JP2008243919A - Method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device that easily forms the thickness of an SiO<SB>2</SB>film in approximately 20 to 100 nm by reducing an interface-level density close to an SiO<SB>2</SB>/SiC interface while increasing the density of the SiO<SB>2</SB>film, when manufacturing the semiconductor device having the SiO<SB>2</SB>film on an SiC board. <P>SOLUTION: The method has (a) a deposition step of supplying the upper section of the SiC board with the raw material gas of silicon and oxygen and depositing the SiO<SB>2</SB>film. The manufacturing method further has (b) an oxidation step of setting the SiC board depositing the SiO<SB>2</SB>film at a temperature from 200°C to 700°C and radical-oxidizing the SiC board by generating oxygen radicals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device using a SiC substrate.

  Power devices with strong demands for high withstand voltage and miniaturization are currently manufactured mainly using Si substrates, but they are approaching the performance limit due to the physical properties of Si. Therefore, a power device using a SiC substrate is expected. Since SiC has a forbidden band that is about three times as large as Si, the breakdown electric field is an order of magnitude larger. That is, the same breakdown voltage can be obtained with a thickness of 1/10. In addition, since the current density that can be handled is increased, the overall size can be reduced. If the power device is a MOSFET, the loss during power conversion can be reduced by two orders of magnitude or more compared to Si when a SiC substrate is used. Moreover, since the thermal conductivity is about 3 times larger than that of Si, the heat dissipation is good and the cooling of the equipment can be simplified. In other words, using a SiC substrate instead of a Si substrate has significant advantages such as small size, low loss, high efficiency, and simple cooling.

Since a gate insulating film of a transistor such as a MOSFET is required to have high insulating characteristics, a thermal oxide film is used in a Si power device. Thermal oxide film, Si substrate _{O 2, H 2 O, N} 2 O, by high-temperature annealing in an oxidizing gas atmosphere such as NO, is oxidized to the Si substrate thermally, the SiO ₂ film on the surface thereof It is a method of forming. In general, a high temperature of about 700 to 1200 ° C. is necessary, the insulating properties are excellent, and the SiO ₂ film / Si interface state density is very small. A thick film of 100 nm or more can also be formed.

However, when thermal oxidation is applied to the gate insulating film of a SiC power device, a problem not found in the Si power device occurs. When a SiC substrate is thermally oxidized, SiC is oxidized to form a SiO ₂ film, and at the same time, C is also oxidized to generate CO ₂ , CO, and the like. The generated CO _2, CO is discharged to the outside of the SiO ₂ film, without a portion of the C is oxidized, becomes C induced defects remaining on the SiO ₂ film of SiO ₂ film / SiC interface area, the interface Increase level density. For this reason, the problem that carrier mobility cannot be made high enough and the power loss by increase in channel resistance arise. In order to obtain an oxidation rate sufficient to obtain a 20-100 nm thick film necessary for the gate insulating film, a very high temperature of 900-1200 ° C. is required. Therefore, there is a problem that the production cost is higher than that of the Si power device, and the low oxidation temperature is one of the requirements.

As a countermeasure against this, a method of thermal nitridation using NO, N ₂ O, NH ₃ gas or the like after thermal oxidation has been studied. By introducing N in the vicinity of the SiO ₂ film / SiC interface by thermal nitridation, defects caused by C are deactivated and the interface state density is reduced (see, for example, Non-Patent Document 1 below).

In addition to the thermal oxidation, the SiO ₂ film can be formed by various methods, but the following constraints must be satisfied. (1) An SiO ₂ film with few C-induced defects can be formed. (2) A SiO ₂ film with few unoxidized defects (oxygen deficiency defects) can be formed. (3) A thick film of 20 to 100 nm can be formed. (4) A method in which no new defect is formed in the SiO ₂ film.

Typical oxidation methods other than thermal oxidation include radical oxidation methods using oxygen radicals generated by ozone decomposition, plasma decomposition, etc., and deposition methods that deposit SiO ₂ films by CVD or sputtering. is there.

  Since the oxygen radical used in the radical oxidation method has a very strong oxidizing power, the effect of removing C is extremely high when oxidizing SiC, and defects caused by C can be greatly reduced as compared with thermal oxidation. In addition, a high-quality oxide film with few unoxidized defects can be formed as in thermal oxidation.

The deposition method is a method in which Si and O in the SiO ₂ film are supplied from the outside of the SiC substrate to the surface of the SiC substrate, unlike the thermal oxidation method and the radical oxidation method. There are various methods depending on the supply form of Si and O, such as CVD, sputtering, PVD, and vapor deposition. Among the deposition methods, the CVD method can form an SiO ₂ film with the fewest defects and is also suitable for mass production.

As another method, a method in which a CVD-SiO ₂ film is formed on SiC and then only one Si atom layer on the surface of the SiC substrate is thermally oxidized at 700 ° C. or more and 900 ° C. or less is proposed. Utilizing the fact that the temperature dependence of the oxidation rate of thermal oxidation by O ₂ and H ₂ O differs between Si and SiC, the oxidation of SiC is suppressed, and only one Si atom layer is thermally oxidized. The temperature at which a practical oxidation rate can be obtained is about 700 ° C. or higher for Si, but about 900 ° C. or higher for SiC. Therefore, in the temperature range of 700 to 900 ° C., it is possible to suppress the oxidation of SiC and to thermally oxidize Si (for example, see Patent Document 1 below).

JP 2003-124208 A N. Kimizuka, K. Yamaguchi, K. Imai, T. Iisuka, C. T. Liu, R. C. Keller and T. Horiuchi, Symp. VLSI Technology, 2000, p. 92.

In reducing the interface state density in the vicinity of the SiO ₂ film / SiC interface, the thermal oxidation method satisfies the above (2) to (4), but the above (1) is a problem.

  Also, in the method of thermal nitriding after thermal oxidation, when N is introduced, defects due to N are generated and the above (4) becomes a problem, and the effect of reducing the interface state by nitriding is limited.

Further, in the radical oxidation method, oxygen radicals have unpaired electrons and are extremely active, so when passing through the SiO ₂ film, they are immediately deactivated due to scattering of the Si—O network. It also has a very short lifetime because it collides with another oxygen radical and recombines to form O ₂ molecules. Therefore, the diffusion length in the SiO ₂ film is very short, and it is difficult to form a thick film of 5 nm or more, and the above (3) becomes a problem. Since the SiC power device handles a high voltage, a film thickness of about 20 to 100 nm is necessary and cannot be applied as it is.

On the other hand, a CVD method, which is a typical deposition method, can easily form a thick film of 20 to 100 nm or more. However, in thermal oxidation and ozone oxidation, O is introduced into high-density SiC to form a high-density SiO ₂ film, whereas in the deposition method, Si and O are supplied from the outside and applied to the substrate. The density of the deposited SiO ₂ film is clearly lower than that of the thermal oxide film or the ozone oxide film. The Si-O bond network with wide gaps and large ring size occludes H ₂ O in the atmosphere, which usually causes defects such as Si-H and Si-OH, and the Si-O-Si bond angle There are more strained Si-O bonds and Si dangling bonds. For this reason, the defect density is high, and the insulation characteristics such as the withstand voltage and the leakage current are worse by one digit or more than the thermal oxide film and the radical oxide film. In particular, since the flow ratio of Si source gas to O source gas is not stable at the initial stage of film formation, many unoxidized defects such as Si-Si bonds, Si dangling bonds, Si-H, and Si-OH are generated. (2) becomes a problem, and the SiO ₂ film / Si interface state density becomes very high. Among the deposited oxide films, the SiO ₂ film formed by the CVD method is relatively excellent in insulating properties, but is inferior to a thermal oxide film or an ozone oxide film as compared with the deposited oxide film.

Further, according to the method described in Patent Document 1, a single layer of SiO ₂ film with few C-induced defects and unoxidized defects and no new defect generation is provided at the SiO ₂ film / SiC interface, and 20-100 nm. It is possible to form a thick film. However, this method has few defects such as C-induced defects and unoxidized defects in only one layer in the vicinity of the SiO ₂ film / SiC interface, and a large amount of unoxidized defects are present in a portion one or more layers away from the interface. The above (2) becomes a problem. Since the influence of Coulomb scattering of carriers due to these defects cannot be ignored, it cannot be said to be a sufficient countermeasure.

Accordingly, the present invention has been made to solve such a problem. In manufacturing a semiconductor device having a SiO ₂ film on a SiC substrate, the interface state density in the vicinity of the SiO ₂ film / SiC interface is reduced and SiO ₂ is reduced. It is an object of the present invention to provide a method for manufacturing a semiconductor device in which the density of the _two films is increased and the thickness of the SiO ₂ film is easily set to about 20 to 100 nm.

The method of manufacturing a semiconductor device according to the present invention includes: (a) a deposition step in which a source gas of silicon and oxygen is supplied onto a SiC substrate to deposit a SiO ₂ film; and (b) the SiC substrate in which the SiO ₂ film is deposited. Is set to a temperature of 200 ° C. or higher and lower than 700 ° C., and an oxygen radical is generated to oxidize the radical.

As described in claim 1, since the SiO ₂ film is deposited on the SiC substrate by supplying the source gases of silicon and oxygen, it is easy to increase the film thickness to about 20 to 100 nm. Moreover, since it oxidizes at the temperature of 200 degreeC or more and less than 700 degreeC, there is almost no thermal oxidation of SiC by an oxygen molecule, and the generation efficiency of the oxygen radical by the thermal decomposition of ozone is high. Therefore, the interface between the SiO ₂ film and SiC is oxidized by only oxygen radicals to become the SiO ₂ film, and thus becomes the interface between the SiO ₂ film and SiC with few C defects. At the same time, the SiO ₂ film deposited by supplying source gases of silicon and oxygen is also densified by oxygen radicals.

[Embodiment 1]
FIG. 1 is a diagram showing a method of forming a SiO ₂ film according to Embodiment 1 of the present invention, which will be described below. First, a deposition step of depositing a SiO ₂ film by supplying source gases of silicon and oxygen on the cleaned SiC substrate 1 shown in FIG. 1A is performed (FIG. 1B). For this deposition process, CVD, PVD, sputtering, vapor deposition, etc. can be used, but the CVD method is the least suitable and suitable for mass production. The CVD-SiO ₂ film 3 (unmodified) It is preferable to deposit a _high quality CVD-SiO ₂ film).

Si source gases include silane-based gases that do not contain C, such as SiCl ₂ H ₂ (dichlorosilane), SiH ₄ (silane), SiCl ₃ H (trichlorosilane), SiCl ₄ (tetrachlorosilane), Si ₂ H ₆ ( Disilane) or the like is used. Thereby, it is possible to avoid the generation of C-induced defects in the CVD-SiO ₂ film 3. An oxidizing gas such as N ₂ 0, O ₂ ozone is used as the O source gas. The CVD-SiO ₂ film 3 using dichlorosilane and N ₂ O is particularly preferable because a film with few unoxidized defects can be formed.

Although various methods such as thermal CVD, plasma CVD, and cat-CVD can be used for the CVD method, the thermal CVD method that is not affected by plasma damage or the like is preferable. The treatment temperature is from room temperature to 900 ° C. or lower, but 400 ° C. or higher is preferable in order to burn and remove organic contaminants adsorbed on the SiC surface from the clean room atmosphere. Further, in order to prevent SiC from being thermally oxidized due to the atmosphere during film formation of CVD-SiO ₂ , the temperature is preferably less than 700 ° C.

After the CVD-SiO ₂ film 3 is formed in this way, the SiC substrate 1 is set to a temperature of 200 ° C. or higher and lower than 700 ° C., and oxygen radicals are generated to pass the SiC substrate 1 over the CVD-SiO ₂ film 3. An oxidation step for radical oxidation is performed (FIG. 1 (c)). Methods for generating oxygen radicals include a method of decomposing oxygen molecules and ozone by plasma, a method of decomposing oxygen molecules and ozone by UV irradiation, and a method of using thermal decomposition of ozone. In order to prevent the breakage of the -O bond, that is, the formation of new unoxidized defects 4, it is preferable to use thermal decomposition of ozone.

In order to increase the decomposition efficiency of ozone, it is preferable to increase the treatment temperature to 200 ° C. or higher and promote the thermal decomposition of ozone. Diffusion length of the decomposition efficiency and SiO ₂ film of ozone, although better process temperature is higher increases, by recombination of pyrolysis and oxygen radicals ozone, since always 0 ₂ molecule is produced, SiC by O ₂ In order to prevent thermal oxidation of the substrate 1, it is performed at less than 700 ° C. Further, a cold wall furnace for heating only the SiC substrate 1 and the substrate stage is used. The temperature of the inner wall of the furnace is at least 200 ° C. or less, preferably close to room temperature. This is because ozone molecules obtain heat for the first time on the SiC substrate 1 so as to be thermally decomposed so that the concentration of oxygen radicals supplied onto the SiC substrate 1 is as high as possible.

Oxygen radicals generated by the CVD-SiO ₂ film 3 surface is easily oxidized to decompose to remove the organic contamination of CVD-SiO ₂ film 3 surface. Furthermore, to spread the CVD-SiO ₂ film 3 medium oxidizes unoxidized defects 4 in the CVD-SiO ₂ film 3, to extinguish. Oxygen radicals diffused to deeper, CVD-SiO ₂ film 3 / oxidizing the deposited initial defect is one of the unoxidized defects 5 that is present in SiC near the interface, and is extinguished CVD-SiO ₂ film 6 (Kai Formed CVD-SiO ₂ film). In addition, when the CVD-SiO ₂ film 3 is formed at a temperature of 700 ° C. or higher, SiC is partially thermally oxidized by the CVD O source gas to generate C-induced defects. C-induced defects are also eliminated.

The oxygen radicals also radically oxidize the SiC substrate 1 to form a radical oxide film (ozone oxidized SiO ₂ film 2) at the CVD-SiO ₂ film 6 / SiC interface. This radical oxide film (ozone oxidized SiO ₂ film 2) has very few C-induced defects and unoxidized defects 4. Oxygen radical generation uses thermal decomposition of ozone, and UV light irradiation and plasma are not used, so there is no damage caused by these, and no new defects are generated. However, the film thickness is about 5 nm. However, unlike the case where the CVD-SiO ₂ film 3 is added after ozone oxidation, the initial film formation defects at the interface between the CVD-SiO ₂ film 6 and the ozone-oxidized SiO ₂ film 2 are greatly reduced. There are no defects due to organic contamination, and unoxidized defects 4 in the CVD-SiO ₂ film 3 are also reduced. For this reason, there is almost no influence of carrier Coulomb scattering due to defects.

The SiC substrate 1 is oxidized by ozone treatment and a new ozone-oxidized SiO ₂ film 2 is formed. The thickness is preferably at least as thick as 2 atomic layers, that is, 0.8 nm or more. In order to adjust the thickness at which the SiC substrate 1 is oxidized to become the ozone-oxidized SiO ₂ film 2, the thickness is adjusted by controlling the processing time from the formation rate of the ozone-oxidized SiO ₂ film 2 by ozone oxidation. The formation rate of the ozone-oxidized SiO ₂ film 2 can be obtained by measuring the thickness of the CVD film in advance and then measuring the film thickness again after ozone oxidation for a predetermined time. The film thickness can be accurately obtained by using the X-ray reflectivity method. By setting the ozone-oxidized SiO ₂ film 2 by ozone oxidation to 0.8 nm or more, defects caused by C can be sufficiently reduced.

As described above, rather than adding the CVD-SiO ₂ film 3 after ozone oxidation, a great improvement effect can be obtained by oxidizing SiC through the CVD-SiO ₂ film 3 after deposition of the CVD-SiO ₂ film 3. . That is, defects such as C-induced defects, unoxidized defects 4 (including damage caused by UV and plasma), and initial film formation defects can be reduced, and a sufficiently thick SiO ₂ film of 20 to 100 nm can be formed with high productivity. Loss of SiC power devices can be reduced.

The present invention has an unoxidized defects 4 or film formation initial defect in the SiO ₂ film is eliminated by oxidation by ozone treatment, oxidation with ozone to O source gas during CVD-SiO ₂ film 3 formed A case where the power is increased will be described. If the oxidizing power is increased by using ozone as the O source gas when forming the CVD-SiO ₂ film 3, the two-step process is not required as in the present invention, and the CVD-SiO ₂ film 3 with few defects is created from the beginning. I can imagine that I can do it. Further, a mixed gas of oxygen and ozone containing several percent of ozone is actually used as the O source gas.

However, it is extremely difficult to form the CVD-SiO ₂ film 3 with few defects from the beginning by further increasing the concentration of ozone and increasing the oxidizing power. This is because the CVD-SiO ₂ film 3 is formed not only by reducing defects in the SiO ₂ film but also by making the thickness in-plane uniform and preventing the generation of particles. Because there is a demand. If the oxidizing power of the oxidizing gas is increased or the concentration is increased, the reaction between the Si source gas and the O source gas is promoted, so it may react before reaching the substrate and generate SiO ₂ particles on the substrate. Becomes higher. It also becomes difficult to ensure in-plane uniformity. Therefore, by performing the treatment in two stages as in the present method, it is possible to form a SiO ₂ film that does not generate particles, has high in-plane film thickness uniformity, and has few unoxidized defects 4.

Further, it is known that when the unoxidized defects 4 are reduced by oxygen radicals, the Si-O network structure is densified and the film density is increased. This can be examined by performing an X-ray reflectivity analysis. FIG. 3 shows X-ray reflectance spectra of the CVD-SiO ₂ films 3 having different thicknesses. FIG. 4 shows the X-ray reflectivity spectrum of the ozone-treated CVD-SiO ₂ film 6. FIG. 5 shows the density distribution in the depth direction of the CVD-SiO ₂ film 3 obtained by fitting analysis from the spectrum of FIG. FIG. 6 shows the density distribution in the depth direction of the ozone-treated CVD-SiO ₂ film 6 obtained by the fitting analysis from the spectrum of FIG.

Although lower and the density of the CVD-SiO ₂ film 3 is 2.0~2.1g / cm ³ degree before the ozone treatment, density 2.1~2.2g / cm ³ to SiO ₂ membrane surface after ozonation And a high-density layer having a density of 2.2 to 2.3 g / cm ³ are formed at the SiO ₂ film / substrate interface. The high-density layer on the surface of the SiO ₂ film is clearly a densified CVD-SiO ₂ film 3. In the analysis, a simple model in which the density changes sharply is used. However, in reality, it is considered that the density changes continuously as the surface becomes denser and deeper. In other words, since the amount of oxygen radicals passing through the surface is larger, it is considered that the densification due to the reconstruction of the Si-O network structure is remarkable. On the other hand, since the high-density layer at the interface is considered to be the ozone-oxidized SiO ₂ film 2 formed by radical oxidation of the substrate, oxygen radicals reach the CVD-SiO ₂ film 3 / SiC interface, and the CVD-SiO ₂ film It is considered that the unoxidized defects 4 in the CVD-SiO ₂ film 3 are reduced by radical oxidation.

FIG. 7 is a graph showing the temperature dependence of the oxidation rate of the thermal oxidation by O ₂ molecules of the SiC substrate 1 and the temperature dependence of the oxygen radical generation efficiency by the thermal decomposition of ozone. At a temperature of 700 ° C. or higher, the oxidation rate of thermal oxidation by O ₂ molecules increases with temperature. In thermal oxidation with O ₂ molecules, formation of C-induced defects occurs even with oxidation of several nanometers or at the atomic level, so the temperature should be as low as possible. If it is lower than 700 ° C., the oxidation rate of thermal oxidation by O ₂ molecules is reduced by two orders of magnitude or more compared to 1100 ° C., and the generation of defects caused by C can be sufficiently prevented.

  On the other hand, the generation efficiency of oxygen radicals increases with temperature. At 200 ° C., almost all ozone molecules can be thermally decomposed in a very short time of 10 seconds or less and oxygen radicals can be generated. When the temperature is 600 ° C. or higher, the rate of increase in the generation efficiency of oxygen radicals accompanying a rise in temperature is reduced. When the temperature is 700 ° C. or higher, the saturation tendency becomes prominent.

Therefore, in order to prevent thermal oxidation by O ₂ molecules as much as possible and promote oxidation by oxygen radicals as much as possible, the treatment conditions of 200 ° C. or higher and lower than 700 ° C. are the best. Therefore, in the present invention, defects can be most effectively reduced by performing ozone treatment at 200 ° C. or higher and lower than 700 ° C.

[Embodiment 2]
FIG. 2 is a diagram showing a method of forming a SiO ₂ film in the second embodiment of the present invention, which will be described below. Similar to the first embodiment, the step of depositing SiO ₂ on the cleaned SiC substrate 1 shown in FIG. 2A (FIG. 2B) and the ozone oxidation step (FIG. 2C) are performed. Thereafter, a step of depositing a SiO ₂ film having a predetermined thickness (FIG. 2 (d)) and an ozone oxidation step (FIG. 2 (e)) are repeated a plurality of times (FIGS. 2 (f) and (g)).

The thicker the CVD-SiO ₂ film 3, the longer the ozone treatment time must be, and a method that can further improve productivity is desired. The density of the CVD-SiO ₂ film 3 is lower than that of the ozone oxide film or the thermal oxide film, the gap between the Si-O networks is wide, and the diffusion length of oxygen radicals is long. However, as the film becomes thicker as shown in FIG. 6, the oxygen radical concentration in the CVD-SiO ₂ film 6 decreases. Therefore, it is effective to repeat the deposition of the CVD-SiO ₂ film 3 and the ozone treatment a plurality of times, and finally form a 20 to 100 nm SiO ₂ film. That rather than deposit the SiO ₂ film of 20~100nm at a time, after depositing a CVD-SiO ₂ film 3, for example 15nm of at 50nm or less, with constant time ozone treatment, 15nm a CVD-SiO ₂ film 3 again Deposited and again ozone treatment. This is repeated a plurality of times to finally form a 20 to 100 nm SiO ₂ film. The time for the ozone treatment may be a time enough to form an oxide film having a thickness of 1 to 5 nm when ozone is directly oxidized on the SiC surface.

In this method, sufficient productivity can be ensured by continuously switching the deposition of the CVD-SiO ₂ film 3 and the ozone treatment in the same furnace. As described above, a SiO ₂ film having a thickness of 20 to 100 nm can be formed with very few C-induced defects and unoxidized defects 4. Therefore, since there is no defect that hinders the movement of electrons in the channel of the transistor, the power loss is extremely small and a sufficient breakdown voltage can be ensured.

  In addition, the SiC substrate 1 described in the first and second embodiments is not limited to the bulk single crystal SiC substrate 1 but may be formed by forming a SiC film on at least a part of the bulk single crystal SiC substrate 1 or the substrate surface of a different material. The same effect can be obtained even if a simple SiC substrate 1 is used.

It is a diagram showing a method of forming the SiO ₂ film in the first embodiment of the present invention. It is a diagram showing a method of forming the SiO ₂ film in the second embodiment of the present invention. It shows an X-ray reflectivity spectra of CVD-SiO ₂ film. It shows an X-ray reflectivity spectra of ozonated CVD-SiO ₂ film. It is a diagram showing a depth direction density distribution of CVD-SiO ₂ film. It is a diagram showing a depth direction density distribution of ozonated CVD-SiO ₂ film. It illustrates the temperature dependence of the oxidation rate of the thermal oxidation by O ₂ molecules of the SiC substrate, the temperature dependence of oxygen radical generation efficiency by the thermal decomposition of the ozone.

Explanation of symbols

1 SiC substrate, 2 ozone-oxidized SiO ₂ film, 3 CVD-SiO ₂ film (unmodified), 4 unoxidized defect (in the film), 5 unoxidized defect (initial film formation), 6, 7, 8 CVD-SiO ₂ membranes (modified).

Claims (5)

(A) a deposition step of depositing a SiO ₂ film by supplying silicon and oxygen source gases on a SiC substrate;
(B) a method of manufacturing a semiconductor device comprising: an oxidizing step of supplying oxygen radicals to the SiC substrate on which the SiO ₂ film and the SiO ₂ film are deposited at a temperature of 200 ° C. or higher and lower than 700 ° C. to perform radical oxidation .   The method of manufacturing a semiconductor device according to claim 1, wherein the step (a) and the step (b) are repeated a plurality of times. The step (a) is performed by a CVD method,
The source gas of silicon used in the CVD method is SiCl ₂ H ₂ (dichlorosilane), SiH ₄ (silane), SiCl ₃ H (trichlorosilane), SiCl ₄ (tetrachlorosilane), Si ₂ H ₆ (disilane). The method for manufacturing a semiconductor device according to claim 1, wherein the method is at least one of them.   The oxygen radical is at least one of ozone self-decomposition, ozone thermal decomposition, ozone plasma decomposition, ozone UV irradiation decomposition, oxygen molecule plasma decomposition, oxygen molecule UV irradiation decomposition. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the method is generated as described above.   5. The method of manufacturing a semiconductor device according to claim 1, wherein the step (b) is performed using a cold wall type furnace having an inner wall temperature of 200 ° C. or less.

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