Method for manufacturing semiconductor device

Abstract

The invention provides a manufacturing method of a semiconductor device capable of reducing gate leakage. This method for manufacturing a semiconductor device comprises: a step for forming a dielectric oxide film having a higher relative permittivity than that of silica on a nitride semiconductor layer; forming a dielectric nitrogen oxide film by nitriding the dielectric oxide film; and forming a gate electrode on the dielectric nitrogen oxide film. The step of forming the dielectric nitrogen oxide film includes: disposing a substrate including the nitride semiconductor layer and the dielectric oxide film in a reaction furnace having a catalyst metal therein; pyrolyzing ammonia gas in the reaction furnace, and generating nitrous oxide gas from nitrogen atoms contained in the ammonia gas and oxygen atoms diffused from the dielectric oxide film; and pyrolyzing the nitrous oxide gas to generate nitric oxide gas.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a semiconductor device. Background Art

[0002] Conventionally, in order to increase drain current, a high electron mobility transistor (HEMT) has been proposed, in which a hafnium silicate film having a high relative dielectric constant is used as a gate insulating film.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application No. 2009-506537

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 5-223855

[0007] In recent years, there has been an increasing demand for reduction in gate leakage. Summary of the invention

[0008] An object of the present disclosure is to provide a method for manufacturing a semiconductor device capable of reducing gate leakage.

[0009] The manufacturing method of the semiconductor device disclosed in the present invention has the following steps: forming a dielectric oxide film having a relative dielectric constant higher than that of silicon dioxide on a nitride semiconductor layer; nitriding the dielectric oxide film to form a dielectric nitride oxide film; and forming a gate electrode on the dielectric nitride oxide film. The step of forming the dielectric nitride oxide film has the following steps: arranging a substrate including the nitride semiconductor layer and the dielectric oxide film in a reactor having a catalyst metal inside; pyrolyzing ammonia gas in the reactor to generate nitrous oxide gas from nitrogen atoms contained in the ammonia gas and oxygen atoms diffused from the dielectric oxide film; and pyrolyzing the nitrous oxide gas to generate nitric oxide gas.

[0010] Effects of the Invention

[0011] According to the present disclosure, gate leakage can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a cross-sectional view showing a method for manufacturing a semiconductor device according to an embodiment (Part 1).

[0013] Figure 2 This is a cross-sectional view showing the method for manufacturing a semiconductor device according to the embodiment (part 2).

[0014] Figure 3It is a cross-sectional view showing the method for manufacturing a semiconductor device according to the embodiment (part 3).

[0015] Figure 4 It is a cross-sectional view showing the method for manufacturing a semiconductor device according to an embodiment (Part 4).

[0016] Figure 5 This is a cross-sectional view showing a method for manufacturing a semiconductor device according to an embodiment (Part 5).

[0017] Figure 6 It is a cross-sectional view showing the method for manufacturing a semiconductor device according to an embodiment (the sixth).

[0018] Figure 7 This is a cross-sectional view showing a method for manufacturing a semiconductor device according to an embodiment (part seven).

[0019] Figure 8 It is a cross-sectional view showing a method for manufacturing a semiconductor device according to an embodiment (the eighth one).

[0020] Fig. 9 This is a cross-sectional view showing a reactor for nitriding a dielectric oxide film (part 1).

[0021] Fig.10 This is a cross-sectional view showing a reactor for nitriding a dielectric oxide film (part 2).

[0022] Fig.11 This is a graph showing the relationship between the flow rate of ammonia gas and the degree of nitridation of the dielectric oxide film.

[0023] Description of Reference Numerals

[0024] 1: Semiconductor devices;

[0025] 2: Substrate;

[0026] 9: Raw gas;

[0027] 10: Growth substrate;

[0028] 20: nitride semiconductor layer;

[0029] 21: buffer layer;

[0030] 22: barrier layer;

[0031] 23: spacer layer;

[0032] 24: channel layer;

[0033] 24A: upper surface;

[0034] 25: cap layer;

[0035] 26: channel area;

[0036] 31: dielectric nitride oxide film;

[0037] 31D, 31S, 50D, 50G, 50S: open;

[0038] 39: Dielectric oxide film;

[0039] 40D, 40S: concave part;

[0040] 41D, 41S: regrowth layer;

[0041] 42D: drain electrode;

[0042] 42S: source electrode;

[0043] 50: passivation film;

[0044] 52: gate electrode;

[0045] 100, 200: reaction furnace;

[0046] 110, 210: chamber;

[0047] 111: nozzle;

[0048] 120: heater;

[0049] 130: fixture;

[0050] 131: concave part;

[0051] 140: substrate holder;

[0052] 160: dummy component;

[0053] 220: nozzle;

[0054] 230: Base. DETAILED DESCRIPTION

[0055] [Description of Embodiments of the Present Disclosure]

[0056] First, embodiments of the present disclosure will be described by way of examples.

[0057] [1] A method for manufacturing a semiconductor device according to one embodiment of the present disclosure comprises the following steps: forming a dielectric oxide film having a relative dielectric constant higher than that of silicon dioxide on a nitride semiconductor layer; nitriding the dielectric oxide film to form a dielectric nitride oxide film; and forming a gate electrode on the dielectric nitride oxide film, wherein the step of forming the dielectric nitride oxide film comprises the following steps: disposing a substrate including the nitride semiconductor layer and the dielectric oxide film in a reactor having a catalyst metal therein; pyrolyzing ammonia gas in the reactor to generate nitrous oxide gas from nitrogen atoms contained in the ammonia gas and oxygen atoms diffused from the dielectric oxide film; and pyrolyzing the nitrous oxide gas to generate nitric oxide gas.

[0058] The dielectric nitride oxide film functions as a gate insulating film. The dielectric nitride oxide film has higher insulation and withstand voltage than the dielectric oxide film, and can reduce gate leakage. In addition, a catalyst metal is provided inside the reactor, so ammonia gas can be used as a nitrogen source supplied to the reactor, and nitrous oxide gas and nitric oxide gas may not be supplied to the reactor.

[0059] [2] In [1], the dielectric oxide film may include at least one selected from the group consisting of hafnium, lanthanum, and zirconium. In this case, it is easy to obtain a high relative dielectric constant in the dielectric oxynitride film.

[0060] [3] In [2], the dielectric oxide film may include at least one selected from the group consisting of silicon and aluminum. In this case, it is easy to obtain a high relative dielectric constant in the dielectric oxynitride film.

[0061] [4] In any one of [1] to [3], the surface of the nitride semiconductor layer facing the dielectric oxide film may have nitrogen polarity. In this case, it is easy to achieve low resistance.

[0062] [5] In any one of [1] to [4], the step of forming the dielectric oxynitride film may include a step of setting the temperature in the reaction furnace to 600° C. or higher and 800° C. or lower. In this case, nitridation of the dielectric oxide film can be easily advanced, and crystallization of the dielectric oxynitride film can be suppressed.

[0063] [6] In any one of [1] to [5], in the step of forming the dielectric nitride oxide film, the ammonia gas may be supplied into the reaction furnace at a flow rate of 100 sccm or more. In this case, nitridation of the dielectric oxide film can be easily advanced.

[0064] [7] In any one of [1] to [6], the reaction furnace may include a nozzle to which the ammonia gas is supplied, and the catalyst metal may be located at least on a surface of the nozzle. In this case, the ammonia gas is easily thermally decomposed on the surface of the nozzle.

[0065] [8] In any one of [1] to [7], the reaction furnace may include a substrate holder on which the substrate is placed, and the catalyst metal may be located at least on the surface of the substrate holder. In this case, ammonia gas is easily thermally decomposed on the surface of the substrate holder.

[0066] [9] In any one of [1] to [8], the reaction furnace may include: a substrate holder for placing the substrate; and a fixture for supporting the substrate holder, wherein the catalyst metal is located at least on a surface of the fixture. In this case, ammonia gas is easily thermally decomposed on the surface of the fixture.

[0067]

[10] In any one of [1] to [9], the reaction furnace may include: a substrate holder for mounting the substrate; a fixture for supporting the substrate holder; and a dummy member supported by the fixture, wherein the catalyst metal is located at least on the surface of the dummy member. In this case, ammonia is easily thermally decomposed on the surface of the dummy member.

[0068]

[11] In any one of [1] to

[10] , the reaction furnace may include a chamber having the catalyst metal provided at least on an inner surface thereof. In this case, ammonia gas is easily thermally decomposed on the inner surface of the chamber.

[0069]

[12] In any one of [1] to [6], the reaction furnace may include a shower head to which the ammonia gas is supplied, and the catalyst metal may be located at least on a surface of the shower head. In this case, the ammonia gas is easily thermally decomposed on the surface of the shower head.

[0070]

[13] In any one of [1] to

[12] , in the step of forming the dielectric oxynitride film, nitrogen gas may be supplied into the reaction furnace together with the ammonia gas. In this case, it is possible to suppress the supply of excessive ammonia gas.

[0071]

[14] In

[13] , in the step of forming the dielectric oxynitride film, 95% by volume or more of the gas supplied to the reaction furnace may be occupied by the ammonia gas and the nitrogen gas. In this case, the supply of unnecessary gases such as nitrous oxide gas and nitric oxide gas can be suppressed.

[0072] [Details of the embodiments of the present disclosure]

[0073] The following is a detailed description of the embodiments of the present disclosure, but the present disclosure is not limited thereto. It should be noted that in the present specification and the drawings, for components having substantially the same functional configuration, repeated descriptions are sometimes omitted by marking the same reference numerals. In the present disclosure, "looking down" refers to observing an object from above.

[0074] The embodiment relates to a method for manufacturing a semiconductor device including a GaN-based high electron mobility transistor (HEMT). Figures 1 to 8 It is a cross-sectional view showing a method for manufacturing a semiconductor device according to an embodiment.

[0075] First, if Figure 1 As shown, a nitride semiconductor layer 20 is formed on a growth substrate 10 by metal organic chemical vapor deposition (MOCVD) method, for example. In the formation of the nitride semiconductor layer 20, a buffer layer 21, a barrier layer 22, a spacer layer 23, a channel layer 24 and a cap layer 25 are sequentially formed.

[0076] The growth substrate 10 is, for example, a semi-insulating silicon carbide (SiC) substrate. When the growth substrate 10 is a SiC substrate, the upper surface of the growth substrate 10 is a carbon (C) polar surface. When the surface of the growth substrate 10 is a C polar surface, the nitride semiconductor layer 20 can be crystallized with the nitrogen (N) polar surface as the growth surface.

[0077] The buffer layer 21 is formed on the growth substrate 10. The buffer layer 21 is, for example, an aluminum nitride (AlN) layer. The thickness of the AlN layer is, for example, 5 nm to 100 nm. The buffer layer 21 may also include an AlN layer and a gallium nitride (GaN) layer or an aluminum gallium nitride (AlGaN) layer on the AlN layer.

[0078] The barrier layer 22 is formed on the buffer layer 21. The barrier layer 22 is, for example, an AlGaN layer. The band gap of the barrier layer 22 is larger than the band gap of the channel layer 24. The thickness of the barrier layer 22 is, for example, not less than 5 nm and not more than 50 nm. The composition of the barrier layer 22 is, for example, Al Y Ga 1－Y N (0.15≤Y≤0.55). The conductivity type of the barrier layer 22 is, for example, n-type or non-doped (i-type). An indium aluminum nitride (InAlN) layer or an indium aluminum gallium nitride (InAlGaN) layer may be used instead of the AlGaN layer.

[0079] The spacer layer 23 is formed on the barrier layer 22. The spacer layer 23 is, for example, an AlN layer. The thickness of the spacer layer 23 is, for example, in the range of 0.5 nm to 3.0 nm.

[0080] The channel layer 24 is formed on the spacer layer 23. The channel layer 24 is, for example, a GaN layer. The band gap of the channel layer 24 is smaller than the band gap of the barrier layer 22. The thickness of the channel layer 24 is, for example, greater than 5 nm and less than 30 nm. Strain is generated between the channel layer 24 and the barrier layer 22 and the spacer layer 23 due to the difference in their lattice constants, and the strain induces piezoelectric charge at the interface between the two. As a result, a two-dimensional electron gas (2DEG) is generated near the surface of the channel layer 24 that is opposite to the barrier layer 22, forming a channel region 26. The conductivity type of the channel layer 24 is, for example, n-type or non-doped (i-type).

[0081] The cap layer 25 is formed on the channel layer 24. The cap layer 25 is, for example, an AlGaN layer. The thickness of the cap layer 25 is, for example, not less than 1 nm and not more than 5 nm.

[0082] On the C-polarity surface of the SiC substrate, the buffer layer 21, the barrier layer 22, the spacer layer 23, the channel layer 24, and the cap layer 25 are crystallized and grown with the N-polarity surface as the growth surface. Therefore, the upper surfaces of the buffer layer 21, the barrier layer 22, the spacer layer 23, the channel layer 24, and the cap layer 25 have N-polarity, and the lower surfaces have gallium (Ga) polarity.

[0083] Then, if Figure 2 As shown, a dielectric oxide film 39 is formed on the nitride semiconductor layer 20. The dielectric oxide film 39 can be formed, for example, by an atomic layer deposition (ALD) method. The dielectric oxide film 39 is in contact with the upper surface of the nitride semiconductor layer 20. The relative dielectric constant of the dielectric oxide film 39 is higher than the relative dielectric constant of silicon dioxide (SiO2). The dielectric oxide film 39 is a high dielectric constant film. The dielectric oxide film 39 may also include at least one selected from the group consisting of hafnium (Hf), lanthanum (La), and zirconium (Zr). In addition, the dielectric oxide film 39 may also include at least one selected from the group consisting of silicon (Si) and aluminum (Al). For example, the dielectric oxide film 39 is hafnium silicate (HfSiO X ) film or hafnium aluminate (HfAlO X The thickness of the dielectric oxide film 39 is, for example, not less than 5 nm and not more than 30 nm.

[0084] In this way, the substrate 2 including the growth substrate 10, the nitride semiconductor layer 20, and the dielectric oxide film 39 can be obtained. In the substrate 2, the surface of the nitride semiconductor layer 20 facing the dielectric oxide film 39 has nitrogen polarity.

[0085] Then, if Figure 3As shown, the dielectric oxide film 39 is nitrided to form a dielectric nitride oxide film 31. The relative dielectric constant of the dielectric nitride oxide film 31 is higher than the relative dielectric constant of SiO2. The dielectric nitride oxide film 31 is a high dielectric constant film. The dielectric nitride oxide film 31 may also include at least one selected from the group consisting of Hf, La and Zr. In addition, the dielectric nitride oxide film 31 may also include at least one selected from the group consisting of Si and Al. For example, the dielectric nitride oxide film 31 is a hafnium silicon oxynitride (HfSiON) film or a hafnium aluminum oxynitride (HfAlON) film. The details of the method of nitriding the dielectric oxide film 39 will be described later.

[0086] Then, if Figure 4 As shown, an opening 31S for the source and an opening 31D for the drain are formed in the dielectric nitride oxide film 31, and a recess 40S for the source and a recess 40D for the drain are formed in the nitride semiconductor layer 20. The bottom of the recess 40S and the bottom of the recess 40D are closer to the lower surface of the nitride semiconductor layer 20 than the upper surface 24A of the channel layer 24. That is, the recess 40S and the recess 40D can also be formed to be deeper than the upper surface 24A of the channel layer 24. The bottom of the recess 40S and the bottom of the recess 40D can be located in the channel layer 24, can be located in the spacer layer 23, or can be located in the barrier layer 22.

[0087] The opening 31S, the opening 31D, the recess 40S, and the recess 40D can be formed by, for example, reactive ion etching (RIE) using a mask (not shown). For example, chlorine (Cl)-based gas is used as reactive gas in forming the opening 31S, the opening 31D, the recess 40S, and the recess 40D.

[0088] Then, if Figure 5 As shown, in the recess 40S, a regrown layer 41S is formed on the channel layer 24, the spacer layer 23 or the barrier layer 22, and in the recess 40D, a regrown layer 41D is formed on the channel layer 24, the spacer layer 23 or the barrier layer 22. The regrown layer 41S and the regrown layer 41D are, for example, n-type GaN layers. The regrown layer 41S and the regrown layer 41D contain germanium (Ge) or Si as n-type impurities. The resistance of the regrown layer 41S and the regrown layer 41D is lower than that of the channel layer 24. The regrown layer 41S and the regrown layer 41D can be formed by, for example, a physical vapor deposition (PVD) method such as an evaporation method, a sputtering method, or a molecular beam epitaxy (MBE) method.

[0089] Then, if Figure 6As shown, a passivation film 50 is formed on the dielectric oxynitride film 31, the regrown layer 41S, and the regrown layer 41D. The passivation film 50 covers the dielectric oxynitride film 31, the regrown layer 41S, and the regrown layer 41D. The passivation film 50 is, for example, a silicon nitride (SiN) film. The thickness of the passivation film 50 is, for example, not less than 5 nm and not more than 50 nm.

[0090] Then, if Figure 7 As shown, an opening 50S for the source and an opening 50D for the drain are formed in the passivation film 50. The opening 50S and the opening 50D can be formed by, for example, RIE using a mask (not shown). For example, in forming the opening 50S and the opening 50D, F-based gas is used as a reactive gas.

[0091] Next, a source electrode 42S is formed on the regrown layer 41S in the opening 50S, and a drain electrode 42D is formed on the regrown layer 41D in the opening 50D. The source electrode 42S is in contact with the regrown layer 41S, and the drain electrode 42D is in contact with the regrown layer 41D. The source electrode 42S is in ohmic contact with the regrown layer 41S, and the drain electrode 42D is in ohmic contact with the regrown layer 41D. In forming the source electrode 42S and the drain electrode 42D, first, a metal layer (not shown) constituting the source electrode 42S and the drain electrode 42D is formed. When forming the metal layer, for example, film formation is performed using a growth mask (not shown), and then the growth mask is removed together with the metal layer (not shown) formed on the growth mask, wherein the growth mask has an opening in the region where the metal layer is to be formed. That is, lift-off is performed.

[0092] Then, if Figure 8 As shown, an opening 50G for a gate is formed in the passivation film 50. The opening 50G can be formed, for example, by RIE using a mask (not shown). For example, in the formation of the opening 50G, an F-based gas is used as a reactive gas. When viewed from above, the opening 50G is formed between the opening 50S and the opening 50D. A portion of the dielectric oxynitride film 31 is exposed from the opening 50G.

[0093] Next, a gate electrode 52 is formed on the passivation film 50 so as to be in contact with the dielectric oxynitride film 31 through the opening 50G. When forming the gate electrode 52, for example, a metal layer is formed using a growth mask (not shown), and then the growth mask having an opening formed in a region where the gate electrode 52 is to be formed is removed together with the metal layer (not shown) formed on the growth mask. That is, lift-off is performed.

[0094] In this way, the semiconductor device 1 can be manufactured.

[0095] Next, a method of nitriding the dielectric oxide film 39 will be described. Fig. 91 is a cross-sectional view showing a reaction furnace for nitriding the dielectric oxide film 39 .

[0096] like Fig. 9 As shown, the reaction furnace 100 has a chamber 110, a nozzle 111, a heater 120, a clamp 130, and a substrate holder 140. The reaction furnace 100 is, for example, a low pressure chemical vapor deposition (LPCVD) device.

[0097] A nozzle 111 for supplying a raw material gas 9 is provided in the chamber 110. The raw material gas is, for example, a mixed gas of ammonia (NH3) gas and nitrogen (N2) gas. A heater 120 is provided around the chamber 110 and can heat the inside of the chamber 110. A fixture 130 is provided in the chamber 110. A plurality of recesses 131 for supporting a substrate holder 140 are formed in the fixture 130. The substrate 2 is placed on the substrate holder 140. By supporting a plurality of substrate holders 140 each holding a substrate 2 on the fixture 130, the dielectric oxide film 39 can be nitrided on the plurality of substrates 2 at the same time to form a dielectric nitride oxide film 31.

[0098] In this example, the chamber 110, the jig 130, and the substrate holder 140 are made of quartz, and the nozzle 111 is made of stainless steel. The substrate holder 140 may also be made of silicon. In the thermal decomposition of ammonia, quartz does not function as a catalyst, but stainless steel functions as a catalyst. That is, at least on the surface of the nozzle 111, there is a catalyst metal for the thermal decomposition of ammonia.

[0099] When the dielectric oxide film 39 is nitrided, the temperature in the chamber 110 is set to 600° C. or higher and 800° C. or lower by the heater 120, and a mixed gas of ammonia gas and nitrogen gas is supplied into the chamber 110 by the nozzle 111. The flow rate of the ammonia gas is set to 100 sccm or higher, for example, or 200 sccm or higher. If the flow rate of the ammonia gas is 100 sccm or higher, it is easy to advance the nitridation of the dielectric oxide film 39. In addition, the pressure in the chamber 110 is set to 40 Pa or higher and 120 Pa or lower, for example. The temperature in the chamber 110 can also be set to 650° C. or higher and 750° C. or lower. The temperature in the chamber 110 can be measured by a thermocouple or the like.

[0100] When the ammonia gas contacts the stainless steel nozzle 111, the ammonia gas is pyrolyzed. In addition, oxygen atoms diffuse from the dielectric oxide film 39. As a result, nitrous oxide (N2O) gas is generated from nitrogen atoms contained in the ammonia gas and oxygen atoms diffused from the dielectric oxide film 39. Then, the nitrous oxide is pyrolyzed to generate nitric oxide (NO) gas. Nitric oxide has a strong nitriding ability, and the dielectric oxide film 39 is nitrided to form a dielectric nitride oxide film 31.

[0101] The dielectric oxynitride film 31 functions as a gate insulating film in the semiconductor device 1. The dielectric oxynitride film 31 has higher insulation and withstand voltage than the dielectric oxide film 39, and according to the present embodiment, gate leakage can be reduced.

[0102] Furthermore, since the stainless steel nozzle 111 functions as a catalyst in the thermal decomposition of ammonia gas, ammonia gas may be used as a nitrogen source supplied to the reactor 100 , and nitrous oxide gas and nitric oxide gas may not be supplied to the reactor 100 .

[0103] In the case where nitrous oxide gas is supplied to the reactor 100 and the dielectric oxide film 39 is nitrided by the nitrous oxide gas, oxidation and nitridation proceed simultaneously, so the nitrogen concentration in the dielectric nitride oxide film 31 is likely to be insufficient, or it is difficult to control the characteristics of the dielectric nitride oxide film 31. In addition, there is a fear that the density of the interface state will increase and the mobility of the electrons will decrease. Moreover, the load of the nitrous oxide gas on the environment is large. In addition, it is also considered to supply nitrous oxide gas to the reactor 100 and nitridate the dielectric oxide film 39 by the nitrous oxide gas, but the toxicity of the nitrous oxide gas is high, so the handling becomes complicated.

[0104] In this embodiment, nitrous oxide gas and nitric oxide gas are generated in the reaction furnace 100, but the nitrous oxide gas and nitric oxide gas are not discharged to the outside, so environmental load and toxicity can be ignored. In addition, the dielectric oxide film 39 is nitrided by the nitric oxide gas generated by the pyrolysis of the nitrous oxide gas, so the dielectric oxide film 39 is not easily oxidized, and the characteristics of the dielectric nitride oxide film 31 can be easily controlled.

[0105] When the dielectric oxide film 39 includes at least one selected from the group consisting of hafnium, lanthanum, and zirconium, it is easy to obtain a high relative dielectric constant in the dielectric nitride oxide film 31. Furthermore, when the dielectric oxide film 39 includes at least one selected from the group consisting of silicon and aluminum, it is easy to obtain a high relative dielectric constant in the dielectric nitride oxide film 31.

[0106] Since the surface of the nitride semiconductor layer 20 facing the dielectric oxide film 39 and the surface facing the dielectric oxynitride film 31 after nitridation have N polarity, the distance between the channel region 26 and the source electrode 42S and the drain electrode 42D can be easily shortened, thereby easily achieving low resistance.

[0107] It should be noted that the nozzle 111 does not need to be made of stainless steel as a whole, and stainless steel can be provided on the surface portion for contact with ammonia. In addition, the composition of stainless steel is not particularly limited. The catalyst metal is not limited to stainless steel, and any metal that functions as a catalyst in the thermal decomposition of ammonia can be used. Typical examples of catalyst metals include platinum (Pt), rhodium (Rh), palladium (Pd) and ruthenium (Ru).

[0108] Moreover, the component provided with a catalyst metal is not limited to the nozzle 111. For example, the chamber 110 may be composed of a catalyst metal, or a catalyst metal may be provided on the inner surface of the chamber 110. The substrate holder 140 may be composed of a catalyst metal, or a catalyst metal may be provided on the surface of the substrate holder 140. The fixture 130 may be composed of a catalyst metal, or a catalyst metal may be provided on the surface of the fixture 130. In addition, a dummy component 160 composed of a catalyst metal may be supported on a portion of the recess 131 of the fixture 130 instead of the substrate holder 140. As the dummy component 160, a component provided with a catalyst metal on the surface of a base material such as a silicon substrate may also be used. In any case, ammonia gas is easily thermally decomposed on a surface provided with a catalyst metal.

[0109] The structure of the reactor is not particularly limited, and the reactor may be used Fig.10 The reactor shown is used instead Fig. 9 A reactor 100 is shown. Fig.10 1 is a cross-sectional view showing a reaction furnace for nitriding the dielectric oxide film 39 .

[0110] like Fig.10 As shown, the reaction furnace 200 has a chamber 210, a shower head 220 and a susceptor 230. The reaction furnace 200 is, for example, a MOCVD device.

[0111] A showerhead 220 for supplying a raw material gas 9 is provided in the chamber 210. The raw material gas is, for example, a mixed gas of ammonia gas and nitrogen gas. A susceptor 230 is provided in the chamber 210. A plurality of substrates 2 are placed on the susceptor 230 in a manner opposed to the showerhead 220. The susceptor 230 can heat the inside of the chamber 210. The susceptor 230 can directly heat the substrate 2. By placing a plurality of substrates 2 on the susceptor 230, the dielectric oxide film 39 can be nitrided on the plurality of substrates 2 at the same time to form the dielectric nitride oxide film 31.

[0112] In this example, the shower head 220 is made of stainless steel. Alternatively, silicon carbide (SiC) may be provided on the surface of a carbon base material to form the susceptor 230. In this example, a catalyst metal for thermal decomposition of ammonia is present at least on the surface of the shower head 220.

[0113] When the dielectric oxide film 39 is nitrided, the temperature in the chamber 210 is set to 600° C. or higher and 800° C. or lower through the susceptor 230, and a mixed gas of ammonia gas and nitrogen gas is supplied into the chamber 210 through the shower head 220. The flow rate of ammonia gas is set to 200 sccm or higher, for example, or 20,000 sccm or higher. In addition, the pressure in the chamber 210 is set to 7000 Pa or higher and 40,000 Pa or lower, for example. The temperature in the chamber 210 may also be set to 650° C. or higher and 750° C. or lower. The temperature in the chamber 210 may be measured by a thermocouple or the like.

[0114] When the ammonia gas contacts the stainless steel shower head 220, the ammonia gas is thermally decomposed and oxygen atoms are diffused from the dielectric oxide film 39. As a result, the dielectric oxide film 39 is nitrided and the dielectric nitride oxide film 31 is formed, similarly to the case of using the reaction furnace 100.

[0115] Here, the effect of the catalyst metal is described. Fig.11 This is a graph showing the relationship between the flow rate of ammonia gas and the degree of nitridation of the dielectric oxide film. Fig.11 2 shows the trends of the case where the catalyst metal exists in the reactor and the case where the catalyst metal does not exist.

[0116] like Fig.11 As shown in FIG. 1 , in the absence of a catalyst metal, the greater the flow rate of ammonia, the lower the degree of nitridation. This is because the greater the flow rate of ammonia, the higher the pressure in the chamber, and therefore, according to Le Chatelier's principle, it becomes difficult for ammonia to be pyrolyzed. On the other hand, in the presence of a catalyst metal, the greater the flow rate of ammonia, the greater the degree of nitridation. This is because, although according to Le Chatelier's principle, the greater the flow rate of ammonia, the more difficult it is to pyrolyze ammonia, the pyrolysis of ammonia becomes easier to advance due to the action of the catalyst metal. That is, this is because substantially all of the supplied ammonia is pyrolyzed and used for nitridation of the dielectric oxide film.

[0117] Since such a natural phenomenon exists, according to the present embodiment, ammonia gas is supplied to the reaction furnace to form the dielectric oxynitride film 31 , thereby suppressing gate leakage.

[0118] It should be noted that, when the temperature in the reactor is too high when nitriding the dielectric oxide film 39, the dielectric oxynitride film 31 may be crystallized. In addition, when the temperature in the reactor is too low when nitriding the dielectric oxide film 39, the nitridation of the dielectric oxide film 39 may become difficult to advance. When the temperature in the reactor is 600° C. or higher and 800° C. or lower when nitriding the dielectric oxide film 39, the nitridation of the dielectric oxide film 39 is easily advanced, and the crystallization of the dielectric oxynitride film 31 can be suppressed.

[0119] The polarity of the nitride semiconductor layer is not limited. That is, when the nitride semiconductor layer contains gallium, the surface of the nitride semiconductor layer facing the dielectric oxide film may have gallium polarity.

[0120] The raw material gas supplied to the reactor only needs to contain ammonia and does not need to contain nitrogen, but by containing nitrogen, the supply of excess ammonia can be suppressed. In addition, if more than 95% by volume of the gas supplied to the reactor is occupied by ammonia and nitrogen, it is easy to suppress the supply of unnecessary gases such as nitrous oxide gas and nitric oxide gas. It can also be that more than 97% by volume of the gas supplied to the reactor is occupied by ammonia and nitrogen, or it can be that 100% by volume of the gas supplied to the reactor is occupied by ammonia and nitrogen. The reactor can also be a rapid thermal processing (RTA) furnace.

[0121] Although the embodiments have been described in detail above, the present disclosure is not limited to the specific embodiments, and various modifications and changes can be made within the scope described in the claims.

Claims

1. A method for manufacturing a semiconductor device, comprising the following steps: forming a dielectric oxide film having a relative dielectric constant higher than that of silicon dioxide on the nitride semiconductor layer; nitriding the dielectric oxide film to form a dielectric oxynitride film; and forming a gate electrode on the dielectric oxynitride film, The process of forming the dielectric oxynitride film includes the following steps: placing a substrate including the nitride semiconductor layer and the dielectric oxide film in a reactor having a catalyst metal therein; thermally decompose the ammonia gas in the reaction furnace to generate nitrous oxide gas from nitrogen atoms contained in the ammonia gas and oxygen atoms diffused from the dielectric oxide film; and The nitrous oxide gas is pyrolyzed to generate nitric oxide gas.

2. The method for manufacturing a semiconductor device according to claim 1, wherein: The dielectric oxide film includes at least one selected from the group consisting of hafnium, lanthanum, and zirconium.

3. The method for manufacturing a semiconductor device according to claim 2, wherein: The dielectric oxide film includes at least one selected from the group consisting of silicon and aluminum.

4. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: A surface of the nitride semiconductor layer facing the dielectric oxide film has nitrogen polarity.

5. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: The step of forming the dielectric oxynitride film includes the step of setting the temperature in the reaction furnace to 600° C. or higher and 800° C. or lower.

6. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: In the step of forming the dielectric oxynitride film, the ammonia gas is supplied into the reaction furnace at a flow rate of 100 sccm or more.

7. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: The reaction furnace has a nozzle to which the ammonia gas is supplied, The catalyst metal is located at least on the surface of the nozzle.

8. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: The reaction furnace has a substrate holder on which the substrate is placed. The catalyst metal is located at least on a surface of the substrate holder.

9. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: The reactor has: A substrate holder for mounting the substrate; as well as a fixture supporting the substrate holder, The catalyst metal is located at least on the surface of the jig.

10. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: The reactor has: A substrate holder for mounting the substrate; a fixture supporting the substrate holder; as well as a dummy member, supported by the fixture, The catalyst metal is located at least on the surface of the dummy member.

11. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: The reaction furnace has a chamber in which the catalyst metal is provided at least on an inner surface.

12. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: The reaction furnace has a nozzle to which the ammonia gas is supplied, The catalyst metal is at least located on the surface of the showerhead.

13. The method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein: In the step of forming the dielectric oxynitride film, nitrogen gas is supplied into the reaction furnace together with the ammonia gas.

14. The method for manufacturing a semiconductor device according to claim 13, wherein: In the step of forming the dielectric oxynitride film, 95% by volume or more of the gas supplied into the reaction furnace is occupied by the ammonia gas and the nitrogen gas.

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