Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) are thin film formation techniques. That is to say, the crystal structure of the thin film can be adjusted according to the synthetic parameters, it can be used in a variety of applications according to the type of synthetic coating, such as anti-wear and corrosion at high temperatures, smooth surface treatment to reduce friction. and prevent corrosion from harsh chemicals, etc.
1. Chemical Vapor Deposition (CVD) CVD is a type of thin film coating technique widely used in the semiconductor microelectronics industry. and micromechanical and electromechanical
quipment Microelectromechanical system (MEMS) required. Figure 1 shows an example of an integrated circuit (IC) chip.that consists of several layers of material and each The layer is thick in micrometers.
Figure. 1 Integrated circuit chip a) Appearance[Source:Inductiveload/Wikimedia Commons]
b) The internal elements consist of a layer of insulating semiconductor and metal.
[Source: Cepheiden/Wikimedia Commons/CC-BY-2.5]
In addition to using CVD techniques in electronic work also used to create a coating Hardened on machined parts and dies to reduce wear and prolong the life of those parts with chemical vapor deposition (CVD). The coating is in the solid state from the vaporized reactants.
The resulting coating is a result of the direct interaction between the initial chemical vapor and the surface to be coated. Or it could be a reaction between more than one chemical vapor above the surface to form a coating on the desired surface.
It requires a good understanding of chemical reaction design. In general, the CVD coating process starts from the Workpieces to be coated are placed in a closed cabinet to prevent chemical vapor leaks and reduce contamination from outside air, then pump out the air inside the cabinet.
The chemical vapor is then supplied into the coating cabinet to the required pressure while at the same time heating the inside of the coating cabinet to an appropriate level. The coating synthesis chemical reaction Figure 2 shows a simplified schematic of a thermal CVD system. This is because the chemical vapors used will diffuse and fill the gaps in the coating cabinet.
Figure. 2 A simple schematic diagram of a CVD system using heat.
CVD coatings are the hallmark of CVD coatings and have made this technique the preferred choice for thin film coatings on complex shapes. However, the coating CVD Disadvantages that the chemical vapors used are often dangerous and toxic.
The resulting coating may contain adulteration and most of the chemical reactions require relatively high heat
(700-1100℃). CVD coating technique can be done at low temperature. down to prevent damage to the workpiece from heat used in the process. and experimenting with new starting chemicals.
In order to obtain a coating with more demanding properties, CVD coating technology can generally be divided into two main categories. according to the energy source used in the The chemical reaction is thermal CVD coating and plasma-based CVD coating.
1.1 Thermal CVD processes There are two main types of CVD coating processes that use heat energy to cause chemical reactions to synthesize coatings according to the vapor pressure used in the cabinet. Coatings include Atmospheric-Pressure CVD (APCVD) and low-pressure chemical vapor deposition. (Low-Pressure CVD; LPCVD)
1.1.1 Chemical vapor deposition at atmospheric pressure (Atmospheric-Pressure CVD; APCVD): This is the most basic CVD coating. There are both high temperature (700-1200℃) and low temperature (500-700℃) versions. determined by the reactant chemical reaction
1.1.2 Chemical vapor deposition at low pressure (Low-Pressure CVD: LPCVD): It is a coating technique that Developed from APCVD coating, with the key strengths being A large number of workpieces can be coated at a time compared to APCVD cabinets of the same size, i.e. At 0.1-1 Pa pressure commonly used in LPCVD (about 103-106 times less than APCVD).
The chemical vapor diffuses to the workpiece surface more quickly, resulting in the coating synthesis process being controlled by surface chemical reactions rather than the diffusion of chemical vapor onto the surface, so that the dense workpiece placement in the coating cabinet does not affect the The consistency of the coating is very good.
Figure 3 shows a polycrystalline silicon coating covering the workpiece surface thoroughly. even in the grooved area The trench width is only 3-4 µm and the depth is about 10 µm. The thickness of the coating on the three walls. of the groove is uniform However, because the pressure used in the laminator is much lower than that of the APCVD system.
Therefore, the reactant should be selected with the concentration of the reactant. The reaction is higher to keep the coating rate at a competitive level. including the need for a pump High efficiency air to keep the pressure inside the cabinet low.
Figure. 3 A polycrystalline silicon coating applied on a silicon substrate by LPCVD technique.
[Source: Thai Microelectronics Center: TMEC]]
2. Physical Vapor Deposition (PVD)
PVD is a thin film-making technique that uses physical mechanisms such as sputtering and evaporation to vaporize reactants, then vapor (which can be atoms or ions). that happens to fall the coating on chopped straight or workpiece
PVD techniques are now widely used in industries such as the glass coating industry. automotive industry and electronics industry Because it has the advantage that the coating process uses low heat. use non-toxic gas and not complicated
Figure. 4 Physical vapor thin film formation process diagram.
Methods for physical vaporization can be divided into two main groups:
2.1 Sputtering PVD method is a process that The sputtering target atoms are released, causing the inert gas2 to enter the substrate surface to form a plasma state3. and the inert gas ions that occur will continually collide with the surface of the reactant to release the reactant vapor. and move to line up at the surface of the substratum (Figure 5).
Figure. 5 PVD Magnetron Sputtering Thin Film Coating Process
2.2 Evaporative PVD method is a process that allow the reactants to evaporate to vapor by heating the reactants by means of various such as using electricity, using electron beam (E-Beam) and cathodic arc (cathodic arc), etc.
The vapors of the reactants will diffuse and hit the substrate and condense. The mask is a coating similar to the sputtering method.
The reactant vapor produced by the sputtering process has a much higher energy than volatilization and therefore is well embedded in the meat.
Therefore, the adhesion of thin films by sputtering method is much better than evaporation method if the bonding force of thin film to the substrate is low. This allows the thin film to come off easily. The PVD technique has several methods for vaporizing the reactants.
Each system has different advantages and disadvantages, so it must be selected to be suitable for PVD thin film coating applications. can In the coating process, heat may or may not be used.
In the absence of heat, heat sensitive workpieces can be coated. The resulting coating looks like a thin film. There is a thickness in micrometers made. The size of the workpiece after coating does not change from the original and the important thing is environmentally friendly because in a vacuum system and without chemicals
Applications PVD thin film coating can be used to coat a wide range of industrial materials such as
1. Mechanical equipment such as drill bits, milling cutters, and turning blades when coated with hard materials. And high temperature resistance will help extend the service life 3-8 times. The thin film types used are TiC, TiN, CrC, TiAlN, AlTiN and AlCrN, etc.
2. Molds such as metal forming molds plastic mold Even for aluminum injection molds, the thin film surface acts to prevent abrasive wear and bonding of the metal to the mold, thereby reducing waste, prolonging mold life and reducing production time. The thin film types used are TiAlN, TiCrN and AlTiCrN, among others.
3. Jewelry, such as jewelry that needs to be beautiful in different colors, such as straps and watch cases, frames, glasses, earrings and necklaces, etc. The film will make the surface of the jewelry beautiful and resistant to scratches. The thin film types used are TiN, ZrN, TaN and HfN, among others.
4. Equipment related to optical properties, such as coating lenses for eyeglasses anti-reflective coating heat-resistant glass coating, various light filter coatings, etc. PVD thin film coating, in this case it is a coating. Some are multilayered to allow light to pass through or reflect light in a given wavelength range. The thin film types used are SiO2, MgF2, ZrO2, TiO2 and Ta2O5, etc.
5. such as the resistive film coating magnetic film capacitor which the latter example is used in memory device or photoconductor coating (photoconductor), etc. Devices related to electrical properties PVD thin film coatings can be used to solve tribology problems 5. born in the industry Other high-stress tools and components, such as the automotive or aerospace industries, need It is necessary to develop materials A new thin film that can be used in many fields.
To enhance mechanical and chemical Summary Chemical vapor deposition (CVD) and physical vapor deposition (PVD) play a role in many industries. to extend the service life of mechanical parts for production be beautiful to the jewelry surface add optical and electrical properties to the surface properties and performance and applications.
Used in the forming of mechanical and electrical equipment. With the strengths of these two technologies being able to create extremely thin films, it responds to the growth in nanotechnology. very well
Summarize CVD coating provides a uniform coating layer. Always and evenly covered on complex shaped workpieces but in processes often use high temperatures. including related chemicals are dangerous while PVD is suitable for less complex parts. Do not use dangerous chemicals