Growth Law of Vacuum Evaporation Coating Layer
Time：
2023-07-31 09:53
The nucleation and growth patterns of the film layer during evaporation coating are the foundation of various ion coating technologies.
1. Nucleation
In vacuum evaporation plating technology, the film particles evaporate in the form of atoms from the evaporation source and fly directly towards the workpiece in high vacuum, forming a film layer on the surface of the workpiece through nucleation and growth. During vacuum evaporation plating, the energy of the film layer atoms escaping from the evaporation source is about 0.2eV. When the cohesion between the film particles is greater than the binding force between the film atoms and the workpiece, island shaped crystal nuclei are formed. When a single film layer atom undergoes irregular movement, diffusion, migration, or collision with other atoms during its residence on the surface of the workpiece, forming a stable crystal nucleus when the number of atoms in the atomic cluster reaches a certain critical value, known as homogeneous nucleation.
Generally, the surface of a workpiece is not absolutely smooth and contains many defects and steps, which results in differences in the adsorption force of human radiation atoms on different parts of the workpiece. The surface adsorption energy of defects is greater than that of normal surfaces, thus becoming active centers is conducive to preferential nucleation, known as heterogeneous nucleation. When the cohesion is equivalent to the binding force, or the binding force between the film layer atoms and the workpiece is greater than the cohesion between the film layer atoms, a layered structure is formed. In ion plating technology, most cases involve the formation of island like cores.
2. Growth
After the core of the thin film is formed, it continues to capture incident atoms and grow. Each island like atomic cluster grows and combines with each other to form a larger hemisphere, gradually forming a hemispherical island like film layer distributed throughout the surface of the workpiece.
When the atomic energy of the film layer is high, it can fully diffuse on the surface, and when the subsequent atomic clusters are smaller, they can form a smooth continuous film. If the diffusion ability of atoms on the surface is weak and the size of deposited atomic clusters is large, they exist in the form of large peninsula nuclei. The top of the island shaped core has a strong shading effect on the concave part, which produces a shadow effect. The protruding part of the surface is more conducive to capturing subsequent deposited atoms and preferentially growing, increasing the degree of surface concavity and convexity to form sufficiently large conical or columnar crystals. The formation of penetrating voids between conical crystals increases the surface roughness value. Fine and dense tissue can be obtained under high vacuum, and as the vacuum decreases, the film layer structure becomes thicker and thicker.
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2026-09-28
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