Uniform control of magnetron sputtering coating on complex workpiece surface
This paper introduces the film coating mechanism and technical characteristics of the workpiece surface with complex cavity. Aiming at the problems such as uneven consumption of target material, concave erosion ring, and uneven and dense film thickness in the coating process of complex workpiece, a rotating columnar magnetron sputtering target was used in the experiment. Multiple targets and materials were installed in different positions of the coating machine. The target can rotate freely to realize the need of directional coating; Using multiple magnetron sputtering target and set the auxiliary magnetic field of the unbalanced magnetron sputtering cathode target structure improvement, to improve the vacuum coating chamber plasma density, thus improve the sputtering artifacts bias current deposition coating, etc. Series of innovative research, intended to achieve in the same plane, with complex shape and the structure of the inner cavity on the workpiece surface plating thickness uniform, dense and continuous functional composite film.
On edges and much more complex than the cavity surface coating, chemical plating technology on at present at home and abroad are more, as was also carried out on the workpiece surface coating treatment of vacuum magnetron sputtering film technology, at present are mostly in the rule and the flat surface of preparing for a single or composite membrane, and is widely used in machinery, electronics, energy, materials, information, aerospace and other fields, the concrete such as cutting tools, hardware tools, mobile phones, notebook computers, various types of sensors and parts have special requirements, etc. Due to the characteristics of vacuum film forming technology, it is difficult and complicated to control the film thickness, uniformity and bonding force of sputtering film forming process on the surface of complex workpiece. With the rapid development of machinery manufacturing industry, the application range of surface coating technology of workpiece is expanded from cutting tools to precision stamping die, aerospace parts and electronic accessories plug-in. New high-performance film layers keep emerging, such as TiAlCN, AlCrN, TiSiN, diamond-like layer, etc., which improve the service life and machining efficiency of die. It is very important to study the uniform control of magnetron sputtering coating technology on the surface of complex workpiece.
1. Mechanism and technical characteristics of magnetron sputtering coating
1.1 magnetron sputtering coating mechanism
The working mechanism of magnetron sputtering is that under the action of electric field E, electrons collide with argon atoms in the process of flying to the substrate and ionize positive ion Ar and new electrons. New electrons fly to the substrate, Ar ions accelerate to the cathode target under the action of electric field, and bombard the target surface with high energy, so that the target sputters. In the sputtering particles, the neutral target atoms or molecules are deposited on the substrate to form a thin film, and the generated secondary electrons will be affected by the electric field and magnetic field to produce E B drift, whose motion trajectory is similar to cycloid. Electrons move in a circular motion on the target surface and are bound to the plasma region on the target surface. In this region, a large number of Ar ions are ionized to bombard the target, thus achieving a high deposition rate. With the increase of the number of collisions, the energy of the secondary electrons is exhausted, and they gradually move away from the target surface, and finally deposit on the substrate under the action of the electric field E. Magnetron sputtering is the collision process between the incident particles and the target. It passes some momentum to the target atom through the complex scattering process and the collision of the target atom. The target atom collides with other target atoms to form a cascade process.
1.2 characteristics of technical application
Magnetron sputtering is a high-speed sputtering process under low pressure. The ionization rate of the gas must be effectively increased. The plasma density can be increased by introducing a magnetic field on the surface of the target cathode and using the constraint of the magnetic field on charged particles to increase the sputtering rate.
In magnetron sputtering, the movement of electrons in magnetic field by lorentz force, their trajectory is bent and even produce spiral motion, the motion path, thus increased the number of collisions with working gas, the plasma density increases, thus magnetron sputtering rate is greatly improved, and can work under low sputtering voltage and air pressure, reduce the tendency of membrane pollution; At the same time, the atomic energy incident on the substrate surface is increased, so the film quality can be improved to a great extent. Electrons that have lost energy due to repeated collisions reach the anode and become low-energy electrons so that the substrate does not overheat. Therefore, magnetron sputtering has the advantages of "high speed" and "low temperature".The disadvantage of magnetron sputtering coating is that it cannot prepare insulator film, and the uneven magnetic field used in the magnetron electrode will cause significant uneven etching of the target material, resulting in a low utilization rate of the target material, which is generally only 20%~30%.The utilization rate of magnetron sputtering target is an important parameter for the engineering design and production process cost accounting of magnetron sputtering source.In order to improve the utilization rate of target materials, different forms of dynamic targets were studied, among which the rotating magnetic field cylindrical target was the main target and was widely used in industry, and the utilization rate of such target materials was as high as 70%.Common magnetron sputtering targets can be divided into three types from the geometric shape: rectangular plane target, circular plane target and cylindrical target.
2. Uniform control of sputtering coating on the surface of workpieces with complex cavities
2.1 existing technical problems
(1) the cathode target is planar sputtering, which is caused by local strong sputtering caused by uneven magnetic field components, resulting in uneven consumption of the target and concave erosion ring. (2) the surface of the workpiece is deposited and coated with multiple layers of film, and the bonding strength between the bottom layer and the film layer is not uniform and firm. At the same time, there are sputtering phenomena of different components and anti-sputtering effect of the film layer, resulting in great differences in the composition of the film layer and the target.
2.2 technical analysis and scientific conception
(1) the workpiece surface with multiple edges and angles and multiple cavities is deposited and coated with multiple layers of film. It is planned to adopt rotating columnar magnetron sputtering target, and multiple targets and materials are installed in different positions of the coating machine. The target can rotate freely to achieve the need of directional coating. (2) multiple magnetron sputtering targets and auxiliary magnetic fields were set to improve the structure of unbalanced magnetron sputtering cathode targets, improve the plasma density in the vacuum coating chamber, and further improve the bias flow of the sputtering workpiece to achieve deposition and coating. (3) the uneven magnetic field component of the planar sputtering cathode target produces a concave erosion ring in the target. It is intended to change the magnetic field distribution to achieve isotropic internal stress of the complex workpiece in sputtering on the substrate, and to combine the dense, continuous and uniform film.
2.3 experimental methods and technical route
2.3.1 experimental materials
The six-station magnetron sputtering equipment was used in the experiment, which was mainly composed of vacuum acquisition system, vacuum detection, vacuum furnace, cathode magnetron, gas input system and power supply. Physical vapor deposition PVD magnetron sputtering process was used. Cathode materials: Ti, TiN, TiAlN, coated Ti, TiN, TiN, TiAlN multielement multilayer film.
2.3.2 quality detection of film layer (table 1)
2.3.3 experimental methods
The complex surface sputtering film of workpiece was prepared by if sputtering ion plating. In order to solve the technical problems of complex workpiece coating, the following experimental research was carried out.
(1) the cathode target is planar sputtering, and the local strong sputtering caused by uneven magnetic field components leads to uneven target material consumption. By improving the shape and distribution of the magnetic field, making the magnet move inside the cathode, setting the shield and other measures, it is realized that the film coating of the workpiece with multiple edges and angles and multiple cavities sputtering on the substrate can generate isotropic internal stress, and the film is compact, continuous and uniform. The structure of balanced sputtering target is mainly composed of outer magnetic steel, central magnetic steel and magnetic pole boots.
(2) according to the requirement of sputtering on the surface coating of complex workpiece with multiple edges and angles and multiple cavities to achieve the structural requirements of target material and target, rotary columnar magnetron sputtering target was adopted. According to different workpiece conditions, sputtered targets with magnetic structure or sputter structure were used. Gyromagnetic cylindrical magnetron target is the use of the magnetic field around the target tube parallel and vertical target electric field component, on the surface of the tube in the target tube surface orthogonal electromagnetic field, the installation of target in the center of the deposition chamber, to around 360 ° direction spin coating; The cylindrical magnetron sputtering target is mounted on the side of the coating chamber. The target tube rotates continuously during the coating process to meet the need of directional coating.
(3) the selective sputtering phenomenon of different components, the film's anti-sputtering rate and adhesion are different, which will lead to a great difference between the film and the target components. The selection of appropriate process conditions will minimize the anti-sputtering effect on the film.
(4) using multiple magnetron sputtering target, and setting auxiliary magnetic field in the coating room constitute a closed magnetic field, unless there is magnetic field distribution in front of the target, the target between the target and by setting the auxiliary magnetic field effect, form each other crosslinking effect, make the plasma density increase, the artifacts drift, so that more edges and cavity of the workpiece to achieve the objective of the deposited coating. FIG. 1 shows a schematic diagram of closed magnetic field formed by four non-equilibrium magnetron sputtering targets and auxiliary magnetic field.
2.4 experimental results and discussion
From December 2012 to February 2013, sputtering coating tests were carried out on the surface of small stamping die workpiece and communication device respectively.TiN samples of small stamping die workpiece test results: the film appearance is good, no crack;Film thickness between 1 m~5 m;Film uniformity was less than 5%;Small hole rate;Film hardness up to 2000 HV;High bonding strength;Strong adhesion, no peeling of injection layer;Excellent corrosion resistance, heat resistance and abrasion resistance;Isotropic good;The material particle ionization rate is 75%~95%.Film deposition rate is controllable (2.0~2000)nm/s;Film forming speed (2~13) m/h.All the indexes in the trial reached the design requirements, and the results of the composite film on the surface of communication devices also reached the expected effect.It is feasible to study the uniform control measures of magnetron sputtering coating on the workpiece surface with multiple edges and angles and multiple cavities.
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