Vacuum refers to a gas state within a given space that is below one atmospheric pressure. Simply put, it means extracting the vast majority of gas molecules from a container, resulting in a pressure much lower than the external atmospheric pressure.
From a microscopic perspective, vacuum does not mean the complete absence of matter. There may still be small amounts of gas molecules, ions, photons, etc. in vacuum. However, the quantity of these substances is very small, which gives the vacuum environment some special properties, such as low pressure, high insulation, low heat transfer, etc.
Vacuum can generally be divided into the following levels:
Low vacuum: The pressure range is usually around 101325Pa (one standard atmosphere) to 1333Pa. Within this range, there are still quite a few gas molecules, mainly used for some rough vacuum applications such as vacuum drying, vacuum forming, etc.
Medium vacuum: The pressure range is approximately 1333Pa to 1.33 × 10 ⁻¹ Pa. In a medium vacuum environment, the number of gas molecules is further reduced, which can be used in some preliminary stages of vacuum metallurgy and vacuum coating.
High vacuum: pressure range from 1.33 × 10 ⁻¹ Pa to 1.33 × 10 ⁻⁶ Pa. Under high vacuum conditions, gas molecules are very rare and suitable for high-precision vacuum coating, electron beam welding, vacuum heat treatment, etc.
Ultra high vacuum: pressure below 1.33 × 10 ⁻⁶ Pa. In ultra-high vacuum environments, there are almost no gas molecules present, mainly used in some cutting-edge scientific research fields, such as surface science research, certain key processes in semiconductor manufacturing, etc.
The role of vacuum technology in sputtering coating
Exclusion of impurities: In a vacuum environment, the number of gas molecules is greatly reduced, which can effectively eliminate impurities in the air, such as oxygen, nitrogen, water vapor, etc. These impurities will react with the target material and substrate, affecting the quality and performance of the film. Through vacuum technology, a high-purity environment can be created to ensure the purity and stability of the film.
Improve sputtering efficiency: In a vacuum environment, the movement of ions is more free and not affected by factors such as air resistance. This enables ions to collide with the target material at higher speeds and energies, thereby improving sputtering efficiency. In addition, vacuum can reduce ion scattering and collision, and improve ion utilization efficiency.
Control coating parameters: Vacuum technology can accurately control parameters such as air pressure, temperature, and power during the coating process. By adjusting these parameters, control over the thickness, composition, structure, and other aspects of the film can be achieved. For example, by changing the air pressure, the energy and density of ions can be regulated, thereby affecting the growth rate and quality of thin films.
Improving film quality: Thin films prepared under vacuum conditions have higher purity, better uniformity, and lower defect density. This is because vacuum can eliminate impurities and control coating parameters, thereby reducing defects and impurities in the film. In addition, vacuum can reduce the oxidation and contamination of thin films, improve their stability and durability.
