JPH09263936A - Production of thin film and thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a fluoride film free from light absorption by sputtering method at high speed. SOLUTION: The film is formed from a molecular state MgF2 on a substrate by using a granular MgF2 having 0.1-10mm particle diameter as a raw material of the film, applying high frequency power while introducing simultaneously one or more kinds of gases selected from oxygen or nitrogen and a fluorine- containing gas to generate plasma on the MgF2 , keeping the surface of the MgF2 at 650-1,100 deg.C by the plasma and sputtering MgF2 with a positive ion of the introduced gas to eject at least a part of the MgF2 in the molecular state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin film at a high speed, and more particularly to a method for producing an optical thin film such as an antireflection film at a high speed by using a sputtering method and a thin film produced by the method.

[0002]

2. Description of the Related Art Conventionally, when forming a thin film, a vacuum vapor deposition method has been widely used because of its easiness in the method and the speed of film formation. This is the same when forming an optical thin film such as an antireflection film, a half mirror, or an edge filter.

On the other hand, in recent years, there has been an increasing demand for coating by an optical thin film and other thin films, which is advantageous in terms of automation, labor saving and applicability to a large area substrate as compared with the vacuum vapor deposition method. It was However, the sputtering method has a disadvantage that the film formation rate is lower than that of the vacuum evaporation method. In the case of a metal film, it is still at a practical level, but in the case of other films, the film-spreading rate is remarkably slow, so that industrial diffusion tends to be delayed. Further, when a fluoride such as MgF ₂ which is a typical low refractive index material as an optical thin film is sputtered, it is dissociated into Mg and F and F is insufficient in the film, so that visible light is absorbed. However, this has been a major obstacle in applying the sputtering method to optical thin films.

Japanese Patent Laid-Open No. 4-223401 describes a method of forming an optical thin film by a sputtering method. In this method, when MgF ₂ is sputtered, visible light is absorbed. Therefore, sputtering is performed by using MgF ₂ with Si added as a target, thereby forming a low-refractive index film with almost no light absorption.

[0005]

However, the invention described in the above publication has the following drawbacks. That is, even if a high frequency power of 2.8 W / cm or more is applied,
The film formation rate is 10 nm / min or less at the maximum, and the drawback of the sputtering method that the film formation rate is low cannot be solved. At this deposition rate, for example, it takes 10 minutes or more to form a single-layer antireflection film applied in the visible region, which makes industrial diffusion difficult.

According to a follow-up experiment conducted by the present inventor,
According to the above method, even if sputtering is performed with a plate-shaped MgF ₂ on which a Si wafer is placed as a target, light absorption is practically no problem in the visible region, and the refractive index is 1.4 or less. It was not possible to form such a film.

The present invention has been made in view of such conventional problems, and claims 1 to 4 are methods for forming a thin film at a high speed by a sputtering method, and in particular, a fluoride which does not absorb light by the sputtering method. An object is to provide a method capable of forming a film at high speed.

[0008]

The invention according to claim 1 uses a fluoride granule having a particle diameter of 0.1 to 10 mm as a film raw material, and a gas containing at least one of oxygen, nitrogen or hydrogen, and a fluorine-containing gas. While simultaneously introducing and, high frequency power is applied to generate plasma on the film raw material, the temperature of the surface of the film raw material is raised by the plasma, and the film raw material is sputtered with positive ions of the introduced gas. Thus, at least a part of the film raw material is jumped out in a molecular state, and a film is formed on the substrate by the molecular raw material of the film.

For optical applications, it is generally desirable for the thin film to have low light absorption. Therefore, when the film raw material has the same composition as that of the desired thin film, it is preferable that the shape of the jumped-out particles is in the molecular form rather than dissociated into the atomic form. As a result of diligent research, it was found that the morphology of jumping particles depends on the gas species introduced during sputtering. At the time of sputtering, generally used inert gas such as Ar tends to atomize the jumped-out particles into atoms. On the other hand, oxygen, nitrogen, hydrogen, or a gas containing these causes particles to jump out in a molecular state without breaking them apart.

Therefore, especially when manufacturing an optical thin film,
It is advisable to introduce a gas containing at least one of oxygen, nitrogen and hydrogen. However, in the case of a fluoride, the completely jumped-out particles cannot maintain the stoichiometric state, and the fluorine is a little dissociated. By introducing a fluorine-containing gas to supplement the dissociated fluorine, a thin film having the same composition as the film raw material can be formed.

Incidentally, it can be said that oxygen, nitrogen, hydrogen or a gas containing these only sputters the film raw material and hardly mixes with the film raw material. Therefore, it can be considered that the optical thin film manufactured in this manner has substantially the same composition as that when the film is formed on the substrate by heating and evaporating the film raw material.

If the particle size is smaller than 0.1 mm, the heat capacity of the material becomes small, the target temperature does not rise, and a sufficient film formation rate cannot be obtained, which is not preferable. On the other hand, if the particle size is larger than 10 mm, the heat capacity of the material becomes large, the target temperature rises too much, and it is simply vapor deposition, which is not preferable.

According to the second aspect of the invention, the particle size is 0.1 to 10 mm.
While using at least one kind of gas selected from oxygen and nitrogen and a fluorine-containing gas at the same time as the film raw material of MgF ₂ in the form of granules, a high frequency power is applied to generate plasma on MgF _2. , The above-mentioned MgF ₂ by the plasma
While maintaining the surface temperature between 650 ° C. and 1100 ° C., by sputtering the MgF ₂ with positive ions of the introduced gas, at least a part of the MgF ₂ is jumped out in a molecular state, The method for producing a thin film is characterized in that the film is formed on the substrate by MgF ₂ of.

In the case of sputtering MgF _{2 which} is particularly useful as an optical thin film, the film forming rate can be sufficiently increased if the surface temperature of the target is 650 ° C. or higher.
On the other hand, at 1100 ° C. or higher, the vapor pressure of the film raw material rises to the same level as the pressure of the introduced gas, and the vaporized molecules reach the substrate as they are, resulting in simple vapor deposition.
In the case of vapor deposition, unlike the case of sputtering, scratch resistance is low.

In the case of vapor deposition of MgF ₂ , unless the substrate is heated up to about 300 ° C., the scratch resistance becomes extremely low and it cannot be practically used. However, even if the substrate is not heated, the surface temperature of the target can be reduced. If the temperature is kept at 650 ° C or higher, a film having high scratch resistance can be obtained. Among the above-mentioned gases, oxygen or nitrogen is particularly preferable as the gas to be introduced in view of economical efficiency, availability and safety.

The molecules jumped from the target material may collide with electrons in the plasma to become positive ions and collide with the target to cause so-called self-sputtering phenomenon.
_In the case of ₂ , the shape of the particles jumping from the target by self-sputtering seems to be a molecular state, and there is no particular problem. However, since there are some molecules in which fluorine is dissociated, a fluorine-containing gas is introduced to supplement the dissociated fluorine.

The optical thin film produced as described above is
It is close to the stoichiometric ratio and has almost no absorption in the visible region, and its refractive index is about 1.38. Therefore, this optical thin film has a sufficient antireflection effect even if it is a single layer.
It can be used as an optical component / equipment such as an optical fiber, glasses, sunglasses, goggles, a display element such as a cathode ray tube or a liquid crystal, various window materials, and an antireflection film for a screen. In addition, a multi-layered structure in combination with a high refractive index film can form a higher performance antireflection film and other optical thin films such as a half mirror and an edge filter.

Since there is no need to heat the substrate, there is no limitation on the material to which the present technique can be applied. It can be applied to any kind of glass such as optical glass and window glass, various resins such as PMMA, polycarbonate and polyolefin, and other metals and ceramics. The shape of the substrate is not particularly limited to a plate shape, a film shape, or a spherical shape.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a schematic configuration diagram of a film forming apparatus used in this embodiment. Reference numeral 1 denotes a vacuum tank, and a substrate 2 is rotatably installed above the inside of the vacuum tank 1. MgF ₂ granules 3 having a particle size of 1 to 5 mm, which is a raw material for the membrane, are made of quartz dishes 4
And is placed on the magnetron cathode 5 having a diameter of 4 inches (about 100 mm).

The magnetron cathode 5 is connected to a high frequency power source 7 of 13.56 MHz via a matching box 6. Further, in order to keep the temperature of the magnetron cathode 5 constant, cooling water 8 whose water temperature is controlled to 20 ± 0.5 ° C. flows on the lower surface of the magnetron cathode 5. On the side surface of the vacuum chamber 1, three gas inlets 9, 10, 12 connected to different gas sources are provided. A shutter 1 is provided between the magnetron cathode 5 and the substrate 2.
1 is provided.

The formation of a thin film using the apparatus having the above structure is
First, the substrate 2 made of La-type optical glass having a refractive index of 1.75.
And the inside of the vacuum chamber 1 is evacuated to 7 × 10 ⁻⁵ Pa. After that, O ₂ gas was introduced from the gas inlet 9 to 4 × 10 ^-1 P
up to a, SF ₆ gas from the gas inlet 12 to 0.4 × 10
-Introduce up to ¹ Pa. Next, electric power is supplied from the high frequency power source 7 to the magnetron cathode 5 to generate plasma.

The MgF ₂ granules 3 are heated by this plasma, and cooling water 8 flowing under the magnetron cathode 5 is introduced.
Is maintained at a temperature balanced with the cooling capacity of
Sputtered. Here, when the substrate 2 is rotated and the shutter 11 is opened, the MgF ₂ film is formed on the substrate 2. The shutter 11 was closed after a lapse of time when the optical film thickness reached 130 nm.

When the wavelength of the plasma emission spectrum during film formation was examined, when the input power was 400 W or more, light emission was observed from MgF ₂ molecules in addition to Mg atoms, and at least a part of the film raw material jumped in the molecular state. Was confirmed.

Here, the graph of FIG. 2 shows how the surface temperature of the granules 3 and the film formation rate on the substrate 2 change when the applied power is changed. From the graph of FIG. 2, when the input power is 400 W or more, the surface temperature of the granules 3 is about 650.
It can be seen that the temperature rises to ℃ or more and the film formation rate increases rapidly. On the other hand, when the input power is 800 W, the surface temperature of the granules 3 has risen to about 1100 ° C.

As a result of the EPMA analysis of the film formed with an applied power of 400 W to 800 W, the composition ratio was M.
The g: F was 1: 1.8 to 1.99, and the result was that the larger the input power, the larger the amount of F. It was also confirmed that almost no O (oxygen) introduced as the process gas was present in the film. Further, as a result of analysis by FT-IR, the state of Mg in the film was such that the bond with F was recognized, but the bond with O (oxygen) was not recognized. continue,
As a result of analysis by XRD, the crystallinity was low and no clear peak was observed.

Next, a so-called tape peeling test was conducted in which a cellophane tape was attached to the film and then strongly peeled in the direction of 90 °, but no peeling occurred in the film produced under any conditions. Further, when a so-called scratch resistance test was conducted in which the film surface was visually inspected after being strongly rubbed with a lens cleaning paper moistened with alcohol, a scratch was not generated at all with an applied power of less than 800 W. It was observed that the one with 800 W had a thin scratch. Further, with 900 W, the film was easily peeled off from the substrate.

Next, an example of the measurement result of the spectral reflectance of the antireflection film manufactured by the manufacturing method of the present embodiment and the measurement result of the refractive index n and the absorption coefficient k by spectroscopic ellipsometry are shown in FIGS. Shown in the graph. As can be seen from this graph, n is about 1.38 and k is 10 ⁻⁴ or less, and it can be said that both are at a practical level as a low refractive index optical film. As shown in Fig. 3, the reflectance is 0.2% at the center wavelength.
It has fallen to the following level and has a good antireflection property.

Incidentally, if the particle size of the granules used in the present embodiment is in the range of 0.1 mm to 10 mm, similar results were obtained, and there was no problem. The pressure of the introduced O ₂ gas is 5
× 10 ^-2 Pa to 5 Pa, SF ₆ gas pressure is 0.5 × 1
In any range of 0 ^-2 Pa to 0.5 Pa, it was possible to obtain an antireflection film having good optical characteristics and durability although the required input power was slightly different. Further, although oxygen and SF ₆ are introduced to form a film in the present embodiment, similar results are obtained when hydrogen and CF ₄ are introduced.

(Comparative Example 1) Instead of MgF ₂ granules 3, M
The result of the similar experiment using the gF ₂ sintered body is shown in the graph of FIG. As can be seen from the graph, when the sintered body is used, unlike the case of the granule, it is difficult to be heated even if the input electric power is increased, and the temperature hardly rises. That is, it is a state of sputtering that is usually performed, and the film formation rate is extremely slow, which is not practical. For example, input power 600
In the case of W, the film formation time was 18 seconds in the first embodiment, but it takes 11 minutes to obtain the same film thickness in this comparative example. Further, the thin film produced in this comparative example has absorption in the visible region, and cannot be used for optical applications.

The composition ratio of the thin film produced in this comparative example is M
It was confirmed that g: F was 1: 1.5 to 1.7, and the amount of F was considerably insufficient. Further, it was confirmed that the crystallinity was slightly high.

(Embodiment 2) In this embodiment, a thin film is formed by using the same apparatus as in the first embodiment. First,
Gas inlet 9 to N _{2 up} to 1 × 10 ⁻¹ Pa, gas inlet 10 to Ar up to 3 × 10 ⁻² Pa, gas inlet 12
Therefore, CF ₄ was introduced at 0.3 × 10 ⁻² Pa. Compared to the first embodiment, the temperature rise was slightly small, and the target surface temperature rose to 650 ° C. or higher when the applied power was 500 W or higher.

As a result of forming a film on the substrate with an applied power of 650 W and a film forming time of 21 seconds, the spectral reflectance of the film was exactly the same as that in FIG. Light absorption in the visible region was 1% or less, which was at a practical level. As a result of performing various tests similar to those of the first embodiment, no peeling was observed in the tape peeling test, and no scratch was formed in the scratch resistance test.

In place of MgF ₂ , LiF, Ca
_{F 2, SrF 2, AlF 3} , GaF 3, InF 3, or mixtures thereof, in mixtures thereof with MgF _2, although the required input power is different, both without light absorption, adhesion property and scratch It was possible to form a film having excellent properties. All of these are low refractive index substances having a refractive index of about 1.4 and could be used as a single-layer antireflection film. Further, in the present embodiment, nitrogen and CF ₄ were introduced to form a film, but similar results were obtained when hydrogen or oxygen and SF ₆ were introduced.

(Embodiment 3 to 5) FIG. 7 shows Embodiment 3
It is a schematic block diagram of the film-forming apparatus used by ~ 5. The film forming apparatus uses two vacuum chambers 1 and 1a similar to those in the first embodiment, which are partitioned by a gate valve 21 and connected. The substrate is transported between the vacuum chamber 1 and the vacuum chamber 1a by a transport device (not shown). The magnetron cathode 5 a of the vacuum chamber 1 a is connected to the DC power supply 22.

In the vacuum chamber 1, a film was formed by the same method as in the first embodiment. In the vacuum chamber 1a, T is used as the target 3a.
A metal plate such as i, Ta, or Zr is used. O2 was introduced from the gas inlet 9a, Ar was introduced from the gas inlet 10a, and TiO ₂ , Ta ₂ O ₅ , and Z were formed by DC reactive sputtering.
A high refractive index film such as rO ₂ is formed on the substrate.

On the substrate, the vacuum chamber 1 and the vacuum chamber 1a are used, and MgF ₂ , TiO ₂ and T having a desired film thickness are respectively formed.
By alternately forming a ₂ O ₅ or ZrO ₂ or the like,
An antireflection film and a half mirror were formed. Table 1 shows the film configuration
In addition, the spectral characteristics are shown in the graphs of FIGS.

[0037]

[Table 1]

The antireflection film of FIG. 8 has a reflectance of almost zero at a wavelength of 630 nm, and is excellent in the antireflection effect of a single wavelength. The antireflection film of FIG. 9 has a reflectance of approximately 1% or less in the entire wavelength range of 400 to 700 nm which is a visible region, and is not only used as an antireflection film for CRTs but also for high precision optical equipment such as a camera and a microscope. Is an extremely excellent property that can be sufficiently used. The half mirror of FIG. 10 has a wavelength of 450 even though it has only five layers.
It has flat characteristics with a reflectance of 40 to 45% in a wide range of ˜650 nm.

[0039]

According to the present invention, since a solid film raw material is preheated and then sputtered, most of the energy of the accelerated ions is used for the sputtering, so that the sputtering yield is increased. As a result, the film formation rate can be significantly increased as compared with the conventional method. Further, by raising the temperature of the film raw material, a strong binding site and a weak binding site are created due to thermal vibration, and the jumping-out particle may be a molecule. As a result, even a material that is normally dissociated by sputtering can be formed into a film having substantially the same material as the starting material without dissociation. This method is particularly effective when a fluoride-based optical film typified by MgF2 is formed by a sputtering method, and a low refractive index film that does not absorb light can be easily obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a film forming apparatus used in the first embodiment.

FIG. 2 is a characteristic diagram of film formation rate and surface temperature in the first embodiment.

FIG. 3 is a characteristic diagram of spectral reflectance in the first embodiment.

FIG. 4 is a characteristic diagram of a refractive index in the first embodiment.

FIG. 5 is a characteristic diagram showing a relationship between an absorption coefficient and a wavelength in the first embodiment.

FIG. 6 is a characteristic diagram of film formation rate and surface temperature in Comparative Example 1.

FIG. 7 is a cross-sectional view showing another configuration of the film forming apparatus.

FIG. 8 is a characteristic diagram of spectral reflectance according to the third embodiment.

FIG. 9 is a characteristic diagram of spectral reflectance according to the fourth embodiment.

FIG. 10 is a characteristic diagram of spectral reflectance according to the fifth embodiment.

[Explanation of symbols]

1 Vacuum Tank 2 Substrate 3 MgF ₂ Granules 4 Dish 5 Magnetron Cathode 6 Matching Box 7 High Frequency Power Supply 8 Cooling Water 9, 10, 12 Gas Inlet 11 Shutter

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Ken Kawamata 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (72) Inventor Tadashi Watanabe 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Hiroshi Ikeda 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Norikazu Urata 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd.

Claims (4)

[Claims] 1. A high frequency power is applied while using a fluoride granule having a particle diameter of 0.1 to 10 mm as a membrane raw material and at the same time introducing a gas containing at least one of oxygen, nitrogen and hydrogen and a fluorine containing gas. Then, plasma is generated on the film raw material, and the temperature of the surface of the film raw material is raised by the plasma, and at least a part of the film raw material is molecule-formed by sputtering the film raw material with positive ions of the introduced gas. A method for producing a thin film, which comprises jumping out in a state and forming a film on a substrate using the film-state raw material in a molecular state. 2. Granular MgF having a particle size of 0.1 to 10 mm.
₂ as the membrane raw material, while simultaneously introducing at least one gas selected from oxygen or nitrogen and a fluorine-containing gas,
And high frequency power to generate plasma on the MgF _2, 650 ° C. The temperature of the MgF ₂ surface by the plasma
By maintaining the temperature between ˜1100 ° C. and sputtering MgF ₂ with positive ions of the introduced gas,
A method for producing a thin film, characterized in that at least a part of MgF ₂ is jumped out in a molecular state, and a film is formed on a substrate by MgF _{2 in} this molecular state. 3. The fluorine-containing gas is CF ₄ or SF
_{6. The} method for producing a thin film according to claim 1, wherein the method is 6. 4. Mg is 1 and F is 1.8 to 1.99.
3. The method for producing a thin film according to claim ₂ , wherein MgF ₂ which has a composition ratio of 1 and is not crystallized is used.