JPH05160386A - Diamond diode and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a diamond diode having low internal resistance by installing, in distributed condition, a plurality of electrodes to form Schottky junction due to the contact with the surface of the second diamond layer added with low concentration boron which is laminated on a first diamond layer added with high concentration boron which is laminated on a substrate. CONSTITUTION:Scratching treatment is made by the powder of #800 diamond on the surface of a metallic substrate 1 for which a Pt plate is used. Composition of diamond is done on the surface by using mu-wave CVD system. Diamond is composed by the following process: CH4 gas and H2 gas are fed with a flow rate of 0.5SCCM and 99.5SCCM, respectively. Then, B2 gas and H6 gas are mixed with the CH4 gas and H2 gas for B dope. A high concentration B doped diamond film 21 is formed in about one hour by mixing the B2H6 gas so that the B/C ratio gets to 1000ppm. Successively, a low concentration B doped diamond film 22 is formed in about 0 hour by mixing the B2h6 gas so that the B/C ratio gets to 10ppm and 1000ppm. Then, Al is vapor deposited, and a Schottky electrode 3 having small area is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond diode having a Schottky junction with a polycrystalline diamond film which can be formed by a vapor phase synthesis method, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Since diamond, which is a typical gem, is the hardest substance, it is industrially used for cutting tools and abrasives as well known. Besides this,
Diamond belongs to the same group IV as Si and Ge, and also has semiconductor properties. Not only does it have a larger energy gap than Si, but it also has carrier mobility, saturation drift velocity,
Dielectric breakdown electric field and thermal conductivity are also large, and they are promising as materials for high temperature operation devices, high power devices, blue light emitting devices and the like. In recent years, this diamond has been vapor-phase synthesized (CV
D) technology has been developed, and its application as a semiconductor device is drawing more attention. Actually, trial production of thermistors, Schottky diodes, FETs, light emitting elements, etc. has been actively conducted.

Diamond is a crystal composed of carbon atoms.
However, it is not a stable phase under normal environment. In metastable phase
The CVD method is a method for synthesizing a certain diamond. C
H_FourGas composed of carbon and a large amount of H₂Gas
On a substrate such as Si that has been activated and heated to a high temperature of 600 to 1200 ° C
This is a method of forming a diamond film. H₂Gas activated
Will be converted into highly reactive atomic hydrogen and diamond
Simultaneously re-evaporate the graphite component which is a stable phase
Emit. Various ways to activate these gases have been devised
Hot filament CVD method, μ wave plasma CVD
Method, DC plasma jet CVD method, etc.
ing. The synthetic diamond has a diamond substrate
It becomes a polycrystal except when it is made of C-BN or C-BN. That
B₂H ₆When a gas containing boron such as
B can be added to the diamond. CH as a carbon source_Four
When gas is used, the B / C ratio in the gas and the diamond
It almost coincides with the B / C ratio in the film. Like this
B-doped diamond is a P-type semiconductor and is made of metallic aluminum.
Form a Schottky junction with such as titanium or titanium
It For this reason, diamond-based diodes and electric fields
Effect transistors have been developed.

[0004]

The conventional Schottky diode using polycrystalline diamond synthesized by the CVD method has the structure shown in FIG. That is,
A diamond film 2 doped with B is synthesized on an insulating substrate 1 such as SiO ₂ by a CVD method, and a Schottky electrode 3 such as Al and an ohmic electrode 4 such as Au are attached to the surface of the diamond film 2 by vapor deposition. It is a thing. In the diode having this structure, the current density flowing in the diamond film 2 depends on the film thickness. Then, in order to reduce the internal resistance of diamond, a fine processing technique for narrowing the distance between the electrodes 3 and 4 must be used, which is a problem that cannot be easily done.

In order to solve such a problem, a diode having the structure shown in FIG. 3 is manufactured. This diode synthesizes a B-doped diamond film 2 on a heavily doped n ⁺ Si or p ⁺ Si substrate 5, a Schottky electrode 3 on the surface of the diamond film 2 and an ohmic electrode on the surface of the Si substrate 5. 6 is contacted. Although this structure reduces the internal resistance to some extent, the internal resistance of the Si substrate 5 having a resistivity of about 10 ³ Ωcm cannot be avoided. Further, since the diamond film 2 is polycrystalline, a short circuit occurs between the Schottky electrode 3 and the Si substrate 5.

It is an object of the present invention to solve the above problems and provide a diamond diode having a small internal resistance and a method for manufacturing the same.

[0007]

In order to achieve the above object, the diamond diode of the present invention comprises a first diamond layer containing a high concentration of boron on a substrate made of a metal which makes ohmic contact with diamond. , A second diamond layer having a low concentration of boron added is laminated on the first diamond layer, and a plurality of electrodes for contacting the surface of the second diamond layer to form a Schottky junction are provided in a dispersed manner. It is assumed that And the metal substrate is platinum,
Consists of one of copper, gold, silver, tungsten and molybdenum, B concentration of the first diamond layer is 800ppm
And the B concentration of the second diamond layer is 5 or more.
It is effective that the content is up to 200 ppm and that the electrode is made of either aluminum or titanium. In addition, such a diamond diode manufacturing method first forms a first diamond layer having a high B concentration on a metal substrate by vapor phase synthesis using a gas containing a carbon compound and a boron compound,
Next, a second diamond layer having a low B concentration is formed, a metal is deposited on the surface of the second diamond layer, and the metal layer is patterned to form a plurality of electrodes. Then, it is effective to connect each electrode to the terminal except the electrode having no rectifying characteristic with the substrate.

[0008]

[Function] The resistivity of metal is about 1 to 100 Ωcm and 10 ³ Ω of Si
It is smaller than the resistivity of cm or more, and by using a metal substrate, the internal resistance can be suppressed to about 1/100 even if it is small. By increasing the B concentration on the substrate side of the diamond phase to a resistivity of about 0.03 Ωcm, if the layer thickness is sufficiently smaller than the substrate thickness, the increase in internal resistance due to this layer is slight, and the high B concentration is increased. By doing so, the ohmic contact with the substrate is improved and the contact resistance is also reduced. This reduces the internal resistance of the diode. Further, by using a plurality of Schottky electrodes, even if a short circuit with the substrate occurs in some of the electrodes, the rectifying action can be obtained in the other electrodes.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of (a) and a plan view of (b) showing a diamond diode according to one embodiment of the present invention.
The same parts as those in FIG. 3 are designated by the same reference numerals. This diode was manufactured as follows.

A Pt plate was used as the metal substrate 1, and the surface thereof was scratched with # 800 diamond powder. Then, diamond is synthesized on the surface by the μ wave CVD method. The synthesis of diamond CH ₄ gas and H ₂ gas
Flowing at a flow rate of 0.5 SCCM and 99.5 SCCM, the gas is mixed with B ₂ H ₆ gas for B doping. First, B ₂ H ₆ gas B / C ratio to form a high concentration B-doped diamond film 21 in about 1 hour and mixed so that the 1000 ppm, is continuously B ₂ H ₆ gas B / C ratio Low concentration B-doped diamond film was mixed in 10ppm and 100ppm in about 3 hours.
22 formed. In each case, the reaction pressure was adjusted to 30 Torr, and a microwave of 2.45 GHz and 400 W was introduced into the substrate placed in the reaction tube. As a result, the source gas is turned into plasma, and about 10
A diamond film is synthesized on the substrate at 00 ° C. Then, Al was vapor-deposited on the diamond film 22 and patterned to form a total of 16 small-area Schottky electrodes 3 each having a diameter of 2 mm as shown in FIG.

In this diode, the metal substrate 5 and the high-concentration B-doped diamond film 21 are particularly used for the internal resistance.
Ohmic contact between and becomes a problem. Therefore, it was confirmed that the sample in which the low concentration B-doped diamond film 22 was not synthesized was ohmic. Also, similar C
When a high-concentration B-doped diamond film was formed on the SiO ₂ substrate by the VD method and the resistivity was measured, a value of 0.03 Ωcm was obtained.

It was confirmed that the diamond diode having the above structure has a rectifying characteristic. FIG. 4 shows the current / voltage characteristics of the diamond film 22 when B / C = 10 ppm. In this case, about three of the 16 Schottky electrodes 3 were leaked, and therefore the electrodes were disconnected from the terminals. Although Pt was used as the material of the metal substrate 5 in the above embodiment, other than Au, A
It is also possible to use g, Cu, W, Mo and the like. In addition to Al, Ti may be used as the material of the Schottky electrode 3.

[0013]

According to the present invention, as a result of using a metal substrate having a low resistivity as a substrate for forming a diamond layer and doping the high concentration B on the side of the diamond layer which is in contact with the substrate to reduce the contact resistance. We were able to obtain a diamond diode with low internal resistance. Further, by dividing the Schottky electrode into a plurality of pieces, even if a short circuit between the Schottky electrode and the substrate through the polycrystalline diamond layer partially occurs, only the electrode having a rectifying characteristic can be used, and the short circuit can be achieved. Although the characteristics are reduced depending on the number of parts, it has become possible to increase the manufacturing yield.

[Brief description of drawings]

FIG. 1 shows a diamond diode according to an embodiment of the present invention, (a) is a sectional view, and (b) is a plan view.

FIG. 2 is a sectional view of an example of a conventional diamond diode.

FIG. 3 is a sectional view of another example of a conventional diamond diode.

FIG. 4 is a voltage / current characteristic diagram of a diamond diode according to an embodiment of the present invention.

[Explanation of symbols]

 21 high concentration B-doped diamond film 22 low concentration B-doped diamond film 3 Schottky electrode 5 metal substrate

Claims (7)

[Claims] 1. A first diamond layer having a high concentration of boron added on a substrate made of a metal which makes ohmic contact with a diamond, and a second diamond having a low concentration of boron added on the first diamond layer. A diamond diode, wherein layers are laminated, and a plurality of electrodes forming a Schottky junction in contact with the surface of the second diamond layer are dispersedly provided. 2. The diamond diode according to claim 1, wherein the metal substrate is one of platinum, copper, gold, silver, tungsten and molybdenum. 3. The boron concentration of the first diamond layer is 800 ppm.
The diamond diode according to claim 1 or 2, which is the above. 4. The boron concentration of the second diamond layer is 5 to 20.
The diamond diode according to claim 1, 2 or 3, which has an amount of 0 ppm. 5. The diamond diode according to claim 1, wherein the electrode is made of aluminum or titanium. 6. A first diamond layer having a high boron concentration is first formed on a metal substrate by a vapor phase synthesis method using a gas containing a carbon compound and a boron compound, and then a second diamond layer having a low boron concentration is formed. A method for producing diamond / diamond, comprising forming a diamond layer, then depositing a metal on the surface of the second diamond layer, and patterning the metal layer to form a plurality of electrodes. 7. The method of manufacturing a diamond diode according to claim 6, wherein each electrode is connected to a terminal except an electrode having no rectifying characteristic with the substrate.