Semiconductor device and manufacturing method thereof

Abstract

To provide a semiconductor device capable of realizing a metal electrode with low connection resistance to a nitride semiconductor.SOLUTION: A semiconductor device comprises: a first nitride region that is an n-type semiconductor, being a nitride selected from aluminum gallium nitride and aluminum nitride; and a second nitride region that is in contact with the first nitride region, being the nitride and being made of metal, and including a first element that is at least one element selected from a group consisting of Be, Mg, Ca, Sr, Ba, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, V, Nb, Ta, Li, Na, K, Rb, Ce, and Zn.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a semiconductor device and a method for manufacturing the semiconductor device. [Background technology]

[0002] Semiconductor elements such as transistors and diodes are used in circuits such as switching power supply circuits and inverter circuits. These semiconductor elements are required to have high breakdown voltage and low on-resistance. There is a trade-off between breakdown voltage and on-resistance that is determined by the element material.

[0003] Advances in technological development have enabled semiconductor devices to achieve low on-resistance close to the limits of silicon, the primary device material. To further improve breakdown voltage or further reduce on-resistance, a change in device material is necessary. By using nitride semiconductors such as gallium nitride and aluminum gallium nitride as the device material, the trade-off relationship determined by the device material can be improved. This makes it possible to dramatically increase the breakdown voltage and reduce the on-resistance of semiconductor devices.

[0004] When a semiconductor device is formed using a nitride semiconductor, it is desirable to realize a metal electrode with low connection resistance to the nitride semiconductor. By forming a metal electrode with low connection resistance to the nitride semiconductor, high performance of the semiconductor device can be realized. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-68722 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a semiconductor device that can realize a metal electrode having low connection resistance to a nitride semiconductor. [Means for solving the problem]

[0007] The semiconductor device of the embodiment includes a first nitride region which is an n-type semiconductor and is made of a nitride selected from aluminum gallium nitride and aluminum nitride, and a second nitride region which is in contact with the first nitride region and which is selected from beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), and the like. a first element that is at least one element selected from the group consisting of europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn), and the nitride is a metal. target and a second nitride region, The sheet resistance of the second nitride region is 0.1 Ω / sq or less. . [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a semiconductor device according to a first embodiment. [Figure 2] 2A to 2C are diagrams showing a manufacturing flow of the method for manufacturing the semiconductor device according to the first embodiment; [Figure 3] 3A to 3C are explanatory diagrams illustrating the operation and effect of the semiconductor device according to the first embodiment. [Figure 4] 3A to 3C are explanatory diagrams illustrating the operation and effect of the semiconductor device according to the first embodiment. [Figure 5] FIG. 4 is a schematic cross-sectional view of a semiconductor device according to a second embodiment. [Figure 6] FIG. 10 is a schematic cross-sectional view of a semiconductor device according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same or similar components will be denoted by the same reference numerals, and a description of a component that has already been described may be omitted.

[0010] In this specification, in order to indicate the positional relationship of parts, etc., the upward direction of the drawing will be described as "up" and the downward direction of the drawing will be described as "down." In this specification, the concepts of "up" and "down" do not necessarily refer to the direction of gravity.

[0011] In the following description, n + , n, n - and p + , p, p - When the notation is used, it indicates the relative level of impurity concentration in each conductivity type. + has a relatively higher n-type impurity concentration than n, - indicates that the n-type impurity concentration is relatively lower than that of n. + has a relatively higher p-type impurity concentration than p, - indicates that the p-type impurity concentration is relatively lower than that of p. + type, n - The type is simply n-type, p + type, p - The type is sometimes simply referred to as p-type.

[0012] (First embodiment) The semiconductor device of the first embodiment is a nitride selected from aluminum gallium nitride and aluminum nitride, and includes a first nitride region which is an n-type semiconductor, and a second nitride region which is in contact with the first nitride region and contains beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gallium (V), and the like. and a second nitride region that is a metal and that includes a first element that is at least one element selected from the group consisting of fluorine (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn).

[0013] 1 is a schematic cross-sectional view of a semiconductor device according to the first embodiment. The semiconductor device according to the first embodiment is a contact structure 100 that electrically connects a nitride semiconductor and a metal electrode.

[0014] The contact structure 100 of the first embodiment comprises a nitride layer 10 and a metal electrode 11. The nitride layer 10 includes a first nitride region 10a and a second nitride region 10b.

[0015] The nitride layer 10 contains at least a nitride selected from aluminum gallium nitride and aluminum nitride. The nitride layer 10 is, for example, single-crystal aluminum gallium nitride. The nitride layer 10 is, for example, single-crystal aluminum nitride.

[0016] The first nitride region 10a is an n-type semiconductor.

[0017] The first nitride region 10a is a nitride selected from aluminum gallium nitride and aluminum nitride. The first nitride region 10a is, for example, aluminum gallium nitride, an n-type semiconductor. The first nitride region 10a is, for example, aluminum nitride, an n-type semiconductor.

[0018] The first nitride region 10a contains, for example, silicon (Si) as an n-type impurity. The n-type impurity concentration of the first nitride region 10a is, for example, 1×10 15 cm -3 More than 1×10 21 cm -3 The following is the result.

[0019] The second nitride region 10b is provided on the first nitride region 10a. The second nitride region 10b contacts the first nitride region 10a. The second nitride region 10b is provided between the first nitride region 10a and the metal electrode 11.

[0020] The second nitride region 10b is formed of the same nitride as the first nitride region 10a. The second nitride region 10b is formed by ion-implanting gallium or aluminum into the first nitride region 10a, so there are differences, but the base nitride is the same. For example, if the first nitride region 10a is aluminum gallium nitride, the base nitride of the second nitride region 10b is also the same aluminum gallium nitride. Furthermore, for example, if the first nitride region 10a is aluminum nitride, the base nitride of the second nitride region 10b is also the same aluminum nitride.

[0021] The second nitride region 10b is metallic.

[0022] The second nitride region 10b is, for example, metallic aluminum gallium nitride.The second nitride region 10b is, for example, aluminum gallium nitride obtained by metallizing semiconductor aluminum gallium nitride.

[0023] The second nitride region 10b is, for example, a metallic aluminum nitride.The second nitride region 10b is, for example, an aluminum nitride obtained by metallizing a semiconductor aluminum nitride.

[0024] For example, since the second nitride region 10b is metallic, the electrical resistance of the second nitride region 10b increases with increasing temperature. For example, by measuring the temperature dependence of the electrical resistance of the second nitride region 10b, it can be confirmed that the second nitride region 10b is metallic.

[0025] The sheet resistance of the second nitride region 10b is, for example, 0.1 Ω / sq or less.

[0026] The work function of the second nitride region 10b is, for example, 3.7 eV or less. The work function of the second nitride region 10b can be measured using, for example, ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), or Auger electron spectroscopy (AES). Furthermore, using a Kelvin probe, it can be measured as the intermetallic work function difference between the sample and the probe.

[0027] The second nitride region 10b is made of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), , a first element which is at least one element selected from the group consisting of dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn).

[0028] The concentration of the first element contained in the second nitride region 10b is, for example, 1×10 19 cm-3 More than 1×10 22 cm -3 The following is the result.

[0029] The thickness of the second nitride region 10b is, for example, not less than 0.1 μm and not more than 1.0 μm.

[0030] Among the first elements contained in the second nitride region 10b, the sum of the amount of the first element bonding with aluminum (Al) and the amount of the first element bonding with gallium (Ga) is greater than the amount of the first element bonding with nitrogen (N), for example. In other words, among the first elements contained in the second nitride region 10b, the amount of the first element located at the nitrogen site of the crystal structure of the nitride forming the second nitride region 10b is greater than the sum of the amount of the first element located at the aluminum site of the crystal structure of the nitride and the amount of the first element located at the gallium site of the crystal structure of the nitride. In other words, the amount of the first element substituting for nitrogen atoms in the crystal structure of the nitride forming the second nitride region 10b is greater than the sum of the amount of the first element substituting for aluminum atoms and the amount of the first element substituting for gallium atoms in the crystal structure of the nitride.

[0031] Among the first elements contained in second nitride region 10b, the sum of the amount of the first element that bonds with aluminum (Al) and the amount of the first element that bonds with gallium (Ga) is, for example, 10 times or more the amount of the first element that bonds with nitrogen (N). Among the first elements contained in second nitride region 10b, the amount of the first element located at nitrogen sites in the crystal structure of the nitride that forms second nitride region 10b is 10 times or more the sum of the amount of the first element located at aluminum sites and the amount of the first element located at gallium sites in the crystal structure of the nitride.

[0032] The relationship between the sum of the amount of the first element bonded to aluminum (Al) and the amount of the first element bonded to gallium (Ga) and the amount of the first element bonded to nitrogen (N) can be measured using, for example, X-ray photoelectron spectroscopy (XPS).

[0033] The metal electrode 11 is provided on the second nitride region 10b and is in contact with the second nitride region 10b.

[0034] The metal electrode 11 is a metal or a metal compound, and has a chemical composition different from that of the second nitride region 10b.

[0035] The metal electrode 11 includes, for example, titanium, titanium nitride, aluminum, or tungsten, and has, for example, a laminated structure of a titanium film and an aluminum film.

[0036] Next, an example of a method for manufacturing the semiconductor device of the first embodiment will be described.

[0037] The method for manufacturing a semiconductor device according to the first embodiment includes the steps of: forming an n-type nitride semiconductor layer, which is aluminum gallium nitride or aluminum nitride, on a substrate; doping an n-type nitride semiconductor layer, which is aluminum gallium nitride or aluminum nitride, with beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (V), or the like; a first ion implantation is performed to implant a first element, which is at least one element selected from the group consisting of (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn); a second ion implantation is performed to implant aluminum (Al) or gallium (Ga) into the nitride semiconductor layer; a third ion implantation is performed to implant hydrogen (H) into the nitride semiconductor layer; a coating layer is formed on the surface of the nitride semiconductor layer after the first ion implantation, the second ion implantation, and the third ion implantation; a first heat treatment is performed after the coating layer is formed; the coating layer is peeled off after the first heat treatment; and a second heat treatment is performed after the coating layer is peeled off.

[0038] Hereinafter, an example will be described in which the nitride semiconductor layer is an aluminum gallium nitride layer, the first element is magnesium (Mg), and gallium (Ga) is ion-implanted in the second ion implantation.

[0039] 2 is a diagram showing a manufacturing flow of the method for manufacturing the semiconductor device of the first embodiment. The method for manufacturing the semiconductor device of the first embodiment includes an aluminum gallium nitride layer preparation step S101, a magnesium ion implantation step S102 (first ion implantation), a gallium implantation step S103 (second ion implantation), a hydrogen ion implantation step S104 (third ion implantation), a silicon nitride layer formation step S105 (covering layer formation), a first nitrogen annealing step S106 (first heat treatment), a silicon nitride layer peeling step S107 (covering layer peeling), a second nitrogen annealing step S108 (second heat treatment), and a metal film formation step S109.

[0040] The following description will be given with reference to FIG.

[0041] First, an aluminum gallium nitride layer is prepared (S101). The aluminum gallium nitride layer is single-crystal aluminum gallium nitride. The aluminum gallium nitride layer corresponds to the nitride layer 10 in FIG. 1. The aluminum gallium nitride layer is an example of a nitride semiconductor layer.

[0042] An n-type semiconductor aluminum gallium nitride region is formed in the aluminum gallium nitride layer, which corresponds to the first nitride region 10a in FIG.

[0043] Next, magnesium (Mg) ions are implanted into the surface of the aluminum gallium nitride layer using a known ion implantation method (S102). The magnesium ion implantation corresponds to the first ion implantation.

[0044] The region into which magnesium is ion-implanted will ultimately become the second nitride region 10b of the contact structure 100. For example, magnesium may be ion-implanted in multiple steps with different ion-implantation energies.

[0045] The dose of magnesium is, for example, 1×10 14 cm -2 5x10 or more 15 cm -2 The following is the result.

[0046] Next, gallium (Ga) ions are implanted into the surface of the aluminum gallium nitride layer using a known ion implantation method (S103). The gallium ion implantation corresponds to the second ion implantation.

[0047] Gallium is introduced into the region where magnesium has been ion-implanted. For example, gallium may be ion-implanted in multiple steps with different ion-implantation energies.

[0048] The dose of gallium is, for example, higher than the dose of magnesium. The dose of gallium is, for example, 5×10 14 cm -2 More than 1×10 16 cm -2 The following is the result.

[0049] The second ion implantation creates, for example, a large number of nitrogen vacancies in the aluminum gallium nitride layer.

[0050] In the second ion implantation, aluminum (Al) ions may be implanted instead of gallium (Ga). Also, in the second ion implantation, both gallium (Ga) and aluminum (Al) ions may be implanted.

[0051] Next, hydrogen (H) ions are implanted into the surface of the aluminum gallium nitride layer using a known ion implantation method (S104). The hydrogen ion implantation corresponds to the third ion implantation.

[0052] Hydrogen is introduced into the region where magnesium and gallium have been ion-implanted. For example, hydrogen may be ion-implanted in multiple steps with different ion-implantation energies.

[0053] The dose of hydrogen in the third ion implantation is, for example, greater than the dose of magnesium in the first ion implantation. The dose of hydrogen in the third ion implantation is, for example, greater than the dose of gallium in the second ion implantation. The dose of hydrogen is, for example, 1×10 15 cm -2 5x10 or more 16 cm -2 The following is the result.

[0054] Next, a silicon nitride layer is formed on the surface of the aluminum gallium nitride layer using a known film growth method (S105). The silicon nitride layer is an example of a covering layer. The covering layer is not limited to silicon nitride.

[0055] The covering layer is, for example, an insulator, such as silicon nitride, silicon oxide, silicon oxynitride, or aluminum nitride.

[0056] The covering layer is, for example, a conductor or a semiconductor, for example, polycrystalline silicon.

[0057] Next, a first nitrogen anneal is performed (S106). The first nitrogen anneal is performed, for example, in a nitrogen gas atmosphere under the temperature condition of 950° C. or more and 1250° C. or less. The first nitrogen anneal is an example of a first heat treatment.

[0058] The first heat treatment is carried out in a non-oxidizing atmosphere containing, for example, argon, nitrogen, hydrogen, or helium.

[0059] The first heat treatment causes, for example, magnesium to enter the nitrogen sites of the aluminum gallium nitride. The first heat treatment causes, for example, magnesium to enter the nitrogen vacancies. The magnesium that has entered the nitrogen sites of the aluminum gallium nitride is bonded with, for example, hydrogen.

[0060] Next, the silicon nitride layer on the surface of the aluminum gallium nitride layer is removed by a known wet etching method (S107), thereby exposing the surface of the aluminum gallium nitride layer.

[0061] Next, second nitrogen annealing is performed (S108). The second nitrogen annealing is performed, for example, in a nitrogen gas atmosphere at a temperature of 950° C. to 1250° C. The second nitrogen annealing is an example of a second heat treatment.

[0062] The second heat treatment is performed in a non-oxidizing atmosphere containing, for example, argon, nitrogen, or helium, or in an atmosphere not containing hydrogen.

[0063] By the second heat treatment, for example, hydrogen that was bonded to magnesium is desorbed from the magnesium.

[0064] Next, a laminated film of a titanium film and an aluminum film is formed on the aluminum gallium nitride layer (S109). The laminated film of the titanium film and the aluminum film is an example of a metal film. The laminated film of the titanium film and the aluminum film will eventually become the metal electrode 11 of the contact structure 100.

[0065] By the above manufacturing method, the contact structure 100 of the first embodiment shown in FIG. 1 is formed.

[0066] Next, the operation and effects of the semiconductor device and semiconductor manufacturing apparatus of the first embodiment will be described.

[0067] When a semiconductor device is formed using a nitride semiconductor, it is desirable to realize a metal electrode with low connection resistance to the nitride semiconductor. By forming a metal electrode with low connection resistance to the nitride semiconductor, high performance of the semiconductor device can be realized.

[0068] The contact structure 100 of the first embodiment includes the second nitride region 10b of metal, which allows for low connection resistance with the first nitride region 10a of the n-type semiconductor, thereby realizing a highly reliable metal electrode, as will be described in detail below.

[0069] Hereinafter, an example will be described in which the nitride layer 10, the first nitride region 10a, and the second nitride region 10b of the contact structure 100 are made of aluminum gallium nitride, and the first element is magnesium (Mg).

[0070] The junction between the aluminum gallium nitride region of the n-type semiconductor and the metal electrode is a semiconductor-metal junction. From the viewpoint of work function, the metal materials that can form an ohmic junction with the n-type aluminum gallium nitride are extremely limited. Considering the affinity of metal materials for semiconductor processes, it is difficult to form an ohmic junction between the aluminum gallium nitride region of the n-type semiconductor and the metal electrode. Therefore, the junction between the aluminum gallium nitride region of the n-type semiconductor and the metal electrode is likely to be a Schottky junction. Therefore, it is difficult to reduce the connection resistance between the aluminum gallium nitride region of the n-type semiconductor and the metal electrode.

[0071] Furthermore, the interface between the aluminum gallium nitride region of the n-type semiconductor and the metal electrode is a semiconductor-metal interface. Therefore, the strength of the interface may be reduced by the application of temperature or stress. Therefore, for example, peeling may occur at the interface, reducing the reliability of the metal electrode.

[0072] 3(a) and 3(b) are explanatory diagrams of the operation and effect of the semiconductor device of the first embodiment. FIG. 3(a) is an energy band diagram of aluminum gallium nitride in which conductive impurities are not actively introduced. In FIGS. 3(a) and 3(b), the chemical composition of aluminum gallium nitride is Al 0.3 Ga 0.7 3 illustrates the case where the nitride is N. Fig. 3(b) is an energy band diagram of metallic aluminum gallium nitride, which corresponds to the second nitride region 10b of the first embodiment.

[0073] Nitrogen vacancies exist in undoped aluminum gallium nitride. As shown in Figure 3(a), in undoped semiconductor aluminum gallium nitride, the energy level of nitrogen vacancies exists below the lower edge of the conduction band. The energy level (VBE) of the lower edge of the conduction band of aluminum gallium nitride is 3.05 eV. The energy level (VNV) of nitrogen vacancies is 3.42 eV.

[0074] As shown in Figure 3(b), in metallic aluminum gallium nitride, magnesium (Mg) exists at the nitrogen site of aluminum gallium nitride. The work function of magnesium has an energy level near the bottom of the conduction band. In other words, it has an energy level near the energy level of a nitrogen vacancy.

[0075] Specifically, the energy level (VNV) of a nitrogen vacancy is 3.42 eV, while the work function of magnesium is 3.66 eV.

[0076] The inventors' first-principles calculations revealed that when a large number of nitrogen vacancies coexist in aluminum gallium nitride with magnesium present at the nitrogen sites, magnesium functions as an electron source, supplying electrons to the nitrogen vacancies. As shown in Figure 3(b), it was revealed that the supply of electrons from magnesium to the nitrogen vacancies broadens the nitrogen vacancy energy band. Furthermore, it was revealed that the Fermi level of aluminum gallium nitride is located within the conduction band.

[0077] In metallic aluminum gallium nitride, the Fermi level falls within the conduction band due to the interaction between the large number of nitrogen vacancies and the magnesium at the nitrogen sites, causing the aluminum gallium nitride, which is essentially a semiconductor, to become metallic.

[0078] The energy level (VNV) of a nitrogen vacancy is 3.42 eV, while the work function of magnesium is 3.66 eV, which is 0.24 eV larger. In order to supply electrons to the nitrogen vacancy, it is preferable that the work function of the first element serving as the electron source is smaller than the energy level (VNV) of the nitrogen vacancy.

[0079] However, since electrons from the first element enter the nitrogen vacancy, making it easier for the electrons to move, an energy gain equivalent to the kinetic energy is obtained by supplying electrons from the first element. Therefore, even if the work function of the first element is at least 0.25 eV higher than the energy level (VNV) of the nitrogen vacancy, electrons can be supplied from the first element to the nitrogen vacancy. Therefore, even in the case of magnesium, whose work function is 0.24 eV higher than the energy level (VNV) of the nitrogen vacancy, electrons can be supplied to the nitrogen vacancy.

[0080] The contact structure 100 of the first embodiment includes a metal second nitride region 10b between an n-type semiconductor first nitride region 10a and a metal electrode 11. The junction between the metal second nitride region 10b and the metal electrode 11 is a metal-to-metal junction. Therefore, the junction between the metal second nitride region 10b and the metal electrode 11 is an ohmic junction, which can reduce the connection resistance.

[0081] Furthermore, since the interface between the second metal nitride region 10b and the metal electrode 11 is a metal-to-metal interface, it is possible to prevent a decrease in strength due to application of temperature or stress. Therefore, for example, peeling at the interface is prevented, and the reliability of the metal electrode 11 is improved.

[0082] The junction between the n-type semiconductor first nitride region 10a and the metal second nitride region 10b is a semiconductor-metal junction. As described above, the Fermi level of the second nitride region 10b is within the conduction band of aluminum gallium nitride. In other words, the work function of the second nitride region 10b is lower than the energy of the bottom of the conduction band of the first nitride region 10a. Therefore, the junction between the n-type semiconductor first nitride region 10a and the metal second nitride region 10b is an ohmic junction. This allows for a low connection resistance between the n-type semiconductor first nitride region 10a and the metal second nitride region 10b.

[0083] The interface between the n-type semiconductor first nitride region 10a and the metal second nitride region 10b is an interface where the aluminum gallium nitride crystal structure is continuous. Therefore, the strength of the interface is high. Therefore, even if annealing or other processes are performed later, residual oxygen and the like do not penetrate this continuous interface, making it less likely for interfacial peeling to occur.

[0084] As described above, in the contact structure 100 of the first embodiment, by providing the metal second nitride region 10b, the junction between the n-type semiconductor first nitride region 10a and the metal electrode 11 becomes an ohmic junction. Therefore, the connection resistance with the n-type semiconductor first nitride region 10a is low, and a highly reliable metal electrode 11 can be realized. As a secondary effect, the degree of freedom in selecting the metal electrode 11 is greatly improved. For example, a special layered structure such as a layered structure of aluminum and titanium is no longer necessary. For example, titanium nitride (TiN), tungsten (W), polysilicon doped with phosphorus or boron, and other materials with excellent processability can be used.

[0085] From the viewpoint of reducing the contact resistance of the metal electrode 11, the work function of the second nitride region 10b is preferably 3.7 eV or less.

[0086] From the viewpoint of reducing the connection resistance of the metal electrode 11, the sheet resistance of the second nitride region 10b is preferably 0.1 Ω / sq or less.

[0087] From the viewpoint of reducing the contact resistance of the metal electrode 11, the magnesium concentration of the second nitride region 10b is set to 1×10 19 cm -3 It is preferable that the concentration is 1×10 or more. 20 cm -3 More preferably, it is 1×10 or more. 21 cm -3 More preferably, it is equal to or greater than this.

[0088] From the viewpoint of reducing the connection resistance of the metal electrode 11, it is preferable that, among the magnesium contained in the second nitride region 10b, the sum of the amount of magnesium bonding with aluminum and the amount of magnesium bonding with gallium is greater than the amount of magnesium bonding with nitrogen, and it is more preferable that, among the magnesium contained in the second nitride region 10b, the sum of the amount of magnesium bonding with aluminum and the amount of magnesium bonding with gallium is 10 times or more the amount of magnesium bonding with nitrogen.

[0089] In other words, the amount of magnesium located at the nitrogen sites in the second nitride region 10b is preferably greater than the sum of the amount of magnesium located at the aluminum sites and the amount of magnesium located at the gallium sites, and more preferably the amount of magnesium located at the nitrogen sites in the second nitride region 10b is at least 10 times the sum of the amount of magnesium located at the aluminum sites and the amount of magnesium located at the gallium sites.

[0090] Magnesium located at the aluminum site or gallium site functions as a p-type impurity, and therefore its presence is undesirable because it inhibits the metallic properties of second nitride region 10b.

[0091] In the manufacturing method of the first embodiment, the second nitride region 10b is formed by ion implanting magnesium, gallium, and hydrogen into the same region of the aluminum gallium nitride layer. By ion implanting gallium, which has a relatively large ionic radius, a large number of nitrogen vacancies are formed in the aluminum gallium nitride layer. Therefore, a large number of nitrogen vacancies are present in the second nitride region 10b. Note that a large number of nitrogen vacancies can also be formed in the aluminum gallium nitride layer by ion implanting aluminum instead of gallium.

[0092] Magnesium then enters the large number of nitrogen vacancies that are formed. In other words, magnesium enters the nitrogen sites. As mentioned above, if magnesium enters the aluminum or gallium sites, it functions as a p-type impurity, which is not desirable.

[0093] In the manufacturing method of the first embodiment, gallium ions are implanted, so that gallium ions are preferentially inserted into the formed aluminum vacancies and gallium vacancies over magnesium. Therefore, magnesium is prevented from entering the gallium sites. Note that even if aluminum ions are implanted instead of gallium, magnesium is prevented from entering the gallium sites.

[0094] Furthermore, hydrogen ion implantation promotes magnesium to enter the nitrogen vacancies, and magnesium bonded with hydrogen can exist more stably in the nitrogen vacancies than magnesium alone.

[0095] On the other hand, magnesium bonded with hydrogen does not act as a source of electrons to the nitrogen vacancy energy level. Therefore, the second heat treatment after peeling off the coating layer causes hydrogen to be desorbed from the magnesium, allowing the magnesium to function as an electron source.

[0096] Note that even when the nitride layer 10, the first nitride region 10a, and the second nitride region 10b of the contact structure 100 are made of aluminum nitride and the first element is other than magnesium (Mg), the junction between the first nitride region 10a of the n-type semiconductor and the metal electrode 11 becomes an ohmic junction. Therefore, the contact resistance with the first nitride region 10a of the n-type semiconductor is low, and a highly reliable metal electrode 11 can be realized.

[0097] Next, the selection of a desirable first element according to the chemical composition of the nitride in the second nitride region 10b will be described.

[0098] FIG. 4 is an explanatory diagram of the operation and effects of the semiconductor device of the first embodiment.

[0099] FIG. 4 is an energy band diagram of a nitride semiconductor whose chemical composition is represented by the following (Formula A). Al x Ga 1-x N (0 ≦ x ≦ 1) (Formula A)

[0100] In (Formula A), when x = 0, it is gallium nitride (GaN), when 0 < x < 1, it is aluminum gallium nitride, and when x = 1, it is aluminum nitride (AlN). In FIG. 4, when the aluminum gallium nitride has a chemical composition of x = 0.3, that is, Al 0.3 Ga 0.7 N is exemplified.

[0101] As shown in FIG. 4, as the chemical composition of the nitride semiconductor changes, the energy band changes. The bandgap becomes wider as the composition changes from gallium nitride (GaN) to aluminum nitride (AlN). The energy (VBE) at the lower end of the conduction band becomes smaller as the composition changes from gallium nitride (GaN) to aluminum nitride (AlN).

[0102] The energy level of the nitrogen vacancy (VNV) has an energy greater than the energy of the lower end of the conduction band (VBE). The difference between the energy level of the nitrogen vacancy (VNV) and the energy of the lower end of the conduction band (VBE) is 0.25 eV in the case of gallium nitride (GaN) and 0.65 eV in the case of aluminum nitride (AlN).

[0103] When the energy level of the nitrogen vacancy (VNV) is expressed as a variable of x, it becomes the following (Formula B). (Formula B) is represented by a dotted line segment in FIG. 4. VNV = 3.90×(1 - X) + 2.30×x (Formula B)

[0104] When the chemical composition of the nitride in the second nitride region 10b is expressed by the following (Formula 1), it is preferable that the work function WF (eV) of the first element satisfies (Formula 2). Al x Ga 1-x N(0 < x ≦ 1) (Formula 1) 3.90×(1 - X) + 2.30×x + 0.25 ≧ WF (Formula 2)

[0105] Using (Formula B), (Formula 2) can be transformed as follows (Formula 2'). VNV + 0.25 ≧ WF (Formula 2')

[0106] As can be seen from (Formula 2'), (Formula 2) indicates that the work function WF of the first element is less than or equal to the value obtained by adding 0.25 eV to the energy level of the nitrogen vacancy (VNV).

[0107] As described above, since electrons move more easily when electrons enter the nitrogen vacancy from the first element, an energy gain corresponding to the kinetic energy is obtained by the supply of electrons from the first element. Therefore, even if the work function of the first element is greater than the energy level of the nitrogen vacancy (VNV) by at least about 0.25 eV, the supply of electrons from the first element to the nitrogen vacancy is possible. By the work function WF (eV) of the first element satisfying (Formula 2), it becomes easy to make the nitride in the second nitride region 10b a metal.

[0108] For example, the work functions of magnesium (Mg), scandium (Sc), and cesium (Cs) are shown in Figure 4. The work function of magnesium (Mg) is 3.66 eV, the work function of scandium (Sc) is 3.5 eV, and the work function of cesium (Cs) is 1.9 eV.

[0109] Gallium nitride (GaN) and Al 0.3 Ga 0.7 In the case of aluminum gallium nitride, which has a chemical composition of N, the work functions of magnesium (Mg), scandium (Sc), and cesium (Cs) all satisfy (Equation 2). On the other hand, in the case of aluminum nitride (AlN), only the work function of cesium (Cs) satisfies (Equation 2).

[0110] From the viewpoint of making it easier to convert the nitride of the second nitride region 10b into a metal, it is more preferable that the work function WF (eV) of the first element satisfies the following (Equation 3), it is even more preferable that it satisfies the following (Equation 4), and it is most preferable that it satisfies the following (Equation 5). 3.90×(1-X)+2.30×x+0.15≧WF (Formula 3) 3.90×(1-X)+2.30×x+0.05≧WF (Formula 4) 3.90×(1-X)+2.30×x≧WF (Formula 5)

[0111] The work functions of some first elements are exemplified below: For example, the work function of cesium (Cs) is 1.9 eV, potassium (K) is 2.3 eV, niobium (Nb) is 2.3 eV, sodium (Na) is 2.4 eV, strontium (Sr) and barium (Ba) are 2.5 eV, calcium (Ca) is 2.8 eV, lithium (Li) is 2.9 eV, yttrium (Y) is 3.1 eV, scandium (Sc) is 3.5 eV, zinc (Zn) is 3.6 eV, and magnesium (Mg) is 3.66 eV.

[0112] As described above, according to the semiconductor device and the method for manufacturing the semiconductor device of the first embodiment, it is possible to provide a semiconductor device that can realize a metal electrode with low connection resistance to a nitride semiconductor.

[0113] (Second embodiment) The semiconductor device of the second embodiment is a lateral high electron mobility transistor (HEMT) including the contact structure of the first embodiment. Hereinafter, some of the description overlapping with the first embodiment may be omitted.

[0114] 5 is a schematic cross-sectional view of a semiconductor device according to the second embodiment, which is a lateral HEMT 200.

[0115] The lateral HEMT 200 of the second embodiment includes a nitride layer 10, a source electrode 12 (metal electrode), a drain electrode 13 (metal electrode), a gate electrode 14, and an interlayer insulating layer 16. The nitride layer 10 includes a gallium nitride region 21, an aluminum gallium nitride region 22 (first nitride region), a first metal region 23 (second nitride region), and a second metal region 24 (second nitride region).

[0116] In the lateral HEMT 200, a two-dimensional electron gas (2DEG) is formed at the interface between the gallium nitride region 21 and the aluminum gallium nitride region 22. The formation of the two-dimensional electron gas causes an on-current to flow between the source electrode 12 and the drain electrode 13. The on and off operations of the lateral HEMT 200 are controlled by changing the gate voltage applied to the gate electrode 14.

[0117] An interlayer insulating layer 16 is formed on the nitride layer 10. The interlayer insulating layer 16 is, for example, silicon oxide.

[0118] The gallium nitride region 21 is a semiconductor. The gallium nitride region 21 is in contact with the aluminum gallium nitride region 22. The aluminum gallium nitride region 22 is provided between the gallium nitride region 21 and the first metal region 23. The aluminum gallium nitride region 22 is provided between the gallium nitride region 21 and the second metal region 24.

[0119] The aluminum gallium nitride region 22 is an example of a first nitride region. The aluminum gallium nitride region 22 is an n-type semiconductor.

[0120] The first metal region 23 is an example of a second gallium nitride region.

[0121] The first metal region 23 is provided on the aluminum gallium nitride region 22. The first metal region 23 is in contact with the source electrode 12. The first metal region 23 is provided between the aluminum gallium nitride region 22 and the source electrode 12.

[0122] The first metal region 23 is a metal. The first metal region 23 is metallic aluminum gallium nitride. The first metal region 23 is aluminum gallium nitride that is a metallized version of semiconductor aluminum gallium nitride.

[0123] First metal region 23 includes a first element, which is at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn).

[0124] The source electrode 12 is an example of a metal electrode. The source electrode 12 is provided on the first metal region 23. The source electrode 12 is in contact with the first metal region 23.

[0125] The second metal region 24 is an example of a second nitride region.

[0126] The second metal region 24 is provided on the aluminum gallium nitride region 22. The second metal region 24 is in contact with the drain electrode 13. The second metal region 24 is provided between the aluminum gallium nitride region 22 and the drain electrode 13.

[0127] The second metal region 24 is a metal. The second metal region 24 is metallic aluminum gallium nitride. The second metal region 24 is aluminum gallium nitride that is a metallized version of semiconductor aluminum gallium nitride.

[0128] Second metallic region 24 includes a first element, which is at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn).

[0129] The drain electrode 13 is an example of a metal electrode. The drain electrode 13 is provided on the second metal region 24. The drain electrode 13 is in contact with the second metal region 24.

[0130] In the lateral HEMT 200 of the second embodiment, a contact structure similar to the contact structure 100 of the first embodiment is applied to the contact structure between the source electrode 12 and the nitride layer 10. Therefore, the connection resistance between the source electrode 12 and the nitride layer 10 is reduced. Also, the reliability of the source electrode 12 is improved.

[0131] Furthermore, in the lateral HEMT 200 of the second embodiment, a contact structure similar to the contact structure 100 of the first embodiment is applied to the contact structure between the drain electrode 13 and the nitride layer 10. This reduces the connection resistance between the drain electrode 13 and the nitride layer 10. Furthermore, the reliability of the drain electrode 13 is improved.

[0132] Therefore, for example, a lateral HEMT 200 with reduced on-resistance and improved reliability can be realized.

[0133] Furthermore, the lateral HEMT 200 of the second embodiment includes a second metal region 24 on the drain electrode 13 side. For example, the second metal region 24 blocks an electric field caused by charges injected into the interlayer insulating layer 16 and trapped in the interlayer insulating layer 16 during on-state operation of the lateral HEMT 200. Also, for example, charges injected into the interlayer insulating layer 16 during on-state operation of the lateral HEMT 200 pass through the second metal region 24 and escape to the drain electrode 13. This suppresses current collapse in the lateral HEMT 200, improving the reliability of the lateral HEMT 200.

[0134] (Variation) The semiconductor device of the modified example of the second embodiment differs from the semiconductor device of the second embodiment in that the second nitride region is in contact with the gallium nitride region.

[0135] 6 is a schematic cross-sectional view of a semiconductor device according to a modification of the second embodiment. The semiconductor device according to the second modification is a lateral HEMT 201.

[0136] In the lateral HEMT 201 of the second embodiment, the first metal region 23 (second nitride region) is in contact with the gallium nitride region 21. Also, the second metal region 24 (second nitride region) is in contact with the gallium nitride region 21.

[0137] As described above, according to the semiconductor device of the second embodiment and the modified example, it is possible to provide a semiconductor device that can realize a metal electrode with low connection resistance to a nitride semiconductor.

[0138] Although the second embodiment has been described using a lateral HEMT as an example of a semiconductor device, the present invention can also be applied to other semiconductor devices. For example, the present invention can also be applied to optical semiconductor devices such as a vertical HEMT, a diode, or an LED (Light Emmitting Diode), or an electron gun.

[0139] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. For example, components of one embodiment may be replaced or changed with components of another embodiment. These embodiments and modifications thereof are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0140] 10 nitride layer 10a First nitride region 10b Second nitride region 11 Metal electrode 12 Source electrode (metal electrode) 13 Drain electrode (metal electrode) 21 Gallium nitride region 22 Aluminum gallium nitride region (first nitride region) 23 First metal region (second nitride region) 24 Second metal region (second nitride region) 100 Contact structure (semiconductor device) 200 Lateral HEMT (semiconductor device)

Claims

1. a first nitride region that is an n-type semiconductor and is made of a nitride selected from aluminum gallium nitride and aluminum nitride; a second nitride region in contact with the first nitride region, the second nitride region comprising a first element, the first element being at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn), the second nitride region being the nitride and metallic; Equipped with The semiconductor device, wherein the sheet resistance of the second nitride region is 0.1 Ω / sq or less.

2. A first nitride region which is a nitride selected from aluminum gallium nitride and aluminum nitride and is an n-type semiconductor; a second nitride region in contact with the first nitride region, the second nitride region comprising a first element, the first element being at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn), the second nitride region being the nitride and metallic; Equipped with When the chemical composition of the nitride of the second nitride region is expressed by (Formula 1), a work function WF (eV) of the first element satisfies (Formula 2). Al ｘ Ga 1－ｘ N (0<x≦1) (Formula 1) 3.90×(1-x)+2.30×x+0.25≧WF (Formula 2)

3. A first nitride region which is a nitride selected from aluminum gallium nitride and aluminum nitride and is an n-type semiconductor; a second nitride region in contact with the first nitride region, the second nitride region comprising a first element, the first element being at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn), the second nitride region being the nitride and metallic; Equipped with In the second nitride region, the sum of the amount of the first element that bonds with aluminum (Al) and the amount of the first element that bonds with gallium (Ga) is greater than the amount of the first element that bonds with nitrogen (N).

4. 4. The semiconductor device according to claim 1, further comprising a metal electrode in contact with the second nitride region.

5. The concentration of the first element in the second nitride region is 1×10 １９ cm －３ 3. The semiconductor device according to claim 2.

6. 4. The semiconductor device according to claim 1, further comprising a gallium nitride region in contact with the first nitride region, the first nitride region being provided between the gallium nitride region and the second nitride region.

7. The semiconductor device of claim 6 , wherein the second nitride region is in contact with the gallium nitride region.

8. A semiconductor device as described in claim 5, wherein the concentration of the first element in the second nitride region is equal to or greater than the concentration of silicon (Si) in the second nitride region.

9. a first nitride region that is an n-type semiconductor and is made of a nitride selected from aluminum gallium nitride and aluminum nitride; In contact with the first nitride region, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbi a second nitride region including a first element, the first element being at least one element selected from the group consisting of yttrium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn), the nitride region being such that the sum of the amount of the first element bonded to aluminum (Al) and the amount of the first element bonded to gallium (Ga) is greater than the amount of the first element bonded to nitrogen (N); A semiconductor device comprising:

10. 10. The semiconductor device according to claim 9, wherein when the chemical composition of the nitride of the second nitride region is expressed by (Formula 1), the work function WF (eV) of the first element satisfies (Formula 2). Al ｘ Ga 1－ｘ N (0<x≦1) (Formula 1) 3.90×(1-X)+2.30×x+0.25≧WF (Formula 2)

11. The semiconductor device according to claim 9 , further comprising a metal electrode in contact with the second nitride region.

12. 10. The semiconductor device according to claim 9, wherein the sheet resistance of said second nitride region is 0.1 Ω / sq or less.

13. The concentration of the first element in the second nitride region is 1×10 １９ cm －３ 10. The semiconductor device according to claim 9.

14. 10. The semiconductor device according to claim 9, further comprising a gallium nitride region in contact with said first nitride region, said first nitride region being provided between said gallium nitride region and said second nitride region.

15. The semiconductor device of claim 14 , wherein the second nitride region abuts the gallium nitride region.

16. a first ion implantation step of implanting a first element, which is at least one element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), vanadium (V), niobium (Nb), tantalum (Ta), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and zinc (Zn), into an n-type nitride semiconductor layer which is aluminum gallium nitride or aluminum nitride; performing a second ion implantation of aluminum (Al) or gallium (Ga) into the nitride semiconductor layer; performing a third ion implantation of implanting hydrogen (H) into the nitride semiconductor layer; forming a covering layer on a surface of the nitride semiconductor layer after the first ion implantation, the second ion implantation, and the third ion implantation; performing a first heat treatment after forming the coating layer; peeling off the coating layer after the first heat treatment; A method for manufacturing a semiconductor device, comprising the steps of: performing a second heat treatment after removing the covering layer;

17. 17. The method for manufacturing a semiconductor device according to claim 16, further comprising forming a metal film on the nitride semiconductor layer after the second heat treatment.

18. 17. The method for manufacturing a semiconductor device according to claim 16, wherein a dose of hydrogen in the third ion implantation is greater than a sum of a dose of aluminum (Al) and a dose of gallium (Ga) in the second ion implantation, and the sum of a dose of aluminum (Al) and a dose of gallium (Ga) in the second ion implantation is greater than a dose of the first element in the first ion implantation.

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