JP7416171B1 - Epitaxial wafer manufacturing method - Google Patents

Abstract

【assignment】
It is an object of the present invention to provide an epitaxial wafer and a method for manufacturing the epitaxial wafer that can be manufactured with a small number of steps and that achieves a sufficient amount of oxygen capture by using a new gettering mechanism.
[Solution]
An epitaxial wafer 1 having a silicon substrate 10 and a silicon epitaxial film 12 formed on the silicon substrate 10, the distance being 600 nm or less from the interface between the silicon substrate 10 and the silicon epitaxial film 12 to the silicon epitaxial film 12 side. An epitaxial wafer 1 characterized in that a void defect region 11 is provided in a range of .
[Selection diagram] Figure 1

Description

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

Epitaxial wafers are widely used as substrates for electronic devices from the viewpoint of crystal perfection and impurity (oxygen, etc.) concentration. It is known that epitaxial wafers have extremely high purity immediately after film formation, but their quality deteriorates as they go through the device manufacturing process. The main causes include the external environment to which the wafer is exposed during the device manufacturing process and impurity diffusion from the silicon wafer, which is the bulk part of the epitaxial wafer. Due to heat treatment during the device manufacturing process, contaminated metals adhering to the surface and oxygen in the silicon wafer diffuse into the epitaxial film, which is the active layer of the device, forming defect levels in the epitaxial film, resulting in a decrease in manufacturing yield. or cause deterioration of electrical characteristics. Particularly in the field of solid-state imaging devices (CCD, CIS), defects caused by oxygen diffused into the device active layer have been regarded as a problem as one of the factors that deteriorate device characteristics. Therefore, the development of epitaxial wafer technology is progressing to reduce the oxygen concentration of the epitaxial film, which is the active layer at the bottom of the device, as much as possible.

A typical technique for reducing the oxygen concentration in a device active layer is to place an oxygen gettering site near the interface between an epitaxial film and a silicon substrate.

For example, Patent Document 1 describes a technology in which a silicon substrate used for epitaxial film formation is pretreated with an RTA device to form a surface-modified layer, and then epitaxial growth is performed on the surface-modified layer to capture oxygen diffused from the bulk portion. is disclosed. This is a technology that utilizes BMD that precipitates in a surface modification layer, but it is difficult to control the amount of BMD precipitation and the thickness of the modification layer, and it is difficult to control the amount of oxygen capture required by the device. I can't. There is also a limit to the temperature range that shows oxygen capture ability.

Therefore, in Patent Document 2, an ion implantation layer is formed by irradiating the silicon substrate surface with gettering atoms such as carbon at a high concentration, and silicon is epitaxially grown on the ion implantation layer to diffuse it from the bulk part. Techniques for capturing oxygen are disclosed. This is a technology that forms a surface modification layer by ion implantation for the purpose of selectively arranging gettering sites near the interface between the epitaxial film and the silicon substrate. This is an excellent method for reducing the concentration of oxygen that diffuses from the silicon epitaxial film into the silicon epitaxial film. Furthermore, the amount of oxygen captured can be adjusted by adjusting the irradiation conditions. However, there are problems such as an increase in the number of steps and cross contamination due to the use of an ion implantation device.

Here, as a technology for manufacturing an epitaxial wafer containing gettering atoms at low cost and with low contamination, there is an epitaxial wafer containing a high concentration of carbon formed by chemical vapor deposition using a CVD furnace. Patent Document 3 discloses that an epitaxial film containing a high concentration of carbon, which is a gettering atom, is formed on a silicon substrate by chemical vapor deposition, and a silicon epitaxial film is formed on the epitaxial film containing carbon. A technique for producing an epitaxial wafer using the same method is described. By using this technology, a structure in which an epitaxial film containing carbon, which is an oxygen gettering atom, is arranged near the interface between the epitaxial film and a silicon substrate can be used at low cost and with low contamination. However, the gettering characteristics exhibited by the high-concentration carbon-containing layer described in Patent Document 3 are a general mechanism that utilizes the solid solubility difference and micro defects between the substrate and the silicon epitaxial film. With a thickness of about 2 μm as shown in FIG. 4, it is difficult to achieve a high impurity trapping ability exceeding 2.0×10 ¹⁴ atoms/cm ² .

Japanese Patent Application Publication No. 2013-143504 Japanese Patent Application Publication No. 2017-175144 Japanese Patent Application Publication No. 2013-51348

As shown above, a substrate with a structure in which an ion-implanted layer of carbon, which is a gettering atom, and an epitaxial film containing high concentration of carbon formed by chemical vapor deposition are sandwiched between the substrate and a silicon epitaxial film is used. By doing so, it becomes possible to reduce the oxygen concentration in the device active layer.

However, the thickness of the carbon ion-implanted layer that can be formed by the ion implantation described in Patent Document 2 is as thin as about 0.3 μm, and furthermore, the trapping layer is formed by multiple operations (ion implantation, recovery heat treatment, etc.) at the stage before epitaxial film formation. , which increases the number of manufacturing steps. Such epitaxial wafers cannot easily capture a sufficient amount of impurities.

In addition, the epitaxial film containing a high concentration of carbon in an epitaxial wafer using a CVD furnace described in Patent Document 3 is a technology developed with the gettering effect of heavy metal impurities in mind as the main application, and the prior art document There is no mention of the oxygen capturing ability of the epitaxial film containing carbon. Furthermore, considering the available gettering mechanisms, a sufficient amount of oxygen capture cannot be expected.

From this point of view, in the field of devices that are sensitive to the oxygen concentration in the active layer of devices, such as solid-state imaging devices, epitaxial wafers that have a new gettering mechanism and sufficient oxygen capture ability that contributes to improved characteristics. development was required.

The present invention has been made in view of the above problems, and provides an epitaxial wafer that can be manufactured with a small number of steps and that achieves a sufficient amount of oxygen capture by using a new gettering mechanism, and a method for manufacturing the same. The purpose is to

The present invention has been made to achieve the above object, and is an epitaxial wafer having a silicon substrate and a silicon epitaxial film formed on the silicon substrate, the invention being an epitaxial wafer comprising a silicon substrate and a silicon epitaxial film formed on the silicon substrate. There is provided an epitaxial wafer characterized in that a void defect region is provided in a range of 600 nm or less from the interface to the silicon epitaxial film side.

According to such an epitaxial wafer, a sufficient amount of oxygen can be captured. In particular, with such an epitaxial wafer, void defects can be selectively placed as gettering sites near the interface between the silicon epitaxial film and the silicon substrate below the device active layer, greatly reducing the oxygen concentration. become something that can be done. Moreover, it can be manufactured with a small number of steps.

At this time, the silicon epitaxial film can have a carbon concentration and film thickness that satisfy the following formula (1).
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)

This makes it possible to achieve a sufficient amount of oxygen capture. In particular, by satisfying formula (1), a void defect region can be sufficiently formed near the interface between the silicon epitaxial film and the silicon substrate.

At this time, another silicon epitaxial film may be provided on the silicon epitaxial film, and the carbon concentration of the another silicon epitaxial film may be less than 2.0×10 ¹⁹ atoms/cm ³ .

Thereby, it is possible to provide an epitaxial wafer having an oxygen capturing ability useful for solid-state image sensing devices. In other words, by forming an epitaxial wafer structure based on a silicon substrate on which a silicon epitaxial film is formed, and further forming a silicon epitaxial film that does not contain carbon, an epitaxial wafer having an oxygen trapping ability useful for solid-state image sensing devices is provided. be able to.

At this time, the silicon epitaxial film can have insulation properties and high frequency characteristics.

This makes it possible to provide an epitaxial wafer having an oxygen capturing ability that is more useful for solid-state image sensing devices.

The present invention has been made to achieve the above object, and is a method for manufacturing an epitaxial wafer, which uses a raw material gas containing a carbon source gas to obtain a carbon concentration and a film thickness that satisfy the following formula (1). An epitaxial method comprising the steps of: forming a silicon epitaxial film on a silicon substrate, and then performing heat treatment at a heat treatment temperature of 900° C. or higher and a heat treatment time of 1 hour or longer. A wafer manufacturing method is provided.
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)

According to such an epitaxial wafer manufacturing method, a void defect region can be provided in a range of 600 nm or less from the interface between the silicon substrate and the silicon epitaxial film toward the silicon epitaxial film. In particular, a void defect region can be formed by heat treatment at a heat treatment temperature within this range. Further, it can be manufactured with a small number of steps.

At this time, the heat treatment can be performed under the conditions that the heat treatment temperature is 1100° C. or less and the heat treatment time is 36 hours or less.

By setting the heat treatment temperature to 1100° C. or lower, the influence of heavy metal diffusion can be suppressed. Further, by setting the heat treatment time to 36 hours or less, an epitaxial wafer that is excellent in terms of manufacturing efficiency can be obtained.

At this time, after the step of forming the silicon epitaxial film and before the step of heat treatment, a carbon concentration of 2.0×10 ¹⁹ atoms/ The process may include forming another silicon epitaxial film less than cm ³ .

Thereby, it is possible to provide an epitaxial wafer having an oxygen trapping ability useful for solid-state image sensing devices.

According to the epitaxial wafer of the present invention, a sufficient amount of oxygen capture can be achieved. In particular, it is possible to obtain an epitaxial wafer having a structure having a void defect region exhibiting excellent gettering characteristics near the interface between the silicon epitaxial film, which is the device active layer, and the silicon substrate. Moreover, it can be manufactured with a small number of steps.
According to the epitaxial wafer manufacturing method of the present invention, it is possible to provide a void defect region in a range of 600 nm or less from the interface between the silicon substrate and the silicon epitaxial film to the silicon epitaxial film side. Moreover, it can be manufactured with a small number of steps.

FIG. 1 is a schematic diagram showing an epitaxial wafer according to a first embodiment of the present invention. 1 is a flow diagram showing a method for manufacturing an epitaxial wafer according to a first embodiment of the present invention. It is a schematic diagram showing an epitaxial wafer of a 2nd embodiment of the present invention. FIG. 2 is a flow diagram showing a method for manufacturing an epitaxial wafer according to a second embodiment of the present invention. It is a cross-sectional TEM image of an epitaxial wafer of an experimental example (Example 1). They are a high-magnification TEM image (plane, cross-section) and a structural diagram of a Void defect in an experimental example (Example 1). This is a planar TEM image of a thin sample (about 500 nm thick) cut out from the epitaxial wafers of Examples 1 to 6 at a depth that includes the interface between the silicon epitaxial film and the substrate. 3 shows SIMS measurement results of epitaxial wafers of Examples 1 to 6. 1 is a graph showing conditions of carbon concentration and film thickness of a silicon epitaxial film in which a void defect region is formed near the interface between the silicon epitaxial film and a silicon substrate in an epitaxial wafer of the present invention. 2 is a graph showing the amount of oxygen captured in the epitaxial wafers of Examples 1 to 6. 3 is a graph comparing the amount of oxygen captured in the epitaxial wafer implanted with carbon ions of Comparative Example 1, the amount of oxygen captured in the epitaxial wafer of Comparative Example 2, and the amount of oxygen captured in the epitaxial wafer of Example 5.

Hereinafter, the present invention will be explained in detail, but the present invention is not limited thereto.

As described above, there has been a need for an epitaxial wafer and a method for manufacturing the same that can achieve a sufficient amount of oxygen capture.

As a result of extensive studies on the above-mentioned problems, the present inventors have discovered an epitaxial wafer having a silicon substrate and a silicon epitaxial film formed on the silicon substrate, the interface between the silicon substrate and the silicon epitaxial film. An epitaxial wafer characterized in that a Void defect region is provided in a range of 600 nm or less from the silicon epitaxial film side to the silicon epitaxial film side, whereby a sufficient amount of oxygen capture can be realized, and
A method for manufacturing an epitaxial wafer, using a raw material gas containing a carbon source gas, using the following formula (1),
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)
A step of forming a silicon epitaxial film on a silicon substrate so as to have a carbon concentration and film thickness that satisfy , and then a heat treatment temperature of 900°C or more and 1100°C or less and a heat treatment time of 1 hour or more and 36 hours or less. The present invention was completed based on the discovery that a sufficient amount of oxygen capture can be achieved by a method for producing an epitaxial wafer characterized by a step of heat treatment under certain conditions.

Hereinafter, the present invention will be explained in more detail with reference to the drawings, but the present invention is not limited thereto.

(Epitaxial wafer of the first embodiment)
FIG. 1 is a schematic diagram showing an epitaxial wafer according to a first embodiment of the present invention.
As shown in FIG. 1, the epitaxial wafer 1 according to the first embodiment of the present invention has a silicon epitaxial film 12 formed on a silicon substrate 10 and a silicon substrate 10 that extend within a range of 600 nm or less from the interface between the silicon epitaxial film 12 and the silicon substrate 10 to the epitaxial film 12 side. It has a structure having a void defect region 11.

With the epitaxial wafer 1 according to the first embodiment of the present invention, it becomes possible to largely capture oxygen diffused from the silicon substrate 10 to the silicon epitaxial film 12 in the void defect region 11, and compared to the conventional epitaxial wafer implanted with carbon ions. A superior amount of oxygen capture can be achieved compared to wafers.

In this way, by realizing the structure of the epitaxial wafer 1 having the void defect region 11 in a range of 600 nm or less from the interface between the silicon epitaxial film 12 and the silicon substrate 10 to the epitaxial film 12 side, oxygen capture that exceeds that of the conventional technology is realized. epitaxial wafers can be provided that have oxygen scavenging capabilities that are useful, for example, for solid-state imaging devices.

At this time, the lower limit of the range of the void defect region 11 is not particularly limited, but may be, for example, 100 nm or more. Such a material has a high void density and sufficient oxygen capturing ability.

The silicon substrate 10 is not particularly limited, and can be obtained by slicing a single crystal ingot manufactured by, for example, the Czochralski method or the floating zone method, and has a diameter of, for example, 200 mm, or even 300 mm or more. It can be done. The resistivity and oxygen concentration of the substrate are not limited and can be adjusted depending on the application.

The relationship between the carbon concentration contained in the silicon epitaxial film 12 and the film thickness is expressed by the following equation (1):
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)
In addition, the carbon concentration can be in a range of 2.0×10 ¹⁹ atoms/cm ³ or more and 5.0×10 ²¹ atoms/cm ³ or less.

If the relationship between the carbon concentration contained in the silicon epitaxial film 12 and the film thickness shown in the above formula (1) is not satisfied, the void defect region 11 will not be formed and the amount of oxygen captured will not be sufficient.
In the present invention, the film thickness and carbon concentration are values measured using SIMS.

If the silicon epitaxial film 12 has such a film thickness and carbon concentration, a void defect region 11 is formed in a range of 600 nm or less from the interface between the silicon epitaxial film 12 and the silicon substrate 10 to the silicon epitaxial film 12 side. In addition to realizing a sufficient amount of oxygen capture as a gettering site, the crystallinity of the silicon epitaxial film 12 becomes more excellent, resulting in a high-quality epitaxial wafer 1.

The epitaxial wafer 1 according to the first embodiment of the present invention is suitable for, for example, manufacturing a back-illuminated solid-state image sensor, but its use is not particularly limited.

In the present invention, the upper and lower limits of the thickness of the silicon epitaxial film 12 are not particularly limited, but may be set to, for example, 0.1 μm or more and 10 μm or less in consideration of productivity and cost. Such a material will have a sufficient oxygen capturing ability at a lower cost.
Further, in the present invention, the upper limit value of the carbon concentration of the silicon epitaxial film 12 is not limited, but it can be set to, for example, 5.0×10 ²¹ atoms/cm ³ or less. Such a structure has a void defect region 11 that achieves sufficient oxygen trapping ability.
Although the lower limit of the thickness of the Void defect region 11 formed by heat treatment is not particularly limited, it can be, for example, 100 nm or more. Such a material has a high void density and sufficient oxygen capturing ability.

(Method for manufacturing epitaxial wafer of first embodiment)
FIG. 2 is a flow diagram showing the method for manufacturing an epitaxial wafer according to the first embodiment of the present invention. That is, it is a flow diagram showing a process for forming an epitaxial wafer 1 according to the first embodiment, which has a void defect region 11 extending 600 nm or less from the interface between the silicon epitaxial film 12 and the silicon substrate 10 to the epitaxial film 12 side.

<Step 1: Formation of silicon epitaxial film under reduced pressure>
First, the silicon substrate 10 described above is prepared, and a silicon epitaxial film 12 is formed by epitaxial growth under reduced pressure using a reduced pressure CVD apparatus.

Note that the same low-pressure CVD apparatus as that conventionally used can be used. For example, as a silicon source gas in a mixed gas atmosphere for forming the silicon epitaxial film 12 with a controlled carbon concentration, for example, SiH ₂ Cl ₂ can be used, and as a source gas for doping carbon, For example, at least one of SiH ₃ (CH ₃ ) and SiH ₂ (CH ₃ ) ₂ can be used. However, it is not particularly limited as long as it is a raw material gas or doping gas containing carbon that can be doped with carbon while forming the silicon epitaxial film 12, but these source gases are commonly used and are suitable because they are easily available. Further, the holding temperature within the chamber can be set to, for example, 550°C to 800°C. However, the temperature is not particularly limited as long as it is a temperature at which a highly crystalline silicon epitaxial film 12 is formed.

The lower limit of the thickness of the silicon epitaxial film 12 formed by the aforementioned low pressure CVD apparatus is determined depending on the carbon concentration introduced under control. The relationship between the carbon concentration contained in the silicon epitaxial film 12 and the film thickness is expressed by the following formula (1):
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)
The epitaxial wafer 1 of the present invention can be manufactured by forming a film within a range that satisfies the following.

Regarding the silicon epitaxial film 12, the film thickness and carbon concentration can be adjusted to a greater extent by adjusting the length of processing time and the amount of source gas introduced, for example, within a range that satisfies equation (1).

<Step 2: Formation of Void defect region>
By heat treatment after film formation, a void defect region 11 can be formed near the interface between the silicon epitaxial film 12 and the silicon substrate 10.

The method of this heat treatment is not particularly limited, and for example, a general heat treatment furnace for silicon wafers can be used.
Although the heating time in the heat treatment is not particularly limited, the heat treatment temperature can be 900° C. or higher. By doing so, the formation of the void defect region 11 is promoted and manufacturing efficiency is improved.
The upper limit of the heat treatment temperature is not particularly limited, but may be, for example, 1100° C. or lower. By doing so, the influence of heavy metal diffusion can be suppressed.

Moreover, the heat treatment time can be 1 hour or more. By doing so, sufficient void defects are formed and the quality is improved.
The upper limit of the heat treatment time is also not particularly limited, and may be, for example, 36 hours or less.
By doing so, an epitaxial wafer that is excellent in terms of manufacturing efficiency can be obtained.

Based on the above, by placing the epitaxial wafer directly into a heat treatment furnace heated to around 1000°C and heat-treating it for about 1 to 36 hours, the interface between the silicon epitaxial film 12 formed in step 1 and the silicon substrate 10 can be removed. A Void defect region 11 is formed on the epitaxial film 12 side in a range of 600 nm or less.
At this time, the type of gas during the heat treatment can be selectively used depending on the purpose, and can be, for example, oxygen gas, or an inert gas such as argon or nitrogen.
From the above, the epitaxial wafer 1 of the first embodiment of the present invention can be obtained.

(Epitaxial wafer of second embodiment)
FIG. 3 is a schematic diagram showing an epitaxial wafer according to a second embodiment of the present invention.
The epitaxial wafer 2 of the second embodiment of the present invention is the epitaxial wafer of the first embodiment except that the silicon epitaxial film 12 is not doped, so that another silicon epitaxial film 13 that does not contain carbon is formed. It has the same configuration as 1.

Another silicon epitaxial film 13 that does not contain carbon refers to a silicon epitaxial film with a carbon concentration of less than 2.0×10 ¹⁹ atoms/cm ³ .
The lower the carbon concentration of another silicon epitaxial film 13 that does not contain carbon, the more preferable it is, but the carbon content can be at the level of unavoidable impurities, for example, 5.0 × 10 ¹⁵ atoms, which is the lower limit of detection in SIMS measurement. /cm ³ or less is more preferable.

In the present invention, the upper limit value of the carbon concentration of the silicon epitaxial film 12 is not limited either, but it can be set to, for example, 5.0×10 ²¹ atoms/cm ³ or less. If it is like this, it has a void defect region 11 that realizes sufficient oxygen trapping ability, and the other silicon epitaxial film 13 that does not contain carbon and is formed on the silicon epitaxial film 12 also has good crystallinity. Become.

(Method for manufacturing epitaxial wafer of second embodiment)
FIG. 4 is a flow diagram showing an example of the method for manufacturing an epitaxial wafer according to the second embodiment of the present invention.
The process is the same as in Embodiment 1, except that after step 1 is performed, step 1' is performed, and then heat treatment is performed.

<Step 1': Formation of carbon-free silicon epitaxial film>
Depending on the use of the wafer, another silicon epitaxial film 13 that does not contain carbon can be formed using the silicon epitaxial film 12 as a base. The method for forming this other silicon epitaxial film 13 is not particularly limited, and it can be formed by a conventional method. For example, without using the carbon source gas described above, it is possible to introduce a silicon source gas into the chamber and to form the film at a holding temperature of about 1000°C. By controlling the processing time and the dope gas for resistivity adjustment, a carbon-free silicon epitaxial film 13 having a desired film thickness and conductivity type resistivity can be formed on the silicon epitaxial film 12 formed in step 1. can.

<Step 2: Formation of Void defect region>
After forming the carbon-free silicon epitaxial film 13 on the silicon epitaxial film 12 formed in step 1', a Void defect region 11 is formed near the interface between the silicon epitaxial film 12 and the silicon substrate 10 by heat treatment after film formation. can be formed.
The conditions for this heat treatment are the same as in step 2 of the first embodiment.
From the above, the epitaxial wafer 2 of the second embodiment of the present invention can be obtained.

EXAMPLES Hereinafter, the present invention will be explained in more detail by showing Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.

(Example 1)
A silicon epitaxial film (carbon concentration: 2.0 mm) was formed on a silicon substrate with a diameter of 300 mm obtained by slicing an ingot manufactured by the Czochralski method using a low-pressure CVD apparatus using SiH ₃ (CH ₃ ) as a carbon source gas. 0×10 ¹⁹ atoms/cm ³ , film thickness: 5.5 μm).
Note that when the carbon concentration of the silicon epitaxial film is 2.0×10 ¹⁹ atoms/cm ³ , the thickness of the silicon epitaxial film determined from equation (1) is about 2.2 μm or more.
After film formation, a Void defect region was formed by performing heat treatment at 1000° C. in an oxygen atmosphere for 36 hours until a thermal equilibrium state was reached, and the epitaxial wafer of Example 1 was prepared.

In order to investigate the structure of this epitaxial wafer, TEM images were taken from a cross-sectional direction to include the surface of the silicon epitaxial film and the interface between the silicon epitaxial film and the silicon substrate, and a TEM image was taken from a plane view to include the interface between the silicon epitaxial film and the silicon substrate. TEM images were acquired from each direction.
Further, the thickness of the void defect region and the amount of oxygen captured were measured by SIMS.

As a result, it was confirmed that a void defect region was formed in a range of about 600 nm from the interface between the silicon substrate and the silicon epitaxial film toward the epitaxial film in the epitaxial wafer of the present invention. (See Figures 5, 6, 7, 8)

Further, the amount of oxygen captured was approximately 4.3×10 ¹⁴ atoms/cm ² . (See Figure 10)

(Example 2)
An epitaxial wafer was manufactured under the same conditions as in Example 1 except that the thickness of the silicon epitaxial film was 3 μm.
Further, a silicon epitaxial film containing no carbon was formed to a thickness of approximately 2 μm using this silicon epitaxial film as a base.
The film thickness was adjusted by changing the treatment time in the low pressure CVD furnace.

In order to investigate the structure of this epitaxial wafer, a TEM image was obtained from a plane direction so as to include the interface between the silicon epitaxial film and the silicon substrate.
Further, the thickness of the void defect region and the amount of oxygen captured were measured by SIMS.

As a result, it was confirmed that a void defect region was formed in a range of about 580 nm from the interface between the silicon substrate and the silicon epitaxial film toward the epitaxial film in the epitaxial wafer of the present invention. (See Figures 7 and 8)

Further, the amount of oxygen captured was approximately 2.0×10 ¹⁴ atoms/cm ² . (See Figure 10)

(Example 3)
An epitaxial wafer was manufactured under the same conditions as in Example 1, except that the silicon epitaxial film had a carbon concentration of 1.0×10 ²⁰ atoms/cm ³ and a thickness of 3 μm.
Note that when the carbon concentration of the silicon epitaxial film is 1.0×10 ²⁰ atoms/cm ³ , the thickness of the silicon epitaxial film determined from equation (1) is about 1.2 μm or more.

In order to investigate the structure of this epitaxial wafer, a TEM image was obtained from a plane direction so as to include the interface between the silicon epitaxial film and the silicon substrate. Further, the thickness of the void defect region and the amount of oxygen captured were measured by SIMS.

As a result, it was confirmed that in the epitaxial wafer of the present invention, a void defect region was formed in a range of about 350 nm or less from the interface between the silicon substrate and the silicon epitaxial film toward the epitaxial film. (See Figures 7 and 8)

Further, the amount of oxygen captured was approximately 1.2×10 ¹⁵ atoms/cm ² . (See Figure 10)

(Example 4)
An epitaxial wafer was manufactured under the same conditions as in Example 3 except that the thickness of the silicon epitaxial film was 2 μm.

In order to investigate the structure of this epitaxial wafer, a TEM image was obtained from a plane direction so as to include the interface between the silicon epitaxial film and the silicon substrate. Further, the thickness of the void defect region and the amount of oxygen captured were measured by SIMS.

As a result, it was confirmed that a void defect region was formed in a range of about 390 nm from the interface between the silicon substrate and the silicon epitaxial film toward the epitaxial film in the epitaxial wafer of the present invention. (See Figures 7 and 8)

Further, the amount of oxygen captured was approximately 1.2×10 ¹⁵ atoms/cm ² . (See Figure 10)

(Example 5)
An epitaxial wafer was manufactured under the same conditions as in Example 1, except that the silicon epitaxial film had a carbon concentration of 3.0×10 ²⁰ atoms/cm ³ and a thickness of 1 μm.
Note that when the carbon concentration of the silicon epitaxial film is 3.0×10 ²⁰ atoms/cm ³ , the thickness of the silicon epitaxial film determined from equation (1) is about 0.5 μm or more.

In order to investigate the structure of this epitaxial wafer, a TEM image was obtained from a plane direction so as to include the interface between the silicon epitaxial film and the silicon substrate.
Further, the thickness of the void defect region and the amount of oxygen captured were measured by SIMS.

As a result, it was confirmed that in the epitaxial wafer of the present invention, a void defect region was formed in a range of about 250 nm or less from the interface between the silicon substrate and the silicon epitaxial film toward the epitaxial film. (See Figures 7 and 8)

Further, the amount of oxygen captured was approximately 2.1×10 ¹⁵ atoms/cm ² . (See Figure 10)

(Example 6)
An epitaxial wafer was manufactured under the same conditions as in Example 1 except that the silicon epitaxial film had a carbon concentration of 1.0×10 ²¹ atoms/cm ³ and a thickness of 1 μm.
Note that when the carbon concentration of the silicon epitaxial film is 1.0×10 ²¹ atoms/cm ³ , the thickness of the silicon epitaxial film determined from equation (1) is the lower limit of 0.1 μm or more.

In order to investigate the structure of this epitaxial wafer, a TEM image was obtained from a plane direction so as to include the interface between the silicon epitaxial film and the silicon substrate. Further, the thickness of the void defect region and the amount of oxygen captured were measured by SIMS.

As a result, it was confirmed that in the epitaxial wafer of the present invention, a void defect region was formed in a range of about 320 nm or less from the interface between the silicon substrate and the silicon epitaxial film toward the epitaxial film. (See Figures 7 and 8)

Further, the amount of oxygen captured was approximately 3.6×10 ¹⁵ atoms/cm ² . (See Figure 10)

(Comparative example 1)
A ^surface modified layer (carbon ^{concentration} A silicon wafer having a density of 1.0×10 ²⁰ atoms/cm ³ ) was prepared.

By forming a silicon epitaxial film on this silicon wafer, an epitaxial wafer having a modified layer immediately below the epitaxial film, which is a device active layer, was prepared.
The silicon epitaxial film was formed at a temperature of 1000° C. and a thickness of 9 μm.

In order to evaluate the amount of oxygen captured in this epitaxial wafer, the obtained epitaxial wafer was subjected to heat treatment at 1000° C. in an oxygen atmosphere until a thermal equilibrium state was reached.

Further, the ion implantation depth (position of the carbon-containing layer) was 9.1 μm from the surface of the silicon epitaxial film, and the thickness of the carbon-containing layer was 0.3 μm.

When the amount of oxygen captured in this epitaxial wafer was measured by SIMS, the amount of oxygen captured was approximately 5.7×10 ¹³ atoms/cm ² .

(Comparative example 2)
An epitaxial wafer was manufactured under the same conditions as in Example 1 except that the thickness of the silicon epitaxial film was 1 μm.
This does not satisfy formula (1), and no void defect region is formed by heat treatment.

When the amount of oxygen captured in this epitaxial wafer was investigated by SIMS, the amount of oxygen captured was approximately 8.1×10 ¹³ atoms/cm ² .

FIG. 11 is a graph comparing the amount of oxygen captured in the epitaxial wafer implanted with carbon ions of Comparative Example 1, the amount of oxygen captured in the epitaxial wafer of Comparative Example 2, and the amount of oxygen captured in the epitaxial wafer of Example 5.
The epitaxial wafer of Example 5 (this proposed substrate), which has a structure in which a Void defect layer is formed directly under the silicon epitaxial film, has an exceptionally superior capture amount compared to epitaxial wafers using conventional modified layers. I understand.

From the above, in the epitaxial wafer of the present invention, the relationship between the carbon concentration contained in the silicon epitaxial film and the film thickness is expressed by formula (1):
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)
By forming a film within a range that satisfies the above, it is possible to manufacture an epitaxial wafer with a structure in which a void defect layer is formed directly under the silicon epitaxial film, and the void defect layer is formed on the silicon epitaxial film side (active It has been shown that it is possible to provide an epitaxial wafer with a significantly improved effect of reducing the amount of oxygen diffusion into the layer).

Furthermore, based on the above examples and comparative examples, and with reference to FIGS. 5 to 11, the circumstances leading to the present invention will be explained in the following experimental examples.

(Experiment example)
There has been a demand for epitaxial wafers with sufficient oxygen trapping ability in the field of devices that are sensitive to defect levels caused by oxygen, such as image pickup devices.

In view of the above background, the inventors applied the phenomenon in which carbon contained in a silicon epitaxial film formed by a CVD apparatus changes into interstitial carbon and vacancies through heat treatment, and created voids, which are aggregates of vacancies. I came up with a method to use it as a gettering site.
The inventors formed a silicon epitaxial film (carbon concentration: 2.0×10 ¹⁹ atoms/cm ³ , film thickness: 5.5 μm) on a silicon substrate using a low pressure CVD apparatus. Note that the carbon concentration and thickness of the silicon epitaxial film were adjusted by changing the amount of raw material gas supplied and the processing time in the low-pressure CVD furnace.

As a preliminary experiment, the obtained epitaxial wafer was subjected to heat treatment at 1000° C. in an oxygen atmosphere for 12 to 36 hours. When the oxygen concentration of the epitaxial wafer after heat treatment was measured by SIMS, it was found that a steep oxygen peak occurred in the SIMS profile in a range of 600 nm or less from the interface between the silicon epitaxial film and the silicon substrate to the epitaxial film side. Ta. It was also found that the oxygen atom concentration continued to change slowly near the interface between the silicon epitaxial film and the silicon substrate within the heat treatment time range of 12 hours to 36 hours.
The above results suggested that a specific defect region may be formed in a range of about 600 nm from the interface between the silicon epitaxial film and the silicon substrate of the epitaxial wafer toward the silicon epitaxial film. Further, when the amount of oxygen captured by the epitaxial wafer was calculated from the SIMS results, it was an excellent value exceeding 2.0×10 ¹⁴ atoms/cm ² .

The inventors believed that by clarifying the cause of the steep oxygen peak observed in SIMS measurements, it is likely that epitaxial wafers that are superior in terms of manufacturing efficiency will be realized.
Therefore, a silicon epitaxial film (carbon concentration: 2.0×10 ¹⁹ atoms/cm ³ , film thickness: 5.5 μm) that had been heat-treated at 1000° C. for 36 hours was subjected to TEM observation from the cross-sectional direction.

FIG. 5 is a cross-sectional TEM image of the epitaxial wafer of the experimental example (Example 1).
A void defect region was confirmed in a range of 600 nm or less from the interface between the silicon epitaxial film and the silicon substrate to the epitaxial film side.
In the right enlarged view, the dashed circular part is a void, and the rectangular area containing a plurality of voids is a void defect area.
This corresponds to the oxygen peak position in the SIMS profile described above, and indicates that a large amount of oxygen is captured in the Void defect region.

In order to investigate the structure of the void defect in more detail, high-magnification TEM images were obtained from both the planar direction and the cross-sectional direction.
FIG. 6 is a high-magnification TEM image (plane, cross-section) and structural diagram of a Void defect in an experimental example (Example 1).
By acquiring TEM images in two directions, one perpendicular to the silicon substrate and the other in cross section, it was revealed that the shape of the void was a regular octahedron and that it had a structure with silicon oxide on the inner wall. .
In other words, as shown in the TEM image and schematic diagram of FIG. 6, Void defects formed in a range of 600 nm or less from the interface between the silicon epitaxial film and the silicon substrate to the epitaxial film side have a regular octahedral structure, and the inner wall It was found that the material had a silicon oxide layer of about 10 nm. The regular octahedral shape suggests that the void defect is surrounded by {111} planes of matrix silicon, and the silicon oxide on the inner wall is thought to have grown by capturing oxygen diffused from the silicon substrate during heat treatment. It will be done.

From the above results, when the carbon concentration in the silicon epitaxial film is 2.0×10 ¹⁹ atoms/cm ³ , by applying heat treatment after film formation, it is possible to increase the amount of carbon from the interface between the silicon epitaxial film and the silicon substrate to the epitaxial film side. It has become possible to form a void defect region in a range of 600 nm or less, and it has been found that this makes it possible to realize an excellent oxygen trapping ability exceeding 2.0×10 ¹⁴ atoms/cm ² .

However, from the viewpoint of manufacturing efficiency, it is desirable to achieve excellent oxygen trapping ability with a thinner film thickness. Therefore, a silicon epitaxial film containing 2.0×10 ¹⁹ atoms/cm ³ or more of carbon and having a varying thickness (film thickness: 1 μm for a sample with a carbon concentration of 2.0×10 ¹⁹ atoms/cm ^{3 )} was used. For samples of 1.5 μm, 2 μm, 3 μm, and 5.5 μm, carbon concentration: 1.0×10 ²⁰ atoms/cm ³ , film thickness: 1 μm, 2 μm, and 3 μm, carbon concentration: 3.0×10 ²⁰ atoms/cm For samples of ³ and 1.0×10 ²¹ , a film thickness of 1 μm) was formed on a silicon substrate. Note that the carbon concentration and thickness of the silicon epitaxial film were adjusted by changing the amount of source gas introduced and the processing time.

In order to evaluate the presence or absence of Void defect regions in these epitaxial wafers, the obtained epitaxial wafers were subjected to heat treatment at 1000° C. in an oxygen atmosphere for 36 hours. After the heat treatment, planar TEM observation was performed using a thin sample (about 500 nm thick) containing the interface between the silicon epitaxial film and the silicon substrate of each epitaxial wafer.

FIG. 7 is a planar TEM image of a thin sample (thickness: about 500 nm) cut out from the epitaxial wafers of Examples 1 to 6 at a depth that includes the interface between the silicon epitaxial film and the substrate.
A sample with a carbon concentration of 2.0×10 ¹⁹ atoms/cm ³ has a film thickness of 3 μm or more, and a sample with a carbon concentration of 1.0×10 ²⁰ atoms/cm ³ has a film thickness of 2 μm or more and a carbon concentration of 3 μm. It was found that in the sample with .0×10 ²⁰ atoms/cm ³ or more, the film thickness was 1 μm, and a void defect amount region was formed near the interface between the silicon epitaxial film and the silicon substrate.

By performing SIMS measurements on these samples, we have also confirmed that a steep oxygen peak appears in a range of 600 nm or less from the interface between the silicon epitaxial film and the silicon substrate to the epitaxial film side (FIG. 8).
FIG. 8 shows the SIMS measurement results of the epitaxial wafers of Examples 1 to 6. When the carbon concentration of the silicon epitaxial film formed on the silicon substrate is 2.0×10 ¹⁹ atoms/cm ³ and the film thickness is 3 μm, the thickness of the Void defect region is about 580 nm, and the carbon concentration is 2.0×10 ¹⁹ When the carbon concentration is 1.0×10 20 atoms/cm ³ and the film thickness is 2 μm, the thickness of the void defect region is approximately 600 nm. When the carbon concentration is 1.0×10 ²⁰ atoms/cm ³ and the film thickness is 2 μm, the thickness of the void defect region is approximately 390 nm. , when the carbon concentration is 1.0×10 ²⁰ atoms/cm ³ and the film thickness is 3 μm, the thickness of the void defect region is about 350 nm, and when the carbon concentration is 3.0×10 ²⁰ atoms/cm ³ and the film thickness is 1 μm, the void defect region is about 350 nm The thickness of the void defect region is approximately 250 nm, the thickness of the void defect region is approximately 320 nm when the carbon concentration is 1.0×10 ²¹ atoms/cm ³ and the film thickness is 1 μm, and the thickness of the void defect region is approximately 320 nm. It can be seen that a Void defect region is formed in the side range.

Based on the above results, the inventors determined that the conditions under which Void defects are formed in a range of 600 nm or less from the interface between the silicon epitaxial film and the silicon substrate to the epitaxial film side by heat treatment are the carbon concentration contained in the silicon epitaxial film and the silicon It is concluded that both depend on the thickness of the epitaxial film.

Therefore, FIG. 9 shows the results of sorting out the presence or absence of a void defect region shown in a series of experiments based on the carbon concentration contained in the silicon epitaxial film and the film thickness of the silicon epitaxial film.
FIG. 9 is a graph showing the conditions of the carbon concentration and film thickness of the silicon epitaxial film in which a Void defect region is formed near the interface between the silicon epitaxial film and the silicon substrate in the epitaxial wafer of the present invention.
At this time, the effective region where a Void defect region is formed at the interface between the silicon epitaxial film and the silicon substrate after the heat treatment is shown by the broken line and the shaded area in the figure. This is 6.6×10 ²⁰ ×exp(-1.6×[thickness of silicon epitaxial film (μm)])<[silicon Carbon concentration of epitaxial film (atoms/cm ³ )].

The reason why the effective range in which a Void defect region is formed, within a range of 600 nm or less from the interface between the silicon epitaxial film and the substrate to the epitaxial film side, is influenced by the carbon concentration contained in the silicon epitaxial film and the thickness of the silicon epitaxial film is as follows. We are considering the possibility that Void is involved in the stress relaxation mechanism that occurs due to the fact that the lattice constant of the silicon epitaxial film is different from that of the silicon substrate.

In addition, from experimental examples, in an epitaxial wafer having a structure having a void defect region in a range of 600 nm or less from the interface between the silicon epitaxial film and the silicon substrate to the epitaxial film side in the present invention, it was found that the thickness of the silicon epitaxial film and the silicon epitaxial film It has been found that the carbon concentration included can be varied as required within the scope of the present invention.

The specification includes the following aspects.
[1]: An epitaxial wafer having a silicon substrate and a silicon epitaxial film formed on the silicon substrate,
An epitaxial wafer characterized in that a void defect region is provided in a range of 600 nm or less from an interface between the silicon substrate and the silicon epitaxial film toward the silicon epitaxial film.
[2]: The epitaxial wafer of [1] above, wherein the silicon epitaxial film has a carbon concentration and film thickness that satisfy the following formula (1).
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)
[3]: The above silicon epitaxial film has another silicon epitaxial film on the silicon epitaxial film, and the carbon concentration of the another silicon epitaxial film is less than 2.0×10 ¹⁹ atoms/cm ³ . [1] or the epitaxial wafer of [2] above.
[4]: The epitaxial wafer according to any one of [1] to [3] above, wherein the silicon epitaxial film has insulating properties and high frequency characteristics.
[5]: A method for manufacturing an epitaxial wafer, in which a silicon epitaxial film is formed on a silicon substrate using a raw material gas containing a carbon source gas so as to have a carbon concentration and film thickness that satisfy the following formula (1). A method for producing an epitaxial wafer, comprising a step of forming the epitaxial wafer, and a step of performing heat treatment at a heat treatment temperature of 900° C. or higher and a heat treatment time of 1 hour or longer.
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1)
[6]: The method for manufacturing an epitaxial wafer according to the above [5], characterized in that the heat treatment is performed under conditions that the heat treatment temperature is 1100° C. or less and the heat treatment time is 36 hours or less.
[7]: After the step of forming the silicon epitaxial film and before the step of heat treatment, a carbon concentration of 2.0×10 ¹⁹ atoms is formed on the silicon epitaxial film using a raw material gas that does not contain a carbon source gas. The method for manufacturing an epitaxial wafer according to [5] or [6] above, which comprises a step of forming another silicon epitaxial film with a thickness of less than /cm ³ .

Note that the present invention is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any embodiment that has substantially the same configuration as the technical idea stated in the claims of the present invention and has similar effects is the present invention. covered within the technical scope of

DESCRIPTION OF SYMBOLS 1, 2...Epitaxial wafer, 10...Silicon substrate, 11...Void defect region, 12...Silicon epitaxial film, 13...Another silicon epitaxial film.

Claims (3)

A method for manufacturing an epitaxial wafer, the method comprising:
A process of forming a silicon epitaxial film on a silicon substrate using a source gas containing a carbon source gas and not containing a gas containing oxygen atoms so as to have a carbon concentration and film thickness that satisfy the following formula (1). and,
A method for manufacturing an epitaxial wafer, comprising the step of thereafter performing heat treatment at a heat treatment temperature of 1000 ° C. or more and a heat treatment time of 1 hour or more.
6.6×10 ²⁰ ×exp(−1.6×[thickness of silicon epitaxial film (μm)])<[carbon concentration of silicon epitaxial film (atoms/cm ³ )]…(1) 2. The method for manufacturing an epitaxial wafer according to claim 1, wherein the heat treatment is performed under conditions that the heat treatment temperature is 1100° C. or less and the heat treatment time is 36 hours or less. After the step of forming the silicon epitaxial film and before the step of heat treatment,
It is characterized by comprising the step of forming another silicon epitaxial film having a carbon concentration of less than 2.0×10 ¹⁹ atoms/cm ³ on the silicon epitaxial film using a source gas that does not contain a carbon source gas. The method for manufacturing an epitaxial wafer according to claim 1 or 2 .

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