CN112514036B - Method for manufacturing epitaxial silicon wafer and epitaxial silicon wafer - Google Patents

Method for manufacturing epitaxial silicon wafer and epitaxial silicon wafer Download PDF

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CN112514036B
CN112514036B CN201980037347.4A CN201980037347A CN112514036B CN 112514036 B CN112514036 B CN 112514036B CN 201980037347 A CN201980037347 A CN 201980037347A CN 112514036 B CN112514036 B CN 112514036B
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silicon wafer
epitaxial
carbon
diffusion layer
carbon diffusion
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CN112514036A (en
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古贺祥泰
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Sumco Corp
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Sumco Corp
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Abstract

The invention provides a method for manufacturing an epitaxial silicon wafer with high gettering capability while suppressing the 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 performing a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere on a silicon wafer having a front surface, a back surface and an edge region, and forming a carbon diffusion layer on at least a front surface side surface layer portion of the silicon wafer; and a step (2) in which a silicon epitaxial layer is formed on the carbon diffusion layer formed on the front surface side surface layer of the silicon wafer at a temperature of 900 ℃ to 1000 ℃.

Description

Method for manufacturing epitaxial silicon wafer and epitaxial silicon wafer
Technical Field
The present invention relates to a method for manufacturing an epitaxial silicon wafer and an epitaxial silicon wafer.
Background
Conventionally, a silicon wafer has been widely used as a substrate for a semiconductor device, but if heavy metals are mixed in the silicon wafer, significant adverse effects (for example, poor pause time, poor holding, poor junction leakage, dielectric breakdown of an oxide film, etc.) are caused on device characteristics. Therefore, by forming a gettering layer for capturing 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 immediately below the device formation region so that heavy metals such as titanium and molybdenum having a slow diffusion rate can be trapped.
In recent years, there has been a demand for an epitaxial silicon wafer having a silicon epitaxial layer formed on a silicon wafer, as a substrate, without having crystal defects in a device formation region. The epitaxial silicon wafer is formed, for example, by: after forming a gettering layer 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 a silicon wafer to form a gettering layer containing high concentration of carbon at the surface portion of the wafer, and a silicon epitaxial layer is formed on the formed gettering layer.
In order to form a gettering layer directly under a silicon epitaxial layer by an ion implantation method, ions need to be implanted to a shallower position from the surface of a silicon wafer. However, if ions are implanted to a position shallower 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 method is 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 as follows: a layer containing a thermally decomposed carbon gas is formed by supplying a carbon-containing gas to a silicon wafer at a temperature of 1000 ℃ to 1200 ℃ inclusive, and an epitaxial layer is formed thereon, whereby an epitaxial wafer having a gettering layer directly below the epitaxial layer is produced.
Patent document 3 describes a method for manufacturing an epitaxial wafer as follows: 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 subjected to a heat treatment at a temperature of 500 to 750 ℃ to thermally diffuse carbon in the carbon-containing film into the surface layer portion of the silicon wafer, and thereafter an epitaxial layer is formed on the formed carbon diffusion layer.
Prior art literature
Patent literature
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 publication No. 2010-34330
Disclosure of Invention
Technical problem to be solved by the invention
However, it is known that many epitaxial defects are formed also in the epitaxial wafer manufactured by the method described in patent document 2. Further, it is also known that the epitaxial wafer manufactured by the method described in patent document 3 has insufficient gettering capability.
Accordingly, an object of the present invention is to provide a method for manufacturing an epitaxial silicon wafer and an epitaxial silicon wafer capable of suppressing the formation of epitaxial defects and having high gettering capability.
Solution for solving the technical problems
The present invention to solve 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 performing a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere on a silicon wafer having a front surface, a back surface and an edge region, and forming a carbon diffusion layer on at least a surface layer portion on the front surface side of the silicon wafer; and
and a step 2 of forming a silicon epitaxial layer on the carbon diffusion layer formed on the surface layer portion on the front side of the silicon wafer at a temperature of 900 ℃ to 1000 ℃.
[2] The method for producing an epitaxial silicon wafer according to the above [1], wherein,
in the step 1, the carbon diffusion layer is formed only on the surface layer portion on the front surface side of the silicon wafer.
[3] The method for producing an epitaxial silicon wafer according to [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 4, removing the protective film before or after the 2 nd step.
[4] The method for producing an epitaxial silicon wafer according to the above [2], wherein,
in the step 1, the carbon diffusion layer is formed on a surface layer portion of the silicon wafer on both the front surface side and the back surface side,
the method for manufacturing an epitaxial silicon wafer further includes 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 producing an epitaxial silicon wafer according to the above [2], wherein,
in the step 1, the carbon diffusion layer is formed on at least the front surface side surface layer portion of each of the two silicon wafers having the back surfaces overlapped with each other,
the method for manufacturing an epitaxial silicon wafer further includes a 6 th step, after the 1 st step, of peeling the two silicon wafers.
[6] The method for producing 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 on 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 1 st step is performed in an epitaxial growth furnace in which the 2 nd step is performed.
[8] The method for producing an epitaxial silicon wafer according to any one of the above [1] to [6], wherein,
the 1 st step is performed by introducing the silicon wafer into a heat treatment apparatus capable of introducing the carbon-containing gas, and the 2 nd step is performed by introducing the heat-treated silicon wafer 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 1×10 17 /cm 3 Above and 1×10 20 /cm 3 The heat treatment is performed in the following manner,
in the step 2, the peak concentration of hydrogen in the carbon diffusion layer is 1×10 18 Atoms/cm 3 Above and 1×10 20 Atoms/cm 3 The epitaxial growth process was performed in the following manner.
[10] An epitaxial silicon wafer comprising:
a carbon diffusion layer formed on a surface layer portion of a silicon wafer having a front surface, a back surface, and an edge region, at least on the front surface side; and
a silicon epitaxial layer formed on the carbon diffusion layer of the surface layer portion on the front side,
the carbon diffusion layer has a carbon peak concentration of 1×10 17 /cm 3 Above and 1×10 20 /cm 3 In the following the procedure is described,
the peak hydrogen concentration of the carbon diffusion layer is 1×10 18 Atoms/cm 3 Above and 1×10 20 Atoms/cm 3 The following is given.
[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 in the surface layer portion on the front side.
[13] The epitaxial silicon wafer according to any one of the above [10] to [12], wherein,
the carbon diffusion layer is not formed in 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 the formation of epitaxial defects can be manufactured.
Drawings
Fig. 1 is a flowchart showing a process of a method for producing an epitaxial silicon wafer according to the present invention.
Fig. 2 is a diagram showing an epitaxial silicon wafer having carbon diffusion layers on both the front and back surfaces.
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. 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 diagram showing two silicon wafers having back surfaces overlapping each other.
Fig. 6 is a graph showing the concentration distribution 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 1 st step of performing a heat treatment at a temperature of 800 ℃ to 980 ℃ in a carbon-containing gas atmosphere on a silicon wafer 11 having a front surface 11a, a rear surface 11b, and an edge region 11c (fig. 1 (a) in fig. 1), thereby forming a carbon diffusion layer 12 on at least a surface layer portion on the front surface 11a side of the silicon wafer 11 (fig. 1 (b) in fig. 1); and a step 2 of forming a silicon epitaxial layer 13 on the carbon diffusion layer 12 formed on 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 document 2 and patent document 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 have studied the cause of the above-mentioned problems in detail. As a result, it was determined that the reason why the gettering ability 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 ℃, the carbon in the carbon-containing film is not sufficiently diffused 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 on the surface layer portion of the silicon wafer by heat treatment, the heat treatment temperature is as high as 1000 to 1200 ℃, so that silicon constituting the carbon diffusion layer sublimates, and residual carbon is bonded to each other to be deposited, and the crystal structure of the surface layer portion of the wafer is disordered.
From the above-described study, it is desired that an epitaxial wafer having high gettering capability while suppressing the formation of epitaxial defects can be produced 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 many epitaxial defects are still formed when the inventors of the present invention perform heat treatment in the above temperature range to manufacture an epitaxial silicon wafer. Therefore, the inventors of the present invention have investigated the cause thereof. The reason for this is known to be: the general formation temperature of the silicon epitaxial layer formed on the carbon diffusion layer is 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 study, the inventors of the present invention have concluded that: in order to manufacture an epitaxial silicon wafer having high gettering capability while suppressing the formation of epitaxial defects, it is necessary to perform heat treatment of the silicon wafer under a carbon-containing gas atmosphere at a temperature at which carbon sufficiently diffuses into the interior of the silicon wafer and does not cause carbon precipitation due to sublimation of silicon of the formed carbon diffusion layer, and also the silicon epitaxial layer is required to be formed at a lower temperature at which carbon precipitation due to sublimation of silicon of the formed carbon diffusion layer does not occur.
Further, the present inventors 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 ℃ or more and 980 or less and performing formation of a silicon epitaxial layer at a temperature of 900 ℃ or more and 1000 ℃ or less, and have completed the present invention. Hereinafter, each step will be described.
< procedure 1 >
First, a silicon wafer 11 having a front surface 11a, a rear surface 11b, and an edge region 11c (fig. 1 (a) in fig. 1) 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 on at least a surface layer portion on the front surface 11a side of the silicon wafer 11 (fig. 1 (b) in fig. 1).
As the silicon wafer 11, a silicon wafer obtained by performing wafer processing on a single crystal silicon ingot grown by a czochralski method (CZ method) or a floating zone melting method (FZ method) can be used. Carbon and/or nitrogen may be added to the silicon wafer 11 in order to obtain higher gettering capability. Further, any appropriate impurity may be added to make n-type or p-type. The diameter of the silicon wafer 11 can be set to 200mm, 300mm, or 450mm, for example. The resistivity may be appropriately set according to the design.
In the present invention, the "carbon-containing gas atmosphere" refers to an atmosphere composed of a gas containing carbon. Examples of the carbon-containing gas include methane gas, ethane gas, propane gas, and the like. Among them, from the viewpoint of improving the reaction efficiency of carbon with the silicon wafer 11, propane gas or ethane gas is preferably used.
Further, the oxygen concentration of the silicon wafer 11 is preferably 1×10 17 Atoms/cm 3 Above and 1×10 18 Atoms/cm 3 The following is given. This can suppress the occurrence of slip (slip) and suppress 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 ℃ or higher and 980 ℃ or lower. When the heat treatment temperature is less than 800 ℃, the carbon-containing gas, 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 interior.
On the other hand, in the case where the heat treatment temperature exceeds 980 ℃, the silicon in the formed carbon diffusion layer 12 sublimates due to the high thermal energy. As a result, the carbon remaining in the carbon diffusion layer 12 is bonded to each other and precipitated, and the crystal structure of silicon is disordered, so that 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. More preferably, the heat treatment temperature is 800 ℃ to 950 ℃.
By performing the heat treatment at the temperature within the above range, carbon can be diffused into the wafer without disturbing the crystal structure of the surface layer portion of the silicon wafer 11, and the carbon diffusion layer 12 can be formed. The concentration of carbon contained in the carbon diffusion layer 12 was 1×10 17 /cm 3 Above and 1×10 20 /cm 3 The carbon diffusion layer 12 can be made to contain carbon at a sufficient concentration for heavy metal gettering. The carbon concentration is the maximum concentration inside the silicon wafer 11, and the carbon concentration is the maximum (peak value) at the interface between the silicon wafer 11 and the silicon epitaxial layer 13.
The heat treatment time is preferably 1 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 of carbon 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 when the heat treatment is performed for more than 40 minutes, 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 formed carbon diffusion layer 12 is approximately 200nm.
As shown in fig. 2, the carbon diffusion layer 12 may be formed not only on the front surface 11a side but also on the back surface 11b side of the silicon wafer 11. Thus, the carbon diffusion layer 12 formed on the surface layer portion on the rear surface 11b side can be used as a gettering layer, and the gettering capability can be further improved.
The carbon diffusion layer 12 may be formed only in the surface layer portion on the front surface 11a side of the silicon wafer 11. This can suppress pollution caused by carbon. The carbon diffusion layer 12 may be formed in the edge region 11c.
Regarding the formation of the surface layer portion of the carbon diffusion layer 12 on only the front surface 11a side of the silicon wafer 11, for example, it can be performed using a susceptor as shown in fig. 3, instead of using a susceptor of the type that supports the edge region 11c of the silicon wafer 11 by line 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 the heat treatment in a state where the back surface 11b is in contact with the bottom surface 21b, the carbon diffusion layer 12 can be formed only in the surface layer portion on the front surface 11a side.
As shown in fig. 4, the protective film 14 is formed on the back surface 11b of the silicon wafer 11 (step 3), and the heat treatment is performed in a state where the protective film 14 is formed, whereby 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. The formed protective film 14 can be removed by polishing, for example, before or after step 2 (step 4) described later. The protective film 14 may be any film that can prevent diffusion of carbon, and an oxide film, a nitride film, or the like may be used.
Further, after the carbon diffusion layer 12 is temporarily formed on the surface layer portion 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 of the back surface 11b side may be removed, whereby the carbon diffusion layer 12 may be formed only on the surface layer portion of the front surface 11a side. The carbon diffusion layer 12 formed on the surface layer portion on the back surface 11b side can be removed by polishing, for example, before or after step 2 (step 5) described later.
In order to form the carbon diffusion layer 12 only on the front surface 11a side surface layer portion 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 step 1, the carbon diffusion layer 12 may be formed on the front surface 11a side surface layer portion of each of the two silicon wafers 11. In this case, after the 1 st step, the two silicon wafers are separated 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 on 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 in the above-described manner, the carbon diffusion layer 12 is also formed on the surface layer portion of the edge region 11c where 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 subjected to heat treatment performed in a subsequent device process, and thus diffuses outward from the wafer, and there is a possibility that the carbon is absorbed in the silicon epitaxial layer (device formation region) 13. Therefore, the carbon diffusion layer 12 formed on the surface layer portion of the edge region 11c is preferably removed before the step 2 (step 7). The carbon diffusion layer 12 formed on the surface layer portion of the edge region 11c can be removed by polishing.
The above-mentioned step 1 can be performed in an epitaxial growth furnace in which the following step 2 is performed. Specifically, first, the silicon wafer 11 is introduced into an epitaxial growth furnace, hydrogen gas is introduced into the furnace, and hydrogen baking is performed by heating to 1100 to 1150 ℃ to remove a natural oxide film on the surface of the silicon wafer 11. Then, the temperature in the furnace is lowered to a temperature of 800 to 980 ℃, and a carbon-containing gas such as hydrogen gas (carrier gas) or methane gas is introduced into the furnace and kept for 1 minute, for example. Thereby, carbon is diffused from the surface of the silicon wafer 11 into the wafer interior, and the carbon diffusion layer 12 can be formed at least on the front surface 11 a. Next, the silicon epitaxial layer 13 of step 2 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, and then the carbon-containing gas is introduced into the furnace to form a carbon-containing gas atmosphere in the furnace, 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 for processing one wafer like an RTA apparatus may be used, but a batch type heat treatment apparatus capable of simultaneously heat-treating a plurality of wafers is preferably used. In this case, the step 2 can be performed by introducing the heat-treated silicon wafer 11 into the epitaxial growth furnace.
< procedure 2 >
Next, in step 1, a silicon epitaxial layer 13 is formed on the carbon diffusion layer 12 formed on the surface layer portion on the front surface 11a side at a temperature of 900 ℃ or higher and 1000 ℃ or lower (fig. 1 (c) in fig. 1). This can be performed by a vapor phase growth method such as CVD.
Specifically, the silicon wafer 11 having the carbon diffusion layer 12 formed in step 1 is introduced into an epitaxial growth furnace, hydrogen gas is introduced into the furnace, and the temperature is raised to about 1100 to 1150 ℃ to perform hydrogen baking, thereby removing a natural oxide film on the surface of the silicon wafer 11. Then, for example, hydrogen is used as a carrier gas, monosilane gas (SiH 4 ) Dichlorosilane gas (SiH) 2 Cl 2 ) And a silane-based gas which can decompose at 900 ℃ to 1000 ℃ as a source gas. Thereby, the silicon epitaxial layer 13 can be formed on the carbon diffusion layer 12. Further, from the viewpoint of increasing the hydrogen concentration in the carbon diffusion layer 12, monosilane gas (SiH) having a large number of hydrogen bonds is preferably used 4 )。
The thickness of the silicon epitaxial layer 13 can be set appropriately according to the design, but can be set in a range of 1 μm to 15 μm, for example. 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 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 step 1 sublimates and carbon is bonded to each other and deposited. 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 way, the epitaxial silicon wafer 1 according to the present invention can be manufactured. Hydrogen contained in the source gas or hydrogen gas as a 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 in the heat treatment in the device forming step. In the present invention, the silicon epitaxial layer 13 is formed at a relatively low temperature of 900 ℃ or more and 1000 ℃ or less. Therefore, 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 be made to trap hydrogen at a high concentration, and the passivation effect of defects can be improved.
Here, the peak concentration of hydrogen trapped by the carbon diffusion layer 12 is 1×10 18 Atoms/cm 3 Above and 1×10 20 Atoms/cm 3 The following is given. The hydrogen concentration is the maximum concentration inside the silicon wafer 11, and the hydrogen concentration is the maximum (peak value) 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 comprises: a carbon diffusion layer 12 formed on a surface layer portion of the silicon wafer 11 having a front surface 11a, a rear surface 11b, and an edge region 11c, at least on the front surface 11a side; 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 diffusion layer 12 has a carbon peak concentration of 1×10 17 /cm 3 Above and 1×10 20 /cm 3 Hereinafter, the peak hydrogen concentration of the carbon diffusion layer 12 is 1×10 18 Atoms/cm 3 Above and 1×10 20 Atoms/cm 3 The following is given.
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 the carbon-containing gas atmosphere is performed at a relatively low temperature of 800 ℃ or more and 980 ℃ or less. Thus, the carbon peak concentration of the carbon diffusion layer 12 becomes 1×10 17 /cm 3 Above and 1×10 20 /cm 3 Hereinafter, the carbon diffusion layer 12 has high gettering ability.
In addition to the above-described 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 epitaxial defects having a size of 90nm or more are four or less. As described above, the epitaxial silicon wafer 1 according to the present invention has not only few epitaxial defects but also high gettering capability.
The thickness of the carbon diffusion layer 12 is 20nm or more and 200nm or less. The carbon diffusion layer 12 contains 1×10 18 Atoms/cm 3 Above and 1×10 20 Atoms/cm 3 The following high peak concentration of hydrogen has the effect of diffusing into the silicon epitaxial layer 13 and passivating defects when heat treatment in the device forming process is performed.
The carbon diffusion layer 12 may be provided only in the surface layer portion on the front surface 11a side of the silicon wafer 11, or the carbon diffusion layer 12 may be provided in the surface layer portions on both the front surface 11a side and the back surface 11b side. Further, the carbon diffusion layer 12 is preferably not formed in the surface layer portion of the edge region 11c.
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 for an epitaxial silicon wafer, an n-type silicon wafer (resistivity: 50Ω·cm, dopant: phosphorus, phosphorus concentration: 8.6X10) having a diameter of 200mm obtained by subjecting a single crystal silicon ingot grown by the CZ method to wafer processing was prepared 13 Atoms/cm 3 Oxygen concentration: 9×10 17 Atoms/cm 3 ). The silicon wafer is introduced into a heat treatment furnace and placed on a susceptor shown in fig. 3. Then, after introducing ethane gas into the furnace to set the atmosphere of ethane gas, the temperature in the furnace was raised to 800 ℃, and the silicon wafer was subjected to heat treatment for 1 minute, whereby a carbon diffusion layer was formed on the surface layer portion on the front side of the silicon wafer. After the silicon wafer with the carbon diffusion layer formed thereon is taken out from the heat treatment furnace, the silicon wafer with the carbon diffusion layer formed thereon is introduced into the epitaxial growth furnace, and hydrogen gas is introduced into the furnace. Then, the temperature in the furnace was lowered to 980℃and then monosilane gas (SiH) was obtained by using hydrogen as a carrier gas 4 ) Phosphine (PH) 4 ) Is 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 inventive example 1. However, the heat treatment temperature in the step 1 was set to 950 ℃, and an epitaxial silicon wafer according to the invention example 2 was obtained. Other conditions were exactly the same as in inventive example 1.
Inventive example 3
An epitaxial silicon wafer was produced in the same manner as in inventive example 1. However, the epitaxial silicon wafer of invention example 3 was obtained by setting the heat treatment temperature in step 1 to 980 ℃. Other conditions were exactly the same as in inventive example 1.
Comparative example 1
An epitaxial silicon wafer was produced in the same manner as in inventive example 1. However, the heat treatment temperature in step 1 was set to 750 ℃, and an epitaxial silicon wafer of comparative example 1 was obtained. Other conditions were exactly the same as in inventive example 1.
Comparative example 2
An epitaxial silicon wafer was produced in the same manner as in inventive example 1. However, the heat treatment temperature in step 1 was set at 1000 ℃, and an epitaxial silicon wafer of comparative example 2 was obtained. Other conditions were exactly the same as in inventive example 1.
Comparative example 3
An epitaxial silicon wafer was produced in the same manner as in inventive example 1. However, the heat treatment temperature in step 1 was set to 1100 ℃, and an epitaxial silicon wafer of comparative example 3 was obtained.
Example 4 of the invention
An epitaxial silicon wafer was produced in the same manner as in inventive example 2. However, the epitaxial layer formation temperature in step 2 was set to 900 ℃. Other conditions were exactly the same as in inventive example 2.
Example 5 of the invention
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 by setting the formation temperature of the silicon epitaxial layer in step 2 to 1000 ℃. Other conditions were exactly the same as in inventive example 2.
Comparative example 4
An epitaxial silicon wafer was produced in the same manner as in inventive example 2. However, the formation temperature of the epitaxial layer in step 2 was set at 850 ℃. As a result, the 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 layer formation temperature in step 2 was set to 1180 ℃, and an epitaxial silicon wafer of comparative example 5 was obtained. Other conditions were exactly the same as in inventive example 2.
< evaluation of epitaxial Defect >
The number of epitaxial defects formed in the silicon epitaxial layer was evaluated for each of the epitaxial silicon wafers of the above invention examples 1 to 5 and comparative examples 1 to 3 and 5. Specifically, the surface of the epitaxial wafer of each sample was observed and evaluated by using a surface defect inspection apparatus (manufactured by KLA-Tencor Co., ltd.: surfscan SP-2), and the occurrence of bright point defects (Light Point Defect, LPD) of 90nm or more was examined. At this time, the observation mode was set to an Oblique mode (Oblique incidence mode), and surface dishing was estimated from the detection size ratio of the Wide Narrow channel. Next, the site of LPD production was observed and evaluated using a scanning electron microscope (Scanning Electron Microscope, SEM), and whether the LPD was Stacking Fault (SF) was evaluated. The number of epitaxial defects detected (per wafer) is shown in table 1.
TABLE 1
As is apparent from table 1, the number of epitaxial defects formed in each wafer was smaller than 5 in each of 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 ℃ or higher and in comparative example 5 in which the silicon epitaxial layer formation temperature exceeded 1000 ℃, many epitaxial defects were formed. The reason for this is considered to be: the silicon of the formed carbon diffusion layer sublimates and carbon is precipitated.
< evaluation of gettering ability >
The gettering capability was evaluated for each of the epitaxial silicon wafers of the above-described invention examples 1 to 5, comparative examples 1 to 3, and comparative example 5. Specifically, ni-contaminated liquid (1.0X10) 13 /cm 2 ) And the surface of the epitaxial layer of each epitaxial wafer was intentionally contaminated by spin-coating contamination, followed by 3 minutes at 1000℃in a nitrogen atmosphereDiffusion heat treatment of the clock. Then, photolithography was performed for 3 minutes, and the recesses observable on the surface of the epitaxial layer were observed using an optical microscope, and the gettering ability was evaluated by the presence or absence of the recesses. The evaluation results are shown in table 1.
As is apparent from Table 1, although no dishing was observed in the invention examples 1 to 5, the comparative example 2, the comparative example 3 and the comparative example 5, dishing was observed in the comparative example 1 having a heat treatment temperature as low as 750 ℃. The reason for this is considered to be: in comparative example 1, since the heat treatment temperature was low, carbon was not sufficiently diffused into the wafer.
< evaluation of carbon concentration and Hydrogen concentration >
The obtained epitaxial silicon wafers were subjected to SIMS (Secondary Ion Mass Spectrometry: secondary ion mass spectrometry) measurement to measure the carbon concentration and the hydrogen concentration in examples 1 to 5, comparative examples 1 to 3, and comparative example 5. 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, comparative examples 2, 3 and 5, which were inventive examples 1 to 5 and had high heat treatment temperatures, had carbon concentrations of 5X 10 18 Atoms/cm 3 The above has high gettering ability. In contrast, in comparative example 1, since the heat treatment temperature was low, carbon was not sufficiently diffused into the wafer, and the gettering ability was insufficient.
In addition, in invention examples 1 to 5 having high gettering ability, the heat treatment temperature was relatively low, and the hydrogen concentration was 10 in invention example 1 18 Atoms/cm 3 To the extent, however, examples 2 to 5 are 10 19 Atoms/cm 3 To the extent that the carbon diffusion layer contains a high concentration of hydrogen. In comparative examples 2 and 3, in which the formation temperature of the silicon epitaxial layer was within the range defined in the present invention, the hydrogen concentration was 10 19 Atoms/cm 3 Degree of the degree.
Industrial applicability
According to the present invention, an epitaxial silicon wafer having high gettering capability while suppressing the 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 side.

Claims (13)

1. A method for manufacturing an epitaxial silicon wafer is characterized by comprising the following steps:
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 having a front surface, a back surface and an edge region, and forming a carbon diffusion layer on at least a surface layer portion on the front surface side of the silicon wafer; and
and a step 2 of forming a silicon epitaxial layer on the carbon diffusion layer formed on the surface layer portion on the front side of the silicon wafer at a temperature of 900 ℃ to 1000 ℃.
2. The method for producing 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 on 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 4, removing the protective film before or after the 2 nd step.
4. The method for producing an epitaxial silicon wafer according to claim 2, wherein,
in the step 1, the carbon diffusion layer is formed on a surface layer portion of the silicon wafer on both the front surface side and the back surface side,
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 producing an epitaxial silicon wafer according to claim 2, wherein,
in the step 1, the carbon diffusion layer is formed on at least the front surface side surface layer portion of each of the two silicon wafers having the back surfaces overlapped with each other,
the method for manufacturing an epitaxial silicon wafer further comprises: and 6, after the 1 st step, peeling the two silicon wafers.
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 on the 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 claims 1 to 5, wherein,
the 1 st step is performed in an epitaxial growth furnace in which the 2 nd step is performed.
8. The method for producing an epitaxial silicon wafer according to any one of claims 1 to 5, wherein,
the 1 st step is performed by introducing the silicon wafer into a heat treatment apparatus capable of introducing the carbon-containing gas, and the 2 nd step is performed by introducing the heat-treated silicon wafer into an epitaxial growth furnace.
9. The method for producing an epitaxial silicon wafer according to any one of claims 1 to 5, wherein,
in the step 1, the peak concentration of carbon in the carbon diffusion layer is 1×10 17 /cm 3 Above and 1×10 20 /cm 3 The heat treatment is performed in the following manner,
in the step 2, the peak concentration of hydrogen in the carbon diffusion layer is 1×10 18 Atoms/cm 3 Above and 1×10 20 Atoms/cm 3 The epitaxial growth process was performed in the following manner.
10. An epitaxial silicon wafer comprising:
a carbon diffusion layer formed on a surface layer portion of a silicon wafer having a front surface, a back surface, and an edge region, at least on the front surface side; and
a silicon epitaxial layer formed on the carbon diffusion layer of the surface layer portion on the front side,
the carbon diffusion layer has a carbon peak concentration of 1×10 17 /cm 3 Above and 1×10 20 /cm 3 In the following the procedure is described,
the peak hydrogen concentration of the carbon diffusion layer is 1×10 18 Atoms/cm 3 Above and 1×10 20 Atoms/cm 3 In the following the procedure is described,
the number of epitaxial defects with a size of 90nm or more is 4 or less.
11. The epitaxial silicon wafer of claim 10, wherein,
the thickness of the carbon diffusion layer is 200nm or less.
12. Epitaxial silicon wafer according to claim 10 or 11, wherein,
the carbon diffusion layer is formed only in the surface layer portion on the front side.
13. Epitaxial silicon wafer according to claim 10 or 11, wherein,
the carbon diffusion layer is not formed in the surface layer portion of the edge region.
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