JP2725442B2 - Method for producing composite oxide thin film and method for producing spatial light modulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a composite oxide thin film containing bismuth and silicon as main components, and a method for manufacturing a spatial light modulator used for an optical arithmetic device or a projection display. About.

2. Description of the Related Art A Pockels lead-out, which is a kind of spatial light modulator using the Pockels effect, using a single crystal substrate of bismuth silicon oxide (Bi ₁₂ SiO ₂₀ , hereinafter referred to as BSO) which is a photoconductive electro-optic crystal. Devices (hereinafter referred to as PROM devices) have been developed by researchers at Itek and applied to logic gates and image storage devices in optical arithmetic devices. Recently, application to a neural network circuit that performs input / output operations similar to those of the nervous system, for example, pattern recognition and associative memory, has begun to be studied.

FIG. 5 shows a cross-sectional structure of a conventional PROM element. An insulating layer 20 is formed on both sides of a surface-polished BSO single crystal substrate 19 having a thickness of several hundred μm.
Is a structure in which poly-p-paraxylylene is deposited to a thickness of about 5 μm, and ITO is deposited thereon as a transparent electrode 21 to a thickness of 200 nm.

The PROM element has both photoconductivity and Pockels effect, and writing of an image is performed by photoconductivity and reading is performed by Pockels effect. When light with image information is irradiated with a voltage applied to the PROM element, the BSO varies depending on the input light intensity due to the photoconductivity of the BSO.
Charge is generated in the single crystal, and the charge apparently reduces the voltage applied to the crystal. That is, the input image information is recorded as a voltage distribution in the crystal. Next, for reading the recorded image, the linearly polarized light is
When the light enters the PROM element, it becomes elliptically polarized light according to the applied voltage due to the Pockels effect. By installing an analyzer that is rotated 90 degrees to the polarization direction of the incident light on the output side, BS
The voltage distribution of the O crystal can be extracted in the form of a light intensity distribution.

In addition to the application as a PROM element described above, an application of a BSO to a spatial light modulation element having a threshold processing function in which a photoconductive layer and a liquid crystal layer are stacked has been proposed (Kuniharu Takizawa)
Proceedings of the 35th Annual Conference of the Japan Society of Applied Physics, Showa
Spring 63, 30P-ZF-3, 30P-ZF-4).

As described above, the conventional PROM element is manufactured using a BSO single crystal, but since a BSO single crystal is generally grown from a melt at about 900 ° C. by the Czochralski method, the crystal growth and substrate processing are complicated. Needs a process.

On the other hand, BS by the sputtering method generally used for film formation
O thin film formation is conceivable. Among them, the sputtering method using the electron cyclotron resonance plasma has a higher deposition rate because a larger amount of plasma can be extracted and a relatively high vacuum (10 ⁻⁵⁾ , compared with the conventional RF plasma sputtering method. Torr to 10 ^-4 Torr)
Since a high quality thin film can be formed with little incorporation of impurities, it can be applied to the formation of a BSO thin film.

Problems to be Solved by the Invention However, the above-described conventional configuration has the following problems.

First, using a target electrode composed of ceramics sintered by mixing their respective compositions, or an alloy or a piece of metal pieces composed of a number of different compositions, obtains a uniform and high-quality BSO thin film that can be used in PROM devices. Had the problem of being difficult.

That is, when a ceramic target electrode composed of two or more main components is sputtered by electron cyclotron resonance plasma to form a composite thin film, the composition of the surface of the target electrode is sometimes changed because the sputtering speed of each particle during sputtering is different. It changes every moment, which causes poor reproducibility of the composition ratio of the composite compound thin film. In addition, ceramic target electrodes generally have many impurities, and if these enter the film, they have problems such as generating defects and becoming an electron trap. Was.

Further, in the case of a target electrode in which an alloy or a large number of small metal pieces are bonded, there are problems such as difficulty in manufacturing the target electrode and variation in the in-plane composition ratio.

Furthermore, when manufacturing a PROM element, the thinner the BSO single crystal substrate, the higher the resolution of the element, but the thinner the mechanical strength decreases, the limit is about 200 μm, and the resolution is also 20 lp / mm (line pair). / mm) as low as BS
O When forming an insulating film on the surface of a single crystal substrate, it is once left in the air so that the surface is contaminated, pinholes and defects are formed in the insulating film, and dielectric breakdown occurs during driving. Was.

The present invention solves the above-mentioned conventional problems, and provides a method for producing a composite oxide thin film made of BSO having stable characteristics with good reproducibility, and a method for producing a spatial light modulator having excellent reliability. The purpose is to:

Means for Solving the Problems To achieve this object, a method for producing a composite oxide thin film according to the present invention is directed to an electron cyclotron resonance generated by introducing an arbitrary gas into a vacuum vessel and applying an electric field and a magnetic field. A method in which plasma is drawn into a target electrode to which an electric field is applied, and the target electrode is sputtered to form a thin film on a substrate held in the plasma, wherein the target electrode is a first electrode containing at least bismuth as a main component And a second electrode containing at least silicon as a main component, including a step of applying an independent electric field to each of the first and second target electrodes to perform sputtering, and forming at least bismuth and silicon as main components on a substrate. To form a composite oxide thin film.

Operation With this configuration, a target electrode having a single composition can be used, so that a composite oxide thin film having the same composition can be formed with good reproducibility. In addition, since a target electrode made of a high-purity metal can be easily used, contamination of the composite oxide thin film with impurities can be reduced, and a composite oxide thin film made of BSO with few defects and electron traps can be used more efficiently. Can be formed at speed. In addition, since an electric field is independently applied to each target electrode, the composition can be arbitrarily changed and material design can be easily performed. Further, even when applied to a PROM element or the like, since it is a thin film, there is no need for polishing, and an element with high resolution can be formed.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a schematic configuration diagram of a sputtering apparatus using electron cyclotron resonance plasma used in a method of manufacturing a composite oxide thin film in one embodiment of the present invention.

This sputtering apparatus is divided into a plasma chamber 1 and a sample chamber 2. The plasma chamber 1 is equipped with a microwave source of 2.45 GHz (not shown in the figure), and has a 0.0875 T or more required to satisfy electron cyclotron resonance conditions. Are generated. In the sample chamber 2, a support 5 for supporting a substrate 4, a target electrode sputtered by plasma, and gas inlets 6 and 7 are provided. The target electrode is a first electrode made of bismuth having a purity of 99.999% or more, which is connected to the first power supply 10.
99.999% connected to the second electrode 8 and the second power supply 11
It is composed of a second electrode 9 made of silicon having the above purity, and is arranged so as to surround the plasma outlet 12.

A method for forming a BSO thin film using this apparatus will be described below.

Evacuation is performed by a turbo pump and an oil rotary pump, and the degree of vacuum before forming the BSO thin film is 10 ^-5 to 10 ^-6 Torr. Argon and oxygen gas were introduced at a flow rate of 2 ml / min from the gas inlets 6 and 7, respectively, the degree of vacuum in the sample chamber 2 was adjusted to 10 ^-3 Torr by adjusting the pumping amount, and the microwave power was set to 300 W. , To generate plasma. Next, an arbitrary DC bias is applied from the first power supply 10 and the second power supply 11 to the first and second electrodes. The sputtering rates of the first and second electrodes are almost proportional to the applied DC bias.

In order to form a commercial-grade BSO thin film, it is necessary to make the chemical composition as close as possible to the stoichiometric ratio. However, according to the method of this embodiment, the sputter rates of the first and second electrodes are arbitrarily independent. Therefore, a high-quality thin film can be formed with good reproducibility. For example, when the applied voltage to the first electrode (bismuth) is fixed at 200 V and the applied voltage to the second electrode (silicon) is changed, the atomic ratio of silicon in the BSO thin film obtained by X-ray micro FIG. 2 shows the result of measurement by the analyzer. As shown in FIG. 2, the composition ratio can be easily controlled. In FIG. 2, the composition indicated by (a) is closest to the stoichiometric ratio of BSO, and the wavelength dependence of its photoconductive characteristics shows extremely good characteristics as shown in FIG.

Further, it was found that the electrical characteristics were further improved by annealing the obtained BSO thin film at a temperature of 400 ° C. or more in an atmosphere containing oxygen gas.

Example 2 Next, a method for manufacturing a spatial light modulator using a BSO thin film will be described below with reference to FIG.

A transparent electrode 14 made of ITO having a thickness of about 200 nm is formed on an insulating substrate 13 (for example, glass or the like) that transmits light by an electron beam evaporation method or the like. Next, using the sputtering apparatus shown in FIG. 1, argon and oxygen gas were introduced at a flow rate of 2 ml / min from the gas introduction ports 6 and 7, respectively.
The degree of vacuum in the sample chamber 2 is adjusted to 10 ^-3 Torr by adjusting the exhaust amount, and the power of the microwave is set to 300 W to generate plasma. Next, a DC bias of 300 V is applied only to the second power supply 11, and only the second electrode 9 made of silicon is sputtered to form an insulating film 15 made of silicon oxide (SiO ₂ ) with a thickness of about 1 μm. I do.

Next, without breaking the vacuum, the power of the microwave is 30
At 0 W, the first power supply 10 and the second power supply 11
By applying a DC bias of 0 V and 150 V, the first electrode 8 made of bismuth and the second electrode 9 made of silicon are simultaneously sputtered to form a BSO thin film 16 with a thickness of about 10 μm.

In addition, a second power supply 11 without breaking the vacuum
By applying a DC bias of 300 V to only the second electrode 9 and sputtering only the second electrode 9 made of silicon, an insulating film 17 made of silicon oxide (SiO ₂ ) is formed with a thickness of about 1 μm.

Finally, a transparent electrode 18 made of ITO having a thickness of about 200 nm is formed by an electron beam evaporation method or the like.

According to the method of the present invention, a spatial light modulator using BSO can be easily formed in the same vacuum. Also BS
The thickness of the O thin film is about 10 μm, which is about one tenth that when single crystal BSO is used, and a resolution of 100 lp / mm is possible.

Further, since the insulating film and the BSO thin film are formed in the same vacuum, the number of pinholes and defects is extremely small, the withstand voltage is greatly improved, and the reliability of the device is increased.

In the above-described embodiment, the same applies even when nitrogen gas is introduced from the gas inlet 7 at a flow rate of 2 ml / min instead of oxygen gas to form silicon nitride (Si ₃ N ₄ ) as the insulating films 15 and 17. The effect was obtained.

Effect of the Invention As described above, the present invention introduces an arbitrary gas into a vacuum vessel, draws an electron cyclotron resonance plasma generated by applying an electric field and a magnetic field to a target electrode to which an electric field is applied, and discharges the target electrode. The method uses a method in which a thin film is formed on a substrate held in plasma by sputtering, and the target electrode includes at least a first electrode containing bismuth as a main component and at least a second electrode containing silicon as a main component. And a method of manufacturing an excellent composite oxide thin film capable of forming a high-performance composite oxide thin film containing bismuth and silicon as main components on a substrate by applying sputtering while applying an independent electric field to the second electrode. Can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an electron cyclotron resonance plasma sputtering apparatus used in a method of manufacturing a composite oxide thin film according to one embodiment of the present invention, and FIG. FIG. 3 is a diagram showing the relationship between the atomic ratio of silicon in a BSO thin film, FIG. 3 is a typical photoconductive characteristic diagram of the BSO thin film of the present invention, and FIG. 4 is spatial light produced by one embodiment of the present invention. FIG. 5 is a sectional view of a modulation element, and FIG. 5 is a sectional view of a conventional PROM element. DESCRIPTION OF SYMBOLS 1 ... Plasma chamber (vacuum container), 2 ... Sample chamber (vacuum container), 4 ... Substrate, 5 ... Support base, 6, 7 ... Gas inlet, 8 ... First electrode, 9 ... ... second electrode, 10 ... first
Power supply, 11 ... second power supply.

Claims (3)

(57) [Claims] 1. An arbitrary gas is introduced into a vacuum vessel, an electron cyclotron resonance plasma generated by applying an electric field and a magnetic field is drawn into a target electrode to which an electric field is applied, and the target electrode is sputtered into the plasma. Using a method of forming a thin film on a held substrate, the target electrode is composed of at least a first electrode mainly containing bismuth and at least a second electrode mainly containing silicon;
A method of manufacturing a composite oxide thin film, comprising forming a composite oxide thin film containing at least bismuth and silicon as main components, including a step of performing sputtering while applying an independent electric field to each of the first and second electrodes. 2. The composite oxide thin film according to claim 1, wherein after forming a composite oxide thin film containing bismuth and silicon as main components on the substrate, annealing is performed at a temperature of 400 ° C. or more in an atmosphere containing oxygen gas. Manufacturing method. 3. An arbitrary gas is introduced into a vacuum vessel, an electron cyclotron resonance plasma generated by applying an electric field and a magnetic field is drawn into a target electrode to which the electric field is applied, and the target electrode is sputtered into the plasma. Using a method of forming a thin film on a held substrate, the target electrode is composed of at least a first electrode mainly containing bismuth and at least a second electrode mainly containing silicon;
Applying a voltage only to the second electrode to form an oxide or nitride containing at least silicon as a main component, and applying an independent electric field to the first and second electrodes, respectively; A step of forming a composite oxide containing at least bismuth and silicon as main components, and further applying a voltage only to the second electrode to form an oxide or nitride containing at least silicon as a main component A method for manufacturing a spatial light modulation element including a step.