JPH0995768A - Method for sputtering on silicon dioxide series base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a stably window material free from the generation of peeling and cracking by shielding the surface of the base material other than the thin film forming face from the electric field by inert element plasma. SOLUTION: A metallic oxide thin film is formed on an SiO2 series base material by a sputtering method. At this time, sputtering is executed in such a manner that an inert element gas is used as a discharge gas, and the surface of the base material other than the face on which the thin film shall be formed is shielded from the electric field by inert gas plasma. It is applied to a transparent ceramics substrate as a window material to form a coating film excellent in fluorine plasma resistance. At this time, the sputtering is executed while the side face side and back face side of the substrate are shielded from the electric field by inert gas plasma, by which an Al2 O3 thin film is formed. This Al2 O3 thin film is preferably composed of amorphous one, and the film thickness is regulated to about 0.1 to 20μm. Thus, the Al2 O3 thin film showing excellent corrosion resistances to halogen gases and halogen plasma can uniformly be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION In a vacuum apparatus represented by a CVD apparatus, for example, a SiO ₂ transparent window material for introducing microwaves is installed. Such a window material is generated inside the vacuum apparatus. The corrosive gas that is generated may cause physical or chemical damage and make long-term use difficult. The present invention relates to a technique for forming a metal oxide thin film on a SiO ₂ base material typified by such a window material to protect the base material, and more specifically to a homogeneous metal oxide having no inclusions. It is intended to form a thin film to improve its corrosion resistance.

[0002]

2. Description of the Related Art A CVD method is known as one of the methods for forming a thin film of metal, ceramics or the like on a substrate. A thin film forming apparatus (CVD apparatus) for carrying out the CVD method may be a thermal CVD apparatus, a plasma CVD apparatus, a photo CVD apparatus, or a thermal CVD apparatus, depending on the method of decomposing or reacting the gas introduced into the vacuum chamber. An apparatus that implements a combination of methods, such as a thermal / plasma CVD apparatus, has been developed.

A thermal / plasma CVD apparatus will be described as a typical example. As shown in FIG. 1, a lamp heater 3 is arranged below a chamber (reaction chamber) 1 and transparent ceramics such as transparent quartz glass or a transparent glass composition. The susceptor 6 is heated through the window 2 formed in 1. Susceptor 6
A substrate 7 is placed on the substrate 7, and the substrate 7 is heated to about 300 ° C. by heat transfer from the susceptor 6. On the other hand, by exhausting the air in the chamber 1 through the exhaust port 5, the chamber 1 is evacuated or depressurized, and the material gas such as WF ₆ or the etching gas is introduced from the inlet port 4. . When a high frequency voltage is applied between the susceptor 6 and the chamber wall in this state and a high frequency is introduced from the inlet 4, the material gas or the like is turned into plasma, and a thin film having a desired composition, for example, a W film is formed on the substrate 7. To be done. That is, the heating of the lamp heater 3 is transmitted to the inside of the chamber 1 through the window 2, the decomposition and the initiation and promotion of the reaction of the material gas, the promotion of the thin film deposition reaction on the substrate 7, the structure of the thin film and the substrate. It plays an important role in improving adhesion to 7.

Therefore, the window 2 is designed to efficiently transmit light rays (mainly infrared rays) from the lamp heater 3,
It is essential that the material is transparent, and the material having good transparency as described above is used. On the other hand, since the inner surface of the window is exposed to the high heat of the chamber 1, it is also necessary that it has heat resistance.
Furthermore, for the reasons described below, it is also necessary to have excellent corrosion resistance, particularly halogen gas corrosion resistance and halogen plasma corrosion resistance.

That is, in the CVD apparatus, a halogen gas or a halogen compound gas is often used, and typical ones are F ₂ and WF ₆ . After the film formation, an etching gas containing NF ₃ or the like is introduced into the chamber for cleaning. When such a halogen-based gas is used, a halogen-based gas plasma (hereinafter typically referred to as fluorine plasma) is generated during film formation or etching, and the inner surface of the window is exposed to these. . However, the above-mentioned transparent ceramics, especially SiO ₂
Quartz glass composed of a simple substance has low fluorine gas resistance and fluorine plasma resistance, and is significantly eroded and damaged.

When such erosion damage occurs on the inner surface of the window, the transparency of the window is lowered even if the extent of the erosion damage is slight, and the qualification of the lamp heater as a window material is lost. In addition, if the degree of damage progresses further, local corrosion in the form of pits may occur, which may be the starting point of cracks. Therefore, it cannot be used continuously. Alternatively, SiO ₂ separated from the window surface due to erosion may become fine particles that float in the chamber and adhere to the substrate. In such a case, there is a fatal problem that a device for a semiconductor device is defective. .

Therefore, it is necessary to prevent the erosion of the window material by fluorine plasma or the like, and the first countermeasure is S
The use of transparent material which does not include the iO ₂ is considered. However, for example, plastics materials have the problems of heat resistance and gas release even though they are transparent, and thermal / plasma CVD
It is not suitable as a window material for chambers of equipment. Therefore, as appropriate in terms of heat resistance and gas release characteristics, SiO
_A ceramic material not containing ₂ is considered, but there is a problem with transparency in polycrystalline ceramics, and in order to ensure transparency, it must be in a single crystal or amorphous state,
Both encounter manufacturing problems. That is, it is very difficult to manufacture a single crystal with a large diameter and a large wall thickness at the current level of manufacturing technology. Especially, it is a mainstream to use a large diameter wafer having a diameter of 8 inches or more in a CVD apparatus. Therefore, it must be said that the development of a single crystal window material is unrealistic because a window material with a larger diameter than that is naturally required. On the other hand, also in the production of amorphous materials, making large bulk materials amorphous is a technical problem from the viewpoint of thermal equilibrium, and it is extremely difficult to produce large-diameter window materials with amorphous materials. Is.

On the other hand, since the operation of the CVS device is basically a batch treatment method, the chamber 1 is once opened after the film formation is completed, and the temperature is around room temperature until various preparations are made in preparation for the next operation. Is cooled down. Therefore, heating / cooling is repeated in the temperature range between room temperature and 300 ° C. in the chamber 1 each time batch processing is performed, and the window material, which is a member of the chamber 1, is also subjected to heating / cooling heat shock. become.

By the way, the coefficient of thermal expansion of quartz glass is about 5 ×.
10 ^-7 / a ° C., the thermal expansion coefficient of Al ₂ O ₃ is about 8 × 1
Since it is 0 ⁻⁶ / ° C., there is a large difference in thermal expansion coefficient between the two of 10 times or more. Therefore, during the heating / cooling process, a large thermal stress caused by the difference in thermal expansion coefficient between the _two is applied to the Al ₂ O ₃ film. Therefore, the Al ₂ O ₃ film may be cracked or partially peeled. When a crack occurs, an accident occurs in which halogen gas penetrates into the surface of the window material from the deep portion of the film, which itself becomes a new cause of peeling. Since the quartz glass is exposed to the fluorine plasma at the peeling portion, the above-mentioned S
This leads to the problem of generation of iO ₂ fine particles.

Therefore, from the viewpoint of preventing the coating film from cracking due to the thermal stress as described above, a method has been proposed in which a quartz glass substrate is laminated and coated with an Al film and an Al ₂ O ₃ film (Actual Publication No. 61-13555). Since the Al film is opaque, the light of the lamp heater is blocked and the heating effect is impaired.

In addition, a method of coating the surface of the window material with zirconia, alumina or a mixed oxide thereof has been developed (Japanese Patent Laid-Open Nos. 53-146717 and 54-3118), but in the above invention, the material of the coating material is crystalline. Because of its quality and physical properties, it is hard and brittle, so cracks and pinholes are likely to occur due to the temperature rise when the substrate is heated or when plasma is generated. There was a risk that an accident of etching the material would occur.

[0012]

A common challenge in THE INVENTION It is an object of the addition of these thin film forming method, the metal oxide of interest to the SiO ₂ based base on (typically as a metal oxide other than SiO _2, SiO ₂ with different film quality from the base material SiO ₂
(There is no limitation on the type of metal oxide, since ₂ may be formed.) When forming a thin film by sputtering, part of the base material mixes into the metal oxide thin film and impairs the homogeneity of the thin film. There is a problem. This point is also a problem encountered when forming a metal oxide thin film on a window material for a CVD apparatus, and it is desired to establish some solution.

The present invention has been made in view of such circumstances, and basically establishes a sputtering method capable of suppressing mixing of a base material component into a thin film in carrying out the sputtering method as much as possible. It is intended. Further, in an example of a concrete development in which the window material for the CVD apparatus is sputtered, by preventing the mixture from the window material components, the heat resistance and the halogen resistant system can be achieved without impairing the transparency as the window material. Provided is a method capable of reliably producing a window material for a vacuum device having a protective film that exhibits gas corrosion resistance and halogen-based plasma corrosion resistance and does not cause cracks or peeling due to the above-mentioned thermal influence. It is intended.

[0014]

The sputtering method provided by the present invention is to use an inert gas as a discharge gas in forming a metal oxide thin film on a base material mainly composed of SiO ₂ , The basic structure is that the surface of the base material other than the surface on which the thin film is to be formed is shielded from the electric field generated by the inert gas plasma to perform sputtering. Then, when this method is applied to the transparent ceramic substrate as the window material to form a coating film excellent in fluorine plasma resistance, the side surface and the back surface of the substrate are shielded from the electric field by the inert gas plasma. By performing sputtering, an Al ₂ O ₃ thin film is formed on the front surface side (inner surface side as the window material) of the substrate.
It is particularly preferable that the Al ₂ O ₃ thin film is amorphous as described later, and the film thickness is 0.1 to 2
It is recommended to form it to about 0 μm.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described with a focus on an application example to a window material for a CVD apparatus. It is known that the Al ₂ O ₃ film is formed on the transparent window material made of transparent ceramics to improve the fluorine plasma resistance, but the present inventors have found that the film quality of the Al ₂ O ₃ film should be improved. Attention was paid to various studies on the relationship between film quality and fluorine plasma resistance. As a result, it has been found that the film quality of the Al ₂ O ₃ film is an important control item in order to exert strong corrosion resistance in highly corrosive fluorine plasma.

That is, Al₂ O_Three The film was subjected to X-ray diffraction measurement
At this time, a diffraction peak with a half-value width of 5 ° or less originating from the crystalline
Not having, in other words, being substantially amorphous
Is useful for exhibiting excellent fluorine plasma resistance
It has been found. This Al₂ O _Three The film is crystalline and polycrystalline
When you are a body, or crystalline and amorphous parts are mixed
At this time, the grain boundary and the interface between crystalline and amorphous are fluorine-resistant.
Since the plasma property is inferior, selective corrosion progresses from this part.
And develop into cracks and pinholes. Al
₂ O_Three When the film is formed as a single crystal, the above selection
Selective corrosion can be avoided, but
If it is, the fluorine plasma resistance is inferior overall,
Since the residual film stress is large, before using window material (direct coating
After) and peeling and cracking of the coating layer during use of window materials
It is easy to use. Therefore, it is possible to make the whole substantially amorphous.
Both were confirmed to be advantageous.

[0017] Next the present inventors have made various studies on the quality of the amorphous the Al ₂ O ₃ film, for amorphous the Al ₂ O ₃ film improve耐弗oxygen plasma by the uniformity of the film quality It has been found that is extremely important, and that it is particularly necessary to avoid inclusion of inclusions composed of components other than Al ₂ O ₃ as much as possible. When such inclusions are mixed in the amorphous Al ₂ O ₃ film, the interface between the inclusions and the amorphous Al ₂ O ₃ part allows the penetration of fluorine plasma, and the surface of the window material as the substrate. Is exposed to fluorine plasma and is etched, and this local damage causes cracks and peeling of the amorphous Al ₂ O ₃ film. Moreover, the inventors of the present invention further studied and found that when the inclusions are Si compounds such as SiO ₂ or metallic Si, it is easily understood from the fact that the inclusions are the same as the window material constituting material. In addition, it was found that the inclusion itself was significantly corroded by oxygen plasma, and the cracks and peeling occurred early.

Then, various investigations were made on the cause of mixing such SiO ₂ or metallic Si into the amorphous Al ₂ O ₃ film, and it was found that it was due to the self-bias of the base material SiO ₂ . That is, in the sputtering process, plasma of Ar gas or the like is formed in the sputter phosphorus chamber, but when Ar ⁺ or the like is formed in the plasma, the substrate that is an insulator existing in the vicinity of the plasma is negatively charged. . Then, positive ions such as Ar ⁺ move to the negatively charged portion and a self-bias is formed there. However, the transfer energy causes the positive ions to hit the surface of the substrate, resulting in so-called reverse sputtering. By the way, in an actual process, such a self-bias is not formed on the surface of the substrate on which the formation of the amorphous Al ₂ O ₃ film is currently in progress. However, since the amorphous Al ₂ O ₃ film is scarcely formed on the side surface and the back surface side of the substrate, the substrate is exposed to plasma such as Ar gas, and the self-bias is easily formed. For that reason, the side surface and the back surface of the substrate are subjected to the sputtering to cause the etching of the substrate, and the metal Si, SiO _2, etc., which are ejected by the etching, are mixed into the amorphous Al ₂ O ₃ film to make the film uniform. It inhibits.

The present invention is based on the technical knowledge elucidated as described above, and in order to prevent the above phenomenon, it is useful to shield the side surface and the back surface of the substrate from the electric field of the inert element plasma. I came to the conclusion. As a means for achieving such electrical shielding, a method of covering the side surface and the back surface of the substrate with a holder made of metal such as stainless steel or aluminum alloy is typically exemplified. As another method, in this embodiment, an example of plasma shielding by using a stainless steel ring-shaped holder has been described. However, in addition to the method according to this embodiment, a shielding grid is installed near the surface of the window material. It is conceivable to shield the plasma by a method such as concentrating the plasma in a specific region in the chamber by applying a magnetic field from the. Even when these techniques are used, the object of the present invention can be achieved.

In the above description, the case where a SiO ₂ window material for a CVD apparatus is used as a substrate has been mainly described, but the method of the present invention can be widely applied to a sputtering method in which a substrate mainly containing SiO ₂ is a target. Needless to say.

Regarding the window material for the CVD apparatus, the thickness of the amorphous Al ₂ O ₃ film coated on the window material does not limit the present invention, but if it is less than 0.1 μm, the window surface is completely covered. It is difficult to do so, and the barrier properties are insufficient due to the inherent coating defects, which may lead to partial corrosion of the substrate. Therefore, 0.
1 μm or more is preferred. More preferably, it is 0.5 μm or more. On the other hand, regarding the upper limit, the corrosion resistance effect improves as the film thickness increases, but the absolute stress applied to the film (including thermal stress, stress due to shape and film forming conditions: true stress) increases, and coating From the viewpoint of safety, it is desired that the thickness be 20 μm or less, since the layers are likely to peel and crack.

As a method of forming an amorphous Al ₂ O ₃ film,
Although not particularly limited, a sputtering method is particularly preferable, and in this method, since individual particles for forming a film have large energy, they strongly adhere to the substrate and control the film forming conditions. As a result, amorphous Al
_{It is possible} to form the ₂ O ₃ film uniformly and enjoy good fluorine plasma resistance. Although the sputtering method is not particularly limited, it is typically desired to adopt the RF (high frequency) magnetron sputtering method. Alternatively, a vacuum vapor deposition method can be used. On the other hand, if an ion plating method or a chemical vapor deposition method is adopted, a crystalline Al ₂ O ₃ film is likely to be formed, and there is a risk of composition deviation or the like, which is not preferable.

[0023]

EXAMPLE 1 In a batch type and sputter down type RF magnetron sputtering apparatus, α-A was used as a target material.
a sintered target made of l ₂ O ₃ (purity of 99.99% or more),
Substrate made of fused silica glass [Size: 232]
(Φ) × 12.7 (t) mm], and a film thickness of 5 μm is formed on the surface of the base material by the RF magnetron sputtering method.
m Al ₂ O ₃ film was formed. At this time, pure Ar gas was used as a discharge gas for sputtering. The base material is placed on a stainless steel turntable (substrate holder) in the lower part of the sputtering apparatus chamber, and the side surface of the window material base material is further shielded from the electric field due to Ar plasma on the side surface of the base material. , And a ring-shaped holder made of stainless steel that matches the outer size of the window material base material so that the chamfered portion between the side surface and the surface can be completely covered without a gap, and the ring-shaped holder is formed on the base material. Fit the holder,
Sputtering was performed after the ring-shaped holder was grounded.

Phosphoric acid (purity of 85% or more) was used as an etching solution for the base material on which the Al ₂ O ₃ film was formed at 80 ° C.
After performing etching for a minute, the presence or absence of inclusions observed on the Al ₂ O ₃ film surface after etching is observed by SEM, and the ratio (area ratio) of inclusions to the film surface area at any location on the film surface is determined. The generation status of the product was evaluated.

Comparative Example By the same method as in Example 1, a film thickness of 5 μm was formed on the same base material.
m Al ₂ O ₃ film was formed. At this time, the base material was simply placed on the stainless steel turntable (substrate holder) in the lower part of the chamber of the sputtering apparatus, and the ring-shaped holder used in Example 1 was not used.
With respect to the base material on which the Al ₂ O ₃ film was formed in this manner, the generation state of inclusions in the Al ₂ O ₃ film was evaluated by the same method as in Example 1. Al ₂ O in Example 1 and Comparative Example
Table 1 also shows the generation of inclusions in the _three films.

[0026]

[Table 1]

Table 1 shows the area ratio of the inclusion portion in which the Si element was detected using the energy dispersive X-ray detector attached to the SEM device to the entire film. As is clear from the results of Table 1, when a ring-shaped holder is used (when the side surface and the bottom surface of the base material are shielded from the electric field due to Ar plasma), Si or SiO ₂ etc. is contained in the sputtered Al ₂ O ₃ film. Almost no inclusions made of Si compound are mixed. On the other hand, when the ring-shaped holder is not used (when the side surface and the bottom surface of the base material are not shielded from the electric field due to Ar plasma), the sputtered Al ₂ O ₃ film is uniformly distributed over the entire surface of the film. , Diameter 0.
Many inclusions having a size of 3 to 0.5 μm were observed. From the above results, it can be seen that shielding the side surface and the bottom surface of the base material from the electric field due to Ar plasma is effective in preventing inclusion of inclusions in the Al ₂ O ₃ film.

[0028]

Since the constitution of the present invention is as described above,
When forming the metal oxide thin film on the SiO ₂ base material by the sputtering method, reverse sputtering on the side surface and the back surface of the base material is prevented. Therefore, there is no problem that the Si-based inclusions are mixed in the thin film to impair the homogeneity of the thin film. When this method is applied to a window material for a vacuum device, excellent halogen-based gas corrosion resistance and halogen-based plasma corrosion resistance can be obtained without impairing transparency and heat resistance, which are basic performances of the window material. Al ₂ that can be demonstrated
The O ₃ thin film could be produced homogeneously. As a result, a stable window material that can withstand thermal stress caused by repeated heating / cooling during use for a long period of time and is free from peeling or cracking for a long period of time was provided.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a thermal / plasma CVD apparatus.

[Explanation of symbols]

 1 chamber (reaction chamber) 2 window 3 lamp heater 4 inlet port 5 exhaust port 6 susceptor 7 substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kouki Ikeda 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Prefecture Kobe Steel Institute of Technology, Kobe Steel Co., Ltd. (72) Atsushi Hisamoto Nishi-ku, Kobe-shi, Hyogo Prefecture Takatsukadai 1-5-5 Kobe Steel Co., Ltd. Kobe Research Institute

Claims (2)

[Claims] 1. When forming a metal oxide thin film on a base material mainly composed of SiO ₂ by a sputtering method, an inert element gas is used as a discharge gas, and a base material surface other than the thin film forming surface is covered with the non-active material. A method of sputtering on a SiO ₂ base material, which is characterized by shielding from an electric field by an active element plasma. 2. The base material is a transparent ceramic window material in a vacuum device in which a corrosive gas exists in the chamber,
The method according to claim 1, wherein when forming a thin film of Al ₂ O ₃ on the inner surface side, the side surface side and the back surface side of the transparent ceramic window material are shielded from the electric field by the inert element plasma.