JPH09184902A - Production of thin film and apparatus for production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the film forming speed at the time of forming thin films by sputtering and to control the damage on the quality of the films and a substrate. SOLUTION: An AC is impressed on an electrode 4, on which a film raw material 3 is placed, from a high-frequency power source 7 to hold the electrode 4 at negative potential. Plasma is generated on the film raw material 3 by the electric power of this AC. While the temp. of the film raw material 3 is increased by this plasma, the film raw material 3 is sputtered with positive ions to jump out at least a part of the film raw material 3 in the molecular state. The charged particles of the film raw material in the molecular state are made incident on the substrate 2 while the quantity thereof is controlled, to form the thin films. Since most of the energy of the acceleration ions is usable for the sputtering, the film forming speed increases. Since the quantity of the charged particles is controlled, the quality of the film and the damage on the substrate are controllable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a thin film by using a sputtering method, and more particularly to a method and an apparatus for producing a thin film capable of controlling the physical properties of the thin film and the damage to the substrate.

[0002]

2. Description of the Related Art In the case of forming a thin film, a vacuum vapor deposition method has been widely used because of its easiness of the method and the speed of film formation. This vacuum deposition method is also used when forming an optical thin film such as an antireflection film, a half mirror, and an edge filter. On the other hand, in recent years, in optical thin films and other thin films, there is an increasing demand for coating by a sputtering method, which is more advantageous than the vacuum evaporation method in terms of automation, labor saving, and applicability to a large area substrate. .

[0003] However, the sputtering method has a disadvantage that the film forming 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 formation rate is extremely slow, and therefore industrial diffusion tends to be delayed. Further, when a fluoride such as MgF ₂ which is a typical low refractive index substance is sputtered as an optical thin film, it is dissociated into Mg and F and F is insufficient in the film, so that absorption of visible light may occur. This is a major obstacle to applying the sputtering method to optical thin films.

As an example of applying the sputtering method to the optical thin film, there is a method described in JP-A-4-223401. This method was made in consideration that absorption of visible light occurs when MgF ₂ is sputtered,
A low refractive index film with almost no light absorption is formed by sputtering with a target in which Si is added to MgF ₂ . However, with this method, 2.8
Even if a high frequency power of W / cm ² is applied, the film forming rate is 10 nm / min or less at the maximum, and the defect of the sputtering method that the film forming rate is slow cannot be solved. At such a film-forming speed, it takes 10 minutes or more to form a single-layer antireflection film applied in the visible region, for which reason it must be said that industrial diffusion is difficult. In addition, according to a follow-up experiment of the present inventor for this method, S on MgF ₂
Even if the i-wafer was placed on the target and was sputtered, the light absorption was practically no problem in the visible region, and a film having a refractive index of 1.4 or less could not be formed. .

On the other hand, the present inventor applies an alternating current to the electrode on which the film raw material is placed to bring the electrode to a negative potential, and at the same time, a plasma is generated on the film raw material by the electric power of the alternating current. While raising the temperature of the surface of the film raw material, by sputtering the film raw material with positive ions, at least a part of the film raw material is jumped out in a molecular state, and the film raw material in this molecular state reaches the substrate and reaches the substrate. By forming the film, it has been found that a fluoride film that does not absorb light can be formed at high speed.

[0006]

By the way, the sputtering method utilizing alternating current has a feature that many charged particles easily jump into the substrate and the film formed thereon. From the above, it has been found that in the case of the thin film forming method described above, it may be difficult to obtain a thin film having desired characteristics unless the incident amount of the charged particles is controlled.

The present invention has been made in view of such problems, and an object thereof is to provide a method and an apparatus capable of forming a thin film having desired characteristics at a high speed by a sputtering method.

[0008]

According to the method of the present invention for achieving the above object, an alternating current is applied to a first electrode on which a film raw material is placed so that the first electrode has a negative potential, and Plasma is generated on the film raw material by electric power, and the temperature of the film raw material is raised by this plasma, and the film raw material is sputtered by positive ions to cause at least a part of the film raw material to jump out in a molecular state. When the raw material reaches the substrate to form a thin film, the amount of charged particles incident on the substrate is controlled.

This method can be characterized by forming a thin film used for optical applications.

In the manufacturing apparatus of the present invention, a film raw material is placed,
A first electrode applied to a negative potential, an AC power supply means for generating plasma on the film material to raise the temperature of the film material, and a substrate mounted so as to face the film material,
Means for controlling the amount of charged particles of the film raw material incident on the substrate.

In this apparatus, the means for controlling the amount of charged particles incident on the substrate is composed of a second electrode for holding the substrate and a means for applying a bias voltage to the second electrode. You can

As means for controlling the amount of charged particles incident on the substrate, a third electrode provided separately from the first and second electrodes, and means for applying an electric potential to the third electrode. And can consist of

In the conventional sputtering method, when the ions collide with the target, it is necessary to break the interatomic bond in the target to eject the atom, and a part of the accelerated ion energy cuts the interatomic bond. Since this is spent, the sputtering yield becomes low, and as a result, the film forming rate becomes slow. In the present invention, the binding force is weakened in advance by raising the temperature of the film raw material, and the ions are made to collide with the target which is the film raw material. Therefore, most of the accelerated ion energy can be used for sputtering. . For this reason, the sputtering yield is increased, and the film formation rate can be significantly increased as compared with the conventional method.

In this case, the means for heating the film raw material can be appropriately selected, but since sputtering is performed,
By applying an alternating current to the electrode on which the film raw material is placed, plasma is generated on the electrode to have a negative potential, and the film raw material can be heated by this plasma. Therefore, the present invention uses this means. . In the present invention, alternating current is 1
It also includes a high frequency of 3.56 MHz and a medium frequency of about 10 KHz.

In the conventional sputtering method, the interatomic bond is broken and the atom jumps out from the target. However, in the present invention, by raising the temperature of the film raw material, a portion having a strong binding force and a portion having a weak binding force due to thermal vibration are generated. It is possible to control the morphology of particles that jump out into molecules. The molecule here includes not only a single molecule but also multiple molecules that form an aggregate in a cluster. It can be considered that the shape of the molecule jumping out from such a target is almost the same as that of the vaporized molecule by heat.

In the present invention, since the amount of charged particles incident on the substrate is controlled, the influence of the charged particles on the substrate or film can be controlled. The charged particles refer to electrons generated by jumping from a target which is a film raw material, or ions generated by collision of an introduced gas or jumped film raw material with electrons. When these are incident on the substrate or the film formed on the substrate, the temperature of the substrate is increased or the quality of the film is changed, the film is re-sputtered, the film composition, the internal stress, or the step coverage is changed. For example, the main cause of the temperature rise of the substrate during sputtering is due to the electrons flowing into the substrate. Therefore, when the temperature rise is not desirable, control is performed so as to suppress the flow of electrons into the substrate. In the present invention,
Of course, the amount of charged particles incident on the substrate may be changed during film formation as needed.

The means for controlling the amount of charged particles incident on the substrate is not particularly limited, and a plurality of methods may be used together. The easiest way is to apply a bias voltage to the second electrode holding the substrate. If the bias voltage is made positive, the inflow of electrons can be increased and the incidence of positive ions can be decreased, and if it is made negative, the opposite is also possible. By forming a magnetic field around the substrate in addition to applying a bias voltage, it becomes easier to control charged particles incident on the substrate.

As another means for controlling the amount of charged particles incident on the substrate, a third electrode may be arranged in the path of incidence of charged particles on the substrate. The third electrode is installed separately from the first electrode on which the film raw material is placed and the second electrode holding the substrate, and is applied to the substrate by applying a potential to this electrode. It becomes easy to control the charged particles. The specific structure includes the first and second
Electrodes of mesh shape or rod shape are provided between or near the electrodes, and ions or electrons are trapped or accelerated by controlling the potential of these electrodes to control the amount and energy of charged particles incident on the substrate. can do. Note that this third
It is not necessary to have one electrode, and a plurality of electrodes may be installed.

When the thin film produced by the present invention is used for optical purposes, it is necessary to strictly control the thin film production process, in particular. In the present invention, since particles jumping out of the target are in a molecular form, it is easy to obtain a thin film having the same composition as the film raw material, but it is easier to obtain desired characteristics by controlling the charged particles incident on the substrate. . For example,
If the substrate material can be heated with glass, etc., it is better in terms of density, crystallinity, durability, etc. to form a film while raising the substrate temperature so that a large amount of electrons flow into the substrate. A film is obtained.

On the other hand, when it is better not to heat the substrate material with resin or the like, it is possible to reduce the electrons flowing into the substrate so that the substrate temperature does not rise. Also, while ions are incident on the film during sputtering, increasing the incident amount increases the amount of re-sputtering of the film, leaving only strongly bonded atoms, improving the film quality and improving step coverage. Has the effect of On the other hand, if the substrate or film may be damaged by the incidence of ions, for example, if the substrate material is optical glass and its components are easily reduced by the incidence of ions to cause light absorption, or if the substrate material is In the present invention, in the case of a resin such as PMMA, which deteriorates the adhesion of the film due to the formation of an altered layer on the surface due to the incidence of ions, or a fluoride which is easily damaged by the incidence of ions. Reduce the amount of incident ions.

The film raw material of the present invention is not particularly limited, and basically any material can be applied. Fluorides, oxides, nitrides, sulfides and the like can be used in the case of a material suitable for the application, for example, a thin film for optical use.
In particular, the application of the present invention has a great effect in the case of a fluoride such as MgF ₂ which has been difficult to form a film by sputtering.

The above-mentioned fluoride thin film produced by the present invention has a near stoichiometric ratio, almost no absorption in the visible region, its refractive index is sufficiently low, and even a single layer has a sufficient antireflection effect. Therefore, it can be used as an antireflection film for optical components such as lenses, prisms, optical fibers, spectacles, sunglasses, goggles and the like, display devices such as cathode ray tubes and liquid crystals, various window materials and screens. Further, by using a multi-layered structure in combination with a high refractive index film, it is possible to form a higher performance antireflection film and other optical thin films such as half mirrors and edge filters.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 shows a film forming apparatus used in Embodiment 1. Reference numeral 1 denotes a vacuum chamber, and a substrate 2 made of optical glass is rotatably arranged in an upper portion of the vacuum chamber 1. The substrate 2 is connected to a variable power source 11, and the power source 11 applies a bias voltage V _B to the substrate 2.

As the film raw material 3, MgF ₂ granules having a particle size of 0.5 to ₂ mm are used. The MgF ₂ granules 3 are filled in a quartz dish 4, which is placed on a magnetron cathode 5 having a diameter of 3 inches (about 75 mm). The magnetron cathode 5 constitutes the first electrode. The magnetron cathode 5 is connected to a high frequency power source 7 having an output of 13.56 MHz via a matching box 6. Also, in order to keep the temperature of the cathode constant, the water temperature is 25 ±
Cooling water 8 controlled at 0.5 ° C. is flowing. Further, a gas inlet 9 is provided on the side surface of the vacuum chamber 1, and a shutter 10 is provided between the cathode 5 and the substrate 2.

In the above structure, the substrate 2 which is an optical glass is set, and the vacuum chamber 1 is evacuated to a vacuum degree of 7 × 10 ^-5 Pa. After that, N ₂ gas was introduced from the gas inlet 9 to 1 Pa.
It is introduced until the degree of vacuum reaches. Bias voltage V _B is +1
A thin film is formed by changing the voltage from 0V to -15V in 5V increments.

Electric power of 500 W is supplied from the high frequency power source 7 to the magnetron cathode 5 to generate plasma. M
The gF ₂ granules 3 are heated by this plasma, kept at a temperature balanced with the cooling capacity of the cooling water 8 on the lower surface of the cathode, and sputtered. Here, the substrate 2
Is rotated and the shutter 11 is opened, an MgF ₂ film is formed on the substrate 2. And this optical film thickness is 1
The shutter was closed to 30 nm.

When the wavelength of the plasma emission spectrum during film formation was examined, it was confirmed that light was emitted from MgF molecules in addition to Mg atoms, and at least a part of the film raw material jumped in the molecular state.

Table 1 shows the bias voltage V applied to the substrate 2._B
Shows the results when different. Bias voltage V_BIs a positive place
In this case, the substrate temperature at the end of film formation is high. next,
Adhesive tape (trade name "Cello-Hante
), And then peel it off strongly in the 90 ° direction.
Adhesion test was carried out, but the film produced under any condition
No peeling occurred. Also moistened with alcohol
Rubbed 20 times with lens cleaning paper
After that, a scratch resistance test was conducted to observe the film surface with the naked eye.
If the substrate 2 is a glass material of BK7 or KzFS4
Also the bias voltage V _BScratch resistance of the film as the value becomes positive
Has improved. This correlates with the rise in substrate temperature.
It is thought to be.

Subsequently, the optical absorptance at a wavelength of 400 nm was measured when the optical film thickness was 130 nm. As a result, when the substrate 2 is BK7, the bias voltage V _B is −10.
Above V, there was no problem at 0.5% or less, but −
In the case of 15V, about 1% of light absorption occurred. This is because a portion of the MgF ₂ film was sputtered by the incident ions and the F was dissociated. On the other hand, the substrate is KzFS4
In the case of, the light absorption increased as the bias voltage V _B became 0 to negative. This is because PbO, which is a component in the substrate, is reduced by the ion incidence on the substrate, in addition to the influence of the ion incidence on the film described above.

The above results are shown in Table 1. In the table,
In the “Adhesiveness” column, “◯” indicates that there was no peeling, and “x” indicates that there was peeling. In the “Scratch resistance” column, “◯” indicates that there is no scratch, “Δ” indicates that there is a scratch that can be distinguished by a microscope, and “x” indicates that there is a scratch that can be distinguished by the naked eye. In the "light absorption" column, "○" means light absorption of 0.5% or less, and "△" means light absorption of 0.5 to 1.5%.
“X” indicates light absorption of 1.5% or more.

[0031]

[Table 1]

In this embodiment, the MgF ₂ film was formed on various optical glasses other than the above optical glasses, but a positive bias is applied to the substrate to form a thin film having excellent characteristics. I was able to. Further, as a film material, LiF, CaF ₂ , SrF ₂ , A instead of MgF ₂
A thin film was formed using 1F ₃ , GaF ₃ , and InF _3, and the same result was obtained in each case. Similar results could be obtained when the gas to be introduced was changed from N ₂ to O ₂ , and further, as a mixed gas thereof.

(Embodiment 2) The same apparatus as in Embodiment 1 is used, and MgF is formed on a glass diffraction grating by the same method.
_Two films were formed. FIG. 2 shows the cross-sectional structure of the film when the bias voltage V _B for the substrate 2 is changed. In the figure,
Reference numeral ₂ is a substrate made of a diffraction grating, 12 is a MgF ₂ thin film formed on the substrate 2, (a) is a case where the bias voltage V _B is positive, (b) is a case where V _B is zero, (c). Indicates the case where V _B is negative. It can be seen that when the bias voltage V _B is 0 or positive, the step coverage is bad, but when it is negative, the step coverage is good. This is an effect due to the large number of positive ions such as N ⁺ incident when the bias voltage V _B is negative. Similar results were obtained even when an RF bias was applied to the substrate 2.

As described above, by changing the bias voltage applied to the substrate 2, it is possible to improve the step coverage for a substrate having a step like a diffraction grating.

(Embodiment 3) Using the same apparatus as in Embodiment 1, a MgF ₂ film was formed on a resin substrate made of polycarbonate by the same method. If the bias voltage V _B of the substrate remains positive during film formation, a large amount of electrons flow in to raise the temperature of the substrate and the surface shape changes, but the bias voltage V _B is 0 or negative. Although the rise in substrate temperature was suppressed, the scratch resistance of the film was slightly lowered.
In addition, when the internal stress of the film was inspected, the bias voltage V
_{When B} was positive or 0, there was compressive stress.

Therefore, -10V is applied to the substrate for the first 10 seconds.
Was applied and then +10 V was applied to form a film. As a result, an increase in the substrate temperature was suppressed, the surface shape did not change, and a film having high scratch resistance was formed on the surface. Moreover, the internal stress of the entire film is almost zero, and even if it is left under high temperature and high humidity such as 70 ° C. and 80%,
There were no problems such as cracks in the film. Similar results were obtained even when the bias voltage was continuously changed from negative to positive.

As described above, in this embodiment, it was possible to form a thin film having desired characteristics by changing the bias voltage during film formation.

(Embodiment 4) FIG. 3 shows a film forming apparatus of this embodiment, and the same elements as those in FIG. 1 are designated by the same reference numerals and correspond to each other. In this embodiment, the mesh anode 13 as the second electrode is arranged. The mesh anode 13 is arranged so as to surround the dish 4 filled with the film raw material as the target. Further, the mesh anode 13 is connected to a variable power source 14, and an anode voltage V _A is applied from the power source 14.

In this embodiment, oxides such as SiO ₂ , WO ₃ , In ₂ O ₃ and SnO ₂ are used as the target material. When the anode voltage V _A applied to the mesh anode 13 is set to about +5 to 10 V, all the electrons toward the substrate 2 are trapped here, so that the temperature of the substrate 2 hardly rises. On the other hand, the anode voltage V _{A is set} to −5
When the voltage is set to about 20 V, the incidence of positive ions incident on the substrate 2 can be suppressed, and damage to the substrate 2 can be eliminated.

(Embodiment 5) FIG. 4 shows a film forming apparatus according to an embodiment. This apparatus is provided with a magnetic field generating means 15 in addition to the configuration shown in FIG. 3, and the magnetic field generating means 15 is provided outside the vacuum chamber 1. By forming a magnetic field parallel to the substrate surface by the magnetic field generation means 15, it is possible to prevent electrons from entering the substrate 2. At the same time, the anode voltage V _A applied to the mesh anode 13 is set to about −5 to 20 V to suppress the positive ions incident on the substrate 2, thereby almost completely eliminating the incidence of charged particles on the substrate 2. You can The magnetic field generating means 15
The same effect can be obtained even if it is installed near the back surface of the substrate 2.

(Sixth Embodiment) FIG. 5 shows a film forming apparatus according to a sixth embodiment. This device is provided with a mesh anode 16 as a third electrode in addition to the structure shown in FIG. The mesh anode 16 is arranged between the mesh anode 13 as the second electrode and the substrate 2, and is thereby positioned in the incident path of the charged particles to the substrate 2. The mesh anode 16 is a variable power source 17
, And the bias voltage V _C is applied thereby. In this case, the bias voltages V _A and V _C to the mesh anodes 13 and 17 and the bias voltage V _B to the substrate 2
All can set the potential independently. By doing so, it is possible to almost completely control the incidence of charged particles on the substrate.

For example, by setting the bias voltage V _A to ground and the bias voltage V _C to a negative potential, positive ions can be accelerated and made incident on the substrate 2. Furthermore, by setting the bias voltage V _B to a negative potential, it is possible to create a situation in which electrons are not incident on the substrate 2 and the substrate 2 is strongly hit by positive ions. Such a configuration was very effective, for example, when it was necessary to improve the step coverage with respect to the substrate having the steps as in the second embodiment.

(Embodiment 7) FIG. 6 shows a film forming apparatus according to Embodiment 7. In this apparatus, the substrate 2 moves at a constant speed in the linear direction indicated by the arrow during film formation. Also, two magnetron cathodes 5 are arranged in parallel,
Each magnetron cathode 5 has a 30 KHz AC power supply 7
The alternating current is applied with a shift of a half cycle from.
For this magnetron cathode 5, MgF ₂ which is a film raw material is used.
Granules 3 are placed on each. Furthermore, a rod-shaped electrode 18 is provided upright next to the target. This electrode 18
A voltage V _D is applied from the variable power source 19. Cooling water 8 is made to flow on the lower surface of each magnetron cathode 5.

In the above structure, after the inside of the vacuum chamber 1 is evacuated, a mixed gas of H ₂ and O ₂ is introduced from the gas inlet 9 to 0.1 Pa. The potential V _{D of the} electrode 18 is maintained at a positive potential and is set so as to trap electrons. Electric power is supplied from the AC power supply 7 to the cathode 5 to generate plasma. The MgF ₂ is heated and sputtered by this plasma, and an MgF ₂ film is formed on the substrate 2. When the thin film was formed by this method, the temperature of the substrate 2 did not rise at all because the electrode 18 for trapping electrons was installed.

According to the embodiment of the present invention described above, the following constitution can be obtained. [Supplementary Note 1] An alternating current is applied to the first electrode on which the film raw material is placed to make the first electrode have a negative potential, and plastic is generated on the film raw material by the AC power, and the plasma is used to generate the film raw material. The film raw material is sputtered with positive ions while the temperature of the film is raised to cause at least a part of the film raw material to jump out in a molecular state. Forming a thin film. [Supplementary Note 2] The method for producing a thin film according to Supplementary Note 1, wherein a thin film used for optical applications is formed. [Supplementary Note 3] First, in which a film raw material is placed and applied to a negative potential
Electrode, an AC power supply means for generating plasma on the film material to raise the temperature of the film material, a substrate placed so as to face the film material and applied with a positive potential, and And a means for controlling the amount of charged particles of the film raw material incident thereon. [Supplementary Note 4] A means for controlling the amount of charged particles incident on the substrate is a second electrode that holds the substrate and is applied to a positive potential, and a means that applies a bias voltage to the second electrode.
5. The thin film manufacturing apparatus as described in appendix 3, comprising: [Supplementary Note 5] A means for controlling the amount of charged particles incident on the substrate is a third electrode provided separately from the first and second electrodes, and means for applying a potential to the third electrode. The thin-film manufacturing apparatus as set forth in appendix 3, comprising:

[0046]

As described above, according to the present invention, a solid film raw material is preheated and then sputtered. Since most of the accelerated ion energy can be used for sputtering, the sputtering yield can be improved. As a result, the film forming rate can be significantly increased as compared with the conventional method. Further, since the means for controlling the amount of charged particles incident on the substrate is provided, the quality of the film and the damage to the substrate can be controlled. Accordingly, it can be effectively applied to the formation of a fluoride-based optical film typified by MgF ₂ by the sputtering method.

[Brief description of the drawings]

FIG. 1 is a sectional view of a film forming apparatus according to a first embodiment.

2A to 2C are cross-sectional views of a thin film formed according to the second embodiment.

FIG. 3 is a sectional view of a film forming apparatus according to a fourth embodiment.

FIG. 4 is a sectional view of a film forming apparatus according to a fifth embodiment.

FIG. 5 is a sectional view of a film forming apparatus according to a sixth embodiment.

FIG. 6 is a sectional view of a film forming apparatus according to a seventh embodiment.

[Explanation of symbols]

 2 substrate 3 film material 5 magnetron cathode 7 high frequency power supply 11 variable power supply

Claims (5)

[Claims] 1. An alternating current is applied to a first electrode on which a film raw material is placed so that the first electrode has a negative potential, and plasma is generated on the film raw material by the electric power of the alternating current. While raising the temperature of the raw material, the film raw material is sputtered with positive ions to cause at least a part of the film raw material to jump out in the molecular state, and when the thin film is formed by making the molecular raw material reach the substrate, a film is formed on the substrate. A method for producing a thin film, which comprises controlling the amount of incident charged particles. 2. The method for producing a thin film according to claim 1, which comprises forming a thin film used for optical applications. 3. A first electrode on which a film material is placed and which is applied to a negative potential, an AC power supply means for generating plasma on the film material to raise the temperature of the film material, and the film material. An apparatus for producing a thin film, comprising: substrates placed so as to face each other; and means for controlling the amount of charged particles of a film raw material incident on the substrate. 4. The means for controlling the amount of charged particles incident on the substrate comprises a second electrode for holding the substrate and a means for applying a bias voltage to the second electrode. The thin film manufacturing apparatus according to claim 3. 5. A means for controlling the amount of charged particles incident on the substrate, a third electrode provided separately from the first and second electrodes, and means for applying a potential to the third electrode. 4. The thin film manufacturing apparatus according to claim 3, comprising: