JP2004343133A - Manufacturing method of silicon carbide, silicon carbide, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of silicon carbide that can manufacture silicon carbide with sufficient productivity, while adding impurities under high control without having restrictions of impurity sources and impurity concentration, or the depth restrictions of an impurity addition range, etc., as well as a silicon carbide, and a semiconductor device. <P>SOLUTION: A unit process composed of following steps is repeated 2000 times to form a cubic silicon carbide film on a substrate 4 (silicon substrate) through the epitaxial growth, i.e., a single-crystal silicon substrate 4 is set up onto a plate 3 within a CVD (chemical vapor deposition) unit 10 and is heated to 1,200<SP>o</SP>C through a heating means 5, the inside of a deposition chamber 1 is provided under an atmosphere of an H<SB>2</SB>gas, after that, SiH<SB>2</SB>Cl<SB>2</SB>gas is supplied for five seconds (to form a silicon layer), next, the SiH<SB>2</SB>Cl<SB>2</SB>gas is stopped and N<SB>2</SB>gas is supplied for 5 seconds (N (donor) doping to the silicon layer), then, the N gas is stopped and C<SB>2</SB>H<SB>2</SB>gas is supplied for five minutes (to carbonize the N-doped silicon layer). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a substrate material and a sensor of a semiconductor device, as a member of a semiconductor manufacturing apparatus, as a silicon carbide thin film or an ingot or a structure used for a dummy wafer in a semiconductor element manufacturing process, as a solar cell, and further as an X-ray mask. The present invention relates to a silicon carbide manufacturing method and silicon carbide that can be used, and a semiconductor device using the silicon carbide.

  Silicon carbide is a semiconductor having a wide band gap of 2.2 eV or more, and is a crystal that is thermally, chemically, and mechanically stable. Further, because of its high thermal conductivity, it is expected to be applied as a semiconductor element material under conditions such as high frequency, large power, and high temperature.

  As a method for producing silicon carbide, a method of reacting silicon on the surface of a heated coke to precipitate silicon carbide on the surface of the coke (Acheson method) or heating and sublimating silicon carbide produced by the Acheson method to cause recrystallization. There are known methods (sublimation method, modified Rayleigh method), liquid phase growth method in which silicon is melted in a carbon crucible and pulled up while reacting suspended carbon with silicon in the crucible.

  Further, as a method for obtaining a silicon carbide film having high purity and few crystal defects, a chemical vapor deposition method is used in which a gas of a carbon source and a gas of a silicon source are thermally reacted under normal pressure or reduced pressure atmosphere to deposit on a substrate surface. An atomic layer epitaxy (ALE) method in which silicon source molecules and carbon source molecules are alternately adsorbed on the substrate surface and silicon carbide is epitaxially grown while inheriting the crystallinity of the substrate is used.

Incidentally, when silicon carbide is used as a material of a semiconductor device, control of impurities is extremely important. For example, when silicon carbide is used as a substrate of a discrete-type power semiconductor device (such as a Schottky barrier diode), the series resistance (on-resistance) when the device is in an on-state leads to power loss inside the device, and as much as possible. Must be reduced. In order to reduce such ON resistance, the substrate is required to be doped with impurities up to 10 ²¹ / cm ³ .

On the other hand, since the breakdown voltage of a semiconductor device is generally proportional to the -0.5 power of the impurity concentration, the impurity concentration in the portion where the electric field is concentrated inside the device must be reduced to 1 × 10 ¹⁴ / cm ³ or less. . When manufacturing a semiconductor device using silicon as a material, a thermal diffusion method is used as a method for adding impurities. The thermal diffusion method is a method in which an impurity is applied to the surface of a substrate to be added, or a desired impurity is diffused into the substrate by heating while exposing the substrate to an impurity atmosphere. However, the diffusion coefficient of impurities in silicon carbide is significantly lower than that of silicon, and impurities are added so that a semiconductor device can be manufactured (depth: 1 μm or more, addition concentration range: 1 × 10 ¹⁴ to 1 × 10 ²¹ / cm ³ ). It is impossible to do.

  In order to control such a wide range of impurity concentration in silicon carbide, silicon carbide is subjected to impurity addition by an ion implantation method. However, in the ion implantation method, since the depth distribution of the impurity addition is limited to the range of the implanted ions, for example, as disclosed in JP-A-11-503571, the method of introducing the dopant into the semiconductor layer of silicon carbide is as follows. An amorphous surface proximity layer is formed in the step of ion-implanting a dopant into the semiconductor layer at a low temperature, and at a high temperature at which the dopant diffuses into the non-implanted lower layer of the semiconductor layer following the surface proximity layer after this step. Must be carried out. Moreover, even if this method is used, it is difficult to add high-concentration impurities to the entire substrate.

Further, since the electrical activation of the implanted ions is insufficient, or crystal defects are generated inside the silicon carbide due to the ion implantation, for example, carbon (C) is not used as disclosed in Japanese Patent Application Laid-Open No. 12-068225. ) By additionally implanting atoms, the electrical activation rate of the acceptor atoms implanted into silicon carbide can be improved, and diffusion due to heat treatment can be suppressed. As disclosed in JP-A-10-256173, After forming a mask made of SiO ₂ on the silicon surface of the silicon substrate and ion-implanting nitrogen as an impurity element, ion implantation in the direction perpendicular to the silicon surface (channeling implantation) and from the direction perpendicular to the (0001) silicon surface It is necessary to perform ion implantation (random implantation) in a direction inclined by 7 °. Further, as described in JP-A-11-121393, when phosphorus atoms are ion-implanted into a silicon carbide semiconductor at a high temperature, the phosphorus atoms are implanted into the silicon carbide semiconductor at a temperature of 1200 ° C. or higher. It is necessary to adopt a method of doping impurities.

  For example, a method of adding an impurity simultaneously with the formation of silicon carbide (in-situ doping) is used when performing the impurity addition over the entire substrate, but in this case, the impurity source and concentration to be added are limited. Can be For example, in the invention disclosed in Japanese Patent Application Laid-Open No. 09-063968, when a gas containing carbon and silicon is caused to flow and a gas containing boron is caused to flow at the same time, the p-type silicon carbide semiconductor layer is vapor-phase grown. It is required that the relationship of 1 <Qc / Qsi <5 be satisfied between the supply amount Qc of carbon contributing to crystal growth and the supply amount Qsi of silicon contributing to crystal growth.

In the formed p-type silicon carbide semiconductor layer, there is a limit of 1 <d _C / d _Si ≦ 32/31 between the atomic density d _{C of} carbon as a component element and the atomic density d _{Si of} silicon. is there. Alternatively, as described in Japanese Patent Publication No. 10-507734, in a CVD process or a sublimation process, at least one boron atom is converted into at least one carbon atom in a molecule of a silicon carbide single crystal during doping thereof. A preferred organoboron compound when using a chemically bound organoboron compound is a trialkylboron.

When the concentration of nitrogen as an impurity is to be changed in a wide range by in-situ doping, for example, Appl. Phys. Lett. 65 (13), 26
As described in (1994), a method of changing the concentration of C in which the occupancy of the crystal lattice in silicon carbide competes with N has been reported. Since the concentration changes sensitively with respect to the C concentration, it is necessary to strictly control the composition ratio between the silicon source and the C source during the growth of silicon carbide, and it is difficult to apply this method to mass production.

  When impurities are introduced by a sublimation recrystallization method, silicon carbide powder as a raw material and an impurity source (Al, B, etc.) are mixed in a predetermined ratio, and the mixture is sublimated and recrystallized on a seed crystal. However, since the vapor pressure of the impurity source at the sublimation temperature greatly exceeds the vapor pressure of silicon carbide, the impurity concentration is high in the initial stage of silicon carbide growth, and the impurity source volatilizes and disappears at the end of the growth. Is formed.

  Therefore, even if the silicon carbide formed by the sublimation recrystallization method is sliced to obtain a silicon carbide substrate, variation in impurity concentration (variation in resistivity) between the substrates increases, and stable device characteristics cannot be obtained. . Further, since the surface of silicon carbide grown by the sublimation recrystallization method is not always flat, it is difficult to obtain a steep pn junction or a smooth pn junction.

  Further, when impurities are introduced while growing silicon carbide by a conventional vapor phase growth method (in-situ doping), the incorporation of impurities proceeds simultaneously with the growth of silicon carbide. Even if switching is performed to obtain a pn junction, a certain amount of impurity gas stays in the reaction system, so that a clear (having a steep concentration gradient) pn junction cannot be obtained. In addition, since both the donor impurity and the acceptor impurity exist near the junction, the degree of compensation increases, and it is difficult to increase the mobility at the junction. Further, the in-plane impurity concentration becomes non-uniform due to the flow of the raw material gas or the like, and it is difficult to make the in-plane impurity concentration uniform over a large area. Therefore, strict control of the impurity concentration cannot be performed, and silicon carbide having a desired impurity concentration distribution with high yield cannot be obtained.

  SUMMARY OF THE INVENTION The present invention has been made to overcome the above-described problems, and has high control over a large area of 4 inches or more in diameter without being restricted by an impurity source, an impurity concentration, or a depth of an impurity doping range. It is an object of the present invention to provide a method for manufacturing silicon carbide, a silicon carbide and a semiconductor device which can be manufactured with sufficient productivity while adding impurities under the same conditions.

As means for solving the above-mentioned problems, the first means is:
In a silicon carbide production method of forming a silicon carbide by depositing a thin film from a gas phase or a liquid phase on a substrate,
A silicon layer forming step of forming a silicon layer on a substrate,
Addition of at least one element selected from N, B, Al, Ga, In, P, As, Sb, Se, Zn, O, Au, V, Er, Ge, and Fe to the silicon layer as an impurity. Process and
Carbonizing the silicon layer to which the impurities are added to form a silicon carbide layer to which the impurities are added.
The second means is
The silicon layer forming step, the impurity adding step and the carbonizing step are performed while epitaxially growing a thin film on a substrate using a chemical vapor deposition method, and a silane-based or dichlorosilane-based gas is used as a silicon raw material in the silicon layer-forming step. And a method for producing silicon carbide according to a first means, wherein an unsaturated hydrocarbon gas is used as a carbon raw material in the carbonization step.
The third means is
An impurity adding step is performed after the silicon layer forming step, and then a carbonizing step is performed.
The fourth means is
A silicon carbide manufacturing method according to the first or second means, wherein the silicon layer forming step and the impurity adding step are performed simultaneously, and thereafter, the carbonizing step is performed.
The fifth means is
A method for producing silicon carbide according to a first or second means, characterized in that a carbonization step is performed after a lapse of a predetermined time from the start of these steps while simultaneously performing the silicon layer forming step and the impurity adding step.
Sixth means,
A first silicon carbide layer having a desired thickness is formed by repeatedly performing a series of unit steps of forming a thin-film silicon carbide by the silicon layer forming step, the impurity adding step, and the carbonizing step; A method for producing silicon carbide according to any one of the fifth means.
Seventh means,
A silicon carbide manufacturing method according to a sixth means, wherein a silicon carbide layer having a different impurity concentration in a thickness direction is formed by changing an impurity amount added in each of the unit steps.
Eighth means,
Any one of the first to seventh aspects, wherein the impurity addition amount is controlled so that the impurity concentration of the obtained silicon carbide is in the range of 1 × 10 ¹³ / cm ³ to 1 × 10 ²¹ / cm ³ . It is a method for producing silicon carbide according to the means.
The ninth means is
A first to a first aspect wherein the impurity addition amount is controlled such that the impurity concentration gradient in the obtained silicon carbide thickness method is in the range of 1 × 10 ¹⁸ / cm ⁴ to 4 × 10 ²⁴ / cm ⁴ . 8. A method for producing silicon carbide according to any one of (8) to (9).
The tenth means is
At least the surface of the base is made of single crystal silicon, cubic silicon carbide or hexagonal silicon carbide, and the silicon carbide formed on the surface of the base is cubic silicon carbide or hexagonal silicon carbide. The method according to any one of the first to ninth means.
The eleventh means is
A method for producing silicon carbide according to any one of the first to tenth means, wherein after forming a silicon carbide layer on a substrate, the substrate is removed to form silicon carbide in a wafer form.
The twelfth means is
A sixth aspect of the present invention is a method for manufacturing a silicon carbide according to any one of the sixth to eleventh means, wherein a pn junction is provided in a silicon carbide layer by changing a type of an impurity added in an impurity adding step in a unit process.
The thirteenth means is
Silicon carbide produced by the silicon carbide production method according to the first to twelfth means is used as a seed crystal to grow silicon carbide by a vapor phase growth method, a sublimation recrystallization method, or a liquid phase growth method. Silicon carbide manufacturing method.
Fourteenth means,
Silicon carbide having a layer region in which the impurity concentration gradient in the thickness method is 1 × 10 ²² / cm ⁴ to 4 × 10 ²⁴ / cm ⁴ .
The fifteenth means is
A semiconductor device using the silicon carbide manufactured by the silicon carbide manufacturing method according to the first to thirteenth means or the silicon carbide according to the fourteenth means.

According to the above-described first to fifth means, since silicon carbide containing an impurity is formed by adding an impurity to silicon and then carbonizing the same, a conventional method of adding an impurity to silicon carbide is used. As compared with the case, it is possible to easily and accurately add a desired high concentration of impurities. That is, in general, the impurity concentration that can be added to silicon carbide is limited, but the impurity can be relatively freely added to silicon. The above means focuses on this point, and the above means can realize high-concentration impurity addition exceeding the diffusion coefficient and solid solubility limits of impurities in silicon carbide. According to the above means, since the amount of impurities finally taken into the silicon carbide layer matches the amount of impurities added to silicon in advance, the amount of impurities in the silicon carbide depends on the impurity addition conditions during the formation of the silicon layer ( For example, it can be strictly controlled by the supply amount and supply time of the impurity. In addition, since the diffusion coefficient of the impurity with respect to the already formed silicon carbide is much lower than the diffusion coefficient with respect to silicon, it is possible to prevent the impurity concentration distribution from being disturbed by inner diffusion or the like during the growth of silicon carbide. Therefore, the range of impurity addition can be precisely controlled by the thickness of the silicon layer formed in advance. Thereby, for example, silicon carbide having an impurity concentration in an extremely wide range as defined in the eighth means can be easily obtained over a region having a thickness of 1 μm or more. This enables a wide range of applications as a semiconductor device.
It is important that both the silicon layer forming step and the impurity adding step be performed in the absence of a carbon material. If no carbon source is present, the impurity adding step may be performed simultaneously with the silicon layer forming step, or may be performed after the silicon layer forming step. In any case, it is essential that the carbonizing step be performed after the silicon layer forming step and the impurity adding step. The reason is as follows.
That is, when a carbon material and an impurity material are simultaneously introduced onto a substrate on which a silicon layer is formed, the formation of silicon carbide is more predominant than the addition of impurities. This is because while carbonization of the silicon surface is a surface reaction, diffusion of impurities is a phenomenon proportional to the square root of time, and therefore the carbonization phenomenon is completed in a shorter time. Therefore, sufficient impurity cannot be added in the presence of carbon. Further, since the carbon material is preferentially adsorbed on the substrate surface, the impurity material is prevented from diffusing into the substrate.
Therefore, in order to add a sufficient impurity, it is necessary to introduce the impurity source into the substrate on which the silicon layer is formed in the absence of the carbon source. In this case, the silicon source and the impurity source may be introduced at the same time.
Then, after the silicon layer to which the impurity element is added is formed, the carbon material may be introduced onto the base. In the carbonization step, an impurity raw material may be introduced together with the carbon raw material. This is because carbonization is considered to occur preferentially even when the impurity raw material and the carbon raw material are present at the same time, and as a result, the result is the same as when the carbon raw material is introduced alone.
In addition, in the carbonization step, the silicon raw material may be present together with the carbon raw material as long as the flow ratio is within a predetermined range (determined by the adhesion coefficient ratio between the carbon raw material and the silicon raw material). This is because when the flow rate ratio is within the range, the carbon material forms an adsorption layer on the substrate surface, and no more silicon carbide is formed even when the carbon material and the silicon material are supplied simultaneously. Because you can.
Specific means for depositing a thin film from a gas phase or a liquid phase include, for example, a chemical vapor deposition (growth) method (CVD method), a molecular beam epitaxy method (MBA method), and a liquid phase epitaxy method (LPE method). There is.
As the substrate, a substrate having silicon, silicon carbide, TiC, sapphire, or the like at least on its surface can be used.
Examples of impurities to be added include N, B, Al, Ga, In, P, As, Sb, Se, Zn, O, Au, V, Er, Ge, and Fe. Among them, B, Al, Ga, and In which are Group III elements are used to form a P-type semiconductor as an acceptor, and N, P, As and V which are Group V elements are used to form an n-type semiconductor as a donor. Se, which is a group IV element, is one in which Sb forms a level in a forbidden band due to a difference in electron affinity and changes electric resistance. In addition, Zn, O, Au, V, Ge, and Fe may be used to form a deep level and change the lifetime and resistivity of minority carriers.
The impurities described above may be used alone or in combination. For example, even if impurities of the same type are formed at different levels in the forbidden band and change in resistivity with respect to temperature are different, if it is desired to adjust the resistivity at a certain temperature, multiple types of impurities are added simultaneously. I do. For example, two arbitrary elements are selected from the above-mentioned group V elements and are added simultaneously. For example, N and P are added.
Further, by adding a donor and an acceptor at the same time and compensating for carriers, the resistivity can be increased. Thereby, for example, the i layer of the PiN diode can be formed. For example, N as a donor and B as an acceptor are simultaneously added. In addition, in order to offset the increase in resistivity due to impurities that inevitably enter during crystal growth, impurities are introduced when an impurity having the opposite property to the impurity is added or when a donor and an acceptor are simultaneously added. By adjusting these properties so as to offset the properties of the impurities and adding them, silicon carbide having a high resistivity can be formed.
The silicon layer forming step, the impurity adding step, and the carbonizing step can be performed by controlling the supply of the raw material to the gas phase or the liquid phase. For example, the concentration ratio of the impurity source mixed with the silicon carbide raw material is changed, or the time during which the impurities are mixed is adjusted.
Examples of the silane-based gas or dichlorosilane-based gas include dichlorosilane, tetrachlorosilane, trichlorosilane, and hexachlorosilane. In addition, examples of the unsaturated hydrocarbon gas include acetylene, ethylene, and propane. By using these raw materials, the formation temperature of silicon carbide is low, the allowable range of change in the gas flow ratio is large, and the crystallinity of the obtained silicon carbide can be improved.
In the case of manufacturing by the second means, the temperature of the substrate such as the substrate during the reaction is set to 900 to 1400 ° C, preferably 1000 to 1400 ° C. If the reaction temperature is too high, silicon will be melted when silicon is used as the substrate, and if the reaction temperature is too low, the reaction rate will be significantly reduced.
Further, according to the sixth means, an impurity-added layer having an arbitrary concentration profile can be formed. In addition, when this method is used, any impurity that diffuses into silicon can be used without any restrictions.
According to the seventh means, it is possible to obtain one having an arbitrary concentration gradient. That is, it is possible to easily obtain a steep concentration gradient that could not be obtained conventionally, for example, a steep concentration gradient as defined in the ninth means.
According to the tenth means, good silicon carbide can be obtained. For example, when silicon carbide is formed on a silicon carbide substrate, it can be used as it is as a silicon carbide substrate for semiconductors. Here, as the silicon carbide of the base, silicon carbide formed by the Acessason method or the sublimation recrystallization method can also be used. Further, a material obtained by carbonizing the surface of silicon may be used.
In this case, as the substrate, for example, a substrate having a slightly inclined normal axis of the surface (a substrate having an off-angle) can be used. An example of such a substrate is a silicon (100) substrate whose surface normal axis is slightly inclined from the [001] direction to the [110] direction. Further, as the substrate, a substrate having a plurality of undulations extending in parallel in one direction on the surface can be used. For example, a silicon substrate or a cubic silicon carbide substrate provided with undulations extending in parallel to the [011] direction on the surface of a certain substrate on the (001) plane can be given. In this case, defects in the formed silicon carbide layer can be reduced, and high-quality silicon carbide can be obtained.
According to the eleventh means, a silicon carbide semiconductor wafer having a desired uniform impurity concentration or a desired strictly controlled impurity concentration distribution can be obtained. When a silicon substrate is used as the substrate, for example, a silicon carbide layer is formed on the substrate, and then the substrate is removed by etching, cutting, or the like. When the silicon carbide layer is formed thick on the substrate, the formed silicon carbide layer is cut and sliced by means such as a wire saw to obtain a wafer. In this case, when the diameter of the wafer is 6 inches, the thickness is 0.65 mm, and when the diameter of the wafer is 5 inches, the thickness is 0.5 mm, and the diameter of the wafer is 4 inches or 3 inches. In this case, the thickness is about 0.36 mm. Even in the case of such a large area and relatively thick, it is possible to obtain an accurately controlled impurity concentration over the entire wafer. Specifically, it is possible to reduce the variation of the impurity concentration over the entire surface in the thickness direction of 4 inches or more to 5% or less and the variation of the impurity concentration over the entire thickness direction to 5% or less. Here, the variation (%) of the impurity concentration is obtained by an equation of variation of the impurity concentration = {(maximum concentration−minimum concentration) / average concentration} × 100 (%). Further, the impurity concentration gradient can be provided in the ninth means or the fourteenth means by controlling it accurately within a range.
According to the twelfth means, a pn junction in which the impurity concentration is accurately controlled can be obtained with good reproducibility, so that a large number of desired semiconductor devices can be manufactured with high yield.
According to the thirteenth means, by appropriately setting the impurity concentration of silicon carbide used as a seed crystal, the electric resistivity thereof is controlled to an appropriate value, thereby preventing adhesion of particles during crystal growth. As a result, it is possible to obtain a high-quality silicon carbide ingot.
According to the fourteenth means, silicon carbide having a concentration gradient in the thickness direction is cut and formed into a large number of slices in the thickness direction, so that slices having a desired concentration can be easily obtained. As a result, the control range of the internal electric field of the semiconductor is widened, which is extremely advantageous in designing the operating characteristics of the semiconductor device.
According to the fifteenth means, a high-speed, high withstand voltage, high-efficiency power semiconductor or the like can be obtained.

(Example 1)
FIG. 1 is a diagram showing a schematic configuration of a CVD apparatus for performing the silicon carbide manufacturing method according to the first embodiment, and FIG. 2 is an illustration of a raw material gas supply timing in the silicon carbide manufacturing method according to the first embodiment. Hereinafter, the method for manufacturing silicon carbide according to the first embodiment will be described with reference to FIGS. 1 and 2, and the silicon carbide according to the embodiment of the present invention will be described. This embodiment is an example in which an impurity adding step is performed after a silicon layer forming step, and then a carbonizing step is performed.

In FIG. 1, a CVD apparatus 10 is provided in a film forming chamber 1 in a state where a gas introduction pipe 2 stands substantially vertically so that a tip nozzle 2 a thereof is located at the center of the film forming chamber 1. A plate 3 is attached to the tip of the gas introduction pipe 2. A heating means 5 for heating the substrate 4 and the like disposed on the plate 3 is provided below the plate 3. Note that the substrate 4 constitutes the base in the present invention. The gas supply side of the gas introduction pipe 2 is provided outside the film forming chamber 1 and includes H ₂ gas, N ₂ gas, SiH ₂ Cl ₂ gas, and C ₂ H via valves 2b, 2c, 2d, and 2e, respectively. Connected to _two gas sources. Further, an exhaust pipe 6 is connected to the film forming chamber 1, and the exhaust pipe 6 is connected to an exhaust pump (not shown) via a pressure adjusting valve 7 so that the inside of the film forming chamber 1 can be evacuated. .

  The above-described CVD apparatus 10 is a known so-called cold-wall type low-pressure CVD apparatus, in which a substrate 4 arranged on a plate 3 is heated to an appropriate temperature by a heating means 5, and the inside of the film forming chamber 1 is exhausted by an exhaust pipe 6. A thin film is grown on the substrate 4 by evacuating and supplying an appropriate gas from the nozzle 2 a of the gas introduction pipe 2 to form an appropriate gas phase in the film forming chamber 1.

Silicon carbide is manufactured by the above-described low-pressure CVD apparatus 10 as follows. Here, as the substrate 4, a single crystal silicon substrate having a diameter of 6 inches and a {001} plane of the crystal appearing on the surface is used. Then, as a pretreatment, the surface layer of the silicon substrate is carbonized, and a thin silicon carbide layer is formed as a buffer layer between the silicon carbide layer to be grown on the substrate and the silicon substrate, thereby growing a silicon carbide layer having good crystallinity. It can be so. That is, the inside of the film forming chamber 1 is evacuated through the exhaust pipe 6, the valve 2b and the valve 2e are opened, H ₂ gas is introduced at 200 sccm, and C ₂ H ₂ gas is introduced at 50 sccm. , And the temperature of the substrate 4 is heated to 1200 ° C. in about one minute by the heating means 5. Thereby, the surface layer of the substrate 4 is carbonized in advance. When this process is completed, the valve 2e is closed and the introduction of the C ₂ H ₂ gas is temporarily stopped. Thereafter, the pressure is controlled by controlling the amount of exhaust by the pressure adjusting valve 7 through the exhaust pipe 6 so that the pressure in the film forming chamber 1 becomes 60 mTorr while the H ₂ gas is constantly supplied at 200 sccm while maintaining the substrate temperature. The following film forming operation is performed while performing the adjustment.

As shown in FIG. 2, first, the valve 2c is opened, and a SiH ₂ Cl ₂ gas is supplied at a supply amount of 30 sccm for 5 seconds (formation of a silicon layer). Next, the valve 2c is closed to stop the supply of the SiH ₂ Cl ₂ gas, and the valve 2d is opened to supply the N ₂ gas at a supply rate of 50 sccm for 5 seconds (addition of N (donor) to the silicon layer). Next, the valve 2d is closed to stop the supply of the N ₂ gas, and the valve 2e is opened to supply the C ₂ H ₂ gas at a supply rate of 10 sccm for 5 seconds (carbonization of the N-added silicon layer). Assuming that the above series of steps (the step of forming the silicon layer, the step of adding N to the silicon layer, and the step of carbonizing the silicon layer to which N is added) are unit steps, this unit step is repeated 2000 times. Thus, a cubic silicon carbide film is formed on substrate 4 (silicon substrate) by epitaxial growth.

The time required to grow the silicon carbide film is 8.3 hours. As a result of the growth, a single-crystal silicon carbide semiconductor film of 54 μm was formed on substrate 4 (silicon substrate). The N concentration in the silicon carbide grown on the substrate 4 (silicon substrate) was measured by SIMS (Secondary Ion Mass Spectroscopy) and found to be uniformly distributed at 7.4 × 10 ¹⁹ / cm ^3. did. When the electron concentration in the silicon carbide at room temperature was measured using the Hall effect, it was found to be 7.2 × 10 ¹⁹ / cm ³ . Further, the resistivity of the silicon carbide was 0.007 Ωcm. The variation in the impurity concentration was 3.7% both in the plane and in the thickness direction.

(Example 2)
FIG. 3 is an illustration of a raw material gas supply timing in the silicon carbide manufacturing method according to the second embodiment. Second Embodiment A silicon carbide manufacturing method and silicon carbide according to a second embodiment will be described with reference to FIG. The method for manufacturing silicon carbide of this embodiment has almost the same configuration except that the unit process in the method for manufacturing silicon carbide of the first embodiment is different. Description is omitted. This embodiment is an example in which the silicon layer forming step and the impurity adding step are performed simultaneously, and thereafter, the carbonizing step is performed.

As shown in FIG. 3, in the unit process of this embodiment, first, the valve 2c is opened to supply SiH ₂ Cl ₂ gas at a supply amount of 30 sccm for 5 seconds (formation of a silicon layer), and at the same time, the valve 2d is opened. N ₂ gas is supplied at a supply amount of 50 sccm for 5 seconds (N (donor) addition to the silicon layer). That is, by simultaneously supplying the SiH ₂ Cl ₂ gas and the N ₂ gas for 5 seconds, the formation of the silicon layer and the addition of N (donor) to the silicon layer are performed simultaneously. Next, the valves 2c and 2d are closed to stop the supply of the SiH ₂ Cl ₂ gas and the N ₂ gas, and the valve 2e is opened to supply the C ₂ H ₂ gas at a supply rate of 10 sccm for 5 seconds (the silicon layer added with N). Carbonization). The above unit process is repeated 2000 times. Thus, a cubic silicon carbide semiconductor film is formed on substrate 4 (silicon substrate) by epitaxial growth.

The time required for the growth of silicon carbide is 5.6 hours. As a result of the growth, single-crystal silicon carbide of 54 μm was obtained on substrate 4 (silicon substrate). Impurities in the silicon carbide grown on the silicon substrate were measured by SIMS (Secondary Ion Mass Spectroscopy). As a result, although the N ₂ supply amount was the same as that in Example 1, the N concentration in the silicon carbide was Was found to be uniformly distributed at 7.4 × 10 ¹⁹ / cm ³ . When the electron concentration in the silicon carbide at room temperature was measured using the Hall effect, it was found to be 7.2 × 10 ¹⁹ / cm ³ . The resistivity of the silicon carbide was 0.007 Ωcm. The variation in the impurity concentration was 3.7% both in the plane and in the thickness direction. According to this example, it has been clarified that the effect of the present invention does not change even if the step of depositing the silicon layer and the step of adding impurities to the silicon layer are overlapped in time or separated. Further, a similar silicon carbide semiconductor can be obtained in a shorter time than in Example 1.

(Example 3)
FIG. 4 is an illustration of a raw material gas supply timing of the method for manufacturing silicon carbide according to the third embodiment. Third Embodiment A silicon carbide manufacturing method and silicon carbide according to a third embodiment will be described with reference to FIG. The method for manufacturing silicon carbide of this embodiment also has almost the same configuration except that the unit process in the method for manufacturing silicon carbide of the above-described first embodiment is different. Description is omitted. This embodiment is an example in which the carbonization step is performed a fixed time after the start of these steps while simultaneously performing the silicon layer forming step and the impurity adding step.

As shown in FIG. 4, in the unit process of this embodiment, first, the valve 2c is opened and the SiH ₂ Cl ₂ gas is continuously supplied at a supply amount of 30 sccm (formation of a silicon layer), and at the same time, the valve 2d is opened. Open to continuously supply N ₂ gas at a supply rate of 50 sccm (addition of N (donor) to the silicon layer). That is, by simultaneously and continuously supplying the SiH ₂ Cl ₂ gas and the N ₂ gas, formation of the silicon layer and addition of N (donor) to the silicon layer are continuously performed. Next, 5 seconds after the start of the supply of the SiH ₂ Cl ₂ gas and the N ₂ gas, the valve 2e is opened to supply the C ₂ H ₂ gas at a supply amount of 10 sccm for 5 seconds (for the N-added silicon layer). Carbonized). In this case, even when the C ₂ H ₂ gas is supplied, the supply of the SiH ₂ Cl ₂ gas and the N ₂ gas is continued.

The above unit process is repeated 2000 times. Thus, a cubic silicon carbide semiconductor film is formed on substrate 4 (silicon substrate) by epitaxial growth. The time required for the growth of silicon carbide is 5.6 hours. As a result of the growth, single-crystal silicon carbide of 54 μm was obtained on substrate 4 (silicon substrate). Impurities in the silicon carbide grown on the silicon substrate were measured by SIMS (Secondary Ion Mass Spectroscopy). As a result, although the N ₂ supply amount was the same as that in Example 1, the N concentration in the silicon carbide was Was found to be uniformly distributed at 7.3 × 10 ¹⁹ / cm ³ . When the electron concentration in the silicon carbide at room temperature was measured using the Hall effect, it was found to be 7.2 × 10 ¹⁹ / cm ³ . The resistivity of the silicon carbide was 0.007 Ωcm. The variation in the impurity concentration was 3.7% both in the plane and in the thickness direction. According to this embodiment, even if the supply of SiH ₂ Cl _{2 and the} supply of N ₂ are continuous and the supply of C ₂ H ₂ is performed intermittently, the addition of impurities into silicon carbide is substantially the same as the supply of C ₂ H _2. It does not occur at the time (at the time of carbonization of the silicon layer), indicating that the impurity addition process and the carbonization process are temporally separated. Also in this embodiment, a substantially similar silicon carbide semiconductor can be obtained in a shorter time than in the first embodiment. According to this embodiment, the control of gas supply can be simplified as compared with the other embodiments.

(Example 4)
Next, FIG. 5 is an explanation of the raw material gas supply timing of the method for manufacturing silicon carbide according to the fourth embodiment. Example 4 A method for manufacturing silicon carbide and silicon carbide according to Example 4 will be described with reference to FIG. In the silicon carbide manufacturing method of this embodiment, as a unit step in the silicon carbide manufacturing method of the above-described third embodiment, a BCl ₃ gas is supplied at a flow rate of 20 sccm instead of the N ₂ gas. , N (donor) in place of adding B (acceptor), and except that the supply amount of C ₂ H ₂ gas was set to 5 sccm, is the same as that of Example 3, and the detailed description is omitted. I do.

The time required for the growth of silicon carbide is 5.6 hours. As a result of the growth, single-crystal silicon carbide of 54 μm was obtained on substrate 4 (silicon substrate). The B concentration in the silicon carbide grown on the silicon substrate was measured by SIMS (Secondary Ion Mass Spectroscopy) and found to be uniformly distributed at 1.3 × 10 ¹⁹ / cm ³ . The hole concentration at room temperature in the silicon carbide was measured using the Hall effect, and was found to be 1.0 × 10 ¹⁹ / cm ³ . The resistivity of this silicon carbide was 0.01 Ωcm. The variation in the impurity concentration was 3.7% both in the plane and in the thickness direction.

(Example 5)
Next, FIG. 6 illustrates the timing of supplying the source gas in the method for manufacturing silicon carbide according to the fifth embodiment. Example 5 A method for manufacturing silicon carbide and silicon carbide according to Example 5 will be described with reference to FIG. In the silicon carbide manufacturing method of this embodiment, the supply amount (fn) of the N ₂ gas is changed and the supply of the SiH ₂ Cl ₂ gas and the N ₂ gas is performed in the unit process in the silicon carbide manufacturing method of the third embodiment. Example 3 is the same as Example 3 except that the time (ts) between the start point and the point at which the supply of the C ₂ H ₂ gas is started is changed, and the detailed description is omitted.

FIG. 7 is a graph showing the result of observing the electron concentration in a number of silicon carbide semiconductors formed by changing ts and fn. As shown in FIG. 7, the electron concentration is proportional to both ts and fn, and the value is in a range from 3 × 10 ¹⁴ / cm ³ to 1.8 × 10 ²⁰ / cm ^{3 where} a device can be formed. It turned out that high-precision control was possible. Further, it is also understood that a higher electron density can be achieved by extending ts to 10 seconds or more.

(Example 6)
Next, an example of forming a semiconductor device having a pn junction on a substrate 4 (single-crystal silicon substrate) will be described as a sixth embodiment. In this embodiment, an n-type semiconductor is formed on the substrate 4 by performing the unit process in the method of the third embodiment 1,000 times, and then the unit process in the method of the fourth embodiment is performed 1,000 times. A p-type semiconductor is formed on the n-type semiconductor to form a pn junction silicon carbide semiconductor having a thickness of 54 μm on the substrate 4. The formation time is 5.6 hours. The film forming conditions are the same as those in Examples 3 and 4, except for the number of unit processes.

Next, substrate 4 (single crystal silicon substrate) is removed using a mixed solution of HF and HNO ₃ , and Ni electrodes are deposited on the upper surface side (p type side) and the lower surface side (n type side) of the silicon carbide semiconductor. I do. Next, a conductive wire was adhered to the upper and lower electrodes, and the capacitance of the pn junction was measured while applying a DC voltage. The applied voltage was a direct current of -10 V to +10 V, and the capacity measurement used an AC voltage of 1 MHz (0.2 V). From the change in capacitance with respect to the applied voltage, it was found that the built-in potential of the pn junction formed by this method was 1.56 V, and the impurity concentration gradient of the pn junction was 1.4 × 10 ²⁴ / cm ⁴ . It was calculated that there is. Next, when a voltage was applied to the pn junction in the silicon carbide semiconductor with the upper electrode being on the negative side and the lower electrode being on the positive side, a breakdown phenomenon was observed at 3V.

(Example 7)
This embodiment is an example in which silicon carbide manufactured by the method of the above embodiment is used as a seed crystal to manufacture silicon carbide by a sublimation recrystallization method. This will be described below. First, the value of fn or ts is set so that the resistivity of silicon carbide to be formed is 0.001 Ωcm by using the method of the above-described fifth embodiment, and a cubic of 6 inches in diameter is formed on a silicon substrate having 6 inches in diameter. A first seed crystal of crystalline silicon carbide is formed. Similarly, the value of fn or ts is set so that the resistivity of the formed silicon carbide is 50 Ωcm, and the second seed crystal of cubic silicon carbide having a diameter of 6 inches is formed on a silicon substrate having a diameter of 6 inches. Form.

  Next, the substrate on which the silicon carbide serving as the seed crystal was formed was placed downward in a graphite crucible, and SiC powder was inserted into the lower portion of the crucible. Then, SiC was recrystallized on the substrate. In this case, the distance between the substrate surface and the upper part of the powder is 100 mm. The growth rate of SiC is 0.5 mm / hr.

The surface after the growth of 10 mm was etched with molten KOH at 500 ° C. for 10 minutes, and the etch pit density of the surface was measured. When the first seed crystal (resistivity 0.001 Ωcm) was used, 10 / cm ² or less, whereas the value was 3500 / cm ² when the second seed crystal (resistivity was 50 Ωcm) was used. That is, by keeping the resistivity extremely low, the adhesion of particles (mainly silicon carbide powder as a raw material) due to static electricity in sublimation recrystallization can be suppressed, and the defect concentration is extremely low, the diameter is 6 inches, and the thickness is 10 mm. A graded cubic silicon carbide ingot is obtained.

Next, for comparison, SiC was sublimated and recrystallized using a commercially available 6H—SiC (micropipe concentration 100 / cm 2, diameter 2 inches, resistivity 40 Ωcm) as a substrate under the same conditions. Was 1000 / cm ² and the number of particles was 3000 / cm ² .

As described above, according to the above embodiment, a steep impurity concentration gradient exceeding 10 ²⁴ / cm ⁴ can be formed at the pn junction. Further, as shown in the above-described fifth embodiment, since the impurity concentration can be controlled and changed in the range of 1 × 10 ¹⁴ to 1 × 10 ²¹ / cm ³ , the concentration gradient also ranges from 10 ¹⁷ / cm ⁴ to 10 ^24. / it in the range of cm ⁴ can be controlled is obvious, it is clear that the pn junction of the semiconductor device can control the breakdown voltage from 3 in a wide range of 10000 V.

As described above based on the embodiments, when the present invention is used, impurity concentration control and impurity concentration gradient control over a wide range can be performed with high accuracy, and the built-in potential and breakdown voltage of a semiconductor device can be controlled with high accuracy. It is possible to do. The effect of the present invention is not limited to the case where N ₂ or BCl ₃ is used as an impurity, and the effect of the present invention is exhibited without any limitation as long as the impurity can diffuse into silicon. . Although SiH ₂ Cl ₂ and C ₂ H ₂ were used as the raw materials for silicon carbide, the present invention can be implemented by combining other raw materials for depositing silicon on a substrate with a carbon source capable of carbonizing the silicon. The effect appears.

  Although 1200 ° C. was used as the growth temperature of silicon carbide, the effect of the present invention can be exhibited if the temperature is 900 ° C. or more at which decomposition of the silicon source and carbonization of the silicon layer can occur. The gas supply time during the growth of silicon carbide is not limited to the embodiment of the present invention, and a gas introduction time and a gas introduction frequency necessary for obtaining a desired silicon carbide film thickness can be selected. The crystal phase of silicon carbide is not limited to cubic, and the effects of the present invention are not changed even if hexagonal or rhombohedral silicon carbide is used.

Further, in the above-described embodiment, an example of the case of the vapor phase growth method is given, but the present invention can be applied to the liquid phase growth method. In the case of the liquid phase growth method, first, the substrate surface is brought into contact with a Si melt to grow a Si layer on the substrate surface, and then the Si layer is exposed to an impurity atmosphere (for example, a gas phase or impurities in the impurity atmosphere are removed). Impurities) are diffused into the Si layer, and then the Si surface containing the impurities is exposed to a hydrocarbon atmosphere. Thus, the same effect as the vapor phase growth method can be obtained by the liquid phase growth method. Further, in the above embodiment, an example in which the impurity concentration gradient is set to 1.4 × 10 ²⁴ / cm ⁴ is given. However, according to the method of the present invention, the impurity concentration gradient is set to 1 × 10 ¹⁸ / cm ⁴ to 4 ×. It has been confirmed that it can be arbitrarily selected within the range of 10 ²⁴ / cm ⁴ . Hereinafter, for comparison with the present invention, specific examples of the conventional manufacturing method will be listed as comparative examples.

(Comparative Example 1)
In this comparative example, a film is formed under the same film forming conditions as in Example 1 except that the unit process in Example 1 is different. That is, as shown in FIG. 8, instead of repeating the unit process in Example 1, H ₂ gas, SiH ₂ Cl ₂ gas, N ₂ gas and C ₂ H ₂ gas are simultaneously supplied continuously for 60 minutes. In addition, impurities are added simultaneously with the formation of silicon carbide. The supply amount of each gas is the same as in the first embodiment.

Thus, a 77 μm cubic silicon carbide semiconductor film was obtained on substrate 4 (single crystal silicon substrate). Impurities in the silicon carbide grown on the silicon substrate were measured by SIMS (Secondary Ion Mass Spectroscopy). As a result, the N concentration in the silicon carbide was uniformly distributed at 3.2 × 10 ¹⁶ / cm ³ . There was found. When the electron concentration in the silicon carbide at room temperature was measured using the Hall effect, it was found to be 2.7 × 10 ¹⁶ / cm ³ . The resistivity of the silicon carbide was 0.42 Ωcm. The variation in the impurity concentration was 8.2% both in the plane and in the thickness direction.

  As is apparent from Comparative Example 1, according to the above-described embodiment, a silicon layer is formed on a substrate once, an impurity is added simultaneously with the formation, and then the silicon layer containing the impurity is carbonized. Therefore, as compared with the case where impurities are added simultaneously with the formation of silicon carbide, the impurity concentration is increased by three digits or more even with the same amount of impurity gas introduced, and the resistivity of silicon carbide can be significantly reduced. It becomes.

(Comparative Example 2)
This comparative example is the same as the comparative example 1 except that the BCl ₃ gas was supplied at 20 sccm instead of the N ₂ gas supply as shown in FIG. This is the same as Comparative Example 1 except that B (acceptor) is added instead of N (donor) as an impurity to be added to the silicon layer, and thus detailed description is omitted.

Thus, a 77 μm cubic silicon carbide film was obtained on the silicon substrate. Impurities in the silicon carbide grown on the silicon substrate were measured by SIMS (secondary ion mass spectrometry), and it was found that the B concentration in the silicon carbide was uniformly distributed at 2.2 × 10 ¹⁶ / cm ^3. did. The hole concentration in the silicon carbide at room temperature was measured using the Hall effect and found to be 7.5 × 10 ¹⁵ / cm ³ . The resistivity of this silicon carbide was 1.74 Ω-cm. The variation in the impurity concentration was 8.2% both in the plane and in the thickness direction.

  As is apparent from Comparative Example 2, according to the above-described embodiment, a silicon layer is once formed on a substrate, an impurity is added simultaneously with the formation, and then the silicon layer containing the impurity is carbonized. Therefore, as compared with the case where impurities are added simultaneously with the formation of silicon carbide, the impurity concentration becomes three orders of magnitude or more even with the same amount of impurity gas introduced, and the resistivity of silicon carbide can be significantly reduced. It becomes possible.

(Comparative Example 3)
Next, a method for manufacturing silicon carbide and silicon carbide according to Comparative Example 3 will be described with reference to FIG. The method for producing silicon carbide of this comparative example is the same as that of comparative example 1 except that a large number of silicon carbide semiconductors were formed by changing the supply amount (fn) of N ₂ gas in the method for producing silicon carbide of comparative example 1 described above. Therefore, detailed description is omitted.

FIG. 11 is a graph showing the result of observing the electron concentration in a number of silicon carbide semiconductors formed by changing fn. As shown in FIG. 11, the electron concentration tends to increase with fn, but the relationship is not proportional, and the tendency of the electron concentration to increase with fn tends to slow down. Further, the variable range of the electron concentration in the present comparative example is about 1 × 10 ¹³ / cm ³ to 4 × 10 ¹⁶ / cm ^3, which is narrower than that in the above-described embodiment, and is not suitable for manufacturing a semiconductor device. It is enough.

(Comparative Example 4)
Next, a comparative example in which a semiconductor device having a pn junction is formed on a substrate 4 (single-crystal silicon substrate) will be described as a comparative example 4. In this comparative example, the method of Comparative Example 1 is performed for 30 minutes to form an n-type semiconductor on the substrate 4, and then the method of Comparative Example 3 is performed for 30 minutes, so that the n-type semiconductor is formed on the substrate 4. A p-type semiconductor is formed to form a pn junction silicon carbide semiconductor having a thickness of 77 μm on the substrate 4. The film forming conditions are the same as those of Comparative Examples 1 and 2 except for the film forming time.

Next, substrate 4 (single crystal silicon substrate) is removed using a mixed solution of HF and HNO ₃ , and Ni electrodes are deposited on the upper surface side (p type side) and the lower surface side (n type side) of the silicon carbide semiconductor. I do. Next, a conductive wire was bonded to the upper and lower electrodes, and the capacitance of the pn junction was measured while applying a DC voltage. The applied voltage was a direct current of -10 V to +10 V, and the capacity measurement used an AC voltage of 1 MHz (0.2 V). From the change in capacitance with respect to the applied voltage, it was found that the built-in potential of the pn junction formed by this method was 0.92 V, and the impurity concentration gradient of the pn junction was 4.5 × 10 ¹⁸ / cm ^4. Was calculated. Next, when a voltage was applied to the pn junction in the silicon carbide with the upper electrode being on the negative side and the lower electrode being on the positive side, a breakdown phenomenon was observed at 124V.

  As described in detail above, the present invention relates to a silicon carbide manufacturing method for forming a silicon carbide semiconductor by depositing a thin film from a gas phase or a liquid phase on a base, and a silicon layer forming step of forming a silicon layer on the base. An impurity in which at least one element selected from the group consisting of N, B, Al, Ga, In, P, As, Sb, Se, Zn, O, Au, V, Er, Ge, and Fe is added to the silicon layer; And a carbonization step of carbonizing the silicon layer to which the impurity is added to form a silicon carbide layer to which the impurity is added, thereby limiting an impurity source and an impurity concentration. Alternatively, a silicon carbide manufacturing method, a silicon carbide, and a semiconductor device capable of manufacturing with sufficient productivity while performing impurity addition with high controllability without being subject to the depth limitation of the impurity addition range, etc. It is what you are getting.

FIG. 2 is a diagram showing a schematic configuration of a CVD apparatus for performing the silicon carbide manufacturing method according to the first embodiment. 4 is an illustration of a raw material gas supply timing of the silicon carbide production method according to the first embodiment. 4 is an illustration of a raw material gas supply timing of the method for manufacturing silicon carbide according to the second embodiment. 9 is an illustration of a source gas supply timing of the method for manufacturing silicon carbide according to the third embodiment. 11 is an illustration of a raw material gas supply timing of the method for manufacturing silicon carbide according to the fourth embodiment. 13 is an illustration of a source gas supply timing of the method for manufacturing silicon carbide according to the fifth embodiment. 5 is a graph showing the results of observing electron concentrations in a number of silicon carbide films formed by changing ts and fn. 4 is an illustration of a raw material gas supply timing of the silicon carbide production method according to Comparative Example 1. 5 is an illustration of a source gas supply timing of the method for manufacturing silicon carbide according to Comparative Example 2. 9 is an illustration of a raw material gas supply timing of the silicon carbide production method according to Comparative Example 3. 5 is a graph showing a result of observing electron concentrations in a large number of silicon carbide films formed by changing fn. 13 is an illustration of a source gas supply timing of the method for manufacturing silicon carbide according to Comparative Example 4.

Explanation of reference numerals

  DESCRIPTION OF SYMBOLS 1 ... Film-forming chamber, 2 ... Gas introduction pipe, 3 ... Plate, 4 ... Substrate, 5 ... Heating means, 6 ... Exhaust pipe.

Claims (1)

In a silicon carbide manufacturing method of forming a silicon carbide by depositing a thin film from a gas phase on a substrate,
A silicon layer forming step of forming a silicon layer on the substrate,
N, B, Al, Ga, In, P, As, Sb, Se, Zn, O, Au,
An impurity adding step of adding at least one element selected from V, Er, Ge, and Fe as impurities;
A carbonization step of carbonizing the silicon layer to which the impurities are added to form a silicon carbide layer to which the impurities are added;
A method for producing silicon carbide, comprising:

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