Study on the uniformity of TiN deposited on stainless steel plate by multi-arc ion plating
Multi-arc ion plating is a coating process developed for good diffraction, which can be used to prepare metal films, alloy films, compound films and multilayer structure films. Due to its high metal ionization rate and high ion energy, this technology can improve the coating uniformity and adhesion, and has become the best technology for deposition of TiN decorative film.
Multi arc ion plating deposition TiN, the essence of which is introduced in the process of general multi arc ion plating chemical process, which at the same time of evaporation of titanium import can react with titanium nitrogen, with the evaporation of titanium mixed into plasma, under low temperature was biochemistry reaction, sediments formed in the substrate compounds.
Although multi-arc ion plating has good diffraction property and can be used for all kinds of decorations, it is not easy to obtain uniform TiN coating on the large area of stainless steel substrate for architectural decoration.
1. Proposing problems
In order to obtain satisfactory uniformity, the transverse width of the target is required to be larger than the width of the substrate, and the target is a continuous whole in the width direction of the substrate. And many arc ion equipment each arc is discontinuous on the space between the arc and arc has a certain distance, if improper adjustment hardware part of the equipment, or improper selection process parameters of the equipment software, it is possible to make the substrate in the opposite the arc part and a larger part of the color difference between arc and arc, arc is opposite the deep part of the color (or light), between the arc and arc section color shallow or deep, curving stripes depth, commonly known as the "zebra", make the product of the decorative decline, even become defective.
The problem of uniformity of ion-plated stainless steel plates is discussed in this paper
2. Influencing factors of hardware
2.1 the distance between arcs and substrates
The distance between arc and substrate has great influence on the uniformity of ion plating coating. The arc base distance is too small, the number of particle collisions before reaching the substrate is too small, the scattering effect is weakened, and the coating uniformity decreases. Arc base distance is too large, not only a waste of space, increase unnecessary exhaust time, but also make the particles reach the substrate when the energy is too small, coating firmness and decline. Theoretical and experimental results show that the desired film thickness uniformity can be achieved when the arc base distance is above 200mm.
2.2 magnetic field strength
Magnetic field strength and the coating evenly relationship closely, it is well known that the magnetic field in the arc source system can improve the performance of the electric arc source, make the arc plasma accelerated motion, increase the number of the cathode emission electrons and ions, increase the density of the beams and directionality, reduce the content of micro drip, but the strength of the magnetic field to moderate, too much can make particles concentration, the uniformity of coating fall; Too weak and easy to cause arc extinguishing, can not reach the role of stable arc.
Experiments show that the maximum horizontal component of the source material on the surface of magnetic field strength in the 20 ~ 35 gs is the best, before using all arc source material on the surface of the magnetic field strength needed to use gauss meter unified adjustment, as the source of material consumption, the source of material surface due to the distance from the magnet smaller and make the magnetic field strength increase, so it is necessary to adjust its periodically according to the source of material consumption on the surface of the magnetic field intensity, the surface morphology defects serious source of material to be reprocessed.
3. Software influencing factors
3.1 gas pressure
In the process of ion plating, the gas pressure has a great influence on the uniformity of the coating. Generally speaking, the higher the gas pressure is, the better the ion diffraction is and the better the uniformity of the coating is. However, excessive pressure will also reduce the energy carried by particles when they reach the substrate and affect the adhesion strength of the coating. Experiments show that the optimum partial pressure of nitrogen is 3.0*10-1~1Pa for the deposition of TiN on a large area of stainless steel substrate by ion plating.
3.2 substrate bias
In setting negative substrate bias can improve the speed of the incident particles, substrate to obtain larger energy, thereby increasing the adhesion strength between coating and substrate, but excessive bias would make the particles to scattering is attracted to the substrate, the uniformity of coating, ion plating deposition of TiN film bias between 50 ~ 100 v is better.
3.3 the magnitude of arc current
The arc current reflects the evaporation rate of the film. Experiments show that when the arc current increases when the coating uniformity will decline, this is because of scattering particle deposition on the substrate, and deposition in facing because of the increased incidence of arc source, however, from improving production efficiency, hope that the greater the arc current, the better, this requires us to make the compromise choice, in addition to the source material area of different devices, the choice of parameters will be different, for the source material of a diameter of 65 mm arc, arc current should be between 50 ~ 100 a.
3.4 substrate temperature
Substrate temperature on the effect of ion plating coating uniformity, main is to remove the vacuum indoor moisture and improve coating adhesion, vacuum indoor moisture is prompted a zebra coating of a very important reason, especially for the layers with water-cooled vacuum chamber equipment, summer air humidity is bigger, pressure in the vacuum freezing indoor wall condensation water easily, this is the main cause of water, in addition, after cleaning the substrate drying incomplete will also bring moisture into the vacuum chamber, water heated to steam, on the one hand, easy to cause the discharge of substrate in vacuum chamber body, Burns substrate surface (on the other hand, under the action of electric arc, decompose the oxygen, nitrogen and oxygen react with titanium faster, it will inevitably cause the change of the coating composition, resulting in uneven coating color, the substrate temperature should be between 120 ℃ ~ 200 ℃, because temperature is too high may cause difficulties for loading and unloading of substrate, reduce the production efficiency, on the other hand, when damage to the vacuum close vacuum chamber of the cooling water and keep the indoor temperature, vacuum in the very great degree can improve this state.
In order to obtain uniform ion plating coating adhesion good N, adjust device about the hardware part and the alternative process parameters of the equipment software is very important, for different structure of the equipment, various factors must be taken into account comprehensively, a unified regulation of various process parameters, find the corresponding to the optimum process conditions of the specific equipment.
In addition, the workpiece before plating cleaning and reaction gas purity on the coating uniformity also has a greater impact, because these two aspects can generally cause enough attention, and get a good cleaning effect (using ultrasonic cleaning equipment) and high purity nitrogen is relatively easy, so not in the scope of this paper.
In the end, the typical process parameters of TiN coating deposited on 3000mm*1000mm stainless steel plate by multi-arc ion plating equipment with diameter of 1500mm and length of 3500mm and 24 arc sources are given for discussion by colleagues.
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