Process for preparing a metal microcavity of an infrared detector

Abstract

This invention discloses a fabrication process for a metal microcavity in an infrared detector. The metal microcavity includes a mesa structure and an insulating dielectric layer and a gold thin film layer sequentially covering the outer side of the mesa structure. The fabrication process includes the following steps: S1: Fabricating the mesa structure on a substrate using an etching process; S2: Depositing an insulating dielectric layer on the mesa structure; S3: Depositing a gold thin film layer on the insulating dielectric layer; S4: Forming a photolithographic pattern on the gold thin film layer and etching the gold thin film layer using a dry etching process; S5: Removing the residual gold thin film layer and metal byproducts generated by the dry etching process using a wet etching process, and finally cleaning to remove the photolithographic pattern layer. This invention proposes a metal microcavity structure fabrication scheme combining atomic layer deposition and composite etching processes, focusing on solving the technological challenges of controlling the optical flatness of the surface and sidewall metal films of the microcavity structure at deep subwavelength scales and ensuring reliable electrical isolation between the microcavity structure and the upper and lower electrodes and active layers.

Description

Technical Field

[0001] This invention relates to micro-nano fabrication technology for complex mesa-structured microcavity infrared detectors, and more particularly to a metal microcavity fabrication process for infrared detectors. Background Technology

[0002] The Metal Cavity-Quantum Well Infrared Photodetector (MC-QWIP) is a detector that utilizes the resonant frequency selection characteristics of a metal microcavity and the infrared absorption of the quantum well material to achieve spectral selectivity. Specifically, a quantum well material is placed inside a metal microcavity. Based on the resonance mechanism of the microcavity structure, only incident infrared light of a specific wavelength can couple into the microcavity to form a resonant mode, which is then absorbed and detected by the built-in quantum well material. Due to the resonant frequency selection of the metal microcavity, incident photons will be absorbed multiple times within the cavity until they are exhausted. Simultaneously, the device's response bandwidth is significantly compressed (to a typical bandwidth of around 300 nm for narrowband target recognition and detection), resulting in a significant improvement in absorption quantum efficiency.

[0003] In metallic microcavity quantum well infrared detectors, the metallic microcavity is a subwavelength optical resonant structure formed by the detector's metallic sidewalls and upper and lower interfaces. Essentially, it utilizes the electromagnetic standing wave field formed by the metallic boundaries; therefore, the quality of the metallic microcavity is the key physical basis for achieving high optical coupling efficiency and optical absorption performance. First, a smooth and steep metallic microcavity provides a definite and consistent reflection boundary and phase abrupt change condition for electromagnetic waves, which is a prerequisite for accurately controlling the resonant wavelength and achieving precise spectral modulation. Second, the smoothness of the metallic microcavity directly determines the scattering loss of light propagating within the cavity. An ideal, smooth metallic sidewall allows light waves to circulate multiple times within the cavity via specular reflection, resulting in slow energy decay and the formation of a narrow-band, high-intensity resonance peak. The quality of the metallic microcavity is a core factor affecting the overall performance of the device; therefore, its fabrication process plays a crucial role in the entire detector fabrication process.

[0004] In the fabrication of metal microcavity quantum well infrared detectors, several key challenges arise, primarily in the selection and growth process of the dielectric film, and the fabrication and patterning etching of the metal film. Firstly, the dielectric film, as a crucial component of the metal microcavity structure, directly impacts the device's electrical isolation and optical resonance quality. An ideal dielectric film must meet several requirements: 1. The optical absorption of the dielectric film should be as low as possible to minimize its influence on the light absorbed by the QWIP material; 2. The dielectric strength of the dielectric film should be sufficiently high to withstand the operating voltage; 3. The film itself should have a good stress state to avoid warping or cracking due to excessive stress; 4. The film should have good adhesion to the layers above and below it to prevent delamination or detachment; 5. The dielectric film must be compatible with subsequent processes to ensure device performance and yield. However, traditional PECVD technology suffers from poor step coverage and difficulty in controlling film thickness uniformity, making it challenging to meet the consistency and morphological fidelity requirements of high-precision microcavities.

[0005] Secondly, the fabrication and patterning of the metal film are particularly complex. The thickness and morphology of the metal sidewalls have a decisive influence on the resonant performance of the microcavity. Due to the limitations of the three-dimensional structure, electron beam evaporation cannot be used to ensure the thickness of the metal film on the sidewalls of the metal microcavity. Instead, magnetron sputtering technology is required, and the process parameters must be precisely controlled to achieve uniform coverage of the sidewall metal. During the patterning process, in order to achieve stable electrical isolation between detector pixels, metal patterning must use etching rather than stripping. However, the etching of metals, especially for materials like gold, has three fundamental limitations with traditional dry etching: 1. The reaction products of dry etching have extremely poor volatility. Taking typical gold chloride (AuCl3) as an example, its sublimation temperature at atmospheric pressure is as high as 254℃, far exceeding the tolerance limit of conventional etching cavities (<200℃). This forces the process to rely on continuous bombardment of ions with energies higher than 500 eV to provide sufficient desorption kinetic energy, resulting in etching rates generally lower than 8 nm / min, only 1 / 30 of the etching rate of silicon. Meanwhile, the selectivity ratio of the mask and underlying material in this process is less than 3:1, resulting in severe non-target etching and structural damage. 2. Dry etching can induce difficult-to-eliminate redeposition defects. Due to the short mean free path of gold atoms (<50 nm), gold atoms displaced under high-energy ion bombardment are easily redeposited on the sidewalls under the drive of the plasma sheath electric field, forming a nanoscale "fence" structure composed of dense gold atoms. Due to its chemical inertness and high density, this structure is firmly wrapped around the photoresist pattern and cannot be removed by conventional post-processing methods, severely damaging the integrity and precision of the structure. 3. Dry etching faces the challenge of selectivity imbalance when integrating heterogeneous materials. When gold coexists with key dielectric layers such as hafnium oxide (HfO2), the etching rate ratio (Au:HfO2) in Cl2-based plasma is as low as 0.7:1. This means that while etching through a 100 nm gold layer, more than 140 nm of dielectric layer will be removed simultaneously. The trench effect that appears around the mesa can exacerbate the etching effect around the mesa. Even a slight over-etching of only 10% can easily lead to perforation of the dielectric layer, causing it to completely lose its electrical isolation function and directly leading to device failure. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a process for fabricating metal microcavities for infrared detectors. Through rational process design and specific etching methods, this invention manufactures metal microcavity structures with smooth surfaces, intact structures, no residues, and no damage to the underlying material during processing.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A fabrication process for a metal microcavity in an infrared detector, the metal microcavity comprising a mesa structure and an insulating dielectric layer and a gold thin film layer sequentially coated on the outer side of the mesa structure; the fabrication process includes the following steps:

[0009] S1: Mesa structure is fabricated on the substrate by etching process;

[0010] S2: Deposit an insulating dielectric layer on the platform structure;

[0011] S3: Deposit a gold thin film layer on the insulating dielectric layer;

[0012] S4: A photolithographic pattern is formed on the gold thin film layer and the gold thin film layer is etched using a dry etching process;

[0013] S5: Wet etching is used to remove the residual gold film layer and the metal byproducts produced by dry etching. Finally, the photolithographic material pattern layer is removed by cleaning.

[0014] The etching process in step S1 is as follows: cavity temperature: 20℃; BCl3: 5sccm; Cl2: 5sccm; pressure: 4mTorr; Ar: 20sccm; ICP power: 280W; RF: 25W; Helium: 10mTorr.

[0015] In step S1, the sidewall surface of the platform structure is smooth and steep.

[0016] In step S2, an insulating dielectric layer is deposited on the mesa structure using atomic layer deposition.

[0017] In step S2, the insulating dielectric layer grows uniformly and smoothly on the mesa structure.

[0018] In step S3, the thickness of the gold thin film layer is greater than 100 nanometers.

[0019] In step S3, a gold thin film layer is deposited by magnetron sputtering.

[0020] Specifically, the dry etching in step S4 is performed using ion beam etching (IBE) technology.

[0021] In step S4, the etching angle of the ion beam etching technique is 60°-90°.

[0022] Specifically, the wet etching in step S5 uses Sigma-Aldrich 651842 etchant.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) This invention proposes a metal microcavity structure fabrication scheme combining atomic layer deposition (ALD) and composite etching processes, which focuses on solving the process challenges of controlling the optical flatness of the surface and sidewall metal films of the microcavity structure at the deep subwavelength scale and ensuring reliable electrical isolation between the metal films and the upper and lower electrodes and active layers. The specific process flow includes: first, forming a mesa-shaped device structure using ICP etching; then, combining ALD and magnetron sputtering processes, growing an insulating dielectric layer and a metal film covering the mesa in sequence to construct a high-quality metal microcavity. Among them, the dielectric film ALD technology not only achieves effective electrical isolation of the sidewalls, but also significantly improves the sidewall roughness problem caused by ICP etching, thereby improving the optical flatness of the metal film layer and optimizing the resonant frequency selection characteristics and optocoupler efficiency of the device.

[0025] (2) The fabrication process of this invention combines functionality and processability. While effectively protecting the electrical properties of the pixels after mesa etching, it can significantly flatten the exposed steep mesa sidewalls. This characteristic provides a smoother substrate for subsequent metal microcavity deposition and is the key process basis for the final formation of a high-performance "metal mirror" structure.

[0026] (3) This invention successfully overcomes the inherent limitations of single etching techniques by synergistically integrating physical dry etching and wet etching. This scheme utilizes wet etching to effectively remove redeposited materials generated by dry etching and alleviate their physical damage to the dielectric film material. At the same time, it utilizes the anisotropic characteristics of dry etching to suppress the lateral drilling of wet etching. This synergistic process allows the two to complement each other under existing equipment conditions, significantly improving the morphology quality and fabrication yield of metal microcavities. Specifically, in the pixel isolation stage, a composite process combining dry etching and wet etching is adopted to effectively remove the metal layer in the micron-scale pixel gaps, overcome the "fence effect" and "channel effect" commonly found in dry etching, reduce metal product residue while avoiding damage to the electrical performance of the device, and ensure the integrity of the microcavity structure and the reliability of electrical isolation.

[0027] (4) The device fabrication process proposed in this invention is fully compatible with existing focal plane array technology and has excellent inheritance and scalability. This method has significant advantages in improving the optical and electrical performance of metal microcavities, which is beneficial to improving the fabrication yield and overall performance of infrared focal plane array detectors. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the metal microcavity of the present invention, wherein... Figure 1 (a) in the diagram is a schematic diagram of the basic structure of a metal microcavity. Figure 1 (b) in the figure is a schematic diagram of the cross-section of the metal microcavity.

[0029] Figure 2This is a schematic flowchart of the metal microcavity fabrication process for the infrared detector of the present invention.

[0030] Figure 3 This is a schematic flowchart of the metal cavity etching process steps of the present invention.

[0031] Figure 4 This is a schematic diagram of a focal plane array device.

[0032] In the attached figures, the labels are: 1-gold thin film layer, 2-insulating dielectric layer, 3-upper electrode layer, 4-quantum well light absorption layer, and 5-lower electrode layer. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0034] This invention proposes a metal microcavity fabrication process for infrared detectors that can meet the requirements of dielectric films and effectively solve problems such as product deposition, fence effect and channel effect generated during the etching process of gold thin films, ensuring optical and electrical performance, and is compatible with infrared focal plane array device processes.

[0035] The structure of the metal microcavity of the present invention is as follows: Figure 1 As shown, where Figure 1 (a) in the diagram is a schematic diagram of the basic structure of a metal microcavity. Figure 1 (b) is a schematic cross-sectional view of the metal microcavity. Specifically, the metal microcavity consists of a gold thin film layer 1, an insulating dielectric layer 2, an upper electrode layer 3, a quantum well light absorption layer 4, and a lower electrode layer 5 from top to bottom. That is, the metal microcavity includes a mesa structure and an insulating dielectric layer 2 and a gold thin film layer 1 sequentially covering the outside of the mesa structure; the mesa structure includes the upper electrode layer 3, the quantum well light absorption layer 4, and the lower electrode layer 5. The pixel arrangement period, mesa size, grating parameters, mesa height, and quantum well structure parameters in the detector structure design are obtained through finite element simulation. The mesa structure (specifically including the upper electrode layer 3, the quantum well light absorption layer 4, and the lower electrode layer 5) is obtained by ICP etching on the quantum well substrate material. The insulating dielectric layer 2 and the gold thin film layer 1 covering the mesa device are grown on the mesa structure by atomic layer deposition and magnetron sputtering processes. A patterned mask layer is obtained by photoresist. Then, the metal at the edge of the mesa device is removed by a device process combining dry etching and wet etching to fabricate the metal microcavity.

[0036] In this invention, the high-quality metal microcavity structure is based on two key processes: precise mesa etching and uniform dielectric film deposition.

[0037] See Figure 2 This invention, through a precisely controlled mesa etching process, first forms steep and smooth mesa sidewalls, providing an excellent initial morphological foundation for achieving the ideal microcavity resonance mode. Based on this, the dielectric film grown using atomic layer deposition (ALD) technology exhibits several comprehensive advantages: In terms of process morphology, its superior step coverage capability allows it to uniformly cover high aspect ratio mesa structures, effectively filling microscopic defects that may be introduced by dry etching and providing a smooth and continuous substrate surface for subsequent gold thin film deposition; in terms of mechanical properties, precise control of internal stress is achieved through layer-by-layer reaction, effectively avoiding film cracking or substrate warping caused by stress mismatch, ensuring the mechanical stability and morphological integrity of the microcavity structure; in terms of process compatibility… Atomic layer deposition (ALD) exhibits excellent compatibility with preceding and subsequent process steps, avoiding thermal or mechanical damage to the formed mesa structure while providing ideal interface conditions for subsequent metal deposition, ensuring smooth and reliable overall process flow. In terms of electrical performance, the insulating dielectric layer 2, with its excellent dielectric strength and uniformity, forms a dense, non-porous, high-quality insulating layer between the metal microcavity and the pixel electrode, effectively preventing electrical short circuits between the microcavity and the electrode. Its stable chemical properties and low defect density ensure long-term reliability of the device under operating voltage, avoiding premature breakdown or leakage failure. The synergistic effect of these two processes not only creates ideal morphological conditions for the construction of the metal microcavity but also lays a solid foundation in multiple dimensions such as stress control, process compatibility, and electrical isolation, thus jointly guaranteeing the final formation of a smooth, continuous, and highly reflective "metal mirror" structure.

[0038] See Figure 3This invention further employs magnetron sputtering to deposit a gold thin film layer 1, and utilizes a composite etching technique combining dry and wet methods to achieve high-precision patterning of the metal microcavity. The specific process is as follows: First, the gold thin film layer 1 is initially thinned using IBE ion beam etching. By optimizing the etching angle, the normal bombardment intensity of high-energy ions on the substrate is reduced, thus minimizing physical damage to the dielectric layer. Subsequently, by adjusting the wet etching solution containing isopropanol, lateral corrosion is suppressed while shortening the etching time, ensuring the perpendicularity and dimensional accuracy of the patterned structure. This fabrication scheme effectively overcomes problems such as "fence" redeposition, dielectric layer perforation, and isotropic corrosion in traditional metal etching. Combining precise mesa etching and uniform dielectric film deposition processes, a metal microcavity structure with smooth continuity, steep sidewalls, and high reflectivity is ultimately formed. While ensuring the electrical isolation performance of the detector, it significantly improves optical coupling efficiency and pixel yield, providing key technical support for the development of high-performance metal microcavity infrared focal plane array devices.

[0039] Example 1

[0040] All equivalent transformations or substitutions made based on the technical solution of this invention should be covered within the protection scope of this invention. This embodiment is only one specific implementation method. This embodiment uses quantum well materials as an example to briefly describe the specific implementation method of this invention. The basic structure of the metal microcavity detector of this invention is as follows: Figure 1 As shown. Specifically, the mesa structure has a width of 30 μm and a height of 10 μm. Nine grating slots are evenly distributed in 3 rows and 3 columns on the mesa, with a width w = 3 μm, a depth of 3 μm, and a distance p = 7 μm between two slots. In this embodiment, the insulating medium used is HfO2, with a thickness of 200 nm; the gold thin film layer has a thickness of 1 μm.

[0041] See Figure 2 and Figure 3 The fabrication process of the metal microcavity of the infrared detector in this embodiment specifically includes the following steps:

[0042] S1: Mesa etching: A mesa structure of the above dimensions is prepared on the substrate by etching process.

[0043] S2: Dielectric film deposition: An insulating dielectric layer 2 with a thickness of 200 nm is grown by atomic layer deposition process. In this embodiment, the insulating dielectric layer 2 is an HfO2 insulating dielectric layer.

[0044] S3: Gold deposition: A 1 μm Au film is sputtered on the mesa surface and mesa sidewalls by physical vapor deposition as a gold thin film layer 1.

[0045] S4: Photolithography and development: Use photoresist to homogenize and photolithographically create a pattern that covers the entire mesa and creates a hole with a diameter of 16μm above the mesa;

[0046] S5: Gold Etching and Resin Removal: After development, etching of the metal microcavities can begin, with the final result as shown. Figure 2 As shown in S5.

[0047] This embodiment employs a composite etching technique combining dry and wet etching to etch the metal microcavity, achieving high-precision patterning of the metal microcavity. See also... Figure 3 Step S5 specifically includes the following steps:

[0048] S51: IBE Etching: The device is etched using an IBE etching system (ion beam etching system) at 400 eV, 90 degrees, and a etching rate of 10 nm / min for 20 minutes. Figure 3 As shown in S51.

[0049] S52: Wet Etching: The metal microcavity was further etched using Sigma-Aldrich gold etchant 651842 modified with isopropanol. The Sigma-Aldrich gold etchant 651842 was mixed with isopropanol at a volume ratio of 1:1 and stirred thoroughly until homogeneous. The sample was placed in the prepared gold etching solution at 25°C and 45% humidity and etched at a rate of 10 nm / s. After 80 s of etching, the sample was immediately transferred to deionized water for 3 min of cleaning. Figure 3 As shown in S52.

[0050] S53: Remove photoresist: Clean the photoresist mask with acetone, such as... Figure 3 As shown in S54.

[0051] The process described in this case is fully compatible with existing focal plane array technologies. When applied to the design of focal plane array devices, its process effect is as follows: Figure 4 As shown. Figure 4 This is a schematic diagram of the structure of a focal plane device obtained by applying the metal microcavity fabrication process of the infrared detector of the present invention to the design of a focal plane device. Figure 4 As shown, the focal plane array in this embodiment includes 1024 pixels in both the horizontal and vertical directions.

[0052] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention. The above embodiments are provided only for the purpose of describing the present invention and are not intended to limit the present invention. Parts not described in detail in this specification are well-known in the art and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be covered within the scope of the present invention.

Claims

1. A process for fabricating a metal microcavity for an infrared detector, characterized in that, The metal microcavity comprises a mesa structure and an insulating dielectric layer and a gold thin film layer sequentially coated on the outside of the mesa structure; the fabrication process of the metal microcavity includes the following steps: S1: Mesa structure is fabricated on the substrate by etching process; S2: Deposit an insulating dielectric layer on the platform structure; S3: Deposit a gold thin film layer on the insulating dielectric layer; S4: A photolithographic pattern is formed on the gold thin film layer and the gold thin film layer is etched using a dry etching process; S5: Wet etching is used to remove the residual gold film layer and the metal byproducts produced by dry etching. Finally, the photolithographic material pattern layer is removed by cleaning.

2. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, The etching process in step S1 is as follows: chamber temperature: 20℃; BCl3: 5 sccm; Cl2: 5 sccm; pressure: 4 mTorr; Ar: 20 sccm; ICP power: 280W; RF: 25W; Helium: 10mTorr.

3. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, The sidewall surface of the platform structure obtained in step S1 is smooth and steep.

4. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, Step S2 uses atomic layer deposition to deposit an insulating dielectric layer on the mesa structure.

5. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, The insulating dielectric layer in step S2 grows uniformly and smoothly on the mesa structure.

6. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, The thickness of the gold thin film layer in step S3 is greater than 100 nanometers.

7. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, In step S3, a gold thin film layer is deposited by magnetron sputtering.

8. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, The dry etching in step S4 specifically uses ion beam etching technology.

9. The fabrication process of the metal microcavity for the infrared detector according to claim 8, characterized in that, The etching angle of the ion beam etching technique in step S4 is 60°-90°.

10. The fabrication process of the metal microcavity for the infrared detector according to claim 1, characterized in that, The wet etching in step S5 specifically uses Sigma-Aldrich 651842 etchant.

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