Development and application of magnetron sputtering coating technology
In recent years, with the development of new materials, especially the development and application of thin film materials, the rapid development of sputter deposition technology has played an irreplaceable role in the field of scientific research and industrial production. This paper mainly introduces the process and development of sputter deposition coating technology, the characteristics of various major magnetron sputtering plating technology, and introduces the main application of magnetron sputtering technology in various fields.
The process of sputtering coating is mainly to make target materials into thin films, which are fixed on the cathode of the sputtering deposition system, and the substrate of thin films to be deposited is placed on the anode of the opposite target surface.The sputtering system is pumped to a high vacuum and filled with argon, etc. A high pressure is applied between cathode and anode, and a low pressure glow discharge is generated between anode and cathode.In the plasma generated by discharge, argon positive ions move towards the cathode under the action of electric field and collide with the target surface. The target atoms emitted from the target surface after being collided are called sputtering atoms. The energy of sputtering atoms is generally in the range of one to dozens of electron volts.Sputtering coating is to use argon positive ions generated by low pressure glow discharge to bombard cathode target at high speed under the action of electric field. Particles such as atoms or molecules in the target are sputtered and deposited on the surface of substrate or workpiece to form the required film layer.However, the sputter deposition process sputtering particles of very low energy, resulting in a low film rate.
Magnetron sputtering technology is to improve the film forming rate on the basis of sputtering coating, establishment and electric field perpendicular magnetic field in the surface of target, argon gas ionization rate a 0.5% increase from 0.3% to 5% 6%, so that it can solve the problem of sputtering coating deposition rate is low, one of the main methods are precise coating industry. Magnetron sputtering cathode materials can be prepared from a wide range of materials, all metals, alloys and ceramics can be prepared into targets. Magnetron sputtering coating is suitable for mass and high efficiency industrial production due to its rapid deposition rate and compact film and good adhesion to substrate under the effect of vertical magnetic field and electric field.
1. The process of magnetron sputtering
In the magnetron sputtering process, the specific process has a great impact on the film performance, and the main process is as follows:
(l) substrate cleaning, mainly by steam cleaning with isopropyl alcohol, followed by rapid drying after soaking the substrate with ethanol and acetone to remove oil on the surface;
(2) vacuum. The vacuum must be controlled above 2 * 10-4 Pa to ensure the purity of the film;
(3) heating, in order to remove the substrate surface moisture, improve the adhesion strength of the film and substrate, need to heating substrate, temperature usually choose between 150 ℃ ~ 150 ℃;
(4) argon partial pressure, generally within the range of 0.01 lPa, to meet the pressure condition of glow discharge;
(5) presputtering. Presputtering is to remove the oxide film on the surface of target material by ion bombardment so as not to affect the film quality.
(6) sputtering. The positive ions formed by argon ionized can, under the action of orthogonal magnetic field and electric field, bombard the target material at high speed, making the target particles emitted by sputtering reach the surface of the substrate and deposit into a film.
(7) during annealing, the thermal expansion coefficient of the film and the substrate is different, and the binding force is small. The mutual diffusion of the film and the substrate atoms during annealing can effectively improve the adhesion.
2. Development of magnetron sputtering coating technology
In recent years, the development of magnetron sputtering technology is very rapid. Typical methods include balanced magnetron sputtering, reactive magnetron sputtering, medium frequency magnetron sputtering and high-energy pulse magnetron sputtering.
Balanced magnetron sputtering: the most traditional magnetron sputtering technique involves placing a permanent magnet or an electromagnetic coil behind the target, which forms a magnetic field perpendicular to the direction of the electric field on the surface of the target. In argon gas ionization under high pressure into a plasma, Ar + ion by the electric field acceleration bombarding cathode material, secondary electrons are sputtering target material, and electron in the role of perpendicular electric field and magnetic field, bound at the cathode, near the surface of the target material increases the risk of collision between electron and gas, which increased the argon gas ionization rate, make the argon gas can also maintain the discharge under low gas, thus magnetron sputtering is both reduced the sputtering gas pressure, but also improve the efficiency of sputtering and deposition rate. However, there are some disadvantages of conventional magnetron sputtering. For example, both the electrons generated by low-pressure discharge and the second electrons emitted by sputtering target are bound to the area around the target surface of about 60 mm, so that the workpiece can only be placed within the range of 50 mm and 100 mm on the target surface. Such a small range of coating limits the size of the workpiece to be plated.
Reactive magnetron sputtering: with the development of surface engineering, various kinds of compound thin films are used more and more. Compound films can be prepared by sputtering on targets made of compound materials directly or by reactive gases when sputtering on metal or alloy targets. The latter is called reactive magnetron sputtering. In general, it is easier to obtain high quality compound films by using pure metal as the target and gas reactions.
Medium frequency magnetron sputtering: this coating method changes the magnetron sputtering power supply from conventional dc to medium frequency ac power supply.In the sputtering process, when the voltage applied by the system is in the negative half cycle of alternating current, the target material is bombarded and sputter by positive ions, while in the positive half cycle, the surface of the target material is bombarded and sputter by electrons in the plasma, and at the same time, the accumulated positive charges on the surface of the target material are neutralized and arc-striking phenomenon is suppressed.If the frequency of magnetron sputtering power source is usually between 10 and 80 kHz, the frequency is high, the acceleration time of positive ions is short, the energy is low when hitting the target, and the sputtering deposition rate drops accordingly.Medium frequency magnetron sputtering system generally has two targets, which take turns to be cathode and anode periodically.On the other hand, it also eliminates the arc-striking phenomenon.
High energy pulsed magnetron sputtering: for the first time since the Swedish scientists using high-energy pulse as magnetron sputtering power supply mode and the Cu thin film deposition, HPPMS since, with its high metal ionization rate increasing attention in recent years, high energy pulsed magnetron sputtering technology is the use of high pulse peak power and low pulse duty ratios produce high sputtering metal ionization rate of a magnetron sputtering technology, due to the short pulse duration, the average power is not high, this cathode not in overheating and increase the target cooling requirements.Its peak power is 100 times that of ordinary magnetron sputtering, which is about 1000-3000w /cm2. The plasma density can be as high as 1018m-3 order of magnitude. The ionization rate of sputtering material is very high, and the sputtering Cu target can be up to 70%.
3. Application of magnetron sputtering coating technology
Magnetron sputtering coating technology is mainly used for the deposition of metal or compound thin films of plastics, ceramics, glass, silicon and other products to obtain bright, beautiful and economical surface metallization products of plastics and ceramics. The film making technology of decoration, lamps, furniture, toys, arts and crafts, decoration and other living fields usually USES magnetron sputtering method, which is also applied in the industrial fields of military protective film, optical product, magnetic recording medium, circuit board, moisture-proof and permeable film, wear-resistant film, rust resistance and corrosion resistance.
Magnetron sputtering is not only applied in scientific research and industrial fields, but also extended to many daily supplies, mainly used in the preparation of difficult thin films by chemical vapor deposition. Magnetron sputtering technology has been used for many years in the preparation of electronic packaging and optical thin films, especially the advanced intermediate frequency non-equilibrium magnetron sputtering technology has also been applied in optical thin films and transparent conductive glass. Transparent conductive glass is widely used at present, such as TV computer panel display devices, electromagnetic microwave and radio frequency shielding devices and devices, solar cells and so on. In addition, the magnetron sputtering coating technology plays an important role in optical memory. Moreover, this technology is widely used in surface functional film, self-lubricating film, ultra-hard film and so on.
In addition to the fields mentioned above that have been widely used, magnetron sputtering coating technology also plays an important role in the research of high temperature, superconducting thin films, giant magnetoresistive thin films, ferroelectric thin films, luminescent thin films, shape memory alloy thin films and solar cells.
Magnetron sputtering coating technology has become one of the main techniques for preparing thin films due to its remarkable advantages. The non-equilibrium magnetron sputtering improves the distribution of plasma and the quality of film. The development of medium frequency sputtering coating technology has effectively overcome the arc-striking phenomenon in the reactive sputtering process, reduced the structural defects of the film and significantly increased the deposition rate of the film. High - speed sputtering and high - energy pulsed magnetron sputtering technology open up a new research field for sputtering films. In future studies, new sputtering technology to promote in the field of life, the combination of magnetron sputtering deposition technology and the computer will become a hot research topic, using the computer simulation of the coating when the magnetic field, electric field, temperature field, and the distribution of the plasma, will offer sputtering coating technology for the development of the expansion of the huge space, promote the magnetron sputtering coating technology to the transformation of industrial and living fields.