JP2013004643A - Manufacturing method of silicon carbide semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a silicon carbide semiconductor device capable of controlling a threshold voltage while suppressing channel mobility.SOLUTION: A manufacturing method of a silicon carbide semiconductor device comprises a step (b) of nitriding a silicon carbide substrate on which a silicon dioxide film is formed and a step (c) of heat-treating the nitrided silicon carbide substrate in an oxygen atmosphere including moisture vapor. The step (c) includes a step (c1) of raising or lowering a temperature of a heat treatment furnace into which the nitrided silicon carbide substrate was placed in an inert gas atmosphere. The step (c1)determines a temperature rising rate and/or a temperature dropping rate so that a decreasing rate of channel mobility in the silicon carbide substrate calculated by an expression (1) becomes less than or equal to 10% when channel mobility immediately after nitriding is μ, a temperature rising or dropping start time is t=0, heat treatment start time is t=t, heat treatment end time is t=t, time at which the substrate is taken out from the heat treatment furnace is t=t, a Boltzmann constant is k, and a temperature of the heat treatment furnace at time t is T(K).

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device, and more particularly to control of a threshold voltage.

  Silicon carbide has excellent physical properties, and enables the realization of a power device with high breakdown voltage and low loss. However, many interface states exist at the silicon carbide / silicon dioxide interface immediately after thermal oxidation. Due to this interface state, the channel mobility of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) becomes extremely smaller than the electron mobility in the bulk, and the on-resistance value becomes higher than the ideal value.

  As a cause of the generation of this interface state, it is considered that carbon atoms in silicon carbide are precipitated in the silicon dioxide film.

Therefore, after forming a silicon dioxide film on the silicon carbide layer, by performing a heat treatment in a nitrogen oxidizing gas atmosphere such as nitrogen monoxide (NO) or dinitrogen monoxide (N 2 O) or an ammonia (NH ₃ ) gas atmosphere, The interface state is reduced, and oxynitriding with nitrogen monoxide gas is particularly effective. By performing heat treatment in a nitrogen monoxide gas atmosphere, the interface states generated at the interface between the silicon carbide layer and the silicon dioxide film are electrically inactivated.

  By the way, when using a silicon carbide semiconductor device as a power device, ensuring high withstand voltage characteristics is a top priority. In order to realize this, the threshold voltage needs to have a certain level. However, when the above nitriding treatment is performed on a device having a relatively complicated structure such as a storage MOSFET in order to realize a low-resistance device, the threshold voltage approaches a theoretical value as the acceptor-type interface state decreases. If the power device is too low or bad, the normally-on characteristic is obtained.

For these reasons, in the development of silicon carbide MOSFETs, there is an urgent need to control the threshold voltage as well as improve the channel mobility. Patent Document 1 discloses a method of performing a heat treatment in an oxygen (O ₂ ) atmosphere containing water vapor (H ₂ O) after nitriding as a means for increasing the threshold voltage of the silicon carbide semiconductor device after nitriding. . A temperature range of 800 ° C. or higher and lower than 1100 ° C. is considered particularly good. For example, the threshold voltage is greatly increased to +8 V by heat treatment at 950 ° C. for 1 hour.

JP 2005-223003 A

G. Y. Chung et al., “Interface state density and channel mobility for 4H-SiC MOSFETs with nitrogen generation passivation,” Applied Surface Science 184, pp.399-403, 2001.

  However, if the silicon carbide semiconductor device is exposed to an inert gas atmosphere at 500 ° C. or higher after the nitriding treatment and before the heat treatment in an oxygen atmosphere containing water vapor, the interface state reduced by the nitriding treatment is again reduced. There is a problem that the channel mobility is lowered due to activation.

  In view of the above problems, an object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device that controls a threshold voltage while suppressing a decrease in channel mobility.

The method for manufacturing a silicon carbide semiconductor device of the present invention includes (a) a step of forming a silicon dioxide film on a silicon carbide substrate, (b) a step of nitriding the silicon carbide substrate on which the silicon dioxide film is formed, c) heat-treating the nitrided silicon carbide substrate in an oxygen atmosphere containing water vapor, and step (c) includes (c1) inactivating the temperature of the heat treatment furnace in which the nitrided silicon carbide substrate is charged. The step (c1) includes a channel mobility immediately after the nitriding treatment, μ _ch , the temperature rise or temperature drop start time in the step (c1) is t = 0, and the heat treatment The start time is t = t ₁ , the heat treatment finish time is t = t ₂ , the substrate removal time from the heat treatment furnace is t = t ₃ , the Boltzmann constant is k, and the temperature of the heat treatment furnace at time t is T (K). If

The rate of temperature increase and / or the rate of temperature decrease is determined so that the rate of decrease in channel mobility in the silicon carbide substrate in step (c1) obtained by the above is 10% or less.

The method for manufacturing a silicon carbide semiconductor device of the present invention includes (c) a step of heat-treating a nitrided silicon carbide substrate in an oxygen atmosphere containing water vapor, and step (c) includes (c1) nitridation treatment. Including a step of raising or lowering the temperature of the heat treatment furnace containing the silicon carbide substrate in an inert gas atmosphere, wherein the step (c1) has a channel mobility of μ _ch immediately after the nitriding treatment, and the step (c1). The temperature rising or cooling start time is t = 0, the heat treatment start time is t = t ₁ , the heat treatment end time is t = t ₂ , the substrate removal time from the heat treatment furnace is t = t ₃ , the Boltzmann constant is k, When the temperature of the heat treatment furnace at time t is T (K), the rate of decrease in channel mobility in the silicon carbide substrate in step (c1) obtained by equation (1) is 10% or less. Decide the heating rate and / or cooling rate Since, it is possible to control the threshold voltage while suppressing a reduction in channel mobility.

It is a figure which shows the process sequence of the heat processing in the oxygen atmosphere containing water vapor | steam. It is a figure which shows the change of the channel mobility with respect to the exposure time when a silicon carbide semiconductor device is exposed to 950 degreeC inert gas atmosphere. It is a figure which shows the change of the channel mobility with respect to the exposure temperature when a silicon carbide semiconductor device is exposed to inert gas atmosphere. It is sectional drawing which shows the structure of n channel lateral type | mold MOSFET. It is sectional drawing which shows the manufacturing process of n channel lateral type | mold MOSFET. It is sectional drawing which shows the manufacturing process of n channel lateral type | mold MOSFET. It is sectional drawing which shows the manufacturing process of n channel lateral type | mold MOSFET. It is sectional drawing which shows the manufacturing process of n channel lateral type | mold MOSFET. It is sectional drawing which shows the manufacturing process of n channel lateral type | mold MOSFET. It is sectional drawing which shows the manufacturing process of n channel lateral type | mold MOSFET.

(Prerequisite technology)
FIG. 1 shows a process sequence of heat treatment in an oxygen atmosphere containing water vapor. After the silicon carbide substrate on which the silicon dioxide film is formed is subjected to nitriding treatment to inactivate the interface states, heat treatment in an oxygen atmosphere containing water vapor is performed to raise the threshold voltage.

  A silicon carbide substrate is put into a furnace for performing the heat treatment, and the temperature is raised from the substrate charging temperature to the heat treatment temperature. When the heat treatment temperature is reached, the heat treatment is performed by switching the inflow gas from an inert gas to an oxygen gas containing water vapor. When the heat treatment is finished, the inflow gas is switched to the inert gas again, and the temperature is lowered from the heat treatment temperature to the substrate take-out temperature.

  As described above, the silicon carbide substrate is exposed to a high-temperature inert gas atmosphere in the temperature raising step and the temperature lowering step (the hatched region in FIG. 1) before and after the heat treatment step, and the channel mobility increases as this region increases. descend.

  FIG. 2 shows a change in channel mobility with respect to the exposure time when the silicon carbide substrate is exposed to an inert gas atmosphere at 950 ° C. When the temperature is constant, the channel mobility is expressed as a linear function of time, and the longer the exposure time, the lower the channel mobility. The decrease in channel mobility with respect to exposure time becomes reaction-limited.

  FIG. 3 shows changes in channel mobility with respect to exposure temperature for exposure times of 30 minutes and 1 hour, respectively. It can be seen that the longer the exposure time and the higher the exposure temperature, the more the channel mobility decreases.

Here, the amount of decrease in channel mobility is expressed by the Arrhenius equation. Since the activation energy of the interface state is 1.05 eV, when the exposure temperature is T [K], the channel mobility decreases in proportion to exp (−1.05 / kT) [cm ² / Vs]. . Further, when the exposure time is t [s], the amount of decrease in channel mobility is expressed as t × 750 × exp (−1.05 / kT) [cm ² / Vs]. In the temperature increasing / decreasing process indicated by hatching in FIG. 1, since the exposure temperature T [K] is a function of time t [s], the amount of decrease in channel mobility is ∫750 × exp (−1.05 / kT) dt. It is expressed as [cm ² / Vs].

  In consideration of this, the present invention prevents the channel mobility from exceeding the allowable amount by adjusting the exposure time of the inert gas atmosphere performed before and after the heat treatment process for threshold voltage control. It is.

(Embodiment 1)
<Configuration>
FIG. 4 is a cross-sectional view showing the structure of an n-channel lateral MOSFET (Metal-Oxide-Semiconductor Field-effect Transistor) as an example of the silicon carbide semiconductor device according to the present invention. The n-channel lateral MOSFET includes an n-type silicon carbide substrate 1, an epitaxial layer 2 made of p-type silicon carbide, an n-type drain region 3 and a source region 4, and a p-type well contact 5. Epitaxial layer 2 is formed on the surface of silicon carbide substrate 1. The drain region 3 and the source region 4 are formed apart from each other from the surface of the epitaxial layer 2 to a predetermined depth. Well contact 5 is formed on the surface of epitaxial layer 2 adjacent to source region 4.

  The n-channel lateral MOSFET further includes a gate oxide film 6, a gate electrode 7, a drain electrode 8, and a source electrode 9. Gate oxide film 6 is formed on epitaxial layer 2, drain region 3, and source region 4. The drain electrode 8 is formed on the drain region 3, and the source electrode 9 is formed on the source region 4 and the well contact 5. The gate electrode 7 is formed on the oxide film 6 so that both ends thereof overlap the drain region 3 and the source region 4 in the gate plan view.

<Operation>
When a voltage is applied to the gate electrode 7, an inversion channel layer is formed on the surface of the epitaxial layer 2 immediately below the gate electrode 7, and a path through which charges flow is formed between the drain region 3 and the source region 4. In the n-channel MOSFET, electrons are majority carriers, and electrons flowing from the source region 4 to the surface of the epitaxial layer 2 reach the drain electrode 8 through the surface of the epitaxial layer 2 according to the electric field formed by the voltage applied to the drain electrode 8. . Therefore, a current flows from the drain electrode 8 to the source electrode 9 by applying a voltage to the gate electrode 7.

<Manufacturing process>
5 to 8 are diagrams showing manufacturing steps of the n-channel lateral MOSFET shown in FIG. First, epitaxial layer 2 made of p-type silicon carbide is formed on n-type silicon carbide substrate 1 using an epitaxial crystal growth method (FIG. 5). The thickness of the epitaxial layer 2 may be about 1 to 50 μm, and the impurity concentration may be about 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ .

  As the plane orientation of silicon carbide substrate 1, (0001) plane, (000-1) plane, (11-20) plane, or the like can be used. Moreover, 4H, 6H, or 3C can be used for the silicon carbide substrate 1 as a polytype.

  Next, a mask is formed with resist, silicon dioxide, silicon nitride, or the like using a photoengraving technique so that the regions where the drain region 3 and the source region 4 are formed are exposed on the surface of the epitaxial layer 2. Impurities are ion-implanted using this mask as an impurity implantation blocking film to form a pair of n-type drain region 3 and source region 4 (FIG. 6). FIG. 6 shows a cross-sectional structure after removing the ion implantation mask.

  Next, a mask is formed on the surface of the epitaxial layer 2, the source region 4, and the drain region 5 using a photoengraving technique so that a portion where the well contact 5 is to be formed is exposed. Using this mask as an impurity implantation blocking film, p-type impurities are ion-implanted to form a well contact 5 adjacent to the source region 4 (FIG. 7). FIG. 7 shows a cross-sectional structure after the well contact 5 forming mask is removed.

For example, phosphorus (P) or nitrogen (N) can be used as the n-type impurity introduced into the drain region 3 and the source region 4, and the impurity concentration thereof is, for example, 1 × 10 ¹⁸ to 1 × 10 ²¹ cm. If it is about ^-3 . The drain region 3 and the source region 4 are formed shallower than the epitaxial layer 2. For example, boron (B) or aluminum (Al) can be used as the p-type impurity introduced into the well contact 5, and the impurity concentration thereof is, for example, 1 × 10 ¹⁸ to 1 × 10 ²¹ cm ^−3. Any degree is acceptable.

  Subsequently, the silicon carbide substrate 1 is heat-treated, for example, for 30 seconds to 1 hour under a high temperature condition of 1300 to 1900 ° C., for example, by a heat treatment apparatus. By this heat treatment, ions implanted into the drain region 3, the source region 4, and the well contact 5 are electrically activated. In the following description, the state in which epitaxial layer 2 is formed on the surface of silicon carbide substrate 1, the state in which various ion implantations are performed on the surface of epitaxial layer 2, and the state in which gate oxide film 6 is formed This is simply referred to as a silicon carbide substrate depending on the context.

  Next, gate oxide film 6 is formed on the silicon carbide substrate (FIG. 8). In the method for manufacturing the silicon carbide semiconductor device according to the present embodiment, after forming a silicon dioxide film as gate oxide film 6 by thermal oxidation, a step of nitriding, and then a step of further heat-treating in an oxygen atmosphere containing water vapor are performed. Prepare. In the following description, the silicon dioxide film is referred to as a silicon dioxide film 6 similarly to the gate oxide film 6.

  The silicon dioxide film 6 can be formed not only by thermally oxidizing the silicon carbide substrate in an atmosphere containing oxygen atoms but also by chemical vapor deposition. Alternatively, the silicon dioxide film 6 may be formed by chemical vapor deposition after oxidizing the surface of the silicon carbide substrate in an atmosphere containing oxygen or a nitrogen oxidizing gas atmosphere.

  After forming silicon dioxide film 6, the silicon carbide substrate is taken out of the heat treatment furnace and introduced into the nitriding furnace. The temperature of the nitriding furnace is raised, and when the inside of the furnace reaches the processing temperature, the inflow gas is switched to a nitrogen monoxide gas or nitrous oxide atmosphere, and the processing temperature is maintained for a predetermined time in this state. By performing such a nitriding process, the interface state between the silicon dioxide film 6 (gate oxide film 6) and the silicon carbide epitaxial layer 2 is deactivated, and the channel mobility is increased.

  As the inflow gas in the nitriding furnace, nitrogen monoxide gas or dinitrogen monoxide gas diluted with an inert gas such as nitrogen, argon, helium or krypton may be used. An atmosphere in which nitrous oxide gas is mixed may be used. Further, nitrogen dioxide gas or ammonia gas may be used, and the silicon carbide substrate may be exposed to plasma generated using a gas containing nitrogen element.

  The nitriding temperature is desirably 900 ° C. to 1450 ° C. This is because the nitriding rate is very slow at a low temperature of 900 ° C. or lower, and the inactivation of the interface state by nitrogen atoms hardly proceeds. Further, under high temperature conditions of 1450 ° C. or higher, thermal oxidation proceeds due to oxygen generated by decomposition of nitric oxide or dinitrogen monoxide, and a new interface state increases. The nitriding time is preferably about 10 minutes to 10 hours. After the nitriding treatment, the temperature inside the furnace is lowered to the substrate take-out temperature, and then the silicon carbide substrate is taken out.

  When the formation of the silicon dioxide film 6 and the nitriding process are completed, the silicon carbide substrate is moved to a heat treatment furnace and the temperature inside the furnace is increased from the substrate charging temperature to the heat treatment temperature in order to perform heat treatment in an oxygen atmosphere containing water vapor. Warm up. Here, it is important that the heat treatment temperature is sufficiently lower than the temperature at which the silicon carbide substrate is thermally oxidized. The inside of the heat treatment furnace is filled with an inert gas such as nitrogen gas, and the silicon carbide substrate is exposed to an inert gas atmosphere until just before the start of the heat treatment.

  When the furnace temperature approaches the heat treatment temperature, heat treatment is performed by switching the inflow gas from an inert gas to an oxygen gas containing water vapor.

  After completion of the heat treatment in an oxygen atmosphere containing water vapor, the temperature inside the heat treatment furnace is lowered to the substrate take-out temperature, and the silicon carbide substrate is taken out of the furnace.

  The silicon carbide substrate is exposed to an inert gas atmosphere in the temperature increasing / decreasing process before and after the heat treatment process in an oxygen atmosphere containing water vapor, whereby the interface state between the epitaxial layer 2 and the silicon dioxide film 6 is activated, and the channel Mobility decreases. Therefore, it is not desirable to expose the silicon carbide substrate to an inert gas atmosphere for a long time. Therefore, by controlling the temperature increase rate and temperature decrease rate of the heat treatment furnace, the decrease in channel mobility does not exceed the allowable amount.

That is, the channel mobility immediately after the nitriding treatment is μ _ch , the substrate loading time into the heat treatment furnace is t = 0 [s], the heat treatment start time is t = t ₁ [s], and the heat treatment end time is t = t ₂ [s. ], When the substrate removal time from the heat treatment furnace is t = t ₃ [s], the Boltzmann constant is k, and the temperature of the heat treatment furnace at time t is T [K], based on the Arrhenius equation

The rate of temperature increase and the rate of temperature decrease of the heat treatment furnace are determined so that the rate of decrease in channel mobility obtained by the above is less than the allowable value.

  For example, when the rate of temperature increase and the rate of temperature decrease are 10 ° C./min and 3 ° C./min, respectively, the rate of decrease in channel mobility exceeds 1% when the heat treatment temperature is 800 ° C. or higher according to equation (1).

  Therefore, when the channel mobility reduction allowable rate is 1%, the inflow gas is switched from an inert gas to an oxygen gas containing water vapor when the furnace temperature reaches 800 ° C.

  When the temperature increasing / decreasing rate changes, the heat treatment temperature that satisfies the permissible decrease rate of the channel mobility also changes according to the equation (1). For example, when the rate of temperature increase and the rate of temperature decrease are both 10 ° C. per minute, when the heat treatment temperature is 860 ° C. or higher, the rate of decrease in channel mobility exceeds 1%.

  Further, when the allowable rate of decrease in channel mobility changes, the upper limit of the heat treatment temperature that satisfies the allowable decrease rate of channel mobility also changes according to the equation (1). For example, if the temperature increase rate and the temperature decrease rate are 10 ° C./min and 3 ° C./min, respectively, and the allowable rate of decrease in channel mobility is 3%, the upper limit of the heat treatment temperature is 890 ° C. When the allowable rate of decrease in channel mobility is relaxed to 5% under the same temperature increase / decrease rate condition, the upper limit of the heat treatment temperature increases to 940 ° C.

  Of course, the lowering rate of channel mobility is better. However, in order to increase the threshold voltage, it is necessary to realize a constant high heat treatment temperature, and since the temperature increasing / decreasing rate is a finite value, it is necessary to allow a constant value for the rate of decrease in channel mobility. is there. As a result of practical verification in consideration of these points, it was found that the allowable rate of decrease in channel mobility is preferably 5%. Note that 3% or 1% may be used to further suppress the decrease in channel mobility, and 10% may be used to further increase the threshold voltage.

  In the above-described series of processing steps relating to the gate oxide film 6, the formation of the silicon dioxide film 6, the nitriding process, and the heat treatment in an oxygen atmosphere containing water vapor are performed in different processing furnaces. However, these steps may be performed continuously in the same furnace. By processing in the same furnace, the process time is shortened, and the substrate contamination accompanying the movement between apparatuses is reduced.

  Next, a gate electrode 7 is formed on the gate oxide film 6, and then the gate electrode 7 is patterned using photolithography (FIG. 9). The gate electrode 7 is patterned in such a shape that the drain region 3 and the source region 4 overlap with both ends in plan view, and the epitaxial layer 2 exposed between the drain region 3 and the source region 4 is located in the center thereof. .

  As a material for the gate electrode 7, n-type or p-type polycrystalline silicon (polysilicon) can be used. In addition, it may be n-type or p-type polycrystalline silicon carbide. Furthermore, aluminum or a low-resistance refractory metal such as titanium, molybdenum, tantalum, niobium, or tungsten may be used, or a nitride of a refractory low-resistance metal may be used.

  After patterning the gate electrode 7, unnecessary portions of the gate oxide film 6 are removed by patterning using a photoengraving technique and wet or dry etching to expose the surfaces of the drain region 3, the source region 4 and the well contact 5 ( FIG. 10). The gate oxide film 6 is formed longer than the gate electrode 7, and reliably separates the drain electrode and the source electrode formed in the next step from the gate electrode 7.

  Next, the drain electrode 8 and the source electrode 9 are formed on the drain region 3, the source region 4, and the exposed portions of the well contact 5 by film formation and patterning.

  As the material for the drain electrode 8 and the source electrode 9, aluminum, nickel, titanium, gold, or a composite thereof can be used. Further, in order to obtain ohmic contact with the drain region 3, the source region 4 and the well contact 5, a heat treatment at about 1000 ° C. may be performed after the drain electrode 8 and the source electrode 9 are formed.

  Through the above steps, the main part of the MOSFET whose sectional structure is shown in FIG. 4 is completed.

  In the above description, the MOSFET is taken up as the silicon carbide semiconductor device of the present invention. In addition, as an insulated gate transistor element having a silicon dioxide film formed on a silicon carbide layer as a gate insulating film, it is applied to an IGBT. Also good. In addition, as an insulated gate transistor element, a vertical semiconductor device in which a source, a gate electrode, and a drain electrode are formed with a substrate interposed therebetween is also used for a lateral semiconductor device in which a source, a gate, and a drain electrode are formed on the same main surface. It may be a type semiconductor element.

<Effect>
The method for manufacturing a silicon carbide semiconductor device of the present invention includes: (a) a step of forming a silicon dioxide film 6 on a silicon carbide substrate; and (b) a step of nitriding the silicon carbide substrate on which the silicon dioxide film 6 is formed. (C) heat-treating the nitrided silicon carbide substrate in an oxygen atmosphere containing water vapor, and the step (c) includes (c1) a heat treatment furnace charged with the nitrided silicon carbide substrate. In the inert gas atmosphere, the step (c1) includes the channel mobility immediately after the nitriding treatment as μ _ch , and the temperature rise or temperature drop start time in the step (c1). t = 0, the heat treatment start time is t = t ₁ , the heat treatment finish time is t = t ₂ , the substrate removal time from the heat treatment furnace is t = t ₃ , the Boltzmann constant is k, and the heat treatment furnace at time t When the temperature is T (K), ( ) The temperature increase rate and / or the temperature decrease rate is determined so that the rate of decrease in channel mobility in the silicon carbide substrate in the step (c1) obtained by the formula is 10% or less. The threshold voltage can be increased while minimizing the decrease.

  In the step (c1), since the temperature increase rate and / or the temperature decrease rate is determined so that the rate of decrease in channel mobility is 5% or less, the threshold value is maintained while minimizing the decrease in channel mobility. The voltage can be increased.

  In the step (c1), since the temperature increase rate and / or the temperature decrease rate is determined so that the rate of decrease in channel mobility is 3% or less, the threshold value is maintained while minimizing the decrease in channel mobility. The voltage can be increased.

  In the step (c1), the temperature increase rate and / or the temperature decrease rate is determined so that the rate of decrease in channel mobility is 1% or less, so that the threshold value is maintained while minimizing the decrease in channel mobility. The voltage can be increased.

  Further, by performing the nitriding treatment in the step (b) and the heat treatment in the step (c) in the same furnace, the process time can be shortened and the substrate contamination accompanying the movement between apparatuses can be reduced.

  In the step (c), since the heat treatment is performed at atmospheric pressure, the threshold voltage can be increased while minimizing the decrease in channel mobility.

  In step (a), silicon dioxide film 6 can be formed on the silicon carbide substrate by thermally oxidizing silicon carbide substrate 1 in an atmosphere containing oxygen atoms.

  Alternatively, in the step (a), the silicon dioxide film 6 can be formed on the silicon carbide substrate by chemical vapor deposition.

  Alternatively, in the step (a), even if the chemical vapor deposition method is applied after the surface of the silicon carbide substrate 1 is oxidized in an atmosphere containing oxygen or a nitrogen oxidizing gas atmosphere, the silicon dioxide film 6 is formed on the silicon carbide substrate. Can be formed.

  In the step (b), the silicon carbide substrate is heat-treated in a gas atmosphere containing at least one selected from nitrogen monoxide gas, dinitrogen monoxide gas, and nitrogen dioxide gas to perform nitriding treatment.

  Alternatively, in the step (b), a nitriding treatment is performed by heat-treating the silicon carbide substrate in an ammonia gas atmosphere.

  Alternatively, in the step (b), nitriding is performed by exposing the silicon carbide substrate to plasma generated using a gas containing a nitrogen element.

  The present invention can be applied to an insulated gate transistor element such as a MOSFET or IGBT having a silicon dioxide film formed on a silicon carbide substrate layer as a gate insulating film. According to the present invention, it is possible to suppress an excessive decrease in channel mobility in a heat treatment step in an oxygen atmosphere containing water vapor after nitriding.

  1 substrate 2 epitaxial layer 3 drain region 4 source region 5 well contact 6 gate oxide film 7 gate electrode 8 drain electrode 9 source electrode

Claims (12)

(A) forming a silicon dioxide film on the silicon carbide substrate;
(B) nitriding the silicon carbide substrate on which the silicon dioxide film is formed;
(C) heat-treating the nitrided silicon carbide substrate in an oxygen atmosphere containing water vapor,
The step (c)
(C1) including a step of raising or lowering the temperature of a heat treatment furnace charged with the nitrided silicon carbide substrate in an inert gas atmosphere,
In the step (c1), the channel mobility immediately after the nitriding treatment is μ _ch , the temperature increase or temperature decrease start time in the step (c1) is t = 0, the heat treatment start time is t = t ₁ , and the heat treatment end time Where t = t ₂ , the substrate removal time from the heat treatment furnace is t = t ₃ , the Boltzmann constant is k, and the temperature of the heat treatment furnace at time t is T (K),

The temperature increase rate and / or the temperature decrease rate is determined so that the rate of decrease in channel mobility in the silicon carbide substrate in the step (c1) obtained by the step is 10% or less.
A method for manufacturing a silicon carbide semiconductor device. In the step (c1), the temperature increase rate and / or the temperature decrease rate is determined so that the rate of decrease in the channel mobility is 5% or less.
A method for manufacturing a silicon carbide semiconductor device according to claim 1. In the step (c1), the rate of temperature increase and / or the rate of temperature decrease is determined so that the rate of decrease in channel mobility is 3% or less.
A method for manufacturing a silicon carbide semiconductor device according to claim 1. In the step (c1), the temperature increase rate and / or the temperature decrease rate is determined so that the rate of decrease in channel mobility is 1% or less.
A method for manufacturing a silicon carbide semiconductor device according to claim 1. The nitriding treatment in the step (b) and the heat treatment in the step (c) are performed in the same furnace.
The manufacturing method of the silicon carbide semiconductor device in any one of Claims 1-4. The step (c) is a step of performing the heat treatment at atmospheric pressure.
The manufacturing method of the silicon carbide semiconductor device in any one of Claims 1-5. The step (a) is a step of forming the silicon dioxide film by thermally oxidizing the silicon carbide substrate in an atmosphere containing oxygen atoms.
The manufacturing method of the silicon carbide semiconductor device in any one of Claims 1-6. The step (a) is a step of forming the silicon dioxide film by chemical vapor deposition.
The manufacturing method of the silicon carbide semiconductor device in any one of Claims 1-6. The step (a) is a step of forming the silicon dioxide film by chemical vapor deposition after oxidizing the surface of the silicon carbide substrate in an oxygen-containing atmosphere or a nitrogen oxidizing gas atmosphere.
A method for manufacturing a silicon carbide semiconductor device according to claim 8. The step (b) is a step of heat-treating the silicon carbide substrate in a gas atmosphere containing at least one selected from nitrogen monoxide gas, dinitrogen monoxide gas, and nitrogen dioxide gas.
The manufacturing method of the silicon carbide semiconductor device in any one of Claims 1-9. The step (b) is a step of heat-treating the silicon carbide substrate in an ammonia gas atmosphere.
The manufacturing method of the silicon carbide semiconductor device in any one of Claims 1-9. The step (b) is a step of exposing the silicon carbide substrate to plasma generated using a gas containing nitrogen element.
The manufacturing method of the silicon carbide semiconductor device in any one of Claims 1-9.

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