CN1629663A - Silicon-on-insulator ridge optical waveguide with new cross-sectional shape and its manufacturing method - Google Patents

Abstract

The invention relates to the field of optical waveguide technology, in particular to a silicon-on-insulator ridge-shaped optical waveguide with a new cross-sectional shape and a manufacturing method thereof. The cross-sectional shape of the ridge part of the waveguide is composed of a rectangular top and an isosceles trapezoidal bottom, the lower light limiting layer of the waveguide is an insulating layer, and the upper surface of the waveguide is covered by silicon oxide and/or nitride. Its manufacturing method includes: a. On the SOI wafer, the mask of the optical waveguide is made by photolithography; b. On the top layer of silicon, a ridge waveguide with a rectangular cross section is etched by dry method; c. On the basis of the original mask above, performing secondary etching on the rectangular ridge waveguide by wet etching; d. removing the mask, and covering the ridge waveguide with an oxide and/or nitride layer. The structure and manufacture of the invention are relatively simple, the etching surface is smooth without damage and polymer residue, the coupling efficiency is relatively high, and the optical performance and electrical performance of the waveguide can be improved.

Description

Silicon-on-insulator ridge optical waveguide with new cross-sectional shape and its manufacturing method

technical field

The invention relates to the field of optical waveguide technology, in particular to a silicon-on-insulator (SOI, silicon-on-insulator) ridge optical waveguide with a new cross-sectional shape and a manufacturing method thereof, which can be applied to single-multimode SOI optical waveguides and SOI waveguide devices in the making.

Background technique

The current research on optical devices is developing in the direction of diversification of materials and structures, and silicon-based integrated optics has always been an important research direction. SOI materials can be used to make high-speed CMOS devices. At the same time, the technology of SOI materials is very mature. The thickness of the top silicon film is not limited, and SOI optical waveguides of various sizes can be produced. The SOI optical waveguide process is compatible with CMOS circuit technology. Therefore, SOI materials are very suitable for making photoelectric hybrid integrated chips. In recent years, various SOI-based optical passive devices, such as waveguide couplers made of SOI materials, waveguided optical modulators, electro/thermo-optical switches, and AWGs, have gained more and more attention. SOI-based optical waveguides are the basis of these devices and the realization of silicon-based integrated optical interconnection, so it is of great significance to design and manufacture SOI-based optical waveguides with excellent performance. SOI optical waveguides are usually produced by wet etching or dry etching. Wet etching usually uses anisotropic solution for etching, and a waveguide with a trapezoidal cross-section can be obtained as shown in Figure 1, including ridges with a trapezoidal cross-section. The waveguide 1, the insulating layer 2, and the silicon substrate 3, the sidewall and the bottom surface of the waveguide are relatively smooth, there is no damaged layer on the etched surface, and there are few etching residues. However, the SOI ridge waveguide with trapezoidal cross-section obtained by wet etching (generally, it is photolithographically etched along the <110> crystal direction on {100} silicon wafers by wet method, and the etching side is {111} plane, {111} plane The angle θ with the {100} plane is 54.74°), such as the AWG of SOI material, it is difficult to obtain good polarization-dependent loss performance. The dry etching has good anisotropy, and the etching rate has nothing to do with the crystal orientation. A ridge waveguide with a rectangular cross section as shown in FIG. 2 can be obtained, including a ridge waveguide 4 with a rectangular cross section, an insulating layer 2, and a silicon substrate 3. Polarization is insensitive, but the roughness of the side wall and bottom surface is much higher than that of wet etching, and the roughness of the etched surface will have a direct impact on the transmission characteristics of light. In the case of similar parameters, the coupling efficiency with single-mode fiber is slightly lower than that of SOI optical waveguide with trapezoidal cross-section shape. Dry etching will inevitably form a layer of thin or thick damage layer on the etching surface. When some bromine-based or fluorocarbon-containing gases are used for etching, there will also be a thin layer of polymer on the etching surface. It will have a bad effect on the optical and electrical properties of the device. In addition, when making some waveguide devices, such as thermo-optic or electro-optic SOI switches, if the bottom corner of the waveguide side wall is too steep, it is not conducive to the climbing of the electrodes, and the electrodes are easily burned, resulting in device failure.

Contents of the invention

The object of the present invention is to provide a SOI optical waveguide with a new cross-sectional shape with relatively simple structure, smooth etched surface, no damage and no polymer residue, and relatively high coupling efficiency, so as to improve the optical and electrical properties of the waveguide.

In order to achieve the above object, the technical solution of the present invention is to provide a kind of SOI ridge optical waveguide of new cross-sectional shape, and its structure comprises: a silicon substrate, one layer of oxide layer on the silicon substrate top, and a layer A single crystal silicon layer on the top layer of oxide, wherein there is a ridge-shaped optical waveguide on the silicon layer on the top oxide layer, and the cross-sectional shape of the ridge part of the waveguide is composed of a rectangular top and an isosceles trapezoidal bottom. The lower confinement layer is an insulating layer, and the upper surface of the waveguide is covered by silicon oxide or nitride.

In the silicon optical waveguide, the ratio of the height of the rectangular portion and the height of the trapezoidal portion of the ridge waveguide to the total height of the ridge can be changed.

In the silicon optical waveguide, the base angle of the isosceles trapezoid is 54.74°.

A method for fabricating a silicon-on-insulator optical waveguide with a new cross-sectional shape, comprising the following steps:

a. On the SOI wafer, an optical waveguide mask along the <110> crystal direction is fabricated on the top {100} silicon crystal surface through a photolithography process;

b. Dry etching a ridge waveguide with a rectangular cross-section on the top silicon;

c. On the basis of the original mask, the rectangular ridge waveguide is etched twice by wet etching;

d. Remove the mask, and cover the ridge waveguide with an oxide and/or nitride layer as an upper cladding layer of the waveguide.

In the method, the silicon layer on the insulating layer is a {100} silicon crystal plane, and the dry etching direction is along the <100> crystal direction.

In the method described above, when the ridge waveguide is etched twice by a wet method, the wet etching solution used is an anisotropic etching solution, and the side surfaces of the obtained trapezoidal waveguide are {111} planes, {111} The angle between the plane and the {100} plane is 54.74°.

The method, the mask, and the material can be metal and/or silicon oxide and/or silicon nitride.

According to the method, different anisotropic wet etching solutions can be used according to different mask materials.

In the method, by changing the etching parameters and etching time of the dry method and the wet method, the ratio of the height of the rectangular part of the ridge waveguide and the height of the trapezoidal part to the total height of the ridge can be changed.

The present invention adopts the dry-wet combination method to obtain the SOI ridge optical waveguide whose cross-sectional shape is shown in Fig. 3 , which solves or improves the problems existing in the prior art.

The invention has relatively simple structure and manufacture, smooth etched surface, no damage, no polymer residue, relatively high coupling efficiency, is conducive to electrode climbing, and can improve the optical performance of the waveguide and the electrical performance of the optical waveguide device.

Description of drawings

Fig. 1 Schematic diagram of a conventional anisotropic wet-etched waveguide section;

Fig. 2 Schematic diagram of conventional dry etching waveguide section;

Fig. 3 is a schematic diagram of a cross section of a waveguide obtained by combining dry and wet methods in the present invention;

4-7 are schematic diagrams of the implementation steps of the process of the present invention.

Detailed ways

As shown in FIG. 4, firstly, an optical waveguide mask 9 along the <110> direction is made on the top layer {100} silicon thin layer 8 of SOI material including a silicon substrate 3 and an insulating layer 2 by a photolithography process, and the mask material Metal, silicon oxide, and silicon nitride can be used, and then etched along the <100> crystal direction through a dry etching process to obtain a ridge waveguide 10 with a rectangular cross-sectional shape as shown in Figure 5, and the obtained rectangular waveguide The sidewalls are {110} planes. Depending on the mask material used, different etching solutions are used or the ratio of the solution is changed, and secondary etching is performed on the basis of dry etching. In the process of secondary etching, due to the use of anisotropic etching Solution, the sidewall of the rectangular waveguide is etched, the width becomes smaller, and the etching proceeds downward at the same time, and the trapezoidal waveguide 11 as shown in FIG. 6 is obtained, the sidewall of which is a {111} crystal plane. The θ angle is the angle between the {100} plane and the {111} plane, which is 54.74°. After the waveguide with the cross-sectional shape shown in FIG. 6 is obtained, the mask 9 is removed, and the upper surface of the waveguide is covered with a silicon oxide and/or nitride layer 7 , as shown in FIG. 7 . Ridge waveguides with different proportions of rectangular height and trapezoidal waveguide height can be obtained by changing the etching parameters and etching time of dry and wet etching during the waveguide fabrication process.

Claims (9)

1. the silicon-on-insulator ridge optical waveguide of a new cross sectional shape, its structure comprises: a silicon substrate, one oxide skin(coating) on silicon substrate top, and a monocrystalline silicon layer on the oxide top layer, wherein on the silicon layer on the oxide top layer ridge optical waveguide is arranged, it is characterized in that: the ridged partial cross section shape of waveguide is made of a rectangular top and an isosceles trapezoid bottom, and waveguide is an insulation course to the lower limit layer of light, and the upper surface of waveguide is by the oxide or the nitride covering of silicon.

2. silicon-on-insulator ridge optical waveguide as claimed in claim 1 is characterized in that: the height of the rectangle part of described ridge waveguide and the height of trapezoidal portions, the ratio that accounts for the ridged overall height can change.

3. silicon-on-insulator ridge optical waveguide as claimed in claim 1 is characterized in that: the base angle of described isosceles trapezoid is 54.74 °.

4. the method for making of the silicon-on-insulator ridge optical waveguide of a new cross sectional shape is characterized in that: may further comprise the steps:

A. on the SOI wafer,, { make optical waveguide mask on the 100} silicon wafer face along＜110〉crystal orientation at top layer by photoetching process;

B. the ridge waveguide that on top layer silicon, is rectangle with cross section of dry etching;

C. on the basis of former mask, carry out secondarily etched to the rectangular ridge waveguide with wet etching;

D. remove mask, capping oxide and/or nitride layer on ridge waveguide are as the waveguide top covering.

5, method as claimed in claim 4 is characterized in that, the silicon on the insulation course is that { 100} silicon wafer face, the dry etching direction is along＜100〉crystal orientation.

6, method as claimed in claim 4, it is characterized in that with wet method ridge waveguide is carried out when secondarily etched, used wet etching solution is anisotropic etching solution, the side of resulting trapezoidal waveguide is that { the 111} face, { the 111} face is with { angle of 100} face is 54.74 °.

7, method as claimed in claim 4 is characterized in that, described mask, material can adopt the oxide and/or the silicon nitride of metal mask and/or silicon.

8, as claim 4 or 7 described methods, it is characterized in that,, can adopt different anisotropic wet etch solution according to the difference of mask material.

9, method as claimed in claim 4 is characterized in that, by changing the etching parameters and the etching time of dry method and wet method, the height that can change the height of rectangle part of ridge waveguide and trapezoidal portions accounts for the ratio of ridged overall height.

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