Method for plating pixelated noble metal electrode on crystal surface and radiation detection imaging element
By using bromine-methanol corrosion and hydrochloric acid activation treatment on the CdZnTe crystal surface, combined with chemical plating solution replacement reaction, the problems of mechanical stability and thickness uniformity were solved, and the preparation of high-precision pixelated precious metal electrodes was achieved to meet the needs of high-performance radiation detection imaging elements.
Patent Information
- Application Number
- CN202510913091.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-03
- Publication Date
- 2025-10-17
AI Technical Summary
In the existing technology, when preparing high-quality, uniform and tiny precious metal electrode arrays on the surface of CdZnTe crystals, there are problems such as insufficient mechanical stability, uneven coating thickness and poor compatibility with photolithography processes, which makes it difficult to meet the preparation requirements of high-precision, small-size pixelated electrodes.
The crystal surface is treated with a bromine-methanol etching solution, and a grid-shaped photoresist protection area is formed through a photolithography process. A hydrochloric acid solution is used to activate the crystal surface, and then a chemical plating solution replacement reaction of precious metal ions is carried out in the exposed area to form a pixelated electrode.
The prepared pixelated noble metal electrodes have excellent edge clarity and graphic fidelity, the coating structure is dense and uniform, the electrodes are firmly bonded to the crystalline substrate, the mechanical stability is enhanced, and they are highly compatible with the photolithography process.
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Figure CN120813087A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of radiation detection, and particularly relates to a method for plating a pixelated noble metal electrode on a crystal surface and a radiation detection imaging element. BACKGROUND
[0002] As a wide-bandgap semiconductor material, cadmium zinc telluride (CdZnTe) is very suitable for preparing imaging elements of room-temperature radiation detectors / imagers due to its excellent X / γ-ray stopping power. At present, the material has been applied to the fields of medical imaging, homeland security, industrial analysis and astrophysics.
[0003] The key to realizing the function of radiation spectral imaging in a CdZnTe device lies in the preparation of a fine pixelated electrode array on the anode surface. Based on the small pixel effect, a smaller pixel pitch can realize higher spatial resolution. However, as the pixel pitch decreases, the charge cloud generated by the interaction of X / γ rays is shared by more and more pixels. Studies have shown that for X / γ rays with an energy of up to 200 keV, a pixel pitch of 250 μm can ensure good spatial resolution and avoid significant impact on imaging quality due to charge sharing.
[0004] However, there are still severe technical challenges in the current preparation of high-quality, uniform and small noble metal electrode arrays on the surface of CdZnTe crystals. One of the main problems in the preparation of gold or platinum electrodes on the surface of CdZnTe by using a thermal evaporation or sputtering process is the poor mechanical stability of the electrodes. Since CdZnTe exhibits thermal instability above 150℃, the deposited electrodes cannot be improved in performance by thermal annealing, which further exacerbates the above problem.
[0005] Although studies have shown that chemical gold plating or platinum plating using water or methanol as a solvent at room temperature can obtain electrodes with good mechanical stability, the existing chemical plating process still has obvious defects: a water-based chemical plating solution easily leads to uneven thickness of the electrode; and an alcohol-based (such as methanol, ethanol, etc.) chemical plating solution easily dissolves photoresist, affecting the implementation of subsequent pixelation processes.
[0006] In summary, the existing sputtering / thermal evaporation electrode process cannot be annealed due to the thermal sensitivity of the material, resulting in insufficient mechanical stability of the electrode; and in the chemical plating process, the water-based system has a problem of uniformity of the thickness of the plated layer, and the alcohol-based system has poor compatibility with the photoetching process. These defects are difficult to meet the preparation requirements of high-precision and small-size pixelated electrodes, and have become a key bottleneck restricting the development of high-performance CdZnTe radiation detection imaging elements. Therefore, it is urgent to develop a new method for directly preparing pixelated noble metal electrodes with high uniformity, strong mechanical stability and good compatibility with photoetching processes on the surface of CdZnTe wafers at room temperature. SUMMARY
[0007] In view of the deficiencies of the prior art, the application provides a method for plating a pixelated noble metal electrode on a crystal surface and a radiation detection imaging element.
[0008] The application aims to provide a method for plating a pixelated noble metal electrode on a crystal surface and a radiation detection imaging element, so as to solve the problems of insufficient mechanical stability, poor thickness uniformity and poor compatibility with a photolithography process in the prior art.
[0009] The first aspect of the application provides a method for plating a pixelated noble metal electrode on a crystal surface, preparing a tellurium cadmium compound wafer with an exposed flat and clean (111) crystal surface, etching with a bromine-methanol etching solution, forming a grid-shaped photoresist protection area and leaving an unprotected pixel column by a photolithography process, activating the unprotected area of the crystal surface with a hydrochloric acid solution, and applying a chemical plating solution containing noble metal ions to the activated layer to deposit a pixelated electrode in the exposed area through a displacement reaction.
[0010] As a further optimization scheme, the following steps are included:
[0011] Step (1): cutting a wafer along the (111) crystal surface of a tellurium cadmium compound ingot and performing surface grinding and polishing;
[0012] Step (2): cleaning the surface of the wafer with an organic solvent and deionized water;
[0013] Step (3): bromine-methanol (Br-MeOH) etching solution;
[0014] Step (4): immersing the cleaned wafer in the bromine-methanol etching solution for 1-5 minutes, and then cleaning with methanol and deionized water to remove the etching solution;
[0015] Step (5): spin coating a negative photoresist on the surface of the wafer, exposing through a mask after baking, and developing to form an exposed area of a pixel array and a grid-shaped photoresist protection area;
[0016] Step (6): dropping a hydrochloric acid solution onto the surface of the wafer on a spin coater, and spinning at a speed of 2000-3000 r / min after standing for 10-40 seconds;
[0017] Step (7): spin coating a chemical plating solution containing noble metal ions on the activated surface, standing for 1-15 minutes and then spinning, and a displacement reaction occurs in the exposed area to form a pixelated electrode;
[0018] Step (8) post-treatment: rinsing with deionized water to remove residual liquid and blowing dry.
[0019] As a further optimization scheme, the tellurium cadmium compound is cadmium zinc telluride or cadmium telluride; and the noble metal is gold or platinum.
[0020] As a further optimization scheme, in step (1), the wafer size is 5mm*5mm*1mm to 20mm*20mm*5mm; the polishing process comprises rough polishing and fine polishing, the rough polishing uses Al2O3 polishing liquid with a particle size of 1-5μm, and polishing is performed for 10-20 minutes; the fine polishing uses Al2O3 polishing liquid with a particle size of 0.1-1μm, and polishing is performed for 20-40 minutes.
[0021] As a further optimization scheme, in step (3), the bromine-methanol etching solution has a bromine concentration of 1-5wt%.
[0022] As a further optimization scheme, in step (5), after etching, the wafer is placed on a spin coater, negative glue is added dropwise on the sample surface to form a uniform glue layer on the sample surface, and after baking, a direct exposure machine is used to expose the sample surface through a mask plate; after exposure, the sample is immersed in a developing solution for 30-50s, and the negative glue that is not exposed and solidified is dissolved and removed, thereby forming an exposed area in the shape of a pixel array and a photoresist reserved area in the shape of a grid on the sample surface; then, deionized water is used to wash and remove the residual developing solution.
[0023] As a further optimization scheme, in step (6), after the sample is patterned by photolithography, the sample is placed on a spin coater, 3-7% HCl solution is added dropwise on the sample surface and allowed to stand for 10-40s, so that the solution infiltrates the exposed crystal surface; then, the spin coater is started, and the HCl solution is spun dry at a speed of 2000-3000r / min for 30-60s, thereby forming an activated crystal surface.
[0024] As a further optimization scheme, in step (7), a chemical plating solution containing noble metal ions is prepared; then, the chemical plating solution is added dropwise to the sample surface, the spin coater is rotated at a speed of 50-100r / min for 5-10s to uniformly spin coat the solution, and after standing for 1-15min, the spin coater is rotated at a speed of 2000-3000r / min for 60-90s to spin dry the solution.
[0025] As a further optimization scheme, in step (7), a chemical plating solution containing noble metal ions is prepared, a 4% chloroauric acid solution is prepared according to a mass ratio of gold chloride to deionized water of 4:100, and a chemical gold plating solution is prepared according to a mass ratio of the chloroauric acid solution, glycerol and methanol of 4:8:2.
[0026] The second aspect of the present application provides a radiation detection imaging element, which is prepared by the above method and comprises a tellurium cadmium compound crystal and a pixelated noble metal electrode array prepared on the surface of the tellurium cadmium compound crystal.
[0027] Advantages
[0028] The application provides a new method for preparing pixelated noble metal electrodes on the surface of tellurium cadmium compound crystals, which can solve the problems of poor mechanical stability of electrodes, uneven thickness of plating layer and poor compatibility with photolithography process in the prior art. The pixelated electrode prepared by the method has excellent edge definition and pattern fidelity, and no adhesion phenomenon; the plating layer structure is dense and has high uniformity; the electrode is firmly combined with the crystal substrate, and the mechanical stability is significantly enhanced; meanwhile, the entire process is highly compatible with the photolithography technology, and the photoresist damage problem is avoided. BRIEF DESCRIPTION OF DRAWINGS
[0029] Figure 1 Figure 1 is a process flow diagram of the method for electroless plating pixelated noble metal on the surface of tellurium cadmium compound according to the application.
[0030] Figure 2 Figure 2 is an optical micrograph of the surface of a gold-plated wafer sample prepared according to the method of Example 1.
[0031] Figure 3 Figure 3 is an SEM image of a single gold-plated pixel in a gold-plated wafer sample prepared according to the method of Example 1.
[0032] Figure 4 Figure 4 is an SEM image of the side view of a gold-plated layer in a gold-plated wafer sample prepared according to the method of Example 1.
[0033] Figure 5 Figure 5 is an SEM image of a gold-plated layer and the corresponding energy dispersive X-ray spectroscopy element distribution curve of a gold-plated wafer sample prepared according to the method of Example 1.
[0034] Figure 6 Figure 6 is the tape adhesion test result of a gold-plated wafer sample prepared according to the method of Example 1, wherein Figure 6 a is an optical micrograph of the surface of the sample after the tape is peeled off, Figure 6 b is the surface state of the peeled-off tape. DETAILED DESCRIPTION
[0035] Figure 1 Figure 1 is a process flow diagram of the method for electroless plating pixelated noble metal on the surface of tellurium cadmium compound according to the application, wherein the tellurium cadmium compound includes cadmium telluride and cadmium zinc telluride, and the noble metal electrode includes a gold electrode and a platinum electrode.
[0036] Step 1: A tellurium cadmium compound crystal ingot is taken, and a wafer is prepared by cutting the wafer along the (111) crystal surface of the crystal ingot, and then the wafer is ground and polished.
[0037] Step 2: The surface of the sample obtained in step 1 is cleaned with an organic solvent and water.
[0038] Step 3: A Br-MeOH etching solution with a concentration of 1-5% is prepared.
[0039] Step 4, the sample after cleaning in step 2 is placed in a Br-MeOH solution for 1-5 min to remove the mechanical damage layer caused by polishing, and then washed with methanol and deionized water to remove the residual solution.
[0040] Step 5, the sample after etching is placed on a spin coater, and negative glue is added dropwise on the surface of the sample to form a uniform glue layer, and then the sample is placed on a hot plate for baking; then a direct exposure machine is used to expose the sample surface through a mask; after exposure, the sample is immersed in a developing solution for 30-50 s to dissolve and remove the negative glue that has not been exposed and cured, forming a pixel array-shaped exposed area and a grid-shaped photoresist reserved area on the sample surface, and then washed with deionized water to remove the residual developing solution.
[0041] Step 6, the sample after photoetching is placed on a spin coater, and 3-7% HCl solution is added dropwise on the surface of the sample and left for 10-40 s to allow the solution to fully soak the exposed CdZnTe crystal surface; then start the spin coater and keep it at a speed of 2000-3000 r / min for 30-60 s to dry the HCl solution and form a clean and activated crystal surface.
[0042] Step 7, prepare a chemical plating solution containing noble metal ions; then add the chemical plating solution to the surface of the sample, and rotate the spin coater at a speed of 50-100 r / min for 5-10 s to evenly spin the solution, and then leave it for 1-15 min, and then rotate the spin coater at a speed of 2000-3000 r / min for 60-90 s to dry the solution.
[0043] Step 8, rinse the sample surface with deionized water to remove the residual solution, and then dry it with a nitrogen gun to obtain a pixelated tellurium cadmium crystal wafer plated with noble metal.
[0044] The following specific examples will be used to illustrate the process and effects of chemical gold plating on the surface of tellurium zinc cadmium.
[0045] Example 1
[0046] Step 1, cut along the (111) crystal plane of the tellurium zinc cadmium ingot to obtain a wafer with a size of 10 mm x 10 mm x 2 mm; use a two-step polishing process to treat the wafer surface: first use Al2O3 polishing liquid with a particle size of 3 μm to polish both sides of the wafer for 15 minutes to quickly remove the surface damage layer and processing marks generated during cutting; then replace it with Al2O3 polishing liquid with a particle size of 0.5 μm for double-sided fine polishing, polishing time 30 minutes, further reduce the surface roughness of the wafer.
[0047] Step 2, the wafer prepared in step 1 is placed in a container, and a sufficient amount of acetone is added, and then placed in a constant temperature ultrasonic cleaner, and the cleaning temperature is set to 40°C, and the cleaning time is 15 minutes. After ultrasonic cleaning, rinse with deionized water to remove residual acetone.
[0048] Step 3, according to the mass ratio of bromine and methanol 1:100, 1% Br-MeOH etching solution is prepared.
[0049] Step 4, the sample washed in step 2 is placed in 1% Br-MeOH solution for etching for 1 min, and then rinsed with methanol and deionized water to remove residual liquid after etching.
[0050] Step 5, place the etched sample on the chuck of the spin coater, and start the vacuum pump to form negative pressure to fix the sample on the chuck of the spin coater; drop the negative glue on the surface of the sample to spin coating and form a uniform glue layer on the surface of the sample, then place the sample on the hot plate for baking; then use a direct exposure machine to expose the sample surface through a mask; after exposure, immerse the sample in the developing solution for 40s to dissolve and remove the unexposed negative glue, forming a pixel array-shaped exposed area and a grid-shaped photoresist reserved area on the sample surface, and then rinse with deionized water to remove residual developing solution.
[0051] Step 6, place the sample after photoetching on the chuck of the spin coater, and start the vacuum pump to fix the sample; drop 5% HCl solution on the surface of the sample and stand for 20s to allow the solution to fully soak the exposed CdZnTe crystal surface; then start the spin coater and keep it at 2000r / min for 30s to dry the HCl solution, forming a clean and activated crystal surface.
[0052] Step 7, prepare a 4% chloroauric acid (HAuCl4) solution according to the mass ratio of gold chloride to deionized water 4:100; prepare a chemical gold plating solution according to the mass ratio of chloroauric acid solution, glycerol, and methanol 4:8:2; then drop the chemical gold plating solution onto the surface of the sample, and spin the solution evenly with the spin coater at a speed of 50r / min for 5s, stand for 10min, and then spin the solution at a speed of 2000r / min for 60s.
[0053] In this step, the tellurium zinc cadmium crystal undergoes a displacement reaction with the chemical gold plating solution, and the reaction is as follows:
[0054] 2AuCl4+3Cd(Zn) Surface →2Au Surface +8Cl - +3Cd 2+ ;
[0055] 4AuCl4+3Te Surface →4Au Surface+ 16 Cl - + 3 Te 4+ .
[0056] Step 8, rinse the surface of the gold-plated sample with deionized water to remove residual liquid, and then dry it with a nitrogen gun to obtain a pixelated gold-plated CdZnTe wafer.
[0057] Effect verification
[0058] According to the process steps of Example 1, a gold-plated wafer sample was prepared. Figure 2 The optical micrograph of the sample surface is shown, and the pixelated structure after chemical gold plating can be observed by optical microscope, and there is no adhesion phenomenon between each electrode unit. The results show that the chemical gold plating solution does not cause dissolution damage to the photoresist, and the integrity is maintained, which verifies the feasibility of the method for preparing the surface pixelated gold-plated CdZnTe wafer.
[0059] The microstructure and composition of the gold-plated sample were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Figure 3 The SEM image of a single gold-plated pixel is shown, and the pixel edge is regular and clear, without burrs or agglomeration, indicating that the chemical gold plating process has good fidelity to the pixelated pattern. Figure 4 The SEM image is a side view of the gold-plated layer, and the results show that the gold-plated layer is continuous and dense, and the thickness is uniform, which is about 36 nm, indicating that the method can realize the controllable deposition of uniform nanoscale coating. Figure 5 The SEM image and EDS elemental distribution curve across the gold-plated layer are shown, and the results show that in the gold-plated layer region, the gold element content presents a peak-shaped feature, which is obviously distinguished from the signal of the substrate region, which again indicates the effective formation of the coating layer, further verifying the effectiveness of the chemical plating of noble metal process.
[0060] According to the process steps of Example 1, a gold-plated wafer sample was prepared, and 3M600 standard test tape was used. The tape was tightly adhered to the electrode surface and uniform pressure was applied, and after 30 min of standing to stabilize the adhesive force, the tape was quickly peeled off at a 90° vertical direction. The test results are shown in Figure 6 Figure 6 a is the optical micrograph of the sample surface after the tape is peeled off, showing that the electrode array has no peeling or skinning phenomenon; Figure 6 b is the surface state of the peeled tape, and no metal coating residue is found in the adhesive layer of the tape. This test shows that the chemical gold-plated electrode prepared by this method has excellent adhesion strength with the CdZnTe substrate, meeting the requirements of mechanical stability for practical application.
[0061] In conclusion, the method can plate pixelated noble metal electrodes on the surface of tellurium cadmium compound, can realize the preparation of nanoscale uniform plating layer, and the prepared pixelated noble metal electrode has regular edge and no adhesion, and has strong interface bonding force and mechanical stability. The method provides a technical path with process feasibility and cost advantage for the preparation of high-performance radiation detection imaging elements, and has significant application potential in the fields of medical imaging, safety detection and the like.
[0062] The above embodiments are exemplary, and the purpose is to illustrate the technical concept and characteristics of the present application, so that those skilled in the art can understand the content of the present application and implement it, and the protection scope of the present application cannot be limited thereto. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.
Claims
1. A method for plating pixelated noble metal electrodes on a crystal surface, characterized in that: A cadmium telluride wafer with a flat and clean (111) crystal surface is prepared and exposed. It is etched with a bromine-methanol etching solution. A grid-like photoresist protection area is formed through a photolithography process, and unprotected pixel columns are left. The unprotected area of the crystal surface is activated with a hydrochloric acid solution. A chemical plating solution containing noble metal ions is applied to the activation layer, and pixelated electrodes are deposited on the exposed area through a replacement reaction.
2. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 1, characterized in that: The following steps are involved: Step (1): cutting the cadmium telluride ingot along the (111) crystal plane to obtain a wafer, and performing surface grinding and polishing; Step (2): Cleaning the wafer surface with an organic solvent and deionized water; Step (3): bromine-methanol (Br-MeOH) etching solution; Step (4): Immerse the cleaned wafer in a bromine-methanol etching solution for 1-5 minutes, and then rinse with methanol and deionized water to remove the etching solution; Step (5): Spin-coating a negative photoresist on the wafer surface, baking it, exposing it through a mask, and developing it to form an exposed area of the pixel array and a grid-like photoresist protection area; Step (6): Add hydrochloric acid solution dropwise to the surface of the crystal on a sizing machine, let it stand for 10-40 seconds, and then spin dry at a speed of 2000-3000 r / min; Step (7): Spin-coat the activated surface with a chemical plating solution containing noble metal ions, let it stand for 1-15 minutes, and then spin dry. A replacement reaction occurs in the exposed area to form a pixelated electrode; Step (8) post-treatment: rinse with deionized water to remove residual liquid and blow dry.
3. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 2, characterized in that: The cadmium telluride is cadmium zinc telluride or cadmium telluride; and the noble metal is gold or platinum.
4. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 2, wherein: In step (1), the chip size is 5 mm × 5 mm × 1 mm to 20 mm × 20 mm × 5 mm; the grinding and polishing process includes rough polishing and fine polishing, the rough polishing uses Al2O3 polishing liquid with a particle size of 1-5 μm and polishing for 10-20 minutes; the fine polishing uses Al2O3 polishing liquid with a particle size of 0.1-1 μm and polishing for 20-40 minutes.
5. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 2, wherein: In step (3), the bromine concentration of the bromine-methanol etching solution is 1-5 wt%.
6. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 2, wherein: In step (5), the etched wafer is placed on a photoresist spreader, a negative photoresist is dripped onto the sample surface and spin-coated to form a uniform photoresist layer on the sample surface. After baking, the sample surface is exposed through a mask using a direct exposure machine. After exposure, the sample is immersed in a developer for 30-50 seconds to dissolve and remove the negative photoresist that has not been exposed and cured, forming a pixel array-shaped exposed area and a grid-shaped photoresist retention area on the sample surface. The residual developer is then removed by rinsing with deionized water.
7. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 2, wherein: In step (6), the sample after photolithography patterning is placed on a coating machine, and a 3-7% HCl solution is dripped onto the sample surface and left to stand for 10-40 seconds to allow the solution to infiltrate the exposed crystal surface; then the coating machine is started and maintained at a speed of 2000-3000 r / min for 30-60 seconds to spin dry the HCl solution to form an activated crystal surface.
8. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 2, wherein: In step (7), a chemical plating solution containing precious metal ions is prepared; the chemical plating solution is then added dropwise to the sample surface, and the solution is evenly spin-coated by rotating the coating machine at a speed of 50-100 r / min for 5-10 seconds. After standing for 1-15 minutes, the coating machine is rotated at a speed of 2000-3000 r / min for 60-90 seconds to dry the solution.
9. The method for plating pixelated noble metal electrodes on a crystal surface according to claim 8, characterized in that: In step (7), a chemical plating solution containing precious metal ions is prepared, a 4% chloroauric acid solution is prepared according to a mass ratio of gold chloride to deionized water of 4:100, and a chemical gold plating solution is prepared according to a mass ratio of chloroauric acid solution, propylene glycol, and methanol of 4:8:
2.
10. A radiation detection imaging element, characterized in that: Prepared by the method according to any one of claims 1 to 9, comprising a cadmium telluride crystal and a pixelated noble metal electrode array prepared on the surface of the cadmium telluride crystal.