JP2012150282A - Manufacturing method and manufacturing device for optical wavelength conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method and a manufacturing device for optical wavelength conversion element that facilitate control over the size of a polarization inversion region by generating polarization inversion nuclei with high density.SOLUTION: The manufacturing method for optical wavelength conversion element includes a back electrode forming process 300 of forming a back electrode on a back surface of a ferroelectric crystal substrate; a fine electrode forming process 301 of forming a fine electrode having a fine line pattern on a top side of the ferroelectric crystal substrate; an etching process 302 of forming grooves at the fine line pattern part by etching the top side of the ferroelectric crystal substrate; a first polarization inverting process 303 of applying a voltage between the back electrode and the fine electrode; a fine electrode removing process 304 of removing the fine electrode; a periodic electrode forming process 305 of forming a plurality of periodic electrodes so as to cover a plurality of grooves; and a second polarization inverting process 306 of applying a voltage having the reversed polarity to the polarity of the voltage of the first polarization inverting process between the back electrode and periodic electrodes.

Description

  The present invention relates to a method for manufacturing an optical wavelength conversion element and an apparatus for manufacturing the same.

A method of performing pseudo phase matching by periodically reversing the dielectric polarization direction of a ferroelectric crystal such as LiNbO ₃ or LiTaO ₃ by 180 degrees (polarization inversion) is known as quasi phase matching (QPM: Quasi Phase Matching). being called. With the above technique, it becomes possible to obtain a laser beam having a higher frequency by using an inexpensive laser light source.
As a method for forming the domain-inverted region, various methods such as a Ti diffusion method, an electron beam irradiation method, and a voltage application method have been researched and developed. In polarization reversal by the voltage application method, polarization reversal nuclei are generated from the edge portion of the electrode, and the first surface (+ Z surface) to the second surface (−Z surface) of the ferroelectric substrate starting from the polarization reversal nucleus. Then, the domain-inverted region penetrates, and then the domain-inverted regions are combined to complete the formation of the domain-inverted region (see Non-Patent Document 1). Since the domain-inverted nuclei are generated from the edge portion of the electrode, there is a problem that when the entire domain-inverted width is inverted, the domain-inverted region extends to the outside of the electrode. Although there is a method of narrowing the electrode width in advance in consideration of the spread of the polarization inversion width, the polarization inversion nucleus is not generated from the edge portion of the electrode, so the size of the polarization inversion region should be controlled. It was difficult. Therefore, Patent Document 1 discloses a first metal electrode forming step of forming a first metal electrode on a processed surface after processing one surface of a substrate made of a ferroelectric material to a predetermined roughness, A second metal electrode forming step of forming a second metal electrode so as to cover the entire surface opposite to the surface on which the first metal electrode is formed; and the first metal electrode and the second metal electrode A manufacturing method of an optical wavelength conversion element comprising a polarization reversal forming step of forming a polarization reversal portion on the substrate by applying an electric field between the electrodes is disclosed.

JP 2008-309828 A

Nao Kurita and nine others, “Selective Nuclear Growth Method I in LiNbO3 Polarization Inversion I: Motivation and Background”, Proceedings of the 49th Joint Conference on Applied Physics (March 2002 27a-ZS-9)

  However, in the above prior art, the uniformity of the polarization direction in the region where the polarization inversion is not performed depends on the quality of the first ferroelectric crystal substrate and the ease of controlling the formation position of the polarization inversion nucleus. was there.

  The present invention has been made in view of the above circumstances, and the inventors have devised the present invention, considering that the uniformity of domain-inverted nuclei affects the dimensional accuracy of domain-inverted regions. An object of the present invention is to provide a method of manufacturing an optical wavelength conversion element and a manufacturing apparatus thereof that can easily control the size of a domain-inverted region by generating domain-inverted nuclei uniformly and with high density.

  In order to solve the above-mentioned problems, a method for manufacturing an optical wavelength conversion element according to the present invention includes a back electrode forming step of forming a back electrode on the back side surface of a ferroelectric crystal substrate, and a fine pattern on the front side surface of the ferroelectric crystal substrate. A fine electrode forming step of forming a fine electrode having a line pattern, an etching step of etching the front side surface of the ferroelectric crystal substrate to form a groove in the fine line pattern portion, the back electrode and the fine electrode A first polarization reversal step of applying a voltage between, a fine electrode removal step of removing the fine electrode, and a periodic electrode formation step of forming a plurality of periodic electrodes so as to cover the plurality of grooves And a second polarization reversing step of applying a voltage having a polarity opposite to the voltage of the first polarization reversing step between the back electrode and the periodic electrode.

  According to said manufacturing method, the optical wavelength conversion element in which the dimensional accuracy of the polarization inversion area | region improved can be manufactured.

  Note that the order of the back electrode forming step and the fine electrode forming step may be reversed.

  In the manufacturing method described above, the groove in the fine electrode forming step is a line-shaped electrode pattern formed by an electron beam (EB), the electrode width of the remaining fine electrode portion being 20 nm to 100 nm, and the depth of the groove is It is desirable to be 20 nm to 100 nm.

  According to this method, only the fine line pattern region in which the fine electrode is eliminated is etched by hydrofluoric acid or hydrofluoric acid, so that a plurality of fine line-shaped grooves can be formed. And by making groove depth into 20-100 nm, the damage to a fine electrode pattern can be decreased and a fine etching pattern can be formed. The line-shaped grooves can improve the nucleation density at the time of periodic polarization inversion, and improve the dimensional accuracy of the periodic polarization inversion region.

  Furthermore, it is desirable that the longitudinal direction of the fine electrode and the longitudinal direction of the periodic electrode are parallel. According to this method, it is possible to form periodic polarization inversion with good linearity.

  The ferroelectric crystal substrate is preferably made of lithium niobate doped with magnesium or lithium tantalate doped with magnesium. Further, lithium niobate or lithium tantalate not doped with magnesium may be used.

  Further, as an example of the manufacturing method described above, when lithium niobate doped with magnesium or lithium tantalate doped with magnesium is used, the back side surface of the ferroelectric crystal substrate is the + Z plane side of the crystal, The side surface is the −Z plane side of the crystal, and the etching step is characterized in that the front side surface is etched using hydrofluoric acid or hydrofluoric acid.

  Since the above ferroelectric crystal substrate is etched only in the −Z plane by hydrofluoric acid or hydrofluoric acid, a groove having a fine line pattern is formed in the −Z plane of the crystal substrate. After the etching process, by reversing the entire polarization direction of the crystal substrate and replacing the original + Z plane with the −Z plane, the fine uneven pattern formed by the etching process becomes the + Z plane. A polarization inversion nucleus is formed from the fine uneven pattern.

  Further, the optical wavelength conversion element manufacturing apparatus of the present invention includes a back electrode forming apparatus for forming a back electrode on the back side surface of the ferroelectric crystal substrate, and a fine electrode having a fine line pattern on the front side surface of the ferroelectric crystal substrate. A voltage is applied between the back electrode and the fine electrode, a fine electrode forming device that forms a groove, an etching device that etches the front side surface of the ferroelectric crystal substrate to form a groove in the fine line pattern portion, and A first voltage applying device to be applied; a fine electrode removing device for removing the fine electrode; a periodic electrode forming device for forming a plurality of periodic electrodes so as to cover the plurality of grooves; the back electrode; And a second voltage applying device for applying a voltage having a polarity opposite to the voltage of the first voltage applying device between the periodic electrodes.

  According to said manufacturing apparatus, the optical wavelength conversion element in which the dimensional accuracy of the polarization inversion area | region improved can be manufactured.

  According to the present invention, since the entire polarization is reversed, the uniformity can be ensured even if the polarization of the first ferroelectric crystal substrate is not uniform, and the formation position of the polarization reversal nucleus is controlled. In addition, the domain-inverted nuclei can be generated uniformly and with high density, and the dimensions of the domain-inverted regions can be easily controlled, so that domain-inverted regions with high uniformity can be formed.

Flow diagram of a method of manufacturing an optical wavelength conversion element in an embodiment of the present invention Sectional drawing of the ferroelectric crystal substrate after passing through the electrode forming apparatus in the embodiment of the present invention Sectional drawing of the ferroelectric crystal substrate after the process by the image development apparatus of the microelectrode formation process in embodiment of this invention Sectional drawing of the ferroelectric crystal substrate after the process by the electrode etching apparatus of the fine electrode formation process in embodiment of this invention Sectional drawing of the ferroelectric crystal substrate after the fine electrode formation process in the embodiment of the present invention Sectional drawing of the ferroelectric crystal substrate after the etching process in the embodiment of the present invention Top view of FIG. Sectional drawing of the ferroelectric crystal substrate after the 1st polarization inversion process in embodiment of this invention Sectional drawing of the ferroelectric crystal substrate after the fine electrode removal process in embodiment of this invention The top view of the ferroelectric crystal substrate after forming the insulating film pattern in the periodic electrode formation process in the embodiment of the present invention Sectional drawing of the ferroelectric crystal substrate after forming an insulating film pattern and a periodic electrode in the periodic electrode formation process in the embodiment of the present invention Sectional drawing of the ferroelectric crystal substrate in the early stage of the 2nd polarization inversion process in embodiment of this invention Sectional drawing of the ferroelectric crystal substrate after the 2nd polarization inversion process in embodiment of this invention Sectional view after the domain-inverted structure in the comparative example is formed The system block diagram of the optical wavelength conversion element manufacturing apparatus in embodiment of this invention The figure which showed the inside of the fine electrode formation apparatus of FIG. 13 in detail The figure which showed the inside of the insulating film pattern formation apparatus of FIG. 13 in detail

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment, In the range which does not change the summary, it can implement suitably.

In this embodiment, Mg-doped stoichiometric lithium niobate (LiNbO ₃ ) was used as the ferroelectric crystal substrate. As the size of the substrate, a diameter of 3 inches and a thickness of 0.5 mm were used.

  FIG. 1 shows a manufacturing process of an optical wavelength conversion element in an embodiment of the present invention. In the method for manufacturing an optical wavelength conversion element according to one embodiment of the present invention, a back electrode forming process 300 for forming a back electrode on the back side surface of the ferroelectric crystal substrate, and a front side surface of the ferroelectric crystal substrate. A fine electrode forming step 301 for forming a fine electrode having the fine line pattern 10, an etching step 302 for etching the front side surface of the ferroelectric crystal substrate to form a groove in the fine line pattern 10, and the back surface A first polarization inversion step 303 for applying a voltage between an electrode and the fine electrode; a fine electrode removal step 304 for removing the fine electrode; and a plurality of periodic electrodes periodically covering the plurality of grooves. A periodic electrode forming step 305 to be formed, and a second polarization inversion step 306 in which a voltage having a polarity opposite to that of the first polarization inversion step is applied between the back electrode and the periodic electrode. To run. Note that the order of the back electrode forming step 300 and the fine electrode forming step 301 may be reversed.

  2 to 13 are sectional views and top views of the ferroelectric crystal substrate in each process. 15 to 17 are system configuration diagrams of the optical wavelength conversion element manufacturing apparatus according to the embodiment of the present invention. In the drawing, the ferroelectric crystal substrate processed in each apparatus is sequentially transferred to the next apparatus indicated by an arrow. The optical wavelength conversion element manufacturing apparatus includes a substrate cleaning apparatus 110, electrode forming apparatuses 120 and 180, a fine electrode forming apparatus 130, an etching apparatus 140, voltage applying apparatuses 150 and 190, an electrode removing apparatus 160, an insulating film pattern forming apparatus 170, And a dicing device 180.

  As shown in FIG. 16, the fine electrode forming apparatus 130 includes an EB resist film coating apparatus 131, a pre-baking furnace 132, an EB drawing apparatus 133, a PE baking furnace 134, a developing apparatus 135, a post-baking furnace 136, and an electrode etching apparatus 137. It has.

  As shown in FIG. 17, the insulating film pattern forming device 170 includes a substrate drying device 171, a photoresist film coating device 172, a pre-baking furnace 173, an exposure device 174, a developing device 175, and a post-baking furnace 176.

  The developing devices 135 and 175 have a container for holding a developing solution, and the ferroelectric crystal substrate 1 is immersed in the container for a predetermined period, whereby a resist film after exposure with EB drawing or photo is performed. Develop. The developed ferroelectric crystal substrate 1 was washed with pure water and then dried using an air gun or a spin dryer. The developing devices 135 and 175 may perform the above-described processing automatically or may be performed manually.

  The electrode forming devices 120 and 180 are, for example, vapor deposition devices or sputtering devices.

  The voltage application devices 150 and 190 are devices for applying a voltage to the electrodes formed on the ferroelectric crystal substrate 1 and have a high voltage power source.

  Hereinafter, a more specific description of each part will be given.

  In the substrate cleaning apparatus 110, the ferroelectric crystal substrate 1 was cleaned with acetone, then with pure water, and dried.

  In the electrode forming apparatus 120, a Cr layer (10 nm) and an Au layer (40 nm) are vapor-deposited in this order on the first surface 1-2 (+ Z surface side) and the second surface 1-3 (−Z surface side). Electrode 2 and back electrode 3 were prepared. The reason why the Au layer is formed on the Cr layer is to prevent the Cr layer from being corroded in an etching process using hydrofluoric acid or hydrofluoric nitric acid described later.

  In the fine electrode forming apparatus 130, a part of the electrode on the second surface 1-3 (−Z plane side) is removed by a patterning technique using an electron beam (EB) drawing apparatus to create a fine line pattern 10. Pattern 2-2 was formed. With reference to FIG. 16, the detailed content of the process of the fine electrode forming apparatus 130 will be described below.

  First, an EB resist solution (for example, OEBR-CAP112PM manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied by spin coating on the electrode on the first surface 1-2 of the substrate with the EB resist film coating apparatus 131. Then, pre-baking was performed at 130 ° C. in the pre-baking furnace 132 to form the EB resist film 11. Thereafter, similarly to this treatment, the EB resist film 12 was applied to the second surface 1-3 by spin coating, and then pre-baked at 130 ° C. In order to prevent the substrate from reciprocating between the EB resist film coating apparatus 131 and the pre-baking furnace 132, two of each of these apparatuses may be prepared and arranged in series.

  In the EB drawing apparatus 133, the EB resist film 12 was exposed with an exposure pattern of a fine line pattern 10 in which a plurality of lines as shown in FIG. Note that a conductive aqueous solution may be applied by spin coating, if necessary, before applying the EB resist film 12 to the second surface 1-3. The fine line pattern 10 was formed so that the length direction thereof was parallel to the Y axis of the crystal. The electron beam irradiation range corresponds to the position of the groove 5 in FIG. Specifically, the electron beam is irradiated so that the portion with the EB resist film 12 and the portion without the EB resist film 12 have the same width (for example, at an interval of 50 nm) so that the stripe-like fine line pattern 10 is obtained. did.

  Thereafter, post-exposure baking (PEB) was performed at 110 ° C. in a PE baking furnace 134. The developing device 135 develops the EB resist to obtain the EB resist film 12. The purpose of the PE baking furnace is a furnace that performs a heat treatment for advancing a chemical reaction in the resist after EB exposure. If this step is not performed, development cannot be performed at all. If the EB exposure time is increased, development can be performed to some extent, but the exposure time is considerably increased.

  Next, post-baking is performed at 100 ° C. in the post-baking furnace 136, and then the Au layer exposed in the region without the EB resist is removed by the Au etching solution with the electrode etching device 137, and the exposed Cr is thereby removed. The layer was removed with a Cr etchant. Thereafter, the EB resist films 11 and 12 were removed with an EB resist stripping solution, and the structures shown in FIGS. 5 and 7 were produced. As shown in FIG. 7, the fine electrode pattern 2 is connected to form one electrode.

  In this way, the formation of the fine electrode pattern 2 is completed. The electrode width of the fine electrode portion is desirably a linear electrode pattern of 20 nm to 100 nm, and can be controlled by dimensional conditions in electron beam irradiation. Note that the pre-bake, PE bake, and post-bake times are appropriately adjusted depending on the apparatus used. The atmosphere of the pre-bake, PE bake or post-bake is air.

  Thereafter, in the etching apparatus 140, the ferroelectric crystal substrate 1 on which the fine electrode pattern 12 is formed is immersed in fluorinated nitric acid at room temperature for about 3 minutes, and the first portion of the ferroelectric crystal substrate 1 exposed in the opening where there is no electrode is exposed. The groove 5 was formed by etching the surface of the second surface 1-3. The depth of the groove formed by etching is about 50 nm. The depth of the groove is desirably 20 nm to 100 nm, and can be controlled by appropriately changing the etching conditions.

  After that, as shown in FIG. 8, the voltage application device 150 applies a 1.5 kV, 1 ms pulse 20,000 times, with the back electrode 3 set to a positive potential and the fine electrode pattern 2 set to a negative potential, and is directed downward. The entire polarization direction was reversed upward. The application conditions of the high voltage pulse may be any conditions as long as the polarization direction is entirely reversed and the crystal is not broken, and can be appropriately changed.

  After reversing the polarization direction over the entire surface, the electrode removing apparatus 160 removed the fine electrode pattern 2 with an Au etching solution and a Cr etching solution (FIG. 9). At this time, the back electrode 3 is protected beforehand with a tape or the like so as not to be etched.

Next, in the insulating film pattern forming apparatus 170, the insulating film pattern 6 was formed on the second surface 1-3 changed to the + Z plane. More detailed contents are shown in FIG.
First, the substrate drying apparatus 171 dry-baked the substrate.
Next, in the photoresist film coating apparatus 172, first, hexamethyldisilazane treatment (also referred to as OAP treatment, OAP (trade name) manufactured by Tokyo Ohka Kogyo Co., Ltd.) is performed, and then a photoresist (for example, on the second surface 1-3). , Tokyo Ohka Kogyo Co., Ltd. OFPR-800) was applied by spin coating. Next, the substrate was prebaked at 90 ° C. in a prebaking furnace 173. Thereafter, a desired pattern was exposed to the photoresist by an exposure device 174 using an exposure machine such as a mask aligner. Thereafter, development was performed in the developing device 175, and then the substrate was post-baked at 130 ° C. in a post-baking furnace 176. By these processes, the insulating film pattern 6 corresponding to the periodic polarization inversion pattern was formed.

  The insulating film pattern 6 formed in the example was a striped line pattern having a resist-free portion of 3 μm and a period of 6.8 μm. The length direction of the line pattern was formed so as to be parallel to the groove 5 formed by hydrofluoric acid etching (so as to be parallel to the Y axis of the crystal) (see the plan view of FIG. 10). In this embodiment, the portion without the resist is 3 μm, so that there are about 30 grooves 5 in the width. In order to simplify the drawing, FIGS. 11 to 13 show only two grooves 5 covered by one insulating film 6, but originally, a large number of grooves 5 are shown. Exists.

  Next, in the electrode forming apparatus 180, as shown in FIG. 11, the periodic electrode 7 was formed on the entire surface of the front side surface 1-3 of the ferroelectric crystal substrate so as to cover the insulating film pattern 6 by using a vapor deposition apparatus. . In this example, Cr (thickness 200 nm) was used. By forming the portion covered with the insulating film and the portion not covered with an arbitrary periodicity, the insulating film pattern 6 and the conductive region where the front side surface 1-3 of the ferroelectric crystal substrate is in contact with the periodic electrode 7 are formed. Creates a periodic pattern of covered non-energized areas.

  Next, in the voltage application device 190, as shown in FIGS. 12 and 13, the second surface 1-3 is positive between the second surface 1-3 and the first surface 1-2 of the ferroelectric crystal substrate 1. A high voltage pulse was applied so as to obtain a voltage. As application conditions of the high voltage pulse, in the example, the back electrode 3 was set to a negative potential and the periodic electrode 7 was set to a positive potential, and a pulse of 1.3 kV and 1 ms was applied 40,000 times. As shown in FIG. 12, inversion nuclei were generated from below the grooves 5, and finally a periodic polarization inversion pattern was formed as shown in FIG.

  Next, in the dicing apparatus 200, a dicing tape is attached to the back surface of the substrate, and the substrate is separated into individual quasi phase matching elements. Note that the processing by the voltage application device 190 may be performed after the dicing device 180 first separates into pieces.

In the case of the example of the present invention (FIG. 13), as compared with a comparative example described later, a large number of grooves 5 exist below the periodic electrode 7, and therefore a large number of domain-inverted nuclei are generated efficiently and uniformly. Due to the effect, polarization inversion with a high aspect ratio was formed, and it was possible to suppress the spread of the inversion region and improve controllability compared to the comparative example. When the interval between the grooves 5 is smaller than 20 nm, the neighboring grooves 5 are bonded to each other by the wraparound under the electrode during the hydrofluoric acid or hydrofluoric acid etching, and the effect is reduced. For example, when the polarization inversion period is 6.8 μm, if the interval between the grooves 5 is made larger than 100 nm, the nuclear density of the polarization inversion is lowered, and the effect of the grooves is reduced. However, when the polarization inversion period is larger than 6.8 μm, the effect can be obtained even if the interval between the grooves 5 is increased more than 100 nm in proportion thereto. The depth of the groove 5 is preferably the same as the distance from the neighboring groove 5.
(Comparative example)
A cross-sectional view of the comparative example is shown in FIG. The manufacturing method of the comparative example is obtained by removing the fine electrode removing step 304 from the fine electrode forming step 301 from the method of the example. Specifically, after passing through the substrate cleaning apparatus 110, the substrate was formed only by the electrode forming apparatus 120 on the back surface electrode (in the case of the comparative example, formed on the second surface 1-3: -Z surface). Thereafter, the steps after the insulating film pattern forming apparatus 170 are the same as those in the embodiment (the insulating film pattern 6 and the periodic electrode 7 are formed on the first surface 1-2: + Z surface). In the case of the comparative example, the polarization inversion progresses to the lower inside of the resist film 6 without the electrode 7, and the polarization inversion region expands, so that it is quite close to the adjacent region.

1 Ferroelectric Crystal Substrate 1-2 First Surface 1-3 of Ferroelectric Crystal Substrate Second Surface 2 of Ferroelectric Crystal Substrate 2 Front Electrode 2-2 Fine Electrode Pattern 3 Back Electrode 4-1 and 4-2 Polarization Direction 5 Groove 6 Insulating film pattern 7 Periodic electrode 10 Fine line pattern 11, 12 EB resist film 110 Substrate cleaning device 120, 180 Electrode forming device 130 Fine electrode forming device 131 EB resist film coating device 132 Prebaking furnace 133 EB drawing device 134 PE Baking furnace 135 Developing apparatus 136 Post baking furnace 137 Electrode etching apparatus 140 Etching apparatus 150, 190 Voltage application apparatus 160 Electrode removal apparatus 170 Insulating film pattern forming apparatus 171 Substrate drying apparatus 172 Photo resist film coating apparatus 173 Prebaking furnace 174 Exposure apparatus 175 Development Equipment 176 Post-baking furnace 200 Daishin Device 105,190 voltage application device 300 back electrode forming step 301 fine electrode forming step 302 etching process 303 first poled step 304 microelectrodes removing step 305 periodically electrode forming step 306 second polarization reversal process

Claims (8)

A back electrode forming step of forming a back electrode on the back side surface of the ferroelectric crystal substrate;
A fine electrode forming step of forming a fine electrode having a fine line pattern on the front side surface of the ferroelectric crystal substrate;
An etching step of etching the front side surface of the ferroelectric crystal substrate to form a groove in the fine line pattern portion;
A first polarization inversion step of applying a voltage between the back electrode and the fine electrode;
A fine electrode removal step of removing the fine electrode;
A periodic electrode forming step of forming a plurality of periodic electrodes so as to cover the plurality of grooves;
A method of manufacturing an optical wavelength conversion element, comprising: a second polarization reversal step of applying a voltage having a polarity opposite to the voltage of the first polarization reversal step between the back electrode and the periodic electrode. The manufacturing method of the optical wavelength conversion element of Claim 1 which reversed the order of the said back surface electrode formation process and the said fine electrode formation process. The optical wavelength conversion element according to claim 1 or 2, wherein the groove in the fine electrode forming step is a linear electrode pattern formed by an electron beam and having an electrode width of a remaining fine electrode portion of 20 nm to 100 nm. Manufacturing method. The method for manufacturing an optical wavelength conversion element according to any one of claims 1 to 3, wherein the depth of the groove is 20 nm to 100 nm. 5. The method of manufacturing an optical wavelength conversion element according to claim 1, wherein a longitudinal direction of the fine electrode and a longitudinal direction of the periodic electrode are parallel to each other. 6. The optical wavelength conversion device according to claim 1, wherein the ferroelectric crystal substrate is lithium niobate doped with magnesium or lithium tantalate doped with magnesium. Method. The back side surface of the ferroelectric crystal substrate is the + Z plane side of the crystal, the front side surface is the −Z plane side of the crystal,
6. The method of manufacturing an optical wavelength conversion element according to claim 1, wherein the etching step etches the front side surface using hydrofluoric acid or hydrofluoric acid. A back electrode forming apparatus for forming a back electrode on the back side surface of the ferroelectric crystal substrate;
A fine electrode forming apparatus for forming a fine electrode having a fine line pattern on a front side surface of the ferroelectric crystal substrate;
An etching apparatus for etching the front side surface of the ferroelectric crystal substrate to form a groove in the fine line pattern portion;
A first voltage applying device for applying a voltage between the back electrode and the fine electrode;
A fine electrode removing device for removing the fine electrode;
A periodic electrode forming apparatus that forms a plurality of periodic electrodes so as to cover the plurality of grooves;
An optical wavelength conversion device manufacturing apparatus comprising: a second voltage application device that applies a voltage having a polarity opposite to that of the voltage of the first voltage application device between the back electrode and the periodic electrode.

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