JPH07267681A - Production of optical thin film - Google Patents

Abstract

PURPOSE:To provide a method for producing an optical thin film, capable of extremely improving a film forming rate. CONSTITUTION:In producing an optical thin film by a sputtering method, an inert gas is introduced from inlets 11 and 16 in the vicinity of metal targets 4 and 5 and an oxidizing gas is fed from inlets 9 and 14 in the vicinity of a base 17 separately from the inert gas.

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 an optical thin film such as an antireflection film, a half mirror, an interference filter and the like by sputtering.

[0002]

2. Description of the Related Art An optical thin film of this type is formed by alternately stacking a high refractive index substance and a low refractive index substance. In general, a metal oxide such as TiO ₂ or WO ₃ is used as the high refractive index substance, and SiO ₂ is used as the low refractive index substance. The reason why oxides are used for all the substances is that they are excellent in chemical stability.

When laminating these oxides on the surface of a substrate such as a prism, in principle, TiO ₂ or SiO _{2 is used.}
The oxide may be used as it is as a target for sputtering. However, when such an oxide target is used, there is a problem that the film formation rate is extremely slow and the productivity is low. In addition, the oxide target is expensive and brittle and easily cracked, which makes it inconvenient to handle.

Therefore, it is desired to form an oxide thin film such as TiO ₂ or SiO ₂ by using a simple substance such as Ti or Si as a target. Then, for that purpose, it is considered that sputtering is carried out in an oxidizing atmosphere so that the atomized atoms of Ti or the like are turned into oxides such as TiO ₂ and laminated on the substrate surface.

Such an attempt is made, for example, in Japanese Patent Laid-Open No. 2-10
It is also disclosed in Japanese Patent No. 3002. In this publication, Ti is used as a target and D is introduced while introducing oxygen gas.
A TiO2 film is formed by C-reactive sputtering.

[0006]

However, as described in the above publication, when a metal target is sputtered in an oxygen gas atmosphere, the deposition rate is certainly improved as compared with the conventional oxide target. However, it was still impossible to obtain a satisfactory film formation rate.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing an optical thin film capable of dramatically improving the film forming rate.

[0008]

In order to achieve the above object, in the method for producing an optical thin film of the present invention according to claim 1, in producing an optical thin film by a sputtering method, an inert gas is added in the vicinity of the metal target. Along with the introduction, it is characterized in that the oxidizing gas is introduced from a place different from this inert gas.

In the present specification, the metal target includes, in particular, Si in addition to simple metals such as Ti and W. Further, as the inert gas, Ar, He, N
Although e, Kr, Xe and the like can be used, Ar is preferable from the viewpoint of economy. Oxidizing gas is O
_It is preferable to use ₂ , but a gas containing an oxygen atom such as CO ₂ or CO or NO _x can also achieve the purpose.

In this case, the oxidizing gas may be introduced from the vicinity of the substrate, and the metal targets may be Si, Ta, Ti, Al, Zr, Hf, Y,
W or a mixture thereof may be used.

[0011]

The operation of claim 1 of the present invention having the above-mentioned structure is as follows. To increase the film formation speed,
It is desirable to introduce an inert gas in addition to the oxidizing gas for the reaction. This is because the inert gas has a significantly higher sputtering rate than oxygen and the like. At this time, generally, a pressure distribution is generated in the vacuum chamber into which the gas is introduced, so the position where the inert gas is introduced is important. That is, since the inert gas is introduced to knock out the molecules constituting the target, it is desirable that the partial pressure be high only in the vicinity of the target. A simple way to achieve this is to introduce an inert gas near the target. At this time, if a gas having a low sputtering rate other than the inert gas is present in the vicinity of the target, the action of the inert gas is hindered, which causes the film formation rate to be slowed. Therefore, the oxidizing gas should be introduced from another place.

The operation of claim 2 is as follows. The introduction position of the oxidizing gas does not significantly affect the film formation rate unless it is near the target. However, since visible light is absorbed unless the molecules knocked out from the target are completely oxidized on the substrate, it is necessary to supply a sufficient oxidizing gas on the substrate. In particular, it is necessary to more efficiently supply the oxidizing gas onto the substrate as the film forming speed increases. Therefore, it is preferable to introduce the oxidizing gas from the vicinity of the substrate.

The operation of claim 3 is as follows. In the present invention, the material of the target is not particularly limited and can be applied to various materials. However, considering practicality, economic efficiency, film durability, etc., the target may be Si, Ta, Ti, It is preferable to use Al, Zr, Hf, Y, W, or a mixture thereof. Among them,
It is preferable that the targets are Si, Ta, and Ti, and the thin film to be formed is SiO ₂ , Ta ₂ O ₅ , and TiO ₂ .

Embodiments of the method for producing an optical thin film according to the present invention will be described below with reference to the accompanying drawings.

[0015]

First Embodiment First, a first embodiment of the present invention will be described. Figure 1
FIG. 3 is a sectional view showing a sputtering apparatus used in the method for producing an optical thin film of the present invention. As shown, this device
It is an in-line type chamber in which a total of four tanks including a first tank A for setting a substrate, a second tank B and a third tank C for film formation, and a fourth tank D for taking out a substrate are arranged. Each tank is partitioned by openable and closable gate valves 1 to 3, and the flow rate and partial pressure of the gas to be introduced can be set independently. 4-inch targets 4 and 5 are attached to the ceilings of the second tank B and the third tank C, and one cathode (not shown) using a magnetron is provided for each of them. Power source 6 or RF power source 7
Either one of them is connected via the changeover switches 12 and 21. An exhaust system including a rotary pump (not shown) and a turbo molecular pump is connected to each tank.

In the second tank B and the third tank C, inlets 11 and 16 for introducing an inert gas are arranged near the targets 4 and 5. On the other hand, the inlets 9 and 14 for introducing the oxidizing gas are the substrates 17 and 17 near the bottom of the tank.
It is arranged in the vicinity. Reference numeral 18 denotes a substrate holder that holds and conveys the substrate 17, and 19 and 20 denote openable and closable shutters for partitioning the targets 4 and 5 from the substrates 17 and 17.

Next, a method for producing an optical thin film by using the sputtering apparatus configured as above will be described.

First, the substrate 17 is held by the substrate holder 18 and set in the first tank A. 1 by turbo molecular pump
After exhausting to × 10 ^-3 Pa, open the gate valve 1,
After transferring the substrate 17 to the second tank B, the gate valve 1 is closed.

In the second tank B, Ti is attached as the target 4, and the inside of the tank is sufficiently evacuated in advance. The valve 8 is opened to introduce O ₂ gas with a partial pressure of 0.1 Pa from the inlet 9, while the valve 10 is opened from the inlet 11 to introduce Ar gas with a partial pressure of 1.9 Pa. When the changeover switch 12 is switched to the DC side and 400 W of electric power is applied and the shutter 19 is opened for a predetermined time (10 seconds in this embodiment), a TiO ₂ film is formed by reactive DC magnetron sputtering. Then, the gate valve 2 is opened and the substrate 17 is transferred to the third tank C.

Si is attached as a target 5 to the third tank C, and the inside of the tank is sufficiently evacuated in advance. The valve 13 is opened to introduce an O ₂ gas having a partial pressure of 0.1 Pa from the introduction port 14, while the valve 15 is opened to introduce an Ar gas having a partial pressure of 3.9 Pa from the introduction port 16. Changeover switch 2
When the power of 700 W is applied with 1 as the RF side and the shutter 20 is opened for a predetermined time (70 seconds in this embodiment), a SiO ₂ film is formed by reactive RF magnetron sputtering. After that, the gate valve 3 is opened and the substrate 17 is transferred to the fourth tank D.

After closing the gate valve 3, the fourth tank D is opened and the substrate 17 is taken out. In the in-line type chamber as in the present embodiment, since the substrate 17 can be continuously flowed, the substrate 17 after the film formation is completed every 70 seconds which is the maximum time among the processing times of the first to fourth baths. You can take it out.

The antireflection film obtained as above is summarized as follows. Target / Film material Thickness method Ar pressure Power time Second layer Si / SiO ₂ 180nm RF 3.9Pa 700W 70sec First layer Ti / TiO ₂ 17nm DC 1.9Pa 400W 10sec Substrate BK7 (n = 1.52)

FIG. 2 shows the spectral reflection characteristics of the antireflection film formed according to this example. The reflectance is 4% or less in the visible region and the minimum is about 1% even though the number of layers is only two, and it can be seen that the required effect is obtained. Also,
There were no problems in appearance and problems such as visible light scattering and absorption. Furthermore, a peeling test using an adhesive tape was conducted, but it did not peel off. The scratching property was also very good and practically no problem.

[0024]

Comparative Example Next, in order to investigate the effect of the present invention, a comparative example was prepared by changing the introduction positions of the inert gas and the oxidizing gas. The results are shown below. The film thickness is 18
The film formation time required to form a 0 nm SiO ₂ film was investigated, and RF magnetron sputtering was performed at a power of 700 W using the apparatus shown in FIG. All Ar gas partial pressure is 3.9 Pa, O ₂ gas partial pressure is 0.1 P
a.

The introduction positions 11 and 9 in the table are shown in FIG.
Corresponds to the sign of.

Comparative Example 1 uses oxide Si as a target.
Although O ₂ is used, it can be seen that the film forming rate is extremely slow as described in the prior art. It should be noted that when an oxide target is used, it is not necessary to introduce O ₂ in particular, but the conditions are prepared for comparison.

Comparative Examples 2 to 4 are cases in which simple substance Si, that is, the metal target according to the present invention is used. In Comparative Example 2, a mixed gas of Ar and O ₂ was introduced through the inlet 11 near the target. In Comparative Example 3, the same gas was introduced through the inlet 9 near the substrate. Comparative Example 4 is Example 1
And the introduction position is reversed. It can be seen that the film forming rate in Example 1 is faster than that in any of the comparative examples. Further, in Comparative Example 2, film formation was performed in a relatively short time of 150 seconds, and it was found that some effects can be obtained by introducing at least an inert gas from the vicinity of the target.

Next, tests were conducted using metal targets other than Si and Ti. The results are shown below. In addition, in all cases, the film formation time until the film thickness reaches 17 nm was examined, and DC was obtained by using the apparatus of FIG.
It was magnetron sputtered. Ar
Gas was introduced from the inlet 11 and O ₂ gas was introduced from the inlet 9 at the following partial pressure. In each case, the film formation time is within 20 seconds, which shows that the film formation can be performed extremely quickly.

[0029]

[0030]

[Embodiment 2] In this embodiment, Ta ₂ is used by using the apparatus shown in FIG.
A film of O ₅ was formed. This device is basically the same as the second tank in FIG. 1, but the gas introduction position is different. That is, there are eight inlets 11 '(only two are shown in the drawing) so as to surround the target 4 and another inlet 9'is provided at the substantially central portion of the chamber.

After Ta was attached as the target 4 and the inside of the tank was sufficiently evacuated, O ₂ gas having a partial pressure of 0.5 Pa was introduced from the inlet 9 ', and then a partial pressure of 3.0 Pa was introduced from the inlet 11'.
Ar gas was introduced. The applied power is set to 500 W, and T is deposited on the substrate by the reactive DC magnetron sputtering method.
An a ₂ O ₅ film was formed. At this time, the film formation rate is 150 nm
It was fast enough / minute.

As shown in this embodiment, a sufficient film formation rate can be obtained even if the oxygen inlet is not necessarily located near the substrate. Further, in this embodiment, since the Ar inlet is arranged so as to surround the target, the gas pressure distribution in the target surface becomes uniform, and as a result, the film thickness distribution on the substrate tends to be uniform. There is. In this example, when Kr or Xe was used as the inert gas instead of Ar gas, the film formation rate was further improved. Further, even if CO ₂ or CO was used instead of O ₂ gas, the film formation rate was slightly improved as compared with the case of using O ₂ .

In each of the above embodiments, an example in which two layers of antireflection layers are formed has been shown, but the present invention is not limited to this, and for example, a single layer or about 3 to 6 layers of antireflection layer is formed. It goes without saying that it can be applied to form a film, to produce a half mirror, an interference filter, and the like. Further, the sputtering device may be either an in-line type or a batch type.

[0034]

As described above, according to the method for producing an optical thin film of the present invention, sputtering is performed while introducing an inert gas from the vicinity of the target, so that the film formation rate can be dramatically improved. . Therefore, the productivity is improved and the manufacturing cost can be reduced.

If the oxidizing gas is introduced from the vicinity of the substrate as described in claim 2, the oxidizing gas can be efficiently supplied onto the substrate, so that the target is hit even when the film forming speed is high. The emitted molecules can be completely oxidized on the substrate without causing absorption of visible light.

Further, as described in claim 3, as targets, Si, Ta, Ti, Al, Zr, Hf,
By using Y, W, or a mixture thereof, an optical thin film excellent in practicality, economy and durability can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a sputtering apparatus used in a method for producing an optical thin film according to the present invention.

FIG. 2 is a graph showing characteristics of the optical thin film obtained in Example 1 of the present invention.

FIG. 3 is a cross-sectional view showing another example of the sputtering apparatus used in the method for producing an optical thin film according to the present invention.

[Explanation of symbols]

 1,2,3 Gate valve 4,5 Target 6,7 Power supply 8,10,13,15 Valve 9,11,14,16 Inlet port 12,21 Changeover switch 17 Substrate 18 Substrate holder 19,20 Shutter

Claims (3)

[Claims] 1. An optics characterized by introducing an inert gas in the vicinity of a metal target when producing an optical thin film by a sputtering method, and introducing an oxidizing gas from a place different from the inert gas. Thin film manufacturing method. 2. The method for producing an optical thin film according to claim 1, wherein the oxidizing gas is introduced from near the substrate. 3. The metal target is Si, Ta, T
3. The method for producing an optical thin film according to claim 1, which is i, Al, Zr, Hf, Y, W, or a mixture thereof.