JP2003209251A - Silicon carbide semiconductor element and method for forming its insulation film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulation film of a silicon carbide semiconductor element in which an interface state density sufficient as the semiconductor element is reduced in the insulation film/silicon carbide interface of the semiconductor element, and to provide a method for forming the same. <P>SOLUTION: The silicon carbide semiconductor element comprises a silicon carbide board having a step including a height of two atomic layers or more on a surface, and an oxide film formed on a surface of the silicon carbide board so that an interface state density of the oxide film and a silicon carbide is 1.5×10<SP>12</SP>cm<SP>-2</SP>or less. The method for forming the insulation film of the silicon carbide semiconductor element comprises the steps of holding a plurality of set temperatures in an atmosphere containing an oxygen, annealing the film, second time annealing at a temperature set lower than the first time annealing set temperature continued to the first time annealing, and annealing n times (n≥2) in the atmosphere containing the oxygen held at at least two more different temperatures. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide semiconductor device made of silicon carbide, particularly to a gate insulating film of a power MOS semiconductor device and a method for forming the same, and particularly to a high speed, high breakdown voltage and low loss power. This makes it possible to realize a semiconductor device.

[0002]

2. Description of the Related Art An insulated gate type semiconductor device 21 made of conventional silicon carbide described as Conventional Example 1 has an n type epitaxial growth layer (n type layer) 23 on an n type substrate 22 as shown in FIG. Then, a p-type portion 24 is formed by diffusing or ion-implanting an impurity forming a p-type semiconductor such as Al into a part of the formed p-type semiconductor. The n-type portion 25 is formed by diffusing or ion-implanting impurities forming such an n-type semiconductor. The p-type portion 2 sandwiched between the portion where the n-type layer 23 reaches the surface and the n-type portion 25.
An oxide insulating film 26 is formed on the surface of No. 4, and a gate electrode 27a is further provided on the surface. The drain electrode 27c is formed on the back surface of the substrate, and the source electrode 27b is formed in contact with the n-type portion 25 and the p-type portion 24. This insulated gate type semiconductor device is p-typed by the bias applied to the gate electrode 27a.
The inversion layer formed on the surface of the mold portion 24 functions as a channel.

The contents of this prior art are, for example, Silicon C
arbide; A Review of FundamentalQuestions and Appli
cations to Current Device Technology, edited by W.
J. Choyke, H. Matsunami, and G. Pensl, Akademie Verlag
It is disclosed in Vol.II pp.369-388 of 1997. A silicon carbide semiconductor element provides a semiconductor element that contributes to energy saving by operating at high temperature with low loss, by utilizing the physical properties of silicon carbide, such as wide gap property, high dielectric strength, sufficient mobility, and high thermal conductivity. Is expected.

However, conventional silicon carbide semiconductor devices, especially
A semiconductor element including an oxide insulating film / silicon carbide interface such as MOSFET has insufficient characteristics at the oxide insulating film / silicon carbide interface.
It wasn't practical. The oxide insulating film 26 formed on the surface of the channel portion when the above-mentioned insulated gate semiconductor element is formed is formed by oxidizing the silicon carbide substrate on which the element pattern is formed by ion implantation or the like. Further, reoxidation annealing for treating in an atmosphere containing oxygen at a temperature lower than the temperature when the oxide insulating film is formed after the oxide insulating film is formed is used to remove the oxide insulating film and the oxide insulating film / silicon carbide interface. Higher performance has been reported.

Such a conventional oxide film forming method is disclosed in, for example, the literature P-type SiC MOS reliability with improved oxida.
tion procedures and aluminum or boron p-type dopan
ts, LALipkin and JW Palmour, proceedings of hig
As shown in h temperature electronics XIV-15-XIV-20, the formed oxide film is exposed to an oxidizing atmosphere at a temperature lower than the oxidation temperature, and the residual impurities existing near the interface are oxidized again to reduce the electrical characteristics. This is an attempt (reoxidation) to reduce the interface state density that is the cause. Until now, the temperature used for reoxidation was limited to one type.

Although these conventional methods of forming an insulating film of a silicon carbide semiconductor element certainly reduce the interface state density of the oxide insulating film / silicon carbide interface, the interface state density sufficient for a semiconductor element is obtained. By the time, it was necessary to further decrease by one digit or more, which was insufficient as a method for forming an insulating film. Furthermore, with respect to the breakdown voltage, in many cases it is less than 1MVcm ^-1 ,
It was insufficient. A breakdown voltage of about 10 MVcm ^-1 is necessary to realize a high breakdown voltage element. In addition, the oxide insulating film of the above conventional example
/ Interface state density Nit of silicon carbide interface ¹ × 10 1 ³ cm
^-2 or more, and the silicon carbide semiconductor device MOSFET of FIG. 2 formed by using this insulating film has a low channel mobility of about 10 cm ² / Vs, which is not sufficient for a practical semiconductor device. there were.

[0007]

SUMMARY OF THE INVENTION In order to realize a silicon carbide semiconductor device that can withstand practical use, at least 2 × 10 ¹² cm ^-2
The following interface state density Nit and channel mobility of 100 cm ² / Vs or more are required. When this channel mobility is achieved, the channel resistance of the MOSFET is reduced to be in parallel with the drift mobility in the case of a power device with a withstand voltage of several hundreds of volts, and the semiconductor device can be practically used as a power device.

Overcoming the problems of the prior art, the present invention provides
It is an object of the present invention to realize a low loss and high breakdown voltage semiconductor element that makes use of the properties of a wide gap semiconductor such as silicon carbide.

[0009]

DISCLOSURE OF THE INVENTION In the above-mentioned conventional example, the present inventors have examined that the dielectric strength of the oxide insulating film is small and insufficient and that the level density is large and insufficient. As a result, the following things became clear.
That is, the surface of the silicon carbide semiconductor substrate currently used uses the α-SiC (0001) offcut surface, and the surface has α-SiC (0001) offcut surface.
The present inventors have found that the inclusion of the (001) terrace and the (1-210) step is the cause of the low withstand voltage and the high level density, and based on this finding, the insulation of the present invention was found. A method of forming a film was invented.

The difference in the oxidation rate between the α-SiC (0001) plane (Si plane) and the (1-210) plane is, for example, Silicon Carbide;
A Review of Fundamental Questions and Application
s to Current Device Technology, edited by WJChoy
ke, H.Matsunami, and G.Pensl, Akademie Verlag 1997
No. Vol.II pp.369-388, but the evaluation of the characteristics of the oxide insulating film / silicon carbide interface was insufficient. Even for the method of forming the oxide insulating film, optimization based on the evaluation has not been made, and based on the evaluation result first revealed by the present inventors, the optimum method of forming the insulating film is established. Furthermore, a silicon carbide semiconductor device using this has been invented, which has never existed in the past.

A silicon carbide semiconductor device of the present invention includes a silicon carbide substrate including a step having a height of two atomic layers (monolayer) or more, and an oxide film formed on the surface of the silicon carbide substrate. The interface state density Nit of silicon carbide is 1.5 × 10 ¹² cm ⁻² or less.

In the silicon carbide semiconductor device of the above invention,
Silicon carbide substrates including steps having a height of two atomic layers or more are β-SiC (111), α-SiC (0001) such as 6H, 4H, 15R-SiC
Si surface, β-SiC (100), β-SiC (110), α-SiC such as 6H, 4H
It is preferable that the silicon carbide substrate has an off-cut surface of one or more crystal faces selected from (1-100) and / or α-SiC (11-20) as a surface.

A method of forming an insulating film of a silicon carbide semiconductor device according to the present invention includes a silicon carbide substrate including a step having a height of two atomic layers or more, and a silicon carbide including an oxide film formed on the surface of the silicon carbide substrate. A method of forming an insulating film of a silicon carbide semiconductor element, comprising: annealing a semiconductor element at a plurality of set temperatures in an atmosphere containing oxygen, the method comprising: a first annealing treatment; Characterized by performing a second annealing treatment at a set temperature lower than the set temperature and performing n times (n ≧ 2) of the annealing treatment under an atmosphere containing oxygen kept at at least two different set temperatures. And

In the method for forming an insulating film of a silicon carbide semiconductor device according to the above invention, the first annealing treatment in an atmosphere containing oxygen is 900 ° C. or higher, and the set temperature is 850 ° C.
It is preferable to include at least the following n-th annealing treatment.

Further, in the method for forming an insulating film of a silicon carbide semiconductor element according to the present invention, it is preferable that the annealing treatment at least n times in an atmosphere containing oxygen is a wet oxygen atmosphere.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The silicon carbide semiconductor device of the present invention comprises:
As shown in the enlarged view of the insulating film / silicon carbide interface in FIG. 1 (a), the silicon carbide substrate 1 including step 2 having a height of two atomic layers or more, and the oxide formed on the surface of the silicon carbide substrate. An insulating film 4 including the film 4, wherein the interface state density Nit at the interface 3 between the oxide insulating film 4 and the silicon carbide 1 is 1.5 × 10 ¹² cm ⁻² or less. To do.

A semiconductor device using an off-cut silicon carbide substrate 1 including a step 2 having a height of two monolayers or more, particularly a vertical insulated gate semiconductor device (M) for high power.
In the case of OSFET), the low interface state density of the insulating film / silicon carbide was realized for the first time by the present invention, and the channel resistance in the range where the interface state density Nit is 1.5 × 10 ¹² cm ⁻² or less is obtained. It was confirmed for the first time that it was at the same level as the drift resistance.

It was confirmed that a MOS semiconductor device capable of controlling a large current can be realized by utilizing this insulating film / silicon carbide interface having a low interface state density. Interface state density Ni
When t becomes 1.5 × 10 ¹² cm ^-2 or more, the MOSFET
When a semiconductor element is formed, the channel resistance becomes one digit or more larger than the drift resistance, and the loss becomes large.
It was confirmed that it is not suitable as a large current control power semiconductor device.

In the above-described silicon carbide semiconductor device of the present invention, the silicon carbide substrate including steps having a height of two atomic layers or more is α-SiC (111), 6H, 4H or the like α-SiC (0001), 15
Si surface of R-SiC, β-SiC (100), β-SiC (110), α of 6H, 4H, etc.
It has been confirmed that a silicon carbide substrate having an off-cut surface of one or more crystal faces selected from -SiC (1-100) and / or α-SiC (11-20) as a surface is preferable. Here, since it is difficult to grow an epitaxial film having good crystallinity on a substrate having an off-cut angle of 1 degree or less, it is not preferable. Further, it was confirmed that the present invention can be easily realized for a substrate having an off-cut angle of 10 degrees or less. Here, it was difficult to obtain a good epitaxial film for the off angle of 10 degrees or more of the silicon carbide substrate, and it was sometimes difficult to form a good insulating film of the present invention.

In the method for forming an insulating film of a silicon carbide semiconductor element according to the present invention, the oxidation treatment temperature is changed as shown in FIG. 1 (b) during the oxidation treatment of silicon carbide. Usually, (reoxidation) annealing treatment is performed after the oxidation treatment 7 at a high temperature of 1000 ° C. or higher.
In other words, the commonly used SiC epi film is from 3.5 degrees to 8 degrees.
It is grown on a silicon carbide substrate 1 having an OFF angle in the direction of (11-20) degrees, and its surface 3 is physically (0001) plane 5 as shown in FIG. 1 (a). (11-2
0) It is composed of plane 6. In particular, in the silicon carbide substrate 1 including the step 2 having a height of 2 atomic layers or more, (00
For a substrate whose OFF angle from the (01) plane 5 reaches 8 degrees,
As shown in (a), 14% of the substrate surface is (11-20)
It is constituted by the surface 6. The oxidation rate of the SiC epi film is
A thick oxide insulating film is formed about 3 times faster in the (11-20) plane than in the (0001) plane, and the optimum oxidation temperature in the reoxidation annealing treatment for eliminating the residual impurities described in the description of the conventional example. Is also different.

According to the method of forming an insulating film of a silicon carbide semiconductor element of the present invention, after performing reoxidation annealing treatment 8 on an (0001) plane in an atmosphere containing oxygen, (11-20)
It is based on a two-step annealing in which reoxidation annealing treatment 9 is performed on the surface in an atmosphere containing oxygen. (0001)
The face is less likely to be oxidized than the (11-20) face, so (0
The reoxidation annealing process for the (001) plane requires high temperature. After performing the first reoxidation annealing treatment 8 on the (0001) plane at a high set temperature, the (11-20) plane is regenerated at a temperature lower than the set temperature of the first reoxidation annealing treatment 8. It was effective to perform the oxidation annealing treatment 9.

Regarding the above-mentioned (11-20) plane, if it is a plane orthogonal to the (0001) plane, the same effect was confirmed for the (1-100) plane, and the present invention was effective. That is, by performing the above-described two-step annealing treatment of the present invention, it becomes possible to form an oxide insulating film on silicon carbide having a high breakdown voltage and a low level density. After that, even if annealing treatment is further added and annealing treatment is performed n times, the present invention can be realized as long as n is 2 or more.

The case of a silicon carbide substrate having an off-cut surface of a (0001) Si surface is shown above, but in general, the above-mentioned (000
The present invention is effective for off-cut planes composed of 1) plane, (11-20) plane, and equivalent planes such as (1-100) plane orthogonal to (0001) plane. confirmed. That is, a method for forming a silicon carbide semiconductor device and an insulating film therefor according to the present invention includes an oxide film formed on the surface of β-SiC (1
11), 6H, 4H, etc. α-SiC (0001), 15R-SiC Si surface, β-SiC
(100), β-SiC (110), 6H, 4H etc. α-SiC (1-100) and / or α-SiC (11-20) selected from the crystal planes of 1 or more off-cut plane It was confirmed to be effective for a silicon carbide substrate having a surface of.

That is, the above-mentioned off-cut surface is shown in FIG.
As shown in (a), a silicon carbide semiconductor device including a silicon carbide substrate 1 including step 2 having a height of two atomic layers or more, and a silicon carbide semiconductor element including an oxide film 4 formed on the surface 3 of the silicon carbide substrate,
A method of forming an insulating film of a silicon carbide semiconductor element, comprising performing annealing treatment while maintaining a plurality of preset temperatures in an atmosphere containing oxygen, wherein the first annealing treatment is followed by a temperature higher than the first annealing treatment setting temperature. Confirmed that it is effective to perform the second annealing treatment at a low set temperature and to include n times (n ≧ 2) annealing treatment in an atmosphere containing oxygen kept at at least two different set temperatures. did.

Further, it was confirmed that the present invention can be easily realized by carrying out the annealing treatment in an atmosphere containing oxygen at 1000 ° C. or lower. Here, if the annealing treatment in an atmosphere containing oxygen is performed at 1000 ° C. or higher, the oxidation progresses at the oxide film / silicon carbide interface during the annealing treatment, and the impurities remaining at the interface increase, which is favorable for the present invention. It was also confirmed that a good insulating film could not be formed.

Further, in the method for forming a silicon carbide semiconductor device and the insulating film thereof according to the present invention, the set temperature of the first annealing treatment 8 in an atmosphere containing oxygen is 900 ° C. or higher,
It is preferable that the set temperature of the second and subsequent annealing processes 9 is 850 ° C. or lower. When the set temperature of the annealing process 8 in the first atmosphere containing oxygen becomes 900 ° C. or lower, (0
The remaining impurities cannot be sufficiently eliminated by reoxidation annealing in an atmosphere containing oxygen with respect to the (001) plane, and it is difficult to form a good insulating film of the present invention. Further, when the set temperature of the second and subsequent annealing treatments 9 is 850 ° C. or higher, for example, the first oxidation treatment is performed on the (11-20) plane perpendicular to the (0001) plane to eliminate impurities. Oxidation of the oxide film / silicon carbide interface normalized by the reoxidation anneal progresses and the interface is reopened, making it difficult to form a good insulating film of the present invention.

Further, in the method for forming a silicon carbide semiconductor element and the insulating film thereof according to the present invention, the first annealing treatment 8 in an atmosphere containing oxygen is a wet oxygen atmosphere.
It is preferable that the annealing treatment 9 after the first time also be in a wet oxygen atmosphere. When the annealing treatment in the atmosphere containing oxygen is a wet oxygen atmosphere containing water vapor, even if the annealing treatment in the wet oxygen atmosphere is performed only once in n times, the impurities remaining at the interface are removed. Was more efficient and effective.

For the first time, using the above-described method for forming an insulating film of a silicon carbide semiconductor element according to the present invention, an oxide insulating film in which the interface state density Nit between the insulating film and silicon carbide is 1.5 × 10 ¹² cm ⁻² or less. A film was formed. This low interface state density (Nit
For the first time, an insulating film having a thickness of 1.5 × 10 ¹² cm ⁻² ) has realized a silicon carbide semiconductor device MOSFET having a structure as shown in FIG. 2 and having a high mobility and capable of controlling a large current.

[0029]

EXAMPLES Example 1 As Example 1, a first example of the silicon carbide semiconductor device of the present invention will be described with reference to FIG.
The insulated gate semiconductor device 21 of Example 1 of the silicon carbide semiconductor device of the present invention is 5 × 10 ¹⁵ cm ^-3 on an n-type substrate 22 having a doping concentration of 5 × 10 ¹⁸ cm ^-3 as shown in FIG. An n-type epitaxial growth layer (n-type layer) 23 having a doping concentration of 10 μm is formed with a thickness of 10 μm, and Al (impurity forming a p-type semiconductor) ions are implanted into a part thereof to form the p-type portion 24. 5 × 10 ¹⁷ cm at a concentration of ^-3 is formed by a 2 micron thick, by ion implantation of n dopant to form the n-type semiconductor in a portion near the surface of the p-type portion of 10 ¹⁹ cm ^-3 An n-type portion 25 having a doping concentration is formed with a thickness of 0.3 micron. A silicon carbide substrate including a step having a height of two atomic layers or more of the present invention on the surface of a p-type portion sandwiched between the portion where the n-type layer 23 reaches the surface and the n-type portion 25. An oxide insulating film 26 formed on the surface and having an interface state density Nit of the oxide film and silicon carbide of 1.5 × 10 ¹² cm ⁻² or less was formed to a thickness of 25 nm. Further, an Al gate electrode 27a was provided on the surface thereof. The drain electrode 27c is alloyed by depositing Ni on the back surface of the substrate (heat treatment 10
The ohmic electrode was formed at 00 ° C. for 5 minutes, and the source electrode 27b was made of Ni so as to make ohmic contact with the n-type portion 25 and the p-type portion 24. In this insulated gate semiconductor device 21, the inversion layer formed on the surface of the p-type portion 24 by the bias to the gate electrode 27a acts as the channel region 28, and a current flows from the drain to the source to generate the gate voltage. The source / drain current was modulated by the FET operation.

As Example 1 of the silicon carbide semiconductor device of the present invention in this case, a device having a gate length of 2 microns and a gate width of 500 microns was formed. When the gate voltage was 10V, the source / drain current when applying 10V was more than 20mA. On the other hand, in the conventional silicon carbide semiconductor device having the interface state density of the insulating film, that is, the oxide film and silicon carbide of 10 ¹³ cm ^-2 or more, the semiconductor device of Example 1 of the first embodiment of the present invention is It has been confirmed that a current of 1 mA or less only flows under the same condition in a semiconductor element having a similar size.

The present inventors have found that the oxide insulating film of the semiconductor element of the present invention is the interface state density Nit of the oxide film and silicon carbide.
Was 1.5 × 10 ¹² cm ⁻² or less by the method described in Example 2. This low interface state density Nit
= 1.5 × 10 ¹² cm ⁻² or more, it was also confirmed that the source / drain current value was remarkably reduced to 1 mA or less. That is, it was also confirmed that when the interface state density Nit of the oxide film and silicon carbide is 1.5 × 10 ¹² cm ⁻² or more, the performance of the semiconductor element is significantly deteriorated and the semiconductor element becomes unusable. did.

In this case, the surface of the silicon carbide semiconductor element is
The surface is off-cut by 8 degrees with respect to the SiC (0001) crystal plane, and always has a step on the substrate surface (insulating film / silicon carbide interface). Here, when the step of the insulating film / silicon carbide interface is bunching and has a step of a height of two atomic layers or more, the interface state density Nit is 1.5 ×
It has been confirmed that it is particularly important that it is 10 ¹² cm ⁻² or less. According to the present invention, a significant increase in the source / drain current was confirmed, and a silicon carbide semiconductor element that can withstand the practical use of the present invention was realized.

Further, it includes a silicon carbide substrate including a step having a height of two atomic layers or more, and an oxide film formed on the surface of the silicon carbide substrate, and the interface state density Nit of the oxide film and silicon carbide is 1. In the semiconductor device of the present invention having a size of 5 × 10 ¹² cm ⁻² or less, when an ACCUFET having an n-type layer inserted in the channel portion 28 of the semiconductor device of Example 1 is formed, a channel of 100 cm ² / Vs or more is formed. Mobility was confirmed. The channel mobility of a similar conventional silicon carbide semiconductor device is 10 cm ² / Vs or less, and it was confirmed that the present invention can realize a silicon carbide semiconductor device that can be used practically. MOS formed in the first embodiment
When the channel resistance and drift resistance of the FET were estimated to be on, the values were in the order of approximately the same, and it was confirmed that a low-loss power element was formed. The interface state density is 1.5 x 1 using the conventional insulating film / silicon carbide interface.
When it was as large as 0 ¹² cm ^-2 or more, the channel resistance was larger than the drift resistance by one digit or more, which was not practical.

Further, in a semiconductor device including a silicon carbide substrate including a step having a height of two atomic layers or more and an oxide film formed on the surface of the silicon carbide substrate, the interface state density between the oxide film and silicon carbide is Nit is 1.5 × 10 ¹² cm ^-2
It was also confirmed that the dielectric strength of the oxide insulating film was 10 MVcm ^-1 or more when it was below. In a conventional silicon carbide semiconductor device including a silicon carbide substrate including a step having a height of two atomic layers or more and an oxide film having a large interface state density formed on the surface of the silicon carbide substrate, a withstand voltage is ¹ MVcm ^−1. This is the following, and for the first time in the semiconductor device of the present invention, sufficient withstand voltage that can be practically used was achieved.

The silicon carbide semiconductor device of the present invention contributes to energy saving by operating at high temperature with low loss, by utilizing the physical properties of silicon carbide such as wide gap property, high dielectric strength, sufficient mobility and high thermal conductivity. Provided is a semiconductor device.

In Example 1, the 8 ° off-cut surface of SiC (0001) was used as the substrate, and the silicon carbide semiconductor element formed on the surface was described. However, a step having a height of 2 atomic layers or more was used. Silicon carbide substrate containing other β-SiC
Α-SiC (0001) such as (111), 6H, 4H, Si surface of 15R-SiC, β-Si
C (100), β-SiC (110), α-SiC (1-100) such as 6H, 4H and /
Alternatively, it was confirmed that the present invention is effective even for a silicon carbide substrate having an off-cut surface of one or more crystal faces selected from α-SiC (11-20) as a surface.

(Embodiment 2) As an embodiment 2, an embodiment of a method for manufacturing an insulating film of a silicon carbide semiconductor device of the present invention is shown in FIG.
Will be explained. The single crystal wafer used to prepare the metal-oxide-semiconductor (MOS) sample is commercially available n-type 4-period hexagonal silicon carbide (4H-SiC). This single crystal wafer has a diameter of 2 inches and an off angle of 8 ° with respect to the (0001) plane, and an epitaxial film having an impurity concentration of 5 × 10 ¹⁵ cm ⁻³ is grown on the crystal surface. This single crystal was cut into a 5 mm × 5 mm square and used as a substrate for preparing a MOS sample. Before sample preparation, immediately after the surface of the substrate was organically cleaned, hydrogen was blown into oxygen at 1100 ° C to oxidize it with high-temperature steam generated (hydrogen combustion oxidation) to sacrifice the surface of the single crystal. The oxide film was melted with 3% thin hydrofluoric acid to expose the cleaned surface.
The silicon surface of the silicon carbide 4H-SiC substrate having this cleaned surface was subjected to hydrogen combustion oxidation at 1100 ° C for 1 hour to form a gate oxide film having a thickness of 25 nm.

Then, the oxidation temperature is lowered to 950 ° C.
The first annealing treatment was performed in a hydrogen combustion oxidizing atmosphere (wet oxygen atmosphere containing oxygen and water vapor) for a time. Then, lower the temperature to 800 ° C and continue for 3 hours in a hydrogen combustion oxidizing atmosphere (wet oxygen atmosphere containing oxygen and water vapor).
The second annealing treatment was performed. After completion of the multi-stage annealing treatment, the sample was pulled out from the reaction tube, and the sample temperature was rapidly cooled to room temperature to interrupt the chemical reaction near the SiO ₂ / 6H-SiC interface. Immediately after forming the gate oxide film, aluminum (Al) was vapor-deposited to form a MOS structure having an electrode with a diameter of 0.5 mm. Also,
The Mick electrode was prepared by removing the oxide film grown on the back surface and then depositing Al on the exposed surface of the 4H-SiC substrate.

The capacitance-weight (CV) characteristic of the 4H-SiCMOS structure is measured by a low frequency capacitance measurement / high frequency capacitance measurement / simultaneous measurement device (package
The measurement was performed at room temperature in the dark. In acquiring this CV characteristic, a voltage was swept from the inversion region to the accumulation region (forward sweep) and a measurement voltage was swept from the accumulation region to the inversion region (reverse sweep). In the forward sweep, the sample gate electrode surface was irradiated with ultraviolet rays before the sweep was started to form an inversion layer. After the inversion layer is formed, the ultraviolet irradiation is stopped, and then the measurement is performed at room temperature and in a dark state. On the other hand, when performing the backward sweep, ultraviolet irradiation is not performed.

FIG. 3A shows a steam annealing treatment at 950 ° C. for 3 hours and 800 ° C. for 3 hours, which is an example of the annealing treatment in the method for forming the insulating film of the silicon carbide semiconductor element of the present invention after the gate oxide film is formed. CV characteristics when continuously performed, and FIG. 3 (b) shows CV when only the steam annealing treatment at 950 ° C. for 3 hours, which is the annealing treatment of the conventional method for forming the insulating film of the silicon carbide semiconductor element, is performed. Show the characteristics.

In FIG. 3 (a), the high frequency CV curve changes from -13V to +
It is swept up to 10V. As the sweep voltage decreases, the capacity temporarily decreases (redistribution of minority carriers). Then voltage 0
The capacitance starts to increase from around V, but immediately it is understood that the capacitance is suppressed and bent (capacitance ledge). Also, in the quasi-static CV curve, it can be seen that a large wedge-shaped capacitance decrease is caused in the 0 V voltage region where the capacitance ledge appears. These facts mean that SiO ₂ / 4H-
This indicates that the interface state of the SiC interface is small.

On the other hand, in the sample subjected to only the steam annealing treatment at 950 ° C. for 3 hours in FIG. 3B, the redistribution of minority carriers and the capacitance ledge in the high frequency CV characteristic are not clear. In addition, the capacity decrease of the quasi-static CV curve is not clear, indicating that the interface state quantity is large.

As is clear from the comparison between FIGS. 3 (a) and 3 (b), the multistage steam annealing treatment, which is the method of forming the insulating film of the silicon carbide semiconductor device of the present invention, has the effect of reducing the interface state. Understand. This result shows that the oxidization atmosphere annealing treatment at 950 ° C. for 3 hours, which has a reoxidation effect on the (0001) plane, is followed by 800 ° C. for 3 hours, which has a reoxidation effect on the (11-20) plane. This is the result of performing the annealing treatment in the oxidizing atmosphere. As a result, the shape of the low-frequency CV characteristics has changed to a wedge shape, and the interface state amount has been reduced compared to the single-temperature annealing treatment that is the conventional method of forming an insulating film of a silicon carbide semiconductor device. I understand.

Shape of Insulating Film of Silicon Carbide Semiconductor Element of the Present Invention
The interface state density Nit in the example of the forming method is Nit = 1.09 × 10.¹²c
m^-2And the interface state density Nit = 5.15 × 10 in the conventional example.
¹²cm ^-2Is much smaller than that of the insulation of the present invention.
The effectiveness of the film forming method was confirmed.

In the second embodiment, the method of manufacturing the insulating film of the silicon carbide semiconductor device formed on the surface of the 8H off-cut surface of 4H-SiC (0001) is described. Silicon carbide substrate including a step having a height of other β-SiC (111), 6H, 4H α-SiC (0001),
15R-SiC Si face, β-SiC (100), β-SiC (110), α-SiC (1-100) such as 6H, 4H and / or α-SiC (11-20) It has been confirmed that the present invention is effective even for a silicon carbide substrate whose surface is an off-cut surface of one or more crystal planes.

In the second embodiment, the annealing treatment is 2 times.
Although the case of the number of times of annealing has been described, the carbonization including the step having a height of two atomic layers or more according to the present invention is performed even when the annealing is performed n times including changing the set temperature more times. Method for forming insulating film of silicon carbide semiconductor element, in which silicon carbide semiconductor element including silicon substrate and oxide film formed on the surface of silicon carbide substrate is annealed at a plurality of set temperatures in an atmosphere containing oxygen That is, following the first annealing treatment, the second annealing treatment is performed at a setting temperature lower than the first annealing treatment setting temperature, and oxygen containing at least two or more different setting temperatures is included. It was confirmed that it is effective if the annealing treatment of n times (n ≧ 2) in the atmosphere is included.

In the second embodiment, the case where the set temperature of the first annealing process is 950 ° C. and the set temperature of the second annealing process is 800 ° C. is described. However, the insulating film of the silicon carbide semiconductor device of the present invention is described. It is also confirmed that it is effective if the first annealing treatment in an atmosphere containing oxygen is 900 ° C. or higher and at least the nth annealing treatment whose set temperature is 850 ° C. or lower is included. did.

In the second embodiment, the case where the annealing treatment is performed in the hydrogen burning oxidation atmosphere which is a kind of the wet oxygen atmosphere has been described, but it is the method of forming the insulating film of the silicon carbide semiconductor element of the present invention. It was confirmed that at least the n-th annealing treatment in an atmosphere containing oxygen was effective when performed in a wet oxygen atmosphere containing at least water vapor and oxygen.

[0049]

As described above, according to the silicon carbide semiconductor device of the present invention, it is possible to realize a control device having a low loss and a high breakdown voltage for controlling a high power, for example, a high performance inverter for controlling an air conditioner or the like. Provide an energy-saving power element that can be used for practical use.

Further, according to the method for forming an insulating film of a silicon carbide semiconductor element of the present invention, a high withstand voltage, a low fixed charge density, and a low interface state density applicable to a gate insulating film of a low loss power element can be obtained. It is possible to obtain an insulating film of a silicon carbide semiconductor device, and to form a high-speed low-loss semiconductor device suitable for large power having a high breakdown voltage and a large current capacity.

[Brief description of drawings]

FIG. 1 (a) is an enlarged view of an insulating film / silicon carbide interface of a silicon carbide semiconductor device of the present invention. (b) It is a figure which shows the formation method of the insulating film of the silicon carbide semiconductor element of this invention.

FIG. 2 is a diagram showing a structure of an insulated gate semiconductor device.

FIG. 3 (a) is a diagram showing CV characteristics of an oxide insulating film / silicon carbide interface by the method for forming a silicon carbide semiconductor device and an insulating film thereof according to the present invention. (b) is a diagram showing CV characteristics of an oxide insulating film / silicon carbide interface by an insulating film forming method of a conventional example.

[Explanation of symbols]

1 substrate Two steps 3 Insulating film / silicon carbide substrate interface 4 Oxide insulation film 5 (0001) Terrace surface 6 (11-20) side 7 Oxidation set temperature 8 1st annealing set temperature 9 Second annealing set temperature 21 Insulated gate type semiconductor device 22 n type substrate 23 n-type epitaxial growth layer (n-type layer) 24 p-type part (p-type layer) 25 n + type layer 26 Oxide insulation film 27a Gate electrode 27b Source electrode ohmic junction 27c drain electrode 27d Schottky junction of source electrode 28 channel area

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hisayoshi Ito             1233 Watanuki-cho, Takasaki-shi, Gunma Japan Nuclear Power             Research Institute Takasaki Research Center (72) Inventor Makoto Kitahata             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kenya Yamashita             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Osamu Kusumoto             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Masao Uchida             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kunikata Takahashi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Ryoko Miyanaga             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 5F058 BA20 BC02 BF56 BF63 BH03                       BH20 BJ01

Claims (5)

[Claims] 1. A silicon carbide substrate including a step having a height of two atomic layers or more on a surface thereof, and an oxide film formed on the surface of the silicon carbide substrate, wherein an interface state density Nit of the oxide film and the silicon carbide is A silicon carbide semiconductor device having a size of 1.5 × 10 ¹² cm ⁻² or less. 2. The silicon carbide semiconductor device according to claim 1, wherein the silicon carbide substrate including a step having a height of two atomic layers or more is α-SiC such as β-SiC (111), 6H, 4H. (0001), 15
Si surface of R-SiC, β-SiC (100), β-SiC (110), α of 6H, 4H, etc.
-SiC (1-100) and / or α-SiC (11-20), which is a silicon carbide substrate having an off-cut surface of one or more crystal planes selected from the surface thereof as a surface. Semiconductor device. 3. A plurality of silicon carbide substrates including a step having a height of two atomic layers or more on the surface and a silicon carbide semiconductor element including an oxide film formed on the surface of the silicon carbide substrate in an atmosphere containing oxygen. A method of forming an insulating film of a silicon carbide semiconductor element, which comprises performing annealing treatment while maintaining the set temperature of
Subsequent to the first annealing treatment, the second annealing treatment is performed at a setting temperature lower than the first annealing treatment setting temperature, and n in an atmosphere containing oxygen kept at at least two different setting temperatures is used. A method for forming an insulating film of a silicon carbide semiconductor element, characterized in that the method includes a step (n ≧ 2) of annealing treatments. 4. The method for forming an insulating film of a silicon carbide semiconductor device according to claim 3, wherein the first annealing treatment in an atmosphere containing oxygen is 900 ° C. or higher, and the set temperature is 8.
A method for forming an insulating film of a silicon carbide semiconductor device, comprising at least an n-th annealing treatment at 50 ° C. or lower. 5. The method for forming an insulating film of a silicon carbide semiconductor device according to claim 3, wherein the annealing treatment in an atmosphere containing oxygen at least n times is a wet oxygen atmosphere. Method for forming insulating film of semiconductor element.