Method for manufacturing a group III nitride semiconductor device

Abstract

To provide a method for manufacturing a group III nitride semiconductor element capable of depositing a group III nitride semiconductor with good crystallinity.SOLUTION: A method for manufacturing a group III nitride semiconductor element includes the steps of: preparing a substrate in which a base GaN layer is formed on an Si (111) substrate; growing a first GaN layer having a higher electric resistivity than the base GaN layer on the base GaN layer; and growing a second GaN layer on the first GaN layer. The step of growing the first GaN layer plasmatizes a mixed gas of N2 and H2 and supplies the plasmatized gas to the substrate and supplies an organic metal gas to the substrate without plasmatizing the organic metal gas. The step of growing the second GaN layer plasmatizes N2 and supplies the same to the substrate, supplies the organic metal gas to the substrate without plasmatizing the same, and pulse-grows the second GaN layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technical field of the present specification relates to a method for manufacturing a Group III nitride semiconductor device using plasma. [Background technology]

[0002] In Group III nitride semiconductors, such as GaN, the band gap can be varied from 0.6 eV to 6 eV by changing the composition, and therefore Group III nitride semiconductors are used in light-emitting devices, laser diodes, photodetectors, and other devices that emit light over a wide range of wavelengths, from near infrared to deep ultraviolet.

[0003] Furthermore, Group III nitride semiconductors have high breakdown field strength and high melting points. Therefore, Group III nitride semiconductors are expected to replace GaAs-based semiconductors as materials for high-power, high-frequency, and high-temperature semiconductor devices. Accordingly, research and development of HEMT elements and other devices is being conducted.

[0004] One method for epitaxially growing Group III nitride semiconductors is metalorganic chemical vapor deposition (MOCVD). MOCVD uses large amounts of ammonia gas. This requires the MOCVD furnace to be equipped with an ammonia removal device. The running costs of ammonia are also high. The semiconductor layer is formed by a reaction between the metalorganic gas and ammonia. For this reaction to occur, the substrate temperature must be high. A high substrate temperature makes it difficult to grow a high-quality InGaN layer with a high In concentration. Furthermore, warping is likely to occur due to the difference in thermal expansion between the growth substrate and the semiconductor layer.

[0005] Therefore, the present inventors developed a radical enhanced metal organic chemical vapor deposition (REMOCVD) method in which a plasma of a gas containing nitrogen atoms is generated and supplied to a growth substrate, rather than a plasma of an organometallic gas containing a group III metal (Patent Document 1). The technique of Patent Document 1 allows GaN and other materials to be grown at low temperatures. As a result, stress caused by differences in thermal expansion coefficients can be suppressed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-99866 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-20299 Summary of the Invention [Problem to be solved by the invention]

[0007] However, sapphire substrates and GaN substrates are expensive. Therefore, it is preferable to form a Group III nitride semiconductor film on an inexpensive Si(111) substrate. However, it is not necessarily easy to form a high-quality Group III nitride semiconductor film that exhibits high-performance device characteristics on a Si(111) substrate (Patent Document 2).

[0008] MOCVD and MBE methods are sometimes used to form Group III nitride semiconductor films. A commonly used HEMT structure involves growing high-resistivity GaN on a GaN / Si template grown via a buffer layer, and then growing an AlGaN cladding layer on top of that. In this case, the energy band of the GaN is bent to generate two-dimensional electron gas on the GaN side of the AlGaN / GaN interface. Another HEMT structure involves growing a thin, low-resistivity GaN layer on top of high-resistivity GaN, and then growing an AlGaN cladding layer on top of that.

[0009] However, growing nitride semiconductors using conventional MOCVD methods requires high-temperature growth at 1150°C or higher to activate neutral NH3. This generates stress due to the difference in thermal expansion coefficients between the growth substrate and the semiconductor. This can lead to poor crystallinity in the grown semiconductor. This stress can cause problems such as warping and cracking. Furthermore, conventional MOCVD methods use large amounts of ammonia, resulting in poor productivity.

[0010] The technology of the present specification provides a method for manufacturing a Group III nitride semiconductor device that can form a Group III nitride semiconductor film with excellent crystallinity. [Means for solving the problem]

[0011] A first aspect of the method for manufacturing a Group III nitride semiconductor device includes the steps of preparing a substrate having an underlying GaN layer formed thereon, growing a first GaN layer on the underlying GaN layer, the first GaN layer having a higher electrical resistivity than the underlying GaN layer, and growing a second GaN layer on the first GaN layer. In the step of growing the first GaN layer, a mixed gas of N2 and H2 is turned into plasma and supplied to the substrate, and an organometallic gas is supplied to the substrate without being turned into plasma. In the step of growing the second GaN layer, N2 Gas only is turned into plasma and supplied to the substrate, and an organometallic gas is supplied to the substrate without being turned into plasma, thereby growing a second GaN layer in a pulsed manner.

[0012] This method for manufacturing a Group III nitride semiconductor device involves pulse growth of a second GaN layer on a high-resistivity first GaN layer, resulting in the formation of a nitride semiconductor layer with excellent crystallinity. [Effects of the Invention]

[0013] This specification provides a method for manufacturing a Group III nitride semiconductor device that can form a Group III nitride semiconductor film with excellent crystallinity. [Brief explanation of the drawings]

[0014] [Figure 1] 1A and 1B are diagrams illustrating a structure of a semiconductor wafer according to a first embodiment. [Figure 2] FIG. 1 is a diagram showing a schematic configuration of a manufacturing apparatus according to a first embodiment. [Figure 3] 1 is a timing chart (part 1) showing the relationship between gas supply and the output of a high-frequency potential applied to a shower head electrode by an RF power supply in the first embodiment. [Figure 4] 10 is a timing chart (part 2) showing the relationship between the supply of gas and the output of the high-frequency potential applied to the shower head electrode by the RF power supply in the first embodiment. [Figure 5] 1 is a schematic configuration diagram showing the structure of a HEMT according to a first embodiment. [Figure 6] 1 is a graph showing the semi-insulating properties of GaN. [Figure 7] 1 is a scanning electron microscope photograph showing a cross section of a GaN layer in Example 1. [Figure 8] 1 is a scanning electron microscope photograph showing the surface of the GaN layer of Example 1. [Figure 9] 1 is a graph showing the full width at half maximum of the X-ray diffraction of the GaN layer of Example 1. [Figure 10] 1 is a scanning electron microscope photograph showing a cross section of a GaN layer in Example 2. [Figure 11] 1 is a scanning electron microscope photograph showing the surface of the GaN layer of Example 2. [Figure 12] 10 is a graph showing the full width at half maximum of the X-ray diffraction of the GaN layer of Example 2. [Figure 13] 1 is a scanning electron microscope photograph showing a cross section of a GaN layer of a comparative example. [Figure 14] 1 is a scanning electron microscope photograph showing the surface of a GaN layer of a comparative example. [Figure 15] 10 is a graph showing the full width at half maximum of X-ray diffraction of a GaN layer of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Specific embodiments will be described below with reference to the drawings, taking as an example a method for manufacturing a Group III nitride semiconductor device.

[0016] (First embodiment) 1.Semiconductor wafers FIG. 1 is a diagram showing the structure of a semiconductor wafer Wa1 according to a first embodiment. The semiconductor wafer Wa1 includes a substrate Sa1, a high-resistance nitride layer F1, and a pulse-grown nitride layer F2. The substrate Sa1 is a nitride template substrate or nitride substrate in which a nitride layer is grown on a Si(111) substrate. The high-resistance nitride layer F1 is a nitride layer grown by converting a mixed gas of N2 and H2 into plasma and reacting it with an organometallic gas. The pulse-grown nitride layer F2 is a nitride layer grown by converting only N2 gas into plasma and reacting it with an organometallic gas. Both the high-resistance nitride layer F1 and the pulse-grown nitride layer F2 are, for example, GaN layers. In this way, the semiconductor wafer Wa1 is formed by epitaxially growing a Group III nitride semiconductor on the main surface of the wafer.

[0017] 2. Effects of the semiconductor wafer according to the first embodiment The semiconductor wafer Wa1 of the first embodiment is a template or bulk substrate in which a GaN layer is grown on a Si(111) substrate via a buffer layer. The Si(111) substrate may be one in which a buffer layer and a GaN layer are grown in a growth apparatus. After growing a high-resistivity nitride layer F1 on this Si(111) substrate, a pulse-grown nitride layer F2 is pulse-grown under precise control. This semiconductor has excellent crystallinity.

[0018] 3. Group III nitride semiconductor device manufacturing equipment 2 is a schematic diagram of a manufacturing apparatus 1000 for manufacturing a semiconductor wafer Wa1 according to the first embodiment. The manufacturing apparatus 1000 is used for epitaxially growing a Group III nitride semiconductor. The manufacturing apparatus 1000 is a plasma generating apparatus that generates a plasma generation region inside a chamber. The manufacturing apparatus 1000 supplies an organometallic gas (first gas) containing a Group III metal to the growth substrate without passing it through the plasma generation region, and supplies a gas (second gas) containing nitrogen atoms to the growth substrate after passing it through the plasma generation region.

[0019] The manufacturing apparatus 1000 includes a furnace body 1001, a showerhead electrode 1100, a susceptor 1200, a heater 1210, a first gas supply pipe 1300, a gas introduction chamber 1410, a second gas supply pipe 1420, a metal mesh 1500, an RF power supply 1600, a matching box 1610, a plasma power pulse control unit 1620, a first gas supply unit 1710, a second gas supply unit 1810, gas containers 1910, 1920, and 1930, constant temperature baths 1911, 1921, and 1931, mass flow controllers 1720, 1820, 1830, and 1840, and a pulse valve 1850. The manufacturing apparatus 1000 also includes an exhaust port (not shown).

[0020] The showerhead electrode 1100 is a first electrode to which a periodic potential is applied. The showerhead electrode 1100 is made of, for example, stainless steel. Of course, other metals may also be used. The showerhead electrode 1100 is a flat electrode. The showerhead electrode 1100 has a plurality of through-holes (not shown) that penetrate from the front surface to the back surface. These through-holes communicate with the gas introduction chamber 1410 and the second gas supply pipe 1420. Therefore, the second gas supplied from the gas introduction chamber 1410 to the inside of the furnace body 1001 is suitably converted into plasma.

[0021] The RF power supply 1600 is a potential applying unit that applies a high frequency potential to the shower head electrode 1100. The plasma power pulse control unit 1620 is a device that applies a high frequency pulse to the shower head electrode 1100.

[0022] The susceptor 1200 is a substrate support portion for supporting the substrate Sa1. The material of the susceptor 1200 is, for example, graphite. Alternatively, other conductive materials may be used. Here, the substrate Sa1 is a growth substrate for growing a Group III nitride semiconductor.

[0023] The first gas supply pipe 1300 is used to supply a first gas to the susceptor 1200. In practice, the first gas is supplied to the substrate Sa1 supported by the susceptor 1200. Here, the first gas is an organometallic gas containing a Group III metal. The first gas may also contain other carrier gases. The first gas supply pipe 1300 has a ring-shaped ring portion 1310. The ring portion 1310 of the first gas supply pipe 1300 has 12 through-holes (not shown) formed inside the ring portion 1310. Thus, the first gas supply pipe 1300 has at least one through-hole. These through-holes are ejection ports from which the first gas is ejected. Therefore, the first gas is ejected toward the inside of the ring portion 1310. These through-holes are located between the susceptor 1200 and the metal mesh 1500. Therefore, the first gas supply pipe 1300 is located at a position away from the plasma generation region.

[0024] The second gas supply pipe 1420 is for supplying a second gas to the susceptor 1200. In practice, the second gas is supplied to the space between the showerhead electrode 1100 and the metal mesh 1500, and then supplied to the substrate Sa1 supported by the susceptor 1200. Here, the second gas is a gas containing nitrogen gas. The second gas may be a mixed gas of nitrogen gas and hydrogen gas.

[0025] The gas introduction chamber 1410 is used to temporarily store a mixed gas of nitrogen gas and hydrogen gas, and to supply this mixed gas to the through-holes of the shower head electrode 1100 .

[0026] The metal mesh 1500 is a metal mesh member for capturing charged particles. The metal mesh 1500 is made of, for example, stainless steel. Of course, other metals may also be used. The metal mesh 1500 is disposed between the shower head electrode 1100 and the susceptor 1200. Therefore, as described below, the metal mesh 1500 can prevent charged particles generated in the plasma generation region from moving toward the growth substrate Sa1 supported by the susceptor 1200. The metal mesh 1500 is also disposed between the shower head electrode and the ring portion 1310 of the first gas supply pipe 1300. Therefore, the charged particles can be prevented from colliding with organometallic molecules containing a Group III metal ejected from the ring portion 1310 of the first gas supply pipe 1300. The metal mesh 1500 is formed by overlapping multiple meshes with slight offsets. In other words, the linear portions of the second mesh are disposed at the positions of the openings of the first mesh. Therefore, light traveling in a straight line cannot pass through the metal mesh 1500. In other words, the metal mesh 1500 does not allow electrons, ions, or light to pass through, but allows neutral radicals to pass through.

[0027] The furnace body 1001 accommodates at least the showerhead electrode 1100, the susceptor 1200, the ring portion 1310 of the first gas supply pipe 1300, and the metal mesh 1500. The furnace body 1001 is made of, for example, stainless steel. The furnace body 1001 may be made of a conductive material other than those mentioned above.

[0028] The furnace body 1001, the metal mesh 1500, and the first gas supply pipe 1300 are all conductive members and are grounded. Therefore, when a potential is applied to the showerhead electrode 1100, a voltage is applied between the showerhead electrode 1100 and the furnace body 1001 and the metal mesh 1500. It is believed that a discharge occurs between the showerhead electrode 1100 and at least one of the furnace body 1001 and the metal mesh 1500. A high-frequency, high-intensity electric field is formed directly below the showerhead electrode 1100. Therefore, the position directly below the showerhead electrode 1100 is a plasma generation region.

[0029] The second gas is converted into plasma in the plasma generation region. Plasma products are generated in the plasma generation region. The plasma products in this case include, for example, nitrogen radicals, hydrogen radicals, hydrogen nitride-based compounds, electrons, and other ions. The hydrogen nitride-based compounds include NH, NH2, NH3, and their excited states, as well as other ions.

[0030] The showerhead electrode 1100 and the susceptor 1200 are sufficiently separated from each other. The distance between the showerhead electrode 1100 and the susceptor 1200 is 40 mm or more and 200 mm or less, and more preferably 40 mm or more and 150 mm or less. If the distance between the showerhead electrode 1100 and the susceptor 1200 is short, the plasma generation region may extend to the susceptor 1200. If the distance between the showerhead electrode 1100 and the susceptor 1200 is 40 mm or more, the plasma generation region is unlikely to extend to the susceptor 1200. Therefore, charged particles can be prevented from reaching the substrate Sa1. If the distance between the showerhead electrode 1100 and the susceptor 1200 is large, nitrogen radicals, hydrogen nitride-based compounds, and the like are less likely to reach the substrate Sa1 held by the susceptor 1200. These distances also depend on the size of the plasma generation region and other plasma conditions.

[0031] The showerhead electrode 1100 is positioned farther from the susceptor 1200 than the through-hole of the ring portion 1310 of the first gas supply pipe 1300. The distance between the showerhead electrode 1100 and the through-hole of the ring portion 1310 of the first gas supply pipe 1300 is 30 mm or more and 190 mm or less, and more preferably 30 mm or more and 140 mm or less. This is to prevent charged particles from being mixed into the first gas and to facilitate the arrival of nitrogen radicals, hydrogen nitride-based compounds, and the like at the substrate Sa1. Therefore, a semiconductor layer is deposited on the substrate Sa1 using the second gas in plasma form and the first gas that is not in plasma form. Note that these distances also depend on the size of the plasma generation region and other plasma conditions.

[0032] The heater 1210 heats the substrate Sa1 supported by the susceptor 1200 via the susceptor 1200.

[0033] Mass flow controllers 1720, 1820, 1830, and 1840 are used to control the flow rates of the respective gases. Pulse valve 1850 is used to supply organometallic gas containing a Group III metal in synchronization with the high-frequency potential pulse. Thermostatic chambers 1911, 1921, and 1931 are filled with antifreeze solutions 1912, 1922, and 1932. Gas containers 1910, 1920, and 1930 are used to store organometallic gas containing a Group III metal. Gas containers 1910, 1920, and 1930 contain trimethylgallium, trimethylindium, and trimethylaluminum, respectively. Of course, organometallic gas containing other Group III metals, such as triethylgallium, may also be used.

[0034] The manufacturing apparatus 1000 has an electron gun 1010 and a detector 1020. The electron gun 1010 is for emitting electrons from a solid by heat or an electric field. The detector 1020 is for detecting electrons scattered on the surface of the substrate Sa1. The electron gun 1010 and the detector 1020 constitute a part of an RHEED device.

[0035] 4. Manufacturing conditions of manufacturing equipment The manufacturing conditions for the manufacturing apparatus 1000 are shown in Table 1. The numerical ranges listed in Table 1 are merely guidelines and do not necessarily have to be these numerical ranges. The RF power is in the range of 100 W or more and 1000 W or less. The frequency of the periodic potential applied to the shower head electrode 1100 by the RF power supply 1600 is in the range of 30 MHz or more and 300 MHz or less. The substrate temperature is in the range of 0°C or more and 900°C or less. The internal pressure of the manufacturing apparatus 1000 is in the range of 1 Pa or more and 10,000 Pa or less.

[0036] [Table 1] RF power 100W or more 1000W or less Frequency: 30MHz or more, 300MHz or less Substrate temperature 0℃ or more but 900℃ or less Internal pressure: 1 Pa or more, 10,000 Pa or less

[0037] 5. Gas and pulse voltage The pulse-grown nitride layer F2 is formed by pulse growth. The relationship between the gas supply and the applied voltage will be described. During pulse growth, a first period and a second period are repeated. In the first period, an organometallic gas is supplied, and in the second period, no organometallic gas is supplied.

[0038] 5-1. First pattern 3 is a timing chart (part 1) showing the relationship between the gas supply and the output of the high-frequency potential applied to the shower head electrode by the RF power supply in the first embodiment. The horizontal axis of FIG. 3 represents time. The vertical axis of FIG. 3 represents the flow rate of the source gas or the power of the RF power supply.

[0039] As shown in Figure 3, the manufacturing apparatus 1000 deposits a semiconductor film by alternately repeating a first period T1 and a second period T2. N2 gas flows constantly regardless of time. That is, N2 gas is continuously supplied during the first period T1 and the second period T2. The supply of TMG (trimethylgallium) and RF power are changed at regular intervals.

[0040] During the first period T1, TMG and N2 are supplied, and RF power is on. The flow rate of TMG is SB1, the flow rate of N2 is constant, and the RF power output is W1. That is, during the first period T1, power is supplied to turn N2 gas into plasma. During the second period T2, only N2 is supplied, TMG is not supplied, and the RF power output is W2, which is smaller than W1. This is to prevent nitrogen dissociation. That is, during the second period T2, the power to turn N2 gas into plasma is weaker than the power to turn N2 gas into plasma in the first period T1.

[0041] 5-2. Second pattern 4 is a timing chart (part 2) showing the relationship between the gas supply and the output of the high-frequency potential applied to the shower head electrode by the RF power supply in the first embodiment. The horizontal axis of FIG. 4 represents time. The vertical axis of FIG. 4 represents the flow rate of the source gas or the power of the RF power supply. N2 gas is continuously supplied during the first period T1 and the second period T2.

[0042] During the first period T1, TMG and N2 are supplied, and the RF power is off. During the second period T2, TMG is not supplied, N2 is supplied, and the RF power is on. That is, the flow rate of TMG is 0, the flow rate of N2 is constant, and the RF power output is W1. That is, during the first period T1, no power is supplied to turn the N2 gas into plasma, and during the second period T2, power is supplied to turn the N2 gas into plasma.

[0043] 5-3. Differences in patterns When growing semiconductors at low temperatures, the vapor pressure of the Group III metal decomposed from the metalorganic gas is relatively low. For this reason, the second pattern shown in Figure 4 is preferable for low-temperature growth. In the second pattern, Ga is temporarily deposited on the substrate surface during the first period T1 to form a Ga layer, and then the Ga layer is nitrided during the second period T2.

[0044] When growing semiconductors at high temperatures, the vapor pressure of the Group III metals decomposed from the metalorganic gas is relatively high. For this reason, the first pattern shown in Figure 3 is preferable for high-temperature growth. In the first pattern, it is difficult to temporarily retain Ga on the substrate surface during the first period T1. Therefore, Ga and N are supplied during the first period T1 to form GaN on the substrate surface.

[0045] 5-4.Effects of pulse growth During the first period T1 of the first pattern, nitrogen radicals reach the substrate Sa1, causing the growth of a semiconductor. During the second period T2, the nitrogen radicals do not reach the substrate Sa1, causing the growth of a semiconductor. Furthermore, during the second period T2, impurities such as carbon are released from the semiconductor, causing the grown film to become flat. During the first period T1 of the second pattern, TMG becomes Ga on the surface, causing the carbon to be released. During the second period T2 of the second pattern, this Ga reacts with the nitrogen radicals, causing the growth of a low-carbon semiconductor.

[0046] 6. Semiconductor wafer manufacturing method In the method for manufacturing a semiconductor wafer according to this embodiment, a semiconductor layer is grown by a radical enhanced metal organic chemical vapor deposition (REMOCVD) method. That is, a group III nitride semiconductor is epitaxially grown on the primary surface of the substrate Sa1 using the manufacturing apparatus 1000 according to the first embodiment.

[0047] 6-1. Cleaning the board Here, a method for manufacturing a semiconductor wafer using the manufacturing apparatus 1000 of the first embodiment will be described. First, a substrate Sa1 is prepared, which is a substrate having an underlying GaN layer formed on a Si(111) substrate. The substrate Sa1 is placed on a susceptor 1200 inside the manufacturing apparatus 1000, and the substrate temperature is raised to approximately 900°C while supplying hydrogen gas. This reduces the surface of the substrate Sa1 and cleans the surface of the substrate Sa1. The substrate temperature may be raised to a higher temperature. Alternatively, the hydrogen gas may be turned into plasma.

[0048] 6-2. High-resistance nitride layer formation process A high-resistivity nitride layer F1 (first GaN layer) is formed on the underlying GaN layer of the substrate Sa1. In this high-resistivity nitride layer formation process, the first gas supply pipe 1300 supplies a first gas to the susceptor 1200. A mixed gas of N2 and H2 is supplied from the second gas supply pipe 1420. The RF power supply 1600 is also continuously turned on to grow a GaN film of the required thickness. That is, the mixed gas of N2 and H2 is plasma-converted and supplied to the substrate Sa1, and an organometallic gas is supplied to the substrate Sa1 without being plasma-converted. The ratio of N2 to H2 is determined based on the device configuration. The flow rate of H2 in the mixed gas is, for example, between 10% and 60%. In this process, carbon easily penetrates into the semiconductor, becoming a deep acceptor. As a result, the high-resistivity nitride layer F1 has high resistance.

[0049] 6-3. Pulse-grown nitride layer formation process Next, a pulse-grown nitride layer F2 (second GaN layer) is formed on the high-resistance nitride layer F1 (first GaN layer). As shown in FIG. 3 or 4, the semiconductor layer is pulse-grown. During this process, the first gas supply pipe 1300 supplies a first gas to the susceptor 1200. N2 gas is supplied from the second gas supply pipe 1420, but H2 gas is not. In this process, only N2 gas is converted into plasma, and H2 gas is not converted into plasma. Therefore, in the pulse-grown nitride layer formation process, nitrogen radicals reach the substrate surface, but hydrogen radicals do not. Thus, N2 is converted into plasma and supplied to the substrate Sa1, and an organometallic gas is supplied to the substrate Sa1 without being converted into plasma, thereby pulse-growing the second GaN layer. In the process of growing the second GaN layer, the temperature of the heater for heating the substrate is preferably set to 200°C or higher and lower than 600°C. In the step of growing the second GaN layer, the temperature of the heating unit that heats the substrate may be set to 600°C or higher and 1150°C or lower.

[0050] 7. Semiconductor elements Fig. 5 is a schematic diagram showing the structure of a HEMT according to the first embodiment. The HEMT in Fig. 5 includes a Si(111) substrate, a buffer layer, an i-GaN layer (high-resistance nitride layer), a GaN active layer (pulse-grown nitride layer), and an i-AlGaN layer. The carbon concentration of the i-GaN layer (high-resistance nitride layer) is higher than that of the GaN active layer (pulse-grown nitride layer). Two-dimensional electron gas is generated in the pulse-grown nitride layer. The crystallinity of the pulse-grown nitride layer F2 is excellent.

[0051] 8. Effects of the First Embodiment In the method for manufacturing a Group III nitride semiconductor device according to the first embodiment, a Group III nitride semiconductor with excellent crystal quality can be grown by pulse growth, because pulse growth favorably removes carbon atoms from the semiconductor layer and improves flatness.

[0052] Figure 6 is a graph showing the semi-insulating properties of GaN. When the concentration of shallow donors is between that of deep and shallow acceptors, the Fermi level is pinned between the energy bands, resulting in semi-insulating GaN and an immeasurably high resistivity.

[0053] 9. Variations 9-1. Period during which plasma is generated in the plasma generation region As shown in Figure 3, when the metal-organic gas is stopped, plasma is generated in the plasma generation region. This is to prevent the grown nitride from decomposing when the metal-organic gas is stopped. However, it is not necessary to generate plasma when the metal-organic gas is stopped.

[0054] 9-2. Nitrogen gas flow period 3 and 4, nitrogen gas is continuously flowed while TMA is flowing and while it is stopped, but it may be flowed intermittently as needed. That is, nitrogen gas does not need to be flowed while the metalorganic gas is stopped in FIG. 3, or while the metalorganic gas is flowing in FIG. 4.

[0055] 9-3. Pulse-grown nitride layer formation process In the pulse-grown nitride layer formation step, the film may be formed at the atomic layer level by pulse growth, which improves the crystallinity of the pulse-grown nitride layer F2 but increases the film formation time.

[0056] 9-4. Length of the First and Second Periods The lengths of the first period T1 and the second period T2 can be selected appropriately depending on the device configuration, growth conditions, etc. The crystallinity can be determined based on the detection results by RHEED, or by the flatness, crystallinity, and impurity concentration of the grown film.

[0057] 9-5. Combinations The above modifications may be freely combined.

[0058] Example 1 1. First step This experiment was carried out using the manufacturing apparatus 1000 shown in Fig. 2. The internal pressure of the manufacturing apparatus 1000 was 300 Pa. A bulk GaN substrate measuring 10 mm square and 300 µm thick was used as the growth substrate.

[0059] The bulk GaN substrate was heated to 800°C while flowing N2 / H2 gas at 750 sccm / 250 sccm, and was heat-treated for 10 minutes without plasma power (cleaning step).

[0060] Thereafter, a GaN film was continuously formed under the following conditions.

[0061] TMG temperature +5℃ H2 carrier gas 20sccm Growth temperature 800℃ Plasma power 600W Furnace pressure 300Pa N2 / H2 gas flow rate 1500sccm / 1500sccm Growth time: 10 minutes

[0062] The thickness of the grown GaN was 1.3 μm.

[0063] 2. Second process Next, pulse growth was carried out in the manufacturing apparatus 1000 shown in FIG. 2 under the following conditions.

[0064] Furnace pressure 150Pa TMG temperature +5℃ H2 carrier gas 20sccm Plasma power P1 600W P2 300W N2 gas flow rate 1500sccm Growth time 120 minutes

[0065] The pulse growth time was set to 5 seconds for the first period T1 and 10 seconds for the second period T2.

[0066] 3.SEM FIG. 7 is a scanning electron microscope photograph showing the cross section of the GaN layer of Example 1. FIG. 8 is a scanning electron microscope photograph showing the surface of the GaN layer of Example 1. As shown in FIG. 8, the surface of the GaN layer is relatively flat. The film thickness of the pulse-grown GaN was 1.4 μm. The surface of the pulse-grown GaN is flat. The growth rate of the pulse-grown GaN was as high as 0.7 μm / hr.

[0067] 4.XRD Fig. 9 is a graph showing the half-width of the X-ray diffraction of the GaN layer of Example 1. As shown in Fig. 9, the half-width of the X-ray diffraction of the GaN layer of Example 1 was 345 arcsec.

[0068] Example 2 1. First step In this experiment, the manufacturing apparatus 1000 shown in Fig. 2 was used. A Mo electrode was used as the plasma electrode. The internal pressure of the manufacturing apparatus 1000 was 100 Pa. A bulk GaN substrate measuring 10 mm square and 300 µm thick was used as the growth substrate.

[0069] The bulk GaN substrate was heated to 800°C while flowing N2 / H2 gas at 750 sccm / 250 sccm, and was heat-treated for 10 minutes without plasma power (cleaning step).

[0070] Thereafter, a GaN film was continuously formed under the following conditions.

[0071] TMG temperature 0℃ H2 carrier gas 5sccm Growth temperature 800℃ Plasma power 150W N2 / H2 gas flow rate 750sccm / 250sccm Growth time 60 minutes

[0072] 2. Second process Next, pulse growth was carried out in the manufacturing apparatus 1000 shown in FIG. 2 under the following conditions.

[0073] Furnace pressure: 85Pa TMG temperature 0℃ H2 carrier gas 5sccm Plasma power P1 150W P2 150W N2 gas flow rate 750sccm Growth time 180 minutes

[0074] The pulse growth time was 180 minutes. The first period T1 was 10 seconds, and the second period T2 was 10 seconds. The plasma power P1 was 150W, and P2 was 150W.

[0075] 3.SEM Figure 10 is a scanning electron microscope photograph showing the cross section of the GaN layer of Example 2. Figure 11 is a scanning electron microscope photograph showing the surface of the GaN layer of Example 2. As shown in Figure 11, the surface of the GaN layer is relatively flat. The thickness of the GaN grown in the first step was 0.1 μm. When using a Mo electrode, arcing occurred, making it impossible to use high plasma power. The thickness of the GaN grown in the second step was 0.72 μm. The surface of this GaN layer was flat. Because the plasma power was low, the growth rate was 0.36 μm / hr.

[0076] 4.XRD Fig. 12 is a graph showing the half-width of the X-ray diffraction of the GaN layer of Example 2. As shown in Fig. 12, the half-width of the X-ray diffraction of the GaN layer of Example 2 was 169 arcsec.

[0077] (Comparative Example 1) 1. First step This experiment was carried out using the manufacturing apparatus 1000 shown in Fig. 2. The internal pressure of the manufacturing apparatus 1000 was 300 Pa. A GaN template on a Si (111) substrate measuring 10 mm square and 625 µm thick was used as the growth substrate.

[0078] The bulk GaN substrate was heated to 800°C while flowing N2 / H2 gas at 750 sccm / 250 sccm, and was heat-treated for 10 minutes without plasma power (cleaning step).

[0079] Thereafter, a GaN film was continuously formed under the following conditions.

[0080] Growth temperature 800℃ Furnace pressure 300Pa TMG temperature +5℃ N2 carrier gas 20sccm Plasma power 600W N2 / H2 gas flow rate 1500sccm / 1500sccm Growth time 20 minutes

[0081] The thickness of the grown GaN was 0.6 μm.

[0082] 2. Second process Next, pulse growth was carried out in the manufacturing apparatus 1000 shown in FIG. 2 under the following conditions.

[0083] Furnace pressure 300Pa TMG temperature +5℃ H2 carrier gas 20sccm Plasma power P1 600W P2 400W N2 / H2 gas flow rate 1500sccm / 1500sccm Growth time 120 minutes

[0084] The pulse growth time was set to 5 seconds for the first period T1 and 10 seconds for the second period T2.

[0085] The surface morphology of the pulse-grown GaN was considerably worse than that of Examples 1 and 2, and the growth rate was also extremely slow. This is thought to be due to the etching effect of H radicals when hydrogen is introduced during pulse growth.

[0086] 3.SEM FIG. 13 is a scanning electron microscope photograph showing the cross section of the GaN layer of the comparative example. FIG. 14 is a scanning electron microscope photograph showing the surface of the GaN layer of the comparative example. As shown in FIG. 14, the surface of the GaN layer has minute irregularities and is not flat. The thickness of the GaN layer in the first step was 0.6 μm. The thickness of the GaN layer in the second step was 0.7 μm. The growth rate of the pulse-grown GaN layer was slower than that of the pulse-grown GaN layer in Example 1.

[0087] 4.XRD Fig. 15 is a graph showing the half-width of the X-ray diffraction of the GaN layer of the comparative example. As shown in Fig. 15, the half-width of the X-ray diffraction of the GaN layer of the comparative example was 954 arcsec.

[0088] (Addendum) A first aspect of the present invention relates to a method for manufacturing a Group III nitride semiconductor device, which includes the steps of: preparing a substrate having an underlying GaN layer; growing a first GaN layer on the underlying GaN layer, the first GaN layer having a higher electrical resistivity than the underlying GaN layer; and growing a second GaN layer on the first GaN layer. In the step of growing the first GaN layer, a mixed gas of N2 and H2 is turned into plasma and supplied to the substrate, and an organometallic gas is supplied to the substrate without being turned into plasma. In the step of growing the second GaN layer, N2 is turned into plasma and supplied to the substrate, and an organometallic gas is supplied to the substrate without being turned into plasma, thereby pulse-growing the second GaN layer.

[0089] In the method for manufacturing a Group III nitride semiconductor device according to the second aspect, in the step of growing the second GaN layer, a first period and a second period are repeated, and an organometallic gas is supplied in the first period, and is not supplied in the second period.

[0090] In the method for manufacturing a Group III nitride semiconductor device according to the third aspect, in the step of growing the second GaN layer, power is supplied for generating plasma from N2 gas during the first period.

[0091] In a fourth aspect of the method for manufacturing a Group III nitride semiconductor device, in the step of growing a second GaN layer, N2 gas is continuously supplied during a first period and a second period. During the first period, power is supplied to turn the N2 gas into plasma. During the second period, the power to turn the N2 gas into plasma is made weaker than the power to turn the N2 gas into plasma during the first period.

[0092] In the method for manufacturing a Group III nitride semiconductor device according to the fifth aspect, in the step of growing the second GaN layer, N gas is continuously supplied during the first period and the second period, power for turning the N gas into plasma is not supplied during the first period, and power for turning the N gas into plasma is supplied during the second period.

[0093] In the method for manufacturing a Group III nitride semiconductor device according to the sixth aspect, the temperature of the heating unit that heats the substrate is set to 200°C or higher and lower than 600°C in the step of growing the second GaN layer.

[0094] In the method for manufacturing a Group III nitride semiconductor device according to the seventh aspect, the temperature of the heating unit that heats the substrate is set to 600°C or higher and 1150°C or lower in the step of growing the second GaN layer. [Explanation of symbols]

[0095] 1000…Manufacturing equipment 1001...furnace body 1010...Electron gun 1020: Detector 1100...Shower head electrode 1200...Susceptor 1210…heater 1300...First gas supply pipe 1410...Gas introduction chamber 1420...Second gas supply pipe 1500...Metal mesh 1600...RF power supply 1610…Matching box

Claims

1. preparing a substrate on which an underlying GaN layer is formed; growing a first GaN layer on the underlying GaN layer, the first GaN layer having a higher electrical resistivity than the underlying GaN layer; growing a second GaN layer on the first GaN layer; and In the step of growing the first GaN layer, N ２ and H ２ a mixed gas of the above and the above-mentioned metalorganic gas is supplied to the substrate without being turned into plasma; In the step of growing the second GaN layer, N ２ The second GaN layer is pulse-grown by supplying only the gas to the substrate in a plasma state and supplying the metalorganic gas to the substrate without plasma-grown it. A method for manufacturing a Group III nitride semiconductor device, comprising:

2. preparing a substrate on which an underlying GaN layer is formed; growing a first GaN layer on the underlying GaN layer, the first GaN layer having a higher electrical resistivity than the underlying GaN layer; growing a second GaN layer on the first GaN layer; and In the step of growing the first GaN layer, N ２ and H ２ a mixed gas of the above and the above-mentioned metalorganic gas is supplied to the substrate without being turned into plasma; In the step of growing the second GaN layer, repeating the first period and the second period to pulse-grow the second GaN layer; In the first period, power for generating plasma is not supplied. ２ supplying a gas to the substrate, and supplying the metal-organic gas to the substrate without converting it into plasma; In the second period, power is supplied to generate plasma. ２ A gas is plasmatized and supplied to the substrate, while the metalorganic gas is not supplied to the substrate; During the first period and the second period, ２ Continue to supply gas A method for manufacturing a Group III nitride semiconductor device, comprising:

3. 2. The method for manufacturing a Group III nitride semiconductor device according to claim 1, In the step of growing the second GaN layer, Repeating the first period and the second period, During the first period, the metal-organic gas is supplied; During the second period, the metal-organic gas is not supplied. A method for manufacturing a Group III nitride semiconductor device, comprising:

4. 4. The method for manufacturing a Group III nitride semiconductor device according to claim 3, In the step of growing the second GaN layer, In the first period, the N ２ Supplying power to turn gas into plasma A method for manufacturing a Group III nitride semiconductor device, comprising:

5. 5. The method for manufacturing a Group III nitride semiconductor device according to claim 4, In the step of growing the second GaN layer, During the first period and the second period, ２ Continue to supply gas In the first period, the N ２ It supplies electricity to turn the gas into plasma, In the second period, the N ２ The power for turning the gas into plasma is set to be weaker than the power for turning the N2 gas into plasma in the first period. A method for manufacturing a Group III nitride semiconductor device, comprising:

6. 4. The method for manufacturing a Group III nitride semiconductor device according to claim 3, In the step of growing the second GaN layer, During the first period and the second period, ２ Continue to supply gas In the first period, the N ２ No power is supplied to turn the gas into plasma. In the second period, the N ２ Supplying power to turn gas into plasma A method for manufacturing a Group III nitride semiconductor device, comprising:

7. 7. The method for manufacturing a Group III nitride semiconductor device according to claim 1, In the step of growing the second GaN layer, The temperature of the heating unit for heating the substrate is set to 200°C or higher and lower than 600°C. A method for manufacturing a Group III nitride semiconductor device, comprising:

8. 7. The method for manufacturing a Group III nitride semiconductor device according to claim 1, In the step of growing the second GaN layer, The temperature of the heating unit for heating the substrate is set to 600° C. or more and 1150° C. or less. A method for manufacturing a Group III nitride semiconductor device, comprising:

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