JP2017112127A - Laminate, schottky barrier diode and electrical equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate and a Schottky barrier diode which enable a Schottky barrier diode which is excellent in mass productivity, exhibits a low defect density and exhibits an excellent breakdown electric field.SOLUTION: A multilayer body 1 includes an n-type oxide semiconductor layer 10 and a Schottky electrode layer 20. A terminal surface 11 of the n-type oxide semiconductor layer 10 has a monomolecular film 70. The monomolecular film 70 is composed of a compound molecule containing at least one selected from a carboxylic acid group, a phosphonic acid group and a phosphoric acid ester group, or an organic silane molecule.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a stacked body including an electrode layer having a Schottky characteristic (Schottky electrode layer) and an n-type oxide semiconductor layer, a Schottky barrier diode including the stacked body, and an electric device.

As Schottky barrier diodes that realize large current and high power consumption, examples in which SiC or GaN is epitaxially grown on an inexpensive Si wafer substrate are disclosed (for example, Patent Documents 1 to 3).
Regarding SiC, the crystal structure suitable as a power semiconductor is 4H—SiC, and a dielectric breakdown electric field of 3 MV / cm or more is realized. However, since the lattice mismatch is large, it is difficult to epitaxially grow a single crystal with few defects on Si with a high yield. If it is 3C-SiC, it can be epitaxially grown by performing microfabrication on the Si wafer or using the Si (211) surface, but since the band gap becomes narrow, the dielectric breakdown electric field remains at 1.2 MV / cm. .

  On the other hand, GaN also has a dielectric breakdown electric field of 3 MV / cm or more like 4H-SiC, and attempts have been made to grow crystals on Si for mass production. However, although it is not as high as SiC in terms of mismatch between Si and lattice, crystal growth is difficult without passing through a buffer layer such as AlN, and there is a problem in mass productivity.

JP 2009-164638 A JP 2010-40972 A JP 2013-227198 A

  The present invention has been made in view of the above problems, and provides a multilayer body and a Schottky barrier diode that enable a Schottky barrier diode that is excellent in mass production, has a low defect density, and exhibits an excellent breakdown electric field. The purpose is to do.

According to the present invention, the following laminates and the like are provided.
1. an n-type oxide semiconductor layer and a Schottky electrode layer;
A stacked body, wherein a termination surface of the n-type oxide semiconductor layer has a monomolecular film.
2. 2. The laminate according to 1, wherein the monomolecular film is composed of a compound molecule containing one or more selected from a carboxylic acid group, a phosphonic acid group, and a phosphate ester group, or an organic silane molecule.
3. 3. The laminate according to 1 or 2, wherein the monomolecular film is a self-assembled molecular film.
4). The laminated body according to any one of 1 to 3, wherein the n-type oxide semiconductor layer includes one or more selected from indium oxide and gallium oxide.
5. A Schottky barrier diode having the laminate according to any one of 1 to 4.
An electric apparatus having the Schottky barrier diode described in 6.5.

  ADVANTAGE OF THE INVENTION According to this invention, the laminated body which enables the Schottky barrier diode which is excellent in mass-productivity, has the defect density, and shows the outstanding dielectric breakdown electric field, and a Schottky barrier diode can be provided.

It is a schematic sectional drawing of the Schottky barrier diode containing the laminated body which concerns on one Embodiment of this invention. It is a schematic sectional drawing of the semiconductor part and back surface electrode part of the Schottky barrier diode shown in FIG.

  The laminate of the present invention includes an n-type oxide semiconductor layer and a Schottky electrode layer, and the termination surface of the n-type oxide semiconductor has a monomolecular film.

  The terminal portion of the n-type oxide semiconductor is a portion where the n-type oxide semiconductor layer of the Schottky barrier diode individually cut from the wafer comes into contact with the outside air. When this terminal part is covered with a monomolecular film, moisture, oxygen, carbon dioxide in the air, sulfides, nitrogen oxides, hydrocarbon components, halogens, alkali metal components, etc. are adsorbed on the surface of the terminal part, or n-type oxidation It is possible to suppress the influence on the characteristics of the Schottky barrier diode by diffusing into the physical semiconductor layer. In particular, changes in characteristics can be suppressed when used for a long time.

  In addition, an insulating film is preferably interposed between part of the n-type oxide semiconductor layer and the Schottky electrode layer. When an insulating layer is interposed between the n-type oxide semiconductor and the Schottky electrode layer, power concentration on the Schottky electrode layer can be reduced, and the voltage resistance can be improved.

  FIG. 1 is a schematic cross-sectional view of a Schottky barrier diode including a multilayer body according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a semiconductor portion and a back electrode portion of the Schottky barrier diode shown in FIG.

The stack 1 in FIG. 1 includes an n-type oxide semiconductor layer 10 and a Schottky electrode layer 20 on the n-type oxide semiconductor layer 10, and an insulating layer is formed between the n-type oxide semiconductor layer 10 and the Schottky electrode layer 20. A film 30 is formed. A monomolecular film 70 is formed on the termination surface 11 of the n-type oxide semiconductor 10.
As shown in the figure, there are an insulating film intervening region A and an insulating film non-intervening region B. In the insulating film non-intervening region B, the n-type oxide semiconductor layer 10 and the Schottky electrode layer 20 are in contact with each other. The insulating film 30 becomes thinner toward the insulating film non-intervening region B, and is tapered at an angle θ (30 degrees).
An aluminum layer 40 is formed on the Schottky electrode layer 20.

  In this embodiment, the Schottky electrode layer 20 is a stacked body of a first layer 21 made of a metal having Schottky characteristics and a second layer 22 made of a metal having Schottky characteristics. The first layer 21 and the second layer 22 are preferably separate metal layers. The first layer 21 is a layer that contacts (acts) with the n-type oxide semiconductor layer 10 and exhibits Schottky characteristics. The second layer 22 itself has Schottky characteristics, and aluminum atoms enter the first layer 21 from the aluminum layer stacked on the second layer 22 to reduce the Schottky characteristics, It plays a role to prevent becoming a new resistance layer. Even if the thickness of the first layer 21 is increased, it is difficult to suppress the diffusion and reaction of aluminum. Therefore, it is preferable to provide the second layer 22 and have a laminated structure of different materials. By separating the functions in this way, the Schottky characteristics can be maintained more stably.

  There is an ohmic electrode layer 50 on the surface of the n-type oxide semiconductor layer 10 facing the surface on which the Schottky electrode layer 20 is provided. Details of the ohmic electrode layer 50 are shown in FIG. In FIG. 2, reference numeral 10 denotes an n-type oxide semiconductor layer, reference numeral 50 denotes an ohmic electrode layer, and the ohmic electrode layer may include a support substrate.

In this embodiment, the ohmic electrode layer 50 includes a layer 51 made of a metal or conductive metal oxide that is conductive even when oxidized, a diffusion prevention layer 52 that prevents diffusion of oxygen, and a contact resistance with silicon. It consists of a metal layer 53 for forming silicide and a silicon wafer 54. Further, preferably, a back contact layer 60 for taking out the electrode is formed. The ohmic electrode layer 50 can also be used for a β-Ga ₂ O ₃ substrate, α-Ga ₂ O ₃ substrate, and InGaO ₃ substrate that are highly doped n-type. When an oxide substrate is used, the back contact layer 60 for taking out an electrode may be formed through or without an ohmic electrode layer. In the case of performing epitaxial growth, an epitaxial film with few defects can be easily obtained by epitaxially growing the oxide after treating the surface of the oxide substrate with oxygen plasma.

As the n-type oxide semiconductor layer, an n-type doped β-Ga ₂ O ₃ layer, an n-type doped α-Ga ₂ O ₃ layer, or the like can be used.

A substrate that is preferable in terms of easy performance is a substrate including an n-type oxide semiconductor layer made of β-Ga ₂ O ₃ or α-Ga ₂ O ₃ doped with n-type having a large band gap. These substrates are advantageous for forming an n-type oxide semiconductor layer with good crystallinity and few defects. A more preferred substrate is an n-type oxide semiconductor formed on an n-type doped silicon wafer. In general, silicon wafers are mass-produced, are easily available, and are preferably used by forming an n-type oxide semiconductor layer via an ohmic contact layer.

  The thickness of the insulating film is preferably 0.1 μm to 30 μm in order to withstand a high voltage. If the thickness is less than 0.1 μm, the withstand voltage of the Schottky barrier diode element may decrease, and if it exceeds 30 μm, it takes too much time to form and may be expensive. More preferably, it is 0.5 μm to 15 μm, and further preferably 1 μm to 10 μm.

In the boundary region between the insulating film intervening region and the insulating film non-intervening region, the insulating film is preferably tapered. By taper processing, rapid fluctuations in the film thickness in the boundary region can be suppressed, and the withstand voltage of the element is not lowered. The taper angle is preferably 15 to 70 degrees. If it is less than 15 degrees, the boundary region becomes too wide, and the number of elements may be reduced. If it exceeds 70 degrees, the withstand voltage may decrease due to a sudden film thickness fluctuation. More preferably, it is 20 to 60 degrees, and further preferably 25 to 50 degrees.
For etching the tapered insulating film, a commonly used method such as dry etching or wet etching can be used.

  The insulating film is preferably a single film or a stacked film of one or more selected from silicon oxide, aluminum oxide, and silicon nitride. The insulating film in contact with the n-type oxide semiconductor layer is preferably an oxide. This is because when forming a nitride film, the n-type oxide semiconductor layer may be reduced to generate carriers. When silicon oxide and aluminum oxide are compared, aluminum oxide is preferable as an insulating film because it has an action as an oxygen nonconductor.

  The n-type oxide semiconductor layer preferably contains one or more selected from indium oxide and gallium oxide.

Specifically, it preferably comprises a single crystal phase of β-Ga ₂ O ₃ phase, α-Ga ₂ O ₃ phase or InGaO ₃ phase.
The composition forming the single crystal phase is Ga / (In + Ga) = 90 to 100 atomic% or Ga / (In + Ga) = 45 to 55 atomic%. In the case of Ga / (In + Ga) = 90 to 100 atomic%, β-Ga ₂ O ₃ or α-Ga ₂ O ₃ doped with In or not doped can be formed. Β-Ga ₂ O ₃ and α-Ga ₂ O ₃ can be formed depending on the selection of the substrate, film formation conditions, the crystallization temperature, and the like. In the case of forming β-Ga ₂ O ₃ , an n-type doped β-Ga ₂ O ₃ substrate can be used. On the other hand, when α-Ga ₂ O ₃ is formed, the film can be formed on sapphire and then peeled off. Specifically, a Ga ₂ O ₃ film doped n-type by mist CVD, ion plating, sputtering, etc. can be formed under heating on a sapphire substrate, or can be formed by crystallization by heating after formation. It can be peeled from the sapphire substrate and used as a substrate.
When the composition is Ga / (In + Ga) = 45 to 55 atomic%, an InGaO ₃ phase can be formed.

  The thickness of the n-type oxide semiconductor layer is not particularly limited, but is usually 0.1 μm or more and 100 μm or less, and preferably 0.5 μm or more and 50 μm or less.

As a Schottky electrode layer, a laminate in which two or more metal layers made of a metal having a high work function are stacked, or a metal oxide layer made of a metal layer made of a metal having a high work function and an oxide of a metal having a high work function Can be used. The work function is usually 4.4 eV or more, preferably 4.5 eV or more. The upper limit of the work function is usually 6.5 eV. Specific metals include Au, Pt, Pd, Ni, Ru, Mo, Ti, and the like, and Ni, Ru, Mo, Ti, and the like are preferably used.
When the metal having a high work function is an expensive metal, the metal is used as a very thin layer in contact with the n-type oxide semiconductor, and a layer made of another metal is preferably stacked.
The work function can be measured by photoelectron spectroscopy.

  The Schottky electrode layer is a stacked body including a metal layer having a Schottky characteristic and a metal oxide layer having a Schottky characteristic including a metal oxide of the metal layer on the n-type oxide semiconductor layer side. Can do. When using a laminate of a metal layer and a metal oxide layer as the Schottky electrode layer, after forming a metal layer having a large work function, the portion of the metal layer that is in contact with the n-type oxide semiconductor layer by heat treatment or the like Can be oxidized to form a metal oxide layer, and an unoxidized portion of the metal layer can also be used as a metal layer.

  The thickness of the Schottky electrode layer is not particularly limited, but is usually 0.02 μm or more and 10 μm or less, preferably 0.05 μm or more and 5 μm or less. In FIG. 1, the first Schottky layer 21 is usually 0.02 μm or more and 1 μm or less, preferably 0.03 μm or more and 0.5 μm or less. The second Schottky layer 22 is usually 0.02 μm or more and 1 μm or less, preferably 0.03 μm or more and 0.5 μm or less.

The monomolecular film can be composed of a compound molecule containing one or more selected from a carboxylic acid group, a phosphonic acid group, and a phosphate ester group, or an organic silane molecule.
Examples of the compound containing a carboxylic acid group include a compound represented by R-COOH. R represents a hydrocarbon group such as an alkyl group or an aryl group.
As compounds containing phosphonic acid groups, compounds represented the R-PO ₃ H ₂ and the like. R represents a hydrocarbon group such as an alkyl group or an aryl group.
Examples of the compound containing a phosphate group include a compound represented by RO-PO ₃ H ₂ . R represents a hydrocarbon group such as an alkyl group or an aryl group.

Examples of the organic silane compound include a compound represented by R-SiX ₃ . X represents, for example, a halogen atom such as chlorine, bromine or iodine, or an alkoxy group such as —OCH ₃ or —OC ₂ H ₅ . R represents, for example, a hydrocarbon group such as an alkyl group or an aryl machine.
Further, a silazane compound such as hexamethyldisilazane: [(CH ₃ ) ₃ Si] ₂ NH can be used.

  The monomolecular film is preferably a self-assembled molecular film. The self-assembled molecular film is a monomolecular film formed by self-assembly / self-assembly. These are molecular aggregates formed on the solid surface during the process of chemisorption of organic molecules. A feature of this is that aggregate-constituting molecules are densely assembled by the interaction between adsorbed molecules, and a highly regular structure in molecular orientation and arrangement is automatically formed. These automatically formed self-assembled / self-assembled films can cover the surface of the cracks, voids, irregularities such as irregularities, etc. on the surface of the end portion generated in the wafer dicing process.

  Although it can be sealed with resin, the self-assembled molecular film can automatically cover the surface of fine cracks, voids, irregularities, scratches and the like that cannot be penetrated by resin by self-assembly / self-assembly. Thereby, an element that operates more stably can be obtained.

  The monomolecular film can be formed by immersing in a liquid containing a monomolecular forming material or by contacting with a vapor of molecules forming the monomolecular film. For example, a Schottky barrier diode element individually separated by dicing is washed and dried, and then brought into contact with a hexamethyldisilazane vapor or a hexamethyldisilazane solution. A self-assembled film is formed.

The ohmic electrode layer has a function for making ohmic contact between the n-type substrate and the n-type oxide semiconductor layer, and a metal indium layer and / or an indium oxide layer between the ohmic electrode layer and the n-type oxide semiconductor layer. The structure which laminates | stacks is used suitably.
In the case where the n-type substrate is an n-type doped silicon wafer, the ohmic layer in contact with the silicon uses a metal that forms a silicide, and even if it is oxidized to a layer in contact with the n-type oxide semiconductor layer, it has conductivity. The metal or conductive metal oxide is used. A diffusion prevention layer for preventing diffusion of oxygen can be sandwiched between the metal layer that forms silicide and the metal or conductive metal oxide layer that has conductivity even when oxidized. Mo, Ti, etc. can be used as the metal for forming silicide. Examples of metals or metal oxides that are conductive even when oxidized include Zn, In, Sn, InSn alloys, Mo, Ti, ZnO, In ₂ O ₃ , SnO ₂ , MoO ₂ , TiO ₂ , indium tin oxide, Indium zinc oxide or the like can be used. Of these, In, Sn, InSn alloy, indium tin oxide, and indium zinc oxide are preferable. As the diffusion preventing layer for preventing oxygen diffusion, Mo, Ti, Zn, In, Sn, InSn alloy, Pt, Pd, Ru, or the like can be used.

  The Schottky barrier diode of the present invention can be suitably used for electrical equipment such as a converter that converts alternating current into direct current.

  Although the embodiments of the present invention have been described above, those skilled in the art can easily make many changes to these illustrative embodiments without substantially departing from the features of the present invention. These modifications are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Stacked body 10 N-type oxide semiconductor layer 11 Termination surface of n-type oxide semiconductor layer 20 Schottky electrode layer 21 First Schottky layer 22 Second Schottky layer 30 Insulating film 40 Aluminum layer 50 Ohmic electrode layer 51 Layer made of metal or conductive metal oxide that is conductive even if oxidized 52 Diffusion prevention layer 53 Metal layer forming silicide 54 Silicon wafer 60 Back contact layer 70 Monomolecular film θ Taper angle A Insulating film intervening region B Insulation Non-membrane region

Claims (6)

an n-type oxide semiconductor layer and a Schottky electrode layer;
A stacked body, wherein a termination surface of the n-type oxide semiconductor layer has a monomolecular film.   The multilayer according to claim 1, wherein the monomolecular film is composed of a compound molecule containing one or more selected from a carboxylic acid group, a phosphonic acid group, and a phosphate ester group, or an organic silane molecule. body.   The laminate according to claim 1, wherein the monomolecular film is a self-assembled molecular film.   The laminate according to any one of claims 1 to 3, wherein the n-type oxide semiconductor layer contains one or more selected from indium oxide and gallium oxide.   The Schottky barrier diode which has a laminated body in any one of Claims 1-4.   An electric device having the Schottky barrier diode according to claim 5.

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