusion layer 12.

(Epitaxial silicon wafer)
Next, the epitaxial silicon wafer according to the present invention will be described. The epitaxial silicon wafer 1 according to the present invention includes a carbon diffusion layer 12 formed at least on a surface layer on the front surface 11a side of a silicon wafer 11 having a front surface 11a, a back surface 11b, and an edge region 11c. And a silicon epitaxial layer 13 formed on the carbon diffusion layer 12 in the surface layer on the surface 11a side. Here, the carbon peak concentration of the carbon diffusion layer 12 is 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less, and the hydrogen peak concentration of the carbon diffusion layer 12 is 1 × 10 ¹⁸ atoms / cm ³ or more. × 10 ²⁰ atoms / cm ³ or less.

As described above, in the method for manufacturing an epitaxial silicon wafer according to the present invention, the heat treatment of the silicon wafer 11 in a carbon-containing gas atmosphere is performed at a relatively low temperature of 800 ° C. or more and 980 ° C. or less. Thereby, the carbon peak concentration of the carbon diffusion layer 12 becomes 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less, and the carbon diffusion layer 12 has a high gettering ability.

  In addition to the heat treatment at a relatively low temperature, the formation of the silicon epitaxial layer 13 is also performed at a relatively low temperature. As a result, the formation of epitaxial defects is suppressed, and the number of epitaxial defects is 90 nm or more and 4 or less. Thus, the epitaxial silicon wafer 1 according to the present invention has few epitaxial defects and high gettering ability.

The thickness of the carbon diffusion layer 12 is not less than 20 nm and not more than 200 nm. Further, the carbon diffusion layer 12 contains a high peak concentration of hydrogen of 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. It has the effect of diffusing inside and passivating defects.

  The carbon diffusion layer 12 may be provided only on the surface portion on the front surface 11a side of the silicon wafer 11, or may be provided on both the front surface 11a and the back surface 11b. Further, it is preferable that the carbon diffusion layer 12 is not formed on the surface layer of the edge region 11c.

  Hereinafter, although an example of the present invention is described, the present invention is not limited to an example.

(Invention Example 1)
First, as a substrate for an epitaxial silicon wafer, an n-type silicon wafer having a diameter of 200 mm obtained by subjecting a single crystal silicon ingot grown by the CZ method to wafer processing (resistivity: 50 Ω · cm, dopant: phosphorus, phosphorus A concentration: 8.6 × 10 ¹³ atoms / cm ³ and an oxygen concentration: 9 × 10 ¹⁷ atoms / cm ³ ) were prepared. This silicon wafer was introduced into the heat treatment furnace, and was placed on the susceptor shown in FIG. Next, ethane gas is introduced into the furnace to form an ethane gas atmosphere. Then, the temperature in the furnace is increased to 800 ° C., and the silicon wafer is subjected to a heat treatment for 1 minute, and the silicon wafer is heated on the front side. A carbon diffusion layer was formed on the surface layer. Subsequently, after the silicon wafer on which the carbon diffusion layer was formed was taken out of the heat treatment furnace, the silicon wafer on which the carbon diffusion layer was formed was introduced into an epitaxial growth furnace, and hydrogen gas was introduced into the furnace. After the temperature in the furnace was lowered to 980 ° C., hydrogen gas was introduced into the furnace as a carrier gas, monosilane gas (SiH ₄ ) as a source gas, and phosphine (PH ₄ ) as a dopant gas. An n-type silicon epitaxial layer (dopant: phosphorus, resistivity: 10 Ω · cm, thickness: 4 μm) was formed. Thus, an epitaxial silicon wafer according to Inventive Example 1 was obtained.

(Invention Example 2)
An epitaxial silicon wafer was produced in the same manner as in Invention Example 1. However, an epitaxial silicon wafer according to Invention Example 2 was obtained by setting the heat treatment temperature in the first step to 950 ° C. Other conditions are all the same as those of Inventive Example 1.

(Invention Example 3)
An epitaxial silicon wafer was produced in the same manner as in Invention Example 1. However, an epitaxial silicon wafer according to Invention Example 3 was obtained by setting the heat treatment temperature in the first step to 980 ° C. Other conditions are all the same as those of Inventive Example 1.

(Comparative Example 1)
An epitaxial silicon wafer was produced in the same manner as in Invention Example 1. However, an epitaxial silicon wafer according to Comparative Example 1 was obtained by setting the heat treatment temperature in the first step to 750 ° C. Other conditions are all the same as those of Inventive Example 1.

(Comparative Example 2)
An epitaxial silicon wafer was produced in the same manner as in Invention Example 1. However, an epitaxial silicon wafer according to Comparative Example 2 was obtained by setting the heat treatment temperature in the first step to 1000 ° C. Other conditions are all the same as those of Inventive Example 1.

(Comparative Example 3)
An epitaxial silicon wafer was produced in the same manner as in Invention Example 1. However, an epitaxial silicon wafer according to Comparative Example 3 was obtained by setting the heat treatment temperature in the first step to 1100 ° C.

(Invention Example 4)
An epitaxial silicon wafer was produced in the same manner as in Inventive Example 2. However, an epitaxial silicon wafer according to Inventive Example 4 was obtained by setting the temperature for forming the epitaxial layer in the second step to 900 ° C. Other conditions are the same as those of the invention example 2.

(Invention Example 5)
An epitaxial silicon wafer was produced in the same manner as in Inventive Example 2. However, an epitaxial silicon wafer according to Inventive Example 5 was obtained by setting the formation temperature of the silicon epitaxial layer in the second step to 1000 ° C. Other conditions are the same as those of the invention example 2.

(Comparative Example 4)
An epitaxial silicon wafer was produced in the same manner as in Inventive Example 2. However, the temperature for forming the epitaxial layer in the second step was 850 ° C. As a result, a silicon epitaxial layer could not be grown.

(Comparative Example 5)
An epitaxial silicon wafer was produced in the same manner as in Inventive Example 2. However, an epitaxial silicon wafer according to Comparative Example 5 was obtained by setting the formation temperature of the epitaxial layer in the second step to 1180 ° C. Other conditions are the same as those of the invention example 2.

<Evaluation of epitaxial defects>
The number of epitaxial defects formed in the silicon epitaxial layer was evaluated for each of the epitaxial silicon wafers of Invention Examples 1 to 5 and Comparative Examples 1 to 3. Specifically, the surface of the epitaxial wafer of each sample was observed and evaluated using a surface defect inspection device (Surfscan SP-2 manufactured by KLA-Tencor), and a bright point defect (Light Point Defect, LPD) having a size of 90 nm or more was observed. Was investigated. At that time, the observation mode was the Oblique mode (oblique incidence mode), and the estimation of the surface pits was performed based on the detection size ratio of the Wide Narrow channel. Subsequently, the occurrence site of LPD was observed and evaluated using a scanning electron microscope (Scanning Electron Microscope, SEM) to evaluate whether the LPD was a stacking fault (SF). Table 1 shows the number of detected epitaxial defects (pieces / wafer).

  As is clear from Table 1, formation of epitaxial defects per wafer was less than 5 in Invention Examples 1 to 5 and Comparative Example 1. On the other hand, in Comparative Examples 2 and 3 in which the heat treatment temperature was 1000 ° C. or higher, and in Comparative Example 5 in which the formation temperature of the silicon epitaxial layer exceeded 1000 ° C., many epitaxial defects were formed. This is considered to be due to sublimation of silicon in the formed carbon diffusion layer and deposition of carbon.

<Evaluation of gettering ability>
The gettering ability of each of the epitaxial silicon wafers of Invention Examples 1 to 5 and Comparative Examples 1 to 3 and 5 was evaluated. Specifically, the surface of the epitaxial layer of each epitaxial wafer is intentionally contaminated with a Ni contaminated liquid (1.0 × 10 ¹³ / cm ² ) using a spin coat contaminant method, and then continuously at 1000 ° C. for 3 minutes in a nitrogen atmosphere. Was subjected to a diffusion heat treatment. Thereafter, light etching was performed for 3 minutes, pits observed on the epitaxial layer surface were observed using an optical microscope, and the gettering ability was evaluated based on the presence or absence of the pits. Table 1 shows the evaluation results.

  As is clear from Table 1, no pits were observed in Invention Examples 1 to 5 and Comparative Examples 2, 3 and 5, but pits were observed in Comparative Example 1 in which the heat treatment temperature was as low as 750 ° C. Insufficient ability. This is probably because in Comparative Example 1, the heat treatment temperature was low, so that carbon could not be sufficiently diffused into the inside of the wafer.

<Evaluation of carbon concentration and hydrogen concentration>
Regarding Invention Examples 1 to 5 and Comparative Examples 1 to 3, SIMS (Secondary Ion Mass Spectrometry) measurements were performed on the obtained epitaxial silicon wafers to measure the carbon concentration and the hydrogen concentration. Table 1 shows the obtained carbon and hydrogen concentrations. FIG. 6 shows the concentration profiles of carbon and hydrogen in the epitaxial silicon wafer of Inventive Example 2.

As shown in Table 1, the carbon concentration is 5 × 10 ¹⁸ atoms / cm ³ or more for Invention Examples 1 to 5 and Comparative Examples 2, 3, and 5 having high heat treatment temperatures, and has high gettering ability. Was. On the other hand, in Comparative Example 1, since the heat treatment temperature was low, carbon could not be sufficiently diffused into the inside of the wafer, and the gettering ability was insufficient.

In addition, among the invention examples 1 to 5 having high gettering ability, the hydrogen concentration was in the order of 10 ¹⁸ atoms / cm ^{3 for} invention example 1 in which the heat treatment temperature was relatively low. The order was 10 ¹⁹ atoms / cm ³ , and the carbon diffusion layer contained a high concentration of hydrogen. Also, in Comparative Examples 2 and 3, in which the formation temperature of the silicon epitaxial layer was within the range specified in the present invention, the hydrogen concentration was on the order of 10 ¹⁹ atoms / cm ³ .

  According to the present invention, an epitaxial silicon wafer having high gettering ability can be manufactured while suppressing formation of epitaxial defects, and thus is useful in the semiconductor wafer manufacturing industry.

DESCRIPTION OF SYMBOLS 1 Epitaxial silicon wafer 11 Silicon wafer 11a Front surface 11b Back surface 11c Edge region 12 Carbon diffusion layer 13 Silicon epitaxial layer 14 Protective layer 20 Susceptor 21 Depression 21a Side wall 21b Bottom

Claims (13)

A silicon wafer having a front surface, a back surface, and an edge region is subjected to a heat treatment at a temperature of 800 ° C. or more and 980 ° C. or less in a carbon-containing gas atmosphere, and at least a surface layer portion of the silicon wafer on the front surface side A first step of forming a carbon diffusion layer on
A second step of forming a silicon epitaxial layer at a temperature of 900 ° C. or more and 1000 ° C. or less on the carbon diffusion layer formed on the surface layer on the front surface side of the silicon wafer;
A method for producing an epitaxial silicon wafer, comprising:   2. The method of manufacturing an epitaxial silicon wafer according to claim 1, wherein in the first step, the carbon diffusion layer is formed only on a surface layer on the front side of the silicon wafer. 3.   3. The method according to claim 1, further comprising: a third step of forming a protective film on the back surface of the silicon wafer before the first step; and a fourth step of removing the protective film before or after the second step. 3. The method for producing an epitaxial silicon wafer according to item 2. In the first step, the carbon diffusion layer is formed on both the front surface side and the back surface side of the silicon wafer,
3. The method of manufacturing an epitaxial silicon wafer according to claim 2, further comprising a fifth step of removing the carbon diffusion layer formed in the surface layer on the back surface before or after the second step. 4. In the first step, the carbon diffusion layer is formed on at least the front surface side of each of the two silicon wafers with respect to the two silicon wafers whose back surfaces are overlapped,
The method of manufacturing an epitaxial silicon wafer according to claim 2, further comprising a sixth step of separating the two silicon wafers after the first step.   The method according to any one of claims 1 to 5, further comprising a seventh step of removing the carbon diffusion layer formed on a surface portion of the edge region of the silicon wafer after the first step and before the second step. A method for producing an epitaxial silicon wafer according to claim 1.   The method of manufacturing an epitaxial silicon wafer according to any one of claims 1 to 6, wherein the first step is performed in an epitaxial growth furnace in which the second step is performed.   The first step is performed by introducing the silicon wafer into a heat treatment apparatus capable of introducing the carbon-containing gas, and the second step is performed by introducing the heat-treated silicon wafer into an epitaxial growth furnace. Item 7. The method for producing an epitaxial silicon wafer according to any one of Items 1 to 6. In the first step, heat treatment is performed so that the carbon peak concentration in the carbon diffusion layer is 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less.
9. The method according to claim 1, wherein in the second step, an epitaxial growth process is performed such that a hydrogen peak concentration in the carbon diffusion layer is 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. Item 13. The method for producing an epitaxial silicon wafer according to Item 1. Front surface, a carbon diffusion layer formed on at least the front surface side of the silicon wafer having a back surface and an edge region,
A silicon epitaxial layer formed on the carbon diffusion layer in the surface layer on the front side,
Has,
The carbon diffusion layer has a carbon peak concentration of 1 × 10 ¹⁷ / cm ³ or more and 1 × 10 ²⁰ / cm ³ or less;
An epitaxial silicon wafer, wherein the carbon diffusion layer has a hydrogen peak concentration of 1 × 10 ¹⁸ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less.   The epitaxial silicon wafer according to claim 10, wherein the thickness of the carbon diffusion layer is 200 nm or less.   The epitaxial silicon wafer according to claim 10, wherein the carbon diffusion layer is formed only on a surface layer on the front surface side.   The epitaxial silicon wafer according to any one of claims 10 to 12, wherein the carbon diffusion layer is not formed on a surface portion of the edge region.

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