JP6785202B2 - Silicon carbide semiconductor device - Google Patents

Description

The present invention relates to a silicon carbide semiconductor device.

Conventionally, silicon carbide (hereinafter, may be referred to as "SiC") has attracted attention as a material for power devices applied to, for example, motor control systems. Research on devices using SiC is underway, and for example, a silicon carbide semiconductor device using SiC as a semiconductor substrate is known (see, for example, Patent Document 1).

For example, Patent Document 1 states, "Insulation in which an insulating film having a composition ratio of 90% or more as a base and mainly composed of 10% or less of nitrogen is formed on a substrate of a wide bandgap semiconductor material. The film structure has a transition region in which the silicon composition ratio and the carbon composition ratio change rapidly in the vicinity of the interface between the insulating film and the wide bandgap semiconductor material substrate, and the oxygen concentration in the transition region. When the position where is 90% of the oxygen concentration in the silicon dioxide is defined as the interface, the nitrogen concentration contained in the region where the distance from the interface is 5 nm or less on the silicon dioxide side and 5 nm or less on the silicon carbide side is the area density. It is higher than 5.0 × 10 ¹³ cm ^{- 2 and} less than 1.6 × 10 ¹⁴ cm- ^2. ”Insulation film structures are disclosed.

Japanese Unexamined Patent Publication No. 2011-082454

An object of the present invention is to provide a silicon carbide semiconductor device having stable semiconductor device characteristics even when a stress voltage is applied to a gate electrode.

The means for solving the above problems include the following aspects.
<1> With the gate electrode
With an insulating film of silicon dioxide,
With a silicon carbide semiconductor substrate,
At the interface between the silicon dioxide insulating film and the silicon carbide semiconductor substrate, an insulating gate type in which a nitrogen atom is coordinated to at least a part of carbon sites bonded to only two silicon atoms on the silicon carbide side. Silicon carbide semiconductor device.
<2> The crystal plane on the silicon carbide side at the interface is any one of the m-plane, a-plane, Si-plane and C-plane, and the deviation of each crystal plane is ± 10%. The silicon carbide semiconductor device according to <1>, which is within.
<3> The silicon carbide semiconductor device according to <2>, wherein the crystal plane on the silicon carbide side at the interface is the m-plane.

According to the silicon carbide semiconductor device of the present invention, there is provided a silicon carbide semiconductor device having stable semiconductor element characteristics even when a stress voltage is applied to the gate electrode.

It is a schematic diagram which shows an example of the crystal structure on the silicon carbide side of the interface between silicon carbide and silicon oxide in the silicon carbide semiconductor device of this embodiment. It is a schematic diagram which shows another example of the crystal structure on the silicon carbide side of the interface between silicon carbide and silicon oxide in the silicon carbide semiconductor device of this embodiment. It is a schematic diagram which shows an example of the silicon carbide semiconductor device of this embodiment. It is a schematic diagram which shows another example of the silicon carbide semiconductor device of this embodiment. It is a graph which shows the capacitance at the time of a gate voltage sweep. It is a graph which shows the X-ray absorption spectroscopic analysis result.

Hereinafter, a preferred embodiment which is an example of the silicon carbide semiconductor device of the present invention will be described.

The silicon carbide semiconductor device of the present embodiment includes a gate electrode, an insulating film of silicon dioxide (hereinafter, may be referred to as “SiO ₂ ”), and a semiconductor substrate of silicon carbide (SiC). Then, at the interface between the insulating film of silicon dioxide (SiO ₂ ) and the semiconductor substrate of silicon carbide (SiC) (hereinafter, may be referred to as "SiC / SiO ₂ interface"), two silicon atoms on the silicon carbide side are used. (Hereinafter, it may be referred to as "Si atom".) A nitrogen atom is coordinated to at least a part of a carbon site that is bonded only. That is, the nitrogen atom is bonded to the two Si atoms on the SiC side regardless of the bond to the atom of the insulating film of SiO ₂ .
In addition, the fact that a nitrogen atom is coordinated to at least a part of a carbon site bonded to only two Si atoms means that the carbon atom is substituted with a carbon atom bonded to only two Si atoms. It is also a concept that includes the introduction of a nitrogen atom into a carbon site in which a carbon atom bonded to only two Si atoms is defective.

Further, the silicon carbide semiconductor device of the present embodiment is an insulated gate type semiconductor device. The silicon carbide semiconductor device of the present embodiment includes a gate electrode, a SiO ₂ insulating film (SiO ₂ insulating film), and a SiC semiconductor substrate (SiC semiconductor substrate), and is located on the SiC side at the SiC / SiO ₂ interface. The structure of the insulated gate type semiconductor device is not particularly limited as long as the nitrogen atom is coordinated to at least a part of the carbon site bonded to the two Si atoms.

The silicon carbide semiconductor device of the present embodiment may have, for example, a MOS (Metal Oxide Semiconductor) structure or an IGBT (Insulated Gate Bipolar Transistor) structure. Further, it may have a planar structure or a trench structure. In the silicon carbide semiconductor device of the present embodiment, a known structure may be adopted for the structure other than the gate electrode, the SiO ₂ insulating film, and the SiC semiconductor substrate, depending on the target structure. Further, as a method for providing a structure other than the gate electrode, the SiO ₂ insulating film, and the SiC semiconductor substrate, a known method may be adopted.

Here, the silicon carbide semiconductor device of this embodiment will be described with reference to the drawings.
FIG. 1 is a schematic view showing an example of a crystal structure on the silicon carbide side of the interface between silicon carbide and silicon oxide in the silicon carbide semiconductor device of the present embodiment. Specifically, the schematic diagram shown in FIG. 1 shows a crystal structure seen from the a-plane on the SiC side at the SiC / SiO ₂ interface. That is, the front surface of the schematic view shown in FIG. 1 represents the a-plane of SiC. Further, in FIG. 1, the upper side of the crystal structure represents the m-plane. In FIG. 1, 11 represents a silicon (Si) atom, 12 represents a carbon (C) atom, and 13 represents a nitrogen (N) atom. As shown in FIG. 1, the nitrogen atom coordinates at least a part of the carbon site bonded to the two Si atoms at the SiC / SiO ₂ interface on the m-plane on the SiC side.

Further, FIG. 2 is a schematic view showing another example of the crystal structure on the silicon carbide side of the interface between silicon carbide and silicon oxide in the silicon carbide semiconductor device of the present embodiment. Specifically, the schematic diagram shown in FIG. 2 is a diagram showing the crystal structure on the SiC side at the SiC / SiO ₂ interface as a three-dimensional display. In the schematic view shown in FIG. 2, the upper surface side of the crystal structure represents the m-plane. As shown in FIG. 2, the nitrogen atom coordinates at least a part of the carbon site bonded to the two Si atoms at the SiC / SiO ₂ interface on the m-plane on the SiC side. In FIG. 2, the same atoms as those in the schematic diagram shown in FIG. 1 are designated by the same reference numerals.

FIG. 3 is a schematic view showing an example of the silicon carbide semiconductor device of the present embodiment. In FIG. 3, 300 is a silicon carbide semiconductor device, 31 is a SiC semiconductor substrate, 33 is an insulating film of SiO ₂ , and 35 is a gate electrode. Further, in FIG. 3, 39 indicates a SiC / SiO ₂ interface, and the silicon carbide semiconductor device 300 shown in FIG. 3 has a SiO ₂ insulating film (SiO ₂ insulating film) on a SiC semiconductor substrate (SiC semiconductor substrate) 31. ) 33 is provided, and the gate electrode 35 is provided on the SiO ₂ insulating film 33. A SiC / SiO ₂ interface 39 exists between the SiC semiconductor substrate 31 and the SiO ₂ insulating film 33. When observed from the surface a on the SiC side at the SiC / SiO ₂ interface 39, the schematic diagram shown in FIG. 1 is obtained.

FIG. 4 is a schematic view showing another example of the silicon carbide semiconductor device of the present embodiment. Specifically, the schematic diagram shown in FIG. 4 is a diagram showing a semiconductor device having a trench structure. In FIG. 4, 400 is a silicon carbide semiconductor device, 41 is a SiC semiconductor substrate, 43 is a SiO ₂ insulating film, and 45 is a gate electrode. The silicon carbide semiconductor device shown in FIG. 4 is provided with a trench extending from the upper surface to the lower surface of the SiC semiconductor substrate 41. Further, a SiO ₂ insulating film 43 is provided on the SiC semiconductor substrate 41 in the portion where the trench is provided. A gate electrode 45 is provided in a portion where the trench is provided so as to be in contact with the SiO ₂ insulating film 43. In FIG. 4, the portion indicated by M has the same structure as that of the silicon carbide semiconductor device shown in FIG. That is, in the semiconductor device 400, the SiO ₂ insulating film 43 is provided on the SiC semiconductor substrate 41, and the gate electrode 45 is provided on the SiO ₂ insulating film 43.
Hereinafter, the reference numerals will be omitted.

In the present specification, the "interface" between the insulating film of silicon dioxide and the semiconductor substrate of silicon carbide means the following range.
The "interface" is a range from the center to within 5 nm on the silicon carbide side, centering on the position where the oxygen concentration is 50% as the oxygen concentration in SiO ₂ in the transition region between SiO ₂ and SiC. And the range up to 5 nm on the silicon dioxide side is shown.
In the present specification, the m plane represents the (1-100 plane), the a plane represents the (11-20) plane, the Si plane (0001), and the C plane represents the (000-1) plane. The "-" is attached above the number to the right of the "-", but for convenience, it is attached to the left of the number.

Conventionally, for example, a semiconductor device in which a silicon dioxide film (SiO ₂ ) SiO ₂ insulating film is formed on a SiC semiconductor substrate by using SiC as a semiconductor substrate and thermally oxidizing the SiC semiconductor substrate is known. ing. A transition region is formed at the interface between the SiC semiconductor substrate and the SiO ₂ insulating film formed on the SiC semiconductor substrate. Since there are many defects inside this transition region, the interface state density is high and the channel mobility is inferior.
In addition, as a countermeasure, for example, by heat-treating in a nitrogen-containing gas (ammonia, nitrous oxide, nitric oxide, etc.) atmosphere, nitrogen is contained in the SiC / SiO ₂ interface to eliminate defects in the transition layer. It is known to improve channel mobility by reducing the amount.

For example, Patent Document 1 discloses an insulating film structure in which nitrogen is contained in a transition region near the SiC / SiO ₂ interface by performing heat treatment in a gas atmosphere such as nitric oxide (NO). To. Further, in this insulating film structure, the nitrogen concentration in the region from the SiC / SiO ₂ interface defined in the transition region to 5 nm on the SiC side and 5 nm on the SiO ₂ side is within a certain range. It is said that in a semiconductor device using this insulating film structure, fluctuations in the threshold voltage hardly occur, and stable electrical characteristics can be obtained.

However, even if the nitrogen concentration in the region from the SiC / SiO ₂ interface to the SiC side and the region to the SiO ₂ side is specified, stable semiconductor element characteristics (electrical characteristics) are sufficiently obtained, especially when a stress voltage is applied. I can't get it. In a semiconductor device using SiC, it is considered that it is not enough to specify the nitrogen concentration in a specific region from the SiC / SiO ₂ interface in the transition region in order to obtain stable electrical characteristics.
As described above, the conventional semiconductor device using SiC is required to have stable electrical characteristics, and further improvement in performance is desired.

Therefore, in the silicon carbide semiconductor device of the present embodiment, even the site where the nitrogen atom is coordinated at the SiC / SiO ₂ interface is specified. It is believed that this allows nitrogen to enter the appropriate sites, reducing dangling bonds and reducing carrier traps at the SiC / SiO ₂ interface. As a result, even when a stress voltage is applied to the gate electrode, it is considered that the semiconductor element has stable characteristics (for example, fluctuation of the threshold voltage is suppressed).

Hereinafter, the silicon carbide semiconductor device of the present embodiment will be described together with the manufacturing method.
As an example of a preferable manufacturing method of the silicon carbide semiconductor device of the present embodiment, for example, a step of providing an insulating film of SiO ₂ on a SiC semiconductor substrate (insulating film forming step) in which the manufacturing method is preferable, and a gas containing a nitrogen atom. It has a step of heat treatment in an atmosphere (heat treatment step) and a step of forming a gate electrode on the insulating film of SiO ₂ (gate electrode forming step).

(Insulating film forming process)
The insulating film forming step is a step of forming an insulating film of SiO ₂ on a SiC semiconductor substrate.

Examples of the SiC used for the semiconductor substrate include 2H-SiC, 4H-SiC, and 6H-SiC. Among these, 4H-SiC is preferable as SiC, for example, in terms of carrier electron mobility and the like.

The SiO ₂ insulating film is provided on the SiC semiconductor substrate, for example, by thermally oxidizing the SiC semiconductor substrate. As for the conditions of thermal oxidation, for example, it is preferable to perform thermal oxidation using oxygen gas at a temperature of 1100 ° C. to 1300 ° C. (for example, 1200 ° C.) in a dry atmosphere. Further, for example, thermal oxidation may be performed at a temperature of 1000 ° C. to 1300 ° C. (for example, 1100 ° C.) in a moist atmosphere containing water vapor. The thermal oxidation treatment time may be set according to the target film thickness of the insulating film.
The SiO ₂ insulating film is not limited to the thermal oxide film produced by thermal oxidation, and may be deposited on a SiC semiconductor substrate by, for example, a CVD (Chemical Vapor Deposition) method.

The SiO ₂ insulating film may be formed on any one of the m-plane, a-plane, Si-plane and C-plane of the SiC semiconductor substrate.

(Heat treatment process)
In the heat treatment (annealing) step, a SiC semiconductor substrate provided with a SiO ₂ insulating film is heat-treated in a gas atmosphere containing nitrogen atoms, so that only two Si atoms on the SiC side are formed at the SiC / SiO ₂ interface. This is a step of coordinating a nitrogen atom to at least a part of the carbon site to be bonded. It is believed that this step reduces dangling bonds and reduces carrier traps at the SiC / SiO ₂ interface. As a result, a silicon carbide semiconductor device having stable semiconductor element characteristics can be obtained even when a stress voltage is applied to the gate electrode.

At the SiC / SiO ₂ interface, the crystal plane in which the nitrogen atom coordinates with at least a part of the carbon site bonded to only two Si atoms on the SiC side is any of m-plane, a-plane, Si-plane and C-plane. It is often one plane and the deviation of each crystal plane is within ± 10%, and it is preferably m plane. For example, when a SiO ₂ insulating film is formed on the m-plane side of a SiC semiconductor substrate, nitrogen is present in at least a part of carbon sites bonded to only two Si atoms on the m-plane on the SiC side at the SiC / SiO ₂ interface. Atoms are coordinated. Similarly, when the SiO ₂ insulating film is formed on the a-plane side of the SiC semiconductor substrate, at least a part of the carbon sites bonded to only two Si atoms on the a-plane on the SiC side at the SiC / SiO ₂ interface. Nitrogen atoms are coordinated.

Gas containing nitrogen atoms is, for example, _NO, N 2 O, nitrogen oxide gas, such as NO _2; NH _3; and the like. The gas containing these nitrogen atoms may be used alone or in combination of two or more. Further, an inert gas such as nitrogen gas, argon gas, or helium gas may be used in combination with the gas containing a nitrogen atom.

The heat treatment temperature in a gas atmosphere containing nitrogen atoms is preferably in the range of, for example, 1250 ° C to 1350 ° C. If the heat treatment temperature is too low, the rate of coordination of nitrogen atoms will be too slow, and it will be difficult to obtain stable semiconductor device characteristics. Further, when the temperature of the heat treatment is too high, when the gas containing nitrogen atoms is, for example, nitrogen oxides, it is conceivable that the nitrogen oxides are decomposed and thermal oxidation proceeds instead. The heat treatment time in the heat treatment step includes, for example, a range of 10 minutes to 10 hours.

(Gate electrode forming process)
The gate electrode forming step is a step of forming a gate electrode on the SiO ₂ insulating film of the SiC semiconductor substrate on which the SiO ₂ insulating film is formed. The gate electrode may be polysilicon doped with impurities (either p-type polysilicon or n-type polysilicon). Further, the gate electrode may be a metal such as aluminum or a metal compound (for example, TiSi).
When the silicon carbide semiconductor device of the present embodiment has a trench structure, the gate electrode can be obtained, for example, as follows. A trench is formed on the surface of the SiC semiconductor substrate by dry etching or the like. Next, a SiO ₂ insulating film is formed on the SiC semiconductor substrate in which the trench is formed by the above-mentioned thermal oxidation or CVD method. Then, in the trench which SiO ₂ insulating film is formed, as can be provided on the SiO ₂ insulating film, for example, by depositing polysilicon doped with impurities, a gate electrode is formed.
Further, when the silicon carbide semiconductor device of the present embodiment has a planar structure, for example, a gate electrode such as polysilicon doped with impurities is formed so as to be on the SiO ₂ insulating film by the CVD method or the like. ..
Through the above steps, the silicon carbide semiconductor device of the present embodiment is obtained.

In the silicon carbide semiconductor device of the present embodiment, a known layer may be formed in addition to the layers described above. The method of providing the known layer is not particularly limited, and the known layer may be formed by a known method.

Examples will be described below, but the silicon carbide semiconductor device of the present embodiment is not limited to the examples.

<Example>
The silicon oxide semiconductor devices of Examples and Comparative Examples were produced as follows.
First, a commercially available 4H-SiC single crystal SiC semiconductor substrate is prepared. Next, a trench is formed on the surface of the prepared SiC semiconductor substrate by a dry etching method. Next, thermal oxidation is performed to form a SiO ₂ insulating film on the SiC semiconductor substrate inside the trench. The conditions for thermal oxidation of the silicon carbide substrate are 1300 ° C. and 0.1 hour under a dry oxygen atmosphere. Next, the silicon carbide substrate on which the SiO ₂ insulating film is formed is heat-treated (annealed) under the condition of 0.5 hours so that the temperature becomes 1250 ° C. or higher in nitric oxide having a concentration of 10%. .. Next, in contact with the SiO ₂ insulating film, on the SiO ₂ insulating film, by depositing polysilicon doped with impurities, providing a gate electrode in the trench. The SiO ₂ insulating film is a gate insulating film.
As described above, the silicon oxide semiconductor device of the example having the SiO ₂ insulating film and the gate electrode provided on the SiC semiconductor substrate was produced.
Further, the silicon oxide semiconductor device of the comparative example was manufactured in the same procedure as the silicon oxide semiconductor device of the example, except that the condition of the annealing treatment temperature was changed to 1150 ° C.

[Evaluation]
The obtained silicon oxide semiconductor device was analyzed by an X-ray absorption spectrophotometer (analysis conditions / facility used: Kyushu Synchrotron Optical Research Center, beamline used: BL12, measurement method: total electron yield method). The result of the analysis is shown in FIG. In FIG. 6, A represents the analysis result of the X-ray absorption spectroscopy of the silicon carbide semiconductor device of the example, and B represents the analysis result of the X-ray absorption spectroscopy of the silicon carbide semiconductor device of the comparative example. As shown in FIG. 6, no shoulder is seen in the absorption spectrum of the silicon carbide semiconductor device (A) of the example. Therefore, in the silicon oxide semiconductor device (A) of the embodiment, as shown in the schematic diagram shown in FIG. 1, nitrogen atoms are coordinated to at least a part of carbon sites bonded to only two Si atoms on the m-plane. I confirmed that it was there.
On the other hand, as shown in FIG. 6, in the absorption spectrum of the silicon oxide semiconductor device (B) of the comparative example, a shoulder is seen at the position indicated by the arrow S. Therefore, in the silicon carbide semiconductor device (B) of the comparative example, it was confirmed that the nitrogen atom is coordinated to at least a part of the carbon sites bonded to the three Si atoms. However, in the silicon oxide semiconductor device (B) of the comparative example, the nitrogen atom is coordinated to the carbon site that is bonded to only two Si atoms on any of the m-plane, a-plane, Si-plane and C-plane. I could not confirm that it was there.

Further, with respect to the obtained silicon oxide semiconductor device, a voltage was applied to the gate electrode to perform CV measurement (capacity-voltage measurement). FIG. 5 is a graph showing the capacitance at the time of sweeping the gate voltage. In FIG. 5, A represents the CV measurement result of the silicon carbide semiconductor device of the example, and B represents the CV measurement result of the silicon carbide semiconductor device of the comparative example. As shown in FIG. 5, it can be seen that the silicon carbide semiconductor device (A) of the example has a smaller hysteresis and a smaller fluctuation of the threshold voltage than the silicon carbide semiconductor device (B) of the comparative example.
Therefore, in the silicon carbide semiconductor device of the embodiment in which the nitrogen atom is coordinated to at least a part of the carbon site bonded to only two Si atoms, the fluctuation of the threshold voltage generated when the stress voltage is applied to the gate electrode. It can be seen that the semiconductor element has stable characteristics.

Claims (2)

With the gate electrode
With an insulating film of silicon dioxide,
With a silicon carbide semiconductor substrate,
At the interface between the silicon dioxide insulating film and the silicon carbide semiconductor substrate, nitrogen atoms are coordinated to at least a part of carbon sites that bond with only two silicon atoms on the silicon carbide side .
An insulated gate type silicon carbide semiconductor device in which the crystal plane on the silicon carbide side at the interface is the m-plane . The silicon carbide semiconductor device according to claim 1, wherein the deviation of the crystal plane is within ± 10%.