A method for manufacturing an electrode contact hole of an infrared detector

Abstract

The application discloses a kind of electrode contact hole manufacturing method of infrared detector, with normal temperature ICP etching system, with 3~4 μm photoresist single-layer film as etching mask, with low-power, small substrate direct current biasing mild etching parameters, etching preparation 0.3~0.5 μm electrode contact hole, save medium mask deposition, secondary lithography and other complex processes;Through subsequent high-temperature annealing process under saturated Hg vapor pressure atmosphere, repair etching lattice damage, greatly improve the quality of contact hole.The application process is simple, low in cost, good in etching uniformity, low in interface damage, can stably prepare small center distance high-density electrode contact hole, suitable for tellurium cadmium mercury infrared focal plane detector batch production, with very high engineering application and industrialization value.

Description

Technical Field

[0001] This invention relates to the fields of infrared focal plane detector chip manufacturing and semiconductor micro / nano etching technology, specifically to a method for fabricating electrode contact holes for an infrared detector. Background Technology

[0002] Mercury cadmium telluride (MCT) and cadmium telluride (CdTe) are core semiconductor materials for fabricating infrared focal plane array detectors. Due to their excellent infrared photoelectric response characteristics and tunable bandgap, they are widely used in military detection, infrared imaging, and security monitoring. The electrode contact hole is the core microstructure of the MCT infrared detector; its sidewall steepness, dimensional uniformity, and interface damage directly determine the detector's photoelectric response consistency, imaging resolution, and long-term operational stability.

[0003] Currently, the mainstream process for fabricating contact holes for MCT / CdTe materials in the industry is low-temperature ICP etching combined with wet etching. Because photoresist materials are prone to carbonization, cracking, and detachment under low-temperature etching conditions, rendering them unusable as effective masks, existing processes require the pre-growth of a SiO2 hard dielectric mask. This necessitates multiple steps, including secondary photolithography, mask etching, and resist removal, to complete the pattern transfer before low-temperature ICP etching can proceed. This process has significant drawbacks: firstly, the process flow is cumbersome, involving redundant steps such as dielectric deposition, mask etching, and multiple photolithography alignments, resulting in long production cycles and high manufacturing costs; secondly, the combination of low-temperature etching with high RF power and large bias parameters leads to intense ion bombardment, which easily generates lattice defects and etching damage on the contact hole sidewalls and concave surfaces, increasing dark current and reducing detector performance. This fails to meet the integration requirements of large-area, high-density infrared focal plane detectors with a resolution of 640×512 or higher.

[0004] Currently, there is no complete process solution for fabricating electrode contact holes for high-density mercury cadmium telluride detectors using a room-temperature ICP etching system without requiring a SiO2 hard dielectric mask, nor is there an integrated annealing damage repair process adapted to room-temperature low-power etching. Addressing the pain points of existing technologies—complex processes, high costs, and inability to adapt to high-density integration—there is an urgent need to develop a simplified, low-damage, and highly uniform room-temperature ICP contact hole fabrication method. Summary of the Invention

[0005] The purpose of this invention is to provide a method for fabricating electrode contact holes for infrared detectors. This method overcomes the shortcomings of existing low-temperature ICP etching and humidification etching processes for preparing contact holes for mercury cadmium telluride detectors, which are complex in process, prone to lattice defects and etching damage on the sidewalls and concave surfaces of the contact holes, increase dark current of the device, reduce detector performance, and cannot meet the integration requirements of large-area array, high-density infrared focal plane detectors of 640×512 and above. This method simplifies the process, reduces production costs, reduces etching damage, and improves the uniformity of the contact holes, making it suitable for mass production of large-area array, high-density infrared focal plane detectors.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for fabricating electrode contact holes in an infrared detector, used for the fabrication of a high-density mercury cadmium telluride (HCdT) infrared detector, eliminates the need to grow a SiO2 hard mask as an etching mask on the surface of the HCdT / cadmium telluride material to be processed. The electrode contact holes are fabricated using room-temperature ICP etching. The method specifically includes the following steps:

[0008] S1, Photoresist Coating: Select a mercury cadmium telluride epitaxial wafer adapted for infrared detection, and uniformly coat the surface of the mercury cadmium telluride / cadmium telluride material to be processed with AZ4330 positive photoresist to form a photoresist film.

[0009] S2, Photolithography Pattern Transfer: The coated epitaxial wafer is placed into a photolithography machine. Through photolithography, exposure, and development processes, the electrode contact hole pattern is transferred on the photoresist film, exposing the mercury cadmium telluride functional layer region to be etched.

[0010] S3, Underfilm removal process: The plasma resist removal process is used to remove the residual photoresist underfilm in the patterned opening area to ensure that the surface of the material to be etched is clean and free of residue.

[0011] S4, wafer bonding and fixing: The epitaxial wafer processed in S3 is fixed onto the tray of the ICP etching machine by vacuum adsorption or high temperature bonding. The cavity is closed and vacuum is drawn to complete the cavity vacuum pretreatment.

[0012] S5, room temperature ICP etching, maintaining the cavity temperature at 10~15℃, using low RF power and small substrate DC bias parameters, and introducing etching process gas to perform ICP etching on the exposed epitaxial wafer to prepare electrode contact holes with a depth of 0.3~0.5μm;

[0013] S6, Annealing damage repair: Take out the etched epitaxial wafer and perform high-temperature annealing to eliminate lattice damage, interface defects and residual stress generated during ICP etching.

[0014] S7, Photoresist Removal: A combination of plasma and wet photoresist removal is used to thoroughly remove residual photoresist from the surface, completing the fabrication of the electrode contact holes for the mercury cadmium telluride infrared detector.

[0015] In step S1, AZ4330 photoresist is uniformly coated on the surface of the epitaxial wafer using a spin coating process. The spin coating speed is 3000 rpm and the spin coating time is 30 s. After drying, a photoresist film with a uniform thickness of 3~4 μm is formed.

[0016] In step S3, the patterned epitaxial wafer is placed in a plasma cleaner and oxygen is used to remove the underlying film. The processing power is 300W and the processing time is 5 minutes.

[0017] In step S5, the ICP etching process parameters include: ICP source power of 800W, RF power of 10W, and small substrate bias voltage of 22~25V.

[0018] The etching process gases include a main etching gas and an auxiliary gas. The gas types and flow ratios of the main etching gas and the auxiliary gas are Ar:N2:CH4 = 30 sccm:5 sccm:1 sccm. The vacuum pressure of the etching chamber is 2.0 mTorr, the etching time is 15 min, and the etching selectivity ratio PR:MCT≈5:1 and PR:CdTe>3:1.

[0019] In step S6, the high-temperature annealing process involves placing the epitaxial wafer into a mercury-rich annealing furnace and annealing it in a saturated Hg vapor pressure atmosphere at a temperature of 265°C. The annealing holding time is 2 hours, followed by natural cooling.

[0020] In step S7, most of the remaining adhesive layer and carbonized layer on the surface are first thoroughly removed by plasma adhesive removal process. Then, the residual thin adhesive is removed by adhesive removal solution, acetone and ethanol in sequence. Finally, the surface damage layer is removed by bromomethanol rinsing. After rinsing with deionized water and drying with nitrogen, the electrode contact hole preparation is completed.

[0021] The sidewall steepness of the electrode contact hole made in step S7 is ≥85°, and the contact hole size uniformity error is ≤5%.

[0022] In view of the above technical features, the present invention has the following beneficial effects: 1. The present invention adopts a room-temperature inductively coupled plasma (ICP) preparation method, which simplifies the process flow and significantly reduces costs. It eliminates the traditional processes of SiO2 hard mask deposition, mask etching, and secondary photolithography, and the mask preparation can be completed with only a single photoresist pattern transfer, reducing the number of processes by more than 40%, significantly shortening the production cycle, and reducing equipment and material costs; 2. The present invention uses a room-temperature ICP etching system, combined with low radio frequency power, low RF power, small substrate DC bias, and suitable gas ratio etching parameters, which reduces the bombardment damage of high-energy ions to mercury cadmium telluride / cadmium telluride materials and ensures the integrity of the concave surface; 3. The 3~4μm photoresist AZ4330(PR) after photolithography pattern transfer is used directly as the only etching mask, eliminating the need to deposit a hard dielectric mask, simplifying the preparation process, and providing good mask formability and high pattern accuracy, which can accurately prepare 0.3~0.5μm contact holes; 4. After etching, in conjunction with the subsequent The annealing process at 265℃ for 2 hours in a saturated Hg vapor pressure atmosphere completely eliminates lattice defects and residual stress introduced by etching, repairs trace lattice defects and interface damage caused by room temperature etching, effectively reduces detector dark current, improves photoelectric response stability, and results in extremely low etching damage and excellent device performance. 5. High-quality contact holes, suitable for high-density integration, high precision of photoresist thick film mask pattern, excellent anisotropy of room temperature etching, and the prepared 0.3~0.5μm contact holes have steep sidewalls, no collapse, and no burrs. The dimensional uniformity is far superior to traditional processes, enabling small center-pitch array arrangement, perfectly meeting the integration requirements of large-area high-density mercury cadmium telluride infrared detectors. 6. Strong process stability, suitable for mass production: The entire process is at room temperature, with strong parameter controllability, avoiding process deviations caused by temperature fluctuations in low-temperature processes, resulting in high product yield and enabling industrial-scale mass production of high-performance mercury cadmium telluride infrared detectors. Attached Figure Description

[0023] Figure 1 A schematic diagram of the process flow for fabricating electrode contact holes using room-temperature ICP;

[0024] Figure 2 Laser confocal images of electrode contact holes prepared according to the present invention;

[0025] Figure 3 The images show a comparison of the SEM morphology of the electrode contact holes prepared in this invention. (a) shows the etching morphology of the single mask etched by the room temperature ICP photoresist of this invention, with smooth and steep sidewalls; (b) shows the low-temperature etching morphology of the SiO2 hard mask in the prior art, with a rough bottom and severely damaged sidewalls.

[0026] Figure 4 This is an image of the device produced by the room temperature etching process of this invention. It is uniform, free of dark spots, and has high contrast. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these drawings and embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that some components well-known to those skilled in the art but not related to the main content of the present invention may be omitted in the drawings or description. Additionally, for ease of description, some components in the drawings may be omitted, enlarged, or reduced, but this does not represent the actual size or complete structure of the product.

[0028] To address the technical challenges of existing technologies for fabricating electrode contact holes in MCT / CdTe materials for large-area, high-density MCT / CdTe infrared detectors with small pixel center-to-center spacing, which employs low-temperature (LN2) ICP dry etching, requiring additional SiO2 hard mask growth, resulting in complex processes, high production costs, and difficulties in large-scale production, this invention utilizes a room-temperature ICP etching system. This system incorporates etching parameters with low RF power, low RF power, small substrate DC bias, and suitable gas ratios. The photoresist AZ4330(PR) after photolithographic pattern transfer is used as the sole etching mask, eliminating the need for a hard dielectric mask and simplifying the fabrication process. After etching, a high-temperature annealing process eliminates interface damage and lattice defects introduced by room-temperature ICP etching, ultimately producing electrode contact holes with steep sidewalls and uniform dimensions of 0.3–0.5 μm. The present invention features a simple process, low cost, and minimal etching damage. It can stably prepare electrode contact holes with small center distance and high density, and is suitable for the mass production of mercury cadmium telluride infrared focal plane detectors of different specifications and wavelengths, effectively improving the uniformity of the detector's photoelectric response and imaging performance.

[0029] A method for fabricating electrode contact holes in an infrared detector, used for the fabrication of a high-density mercury cadmium telluride (HCdT) infrared detector, eliminates the need to grow a SiO2 hard mask as an etching mask on the surface of the HCdT / cadmium telluride material to be processed. The electrode contact holes are fabricated using room-temperature ICP etching. Figure 1 As shown, the specific steps include:

[0030] S1, Photoresist Coating: Select a mercury cadmium telluride epitaxial wafer adapted for infrared detection, and uniformly coat the surface of the mercury cadmium telluride / cadmium telluride material to be processed with AZ4330 positive photoresist to form a photoresist film.

[0031] Preferably, AZ4330 photoresist is uniformly coated on the surface of the epitaxial wafer using a spin coating process. The spin coating speed is 3000 rpm and the spin coating time is 30 s. After drying, a photoresist film with a uniform thickness of 3~4 μm is formed.

[0032] S2, Photolithography Pattern Transfer: The coated epitaxial wafer is placed into a photolithography machine. Through photolithography, exposure, and development processes, the electrode contact hole pattern is transferred on the photoresist film, exposing the mercury cadmium telluride functional layer region to be etched.

[0033] S3, Underfilm Removal Process: The plasma resist removal process is used to remove the residual photoresist underfilm in the patterned opening area, ensuring that the surface of the material to be etched is clean and free of residue. Specifically, the patterned epitaxial wafer is placed in a plasma cleaner and oxygen is used for underfilm removal. The processing power is 300W and the processing time is 5 minutes.

[0034] S4, wafer bonding and fixing: The epitaxial wafer processed in S3 is fixed on the ICP etching machine tray by vacuum adsorption or high temperature bonding. The cavity is closed and vacuum is drawn to complete the cavity vacuum pretreatment.

[0035] S5, room temperature ICP etching, maintaining the cavity temperature at 10~15℃, using low RF power and small substrate DC bias parameters, and introducing etching process gas to perform ICP etching on the exposed epitaxial wafer to prepare electrode contact holes with a depth of 0.3~0.5μm.

[0036] The ICP etching process parameters include an ICP source power of 800W, an RF power of 10W, and a small substrate bias voltage of 22~25V.

[0037] The etching process gases include a main etching gas and an auxiliary gas. The gas types and flow ratios of the main etching gas and the auxiliary gas are Ar:N2:CH4 = 30 sccm:5 sccm:1 sccm. The vacuum pressure of the etching chamber is 2.0 mTorr, the etching time is 15 min, and the etching selectivity ratio PR:MCT≈5:1 and PR:CdTe>3:1.

[0038] S6. Annealing damage repair: The etched epitaxial wafer is taken out and subjected to high-temperature annealing to eliminate lattice damage, interface defects and residual stress generated during ICP etching. Preferably, the high-temperature annealing process involves sending the epitaxial wafer into a mercury-rich annealing furnace and performing the process under a saturated Hg vapor pressure atmosphere. The annealing temperature is 265°C, and the annealing holding time is 2 hours followed by natural cooling.

[0039] S7. Photoresist Removal: A combination of plasma and wet photoresist removal is used to thoroughly remove residual photoresist from the surface, completing the fabrication of the electrode contact holes for the mercury cadmium telluride infrared detector. Specifically, plasma photoresist removal is first used to thoroughly remove most of the remaining photoresist and carbonized layer from the surface. Then, photoresist remover solution, acetone, and ethanol are used in sequence to remove the residual thin photoresist. Finally, bromomethanol is used to rinse and remove the surface damage layer. After rinsing with deionized water and drying with nitrogen, the electrode contact hole fabrication is completed.

[0040] like Figure 2 As shown, the electrode contact holes finally produced through these steps were tested and verified to be steep, with smooth sidewalls, no tilting or collapse, and the steepness angle of the sidewalls of the electrode contact holes was ≥85°. The uniformity error of the contact hole size was ≤5%. The device has low dark current and the photoelectric response uniformity is significantly improved compared with the device prepared by traditional process, which fully meets the mass production requirements of high-density integrated infrared focal plane detectors.

[0041] like Figure 3 As shown, compared with the prior art, (a) the etching morphology of the room temperature ICP photoresist single mask of the present invention has smooth and steep sidewalls; (b) is the low temperature etching morphology of the SiO2 hard mask of the prior art, with a rough bottom and severely damaged sidewalls.

[0042] like Figure 4 As shown, the image of the detector containing the device of the present invention is uniform, without dark spots, and has high contrast.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. All equivalent changes and modifications made within the scope of the claims of this invention should be considered within the technical scope of this invention.

Claims

1. A method for manufacturing an electrode contact hole for an infrared detector, characterized in that: Used for fabricating high-density mercury cadmium telluride infrared detectors, the fabrication process does not require growing a SiO2 hard mask as an etching mask on the surface of the mercury cadmium telluride / cadmium telluride material to be processed, and the electrode contact holes are fabricated using room temperature ICP etching. specific Includes the following steps, S1, photoresist coating; Select a mercury cadmium telluride epitaxial wafer adapted for infrared detection, and uniformly coat the surface of the mercury cadmium telluride / cadmium telluride material to be processed with AZ4330 positive photoresist to form a photoresist film. S2, Photolithography Pattern Transfer: The coated epitaxial wafer is placed into a photolithography machine. Through photolithography, exposure, and development processes, the electrode contact hole pattern is transferred on the photoresist film, exposing the mercury cadmium telluride functional layer region to be etched. S3, Underfilm removal process: The plasma resist removal process is used to remove the residual photoresist underfilm in the patterned opening area, ensuring that the surface of the material to be etched is clean and free of residue. S4, wafer bonding and fixing: The epitaxial wafer processed in S3 is fixed onto the tray of the ICP etching machine by vacuum adsorption or high temperature bonding. The cavity is closed and vacuum is drawn to complete the cavity vacuum pretreatment. S5, room temperature ICP etching, maintaining the cavity temperature at 10~15℃, using low RF power and small substrate DC bias parameters, and introducing etching process gas to perform ICP etching on the exposed epitaxial wafer to prepare electrode contact holes with a depth of 0.3~0.5μm; S6, Annealing damage repair: The etched epitaxial wafer is taken out and subjected to high-temperature annealing to eliminate lattice damage, interface defects and residual stress generated during ICP etching. S7, Photoresist Removal: A combination of plasma and wet photoresist removal is used to thoroughly remove residual photoresist from the surface, completing the fabrication of the electrode contact holes for the mercury cadmium telluride infrared detector.

2. The method for manufacturing an electrode contact hole according to claim 1, characterized in that: In step S1, AZ4330 photoresist is uniformly coated on the surface of the epitaxial wafer using a spin coating process. The spin coating speed is 3000 rpm and the spin coating time is 30 s. After drying, a photoresist film with a uniform thickness of 3~4 μm is formed.

3. The method for manufacturing an electrode contact hole according to claim 1, characterized in that: In step S3, the patterned epitaxial wafer is placed in a plasma cleaner and oxygen is used to remove the underlying film. The processing power is 300W and the processing time is 5 minutes.

4. The method for manufacturing an electrode contact hole according to claim 1, characterized in that: In step S5, the ICP etching process parameters include: ICP source power of 800W, RF power of 10W, and small substrate bias voltage of 22~25V. The etching process gases include a main etching gas and an auxiliary gas. The gas types and flow ratios of the main etching gas and the auxiliary gas are Ar:N2:CH4 = 30 sccm:5 sccm:1 sccm. The vacuum pressure of the etching chamber is 2.0 mTorr, the etching time is 15 min, and the etching selectivity ratio PR:MCT≈5:1 and PR:CdTe>3:

1.

5. The method for manufacturing an electrode contact hole according to claim 1, characterized in that: In step S6, the high-temperature annealing process involves placing the epitaxial wafer into a mercury-rich annealing furnace and annealing it in a saturated Hg vapor pressure atmosphere at a temperature of 265°C. The annealing holding time is 2 hours, followed by natural cooling.

6. The method for manufacturing an electrode contact hole according to claim 1, characterized in that: In step S7, most of the remaining adhesive layer and carbonized layer on the surface are first thoroughly removed by plasma adhesive removal process. Then, the residual thin adhesive is removed by adhesive removal solution, acetone and ethanol in sequence. Finally, the surface damage layer is removed by bromomethanol rinsing. After rinsing with deionized water and drying with nitrogen, the electrode contact hole preparation is completed.

7. The method for manufacturing an electrode contact hole according to claim 1, characterized in that: The sidewall steepness of the electrode contact hole made in step S7 is ≥85°, and the contact hole size uniformity error is ≤5%.

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