JP4822167B2 - Diamond semiconductor manufacturing method and diamond semiconductor - Google Patents

Description

  The present invention relates to a method for manufacturing a diamond semiconductor and a diamond semiconductor, and more particularly to an n-type doping method on a diamond {100} substrate.

  Attempts to artificially synthesize diamond have been made for a long time, but in the 1980s, practical synthesis under low pressure such as microwave plasma CVD method and hot filament CVD method began to succeed. . In line with this, there has been a growing movement to make semiconductor devices using diamond epitaxial films.

Diamonds
(1) High carrier mobility and high speed operation can be expected.
(2) A wide band gap (5 eV or more), which is expected to operate without being destroyed even at a temperature of 500 ° C. or more.
(3) The thermal conductivity is as large as five times that of copper, and the generated heat can be quickly released.
(4) The radiation resistance is high, and it is expected that soft errors due to α rays, which is a problem in VLSI, are reduced.
(5) Since it is a single element material, the problem of structural defects peculiar to compound semiconductors can be avoided.
It is expected to be used in high-speed devices that cannot be handled by conventional semiconductors and in severe usage environments.

However, several problems have been pointed out in practical use.
(A) Single crystallization technology,
(B) n-type doping (c) Circuit formation technology and the like are main problems to be solved in the future.

  Regarding (a), recently, heteroepitaxial growth of iridium on {100} (see Non-Patent Document 1), enlargement method using a plurality of Ib type crystals by high-pressure synthesis as seed crystals (non- Patent Document 2) has been developed. On the other hand, as for (b) n-type doping, it has been reported that it is desirable to obtain n-type diamond by using a (111) substrate with phosphorus (P) as a dopant (see Non-Patent Document 3).

  (111) and {100} are the main crystal planes of diamond, but (111) is the most difficult to polish even for diamonds with the highest hardness in the material. As for the increase in the area of the substrate, research on the assumption of {100} for both the above-described bonded substrate and heteroepitaxial growth is in progress. In addition, the current situation is that the technology in {100} is also advanced in that homo-epitaxial growth is performed on a flat surface.

  The above-mentioned doping of P is difficult because it is difficult to dope P into the film in the growth on the {100} substrate. Therefore, Namba et al. Proposed a method of forming an n-type region on a {100} substrate by forming an unevenness having a (111) plane on a {100} substrate by an etching technique (Non-patent Document 4). reference). However, this method cannot avoid an increase in cost due to increased processes such as patterning and etching.

Maeda et al .: New Diamond Forum 18th Diamond Symposium Proceedings (2004) p10 Meguro et al .: New Diamond Forum Proceedings of the 16th Diamond Symposium (2002) p8 S. Koizumi et al .: Appl. Phys. Lett. 71 (1997) 25 Namba et al .: New Diamond Forum Proceedings of the 17th Diamond Symposium (2003) p54

In view of the above prior art, a method of epitaxially growing n-type diamond on a substantial {100} substrate by an inexpensive method that does not use patterning or the like is desired.
The present invention has been made in view of such problems, and provides an inexpensive method for growing P-doped n-type diamond on a {100} substrate.

As a result of earnest research, the inventors have reached the following invention.
(1) The nitrogen atom concentration / carbon atom concentration in the gas is set to 0.001 or more and 0.00 on the diamond substrate tilted by 10 degrees or less from {100} to within <110> ± 10 degrees by plasma CVD . A method for producing a diamond semiconductor, comprising growing diamond with a film thickness of 0.1 μm or more under nitrogen addition conditions of 05 or less, and subsequently growing diamond under phosphorus addition conditions.

(2) On a diamond substrate tilted by 10 degrees or less from {100} to within <110> ± 10 degrees, a diamond having a thickness of 0.1 μm or more is grown by plasma CVD under nitrogen addition conditions. A method for producing a diamond semiconductor, comprising: forming a step bunch having a thickness of 1 nm to 10 nm and subsequently growing diamond under a phosphorus addition condition.
(3) A diamond semiconductor manufactured by the method for manufacturing a diamond semiconductor according to (1) or (2) above, wherein the n-type includes a region doped with phosphorus in a periodic layer shape having an average period of 0.5 μm or less Ri Ah diamond, periodic layers phosphorus doped are inclined with respect to the substrate principal plane, the inclination angle of the diamond semiconductor, characterized in der Rukoto to 60 degrees 1 degree.

This mechanism is considered as follows.
Under nitrogen addition conditions, a large step is formed by step bunching. (FIG. 1, the height direction is enlarged) The height and interval of this step vary depending on the orientation deviation of the substrate and the film formation conditions. In general, the large step slope cannot be represented by a low index surface, but has a large uneven surface (bottom of FIG. 1). However, since the growth mode is different from {100} in this growth, P is in the film. It is captured. As a result, as shown in FIG. 2 (again, the height direction is enlarged), the cross-section becomes a stripe-like shape, resulting in an n-type diamond including a parallel layered P-doped region. An epitaxial film can be obtained. Such a striped region is formed by the competition between the growth on the step slope and the growth on the terrace, but when the inclination with respect to the main surface of the substrate is increased, the vertical distance between the layers is increased and the conduction between the layers is deteriorated. Therefore, it is desirable that it is 60 degrees or less.

  The off orientation is preferably the <110> orientation. This is because when the <110> orientation is off, large steps formed on the diamond surface are likely to be parallel (FIG. 3A), and homogeneity can be expected. On the other hand, for example, when the <100> orientation is off, the step becomes wavy as shown in FIG. 3B, and the surface is a mixture of steps in various directions. And homogeneity is impaired.

  The width of the layered region, the interval, and the inclination with the substrate vary depending on the height and interval of the step bunches at the time of forming the P-doped film, and further depending on the conditions of P-doped growth. If the period of the region becomes too large, the doped region of P becomes local, and the conductivity as a film cannot be expected. Such a P-doped region preferably has an average period of 0.5 μm or less. Therefore, it is necessary to start the growth of the P-doped film at a stage where the macro step due to the step bunch does not become too large.

  According to the present invention, an n-type diamond epitaxial film doped with P can be grown on a {100} substrate, and a diamond semiconductor can be easily provided.

An example in which the present invention is used for doping an actual diamond semiconductor will be described below.
Example 1
As the substrate, a 3 mm × 3 mm substrate tilted by 3 ± 1 degree in the <110> direction (within ± 2 degrees) from {100} was used. In addition, a diamond epitaxial film was first grown under nitrogen addition conditions by a so-called inorganic material type microwave plasma CVD method by Kamo et al. The introduced gases are CH ₄ , H ₂ , and N ₂ (diluted 1% in H ₂ ), 2.5 sccm, 500 sccm, and 2.5 sccm, respectively, and the gas pressure during film formation is 60 Torr. The substrate temperature was 870 ° C., and the film was formed for 10 minutes. The film thickness was estimated to be 0.15 μm.

After film formation under nitrogen addition conditions, the surface was observed with a scanning tunneling microscope, and it was observed that steps having a height of 1 to 2 nm were formed in parallel at intervals of approximately 30 nm to 50 nm. In the flat region sandwiched between large steps, a single atom step, a step that appears to be a two atom step, and an island of a monoatomic layer were also observed.
Thereafter, P-dope was grown using the same microwave plasma CVD apparatus. Introducing gas CH ₄ (10% diluted in _{H 2),} and in H _2, PH ₃ (1% dilution in _{H 2),} respectively 5 sccm, 500 sccm, 1 sccm, the gas pressure during film formation and 100 Torr, the film thickness A film thickness of about 2.5 μm was formed.
Ti / Pt / Au electrodes were formed at the four corners of the sample, and AC magnetic field hole measurement was performed by the van der Pauw method. The resistivity was 6 × 10 ³ Ωcm at room temperature and 4 × 10 ² Ωcm at 100 ° C. as values assuming a homogeneous film. In the latter measurement, n-type determination was obtained.

Example 2
As the substrate, a 3 mm × 3 mm substrate tilted by 5 ± 1 degree in the <110> direction (within ± 2 degrees) from {100} was used. In addition, a diamond epitaxial film was first grown under nitrogen addition conditions by a so-called inorganic material type microwave plasma CVD method by Kamo et al. The introduced gases are CH ₄ , H ₂ , and N ₂ (diluted 1% in H ₂ ), 1 sccm, 500 sccm, 1 sccm, respectively, and the gas pressure during film formation is 60 Torr. The substrate temperature was 870 ° C., and the film was formed for 10 minutes. The film thickness formed was estimated to be 0.1 μm.
After film formation under nitrogen addition conditions, the surface was observed with an atomic force microscope, and it was observed that steps having a height of 1 to 2 nm were formed in parallel at intervals of approximately 20 nm to 30 nm.

Thereafter, P-dope was grown using the same microwave plasma CVD apparatus. Introducing gas CH ₄ (10% diluted in H _2), with H _2, PH ₃ (1% dilution in H _2), respectively 5 sccm, 500 sccm, 10 sccm, gas pressure during film formation was set to 100 Torr, the film thickness A film thickness of about 4 μm was formed.
Using a microprober, the resistivity was measured by a four-probe method, and the resistivity was estimated as a homogeneous film.
When the four probes were arranged in the off direction (perpendicular to the step), they were 3 × 10 ² Ωcm at room temperature and 2 × 10 ² Ωcm at 100 ° C. On the other hand, when arranged in the off-vertical direction (parallel to the step), it was 2 × 10 ² Ωcm at room temperature and 1 × 10 ² Ωcm at 100 ° C.

Example 3
As the substrate, a 4 mm × 4 mm substrate inclined by 2 ± 1 degree in the <100> direction (within ± 3 degrees) from {100} was used. First, a diamond epitaxial film was grown under the condition of nitrogen addition by an inorganic material type microwave plasma CVD method. The introduced gases are CH ₄ , H ₂ , and N ₂ (1% dilution in H ₂ ), 2.5 sccm, 500 sccm, and 1 sccm, respectively, and the gas pressure during film formation is 60 Torr. The substrate temperature was 870 ° C. and the film was formed for 20 minutes. The film thickness was estimated to be 0.2 μm.

  After film formation under nitrogen addition conditions, the surface was observed with a scanning tunneling microscope, and it was observed that bent steps having a height of 1 to 2 nm were formed at intervals of approximately 30 nm to 50 nm. We were able to observe the splitting and merging of steps. In the flat region sandwiched between large steps, a single atom step or a step that appears to be a two atom step, and an island of a monoatomic layer or a two atomic layer were also observed.

Thereafter, P-dope was grown using the same microwave plasma CVD apparatus. Introducing gas CH ₄ (10% diluted in H _2), and in H _2, PH ₃ (1% dilution in H _2), respectively 5 sccm, 500 sccm, 1 sccm, the gas pressure during film formation and 100 Torr, the film thickness A film thickness of about 3 μm was formed.
Ti / Pt / Au electrodes were formed at the four corners of the sample, and AC magnetic field hole measurement was performed by the van der Pauw method. The resistivity was 1.5 × 10 ⁴ Ωcm at room temperature and 7 × 10 ² Ωcm at 100 ° C. as values assuming a homogeneous film. In the latter measurement, n-type determination was obtained.

Comparative Example 1
A film was formed on a substrate having an inclination from {100} within 0.3 degrees under the same conditions as the P-doping conditions of Example 1. However, pre-deposition with nitrogen addition condition not performed, by using a microwave plasma CVD apparatus, introducing gas (diluted 10% in _{H 2) CH 4, H 2} , PH 3 ( in H ₂ 1 % Dilution) at 5 sccm, 500 sccm, 1 sccm, the gas pressure during film formation was 100 Torr, and a film thickness of about 5 μm was formed.
Ti / Pt / Au electrodes were formed at the four corners of the sample, and AC magnetic field Hall measurement was performed by the van der Pauw method. However, the resistivity was high and could not be measured.

Comparative Example 2
As the substrate, a substrate tilted by 4 ± 1 degrees in the <100> direction (within ± 3 degrees) from {100} was used. To this, a diamond epitaxial film was first grown under the condition of nitrogen addition by the inorganic material type microwave plasma CVD method. The introduced gases are CH ₄ , H ₂ , and N ₂ (diluted 1% in H ₂ ), 2.5 sccm, 500 sccm, and 2.5 sccm, respectively, and the gas pressure during film formation is 60 Torr. The substrate temperature was 870 ° C., and film formation was performed for 4 hours. The film thickness was estimated to be 5 μm.

After film formation under nitrogen addition conditions, the surface was observed with a scanning electron microscope. Steps with an interval of approximately 0.5 to 1 μm were observed, and the height was approximately 10 to 30 nm. Numerous steps were also observed.
Thereafter, P-dope was grown using the same microwave plasma CVD apparatus. Introducing gas CH ₄ (10% diluted in H _2), and in H _2, PH ₃ (1% dilution in H _2), respectively 5 sccm, 500 sccm, 1 sccm, the gas pressure during film formation and 100 Torr, the film thickness A film thickness of about 5 μm was formed. Ti / Pt / Au electrodes were formed at the four corners of the sample, but the resistivity was high and could not be measured.
When two-terminal measurement was performed with a micro prober, it was found that the region showing conductivity and the region showing insulation were finely distributed.

  As mentioned above, although each Example of this invention was demonstrated by the microwave plasma CVD method, this invention is not limited to these, The film-forming method can be changed suitably in the range which does not deviate from the main point of this invention. . For example, ECR plasma, helicon wave plasma, ICP (Inductive Coupled Plasma), TCP (Transformer Coupled Plasma), DC plasma, or the like may be used. However, a hot filament, which is a typical diamond synthesis method as well as a plasma CVD method, is not suitable because the film quality deteriorates when synthesized under nitrogen addition conditions.

Schematic diagram of the macrostep surface after nitrogen addition growth (cross section) Distribution diagram of P-doped diamond grown on macrostep surface (shaded area is P-doped region) Macro step surface schematic diagram after nitrogen addition growth (top view) off orientation (arrow) (a) <110> (b) <100>

Claims (3)

The nitrogen atom concentration / carbon atom concentration in the gas is set to 0.001 or more and 0.05 or less by a plasma CVD method on a diamond substrate inclined by 10 degrees or less from {100} to within <110> ± 10 degrees. A method for producing a diamond semiconductor, comprising: growing a diamond having a thickness of 0.1 μm or more under the added nitrogen condition, and subsequently growing the diamond under the added phosphorus condition. A diamond substrate having a thickness of 0.1 μm or more is grown on a diamond substrate tilted by 10 degrees or less from {100} to within <110> ± 10 degrees by a plasma CVD method under nitrogen addition conditions, and a height of 1 nm or more. A method for producing a diamond semiconductor, comprising performing diamond growth under a phosphorus addition condition after forming a step bunch of 10 nm or less. A diamond semiconductor produced by the process of the diamond semiconductor manufacturing according to claim 1 or 2, Ri Ah with n-type diamond containing phosphorus below periodic layered average period 0.5μm doped region, phosphorus There doped periodic layers are inclined with respect to the substrate principal plane, the inclination angle of the diamond semiconductor, characterized in der Rukoto to 60 degrees 1 degree.

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