JP2006237179A - Method of forming ohmic joint of diamond - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of easily forming an ohmic joint on diamond. <P>SOLUTION: The method includes a step wherein, with laser light being irradiated on a predetermined range on a diamond substrate (1) in a vacuum bath (2), a dopant ion beam is injected into the same region to form a conductive layer; and a step of forming a metal electrode on the conductive layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diamond semiconductor device, and more particularly to a method for forming an ohmic junction of diamond.

  Diamond is the hardest material, has excellent heat resistance, has a large band gap of 5.47 eV, is usually an insulator, but can be made into a semiconductor by doping with a dopant. In addition, the dielectric breakdown voltage and saturation drift speed are high, and the electrical characteristics such as low dielectric constant are also excellent. Furthermore, it has the highest thermal conductivity among substances at around room temperature and has high heat dissipation. Due to such characteristics, diamond is expected to be used as a next-generation element for extreme environments such as high temperature resistance and radiation resistance, and as a semiconductor for high frequency and high output elements, and is currently under development.

  In order to use diamond as a semiconductor device material, it is necessary to control p-type and n-type conductivity. Specifically, in the process of manufacturing an element, a donor-type or acceptor-type impurity is introduced from the outside into an appropriate portion of diamond, and p-type or n-type conductivity is imparted to the necessary portion. Further, in order to function as an element, it is necessary to form a metal electrode for current input / output on the conductive portion and to wire the conductive portions to each other. At that time, it is required that the junction between the conductive portion and the metal electrode have ohmic electrical characteristics. That is, the contact between the conductive portion and the metal needs to be an ohmic contact in which the current-voltage characteristic of the contact portion is linear.

Conventionally, after imparting conductivity to diamond by introducing impurities, and depositing a metal electrode on the conductive portion, heat treatment was performed to recover lattice defects, and a good ohmic junction was obtained ( Non-patent document 1).
Electrical properties of graphite / homoepitaxial diamond contact, YG Chen, et.al., Diamond and Related Materials 11 (2002) 451-457.

  However, in the above-described conventional technique, a donor-type or acceptor-type impurity is introduced into diamond from the outside to form a conductive portion, and a metal electrode is formed on the conductive portion, depending on the amount of impurities implanted. There has been a problem that it may be difficult to impart ohmic electrical characteristics to the joint.

  The present invention has been made in order to solve the above-described conventional problems, and can easily provide ohmic electrical characteristics to a joint portion of a diamond conductive portion and another material, particularly a metal electrode. It is an object of the present invention to provide a method for forming a diamond ohmic joint.

  In order to solve the above-mentioned problems, the diamond ohmic junction forming method according to the present invention forms a conductive layer by ion-implanting impurities into a predetermined region while irradiating the predetermined region of the diamond surface with laser light. Including the step of: This makes it possible to obtain an ohmic junction in the conductive layer.

The diamond ohmic bonding portion forming method according to the present invention further includes a step of forming a metal electrode on the conductive layer. This provides an ohmic electrode on the diamond conductive layer.

Boron or phosphorus can be used as the impurity, but it is an element that can form an n-type or p-type conductive layer in diamond, that is, an n-type or p-type element for carbon. Does not matter.

The energy of the impurity ion beam is about 10 keV to several MeV, and the amount of current is about 0.1.
It can be from μA / cm ² to 10 mA / cm ² .

It is desirable that the laser beam has a wavelength of about 400 nm to 100 nm and an energy density of about 100 mJ / cm ² or more.

The conductive layer is preferably formed in a vacuum environment, and the degree of vacuum is about 10 ⁻² Pa or less.

  According to the method for forming an ohmic junction of diamond according to the present invention, it becomes possible to form an ohmic junction at a conductive portion of diamond. It is possible to impart ohmic properties to the joint between the conductive portion and the metal electrode that have been generated. Thereby, diamond can be used more widely as a material for semiconductor elements.

  Hereinafter, a method for forming an ohmic joint of diamond according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram for explaining a method for forming an ohmic junction of diamond according to an embodiment of the present invention.

First, the diamond substrate 1 is placed in the irradiation vacuum chamber 2, and an ion beam of an impurity element (boron, phosphorus, etc.) for conductivity control is introduced into the irradiation vacuum chamber 2 and irradiated on the surface of the diamond substrate 1. The energy of the impurity ion beam is selected according to the depth and distribution necessary for imparting conductivity. Usually, it is in the range of 10 keV to several MeV. Current of the ion beam is not particularly limited, usually ^{0.1μA / cm 2 ~10 mA / cm} 2 or so, preferably ^{1μA / cm 2 ~1 mA / cm} 2 approximately.

When irradiating the surface of the diamond substrate 1 with the ion beam, simultaneously, a laser beam is irradiated onto a region on the surface of the diamond substrate 1 where the ion beam is irradiated. The wavelength and energy density of the laser beam are not particularly limited, but the wavelength is preferably about 400 nm to 100 nm, and the energy density is preferably about 100 mJ / cm ² or more. That is, it is desirable that the wavelength of the laser light be in a region where light absorption by diamond is significant. Specifically, a wavelength exceeding the energy between the forbidden bands of diamond, a wavelength at which absorption by impurities or defects can occur, and the like are desirable.

The vacuum in the irradiation vacuum chamber 2 in which the diamond substrate 1 is installed at the time of ion irradiation is not particularly limited, but a higher vacuum is desirable. The degree of vacuum in the irradiation vacuum chamber 2 is about 10 ⁻² Pa or less, preferably about 10 ⁻⁴ Pa or less.

  There is no particular limitation on the temperature of diamond when the ion beam or laser beam is irradiated.

  Next, an Example is given and this invention is demonstrated more concretely. Of course, the following examples are merely specific examples for understanding the present invention, and the present invention is not limited thereby.

As in FIG. 1, the diamond substrate 100 synthesized at high temperature and high pressure was placed in an irradiation vacuum chamber, and the inside of the vacuum chamber was evacuated to 7 × 10 ⁻⁶ Pa.

Thereafter, in order to impart p-type conductivity to the diamond substrate 100, boron was introduced by ion implantation. Specifically, the boron element was introduced by ionizing the boron element to generate a boron ion beam and irradiating the surface of the diamond substrate 100 with it. Thereby, the conductive layer 110 (see FIG. 2) was formed on the surface of the diamond substrate 100. At this time, the energy and irradiation amount of the ion beam were adjusted so that the boron concentration was uniform at 5 × 10 ¹⁹ cm ⁻³ at a depth from the surface of the diamond substrate 100 to 450 nm. The temperature of the diamond substrate 100 during ion implantation was set to 400 ° C.

Simultaneously with the irradiation of the ion beam, the surface of the diamond substrate 100 was also irradiated with a laser beam. As the laser light, a XeCl excimer laser with a wavelength of 308 nm was used. The pulse width of the laser beam was set to 20 ns, the repetition rate was set to 100 Hz, and the energy density of the laser beam at the surface position of the diamond substrate 100 was set to about 0.2 J / cm ² .

  After ion implantation, heat treatment was performed at 1400 ° C. to remove lattice defects formed simultaneously with boron introduction.

  After heat treatment, a metal electrode was deposited on the conductive layer 110 into which boron was introduced. Specifically, two metal electrodes were formed by vapor-depositing each metal in the order of titanium Ti (thickness 30 nm), platinum Pt (thickness 30 nm), and gold Au (thickness 100 nm) ( (See FIG. 2).

  After forming the metal electrode, heat treatment was again performed at 400 ° C.

  For comparison, a metal electrode was similarly formed after irradiating only the ion beam to the diamond substrate without performing laser irradiation.

  FIGS. 3A and 3B are diagrams showing the logarithm of the current-voltage characteristics between the two metal electrodes when laser irradiation is performed and when laser irradiation is not performed.

When the laser irradiation shown in FIG. 3B is not performed, the current and voltage measured values are not plotted on a straight line (n = 1) with a logarithmic display and a slope n of 1; Is not proportional, i.e., not ohmic. On the other hand, when the laser irradiation shown in FIG. 3 (a) is performed, the plot of the measured values of current and voltage is on a straight line of n = 1, and the current and voltage are in a proportional relationship, that is, ohmic. It turns out that it is.

  In this example, the current-voltage characteristics between the two metal electrodes formed on the diamond substrate were in a proportional relationship including the case of sign inversion. That is, even if the polarity of the applied voltage is reversed, the current and the voltage are still in a proportional relationship.

As described above, in the method for forming an ohmic junction of diamond according to the present invention, an ion beam of impurities is irradiated while irradiating a laser beam when forming a conductive layer of diamond. In particular, when a metal electrode is formed on the conductive layer, the junction between the conductive layer and the metal electrode can surely have ohmic properties. Thereby, an ohmic electrode can be easily formed on the diamond.

  The method for forming an ohmic junction of diamond according to the present invention has an effect that an ohmic junction and an ohmic electrode can be easily formed on diamond, and a semiconductor using diamond. This is useful in manufacturing the device.

It is a figure explaining the formation method of the ohmic junction of the diamond which concerns on embodiment of this invention. It is sectional drawing of the diamond substrate which formed the metal electrode, after irradiating an ion beam, irradiating a laser beam. It is the figure which carried out the logarithm display of the current-voltage characteristic of the ohmic junction obtained in the said Example, (a) is a case where laser irradiation is performed, (b) is a case where laser irradiation is not performed.

Explanation of symbols

1, 100 Diamond substrate 2 Irradiation vacuum chamber 110 Conductive layer introduced with boron

Claims (6)

  A method for forming an ohmic junction of diamond, comprising the step of forming a conductive layer by irradiating a predetermined region of a diamond surface with laser light and implanting impurities into the predetermined region.   The method according to claim 1, further comprising forming a metal electrode on the conductive layer.   The method for forming an ohmic junction of diamond according to claim 1, wherein the impurity is a p-type or n-type element for carbon. The energy of the ion beam of the impurity is about 10 keV to several MeV,
4. The diamond ohmic junction according to claim 1, wherein an ion beam current amount of the impurity is about 0.1 μA / cm ² to 10 mA / cm ^2. Method. The wavelength of the laser light is about 400 nm to 100 nm,
The method for forming an ohmic bonding portion of diamond according to any one of claims 1 to 4, wherein the energy density of the laser beam is about 100 mJ / cm ² or more. 6. The method for forming an ohmic junction of diamond according to claim 1, wherein the conductive layer is formed in an environment having a degree of vacuum of about 10 ⁻² Pa or less. .

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