JP6524888B2 - Compound semiconductor device and method of manufacturing the same - Google Patents

Description

  The present invention relates to a compound semiconductor device and a method of manufacturing the same.

  Compound semiconductor devices, in particular nitride semiconductor devices, have been actively developed as high breakdown voltage and high output semiconductor devices by utilizing features such as high saturation electron velocity and wide band gap. As nitride semiconductor devices, many reports have been made on field effect transistors, in particular, high electron mobility transistors (HEMTs). In particular, GaN-based HEMTs that can use GaN as a main material and can realize breakdown voltage and high output have attracted attention.

JP, 2014-11167, A JP 2012-119638 A

  In forming a source electrode and a drain electrode which are ohmic electrodes in the HEMT, after forming the source electrode and the drain electrode, it is necessary to perform a heat treatment to obtain an ohmic contact with the compound semiconductor layer. However, due to the heat treatment, the surface morphology is deteriorated due to reaction with the outside air (predetermined atmosphere) on the surface of the ohmic electrode, which causes a problem of electric field concentration when used as an electrode.

  In order to cope with the above problems, there is a technique of forming a high melting point metal such as Mo, Pt, Ta or the like as a cap film on the ohmic electrode to protect the electrode surface. In the GaN-based HEMT, aluminum (Al) is used as a part of the material for the ohmic electrode, and gold (Au) is used as the material of the wiring connected thereto. When the ohmic electrode and the wiring are in direct contact with each other, an Au-Al compound is easily generated during operation, resulting in high resistance. The formation of the high melting point metal cap film is also intended to suppress the formation of the Au-Al compound.

  However, even if a cap film of high melting point metal is formed, the high melting point metal of the cap film may be aggregated or alloyed with Al of the ohmic electrode depending on the temperature of heat treatment for obtaining ohmic contact. There are also reports of cases leading to surface roughness of the electrode.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a highly reliable compound semiconductor device which reliably suppresses the occurrence of surface roughness of an electrode containing Al due to heat treatment, and a method of manufacturing the same. To aim.

One embodiment of a compound semiconductor device includes a compound semiconductor layer, a first electrode containing aluminum formed on the compound semiconductor layer and in ohmic contact with the compound semiconductor layer, and formed above the compound semiconductor layer and a second electrode, covering over the side surface from the upper surface of the first electrode, seen including a protective layer containing aluminum compound, wherein the protective layer is formed on the first electrode, the compound semiconductor There is a non-forming site on the layer, which is remote from the second electrode .

One aspect of the production method of a compound semiconductor device has, on a compound semiconductor layer, forming a step of forming a first electrode containing aluminum, covering the first electrode, a protective film containing aluminum compound When the state in which the first electrode was covered with the protective film, the first electrode by heat-treating, the first a step of electrodes and the said compound semiconductor layer Ru is ohmic contact, said protective film a step of processing the island shape corresponding to the first electrode, seen including a step of forming a second electrode above the compound semiconductor layer, wherein the protective film is not in the compound semiconductor layer There is a site of formation, which is remote from the second electrode .

  According to the above aspects, a highly reliable compound semiconductor device is realized which reliably suppresses the occurrence of surface roughness of the Al-containing electrode due to the heat treatment.

FIG. 6 is a schematic cross-sectional view showing the method of manufacturing the Schottky type AlGaN / GaN.HEMT according to the first embodiment in the order of steps. FIG. 2 is a schematic cross-sectional view showing the method of manufacturing the Schottky type AlGaN / GaN.HEMT according to the first embodiment in order of processes subsequent to FIG. 1; FIG. 3 is a schematic cross-sectional view showing the method of manufacturing the Schottky type AlGaN / GaN.HEMT according to the first embodiment in order of processes subsequent to FIG. 2; FIG. 4 is a schematic cross-sectional view showing the method of manufacturing the Schottky type AlGaN / GaN.HEMT according to the first embodiment in order of steps, following FIG. 3; It is a figure of the photograph which shows the appearance of the surface of an ohmic electrode (a source electrode and a drain electrode) after performing heat treatment for obtaining ohmic contact in a 1st embodiment based on comparison with various comparative examples. It is a characteristic view shown based on comparison with various comparative examples about ohmic characteristics after performing heat treatment for obtaining ohmic contact in a 1st embodiment. It is a schematic sectional drawing which shows the main processes of the manufacturing method of the Schottky type | mold AlGaN / GaN HEMT by 2nd Embodiment. 7 is a schematic cross-sectional view showing the main steps of a method of manufacturing a Schottky-type AlGaN / GaN HEMT according to the second embodiment, following FIG. 7; It is a schematic sectional drawing which shows the main processes of the manufacturing method of the Schottky-type AlGaN / GaN HEMT by 3rd Embodiment. FIG. 9 is a schematic cross-sectional view showing main steps of a method of manufacturing a Schottky-type AlGaN / GaN.HEMT according to the third embodiment, following FIG. 9; It is a wiring diagram which shows schematic structure of the power supply device by 4th Embodiment. It is a wiring diagram which shows schematic structure of the high frequency amplifier by 5th Embodiment.

Hereinafter, various embodiments will be described in detail with reference to the drawings. In the following embodiments, the configuration of a compound semiconductor device will be described together with a method of manufacturing the same.
In the following drawings, for convenience of illustration, there are components which are not shown in relatively accurate sizes and thicknesses.

First Embodiment
In the present embodiment, a Schottky-type AlGaN / GaN HEMT is disclosed as a compound semiconductor device.
1 to 4 are schematic cross-sectional views showing the method of manufacturing the Schottky type AlGaN / GaN.HEMT according to the first embodiment in the order of steps.

First, as shown in FIG. 1A, a compound semiconductor layer 2 having a layered structure of compound semiconductors is formed on, for example, a semi-insulating SiC substrate 1 as a growth substrate.
As a growth substrate, an Si substrate, a sapphire substrate, a GaAs substrate, a GaN substrate or the like may be used instead of the SiC substrate. The conductivity of the substrate may be either semi-insulating or conductive.
The compound semiconductor layer 2 includes a buffer layer 2a, an electron transit layer 2b, an intermediate layer 2c, an electron supply layer 2d, and a cap layer 2e. In the AlGaN / GaN HEMT, a two-dimensional electron gas (2DEG) is generated in the vicinity of the interface between the electron transit layer 2b and the electron supply layer 2d (precisely, the intermediate layer 2c).

  Specifically, the following compound semiconductors are grown on the SiC substrate 1 by, for example, metal organic vapor phase epitaxy (MOVPE). Molecular beam epitaxy (MBE) method or the like may be used instead of the MOVPE method.

  AlN, i (intentionally undoped) -GaN, i-AlGaN, n-AlGaN, and n-GaN are sequentially deposited on the SiC substrate 1 to form a buffer layer 2a, an electron transit layer 2b, an intermediate layer 2c, electrons The supply layer 2d and the cap layer 2e are laminated. As growth conditions of AlN, GaN, AlGaN, and GaN, a mixed gas of trimethylaluminum gas, trimethylgallium gas, and ammonia gas is used as a source gas. Depending on the compound semiconductor layer to be grown, the presence or absence and supply flow rate of trimethylaluminum gas as an Al source and trimethylgallium gas as a Ga source are appropriately set. The flow rate of ammonia gas, which is a common source, is about 100 sccm to 10 LM. The growth pressure is about 50 Torr to 300 Torr, and the growth temperature is about 1000 ° C. to 1200 ° C.

When growing GaN and AlGaN as n-type, for example, SiH ₄ gas containing Si as an n-type impurity is added to the source gas at a predetermined flow rate, and Si is doped to GaN and AlGaN. The doping concentration of Si is about 1 × 10 ¹⁸ / cm ^{3 to} about 1 × 10 ²⁰ / cm ³ , for example, about 5 × 10 ¹⁸ / cm ³ .
Here, the buffer layer 2a has a film thickness of about 0.1 μm, the electron transit layer 2b has a film thickness of about 3 μm, the intermediate layer 2c has a film thickness of about 5 nm, and the electron supply layer 2d has a film thickness of about 20 nm. The surface layer 2e is formed to a film thickness of about 10 nm.

Subsequently, as shown in FIG. 1B, the element isolation structure 3 is formed.
Specifically, for example, argon (Ar) is injected into the element isolation region of the compound semiconductor layer 2. Thereby, the element isolation structure 3 is formed in the surface layer portion of the compound semiconductor layer 2 and the SiC substrate 1. The element isolation structure 3 defines an active region on the compound semiconductor layer 2.
Note that element isolation may be performed using, for example, STI (Shallow Trench Isolation) method instead of the above-described implantation method.

Subsequently, as shown in FIG. 1C, the source electrode 4 and the drain electrode 5 are formed.
Specifically, first, the electrode grooves 2A and 2B are formed in the cap layer 2e at the planned formation positions of the source electrode and the drain electrode on the surface of the compound semiconductor layer 2.
A resist mask is formed to open the planned formation positions of the source electrode and the drain electrode on the surface of the compound semiconductor layer 2. The cap layer 2e is removed by dry etching using this resist mask. Thereby, the electrode grooves 2A and 2B are formed. In dry etching, an inert gas such as Ar and a chlorine-based gas such as Cl ₂ are used as an etching gas. Here, the electrode groove may be formed by dry etching through the cap layer 2e to the surface layer portion of the electron supply layer 2d.

  For example, Ti / Al is used as an electrode material. For the electrode formation, for example, a double-layered resist having a wedge structure suitable for a vapor deposition method and a lift-off method is used. This resist is applied on the compound semiconductor layer 2 to form a resist mask which opens the electrode grooves 2A and 2B. Ti / Al is deposited using this resist mask. The thickness of Ti is about 20 nm, and the thickness of Al is about 200 nm. The liftoff method is used to remove the resist mask of the crucible structure and Ti / Al deposited thereon. As described above, the source electrode 4 and the drain electrode 5 are formed to embed the electrode grooves 2A and 2B in the lower part of Ti / Al.

  The source electrode 4 is formed with the first electrode layer 4a of high melting point metal Ti as a lower layer and the second electrode layer 4b of Al as an upper layer, and the upper portion of the first electrode layer 4a is a compound semiconductor layer It protrudes from the surface of 2. The drain electrode 5 is formed with the first electrode layer 5a of high melting point metal Ti as a lower layer and the second electrode layer 5b of Al as an upper layer, and the upper portion of the first electrode layer 4a is a compound semiconductor layer Projecting upward from the surface of 2.

Subsequently, as shown in FIG. 2A, an Al compound film 6 is formed on the entire surface.
In detail, the material contained by the source electrode 4 and the drain electrode 5 on the entire surface of the compound semiconductor layer 2 so as to cover the source electrode 4 and the drain electrode 5, in this case, Al which is the material of the second electrode layers 4b and 5b. The Al compound film 6 which is a compound of the above is formed as a protective film. As the Al compound film 6, at least one selected from aluminum oxide (AlO), aluminum nitride (AlN), aluminum oxynitride (AlON), and aluminum carbide (AlC) is used. In the case of aluminum oxide, in view of the electrode protection function of the Al compound film 6, it is preferable to set the O / Al ratio to 1.5 or more. In the case of aluminum nitride, the N / Al ratio is preferably 1 or more. Here, aluminum oxide is selected as the Al compound film 6. Aluminum oxide is deposited to a thickness of about 2 nm to about 50 nm, for example, about 5 nm, by atomic deposition, for example. Thereby, the Al compound film 6 is formed. The Al compound film 6 has the entire top and side surfaces (including the boundary between the first electrode layer 4 a and the second electrode layer 4 b) of the source electrode 4 and the top and side surfaces (first electrode) of the drain electrode 5. Covering the entire surface of the layer 5a and the boundary portion between the second electrode layer 5b).

  Thereafter, in a state where the source electrode 4 and the drain electrode 5 are covered with the Al compound film 6, the SiC substrate 1 is heat-treated at, for example, about 400 ° C. to about 1000 ° C., for example, about 600 ° C. in a nitrogen atmosphere. As a result, the source electrode 4 and the drain electrode 5 are in ohmic contact with the compound semiconductor layer 2 to establish ohmic characteristics.

  In the present embodiment, in a state where the source electrode 4 and the drain electrode 5 are covered with the Al compound film 6, heat treatment for obtaining ohmic contact is performed. The Al compound film 6 is a compound of the electrode material (Al) itself, and has a high melting point (2072 ° C. for AlO, 2200 ° C. for AlN). Therefore, surface roughening due to reaction with external air (predetermined atmosphere) of the surface of source electrode 4 and the surface of drain electrode 5 is suppressed, and aggregation of high melting point metal (Ti) or high melting point metal (Ti) and electrode material ( It is possible to prevent alloying with Al). The heat treatment is performed in a state where the boundary between the first electrode layers 4a and 5a and the second electrode layers 4b and 5b is also covered with the Al compound film 6, and therefore, the refractory metal (Ti) at the boundary And the alloying of the high melting point metal (Ti) and the electrode material (Al) are also suppressed. If heat is applied in a state where the boundary portions (Ti and Al) between the first electrode layers 4a and 5a and the second electrode layers 4b and 5b are not protected, the interface between Ti and Al in contact with the outside air is Alloying progresses. When alloying progresses at the interface between Ti and Al, the interface between Ti and Al is roughened (concavities and convexities are formed at the interface), and an electric field is concentrated in the roughened (concave and convex) region, and the source electrode 4 and drain electrode 5 is destroyed. In this embodiment, since the boundary portion (Ti and Al) is protected by an Al compound having a high melting point, interface roughening between Ti and Al can be suppressed, and the source electrode 4 and the drain electrode 5 are broken. It will not be done.

Subsequently, as shown in FIG. 2B, the Al compound film 6 is left only in the portion covering the source electrode 4 and the drain electrode 5.
In detail, the Al compound film 6 is processed by lithography and wet etching and left only in a portion covering the source electrode 4 and the drain electrode 5. For wet etching, for example, tetramethyl ammonium hydroxide (TMAH) is used. Thereby, the Al compound film 6 is separated corresponding to the source electrode 4 and the drain electrode 5 and remains in an island shape. Between the source electrode 4 and the drain electrode 5 on the surface of the compound semiconductor layer 2, a non-formation site of the Al compound film 6 is present.

Subsequently, as shown in FIG. 2C, the insulating protective film 7 is formed on the entire surface.
Specifically, an insulator such as silicon nitride (SiN) is applied to the entire surface including the upper surface of the Al compound film 6 of the compound semiconductor layer 2 by plasma CVD or the like to a thickness of about 10 nm to about 100 nm, for example, about 50 nm. accumulate. Thereby, the protective insulating film 7 is formed. The protective insulating film 7 has a function of protecting the surface of the compound semiconductor layer 2. As the protective insulating film 7, instead of single-layer SiN, single-layer silicon oxide (SiO), single-layer silicon oxynitride (SiON), single-layer aluminum nitride (AlN) or single-layer aluminum oxide (AlO) ) May be formed. Further, it is preferable to form a laminated film of any two or more layers selected from SiN, SiON, AlN and AlO.

Subsequently, as shown in FIG. 3A, the gate electrode 8 is formed.
Specifically, dry etching is first performed to form an electrode groove 7a penetrating the protective insulating film 7 and exposing the surface of the compound semiconductor layer 2 on the gate electrode formation planned portion of the protective insulating film 7 by lithography and dry etching. For example, a fluorine-based gas is used.
The resist used for lithography is removed by ashing treatment or wet treatment using a predetermined chemical solution.

  Next, a resist mask for forming a gate electrode is formed. Here, for example, a two-layered resist having a wedge structure suitable for the vapor deposition method and the lift-off method is used. This resist is applied on the protective insulating film 6 to form an opening for exposing the portion of the electrode groove 7 a of the protective insulating film 7. Thus, a resist mask having the opening is formed.

  Using this resist mask, for example, Ni / Au as an electrode material is deposited on the resist mask including the inside of the opening for exposing the portion of the electrode groove 7a of the protective insulating film 7 by, for example, a vapor deposition method. The thickness of Ni is about 30 nm, and the thickness of Au is about 400 nm. The resist mask and Ni / Au deposited thereon are removed by a lift-off method. Thus, the inside of the electrode groove 7a is filled with a part of the electrode material, and the gate electrode 8 having a shape that rides on the protective insulating film 7 is formed.

Subsequently, as shown in FIG. 3B, an interlayer insulating film 9 is formed.
In detail, an insulating material such as methylsilsesquioxane is applied by spin coating on the entire surface including the source electrode 4 and the drain electrode 5 and the gate electrode 8. Thus, the interlayer insulating film 9 is formed.

Subsequently, as shown in FIG. 4A, an opening 10 is formed in the Al compound film 6, the protective insulating film 7, and the interlayer insulating film 9.
Specifically, the Al compound film 6, the protective insulating film 7, and the interlayer insulating film 9 are processed by lithography and dry etching. Thus, an opening 10 is formed to penetrate the Al compound film 6, the protective insulating film 7, and the interlayer insulating film 9 to expose the surface of the source electrode 4 (drain electrode 5). At this time, an opening for exposing the surface of the gate electrode 8 is also formed in the interlayer insulating film 9.

Subsequently, as shown in FIG. 4B, the barrier metal layer 11 and the wiring layer 12 are formed.
Specifically, first, the barrier metal layer 11 and a not-shown seed metal layer are formed on the entire surface of the interlayer insulating film 9 by sputtering or the like so as to cover the inner wall surface of the opening 10. The barrier metal layer 11 is formed, for example, in a two-layer structure of Ti / Pt. As a seed metal layer, Au which is a wiring metal is formed.

Next, a resist mask is opened on the seed metal layer to open the wiring formation planned site, and Au is deposited in the opening by Au plating to form a wiring layer 12.
After removing the resist mask, the excess barrier metal layer 11 and the seed metal layer are removed.
Thus, the AlGaN / GaN.HEMT according to the present embodiment is formed.

  Hereinafter, the operation and effect of the AlGaN / GaN HEMT according to the present embodiment will be described based on comparison with various comparative examples.

  FIG. 5 is a photograph showing the appearance of the surface of the ohmic electrode (source electrode and drain electrode) after heat treatment for obtaining ohmic contact in the present embodiment, based on comparison with various comparative examples. . FIG. 5 shows the results of the present embodiment, the results of Comparative Example 1, and the results of Comparative Example 2 side by side. Also in the second and third embodiments described later, the same results as in the present embodiment of FIG. 5 are obtained.

  In Comparative Example 1, a cap film of Pt (about 5 nm thick) is formed on the source electrode and the drain electrode instead of forming the Al compound film in the present embodiment, and the cap film is formed. Heat treatment (about 600 ° C.) was performed to obtain ohmic contact. Others are the same as in this embodiment.

  In Comparative Example 2, without forming the Al compound film in the present embodiment, a cap film of Ta (approximately 5 nm thick) is formed on the source electrode and the drain electrode instead, and the cap film is formed. Heat treatment (about 600 ° C.) was performed to obtain ohmic contact. Others are the same as in this embodiment.

  From the results shown in FIG. 5, it was confirmed that the occurrence of surface roughness of the source electrode and the drain electrode due to the heat treatment for obtaining the ohmic contact is suppressed by using aluminum oxide (AlO) as the cap film.

  FIG. 6 is a characteristic diagram showing ohmic characteristics after heat treatment for obtaining ohmic contact in the present embodiment based on comparison with various comparative examples. (A) shows the result of the present embodiment, and (b) shows the result of Comparative Example 3. Also in the second and third embodiments described later, the same result as that shown in FIG. 6A is obtained.

  In Comparative Example 3, heat treatment (about 600 ° C.) for obtaining ohmic contact in a state where the surface of the source electrode and the surface of the drain electrode are exposed is performed in an oxygen atmosphere without forming the Al compound film in this embodiment. The By this heat treatment, an aluminum oxide (AlO) cap film was formed covering the surface of the source electrode and the surface of the drain electrode, and an ohmic contact was obtained. Others are the same as in this embodiment.

  From the results shown in FIG. 6, it is confirmed in the present embodiment that good ohmic characteristics are secured. On the other hand, when the cap film of AlO is formed by heat treatment as in Comparative Example 3, the contact resistance is about twice that of the case where the cap film of AlO is formed before heat treatment as in this embodiment. It is understood that it is high. This is because when the cap film of AlO is formed by heat treatment, oxidation proceeds through the grain boundaries of Al, so it is difficult to control the thickness of AlO, and the resistance of Ti / Al of the source electrode and the drain electrode It is considered to be a rising effect.

  As described above, according to the present embodiment, highly reliable AlGaN / GaN.HEMT in which the occurrence of surface roughness of the source electrode 4 and the drain electrode 5 which are electrodes containing Al due to heat treatment is reliably suppressed. Is realized.

Second Embodiment
In the present embodiment, as in the first embodiment, a Schottky-type AlGaN / GaN.HEMT is disclosed, but it is different from the first embodiment in that the formation mode of the Al compound film is different.
7 to 8 are schematic cross-sectional views showing main steps of a method of manufacturing a Schottky-type AlGaN / GaN.HEMT according to the second embodiment. In the second embodiment, the components corresponding to the first embodiment are denoted by the same reference numerals, and the detailed description thereof is omitted.

  First, as in the first embodiment, the steps of FIG. 1A to FIG. 2A are performed. The state corresponding to FIG. 2 (a) is shown in FIG. 7 (a). Then, in a state where the source electrode 4 and the drain electrode 5 are covered with the Al compound film 6 as in the first embodiment, a heat treatment for obtaining an ohmic contact is performed.

  The Al compound film 6 is a compound of the electrode material (Al) itself, and has a high melting point (2072 ° C. for AlO, 2200 ° C. for AlN). Therefore, surface roughening due to reaction with external air (predetermined atmosphere) of the surface of source electrode 4 and the surface of drain electrode 5 is suppressed, and aggregation of high melting point metal (Ti) or high melting point metal (Ti) and electrode material ( It is possible to prevent alloying with Al). The heat treatment is performed in a state where the boundary between the first electrode layers 4a and 5a and the second electrode layers 4b and 5b is also covered with the Al compound film 6, and therefore, the refractory metal (Ti) at the boundary And the alloying of the high melting point metal (Ti) and the electrode material (Al) are also suppressed.

Subsequently, as shown in FIG. 7B, the insulating protective film 7 is formed on the entire surface of the Al compound film 6 with the Al compound film 6 left on the entire surface without being etched.
Specifically, an insulator such as silicon nitride (SiN) is deposited on the entire surface of the Al compound film 6 to a thickness of about 10 nm to about 100 nm, for example, about 50 nm, using plasma CVD or the like. Thereby, the protective insulating film 7 is formed. The protective insulating film 7 has a function of protecting the surface of the compound semiconductor layer 2.

Subsequently, as shown in FIG. 7C, the gate electrode 8 is formed.
Specifically, first, the Al compound film 6 and the protective insulating film 7 are penetrated to expose the surface of the compound semiconductor layer 2 at the planned gate electrode formation portions of the Al compound film 6 and the protective insulating film 7 by lithography and dry etching. For example, a fluorine-based gas is used for dry etching for forming the electrode groove 13 to be formed.
The resist used for lithography is removed by ashing treatment or wet treatment using a predetermined chemical solution.

  Next, a resist mask for forming a gate electrode is formed. Here, for example, a two-layered resist having a wedge structure suitable for the vapor deposition method and the lift-off method is used. This resist is applied on the protective insulating film 6 to form an opening for exposing the portions of the protective insulating film 6 and the electrode groove 13 of the protective insulating film 7. Thus, a resist mask having the opening is formed.

  Using this resist mask, for example, Ni / Au as an electrode material is deposited on the resist mask including the inside of the opening that exposes the portions of the electrode grooves 13 of the protective insulating film 6 and the protective insulating film 7 by evaporation, for example. . The thickness of Ni is about 30 nm, and the thickness of Au is about 400 nm. The resist mask and Ni / Au deposited thereon are removed by a lift-off method. As described above, the inside of the electrode groove 13 is filled with a part of the electrode material, and the gate electrode 8 having a shape that rides on the protective insulating film 7 is formed.

Subsequently, as shown in FIGS. 8 (a) and 8 (b), the same steps as those in FIGS. 3 (b) and 4 (a) and 4 (b) of the first embodiment are performed.
Thus, the AlGaN / GaN.HEMT according to the present embodiment is formed.

  As described above, according to the present embodiment, highly reliable AlGaN / GaN.HEMT in which the occurrence of surface roughness of the source electrode 4 and the drain electrode 5 which are electrodes containing Al due to heat treatment is reliably suppressed. Is realized.

Third Embodiment
In the present embodiment, as in the first embodiment, a Schottky-type AlGaN / GaN.HEMT is disclosed, but it is different from the first embodiment in that the formation mode of the Al compound film is different.
9 to 10 are schematic cross-sectional views showing the main steps of a method of manufacturing a Schottky-type AlGaN / GaN.HEMT according to the third embodiment. In the second embodiment, the components corresponding to the first embodiment are denoted by the same reference numerals, and the detailed description thereof is omitted.

  First, as in the first embodiment, the steps of FIG. 1A to FIG. 2A are performed. A state corresponding to FIG. 2 (a) is shown in FIG. 9 (a). Then, in a state where the source electrode 4 and the drain electrode 5 are covered with the Al compound film 6 as in the first embodiment, a heat treatment for obtaining an ohmic contact is performed.

  The Al compound film 6 is a compound of the electrode material (Al) itself, and has a high melting point (2072 ° C. for AlO, 2200 ° C. for AlN). Therefore, surface roughening due to reaction with external air (predetermined atmosphere) of the surface of source electrode 4 and the surface of drain electrode 5 is suppressed, and aggregation of high melting point metal (Ti) or high melting point metal (Ti) and electrode material ( It is possible to prevent alloying with Al). The heat treatment is performed in a state where the boundary between the first electrode layers 4a and 5a and the second electrode layers 4b and 5b is also covered with the Al compound film 6, and therefore, the refractory metal (Ti) at the boundary And the alloying of the high melting point metal (Ti) and the electrode material (Al) are also suppressed.

Subsequently, as shown in FIG. 9B, the gate electrode 8 is formed.
In the present embodiment, the Al compound film 6 doubles as a protective function of the surface of the compound semiconductor layer 2 without forming the insulating protective film 7 of the first embodiment. This reduces the number of processes.

Specifically, dry etching is first performed to form an electrode groove 6 a penetrating the Al compound film 6 to expose the surface of the compound semiconductor layer 2 at the gate electrode formation planned portion of the Al compound film 6 by lithography and dry etching. For example, a fluorine-based gas is used.
The resist used for lithography is removed by ashing treatment or wet treatment using a predetermined chemical solution.

  Next, a resist mask for forming a gate electrode is formed. Here, for example, a two-layered resist having a wedge structure suitable for the vapor deposition method and the lift-off method is used. This resist is applied on the protective insulating film 6 to form an opening for exposing the portion of the electrode groove 6 a of the protective insulating film 6. Thus, a resist mask having the opening is formed.

  Using this resist mask, for example, Ni / Au as an electrode material is deposited on the resist mask including the inside of the opening for exposing the portion of the electrode groove 6 a of the protective insulating film 6 by, for example, a vapor deposition method. The thickness of Ni is about 30 nm, and the thickness of Au is about 400 nm. The resist mask and Ni / Au deposited thereon are removed by a lift-off method. As described above, the gate electrode 8 is formed in such a shape that the inside of the electrode groove 6a is embedded with a part of the electrode material, and the protective insulating film 7 rides on it.

Subsequently, as shown in FIGS. 10A and 10B, the same steps as those in FIGS. 3B and 4A in the first embodiment are performed.
Thus, the AlGaN / GaN.HEMT according to the present embodiment is formed.

  As described above, according to the present embodiment, highly reliable AlGaN / GaN.HEMT in which the occurrence of surface roughness of the source electrode 4 and the drain electrode 5 which are electrodes containing Al due to heat treatment is reliably suppressed. Is realized.

  In the first to third embodiments, the Schottky type InAlGaN / InAlN / GaN HEMT in which the gate electrode 8 is in contact with the surface of the compound semiconductor layer 2 has been described. However, MIS type InAlGaN / InAlN / GaN · It is also possible to apply to HEMT. In the case of the MIS type, for example, in the first embodiment, for example, the protective insulating film 7 is used as a gate insulating film. The gate electrode 8 may be formed on the compound semiconductor layer 2 via the protective insulating film 7 without forming the electrode groove 7 a in the protective insulating film 7.

Fourth Embodiment
The present embodiment discloses a power supply apparatus to which one type of AlGaN / GaN HEMT selected from the first to third embodiments is applied.
FIG. 11 is a connection diagram showing a schematic configuration of the power supply device according to the fourth embodiment.

The power supply device according to the present embodiment includes a high voltage primary side circuit 21 and a low voltage secondary side circuit 22, and a transformer 23 disposed between the primary side circuit 21 and the secondary side circuit 22. Ru.
The primary side circuit 21 is configured to include an AC power supply 24, a so-called bridge rectifier circuit 25, and a plurality of (here, four) switching elements 26a, 26b, 26c and 26d. The bridge rectifier circuit 25 also has a switching element 26e.
The secondary side circuit 22 is configured to include a plurality of (here, three) switching elements 27a, 27b, and 27c.

  In the present embodiment, the switching elements 26a, 26b, 26c, 26d, 26e of the primary side circuit 21 are one type of AlGaN / GaN HEMT selected from the first to third embodiments. On the other hand, the switching elements 27a, 27b and 27c of the secondary side circuit 22 are assumed to be ordinary MIS-FETs using silicon.

  In the present embodiment, an AlGaN / GaN.HEMT in which the occurrence of surface roughness of the source electrode and the drain electrode which are electrodes containing Al due to the heat treatment is surely suppressed is applied to the power supply circuit. Thereby, a highly reliable power supply circuit of high power is realized.

Fifth Embodiment
The present embodiment discloses a high frequency amplifier to which one type of AlGaN / GaN HEMT selected from the first to third embodiments is applied.
FIG. 12 is a connection diagram showing a schematic configuration of the high frequency amplifier according to the fifth embodiment.

The high frequency amplifier according to the present embodiment is configured to include a digital predistortion circuit 31, mixers 32a and 32b, and a power amplifier 33.
The digital predistortion circuit 31 compensates for non-linear distortion of the input signal. The mixer 32a mixes an AC signal with an input signal whose nonlinear distortion has been compensated. The power amplifier 33 amplifies an input signal mixed with an alternating current signal, and includes one type of AlGaN / GaN HEMT selected from the first to third embodiments. In FIG. 12, for example, by switching the switch, the signal on the output side can be mixed with an AC signal by the mixer 32b and sent to the digital predistortion circuit 31.

  In the present embodiment, an AlGaN / GaN.HEMT in which the occurrence of surface roughness of the source electrode and the drain electrode which are electrodes containing Al due to heat treatment is reliably suppressed is applied to a high frequency amplifier. As a result, a highly reliable high voltage high frequency amplifier is realized.

(Other embodiments)
In the first to fifth embodiments, an AlGaN / GaN HEMT is illustrated as a compound semiconductor device. The compound semiconductor device can be applied to the following HEMT as well as the AlGaN / GaN.HEMT.

・ Other HEMT example 1
In this example, an InAlN / GaN HEMT is disclosed as a compound semiconductor device.
InAlN and GaN are compound semiconductors whose lattice constants can be made close to each other depending on the composition. In this case, in the first to fifth embodiments described above, the electron transit layer is formed of i-GaN, the intermediate layer is formed of i-InAlN, the electron supply layer is formed of n-InAlN, and the cap layer is formed of n-GaN. Further, since the piezoelectric polarization in this case hardly occurs, the two-dimensional electron gas is mainly generated by the spontaneous polarization of InAlN.

  According to this example, similarly to the above-described AlGaN / GaN HEMT, highly reliable InAlN / GaN in which the occurrence of surface roughness of the source electrode and the drain electrode which are electrodes containing Al by heat treatment is reliably suppressed.・ HEMT is realized.

・ Other HEMT example 2
In this example, an InAlGaN / GaN HEMT is disclosed as a compound semiconductor device.
GaN and InAlGaN are compound semiconductors whose lattice constant can be made smaller by the composition than the former. In this case, in the first to fifth embodiments described above, the electron transit layer is formed of i-GaN, the intermediate layer is formed of i-InAlGaN, the electron supply layer is formed of n-InAlGaN, and the cap layer is formed of n-GaN.

  According to this example, similarly to the above-described AlGaN / GaN HEMT, highly reliable InAlGaN / GaN in which the occurrence of surface roughness of the source electrode and the drain electrode which are electrodes containing Al by heat treatment is reliably suppressed.・ HEMT is realized.

  Hereinafter, various aspects of a compound semiconductor device and a method of manufacturing the same, and a power supply device and a high frequency amplifier will be collectively described as a note.

(Supplementary Note 1) Compound Semiconductor Layer
An electrode containing aluminum,
What is claimed is: 1. A compound semiconductor device comprising: a protective film containing an aluminum compound, which covers and covers the upper surface and the side surface of the electrode.

  (Supplementary Note 2) The compound semiconductor device according to Supplementary Note 1, wherein the protective film contains at least one selected from aluminum oxide, aluminum nitride, aluminum oxynitride, and aluminum carbide.

(Supplementary Note 3) The electrode includes a first electrode layer and a second electrode layer formed on the first electrode layer,
The compound semiconductor device according to claim 1 or 2, wherein the protective film covers a boundary portion between the first electrode layer and the second electrode layer.

  (Supplementary Note 4) The protective film is separately formed corresponding to the electrode, and there is a non-formed portion on the compound semiconductor layer. The compound semiconductor device of description.

  (Supplementary Note 5) The compound semiconductor device according to any one of supplementary notes 1 to 4, further including an upper protective film covering the protective film.

(Supplementary Note 6) A step of forming an electrode containing aluminum on the compound semiconductor layer
Forming a protective film containing an aluminum compound covering the electrode;
Heat treating the electrode in a state in which the electrode is covered with the protective film.

  (Supplementary Note 7) The method for producing a compound semiconductor device according to Supplementary Note 6, wherein the protective film contains at least one selected from aluminum oxide, aluminum nitride, aluminum oxynitride, and aluminum carbide. .

(Supplementary Note 8) The electrode includes a first electrode layer and a second electrode layer formed on the first electrode layer,
The method of manufacturing a compound semiconductor device according to claim 6 or 7, wherein the protective film covers a boundary between the first electrode layer and the second electrode layer.

(Supplementary Note 9) The method further includes the step of separating the protective film corresponding to the electrode,
The method for manufacturing a compound semiconductor device according to any one of appendices 6 to 8, wherein there is a non-formation part of the protective film on the compound semiconductor layer.

  (Supplementary Note 10) A method of manufacturing a compound semiconductor device according to any one of Supplementary notes 6 to 9, further comprising the step of forming an upper protective film covering the protective film.

(Supplementary note 11) A power supply circuit including a transformer and a high voltage circuit and a low voltage circuit sandwiching the transformer,
The high voltage circuit comprises a transistor,
The transistor is
A compound semiconductor layer,
An electrode containing aluminum,
A protective film containing an aluminum compound, which covers and covers the upper surface and the side surface of the electrode.

(Supplementary Note 12) A high frequency amplifier that amplifies and outputs an input high frequency voltage, and
Have a transistor,
The transistor is
A compound semiconductor layer,
An electrode containing aluminum,
And a protective film containing an aluminum compound, which covers and covers the upper surface and the side surface of the electrode.

Reference Signs List 1 SiC substrate 2 compound semiconductor layer 2a buffer layer 2b electron traveling layer 2c intermediate layer 2d electron supply layer 2e cap layer 3 element isolation structure 4 source electrode 4a, 5a first electrode layer 4b, 5b second electrode layer 5 drain electrode 6 Al compound film 6a, 7a, 13 electrode groove 7 protective insulating film 10 opening 8 gate electrode 9 interlayer insulating film 11 barrier metal layer 12 wiring layer 21 primary side circuit 22 secondary side circuit 23 transformer 24 AC power supply 25 bridge rectification circuit 26a , 26b, 26c, 26d, 26e, 27a, 27b, 27c switching element 31 digital predistortion circuit 32a, 32b mixer 33 power amplifier

Claims (8)

A compound semiconductor layer,
An aluminum-containing first electrode formed on the compound semiconductor layer and in ohmic contact with the compound semiconductor layer ;
A second electrode formed above the compound semiconductor layer;
Covering over the side surface from the upper surface of the first electrode, seen including a protective layer containing aluminum compound,
The compound semiconductor device, wherein the protective film is formed on the first electrode, has a non-formed portion on the compound semiconductor layer, and is separated from the second electrode .   The compound semiconductor device according to claim 1, wherein the protective film contains at least one selected from aluminum oxide, aluminum nitride, aluminum oxynitride, and aluminum carbide. The first electrode has a first electrode layer and a second electrode layer formed on the first electrode layer,
The compound semiconductor device according to claim 1, wherein the protective film covers a boundary portion between the first electrode layer and the second electrode layer. The compound semiconductor device according to any one of claims 1 to 3 , further comprising an upper protective film covering the protective film. Forming a first electrode containing aluminum on the compound semiconductor layer;
Forming an aluminum compound-containing protective film covering the first electrode;
In a state where the first electrode is covered with the protective film, and then heat treating the first electrode, and said first electrode said compound semiconductor layer Ru is ohmic contact process,
Processing the protective film into an island corresponding to the first electrode;
Look including a step of forming a second electrode above the compound semiconductor layer,
The method for manufacturing a compound semiconductor device, wherein the protective film has a non-formed portion on the compound semiconductor layer and is separated from the second electrode . 6. The method of manufacturing a compound semiconductor device according to claim 5 , wherein the protective film contains at least one selected from aluminum oxide, aluminum nitride, aluminum oxynitride, and aluminum carbide. The first electrode has a first electrode layer and a second electrode layer formed on the first electrode layer,
The protective film manufacturing method of a compound semiconductor device according to claim 5 or 6, characterized in that covering the boundary portion between the second electrode layer and the first electrode layer. The method of manufacturing a compound semiconductor device according to any one of claims 5 to 7 , further comprising the step of forming an upper protective film covering the protective film.