Vapor Deposition Technology

       Vapor deposition technology is the use of physical and chemical processes in the gas phase to form functional or decorative metal, non-metal or compound coatings on the surface of workpieces. Vapor deposition technology can be divided into chemical vapor deposition, physical vapor deposition and plasma vapor deposition according to the film-forming mechanism.



At present, physical or chemical vapor deposition methods can be used to prepare tungsten coatings, or vapor deposition methods can be combined with other preparation techniques to improve the performance of tungsten coatings.



Chemical vapor deposition [CVD (Chemical Vapor Deposition)] refers to the process of introducing the vapor containing the gaseous reactant or liquid reactant and other gases required for the reaction into the reaction chamber, and a chemical reaction occurs on the surface of the substrate to form a thin film. . Many thin films in VLSI are prepared by CVD method.



CVD features: low deposition temperature, easy control of film composition, film thickness proportional to deposition time, good uniformity, repeatability, and excellent step coverage.



Chemical Vapor Deposition (CVD)



The workpiece is placed in the reaction chamber, evacuated and heated to 900~1100°C. If a TiC layer is to be coated, titanium is introduced into the reaction chamber together with volatile chlorides (such as TiCl4) and gaseous hydrocarbons (such as CH4), and then a chemical reaction occurs on the work surface to generate TiC, which is deposited on the A 6~8μm thick cover layer is formed on the surface of the workpiece. After the workpiece is plated by vapor deposition, quenched and tempered, the surface hardness can reach 2000~4000HV



Physical Vapor Deposition (PVD)



Physical vapor deposition is a process such as evaporation, ionization or sputtering, which produces metal particles and reacts with reactive gases to form compounds that are deposited on the surface of the workpiece. There are three kinds of physical vapor deposition methods: vacuum plating, vacuum sputtering and ion plating. At present, ion plating is widely used.



Ion plating is to make the plating material (such as metal titanium) vaporize, evaporate and ionize by means of inert gas glow discharge. The ions are accelerated by the electric field and bombard the surface of the workpiece with high energy. TiC and TiN coating layers can be obtained on the surface of the workpiece with a hardness of up to 2000HV. The important feature of ion plating is that the deposition temperature is only about 500 ℃, and the adhesion of the covering layer is strong, which is suitable for high-speed steel tools, hot forging dies, etc.



Detailed explanation of chemical vapor deposition



Chemical vapor deposition is a chemical technology, which mainly uses one or several gas-phase compounds or elemental substances containing thin film elements to perform chemical reactions on the surface of the substrate to form thin films. Chemical vapor deposition is a new technology for preparing inorganic materials developed in recent decades. Chemical vapor deposition has been widely used to purify substances, develop new crystals, and deposit various single crystal, polycrystalline or glassy inorganic thin film materials. These materials can be oxides, sulfides, nitrides, carbides, or binary or multi-element interelement compounds in III-V, II-IV, IV-VI groups, and their physical functions can be passed through the gas phase. The doping deposition process is precisely controlled. At present, chemical vapor deposition has become a new field of inorganic synthetic chemistry.



application

Modern science and technology require the use of a large number of new inorganic materials with different functions. These functional materials must be high-purity, or doped materials formed by intentionally incorporating certain impurities into high-purity materials. However, many preparation methods that we are familiar with in the past, such as high-temperature smelting, precipitation and crystallization in aqueous solution, are often difficult to meet these requirements, and it is difficult to ensure high-purity products. Therefore, the synthesis of new inorganic materials has become a major subject in modern materials science.



principle

Chemical vapor deposition technology is a process that uses gaseous substances to describe chemical reactions on solids and produce solid deposits. It roughly includes three steps:



(1) The formation of volatile substances;



(2) Transfer the above-mentioned substances to the deposition area;



(3) A chemical reaction occurs on a solid and a solid substance is produced.



The most basic chemical vapor deposition reactions include thermal decomposition reactions, chemical synthesis reactions, and chemical transport reactions.



Features

1) At medium or high temperature, a solid substance is formed and deposited on a substrate by a gas-phase chemical reaction between gaseous initial compounds.



2) It can be deposited under normal pressure or vacuum conditions (negative pressure ", usually the quality of the vacuum deposition film is better).



3) The use of plasma and laser-assisted techniques can significantly promote chemical reactions, enabling deposition to be performed at lower temperatures.



4) The chemical composition of the coating can be changed with the change of the gas phase composition, so as to obtain gradient deposits or obtain mixed coatings.



5) The density and purity of the coating can be controlled.



6) The plated parts are good. Coatings are possible on complex shaped substrates as well as on granular materials. Suitable for coating workpieces of various complex shapes. Because of its good wrapping performance, it can coat workpieces with grooves, grooves, holes, and even blind holes.



7) The deposited layer usually has a columnar crystal structure, which is not resistant to bending, but the chemical reaction can be perturbed in the gas phase by various techniques to improve its structure.



8) Various metal, alloy, ceramic and compound coatings can be formed through various reactions.



type of technology

The most important element of a chemical vapor deposition apparatus is the reactor. According to the difference in the reactor structure, we can divide the chemical vapor deposition technology into two types: open tube/closed tube gas flow method:



1 Sealing method



This reaction method is to place a certain amount of reactive substances and groups on both sides of the reactor, evacuate the reactor into a vacuum, inject part of the transport gas into it, and then seal it again, and then control the temperature at both ends of the reactor to make it There are certain differences. Its advantages are: ① It can effectively avoid external pollution; ② It can keep the interior vacuum without continuous pumping. Its disadvantages are: ① the material is produced slowly; ② the pressure in the tube is not easy to grasp.



2 open tube method



A feature of this preparation method is that the reactive gas mixture can be replenished at any time. The exhaust gas can also be discharged from the reaction device in time. According to the heating method, the open-tube airflow method should be divided into two types: hot wall and cold wall. The heating of the former will cause the entire deposition chamber wall to heat up, so deposition will also occur on the tube wall. In the latter, only the body itself will be heated, so there is no such disadvantage. Cold-wall heating generally uses induction heating, electrical heating, and infrared heating.



Chemical vapor deposition technique used in material preparation

1 Chemical vapor deposition method to produce crystal, crystal thin film



Chemical vapor deposition can not only help improve the properties of crystals or crystal thin films, but also produce some crystals that cannot be prepared by other means. The most common use of chemical vapor deposition is to create a new epitaxial single crystal layer on a crystalline substrate, initially for silicon and later for epitaxial compound semiconductor layers. It is also common in the preparation of metal single crystal thin films (such as the preparation of W, Mo, Pt, Ir, etc.) and individual compound single crystal thin films (such as nickel ferrite thin films, yttrium iron garnet thin films, cobalt ferrite thin films, etc. ).



2 Production of whiskers



Whiskers belong to a well-developed single crystal, which plays a very important role in the field of conforming materials and can be used to produce some new composite materials. Chemical vapor deposition uses the hydrogen-reducing properties of metal halides in the production of whiskers. Chemical vapor deposition can not only prepare various metal whiskers, but also produce compound whiskers, such as alumina, emery, titanium carbide whiskers and so on.



3 Chemical vapor deposition technology to produce polycrystalline/amorphous material films



Chemical vapor deposition is widely used in the semiconductor industry. For example, a polysilicon deposition layer as an edge dielectric isolation layer. In contemporary times, more and more new amorphous materials are used in miniature electronic components, such materials include phosphosilicate glass, borosilicate glass, SiO2 and Si3N4, etc. In addition, there are also some materials that may be developed into switches and storage memory materials in the future, such as copper oxide-phosphorus pentoxide, copper oxide-vanadium pentoxide-phosphorus pentoxide, and vanadium pentoxide-phosphorus pentoxide, etc. Produced using chemical vapor deposition.



Application of Chemical Vapor Deposition in Precious Metal Materials

1. Production of several precious metal thin films by chemical vapor deposition



Precious metal thin films have attracted the interest of researchers because of their good anti-oxidation ability, high electrical conductivity, strong catalytic activity, and extreme stability. Compared with other methods of producing precious metal thin films, chemical vapor deposition has more technical advantages, so most precious metal thin films are prepared by this method. There are a wide variety of depositors for depositing precious metal thin films, but most of them are halides and organic compounds of precious metal elements, such as COCl2, carbonyl platinum chloride, iridium carbonyl chloride, DCPD compounds, and so on.



The purpose of introducing oxygen into the device during deposition is to eliminate the carbon produced by the thermal decomposition of the raw materials, and to prepare a more metallic noble metal thin film. Otherwise, the final result is an iridium carbon cluster film, that is, a nano-scale crystallized film. Iridium particles encased in a carbon layer. The iridium-carbon cluster films deposited on YSZ have the best electrical properties and catalytic activity. At relatively low temperatures, the interfacial conductivity of the iridium-carbon cluster film can reach more than a hundred times that of pure iridium or pure platinum. The cluster membrane composed of noble metal and carbon is a kind of cluster membrane with strong transport porous catalytic activity, and its use in electrode materials will have great potential in the future.



2. Production of precious metal iridium high temperature coatings by chemical vapor deposition



Beginning in the 1980s, NASA began to try to use metal organic compound chemical vapor deposition to produce composite nozzles using rhenium-based iridium as a coating, and achieved success. At this time, chemical vapor deposition was only used in the production of precious metal coatings. a breakthrough to some extent.



NASA used C15H21IrO6 as the material for the preparation of iridium coatings, and used the thermal decomposition reaction of C15H21IrO6 for deposition. The deposition rate of iridium is very fast, up to 3~20μm/h. The deposition thickness also reached 50 μm, and the preparation efficiency of C15H21IrO6 was as high as 70%.



3. Chemical vapor deposition of palladium



Pd and its alloys have a strong adsorption effect on hydrogen and special selective permeation properties, and are ideal materials for storing or purifying hydrogen. Most of the current use of Pd is to produce hydrogen purification equipment from palladium alloys or palladium coatings. Some scholars also use chemical vapor deposition to make palladium into thin films or thin layers. The specific method is to use metal organic compounds with extremely low decomposition temperature as materials for the preparation of palladium, including: allyl [β-ketimine] Pd (II), Pd (η3-C3H5) (η5-C5H5) and Pd ( η3-C3H5) (CF3COCHCOCF3) and other materials, using this method can produce very high purity palladium films.



Chemical vapor deposition technology is an important material preparation method, which plays an important role in precious metal thin films and coatings. At present, my country is still in the development stage in the field of aerospace, and the use of chemical vapor deposition technology still has great exploration. space, we need to devote more energy to research.



Detailed explanation of physical vapor deposition



Physical vapor deposition (Physical Vapor Deposition, PVD) technology refers to the use of physical methods under vacuum conditions, the material source - solid or liquid surface is vaporized into gaseous atoms, molecules or partially ionized into ions, and passed through low-pressure gas (or plasma). ) process, a technique for depositing a thin film with a special function on the surface of the substrate. The main methods of physical vapor deposition are vacuum evaporation, sputtering coating, arc plasma coating, ion coating, and molecular beam epitaxy. Up to now, physical vapor deposition technology can not only deposit metal films, alloy films, but also compounds, ceramics, semiconductors, polymer films, etc.



Introduction

Physical vapor deposition technology has some applications as early as the early 20th century, but it has developed rapidly in the past 30 years and has become a new technology with the most broad application prospects, and it is developing towards the trend of environmental protection and cleanliness. Since the early 1990s, it has been widely used in the watch industry, especially the surface treatment of metal exterior parts of precious watches.



The basic principle of vacuum evaporation is to evaporate metals, metal alloys or compounds under vacuum conditions, and then deposit them on the surface of the substrate. The methods of evaporation are commonly used resistance heating, high-frequency induction heating, electron beam, laser beam, ion beam high-energy bombardment plating The material is evaporated into a gas phase and then deposited on the surface of the substrate. Historically, vacuum evaporation was the earliest technology used in the PVD method.



The basic principle of sputtering coating is to make argon gas glow discharge under vacuum conditions filled with argon (Ar) gas. At this time, argon (Ar) atoms are ionized into argon ions (Ar+), and argon ions are accelerated under the action of electric field force. Bombarding the cathode target made of plating, the target will be sputtered and deposited on the surface of the workpiece. If DC glow discharge is used, it is called direct current (Qc) sputtering, and radio frequency (RF) glow discharge is called radio frequency sputtering. Magnetron (M) glow discharge caused by magnetron sputtering. The basic principle of arc plasma coating is to use an arc ignition needle to strike the arc under vacuum conditions, so that arc discharge is carried out between the vacuum gold wall (anode) and the plating material (cathode), and the cathode surface moves rapidly with multiple cathode arc spots. Quickly evaporate or even "different" plating material, ionize it into arc plasma with plating material as the main component, and quickly deposit the plating material on the substrate. Because there are many arc spots, it is also called multi-arc evaporation ionization process.



The basic principle of ion plating is to use a certain plasma ionization technology under vacuum conditions to partially ionize the atoms of the plating material into ions, and at the same time generate many high-energy neutral atoms, which are negatively biased on the substrate to be plated. In this way, under the action of a deep negative bias, ions are deposited on the surface of the substrate to form a thin film.



The basic principle of physical vapor deposition technology can be divided into three process steps:



(1) Evaporation of the plating material: Even if the plating material is evaporated, sublimated or sputtered, that is, through the vaporization source of the plating material.



(2) Migration of the atoms, molecules or ions of the plating material: After the atoms, molecules or ions supplied by the gasification source are collided, various reactions occur.



(3) The atoms, molecules or ions of the plating material are deposited on the substrate.



The physical vapor deposition technology has a simple process, improved environment, no pollution, less consumables, uniform and dense film formation, and strong bonding force with the substrate. This technology is widely used in aerospace, electronics, optics, machinery, construction, light industry, metallurgy, materials and other fields. Films with properties such as superconductivity.



With the development of high technology and emerging industries, many new and advanced physical vapor deposition technology has appeared, such as multi-arc ion plating and magnetron sputtering compatible technology, large rectangular long arc target and sputtering target, unbalanced magnetron Sputtering target, twin target technology, strip foam multi-arc deposition winding coating technology, strip fiber fabric winding coating technology, etc., the coating equipment used is fully automatic and large-scale industrial scale.



Vacuum evaporation

(1) Principle of vacuum evaporation



(1) Vacuum evaporation is to heat and evaporate the plating material under vacuum conditions, so that a large number of atoms and molecules are vaporized and leave the liquid plating material or leave the surface of the solid plating material (sublimation).



(2) Gaseous atoms and molecules migrate to the matrix after few collisions in vacuum.



(3) The atoms and molecules of the plating material are deposited on the surface of the substrate to form a thin film.



(2) Evaporation source



The plating material is heated to the evaporation temperature and vaporized, this heating device is called