Manufacturing method of nitride semiconductor wafers, and nitride semiconductor wafers

Abstract

This invention relates to a method for manufacturing a nitride semiconductor wafer, wherein a nitride semiconductor film is formed on a single-crystal silicon substrate. The method is characterized in that the single-crystal silicon substrate used is doped with 5×10⁻⁶ silicon. 14 atoms / cm 3 or more and 5×10 16 atoms / cm A method for manufacturing a single-crystal silicon substrate with a nitrogen concentration of 3 or less includes the following steps: forming the aforementioned nitride semiconductor film on the single-crystal silicon substrate; and irradiating the single-crystal silicon substrate with electron beams to increase its resistivity compared to before irradiation. This provides a method for manufacturing a nitride semiconductor wafer that, for nitride semiconductor wafers obtained by growing a nitride semiconductor film on a single-crystal silicon substrate, prevents the resistivity of the single-crystal silicon substrate, which becomes high-resistivity due to electron beam irradiation, from being restored and reduced by epitaxial growth or other thermal treatment steps.

Description

[Technical Field]

[0001] This invention relates to a nitride semiconductor wafer and a method for manufacturing the same, and more particularly to a method for manufacturing a nitride semiconductor wafer suitable for use in high-frequency devices. [Previous Technology]

[0002] High-frequency devices are being developed to integrate antennas, amplifiers, switches, filters, and other components for miniaturization and cost reduction. Furthermore, with increasing frequency and circuit complexity, the materials used in these devices are becoming increasingly diverse: devices using silicon complementary metal-oxide-semiconductor (SiCMOS), III-V semiconductors, or nitride semiconductors, and filters using piezoelectric elements, etc. Single-crystal silicon substrates with inexpensive and large-diameter wafers are considered suitable as substrates for these devices. [Previous Art Documents] (Patent Documents)

[0003] Patent Document 1: International Publication No. 2005 / 020320 [Summary of the Invention]

[0004] [The problem the invention aims to solve]

[0005] However, in the conventional high-frequency devices described above, characteristic degradation caused by the substrate, losses due to the substrate, and degradation of second and third harmonic characteristics have been observed.

[0006] Here, harmonics refer to higher-order frequency components that are integer multiples of the fundamental frequency. The fundamental frequency is defined as the fundamental wave. A frequency twice the fundamental wave (half the wavelength) is defined as the second harmonic, and a frequency three times the fundamental wave (one-third the wavelength) is defined as the third harmonic. In high-frequency circuits, a substrate with lower harmonics is required to avoid interference caused by harmonics.

[0007] Patent document 1 describes irradiating a wide bandgap bipolar semiconductor (SiC) for power applications with one of gamma rays, electron beams, or charged particle beams in advance to adjust the carrier lifetime to a specified range, thereby improving the switching characteristics, but does not mention the degradation of the second harmonic characteristics.

[0008] Furthermore, the inventors have discovered that by irradiating a single-crystal silicon substrate with electron beams, the resistivity of the substrate can be increased, thereby improving high-frequency characteristics, regardless of the substrate resistivity. However, if annealing or epitaxial growth is performed after electron beam irradiation, the resistivity sometimes reverts to its original state and becomes lower.

[0009] This invention was made to solve the above-mentioned problems, and its object is to provide a method for manufacturing a nitride semiconductor wafer. For nitride semiconductor wafers obtained by growing a nitride semiconductor film on a single-crystal silicon substrate, this method prevents the resistivity of the single-crystal silicon substrate, which has become high-resistivity due to electron beam irradiation, from being restored and reduced by epitaxial growth or other heat treatment steps. [Technical Means for Solving the Problem]

[0010] In order to solve the above problems, the present invention provides a method for manufacturing a nitride semiconductor wafer, wherein a nitride semiconductor film is formed on a single-crystal silicon substrate, wherein the single-crystal silicon substrate is a single-crystal silicon substrate doped with nitrogen at a concentration of 5×10¹⁴ atoms / cm³ or more and 5×10¹⁶ atoms / cm³ or less, and the manufacturing method includes the following steps: forming the aforementioned nitride semiconductor film on the single-crystal silicon substrate; and irradiating the aforementioned single-crystal silicon substrate with electron beams to make the resistivity of the aforementioned single-crystal silicon substrate higher than that before irradiation.

[0011] If such a method of manufacturing nitride semiconductor wafers is used, the single-crystal silicon substrate that has become high resistivity due to irradiation with electron beams can be restored and its resistivity reduced by epitaxial growth or other heat treatment steps.

[0012] Furthermore, it is preferable that, in the step of irradiating the aforementioned electron beams, the irradiation dose of the aforementioned irradiated electron beams is set to be 1×10¹⁴e / cm² or more and 1×10¹⁶e / cm² or less.

[0013] By setting the irradiation amount of electron beams within such a range, a nitride semiconductor wafer can be manufactured, which further improves loss and suppresses the degradation of second harmonic characteristics, and the irradiation time does not become too long, thus achieving efficiency.

[0014] In this invention, the step of irradiating the aforementioned electron beam can be performed before the step of forming the aforementioned nitride semiconductor film.

[0015] The present invention can be performed in such a sequence.

[0016] In this invention, the step of irradiating the aforementioned electron beam can also be performed after the step of forming the aforementioned nitride semiconductor film.

[0017] If this is done, it is possible to avoid the decrease in resistivity due to epitaxial growth.

[0018] Furthermore, the present invention provides a nitride semiconductor wafer, which is obtained by forming a nitride semiconductor film on a single-crystal silicon substrate, wherein the aforementioned single-crystal silicon substrate is doped with nitrogen at a concentration of 5×10¹⁴ atoms / cm³ or more and 5×10¹⁶ atoms / cm³ or less, and is irradiated with electron beams.

[0019] If it is such a nitride semiconductor wafer, then the high resistivity of the single-crystal silicon substrate, which is protected from electron beam irradiation, can be restored and its resistivity reduced by epitaxial growth or other heat treatment steps. [Effects of the Invention]

[0020] As described above, if it is the method for manufacturing nitride semiconductor wafers of the present invention, then in the high-frequency device manufactured by the nitride semiconductor wafer obtained by growing a nitride semiconductor film on a single-crystal silicon substrate, it is possible to prevent the resistivity of the substrate from being restored and reduced due to epitaxial growth or other heat treatment steps. The substrate is irradiated with electron beams to improve the loss and second harmonic characteristics caused by the substrate, thereby making it high resistivity.

Implementation Method

[0022] As described above, it is sought to develop a method for manufacturing a nitride semiconductor wafer, which, for a nitride semiconductor wafer obtained by growing a nitride semiconductor film on a single-crystal silicon substrate, can prevent the resistivity of the single-crystal silicon substrate, which has become high resistivity due to electron beam irradiation, from being restored and reduced by epitaxial growth or other heat treatment steps.

[0023] The inventors have repeatedly and diligently studied the above-mentioned problems and found that by doping the single-crystal silicon substrate with a predetermined concentration of nitrogen in advance, even if the resistivity of the substrate is increased by electron beam irradiation and then subjected to heat treatment, the resistivity will not return to the value before electron beam irradiation, thereby completing the present invention.

[0024] That is, the present invention is a method for manufacturing a nitride semiconductor wafer, wherein a nitride semiconductor film is formed on a single-crystal silicon substrate, wherein the single-crystal silicon substrate is a single-crystal silicon substrate doped with nitrogen at a concentration of 5×10¹⁴ atoms / cm³ or more and 5×10¹⁶ atoms / cm³ or less, and the manufacturing method includes the following steps: forming the aforementioned nitride semiconductor film on the single-crystal silicon substrate; and irradiating the aforementioned single-crystal silicon substrate with electron beams to make the resistivity of the aforementioned single-crystal silicon substrate higher than before irradiation.

[0025] Hereinafter, the present invention will be described in detail, but the present invention is not limited to these descriptions.

[0026] [Method for Manufacturing a Nitride Semiconductor Wafer] The method for manufacturing a nitride semiconductor wafer according to the present invention will be described using Figure 1. Furthermore, the structure of the nitride semiconductor wafer described below is an example and is not limited thereto. Also, the present invention will be described below as an example in which the step of irradiating with electron beams is performed first, followed by the step of forming a nitride semiconductor film. The present invention can also be performed by first forming a nitride semiconductor film and then performing the step of irradiating with electron beams.

[0027] <Monocrystalline Silicon Substrate> First, a monocrystalline silicon substrate is prepared. This monocrystalline silicon substrate is doped with nitrogen at a concentration of 5×10¹⁴ atoms / cm³ or higher and 5×10¹⁶ atoms / cm³ or lower. By setting the nitrogen concentration to 5×10¹⁴ atoms / cm³ or higher, the effect of preventing differential runoff is obtained, thereby preventing the resistivity, which has increased due to electron beam irradiation, from returning to its original value; by setting it to 5×10¹⁶ atoms / cm³ or lower, the decrease in the monocrystalline rate can be suppressed when growing monocrystalline silicon by doping with nitrogen.

[0028] There are no particular limitations on the resistivity of the prepared monocrystalline silicon substrate. For example, a monocrystalline silicon substrate with a high resistivity of 100 Ωcm or higher can be used. There are no particular limitations on the upper limit of the resistivity. For example, it can be set to 10000 Ωcm or lower. Furthermore, a monocrystalline silicon substrate with a typical resistivity of 1 Ωcm or higher but lower than 100 Ωcm, or a monocrystalline silicon substrate with a low resistivity of less than 1 Ωcm, can also be used.

[0029] Furthermore, from the viewpoint of being able to more fully obtain the effects of the present invention, it is preferable to have a single-crystal silicon substrate with higher resistivity, because the resistivity can be increased more significantly when subjected to electron beam irradiation.

[0030] <Step of irradiating with electron beams> Subsequently, by irradiating the above-mentioned single-crystal silicon substrate with electron beams, the resistivity of the single-crystal silicon substrate is increased to be higher than that before irradiation.

[0031] By irradiating with electron beams, it is possible to significantly achieve the effect of deactivating carriers such as dopants and / or impurities derived from the raw materials in a single-crystal silicon substrate. That is, this deactivation is caused by the reaction between point defects and dopants and / or carriers: by irradiating with electron beams, point defects are formed in the single-crystal silicon substrate, and these point defects trap carriers in the single-crystal silicon substrate. Furthermore, it is believed that point defects lead to a decrease in the mobility of dopants and / or carriers, resulting in a change in resistivity. The deactivation of dopants and / or carriers in the single-crystal silicon substrate is considered to result in a higher resistivity of the single-crystal silicon substrate.

[0032] There are no particular limitations on the irradiation conditions of electron beams. For example, irradiation with electron beams at 2 MeV at a level of 1×10¹⁴ e / cm² or higher and 1×10¹⁶ e / cm² or lower is permitted. Preferably, this electron beam irradiation is set at a level of 1×10¹⁵ e / cm² or higher and 1×10¹⁶ e / cm² or lower.

[0033] By irradiating with electron beams of 1×10¹⁴ e / cm² or higher, a nitride semiconductor wafer can be manufactured, which further improves loss and suppresses second harmonic characteristic degradation. Furthermore, by setting it to 1×10¹⁶ e / cm² or lower, the irradiation time does not become too long, thus achieving high efficiency.

[0034] There is no particular limitation on the irradiation energy of the electron beam; for example, electrons with energies of 250 keV or higher can be used. If it is about 250 keV or higher, point defects can be formed more reliably in the single-crystal silicon substrate, and carriers such as dopants and / or impurities from the raw materials in the single-crystal silicon substrate can be deactivated. Furthermore, there is no particular upper limit on the irradiation energy.

[0035] Furthermore, this electron beam irradiation can also be performed after the growth of the nitride semiconductor film described below. If it is performed in this way, the decrease in resistivity due to epitaxial growth can be effectively avoided.

[0036] By performing such electron beam irradiation, the resistivity of the single-crystal silicon substrate can be made higher than that before irradiation.

[0037] <Step of forming a nitride semiconductor film> Subsequently, a nitride semiconductor film is epitaxially grown on a single-crystal silicon substrate. The grown nitride semiconductor film is not particularly limited, as long as it contains at least one nitride semiconductor layer, it can be a single layer or multiple layers.

[0038] For example, when the nitride semiconductor layer forming multiple layers is used as the nitride semiconductor film, as shown in Figure 1, an intermediate layer is formed first. The intermediate layer can form, for example, an AlN layer 2 with a thickness of 150 nm on a single crystal silicon substrate 1, and an AlGaN layer 3 with a thickness of 160 nm on it, and further form an intercalated layer, for example, 40 sets of GaN layers and AlN layers to obtain a superlattice layer (SLs) 4.

[0039] A device layer is then formed. The device layer can form, for example, a GaN layer 5 with a thickness of 800 nm, on which an AlGaN layer 6 with a thickness of 25 nm is formed, and further form, for example, a GaN layer 7 with a thickness of 3 nm.

[0040] Furthermore, the total thickness of the formed nitride semiconductor film can be set to, for example, 0.1 to 20 μm, preferably 0.5 to 10 μm, more preferably 1 to 5 μm, and most preferably 1.8 μm.

[0041] Subsequently, the nitride semiconductor wafer obtained by epitaxial growth can be removed, and electrodes 8 can be formed by photolithography.

[0042] A high-frequency device manufactured from a nitride semiconductor wafer irradiated with electron beams in this manner can be made into a high-frequency device that suppresses the degradation of second harmonic characteristics. Furthermore, since the single-crystal silicon substrate is doped with nitrogen at a concentration of 5×10¹⁴ atoms / cm³ or more and 5×10¹⁶ atoms / cm³ or less, it is possible to prevent the resistivity that has increased due to electron beam irradiation from being restored to its original low resistivity by epitaxial growth or other heat treatment steps.

[0043] [Nitride Semiconductor Wafer] Furthermore, the present invention provides a nitride semiconductor wafer, which is obtained by forming a nitride semiconductor film on a single-crystal silicon substrate, wherein the aforementioned single-crystal silicon substrate is doped with nitrogen at a concentration of 5×10¹⁴ atoms / cm³ or more and 5×10¹⁶ atoms / cm³ or less, and is irradiated with electron beams.

[0044] If it is such a nitride semiconductor wafer, it can prevent the high resistivity of a single-crystal silicon substrate from being irradiated with electron beams, and the resistivity can be restored by epitaxial growth or other heat treatment steps, thus reducing the resistivity. [Example]

[0045] Hereinafter, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited to these examples.

[0046] (Example 1, Comparative Example 1) The following substrates for recovery heat treatment were prepared. Example 1: 471 Ωcm (Czickallski method (N) doping, 5 × 10¹⁴ atoms / cm³) Comparative Example 1: 37 Ωcm (Cz method, non-N doped)

[0047] The substrate for the above-mentioned restoration heat treatment was subjected to electron beam irradiation at 2MeV and 1×10¹⁶e / cm². In an organometallic chemical vapor deposition (MOCVD) furnace, the substrate for the restoration heat treatment after electron beam irradiation was subjected to defect restoration heat treatment at 1200°C for 90 minutes and 100mbar in a hydrogen atmosphere. Then the change in resistivity was confirmed.

[0048] It was confirmed that the N-doped single-crystal substrate (471 Ωcm) obtained according to the CZ method in Example 1 had its resistivity increased to a high resistivity of 20568 Ωcm after electron beam irradiation. Even after subsequent hydrogen thermal treatment, the resistivity did not return to its original value, remaining at a high resistivity of 3041 Ωcm. It was confirmed that the CZ single-crystal substrate (37 Ωcm) in Comparative Example 1 had its resistivity increased to a high resistivity of 1892 Ωcm after electron beam irradiation, but the resistivity returned to near its original value (67 Ωcm) before electron beam irradiation due to subsequent hydrogen thermal treatment.

[0049] (Examples 2, Comparative Examples 2 and 3) The following epitaxial growth substrates were prepared. Example 2: 100 Ωcm (CZ method, N-doped, 5 × 10¹⁴ atoms / cm³) Comparative Example 2: 4344 Ωcm (Floating zone melting method (FZ method), non-N-doped) Comparative Example 3: 13 Ωcm (CZ method, non-N-doped)

[0050] The epitaxial growth substrate was irradiated with electron beams at 2 MeV and 1 × 10¹⁶ e / cm². Epitaxial growth of a 1.8 μm high electron mobility transistor (HEMT) as shown in Figure 1 was then performed on the irradiated substrate in an MOCVD furnace, and the change in resistivity was then confirmed. Figure 2 shows a cross-sectional SEM image of the epitaxially grown substrate.

[0051] It was confirmed that the N-doped single-crystal substrate (100 Ωcm) obtained according to the CZ method in Example 2 had a resistivity of 7942 Ωcm after electron beam irradiation. Even after subsequent 1.8 μm HEMT epitaxy, the resistivity did not return to its original value, but remained at a high resistivity of 3108 Ωcm. It was confirmed that the FZ single-crystal substrate (4344 Ωcm) of Comparative Example 2 and the CZ single-crystal substrate (13 Ωcm) of Comparative Example 3 had high resistivity (202211 Ωcm, 50713 Ωcm) after electron beam irradiation, but after 1.8 μm HEMT epitaxial growth, the resistivity returned to near the original resistivity before electron beam irradiation (4922 Ωcm, 14 Ωcm).

[0052] Furthermore, the present invention is not limited to the above-described embodiments. The above-described embodiments are examples; any invention having a substantially similar structure and performing the same function as the technical concept described in the claims of the present invention is included within the technical scope of the present invention. [Simplified Explanation of the Diagram]

[0021] Figure 1 is a schematic cross-sectional view of an example of the nitride semiconductor wafer manufactured in this invention. Figure 2 is a cross-sectional scanning electron microscope (SEM) photograph of the nitride semiconductor wafer manufactured in the embodiment. [Biomaterial Storage]

[0054] Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None.

Claims

1. A method for manufacturing a nitride semiconductor wafer, comprising forming a nitride semiconductor film on a single-crystal silicon substrate, characterized in that, as the aforementioned single-crystal silicon substrate, a single-crystal silicon substrate doped with nitrogen at a concentration of 5×10¹⁴ atoms / cm³ or more and 5×10¹⁶ atoms / cm³ or less is used, the manufacturing method comprising the steps of: forming the aforementioned nitride semiconductor film on the single-crystal silicon substrate; and irradiating the aforementioned single-crystal silicon substrate with electron beams to increase the resistivity of the aforementioned single-crystal silicon substrate compared to before irradiation; and setting the resistivity of the aforementioned single-crystal silicon substrate before irradiation with electron beams to 471 Ωcm or less.

2. The method for manufacturing a nitride semiconductor wafer as described in claim 1, wherein, In the step of irradiating the aforementioned electron beams, the irradiation dose of the aforementioned electron beams is set to be 1×10¹⁴e / cm² or more and 1×10¹⁶e / cm² or less.

3. A method for manufacturing a nitride semiconductor wafer as described in claim 1 or 2, wherein, The step of irradiating with electron beams is performed before the step of forming the aforementioned nitride semiconductor film.

4. A method for manufacturing a nitride semiconductor wafer as described in claim 1 or 2, wherein, After forming the aforementioned nitride semiconductor film, the step of irradiating with the aforementioned electron beam is performed.

Images