JP2014160761A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device in which leakage current is reduced.SOLUTION: The semiconductor device comprises: an electron transit layer made of nitride semiconductor; an electron supply layer which is formed on the electron transit layer and made of nitride semiconductor having a bandgap larger than that of the electron transit layer; a field plate layer which is formed on a part of the electron supply layer and made of nitride semiconductor having a bandgap energy smaller than that of the electron supply layer; a lower electrode layer made of metal, which is formed so as to be in contact with the electron supply layer and the field plate layer and is in Schottky contact with the electron supply layer and the field plate layer; and an upper electrode layer which is formed so as to cover the lower electrode layer and made of metal having a work function smaller than that of the metal making up the lower electrode layer. The electron supply layer and the field plate layer are separated from the upper electrode layer.

Description

  The present invention relates to a semiconductor device.

  Conventionally, in a semiconductor device using a two-dimensional electron gas (2DEG) layer as a current path, an electron transit layer is made of GaN, and an electron supply layer is formed on a semiconductor stacked portion made of AlGaN, and a field plate layer made of GaN is formed, There has been proposed a semiconductor device in which an electrode is formed so as to be in contact with an electron supply layer and a field plate layer. (For example, refer to Patent Document 1). In a semiconductor device using the 2DEG layer as a current path, there is a problem that the breakdown voltage of the element is lowered due to electric field concentration at the electrode end, and reliability is impaired. For this reason, the field plate layer is formed, and the electron gas in the 2DEG layer below the field plate layer is diluted to reduce the electric field concentration at the electrode end.

  FIG. 18 is a schematic diagram illustrating a cross section of a semiconductor device according to the related art. A nitride semiconductor device 1000 illustrated in FIG. 18 is a Schottky barrier diode (SBD), and includes an anode electrode 1003 that is in Schottky contact with the semiconductor stacked portion 1001 and a cathode electrode 1004 that is in ohmic contact with the semiconductor stacked portion 1001. Furthermore, the anode electrode 1003 includes a lower electrode layer 1003a and an upper electrode layer 1003b. The lower electrode layer 1003a is in Schottky contact with the semiconductor stacked portion 1001 and the field plate layer 1002, and the upper electrode layer 1003b formed on the lower electrode layer 1003a is formed to improve the bonding with the wiring electrode ( For example, see Patent Document 2).

JP 2001-230407 A JP 2011-54845 A

  However, when the upper electrode layer 1003b is formed on the lower electrode layer 1003a in this way, the upper electrode layer 1003b comes into contact with the field plate layer 1002, and a large leakage current is generated from the contact portion. It became clear by the people.

  The present invention has been made in view of the above, and an object thereof is to provide a semiconductor device in which leakage current is suppressed.

  In order to solve the above-described problems and achieve the object, a semiconductor device according to the present invention is formed on an electron transit layer made of a nitride semiconductor and the electron transit layer, and has a band gap larger than that of the electron transit layer. An electron supply layer made of a large nitride semiconductor, a field plate layer made of a nitride semiconductor having a band gap energy smaller than that of the electron supply layer formed on a part of the electron supply layer, the electron supply layer, and the field A lower electrode layer made of metal in Schottky contact with the electron supply layer and the field plate layer, and a metal formed to cover the lower electrode layer and forming the lower electrode layer; An upper electrode layer made of a metal having a lower work function than the electron supply layer and the field. Characterized in that the rate layer and the upper electrode layer are separated.

  In the semiconductor device according to the present invention, in the above invention, the entire upper electrode layer is formed in a region on the lower electrode layer, and the lower electrode layer is interposed between the field plate layer and the upper electrode layer. By doing so, the field plate layer and the upper electrode layer are separated from each other.

  In the semiconductor device according to the present invention, in the above invention, an insulating film is formed between the field plate layer and the upper electrode layer, and the field plate layer and the upper electrode layer are separated by the insulating film. It is characterized by.

  In the semiconductor device according to the present invention as set forth in the invention described above, the lower electrode layer and the upper electrode layer are formed by a lift-off method.

  The semiconductor device according to the present invention is characterized in that, in the above invention, the insulating film has a higher breakdown field strength than the field plate layer.

In the semiconductor device according to the present invention as set forth in the invention described above, the insulating film contains SiO ₂ or SiN _x .

  In the semiconductor device according to the present invention as set forth in the invention described above, the insulating film is formed of two or more kinds of stacked films.

  In the semiconductor device according to the present invention, in the above invention, the insulating film has at least one or more stepped portions, and the electrodes run on at least one or more stepped portions of the previous stepped portions. It is characterized by.

  In the semiconductor device according to the present invention, the lower electrode layer is made of Ni and the upper electrode layer is made of Ti or Al.

  In the semiconductor device according to the present invention, the electrode is an anode electrode, a cathode electrode formed so as to be in contact with the electron supply layer, and a diode.

  In the semiconductor device according to the present invention, in the above invention, the electrode is a gate electrode, is formed so as to be in contact with the electron supply layer, and has a source electrode and a drain electrode formed so as to sandwich the gate electrode. And a field effect transistor.

  According to the present invention, a semiconductor device in which leakage current is suppressed can be realized.

FIG. 1 is a schematic diagram showing a cross section of the semiconductor device according to the first embodiment of the present invention. FIG. 2 is a schematic diagram showing a cross section of a semiconductor stacked portion in the semiconductor device according to the first embodiment of the present invention. FIG. 3 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 4 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 6 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 7 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 8 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 9 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 10 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 11 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 12 is a diagram for explaining an example of a method of manufacturing a semiconductor device according to the first embodiment of the present invention. FIG. 13 is a schematic diagram showing a cross section of the semiconductor device according to the second embodiment of the present invention. FIG. 14 is a schematic diagram showing a cross section of a semiconductor device according to the third embodiment of the present invention. FIG. 15 is a diagram showing a cross section of a semiconductor device according to the fourth embodiment of the present invention. FIG. 16 is a schematic diagram showing a cross section of a semiconductor device according to the fifth embodiment of the present invention. FIG. 17 is a schematic diagram showing a cross section of a semiconductor device according to the sixth embodiment of the present invention. FIG. 18 is a schematic diagram illustrating a cross section of a semiconductor device according to the related art.

  Embodiments of a semiconductor device according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments. In the description of the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. Further, the drawings are schematic, and it should be noted that the relationship between the thickness and width of each layer, the ratio of each layer, and the like may differ from the actual situation. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included.

(Embodiment 1)
First, the semiconductor device according to the first embodiment of the present invention will be described in comparison with the nitride semiconductor device 1000 according to the prior art. FIG. 1 is a schematic diagram showing a cross section of the semiconductor device according to the first embodiment of the present invention. As shown in FIG. 1, the nitride semiconductor device 100 is an SBD, like the nitride semiconductor device 1000 according to the prior art, and includes an anode electrode 103 that is in Schottky contact with the semiconductor stacked portion 101, a semiconductor stacked portion 101, and A cathode electrode 104 in ohmic contact is provided. Furthermore, the anode electrode 103 includes a lower electrode layer 103a and an upper electrode layer 103b. The lower electrode layer 103a is in Schottky contact with the semiconductor stacked portion 101 and the field plate layer 102, and the upper electrode layer 103b formed on the lower electrode layer 103a is formed to improve the bonding with the wiring electrode. On the other hand, in the nitride semiconductor device 100, unlike the nitride semiconductor device 1000 according to the prior art, the field plate layer 102 and the upper electrode layer 103b are separated by an insulating film 105 composed of two layers.

  Next, the structure of nitride semiconductor device 100 according to the first embodiment of the present invention will be described. First, the semiconductor stacked unit 101 constituting the nitride semiconductor device 100 according to the first embodiment will be described. FIG. 2 is a schematic diagram showing a cross section of a semiconductor stacked portion in the semiconductor device according to the first embodiment of the present invention. In the semiconductor stacked unit 101, a plurality of AlN layers and GaN layers are alternately stacked as a buffer layer 12 on a substrate 11 made of silicon (Si). However, the substrate is not limited to Si, but may be sapphire, SiC, ZnO, GaN, or the like.

Further, an electron transit layer 13 made of GaN and an electron supply layer 14 made of AlGaN are sequentially stacked on the buffer layer 12. AlGaN constituting the electron supply layer 14 is a mixed crystal of AlN and GaN, and has a larger band gap energy than GaN constituting the electron transit layer 13, and the characteristics of the band gap, spontaneous polarization, and piezo polarization change depending on the composition ratio. . The electron supply layer 14 is a single layer of, for example, Al _0.25 Ga _0.75 N. However, the electron supply layer 14 is not limited to an AlGaN single layer, and may be a pseudo mixed crystal layer in which a plurality of AlN layers and GaN layers are alternately stacked. In that case, the band gap energy when the pseudo mixed crystal layer is averaged in the thickness direction may be larger than that of the electron transit layer. Further, the thicknesses of the AlN layer and the GaN layer may be adjusted so that 2DEG is not generated in the pseudo mixed crystal layer.

  At the interface between the electron transit layer 13 and the electron supply layer 14, a 2DEG layer 13 a whose concentration is controlled by controlling the Al composition ratio and thickness of the electron supply layer 14 is formed. The 2DEG layer 13a serves as a current path through which electrons flow. Since the 2DEG layer 13a has a small electron impurity scattering, the 2DEG layer 13a becomes a high mobility and low resistance electric conductive layer, and provides a current path between the electrodes formed on the electron supply layer. Thereby, the semiconductor stacked portion 101 is configured. Note that the semiconductor stacked units 201, 301, 401, 501, and 601 according to each embodiment described later and the semiconductor stacked unit 1001 according to the related art have the same structure as the semiconductor stacked unit 101, and thus description thereof is omitted.

  Next, a part of the semiconductor stacked portion 101 has a band gap energy smaller than that of the electron supply layer 14 which is the outermost portion of the semiconductor stacked portion 101, for example, AlGaN or GaN having an Al composition ratio lower than that of the electron supply layer 14. A field plate layer 102 made of, for example, is formed. Further, in order to constitute the SBD, an anode electrode 103 in Schottky contact with the electron supply layer 14 and the field plate layer 102 and a cathode electrode 104 in ohmic contact with the electron supply layer 14 are formed. Here, the anode electrode 103 is in Schottky contact with the electron supply layer 14 and the field plate layer 102, for example, a lower electrode layer 103a made of Ni, and an upper electrode made of, for example, Ti or Al, which is well-bonded to the wiring electrode. Layer 103b.

Here, when the nitride semiconductor device 100 according to the first embodiment is compared with the nitride semiconductor device 1000 according to the prior art, the nitride semiconductor device 100 according to the first embodiment has an insulating film 105. Is formed. The insulating film 105 is made of, for example, SiO ₂ and may have a stepped portion as shown in FIG. Such a step portion has an effect of dispersing the electric field concentration generated at the electrode end. By this insulating film 105, the field plate layer 102 and the upper electrode layer 103b are separated from each other. The insulating film 105 is not limited to SiO ₂ but may be SiN _x .

Further, in the above embodiment, what is described as SiO _2, it refers to a collection of what is referred to as SiO ₂ as a general designation. That is, for example, it includes SiON in which nitrogen is partially mixed when SiO ₂ is formed by PCVD.

  Next, the operation of nitride semiconductor device 100 according to the first embodiment will be described in comparison with the operation of nitride semiconductor device 1000 according to the prior art. First, when a voltage is applied to the anode electrode 1003 and the cathode electrode 1004 of the nitride semiconductor device 1000 according to the prior art, a current flows for a positive voltage from the anode electrode 1003 toward the cathode electrode 1004. On the other hand, it is desirable that no current flows in the nitride semiconductor device 1000 that is an SBD due to the Schottky barrier of the anode electrode 1003 with respect to the reverse voltage. However, as shown in FIG. 18, in the nitride semiconductor device 1000, the upper electrode layer 1003b and the field plate layer 1002 are in contact with each other. Therefore, when the work function of the metal forming the upper electrode layer 1003b is smaller than the work function of the metal forming the lower electrode layer 1003a, when a reverse voltage is applied, the field plate layer 1002 and the lower electrode layer 1003a A current flows through the upper electrode layer 1003b having a small Schottky barrier, and a large leak current is generated.

  On the other hand, in nitride semiconductor device 100 according to the first embodiment, since insulating film 105 is formed, upper electrode layer 103b and field plate layer 102 are separated from each other. Therefore, no leakage current flows from the field plate layer 102 to the upper electrode layer 103b. Thereby, a semiconductor device in which leakage current is suppressed can be realized.

  Leakage current is a very important parameter for practical use because it directly affects the rectification action in a diode, for example. The occurrence of such a leak current has not been clarified at all so far, and has been newly clarified by the present inventors' research, and further, means for solving by the present invention have been presented.

  Furthermore, in such a semiconductor device, as described above, there is a problem that the reliability of the semiconductor device is impaired because electric field concentration occurs at the electrode end portion of the anode electrode and the breakdown voltage decreases. Therefore, the nitride semiconductor device 100 according to the first embodiment reduces the electric field concentration at the electrode end by forming the field plate layer 102 and diluting the electron gas in the 2DEG layer below the field plate layer 102. It has a structure to let you. Further, by providing a stepped portion in the insulating film 105, electric field concentration is dispersed.

Here, in the nitride semiconductor device 100 according to the first embodiment, the dielectric breakdown field strength of GaN forming the field plate layer 102 is about 3.3 MV / cm, whereas the insulating film 105 is formed. The dielectric breakdown electric field strength of SiO ₂ is about 9 MV / cm. Therefore, in nitride semiconductor device 100 according to the first embodiment, the end of anode electrode 103 where electric field concentration is likely to be in contact is in contact with SiO ₂ having a high dielectric breakdown electric field strength. Thus, the nitride semiconductor device 100 according to the first embodiment realizes a highly reliable semiconductor device that not only suppresses the leakage current but also has an improved breakdown voltage.

  As described above, the nitride semiconductor device 100 according to the first embodiment is a highly reliable semiconductor device that suppresses leakage current and has high reliability.

  Next, a method for manufacturing the nitride semiconductor device 100 according to the first embodiment will be described. 3 to 12 are diagrams for explaining an example of the method for manufacturing the semiconductor device according to the first embodiment of the present invention. First, as illustrated in FIG. 3, the semiconductor stacked unit 101 is prepared. The semiconductor stacked unit 101 forms a buffer layer 12 having a film thickness of, for example, about 2 μm by alternately forming a plurality of AlN layers and GaN layers on a substrate 11 made of Si as a support substrate. Subsequently, an electron transit layer 13 made of GaN is formed on the buffer layer 12 so as to have a thickness of about 1 μm, for example. For example, a metal organic chemical vapor deposition method (MOCVD method) can be used for forming each thin film in the buffer layer 12 and the electron transit layer 13. However, the present invention is not limited to this, and various film forming methods such as a hydride vapor phase epitaxy method (HVPE method) and a molecular beam epitaxy method (MBE method) may be used.

Next, by forming an Al _0.25 Ga _0.75 N film on the electron transit layer 13, the electron supply layer 14 made of AlGaN having a thickness of, for example, about 25 nm is formed. For the film formation of the electron supply layer 14, as with the electron transit layer 13, various film formation methods such as the HVPE method and the MBE method can be used in addition to the MOCVD method. However, in this embodiment, the electron supply layer 14 is formed so that the carbon (C) concentration in the film is about 2 × 10 ¹⁷ cm ⁻³ or more, for example, about 2.5 × 10 ¹⁷ cm ⁻³ . For example, when the MOCVD method is used, the electron supply layer 14 containing C as an acceptor can be formed by autodoping with C contained in an organometallic element.

  As described above, the semiconductor stacked portion 101 including the electron transit layer 13 and the electron supply layer 14 is formed on the substrate 11 with the buffer layer 12 interposed therebetween. Further, as shown in FIG. 4, a field plate layer 102 made of GaN is formed on a part of the semiconductor stacked portion 101 by a photolithography process using a photoresist as an etching mask.

  Here, the cathode electrode 104 is formed by a lift-off method. First, as shown in FIG. 5, a resist R is formed in a region other than the region where the cathode electrode 104 is to be formed. Thereafter, as shown in FIG. 6, Ti and Al are vapor-deposited in this order as the metal that becomes the cathode electrode 104. Here, when the resist R is removed, the cathode electrode 104 is formed as shown in FIG.

  Next, as shown in FIG. 8, the insulating film 105 is formed by a photolithography process using a photoresist as an etching mask. Furthermore, the insulating film 105 preferably has a stepped portion in order to reduce electric field concentration, and the stepped portion is formed in the two-layered insulating film 105 as shown in FIG.

Next, the anode electrode 103 is formed. First, in order to form the anode electrode 103, as shown in FIG. 10, a resist R is formed in a region other than the region where the anode electrode 103 is to be formed. Thereafter, as shown in FIG. 11, Ni is vapor-deposited as a metal that becomes the lower electrode layer 103 a of the anode electrode 103. At this time, a region where no metal is deposited is formed in the shadowed portion of the resist R. Further, Al is vapor-deposited as a metal that becomes the upper electrode layer 103b. Then, the upper electrode layer 103b is formed so as to cover the region where the lower electrode layer 103a is not formed. At this time, in the nitride semiconductor device 100 according to the first embodiment, the end portion of the upper electrode layer 103b and the insulating film 105 are in contact with each other as shown in FIG. On the other hand, in nitride semiconductor device 1000 according to the prior art that does not have an insulating film, the end portion of upper electrode layer 1003b and field plate layer 1002 come into contact with each other, and a leak current is generated from this contact portion. Thus, the nitride semiconductor device 100 according to the first embodiment suppresses the leakage current. Further, the nitride semiconductor device 100 according to the first embodiment has a high breakdown voltage and a highly reliable semiconductor device because the end portion of the anode electrode 103 is in contact with SiO ₂ having a high dielectric breakdown electric field strength. Realized.

  As described above, the nitride semiconductor device 100 according to the first embodiment is manufactured, and a semiconductor device with reduced leakage current and high reliability is realized.

(Embodiment 2)
Next, the nitride semiconductor device 200 according to the second embodiment of the present invention will be described. FIG. 13 is a schematic diagram showing a cross section of the semiconductor device according to the second embodiment of the present invention. As shown in FIG. 13, the nitride semiconductor device 200 according to the second embodiment is an SBD, and an anode electrode 203 and a cathode electrode 204 are formed on a semiconductor stacked portion 201. The anode electrode 203 includes a lower electrode layer 203a and an upper electrode layer 203b. In addition, a field plate layer 202 and an insulating film 205 are formed to reduce electric field concentration. Here, the insulating film 205 is composed of two layers of an insulating film 205a made of SiN _x and an insulating film 205b made of SiO ₂ . Thus, the nitride semiconductor device 200 according to the second embodiment realizes a semiconductor device in which the field plate layer 202 and the upper electrode layer 203b are separated from each other and leakage current is suppressed. In this case, since the insulating film 205a made of SiN _x is formed on the semiconductor layer, the interface state density is reduced, and the effect of suppressing the collapse can be obtained.

(Embodiment 3)
Next, a nitride semiconductor device 300 according to the third embodiment of the present invention will be described. FIG. 14 is a schematic diagram showing a cross section of a semiconductor device according to the third embodiment of the present invention. As shown in FIG. 14, the nitride semiconductor device 300 according to the third embodiment is an SBD, and an anode electrode 303 and a cathode electrode 304 are formed on a semiconductor stacked portion 301. The anode electrode 303 includes a lower electrode layer 303a and an upper electrode layer 303b. In addition, a field plate layer 302 and an insulating film 305 are formed to reduce electric field concentration. Here, in contrast to the second embodiment, the insulating film 305 includes two layers of an insulating film 305a made of SiO ₂ and an insulating film 305b made of SiN _x . Thereby, the nitride semiconductor device 300 according to the third embodiment realizes a semiconductor device in which the field plate layer 302 and the upper electrode layer 303b are separated from each other and leakage current is suppressed.

  As described above, as in the second and third embodiments, the insulating film may be formed of two or more layers having different compositions. As a result, a semiconductor device having a high breakdown voltage and high reliability can be realized by using a material having a higher dielectric breakdown electric field strength in a region where electric field concentration is likely to occur, as well as suppressing leakage current.

(Embodiment 4)
Next, a nitride semiconductor device 400 according to the fourth embodiment of the present invention will be described. FIG. 15 is a diagram showing a cross section of a semiconductor device according to the fourth embodiment of the present invention. As shown in FIG. 15, the nitride semiconductor device 400 according to the fourth embodiment is an SBD, and an anode electrode 403 and a cathode electrode 404 are formed on a semiconductor stacked portion 401. The anode electrode 403 includes a lower electrode layer 403a and an upper electrode layer 403b. In addition, a field plate layer 402 is formed to reduce electric field concentration. Here, the nitride semiconductor device 400 does not have an insulating film, but the entire upper electrode layer 403b is formed in a region on the lower electrode layer 403a. At this time, the lower electrode layer 403a is always interposed between the field plate layer 402 and the upper electrode layer 403b. That is, the field plate layer 402 and the upper electrode layer 403b are separated from each other. Thus, the nitride semiconductor device 400 according to the fourth embodiment realizes a semiconductor device in which the field plate layer 402 and the upper electrode layer 403b are separated from each other and leakage current is suppressed. As described above, the leakage current can also be suppressed by structurally separating the field plate layer and the upper electrode layer regardless of the insulating film.

  Next, a method for manufacturing the nitride semiconductor device 400 according to the fourth embodiment will be described. The process until the semiconductor stacked unit 401 is prepared and the field plate layer 402 is stacked thereon is the same as the method for manufacturing the nitride semiconductor device 100 according to the first embodiment shown in FIGS. Here, when the electrode is formed using the lift-off method, the upper electrode layer and the field plate layer come into contact as described in the manufacturing method of the first embodiment. Thus, for example, the nitride semiconductor device 400 according to the fourth embodiment can be realized by dry etching. First, for example, Ni, which becomes the lower electrode layer 403a of the anode electrode 403, is uniformly deposited on the semiconductor stacked portion 401 and the field plate layer 402 formed on the semiconductor stacked portion 401. Next, a region where the lower electrode layer 403a is to be formed is covered with a mask, and Ni in other regions is removed by dry etching. Further, for example, Ti or Al, which will become the upper electrode layer 403b and the cathode electrode 404 of the anode electrode 403, is uniformly deposited. Then, a region where the upper electrode layer 403b is to be formed is covered with a mask, and Ti or Al in other regions is removed by dry etching. Thus, the nitride semiconductor device 400 according to the fourth embodiment is realized.

(Embodiment 5)
Next, a nitride semiconductor device 500 according to the fifth embodiment of the present invention will be described. FIG. 16 is a schematic diagram showing a cross section of a semiconductor device according to the fifth embodiment of the present invention. As shown in FIG. 16, the nitride semiconductor device 500 according to the fifth embodiment is an SBD, and an anode electrode 503 and a cathode electrode 504 are formed on a semiconductor stacked unit 501. The anode electrode 503 includes a lower electrode layer 503a and an upper electrode layer 503b. In addition, a field plate layer 502 and an insulating film 505 are formed to reduce electric field concentration. Here, an insulating film 505 made of SiO _2, separated and the field plate layer 502 and the upper electrode layer 503b is, and the entire upper electrode layer 503b is formed in a region on the lower electrode layer 503a. Thereby, the nitride semiconductor device 500 according to the fifth embodiment realizes a semiconductor device in which the field plate layer 502 and the upper electrode layer 503b are separated from each other and leakage current is suppressed. As described above, the effect of the present invention that suppresses the leakage current can also be exhibited by the structure having the configurations of the first embodiment and the fourth embodiment.
The insulating film 505 is composed of three layers and has two steps. In this way, a plurality of step portions may be formed in order to further distribute the electric field concentration.

(Embodiment 6)
Next, a nitride semiconductor device 600 according to the sixth embodiment of the present invention will be described. FIG. 17 is a schematic diagram showing a cross section of a semiconductor device according to the sixth embodiment of the present invention. As shown in FIG. 17, the nitride semiconductor device 600 according to the sixth embodiment is a high electron mobility transistor (HEMT: High Electron Mobility Transistor). A gate electrode 603g including two layers of a lower electrode layer 603a and an upper electrode layer 603b is formed on the semiconductor stacked portion 601. The upper electrode layer 603b of the gate electrode 603g is made of SiO ₂ and is separated from the field plate layer 602 by a two-layer insulating film 605. A source electrode 604s and a drain electrode 604d are formed so as to sandwich the gate electrode 603g. Thereby, the nitride semiconductor device 600 according to the sixth embodiment realizes a semiconductor device that is a HEMT in which the field plate layer 602 and the upper electrode layer 603b are separated from each other and leakage current is suppressed. Further, the end portion of the gate electrode 603g is in contact with SiO ₂ having high breakdown field strength, so that a semiconductor device with high breakdown voltage and high reliability is realized.

  As described above, according to the present embodiment, it is possible to provide a semiconductor device in which leakage current is suppressed.

  The lower electrode layer of the anode electrode of the diode and the gate electrode of the transistor is an electrode that makes Schottky contact with the outermost surface portion of the semiconductor stacked portion and the field plate layer, and is formed of, for example, Ni. However, the present invention is not limited to this. For example, nickel (Ni), platinum (Pt), palladium (Pd), tungsten (W), gold (Au), silver (Ag), copper (Cu), tantalum (Ta ), A metal film containing at least one of aluminum (Al), or a metal film made of an alloy containing at least one of Ni, Pt, Pd, W, Au, Ag, Cu, Ta, and Al, Any metal material that satisfies the above conditions, such as a metal film including at least one, may be used.

  Further, the upper electrode layer of the anode electrode of the diode and the gate electrode of the transistor is made of a metal having a work function smaller than that of the lower electrode layer, and is, for example, Ti or Al. However, the present invention is not limited to this. For example, a metal film containing at least one of titanium (Ti) and aluminum (Al), a metal film made of an alloy containing at least one of Ti and Al, or Ti Any metal material satisfying the above conditions may be used, such as a metal film made of a silicide alloy containing at least one of Al and a metal film containing at least one.

  Further, the cathode electrode of the diode and the source electrode and drain electrode of the transistor are electrodes that are in ohmic contact with the outermost surface portion of the semiconductor stacked portion or in a state where the contact resistance is sufficiently small, and are, for example, Al. However, the present invention is not limited to this. For example, at least one of titanium (Ti), aluminum (Al), silicon (Si), lead (Pb), chromium (Cr), indium (In), and tantalum (Ta). A metal film made of an alloy containing at least one of Ti, Al, Si, Pb, Cr, In, Ta, or a silicide alloy containing at least one of Ti, Al, Si, Ta Any metal film satisfying the above conditions, such as a metal film including at least one of the metal films formed, may be used.

  In the above embodiment, the SBD and the HEMT are given as examples of the semiconductor device according to the present invention. However, the present invention is not limited to this, and various semiconductor devices such as a MESFET (Metal Semiconductor FET) are used. The present invention can be applied.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

DESCRIPTION OF SYMBOLS 11 Board | substrate 12 Buffer layer 13 Electron transit layer 13a 2DEG layer 14 Electron supply layer 100, 200, 300, 400, 500, 600, 1000 Nitride semiconductor device 101, 201, 301, 401, 501, 601, 1001 Semiconductor laminated part 102 202, 302, 402, 502, 602, 1002 Field plate layer 103, 203, 303, 403, 503, 1003 Anode electrode 103a, 203a, 303a, 403a, 503a, 603a, 1003a Lower electrode layer 103b, 203b, 303b, 403b, 503b, 603b, 1003b Upper electrode layer 603g Gate electrode 104, 204, 304, 404, 504, 1004 Cathode electrode 604d Drain electrode 604s Source electrode 105, 205, 205a, 2 5b, 305,305a, 305b, 505,605 insulating film R resist

Claims (11)

An electron transit layer made of a nitride semiconductor;
An electron supply layer formed on the electron transit layer and made of a nitride semiconductor having a larger band gap than the electron transit layer;
A field plate layer formed on a part of the electron supply layer and made of a nitride semiconductor having a band gap energy smaller than that of the electron supply layer;
A lower electrode layer formed of metal in contact with the electron supply layer and the field plate layer, and made of a metal in Schottky contact with the electron supply layer and the field plate layer;
An electrode having an upper electrode layer formed to cover the lower electrode layer and made of a metal having a work function smaller than that of the metal forming the lower electrode layer;
With
The semiconductor device, wherein the electron supply layer and the field plate layer are separated from the upper electrode layer.   The entire upper electrode layer is formed in a region on the lower electrode layer, and the lower electrode layer is interposed between the field plate layer and the upper electrode layer, whereby the field plate layer, the upper electrode layer, The semiconductor device according to claim 1, wherein the two are separated from each other.   2. The semiconductor according to claim 1, wherein an insulating film is formed between the field plate layer and the upper electrode layer, and the field plate layer and the upper electrode layer are separated by the insulating film. apparatus.   The semiconductor device according to claim 3, wherein the lower electrode layer and the upper electrode layer are formed by a lift-off method.   5. The semiconductor device according to claim 3, wherein the insulating film has a higher breakdown field strength than the field plate layer. The semiconductor device according to claim 3, wherein the insulating film contains SiO ₂ or SiN _x .   The semiconductor device according to claim 3, wherein the insulating film is formed of two or more kinds of stacked films.   8. The insulating film according to claim 1, wherein the insulating film has at least one stepped portion, and the electrode rides on at least one stepped portion of the stepped portions. A semiconductor device according to 1.   9. The semiconductor device according to claim 1, wherein the lower electrode layer is made of Ni, and the upper electrode layer is made of Ti or Al.   The semiconductor device according to claim 1, wherein the electrode is an anode electrode, includes a cathode electrode formed so as to be in contact with the electron supply layer, and is a diode.   The electrode is a gate electrode, is formed to be in contact with the electron supply layer, includes a source electrode and a drain electrode formed so as to sandwich the gate electrode, and is a field effect transistor. Item 11. The semiconductor device according to any one of Items 1 to 10.

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