JP4840798B2 - Device having diamond electrode structure for suppressing breakdown voltage of electrode and manufacturing method thereof - Google Patents

Description

  The present invention relates to a device having a diamond electrode structure for suppressing an electrode breakdown voltage due to electric field concentration of a diamond device, and a method for manufacturing the same.

Compared to conventional semiconductor materials, the dielectric breakdown electric field is high, the thermal conductivity is extremely good, the heat dissipation is excellent, the chemical is very stable, and the band gap is as large as 5.5 eV. It is attracting attention as an electronic device that operates even under harsh environments such as radiation and as a device for high power.
As such a diamond device material, a diamond epitaxial layer having excellent flatness and crystallinity is formed and doped with impurities such as boron and aluminum, and used as a P-type semiconductor and an N-type semiconductor.

As a means for forming the diamond epitaxial layer, the source gas is formed by using a direct current, a high frequency or microwave electric field discharge method, an ion bombardment method, or using a laser beam or the like to decompose the source gas. And a method of activating a source gas using thermoelectrons are already known, and a good diamond epitaxial layer can be formed by these methods.
An ohmic electrode (ohmic electrode) and a Schottky electrode (rectifying electrode) are formed on the surface of the semiconductor diamond thus obtained, and a semiconductor electrode structure corresponding to various uses is obtained. The P-type semiconductor and the N-type semiconductor are distinguished by doping depending on the kind of the semiconductor substrate, whereby a corresponding ohmic electrode and Schottky electrode can be obtained. This is already known per se, and further improvements have been made to improve the characteristics.

On the other hand, there are some proposals as materials for Schottky electrodes. For example, as a material for the electrode layer for the Schottky barrier, a layer of gold, platinum, palladium, and molybdenum is cited, and it is proposed to form the layer by vapor deposition, ion beam vapor deposition, or sputtering (see Patent Document 1). ).
As materials for Schottky electrodes, heat-resistant tungsten, molybdenum, niobium, tantalum, polycrystalline silicon, nickel, gold, platinum, tungsten carbide, molybdenum carbide, tantalum carbide, niobium carbide, tungsten silicide, molybdenum silicide It is preferable that it is formed by vapor deposition, ion plating, sputtering, CVD, or plasma CVD (see Patent Document 2).

In addition, as a material for the Schottky barrier electrode layer, a metal having a melting point of 400 to 700 ° C., specifically, aluminum, antimony, tellurium, and zinc are used, and aluminum is particularly preferable (see Patent Document 3). .
In addition, two metal materials are used for the Schottky electrode layer, tungsten, zirconium, tantalum, molybdenum, and niobium are used as the first metal, and aluminum that has a work function of 5 eV or less as the second metal. There is a proposal of using zinc as a composite metal (see Patent Document 4).
In addition, as a Schottky electrode layer, a metal having a low electronegativity of 1.8 or less is used as an electrode, and in particular, Mg, Hf, Zr, and Al are used. When used at high temperatures, Pt or Au is capped to prevent electrode oxidation. It has been proposed to stack as a layer (see Patent Document 5).

In the above known documents, the electrode formation method is not particularly problematic. Usually, as shown in Patent Document 3, it is formed and processed into a disk shape on a diamond layer. Further, in such a disk-shaped electrode, a breakdown voltage due to the concentration of the electric field of the electrode is likely to be generated, but there is no consideration on means for suppressing the breakdown voltage.
Therefore, as described above, diamond itself has a higher breakdown electric field, extremely good thermal conductivity, excellent heat dissipation, and chemically very stable compared to conventional semiconductor materials. There was a problem that the electrode did not have the characteristics to meet it, while having the excellent characteristics of being able to operate in harsh environments such as under.
Japanese Unexamined Patent Publication No. 1-161759 Japanese Unexamined Patent Publication No. 1-246867 Japanese Patent Laid-Open No. 3-110824 JP-A-8-55819 JP-A-8-316498

  The present invention aims to solve the above problems, and has a high dielectric breakdown electric field, extremely good thermal conductivity, excellent heat dissipation, and chemically stable compared to ordinary semiconductor materials, In addition, in order to make the most of the characteristics of a diamond semiconductor having a large band gap, a device having a diamond electrode structure for suppressing the breakdown voltage of the electrode due to electric field concentration of the diamond device and a method for manufacturing the same are provided. is there.

In view of the above problems, the present invention forms a semiconductor diamond layer on an insulator diamond layer or a metallic diamond layer, and etches a portion to be an electrode buried portion of the semiconductor diamond layer to form a groove. Next, an electrode material is formed on the entire surface of the semiconductor diamond layer including the groove thus formed.
Then, the excess electrode material on the semiconductor diamond layer is polished to obtain a device in which the electrode is embedded only in the groove provided in the semiconductor diamond. As a result, the shape of the electrode / diamond interface becomes gentle, and breakdown due to electric field concentration can be reduced. This structure can effectively suppress the breakdown voltage of the electrode due to the electric field concentration of the diamond device.

That is, in a conventional device having an electrode mounted on diamond, the electric field concentration is only on the bottom surface of the electrode, and in particular, the electric field is concentrated on the edge portion (circumferential portion), but it has a buried structure as in the present invention. Then, the electric field concentration is on the electrode bottom surface and the cylindrical side surface (circumference × depth). Therefore, since the area corresponding to the edge portion is increased, the electric field concentration can be suppressed.
In addition, such an electrode structure has a feature that a high voltage device can be easily realized because surface modification such as ion implantation or plasma treatment is facilitated in a later process.

As the electrode material, one or more electrode materials selected from metals, metal nitrides, metal silicides, metal borides, metal carbides, metal oxides, and metal nitrides can be used. There is no restriction | limiting in particular in this electrode material. Depending on the purpose, ohmic electrodes (ohmic electrodes) or Schottky electrodes can be formed. The electrode can be formed in a single layer or a multilayer. The present invention includes all of these.
Further, a high resistance material layer can be formed around the electrode layer embedded in the semiconductor diamond. This has a function of relaxing the electric field distribution and can further improve the breakdown electric field.

  An ohmic electrode can be formed on the back side of the electrode layer embedded with semiconductor diamond. An ohmic electrode is formed. This electrode can also be a normal electrode, and the ohmic electrode is made of a material having excellent conductivity and chemical resistance, and has heat dissipation and improved heat resistance, and at the same time has excellent oxidation resistance and the like. It can also be a material. The electrode structure and the ohmic electrode can be formed by a known vapor deposition method, ion plating method, sputtering method, CVD method, or plasma CVD method. There is no restriction | limiting in particular about the formation method of various layers.

By forming a gate insulating film / metal layer on the semiconductor diamond surface, a transistor as a device having a diamond electrode structure can be manufactured. A structure in which a layer made of a gate insulating film / metal is embedded in a groove provided in the semiconductor diamond so that the surface of the semiconductor diamond and the surface of the layer made of the gate insulating film / metal are flush with each other can also be adopted. .
In this case, as described above, a groove is formed by dry etching or etching with an ion beam or the like at a portion to be an electrode buried portion. Next, an electrode material is formed on the entire surface of the semiconductor diamond layer including the groove thus formed. Then, the excess electrode material on the semiconductor diamond layer is polished to obtain a device in which the electrode is embedded only in the groove provided in the semiconductor diamond.

Such an embedded structure is characterized in that, like the above-described electrode, surface modification by post-processes such as ion implantation and plasma treatment is facilitated, and a high withstand voltage device can be easily realized. Have.
For example, when surface modification is performed to increase the breakdown voltage by increasing the resistance where metal, diamond, air (or passivation film, etc.) are in contact, the interface between the electrode and diamond is the bottom of the electrode The edge portion (circumference) is formed, and particularly when ion implantation is performed on the edge portion, it is necessary to modify the region extending over the lower portion of the electrode and the diamond.
However, in the case of an embedded electrode as in the present invention, since the place where the electrode, diamond, and atmosphere (or a passivation film, etc.) are in contact only in the vicinity of the surface, there is an effect that the modification is facilitated.

  As described above, the characteristics of diamond semiconductors are maximized because they have a high dielectric breakdown electric field, excellent thermal conductivity, excellent heat dissipation, chemical stability, and a large band gap compared to ordinary semiconductor materials. Therefore, it is possible to provide a device having a diamond electrode structure for suppressing the breakdown voltage of the electrode due to electric field concentration of the diamond device and a manufacturing method thereof.

  Next, the features of the present invention will be specifically described with reference to the drawings. In addition, the following description is for making an understanding of this invention easy, and is not restrict | limited to this. That is, modifications, embodiments, and other examples based on the technical idea of the present invention are included in the present invention.

FIG. 1 shows the process of making a diode. The lower layer shows the metallic diamond layer 1. In general, a diamond epitaxial layer is formed. The diamond epitaxial layer is excellent in flatness and crystallinity.
There is no restriction | limiting in particular as a means to form such a metallic diamond layer 1, A well-known method can be used. For example, a method of using a direct current, high frequency or microwave electric field discharge, a method of using ion bombardment, a method of decomposing and forming a raw material gas using light such as laser light, and thermionics. And a method of activating the source gas. Thereby, a good metallic diamond layer 1 can be formed.

A semiconductor diamond layer 2 is formed on the surface of the metallic diamond layer 1 thus obtained. An ohmic electrode 3 is formed on the back surface of the semiconductor diamond layer 2.
This is already known per se, and the present invention is not particularly limited by these. The ohmic electrode 4 is an example of a three-layer electrode in which titanium, platinum / molybdenum 5 and gold 6 are coated (capned) on a semiconductor diamond layer. The cap 6 is important for providing heat dissipation of the electrode structure and improving heat resistance.

FIG. 2 shows a structure in which a groove 7 is formed by patterning the semiconductor diamond layer 2 and further etching the electrode buried portion. As in FIG. 1, the lower layer shows a metallic diamond layer 1. The description common to FIG. 1 is omitted.
As shown in FIG. 3, one or more electrode structure materials 8 selected from metals, metal nitrides, metal silicides, metal borides, metal carbides, and metal oxides (including complex oxides) are deposited, sputtered, for example. The entire surface of the semiconductor diamond layer 2 including the grooves 7 is covered by, for example. A known method can be used as the coating method, and there is no particular limitation. Moreover, it can also be set as a single phase or a multilayer film.

Next, as shown in FIG. 4, the surface of the semiconductor diamond layer 2 is polished to remove the excess electrode material 8 so that the electrode material 8 remains only in the groove 7. Thus, a diode having a diamond embedded electrode structure can be obtained.
In this way, the shape of the electrode / diamond interface becomes gentle and the breakdown due to electric field concentration can be reduced. That is, this structure can effectively suppress the breakdown voltage of the electrode due to the electric field concentration of the diamond device. Such an electrode structure also has an effect that a high voltage device can be easily realized because surface modification such as ion implantation or plasma treatment is facilitated in a later process.

  5 shows a high resistance layer 10 obtained by ion-implanting hydrogen, phosphorus, antimony, carbon, nitrogen, and argon around the electrode 9 into the diode having the diamond embedded electrode structure obtained in FIG. Is formed. The high resistance layer 10 has a function of relaxing the electric field distribution, and can obtain characteristics with a further improved breakdown electric field. As shown in this example, it has a feature that surface modification by a post-process such as ion implantation or plasma treatment becomes extremely easy. This is due to the structure of the embedded electrode 9.

FIG. 6 shows an example of a diamond embedded electrode type transistor. The semiconductor diamond layer 2 is formed on the insulating diamond layer 11. The insulating diamond layer 11 is manufactured by a known epitaxial method, and the manufacturing method is not particularly limited.
The creation of the source or drain electrode 12 formed on the semiconductor diamond layer 2 is the same as the method described with reference to FIGS. 1 to 4 and will not be described here.
In manufacturing the transistor, a gate insulating film / metal layer 13 is formed on the semiconductor diamond layer 2. This layer can be formed by a known method such as ordinary vapor deposition or sputtering.

FIG. 7 shows an example in which the gate insulating film / metal layer 13 is embedded in the semiconductor diamond layer 2 in the transistor example. Also in this case, a groove is formed by etching a portion to be an electrode buried portion. Next, an electrode material is formed on the entire surface of the semiconductor diamond layer including the groove thus formed.
Then, an excess electrode material on the semiconductor diamond layer is polished to obtain a device in which an electrode is embedded only in a groove provided in the semiconductor diamond. The insulating film / metal layer 14 having the embedded structure can have an effect of further improving processing accuracy in a later process.

FIG. 8 shows a structure in which the high resistance layer 15 is formed by ion implantation of hydrogen, phosphorus, antimony, carbon, nitrogen, and argon around the source or drain electrode 12 in the structure of FIG. The high resistance layer 15 has a function of relaxing the electric field distribution, and has a function of further improving the breakdown electric field.
FIG. 9 similarly shows the structure of FIG. 7 in which hydrogen, phosphorus, antimony, carbon, nitrogen, and argon are ion-implanted around the source or drain electrode 12 to form the high resistance layer 15. Similarly, the high resistance layer 15 has a function of relaxing the electric field distribution, and can have a function of further improving the breakdown electric field.

  In the example, the surface of the high resistance material layer 15 is in the same plane as the surface of the semiconductor diamond layer 2 and the surface of the source or drain electrode 12. Examples of the material of the high resistance layer 11 include a diamond layer in which hydrogen, phosphorus, antimony, carbon, nitrogen, and argon are ion-implanted.

  Since the device having the diamond electrode structure of the present invention and the manufacturing method thereof can suppress the breakdown voltage of the electrode due to the electric field concentration of the diamond device, the dielectric breakdown electric field is higher than that of a normal semiconductor material, and the heat conduction. The diamond emission device, diamond emitter, diamond diode, diamond can be used to the fullest extent, with the characteristics of diamond semiconductors being extremely high, excellent in heat dissipation, chemically stable, and having a large band gap. As a transistor or the like, it is extremely useful as a device used under a severe environment such as a high temperature atmosphere or radiation.

It is explanatory drawing of the example which shows the example of the process which produces the device which has a semiconductor diamond embedded electrode, especially a diode, and forms an ohmic electrode on the back. It is explanatory drawing of the example which patterns and etches the electrode part formed in a semiconductor diamond in the process same as the above, and forms a groove | channel. It is explanatory drawing of the example which coat | covers the electrode material on the whole surface in a semiconductor diamond in the process same as the above. It is explanatory drawing of the example which removes an excess electrode material from a semiconductor diamond and forms an electrode in a groove | channel in the process same as the above. It is explanatory drawing of the example which formed the high resistance layer around the electrode material in the process same as the above. It is explanatory drawing which formed the embedded electrode for transistors, and formed the gate electrode / metal layer on the semiconductor diamond. It is explanatory drawing which formed the embedding type electrode and metal layer in semiconductor diamond while forming the embedding electrode for transistors. FIG. 5 is an explanatory diagram in which a buried electrode for a transistor is formed, a gate electrode / metal layer is formed on semiconductor diamond, and a high resistance layer is formed around the gate electrode / metal layer. FIG. 5 is an explanatory diagram in which a buried electrode for a transistor is formed, a buried gate electrode / metal layer is formed on semiconductor diamond, and a high resistance layer is formed around the gate electrode / metal layer.

Explanation of symbols

1: Metallic diamond layer 2: Semiconductor diamond layer 3: Ohmic electrode 4: Titanium 5: Platinum, molybdenum film 6: Gold 7: Groove
8: Electrode material 9: Electrode 10, 15: High resistance layer 11: Insulator diamond layer 12: Source or drain electrode 14: Gate insulating film / metal 15: High resistance layer

Claims (12)

A diamond device having an electrode structure for suppressing a breakdown voltage of the electrode due to electric field concentration of the diamond device,
The surface of the semiconductor diamond and the surface of the electrode are flush with the electrode embedded in the groove provided in the semiconductor diamond,
A diamond device comprising a high resistance material layer around the electrode embedded in the semiconductor diamond.   2. The diamond device according to claim 1, wherein the electrode comprises one or more electrode structures selected from metals, metal nitrides, metal silicides, metal borides, metal carbides, and metal oxides.   The diamond device according to claim 1 or 2, wherein the electrode is formed in a single layer or a multilayer.   The diamond device according to any one of claims 1 to 3, further comprising an ohmic electrode on the back side of the electrode layer embedded with semiconductor diamond.   The diamond device according to claim 1, further comprising a gate insulating film / metal layer on a semiconductor diamond surface. The semiconductor diamond has a structure in which a gate insulating film / metal layer is embedded in a groove provided in the semiconductor diamond so that the surface of the semiconductor diamond and the surface of the gate insulating film / metal layer are flush with each other. The diamond device according to any one of claims 1 to 3. A method of manufacturing a diamond device having an electrode structure for suppressing the breakdown voltage of the electrode due to electric field concentration of the diamond device,
A semiconductor diamond layer is formed on an insulator diamond layer or a metallic diamond layer, and then a groove is formed by etching a portion of the semiconductor diamond layer where an electrode is embedded, and an electrode is formed on the entire surface of the semiconductor diamond layer including the groove. The material is formed, and the electrode is embedded in a groove provided in the semiconductor diamond by polishing the excess electrode material on the semiconductor diamond layer,
A method of manufacturing a diamond device, comprising forming a high resistance material layer around the electrode embedded in the semiconductor diamond.   8. The method of manufacturing a diamond device according to claim 7, wherein at least one electrode material selected from metals, metal nitrides, metal silicides, metal borides, metal carbides, and metal oxides is used as the electrode material. .   9. The method for manufacturing a diamond device according to claim 7, wherein the electrode is formed in a single layer or a multilayer.   The method for manufacturing a diamond device according to any one of claims 7 to 9, wherein an ohmic electrode is formed on the back side of the electrode layer embedded with semiconductor diamond.   The method for producing a diamond device according to any one of claims 7 to 9, wherein a layer made of a gate insulating film / metal is formed on the surface of the semiconductor diamond.   A feature is that the gate insulating film / metal layer is embedded in a groove provided in the semiconductor diamond so that the surface of the semiconductor diamond and the surface of the gate insulating film / metal layer are flush with each other. The method for manufacturing a diamond device according to any one of claims 7 to 9.

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