JPH03137017A - Optical thin film and its production - Google Patents

Abstract

PURPOSE:To produce an optical thin film having high refractive index and high transmittance at low cost by sputtering a target containing Zn, S, and O in a mixture atmosphere of Ar gas and N2 gas and then annealing the obtd. thin film. CONSTITUTION:While a mixture gas atmosphere of Ar and N2 is maintained at specified reduced pressure in a chamber 10, an electric power is applied on a ZnS target containing a minute amt. of O to effect reactive sputtering. With applying a magnetic field perpendicular to the target surface from a magnet 14, production rate of Ar<+> is increased, which raise the sputtering speed. The sputtered particles from the target 12 deposite on a glass substrate 11 separated from the plasma and thus a thin film is formed into which N in the chamber is incorporated. The obtd. thin film on the substrate consists of Zn, S, O and N. By annealing the film, transmittance is further improved for any wavelength of incident light, and especially transmittance for short wavelength is significantly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical thin film having a high refractive index and high transmittance, and a method for manufacturing the same.

[Prior Art and Problems to be Solved by the Invention] A ZnS thin film is known as a material having a high refractive index and high transmittance.

A ZnS thin film has conventionally been produced by a vapor deposition method or a sputtering method, and it has been reported that the refractive index of this thin film for light with a wavelength of 633 nm is as high as 2.35.

However, when applying conventional ZnS thin films to applications that require high transmittance but extremely high refractive index, such as antireflection coatings, broadband mirrors, uniform guides, and microlenses, their optical properties are insufficient. However, it has the disadvantage that the film thickness must be increased or the number of laminated layers must be increased, resulting in high manufacturing costs.

The present invention was made in view of the above circumstances, and an object thereof is to provide an optical thin film that has a high refractive index, high transmittance, and low manufacturing cost, and a method for manufacturing the same.

[Means for Solving the Problems] The optical thin film according to the present invention contains substantially ZnS as a constituent element.
, O, N.

This thin film may contain polycrystalline material or may be composed of an amorphous material.

Further, the method for manufacturing an optical thin film according to the present invention includes, firstly,
A6 is characterized in that the process of forming a mixed atmosphere of argon gas and nitrogen gas and the process of sputtering a target containing Zn, S, and 0 in this atmosphere are performed.

A second feature is that the method includes a step of annealing the thin film formed by the first method.

[Operation: The optical thin film consisting essentially of Zn, S, O, and N has a larger refractive index than a conventional ZnS thin film, and by selecting the composition, it can have the largest refractive index among high transmittance materials. It can have a higher refractive index than diamond.

In addition, the transmittance can be made higher than that of the ZnS thin film,
In particular, the transmittance on the short wavelength side can be increased. Therefore, a thin film having desired optical characteristics can be produced without increasing the film thickness or the number of laminated layers, and the manufacturing cost can be reduced. Moreover, this thin film can be manufactured without difficulty by sputtering in a mixed atmosphere of argon gas and nitrogen gas. Furthermore, by annealing the thin film produced in this manner, the transmittance can be further improved, particularly the transmittance on the short wavelength side.

[Example] This invention will be explained in detail below.

The optical thin film in this invention is substantially composed of Zn, S10 and N. Such thin films can exhibit higher transmittance and higher refractive index than ZnS thin films. Regarding the refractive index, the wavelength 633 of the irradiated light can be adjusted by selecting the composition.
It can be larger than diamond, which has the highest refractive index of high transmittance materials at r+m. The transmittance can be increased particularly when the irradiated light has a short wavelength from the visible light region to the ultraviolet region. Note that a composition having a basic composition of ZnS and containing 10 at % or less of 0 and 10 at % or less of N has a particularly high refractive index. In addition, 10 to 30 at% of 0 and 10 at% of N
Those having the following compositions have particularly high transmittance.

For this reason, this optical thin film is suitable for materials that require high transmittance and high refractive index, such as the aforementioned anti-reflection film and wide-area mirror.
The present invention is expected to be applied to Unibu guides, microlenses, and even enhancement films for increasing the Kerr rotation angle of photothermal magnetic recording media.

The refractive index of this optical thin film largely depends on its composition, for example the N content, and can be varied over a wide range by adjusting the composition.

Further, by adjusting the composition of this optical thin film, particularly the N content and the ratio of Zn to S, the state of the thin film can be changed between polycrystalline and amorphous.

When the thin film is polycrystalline, the refractive index can be particularly increased. Further, when the thin film is amorphous, the transmittance can be particularly increased. The effect of increasing transmittance in this case is particularly noticeable on the short wavelength side.

Furthermore, the wavelength position of the absorption edge can be changed by adjusting the N content of this optical thin film.

Next, a method for manufacturing such an optical thin film will be explained. FIG. 1 schematically shows an example of an apparatus for producing an optical thin film according to the present invention (J4 configuration, and shows a facing target sputtering apparatus.

In FIG. 1, a pair of targets 12 made of a ZnS sintered body are arranged in a chamber 10. Note that a ZnS sintered target containing a slight amount of oxygen (0) is used.

Above the target 12, a substrate 11 is rotatably supported by a rotation support member (not shown). A magnet 14 is attached to the outer edge of the back side of each target over the entire circumference.
is provided, and a magnetic field H exists between the targets. An AC power supply 16 is connected to each target,
Power is supplied to the target 12 from this power source 16. Note that the outer edge of each target 12 is covered with a cylindrical target cover 15.

The chamber 10 has a gas inlet 17 and a gas outlet 1.
8 is formed. An Ar gas supply source and a N2 gas supply source (both not shown) are connected to the gas introduction port 17, and A gas is supplied from these gas supply sources into the chamber 10.
A mixed gas of r gas and N2 gas is supplied. Further, a vacuum pump (not shown) is connected to the gas exhaust port 18, and by operating the vacuum pump, the inside of the chamber 10 is adjusted to a predetermined gas pressure.

In such an apparatus, a mixed gas of Ar gas and N2 gas is introduced into the chamber 10, and the chamber 10
Reactive sputtering is performed by applying power to each target 12 while maintaining a predetermined reduced pressure state of the mixed gas atmosphere inside. At this time, magnet 1
4 applies a magnetic field perpendicular to the target surface, this magnetic field increases the generation rate in Ar, making it possible to increase the sputtering rate.

During this sputtering, sputtered particles ejected from the target 12 are deposited on the glass substrate 11 separated from the plasma to form a thin film, and N in the chamber is taken into the thin film. Furthermore, since some O is present in the ZnS target, some O is included in the thin film. As a result, substantially Zn, S, O, N are formed on the substrate.
A lζ film is formed. At this time, since the substrate 11 is in a plasma-free state due to the magnetic field, Mll& is maintained at around room temperature. Furthermore, since the targets are facing each other, it is easy to control the thin film composition.

In addition, substantially Zn produced in this way.

The optical thin film made of S, O, and N is
As mentioned above, it has a high transmittance above 500 r+a as shown in Figure 4, which will be described later.
The transmittance decreases from around +, and at 250 nm, the transmittance is about 50%, and the optical properties on the short wavelength side are still not sufficient. For example, when this thin film is applied to optical components used in the entire visible light region,
Since the nc transmittance is low and the film itself is colored, its range of applications is narrowed. Furthermore, when used in the ultraviolet region with a wavelength of 350 to 200 nm, the transmittance becomes even lower, resulting in poor efficiency.

In order to avoid such inconveniences, in the present invention, the optical thin film formed by sputtering as described above is further subjected to an annealing treatment. As a result, the transmittance is further increased regardless of the wavelength of the irradiated light, and in particular, the transmittance on the short wavelength side can be significantly increased, and the transmittance in the visible light region is more uniform than that before heat treatment. Become. Therefore, it is convenient for application in the visible light region and the ultraviolet region.

Note that the annealing treatment can be performed in the atmosphere, and the temperature may be as low as about 150°C.

Next, the results of actual tests based on this invention will be explained.

Using the facing target sputtering apparatus shown in Fig. 1, a ZnS sintered body (containing some O) was used as the target.
A thin film sample was prepared by sputtering. At this time, among the mixed gases supplied into the chamber, the amount of Ar gas was fixed at 27 cc/min, and the flow rate of N2 gas was set at 0.3 cc/min, 1.0 cc/min, and 3.0 cc/min, respectively.
0cc/min, 8. Five types of samples were prepared at Occ/min and 20.0cc/min (Examples 1 to 5 in the order of N2 gas flow 2). For comparison, a sample prepared by sputtering using only Ar gas without introducing N2 gas was also prepared (referred to as Comparative Example 1). Moreover, the gas pressure in the chamber during sputtering is 1.1 to 1. 5
X 10-3 Torr. During sputtering, the substrate temperature was only a few degrees above room temperature because the substrate was isolated from the plasma.

For the elemental analysis, X-ray diffraction, and refractive index measurements described below, the substrate was quartz glass, and the film deposition rate was 3.5 to 4.
For transmittance measurements, the substrate was Pyrex alkali-free glass and the film deposition rate was 0.4 nm/min.
Samples with a film thickness of 18 to 40r+I11 were used.

Among these samples, Example 1.3.5 and Comparative Example 1
Varnish power (ESCA; Elcctrum 5p
cctr.

5copy f'or Chemical Analyses
As a result of the compositional analysis using the following method, the results shown in Table 1 were obtained. For reference, the analysis values of the ZnS standard sample are also listed.

Table 1 In Table 1, tr indicates that it was not detected due to the varnish force. As shown in this table, as the N2 gas flow rate increases, the Nm in the thin film increases, and the composition ratio of S to Zn (S/Zn) decreases, and when the N2 gas flow rate is 20 cc/min, The N content was 9.4 at% and the S/Z n was 0.66. Furthermore, each thin film contains 7 to 8 atomic percent of zero. In addition, Z
It was confirmed that the nS standard sample also contained 0 as an impurity.

FIGS. 2(a) to 2(f) are diagrams showing X-ray diffraction patterns of each sample in which a thin film was formed by changing the N2 gas flow rate as described above. Note that the large peak near the diffraction angle of 20° is due to the substrate. N2 gas flow rate is O~
At 0.3 cc/min (a) and (b), a hexagonal diffraction peak was confirmed around the diffraction angle of 27°, and
A hexagonal or cubic diffraction peak was confirmed near 9″47.5′ 56.5@. Therefore, the thin film contains a polycrystalline body consisting of hexagonal crystals or a mixed crystal of hexagonal crystals and cubic crystals. It can be seen that the N2 gas flow rate is 1.0c.
A large diffraction peak was confirmed near the diffraction angle of 47.5'' at c/min (C), indicating the presence of polycrystals in the thin film. This is presumed to indicate that the crystal plane, which is considered to be the (110) plane, is preferentially oriented.

On the other hand, when the N2 gas flow rate is 3.0 to 20. In OCC/min (d) to (f), no diffraction peaks other than the diffraction peak based on the substrate are observed, indicating that the thin film is in an amorphous state. That is, N during sputtering
It was confirmed that the thin film could change between crystalline and amorphous depending on the two gas flow rates. From these X-ray diffraction patterns and the above thin film composition, it is clear that the N content is high and the S/
It was confirmed that if Zn is small, it tends to become amorphous.

FIG. 3 is a diagram showing the relationship between the N2 gas flow rate during thin film formation and the refractive index when the wavelength of light irradiating the thin film is 633 nm.

As shown in this figure, the refractive index is relatively high in all samples, and the N2 gas flow rate is 0.3 cc/min and 1 cc/min.
．． For the 0cc/min sample, the refractive index n=2.41 (λ-
633run). In particular, at an N2 gas flow rate of 0.3 cc/min, 2
, 55, an extremely large refractive index was obtained.

FIG. 4 is a diagram showing the relationship between the wavelength of irradiation light and the transmittance for each N2 gas flow rate during thin film formation. As shown in this figure, all samples have wavelengths in the visible light range of 50
The transmittance tends to decrease as the wavelength becomes shorter from around 0 r++n, but for samples with a large flow rate of N2 gas, the transmittance is high and the absorption edge shifts to the shorter wavelength side.
It was observed that the wavelength range showing high transmittance was expanded toward shorter wavelengths. That is, it was confirmed that as the N2 gas flow rate increased, the transmittance, especially the transmittance on the short wavelength side, increased.

Next, the results of annealing a thin film produced by sputtering will be described. Anilization was carried out at 150° C. for a maximum of 440 hours in a dry air atmosphere. Then, the transmittance of the sample subjected to this annealing treatment was measured.

As a result, almost no change in transmittance was observed in the sample of the comparative example in which N2 gas was not supplied even after the annealing treatment. Further, even in the samples of the example in which N2 gas was supplied, the improvement in transmittance was only slight for samples where the N2 gas flow rate was up to 1 cc/min.

For a sample with a N2 gas flow rate of 3 cc/min, as shown in Figure 5, the irradiation light wavelength was 470 to 250 na+.
A clear improvement in transmittance was seen on the shorter wavelength side.

In addition, for the sample with a N2 gas flow rate of 8 cc/min, as shown in Figure 6, an even more significant increase in transmittance was confirmed on the short wavelength side, and this effect was greater than that of the one annealed for 130 hours. , it was observed that the one annealed for 440 hours was larger. Furthermore, the N2 gas flow rate is 20
For the cc/min sample, as shown in Figure 7,
- The layer transmittance was improved, and in particular, the one annealed for 440 hours achieved a high transmittance of 90% or more even in the ultraviolet region with a wavelength of about 300 nm. Although not shown, the change in transmittance due to annealing is due to the annealing time of 300
It was observed that although the time is large, the time after that is small up to 440 hours, and it is saturated at about 300 hours.

FIG. 8 is a diagram showing the effect of annealing depending on the irradiation light wavelength on samples with different N2 gas flow rates.

Note that ΔT on the vertical axis indicates a value obtained by subtracting the transmittance of the unannealed sample from the transmittance of the sample after 440 hours of annealing.

As shown in this figure, for samples with a N2 gas flow rate of 3 cc/min or more, the transmittance was improved by annealing, and the effect of transmittance improvement was particularly large in the short wavelength ultraviolet region of 350 to 20 Onl11. It was confirmed that the amount by which the permeability is improved increases as the N2 flow rate increases.

In addition, as a result of compositional analysis of the sample by Auger, N
In the sample where the N2 gas flow rate was Occ (comparative example), no composition change was observed due to annealing, but in the sample where the N2 gas flow rate was 0.3cc/min or more, the O content decreased to 10 atoms compared to before annealing. % to about 20 at.%.

[Effects of the Invention] According to the present invention, it is possible to provide an optical thin film that has a higher refractive index than a conventional ZnS thin film and also has a high transmittance. Therefore, a thin film having desired optical properties can be obtained without increasing the film thickness or the number of laminated layers, and manufacturing costs can be reduced. Furthermore, since the number of laminated layers may be small, stress strain can be reduced and the life span can be extended. Moreover, this thin film can be manufactured without difficulty by sputtering in a mixed atmosphere of argon gas and nitrogen gas.

Furthermore, by annealing the thin film produced in this way, the transmittance can be further improved, particularly the transmittance on the short wavelength side.

For this reason, components that require high transmittance and high refractive index, such as the aforementioned anti-reflection coating, wide-band mirror guide, microlens, and enhancement for increasing the Kerr rotation angle of photothermal magnetic recording media, are used. It is expected to be applied to membranes.

For example, the effective wavelength range of a broadband mirror can be expanded, and excess ripple can be reduced. It can also be used as a reflective film for high-power lasers, which has a non-uniform refractive index in the film thickness direction.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a sputtering apparatus for manufacturing an optical thin film according to the present invention, and FIG. 2 is an X-ray diffraction diagram of a thin film sample when varying the flow rate of N2 gas supplied during sputtering. Figure 3 is a diagram showing the relationship between the N2 gas flow supplied during sputtering and the refractive index.
The figure shows the relationship between the wavelength of the irradiated light and the transmittance of the thin film when varying the N2 gas flow rate supplied during sputtering. FIG. 8 is a diagram showing the influence of annealing on the transmittance when expressed as a value, and FIG. 8 is a diagram showing the change in transmittance depending on the wavelength of irradiation light. 10; chamber, 11: substrate, 12; target, 14
; Magnet, 16; Power supply.

Claims (1)

[Scope of Claims] (1) An optical thin film characterized in that the constituent elements are substantially Zn, S, O, and N. (2) Claim 1 characterized in that it contains a polycrystalline body.
The optical thin film described in . (3) The optical thin film according to claim 1, wherein the optical thin film is made of an amorphous material. (4) A method for producing an optical thin film, comprising the steps of forming a mixed atmosphere of argon gas and nitrogen gas, and sputtering a target containing Zn, S, and O in this atmosphere. . (5) A step of forming a mixed atmosphere of argon gas and nitrogen gas, a step of sputtering a target containing Zn, S, and O in this atmosphere, and a step of annealing the thin film formed by this step. A method for producing an optical thin film, comprising: