Method for selectively reverse sputter etching oxide layer on surface of niobium film without photoresist
By employing a photoresist-free selective backsputtering method on the oxide layer of the niobium film surface and using a metal layer as a mask, the problems of low backsputtering rate and photoresist contamination in traditional methods are solved, the etching efficiency and device reliability are improved, and periodic, contamination-free rate calibration is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JINAN INST OF QUANTUM TECH
- Filing Date
- 2026-03-09
- Publication Date
- 2026-06-09
AI Technical Summary
Traditional methods for etching the oxide layer on the surface of niobium films suffer from problems such as low backsputtering rate, risk of photoresist contamination, and difficulty in periodic calibration, which affect the performance and reliability of superconducting electronic devices.
A photoresist-free selective backsputtering method is adopted, using a metal layer as a natural mask. Selective etching of the oxide layer on the niobium film surface is performed through a magnetron sputtering PC chamber, avoiding photoresist contamination. Rate calibration is performed in an ultra-high vacuum magnetron sputtering system.
This improved etching efficiency, avoided photoresist contamination, ensured the performance and reliability of superconducting devices, and enabled regular, contamination-free rate calibration.
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Figure CN122180307A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of superconducting electronic device fabrication and micro / nano fabrication technology, and in particular to a method for selectively backsputtering niobium film surface oxide layer etching without photoresist. Background Technology
[0002] The oxide layer on the surface of a niobium (Nb) film is an insulating layer. In Nb-based superconducting electronic devices, this oxide layer blocks interlayer electrical connections. Before fabricating interconnect layers (superconducting layers, metal layers) via ultra-high vacuum magnetron sputtering, this oxide layer needs to be completely etched. To completely etch the oxide layer on the Nb surface, the etching rate of the Nb oxide layer within the sputtering chamber needs to be obtained and periodically calibrated. In the field of Nb film superconducting electronics, conventional processes typically employ magnetron sputtering to deposit the niobium layer, followed by patterning using photoresist masking techniques (including coating, exposure, development, and etching steps). Subsequently, backsputtering is performed in the Loadlock (LL) cavity of the ultra-high vacuum magnetron sputtering system using photoresist as a mask to remove the oxide layer on the niobium surface, ensuring interlayer connectivity. However, this method has the following main problems:
[0003] 1. Low backsputtering rate of traditional Loadlock chambers: The limitations of LL chamber design lead to low backsputtering efficiency and long etching time. Nb films and superconducting devices based on Nb films and Josephson structures are exposed to high-energy etching ion beams for a long time, which can easily cause junction damage or uneven etching, affecting the performance and reliability of Josephson junctions.
[0004] 2. Photoresist Contamination Risk: To achieve selective backsputtering, photoresist is typically used as a mask. In practice, organic matter in the photoresist may volatilize and deposit within the cavity or on the target surface, contaminating both. For the Josephson junction process, which fabricates ultrathin junctions, the cleanliness of the ultra-high vacuum deposition chamber is crucial. Photoresist residues can lead to decreased film quality and process instability, potentially affecting process stability and even causing product quality issues.
[0005] 3. Periodic calibration of the backsputtering rate requires a high degree of cleanliness, which traditional methods cannot meet: Due to the changes and fluctuations in equipment performance during operation, the need for consistency and stability of the wafer fabrication process, the need for quality control, and the need to ensure optimal preparation conditions, periodic pollution-free rate calibration is also very necessary. Calibration with photoresist cannot guarantee pollution-free operation.
[0006] Therefore, how to improve the etching process of the oxide layer on the surface of niobium film to increase etching efficiency has become an urgent problem to be solved. Summary of the Invention
[0007] This invention provides a method for selective reverse sputtering etching of the oxide layer on the surface of a niobium film without photoresist, in order to solve the problem of how to improve the etching process of the oxide layer on the surface of the niobium film to increase etching efficiency.
[0008] This invention provides a method for selectively backsputtering niobium film surface oxide layer without photoresist, comprising:
[0009] A niobium film is deposited on the surface of a silicon substrate, a metal layer is deposited on the niobium film, a photoresist layer is coated on the metal layer, and the photoresist layer is exposed to expose the target pattern.
[0010] The metal layer that is not covered by the target pattern is etched until the niobium film layer is exposed, and the photoresist layer of the target pattern is removed to obtain the remaining metal layer and the surface oxide layer of the niobium film layer that is not covered by the metal layer.
[0011] The surface oxide layer is reverse sputtered to remove it, and the remaining metal layer is etched to expose a portion of the niobium film layer from which the surface oxide layer has been etched, thereby obtaining a semiconductor composed of the silicon substrate and the etched niobium film layer.
[0012] Optionally, after removing the photoresist layer of the target pattern to obtain the remaining metal layer and the surface oxide layer of the niobium film layer not covered by the metal layer, the method further includes:
[0013] At a preset rotation speed, the remaining metal layer, the niobium film layer, and the silicon base are spun dry for a first preset time to ensure that there are no water marks on the surface.
[0014] Optionally, the preset rotation speed is 500-4000 rpm, and the first preset time is 30s to 150s.
[0015] Optionally, the step of reverse sputtering to remove the surface oxide layer includes:
[0016] Using an ultra-high vacuum magnetron sputtering process chamber (PC chamber), the surface oxide layer is back-sputtered for a second preset time at a preset chamber pressure and a preset sputtering power to remove the surface oxide layer.
[0017] Optionally, the preset chamber pressure is 0.5 Pa to 2 Pa, the preset sputtering power is 50 W to 300 W, and the second preset time is 1 min to 15 min.
[0018] Optionally, coating the photoresist layer on the metal layer includes:
[0019] After coating the metal layer with a photoresist adhesion promoter, a photoresist layer of a predetermined thickness is coated to form a photoresist layer.
[0020] Optionally, the metal layer is a wet-etched metal layer in which the etching solution does not corrode Nb and Nb2O5, and the metal layer includes an aluminum layer or a molybdenum layer.
[0021] Optionally, after obtaining the semiconductor composed of the silicon substrate and the etched niobium film layer, the method further includes:
[0022] By collecting data at least five times, the depth of the partially etched surface oxide layer is measured. Based on the collected depth, the consistency of the etching depth is evaluated to obtain a first evaluation result.
[0023] The etching rate of the semiconductor is collected, the etching rate is evaluated, and a second evaluation result is obtained;
[0024] Electrical tests and elemental analysis were performed on the portion of the surface oxide layer that was partially etched away to obtain a third evaluation result;
[0025] The etching process parameters are obtained, and the process parameters are optimized based on the first evaluation result, the second evaluation result, and the third evaluation result to obtain the optimized process parameters.
[0026] The technical advantages of this invention compared to existing technologies are as follows: This invention deposits a niobium film on a silicon substrate, deposits a metal layer on the niobium film, coats a photoresist layer on the metal layer, exposes the photoresist layer to reveal a target pattern, etches the unmasked metal layer of the target pattern until the niobium film is exposed, and removes the photoresist layer of the target pattern, obtaining a remaining metal layer and a surface oxide layer of the niobium film layer not covered by the metal layer. The surface oxide layer is then back-sputtered to remove it, and the remaining metal layer is etched to expose a portion of the niobium film layer with the surface oxide layer etched away, resulting in a semiconductor composed of the silicon substrate and the etched niobium film layer. Using a metal layer as a natural mask instead of photoresist avoids contamination of the sputtering PC cavity and target material introduced by photoresist, effectively improving sputtering efficiency and etching efficiency, and achieving periodic, contamination-free rate calibration. Furthermore, selective backsputtering in the magnetron sputtering PC cavity to remove the Nb surface oxide layer can avoid the problems of low backsputtering rate and damage to the junction region in traditional loadlock chambers. Attached Figure Description
[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0028] Figure 1 This is a schematic flowchart of a method for selectively etching the oxide layer on the surface of a niobium film without photoresist, provided in an embodiment of the present invention.
[0029] Figure 2 This is a schematic diagram of a method for selectively etching the oxide layer on the surface of a niobium film without photoresist, provided in an embodiment of the present invention.
[0030] Figure 3 This is a schematic diagram of a process parameter optimization method provided by an embodiment of the present invention. Detailed Implementation
[0031] To make the technical problems solved, the technical solutions, and the beneficial effects 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 of the invention and are not intended to limit the invention.
[0032] like Figure 1 The diagram shown is a flowchart of a method for selectively etching the oxide layer on the surface of a niobium film without photoresist, according to Embodiment 1 of the present invention. This method for etching the oxide layer on the surface of a niobium film may include the following steps:
[0033] Step S101: Deposit a niobium film on the surface of a silicon substrate, deposit a metal layer on the niobium film, coat a photoresist layer on the metal layer, and expose the photoresist layer to expose the target pattern.
[0034] The target pattern is the circuit pattern that is ultimately to be formed on the surface of the niobium film. In this step, a surface oxide layer will be formed on the surface of the niobium film layer. That is, the niobium film layer consists of two parts: the niobium film part and the surface oxide layer. A metal layer is deposited on the surface oxide layer. The metal used in this metal layer includes, but is not limited to, aluminum, molybdenum, etc.
[0035] The use of photoresist in step S101 is essentially a preliminary step for etching the metal layer to form the target pattern.
[0036] Step S102: Etch the metal layer that is not covered by the target pattern until the niobium film layer is exposed, and remove the photoresist layer of the target pattern to obtain the remaining metal layer and the surface oxide layer of the niobium film layer that is not covered by the metal layer.
[0037] In step S101, the photoresist layer forms the target pattern, which masks part of the metal layer. A part of the metal layer is not masked. The unmasked metal layer is etched to directly expose the niobium film layer, which is the surface oxide layer on the niobium film layer. Then the photoresist is removed, so that the remaining metal layer becomes a protective layer for the niobium film layer to be exposed and developed.
[0038] Step S103: The surface oxide layer is back sputtered to remove the surface oxide layer, and the remaining metal layer is etched to expose a portion of the niobium film layer from which the surface oxide layer has been etched, thereby obtaining a semiconductor composed of the silicon substrate and the etched niobium film layer.
[0039] The sample entering the anti-sputtering process has no photoresist layer, so it will not contaminate the sputtering chamber, effectively ensuring the normal use of sputtering and improving the efficiency of sputtering and etching.
[0040] Of course, the surface oxide layer on the exposed niobium film can be removed after sputtering. The niobium film layer that is covered by the metal layer is unaffected. After removing the metal layer, the entire niobium film layer is divided into two types of regions: one is the niobium film layer + surface oxide layer, and the other is the niobium film layer. The surface oxide layer will block the interlayer electrical connection. The remaining exposed niobium film layer can be used to prepare interconnect layers (superconducting layer, metal layer).
[0041] The aforementioned anti-sputtering equipment can use loadlock chambers, magnetron sputtering PC chambers, etc. It is preferable to use magnetron sputtering PC chambers, which can effectively improve sputtering efficiency and avoid the problems of low anti-sputtering rate and damage to the junction region in traditional loadlock chambers.
[0042] This invention involves depositing a niobium film on a silicon substrate, depositing a metal layer on the niobium film, coating a photoresist layer on the metal layer, exposing the photoresist layer to reveal a target pattern, etching the unmasked metal layer of the target pattern until the niobium film is exposed, and then removing the photoresist layer of the target pattern to obtain the remaining metal layer and a surface oxide layer of the niobium film layer not covered by the metal layer. The surface oxide layer is then back-sputtered to remove it, and the remaining metal layer is etched to expose a portion of the niobium film layer with the surface oxide layer etched away, resulting in a semiconductor composed of the silicon substrate and the etched niobium film layer. Using a metal layer as a natural mask instead of photoresist avoids the contamination of the sputtering PC cavity and target material introduced by photoresist, effectively improving sputtering efficiency and etching efficiency. Furthermore, selective back-sputtering in the magnetron sputtering PC cavity to remove the Nb surface oxide layer avoids the problems of low back-sputtering rates and junction damage associated with traditional loadlock chambers.
[0043] Optionally, after removing the photoresist layer of the target pattern to obtain the remaining metal layer and the surface oxide layer of the niobium film layer not covered by the metal layer, the method further includes:
[0044] At a preset temperature, the remaining metal layer, the niobium film layer, and the silicon base are spun dry for a first preset time to ensure that there are no water marks on the surface.
[0045] Optionally, the preset rotation speed is 500-4000 rpm, and the first preset time is 30s to 150s.
[0046] Optionally, the step of reverse sputtering to remove the surface oxide layer includes:
[0047] Using a magnetron sputtering PC cavity, the surface oxide layer is back-sputtered for a second preset time at a preset chamber pressure and a preset sputtering power to remove the surface oxide layer.
[0048] In this embodiment, the Nb oxide layer is etched by backsputtering and interconnect layers (superconducting metal, metal layer, etc.) are prepared in situ in an ultra-high vacuum magnetron sputtering PC cavity with a relatively fast etching rate. Compared with the Loadlock chamber, this can improve the backsputtering efficiency and effectively avoid junction damage.
[0049] Optionally, the preset chamber pressure is 0.5 Pa to 2 Pa, the preset sputtering power is 50 W to 300 W, and the second preset time is 1 min to 15 min.
[0050] Optionally, coating the photoresist layer on the metal layer includes:
[0051] After coating the metal layer with a photoresist adhesion promoter, a photoresist layer of a predetermined thickness is coated to form a photoresist layer.
[0052] Optionally, the metal layer is a wet-etched metal layer that does not corrode Nb and Nb2O5, such as an aluminum layer or a molybdenum layer. The etching process of Al or Mo layers is highly controllable and easy to precisely etch using a developing solution.
[0053] like Figure 2 The diagram shown is a schematic representation of a method for selective backsputtering etching of a niobium film surface oxide layer without photoresist, according to an embodiment of the present invention. Taking an Al layer as an example, the specific details are as follows:
[0054] 1. Substrate preparation:
[0055] A certain thickness of Nb layer and Al layer are sequentially deposited on a silicon substrate by magnetron sputtering.
[0056] 2. Graphical processing:
[0057] A photoresist thickener is coated onto the Nb / Al film, and the Nb / Al film is exposed and developed using a photoresist of a certain thickness to form the desired pattern.
[0058] 3. Selective etching and adhesive removal:
[0059] After development, the Al film is selectively etched using AZ400K developer to expose the oxide layer on the Nb surface. The etching process can be automated using a wet cleaning machine or manually, ensuring complete removal of Al from the developed areas. Color changes in the developed areas are observed to confirm the etching effect. After etching, a stripping process ensures no residue remains on the surface, and the film is then spun dry at 500-4000 rpm for 30-150 seconds to ensure no watermarks remain.
[0060] 4. Anti-splashing:
[0061] The sample was transferred to the magnetron sputtering PC cavity, and the chamber pressure and sputtering power were adjusted to test the etching effect at different back-sputtering times, thus exploring suitable process parameters. Specific parameters include, but are not limited to:
[0062] Anti-sputtering pressure range: recommended from 0.5 Pa to 2 Pa;
[0063] Anti-sputtering power range: recommended from 50W to 300W;
[0064] Anti-sputtering time control: usually 1min-15min.
[0065] 5. Secondary corrosion:
[0066] After anti-sputtering, the undeveloped Al layer was etched again using AZ400K developer to expose the undeveloped Nb layer and observe the color change to confirm the etching effect.
[0067] After etching is completed, AFM can be used to observe the etching depth and other parameters, thereby allowing for reverse control of the specific values of process parameters.
[0068] This method utilizes metal layers such as Al or Mo, which can be wet-etched and whose etchant does not corrode Nb and Nb2O5, as a natural mask to replace photoresist. This avoids the contamination of the PC cavity and target material introduced by photoresist, and also solves the problem of the need for regular calibration of the backsputtering rate in magnetron sputtering, which requires frequent calibration and minimizing contamination during the calibration process. Selective backsputtering is performed in the magnetron sputtering PC cavity to remove the Nb surface oxide layer, avoiding the problems of low backsputtering rate and junction damage in traditional loadlock chambers.
[0069] like Figure 3As shown in the figure, this embodiment of the invention also provides a process parameter optimization flowchart, wherein, after obtaining the semiconductor composed of the silicon substrate and the etched niobium film layer, the following steps are further included:
[0070] Step S301: The depth of the partially etched surface oxide layer is collected by at least five collection points. The consistency of the etching depth is evaluated based on the collected depth to obtain a first evaluation result.
[0071] Step S302: Collect the etching rate of the semiconductor, evaluate the etching rate, and obtain a second evaluation result.
[0072] Step S303: Perform electrical testing and elemental analysis on the portion of the surface oxide layer that has been partially etched away to obtain a third evaluation result.
[0073] Step S304: Obtain the process parameters for this etching process, and optimize the process parameters based on the first evaluation result, the second evaluation result, and the third evaluation result to obtain the optimized process parameters.
[0074] Among them, the height of the pattern step in the anti-sputtering area is measured using a semiconductor process step test equipment. This step height is the depth of NbOx / Nb etched by the PC cavity anti-sputtering (i.e., the surface oxide layer is etched away in the niobium film layer).
[0075] Each sample was measured using a method with at least 5 points to analyze the step height consistency (i.e., the first evaluation result) and etching rate (i.e., the second evaluation result) under different process parameters. Combined with electrical testing and elemental analysis, the method was used to verify whether the niobium surface oxide layer was completely etched away (i.e., the third evaluation result). Based on the evaluation of the three parts, the optimal anti-sputtering process parameters (such as pressure, power, and time) were optimized.
[0076] Through systematic research on key parameters such as anti-sputtering pressure, power, and time, selective etching of the niobium surface oxide layer was achieved, resulting in efficient removal and precise etching. This ensures good interlayer connectivity while guaranteeing the safety of the junction region and the integrity of the mask structure, thus safeguarding the performance of the superconducting device.
[0077] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.
Claims
1. A method for selectively etching the oxide layer on the surface of a niobium film using photoresist-free back sputtering, characterized in that, include: A niobium film is deposited on the surface of a silicon substrate, a metal layer is deposited on the niobium film, a photoresist layer is coated on the metal layer, and the photoresist layer is exposed to expose the target pattern. The metal layer that is not covered by the target pattern is etched until the niobium film layer is exposed, and the photoresist layer of the target pattern is removed to obtain the remaining metal layer and the surface oxide layer of the niobium film layer that is not covered by the metal layer. The surface oxide layer is reverse sputtered to remove it, and the remaining metal layer is etched to expose a portion of the niobium film layer from which the surface oxide layer has been etched, thereby obtaining a semiconductor composed of the silicon substrate and the etched niobium film layer.
2. The method for etching the oxide layer on the surface of a niobium film according to claim 1, characterized in that, After removing the photoresist layer of the target pattern to obtain the remaining metal layer and the surface oxide layer of the niobium film layer not covered by the metal layer, the process further includes: At a preset rotation speed, the remaining metal layer, the niobium film layer, and the silicon substrate are spun dry for a first preset time to ensure that there are no watermarks on the surface.
3. The method for selectively etching the oxide layer on the surface of a niobium film using photoresist-free back sputtering according to claim 2, characterized in that, The preset rotation speed is 500-4000 rpm / min, and the first preset time is 30s to 150s.
4. The method for selectively etching the oxide layer on the surface of a niobium film using photoresist-free back sputtering according to claim 1, characterized in that, The step of removing the surface oxide layer by reverse sputtering includes: Using a magnetron sputtering PC cavity, the surface oxide layer is back-sputtered for a second preset time at a preset chamber pressure and a preset sputtering power to remove the surface oxide layer.
5. The method for selectively etching the oxide layer on the surface of a niobium film using photoresist-free selective back sputtering according to claim 4, characterized in that, The preset chamber pressure is 0.5 Pa to 2 Pa, the preset sputtering power is 50 W to 300 W, and the second preset time is 1 min to 15 min.
6. The method for selectively etching the oxide layer on the surface of a niobium film using photoresist-free back sputtering according to claim 1, characterized in that, The process of coating a photoresist layer on the metal layer includes: After coating the metal layer with a photoresist adhesion promoter, a photoresist layer of a predetermined thickness is coated to form a photoresist layer.
7. The method for selectively etching the oxide layer on the surface of a niobium film using photoresist-free back sputtering according to claim 1, characterized in that, The metal layer is a wet-etched metal layer in which the etching solution will not corrode Nb and Nb2O5, and the metal layer includes an aluminum layer or a molybdenum layer.
8. The method for selective reverse sputtering etching of the oxide layer on the surface of a niobium film without photoresist according to any one of claims 1 to 7, characterized in that, After obtaining the semiconductor composed of the silicon substrate and the etched niobium film layer, the method further includes: By collecting data at least five times, the depth of the partially etched surface oxide layer is measured. Based on the collected depth, the consistency of the etching depth is evaluated to obtain a first evaluation result. The etching rate of the semiconductor is collected, the etching rate is evaluated, and a second evaluation result is obtained; Electrical tests and elemental analysis were performed on the portion of the surface oxide layer that was partially etched away to obtain a third evaluation result; The etching process parameters are obtained, and the process parameters are optimized based on the first evaluation result, the second evaluation result, and the third evaluation result to obtain the optimized process parameters.