In vacuum coating (Vacuum Coating) processes, the deposition rate is one of the core parameters that determines both production efficiency and film characteristics. However, excessively high or low deposition rates can directly affect film quality, thereby influencing the optical, electrical, and mechanical properties of the coating. Finding the right balance between rate and quality is a key factor in thin-film process optimization.
1. Basic Concept of Deposition Rate
The deposition rate is usually expressed in nm/s or Å/s, indicating the thickness of film deposited on the substrate per unit time. Several factors affect the deposition rate, including:
Vacuum Level: Higher background pressure increases particle scattering, reducing effective deposition.
Energy Input: Heating power of evaporation sources or current of magnetron targets determines the sputtering rate.
Process Gas Flow: In reactive sputtering, gas concentration directly affects the deposition rate.
2. Mechanisms Linking Deposition Rate and Film Quality
Effects of Excessively High Rate:
Low Film Density: At high deposition rates, atoms or molecules have insufficient surface mobility, leading to porous structures.
Stress & Adhesion Issues: Rapid accumulation concentrates internal stress, reducing adhesion strength.
Optical Variability: Thickness control accuracy decreases, causing deviations in refractive index or transmittance.
Effects of Excessively Low Rate:
Low Productivity: Extended deposition time reduces throughput for large-area substrates.
Increased Contamination Risk: Longer deposition times raise the probability of residual gas or impurity incorporation.
Abnormal Grain Growth: In some materials, overly slow deposition can increase surface roughness.
Optimal Deposition Window:
A moderate deposition rate balances film density, stress control, and thickness uniformity. In practice, rate calibration and Quartz Crystal Monitoring (QCM) are employed to achieve precise control.
3. Rate Control in Different Processes
Thermal Evaporation: Excessive rate may cause spattering and particle defects; stepwise temperature control is used to manage evaporation rate.
Magnetron Sputtering: Rate is influenced by target power and gas flow, requiring a balance between target utilization and film uniformity.
Reactive Sputtering: Deposition rate is closely related to target poisoning, necessitating closed-loop control.
4. Practical Applications in Industry
In optical coating, rate control directly affects refractive index and interference color accuracy.
In semiconductor thin films, excessive rate may cause resistivity deviations, impacting device performance.
In decorative coatings, for large-area production, moderate rate increases are adopted while ensuring uniformity.
Conclusion
Deposition rate is closely linked to film quality: too fast compromises density and adhesion, while too slow reduces efficiency and increases contamination risk. Only through precise rate control and process optimization can an optimal balance between efficiency and quality be achieved, meeting the requirements of optical, electronic, and decorative applications.
—This article was published by vacuum coating equipment manufacturer Zhenhua Vacuum
Post time: Nov-03-2025