JP4653391B2 - Manufacturing method of light control element - Google Patents

Description

  The present invention relates to a light control element using a dielectric thin film made of an electro-optic material or a nonlinear optical material.

  There are various methods for forming a thin film layer on a substrate, but a crystal growth technique is often used to form a high-quality thin film layer. In the crystal growth technique, it is possible to control the film thickness with high accuracy and to form different materials with multilayer films. However, in order to form a high-quality thin film layer, the lattice constant between the substrate to be grown and the thin film material needs to be close, and the existence and establishment of stable growth conditions is necessary, and the materials for growth are limited. This hetero-growth can only be used with limited materials.

  In crystal growth in the case of a semiconductor, it is possible to form an AlGaAs thin film layer on a GaAs substrate by crystal growth technology, but it is difficult to form AlGaAs on a semiconductor substrate having a different lattice constant. It is even more difficult to form on a substrate such as no glass. In addition, a lithium niobate thin film used as an electro-optic or nonlinear optical material can be formed by a high-frequency sputtering method or the like, but these generally used methods have a large electro-optic constant that is important for optical applications. It is extremely difficult to form a high-quality thin film having a nonlinear optical constant or the like.

  Although lithium niobate has excellent characteristics as an electro-optic material or a nonlinear optical material, Patent Document 1 describes a liquid phase growth method as a method for forming a high-quality lithium niobate thin film on a different material. . This is a method of forming a lithium niobate single crystal thin film on a lithium tantalate substrate by liquid crystal growth. By manipulating the growth conditions, lattice matching between the lithium niobate thin film and the lithium tantalate substrate is realized, and the thin film can be formed. However, since it is necessary to match the lattice for thin film growth, the selection range of the substrate is extremely narrow, and it is required that the material is almost the same series. Lithium niobate thin film doped with manganese oxide on the lithium niobate substrate The growth of this is to the extent that it has been put to practical use.

With respect to semiconductors, as a technique for forming a thin film layer of silicon, there is a smart cut method which is a method for manufacturing an SOI (Silicon on insulator) substrate, which is described in Patent Document 2, for example. In this method, hydrogen ions are implanted into an oxidized silicon wafer to form a microbubble layer inside the wafer. Thereafter, the ion-implanted surface of the silicon wafer into which the ions are implanted is brought into close contact with another silicon wafer through an oxide film, and a heat treatment of 500 ° C. or more is applied to separate the wafer into a thin film to form an SOI substrate. A method is described. Since the substrate from which the thin film has been separated can be reused in a similar process after the surface treatment, mass production considering cost can be performed without wasting the substrate. However, in this method, in order to increase the adhesive strength between the SiO ₂ layers, a bonding heat treatment is actually performed at 1100 degrees. Therefore, a substrate having strong adhesive strength cannot be formed unless the material can withstand this bonding heat treatment. In addition, a method of bonding silicon and SiO ₂ without using an SiO ₂ layer is also possible. However, since there is no strong bonding due to high temperature, the interface between the thin film silicon layer and the thin film silicon layer is reduced when the temperature is returned to room temperature. In other words, stress is generated in the parallel direction, and the strength of the joint surface and the crystal quality of the interface cannot be maintained.

Patent Document 3 proposes a method for forming a photonic crystal on a GaAs thin film by bonding a compound semiconductor made of GaAs and SiO ₂ instead of silicon as a semiconductor. A GaAs layer having an etch stop layer formed of InGaAs or the like is formed by a crystal growth technique, and a SiO ₂ layer is formed on the surface thereof. The wafer is bonded through the SiO ₂ layer, the substrate side is etched to the etch stop layer by wet etching, and finally the etch stop layer is etched to form a GaAs thin film layer. In this method, it is necessary to form a required GaAs layer with high quality after forming the etch stop layer. For compound semiconductors, epitaxial growth techniques such as metal organic vapor phase epitaxy have been established and can be formed relatively easily. However, it is not possible to form such an etch stop layer for materials other than semiconductors. Material is limited. In addition, this method is a substrate manufacturing method in which, if wet etching is performed up to the etch stop layer, all the substrates up to that portion are wasted, and mass production is difficult. In addition, the etching stop layer itself needs to produce crystals of materials with considerably different characteristics. However, unlike the case of semiconductor GaAs or silicon, it is difficult to form a good etching stop layer by crystal growth in the case of a dielectric material made of an electro-optic material or a nonlinear optical material.

  On the other hand, Patent Document 3 describes a multilayer substrate having a plurality of silicon layers having a photonic crystal structure by using an SOI substrate and laminating them by thermocompression bonding. However, even when a plurality of silicon layers are produced on this multilayer substrate, it is fundamental to remove the SiO2 layer by etching, and it is necessary to form an etching stop layer, and a dielectric made of an electro-optic material or a nonlinear optical material. It is difficult to apply in the case of materials.

Japanese Patent No. 2893212 Japanese Patent No. 3048201 JP 2000-232258 A

  As described above, dielectric substrates made of electro-optic materials or nonlinear optical materials are often difficult to grow thin-film crystals, and are difficult to degrade crystal quality due to high-temperature heating and to form a sacrificial layer. . Therefore, since none of the above methods can be used, it is extremely difficult to stably mass-produce thin film layers of these materials on materials having different lattice constants by hetero-growth. For this reason, it is difficult to fabricate a light control element using a thin film using these by either direct heterogrowth or heterogrowth of an etching stop layer.

  A first object of the present invention is to provide a light control element that is highly functional and economical.

  A second object of the present invention is to provide a light control element having a uniform thin film thickness and small element variation.

  A third object of the present invention is to provide a light control element that has a high yield at the time of bonding and at the same time has a high fine shape accuracy.

  A fourth problem of the present invention is to provide a light control element that has a very high fine shape processing and thereby has high wavelength accuracy.

  The fifth object of the present invention is to provide a light control element in which the thickness of the thin film is further uniform and the loss due to scattering is small.

  The sixth problem of the present invention is to reduce the optical characteristics of the dielectric thin film material by heat and to make it more efficient, so that the stress caused by the stress caused by the difference in thermal expansion coefficient of different materials at the same time is small and low power consumption. It is an object of the present invention to provide a light control element that can reduce dielectric thin film breakage and optical function reliability degradation.

  The seventh problem of the present invention is to increase the bonding force between different materials, and at the same time, reduce the dielectric thin film breakage due to the stress caused by the difference in the thermal expansion coefficient of the dielectric material, and reduce the reliability of the optical function. It is to provide a light control element.

  An eighth object of the present invention is to provide a light control element having a light control element that has a higher function, a smaller size, and lower power consumption by enhancing the electro-optic effect or the nonlinear effect.

  The ninth problem of the present invention is that the non-linear effect is enhanced by delaying the group velocity at the same time as making the steep propagation light deflection by the photonic band effect. It is to provide a light control element.

  A tenth problem of the present invention is to provide a light control element capable of combining light control effects.

One form of the present invention is a manufacturing method of an optical control device having a dielectric thin film made of a supporting lifting the substrate and the electro-optic material or non-linear optical material, an ion implantation separation layer by implanting ions into the dielectric substrate A separation layer forming step to be formed; a bonding step of bonding a surface of the dielectric substrate into which ions are implanted; and the ion implantation separation layer so that the remaining dielectric substrate becomes the dielectric thin film. A separation step of separating and removing a part of the dielectric substrate at the portion, and a light control structure forming step of forming a light control structure on the dielectric substrate between the separation layer forming step and the bonding step ; A method for manufacturing a light control element comprising: Another embodiment of the present invention is a method of manufacturing a light control element having a support substrate and a dielectric thin film made of an electro-optic material or a non-linear optical material, and ion implantation is performed by implanting ions into the dielectric substrate. A separation layer forming step of forming a layer; a bonding step of bonding the surface of the dielectric substrate into which ions are implanted; and the ion implantation so that the remaining dielectric substrate becomes the dielectric thin film. A separation step of separating and removing a part of the dielectric substrate at a separation layer portion; and a light control structure formation step of forming a light control structure on the dielectric substrate before the separation layer formation step. This is a method for manufacturing a light control element.

After the previous SL separation step may be facilities polished on the dielectric the dielectric surface of the thin film part is formed separately removal of the substrate.

Before SL bonding step may also contains I ion irradiation treatment or plasma irradiation treatment to said substrate surface in a vacuum.

Before SL bonding step, said prior to the separation layer forming step, the supporting substrate and the step of forming the bonding layer on the surface to be bonded to each other with the dielectric film may also do free.

Before Symbol light control structure formation step, a light control structure may be formed a channel type optical waveguide structure.

Before Symbol light control structure formation step, a light control structure may be formed a photonic crystal structure.

After the previous SL separation step, by implanting ions into another dielectric substrate ion implantation and the second separation layer forming step of forming a separation layer, the said further dielectric ions have been implanted face of the substrate support A second bonding step for bonding to the dielectric thin film already formed on the substrate; and the other dielectric substrate at the ion implantation separation layer so that the remaining dielectric substrate becomes the dielectric thin film. A multi-layering process including a second separation process for separating and removing a part of the body substrate may be executed once or a plurality of times .

  The invention according to claim 1 can provide a light control element that is highly functional and excellent in economy when light control is performed by a dielectric thin film made of an electro-optic material or a non-linear optical material.

According to the first aspect of the present invention , the light control structure is formed before the ion implantation separation layer is provided. When the light control is performed by a dielectric thin film made of an electro-optic material or a nonlinear optical material, the light control structure is highly functional. It is possible to provide a light control element that is excellent in economic efficiency, has a high yield at the time of bonding, and has a high fine shape accuracy.

In the invention according to claim 2 , the light control structure is formed before separation of the dielectric thin film after the ion implantation separation layer, and light control is performed by a dielectric thin film made of an electro-optic material or a nonlinear optical material. In addition, it is possible to provide a light control element with high function and economy, and at the same time having a very high fine shape processing, and thereby high wavelength accuracy.

According to the third aspect of the present invention, when light control is performed by a dielectric thin film made of an electro-optic material or a non-linear optical material, it is highly functional and economical, and at the same time, the thickness of the thin film is more uniform and due to scattering. A light control element with small loss can be provided.

In the invention according to claim 4, when optical control is performed with a dielectric thin film made of an electro-optic material or a non-linear optical material, it is highly functional and economical, and at the same time, optical characteristics due to heat of the dielectric thin film material are reduced. It is possible to provide a light control element that is small in size and low in power consumption through higher efficiency, and at the same time reduces damage to the dielectric thin film due to the stress caused by the difference in thermal expansion coefficient between different materials and reduced optical function reliability. it can.

In the invention of claim 5, when performing light control with a dielectric thin film made of an electro-optic material or a non-linear optical material, it is highly functional and economical, and at the same time increases the bonding force between different materials, It is possible to provide a light control element in which the dielectric thin film breakage due to the stress caused by the stress caused by the difference in the thermal expansion coefficient of the dielectric material and the reliability of the optical function are reduced.

According to the sixth aspect of the present invention, when light control is performed by a dielectric thin film made of an electro-optic material or a non-linear optical material, it is highly functional and excellent in economic efficiency, and at the same time, confines the light in the horizontal direction of the propagation light. By performing the electro-optic effect or the non-linear effect, it is possible to provide a light control element having a light control element that has higher functionality, smaller size, and lower power consumption.

According to the seventh aspect of the present invention, when optical control is performed by a dielectric thin film made of an electro-optic material or a non-linear optical material, it is highly functional and economical, and at the same time, a steep light propagation light due to the photonic band effect. At the same time as the deflection, by delaying the group velocity and enhancing the nonlinear effect, it is possible to provide a light control element that has a higher function and a smaller size and lower power consumption.

The invention according to claim 8 provides a light control element capable of combining a light control effect while at the same time being highly functional and economical when performing light control with a dielectric thin film made of an electro-optic material or a non-linear optical material. can do.

[First Embodiment (Embodiments of the Inventions of Claims 1 and 5)]
A first embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic diagram showing a method for manufacturing a light control element as a first embodiment of the present invention.

As shown in FIGS. 1A and 1B, in this embodiment, a dielectric substrate (hereinafter referred to as substrate A) made of an electro-optic material or a nonlinear optical material and a support substrate (hereinafter referred to as substrate B) serving as a base. ) To form the light control element 101. As steps for that purpose, the present embodiment includes a separation layer forming step, a bonding step, a separation step, and a polishing step.
(1) Separation Layer Formation Step As shown in FIG. 1 (c), rare gas ions are implanted by ion implantation to form an ion implantation separation layer 201 inside the wafer. For example, in the case of lithium niobate, an ion implantation separation layer 201 is formed in a portion having a thickness of about 1 μm at an acceleration voltage of 500 kV and an ion concentration of 5 × 10 ¹⁶ [1 / piece] in the ion implantation of helium ion gas ( The line with x in the figure indicates the ion implantation separation layer 201). Since this value varies depending on the characteristics of the material, it must be optimally controlled. The implantation depth can be controlled by changing the acceleration voltage of ions. When the implantation depth is as deep as several μmm or more, the acceleration voltage needs to be large, and a large apparatus is required, but when a dielectric substrate made of an electro-optic material or a nonlinear optical material is used as the light control element 101, Since the ion implantation separation layer 201 may be as thin as about 1 μm or 1 μm or less in order to function as a waveguide, the implantation depth that is the depth of the ion implantation separation layer 201 may be thin. For this reason, the implantation energy is small. In the case where a three-layer flat optical waveguide is formed by sandwiching a lithium niobate thin film between upper and lower substrates with SiO ₂ , the thickness of the core layer that gives a single mode in which the optical signal can be easily controlled, that is, the thickness of the lithium niobate layer The length is about 0.5 μm for an electrical transverse wave and a magnetic transverse wave for a wavelength of 1.3 μm. Since a film thickness of 0.5 μm is sufficient, a high acceleration voltage is not required, and ion implantation with an acceleration voltage of 1 MeV or less that is relatively easy to control becomes possible. The ion implantation separation layer 201 by ion implantation may be subjected to ion diffusion by heat treatment to change the implantation depth and ion concentration. In the on implantation, other rare gas ions may be used instead of helium gas or ions other than the rare gas may be used depending on the material.
(2) Bonding Step Next, as shown in FIG. 1D, the substrate A and the substrate B are bonded so that the ion implantation surface of the substrate A is in contact. For the bonding, the substrate A and the substrate B can be firmly bonded at the atomic level by using an anodic bonding method, a heat bonding method, or the like. The light control element 101 using a dielectric substrate made of an electro-optic material or a non-linear optical material requires bonding at a temperature at which the optical characteristics of the dielectric material do not change. Since optical properties of lithium niobate may deteriorate due to phase change at 700 ° C. or higher, it is necessary to set the bonding temperature within 600 ° C. when bonding lithium niobate and SiO ₂ .

Further, when different types of materials are directly joined by joining with heating, the joining surface is deteriorated due to the stress when cooled due to the difference in thermal expansion coefficient. In the combination of lithium niobate and SiO ₂ , the thermal expansion coefficients of the two materials are almost the same. Therefore, heat bonding at a high temperature within a range where the optical properties of lithium niobate do not change is possible. However, in the case of a combination of other materials, it is necessary to consider a decrease in reliability due to thermal stress with respect to the bonding temperature.
(3) Separation process As shown in FIG. 1 (e), by heating the bonded substrate simultaneously with the previous process or as the next process, the substrate is peeled off from the separation surface in the dry process, and the electro-optic material or A thin film structure having a film thickness of about 1 μm can be formed by a dielectric substrate made of a nonlinear optical material. In the lithium niobate substrate, the dielectric thin film 301 which is an optical thin film of the dielectric substrate can be separated from the dielectric substrate by the ion implantation separation layer 201 by heating at 400 ° C. or higher. At this time, when different types of materials are directly bonded, stress is generated in the ion implantation separation layer 201 at the same time as stress is generated on the bonding surface during heating due to the difference in thermal expansion coefficient. This stress is one of the driving forces when the substrate is peeled off from the ion implantation separation layer 201. Therefore, the temperature, speed, and time of heating are controlled while reducing the decrease in reliability at the bonding surface. It is preferable to optimize the stress in the ion implantation separation layer 201. Further, as shown in FIG. 1, since the substrate B is bonded to the substrate A in advance and then peeled off from the ion implantation separation layer 201, the separated very thin dielectric thin film 301 is broken by the stress at the time of separation, It is reduced that it is destroyed by the force applied in the subsequent process. For this reason, compared with the case where the ion implantation separation layer 201 is formed on a dielectric substrate made of an electro-optic material or a nonlinear optical material and heated to form the dielectric thin film 301, the ion implantation separation is performed near the junction. In the case where the layer 201 is present, the dielectric thin film 301 having a uniform and few defects can be formed.
(4) Polishing process The dielectric thin film 301 separated by the process of FIG. 1 (e) has the ion-implanted depth and the non-uniformity of the ion accelerating voltage at the time of ion implantation and the defects and non-uniformity of the crystal serving as the substrate. The concentration varies, and as a result, the surface and thickness of the dielectric thin film 301 may be non-uniform. However, as shown in FIG. 1 (f), the surface roughness and thickness of the dielectric thin film 301 are reduced by reducing the number of defective portions while simultaneously smoothing the thin film surface by polishing or chemical treatment. At the same time as reducing optical loss due to unevenness, it is possible to reduce long-term deterioration of optical characteristics. In particular, when light is propagated in the in-plane direction of the dielectric thin film 301, the loss can be reduced, which is very effective. As the polishing process, a method such as CMP (Chemical Mechanical Polishing) or laser processing may be used other than normal optical polishing.

  Since the light control element 101 shown in FIG. 1 is different from the conventional method of forming the dielectric thin film 301 on the support substrate using the etching stopper layer, an etching stopper layer having a large etching selectivity is formed by hetero-growth or post-processing. Even for materials that cannot be formed, the dielectric thin film 301 made of a dielectric material made of an electro-optic material or a non-linear optical material can be easily formed on the support substrate. As a result, light is propagated through the dielectric thin film 301 to cause the electro-optic effect or the non-linear optical effect to act on the propagating light, whereby the directional coupling as the light control element 101 by the refractive index difference using conventional ion diffusion is performed. Devices, Mach-Zehnder interferometers, wavelength conversion elements, diffraction gratings, optical routing elements using these, optical modulators, DEMUX / MUX elements, laser oscillation elements, etc. are much smaller and have higher performance than before. Can be realized. Furthermore, they use a very small amount of dielectric material made of electro-optic material or non-linear optical material as the dielectric thin film 301 on the supporting substrate, and the dielectric substrate itself can be reused many times to form a dielectric material. Since the thin film 301 can be separated, almost no dielectric material consisting of expensive electro-optic material or nonlinear optical material is consumed, so that it is very economical and suitable for mass production.

  In the invention of the present embodiment, the substrate A is a dielectric substrate made of an electro-optic material or a nonlinear optical material. Examples of the dielectric material made of this electro-optic material or nonlinear optical material include lithium niobate and niobate. Use inorganic optical crystals such as titanium, KTP, KDP, and SBN (strontium niobium barium acid), optical ceramics such as PZT and PLZT, or materials having organic molecules such as azo dyes, stilbene dyes, and DAST, or organic optical crystals. be able to. In addition, these materials have large electro-optic constants and nonlinear constants compared to semiconductors, but their physical properties are significantly different from those of semiconductors, and even if the bulk refractive index is high, it is about 2.5. The refractive index is smaller than 3, and the material to be bonded is preferably a low refractive index material in order to confine light. In order to generate the electro-optic effect, it is necessary to provide an electrode in the vicinity of the dielectric thin film 301 in order to apply an electric field. However, since it is not a semiconductor, it is used as an electrode by being bonded to a semiconductor or metal. Driving with a low voltage can be realized by forming an electrode between the gaps.

[Second Embodiment (Embodiment of the Invention of Claim 2)]
A second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are denoted by the same drawings and the same reference numerals, and the description thereof is also omitted (the same applies hereinafter).

  FIG. 2 is a schematic diagram showing a method for manufacturing the light control element 101 as the second embodiment of the present invention.

  As shown in FIG. 2C, an ion implantation separation layer 201 is formed by ion implantation on a substrate A made of an electro-optic material or a nonlinear optical material.

  Thereafter, as shown in FIGS. 2D and 2E, the substrate B and the substrate A of different materials are joined, heated, and peeled off by the ion implantation separation layer 201, whereby an electro-optic material or a nonlinear material is obtained. An optical substrate on which the light control element 101 is formed can be formed with a thin film structure having a thickness of 1 μm or less.

  Next, as shown in FIG. 2F, the thin film surface is smoothed by polishing or chemical treatment. On the substrate A from which the thin film has been separated, there are irregularities in the pattern when the optical element is formed. Therefore, the irregularities are removed by polishing or chemical treatment and reused.

  Then, as shown in FIG. 2G, a light control structure 401 to be the light control element 101 is formed (light control structure forming step). The light control structure 401 is formed by lithography and etching used in a semiconductor process. A photosensitive resist is attached to the ion-implanted lithium niobate substrate A by spin coating, and after covering with a mask, the optical element is patterned by light irradiation and development. Thereafter, the resist is used as a mask by dry etching with a chlorofluorocarbon gas and transferred to a lithium niobate substrate. At this time, etching is performed up to the ion-implanted separation layer 201 into which ions have been implanted. Thereafter, the resist is removed and the surface is washed to form the substrate A on which the dielectric thin film 301 is patterned as the light control structure 401.

  A light control structure 401 in FIG. 2 is a light propagation structure formed by fine processing of about 1/10 of a wavelength to processing of a size of about several centimeters. Processing in the direction perpendicular to the surface of the body thin film 301 is shown. A periodic structure is provided on the dielectric thin film 301 to form a diffraction grating type optical coupling element, a vertical mirror is formed to form a deflecting element or a condensing lens, and a waveguide is also produced. By forming a light control structure 401 capable of propagating light in the dielectric thin film 301 due to a fine structure, and forming means for imparting an electro-optic effect or a nonlinear optical effect to the dielectric thin film 301, light modulation, High-performance optical control such as optical routing and wavelength conversion can be performed.

  In FIG. 2, ion implantation is performed on a smooth surface subjected to optical polishing or chemical treatment to form an ion implantation separation layer 201, and then a light control structure 401 is formed, so that ion implantation can be performed uniformly, In addition, since the heating for separation and the stress accompanying the heating can be applied uniformly, the light control element 101 having a uniform thickness of the dielectric thin film 301 separated on the support substrate and small element variations can be provided. .

[Third Embodiment (Embodiment of Invention of Claim 3)]
A third embodiment of the present invention will be described with reference to FIG.

  FIG. 3 is a schematic view showing a method for manufacturing the light control element 101 as the third embodiment of the present invention.

  As shown in FIG. 3C, a light control structure 401 as shown in FIG. 3D is formed on a substrate in which an ion implantation separation layer 201 is formed by ion implantation on a substrate A of an electro-optic material or a nonlinear optical material. (Light control structure forming step). The light control structure 401 can be formed using lithography and etching used in a semiconductor process.

  A photosensitive resist is attached to the ion-implanted lithium niobate substrate A by spin coating, and after covering with a mask, the optical element is patterned by light irradiation and development. Thereafter, the resist is used as a mask by dry etching with a chlorofluorocarbon gas and transferred to a lithium niobate substrate. At this time, etching is performed up to the ion-implanted separation layer 201 into which ions have been implanted.

  Thereafter, the patterned substrate A can be formed by removing the resist and washing the surface.

  Then, as shown in FIGS. 3E and 3F, the substrate B and the substrate A made of different materials are bonded, heated, and the substrate is peeled off by the ion implantation separation layer 201. An optical substrate in which the light control structure 401 is formed with a thin film structure having a thickness of 1 μm or less can be formed. Next, as shown in FIG. 3G, the light control element 101 is formed by smoothing the surface of the thin film by polishing or chemical treatment.

  In FIG. 3, since the light control structure 401 is formed on the dielectric substrate provided only with the ion implantation separation layer 201, the light control structure 401 is directly formed on a good substrate surface close to a smooth surface subjected to optical polishing or chemical treatment. Since the light control structure 401 having a fine structure is formed, the fine structure can be uniformly formed, and at the same time, the resolution of patterning by light or an electric field can be improved. It is also possible to form a fine structure. As a result, the uniformity of the light control structure 401 is improved when used as the light control element 101, so that the applied wavelength accuracy as the light control element 101 is improved and a fine shape is also possible, thereby improving the light utilization efficiency. You can also Further, since the ion implantation is performed in advance before the formation of the light control structure 401, the light control element 101 having a uniform thickness of the dielectric thin film 301 separated on the support substrate and small element variations is provided. You can also

[Fourth Embodiment (Embodiment of Invention of Claim 4)]
A fourth embodiment of the present invention will be described with reference to FIG.

  FIG. 4 is a schematic view showing a method of manufacturing the light control element 101 as the fourth embodiment of the present invention.

  As shown in FIG. 4C, a light control structure 401 is formed by lithography and etching on a substrate A made of an electro-optic material or a nonlinear optical material (light control structure forming step).

  Thereafter, the wafer surface is cleaned, and an ion implantation separation layer 201 is formed on the substrate A by ion implantation, as shown in FIG.

  Then, as shown in FIG. 4 (e), the patterned substrate surface and the substrate B made of a material different from the substrate A are joined, and as shown in FIGS. 4 (f) and 4 (g). Then, the patterned thin film layer is separated by heating and polishing.

  In FIG. 4, since the light control structure 401 is formed directly on a smooth surface that has been optically polished or chemically processed without any ion implantation or the like, the light control structure 401 is formed. In addition, the fine structure can be uniformly formed with high definition, and at the same time, the resolution of patterning by light or an electric field can be improved, so that a further fine structure can be formed. As a result, the uniformity of the light control structure 401 is improved when used as the light control element 101, so that the applied wavelength accuracy as the light control element 101 is improved and a fine shape is also possible. You can also improve. However, since the ion implantation is performed after the formation of the light control structure 401, the light control structure 401 undergoes shape deformation by the ion implantation and the separation process associated therewith. Therefore, the light control structure 401 corresponding to the shape deformation is manufactured in advance. Therefore, since the device design is slightly restricted, it is necessary to optimize the light control structure 401 in advance for the ion implantation process in the subsequent process.

  FIG. 5 is a schematic view showing a method for manufacturing the light control element 101 as a reference example of the present invention. In FIG. 5, a bonding portion is provided between a substrate A, which is a dielectric substrate made of an electro-optic material or a nonlinear optical material, and a substrate B, which is a support substrate, and a part of the dielectric substrate is polished by a polishing process. As an example, a substrate B as the support substrate and a dielectric thin film 301 substrate made of the dielectric thin film are formed.

  In FIG. 5, as shown in FIG. 5C, a substrate A made of an electro-optic material or a nonlinear optical material and a substrate B made of a material different from the substrate A are joined, and the joining surface of the substrate A is The opposite side is thinned by polishing (FIG. 5D) and surface-treated (FIG. 5E) to form a thin film substrate.

  In FIG. 5, since an ion implantation process is necessary, it is difficult to manufacture by the ion implantation method shown in FIGS. 1 to 4, or the dielectric thin film 301 or the support substrate is damaged by the ion implantation, and the function is deteriorated. In this case, a thin film layer having a thickness of several μm can be manufactured. 5 can be combined with the steps in FIGS. 1 to 4 to form a dielectric thin film 301 made of an electro-optic material or a nonlinear optical material with respect to various materials. In the polishing process, it is effective to form a smooth surface by using a method by CMP (Chemical Mechanical Polishing) in addition to normal optical polishing.

[Fifth Embodiment (Embodiment of the Invention of Claim 6)]
A fifth embodiment of the present invention will be described.

In FIGS. 1 to 4, after the surface activation treatment, the substrates are bonded to each other at a normal temperature or a low temperature, thereby reducing the optical characteristics due to the heat of the dielectric thin film material and increasing the efficiency. Can provide the light control element 101 that is small in size and low in power consumption, and at the same time, reduced in the dielectric thin film damage due to the stress caused by the stress caused by the difference in thermal expansion coefficient of different materials and reduced in optical function reliability. It is effective. The surface activation treatment here means that the substrate is irradiated with an atom, ion beam or plasma beam in a vacuum. As a result, the natural oxide film on the surface of the substrate is removed, the bonding state of atoms is activated, and dangling bonds are generated. After that, before joining again, the wafers are bonded together in a vacuum to realize bonds between atoms that have generated bonds at the atomic level. Since the degree of vacuum affects the amount of recombination of oxygen, an ultrahigh vacuum is preferable, but it may be about 1 × 10 ⁻⁷ Torr. With this method, it is possible to bond many materials such as metal and dielectric, polymer dielectric and inorganic dielectric, and the like.

As a result, by bonding different materials without heating or with a low temperature rise due to heating, it is possible to avoid peeling due to a difference in thermal expansion coefficient or deterioration of optical characteristics due to stress. In particular, since the thin film formed is extremely thin with a thickness of 1 μm or less, damage to the joint surface due to a difference in expansion coefficient is a big problem. If the thermal expansion coefficients are almost the same as in the case of lithium niobate and SiO _2, the difference in thermal expansion coefficient is not affected, but in the combination of ordinary dissimilar materials, the thermal expansion coefficient is inconsistent. At the same time, the optical characteristics are deteriorated by increasing the temperature, so that the optical characteristics of the optical material can be minimized. Furthermore, in the present invention, by combining this surface activation treatment on the substrate, it becomes possible to form a sandwich structure of a metal electrode, a dielectric, an electro-optic material, a dielectric, and a metal electrode with a width of several μm. Application can be performed with high efficiency, and an ultra-compact light control element 101 with low power consumption can be realized.

[Sixth Embodiment (Embodiment of the Invention of Claim 7)]
A sixth embodiment of the present invention will be described with reference to FIG.

  FIG. 6 is a schematic view showing a manufacturing method of the light control element 101 as the sixth embodiment of the present invention.

  As shown in FIG. 6C, the substrate B, which is a dielectric substrate made of an electro-optic material or a nonlinear optical material, and the substrate A, which is a support substrate, are made of different materials from the original substrates A and B, respectively. The bonding layer 501 is formed using the same material. The bonding layer 501 is made of a material that can bond to each other even at a low temperature. Thereafter, as shown in FIG. 6D, ion implantation separation layer 201 is formed by performing ion implantation only on substrate B which is a dielectric substrate made of an electro-optic material or a nonlinear optical material. Then, as shown in FIG. 6E, the bonding layers 501 provided on the substrates A and B, each of which is a substrate B which is a dielectric substrate on which the ion implantation separation layer 201 is formed and a substrate A which is a support substrate. Join with. Thereafter, as shown in FIG. 6 (f), the dielectric is partially separated from the ion implantation separation layer 201 by heating. Then, as shown in FIG. 6G, the surface is polished to form a dielectric thin film 301 containing a dielectric on a substrate A that is a support substrate.

  In bonding a dielectric substrate (substrate B) made of an electro-optic material or a non-linear optical material, even if the temperature can be raised and the substrate can be firmly joined, in order to function as the light control element 101, an electric property is changed by a change in optical characteristics due to a phase change. The temperature cannot be increased to a temperature at which the optical effect or the nonlinear optical effect is reduced. However, as shown in FIG. 6, a material that can be bonded even at a low temperature is formed in advance as a bonding layer 501 on each of the substrates A and B or one of the substrates A or B, so A simple bonding interface can be obtained. As a method for forming the bonding layer 501, a method such as vapor deposition, high-frequency sputtering, spin coating, vapor phase epitaxial growth, liquid phase epitaxial growth, or the like is performed in advance on one or both of the substrates A and B before bonding. It is formed by. Thereafter, the substrates A and B can be bonded directly, or can be bonded by heating within a range in which the optical characteristics do not change when they are in close contact with each other. With this method, it is not necessary to perform room temperature bonding in a vacuum, and the manufacturing method is simple. In addition to the optical material, optical crystal, and polymer material, it is also effective to use a material that solidifies at the evaporation temperature of water, such as water glass, as the bonding layer 501 as the material of the bonding layer 501.

[Seventh Embodiment (Embodiment of Invention of Claim 8)]
A seventh embodiment of the present invention will be described.

  In addition to the upper and lower confinement with respect to the substrate having a thin film structure as the dielectric thin film 301 on the support substrate (substrate A), a channel-type optical waveguide in which the left and right sides are completely separated from each other is configured. A structure that strongly confines light in a three-dimensional manner is very effective when light control is performed by an electro-optic effect or a nonlinear optical effect. This is because the propagation light is confined in the channel type optical waveguide, so that very strong light intensity can be propagated per volume, and at the same time, the effect is greatly increased by applying a voltage to the left and right sides of the channel type optical waveguide. can do. Also, optical waveguide branching structure formed by channel type optical waveguide, dispersion compensation structure by grating, wavelength filter, directional coupler, optical modulator and optical switch by Mach-Zehnder interference, wavelength conversion element using nonlinear effect Optical devices such as optical devices, optical circuits, and optical integrated circuits that combine them can be constructed, and at the same time, the refractive index difference can be increased, so that the curvature of the waveguide can be increased. realizable.

  In order to form an optical waveguide on a dielectric substrate (substrate B) made of an electro-optic material or a non-linear material by conventional techniques, in the case of lithium niobate, the refractive index is slightly increased by diffusing titanium. The optical waveguide was formed with this portion as the core and the other low refractive index portions as the cladding. However, since the refractive index change is slight, the curvature of the waveguide cannot be increased, and the light control element 101 has to be increased. Since the substrate surface was flat, voltage could not be applied effectively only to the small core part, and voltage was also applied to part of the cladding at the same time, and the operating voltage had to be increased accordingly. there were. However, in the present invention, since the channel waveguide is formed using a dielectric thin film made of an electro-optic material or a nonlinear material, it is easy to increase the bending rate. Furthermore, since the present invention can also control the thickness of the dielectric thin film 301, it is also possible to control the confinement in the vertical direction, the confinement of strong light intensity in a single mode is possible, and the electro-optic effect and the nonlinear effect Can be increased.

[Eighth Embodiment (Embodiment of Claim 9)]
An eighth embodiment of the present invention will be described with reference to FIG.

  FIG. 7 is a schematic diagram showing a light control element 101 having a two-dimensional photonic crystal arrangement.

  In FIG. 7, a photonic crystal is formed by dry etching a plurality of periodic fine holes indicated by black circles in the dielectric thin film 301. The photonic crystal shown in FIG. 7 has a dielectric periodic arrangement of about the wavelength, and can form a photonic band similar to an electron band in the crystal. Due to the nature of this photonic band, a photonic band gap that is a forbidden band of light is formed, strong wavelength dispersion, and light control effects on propagating light peculiar to photonic crystals such as specific light propagation at the band edge, It becomes possible to make the size of the light control element 101 different from the past and the size of the light control element 101 so far very small.

  More specific examples of the light control element 101 include a polarization separation element using a photonic band gap, an optical waveguide having a sharp bend introduced with a defect, an electro-optic material such as a low threshold laser, an anomalous dispersion prism, and a nonlinear material. In addition to the light control element 101 that passively uses the dielectric thin film, the light control element 101 such as the light control element 101 that is actively used such as a light modulator, a routing element, a wavelength conversion element, and a MEMUX element using a four-wave mixing element. Can be realized.

  The photonic crystal is a three-dimensional photonic crystal having a periodic structure with respect to a three-dimensional direction capable of completely confining light, and a two-dimensional photo capable of confining light as a photonic crystal only in the two-dimensional direction. There is a nick crystal. A two-dimensional photonic crystal structure formed in a certain plane can be formed relatively easily by comparison with a three-dimensional photonic crystal structure by diverting semiconductor process technology. A pattern can be formed by lithography in a two-dimensional plane, and the pattern can be transferred by etching. The two-dimensional photonic crystal needs to realize light confinement in a direction perpendicular to the plane constituting the crystal, and in many cases, a slab structure is adopted. The slab structure is a structure in which a sub-μm high refractive index medium is formed on a low refractive index medium. For this reason, a dielectric thin film 301 made of a dielectric material made of an electro-optic material or a non-linear material formed on the support substrate of the present invention is used, and the dielectric thin film 301 is finely processed to form a two-dimensional photonic crystal. Constructing is effective in simplifying the manufacturing process.

  In addition to the slab type photonic crystal, it is possible to realize a two-dimensional photonic crystal whose upper and lower sides are confined by a multilayer structure or a metal film. In this case as well, the electro-optic material formed on the support substrate of the present invention In addition, it can be formed relatively easily by forming a photonic crystal using a dielectric thin film 301 made of a dielectric material made of a nonlinear material.

  In FIG. 7, the photonic crystal is composed of a triangular array of air holes. This photonic crystal structure can have a photonic band gap, which is a light forbidden body, by adjusting the periodic structure, and the characteristics of this photonic crystal are the structure formed with the substrate, Here, it is determined by the difference in permittivity of the air holes, its arrangement, the wavelength of light and the size and shape of the structures, the distance between the structures, and the like. Therefore, by changing any of these, the characteristics of the photonic crystal can be optimally controlled according to the wavelength used as the light control element 101. Further, the photonic crystal arrangement may be a structure in which a dielectric pillar is used and the periphery is a low refractive index medium in addition to the air hole. Further, the dielectric periodic structure does not have to be circular, and may be polygonal.

  A modification of the eighth embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 8, an optical waveguide having a line defect structure can be formed by eliminating the linear arrangement in a part of the photonic crystal arrangement. By combining such a line defect waveguide, a small optical circuit such as a directional coupler or a Mach-Zehnder interferometer constituted by the line defect waveguide formed by the photonic crystal can be formed. In addition, a group velocity delay element can be realized by utilizing a group velocity reduction effect peculiar to a line defect waveguide by a photonic crystal.

  In the two-dimensional photonic crystal in FIG. 8, light is confined by total reflection in the layer thickness direction, and the photonic crystal is formed in a portion where the layer is formed. In addition, since the light is confined by total reflection in the layer thickness direction, the light confinement may not be possible depending on the wave number of the propagating light. The light confinement due to the total reflection cannot be performed when the wave number changes greatly in the portion where the light is confined or when a mode having a large wave number distribution is excited. However, this phenomenon is greatly influenced by the refractive index of the material of the upper and lower cladding parts, and the difference in refractive index between this part and the core part determines whether or not the optical confinement due to total reflection becomes invalid. It is necessary to use a material that is optimized according to the light control so that the refractive index difference is increased when confining the refractive index of the clad part of the cladding, and the refractive index difference is decreased for leakage. is there. For this reason, it is necessary to use a plurality of types of materials as the cladding material. For this purpose, the present invention in which an optical waveguide is formed on a dielectric substrate made of an electro-optic material or a nonlinear material is very effective. is there. In the case of total reflection, it is optically stable to increase the difference in refractive index as much as possible by combining a material with a high refractive index for the core and a material with a low refractive index for the cladding. It is preferable to use a material having a physical property value. Also in this respect, the light control element 101 formed by forming the optical waveguide on the dielectric substrate made of the electro-optic material or the nonlinear material of the present invention is a light control element of a two-dimensional photonic crystal. 101 is very effective.

The configuration of the two-dimensional photonic crystal array shown in FIG. 7 and FIG. 8 is a circular hole having a half wavelength of light in a dielectric thin film 301 formed on a dielectric substrate made of an electro-optic material or a nonlinear material as a core. Can be formed by lithography and etching using a semiconductor process. Lithography can be performed by patterning the resist by electron beam exposure, short wavelength photolithography, or the like. In addition, the resist pattern can be transferred by using a dry etching technique. More specifically, when lithium niobate (LN) is used as the electro-optic material, the formation of a fine periodic structure as a photonic crystal can be achieved by applying the surface of the Z-axis cut crystal substrate of the optical crystal to CF Fine etching with a depth of 1 μm or less can be formed by dry etching using a metal containing a noble metal or a nitride mask with respect to the system gas. In this case, since the etching depth of the dielectric thin film 301 is extremely thin of 1 μm or less, an etching process giving a high aspect ratio is not necessary and can be easily formed. In addition, if an electrode is provided in the fine hole, strong electrolysis can be applied to the minute space, which is more effective. Furthermore, an electric drive element is provided on silicon, and an electrode on the LN and an electric drive element on silicon are electrically connected by electrophoresis to form an electric drive element integrated type light control element 101 using a composite substrate. It is also very effective.

  Similarly, instead of lithium niobate, optical inorganic crystals of titanium niobate, KTP, SBN (strontium barium niobate), organic materials with a high refractive index, and inorganic optical ceramics such as PZT and PZLT are similarly used. You may produce a micropore by dry etching. Further, instead of the silicon substrate, other substrates such as a lithium niobate substrate and an MgO-doped lithium niobate substrate may be used. Furthermore, some of these LN photonic crystals may be combined with a waveguide by proton diffusion or titanium diffusion, or may be combined by forming a ridge or buried waveguide by dicing or dry etching. good.

The dielectric thin film 301 or photonic crystal structure thin film of lithium niobate or PZT is not limited to the use of crystals, but is prepared by a precursor using a sol-gel method and dry etching of the precursor. Also good. It is also effective to use a liquid crystal photonic crystal formed by filling a liquid crystal into a fine hole formed by dry etching in a dielectric thin film 301 made of a SiO ₂ substrate. At this time, the orientation of the liquid crystal is set in a direction perpendicular to the substrate, and by applying a lateral electric field, the response speed can be realized using the electro-optic effect and the alignment regulating force of the liquid crystal. Furthermore, instead of a simple substrate, a liquid crystal may be partially filled in a substrate having an electro-optic effect such as an LN substrate to produce the electro-optic effect in a composite manner.

[Ninth Embodiment (Embodiment of Claim 10)]
A ninth embodiment of the present invention will be described with reference to FIG.

  FIG. 9 is a configuration diagram schematically showing a ninth embodiment of the present invention. By repeating the formation of the light control element 101 described above, the dielectric thin films 301 of electro-optic material or nonlinear optical material can be arranged in multiple layers (second separation layer forming step, second bonding step, second A multi-layered process consisting of the separation process.

  A substrate A made of an electro-optic material or a nonlinear optical material and a substrate B different from the substrate A are prepared. The substrate A and the substrate B are materials that can form the ion implantation separation layer 201 by ion implantation. The substrate A on which the ion implantation separation layer 201 is formed by ion implantation and the substrate B are joined, and the thin film layer portion of the substrate A is separated from the ion implantation separation layer 201 by heating, and a thin film layer is formed on the substrate B. The The substrate B on which the thin film layer of the substrate A is formed is joined to the substrate C on which the ion implantation separation layer 201 is formed by ion implantation with the same material as the substrate B, and the thin film of the substrate C is heated from the ion implantation separation layer 201 by heating. The layers are separated. By repeating this process, the thin film layers of the substrate A and the substrate C are formed. The material of the substrate C is not necessarily the same as that of the substrate B. Different materials may be used for the substrate A and the substrate B. It is also effective to combine the formation of the dielectric thin film 301 layer by the polishing step shown in FIG.

  In FIG. 9, a multilayer structure is used so that light control is performed for each layer, light control is performed between each layer, and furthermore, a multi-layer propagation structure is formed to control light in a plurality of layers. Thus, it is possible to provide a light control element 101 having a higher function capable of combining light control effects.

  In addition, in order to completely control the light by the photonic crystal, it is necessary to control the light by forming the photonic crystal in the three-dimensional direction. However, in order to stably manufacture the three-dimensional photonic crystal in a large area, it is extremely difficult. Advanced technology is required. However, according to the present invention, a three-dimensional photonic structure is formed using a conventional semiconductor process by forming a multilayer structure having a photonic crystal structure by repeating peeling of the ion implantation separation layer 201 having the light control structure 401. The crystal structure can be formed more easily than in the past. In addition, according to the present invention, it is also effective to form a multilayer structure of two-dimensional photonic crystals and to perform mutual optical control between the multilayered photonic crystal layers.

FIG. 6 is a schematic diagram showing a method for manufacturing the light control element 101 as the first embodiment of the present invention. FIG. 6 is a schematic diagram showing a method for manufacturing a light control element 101 as a second embodiment of the present invention. FIG. 6 is a schematic diagram showing a method for manufacturing a light control element 101 as a third embodiment of the present invention. FIG. 10 is a schematic diagram showing a method for manufacturing a light control element 101 as a fourth embodiment of the present invention. FIG. 6 is a schematic diagram showing a method for manufacturing the light control element 101 as a reference example of the present invention. FIG. 10 is a schematic diagram showing a method for manufacturing a light control element 101 as a sixth embodiment of the present invention. It is a schematic diagram which shows the light control element which has a two-dimensional photonic crystal arrangement | sequence as the 7th Embodiment of this invention. It is a schematic diagram which shows the light control element which has a two-dimensional photonic crystal arrangement | sequence as a modification of the 7th Embodiment of this invention. It is a side view which shows the light control element 101 as the 9th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Light control element 201 Ion implantation isolation | separation layer 301 Dielectric thin film 401 Light control structure 501 Junction layer

Claims (8)

A method of manufacturing a light control element having a support substrate and a dielectric thin film made of an electro-optic material or a nonlinear optical material,
A separation layer forming step of implanting ions into a dielectric substrate to form an ion implantation separation layer;
A bonding step of bonding a surface into which the ions of the dielectric substrate are implanted to the support substrate;
A separation step of separating and removing a part of the dielectric substrate at a portion of the ion implantation separation layer so that the remaining dielectric substrate becomes the dielectric thin film;
A light control structure forming step of forming a light control structure on the dielectric substrate between the separation layer forming step and the bonding step ;
A method of manufacturing a light control element comprising: A method of manufacturing a light control element having a support substrate and a dielectric thin film made of an electro-optic material or a nonlinear optical material,
A separation layer forming step of implanting ions into a dielectric substrate to form an ion implantation separation layer;
A bonding step of bonding a surface into which the ions of the dielectric substrate are implanted to the support substrate;
A separation step of separating and removing a part of the dielectric substrate at a portion of the ion implantation separation layer so that the remaining dielectric substrate becomes the dielectric thin film;
A light control structure forming step of forming a light control structure on the dielectric substrate before the separation layer forming step ;
A method of manufacturing a light control element comprising: 3. The method of manufacturing a light control element according to claim 1, wherein after the separation step, a surface of the dielectric thin film formed by separating and removing a part of the dielectric substrate is polished. . The bonding step, the method for manufacturing an optical control element according to any one of claims 1 to 3, characterized in that it comprises an ion irradiation treatment or plasma irradiation process on the substrate surface in a vacuum. The joining step, said prior to the separation layer forming step, the supporting substrate and the claims 1 to one any of the 4, characterized in that it comprises a step of forming a bonding layer on a surface to be bonded to each other with the dielectric film The manufacturing method of the light control element of description. The light control structure forming step, the light control structure, manufacturing method of an optical control element according to any one of claims 1 to 5, wherein forming a channel type optical waveguide structure. The light control structure forming step, the light control structure, manufacturing method of an optical control element according to any one of claims 1 to 6, characterized in that to form the photonic crystal structure. After the separation step,
A second separation layer forming step of implanting ions into another dielectric substrate to form an ion implantation separation layer;
A second bonding step of bonding the surface of the other dielectric substrate into which ions are implanted to the dielectric thin film already formed on the support substrate;
A second separation step of separating and removing a part of the other dielectric substrate at the ion implantation separation layer so that the remaining dielectric substrate becomes the dielectric thin film. method for manufacturing an optical control element according to any one of claims 1 to 7, characterized in that to perform one or more times a step.

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