JPH0769794A - Semiconductor diamond and method for forming the same - Google Patents

Abstract

PURPOSE:To obtain an n-type semiconductor of low resistance by doping diamond with a nitrogen atom and a boron atom in specific concentration ranges. CONSTITUTION:Diamond is doped with a reaction gas obtained by adding a nitrogen atom-containing gas such as N2 or N2O and a boron atom-containing gas such as B2H6 or B3O3 to a mixed gas prepared by diluting CH4 with H2 by CVD method (chemical vaporphase growth method) to dope diamond with 1X10<19>cm<-3> nitrogen atom and boron atom in 100CB2CN>CB wherein C''s nitrogen atom concentration and CB is boron atom concentration to give an n-type semiconductor diamond which has >=1mu10<16>-cm<-3> carrier concentration, <=40 seconds half-value width of rocking curve in 2 crystallization method of X-ray diffraction. This diamond is applicable to both artificial (high-pressure synthesis) bulk single crystal or thin-film polycrystal or thin-film single crystal (epitaxial film) by a vapor-phase synthesis method and has <=1X105OMEGA.cm specific resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor diamond that can be used for semiconductor devices such as diodes and transistors.

[0002]

2. Description of the Related Art Diamond has attracted attention for its application as a device that operates stably under severe conditions such as high temperature and radiation irradiation, or as a device that can withstand operation at high output.

The reason why diamond can operate even at high temperature is that the band gap is as large as 5.5 eV. This is because it indicates that the temperature range (intrinsic region) where semiconductor carriers are not controlled does not exist below 1400 ° C.

However, diamond has not been able to obtain an n-type semiconductor having a low resistance until now, and this has been a great obstacle to the development of device application products.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low resistance n-type semiconductor of diamond semiconductor and a method for forming the same.

[0006]

Similar to silicon (Si), diamond is expected to become a p-type semiconductor by adding a group III element and become an n-type semiconductor by adding a group V element. However, since carbon that constitutes diamond has a small atomic radius and a large density, it is not possible to mix any impurities into diamond, and elements such as boron, nitrogen, or phosphorus with a relatively small atomic radius are mixed. It is possible.

However, if nitrogen atoms are doped into the diamond as a donor, the donor level becomes very deep (from 1 eV to 2 eV).
This is the boron acceptor level (0.37 eV)
Since it is much larger than that of No. 1, a low resistance n-type semiconductor cannot be obtained by simply doping nitrogen into the diamond as a donor.

As a result of earnest research, the present inventor has made it possible to conduct carriers between nitrogen levels by making the concentration of nitrogen atoms in diamond extremely high, and to obtain low resistance conductivity even at room temperature. I found a thing.

The semiconductor diamond of the present invention is based on the above findings, and more specifically, it is characterized in that the diamond is doped with nitrogen atoms at 1 × 10 ¹⁹ cm ⁻³ or more.

As described above, according to the present invention, a low resistance n-type diamond semiconductor can be obtained by making the nitrogen atom concentration extremely high. Considering that pure Si having a bandgap of 1.1 eV has a very high resistivity, a low resistance semiconductor is obtained by using a dopant (nitrogen atom) having an impurity level of 1 to 2 eV. The idea of the present invention is totally different from the conventional one.

As a result of further research conducted by the present inventor, it was found that doping not only nitrogen atoms but also boron atoms in a specific concentration range into diamond is extremely effective in solving the above-mentioned problems. It started.

Therefore, according to the present invention, the diamond is further doped with nitrogen atoms and boron atoms, and the nitrogen atom concentration (CN) and the boron atom concentration (CB) are 100 CB ≧ CN> An n-type semiconductor diamond is provided that is in the CB range.

According to the knowledge of the inventor of the present invention, when nitrogen is doped in a low concentration in diamond, the nitrogen level is deep because the nitrogen atom is introduced into the diamond so that the crystal structure is locally changed. It is thought that it is distorted. Therefore, according to the knowledge of the inventor of the present invention, the lattice distortion caused by the incorporation of nitrogen atoms into diamond is relaxed by the addition of boron atoms as described above to make the nitrogen level shallow, and thus even at room temperature. It is considered that low resistance conductivity can be obtained.

[0014]

Function: Diamond has a band gap of 5.5 eV
Therefore, the temperature region corresponding to the intrinsic region does not exist below 1400 ° C. at which diamond is thermally stable, and furthermore, diamond is also chemically very stable. Further, the thermal conductivity of diamond is 20 (W / cm · K), which is 10 times or more that of Si, and is excellent in heat dissipation. Furthermore, diamond has a high carrier mobility (electron mobility: 2000 (cm ² / V · sec)) and hole mobility:
2100 (cm ² / V · sec), 300K), small inductivity (K = 5.5), large breakdown electric field (E = 5 × 10)
⁶ V / cm) and the like, it is possible to fabricate a device for high power at high frequency by using diamond.

In the present invention, in order to realize an n-type or p-type semiconductor which is indispensable in a diamond device, a large amount of nitrogen atoms are doped into diamond, or boron atoms are simultaneously doped into diamond. ing.

The present invention will be described in more detail below.

(Semiconductor Diamond) The semiconductor diamond to which the present invention is applicable is not particularly limited. For example, the effect of the present invention does not change whether the diamond is an artificial (high pressure synthetic) bulk single crystal or a thin film polycrystal or a thin film single crystal (epitaxial film) produced by a vapor phase synthesis method.

The semiconductor diamond of the present invention may be either n-type or p-type, but is preferably n-type for application to a device.

The resistivity of the semiconductor diamond of the present invention is preferably 1 × 10 ⁵ Ω · cm or less, more preferably 1000 Ω · cm or less (particularly 100 Ω · cm or less).
Is preferred.

In measuring the resistivity, for example, the following measurement conditions can be preferably used.

Measurement method: four-terminal method Measurement conditions: voltage measurement (1 to 100 v) is performed under a constant current (10 μA to 1 mA).

(Diamond forming method) When the diamond film is formed by vapor phase synthesis, the following various methods can be used as the forming method.

(1) A method of activating a raw material gas by causing a discharge by a direct current or an alternating current electric field, (2) a method of heating a thermoelectron emitting material to activate the raw material gas, (3) a surface on which diamond is grown A method of bombarding with,
(4) Method of exciting source gas with light such as laser or ultraviolet ray, and (5) Method of burning source gas Any of the above methods can be used in the present invention. However, the effect of the invention does not change.

In the present invention, the CVD method (chemical vapor deposition method) is preferably used as a method for doping diamond with nitrogen atoms from the viewpoint of easy adjustment of the dopant amount.

(CVD method) The reaction gas (or raw material gas) used in the CVD method is not particularly limited as long as the diamond can be deposited and grown on the substrate. More specifically, for example, as the reaction gas, a mixed gas of CH ₄ diluted with H ₂ , a mixed gas of ethyl alcohol or acetone diluted with H ₂ , or a mixed gas of CO diluted with H ₂ is suitable. Can be used for.

In the present invention, when a diamond doped with nitrogen atoms is obtained, the reaction gas may be added with a nitrogen atom-containing gas in an amount corresponding to a desired nitrogen atom concentration. As such a nitrogen atom-containing gas, for example, N ₂ , N ₂ O, NO ₂ , NH _{3 and the} like can be preferably used.

In the present invention, when a diamond doped with nitrogen atoms and boron atoms is obtained, the reaction gas is supplied with nitrogen atom-containing gas and boron atom-containing gas in amounts corresponding to the desired nitrogen atom concentration and boron atom concentration, respectively. It may be added and used. Examples of such boron atom-containing gas include B ₂ H ₆ , B ₂ O ₃ , and B.
₂ (CH ₃ ) ₃ , B ₂ (OCH ₃ ) _{3 and the} like can be preferably used.

(High-pressure synthesis method) When the high-pressure synthesis method is used,
Even if a nitrogen-containing raw material is added to a raw material, a solvent, and / or a high-pressure synthesis container to form a nitrogen-containing diamond by the high-pressure synthesis method, or a raw material containing nitrogen and boron is added, nitrogen is added by the high-pressure synthesis method. Forming diamond containing boron and boron does not change the effect of the present invention.

(Ion Implantation Method) Also, a method of adding nitrogen by ion implantation can be used. In this case, it is usually difficult to obtain the above effect in the sample immediately after the injection, but for example, the injection condition is adjusted (injection at a high temperature state) or the crystallinity recovery process (hydrogen plasma is performed). It is possible to obtain the above-mentioned effects by adjusting the treatment etc.).

(Concentration of Nitrogen Atoms) The concentration of nitrogen atoms doped in the semiconductor diamond of the present invention is 1 × 10 ^19.
It is preferably cm ⁻³ or more. When nitrogen atoms are doped into diamond together with other dopants, the concentration of nitrogen atoms is 1 × 1 from the viewpoint of semiconductor characteristics.
It is preferably 0 ¹⁷ cm ⁻³ or more.

The nitrogen atom concentration can be measured by, for example, secondary ion mass spectrometry (SIMS). In this SIMS, for example, the following measurement conditions can be preferably used.

(N analysis) (B analysis) Primary ion: Cs ⁺ O ₂ ⁺ Accelerating voltage: 10 kV 15 kV Current: 580 nA 2000 nA Raster size: 250 μm square 250 μm square Analysis area: Diameter 62 μmφ 62 μmφ (concentration of boron atom) The present invention When the n-type semiconductor diamond is doped with nitrogen atoms and boron atoms, the concentration of the doped nitrogen atoms (CN) and the concentration of boron atoms (CB) are the characteristics and conductivity of the n-type semiconductor. From a balance point, 100CB ≧ CN> CB
It is preferable to have a relationship of 10 CB ≧
It is preferable to have a relationship of CN> CB. In this case, from the viewpoint of conductivity, the concentration of nitrogen atoms is 10 ¹⁷ cm ^-3.
The above is preferable.

The concentration of the boron atom is, for example, S
It can be measured by IMS, and the measurement conditions (B analysis) shown above can be used in this SIMS measurement.

(Carrier Concentration) In the semiconductor diamond of the present invention, the carrier concentration is 1 × from the viewpoint of conductivity.
It is preferably 10 ¹⁶ cm ⁻³ or more.

The carrier concentration can be obtained, for example, based on the measurement of the Hall coefficient (eg, Shoji Aoki and Yasuo Minamihitsu, "Physics of Semiconductors", p. 46, 196).
9 years, see industry books).

In measuring the Hall coefficient, for example, the following measurement conditions can be preferably used.

Applied magnetic field: 5000 gauss Sample current: 0.01 to 1 mA (In this range, the value of current has almost no effect on the carrier concentration measurement result.) (Crystallinity) Crystallinity of the semiconductor diamond of the present invention Is X
It can be evaluated by the double-crystal method of line diffraction. More specifically, in the semiconductor diamond of the present invention, the full width at half maximum of the rocking curve in the two-crystal method of X-ray diffraction is 40 seconds or less (further 20 seconds or less, particularly 10 seconds or less).
Is preferred.

Here, the “two-crystal method of X-ray diffraction” means 1
Another crystal C ₁ (the first crystal that functions as a monochromator and a collimator) is placed in front of the second crystal C ₂ which is a sample in the crystallization method to improve the parallelism and monochromaticity of X-ray diffraction. Say the method. In the present invention,
The arrangement is such that the deflection of the path of the X-ray beam due to the reflection of C ₁ and C ₂ is in the opposite direction (− arrangement), and the order of reflection by C ₁ (m) and the order of reflection by C ₂ (n). Are used (−parallel arrangement). This "-parallel arrangement"
Has extremely high resolution with respect to angle. On the other hand, the "rocking curve" refers to the intensity distribution curve of the diffraction line when a monochromatic X-ray is applied to the crystal and the crystal is rotated in the vicinity of the orientation that satisfies the Bragg condition.

The half-value width ([Delta] W _D) of the rocking curve measured by the double crystal method described above is approximately given by the following equation.

[0040] (- case of the ^{_{arrangement) (ΔW D) 2 = (}} Δ
W ₁ ) ² + (ΔW ₂ ) ² + δ ² where ΔW ₁ and ΔW ₂ are the Darwin plateux widths of the first and second crystals, respectively, and δ = (Δλ / λ) (tan θ _B1 −tan θ _B2 ). In the above equation, θ _B1 and θ _B2 are Bragg angles in the respective crystals, λ is the wavelength of X-rays,
Δλ is the full width at half maximum of the characteristic X-ray (for example, 5.8 × 10 ⁻⁴ angstrom for CuKα ₁ ray). In addition,
For details of the above-mentioned “two-crystal method of X-ray diffraction”, see the literature (Nishibayashi et al., 53rd Autumn Meeting, 408, 19).
1992; "Evaluation of single crystal diamond by two-crystal method").

In measuring the rocking curve,
For example, the following measurement conditions can be preferably used.

X-Ray Tube, 35 kV, 10 mA Diamond (004) Parallel Arrangement The present invention will be described in more detail based on the following examples.

[0043]

Example 1 A non-doped diamond layer was formed on a (100) plane of an artificial single crystal diamond substrate (Ib type) synthesized by a high-pressure high-temperature synthesis method and on a Si substrate by a microwave plasma CVD method, respectively. A sample was prepared in which a nitrogen-doped diamond layer was further formed on the non-doped layer. Each film was typically formed under the following conditions.

(Non-doped layer) H ₂ flow rate: 100 SCCM CH ₄ flow rate: 0.5 to 6 SCCM pressure: 40 Torr power: 300 W Substrate temperature: about 800 ° C. Film thickness: about 2 μm (nitrogen-doped layer) H ₂ flow rate: 100 SCCM CH ₄ Flow rate: 0.5 to 6 SCCM NH ₃ Flow rate: 5 SCCM Pressure: 40 Torr Power: 300 W Substrate temperature: about 800 ° C. Film thickness: about 1 μm On the other hand, as a sample for comparison, a non-doped diamond layer (film that does not form a nitrogen-doped film) A sample having only a thickness of 2 μm was also formed. The conductivity of the film of the comparative sample thus formed could not be specified because the resistivity was extremely high. The resistivity was 10 ¹⁰ Ω · cm or more.

When the Hall effect of the film (nitrogen-doped layer) of the nitrogen-doped sample formed as described above was measured,
The conductivity type was found to be n-type. The amount of nitrogen atoms contained in the nitrogen-doped layer is measured by SIMS,
And the resistivity was measured by the 4-terminal method. The measurement results are summarized in Table 1 below (when a film is formed on the diamond substrate).

[0046]

[Table 1]

As shown in Table 1, when the nitrogen atom concentration in the film was 1 × 10 ¹⁹ cm ^-3 or more, a low resistance n-type semiconductor diamond could be formed.

Furthermore, when the temperature dependence of the carrier concentration of the nitrogen-doped film was examined, the results shown in FIG. 1 (when formed on a diamond substrate) were obtained. As shown in FIG. 1, it was found that when the nitrogen atom concentration (N) is a certain value or more, the carrier concentration is hardly affected by temperature. From the results of the above measurement, if the carrier concentration is 1 × 10 ¹⁶ cm ⁻³ or more, 1 × 10 ⁵ Ω ·
It was also found that a resistivity of cm or less can be obtained.

Other than changing the film forming conditions for the nitrogen-doped film,
A nitrogen-doped film was formed in the same manner as above. The obtained results are shown in Table 2 below (when a film is formed on a diamond substrate).
Shown in.

[0050]

[Table 2]

When the nitrogen-doped film was formed on the Si substrate, the same tendency as the results shown in Tables 1 and 2 and FIG. 1 (when the film was formed on the single crystal diamond substrate) was observed. . As compared with the case where the nitrogen-doped film was formed on the Si substrate, the case where the nitrogen-doped film was formed on the single crystal diamond substrate had a lower resistivity and a good nitrogen-doped film was obtained.

Example 2 (100) of artificial single crystal diamond substrate (Ib type)
A sample was prepared in which a non-doped diamond layer was formed on each of the surface and the Si substrate by a microwave plasma CVD method, and a diamond layer simultaneously doped with nitrogen and boron was formed on the non-doped layer. Each film was typically formed under the following conditions.

(Non-doped layer) H ₂ flow rate: 100 SCCM CH ₄ flow rate: 0.5 to 6 SCCM pressure: 40 Torr power: 300 W Substrate temperature: about 850 ° C. Film thickness: about 2 μm (nitrogen and boron doped layer) H ₂ flow rate: 100 SCCM CH ₄ Flow rate: 0.5 to ₆ SCCM B ₂ H ₆ (hydrogen dilution 100 ppm) Flow rate: 1 SCCM NH ₃ Flow rate: 0.5 SCCM Pressure: 40 Torr Power: 300 W Substrate temperature: about 850 ° C. Film thickness: about 1 μm On the other hand, a sample for comparison As a non-doped diamond layer (film thickness: 2
A sample of only μm) was also formed. The resistivity of the film of the comparative sample thus formed is 10 ¹⁰ Ω as in Example 1.
・ It was more than cm.

When the Hall effect of the film (nitrogen / boron doped layer) of the nitrogen and boron doped sample formed as described above was measured, it was found that its conduction type was n type. The amounts of nitrogen atoms and boron atoms contained in the nitrogen / boron doped layer are measured by SIMS, and
The resistivity was measured by the 4-terminal method. The measurement results (the amount of nitrogen atoms in the film, the amount of boron atoms, and the resistivity) are collectively shown in Table 3 below (when the film is formed on the diamond substrate).

[0055]

[Table 3]

As shown in Table 3, the concentration of nitrogen atoms (C
N) and the boron atom concentration (CB) are 100 CB ≧ C
In the range satisfying N> CB, low resistance n-type semiconductor diamond could be formed.

Further, when the temperature dependence of the carrier concentration of the nitrogen / boron doped film was examined, the results shown in FIG. 2 (when formed on a diamond substrate) were obtained. As shown in FIG. 21, the activation energy was much smaller than that of the film containing no boron, and it was found that low resistance was achieved even at room temperature.

A nitrogen / boron-doped film was formed in the same manner as above except that the conditions for forming the nitrogen / boron-doped film were changed. The obtained results are shown in Table 4 below (when a film is formed on the diamond substrate).

[0059]

[Table 4]

When the nitrogen / boron doped film is formed on the Si substrate, the same results as those shown in Tables 3 and 4 and FIG. 2 (when formed on the single crystal diamond substrate) are obtained. It was The resistivity was lower when the nitrogen / boron-doped film was formed on the single crystal diamond substrate than when the nitrogen / boron-doped film was formed on the Si substrate.

Example 3 A nitrogen-doped film and a nitrogen-boron-doped film were formed in the same manner as in Examples 1 and 2 except that the (100) plane of natural IIa and Ia diamond was used as the substrate. Results similar to those of Examples 1 and 2 were obtained.

[0062]

As described above, according to the present invention, it is possible to obtain semiconductor diamond in which diamond is doped with nitrogen atoms at 1 × 10 ¹⁹ cm ⁻³ or more.

In the semiconductor diamond of the present invention,
In the temperature range of room temperature to 600 ° C., the carrier concentration has almost no temperature dependence, and it is possible to form the carrier by controlling the carrier density in diamond. The n-type semiconductor diamond having low resistance even at room temperature obtained by the present invention is
It can be applied to various devices, for example, to a semiconductor device that exhibits stable diode characteristics, transistor characteristics, etc. in the temperature range from room temperature to high temperature or under irradiation of radiation and / or operation at high output. It is possible.

[Brief description of drawings]

FIG. 1 is a graph showing the temperature dependence of carrier concentration in a nitrogen-doped diamond film obtained in Example 1.

2 is a graph showing the temperature dependence of carrier concentration in the nitrogen-boron-doped diamond film obtained in Example 2. FIG.

Claims (8)

[Claims] 1. Nitrogen atoms in the diamond are 1 × 10 ¹⁹
Semiconductor diamond doped with cm ^-3 or more. 2. A diamond is doped with nitrogen atoms and boron atoms, and a nitrogen atom concentration (CN) and a boron atom concentration (CB) are 100 CB.
An n-type semiconductor diamond having a range of ≧ CN> CB. 3. A method of forming a diamond by a vapor phase synthesis method, wherein a reaction gas to which a gas containing a nitrogen atom is added is used to add 1 × 10 ¹⁹ cm ⁻³ nitrogen atom in the diamond.
A method for forming a semiconductor diamond, which comprises the above doping. 4. A method for forming diamond by a vapor phase synthesis method, wherein a reaction gas obtained by adding a gas containing a nitrogen atom and a gas containing a boron atom is used to add 100 CB ≧ nitrogen atoms and boron atoms in the diamond. A method for forming an n-type semiconductor diamond, which comprises doping in a range of CN> CB (CN: nitrogen atom content concentration, CB: boron atom content concentration). 5. Nitrogen atoms in the diamond are 1 × 10 ¹⁹
A semiconductor diamond, which is doped with cm ⁻³ or more and has a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ or more. 6. The diamond is doped with nitrogen atoms and boron atoms, and the nitrogen atom concentration (CN) and the boron atom concentration (CB) are 100 CB ≧ CN> CB.
And the carrier concentration is 1 × 10 ¹⁶ cm ⁻³
The above is an n-type semiconductor diamond characterized by the above. 7. Nitrogen atoms in the diamond are 1 × 10 ¹⁹
cm ⁻³ or more, and X-ray diffraction of 2
A semiconductor diamond having a rocking curve full width at half maximum of 40 seconds or less in the crystallization method. 8. The concentration of nitrogen atoms (CN), wherein the diamond is doped with nitrogen atoms and boron atoms.
And the boron atom concentration (CB) are 100CB ≧ CN> C
An n-type semiconductor diamond in the range of B and having a full width at half maximum of a rocking curve in the two-crystal method of X-ray diffraction of 40 seconds or less.