JPH08288283A - Silicon oxide film forming method and silicon oxide film forming apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] It is possible to remove structural defects in the silicon oxide film without introducing foreign atoms into the silicon oxide film, thereby forming a high quality ultra-thin silicon oxide film. . A step of forming an oxide film 203 by thermal oxidation, and a step of removing a defect 204 in the silicon oxide film 203 in an atmosphere in which the sublimation rate of silicon monooxide (SiO) is higher than the oxidation rate. Is continuously repeated to perform initial oxidation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon oxide film forming method and a silicon oxide film forming apparatus used for a gate insulating film or a capacitor insulating film of a semiconductor device.

[0002]

2. Description of the Related Art As a gate oxide film forming a semiconductor device, a silicon oxide film (SiO ₂ ) formed by thermally oxidizing a Si (silicon) substrate is usually used. With the integration, it is required to reduce the thickness of this silicon oxide film. For example, an oxide film having a film thickness of 100Å is used in 64M DRAM of 0.35 μm process technology and 256 MDRA of 0.25 μm process technology.
For M, an oxide film with a thickness of 80Å is used. In addition, CMOS logic that aims for higher performance is more
The generation of thin films is required in the early generation, and an oxide film having a film thickness of 60 Å is used in the CMOS logic of the 0.25 μm process technology.

By the way, in such an ultrathin silicon oxide film, the influence of certain defects (structural defects) existing in the film cannot be ignored, and for this reason, it cannot be seen in the conventional thick oxide film. Problems have arisen, making it difficult to ensure the reliability of the device.

First, structural defects in the silicon oxide film will be described. Silicon oxide film has an amorphous structure with a short-range order of Si-O ₄ tetrahedral structure (tetrahedra). In this case, the structural defect is a portion deviated from the tetrahedral structure due to the destruction of the short-range order. In this portion, the chemical bond of the bridging oxygen atom is broken, and the silicon dangling bond, Si-Si, S
There are incomplete bonds such as i-O-H bonds. Although the cause of generation of such structural defects is not clear,
It has been pointed out that the state of the i-substrate surface has an effect. Bulk silicon is a very high quality single crystal, but there are many uncontrollable factors (surface defects) on its surface. For example, minute irregularities, a natural oxide film, impurities adsorbed on the surface (water, heavy metals, carbides, particles, chemical residues, mobile ions) can be cited. It is impossible to perfect the surface condition of the substrate, and surface defects remain even after pretreatment with various chemicals. It is considered that such surface defects are incorporated into the film due to oxidation to form structural defects. This type of unstable bond is broken by the application of high electric field stress. The resulting dangling bond becomes an electron trap site, which causes a change in characteristics over time and reduces reliability.

From the above, it is necessary to control the structure of the silicon oxide film at the atomic level in order to obtain an ultrathin oxide film having excellent reliability. Several methods are available for achieving such an object. Is proposed.

For example, JP-A-6-45320, JP-A-5-315318 and JP-A-3-257828 disclose:
A method of introducing nitrogen atoms into a silicon oxide film has been proposed. That is, JP-A-6-45320 proposes a method of adding nitrogen in an excited state into an oxidizing atmosphere and introducing it into an oxide film, and JP-A-5-315318 discloses a surface of a silicon substrate before oxidation. A method of implanting nitrogen atoms by an ion implantation method and oxidizing the surface thereof to introduce nitrogen atoms into the oxide film has been proposed, and JP-A-3-2578 is also available.
No. 28 proposes a method in which a silicon substrate is thermally oxidized and then heat-treated in a nitrogen atmosphere to introduce nitrogen atoms into the film. These methods are intended to replace the oxygen atom and the nitrogen atom to make a more stable bond state.

Further, JP-A-6-85278 and JP-A-6-85278.
-13372 and Japanese Patent Laid-Open No. 5-74762 propose a method of introducing fluorine or chlorine atoms into an oxide film. These methods are intended to terminate a silicon dangling bond with a fluorine or chlorine atom that has a strong bond with silicon.

As described above, conventionally, atoms other than silicon and oxygen, such as nitrogen, chlorine, and fluorine (hereinafter referred to as "heteroatoms") are introduced into the oxide film, and silicon dangling bonds such as dangling bonds are introduced. By terminating or forming a more stable bond state, the influence of structural defects on the characteristics is mitigated.

[0009]

However, the above-mentioned conventional methods for forming a high quality ultra-thin silicon oxide film have the following problems.

(Problem 1) In other words, it is considered that structural defects do not exist two-dimensionally uniformly but exist discretely. Therefore, it is most effective to selectively introduce different atoms into the defect portion. However, in the conventional method described above,
Heterogeneous atoms such as nitrogen, chlorine, and fluorine are also introduced into the oxide film having no defects, and when these heterogeneous atoms are introduced into the interstitial space, etc., they can become new trap sites. Further, when the heteroatoms are introduced by ion implantation, secondary defects due to the implantation are also introduced into the oxide film. In order to remove these defects or interstitial atoms by outdiffusion, high temperature heat treatment is required, and there is a problem that the lowering of the process temperature is hindered.

(Problem 2) Further, according to the above-described conventional method, it is impossible to selectively introduce the heteroatom only into the oxide film, and the heteroatom is simultaneously introduced into silicon near the interface. . In the MOS structure element, the portion directly under the oxide film is the channel portion. Therefore, when the oxide film structure is improved by the above-mentioned conventional method to form the MOS structure element, the channel portion is also covered with nitrogen, chlorine, fluorine or the like. Heterogeneous atoms are included. In the MOS structure element, it is desired that the channel portion does not have atoms that may be carriers of confusion as much as possible. However, in the MOS structure element in which the oxide film is formed by the above-described conventional method, different kinds of atoms are present in the channel portion. Are included, and these foreign atoms become an obstacle to carriers moving in the channel portion, which causes a decrease in carrier mobility in the channel.

(Problem 3) Further, in the above-mentioned conventional method, the concentration distribution in the wafer of the heteroatoms introduced into the oxide film by the heat treatment after the oxidation, the ion implantation and the like, and the reproducibility between batches. It is difficult to ensure the above characteristics, and this causes a problem that variations in element characteristics occur.

As described above, conventionally, various methods of introducing different kinds of atoms have been proposed in order to improve the structure of the silicon oxide film. In these methods, except for the defective portion in the oxide film, However, the heteroatom is introduced, which causes many problems as described above. Therefore, a method of removing structural defects in the oxide film without introducing foreign atoms into the oxide film is desired.

The present invention can remove structural defects in a silicon oxide film without introducing foreign atoms into the silicon oxide film, thereby forming a high quality ultrathin silicon oxide film. An object of the present invention is to provide a silicon oxide film forming method and a silicon oxide film forming apparatus that can be used.

[0015]

As described above, most of the causes of structural defects in the silicon oxide film exist on the surface of the silicon substrate before oxidation. Therefore, in order to form a high-quality silicon oxide film, particular attention must be paid to the initial process of oxidation. The present invention is an improvement of this initial oxidation process over the conventional method of forming a silicon oxide film.

Here, the initial oxidation process refers to a region where the oxide film thickness is approximately 50 Å or less. In the oxidation process according to the present invention, in this initial oxidation process, a basic process includes a step of forming a silicon oxide film by a thermal oxidation method and a step of selectively removing a structural defect portion formed in the silicon oxide film. The basic process is repeated a plurality of times to form an ultrathin oxide film, and then a silicon oxide film having a desired film thickness is formed by, for example, an ordinary thermal oxidation method. According to this method, unlike the conventional method, it is possible to form a silicon oxide film having no structural defects without introducing foreign atoms.

The method for forming a silicon oxide film and the method for removing structural defects in the present invention will be described below. Normal thermal oxidation is performed in an oxidizing atmosphere near atmospheric pressure,
In the method of the present invention, thermal oxidation is performed in an atmosphere having a low partial pressure of oxidizing gas. Especially when the oxidizing atmosphere is in the high vacuum region, the etching and oxidation of the silicon surface are very sensitive to the oxidizing conditions.

FIG. 1 shows this state. In FIG. 1, the horizontal axis represents the oxidation temperature and the vertical axis represents the oxidizing gas partial pressure in the atmosphere. In the figure, the shaded portion 102 is a region where etching of the silicon surface occurs, and the other portion 101 is a region where the silicon surface is oxidized. That is, when the oxidation temperature under the oxidation conditions is constant, the etching and oxidation of the surface can be controlled as indicated by arrow A by adjusting the partial pressure of the oxidizing gas. When the oxidizing gas partial pressure is constant, the etching temperature and the oxidation of the surface can be controlled as shown by arrow B by adjusting the oxidation temperature.

Here, the etching of the Si surface occurs when silicon monoxide (Si-O) produced by the reaction between the oxidizing gas and Si sublimes into the gas phase. This process is used for surface cleaning when crystal-growing a thin film on a silicon substrate.

By the way, as described above, the structural defects in the silicon oxide film are Si having a smaller oxidation number than SiO _2.
O _X and a Si-Si bond defects of this kind is considered to discretely distributed within the wafer surface. The inventor of the present application paid attention to such a structure of defects in the silicon oxide film. Incomplete coupling portions such as SiO _X or Si-Si, compared to the portion having a tetrahedral structure, it is in a transient state of easily more SiO bonds. Therefore, when the silicon oxide film containing structural defects is exposed to the above-mentioned conditions in which the sublimation of Si—O occurs, the portion where the bond is incomplete, that is, the structural defect portion sublimates first. If this state is maintained thereafter, the silicon oxide film over the entire area of the silicon substrate will sublime. Therefore, by appropriately setting the processing condition (processing time), it becomes possible to selectively remove only the structural defect portion in the silicon oxide film.

In the present invention, the above-mentioned structural defect removing method is incorporated into the thermal oxidation method, and the oxide film forming step by thermal oxidation and the sublimation rate of silicon monooxide (SiO) are higher than the oxidation rate. The initial oxidation is performed by continuously repeating the defect removing step of removing defects in the silicon oxide film in the atmosphere.

FIG. 2 is a diagram showing an outline of this method of the present invention. As shown in FIG. 2A, generally, the silicon substrate 3
On the surface of 10, there are surface defects 202 that cannot be completely removed by pretreatment with various chemicals. When the surface of the silicon substrate in this state is oxidized by forming an atmosphere 207 which causes oxidation as shown in FIG. 2B, the silicon oxide film 203 contains structural defects 204.

In the present invention, the oxidation is suspended in this state, and as shown in FIG. 2 (c), an atmosphere 2 in which sublimation of Si--O occurs.
By forming 06, the structural defect 204 is removed. That is, in this defect removal step, the structural defect portion 204 in the silicon oxide film is sublimated and removed in the Si—O state as indicated by reference numeral 205, resulting in the state shown in FIG. Note that, hereinafter, the two steps of the oxidation step as shown in FIG. 2B and the defect removal step as shown in FIGS. 2C and 2D are collectively referred to as a basic step. The process is repeated to form a silicon oxide film.

That is, thereafter, again, as shown in FIG. 2 (e), an atmosphere 207 that causes oxidation is formed. In this oxidation step, oxidation occurs even in the portion where the structural defects are removed in the steps of FIGS. 2C and 2D, and the silicon oxide film 2
03 is formed, and with respect to this silicon oxide film 203,
By repeating the basic steps such as performing the same defect removing step as in FIGS. 2C and 2D, a silicon oxide film having no structural defects can be finally formed. The silicon oxide film is formed by repeating the above basic steps until the silicon oxide film having a thickness of 10 to 50 Å is formed, and the subsequent oxidation may be performed in a normal atmosphere. The process may be repeated to continue formation.

In the above basic process, the oxidation process and the defect removal process in the oxide film by sublimation of Si—O can be achieved by adjusting the following conditions.

First, in the case of oxidizing at a constant oxidizing temperature, the partial pressure of the gas forming the oxidizing atmosphere is adjusted as shown by the arrow A in FIG. If the gas partial pressure is high, oxidation is likely to occur, and if the gas partial pressure is low, defect removal is likely to occur.
Further, in the case of oxidizing with the partial pressure of the gas forming the oxidizing atmosphere being constant, the oxidation and the defect removal can be controlled by adjusting the oxidizing temperature, as shown by the arrow B in FIG. That is, when the partial pressure is constant, sublimation in the Si—O state is more likely to occur when the oxidation temperature is high,
Oxidation is more likely to occur when the oxidation temperature is low.

Gases such as oxygen (O ₂ ), water vapor (H ₂ O) and ozone (O ₃ ) can be used as the oxidizing gas forming the oxidizing atmosphere. These oxidizing gases may be used alone, or may be argon (Ar), nitrogen (N ₂ ), helium (H).
You may use it after diluting it with an inert gas such as e). Also,
Gas partial pressure during oxidation is 760 Torr (atmospheric pressure) to 10 ^-7
It is preferable to adjust in the range of Torr. The oxidation temperature is preferably in the range of 500 to 1200 ° C.
In addition, the defect removal process is 10 ^-2 Torr to ^{10 -10} T.
It is preferable to perform the above inert gas atmosphere or vacuum atmosphere under the partial pressure of orr. When an oxidizing gas is present in the atmosphere, the partial pressure of the oxidizing gas is set to 10 ⁻⁴ Torr to 10 ⁻⁸ Torr.
Adjust to the range of. The processing temperature at this time is 700 ° to 13 °
It is better to set it in the range of 00 ° C.

Further, in the process of removing defects (that is, when the oxidizing gas partial pressure is low or the oxidation temperature is high among the two oxidizing conditions formed alternately), Si atoms are converted into silicon. By supplying to the substrate surface,
Sublimation of Si-O becomes easier to proceed. This is because active Si atoms and oxygen in the silicon oxide film are bonded to each other, so that transition to Si—O is likely to occur.
Here, the film formation of Si is performed in the same vacuum chamber as the oxidation by a method such as an electron beam (EB) vapor deposition method, a resistance heating vapor deposition method, and a vapor phase growth method (CDV method). The supply amount of Si atoms is set, for example, so that Si atoms are deposited on the surface of the silicon oxide film in at least a monoatomic layer or more, more specifically, the film thickness of Si is 1 ML to 10 ML. After that, the Si deposited on the silicon oxide film is also oxidized. By repeating these steps to form a silicon oxide film, a high quality silicon oxide film with extremely few structural defects can be obtained.

In other words, according to the method for forming a silicon oxide film of the present invention, in the method for forming a silicon oxide film by heating the surface of the silicon substrate in an oxidizing atmosphere, the step of oxidizing the surface of the silicon substrate The basic step is a defect removal step of removing defects in the silicon oxide film in an atmosphere in which the sublimation rate of monooxide (SiO) is higher than the oxidation rate, and the basic step is repeated to form the silicon oxide film. It is characterized by that.

Here, in the basic process, the oxidizing gas partial pressure is adjusted to a range of 10 ^-2 Torr to 10 ^-8 Torr,
The basic process can be performed in an atmosphere in which oxidizing gas partial pressures of at least two points in the gas partial pressure range are alternately formed.

Alternatively, the oxidation temperature of the basic process is set to 70
The temperature is adjusted within the range of 0 ° C to 1300 ° C, the basic process is performed in an atmosphere in which the oxidation temperatures of at least two points of the oxidation temperature range are alternately formed, and the high oxidation temperature of the at least two points. The partial pressure of the oxidizing gas can be performed in an atmosphere smaller than the partial pressure of the oxidizing gas at the low oxidation temperature.

Alternatively, in the basic step, two oxidation conditions are alternately formed. Of these two oxidation conditions, if the oxidizing gas partial pressure is low or the oxidation temperature is high, In addition, Si atoms are deposited on the surface of the silicon oxide film in at least a monoatomic layer or more.

[0033]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a diagram showing a structural example of a silicon oxide film forming apparatus according to the present invention. This silicon oxide film forming apparatus is composed of three chambers, a sample introducing chamber 301, an initial oxidizing chamber 302, and an oxidizing chamber 303.
2, 303 are partitioned by gate valves 304, 305.

The chambers 301, 302, 303 can be individually evacuated. That is, in the oxidation chamber 303, it is possible to oxidize in a low-vacuum depressurized state from atmospheric pressure to 10 ^-2 Torr, and in the initial oxidation chamber 302, 10 ^-2 Torr.
Oxidation is possible in the high vacuum region of -10 ^-7 Torr.

Further, a substrate transfer mechanism (not shown) does not expose the substrate 310 to the atmosphere, so that the chambers 301, 302, 30 are not exposed.
It can be moved along the transport route TR between the three.

Further, although the oxidation chamber 303 is constructed as a general RTP device, the initial oxidation chamber 302 is constructed so that an ultrahigh vacuum can be exhausted by the exhaust system 306.
A substrate heating system 307 and a Si film forming apparatus (for example, an electron beam vapor deposition apparatus) 309 are provided in the initial oxidation chamber 302. Here, the substrate heating system 307 is configured such that the back surface and the front surface of the substrate 310 can be independently heated and controlled by an infrared lamp, for example. The back surface heating can be mainly used for bias heating, and the front surface heating can be used for rapid temperature rising. Further, when an electron beam evaporation apparatus is used as the Si film forming apparatus 309, the supply timing can be controlled by opening and closing the shutter.

Further, this silicon oxide film forming apparatus has
An inert gas supply source 311 and an oxidizing gas supply source 312 are provided, and the inert gas from the inert gas supply source 311 is supplied to the initial oxidation chamber 3 by valves 313 and 314.
02, supply to the oxidation chamber 303 is controlled respectively. The supply of the oxidizing gas from the oxidizing gas supply source 312 to the initial oxidizing chamber 302 and the oxidizing chamber 303 is controlled by valves 315 and 316, respectively.

The heating control of the substrate 310 and the supply timing control of the inert gas, the oxidizing gas, and the Si raw material are
For example, it can be collectively performed by a timing control device (not shown) using a processor or the like (program control of each condition is possible).

In other words, the silicon oxide film forming apparatus according to this embodiment includes a substrate heating device 307, an exhaust device 306,
Gas supply devices 311, 312 and Si thin film deposition device 30
9 and a timing control device, and a substrate heating device 30
7 is capable of periodically adjusting the amount of heating to the substrate, and the exhaust device 306 is capable of performing ultra-high vacuum exhaust and being capable of periodically adjusting the exhaust speed, and the gas supply device 3
11, 312 can adjust the gas supply amounts of the inert gas and the oxidizing gas periodically, and the Si thin film deposition apparatus 30
In 9, the supply amount of Si can be adjusted periodically.

With such a silicon oxide film forming apparatus, a silicon oxide film with extremely few structural defects can be formed in the manner described above. An embodiment of the silicon oxide film forming method using the silicon oxide film forming apparatus of FIG. 3 will be described in detail below.

Example 1 In Example 1, first, a Si substrate 310 thoroughly washed with chemicals and pure water was inserted into a sample introduction chamber 301 shown in FIG. 3, and each chamber 301, 302,
The 303 was evacuated. Each chamber 301, 3 by evacuation
After confirming that the back pressure of 02 and 303 was sufficiently reduced, the Si substrate 310 was transferred to the initial oxidation chamber 302. After setting the Si substrate 310 in the initial oxidation chamber 302, first, the Si is heated by thermal etching by the substrate heating system 307.
The native oxide film on the substrate surface was removed. The natural oxide film was removed under a heat treatment condition of a back pressure of 10 ⁻⁹ Torr and a substrate temperature of 1000 ° C. for about 10 minutes. In order to suppress reoxidation of the surface after removing the natural oxide film, the above treatment was performed in an atmosphere in which the water pressure in the atmosphere was very small.

Then, a silicon oxide film was formed by the process sequence shown in FIG. In the process sequence of FIG. 4, the oxidation temperature was kept constant at 1000 ° C. The oxidation process was performed using Ar gas as the inert gas from the inert gas supply source 311 and O ₂ gas as the oxidizing gas from the oxidizing gas supply source 312. Here, the Ar gas is the inert gas supply source 3
By controlling the supply amount of Ar gas from 11 with valves 313 and 314, it is used to control the back pressure of the chambers 302 and 303 and to replace the oxidizing gas and the defect removal atmosphere with gas. It can also be used for adjusting the pressure when the substrate is transferred from the initial oxidation chamber 302 to the oxidation chamber 303.

Referring to the process sequence of FIG.
First, the initial oxidation chamber 302 is evacuated, and then
The valve 313 is opened to introduce Ar gas from the inert gas supply source 311 into the initial oxidation chamber 302,
The degree of vacuum in 02 is adjusted to 10 ⁻⁵ Torr. When the degree of vacuum becomes stable, the valve 313 is closed to stop the supply of Ar gas. Next, the valve 315 is opened to introduce the oxygen gas from the oxidizing gas supply source 312 into the initial oxidation chamber 302, and the flow rate of the oxygen gas is adjusted to adjust the total pressure to 10 ⁻³ Torr.
So that Maintaining this atmosphere for time t ₁ ,
A silicon oxide film is formed on the substrate 310. Next, the valve 315 is closed to stop the supply of oxygen gas. Next, the valve 313 is opened to introduce Ar gas into the initial oxidation chamber 302, and the atmosphere in the initial oxidation chamber 302 is replaced with Ar atmosphere. This state is maintained for time t ₂ , and after confirming that the total pressure in the initial oxidation chamber 302 has reached 10 ⁻⁵ Torr, the valve 313 is closed and the exhaust system 306 is used to set the initial oxidation chamber 30.
The inside of 2 is evacuated to an ultra-high vacuum to form an ultra-high vacuum atmosphere on the order of 10 ^-8 Torr. By maintaining this ultra-high vacuum atmosphere for time t ₃ , defects in the silicon oxide film can be removed by sublimation into the vapor phase.

The oxide film forming step, the atmosphere replacing step and the defect removing step were repeated to form a silicon oxide film having a film thickness of 20 Å. Here, the film thickness of the silicon oxide film was obtained from the intensity ratio of the peak from the silicon substrate and the peak from the silicon oxide film in the Si-2p photoelectron spectrum by X-ray photoelectron analysis (XPS) described below. .

The quality of the silicon oxide film formed as described above by the process sequence of FIG. 4 can be evaluated from the state of the Si-2p photoelectron spectrum of this silicon oxide film by X-ray photoelectron analysis (XPS). First of all Si
The -2p spectrum will be described. Figure 5 shows a conventional RT
It is a figure which shows the Si-2p spectrum of the silicon oxide film formed with the P apparatus. The silicon oxide film used in FIG. 5 is formed by heat-treating silicon at a temperature of 1000 ° C. for 30 seconds in an oxygen atmosphere at atmospheric pressure to a film thickness of 50 Å. In the spectrum of FIG. 5, the peak 501 on the high energy side is the signal from the silicon oxide film, and the peak 502 on the low energy side is the signal from the Si substrate. As described above, the silicon oxide film formed by the usual method has structural defects that are insufficiently oxidized.
When the silicon oxide film is analyzed by XPS, such an unstable bond state can be detected as a sub-oxide spectrum of Si-2p spectrum. Si-2p in FIG.
In the example of the spectrum, the peak 50 from the silicon oxide film is obtained.
A small peak 503 is seen between 1 and the peak 502 from the silicon substrate, and this peak 503 corresponds to the signal from the suboxide. This spectrum (peak 50
3) corresponds to the amount of structural defects in the silicon oxide film. Therefore, the integrated intensity of the sub-oxide spectrum of the silicon oxide film formed by the conventional method and the method of Example 1 (process of FIG. 4). By obtaining the intensity ratio with the integrated intensity of the suboxide spectrum of the silicon oxide film formed by the (sequence), the quality of the oxide film by the conventional method and the quality of the oxide film by the method of Example 1 can be compared.

FIG. 6 shows the intensity ratio of the integrated intensity of the sub-oxide spectrum of the silicon oxide film by the conventional method and the integrated intensity of the sub-oxide spectrum of the silicon oxide film formed by the method of Example 1 (method of Example 1 / conventional method). It is a figure which shows the measurement result of (method). In FIG. 6, the horizontal axis represents FIG.
The time (t ₃ ) of the defect removal process shown in FIG. Figure 6
From the above, it can be seen that the integrated intensity ratio of the sub-oxide spectrum decreases as the time t ₃ of the defect removal process increases, and thus the amount of structural defects decreases.

As described above, from the result of FIG. 6, Si-2p is contained in the silicon oxide film formed by the method of the first embodiment.
It can be seen that the amount of structural defects detected as suboxide in the spectrum is smaller than that of the silicon oxide film of the conventional method.

Example 2 In Example 1, defects were removed by keeping the oxidation temperature constant and adjusting the oxygen partial pressure in the atmosphere. In Example 2, however, the oxidation temperature was mainly adjusted. Then, the defect was removed.

Also in the second embodiment, first, as in the first embodiment, the Si substrate 31 thoroughly washed with chemicals and pure water is used.
0 into the sample introduction chamber 301 shown in FIG.
1,302,303 were evacuated. After confirming that the back pressure of each chamber 301, 302, 303 was sufficiently reduced by vacuum exhaust, the Si substrate 310 was transferred to the initial oxidation chamber 302. After setting the Si substrate 310 in the initial oxidation chamber 302, first, the natural oxide film on the surface of the Si substrate was removed by thermal etching by the substrate heating system 307. Removal of natural oxide film was performed with back pressure of 10 ^-9 Torr and substrate temperature of 1000.
It was carried out for about 10 minutes under the heat treatment condition of ° C. In order to suppress reoxidation of the surface after removing the natural oxide film, the above treatment was performed in an atmosphere in which the water pressure in the atmosphere was very small.

Then, in Example 2, a silicon oxide film was formed by the process sequence of FIG. Referring to the process sequence of FIG. 7, first, the initial oxidation chamber 302 is evacuated to vacuum, and then the valve 313 is opened to suppress the oxidation during the temperature rise process of the substrate temperature from the inert gas supply source 311. Was introduced into the initial oxidation chamber 302, and an Ar gas atmosphere of 1 Torr was formed in the initial oxidation chamber 302. In this atmosphere, the back surface of the substrate 310 is heated by the substrate heating system 307, and the substrate temperature is set to 850 ° C. After setting the substrate temperature to 850 ° C, the valve 31
3 was closed to stop the supply of Ar gas, and then the valve 315 was opened to introduce oxygen gas into the initial oxidation chamber 302 to start oxidation. Here, the atmospheric pressure during oxidation is 1
0 ^-3 Torr, maintain this atmosphere for time t ₁ ', S
A silicon oxide film was formed on the i substrate 310. Fixed time t
₁ 'After oxidation, the substrate 310 by a substrate heating system 307
The surface of the substrate was heated to raise the substrate temperature to 1000 ° C. Together with this temperature increase, the oxygen supply rate is controlled to reduce the oxidizing atmosphere to 1
It was set to 0 ^-5 Torr. By maintaining this atmosphere for a time t ₂ ′, the defective portion in the silicon oxide film can be removed into the vapor phase by sublimation under this atmosphere. The oxide film forming process and the defect removing process are repeated to obtain a film thickness of 2
A 0Å silicon oxide film was formed. In the example of FIG. 7, the processing time t ₃ ′ of the oxide film forming process after the second time is
It is different from the processing time t ₁ 'of the _first oxide film forming step. In this way, after forming an oxide film of 20 Å, Ar gas is introduced so that 1
An Ar atmosphere of Torr was formed.

In this state, the substrate 310 was transferred to the oxidation chamber 303 in which an Ar atmosphere of 1 Torr was similarly formed. After the substrate 310 was transferred to the oxidation chamber 303, the substrate 310 in the oxidation chamber 303 was heated in Ar atmosphere and the substrate temperature was set to 1000 ° C. After that, the supply of Ar gas to the oxidation chamber 303 was stopped, oxygen gas was introduced into the oxidation chamber 303 to form an oxygen atmosphere at atmospheric pressure, and oxidation of the substrate 310 was started. The treatment was performed for 30 seconds in this atmosphere to adjust the oxide film thickness to 70 Å. The thickness of the silicon oxide film at this time is measured by ellipsometry immediately after the oxidation.

In this way, the characteristics of the silicon oxide film formed by the method of Example 2 with the predetermined time t ₂ ′ in the defect removing step were evaluated by the initial breakdown voltage. FIG. 8 is a diagram showing this evaluation result. In FIG. 8, the vertical axis represents the non-defective product rate with a breakdown voltage of 8 MV / cm or more, and the horizontal axis represents the defect removal time (t ₂ 'in the sequence of FIG. 7) in the oxidation process. As can be seen from FIG. 8, as the defect removal time t ₂ ′ is increased, the withstand voltage non-defective rate is obviously increased, and when the oxide film is formed by the method of the second embodiment, the withstand voltage characteristic of the oxide film is improved. be able to.

Example 3 Example 1 and Example 2 described above
In the initial oxidation chamber 302, the oxidation process and the defect removal process were repeated to form an oxide film.
Then, in this repeating step, the Si film forming apparatus is further added.
(Electron beam evaporation apparatus) 309 has a step of supplying Si to the surface of the substrate. Here, the timing of supplying Si can be controlled by opening and closing the shutter.

Specifically, in the third embodiment, first, the first embodiment
Similarly to the above, after removing the natural oxide film on the surface of the Si substrate 310 in the initial oxidation chamber 302, a silicon oxide film was formed by the process sequence of FIG. The method for forming the silicon oxide film was the same as in Example 1 except that the process temperature was kept constant at 1000 ° C. The difference from the method of Embodiment 1 is the step of forming a super high vacuum to remove structural defects in the silicon oxide film, and further depositing Si on the substrate surface by a Si film forming apparatus (electron beam evaporation apparatus) 309. It is to let. As can be seen by comparing FIG. 9 with FIG. 4,
In the method of Example 3, the oxidation step (time t ₁ ) is performed, and then the atmosphere removal step (time t ₂ ) is performed, and then the defect removal step (time t ₃ ) is performed. Of Si was deposited. Back pressure during film formation is 10 ^-8 Tor
r. Thereafter, the vapor deposition of Si is stopped, oxygen gas is introduced again to form an oxygen atmosphere of 10 ⁻³ Torr, and this atmosphere is held for time t ₁ to form an oxide film. In Example 3, such a process was repeated in the initial oxidation chamber 302 to form a silicon oxide film having a film thickness of 20Å. The film quality of the formed silicon oxide film was evaluated by XPS analysis as in the case of Example 1. This result is shown in FIG. 6 for comparison with the result of Example 1. The method of Example 3 also reduced the integrated intensity of suboxide in the Si-2p spectrum as in Example 1. Further, from FIG. 6, in the method of the third embodiment, compared with the method of the first embodiment, even if the processing time t ₃ of the defect removal step is shortened,
The defect could be removed. In the case of the method of Example 3, this is the active Si deposited on the surface of the silicon oxide film.
It is considered that this is because the reaction between the silicon oxide film and the silicon oxide film occurs and Si—O is more easily formed as compared with the method of the first embodiment. Therefore, the method of Example 3 can form a higher quality silicon oxide film in a shorter processing time than the method of Example 1.

[0056]

As described above, according to the first to fourth aspects of the invention, in the initial formation process of the silicon oxide film, the step of forming the oxide film by the thermal oxidation method and the step of forming the oxide film The ultra-thin oxide film is formed by repeatedly performing the step of selectively removing the structural defect portion formed on the surface of the oxide film.Therefore, structural defects in the oxide film can be formed without introducing foreign atoms into the oxide film. Can be removed and a high quality ultra-thin silicon oxide film can be formed.

According to the invention of claim 5, a substrate heating device for heating a silicon substrate, an exhaust device for vacuum evacuation, a gas supply device for supplying an oxidizing gas and an inert gas, and a Si substrate for Si. It has a Si thin film deposition device for depositing a film and a timing control device for controlling the overall operation timing, the substrate heating device can periodically adjust the heating amount to the substrate, and the evacuation device uses ultra-high vacuum evacuation. It is possible and the exhaust speed can be adjusted periodically, the gas supply device can adjust the gas supply amount of the oxidizing gas and the inert gas periodically, and the Si thin film deposition device can adjust the Si supply amount periodically. It is possible to realize the method for forming a silicon oxide film according to any one of claims 1 to 4 by using this apparatus.

[Brief description of drawings]

FIG. 1 is a diagram showing conditions for etching and oxidizing a silicon surface.

FIG. 2 is a diagram for explaining a defect removal process of a silicon oxide film according to the present invention.

FIG. 3 is a diagram showing a configuration example of a silicon oxide film forming apparatus according to the present invention.

FIG. 4 is a diagram for explaining the process sequence of the first embodiment.

FIG. 5: Si of silicon oxide film by X-ray photoelectron spectroscopy
It is a figure which shows a -2p photoelectron spectrum.

FIG. 6 is a diagram showing a measurement result of a ratio between an integrated intensity of a suboxide spectrum of a silicon oxide film by a conventional method and an integrated intensity of a suboxide spectrum of a silicon oxide film formed by the method of the present invention.

FIG. 7 is a diagram for explaining the process sequence of the second embodiment.

FIG. 8 is a diagram showing a withstand voltage non-defective rate of a silicon oxide film with respect to a defect removal process time.

FIG. 9 is a diagram for explaining the process sequence of the third embodiment.

[Explanation of symbols]

 310 Silicon substrate 301 Sample introduction chamber 302 Initial oxidation chamber 303 Oxidation chamber 304,305 Gate valve 306 Exhaust system 307 Substrate heating system 309 Si film forming apparatus 311 Inert gas supply source 312 Oxidizing gas supply source

Claims (5)

[Claims] 1. A method for forming a silicon oxide film by heating the surface of a silicon substrate in an oxidizing atmosphere to form a silicon oxide film, wherein the step of oxidizing the surface of the silicon substrate and the sublimation rate of silicon monooxide (SiO) are the same as the oxidation rate. On the other hand, a method for forming a silicon oxide film is characterized in that a defect removing step of removing defects in a silicon oxide film in an atmosphere having a large size is used as a basic step, and the silicon oxide film is formed by repeating the basic step. 2. The method for forming a silicon oxide film according to claim 1, wherein the partial pressure of the oxidizing gas in the basic step is 10 ⁻² To.
A method for forming a silicon oxide film, which is adjusted to a range of rr to 10 ^-8 Torr and is performed in an atmosphere in which oxidizing gas partial pressures of at least two points in the gas partial pressure range are alternately formed. . 3. The method for forming a silicon oxide film according to claim 1, wherein the oxidation temperature in the basic step is 700 ° C. to 1 ° C.
The oxidizing property is adjusted within the range of 300 ° C., and the basic process is performed in an atmosphere in which at least two oxidation temperatures in the oxidation temperature range are alternately formed, and at a high oxidation temperature of at least two oxidation temperatures. A method for forming a silicon oxide film, characterized in that the partial pressure of gas is performed in an atmosphere smaller than the partial pressure of oxidizing gas at a low oxidation temperature. 4. The method for forming a silicon oxide film according to claim 1, wherein the basic step is to alternately form two oxidizing conditions, and the oxidizing gas partial pressure is one of the two oxidizing conditions. A method for forming a silicon oxide film, characterized in that Si atoms are deposited on the surface of the silicon oxide film in at least a monoatomic layer or more under the condition of being small or having a high oxidation temperature. 5. A substrate heating device for heating a silicon substrate, an exhaust device for evacuating, a gas supply device for supplying an oxidizing gas and an inert gas, and a Si thin film deposition device for depositing Si on a silicon substrate. , A timing control device for controlling the overall operation timing, the substrate heating device is capable of periodically adjusting the amount of heating to the substrate, the exhaust device is capable of ultra-high vacuum exhaust and exhaust speed The gas supply device is periodically adjustable, and the gas supply amount of the oxidizing gas and the inert gas is periodically adjustable.
The i thin film deposition apparatus is capable of periodically adjusting the amount of Si supplied, and is a silicon oxide film forming apparatus.