Resistive Evaporation

Vacuum evaporation, referred to as evaporation, refers to the process method of evaporating the coating material (or film material) and vaporizing it by a certain heating and evaporation method under vacuum conditions, and the particles fly to the surface of the substrate to form a film. Evaporation is an earlier and most widely used vapor deposition technology, which has the advantages of simple film-forming method, high purity and compactness of thin film, and unique film structure and performance.

The physical process of evaporation includes: the evaporation or sublimation of the deposited material into gaseous particles→ the rapid transport of gaseous particles from the evaporation source to the surface of the substrate→ the gaseous particles attach to the surface of the substrate to nucleate, grow into a solid film→ reconstitution of thin film atoms or produce chemical bonding.

The substrate is placed in a vacuum chamber and heated by resistance, electron beam, laser and other methods to evaporate or sublimate the film material and vaporize it into particles (atoms, molecules or clusters) with a certain energy (0.1~0.3eV). The gaseous particles are transported to the substrate in a linear motion that is basically collision-free, and some of the particles that reach the surface of the substrate are reflected, and the other part is adsorbed on the substrate and spreads on the surface, resulting in two-dimensional collisions between the deposited atoms to form clusters, and some may stay on the surface for a short time and then evaporate. Clusters of particles are constantly colliding with diffuse particles, either adsorbing or emitting single particles. This process is repeated repeatedly, and when the number of particles gathered exceeds a certain critical value, it becomes a stable nucleus, and then continues to adsorb and diffuse particles and gradually grows, and finally forms a continuous thin film through the contact and merger of adjacent stable nuclei.

Saturation vapor pressure (PV): The pressure at which the vapor of the evaporated material in a vacuum chamber is in equilibrium with a solid or liquid at a certain temperature. The relationship curve between saturation vapor pressure and temperature is of great significance for film fabrication technology, which can help us to rationally select evaporation materials and determine evaporation conditions.