Densification Process
A deposition phenomenon involving the bombardment of a growing thin film by energetic neutral particles alters the density and stress state of the material. In sputter deposition, atomic peening drives species from the target or working gas into the film, compressing the lattice structure. This energetic bombardment occurs when high energy particles are reflected from the sputter target toward the substrate.
Stress Generation
Compressive stress is introduced when these energetic neutrals force atoms into interstitial positions within the crystal lattice. This stress modification remains a primary mechanism for adjusting the mechanical properties of hard coatings. Controlling the sputtering pressure and substrate bias allows operators to regulate the kinetic energy of the incoming species, which modifies the residual stress from tensile to compressive.
Lower gas pressures reduce collisions in the plasma, yielding more energetic neutral reflections and greater film compression.
Substrate Interaction
Interfacial adhesion increases because the bombarding particles create a mixing zone at the boundary between the film and the underlying material. This mixing improves the mechanical anchoring of the deposited layer. Excessively high bombardment energy can damage the substrate surface, causing defect generation that reduces the overall reliability of the sensor assembly.
Microstructural Effect
Microstructural refinement occurs as a direct consequence of the continuous disruption of grain growth during the deposition process. The resulting thin film displays a dense, fibrous structure with fewer voids, which prevents moisture ingress and stabilizes the electrical characteristics of the sensor over long periods of time.
