CN105334579B - A kind of silicon-based grating coupler and preparation method thereof - Google Patents

Abstract

The invention discloses a silicon-based grating coupler and a manufacturing method thereof. The coupler can directly couple with the chip vertically when the optical fiber is coupled with the chip, without making the vertical direction of the optical fiber and the chip form a certain deflection angle. The fabrication method is: using MEMS technology, corroding and hollowing out the buried insulator below the top silicon layer optical waveguide with the coupling grating, tilting the silicon optical waveguide and attaching it to the silicon substrate by electrostatic adsorption , so that the coupling between the silicon optical waveguide and the vertical optical fiber is realized by fabricating a coupling grating on the inclined silicon optical waveguide. The grating coupler with this structure is coupled with the external optical fiber, which not only reduces the second-order reflection and improves the coupling efficiency, but also facilitates chip detection and packaging due to its simple manufacturing method and vertical coupling characteristics, and facilitates large-scale integration.

Description

A silicon-based grating coupler and its manufacturing method

technical field

The invention relates to the field of optical coupling technology and photoelectric integration, in particular to a silicon-based grating coupler and a manufacturing method thereof.

Background technique

With the rapid development of communication technology and the advent of cloud computing and big data era, the bandwidth requirements are increasing. People pay more and more attention to the bandwidth and density of data centers and high-performance computing applications. Due to the limitation of physical characteristics, the traditional electrical interconnection urgently needs fundamental breakthroughs in terms of bandwidth expansion, transmission delay, loss control, and signal-to-noise improvement. To meet the requirements of fast processing speed, large data storage and low power consumption, optoelectronic chips are urgently needed to break the limitations of Moore's Law in the microelectronics industry.

Silicon-based photonic devices use light to transmit signals. Compared with electrons, photon transmission speed is much faster than electron movement speed, and the mechanism of light transmission signal is wave impedance transformation. This transformation consumes very low energy, and the signal is not easy to be distorted during transmission. , a larger transmission capacity can be obtained under the condition of large bandwidth. Moreover, silicon-based photonic devices also have the advantages of being compatible with complementary metal oxide semiconductor processes, small in size, transparent in communication bands, and resistant to radiation. It is precisely because of the advantages of large bandwidth, low delay, low energy consumption, and low crosstalk that emerging information technologies such as optical communication, optical interconnection, and optical sensing based on silicon photonics integration show the development trend of building new information hardware and are becoming a new generation of information technology. An important foundation of information systems and networks.

For silicon-based photonic integrated chips, a key issue that cannot be ignored is the input and output of optical signals. Especially silicon is used as an indirect bandgap material, and the luminous efficiency has not yet reached the practical requirements. In order to overcome the above defects, in the prior art, an independent light source is introduced from the outside of the photonic chip or an on-chip hybrid integrated optical gain material is used. Therefore, photonic integrated chips need high-efficiency, large-bandwidth, and easy-to-integrate optical coupling structures both on-chip and off-chip. The commonly used coupling method is to make a grating structure on the silicon waveguide, and realize effective coupling with the optical fiber placed near the vertical direction of the chip through the grating diffraction effect.

In order to reduce the second-order reflection and improve the coupling efficiency, the diffraction direction of the grating coupler needs to avoid being completely perpendicular to the chip as far as possible, usually at an off angle of about 10°. This makes packaging difficult and has a certain impact on system performance.

Therefore, it is very necessary and important to design a silicon-based grating coupler that is easy to package and can perform high-efficiency optical coupling.

Contents of the invention

An object of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide a silicon-based grating coupler, which can directly couple with the chip vertically when the optical fiber is coupled with the chip, which reduces the second-order reflection and improves the coupling. efficiency, and has a large operating wavelength bandwidth.

Another object of the present invention is to provide a manufacturing method of the above-mentioned silicon-based grating coupler, the manufacturing method is simple, and the manufactured silicon-based grating coupler is convenient for large-scale integration.

The object of the present invention is achieved through the following technical solutions: a silicon-based grating coupler, comprising a silicon-on-insulator chip and an optical fiber, the optical fiber is placed vertically above the silicon-on-insulator chip; the silicon-on-insulator chip is made of top silicon Layer, a buried insulator layer, and a silicon substrate. A section of silicon optical waveguide is fabricated on the surface of the top silicon layer. The silicon optical waveguide includes a first bonding section, an inclined section, and a second bonding section connected in sequence. The first The bonding segment is bonded and fixed on the buried insulator layer. Starting from the intersection of the first bonding segment and the inclined segment, the buried insulator layer under the top silicon layer is corroded and hollowed out, so the second bonding segment is bonded and fixed on the silicon On the substrate, a coupling grating is fabricated on the inclined section, and the optical fiber is placed above the coupling grating.

Preferably, the thickness of the top silicon layer of the silicon-on-insulator chip is less than 500 nm, and the thickness of the buried insulator layer is between 1-5 μm.

Further, the etching depth of the silicon optical waveguide is 70-500nm, and the etching depth of the coupling grating is 70-500nm.

Preferably, the included angle between the inclined section and the horizontal direction is between 4°-15°.

The manufacturing method of the above-mentioned silicon-based grating coupler comprises the steps of:

(1) Fabricate a buried insulator layer and a top silicon layer sequentially on a silicon substrate to form a silicon-on-insulator chip;

(2) Using traditional electron beam lithography or deep ultraviolet lithography to form silicon optical waveguides and coupling grating patterns, and then dry-etching methods to fabricate silicon optical waveguides and coupling gratings on the top silicon layer;

(3) Spin-coat a layer of photoresist on the chip obtained in step (2), and carry out pre-baking; by the traditional photolithography method of exposure and development, only the photoresist at the vicinity of the coupling grating is removed;

(4) placing the chip processed in step (3) in hydrofluoric acid solution or hydrogen fluoride vapor phase etching equipment, and corroding and hollowing out the buried insulator below the top silicon layer with the coupling grating;

(5) Remove the photoresist on the current chip with acetone or other glue remover, rinse the chip with deionized water, and then dry it so that one end of the silicon optical waveguide is inclined and fixed to the silicon substrate;

(6) An optical fiber is placed vertically above the silicon-on-insulator chip, and the optical fiber is above the coupling grating.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

The present invention can realize the coupling between the silicon optical waveguide and the optical fiber placed in the vertical direction under the requirements of maintaining high coupling efficiency, low reflectivity and large working wavelength bandwidth, which can reduce the alignment difficulty in the testing process, and at the same time Because of its vertical coupling structure design, it is easier to integrate and can improve the integration degree.

Description of drawings

Fig. 1 is a schematic diagram of the structure of a silicon-on-insulator chip of the present invention.

Fig. 2 is a schematic structural diagram of the silicon-based grating coupler of the present invention.

Fig. 3(a) is a schematic top view of the intermediate structure obtained in step 2 of the preparation method of the present invention.

Fig. 3(b) is a schematic front view of the intermediate structure obtained in step 2 of the preparation method of the present invention.

Fig. 4(a) is a schematic top view of the intermediate structure obtained in step 3 of the preparation method of the present invention.

Fig. 4(b) is a schematic front view of the intermediate structure obtained in step 3 of the preparation method of the present invention.

Fig. 5(a) is a schematic top view of the intermediate structure obtained in step 4 of the preparation method of the present invention.

Fig. 5(b) is a schematic front view of the intermediate structure obtained in step 4 of the preparation method of the present invention.

Fig. 6(a) is a schematic top view of the intermediate structure obtained in step 5 of the preparation method of the present invention.

Fig. 6(b) is a schematic front view of the intermediate structure obtained in step 5 of the preparation method of the present invention.

Fig. 7 is a side view of the inclined silicon optical waveguide fabricated in this embodiment.

Fig. 8(a) is a light field distribution diagram of a steady state field at a certain moment when simulated light is transmitted in the grating coupler of the present invention.

Fig. 8(b) is a diagram of the steady-state field phase distribution when simulated light is transmitted in the grating coupler of the present invention.

Among them: 1—top silicon layer, 2—buried insulator, 3—silicon substrate, 4—optical fiber, 5—first bonding section, 6—inclined section, 7—second bonding section, 8—coupling grating.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

As shown in FIG. 1 , a silicon-based grating coupler in this embodiment is based on a silicon-on-insulator chip structure, which includes a top silicon layer 1 , a buried insulator 2 , and a silicon substrate 3 . The thickness of the top silicon layer 1 is below 500nm, and the thickness of the buried insulator layer is between 1 μm and 5 μm.

As shown in Figure 2, in the grating coupler described in this embodiment, a section of silicon optical waveguide is formed on the surface of the top silicon layer 1, and the silicon optical waveguide includes a first bonding section 5, an inclined section 6 and a second bonding section connected in sequence. Two bonding segments 7, the first bonding segment 5 is bonded and fixed on the buried insulator layer 2, starting from the intersection position of the first bonding segment 5 and the inclined segment 6, the buried insulator layer 2 below the top silicon layer is etched out empty, the second bonding segment 7 is bonded and fixed on the silicon substrate 3 . The coupling grating 8 is fabricated on the inclined section 6 of the silicon optical waveguide, which can realize optical coupling between the vertically placed optical fiber 4 and the silicon optical waveguide. Although the optical fiber 4 is perpendicular to the silicon chip on the insulator, because the silicon optical waveguide with the coupling grating 8 has a certain inclination in the horizontal direction, the optical fiber 4 and the silicon optical waveguide in the coupling region, that is, the inclined section 6, are actually at a certain angle. inclination. Therefore, the vertical grating coupler realized in the present invention can achieve performance close to that of the conventional grating coupler.

In this embodiment, the etching depth of the silicon optical waveguide is 70-500 nm, and the etching depth of the coupling grating 8 is 70-500 nm. The coupling grating 8 has a width of 9-14 μm and an area of 70-130 μm ² , which is equivalent to the mode spot size of a single-mode optical fiber. The coupling grating 8 is composed of a submicron periodic structure, the period number is more than 5, and the period is 250nm-750nm. The included angle between the inclined section 6 and the horizontal direction is between 4°-15°.

This embodiment provides a method for manufacturing the above-mentioned silicon-based grating coupler, and the specific steps are as follows:

Step 1: sequentially fabricate a buried insulator 2 and a top silicon layer 1 on a silicon substrate 3 to form a silicon-on-insulator chip.

Step 2: Using traditional electron beam lithography or deep ultraviolet lithography to form patterns of silicon optical waveguides and coupling gratings, and then dry-etching methods to fabricate silicon optical waveguides and coupling gratings 8 on the top silicon layer 1 . If the silicon optical waveguide and the coupling grating are etched to different depths, the method can be repeated many times to make corresponding fabrications for each etching depth. After this step is completed, its structure is shown in Figure 3 (a), (b).

Step 3: Spin-coat a layer of photoresist on the above chip, and perform pre-baking. Through the traditional photolithography method of exposure and development, the photoresist at the coupling grating area is removed, so that the remaining parts are protected by photoresist. After this step is completed, its structure is shown in Figure 4 (a), (b).

Step 4: Place the chip in hydrofluoric acid solution or hydrogen fluoride vapor phase etching equipment, etch and hollow out the exposed part of the buried insulator (that is, the buried insulator under the top silicon layer on which the coupling grating is made). Since hydrogen fluoride cannot corrode silicon and photoresist, the grating structure, silicon optical waveguide and the parts protected by photoresist will not be damaged. For the silicon optical waveguide, a suspended structure is finally formed, which is supported on the buried insulator layer through the first bonding segment 5 of the silicon optical waveguide. After this step is completed, its structure is shown in Figure 5(a), (b).

Step 5: Remove the photoresist with acetone or other glue remover, rinse the chip with deionized water, and then dry it. Due to the surface tension of water during the drying process, the suspended structure of the silicon optical waveguide will be pulled to the silicon substrate 3, and will be adsorbed on the silicon substrate 3 due to the electrostatic adsorption force, and finally form the inclined section 6 and the second Fit segment 7. After this step is completed, its structure is shown in Figure 6 (a), (b).

Step 6: Place an optical fiber vertically above the silicon-on-insulator chip, with the optical fiber above the coupling grating. The structure is shown in Figure 2, that is, the fabrication of the silicon-based grating coupler is completed.

Fig. 7 is a physical diagram of an inclined silicon waveguide fabricated by the above method. In this case, the slanted silicon waveguide is at an angle of 7° to the horizontal.

In Fig. 8(a) and (b), the numerical simulation is performed on the transmission of light in the grating coupler realized by the present invention. Light is input from the silicon optical waveguide on the left, and is diffracted by the coupling grating 8 on the inclined section 6 . From Figure 8(a), it can be seen that part of the light wave is emitted upward. The phase diagram of Fig. 8(b) clearly shows that the wavefront of the upwardly emitted light is basically located in the horizontal direction, which further illustrates that the light is emitted upwardly from the vertical direction.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (1)

1. a kind of production method of silicon-based grating coupler, it is characterised in that including step：

(1) buried insulator layer and top silicon layer are made successively on a silicon substrate, forms silicon-on-insulator chip；

(2) figure of silicon optical waveguide and coupling grating is formed using the photoetching of conditional electronic beam or deep ultraviolet light carving method, afterwards By the method for dry etching, silicon optical waveguide and coupling grating are produced on the silicon layer of top；

(3) one layer of photoresist of spin coating on step (2) gained chip, and carry out front baking；Pass through exposed and developed conventional lithography Method, only gets rid of the photoresist at coupling grating near zone；

(4) chip that will be handled by step (3), is placed among hydrofluoric acid solution or hydrogen fluoride gaseous corrosion equipment, will make Making, which has the buried insulators below the top silicon layer of coupling grating to carry out corrosion, empties；

(5) by going glue to remove the photoresist on current chip, and with deionized water rinsing chip, then dry, make silicon light Waveguide end is tilted and is adhesively secured on silicon substrate；

(6) fiber perpendicular is placed on to the top of silicon-on-insulator chip, optical fiber is in the top of coupling grating；

Silicon optical waveguide after completing includes the first fitting section, tilting section and the second fitting section being sequentially connected, the first fitting Section fitting is fixed on buried insulator layer, since the first fitting section and tilting section intersection location, pushes up covering below silicon layer Bury insulator layer and be corroded and empty, then the second fitting section fitting is fixed on a silicon substrate, and being made on the tilting section has coupling Grating.