Epitaxial wafer and production method therefor

Abstract

The present invention is an epitaxial wafer comprising a single-crystal silicon substrate having a resistivity of 10-5,000 Ω·cm and having, formed thereon in the following order, an epitaxial silicon film having a carbon concentration of 2×1019 atoms / cm3 or higher but less than 3×1020 atoms / cm3 and containing carbon defects and a dielectric layer. The epitaxial silicon film has a thickness satisfying the formula: 6.6×1020×exp\{-1.6×[thickness (μm) of epitaxial silicon film]\}>[carbon concentration (atoms / cm3) of epitaxial silicon film]. As a result, the present invention provides: an epitaxial silicon wafer for high-frequency integrated circuit boards which is obtained by forming the epitaxial silicon film on a silicon substrate having an ordinary resistivity and which has the excellent ability to reduce higher harmonics and is easy to process; and a method for producing the epitaxial silicon wafer.

Description

Epitaxial wafer and method for manufacturing the same

[0001] The present invention relates to an epitaxial wafer and a method for manufacturing the same.

[0002] In recent years, demand for high-capacity communications has been extremely high, accelerating the development of devices compatible with fifth- and sixth-generation mobile communications systems (commonly known as 5G and 6G). These communications devices incorporate integrated circuits, and the active elements (e.g., transistors) and passive elements (e.g., inductors) that make up the integrated circuits must be highly stable in 5G and 6G environments. In particular, because these high-capacity communications systems are expected to use high-frequency bands (millimeter waves to sub-terahertz bands), there is a social demand for device designs and material development that combine excellent high-frequency characteristics with power-saving performance.

[0003] Looking at the materials required for semiconductor integrated circuits, silicon wafers produced by the Czochralski (CZ) method are sometimes used as substrates for high-frequency integrated circuits. The silicon wafers used in this case must have high substrate resistivity in order to achieve low resistance loss and good high-frequency characteristics.

[0004] Furthermore, in applications requiring superior high-frequency characteristics, wafers having a trap-rich layer formed thereon, as described in Patent Document 1 and Patent Document 2, are widely used. This is because it is known that when a high-frequency signal is input to a device formed on a high-resistivity substrate, the resistivity changes due to the formation of an inversion layer in the substrate, and high substrate resistivity can be maintained by capturing carriers generated in the inversion layer at deep levels in the trap-rich layer. In particular, for passive elements, wafers having a polysilicon layer formed as a trap-rich layer on a high-resistivity substrate are used. In contrast, SOI wafers having a trap-rich layer are widely used for active elements. In the structure of such an SOI wafer, a polysilicon layer as a trap-rich layer, an oxide film as a dielectric layer, and a single-crystal silicon layer are stacked in this order on a high-resistivity substrate.

[0005] However, the manufacture of high-resistivity substrates, which are widely used as substrates for high-frequency integrated circuits, is technically difficult to control resistivity, resulting in low yields. In addition, polysilicon, which is used as a trap-rich layer, is difficult to process, leading to reduced productivity, and SOI structures using polysilicon as a trap-rich layer have a complex manufacturing process and significant cost issues. Therefore, there has been a demand for technology development that does not use high-resistivity substrates but instead exhibits excellent high-frequency characteristics, particularly reducing harmonics, in epitaxial wafers in which a silicon epitaxial film is formed on a silicon single crystal substrate (hereinafter simply referred to as "silicon substrate").

[0006] Furthermore, wafers in which a carbon-doped epitaxial film is formed on a silicon substrate are described in Patent Documents 3 and 4. However, the wafers in Patent Documents 3 and 4 are epitaxial wafers that are basically composed of a silicon substrate, a carbon-doped epitaxial film, and a silicon epitaxial film and are intended to be used mainly in image sensors, and there is no description of performing heat treatment after forming the epitaxial film, so no trap-rich layer is formed in the epitaxial film.

[0007] Furthermore, Patent Document 5 describes an epitaxial wafer in which a wafer having a carbon-doped epitaxial film formed on a silicon substrate is subjected to a heat treatment. However, it does not mention the use of the epitaxial wafer as a wafer for high frequency devices or an epitaxial wafer in which a trap rich layer is formed.

[0008] In Patent Document 5, the technology was developed with the aim of using a silicon epitaxial film containing a high concentration of carbon as a gettering layer, and the heat treatment is intended to drive gettering. Therefore, the heat treatment conditions are described as being in the range of 450 to 750°C for approximately 30 minutes. Heat treatment at 800 to 1000°C is also mentioned to drive gettering in a shorter time, but the heat treatment time is estimated to be 30 minutes or less. However, it is difficult to obtain stable high-frequency characteristics under such conditions.

[0009] For the reasons described above, it is difficult to use the wafers disclosed in Patent Documents 3, 4, and 5 as wafers for high frequency devices.

[0010] Japanese Patent Publication No. 2015-503853 Japanese Patent Publication No. 2019-129195 Japanese Patent Publication No. 2009-164590 Japanese Patent Publication No. 2009-200231 Japanese Patent Publication No. 2006-216934

[0011] As described above, there has been a demand for an epitaxial wafer that can reduce harmonics without using a high-resistivity substrate and has a trap-rich layer as a substrate for high-frequency integrated circuits. The inventors conducted extensive research aimed at developing a material that meets these demands, and as a result, found that an epitaxial wafer obtained by forming a silicon epitaxial film containing a high concentration of carbon on a substrate with normal resistivity and then performing a heat treatment on the epitaxial wafer is promising. This makes it possible to provide a substrate for high-frequency integrated circuits that can be manufactured with a small number of steps and has an easy processing process.

[0012] However, even these substrates do not have the ability to reduce harmonics to the same level as epitaxial wafers that use conventional polysilicon layers as trap-rich layers, and there is an urgent need to develop epitaxial wafers that exhibit better high-frequency characteristics.

[0013] The present invention has been made in view of the above problems, and has an object to provide a silicon epitaxial wafer for use in high frequency integrated circuit substrates, which is a silicon epitaxial wafer in which a silicon epitaxial film is formed on a silicon substrate of normal resistivity, which has an excellent ability to reduce harmonics, and which can be easily processed, and a method for manufacturing the same.

[0014] The present invention has been made to achieve the above object, and provides a method for manufacturing a silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less, the method comprising: １９ atoms / cm ３ 3x10 or more ２０ atoms / cm ３a silicon epitaxial film containing carbon defects, and a dielectric layer in this order, and the silicon epitaxial film has a thickness of less than 6.6×10 ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) is satisfied.

[0015] In such an epitaxial wafer, the dielectric layer on the silicon epitaxial film having the above carbon concentration improves the insulating properties of the substrate, and the film quality of the epitaxial wafer is stabilized at a high level. Furthermore, minute carbon defects can be contained in the silicon epitaxial film, which acts to provide excellent high-frequency characteristics.

[0016] In this case, the epitaxial wafer can be a wafer for a high frequency device.

[0017] The dielectric layer on the silicon epitaxial film having the above carbon concentration improves the insulating properties of the substrate, and the epitaxial wafer also has a high and stable film quality. Furthermore, the silicon epitaxial film can contain minute carbon defects, which act to provide excellent high-frequency characteristics, making the epitaxial wafer suitable for use as a wafer for high-frequency devices.

[0018] At this time, the carbon defects have a size of 10 nm or less and a density of 1×10 in the silicon epitaxial film. １０ cm －２ It can be the above.

[0019] If such carbon defects are present, the silicon epitaxial film containing minute carbon defects at a high density will have excellent high frequency characteristics.

[0020] The present invention also provides a method for manufacturing a silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less, and a method for manufacturing a silicon single crystal substrate having a carbon concentration of 2×10 １９ atoms / cm ３ 3x10 or more ２０ atoms / cm３ a step of vapor-growing a carbon-doped silicon epitaxial film having a thickness of less than 6.6×10; a step of forming a dielectric layer on the silicon epitaxial film; and a step of forming carbon defects in the silicon epitaxial film by heat-treating the silicon single crystal substrate on which the dielectric layer has been formed at a heat treatment temperature of 900° C. to 1100° C. for a heat treatment time of 3 hours to 36 hours, wherein in the step of vapor-growing the silicon epitaxial film, the thickness of the silicon epitaxial film is less than 6.6×10. ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ The present invention provides a method for producing an epitaxial wafer, characterized by forming a silicon epitaxial film that satisfies the following conditions:

[0021] Such a method for manufacturing an epitaxial wafer in which minute carbon defects are formed at a high density inside the silicon epitaxial film by vapor phase growth of the silicon epitaxial film, formation of the dielectric layer, and subsequent heat treatment makes it possible to easily manufacture an epitaxial wafer that exhibits the above-mentioned excellent high frequency characteristics.

[0022] In this case, the epitaxial wafer manufactured using the above-described method for manufacturing an epitaxial wafer can be used as a wafer for a high frequency device.

[0023] The dielectric layer on the silicon epitaxial film having the above carbon concentration improves the insulating properties of the substrate, and the epitaxial wafer also has a high and stable film quality. Furthermore, minute carbon defects can be formed at a high density in the silicon epitaxial film, which results in excellent high-frequency characteristics, making the epitaxial wafer suitable for use as a wafer for high-frequency devices.

[0024] At this time, the carbon defects have a size of 10 nm or less and a density of 1×10 in the silicon epitaxial film. １０ cm －２ It can be the above.

[0025] It is possible to manufacture an epitaxial wafer having a silicon epitaxial film containing such minute carbon defects at a high density and having superior high frequency characteristics.

[0026] As described above, the silicon epitaxial wafer of the present invention does not require a high resistivity substrate, and due to the action of the silicon epitaxial film containing a high density of minute carbon defects and the dielectric layer provided on the epitaxial film, it has superior harmonic reduction capability compared to epitaxial wafers in which a polysilicon layer is formed as a trap rich layer on a conventional high resistivity substrate, making it suitable as a wafer for high frequency devices. Furthermore, the method for producing an epitaxial wafer of the present invention makes it possible to easily produce epitaxial wafers exhibiting the above-mentioned excellent harmonic reduction capability.

[0027] 1 is a schematic diagram showing an epitaxial wafer of the present invention; 2 is a flow chart showing an example of a manufacturing method of an epitaxial wafer of the present invention; 3 is a graph showing the conditions of carbon concentration and film thickness of a silicon epitaxial film under 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; 4 is a plot showing changes in the second harmonic and third harmonic characteristics of an epitaxial wafer when heat treatment is performed on the epitaxial wafer with varying heat treatment times in Experimental Example 2; and 5 is a graph showing the relationship between the second harmonic characteristics and third harmonic characteristics of epitaxial wafers in Example 1 and Comparative Examples 1 and 2 and the carbon concentration.

[0028] The present invention will be described in detail below, but the present invention is not limited thereto.

[0029] As described above, the demand for smaller, more energy-efficient, and less expensive communication devices has led to a demand for inexpensive epitaxial wafers that can further improve high-frequency characteristics, particularly reduce harmonics.

[0030] As a result of extensive research into the above-mentioned problems, the present inventors have discovered that a silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less can be formed with a carbon concentration of 2×10 １９ atoms / cm ３3x10 or more ２０ atoms / cm ３ a silicon epitaxial film containing carbon defects, and a dielectric layer in this order, and the silicon epitaxial film has a thickness of less than 6.6×10 ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ))], the dielectric layer provided on the silicon epitaxial film containing minute carbon defects acts to provide an epitaxial wafer with excellent harmonic reduction capability, and the present invention has been completed based on this finding.

[0031] The present inventors have also discovered a method for producing a silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less, and forming a carbon film having a carbon concentration of 2×10 １９ atoms / cm ３ 3x10 or more ２０ atoms / cm ３ a step of vapor-growing a carbon-doped silicon epitaxial film having a thickness of less than 6.6×10; a step of forming a dielectric layer on the silicon epitaxial film; and a step of forming carbon defects in the silicon epitaxial film by heat-treating the silicon single crystal substrate on which the dielectric layer has been formed at a heat treatment temperature of 900° C. to 1100° C. for a heat treatment time of 3 hours to 36 hours, wherein in the step of vapor-growing the silicon epitaxial film, the thickness of the silicon epitaxial film is less than 6.6×10. ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ The present inventors have found that an epitaxial wafer having the above-mentioned excellent harmonic reduction capability can be easily manufactured by a method for manufacturing an epitaxial wafer, which method is characterized by forming a silicon epitaxial film that satisfies the above-mentioned requirement.

[0032] [Epitaxial Wafer of the Present Invention] The epitaxial wafer of the present invention will be described below with reference to Fig. 1. As shown in Fig. 1, the epitaxial wafer 1 of the present invention includes, on a silicon substrate 2, a silicon epitaxial film 3 containing carbon defects, and a dielectric layer 4, in this order.

[0033] The silicon substrate 2 has a resistivity of 10 Ω cm or more and 5000 Ω cm or less. A silicon substrate 2 with a resistivity in this range can be used for high-frequency devices. The resistivity is more preferably about 1000 to 5000 Ω cm, which provides good high-frequency characteristics and allows resistivity control in single crystal production.

[0034] The silicon epitaxial film 3 has a general carbon solid solubility of 3×10 １７ atoms / cm ３ (the maximum solid solubility of carbon at the melting point of silicon) is 2 × 10 １９ atoms / cm ３ 3x10 or more ２０ atoms / cm ３ The alloy contains carbon at a concentration of less than 10 ...

[0035] The minute carbon defects contained in the silicon epitaxial film 3 have a size of about 10 nm or less and a density in the silicon epitaxial film 3 of about 1×10 １０ cm －２ (When the carbon concentration of the carbon-doped silicon epitaxial film 3 is low according to the present invention, carbon defects of about 25 nm or more are contained at a low density.) The lower limit of the size and the upper limit of the density are not particularly limited, but are preferably 3 nm or more and 1×10 １２ cm －２ The size of the carbon defects is a value measured by measuring the longest part of the defect detected by cross-sectional TEM. This also applies to the epitaxial wafer manufacturing method described below.

[0036] The thickness and carbon concentration of the silicon epitaxial film 3 are set to 6.6×10 so that the silicon epitaxial film 3 does not contain void defects.２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) ] relationship is satisfied.

[0037] The dielectric layer 4 on the surface of the silicon epitaxial film 3 functions as an insulating film, improves the insulating properties of the substrate, and also has the effect of preventing roughening of the silicon epitaxial film 3 due to heat treatment, thereby stabilizing the film quality at a high level.

[0038] Furthermore, by performing a heat treatment after the deposition of the dielectric layer 4, the silicon epitaxial film 3 contains a high density of minute carbon defects, which act to provide excellent high frequency characteristics. The reason for this is thought to be that the heat treatment forms minute carbon defects in the silicon epitaxial film, which form deep levels, enhancing its function as a trap rich layer and inhibiting the formation of an inversion layer.

[0039] Such epitaxial wafers have the advantage of minute carbon defects inside the silicon epitaxial film, and the high insulating properties of the substrate result in excellent harmonic characteristics, making them suitable substrates for high-frequency device wafers and active elements.

[0040] The upper and lower limits of the carbon concentration of the silicon epitaxial film 3 are 2.0×10 １９ atoms / cm ３ 3x10 or more ２０ atoms / cm ３ At such a concentration, the carbon concentration is much higher than the general carbon solid solubility, so it is possible to form minute carbon defects at a high density by heat treatment, and sufficient high-frequency characteristics can be realized. If the carbon concentration is below the lower limit, the degree of carbon supersaturation is small, so coarse carbon defects are formed, resulting in low density and making it impossible to realize sufficient high-frequency characteristics. On the other hand, if the carbon concentration is 2.0 × 10 １９ atoms / cm ３In the above cases, when the film thickness exceeds a predetermined value, void defects are formed, and if these coexist with minute carbon defects inside the film, the high frequency characteristics are improved by heat treatment, but the extent of the improvement is small. This is thought to be because the volume of void defects is much larger than that of carbon defects, so the influence of void defects becomes dominant. Therefore, in order to obtain an epitaxial wafer with excellent high frequency characteristics, it is important that the film thickness of the silicon epitaxial film 3 is thin enough to prevent the formation of void defects. Also, when the carbon concentration is 3×10 ２０ atoms / cm ３ If the carbon concentration is more than this, the film quality of the carbon-doped silicon epitaxial film 3 deteriorates and productivity also decreases. The upper limit of the carbon concentration depends on the silicon epitaxial film thickness. ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) ]. At such a concentration, stable and excellent high frequency characteristics are obtained. This also applies to the manufacturing method of the epitaxial wafer described later.

[0041] The upper and lower limits of the thickness of the silicon epitaxial film 3 can be set to, for example, 0.1 μm or more and 2.5 μm or less, taking into consideration productivity and costs. Within this range, the silicon epitaxial film can have sufficient high-frequency characteristics at a lower cost. However, if the carbon concentration of the silicon epitaxial film is 2.0×10 １９ atoms / cm ３ In the above cases, when the silicon epitaxial film is heat-treated, void defect regions are likely to form at the interface between the silicon epitaxial film and the silicon substrate. Since void defects are aggregates of vacancies, reducing the thickness of the silicon epitaxial film 3 reduces the number of vacancies generated inside the film, thereby suppressing the formation of void defects. Therefore, it is necessary to adjust the film thickness according to the carbon concentration. From the above, the relationship between the thickness of the silicon epitaxial film 3 and the carbon concentration is 6.6×10 ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm３ ) ] must be met.

[0042] Experimental Example 1 The following describes the results of an experiment evaluating the relationship between the carbon concentration and film thickness of a carbon-doped silicon epitaxial film formed on a silicon substrate, which prevents void defects from forming in the epitaxial film.

[0043] The inventors used a low-pressure CVD apparatus to １９ atoms / cm ３ A silicon epitaxial film containing carbon of 2.0×10 or more and varying the thickness (carbon concentration: 2.0×10 １９ atoms / cm ３ The samples had film thicknesses of 1 μm, 1.5 μm, 2 μm, 3 μm, and 5.5 μm, and carbon concentrations of 1.0×10 ２０ atoms / cm ３ In the samples, the film thickness was 1 μm, 2 μm, and 3 μm, and the carbon concentration was 3.0×10 ２０ atoms / cm ３ and 1.0 x 10 ２１ In the sample (2), a film having a thickness of 1 μm was formed on a silicon substrate. The carbon concentration and thickness of the silicon epitaxial film were adjusted by changing the amount of source gas introduced into the low-pressure CVD furnace and the processing time.

[0044] 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 for 36 hours in an oxygen atmosphere. After the heat treatment, planar TEM observation was performed using thin section samples (approximately 500 nm thick) including the interface between the silicon epitaxial film and the silicon substrate of each epitaxial wafer.

[0045] As a result of Experimental Example 1, the carbon concentration was 2.0 × 10 １９ atoms / cm ３ In the sample, the film thickness is 3 μm or more, and the carbon concentration is 1.0 × 10 ２０ atoms / cm ３ In the sample, the film thickness is 2 μm or more, and the carbon concentration is 3.0 × 10 ２０ atoms / cm ３In the above samples, it was found that the film thickness was 1 μm and a void defect region was formed near the interface between the silicon epitaxial film and the silicon substrate.

[0046] From the above results, the inventors concluded that the conditions under which void defects are formed in a silicon epitaxial film by heat treatment vary depending on both the carbon concentration contained in the silicon epitaxial film and the thickness of the silicon epitaxial film.

[0047] The presence or absence of void defect regions shown in Experimental Example 1 was analyzed based on the carbon concentration contained in the silicon epitaxial film and the film thickness of the silicon epitaxial film, and the results are shown in Figure 3. Figure 3 is a graph showing the conditions for the carbon concentration and film thickness of the silicon epitaxial film under which void defect regions are formed near the interface between the silicon epitaxial film and the silicon substrate in the epitaxial wafer of the present invention. The region in which void defect regions are formed at the interface between the silicon epitaxial film and the silicon substrate after heat treatment is shown by the dashed line and the shaded area in the figure. That is, the white area in the figure is the region in the silicon epitaxial film in which void defect regions are not formed. This is because, in the relationship between the carbon concentration contained in the silicon epitaxial film and the film thickness, ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) can be set to a range that satisfies the above.

[0048] The silicon epitaxial wafer of the present invention does not require a high resistivity substrate, and due to the action of the silicon epitaxial film containing a high density of minute carbon defects and the dielectric layer provided on the epitaxial film, the silicon epitaxial wafer has superior harmonic reduction capability compared to epitaxial wafers in which a polysilicon layer is formed as a trap rich layer on a conventional high resistivity substrate, making the wafer suitable as a wafer for high frequency devices.

[0049] [Method for Manufacturing an Epitaxial Wafer] An example of a method for manufacturing an epitaxial wafer according to the present invention is shown in Fig. 2. This method is a method for manufacturing an epitaxial wafer in which a dielectric layer is formed on a silicon epitaxial film in which minute carbon defects are formed at a high density as a trap rich layer.

[0050] (Step of Preparing a Silicon Single Crystal Substrate) First, a silicon substrate having a resistivity of 10 to 5000 Ω·cm is prepared.

[0051] (Step of Vapor-Depositing Carbon-Doped Silicon Epitaxial Film) Next, a gas containing silicon atoms and carbon atoms is supplied onto the silicon substrate under reduced pressure, and 2×10 １９ atoms / cm ３ 3x10 or more ２０ atoms / cm ３ and the relationship between the thickness of the silicon epitaxial film and the carbon concentration is 6.6×10 ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) is vapor-grown. A dielectric layer is then formed on the epitaxial film. The epitaxial wafer with the dielectric layer formed on the epitaxial film is then heat-treated, thereby forming a high density of minute carbon defects in the epitaxial film.

[0052] By performing vapor phase growth of the epitaxial film under reduced pressure, the concentration of impurities other than carbon doped into the epitaxial film can be reduced. The pressure for forming the epitaxial film need not be particularly limited as long as it is reduced pressure, but it is preferable to perform the growth at about 10 Torr (about 1.3 kPa), for example, between 5 Torr (about 0.67 kPa) and 20 Torr (about 2.7 kPa).

[0053] As described above, carbon doping in vapor phase growth of an epitaxial film uses a gas (source gas) containing silicon atoms and carbon atoms. The source gas preferably contains at least one of monomethylsilane gas and trimethylsilane gas. By using these gases, good carbon doping can be easily achieved in the silicon epitaxial film. Furthermore, the vapor phase growth atmosphere may contain hydrogen, argon, or the like as a carrier gas when supplying the source gas.

[0054] The epitaxial film can be formed satisfactorily under reduced pressure by vapor-phase growth at 600 to 1000°C.

[0055] It is also preferable to appropriately set the pressure, temperature, time, and source gas concentration of the vapor phase growth so that the epitaxial film to be formed has a desired thickness. The thickness of the epitaxial film can be, for example, 0.1 μm or more and 2.5 μm or less, but 6.6×10 ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) )] is not limited to this. If the relationship between the carbon concentration and the film thickness of the epitaxial film is as described above, void defects will not be formed in the epitaxial film.

[0056] (Step of forming a dielectric layer) The method and material for forming the dielectric layer on the epitaxial film are not particularly limited, and a silicon oxide film formed by a general pyrogenic oxidation method can be used. This allows the dielectric layer to be efficiently formed to any desired thickness.

[0057] The thickness of the dielectric layer is not particularly limited, but may be, for example, 10 nm to 5 μm, which provides sufficient high frequency characteristics at lower cost.

[0058] The temperature for forming the dielectric layer can be a high-temperature process of 800° C. to 1200° C. using a heat treatment furnace capable of carrying out pyrogenic oxidation, a general method for forming a thermal oxide film. In this case, if a high-temperature heat treatment (e.g., a heat treatment temperature of 1000° C. for 3 hours or more) is performed in the process of forming the dielectric layer on the epitaxial film so that minute carbon defects are sufficiently formed inside the epitaxial film, the heat treatment after the formation of the dielectric layer can be omitted.

[0059] (Step of forming carbon defects) The method of heat treatment of an epitaxial wafer in which a dielectric layer is formed on an epitaxial film is not particularly limited, and for example, a heat treatment furnace for a general silicon wafer or a heat treatment furnace used for growing a dielectric layer can be used.

[0060] The lower limit of the heat treatment temperature is set to 900° C. or higher and the upper limit is set to 1100° C. In this way, minute carbon defects can be formed at a high density using a general heat treatment furnace, and the influence of heavy metal diffusion can be suppressed, improving manufacturing efficiency.

[0061] The heat treatment time is set to 3 hours or more and 36 hours or less, which allows for the formation of sufficiently small carbon defects, resulting in an epitaxial wafer of high quality and superior manufacturing efficiency.

[0062] The results of the investigation into the heat treatment time in the heat treatment will be explained in Experimental Example 2 below.

[0063] (Experimental Example 2) The heat treatment time required to form minute carbon defects at a high density was determined by the following experiment. In order to fundamentally investigate the heat treatment time required to manufacture an epitaxial wafer that exhibits excellent harmonic characteristics, the carbon concentration during film formation was set to 1.0 × 10 ２０ atoms / cm ３ The epitaxial wafer was subjected to heat treatment in an oxygen atmosphere at 1000°C for a heat treatment time varying from 15 minutes to 12 hours. Then, in order to investigate the high frequency characteristics of this epitaxial wafer, the second harmonic characteristics and the third harmonic characteristics were measured.

[0064] The high-frequency characteristics of epitaxial wafers are measured as follows. To measure harmonic characteristics [second-harmonic characteristics (2HD) and third-harmonic characteristics (3HD)], a coplanar waveguide (CPW) is first formed using metal (e.g., aluminum) on a dielectric layer (e.g., an oxide film), and probes are grounded to both ends of this metal electrode. A high-frequency signal is then input to one of the electrodes, and the second-harmonic and third-harmonic signals output from the other side are measured (e.g., input signal frequency: 1 GHz, input power: 15 dBm).

[0065] Specifically, an aluminum electrode with a line length of 2200 μm was formed on a silicon epitaxial film that had been heat-treated for the above-mentioned heat treatment time range, and the second- and third-harmonic characteristics were measured. The measurement results are shown in Figure 4. As shown in Figure 4, for samples that had been heat-treated for 3 hours or more and had an input signal frequency of 1 GHz, the second-harmonic characteristics were all around -50 dBm, and the third-harmonic characteristics were all below -60 dBm.

[0066] This result indicates that in order to manufacture an epitaxial wafer that exhibits excellent harmonic characteristics by forming minute carbon defects at a high density, it is necessary to perform heat treatment at 1000°C for at least 3 hours. Therefore, the heat treatment time is set to 3 hours or more and 36 hours or less. Note that the upper limit is set to 36 hours or less in consideration of productivity, since even if the treatment is performed for an excessively long time, the effect of forming carbon defects does not change. By doing so, sufficiently minute carbon defects are formed, improving quality and resulting in an epitaxial wafer that is excellent in terms of manufacturing efficiency.

[0067] In view of the above, by directly placing the epitaxial wafer in a heat treatment furnace heated to about 1000°C and heat treating it for about 3 to 36 hours, minute carbon defects are formed at a high density in the epitaxial film formed by vapor phase growth under reduced pressure. At this time, the type of gas used in the heat treatment is not particularly limited, and can be, for example, oxygen gas or an inert gas such as argon or nitrogen.

[0068] In this manner, the epitaxial wafer of the present invention can be manufactured. The dielectric layer on the epitaxial film functions as an insulating film, resulting in a wafer that exhibits excellent high-frequency characteristics. Therefore, the epitaxial wafer of the present invention is suitable as a wafer for high-frequency devices.

[0069] According to the method for producing a silicon epitaxial wafer of the present invention, it is possible to easily produce an epitaxial wafer having a high density of minute carbon defects formed in the epitaxial film without using a high-resistivity substrate. The produced epitaxial wafer has superior harmonic reduction capability due to the action of the epitaxial film and the dielectric layer formed thereon, compared to epitaxial wafers in which a polysilicon layer is formed as a trap-rich layer on a conventional high-resistivity substrate. As a result, the epitaxial wafer is suitable as a wafer for high-frequency devices.

[0070] [High Frequency Characteristics] The high frequency characteristics of the epitaxial wafer of the present invention will be described.

[0071] In the epitaxial wafer of the present invention, since a high density of minute carbon defects is formed in the carbon-doped silicon epitaxial film on the silicon substrate by the heat treatment, the trap density of the trap rich layer is increased compared to before the heat treatment, and as a result, the carrier capture ability is improved, so that even if the silicon substrate does not have a high resistivity, it can obtain superior high-frequency characteristics compared to epitaxial wafers in which a polysilicon layer is formed as a trap rich layer on a conventional high-resistivity substrate. Furthermore, the dielectric layer on the carbon-doped silicon epitaxial film improves the insulation properties of the substrate and stabilizes the film quality, thereby obtaining even better high-frequency characteristics.

[0072] In this way, the epitaxial wafer of the present invention can improve the second harmonic characteristics and the third harmonic characteristics, and is suitable as a wafer for high frequency devices.

[0073] EXAMPLES The present invention will be explained in more detail below by showing examples and comparative examples of the present invention, but the present invention is not limited to these.

[0074] Example 1 An epitaxial wafer according to the present invention was manufactured according to the method shown in Figure 2. A carbon-doped silicon epitaxial film (carbon concentration: 2.0 x 10) was formed on a silicon substrate (P-type, resistivity: 10 Ω cm) having a diameter of 300 mm, obtained by slicing an ingot manufactured by the Czochralski method using a low-pressure CVD apparatus, using monomethylsilane as a carbon source gas. １９ ~1.0 x 10 ２０ atoms / cm ３ In this carbon concentration range, void defects are not formed if the film thickness is 0.1 to 1.1 μm. After film formation, the obtained wafer was treated at 1000°C for 2 hours using a pyrogenic oxidation method to form a silicon oxide film of 400 nm. The epitaxial wafer on which the silicon oxide was formed was subjected to a heat treatment in an oxidizing atmosphere at 1000°C for 10 hours, thereby forming a high density of minute carbon defects in the silicon epitaxial film.

[0075] The concentration of the carbon-doped silicon epitaxial film is (1) 2.0 × 10 １９ atoms / cm ３ , (2) 3.0 × 10 １９ atoms / cm ３ , (3) 6.0 × 10 １９ atoms / cm ３ , (4) 1.0 × 10 ２０ atoms / cm ３ There were four types:

[0076] The second harmonic characteristics and the third harmonic characteristics were measured to investigate the high frequency characteristics of the epitaxial wafer produced in Example 1. On the surface of the produced epitaxial wafer, an aluminum electrode with a line length of 2200 μm was formed on the surface of a dielectric layer (silicon oxide, 400 nm) formed on the surface of a silicon epitaxial film (carbon concentration: (1) to (4), film thickness: 1 μm) in which minute carbon defects were formed at a high density, and the high frequency characteristics were measured.

[0077] The measurement results are shown in Figure 5. As shown in Figure 5, the second harmonic characteristics when the input signal frequency was 1 GHz were (1) -55.0 dBm, (2) -47.3 dBm, (3) -52.4 dBm, and (4) -59.5 dBm for the carbon concentrations of the silicon epitaxial film (1) to (4), respectively. The third harmonic characteristics were (1) -85.2 dBm, (2) -87.1 dBm, (3) -91.2 dBm, and (4) -84.1 dBm. These results demonstrate that the epitaxial wafer of Example 1 can significantly reduce harmonics.

[0078] Comparative Example 1 An epitaxial wafer was manufactured using the same method as in Example 1, except that no dielectric layer was formed after the formation of the carbon-doped silicon epitaxial layer. Specifically, the epitaxial wafer obtained using the same method as in Example 1 was subjected to a heat treatment in an oxidizing atmosphere at 1000°C for 12 hours to form a high density of minute carbon defects in the silicon epitaxial film. This was used as the epitaxial wafer of Comparative Example 1.

[0079] The second-harmonic and third-harmonic characteristics of the epitaxial wafer of Comparative Example 1 were measured using the same method as in Example 1, and the results are shown in Figure 5. The oxide film formed on the surface by heat treatment in an oxidizing atmosphere was removed with hydrofluoric acid (hydrofluoric acid), and then an aluminum electrode with a line length of 2200 μm was formed on the surface where no dielectric layer was formed, and the high-frequency characteristics were evaluated. As shown in Figure 5, the second-harmonic characteristics of the wafer were (1) -44.8 dBm, (2) -43.5 dBm, (3) -47.4 dBm, and (4) -52.2 dBm for the carbon concentrations of the silicon epitaxial film (1) to (4), respectively. The third-harmonic characteristics were (1) -60.0 dBm, (2) -61.3 dBm, (3) -63.3 dBm, and (4) -67.4 dBm. From these results, it was found that the second harmonic characteristics and the third harmonic characteristics of Comparative Example 1 were both inferior to those of Example 1.

[0080] From the above results, it was found that the epitaxial wafer of the present invention has improved high frequency characteristics due to the effect of the dielectric layer formed on the carbon-doped silicon epitaxial film.

[0081] Comparative Example 2 Epitaxial wafers were manufactured using the same method as in Example 1 and Comparative Example 1, but differing only in the carbon concentration contained in the carbon-doped silicon epitaxial film. First, a carbon-doped silicon epitaxial film (carbon concentration: 3.0×10) was formed on a silicon substrate (P-type, resistivity: 10 Ω cm) with a diameter of 300 mm, obtained by slicing an ingot manufactured by the Czochralski method using a low-pressure CVD apparatus, using monomethylsilane as a carbon source gas. ２０ ~1.0 x 10 ２１ atoms / cm ３ A carbon-doped silicon epitaxial film (film thickness: 1 μm) was then formed. An epitaxial wafer was then prepared in which a silicon oxide film of 400 nm was formed on the carbon-doped silicon epitaxial film, and an epitaxial wafer without a silicon oxide film formed thereon. These epitaxial wafers were subjected to a heat treatment at 1000°C in an oxidizing atmosphere under conditions adjusted so that the total heat treatment time was 12 hours. This epitaxial wafer was designated as Comparative Example 2. It has been found that within this carbon concentration range, void defects are formed at film thicknesses of 1 μm or more.

[0082] The concentration of the carbon-doped silicon epitaxial film is (1) 3.0 × 10 ２０ atoms / cm ３ , (2) 1.0 × 10 ２１ atoms / cm ３ , and there were two types.

[0083] The second-harmonic characteristics and third-harmonic characteristics of the epitaxial wafer of Comparative Example 2 were measured using the same method as in Example 1, and the results are shown in Figure 5. For epitaxial wafers without a silicon oxide film, the oxide film formed on the surface by heat treatment in an oxidizing atmosphere was removed with hydrofluoric acid (hydrofluoric acid), and then an aluminum electrode with a line length of 2200 μm was formed on the surface without the dielectric layer, and the high-frequency characteristics were evaluated. As shown in Figure 5, when the input signal frequency was 1 GHz, the second-harmonic characteristics (with dielectric layer) of the epitaxial wafer were (1) -29.5 dBm and (2) -28.5 dBm for the carbon concentrations of the silicon epitaxial film (1) and (2), respectively, and the second-harmonic characteristics (without dielectric layer) were (1) -26.7 dBm and (2) -26.0 dBm. The third harmonic characteristics (with dielectric layer) were (1) -49.7 dBm and (2) -64.2 dBm, and the third harmonic characteristics (without dielectric layer) were (1) -58.8 dBm and (2) -61.7 dBm. As a result, both the second harmonic characteristics and the third harmonic characteristics of Comparative Example 2 were inferior to those of Example 1.

[0084] As described above, according to the examples of the present invention, it was possible to easily manufacture an epitaxial wafer having superior high frequency characteristics to conventional epitaxial wafers, without using a high resistivity substrate, and by virtue of the action of the silicon epitaxial film containing a high density of minute carbon defects and the dielectric layer.

[0085] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A silicon single crystal substrate with a resistivity of 10 Ω cm or more and 5000 Ω cm or less is formed with a carbon concentration of 2×10 １９ atoms / cm ３ Above 3 x 10 ２０ atoms / cm ３ a silicon epitaxial film having a thickness of less than 6.6×10 and containing carbon defects, and a dielectric layer in this order; ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) is satisfied.

2. The epitaxial wafer according to claim 1, which is a wafer for use in high frequency devices.

3. The carbon defects have a size of 10 nm or less and a density of 1×10 in the epitaxial film. １０ cm －２ 3. The epitaxial wafer according to claim 1 or 2, characterized in that:

4. A step of preparing a silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less; and forming a carbon layer having a carbon concentration of 2×10 on the silicon single crystal substrate under reduced pressure. １９ atoms / cm ３ Above 3 x 10 ２０ atoms / cm ３ a step of vapor-growing a carbon-doped silicon epitaxial film having a thickness of less than 6.6×10; a step of forming a dielectric layer on the silicon epitaxial film; and a step of heat-treating the silicon single crystal substrate having the dielectric layer formed thereon at a heat treatment temperature of 900° C. to 1100° C. for a heat treatment time of 3 hours to 36 hours to form carbon defects in the silicon epitaxial film, ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) ) ) is formed on a silicon epitaxial film.

5. A method for producing an epitaxial wafer, comprising the steps of: producing an epitaxial wafer by the method for producing an epitaxial wafer according to claim 4; and using the epitaxial wafer as a wafer for a high frequency device.

6. The carbon defects are formed so that the size of the carbon defects is 10 nm or less and the density of the carbon defects in the epitaxial film is 1×10 １０ cm －２ 6. The method for producing an epitaxial wafer according to claim 4 or 5, characterized in that:

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