An InP microlens array based on intermittent three-stage etching and a preparation method thereof

Abstract

The present application relates to the field of photoelectric detection and micro-nano manufacturing, and particularly relates to a preparation method of an InP microlens array based on intermittent three-stage etching, which comprises the following steps: first, forming a photoresist pattern on the surface of an InP substrate; second, performing a heat reflow treatment on the photoresist pattern to make the photoresist pattern into a continuous curved surface structure; third, using an inductively coupled plasma etching process to transfer the morphology of the continuous curved surface structure to the InP substrate; the etching process is an intermittent etching transfer process; then, repeating the etching process until the morphology transfer on the surface of the InP substrate is completed; after the morphology transfer is completed, performing a multi-stage surface cleaning on the surface of the InP substrate; finally, obtaining the InP microlens array. The present application also comprises an InP microlens array based on intermittent three-stage etching. The present application can realize high-fidelity transfer of the curved surface morphology of the microlens in a large range of sag height, has low surface roughness and good array consistency, and is suitable for manufacturing of InP-based high-performance and high-yield photoelectric devices.

Description

Technical Field

[0001] This invention relates to the fields of photoelectric detection and micro / nano manufacturing, and in particular to an InP microlens array based on intermittent three-stage etching and its fabrication method. Background Technology

[0002] With the rapid development of quantum communication, lidar, and high-speed optical communication, infrared detectors are continuously evolving towards larger arrays, smaller pixels, and higher bandwidth. In typical devices such as InGaAs / InP avalanche photodiodes, to meet the requirements of high-speed response and low noise, the active region size usually needs to be reduced to decrease junction capacitance and suppress dark current. However, pixel reduction leads to a decrease in the effective photosensitive area, and the incident light cannot be fully utilized. The reduced optical coupling efficiency has become a key bottleneck restricting the improvement of detection efficiency. With the space for electrical optimization gradually becoming limited, monolithically integrating microlens arrays on the surface of InP-based devices and focusing the incident light to the effective photosensitive area through curved surface topography can compensate for the light energy loss caused by pixel reduction, improve the equivalent fill factor and light energy utilization, and thus become an important technical path to improve device performance.

[0003] Currently, the mainstream fabrication method for InP-based microlens arrays is a combination of photoresist thermal reflow and chlorine-containing ICP etching to transfer the photoresist curved structure to the substrate. However, this process faces three major problems in practical engineering. First, during continuous ICP etching, plasma bombardment and substrate heat buildup cause deformation of the photoresist mask, resulting in a significant deviation of the etched lens surface from the designed spherical cap contour, especially prominent in large-sagittal structures requiring deep etching. Second, InP's Cl-based etching byproducts (such as InCl...) X InP microlens arrays have low volatility and readily deposit polymers on the chamber walls and substrate surface. As etching depth increases, byproducts gradually cover the mask and etching interface, causing localized etching rate decreases, sidewall roughness, and pattern transfer distortion, and in severe cases, even leading to etching termination. Thirdly, after etching, residual chlorides and microparticle contaminants on the InP surface are difficult to remove completely using conventional single-step wet cleaning. These residues increase surface roughness, raise device dark current, and reduce long-term reliability. These intertwined problems restrict the engineering application of InP-based microlens arrays in large-area, high-performance optoelectronic devices. Therefore, a high-fidelity conformal fabrication method that can simultaneously solve the problems of mask conformal preservation, in-situ byproduct removal, and surface purification is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide an InP microlens array based on intermittent three-stage etching and its fabrication method, which mainly solves the problems existing in the prior art. It achieves high-fidelity and shape-preserving transfer of the microlens curved structure on the InP substrate by introducing a synergistic control mechanism of curved structure conformal enhancement, dynamic control of the etching process, and surface repair after etching, and obtains an array structure with low roughness and high consistency.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is to provide a method for fabricating an InP microlens array based on intermittent three-stage etching, characterized by comprising the following steps:

[0006] Step S100: A photoresist pattern is formed on the surface of the InP substrate;

[0007] Step S200: Perform thermal reflow treatment on the photoresist pattern to make the photoresist pattern a continuous curved surface structure;

[0008] Step S300: The morphology of the continuous curved surface structure is transferred to the InP substrate using an inductively coupled plasma etching process; the etching process is an intermittent etching transfer process.

[0009] Step S400, repeat step S300 until the morphology transfer of the InP substrate surface is completed;

[0010] Step S500: After the morphology transfer is completed, the surface of the InP substrate is subjected to multi-stage surface cleaning.

[0011] Step S600: Obtain the InP microlens array.

[0012] Furthermore, in step S200, the heat reflux process is a segmented heating heat reflux process, which includes multiple heating stages; the temperature of each heating stage increases progressively.

[0013] Furthermore, the segmented heating and reflux treatment includes three heating stages; the target temperature range for each heating stage is 100°C to 200°C, and the heating rate is 10°C / min to 50°C / min.

[0014] Furthermore, between steps S200 and S300, step S250 is included to perform a low-temperature stabilization treatment on the continuous curved surface structure to enhance the shape retention capability of the continuous curved surface structure in the subsequent etching process.

[0015] Furthermore, the low-temperature stabilization treatment temperature is 60°C to 100°C, and the treatment time is 1 to 3 hours.

[0016] Furthermore, in step S300, the intermittent etching transfer process is an intermittent three-stage etching transfer process, which includes an etching stage, an inert gas purging stage, and a vacuum stage performed sequentially, in order to reduce the deposition of chlorine-containing etching byproducts and reduce substrate heat accumulation.

[0017] Furthermore, the duration of the etching stage, the inert gas purging stage, and the vacuuming stage is 1 to 5 minutes each; the etching stage uses a chlorine-containing gas system; the chlorine-containing gas system includes Cl2 with a flow rate of 6 to 15 sccm and BCl3 with a flow rate of 5 to 20 sccm.

[0018] Furthermore, in step S500, the multi-stage surface cleaning includes sequential fluorine-based plasma cleaning, a first deionized water rinse, an acidic solution cleaning, and a second deionized water rinse.

[0019] Furthermore, in the fluorine-based plasma cleaning, plasma containing SF6 is used; in the acidic solution cleaning, dilute hydrochloric acid with a concentration of 1% to 10% is used for cleaning, and the cleaning time is 0.5 to 3 minutes.

[0020] The present invention also discloses an InP microlens array prepared by the above preparation method, characterized in that the diameter of the microlens is 10 to 500 μm and the sagittal height is 2 to 15 μm.

[0021] In view of the above technical features, the InP microlens array based on intermittent three-stage etching and its fabrication method of the present invention have the following significant advantages compared with the prior art:

[0022] 1. This invention significantly improves the thermal stability and bombardment resistance of the photoresist spherical crown structure in the plasma etching environment by introducing a long-term low-temperature baking hardening step after hot melt reflow. It effectively suppresses the softening deformation, collapse or carbonization of the mask during the etching process and ensures high-fidelity transfer of the lens surface shape from the photoresist to the InP substrate.

[0023] 2. This invention employs an intermittent three-stage etching process, which divides continuous etching into a short etching stage, a purging stage, and a vacuuming stage. In each short cycle, inert gas is used to purge and vacuum in a timely manner, which can remove the low-volatility etching byproducts accumulated in the chamber and on the substrate surface in real time. At the same time, it effectively reduces substrate heat accumulation, thereby avoiding pattern distortion caused by byproduct deposition and mask damage caused by heat accumulation, and significantly improving the fidelity of topography transfer and process stability.

[0024] 3. This invention proposes a multi-stage surface repair process involving fluorine-based plasma cleaning, deionized water cleaning, acidic solution cleaning, and deionized water rinsing. This process can remove residual photoresist, chlorides, and metal oxides in steps, resulting in a sub-nanometer smooth surface. This significantly reduces the surface roughness of the microlens, which is beneficial for improving the optical performance and long-term reliability of the device.

[0025] 4. In this invention, the synergistic effect of the above-mentioned technical features enables the fabrication of large-area microlens arrays to achieve sub-nanometer-level low surface roughness, high vector accuracy, low curvature error, and excellent intra-array uniformity, providing a reliable process foundation for the engineering application of InP-based optoelectronic devices. Attached Figure Description

[0026] Figure 1 This is a flowchart of a preferred embodiment of the method for fabricating an InP microlens array based on intermittent three-stage etching according to the present invention.

[0027] Figure 2 This is a schematic diagram of the etching process in a preferred embodiment of the InP microlens array fabrication method based on intermittent three-stage etching of the present invention.

[0028] Figure 3 This is a schematic diagram of a preferred embodiment of the InP microlens array based on intermittent three-stage etching of the present invention.

[0029] Figure 4 This is a schematic diagram of a 3D graphic obtained by laser confocal scanning of a preferred embodiment of the InP microlens array based on intermittent three-stage etching of the present invention.

[0030] In the figure, 1-InP substrate, 2-microlens, 3-photoresist. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] Please see Figure 1 and Figure 2 This invention discloses a method for fabricating an InP microlens array based on intermittent three-stage etching. As shown in the figure, a preferred embodiment includes the following steps:

[0033] Step S100: Forming a photoresist pattern.

[0034] An InP substrate is selected, and its surface is cleaned using a standard semiconductor cleaning process. After cleaning, a positive photoresist (e.g., SPR220-3.0 photoresist) is spin-coated onto the InP substrate surface. The spin-coating speed and time are adjusted according to the target film thickness. In this embodiment, the photoresist thickness after spin-coating is 2 to 4 μm. Then, using ultraviolet lithography, a photoresist microstructure array, such as a cylindrical or prismatic photoresist pattern array, is formed on the InP substrate surface through exposure and development using a photomask. The microlens diameter can cover a range of 10 to 500 μm, thus corresponding to the photoresist pattern diameter. In this embodiment, the microlens diameter is 50 μm.

[0035] Step S200: Segmented heating and reflux treatment.

[0036] An InP substrate with photoresist pattern is placed on a hot stage for segmented heating and reflow processing. This embodiment employs three heating stages, each with a target temperature range of 100°C to 200°C and a heating rate of 10°C / min to 50°C / min. Specifically, the first heating stage begins at 100°C, increasing to 120°C at a rate of 20°C / min and holding for 2 minutes. The second heating stage increases the temperature to 160°C at a rate of 20°C / min and holds for 2 minutes. The third heating stage increases the temperature to 180°C at a rate of 20°C / min and holds for 2 minutes. During the reflow process, the photoresist softens and flows under surface tension, gradually forming a smooth, continuous spherical cap-shaped curved surface structure from an initial cylindrical shape.

[0037] Step S250: Low-temperature stabilization treatment.

[0038] This process is used to complete the conformal aging process of the photoresist. After reflow, the sample is removed from the hot stage and transferred to an oven for low-temperature stabilization. The treatment temperature is 60°C to 100°C, and the treatment time is 1 to 3 hours. In this embodiment, the treatment temperature is 80°C, and the treatment time is 2 hours. This step allows the curved surface structure of the photoresist to cross-link and solidify, enhancing its thermal stability and resistance to plasma bombardment during subsequent plasma etching processes, thereby ensuring high-fidelity transfer of the spherical cap morphology.

[0039] Step S300: Intermittent three-stage ICP etching.

[0040] By using intermittent three-stage ICP etching, the morphology of photoresist is transferred onto an InP substrate. This effectively suppresses byproduct deposition and heat accumulation, thereby improving the fidelity of microlens transfer to the InP substrate.

[0041] Specifically, the sample, after low-temperature stabilization, is placed in the reaction chamber of an inductively coupled plasma (ICP) etching apparatus and fixed on a temperature-controlled substrate stage, with the etching temperature set at 20°C. The ICP etching apparatus generates high-density plasma via an ICP power supply, and the ion bombardment energy and direction are controlled by an RF bias power supply. This embodiment employs an intermittent three-stage etching transfer process, with each etching cycle including a sequential etching stage, an inert gas purging stage, and a vacuuming stage.

[0042] Step S301, etching stage.

[0043] A chlorine-containing gas system, including Cl2 and BCl3, is introduced as the etching gas. The Cl2 flow rate is 6 to 15 sccm (10 sccm in this embodiment), the BCl3 flow rate is 5 to 20 sccm (12 sccm in this embodiment), the RF power is 100 to 300 W (150 W in this embodiment), and the ICP power is 400 to 1000 W (800 W in this embodiment). This stage lasts for 1 to 5 minutes (2 minutes in this embodiment). During this stage, Cl2 and BCl3 react chemically with InP to generate volatile products such as InCl3 and PCl3. Simultaneously, under ion bombardment, the morphology of the photoresist surface gradually transfers onto the InP substrate.

[0044] Step S302, inert gas purging stage.

[0045] Turn off the etching gas and power source, and introduce inert gas at a flow rate of 50 sccm. Use the gas to purge the chamber and sample surface to remove the low-volatility etching byproducts remaining thereafter. This stage lasts for 1 to 5 minutes (2 minutes in this example).

[0046] Step S303, vacuuming stage.

[0047] All gases are shut off, and the reaction chamber is evacuated to a low vacuum using a vacuum pump to completely remove residual byproducts and effectively reduce substrate heat accumulation. This stage lasts for 1 to 5 minutes (2 minutes in this embodiment).

[0048] Step S400: Determine whether the designed etching depth has been reached.

[0049] If the designed etching depth is not reached, proceed to step S300 and repeat the cycle consisting of the etching stage, inert gas purging stage, and vacuuming stage. Once the morphology of the photoresist surface has been completely transferred to the InP substrate and the designed etching depth has been reached (corresponding to a microlens sagitta of 2 to 15 μm), proceed to step S500.

[0050] Step S500: Multi-stage surface cleaning.

[0051] After etching, the sample surface undergoes multi-stage cleaning to remove residual photoresist, chlorides, and other contaminants. This process includes the following four sub-steps:

[0052] Step S501, fluorine-based plasma cleaning.

[0053] The sample is placed in the reaction chamber of an inductively coupled plasma (ICP) etching apparatus, and SF6 gas is introduced at a flow rate of 5 to 20 sccm (10 sccm in this embodiment), with an RF power of 20 to 100 W (80 W in this embodiment) and an ICP power of 200 to 800 W (400 W in this embodiment), for 1 to 3 minutes. SF6 plasma can effectively remove residual organic contaminants and some chlorides from the surface.

[0054] Step S502, first deionized water rinse.

[0055] Remove the sample and rinse the surface with plenty of deionized water to remove water-soluble residues.

[0056] Step S503: Clean with acidic solution.

[0057] The sample was immersed in a 1% to 10% dilute hydrochloric acid solution for 0.5 to 3 minutes. In this example, 5% dilute hydrochloric acid was used for 1 minute. Dilute hydrochloric acid can dissolve residual metal oxides and chlorides on the surface.

[0058] Step S504, second deionized water rinse.

[0059] Rinse the sample surface again with plenty of deionized water to remove residual acid and reaction products, and finally dry it with nitrogen.

[0060] Step S600: Obtain the InP microlens array.

[0061] After the above steps, an InP microlens array with high-fidelity curved surface morphology, low surface roughness and good array consistency is obtained on the InP substrate surface.

[0062] Please see Figure 2 and Figure 3 The present invention also discloses an InP microlens array based on intermittent three-stage etching, manufactured using the above-described fabrication method. As shown in the figure, a preferred embodiment includes an InP substrate 1 and a plurality of microlenses 2 integrally formed on the surface of the InP substrate. The microlenses 2 have a continuous curved surface profile in the shape of a spherical cap or approximately a spherical cap.

[0063] The InP substrate 1 and the microlens 2 are made of the same material (both InP), and are integrally formed by etching without the need for additional bonding or assembly steps. This InP microlens array can be monolithically integrated onto the light-incident surface of InP-based optoelectronic devices (such as InGaAs / InP avalanche photodiode arrays) to focus incident light onto the effective photosensitive area, thereby improving optical coupling efficiency and equivalent fill factor.

[0064] The diameter of the microlens 2 fabricated using the above method is between 20 and 300 μm. In this embodiment, depending on the mask design, the diameter of the microlens 2 can specifically be 50 μm, 100 μm, 150 μm, or 200 μm, etc. The height of the microlens 2 is between 2 and 15 μm. The ratio of height to diameter (height-to-diameter ratio) can be controlled by adjusting the photoresist thickness, thermal reflow parameters, and etching depth according to the actual optical design requirements. In this embodiment, typical heights are 5 μm, 8 μm, or 10 μm.

[0065] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for fabricating an InP microlens array based on intermittent three-stage etching, characterized in that, Includes the following steps: Step S100: A photoresist pattern is formed on the surface of the InP substrate; Step S200: Perform thermal reflow treatment on the photoresist pattern to make the photoresist pattern a continuous curved surface structure; Step S300: The morphology of the continuous curved surface structure is transferred to the InP substrate using an inductively coupled plasma etching process. The etching process is an intermittent etching transfer process; Step S400, repeat step S300 until the morphology transfer of the InP substrate surface is completed; Step S500: After the morphology transfer is completed, the surface of the InP substrate is subjected to multi-stage surface cleaning. Step S600: Obtain the InP microlens array.

2. The preparation method according to claim 1, characterized in that, In step S200, the heat reflux process is a segmented heating heat reflux process, which includes multiple heating stages; the temperature of each heating stage increases progressively.

3. The preparation method according to claim 2, characterized in that, The segmented heating and reflux process includes three heating stages; the target temperature range for each heating stage is 100°C to 200°C, and the heating rate is 10°C / min to 50°C / min.

4. The preparation method according to claim 1, characterized in that, Between steps S200 and S300, there is also step S250, which involves performing a low-temperature stabilization treatment on the continuous curved surface structure to enhance its shape retention capability during subsequent etching processes.

5. The preparation method according to claim 4, characterized in that, The low-temperature stabilization treatment is performed at a temperature of 60°C to 100°C for a duration of 1 to 3 hours.

6. The preparation method according to claim 1, characterized in that, In step S300, the intermittent etching transfer process is an intermittent three-stage etching transfer process, which includes an etching stage, an inert gas purging stage, and a vacuum stage performed sequentially, in order to reduce the deposition of chlorine-containing etching byproducts and reduce substrate heat accumulation.

7. The preparation method according to claim 6, characterized in that, The duration of the etching stage, the inert gas purging stage, and the vacuuming stage is 1 to 5 minutes each; the etching stage uses a chlorine-containing gas system; the chlorine-containing gas system includes Cl2 with a flow rate of 6 to 15 sccm and BCl3 with a flow rate of 5 to 20 sccm.

8. The preparation method according to claim 1, characterized in that, In step S500, the multi-stage surface cleaning includes sequential fluorine-based plasma cleaning, a first deionized water rinse, an acidic solution cleaning, and a second deionized water rinse.

9. The preparation method according to claim 8, characterized in that, In the fluorine-based plasma cleaning, plasma containing SF6 is used; in the acidic solution cleaning, dilute hydrochloric acid with a concentration of 1% to 10% is used for cleaning, and the cleaning time is 0.5 to 3 minutes.

10. An InP microlens array prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The microlens has a diameter of 10 to 500 μm and a sagittal height of 2 to 15 μm.

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