JPH09228028A - Composite thin film and forming of thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide thin film applicable to optical elements and color materials on substrates in a wide range from plastic stocks to inorganic stocks by using a zinc compound wide in optical band gap energy and high in cost performance. SOLUTION: This is composite thin film composed of a nitrogen compound and an oxygen compound, particularly, of zinc nitride and zinc oxide, and the method for forming thin film composed of nitrogen compound thin film or thin film composed of a nitrogen compound and an oxygen compound, particularly, and zinc nitride thin film or thin film composed of zinc nitride and zinc oxide by a sputtering method using at least one kind of plasma gases 6 among nitrogen, oxygen and argon is provided, by which the thin film of the compound having desired optical band gap energy and color can be formed, and, since low temp. film formation is made possible, the width of the selection of the materials of the substrates 1 is extended.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a composite thin film and a method for forming the thin film, and more particularly to a composite thin film and a method for forming the thin film having a desired optical bandgap and color.

[0002]

2. Description of the Related Art Zinc phosphide (Zn ₃ P ₂ ) which is one of the nitrogen compounds, and zinc oxide (ZnO) which is one of the oxygen compounds are reported on the crystal structure and chemical properties. There are many examples. For example, Zn ₃ P ₂ is II
A group V zinc compound having a tetragonal antifluorite type crystal structure, a direct transition type band structure, and an optical bandgap energy Eg (hereinafter referred to as “Eg”)
Is reported to be 1.5 eV, and further, zinc phosphide thin films are attracting attention as materials for solar cells.
On the other hand, ZnO has a hexagonal wurtzite crystal structure,
It is reported that the band structure is a direct transition type and Eg is 3.2 eV. Further, the zinc oxide thin film is widely applied as a dielectric material and a semiconductor material.

By analogy with these two types of zinc compounds, zinc nitride, which is a type of nitrogen compound, is expected to show interesting physical properties, and is expected to be applied as semiconductor materials, optical element materials, and the like.

However, zinc nitride (Zn ₃ N ₂ ) is one of the compounds with few studies, and the first synthesis of Zn ₃ N ₂ was performed by Juza et al. In 1940. In recent years, the structure and physical properties of a zinc nitride thin film have been reported by Takai, the inventor of the present application (Osamu Takai, “Surface Technology” 40 (1) 98).
(1989)). Here, Takai confirmed that the zinc nitride thin film prepared by the reactive high frequency ion plating method was Zn ₃ N ₂ by Auger electron spectroscopy, and that the thin film was yellowish brown or grayish brown, It has optical transparency in the visible and near-infrared region and is expected to be applied as a material for optical functional devices. The reactive high frequency ion plating method used by Takai usually generates nitrogen plasma by high frequency and has a purity of 99.99 by resistance heating of a tungsten (W) linear basket.
In this method, 99% of zinc is evaporated in nitrogen plasma to form a zinc nitride thin film on a substrate placed below. The film formation time on the substrate is 60 to 90 minutes, and the temperature of the substrate during film formation is 70 to 140 ° C.

Kuriyama et al. Reported on the optical band gap of Zn ₃ N ₂ thin films (Kuriyama et al., Th.
e American Physical Society, PYSICASL REVIEW B, 48
(4) 2781 (1993)). Kuriyama et al., Zn ₃ by a direct nitriding method
An N ₂ thin film was formed and confirmed to be Zn ₃ N ₂ by X-ray diffraction (XD) and Rutherford's light scattering spectrum (RBS). In the direct nitriding method used by Kuriyama et al., A zinc thin film is formed on a substrate, and then the substrate is heated while blowing ammonia gas (NH ₃ ) in a nitrogen atmosphere,
In this method, a zinc thin film formed on a substrate is annealed at 410 ° C. for 4 hours to obtain a Zn ₃ N ₂ thin film. Therefore, as the substrate, a metal plate having a high heat resistance, a quartz plate, a heat-resistant glass plate or the like is used.

[0006]

However, the film-forming method of Kuriyama et al. Has a problem that the material of the substrate is limited because the film is formed at a high temperature and the application range of the application is limited. It was Furthermore, in the reactive high frequency ion plating method used by Takai, an amorphous material is used.
Only the film of can be produced.

Further, in any of the above film forming methods, only a thin film of a single compound can be formed, and only a single Eg can be obtained. Therefore, it was impossible to use this thin film alone as a semiconductor. As a semiconductor material, a III-V group, such as a GnN-InN thin film, whose Eg can be controlled from 2.0 to 6.0 eV is generally used, but a III-V group compound is expensive and its use is limited. There was a problem that it would end up. Further, when Eg is 2.0, visible light cannot be completely blocked, and therefore a black film cannot be formed on the substrate.

Further, in the above film forming method, only a single compound thin film can be formed on the substrate. In general, thin films of IVN group TiN, ZrN, HfN, and similar compounds are known as a decorative material for substrates, but there is a problem that their applications are limited because they are expensive. .

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to form a composite thin film composed of a compound having a desired band gap or color, and a thin film on a substrate at a low temperature and to obtain a desired band. It is an object of the present invention to provide a thin film forming method for forming a thin film made of a compound having a gap or a color.

[0010]

In order to achieve the above object, the composite thin film of the present invention is composed of a nitrogen compound and an oxygen compound. Therefore, a thin film of a compound having a desired bandgap and color can be formed depending on the composition ratio of the nitrogen compound and the oxygen compound.

In the composite thin film of the present invention, the nitrogen compound is zinc nitride and the oxygen compound is zinc oxide. Therefore, it is possible to form a thin film of a compound having a desired band gap and color as described above by simply changing the mixing ratio of zinc nitride and zinc oxide using zinc that is abundant in terms of resources and is inexpensive.

Further, in the thin film forming method of the present invention, a nitrogen compound thin film or a thin film composed of a nitrogen compound and an oxygen compound is formed by a sputtering method using at least one plasma gas of nitrogen, oxygen and argon. Therefore,
A nitrogen compound thin film or a thin film composed of a nitrogen compound and an oxygen compound can be formed by arbitrarily selecting the plasma gas. Further, in the sputtering method, it is easy to introduce the plasma gas into the processing system while changing the plasma gas to a desired ratio. Therefore, by changing the mixing ratio of the mixed plasma gas of nitrogen and oxygen, the desired optical band similar to the above can be obtained. A thin film of a compound having gap energy and color can be formed on a substrate. In addition, since the sputtering method allows low-temperature film formation and large-area film formation, the material of the substrate on which the film is formed is not restricted as in the past and can be used immediately industrially. There is an advantage that it is a possible film forming method.

In the thin film forming method of the present invention, the nitrogen compound is zinc nitride and the oxygen compound is zinc oxide. Therefore, by changing the mixing ratio of the two gases in the mixed plasma gas of nitrogen and oxygen,
It is possible to form a thin film of a compound having a desired band gap and color by changing the mixing ratio of zinc nitride and zinc oxide by using zinc which is abundant in resources and inexpensive.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The composite thin film of the present invention is composed of a nitrogen compound and an oxygen compound, preferably the nitrogen compound is zinc nitride (Zn ₃ N ₂ ) and the oxygen compound is zinc oxide (ZnO). . When the composite thin film of the present invention is composed of zinc nitride (Zn ₃ N ₂ ) and zinc oxide (ZnO), the optical bandgap energy Eg of the composite thin film is changed according to the film composition ratio of zinc nitride and zinc oxide. (Hereinafter "E
“G”) is in the range of 1.2 eV to 3.2 eV. Incidentally, the Eg of zinc nitride is usually 1.2 eV, and the Eg of zinc oxide is 3.2 eV. Furthermore, as the film composition ratio of zinc oxide to zinc nitride increases, the color of the thin film changes from black to reddish brown to red to orange to yellow to transparent.

Therefore, the composite thin film of the present invention has an Eg of 1.
Since it can be controlled within the range of 2 eV to 3.2 eV, it can be used as a semiconductor material for optoelectronics, such as solar cells, light emitting elements (EL, PL), switching elements, rectifying elements, and the like. Furthermore, since the color of the thin film can be changed by changing the film composition ratio of zinc nitride and zinc oxide as described above, it can be applied to optically functional glass, such as selective transparent film and black film (CF, visible light absorbing film). It can be applied as a decorative material.

The thickness of the composite thin film of the present invention is 0.0
5 to 1 μm is preferable, and 0.1 to 0.5 is more preferable.
μm. When the thickness of the composite thin film is less than 0.05 μm, transparency is obtained, but there is a disadvantage that the color is more difficult to recognize as the absorption becomes insufficient and the color becomes lighter. On the other hand, when the thickness exceeds 1 μm. Has the disadvantage that fine cracks are likely to occur and the transparency is impaired, and that if the substrate is a resin film, problems occur in the physical properties (adhesion, bending, etc.).

In the thin film forming method of the present invention, a thin film of a nitrogen compound or a thin film of a nitrogen compound and an oxygen compound, preferably a nitride film, is formed by a sputtering method using at least one plasma gas of nitrogen, oxygen and argon. It is a method of forming a zinc thin film or a thin film composed of zinc nitride and zinc oxide.

The thin film forming method of the present invention will be described below.

The thin film forming method of the present invention uses the sputtering method as described above, but the sputtering method which can be used in the present invention is roughly classified into a plasma method and a beam method. Examples of the plasma method include a high frequency sputtering method (for example, the bipolar sputtering method shown in FIG. 1), a high frequency magnetron sputtering method (the method shown in FIG. 2), a reactive sputtering method, and the like, and a beam method includes an ion beam sputtering method. Law etc. are mentioned. 1 and 2, DC means direct current and RF means high frequency.

The high frequency sputtering method is a method of forming a thin film on a substrate by the following steps. That is,
First, after cleaning the substrate, as shown in FIG. 1, the substrate 1 and the target 2 are mounted in a sputtering chamber 5 (hereinafter referred to as "chamber 5"). At this time, the distance between the substrate 1 and the target 2 is preferably about 30 to 150 mm. After that, the chamber 5 is evacuated to about 10
^-4 Pa. Next, argon gas is injected into the chamber 5 through the gas injection port 3 and the argon gas is turned into plasma by high frequency. Then, the surface of the target 2 is pre-etched by this plasma. The target here means a metal supply source for forming a thin film. After the target 2 is pre-etched, the chamber 5 is evacuated again to about 10 ⁻⁴ Pa, and plasma gas is introduced into the chamber 5 to start film formation. After forming a thin film having a desired composition to a predetermined thickness, the substrate 1 is taken out from the chamber 5 after cooling if necessary.

The total pressure when introducing the plasma gas in the chamber 5 is 0.5 to 10 Pa, preferably 0.6.
~ 5 Pa. If the total pressure is less than 0.5 Pa, there is an inconvenience that the plasma is not stable. On the other hand, if the total pressure is more than 10 Pa, economical waste occurs and the film formation time is too short, which makes it difficult to control the film thickness. There is an inconvenience.

In the method for forming a thin film of the present invention,
The temperature of the substrate is room temperature (about 25 ° C.) to 60 ° C., and a thin film can be sufficiently formed on the substrate. However, in order to increase the thin film formation rate, the temperature may be higher than the above temperature, for example, about 150 ° C.
It may be performed at (423K). Therefore, according to the thin film forming method of the present invention, since the temperature of the substrate during film formation can be suppressed to a low temperature, the range of choices for the material of the substrate is widened. Therefore, for example, general glass, resin film, non-heat-resistant metal or the like can be newly used, and naturally, heat-resistant metal, quartz glass or the like which has been conventionally used can also be used. Therefore, there is an advantage that a wide range of materials from plastic materials to inorganic materials can be used as substrates for the materials in the above-mentioned fields of use.

As the plasma gas, nitrogen, oxygen,
At least one plasma gas of argon is preferred,
Further, a plasma gas obtained by mixing two kinds of the above gases is more preferable. Examples of the plasma gas of two kinds mixed include nitrogen / argon (N ₂ / Ar), nitrogen / oxygen (N ₂ / O ₂ ), and oxygen / argon (O ₂ / Ar).

When nitrogen / argon (N ₂ / Ar) is used as the plasma gas and a pure metal is used as the target,
A thin film of a nitrogen compound is deposited on the substrate. When a metal oxide is used as the target, a thin film made of a nitrogen compound and an oxygen compound is formed on the substrate. Therefore, when zinc is used as the target, a thin film of zinc nitride is formed on the substrate. When zinc oxide is used as the target, a thin film made of zinc nitride and zinc oxide is formed on the substrate. Here, the nitrogen gas concentration in the plasma gas is preferably 2.5 to 100%, more preferably 20 to 100%. When the nitrogen gas concentration is less than 2.5%, the nitrogen compound does not form a film,
A metal film is formed. By setting the nitrogen gas to 20% or more, for example, in the case of a zinc nitride thin film, a polycrystalline thin film can be industrially stably obtained.

When nitrogen / oxygen (N ₂ / O ₂ ) is used as the plasma gas and a target of pure metal, metal oxide, or metal nitride is used, a thin film made of a nitrogen compound and an oxygen compound is obtained. The film is formed on the substrate. Therefore, regardless of whether zinc, zinc oxide, or zinc nitride is used as the target, a thin film made of zinc nitride and zinc oxide is formed on the substrate.

Furthermore, when oxygen / argon (O ₂ / Ar) is used as a plasma gas and a metal nitride is used as a target, a thin film composed of a nitrogen compound and an oxygen compound is formed on the substrate. Therefore, when zinc nitride is used as the target, a thin film made of zinc nitride and zinc oxide is formed on the substrate.

Therefore, according to the thin film forming method of the present invention, a desired nitrogen compound-only thin film and a nitrogen compound and an oxygen compound can be formed by selecting an arbitrary mixed plasma gas from the combination of the above plasma gases. The composite thin film can be easily formed on the substrate. Furthermore, when a composite thin film is formed on a substrate, it can be easily performed by changing the mixing ratio of nitrogen gas and oxygen gas of plasma gas and by adjusting the concentration of nitrogen gas in the target of oxygen compound and plasma gas. The composition ratio of the nitrogen compound and the oxygen compound in the composite thin film can be controlled. In addition, by changing the mixing ratio of the nitrogen gas and the oxygen gas of the plasma gas during film formation, or by changing the nitrogen gas concentration in the plasma gas when the target is an oxygen compound. Further, thin films having different compositions or thin films having a multi-layered structure having different compositions can be easily formed on the substrate.

Further, in the thin film forming method of the present invention, it is possible to form a thin film having a multi-layer structure on the substrate by a sputtering method while changing the kind of the target metal.
Alternatively, a plurality of target metals may be evaporated at the same time to form a thin film on the substrate.

The above Eg is determined by the method described below.

[0030]

(1) (hνα) ² = β (hνα · Eg) (where, hν: photon energy, α: absorption coefficient, Eg:
Optical bandgap energy, β: A parameter that characterizes the transition type and can be easily treated as a constant. ) First, by calculating and substituting the absorption coefficient α from the transmission spectrum of the thin film, and substituting hν obtained by the experiment into the equation showing the relationship with the light energy near the absorption edge wavelength,
The relationship between the absorption coefficient near the absorption edge and the photon energy is plotted with hν as the horizontal axis and (hνα) ² as the vertical axis.
In the graph in which these values are plotted, a linear relationship is established in a wide energy range, but this linear portion is extended and the value of hν (eV) at the point where (hνα) ² = 0 intersects is Eg.

The film forming treatment time in the thin film forming method of the present invention is, for example, about 30 minutes to 100 minutes for forming a thin film having a thickness of 0.2 μm on a substrate.

Further, other preferred embodiments of the present invention other than those described in the claims are shown below.

1. The optical bandgap energy Eg of the composite thin film composed of zinc nitride (Zn ₃ N ₂ ) and zinc oxide (ZnO) is in the range of 1.2 eV to 3.2 eV depending on the film composition ratio of zinc nitride and zinc oxide. is there.

2. The color of the composite thin film composed of zinc nitride (Zn ₃ N ₂ ) and zinc oxide (ZnO) is black to reddish brown to red to orange to yellow as the film composition ratio of zinc oxide to zinc nitride increases. ~ Change to transparent.

3. The thickness of the composite thin film composed of the nitrogen compound and the oxygen compound is 0.05 to 1 μm.

4. The thickness of the composite thin film composed of the nitrogen compound and the oxygen compound is 0.1 to 0.5 μm.

5. The thin film is formed by using a plasma gas composed of a mixed gas of nitrogen / argon (N ₂ / Ar), nitrogen / oxygen (N ₂ / O ₂ ) and oxygen / argon (O ₂ / Ar). Method to form a nitrogen compound thin film or a thin film composed of a nitrogen compound and an oxygen compound.

6. The thin film is formed by using a plasma gas composed of a mixed gas of nitrogen / argon (N ₂ / Ar), nitrogen / oxygen (N ₂ / O ₂ ) and oxygen / argon (O ₂ / Ar). Method to form a thin film of zinc nitride or a thin film of zinc nitride and zinc oxide.

7. In the method of forming a thin film, when a zinc nitride thin film or a thin film of zinc nitride and zinc oxide is formed by a sputtering method using a plasma gas composed of a mixed gas of nitrogen / argon (N ₂ / Ar), The nitrogen gas concentration is 2.5 to 100%.

8. In the method of forming a thin film, when a zinc nitride thin film or a thin film of zinc nitride and zinc oxide is formed by a sputtering method using a plasma gas composed of a mixed gas of nitrogen / argon (N ₂ / Ar), The nitrogen gas concentration is 20 to 100%.

9. In the method for forming a thin film, the temperature of the substrate on which the thin film is formed is room temperature (about 25 ° C.) to 60 ° C.

10. In the thin film forming method, the temperature of the substrate when forming the thin film on the substrate by increasing the thin film forming speed is
It is 60 to 200 ° C.

[0043]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

Examples 1 to 14 Substrate ; PET (polyethylene terephthalate) film: transparent P
ET film (film thickness 2 mm) ITO thin film (one kind of transparent conductive film): commercially available ITO thin film glass plate: commercially available borosilicate glass target ; zinc: high-purity zinc metal disk (purity 99.9)
Zinc oxide: A process for forming a zinc oxide disc thin film in which high-purity zinc oxide (purity 99.99%) is fixed on a stainless disc by a sintering method; in the present embodiment, the high frequency magnetron sputtering method shown in FIG. 2 is used. Was used to form a thin film. First, after cleaning the substrate, as shown in FIG. 2, the target 2 was placed on the magnet 4, and the substrate 1 was also mounted in the sputtering chamber 5 (hereinafter referred to as “chamber 5”). The distance between the substrate 1 and the target 2 at this time was 70 mm. Then, exhaust the inside of the chamber 5
× 10 ^-4 Pa. Next, while the high frequency was being output at 25 W, argon gas was injected into the chamber from the gas injection port 3 (pressure of argon gas was 0.6 Pa), and the argon gas was turned into plasma by the high frequency. Then, the surface of the target 2 was pre-etched for 20 minutes with this plasma. After the target 2 was pre-etched, the chamber 5 was evacuated again to 5 × 10 ⁻⁴ Pa, and a plasma gas having a predetermined composition ratio was introduced into the chamber 5 to start film formation. The thin film forming conditions, that is, the composition of the plasma gas, the target, the substrate, the temperature of the substrate, etc. are as shown in Table 1. The processing time was set so that the thickness of the thin film was 0.2 μm. After forming a thin film having a desired composition to a predetermined thickness, the substrate 1 was taken out from the chamber 5 after cooling and its performance was evaluated.

Regarding the structure of the thin film formed on the substrate, X-ray diffraction (XD) measurement and X-ray electron spectroscopic analysis (XP
S) and the composition of the thin film was confirmed by X-ray electron spectroscopy (XPS). The optical property of the formed thin film was measured by a transmission spectrum with a spectrophotometer. For the measurement of the transmittance, the borosilicate glass plate used as the substrate was used as a blank.

Evaluation items ; (1) Optical bandgap energy Eg; As described above, the relationship between the optical energy and the absorption function was obtained by experiment, and Y = 0 ((hνα) ² = 0) was extrapolated to the linear part. Eg was determined.

(2) Color of thin film: The appearance was visually evaluated.

(3) Absorption edge wavelength: The transmission spectrum of the obtained thin film was measured at measurement wavelengths of 3200 to 300 nm, the horizontal axis represents the measurement wavelength, and the vertical axis represents the transmittance to obtain the transmittance. From the obtained spectrum, the linear portion from the portion where absorption was started was extended, and the value of the wavelength intersecting the x axis was taken as the absorption edge wavelength.

The above evaluations were performed, and the results are also shown in Table 1.

[0050]

[Table 1] From these results, according to the composite thin film and the method for forming a thin film of the present invention, it is possible to form a thin film of a desired Eg on the substrate in the range of Eg of 1.2 eV to 3.2 eV, and further form a thin film in a desired color. It turned out to be possible. Further, according to the composite thin film of the present invention, as can be seen from the above results, it can be used as a selective transmission film that blocks arbitrary visible light.

[0051]

As described above, according to the composite thin film of the present invention, a thin film of a compound having a desired band gap and color can be easily produced depending on the composition ratio of the nitrogen compound and the oxygen compound of the composite thin film. .

Further, according to the thin film forming method of the present invention, a nitrogen compound thin film or a nitrogen compound and oxygen can be obtained by arbitrarily selecting a plasma gas as at least one plasma gas of nitrogen, oxygen and argon. A thin film composed of a compound can be formed. Further, in the sputtering method, it is easy to introduce the plasma gas into the processing system while changing the plasma gas to a desired ratio. Therefore, by changing the mixing ratio of the mixed plasma gas of nitrogen and oxygen, the desired optical band similar to the above can be obtained. Thin films of compounds having gap energy and color can be produced. In addition, since the sputtering method can form a film at a low temperature and can form a large area, the material of the substrate to be formed is not restricted as compared with the conventional one, and the above-mentioned film forming method is industrially used. Can be used.

Further, by changing the composition ratio of the plasma gas with time, thin films having different compositions or thin films having a multi-layered structure having different compositions can be easily formed on the substrate.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an apparatus configuration used in a high frequency sputtering method according to the present invention.

FIG. 2 is a diagram showing an outline of an apparatus configuration used in a high frequency magnetron sputtering method according to the present invention.

[Explanation of reference numerals] 1 substrate, 2 target, 3 gas inlet, 4 magnet, 5 sputtering chamber, 6 plasma gas.

Claims (4)

[Claims] 1. A composite thin film comprising a nitrogen compound and an oxygen compound. 2. The composite thin film according to claim 1, wherein the nitrogen compound is zinc nitride and the oxygen compound is zinc oxide. 3. A method for forming a thin film, comprising forming a nitrogen compound thin film or a thin film containing a nitrogen compound and an oxygen compound by a sputtering method using at least one plasma gas of nitrogen, oxygen and argon. 4. The thin film forming method according to claim 3, wherein the nitrogen compound is zinc nitride and the oxygen compound is zinc oxide.