Tilt bonding method of progressive grating coupler based on off-chip light source and silicon substrate integration

Abstract

The present invention provides a method for tilt bonding of an off-chip light source and a silicon-based integrated progressive grating coupler, comprising: pre-treating a sample; evenly coating a layer of photoresist on the surface of the sample, and baking the coated sample; transferring a preset pattern to the photoresist layer on the surface of the sample by exposure technology; placing the exposed sample in a developer to dissolve excess photoresist; transferring the pattern of the photoresist layer to the surface of the silicon layer of the sample by etching; plating silicon dioxide as a covering layer on the sample by plasma enhanced chemical vapor deposition; preparing gallium-indium alloy liquid metal according to a preset ratio, assembling the gallium-indium alloy liquid metal on a bonding pad of an off-chip light source with graphene, and controlling the off-chip light source to form a preset input light angle; filling the remaining space when the off-chip light source is bonded to the sample with a matching refractive index liquid to obtain a progressive grating coupler. The grating coupler designed by the present invention has a compact structure and is easy to integrate.

Description

Technical Field

[0001] The invention relates to the field of silicon photonic integration and semiconductor laser technology, and in particular to a tilt-angle bonding method based on an off-chip light source and a silicon-based integrated progressive grating coupler. Background Art

[0002] In the past few decades, integrated circuit technology has been widely used and has formed a complete industrial chain. However, with the development of big data, the Internet of Things, and cloud computing, the requirements for ultra-high transmission rates, ultra-fast processing capabilities, and low latency are increasing. Integrated circuit technology based on electrical interconnection is approaching physical limits, and issues such as speed, bandwidth, and energy consumption are gradually becoming prominent. In order to break through the development bottleneck, integrated optoelectronic technology uses photons as information carriers, combines microelectronics technology and photonics, and has the advantages of fast transmission rates and low energy consumption. A major challenge facing silicon-based photonic integration is the realization of silicon-based efficient electrically pumped light sources. Due to the low luminescence efficiency of direct carrier transition recombination in silicon, it is difficult to directly epitaxially grow efficient light-emitting devices on silicon photonic chips, and on-chip optical interconnection chips must have reliable light sources to work properly. At present, the use of off-chip light source hybrid integration has become the main means of light input for silicon-based photonic integrated chips.

[0003] As an input / output device for optical chips, grating couplers realize high-density optical interconnection between integrated circuits and lasers. However, in simulations, at most 50% of the light produced by conventional vertically incident uniform grating couplers theoretically produces interference coherent superposition, so the input light can have higher coupling efficiency when it is incident at an angle, and then it is diffracted by the grating in the top silicon to the waveguide for transmission. The advantages of grating couplers include easy manufacturing, flexible position, and large alignment tolerance, but they also have disadvantages such as low coupling efficiency, narrow bandwidth, large size, and polarization sensitivity. Summary of the invention

[0004] In view of this, the present invention provides a tilt bonding method based on an off-chip light source and a silicon-based integrated progressive grating coupler to solve the above problems.

[0005] The present invention provides a method for angle bonding of a silicon-based integrated progressive grating coupler based on an off-chip light source, comprising: step 1: pre-treating a sample, wherein the pre-treating comprises brushing, cleaning and drying; step 2: uniformly coating a layer of photoresist on the surface of the sample, and baking the coated sample; step 3: transferring a preset pattern to the photoresist layer on the surface of the sample by using an exposure technology; step 4: placing the exposed sample in a developer to dissolve excess photoresist, cleaning and baking the developed sample to remove the remaining solvent on the sample; step 5: etching the sample by etching The etching process transfers the pattern of the photoresist layer to the surface of the silicon layer of the sample, and removes the remaining etchant and impurities on the surface of the sample; Step 6: Plating a layer of silicon dioxide as a covering layer on the sample by plasma enhanced chemical vapor deposition; Step 7: Prepare gallium-indium alloy liquid metal according to a preset ratio, assemble the gallium-indium alloy liquid metal to the bonding pad of an off-chip light source with graphene, and control the off-chip light source to form a preset input light angle; Step 8: Fill the remaining space when the off-chip light source is bonded to the sample with a matching refractive index liquid to obtain a progressive grating coupler.

[0006] In another implementation of the present invention, the sample is pretreated, and the pretreatment includes brushing, cleaning and drying, including: brushing the sample; placing the brushed sample into a beaker, adding high-purity acetone for ultrasonic cleaning; after cleaning, replacing ethanol with acetone, and ultrasonic cleaning again; after rinsing with distilled water, the sample is dried with a nitrogen gun.

[0007] In another implementation of the present invention, the grating layer of the progressive grating coupler includes a progressively changing grating structure and a uniform grating structure, and the designed grating size is 15×15 μm. 2 , connected to a 5mm straight waveguide through a 50μm tapered converter.

[0008] In another implementation of the present invention, the grating period of the progressive grating coupler is expressed as:

[0009]

[0010] Among them, n eff is the effective refractive index of the grating, Λ is the grating period, λ c is the coupling wavelength, θ air is the diffraction angle; the grating period is linearly changed along the grating, and the equation for apodizing the grating is expressed as:

[0011] W=W 0 -Rz

[0012] Among them, W 0is the initial fill factor of the first radiating element, R is the linear apodization factor, and z is the distance of each radiating element from the start of the grating.

[0013] The invention designs a highly efficient progressive grating coupler suitable for VCSEL based on the tilt bonding method of an off-chip light source and a silicon-based integrated progressive grating coupler, which has a compact structure and is easy to integrate, and the grating can be prepared by a method combining electron beam lithography and traditional lithography; and proposes a method for controlling the steady tilt angle of a laser, which uses liquid metal prepared from gallium-indium alloy as an interface, and can realize a coupling structure of the laser's steadily tilted output light, and the structure has a large adjustment angle range, a simple method and process, and a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. By reading the detailed description of the following implementations, the advantages and benefits of the solutions become clear to those skilled in the art. The drawings are only used to illustrate the preferred implementations and are not to be considered as limiting the present invention.

[0015] In the attached picture:

[0016] Figure 1 The present invention is a flowchart of a method for angle bonding of an off-chip light source and a silicon-based integrated progressive grating coupler according to an embodiment of the present invention.

[0017] Figure 2 It is a schematic cross-sectional diagram of bonding between a laser tilt stabilization device and a progressive grating coupler according to an embodiment of the present invention.

[0018] Figure 3 This is a cross-sectional view of a progressive grating coupler filled with gallium-indium alloy according to an embodiment of the present invention.

[0019] Figure 4 FIG. 1 is a top view of a progressive grating coupler bonding according to an embodiment of the present invention.

[0020] Figure 5 FIG. 1 is a top view of a progressive grating structure according to an embodiment of the present invention.

[0021] Figure 6 FIG. 1 is a top view of a progressive grating coupler structure according to an embodiment of the present invention.

[0022] Figure 7 FIG. 4 is a cross-sectional view of a progressive grating structure according to an embodiment of the present invention.

[0023] Figure 8 This is a simulation result diagram of the coupling efficiency of the oblique-incidence progressive grating according to an embodiment of the present invention.

[0024] Fig. 9 A three-dimensional diagram of a progressive grating structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be described clearly and in detail below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in the field based on the embodiments in the embodiments of the present invention should fall within the scope of protection of the embodiments of the present invention.

[0026] In order to solve the challenges existing in the current technology, the present invention aims to propose an efficient progressively variable grating coupler for bonding a vertical-cavity surface-emitting laser (VCSEL) with a silicon-based photonic integrated circuit when the incident light is obliquely incident. In the field of photonic integrated circuits, the coupling efficiency of oblique incident light has always been an important issue. The existing vertical grating coupler can only couple light to one side of the coupler, and due to the symmetry of the design, the maximum coupling efficiency is usually only 50%. In order to solve the back reflection problem introduced by the negative second-order diffraction order, the output / input beam angle of the grating coupler usually deviates from the vertical direction by about 10°. However, when the VCSEL has a certain oblique angle incident progressive grating structure, the simulation results show that the coupling efficiency is higher, and the progressively variable grating can reduce the mode field mismatch loss and improve the directivity.

[0027] Figure 1 A schematic flow chart of a tilt bonding method based on an off-chip light source and a silicon-based integrated progressive grating coupler provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, this embodiment mainly includes:

[0028] Step 1: Pre-treat the sample, including brushing, cleaning and drying.

[0029] Exemplarily, the sample pretreatment is to ensure the cleanliness of the chip surface. The pretreatment step first requires brushing the chip; the next step is cleaning, placing the sample in a clean beaker, and then adding a certain amount of high-purity acetone for ultrasonic cleaning; after the ultrasound is completed, replace the acetone with ethanol and repeat the previous step; after rinsing with distilled water, blow dry the sample with a nitrogen gun.

[0030] Step 2: evenly apply a layer of photoresist on the surface of the sample, and bake the sample after the coating.

[0031] For example, pre-baking is to bake the sample after coating to improve the viscosity of the photoresist and ensure the development quality.

[0032] Step 3: Transferring the preset pattern to the photoresist layer on the surface of the sample by using exposure technology.

[0033] Exemplarily, the exposure is a process of transferring a desired pattern onto a photoresist using an EBL technique or other exposure techniques.

[0034] Step 4: placing the exposed sample in a developer to dissolve excess photoresist, and washing and baking the developed sample to remove the remaining solvent on the sample.

[0035] Exemplarily, development and fixing, development is the process of placing the exposed silicon wafer in a developer of positron etchant or negative electron etchant to dissolve excess photoresist; fixing is used to wash away the remaining developer; post-baking is to bake the sample again after fixing to remove the remaining solvent on the sample to ensure the quality of development.

[0036] Step 5: Transfer the pattern of the photoresist layer to the surface of the silicon layer of the sample by etching, and remove the remaining etchant and impurities on the surface of the sample.

[0037] For example, etching is the process of transferring the pattern on the photoresist to the surface of the silicon wafer; stripping is the process of removing the remaining etchant and other impurities on the surface of the sample.

[0038] Step 6: A layer of silicon dioxide is deposited on the sample as a covering layer by plasma enhanced chemical vapor deposition.

[0039] For example, a layer of silicon dioxide (SiO2) is deposited on the obtained structure pattern conforming to the design pattern by plasma enhanced chemical vapor deposition (PECVD). 2 ) as a covering layer.

[0040] Step 7: Prepare gallium-indium alloy liquid metal according to a preset ratio, assemble the gallium-indium alloy liquid metal onto a bonding pad of an off-chip light source having graphene, and control the off-chip light source to form a preset input light angle.

[0041] For example, Figure 3As shown, a VCSEL that meets the required wavelength and requirements is flip-chip bonded on top of a grating coupler, and a gallium-indium alloy is prepared in a certain proportion to control the angle of the oblique incident VCSEL. Liquid metals (LM) of the gallium-indium alloy are assembled on the bonding pad of the VCSEL with graphene electrical and thermal conductivity to control the angle of the required input light.

[0042] In order to ensure the VCSEL laser achieves a stable tilt angle after flip-chip bonding, the height of the LM after reflow soldering is controlled. Using the solid-liquid phase transition and plastic deformation of liquid metal, gallium-indium alloy can be used to manufacture flexible electronic devices with three-dimensional circuits. The solid but plastically deformable LM deforms in different temperature ranges, thereby changing the tilt angle of the input light.

[0043] Step 8: Fill the remaining space when the off-chip light source is bonded to the sample with a matching refractive index liquid to obtain a progressive grating coupler.

[0044] For example, Figure 2 , Figure 4 and Figure 6 As shown, the coupling structure includes: a VCSEL with a conductive, heat-conducting and heat-dissipating layer, an inclined liquid metal interface, and a progressive silicon grating coupler (a substrate layer, an oxide layer, a waveguide grating layer, and a cover layer stacked in sequence from bottom to top). Based on the uniform grating, an additional progressive grating is added on top of the top silicon grating area. The added progressive grating helps to reduce light energy consumption and reflection, so that more light energy is coupled into the waveguide, improving coupling efficiency.

[0045] The invention designs a highly efficient progressive grating coupler suitable for VCSEL based on the tilt bonding method of an off-chip light source and a silicon-based integrated progressive grating coupler, which has a compact structure and is easy to integrate, and the grating can be prepared by a method combining electron beam lithography and traditional lithography; and proposes a method for controlling the steady tilt angle of a laser, which uses liquid metal prepared from gallium-indium alloy as an interface, and can realize a coupling structure of the laser's steadily tilted output light, and the structure has a large adjustment angle range, a simple method and process, and a low cost.

[0046] In another implementation of the present invention, the sample is pretreated, and the pretreatment includes brushing, cleaning and drying, including: brushing the sample; placing the brushed sample into a beaker, adding high-purity acetone for ultrasonic cleaning; after cleaning, replacing ethanol with acetone, and ultrasonic cleaning again; after rinsing with distilled water, the sample is dried with a nitrogen gun.

[0047] In another implementation of the present invention, Figure 5 , Figure 7 and Fig. 9 As shown, the grating layer of the progressive grating coupler includes a progressively changing grating structure and a uniform grating structure, and the designed grating size is about 15×15 μm 2 , connected to a 5mm straight waveguide through a 50μm tapered converter.

[0048] In another implementation of the present invention, the grating period of the progressive grating coupler is expressed as:

[0049]

[0050] Among them, n eff is the effective refractive index of the grating, Λ is the grating period, λ c is the coupling wavelength, θ air is the diffraction angle; the grating period is linearly changed along the grating, and the equation for apodizing the grating is expressed as:

[0051] W=W 0 -Rz

[0052] Among them, W 0 is the initial fill factor of the first radiating element, R is the linear apodization factor, and z is the distance of each radiating element from the start of the grating.

[0053] For example, the designed non-traditional progressive grating coupler can reduce the mode field mismatch loss and improve the directivity. According to the first-order Bragg condition, the grating period Λ is given by:

[0054]

[0055] Among them, n eff is the effective refractive index of the grating, Λ is the grating period, λ c is the coupling wavelength, θ air is the diffraction angle.

[0056] Starting from the basic structure of a uniform grating coupler, the coupling efficiency can be improved by introducing linear apodization on the grating. By linearly varying the Λ value along the grating, two positive effects can be achieved: the amount of optical power radiated by the first element of the grating is reduced, and the optical impedance matching between the waveguide and the grating section is improved.

[0057] It should be understood that the period, duty cycle, and etching depth of the grating are optimized; the duty cycle and period of the grating are linearly modulated and comprehensively optimized; and the final grating coupler structure that meets the VCSEL incident at an inclined angle is obtained, such as Figure 8 As shown, the designed progressive grating coupler achieves higher coupling efficiency in the simulation.

[0058] In the present invention, gallium alloy-based liquid metal, due to its inherent fluidity and high conductivity, can be used to control the solid-liquid phase transition and plastic deformation of liquid metal, so as to achieve electrical contact and mechanical bonding between VCSEL and silicon photonic integrated circuit. By controlling the reflow of liquid metal gallium alloy, the required tilt angle can be adjusted, thereby creating a method for direct VCSEL-PIC electrical connection. This method can redesign the VCSEL bonding pad originally used for wire bonding connection so that it can be tightly combined and achieve efficient electrical connection without surface treatment or post-treatment, ensuring maximum compatibility with biosensing applications, keeping the functional layer clean and compact, so that the PIC waveguide and resonator structure can fully function. The bonding tilt angle is achieved by stable shaping of gallium-indium alloy liquid metal, which is easy to integrate with silicon photonic chips, and improves the signal reception efficiency of silicon-based optical chips.

[0059] This technological breakthrough brings new development possibilities to the field of photonic integrated circuits, and also brings innovative applications to the fields of optical communications, sensors, and biomedicine. By efficiently combining VCSEL with silicon photonic integrated circuits, more stable and efficient optical performance can be achieved, providing new ideas and approaches for the research and development and application of photonic integrated circuit equipment.

[0060] Thus far, specific embodiments of the present invention have been described. Other embodiments are within the scope of the appended claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve the desired results. Additionally, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing may be advantageous.

[0061] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0062] In the description of the present invention, the terms "first" and "second" are only used to facilitate the description of different components or names, and cannot be understood as indicating or implying a sequential relationship, relative importance, or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0064] It should be noted that although the specific embodiments of the present invention are described in detail in conjunction with the accompanying drawings, it should not be understood as limiting the scope of protection of the present invention. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still belong to the scope of protection of the present invention.

[0065] The examples of the embodiments of the present invention are intended to concisely illustrate the technical features of the embodiments of the present invention so that those skilled in the art can intuitively understand the technical features of the embodiments of the present invention, and are not intended to be improper limitations of the embodiments of the present invention.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tilt bonding method based on an off-chip light source and a silicon-based integrated progressive grating coupler, characterized in that: include: Step 1: pre-treating the sample, including brushing, cleaning and drying; Step 2: evenly apply a layer of photoresist on the surface of the sample, and bake the sample after the coating; Step 3: Transferring the preset pattern to the photoresist layer on the surface of the sample by using exposure technology; Step 4: placing the exposed sample in a developer to dissolve excess photoresist, and washing and baking the developed sample to remove the remaining solvent on the sample; Step 5: transferring the pattern of the photoresist layer to the surface of the silicon layer of the sample by etching, and removing the remaining etchant and impurities on the surface of the sample; Step 6: coating a layer of silicon dioxide as a covering layer on the sample by plasma enhanced chemical vapor deposition; Step 7: preparing gallium-indium alloy liquid metal according to a preset ratio, assembling the gallium-indium alloy liquid metal onto a bonding pad of an off-chip light source having graphene, and controlling the off-chip light source to form a preset input light angle; Step 8: Fill the remaining space when the off-chip light source is bonded to the sample with a matching refractive index liquid to obtain a progressive grating coupler.

2. The method according to claim 1, characterized in that The sample is pre-treated, and the pre-treatment includes brushing, cleaning and drying, including: Performing brushing treatment on the sample; Place the brush-treated sample into a beaker and add high-purity acetone for ultrasonic cleaning; After cleaning, ethanol was replaced with acetone and ultrasonic cleaning was performed again; After rinsing with distilled water, the coupons were blown dry with a nitrogen gun.

3. The method according to claim 1, characterized in that The grating layer of the progressive grating coupler includes a progressively changing grating structure and a uniform grating structure, and the designed grating size is 15×15 μm 2 , connected to a 5mm straight waveguide through a 50μm tapered converter.

4. The method according to claim 3, characterized in that The grating period of the progressive grating coupler is expressed as: Among them, n eff is the effective refractive index of the grating, Λ is the grating period, λ c is the coupling wavelength, θ air is the diffraction angle; The equation for apodizing the grating by linearly changing the grating period along the grating is expressed as: W=W0-Rz Where W0 is the initial fill factor of the first radiating element, R is the linear apodization factor, and z is the distance of each radiating element from the start of the grating.

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