Corrosion method for simultaneously corroding zns and tellurium-cadmium-mercury

Abstract

The invention discloses a corrosion method for simultaneously corroding zns and tellurium-cadmium-mercury, and relates to the technical field of chip manufacturing, and the method comprises the following steps: providing a chip with a zinc sulfide layer and a tellurium-cadmium-mercury layer on the surface, forming a graphical photoresist mask, and exposing an area to be corroded; mixing hydrobromic acid with bromine, fully stirring, and standing for 10-20 minutes to obtain a corrosive liquid; immersing the processed chip into a corrosive liquid, and standing and corroding for 30-60 seconds; taking out the corroded chip, and immediately placing the corroded chip in flowing pure water for standing so as to terminate the corrosion reaction; the photoresist mask is removed, and graphical corrosion of the chip is completed; according to the method, high-quality one-step synchronous corrosion of the ZnS / HgCdTe double-layer structure is realized, inherent defects of a step-by-step process are fundamentally avoided, the corrosion morphology is uniform and consistent, lateral undercutting is effectively inhibited, the quality is greatly improved, a complex multi-step process is simplified into one step, the dependence on high-skill operators is reduced, the production period is shortened, and the production cost is reduced. The method is more suitable for large-scale automatic production.

Description

Technical Field

[0001] This invention relates to the field of chip manufacturing technology, and more specifically to an etching method for simultaneously etching Zns and mercury cadmium telluride. Background Technology

[0002] In the field of infrared focal plane detector chip manufacturing technology, it is often necessary to prepare a zinc sulfide (ZnS) antireflection film on the surface of a mercury cadmium telluride (HgCdTe) chip to optimize optical performance. To form specific electrode or optical structures, the ZnS and HgCdTe bilayer material must be patterned and etched.

[0003] Due to the significant differences in the chemical properties of the two materials, traditional processes generally employ a stepwise etching method: First, the ZnS layer is etched using hydrochloric acid (HCl) or a mixed solution of potassium iodide and iodine (KI / I2). This type of etching is isotropic, fast-paced, and time-sensitive, easily leading to lateral drilling, which deteriorates the pattern morphology. The process window is very narrow and highly dependent on the operator's experience. Subsequently, the HgCdTe layer is etched using a bromine-ethylene glycol solution or a bromine-hydrobromic acid solution. Its etching mechanism and rate control are different from those of ZnS.

[0004] The existing step-by-step etching process is cumbersome and inefficient, requiring two photolithography alignments, two etching processes, and two cleaning processes. This results in a long production cycle, difficulty in quality control, and difficulty in accurately controlling the endpoint when etching ZnS, which can easily lead to "over-etching" or "under-etching". Furthermore, the risk of interface contamination and mechanical damage is high, and the cleaning and transfer between the two processes may introduce contaminants or damage the chip. At the same time, pattern alignment errors are unavoidable, and the precision limit of the two photolithography alignments affects the accuracy of the final pattern overlay. Summary of the Invention

[0005] The purpose of this invention is to provide a corrosion method for simultaneously corroding Zns and mercury cadmium telluride, in order to overcome the above-mentioned shortcomings of the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for simultaneously etching ZnS and mercury cadmium telluride, comprising the following steps: S1: providing a chip with a zinc sulfide layer and a mercury cadmium telluride layer on its surface, and forming a patterned photoresist mask on the chip surface using a photolithography process to expose the area to be etched; S2: mixing hydrobromic acid and bromine, stirring thoroughly, and letting stand for 10-20 minutes to activate the mixture, thereby obtaining a composite etching solution; S3: immersing the chip treated in step S1 into the etching solution prepared and activated in step S2, and allowing it to etch for 30-60 seconds; S4: removing the etched chip and immediately placing it in flowing pure water to stop the etching reaction; S5: removing the photoresist mask to complete the patterned etching of the chip.

[0007] Preferably, the composite corrosion solution in S2 is a mixture of hydrobromic acid and bromine in a volume ratio of 100-300:1-5.

[0008] Preferably, the concentration of hydrobromic acid in the composite corrosion solution in S2 is 40%~100%, and the concentration of bromine is 99.5%~100%.

[0009] Preferably, in step S3, the temperature of the etchant is 20~25℃.

[0010] Preferably, in step S4, the chip is left to stand in flowing pure water for 80±10 seconds.

[0011] Preferably, in step S5, the chip is first rinsed with acetone solution 1 to 3 times, each rinse lasting 2 to 10 seconds, and then rinsed with an alcohol spray gun for 30 to 60 seconds; acetone is an efficient solvent for dissolving photoresist.

[0012] In the above technical solution, the present invention provides a corrosion method for simultaneously corroding ZnS and HgCdTe, which has the following beneficial effects: The present invention achieves high-quality one-step synchronous corrosion of ZnS / HgCdTe double-layer structure, fundamentally avoiding the inherent defects of step-by-step process, with uniform corrosion morphology, effectively suppressing lateral drilling corrosion, greatly improving quality, simplifying complex multi-step process into one step, reducing dependence on highly skilled operators, shortening production cycle, and making it more suitable for large-scale automated production. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0014] Figure 1 This is a schematic diagram of the chip after being protected by homogenized adhesive in the process of this invention;

[0015] Figure 2 This is a schematic diagram of the chip after etching and resist removal using the process of this invention.

[0016] Explanation of reference numerals in the attached figures:

[0017] 1. Silicon substrate; 2. Mercury cadmium telluride layer; 3. Zinc sulfide layer; 4. Photoresist mask. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] Please see Figure 1-2 A method for simultaneously etching ZnS and mercury cadmium telluride (HgCdTe) includes the following steps: S1: A chip with a zinc sulfide layer 2 and a mercury cadmium telluride layer 3 on its surface is provided. The bottom of the chip is a silicon substrate 1, the mercury cadmium telluride layer 3 is on the silicon substrate 1, and the zinc sulfide layer 2 is on the mercury cadmium telluride layer 3. A patterned photoresist mask 4 is formed on the surface of the zinc sulfide layer 2 of the chip by photolithography to expose the area to be etched. A HgCdTe chip with a ZnS antireflection film deposited on its surface is taken, and photoresist is spin-coated on the chip surface and exposed and developed to form a photoresist mask 4 with the required pattern, protecting the areas that do not need to be etched and precisely exposing the ZnS / HgCdTe bilayer material area that needs to be fabricated into a specific electrode or optical structure. S2: After mixing hydrobromic acid and bromine, stir thoroughly and let stand for 10-20 minutes to activate the composite etching solution. Let stand for 10-20 minutes to allow bromine molecules to fully diffuse and dissolve in the hydrobromic acid solution and reach a stable reaction equilibrium with the acid environment, thus forming a homogeneous and stable active etching solution. S3: Immerse the chip treated in step S1 into the etching solution prepared and activated in step S2, and let it stand for 30-60 seconds for etching. Hydrobromic acid, as a strong acid, provides H⁺ to promote the acidic dissolution of ZnS. At the same time, bromine, as a strong oxidant, can oxidize S²⁻ in ZnS to elemental sulfur or soluble sulfur oxides with higher valence states, thereby achieving effective etching of ZnS. For HgCdTe, the bromine-hydrobromic acid system itself is an effective etchant. The key lies in the specific ratio of this invention, which matches the rates of the two etching paths, achieving high-quality pattern transfer. Room temperature operation avoids the process complexity and energy consumption introduced by heating, improving process controllability. The short time window of 30-60 seconds is an ideal range determined through extensive experimentation, ensuring complete etching of ZnS while achieving the required etching depth for HgCdTe, and significantly suppressing the inherent lateral drilling of isotropic etching. S4: Remove the etched chip and immediately place it in flowing pure water to stop the etching reaction; quickly transfer the chip to a large volume of flowing pure water to dilute and rinse away residual etching solution, immediately stopping the etching reaction and preventing "over-etching" caused by the continued action of residual liquid; thoroughly clean the etching byproducts and ion residues on the chip surface to prepare a clean surface for subsequent resist removal steps, avoiding contaminants affecting device performance. S5: Remove the photoresist mask 4 to complete the patterning etching of the chip; the resist removal process must be thorough and gentle, avoiding strong peeling methods that may damage the etched pattern.

[0020] Furthermore, the composite etching solution in S2 is composed of hydrobromic acid and bromine mixed at a volume ratio of 100-300:1-5. When the bromine ratio is too low (<1:300), the oxidizing power of bromine is insufficient, and the etching rate of ZnS is too slow, making it impossible to effectively remove ZnS within the process time (30-60 seconds), resulting in ZnS residue. When the bromine ratio is too high (>5:100), the oxidizing power is too strong, and the etching of HgCdTe becomes too severe, resulting in surface roughness, pitting, and damage to device performance. When the volume ratio of bromic acid to bromine is 100-300:1-5, ZnS can be completely etched away, while HgCdTe can also reach the required depth and have a smooth surface, thus achieving high-quality synchronous etching, and neither of them experienced significant lateral drilling.

[0021] Furthermore, the concentration of hydrobromic acid in the S2 composite corrosion solution is 40%~100%, and the concentration of bromine is 99.5%~100%. The hydrobromic acid concentration is ≥40%: this lower limit ensures a sufficiently high H⁺ ion concentration in the solution to meet the basic requirements for acid dissolution corrosion of ZnS. If the concentration is too low (e.g., using dilute hydrobromic acid), the acid dissolution effect will be greatly reduced, potentially leading to incomplete ZnS corrosion. High-purity bromine ensures its effectiveness as a strong oxidant. Trace impurities may consume bromine or affect its reactivity, thus failing to effectively oxidize S²⁻ in ZnS and disrupting the balance of synergistic corrosion. The 99.5% concentration requirement provides purity assurance for the process effect.

[0022] Specifically, in step S3, the temperature of the etchant is 20~25℃. Temperatures below 20℃ will slow down molecular thermal motion and decrease the corrosion rate. It may not be possible to completely etch away ZnS within the specified 30-60 seconds, resulting in "insufficient corrosion" and residue. Temperatures above 25℃ will drastically accelerate the reaction, especially the oxidation and volatilization of bromine and the corrosion of HgCdTe will become difficult to control, easily leading to "over-corrosion," manifested as surface roughness, pitting, and damage to the pattern morphology. At a temperature of 20~25℃, the etchant can exert the best synergistic effect, completing high-quality pattern transfer in a short time, while keeping lateral drilling at a very low level.

[0023] Furthermore, in step S4, the chip is placed in flowing pure water for 80±10 seconds. After the chip is removed, active etching solution will still adhere to its surface and microstructure. The "80±10 seconds" placement time is the effective time required under flowing pure water conditions to ensure sufficient diffusion and displacement of water molecules, and to completely neutralize and dilute the residual etching solution. If the time is too short (e.g., <70 seconds), the residual solution may continue to react, leading to accidental damage to the pattern (over-etching); if the time is too long, the efficiency will be low. This time window is crucial to ensuring that the final edge shape of the pattern is steep and defect-free.

[0024] In step S5, the chip is first rinsed with acetone solution 1-3 times, each rinse lasting 2-10 seconds, followed by rinsing with an alcohol spray gun for 30-60 seconds. Acetone is a highly efficient solvent for dissolving photoresist. This "rinsing" method quickly dissolves and removes most of the photoresist while avoiding potential impacts of acetone on other materials or the underlying structure. The short contact time and limited number of rinses effectively remove the photoresist while preventing over-processing. The alcohol spray gun further removes any residual traces of photoresist and acetone. Simultaneously, the rapid evaporation of alcohol and its moderate surface tension effectively prevent water residue, allowing for a more thorough cleaning of the pattern sidewalls and microstructures, ensuring no contaminant residue remains.

[0025] Example 1

[0026] Pretreatment: Take an HgCdTe chip with a ZnS antireflection film deposited on its surface, spin-coate photoresist on the chip surface using standard photolithography, and expose and develop it to form a photoresist mask 4 with the desired pattern, exposing the ZnS / HgCdTe area to be etched.

[0027] Preparation of etching solution: Measure 200 ml of 48.5% hydrobromic acid and 2 ml of analytical grade bromine (99.5% concentration) into a polytetrafluoroethylene beaker, stir thoroughly with a glass rod for 1 minute, and then let stand for 15 minutes to complete the activation.

[0028] Synchronous etching: Fix the chip with a Teflon clamp and immerse it vertically in the activated etching solution. Let it stand for 40 seconds at room temperature of 23°C.

[0029] Water washing: Quickly remove the chip from the etching solution and transfer it to a flowing pure water tank. Let it stand and soak for 80 seconds to completely stop the reaction and wash away any residual etching solution.

[0030] Resin Removal and Drying: The chip was transferred to a beaker containing 99.5% acetone and gently rinsed twice, approximately 5 seconds each time. Then, using an anhydrous ethanol spray gun, the chip surface was uniformly sprayed for 40 seconds to remove the photoresist. Finally, it was dried with nitrogen gas. Results: Microscopic examination showed that the ZnS layer was completely removed, the HgCdTe surface was smooth, the pattern edges were clear and steep, and there was no side corrosion.

[0031] Example 2

[0032] The pretreatment is the same as in Example 1.

[0033] Prepare the etching solution: Measure 150 ml of 40% hydrobromic acid and 3 ml of 100% bromine, mix them, stir and let stand for 20 minutes.

[0034] Synchronous corrosion: at 25°C, the corrosion time is 50 seconds.

[0035] Post-processing was the same as in Example 1. Results: The etching effect was good, the pattern transfer fidelity was high, and the process requirements were met.

[0036] Comparative Example: Using a traditional step-by-step process: ZnS was first etched with dilute hydrochloric acid for about 10 seconds (the endpoint needs to be closely observed under a microscope), then rinsed with water, and finally HgCdTe was etched with a 2% bromine-ethylene glycol solution for 60 seconds. The results showed that due to human error in timing, the ZnS etching step repeatedly resulted in lateral drilling (>1.5μm) or localized residue, leading to poor product quality consistency.

[0037] By comparing Comparative Examples 1 and 2 with the comparative examples, it can be seen that the present invention, by using a bromine-hydrobromic acid composite etching solution with a specific ratio, successfully achieves high-quality one-step simultaneous etching of the chemically distinct ZnS and HgCdTe bilayer structures. This not only fundamentally overturns the traditional cumbersome, inefficient, and inconsistent step-by-step process, shortening the production cycle by more than 50%, but also effectively suppresses lateral drilling (from >1.5μm to negligible) through precise parameter control (such as 40-50 seconds of etching and 80 seconds of water washing in the examples), resulting in a pattern with steep edges and perfect morphology, greatly improving product yield and performance consistency. At the same time, this process transforms the operation from relying on human experience to being standardized and easily automated, significantly reducing the dependence on human factors, interface contamination, and mechanical damage, thus demonstrating comprehensive and outstanding advantages in simplifying the process, improving efficiency, ensuring quality, and reducing costs.

[0038] Although the bromine-hydrobromic acid system is the preferred embodiment of this invention, those skilled in the art may also try other strong oxidizing acid systems (such as bromine-hydrochloric acid) as alternatives. As long as they can simultaneously corrode ZnS and HgCdTe, they are all equivalent substitutions of the concept of this invention.

[0039] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A corrosion method for simultaneously corroding Zns and mercury cadmium telluride, characterized in that, Includes the following steps, S1: Provide a chip with a zinc sulfide layer (2) and a mercury cadmium telluride layer (3) on its surface, and form a patterned photoresist mask (4) on the chip surface through photolithography to expose the area to be etched; S2: Mix hydrobromic acid and bromine, stir thoroughly and let stand for 10-20 minutes to activate, and obtain a composite etching solution; S3: Immerse the chip treated in step S1 into the etching solution prepared and activated in step S2, and let it stand for 30-60 seconds to etch; S4: Remove the etched chip and immediately place it in running pure water to stop the etching reaction; S5: Remove the photoresist mask (4) to complete the patterning etching of the chip.

2. The corrosion method for simultaneously corroding Zns and mercury cadmium telluride according to claim 1, characterized in that, The composite corrosion solution in S2 is composed of hydrobromic acid and bromine mixed in a volume ratio of 100-300:1-5.

3. The corrosion method for simultaneously corroding Zns and mercury cadmium telluride according to claim 2, characterized in that, The concentration of hydrobromic acid in the composite corrosion solution in S2 is 40%~100%, and the concentration of bromine is 99.5%~100%.

4. The corrosion method for simultaneously corroding Zns and mercury cadmium telluride according to claim 3, characterized in that, In step S3, the temperature of the etchant is 20~25℃.

5. The corrosion method for simultaneously corroding Zns and mercury cadmium telluride according to claim 4, characterized in that, In step S4, the chip is left to stand in flowing pure water for 80±10 seconds.

6. The corrosion method for simultaneously corroding Zns and mercury cadmium telluride according to claim 5, characterized in that, In step S5, the chip is first rinsed with acetone solution 1 to 3 times, each rinse lasting 2 to 10 seconds, and then sprayed with an alcohol spray gun for 30 to 60 seconds; acetone is a highly efficient solvent for dissolving photoresist.

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