Pros & Cons of 4 Film Manufacturing Methods

The properties of the thin film are determined by the manufacturing method, and different methods have their own advantages and disadvantages. Commonly used preparation processes include magnetron sputtering, chemical vapor deposition, vacuum evaporation, pulsed laser deposition, etc. Among them, magnetron sputtering deposition technology has been widely researched and applied due to its high film formation rate and good uniformity.


Magnetron Sputtering

The basic principle of the method is that under the action of electric and magnetic fields, the accelerated high-energy particles (A, +) bombard the surface of the target, and after the energy is exchanged, the atoms on the surface of the target escape from the original lattice, and finally, the sputtering particles are deposited on the surface of the substrate and react with oxygen atoms to form an oxide film. The magnetron sputtering process is characterized by excellent optical and electrical properties of the film deposited at low temperatures. In addition, it has the advantages of a high deposition rate, low substrate temperature, good film adhesion, easy to control, and large-area film formation. Therefore, it has become the most researched and widely used film-forming technology in industrial production today as well as a research hotspot in ITO film preparation technology.

Chemical Vapor Deposition

The chemical vapor deposition method is a process in which a gaseous reactant (including a gaseous reactant that becomes a vaporized condensed matter after evaporation) is chemically reacted on the surface of the substrate to deposit a film. This chemical reaction occurring on the surface of the substrate is usually the thermal decomposition and in-situ oxidation of the source material. The reaction system selected by the CVD method must satisfy:

(1) At the deposition temperature, the reactant must have a sufficiently high vapor pressure;
(2) The chemical reaction product must be in a gaseous state except for the solid matter deposited on the substrate;
(3) The vapor pressure of the deposit should be low enough to ensure good adsorption on a substrate having a certain temperature.

Vacuum Evaporation

The vacuum evaporation method is a method in which a raw material of a to-be-formed film in an evaporation vessel is vaporized from a surface to form a vapor stream, and is incident on a surface of the substrate to react with a gas to form a film in a vacuum chamber. A high-quality ITO film can be prepared by the electron beam evaporation deposition method, in which the evaporation substance is In2Odoped with SnO2, and the mass percentage of SnO2 is 10%. Under suitable process conditions, the deposited film has a minimum resistivity of 4×10-4 Ω•cm and an average transmittance in the visible range of more than 90%.

Pulsed Laser Deposition

The pulsed laser deposition (PLD) process is a very competitive new vacuum physical deposition process developed in recent years. Compared with other processes, it has the advantages of precise control of stoichiometry, synthesis, and deposition, and no requirement for the shape and surface quality of the target, so the surface of the solid material can be processed without affecting the material body.

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Introduction to the Process and Steps of Evaporation Coating

The basic process flow for evaporation coating is:

Preparation before coating→ vacuum→ ion bombardment→ baking→ premelting→ evaporation→ removing parts→ film surface treatment→ finished product

1. Preparation before coating

The process includes vacuum chamber coating part cleaning, evaporation source making and cleaning, installation of evaporation source and evaporation materials.

The amount of bonding between the film layer and the surface of substrate is an important indicator of product quality. It is determined by many factors, and the surface treatment before coating is one of the most basic factors. If there is grease on the surface of the coating part, adsorbing water, dust, etc., it will reduce the bonding force of the film layer and affect the surface roughness. Cleaning is generally done by several methods: chemical degreasing, electrostatic dedusting and primer application.

According to the requirements of the product and the material of the coating parts, selecting the appropriate evaporation material is the basic condition for obtaining a high-quality film layer. For different evaporation materials, the corresponding evaporation source and the evaporation method should be selected.

The basic principle of selecting metal evaporation materials is: good thermal stability and chemical stability, high mechanical strength, low internal stress, and certain toughness, good bonding with primer, high reflectivity, and small gas release in vacuum; the material source is wide, the price is low, and it has a corresponding evaporation source.

2. Vacuum step

Open the cooling water valve, adjust to the required water pressure, turn on the main power supply, close the atmospheric valve leading to the vacuum chamber, close the pipeline valve, start the mechanical pump power supply, and open the pre-vacuum valve; At this time, the vacuum chamber is evacuated using a diffusion pump or a mechanical pump, and baking, pre-melting, and evaporation are performed when the degree of vacuum reaches a certain value.

3. Ion bombardment

In the glow discharge, the ion bombardment electrons obtain a high speed, and the negative charge is rapidly generated around the substrate due to the large mobility of the electron. Under the action of the negative charge attraction, the positive ion bombards the surface of the coating part, and the substrate. There is energy exchange on the surface, and a chemical reaction occurs between the adsorption layer of the coating member and the active gas to achieve the effect of cleaning the surface.
The conditions of ion bombardment are that the residual gas pressure is stable at 0.13~13Pa, the voltage is 1.5~10kV, and the time is 5~60min.

4. Baking

It can accelerate the rapid escape of the gas adsorbed by the coating parts or the clamp, which is beneficial to improve the vacuum degree and the film bonding force. When baking, it should be noted that the non-metal baking temperature is lower than the hot deformation temperature of the coating part by 20~30 °C, and the metal baking is generally not more than 200 °C.

5. Pre-melting

This step can remove the low melting point impurities in the evaporation material and the gas adsorbed in the evaporation source and the evaporation material, which is favorable for the smooth progress of evaporation. The pre-melted vacuum is generally 6.6 x 10-3 Pa. For materials with high hygroscopicity, it should be pre-melted repeatedly. The overall requirement is that the vacuum does not drop as the evaporating material warms to the evaporating temperature.

6. Evaporation

Evaporation technology has a great impact on film quality. There are different requirements for general metals, special metals and compound evaporating pellets. For example, some metal particles need to be evaporated quickly, while others are not suitable. The heating method and the shape of the evaporation source should also be different depending on the evaporation material.

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Differences between vacuum evaporation and sputter coating

It is well known that vacuum coating has two common methods: vacuum evaporation and sputter coating. However, many people have doubts about the difference between evaporation and sputter coating. Let SAM Sputter Targets answer it for you.

sputter coating3First, let’s take a look at the definition of these two words. The vacuum evaporation is carried out by means of resistance heating, electron beam or laser bombardment in an environment with a vacuum of not less than 10-2 Pa, and the evaporation material is heated to a certain temperature to evaporate or sublimate a large number of molecules or atoms, and then directly deposited on a substrate to form a film. Continue reading “Differences between vacuum evaporation and sputter coating”

Five evaporation sources for heating

The evaporation source is a heating element used to vaporize  the molding material. The evaporation sources currently used mainly include the following types:

Resistance evaporation heating source

The resistance heating method is simple and easy to operate, and is a common application method: a filament-like or sheet-like high melting point metal (such as Tungsten, Molybdenum, Titanium, etc.) is made into an evaporation source of a suitable shape. It is equipped with an evaporation material to turn on the power supply, and the evaporation material is directly heated and evaporated. The resistance heating method should mainly consider two problems, the melting point and vapor pressure of the evaporation material; the reaction of the evaporation material with the coating material and the wettability caused by the coating material.

Electron beam evaporation source

The evaporation material is placed in a water-cooled copper dry pot and directly heated by an electron beam, which is called electron beam heating. It can vaporize the evaporation material and form a film on the surface of the substrate. It is an important heating method and development direction in the vacuum evaporation coating technology. In the resistance heating method, the coating material and the evaporation material are in direct contact, and the temperature of the evaporation material is higher than that of the coating material, and is easily mixed into the coating material, especially in the semiconductor device coating. Electron beam evaporation can overcome many shortcomings of general resistance heating evaporation, and is particularly suitable for preparing high melting point film materials and high purity film materials.

High frequency induction heating evaporation source

The high-frequency induction heating evaporation source places the graphite or quartz crucible containing the evaporation material in the center of the water-cooled high-frequency spiral coil, so that the evaporation material generates strong eddy current loss and hysteresis loss under the induction of the magnetic field in the high frequency band (to Ferromagnetic), causing the evaporating material to heat up until evaporation. The smaller the volume of the evaporated material is, the higher the frequency of induction is. In the large-scale vacuum aluminum plating equipment on the steel strip, the high-frequency induction heating evaporation process has achieved great success.

Radiant heating evaporation source

For materials with high absorption of infrared radiation, it can be evaporated by radiant heating, and many substances are evaporated by this method. In addition, the reflectivity of the metal for infrared radiation is high, and the absorption rate of quartz for infrared radiation is low, so they are difficult to be evaporated by radiation heating. The main advantage of the radiant heating method is that the evaporation is only heated on the surface, and the adsorbed gas is released on the surface without splashing the material.

Laser beam evaporation source

The evaporation technique using a laser beam evaporation source is an ideal film preparation method because the laser can be installed outside the vacuum chamber. This not only simplifies the space arrangement inside the vacuum chamber and reduces the abandonment of the heating source, but also completely avoids the contamination of the evaporation material by the evaporator, thus it is advantageous for obtaining a high-purity film.


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