JPH0995773A - Production of window material for vacuum device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of peeling and cracking by executing coating with Al2 O3 as a target material in a discharge gas contg. specified amounts of Ar and O2 by a high frequency magnetron sputtering method to produce a transparent window material made of ceramics. SOLUTION: A thin film is formed by a CDV method. A lump heater 3 is arranged on the lower direction of a vacuum chamber 1, and a susceptor 6 is heated through a window 2. This window 2 requires transparency, corrosion resistance, corrosion resistance to halogen series gases and corrosion resistance to halogen series plasma. With Al2 O3 as a target material, and an Al2 O3 film is formed on a transparent ceramics material in a discharge gas essentially consisting of Ar and contg. O2 by 5atom% into a window 2. The formed window is small in film stress and furthermore excellent in heat resistance and crack resistance. Since Al2 O3 is sufficient in corrosion resistance or the like, it can stably be used as the window 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION In a vacuum apparatus represented by a CVD apparatus or the like, a transparent window material for introducing microwaves, for example, is installed. Such a window material is corrosive, which is generated inside the vacuum apparatus. The gas may cause physical or chemical damage that makes long-term use difficult. Therefore, the present invention is intended to provide a new coating technique capable of stably forming a coating film having higher reliability, by researching a coating film forming technique capable of improving the corrosion resistance of such a window material. is there.

[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]

[Problems to be Solved by the Invention] From the above situation,
Highly reliable heat resistance, halogen gas corrosion resistance and halogen plasma corrosion resistance without impairing transparency, and protection that does not cause cracks or peeling due to the above-mentioned thermal effects. There is a need to provide a window material for a vacuum device provided with a membrane, and the present invention has been made to respond to this.

[0013]

The novel coating technology provided by the present inventors is such that the surface of the window material, which is the inside of the chamber, contains Ar as a main component and the O ₂ gas content is 5 atm% or less. It is a gist to form a coating film by a high frequency magnetron sputtering method using a target material made of Al ₂ O ₃ in a certain discharge gas.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been publicly known that an Al ₂ O ₃ film is formed on a transparent window material made of transparent ceramics to improve the fluorine plasma resistance as described above.
Focusing on the film quality of the Al ₂ O ₃ film, various studies were conducted on the relationship between the film quality and the fluorine plasma resistance, heat resistance, peeling resistance, and the like. As a result, in order to exert strong corrosion resistance in highly corrosive fluorine plasma and to improve the above-mentioned various characteristics, A
It was found that the film quality of the l ₂ O ₃ film is an important control item.

The control items that the present inventors have reached as important film quality characteristics are as follows. In the Al ₂ O ₃ film in the the Al ₂ O ₃ film satisfies a substantially uniform amorphous, pin the Al ₂ O ₃ film in that it does not contain inclusions of crystalline material portion or impurity components No film defects such as holes are present Small stress (especially compressive stress) in the Al ₂ O ₃ film

In order to satisfy each of these control items, it is necessary to control the film forming method and the film forming conditions for forming the Al ₂ O ₃ film.
As a result of examining the method, etc., a high-frequency (RF) method is used as a film forming method.
It has been found that the adoption of magnetron sputtering method is most advantageous.

When this method is not adopted, for example, when the coating film is formed by the RF conventional sputtering method which does not use a magnet or the ion beam evaporation method which is generally used, the film stress becomes extremely high, and immediately after coating, In addition, the coating layer is peeled or cracked as the substrate used as a window material is heated or the temperature is increased by plasma. Further, for example, when coating is performed by a reactive sputtering method using a metal Al as a target, it is necessary to mix a large amount (5% or more in terms of partial pressure ratio) of O ₂ in the discharge gas for sputtering. The film quality of the Al ₂ O ₃ film is considerably inferior.

On the other hand, the present inventors
Al by the sputtering method₂ O _Three When forming a film
Has a low film stress and excellent heat resistance and crack resistance.
Al₂ O_Three It was found that a film was formed.
Moreover, Al produced by this method₂ O_Three X-ray film
When subjected to folding measurement, the half-value width of 5 ° or less due to the crystalline
It has no lower diffraction peak, in other words, it is substantially non-
It was found to be crystalline and this is an excellent resistance to fluorine.
Plays an important role in exhibiting elementary plasma properties
That was clarified. This Al₂ O_Three Membrane is crystalline
And when it is a polycrystal, or a crystalline part and an amorphous part
When is mixed, the grain boundary or the interface between crystalline and amorphous
Is inferior in fluorine plasma resistance, so selective from that part
Corrosion progresses and develops into cracks and pinholes.
You. Al₂ O_Three When the film is formed as a single crystal,
Although selective corrosion as described above can be avoided, the whole is amorphous.
Fluorine plasma resistance is generally inferior to that of
In addition, the residual film stress during film formation is large,
Immediately after opening and during use of window materials, peeling and cracking of the coating layer
It is easy to cause this. Therefore, make the whole substantially amorphous.
Was confirmed to be extremely advantageous. Crystalline Al₂ 
O_Three As an aggressive method to further reduce the contamination of
Cool the window material, which is the base material, during the coating film formation process.
It can be cited as continuing to reject. If cooling is omitted,
As the substrate temperature rises during coating, Al₂ O_Three One
This is because the part may be crystallized.

Another advantage of adopting the RF magnetron sputtering method is that the formation of inclusions due to the incorporation of other impurity elements is suppressed as much as possible. It becomes possible that the quality film becomes more homogeneous and contributes to the improvement of fluorine plasma resistance.

Furthermore, regarding the composition of the discharge gas during sputtering,
That is, a large amount in the discharge gas, a partial pressure ratio of 5%
O beyond₂ When gas is mixed, Al₂ O_Three In the membrane
It was found that a large number of fine pinholes were formed.
It can be used as a window material with such pinholes still existing.
Then, fluorine plasma penetrates through the pinhole, and the substrate
The window material is etched and the life of the window material is shortened at a stretch.
Become. Therefore Al₂ O _Three O in discharge gas during film formation₂ Is
The partial pressure ratio is 5% or less, preferably 3% or less. Take
In terms of meaning, adopting the reactive sputtering method
Not Al ₂ O_Three Vapor Deposition Method Using As Target Material
Is recommended.

The thickness of the formed amorphous Al ₂ O ₃ film does not limit the present invention, but if it is less than 0.1 μm, it is difficult to completely cover the window surface, and coating defects are inherent. Insufficient barrier properties may lead to partial corrosion of the substrate. Therefore, 0.1 μm or more is preferable. 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.

[0022]

【Example】Example 1 On the surface of a Si wafer (100) with a diameter of 2 inches, Al was formed by the following methods: high-frequency magnetron sputtering method, high-frequency conventional sputtering method, and ion beam evaporation method.₂ O_Three The thickness of each film is 0.5 μm
Samples 1 to 3 were formed so that The above trial
While scanning laser light for materials 1 to 3,
Measure the amount of warp of the board based on the degree of displacement,
The stress generated in the thin film was calculated from the change in the amount of the coating. Various
Al created by coating method₂ O _Three Membrane stress measurement
The results of the determination are shown in Table 1.

[0023]

[Table 1]

The Al ₂ O ₃ film (Sample 1) coated by the high frequency magnetron sputtering method has a small film stress of about 100 MPa on the compression side, but the method other than the above (Al coated by the high frequency sputtering method and the ion beam evaporation method). It can be seen that the ₂ O ₃ films (Samples 2 and 3) have significantly high film stress on the compression side.

Example 2 On the surface of a substrate (window material base material) made of fused silica glass, an Al ₂ O ₃ film was formed to a thickness of 5 μm by using the same method as in Example 1. The obtained samples 1'to 3'are set in the same apparatus as the window material 2 of the thermal / plasma CVD apparatus shown in FIG. 1, and the NF ₃ plasma is discharged at an RF output of 300 W while heating the inside of the chamber to 485 ° C. As a result, the plasma irradiation test for Samples 1 ′ to 3 ′ was performed for a total of 500 minutes, and the fluorine plasma resistance was evaluated from the appearance after the test.

Another sample 1'to 3'prepared in the same manner
To 50 ° C. to 550 ° C. at a heating rate of 50 ° C./min, and holding at 550 ° C. for 10 minutes, then cooling rate 1
A heat cycle test was conducted in which a heating / cooling cycle of cooling at 5 ° C./min and holding at 50 ° C. for 10 minutes was repeated 10 times. From the appearance after the test (the state of cracking of Al ₂ O ₃ film), heat resistance evaluated. Table 2 shows the evaluation results.

[0027]

[Table 2]

From Table 2, it can be seen that Sample 1'satisfying the conditions of the present invention has good results in both the plasma irradiation test and the heat cycle test, and has excellent fluorine plasma resistance and heat resistance.

Example 3 α-A was formed on the surface of a substrate (window material base material) made of fused silica glass.
By using a sintered target made of l ₂ O ₃ (purity of 99.99% or more) by a high frequency magnetron sputtering method,
An Al ₂ O ₃ film having a film thickness of 5 μm was formed and used as a sample. At the time of formation, A was used as a discharge gas for sputtering.
Using a gas in which r (argon) and O ₂ (oxygen) are mixed,
Samples 1 to 8 were prepared by changing the mixing ratio.

For samples 1 to 8 above, phosphoric acid (purity 85
% Or more) as an etching solution at 80 ° C. for 1 minute, and the surface of the Al ₂ O ₃ film after the etching is SEM.
Then, the hole area ratio of the pinhole portion to the film surface was obtained, and the occurrence of pinholes was evaluated.

The above samples were evaluated for fluorine plasma resistance by the same method as described in Example 2. Table 3 shows the evaluation results.

[0032]

[Table 3]

From Table 3, it can be seen that Samples 1 to 3 satisfying the conditions of the present invention have a low pinhole area ratio of less than 1% and are excellent in fluorine plasma resistance.

[0034]

Since the constitution of the present invention is as described above,
We have succeeded in forming a coating layer that can exhibit excellent halogen-based gas corrosiveness and halogen-based plasma corrosiveness without impairing the transparency and heat resistance of the window material for vacuum equipment. The window material thus obtained withstood thermal stress due to repeated heating / cooling during long-term use, and could be a stable window material free from peeling or cracking over a long period of time.

[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 (1)

[Claims] 1. When manufacturing a transparent ceramic window material in a vacuum device in which a corrosive gas exists in a chamber, Ar is the main component and the O ₂ gas content is 5 atm%.
A method for producing a window material for a vacuum device, comprising coating a target material made of Al ₂ O ₃ in the following discharge gas by a high frequency magnetron sputtering method.