KR0161897B1 - Fabrication method of pole-inversion layer of lithium niobate crystal - Google Patents
Fabrication method of pole-inversion layer of lithium niobate crystal Download PDFInfo
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- KR0161897B1 KR0161897B1 KR1019940035563A KR19940035563A KR0161897B1 KR 0161897 B1 KR0161897 B1 KR 0161897B1 KR 1019940035563 A KR1019940035563 A KR 1019940035563A KR 19940035563 A KR19940035563 A KR 19940035563A KR 0161897 B1 KR0161897 B1 KR 0161897B1
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- 238000000034 method Methods 0.000 title claims abstract description 34
- 238000004519 manufacturing process Methods 0.000 title abstract description 14
- 239000013078 crystal Substances 0.000 title description 17
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title description 2
- 230000010287 polarization Effects 0.000 claims abstract description 77
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims abstract description 65
- 239000010936 titanium Substances 0.000 claims abstract description 65
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 65
- 239000010409 thin film Substances 0.000 claims abstract description 38
- 239000000758 substrate Substances 0.000 claims abstract description 21
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 17
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 17
- 238000010438 heat treatment Methods 0.000 claims abstract description 15
- 238000009792 diffusion process Methods 0.000 abstract description 28
- 230000003287 optical effect Effects 0.000 abstract description 13
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 abstract description 7
- 229910001947 lithium oxide Inorganic materials 0.000 abstract description 7
- 230000015572 biosynthetic process Effects 0.000 abstract 1
- 230000000694 effects Effects 0.000 description 8
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical group [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
- 230000002411 adverse Effects 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 230000005684 electric field Effects 0.000 description 3
- 229910001416 lithium ion Inorganic materials 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 229910013641 LiNbO 3 Inorganic materials 0.000 description 1
- 239000008896 Opium Substances 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- XUCJHNOBJLKZNU-UHFFFAOYSA-M dilithium;hydroxide Chemical compound [Li+].[Li+].[OH-] XUCJHNOBJLKZNU-UHFFFAOYSA-M 0.000 description 1
- 238000005566 electron beam evaporation Methods 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229960001027 opium Drugs 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000001259 photo etching Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000007517 polishing process Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 238000007669 thermal treatment Methods 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
- H01L21/283—Deposition of conductive or insulating materials for electrodes conducting electric current
- H01L21/285—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation
- H01L21/28506—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers
- H01L21/28512—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers on semiconductor bodies comprising elements of Group IV of the Periodic Table
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
- H01L21/283—Deposition of conductive or insulating materials for electrodes conducting electric current
- H01L21/285—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation
- H01L21/28506—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers
- H01L21/28512—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers on semiconductor bodies comprising elements of Group IV of the Periodic Table
- H01L21/2855—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers on semiconductor bodies comprising elements of Group IV of the Periodic Table by physical means, e.g. sputtering, evaporation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/324—Thermal treatment for modifying the properties of semiconductor bodies, e.g. annealing, sintering
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Abstract
본 발명은 +Z면 리튬나오베이트 기판 위에 티타늄박막을 확산시켜 분극반전을 얻는 방법에 관한 것으로, 표면 분극반전층을 형성하지 않으며, 횡방향 확산된 티타늄 농도를 조절함으로써 분극반전의 깊이 조절이 가능하고, 기판으로부터의 리튬옥사이드 외부확산량이 적어 광도파로 형성후 표면도파현상이 거의 없는 분극반전층의 제조방법에 관한 것이다.The present invention relates to a method of obtaining a polarization inversion by diffusing a titanium thin film on a + Z plane lithium naobate substrate, without forming a surface polarization inversion layer, and controlling the depth of the polarization inversion by controlling the concentration of the titanium diffused in the lateral direction. In addition, the present invention relates to a method of manufacturing a polarization inversion layer having a small amount of external diffusion of lithium oxide from a substrate and having almost no surface waveguide after optical waveguide formation.
본 발명에 의한 분극반전층 형성방법은 +Z면 리튬나오베이트 기판 위의 분극반전층을 형성하지 않을 부분에 티타늄박막을 형성한 후, 열처리를 행하여 티타늄을 횡방향으로 확산시켜 분극반전층을 형성하는 것이다.In the method of forming a polarization inversion layer according to the present invention, a titanium thin film is formed on a portion where a polarization inversion layer is not to be formed on a + Z plane lithium naobate substrate, followed by heat treatment to diffuse titanium in a transverse direction to form a polarization inversion layer. It is.
본 발명에 의하면, 횡방향 확산된 티타늄농도를 조절하여 표면 분극반전층의 형성없이 분극반전 깊이를 조절할 수 있으며, 이에 따라 준위상정합된 집적광학 광도파로형 제2고조파 발생소자의 변화효율의 최대화를 매우 용이하게 실현할 수 있게 된다.According to the present invention, it is possible to control the polarization inversion depth without forming the surface polarization inversion layer by controlling the titanium concentration diffused in the lateral direction, thereby maximizing the change efficiency of the quasi-phase matched integrated optical waveguide type second harmonic generating element. Can be realized very easily.
Description
제1도 (a)~(b)는 종래의 티타늄 내부확산에 의한 분극반전 형성방법을 도시한 도면.1 (a) to (b) is a view showing a polarization inversion forming method by the conventional internal diffusion of titanium.
제2도 (a)~(c)는 본 발명에 의한 리튬나오베이트 결정의 분극반전층 제조방법을 도시한 도면.2 (a) to 2 (c) show a method of manufacturing a polarized inverted layer of lithium naobate crystals according to the present invention.
* 도면의 주요부분에 대한 부호의 설명* Explanation of symbols for the main parts of the drawings
1 : +Z면 리튬나오베이트 기판 2 : 티타늄박막1: + Z surface lithium nanobait substrate 2: titanium thin film
3 : 횡확산된 티타늄박막3: Tungsten Thin Film
4 : 열처리중의 기판 내부에서의 동일 티타늄 농도 분포4: distribution of the same titanium concentration in the substrate during heat treatment
5 : 분극반전층5: polarization inversion layer
본 발명은 리튬나오베이트 결정의 분극반전층 제조방법에 관한 것으로, 특히 표면분극반전층을 형성하지 않으며, 표면도파 현상이 거의 없는 분극반전층의 제조방법에 관한 것이다.BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polarization inversion layer of lithium naobate crystals, and more particularly, to a method for manufacturing a polarization inversion layer having no surface polarization inversion layer and almost no surface waveguide phenomenon.
유전체 광도파로를 기반으로 하는 집적광학(integrated optics) 소자의 기판재료중 단일결정 리튬나오베이트(lithium niobate;LiNbO3)는 우수한 전기광학 효과(electro optic effect) 및 압전효과(piezoelectric effect)등을 가지고 있어 광신호처리 소자 및 압전소자로서 널리 응용되고 있다. 특히, 리튬나오베이트는 가시광 영역에서 흡수가 없으며 2차 비선형 계수가 다른 집적광학 유전체 기판중 가장 커 최근에는 다이오드 레이저의 제2고조파 발생(second-harmonic generation)방법으로 청색 레이저 광파를 생성하려는 연구가 활발하게 진행되고 있다.Single crystal lithium niobate (LiNbO 3 ) among substrate materials of integrated optical devices based on dielectric optical waveguide has excellent electro optic effect and piezoelectric effect. It is widely applied as an optical signal processing element and a piezoelectric element. In particular, lithium naobate is the largest integrated optical dielectric substrate that has no absorption in the visible region and has a different secondary nonlinear coefficient. Recently, researches on generating blue laser light waves by the second-harmonic generation method of diode laser have been conducted. It is actively going on.
단일결정 리튬나오베이트는 강유전체로 외부에서 전계를 걸어주지 않아도 항상 일정한 방향으로 쌍극자(dipole)들이 정렬되어 있어 자연분극(spontaneous polarizatiSingle crystal Lithium Naobate is a ferroelectric material, so spontaneous polarizati is always aligned with dipoles in a constant direction even without an external electric field.
on)이 존재하는 결정이다. 리튬나오베이트의 비선형 광학계수의 부호는 결정의 자연분극 방향에 의하여 결정된다. 효율적인 제2고조파 발생을 위해서는 펌핑광파와 발생된 제2고조파간의 위상정합(phase-matching)이 필수적으로 요구되는데, 공간적인 비선형 계수의 주기적 교번(alternation)에 의하여 이를 성취할 수 있다.on) is a decision. The sign of the nonlinear optical coefficient of lithium naobate is determined by the natural polarization direction of the crystal. In order to efficiently generate second harmonics, phase-matching between the pumped light waves and the generated second harmonics is essential, which can be achieved by periodical alternation of spatial nonlinear coefficients.
이 위상정합 방법을 준위상정합(우리말로는 準位相整合, 영어로는 Quasi-Phase Matching, 일본말로는 疑似相整合이라 함)방법이라 한다This phase matching method is called quasi-phase matching (in Korean, Quasi-Phase Matching, and in Japanese).
준위상정합 방법은 자연분극의 교번 주기를 적절히 택함으로써 임의의 펌핑광 파장에서 위상정합을 시킬 수 있으며, 리튬나오베이트 결정의 가장 큰 비선형 계수인 d33을 사용할 수 있는 장점이 있다. 자연분극의 교번은 주기적으로 공간상의 특정 부분의 자연분극을 반전시키면 된다. 리튬나오베이트를 비롯한 강유전체의 자연분극을 반전시키는 것을 특별히 분극반전(pole-inversion 또는 domain-inversion)이라 한다. 단일결정 리튬나오베이트의 분극반전은 결정의 전하 중심을 이루고 있는 산소삼각형(oxygen triangle) 중심에 대하여 리튬이온(Li+)의 위치와 또하나의 전하중심인 산소팔면체(oxygen octahedron) 중심에 대하여 나이오븀이온(Nb5+)의 위치를 이동시킴으로써 이루어진다. 이들 양이온(positive ion)의 위치를 이동시키기 위해서는 산소삼각형의 결합을 느슨하게 해주는 열 또는 전자빔과 같은 에너지과 결정의 자연분극방향과 반대방향의 분극반전 전계가 필요하다.The phase-matching method can be phase-matched at any pumping wavelength by appropriately selecting the alternating period of natural polarization, and has the advantage of using d 33 , the largest nonlinear coefficient of lithium nanobait crystals. The alternating natural polarization can be reversed by periodically inverting the natural polarization of a specific part of space. Inverting the natural polarization of ferroelectrics, such as lithium naobate, is particularly called polar-inversion or domain-inversion. The polarization reversal of monocrystalline Lithium Naobate is related to the position of lithium ion (Li + ) with respect to the center of the oxygen triangle, which forms the charge center of the crystal, and the age with respect to the center of oxygen octahedron, another charge center. This is achieved by shifting the position of the opium ion (Nb 5+ ). To shift the position of these positive ions requires a polarization inversion field opposite to the natural polarization direction of the crystal and energy, such as heat or electron beams, which loosen the oxygen triangle bonds.
지금까지 개발된 리튬나오베이트의 분극반전을 위한 방법은 분극반전 전계를 가해주는 방식에 따라 크게 두가지 방식으로 분류될 수 있다.The methods for polarization inversion of lithium naobate developed so far can be classified into two types according to the method of applying a polarization inversion electric field.
첫번째로 결정의 항전계(coercive force, 약 200KV/㎝)보다 강한 외부 펄스전계를 결정에 인가하여 분극반전을 얻는 방법으로 결정이 전자사태(electron avalanchFirst, an electron avalanch is obtained by applying an external pulse field stronger than the crystal coercive force (about 200 KV / cm) to the crystal to obtain polarization inversion.
e)에 의하여 파괴되는 것을 막기 위하여 특별히 결정을 얇게 해야만 한다. 이 방식은 분극반전 폭에 비해 깊은 분극반전을 얻을 수 있는 장점이 있으나 제작이 매우 까다롭고 공정단가가 비싸 대량생산이 어려운 단점이 있다.Special crystals must be thinned to prevent them from being destroyed by e). This method has the advantage of obtaining a deep polarization inversion compared to the width of the polarization inversion, but it is very difficult to manufacture and has a disadvantage in that it is difficult to mass-produce due to high process cost.
두번째로 불순물 원자를 결정에 내부확산(indiffusion)시키거나 결정내의 리튬옥사이드(Li2O)를 외부확산(outdiffusion)시킴으로써 분극반전 전계를 내부에서 생성시켜 분극반전시킨다. 이 방식의 장점을 제작의 용이성으로 인해 저가로 대량생산할 수 있는 등의 장점이 있는 반면 분극반전 폭에 비해 깊이가 얕은 단점을 가지고 있다.Second, a polarization inversion field is generated internally by polarization inversion by infusing impurity atoms into the crystal or outdiffusion of lithium oxide (Li 2 O) in the crystal. The advantage of this method is that it can be mass-produced at low cost due to its ease of manufacture, but has the disadvantage of having a shallow depth compared to the polarization inversion width.
이상 분극반전 전계에 따른 두가지 방식의 리튬나오베이트 결정의 분극반전에 대하여 설명하였는바, 이들 중 두번째 방식인 티타늄 박막의 확산에 의한 분극반전방법은 분극반전 깊이가 얕은 삼각형 모양의 분극반전이 얻어지는 한계를 갖고 있으나 제작공정이 용이한 이유로 이를 이용한 많은 소자제작 연구가 이루어졌다. 기존의 티타늄 내부확산에 의한 분극반전 방법을 제1도를 참조하여 설명하면 다음과 같다.As described above, the polarization inversion of two types of lithium naobate crystals according to the polarization inversion electric field has been described. The second method of the polarization inversion by diffusion of a titanium thin film has a limitation in that the polarization inversion of the triangular shape with shallow polarization inversion depth is obtained. However, because of the easy manufacturing process, many device fabrication researches have been conducted. Referring to FIG. 1, the polarization reversal method by conventional titanium internal diffusion is as follows.
제1도 (a)에 도시된 바와 같이 얇은 두께의 티타늄박막(보통 5nm)을 +Z단면 리튬나오베이트(1) 표면의 분극반전을 원하는 곳에 스퍼터링(sputtering) 또는 전자빔 증착(electron-beam evaporation)방법 등으로 증착한 후, 주기적(주기 9㎛)으로 티타늄 박막층(3)을 형성하고 이를 1000-1100℃의 고온에서 대략 1시간 정도 내부확산시키면 티타늄박막이 있었던 곳의 아래에 사잇각이 129°인 삼각형 모양의 분극반전(6)이 얻어진다. 이와 같이 매우 간단한 과정만으로 분극반전을 할 수 있음에도 불구하고 이 방법은 티타늄박막의 내부확산과 동시에 일어나는 두가지의 역효과에 의해 이를 이용하는 소자제작에 제한을 준다. 이 역효과로는 티타늄박막을 내부확산시킬때 깊이방향 확산과 더불어 원치 않는 횡방향 확산이 매우 크게 일어나는 점과 기판 전면에 걸쳐서 리튬옥사이드의 외부 확산이 일어남을 들 수 있다. 이 역효과로 인해 제1도 (b)에 도시된 바와 같이 분극반전을 원하지 않던 곳에 티타늄박막의 횡획산과 리튬옥사이드의 외부확산에 의하여 기판의 자연분극이 반전되어 기판 전체적으로 볼때 소위 평면 분극반전층(planar-inverted layer)이라고 일컬어지는 층이 형성된다. 이 평면 분극반전층은 근본적으로 주기적 분극반전을 이용하는 준위상정합된 집적광학 광도파로형 제2고조파 발생소자의 변환효율의 증대를 위한 열처리로(furnace)의 환경(예를 들어 열처리 분위기의 가스종류, 압력 및 습도등)에 민감하게 변화하기 때문에 평면 분극반전층의 두께를 항상 일정하게 얻을 수 없어 그나마 소자제작의 재현성마저 떨어뜨릴 수 있다. 이와 더불어 결정으로부터의 리튬옥사이드 외부확산은 결정표면의 이상굴절율을 증가시켜 분극반전 공정후 이 기판 위에 광도파로를 만들었을 때 빛이 채널 광도파로에만 집중되어 도파하지 못하고 표면전체에 걸쳐 도파하는 표면도파현상(surface-guiding effect)을 유발하는 등의 문제점을 안고 있다. 이를 해결하기 위하여 일본의 소니사에서는 기판의 윗부분을 기계적인 연마과정을 통해 제거하는 방법을 제안하기도 하였으나 이 방법 역시 기판 전체에 걸쳐 매우 정밀한 연마두께 조절이 이루어져야 하는 어려움과 이 과정으로 인한 제작단가의 상승 등의 문제점을 안고 있다.(日本國特許, 특허출원공개번호 : 特開平 4-296829, 발명의 명칭 : 광도파로형 재2고조파 발생소자의 제법).As shown in FIG. 1 (a), sputtering or electron-beam evaporation of a thin titanium thin film (typically 5 nm) where desired polarization reversal of the surface of + Z section lithium nanobait (1) is desired. After deposition by a method or the like, the titanium thin film layer 3 was formed periodically (period 9 μm) and internally diffused for about 1 hour at a high temperature of 1000-1100 ° C., where the angle of 129 ° below the titanium thin film was present. A triangular polarization inversion 6 is obtained. Although polarization reversal can be performed by this very simple process, this method limits the device fabrication by using two adverse effects simultaneously with the internal diffusion of the titanium thin film. This adverse effect is that when the titanium thin film is internally diffused, the diffusion in the depth direction and the unwanted lateral diffusion are very large and the external diffusion of lithium oxide occurs over the entire surface of the substrate. Due to this adverse effect, as shown in FIG. 1 (b), the natural polarization of the substrate is reversed by the transverse diffusion of the titanium thin film and the external diffusion of the lithium oxide where the polarization inversion is not desired. A layer called an inverted layer is formed. This planar polarization inversion layer is basically used in a heat treatment furnace environment (e.g., in a heat treatment atmosphere) to increase conversion efficiency of a quasi-phase matched integrated optical optical waveguide-type second harmonic generating element using periodic polarization inversion. , Pressure, humidity, etc.), so that the thickness of the planar polarization inversion layer can not always be uniformly obtained, however, the reproducibility of device fabrication can be reduced. In addition, the external diffusion of lithium oxide from the crystal increases the refractive index of the crystal surface, and when the optical waveguide is made on the substrate after the polarization inversion process, the light is concentrated on only the channel optical waveguide and the surface waveguides the entire waveguide. There are problems such as causing a surface-guiding effect. In order to solve this problem, Sony in Japan has proposed a method of removing the upper part of the substrate through mechanical polishing process, but this method also has a difficulty in controlling the very precise polishing thickness over the entire substrate, and the manufacturing cost increases due to this process. (Japanese Patent Application Publication No .: 特 開平 4-296829, Name of the Invention: Preparation of Optical Waveguide Type 2 Harmonic Generation Device).
따라서 본 발명은 상술한 문제점을 해결할 수 있는 티타늄 횡확산 분극반전방법을 제공하는데 그 목적이 있다.Accordingly, an object of the present invention is to provide a titanium lateral diffusion polarization inversion method that can solve the above problems.
상기 목적을 달성하기 위한 본 발명의 분극반전층 형성방법은 +Z면 리튬나오베이트기판상의 분극반전을 원치 않는 부분에 소정의 폭과 두께를 갖는 티타늄박막을 형성하는 단계와, 열처리공정에 의해 상기 티타늄박막을 횡방향으로 확산시켜 티타늄이 확산된 기판부분에 분극반전층을 형성하는 단계로 이루어진다.The polarization inversion layer forming method of the present invention for achieving the above object is to form a titanium thin film having a predetermined width and thickness on the portion where the polarization inversion on the + Z plane lithium naobate substrate is not desired, and by the heat treatment process The titanium thin film is spread in the transverse direction to form a polarization inversion layer on the substrate portion where titanium is diffused.
본 발명은 분극반전을 위해 티타늄박막이 열처리시간내에 충분히 확산되어 티타늄 농도가 적을 때에만 분극반전이 일어나는 것을 이용하고, 티타늄박막이 확산된 곳에서는 리튬옥사이드의 외부확산이 억제되는 점을 이용하며, 또한 티타늄박막이 횡방향으로 폭이 좁은 띠(strip) 형태의 경우 박막이 확산될 때 횡방향으로 확산이 매우 크게 일어나는 점을 이용한다.The present invention utilizes the fact that the titanium thin film is sufficiently diffused within the heat treatment time for polarization inversion so that the polarization inversion occurs only when the titanium concentration is low, and the diffusion of lithium oxide is suppressed in the place where the titanium thin film is diffused. In addition, in the case of a strip form having a narrow width in the transverse direction, the titanium thin film uses a point in which the diffusion is very large in the transverse direction.
상기의 효과들을 이용하여 티타늄박막의 횡확산 양을 조절함으로써 표면분극반전층이 형성되지 않으며 분극반전의 깊이 조절이 용이하고 또한 표면도파 현상이 거의 없는 분극반전을 알 수 있다.By controlling the amount of lateral diffusion of the titanium thin film using the above effects, it is possible to know that the polarization inversion is not formed, the depth of the polarization inversion is easily controlled, and the surface waveguide phenomenon is almost absent.
본 발명에 의한 분극반전층 제조방법을 제2도를 참조하여 설명하면 다음과 같다.The polarization inversion layer manufacturing method according to the present invention will be described with reference to FIG.
먼저, 제2도 (a)에 도시된 바와 같이 +Z단면 리튬나오베이트기판(1)상에 통상의 티타늄 내부확산방법에서 사용하는 티타늄 박막두께(5nm)보다 두꺼운 티타늄박막(10~40nm)을 증착한 후 포토엣칭법을 이용 분극반전을 원하지 않는 부분에 소정의 폭을 가지도록 주기적으로 티타늄 박막층(2)을 형성한 다음, 이를 1000-1050℃정도의 고온에서 종래의 티타늄 내부확산 방법에서 사용하는 열처리시간보다 긴 시간(2-5시간)동안 열처리한다. 이때, 티타늄박막은 횡방향으로의 확산경향이 크기 때문에 제2도 (b)에 도시된 바와 같이 분극반전을 원하는 곳에 티타늄이 확산되어(참조부호 3) 이곳에 타타늄 농도가 존재하게 된다. (참조부호4는 열처리중의 기판 내부에서의 동일 티타늄 농도 분포를 나타낸다) 이곳에 존재하는 티타늄 농도가 분극반전을 일으킬 수 있을 정도로 충분히 낮으면 이곳에 분극반전이 형성된다. 이때 초기 티타늄박막이 있던 곳은그 옆쪽에 비해 티타늄 농도가 높으며, 분극반전이 일어나지 않을 정도로 티타늄 농도가 크도록 열처리조건을 설정할 경우, 이곳에 어떠한 분극반전도 일어나지 않도록 할 수 있다. 따라서 제2도 (c)에 도시된 바와 같이 표면 분극반전층을 형성하지 않고 분극반전층(5)을 제조할 수 있다.First, as shown in FIG. 2A, a titanium thin film (10 to 40 nm) thicker than the titanium thin film thickness (5 nm) used in a conventional titanium internal diffusion method is formed on the + Z cross-section lithium nanobait substrate (1). After the deposition, the titanium thin film layer 2 is periodically formed to have a predetermined width in a portion where polarization inversion is not desired by using photoetching, and then it is used in a conventional titanium internal diffusion method at a high temperature of about 1000-1050 ° C. The heat treatment is performed for a time longer than the heat treatment time (2-5 hours). At this time, since the titanium thin film has a large diffusion tendency in the transverse direction, as shown in FIG. 2 (b), titanium is diffused where desired polarization inversion (reference 3), whereby the titanium concentration exists. (Reference numeral 4 indicates the same titanium concentration distribution inside the substrate during heat treatment.) If the titanium concentration present here is low enough to cause polarization inversion, polarization inversion is formed here. At this time, where the initial titanium thin film was higher than the side of the titanium concentration, and if the heat treatment conditions are set so that the titanium concentration is large enough that the polarization inversion does not occur, it can prevent any polarization inversion here. Accordingly, as shown in FIG. 2C, the polarization inversion layer 5 may be manufactured without forming the surface polarization inversion layer.
즉, 티타늄 확산농도가 어느 이상이 되면 오히려 분극반전이 형성되지 않는다는 점과 티타늄박막이 띠형태일 때 타타늄이 횡방향으로 화산되는 점을 이용하여 티타늄박막을 기존보다 두껍게(10~40nm)하고 열처리시간을 길게 하면 티타늄박막이 있는 바로 밑은 티타늄의 농도가 높아 분극반전기 일어나지 않으며, 또 티타늄박막의 두께가 두껍기 때문에 리튬이온이 외부로 빠져나가지 어려워 리튬이온의 외부확산에 의한 분극반전도 일어나지 않게 되나, 티타늄박막이 없는 곳에서는 티타늄이 횡방향으로 확산되어 티타늄 농도가 분극반전이 일어나기 알맞은 정도가 되어 쉽게 분극반전이 형성하게 되어 제2도 (c)에 도시된 바와 같이, 종래의 방법과는 달리 티타늄박막이 없는 곳에 분극반전이 형성되는 것이다.That is, if the titanium diffusion concentration is more than a certain point, the polarization inversion is not formed, and when the titanium thin film is in the form of a band, the titanium thin film is thicker (10-40 nm) than the conventional one by using the point where the titanium is laterally volcanoed. The longer the heat treatment time, the lower the titanium concentration, the higher the concentration of titanium does not occur polarization reversal, and because the thickness of the titanium film is thick, it is difficult for lithium ions to escape to the outside, and polarization reversal also occurs due to external diffusion of lithium ions. However, where there is no titanium thin film, titanium diffuses in the transverse direction so that the titanium concentration becomes a suitable degree of polarization inversion, so that polarization inversion is easily formed, as shown in FIG. In other words, the polarization inversion is formed where there is no titanium thin film.
이 방법은 초기 증착한 티타늄박막의 두께 및 폭 그리고 열처리 조건을 조절하여 전혀 평면 분극반전층을 형성하지 않고서도 분극반전 깊이를 용이하게 조절할 수 있다. 또한, 분극반전 공정중 기판의 전면에 티타늄이 확산되기 때문에(초기 티타늄박막이있던 곳은 내부확산에 의해, 티타늄박막이 없던 곳은 횡확산에 의해) 기판전면에 걸쳐 리튬옥사이드의 외부확산을 억제할 수 있다.This method can easily control the polarization inversion depth without forming a planar polarization inversion layer by controlling the thickness and width of the initially deposited titanium thin film and the heat treatment conditions. In addition, since titanium is diffused on the entire surface of the substrate during the polarization inversion process (by internal diffusion where the initial titanium thin film was present, and by lateral diffusion where no titanium thin film was present), external diffusion of lithium oxide is suppressed over the entire surface of the substrate. can do.
이와 같이 본 발명은 티타늄박막의 두께, 열치리시간을 기존의 티타늄 박막확산방법과 다르게 하여 기존의 티타늄 내부확산방법에서의 단점을 주효과로 사용한다. 본 발명은 기존의 티타늄 내부확산 방법의 장점(제작의 용이성)을 그대로 포함하며, 나아가 기존의 티타늄 내부확산방법으로는 불가능했던 표면 분극반전 미생성 및 리튬옥사이드 외부확산 억제 등의 새로운 장점을 갖는 획기적인 방법이다.As described above, the present invention uses the disadvantages of the conventional titanium internal diffusion method as a main effect by varying the thickness and thermal treatment time of the titanium thin film from the conventional titanium thin film diffusion method. The present invention includes the advantages (easiness of manufacture) of the existing titanium internal diffusion method as it is, and further breakthroughs with new advantages such as surface polarization inversion generation and lithium oxide external diffusion suppression that were not possible with the conventional titanium internal diffusion method. Way.
본 발명의 분극반전 형성방법에 의해 준위상정합된 집적광학 광도파로형 제2고조파 발생소자를 제작할 경우, 표면 분극반전층이 전혀 형성되지 않은 상태에서 분극반전 깊이를 조절할 수 있기 때문에 제2고조파 발생소자의 최적화가 매우 용이해진다.In the case of fabricating the second optical waveguide type second harmonic generating element of the phase matching according to the polarization inversion forming method of the present invention, since the polarization inversion depth can be adjusted without the surface polarization inversion layer being formed at the second harmonic generation Optimization of the device becomes very easy.
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|---|---|---|---|---|
| WO2019066259A1 (en) * | 2017-09-28 | 2019-04-04 | 광주과학기술원 | Optical phased array antenna and lidar including same |
| US11575199B2 (en) | 2017-09-28 | 2023-02-07 | Gwangju Institute Of Science And Technology | Optical phased array antenna and LiDAR including same |
Also Published As
| Publication number | Publication date |
|---|---|
| KR960026998A (en) | 1996-07-22 |
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