Epitaxial wafer and method for manufacturing the same

Abstract

To provide a silicon epitaxial wafer for high frequency integrated circuit substrate, capable of forming a silicon epitaxial film on a silicon substrate having a usual resistivity, excellent in capability of reducing a higher harmonic wave and easy in a processing process, and a method for manufacturing the same.SOLUTION: An epitaxial wafer having a carbon concentration of 2×1019 atoms / cm3 or more and less than 3×1020 atoms / cm3 includes a silicon epitaxial film including carbon defects and a dielectric layer in this order on a silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less. The thickness of the silicon epitaxial film satisfies 6.6×1020×exp{-1.6×[the thickness (μm) of the epitaxial film]}>[the carbon concentration (atoms / cm3) of the epitaxial film].SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, the demand for large-capacity communications has been extremely high, and the development of devices applicable to the fifth and sixth generation mobile communications systems (commonly known as 5G and 6G) ​​has accelerated. 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 are required to have a high degree of operational stability in 5G and 6G environments. In particular, because these large-capacity communications systems are scheduled 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 need to have high substrate resistivity in order to achieve low resistance loss and good high-frequency characteristics.

[0004] Furthermore, in applications requiring better high-frequency characteristics, wafers with a trap-rich layer formed thereon as described in Patent Document 1 and Patent Document 2 are often used. This is because, when a high-frequency signal is input to a device formed on a high-resistivity substrate, a phenomenon is known in which 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 a deep level of the trap-rich layer. In particular, for passive elements, wafers with a polysilicon layer formed as a trap-rich layer on a high-resistivity substrate are used. On the other hand, SOI wafers with 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 production of high resistivity substrates, which are widely used as substrates for high frequency integrated circuits, is technically difficult to control the resistivity, resulting in low yields. In addition, the polysilicon used as the trap rich layer is difficult to process, leading to poor productivity, and the SOI structure using polysilicon as the trap rich layer has a complex manufacturing process and significant cost issues. Therefore, there has been a demand for the development of technology that does not use high resistivity substrates, but instead shows excellent high frequency characteristics in epitaxial wafers, in which a silicon epitaxial film is formed on a silicon single crystal substrate (hereinafter simply referred to as "silicon substrate"), and in particular reduces harmonics.

[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 for image sensors, and there is no description of performing heat treatment after the formation of the epitaxial film, so that no trap rich layer is formed in the epitaxial film.

[0007] In addition, an epitaxial wafer in which a wafer having a carbon-doped epitaxial film formed on a silicon substrate is subjected to a heat treatment is described in Patent Document 5. However, there is no mention of its use 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 silicon epitaxial film containing a high concentration of carbon was developed with the aim of using it as a gettering layer, and the heat treatment is aimed at driving gettering. Therefore, the heat treatment conditions are described as being in the range of 450 to 750°C for about 30 minutes. Although heat treatment at 800 to 1000°C is also mentioned in order to drive gettering in a shorter time, 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 mentioned above, it is difficult to use the wafers disclosed in Patent Documents 3, 4, and 5 as wafers for high frequency devices. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Special Publication No. 2015-503853 [Patent Document 2] JP 2019-129195 A [Patent Document 3] JP 2009-164590 A [Patent Document 4] JP 2009-200231 A [Patent Document 5] JP 2006-216934 A Summary of the Invention [Problem to be solved by the invention]

[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 a high frequency integrated circuit. The inventors of the present invention have conducted extensive research aimed at developing a material that meets such demands, and have found that an epitaxial wafer obtained by subjecting an epitaxial wafer in which a silicon epitaxial film containing a high concentration of carbon is formed on a substrate with normal resistivity to a heat treatment is promising. This makes it possible to provide a substrate for a high frequency integrated circuit 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 at 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 superior high frequency characteristics.

[0013] The present invention has been made in consideration 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 having a silicon epitaxial film formed on a silicon substrate having normal resistivity, has an excellent ability to reduce harmonics, and is easy to process, and a method for manufacturing the same. [Means for solving the problem]

[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 More than 3×10 20 atoms / cm 3 a silicon epitaxial film having a thickness of less than 6.6×10 20 ×exp{-1.6×[thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm 3The present invention provides an epitaxial wafer which satisfies the above condition (1).

[0015] In such an epitaxial wafer, the dielectric layer on the silicon epitaxial film having the above carbon concentration improves the insulation of the substrate, and the film quality of the epitaxial wafer is stabilized at a high level. Furthermore, minute carbon defects can be included 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 epitaxial wafer has improved insulation of the substrate due to the dielectric layer on the silicon epitaxial film having the above carbon concentration, and the film quality of the epitaxial wafer is stable at a high level. Furthermore, the epitaxial wafer can contain minute carbon defects in the silicon epitaxial film, which acts to provide the epitaxial wafer with 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 10 cm -2 The above may be possible.

[0019] A material having such carbon defects has excellent high frequency characteristics due to the effect of the silicon epitaxial film containing minute carbon defects at a high density.

[0020] The present invention also relates to 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 More than 3×10 20 atoms / cm 3a 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, 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, which is characterized by forming a silicon epitaxial film that satisfies the above-mentioned condition (1).

[0021] Such a method for producing 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 produce an epitaxial wafer exhibiting the above-mentioned excellent high frequency characteristics.

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

[0023] The dielectric layer on the silicon epitaxial film having the above carbon concentration improves the insulation of the substrate, and the epitaxial wafer has a high and stable film quality. Furthermore, minute carbon defects can be formed in the silicon epitaxial film at a high density, 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 10 cm -2 The above may be possible.

[0025] It is possible to manufacture an epitaxial wafer having a silicon epitaxial film that contains such minute carbon defects at a high density and has superior high frequency characteristics. Effect of the Invention

[0026] As described above, the silicon epitaxial wafer of the present invention does not need to be 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 a conventional epitaxial wafer in which a polysilicon layer is formed as a trap rich layer on a high resistivity substrate, and is suitable as a wafer for high frequency devices. Also, according to the method for producing the epitaxial wafer of the present invention, it is possible to easily produce an epitaxial wafer exhibiting the above-mentioned superior harmonic reduction capability. [Brief description of the drawings]

[0027] [Figure 1] 1 is a schematic diagram showing an epitaxial wafer of the present invention. [Diagram 2] FIG. 2 is a flow diagram showing an example of a method for producing an epitaxial wafer according to the present invention. [Diagram 3] 1 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 a silicon substrate in an epitaxial wafer of the present invention. [Figure 4] 13 is a plot showing changes in second harmonic and third harmonic characteristics of an epitaxial wafer when heat treatment is performed on the epitaxial wafer with different heat treatment times in Experimental Example 2. [Diagram 5] 1 is a graph showing the relationship between the second harmonic characteristics and the third harmonic characteristics of epitaxial wafers and the carbon concentration in Example 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 costly communications equipment has created a demand for inexpensive epitaxial wafers that can further improve high-frequency characteristics, in particular by reducing harmonics.

[0030] As a result of intensive research into the above-mentioned problem, the inventors have discovered that a carbon concentration of 2×10 19 atoms / cm 3 More than 3×10 20 atoms / cm 3 a silicon epitaxial film having 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 inventors have found that an epitaxial wafer characterized by satisfying the above condition (1) above and (2) above, which has an excellent harmonic reduction capability due to the action of a dielectric layer provided on a silicon epitaxial film containing minute carbon defects, has been provided with an excellent harmonic reduction capability, and have completed the present invention.

[0031] The present inventors 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 depositing a carbon-containing gas having a carbon concentration of 2×10 19 atoms / cm 3 More than 3×10 20 atoms / cm 3a 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, 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 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 is characterized by forming a silicon epitaxial film that satisfies the above-mentioned requirement (1). Thus, the present invention has been completed.

[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 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 has good high frequency characteristics and allows resistivity control in single crystal production.

[0034] The silicon epitaxial film 3 has a typical carbon solid solubility of 3 × 10 17 atoms / cm 3 (the maximum solid solubility of carbon at the melting point of silicon) is much higher than 2×10 19 atoms / cm 3 More than 3×10 20 atoms / cm 3It contains carbon at a concentration of less than 1000 nm and contains minute carbon defects. It also does not contain void defects.

[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 It is preferable that the above is the case (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 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 manufacturing method of the epitaxial wafer described later.

[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 the silicon epitaxial film 3 from becoming rough due to heat treatment, thereby stabilizing the film quality at a high level.

[0038] Furthermore, by carrying out 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 acts to provide excellent high frequency characteristics. This is thought to be because minute carbon defects are formed in the silicon epitaxial film by the heat treatment, which form deep levels, enhancing the function of the film as a trap rich layer and inhibiting the formation of an inversion layer.

[0039] Such an epitaxial wafer has 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 it an ideal substrate for use as a wafer for high frequency devices or 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 More than 3×10 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 3 In the above cases, when the film thickness exceeds a certain value, void defects are formed, and if these coexist with minute carbon defects inside the film, the high frequency characteristics improve 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 effect 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 less than 3×10 20 atoms / cm 3 Above this concentration, the film quality of the carbon-doped silicon epitaxial film 3 deteriorates, and the 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, the high frequency characteristics are stable and excellent. 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, sufficient high-frequency characteristics can be obtained 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, the formation of void defects can be suppressed by reducing the thickness of the silicon epitaxial film 3, thereby reducing the amount of vacancies generated inside the film. For this reason, 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 / cm 3 ) must be satisfied.

[0042] (Experimental Example 1) The following describes the results of an experiment evaluating the relationship between the carbon concentration and the thickness of a carbon-doped silicon epitaxial film formed on a silicon substrate, which does not cause void defects in the epitaxial film.

[0043] The inventors used a low-pressure CVD apparatus to 19 atoms / cm 3 Silicon epitaxial film containing more than 2.0×10 carbon and varying 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 The samples had film thicknesses of 1 μm, 2 μm, and 3 μm, and carbon concentrations of 3.0×10 20 atoms / cm 3 and 1.0×1021 In the sample, a silicon epitaxial film (thickness: 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 epitaxial wafers obtained 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 specimens (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 3 In the above samples, the film thickness was 1 μm, and it was found that 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 for forming void defects 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] FIG. 3 shows the results of the presence or absence of void defect regions shown in Experimental Example 1, organized according to the carbon concentration contained in the silicon epitaxial film and the film thickness of the silicon epitaxial film. 3 is a graph showing the carbon concentration and film thickness conditions of the 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. The region in which a void defect region is 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. In other words, the white area in the figure is the region in which no void defect region is formed in the silicon epitaxial film. This is because, in the relationship between the carbon concentration 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 as a range that satisfies the above.

[0048] Such a silicon epitaxial wafer of the present invention does not need to be 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 a conventional epitaxial wafer in which a polysilicon layer is formed as a trap rich layer on a high resistivity substrate, making it suitable as a wafer for high frequency devices.

[0049] [Epitaxial wafer manufacturing method] An example of a method for producing an epitaxial wafer according to the present invention is shown in Fig. 2. This method is a method for producing 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 with a resistivity of 10 to 5000 Ω·cm is prepared.

[0051] (Step of vapor-depositing a carbon-doped silicon epitaxial film) Next, a gas containing silicon atoms and carbon atoms was supplied onto the silicon substrate under reduced pressure, and 2×10 19 atoms / cm 3 More than 3×10 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 In this method, a carbon-doped silicon epitaxial film (hereinafter, simply referred to as "epitaxial film") that satisfies the above condition is vapor-grown. Then, a dielectric layer is formed on the epitaxial film. Next, the epitaxial wafer with the dielectric layer formed on the epitaxial film is heat-treated, thereby forming a high density of minute carbon defects in the epitaxial film.

[0052] By performing the vapor phase growth of the epitaxial film under reduced pressure, the concentration of impurities other than carbon doped in 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, 5 Torr (about 0.67 kPa) to 20 Torr (about 2.7 kPa).

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

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

[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 to 2.5 μm, but is not limited to 6.6×10 20 ×exp{-1.6×[thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm 3 The above relationship between the carbon concentration and the film thickness of the epitaxial film is not limited to this, so long as it satisfies the above-mentioned range. Void defects are not 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. With such a method, the dielectric layer can 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 a lower cost.

[0058] The deposition temperature of 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 as a method for forming a general 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 deposition process of the dielectric layer formed on the epitaxial film such that minute carbon defects are sufficiently formed inside the epitaxial film, the heat treatment after deposition of the dielectric layer can be omitted.

[0059] (Step of forming carbon defects) The method of heat treatment of an epitaxial wafer having a dielectric layer 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 the dielectric layer can be used.

[0060] The lower limit of the heat treatment temperature in the heat treatment is 900° C. or more, and the upper limit is 1100° C. or less. In this way, minute carbon defects can be formed at a high density using a general heat treatment furnace, and the effects 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. By doing so, sufficiently small carbon defects are formed, improving the quality and resulting in an epitaxial wafer that is excellent from the viewpoint of manufacturing efficiency.

[0062] Here, the results of the investigation into the heat treatment time in the heat treatment will be explained in the following Experimental Example 2.

[0063] (Experimental Example 2) The heat treatment time required to form minute carbon defects at a high density was determined by the following experiment. To investigate the heat treatment time required for the manufacture of epitaxial wafers with 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 a heat treatment in an oxygen atmosphere at 1000°C for a heat treatment time varying from 15 minutes to 12 hours. In order to investigate the high frequency characteristics of the epitaxial wafer, the second harmonic characteristics and the third harmonic characteristics were measured.

[0064] The high frequency characteristics of the epitaxial wafer are measured as follows. To measure harmonic characteristics [second harmonic characteristics (2HD) and third harmonic characteristics (3HD)], first, a co-planar waveguide (CPW) is formed using metal (e.g., aluminum) on a dielectric layer (e.g., oxide film), and probes are grounded to both ends of this metal electrode. After that, a high-frequency signal is input from one of the electrodes, and the second and third harmonics 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 range of heat treatment times, and the second and third harmonic characteristics were measured. The measurement results are shown in Figure 4. As shown in Figure 4, when the input signal frequency of the samples that had been heat-treated for 3 hours or more was 1 GHz, the second harmonic characteristics were all around -50 dBm, and the third harmonic characteristics were all below -60 dBm.

[0066] This result shows that in order to manufacture epitaxial wafers that exhibit excellent harmonic characteristics by forming minute carbon defects at a high density, heat treatment at 1000°C must be performed for at least 3 hours. Therefore, the heat treatment time is set to 3 hours or more and 36 hours or less. 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 period of time, there is no change in the effect of forming carbon defects. By doing so, sufficiently small 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, the epitaxial wafer is directly placed in a heat treatment furnace heated to about 1000°C and heat-treated for about 3 to 36 hours, whereby 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 during 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 in which minute carbon defects are formed at a high density in the epitaxial film without using a high resistivity substrate. The produced epitaxial wafer has a superior harmonic reduction capability due to the action of the epitaxial film and the dielectric layer formed thereon, compared to a conventional epitaxial wafer in which a polysilicon layer is formed as a trap rich layer on a 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 now be described.

[0071] In the epitaxial wafer of the present invention, minute carbon defects are formed at a high density in the carbon-doped silicon epitaxial film on the silicon substrate by heat treatment, so that 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 is possible to 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 of the substrate and stabilizes the film quality, so that more superior high frequency characteristics can be obtained.

[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. EXAMPLES

[0073] The present invention will be described in more detail below with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

[0074] Example 1 The epitaxial wafer of the present invention was manufactured according to FIG. 2. A carbon-doped silicon epitaxial film (carbon concentration: 2.0×10) 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. 19 ~1.0×10 20 atoms / cm 3 In this carbon concentration range, if the film thickness is 0.1 to 1.1 μm, no void defects are formed. After film formation, the obtained wafer was treated at 1000°C for 2 hours using pyrogenic oxidation to form a silicon oxide film of 400 nm. The epitaxial wafer on which the silicon oxide was formed was then heat-treated in an oxidizing atmosphere at 1000°C for 10 hours, 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 The four types were:

[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 above measurement results are shown in Figure 5. As shown in Figure 5, when the input signal frequency was 1 GHz, the second harmonic characteristics 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. This result shows that the epitaxial wafer of Example 1 can significantly reduce harmonics.

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

[0079] The second harmonic characteristics and third harmonic characteristics of the epitaxial wafer of Comparative Example 1 were measured in the same manner as in Example 1, and the results are shown in Fig. 5. At this time, the oxide film formed on the surface by the 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 on which the dielectric layer was not formed, and the high frequency characteristics were evaluated. As shown in FIG. 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 when the carbon concentrations of the silicon epitaxial film were (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 Comparative Example 1 was inferior to Example 1 in both the second harmonic characteristics and the third harmonic characteristics.

[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 the manufacturing method of the epitaxial wafers of Example 1 and Comparative Example 1, with only the carbon concentration contained in the carbon-doped silicon epitaxial film being different. First, a carbon-doped silicon epitaxial film (carbon concentration: 3.0×10) was formed using monomethylsilane as a carbon source gas 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. 20 ~1.0×10 21 atoms / cm 3 Then, an epitaxial wafer 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 were prepared. 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 was used as the epitaxial wafer in Comparative Example 2. It has been found that in this carbon concentration range, void defects are formed when the film thickness is 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 in the same manner as in Example 1, and the results are shown in Fig. 5. For the epitaxial wafer not having 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 not having the dielectric layer, and the high frequency characteristics were evaluated. As shown in FIG. 5, when the input signal frequency was 1 GHz, the second harmonic characteristics of the epitaxial wafer (with dielectric layer) 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. Moreover, 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, 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 is 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 embodiment. The above-described embodiment is merely an example, 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 in the technical scope of the present invention. [Explanation of symbols]

[0086] 1... epitaxial wafer, 2... silicon substrate, 3...silicon epitaxial film containing carbon defects, 4...dielectric layer.

Claims

1. A silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less is provided 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 100 nm and containing carbon defects, and a dielectric layer, in this order; The thickness of the silicon epitaxial film is 6.6×10 ２０ × exp{−1.6 × [thickness of epitaxial film (μm)]}>[carbon concentration of epitaxial film (atoms / cm ３ ) is satisfied.

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

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

4. preparing a silicon single crystal substrate having a resistivity of 10 Ω cm or more and 5000 Ω cm or less; The silicon single crystal substrate is then heated under reduced pressure until the carbon concentration reaches 2×10 １９ atoms / cm ３ Above 3 x 10 ２０ atoms / cm ３ vapor depositing a carbon-doped silicon epitaxial film having an average thickness of less than 100 nm; forming a dielectric layer on the silicon epitaxial film; and forming carbon defects in the silicon epitaxial film by subjecting the silicon single crystal substrate on which the dielectric layer is formed to a heat treatment temperature of 900° C. or more and 1100° C. or less for a heat treatment time of 3 hours or more and 36 hours or less, In the step of growing the silicon epitaxial film in a vapor phase, the thickness of the silicon epitaxial film is 6.6×10 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. 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 set to have a size of 10 nm or less and a density of 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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