CN111965854A - Electro-optical crystal film, method for producing the same, and electro-optical modulator - Google Patents

Electro-optical crystal film, method for producing the same, and electro-optical modulator Download PDF

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CN111965854A
CN111965854A CN202010887317.7A CN202010887317A CN111965854A CN 111965854 A CN111965854 A CN 111965854A CN 202010887317 A CN202010887317 A CN 202010887317A CN 111965854 A CN111965854 A CN 111965854A
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silicon
isolation layer
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CN111965854B (en
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张秀全
张涛
王金翠
李真宇
李洋洋
刘桂银
孔霞
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Jinan Jingzheng Electronics Co Ltd
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    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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  • Optical Integrated Circuits (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The embodiment of the application provides an electro-optical crystal film, a preparation method thereof and an electro-optical modulator, wherein the electro-optical crystal film sequentially comprises the following components from bottom to top: the device comprises a silicon substrate layer, a silicon dioxide layer, a silicon waveguide layer, a coating isolation layer, a measurement reflection layer, an isolation layer and a functional thin film layer; the silicon waveguide layer is embedded in the cladding isolation layer; the measurement reflecting layer is metal or nonmetal with low microwave loss and high reflectivity of a visible light wave band, and is used for monitoring the thickness and uniformity of the isolation layer and the functional thin film layer. The isolation layer is planarized and can be bonded with the functional thin film layer. By adopting the scheme, the thickness of the isolation layer is controllable by arranging the measuring reflection layer in the structure, the thickness deviation of the isolation layer is reduced, the surface of the isolation layer is smoother, the uniformity is better, and the bonding coupling loss is reduced, so that the optical signal of the electro-optical modulator prepared can be well coupled between the functional thin film layer and the silicon waveguide layer, the prepared device has wide bandwidth, low loss and good device consistency.

Description

Electro-optical crystal film, method for producing the same, and electro-optical modulator
Technical Field
The application relates to the technical field of semiconductors, in particular to an electro-optical crystal film, a preparation method thereof and an electro-optical modulator.
Background
At present, the processing technology of silicon materials is very mature, and the silicon materials are semiconductor materials with more industrial applications, so the silicon materials are widely applied to electronic components. The silicon material is in a centrosymmetric crystal structure, so that the silicon does not have a linear electro-optic effect, and therefore, the silicon material cannot be directly used for preparing a high-performance electro-optic modulator. Therefore, the conventional silicon-based electro-optic modulator usually needs to solve the above problem by means of a plasma dispersion effect, and a specific method is to form a PN junction by means of ion implantation, change the refractive index of a silicon waveguide in the silicon-based electro-optic modulator by changing the carrier concentration of the PN junction, and further realize modulation of the amplitude of an optical wave. However, the method changes the refractive index of the silicon waveguide and the loss of the silicon waveguide at the same time, and realizes high bandwidth on the basis of sacrificing extinction ratio, so that the application of the silicon-based electro-optical modulator is limited.
And the lithium niobate and other crystals have excellent nonlinear optical characteristics, electro-optical characteristics and acousto-optical characteristics, and have wide application in the aspects of optical signal processing, information storage and the like. Therefore, at present, researchers propose that a silicon material and a lithium niobate crystal are combined to form an electro-optic crystal film to be applied to an electro-optic modulator, so that the characteristics of the silicon waveguide light guide and the lithium niobate electro-optic modulation characteristics can be utilized, namely, one part of a light field takes a silicon waveguide as a traveling light path, and the other part of the light field is modulated in the lithium niobate film layer, namely, by means of the advantages of the lithium niobate crystal, the short plate of the silicon material is effectively compensated, and the performance of the electro-optic modulator is improved.
At present, a mode of combining a silicon material and a lithium niobate crystal is to bond by using a bonding agent, but the thickness and the uniformity of the bonding agent cannot be accurately controlled, a good modulation effect can be achieved only when the thickness uniformity of an isolation layer between the lithium niobate crystal and a silicon waveguide is smaller than a certain value, the thickness uniformity of the isolation layer is better, and the modulation effect of an optical field on a lithium niobate thin film layer is more stable, so that the bonding agent is used as the isolation layer between the silicon material and the lithium niobate, the thickness and the uniformity of the isolation layer cannot be accurately controlled, and further the modulation of the optical field in the lithium niobate layer can be influenced, and the performance of an electro-optic modulator is further influenced.
Disclosure of Invention
The application provides an electro-optical crystal film, a preparation method thereof and an electro-optical modulator, which aim to solve the problem that the modulation of an optical field in a lithium niobate layer can be influenced by using an adhesive as an isolation layer of a silicon material and the lithium niobate, so that the performance of the electro-optical modulator is influenced.
In a first aspect, an embodiment of the present application provides an electro-optic crystal film, which sequentially includes, from bottom to top: the device comprises a silicon substrate layer, a silicon dioxide layer, a silicon waveguide layer, a coating isolation layer, a measurement reflection layer, an isolation layer and a functional thin film layer; wherein the silicon waveguide layer is embedded into the cladding isolation layer;
the measurement reflecting layer is metal or nonmetal with low microwave loss and high visible light waveband reflectivity and is used for monitoring the thickness and uniformity of the isolation layer and the functional thin film layer;
the refractive index of the isolation layer is lower than that of the functional thin film layer, and the isolation layer is subjected to planarization treatment and can be bonded with the functional thin film layer.
With reference to the first aspect, in one implementation form, the material of the measurement reflection layer is chromium or molybdenum.
With reference to the first aspect, in one implementation manner, the thickness of the isolation layer is: 50nm-2000nm, and the thickness uniformity is less than 5%; the isolation layer is made of silicon dioxide or silicon nitride, the roughness of the isolation layer is less than 0.5nm, and the flatness of the isolation layer is less than 1 nm.
With reference to the first aspect, in one implementation, the cladding isolation layer is silicon dioxide or silicon nitride; the coating isolation layer consists of a first coating isolation layer and a second coating isolation layer;
the thickness of the first coating isolation layer is as follows: 10nm-1000 nm; the thickness of the second coating isolation layer is equal to that of the silicon waveguide layer;
the first coating isolation layer and the second coating isolation layer are integrally formed.
With reference to the first aspect, in an implementation manner, the shape of the silicon waveguide in the silicon waveguide layer is a ridge-type stripe structure, the thickness of the silicon waveguide layer is 50nm to 50 μm, and the width of the silicon waveguide is 50nm to 50 μm.
With reference to the first aspect, in one implementation manner, the functional thin film layer is a lithium niobate crystal, a lithium tantalate crystal, a rubidium titanyl phosphate crystal, or a potassium titanyl phosphate crystal, and the thickness of the functional thin film layer is 50nm to 3000nm or 400nm to 100 μm.
In combination with the first aspect, in one implementation form, the silicon waveguide layer and the silicon dioxide layer are provided with silicon layers, the sum of the thicknesses of the silicon waveguide layer and the silicon layer is 50nm to 50 μm, and the thickness of the silicon dioxide layer is 50nm to 5 μm.
In a second aspect, embodiments of the present application provide, in part, an electro-optic modulator comprising an electro-optic crystal film as described in any one of the first aspect.
In a third aspect, an embodiment of the present application provides a method for preparing an electro-optic crystal film, where the method is used to prepare the electro-optic crystal film described in any one of the first aspect, and the method includes the following steps:
preparing a silicon-on-insulator structure, and etching the top silicon of the silicon-on-insulator structure by adopting an etching method to form a silicon waveguide layer; the silicon-on-insulator structure sequentially comprises a silicon substrate layer, a silicon dioxide layer and top silicon from bottom to top; forming a groove structure in the silicon waveguide layer after etching;
filling a coating isolation layer in the groove structure, and flattening the groove structure;
depositing a measurement reflecting layer on the flattened coating isolation layer;
depositing an isolation layer on the measurement reflection layer and flattening the isolation layer;
and preparing a functional thin film layer on the isolation layer to obtain the electro-optic crystal thin film.
With reference to the third aspect, in one implementation manner, etching the top silicon of the silicon-on-insulator structure includes: etching the top silicon layer by a dry etching method to form a ridge-shaped strip-shaped silicon waveguide; wherein the top layer silicon is completely etched or partially etched.
With reference to the third aspect, in an implementation manner, filling a cladding isolation layer in the groove structure, and planarizing the groove structure includes:
filling a coating isolation layer in the groove structure, wherein the coating isolation layer fills the groove structure and covers the silicon waveguide layer, and the step is repeated for at least three times;
and finally, the coating isolation layer with the target thickness is reserved above the silicon waveguide layer through polishing, the roughness of the coating isolation layer is less than 0.5nm, and the surface flatness is less than 1 nm.
With reference to the third aspect, in one implementation, the method of preparing the measurement reflection layer is magnetron sputtering.
With reference to the third aspect, in one implementation, depositing an isolation layer on the measurement reflection layer and planarizing the isolation layer includes:
and depositing an isolation layer on the surface of the measuring reflection layer, determining the thickness and the thickness uniformity of the isolation layer according to the measuring reflection layer, and flattening the isolation layer until the surface roughness of the isolation layer is less than 0.5nm and the surface flatness of the isolation layer is less than 1 nm.
With reference to the third aspect, in one implementation manner, the preparation method for filling the cladding isolation layer in the groove structure and depositing the isolation layer on the measurement reflection layer is PECVD, magnetron sputtering, evaporation or electroplating.
With reference to the third aspect, in one implementation manner, a functional thin film layer is prepared on the cladding isolation layer by using an ion implantation method and a bonding separation method, or by using a bonding method and a grinding and polishing method.
The embodiment of the application provides an electro-optical crystal film, a preparation method thereof and an electro-optical modulator, wherein the electro-optical crystal film sequentially comprises the following components from bottom to top: the device comprises a silicon substrate layer, a silicon dioxide layer, a silicon waveguide layer, a coating isolation layer, a measurement reflection layer, an isolation layer and a functional thin film layer. The silicon waveguide layer is embedded into the cladding isolation layer; the measurement reflecting layer is metal or nonmetal with low microwave loss and high reflectivity of a visible light wave band, and is used for monitoring the thickness and uniformity of the isolation layer and the functional thin film layer. The refractive index of the isolation layer is lower than that of the functional thin film layer, and the isolation layer is subjected to planarization treatment and can be bonded with the functional thin film layer. By adopting the scheme, the thickness of the isolation layer is controllable by arranging the measuring reflection layer in the structure, the thickness deviation of the isolation layer is reduced, the surface of the isolation layer is smoother, the uniformity is better, and the bonding coupling loss is reduced, so that the optical signal of the electro-optical modulator prepared can be well coupled between the functional thin film layer and the silicon waveguide layer, the prepared device has wide bandwidth, low loss and good device consistency.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an electro-optic crystal film provided by an embodiment of the present application;
FIG. 2 is a schematic illustration of a planarized isolation layer of the present application;
FIG. 3 is a schematic structural diagram of a method for manufacturing an electro-optic crystal film according to an embodiment of the present disclosure;
FIG. 4 is a schematic flow chart of a method for manufacturing an electro-optic crystal film according to an embodiment of the present disclosure.
Wherein, 100-top silicon; 110-a silicon substrate layer; 120-a silicon dioxide layer; 130-a silicon waveguide layer; 140-a wrapped isolation layer, 1401-a first wrapped isolation layer, 1402-a second wrapped isolation layer; 150-measuring the reflective layer; 160-an isolation layer; 170-functional film layer.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.
As described in the background of the present application, in the prior art, a silicon material and a lithium niobate crystal are bonded by using an adhesive, but the adhesive used in the prior art is benzocyclobutene resin, but the benzocyclobutene resin as the adhesive is easy to generate bubbles during the curing process of bonding lithium niobate and silicon material, and particularly, the problem is more obvious when large-size (4inch and above) lithium niobate and silicon material are bonded, in addition, the usage temperature of the benzocyclobutene resin is usually lower than 400 ℃, and may fail above this temperature, and the damage recovery of lithium niobate and the like by ion implantation usually requires a temperature of 400 ℃ or above, so the preparation of a lithium niobate single crystal film with a thickness of several hundred nanometers by the benzocyclobutene resin bonding method is also limited. Furthermore, benzocyclobutene resin belongs to high polymers, and can not be flattened by using a conventional chemical mechanical polishing process, so that silicon materials and lithium niobate crystals can not be tightly attached, and the performance of the electro-optical modulator is influenced.
In addition, the silicon waveguide layer in the electro-optical modulator needs to be polished and polished to be flat in the preparation process so as to control the surface flatness of the silicon waveguide layer, and the polishing and polishing operation can cause local damage of the silicon waveguide layer, poor thickness uniformity and poor surface flatness and influence the propagation performance of an optical signal, which can simultaneously cause uncontrollable coupling of light in the lithium niobate and the waveguide layer, thereby causing poor consistency of devices and being very unsuitable for industrial production.
More importantly, the hybrid integration of the silicon, lithium niobate and other photoelectric crystal films utilizes the characteristics of silicon waveguide light guiding and lithium niobate electro-optical modulation characteristics, one part of the light field takes the silicon waveguide as a traveling light path, and the other part of the light field is modulated in the lithium niobate thin film layer, so that a good modulation effect can be achieved when the thickness uniformity of the isolation layer between the lithium niobate thin film layer and the silicon waveguide is smaller than a certain value, the thickness uniformity of the isolation layer is better, the modulation effect of the light field on the lithium niobate thin film layer is more stable, and the thickness of the isolation layer cannot be accurately monitored by adopting a bonding agent bonding mode.
Therefore, in order to solve the above problem, an embodiment of the present application provides a structure diagram of an electro-optical crystal film, 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, a measurement reflection layer 150, an isolation layer 160 and a functional thin film layer 170.
The silicon waveguide layer 130 is embedded in a cladding isolation layer 140, that is, the cladding isolation layer 140 claddes the silicon waveguide layer 130.
Wherein the silicon substrate layer 110 and the silicon dioxide layer 120 may be obtained from a silicon-on-insulator (SOI) structure.
The measurement reflection layer 150 is a metal or nonmetal having low microwave loss and high reflectivity in a visible light band, and is used for monitoring the thickness and uniformity of the isolation layer 160 and the functional thin film layer 170.
The measurement reflection layer 150 can accurately measure the thickness of the isolation layer 160 and the functional thin film layer 170, so as to control the thickness uniformity, and particularly, the thickness of the isolation layer 160 can be accurately monitored, and the measurement principle is a white light interference method.
The refractive index of the isolation layer 160 is lower than that of the functional thin film layer 170, and the isolation layer 160 is planarized and may be bonded to the functional thin film layer 170.
The thickness of the isolation layer 160 can be monitored by using the measurement reflection layer 150, after planarization treatment, the surface of the isolation layer can be smoother, the thickness uniformity is good, and further, after the electro-optic modulator is prepared, optical signals can be well coupled between the functional thin film layer 170 and the silicon waveguide layer 130, the electro-optic performance of the electro-optic crystal thin film is improved, the consistency is good, and the finally prepared electro-optic modulator is wide in bandwidth, low in loss and good in device consistency.
In addition, the material of the isolation layer 160 is selected to have a refractive index lower than that of the material of the functional thin film layer 170, and the refractive index difference between the functional thin film layer 170 and the cladding isolation layer 140 can reduce the loss of the optical signal better.
The embodiment of the application provides an electro-optical crystal film, the electro-optical crystal film from the bottom up includes in proper order: a silicon substrate layer 110, a silicon dioxide layer 120, a silicon waveguide layer 130, a cladding isolation layer 140, a measurement reflection layer 150, an isolation layer 160 and a functional thin film layer 170. The silicon waveguide layer 130 is embedded in the cladding isolation layer 140, and the measurement reflection layer 150 is a metal or nonmetal with low microwave loss and high reflectivity in the visible light band, and is used for monitoring the thickness and uniformity of the isolation layer 160. The refractive index of the isolation layer 160 is lower than that of the functional thin film layer 170, and the isolation layer 160 is planarized and may be bonded to the functional thin film layer 170. By adopting the scheme provided by the embodiment of the application, the thickness of the isolation layer 160 is controllable by arranging the measurement reflection layer 150 in the structure, the thickness deviation is reduced, the surface of the isolation layer is smoother, the uniformity is better, and the bonding coupling loss is reduced, so that the optical signal of the prepared electro-optical modulator can be well coupled between the functional thin film layer 170 and the silicon waveguide layer 130, the bandwidth of the prepared device is wide, the loss is low, and the consistency of the device is good.
In one embodiment, the material of the measurement reflection layer 150 is chromium or molybdenum.
Chromium or molybdenum is selected as the material of the measurement reflection layer 150 because chromium or molybdenum is a material with low microwave loss and high reflectivity in the visible light band, and may be other materials meeting the requirements, which is not specifically limited in this application.
In one embodiment, the thickness of the isolation layer 160 is: 50nm-2000nm, and the thickness uniformity is less than 5%.
Wherein, the thickness uniformity of the isolation layer 160 is controlled by the measurement reflection layer 150 to be less than 5%, so as to achieve the effect of stably modulating the optical field in the lithium niobate thin film layer.
In one embodiment, the isolation layer 160 is silicon dioxide or silicon nitride, and the roughness of the isolation layer 160 is less than 0.5nm and the flatness is less than 1 nm.
Wherein, the refractive index of silicon dioxide, silicon nitride and other materials is lower than that of the photoelectric crystal film, and the surface roughness of the isolation layer 160 is less than 0.5nm and the flatness is less than 1nm after the planarization treatment.
In one embodiment, the cladding isolation layer 140 is silicon dioxide or silicon nitride; the wrapped-isolation layer 140 is comprised of a first wrapped-isolation layer 1401 and a second wrapped-isolation layer 1402; the thickness of the first encapsulating spacer 1401 is: 10nm-1000 nm; the thickness of the second cladding spacer layer 1402 is equal to the thickness of the silicon waveguide layer 130; the first encapsulating spacer 1401 is integrally formed with the second encapsulating spacer 1402.
The cladding isolation layer 140 also needs to be planarized, so that the surface uniformity is better.
In this embodiment, the cladding spacer 140 may include two parts, a first cladding spacer 1401 and a second cladding spacer 1402, where the first cladding spacer 1401 and the second cladding spacer 1402 are integrally formed, and the thickness of the second cladding spacer 1402 is the thickness of the silicon waveguide layer 130.
In a specific embodiment, the shape of the silicon waveguide in the silicon waveguide layer 130 is a ridge stripe structure, the thickness of the silicon waveguide layer 130 is 50nm-50 μm, and the width of the silicon waveguide is 50nm-50 μm.
In this embodiment, the silicon waveguide layer 130 may include a plurality of ridge-type stripe silicon waveguides uniformly distributed, waveguide grooves (groove structures) exist between the ridge-type stripe silicon waveguides, the cladding isolation layer 140 at the ridge-type silicon waveguides is higher than the waveguide grooves, when the silicon waveguide layer 130 is polished, the cladding isolation layer 140 at the waveguide grooves is over-polished, as shown in fig. 2, if a single polishing process cannot achieve the effect of flattening the silicon waveguides, the application adopts multiple polishing, and the deposition and polishing processes are repeated after polishing to the silicon waveguide layer 130 each time, so as to achieve the purpose of flattening the silicon waveguides, and finally, the material deposited at the waveguide grooves is the second cladding isolation layer 1402, and is integrally formed with the finally formed first cladding isolation layer 1401, so that the coupling effect between the functional thin film layer 170 and the silicon waveguide layer 130 is improved.
The functional thin film layer 170 is an electro-optic crystal material for modulating an optical signal. Since light is transmitted in a material having a large refractive index, the refractive index of the isolation layer 160 is lower than that of the functional thin film layer 170, and the thickness of the functional thin film layer 170 is 50nm to 3000nm or 400nm to 100 μm.
In the embodiment of the present application, the material of the functional thin film layer 170 may be selected according to the actual function to be realized, and the functional thin film layer 170 is selected from lithium niobate, lithium tantalate, and KTP (potassium titanyl phosphate, whose molecular formula is KTiOPO)4) And RTP (rubidium titanyl phosphate, molecular formula RbTiOPO)4) One kind of (1).
Optionally, the silicon waveguide layer 130 and the silicon dioxide layer 120 are provided with silicon layers, the sum of the thicknesses of the silicon waveguide layer 130 and the silicon layers is 50nm to 50 μm, and the thickness of the silicon dioxide layer 120 is 50nm to 5 μm.
In this embodiment, there may also be a silicon layer between the silicon waveguide layer 130 and the silicon dioxide layer 120, the sum of the thicknesses of which and the silicon waveguide layer is 50nm-50 μm; the SOI wafer structure is 50nm-50 μm Si/50nm-5 μm SiO from top to bottom2and/Si, if the etching depth of the top layer silicon is equal to the thickness of the top layer silicon, namely, in the case of complete etching, the SOI wafer subjected to the etching treatment forms a three-layer structure of a silicon substrate layer 110, a silicon dioxide layer 120 and a silicon waveguide layer 130. Since the complete etching has a high process requirement and is prone to over-etching, once the silicon dioxide layer 120 is etched, the planarization effect of the silicon waveguide layer 130 will be affected, and therefore, in another embodiment, an incomplete etching process is adopted, in which the etching depth is less than the thickness of the top silicon layer, so that a silicon layer is formed between the silicon waveguide layer 130 and the silicon dioxide layer 120. The incomplete etching method enables the etching depth of the silicon waveguide layer 130 to be adjusted and controlled within a certain range, and the transmission performance of light can be adjusted and controlled when the etching depth is different, that is, the thickness of the silicon waveguide layer 130 is different. In addition, after the top silicon is etched into the silicon waveguide layer 130, the strength will beThe silicon layer can improve the strength after being etched, becoming lower.
Based on the electro-optic crystal film provided by the previous embodiment of the present application, the embodiment of the present application provides an electro-optic modulator, which comprises the electro-optic crystal film as described in any one of the above embodiments.
The electro-optical crystal thin film provided by the embodiment of the application is applied to the electro-optical modulator, the electro-optical modulator has the advantages of two materials, namely silicon, lithium niobate and other electro-optical crystals, takes the silicon waveguide with high refractive index as a loading strip, simultaneously realizes the optical modulation effect on the lithium niobate layer, and can be widely applied.
The embodiment of the application also provides a method for preparing the electro-optic crystal film, as shown in fig. 3, and fig. 3 is a schematic structural diagram of a preparation process of the electro-optic crystal film.
Specifically, as shown in fig. 4, the preparation method comprises the following steps:
s11, preparing a silicon-on-insulator structure, and etching the top silicon 100 of the silicon-on-insulator structure by adopting an etching method to form a silicon waveguide layer 130; the silicon-on-insulator structure comprises a silicon substrate layer 110, a silicon dioxide layer 120 and top silicon 100 from bottom to top in sequence; after etching, a trench structure is formed in the silicon waveguide layer 130.
The SOI wafer structure is also called as an SOI wafer, and the structure of the SOI wafer is as follows from top to bottom: 50nm-50 mu m Si/50nm-5 mu m SiO2/Si。
Optionally, in this step, a plurality of uniformly distributed ridge-type strip silicon waveguides are etched on one surface of the top silicon 100 by a dry method to form the silicon waveguide layer 130, and the silicon waveguide layer 130 may also be completed by a process combining a mechanical processing, a wet etching and a plurality of processing modes; the dimensions of the ridge-type silicon waveguide are width: 50nm-50 μm, thickness: 50nm-50 μm, wherein the top layer silicon 100(Si) is completely etched or partially etched, and after etching, a groove structure is formed between adjacent ridge type strip-shaped silicon waveguides.
S12, filling the trench structure with a cladding isolation layer 140, and planarizing the trench structure.
Optionally, in this step, a cladding isolation layer 140 is deposited on the surface of the silicon waveguide, the cladding isolation layer 140 fills the groove structure and covers the silicon waveguide layer, the cladding isolation layer 140 is ground and polished to the silicon waveguide layer 130, when the removal rate of polishing is almost zero, the polishing is stopped, and this step is repeated at least three times; wherein the final polishing leaves a cladding isolation layer 140 of a target thickness (e.g., 50nm, 100nm, 500nm, 1000nm, 2000nm, etc.) over the silicon waveguide layer 130 until the roughness of the cladding isolation layer 140 is less than 0.5nm and the surface flatness is less than 1 nm. The final effect of this step is that the thickness of the silicon dioxide covering the silicon waveguide layer 130 is 10nm-1000nm, and the actual thickness of the silicon dioxide covering the silicon waveguide layer 130 is 10nm + -0.5 nm-1000nm + -50 nm calculated by 5% non-uniformity.
Wherein, the deposition method of the cladding isolation layer 140 is PECVD, sputtering, evaporation, electroplating, etc.; the polishing method may adopt CMP.
S13, a measurement reflection layer 150 is deposited on the planarized cladding isolation layer 140.
The deposition method of the measurement reflection layer 150 may be magnetron sputtering.
S14, an isolation layer 160 is deposited on the measurement reflection layer 150 and planarized.
The step is to deposit an isolation layer 160 on the surface of the measurement reflection layer 150, determine the thickness and the thickness uniformity according to the measurement reflection layer 150, and planarize the isolation layer 160 until the surface roughness is less than 0.5nm and the surface flatness is less than 1 nm. Wherein, the thickness of the final isolation layer 160 in this step is 50nm-2000nm, and the thickness of the isolation layer 160 actually covered on the measurement reflection layer 150 is 50nm + -2.5 nm-2000nm + -100 nm calculated by 5% non-uniformity.
S15, preparing a functional film layer 170 on the isolation layer 160 to obtain the electro-optic crystal film.
In this step, the preparation method of the functional thin film layer 170 may select an ion implantation method and a bonding separation method, and may also select a bonding method and a grinding and polishing method, which is not specifically limited in this application.
When selected using ion implantation and bondingIn the separation method, the scheme comprises the following steps: performing ion implantation on the functional film, wherein the implantation energy of the ion implantation is 50-1000KeV, and the dosage is 1E16-1E17 ions/cm2Forming a functional thin film wafer with a three-layer structure of a thin film layer, a separation layer and a residual material layer; preparing and forming a bonding body by adopting a plasma bonding mode; under vacuum environment or under 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 single crystal film; polishing the lithium niobate single crystal film to 50nm-3000nm (such as 100nm, 400nm, 500nm, 800nm, 1000nm, 2000nm, etc.) to obtain the electro-optic crystal film with nanometer-level 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 environment or under 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 the film to 1-102 μm by mechanical grinding, and polishing to 400nm-100 μm (such as 500nm, 1 μm, 5 μm, 10 μm, 50 μm, etc.), to obtain the lithium niobate single crystal film with micron-scale thickness.
The purpose of the bonding body heat preservation is to improve the bonding force of the bonding body to be more than 10 MPa.
The thickness of the functional thin film layer 170 can be adjusted by adjusting the ion implantation depth, specifically, the greater the ion implantation depth, the greater the thickness of the prepared functional thin film layer 170; conversely, the smaller the depth of ion implantation, the smaller the thickness of the functional thin film layer 170 is prepared.
After ion implantation and before bonding, it is usually necessary to clean the two contacting bonding surfaces to enhance the bonding effect.
In the application, different activation means are selected according to the thickness of the selected electro-optic crystal material. Since the thickness of the ion implantation is limited, it is not suitable for electro-optic crystal materials with a relatively large thickness. When the thickness of the selected electro-optic crystal material is thicker, ion implantation is not carried out, and direct bonding is carried out.
According to the preparation method disclosed by the embodiment of the application, 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.
In the embodiments of the present application, the embodiments of the structural portion and the embodiments of the preparation method portion may be referred to each other, and are not described herein again.
In order to make the scheme of the application clearer, specific examples are further disclosed in the embodiment of the application.
Example 1 (ion implantation + bonding separation method)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2and/Si, cleaning the top silicon (Si) of the SOI wafer, etching the top silicon of the SOI wafer by using a dry etching method to obtain a ridge-type strip silicon waveguide, completely etching the top silicon, wherein the ridge-type strip silicon waveguide has the size of 1 mu m in width and 220nm in thickness, and forming a groove structure in the silicon waveguide layer after etching, wherein the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge-type silicon waveguide surface, and depositing a layer of 520nm silicon dioxide (SiO) in the groove structure by adopting PECVD (or sputtering, evaporation, electroplating and the like)2) And as a coating isolation layer, filling the groove structure with silicon dioxide, covering the silicon waveguide layer, polishing (flattening) the silicon dioxide coating isolation layer covering the silicon waveguide layer to the silicon waveguide layer by adopting CMP, repeating PECVD deposition of the silicon dioxide, then polishing to the silicon waveguide layer for 3 times, and finally polishing to keep the coating isolation layer with the thickness of 50nm above the silicon waveguide layer, wherein the roughness of the coating isolation layer is finally improved to be less than 0.5nm, and the surface flatness is less than 1 nm. Wherein, the thickness of the silicon dioxide actually covered on the silicon waveguide layer is 50nm +/-2.5 nm calculated by 5 percent of nonuniformity.
3) SiO coating isolation layer for covering ridge type silicon waveguide in step 2)2Cleaning the surface, and depositing a layer of Cr in a magnetron sputtering mode for measurementA reflective layer, wherein Cr is 50nm thick.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of SiO with the thickness of 500nm on the surface of the reflection layer measured by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)2As an isolation layer. Then polishing the isolation layer to 200nm to improve SiO2The roughness is less than 0.5nm, and the surface flatness is less than 1 nm. The thickness of the silicon dioxide isolation layer actually covering the measurement reflective layer Cr is 200nm +/-10 nm calculated according to 5% of nonuniformity.
5) Preparing a lithium niobate wafer having a size of 4 inches, and implanting helium ions (He) by ion implantation+) Implanting helium ions into the lithium niobate wafer at an implantation energy of 200KeV and a dose of 4E16ions/cm2And forming the lithium niobate wafer with a three-layer structure of a thin film layer, a separation layer and a residual material layer.
6) And (3) cleaning the silicon dioxide surface in the step (4) and the film surface in the step (5), and bonding the film layer of the cleaned lithium niobate wafer and the isolation layer (silicon dioxide) by adopting a plasma bonding method to form a bonded body.
7) And then putting the bonding body into heating equipment, and preserving heat 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 of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa, and the damage of ion implantation to the thin film layer can be recovered, so that the obtained lithium niobate thin film layer has the property close to that of a lithium niobate wafer.
8) And polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with the nanoscale thickness.
As can be seen, example 1 is a method of ion implantation + bonding separation, in which the coating isolation layer is SiO2The isolation layer is SiO2The measuring reflecting layer is Cr, the functional film layer is lithium niobate, and the functional film layer is bonded and separated with the isolating layer after ion implantation.
Example 2 (ion implantation + bonding separation method)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2and/Si, cleaning the top silicon Si of the SOI wafer, etching the top silicon of the SOI wafer to obtain a ridge-type strip silicon waveguide by using a dry etching method, wherein the top silicon is not completely etched, the ridge-type strip silicon waveguide has the size of 1 mu m and the thickness of 100nm, and a groove structure is formed in the silicon waveguide layer after etching, and the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge type strip silicon waveguide surface, and depositing a layer of 520nm silicon nitride (Si) on the ridge type strip silicon waveguide surface by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)3N4) And filling the groove structure with the coating isolation layer as a coating isolation layer, covering the silicon waveguide layer, polishing the silicon nitride coating isolation layer covering the silicon waveguide layer to the silicon waveguide layer by adopting CMP (chemical mechanical polishing), repeating PECVD (plasma enhanced chemical vapor deposition) to deposit silicon nitride, then polishing to the silicon waveguide layer for 3 times, retaining the coating isolation layer with the thickness of 50nm above the silicon waveguide layer by final polishing, and finally improving the roughness of the coating isolation layer to be less than 0.5nm and the surface flatness to be less than 1 nm. The final effect of this step is that the thickness of the silicon nitride coated on the silicon waveguide layer is 50nm, calculated as 5% non-uniformity, and the thickness of the silicon nitride coating isolation layer actually coated on the silicon waveguide layer is 50nm +/-2.5 nm.
3) For the coating isolation layer Si covering the ridge type silicon waveguide in the step 2)3N4And cleaning the surface, and depositing a layer of Cr as a measurement reflecting layer in a magnetron sputtering mode, wherein the thickness of the Cr is 50 nm.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of 500nm silicon nitride on the surface of the reflection layer to be measured by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like) as an isolating layer. Then polishing the isolation layer to a thickness of 200nm to improve Si3N4The roughness is less than 0.5nm, and the surface flatness is less than 1 nm. The thickness of the silicon nitride isolation layer actually covering the measurement reflective layer Cr is 200nm +/-10 nm calculated according to 5% of non-uniformity.
5) Preparing a lithium niobate wafer having a size of 4 inches, and implanting helium ions (He) by ion implantation+) Implanting helium ions into the lithium niobate wafer at an implantation energy of 200KeV and a dose of 4E16ions/cm2And forming the lithium niobate wafer with a three-layer structure of a thin film layer, a separation layer and a residual material layer.
6) And (3) cleaning the silicon nitride isolation layer surface in the step (4) and the film surface in the step (5), and bonding the film layer of the cleaned lithium niobate wafer and the isolation layer (silicon nitride) by adopting a plasma bonding method to form a bonding body.
7) And then putting the bonding body into heating equipment, and preserving heat 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 of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa, and the damage of ion implantation to the thin film layer can be recovered, so that the obtained lithium niobate thin film layer has the property close to that of a lithium niobate wafer.
8) And polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with the nanoscale thickness.
As can be seen, example 2 is a method of ion implantation + bonding separation, in which the cladding isolation layer is Si3N4The isolating layer is Si3N4The measuring reflecting layer is Cr, the functional film layer is lithium niobate, and the functional film layer is prepared by ion implantation and then bonding and separating with the isolating layer.
Example 3 (direct bonding + lapping and polishing method)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2and/Si, cleaning the top Si layer of the SOI wafer, etching the top silicon layer of the SOI wafer to obtain a ridge type strip silicon waveguide by using a dry etching method, completely etching the top silicon layer, wherein the ridge type strip silicon waveguide has the size of 1 mu m and the thickness of 220nm, and forming a groove junction in the silicon waveguide layer after etchingAnd the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge-type silicon waveguide surface, and depositing a layer of 520nm silicon dioxide (SiO) on the ridge-type silicon waveguide surface by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)2) Filling the groove structure as a coating isolation layer, covering the silicon waveguide layer, polishing (flattening) the silicon dioxide coating isolation layer covering the silicon waveguide layer to the silicon waveguide layer by adopting CMP, repeating PECVD to deposit silicon dioxide, then polishing to the silicon waveguide layer for 3 times, retaining the coating isolation layer with the thickness of 50nm above the silicon waveguide layer by final polishing, and finally improving the roughness of the coating isolation layer to be less than 0.5nm and the surface flatness to be less than 1 nm. The step can be repeated for many times, and the final effect is that the thickness of the coating isolation layer covered above the silicon waveguide layer is 50nm, the thickness of the silicon dioxide actually covered above the silicon waveguide layer is 50nm +/-2.5 nm calculated by 5% of non-uniformity.
3) SiO coating isolation layer for covering ridge type silicon waveguide in step 2)2And cleaning the surface, and depositing a layer of Cr as a measurement reflecting layer in a magnetron sputtering mode, wherein the thickness of the Cr is 50 nm.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of SiO with the thickness of 500nm on the reflection layer by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)2As an isolation layer. Then polishing the isolation layer to 200nm to improve SiO2The roughness is less than 0.5nm, and the surface flatness is less than 1 nm. The thickness of the silicon dioxide isolation layer actually covering the measurement reflective layer Cr is 200nm +/-10 nm calculated according to 5% of nonuniformity.
5) Preparing a lithium niobate wafer with the size of 4 inches, cleaning a process surface, and bonding the process surface of the cleaned lithium niobate wafer with an isolation layer (silicon dioxide) of an SOI substrate by adopting a plasma bonding method to form a bonding body.
6) And then, putting the bonding body into heating equipment for heat preservation at high temperature, wherein the heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa through the link.
7) And then 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 micron-sized thickness.
As can be seen, example 3 is a method using direct bonding plus lapping and polishing, in which the cladding isolation layer is SiO2The isolation layer is SiO2The measuring reflecting layer is Cr, the functional film layer is lithium niobate, and the functional film layer is directly bonded with the isolating layer and then is ground and polished.
Example 4 (direct bonding + lapping and polishing method)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2and/Si, cleaning the top Si layer of the SOI wafer, etching the top silicon layer of the SOI wafer to obtain the ridge type strip silicon waveguide by using a dry etching method, wherein the top silicon layer is not completely etched, the ridge type strip silicon waveguide has the size of 1 mu m and the thickness of 100nm, and a groove structure is formed in the silicon waveguide layer after etching, and the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge-type silicon waveguide surface, and depositing a layer of 520nm silicon nitride (Si) on the ridge-type silicon waveguide surface by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)3N4) Filling the groove structure as a coating isolation layer, covering the silicon waveguide layer, polishing (flattening) the silicon nitride coating isolation layer covering the silicon waveguide layer to the silicon waveguide layer by adopting CMP, repeating PECVD to deposit silicon nitride, then polishing to the silicon waveguide layer for 3 times, retaining the coating isolation layer with the thickness of 50nm above the silicon waveguide layer by final polishing, and finally improving the roughness of the coating isolation layer to be less than 0.5nm and the surface flatness to be less than 1 nm. The final effect of this step is that the thickness of the silicon nitride coated on the silicon waveguide layer is 50nm, calculated as 5% non-uniformity, and the thickness of the silicon nitride coating isolation layer actually coated on the silicon waveguide layer is 50nm +/-2.5 nm.
3) Coating isolation layer Si for covering ridge type strip silicon waveguide in step 2)3N4And cleaning the surface, and depositing a layer of Cr as a measurement reflecting layer in a magnetron sputtering mode, wherein the thickness of the Cr is 50 nm.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of 500nm silicon nitride on the reflection layer by adopting PECVD (or sputtering, evaporation, electroplating and the like) as an isolation layer. Then polishing the isolation layer to a thickness of 200nm to improve Si3N4The roughness is less than 0.5nm, and the surface flatness is less than 1 nm. The thickness of the silicon nitride isolation layer actually covering the measurement reflective layer Cr is 200nm +/-10 nm calculated according to 5% of non-uniformity. The thickness and the thickness nonuniformity of the silicon nitride in the steps 2) and 4) are 250nm +/-12.5 nm.
5) Preparing a lithium niobate wafer with the size of 4 inches, cleaning a process surface, and bonding the process surface of the cleaned lithium niobate wafer with a silicon nitride layer (an isolation layer) of an SOI substrate by adopting a plasma bonding method to form a bonding body.
6) And then, putting the bonding body into heating equipment for heat preservation at high temperature, wherein the heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa through the link.
7) And then 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 micron-sized thickness.
As can be seen, example 4 is a method using direct bonding plus lapping and polishing, in which the cladding isolation layer is Si3N4The isolating layer is Si3N4The measuring reflecting layer is Cr, the functional film layer is lithium niobate, and the functional film layer is directly bonded with the isolating layer and then is ground and polished.
Example 5 (ion implantation + bonding separation method)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2The Si is cleaned on the top layer Si of the SOI wafer and then used on the top layer Si of the SOI waferAnd etching the ridge type strip silicon waveguide by a dry etching method, completely etching the top silicon layer, forming a groove structure in the silicon waveguide layer after etching, wherein the size of the ridge type strip silicon waveguide is 1 mu m and 220nm, and the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge-type silicon waveguide surface, and depositing a layer of 520nm silicon dioxide (SiO) in the groove structure by adopting PECVD (or sputtering, evaporation, electroplating and the like)2) Filling the groove structure as a coating isolation layer, covering the silicon waveguide layer, polishing (flattening) the silicon dioxide coating isolation layer covering the silicon waveguide layer to the silicon waveguide layer by adopting CMP, repeating PECVD to deposit silicon dioxide, then polishing to the silicon waveguide layer for 3 times, retaining the coating isolation layer with the thickness of 50nm above the silicon waveguide layer by final polishing, and finally improving the roughness of the coating isolation layer to be less than 0.5nm and the surface flatness to be less than 1 nm. The final effect of the step is that the thickness of the coating isolation layer covering the silicon waveguide layer is 50nm, calculated by 5% of non-uniformity, and the thickness of the silicon dioxide actually covering the silicon waveguide layer is 50nm +/-2.5 nm.
3) SiO coating isolation layer for covering ridge type strip-shaped silicon waveguide in step 2)2And cleaning the surface, and depositing a layer of Cr as a measurement reflecting layer in a magnetron sputtering mode, wherein the thickness of the Cr is 50 nm.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of 500nm silicon nitride (Si) on the surface of the reflection layer measured by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)3N4) As an isolation layer. Then polishing the thickness of the isolation layer to 200nm, improving the roughness of the silicon nitride to be less than 0.5nm and the surface flatness to be less than 1 nm. The thickness of the silicon nitride isolation layer actually covering the measurement reflective layer Cr is 200nm +/-10 nm calculated according to 5% of non-uniformity.
5) Preparing a lithium niobate wafer having a size of 4 inches, and implanting helium ions (He) by ion implantation+) Implanting helium ions into the lithium niobate wafer at an implantation energy of 200KeV and a dose of 4E16ions/cm2Forming lithium niobate with three-layer structure of thin layer, separation layer and residual material layerAnd (5) a wafer.
6) And (3) cleaning the silicon nitride surface in the step (4) and the film surface in the step (5), and bonding the film layer of the cleaned lithium niobate wafer and the isolation layer (silicon nitride) by adopting a plasma bonding method to form a bonding body.
7) And then putting the bonding body into heating equipment, and preserving heat 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 of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa, and the damage of ion implantation to the thin film layer can be recovered, so that the obtained lithium niobate thin film layer has the property close to that of a lithium niobate wafer.
8) And polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with the nanoscale thickness.
As can be seen, example 5 is an ion implantation + bonding separation method, in which the coating isolation layer is SiO2The isolating layer is Si3N4The measuring reflecting layer is Cr, the functional film layer is lithium niobate, and the functional film layer is prepared by bonding and separating the functional film layer and the isolating layer after ion implantation.
Example 6 (direct bonding + lapping and polishing method)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2and/Si, cleaning the top Si layer of the SOI wafer, etching the top silicon layer of the SOI wafer by using a dry etching method to obtain the ridge type strip silicon waveguide, completely etching the top silicon layer, wherein the ridge type strip silicon waveguide has the size of 1 mu m and the thickness of 220nm, forming a groove structure in the silicon waveguide layer after etching, and the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge-type silicon waveguide surface, and depositing a layer of 520nm silicon dioxide (SiO) on the ridge-type silicon waveguide surface by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)2) As a cladding isolation layer, filling the groove structure and covering the silicon waveguide layerAnd then, polishing the silicon dioxide coating isolation layer covering the silicon waveguide layer to the silicon waveguide layer by adopting CMP, repeating PECVD to deposit silicon dioxide, then polishing to the silicon waveguide layer for 3 times, and finally, retaining the coating isolation layer with the thickness of 50nm above the silicon waveguide layer by polishing for the last time, wherein the roughness of the coating isolation layer is finally improved to be less than 0.5nm, and the surface flatness is less than 1 nm. The final effect of the step is that the thickness of the coating isolation layer covering the silicon waveguide layer is 50nm, calculated by 5% of non-uniformity, and the thickness of the silicon dioxide actually covering the silicon waveguide layer is 50nm +/-2.5 nm.
3) SiO coating isolation layer for covering ridge type silicon waveguide in step 2)2And cleaning the surface, and depositing a layer of Cr as a measurement reflecting layer in a magnetron sputtering mode, wherein the thickness of the Cr is 50 nm.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of 500nm silicon nitride (Si) on the surface of the reflection layer measured by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)3N4) As an isolation layer. Then polishing the thickness of the isolation layer to 200nm, improving the roughness of the silicon nitride to be less than 0.5nm and the surface flatness to be less than 1 nm. The thickness of the silicon nitride isolation layer actually covering the measurement reflective layer Cr is 200nm +/-10 nm calculated according to 5% of non-uniformity.
5) Preparing a lithium niobate wafer with the size of 4 inches, cleaning a process surface, and bonding the process surface of the cleaned lithium niobate wafer with a silicon nitride layer (an isolation layer) of an SOI substrate by adopting a plasma bonding method to form a bonding body.
6) And then, putting the bonding body into heating equipment for heat preservation at high temperature, wherein the heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa through the link.
7) And then 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 micron-sized thickness.
As can be seen, example 6 is a direct bond plus lapping polishThe method, wherein the coating isolation layer is SiO2The isolating layer is Si3N4The measuring reflecting layer is Cr, the functional film layer is lithium niobate, and the functional film layer is directly bonded with the isolating layer and then is ground and polished.
Example 7 (ion implantation + bonding separation method)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2and/Si, cleaning the top Si layer of the SOI wafer, etching the top silicon layer of the SOI wafer by using a dry etching method to obtain the ridge type strip silicon waveguide, completely etching the top silicon layer, wherein the ridge type strip silicon waveguide has the size of 1 mu m and the thickness of 220nm, forming a groove structure in the silicon waveguide layer after etching, and the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge-type silicon waveguide surface, and depositing a layer of 520nm silicon nitride (Si) on the ridge-type silicon waveguide surface by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)3N4) Filling the groove structure as a coating isolation layer, covering the groove structure, polishing the silicon nitride coating isolation layer covering the silicon waveguide layer to the silicon waveguide layer by adopting CMP (chemical mechanical polishing), repeating the PECVD (plasma enhanced chemical vapor deposition) to deposit silicon nitride, then polishing the silicon waveguide layer for 3 times, and finally, retaining the coating isolation layer with the thickness of 50nm above the silicon waveguide layer by polishing for the last time, wherein the roughness of the coating isolation layer is finally improved to be less than 0.5nm, and the surface flatness is less than 1 nm. The final effect of this step is that the thickness of the silicon nitride coated on the silicon waveguide layer is 50nm, calculated as 5% non-uniformity, and the thickness of the silicon nitride coating isolation layer actually coated on the silicon waveguide layer is 50nm +/-2.5 nm.
3) Coating isolation layer Si for covering ridge type strip silicon waveguide in step 2)3N4And cleaning the surface, and depositing a layer of Mo serving as a measurement reflecting layer in a magnetron sputtering mode, wherein the thickness of the Mo is 50 nm.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of 500nm silicon nitride on the surface of the reflection layer to be measured by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like) as an isolating layer. Then polishingThe thickness of the isolation layer is 200nm, and Si is improved3N4The roughness is less than 0.5nm, and the surface flatness is less than 1 nm. Calculated by 5% non-uniformity, the thickness of the silicon nitride isolation layer actually covered on the measurement reflection layer Mo is 200nm +/-10 nm.
5) Preparing a lithium niobate wafer having a size of 4 inches, and implanting helium ions (He) by ion implantation+) Implanting helium ions into the lithium niobate wafer at an implantation energy of 200KeV and a dose of 4E16ions/cm2And forming the lithium niobate wafer with a three-layer structure of a thin film layer, a separation layer and a residual material layer.
6) And (3) cleaning the silicon nitride surface in the step (4) and the film surface in the step (5), and bonding the film layer of the cleaned lithium niobate wafer and the isolation layer (silicon nitride) by adopting a plasma bonding method to form a bonding body.
7) And then putting the bonding body into heating equipment, and preserving heat 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 of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa, and the damage of ion implantation to the thin film layer can be recovered, so that the obtained lithium niobate thin film layer has the property close to that of a lithium niobate wafer.
8) And polishing and thinning the lithium niobate single crystal film to 400nm to obtain the lithium niobate single crystal film with the nanoscale thickness.
As can be seen, example 7 is a method of ion implantation + bonding separation, in which the cladding isolation layer is Si3N4The isolating layer is Si3N4The measuring reflecting layer is Mo, the functional film layer is lithium niobate, and the functional film layer is bonded with the isolating layer after ion implantation.
Example 8 (direct bonding + method of lapping and polishing)
1) An SOI wafer having a size of 4 inches, a thickness of 0.5mm and a smooth surface was prepared, and the SOI wafer structure was 220nm Si/2 μm SiO from the top down2The Si on the top layer of the SOI wafer is cleaned, and then the SOI wafer is cleanedAnd etching the top silicon layer of the circle by using a dry etching method to form a ridge-type strip silicon waveguide, wherein the top silicon layer is completely etched, the ridge-type strip silicon waveguide has the size of 1 mu m width and 220nm thickness, and a groove structure is formed in the silicon waveguide layer after etching, and the height of the groove structure is equal to the thickness of the silicon waveguide layer.
2) Cleaning the etched ridge-type silicon waveguide surface, and depositing a layer of 1000nm silicon nitride (Si) on the ridge-type silicon waveguide surface by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)3N4) Filling the groove structure as a coating isolation layer, covering the groove structure, polishing the silicon nitride coating isolation layer covering the silicon waveguide to a silicon waveguide layer by adopting CMP (chemical mechanical polishing), repeating the PECVD (plasma enhanced chemical vapor deposition) to deposit silicon nitride, then polishing the silicon waveguide layer for 3 times, and finally, retaining the coating isolation layer with the thickness of 200nm above the silicon waveguide layer by polishing for the last time, and finally improving the roughness of the coating isolation layer to be less than 0.5nm and the surface flatness to be less than 1 nm. The final effect of this step is that the thickness of the silicon nitride layer covered on the silicon waveguide layer is 200nm, calculated as 5% non-uniformity, and the thickness of the silicon nitride coating isolation layer actually covered on the silicon waveguide layer is 200nm +/-10 nm.
3) For the coating isolation layer Si covering the ridge type silicon waveguide in the step 2)3N4And cleaning the surface, and depositing a layer of Mo serving as a measurement reflecting layer in a magnetron sputtering mode, wherein the thickness of the Mo is 100 nm.
4) Cleaning the process surface of the reflection layer measured in the step 3), and depositing a layer of 1000nm silicon nitride (Si) on the surface of the reflection layer measured by adopting PECVD (or adopting sputtering, evaporation, electroplating and the like)3N4) As an isolation layer. Then polishing the isolation layer to a thickness of 500nm to improve Si3N4The roughness is less than 0.5nm, and the surface flatness is less than 1 nm. Calculated by 5% non-uniformity, the thickness of the silicon nitride isolation layer actually covered on the measurement reflection layer Mo is 500nm +/-25 nm.
5) Preparing a lithium niobate wafer with the size of 4 inches, cleaning a process surface, and bonding the process surface of the cleaned lithium niobate wafer with a silicon nitride layer (an isolation layer) of an SOI substrate by adopting a plasma bonding method to form a bonding body.
6) And then, putting the bonding body into heating equipment for heat preservation at high temperature, wherein the heat preservation process is carried out in a vacuum environment or in a protective atmosphere formed by at least one of nitrogen and inert gas, the heat preservation temperature is 400 ℃, and the heat preservation time is 3 hours. The bonding force can be improved by more than 10MPa through the link.
7) And then 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 micron-sized thickness.
As can be seen, example 8 is a method using direct bonding plus lapping and polishing, in which the cladding isolation layer is Si3N4The isolating layer is Si3N4The measuring reflecting layer is Mo, the functional film layer is lithium niobate, and the functional film layer is directly bonded with the isolating layer and then is ground and polished.
In addition, on the basis of the above embodiments, other embodiments may also be derived, such as: on the basis of each embodiment, the functional thin film layer in the embodiment is replaced by lithium tantalate, KTP or RTP, and other process parameters can be changed without changing or according to needs; that is, one skilled in the art can combine alternative materials and process parameters according to the above embodiments, and the application is not limited specifically.
In the embodiment, the lithium niobate single crystal film with the nanometer-scale thickness can be obtained by adopting the ion implantation and direct bonding method; the method for preparing the lithium niobate single crystal thin film by direct bonding and grinding and polishing can obtain the lithium niobate single crystal thin film with micron-sized thickness, and the single crystal thin film has the advantages of easy processing of a silicon waveguide and excellent electro-optic characteristics of a lithium niobate crystal, so that the electro-optic crystal thin film and the preparation method disclosed by the embodiment of the application can be widely applied.
The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.

Claims (15)

1. An electro-optic crystal film, comprising, in order from bottom to top: the device comprises a silicon substrate layer, a silicon dioxide layer, a silicon waveguide layer, a coating isolation layer, a measurement reflection layer, an isolation layer and a functional thin film layer; wherein the silicon waveguide layer is embedded into the cladding isolation layer;
the measurement reflecting layer is metal or nonmetal with low microwave loss and high visible light waveband reflectivity and is used for monitoring the thickness and uniformity of the isolation layer and the functional thin film layer;
the refractive index of the isolation layer is lower than that of the functional thin film layer, and the isolation layer is subjected to planarization treatment and can be bonded with the functional thin film layer.
2. The electro-optic crystal film of claim 1, wherein the material of the measurement reflective layer is chromium or molybdenum.
3. An electro-optic crystal film as claimed in claim 1 or claim 2 wherein the spacer layer has a thickness of: 50nm-2000nm, the thickness uniformity is less than 5%, the isolation layer is silicon dioxide or silicon nitride, the roughness of the isolation layer is less than 0.5nm, and the flatness is less than 1 nm.
4. The electro-optic crystal film of claim 1 or 2, wherein the cladding spacer layer is silicon dioxide or silicon nitride, and the cladding spacer layer is composed of a first cladding spacer layer and a second cladding spacer layer;
the thickness of the first coating isolation layer is as follows: 10nm-1000 nm; the thickness of the second coating isolation layer is equal to that of the silicon waveguide layer;
the first coating isolation layer and the second coating isolation layer are integrally formed.
5. The electro-optic crystal film of claim 1 or 2, wherein the silicon waveguide layer has a ridge-type stripe structure, the thickness of the silicon waveguide layer is 50nm-50 μm, and the width of the silicon waveguide layer is 50nm-50 μm.
6. The electro-optic crystal film of claim 1 or 2, wherein the functional thin film layer is a lithium niobate crystal, a lithium tantalate crystal, a rubidium titanyl phosphate crystal, or a potassium titanyl phosphate crystal, and the functional thin film layer has a thickness of 50nm to 3000nm or 400nm to 100 μm.
7. The electro-optic crystal film of claim 1, wherein the silicon waveguide layer and the silicon dioxide layer are provided with silicon layers, the sum of the thicknesses of the silicon waveguide layer and the silicon layers being 50nm-50 μm, and the thickness of the silicon dioxide layer being 50nm-5 μm.
8. An electro-optic modulator comprising the electro-optic crystal film of any one of claims 1-7.
9. A method for producing an electro-optic crystal film, the method being used for producing the electro-optic crystal film according to any one of claims 1 to 7, the method comprising the steps of:
preparing a silicon-on-insulator structure, and etching the top silicon of the silicon-on-insulator structure by adopting an etching method to form a silicon waveguide layer; the silicon-on-insulator structure sequentially comprises a silicon substrate layer, a silicon dioxide layer and top silicon from bottom to top; forming a groove structure in the silicon waveguide layer after etching;
filling a coating isolation layer in the groove structure, and flattening the groove structure;
depositing a measurement reflecting layer on the flattened coating isolation layer;
depositing an isolation layer on the measurement reflection layer and flattening the isolation layer;
and preparing a functional thin film layer on the isolation layer to obtain the electro-optic crystal thin film.
10. The method of claim 9, wherein etching the top silicon of the silicon-on-insulator structure comprises: etching the top silicon layer by a dry etching method to form a ridge-shaped strip-shaped silicon waveguide; wherein the top layer silicon is completely etched or partially etched.
11. The method according to claim 9, wherein filling a cladding isolation layer in the groove structure and planarizing the groove structure comprises:
filling a coating isolation layer in the groove structure, wherein the coating isolation layer fills the groove structure and covers the silicon waveguide layer, and the step is repeated for at least three times;
and finally, the coating isolation layer with the target thickness is reserved above the silicon waveguide layer through polishing, the roughness of the coating isolation layer is less than 0.5nm, and the surface flatness is less than 1 nm.
12. The production method according to claim 9, wherein the method for producing the measurement reflection layer is magnetron sputtering.
13. The method of claim 9, wherein depositing an isolation layer on the measurement reflection layer and planarizing it comprises:
and depositing an isolation layer on the surface of the measuring reflection layer, determining the thickness and the thickness uniformity of the isolation layer according to the measuring reflection layer, and flattening the isolation layer until the surface roughness of the isolation layer is less than 0.5nm and the surface flatness of the isolation layer is less than 1 nm.
14. The method according to claim 9, wherein the step of filling the groove structure with the cladding isolation layer and depositing the isolation layer on the measurement reflection layer is performed by PECVD, magnetron sputtering, evaporation or electroplating.
15. The production method according to claim 9, wherein a functional thin film layer is produced on the clad separator layer by an ion implantation method and a bonding separation method, or by a bonding method and a lapping polishing method.
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