A method for improving the uniformity and quality of DLC coating prepared by PECVD method

Abstract

This invention belongs to the field of thin film deposition technology and relates to a method for improving the uniformity and quality of DLC coatings prepared by PECVD. Based on PECVD equipment, a method for preparing uniform, highly wear-resistant / corrosion-resistant DLC coatings on irregularly shaped workpieces by controlling a rotating magnetic field is provided. The method includes a vacuum chamber system, a dynamic magnetic field generator, a radio frequency plasma excitation system, a dual-path gas supply system, and a vacuum and pressure regulation system. The dynamic magnetic field generator uses two sets of ring-arranged neodymium iron boron permanent magnets, driven by a motor to rotate the magnetic field vector. The top spray electrode and the bottom ring ground electrode form the main discharge circuit. The rotating magnetic field increases the number density of active groups and molecular kinetic energy during deposition. Different gas ratios are used during coating deposition to achieve high-density, high-quality DLC coatings. The workpiece for DLC coating deposition is placed at the bottom of the reaction chamber. This method is used to deposit uniform, highly wear-resistant, and highly corrosion-resistant DLC coatings on planar or irregularly shaped workpieces.

Description

Technical Field

[0001] This invention belongs to the field of physical vapor deposition technology, specifically relating to a method for preparing a DLC coating with high uniformity, high wear resistance, and high corrosion resistance on the surface of irregularly shaped workpieces by controlling a rotating magnetic field using a PECVD device. Technical Background

[0002] Diamond-like carbon (DLC) coatings have become key functional coatings in mechanical, optical, and medical fields due to their high hardness, low coefficient of friction, excellent chemical stability, and biocompatibility. DLC coatings form an amorphous network with short-range order and long-range disorder through the sp3 / sp2 hybrid structure of carbon atoms. The sp3 bond content directly affects the coating's hardness and wear resistance, while the sp2 bond and hydrogen content are closely related to the coating's lubricity and chemical stability. Currently, DLC coating preparation technologies mainly include physical vapor deposition (PVD) and chemical vapor deposition (CVD). Plasma-enhanced chemical vapor deposition (PECVD) has become the mainstream method because it can achieve high-purity and uniform coating deposition at lower temperatures.

[0003] However, existing technologies still face the following core challenges in the preparation of DLC coatings for irregularly shaped workpieces, especially complex curved surface structures such as gears and molds: 1) Insufficient gas dissociation and uneven distribution of active molecules. Traditional PECVD equipment relies on static magnetic fields or single electric fields to excite plasma, and the dissociation efficiency of gas molecules (such as CH4 and Ar) is generally low (dissociation degree less than 70%), resulting in insufficient density of active carbon groups (such as C2 and CHx). In complex curved surface areas of irregularly shaped workpieces (such as recesses and grooves), the plasma density exhibits a significant gradient distribution, resulting in a difference of 20%-30% in the number density of active groups, ultimately leading to non-uniformity in coating thickness and crystal structure, seriously affecting wear resistance and corrosion resistance. 2) Defects in ion kinetic energy control and internal stress problems. Existing technologies mostly rely on fixed-frequency bias power supplies (such as single DC or RF bias) to accelerate ion bombardment of the substrate, resulting in a wide range of discrete ion kinetic energy distribution, which easily causes surface sputtering damage and enrichment of structural defects. Especially on high-strength alloy substrates such as 30SiMn2MoVA [containing easily oxidizable elements such as Mn and Mo], traditional processes easily generate high-density interfacial stress, leading to crack propagation in the coating under alternating loads or corrosive environments, accelerating the penetration of corrosive media. 3) Poor plasma uniformity and compatibility with irregularly shaped workpieces. The plasma distribution in PECVD is significantly constrained by geometric structure, and traditional equipment lacks active control methods for complex curved surfaces.

[0004] In summary, to address the aforementioned needs, this invention proposes a method for improving the uniformity and quality of DLC coatings prepared by PECVD. Its core innovations are: 1) A top spray electrode [iridium-doped molybdenum boat material, 0.8mm aperture] and a bottom annular ground electrode form the main discharge circuit. A supplementary sidewall auxiliary electrode (RF frequency 400-800kHz) is added, and plasma uniformity is improved through a phase synchronization controller; 2) Two sets of annularly arranged neodymium iron boron permanent magnets [N42 grade, magnetic energy product ≥39MGOe] are installed, and the magnetic field vector rotation is achieved by motor drive [rotation frequency 10-50Hz]; the angle between the magnetic field rotation plane and the workpiece surface is 15-30°; the magnetic field strength is controlled by an air gap adjustment mechanism, with an adjustment range of 0.3-1.2T; 3) The reaction chamber structure adopts a double-layer nested reaction chamber design, with an inner quartz treatment chamber body and an outer stainless steel vacuum chamber, achieving airtight connection through O-rings [sealing level ≥1×10]. -3 4) A dual-gas supply system is used with a mixed gas module. Argon [high purity Ar 99.999%] and methane [CH4 99.999%] are mixed through a mass flow controller [accuracy ±0.5 sccm]. A premixing chamber [volume 2L, gas mixing residence time >3s] is set to ensure gas mixing uniformity CV value ≤2%. Dynamic ratios are used during deposition, i.e., the gas ratio is switched at different stages of coating: pre-deposition stage: Ar:CH4 = 8:1 [surface activation]; film formation stage: Ar:CH4 = 6:1 [dense layer formation]; annealing stage: Ar:CH4 = 4:1 [defect repair]. 5) The vacuum and pressure regulation system uses a series system configuration: roughing stage: rotary vane vacuum pump [ultimate vacuum 2×10 -2 Pa]; Precision pumping: Two-stage turbomolecular pump [Ultimate vacuum 1×10] -4 Pa; Pressure control accuracy ±0.1 Torr [Working range 0.8-1.5 Torr]. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to propose a method for improving the uniformity and quality of DLC coatings prepared by PECVD. This method addresses the issues of low gas pyrolysis efficiency and geometrically constrained plasma distribution in traditional PECVD equipment. A main discharge circuit is constructed using a top spray electrode and a bottom annular ground electrode. Sidewall auxiliary electrodes are supplemented, and plasma uniformity is improved through a phase synchronization controller. Simultaneously, two sets of annularly arranged NdFeB permanent magnets are installed, and the magnetic field vector is rotated via a motor drive. The rotating magnetic field increases the number density of active groups and molecular kinetic energy during deposition. Subsequently, a dynamic gas ratio is used during deposition, i.e., the gas ratio is switched at different stages of coating to achieve a high-quality, high-density, low-stress DLC coating, thereby improving its wear resistance and corrosion resistance.

[0006] The technical solution of this invention is:

[0007] A method for improving the uniformity and quality of DLC coatings prepared by PECVD is characterized by comprising a vacuum chamber system, a dynamic magnetic field generator, a radio frequency plasma excitation system, a dual-channel gas supply system, and a vacuum and pressure regulation system. The radio frequency plasma excitation system uses a multi-electrode configuration, with a top spray electrode and a bottom annular ground electrode forming the main discharge circuit. The dynamic magnetic field generator achieves magnetic field vector rotation by installing two sets of annularly arranged NdFeB permanent magnets and driving them with a motor.

[0008] Furthermore, the top spray electrode [made of iridium-doped molybdenum boat material, with an aperture of 0.8 mm] and the bottom annular ground electrode form the main discharge circuit. Auxiliary sidewall electrodes [RF frequency 400-800 kHz] are added, and plasma uniformity is improved through a phase synchronization controller.

[0009] Furthermore, two sets of ring-arranged neodymium iron boron permanent magnets [N42 grade, magnetic energy product ≥39MGOe] are installed, and the magnetic field vector is rotated by a motor [rotation frequency 10-50Hz]; the angle between the magnetic field rotation plane and the workpiece surface is 15-30°; the magnetic field strength is controlled by an air gap adjustment mechanism, with an adjustment range of 0.3-1.2T.

[0010] Furthermore, the reaction chamber structure adopts a double-layer nested design, with the inner layer being a quartz treatment chamber body and the outer layer being a stainless steel vacuum chamber, achieving airtight connection through O-rings [sealing level ≥ 1×10]. -3 Pa].

[0011] Furthermore, the dual-gas supply system utilizes a mixing module, where argon [high-purity Ar 99.999%] and methane [CH4 99.999%] are mixed via a mass flow controller [accuracy ±0.5 sccm]. A premixing chamber [volume 2L, gas residence time >3s] is set up to ensure gas mixing uniformity (CV value) ≤2%. Dynamic proportions are used during deposition, switching the gas ratio at different stages of the coating process: pre-deposition stage: Ar:CH4 = 8:1 [surface activation]; film formation stage: Ar:CH4 = 6:1 [dense layer formation]; annealing stage: Ar:CH4 = 4:1 [defect repair].

[0012] Furthermore, the vacuum and pressure regulation system uses a series configuration. Roughing stage: Rotary vane vacuum pump [ultimate vacuum 2×10⁻⁶] -2 Pa]; Precision pumping: Two-stage turbomolecular pump [Ultimate vacuum 1×10] -4 Pa; Pressure control accuracy ±0.1 Torr [Working range 0.8-1.5 Torr].

[0013] The key to the implementation of this invention lies in:

[0014] This invention proposes a method to improve the uniformity and quality of DLC coatings prepared by PECVD. It mainly includes a vacuum chamber system, a dynamic magnetic field generator, a radio frequency plasma excitation system, a dual-channel gas supply system, and a vacuum and pressure regulation system. The dynamic magnetic field generator uses two sets of ring-arranged NdFeB permanent magnets, driven by a motor to rotate the magnetic field vector. The radio frequency plasma excitation system uses a multi-electrode configuration, with the top spray electrode and the bottom ring ground electrode forming the main discharge circuit. The rotating magnetic field increases the number density of active groups and molecular kinetic energy during deposition. The workpiece for DLC coating deposition is placed at the bottom of the reaction chamber, and the substrate stage can rotate horizontally to improve deposition uniformity. This device is mainly used for depositing uniform, highly wear-resistant, and highly corrosion-resistant DLC coatings on planar or irregularly shaped workpieces.

[0015] This device is mainly used for the deposition of DLC coatings with high uniformity, high wear resistance, and high corrosion resistance.

[0016] The key to generating plasma and performing DLC ​​deposition lies in:

[0017] First, the workpiece is cleaned. It is placed in a 20% diluted sulfuric acid solution, heated to 60°C, and ultrasonically cleaned for 20 minutes. Then, the workpiece is sequentially placed in acetone and anhydrous ethanol and ultrasonically cleaned for 20 minutes each to remove surface impurities and ensure high adhesion. Finally, the workpiece is placed on a vacuum chamber substrate stage, and the chamber is evacuated to 1.0 × 10⁻⁶. -4 After evacuating to a predetermined vacuum, argon and methane are introduced into the chamber to maintain a pressure of 100–200 Pa. The radio frequency power supply is turned on, and the output power is adjusted to 200–1000 W. The reactive gas is ionized to form a plasma composed of high-energy electrons, ions, and free radicals. During DLC ​​coating deposition, the magnetic field vector is rotated via a motor drive, with the magnetic field strength adjusted to above 0.3 T to increase the number density of active groups and molecular kinetic energy. Different gas ratios are used at different deposition stages to experimentally achieve the deposition of high-quality, high-density, and low-stress DLC coatings. After coating deposition is complete, the power and gas are turned off, and the chamber is shut down after evacuating to an ultimate vacuum.

[0018] The advantages of this invention compared to the prior art are as follows:

[0019] This invention proposes a method to improve the uniformity and quality of DLC coatings prepared by PECVD. Compared with traditional PECVD methods for DLC coating deposition, this method aims to solve the problems of low gas pyrolysis efficiency and geometric constraints on plasma distribution in traditional PECVD equipment. A main discharge circuit is formed by a top spray electrode and a bottom annular ground electrode. Sidewall auxiliary electrodes are added, and plasma uniformity is improved through a phase synchronization controller. Simultaneously, two sets of annularly arranged NdFeB permanent magnets are installed, and the magnetic field vector is rotated by a motor. The rotating magnetic field increases the number density of active groups and molecular kinetic energy during deposition. Subsequently, a dynamic gas ratio is used during deposition, i.e., the gas ratio is switched at different stages of coating to achieve a high-quality, high-density, low-stress DLC coating, thereby improving its wear resistance and corrosion resistance. Attached Figure Description

[0020] Figure 1 This is a diagram showing the magnetic flux density modulus and flux density streamline distribution within the PECVD chamber after the addition of a rotating magnetic field;

[0021] Figure 2 This is a cross-sectional topography of the DLC coating deposited using this method;

[0022] Figure 3 This is the Raman spectrum of the DLC coating deposited using this method. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to specific embodiments:

[0024] Example 1

[0025] First, the 25Cr3Mo3NiNbZr alloy sample was ultrasonically cleaned sequentially in 20% dilute sulfuric acid acetone and anhydrous ethanol for 20 minutes each. Then, the workpiece was placed in a PECVD machine and evacuated to a vacuum of 1×10⁻⁶. -4 Below Pa. Ar and CH4 gases are introduced at initial flow rates of 180 and 20 sccm, respectively. The RF power supply is turned on, and the output power is adjusted to 400W. The reactive gas is ionized, forming a plasma composed of high-energy electrons, ions, and free radicals. Simultaneously, the magnetic field drive motor is turned on, driving the magnetic field vector rotation. The magnetic field strength is adjusted to 0.5T, the rotation frequency is set to 30Hz, and the magnetic field rotation plane forms a 25° angle with the workpiece to increase the number density of active groups and molecular kinetic energy. The furnace temperature is maintained at 150℃ during deposition. This process is maintained for 10 minutes. Then, the Ar and CH4 gas flow rates are adjusted to 120 and 20 sccm, respectively, and this process is maintained for 30 minutes. Finally, the Ar and CH4 gas flow rates are adjusted to 80 and 20 sccm, respectively, and this process is maintained for 10 minutes.

[0026] Example 2

[0027] First, the 30SiMn2MoVA alloy sample was ultrasonically cleaned sequentially in 20% dilute sulfuric acid acetone and anhydrous ethanol for 20 minutes each. Then, the workpiece was placed in a PECVD machine and evacuated to a vacuum of 1×10⁻⁶. -4 Below Pa. Ar and CH4 gases are introduced at initial flow rates of 180 and 20 sccm, respectively. The RF power supply is turned on, and the output power is adjusted to 500W. The reactive gases are ionized, forming a plasma composed of high-energy electrons, ions, and free radicals. Simultaneously, the magnetic field drive motor is turned on, driving the magnetic field vector rotation. The magnetic field strength is adjusted to 0.8T, the rotation frequency is set to 40Hz, and the magnetic field rotation plane forms a 15° angle with the workpiece to increase the number density of active groups and molecular kinetic energy. The furnace temperature is maintained at 180℃ during deposition. This process is maintained for 10 minutes. Then, the Ar and CH4 gas flow rates are adjusted to 120 and 20 sccm, respectively, and this process is maintained for 30 minutes. Finally, the Ar and CH4 gas flow rates are adjusted to 80 and 20 sccm, respectively, and this process is maintained for 10 minutes.

Claims

1. A method for improving the uniformity and quality of DLC coatings prepared by PECVD, characterized in that, It includes a vacuum chamber system, a dynamic magnetic field generator, a radio frequency plasma excitation system, a dual-channel gas supply system, and a vacuum and pressure regulation system. The radio frequency plasma excitation system uses a multi-electrode configuration, with the top spray electrode and the bottom annular ground electrode forming the main discharge circuit. The dynamic magnetic field generator uses two sets of annularly arranged neodymium iron boron permanent magnets, driven by a motor to achieve magnetic field vector rotation. Different gas ratios are used during coating deposition to achieve high-density, high-quality DLC coatings.

2. The method for improving the uniformity and quality of DLC coatings prepared by PECVD according to claim 1, characterized in that, The top spray electrode (made of iridium-doped molybdenum boat material, with an aperture of 0.8 mm) and the bottom annular ground electrode form the main discharge circuit, supplemented by the side wall auxiliary electrode (RF frequency 400-800 kHz). The plasma uniformity is improved through the phase synchronization controller.

3. The method for improving the uniformity and quality of DLC coatings prepared by PECVD according to claim 1, characterized in that, Two sets of ring-arranged neodymium iron boron permanent magnets [N42 grade, magnetic energy product ≥39MGOe] are installed, and the magnetic field vector is rotated by a motor [rotation frequency 10-50Hz]; the angle between the magnetic field rotation plane and the workpiece surface is 15-30°; the magnetic field strength is controlled by an air gap adjustment mechanism, with an adjustment range of 0.3-1.2T.

4. The method for improving the uniformity and quality of DLC coatings prepared by PECVD according to claim 1, characterized in that, The reaction chamber structure adopts a double-layer nested design, with the inner layer being a quartz treatment chamber and the outer layer being a stainless steel vacuum chamber. Airtight connection is achieved through O-ring seals [sealing level ≥ 1×10]. -3 Pa].

5. The method for improving the uniformity and quality of DLC coatings prepared by PECVD according to claim 1, characterized in that, The dual-gas supply system uses a mixing module, where argon (high purity Ar 99.999%) and methane (CH4 99.999%) are mixed via a mass flow controller (accuracy ±0.5 sccm). A premixing chamber (2L volume, mixing residence time >3s) is set up to ensure gas mixing uniformity (CV value ≤2%). Dynamic proportions are used during deposition, switching the gas ratio at different stages of the coating process: pre-deposition stage: Ar:CH4 = 8:1 (surface activation); film formation stage: Ar:CH4 = 6:1 (dense layer formation). Annealing stage: Ar:CH4 = 4:1 [Defect repair].

6. The method for improving the uniformity and quality of DLC coatings prepared by PECVD according to claim 1, characterized in that, The vacuum and pressure regulation system uses a series configuration: Roughing stage: Rotary vane vacuum pump [Ultimate vacuum 2×10⁻⁶] - 2 Pa]; Precision pumping: Two-stage turbomolecular pump [Ultimate vacuum 1×10] -4 Pa; Pressure control accuracy ±0.1 Torr [Operating range 0.8-1.5 Torr].

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