Name: Suzhou cycas Microelectronics Co., Ltd.
Address: 1st floor,B06 building,No.2,Fuxing Road,Zhangjiagang Economic Development Zone,Jiangsu Province 215600PRC
The direct current sputtering method requires that the target can transfer the positive charge from the ion bombardment process to the cathode in close contact with it, so this method can only sputtering the conductor material, which is not suitable for the insulating material, because the ion charge on the surface of the insulating target can not be neutralized when bombarding, which will lead to the potential rise of the target surface, and the applied voltage is almost added to the target, and the ion acceleration and ionization between the two poles The chance will be smaller, even can not ionize, resulting in not continuous discharge or even discharge stop, sputtering stop. Therefore, RF sputtering should be used for insulating target or non-metallic target with poor conductivity.
The sputtering process involves complex scattering process and many kinds of energy transfer processes. Firstly, the incident particles collide with the target atoms elastically, and part of the kinetic energy of the incident particles will be transmitted to the target atoms. The kinetic energy of some target atoms exceeds the potential barrier (5-10ev for metals) formed by other atoms around them, so they are collided out of the lattice lattice and generate dislocations Atoms, and further and adjacent atoms in turn repeatedly collide, resulting in a collision cascade. When the collision cascade reaches the target surface, if the kinetic energy of the atoms near the target surface is greater than the surface binding energy (1-6ev for metals), these atoms will separate from the target surface and enter the vacuum.
Sputtering coating is a technology that bombards the target surface with charged particles in vacuum to deposit the bombarded particles on the substrate. Usually, the incident ions are produced by glow discharge of low pressure inert gas. The cathode target is made of coating material, the substrate is used as anode, argon or other inert gas of 0.1-10Pa is introduced into the vacuum chamber, and glow discharge is produced under the action of 1-3KV DC negative high voltage or 13.56MHz RF voltage of the cathode (target). The ionized argon ions bombard the target surface, making the target atoms splash and deposit on the substrate, forming a thin film. There are many sputtering methods, including secondary sputtering, tertiary or quaternary sputtering, magnetron sputtering, target sputtering, RF sputtering, bias sputtering, asymmetric AC RF sputtering, ion beam sputtering and reactive sputtering.
Because the sputtered atoms are splashed out after exchanging kinetic energy with positive ions with tens of electron volts energy, the sputtered atoms have high energy, which is conducive to improving the diffusion ability of atoms during deposition, improving the density of deposited structure, and making the film and substrate have strong adhesion.
During sputtering, after the gas is ionized, the gas ions fly to the cathode target under the action of electric field, and the electrons fly to the grounded wall cavity and substrate. In this way, under low voltage and low pressure, the number of ions produced is small, and the sputtering efficiency of the target is low; while under high voltage and high pressure, although more ions can be produced, the high energy carried by the electrons flying to the substrate is easy to heat the substrate or even cause secondary sputtering, which affects the film quality. In addition, the collision probability between the target atoms and the gas molecules increases greatly in the process of flying to the substrate, so it will be scattered to the whole cavity, which will not only cause the target waste, but also cause the pollution of each layer in the preparation of multilayer.
In order to solve the defects of cathode sputtering, DC magnetron sputtering technology was developed in 1970s. It effectively overcomes the weaknesses of low cathode sputtering rate and high substrate temperature caused by electrons, so it has been rapidly developed and widely used.
The principle is as follows: in magnetron sputtering stage, due to the Lorentz force on the moving electrons in the magnetic field, their motion path will be bent or even spiral, and their motion path will become longer, so the number of collisions with the working gas molecules will be increased, the plasma density will be increased, and the magnetron sputtering rate will be greatly improved On the other hand, it also improves the energy of the atoms incident on the substrate surface, so it can improve the quality of the film to a great extent. At the same time, the electrons that lost energy after many collisions have become low energy electrons when they reach the anode, so that the substrate will not overheat. Therefore, magnetron sputtering has the advantages of "high speed" and "low temperature". The disadvantage of this method is that the insulator film can not be prepared, and the inhomogeneous magnetic field used in the magnetic control electrode will cause significant inhomogeneous etching of the target, resulting in low utilization rate of the target, generally only 20% - 30%.