Thin Film Deposition Using Thermal Evaporation

Thermal evaporation is one of the most widely used physical vapour deposition (PVD) methods for creating thin films in research and manufacturing. By heating a source material under high-vacuum conditions until it vapourises, atoms or molecules travel line-of-sight to the target substrate, where they condense and form a film.

This straightforward process makes thermal evaporation a go-to technique for metals, semiconductors, organics, and certain dielectrics.

How It Works

1.High Vacuum Environment
A robust vacuum (often in the 10⁻⁶ to 10⁻7 mbar range) ensures mean free paths are long enough for evaporated particles to reach the substrate without colliding with residual gas molecules.

2.Heating the Source
Resistive (tungsten coil) or electron beam (e-beam) heating is used to raise the source material to its evaporation or sublimation point. The choice depends on the material’s melting point and desired deposition rate.

3.Line-of-Sight Deposition
Material flux travels in essentially straight lines from source to substrate. Substrate holders often feature rotation or tilting to enhance film uniformity.

4.Condensation and Film Formation
Once vapourised particles reach the cooler substrate, they condense and form a thin film. Thickness control can be achieved through quartz crystal monitors, time-based recipes, or advanced feedback loops.

Key Considerations

Material Properties

• Melting/Vapourisation Points: Materials with very high melting points can require specialized high-power sources (e.g., e-beam). Conversely, for organic materials lower temperatures with precise control are required.
• Vapour Pressure: Elements with low vapour pressure are more challenging to evaporate uniformly.
• Stoichiometry: Multi-component sources (e.g., alloys) may suffer from differential evaporation rates.

Process Parameters

• Base Pressure: A lower base pressure (high vacuum) reduces contamination and ensures stable evaporation rates.
• Evaporation Rate: Too high a rate can lead to poor film adhesion or unwanted morphology; too low can be time-consuming.
• Substrate Temperature: Elevated substrate temperatures can improve film density but may damage temperature-sensitive substrates. This is particularly important for Lift-Off applications.

Uniformity and Coverage

• Geometric Placement: Because it’s a line-of-sight technique, substrate positioning relative to the source heavily influences coverage.
• Rotation & Manipulation: Substrate rotation is often employed to achieve better film uniformity across larger areas or 3D objects.

Contamination and Purity

• Crucible/Boat Material: Interaction between the source material and crucible can introduce impurities. Choosing inert container materials (e.g., alumina, tungsten, molybdenum) is crucial.
• Chamber Cleanliness: Proper cleaning and dedicated vacuum lines help maintain film purity.

Our Thermal Evaporation Solutions

At Moorfield, we’ve harnessed decades of vacuum and materials expertise to develop PVD systems that streamline thermal evaporation for both R&D and low-volume production:

• Compact Yet Capable: Small footprints maximize valuable lab space without sacrificing professional-grade performance. Available in benchtop or modular platforms.

• Modular Designs: Customize with various source types (resistive or e-beam), substrate holders, and pump configurations tailored to your materials and thickness goals.
• Process Control & Automation: Our intuitive software suite simplifies parameter tuning (pressure, temperature, deposition rate) and recipe management.
• Advanced Monitoring: Integrated quartz crystal sensors ensure real-time tracking of film growth, enabling precise control of deposition rates and total thickness.
• User-Centric Upgrades: Whether you need multi-source evaporation for alloys or advanced fixturing for large substrates, our MiniLab systems evolve alongside your research demands.

Contact Moorfield today to discuss your application.