JP2017168601A - Silicon carbide semiconductor device and silicon carbide semiconductor device manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device and a semiconductor device manufacturing method which achieve effective reduction of an interface state density.SOLUTION: A silicon carbide semiconductor device comprises: a first conductivity type silicon carbide semiconductor substrate 1; and a gate insulation film 3 having a first film 311 which is provided on a surface of the silicon carbide semiconductor substrate 1 and formed by thermal oxidation and has a film thickness within a range from 0.5 nm to 10 nm, and a second film 312 formed by deposition of an insulation film on a surface opposite to the first film 311 on the silicon carbide semiconductor substrate 1 side. And atmosphere of thermal oxidation for forming the first film 311 is in a hydrogen and moisture-containing gas not containing oxygen.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a silicon carbide semiconductor device and a method for manufacturing a silicon carbide semiconductor device.

  Research and development of next-generation semiconductor devices using a silicon carbide (SiC) substrate is underway. Silicon carbide can form an insulating film by thermal oxidation like silicon (Si), but has a characteristic that channel mobility of a MOS (Metal Oxide Semiconductor) interface differs depending on a crystal plane or an oxidation method.

Silicon carbide oxidation methods include dry oxidation using dry oxygen (O ₂ ) as an oxidizing species, wet oxidation using water vapor (H ₂ O) as an oxidizing species, and the like. Further, the (000-1) plane and the (11-20) plane of the silicon carbide substrate are said to exhibit higher channel mobility than the (0001) plane when wet-oxidized. 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. Further, there is an interface state density as an index for evaluating channel mobility as an alternative, and it is generally known that the channel mobility tends to increase as the interface state density decreases.

In addition, as a method for generating water vapor in wet oxidation, there are pure water heating, pure water bubbling with oxygen gas, and the like, but at present, a pyrogenic method using a combustion reaction of O ₂ gas and H ₂ gas is common. . In this method, the flow rate ratio between O ₂ gas and H ₂ gas is explosive if the H ₂ gas is excessive, so that it is generally used at a flow rate ratio rich in O ₂ . Therefore, the oxidizing atmosphere is an atmosphere of H ₂ O generated and H ₂ O + O ₂ of unreacted O ₂ .

  With respect to the thermal oxidation of silicon carbide, a hysteresis and a flat having a step of annealing with hydrogen and a step of annealing with an inert gas following thermal oxidation of the silicon carbide substrate in oxygen or humidified oxygen. There is a method of improving a thermal oxide film of silicon carbide on a silicon carbide substrate that reduces band shift (see, for example, Patent Document 1).

Further, regarding the reduction of the interface state density, the (000-1) plane of the silicon carbide substrate is oxidized in a wet atmosphere composed of H ₂ O gas and O ₂ gas, or H ₂ O gas, O ₂ gas and inert gas. Then, there is a method of reducing the interface state density by heat treatment in an atmosphere containing H ₂ gas (see, for example, Patent Document 2).

In addition, with regard to the method of generating water vapor in wet oxidation, the platinum catalyst is used to increase the reactivity of hydrogen and oxygen, and the reaction is carried out at a temperature lower than the ignition temperature of the hydrogen mixed gas to generate moisture without burning at high temperature. There is a method (for example, refer to Patent Document 3). In this system, since there is no danger of explosion even if H ₂ gas is excessive, it can be used at a flow rate ratio rich in H ₂ .

JP-A-9-199497 Japanese Patent No. 4374437 JP 2000-72405 A

The (000-1) plane or the (11-20) plane of the silicon carbide substrate is wet-oxidized in a gas containing H ₂ O and O ₂ and heat-treated in an atmosphere containing H ₂ as hydrogen POA (Post Oxidation Annealing). By doing so, the interface state density is reduced. This is said to be because hydrogen or a hydroxyl group terminates the interface state.

  On the other hand, since the interface state density when dry oxidation is performed on the (000-1) plane or the (11-20) plane of the silicon carbide substrate in an atmosphere containing only dry oxygen, the MOS interface characteristics are poor. Further, when hydrogen POA is performed after dry oxidation, the interface state density is reduced, but it does not reach the interface characteristics when wet oxidation and hydrogen POA are combined.

Thus, in the formation of the gate insulating film on the (000-1) or (11-20) plane of the silicon carbide substrate, O ₂ is not effective in reducing the interface state density, and H ₂ O and H ₂ are effective. It is.

  Note that hydrogen or a hydroxyl group introduced by gate oxidation and POA effectively terminates the interface state, and if it exists in the gate insulating film, it causes electron trapping. Therefore, it segregates in a thin region including the interface. It is desirable that

Further, in the thermal oxidation of silicon carbide, surplus carbon is generated as the oxide film (SiO ₂ ) is formed. If oxidation progresses and the oxide film thickness increases, and this surplus carbon remains in the MOS interface or oxide film, there is a concern that the interface state density increases or the reliability decreases. On the other hand, there is a method of improving the MOS interface by first depositing an insulating film by CVD (Chemical Vapor Deposition) method, etc., and then oxidizing it, but first, surplus carbon generated by reoxidation is removed. It is difficult to penetrate and desorb the deposited insulating film.

As described above, in the prior art, O ₂ which is not effective in reducing the interface state density is used for wet oxidation of the (000-1) plane or the (11-20) plane of the silicon carbide substrate. The generated surplus carbon stays in the insulating film, and it is difficult to sufficiently reduce the interface state density.

  An object of the present invention is to provide a silicon carbide semiconductor device and a method for manufacturing the silicon carbide semiconductor device in which the interface state density is more effectively reduced.

  In order to solve the above-described problems and achieve the object of the present invention, a silicon carbide semiconductor device according to the present invention has the following characteristics. The silicon carbide semiconductor device includes a first conductivity type silicon carbide semiconductor substrate and a gate insulating film. The gate insulating film includes a first film having a thickness of 0.5 nm to 10 nm formed by thermal oxidation provided on the front surface of the silicon carbide semiconductor substrate, and the silicon carbide of the first film. And a second film in which an insulating film of an oxide film, a nitride film, or an oxynitride film is deposited on a surface opposite to the semiconductor substrate side.

  In order to solve the above-described problems and achieve the object of the present invention, a method for manufacturing a silicon carbide semiconductor device according to the present invention has the following characteristics. In the method for manufacturing the silicon carbide semiconductor device, first, a part of the gate insulating film is formed on the front surface of the first conductivity type silicon carbide semiconductor substrate by thermal oxidation. Next, an oxide film, a nitride film, or an oxynitride film is deposited on a part of the surface of the gate insulation film to form a gate insulation film. When forming a part of the gate insulating film, the thermal oxidation atmosphere is characterized by being in a gas not containing oxygen but containing hydrogen and water vapor.

  Further, in the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, the step of forming a part of the gate insulating film is performed in the atmosphere of either or both of temperature increase and temperature decrease in the thermal oxidation. , Hydrogen gas or diluted hydrogen gas.

  Also, in the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, the step of forming a part of the gate insulating film is replaced with hydrogen gas or diluted hydrogen gas before the temperature drop in the thermal oxidation. And holding for a predetermined time.

  Further, the method for manufacturing a silicon carbide semiconductor device according to the present invention is the above-described invention, wherein in the above-described invention, after the step of forming the gate insulating film, an inert gas of any of nitrogen, helium or argon, hydrogen gas at a predetermined temperature Alternatively, heat treatment is performed in an atmosphere of hydrogen gas diluted with the inert gas.

  In the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, the step of forming a part of the gate insulating film includes forming a part of the gate insulating film to a thickness of 0.5 nm to 10 nm. It is characterized by forming.

  According to the above-described invention, the gate insulating film has the film formed by thermal oxidation with a film thickness of 0.5 nm to 10 nm and the film on which the insulating film is deposited. By forming a deposited film after first forming from 0.5 nm to 10 nm in thickness by thermal oxidation, excess carbon is easily removed during thermal oxidation. For this reason, the interface state density is reduced, and high channel mobility of the silicon carbide semiconductor device can be realized.

In addition, by forming an oxide film by thermal oxidation in an atmosphere that does not contain O ₂ and contains H ₂ and H ₂ O, hydrogen or a hydroxyl group introduced by thermal oxidation can efficiently terminate the interface state. For this reason, the interface state density is greatly reduced, and high channel mobility of the silicon carbide semiconductor device can be realized.

Further, in the thermal oxidation atmosphere containing H ₂ and H ₂ O containing no O _2, by forming a thin oxide film from 0.5nm of 10 nm, hydrogen or hydroxyl, segregated at the thin region including the interface be able to. For this reason, it can prevent becoming a factor of an electron trap.

  According to the silicon carbide semiconductor device and the method for manufacturing the silicon carbide semiconductor device according to the present invention, there is an effect that the interface state density can be more effectively reduced.

It is sectional drawing which shows the structure of the MOS capacitor concerning embodiment. It is sectional drawing which shows the state in the middle of manufacture of the MOS capacitor concerning Embodiment (the 1). It is sectional drawing which shows the state in the middle of manufacture of the MOS capacitor concerning Embodiment (the 2). It is a figure which shows the measurement of the interface state density of a MOS capacitor. It is a figure which shows the interface state density obtained from the measurement result of each MOS capacitor produced in order to contrast with the MOS capacitor concerning Embodiment. It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 1). It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 2). It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 3). It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 4). It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 5). It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 6). It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 7). FIG. 8 is a cross-sectional view showing a state during the manufacture of the MOSFET according to the embodiment (No. 8). It is sectional drawing which shows the state in the middle of manufacture of MOSFET concerning a present Example (the 9). It is sectional drawing which shows an example of the semiconductor device which has a complicated MOS gate structure concerning this invention.

  Exemplary embodiments of a silicon carbide semiconductor device and a method for manufacturing the silicon carbide semiconductor device according to the present invention will be explained below 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. When the notations of n and p including + and − are the same, it indicates that the concentrations are close to each other, and the concentrations are not necessarily equal. 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)
In the embodiment, a silicon carbide semiconductor device will be described by taking the structure of a MOS capacitor as an example. FIG. 1 is a cross-sectional view showing the configuration of the MOS capacitor according to the embodiment. As shown in FIG. 1, the MOS capacitor according to the embodiment includes an n-type epitaxial film 2 on a first main surface (front surface) of an n-type silicon carbide substrate (first conductivity type silicon carbide semiconductor substrate) 1. Is deposited.

  N-type silicon carbide substrate 1 is a silicon carbide single crystal substrate doped with, for example, nitrogen (N). N-type epitaxial film 2 is a low-concentration n-type drift layer doped with, for example, nitrogen at an impurity concentration lower than that of n-type silicon carbide substrate 1. Hereinafter, n-type silicon carbide substrate 1 and n-type epitaxial film 2 are collectively referred to as a silicon carbide semiconductor substrate.

  Insulating film 3 is provided on the surface of n-type epitaxial film 2 opposite to n-type silicon carbide substrate 1. The insulating film (gate insulating film) 3 includes a first film 311 provided on the surface of the n-type epitaxial film 2 opposite to the n-type silicon carbide substrate 1, and an n-type carbonization of the first film 311. And a second film 312 provided on the surface opposite to the silicon substrate 1. The first film 311 is a film formed by thermal oxidation with a film thickness of 0.5 nm to 10 nm, and the second film 312 is an insulating film such as an oxide film, a nitride film, or an oxynitride film deposited thereon. It is a membrane.

  An aluminum gate electrode 4 made of aluminum (Al) is provided on a part of the surface of the insulating film 3 opposite to the n-type silicon carbide substrate 1. An aluminum back electrode 5 on which aluminum is deposited is provided on the second main surface (back surface) of n-type silicon carbide substrate 11.

(Manufacturing method of MOS capacitor according to embodiment)
Next, a method for manufacturing the MOS capacitor according to the embodiment will be described. 2 and 3 are cross-sectional views showing a state in the middle of manufacturing the MOS capacitor according to the embodiment.

(1) Step 1
First, as the n-type silicon carbide substrate 1, an n-type 4H—SiC (four-layer periodic hexagonal silicon carbide) substrate is prepared. An n-type epitaxial film 2 having a donor density of about 1.0 × 10 ¹⁶ / cm ^{3 is formed} on an n-type 4H—SiC (000-1) substrate (off substrate of 0 to 8 degrees from the (000-1) plane). Grow 10 μm. The state so far is described in FIG. The 4H—SiC substrate alone or the 4H—SiC substrate and the n-type epitaxial film 2 are collectively referred to as a 4H—SiC semiconductor.

(2) Step 2
Then, after washing the 4H-SiC semiconductor, 1 slm of H ₂ at 1000 ℃ (standard liter per minute) , in an atmosphere of flowing 2slm of H ₂ O, the n-type front surface side of the silicon carbide substrate 1 heat Oxidation is performed to form a part of the first film 311 of the insulating film 3 with a thickness of 0.5 nm to 10 nm.

Atmosphere thermal oxidation, the O ₂ in H ₂ and 1slm of 3 slm, is reacted with a platinum catalyst, the flow ratio of H ₂ and O ₂ by with H _{2 rich, 2H 2 + O 2 → 2H} 2 O In this reaction, there is no unreacted O ₂ , and an atmosphere of unreacted 1 slm H ₂ and generated ₂ slm H ₂ O is used. The thermal oxidation treatment temperature is preferably 800 ° C to 1200 ° C, more preferably 900 ° C to 1100 ° C. The thermal oxidation treatment time is appropriately adjusted according to the desired film thickness.

Further, the flow rate ratio between H ₂ and O ₂ may be H ₂ / O ₂ = 2 or more so that unreacted O ₂ is not generated. The H ₂ O concentration in the oxidizing atmosphere is preferably 1% or more, more preferably 7% or more. The upper limit of the H ₂ O concentration is not limited and may be 100% or less. Moreover, you may dilute with the inert gas in any one of nitrogen, helium, and argon which does not contribute to reaction.

Further, the temperature is raised in a nitrogen atmosphere, and the temperature is lowered in a hydrogen atmosphere. Before the temperature is lowered, the gas is replaced with hydrogen gas or diluted hydrogen gas, and kept in a hydrogen atmosphere for 30 minutes. Both the temperature rise and fall may be a hydrogen atmosphere or an inert gas atmosphere, and hydrogen may be diluted with an inert gas. Further, while the atmosphere containing the same H ₂ and between H ₂ O thermal oxidation, or may be cooled in an atmosphere containing H ₂ and H ₂ O diluted in an inert gas.

Here, Patent Document 1 performs heat treatment in an inert gas atmosphere or a hydrogen atmosphere after thermal oxidation of a silicon carbide substrate in oxygen or humidified oxygen, and includes H ₂ and H ₂ O of the present invention. It is different from thermal oxidation of the atmosphere.

Patent Document 2 is for performing heat treatment of an atmosphere containing H ₂ gas after thermal oxidation of an atmosphere made of H ₂ O gas and oxygen or H ₂ O gas, oxygen gas and inert gas. This is different from the thermal oxidation of the atmosphere containing H ₂ and H ₂ O of the present invention. In addition, Patent Document 2 describes that if a hydrogen heat treatment at 1000 ° C. is performed after silicon carbide is oxidized, the temperature is too high and the oxide film is reduced by hydrogen, but the H ₂ and H ₂ O of the present invention are reduced. No reduction of the oxide film at 1000 ° C. has been confirmed by the heat treatment in the atmosphere. This is presumably because H ₂ O is contained in the atmosphere.

(3) Process 3
Next, an insulating film of an oxide film, a nitride film, or an oxynitride film is deposited to form a second film 312, and the insulating film having a film thickness of about 50 nm is combined with the first film 311 formed by thermal oxidation in Step 2. 3 is formed. A method for depositing the insulating film 3 includes a method using silane (SiH ₄ ) or TEOS (tetraethoxysilane) (C ₈ H ₂₀ O ₄ Si) by a CVD method, but is not particularly limited. The film thickness of the insulating film 3 may be any film thickness that does not cause dielectric breakdown in the evaluation of the interface state density. Preferably it is 30 nm-150 nm.

(4) Step 4
Next, heat treatment is performed as POA for 30 minutes in an H ₂ gas atmosphere at 1000 ° C. The atmosphere of POA may be an inert gas such as nitrogen, helium (He), or argon (Ar), or an atmosphere in which H ₂ gas is diluted with an inert gas. The state so far is described in FIG.

(5) Process 5
Next, a circular aluminum gate electrode 4 is deposited on the insulating film 3 at room temperature, and an aluminum back electrode 5 is formed by depositing aluminum on the entire back surface. Thereby, the MOS capacitor shown in FIG. 1 is manufactured (manufactured).

(Measurement example of interface state density)
Next, it was verified how the interface state density is reduced by the present invention. In order to verify the control effect of the MOS interface according to the present invention, as a comparative example, a MOS capacitor in which the process 2 was not performed and a MOS capacitor in which the order of the process 2 and the process 3 was exchanged were manufactured. FIG. 4 is a diagram showing the measurement of the interface state density of the MOS capacitor. As shown in FIG. 4, the completed MOS capacitors were measured with a CV (Capacitance-Voltage) meter 6, and interface state densities were calculated and compared.

  FIG. 5 is a diagram showing the interface state density obtained from the measurement results of the MOS capacitor according to the embodiment and the MOS capacitor manufactured for comparison.

In FIG. 5, (e) only the deposited film (plotted with x) is the case where the thermal oxidation of step 2 is not performed, while (a) to (d) are the cases where the thermal oxidation of step 2 is performed. It is. As can be seen from FIG. 5, when the thermal oxidation of (a) to (d) is performed, the interface state density is reduced as compared with the case where the thermal oxidation of (e) is not performed. This shows that the interface state density is significantly reduced by thermal oxidation of the atmosphere containing H ₂ and H ₂ O.

  Further, (d) deposited film → thermal oxidation 1 nm (triangular plot) is a case where the order of steps 2 and 3 is changed and a film thickness of 1 nm is formed by thermal oxidation. Further, (c) Thermal oxidation 20 nm → deposited film (marked with □) is a case where an insulating film is formed in Step 3 after forming a film thickness of 20 nm by thermal oxidation in Step 2. On the other hand, (b) Thermal oxidation 10 nm → deposition film (plotted with ◇) is a case where an insulating film is formed in Step 3 after forming a film thickness of 10 nm by thermal oxidation in Step 2. (A) Thermal oxidation 1 nm → deposited film (circled plot) is a case where a film thickness of 1 nm is formed by thermal oxidation in step 2 and then an insulating film is formed in step 3.

  According to FIG. 5, when an insulating film is formed in step 3 after forming a film thickness of 1 or 10 nm by thermal oxidation in step 2 of (a) and (b), steps 2 and 3 in (d). It can be seen that the interface state density is reduced as compared with the case of changing the order. Accordingly, it can be seen that when the thermal oxide film and the deposited film are combined, the interface state density is further reduced by forming the deposited film after the thermal oxidation is first formed.

  In addition, after forming a film thickness of 1 or 10 nm by thermal oxidation in step 2 of (a) and (b), if an insulating film is formed in step 3, it is 20 nm by thermal oxidation of step 2 of (c). It can be seen that after the film thickness is formed, the interface state density is reduced as compared with the case where the insulating film is formed in Step 3. Thus, it is understood that the interface state density is further reduced by forming the deposited film after forming the thermal oxidation film with a thickness of 1 to 10 nm.

From the above, it can be seen that the interface state density is significantly reduced by thermal oxidation of the atmosphere containing H ₂ and H ₂ O. This is probably because hydrogen or hydroxyl group introduced by thermal oxidation effectively terminates the interface state. In the case where a thermal oxide film and a deposited film are combined, the interface state density is further reduced by forming the deposited film after first forming the film to a thickness of 1 to 10 nm by thermal oxidation. This is thought to be due to the ease of carbon removal during thermal oxidation. If a deposited film is formed first or the thickness of the thermal oxidation is increased, it is assumed that excess carbon generated due to the thermal oxidation is difficult to escape.

  As an example of the present invention, a silicon carbide MOSFET (Metal Oxide Semiconductor Field Effect Transistor) was fabricated, and channel mobility was evaluated as a characteristic of the silicon carbide MOSFET.

Example 1
Next, an embodiment of the present invention will be described with reference to FIGS. 6 to 14 are cross-sectional views showing states during the manufacture of the MOSFET according to this example. 6-14 is sectional drawing for every process for demonstrating the processes 1-9 at the time of manufacturing MOSFET on a silicon carbide (000-1) surface.

(1) Step 1
First, as shown in FIG. 6, an acceptor is formed on a p ⁺ type 4H—SiC (000-1) substrate 7 (0 to 8 degrees off substrate, preferably 0 to 4 degrees off substrate from the (000-1) plane). A p-type epitaxial film 8 having a density of 1 × 10 ¹⁶ / cm ³ is grown.

(2) Step 2
Next, as shown in FIG. 7, a SiO ₂ film having a thickness of 1 μm is deposited on the surface of the p-type epitaxial film 8 by a low pressure CVD method, and a mask 9 is formed by patterning by photolithography. Thereafter, for example, phosphorus (P) ions 10 are ion-implanted so that the substrate temperature is 500 ° C., the acceleration energy is 40 keV to 250 keV, and the impurity concentration is 2 × 10 ²⁰ / cm ³ . In FIG. 7, the region into which phosphorus is ion-implanted is a hatched region.

(3) Process 3
Next, as shown in FIG. 8, the mask 9 is removed, a 1 μm thick SiO ₂ film is deposited on the surface by low pressure CVD, and a mask 11 is formed by patterning by photolithography. Thereafter, for example, aluminum ions 12 are ion-implanted so that the substrate temperature is 500 ° C., the acceleration energy is 40 keV to 200 keV, and the impurity concentration is 2 × 10 ²⁰ / cm ³ . In FIG. 8, the region into which aluminum is ion-implanted is a region hatched more thinly than the region into which phosphorus is ion-implanted.

(4) Step 4
Next, as shown in FIG. 9, the mask 11 is removed, and activation annealing is performed in an argon atmosphere at 1600 ° C. for 5 minutes to form the drain region 13, the source region 14, and the ground region 15.

(5) Process 5
Next, as shown in FIG. 10, a field oxide film 16 having a thickness of 0.5 μm is deposited by low pressure CVD, and a part of the field oxide film 16 is removed by photolithography and wet etching to form an active region 17. To do.

(6) Step 6
Next, as shown in FIG. 11, a gate insulating film 18 having a thickness of 50 nm is formed by thermal oxidation and a deposited film. H ₂ and O ₂ are reacted using a platinum (Pt) catalyst to form an atmosphere containing H ₂ and H ₂ O having a moisture concentration of 67%, and after forming about 1 nm by thermal oxidation at 1000 ° C., A 49 nm deposited film was formed by the CVD method used. The temperature of thermal oxidation was raised in an N ₂ gas atmosphere, and the temperature was lowered in an H ₂ gas atmosphere, and held in an H ₂ gas atmosphere for 30 minutes before the temperature was lowered.

Next, heat treatment was performed for 30 minutes in a H ₂ gas atmosphere at 1000 ° C. as POA. The film thickness of the insulating film 18 may be determined according to a desired threshold voltage or dielectric breakdown voltage, and is preferably several nm to 150 nm. When the film thickness is 10 nm or less, the gate insulating film 18 may be formed only by thermal oxidation without using a deposited film.

  Next, polycrystalline silicon is deposited to a thickness of 0.3 μm on the gate insulating film 18 by a low pressure CVD method, and a gate electrode 19 is formed by patterning by photolithography.

(7) Step 7
Next, as shown in FIG. 12, contact holes are formed on the drain region 13, the source region 14 and the ground region 15 by photolithography and hydrofluoric acid etching, from which 10 nm thick aluminum and 60 nm nickel ( Ni) is deposited and patterned by lift-off to form the contact metal 20.

(8) Step 8
Next, as shown in FIG. 13, annealing is performed at 950 ° C. for 2 minutes in an atmosphere of an inert gas or a mixed gas of inert gas and hydrogen as ohmic contact annealing, and the contact metal 20 and the silicon carbide reaction layer 21 are formed. Form. The inert gas is nitrogen, helium, or argon.

(9) Step 9
Next, as shown in FIG. 14, 300 nm of aluminum is vapor-deposited on the surface, pad electrode 22 is formed on gate electrode 19 and reaction layer 21 by photolithography and phosphoric acid etching, and 100 nm of aluminum is vapor-deposited on the back surface. 23 is formed.

Here, when the characteristics of the silicon carbide MOSFET manufactured by the method for manufacturing the silicon carbide MOSFET shown in FIGS. 6 to 14 were evaluated, the channel mobility was as high as about 78 cm ² / Vs. It is considered that the interface state density is small because of high channel mobility.

(Comparative example)
In the step 6 of the first embodiment, the manufacturing method is the same as that of the first embodiment, except that the thermal oxidation in the atmosphere containing H ₂ and H ₂ O is not performed and the gate insulating film 18 having a thickness of 50 nm is formed only by the deposited film. When a silicon carbide MOSFET was fabricated and the characteristics were evaluated, the channel mobility was a low value of about 9 cm ² / Vs. This is presumably because the interface state density is not reduced because there is no thermal oxidation of the atmosphere containing H ₂ and H ₂ O.

(Example 2)
A silicon carbide MOSFET was manufactured by the same manufacturing method as in Example 1 except that the moisture concentration in the thermal oxidation atmosphere was changed to 1% in Step 6 of Example 1, and the channel mobility was about 14 cm ² / Vs. The value was lower than that of Example 1, but higher than that of Comparative Example. This is presumably because the concentration of H ₂ O and O ₂ is lower than that in Example 1, so that hydrogen or hydroxyl cannot sufficiently terminate the interface state, and the interface state density is not reduced.

(Example 3)
A silicon carbide MOSFET was manufactured by the same manufacturing method as in Example 1 except that the moisture concentration in the thermal oxidation atmosphere was changed to 7% in Step 6 of Example 1, and the channel mobility was about 37 cm ² / Vs. Although the value was lower than that of Example 1, it was higher than that of Comparative Example and Example 2. This is because the concentration of H ₂ O and O ₂ is higher than that of Example ₂ , but since the concentration of H ₂ O and O ₂ is lower than that of Example 1, hydrogen or a hydroxyl group cannot sufficiently terminate the interface state. This is probably because the unit density is not reduced.

Example 4
A silicon carbide MOSFET was manufactured by the same manufacturing method as in Example 1 except that in Step 6 in Example 1, both the temperature increase and decrease in thermal oxidation in an atmosphere containing H ₂ and H ₂ O were performed in a hydrogen atmosphere. However, the same characteristics as in Example 1 were exhibited. Thus, it can be seen that the interface state density can be reduced even if the atmosphere of temperature increase and decrease in thermal oxidation is a hydrogen atmosphere.

(Example 5)
A silicon carbide MOSFET was manufactured by the same manufacturing method as in Example 1 except that heat treatment was performed at 1000 ° C. for 30 minutes in an N ₂ atmosphere as POA in Step 6 in Example 1, and the channel mobility was about 38 cm ² / Although Vs and the value lower than Example 1 were shown, the value was higher than the comparative example. Accordingly, it can be seen that the interface state density can be reduced even if heat treatment is performed in an N ₂ atmosphere.

(Example 6)
In Step 6 of Example 1, a silicon carbide MOSFET was manufactured by the same manufacturing method as in Example 1 except that the deposited film was formed by CVD using silane and ammonia (NH ₃ ). Showed the same characteristics. Thus, it can be seen that the interface state density can be reduced even if the deposited film is formed by a CVD method using silane and ammonia.

  In Examples 1 to 6, a (000-1) substrate (0 to 8 degrees off substrate) having a crystal structure of 4H—SiC was used, but a (0001) substrate having a crystal structure of 4H—SiC ( 11-20) The same effect can be obtained with a substrate having another plane orientation such as a substrate.

As described above, the present invention has been described by taking the manufacturing method of the MOS capacitor and the lateral MOSFET using the p ⁺ type semiconductor substrate as the silicon carbide MOSFET as an example. However, the present invention is not limited to this, and the n ⁺ type semiconductor substrate is not limited thereto. The present invention can also be applied to a semiconductor device having a high breakdown voltage structure such as a vertical MOSFET using GaN, a semiconductor device having a trench gate or a complicated MOS gate structure, and the same effect can be obtained. Therefore, the present invention can be applied to various semiconductor device manufacturing methods without departing from the scope of the invention described in the claims.

The complex MOS gate structure is, for example, an element structure in which a channel is formed in the vicinity of the surface of the SiC epitaxial substrate in the on state. FIG. 15 is a sectional view showing an example of a semiconductor device having a complicated MOS gate structure according to the present invention. As shown in FIG. 15, in the vertical MOSFET, an n-type epitaxial layer 32 is formed on the front surface of an n ⁺ -type silicon carbide substrate 31.

The impurity concentration of n type epitaxial layer 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 layer 32. P type region 36 is exposed on the surface of n type epitaxial layer 32 opposite to the n ⁺ type silicon carbide substrate 31 side. A p-type SiC layer 37 having a lower concentration than p-type region 36 is formed over the surfaces of n-type epitaxial layer 32 and p-type region 36. An n-type region 33 that penetrates the p-type SiC layer 37 in the depth direction and reaches the n-type epitaxial layer 32 is formed in the p-type SiC layer 37 on the n-type epitaxial layer 32 where the p-type region 36 is not formed. . The n-type epitaxial layer 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 layer 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 19 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 the gate insulating film 18. The gate electrode 19 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 39 in contact with the n ⁺ -type silicon carbide substrate 31 is formed. By forming the gate insulating film 18 by the method of the present invention, a semiconductor device having a complicated MOS gate structure in which the interface state density is reduced and high channel mobility is realized can be manufactured.

  As described above, according to the silicon carbide semiconductor device according to the embodiment, the gate insulating film is a film formed by thermal oxidation with a film thickness of 0.5 nm to 10 nm, and an insulating film is deposited thereon. And having a film formed. By forming a deposited film after first forming from 0.5 nm to 10 nm in thickness by thermal oxidation, excess carbon is easily removed during thermal oxidation. For this reason, the interface state density is reduced, and high channel mobility of the silicon carbide semiconductor device can be realized.

In addition, by forming an oxide film by thermal oxidation in an atmosphere that does not contain O ₂ and contains H ₂ and H ₂ O, hydrogen or a hydroxyl group introduced by thermal oxidation can efficiently terminate the interface state. For this reason, the interface state density is greatly reduced, and high channel mobility of the silicon carbide semiconductor device can be realized.

Further, in the thermal oxidation atmosphere containing H ₂ and H ₂ O containing no O _2, by forming a thin oxide film from 0.5nm of 10 nm, hydrogen or hydroxyl, segregated at the thin region including the interface be able to. For this reason, it can prevent becoming a factor of an electron trap.

  As described above, the silicon carbide semiconductor device according to the present invention is useful for a high voltage semiconductor device used for a power supply device such as a power conversion device and various industrial machines.

1 n-type silicon carbide substrate 2 n-type epitaxial film 3 insulating film 311 first film 312 second film 4 aluminum gate electrode 5 aluminum back electrode 6 CV meter 7 p ⁺ type 4H-SiC (000-1) substrate 8 p-type epitaxial film 9 mask 10 phosphorus ion 11 mask 12 aluminum ion 13 drain region 14 source region 15 ground region 16 field oxide film 17 active region 18 gate insulating film 19 gate electrode 20 contact metal 21 reaction layer 22 pad electrode 23 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 drain electrode

Claims (6)

A first conductivity type silicon carbide semiconductor substrate;
A first film having a thickness of 0.5 nm to 10 nm formed by thermal oxidation provided on the front surface of the silicon carbide semiconductor substrate, and the silicon carbide semiconductor substrate side of the first film; A gate insulating film having a second film in which an insulating film of an oxide film, a nitride film, or an oxynitride film is deposited on the opposite surface,
A silicon carbide semiconductor device comprising: Forming a part of the gate insulating film on the front surface of the first conductivity type silicon carbide semiconductor substrate by thermal oxidation;
Depositing an insulating film of an oxide film, a nitride film or an oxynitride film on a part of the surface of the gate insulating film to form a gate insulating film;
Including
In the method of forming a part of the gate insulating film, the thermal oxidation atmosphere is in a gas not containing oxygen but containing hydrogen and water vapor.   3. The step of forming a part of the gate insulating film is characterized in that an atmosphere of either or both of temperature rise and temperature drop in the thermal oxidation is hydrogen gas or diluted hydrogen gas. A method for manufacturing a silicon carbide semiconductor device.   4. The method according to claim 2, wherein the step of forming a part of the gate insulating film is replaced with hydrogen gas or diluted hydrogen gas before the temperature is lowered in the thermal oxidation, and held for a predetermined time. A method for manufacturing a silicon carbide semiconductor device.   After the step of forming the gate insulating film, heat treatment is performed in an atmosphere of an inert gas of nitrogen, helium or argon, hydrogen gas, or hydrogen gas diluted with the inert gas at a predetermined temperature. The manufacturing method of the silicon carbide semiconductor device as described in any one of Claims 2-4.   The step of forming a part of the gate insulating film forms the part of the gate insulating film with a film thickness of 0.5 nm to 10 nm. A method for manufacturing a silicon carbide semiconductor device.

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