JP2006216918A - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor element having high channel mobility and a method of manufacturing the element. <P>SOLUTION: The method of manufacturing a semiconductor element, in which an oxide film is formed on a semiconductor substrate including SiC, includes a step of oxide film formation of forming an oxide film including SiO<SB>2</SB>on the semiconductor substrate in a condition where the SiC is not oxidized; and a step of oxynitride film formation for forming an oxynitride film by oxynitriding SiC at an interface between the oxide film and the semiconductor substratre. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor device having a high channel mobility of a MOS transistor and a manufacturing method thereof, and more particularly to a semiconductor device using SiC as a semiconductor substrate and a manufacturing method thereof.

  Silicon carbide (SiC) is a promising semiconductor material for high power, high frequency, high temperature device applications. The realization of high-performance transistors using SiC that cannot be achieved with existing semiconductor materials is expected. However, when a semiconductor element is manufactured using SiC as a semiconductor substrate, high-density defects are formed at the interface between the oxide film and SiC. It is known that the resistance component in this portion significantly reduces device performance.

Specifically, when a SiC MOS transistor is manufactured, a thick oxide film is conventionally formed by oxidizing SiC in a gas atmosphere such as O ₂ . However, in the MOS transistor formed by this method, many defects are generated at the interface between the oxide film and SiC. Then, the electron travel is significantly hindered by this defect, and the channel mobility that is a performance index of the transistor remains at 5 to ²⁰ cm ² / Vs.

Therefore, in order to improve channel mobility, for example, after forming a gate insulating film on SiC which is a semiconductor substrate, heat treatment is performed with H ₂ O (see Patent Document 1), or two steps at different temperatures are performed. It has been proposed to perform an oxidation process (see Patent Document 2).
JP 2003-86792 A (publication date; March 20, 2003) JP 2002-222945 A (publication date; August 9, 2002)

  However, the conventional configuration described above does not provide channel mobility at a level that can be actually used as a semiconductor device.

  The present invention has been made in view of the above problems, and an object thereof is to provide a semiconductor device having a high channel mobility and a method for manufacturing the same.

In order to solve these problems, the present inventors diligently studied a semiconductor element and a manufacturing method thereof. As a result, as one of the factors that hinder the increase in channel mobility, it has been found that an “interface transition layer” is generated at the interface between SiC and SiO ₂ that is an oxide film in the conventional method.

Specifically, for example, when fabricating a semiconductor element such as a MOS device (MOSFET (Metal Oxide Semiconductor Field Effect Transistor), etc.), it is essential to form a SiO ₂ film, which is an oxide film, on the surface of a semiconductor substrate, which is SiC. It is. Conventionally, the SiO ₂ film is formed by thermally oxidizing the SiC. However, in the conventional method of forming a SiO ₂ film by thermally oxidizing SiC, a large amount of defects are generated at the interface between SiO ₂ and SiC, and the speed of electrons traveling in this region is remarkably reduced. As a result, the device performance decreases, for example, the resistance increases. For example, when the present inventors form SiO ₂ on the SiC surface by heating and oxidizing SiC in an atmosphere of O ₂ , H ₂ O, N ₂ O, or the like, the above-described interface is formed at the interface between SiO ₂ and SiC. It has been found that a thick “interface transition layer (intermediate layer that is neither SiO ₂ nor SiC)” represented by SiC _x O _y, which causes a problem, is formed.

Then, the present inventors have further made intensive studies, as a result, together with eliminating the interfacial transition layer generated at the interface between the SiO ₂ and SiC, the interface between the SiO ₂ and SiC, a separate layer different from the interfacial transition layer As a result, it has been found that the channel mobility can be remarkably improved as compared with the conventional case, and the present invention has been completed.

That is, in order to solve the above-described problem, a method for manufacturing a semiconductor device according to the present invention provides a method for manufacturing a semiconductor device in which an oxide film is formed on a semiconductor substrate made of SiC, under the condition that the SiC is not oxidized. by forming a SiO ₂ on a semiconductor substrate, the oxide film forming step of forming an oxide film consisting of SiO _2, by oxynitride of SiC at the interface between the oxide film and the semiconductor substrate, the oxynitride film And an oxynitride film forming step of forming.

In the above-described method, an oxide film made of SiO ₂ that is not obtained by oxidizing SiC is formed on SiC that is a semiconductor substrate, and thereafter, SiC present at the interface between SiC and SiO ₂ is oxynitrided. A SiC oxynitride film is formed. Thereby, an interface transition layer represented by SiC _x O _y generated when SiC is oxidized as in the prior art is not generated. Therefore, it is possible to prevent a decrease in channel mobility due to the occurrence of the interface transition layer. Further, since the SiC oxynitride film is formed at the interface between SiC and SiO ₂ , the channel mobility can be further improved.

  In the method of manufacturing a semiconductor element according to the present invention, it is more preferable that the oxide film forming step is a method of forming the oxide film by CVD (vapor phase chemical deposition method).

The method for manufacturing a semiconductor device according to the present invention includes a heat treatment step of forming an oxide film made of SiO ₂ by heat-treating the Si film deposited on the SiC in a gas atmosphere containing oxygen. Is more preferable.

With the above configuration, an oxide film made of SiO ₂ can be formed more reliably without oxidizing SiC.

In the method for manufacturing a semiconductor device according to the present invention, it is more preferable that the oxynitride film forming step is heat-treated in an N ₂ O or NO atmosphere.

With the above configuration, SiC existing at the interface between SiC and SiO ₂ can be reliably oxynitrided.

In the method of manufacturing a semiconductor element according to the present invention, it is more preferable to form an oxynitride film having a thickness of 1 nm to 10 nm, more preferably 1 nm to 6 nm in the oxynitride film forming step. When the thickness of the oxynitride film is smaller than 1 nm, it is strongly affected by defects generated at the SiO ₂ film / SiC interface, and there is a possibility that the channel mobility is lowered. On the other hand, when the thickness of the oxynitride film is larger than 10 nm, the interface transition layer is also formed at the time of forming the oxynitride film, and there is a possibility that the channel mobility is lowered. Therefore, channel mobility can be further improved by forming the oxynitride film within the above range.

According to another aspect of the present invention, there is provided a method for manufacturing a semiconductor device comprising: forming SiO ₂ on a semiconductor substrate under a condition that the SiC is not oxidized in the method for manufacturing a semiconductor device in which an oxide film is formed on a semiconductor substrate made of SiC. Thus, a method including an oxide film forming step of forming an oxide film made of the SiO ₂ and a heat treatment step of heat-treating the semiconductor substrate on which the oxide film is stacked in an N ₂ O or NO atmosphere may be used. .

  The semiconductor element according to the present invention is obtained by the above manufacturing method. Thereby, a semiconductor element with further improved channel mobility can be provided.

In the method of manufacturing a semiconductor device according to the present invention, the oxide film forming step includes forming an oxide film made of SiO ₂ by forming SiO ₂ on the semiconductor substrate, or depositing Si on the semiconductor substrate. The channel mobility is increased by including a thin film forming step for forming a Si film by heat treatment and a heat treatment step for forming an oxide film made of SiO ₂ by heat-treating the Si film in a gas atmosphere containing oxygen. A further improved semiconductor element can be provided.

An embodiment of the present invention will be described as follows. In the method of manufacturing a semiconductor element according to the present embodiment, an SiC film made of SiO ₂ is formed on SiC, which is a semiconductor substrate, under the condition that the SiC is not thermally oxidized (oxide film forming step), and then SiC and SiO ₂ is a method of forming an SiC oxynitride film (SiO _x N _y ) obtained by oxynitriding SiC existing at the interface with the substrate 2 (oxynitride film forming step). This will be described.

(Oxide film formation process)
The following describes oxide film forming step of forming a SiO ₂ film on the SiC. In the present embodiment, the method is different from a SiO ₂ film formed by heating SiC to a high temperature (usually 1000 to 1200 ° C.) in an atmospheric gas such as O ₂ , H ₂ O, N ₂ O, or NO. The SiO ₂ film formed in (1) is formed on the SiC or on the SiC surface.

As a specific forming method, for example, (A) a method of depositing a SiO ₂ film on SiC by performing CVD under the condition that the SiC is not thermally oxidized, and (B) after forming a Si film on SiC. A method of forming a SiO ₂ film by oxidizing the Si under conditions where the SiC is not thermally oxidized can be mentioned. As will be described in detail below these methods, a method for forming the specific SiO ₂ film, is not limited to the above, SiC in a method other than a method of obtaining a SiO ₂ film by thermal oxidation Any method for forming a SiO ₂ film may be used.

Here, (A) a method of depositing the SiO ₂ film on the SiC by the CVD method will be described. Examples of the CVD method include thermal CVD and plasma CVD. Note that using these CVD, when depositing a SiO ₂ film on SiC, performing the CVD under the condition that the SiC is not thermally oxidized.

Specifically, the operating conditions for depositing (forming) a SiO ₂ film on the SiC by thermal CVD are, for example, SiH ₄ flow rate: ₂ sccm, N ₂ O flow rate: 250 sccm, N ₂ flow rate: 1000 sccm, pressure : 2660 Pa, substrate temperature: 600 ° C. The deposition time may be appropriately set depending on the thickness of the SiO ₂ film to be deposited, and may be about 3 minutes, for example.

Further, by plasma CVD, as the operating conditions for depositing an SiO ₂ film on the SiC, SiH ₄ flow rate: 3 sccm, _{N 2} O flow rate: 200 sccm, _{N 2} flow rate: 200 sccm, pressure: 50 Pa, RF power: 120 W, The substrate temperature may be a condition such as 450 ° C. The deposition time (processing time) may be appropriately set depending on the thickness of the SiO ₂ film to be deposited, and may be, for example, about 2 minutes.

When thermal CVD or plasma CVD is performed under the above conditions, a SiO ₂ film can be formed on the SiC without thermally oxidizing the SiC.

Next, (B) a method of forming a SiO ₂ film by forming a Si film on SiC and then oxidizing the Si under conditions where the SiC is not thermally oxidized will be described.

  As a method for depositing the Si film on the SiC, for example, a method of depositing using thermal CVD can be cited. Note that a Si film may be deposited on SiC by using a method other than the above. However, even if thermal CVD is used or other methods are used, Si is not thermally oxidized under the conditions. A film needs to be deposited.

Specifically, when the Si film is deposited by thermal CVD, for example, the SiH ₄ flow rate: 3 sccm, the H ₂ flow rate: 2000 sccm, the pressure: 10640 Pa, and the substrate temperature: 700 ° C. may be used. The deposition time (processing time) may be appropriately set depending on the thickness of the Si film to be deposited, and may be about 4 minutes, for example.

Next, by heat-treating the deposited Si film, for example, in a dry O ₂ atmosphere, a SiO ₂ film in which Si is thermally oxidized can be formed. In other words, the Si film deposited on SiC is oxidized to form a SiO ₂ film. Specifically, by reacting at a flow rate of O _{2 of} 1000 sccm and a temperature of about 800 ° C. for 2 hours, a SiO ₂ film in which Si is thermally oxidized can be formed. A high-quality (small defect) SiO ₂ / SiC interface can be formed by thermally oxidizing the Si deposited on the SiC without thermally oxidizing the SiC. The atmosphere for oxidizing the deposited Si film may be wet O ₂ , N ₂ O, or the like.

As described above, by forming the SiO ₂ film on the SiC without oxidizing the SiC, a thick interface transition layer may be generated as in the conventional method of oxidizing the SiC to obtain the SiO ₂ film. Absent.

Here, the reason why the methods (A) and (B) do not thermally oxidize SiC will be described. SiC differs in the rate of thermal oxidation and the temperature at which thermal oxidation occurs depending on the crystal plane. The most frequently used (0001) plane starts thermal oxidation at a temperature of about 900 ° C. or higher. Further, the (000-1) plane and the (11-20) plane are likely to oxidize and are oxidized from about 850 ° C. Therefore, in order to thermally oxidize the SiC and form the SiO ₂ film, the above temperature is required. Actually, since the formation speed is too slow at 900 ° C., in order to form a SiO ₂ film (oxide film) having a thickness (about 40 to 80 nm) necessary for device production from the relationship of the film formation speed in practical use, Usually, a high temperature of 1100 to 1200 ° C. is used.

However, in the methods (A) and (B), since the SiO ₂ film is deposited at a temperature lower than the temperature at which the SiC is thermally oxidized, the SiO ₂ film can be obtained without thermally oxidizing the SiC. Can be deposited. In crystallography, it is customary to add − on a number, but in this embodiment, a negative display is used.

In the oxide film forming step, the film thickness of the SiO ₂ film deposited on the semiconductor substrate SiC varies depending on the use and conditions used, but for example, in the case of power device application, about 40 to 80 nm. SiO ₂ film thickness of, SiO ₂ film thickness of about 5~40nm case of the high frequency device applications is more preferable.

(Oxynitride film formation process)
Then, after forming a SiO ₂ film on the SiC, described oxynitride film forming step of forming an oxynitride film of SiC the SiC by oxynitride at the interface between SiC and SiO ₂ film.

In order to form the SiC oxynitride film, for example, heat treatment may be performed in an N ₂ O or NO atmosphere.

Specifically, for example, heat treatment may be performed for 3 hours under the conditions of N ₂ O flow rate: 100 sccm, N ₂ flow rate: 1000 sccm, pressure: 1 atm, and temperature: 1300 ° C. Alternatively, heat treatment may be performed, for example, for 2 hours under the conditions of N ₂ O flow rate: 1000 sccm, pressure: 1 atm, and temperature: 1300 ° C. The optimum oxynitriding condition varies depending on the thickness of the SiO ₂ film formed on the SiC. That is, when the SiO ₂ film formed on the SiC is thin, a relatively short oxynitriding process is desirable, and when the SiO ₂ film formed on the SiC is thick, an optimal oxynitriding process is performed. Time is relatively long. This reason is deeply related to the thickness of the oxynitride film formed by the oxynitriding process, as will be described later. Moreover, although the above description shows the condition when N ₂ O is used, the same applies to the case of NO.

In the oxynitride film forming step, the thickness of the oxynitride film to be formed may be as small as possible, but is preferably in the range of 1 to 10 nm, and more preferably in the range of 1 to 6 nm. The range of 2 to 5 nm is particularly preferable. When the thickness of the oxynitride film is smaller than 1 nm, it is strongly affected by defects generated at the SiO ₂ film / SiC interface, and the effective channel mobility may be lowered. On the other hand, when the thickness of the oxynitride film is larger than 10 nm, the interface transition layer is also formed at the time of forming the oxynitride film, and there is a possibility that the channel mobility is lowered.

(Semiconductor element)
Then, by performing the oxide film formation step and the oxynitride film formation step, a semiconductor element in which an oxide film is formed on a semiconductor substrate made of SiC can be manufactured.

Specifically, when the insulating film is formed using the method (A) in the oxide film forming step, for example, as shown in FIG. 1, a SiO ₂ film is deposited by CVD on SiC as a semiconductor substrate. Then, an oxynitride film is formed by oxynitriding SiC present at the interface between SiC and SiO ₂ .

In the case of forming the insulating film by using the method (B) in the oxide film forming step, for example, as shown in FIG. 2, after forming a Si film on the semiconductor substrate SiC by CVD, The SiO ₂ film is laminated on the SiC by thermally oxidizing the Si deposited film under the condition that is not thermally oxidized. Then, an oxynitride film is formed by oxynitriding SiC existing at the interface between SiC and SiO ₂ .

  Thus, by manufacturing a semiconductor element, the oxynitride film is formed without being in contact with the atmosphere. Thereby, the defect which arises when the said oxynitride film contacts air | atmosphere can be prevented.

The semiconductor element according to the present embodiment has a configuration in which an oxynitride film obtained by oxynitriding SiC and SiO ₂ are sequentially stacked on SiC, which is a semiconductor substrate, and SiC, an oxynitride film, In addition, the oxynitride film and SiO ₂ are in direct contact with each other. More specifically, the semiconductor element according to the present embodiment has an interface transition layer (intermediate layer that is neither SiO ₂ nor SiC) represented by SiC _x O _y generated when SiC is oxidized. Absent.

As described above, the manufacturing method of the semiconductor element according to the present embodiment is made of SiO _{2 under the} condition that the SiC is not oxidized in the manufacturing method of the semiconductor element in which the oxide film is formed on the semiconductor substrate made of SiC. An oxide film forming step for forming an oxide film on the semiconductor substrate; and an oxynitride film forming step for forming an oxynitride film by oxynitriding SiC at an interface between the oxide film and the semiconductor substrate. Is the method.

In the above-described method, an SiC oxide film made of SiO ₂ that is not obtained by oxidizing SiC is deposited on SiC, which is a semiconductor substrate, and SiC existing at the interface between SiC and SiO ₂ is oxidized and nitrided. An oxynitride film is formed. Thereby, the interface transition layer represented by SiC _x O _y generated when SiC is oxidized is not generated. Thereby, it is possible to prevent a decrease in channel mobility due to the occurrence of the interface transition layer. Further, since the SiC oxynitride film is formed at the interface between SiC and SiO ₂ , the channel mobility can be further improved.

Also, in the method of manufacturing a semiconductor element according to the present embodiment, the oxide film forming step (A) deposits an oxide film made of SiO ₂ on the semiconductor substrate by a CVD method, or (B) A thin film forming step of depositing a Si thin film made of Si on a semiconductor substrate, and a heat treatment step of heat-treating the Si thin film in a gas atmosphere containing oxygen to form an oxide film made of SiO _2. It is more preferable. Thereby, an oxide film made of SiO ₂ can be formed more reliably without oxidizing SiC.

Further, in the method of manufacturing a semiconductor element according to the present embodiment, the oxynitride film forming step is a method of performing a heat treatment in an N ₂ O or NO atmosphere, so that SiC existing at the interface between SiC and SiO ₂ can be obtained. Can be reliably oxynitrided.

In addition, in the method for manufacturing a semiconductor element according to the present embodiment, in the oxynitride film forming step, a method of forming an oxynitride film having a thickness of 1 nm to 10 nm, more preferably 1 nm to 6 nm is more preferable. When the thickness of the oxynitride film is smaller than 1 nm, it is strongly affected by defects generated at the SiO ₂ film / SiC interface, and there is a possibility that the channel mobility is lowered. On the other hand, when the thickness of the oxynitride film is larger than 10 nm, the interface transition layer is also formed at the time of forming the oxynitride film, and there is a possibility that the channel mobility is lowered. Therefore, channel mobility can be further improved by forming the oxynitride film within the above range.

  Further, since the semiconductor element according to the present embodiment is obtained by the above manufacturing method, a semiconductor element with further improved channel mobility can be provided.

As a method for confirming whether the interfacial transition layer _(SiC x _{O y)} is present, for example, a method of depth analysis of secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) Is mentioned. Specifically, the presence / absence and thickness of the interface transition layer can be determined by analyzing the depth distribution of C, O, N, and Si atoms by SIMS.

The method for manufacturing a semiconductor element according to the present embodiment is obtained by thermally oxidizing SiC on the semiconductor substrate in the method for manufacturing a semiconductor element in which an oxide film is formed on a semiconductor substrate made of SiC. An oxide film forming step for forming an oxide film made of SiO ₂ by a method other than SiO ₂ , and an oxynitride film for forming an oxynitride film by oxynitriding SiC at the interface between the oxide film and the semiconductor substrate And a method including a forming step. According to the above configuration, on the SiC is a semiconductor substrate, by forming the oxide film composed of SiO ₂ without oxidizing the SiC, the interface between SiC and SiO _2, the composition and the SiC and SiO ₂ Can be prevented from forming another layer (SiC _x O _y (where x and y are arbitrary constants)). In addition, by forming the oxynitride film, defects generated at the interface between SiC and SiO ₂ can be prevented as in the conventional case, so that the interface can be made steep.

The semiconductor device according to the present invention may be manufactured by a method other than the above. For example, after forming an oxynitride film of several nm on SiC, an SiO ₂ film is deposited by CVD, and further N ₂ It may be produced by oxynitriding with O or NO.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these.
[Example 1]
In this example, an inverted n-channel MOSFET, which is a semiconductor device provided with the above-described semiconductor element, was created and the effective channel mobility was evaluated. The manufacturing process of the MOSFET will be described below.
(MOSFET)
In the present embodiment, the MOSFET manufacturing process includes (A) a source / drain region forming process, (B) a gate insulating film forming process, (C) a source / drain electrode forming process, and (D) a gate electrode forming process. It includes four steps. In the following description, an example in which a 4H—SiC (0001) epitaxial substrate is used as the semiconductor substrate is described.

(A) Source / Drain Region Forming Process FIG. 3 is a diagram for explaining a source / drain region forming process, which is a process of manufacturing a MOSFET according to the present embodiment.

First, as shown in FIG. 3A, using an epitaxial substrate having a substrate 31 and an epitaxial layer (corresponding to a semiconductor substrate (SiC) in the present invention) 32, an Al film 33 is formed on the surface of the epitaxial layer 32. After the formation, a resist was applied onto the Al film 33, and exposure / development was performed to pattern the resist 38. Next, as shown in FIG. The Al film 33 was patterned by etching the Al film 33 using the patterned resist 38 as a mask. Thereafter, as shown in FIG. 3C, P (phosphorus) ions (P ⁺ ) are implanted into the epitaxial layer 32 in a portion where the surface is exposed using the patterned resist 38 and the Al film 33 as a mask. Went. Next, as shown in FIG. 3D, after removing the resist 38 and the Al film 33, n ⁺ diffusion layers 40 and 41 were formed by annealing. P ⁺ ion implantation was performed at 300 ° C. The implantation dose is 4 × 10 ¹⁵ cm ⁻² . Further, after the implantation, annealing was performed at 1600 ° C. for 20 minutes to reduce crystal defects generated by the ion implantation.

  Thereby, source / drain regions were formed in the epitaxial substrate.

(B) Formation Process of Gate Insulating Film FIG. 4 is a drawing for explaining the forming process of the gate insulating film, which is one process of the MOSFET manufacturing process according to this example.

First, an SiO ₂ film (oxide film) 42 was formed on the 4H—SiC (0001) epitaxial layer 32 by thermal CVD. The treatment conditions at this time were SiH ₄ flow rate: ₂ sccm, N ₂ O flow rate: 250 sccm, N ₂ flow rate: 1000 sccm, pressure: 2660 Pa, and substrate temperature: 600 ° C., and the treatment was performed under these treatment conditions for 3 minutes. Thus, a 70 nm SiO ₂ film 42 was deposited on the epitaxial layer (SiC) 32 (oxide film forming step). At this time, an interface transition layer generated by oxidation of the SiC was not generated at the interface between SiC and SiO ₂ .

Next, SiC, which is the epitaxial layer 32, is deposited on the SiC by performing heat treatment for 3 hours under the conditions of N ₂ O flow rate: 100 sccm, N ₂ flow rate: 1000 sccm, pressure: 1 atm, and temperature: 1300 ° C. An SiC oxynitride film was formed at the interface with the SiO ₂ film 42 (oxynitride film forming step). That is, SiC oxynitride film 39 was formed by oxynitriding SiC existing at the interface between SiC and SiO ₂ .

Thus, a gate insulating film composed of the SiO ₂ film 42 and the SiC oxynitride film 39 was formed.

(C) Source / Drain Electrode Formation Process FIG. 5 is a drawing for explaining a contact hole formation process, which is a process for manufacturing a MOSFET according to this embodiment.

First, as shown in FIG. 5A, a resist pattern 43 for forming a contact hole was formed on the gate insulating film (SiO ₂ film 42 and SiC oxynitride film 39) by photolithography. Next, as shown in FIG. 5B, the gate insulating film was etched using the resist pattern 43 as a mask. Thereafter, as shown in FIG. 5C, a Ni film 44 was deposited on the resist pattern 43. Next, as shown in FIG. 5D, source / drain electrodes 45 and 46 were formed by removing the Ni film 44 and the resist pattern 43 formed on the gate insulating film. Further, a Ti / Al electrode film 47 was deposited on the back side of the substrate 31. In order to reduce the contact resistance of these electrodes, heat treatment was performed at 1000 ° C. for 2 minutes in an N ₂ gas atmosphere.

(D) Gate Electrode Formation Process FIG. 6 is a diagram for explaining a gate electrode formation process, which is a process of manufacturing a MOSFET according to this embodiment.

  First, as shown in FIG. 6A, a resist 48 was applied to the surfaces of the source / drain electrodes 45 and 46 and the gate insulating film, and the resist 48 was patterned by exposure and development.

  Next, as shown in FIG. 6B, an Al film 49 was deposited on the patterned resist 48. Thereafter, as shown in FIG. 6C, the gate electrode 50 was formed by removing the resist 48 and the Al film 49 formed on the resist. Finally, heat treatment was performed at 400 ° C. for 10 minutes in a forming gas atmosphere.

Thereby, the MOSFET according to this example was manufactured.
(Measurement of effective channel mobility)
The effective channel mobility of the MOSFET obtained as described above was measured. Specifically, in the oxynitride film forming step (B), the film thickness of the SiC oxynitride film 39, in other words, the oxide film thickness is changed by changing the heat treatment time. The effective channel mobility was measured. The results are shown in Table 1 and FIG. When the thickness of the SiC oxynitride film is 2 to 10 nm, high channel mobility is obtained. In particular, when the thickness of the SiC oxynitride film is ² to 5 nm, the channel mobility is 50 to 60 cm ² / Vs, which is about 8 times the value in the case of conventional dry O ₂ oxidation (no oxynitride film). became.

[Example 2]
A MOSFET was manufactured in the same manner as in Example 1 except that a 4H—SiC (000-1) epitaxial substrate was used. Then, the effective channel mobility of the obtained MOSFET was measured. The measurement results are shown in FIG. The maximum value of the effective channel mobility was 81 cm ² / Vs when the thickness of the SiC oxynitride film was ^{2 to} 3 nm.
Example 3
A MOSFET was manufactured in the same manner as in Example 1 except that a 4H—SiC (11-20) epitaxial substrate was used. Then, the effective channel mobility of the obtained MOSFET was measured. The measurement results are shown in FIG. The maximum value of the effective channel mobility was 128 cm ² / Vs when the thickness of the SiC oxynitride film was ^{2 to} 3 nm.
Example 4
A MOSFET was manufactured in the same manner as in Example 1 except for the (B) gate insulating film forming step (oxide film forming step) among the MOSFET manufacturing steps. The steps other than the step (B) of forming the gate insulating film in this embodiment will be described below.
(Oxide film formation process)
First, a Si film was formed on the epitaxial layer by thermal CVD. The treatment conditions at this time were SiH ₄ flow rate: 3 sccm, H ₂ flow rate: 2000 sccm, pressure: 10640 Pa, substrate temperature: 700 ° C., and the treatment was performed under these conditions for 4 minutes. Thereby, a Si film having a thickness of about 40 nm was deposited on the epitaxial layer (SiC).

Next, the Si film was thermally oxidized by reacting the epitaxial substrate on which the Si film was deposited at an O ₂ flow rate of 1000 sccm and a temperature of about 800 ° C. for 2 hours, whereby the SiO ₂ film 42 was formed.

Thus, the MOSFET according to this example was manufactured. Then, the effective channel mobility of the obtained MOSFET was measured. Specifically, in the oxynitride film forming step (B), the film thickness of the SiC oxynitride film 39, in other words, the increment of the oxide film thickness is changed by changing the heat treatment time. The effective channel mobility was measured. The results are shown in Table 2 and FIG. When the thickness of the SiC oxynitride film was 2 to 10 nm, improvement in channel mobility was confirmed. In particular, when the thickness of the SiC oxynitride film is ² to 5 nm, the channel mobility is 50 to 60 cm ² / Vs, which is about 8 times the value in the case of conventional dry O ₂ oxidation (no oxynitride film). became.

[Comparative Example 1]
Instead of the above (B) a gate insulating film formation step, _{O 2} atmosphere, 1150 ° C., except for a gate insulating film by SiC thermal oxidation of 4 hours, in the same manner as in Example 1, MOSFET of this comparative example Manufactured. That is, in this comparative example, there is no SiC oxynitride film, and the SiO ₂ film, which is a gate insulating film, is formed by thermally oxidizing SiC. And when the channel mobility of MOSFET obtained on 4H-SiC (0001) was measured, it was 7.3 cm < ² > / Vs.
[Comparative Example 2]
Instead of the above (B) a gate insulating film formation step, H 2 _O atmosphere, 1100 ° C., except for a gate insulating film by SiC thermal oxidation of 2 hours, in the same manner as in Example 1, the present comparative example A MOSFET was manufactured. That is, in this comparative example, there is no SiC oxynitride film, and the SiO ₂ film, which is a gate insulating film, is formed by thermally oxidizing SiC. And when the channel mobility of MOSFET obtained on 4H-SiC (0001) was measured, it was 12 cm < ² > / Vs.
[Comparative Example 3]
The MOSFET of this comparative example is the same as that of Example 1 except that the gate insulating film is formed by SiC thermal oxidation for 2 hours in an O ₂ atmosphere at 1250 ° C. instead of the step (B) of forming the gate insulating film. Manufactured. That is, in this comparative example, there is no SiC oxynitride film, and the SiO ₂ film, which is a gate insulating film, is formed by thermally oxidizing SiC. And when the channel mobility of MOSFET obtained on 4H-SiC (0001) was measured, it was 2.6 cm < ² > / Vs.
[Comparative Example 4]
Instead of the above (B) a gate insulating film formation step, N 2 _O atmosphere, is 1300 ° C., except for forming a gate insulating film by SiC thermal oxidation of 8 hours, in the same manner as in Example 1, the present comparative example A MOSFET was manufactured. That is, in this comparative example, the gate insulating film is formed by oxynitriding SiC. And when the channel mobility of MOSFET obtained on 4H-SiC (0001) was measured, it was 21 cm < ² > / Vs.
[Comparative Example 5]
(B) Instead of the step of forming the gate insulating film, after depositing a SiO ₂ film on SiC by CVD, the gate insulating film was formed by heat treatment at 1200 ° C. for 60 minutes in an O ₂ atmosphere. In the same manner as in Example 1, a MOSFET of this comparative example was manufactured. That is, in this comparative example, the gate insulating film deposited without SiC oxynitriding is formed. And when the channel mobility of MOSFET obtained on 4H-SiC (0001) was measured, it was 7.0 cm < ² > / Vs.
[Reference Comparative Example]
Instead of the above (B) a gate insulating film formation step, after the 4H-SiC (the 0001) is thermally oxidized in an _{O 2} atmosphere, a method of heat treatment at _{N 2} O atmosphere, literature [Fujihira, Tarui, Imaizumi, Otsuka, Takami, Ozeki, Applied Physics Society of SiC and related wide gap semiconductor research group 12th lecture proceedings collection p.73]. The channel mobility at this time is 25 cm ² / Vs.

  Table 3 shows the results of these examples and comparative examples. In addition, the maximum value is described about the effective channel mobility of Example 1 and 4 in a table | surface.

From the results shown in Table 3, an SiO ₂ film, which is an oxide film, is formed on SiC without thermally oxidizing SiC (non-thermal oxidation of SiC), and thereafter, SiC at the interface between SiC and SiO ₂ is oxynitrided. Thus, it can be seen that the effective channel mobility is remarkably improved.

Specifically, for example, when Example 1 and Comparative Example 5 are compared, it can be seen that the effective channel mobility is low only by forming the SiO ₂ film without thermally oxidizing SiC. Further, comparing Example 1 with the reference comparative example, it can be seen that the effective channel mobility is low only by oxynitriding the SiO ₂ film. Further, comparing Example 1 with Comparative Examples 1 and 3, it can be seen that the effective channel mobility is the worst unless an SiO ₂ film is formed by thermally oxidizing SiC and oxynitrided.

That is, in order to improve the effective channel mobility as compared with the prior art, (1) non-thermal oxidation of SiC (not to form an interface transition layer) and (2) oxynitriding SiC at the interface between SiC and SiO ₂ It can be seen that the following two conditions are necessary. It can be seen that the MOSFET according to the present invention satisfying the two conditions can obtain 2 to 8 times the characteristics as compared with the MOSFET manufactured by the conventional method (comparative example).

  From the results shown in Tables 1 and 2, the thickness of the oxynitride film to be formed is more preferably in the range of 1 to 10 nm, more preferably in the range of 1 to 6 nm, and particularly preferably in the range of 2 to 5 nm. I understand.

  The semiconductor element according to the present invention can be suitably applied to a semiconductor device such as a MOSFET.

Manufacturing of manufacturing a semiconductor device by forming an oxynitride film by depositing an SiO ₂ film on SiC, which is a semiconductor substrate, by CVD and then oxynitriding SiC present at the interface between SiC and SiO ₂ It is drawing explaining a method. After forming the Si film by CVD on the SiC is a semiconductor substrate, by thermally oxidizing the Si film under the conditions SiC is not thermally oxidized, acid upon by stacking an SiO ₂ film, and oxinitriding that on SiC It is drawing explaining the manufacturing method which manufactures a semiconductor element by forming a nitride film. It is drawing explaining the formation process of the source / drain area | region which is 1 process of the manufacturing process of MOSFET concerning a present Example. It is drawing explaining the formation process of the gate insulating film which is 1 process of the manufacturing process of MOSFET concerning a present Example. It is drawing explaining the formation process of the source / drain electrode which is one process of the manufacturing process of MOSFET concerning a present Example. It is drawing explaining the formation process of the gate electrode which is one process of the manufacturing process of MOSFET concerning a present Example. It is the graph which measured the effective channel mobility when changing the oxide film thickness in Examples 1-3. It is the graph which measured the effective channel mobility when the oxide film thickness in Example 4 was changed.

Explanation of symbols

31 Substrate 32 Epitaxial layer 38 Resist 39 Oxynitride film 40 Ion implantation layer 43 Resist pattern 45 Source / drain electrode (Ni)
46 Source / Drain Electrode (Ni)
47 Ti / Al electrode film 48 Resist 50 Gate electrode (Al)

Claims (7)

In a method for manufacturing a semiconductor element in which an oxide film is formed on a semiconductor substrate made of SiC,
Under conditions that do not oxidize the SiC, by forming a SiO ₂ on the semiconductor substrate, and the oxide film forming step of forming an oxide film consisting of the SiO _2,
A method of manufacturing a semiconductor device, comprising: an oxynitride film forming step of forming an oxynitride film by oxynitriding SiC at an interface between the oxide film and the semiconductor substrate.   2. The method of manufacturing a semiconductor element according to claim 1, wherein the oxide film forming step forms the oxide film by a CVD method. The oxide film forming step includes a thin film forming step of forming a Si film by depositing Si on the semiconductor substrate,
The by Si film is heat-treated in a gas atmosphere containing oxygen, a method of manufacturing a semiconductor device according to claim 1, characterized in that it comprises a heat treatment step of forming an oxide film made of the SiO _2. The oxynitride film forming step, a method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment under N 2 _O or NO atmosphere.   2. The method of manufacturing a semiconductor element according to claim 1, wherein in the oxynitride film forming step, an oxynitride film having a thickness of 1 nm to 10 nm is formed.   2. The method of manufacturing a semiconductor element according to claim 1, wherein in the oxynitride film forming step, an oxynitride film having a thickness of 1 nm to 6 nm is formed. In a method for manufacturing a semiconductor element in which an oxide film is formed on a semiconductor substrate made of SiC,
Under conditions that do not oxidize the SiC, by forming a SiO ₂ on the semiconductor substrate, and the oxide film forming step of forming an oxide film consisting of the SiO _2,
And a heat treatment step of heat-treating the semiconductor substrate on which the oxide film is laminated in an N ₂ O or NO atmosphere.

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