Design Method For Thickness Uniformity Of Magnetron Sputtering Coatings

- Mar 01, 2019-

Design method for thickness uniformity of magnetron sputtering coatings


Magnetron sputtering coating is one of the indispensable technologies in modern industry. Magnetron sputtering coating technology is widely used in transparent conductive film, optical film, super hard film, anti-corrosion film, magnetic film, anti-reflection film, anti-reflection film and various decorative film. It plays an increasingly powerful role in national defense and national economic production. The problems of film thickness uniformity, deposition rate and target material utilization rate in the coating process are very concerned in the actual production. The method to solve these problems is to optimize the overall design of all factors involved in the process of sputtering deposition and establish a comprehensive design system for sputtering coating. Film thickness uniformity is one of the most important parameters in the process of sputtering deposition, so it is of great theoretical and practical value to study the comprehensive design of film thickness uniformity.


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During the development of magnetron sputtering technology, breakthroughs in various technologies generally focus on the generation of plasma and the control of plasma. By controlling the distribution parameters of different kinds of particles in electromagnetic field, temperature field and space, the film quality and properties can meet the requirements of various industries.


The uniformity of film thickness is closely related to the working state of magnetron sputtering target, such as the etching state of the target and the electromagnetic field setting of the target, etc. Therefore, in order to ensure the uniformity of film thickness, foreign film preparation companies or coating equipment manufacturing companies have their own complete set of design schemes for coating equipment (including the core component "target"). At the same time, there are many companies specializing in target analysis, design and manufacturing, and the development of relevant application design software, according to customer requirements for equipment optimization design. There is still a big gap between domestic and international advanced level in the analysis and design of coating equipment.


Therefore, it is imperative to establish a comprehensive design system for sputtering coating. The establishment of the system can be carried out in accordance with the overall comprehensive design to part of the design, and then by part of the design gradually into the overall comprehensive design, that is, "the whole to the part, and then to the whole" this dynamic design concept, constantly improve the design system. Will sputter coating list the important factors involved, find out the inner link between them, and then establish a sputtering coating, a comprehensive design system based on the study of film thickness uniformity and do foreshadowing for late into design system software, to implement the preparation of thin film uniformity good film large area, provide strong guarantee for production.


1. Design system properties


Sputtering film thickness uniformity is one of the final standards for indirect measurement of coating process, which involves all aspects of the coating process. Therefore, it is necessary to establish a comprehensive design system for the uniformity of sputtering film thickness to prepare high-quality films with good uniformity of film thickness, classify, summarize and summarize all aspects of sputtering film, and find out their internal relations. Generally speaking, the establishment of design system should have certain principles to determine its basic organizational framework. Its nature is described from the following four aspects: (1) general: the system is required within a certain range is applicable or universal. For this project, the system can meet the basic process requirements of sputtering film on the industrial flat substrate, that is, the common problems of sputtering film process. (2) particularity: the system for specific research objects to achieve the best applicability. For large-area flat substrate sputtering films, it means that the size effect in sputtering films becomes an important part of the system, such as film uniformity, substrate heating uniformity, linear expansion and deformation of materials, target surface current distribution, gas distribution and electromagnetic field distribution. This series of problems is highlighted by the size effect. So the size effect becomes the personality problem of the system. (3) openness: each part of the system is organic combination and continuous development. With the progress of technology, each part of the function will be further developed, so as to improve the overall performance of the system. The development of automatic control technology makes the system powerful: the monitoring technology of plasma spectrum in sputtering process and the control ability of electromagnetic field enable the system to control the parameters of the whole sputtering process to the maximum extent and realize fine design. The openness of the system belongs to the horizontal development. (4) inheritance: the system develops to a certain extent, it will happen by the quantitative change to the process of qualitative change. On the basis of the original function of baowang, the system is constantly improved and improved. The technology of thin film preparation will be developed with the development of theory. The theoretical research on non-equilibrium magnetron sputtering and plasma has promoted the further development of sputtering technology. Then the system is upgraded to achieve new functions. Inheritance is the vertical development of the system.


2. Establishment of the design system


In general, the enhancement of one part of the system will lead to the enhancement of the overall function, while reducing the dependence of the system on some parts, or it can be understood as: the organic combination of two essential factors of the system into one part. The establishment of integrated design system is helpful to the study of the internal logical relations of each part of the system.


The comprehensive design system of large-area sputtering coating can be divided into three parts: T process design of coating equipment, design of coating process and computer numerical simulation design of each process, referring to figure l. Each part is divided into thousands of aspects, and the parts interact with each other. Because of the complexity of the system, the primary stage of the system should be established to simplify the design parameters to improve its practicability.


2.1 engineering design of coating equipment


For sputtering coating, it can be calculated from vacuum system, electromagnetic field, gas distribution, thermal system and other aspects. Mechanical manufacturing and control run through the whole engineering design process, as shown in figure 2.


2.1.1 vacuum system


Vacuum system design is a relatively mature design part, mainly including the following four parts:

(1) chamber structure -- its design form is set by the system working mode. Vacuum chamber can be designed as single chamber, multi - chamber and production line. For the chamber producing flat substrate, the strength, stiffness, stability and other optimization design should be carried out, while considering the feasibility and simplicity of processing technology.

(2) material selection -- in accordance with the requirements of vacuum process, select materials that meet the requirements of low saturation vapor pressure, good thermal and chemical stability, easy degassing and low air permeability. For example, austenitic stainless steel, aluminum alloy, anaerobic copper and so on. For large size equipment, in order to reduce the overall weight of the equipment or moving parts, priority can be given to the selection of aluminum alloy and other light metal materials.

(3) design of vacuum components -- vacuum seal, electrode introduction, pipeline and valve, etc. Vacuum elements used in different process conditions are different.

(4) selection of vacuum pump and vacuum gauge -- generally can be designed according to common engineering requirements. Accurate design requires quantitative calculation of process gas density distribution in a vacuum chamber. Different types of gas and different vacuum chamber cleaning requirements need to choose different vacuum pumps and vacuum meters. The return oil of the vacuum pump will cause pollution to the substrate, and the reaction gas such as oxygen will oxidize the pump oil. Therefore, dry oil-free vacuum pump is often chosen as the vacuum pumping system.


2.1.2 the electromagnetic field


The relatively accurate electromagnetic field design is to simulate the electromagnetic field in the process of sputtering, rather than only simulate the electromagnetic field of the magnetron sputtering equipment when it is not working.


The choice of power supply: the choice of "power supply" should be determined according to different process, common dc power supply, if power supply, rf power supply and can realize a variety of power supply mode of hybrid power supply.


Material selection: for rf power supply, the manned power and matching is a very important issue. The electrode loading material of high power rf power supply requires high surface conductivity and good chemical stability. The materials in the magnetic controlled target can be divided according to the level of magnetic permeability. The magnetic boots are high permeability materials, which are generally pure industrial iron.


Anode and shield: the space position, potential relation, size and area as well as material properties of anode should be considered in the anode design to ensure stable sputtering process. In the design of shield, the electric field design and potential relationship should be considered first to prevent non-target materials from being sputtered and contaminating the film. Secondly, considering the performance of shielding materials, materials with low saturation vapor pressure, high sputtering threshold and conforming to the requirements of vacuum process are generally selected.


2.1.3 gas distribution


The distribution of gas is extremely important for the plate substrate coating. Through the mechanical structure design, the change rate of gas density is minimized in the sputtering deposition area, while outside the area, the flow guide of the system is maximized to improve the utilization rate of gas and the efficiency of the extraction system. The mechanical parts or structures controlling the gas distribution include the air distribution system, the structure of the vacuum chamber and the pumping system.


2.1.4 heating system


Heating system to meet the vacuum system of baking and film growth required temperature conditions.

The above four aspects and others not described all involve the two aspects of mechanical manufacturing and control, so factors such as machinability and response time should be considered.


2.2 coating process design


Between different membrane materials should be considered need different deposition process, the implementation of the different sputtering technology (dc, intermediate frequency, radio frequency, pulse, reaction sputtering, and the combination between them and the development of technology, or the application of new technology, etc.), the same technology adjustment of different process parameters (power, air pressure, deposition methods, etc.), pretreatment (cleaning, preheating, etc.), reprocessing, heat treatment, etc.).


The whole process of coating is divided into four relatively independent processes, referring to figure 3. Generally speaking, parameters that involve plasma, target surface and substrate state change greatly are parameters that need to be controlled in the process.


Gas discharge: glow discharge generates plasma, dissociates working gas, generates cations, and bombards cathode under the action of electric field, accompanied by secondary electron emission and other phenomena. The study of glow discharge plasma is the only way to study the sputtering deposition process.


Sputtering collision: generally, sputtering collision is to study the interaction between charged ions and surface particles of the target, and the generation process of target atoms and atomic clusters. The most widely used theory is the cascade collision theory. SRIM and other mature simulation software have been widely used in the process of sputtering simulation.


Transport process: the movement of target atoms towards the substrate and other surfaces with a certain initial velocity, accompanied by changes in energy and momentum, and finally the net directional transport volume (number of particles). Under the action of external field (mass, momentum, energy), the transport process is more complicated. MC and other methods (PIC, CIC, CFD, etc.) are commonly used to obtain the number of particles deposited on the substrate. The simplified particle transport calculation method divides the sedimentary particles into fast particles (no collision, direct to the substrate surface) and slow particles (collision, diffusion movement to the substrate surface). The effects of gas heating, thinning and sputter wind (high energy neutral particles) are the result of momentum and energy exchange between gas and energetic particles through collision.


Film growth: the diffusion, migration and aggregation of target atoms on the substrate eventually lead to the growth of film. The properties of thin films are closely related to the temperature, lattice constants, surface states and electromagnetic fields of the substrates. The properties of the film will be seriously affected by the treatment of the film in the later stage, such as annealing. MC and other methods are generally used to simulate the growth of thin films. At the same time, some companies can achieve professional software membrane system design.


2.3 numerical simulation design


The process of sputtering deposition was reproduced by computer simulation, and the design results were displayed and analyzed to optimize the engineering and process design, as shown in figure 4.


Engineering design can achieve parametric design: the use of existing commercial software: Pro/E, UG, Ansys and other secondary development. Process design is to simulate sputtering process by designing or using existing software to analyze and optimize the process and analyze the influence of mechanical structure on the process.


The design process is developed into general design software to realize 3d modeling and mechanical comprehensive performance analysis of mechanical structure (part of engineering design), real-time simulation of process and analysis of electromagnetic field, thermal field and particle spatial distribution, as well as visualization of simulation process for optimization of process and mechanical structure. Able to exchange data with other software.


The further development is to transfer the whole design process from partial design to overall design to eliminate human factors to the greatest extent. Develop intelligent software system with expert system, parametric design, automatic control and remote operation.


The engineering design of the coating equipment, the design of the coating process and the computer numerical simulation of the two are complementary to each other: the coating equipment determines the realization of the coating process, the coating process promotes the upgrading of the coating equipment, and the high performance computer simulation design provides strong support for the design of the two.