JPH10284484A - Formation of silicon oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely form a very thin silicon oxide film having high film thickness uniformity by heat-treating a silicon oxide film in an atmosphere containing steam after the silicon oxide film is formed on the surface of a silicon layer in an atmosphere containing a dry oxygen gas. SOLUTION: After fine particles, etc., are removed form the surface of a silicon semiconductor substrate 10 by the RCA cleaning, etc., the surface of the substrate 10 is exposed by treating the surface with a hydrofluoric acid solution. Then, after a silicon oxide film 12 having a thickness of about 3 nm is formed on the surface of the substrate 10 by performing oxidation treatment for about five minutes by introducing 100% dry oxygen gas into a treatment chamber, first heat treatment is performed on the silicon oxide film 12 for about five minutes at 400 deg.C by supplying steam generated in a combustion chamber to the treatment chamber. In addition, second heat treatment is performed on the film 12 for about 30 minutes by introducing a nitrogen gas containing hydrogen chloride to the treatment chamber after the atmospheric temperature in the chamber is raised to about 700-950 deg.C with a heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a silicon oxide film in the manufacture of a semiconductor device.

[0002]

2. Description of the Related Art For example, in manufacturing a MOS type semiconductor device, it is necessary to form a gate oxide film made of a silicon oxide film on the surface of a silicon semiconductor substrate. Also, in manufacturing a thin film transistor (TFT), it is necessary to form a gate oxide film made of a silicon oxide film on the surface of a silicon layer provided on an insulating substrate. It is not an exaggeration to say that such a silicon oxide film is responsible for the reliability of the semiconductor device. Therefore, a silicon oxide film is always required to have high dielectric breakdown voltage and long-term reliability.

[0003] For example, in the case of manufacturing a MOS type semiconductor device, conventionally, NH ₄ OH /
The surface of the silicon semiconductor substrate is cleaned by RCA cleaning in which the surface is washed with an H ₂ O ₂ aqueous solution and further washed with an HCl / H ₂ O ₂ aqueous solution, and fine particles and metal impurities are removed from the surface. When the RCA cleaning is performed, the surface of the silicon semiconductor substrate reacts with the cleaning liquid to form a silicon oxide film having a thickness of about 0.5 to 1 nm (hereinafter, such a silicon oxide film is simply referred to as an oxide film). The thickness of such an oxide film is not uniform, and the cleaning liquid component remains in the oxide film. Therefore, the silicon semiconductor substrate is immersed in a hydrofluoric acid aqueous solution to remove such an oxide film, thereby exposing a clean surface of the silicon semiconductor substrate. Thereafter, the silicon semiconductor substrate is carried into a processing chamber (oxidizing furnace) of a silicon oxide film forming apparatus, and a silicon oxide film is formed on the surface of the silicon semiconductor substrate. Most of the surface of the silicon semiconductor substrate after the cleaning with the hydrofluoric acid aqueous solution is terminated with hydrogen, and part of the surface is terminated with fluorine.

As a silicon oxide film forming apparatus, as the gate oxide film becomes thinner and the substrate becomes larger in diameter, a quartz type processing chamber (oxidizing furnace) is held horizontally and a vertical type is held vertically. The shift to a silicon oxide film forming apparatus of the system is in progress. This is because the vertical type silicon oxide film forming apparatus is easier to cope with the enlargement of the substrate than the horizontal type silicon oxide film forming apparatus, and the silicon semiconductor substrate is carried into the processing chamber. This is because a silicon oxide film generated by the entrainment of the atmosphere at the time (hereinafter, such a silicon oxide film is called a natural oxide film) can be reduced.
However, even when a vertical silicon oxide film forming apparatus is used, a natural oxide film having a thickness of about 2 nm is formed on the surface of the silicon semiconductor substrate. for that reason,
(1) A method in which a large amount of nitrogen gas flows into a substrate loading / unloading section provided in a silicon oxide film forming apparatus to form a nitrogen gas atmosphere (nitrogen gas purge method). (2) Once the inside of the substrate loading / unloading section is evacuated. After that, a method has been proposed in which the inside of the substrate carry-in / out section is replaced with nitrogen gas or the like to exclude the atmosphere (vacuum load lock method) or the like, and the formation of a natural oxide film is suppressed as much as possible.

[0005] Then, the silicon semiconductor substrate is carried into the processing chamber (oxidizing furnace) with the processing chamber (oxidizing furnace) in an inert gas atmosphere, and then the processing chamber (oxidizing furnace) is oxidized. The gate oxide film is formed by switching and heat-treating the silicon semiconductor substrate. For forming a gate oxide film, a method (thermal wet oxidation method) of thermally oxidizing the surface of a silicon semiconductor substrate by introducing high-purity water vapor into a processing chamber maintained at a high temperature is employed. This makes it possible to form a gate oxide film having higher electrical reliability than the method of oxidizing the surface of the silicon semiconductor substrate (dry oxidation method). As one of the wet oxidation methods, there is a pyrogenic oxidation method (also referred to as a hydrogen combustion oxidation method) using water vapor generated by mixing hydrogen gas with oxygen gas at a high temperature and burning the mixture. Usually, in this pyrogenic oxidation method, the pyrogen oxidation method is provided outside a processing chamber (oxidizing furnace),
Oxygen gas is introduced into the combustion chamber maintained at 0 ° C., and then hydrogen gas is introduced into the combustion chamber to burn the hydrogen gas at a high temperature. The water vapor thus obtained is used as an oxidizing species.

[0006]

The wet oxidation method can form a gate oxide film having higher electrical reliability than the dry oxidation method. However, due to the difference in the ease of diffusion of oxidizing species in the silicon oxide film, the oxidation rate at the same oxidation temperature is faster in the wet oxidation method than in the dry oxidation method. Further, for example, when the partial pressure of water vapor is increased to take advantage of the characteristics of the pyrogenic oxidation method, the oxidation rate is further increased.

The point of high oxidation rate in the wet oxidation method is that
It is advantageous to form a thick (for example, 0.1 μm or more) silicon oxide film as in the case of forming an element isolation region. However, in the formation of a gate oxide film which is required to form an extremely thin silicon oxide film uniformly and with good controllability on the surface of a silicon semiconductor substrate, the fact that the oxidation rate of the wet oxidation method is high can be a serious problem. . That is, 2
The oxidation time required for forming an ultrathin silicon oxide film of 3 nm is about several minutes, depending on the oxidation temperature, the partial pressure of water vapor, and the like. Furthermore, when the nitrogen gas purging method or the vacuum load lock method is not adopted, the oxidation time may be 1 minute or less.

On the other hand, such an ultra-thin silicon oxide film is used for a highly integrated LSI.
In the manufacture of, the diameter 2
A silicon semiconductor substrate having a large diameter of at least 00 mm is used. Therefore, when an ultra-thin silicon oxide film is formed based on the wet oxidation method, a silicon oxide film having a high in-plane thickness uniformity in the silicon semiconductor substrate due to the high oxidation rate and the size of the silicon semiconductor substrate. Forming films is becoming more difficult.

One method of forming an ultra-thin silicon oxide film with good film thickness uniformity is an oxide film forming apparatus by lamp heating provided with a lamp that emits infrared light or visible light (hereinafter referred to as an oxide film of this type). A rapid high-temperature oxidation method (RTO: Ra) using a forming apparatus (sometimes simply referred to as an oxide film forming apparatus).
pid Thermal Oxidation). Usually, this oxide film forming apparatus is of a cold wall type. Therefore, when this RTO method is applied to the wet oxidation method, when the temperature inside the oxide film forming apparatus is lowered, there is a problem that water vapor introduced into the oxide film forming apparatus may be condensed. It may be difficult to realize a wet oxidation method based on the RTO method using a forming apparatus.

Therefore, an object of the present invention is to form a very thin silicon oxide film having a high film thickness uniformity and to obtain a gate oxide with higher electrical reliability than the conventional dry oxidation method. An object of the present invention is to provide a method for forming a silicon oxide film capable of forming a film.

[0011]

According to the present invention, there is provided a method for forming a silicon oxide film on a surface of a silicon layer in an atmosphere containing dry oxygen gas. And (b) heat-treating the silicon oxide film in an atmosphere containing water vapor.

The final thickness of the silicon oxide film after the step (b) may be a predetermined thickness required for the semiconductor device. However, in most cases, the plane orientation of a silicon semiconductor substrate currently used for manufacturing a semiconductor device is (10
0), and no matter how the surface of the silicon semiconductor substrate is smoothed, a step called a step is always formed on the surface of the (100) silicon. This step is usually for one layer of silicon atoms, but in some cases, a step for two to three layers may be formed. Therefore, the thickness of the silicon oxide film after the step (b) is (10
0) When a silicon semiconductor substrate is used, the thickness is preferably 1 nm or more.

In the method of forming a silicon oxide film according to the present invention, the heat treatment may be performed in the step (b) under the conditions of temperature and time so as to increase the thickness of the silicon oxide film. From the viewpoint of controlling the thickness of the film with high accuracy, the increase in the thickness of the silicon oxide film formed in the step (a) can be detected at a temperature that cannot be detected by ellipsometry (so-called ellipsometry). It is preferable to perform heat treatment (hereinafter, may be referred to as first heat treatment). Here, the ellipsometry is a technique of dividing light into two vibration components in the same optical path and measuring the thickness of a thin film by knowing the polarization state of incident light and reflected light. The applied film thickness measuring device is called an ellipsometer. Note that it is assumed that the silicon oxide film does not increase in the first heat treatment even if the thickness increases (for example, the thickness increases to 0.1 nm or less) that can be detected by an electron microscope or the like. The increase in the thickness of the silicon oxide film that cannot be detected by the ellipsometry is, for example, about 0.1 nm or less, depending on the resolution of the measuring device used. Specifically, the upper limit of the temperature in the first heat treatment is 550 ° C., preferably 500 ° C., and more preferably 400 ° C. The lower limit of the temperature in the first heat treatment is a temperature at which water vapor does not condense in a processing chamber (oxidizing furnace) of a single-wafer type or batch type silicon oxide film forming apparatus, preferably 100 ° C. The process (b)
Is preferably generated by at least one of combustion of hydrogen gas, heating of pure water, and bubbling of heated pure water with an oxygen gas or an inert gas. Note that the atmosphere in the step (b) may contain an inert gas such as a nitrogen gas, an argon gas, and a helium gas. Step (a) and step (b) may be performed in the same device, or may be performed in different devices.

The formation of the silicon oxide film in the step (a) may be performed by using a batch type silicon oxide film forming apparatus (furnace annealing apparatus). For example, a lamp that emits infrared light or visible light is provided. It is preferable to perform a rapid high-temperature oxidation method using a single-wafer-type oxide film forming apparatus by lamp heating from the viewpoint that a thinner silicon oxide film can be formed in a short time. In the rapid high-temperature oxidation method,
A temperature rise rate of several tens of degrees C / sec or more can be obtained. The atmosphere for forming the silicon oxide film in the step (a) may be an atmosphere of 100% of dry oxygen gas. Alternatively,
A dry inert gas (eg, nitrogen gas, argon gas, helium gas) atmosphere containing dry oxygen gas may be used, or a dry oxygen gas atmosphere containing hydrochloric acid (HCl), or hydrochloric acid (HCl) and dry oxygen gas may be used. An inert gas atmosphere may be used. In these cases, the dry oxygen gas concentration is determined based on the formation rate (oxidation rate) of the silicon oxide film.
It may be determined appropriately.

In order to further improve the characteristics of the formed silicon oxide film, in the method of forming a silicon oxide film according to the present invention, after the step (b), the formed silicon oxide film is subjected to a second heat treatment. Is preferred. Note that the first heat treatment and the subsequent second heat treatment may be performed in the same apparatus or different apparatuses, but it is preferable to use a furnace annealing apparatus.

It is desirable that the atmosphere for the second heat treatment is an inert gas atmosphere containing a halogen element.
By performing the second heat treatment on the silicon oxide film in an inert gas atmosphere containing a halogen element, the time-zero dielectric breakdown (TZDB) characteristic and the time-dependent dielectric breakdown (T
A silicon oxide film having excellent DDB) characteristics can be obtained. Examples of the inert gas include a nitrogen gas, an argon gas, and a helium gas. In addition, examples of the halogen element include chlorine, bromine, and fluorine, and among them, chlorine is preferable. As the form of the halogen element contained in the inert gas, for example, hydrogen chloride (HCl), CCl ₄ , C ₂ HCl ₃ , C ₂
l _2, HBr, mention may be made of the NF _3. The content of the halogen element in the inert gas is 0.001 to 10% by volume, preferably 0.1 to 10% by volume, based on the form of the molecule or the compound.
005 to 10% by volume, more preferably 0.02 to 10% by volume. For example, when using hydrogen chloride gas, the content of hydrogen chloride gas in the inert gas is preferably 0.02 to 10% by volume. The temperature of the second heat treatment is 700 to
It is desirable that the temperature is 1200 ° C, preferably 700 to 1000 ° C, and more preferably 700 to 950 ° C.

The second heat treatment may be performed in a state in which the atmosphere of an inert gas containing a halogen element is reduced in pressure from atmospheric pressure. In this case, the pressure during the second heat treatment is 1.3 ×
It is preferably at most 10 ⁴ Pa (100 Torr). The lower limit of the pressure depends on the apparatus for heat-treating the silicon oxide film, but is preferably as low as possible.

After the second heat treatment, the silicon oxide film may be nitrided. In this case, the nitriding treatment is preferably performed in an N ₂ O gas, NO gas, or NO ₂ gas atmosphere, and particularly preferably in an N ₂ O gas atmosphere. Alternatively, nitriding is performed in an atmosphere of NH ₃ gas, N ₂ H ₄ , or hydrazine derivative, and then N ₂ O gas, O ₂
It is desirable to perform the annealing treatment in an atmosphere. 700 to 1200 ° C, preferably 800 to 1
It is desirable that the heating be performed at a temperature of 150 ° C., more preferably 900 to 1100 ° C. In this case, the silicon semiconductor substrate is preferably heated by infrared irradiation or furnace annealing.

Alternatively, the atmosphere for the second heat treatment may be a nitrogen-based gas atmosphere. Here, N ₂ , NH ₃ , N ₂ O, and NO ₂ can be exemplified as the nitrogen-based gas.

The silicon layer means not only a substrate itself such as a silicon semiconductor substrate, but also an epitaxial silicon layer, a polycrystalline silicon layer, or an amorphous silicon layer formed on the substrate, so-called bonding method or SIMOX method. Means a silicon layer on which a silicon oxide film is to be formed, such as a silicon layer in an SOI structure manufactured on the basis of the above, and a semiconductor element or a component of a semiconductor element formed on a substrate or these layers. The silicon semiconductor substrate may be manufactured by any method such as the CZ method, the MCZ method, the DLCZ method, and the FZ method, or may be a method in which a high-temperature hydrogen annealing treatment has been performed to remove crystal defects.

The method of forming a silicon oxide film according to the present invention includes, for example, formation of a gate oxide film of a MOS transistor, formation of an interlayer insulating film and an element isolation region, formation of a gate oxide film of a top gate or bottom gate thin film transistor, flash memory For example, the present invention can be applied to formation of a silicon oxide film in various semiconductor devices, such as formation of a tunnel oxide film.

In the method for forming a silicon oxide film of the present invention, first, a silicon oxide film is formed on the surface of a silicon layer in an atmosphere containing dry oxygen gas. That is, a so-called dry oxidation method is performed. In this step, the diffusion rate of oxygen molecules, which are oxidizing species, in the silicon oxide film is lower than that of water molecules. Therefore, the oxidation rate of the silicon layer in the step (a) is lower than that of the wet oxidation method at the same oxidation temperature. As a result, even when a thin silicon oxide film is formed, a silicon oxide film having a uniform film thickness can be formed with good controllability. Further, since the silicon oxide film is formed on the surface of the silicon layer in an atmosphere containing a dry oxygen gas, the silicon layer can be oxidized based on the RTO method.

However, in the silicon oxide film formed in the step (a), an unoxidized Si—Si bond or a silicon dangling bond (Si.) Called oxygen vacancy or oxygen vacancy exists, or At the interface between the silicon oxide film and the silicon layer, structural distortion (compression stress and tensile stress) remains. Incidentally, in the step (b), a first heat treatment is performed on the silicon oxide film in an atmosphere containing water vapor. As a result, water molecules are introduced into the silicon oxide film, and the silicon dangling bonds (Si.) Are terminated by an oxidation reaction by the water molecules in the silicon oxide film to form Si-OH bonds.
As a result, the above-described oxygen vacancies and silicon dangling bonds disappear.

After the step (b), if the formed silicon oxide film is subjected to a second heat treatment in an atmosphere of an inert gas containing a halogen element, an oxidation reaction due to water molecules in the silicon oxide film is performed. Of oxygen vacancies based on silicon, termination of silicon dangling bond at interface of silicon oxide film / silicon layer (Si. + Cl → SiCl) or dehydration effect (SiOH + HCl → SiCl + H ₂ O)
As a result, factors that lower the reliability of the silicon oxide film are further eliminated, and a highly desirable silicon oxide film is formed.

Incidentally, if the first heat treatment is performed at a temperature at which the increase in the thickness of the silicon oxide film formed in the step (a) cannot be detected by the ellipsometry, the first heat treatment It is possible to form a silicon oxide film having high film thickness accuracy without a substantial increase in film thickness.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

(Example 1) In Example 1, the silicon layer was formed from a silicon semiconductor substrate. The formed silicon oxide film functions as a gate oxide film. Example 1
In the above, a silicon oxide film is formed on the surface of the silicon layer in a dry oxygen gas atmosphere. This silicon oxide film was formed using a batch type vertical silicon oxide film forming apparatus whose schematic diagram is shown in FIG. Then, at a temperature at which an increase in the thickness of the silicon oxide film formed in this step cannot be detected by the ellipsometry, the first silicon oxide film is formed on the silicon oxide film in an atmosphere containing water vapor generated by the combustion of hydrogen gas. Heat treatment was applied. That is, steam was generated by the same method as the pyrogenic oxidation method. Further, after the first heat treatment is performed on the silicon oxide film in an atmosphere containing water vapor, an inert gas atmosphere containing a halogen element (specifically, hydrogen chloride is applied to the formed silicon oxide film). A second heat treatment (furnace annealing treatment) was performed in a nitrogen gas atmosphere containing nitrogen gas. In Example 1, the formation of the silicon oxide film, the first heat treatment, and the second heat treatment were performed using the same silicon oxide film forming apparatus. Hereinafter, FIG.
The method of forming the silicon oxide film according to the first embodiment will be described with reference to FIGS.

As shown in the schematic diagram of FIG. 2, this vertical type silicon oxide film forming apparatus includes a processing chamber 20 having a double tube structure made of quartz and a chamber for introducing water vapor or the like into the processing chamber 20. A gas introduction unit 22, a gas exhaust unit 23 for exhausting gas from the processing chamber 20, a heater 24 for maintaining the inside of the processing chamber 20 at a predetermined atmospheric temperature via a cylindrical soaking tube 26 made of SiC, A substrate loading / unloading section 27, a gas introduction section 28 for introducing nitrogen gas into and out of the substrate loading / unloading section 27, a gas exhaust section 29 for exhausting gas from the substrate loading / unloading section 27, a processing chamber 20, and a substrate loading / unloading section. A shutter 25 that separates 27 from
An elevator mechanism 30 is provided for carrying the silicon semiconductor substrate 10 into and out of the processing chamber 20. A quartz boat 31 for mounting the silicon semiconductor substrate 10 is attached to the elevator mechanism 30. The temperature of the silicon semiconductor substrate 10 is measured by an ellipsometer (not shown) whose measurement principle is based on ellipsometry (so-called ellipsometry). Further, the hydrogen gas supplied to the combustion chamber 32 is mixed with the oxygen gas at a high temperature in the combustion chamber 32 and burned to generate steam. The water vapor is supplied into the processing chamber 20 via the pipe 33, the gas flow path 21, and the gas introduction unit 22. The gas flow path 21 is located outside the processing chamber 20 having a double pipe structure.

[Step-100] First, an element isolation region 11 having a LOCOS structure is formed in a silicon semiconductor substrate 10 by a known method, and well ion implantation, channel stop ion implantation, and threshold adjustment ion implantation are performed. Note that the element isolation region may have a trench structure. afterwards,
Fine particles and metal impurities on the surface of the silicon semiconductor substrate 10 are removed by RCA cleaning, and then the surface of the silicon semiconductor substrate 10 is cleaned with a 0.1% aqueous hydrofluoric acid solution to expose the surface of the silicon semiconductor substrate 10 ( FIG.
(A)). Since most of the surface of the silicon semiconductor substrate 10 is terminated with hydrogen and part of the surface is terminated with fluorine, even if the silicon semiconductor substrate 10 is left in the air, a silicon oxide film is not generated. Absent.

[Step-110] Next, the silicon semiconductor substrate is loaded into the substrate loading / unloading section 27 of the silicon oxide film forming apparatus shown in FIG. 2 from a door (not shown) and placed on the quartz boat 31 (FIG. 3 (A)). A nitrogen gas is introduced into the processing chamber 20 from the gas introduction unit 22, the inside of the processing chamber 20 is set to an inert gas atmosphere such as a nitrogen gas (a reduced-pressure atmosphere may be used), and a heater is provided through the soaking tube 26. 24, the atmosphere temperature in the processing chamber 20 is maintained at 850 ° C.
In this state, the shutter 25 is closed.

[Step-120] Then, the substrate loading / unloading section 2
After the loading of the silicon semiconductor substrate into the substrate 7 is completed, a door (not shown) is closed, nitrogen gas is introduced into the substrate loading / unloading unit 27 from the gas introduction unit 28, exhausted from the gas exhaust unit 29, and discharged into the substrate loading / unloading unit 27 Is a nitrogen gas atmosphere. The oxygen gas concentration in the substrate loading / unloading section 27 is monitored, and if the oxygen gas concentration becomes, for example, 20 ppm or less, the substrate loading / unloading section 2
It is determined that the inside of 7 has become a sufficient nitrogen gas atmosphere. Thereafter, the shutter 25 is opened (see FIG. 3B), the elevator mechanism 30 is operated to raise the quartz boat 31, and the silicon semiconductor substrate 10 is carried into the processing chamber 20 having a double tube structure made of quartz. (See FIG. 4A). When the elevator mechanism 30 reaches the highest position, the quartz boat 31
No communication is established between the processing chamber 20 and the substrate loading / unloading section 27 by the base.

[Step-130] Next, 100% dry oxygen gas is introduced into the processing chamber 20 from the gas introduction part 22.
The oxidation time was 5 minutes. As a result, a silicon oxide film 12 having a thickness of 3 nm was formed on the silicon layer (the surface of the silicon semiconductor substrate 10 in Example 1) (see FIG. 1B and FIG. 4B). A conceptual diagram of the structure of the silicon oxide film at this time is shown in FIG. 8A. The silicon oxide film has oxygen vacancies such as “Si—Si” bonds and silicon dangling bonds such as “Si.” And other defects.

[Step-140] After that, the supply of the dry oxygen gas into the processing chamber 20 is stopped, and the inert gas (nitrogen gas) is supplied from the gas inlet 22 into the processing chamber 20 while the silicon oxide film is formed. The temperature of the atmosphere in the processing chamber 20 of the film forming apparatus is set to 400 ° C. by controlling the heater 24. Then, the temperature of the silicon semiconductor substrate 10 in the processing chamber 20 becomes 4
After the temperature reaches 00 ° C. (that is, if the increase in the thickness of the formed silicon oxide film becomes a temperature that cannot be detected by ellipsometer measurement by ellipsometry), the processing chamber 20 is maintained at this temperature. Therefore, in the first embodiment, 75
Hydrogen gas: oxygen gas is introduced in a ratio of 1: 4 into the combustion chamber 32 maintained at 0 ° C. to burn the hydrogen gas, and the steam generated in the combustion chamber 32 is supplied with the steam 33, the gas flow path 21, The gas is supplied into the processing chamber 20 via the gas introduction unit 22. Then, a first heat treatment was performed on the silicon oxide film 12 at 400 ° C. for 5 minutes (see FIG. 1C and FIG. 5A). A conceptual diagram of the structure of the silicon oxide film at this time is shown in FIG. 8B. The silicon dangling bonds generated in the silicon oxide film are terminated by “OH” and the H ₂ O molecule Is contained inside.

[Step-150] Then, the supply of water vapor is stopped, and the temperature of the atmosphere in the processing chamber 20 is raised to 850 ° C. by the heater 24 while the nitrogen gas is introduced into the processing chamber 20 from the gas inlet 22. Let it. Thereafter, for example, a nitrogen gas containing 0.1% by volume of hydrogen chloride was introduced into the processing chamber 20 from the gas introduction unit 22, and a second heat treatment was performed for 30 minutes (FIG. 1D and FIG. 5). (B)). A conceptual diagram of the structure of the silicon oxide film at this time is shown in FIG. 8C. The oxygen vacancies are replaced by “Si—O—Si” bonds, and the “Si—OH” bonds are stable. [Si-C
This replaces the "1" bond, and a silicon oxide film having extremely excellent characteristics is formed.

[Step-160] With the above, the formation of the silicon oxide film 12 on the surface of the silicon semiconductor substrate is completed. Thereafter, the interior of the processing chamber 20 is set to a nitrogen gas atmosphere, the elevator mechanism 30 is operated to lower the quartz boat 31, and then the silicon semiconductor substrate is carried out from the substrate carry-in / out section 27.

Example 2 In Example 1, the silicon oxide film was formed using a batch type vertical silicon oxide film forming apparatus. On the other hand, in Example 2, a rapid high-temperature oxidation method using an oxide film forming apparatus (hereinafter simply referred to as an oxide film forming apparatus) by a single-wafer type lamp heating equipped with an infrared lamp whose conceptual diagram is shown in FIG. A silicon oxide film was formed based on the (RTO method). Also in Example 2, after the first heat treatment was performed on the silicon oxide film in an atmosphere containing water vapor, an inert gas atmosphere containing a halogen element was applied to the formed silicon oxide film (specifically, The first heat treatment and the second heat treatment were performed in the same silicon oxide film forming apparatus (furnace annealing apparatus) as in the first embodiment. It was performed using.

FIG. 6 is a schematic view of the oxide film forming apparatus used in the second embodiment. This oxide film forming apparatus includes a processing chamber 40 formed of a quartz furnace core tube, and a plurality of infrared lamps 41 as heating means for heating the silicon semiconductor substrate 10 corresponding to a silicon layer. Infrared lamp 41
Are disposed outside the processing chamber 40 and substantially parallel to the surface of the silicon layer. For example, the silicon semiconductor substrate 10 corresponding to the silicon layer
And is carried into and out of the processing chamber 40 via a gate valve 43 provided at one end of the processing chamber 40. The oxide film forming apparatus further includes a gas introduction unit 44 for introducing oxygen gas or the like into the processing chamber 40 via the pipe 46, and a gas exhaust unit 45 for exhausting gas from the processing chamber 40.
In some cases, as shown in the schematic diagram of FIG. 7, an oxide film forming apparatus having a resistance heater 41A may be used instead of the infrared lamp 41.

[Step-200] First, after forming an element isolation region and the like in the silicon semiconductor substrate 10 in the same manner as in the first embodiment, fine particles and metal impurities on the surface of the silicon semiconductor substrate are removed by RCA cleaning. Then, the surface of the silicon semiconductor substrate 10 is cleaned with a 0.1% aqueous solution of hydrofluoric acid to expose the surface of the silicon semiconductor substrate 10.

[Step-210] Next, the silicon semiconductor substrate 10 placed on the wafer stage 42 is carried into the processing chamber 40 via the gate valve 43 provided at one end of the processing chamber 40. Before the transfer, the gas introduction unit 4 is introduced into the processing chamber 40.
A nitrogen gas is introduced from Step 4 and the inside of the processing chamber 40 is set to an inert gas atmosphere such as a nitrogen gas (a reduced pressure atmosphere may be used).

[Step-220] After the loading of the silicon semiconductor substrate 10 into the processing chamber 40 is completed, the gate valve 43 is closed, and the infrared lamp 41 is operated to activate the temperature of the silicon semiconductor substrate 10 in the processing chamber 40. To 800 ° C. Then, the gas introduction units 44 to 10
0% dry oxygen gas is introduced. As a result, a silicon oxide film having a thickness of 1.5 nm was formed on the silicon layer (the surface of the silicon semiconductor substrate 10 in Example 2).

[Step-230] Then, the infrared lamp 4
1 is stopped, the gate valve 43 is opened, and the silicon semiconductor substrate 10 is carried out of the processing chamber 40.

[Step-240] Next, the silicon semiconductor substrate 10 is loaded into the substrate loading / unloading section 27 of the vertical type silicon oxide film forming apparatus described in the first embodiment from a door (not shown), and is loaded into the quartz boat 31. Place. A nitrogen gas is introduced into the processing chamber 20 from the gas introduction unit 22, the inside of the processing chamber 20 is set to an inert gas atmosphere such as a nitrogen gas (a reduced-pressure atmosphere may be used), and a heater is provided through the soaking tube 26. At 24, the atmosphere temperature in the processing chamber 20 is maintained at 400 ° C.
In this state, the shutter 25 is closed. After the loading of the silicon semiconductor substrate into the substrate loading / unloading section 27 is completed, a door (not shown) is closed, nitrogen gas is introduced into the substrate loading / unloading section 27 from the gas introducing section 28, and the nitrogen gas is discharged from the gas exhausting section 29, The inside of the substrate loading / unloading section 27 is set to a nitrogen gas atmosphere. The oxygen gas concentration in the substrate loading / unloading section 27 is monitored, and when the oxygen gas concentration becomes, for example, 20 ppm or less, it is determined that the inside of the substrate loading / unloading section 27 has a sufficient nitrogen gas atmosphere. Thereafter, the shutter 25 is opened, the elevator mechanism 30 is operated, the quartz boat 31 is raised, and the silicon semiconductor substrate 10 is carried into the processing chamber 20 having a double tube structure made of quartz. Next, when the silicon semiconductor substrate 10 reaches 400 ° C. (ie,
If the increase in the thickness of the formed silicon oxide film becomes a temperature that cannot be detected by an ellipsometer (not shown) by an ellipsometry, the combustion chamber 32 is processed similarly to [Step-140] of the first embodiment. Hydrogen gas and oxygen gas are introduced therein to burn the hydrogen gas, and steam generated in the combustion chamber 32 is supplied into the processing chamber 20 through the pipe 33, the gas flow path 21 and the gas introduction unit 22, A first heat treatment was performed on the silicon oxide film for 10 minutes at ゜ C.

[Step-250] Next, in the same manner as in [Step-150] of Example 1, a second heat treatment is performed for 30 minutes in a nitrogen gas atmosphere containing 0.1% by volume of hydrogen chloride, for example. Applied to the membrane. Thus, the formation of the silicon oxide film on the surface of the silicon semiconductor substrate 10 is completed. Thereafter, the interior of the processing chamber 20 is set to a nitrogen gas atmosphere, the elevator mechanism 30 is operated to lower the quartz boat 31, and then the silicon semiconductor substrate is carried out from the substrate carry-in / out section 27.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to these embodiments. The various conditions and the structure of the silicon oxide film forming apparatus and the structure of the oxide film forming apparatus using lamp heating described in the embodiments are merely examples, and can be changed as appropriate. The method of generating steam is not only the combustion of hydrogen gas, but also steam generated by heating pure water, steam generated by bubbling heated pure water with an oxygen gas or an inert gas, or a method of generating these steams. The method can be used in combination. In the embodiment, the silicon oxide film is formed exclusively on the surface of the silicon semiconductor substrate. However, in the manufacturing process of the silicon semiconductor substrate, the silicon oxide film is formed on the surface of the silicon semiconductor substrate manufactured by the CZ method or the MCZ method by the epitaxial growth method. A silicon substrate having a 10 μm epitaxial silicon layer formed thereon, an epitaxial silicon layer formed on a silicon semiconductor substrate surface in a semiconductor device manufacturing process, and a polycrystalline silicon layer formed on an insulating layer formed on the substrate Alternatively, a silicon oxide film can be formed on the surface of an amorphous silicon layer or the like. Alternatively, a silicon oxide film may be formed on the surface of the silicon layer in the SOI structure, or a substrate on which a semiconductor element or a component of the semiconductor element is formed, or an underlayer formed on these layers. A silicon oxide film may be formed on the surface of the silicon layer formed on the insulating layer. The second heat treatment after the formation of the silicon oxide film is not essential and can be omitted in some cases.

In the first embodiment, the formation of the silicon oxide film, the first heat treatment, and the second heat treatment were performed using a batch type vertical silicon oxide film forming apparatus.
The silicon oxide film may be formed using a batch type vertical silicon oxide film forming apparatus, and the first heat treatment and the second heat treatment may be performed using different batch furnace annealing apparatuses. it can. On the other hand, in Example 2, the first heat treatment and the second heat treatment were performed using the same silicon oxide film deposition apparatus as in Example 1, but instead, each of these heat treatments was performed in a separate batch. It can also be performed using a furnace annealing apparatus of the type.

[0046]

According to the method for forming a silicon oxide film of the present invention, first, the silicon oxide film is formed on the surface of the silicon layer in an atmosphere containing dry oxygen gas. A silicon oxide film having a uniform thickness can be formed on the silicon layer. Next, by performing a first heat treatment on the silicon oxide film in an atmosphere containing water vapor, a factor that reduces reliability such as oxygen vacancies generated in the silicon oxide film by a so-called dry oxidation method is removed from the silicon oxide film. It is eliminated and a silicon oxide film having very desirable properties is formed. Therefore, a decrease in channel mobility can be prevented, the drive current of the MOS transistor element hardly deteriorates, and the occurrence of a stress leak phenomenon that causes deterioration of data retention characteristics in a flash memory or the like can be suppressed. It is possible to form a very thin, for example, gate oxide film having excellent long-term reliability. Note that by performing the first heat treatment at a temperature at which an increase in the thickness of the silicon oxide film cannot be detected by the ellipsometry, a silicon oxide film having high film thickness accuracy can be formed. Further, if the formed silicon oxide film is further subjected to a second heat treatment in an inert gas atmosphere containing a halogen element, the time-zero dielectric breakdown (TZDB) characteristic and the temporal dielectric breakdown (TDDB) characteristic are excellent. In addition, a silicon oxide film having more preferable electric characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic partial cross-sectional view of a silicon semiconductor substrate and the like for describing a method for forming a silicon oxide film of the present invention.

FIG. 2 is a schematic view of a batch type vertical silicon oxide film forming apparatus used in Example 1.

FIG. 3 is a conceptual diagram of a silicon oxide film forming apparatus and the like for describing a method of forming a silicon oxide film in Example 1.

FIG. 4 is a conceptual diagram of a silicon oxide film forming apparatus and the like for explaining a method of forming a silicon oxide film in Example 1, following FIG. 3;

FIG. 5 is a conceptual diagram of a silicon oxide film forming apparatus and the like for explaining a method of forming a silicon oxide film in Example 1, following FIG. 4;

FIG. 6 is a schematic diagram of an apparatus for forming an oxide film by single-wafer-type lamp heating used in Example 2.

FIG. 7 is a schematic view of another type of single-wafer annealing apparatus.

FIG. 8 is a conceptual diagram of the structure of a silicon oxide film formed in each step of the method for forming a silicon oxide film of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Silicon semiconductor substrate, 11 ... Element isolation area, 12 ... Silicon oxide film, 20 ... Processing chamber, 2
DESCRIPTION OF SYMBOLS 1 ... gas flow path, 22 ... gas introduction part, 23 ...
Gas exhaust unit, 24 heater, 25 shutter, 26 soaking tube, 27 substrate loading / unloading unit, 28
... gas introduction part, 29 ... gas exhaust part, 30 ...
Elevator mechanism, 31 ... quartz boat, 32 ... combustion chamber, 33, 46 ... piping, 40 ... processing chamber, 41
... Infrared lamp, 42 ... Wafer stand, 43 ...
Gate valve, 44: gas introduction part, 45: gas exhaust part

Claims (11)

[Claims] (A) forming a silicon oxide film on the surface of a silicon layer in an atmosphere containing dry oxygen gas; and (b) heat treating the silicon oxide film in an atmosphere containing water vapor. A method for forming a silicon oxide film. 2. The heat treatment of the step (b) at a temperature at which an increase in the thickness of the silicon oxide film formed in the step (a) cannot be detected by ellipsometry. 2. The method for forming a silicon oxide film according to item 1. 3. The method according to claim 1, wherein the water vapor in the step (b) is generated by at least one of combustion of hydrogen gas, heating of pure water, and bubbling of heated pure water with oxygen gas or inert gas. The method of claim 1, wherein: 4. The silicon oxide film according to claim 1, wherein the formation of the silicon oxide film in the step (a) is performed by a rapid high-temperature oxidation method using an oxide film forming apparatus by lamp heating. Forming method. 5. The method for forming a silicon oxide film according to claim 1, wherein a second heat treatment is performed on the formed silicon oxide film after the step (b). 6. The method for forming a silicon oxide film according to claim 5, wherein the atmosphere for the second heat treatment is an inert gas atmosphere containing a halogen element. 7. The method for forming a silicon oxide film according to claim 6, wherein the halogen element is chlorine. 8. The silicon oxide film according to claim 7, wherein the chlorine is in the form of hydrogen chloride, and the concentration of hydrogen chloride contained in the inert gas is 0.02 to 10% by volume. Formation method. 9. The method according to claim 5, wherein the second heat treatment is performed at a temperature of 700 to 950 ° C. 10. The method according to claim 9, wherein the second heat treatment is a furnace annealing process. 11. The method according to claim 1, wherein the silicon layer comprises an epitaxial silicon layer formed on the substrate.