JP2003086518A - Cvd method of silicon carbide film, cvd unit and susceptor for cvd unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CVD method and a CVD unit by which impurities taken into a CVD film can be reduced to a level using semiconductor processes. SOLUTION: The CVD method is composed of a step of first vacuum baking during time intervals t1-t6, a step of hydrogen (H2 ) purge during time intervals t6-t8, a step of SiC/Si coating during time intervals t8-t11, a step of vacuum evacuation during time intervals t11-t13, a step of second vacuum baking during time intervals t13-t18, a step of wafer loading during time intervals t18-t20 and a step of epitaxial growing during time intervals t20-t25. In the process of the first vacuum baking, the temperature of a graphite susceptor 2 is raised to about 200 deg.C, and the baking is continued. If the pressure is lowered, the temperature is raised to about 500 deg.C. If the pressure is lowered by the baking at 500 deg.C, the temperature is raised in steps to about 800 deg.C, and further to about 1,000 deg.C. If the pressure is lowered by the baking around 1,000 deg.C, the temperature is raised to about 1,200 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CVD method for a high-purity silicon carbide film, a CVD apparatus, and a susceptor used in this CVD apparatus.

[0002]

2. Description of the Related Art Silicon carbide (hereinafter abbreviated as "SiC") has high thermal conductivity, heat resistance, a wide band gap of 2.2 to 3.3 × 10 V, a high breakdown electric field, and a high saturated electron velocity.
Expected as an electronic device material, Al and G
Both aN and the like have similar lattice constants, and are expected to be used as substrates for devices made of deposited films of these materials.

As a method of forming SiC as a semiconductor material, 6H to 4 obtained by the Acheson method or Rayleigh method
It is general that an epitaxial film is formed by a CVD method using the (0001) Si surface of H SiC. In the [1120] direction from the (0001) Si surface as a substrate by Matsunami etc.
It was found that a high quality film can be grown by using the one with an inclination of about 3 to 10 degrees. In such a method, the growth temperature Tg is generally about 1550 ° C., and the growth rate is generally 20 μm / h or less, which is low.
Furthermore, it has recently been found that high-quality epitaxial growth is possible even when using a wafer inclined in the [1100] direction. In this case, it is necessary to set the growth rate to an extremely small value of 1 to 2 μm / h. There is.

1 × 10 for SiC electronic devices
^It is necessary to control the carrier density of ¹⁵ cm ⁻³ or less, and in order to manufacture a high-performance device, it is necessary to reduce the background impurity density by about 2 digits or more. In order to grow a high-purity epitaxial film in CVD growth of SiC, it is necessary to prevent impurities from being mixed from the graphite susceptor, and it is considered effective to apply graphite to the graphite.

In fact, it has been reported that when the SiC coating film peels off, light emission from a deep level increases. Under normal SiC CVD conditions, the etching of SiC is quite active. Particularly, in the back surface portion of the SiC wafer, the SiC coat film of the susceptor is easily sublimated or etched due to the temperature difference between the susceptor and the SiC wafer on the susceptor, and the SiC coat film is deteriorated in a very short period of time.

A tantalum carbide (TaC) coat film and a pyrographite film have been studied for the purpose of solving the problem of the SiC coat film, but as a technique for lowering the density of nitrogen in the epitaxial film so far. Has not been established.

When SiC is epitaxially grown by the CVD method, the addition efficiency of nitrogen and Al differs depending on the plane orientation of the substrate. In the (0001) C plane, nitrogen is taken in more efficiently than in the (0001) Si plane, and the carrier density is 1 × 10 ¹⁵ cm ^−3.
It is difficult to form the following high-purity epitaxial film. Therefore, conventionally, the (0001) Si surface is mainly used in the SiC device.

In SiC semiconductor devices, the short lifetime of minority carriers has been a problem. Regarding this point, it is reported that the lifetime is shortened when the carrier density is high, and the lifetime is shortened when the compensation ratio is high. However, it is not known at all about what element the high impurity density causes the carrier lifetime to become shorter.

[0009]

As described above, in order to grow a high-purity crystal by the conventional CVD method, it is necessary to coat the graphite susceptor with SiC. However, when such a SiC coating is applied, conventional Si
In the CVD or the like, when a graphite susceptor is used, B and the like are mixed, so that the susceptor is often coated with SiC. However, CVD of SiC performed at high temperature
In, it is difficult to apply this method to practical use. This is because the etching rate of the SiC coat film reaches several to several tens of μm / hr under normal SiC growth conditions, and the SiC coat film deteriorates during CVD of SiC. A thick film of about 200 μm is used as the SiC coat film so that even if the SiC coat film is deteriorated, its effect is reduced. However, even if the SiC coat film is deteriorated by several times of crystal growth, it sometimes deteriorates at one time. It is known to deteriorate during growth. In particular, it is known that this phenomenon is likely to occur in a portion where temperature distribution is likely to occur, such as around the substrate. As described above, in CVD of SiC, S
The etching rate of iC is also high, and the SiC coat film having a thickness of 100 μm or more deteriorates due to the temperature distribution around the substrate. Degradation of the SiC coat film means that SiC
Is sublimated and supplied in the gas phase. Conventionally, little attention has been paid to this point, but as a result of the present inventors' studying this point, the deposition rate of the CVD-grown SiC film is greatly affected by using the SiC coat film, and the SiC coat is used. In that case, it was found that there was a problem in the controllability of the growth rate. This state is shown in FIG.

When the SiC coat film is formed, it is necessary to lower the growth temperature Tg in order to prevent its deterioration. By lowering the growth temperature Tg, the upper limit of the growth rate at which high quality crystal growth is possible becomes small. This is a big problem in producing a high voltage electronic device.
The reason is that if a device having a withstand voltage of several thousand volts is to be produced, the thickness of the epitaxial layer that must undergo crystal growth becomes several tens of μm. Crystal growth rate is 10 μm / h
If only a slow value of r is used, the time required for crystal growth will take several hours, which will greatly increase the cost for producing such a device.
In addition, it is difficult to constantly examine the deterioration of the SiC coat of the susceptor that needs to maintain a high-purity state in the CVD furnace, and there is a problem in that reproducibility is ensured.

In the conventional SiC coat, impurities are CVD.
It is considered to have an effect of preventing inclusion in the growth film, and it was considered that the quality of the CVD film deteriorates when the SiC coat film deteriorates. However, the CVD of SiC is performed under the condition that SiC itself sublimes at a high temperature. Therefore, as described above, the present inventors have found a problem that the coating film of SiC adversely affects the growth rate, which does not occur in CVD of Si or the like. The present inventors further conducted a more detailed study in order to investigate what function the SiC coat film has at high temperatures. Hereinafter, the influence of the SiC coat on the CVD film was examined by examining what kind of impurities are mixed in the CVD film during the deterioration of the SiC coat film.

As described above, in CVD of SiC, Si is
It has been considered that the impurity density increases when the SiC coat film is deteriorated and graphite is produced due to the high etching rate of the C coat film. However, the present inventors have found the following new facts. If the crystal is grown until the SiC coat is peeled off, the density in the crystal becomes higher as the SiC coat film deteriorates depending on the impurity species. In the case of Al or Ti, the concentration of Al or Ti in the CVD film increases as the peeled area of the SiC film increases, and Ti or Al in graphite is the source of Ti or Al in the CVD film. Is suggested. However, in the case of nitrogen, the impurity density in the CVD film becomes highest when the SiC coat film deteriorates and the interface between the SiC coat film and graphite appears on the surface. This state is shown in FIG. Although the reason for this is not clear, it is clear that it is not possible to predict a priori the density of impurities taken into the SiC crystal when the method of forming the SiC coat film, the method of removing it, and the degree of removal are changed. became. In other words, the conventional wisdom that impurities in graphite are taken into the CVD film does not hold for taking nitrogen in SiC. It became clear that it was not known whether the nitrogen contained in the CVD film was due to the SiC coating, graphite, or the method of forming the SiC coating film.

As described above, although there are many results suggesting that impurities are taken in from the susceptor, it has been clarified that the conventional idea cannot be applied to SiC and the countermeasure cannot be clarified.

Under such a circumstance, the present invention uses C of SiC.
In VD growth, a CVD method capable of reducing impurities taken in a CVD film to a level applicable in a semiconductor process, a CVD apparatus used for this, and this CVD
It is intended to provide a susceptor for a device.

Another object of the present invention is to provide a graphite susceptor capable of constantly growing high-purity crystals without a SiC coating film, and a CV using this susceptor.
D method and CVD apparatus.

Still another object of the present invention is to obtain a SiC film which is of good quality and has a long carrier lifetime.
A VD method, a CVD apparatus, and a susceptor for the CVD apparatus.

[0017]

In order to achieve the above-mentioned object, the first feature of the present invention is to:
Step of inserting a graphite susceptor having a nitrogen density of 1 × 10 ¹⁷ cm ^-3 or less; (b) Vacuum baking of the graphite susceptor; (c) Bringing the graphite susceptor to a temperature near room temperature and not exposing the graphite susceptor to the atmosphere In this way, the step of placing the substrate on the graphite susceptor; (d) controlling the interior of the reaction vessel to a depressurized state to heat the graphite susceptor to a growth temperature higher than the baking temperature to form a silicon carbide film on the substrate. The method is a CVD method of a silicon carbide film including a step of performing vapor phase epitaxial growth of. For example, CVD
Before heating, the graphite susceptor is heated to a temperature of 1200 ° C. or higher while maintaining a pressure of 2 mPa or lower, and the wafer is placed on the susceptor without exposing the susceptor to air or a nitrogen-containing gas. The amount of impurities contained in the grown film can be made extremely low.

In the first aspect of the present invention, between the step of vacuum baking and the step of placing the substrate, the graphite susceptor is cooled to a first temperature between the baking temperature and room temperature. Heating the graphite susceptor from a first temperature to a coating temperature higher than the baking temperature, and coating the surface of the graphite susceptor with a coating film of at least one of silicon and silicon carbide at the coating temperature. preferable. The coating temperature may be between 1200 ° C and 1450 ° C. Further, between the coating step and the substrate arranging step, the temperature of the graphite susceptor is lowered from the coating temperature to the second temperature between the baking temperature and room temperature, and the inside of the reaction vessel is controlled to a reduced pressure state. Then, the graphite susceptor is heated to a peeling temperature from the second temperature to remove at least a part of the coated film.

The second feature of the present invention is (a) a step of inserting a graphite susceptor into the reaction vessel;
(B) Vacuum baking the graphite susceptor;
(C) A step of lowering the temperature of the graphite susceptor from the baking temperature used for vacuum baking to a temperature near room temperature; (D) After this temperature lowering, the graphite susceptor is taken out of the reaction vessel and the surface layer of the graphite susceptor is removed. Step; (E) After the step of removing the surface layer,
Placing the substrate on the graphite susceptor; (f)
A CVD method for a silicon carbide film, comprising: controlling a pressure inside the reaction container to heat a graphite susceptor to a growth temperature higher than a baking temperature; and vapor-phase epitaxially growing a silicon carbide film on a substrate. The point is that there is.

The third feature of the present invention is (a) a step of inserting a graphite susceptor into the reaction vessel;
(B) Vacuum baking the graphite susceptor;
(C) A step of lowering the temperature of the graphite susceptor from the baking temperature used for vacuum baking to a temperature near room temperature; (d) heating the graphite susceptor to a coating temperature higher than the baking temperature, and at the coating temperature, Coating the surface with a film made of at least one of silicon and silicon carbide; (e) lowering the temperature of the graphite susceptor from the coating temperature to a temperature near room temperature;
(F) A step of removing the graphite susceptor from the reaction vessel after lowering the temperature to around room temperature and removing the surface layer of the graphite susceptor; (g) After removing the surface layer, place the substrate on the graphite susceptor. Arranging step: (h) controlling the inside of the reaction vessel to a depressurized state
Heating the graphite susceptor to a growth temperature higher than the coating temperature to vapor-phase epitaxially grow a silicon carbide film on the substrate.
The point is that it is a method. The coating temperature in the third feature may be a temperature between 1200 ° C and 1450 ° C.

The "vacuum baking step" in the first to third features of the present invention includes a step of evacuating the inside of the reaction vessel to a depressurized state after the step of inserting the graphite susceptor into the reaction vessel. It is preferable to control the inside of the reaction vessel to a decompressed state to raise the temperature of the graphite susceptor stepwise to the baking temperature and remove the gas containing water and carbon in the graphite susceptor.

The fourth feature of the present invention is (a) a step of placing a substrate on a graphite susceptor having a nitrogen density of 1 × 10 ¹⁷ cm ^-3 or less; (b) inserting a graphite susceptor into a reaction vessel. And (c) controlling the inside of the reaction vessel to a reduced pressure state, heating the graphite susceptor to the growth temperature, and vapor-phase epitaxially growing a silicon carbide film on the substrate. Is the gist.

In the first to fourth features of the present invention, the vapor phase epitaxial growth of the silicon carbide film at the growth temperature is
It is preferable to use a carrier gas having a dew point between -85 ° C and -75 ° C. Further, the substrate is an S having a (0001) C plane.
It is also possible to use an iC substrate.

The fifth feature of the present invention is (a) a reaction vessel;
(B) A gas introduction section for introducing gas into this reaction container;
(C) A vacuum evacuation unit for evacuating the reaction vessel; (D) A plurality of graphite members arranged inside the reaction vessel and having a nitrogen density of 1 × 10 ¹⁷ cm ⁻³ or less; (E) A plurality of graphite members A susceptor, which is fitted in a tubular shape, with a resistive member having a region made of a material having a resistivity higher than that of the graphite member at least in a fitting portion with the graphite member; and (f) in the circumferential direction of the susceptor. A gist of the present invention is a CVD apparatus provided with high-frequency induction heating means for heating a plurality of graphite members by circulating an electric current along it.

The sixth feature of the present invention is that the nitrogen density is 1 × 1.
The gist is that it is a susceptor for a CVD apparatus, which is provided with a graphite member of 0 ¹⁷ cm ⁻³ or less.

The sixth feature of the invention is that the nitrogen density is 1 × 10.
^A resistance that fits between a plurality of graphite members of ¹⁷ cm ^-3 or less and a material having a higher resistivity than the graphite member at least in the fitting portion with the graphite member. A gist of the present invention is a susceptor for a CVD apparatus, which is formed by combining a member with a tubular shape, and circulates an electric current along the circumferential direction of the tubular shape by high frequency induction heating to be heated.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Next, first to eighth embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and the relationship between the thickness and the plane dimension, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, the specific thickness and dimensions should be determined in consideration of the following description. Further, it is needless to say that the drawings include portions having different dimensional relationships and ratios.

(CVD Apparatus) FIG. 1 shows a schematic structure of an LPCVD apparatus used in the CVD method according to the first to eighth embodiments of the present invention. The upstream side flange of the reaction container (reaction tube) 1 made of quartz has a gas introducing pipe 36 that constitutes a gas introducing portion.
Are connected. Through the downstream side flange of the reaction tube 1, the graphite susceptor 2 shown in FIG. 2 and FIG.
Is placed in the reaction tube 1 after being housed in the solid carbon wool heat insulating material 3. An SiC substrate (wafer) 31 is mounted on the graphite susceptor (hereinafter referred to as “graphite susceptor”) 2, as shown in FIGS. 2 and 3. Further, a vacuum pipe 35 is connected to the downstream side flange of the reaction tube 1 so that the inside of the reaction tube 1 can be evacuated to a vacuum or the gas introduced into the reaction tube 1 can be discharged. . The pressure control valve 6 is connected to the exhaust side of the vacuum pipe 35. Further, another vacuum pipe 38 is connected to the exhaust side of the pressure control valve 6, and the exhaust pump system 7 is connected to the exhaust side of the vacuum pipe 38. The exhaust pump system 7 is configured, for example, by connecting a mechanical booster pump and a dry pump in series in order to exhaust the inside of the reaction tube 1. The pressure control valve 6 separates the reaction tube 1 and the exhaust pump system 7 as necessary, and adjusts the exhaust conductance.

A high frequency induction heater (RF coil) 33 is arranged around the reaction vessel (reaction tube) 1. 500 KHz from the RF oscillator 34 to the RF coil 33
By applying a high frequency (RF) of up to 5 MHz,
The graphite susceptor 2 is heated. Therefore,
The SiC substrate (wafer) 31 placed directly on the graphite susceptor 2 is also heated to a predetermined temperature. A doping gas such as TMAl or the like is supplied from the gas introduction piping system with its flow rate controlled by a mass flow controller provided in a tank circuit (not shown). These gases are discharged through the vacuum pipe 35. In FIG. 1, only one gas introduction pipe 36 is shown, but a plurality of gas introduction pipes 36 may be provided to configure the gas introduction unit according to the type of gas.

Further, a plurality of gas pipes are connected to the gas introduction pipe 36 connected to the upstream side flange of the reaction pipe 1 via stop valves 13a, 13b, 13c and 13d. Stop valves 13a, 13b, 13c, 1
3d includes mass flow controllers 12a and 1a, respectively.
2b, 12c and 12g are connected to each other to form a gas introduction part. Further, hydrogen (H ₂ ) is supplied to the gas introduction part from the collective gas supply system 4 via the mass flow controller 12d.
Gas is supplied. Mass flow controller 12a, 1
2b, 12c and 12g have propane (C
₃ H ₈ ) gas cylinder 11a, monosilane (SiH ₄ ) gas cylinder 11b, nitrogen (N ₂ ) gas cylinder 11c,
A bubbler 14 of trimethylaluminum (TMAl) is connected. The TMAl bubbler 14 is kept at a constant temperature by a constant temperature bath to keep the vapor pressure at a predetermined value. Mass flow controller 12a, 12b, 12
c and 12g are stop valves 14a and 14g, respectively.
It is connected to a purge line (bypass line) 37 via b, 14c and 14d. The downstream side of the purge line 37 can also be evacuated via the pressure control valve 6. T
The MAL bubbler 14 has a mass flow controller 1
Hydrogen (H ₂ ) gas from the collective gas supply system 4 is introduced through 2f, and part of the mass flow controller 12h
It is discharged to the purge line 37 via. The pressure on the output side of the TMAl bubbler 14 is monitored by a pressure gauge 15. The pressure inside the reaction tube 1 is measured by a pressure gauge 5 connected to the reaction tube 1. As the pressure gauges 5 and 15,
Capacitance manometer or Pirani gauge can be used. A pressure control system (not shown) is connected to the pressure control valve 6, and the conductance of the pressure control valve 6 is adjusted based on the difference between the pressure measurement value measured by the pressure gauge 5 and the set pressure value. Reaches the set value and is maintained at this set value.

The temperature inside the reaction vessel (reaction tube) 1 is measured by a radiation thermometer (pyrometer) 8 and fed back to the RF oscillator 34 to control the temperature. Reduced pressure CV
To form a SiC film by the D method, the inside of the reaction tube 1 is evacuated to a certain reduced pressure, the stop valves 14a and 14b are closed, and the stop valves 13a and 13b are opened, so that monosilane (SiH _{4) is used} as a silicon source. ) gas is introduced into the reaction tube 1 through a mass flow controller 12b, propane as a carbon source (C ₃ H ₈₎ gas is introduced into the reaction tube 1 through a mass flow controller 12a. These gases chemically react inside the high-temperature reaction tube 1 of about 1400 ° C. to 1800 ° C. to form a SiC film on the SiC substrate 31. Mass flow controller 12c
Controls the flow rate of nitrogen (N ₂ ) gas as an n-type dopant. The mass flow controller 12g controls the flow rate of TMAl gas as a p-type dopant.

As shown in FIG. 2A, the graphite susceptor 2 is divided into four parts: an upper graphite 2a, a lower graphite 2b, side wall graphites (side wall members) 2c and 2d. A SiC substrate (wafer) 31 is placed on the lower graphite 2b. The graphite susceptor 2 has a size that can be housed in the through hole 3h provided in the solid carbon wool heat insulating material 3 shown in FIG. 2 (b). Then, as shown in FIG. 3, the graphite susceptor 2 is housed in the through hole 3h of the solid carbon wool heat insulating material 3 and placed inside the reaction vessel (reaction tube) 1 shown in FIG.

FIG. 4 shows a process sequence of CVD growth using the LPCVD apparatus shown in FIG. Note that in the following description of the CVD methods according to the first to eighth embodiments of the present invention, a case where some steps are omitted in the process sequence shown in FIG. 4 is included. I want to be done. The process sequence of the CVD growth shown in FIG. 4 is the first vacuum bake at time t1 to t6, and the time t6 to t8.
Hydrogen (H ₂ ) purge, SiC / S from time t8 to t11
i coat, evacuation at times t11 to t13, time t13
.About.t18 second vacuum bake, times t18 to t20 wafer loading, and times t20 to t25 epi growth stages.

(A) First vacuum bake from time t1 to t6:
At times t1 to t6, the graphite susceptor 2 used for epitaxial growth is replaced with the reaction container (reaction tube) 1
The exhaust pump system 7 is evacuated to gradually raise the processing temperature until the pressure inside the chamber becomes 2 mPa or less. First, time t1
From t6 to t6, the temperature of the graphite susceptor 2 is raised to about 200 ° C. and maintained at a constant temperature of about 200 ° C. for 0.5 to 2 hours. Since the pressure rises in two stages mainly due to the separation of water by baking at about 200 ° C., the pressure inside the reaction tube 1 is maintained so as to be 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure decreases, so at time t2, the temperature rises to about 500 ° C. Even at times t2 to t3, the pressure inside the reaction tube 1 is evacuated by the exhaust pump system 7 so as not to exceed 2 mPa and maintained at a constant temperature of about 500 ° C. for 0.5 to 2 hours. Mainly carbonic acid (CO
₂ ) By the release of gas containing carbon (C) such as gas,
Although the pressure rises, the pressure inside the reaction tube 1 is 2 mPa
Maintain pressure so that: Further, if the vacuum exhaust is continued, the pressure decreases, so at time t3, 800
Raise the temperature to about ℃. Even from time t3 to time t4, the pressure inside the reaction tube 1 is evacuated by the exhaust pump system 7 so as not to exceed 2 mPa and maintained at a constant temperature of about 800 ° C. for 0.5 to 2 hours. By baking at about 800 ° C., the pressure rises mainly due to the release of the hydrocarbon gas, but the pressure is maintained so that the pressure inside the reaction tube 1 becomes 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure drops, so at time t4, 1000 ° C.
Raise the temperature to a certain degree. Reaction tube 1 also at times t4 to t5
The gas is exhausted by the exhaust pump system 7 so that the internal pressure does not exceed 2 mPa and maintained at a constant temperature of about 1000 ° C. for 0.5 to 2 hours. By baking at about 1000 ° C., the pressure rises mainly due to the release of hydrocarbon-based gas, but the pressure is maintained so that the pressure inside the reaction tube 1 becomes 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure decreases, so at time t5, the temperature is raised to about 1200 ° C. which is the baking temperature. At time t5 to t6, the pressure inside the reaction tube 1 is exhausted by the exhaust pump system 7 so that the pressure does not exceed 2 mPa, and the time is about 0.5 hours.
Maintain a constant temperature (baking temperature) of about 1200 ° C. By baking at about 1200 ° C., etching of SiC is clearly recognized. Further, if the vacuum exhaust is continued, the pressure is lowered, so that at time t6, the temperature reduction is started.

(B) Hydrogen (H ₂ ) purge from time t6 to t8: At time t7, the temperature of the graphite susceptor 2 is 5
When the temperature has dropped to the first temperature of about 00 ° C., hydrogen (H ₂ ) gas is introduced into the reaction tube 1, and the inside of the reaction tube 1 is purged with hydrogen (H ₂ ) gas.

(C) SiC / Si coating from time t8 to t11: When hydrogen (H ₂ ) purging for a certain period of time is completed, the temperature of the graphite susceptor 2 is set to 1 at time t8.
The temperature is raised from the first temperature until it reaches about 200 ° C. Time t
9, the temperature of the graphite susceptor 2 is 120
When the temperature reaches approximately 0 ° C., monosilane (SiH ₄ ) gas is passed through the mass flow controller 12b, and propane (C
₃ H ₈ ) gas through the mass flow controller 12a,
It is introduced into the reaction tube 1. By introducing monosilane gas and propane gas into the reaction tube 1 at a temperature of 1200 ° C. or higher, silicon (S) is formed on the surface of the graphite susceptor 2.
i) and SiC start to deposit. Further, the temperature is raised until the coating temperature reaches about 1400 ° C. Time t9-t
The temperature rising time of 10 is about 20 minutes. The deposition rate of SiC at 1400 ° C (coating temperature) is about 7 μm.
/ Hr, and the coating of at least one of Si and SiC starts to be deposited on the surface of the graphite susceptor 2 for about 1 hour (time t9 to t11). At time t11, the stop valves 13a and 13b are closed, the introduction of monosilane gas and propane gas is stopped, and the temperature reduction from the coating temperature is started. Propane gas cylinder 11
After shutting off a and the monosilane gas cylinder 11b, the monosilane gas and propane gas remaining in the pipe are exhausted from the purge line 37 by opening the stop valves 14a and 14b.

(D) Vacuum evacuation from time t11 to t13: After the temperature starts to be decreased at time t11, when the temperature of the graphite susceptor 2 drops to the second temperature of about 100 ° C., the reaction tube 1
The inside of is evacuated. That is, at times t11 to t13, the exhaust pump system 7 exhausts the pressure inside the reaction tube 1 so as not to exceed 2 mPa and maintains the temperature at a constant temperature of about 100 ° C.

(E) Second vacuum bake from time t13 to t18: During time t13 to t14, the temperature of the graphite susceptor 2 is increased from the second temperature to about 200 ° C.,
Maintain a constant temperature of about 200 ° C. for 0.5 to 2 hours.
Although the pressure rises by baking at about 200 ° C., the pressure is maintained so that the pressure inside the reaction tube 1 becomes 2 mPa or less. Further, when the vacuum exhaust is continued, the pressure is lowered, so that the temperature is raised to about 500 ° C. at time t14. Also from time t14 to t15, the pressure inside the reaction tube 1 is evacuated by the exhaust pump system 7 so as not to exceed 2 mPa and maintained at a constant temperature of about 500 ° C. for 0.5 to 2 hours. Although the pressure rises by baking at about 500 ° C., the pressure is maintained so that the pressure inside the reaction tube 1 becomes 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure decreases, so at time t15, the temperature rises to about 800 ° C. Even from time t15 to t16, the pressure inside the reaction tube 1 is evacuated by the exhaust pump system 7 so as not to exceed 2 mPa and maintained at a constant temperature of about 800 ° C. for 0.5 to 2 hours. Although the pressure rises by baking at about 800 ° C., the pressure is maintained so that the pressure inside the reaction tube 1 becomes 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure drops, so at time t16, 1000
Raise the temperature to about ℃. Even at time t16 to t17, exhaust gas is exhausted by the exhaust pump system 7 so that the pressure inside the reaction tube 1 does not exceed 2 mPa, and the temperature is 1000 ° C. for 0.5 to 2 hours.
Maintain a constant temperature. Although the pressure rises by baking at about 1000 ° C., the pressure is maintained so that the pressure inside the reaction tube 1 becomes 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure decreases, so at time t17, the temperature rises to a peeling temperature of about 1200 ° C. Time t1
Even from 7 to t18, the pressure inside the reaction tube 1 is 2 mPa.
Exhaust with the exhaust pump system 7 so as not to become the above, and
It is maintained at a constant temperature (peeling temperature) of about 1200 ° C. for about 5 hours. The coating (coating film) made of at least one of Si and SiC is removed by baking at a peeling temperature of about 1200 ° C. Further, if the vacuum exhaust is continued, the pressure is lowered, so that the temperature is started to be lowered at the time t18.

(F) Wafer loading from time t18 to t20: After the temperature starts to be decreased at time t18, the inside of the reaction tube 1 is evacuated until the temperature of the graphite susceptor 2 drops to near room temperature (time t19). Then, at time t19, the downstream side flange of the reaction tube 1 is opened and taken out into a glove box in a hydrogen atmosphere or a rare gas atmosphere such as helium (He). Then, the SiC substrate (wafer) is attached to the graphite susceptor 2 in the glove box.
31 is mounted, the graphite susceptor 2 is housed inside the reaction tube 1 again, and the exhaust pump system 7 is used to perform vacuum exhaust. Alternatively, although omitted in FIG. 1, the reaction tube 1
A vacuum preliminary chamber is connected to the downstream side flange of the substrate via a substrate transfer gate valve, the inside of the vacuum preliminary chamber is set to hydrogen or a rare gas atmosphere, and the graphite susceptor 2 is covered with SiC.
A substrate (wafer) 31 may be mounted. Further, a second vacuum preliminary chamber connected to the vacuum preliminary chamber (first vacuum preliminary chamber) is prepared, and the graphite susceptor 2 is made to have SiC in vacuum by using a loader robot arm.
Processing for mounting the substrate 31 may be performed. Then, the vacuum preliminary chamber (first vacuum preliminary chamber) is evacuated, the substrate transfer gate valve is opened, and the vacuum preliminary chamber (first vacuum preliminary chamber) is opened.
It is also possible to transfer the SiC substrate 31 set in step 1 into the reaction tube 1 by a loader robot arm. In this case, thereafter, the loader robot arm is returned and the substrate transfer gate valve is closed. In this way
The graphite susceptor 2 may be returned to the inside of the reaction tube 1 without being exposed to the atmosphere. From time t18
At the wafer loading stage of t20, after the graphite susceptor 2 is returned to the inside of the reaction tube 1, the exhaust pump system 7 is operated until the pressure inside the reaction tube 1 becomes 0.1 mPa or less.
Exhaust with.

(G) Epi growth from time t20 to t25: If the pressure inside the reaction tube 1 becomes 0.1 mPa or less, the temperature of the graphite susceptor 2 is increased to 2 at time t20.
The temperature is raised to about 00 ° C. From time t20 to t21, the temperature of the graphite susceptor 2 is maintained at a constant temperature of about 200 ° C. for 0.5 hours or more. Although the pressure rises by baking at about 200 ° C., the pressure is maintained so that the pressure inside the reaction tube 1 becomes 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure decreases, so at time t21, the temperature rises to about 500 ° C. Time t
Even at 21 to t22, the pressure inside the reaction tube 1 is 2 mP.
Exhaust with the exhaust pump system 7 so that it does not exceed a,
Maintain a constant temperature of about 500 ° C. for 0.5 hours or more.
The pressure rises due to baking at about 500 ℃,
The pressure is maintained so that the pressure inside the reaction tube 1 is 2 mPa or less. Further, if the vacuum exhaust is continued, the pressure decreases, so at time t22, the mass flow controller 1
Hydrogen (H ₂ ) gas is supplied into the reaction tube 1 via 2d, and the temperature is raised to 1400 ° C. At time t23,
When the temperature of the graphite susceptor 2 reaches about 1400 ° C., propane (C ₃ H ₈ ) gas is introduced into the reaction tube 1 via the mass flow controller 12a. Furthermore, 140
One minute after reaching 0 ° C. (time t24), the graphite susceptor 2 is grown at a growth temperature Tg of, for example, 1500 to 1800.
Heat up to ℃. Three minutes after reaching the growth temperature Tg,
Monosilane (SiH ₄ ) gas is introduced into the reaction tube 1 via the mass flow controller 12b to start the growth of SiC. When the desired film thickness is obtained, at time t25,
The stop valve 13b is closed to stop the introduction of monosilane gas. 0.5 minutes later, the stop valve 13a
Is closed, the introduction of propane gas is stopped, and at the same time the temperature is lowered. After shutting off the propane gas cylinder 11a and the monosilane gas cylinder 11b, the monosilane gas and propane gas remaining in the pipe are stopped by the stop valve 1
The air is exhausted from the purge line 37 by opening 4a and 14b.

(First Embodiment) First, a method of manufacturing a semiconductor device (Schottky diode) using the CVD method according to the first embodiment of the present invention will be described.

(A) As shown in FIG. 16 (a), first,
A purity n-SiC epilayer 52 is deposited on the SiC substrate 51 by the LPCVD method using the LPCVD apparatus shown in FIG. In the CVD method according to the first embodiment of the present invention, at the time t during the process sequence shown in FIG.
1st-t6 1st vacuum bake, time t6-t8 hydrogen (H
₂ ) Purge, SiC / Si coat from time t8 to t11,
The steps of vacuum evacuation at times t11 to t13 and the second vacuum baking at times t13 to t18 are omitted, and only the step of epi growth at times t20 to t25 is performed. The conditions of the CVD are as follows: the growth temperature Tg is 1600 ° C., the growth pressure is 20 kPa, the SiH ₄ supply flow rate is 6.67 sccm, and the C ₃ H ₈ supply flow rate is 3.
33 sccm, the supply flow rate of N _{2 as} a dopant material is 0.1
2 sccm, the supply flow rate of hydrogen as carrier gas is 40
It is 000 sccm. As a result, the carrier density is 5 ×
The high-purity n-SiC epilayer 52 of 10 ¹⁵ cm ^-3 is epitaxially grown.

(B) Next, as shown in FIG.
A back surface metal 63 is formed on the back surface of the SiC substrate 51 by a vacuum deposition method,
Alternatively, it is deposited by a sputtering method. Further, sintering (heat treatment) is performed, and the SiC substrate 51 and the back surface metal 63 are
Lower the contact resistance with.

(C) Next, as shown in FIG.
A Schottky diode is completed by depositing a Schottky metal 62 such as i by a vacuum evaporation method or a sputtering method.

The n-SiC epilayer 5 having a thickness of 10 μm
2 is deposited by LPCVD, and then the n-SiC epilayer 5
The result of having measured the surface of No. 2 by SIMS is shown in FIG. FIG. 7A shows a case where a plurality of graphite susceptors 2 having different nitrogen densities are prepared, and the nitrogen density in the growth film and the nitrogen in the graphite susceptors obtained by LPCVD growth when the plurality of graphite susceptors 2 are used. The relationship with the density is shown. If the nitrogen density in the graphite susceptor 2 is 1 × 10 ¹⁷ cm ⁻³ or less, the nitrogen density in the growth film derived from the graphite susceptor 2 is 1 × 10 ¹⁴ cm 2.
cm ^-3 or less. This is 3% or less with respect to the control impurity density of the high-purity n-SiC epilayer 52. FIG. 16 (c)
In the Schottky diode shown in, since 70% or more of the forward resistance is the running resistance of the high-purity n-SiC epi layer 52,
According to the CVD method according to the first embodiment of the present invention,
The variation in the element resistance of the Schottky diode can be kept within ± several percent within the design margin of a normal Si-based semiconductor element.

Next, a plurality of graphite susceptors 2 having different aluminum (Al) densities are prepared, and the plurality of graphite susceptors 2 are used to make n-thickness of 7 μm.
After depositing the SiC epi layer 52 by the LPCVD method, the n-
The result of measuring the surface of the SiC epi layer 52 by SIMS is shown in FIG. The density of nitrogen is controlled to 1 × 10 ¹⁶ cm ^-3 . Regarding the density of Al, it was found that when the SiC coating is performed, the Al density taken into the CVD film becomes high even if the Al density in the graphite susceptor used for the graphite susceptor 2 is the same. Although the reason for this is not clear, the Al density in the CVD film is also high corresponding to the Al density in the graphite susceptor as the base material. From this, it is presumed that Al, which originally existed in the graphite susceptor, assists in moving into the CVD film when the SiC coated film sublimes.

As shown in FIG. 7B, the ratio of the Al density in the graphite susceptor 2 to the Al density measured by SIMS in the grown film is 3: 1 when there is no SiC coating. Therefore, Al in the graphite susceptor 2
If the density is set to 3 × 10 ¹⁴ cm ^-3 or less, high-purity n-SiC
The Al density in the epi layer 52 is 1 × 10 ¹⁴ cm ⁻³ or less. In this case, the control impurity density in the grown film is 1 × 10 ¹⁶ c
Since it is m ⁻³ , the compensation ratio is 0.01. That is, the compensation ratio 0
The change in mobility is a few percent compared to the design value, and the resistance rise of the entire device is about 1%, which can be suppressed to a practical level. Here, under the same conditions, the Al density is 1 × 10 ¹⁶ cm ^−3.
In the case of using the graphite susceptor 2 of the ordinary level, the element resistance is several percent or more higher than the design value, and the characteristics are extremely unsatisfactory as a Schottky diode.

Next, a plurality of graphite susceptors 2 having different boron (B) densities are prepared, and an n-SiC epilayer 52 having a thickness of 7 μm is deposited by the LPCVD method using the plurality of graphite susceptors 2. 7C shows the result of measurement of the surface of the n-SiC epilayer 52 by SIMS.
Shown in. The density of nitrogen is controlled to 1 × 10 ¹⁶ cm ^-3 .

As shown in FIG. 7C, it can be seen that the impurity density in the grown film drops sharply as the B density in the graphite susceptor 2 decreases. If the B density in the graphite susceptor 2 is set to 1 × 10 ¹⁵ cm ^-3 or less, n-
It can be seen that the B density in the SiC epi layer 52 is 1 × 10 ¹⁴ cm ⁻³ or less. In this case, since the control impurity density in the n-SiC epilayer 52 is 1 × 10 ¹⁶ cm ⁻³ , the compensation ratio is 1%.
The change in mobility is within a few percent, and the resistance increase of the entire device is within a few percent, which is suppressed to a practical level.
Also, 4H- formed by using the SiC film growth method of the present invention.
When the mobility of the SiC film was measured by the Hall measurement method, a good value of 1100 cm ² / v · s was obtained at room temperature. When measured at low temperature, it was 350 at 55K.
A value of 00 cm ² / v / s, which was not obtained in the past, was obtained. In the corresponding conventional example, the value of 25000 cm ² / v / s is the highest value. The fact that a large mobility was obtained at a low temperature as compared with the previously reported example indicates that the impurity density in the crystal is low, and the crystal growth method of the present invention reduces p-type impurities. Indicates that it is extremely effective.

(Second Embodiment) The second embodiment of the present invention will be described below.
The CVD method according to the embodiment will be described with reference to the schematic sectional view of the semiconductor device shown in FIG.

(A) As shown in FIG. 17 (a), first,
A purity n-SiC epilayer 52 is deposited on the SiC substrate 51 by the LPCVD method using the LPCVD apparatus shown in FIG. In the CVD method according to the second embodiment of the present invention, at the time t during the process sequence shown in FIG.
1st-t6 1st vacuum bake, time t6-t8 hydrogen (H
₂ ) Purge, SiC / Si coat from time t8 to t11,
The steps of vacuum evacuation at times t11 to t13 and the second vacuum baking at times t13 to t18 are omitted, and only the step of epi growth at times t20 to t25 is performed. The conditions of the CVD are as follows: the growth temperature Tg is 1600 ° C., the growth pressure is 20 kPa, the SiH ₄ supply flow rate is 6.67 sccm, and the C ₃ H ₈ supply flow rate is 3.
33 sccm, the supply flow rate of N _{2 as} a dopant material is 0.1
2 sccm, the supply flow rate of hydrogen as carrier gas is 40
It is 000 sccm. As a result, the carrier density is 5 ×
The high-purity n-SiC epilayer 52 of 10 ¹⁵ cm ^-3 is epitaxially grown.

(B) Further, as shown in FIG.
On the n-SiC epi layer 52, the LPCVD device shown in FIG.
Of p-SiC epilayer 53 is deposited by LPCVD using
To do. The CVD condition is that the growth temperature Tg is 1600 ° C.
Long pressure 20kPa, SiH _FourSupply flow rate of 6.67s
ccm, C₃H₈Supply flow rate of 3.33 sccm, dopa
The supply flow rate of TMAl, which is the raw material for the component, is 0.01 sccm,
Supply flow rate of hydrogen as carrier gas is 40,000 sccm
Is.

(C) Next, as shown in FIG.
The ohmic metal is deposited by the vacuum evaporation method or the sputtering method to form the anode electrode 64. Then, as shown in FIG. 17C, an ohmic metal is deposited on the back surface of the SiC substrate 51 by a vacuum vapor deposition method or a sputtering method to form a cathode electrode 65. Furthermore,
Sintering (heat treatment) is performed to form the p-SiC epi layer 53.
A pn junction diode is completed by reducing the contact resistance between the anode electrode 64 and the anode electrode 64, and the contact resistance between the SiC substrate 51 and the cathode electrode 65.

Next, a plurality of graphite susceptors 2 having different titanium (Ti) densities are prepared, and using the plurality of graphite susceptors 2, n-Si having a thickness of 10 μm is prepared.
C epi layer 52 and p-SiC epi layer 53 having a thickness of 2 μm
Of the n-SiC epilayer 52 after the LPCVD
The result of having measured the surface of this by SIMS is shown in FIG.8 (a).
The density of nitrogen is controlled to 1 × 10 ¹⁴ cm ^-3 . p-S
Al of 5 × 10 ¹⁸ cm ⁻³ is added to the iC epi layer 53. Here, the CVD conditions for epitaxially growing the high-purity n-SiC epi layer 52 are the same as those in the first embodiment. As shown in FIG. 8A, if the Ti density in the graphite susceptor 2 is 2 × 10 ¹⁴ cm ⁻³ or less,
It can be seen that the density of Ti in the growth film can be set to 1 × 10 ¹³ cm ⁻³ or less. That is, under the above growth conditions, the ratio of the Ti density in the graphite susceptor 2 to the impurity density in the growth film is about 1:20, and the Ti density of 24 in the high-purity n-SiC epilayer 52 is 1 × 10 ¹³ cm ^-3 or less.

FIG. 9A shows the relationship between the Ti density in the grown film and the carrier lifetime. It can be seen that the lifetime is different for the graphite susceptor 2 with and without the SiC coat, and with the SiC coat, the lifetime becomes longer. In either case with or without the SiC coat, the lifetime becomes longer as the Ti density in the growth film decreases. However, SiC
It can be seen that, in the case where there is no coating, a Ti value of 1 × 10 ¹³ cm ⁻³ or less can provide a lifetime value of 1 μs or more, which is indispensable for manufacturing a normal bipolar device.

Further, C according to the second embodiment of the present invention
In the pn junction diode formed by the VD method, the resistance value in the on state is almost equal to the band gap of SiC, and it is determined that the running resistance is hardly generated.

Next, a plurality of graphite susceptors 2 having different vanadium (V) densities are prepared, and the plurality of graphite susceptors 2 are used to make n-thickness of 10 μm.
FIG. 8B shows the result of measuring the surface of the n-SiC epi layer 52 by SIMS after depositing the SiC epi layer 52 and the p-SiC epi layer 53 having a thickness of 2 μm by the LPCVD method. The density of nitrogen is controlled to 1 × 10 ¹⁴ cm ^-3 . The conditions for epitaxially growing the high-purity n-SiC epitaxial layer 52 are the same as those in the first embodiment. Figure 8
As shown in (b), V in the graphite susceptor 2
If the density is 1 × 10 ¹⁴ cm ^-3 or less, high-purity n-SiC
It can be seen that the V density in the epi layer 52 is 3 × 10 ¹⁰ cm ⁻³ or less.

As shown in FIG. 9B, the lifetime of carriers increases as the V density decreases, and the V density becomes 3 ×.
It can be seen that the lifetime exceeds 1 μs in the case of 10 ¹⁰ cm ⁻³ . In the pn junction diode of the present invention, the resistance value in the ON state is substantially equal to the band gap of SiC, and it is determined that running resistance is hardly generated.

(Third Embodiment) A CVD method according to a third embodiment of the present invention will be described below. First and second
In the CVD method according to the embodiment, the first vacuum bake at times t1 to t6, the hydrogen (H ₂ ) purge at times t6 to t8, and the SiC at times t8 to t11 in the process sequence shown in FIG. / Si coat, time t11 to t1
The method of performing the vacuum evacuation of 3 and the second vacuum baking step of times t13 to t18 and performing only the epi growth step of times t20 to t25 was carried out. CV according to the third embodiment
In the D method, the Si vacuum corresponding to the first vacuum bake at times t1 to t6 in the process sequence shown in FIG.
Before growing the C growth film, the graphite susceptor 2 is baked in vacuum.

When the first vacuum bake is performed, the pressure inside the reaction tube 1 should not exceed 2 mPa, as described above. As shown in FIG. 4, while maintaining the internal pressure of 2 mPa or less, the treatment temperature is gradually raised through five stages, and finally vacuum baking is performed to a baking temperature of about 1230 ° C.

In order to form the graphite susceptor 2 with good controllability, the graphite susceptor 2 is shown in FIG.
As shown in (a), the upper graphite 2a, the lower graphite 2b, and the side wall graphites (side wall members) 2c and 2d are divided into four parts. When the graphite susceptor 2 is divided into four, when the graphite susceptor 2 is heated by RF, electric discharge occurs in a vacuum, and there arises a problem that the vacuum baking cannot be performed. In the CVD method according to the third embodiment of the present invention, when two side wall graphites (side wall members) 2c and 2d apart from the inner wafer 31 of the graphite susceptor 2 are coated with SiC and heated, discharge occurs. Did not happen. This is because the high resistance portion is formed in a part of the graphite susceptor 2, so that the current flows in each part and the concentration of the current in the contact part between the parts is prevented.

In the CVD method according to the third embodiment of the present invention, after performing the first vacuum bake in this way, the wafer 31 is loaded and the CVD is performed without exposing the graphite susceptor 2 to the air. went.
CVD temperature is 1550 ° C., growth pressure is 20 kPa, S
iH ₄ is 6.67 sccm, C ₃ H ₈ is 3.33 sccm
Is. When the CVD film is grown after the first vacuum baking of the graphite susceptor 2 as described above, a film having a purity of 5 × 10 ¹⁴ cm ⁻³ or less is obtained.

When the Schottky diode of the first embodiment is formed after baking the graphite susceptor 2 using the same method, a high-purity n-SiC film 52 is formed.
The impurity density of can be controlled with a control accuracy of 10%. On the other hand, when the graphite susceptor 2 is not subjected to the first vacuum bake, the impurity density in the growth film is about 1 × 10 ¹⁵ cm ⁻³ when no impurities are intentionally added. When forming the Schottky diode of the first embodiment,
The impurity density of the high-purity n-SiC film 52 includes an error of about 20%, and practical control accuracy cannot be obtained. If the first vacuum bake is performed under the condition that the pressure is increased to 2 mPa or more, the entire CVD apparatus will be contaminated due to the sudden degassing from the graphite susceptor 2, which is not preferable. Further, the impurity density of the actually grown growth film is about 8 × 10 ¹⁴ cm ⁻³ , and a sufficient baking effect cannot be obtained.

In the third embodiment, the wafer 31
For the lower graphite 2b in the portion close to, a solid graphite material was used. When the lower graphite 2b near the wafer 31 was also coated with SiC, it became clear that SiC was deposited on a part of the wafer 31 before the growth and uniform growth could not be performed with good controllability. It is not preferable to coat the lower graphite 2b with SiC.

(Fourth Embodiment) The fourth embodiment of the present invention will be described below.
The CVD method according to the embodiment will be described. Prior to growing the SiC growth film, the graphite susceptor 2 was
The first vacuum bake is performed under the same conditions as in the above embodiment. In the CVD method according to the fourth embodiment of the present invention, from time t6 of the process sequence of the CVD growth shown in FIG.
After hydrogen (H ₂ ) purge at t8, SiC / Si coating is performed at times t8 to t11.

That is, the flow rate of hydrogen (H ₂ ) gas is 4,000.
The graphite susceptor 2 is heated in hydrogen to 500 ° C. to 1200 ° C. while being supplied at 0 sccm. Furthermore, time t
9, SiH ₄ is 20 sccm and C ₃ H ₈ is 3.3.
Heating temperature from 1200 ℃ to 140 ℃ while supplying 3sccm
Raise to 0 ° C. The temperature rising time from time t9 to t10 is
It takes about 20 minutes. The deposition rate of SiC at the coating temperature of 1400 ° C. is about 7 μm / hr, and the time t
A coating of at least one of Si and SiC is deposited on the surface of the graphite susceptor 2 to a thickness of 5 to 15 μm for about 1 hour from 9 to t11.

In the CVD method according to the fourth embodiment of the present invention, the graphite susceptor 2 is operated by this operation.
A coating film of Si and SiC is deposited on the surface of the. After performing such processing, the temperature is lowered from the coating temperature to near room temperature, and the wafer 31 is loaded and CVD is performed without exposing the graphite susceptor 2 to air. The CVD temperature is 1550 ° C., the growth pressure is 20 kPa, SiH ₄ is 6.67 sccm, and C ₃ H ₈ is 3.33 sccm.

As described above, in the CVD growth process sequence shown in FIG. 4, the first vacuum bake at times t1 to t6, the hydrogen (H ₂ ) purge at times t6 to t8, and the time t8.
After the treatment of SiC / Si coat from ~ t11, C
When the VD film is grown, a film having a purity of 5 × 10 ¹³ cm ⁻³ or less is obtained.

When the graphite susceptor 2 is subjected to the first vacuum baking and the SiC / Si coating by using the CVD method according to the fourth embodiment of the present invention, the Schottky diode of the first embodiment is manufactured. , High purity n-
The impurity density of the SiC film 52 can be controlled within a control accuracy of several percent.

(Fifth Embodiment) In the CVD method according to the fifth embodiment of the present invention, the CVD shown in FIG.
First vacuum bake from time t1 to t6, hydrogen (H ₂ ) purge from time t6 to t8, SiC / Si coat from time t8 to t11, time t11 to t1 in the growth process sequence.
3 vacuum evacuation, second vacuum bake from time t13 to t18,
Wafer loading from time t18 to t20 and time t20 to.
Description will be made regarding the case where all of the respective stages of the epi growth of t25 are carried out.

That is, before growing the SiC growth film, the graphite susceptor 2 is processed under the conditions of the fourth embodiment. Then, while maintaining the pressure inside the reaction tube 1 at 2 mPa or less, as shown in FIG. 4, the treatment temperature is gradually increased in five stages, and finally, at the peeling temperature of 1230 ° C., the second vacuum is applied. Bake. By performing the operation of the second vacuum bake at this peeling temperature, a part of the coating film (coating film) made of at least one of Si and SiC deposited on the surface of the graphite susceptor 2 under the treatment of the conditions of the fourth embodiment. Was removed. Such time t1
After performing the second vacuum baking process of 3 to t18, at time t18 to t20, the wafer 31 is loaded and CVD is performed without exposing the graphite susceptor 2 to air.

The temperature of CVD is 1550 ° C., the pressure inside the reaction tube 1 during growth is 20 kPa, and the flow rate of SiH ₄ is 6.
The flow rate of 67 sccm and C ₃ H ₈ is 3.33 sccm. Thus, the first vacuum bake, the hydrogen (H ₂ ) purge, the Si in the CVD growth process sequence shown in FIG.
After performing all the steps of C / Si coating, vacuum evacuation, and second vacuum baking, when a CVD film is grown, CVD
A film having a purity in which the impurity density in the film is 2 × 10 ¹⁴ cm ⁻³ or less is obtained. Compared with the method for treating the graphite susceptor 2 of the fourth embodiment, the impurity density in the growth film is slightly higher, but this treatment makes it difficult to change the state of the coating film. Then, once the treatment is performed, the reproducibility is improved, and a film having the same degree of purity can be obtained with good reproducibility.

Using the CVD method according to the fifth embodiment of the present invention, the whole process sequence of the CVD growth shown in FIG. 4 is carried out to process the graphite susceptor 2, and then the first embodiment is carried out. The Schottky diode of the first embodiment is formed, and the impurity density is measured by CV measurement. The impurity density of the high-purity n-SiC film 52 with good reproducibility is 5% in control accuracy.
It can be controlled within.

(Sixth Embodiment) In the CVD method according to the sixth embodiment of the present invention, the graphite susceptor 2 is subjected to the first vacuum bake processing described in the third embodiment. After the graphite susceptor 2
5 to 20 μm, for example, 10 μm by grinding and removing the surface of
After that, a CVD growth film is formed under the same conditions as in the first embodiment. Alternatively, after performing the first vacuum bake and the treatment of SiC / Si coating described in the fourth embodiment, the surface of the graphite susceptor 2 is 5 to 20 μm,
For example, it is ground and removed by 10 μm, and then a CVD growth film is formed under the same conditions as in the first embodiment. Furthermore,
The first vacuum bake described in the fifth embodiment, SiC /
After the Si coating and the second vacuum baking, the surface of the graphite susceptor 2 is 5 to 20 μm, for example,
After grinding and removing by 10 μm, a CVD growth film is formed under the same conditions as in the first embodiment.

As a result, the impurity density is 1 × 10 ¹⁴ cm ^-3.
The following CVD film is obtained. This is the first vacuum bake, S
When the surface of the graphite susceptor 2 is removed because the surface of the graphite susceptor 2 is destroyed by the treatment of the iC / Si coating and the second vacuum bake and the amount of impurities accumulated on the surface is increased, the graphite susceptor 2 is removed. This is because the amount of impurities released from the can be reduced.

When the Schottky diode of the first embodiment is formed by using the CVD method according to the sixth embodiment of the present invention and the impurity density is measured by CV measurement, the reproducibility and the high value are improved. It is understood that the impurity density of the purity n-SiC film 52 can be controlled within the control accuracy of 5%.

(Seventh Embodiment) In the CVD method according to the seventh embodiment of the present invention, a case where a (0001) C 4H—SiC substrate is used as the SiC substrate 51 will be described.

The CVD conditions are the same as in the first embodiment. However, the supply flow rate of N ₂ is 0.02 sccm. The density of Al, B, and Ti in the growth film of the seventh embodiment is 5 × 10 ¹³ cm ⁻³ or less, and SIMS measurement shows that
Not detected. When the (0001) Si plane is used as usual, these densities are 10 to 50 × 10 ¹³ cm ⁻³ , a clear compensating effect is confirmed, and the control accuracy of impurities intentionally added is confirmed. It is the cause of lowering.

When the graphite susceptor 2 having a normal nitrogen density is used, the nitrogen density unintentionally added is 1 × 1 due to the high efficiency of nitrogen uptake on the (0001) C plane.
It is about 0 ¹⁵ cm ^-3 , which affects the controllability of the impurity density. However, by using the graphite susceptor 2 having a nitrogen density of 1 × 10 ¹⁷ cm ⁻³ or less, the nitrogen density is 1 × 1.
It ^goes down to 0 ¹⁴ cm ^-3 . Since the compensation ratio is small even at such a low density, in the carrier density region of 1 × 10 ¹⁴ cm ⁻³ or more, the nitrogen density of the background is taken into consideration to achieve good controllability and 1 × 10 ¹⁴ cm 3. ^-3 or more carrier density can be controlled.

The CVD temperature is changed from 1500 ° C. to 1600 ° C.
In SiC grown on the (0001) Si surface by
Nitrogen density is 1 × 10¹³cm^-3From 1 × 10¹⁴cm^-3Until
It rose, but when it grows on the (0001) C plane, it is 1 × 10.¹⁵c
m^-3From 1.5 × 10¹⁴cm ^-3Went down. others
Therefore, even if the (0001) C plane is used, the temperature of 1600 ° C or higher
In long, the addition efficiency of nitrogen is higher than that of the (0001) Si surface.
It does not increase, and using the (0001) C plane is 160
It was particularly effective for growth at 0 ° C or higher.

When the Schottky diode of the first embodiment is formed by using the CVD method according to the seventh embodiment of the present invention and the impurity density is measured by CV measurement,
The high-purity n-SiC film 52 has good reproducibility of the impurity density, that is, can be controlled within 5%.

When the (0001) C plane is used, normally, when the SiC-coated graphite susceptor 2 is used, defects such as etch pits are recognized in the grown film. However, by using a graphite base material as the graphite susceptor 2 within a few cm around the wafer 31, it is possible to obtain a crystal having a good surface morphology.

(Eighth Embodiment) In the CVD method according to the eighth embodiment of the present invention, the dew point of hydrogen gas used as a carrier gas will be described.

The conditions of the CVD according to the eighth embodiment are as follows:
As shown in the table of FIG. 15, the growth temperature Tg was 1600 ° C.,
The growth pressure is 25 kPa, and the supply flow rate of SiH ₄ is 6.67.
The supply flow rate of sccm and C ₃ H ₈ is 3.33 sccm, and the supply flow rate of hydrogen is 40000 sccm.

The hydrogen gas is shown in the table of FIG.
, Hydrogen gas with dew point of -93 ° C, -85 ° C, -75 ° C
Was used. The substrate is a 4H-SiC (0001) Si surface.
As shown in the table of FIG. 15, the densities of Ti, Al, and B are
The higher the dew point is, the lower the dew point is from -93 ° C to -75 ° C.
Any impurity density can be increased to 10¹⁴cm ^-3
It can be seen that it will drop by about an order of magnitude until the middle of.

As shown in FIG. 10, the emission intensity near the band edge increases as the dew point is raised. This means that by increasing the dew point, a good quality crystal with small transitions other than band edges in the crystal was obtained. The carrier density grown under these growth conditions is 1 ×
When the reverse breakdown voltage is measured using a wafer having a thickness of 10 ¹⁶ cm ^{−3 and a} thickness of 10 μm, a breakdown voltage of 1000 V or more can be obtained in any case.

The growth rate was 2.5 μm / hr under any dew point condition, but when the dew point was higher than −75 ° C., the growth rate was lowered. In addition, fine particles are contained in the film, which is not practical.

(Other Embodiments) As described above, the present invention has been described by the first to eighth embodiments, but the description and drawings forming a part of this disclosure limit the present invention. Should not be understood to be. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

For example, in the first to eighth embodiments, 4H-SiC has been described, but the same applies to CVD growth of SiC having another crystal structure such as 6H-SiC and 15R-SiC. Of course.

Therefore, the technical scope of the present invention is defined only by the matters specifying the invention according to the scope of claims reasonable from the above description.

[0091]

As described in detail above, C according to the present invention
According to the VD method, the CVD apparatus, and the susceptor for the CVD apparatus, SiC having a low impurity density other than those intentionally added
An epitaxially grown film of the film can be provided.

According to the CVD method, the CVD apparatus and the susceptor for the CVD apparatus according to the present invention, the impurity density can be controlled with good controllability and reproducibility, and a SiC film having a resistance value as designed can be obtained. I can.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic structure of an LPCVD apparatus used in a CVD method according to first to eighth embodiments of the present invention.

2 (a) is a bird's-eye view showing details of a graphite susceptor used in the LPCVD apparatus of FIG.
FIG. 2B is a bird's eye view showing a solid carbon wool heat insulating material into which the graphite susceptor shown in FIG. 2A is inserted.

3 is a graph of the graphite susceptor of FIG. 2 (a) and FIG.
It is a bird's-eye view which shows the state which combined the solid carbon wool heat insulating material of (b).

FIG. 4 is a time chart exemplifying a process sequence used in the CVD method according to the first to eighth embodiments of the present invention, and particularly focusing on the temperature of the graphite susceptor.

FIG. 5 is a diagram showing a change in impurity density in a grown film with a run number.

FIG. 6 is a diagram showing a relationship between titanium (Ti) density in a grown film and photoluminescence emission intensity.

FIG. 7 is a diagram showing a first embodiment of the present invention in which a plurality of graphite susceptors having different impurity densities are prepared,
LP when using these multiple graphite susceptors
It is a graph which shows the relationship between the impurity density in the growth film obtained by CVD growth, and the impurity density in a graphite susceptor.

FIG. 8 is a second embodiment of the present invention, in which a plurality of graphite susceptors having different impurity densities are prepared,
LP when using these multiple graphite susceptors
It is a graph which shows the relationship between the impurity density in the growth film obtained by CVD growth, and the impurity density in a graphite susceptor.

FIG. 9 is a second embodiment of the present invention, in which a plurality of graphite susceptors having different impurity densities are prepared,
LP when using these multiple graphite susceptors
It is a graph which shows the relationship between the lifetime of the minority carrier in the growth film obtained by CVD growth, and the impurity density in a graphite susceptor.

FIG. 10 is a diagram showing a relationship between a dew point of hydrogen gas used as a carrier gas and an impurity density in a grown film, and a dew point of hydrogen gas and photoluminescence emission intensity in a CVD method according to an eighth embodiment of the present invention. It is a figure which shows a relationship.

FIG. 11 is a diagram showing a relationship between a dew point of hydrogen gas used as a carrier gas and a carrier density in a grown film in a CVD method according to an eighth embodiment of the present invention.

FIG. 12 is a CVD according to first to eighth embodiments of the present invention.
It is a diagram showing the relationship between the supply flow rate and the growth rate of the SiH ₄ to be used for law.

FIG. 13 is a table in which ten graphite susceptors having different impurity densities are prepared, and the correspondence relationships between the impurity densities in the ten graphite susceptors and the impurity densities in the growth film are compared for each impurity element.

14 is a table showing carrier densities, photoluminescence emission intensities, and minority carrier lifetimes in grown films grown using the respective graphite susceptors corresponding to the 10 graphite susceptors in FIG.

FIG. 15 is a table showing carrier density, photoluminescence emission intensity, impurity density for each element, etc. in a grown film when hydrogen gas having a dew point of −93 ° C., −85 ° C., −75 ° C. is used. .

FIG. 16 is a process cross-sectional view illustrating the method for manufacturing a semiconductor element (Schottky diode) using the CVD method according to the first embodiment of the present invention.

FIG. 17 is a process cross-sectional view illustrating the method for manufacturing a semiconductor element (pn junction diode) using the CVD method according to the second embodiment of the present invention.

[Explanation of symbols]

1 reaction tube (reaction vessel) 2 graphite susceptor 3 heat insulator 3h through holes 5, 15 pressure gauge 6 a pressure control valve 7 exhaust pump system 8 radiation thermometer (pyrometer) 11a propane (C ₃ H ₈₎ gas cylinder 11b monosilane gas ( SiH ₄ ) gas cylinder 11c Nitrogen (N ₂ ) gas cylinder 12a to 12h Mass flow controller 13a, 13b, 13c, 13d Stop valve 14 Trimethylaluminum (TMAl) bubbler 14a, 14b, 14c, 14d Stop valve 31 SiC substrate ( Wafer) 33 High frequency induction heater (RF coil) 34 RF oscillator 35, 38 Vacuum piping 36 Gas introduction pipe (gas introduction part) 37 Purge line (bypass line) 51 SiC substrate 52 n-SiC epi layer 53 p-SiC epi layer 62 Schottky metal 63 Surface metal 64 anode electrode 65 cathode electrode

   ─────────────────────────────────────────────────── ─── Continued front page    (71) Applicant 000001889             Sanyo Electric Co., Ltd.             2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture (72) Inventor Mitsuhiro Kushibe             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center (72) Inventor Joji Nishio             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center (72) Inventor Takashi Shinohe             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center (72) Inventor Tetsuo Takahashi             1-1-1 Higashi 1-1-1 Tsukuba City, Ibaraki Prefecture             Inside the Tsukuba Center, National Institute of Advanced Industrial Science and Technology (72) Inventor Yuuki Ishida             1-1-1 Higashi 1-1-1 Tsukuba City, Ibaraki Prefecture             Inside the Tsukuba Center, National Institute of Advanced Industrial Science and Technology (72) Inventor Takaya Suzuki             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Hobara Sho             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. (72) Inventor Kazusato Kojima             1-1-1 Higashi 1-1-1 Tsukuba City, Ibaraki Prefecture             Inside the Tsukuba Center, National Institute of Advanced Industrial Science and Technology (72) Inventor Toshiyuki Ohno             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Tomoyuki Tanaka             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. F-term (reference) 4K030 AA06 AA09 BA37 CA04 CA12                       FA04 GA02 JA10 KA46                 5F045 AA06 AB02 AB06 AC01 AC08                       AC15 AD16 AD17 AD18 AF02                       AF13 EB08 EB11 EB12 EC07                       EK03 EM02 EM09 EN04 GB05                       GB06

Claims (13)

[Claims] 1. A nitrogen density of 1 × 10 5 inside the reaction vessel.
A step of inserting a graphite susceptor of ¹⁷ cm ⁻³ or less; a step of vacuum-baking the graphite susceptor; a temperature of the graphite susceptor near room temperature; and a temperature of the graphite susceptor not exposed to the atmosphere. A step of disposing a substrate on the substrate, and controlling the inside of the reaction vessel to a decompressed state to heat the graphite susceptor to a growth temperature higher than the baking temperature to vapor-phase epitaxially grow a silicon carbide film on the substrate. And a step of performing a CVD method for a silicon carbide film. 2. The step of lowering the temperature of the graphite susceptor from the baking temperature to a first temperature between the baking temperature and room temperature between the step of vacuum baking and the step of disposing the substrate, Heating the graphite susceptor from one temperature to a coating temperature higher than the baking temperature, and coating the surface of the graphite susceptor with a coating film of at least one of silicon and silicon carbide at the coating temperature. The CVD method for a silicon carbide film according to claim 1, wherein: 3. The step of lowering the temperature of the graphite susceptor from the coating temperature to a second temperature between the baking temperature and room temperature between the coating step and the step of disposing the substrate, and the reaction vessel. Controlling the inside of the graphite to a decompressed state to raise the temperature of the graphite susceptor from the second temperature to the peeling temperature to remove at least a part of the coated film. The CVD method for a silicon carbide film according to claim 2. 4. A step of inserting a graphite susceptor into a reaction vessel, a step of vacuum baking the graphite susceptor, and a temperature decrease of the graphite susceptor from a baking temperature used for the vacuum baking to a temperature near room temperature. And a step of removing the surface layer of the graphite susceptor from the reaction vessel after the temperature lowering, and a step of removing the surface layer, and arranging a substrate on the graphite susceptor. And a step of controlling the inside of the reaction vessel to a depressurized state to heat the graphite susceptor to a growth temperature higher than the baking temperature and vapor-phase epitaxially grow a silicon carbide film on the substrate. A method for CVD a silicon carbide film, comprising: 5. A step of inserting a graphite susceptor into a reaction vessel, a step of vacuum baking the graphite susceptor, and a temperature decrease of the graphite susceptor from a baking temperature used for the vacuum baking to a temperature near room temperature. Heating the graphite susceptor to a coating temperature higher than the baking temperature, and coating the surface of the graphite susceptor with a film made of at least one of silicon and silicon carbide at the coating temperature; The step of lowering the temperature of the susceptor from the coating temperature to a temperature near room temperature, and after lowering the temperature to a temperature near the room temperature, the graphite susceptor is carried out of the reaction container and the surface layer of the graphite susceptor is removed. A step of placing a substrate on the graphite susceptor after the step of removing the surface layer, and controlling the inside of the reaction vessel to a depressurized state so that the graphite susceptor has a growth temperature higher than the coating temperature. And a step of vapor-phase epitaxially growing a silicon carbide film on the substrate, the CVD method of the silicon carbide film. 6. The step of vacuum-baking, after the step of inserting a graphite susceptor into the reaction vessel, the step of exhausting the inside of the reaction vessel to a depressurized state, and the step of depressurizing the inside of the reaction vessel. 6. The step of controlling the temperature of the graphite susceptor to reach the baking temperature step by step, and removing the gas containing water and carbon in the graphite susceptor. A CVD method for a silicon carbide film according to any one of items. 7. A step of placing a substrate on a graphite susceptor having a nitrogen density of 1 × 10 ¹⁷ cm ⁻³ or less, a step of inserting the graphite susceptor into a reaction vessel, and a state of decompressing the inside of the reaction vessel. And heating the graphite susceptor to a growth temperature to vapor-phase epitaxially grow a silicon carbide film on the substrate. 8. The coating temperature is from 1200 ° C.
CV of the silicon carbide film according to any one of claims 2, 3 and 5, wherein the temperature is between 1450 ° C.
Method D. 9. The vapor phase epitaxial growth of the silicon carbide film at the growth temperature has a dew point of −85 ° C. to −75 ° C.
A carrier gas between the two is used.
9. A CVD method for a silicon carbide film according to any one of items 1 to 8. 10. The substrate is Si having a (0001) C plane.
The CVD method for a silicon carbide film according to claim 1, wherein the CVD method is a C substrate. 11. A reaction vessel, a gas introduction section for introducing a gas into the reaction vessel, a vacuum evacuation section for evacuating the reaction vessel, and a nitrogen density of 1 × 10 ¹⁷ arranged inside the reaction vessel.
A plurality of graphite members having a size of ³ cm ^-3 or less, and a resistance that is fitted between the plurality of graphite members and has a region made of a material having a higher resistivity than the graphite members at least in a fitting portion with the graphite members. A CVD apparatus comprising: a susceptor in which members are combined in a cylindrical shape; and a high-frequency induction heating unit that heats the plurality of graphite members by circulating an electric current along the circumferential direction of the susceptor. 12. A susceptor for a CVD device, comprising a graphite member having a nitrogen density of 1 × 10 ¹⁷ cm ⁻³ or less. 13. A graphite member having a nitrogen density of 1 × 10 ¹⁷ cm ⁻³ or less, and at least a region which is fitted between the graphite members and is made of a material having a higher resistivity than the graphite member. By combining a resistive member having a fitting portion with the graphite member in a tubular shape, by high frequency induction heating,
A susceptor for a CVD apparatus, wherein an electric current is circulated along the circumferential direction of the cylinder to be heated.