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一、 what kinds of coating technology can be distinguished into?
(1) vacuum evaporation (2) electroplating (3) chemical reaction (4) heat treatment (5) physical or mechanical treatment
二、 What are the types of vacuum pumps? What is the applicable exhaust range?
(1) mechanical pump (2) diffusion pump (3) turbo pump (4) adsorption pump (5) suction pump
Pumping and pumping limits:
Mechanical pump 10-1 ~ 10-4 mbar
Dispersion pump 10-3 ~ 10-6 mbar
Turbo pump 10-3 ~ 10-9 mbar
Suction pump 10-3 ~ 10-4 mbar
Suction pump 10-4 ~ 10-10 mbar
三.What are the applications of plasma technology in surface technology?
Sputtering deposition: sputtering is the use of high speed ions hitting solid target, causing the surface molecules to spatter and shoot into the substrate to be plated into a thin film. The initial kinetic energy of sputtering ions is about 100eV. The commonly used plasma gas is argon, which is of proper quality and has no chemical reaction.
(2)Plasmone-assisted deposition: chemical reactions in vapor deposition occur on a high-temperature substrate so that the gas precursors can react with sufficient energy.
(3)Plasma polymerization: the simplest coating technique for a polymer or plastic film is to put it in a solvent and then apply it to a substrate. The coating system of plasma polymerization excites monomer molecules into plasma, and after chemical reaction, a dense polymer is formed and coated on the substrate. As the substrate is hit by plasma, its adhesion is also very strong.
(4)Plasma etching: wet alkaline etching, which is the simplest and least expensive method, has the disadvantage that alkaline etching has the orientation of the crystal plane and can lead to erosion problems.
(5)Plasma coating: ceramic coating is required for metal components operating at high temperature to prevent corrosion at high temperature.
四.What are the heating methods of evaporation? What are their characteristics?
Heating methods are divided into :(1) resistance heating (2) induction heating (3) electron beam heating (4) laser heating (5) arc heating.
Each has its own characteristics:
(1)resistance heating: this is one of the simplest heating methods, with the advantages of cheap equipment and easy operation.
(2)induction heating: good heating efficiency, fast heating, and large capacity heating.
(3)Electron beam heating: this is done by focusing thousands of eV of high-energy electrons through a magnetic field and directly hitting the vaporizer. The temperature can reach up to 30000C. And its electron source has two: the hot electron that high temperature metal produces, another kind of electron source is hollow cathode discharge.
(4)Laser heating: the laser beam can be optically focused on the evaporation source, producing local instantaneous high temperature to make it escape. The first use was the pulsed red laser, and then the uv excimer laser was developed. The advantage of uv is that the energy per photon is much higher than that of infrared, so excimer lasers have a high power density that ACTS like electron beams to heat and evaporate. It is often used to coat complex compounds, and the coating quality is very good. It is fundamentally different from the process of electron beam heating or sputtering, in which excimer lasers break away from fine particles, which break away as molecules.
(5)Arc heating: advantages of cathode arc deposition:
a、Evaporation rate is fast, up to 1.0 micron per second
b、The substrate does not need to be heated
c、High temperature metal and ceramic compounds can be plated
d、Coating high density and good adhesion
五、What industries can vacuum evaporation be used in
The main industries are mostly used in decoration, optics, electrical, mechanical and corrosion prevention, etc., which are described as follows:
(1)anti-reflection coating of the lens (MgO, MgF2, SiO2, etc.), with the lens placed on the top of the hemispheric branch, can be plated over 100 pieces at a time.
(2)metal, alloy or compound coating, used for microelectronics as wires, resistors, photoelectric functions, etc. _
(3)electrode of aluminized or tantalum used as capacitor in insulation.
(4)MCrAlY coated with special alloy has heat resistance and oxidation resistance up to 1100OC, which can be applied to workpiece with high temperature resistance, such as high-speed cutting and forming, turbine engine blade, etc.
(5)gold plating belongs to glass panels for building decoration and uv protection.
(6)ion evaporation, which is applied at a negative high voltage to the plated part, is then heated and evaporated. The vapor is ionized by electron impact and then plated on the steel plate.
(7)aluminized in the film, for decoration or label, and the film has a metal sense. The biggest use is packing, can moistureproof, prevent the infiltration of air and so on.
(8)mechanical parts or knife grinding tools plated dura (TiC, TiN, Al2O3) these super hard film not only hardness is high, can effectively improve the wear resistance, and the required thickness is small, can meet the requirements of high precision workpiece.
(9)manufacture of special alloy sheet.
(10)multilayer coating on steel plate to improve its performance.
(11)silicon plating on CdS solar cells can increase their efficiency.
(12)manufacture of nano-powder, plated on a cold substrate so that it does not adhere.
六、What are the characteristics of TiN titanium nitride coating
It has the following advantages:
(1)resistance to wear
(2)with bright appearance
(3)safe for use in surgery and food utensils.
(4)with lubrication, can reduce friction.
(5)with anti-corrosion function
(6)can withstand high temperature
七、What are the five steps of CVD chemical vapor deposition?
(1)the prereactants in the gas phase of different components come in from the mainstream gas to transfer the substrate surface by diffusion mechanism. Ideally, the concentration of the precursors on the substrate would be zero, which means that they react immediately on the substrate, which is not the case.
(2)the pre-reactant is adsorbed on the substrate, and the pre-reactant is still allowed to conduct a limited degree of lateral surface movement on the substrate.
(3)the precursors undergo chemical reactions on the substrate to produce chemical molecules in the sediments, which then undergo the steps of accumulation, nucleation, migration, growth, and finally combine with a continuous membrane.
(4)adsorption of excess precursors and unnucleated gas products.
(5)the desorbed gas is transferred to the mainstream gas phase by the diffusion mechanism, and is then transported out.
八、What are the features of plasma - assisted VCD system?
Generally, CVD generates deposition reaction under a high-temperature substrate. If Plasma excites the gas, known as Plasma enhanced CVD(PECVD), the substrate temperature can be significantly reduced. However, generally thin layers of photoelectric coating or submicron lines are quite fragile and vulnerable to plasma ion impact, so PECVD is not appropriate.
九、What are the advantages and disadvantages of CVD process?
Advantages ：
(1)the vacuum requirement is not high, even without vacuum, such as hot spray.
(2)with a high deposition rate, APCVD can reach 1μm/min.
(3)compared with PVD, the coating of chemical components or alloys is easier to achieve.
(4)the coating has various components, including metal, nonmetal, oxide, nitride, carbide, semiconductor, photoelectric material, polymer and diamond film.
(5)can be in the complex shape of the substrate coating, and even infiltration of porous ceramics.
(6)the thickness uniformity is good, and LPCVD can even be plated with dozens of chips at the same time.
Disadvantages ：
(1)thermodynamics and chemical reaction mechanism are not easy or well understood.
(2)must be carried out in high temperature, some base material can not bear, and even coating effect.
(3)the reaction gas may be corrosive, toxic or explosive, so extra care should be taken.
(4) the reaction products may remain in the coating and become impurities.
(5) it is difficult to cover the base material.
十、What are the advantages of diamond materials? What industries can it be applied to?
Advantages: high hardness, high wear resistance, low thermal expansion rate, good heat dissipation ability, corrosion resistance and so on.
Applications: acoustic products, consumer products, biomedical products, optical products, super abrasives, aerospace products, diamond manufacturing, chemical products, electronic products, mechanical products.
十一、What methods can be used to obtain diamond film?
In recent years, membrane diamond synthesis technology has advanced by leaps and bounds. Diamond film thickness, from nanometer to mm. Thin films are often formed by physical vapor deposition. Thick films are usually obtained by chemical vapor deposition.
十二、Explain the properties of diamond film grown by PVD method.
When PVD deposits a diamond, except for a few atoms in the impact zone, the other carbon atoms are in a vacuum and at very low temperatures, so it is often considered a low pressure method. Because diamonds are in the medium stable state at low pressure, PVD method is classified as medium stable diamond growth method. But the pressure and temperature on the carbon atoms in the impact zone where diamonds grow are high. Because the area affected by high temperatures is limited, diamonds grow out of equilibrium. In this case, the atoms are not easy to diffuse, and the arrangement of the atoms producing the diamond is only short-range order, but the long-range arrangement contains a lot of defects and even a lot of impurities, so it is called drill-like carbon. Grow diamond or DLC by PVD method because the substrate temperature is very low, the growth rate is slow, usually only sink a thin layer. Because the film is thin, it can be attached to the surface of the complex workpiece. DLC film plating because the workpiece is not affected by high temperature, so the DLC PVD deposition is widely used, can be used for mold coating and hard disk protective film. To grow a thicker diamond film, the atoms must diffuse to a stable position in the crystal lattice, so the substrate temperature must rise, but not high enough to convert the resulting diamond into graphite.
十三、Explain the properties of CVD diamond films?
Methane with a diamond-like structure is often used as a carbon source for the smooth growth of CVD diamonds. Methane can be thought of as a single atomic diamond pressed by hydrogen. So cooking gas contains a lot of suspended single atom diamonds or DLC. When methane is broken down, if hydrogen atoms can be found nearby, the carbon can be deposited to maintain the structure of the diamond, and then bonded to the diamond film and converted into graphite.
十四、What is the importance of hydrogen and carbon concentrations in growing diamond films by CVD method?
The bottleneck for CVD to grow diamond films is to prevent hydrocarbons from forming graphite, so there should be much more hydrogen than carbon sources. The concentration of the carbon source determines the growth rate of the diamond film, but when the carbon source is too high, the hydrogen atoms have too little time to maintain the structure of the diamond to turn the carbon into graphite. So too much carbon lowers the rate of conversion to diamonds. The concentration and temperature of the carbon source determine the difference in the rate of growth of the diamond in each direction, and therefore the crystal shape of the diamond. The concentration of hydrogen atoms determines not only whether the film can grow, but also its mass. The rate of hydrogen production is less dependent on gas, but is directly related to temperature. As the temperature of the heat source decreases and the distance increases, the concentration of hydrogen atom decreases rapidly.
十五、What is chemical vapor vapor deposition (CVD)? What are the main advantages and disadvantages?
Chemical vapor evaporation USES one or more gases to react on a heated solid substrate and to coat it with a solid film.
Advantages:
(1)the vacuum is not required to be high, even without vacuum, such as hot spray
(2)the deposition rate is fast, and atmospheric CVD can reach 1μm/min
(3)compared with PVD. The composition of chemical quantities or alloy coating is easier to achieve
(4)the composition of the coating is diversified, such as metal, non-metal, semiconductor, photoelectric material, diamond film and so on
(5)can be in the complex shape of the substrate coating, and even infiltration of porous ceramics
(6) thickness uniformity is good, low - voltage CVD can even plating dozens of chips at the same time
Disadvantages:
(1)thermodynamics and chemical reaction mechanism are not easy or well understood
(2)need to be carried out at high temperature, some base material can not bear, and even coating effect
(3)the reaction gas may be corrosive, toxic or explosive, so care should be taken when handling
(4)the reaction products may remain on the coating and become impurities
(5)it is difficult to cover the base material
十六、What are the characteristics of a good film? What are the influencing factors?
The popular definition is that under normal conditions, its application function will not fail. To achieve this, the film must generally have strong adhesion, low internal stress, low pinhole density, strong enough mechanical properties, uniform film thickness, and sufficient chemical resistance. The characteristics of the film are mainly influenced by the deposition process, film forming conditions, interface layer formation and substrate, and the subsequent heat treatment also plays an important role.
十七、What are the sources of internal stresses in deposited films?
(1)lattice mismatch between thin film and substrate
(2)difference in thermal expansion coefficient between the film and the substrate
(3)intersqueezing between grain boundaries
十八、What are the essential properties of a thin film for good adhesion?
(1)there must be strong chemical bonds between the atoms in the interface layer, preferably the formation of compounds or chemical adsorption, which is not enough
(2)low residual stress, which may be due to the mismatch between the coating and the substrate lattice or thermal expansion coefficient, or the film itself has impurities or poor structure
(3)there is no surface structure that is easy to deform, such as fault structure. Mechanical rough surface can reduce the aggravation of the problem
(4)there is no long-term deterioration problem. The coating is exposed to the external environment such as the atmosphere. If there is no chemical reaction such as oxidation, the coating will naturally lose its function
十九、What are the measurement methods of film thickness?
It can be divided into two categories: in situ measurement and out of position measurement.
In-situ star measurement refers to medium measurement of coating, which is commonly used in physical vapor deposition, such as microbalance, optical, and resistance measurement.
Off-site measurement refers to the measurement after the completion of the coating, which is common for electroplating and has the purpose of understanding the plating efficiency, such as mass, profile meter and scanning electron microscope.
二十、What is physical evaporation? Describe the steps.
Physical evaporation is the evaporation of material by heat, and then the vapor deposited on a predetermined substrate. Because the evaporation source must heat volatilization, is in the vacuum, so also known as hot evaporation or vacuum evaporation.
It can be divided into three steps
(1)the condensed material is heated and evaporated into vapor phase
(2) the steam moves a distance to the substrate in a vacuum
(3)the steam is cooled on the substrate and condensed into a film
