阅读说明：本技术 一种波导层间耦合结构及其制备方法 (Waveguide interlayer coupling structure and preparation method thereof ) 是由 李彬 李志华 谢玲 李东浩 唐波 张鹏 杨妍 刘若男 于 2021-06-17 设计创作，主要内容包括：本发明公开一种波导层间耦合结构及其制备方法,涉及硅光器件技术领域,以解决现有耦合结构存在层间耦合损耗较大的技术问题。所述波导层间耦合结构包括：基底。形成在基底上的第一波导；其中,第一波导位于基底的第一区域。形成在基底上的第一介质层,且第一介质层覆盖第一波导。以及形成在第一介质层上第二波导,其中,第二波导位于基底的第二区域,第一波导在基底上的投影与第二波导在基底上的投影具有重合区域,以使从第二波导出射的光耦合地进入第一波导中。第二波导靠近第一波导的一端具有台阶状结构,且沿第一波导至第二波导的方向,台阶状结构中的台阶的厚度依次增大。(The invention discloses a waveguide interlayer coupling structure and a preparation method thereof, relates to the technical field of silicon optical devices, and aims to solve the technical problem that the conventional coupling structure has large interlayer coupling loss. The waveguide interlayer coupling structure includes: a substrate. A first waveguide formed on the substrate; wherein the first waveguide is located at a first region of the substrate. A first dielectric layer formed on the substrate, and the first dielectric layer covers the first waveguide. And a second waveguide formed on the first dielectric layer, wherein the second waveguide is located at a second region of the substrate, and a projection of the first waveguide on the substrate and a projection of the second waveguide on the substrate have an overlapping region, so that light exiting from the second waveguide is coupled into the first waveguide. One end of the second waveguide close to the first waveguide is provided with a step-shaped structure, and the thickness of steps in the step-shaped structure is sequentially increased along the direction from the first waveguide to the second waveguide.)

1. A waveguide interlayer coupling structure, comprising:

a substrate;

a first waveguide formed on the substrate; wherein the first waveguide is located at a first region of the substrate;

a first dielectric layer formed on the substrate, and the first dielectric layer covers the first waveguide;

and a second waveguide formed on the first dielectric layer, wherein the second waveguide is located in a second region of the substrate, and a projection of the first waveguide on the substrate and a projection of the second waveguide on the substrate have a coinciding region, so that light exiting the second waveguide is coupled into the first waveguide;

one end of the second waveguide close to the first waveguide is provided with a step-shaped structure, and the thickness of steps in the step-shaped structure is sequentially increased along the direction from the first waveguide to the second waveguide.

2. The waveguide interlayer coupling structure of claim 1, further comprising a second dielectric layer formed on the first dielectric layer, wherein the second dielectric layer covers the second waveguide.

3. The waveguide interlayer coupling structure of claim 1, wherein an end of the first waveguide away from the second waveguide is formed with a silicon optical device.

4. The waveguide interlayer coupling structure of claim 1, wherein when the thickness of the second waveguide is 400nm to 1 μm, the thickness of the thinnest step in the stepped structure is 50nm to 150 nm; and/or the presence of a gas in the gas,

when the thickness of the second waveguide is 400 nm-1 μm, the thickness difference between adjacent steps in the step-shaped structure is 50 nm-150 nm.

5. A waveguide interlayer coupling structure according to any one of claims 1 to 4, wherein the refractive index of the material from which the first waveguide is made is 1.9 to 3.5, and/or the refractive index of the material from which the second waveguide is made is 1.9 to 3.5.

6. A waveguide interlayer coupling structure according to any one of claims 1 to 4, wherein the refractive index of the material from which the first waveguide is made is greater than the refractive index of the material from which the first dielectric layer is made.

7. A waveguide interlayer coupling structure as claimed in any one of claims 1 to 4, wherein the first waveguide is made of silicon, germanium or silicon germanium; and/or the second waveguide is made of silicon, silicon nitride or silicon oxynitride; and/or the first dielectric layer is made of silicon oxide or germanium oxide.

8. A preparation method of a waveguide interlayer coupling structure is characterized by comprising the following steps:

providing a substrate;

forming a first waveguide on the substrate; wherein the first waveguide is located at a first region of the substrate;

forming a first dielectric layer on the substrate, wherein the first dielectric layer covers the first waveguide;

forming a second waveguide on the first dielectric layer; wherein the second waveguide is located at a second region of the substrate, a projection of the first waveguide on the substrate and a projection of the second waveguide on the substrate have a region of coincidence, such that light exiting the second waveguide is coupled into the first waveguide; one end of the second waveguide close to the first waveguide is provided with a step-shaped structure, and the thickness of steps in the step-shaped structure is sequentially increased along the direction from the first waveguide to the second waveguide.

9. The method for preparing the waveguide interlayer coupling structure according to claim 8, wherein the step of forming the second waveguide on the first dielectric layer comprises the steps of:

obtaining the number of steps of the step-shaped structure and the thickness of each step according to the thickness of the second waveguide;

and sequentially forming steps on the first medium layer from bottom to top to obtain the step-shaped structure.

10. The method for preparing a waveguide interlayer coupling structure according to claim 8, further comprising the steps of:

and forming a second dielectric layer covering the second waveguide on the first dielectric layer.

Technical Field

The invention relates to the technical field of silicon optical devices, in particular to a waveguide interlayer coupling structure and a preparation method thereof.

Background

Silicon materials have great benefits as substrate materials for photonic integrated chips, such as compatibility with CMOS (Complementary Metal Oxide Semiconductor) processes, which can reduce large-scale production costs and facilitate optoelectronic integration with electronic chips. However, with the continuous expansion of the application field, the requirements for the photonic devices are more and more complicated, and the simple preparation of the SOI waveguide device with complicated functions On the SOI (Silicon-On-Insulator) substrate cannot meet the requirements of future development.

In order to further improve the performance of the photonic integrated chip, a silicon-based SiN-on-SOI hybrid integrated material platform is receiving wide attention from researchers. Bonding SOI with SiN_xThe material combination can realize a complex and high-performance photonic integrated chip.

However, currently SOI and SiN_xThe photonic integrated chip combined by the materials has larger loss, so that the coupling loss of the existing waveguide interlayer structure is larger.

Disclosure of Invention

The invention aims to provide a waveguide interlayer coupling structure and a preparation method thereof, which are used for solving the technical problem of larger interlayer coupling loss of the existing coupling structure.

In a first aspect, the present invention provides a waveguide interlayer coupling structure, comprising:

a substrate. A first waveguide formed on the substrate; wherein the first waveguide is located at a first region of the substrate. A first dielectric layer formed on the substrate, and the first dielectric layer covers the first waveguide. And a second waveguide formed on the first dielectric layer, wherein the second waveguide is located at a second region of the substrate, and a projection of the first waveguide on the substrate and a projection of the second waveguide on the substrate have an overlapping region, so that light exiting from the second waveguide is coupled into the first waveguide. One end of the second waveguide close to the first waveguide is provided with a step-shaped structure, and the thickness of steps in the step-shaped structure is sequentially increased along the direction from the first waveguide to the second waveguide.

Under the condition of adopting the technical scheme, the waveguide interlayer coupling structure provided by the invention comprises a first waveguide and a second waveguide positioned above the first waveguide, wherein the second waveguide has a step-shaped structure. When the light wave enters the waveguide interlayer coupling structure, the light wave can enter the second waveguide firstly or the first waveguide firstly. For example, when the light wave first enters the second waveguide, the light wave first enters the step with the largest thickness of the second waveguide and then propagates from the step with the largest thickness of the second waveguide to the step with the smallest thickness of the second waveguide at the end in sequence, and the thickness of the second waveguide gradually decreases during the transmission process of the light wave. At this time, the light wave is more easily entered into the first waveguide from the second waveguide, thereby achieving light wave coupling between the second waveguide and the first waveguide. For another example, when the light wave first enters the first waveguide, the light wave enters the step with the smallest thickness of the second waveguide from the first waveguide and propagates to the step with the largest thickness of the second waveguide from the step with the smallest thickness of the second waveguide in sequence, and the thickness of the second waveguide gradually increases during the transmission process of the light wave. Based on this, the light wave is easier to enter the second waveguide from the first waveguide, thereby realizing the light wave coupling between the first waveguide and the second waveguide. Based on the step-shaped structure of the second waveguide, the thickness of the coupling part of the second waveguide and the first waveguide is relatively reduced compared with the prior art, so that the coupling length of the second waveguide and the first waveguide in the invention is relatively reduced compared with the prior art. Therefore, the coupling loss of the waveguide interlayer coupling structure is smaller than that of the prior art.

In practical application, the invention can also properly increase the interlayer distance between the first waveguide and the second waveguide on the premise of ensuring the coupling efficiency, thereby effectively reducing the interlayer crosstalk during high integration.

In a second aspect, the present invention further provides a method for preparing a waveguide interlayer coupling structure, including the following steps:

providing a substrate;

forming a first waveguide on a substrate; wherein the first waveguide is located at a first region of the substrate;

forming a first dielectric layer covering the first waveguide on the substrate;

forming a second waveguide on the first dielectric layer; wherein the second waveguide is located in a second region of the substrate, and a projection of the first waveguide on the substrate and a projection of the second waveguide on the substrate have an overlapping region, so that light exiting from the second waveguide is coupled into the first waveguide; one end of the second waveguide close to the first waveguide is provided with a step-shaped structure, and the thickness of steps in the step-shaped structure is sequentially increased along the direction from the first waveguide to the second waveguide.

Compared with the prior art, the preparation method of the waveguide interlayer coupling structure provided by the invention has the same beneficial effects as the waveguide interlayer coupling structure in the technical scheme, and the details are not repeated here.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:

fig. 1 is a cross-sectional view of a waveguide interlayer coupling structure provided in an embodiment of the present invention;

FIG. 2 is a top view of a waveguide interlayer coupling structure provided by an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a second waveguide provided in an embodiment of the present invention;

fig. 4 is a schematic structural diagram of a first waveguide according to an embodiment of the present invention;

fig. 5 to fig. 11 are schematic process diagrams of a waveguide interlayer coupling structure manufacturing method according to an embodiment of the present invention;

FIG. 12 is a schematic diagram of another configuration of a second waveguide according to an embodiment of the present invention;

reference numerals:

100-substrate, 101-interlayer dielectric layer, 102-silicon substrate, 103-top silicon, 200-first dielectric layer, 300-first waveguide, 301-silicon optical device, 400-second waveguide, 401-step structure, 402-sub-waveguide, 500-second dielectric layer and 600-photoresist layer.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise. The meaning of "a number" is one or more unless specifically limited otherwise.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

As shown in fig. 1 to 4, an embodiment of the present invention provides a waveguide interlayer coupling structure. The method comprises the following steps:

a substrate 100; a first waveguide 300 formed on the substrate 100; wherein the first waveguide is located at a first region of the substrate and is formed on the substrate 100 as a first dielectric layer 200. And the first dielectric layer 200 covers the first waveguide 300. And a second waveguide 400 formed on the first dielectric layer 200, wherein the second waveguide 400 is located at a second region of the substrate 100, and a projection of the first waveguide 300 on the substrate 100 and a projection of the second waveguide 400 on the substrate 100 have an overlapping region, so that light exiting from the second waveguide 400 is coupled into the first waveguide 300;

one end of the second waveguide 400 close to the first waveguide 300 has a stepped structure 401, and the thickness of the steps in the stepped structure 401 increases in sequence along the direction from the first waveguide 300 to the second waveguide 400.

In practical applications, the waveguide interlayer coupling structure may further include a second dielectric layer 500 formed on the first dielectric layer 200 and covering the second waveguide 400.

As a specific example, as shown in fig. 1 to 4, in the waveguide interlayer coupling structure provided in the embodiment of the present invention, an optical wave enters (right side in the figure) the second waveguide 400 and propagates to the stepped structure 401 at the end (left side in the figure), wherein the second waveguide 400 has the stepped structure 401, and the thickness of the steps in the stepped structure 401 increases in sequence along the direction from the first waveguide 300 to the second waveguide 400. The size of the second waveguide 400 is gradually reduced in the direction from the first waveguide 300 to the second waveguide 400, and the effective refractive index of the mode field of the second waveguide 400 becomes smaller. At this time, the light waves more easily enter the first dielectric layer 200, and the light waves in the second waveguide 400 are coupled into the first waveguide 300 through the evanescent field, thereby realizing the light wave coupling between the second waveguide 400 and the first waveguide 300. Based on the step-shaped structure of the second waveguide, the thickness of the coupling part of the second waveguide and the first waveguide is relatively reduced compared with the prior art, so that the coupling length of the second waveguide and the first waveguide in the invention is relatively reduced compared with the prior art. Therefore, the coupling loss of the waveguide interlayer coupling structure is smaller than that of the prior art.

In practice, the coupling coefficient of the waveguide is inversely proportional to the waveguide thickness (specifically, the core half-width, corresponding to half the thickness of the first waveguide 300 or the second waveguide 400), and the coupling length is inversely proportional to the coupling coefficient. Therefore, in order to reduce the absorption loss of the waveguide and improve the waveguide coupling efficiency, the coupling length needs to be shortened. Based on this, the waveguide interlayer coupling structure provided by the embodiment of the present invention improves the coupling coefficient between the first waveguide 300 and the second waveguide 400 by reducing the coupling length between the second waveguide and the first waveguide, thereby improving the waveguide coupling efficiency. Specifically, the above coupling length corresponds to the second waveguide 400 of the embodiment of the present invention, and therefore, the thickness of the second waveguide 400 of the embodiment of the present invention needs to be reduced. Based on this, the second waveguide 400 in the waveguide interlayer coupling structure provided by the embodiment of the present invention is provided with the step-shaped structure 401 with gradually changed thickness, so as to achieve the technical effects of reducing the coupling length, improving the coupling coefficient, and further improving the coupling efficiency.

Referring to fig. 5, the base 100 may be an SOI substrate including a silicon substrate 102, an interlayer dielectric layer 101, and a top silicon 103 stacked from bottom to top, and at this time, the top silicon 103 is patterned to form a corresponding first waveguide 300. Of course, the substrate 100 may be other types of substrates, and the substrate 100 at least has the interlayer dielectric layer 101 as the lower cladding layer of the first waveguide 300.

More specifically, as shown in fig. 2, in the conventional flat coupling structure, both waveguides are parallel and have a rectangular cross section. The first waveguide 300 provided by the embodiment of the present invention may have a tapered shape, in addition to a rectangular shape, at an end close to the second waveguide 400. The more the tapered end is sharp, the more difficult it is to machine. When the waveguide interlayer coupling structure provided by the embodiment of the present invention is adopted, based on the increase of the coupling coefficient, the embodiment of the present invention can increase the tip widths of the end portions of the first waveguide 300 and the second waveguide 400, so as to reduce the processing difficulty in the actual manufacturing process.

The first dielectric layer 200 is a dielectric material having a refractive index smaller than that of the first waveguide 300. The first dielectric layer 200 serves as an upper cladding layer of the first waveguide 300, and the material thereof is preferably the same as that of a lower cladding layer of the first waveguide 300. For example, when the substrate 100 is an SOI substrate, the first waveguide 300 is made of silicon, and the corresponding lower cladding layer (interlayer dielectric layer 101) and upper cladding layer (first dielectric layer 200) of the first waveguide 300 may be made of silicon dioxide. In practical applications, the material for preparing the first waveguide may also be germanium or silicon germanium, and the material for the first dielectric layer may also be other materials, such as: germanium dioxide.

Of course, the first waveguide 300 may also form a step-like structure similar to the second waveguide 400 (refer to the structural schematic of the step-like structure 401 shown in fig. 1, which performs 180 ° rotation), so as to further improve the coupling coefficient of the waveguide interlayer coupling structure in the embodiment of the present invention.

It should be noted that, when the substrate 100 is a substrate of another type, the material of the first waveguide 300 and the corresponding upper cladding and lower cladding may be other materials, for example, the refractive index of the material for preparing the first waveguide 300 is 1.9 to 3.5, and the refractive index of the material for preparing the first dielectric layer 200 and the interlayer dielectric layer 101 is 1 to 1.5.

The second waveguide 400 may be tapered at its end near the first waveguide 300, but may also be rectangular. The first dielectric layer 200 is a dielectric material having a refractive index smaller than that of the second waveguide 400. The top of the second waveguide 400 may also be formed with a second dielectric layer 500 covering the second waveguide 400, and the second dielectric layer 500 serves as an upper cladding layer of the second waveguide 400, and the material of the second dielectric layer 500 is preferably the same as that of a lower cladding layer (first dielectric layer 200) of the second waveguide 400. For example, when the substrate 100 is an SOI substrate, the first waveguide 300 is silicon, and the material of the corresponding lower cladding (the first dielectric layer 200) of the second waveguide 400 is silicon dioxide, in which case the material of the second dielectric layer 500 is the same as that of the first dielectric layer 200. Wherein the second waveguide 400 may be silicon, silicon nitride, or silicon oxynitride.

It should be noted that, when the substrate 100 is a substrate of another type, the second waveguide 400 and the corresponding upper cladding and lower cladding may be made of other materials, for example, the refractive index of the material for making the second waveguide 400 is 1.9 to 3.5, and the refractive indices of the materials for the first dielectric layer 200 and the second dielectric layer 500 are 1 to 1.5.

As shown in fig. 1 and 3, in one possible implementation, the waveguide interlayer coupling structure may further include a silicon optical device 301 formed on an end of the first waveguide 300 away from the second waveguide. For example: an etching is performed through the first waveguide 300 and a waveguide-on-silicon type germanium detector is formed for converting an optical signal into an electrical signal. Of course, the silicon optical device 301 may be other silicon optical devices 301 than the detector, which may be formed on the first waveguide 300.

In one possible implementation, the second waveguide 400 is deposited on the first dielectric layer 200, and has a thickness of 400nm to 1 μm or more. At this time, the thickness of the thinnest step in the stepped structure 401 may be 50nm to 150nm, and/or the thickness difference between adjacent steps in the stepped structure 401 may be 50nm to 150 nm.

As shown in fig. 1 and 4, the second waveguide 400 is optimally formed in a wedge shape, but it is difficult to form a slope by photolithography, and the stepped structure 401 provided in the present invention has a continuous step surface as an achievable alternative to the slope.

As shown in fig. 5 to fig. 11, an embodiment of the present invention further provides a method for preparing a waveguide interlayer coupling structure, including the following steps:

as shown in fig. 5, step S1: a substrate 100 is provided.

The base 100 has at least an interlayer dielectric layer 101 and may be an SOI substrate. The SOI substrate can be prepared by any one of a silicon wafer bonding and back etching method, a smart cut technique and an oxygen implantation isolation method, or by an SOI substrate which has already been prepared.

As shown in fig. 6, step S2: a first waveguide 300 is formed on a substrate 100. Wherein the first waveguide 300 is located at a first region of the substrate 100.

When the base 100 employs an SOI substrate, patterning is performed on the top silicon 103 of the SOI substrate, resulting in the first waveguide 300.

When the substrate 100 does not adopt an SOI substrate, the substrate 100 has an interlayer dielectric layer 101, a first waveguide material layer is formed on the interlayer dielectric layer 101 by deposition, and patterning is performed on the first waveguide material layer to obtain the first waveguide 300.

As shown in fig. 6, step S3: the first waveguide 300 is patterned and a corresponding silicon optical device 301 is formed.

The waveguide etching, the epitaxy, the ion implantation and the thermal electrode preparation of the silicon optical device 301 involve other auxiliary processes, which are all existing mature processes and are not core improvement points of the present invention, and thus, the details are not described again. The silicon optical device 301 includes a silicon optical passive device including, but not limited to, silicon or silicon nitride waveguides, gratings, arrayed waveguide gratings, microring resonators, multimode interferometers, thermo-optic devices, etc., and a silicon optical active device including, but not limited to, modulators and detectors.

As shown in fig. 7, step S4: a first dielectric layer 200 is formed on the substrate 100, wherein the first dielectric layer 200 covers the first waveguide 300.

When the base material is an SOI substrate, the interlayer dielectric layer 101 may be silicon dioxide, and the first dielectric layer 200 may also be silicon dioxide. The first dielectric layer 200 may be formed on the surfaces of the first waveguide 300 and the interlayer dielectric layer 101 by any one of the conventional Deposition processes such as Chemical Vapor Deposition (CVD), Molecular Beam Epitaxy (MBE).

When the base material does not adopt an SOI substrate, the first dielectric layer 200 is formed on the surfaces of the first waveguide 300 and the interlayer dielectric layer 101 by adopting a suitable deposition method according to the material used for the interlayer dielectric layer 101 and according to the actual material.

S410: the first dielectric layer 200 is thinned to a predetermined thickness.

The preset thickness of the first dielectric layer 200 is determined according to the designed distance between waveguide layers, and the thinning mode can be dry etching or chemical mechanical polishing.

As shown in fig. 8 and 9, step S5: forming a second waveguide 400 on the first dielectric layer 200; wherein the second waveguide is located in a second region of the substrate, and a projection of the first waveguide on the substrate and a projection of the second waveguide on the substrate have an overlapping region, so that light exiting from the second waveguide is coupled into the first waveguide; one end of the second waveguide close to the first waveguide is provided with a step-shaped structure, and the thickness of steps in the step-shaped structure is sequentially increased along the direction from the first waveguide to the second waveguide.

The second waveguide 400 is made of a material having a refractive index of 1.9 to 3.5, such as silicon, silicon nitride, or silicon oxynitride. Wherein the second waveguide 400 material layer may be deposited on the first dielectric layer 200 using any of the existing implementations. The second waveguide 400 material layer is then patterned to obtain the second waveguide 400.

In one possible implementation, forming the second waveguide 400 on the first dielectric layer 200 includes the following steps:

s511: according to the thickness of the second waveguide 400, the number of steps of the stepped structure 401 and the thickness of each step are obtained.

The thickness of the conventional second waveguide 400 may be 400nm to 1 μm, and the thickness of each stage of the preset steps may be 100nm, so that the number of the preset steps may be 4 to 10 stages.

S512: steps are sequentially formed on the first medium layer 200 from bottom to top to obtain a step-like structure 401.

After each patterning treatment, the following requirements are met when the thickness of the step is measured:

the thinnest step thickness of the step-like structure 401 is 50-150 nm, and/or the thickness difference between adjacent steps in the step-like structure 401 is 50-150 nm.

The patterning process for the second waveguide 400 is performed by using a corresponding etching method according to a specific material. For example, when the second waveguide 400 is silicon nitride, the step structure 401 may be formed by dry etching, and the reaction gas of the dry etching may be a mixed gas of sulfur hexafluoride and oxygen.

In the steps S511 to S512, the second waveguide 400 and the corresponding step-like structure 401 are formed by etching. The embodiment of the present invention further provides another way to form the second waveguide 400 and the step-like structure 401, as shown in fig. 11 and 12, including:

s521: a photoresist layer 600 is formed on the first dielectric layer 200, and is developed to form a corresponding pattern of sub-waveguides 402.

S522: sub-waveguides 402 are formed in the first dielectric layer 200 in regions where the photoresist layer 600 is absent.

S523: repeating steps S521 and S522 to form a plurality of sub-waveguides 402, and forming a corresponding step between every two adjacent sub-waveguides 402 to obtain the step-like structure 401.

The step-like structure 401 can be obtained without etching in the method, and in step S522, the sub-waveguide 402 and the photoresist layer 600 can be thinned to a corresponding thickness by chemical mechanical polishing or the like. The sub-waveguides 402 may be formed by any deposition method known in the art. At this time, the photoresist layer 600 also includes a plurality of sub photoresist layers 600, and after the formation of all the sub waveguides 402 is completed, the photoresist is removed, so that the formation process of the upper cladding layer of the second waveguide 400 can be performed.

The step-like structure 401 is divided into a plurality of corresponding sub-waveguides 402 according to the thickness of each step, and the corresponding step-like structure 401 can be formed in a manner of not using etching by conventional means of photoresist and deposition, so that another possible implementation manner is provided.

In this case, if the first waveguide 300 also needs to be formed with a step-like structure, reference may be made to the above steps S521-S523, but the method for forming the plurality of sub-waveguides 402 has a stronger applicability for deposition materials, such as silicon dioxide and silicon nitride.

In a possible implementation manner, the preparation method provided by the embodiment of the present invention further includes the following steps:

as shown in fig. 10, step S6: a second dielectric layer 500 is formed on the first dielectric layer 200 to cover the second waveguide 400.

When the base material is an SOI substrate, the interlayer dielectric layer 101 and the first dielectric layer 200 may be silicon dioxide, and the second dielectric layer 500 may also be silicon dioxide. The second dielectric layer 500 may be formed on the surfaces of the second waveguide 400 and the first dielectric layer 200 by any conventional deposition process, such as chemical vapor deposition or molecular beam epitaxy.

When the substrate does not adopt an SOI substrate, the second dielectric layer 500 is formed on the surfaces of the second waveguide 400 and the first dielectric layer 200 by using a suitable deposition method according to the material used for the first dielectric layer 200 and the actual material.

In the foregoing description of embodiments, the particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.