In vacuum coating processes, the deposition rate is one of the key parameters determining both production efficiency and film properties. However, excessively high or low deposition rates can directly impact film quality, thereby affecting its optical, electrical, and mechanical performance. Striking the right balance between deposition rate and quality is critical for thin-film process optimization.
I. Basic Concept of Deposition Rate
Deposition rate is typically expressed in nm/s or Å/s, representing the film thickness deposited per unit time on the substrate surface. It is influenced by multiple factors, including:
Vacuum Level: Higher background pressure leads to particle scattering, reducing the effective deposition rate.
Energy Input: Heating power of the evaporation source or discharge current of the sputtering target dictates the sputtering/evaporation rate.
Process Gas Flow: In reactive sputtering, gas concentration directly impacts the deposition rate.
II. Mechanisms Linking Deposition Rate and Film Quality
Effects of Excessively High Deposition Rate
Low Film Density: Limited surface diffusion time at high rates results in porous structures.
Stress & Adhesion Issues: Rapid accumulation increases intrinsic stress and weakens adhesion.
Optical Variability: Reduced thickness accuracy causes deviations in refractive index or transmittance.
Effects of Excessively Low Deposition Rate
Low Productivity: Longer cycle times for large-area substrates reduce throughput.
Contamination Risk: Extended deposition increases the probability of residual gas or impurity incorporation.
Abnormal Grain Growth: In certain materials, overly slow deposition promotes excessive surface roughness or coarse grains.
Optimal Deposition Window
A moderate deposition rate ensures a balance between film density, stress control, and thickness uniformity.
In practice, rate calibration and Quartz Crystal Monitoring (QCM) are widely used for precise rate control.
III. Rate Control in Different Deposition Techniques
Thermal Evaporation: Excessive rate may cause spitting and particulate defects; stepwise heating is used to stabilize evaporation.
Magnetron Sputtering: Rate is influenced by target power and process gas flow; optimization must balance target utilization efficiency and film uniformity.
Reactive Sputtering: Deposition rate is strongly affected by target poisoning, requiring closed-loop plasma/gas flow control.
IV. Industrial Practices
In optical coatings, rate control is directly linked to refractive index accuracy and interference color consistency.
In semiconductor thin films, excessive rate can alter film resistivity, degrading device performance.
In decorative coatings, higher rates are preferred to maximize large-area productivity, provided uniformity is maintained.
The relationship between deposition rate and film quality is tightly coupled: too high a rate compromises density and adhesion, while too low a rate reduces productivity and increases contamination risks. Only through precise deposition rate control and process optimization can manufacturers achieve an optimal balance between efficiency and quality, meeting the demands of optical, electronic, and decorative applications.
—This article was published by vacuum coating equipment manufacturer Zhenhua Vacuum
Post time: Aug-20-2025