JP4827108B2 - Polarization inversion formation method - Google Patents

Polarization inversion formation method Download PDF

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JP4827108B2
JP4827108B2 JP2010081377A JP2010081377A JP4827108B2 JP 4827108 B2 JP4827108 B2 JP 4827108B2 JP 2010081377 A JP2010081377 A JP 2010081377A JP 2010081377 A JP2010081377 A JP 2010081377A JP 4827108 B2 JP4827108 B2 JP 4827108B2
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太 山本
潤一郎 市川
哲 及川
直 栗村
健二 北村
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Sumitomo Osaka Cement Co Ltd
National Institute for Materials Science
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National Institute for Materials Science
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本発明は、強誘電体基板の所望領域を分極反転させる分極反転形成方法に関し、特に光学素子に用いられる電気光学効果を有する基板に分極反転領域を形成する分極反転形成方法に関する。   The present invention relates to a polarization inversion forming method for inversion of a desired region of a ferroelectric substrate, and more particularly to a polarization inversion formation method for forming a polarization inversion region on a substrate having an electrooptic effect used for an optical element.

光通信や光計測の分野において、波長変換素子や光変調器などの光学素子が利用されている。
波長変換素子の例としては、以下の特許文献１に示すように、強誘電体ＬｉＮｂＯ３などの電気光学効果を有する基板上に周期的な分極反転構造を形成しているものがある。
また、光変調器の例としては、以下の特許文献２に示すように、電気光学効果を有する基板上に光導波路を形成すると共に、該光導波路に係る基板の一部を分極反転させ、チャープ発生の抑制や変調強度の消光比の向上を図るものが提案されている。 Optical elements such as wavelength conversion elements and optical modulators are used in the fields of optical communication and optical measurement.
As an example of the wavelength conversion element, there is one in which a periodic domain-inverted structure is formed on a substrate having an electro-optic effect such as ferroelectric LiNbO 3 as shown in Patent Document 1 below.
Further, as an example of an optical modulator, as shown in Patent Document 2 below, an optical waveguide is formed on a substrate having an electro-optic effect, and a part of the substrate related to the optical waveguide is polarized and inverted to obtain a chirp. Proposals have been made to suppress generation and improve the extinction ratio of modulation intensity.

このような強誘電体基板上に分極反転領域を形成する方法としては、Ｔｉ熱拡散による方法、ＳｉＯ２を装荷した後に熱処理する方法、プロトン交換処理と熱処理とを行う方法などがある。また、強誘電体の自発分極が電界により反転することを利用して、約２０ｋＶ／ｍｍ以上の電界を印加することにより、分極反転領域を形成する方法が知られている。
特に、電界の印加による分極反転は、分極反転領域を正確に形成できると共に、形成方法が簡便であることなどの理由から、分極反転形成方法として良く利用されている。 As a method for forming such a domain-inverted region on a ferroelectric substrate, there are a method using Ti thermal diffusion, a method in which heat treatment is performed after loading SiO 2 , a method in which proton exchange treatment and heat treatment are performed, and the like. In addition, a method is known in which a polarization inversion region is formed by applying an electric field of about 20 kV / mm or more by utilizing the fact that the spontaneous polarization of a ferroelectric substance is inverted by an electric field.
In particular, polarization reversal by application of an electric field is often used as a polarization reversal formation method because the polarization reversal region can be accurately formed and the formation method is simple.

電界を用いた分極反転形成方法としては、図１に示すように、基板１の上面及び下面に電極２，３を形成し、両電極間に電圧４を印加することにより形成する方法や、図２に示すように、基板１の上面に絶縁性のマスクパターン５を施し、電極６及び７により、シール部材８，９を介して該基板を狭持すると共に、基板１と各電極６，７との間に導電性液体を充填し、電極６，７に電圧４を印加する方法などが知られている。なお、電極６及び７の代わりにアクリル板などの絶縁材料を利用する場合には、電圧４からの給電用に、電線を導電性液体に直接接触させるよう構成される。
これらの方法により、図１の場合には、電極２のパターンに応じた分極反転領域が、また、図２の場合には、マスクパターン５が形成されていない領域に対応した分極反転領域が、各々形成される。 As a method for forming domain inversion using an electric field, as shown in FIG. 1, the electrodes 2 and 3 are formed on the upper and lower surfaces of the substrate 1 and a voltage 4 is applied between the electrodes. 2, an insulating mask pattern 5 is applied to the upper surface of the substrate 1, and the substrate 6 is held between the electrodes 6 and 7 via the seal members 8 and 9. A method in which a conductive liquid is filled between the electrodes 6 and 7 and a voltage 4 is applied to the electrodes 6 and 7 is known. When an insulating material such as an acrylic plate is used instead of the electrodes 6 and 7, the electric wire is configured to directly contact the conductive liquid for power supply from the voltage 4.
By these methods, in the case of FIG. 1, the domain-inverted region corresponding to the pattern of the electrode 2, and in the case of FIG. 2, the domain-inverted region corresponding to the region where the mask pattern 5 is not formed, Each is formed.

上記のような電界を用いた分極反転形成方法においては、分極反転領域の幅、例えば、図３の基板１に形成された分極反転領域１０の幅Ｌが、２０μｍ以下の場合には、分極反転を形成する領域全体に均一な電圧が印加されるため、比較的均一な分極反転領域を形成することが可能となる。
これに対し、幅Ｌが５０μｍ以上となるような大面積な分極反転領域を形成する場合には、分極反転を形成する領域の周辺部が優先的に分極反転され、領域全体としては不均一な分極反転状態を有する結果となる。また、基板となるウエハ自体の不均一性、電界を印加する電極の抵抗のバラツキによる電圧効果の差などの要因により、均一な分極反転が難しくなっている。このため、大口径のウエハを用いた場合には、ウエハ内の場所による分極反転状態の差が顕著となる。 In the polarization inversion forming method using the electric field as described above, when the width of the domain inversion region, for example, the width L of the domain inversion region 10 formed on the substrate 1 in FIG. Since a uniform voltage is applied to the entire region for forming, a relatively uniform domain-inverted region can be formed.
On the other hand, when a large-area domain-inverted region having a width L of 50 μm or more is formed, the periphery of the region where the domain-inverted region is formed is preferentially domain-inverted, and the entire region is not uniform. This results in having a polarization reversal state. Further, uniform polarization inversion is difficult due to factors such as non-uniformity of the wafer itself serving as a substrate and a difference in voltage effect due to variations in resistance of electrodes to which an electric field is applied. For this reason, when a large-diameter wafer is used, the difference in the polarization inversion state depending on the location in the wafer becomes significant.

他方、以下の非特許文献１〜６では、分極反転の形成プロセスは、電極端の電界集中領域での核発生、静電エネルギーの増加を嫌いながら深さ方向にマイクロドメインが伸長、横方向に分域壁が移動、分極反転領域が安定化という過程を経て分極反転構造が形成されること、並びに、分極反転の均一性には、核成長密度の高さが重要であることが開示されている。
また、分極反転を形成する領域の幅Lが５０μｍ以上となる大面積の場合では、周辺部が優先的に分極反転されること、幅Ｌが広い場合は、該幅が狭い場合と比較し、核成長密度が低く、均一な分極反転の形成が難しいことなどが、容易に理解できる。
このため、非特許文献１〜６においては、低い電界パルスを基板に印加することにより、分極反転の核となる核成長を行い、次に高い電界パルスを印加することにより、該核から分域壁を進行させ分極反転を実現する方法が提案されている。
しかも、この方法により、均一な分極反転領域が得られることが報告されている。 On the other hand, in the following Non-Patent Documents 1 to 6, the domain inversion formation process is such that the microdomain expands in the depth direction while disabling the generation of nuclei and the increase in electrostatic energy in the electric field concentration region at the electrode end, It is disclosed that a domain-inverted structure is formed through the process of domain wall movement and domain-inverted region stabilization, and that high nuclear growth density is important for the uniformity of domain-inversion. Yes.
Further, in the case of a large area where the width L of the region where polarization inversion is formed is 50 μm or more, the peripheral portion is preferentially reversed in polarity, and when the width L is wide, compared to the case where the width is narrow, It can be easily understood that the nuclear growth density is low and it is difficult to form uniform polarization inversion.
For this reason, in Non-Patent Documents 1 to 6, by applying a low electric field pulse to the substrate, the nucleus grows as a core of polarization reversal, and by applying the next high electric field pulse, a domain is generated from the nucleus. A method has been proposed for realizing polarization reversal by advancing the wall.
Moreover, it has been reported that a uniform domain inversion region can be obtained by this method.

特開２０００−１４７５８４JP 2000-147484 A 特開２００３−２０２５３０JP 2003-202530 A

栗村直、他９名，「ＬｉＮｂＯ３の分極反転における選択的核成長方法Ｉ〜動機とその背景〜」，第４９回応用物理学関連連合講演会講演予稿集，２００２年３月Nao Kurimura and 9 others, “Selective Nuclear Growth Method I in Motivation and Background in LiNbO3 Polarization Inversion”, Proceedings of the 49th Joint Conference on Applied Physics, March 2002 阿久津剛史、他７名，「ＬｉＮｂＯ３の分極反転における選択的核成長方法II〜選択的核成長法による周期分極反転〜」，第４９回応用物理学関連連合講演会講演予稿集，２００２年３月Takeshi Akutsu and 7 others, "Selective nuclear growth method II in polarization reversal of LiNbO3-Periodic polarization reversal by selective nuclear growth method", Proceedings of the 49th Joint Physics Related Lecture, March 2002 丸山真幸、他５名，「ＬｉＮｂＯ３の分極反転における選択的核成長方法III〜核成長密度の粒子解析による定量化〜」，第４９回応用物理学関連連合講演会講演予稿集，２００２年３月Masayuki Maruyama and five others, “Selective Nucleation Method III in LiNbO3 Polarization Inversion III-Quantification of Particle Growth Density by Particle Analysis”, Proceedings of the 49th Joint Conference on Applied Physics, March 2002 野村善行、他７名，「ＬｉＮｂＯ３の分極反転における選択的核成長方法IV〜核成長密度のパルス数依存性〜」，第６３回応用物理学会学術講演会講演予稿集，２００２年９月Yoshiyuki Nomura and 7 others, "Selective nucleation method IV in polarization reversal of LiNbO3-Dependence on pulse number of nuclear growth density", Proceedings of the 63rd Japan Society of Applied Physics, September 2002 丸山真幸、他７名，「ＬｉＮｂＯ３の分極反転における選択的核成長方法V〜短周期分極反転における核成長条件〜」，第６３回応用物理学会学術講演会講演予稿集，２００２年９月Masayuki Maruyama and 7 others, “Selective Nuclear Growth Method V in LiNbO3 Polarization Inversion V—Nuclear Growth Conditions in Short Period Polarization Inversion”, Proceedings of the 63rd Annual Conference of the Japan Society of Applied Physics, September 2002 丸山真幸、他７名，「ＬｉＮｂＯ３の分極反転における選択的核成長方法VII〜高アスペクト比短周期分極反転による第２高調波発生〜」，第５０回応用物理学関連連合講演会講演予稿集，２００３年３月Masayuki Maruyama and 7 others, "Selective nuclear growth method VII in polarization reversal of LiNbO3-Second harmonic generation by high aspect ratio short period polarization reversal-", Proceedings of the 50th Applied Physics Related Conference March 2003

本発明の目的は、上述した問題を解決し、分極反転を形成する領域の幅が、５０μｍ以上となる大面積であっても、分極反転領域内の分極反転状態を均質に形成することが可能であり、さらに、分極反転時に印加される電圧の強度を低減することを可能な分極反転形成方法を提供することである。   The object of the present invention is to solve the above-mentioned problems, and even if the width of the region for forming polarization inversion is a large area of 50 μm or more, the polarization inversion state in the domain inversion region can be formed uniformly. Furthermore, it is to provide a polarization inversion forming method capable of reducing the strength of the voltage applied at the time of polarization inversion.

請求項１に係る発明は、強誘電体基板の所望領域を分極反転させる分極反転形成方法において、該強誘電体基板の表面の該所望領域に対し、電極パターン又はマスクパターンを微細なパターンの集合体として形成し、該所望領域に、前記微細なパターンを有する電極パターン又はマスクパターンを介して所定の電圧を印加することにより核成長を発生させ、該所望領域全体に対応する電極パターン又はマスクパターンを形成し、該所望領域全体に均一な電圧を印加することで、該核に基づいて分極反転を発生させることを特徴とする。
According to a first aspect of the present invention, there is provided a domain inversion forming method for reversing the polarization of a desired region of a ferroelectric substrate, wherein an electrode pattern or a mask pattern is a set of fine patterns for the desired region on the surface of the ferroelectric substrate. formed as a body, to the desired area, the fine pattern via the electrode pattern or mask pattern having caused the nucleus growth by applying a predetermined voltage, the electrode pattern or mask pattern corresponding to the entire said desired region And applying a uniform voltage to the entire desired region to generate polarization inversion based on the nucleus.

請求項２に係る発明は、請求項１に記載の分極反転形成方法において、前記微細なパターンの形状は、ストライプ状、長円状、６角形状、網目状、又は井桁状のいずれかのパターンで形成されていることを特徴とする。The invention according to claim 2 is the polarization inversion forming method according to claim 1, wherein the fine pattern has any one of a stripe shape, an oval shape, a hexagonal shape, a mesh shape, and a grid pattern. It is formed by.

本発明により、微細なパターンを利用することにより、各パターンの周囲に核成長が起こり、分極反転領域全体としてみた場合には、領域の内部に多数の核成長を発生させることが可能となり、大面積の分極反転領域を形成する場合でも、均一な分極反転を実現することが可能となる。   According to the present invention, by using fine patterns, nucleation occurs around each pattern, and when viewed as the entire domain-inverted region, it is possible to generate a large number of nuclei within the region. Even when a domain-inverted region having an area is formed, uniform domain-inversion can be realized.

従来の電極パターンを用いた分極反転方法を示す図である。It is a figure which shows the polarization inversion method using the conventional electrode pattern. 従来の液体電極法を示す図である。It is a figure which shows the conventional liquid electrode method. 基板に形成された分極反転領域を示す図である。It is a figure which shows the polarization inversion area | region formed in the board | substrate. 基板表面に微小欠陥等を形成した状態を示す図である。It is a figure which shows the state which formed the micro defect etc. in the substrate surface. マスクパターンを微細パターンの集合体で構成する場合を示す図である。It is a figure which shows the case where a mask pattern is comprised with the aggregate | assembly of a fine pattern. 肉薄化した基板を液体電極法で分極反転する状態を示す図である。It is a figure which shows the state which carries out the polarization inversion of the thinned board | substrate by the liquid electrode method.

以下、本発明を好適例を用いて詳細に説明する。
図４は、強誘電体基板１の表面に、分極反転領域２０に核成長を多数起こした状態を示す図である。
このような核成長がある場合、強誘電体基板に電界を印加すると、この核を中心に分極反転が進行する。このため、この核が所望の反転領域内に適度に存在していれば、例えば直径２インチを超えるような大口径強誘電体ウエハ内において、分極反転領域幅が２５μｍを超えるような大面積の領域を複数箇所、同時に分極反転させる際においても、大口径ウエハ内に一括して均一な分極反転状態を実現することが可能となる。 Hereinafter, the present invention will be described in detail using preferred examples.
FIG. 4 is a diagram showing a state in which many nuclei have grown in the domain-inverted region 20 on the surface of the ferroelectric substrate 1.
In the case where there is such a nucleus growth, when an electric field is applied to the ferroelectric substrate, the polarization inversion proceeds around the nucleus. For this reason, if this nucleus is present appropriately in the desired inversion region, for example, in a large-diameter ferroelectric wafer having a diameter exceeding 2 inches, the domain inversion region has a large area exceeding 25 μm. Even when a plurality of regions are simultaneously reversed in polarity, a uniform polarization reversal state can be realized in a large-diameter wafer all at once.

核成長の発生方法としては、機械的な衝撃などによる方法や、化学的な方法が利用可能である。特に、機械的な力を利用して微小欠陥等を形成する際には、基板の温度を高くすることで、より効果的に核成長を起こすことが可能となる。
以下、具体的な方法を列挙する。 As a method for generating nuclear growth, a method using mechanical impact or a chemical method can be used. In particular, when a micro defect or the like is formed using a mechanical force, it is possible to cause more effective nuclear growth by increasing the temperature of the substrate.
Hereinafter, specific methods are listed.

（１）マイクロサンドブラスト法
基板表面上の分極反転領域以外をゴム系レジスト膜等で被覆し、微小硬質材料である研磨剤、ドライアイスなどを該基板表面に高速噴射し、その衝撃で核成長を起こす。 (1) Micro sand blasting The area other than the domain-inverted region on the substrate surface is covered with a rubber-based resist film, etc., and a fine hard material abrasive, dry ice, etc. are sprayed onto the substrate surface at high speed, and the nuclear growth is caused by the impact Wake up.

（２）ワイヤブラシ法
マイクロサンドブラスト法と同様に、基板表面上をゴム系レジスト膜等で被覆し、ワイヤブラシなど微小先端径を有する打撃部材で、該基板表面に衝撃を与え、核成長を起こす。 (2) Wire brush method Similar to the micro sand blast method, the substrate surface is coated with a rubber resist film or the like, and a striking member having a minute tip diameter such as a wire brush is applied to the substrate surface to cause nuclear growth. .

（３）ドットインパクトプリンタの利用
ワイヤドットインパクトプリンタのプリンタヘッドにて、基板表面の分極反転領域に対し選択的に衝撃を与え、核成長を起こす。 (3) Use of a dot impact printer A printer head of a wire dot impact printer selectively impacts the domain-inverted region on the substrate surface to cause nuclear growth.

（４）印刷方法の利用
スクリーン印刷法やインクジェットプリンタなどにより、硬質樹脂や研磨材を含有した樹脂インクを用いて、基板表面に分極反転領域の形状パターンの印刷を行い、印刷乾燥後、布または紙などの緩衝材を介して、バレンなどにより印刷部を擦過し、核成長を起こす。 (4) Use of printing method Using a screen printing method, an ink jet printer, or the like, a resin ink containing a hard resin or an abrasive is used to print a polarization inversion region shape pattern on the substrate surface, and after printing and drying, a cloth or Nucleation is caused by rubbing the printing part with valene or the like through a buffer material such as paper.

（５）研磨シート等の利用
基板表面上の分極反転領域以外をゴム系レジスト膜等で被覆し、研磨シートを基板表面に押圧又は擦過する。あるいは、該被覆後、研磨材を基板表面に散布し、研磨材を基板表面に押し当てるように擦過する。さらには、予め分極反転領域の形状にパターニングした研磨シートを作製し、該シートを基板に張り合わせて、研磨シートを基板に押し当てるようにプレスする。 (5) Use of polishing sheet or the like A region other than the domain-inverted region on the substrate surface is covered with a rubber resist film or the like, and the polishing sheet is pressed or rubbed against the substrate surface. Alternatively, after the coating, the abrasive is spread on the substrate surface and rubbed so as to press the abrasive against the substrate surface. Further, a polishing sheet patterned in advance in the shape of the domain-inverted region is prepared, the sheet is attached to the substrate, and pressed so as to press the polishing sheet against the substrate.

以上のように核成長を起こした後は、図１又は図２のような分極反転の形成方法を利用し、基板に分極反転領域を形成することが可能である。
具体的には、基板表面に分極反転領域に対応した電極パターンを形成し、該基板の裏面には、一様な電極を形成する。両電極間にパルス電圧を印加すると、核を中心に分極反転が進行し、該電極パターンに対応した均一な分極反転を形成することが可能となる。 After the nucleus growth as described above, the domain-inverted region can be formed on the substrate by using the domain-inverted formation method as shown in FIG. 1 or FIG.
Specifically, an electrode pattern corresponding to the domain-inverted region is formed on the substrate surface, and a uniform electrode is formed on the back surface of the substrate. When a pulse voltage is applied between both electrodes, the polarization inversion proceeds centering on the nucleus, and it becomes possible to form a uniform polarization inversion corresponding to the electrode pattern.

導電性液体を用いた方法においては、基板表面に絶縁性のマスクパターンを施した後、導電性液体を該基板の両面に配置させ、該導電性液体にパルス電圧を印加することにより、核を中心に分極反転が進行させることが可能となる。
なお、上記核成長を起こす際に利用したゴム系レジスト膜などを、上記の絶縁性マスクパターンの代わりに代用することも可能である。 In the method using a conductive liquid, after applying an insulating mask pattern to the substrate surface, the conductive liquid is arranged on both surfaces of the substrate, and a pulse voltage is applied to the conductive liquid to thereby remove the nucleus. It becomes possible to cause polarization inversion to proceed in the center.
Note that a rubber-based resist film or the like used for causing the nucleus growth can be substituted for the insulating mask pattern.

大面積の分極反転領域を形成する他の方法としては、図１における分極反転領域の電極パターン又は図２におけるマスクパターンを微細なパターンの集合体として構成する方法がある。以下、マスクパターンを例に説明する。
具体的には、図５（ａ）に示すような幅２０μｍ以上の分極反転領域を形成する場合、まず、図５（ｂ）のように、幅４μｍの微細なストライプ状のマスクパターン（絶縁性マスクのストライプ状の部分に開口が形成されているもの）の集合体として、所定の形状の分極反転領域を形成し、次に、図２に示すように該ストライプ状の開口を介して導電性液体を強誘電体基板に接触させ、電界を該基板に印加する。 As another method for forming a domain-inverted region having a large area, there is a method in which the electrode pattern in the domain-inverted region in FIG. 1 or the mask pattern in FIG. 2 is configured as an aggregate of fine patterns. Hereinafter, a mask pattern will be described as an example.
Specifically, when forming a domain-inverted region having a width of 20 μm or more as shown in FIG. 5A, first, as shown in FIG. 5B, a fine stripe-shaped mask pattern (insulating property) having a width of 4 μm. A domain-inverted region having a predetermined shape is formed as an aggregate of the mask in which an opening is formed in the stripe-shaped portion, and then the conductive property is passed through the stripe-shaped opening as shown in FIG. A liquid is brought into contact with the ferroelectric substrate, and an electric field is applied to the substrate.

このような微細なパターンを利用することにより、各パターンの周囲に核成長が起こり、分極反転領域全体としてみた場合には、領域の内部に多数の核成長を発生させることが可能となる。各パターンの線幅は、実施例のものに限らず、１０μｍ以下の場合には、安定的に核成長が可能となる。
また、微細なパターンの形状としては、図５（ｂ）のようなストライプ状のもに限らず、図５（ｃ）のように長円状のもの、図５（ｄ）のように６角形状のもの、図５（ｅ）のように網目状のもの、さらには、図５（ｆ）のように井桁状（あるいは「ひし形状」）のものなど、各種の応用が可能である。なお、各パターンに付してある数字は、ｍｍ単位の幅を示すものである。
さらに、微細なパターンに直線部分を設ける場合には、強誘電体基板の結晶方位との関係で、分極反転領域の結合が起き難い場合があり、直線部分と結晶方位との角度を考慮する必要がある。
そして、本発明の特徴は、最初に、微細パターンにより核成長を行い、その後、通常の電極パターン又はマスクパターンで、電界を印加することで、核を中心に分極反転を発生させることである。 By using such a fine pattern, nucleus growth occurs around each pattern, and when viewed as the entire domain-inverted region, a large number of nucleus growths can be generated inside the region. The line width of each pattern is not limited to that of the embodiment, and when it is 10 μm or less, stable nuclear growth is possible.
Further, the shape of the fine pattern is not limited to the stripe shape as shown in FIG. 5B, but is an oval shape as shown in FIG. 5C, and six corners as shown in FIG. Various applications such as a shape, a mesh shape as shown in FIG. 5 (e), and a cross-like shape (or “diamond shape”) as shown in FIG. 5 (f) are possible. In addition, the number attached | subjected to each pattern shows the width | variety of mm unit.
In addition, when a linear part is provided in a fine pattern, the domain-inverted region may not be easily coupled due to the crystal orientation of the ferroelectric substrate, and it is necessary to consider the angle between the linear part and the crystal orientation. There is.
The feature of the present invention, the outermost first performs nucleation by fine pattern, then, in the usual electrode pattern or mask pattern, by applying an electric field, and this generating a polarization inversion around the nucleus is there.

また、他の分極反転領域の形成方法について説明する。
具体的には、分極反転を所望する領域の厚さを薄くすることにより、該所望領域の電界を該所望領域以外の領域の電界より高くすることが可能となり、マスク等を用いることなく該所望領域のみの分極反転が可能となる。
特に、分極反転領域の基板の厚みを肉薄加工することにより、印加電圧の低減を達成することができる。好ましくは、分極反転領域に対応したパターンで、基板の裏面から肉薄化し、導電性液体を用いて電圧を印加する。
肉薄化の方法としては、基板の裏面上に分極反転領域外をゴム系レジスト膜などで被覆し、砂目が＃６００程度の微小硬質材料を噴射して、サブミクロンから２５μｍ程度掘り込む。その後、図６のような液体電極法により、基板に電圧を印加し、分極反転領域を形成する。
この際、分極反転を所望する肉薄部Ａ部と分極反転を所望しないＢ部とには同電圧が印加されるが、Ａ部の実効電界ａは、Ｂ部の電界ｂに比べ強くなる。よって、Ａ部を分極反転が促進される電界以上にし、Ｂ部を分極反転が促進される電界未満となるように、該電圧、ならびに肉薄部Ａの厚さを制御すれば、該所望部のみの分極反転が可能となる。
また、この場合、仮に過剰な時間にわたって電界を印加したとしても、Ｂ部は分極反転が生じ得ないことから、反転電流等を監視することによる電界印加時間の厳密な制御を用いることなしに、所望の反転領域が得られる。しかも、分極反転に必要な電圧は、肉薄化を行わない場合の電圧よりも、低いものとなる。 Further, another method for forming a domain-inverted region will be described.
Specifically, by reducing the thickness of a region where polarization inversion is desired, the electric field in the desired region can be made higher than the electric field in a region other than the desired region, and the desired region can be obtained without using a mask or the like. Only the region can be inverted.
In particular, the applied voltage can be reduced by thinning the substrate in the domain-inverted region. Preferably, a pattern corresponding to the domain-inverted region is thinned from the back surface of the substrate, and a voltage is applied using a conductive liquid.
As a thinning method, the outside of the domain-inverted region is coated on the back surface of the substrate with a rubber-based resist film or the like, and a fine hard material having a grain size of about # 600 is jetted to dig about 25 μm from submicron. Thereafter, a voltage is applied to the substrate by a liquid electrode method as shown in FIG. 6 to form a domain-inverted region.
At this time, the same voltage is applied to the thin portion A portion where polarization inversion is desired and the B portion where polarization inversion is not desired, but the effective electric field a of the A portion is stronger than the electric field b of the B portion. Therefore, if the voltage and the thickness of the thin portion A are controlled so that the portion A is higher than the electric field that promotes polarization reversal and the B portion is less than the electric field that promotes polarization reversal, only the desired portion is obtained. Can be reversed.
Further, in this case, even if an electric field is applied for an excessive period of time, polarization inversion cannot occur in the B part, so that without using strict control of the electric field application time by monitoring the reversal current or the like, A desired inversion region is obtained. Moreover, the voltage required for polarization reversal is lower than the voltage when thinning is not performed.

基板の肉薄化の他の方法としては、弗酸系ケミカルエッチングや、ＥＣＲ，ＩＳＭ，ＮＬＤなどのドライエッチングなどを利用することができる。
例えば、弗酸系ケミカルエッチングにおいては、基板裏面上の分極反転領域外をポリイミド系レジストなどで被覆し、弗酸エッチングを行う。エッチングの深さはサブミクロンから数μｍ程度であり、その後、液体電極法により、基板に電圧を印加する。
電圧の印加方法としては、上記の微小硬質材料で肉薄化した場合と同様に電圧の印加を行う。ただし、基板の肉薄化前に、基板全体に通常の分極反転より高い電圧を印加し、基板全体の極性を一度反転させ、その後、上記の肉薄化処理を行い、基板の分極反転領域に先に印加した電圧とは逆極性の電圧を印加することで、分極反転領域を形成することも可能である。この場合には、より均一な分極反転領域を形成することが可能となる。 As other methods for thinning the substrate, hydrofluoric acid chemical etching, dry etching such as ECR, ISM, and NLD can be used.
For example, in hydrofluoric acid chemical etching, the outside of the domain-inverted region on the back surface of the substrate is covered with a polyimide resist or the like, and hydrofluoric acid etching is performed. The etching depth is about submicron to several μm, and then a voltage is applied to the substrate by the liquid electrode method.
As a method for applying a voltage, a voltage is applied in the same manner as in the case of thinning with the fine hard material. However, before thinning the substrate, a voltage higher than the normal polarization inversion is applied to the entire substrate, the polarity of the entire substrate is reversed once, and then the above thinning process is performed, and the polarization inversion region of the substrate is preceded. It is also possible to form a domain-inverted region by applying a voltage having a polarity opposite to the applied voltage. In this case, a more uniform domain-inverted region can be formed.

強誘電体基板に光導波路を形成し、光変調器などの導波路素子を製造する際にも、本発明の分極反転形成方法を利用することが可能である。
上述の基板の肉薄化を利用して分極反転領域を形成し、更に、該肉薄化した基板面に導波路を作製する場合には、肉薄化による基板表面の段差が光学損失の原因となるため、研磨などによって、該段差を除去するのが望ましい。
また、強誘電体基板の一方の面を、分極反転領域の形状に合わせて、切削または侵食などにより薄く形成し、基板の他方の面に光導波路を形成する場合には、基板の厚みの変化が光導波路に影響を与えず、光学損失などの特性の劣化の無い導波路素子を提供することが可能となる。なお、この場合には、分極反転領域の形成と光導波路の形成とは、順序がが前後しても、共に導波路素子を製造することができる。 The polarization inversion forming method of the present invention can also be used when an optical waveguide is formed on a ferroelectric substrate and a waveguide element such as an optical modulator is manufactured.
When a domain-inverted region is formed by utilizing the above-described thinning of the substrate, and a waveguide is formed on the thinned substrate surface, a step on the substrate surface due to the thinning causes optical loss. It is desirable to remove the step by polishing or the like.
In addition, when one surface of the ferroelectric substrate is thinly formed by cutting or erosion in accordance with the shape of the domain-inverted region and an optical waveguide is formed on the other surface of the substrate, the thickness of the substrate changes. Therefore, it is possible to provide a waveguide element that does not affect the optical waveguide and does not deteriorate characteristics such as optical loss. In this case, the waveguide element can be manufactured even if the order of the domain-inverted region and the formation of the optical waveguide are reversed.

本発明は、以上説明したものに限られるものではなく、例えば、核成長と基板の肉薄化とを、マイクロサンドブラスト法で兼用するなど、各種の組み合わせが可能である。
また、分極反転における印加電圧を下げる方法として、電圧印加時に紫外線を基板に照射する方法や、基板上の分極反転領域に対応する領域に予め不純物をドープする方法などを、必要に応じて組み合わせることも可能である。 The present invention is not limited to what has been described above, and various combinations are possible, such as, for example, the combination of nucleus growth and substrate thinning by the micro-sandblast method.
In addition, as a method of lowering the applied voltage in polarization reversal, a method of irradiating the substrate with ultraviolet rays at the time of voltage application, a method of doping impurities in a region corresponding to the polarization reversal region on the substrate in advance, and the like are combined as necessary. Is also possible.

以上、説明したように、本発明によれば、分極反転を形成する領域の幅が、５０μｍ以上となる大面積であっても、分極反転領域内の分極反転状態を均質に形成することが可能であり、さらに、分極反転時に印加される電圧の強度を低減することを可能な分極反転形成方法を提供することができる。   As described above, according to the present invention, even if the width of the region for forming polarization inversion is a large area of 50 μm or more, the polarization inversion state in the polarization inversion region can be formed uniformly. Furthermore, it is possible to provide a polarization inversion forming method capable of reducing the strength of the voltage applied at the time of polarization inversion.

１ 強誘電体基板
２ パターン電極
３ 裏面電極
４ 印加電圧
５ 絶縁性マスクパターン
６，７ 電極
８，９ シール部材
１０ 分極反転領域
２０ 微小欠陥又は微小残留応力領域 DESCRIPTION OF SYMBOLS 1 Ferroelectric substrate 2 Pattern electrode 3 Back surface electrode 4 Applied voltage 5 Insulating mask pattern 6,7 Electrode 8,9 Seal member 10 Polarization inversion area | region 20 Minute defect or minute residual stress area | region

Claims (2)

強誘電体基板の所望領域を分極反転させる分極反転形成方法において、該強誘電体基板の表面の該所望領域に対し、電極パターン又はマスクパターンを微細なパターンの集合体として形成し、該所望領域に、前記微細なパターンを有する電極パターン又はマスクパターンを介して所定の電圧を印加することにより核成長を発生させ、
該所望領域全体に対応する電極パターン又はマスクパターンを形成し、該所望領域全体に均一な電圧を印加することで、該核に基づいて分極反転を発生させることを特徴とする分極反転形成方法。 In a polarization inversion formation method for reversing the polarization of a desired region of a ferroelectric substrate, an electrode pattern or a mask pattern is formed as an aggregate of fine patterns on the desired region of the surface of the ferroelectric substrate, and the desired region In addition, nuclear growth is generated by applying a predetermined voltage through the electrode pattern or mask pattern having the fine pattern,
A polarization reversal forming method comprising: forming an electrode pattern or a mask pattern corresponding to the entire desired region, and applying a uniform voltage to the entire desired region to generate polarization reversal based on the nucleus. 請求項１に記載の分極反転形成方法において、前記微細なパターンの形状は、ストライプ状、長円状、６角形状、網目状、又は井桁状のいずれかのパターンで形成されていることを特徴とする分極反転形成方法。   2. The method of forming a domain inversion according to claim 1, wherein the fine pattern is formed in any one of a stripe shape, an oval shape, a hexagonal shape, a mesh shape, and a cross-like shape. A method for forming domain inversion.
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