In modern manufacturing, vacuum coating technology is widely applied across sectors such as electronics, optics, automotive, and aerospace. One of the most critical factors in ensuring coating performance is accurate film thickness control, which directly affects electrical conductivity, optical behavior, corrosion resistance, and other functional properties of the film. As such, film thickness regulation has become a core focus in vacuum deposition engineering. This article outlines the principles, common methods, and influencing factors for precise thickness control, offering insights for optimizing thin film production.
No.1 Key Parameters in Film Thickness Control
1. Deposition Rate
Film thickness is highly dependent on the deposition rate, defined as the thickness of the film deposited per unit time on the substrate surface. In vacuum processes, the deposition rate is influenced by several factors:
Power applied to the evaporation or sputtering source
Chamber pressure
Distance between the substrate and the deposition source
By finely adjusting these parameters, manufacturers can maintain consistent and controllable film growth rates.
2. Deposition Time
Assuming a stable deposition rate, film thickness is linearly proportional to deposition time. By accurately setting the process duration, the target thickness can be achieved. However, during long deposition cycles, fluctuations in rate due to source degradation or process drift must be managed to avoid non-uniform or excessive deposition.
3. Source-to-Substrate Geometry
The relative positioning and angle between the source and the substrate significantly impact deposition uniformity and local film thickness. If too close, the film may become excessively thick; too far, and it may result in under-deposition or poor coverage. Optimizing the source geometry and employing substrate rotation or planetary motion can enhance film uniformity.
No.2 Common Techniques for Thickness Monitoring and Control
1. Optical Monitoring
Optical monitoring is a widely used method, especially for precision optical coatings. Based on optical interference, it tracks changes in reflectance or transmittance at specific wavelengths in real-time. The system can dynamically adjust the deposition parameters to achieve the desired thickness with high precision. Ideal for anti-reflective coatings, dielectric mirrors, and filters.
2. Quartz Crystal Microbalance (QCM)
This technique utilizes a quartz crystal sensor to monitor mass change via frequency shift, allowing for real-time calculation of deposited thickness. QCMs are commonly integrated into thermal evaporation and e-beam evaporation systems, offering high sensitivity and control.
3. Current-Controlled Evaporation
In thermal evaporation of metals, adjusting the current to the resistive heating element directly influences the evaporation rate. This method is simple and cost-effective but requires stable power supply and calibration to maintain deposition accuracy.
4. Substrate Temperature Control
Substrate temperature influences adatom mobility, film density, and microstructure. Controlling substrate heating during deposition can improve film adhesion and uniformity. In applications like semiconductor packaging or hard coatings, temperature control is crucial for consistent thickness and performance.
No.3 Key Factors Affecting Thickness Accuracy
1. Material Properties
Different materials exhibit varying evaporation characteristics and sticking coefficients. Metals like aluminum or silver evaporate readily, while ceramics or alloys (e.g., SiO₂, TiN) require higher temperatures or reactive atmospheres. Process parameters must be tailored to the material’s physical and thermal behavior for effective thickness control.
2. Chamber Pressure and Gas Composition
Working pressure within the chamber plays a pivotal role. High pressure increases scattering and reduces deposition rate; low pressure may destabilize the plasma or reduce reaction rates in reactive sputtering. Maintaining a stable gas flow (e.g., Ar, O₂, N₂) is essential for process stability.
3. Substrate Surface Condition
Surface contamination, oxides, or roughness on the substrate can affect film adhesion and result in uneven thickness. Surface preparation techniques such as solvent ultrasonic cleaning, plasma cleaning, or ion bombardment are employed to ensure a clean and uniform substrate surface.
Conclusion
Accurate control of film thickness is fundamental to achieving high-performance and high-yield vacuum coatings. Through precise regulation of deposition rate, time, source geometry, and real-time monitoring technologies, manufacturers can meet increasingly stringent film specifications. As the demand for nanometer-scale thin films continues to grow in optics, microelectronics, and functional coatings, advanced thickness control techniques will play a central role in production innovation and competitiveness.
—This article was published by vacuum coating equipment manufacturer Zhenhua Vacuum
Post time: Jul-12-2025