JP5220904B2 - GaN compound semiconductor device - Google Patents

Abstract

In this GaN-based HFET, the resistivity (O·µm) of an TiN film that forms a gate electrode (18) is set at 24.7 (O·µm). Consequently, by setting the resistivity of the TiN film that serves as a Schottky electrode layer of the gate electrode (18) at 10 O·µm or higher, the gate leakage current can be remarkably reduced in comparison to the cases wherein the resistivity of TiN that is the metal material constituting the gate electrode (18) (the gate metal resistivity) is less than 10 O·µm as shown in Fig. 8.

Description

  The present invention relates to a GaN-based compound semiconductor device.

Conventionally, as a GaN-based compound semiconductor device, an HFET (Hetero-junction Field Effect Transistor) having a heterojunction of GaN / AlGaN is described in JP-A-2006-196664 (Patent Document 1). Such a structure has been proposed. In this structure, a Ni layer or a Ti _X W _1-X N (0 <X <1) layer having a sufficiently high Schottky barrier is formed on a compound semiconductor layer made of GaN, and this Ni layer or Ti _A low resistance metal layer is formed on the _X W _1-X N layer to form a gate electrode. Further, in Patent Document 1, in the gate electrode having the above structure, the Ti _X W _1-X N layer is useful as a material for forming a Schottky barrier and is formed on the Ti _X W _1-X N layer. It is described that the leakage current to the gate electrode is suppressed because the low-resistance metal layer to be formed serves as a diffusion barrier that suppresses diffusion of the metal into the GaN-based compound semiconductor layer.

JP 2006-196664 A

  By the way, in the above conventional technique, the leakage current to the gate electrode is not sufficiently suppressed, and even if the annealing conditions and the film thickness are devised, the leakage current to the gate electrode can still be reduced to a desired value. could not.

  Therefore, an object of the present invention is to provide a GaN-based compound semiconductor device that can significantly reduce the leakage current to the gate electrode.

  As a result of intensive studies on the leakage current to the gate electrode (hereinafter referred to as gate leakage current), the present inventors have found that the gate leakage current is reduced by using a metal material having a high resistivity as the metal material forming the gate electrode. I found a phenomenon that it decreased significantly.

  Since the gate electrode is a junction by a Schottky barrier, the physical clear reason that the resistivity of the metal material forming the gate electrode is involved in the gate leakage current was unknown. It has been found by experiments by the present inventors that the gate leakage current is greatly reduced by using a metal material having a high resistivity as the metal material to be formed.

  The present invention was created based on the discovery by the present inventors that such a gate electrode resistivity is significantly related to the gate leakage current.

That is, the GaN-based compound semiconductor device of the present invention is
A GaN-based laminate having a heterojunction;
A source electrode and a drain electrode formed on the GaN-based laminate and spaced apart from each other;
A gate electrode formed on the GaN-based laminate and disposed between the source electrode and the drain electrode;
The GaN-based laminate is
A GaN channel layer;
An AlGaN barrier layer formed on the GaN channel layer;
Have
The gate electrode is
Having an electrode metal layer made of TiN or WN that is Schottky-bonded to the AlGaN barrier layer of the GaN-based laminate, or made of the electrode metal layer,
The electrode metal layer has a resistivity of 10 Ωμm or more.

  According to the GaN-based compound semiconductor device of the present invention, the gate electrode has the electrode metal layer made of TiN (titanium nitride) or WN (tungsten nitride) and has a resistivity of 10Ωμm or more (≧ 10Ωμm). As shown in FIG. 8, it was found that the gate leakage current can be remarkably reduced as compared with the case where the resistivity of the metal material forming the gate electrode (gate metal resistivity) is less than 10 Ωμm.

  Note that the gate leakage current shown in FIG. 8 is measured at a room temperature (25 ° C.) under conditions where 0 V is applied to the source electrode, 5 V is applied to the drain electrode, and −10 V is applied to the gate electrode. Is the value of

  According to the GaN-based compound semiconductor device of the present invention, the gate electrode has a structure in which the electrode metal layer is made of TiN or WN and has a resistivity of 10Ωμm or more (≧ 10Ωμm). It has been found that the gate leakage current can be remarkably reduced as compared with the case where the resistivity (gate metal resistivity) of the metal material forming the electrode metal layer is less than 10 Ωμm.

It is sectional drawing explaining the manufacturing process of GaN-type HFET which is 1st Embodiment of the GaN-type compound semiconductor device of this invention. It is sectional drawing explaining the process following the process of FIG. FIG. 3 is a cross-sectional view illustrating a process that follows the process of FIG. 2. FIG. 4 is a cross-sectional view illustrating a step that follows the step of FIG. 3. It is sectional drawing explaining the process following the process of FIG. It is sectional drawing which shows an example of the protective film of the said GaN-type HFET. It is a figure which shows the sputter | spatter conditions at the time of producing the gate electrode of GaN-type HFET by sputtering, the corresponding resistivity, and a list of gate leak current. It is a characteristic view which shows the relationship between the resistivity ((ohm) * micrometer) of the metal material which makes the gate electrode of GaN-type HFET, and gate leakage current. It is sectional drawing explaining the manufacturing process of GaN-type HFET which is 2nd Embodiment of the GaN-type compound semiconductor device of this invention. FIG. 10 is a cross-sectional view illustrating a process that follows the process of FIG. 9. It is sectional drawing explaining the process following the process of FIG. FIG. 12 is a cross-sectional view illustrating a process that follows the process of FIG. 11. FIG. 13 is a cross-sectional view illustrating a process that follows the process of FIG. 12.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

(First embodiment)
1 to 5 are sectional views sequentially showing steps of manufacturing a GaN-based HFET (heterojunction field effect transistor) according to the first embodiment of the present invention.

  First, as shown in FIG. 1, an undoped AlGaN buffer layer 2, an undoped GaN channel layer 3, and an undoped AlGaN barrier layer 4 are sequentially formed on a Si substrate 1 by using MOCVD (metal organic chemical vapor deposition). . The AlGaN buffer layer 2, the GaN channel layer 3 and the AlGaN barrier layer 4 constitute a GaN-based laminate 5. In FIG. 1, reference numeral 6 indicates a two-dimensional electron gas formed at the interface between the AlGaN barrier layer 4 and the GaN channel layer 3 by a band gap difference and a piezoelectric effect.

  Next, a photoresist layer (not shown) is formed on the undoped AlGaN barrier layer 4, and an opening is formed in the photoresist layer by exposure and development, and the photoresist layer in which the opening is formed is formed. As a mask, the AlGaN barrier layer 4 and a part of the GaN channel layer 3 are etched by dry etching. Thus, as shown in FIG. 2, recesses 12 and 13 reaching from the AlGaN barrier layer 4 to the GaN channel layer 3 are formed in the ohmic electrode formation region.

  Next, Ti and Al are sequentially deposited on the photoresist layer in which the opening is formed and on the recesses 12 and 13, and the recesses 12 and 13 are filled and lifted on the AlGaN barrier layer 4 by lift-off as shown in FIG. Ti / Al electrodes 15 and 16 that serve as protruding source and drain electrodes are formed. Next, the Ti / Al electrodes 15 and 16 are heat-treated to form ohmic electrodes, and the source electrode 15 and the drain electrode 16 are formed. The condition of this heat treatment (ohmic annealing) is set to 500 ° C. for 30 minutes as an example, but the condition of the heat treatment is not limited to this. For example, the heat treatment temperature is set within a range of 400 ° C. to 600 ° C. May be.

  Next, as shown in FIG. 4, a SiN protective film 7 which is a silicon nitride film is formed on the AlGaN barrier layer 4 and the Ti / Al electrodes 15 and 16 by using a plasma CVD method. The growth temperature of the SiN protective film 7 is 350 ° C. as an example, but may be set in the range of 200 ° C. to 400 ° C. Moreover, although the film thickness of the said SiN protective film 7 was 150 nm as an example, you may set it in the range of 20 nm-250 nm.

Further, as an example, the gas flow rate ratio when forming the SiN protective film 7 by the plasma CVD method is set to N ₂ / NH ₃ / SiH ₄ = 645 sccm / 85 sccm / 70 sccm. Thereby, the SiN protective film 7 having a silicon Si ratio larger than that of the stoichiometric silicon nitride film can be formed. According to the SiN protective film 7, current collapse can be further suppressed as compared with a stoichiometric silicon nitride film. Further, for example, when the Si: N composition ratio Si: N of the SiN protective film 7 is set to 1.3 to 1.4: 1, the stoichiometric silicon nitride film of Si: N = 0.75: 1 is used. Is also effective in suppressing current collapse.

  Next, the SiN protective film 7 is heat-treated. For example, this heat treatment was performed at 500 ° C. for 5 minutes in a nitrogen atmosphere. Moreover, you may set the temperature of the said heat processing in the range of 400 to 600 degreeC as an example.

  Next, a mask made of a photoresist (not shown) is formed by photolithography, and etching is performed to remove a region where the gate electrode of the SiN protective film 7 is to be formed, as shown in FIG. Form. Next, a TiN film is formed on the photoresist and on the opening 20 by reactive sputtering. Next, the opening 20 is filled by the lift-off and the gate electrode 18 protruding on the SiN protective film 7 is formed. The undoped AlGaN barrier layer 4 is located immediately below the gate electrode 18, and the junction between the gate electrode 18 and the undoped AlGaN barrier layer 4 is a Schottky junction. The gate electrode 18 is made of a TiN (titanium nitride) film as an electrode metal layer.

Here, as shown in the column No. 2 in FIG. 7, the conditions at the time of forming the TiN film by the reactive sputtering are Ar flow rate of 8 (sccm) and N ₂ flow rate of 22.5 (sccm). ), The chamber internal pressure was set to 9.8 (mTorr), and the high frequency output was set to 300 (W). The TiN film thus produced had a resistivity of 24.7 (Ω · μm). The resistivity value 24.7 (Ω · μm) is an average resistivity value of ten samples prepared under the sputtering conditions in the column No. 2.

  Note that the resistivity values 38.3 (Ω · μm), 12.0 (Ω · μm) in the columns of No. 1, No. 3, No. 4, No. 5, and No. 6 in the table of FIG. , 2.8 (Ω · μm), 2.0 (Ω · μm), 1.6 (Ω · μm), and 0.9 (Ω · μm) are the same as the resistivity values in the No. 2 column. The average value of the resistivity of 10 samples prepared under the sputtering conditions in each column. Samples No. 1 to No. 3 having a resistivity value of 10 (Ω · μm) or more correspond to the present invention, and Sample Nos. 4 to 4 having a resistivity value of less than 10 (Ω · μm). No. 6 is a comparative example.

According to the GaN-based HFET of this embodiment manufactured as described above, the gate leakage current in the off state in which 5 V is applied to the drain electrode 16, 0 V is applied to the source electrode 15, and −10 V is applied to the gate electrode 18. Was 0.17 × 10 ⁻⁸ (A), that is, 1.7 (nA), as shown in the No. 2 column of FIG. 7 and FIG.

  FIG. 8 is a graph in which the vertical axis represents the gate leakage current (A) in the off state, and the horizontal axis represents the resistivity (Ω · μm) of the gate metal forming the gate electrode. In the graph of FIG. 8, each open rhombus mark plots a point determined by the average value of the resistivity of 10 samples manufactured under the same sputtering conditions and the average value of the gate leakage current of the 10 samples. It is a thing.

  Referring to FIG. 8, it can be seen that when the resistivity (gate metal resistivity) of the TiN film forming the gate electrode 18 is less than 10 Ωμm, the gate leakage current increases remarkably. That is, the gate electrode 18 has a resistivity of the metal material TiN constituting the gate electrode 18 as shown in FIG. 8 because the resistivity of the TiN film as the electrode metal layer is 10 Ωμm or more (≧ 10 Ωμm). It can be seen that the gate leakage current can be significantly reduced as compared with the case where the metal resistivity is less than 10 Ωμm.

That is, as shown in the list of FIG. 7, in the comparative example of sample No. 4, the Ar flow rate is 50 (sccm), the N ₂ flow rate is 2 (sccm), and the chamber internal pressure is 3.8 (mTorr). And a TiN film was formed at a high frequency output of 300 (W). The TiN film of this comparative example (No. 4) had a resistivity of 2.8 (Ω · μm). In the gate electrode made of the TiN film of this comparative example (No. 4), the gate leakage current is 5.16 × 10 ⁻⁸ (A), which is 30 times or more the gate leakage current of this embodiment. In addition, although examination was performed by doubling the thickness of the TiN film in the comparative example of sample No. 4, the gate leakage current was not changed.

In the comparative example of sample No. 5, the Ar flow rate is set to 50 (sccm), the N ₂ flow rate is set to 1 (sccm), the pressure in the chamber is set to 3.8 (mTorr), and the high frequency output is set to 300 (W ), A TiN film was formed. The TiN film of this comparative example (No. 5) had a resistivity of 2.0 (Ω · μm). In the gate electrode made of the TiN film of this comparative example (No. 5), the gate leakage current was 7.57 × 10 ⁻⁸ (A), which was 40 times or more the gate leakage current of this embodiment.

In the comparative example of sample No. 6, the Ar flow rate is set to 50 (sccm), the N ₂ flow rate is set to 0.5 (sccm), the pressure in the chamber is set to 3.8 (mTorr), and the high frequency output is set to 300. As (W), a TiN film was formed. The TiN film of this comparative example (No. 6) had a resistivity of 1.6 (Ω · μm). In the gate electrode made of the TiN film of this comparative example (No. 6), the gate leakage current was 530 × 10 ⁻⁸ (A), which was 3100 times or more the gate leakage current of this embodiment.

In the first embodiment, the resistivity of the TiN film forming the gate electrode 18 is 24.7 (Ω · μm). However, the resistivity of the TiN film forming the gate electrode 18 is 12.0 (Ω・ It may be μm). This TiN film having a resistivity of 12.0 (Ω · μm) has a film forming condition by reactive sputtering with an Ar flow rate of 8 (sccm) as shown in the column No. 3 in FIG. _{2 The} flow rate is 15 (sccm), the pressure in the chamber is set to 9.8 (mTorr), and the high-frequency output is 300 (W). According to the gate electrode 18 made of a TiN film having a resistivity of 12.0 (Ω · μm), the gate leakage current is 0.43 × 10 ^{−8 as} shown in the column No. 3 in FIG. (A). That is, according to the gate electrode 18 made of a TiN film having a resistivity of 12.0 (Ω · μm), it is made of the TiN film of the comparative example (No. 4) having a resistivity of 2.8 (Ω · μm). Compared with the gate electrode, the gate leakage current could be reduced to 1/10 or less.

(Second embodiment)
Next, FIGS. 9 to 13 are cross-sectional views sequentially showing the steps of the method of manufacturing the GaN-based HFET which is the second embodiment of the present invention.

  First, as shown in FIG. 9, an undoped AlGaN buffer layer 72, an undoped GaN channel layer 73, and an undoped AlGaN barrier layer 74 are formed in this order on a Si substrate 71 using MOCVD (metal organic chemical vapor deposition). . The AlGaN buffer layer 72, the GaN channel layer 73, and the AlGaN barrier layer 74 constitute a GaN-based stacked body 75. In FIG. 9, reference numeral 76 indicates a two-dimensional electron gas formed at the interface between the AlGaN barrier layer 74 and the GaN channel layer 73.

  The GaN-based laminate 75 produced in the second embodiment differs from the GaN-based laminate 5 produced in the first embodiment described above in that the thickness of the AlGaN barrier layer 74 is the same as that of the AlGaN of the first embodiment. It is thinner than the thickness of the barrier layer 4 (for example, 40 nm), for example, 25 nm. As a result, ohmic contacts of electrodes 85 and 86 to be described later are possible without forming the recesses 12 and 13 as in the first embodiment.

  Next, as shown in FIG. 10, a photoresist layer 81 is formed on the AlGaN barrier layer 74 and exposed and developed to form openings 82 and 83 in regions where source and drain electrodes are to be formed. .

  Next, as shown in FIG. 11, Ti and Al are sequentially deposited on the photoresist layer 81 and the AlGaN barrier layer 74 exposed in the openings 82 and 83, and source and drain electrodes are formed by lift-off. Ti / Al electrodes 85 and 86 are formed in a region on the AlGaN barrier layer 74 to be formed. Next, the Ti / Al electrodes 85 and 86 are heat-treated to form ohmic electrodes, and the source electrode 85 and the drain electrode 86 are formed. The condition of this heat treatment (ohmic annealing) is set to 500 ° C. for 30 minutes as an example, but the condition of the heat treatment is not limited to this. For example, the heat treatment temperature is set within a range of 500 ° C. to 600 ° C. May be.

  Next, as shown in FIG. 12, a SiN protective film 77, which is a silicon nitride film, is formed on the AlGaN barrier layer 74 and the Ti / Al electrodes 85 and 86 by plasma CVD. The growth temperature of the SiN protective film 77 is 350 ° C. as an example, but may be set in the range of 200 ° C. to 400 ° C. The thickness of the SiN protective film 77 is 150 nm as an example, but may be set in the range of 20 nm to 250 nm.

As an example, the gas flow rate ratio when forming the SiN protective film 77 by the plasma CVD method is set to N ₂ / NH ₃ / SiH ₄ = 645 sccm / 85 sccm / 70 sccm. Thereby, the SiN protective film 77 having a silicon Si ratio larger than the stoichiometric silicon nitride film can be formed. According to the SiN protective film 77, current collapse can be further suppressed as compared with a stoichiometric silicon nitride film. For example, when the Si: N composition ratio Si: N of the SiN protective film 77 is set to 1.3 to 1.4: 1, the stoichiometric silicon nitride film of Si: N = 0.75: 1 is used. Is also effective in suppressing current collapse.

  Next, the SiN protective film 77 is heat-treated. This heat treatment was performed, for example, at 500 ° C. for 5 minutes in a nitrogen atmosphere. Moreover, you may set the temperature of the said heat processing in the range of 400 to 600 degreeC as an example.

  Next, a mask made of a photoresist (not shown) is formed by photolithography and etched to remove the region where the gate electrode of the SiN protective film 77 is to be formed, as shown in FIG. Form. Next, a TiN film is formed on the photoresist and in the opening 90 by reactive sputtering. Next, a gate electrode 88 that fills the opening 90 and protrudes on the SiN protective film 77 is formed by lift-off. An undoped AlGaN barrier layer 74 is located immediately below the gate electrode 88, and the junction between the gate electrode 88 and the undoped AlGaN barrier layer 74 is a Schottky junction. The gate electrode 88 is made of a TiN film as a Schottky electrode layer.

Here, as shown in the column No. 3 in FIG. 7, the conditions at the time of forming the TiN film by the reactive sputtering are as follows: the Ar flow rate is 8 (sccm), and the N ₂ flow rate is 15 (sccm). The TiN film was formed by setting the pressure in the chamber to 9.8 mTorr or more and setting the high frequency output to 300 (W). The TiN film thus produced had a resistivity of 12.0 (Ω · μm). The resistivity value 12.0 (Ω · μm) is an average resistivity value of 10 samples manufactured under the same sputtering conditions.

According to the GaN-based HFET of this embodiment manufactured as described above, the gate leakage current in the OFF state in which 5 V is applied to the drain electrode 86, 0 V is applied to the source electrode 85, and −10 V is applied to the gate electrode 88. Was 0.43 × 10 ⁻⁸ (A), that is, 4.3 (nA), as shown in the column of No. 3 in FIG. 7 and FIG. As shown in FIG. 8, the gate electrode 88 has a resistivity (gate metal resistivity) of the metal material TiN forming the gate electrode 88 because the resistivity of the TiN film as the electrode metal layer is 10 Ωμm or more (≧ 10 Ωμm). ) Is less than 10 Ωμm, it was found that the gate leakage current can be significantly reduced.

In the first and second embodiments, as shown in the column No. 1 in FIG. 7, a gate electrode made of a TiN film having a resistivity of 38.3 (Ω · μm) may be provided. As shown in the column No. 1 in FIG. 7, this TiN film is formed by the reactive sputtering under the conditions of Ar flow rate of 8 (sccm), N ₂ flow rate of 45 (sccm), chamber The internal pressure was set to 9.8 (mTorr), and the high frequency output was set to 300 (W). According to the gate electrode made of a TiN film having a resistivity of 38.3 (Ω · μm), the gate leakage current was 0.04 × 10 ⁻⁸ (A) as shown in FIG. That is, according to the gate electrode made of a TiN film having a resistivity of 38.3 (Ω · μm), the gate leakage current is smaller than that of the gate electrode made of a TiN film having a resistivity of 2.8 (Ω · μm). Can be reduced to 1/120 or less.

In the first and second embodiments, the gate electrodes 18 and 88 are made of TiN, but they may be made of WN (tungsten nitride). The resistivity of the gate electrode made of WN (tungsten nitride) is, for example, 52 (Ω · μm) and 58 (Ω · μm) as shown by the two diamonds painted black in FIG. . According to a GaN-based HFET having a gate electrode with a resistivity of 52 (Ω · μm) or 58 (Ω · μm), the gate leakage current is almost 0.0 × 10 ⁻⁸ ( A). The gate electrode made of this WN film is produced by, for example, reactive sputtering. The sputtering conditions for this reactive sputtering are as follows: for a WN film with a resistivity of 52 (Ω · μm) and a WN film with a resistivity of 58 (Ω · μm), the Ar flow rate is 16.8 (sccm) and the N ₂ flow rate is The WN film was formed at 50 (sccm), the chamber internal pressure was set to 37.5 (mTorr), the high-frequency output was 300 (W). According to such a GaN-based HFET having a gate electrode made of a WN film as an electrode metal layer having a resistivity of 10 Ωμm or more, as shown in FIG. 8, the resistivity (gate metal resistance) of the metal material forming the gate electrode is shown. It has been found that the gate leakage current can be significantly reduced as compared with the case where the ratio is less than 10 Ωμm.

In the first and second embodiments, the gate electrodes 18 and 88 are composed of a single layer of a TiN / Al film and a WN film as the electrode metal layer. However, Au is formed on the TiN / Al film and the WN film. A two-layer structure in which low resistance metal films such as a film and an Al film are stacked may be used. A three-layer structure is provided by providing a diffusion prevention layer made of a Ti _X W _1-X N (0 <X <1) film or a Pb film between the TiN / Al film, WN film and the low resistance metal film. It is good. This diffusion prevention layer prevents the metal of the low resistance metal film from diffusing into the lower layer (TiN / Al film, WN film or GaN-based laminate).

  In the first and second embodiments, the source electrodes 15 and 85 and the drain electrodes 16 and 86 as the ohmic electrodes are Ti / Al electrodes in which a Ti layer and an Al layer are sequentially stacked. A Ti / Al / TiN electrode in which an Al layer and a TiN layer are sequentially laminated may be used. The source electrode and the drain electrode may be Ti / AlCu / TiN electrodes in which a Ti layer, an AlCu layer, and a TiN layer are sequentially stacked. The source electrode and the drain electrode may be Hf / Al electrodes. Further, as the source electrode and the drain electrode, Ni / Au may be stacked on Ti / Al or Hf / Al, or Pt / Au may be stacked on Ti / Al or Hf / Al. It is good also as what laminated | stacked Au on Ti / Al or Hf / Al.

In the first and second embodiments, the protective film for suppressing current collapse is the SiN protective film 7, 77 made of a single layer of silicon nitride film (SiN film). However, the protective film is made of TaOx, SiO ₂ , HfOx, or the like. A film may be used, and any of a silicon oxide film, an aluminum oxide film, and an aluminum nitride film may be used. Further, the protective film that suppresses current collapse may be composed of a lower SiN film and a stoichiometric upper SiN film having a silicon Si ratio larger than that of the stoichiometric silicon nitride film. Here, the stoichiometric silicon nitride film means that Si and N have a composition of 3: 4. In this case, it is possible to suppress the diffusion of the electrode metal by the stoichiometric upper SiN film and to suppress the current collapse by the lower SiN film having a large silicon Si ratio. Further, an SiO ₂ film or an Al ₂ O ₃ film may be formed on the SiN protective films 7 and 77. In this case, the SiO ₂ film or Al ₂ O ₃ film can suppress the diffusion of the electrode metal into the SiN protective films 7 and 77 during the heat treatment of the electrode, and the gate electrode 18 passes through the SiN protective films 7 and 77. , 88 can be reduced.

Further, as shown in FIG. 6, a protective film 50 in which a lower SiN film 51, an upper SiN film 52 that is stoichiometry, and a SiO ₂ film 53 are sequentially stacked may be used as a protective film that suppresses current collapse. Here, that the upper SiN film 52 is stoichiometric means that Si and N have a composition of 3: 4. According to the protective film 50, since the upper SiN film 52 is stoichiometry and the SiO ₂ film 53 is formed on the upper SiN film 52, the upper and lower SiN layers of the protective film 50 are heat-treated during the heat treatment of the electrode. The diffusion of the electrode metal into the protective layers 52 and 51 can be suppressed, and the leakage current passing through the protective film 50 can be further reduced. Although the lower SiN film 51 is a SiN protective film having a silicon Si ratio larger than that of the stoichiometric silicon nitride film, current collapse can be suppressed as compared with the stoichiometric silicon nitride film. Similar to the upper SiN film 52, a stoichiometric silicon nitride film may be used. In this case, the leakage current can be further reduced by suppressing the diffusion of the electrode metal. Further, instead of the SiO ₂ film 53, an Al ₂ O ₃ film may be used.

  In the first and second embodiments, the Si substrate is used as the substrate. However, a sapphire substrate may be used. Further, a nitride semiconductor layer may be grown on a substrate made of a nitride semiconductor, such as by growing an AlGaN layer on the GaN substrate. Further, a buffer layer may be appropriately formed between the substrate and each layer. A hetero improvement layer made of AlN may be formed between the GaN channel layers 3 and 73 and the AlGaN barrier layers 4 and 74. A GaN cap layer may be formed on the AlGaN barrier layers 4 and 74.

The GaN-based semiconductor laminate in the manufacturing method of the present invention may include a GaN-based semiconductor layer represented by Al _x In _y Ga _1-xy N (x ≧ 0, y ≧ 0, 0 ≦ x + y <1). . That is, the GaN-based semiconductor laminate in the manufacturing method of the present invention may include AlGaN, GaN, InGaN, and the like.

  In the above embodiment, a normally-on type HFET has been described. However, a normally-off type can achieve the same effect. In addition, the GaN-based semiconductor device manufactured by the present invention is not limited to the HFET of the above embodiment, but may be a field effect transistor having another configuration.

  Although specific embodiments of the present invention have been described, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

1,71 Si substrate 2,72 Undoped AlGaN buffer layer 3,73 Undoped GaN channel layer 4,74 AlGaN barrier layer 5,75 GaN-based stack 6,76 Two-dimensional electron gas 7,77 SiN protective film 12,13 Recess 15 , 85 Ti / Al / TiN electrode (source electrode)
16,86 Ti / Al / TiN electrode (drain electrode)
18, 88 Gate electrode 20, 90 Opening 50 Protective film 51 Lower layer SiN film 52 Upper layer SiN film 53 SiO ₂ film

Claims (1)

A GaN-based laminate having a heterojunction;
A source electrode and a drain electrode formed on the GaN-based laminate and spaced apart from each other;
A gate electrode formed on the GaN-based laminate and disposed between the source electrode and the drain electrode;
The GaN-based laminate is
A GaN channel layer;
An AlGaN barrier layer formed on the GaN channel layer;
Have
The gate electrode is
Having an electrode metal layer made of TiN or WN while being Schottky-bonded to the AlGaN barrier layer of the GaN-based laminate, or consisting of the electrode metal layer,
The electrode metal layer has a resistivity of 10 Ωμm or more, and is a GaN-based compound semiconductor device.

Images