JP2766562B2 - Metal film protective film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective film for preventing oxidation of a metal film used for generating a metal surface plasmon in an element such as a sensor or an optical component utilizing the metal surface plasmon.

[0002]

2. Description of the Related Art Conventionally, metal surface plasmons have a high electric field effect and high sensitivity to changes in propagation conditions due to changes in the refractive index of a substrate. It has been proposed and used for some sensors and refractive index measurement of substances.

[0003] Silver, copper, aluminum, gold and the like are known as metals effective in generating metal surface plasmons. Among them, silver is particularly effective because of its high electric field effect and small propagation loss. It is possible to effectively excite metal surface plasmons.

[0004] Hereinafter, a second harmonic light generating element is an example of the use of the conventional metal surface plasmons is described with reference to FIG.

[0005] FIG. 5 is a diagram showing the use of metal surface plasmons.
FIG. 3 is a structural diagram of a second harmonic light generating element, in which a film thickness of 200 is formed on a lithium niobate substrate 16 having nonlinear optical characteristics.
A silver thin film 15 having a Å and an aluminum nitride film 13 having a thickness of 2 μm are sequentially formed. A prism 12 for adjusting the wave number is arranged on the aluminum nitride film 13 of the device having the structure shown in FIG. 5 , and a fundamental wave laser beam 11 for generating a metal surface plasmon is irradiated to the silver thin film 1.
By exciting the metal surface plasmon at 5,
Second harmonic light 17 can be generated.

[0006]

However, silver, copper and aluminum are generally liable to deteriorate in refractive index characteristics due to oxidation, and when a dielectric film made of an oxide is formed on these metal films, Due to the oxidation of the metal film, there arises a problem that the metal surface plasmon cannot be excited. On the other hand, if the refractive indices at both interfaces of the metal film are made the same, it is possible to generate metal surface plasmons with higher efficiency. In the generating element,
Instead of the refractive index value is less aluminum nitride 13 from the structure of lithium niobate substrate 16 in FIG. 5, the use of the oxide dielectric having the same value of refractive index between the lithium niobate substrate 16, is greater than the strength first Although the generation of second harmonic light can be expected, the silver thin film 15 was actually oxidized, and the metal surface plasmon could not be excited, and the second harmonic light 17 could not be generated. As described above, even if an oxide dielectric having characteristics superior to those of other dielectrics is present, it cannot be used, and many restrictions have been placed on the design of the optical thin film.

Further, it is expected that the metal surface is covered with a dielectric material that does not attack the metal, thereby preventing the metal film from being oxidized. It is greatly affected by the refractive index of the constituting dielectric, and in the case of an optical element utilizing the electro-optic effect or the nonlinear optical effect,
It was thought that if another dielectric film was interposed between the metal interface and the dielectric interface, the high electric field effect would not be effectively generated.

The present invention has been made in view of the above circumstances, and provides a protective film for a metal film that can prevent characteristic deterioration caused by oxidation of the metal film by an oxide dielectric and can effectively generate metal surface plasmons. Aim.

[0009]

In order to solve the above-mentioned problems, an element in which a dielectric film made of an oxide is formed on a metal film used for generating a metal surface plasmon is provided. A nitride thin film is formed as a protective film between itself and the body film.

[0010]

According to the present invention, by adopting a nitride thin film as a protective film on the surface of a metal film used for generating metal surface plasmon, which is in contact with an oxide dielectric film,
It is possible to prevent characteristic deterioration caused by oxidation of the metal film by the oxide dielectric and to effectively generate metal surface plasmons.

[0011]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a method using metal surface plasmons.
FIG. 3 is a structural diagram of a second harmonic light generation element. In FIG.
1 is a fundamental wave laser beam for generating metal surface plasmon, 2 is a prism for adjusting the wave number, 3 is a tantalum oxide film as a dielectric thin film, 4 is a nitride thin film for protecting the metal film, 5 Is a metal film, 6 is a lithium niobate substrate which is a nonlinear optical crystal, and 7 is generated second harmonic light.

On a lithium niobate substrate 6 having nonlinear optical characteristics, a metal film 5 having a thickness of 200.degree. Is formed by sputtering, and a nitride thin film 4 for preventing oxidation is similarly formed on the metal film 5 by sputtering. A tantalum oxide film 3 having a thickness of 2 μm was formed on the tantalum oxide film 3 by the sputtering method, and the prism 2 was disposed on the tantalum oxide film 3. Here, an aluminum nitride film, a silicon nitride film, and an indium nitride film were used as the nitride thin film 4, and silver, copper, and aluminum were used as the metal film 5.

In the second harmonic light generating element having the above structure, the second harmonic light 7 can be generated by irradiating the fundamental laser light 1 to excite metal surface plasmons in the metal film 5. Since the generation of the metal surface plasmon of the metal film 5 of the second harmonic light generating element coincided with the theory, the metal film 5 was not oxidized when the tantalum oxide film 3 was manufactured, and the refractive index did not change. I understand.

FIG. 2 shows the results of measuring the intensity of the second harmonic light when the aluminum nitride film is used as the protective thin film 4 and the film thickness is changed in the device having the structure shown in FIG. It is a graph shown. FIG. 3 is a graph showing the results of measuring the intensity of the second harmonic light when the silicon nitride film was used as the nitride thin film 4 as the protective film in the device having the structure shown in FIG. 1 and the film thickness was changed. It is. FIG. 4 is a graph showing the results of measuring the intensity of the second harmonic light when the indium nitride film is used as the nitride thin film 4 serving as a protective film and the film thickness is changed in the device having the structure shown in FIG. It is.

2 and 3 that when using a nitride thin film of aluminum nitride or silicon nitride, the thickness of the nitride thin film is not less than 100 ° in any of silver, copper and aluminum used as the metal film 5. If so, metal film 5
Can be sufficiently prevented, and when the film thickness is up to about 250 °, there is almost no difference from the theoretical prediction of the occurrence of metal surface plasmons in the case of a metal film alone, and does not affect the occurrence of metal surface plasmons. It turns out. FIG.
According to the results, when the nitride thin film of indium nitride was used, any of silver, copper, and aluminum used as the metal film 5 could sufficiently oxidize the metal film 5 if the thickness of the nitride thin film was 100 ° or more. Can be prevented, and the film thickness is 1000 mm
To the extent, it was found that there was almost no difference from the theoretical prediction of the generation of metal surface plasmons when only the metal film was used, and that the generation of metal surface plasmons was not affected.

It is apparent that other similar nitride thin films such as boron nitride and gallium nitride have similar effects.

In the above embodiment, an example is shown in which the protective film of the metal film of the present invention is applied to the second harmonic light generating element for generating the second harmonic light, but it is used for generating metal surface plasmon. Of course, the present invention can be applied to an element in which a dielectric film made of an oxide is formed on a metal film, for example, an element such as a sensor or an optical component using metal surface plasmon.

[0019]

As described above, according to the present invention, the oxidation of the metal film by the oxide dielectric is prevented, and the high electric field effect of the metal surface plasmon and the propagation of the metal surface plasmon highly dependent on the refractive index are affected. Can be obtained, and many of the restrictions on the design of the optical thin film can be eliminated.
High-performance sensors and optical components using metal surface plasmons can be manufactured.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a second harmonic light generating element using metal surface plasmons according to an embodiment of the present invention.

FIG. 2 is a graph showing the results of measuring the intensity of second harmonic light when the aluminum nitride film is used as the protective thin film 4 and the film thickness is changed in the device having the structure shown in FIG. It is.

3 is a graph showing the results of measuring the intensity of the second harmonic light when the silicon nitride film is used as the protective thin film 4 and the film thickness is changed in the device having the structure shown in FIG. It is.

FIG. 4 is a graph showing the results of measuring the intensity of second harmonic light when the thickness of the indium nitride film is changed in the device having the structure of FIG. 1 when an indium nitride film is used as the nitride thin film 4 as a protective film. It is.

FIG. 5 is a structural diagram of a second harmonic light generating element using metal surface plasmons in a conventional technique.

[Explanation of symbols]

 Reference Signs List 1,11 fundamental wave laser beam 2,12 prism 3 tantalum oxide film 4 nitride thin film 5,15 metal film 6,16 lithium niobate substrate 7,17 second harmonic light 13 aluminum nitride film

Claims (1)

(57) [Claims] 1. A protection film for a metal film in an element in which a dielectric film made of an oxide is formed on a metal film used for generating metal surface plasmon, wherein the protection film is formed of a metal film and the dielectric film. A protective film of a metal film formed between and formed of nitride.