Germanium-silicon quasi-suspension micro-ring based on silicon substrate and preparation method of germanium-silicon quasi-suspension micro-ring

Abstract

The invention belongs to the technical field of preparation of semiconductor micro-nano structures, and particularly relates to a germanium-silicon quasi-suspension micro-ring directly based on a silicon substrate and a preparation method of the germanium-silicon quasi-suspension micro-ring. The method comprises the following steps: firstly, preparing a silicon micro-column with a sunken top central area through a micro-nano template, then growing a germanium-silicon thin film in a heteroepitaxial manner, and finally, carrying out selective wet etching on silicon to obtain the quasi-suspended high-quality germanium-silicon micro-ring resonant cavity. The method for preparing the micro-ring is simple, easy to implement, economical and practical, the formed optical resonant cavity has more excellent optical limiting effect and optical resonance characteristic, thermal contact and electric contact between the annular resonant cavity and the substrate are easy to realize, large-area preparation can be directly performed on the silicon substrate, and the preparation cost is reduced. And a new thought is provided for the structural preparation of the optical microcavity and the design of a novel photoelectric device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor micro-nano structure preparation, and particularly relates to a germanium-silicon quasi-suspended micro-ring directly based on a silicon substrate and a preparation method thereof. BACKGROUND

[0002] Silicon-based optoelectronic integrated, using optical signals instead of electrical signals as information carriers, can effectively solve the problems of large energy consumption, low information transmission speed and signal interference of microelectronic integrated chips. At present, the main factor restricting the development of optoelectronic integrated is the lack of high-performance light sources. Since the cornerstone of microelectronic integration is the indirect band gap of silicon-based materials, the preparation of silicon-based high-performance light sources or detectors has always been a great challenge. According to quantum mechanics theory, the photoelectric conversion of materials not only involves the electronic band structure of the material itself, but also relates to the electromagnetic environment of the material. Therefore, by changing the relevant electromagnetic environment of the material through some optical microcavities such as microdisks / micro-rings and photonic crystals, and by using the Purcell effect to enhance the interaction between light and matter, it is possible to greatly improve the photoelectric conversion efficiency of silicon-based materials.

[0003] Microdisk / micro-ring optical microcavities have multiple resonance modes, such as the most common whispering gallery mode, which can achieve high quality factor and effective transverse coupling characteristics. Therefore, people have made very in-depth research and extensive application exploration on microdisk / micro-ring optical microcavities. Compared with microdisks, micro-rings are more conducive to reducing the laser threshold and suppressing the background radiation of spontaneous emission due to the lack of central area. In addition, they are more sensitive to the environment. Therefore, micro-rings have greater potential in applications such as lasers, sensors, filters, modulators and switch devices. However, it is currently impossible to obtain suspended micro-rings with excellent light confinement. Silicon-based micro-rings are usually manufactured on SOI substrates, which greatly limits the heat dissipation and electrical injection of the device, and also greatly increases the cost of the device. For monolithic optoelectronic integrated circuits (MOEIC), it is more ideal to directly prepare micro-rings on a silicon substrate. The technology of the present scheme can directly prepare quasi-suspended micro-rings on a silicon substrate and achieve good thermal and electrical contact between the micro-ring and the silicon substrate, providing a new idea for the preparation of silicon-based novel optical microcavity structures. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a quasi-suspended germanium-silicon micro-ring based on a silicon substrate with good thermal and electrical conductivity.

[0005] The preparation method of the quasi-suspended germanium-silicon micro-ring based on a silicon substrate provided by the present application uses a silicon wafer as a substrate and prepares a quasi-suspended germanium-silicon micro-ring through polystyrene microparticle etching, thermal evaporation, molecular beam epitaxy growth, and dry and wet etching technologies. The specific steps are as follows: (1) taking a silicon single crystal wafer as a substrate, performing chemical cleaning, and then growing a silicon dioxide film on the silicon substrate as a protective layer; (2) preparing a single layer of polystyrene microspheres on the silicon dioxide film as an etching template; (3) reducing the diameter of the polystyrene microspheres to a required micro-ring outer diameter size by using oxygen plasma; (4) performing plasma dry etching under a mixed atmosphere of sulfur hexafluoride and octafluorocarbon, etching through the silicon dioxide film and into the substrate based on the gap between the microspheres of the polystyrene microsphere etching template, and forming silicon micro-pillars on the silicon substrate; (5) reducing the diameter of the polystyrene microspheres to a required micro-ring inner diameter by using oxygen plasma again; (6) growing a layer of chromium hard mask on the top surface of the silicon micro-pillar by thermal evaporation as an etching template for the chromium ring hard mask; (7) removing the remaining polystyrene microspheres; (8) etching a central hollow pit portion of the micro-ring on the top of the silicon micro-pillar according to the etching template of the chromium ring hard mask again under a mixed atmosphere of sulfur hexafluoride and octafluorocarbon, and forming a silicon micro-pillar with a pit; (9) removing the chromium ring hard mask by using a chromium removal solution or by using an IBE method; (10) removing the silicon dioxide film and performing chemical cleaning; (11) growing a germanium-silicon film on the silicon micro-pillar with a pit by using a molecular beam epitaxy method; (12) performing selective etching on the silicon micro-pillar by using a potassium hydroxide solution wet etching process, and obtaining a germanium-silicon quasi-suspended micro-ring with a silicon support pillar.

[0006] In the present application, in step (1), the thickness of the silicon dioxide film is 20-300 nm.

[0007] In the present application, in step (4), in order to increase the etching depth, Bosch process etching is performed in a manner of alternately introducing the protective gas octafluorocarbon and the etching gas sulfur hexafluoride, and a silicon micro-pillar with good collimation is formed on the substrate; Further, the flow ratio of the mixed gas of sulfur hexafluoride and octafluorocarbon is SF6:C4F8=1:2.

[0008] In the present application, in step (11), the component of germanium in the germanium-silicon film is greater than 10%, and the thickness of the germanium-silicon film is 50-1 μm.

[0009] In the present application, in step (12), the concentration of the potassium hydroxide solution is 0.2-2 mol / L.

[0010] In the present application, the radius difference between the germanium-silicon quasi-suspended micro-ring and the silicon support column is greater than the micro-ring width.

[0011] In the present application, the diameter of the silicon support column under the germanium-silicon quasi-suspended micro-ring is 300 nm-1 mm, and the height of the silicon support column is 300 nm-5 μm; the outer ring diameter of the germanium-silicon quasi-suspended micro-ring is 1 mm-10 mm, the micro-ring width is 200 nm-1 mm, and the depth of the central vacancy pit part is 50 nm-1 μm.

[0012] In the present application, a high-quality germanium-silicon quasi-suspended micro-ring is directly realized on a silicon substrate by using a combination of various micro-nano structure etching and growth technologies such as a self-assembled polystyrene microsphere array mask, ICP-RIE, RIE, wet etching, thermal evaporation coating, and molecular beam epitaxy growth.

[0013] The present application can directly obtain a germanium-silicon quasi-suspended optical micro-ring resonant cavity on a silicon substrate, and a large-area and uniform pattern can be prepared at a time.

[0014] The present application has the advantages that a large-area high-quality quasi-suspended micro-ring resonant cavity can be directly prepared on a silicon substrate, and all the preparation processes are compatible with silicon integration processes; the same idea can be widely used in germanium-silicon alloys, silicon nitride, and even III-V semiconductors to meet the needs of different wavebands. The quasi-suspended micro-ring resonant cavity based on a silicon substrate prepared by the present application can solve the shortcomings of existing micro-ring / micro-disk suspended structure preparation schemes, effectively improve the photoelectric conversion efficiency of silicon-based materials, and can be widely applied to silicon-based optoelectronic devices. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The preparation flowchart of the present application is shown.

[0016] Figure 2 The SEM image after the preparation step (5) of Example 1 is shown.

[0017] Figure 3 The SEM image of the uniform quasi-suspended micro-ring array on the silicon substrate of Example 1 is shown.

[0018] Figure 4 The photoluminescence spectrum of the quasi-suspended micro-ring of Example 1 is shown.

[0019] Figure 5 The luminescence spectrum obtained by simulating the ideal suspended micro-ring structure and the quasi-suspended micro-ring structure prepared by the present application in the FDTD commercial simulation software of Example 1 is shown.

[0020] Figure 6 The SEM image of the uniform quasi-suspended micro-ring array on the silicon substrate of Example 2 is shown. DETAILED DESCRIPTION

[0021] The silicon (100) single crystal wafer was provided by Hefei Kejing Materials Technology Co., Ltd.

[0022] Preparation list: Inductively Coupled Plasma Reactive Ion Etching (ICP–RIE) Model: Oxford Plasma LAB 100.

[0023] Thermo Evaporation coating model: Kurt Lesker Nano36.

[0024] Reactive Ion Etching (RIE) Model: Trion T2.

[0025] Scanning electron microscope (SEM) model: Zeiss Sigma 300.

[0026] Molecular beam epitaxy (MBE) model: Riber Eva-32. Example 1

[0027] Process conditions and preparation process, such as Figure 1 As shown, the specific steps are as follows: (1) Immerse the silicon (001) single wafer in acetone and methanol for 5 minutes each; then rinse it with deionized water; then immerse it in a sulfuric acid: hydrogen peroxide mixture for 5 minutes, and then rinse it with deionized water to obtain a clean silicon wafer sample; The cleaned silicon wafer sample was placed in a plasma-enhanced chemical vapor deposition (PECVD) device to grow a 200 nm silicon dioxide protective layer. (2) An ordered 2μm polystyrene microsphere array was prepared on the surface of a silicon wafer sample with a silica protective layer using Langmuir–Blodgett (LB) technology as an etching template; (3) In the RIE equipment, oxygen is introduced through reactive ion etching (RIE) and etching is performed for 100s under the conditions of gas pressure of 70mTorr and radio frequency power of 50mW. The diameter of polystyrene microspheres is appropriately reduced to the set outer diameter of microring. (4) Fabrication of micropillar structures using inductively coupled plasma etching (ICP-RIE): The sample was transferred to an ICP-RIE device, and a mixture of sulfur hexafluoride and carbon octafluoride (SF6:C4F8 = 1:2) was introduced to etch to a depth of approximately 400 nm. The polystyrene microsphere template was then transferred onto the substrate. Subsequently, carbon octafluoride protective gas and sulfur hexafluoride etching gas were alternately introduced at a flow rate of 100 sccm for 6 s and 8 s, respectively. Each cycle lasted 14 s and was repeated 12 times to achieve an etching depth of approximately 1500 nm. (5) After etching is completed, the above sample is transferred to the RIE device and reactive ion etching (RIE) is used again. Oxygen is introduced and etched for 240s under the same conditions as in (3). The diameter of the polystyrene microspheres is appropriately reduced to reach the set inner diameter of the microring. (6) After etching, a 18 nm chromium layer is grown on the sample surface using thermal evaporation coating technology as an etching template for the subsequent chromium ring hard mask. (7) Soak the silicon wafer sample in tetrahydrofuran for 5 min and sonicate for 1 min to remove the polystyrene microsphere array; (8) The silicon wafer sample with the microsphere array removed was transferred to the ICP-RIE equipment again and inductively coupled plasma etching (ICP-RIE) was used. A mixture of sulfur hexafluoride and carbon tetrafluoride (flow rate ratio of SF6:C4F8=1:2) was introduced to etch out the area missing in the center of the micro-ring template. The etching depth was about 250nm, forming silicon micropillars with pits. (9) The prepared suspended microring template substrate was soaked in a dechromium removal solution (perchlorinated ammonium nitrate solution; mass fraction: 16% ammonium nitrate, 3% perchloric acid) for 3 hours, and then the sample was immersed in 5 wt% hydrofluoric acid for 60–180 s to remove the chromium hard mask and silicon dioxide protective layer on the surface. (10) After cleaning the sample surface using the RCA cleaning method, a 220 nm thick germanium-silicon alloy layer was grown by molecular beam epitaxy. In order to verify the optical resonance characteristics of the quasi-suspended microring, the 220 nm thick germanium-silicon alloy layer contained 5 5 nm germanium layers (separated by 5 nm germanium-silicon alloy) as the light-emitting medium. (11) The grown sample was placed in a 0.5 mol / L potassium hydroxide solution and etched at 35°C for 80-110 s to selectively etch part of the silicon to obtain germanium-silicon quasi-suspended microrings.

[0028] The quasi-suspended microrings prepared on a silicon (001) substrate by the above steps have an outer diameter of approximately 1.7 μm, an inner diameter of approximately 0.9 μm, a thickness of approximately 220 nm, and a period of 2 μm (e.g., ...). Figure 3 ).

[0029] Detection of the photoluminescence spectrum of the sample in Example 1 revealed a significant enhancement in luminescence within the wavelength range of 1.4–2.1 μm, with eight distinct emission peaks observed. Figure 4 As shown, these emission peaks are due to the coupling between the emission spectrum of germanium and the resonant mode of the quasi-suspended germanium-silicon microring.

[0030] Simultaneously comparing the simulated emission spectrum of the theoretically quasi-suspended germanium-silicon microring, it can be found that the resonance spectrum and the experimental results agree very well (focusing mainly on the TE mode, as the TE mode is the dominant emission mode); moreover, the dominant resonance spectrum (TE mode) of the quasi-suspended germanium-silicon microring is very close to that of the ideal suspended germanium-silicon microring. In fact, the quasi-suspended microring structure prepared in this example can even target specific wavelengths, such as 1.55 micrometers suitable for optical communication (corresponding to the TE mode in this example). 6,1 The light in the resonant mode has a better resonance effect, and its emission spectrum is stronger than that of an ideal suspended microring, such as... Figure 5 As shown in the upper part; the main difference in the resonant spectral lines between quasi-suspended germanium-silicon microrings and ideally suspended germanium-silicon microrings lies in their TM mode, such as Figure 5 The lower half is shown, but its intensity is much smaller than that of the TE mode. The related results indicate that the optical microcavity prepared by this method can be considered as a quasi-suspended micro-ring optical resonator, and its main resonance mode is close to that of an ideal suspended micro-ring optical resonator. Example 2

[0031] Process conditions and preparation process, such as Figure 1 As shown, the specific steps are basically the same as in Example 1, except that steps (3) and (5) are changed as follows: (3) In the RIE equipment, oxygen is introduced through reactive ion etching (RIE) at a pressure of 70 mTorr. Radio frequency Etching was performed for 110 seconds at a power of 50mW (10 seconds longer than in Example 1), and the diameter of the polystyrene microspheres was appropriately reduced to the set outer diameter of the microring. (5) After etching, the above sample is transferred to the RIE device and reactive ion etching (RIE) is used again. Oxygen is introduced and etched for 150s under the same conditions as in (3) (90s less than in Example 1). The diameter of the polystyrene microspheres is appropriately reduced to reach the set inner diameter of the microring. The quasi-suspended microrings prepared on a silicon (001) substrate by the above steps have an outer diameter of approximately 1.6 μm (100 nm smaller than in Example 1), an inner diameter of approximately 1.1 μm (200 nm larger than in Example 1), a thickness of approximately 220 nm, and a period of 2 μm (e.g., ...). Figure 6 ).

Claims

1. A method for preparing germanium-silicon quasi-suspended microrings based on a silicon substrate, characterized in that, The specific steps are as follows: (1) Take a silicon single crystal wafer as a substrate, perform chemical cleaning, and then grow a silicon dioxide thin film as a protective layer on the silicon substrate. (2) A monolayer of polystyrene microspheres was prepared on a silica film as an etching template; (3) Using oxygen plasma to reduce the diameter of polystyrene microspheres to the required microring outer diameter; (4) In a mixed atmosphere of sulfur hexafluoride and carbon octafluoride, plasma dry etching is performed to etch through the gap between the microspheres of the etching template based on polystyrene microspheres and into the substrate to form silicon micropillars on the silicon substrate. (5) The diameter of the polystyrene microspheres was reduced again to the required inner diameter of the microring using oxygen plasma; (6) A chromium hard mask is grown on the top surface of the silicon micropillar by thermal evaporation, which serves as the etching template for the chromium ring hard mask; (7) Remove the remaining polystyrene microspheres; (8) Again, in a mixed atmosphere of sulfur hexafluoride and carbon octafluoride, the central void of the microring is etched at the top of the silicon micropillar according to the etching template of the chromium ring hard mask to form a silicon micropillar with a pit. (9) Remove the chromium ring hard mask using a chromium removal solution or by IBE method; (10) Remove the silica film and perform chemical cleaning; (11) Growing germanium-silicon thin films on silicon micropillars with pits using molecular beam epitaxy; (12) Selective etching of silicon micropillars was performed using a wet etching process with potassium hydroxide solution to obtain germanium-silicon quasi-suspended microrings with silicon support pillars.

2. The preparation method according to claim 1, characterized in that, In step (1), the thickness of the silicon dioxide film is 20nm–300nm.

3. The preparation method according to claim 1, characterized in that, In step (4), in order to increase the etching depth, the Bosch etching process is performed by alternately introducing the protective gas tetracarbon octafluoride and the etching gas sulfur hexafluoride to form silicon micropillars with good collimation on the substrate.

4. The preparation method according to claim 3, characterized in that, The flow rate ratio of the mixed gas of sulfur hexafluoride and carbon tetrafluoride octafluoride is SF6:C4F8=1:

2.

5. The preparation method according to claim 1, characterized in that, In step (11), the germanium content in the germanium-silicon thin film is greater than 10%, and the thickness of the germanium-silicon thin film is 50nm-1μm.

6. The preparation method according to claim 1, characterized in that, In step (12), the concentration of the potassium hydroxide solution is 0.2-2 mol / L.

7. The preparation method according to claim 1, characterized in that, The radius difference between the germanium-silicon quasi-suspended microring and the silicon support pillar is greater than the width of the microring.

8. Germanium-silicon quasi-suspended microrings based on a silicon substrate prepared by the preparation method according to any one of claims 1 to 7.

9. The germanium-silicon quasi-suspended microring based on a silicon substrate according to claim 1, characterized in that, The diameter of the silicon support pillar under the germanium-silicon quasi-suspended microring is 300nm-1mm, and the height of the silicon support pillar is 300nm-5μm; the outer ring diameter of the germanium-silicon quasi-suspended microring is 1mm-10mm, the microring width is 200nm-1mm, and the depth of the central empty pit is 50nm-1μm.

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