JP3484480B2 - Method for manufacturing semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device having an oxide film.

[0002]

2. Description of the Related Art With the progress of miniaturization of semiconductor integrated circuits, it is desired to reduce the thickness of a gate oxide film to several nm in a CMOS used for a logic element. Conventionally, dry oxygen oxidation, wet oxygen oxidation, hydrochloric acid oxidation, and dichloroethylene (DCE) oxidation have been used for forming a gate oxide film.

In a silicon oxide film formed by dry oxygen oxidation, the oxygen ratio in the film tends to be low, and dangling bonds of silicon atoms generated by the lack of oxygen atoms act as hole traps. Therefore, the time-dependent dielectric breakdown (TDDB) life is shortened.

In a silicon oxide film formed by wet oxygen oxidation, TDDB life is relatively long because dangling bonds of silicon atoms are terminated by hydrogen atoms. However, when the Si—H and SiO—H bonds in the film are broken by the hot carriers, electron traps are generated and the characteristics of the transistor are changed.

In a silicon oxide film formed by hydrochloric acid oxidation or DCE oxidation, hydrogen atoms or chlorine atoms generated when HCl or DCE is decomposed are incorporated into the film, and therefore, similar to the silicon oxide film formed by wet oxygen oxidation, a transistor oxide film is formed. It is easy to cause characteristic changes.

In order to reduce both hole traps and electron traps, it is effective to oxidize with a strong oxidizing agent in a dry atmosphere containing no water. Ozone oxidation is one of the methods, and the silicon oxide film formed by ozone oxidation has a relatively long TDDB life,
Has high hot carrier resistance. However, ozone is easily decomposed into oxygen gas by the heat at the time of oxidation, and the ozone concentration drops to ppb order under atmospheric pressure.

In order to suppress the decomposition of ozone during oxidation and maintain a high ozone concentration, oxidation is performed in a reduced pressure atmosphere,
Methods such as using lamp heating have been proposed. When the atmosphere at the time of oxidation is a reduced pressure atmosphere, the probability of collision of ozone molecules with each other is lowered, so that the decomposition of ozone molecules is suppressed. Further, when the lamp is heated, the heating of the ozone gas itself can be suppressed, so that the decomposition of ozone molecules is suppressed.

[0008]

As described above, in the oxidation using ozone, if the atmosphere during the oxidation is a reduced pressure atmosphere, the decrease of the ozone concentration can be suppressed, but it is necessary to attach a gas exhaust system to the reaction vessel. Yes, the device becomes larger. In particular, since the apparatus also increases in size in response to the increase in the diameter of the silicon substrate, it is not suitable for the increase in the diameter.

Further, although the decrease in ozone concentration can be suppressed by using lamp heating as the heating method, it is difficult to uniformly heat the entire surface of the silicon substrate by lamp heating. Further, the lamp heating is not suitable for batch processing and requires single-wafer processing, resulting in low throughput.

An object of the present invention is to provide a method of manufacturing a semiconductor device capable of forming a high quality oxide film having a long TDDB life.

[0011]

According to one aspect of the present invention, a silicon substrate having a natural oxide film formed on its surface is heated.
Contact with ozone-containing gas under conditions of 0 ° C to 100 ° C
The step of modifying the native oxide film, and
And a step of heat-treating the natural oxide film in an inert gas.
A method of manufacturing a semiconductor device is provided.

[0012]

[0013]

[0014]

[0015]

[0016]

By contacting the natural oxide film with ozone, the natural oxide film can be modified to obtain a good quality film. Further, by setting the temperature at the time of contact to a temperature of 0 ° C. to 100 ° C., it is possible to suppress the oxidation of the surface of the object to be processed below the natural oxide film, so that the oxide film should be modified while being kept thin. You can

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, wherein the step of modifying the natural oxide film brings the silicon substrate into contact with the gas containing ozone in a reduced pressure atmosphere.

By setting the reduced pressure atmosphere, the decomposition of ozone can be suppressed and the ozone concentration can be maintained high.
According to another aspect of the present invention, the gas containing ozone is
There is provided a method for manufacturing a semiconductor device, which is a gas obtained by diluting a mixed gas of ozone and oxygen gas with an inert gas.

By diluting the mixed gas of ozone and oxygen gas with an inert gas, it becomes possible to suppress the decomposition of ozone and maintain the ozone concentration high. According to another aspect of the present invention, there is provided a method for manufacturing a semiconductor device, wherein the step of modifying the natural oxide film further includes the step of irradiating the gas containing ozone near the surface of the silicon substrate with ultraviolet light. To be done.

By irradiating with ultraviolet light, the ozone concentration can be increased.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION First, the factors that decompose ozone molecules (O ₃ molecules) to oxygen molecules (O ₂ molecules) will be considered. Ozone is

[0023]

It is known that decomposition occurs in the reaction process of O ₃ → O ₂ + O (1) O + O ₃ → 2O ₂ (2). The reaction rate constant k ₁ of the reaction formula (1) is

[0024]

## EQU1 ## k ₁ = A × exp (−E _a1 / RT) (3) Here, A is a proportional constant (10 ^15.7 ) called a frequency factor, and E _a1 is activation energy (2.4 kcal).
/ Mol), R is a gas constant, and T is an absolute temperature. Therefore, if the reaction temperature is determined, the reaction rate constant k ₁ is also uniquely determined.

The reaction rate constant k ₂ of the reaction formula (2) is

[0026]

Represented by the [number 2] _{k 2 = pZ × exp (-E} a2 / RT) ... (4). Here, p is a proportional constant called a steric factor, and E _a2 is activation energy (4.1 kcal / mo).
l) and Z are the number of collisions of O radicals and O ₃ molecules in 1 second.

Oxygen (O) radicals are required for the reaction of the reaction formula (2) to occur. O radicals are generated by the decomposition of oxygen molecules, and the activation energy in this case is 494 kJ / mol. On the other hand, reaction formula (1)
Activation energy of the O ₃ molecule is 95 kJ / mol
Which is considerably smaller than the activation energy for decomposition of O ₂ molecule. Therefore, in the mixed gas of O ₂ and O ₃ , the O radicals are substantially supplied by the reaction of the reaction formula (1).

Therefore, in order for the O radical and the O ₃ molecule to collide with each other, it is necessary for the O ₃ molecules to approach each other. O ₃
It is considered that the number of collisions Z in the equation (4) can be reduced if the probability of approaching molecules can be reduced. By reducing the pressure of the mixed gas of O ₂ and O ₃ , it is possible to reduce the proximity probability of the O ₃ molecules to each other, but as described above, the exhaust system for reducing the pressure is required, so that the apparatus becomes large. I will end up.

Oxidation with dry O ₂ tends to reduce the oxygen ratio in the oxide film. Therefore, in order to form a good oxide film, O ₃ gas is used rather than oxidation with O ₂ gas.
It is preferable to carry out the oxidation with a gas. Therefore, it is preferable to increase the ratio of the partial pressure of O ₃ gas to the partial pressure of O ₂ gas in the oxidizing atmosphere.

The first embodiment of the present invention based on the above consideration will be described below. FIG. 1A shows a schematic cross-sectional view of the oxidation device used in this example. The quartz tube 1 is arranged in the heating space of the vertical resistance heater 2. A reaction gas is introduced from a gas introduction pipe 3 provided above the quartz pipe 1 and discharged to the outside from a gas discharge pipe 4 provided below. At the time of oxidation, the silicon substrate 10 is loaded in the quartz tube 1.

The surface of a silicon substrate having a plane orientation (100) and a conductivity type of p-type is washed with ammonia, hydrogen peroxide solution, hydrofluoric acid and nitric acid. The cleaned silicon substrate 10 is replaced with the quartz tube 1
The substrate temperature is set to 800 ° C. by loading it inside and heating. In addition, in this embodiment, eight silicon substrates 1 are simultaneously formed.
Oxidation was carried out by loading 0.

Argon gas and oxygen gas are cooled to -90 ° C. or lower for purification. The purified oxygen gas is supplied to the ozonizer to generate ozone, and the ozone concentration is 4 to 5% by volume.
To obtain a mixed gas of. The partial pressure of the mixed gas of ozone and oxygen is 2
Quartz tube 1 was mixed with O ₃ / O ₂ / Ar mixed gas mixed with 00 Torr and argon gas at a partial pressure of 560 Torr.
Supply in. After performing oxidation for 30 minutes at a substrate temperature of 800 ° C., the supply of the O ₃ / O ₂ / Ar mixed gas is stopped and the inside of the oxidation furnace is replaced with argon gas. The temperature of the silicon substrate 10 is lowered, and the silicon substrate 10 is taken out from the quartz tube 1.

FIG. 1A compares the thickness of the silicon oxide film formed by the method according to the first embodiment with the case of using an O ₂ / Ar mixed gas containing no O _3. Show. In the figure, the symbol ● indicates the film thickness of the silicon oxide film formed by using the O ₂ / Ar mixed gas having an oxygen partial pressure of 200 Torr and an argon partial pressure of 560 Torr when formed by the method according to the first embodiment. Show. The other conditions are the same as those in the first embodiment. The horizontal axis represents the type of the oxidized silicon substrate, and the silicon substrate 10 loaded in the oxidation furnace 1 is shown by numbering 0 to 7 in order from the top. The vertical axis represents the thickness of the silicon oxide film in nm.

FIG. 1B shows the thickness of the silicon oxide film formed in a reduced pressure atmosphere for comparison with the silicon oxide film formed in the first embodiment. The diffusion pump 5 is attached to the gas exhaust pipe 4, and the pressure in the quartz pipe 1 is 200To.
Oxidation was performed in a reduced pressure atmosphere of rr. Symbol in the figure ●
Indicates a case of using an O ₃ / O ₂ mixed gas having an ozone concentration of 4 to 5% by volume, and a symbol ₂ indicates a case of using only O ₂ gas.

As shown in FIGS. 1A and 1B, there is almost no difference in film thickness due to the difference in the loading position of the silicon substrate.
If the oxidation under atmospheric pressure using a mixed gas containing argon, the film thickness of the silicon oxide film oxidized to generate O ₃ gas, about than the thickness of the oxide film obtained by oxidizing only O ₂ gas 0. It is about 4 nm thick. In the case of oxidation in a reduced pressure atmosphere, the difference is about 0.5 nm.

As described above, the difference in the film thickness of the silicon oxide film due to the presence or absence of O ₃ is almost equal between the case of oxidizing under the atmospheric pressure containing argon and the case of oxidizing under a reduced pressure atmosphere. Therefore, O ₃ concentration in the atmospheric atmosphere containing argon is considered to almost equal to the concentration of O ₃ in the case of reduced pressure atmosphere. That is, it is considered that the disappearance of O ₃ molecules is suppressed by diluting the mixed gas of O ₃ and O ₂ with argon gas, as in the case of reducing the pressure.

In both cases, the partial pressure of O ₃ gas is 8 Torr
There is about 10 Torr and they are almost equal. If the partial pressures of O ₃ gas are the same, it is considered that the O ₃ molecules have almost the same probability of approaching each other. From the equation (4), it is estimated that the O ₃ concentrations are almost the same if the O ₃ molecules have the same approach probability.

The variation in the film thickness of the silicon oxide film in the substrate surface within the range of 3σ when oxidized under atmospheric pressure containing argon was within 0.3 nm. FIG. 2 shows the time-dependent dielectric breakdown resistance of the silicon oxide film. The abscissa represents the cumulative charge amount flowing through the silicon oxide film in the unit of C / cm ² , and the ordinate represents the ratio of the sample subjected to dielectric breakdown in the unit of%.

The method of preparing the sample used for the measurement will be described below. A field oxide film with a thickness of 250 nm is formed on the surface of the silicon substrate, and then sacrificial oxidation with a thickness of 5 nm is performed to clean the surface. Next, a silicon oxide film having a thickness of 4 nm is formed by the method according to the first embodiment. A thickness of 1 on a silicon oxide film by CVD at a growth temperature of 450 ° C.
An 80 nm amorphous silicon layer is formed. This amorphous silicon layer is patterned to have an area of 1.0 ×
An electrode of 10 ⁻⁴ cm ² is formed. In this way, MO
An S structure diode is obtained. A current of 100 mA / cm ² was passed through this MOS diode, and the amount of accumulated charge that had flowed until dielectric breakdown was measured.

The broken line in the figure shows the case of oxidation using the O ₃ / O ₂ / Ar mixed gas, and the solid line shows the case of oxidation using the O ₂ / Ar mixed gas. A silicon oxide film oxidized using an O ₂ / Ar mixed gas has a cumulative charge amount of about 1 C / cm.
By the time it reached ² , about 50% of the samples had a dielectric breakdown. On the other hand, in the silicon oxide film oxidized using the O ₃ / O ₂ / Ar mixed gas, no sample had a dielectric breakdown even when the accumulated charge amount became about 1 C / cm ² .

The cumulative charge amount up to 50% destruction of the silicon oxide film oxidized using the O ₃ / O ₂ / Ar mixed gas is the same as that of the silicon oxide film oxidized using the O ₂ / Ar mixed gas. It was about 30 times. Thus, by oxidizing with O ₃ gas, it is possible to form a good silicon oxide film that is hard to cause dielectric breakdown. It is considered that this is because oxygen defects are less likely to occur in the silicon oxide film due to the action of O ₃ gas. Therefore, it becomes possible to obtain a high-quality film having few unbonded Si atoms that act as a hole trap.

In the first embodiment, O ₃ / O ₂ / Ar is used.
Since the pressure of the mixed gas is atmospheric pressure, it is not necessary to install an exhaust system in the oxidizer, which is effective in preventing the device from becoming large.

Further, Ar gas is mixed to reduce the partial pressure of O ₃ gas to reduce the approach probability of O ₃ molecules. If only O ₃ gas and O ₂ gas are mixed and brought to atmospheric pressure, the absolute partial pressure of O ₃ gas can be increased.
_The partial pressure of ₂ gas also becomes high. By mixing Ar gas, the ratio of the partial pressure of O ₃ gas to the partial pressure of O ₂ gas can be increased. Oxidation by O ₂ gas is suppressed, and O ₃
Since the oxidation by the gas is promoted, a good quality film can be formed.

In the first embodiment described above, the ozone concentration in the mixed gas of oxygen and ozone is set to 4 to 5% by volume, but the ozone concentration may be changed. In order to obtain a sufficient effect, it is preferably not less than 100ppb by volume ratio concentration of O ₃ in the mixed gas of O ₂ and O _3.

In the first embodiment described above, the case where the mixed gas of oxygen and ozone is oxidized under the condition that the partial pressure thereof is 200 Torr has been described, but other pressures may be used. For example, the partial pressure of the mixed gas of oxygen and ozone may be 50 Torr, or may be 100 ppb or more in volume ratio.

In the first embodiment described above, the case where the silicon substrate is oxidized has been described, but the first embodiment is made of materials other than silicon as long as it is a material capable of obtaining a good quality oxide film using O ₃ gas. It is also effective when oxidizing the material.

In the first embodiment, O ₃ and O ₂
The case where Ar gas is mixed with the mixed gas of A has been described.
An inert gas other than r gas may be mixed. Here, the inert gas means a gas that does not oxidize the object to be processed and does not react with O ₃ under the processing temperature and the processing pressure. For example, a rare gas such as He or Ne, or N ₂ gas may be used.

In the first embodiment, when the silicon substrate is nitrided with ammonia gas to form the SiN film, or the silicon substrate is oxynitrided with ammonia gas or N ₂ O gas. It can also be applied when forming a SiON film. A mixed gas containing O ₃ is applied to the SiN film, Si
SiN film or SiON film by exposing to ON film
O atoms are bonded to dangling bonds in the film, or H atoms are replaced by O atoms.
Substitution with atoms could reduce traps in the film.

Next, a second embodiment will be described with reference to FIGS. FIG. 3 is a sectional view showing the outline of an oxidizing device used in the second embodiment. A substrate mounting table 25 is arranged in the reaction vessel 21, and a silicon substrate 30 is mounted on the upper surface of the substrate mounting table 25 during the oxidation process. A halogen lamp 22 for heating is arranged outside the reaction vessel 21 so as to face the silicon substrate 30. A reaction gas introduction pipe 23 and a gas discharge pipe 24 are attached to the reaction vessel 21.

The side surface on the right side of the reaction vessel 21 in the figure is formed with a quartz window 21a that transmits ultraviolet light. The ultraviolet light emitted from the ultraviolet lamp 26 is reflected by the reflecting mirror 27, passes through the quartz window 21 a, and is irradiated into the reaction vessel 21.

Next, the oxidation method according to the second embodiment will be described. The silicon substrate is immersed in a mixed solution of sulfuric acid and hydrogen peroxide solution for 5 minutes. Then, pure water rinsing is performed for 10 minutes and immersion in a hydrogen fluoride solution for 1 minute. Rinsing with pure water for 10 minutes, immersing in nitric acid for 10 minutes, and rinsing with pure water for 10 minutes again.

The silicon substrate 30 which has been wet-cleaned by the above procedure is placed on the substrate platform 25 shown in FIG. A mixed gas of O ₂ and O ₃ having an O ₃ gas concentration of 4 to 5% by volume is introduced into the reaction vessel 21, and the surface of the silicon substrate 30 is set to 1 at atmospheric pressure.
It is brought into contact with a mixed gas of O ₂ and O ₃ for 0 minutes (hereinafter, a treatment of bringing a silicon substrate into contact with a mixed gas of O ₃ and O ₂ is referred to as “O ₃ treatment”). Then, the inside of the reaction vessel 21 is replaced with Ar gas at atmospheric pressure, and heat treatment is performed at a temperature of 800 ° C. for 5 minutes.

A MOS electrode is formed by forming a polysilicon electrode having an area of 0.105 cm ² on the surface of the silicon oxide film thus formed, and a voltage is applied between the silicon substrate and the polysilicon electrode to cause dielectric breakdown. Resistance was measured.

FIG. 4A is a histogram showing the dielectric breakdown voltage of the silicon oxide film. The abscissa represents the applied electric field in the unit of MV / cm, and the ordinate represents the ratio of the number of samples subjected to dielectric breakdown in the unit of%. For reference, FIG. 4B shows a silicon oxide film which has been subjected to only wet cleaning and O ₃ treatment.
FIG. 4C shows the dielectric breakdown resistance of the silicon oxide film that has been subjected only to wet cleaning and heat treatment, and FIG. 4D shows the natural oxide film that has been formed only after wet cleaning.

The film thickness of the natural oxide film formed only by wet cleaning was about 1.5 nm, and the film thickness did not increase even after O ₃ treatment and heat treatment. In this specification, the natural oxide film means a silicon oxide film formed on the Si surface in a solution or in the air at room temperature.

As shown in FIG. 4D, in the case of the natural oxide film formed only by wet cleaning, there was an initial defect of about 15%. It is considered that this is due to a pinhole or the like. The breakdown voltage is 8.5 to 12.
It was in the range of 5 MV / cm. On the other hand, in the case of a silicon oxide film that has been subjected to O ₃ treatment or heat treatment, the initial defect rate is reduced and the dielectric breakdown voltage is 11 to 12.5 MV / c.
It was improved to the range of m.

As shown in FIG. 4A, when both the O ₃ treatment and the heat treatment are performed, no initial failure occurs and the dielectric breakdown resistance is within the range of 11.5 to 12.5 MV / cm. Further improved.

FIG. 5 shows the leakage current of the MOS diode. The horizontal axis represents the applied voltage in V, and the vertical axis represents the leakage current density in A / cm ² . Curves a, b, c and d
Shows the leakage current density of the MOS diode using the silicon oxide film shown in FIGS. 4 (A), (B), (C) and (D), respectively.

The leakage current density of the MOS diode using the natural oxide film formed only by wet cleaning is the highest. When the heat treatment or the O ₃ treatment is performed in addition to the wet cleaning, the leak current density decreases, and the leak current density becomes the minimum when both the heat treatment and the O ₃ treatment are performed.

The reason why the breakdown voltage of the silicon oxide film is improved and the leakage current density is reduced by the O ₃ treatment and the heat treatment is considered as follows. In an ideal silicon oxide film, O atoms are bonded to all four bonds of Si atoms. However, in a natural oxide film formed by performing wet cleaning or the like, there is an incompletely bonded region called a suboxide in which Si atoms are directly bonded to each other. Further, many strains are generated in the natural oxide film. Due to this sub-oxide and strain, the breakdown voltage of the natural oxide film is lowered, and the leak current is increased.

It is considered that the sub oxide in the natural oxide film is almost completely oxidized by the O ₃ treatment. In addition,
In the second embodiment, since the O ₃ treatment is performed at the substrate temperature of 20 ° C., the surface of the silicon substrate below the natural oxide film is not oxidized. Therefore, the sub oxide can be eliminated without increasing the oxide film thickness on the substrate surface. Further, it is considered that the heat treatment removes the strain in the natural oxide film. Therefore, it is considered that the film quality of the silicon oxide film is improved, the dielectric breakdown resistance is improved, and the leak current is reduced by performing the O ₃ treatment and the heat treatment.

As described above, the O ₃ treatment is performed in the room temperature region of the substrate temperature of about 20 ° C., and then the heat treatment is performed in the inert gas atmosphere. A film can be formed.

In the above embodiment, the case where the O ₃ treatment is carried out at the substrate temperature of 20 ° C. is shown, but any other temperature may be used as long as it does not substantially oxidize the silicon substrate below the natural oxide film. For example, when the substrate temperature is 0 to 100 ° C., O ₃
Processing may be performed. Further, the O ₃ treatment may be performed at a temperature of 0 ° C. or higher and lower than 20 ° C.

Further, in the above embodiment, the pressure for carrying out the O ₃ treatment is atmospheric pressure, but a reduced pressure atmosphere may be used. For example,
O ₃ the pressure in the reaction vessel 21 of FIG. 3 as 10Torr
Processing may be performed. In addition, the mixed gas of O ₃ and O ₂ contains A
You may mix inert gas, such as r gas. For example, O ₃
Ar and O ₂ mixed gas at a flow rate of 1 liter / min.
O ₃ treatment may be performed while supplying gas at a flow rate of 4 liter / min. As described in the first embodiment, it is possible to increase the concentration of O ₃ in the mixed gas of O ₃ and O ₂ by setting a reduced pressure atmosphere or mixing an inert gas.

During the O ₃ treatment, the ultraviolet gas 26 shown in FIG. 3 may be used to irradiate the mixed gas of O ₃ and O ₂ in the reaction vessel 21 with ultraviolet light. O ₂ by irradiation with ultraviolet light
Since the molecule is changed to the O ₃ molecule, the O ₃ concentration can be increased. It is preferable to irradiate the mixed gas near the surface of the silicon substrate 30 with ultraviolet light. Irradiation with ultraviolet light may be effective also in the first embodiment.

In the second embodiment described above, wet cleaning is performed using sulfuric acid, hydrogen peroxide solution, pure water, hydrogen fluoride solution, and nitric acid. As long as it is a liquid that forms an oxide film, other liquids may be used for wet cleaning. Furthermore, if a natural oxide film is formed on the surface of the silicon substrate, it is not limited to wet cleaning. For example, dry cleaning may be used.

Next, with reference to FIG. 6, a method of manufacturing a MOS transistor using the method according to the second embodiment will be described. As shown in FIG. 6A, the active region is
Masking with an N film (not shown), a field oxide film 41 is formed on a partial region of the surface of the silicon substrate 40 by thermal oxidation. The SiN film is removed and the wet cleaning described in the second embodiment is performed.

As shown in FIG. 6B, a natural oxide film 42 is formed on the surface of the active region by wet cleaning.
While adjusting the pressure in the reaction vessel 21 shown in FIG. 3 to 10 Torr, a mixed gas of O ₃ and O ₂ having an O ₃ concentration of 5% by volume is supplied for 10 minutes to modify the natural oxide film 42. . As a result, a good quality silicon oxide film having a film thickness of about 1.5 nm can be obtained.

As shown in FIG. 6C, a polycrystalline silicon layer 43 is deposited on the surface of the substrate by CVD. If a thicker gate oxide film is required, the surface of the substrate is oxidized to deposit the oxide film 42 before depositing the polycrystalline silicon layer 43.
May be thickened to a desired thickness.

As shown in FIG. 6D, the polycrystalline silicon layer 43 is patterned to form a gate electrode 43a. Using the gate electrode 43a as a mask for ion implantation, impurities of the opposite conductivity type to the silicon substrate are ion-implanted to form a source region 44S and a drain region 44D.

In this way, a MOS transistor having a thin and high-quality gate oxide film can be manufactured. Although the present invention has been described above with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0072]

As described above, according to the present invention,
A good quality oxide film can be formed. As a result, the reliability of the semiconductor device using the oxide film can be improved. In particular, it is possible to manufacture a semiconductor device which is as thin as a natural oxide film and has good dielectric breakdown resistance and leak current characteristics.

[Brief description of drawings]

FIG. 1 is a graph showing the film thickness of a silicon oxide film formed according to a first embodiment of the present invention and the film pressure of a silicon oxide film formed under a conventional reduced pressure atmosphere.

FIG. 2 is a graph showing dielectric breakdown characteristics of a silicon oxide film manufactured according to the first embodiment.

FIG. 3 is a cross-sectional view showing an outline of an oxidation device used in a second embodiment.

FIG. 4 shows the dielectric breakdown resistance of the silicon oxide film formed according to the second embodiment, and the dielectric breakdown resistance of the silicon oxide film formed by only wet treatment, only wet treatment and O ₃ treatment, and only wet treatment and heat treatment. It is a graph which shows.

FIG. 5 shows the leakage current density of the silicon oxide film formed according to the second embodiment, with respect to the dielectric breakdown resistance of the silicon oxide film formed by the wet treatment only, the wet treatment and the O ₃ treatment only, and the wet treatment and the heat treatment only. 5 is a graph showing the leakage current density of FIG.

FIG. 6 is a sectional view of a substrate for explaining a method of manufacturing a MOS transistor by using the method according to the second embodiment.

[Explanation of symbols]

1 quartz tube 2 heater 3 gas introduction pipes 4 gas exhaust pipe 5 diffusion pump 10 Silicon substrate 21 Reaction vessel 22 Halogen lamp 23 Reaction gas introduction pipe 24 gas exhaust pipe 25 Substrate mounting table 26 UV lamp 27 Reflector 30, 40 Silicon substrate 41 Field oxide film 42 Natural oxide film 43 Polycrystalline silicon layer 43a Gate electrode 44S source area 44D drain region

Front page continuation (72) Inventor Satoru Watanabe 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor Kiyo Irino 1015, Ueda-anaka, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited (56) Reference References JP-A-4-145624 (JP, A) JP-A-3-134153 (JP, A) JP-A-7-86271 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/312 H01L 21/314 H01L 21/316 H01L 21/318 H01L 29/78

Claims (4)

(57) [Claims] 1. A step of modifying a natural oxide film by bringing a silicon substrate having a natural oxide film formed on its surface into contact with a gas containing ozone at a temperature of 0 ° C. to 100 ° C. And a step of heat-treating the formed natural oxide film in an inert gas. Wherein the step of modifying the natural oxide film, a method of manufacturing a semiconductor device according to claim 1, contacting said silicon substrate to a gas containing ozone reduced pressure atmosphere. 3. A gas containing ozone, the method of manufacturing a semiconductor device according to the mixed gas to claim 1 or 2 which is a gas diluted with an inert gas of ozone and oxygen gas. Wherein the step of modifying the natural oxide film, further, according to claim 1, comprising the step of irradiating ultraviolet light to the gas containing the ozone in the vicinity of the surface of the silicon substrate Manufacturing method of semiconductor device.