Comparison Of PVD Deposition Methods

PVD (Physical VaporDeposition) is a technique for depositing thin films with a particular function on the surface of a substrate by physically vaporising the surface of the material source into atoms, molecules or ions under vacuum conditions. PVD coating is divided into three main categories: vapour deposition, sputtering and ion deposition.

Vacuum vapour deposition: a technique in which the plating material is heated to evaporate or sublimate under vacuum conditions and the atoms or molecules of the material form a film directly on the substrate. Several common vacuum vapour deposition techniques are described below. 

1. Resistance evaporation

Using resistance heating evaporation source evaporation coating technology, generally used to evaporate low melting point materials, such as aluminum, gold, silver, zinc sulfide, magnesium fluoride, chromium trioxide, etc.; heating resistance is generally used tungsten, molybdenum, tantalum, etc.

2. Electron beam evaporation

The use of high-speed electron beam heating to vaporize the material evaporation, in the substrate surface condensation into a film of technology. The energy density of the electron beam heat source can reach 104-109w/cm2 and can reach more than 3000℃. Electron beam heating evaporation source has straight gun type electron gun and e type electron gun two kinds (also have ring row), electron beam from the source issued, with magnetic field coil to make electron beam focus and deflection, to film material bombardment and heating.

3. Laser evaporation

The use of high-energy laser beam to evaporate the material to form a thin film method, generally known as laser vapour deposition.

4. Induction heating evaporation

The use of high frequency electromagnetic field induction heating, so that the material vaporisation evaporates on the surface of the substrate to condense into a film technology.

Sputter coating: A technique in which high-energy particles bombard the surface of a material in a vacuum, causing its atoms to gain enough energy to escape the surface and reach the substrate to condense into a film.

Compared to true hair coating, sputter coating is suitable for all (including high melting point) materials and has the advantages of strong adhesion, controlled composition and easy production on a large scale.

1. Dipole sputtering

Sputter coating technology in which a high DC voltage is added between the target and the substrate, the gas between the poles (typically Ar2) is ionised and high-speed charged ions bombard the surface of the target. To maintain a self-sustaining discharge, the discharge pressure is typically as high as 10 Pa at a normal sputtering spacing of several centimetres between the two pole plates, which is detrimental to both sputtering efficiency and film quality. Therefore, DC sputtering mostly uses non-self-sustaining discharge, that is, the addition of hot electron emitter and auxiliary anode quadrupole sputtering, which can make sputtering at a low air pressure of 10-1 to 10-2 Pa.

2. RF sputtering

Using RF power supply instead of DC power supply, high frequency voltage is applied between the target and the substrate, when sputtering, the target will produce self-biasing effect (i.e. the target will automatically be in a negative potential state), so that the sputtering of the insulated target is maintained. The commonly used frequency is approximately 13.56 MHz.

3. Magnetron sputtering

The working principle of magnetron sputtering refers to the collision of electrons with argon atoms in the process of flying towards the substrate under the action of electric field E, which ionises them to produce positive Ar ions and new electrons; the new electrons fly towards the substrate and the Ar ions are accelerated towards the cathode target under the action of electric field and bombard the target surface with high energy, causing the target to sputter. In the sputtered particles, neutral target atoms or molecules are deposited on the substrate to form a thin film, while the resulting secondary electrons will be subject to the electric and magnetic fields, producing a drift in the direction indicated by E (electric field) x B (magnetic field), referred to as E x B drift, and its trajectory approximates to a pendulum line. In the case of a toroidal magnetic field, the electrons move in a circular motion around the target surface in an approximate pendulum, their path is not only long, but they are bound in a plasma region close to the target surface and ionise a large amount of Ar in this region to bombard the target, thus achieving a high deposition rate. As the number of collisions increases, the secondary electron is depleted of energy, gradually moves away from the target surface and is Z finally deposited on the substrate in the presence of the electric field E. Due to the low energy of the electron, the energy transferred to the substrate is very small, resulting in a low temperature rise of the substrate. Magnetron sputtering is a collision process between the incident particles and the target. The incident particle undergoes a complex scattering process in the target and collides with the target atom, transferring some of its momentum to the target atom, which in turn collides with other target atoms, forming a cascade process. During this cascade process the target atoms near certain surfaces gain enough momentum to move outwards and leave the target to be sputtered out.