Method for improving precision and reliability of ceramic substrate surface film circuit pattern

Abstract

The invention discloses a method for improving precision and reliability of a thin film circuit pattern on the surface of a ceramic substrate, and belongs to the field of microwave components, and the method comprises the steps of substrate pretreatment, photoresist pattern preparation, thin film preparation through magnetron sputtering, metal film layer electroplating thickening, photoresist removal and the like. Magnetron sputtering and electroplating are carried out on the ceramic substrate carrying the photoresist pattern, the target thin film circuit pattern is prepared, a traditional wet etching process method is replaced, the side edge corrosion phenomenon is avoided, and the prepared thin film circuit pattern is high in reliability, high in consistency and high in line precision.

Description

Technical Field

[0001] The invention relates to the technical field of microwave components, and in particular to a method for improving the accuracy and reliability of thin film circuit patterns on the surface of a ceramic substrate. Background Art

[0002] In recent years, the rapid development of the communications industry has greatly promoted the market demand for microwave devices. Microstrip isolators, circulators, filters, etc. have become the main types in communication systems due to their small size, easy integration, and high performance.

[0003] Currently, there are three main types of microstrip circuit substrates: all-ferrite circuit substrates, ceramic ferrite composite circuit substrates, and all-ceramic circuit substrates. According to the definition of ceramic materials, all inorganic non-metallic materials can be defined as ceramics. This application collectively refers to the above three types of materials as ceramic substrates.

[0004] At present, the above ceramic substrates all use thin film technology to make metal thin film circuits on the corresponding material substrates. The traditional metal thin film circuit manufacturing process includes sputtering, photolithography and etching. With the increasing requirements for device miniaturization and broadband, the requirements for the accuracy of circuit graphics lines are also getting higher and higher.

[0005] At present, the method to improve the accuracy and reliability of thin-film circuit graphics on the surface of ceramic substrates is generally: sputtering-electroplating-photolithography-etching process is used in sequence. For metal film layers with a thickness of microns, wet etching (a type of etching) process is usually used. The wet etching process is to use a corrosive liquid to chemically corrode the surface of the substrate. It has the corrosion characteristics of various anisotropy. There are two states of longitudinal corrosion and lateral corrosion during the corrosion process. This will cause a lot of side corrosion under the metal pattern, making the upper metal in a suspended state. Under the action of external force, the upper metal will fall off. At the same time, due to the existence of side corrosion and the constant change in concentration of the wet etching liquid during the working process, the accuracy of the target circuit pattern is difficult to guarantee, and thus the high-precision requirements of the circuit pattern cannot be met. Specifically, according to the provisions and test methods in GJB1065A-2004 General Specifications for RF Isolators and Circulators and GJB548C-2021 Test Methods and Procedures for Microelectronic Devices, the accuracy of the circuit pattern can be characterized by directly measuring the size of the circuit lines, and the reliability can be characterized by measuring the side corrosion depth of the thin film circuit by cross-sectional microscopy, that is, the width difference between the upper metal and the lower metal at the edge of the circuit line. The circuit pattern accuracy obtained by the current method is ≤±7μm, and the lateral corrosion depth of the film side is ≤10μm. That is, the wet etching process that introduces serious side corrosion problems has become a bottleneck process for further improving the accuracy and reliability of circuit pattern lines. Therefore, based on ceramic substrates, this field is in urgent need of a method for preparing thin film circuits with high reliability and high graphic accuracy. Summary of the invention

[0006] The purpose of the present invention is to provide a method for improving the accuracy and reliability of thin film circuit patterns on the surface of a ceramic substrate to solve the above-mentioned problems.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a method for improving the accuracy and reliability of thin film circuit patterns on the surface of a ceramic substrate, comprising the following steps: (1) Ceramic substrate pretreatment: Plasma etching treatment is performed on the surface of the cleaned ceramic substrate; (2) Preparing a photoresist pattern: performing micro-nano processing on the ceramic substrate processed in step (1) to prepare a target photoresist pattern on the surface of the ceramic substrate; (3) Magnetron sputtering thin film material: the ceramic substrate with the photoresist pattern processed in step (2) is transferred to a magnetron sputtering device, and a seed layer material and a metal layer material are prepared on the surface with the photoresist pattern; (4) Electroplating to thicken the metal film layer: subjecting the ceramic substrate with the seed layer material and the metal layer material after the treatment in step (3) to an electroplating process to increase the thickness of the surface metal film layer; (5) De-resisting treatment: removing the photoresist from the ceramic substrate treated in step (4) to obtain the target thin film circuit pattern.

[0008] The present invention firstly greatly improves the activation degree of the substrate surface through special substrate pretreatment, so that the photoresist has a high-strength bonding force with the surface of the ceramic substrate, and improves the stability of the photoresist in a high-temperature environment; then, by depositing a seed layer and a metal layer on the ceramic substrate with the photoresist, the seed layer greatly improves the bonding force between the film material and the ceramic substrate, and enhances the reliability of the metal film layer; finally, the metal film layer is thickened by electroplating, and the target pattern can be obtained after dry debonding.

[0009] According to the provisions and test methods in GJB1065A-2004 General Specifications for RF Isolators and Circulators and GJB548C-2021 Test Methods and Procedures for Microelectronic Devices, the preparation method provided by the present invention can make the circuit pattern accuracy ≤±4μm and the lateral corrosion depth of the film layer side ≤1μm.

[0010] As a preferred technical solution, in step (1), the plasma etching method is: using plasma etching equipment, bombarding the surface of the substrate with Ar plasma, and the bombardment time is ≥20 minutes.

[0011] As a preferred technical solution, in step (2), the method for preparing the photoresist pattern is: coating the surface of the substrate after Ar plasma bombardment with photoresist, using a mask of the target pattern, and performing the steps of coating, pre-baking, exposure, development, and hardening to obtain the target photoresist pattern.

[0012] In the present application, the method for preparing the photoresist pattern is a prior art known in the art.

[0013] In step (2), if a photoresist with a viscosity of ≥200 cp is used to prepare a photoresist pattern with a thickness of ≥6 μm, after the sputtering of the thin film material is completed, the metal film layer is thickened by electroplating; If a photoresist with a viscosity of ≤200cp is used to prepare a photoresist pattern with a thickness of ≤3μm, after the sputtering of the thin film material is completed, the photoresist is removed, and then a photoresist with a viscosity of ≥200cp is used to prepare a photoresist pattern with a thickness of ≥5μm, and then the metal film layer is thickened by electroplating.

[0014] As a preferred technical solution, in step (3), the seed layer material is selected from TiN, Cr, Ti x W 1-x, TaN, wherein x≤0.5, the thickness is 50-300nm, the sputtering temperature is 200-600℃, and the sputtering power is 150W-400W; the metal layer material is Cu, Au, Ni, one or more, with a thickness ≥200nm.

[0015] As a preferred technical solution, in step (4), the electroplated material is Au.

[0016] As a preferred technical solution, in step (5), the photoresist removal process is performed using a dry photoresist stripping machine.

[0017] Compared with the prior art, the advantages of the present invention are: compared with the traditional thin film circuit manufacturing process of sputtering-electroplating-photolithography-etching, the manufacturing process of sputtering and electroplating a ceramic substrate with a photoresist pattern has unique advantages: (1) Sputtering technology is used to carry photoresist patterns on ceramic substrates. The target circuit pattern can be formed during the sputtering process. The circuit pattern is only determined by the photolithography accuracy and does not introduce side corrosion problems. The lines are very high, which can make the circuit pattern accuracy ≤±4μm and the lateral corrosion depth of the film layer side ≤1μm; (2) Electroplating technology for ceramic substrates carrying photoresist patterns. Based on the formed seed layer, the circuit film layer is thickened by using adhesive electroplating technology; this method replaces the method of making circuits by wet etching process, and the produced microstrip circuit graphics have greater advantages in line consistency, line accuracy, side etching depth, etc. At the same time, the circuit conductive material (gold) can be used more efficiently, reducing the process production cost. The circuit pattern only occupies a part of the area of ​​the entire ceramic substrate. Under the existing technology, gold will completely cover the entire ceramic substrate. The method provided by the present invention only uses gold according to the area of ​​the circuit pattern, that is, the difference between the substrate area and the circuit pattern area is the reduced process cost; (3) Plasma etching is used to pre-treat the substrate, which greatly improves the activation degree of the substrate surface, so that the photoresist and the ceramic substrate surface have a high-strength bonding force, and improves the stability of the photoresist in a high-temperature environment; at the same time, the bonding force between the seed layer material and the ceramic substrate is also improved during sputtering. The "bonding force pull-off method" is used for performance testing according to the ISO4624 standard. The film bonding force obtained using the existing technology is 350g / mm 2 , and the pretreatment method provided by the present invention makes the film bonding strength reach 800g / mm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of a ceramic substrate; Figure 2 , Figure 3 is a schematic diagram of the method of the present invention after preparation through step (2); Figure 4 This is a schematic diagram of the method of the present invention after preparation through step (3); Figure 5 , Figure 6 , Figure 7 is a schematic diagram of the method of the present invention after preparation through step (4); Figure 8 This is a schematic diagram of the method of the present invention after preparation through step (5).

[0019] In the figure: 1. Ceramic substrate; 2. Seed layer and metal layer; 3. Upper metal film layer; 4. Photoresist. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with embodiments.

[0021] A method for improving the accuracy and reliability of thin film circuit patterns on the surface of a ceramic substrate, the manufacturing process of which is as follows Figure 1-8 As shown, the specific steps are as follows: (1) Substrate pretreatment: Use plasma etching equipment to clean the surface of the ceramic substrate 1 ( Figure 1 ) plasma etching treatment was performed, using Ar plasma etching method, with an Ar gas flow rate of 25 sccm, a power of 300 W, and an etching time of 30 min; (2) Preparation of photoresist pattern: Figure 2 As shown, the surface of the ceramic substrate 1 obtained in step (1) is coated with a photoresist 4 with a viscosity of 100 cp and a thickness of 3 μm, and then subjected to micro-nano processing such as pre-baking, exposure, development, and hardening to form a photoresist pattern on the substrate surface, as shown in FIG. Figure 3 As shown; after the hard film is completed, the substrate is placed in a plasma etching device, and Ar plasma etching is adopted, the Ar gas flow rate is 25sccm, the power is 300W, and the etching time is 5min; (3) Magnetron sputtering thin film material: The ceramic substrate with the photoresist pattern after the treatment in step (2) is transferred to a magnetron sputtering device, and a seed layer material and a metal layer material are prepared on the surface with the photoresist pattern to obtain a seed layer and a metal layer 2, such as Figure 4 As shown; the seed layer material is TiW, the sputtering Ar gas flow rate is 25sccm, the power is 200W, and the sputtering thickness is 0.1μm; the metal layer materials are Cu and Ni, the sputtering thickness of the Cu layer is 2μm, and the sputtering thickness of the Ni layer is 0.1μm; (4) Electroplating thickened metal film layer: such as Figure 5 As shown, the substrate obtained in step (3) is subjected to a photoresist removal treatment, and after the treatment is completed, a photoresist pattern is prepared on the substrate again. Figure 6As shown, a photoresist with a viscosity of 300cp is used, and the thickness of the prepared photoresist pattern is 7μm. After the hard film is completed, the substrate is placed in a plasma etching device, and an Ar plasma etching method is adopted. The Ar gas flow rate is 25sccm, the power is 300W, and the etching time is 10min. After completion, the substrate is subjected to an electroplating gold process operation, and the electroplating gold thickness is 2μm, and the following is obtained. Figure 7 The upper metal film layer 3 shown; (5) Resist removal: The substrate treated in step (4) is subjected to a photoresist removal process to obtain a target thin film circuit pattern, such as Figure 8 shown.

[0022] After testing, the line accuracy is ≤±4μm, the side corrosion depth is ≤1μm, and the "bonding force pull-off method" is used for performance testing according to the ISO4624 standard. The film bonding force is 800g / mm 2 .

[0023] Embodiment 2:

[0024] (1) Substrate pretreatment: Use plasma etching equipment to clean the surface of the ceramic substrate 1 ( Figure 1 ) plasma etching treatment was performed, using Ar plasma etching method, with an Ar gas flow rate of 25 sccm, a power of 300 W, and an etching time of 30 min; (2) Preparation of photoresist pattern: Figure 2 As shown, the surface of the ceramic substrate obtained in step (1) is coated with a photoresist 4 with a viscosity of 300cp and a thickness of 7μm. After pre-baking, exposure, development, hardening and other micro-nano processing, a photoresist pattern is formed on the surface of the substrate, as shown in FIG. Figure 3 As shown; after the hard film is completed, the substrate is placed in a plasma etching device, and Ar plasma etching is adopted, the Ar gas flow rate is 25sccm, the power is 300W, and the etching time is 10min; (3) Magnetron sputtering thin film material: The ceramic substrate with the photoresist pattern after the treatment in step (2) is transferred to a magnetron sputtering device, and the seed layer material and the metal layer material are prepared on the surface with the photoresist pattern, such as Figure 4 As shown, the seed layer material is TiW, the sputtering Ar gas flow rate is 25 sccm, the power is 200 W, and the sputtering thickness is 0.1 μm; the metal layer materials are Cu and Ni, the sputtering thickness of the Cu layer is 2 μm, and the sputtering thickness of the Ni layer is 0.1 μm.

[0025] (4) Electroplating thickened metal film layer: such as Figure 5 As shown, the substrate obtained in step (3) is subjected to a gold electroplating process with a gold electroplating thickness of 2 μm to obtain Figure 7 The upper metal film layer structure is shown.

[0026] (5) Resist removal: The substrate treated in step (4) is subjected to a photoresist removal process to obtain a target thin film circuit pattern, such as Figure 8 shown.

[0027] After testing, the line accuracy is ≤±3.5μm, the side corrosion depth is ≤1μm, and the "bonding force pull-off method" is used for performance testing according to the ISO4624 standard. The film bonding force is 800g / mm 2 .

[0028] Comparative Example 1 Compared with Example 2, this comparative example does not perform the substrate pretreatment in step (1), and the rest is the same as Example 2. After testing, the line accuracy is ≤±5μm, the side corrosion depth is ≤1μm, and the performance test is carried out using the "bonding force pulling method" according to the ISO4624 standard, and the film bonding force is 350g / mm 2 .

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the accuracy and reliability of thin film circuit patterns on the surface of a ceramic substrate, characterized in that: The steps include: (1) Ceramic substrate pretreatment: Plasma etching treatment is performed on the surface of the cleaned ceramic substrate; (2) Preparing a photoresist pattern: performing micro-nano processing on the ceramic substrate processed in step (1) to prepare a target photoresist pattern on the surface of the ceramic substrate; (3) Magnetron sputtering thin film material: the ceramic substrate with the photoresist pattern processed in step (2) is transferred to a magnetron sputtering device, and a seed layer material and a metal layer material are prepared on the surface with the photoresist pattern; (4) Electroplating to thicken the metal film layer: subjecting the ceramic substrate with the seed layer material and the metal layer material after the treatment in step (3) to an electroplating process; (5) De-resisting treatment: removing the photoresist from the ceramic substrate treated in step (4) to obtain the target thin film circuit pattern.

2. The method according to claim 1, characterized in that In step (1), the plasma etching treatment method is: using plasma etching equipment, bombarding the surface of the substrate with Ar plasma, and the bombardment time is ≥20 minutes.

3. The method according to claim 1, characterized in that In step (2), the method for preparing the photoresist pattern is: coating the surface of the substrate after Ar plasma bombardment with photoresist, using a mask of the target pattern, and after the steps of coating, pre-baking, exposure, development, and hardening, a target photoresist pattern is obtained.

4. The method according to claim 1, characterized in that: In step (2), a photoresist having a viscosity of ≥200 cp is used to prepare a photoresist pattern having a thickness of ≥6 μm. After the sputtering of the thin film material is completed, the metal film layer is thickened by electroplating.

5. The method according to claim 1, characterized in that In step (2), a photoresist with a viscosity of ≤200cp is used to prepare a photoresist pattern with a thickness of ≤3μm. After the sputtering of the thin film material is completed, the photoresist is removed, and then a photoresist with a viscosity of ≥200cp is used to prepare a photoresist pattern with a thickness of ≥5μm. The metal film layer is then thickened by electroplating.

6. The method according to claim 1, characterized in that In step (3), the seed layer material is selected from TiN, Cr, Ti x W 1-x , TaN, wherein x≤0.5, the thickness is 50-300nm, the sputtering temperature is 200-600℃, and the sputtering power is 150W-400W; the metal layer material is Cu, Au, Ni, one or more, with a thickness ≥200nm.

7. The method according to claim 1, characterized in that In step (4), the electroplated material is Au.

8. The method according to claim 1, characterized in that In step (5), the photoresist removal process is performed using a dry photoresist stripping machine.

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