CN112198588A

CN112198588A - Silicon waveguide and preparation method thereof

Info

Publication number: CN112198588A
Application number: CN202011065987.7A
Authority: CN
Inventors: 唐波; 张鹏; 杨妍; 李志华; 刘若男; 李彬; 黄凯
Original assignee: Institute of Microelectronics of CAS
Current assignee: Institute of Microelectronics of CAS
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2021-01-08

Abstract

The invention relates to a silicon waveguide and a preparation method thereof. A method of fabricating a silicon waveguide, comprising: forming a rectangular silicon waveguide on a semiconductor substrate; introducing hydrogen gas flow to anneal the rectangular silicon waveguide to make the surface smooth, wherein the annealing temperature is 975-1025 ℃. The method of the invention modifies the rectangular optical waveguide into the arc waveguide with smooth surface by using the high-temperature annealing process, thus reducing the roughness and further reducing the transmission loss of the waveguide.

Description

Silicon waveguide and preparation method thereof

Technical Field

The invention relates to the field of photonic devices, in particular to a silicon waveguide and a preparation method thereof.

Background

An Optical Waveguide (Optical Waveguide) is a dielectric device that guides light waves to propagate therein, and is also called a dielectric Optical Waveguide. Dielectric waveguides are the basic building blocks of integrated optical systems and their components. The dielectric waveguide mainly plays the roles of limiting, transmitting and coupling light waves. Rectangular waveguides are commonly used in integrated optics. The materials used to form waveguides are many in variety, and silicon is one of the materials commonly used to form waveguides. The transmission loss of the waveguide is closely related to the roughness of the outer surface (including the side wall and the upper surface) of the waveguide, and the larger the roughness is, the more serious the scattering of light is, and the larger the transmission loss of light in the waveguide is. At present, a common photoelectric device is based on silicon-on-insulator (SOI), a rectangular silicon waveguide is obtained by etching top silicon, and the rectangular silicon waveguide has clear edges and sharp shape, so that the optical loss is large, and the reduction range of the waveguide loss is limited.

Therefore, the invention is especially provided.

Disclosure of Invention

The invention mainly aims to provide a preparation method of a silicon waveguide, which utilizes a high-temperature annealing process to modify a rectangular optical waveguide into an arc-shaped waveguide with a smooth surface, so that the roughness is reduced, and the transmission loss of the waveguide is reduced.

In order to achieve the above purpose, the invention provides the following technical scheme:

a method of fabricating a silicon waveguide, comprising:

forming a rectangular silicon waveguide on a semiconductor substrate;

introducing hydrogen gas flow to anneal the rectangular silicon waveguide to make the surface smooth, wherein the annealing temperature is 975-1025 ℃.

In a hydrogen atmosphere, the rectangular silicon waveguide is subjected to high-temperature thermal annealing, so that silicon atoms can flow again, the appearance is changed, and a spherical-like structure, such as a semi-cylinder, a hemisphere or other shapes with smooth corners, is spontaneously formed under the action of multiple factors such as surface tension and the like, namely the smooth surface is formed, the shapes have lower roughness, and the waveguide transmission loss is smaller.

On the other hand, the optical field of the silicon waveguide with the new shape obtained after high-temperature annealing is circular, and the extra loss of light cannot be generated.

Therefore, compared with the prior art, the invention can fundamentally and greatly reduce the transmission loss by only adding one step of high-temperature annealing process.

The silicon waveguide obtained by the method can be used for any photoelectric device, including but not limited to a typical coupler, a filter, a modulator or a sensor.

Compared with the prior art, the invention achieves the following technical effects:

(1) the waveguide transmission loss is reduced;

(2) only one step of procedure is added, and the procedure before annealing can adopt the same process as the prior art, thereby bringing convenience for process upgrading.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

FIG. 1 is a schematic diagram of a prior art fabricated rectangular waveguide structure;

FIG. 2 is an SEM image of the waveguide profile obtained by annealing at different temperatures;

fig. 3 is a schematic view of the waveguide structure obtained after annealing according to the present invention.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is illustrative only and is not intended to limit the scope of the present disclosure. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure.

Various structural schematics according to embodiments of the present disclosure are shown in the figures. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers, and relative sizes and positional relationships therebetween shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, as actually required.

In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present. In addition, if a layer/element is "on" another layer/element in one orientation, then that layer/element may be "under" the other layer/element when the orientation is reversed.

Taking the waveguide formed on SOI as an example, as shown in fig. 1, the SOI includes three layers of a silicon substrate 1, a buried oxide layer 2(BOX layer), and a top silicon layer, respectively.

Wherein the BOX layer 2 typically has a lower index of refraction and has a lower index of refraction with a thickness that optically isolates the waveguide from the silicon substrate underlying the BOX layer 2.

A rectangular silicon waveguide 3 may be formed by etching the top silicon layer of the SOI. The etching method is arbitrary, for example, dry etching such as ion milling etching, plasma etching, reactive ion etching, etc., or wet etching is adopted, and usable etching agents include acetic acid, nitric acid, hydrofluoric acid, strong base, etc.

How to reduce the waveguide surface roughness is the core of reducing waveguide losses. The rectangular waveguide has a sharp shape, so that the roughness is increased, the invention adds a procedure, and the rectangular silicon waveguide is modified into a semi-cylindrical or spherical silicon waveguide with a smooth curve on the outer surface, and the specific method comprises the following steps:

In a hydrogen atmosphere, the rectangular silicon waveguide is subjected to high-temperature thermal annealing, so that silicon atoms can flow again, the appearance is changed, and a sphere-like structure, such as a semi-cylinder, a hemisphere or other shapes with smooth corners, is spontaneously formed under the action of multiple factors such as surface tension and the like, and the shapes have lower roughness and smaller waveguide transmission loss.

The annealing temperatures are different, the shapes of the silicon waveguides are slightly different, as shown in the SEM image shown in FIG. 2, the shapes of the silicon waveguides obtained by annealing at 950 ℃, 975 ℃, 1000 ℃ and 1025 ℃ are respectively shown, preferably the shape of the silicon waveguide obtained by annealing at 1000 ℃ is smooth arc-shaped, and the corresponding cross-sectional structure is shown in FIG. 3 (the cross section along the length direction of the waveguide) and is a semi-cylindrical waveguide 4.

On the other hand, the optical field of the silicon waveguide with the new shape obtained after high-temperature annealing is circular, and extra light loss is not caused.

Therefore, the transmission loss can be reduced substantially by only adding one high-temperature annealing process.

In some preferred embodiments, the annealing temperature is from 1000 ℃ to 1025 ℃.

In some preferred embodiments, the flow rate of the hydrogen gas stream is from 20to 180L/min.

In some preferred embodiments, the chamber pressure during annealing is: 20Torr-1 atm. atm means one standard atmosphere.

In some preferred embodiments, the annealing is performed for a treatment time of 10 to 300 seconds.

The preferred process conditions described above can be used to promote a smoother, more regular surface.

One preferred embodiment is:

etching on the SOI to form a rectangular waveguide;

then introducing hydrogen gas flow, and annealing the rectangular silicon waveguide, wherein the annealing temperature is 1000 ℃, the flow rate of the hydrogen gas flow is 20-180L/min, and the chamber pressure during annealing is as follows: 20Torr-1atm, and the annealing time is 10-300 s.

This embodiment results in a semi-cylindrical waveguide with significantly reduced optical loss compared to the waveguide prior to annealing.

The embodiments of the present disclosure have been described above. However, these examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The scope of the disclosure is defined by the appended claims and equivalents thereof. Various alternatives and modifications can be devised by those skilled in the art without departing from the scope of the present disclosure, and such alternatives and modifications are intended to be within the scope of the present disclosure.

Claims

1. A method of fabricating a silicon waveguide, comprising:

forming a rectangular silicon waveguide on a semiconductor substrate;

and introducing hydrogen gas flow to anneal the rectangular silicon waveguide at 975-1025 ℃.

2. The method of claim 1, wherein the annealing temperature is 1000 ℃ to 1025 ℃.

3. The method of claim 1, wherein the flow rate of the hydrogen gas stream is 20to 180L/min.

4. The production method according to any one of claims 1 to 3, wherein the chamber pressure at the time of annealing is: 20Torr-1 atm.

5. The method according to claim 1, wherein the annealing is performed for a treatment time of 10 to 300 seconds.

6. The method of manufacturing according to claim 1, wherein the rectangular silicon waveguide is formed by:

and etching the silicon layer to obtain the rectangular silicon waveguide.

7. A silicon waveguide obtained by the production method according to any one of claims 1 to 6.

8. The silicon waveguide of claim 7, wherein the semiconductor substrate is a silicon-on-insulator substrate comprising, in order from bottom to top, a silicon substrate, a buried oxide layer, and a silicon layer.

9. An optoelectronic device comprising a silicon waveguide according to claim 7 or 8.

10. The optoelectronic device according to claim 9, wherein the optoelectronic device is a coupler, a filter, a modulator, or a sensor.