JP2002076008A - Method of forming ohmic electrode on diamond and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an ohmic electrode that makes a good ohmic contact on diamond. SOLUTION: After a diamond like carbon film 2 is formed on a diamond substrate 1, the diamond like carbon film 2 is heat-treated in a hydrogen atmosphere, and a metal film is formed on the heat-treated diamond like carbon film 2 to be an electrode 3. By forming the electrode after forming the diamond like carbon film 2 by the heat-treatment in the hydrogen atmosphere, the ohmic contact characteristic of the electrode 3 is remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an ohmic electrode of an electronic device using diamond as a raw material, such as a radiation detector, and an electronic device having an ohmic electrode.

[0002]

2. Description of the Related Art Electronic devices are used in various fields, but there is a demand for radiation detectors and the like that can withstand severe environments such as outer space. In response to such demands, research is being conducted on devices using diamond having excellent heat resistance and high thermal conductivity instead of generally used semiconductor materials such as Si (silicon). Application of diamond to various fields as a next-generation semiconductor has been studied, for example, when diamond is doped with impurities such as B (boron), it exhibits p-type semiconductor characteristics.

[0003]

There are various problems in putting a diamond semiconductor into practical use. Among them, how to form an electrode having a good ohmic contact is one of the most important problems. Can be The one that formed a metal electrode on a diamond semiconductor,
It shows an IV characteristic (diode characteristic) as shown in FIG. However, when various kinds of metals are directly deposited on diamond to form an ohmic electrode as in the prior art, the rising voltage V1 shown in FIG. 5 is large, and a good ohmic electrode cannot be obtained.

An object of the present invention is to provide a method for forming an ohmic electrode capable of forming an electrode having a good ohmic contact on diamond, and an electronic device having a practical ohmic electrode.

[0005]

An embodiment of the present invention will be described with reference to FIG. (1) The first aspect of the present invention is a method for forming an ohmic electrode in an electronic device using a diamond substrate 1 as a material. After the diamond-like carbon film 2 is formed on the diamond substrate 1, The above object is achieved by performing heat treatment in a gas atmosphere and forming a metal film on the diamond-like carbon film 2 after the heat treatment to form the electrode 3. (2) The invention according to claim 2 is applied to an electronic device using the diamond substrate 1 as a material, and a diamond-like carbon film 2 formed on the diamond substrate 1 and heat-treated in a hydrogen gas atmosphere; The above object is achieved by providing an electrode 3 made of a metal film formed on the carbon film 2.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments of the present invention are used to make the present invention easier to understand. However, the present invention is not limited to the embodiment.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. As described above, conventionally, an electrode is directly formed on a diamond substrate. However, in the electrode forming method according to the present invention, DLC is formed on the diamond substrate.
A film is formed, the DLC film is heat-treated in a hydrogen atmosphere, and an electrode is formed on the heat-treated DLC film. In the following description, the heat treatment in a hydrogen atmosphere will be referred to as a hydrogen termination treatment.

FIGS. 1 and 2 are views for explaining an embodiment of the method for forming an ohmic electrode according to the present invention. The procedure for forming an ohmic electrode on a diamond substrate will be described with reference to FIGS. First, B
A diamond substrate 1 having p-type semiconductor characteristics including (boron) is formed (see FIG. 1A). In the present embodiment, the thickness of the diamond substrate 1 is about 0.3 mm. Next, as shown in FIG. 1B, a diamond-like carbon (hereinafter, referred to as DLC) film 2 having a thickness of about 400 nm is formed on the diamond substrate 1. As a method for forming the DLC film 2, there is a plasma CVD method or the like, and in particular, ECR-CVD using electron cyclotron resonance.
When the method is used, a good DLC film 2 can be obtained.

After the DLC film 2 is formed on the diamond substrate 1, the DLC film 2 is heated in a hydrogen gas atmosphere to perform a hydrogen termination treatment on the DLC film 2. FIG. 2 is a view for explaining a hydrogen termination treatment, (a) is a schematic diagram of a heat treatment apparatus,
(B) is a figure which shows the heating pattern during heat processing. 5
Is a quartz tube furnace in which the diamond substrate 1 is loaded, and the quartz tube furnace 5 is provided with a heater 6 for heating. Also,
An exhaust device 7 and a gas supply device 8 for supplying a mixed gas of Ar (argon) gas and H ₂ (hydrogen) gas (at substantially normal pressure) are connected to the quartz tube furnace 5.

As shown in FIG. 2A, when the diamond substrate 1 on which the DLC film 2 is formed is loaded into the quartz tube furnace 5, a mixed gas is supplied from the gas supply device 8 into the quartz tube furnace 5. To replace the air and gas. When the mixed gas is filled in the quartz tube furnace 5, the quartz tube furnace 5 is heated by the heater 6 in a heating pattern as shown in FIG. FIG.
In the heating pattern (b), the temperature was raised from room temperature to 800 ° C. over 4 hours, and after maintaining at 800 ° C. for 2 hours, 8 to
Reduce the temperature to room temperature over 10 hours.

FIG. 2B shows an example of a heating pattern, which is set as appropriate according to conditions such as the dimensions of the device, the thickness of each of the films 1 and 2 and the mixing ratio of the mixed gas.
By the way, during hydrogen termination, only hydrogen gas may be supplied into the quartz tube furnace 5, but it is dangerous to supply only hydrogen gas and heat it, so dilute hydrogen gas with inert argon gas. The mixed gas used was used. The mixing ratio (volume ratio) of the mixed gas is set in the example shown in the present embodiment such that hydrogen gas is 5% and argon gas is 95%.

In the present embodiment, argon gas is used as a diluting gas, but helium gas or the like may be used.
As a mode of supplying the mixed gas to the quartz tube furnace 5, the heating process may be performed in a state where the mixed gas is filled as described above, or the mixed gas may be supplied from the gas supply device 8 during heating. The gas may be exhausted by the exhaust device 7.

Returning to FIG. 1, when the heat treatment of the DLC film 2 is completed, Au (gold) is formed on the DLC film 2 and Al (aluminum) is formed on the opposite diamond film 1 by vapor deposition. The electrodes 3 and 4 are formed by film formation. Examples of the evaporation method include a resistance heating method, an ion plating method, a sputter evaporation method, and an electron beam evaporation method. The thickness of each of the electrodes 3 and 4 is about 20 nm. The junction between the Al electrode 4 and the diamond substrate 1 exhibits diode characteristics as shown in FIG. Conventionally, both the electrodes 3 and 4 were formed directly on the diamond substrate 1.

When performing an evaluation experiment on the electrode 3, as shown in FIG. 3, a voltage is applied between the electrode 3 and the electrode 4, and the IV characteristic is measured. FIG. 4 shows characteristics of a diode including an ohmic electrode according to the formation method of the present embodiment (forward characteristics).
Is a diagram showing a comparison with a conventional diode characteristic including an ohmic electrode, in which a horizontal axis indicates a bias voltage V and a vertical axis indicates a forward leakage current. In FIG.
Indicates the characteristics of the device according to the present invention, and indicates the characteristics of the device according to the conventional forming method. Is an Au electrode formed on a diamond substrate, is an electrode formed of a three-layer metal film of Ti, Pt, and Au on a diamond substrate, and is an Au electrode formed after hydrogen termination of the diamond substrate. Things.

As shown in FIG. 4, when an ohmic electrode formed by the conventional method is included, the rise voltage of the leakage current is 100 V or more in (-), but the ohmic electrode formed by the method of the present invention is included. Case () is 1V
The rising voltage becomes smaller by two digits or more. That is, when the ohmic electrode according to the formation method of the present invention is used (), a forward leakage current easily flows, and a remarkably good IV characteristic of the diode is obtained. This indicates that a better ohmic electrode than before, that is, a practical ohmic electrode usable for a diamond device could be formed.

In each of the above examples, an Au electrode was directly formed on a diamond substrate. However, when the diamond substrate was subjected to hydrogen termination, the rising current in the forward direction was larger and a better ohmic current was obtained. It is a contact. From this fact, it is presumed that the ohmic contact property is improved by subjecting diamond to hydrogen termination treatment. In particular, in the case of the DLC film 2, it is considered that the ohmic contact property is significantly improved.

By the way, it is known that when the DLC film 2 formed by the plasma CVD method is subjected to a heat treatment, it becomes graphite. However, in this embodiment, a mixed region of diamond and graphite is formed in order to use a plasma CVD method with a large implantation energy, so that a graphite film is formed by sputter deposition.
It is considered that a good ohmic electrode is formed.

[0018]

As described above, according to the present invention,
For electronic devices using diamond as a substrate material,
An electrode having a better ohmic contact than before can be formed, and diamond can be put to practical use in electronic devices such as radiation detectors.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a procedure for forming an ohmic electrode, and the process proceeds in the order of (a) to (c).

FIGS. 2A and 2B are diagrams illustrating a heat treatment, wherein FIG. 2A is a diagram illustrating a heat treatment device, and FIG. 2B is a diagram illustrating a heating pattern during the heat treatment;

FIG. 3 is a diagram illustrating an electrode evaluation method.

FIG. 4 is a diagram showing characteristics (forward characteristics) of an electrode according to a forming method of the present embodiment in comparison with characteristics of a conventional electrode.

FIG. 5 is a diagram showing IV characteristics when a metal electrode is formed on a diamond semiconductor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diamond substrate 2 Diamond-like carbon film 3, 4 Electrode 5 Quartz tube furnace 6 Heater 7 Exhaust device 8 Gas supply device

Continuation of the front page F term (reference) 4M104 AA10 BB09 BB36 CC01 DD78 FF13 HH15

Claims (2)

[Claims] 1. A method for forming an ohmic electrode in an electronic device using a diamond substrate as a material, comprising: forming a diamond-like carbon film on the diamond substrate; and heating the diamond-like carbon film in a hydrogen gas atmosphere. Forming an electrode by forming a metal film on the diamond-like carbon film after the heat treatment. 2. An electronic device using a diamond substrate as a raw material, comprising: a diamond-like carbon film formed on the diamond substrate and heat-treated in a hydrogen gas atmosphere; and a metal formed on the diamond-like carbon film. An electronic device comprising: a film-forming electrode.