CN111965856B - Electro-optic crystal film, preparation method thereof and electro-optic modulator - Google Patents
Electro-optic crystal film, preparation method thereof and electro-optic modulator Download PDFInfo
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- CN111965856B CN111965856B CN202010865004.1A CN202010865004A CN111965856B CN 111965856 B CN111965856 B CN 111965856B CN 202010865004 A CN202010865004 A CN 202010865004A CN 111965856 B CN111965856 B CN 111965856B
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
-
- 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
- G02B6/122—Basic optical elements, e.g. light-guiding paths
-
- 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
- G02B6/136—Integrated optical circuits characterised by the manufacturing method by etching
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0311—Structural association of optical elements, e.g. lenses, polarizers, phase plates, with the crystal
-
- 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
- G02B2006/12133—Functions
- G02B2006/12142—Modulator
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Nonlinear Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Optical Integrated Circuits (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
The application provides an electro-optic crystal film, a preparation method thereof and an electro-optic modulator, wherein the electro-optic crystal film sequentially comprises the following components from bottom to top: the silicon waveguide layer comprises a silicon substrate layer, a silicon dioxide layer, a silicon waveguide layer, a cladding isolation layer and a functional film layer; the refractive index of the coating isolation layer is lower than that of the functional film layer, and the coating isolation layer is subjected to planarization treatment and can be bonded with the functional film layer. According to the method, the coating isolation layer is used for replacing an adhesive layer in the prior art, on one hand, the coating isolation layer can be subjected to planarization treatment, so that the surface roughness of one side close to the functional film layer is reduced, diffuse reflection can be reduced, and therefore light transmission loss is reduced; on the other hand, the coating isolation layer is combined with the functional film layer in a bonding mode, so that the uniformity and the integrity of the functional film layer are ensured.
Description
Technical Field
The application relates to the technical field of semiconductor preparation, in particular to an electro-optic crystal film, a preparation method thereof and an electro-optic modulator.
Background
The silicon-based electro-optical modulator is an important component of a transceiver in an optical communication and optical interconnection system, and is a premise of completing the conversion from an electric signal to an optical signal and realizing the transmission and processing of high-speed information on an optoelectronic integrated chip.
Silicon-based electro-optic modulators are typically integrated with electro-optic crystal films, and thus the preparation of electro-optic crystal films is significant for silicon-based electro-optic modulators. Currently, electro-optic crystal thin films are generally prepared by the following processes: firstly, preparing a silicon oxide film layer above a silicon crystal substrate layer by adopting an oxidation process, and completing silicon crystal growth above the silicon oxide film layer to form a silicon waveguide layer; then, in order to bond the silicon waveguide layer and the lithium niobate thin film layer, an adhesive layer is provided between the silicon waveguide layer and the lithium niobate thin film layer. In the application of the electro-optical crystal film prepared by the process, a part of optical signals are transmitted in a silicon waveguide layer by a silicon waveguide light path, and a part of optical fields are modulated in a lithium niobate film layer to finish the conversion from electric signals to optical signals.
The adhesive layer is typically coated on the surface of the silicon waveguide layer in a spin coating or spray coating manner using BCB (Benzocyclobutene) resin, and then bonded with the lithium niobate thin film layer. After the bonding is completed, the roughness of the BCB resin surface is typically several tens of nanometers or more. However, when an optical signal is transmitted in the silicon waveguide layer and the lithium niobate thin film layer, since the BCB resin has a large roughness on a surface close to the lithium niobate thin film layer, the optical signal may form diffuse reflection on the surface of the adhesive layer during transmission, resulting in a reduction in light intensity in a desired direction and a large optical transmission loss.
Disclosure of Invention
The application provides an electro-optic crystal film, a preparation method thereof and an electro-optic modulator, which are used for solving the problem of large optical transmission loss caused by using BCB resin as an adhesive layer in the prior art.
In a first aspect of the present application, there is provided an electro-optical crystal film, comprising, in order from bottom to top: the silicon waveguide layer comprises a silicon substrate layer, a silicon dioxide layer, a silicon waveguide layer, a cladding isolation layer and a functional film layer; the silicon waveguide layer is embedded into the cladding isolation layer;
the refractive index of the coating isolation layer is lower than that of the functional film layer, and the coating isolation layer is subjected to planarization treatment and can be bonded with the functional film layer.
Optionally, the functional film layer is selected from one of lithium niobate, lithium tantalate, KTP and RTP, and the thickness of the functional film layer is 50-3000nm or 400nm-100 μm.
Optionally, the coating isolation layer is silicon dioxide or silicon nitride, the flatness of the coating isolation layer is less than 1nm, and the roughness is less than 0.5nm;
the coating isolation layer consists of a first coating isolation layer and a second coating isolation layer;
the first cladding isolation layer is positioned above the silicon waveguide layer, and the thickness is 20nm-2000nm; the second cladding isolation layer is arranged in the silicon waveguide layer and is flush with the silicon waveguide layer, and the thickness of the second cladding isolation layer is equal to that of the silicon waveguide;
the first cladding isolation layer and the second cladding isolation layer are integrally formed.
Optionally, the shape of the silicon waveguide layer is a ridge-shaped structure, the width of the ridge waveguide in the silicon waveguide layer is 50nm-50 μm, and the thickness is 50nm-50 μm.
Optionally, the silicon waveguide structure further comprises a silicon connecting layer, wherein the silicon connecting layer is positioned between the silicon dioxide layer and the silicon waveguide layer; the sum of the thicknesses of the silicon connecting layer and the silicon waveguide layer is 50nm-50 mu m, and the thickness of the silicon dioxide layer is 50nm-5 mu m.
In a second aspect of the present application, there is provided an electro-optic modulator comprising an electro-optic crystal film as claimed in any one of the first aspects.
In a third aspect of the present application, there is provided a method for preparing an electro-optical crystal thin film, comprising:
preparing a silicon-on-insulator structure, and etching top silicon of the silicon-on-insulator structure to form a silicon waveguide layer; the silicon-on-insulator structure comprises a silicon substrate layer, a silicon dioxide layer and top silicon in sequence from bottom to top; forming a groove structure in the silicon waveguide layer after etching;
filling a cladding isolation layer in the groove structure, and carrying out planarization treatment on the cladding isolation layer;
and preparing a functional film layer with a target thickness on the coating isolation layer to obtain the electro-optic crystal film.
Optionally, etching the top silicon of the silicon-on-insulator structure includes: etching the top silicon by adopting a dry etching method, and etching the top silicon into a ridge-type strip-structure silicon waveguide; wherein the top layer silicon is etched completely or partially.
Alternatively to this, the method may comprise,
filling a cladding isolation layer in the groove structure, and carrying out planarization treatment on the cladding isolation layer, wherein the method comprises the following steps:
filling a cladding isolation layer in the groove structure, wherein the cladding isolation layer fills the groove structure and covers the silicon waveguide layer, and polishing the cladding isolation layer, and the step is repeated at least three times;
and the final polishing is performed to reserve a coating isolation layer with a target thickness above the silicon waveguide layer, wherein the roughness of the coating isolation layer is less than 0.5nm, and the surface flatness is less than 1nm.
Optionally, the method for preparing the cladding isolation layer on the silicon waveguide layer comprises the following steps: deposition, magnetron sputtering, evaporation or electroplating.
Alternatively, the functional thin film layer is prepared on the coating isolation layer by using an ion implantation method and a bonding separation method, or by using a bonding method and an abrasive polishing method.
In a fourth aspect of the present application, there is provided an electro-optical modulator, including an electro-optical crystal film prepared by a preparation method provided in any one of possible implementation manners of the third aspect.
In the electro-optical crystal film provided by the application, the coating isolation layer is adopted to replace an adhesive layer in the prior art, on one hand, the coating isolation layer can be subjected to planarization treatment, so that the surface roughness of one side close to the functional film layer is reduced, diffuse reflection can be reduced, and the light transmission loss is reduced; on the other hand, the coating isolation layer is combined with the functional film layer in a bonding mode, so that the uniformity and the integrity of the functional film layer are ensured. Furthermore, the SOI wafer is used as a base material, and the three-layer structure of the silicon substrate layer, the silicon dioxide layer and the silicon waveguide layer can be obtained by only etching the top silicon on the surface of the SOI wafer, but in the prior art, the silicon crystal substrate layer is used as the base material, and the three-layer structure of the silicon crystal substrate layer, the silicon oxide film layer and the silicon waveguide layer can be obtained by continuously preparing two-layer structures on the silicon crystal substrate layer, so that the process is simpler and more convenient.
Drawings
In order to more clearly illustrate the technical solutions of the present application, the drawings that are needed in the embodiments will be briefly described below, and it will be obvious to those skilled in the art that other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is a schematic structural diagram of an electro-optical crystal film according to an embodiment of the present disclosure;
FIG. 2 is a schematic view of another electro-optical crystal film according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram of a structure for planarizing a cladding isolation layer in one embodiment of the present application;
FIG. 4 is a schematic structural diagram of a method for preparing an electro-optic crystal thin film according to an embodiment of the present disclosure;
fig. 5 is a schematic flow chart of a method for preparing an electro-optical crystal film according to an embodiment of the present application.
Wherein, 100-top layer silicon; a 110-silicon substrate layer; a 120-silicon dioxide layer; 130-a silicon waveguide layer; 140-coating isolation layer, 1401-first coating isolation layer, 1402-second coating isolation layer; 150-a functional thin film layer; 160-silicon connection layer.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings of the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
As described in the background art of the present application, in the prior art, the bonding of the silicon material and the lithium niobate crystal is usually performed by using an adhesive, and the adhesive that is used more commonly at present is benzocyclobutene resin, however, the benzocyclobutene resin is used as the adhesive to bond the lithium niobate and the silicon material, and bubbles are easily generated in the curing process, especially when the large-size (4 inch and above) lithium niobate is bonded with the silicon material, the problem is more obvious, in addition, the use temperature of the benzocyclobutene resin is usually lower than 400 ℃, the use temperature is higher than the use temperature and may fail, and the damage recovery of the ion implantation to the lithium niobate and the like usually requires more than 400 ℃, so that the benzocyclobutene resin bonding method is limited to prepare the lithium niobate single crystal film with the thickness of several hundred nanometers. Further, benzocyclobutene resins are polymers that cannot be planarized using conventional chemical mechanical polishing processes, resulting in a failure of the close adhesion of the silicon material to the lithium niobate crystal, affecting the performance of the electro-optic modulator.
The SOI wafer structure is directly adopted for preparation, and the three-layer structure of the silicon waveguide layer, the silicon dioxide layer and the silicon substrate layer which are sequentially laminated can be obtained only by carrying out etching treatment on the surface of the SOI wafer, so that the process adopted by the embodiment of the application is simpler, more convenient and more easily obtained.
Fig. 1 is a schematic structural diagram of an electro-optical crystal film according to an embodiment of the present application. As shown in fig. 1, the electro-optical crystal film sequentially includes, from bottom to top: a silicon substrate layer 110, a silicon dioxide layer 120, a silicon waveguide layer 130, a cladding isolation layer 140, and a functional thin film layer 150. The silicon waveguide layer 130 is embedded in a cladding isolation layer 140.
The functional thin film layer 150 may be an electro-optical crystal such as lithium niobate, lithium tantalate, rubidium titanyl phosphate, or potassium titanyl phosphate.
The refractive index of the cladding isolation layer 140 is lower than that of the functional thin film layer 150, and the cladding isolation layer 140 is planarized and can be bonded with the functional thin film layer 150.
The thickness of the cladding isolation layer 140 is controllable, after planarization treatment, the surface of the cladding isolation layer 140 can be smoother, the thickness uniformity is good, and further, optical signals after being prepared into an electro-optical modulator can be well coupled between the functional thin film layer 150 and the silicon waveguide layer 130, so that the electro-optical performance of the electro-optical crystal thin film is improved, the consistency is good, the bandwidth of the finally prepared electro-optical modulator is wide, the loss is low, and the consistency of devices is good.
In addition, the material of the cladding isolation layer 140 is a material with a refractive index lower than that of the functional film layer 150, and the refractive index difference between the functional film layer 150 and the cladding isolation layer 140 can better reduce the loss of the optical signal
The silicon waveguide layer 130 prepared in the embodiment of the present application includes a plurality of ridge stripe waveguides that are continuously and uniformly distributed, and the silicon waveguide layer 130 is used for transmitting optical signals. In one implementation, the ridge stripe waveguide in the silicon waveguide layer 130 has a width of 50nm to 50 μm and a thickness of 50nm to 50 μm.
In order to solve the problem of large optical transmission loss caused by using BCB resin as an adhesive layer in the prior art, the embodiment of the present application employs the clad isolation layer 140 instead of the adhesive layer. The cladding isolation layer 140 is silicon dioxide or silicon nitride.
In the embodiment of the present application, the functional thin film layer 150 is bonded to the clad isolation layer 140 using an ion implantation method and a bonding separation method, or using a bonding method and a polishing method. Bonding refers to a bonding process in which two materials to be bonded are bonded together without an intermediate layer and an external force field. The Si-O structure in silicon dioxide or the Si-N structure in silicon nitride is a hydrophilic structure, and is easily combined with-OH, and weak bonds based on physical force are formed on the contact surface of two materials to be bonded, so that the cladding isolation layer 140 and the functional thin film layer 150 are bonded together.
In one implementation, a silicon-on-insulator structure is prepared, wherein the silicon-on-insulator structure comprises a silicon substrate layer, a silicon dioxide layer and top silicon in sequence from bottom to top; wherein the silicon substrate layer 110 and the silicon dioxide layer 120 may be obtained from a silicon-on-insulator (SOI) structure. Etching the top layer silicon 100 by a dry etching method to form a silicon waveguide layer 130, wherein a groove structure is formed in the silicon waveguide layer 130 after etching, a layer of silicon dioxide or silicon nitride is deposited in the groove structure, the deposited silicon dioxide or silicon nitride fills gaps of the ridge waveguide and covers the silicon waveguide layer 130, so that a cladding isolation layer 140 is formed; the thickness of the cladding isolation layer 140 is 2 μm to 5 μm; the flatness of the cladding isolation layer 140 is less than 1nm, and the roughness is less than 0.5nm;
the coating isolation layer is composed of a first coating isolation layer 1401 and a second coating isolation layer 1402;
the first cladding isolation layer 1401 is positioned above the silicon waveguide layer, and has a thickness of 20nm-2000nm; the second cladding isolation layer 1402 is disposed in the silicon waveguide layer and is flush with the silicon waveguide layer, and the thickness of the second cladding isolation layer 1402 is equal to the thickness of the silicon waveguide layer;
the first wrapping insulating layer 1401 and the second wrapping insulating layer 1402 are integrally formed.
Therefore, the bottom of the cladding isolation layer 140 in the embodiment of the present application extends to the bottom of the silicon waveguide layer 130, and the silicon waveguide layer 130 is embedded in the cladding isolation layer 140, that is, the thickness of the cladding isolation layer 140 is slightly greater than the thickness of the silicon waveguide layer 130. The thickness of the cladding isolation layer 140 refers to a thickness corresponding to a thickness extending from the surface thereof to the bottom of the silicon waveguide layer 130. The size of the light spot is typically several hundred nanometers to several micrometers, and is distributed between the silicon waveguide layer 130 and the functional thin film layer 150, and the cladding isolation layer 140 is typically thin, so that light propagation is not affected.
Since the material used for the cladding isolation layer 140 is silicon dioxide or silicon nitride, and the cladding isolation layer 140 can be tightly combined with the silicon waveguide layer 130, a CMP process can be used to planarize the surface to improve the roughness of the surface of the cladding isolation layer 140, so that the roughness of the surface is less than 0.5mm, the flatness is less than 1mm, the bonding with the functional thin film layer 150 can be facilitated, and the optical signal can be well coupled between the functional thin film layer 150 and the silicon waveguide layer 130. The surface of the wrapping isolation layer 140 in the embodiment of the present application refers to the surface close to the functional thin film layer 150.
In this embodiment, since there are waveguide grooves between the ridge-shaped silicon waveguides, which may include a plurality of uniformly distributed ridge-shaped silicon waveguides, there are waveguide grooves (groove structures) between the ridge-shaped silicon waveguides, the cladding isolation layer 140 at the ridge-shaped waveguide will be higher than the waveguide grooves, and when the cladding isolation layer 140 is deposited, if a single polishing process is adopted, the effect of flattening the silicon waveguide cannot be achieved, as shown in fig. 3, so that the present application adopts multiple polishing, and repeats the process of depositing and polishing again after each polishing, thereby achieving the purpose of flattening the cladding isolation layer 140, and finally, the deposited material at the waveguide groove is the second cladding isolation layer 1402, which is integrally formed with the finally formed first cladding isolation layer 1401, thereby improving the coupling effect between the functional thin film layer 150 and the silicon waveguide layer 130.
The functional thin film layer 150 is an electro-optic crystal material for modulating an optical signal. Since light is transmitted in a material with a large refractive index, the refractive index of the cladding isolation layer 140 in the embodiment of the present application is lower than that of the functional thin film layer 150, and the thickness of the functional thin film layer 150 is 50-3000nm or 400nm-100 μm.
In this embodiment, according to the actual function to be achieved, the material of the functional thin film layer 150 is selected correspondingly, where the functional thin film layer 150 is selected from lithium niobate, lithium tantalate, KTP (potassium titanyl phosphate, molecular formula is KTiOPO) 4 ) And RTP (rubidium titanyl phosphate with molecular formula RbTiOPO) 4 ) One of them.
According to the technical scheme, in the electro-optical crystal film provided by the application, the coating isolation layer is adopted to replace an adhesive layer in the prior art, on one hand, the coating isolation layer can be subjected to planarization treatment, so that the surface roughness of one side close to the functional film layer is reduced, diffuse reflection can be reduced, and the light transmission loss is reduced; on the other hand, in the prior art, BCB resin is used as an adhesive, and an adhesive is filled between two bonding surfaces in contact with each other, and in the bonding process, a solvent in the adhesive volatilizes to generate bubbles, and the solvent in the middle volatilizes slowly, so that the solvent at the edge volatilizes quickly, and bubbles are easily generated in the middle of the bonding surfaces, so that the uniformity and the firmness of the functional film layer are poor. The cladding isolation layer and the functional film layer are combined in a bonding mode, so that uniformity and integrity of the functional film layer are guaranteed.
In the embodiment of the application, the SOI wafer structure is 50nm-5 from top to bottom0μmSi/50nm-5μmSiO 2 and/Si, if the etching depth of the top silicon is equal to the thickness of the top silicon, namely, in the case of complete etching, the SOI wafer subjected to etching treatment forms a three-layer structure of the silicon substrate layer 110, the silicon dioxide layer 120 and the silicon waveguide layer 130. Since the complete etching has high process requirements and is prone to over etching, once the silicon dioxide layer is etched, the planarization effect of the silicon waveguide layer will be affected, and therefore, in another embodiment, referring to the schematic structure shown in fig. 2, the incomplete etching process is adopted, the immediate etching depth is smaller than the thickness of the top silicon, so that the silicon connection layer 160 is formed between the silicon waveguide layer 130 and the silicon dioxide layer 120. The incomplete etching manner enables the etching depth of the silicon waveguide layer 130 to be regulated and controlled within a certain range, and the transmission performance of light is regulated and controlled when the etching depths are different, namely the thicknesses of the silicon waveguide layers are different. In addition, after the top silicon layer is etched into the silicon waveguide layer, the strength becomes low, and the silicon connection layer 160 can improve the strength after being etched.
Based on the above disclosed electro-optical crystal film, the embodiments of the present application also disclose an electro-optical modulator, which includes an electro-optical crystal film as described above.
In this embodiment of the present application, a method for preparing an electro-optical crystal film is also provided, as shown in fig. 4, and fig. 4 is a schematic structural diagram of a preparation process of the electro-optical crystal film.
Specifically, as shown in fig. 5, the preparation method includes the following steps:
step 1, preparing a silicon-on-insulator structure, and etching top silicon of the silicon-on-insulator structure to form a silicon waveguide layer; the silicon-on-insulator structure comprises a silicon substrate layer, a silicon dioxide layer and top silicon in sequence from bottom to top; and forming a groove structure in the silicon waveguide layer after etching.
In this application, the SOI wafer structure is also referred to as an SOI wafer, and a SOI wafer structure with a size of 4 inches may be selected, where the SOI wafer structure is as follows from top to bottom: 50nm-50 mu mSi/50nm-5 mu mSiO 2 Si, etching the top silicon by a dry etching method, and etching the top silicon into ridge-shaped strip waveguides; wherein the top layer of silicon is finishedEither fully etched or partially etched.
If the full etching is adopted, the processed SOI wafer structure sequentially comprises a silicon substrate layer, a silicon dioxide layer and a silicon waveguide layer from top to bottom; if the incomplete etching is adopted, the obtained processed SOI wafer structure sequentially comprises a silicon substrate layer, a silicon dioxide layer, a silicon connecting layer and a silicon waveguide layer from bottom to top.
And 2, filling a cladding isolation layer in the groove structure, and carrying out planarization treatment on the cladding isolation layer.
The method for preparing the cladding isolation layer is not particularly limited in the present application, and the method for preparing the cladding isolation layer on the silicon waveguide layer includes, but is not limited to: the deposition method, the magnetron sputtering, the evaporation or the electroplating, and the polishing method can adopt CMP.
The method comprises the steps of firstly depositing a cladding isolation layer in a groove structure formed by a silicon waveguide surface, filling the groove structure by the cladding isolation layer, covering the silicon waveguide layer, polishing the cladding isolation layer to the silicon waveguide layer, and repeating the step at least three times when the polishing removal rate is almost zero; wherein the final polishing retains a cladding isolation layer of a target thickness (e.g., 50nm, 100nm, 500nm, 1000nm, 2000nm, etc.) over the silicon waveguide layer until the roughness of the cladding isolation layer is less than 0.5nm and the surface flatness is less than 1nm.
And step 3, preparing a functional film layer with a target thickness on the coating isolation layer to obtain the electro-optic crystal film.
In this step, the preparation method of the functional thin film layer may be selected from an ion implantation method and a bonding separation method, or may be selected from a bonding method and an abrasive polishing method, which is not particularly limited in this application.
When the ion implantation method and the bonding separation method are selected to be utilized, the scheme comprises the following steps: ion implantation is carried out on the functional film, the implantation energy of the ion implantation is 50-1000KeV, and the dosage is 1E 16 -1E 17 ions/cm 2 Forming a functional film wafer with a three-layer structure of a film layer, a separation layer and a residual material layer; the bonding body is prepared and formed by adopting a plasma bonding modeThe method comprises the steps of carrying out a first treatment on the surface of the Under vacuum or under a protective atmosphere formed by at least one of nitrogen and inert gas; wherein the heat preservation temperature is 100-600 ℃ and the heat preservation time is 1 min-48 h until the residual material layer is separated from the bonding body to form the lithium niobate monocrystal film; the lithium niobate single crystal thin film is polished to 50 to 3000nm (for example: 100nm, 400nm, 500nm, 800nm, 1000nm, 2000nm, etc.), to obtain an electro-optic crystal thin film having a nano-scale thickness.
When the bonding method and the grinding and polishing method are selected to be used, the scheme comprises the following steps: preparing and forming a bonding body by adopting a plasma bonding mode; under vacuum or under a protective atmosphere formed by at least one of nitrogen and inert gas; wherein the heat preservation temperature is 100-600 ℃, and the heat preservation time is 1 min-48 h; thinning to 1-102 μm by mechanical grinding, and polishing to 400nm-100 μm (e.g. 500nm, 1 μm, 5 μm, 10 μm, 50 μm, etc.), to obtain lithium niobate single crystal film with micrometer-scale thickness.
The purpose of the bond body heat preservation is to promote the bonding force of the bond body to be more than 10MPa.
Wherein, the thickness of the film layer can be adjusted by adjusting the ion implantation depth, specifically, the greater the ion implantation depth is, the greater the thickness of the prepared film layer is; conversely, the smaller the depth of ion implantation, the smaller the thickness of the thin film layer prepared.
After ion implantation, it is often necessary to clean the two contacting bonding surfaces to enhance the bonding effect before bonding.
In this application, different activation means are selected according to the thickness of the electro-optic crystal material selected. The thickness of ion implantation is limited, so that an electro-optic crystal material with a larger thickness is not suitable. When the thickness of the electro-optic crystal material selected is thick, ion implantation is not performed, but direct bonding is performed.
The preparation method of the electro-optic crystal film disclosed by the embodiment of the application is simple in process, easy to operate and suitable for large-scale popularization and application.
The embodiment of the application also provides an electro-optic modulator, which comprises the electro-optic crystal film prepared by the preparation method provided by any one possible implementation manner of the embodiment.
Examples
Example 1
(1) SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer had a structure of 220nmSi/2 μmSiO from top to bottom 2 Si. And etching the top silicon of the SOI wafer by using a dry etching method, completely etching the top SI to obtain a ridge-type strip waveguide, wherein the ridge-type strip waveguide has a width of 1 mu m and a thickness of 220nm, and forming a groove structure in the silicon waveguide layer after etching, wherein the height of the groove structure is the thickness of the ridge-type strip waveguide.
(2) Cleaning the ridge-shaped waveguide surface of the etched SOI wafer, and depositing a layer of SiO with the thickness of 2.5 mu m on the ridge-shaped silicon waveguide surface by adopting PECVD 2 And filling the groove structure, and covering the silicon waveguide layer to form a cladding isolation layer.
(3) For SiO covering ridge waveguide in step (2) 2 Flattening by adopting a CMP process, repeating PECVD to deposit silicon dioxide, then polishing, repeating the process for 3 times, reserving a coating isolation layer with the thickness of 1000nm above a silicon waveguide layer in the last polishing, and finally improving the roughness of the surface of the coating isolation layer to ensure that the surface roughness is less than 0.5nm and the surface flatness is less than 1nm.
(4) A lithium niobate wafer having a size of 4 inches was prepared, and helium ions (He + ) Implanting helium ion into lithium niobate wafer with implantation energy of 200KeV and dosage of 4E 16 ions/cm 2 And forming the lithium niobate wafer with a three-layer structure of a film layer, a separation layer and a residual material layer.
(5) Cleaning the coating isolation layer in the step (3) and the film layer in the step (4), and bonding the film layer of the cleaned lithium niobate wafer with the coating isolation layer in the step (3) by adopting a plasma bonding method to form a bonded body.
(6) And (3) placing the bonding body into heating equipment to perform heat preservation at high temperature until the residual material layer is separated from the bonding body to form the lithium niobate single crystal film. The heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one gas of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The link can promote bonding force to be more than 10MPa, and can recover damage of ion implantation to the film layer, so that the obtained lithium niobate film layer is close to the property of a lithium niobate wafer.
(7) Polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with nano-scale thickness.
It can be seen that example 1 is a method employing ion implantation + bonding separation, wherein the top silicon is completely etched through, and the cladding spacer is SiO 2 The functional film layer is made of lithium niobate, and is prepared by bonding and separating the functional film layer with the coating isolation layer after ion implantation. A lithium niobate single crystal thin film having a thickness of nanometer order can be obtained.
Example 2
(1) SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer had a structure of 220nmSi/2 μmSiO from top to bottom 2 Si. And etching the top layer Si of the SOI wafer by using a dry etching method, completely etching the top layer SI to obtain a ridge-type strip waveguide, wherein the ridge-type strip waveguide has a width of 1 mu m and a thickness of 220nm, and forming a groove structure in the silicon-based groove waveguide layer after etching, wherein the height of the groove structure is the thickness of the ridge-type waveguide.
(2) Cleaning the ridge-shaped waveguide surface of the etched SOI wafer, and depositing a layer of SiO with the thickness of 2.5 mu m on the ridge-shaped silicon waveguide surface by adopting PECVD 2 And filling the groove structure, and covering the silicon waveguide layer to form a cladding isolation layer.
(3) SiO covering the ridge-shaped silicon waveguide in the step (2) 2 Flattening by adopting a CMP process, repeating PECVD to deposit silicon dioxide, polishing, repeating the process for 3 times, reserving a coating isolation layer with the thickness of 2000nm above a silicon-based groove waveguide layer for the last polishing, and finally improving the roughness of the coating isolation surface to ensure that the surface roughness is less than 0.5nm and the surface flatness is less than 1nm.
(4) Preparing a lithium niobate wafer with the size of 4 inches, cleaning the process surface, and bonding the process surface of the cleaned lithium niobate wafer with the silicon dioxide surface (cladding isolation layer) of the SOI substrate by adopting a plasma bonding method to form a bonded body.
(5) The bonding body is placed into heating equipment to carry out heat preservation at high temperature, the heat preservation process is carried out under a vacuum environment or under a protective atmosphere formed by at least one gas of nitrogen and inert gas, the heat preservation temperature is 400 ℃, the heat preservation time is 3 hours, and the bonding force can be improved to be more than 10MPa.
(6) And thinning the lithium niobate single crystal film to 22 mu m by adopting a mechanical grinding mode, and then polishing to 20 mu m to obtain the lithium niobate single crystal film with the micron-sized thickness.
Example 2 is a method of direct bonding + grinding and polishing, wherein the top silicon is completely etched through, the coating isolation layer is silicon dioxide, the functional thin film layer is lithium niobate, the functional thin film layer is directly bonded with the coating isolation layer, and then grinding and polishing are performed to obtain the silicon nitride composite. And obtaining the lithium niobate single crystal film with the thickness of micron order.
Example 3
(1) SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer had a structure of 220nmSi/2 μmSiO from top to bottom 2 Si. And etching the top layer Si of the SOI wafer by using a dry etching method to etch a ridge-shaped strip waveguide, wherein the ridge-shaped strip waveguide has a dimension of 1 mu m in width and 160nm in thickness, the thickness of a reserved silicon connecting layer is 60nm, and a groove structure is formed in the silicon waveguide layer after etching, and the height of the groove structure is the thickness of the ridge-shaped strip waveguide.
(2) And cleaning the etched ridge-type silicon waveguide surface of the SOI wafer, adopting PECVD (depositing a layer of silicon nitride with the thickness of 2.5 mu m on the ridge-type silicon waveguide surface, filling the groove structure, covering the silicon waveguide layer, and forming a cladding isolation layer.
(3) Flattening the silicon nitride covering the ridge-shaped silicon waveguide in the step (2) by adopting a CMP process, repeating PECVD to deposit silicon dioxide, then polishing, repeating the process for 3 times, and reserving a coating isolation layer with the thickness of 1000nm above the silicon waveguide layer for the last polishing, and finally improving the roughness of the surface of the coating isolation layer, so that the surface roughness is less than 0.5nm and the surface flatness is less than 1nm.
(4) A lithium niobate wafer having a size of 4 inches was prepared, and helium ions (He + ) Implanting helium ion into lithium niobate wafer with implantation energy of 200KeV and dosage of 4E 16 ions/cm 2 And forming the lithium niobate wafer with a three-layer structure of a film layer, a separation layer and a residual material layer.
(5) Cleaning the coating isolation layer in the step (3) and the film layer in the step (4), and bonding the film layer of the cleaned lithium niobate wafer with the silicon nitride surface of the SOI substrate by adopting a plasma bonding method to form a bonding body.
(6) And (3) placing the bonding body into heating equipment to perform heat preservation at high temperature until the residual material layer is separated from the bonding body to form the lithium niobate single crystal film. The heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one gas of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The link can promote bonding force to be more than 10MPa, and can recover damage of ion implantation to the film layer, so that the obtained lithium niobate film layer is close to the property of a lithium niobate wafer.
(7) Polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with nano-scale thickness.
It can be seen that, in example 3, the method of ion implantation and bonding separation is adopted, in which the top silicon is not completely etched through, the coating isolation layer is silicon nitride, the functional thin film layer is lithium niobate, and the functional thin film layer is obtained by bonding separation with the coating isolation layer after ion implantation. A lithium niobate single crystal thin film having a thickness of nanometer order can be obtained.
Example 4
(1) SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer had a structure of 220nmSi/2 μmSiO from top to bottom 2 Si. Etching the top Si layer of the SOI wafer into a ridge-shaped strip waveguide by using a dry etching method, wherein the ridge-shaped strip waveguide has a dimension of 1 mu m in width and 160nm in thickness, and the thickness of a reserved silicon connecting layer is 60nmAnd forming a groove structure in the silicon-based groove waveguide layer after etching, wherein the height of the groove structure is the thickness of the ridge waveguide.
(2) And cleaning the etched ridge-shaped waveguide surface of the SOI wafer, depositing a layer of silicon nitride with the thickness of 2.5 mu m on the ridge-shaped silicon waveguide surface by adopting PECVD, filling the groove structure, and covering the silicon waveguide layer to form a cladding isolation layer.
(3) Flattening the silicon nitride covering the ridge-shaped silicon waveguide in the step (2) by adopting a CMP process, repeating PECVD to deposit silicon dioxide, polishing, repeating the process for 3 times, reserving a coating isolation layer with the thickness of 1000nm above the silicon-based groove waveguide layer for the last polishing, and finally improving the roughness of the surface of the coating isolation layer to ensure that the surface roughness is less than 0.5nm and the surface flatness is less than 1nm.
(4) Preparing a lithium niobate wafer with the size of 4 inches, cleaning the process surface, and bonding the process surface of the cleaned lithium niobate wafer with the silicon nitride surface of the SOI substrate by adopting a plasma bonding method to form a bonded body.
(5) The bonding body is placed into heating equipment to carry out heat preservation at high temperature, the heat preservation process is carried out under a vacuum environment or under a protective atmosphere formed by at least one gas of nitrogen and inert gas, the heat preservation temperature is 400 ℃, the heat preservation time is 3 hours, and the bonding force can be improved to be more than 10MPa.
(6) And thinning the lithium niobate single crystal film to 22 mu m by adopting a mechanical grinding mode, and then polishing to 20 mu m to obtain the lithium niobate single crystal film with the micron-sized thickness.
In example 4, a method of direct bonding and polishing was adopted, in which the top silicon was not completely etched through, the cladding isolation layer was silicon nitride, the functional thin film layer was lithium niobate, and the functional thin film layer was directly bonded to the cladding isolation layer, followed by polishing. And obtaining the lithium niobate single crystal film with the thickness of micron order.
In addition, other embodiments may be derived based on the above embodiments, for example: based on each embodiment, the functional film layer in the embodiment is replaced by lithium tantalate or KTP or RTP, and other process parameters can be changed without changing or according to the need; that is, the person skilled in the art can self-combine the replacement materials and the process parameters according to the above embodiments, and the present application is not particularly limited.
The foregoing detailed description has been provided for the purposes of illustration in connection with specific embodiments and exemplary examples, but such description is not to be construed as limiting the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications and improvements may be made to the technical solution of the present application and its embodiments without departing from the spirit and scope of the present application, and these all fall within the scope of the present application. The scope of the application is defined by the appended claims.
Claims (12)
1. An electro-optical crystal film, characterized in that,
the electro-optic crystal film sequentially comprises the following components from bottom to top: a silicon substrate layer (110), a silicon dioxide layer (120), a silicon waveguide layer (130), a cladding isolation layer (140) and a functional thin film layer (150); -the silicon waveguide layer (130) is embedded in the cladding isolation layer (140); the functional film layer (150) is an electro-optic crystal material;
the refractive index of the cladding isolation layer (140) is lower than that of the functional film layer (150), and the cladding isolation layer (140) is subjected to planarization treatment and can be bonded with the functional film layer (150);
the coating isolation layer (140) is composed of a first coating isolation layer (1401) and a second coating isolation layer (1402);
the first cladding isolation layer (1401) is located above the silicon waveguide layer; the second cladding isolation layer (1402) is arranged in the silicon waveguide layer and is flush with the silicon waveguide layer, and the thickness of the second cladding isolation layer (1402) is equal to that of the silicon waveguide;
the first coating isolation layer (1401) and the second coating isolation layer (1402) are integrally formed.
2. The electro-optical crystal film according to claim 1, wherein the functional thin film layer (150) is selected from one of lithium niobate, lithium tantalate, KTP, and RTP, and the functional thin film layer (150) has a thickness of 50-3000nm or 400nm-100 μm.
3. The electro-optic crystal film according to claim 1, characterized in that the cladding isolation layer (140) is silicon dioxide or silicon nitride, the flatness of the cladding isolation layer (140) is less than 1nm, and the roughness is less than 0.5nm;
the thickness of the first coating isolation layer (1401) is 20nm-2000nm.
4. The electro-optical crystal film according to claim 1, wherein the shape of the silicon waveguide layer (130) is a ridge stripe structure, and the ridge waveguide in the silicon waveguide layer (130) has a width of 50nm to 50 μm and a thickness of 50nm to 50 μm.
5. The electro-optic crystal film of any of claims 1-4, further comprising a silicon connection layer (160), the silicon connection layer (160) being located between the silicon dioxide layer (120) and a silicon waveguide layer (130);
the sum of the thicknesses of the silicon connection layer (160) and the silicon waveguide layer (130) is 50nm-50 μm, and the thickness of the silicon dioxide layer (120) is 50nm-5 μm.
6. An electro-optic modulator comprising an electro-optic crystal film according to any one of claims 1 to 5.
7. A method for producing an electro-optical crystal thin film, comprising:
preparing a silicon-on-insulator structure, and etching top silicon of the silicon-on-insulator structure to form a silicon waveguide layer; the silicon-on-insulator structure comprises a silicon substrate layer, a silicon dioxide layer and top silicon in sequence from bottom to top; forming a groove structure in the silicon waveguide layer after etching;
filling a cladding isolation layer in the groove structure, filling the groove structure by the cladding isolation layer, covering the silicon waveguide layer, polishing the cladding isolation layer for at least three times, and stopping polishing when the polishing removal rate reaches a preset value, wherein the cladding isolation layer with the target thickness is reserved above the silicon waveguide layer in the last polishing;
preparing a functional film layer with a target thickness on the coating isolation layer by using a bonding method and a grinding polishing method to obtain an electro-optic crystal film, wherein a cleaned lithium niobate wafer is bonded with the coating isolation layer by adopting a plasma bonding method to form a bonding body, the bonding body is kept in a preset temperature and vacuum environment or at least one inert gas for Wen Yushe time, and the functional film layer is thinned to the target thickness by adopting a mechanical grinding mode.
8. The method according to claim 7, wherein,
etching the top silicon of the silicon-on-insulator structure, including: etching the top silicon by adopting a dry etching method, and etching the top silicon into a ridge-type strip-structure silicon waveguide; wherein the top layer silicon is etched completely or partially.
9. The method of manufacturing according to claim 7, wherein the last polishing retains a cladding spacer of a target thickness over the silicon waveguide layer, comprising:
the roughness of the coating isolation layer is less than 0.5nm, and the surface flatness is less than 1nm.
10. The method of manufacturing as claimed in claim 9, wherein the method of manufacturing the clad spacer layer on the silicon waveguide layer comprises: deposition, magnetron sputtering, evaporation or electroplating.
11. The method of claim 7, wherein the functional thin film layer is formed on the clad spacer layer by ion implantation and bonding separation.
12. An electro-optic modulator comprising an electro-optic crystal film prepared by the method of any one of claims 7 to 11.
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