Method for manufacturing semiconductor device

Abstract

To provide a semiconductor device and a method for manufacturing the semiconductor device capable of reducing gate leakage.SOLUTION: A method for manufacturing a semiconductor device comprises: a step for forming a dielectric oxide film with a higher relative permittivity than silicon dioxide on a nitride semiconductor layer; a step for nitriding the dielectric oxide film to form a dielectric oxynitride film; and a step for forming a gate electrode on the dielectric oxynitride film; and the step for forming the dielectric oxynitride film comprises: a step for placing a substrate containing the nitride semiconductor layer and the dielectric oxide film in a reactor equipped with a catalytic metal inside; a step for thermally decomposing ammonia gas in the reactor to produce dinitrogen monoxide gas from nitrogen atoms contained in the ammonia gas and oxygen atoms diffused from the dielectric oxide film; and a step for thermally decomposing dinitrogen monoxide gas to produce nitrogen monoxide gas.SELECTED DRAWING: Figure 9

Description

[Technical field]

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

[0002] 2. Description of the Related Art Conventionally, high electron mobility transistors (HEMTs) have been proposed in which a hafnium silicate film having a high relative dielectric constant is used as a gate insulating film in order to improve drain current. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2009-506537 [Patent Document 2] Japanese Patent Application Publication No. 5-223855 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been an increasing demand for reducing gate leakage.

[0005] An object of the present disclosure is to provide a method for manufacturing a semiconductor device capable of reducing gate leakage. [Means for solving the problem]

[0006] A method for manufacturing a semiconductor device according to the present disclosure includes the steps of forming a dielectric oxide film having a higher dielectric constant than silicon dioxide on a nitride semiconductor layer, nitriding the dielectric oxide film to form a dielectric oxynitride film, and forming a gate electrode on the dielectric oxynitride film, and the step of forming the dielectric oxynitride film includes the steps of placing a substrate including the nitride semiconductor layer and the dielectric oxide film in a reactor having a catalytic metal therein, thermally decomposing 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 thermally decomposing the nitrous oxide gas to generate nitric oxide gas. Effect of the Invention

[0007] According to the present disclosure, gate leakage can be reduced. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view (part 1) showing a method for manufacturing a semiconductor device according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view (part 2) showing the method for manufacturing the semiconductor device according to the embodiment. [Diagram 3] FIG. 3 is a cross-sectional view (part 3) showing the method for manufacturing the semiconductor device according to the embodiment. [Figure 4] FIG. 4 is a cross-sectional view (part 4) showing the method for manufacturing the semiconductor device according to the embodiment. [Diagram 5] FIG. 5 is a cross-sectional view (part 5) showing the method for manufacturing the semiconductor device according to the embodiment. [Figure 6] FIG. 6 is a cross-sectional view (part 6) showing the method for manufacturing a semiconductor device according to the embodiment. [Figure 7] FIG. 7 is a cross-sectional view (part 7) showing the method for manufacturing a semiconductor device according to the embodiment. [Figure 8] FIG. 8 is a cross-sectional view (part 8) showing the method for manufacturing the semiconductor device according to the embodiment. [Figure 9]FIG. 9 is a cross-sectional view (part 1) showing a reactor used for nitriding a dielectric oxide film. [Figure 10] FIG. 10 is a cross-sectional view (part 2) showing a reactor used for nitriding a dielectric oxide film. [Figure 11] FIG. 11 is a diagram showing the relationship between the flow rate of ammonia gas and the degree of nitridation of a dielectric oxide film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described.

[0010] [1] A method for manufacturing a semiconductor device according to one aspect of the present disclosure includes the steps of forming a dielectric oxide film having a higher dielectric constant than silicon dioxide on a nitride semiconductor layer, nitriding the dielectric oxide film to form a dielectric oxynitride film, and forming a gate electrode on the dielectric oxynitride film, wherein the step of forming the dielectric oxynitride film includes the steps of placing a substrate including the nitride semiconductor layer and the dielectric oxide film in a reactor having a catalytic metal therein, thermally decomposing 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 thermally decomposing the nitrous oxide gas to generate nitric oxide gas.

[0011] The dielectric oxynitride film functions as a gate insulating film. The dielectric oxynitride film has higher insulating properties and withstand voltage than the dielectric oxide film, and can reduce gate leakage. In addition, since a catalytic metal is provided inside the reactor, ammonia gas can be used as the nitrogen source to be supplied to the reactor, and it is not necessary to supply nitrous oxide gas and nitric oxide gas to the reactor.

[0012] [2] In the above [1], the dielectric oxide film may contain at least one selected from the group consisting of hafnium, lanthanum, and zirconium. In this case, a high relative dielectric constant can be easily obtained in the dielectric oxynitride film.

[0013] [3] In the above [2], the dielectric oxide film may contain at least one selected from the group consisting of silicon and aluminum. In this case, a high relative dielectric constant can be easily obtained in the dielectric oxynitride film.

[0014] [4] In any one of [1] to [3], the surface of the nitride semiconductor layer facing the dielectric oxide film may have a nitrogen polarity. In this case, low resistance can be easily achieved.

[0015] [5] In any one of [1] to [4], in the step of forming the dielectric oxynitride film, the temperature in the reaction furnace may be set to 600° C. or more and 800° C. or less. In this case, nitridation of the dielectric oxide film can be easily promoted and crystallization of the dielectric oxynitride film can be suppressed.

[0016] [6] In any one of [1] to [5], in the step of forming the dielectric oxynitride 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 is easily promoted.

[0017] [7] In any one of [1] to [6], the reactor may have a nozzle through which the ammonia gas is supplied, and the catalytic metal may be present at least on a surface of the nozzle. In this case, the ammonia gas is easily thermally decomposed on the surface of the nozzle.

[0018] [8] In any one of [1] to [7], the reactor may have a substrate holder on which the substrate is placed, and the catalytic metal may be present at least on a surface of the substrate holder. In this case, ammonia gas is likely to be thermally decomposed on the surface of the substrate holder.

[0019] [9] In any one of [1] to [8], the reactor may have a substrate holder on which the substrate is placed and a jig for supporting the substrate holder, and the catalytic metal may be present at least on a surface of the jig. In this case, ammonia gas is likely to be thermally decomposed on the surface of the jig.

[0020]

[10] In any one of [1] to [9], the reactor may have a substrate holder on which the substrate is placed, a jig for supporting the substrate holder, and a dummy member supported by the jig, and the catalytic metal may be present at least on a surface of the dummy member. In this case, ammonia is easily thermally decomposed on the surface of the dummy member.

[0021]

[11] In any one of [1] to

[10] , the reactor may have a chamber having at least an inner surface provided with the catalytic metal. In this case, ammonia gas is likely to be thermally decomposed on the inner surface of the chamber.

[0022]

[12] In any one of [1] to [6], the reactor may have a showerhead to which the ammonia gas is supplied, and the catalytic metal may be present at least on a surface of the showerhead. In this case, the ammonia gas is easily thermally decomposed on the surface of the showerhead.

[0023]

[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, the supply of excessive ammonia gas can be suppressed.

[0024]

[14] In the method of

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

[0025] [Details of the embodiment of the present disclosure] Hereinafter, the embodiments of the present disclosure will be described in detail, but the present disclosure is not limited thereto. In this specification and drawings, components having substantially the same functional configurations may be denoted by the same reference numerals to avoid redundant description. In this disclosure, "planar view" refers to viewing an object from above.

[0026] The embodiment relates to a method for manufacturing a semiconductor device including a GaN-based high electron mobility transistor (HEMT). Figures 1 to 8 are cross-sectional views showing a method for manufacturing a semiconductor device according to the embodiment.

[0027] 1, a nitride semiconductor layer 20 is formed on a growth substrate 10 by, for example, metal organic chemical vapor deposition (MOCVD). In forming 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 formed in this order.

[0028] 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) polarity surface. When the surface of the growth substrate 10 is a C polarity surface, the nitride semiconductor layer 20 can grow as a crystal with a nitrogen (N) polarity surface as the growth surface.

[0029] 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, not less than 5 nm and not more than 100 nm. The buffer layer 21 may include an AlN layer and a gallium nitride (GaN) layer or an aluminum gallium nitride (AlGaN) layer on the AlN layer.

[0030] 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, 5 nm to 50 nm. The composition of the barrier layer 22 is, for example, Al Y Ga 1-YN (0.15≦Y≦0.55). The conductivity type of the barrier layer 22 is, for example, n-type or undoped (i-type). Instead of the AlGaN layer, an indium aluminum nitride (InAlN) layer or an indium aluminum gallium nitride (InAlGaN) layer may be used.

[0031] 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.

[0032] 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, 5 nm to 30 nm. Distortion occurs between the channel layer 24 and the barrier layer 22 and the spacer layer 23 due to the difference in lattice constants thereof, and this distortion induces a piezoelectric charge at the interface between the two layers. As a result, a two dimensional electron gas (2DEG) is generated in the channel layer 24 near the surface facing the barrier layer 22, and a channel region 26 is formed. The conductivity type of the channel layer 24 is, for example, n-type or undoped (i-type).

[0033] 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.

[0034] 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 grow as crystals with the N-polarity surface as the growth surface. Therefore, the upper surface of each of the buffer layer 21, the barrier layer 22, the spacer layer 23, the channel layer 24, and the cap layer 25 has N-polarity, and the lower surface of each has gallium (Ga)-polarity.

[0035] 2, a dielectric oxide film 39 is formed on the nitride semiconductor layer 20. The dielectric oxide film 39 can be formed by, for example, atomic layer deposition (ALD). The dielectric oxide film 39 contacts the upper surface of the nitride semiconductor layer 20. The dielectric constant of the dielectric oxide film 39 is equal to that of silicon dioxide (SiO 2 ). The dielectric oxide film 39 is a high dielectric constant film. The dielectric oxide film 39 may contain at least one selected from the group consisting of hafnium (Hf), lanthanum (La) and zirconium (Zr). The dielectric oxide film 39 may also contain 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 ) membrane 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.

[0036] In this manner, the substrate 2 is obtained, which includes the growth substrate 10, the nitride semiconductor layer 20, and the dielectric oxide film 39. In the substrate 2, the surface of the nitride semiconductor layer 20 facing the dielectric oxide film 39 has nitrogen polarity.

[0037] 3, the dielectric oxide film 39 is nitrided to form the dielectric oxynitride film 31. The dielectric constant of the dielectric oxynitride film 31 is SiO 2 The dielectric oxynitride film 31 is a high dielectric constant film. The dielectric oxynitride film 31 may contain at least one selected from the group consisting of Hf, La, and Zr. The dielectric oxynitride film 31 may also contain at least one selected from the group consisting of Si and Al. For example, the dielectric oxynitride film 31 is a hafnium silicon oxynitride (HfSiON) film or a hafnium aluminum oxynitride (HfAlON) film. A method for nitriding the dielectric oxide film 39 will be described later in detail.

[0038] 4, an opening 31S for a source and an opening 31D for a drain are formed in the dielectric oxynitride film 31, and a recess 40S for a source and a recess 40D for a drain are formed in the nitride semiconductor layer 20. The bottom of the recess 40S and the bottom of the recess 40D may be 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 may be formed deeper than the upper surface 24A of the channel layer 24. The bottom of the recess 40S and the bottom of the recess 40D may be in the channel layer 24, the spacer layer 23, or the barrier layer 22.

[0039] 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, a chlorine (Cl)-based gas is used as a reactive gas in forming the opening 31S, the opening 31D, the recess 40S, and the recess 40D.

[0040] Next, as shown in FIG. 5, a regrown layer 41S is formed on the channel layer 24, the spacer layer 23, or the barrier layer 22 in the recess 40S, and a regrown layer 41D is formed on the channel layer 24, the spacer layer 23, or the barrier layer 22 in the recess 40D. 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 an n-type impurity. The electric resistance of the regrown layer 41S and the regrown layer 41D is lower than the electric resistance 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.

[0041] 6, 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, 5 nm or more and 50 nm or less.

[0042] 7, an opening 50S for a source and an opening 50D for a drain are formed in the passivation film 50. The openings 50S and 50D can be formed by, for example, RIE using a mask (not shown). For example, an F-based gas is used as a reactive gas in forming the openings 50S and 50D.

[0043] 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 contacts the regrown layer 41S, and the drain electrode 42D contacts the regrown layer 41D. The source electrode 42S makes ohmic contact with the regrown layer 41S, and the drain electrode 42D makes 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, a film is formed using a growth mask (not shown) having an opening formed in the region where the metal layer is to be formed, and then the growth mask is removed together with the metal layer (not shown) formed thereon. In other words, lift-off is performed.

[0044] 8, an opening 50G for a gate is formed in the passivation film 50. The opening 50G can be formed by, for example, RIE using a mask (not shown). For example, an F-based gas is used as a reactive gas in forming the opening 50G. In a plan view, the opening 50G is formed between the opening 50S and the opening 50D. A part of the dielectric oxynitride film 31 is exposed from the opening 50G.

[0045] Next, a gate electrode 52 that contacts the dielectric oxynitride film 31 through the opening 50G is formed on the passivation film 50. When forming the gate electrode 52, for example, a metal layer is formed using a growth mask (not shown) having an opening formed in the region where the gate electrode 52 is to be formed, and then the growth mask is removed together with the metal layer (not shown) formed thereon. In other words, lift-off is performed.

[0046] In this manner, the semiconductor device 1 can be manufactured.

[0047] Next, a method for nitriding the dielectric oxide film 39 will be described.

[0048] 9, the reactor 100 includes a chamber 110, a nozzle 111, a heater 120, a jig 130, and a substrate holder 140. The reactor 100 is, for example, a low pressure chemical vapor deposition (LPCVD) device.

[0049] A nozzle 111 for supplying a source gas 9 is provided in a chamber 110. The source gas is, for example, ammonia (NH 3 ) gas and nitrogen (N 2 ) gas. Heater 120 is provided around chamber 110 and can heat the inside of chamber 110. Jig 130 is provided inside chamber 110. Jig 130 has a plurality of recesses 131 formed therein for supporting substrate holders 140. Substrate 2 is placed on substrate holder 140. By having jig 130 support a plurality of substrate holders 140, each with substrate 2 placed thereon, it is possible to nitride dielectric oxide films 39 on a plurality of substrates 2 simultaneously, thereby forming dielectric oxynitride films 31.

[0050] 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 be made of silicon. In the thermal decomposition of ammonia, quartz does not function as a catalyst, but stainless steel does. That is, at least the surface of the nozzle 111 has a catalytic metal for the thermal decomposition of ammonia.

[0051] When nitriding the dielectric oxide film 39, the temperature in the chamber 110 is set to 600° C. or more and 800° C. or less by the heater 120, and a mixed gas of ammonia gas and nitrogen gas is supplied into the chamber 110 through the nozzle 111. The flow rate of the ammonia gas is, for example, 100 sccm or more, and may be 200 sccm or more. If the flow rate of the ammonia gas is 100 sccm or more, the nitridation of the dielectric oxide film 39 is easily promoted. The pressure in the chamber 110 is, for example, 40 Pa or more and 120 Pa or less. The temperature in the chamber 110 may be 650° C. or more and 750° C. or less. The temperature in the chamber 110 can be measured by a thermocouple or the like.

[0052] When the ammonia gas comes into contact with the stainless steel nozzle 111, it is thermally decomposed. Also, oxygen atoms diffuse from the dielectric oxide film 39. As a result, nitrogen atoms contained in the ammonia gas and oxygen atoms diffused from the dielectric oxide film 39 are converted into dinitrogen monoxide (N 2 Then, the dinitrogen monoxide is thermally decomposed to generate nitric oxide (NO) gas. Nitric oxide has a strong nitriding ability, so the dielectric oxide film 39 is nitrided to form the dielectric oxynitride film 31.

[0053] In the semiconductor device 1, the dielectric oxynitride film 31 functions as a gate insulating film. The dielectric oxynitride film 31 has higher insulation properties and withstand voltage than the dielectric oxide film 39, and according to this embodiment, the gate leakage can be reduced.

[0054] In addition, since the stainless steel nozzle 111 functions as a catalyst in the thermal decomposition of ammonia gas, ammonia gas can be used as the nitrogen source to be supplied to the reaction furnace 100, and it is not necessary to supply nitrous oxide gas and nitric oxide gas to the reaction furnace 100.

[0055] When nitrous oxide gas is supplied to the reactor 100 to nitride the dielectric oxide film 39 with the nitrous oxide gas, oxidation and nitridation proceed simultaneously, which may result in a shortage of nitrogen concentration in the dielectric oxynitride film 31 and difficulty in controlling the characteristics of the dielectric oxide film 39. In addition, the density of the interface state may increase, and the mobility of electrons may decrease. Furthermore, the nitrous oxide gas places a large burden on the environment. Although it may be possible to supply nitric oxide gas to the reactor 100 to nitride the dielectric oxide film 39 with the nitric oxide gas, the highly toxic nitric oxide gas is difficult to handle.

[0056] In this embodiment, nitrous oxide gas and nitric oxide gas are generated in the reaction furnace 100, but are not discharged to the outside, so that it is not necessary to consider the environmental load and toxicity. In addition, since the dielectric oxide film 39 is nitrided by the nitric oxide gas generated by the thermal decomposition of the nitrous oxide gas, the dielectric oxide film 39 is not easily oxidized, and the characteristics of the dielectric oxynitride film 31 can be easily controlled.

[0057] When the dielectric oxide film 39 contains at least one selected from the group consisting of hafnium, lanthanum, and zirconium, a high relative dielectric constant can be easily obtained in the dielectric oxynitride film 31. Furthermore, when the dielectric oxide film 39 contains at least one selected from the group consisting of silicon and aluminum, a high relative dielectric constant can be easily obtained in the dielectric oxynitride film 31.

[0058] Since the surface of the nitride semiconductor layer 20 facing the dielectric oxide film 39, and after nitridation, the surface facing the dielectric oxynitride film 31, have N polarity, it is easier to shorten the distance between the channel region 26 and the source electrode 42S and the drain electrode 42D, and it is easier to achieve low resistance.

[0059] It is not necessary that the entire nozzle 111 is made of stainless steel, as long as the stainless steel is provided on the surface of the nozzle 111 that comes into contact with the ammonia gas. The composition of the stainless steel is not particularly limited. The catalytic metal is not limited to stainless steel, and any metal that functions as a catalyst in the thermal decomposition of ammonia gas may be used. Typical examples of catalytic metals include platinum (Pt), rhodium (Rh), palladium (Pd), and ruthenium (Ru).

[0060] Furthermore, the member on which the catalytic metal is provided is not limited to the nozzle 111. For example, the chamber 110 may be made of a catalytic metal, and the catalytic metal may be provided on the inner surface of the chamber 110. The substrate holder 140 may be made of a catalytic metal, and the catalytic metal may be provided on the surface of the substrate holder 140. The jig 130 may be made of a catalytic metal, and the catalytic metal may be provided on the surface of the jig 130. Also, a dummy member 160 made of a catalytic metal may be supported in part of the recess 131 of the jig 130 instead of the substrate holder 140. As the dummy member 160, a substrate such as a silicon substrate on which a catalytic metal is provided may be used. In either case, ammonia gas is likely to be thermally decomposed on the surface on which the catalytic metal is provided.

[0061] The configuration of the reaction furnace is not particularly limited, and the reaction furnace shown in Fig. 10 may be used instead of the reaction furnace 100 shown in Fig. 9. Fig. 10 is a cross-sectional view showing a reaction furnace used for nitriding the dielectric oxide film 39.

[0062] 10, the reactor 200 includes a chamber 210, a shower head 220, and a susceptor 230. The reactor 200 is, for example, an MOCVD apparatus.

[0063] A shower head 220 for supplying a source gas 9 is provided in the chamber 210. The source 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 so as to face the shower head 220. The susceptor 230 can heat the inside of the chamber 210. The susceptor 230 can directly heat the substrates 2. By placing a plurality of substrates 2 on the susceptor 230, the dielectric oxide films 39 can be nitrided on the plurality of substrates 2 at the same time to form dielectric oxynitride films 31.

[0064] In this example, the shower head 220 is made of stainless steel. Silicon carbide (SiC) may be provided on the surface of a carbon base material to form the susceptor 230. In this example, at least the surface of the shower head 220 has a catalytic metal for the thermal decomposition of ammonia.

[0065] When nitriding the dielectric oxide film 39, the temperature in the chamber 210 is set to 600° C. or more and 800° C. or less by 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 the ammonia gas is, for example, 200 sccm or more, and may be 20000 sccm or more. The pressure in the chamber 110 is, for example, 7000 Pa or more and 40000 Pa or less. The temperature in the chamber 110 may be 650° C. or more and 750° C. or less. The temperature in the chamber 210 can be measured by a thermocouple or the like.

[0066] When the ammonia gas comes into contact with the stainless steel shower head 220, it is thermally decomposed. Also, oxygen atoms diffuse from the dielectric oxide film 39. As a result, as in the case where the reaction furnace 100 is used, the dielectric oxide film 39 is nitrided and the dielectric oxynitride film 31 is formed.

[0067] Here, the effect of the catalytic metal will be explained. Fig. 11 is a diagram showing the relationship between the flow rate of ammonia gas and the degree of nitridation of the dielectric oxide film. Fig. 11 shows the tendency when the catalytic metal is present in the reactor and when the catalytic metal is not present.

[0068] As shown in FIG. 11, in the absence of a catalytic metal, the degree of nitridation decreases as the flow rate of ammonia gas increases. This is because, as the flow rate of ammonia gas increases, the pressure in the chamber increases, and therefore, according to Le Chatelier's principle, it becomes more difficult for ammonia gas to thermally decompose. On the other hand, in the presence of a catalytic metal, the degree of nitridation increases as the flow rate of ammonia gas increases. This is because, according to Le Chatelier's principle, although the higher the flow rate of ammonia gas, the more difficult it becomes for ammonia gas to thermally decompose, the action of the catalytic metal makes it easier for the thermal decomposition of ammonia gas to proceed. In other words, this is because almost the entire amount of the supplied ammonia gas is thermally decomposed and used for nitriding the dielectric oxide film.

[0069] Because of this natural phenomenon, according to this embodiment, ammonia gas is supplied to the reaction furnace to form the dielectric oxynitride film 31, thereby making it possible to suppress gate leakage.

[0070] If the temperature in the reactor when nitriding the dielectric oxide film 39 is too high, the dielectric oxynitride film 31 may be crystallized. If the temperature in the reactor when nitriding the dielectric oxide film 39 is too low, the nitridation of the dielectric oxide film 39 may not proceed easily. If the temperature in the reactor when nitriding the dielectric oxide film 39 is 600° C. or higher and 800° C. or lower, the nitridation of the dielectric oxide film 39 can be easily promoted and the crystallization of the dielectric oxynitride film 31 can be suppressed.

[0071] 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 a gallium polarity.

[0072] The raw material gas supplied to the reactor does not need to contain nitrogen gas as long as it contains ammonia gas, but containing nitrogen gas can suppress the supply of excess ammonia gas. Furthermore, if 95% by volume or more of the gas supplied to the reactor is occupied by ammonia gas and nitrogen gas, it is easy to suppress the supply of unnecessary gases such as nitrous oxide gas and nitric oxide gas. 97% by volume or more of the gas supplied to the reactor may be occupied by ammonia gas and nitrogen gas, and 100% by volume or more of the gas supplied to the reactor may be occupied by ammonia gas and nitrogen gas. The reactor may be a rapid thermal annealing (RTA) furnace.

[0073] Although the embodiments have been described in detail above, the present disclosure is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the claims. [Explanation of symbols]

[0074] 1: Semiconductor device 2: Substrate 9: Raw material gas 10: Growth substrate 20: Nitride semiconductor layer 21: Buffer layer 22: Barrier layer 23: Spacer layer 24: Channel layer 24A:Top surface 25: Cap layer 26: Channel region 31: Dielectric oxynitride film 31D, 31S, 50D, 50G, 50S: Aperture 39: Dielectric oxide film 40D, 40S: Concave 41D, 41S: Regrowth layer 42D: Drain electrode 42S: Source electrode 50: Passivation film 52: Gate electrode 100, 200: Reactor 110, 210: Chamber 111: Nozzle 120: Heater 130: Jig 131: Recess 140: Substrate holder 160: Dummy material 220: Shower head 230: Susceptor

Claims

1. forming a dielectric oxide film having a higher dielectric constant than silicon dioxide on the nitride semiconductor layer; nitriding the dielectric oxide film to form a dielectric oxynitride film; forming a gate electrode on the dielectric oxynitride film; having The step of forming the dielectric oxynitride film includes: placing a substrate including the nitride semiconductor layer and the dielectric oxide film in a reactor having a catalytic metal therein; a step of thermally decomposing 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; generating nitric oxide gas by thermal decomposition of the nitrous oxide gas; The method for manufacturing a semiconductor device comprising the steps of:

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

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

4. The method for manufacturing a semiconductor device according to claim 1 , wherein a surface of said nitride semiconductor layer facing said dielectric oxide film has a nitrogen polarity.

5. 4. The method for manufacturing a semiconductor device according to claim 1, wherein a temperature in the reaction furnace is set to 600° C. or more and 800° C. or less in the step of forming the dielectric oxynitride film.

6. 4. The method for manufacturing a semiconductor device according to claim 1, 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 reactor has a nozzle through which the ammonia gas is supplied, The method for manufacturing a semiconductor device according to claim 1 , wherein the catalytic metal is present at least on a surface of the nozzle.

8. the reactor has a substrate holder on which the substrate is placed; The method for manufacturing a semiconductor device according to claim 1 , wherein the catalytic metal is present at least on a surface of the substrate holder.

9. The reactor comprises: a substrate holder on which the substrate is placed; A jig for supporting the substrate holder; having The method for manufacturing a semiconductor device according to claim 1 , wherein the catalytic metal is present at least on a surface of the jig.

10. The reactor comprises: a substrate holder on which the substrate is placed; A jig for supporting the substrate holder; A dummy member supported by the jig; having The method for manufacturing a semiconductor device according to claim 1 , wherein the catalytic metal is present at least on a surface of the dummy member.

11. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the reaction furnace has a chamber having at least an inner surface on which the catalytic metal is provided.

12. the reaction furnace has a showerhead to which the ammonia gas is supplied, The method for manufacturing a semiconductor device according to claim 1 , wherein the catalytic metal is present at least on a surface of the shower head.

13. 4. The method for manufacturing a semiconductor device according to claim 1, wherein in the step of forming the dielectric oxynitride film, nitrogen gas is supplied into the reaction furnace together with the ammonia gas.

14. 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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