阅读说明：本技术 外延硅晶片的制造方法及外延硅晶片 (Method for producing epitaxial silicon wafer and epitaxial silicon wafer ) 是由 古贺祥泰 于 2019-06-05 设计创作，主要内容包括：本发明提供一种能够制造在抑制外延缺陷的形成的同时具有高吸杂能力的外延硅晶片的方法及外延硅晶片。本发明的外延硅晶片的制造方法的特征在于,包括：第1工序,对具有正面、背面及边缘区域的硅晶片,在含碳气体气氛下以800℃以上且980℃以下的温度实施热处理,在硅晶片的至少正面侧的表层部形成碳扩散层；以及第2工序,在形成于硅晶片的正面侧的表层部的碳扩散层上,以900℃以上且1000℃以下的温度形成硅外延层。(The present invention provides a method capable of manufacturing an epitaxial silicon wafer having high gettering capability while suppressing formation of epitaxial defects, and an epitaxial silicon wafer. The method for manufacturing an epitaxial silicon wafer according to the present invention is characterized by comprising: a step 1 of subjecting a silicon wafer having a front surface, a back surface and an edge region to a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere to form a carbon diffusion layer at least in a surface layer portion on the front surface side of the silicon wafer; and a 2 nd step of forming a silicon epitaxial layer on the carbon diffusion layer formed on the surface layer portion on the front surface side of the silicon wafer at a temperature of 900 ℃ to 1000 ℃.)

1. A method for manufacturing an epitaxial silicon wafer is characterized by comprising the following steps:

a step 1 of subjecting a silicon wafer having a front surface, a back surface and an edge region to a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere to form a carbon diffusion layer on at least a surface layer portion of the front surface side of the silicon wafer; and

and a 2 nd step of forming a silicon epitaxial layer on the carbon diffusion layer formed on the surface layer portion on the front surface side of the silicon wafer at a temperature of 900 ℃ to 1000 ℃.

2. The method for manufacturing an epitaxial silicon wafer according to claim 1, wherein,

in the step 1, the carbon diffusion layer is formed only on the surface layer portion of the front surface side of the silicon wafer.

3. The method for manufacturing an epitaxial silicon wafer according to claim 2, further comprising the steps of:

a 3 rd step of forming a protective film on the back surface of the silicon wafer before the 1 st step; and

and a 4 th step of removing the protective film before or after the 2 nd step.

4. The method for manufacturing an epitaxial silicon wafer according to claim 2, wherein,

in the step 1, the carbon diffusion layer is formed on the surface layer portions of both the front surface side and the back surface side of the silicon wafer,

the method for manufacturing an epitaxial silicon wafer further comprises: and a 5 th step of removing the carbon diffusion layer formed on the surface layer portion on the back surface side before or after the 2 nd step.

5. The method for manufacturing an epitaxial silicon wafer according to claim 2, wherein,

in the step 1, the carbon diffusion layer is formed on at least the surface layer portion on the front surface side of each of two silicon wafers having back surfaces overlapping each other,

the method for manufacturing an epitaxial silicon wafer further comprises: and a 6 th step of peeling the two silicon wafers after the 1 st step.

6. The method for manufacturing an epitaxial silicon wafer according to any one of claims 1 to 5, further comprising: and a 7 th step of removing the carbon diffusion layer formed in a surface layer portion of the edge region of the silicon wafer after the 1 st step and before the 2 nd step.

7. The method for manufacturing an epitaxial silicon wafer according to any one of claims 1 to 6, wherein,

the step 1 is performed in an epitaxial growth furnace in which the step 2 is performed.

8. The method for manufacturing an epitaxial silicon wafer according to any one of claims 1 to 6, wherein,

the step 1 is performed by introducing the silicon wafer into a heat treatment apparatus capable of introducing the carbon-containing gas, and the step 2 is performed by introducing the silicon wafer after heat treatment into an epitaxial growth furnace.

9. The method for producing an epitaxial silicon wafer according to any one of claims 1 to 8, wherein,

in the step 1, the peak concentration of carbon in the carbon diffusion layer is set to 1 × 10¹⁷/cm³Above and 1 × 10²⁰/cm³The heat treatment is carried out in the following manner,

in the 2 nd step, the peak concentration of hydrogen in the carbon diffusion layer is set to 1 × 10¹⁸Atom/cm³Above and 1 × 10²⁰Atom/cm³The epitaxial growth process is performed in the following manner.

10. An epitaxial silicon wafer, comprising:

a carbon diffusion layer formed on at least a surface layer portion of the front surface side of a silicon wafer having a front surface, a back surface and an edge region; and

a silicon epitaxial layer formed on the carbon diffusion layer of the surface layer portion on the front surface side,

the carbon peak concentration of the carbon diffusion layer is 1 × 10¹⁷/cm³Above and 1 × 10²⁰/cm³In the following, the following description is given,

the carbon diffusion layer has a hydrogen peak concentration of 1X 10¹⁸Atom/cm³Above and 1 × 10²⁰Atom/cm³The following.

11. The epitaxial silicon wafer of claim 10,

the thickness of the carbon diffusion layer is 200nm or less.

12. Epitaxial silicon wafer according to claim 10 or 11,

the carbon diffusion layer is formed only on the surface layer portion on the front surface side.

13. Epitaxial silicon wafer according to any one of claims 10 to 12, wherein,

the carbon diffusion layer is not formed on the surface layer portion of the edge region.

Technical Field

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

Background

Conventionally, silicon wafers have been widely used as substrates of semiconductor devices, but when heavy metals are mixed into silicon wafers, significant adverse effects (for example, a failure in a pause time, a failure in holding, a failure in junction leakage, and an insulation breakdown of an oxide film) are exerted on device characteristics. Therefore, by forming a gettering layer for trapping heavy metals inside the wafer, diffusion of heavy metals to the device formation region is suppressed. Here, it is important to form a gettering layer directly below the device formation region so as to be able to trap heavy metals such as titanium and molybdenum, which have a low diffusion rate.

In recent years, it has been demanded that an epitaxial silicon wafer having a silicon epitaxial layer formed on a silicon wafer be used as a substrate without crystal defects in a device formation region. The epitaxial silicon wafer is formed, for example, by: after a gettering layer is formed in 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, patent document 1 describes the following method: carbon ions are implanted into the surface of the silicon wafer to form a gettering layer containing high concentration of carbon in the surface layer portion of the wafer, and a silicon epitaxial layer is formed on the formed gettering layer.

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

As another method for forming the gettering layer, the following methods are proposed: the silicon wafer is subjected to a heat treatment in a carbon-containing gas atmosphere to diffuse carbon into the silicon wafer, and the formed carbon diffusion layer is used as a gettering layer. For example, patent document 2 describes a method for manufacturing an epitaxial wafer, the method including: an epitaxial wafer having a gettering layer directly below the epitaxial layer is manufactured by supplying a gas containing carbon to a silicon wafer at a temperature of 1000 ℃ to 1200 ℃ to form a layer containing a gas containing thermally decomposed carbon, and forming the epitaxial layer on the layer.

Patent document 3 describes a method for manufacturing an epitaxial wafer, the method including: a silicon wafer is immersed in a solution containing carbon to form a carbon-containing film on the surface of the silicon wafer, and then the silicon wafer is heat-treated at a temperature of 500 to 750 ℃ to thermally diffuse the carbon in the carbon-containing film to the surface layer portion of the silicon wafer, and then an epitaxial layer is formed on the formed carbon diffusion layer.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3384506

Patent document 2: japanese patent laid-open publication No. 2013-51348

Patent document 3: japanese patent laid-open No. 2010-34330

Disclosure of Invention

Technical problem to be solved by the invention

However, it is known that many epitaxial defects are also formed in the epitaxial wafer manufactured by the method described in patent document 2. Further, it is known that the gettering capability of the epitaxial wafer manufactured by the method described in patent document 3 is insufficient.

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

Means for solving the technical problem

The present invention for solving the above problems is as follows.

[1] A method for manufacturing an epitaxial silicon wafer is characterized by comprising the following steps:

a step 1 of subjecting a silicon wafer having a front surface, a back surface and an edge region to a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere to form a carbon diffusion layer on at least a surface layer portion of the front surface side of the silicon wafer; and

and a 2 nd step of forming a silicon epitaxial layer on the carbon diffusion layer formed on the surface layer portion on the front surface side of the silicon wafer at a temperature of 900 ℃ to 1000 ℃.

[2] The method for producing an epitaxial silicon wafer according to [1], wherein,

in the step 1, the carbon diffusion layer is formed only on the surface layer portion of the front surface side of the silicon wafer.

[3] The method for manufacturing an epitaxial silicon wafer according to [2], further comprising:

a 3 rd step of forming a protective film on the back surface of the silicon wafer before the 1 st step; and

and a 4 th step of removing the protective film before or after the 2 nd step.

[4] The method for producing an epitaxial silicon wafer according to [2], wherein,

in the step 1, the carbon diffusion layer is formed on the surface layer portions of both the front surface side and the back surface side of the silicon wafer,

the method for manufacturing an epitaxial silicon wafer further includes a 5 th step of removing the carbon diffusion layer formed in the surface layer portion on the back surface side before or after the 2 nd step.

[5] The method for producing an epitaxial silicon wafer according to [2], wherein,

in the step 1, the carbon diffusion layer is formed on at least the surface layer portion on the front surface side of each of two silicon wafers having back surfaces overlapping each other,

the method for manufacturing an epitaxial silicon wafer further comprises a 6 th step of peeling the two silicon wafers after the 1 st step.

[6] The method for manufacturing an epitaxial silicon wafer according to any one of [1] to [5], further comprising a 7 th step of removing the carbon diffusion layer formed in a surface layer portion of the edge region of the silicon wafer after the 1 st step and before the 2 nd step.

[7] The method for producing an epitaxial silicon wafer according to any one of the above [1] to [6], wherein,

the step 1 is performed in an epitaxial growth furnace in which the step 2 is performed.

[8] The method for producing an epitaxial silicon wafer according to any one of the above [1] to [6], wherein,

the step 1 is performed by introducing the silicon wafer into a heat treatment apparatus capable of introducing the carbon-containing gas, and the step 2 is performed by introducing the silicon wafer after heat treatment into an epitaxial growth furnace.

[9] The method for producing an epitaxial silicon wafer according to any one of the above [1] to [8], wherein,

in the step 1, the peak concentration of carbon in the carbon diffusion layer is set to 1 × 10¹⁷/cm³Above and 1 × 10²⁰/cm³The heat treatment is carried out in the following manner,

in the 2 nd step, the peak concentration of hydrogen in the carbon diffusion layer is set to 1 × 10¹⁸Atom/cm³Above and 1 × 10²⁰Atom/cm³The epitaxial growth process is performed in the following manner.

[10] An epitaxial silicon wafer, comprising:

a carbon diffusion layer formed on at least a surface layer portion of the front surface side of a silicon wafer having a front surface, a back surface and an edge region; and

a silicon epitaxial layer formed on the carbon diffusion layer of the surface layer portion on the front surface side,

the carbon peak concentration of the carbon diffusion layer is 1 × 10¹⁷/cm³Above and 1 × 10²⁰/cm³In the following, the following description is given,

the carbon diffusion layer has a hydrogen peak concentration of 1X 10¹⁸Atom/cm³Above and 1 × 10²⁰Atom/cm³The following.

[11] The epitaxial silicon wafer according to the above [10], wherein,

the thickness of the carbon diffusion layer is 200nm or less.

[12] The epitaxial silicon wafer according to the above [10] or [11], wherein,

the carbon diffusion layer is formed only on the surface layer portion on the front surface side.

[13] The epitaxial silicon wafer according to any one of the above [10] to [12], wherein,

the carbon diffusion layer is not formed on the surface layer portion of the edge region.

Effects of the invention

According to the present invention, an epitaxial silicon wafer having high gettering capability while suppressing formation of epitaxial defects can be manufactured.

Drawings

Fig. 1 is a view showing a flow of a method for manufacturing an epitaxial silicon wafer according to the present invention.

Fig. 2 is a view showing an epitaxial silicon wafer having a carbon diffusion layer on both the front surface and the back surface.

Fig. 3 is a view showing an example of a susceptor for preventing a carbon diffusion layer from being formed on the back surface of a silicon wafer.

Fig. 4 is a view showing a silicon wafer having a protective film for preventing a carbon diffusion layer from being formed on the back surface.

FIG. 5 is a view showing two silicon wafers with their back surfaces overlapped with each other.

Fig. 6 is a graph showing the concentration distributions of carbon and hydrogen in the epitaxial silicon wafer of invention example 2.

Detailed Description

(method for producing 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. The method for manufacturing an epitaxial silicon wafer according to the present invention is characterized by comprising the steps of: a step 1 of performing a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere on a silicon wafer 11 (fig. 1(a) in fig. 1) having a front surface 11a, a back surface 11b, and an edge region 11c to form a carbon diffusion layer 12 (fig. 1(b) in fig. 1) on at least a surface layer portion of the silicon wafer 11 on the front surface 11a side; and a 2 nd step of forming a silicon epitaxial layer 13 on the carbon diffusion layer 12 formed in the surface layer portion on the front surface 11a side of the silicon wafer 11 at a temperature of 900 ℃ to 1000 ℃ (fig. 1(c) in fig. 1).

As described above, patent documents 2 and 3 propose a technique of diffusing carbon into a silicon wafer and using the formed carbon diffusion layer as a gettering layer. However, many epitaxial defects are formed in the epitaxial wafer manufactured by the method of patent document 2, and the gettering capability of the epitaxial wafer manufactured by the method of patent document 3 is insufficient.

The inventors of the present invention investigated the cause of the above-described problem in detail. As a result, it was found that the reason why the gettering capability of the epitaxial wafer obtained by the method of patent document 3 is insufficient is that: since the heat treatment temperature is as low as 500 to 750 ℃, carbon in the carbon-containing film does not sufficiently diffuse into the wafer.

On the other hand, it is known that the reason why many epitaxial defects are formed in the epitaxial wafer obtained by the method of patent document 2 is that: although the carbon diffusion layer is formed in the surface layer portion of the silicon wafer by the heat treatment, since the heat treatment temperature is as high as 1000 to 1200 ℃, silicon constituting the carbon diffusion layer is sublimated, and the remaining carbon is bonded to each other and precipitated, whereby the crystal structure of the surface layer portion of the wafer is disordered.

From the above studies, it is desired that an epitaxial wafer having high gettering capability while suppressing formation of epitaxial defects can be manufactured by performing heat treatment at a temperature between the temperature described in patent document 3 and the temperature described in patent document 2.

However, it is known that when the present inventors perform heat treatment in the above temperature range to manufacture an epitaxial silicon wafer, many epitaxial defects are still formed. Therefore, the inventors of the present invention investigated the cause thereof. The reason for this is found to be: the silicon epitaxial layer formed on the carbon diffusion layer is generally formed at a temperature of about 1150 ℃, but since the formation temperature is high, silicon in the carbon diffusion layer sublimates as described above, and carbon is precipitated.

From the above studies, the inventors of the present invention reached the following conclusions: in order to produce an epitaxial silicon wafer having high gettering ability while suppressing the formation of epitaxial defects, it is necessary to perform heat treatment of the silicon wafer at a temperature at which carbon is sufficiently diffused into the silicon wafer and carbon deposition due to sublimation of silicon of the formed carbon diffusion layer is not caused under a carbon-containing gas atmosphere, and the silicon epitaxial layer is also required to be formed at a low temperature at which carbon deposition due to sublimation of silicon of the formed carbon diffusion layer is not caused.

Further, the inventors of the present invention have conducted intensive studies on specific temperature conditions, and as a result, have found that an epitaxial silicon wafer having high gettering capability while suppressing the formation of epitaxial defects can be obtained by performing heat treatment of a silicon wafer in a carbon-containing gas atmosphere at a temperature of 800 ℃ to 980 ℃ and performing formation of a silicon epitaxial layer at a temperature of 900 ℃ to 1000 ℃, thereby completing the present invention. Hereinafter, each step will be explained.

< step 1 >

First, a silicon wafer 11 (fig. 1(a) in fig. 1) having a front surface 11a, a back surface 11b, and an edge region 11c is subjected to a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere, and a carbon diffusion layer 12 is formed in at least a surface layer portion of the silicon wafer 11 on the front surface 11a side (fig. 1(b) in fig. 1).

As the silicon wafer 11, a silicon wafer obtained by processing a single crystal silicon ingot grown by a czochralski method (CZ method) or a floating zone method (FZ method) can be used. In order to obtain higher gettering capability, carbon and/or nitrogen may be added to the silicon wafer 11. Further, any appropriate impurity may be added to the mixture to form an n-type or p-type semiconductor device. The diameter of the silicon wafer 11 can be set to 200mm, 300mm, or 450mm, for example. The resistivity may be set as appropriate according to design.

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

Further, the oxygen concentration of the silicon wafer 11 is preferably 1X 10¹⁷Atom/cm³Above and 1 × 10¹⁸Atom/cm³The following. This can suppress the occurrence of slip (slip) and the formation of epitaxial defects due to oxygen precipitation.

As described above, in the present invention, it is important to set the heat treatment temperature in the carbon-containing gas atmosphere to 800 ℃ to 980 ℃. When the heat treatment temperature is less than 800 ℃, a gas containing carbon, for example, 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, in the case where the heat treatment temperature exceeds 980 ℃, since the thermal energy is high, silicon in the formed carbon diffusion layer 12 sublimates. As a result, carbon remaining in the carbon diffusion layer 12 is bonded to each other and precipitated, the crystal structure of silicon is disordered, 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 ℃ or higher and 980 ℃ or lower. The heat treatment temperature is more preferably 800 ℃ to 950 ℃.

By performing the heat treatment at the temperature in the above range, carbon can be diffused into the wafer to form the carbon diffusion layer 12 without disturbing the crystal structure of the surface layer portion of the silicon wafer 11. The concentration of carbon contained in the carbon diffusion layer 12 was 1 × 10¹⁷/cm³Above and 1 × 10²⁰/cm³Hereinafter, the carbon diffusion layer 12 can contain carbon at a sufficient concentration for gettering of heavy metals. The carbon concentration is the maximum concentration in the silicon wafer 11, and the carbon concentration is the maximum (peak) at the interface between the silicon wafer 11 and the silicon epitaxial layer 13.

The heat treatment time is preferably 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 carbon at a high concentration can be formed in the surface layer portion of the silicon wafer 11. By setting the heat treatment time to 1 minute or more, the thickness of the carbon diffusion layer 12 becomes 20nm or more. Further, even if the heat treatment is performed for more than 40 minutes, the diffusion of carbon into the wafer is saturated. Therefore, the upper limit of the heat treatment time is preferably 40 minutes or less. The upper limit of the thickness of the carbon diffusion layer 12 formed is approximately 200 nm.

As shown in fig. 2, the carbon diffusion layer 12 may be formed not only on the surface layer portion on the front surface 11a side of the silicon wafer 11 but also on the surface layer portion on the back surface 11b side. This allows the carbon diffusion layer 12 formed on the surface layer portion on the rear surface 11b side to function as a gettering layer, and thus the gettering capability can be further improved.

The carbon diffusion layer 12 may be formed only on the surface layer portion of the silicon wafer 11 on the front surface 11a side. This can suppress contamination by carbon. The carbon diffusion layer 12 may be formed in the edge region 11 c.

The formation of the carbon diffusion layer 12 only at the surface layer portion on the front surface 11a side of the silicon wafer 11 can be performed, for example, by using a susceptor as shown in fig. 3, instead of using a type of susceptor that supports the edge region 11c of the silicon wafer 11 by wire contact. That is, the susceptor 20 shown in fig. 3 has a recess 21 defined by a side wall 21a and a bottom surface 21b, and the bottom surface 21b has a larger diameter than the silicon wafer 11. By disposing the silicon wafer 11 on the bottom surface 21b of the susceptor 20 and performing heat treatment in a state where the bottom surface 21b is in contact with the back surface 11b, the carbon diffusion layer 12 can be formed only on the surface layer portion on the front surface 11a side.

As shown in fig. 4, the carbon diffusion layer 12 can be formed only on the surface layer portion on the front surface 11a side of the silicon wafer 11 by forming the protective film 14 on the back surface 11b of the silicon wafer 11 (step 3) and performing the above-described heat treatment in a state where the protective film 14 is formed. The formed protective film 14 can be removed before or after the 2 nd step (step 4), for example, by polishing. As the protective film 14, any film that can prevent diffusion of carbon may be used, and an oxide film, a nitride film, or the like may be used.

Further, after the carbon diffusion layer 12 is once formed on the surface layer portions of 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 surface layer portion on the back surface 11b side is removed, whereby the carbon diffusion layer 12 can be formed only on the surface layer portion on the front surface 11a side. The carbon diffusion layer 12 formed on the surface layer portion on the rear surface 11b side can be removed, for example, by polishing before or after the later-described 2 nd step (5 th step).

In order to form the carbon diffusion layer 12 only on the surface layer portion on the front surface 11a side of the silicon wafer 11, as shown in fig. 5, two silicon wafers 11 having the back surfaces 11b overlapped with each other may be prepared, and in the 1 st step, the carbon diffusion layer 12 may be formed on the surface layer portion on the front surface 11a side of each of the two silicon wafers 11. In this case, after the 1 st step, the two silicon wafers are peeled off from each other (6 th step), and in the 2 nd step, the silicon epitaxial layer 13 is formed on the carbon diffusion layer 12 formed in the surface layer portion on the front surface 11a side.

In the case where the carbon diffusion layer 12 is formed only on the surface layer portion on the front surface 11a side of the silicon wafer 11 as described above, the carbon diffusion layer 12 is also formed on the surface layer portion of the edge region 11c in which the outer peripheral portion of the wafer 11 is chamfered. The carbon of the carbon diffusion layer 12 formed in the edge region 11c is diffused outward from the wafer by heat treatment performed in a subsequent device process, and there is a possibility that the carbon is absorbed by the silicon epitaxial layer (device formation region) 13. 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 (7 th step) described later. The carbon diffusion layer 12 formed in the surface layer portion of the edge region 11c can be removed by polishing.

The step 1 can be performed in an epitaxial growth furnace that performs a step 2 described later. Specifically, first, the silicon wafer 11 is introduced into an epitaxial growth furnace, hydrogen gas is introduced into the furnace, and the temperature is raised to 1100 to 1150 ℃ to perform hydrogen baking, thereby removing a natural oxide film on the surface of the silicon wafer 11. Then, the temperature in the furnace is lowered to 800 to 980 ℃, and a carbon-containing gas such as hydrogen gas (carrier gas) or methane gas is introduced into the furnace and is held for 1 minute, for example. This allows carbon to diffuse from the surface of the silicon wafer 11 into the wafer, thereby forming the carbon diffusion layer 12 at least on the front surface 11 a. Next, the silicon epitaxial layer 13 in the 2 nd step can be formed.

The 1 st step can be performed as follows: the silicon wafer 11 as a substrate is introduced into a dedicated heat treatment apparatus capable of introducing a carbon-containing gas, the carbon-containing gas is introduced into the furnace to make the furnace have a carbon-containing gas atmosphere, and then the temperature is raised to a predetermined heat treatment temperature. The heat treatment apparatus is not particularly limited, and a vertical or horizontal apparatus can be used. Further, an apparatus that processes one wafer like an RTA apparatus may be used, but a batch type heat treatment apparatus that can heat-treat a plurality of wafers at the same time is preferably used. In this case, the second step 2 can be performed by introducing the silicon wafer 11 after the heat treatment into the epitaxial growth furnace.

< 2 nd step >

Next, in step 1, a silicon epitaxial layer 13 is formed on the carbon diffusion layer 12 formed in the surface layer portion on the front surface 11a side at a temperature of 900 ℃ to 1000 ℃ (fig. 1(c) in fig. 1). This can be performed by a vapor phase growth method such as a CVD method.

Specifically, the silicon wafer 11 having the carbon diffusion layer 12 formed in the step 1 is introduced into an epitaxial growth furnace, and hydrogen gas is introduced into the furnace, and the temperature is raised to about 1100 to 1150 ℃ to perform hydrogen baking, thereby removing the natural oxide film on the surface of the silicon wafer 11. Then, for example, monosilane gas (SiH) is supplied with hydrogen gas as a carrier gas₄) Dichlorosilane gas (SiH)₂Cl₂) And a silane-based gas decomposable at 900 to 1000 ℃ is introduced into the furnace as a source gas. Thereby, 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 preferable to use monosilane gas (SiH) having many hydrogen bonds₄)。

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

When the formation temperature of the silicon epitaxial layer 13 is less than 900 ℃, the decomposition of the silane-based gas as the source gas cannot be performed satisfactorily. When the formation temperature of the silicon epitaxial layer 13 exceeds 1000 ℃, silicon in the carbon diffusion layer 12 formed in the 1 st step sublimates and carbon bonds with each other and precipitates. As a result, the crystal structure of silicon is disordered, and many 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 ℃ or higher and 1000 ℃ or lower.

In this manner, the epitaxial silicon wafer 1 according to the present invention can be manufactured. Hydrogen contained in the source gas or hydrogen of the hydrogen gas as the carrier gas is trapped in the formed carbon diffusion layer 12. The hydrogen trapped in the carbon diffusion layer 12 has the following effects: the defects in the silicon epitaxial layer 13 are passivated by diffusing into the silicon epitaxial layer 13 during the heat treatment in the device forming step. In the present invention, the formation of the silicon epitaxial layer 13 is performed at a relatively low temperature of 900 ℃ to 1000 ℃. Therefore, as compared with the case where the silicon epitaxial layer 13 is formed at a high temperature of about 1150 ℃, the carbon diffusion layer 12 can trap hydrogen at a high concentration, and the effect of passivating the defects can be improved.

Here, the peak concentration of hydrogen trapped in the carbon diffusion layer 12 was 1 × 10¹⁸Atom/cm³Above and 1 × 10²⁰Atom/cm³The following. 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, an epitaxial silicon wafer according to the present invention will be described. The epitaxial silicon wafer 1 according to the present invention has: a carbon diffusion layer 12 formed on at least a surface layer portion of the silicon wafer 11 on the front surface 11a side, the silicon wafer having a front surface 11a, a back surface 11b, and an edge region 11 c; and a silicon epitaxial layer 13 formed on the carbon diffusion layer 12 of the surface layer portion on the front surface 11a side. Here, the epitaxial silicon wafer 1 according to the present invention is characterized in that: the carbon peak concentration of the carbon diffusion layer 12 was 1X 10¹⁷/cm³Above and 1 × 10²⁰/cm³The hydrogen peak concentration of the carbon diffusion layer 12 is 1 × 10¹⁸Atom/cm³Above and 1 × 10²⁰Atom/cm³The following.

As described above, in the epitaxial silicon wafer according to the present inventionIn the manufacturing method, the heat treatment of the silicon wafer 11 in the carbon-containing gas atmosphere is performed at a relatively low temperature of 800 ℃ to 980 ℃. Thus, the carbon peak concentration of the carbon diffusion layer 12 was 1 × 10¹⁷/cm³Above and 1 × 10²⁰/cm³Hereinafter, the carbon diffusion layer 12 has high gettering ability.

In addition, the heat treatment at the relatively low temperature, as described above, is performed at a relatively low temperature to form the silicon epitaxial layer 13. As a result, formation of epitaxial defects is suppressed, and the number of epitaxial defects having a size of 90nm or more is four or less. Thus, the epitaxial silicon wafer 1 according to the present invention has not only a small number of epitaxial defects but also a high gettering capability.

The thickness of the carbon diffusion layer 12 is 20nm to 200 nm. The carbon diffusion layer 12 contains 1 × 10 carbon atoms¹⁸Atom/cm³Above and 1 × 10²⁰Atom/cm³The hydrogen having the following high peak concentration has a function of diffusing in the silicon epitaxial layer 13 to passivate defects when heat treatment in the device formation process is performed.

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

Examples

Hereinafter, examples of the present invention will be described, but the present invention is not limited to the examples.

(inventive example 1)

First, as a substrate of an epitaxial silicon wafer, an n-type silicon wafer (resistivity: 50. omega. cm, dopant: phosphorus, phosphorus concentration: 8.6X 10) having a diameter of 200mm obtained by wafer-processing a single crystal silicon ingot grown by the CZ method was prepared¹³Atom/cm³Oxygen concentration: 9X 10¹⁷Atom/cm³). The silicon wafer was introduced into a heat treatment furnace and placed on a susceptor shown in FIG. 3. Subsequently, after introducing ethane gas into the furnace to form an ethane gas atmosphere, the temperature in the furnace was raised to 800 ℃ to perform heat treatment on the silicon wafer for 1 minute, thereby forming a front surface of the silicon waferThe surface layer portion on the side forms a carbon diffusion layer. Then, after the silicon wafer having the carbon diffusion layer formed thereon was taken out from the heat treatment furnace, the silicon wafer having the carbon diffusion layer formed thereon was introduced into an epitaxial growth furnace, and hydrogen gas was introduced into the furnace. Then, the temperature in the furnace was lowered to 980 ℃, and monosilane gas (SiH) was supplied using hydrogen as a carrier gas₄) As source gas, Phosphine (PH)₄) Introduced into the furnace as a dopant gas, and an n-type silicon epitaxial layer (dopant: phosphorus, resistivity: 10 Ω · cm, thickness: 4 μm). Thus, an epitaxial silicon wafer of invention example 1 was obtained.

(inventive example 2)

An epitaxial silicon wafer was produced in the same manner as in invention example 1. However, the heat treatment temperature in the 1 st step was set to 950 ℃ to obtain an epitaxial silicon wafer of invention example 2. Other conditions were exactly the same as in invention example 1.

(inventive example 3)

An epitaxial silicon wafer was produced in the same manner as in invention example 1. However, the heat treatment temperature in the 1 st step was set to 980 ℃ to obtain an epitaxial silicon wafer of invention example 3. Other conditions were exactly the same as in invention example 1.

Comparative example 1

An epitaxial silicon wafer was produced in the same manner as in invention example 1. However, the heat treatment temperature in the 1 st step was set to 750 ℃ to obtain an epitaxial silicon wafer of comparative example 1. Other conditions were exactly the same as in invention example 1.

Comparative example 2

An epitaxial silicon wafer was produced in the same manner as in invention example 1. However, the heat treatment temperature in the 1 st step was set to 1000 ℃ to obtain an epitaxial silicon wafer of comparative example 2. Other conditions were exactly the same as in invention example 1.

Comparative example 3

An epitaxial silicon wafer was produced in the same manner as in invention example 1. However, the heat treatment temperature in the 1 st step was set to 1100 ℃, and the epitaxial silicon wafer of comparative example 3 was obtained.

(inventive example 4)

An epitaxial silicon wafer was produced in the same manner as in inventive example 2. However, the epitaxial silicon wafer of invention example 4 was obtained with the epitaxial layer formation temperature in step 2 set to 900 ℃. Other conditions were exactly the same as in invention example 2.

(inventive example 5)

An epitaxial silicon wafer was produced in the same manner as in inventive example 2. However, the epitaxial silicon wafer of invention example 5 was obtained with the temperature of formation of the silicon epitaxial layer in step 2 set to 1000 ℃. Other conditions were exactly the same as in 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 2 nd step was set to 850 ℃. As a result, a silicon epitaxial layer cannot be grown.

Comparative example 5

An epitaxial silicon wafer was produced in the same manner as in inventive example 2. However, the epitaxial silicon wafer of comparative example 5 was obtained with the epitaxial layer formation temperature in step 2 set to 1180 ℃. Other conditions were exactly the same as in invention example 2.

< evaluation of epitaxial Defect >

The epitaxial silicon wafers of invention examples 1 to 5, and comparative examples 1 to 3, and 5 were evaluated for the number of epitaxial defects formed in the silicon epitaxial layer. Specifically, the surface of the epitaxial wafer of each sample was observed and evaluated using a surface Defect inspection apparatus (Surfscan SP-2, manufactured by KLA-Tencor), and the occurrence of Light Point Defects (LPDs) having a size of 90nm or more was examined. At this time, the observation mode was changed to the Oblique mode (Oblique incidence mode), and the surface depression was estimated from the detected size ratio of the Wide Narrow channel. Next, the generation site of LPD was observed and evaluated using a Scanning Electron Microscope (SEM), and whether LPD was a Stacking Fault (SF) was evaluated. The number of detected epitaxial defects (number/wafer) is shown in table 1.

[ Table 1]

As is apparent from table 1, in inventive examples 1 to 5 and comparative example 1, the number of epitaxial defects formed per wafer was less than 5. On the other hand, many epitaxial defects were formed in comparative examples 2 and 3 in which the heat treatment temperature was 1000 ℃ or higher, and comparative example 5 in which the formation temperature of the silicon epitaxial layer exceeded 1000 ℃. The reason is considered to be that: the silicon of the formed carbon diffusion layer sublimates and carbon is precipitated.

< evaluation of gettering ability >

The epitaxial silicon wafers of the invention examples 1 to 5, comparative examples 1 to 3 and comparative example 5 were evaluated for gettering capability. Specifically, Ni-contaminated liquid (1.0X 10) was used¹³/cm²) The surface of the epitaxial layer of each epitaxial wafer was intentionally contaminated by spin coating contamination, and then diffusion heat treatment was performed at 1000 ℃ for 3 minutes in a nitrogen atmosphere. Then, the surface of the epitaxial layer was subjected to 3 minutes of photolithography, and pits observed on the surface of the epitaxial layer were observed with an optical microscope, and the gettering capability was evaluated by the presence or absence of pits. The evaluation results are shown in table 1.

As is apparent from table 1, although no dishing was observed in inventive examples 1 to 5, comparative example 2, comparative example 3, and comparative example 5, dishing was observed in comparative example 1 in which the heat treatment temperature was as low as 750 ℃. The reason is considered to be that: in comparative example 1, since the heat treatment temperature was low, carbon could not be sufficiently diffused into the wafer.

< evaluation of carbon concentration and Hydrogen concentration >

In inventive examples 1 to 5, comparative examples 1 to 3, and comparative example 5, the obtained epitaxial silicon wafers were subjected to SIMS (Secondary Ion Mass Spectrometry) measurement, and the carbon concentration and the hydrogen concentration were measured. The obtained carbon concentration and hydrogen concentration are shown in table 1. Fig. 6 shows the concentration distribution of carbon and hydrogen in the epitaxial silicon wafer of invention example 2.

As shown in Table 1, the carbon concentrations of inventive examples 1 to 5 and comparative examples 2, 3 and 5, in which the heat treatment temperatures were high, were 5X 10¹⁸Atom/cm³As described above, the gettering capability is high. In contrast, in comparative example 1, the heat treatment temperature was lowTherefore, carbon cannot be sufficiently diffused into the wafer, and the gettering capability is insufficient.

Further, of invention examples 1 to 5 having high gettering ability with respect to the hydrogen concentration, invention example 1 having a relatively low heat treatment temperature was 10¹⁸Atom/cm³However, the amounts of the components in the invention examples 2 to 5 were 10¹⁹Atom/cm³To the extent that the carbon diffusion layer contains a high concentration of hydrogen. In comparative examples 2 and 3 in which the temperature for forming the silicon epitaxial layer was within the range specified in the present invention, the hydrogen concentration was 10¹⁹Atom/cm³Degree of the disease.

Industrial applicability

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

Description of the reference numerals

1-epitaxial silicon wafer, 11-silicon wafer, 11 a-front side, 11 b-back side, 11 c-edge region, 12-carbon diffusion layer, 13-silicon epitaxial layer, 14-protective layer, 20-pedestal, 21-recess, 21 a-sidewall, 21 b-bottom surface.