JPH08264468A - Impurity doping method to silicon carbide and electrode formation method - Google Patents

Abstract

PURPOSE: To dope an impurity element into SiC at low temperature and hence form an electrode on the SiC by irradiating silicon carbide placed in a gas atmosphere containing the impurity element with a laser beam. CONSTITUTION: An (n) or (p) type SiC substrate 1 is placed in the atmosphere of gas 2 containing a (p) or (n) type impurity element, and the surface of the SiC substrate 1 is irradiated with excimer laser in a pulsed manner at room temperature. As a reuslt, the impurity element in the reaction gas 2 is doped into the SiC substrate 1, and an impurity doped layer 4 is formed from the surface of the SiC substrate 1 up to a predetermined depth. When aluminum is doped as the p-type impurity, trimethyl aluminum is used as the reaction gas 2, while when boron is doped as the p-type impurity gas, diborane is used as the reaction gas 2. Further, when nitrogen is doped as the n-type impurity, H2 is used as the reaction gas 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for doping impurities into silicon carbide and a method for forming an electrode.

[0002]

2. Description of the Related Art SiC (silicon carbide) is easy to control p-type and n-type valence electrons, and SiC (silicon) or GaA
Since it has many excellent physical properties not found in s (gallium arsenide), it has been attracting attention as a material for semiconductor devices that can be used in various environments.

Since SiC has a larger bandgap than Si and GaAs, p-type or n-type can be maintained up to a high temperature. Therefore, with SiC, high temperature operating devices are realized. Also, since the saturation drift velocity of electrons is high, high frequency operation is possible and a large current can be passed. Therefore, a high frequency device and a high power device can be realized. Furthermore, since it has a high dielectric breakdown electric field, a high breakdown voltage device can be realized.

Since SiC has excellent heat resistance and radiation resistance, it is expected as a material for an environment resistant device which can be used in a harsh environment such as a nuclear reactor, space, ocean, and deep underground. Furthermore, since p-type and n-type SiC can be easily produced by doping impurities, a visible short-wavelength light emitting device that emits blue or violet light,
It is most promising as a material for sensors that detect short-wavelength light such as ultraviolet rays.

Generally, a thermal diffusion process is used for doping a semiconductor with a p-type or n-type impurity element. However, since the diffusion coefficient of the impurity element in SiC is small, a high temperature of 1800 ° C. or higher is required to dope the impurity element into SiC. At such a high temperature, there is a problem that the diffusion mask cannot be used. Therefore, it is difficult to dope a p-type or n-type impurity element into SiC using a thermal diffusion process.

Therefore, an ion implantation / annealing method has been studied in order to dope p-type or n-type impurity elements into SiC. In the ion implantation / annealing method, the impurity element is ion-implanted into SiC at room temperature and then 1600 ° C.
By performing the above high heat treatment, the impurity element is doped into SiC.

On the other hand, since SiC has a wide band gap and chemical stability, a relatively high temperature heat treatment is required to form an ohmic contact. S
When forming an ohmic electrode on iC, an electrode material such as Ni (nickel) is deposited on SiC, and the temperature is set to 1000 ° C.
By performing the above high heat treatment, silicide is formed.

[0008]

As described above, when the p-type or n-type impurity element is doped into SiC by using the ion implantation / annealing method, after the impurity element is ion-implanted into SiC at room temperature. It is necessary to perform high heat treatment at 1600 ° C. or higher. Further, there is a defect that many defects are generated in the layer by the ion implantation.

On the other hand, when the ohmic electrode is formed on SiC by the conventional method, it is necessary to deposit the electrode material on the SiC and then perform high heat treatment at 1000 ° C. or higher as described above.

Conventionally, it has been desired to develop a method for doping SiC with an impurity element at a low temperature and a method for forming an electrode on SiC at a low temperature. Therefore, it is an object of the present invention to provide a method for doping SiC with an impurity element at low temperature and a method for forming an electrode on SiC at low temperature.

[0011]

According to a first aspect of the present invention, there is provided a method of doping impurities into silicon carbide, which comprises arranging silicon carbide in a gas atmosphere containing an impurity element and irradiating the silicon carbide with laser light. Is doped with an impurity element.

In particular, it is preferable to use excimer laser light as the laser light from the viewpoint of high output and wavelength. Further, it is preferable to irradiate the laser light in pulses. The silicon carbide may be single crystal silicon carbide, amorphous silicon carbide, polycrystalline silicon carbide or microcrystalline silicon carbide. The impurity doping depth can be controlled by controlling the number of laser light irradiations or the energy density.

In the method for doping impurities into silicon carbide according to the second aspect of the invention, an impurity element layer containing an impurity element is formed on silicon carbide, and the impurity element layer is irradiated with a laser beam to expose the silicon carbide to the impurity element. Doping.

Particularly, it is preferable to use excimer laser light as the laser light from the viewpoint of high output and wavelength. Further, it is preferable to irradiate the laser light in pulses. The silicon carbide may be single crystal silicon carbide, amorphous silicon carbide, polycrystalline silicon carbide or microcrystalline silicon carbide. The impurity doping depth can be controlled by controlling the number of laser light irradiations or the energy density.

According to a third aspect of the present invention, there is provided an electrode forming method on silicon carbide, which comprises forming an electrode material layer on silicon carbide and irradiating the electrode material layer with a laser beam to form an ohmic electrode of metal or silicide on the silicon carbide. Alternatively, a Schottky electrode is formed.

In particular, it is preferable to use excimer laser light as the laser light from the viewpoint of high output and wavelength. Further, it is preferable to irradiate the laser light in pulses. The silicon carbide may be single crystal silicon carbide, amorphous silicon carbide, polycrystalline silicon carbide or microcrystalline silicon carbide.

[0017]

According to the method for doping impurities into silicon carbide according to the first aspect of the present invention, photoreaction occurs by irradiating silicon carbide in a gas atmosphere containing an impurity element with a laser beam, and a photoreaction occurs at room temperature in a gas atmosphere. Impurity elements are doped into silicon carbide. Particularly, by using the excimer laser light, high output light energy can be easily extracted. In addition, the photoreaction can be effectively caused by irradiating the laser light in a pulse shape.

According to the impurity doping method for silicon carbide according to the second aspect of the present invention, a photoreaction occurs by irradiating the impurity element layer on silicon carbide with laser light, so that the impurity element in the impurity element layer is removed at room temperature. Doped in silicon carbide. Particularly, by using the excimer laser light, high output light energy can be easily extracted.
In addition, the photoreaction can be effectively caused by irradiating the laser light in a pulse shape.

According to the method for forming an electrode on silicon carbide according to the third aspect of the invention, a photoreaction occurs by irradiating the electrode material layer on silicon carbide with laser light, so that the electrode material of the electrode material layer is formed at room temperature. Sintering to the surface layer of silicon carbide (the electrode material goes into the silicon carbide without alloying) or the electrode material reacts with the silicon of the silicon carbide to form a silicide. Particularly, by using the excimer laser light, high output light energy can be easily extracted. In addition, the photoreaction can be effectively caused by irradiating the laser light in a pulse shape.

[0020]

【Example】

(1) First Embodiment FIG. 1 is a diagram showing an impurity doping method according to a first embodiment of the present invention. As shown in (a) of FIG. 1, n is added in the atmosphere of the reaction gas 2 containing a p-type or n-type impurity element.
The p-type or p-type SiC substrate 1 is arranged, and the surface of the SiC substrate 1 is irradiated with the excimer laser light 3 in a pulse shape at room temperature.

As a result, as shown in FIG. 1B, the impurity element in the reaction gas 2 is doped into the SiC substrate 1,
Impurity doped layer 4 is formed from the surface of SiC substrate 1 to a predetermined depth.

As the SiC substrate 1, 6H-SiC, 3
Various polytype single crystal SiC substrates such as C-SiC can be used. Note that a substrate having an amorphous SiC layer, a polycrystalline SiC layer, or a microcrystalline SiC layer formed on its surface may be used.

When Al (aluminum) is doped as the p-type impurity, (CH ₃ ) is used as the reaction gas 2.
_{When 3} Al (trimethylaluminum) is used and B (boron) is doped as the p-type impurity, B ₂ H ₆ (diborane) is used as the reaction gas 2. Further, when N (nitrogen) is doped as the n-type impurity, N ₂ is used as the reaction gas 2, and when P (phosphorus) is doped as the n-type impurity, the reaction gas 2 is PH.
_{Use 3} (phosphine).

FIG. 2 is a schematic view of an experimental apparatus used for preparing a sample in this example. A quartz glass window 11 is provided at a predetermined position in the reaction chamber 10, and the quartz glass window 11 in the reaction chamber 10 is provided.
The SiC substrate 1 is installed behind the substrate using a substrate holder (not shown). The reaction gas 2 is introduced into the reaction chamber 10 through the gas introduction port 12. Reaction gas 2 in the reaction chamber 10
Is kept at a predetermined pressure by the turbo molecular pump 13.
Excimer laser light 3 emitted from the excimer laser 14
Through the quartz glass window 11 by the lens 15 and the reaction chamber 1
The light is focused on the surface of the SiC substrate 1 within 0.

Table 1 shows the sample preparation conditions in this example.

[0026]

[Table 1]

As shown in Table 1, as the SiC substrate 1,
Type 6H-SiC single crystal (N-doped: 1 × 10 ¹⁸ c
m ⁻³ , (0001) basal plane) was used, and a mixed gas of H ₂ and (CH ₃ ) ₃ Al was used as the reaction gas 2. H ₂
And (CH ₃ ) ₃ Al in a volume ratio of 99.8: 0.2,
The pressure inside the reaction chamber 10 was maintained at 100 Torr. A KrF excimer laser having a wavelength of 248 nm is used as the excimer laser 14, and the excimer laser light 3 is supplied to the SiC substrate 1 by about 2 times.
The light was collected in an area of × 4 mm ² . The energy density of laser irradiation on the SiC substrate 1 was 1.5 J / cm ² .
The irradiation of the excimer laser light 3 was performed 1000 times (shots) at 1 Hz. The irradiation time of each pulse is 20 ns,
The pulse half width was set to 10 ns. The SiC substrate 1 was kept at room temperature during the irradiation of the excimer laser light 3.

SiC doped with Al in this way
A SiC diode sample was prepared using the substrate 1. FIG.
3A is a plan view of the Al-doped SiC substrate 1, and FIG. 3B is a sectional view schematically showing the structure of the SiC diode sample.

As shown in FIG. 3A, the SiC substrate 1
Al-doped region 4a of 1 × 1.
It was cut into a planar diode with dimensions of 5 mm ² and a thickness of 0.3 mm. Then, as shown in FIG. 3B, an n-type contact portion 22 is formed by welding a thin nickel wire 21 to the back surface of the SiC substrate 1 using an electric spot welding process, and Al-doped impurities are formed. Applying a silver paint to the surface of the dope layer 4 and thin nickel wire 2
By connecting 3 to each other, a p-type contact portion 24 was formed.

The current-voltage characteristics of the SiC diode sample thus manufactured were measured. FIG. 4 shows Si of FIG.
It is a figure which shows the current-voltage characteristic at room temperature of a C diode sample.

The current-voltage characteristic of FIG. 4 shows the rectification characteristic of a diode having a relatively low leakage current. The leakage current was 5 μA with a reverse bias of 5 V and 10 μA with a reverse bias of 10 V. This result shows that at room temperature Si
It clearly shows that the Al atoms doped in the C substrate 1 are electrically activated without heat treatment. This rectifying property did not change even after annealing at 1000 ° C. for 5 minutes.

FIG. 5 is a diagram showing the measurement result of the distribution in the depth direction of the Al-doped SiC substrate 1 in this embodiment. The distribution in the depth direction is measured by SIMS (secondary ion mass spectrometry), and the Al concentration is corrected by a standard sample.

From FIG. 5, Al atoms are about 0.05 from the surface.
It can be seen that it is doped to a depth of μm and has a rectangular distribution with a maximum concentration of 1 × 10 ²² cm ⁻³ . 1 x 1
Since the concentration of 0 ²² cm ⁻³ is the detection limit of SIMS, it is presumed that Al atoms are actually doped at a concentration of 1 × 10 ²² cm ⁻³ or more.

In the impurity doping method of this embodiment, the pressure of the reaction gas 2, the number of pulses of the excimer laser light 3, the irradiation energy density of the excimer laser light 3, or the wavelength of the excimer laser light 3 is changed to change the Si
The doping amount of the impurity element in the C substrate 1 can be controlled.

As described above, according to the doping method of the above embodiment, the pn junction can be formed on the SiC substrate 1 at room temperature, and the current-voltage characteristic of the pn junction is rectified with a low leakage current. Show the characteristics. Further, since the surface of the SiC substrate 1 is doped with high concentration of Al, ohmic contact can be easily made. Therefore, various SiC devices can be easily manufactured at room temperature by using the doping method of the above embodiment.

(2) Second Embodiment FIG. 6 is a diagram showing an impurity doping method according to a second embodiment of the present invention. As shown in (a) of FIG. 6, after depositing an impurity element layer 5 containing a p-type or n-type impurity element on an n-type or p-type SiC substrate 1, SiC is formed at room temperature.
Excimer laser light 3 is formed on the surface of the impurity element layer 5 on the substrate 1.
Is pulsed.

As a result, as shown in FIG. 6B, the impurity element in the impurity element layer 5 is doped into the SiC substrate 1, and the impurity doped layer 6 is formed in the SiC substrate 1 below the impurity element layer 5. It

As the SiC substrate 1, various polytype single crystal SiC substrates such as 6H-SiC and 3C-SiC can be used as in the first embodiment. In addition, an amorphous SiC layer, a polycrystalline SiC layer, or a microcrystalline SiC layer is formed on the surface.
A substrate on which a layer is formed may be used.

For example, when Al is doped as the p-type impurity, Al is deposited as the impurity element layer 5 on the SiC substrate 1. When B is doped as the p-type impurity, B ₂ O ₃ is added as S in the impurity element layer 5.
Deposition is performed on the iC substrate 1.

In this example, similarly to the first example, a sample was prepared using the experimental apparatus shown in FIG. Table 2 shows the preparation conditions of the sample in this example.

[0041]

[Table 2]

As shown in Table 2, as the SiC substrate 1,
Type 6H-SiC single crystal (N-doped: 1 × 10 ¹⁸ c
m ^-3 , (0001) basal plane) and S in the reaction chamber 10
An impurity element layer 5 made of Al and having a film thickness of 2000 Å was formed on the surface of the iC substrate 1 by vapor deposition. Reaction chamber 10 during vapor deposition
The degree of vacuum inside was 1.5 × 10 ⁻⁶ Torr. Similar to the first embodiment, the excimer laser 14 has a wavelength of 248.
nm of KrF excimer laser, and S in reaction chamber 10
The surface of the impurity element layer 5 on the iC substrate 1 was irradiated with excimer laser light 3 at an energy density of 1 J / cm ² . Irradiation with the excimer laser beam 3 was performed four times (shot). The irradiation time of each pulse is 20 ns, and the pulse half width is 10 ns.
And During irradiation of the excimer laser light 3, the SiC substrate 1 is kept at room temperature, and the degree of vacuum in the reaction chamber 10 is 5 × 10 ⁻⁷ Tor.
kept at r. Then, SiC substrate 1 was washed with aqua regia for 1 minute and with a 10% solution of HF (hydrogen fluoride) for 1 minute to remove impurity element layer 5 on the surface.

SiC doped with Al in this way
The Al distribution in the depth direction of the substrate 1 was measured by SIMS. FIG. 7 is a diagram showing the measurement results of Al distribution in the depth direction. It can be seen from FIG. 7 that Al atoms are more highly doped as they are closer to the surface.

In the impurity doping method of this embodiment, the film thickness of the impurity element layer 3 deposited on the SiC substrate 1 and the number of times of irradiation are changed to control the energy density, so that the impurity element in the SiC substrate 1 is doped. The doping amount can be controlled.

As described above, according to the doping method of this embodiment, it is possible to form a pn junction on the SiC substrate 1 at room temperature, and the closer the surface of the SiC substrate 1 is to the higher the concentration of A.
Since l is doped, ohmic contact can be easily made. Therefore, various SiC devices can be easily manufactured at room temperature by using the doping method of the above embodiment.

(3) Third Embodiment FIG. 8 is a diagram showing an electrode forming method according to a third embodiment of the present invention. As shown in FIG. 8A, after the electrode material layer 7 is deposited on the n-type or p-type SiC substrate 1, the excimer laser light 3 is applied to the surface of the electrode material layer 7 on the SiC substrate 1 at room temperature. Is pulsed. As a result, FIG. 8 (b)
As shown in, a sinter layer or a silicide layer 8 is formed on the SiC substrate 1 below the electrode material layer 7. Ohmic characteristics can be obtained in the sinter or silicide electrode thus formed. Further, as an electrode material, Au
A Schottky electrode can be obtained by using.

As the SiC substrate 1, various polytype single crystal SiC substrates such as 6H—SiC and 3C—SiC can be used as in the first and second embodiments.
Alternatively, a substrate having an amorphous SiC layer, a polycrystalline SiC layer, or a microcrystalline SiC layer formed on its surface may be used.

For example, when forming an n-type electrode, Ni, Ti, W, T is formed on the SiC substrate 1 as the electrode material layer 7.
A single layer of a metal such as a, an alloy layer of any of these with other materials (for example, AuTa), or a laminated film of any of these with other materials is formed. When forming a p-type electrode, a single layer of a metal such as Al or an alloy layer of a metal such as Al and another material (for example, AlTi, AlSi) is formed on the SiC substrate 1 as the electrode material layer 7. Or Al
A laminated film of a metal such as the above and another material is formed. As a method of forming the electrode material layer 7, an electron beam vapor deposition method, application of a metal paste or the like is used. It is also possible to form electrode material layer 7 on SiC substrate 1 by leaving it in gas. For example, placing the SiC substrate 1 in a vacuum container,
After the inside of the vacuum container is evacuated to the order of 10 ⁻⁷ Torr, the inside of the vacuum container is maintained in a (CH ₃ ) ₃ Al atmosphere at about 500 Torr.

Also in this example, a sample was prepared using the experimental apparatus shown in FIG. FIG. 9 is a sectional view schematically showing the structure of the sample manufactured in this example. Also, Table 3
The manufacturing conditions of the sample in this example are shown in FIG.

[0050]

[Table 3]

As shown in Table 3, as in the first and second embodiments, an n-type 6H-SiC single crystal (N-doped: 1 × 10 ¹⁸ cm ^-3 , (0001) base) was used as the SiC substrate 1. Plane) and p-type 6H—SiC single crystal (P-doped: 2 ×
Two electrode material layers 7a and 7b were formed on the SiC substrate 1 by electron beam evaporation using 10 ¹⁸ cm ⁻³ ((0001) basal plane), as shown in FIG. 9A.

When forming the n-type electrode, an n-type SiC single crystal substrate is used as the SiC substrate 1, and the electrode material layer 7 is used.
Ni, Ti, W, and AuTa were used as. When forming a p-type electrode, p-type Si is used as the SiC substrate 1.
C single crystal substrate is used, and A is used as the electrode material layers 7a and 7b.
1, AlTa, and AlSi were used. Electrode material layers 7a, 7
The film thickness of b was set to 500 Å or less.

As in the first and second embodiments, a KrF excimer laser having a wavelength of 248 nm is used as the excimer laser 14, and the energy density of 2 J / cm is applied to the electrode material layers 7a and 7b on the SiC substrate 1 in the reaction chamber 10. ^The excimer laser beam 3 was irradiated at ² . Irradiation of excimer laser light 3 is 1
10 shots were taken. The irradiation time of each pulse is 2
The pulse half width was 10 ns. Reaction chamber 1
The inside of 0 was maintained in an Ar (argon) atmosphere of about 500 Torr or less or a vacuum. The SiC substrate 1 was kept at room temperature during the irradiation of the excimer laser light 3.

A voltage was applied between the electrode material layers 7a and 7b of the sample thus produced, as shown in FIG. 9B, and the current-voltage characteristics were measured by a tester. As a result, it was confirmed that ohmic contact was obtained by the silicide layers 8a and 8b formed on the SiC substrate 1 under the electrode material layers 7a and 7b, respectively.

As described above, according to the electrode forming method of the above embodiment, the silicide electrode can be formed on the SiC substrate 1 at room temperature, and ohmic contact can be easily obtained. Further, the ohmic electrode can be easily formed in a minute area or a wide area. Therefore, various Si can be obtained by using the electrode forming method of the above embodiment.
It becomes possible to easily manufacture the C device at room temperature.

[0056]

According to the first aspect of the present invention, silicon carbide can be doped with an impurity element at a low temperature. Therefore, it becomes easy to manufacture a semiconductor device that can be used in various environments.

According to the second invention, it is possible to dope impurities into silicon carbide at a low temperature. Therefore, it becomes easy to manufacture a semiconductor device that can be used in various environments. According to the third invention, it is possible to form a metal or silicide ohmic electrode or Schottky electrode on silicon carbide at a low temperature. Therefore, it becomes easy to manufacture a semiconductor device that can be used in various environments.

[Brief description of drawings]

FIG. 1 is a diagram showing an impurity doping method according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of an experimental apparatus used for producing a sample.

FIG. 3 is a plan view of an Al-doped SiC substrate and a cross-sectional view schematically showing the structure of a SiC diode sample.

4 is a current at room temperature of the SiC diode sample of FIG.
It is a figure which shows a voltage characteristic.

FIG. 5: Al-doped SiC in the first embodiment
It is a figure which shows the measurement result of the distribution of the depth direction of a board | substrate.

FIG. 6 is a diagram showing an impurity doping method according to a second embodiment of the present invention.

FIG. 7: Al-doped SiC in the second embodiment
It is a figure which shows the measurement result of Al distribution in the depth direction of a board | substrate.

FIG. 8 is a diagram showing an electrode forming method according to a third embodiment of the present invention.

FIG. 9 is a cross-sectional view schematically showing the structure of a sample manufactured in a third example.

[Explanation of symbols]

 1 SiC Substrate 2 Reaction Gas 3 Excimer Laser Light 4 Impurity Doped Layer 5 Impurity Element Layer 6 Impurity Doped Layer 7, 7a, 7b Electrode Material Layer 8, 8a, 8b Silicide Layer In addition, the same reference numerals in each drawing indicate the same or corresponding portions. Show.

[Procedure amendment]

[Submission date] September 13, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masanori Watanabe 4547-15 Tsuda, Hirakata, Osaka Prefecture, Ion Engineering Laboratory Co., Ltd. (72) Toshitake Nakata Toshitake Nakata 4547-15, Tsuda, Hirakata, Osaka Prefecture Ion Engineering Research Co., Ltd. In-house (72) Kenshiro Nakajima 10-22 Takairihara, Inaka-cho, Meito-ku, Nagoya-shi, Aichi (72) Inventor Osamu Kouryu 27 Hazama-cho, Showa-ku, Nagoya, Aichi Prefecture 1-25 House

Claims (4)

[Claims] 1. Impurity to silicon carbide, wherein silicon carbide is arranged in a gas atmosphere containing an impurity element, and the silicon carbide is doped with the impurity element by irradiating the silicon carbide with a laser beam. Doping method. 2. A silicon carbide comprising: forming an impurity element layer containing an impurity element on silicon carbide; and irradiating the impurity element layer with laser light to dope the silicon carbide with the impurity element. Impurity doping method. 3. The method for doping impurities into carbon silicon according to claim 1, wherein the impurity doping depth is controlled by controlling the number of times of laser light irradiation or the energy density. 4. An electrode material layer is formed on silicon carbide, and a metal or silicide ohmic electrode or Schottky electrode is formed on the silicon carbide by irradiating the electrode material layer with laser light. For forming an electrode on silicon carbide.