JPH07172867A - Silicon oxide film optical element and its production - Google Patents

Abstract

PURPOSE:To obtain a silicon oxide thin film optical element having high film forming rate, low internal stress and large laminated thickness by forming a specific hydrogen bond in the film at the time of laminating the silicon oxide film. CONSTITUTION:The silicon oxide thin film is formed as a structural film of an optical element used in a near infrared wave length region by using a mixture of Ar and H2 as a sputtering gas and SiO2 as a sputtering target and setting a substrate temp. to <=400 deg.C so that hydrogen is contained in the silicon oxide film and a part or whole of them forms Si-H bond or SiO-H bond by sputtering method. For example, a laminated optical polarizing element having 500mum laminated thickness is obtained by being constituted of an alternate multilayered film of Ge (4.5nm) and silicon oxide film (800nm) in the film forming condition of 4:1 mixing ratio of Ar and H2, 560W sputtering electric power, 0.2Pa sputtering pressure and non-heating of the basic temperature and inserting a Si film (1nm) between the boundary of the films in order to improve the sticking strength of both films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is indispensable as a waveguide or a low refractive index dielectric layer of optical elements such as laminated polarizers, laminated polarization separation elements and optical filters used in the near infrared wavelength region. The present invention relates to a silicon oxide film optical element having a silicon oxide film and a method for manufacturing the same.

[0002]

2. Description of the Related Art Since a silicon oxide film is transparent in the near-infrared wavelength range, a laminated polarizer, a laminated polarization separation element,
It is used as an optical waveguide of an optical thin film device such as an optical filter or a low refractive index dielectric layer.

Here, the method for producing the silicon oxide film is C
Although there are VD method, electron beam method, sputtering method, etc., in the application of silicon oxide to an optical thin film device, the sputtering method is often used because of its high density and film forming rate, and a mixture of argon and oxygen is used as a sputtering gas. Is generally used.

[0004]

Recently, a laminated polarizer (see S. Kawakami, Appl. Opt., 22,2426 (1983)) and a laminated polarization demultiplexer (T. Sato, K. Shiroishi, K). .Tsutida ann
d S. Kawakami, Appl. Phys. Lett., 612633 (1992))
There is an increasing demand for an optical thin film element composed of an alternating multi-layer film of a silicon oxide film and a metal or semiconductor film such as the above.

Here, the laminated polarizer and the laminated polarization separation element are used by bonding the laminated cross section to the core portion of the optical fiber, and in order to facilitate the bonding operation, the laminated thickness of these elements is used. Is preferably large. It is also considered that the signal light is made incident on the cross section of the element by a lens etc. without using an optical fiber in order to widen the use of these elements, but in that case, the incident light becomes larger as the laminated thickness of the element becomes larger. Coupling with light becomes easy.

However, since the internal stress of a conventional sputtering film using a mixed gas of argon and oxygen is large, there is a limit to the increase in the laminated thickness of the multilayer film. That is, the sputtering method has a merit of high element productivity, but a silicon oxide film formed under a general sputtering condition using a mixed gas of argon and oxygen as a sputtering gas is superior to other film forming methods. There is a problem that high internal stress of the film is generated.

The cause of the stress of the film formed by the sputtering method is the peening effect, that is, the sputtering gas such as argon is taken into the film as an impurity,
It is thought to expand the volume of the membrane (Kanehara
"Sputtering phenomenon" (See p. 194, The University of Tokyo Press).

Therefore, it is effective to reduce the amount of argon taken into the film in order to reduce the volume expansion of the film, and a method using a high sputtering pressure has been reported as a concrete method (for example, CTWu, Th
in Solid Films 64,103 (see 1979).

However, this method cannot be said to be a desirable method from the viewpoint of the productivity of the device because the film forming rate of the silicon oxide film is remarkably reduced, and it has both low internal stress and high film forming rate. A method for forming a silicon oxide film is desirable. Therefore, an object of the present invention is to provide a silicon oxide thin film optical element having a high film forming rate, a low internal stress, and a large laminated thickness, and a manufacturing method thereof.

[0010]

Means for Solving the Problems In the present invention, a means for solving the above-mentioned problems is to use a silicon oxide film optical element having a silicon oxide film as a constituent film of an optical element used in a near infrared wavelength region, In the silicon film stack, at least hydrogen is contained in the film, and part or all of the hydrogen contained in the film forms a Si—H or SiO—H bond,
It is to reduce the internal stress of the film and stack them.

A second means of the present invention relates to a method for manufacturing a silicon oxide film optical element according to the first means, wherein a silicon oxide thin film is used as a sputtering gas using a mixture of argon and hydrogen as a sputtering target. That is, it is formed by sputtering using SiO ₂ .

Furthermore, a third means of the present invention is the method of manufacturing a silicon oxide film optical element according to the second means, wherein the temperature of the substrate is 400 ° C. or lower, and the silicon oxide film contains and contains at least hydrogen. That is, some or all of hydrogen forms Si—H or SiO—H bonds.

The present invention will be described in detail below. (1) Dependence of Hydrogen Gas Flow Rate Ratio on Stress and Deposition Rate of Silicon Oxide Film FIGS. 1 and 2 show the dependency of hydrogen gas flow rate ratio on the stress and deposition rate of the silicon oxide film manufactured by the present invention, respectively. . The film stress was measured by the general method of obtaining the warpage of the substrate before and after the film volume (LMMac and A. Reis).
man, J. Electrochem. Soc., 136, 3433 (1989)). The figure shows the compressive stress as a negative value according to the convention (the stress increases as the absolute value increases).

The experimental condition is that the sputtering gas flow rate is 120 SC.
CM, the sputtering gas pressure was 0.2 Pa, the sputtering power was 750 W, and the substrate was not heated. When an argon / hydrogen mixed gas is used as the sputtering gas, the stress decreases as the flow rate of hydrogen increases. On the other hand, in the conventional argon / oxygen mixed system, the dependency of the oxygen flow rate ratio on the stress is not observed.

Looking at the film forming rate under these conditions, the film forming rate decreases with the increase of the mixing flow rate in both hydrogen and oxygen mixed systems, but the rate of decrease of the film forming rate due to hydrogen addition is low. Comparing the absolute values of the film formation rates, in the case of the same flow rate ratio, the film formation rate of the hydrogen mixed system is about twice that of the oxygen mixed system. From these, it can be seen that the silicon oxide film formed by the sputtering method in the atmosphere of mixed gas of argon and hydrogen has a higher film formation rate and lower stress as compared with the conventional method.

(2) Dependence of sputtering power and sputtering pressure on stress of silicon oxide film The dependence of sputtering power and sputtering pressure on the stress of silicon oxide film was investigated. The results are shown in FIGS. 3 and 4, respectively.

The sputtering power dependence experiment was carried out by using a sputtering gas flow rate of 120 SCCM and a sputtering pressure of 0.2 P.
Under the condition of a, the hydrogen flow rate ratio was 20 and 40%. Moreover, the sputtering gas pressure dependence experiment is performed under the conditions of a sputtering gas flow rate of 120 SCCM, a sputtering power of 375 W, and a hydrogen flow rate ratio of 20%, and in any case, the substrate temperature is not heated.

From the figure, it can be seen that the internal stress of the silicon oxide film decreases almost linearly as the sputtering power decreases and the sputtering pressure increases.

(3) Substrate Temperature Dependence of Stress of Silicon Oxide Film The stress of the silicon oxide film was examined when the substrate temperature was changed from natural standing (no heating) to 450 ° C. Argon / hydrogen mixture ratio, sputtering power and sputtering pressure are 4: 1, 560 W and 0.2 P, respectively.
The value obtained by subtracting (thermal stress) fixed to a from the measured value is shown.

FIG. 5 shows the substrate temperature dependence of the stress of the silicon oxide film produced by this method. The stress values in the figure are
The stress (true stress) indicated by the film itself is plotted by subtracting the thermal stress due to the difference in the coefficient of thermal expansion between the substrate and the film. The figure shows that the true stress of silicon oxide tends to increase as the substrate temperature increases.
It can be seen that it is extremely high when manufactured at 0 ° C. Si contained in silicon oxide as the substrate temperature increases
It was confirmed by infrared absorption spectroscopy that the number of —H bonds decreased and that Si—H bonds were not formed in the film at a substrate temperature of 450 ° C. From these, it is considered that the increase in the true stress of the film is due to the decrease in the amount of hydrogen in the silicon oxide film.

[0021]

The silicon oxide film forms a Si-O-Si network structure. According to the present invention, however, a bond such as Si-H is formed in the network to disconnect the network, that is, to remove Si. By terminating the bond with hydrogen, the volume expansion of the film due to the Peening effect is relaxed.

As described above, the stress of the silicon oxide film of the present invention is reduced as compared with the conventional one. In order to investigate this cause, the amount of argon incorporated in the film was measured by the Rutherford backscattering (RBS) method, and the relationship between the film stress and the amount of argon in the film was investigated as shown in FIG.
White circles and black circles in the figure are data of films formed in an argon / hydrogen atmosphere and an argon / oxygen atmosphere, respectively. As previously reported, there is some correlation between the film stress and the amount of argon in the film, and the film stress tends to increase as the amount of argon in the film increases. However, there is a silicon oxide film which shows a low stress in FIG. 6 despite the large amount of argon in the film.
It is suggested that the stress of this sample cannot be explained only from the viewpoint of the amount of argon in the film.

In the infrared spectroscopic spectrum of the silicon oxide film of the present invention, all peaks due to the Si-H vibration mode were observed, and it was confirmed that the Si bond was partially terminated by hydrogen. The integrated intensity of Si-O Bending (S _Si-O ) and the integral intensity of Si-H Bending mode (S _Si- are used as indices for indicating how much Si in the Si-O-Si network is terminated by H. _H ) was used and expressed as {S _Si-H / S _Si-H + S _Si-O }.

When the relationship between this and the film stress is examined, a good linear relationship is obtained as shown in FIG. This indicates that the stress of this sample is largely related to the amount of hydrogen termination in addition to the amount of argon in the film, and the stress of the film decreases as the amount of hydrogen termination increases. That is, a major feature of the present invention is that hydrogen bond species such as Si—H bond are formed in the silicon oxide film.

Since the silicon oxide film of the present invention is applied to an optical element, its optical characteristics were measured. The silicon oxide film of the present invention shows no light absorption in the near-infrared region of 700 nm or more, and is a lossless material for transmitted light in this wavelength region and has the same refractive index as that of the conventional method. This was confirmed from the measurement of the transmission / reflection spectrum. This shows that the silicon oxide film of the present invention, even when used as a constituent film of an optical element, can exhibit exactly the same performance as an optical element using conventional silicon oxide.

[0026]

EXAMPLE As a practical example of the silicon oxide film optical element of the present invention, a laminated optical polarizing element was produced. This element is Ge
(4.5 nm) and a silicon oxide film (800 nm), and a Si film (1 nm) was inserted at the interface between the films in order to improve the adhesion between the films.

When a silicon oxide film according to the conventional method is used, a layer having a thickness of 300 μm or more cannot be formed. On the other hand, by using the silicon oxide film of the present invention, an element having a layer thickness of 500 μm can be manufactured.

The conditions for forming the silicon oxide film are as follows: Argon / hydrogen mixture ratio = 4: 1, sputtering power = 5.
60 W, sputtering pressure = 0.2 Pa, substrate temperature =
No heating.

The optical characteristics of this device at 850 nm are
Extinction ratio 51 dB, insertion loss 0.33 dB (element length 30 μ
m), and it was confirmed that the characteristics of the laminated polarizer produced using the conventional silicon oxide film were not different at all. In addition, since the film formation rate of the silicon oxide film under this condition is about twice as high as that of the conventional method, it is possible to reduce the manufacturing time of the element to about 1/2, which greatly increases the production efficiency. I was able to. This is because the manufacturing time of the device is almost equal to the film forming time of the silicon oxide film.

[0030]

As described above, according to the present invention,
Since the silicon oxide film optical element is laminated by including at least hydrogen in the film and forming a Si—H or SiO—H bond in a part of the silicon oxide film, the optical characteristics are good. Silicon oxide film can be laminated with low internal stress, the silicon oxide film can be laminated with a sufficiently large thickness, and the stacking speed can be shortened and the production efficiency can be improved. .

[Brief description of drawings]

FIG. 1 is a graph showing the dependency of a stress of a silicon oxide film on a flow rate ratio of an added gas.

FIG. 2 is a graph showing dependency of a silicon oxide film forming rate on an additive gas flow rate ratio.

FIG. 3 is a graph showing the dependence of silicon oxide film stress on sputtering power.

FIG. 4 is a graph showing the dependence of stress of a silicon oxide film on sputtering gas pressure.

FIG. 5 is a graph showing the substrate temperature dependence of the stress of a silicon oxide film.

FIG. 6 is a graph showing a relationship between argon in a silicon oxide film and film stress.

FIG. 7 is a graph showing the relationship between the Si-H system fraction in a silicon oxide film and the film internal stress.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G02B 6/13

Claims (3)

[Claims] 1. A silicon oxide film optical element having a silicon oxide film as a constituent film of an optical element used in a near-infrared wavelength region, wherein a silicon oxide film stack contains at least hydrogen and one of hydrogen contained therein. Part or all of Si-H or S
A silicon oxide film optical element characterized by forming an iO-H bond to reduce internal stress of the film and stacking. 2. A silicon oxide thin film optical element according to claim 1, wherein the silicon oxide thin film is formed by a sputtering method using a mixture of argon and hydrogen as a sputtering gas and SiO ₂ as a sputtering target. Method. 3. The temperature of the substrate is set to 400 ° C. or lower, and at least hydrogen is contained in the silicon oxide film, and part or all of hydrogen contained in the silicon oxide film forms Si—H or SiO—H bonds. Item 3. A method for manufacturing a silicon oxide film optical element according to Item 2.