WO2022003765A1 - Guide d'ondes optique et son procédé de fabrication - Google Patents

Guide d'ondes optique et son procédé de fabrication Download PDF

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Publication number
WO2022003765A1
WO2022003765A1 PCT/JP2020/025491 JP2020025491W WO2022003765A1 WO 2022003765 A1 WO2022003765 A1 WO 2022003765A1 JP 2020025491 W JP2020025491 W JP 2020025491W WO 2022003765 A1 WO2022003765 A1 WO 2022003765A1
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WO
WIPO (PCT)
Prior art keywords
silicon nitride
core
clad layer
optical waveguide
silicon
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PCT/JP2020/025491
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English (en)
Japanese (ja)
Inventor
泰 土澤
卓磨 相原
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日本電信電話株式会社
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Priority to PCT/JP2020/025491 priority Critical patent/WO2022003765A1/fr
Priority to JP2022533267A priority patent/JPWO2022003765A1/ja
Publication of WO2022003765A1 publication Critical patent/WO2022003765A1/fr

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • G02B6/132—Integrated optical circuits characterised by the manufacturing method by deposition of thin films

Definitions

  • the present invention relates to an optical waveguide having a core made of silicon nitride and a method for manufacturing the same.
  • a low-loss optical waveguide which is a basic element of optical transmission, is required, but the device can be miniaturized, is economical, and has a wide range of refractive index selectivity.
  • Expectations are high for optical waveguides with Si, SiN, and SiON as cores and SiO 2 as clads, which have a high degree of design freedom.
  • Optical waveguides with Si, SiN, and SiON as cores have long been known as optical waveguides with a higher refractive index difference between the core and clad than quartz-based waveguides, and have been studied for communication network applications.
  • a technique for forming a film of a high-quality core material and a high-precision processing technique are required. Due to the difficulty of manufacturing, a practical device that can be used in a communication network has not been realized.
  • advances in film formation technology and processing technology have made it possible to manufacture devices at a practical level.
  • the present invention has been made to solve the above problems, and an object thereof is to further increase the refractive index of a core composed of silicon nitride.
  • the method for producing an optical waveguide according to the present invention comprises a first step of forming a lower clad layer made of silicon oxide on a substrate, and a compound containing heavy hydrogen and silicon on the lower clad layer.
  • a fourth step of covering the core on the lower clad layer to form an upper clad layer by depositing silicon oxide by a plasma CVD method is provided, and the second step is plasma CVD of silicon nitride having a chemical quantitative composition.
  • the silicon nitride layer is formed under the condition that the amount of the nitrogen raw material is less than the condition to be produced by the method.
  • the optical waveguide according to the present invention includes a lower clad layer made of silicon oxide formed on a substrate, a core made of silicon nitride containing heavy hydrogen formed on the lower clad layer, and a core. It is provided with an upper clad layer made of silicon oxide, which is covered and formed on the lower clad layer, and the core is under the condition that the nitrogen raw material is less than the condition for producing silicon nitride having a stoichiometric composition by the plasma CVD method. It is composed of silicon nitride formed of.
  • the silicon nitride layer is formed to form the core under the condition that the nitrogen raw material is less than the condition for producing silicon nitride having a stoichiometric composition by the plasma CVD method.
  • the refractive index of the core composed of silicon nitride can be further increased.
  • FIG. 1 is an explanatory diagram for explaining a method for manufacturing an optical waveguide according to an embodiment of the present invention.
  • FIG. 2 is a configuration diagram showing the configuration of the ECR plasma CVD apparatus.
  • FIG. 3 is a characteristic diagram showing the relationship between the flow rate of N 2 and the refractive index of the formed silicon nitride layer.
  • FIG. 4A is a characteristic diagram showing the results of measuring the wavelength dependence of the propagation loss of the optical waveguide by the core made of the silicon nitride layer prepared at a flow rate of N 2 gas of 100 sccm.
  • FIG. 1 is an explanatory diagram for explaining a method for manufacturing an optical waveguide according to an embodiment of the present invention.
  • FIG. 2 is a configuration diagram showing the configuration of the ECR plasma CVD apparatus.
  • FIG. 3 is a characteristic diagram showing the relationship between the flow rate of N 2 and the refractive index of the formed silicon nitride layer.
  • FIG. 4A is a characteristic diagram showing the results of measuring
  • FIG. 4B is a characteristic diagram showing the results of measuring the wavelength dependence of the propagation loss of the optical waveguide by the core made of the silicon nitride layer made of the silicon nitride layer made at the flow rate of N 2 gas of 40 sccm.
  • FIG. 5 is a characteristic diagram showing the propagation loss of the optical waveguide formed by the silicon nitride core formed by using SiH 4 and the optical waveguide formed by the silicon nitride core formed by using SiD 4.
  • a lower clad layer 102 made of silicon oxide is formed on the substrate 101.
  • the substrate 101 is made of, for example, single crystal silicon.
  • the lower clad layer 102 is formed to have a layer thickness of 3 ⁇ m or more.
  • the lower clad layer 102 can be formed by thermally oxidizing the surface of the substrate 101 made of silicon. Further, the lower clad layer 102 can be formed by depositing silicon oxide on the substrate 101 by a known CVD (Chemical Vapor Deposition) method. However, when another device is already formed on the substrate 101, it is important to form the lower clad layer 102 at a low temperature of about 200 ° C. In this case, the lower clad layer 102 can be formed by depositing silicon oxide by an electron cyclotron resonance (ECR) plasma CVD method capable of forming a high-quality film at a low temperature.
  • ECR electron cyclotron resonance
  • a silicon raw material composed of a compound containing deuterium and silicon and a nitrogen raw material were used on the lower clad layer 102.
  • the silicon nitride layer 103 is formed by the plasma CVD method.
  • the silicon raw material can be SiD 4.
  • the silicon nitride layer 103 is formed, for example, to have a thickness of about 0.5 to 1 ⁇ m.
  • the silicon nitride layer 103 is a layer for forming a core, and the thickness of the silicon nitride layer 103 can be determined in correspondence with a desired core thickness. Details of the formation of the silicon nitride layer 103 by the plasma CVD method will be described later.
  • the silicon nitride layer 103 is patterned to form the core 104 on the lower clad layer 102 as shown in FIG. 1 (c).
  • the core 104 can have a width of about 1 to 2 ⁇ m and a height of about 0.5 to 1 ⁇ m in a cross-sectional view.
  • a layer of photosensitive photoresist is formed on the silicon nitride layer 103.
  • a resist pattern is formed on the silicon nitride layer 103 by layer patterning the photoresist using a known lithography technique.
  • the silicon nitride layer with the resist pattern as a mask is used.
  • the core 104 can be formed by etching 103. After forming the core 104 in this way, the resist pattern is removed by dissolving it in an organic solvent or the like.
  • silicon oxide is deposited by the plasma CVD method to form the upper clad layer 105 by covering the core 104 on the lower clad layer 102 as shown in FIG. 1 (d). do.
  • the upper clad layer 105 can be formed by depositing silicon oxide by the ECR plasma CVD method capable of forming a high-quality film at a low temperature.
  • the lower clad layer 102 made of silicon oxide formed on the substrate 101
  • the core 104 made of silicon nitride containing deuterium formed on the lower clad layer 102
  • the core 104 made of silicon nitride containing deuterium formed on the lower clad layer 102
  • the core 104 made of silicon nitride containing deuterium formed on the lower clad layer 102
  • An optical waveguide including an upper clad layer 105 made of silicon oxide formed on the lower clad layer 102 is obtained.
  • the core 104 is composed of silicon nitride formed under the condition that the nitrogen raw material is less than the condition for producing silicon nitride having a stoichiometric composition by the plasma CVD method. .. Further, the hydrogen contained in the core 104 contains deuterium as a main component. According to the optical waveguide configured in this way, the refractive index of the core 104 can be made higher, and a lower loss optical waveguide can be realized.
  • the formation (deposition) of the silicon nitride layer by the above-mentioned ECR plasma CVD method will be described.
  • the ECR plasma CVD method the ECR plasma CVD apparatus shown in FIG. 2 is used.
  • This apparatus includes a plasma generation chamber 201, a film forming chamber 202, a substrate base 203, a magnetic coil 204, a waveguide 205, a quartz window 206, a gas introduction pipe 207, a gas introduction pipe 208, and a gas introduction pipe 210.
  • a magnetic field (875 gauss) satisfying the ECR condition is generated in an appropriate region inside the plasma generation chamber 201 by a magnetic coil 204 arranged around the plasma generation chamber 201, and plasma is generated in the film formation chamber 202.
  • a divergent magnetic field for drawing ions is formed in the form of a stream 211.
  • the N 2 gas is introduced into the plasma generation chamber 201 through the gas introduction pipe 207 installed in the film forming chamber 202 or the gas introduction pipe 210 installed in the plasma generation chamber 201, and the pressure in the plasma generation chamber 201 is reduced to 0.
  • a 2.45 GHz microwave (1200 to 1800 W) is introduced from the waveguide 205 into the plasma generation chamber 201 via the quartz window 206 to generate a plasma of nitrogen gas.
  • SiD 4 gas is supplied to the film forming chamber 202 by a gas introduction tube 208 closer to (near) the substrate 209 to obtain N 2 / SiD 4 mixed plasma, and N 2 is obtained. Induces a plasma reaction between and SiD 4 and a surface reaction on the substrate 209, and silicon nitride is deposited on the surface of the substrate 209 to form a silicon nitride layer.
  • ions accelerated by the electric field generated in the plasma flow 211 enter the surface of the substrate 209 and give an impact, and this energy promotes the formation reaction of the silicon nitride layer, resulting in dense high-quality silicon nitride. Layers are formed.
  • ECR plasma is characterized by high gas decomposition efficiency, stable and difficult to decompose N 2 can be efficiently decomposed, and ions in ECR plasma are incident on the substrate 209 with appropriate energy. Therefore, the use of ECR plasma has an advantage that high-quality silicon nitride can be deposited even if the substrate 209 is kept at a low temperature of 200 ° C. or lower. Further, by supplying the SiD 4 gas to a location (near) closer to the substrate 209, the raw material can be decomposed at a location closer to the substrate 209, and the film-forming material can reach the surface of the substrate 209 more efficiently. This makes it possible to carry out film formation and refractive index control more efficiently.
  • the relationship between the flow rate of N 2 and the refractive index of the formed silicon nitride layer in the above-mentioned deposition of silicon nitride will be described with reference to FIG.
  • sccm is a unit of flow rate, and indicates that a fluid at 0 ° C. and 1013 hPa flows 1 cm 3 per minute.
  • the refractive index is almost constant at about 1.88 up to 70 sccm, but when the flow rate of N 2 is less than 70 sccm, the refractive index increases. .. Further, when the N 2 flow rate is made smaller than 40 sccm, the refractive index rises sharply. Consequently, first, with respect to the flow rate of SiD 4 gas, in a state where N 2 is sufficiently supplied, to react all SiD 4 being fed at the same time, the silicon nitride layer with a refractive index 1.89 is formed To. It is considered that this is because a silicon nitride layer having a stoichiometric composition was formed.
  • the layer of silicon nitride to be formed is formed even if the supply amount of each raw material gas is a condition for forming silicon nitride having a stoichiometric composition. , It does not become a stoichiometric composition.
  • the refractive index of the formed silicon changes depending on the supply amount of the nitrogen raw material, and when the supply amount is reduced beyond a certain condition, the refractive index is in a state of sharply increasing.
  • the singularity of the supply amount of the nitrogen raw material differs depending on the manufacturing apparatus.
  • the cause of this weak absorption peak due to the NH group is that the NH group is caused by hydrogen remaining in the device such as water (H 2 O) adsorbed on the inner wall of the film forming chamber of the device forming the silicon nitride layer. It is considered that this is because it is generated in the silicon nitride layer in a small amount. Even if the degree of vacuum is increased, it is not easy to completely remove the hydrogen remaining in the apparatus. On the other hand, as shown below, it was found that NH in the silicon nitride layer can be reduced by reducing the flow rate of the N 2 gas as described above.
  • FIGS. 4A and 4B show the results of measuring the wavelength dependence of the propagation loss of these two samples.
  • FIG. 4A shows the result of an optical waveguide using a core made of a silicon nitride layer made under the condition of N 2 flow rate of 100 sccm.
  • FIG. 4B shows the result of an optical waveguide using a core made of a silicon nitride layer made under the condition of N 2 flow rate of 40 sccm. In either case, the flow rate of the SiD 4 gas is 40 sccm.
  • the peak near 1510 nm disappears, and the loss is about 0.4 dB / cm at any wavelength.
  • This factor, that with a reduced supply of N 2, remains in SiD 4 is a device that can not react with N 2, which is attached to the inner wall of the apparatus, resulting in from the inner wall as a source of NH This is thought to be because it has the effect of effectively suppressing the supply of hydrogen.
  • the refractive index of the silicon nitride layer formed under the condition of N 2 flow rate of 40 sccm is 1.92.
  • reducing the N 2 flow rate is "a condition in which the nitrogen raw material is less than the condition for producing silicon nitride having a stoichiometric composition by the plasma CVD method".
  • the silicon nitride layer is formed to form a core under the condition that the nitrogen raw material is less than the condition for producing silicon nitride having a stoichiometric composition by the plasma CVD method. Therefore, the refractive index of the core composed of silicon nitride can be further increased.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

Selon la présente invention, lors d'une première étape S101, une couche de gainage inférieure (102) constituée d'oxyde de silicium est formée sur un substrat (101), et lors d'une seconde étape S102, une couche de nitrure de silicium (103) est formée sur la couche de gainage inférieure (102) à l'aide d'un procédé de dépôt chimique en phase vapeur (CVD) par plasma qui utilise une matière première à l'azote et une matière première au silicium constituée d'un composé contenant du deutérium et du silicium. La matière première au silicium peut être SiD4. Lors de cette étape, la couche de nitrure de silicium (103) est formée dans un état qui nécessite moins de matière première à l'azote qu'un état pour la production de nitrure de silicium ayant une composition stœchiométrique par le procédé de CVD par plasma.
PCT/JP2020/025491 2020-06-29 2020-06-29 Guide d'ondes optique et son procédé de fabrication WO2022003765A1 (fr)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080253728A1 (en) * 2006-09-07 2008-10-16 Massachusetts Institute Of Technology Microphotonic waveguide including core/cladding interface layer
JP2019203915A (ja) * 2018-05-21 2019-11-28 日本電信電話株式会社 光集積デバイスおよびその製造方法

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080253728A1 (en) * 2006-09-07 2008-10-16 Massachusetts Institute Of Technology Microphotonic waveguide including core/cladding interface layer
JP2019203915A (ja) * 2018-05-21 2019-11-28 日本電信電話株式会社 光集積デバイスおよびその製造方法

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
NG DORIS K. T., WANG QIAN, WANG TING, NG SIU-KIT, TOH YEOW-TECK, LIM KIM-PENG, YANG YI, TAN DAWN T. H.: "Exploring High Refractive Index Silicon-Rich Nitride Films by Low-Temperature Inductively Coupled Plasma Chemical Vapor Deposition and Applications for Integrated Waveguides", APPLIED MATERIALS & INTERFACES, vol. 7, no. 39, 16 September 2015 (2015-09-16), US , pages 21884 - 21889, XP055897635, ISSN: 1944-8244, DOI: 10.1021/acsami.5b06329 *

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