JP5648442B2 - Silicon carbide semiconductor - Google Patents

Description

The present invention relates to a silicon carbide semiconductor, the doping concentration of nitrogen about the uniform silicon carbide semiconductor with particularly wide substrate surface.

A semiconductor device (element) using silicon carbide (in the embodiment, the substrate on which silicon carbide is grown is also silicon carbide. For this reason, SiC is mainly used in the description of the crystal that is mainly epitaxially grown) Due to its excellent characteristics such as wide forbidden band width, high dielectric breakdown electric field, high saturation electron velocity, and high thermal conductivity, it is expected as a device capable of high breakdown voltage, low loss and high temperature operation. In recent years, the supply system of SiC single crystal substrates is being prepared (Non-Patent Document 1). Furthermore, in the SiC thin film crystal growth technology necessary for device fabrication, technologies for growing high-quality single crystals with low crystal defect density, specifically technologies such as appropriate temperature conditions and source gas supply ratios, are established. (Patent Document 1, Non-Patent Document 2).
Under such circumstances, there is a demand for the development of a technique capable of obtaining a uniform concentration distribution with high accuracy when doping an impurity such as nitrogen into a SiC crystal formed on a wide substrate (Patent Document). 2).

  Examples of impurity doping include a diffusion method, an ion implantation method, and a method using epitaxial growth. However, in the case of SiC, the diffusion method is not appropriate because the diffusion coefficient of impurity atoms in the crystal is small. Also, the ion implantation method is not suitable because it is difficult to recover crystal defects caused by ion implantation, and the surface of the crystal is roughened by thermal annealing for the purpose of activating impurities (non-patent) Reference 3).

  For this reason, in SiC, a method using epitaxial growth is used. In this method, for example, silane and propane introduced with hydrogen as a carrier gas by a CVD method (chemical vapor deposition method) are reacted at 1300 ° C. or more, usually about 1500 ° C. to 1600 ° C. to form SiC on a silicon carbide substrate. In this method, a substance containing an impurity atom that becomes a donor or an acceptor is added to a source gas while epitaxially growing the substrate, and impurity atoms are doped into the epitaxially grown SiC crystal.

Japanese Patent Laid-Open No. 11-162850 Japanese Patent Laid-Open No. 8-139048

H. McD. Hobgood, et al. , Mater. Sci. Forum, vols. 457-460 (2004) p. 3. T. T. et al. Kimoto, et al. , Mater. Sci. Forum, vols. 389-393 (2002) p. 165. M.M. A. Capano, J.A. Electron. Mater. , Vol. 28 (1999) p. 214

Nitrogen gas (N ₂ ) is usually used as a nitrogen source for doping nitrogen by using epitaxial growth in CVD, which is easy to use without flammability, combustion support and toxicity. However, since nitrogen gas has a large triple bond energy, it is difficult to control the thermal decomposition reaction process by thermal decomposition. For this reason, when supplying nitrogen as an active species contributing to doping, partial pressure is applied to the substrate surface. It is difficult to control so that it is uniformly distributed.

Furthermore, as a structural feature of the furnace in the CVD method, when a so-called cold wall type growth furnace in which only the substrate is heated is used, since the gas begins to decompose only when it comes directly above the substrate, nitrogen gas as well as Even when a gas containing a nitrogen compound is used, it is difficult to obtain a uniform doping concentration of nitrogen on the substrate surface.
In the case of a cold wall type growth furnace, it is difficult to make the substrate temperature uniform over the entire substrate surface, and from this point, it is difficult to obtain a uniform nitrogen doping concentration on the substrate surface.

For this reason, it has been desired to develop a technique capable of obtaining high uniformity of in-plane distribution of doping concentration when doping SiC atoms with SiC atoms epitaxially grown on a wide substrate by CVD.
In particular, development of a technique for doping nitrogen by an epitaxial growth method has been desired.

The present invention, Ru der been made in order to solve the above problems. The first to eighth techniques related to the present invention will be described below.
The invention of each claim will be described below.

The first technique related to the present invention is:
A silicon carbide semiconductor manufacturing method in which silicon carbide crystals are grown using epitaxial growth and nitrogen is doped therein.
A silicon carbide semiconductor, characterized by having a preheating step for thermally decomposing before introducing a nitrogen compound gas supplied as a nitrogen source onto a substrate on which silicon carbide crystals are formed It is a manufacturing method.

In the first technique , since the nitrogen source gas is thermally decomposed in the preheating step before introducing the gas of the nitrogen source onto the substrate, the nitrogen distribution in the wide substrate surface where epitaxial growth is being performed becomes uniform, As a result, the concentration distribution of nitrogen doped into the growing SiC crystal becomes uniform.
In the first technique , a nitrogen compound gas that is more thermally decomposable than nitrogen gas is used as a nitrogen doping gas instead of nitrogen gas. Nitrogen gas has a triple bond having a high binding energy, but a nitrogen compound does not contain such a bond, and thus thermal decomposition occurs from a lower temperature than in the case of nitrogen gas. For this reason, it can be easily thermally decomposed when the gas reaches the substrate, and the concentration distribution on the substrate surface becomes more uniform.
Here, “semiconductor” usually means a material (semiconductor) having an intermediate electrical resistance between a conductor such as metal and an insulator, and an electrical element manufactured using a semiconductor as the material ( The term “device” such as a transistor is used, but in this specification, any “semiconductor element” or the like is used unless specifically limited. That is, both are included in the present invention.

A second technique related to the present invention is a method of manufacturing the silicon carbide semiconductor,
In the method of manufacturing a silicon carbide semiconductor, the preheating step is a step of flowing the nitrogen compound gas through a room at 1300 ° C. or higher.

In the second technique , since the wall having a wall surface of 1300 ° C. or higher flows in the preheating step, the nitrogen compound can be sufficiently thermally decomposed in advance without causing a large disturbance in the gas flow.
Here, the “room” means a space for heating the flowing gas, and includes a long and thin tube that is heated from the outside, a room in which a heat transfer coil is installed, fins and the like formed on the inner wall surface. Also includes large spaces.
The upper limit of the temperature of the wall surface of the room is preferably 1350 ° C. or higher in order to perform reliable thermal decomposition even if the length of the room is somewhat short, and is preferably 1600 ° C. or lower from the viewpoint of thermal efficiency.

A third technique related to the present invention is a method of manufacturing the silicon carbide semiconductor,
A method for producing a silicon carbide semiconductor, comprising: a bubbling supply step of supplying the nitrogen compound gas by including the nitrogen compound liquid in a gas bubbled in the nitrogen compound liquid.

In the third technique , the nitrogen gas is mixed into the carrier gas by so-called bubbling, in which the carrier gas is bubbled from the bottom of the container filled with the liquid nitrogen compound. For this reason, the nitrogen compound is contained in the carrier gas at an appropriate concentration.

The 4th technique relevant to the present invention is the above-mentioned manufacturing method of the silicon carbide semiconductor,
The bubbling supply step is a method of using a hydrogen gas or an inert gas as a gas to be bubbled, wherein the silicon carbide semiconductor is produced.

  When the above gas is used as the gas to be bubbled, it is possible to suppress unintentional doping of elements other than nitrogen into the SiC crystal. Hydrogen gas can be highly purified by using a hydrogen gas refining machine, and is also a carrier gas for diluting a raw material gas in epitaxial growth, so that it can be easily employed as a gas to be bubbled. Examples of the inert gas include helium and argon.

A fifth technique related to the present invention is the above-described method for manufacturing a silicon carbide semiconductor,
The method for producing a silicon carbide semiconductor, wherein the nitrogen compound is a compound having no atoms other than nitrogen, silicon, carbon, and hydrogen.

In the fifth technique , there is no possibility that other elements that deteriorate the performance of the product are mixed into the silicon carbide crystal.

A sixth technique related to the present invention is a method of manufacturing the silicon carbide semiconductor,
The method of manufacturing a silicon carbide semiconductor, wherein the nitrogen compound is ammonia or a mixture of ammonia and a nitrogen compound other than ammonia.

Since ammonia used as a dopant is thermally decomposed at a temperature lower than that of nitrogen, preheating is facilitated. At this time, hydrogen or hydrogen gas generated by thermal decomposition is a gas widely used as a gas for diluting the carrier gas or the raw material gas, and does not adversely affect the epitaxial growth of silicon carbide.
Examples of the “nitrogen compound other than ammonia” include methylamine.

A seventh technique related to the present invention is a method of manufacturing the silicon carbide semiconductor,
The silicon carbide semiconductor manufacturing method is characterized in that the substrate on which the silicon carbide crystal is formed is silicon carbide.

In the seventh technique , the SiC crystal is grown on the silicon carbide substrate, and nitrogen is doped into the SiC crystal. This makes it easy to dope nitrogen while keeping the crystal structures of the substrate and the epitaxial growth layer the same.

The eighth technique related to the present invention is:
A silicon carbide semiconductor manufacturing apparatus that grows a silicon carbide crystal using epitaxial growth while doping nitrogen therein.
A silicon carbide semiconductor characterized by having a preheating device for thermally decomposing before introducing a nitrogen compound gas supplied as a nitrogen source onto a substrate on which silicon carbide crystals are formed It is a manufacturing apparatus.

The eighth technique captures the first technique, which is a technique of the manufacturing method, from the manufacturing apparatus.
Note that the preheating device only needs to be thermally decomposed without disturbing the flow of the dopant gas until the dopant gas (nitrogen compound gas) arrives on the epitaxially grown substrate. It does not matter whether it is separate from the container or integrated.

A ninth technique related to the present invention is the above-described silicon carbide semiconductor manufacturing apparatus,
The preheating apparatus is a silicon carbide semiconductor manufacturing apparatus having a room of 1300 ° C. or higher for thermally decomposing the nitrogen compound gas flowing inside.

The ninth technique captures the second technique, which is a technique of the manufacturing method, from the manufacturing apparatus. The room at 1300 ° C. or higher may be partially at 1300 ° C. instead of the whole room as long as the gas flowing inside is sufficiently thermally decomposed without disturbing the flow.

A tenth technique related to the present invention is the silicon carbide semiconductor manufacturing apparatus,
An apparatus for producing a silicon carbide semiconductor, comprising: a bubbling supply device that supplies the nitrogen compound gas in a gas bubbled in a liquid of the nitrogen compound.

In the tenth technique , the third technique, which is a technique of the manufacturing method, is captured from the manufacturing apparatus. Since nitrogen compounds, particularly ammonia and methylamine, are gases at room temperature, they may have a device for pressurizing and liquefying and a device for cooling and liquefying.

The eleventh technology related to the present invention is:
A silicon carbide semiconductor manufactured by the method for manufacturing a silicon carbide semiconductor according to any one of the first to seventh techniques .

The eleventh technology captures the technology of the method for manufacturing a silicon carbide semiconductor according to any one of the first technology to the seventh technology from the surface of a product manufactured by those methods. When epitaxially growing a SiC crystal and doping nitrogen inside the SiC crystal, the nitrogen compound gas is thermally decomposed in advance, so that the surface of the substrate is uniform in a plane direction (two-dimensionally) and of course the substrate surface. Since nitrogen is uniformly doped also in the direction perpendicular to the semiconductor substrate, it is possible to obtain excellent silicon carbide semiconductors, silicon carbide semiconductor elements, and electrical and electronic devices using silicon carbide semiconductors.
The concentration of doped nitrogen is generally about 1 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ³ , although it depends on the growth rate of silicon carbide, the partial pressure of the nitrogen compound gas, and the like.

The twelfth technique related to the present invention is:
A silicon carbide semiconductor manufactured by the silicon carbide semiconductor manufacturing apparatus according to any one of the eighth technique to the tenth technique .

Since it is manufactured using the silicon carbide semiconductor manufacturing apparatus according to any one of the eighth technique to the tenth technique , an excellent silicon carbide semiconductor can be obtained.

The present invention is an invention related to the above technique, and the invention of claim 1
An epitaxially grown silicon carbide semiconductor,
Nitrogen compounds containing at least ammonia gas are used as dopants,
Value sigma / m divided by the average value m and the standard deviation sigma of the doping density, in the flow direction of gas in the nitrogen compound is within 6%, within 4% in the direction of Cartesian the flow of gas in the nitrogen compound The silicon carbide semiconductor is characterized in that the substrate surface is uniformly doped with nitrogen having a doping density of 1 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ³ .

The invention of claim 2 is a silicon carbide semiconductor for a Schottky diode. The silicon carbide semiconductor according to claim 1.

  According to the present invention, uniform doping of nitrogen can be performed on a wide substrate surface by utilizing epitaxial growth of SiC. Thereby, an excellent silicon carbide semiconductor can be obtained.

It is a figure which shows the whole structure of the manufacturing apparatus of the 1st Embodiment of this invention.

  Hereinafter, the present invention will be described based on the embodiments. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(First embodiment)
FIG. 1 is a diagram showing an overall configuration of a manufacturing apparatus according to a first embodiment of the present invention. In this figure, 10 is a raw material supply equipment. Reference numeral 20 denotes a preheating device. 30 is a reaction vessel. Reference numeral 40 denotes an exhaust gas cleaning device. Reference numeral 50 denotes a control device. 70 is a substrate made of silicon carbide crystals. An arrow and a solid line including the arrow indicate a gas flow or a gas piping system. A broken line segment attached to the control device 50 and the valve or the like indicates that the control device 50 and the valve or the like are connected by a control line.

  The raw material supply facility 10 includes an ammonia cylinder 11, a hydrogen gas cylinder 12, a silane cylinder 13, a propane cylinder 14, other pressure gauges, a flow control valve, and the like. A hydrogen gas purifier (not shown) is attached to the hydrogen gas cylinder 12. Then, under control of opening and closing of each valve by the control device 50, each gas having a predetermined pressure and flow rate is sent out from the cylinders 11, 12, 13, and 14 to the preheating device 20.

The preheating device 20 heats ammonia gas, hydrogen gas, silane gas, and propane gas sent from the raw material supply facility 10 to 1300 ° C. or higher. For this reason, a coil 21 for heating is wound around the outer peripheral wall, and the temperature becomes considerably high. Therefore, not only the outer periphery but also a necessary part is not shown, but heat insulation is provided, and a thermometer is attached. Has been.
Then, the ammonia gas sent from the raw material supply facility 10 comes into contact with the inner surface of the heated preheating device wall and is thermally decomposed at a temperature of 1300 ° C. or higher.

The reaction vessel 30 is configured such that a substrate 70 made of a silicon carbide crystal can be placed inside the reaction vessel 30 with a predetermined slight inclination, and SiC is epitaxially grown on the surface of the substrate 70. Nitrogen is doped. For this reason, in order to maintain the surface of the substrate 70 at 1600 ° C., which is the SiC crystal growth temperature, an induction heating coil 32 is wound around the susceptor 31 to cause induction heating by flowing a high-frequency current. A heating body 34 is disposed inside 31 via a quartz tube 33. As a result, the gas introduced into the reaction vessel 30 is further heated to 1600 ° C. on the surface of the substrate 70.
It is to be noted that, in the same manner as the preheating device 20, the necessary portions such as the outer peripheral surface of the susceptor 31 and the inner and outer surfaces of the quartz tube 33 are thermally insulated and a thermometer, a pressure gauge and the like are also mounted.

  The exhaust gas cleaning device 40 is a device that cleans the gas sent from the reaction vessel 30 so that it can be exhausted. For this purpose, it is equipped with a cooler, various neutralizer tanks, filters, exhaust fans, and the like.

  The control device 50 introduces raw material silane gas and propane gas, carrier gas hydrogen gas, and dopant ammonia gas into the preheating device 20 from the raw material supply facility 10 at a predetermined flow rate, pressure, and temperature. It is an apparatus that controls the introduction into the reaction vessel 30, the introduction from the reaction vessel 30 into the exhaust gas cleaning device 40, and the exhaust gas cleaning device 40 further enabling exhaust. For this reason, signals from various sensors (not shown) attached to the devices are monitored, and valve opening and closing and coil current are controlled as necessary.

In this embodiment, hydrogen gas has a flow rate of 5 slm (standard litter per minute), a partial pressure of 46663 Pa, a partial pressure of silane of 54 Pa, and a partial pressure of propane of 1.2 C / Si. It was made to become.
Further, the concentration of ammonia gas in the hydrogen gas was about 1 ppm.
Further, the inside of the preheating device 20 was controlled to 1300 ° C. or higher, and the surface of the substrate 70 in the reaction vessel 30 was controlled to 1600 ° C.
Under the above conditions, the homoepitaxial growth rate of the SiC crystal on the substrate 70 was approximately 5 μm / hr. Moreover, the doping amount of nitrogen was approximately 5 × 10 ¹⁵ atoms / cm ³ .

The substrate 70 is made of 4H—SiC having a diameter of 2 inches (50.8 mm), and the substrate surface orientation was subjected to homoepitaxial growth of 4H—SiC with the (0001) Si surface being slightly inclined to 8 ° off.
Ammonia, which is a dopant gas, reaches the substrate 70 and is sufficiently thermally decomposed in contact with the inner wall of the preheating device 20 at 1300 ° C. or higher. For this reason, a SiC thin film in which nitrogen was uniformly doped on the substrate surface was obtained. In particular, since it is a hot wall type growth furnace in which the heating body 34 is disposed facing the susceptor 31, both the heat distribution and the gas flow are stable. For this reason, a SiC thin film doped with nitrogen at a more uniform concentration was obtained both in the gas flow direction and in the direction perpendicular to the gas flow, that is, on the substrate surface.

(Inspection of surface uniformity)
The inspection of the uniformity of the impurity concentration of the SiC thin film obtained by the above apparatus and method was performed using CV measurement of a Schottky diode. Specifically, using a silicon carbide substrate on which an SiC crystal was epitaxially grown, an electrode having a diameter of 1 mm and a thickness of 20 nm was deposited on the substrate to produce a Schottky diode. As an index indicating uniformity, a value obtained by dividing the standard deviation σ by the average value m was used.
[sigma] / m was 5% or less in the gas flow direction and about 3% in the direction perpendicular to the gas flow, which was very uniform, and the reproducibility was sufficiently satisfactory.

(Second Embodiment)
As a second embodiment, nitrogen is doped into SiC using epitaxial growth under the same conditions as in the first embodiment except that methylamine (CH ₃ NH ₂ ) is used as a dopant instead of ammonia. And in-plane uniformity was tested in the same way.
As a result of the inspection, σ / m was 6% or less in the gas flow direction and about 4% in the direction perpendicular to the gas flow, and the reproducibility was sufficiently satisfied.

(Comparative Example 1)
Except for not using the preheating device 20, the SiC was doped with SiC using epitaxial growth under the same conditions as in the first embodiment, and in-plane uniformity was inspected by the same method.
As a result of the inspection, σ / m was about 20% in the gas flow direction and about 10% in the direction orthogonal to the gas flow.

(Comparative Example 2)
Except for using nitrogen gas (N ₂ ) as a dopant gas instead of ammonia, SiC is doped with SiC using epitaxial growth under the same conditions as in the first embodiment, and in-plane by the same method. A uniformity test was performed.
As a result of the inspection, σ / m was about 15% in the gas flow direction and about 6% in the direction orthogonal to the gas flow.
The reason why σ / m is high is that nitrogen gas has a large triple bond energy, so that it is not sufficiently thermally decomposed even if preheating is performed, and gradually decomposes in the reaction vessel 30. This is probably because the concentration of pyrolyzed nitrogen increased along the flow direction, and the concentration of doped nitrogen also increased.
In addition, when nitrogen gas is used as a dopant using a cold wall type growth furnace, the uniformity of nitrogen concentration in the surface of the substrate is not properly decomposed, so when using a hot wall type growth furnace. Worse than.

DESCRIPTION OF SYMBOLS 10 Raw material supply equipment 11 Ammonia cylinder 12 Hydrogen gas cylinder 13 Silane cylinder 14 Propane cylinder 20 Preheating device 21 Heating coil 30 Reaction vessel 31 Susceptor 32 Induction heating coil 33 Quartz tube 34 Heating body 40 Exhaust gas Cleaning device 50 Control device 70 Substrate

Claims (2)

An epitaxially grown silicon carbide semiconductor,
A preheated nitrogen compound containing at least ammonia gas is used as the dopant gas ,
A value σ / m obtained by dividing the standard deviation σ of the doping density by the average value m is within 6% in the nitrogen compound gas flow direction, and within 4% in the direction perpendicular to the nitrogen compound gas flow. A silicon carbide semiconductor, wherein a substrate surface is uniformly doped with nitrogen having a certain doping density of 1 × 10 ¹⁵ to 1 × 10 ¹⁷ atoms / cm ³ .   2. The silicon carbide semiconductor according to claim 1, which is a silicon carbide semiconductor for a Schottky diode.

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