JP2015142078A - Silicon carbide semiconductor device and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve reduction in the interface state between a silicon carbide layer and a gate insulating film, thereby increasing carrier mobility.SOLUTION: A silicon carbide semiconductor device includes at least one or more layers of an oxide film, a nitride film or an oxynitride film, as a gate insulating film 22, on silicon carbide substrates 12a, 12b. The gate insulating film 22 including the interface between the silicon carbide substrates 12a, 12b and the gate insulating film 22 contains 1×10/cmor more of chlorine therein. The gate insulating film 22 is formed by thermal oxidation in dry oxygen containing no moisture.

Description

  The present invention relates to a semiconductor device using a silicon carbide substrate and a manufacturing method thereof, and more particularly to a silicon carbide semiconductor device having an improved gate insulating film and a manufacturing method thereof.

  Since silicon carbide has excellent physical property values, it is expected to be applied to power devices with high breakdown voltage and low loss. When silicon carbide is applied to a silicon carbide vertical metal-oxide film-semiconductor field effect transistor (MOSFET) which is a kind of silicon carbide semiconductor device, a silicon dioxide film or the like is formed on a silicon carbide substrate. The gate insulating film is formed.

  In order to form a silicon dioxide film on a silicon carbide substrate, there are a method of thermally oxidizing the silicon carbide substrate and a method of depositing a silicon dioxide film on the silicon carbide substrate. Whichever method is used, an interface state is formed at the interface between the silicon carbide substrate and the silicon dioxide film, and this interface state determines the field effect mobility (channel mobility) of the MOSFET from the mobility in the silicon carbide bulk. Decreasing the resistance increases the resistance value when the MOSFET is turned on, and the loss may increase.

  As an index for evaluating the interface characteristics between the silicon carbide substrate and the silicon dioxide film, there is an interface state density. In general, interface characteristics represented by channel mobility tend to be better when the interface state density is smaller.

  As a general method for improving the interface characteristics between the silicon carbide substrate and the silicon dioxide film, the silicon carbide substrate is oxidized in an oxygen-containing atmosphere, and post-oxidation annealing (POA: Post Oxidation Annealing) is used. A method using a nitrogen-containing gas containing nitrogen is known. In this case, nitridation occurs simultaneously with oxidation, and nitrogen atoms contribute to termination of dangling bonds (unbonded hands) in the silicon dioxide film or at the interface between the silicon carbide substrate and the silicon dioxide film, thereby reducing the interface state density. It is said that there is an effect (for example, refer to the following Patent Document 1).

JP-T-2004-511101 (pages 8 to 15)

  In the method using a gas containing nitrogen of dinitrogen monoxide or nitrogen monoxide, the interface between the silicon carbide substrate and the gate insulating film (silicon dioxide film) is optimized by optimizing the nitriding conditions with the dinitrogen monoxide gas ( Hereinafter, it is described that the interface state of the silicon carbide substrate / gate insulating film interface is reduced. However, when nitriding is performed by a method as disclosed in Patent Document 1, the silicon carbide substrate is reoxidized by oxygen gas generated by reaction of dinitrogen monoxide gas during nitriding, and is nitrided by this reoxidation. In some cases, the interface proceeds from the interface to the inside of the silicon carbide substrate, and the remaining silicon carbide substrate / gate insulating film interface is not sufficiently nitrided, and the interface state cannot be sufficiently reduced.

  It has been reported that when a gate insulating film is formed on a silicon carbide substrate with oxygen gas, the channel mobility is very low and the interface state density is high. Causes include dangling bonds in the gate insulating film and at the silicon carbide substrate / gate insulating film interface, and carbon compounds that segregate at the silicon carbide substrate / gate insulating film interface. Therefore, in the method using a gas containing dinitrogen monoxide or nitrogen nitrogen monoxide, oxygen gas is generated as a by-product, and the interface characteristics of the silicon carbide substrate / gate insulating film are deteriorated. Is insufficient.

  In view of the above problems, the present invention provides a silicon carbide semiconductor device having a high carrier mobility and a method for manufacturing the same, in which the level of the interface between the silicon carbide substrate and silicon dioxide (gate insulating film) is further reduced. With the goal.

In order to achieve the above object, a silicon carbide semiconductor device according to the present invention includes a silicon carbide semiconductor device having at least one oxide film, nitride film, or oxynitride film as a gate insulating film on a silicon carbide substrate. 1 × 10 ¹⁹ / cm ³ or more of chlorine exists in the gate insulating film including the interface between the silicon substrate and the gate insulating film.

Further, the method for manufacturing a silicon carbide semiconductor device of the present invention is the method for manufacturing a silicon carbide semiconductor device having at least one oxide film, nitride film or oxynitride film as a gate insulating film on a silicon carbide substrate. And a gate insulating film forming step of including 1 × 10 ¹⁹ / cm ³ or more of chlorine in the gate insulating film including an interface between the silicon carbide substrate and the gate insulating film.

  Further, the gate insulating film forming step includes a thermal oxidation process in dry oxygen containing no moisture.

  Further, the gate insulating film forming step includes a thermal oxynitridation treatment in a gas containing at least dinitrogen monoxide or nitric oxide.

  The gate insulating film forming step includes thermal oxidation treatment in a gas containing at least oxygen and moisture.

  The gate insulating film forming step includes a step of depositing an insulating film of an oxide film, a nitride film, or an oxynitride film by a chemical or physical vapor deposition method.

  Further, the gate insulating film forming step includes a step of performing a thermal oxidation process in an atmosphere into which chlorine element is introduced.

  In addition, after the step of forming the gate insulating film, there is a step of performing a heat treatment in an atmosphere into which chlorine element is introduced.

According to the above configuration, by introducing chlorine of 1 × 10 ¹⁹ / cm ³ or more into the interface between the silicon carbide and the gate insulating film, the dangling bond at the interface that is reported to be the cause of the interface state is terminated by chlorine. Effect and the carbon compound segregated at the interface can be removed, and the interface state between the silicon carbide layer and the gate insulating film can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the interface state of a silicon carbide layer and a gate insulating film can be reduced, and a silicon carbide semiconductor device with high carrier mobility can be obtained.

It is a figure which shows the example of a measurement of the MOS capacitor by the silicon carbide semiconductor device concerning Embodiment 1 of this invention. It is a graph which shows the interface state density obtained from the measurement result of the MOS capacitor concerning Embodiment 1 of this invention, and the MOS capacitor of a comparative example. 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Process 1) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Process 2) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Process 3) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Process 4) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Process 5) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Step 6) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Step 7) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Process 8) 7 is a cross-sectional view showing a manufacturing step of the MOSFET according to Example 1. FIG. (Step 9) It is a graph which shows the gate voltage dependence of the field effect channel mobility obtained by measuring MOSFET of Example 1 and a comparative example. 4 is a chart showing a chlorine concentration in a gate insulating film of the MOSFET of Example 1. It is a comparison figure of the present Example concerning the heat processing method after oxide film formation, and the existing method. It is sectional drawing which shows the vertical MOSFET which has a MOS gate structure concerning Example 6 of this invention.

  Hereinafter, preferred embodiments of a semiconductor device according to the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the accompanying drawings, it means that electrons or holes are majority carriers in layers and regions with n or p, respectively. Further, + and − attached to n and p mean that the impurity concentration is higher and lower than that of the layer or region where it is not attached. Also, in this specification, in the Miller index notation, “−” means a bar attached to the index immediately after that, and “−” is added before the index to indicate a negative index. Note that, in the following description of the embodiments and the accompanying drawings, the same reference numerals are given to the same components, and duplicate descriptions are omitted.

(Embodiment 1)
FIG. 1 is a diagram showing a measurement example of a MOS capacitor by the silicon carbide semiconductor device according to the first embodiment of the present invention. First, referring to FIG. 1, a description will be given of an experimental example in which a gate oxide film is formed on a MOS capacitor and a reduction in interface state density at the interface between the silicon carbide substrate and the gate oxide film is verified. The MOS capacitor 1 shown in FIG. 1 is manufactured by the following steps.

(Process 1)
First, 5 n-type epitaxial films 2b having a donor density of about 1 × 10 ¹⁶ cm ⁻³ are formed on an n-type 4H—SiC (000-1) substrate 2a (0 to 8 degrees off substrate from the (000-1) plane). Grow 10 μm. The n-type 4H—SiC substrate 2a alone, or the n-type 4H—SiC substrate 2a and the n-type epitaxial film 2b are collectively referred to as an n-type 4H—SiC semiconductor substrate 2. Hereinafter, the surface on the n-type epitaxial film 2b side of the n-type 4H-SiC semiconductor substrate 2 is defined as a front surface, and the surface on the n-type 4H-SiC substrate 2a side of the n-type 4H-SiC semiconductor substrate 2 is defined as a back surface.

(Process 2)
After cleaning the n-type 4H—SiC semiconductor substrate 2, it was passed for 20 minutes in an atmosphere containing only trans-1,2-dichloroethylene (Trans-LC) at 1350 ° C. and pure oxygen (containing no water) through a purifier. The insulating film 3 having a thickness of 50 nm is formed on the front surface of the n-type 4H—SiC semiconductor substrate 2. Alternatively, the insulating film 3 is formed by performing heat treatment in an atmosphere containing chlorine (Cl) after oxidation. At this time, the supply of the mixed gas is stopped after thermal oxidation or heat treatment so that the oxidation does not proceed at a low temperature, and purged with an inert gas such as argon or nitrogen at the same temperature for 30 minutes or longer (in the furnace Exhaust the gas). The molar ratio of Trans-LC to pure oxygen that has passed through the purifier is in the range of 0.01 to 0.04.

(Process 3)
A MOS capacitor composed of an aluminum back electrode 5 in which an aluminum gate electrode 4 is deposited on the insulating film 3 so as to have a dot-like planar shape at room temperature and aluminum is deposited on the entire back surface of the n-type 4H-SiC semiconductor substrate 2. Produced.

  Next, in order to verify the effect of reducing the MOS interface according to this experimental example, in step 2, a MOS capacitor in which an insulating film was formed only in an atmosphere containing dry oxygen (Comparative Example 1) and dinitrogen monoxide were included. A MOS capacitor (Comparative Example 2) in which an insulating film was formed by performing only oxidation in an atmosphere was produced. The completed MOS capacitors of this experimental example and Comparative Examples 1 and 2 were measured with a C-V meter 7 to verify the difference in interface state density at the interface between the n-type 4H—SiC semiconductor substrate 2 and the insulating film.

  FIG. 2 is a chart showing the interface state density obtained from the measurement results of the MOS capacitor according to the first embodiment of the present invention and the MOS capacitor of the comparative example. The horizontal axis represents the energy level from the conduction band, and the vertical axis represents the interface state density at the interface between the n-type 4H—SiC semiconductor substrate 2 and the insulating film.

  As shown in FIG. 2, when compared in the atmosphere of each heat treatment in step 2, the heat treatment (black triangle plot) in the atmosphere containing trans-1,2-dichloroethylene and oxygen in the first embodiment (a) is as follows. There is a significant interface state reduction effect compared to the heat treatment in the atmosphere (black circle plot) containing dry oxygen in Comparative Example 1 (c), and the atmosphere containing dinitrogen monoxide in Comparative Example 2 (b) ( The black square plot) has the same reduction effect.

  Next, as a silicon carbide semiconductor device according to the first embodiment, a method for manufacturing an example of a lateral silicon carbide MOSFET having a general MOS gate structure will be described. 3 to 11 are cross-sectional views illustrating manufacturing steps of the MOSFET according to the first embodiment.

(Process 1)
First, as shown in FIG. 3, the front surface of the p ⁺ type 4H—SiC (000-1) substrate 12a (0 to 8 degrees off substrate from the (000-1) plane, preferably 0 to 4 degrees off substrate). A p-type epitaxial film 12b having an acceptor density of 1 × 10 ¹⁶ cm ⁻³ is grown on the surface. A 4H-SiC semiconductor substrate in which a p-type epitaxial film 12b is deposited on a p ⁺ -type 4H-SiC (000-1) substrate 12a is manufactured.

(Process 2)
Next, as shown in FIG. 4, the vacuum on the surface of the p-type epitaxial layer 12b CVD (chemical vapor deposition: Chemical Vapor Deposition) by method deposited SiO ₂ film having a thickness of 1 [mu] m, SiO ₂ by photolithography The film is patterned to form a mask 13 having openings in the drain region and source region formation regions. Thereafter, for example, using the mask 13 as a mask, phosphorus ions 14 are ion-implanted in multiple stages at a substrate temperature of 500 ° C. and in an acceleration energy range of 40 keV to 250 keV with an implantation amount of 2 × 10 ²⁰ cm ⁻³ .

(Process 3)
Next, as shown in FIG. 5, the mask 13 is removed, a 1 μm thick SiO ₂ film is deposited on the surface of the p-type epitaxial film 12b by low pressure CVD, and the SiO ₂ film is patterned by photolithography. Then, a mask 15 having an opening in the formation region of the ground region is formed. The opening of the mask 15 is selectively formed at a position different from the opening of the mask 13. Thereafter, for example, aluminum ions 16 are ion-implanted in multiple stages at a substrate temperature of 500 ° C. and an acceleration energy of 40 keV to 200 keV with an implantation amount of 2 × 10 ²⁰ cm ⁻³ .

(Process 4)
Next, as shown in FIG. 6, the mask 15 is removed, and activation annealing is performed in an argon atmosphere at 1600 ° C. for 5 minutes to perform n ⁺ type drain region 17 and source region 18, and p ⁺ type. A ground region 19 is selectively formed.

(Process 5)
Next, as shown in FIG. 7, a field oxide film 20 having a thickness of 0.5 μm is deposited by low pressure CVD, and a part of the field oxide film 20 is removed by photolithography and wet etching to form an active region 21. To do.

(Step 6)
Next, as shown in FIG. 8, thermal oxidation is performed for 20 minutes in an atmosphere containing Trans-LC at 1350 ° C. and pure oxygen that has passed through a purifier, and a gate insulating film having a thickness of 50 nm is formed in the active region 21. 22 is formed. At this time, in order to prevent oxidation from proceeding at a low temperature, the supply of the mixed gas is stopped during or after the thermal oxidation (heat treatment), and the furnace is kept at the same temperature for 30 minutes or more with an inert gas such as argon or nitrogen. Purge the inside (exhaust the gas in the furnace). The molar ratio of Trans-LC to pure oxygen that has passed through the purifier is in the range of 0.01 to 0.04.

  Thereafter, polycrystalline silicon is deposited to a thickness of 0.3 μm on the gate insulating film 22 by a low pressure CVD method, and a gate electrode 23 is formed by patterning the polycrystalline silicon layer by photolithography.

(Step 7)
Next, as shown in FIG. 9, contact holes are formed on the drain region 17, the source region 18, and the ground region 19 by selectively removing the gate insulating film 22 by photolithography and hydrofluoric acid etching. Then, an aluminum film having a thickness of 10 nm and a nickel film having a thickness of 60 nm are further deposited thereon, and a metal laminated film composed of the aluminum film and the nickel film is patterned by lift-off to contact the silicon portion exposed in the contact hole. Metal 24 is formed.

(Process 8)
Next, as shown in FIG. 10, the contact metal 24 and the silicon carbide reaction layer 25 are formed by annealing at 950 ° C. for 2 minutes in an inert gas atmosphere as ohmic contact annealing. The inert gas is nitrogen, helium, or argon.

(Step 9)
Then, as shown in FIG. 11, an aluminum film is deposited to 300 nm on the front surface of the 4H—SiC semiconductor substrate, the aluminum film is patterned by photolithography and phosphoric acid etching, and a pad is formed on the gate electrode 23 and the reaction layer 25. Electrode 26 is formed. Further, an aluminum film is deposited to 100 nm on the back surface of the 4H—SiC semiconductor substrate (the back surface of the p ⁺ -type 4H—SiC (000-1) substrate 12a) to form the back electrode 27. Thereby, the silicon carbide MOSFET according to Example 1 is completed.

  FIG. 12 is a chart showing the gate voltage dependence of the field-effect channel mobility obtained by measuring the MOSFETs of Example 1 and the comparative example. The silicon carbide MOSFET manufactured by the method for manufacturing the silicon carbide MOSFET shown in Example 1 (FIGS. 3 to 11) and the comparative example were manufactured by changing the process of FIG. The characteristic of silicon carbide MOSFET is shown. The horizontal axis is the gate voltage, and the vertical axis is the field effect channel mobility.

The channel mobility of the Trans-LC of Example 1 shown in FIG. 12A and the MOSFET processed in an oxygen atmosphere was about 35 cm ^{2 /} Vs at the maximum. And it is greatly improved with respect to the atmosphere containing oxygen of Comparative Example 1 (c), and the channel mobility at the peak time is also about 2% even with respect to the atmosphere containing Comparative Example 2 (b) containing dinitrogen monoxide. The result was improved by 10%.

  13 is a chart showing the chlorine concentration in the gate insulating film of the MOSFET of Example 1. FIG. Secondary ion mass spectrometry (SIMS) is used to determine the chlorine concentration at the silicon carbide substrate / gate insulating film interface and gate insulating film formed by oxidizing a (000-1) -SiC substrate in Trans-LC and oxygen atmosphere. The result measured by Ion Mass Spectroscopy is shown.

In the case of Trans-LC with improved channel mobility and a MOSFET processed in an oxygen atmosphere as in Example 1, the silicon carbide substrate / gate insulating film interface, or about 10 nm before and after the silicon carbide substrate / gate insulating film interface. In addition, chlorine having a concentration of 1 × 10 ¹⁹ / cm ³ or more is introduced.

  The second embodiment is different from the first embodiment in the formation method of the gate insulating film 22 shown in step 6 (FIG. 8). In Example 2, thermal oxidation is performed in dry oxygen at 1100 ° C. for 50 minutes, and then heat treatment is performed at 1350 ° C. in an atmosphere containing Trans-LC and pure oxygen that has passed through a purifier. A gate insulating film 22 having a thickness of 50 nm is formed.

  At this time, the supply of the mixed gas is stopped so that the oxidation does not proceed at a low temperature, and after the thermal oxidation (heat treatment), the inside of the furnace is purged with an inert gas such as argon or nitrogen at the same temperature for 30 minutes or more. . The molar ratio of Trans-LC to pure oxygen that has passed through the purifier is in the range of 0.01 to 0.04. Other steps are the same as those in the first embodiment. The silicon carbide MOSFET manufactured by such a manufacturing method also showed the same characteristics as in Example 1.

  Also in Example 3, the method of forming the gate insulating film 22 shown in Step 6 (FIG. 8) is different from Example 1. In Example 3, oxynitridation was performed at 1300 ° C. in an atmosphere having a flow rate ratio of dinitrogen monoxide and nitrogen of 1: 5 for 100 minutes, and then at 1350 ° C., Trans-LC and pure oxygen passed through a purifier were added. The gate insulating film 22 having a thickness of 50 nm is formed by performing heat treatment for 10 minutes in the atmosphere.

  At this time, the supply of the mixed gas is stopped after the thermal oxidation (heat treatment) so that the oxidation does not proceed at a low temperature, and the inside of the furnace is purged with an inert gas such as argon or nitrogen at the same temperature for 30 minutes or more. . The molar ratio of Trans-LC to pure oxygen that has passed through the purifier is in the range of 0.01 to 0.04. Other steps are the same as those in the first embodiment. The silicon carbide MOSFET manufactured by such a manufacturing method also exhibited the same characteristics as in Example 1.

  Also in Example 4, the method of forming the gate insulating film 22 shown in Step 6 (FIG. 8) is different from Example 1. In Example 4, oxynitridation was performed at 1200 ° C. in an atmosphere with a flow rate ratio of nitric oxide and nitrogen of 1:10 for 100 minutes, and then trans-LC at 1350 ° C. and pure oxygen passed through a purifier were included. A gate insulating film 22 having a thickness of 50 nm is formed by performing a heat treatment for 10 minutes in an atmosphere.

  At this time, the supply of the mixed gas is stopped after the thermal oxidation (heat treatment) so that the oxidation does not proceed at a low temperature, and the inside of the furnace is purged with an inert gas such as argon or nitrogen at the same temperature for 30 minutes or more. . The molar ratio of Trans-LC to pure oxygen that has passed through the purifier is in the range of 0.01 to 0.04. Other steps are the same as those in the first embodiment. The silicon carbide MOSFET manufactured by such a manufacturing method also exhibited the same characteristics as in Example 1.

  Also in Example 5, the method of forming the gate insulating film 22 shown in Step 6 (FIG. 8) is different from Example 1. In Example 5, an insulating film having a thickness of less than 50 nm is formed by a deposition method, and then heat treatment is performed at 1350 ° C. for 10 minutes in an atmosphere containing Trans-LC and pure oxygen through a purifier. A gate insulating film 22 having a total thickness of about 50 nm is formed.

  At this time, the supply of the mixed gas is stopped after the thermal oxidation (heat treatment) so that the oxidation does not proceed at a low temperature, and the inside of the furnace is purged with an inert gas such as argon or nitrogen at the same temperature for 30 minutes or more. . The molar ratio of Trans-LC to pure oxygen that has passed through the purifier is in the range of 0.01 to 0.04. A method for depositing the insulating film includes a method using silane or TEOS (tetraethoxysilane) by a CVD method, but is not particularly limited. Other steps are the same as those in the first embodiment. The silicon carbide MOSFET manufactured by such a manufacturing method also exhibited the same characteristics as in Example 1.

  Here, Trans-LC and a heat treatment method after forming an oxide film (gate insulating film 22) using a mixed gas are disclosed as an existing method in Japanese Patent Application Laid-Open No. 2011-49368, for example. FIG. 14 is a comparison diagram between the present embodiment and the existing method relating to the heat treatment method after forming the oxide film. In the existing method, heat treatment is performed using a mixed gas of Trans-LC and dinitrogen monoxide or nitric oxide, thereby obtaining an effect of suppressing oxidation and promoting nitridation. Nitric oxide or dinitrogen monoxide The molar ratio of Trans-LC with respect to is 0.02 or more.

  On the other hand, in each of the above-described embodiments, heat treatment is performed using Trans-LC and pure oxygen that has passed through a purifier, so that the effect of oxidation promotion and chlorine introduction can be obtained instead of oxidation suppression and nitridation promotion. It is done. Note that the molar ratio of Trans-LC to pure oxygen that passed through the purifier is in the range of 0.01 to 0.04.

  In each embodiment of the present invention, as a method of introducing chlorine into the interface between the silicon carbide substrate and the gate insulating film, heat treatment was performed in Trans-LC and an oxygen atmosphere. As a method for introducing chlorine into hydrogen chloride, it can be introduced in a liquid or gaseous chloride and oxygen atmosphere at room temperature and normal pressure such as hydrogen chloride and oxygen or chloromethane and oxygen.

The sixth embodiment has a configuration in which the first embodiment is applied to a vertical MOSFET. FIG. 15 is a sectional view showing a vertical MOSFET having a MOS gate structure according to Example 6 of the invention. As shown in FIG. 15, in a vertical MOSFET, an n-type epitaxial film 32 is formed on the front surface of an n ⁺ -type silicon carbide substrate 31. The impurity concentration of n type epitaxial film 32 is lower than the impurity concentration of n ⁺ type silicon carbide substrate 31.

A plurality of p-type regions 36 are selectively formed inside the n-type epitaxial film 32. P type region 36 is exposed on the surface of n type epitaxial film 32 opposite to the n ⁺ type silicon carbide substrate 31 side. A p-type SiC layer 37 having a lower concentration than the p-type region 36 is formed over the surfaces of the n-type epitaxial film 32 and the p-type region 36. In the p-type SiC layer 37 on the n-type epitaxial film 32 where the p-type region 36 is not formed, an n-type region 33 that penetrates the p-type SiC layer 37 in the depth direction and reaches the n-type epitaxial film 32 is formed. Is done. The n-type epitaxial film 32 and the n-type region 33 are n-type drift regions.

The impurity concentration of the n-type region 33 is preferably higher than that of the n-type epitaxial film 32. Inside the p-type SiC layer 37, an n ⁺ type source region 34 and a p ⁺ type contact region 35 are formed so as to be in contact with each other. N ⁺ -type source region 34 and p ⁺ -type contact region 35 are exposed on the surface of p-type SiC layer 37 opposite to the p-type region 36 side. The n ⁺ type source region 34 is formed apart from the n type region 33.

The p ⁺ type contact region 35 is located on the opposite side of the n ⁺ type source region 34 to the n type region 33 side. The impurity concentration of p ⁺ -type contact region 35 is higher than the impurity concentration of p-type SiC layer 37. A portion of the p-type SiC layer 37 excluding the n ⁺ -type source region 34, the p ⁺ -type contact region 35 and the n-type region 33 becomes a p-type base region together with the p-type region 36.

A source electrode 38 is formed on the surfaces of the n ⁺ type source region 34 and the p ⁺ type contact region 35. A gate electrode 40 is formed on the surface of the p-type SiC layer 37 and the n-type region 33 between the adjacent n ⁺ -type source regions 34 via a gate insulating film 39. The gate electrode 40 is electrically insulated from the source electrode 38 by an interlayer insulating film (not shown).

Further, on the back surface of the n ⁺ -type silicon carbide substrate 31, the drain electrode 41 in contact with the n ⁺ -type silicon carbide substrate 31 is formed. In such a vertical MOSFET, the same gate insulating film as in Examples 1 to 5 was formed, but the same interface state density results as in Examples 1 to 5 could be obtained.

As described above, according to the present invention, silicon carbide that has been reported to cause interface states by introducing chlorine of 1 × 10 ¹⁹ / cm ³ or more into the interface between the silicon carbide substrate and the gate insulating film. The dangling bond at the interface between the substrate and the gate insulating film can be terminated with chlorine, and the carbon compound segregated at the interface between the silicon carbide substrate and the gate insulating film can be removed. As a result, a high-performance silicon carbide semiconductor device having a high carrier mobility and a reduced interface state between the silicon carbide substrate and the gate insulating film can be obtained without adding any special treatment.

  In each of the above examples, a (000-1) substrate (off substrate of 0 to 8 degrees) having a crystal structure of 4H—SiC was used, but a (0001) substrate having a crystal structure of 4H—SiC or (11-20) The same effect can be obtained with a substrate.

  As described above, the present invention is not limited to a lateral MOSFET as a silicon carbide MOSFET, but can also be applied to a semiconductor device having a high breakdown voltage structure such as a vertical MOSFET, and the same effect can be achieved. Therefore, the present invention can be applied to various semiconductor devices and manufacturing methods thereof without departing from the scope of the invention described in the claims.

  As described above, the semiconductor device according to the present invention is useful for various semiconductor devices such as a lateral MOSFET and a vertical MOSFET.

1 MOS capacitor 2a n-type 4H-SiC (000-1) substrate 2b n-type epitaxial film 3 insulating film 4 aluminum gate electrode 5 aluminum back electrode 7 C-V meter 12a p-type ⁺ 4H-SiC (000-1) substrate 12b p-type epitaxial film 13 mask 14 phosphorus ion 15 mask 16 aluminum ion 17 drain region 18 source region 19 ground region 20 field oxide film 21 active region 22 gate insulating film 23 gate electrode 24 contact metal 25 reaction layer 26 pad electrode 27 back electrode 31 n ⁺ -type silicon carbide substrate 32 n-type epitaxial layer 33 n-type region 34 n ⁺ -type source region 35 p ⁺ -type contact region 36 p-type region 37 p-type SiC layer 38 source electrode 39 gate insulating film 40 gate electrode 41 drain Very

Claims (8)

In a silicon carbide semiconductor device having at least one oxide film, nitride film or oxynitride film as a gate insulating film on a silicon carbide substrate,
A silicon carbide semiconductor device, wherein 1 × 10 ¹⁹ / cm ³ or more of chlorine exists in the gate insulating film including an interface between the silicon carbide substrate and the gate insulating film. In a method for manufacturing a silicon carbide semiconductor device having at least one oxide film, nitride film, or oxynitride film as a gate insulating film on a silicon carbide substrate,
A method of manufacturing a silicon carbide semiconductor device, comprising: a step of forming a gate insulating film in which chlorine of 1 × 10 ¹⁹ / cm ³ or more is contained in the gate insulating film including an interface between the silicon carbide substrate and the gate insulating film. Method.   The method for manufacturing a silicon carbide semiconductor device according to claim 2, wherein the gate insulating film forming step includes a thermal oxidation treatment in dry oxygen not containing moisture.   3. The method for manufacturing a silicon carbide semiconductor device according to claim 2, wherein the gate insulating film forming step includes a thermal oxynitriding process in a gas containing at least dinitrogen monoxide or nitric oxide.   3. The method for manufacturing a silicon carbide semiconductor device according to claim 2, wherein the gate insulating film forming step includes a thermal oxidation process in a gas containing at least oxygen and moisture.   3. The silicon carbide according to claim 2, wherein the gate insulating film forming step includes a step of depositing an oxide film, a nitride film, or an oxynitride insulating film by chemical or physical vapor deposition. A method for manufacturing a semiconductor device.   The method for manufacturing a silicon carbide semiconductor device according to claim 2, wherein the gate insulating film forming step includes a step of performing a thermal oxidation process in an atmosphere into which chlorine element is introduced. .   The method for manufacturing a silicon carbide semiconductor device according to claim 2, further comprising a step of performing a heat treatment in an atmosphere into which chlorine element is introduced after the step of forming the gate insulating film.

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