Magnetron sputtering: the basics of how it works
In magnetron sputtering, magnetic fields focus plasmas onto target material surfaces, ejecting material that moves through the plasma to coat substrates. Suitable for depositing most materials (with correct choice of sputtering power supply).
Physical Vapour Deposition (PVD) is a widely used technique for depositing thin films and coatings. A magnetron source is a critical component in this process, providing a means to efficiently sputter material from a target onto a substrate. The magnetron enhances the sputtering process by using a magnetic field to confine electrons close to the target surface, increasing the ionisation efficiency and sputter rate.
How The Magnetron Source Works
Magnetron sputtering involves bombarding a target material with high-energy ions (typically Argon ions). The collision dislodges atoms from the target, which then deposit onto the substrate. The magnetron source utilizes a magnetic field, created by magnets behind the target, to trap electrons near the target surface. Electrons, influenced by the magnetic field, follow helical paths, increasing their chance of ionizing the gas. The positively charged Argon ions are attracted to the negatively charged target, causing sputtering.
The sputtered atoms travel through the vacuum and deposit as a thin film on the substrate.
Choice of DC vs. RF Power Supply
DC Power Supply:
Used for sputtering conductive materials such as metals. A direct current (DC) power supply provides a constant voltage and current, creating a stable plasma.
- Advantages: Simplicity, cost-effectiveness, and efficiency for conducting targets.
- Limitations: Not suitable for insulating or dielectric materials, as the constant current can lead to charge buildup and arcing on the target surface.
RF Power Supply:
Used for sputtering both conductive and non-conductive materials. Radio frequency (RF) power supplies operate at high frequencies (typically 13.56 MHz), alternating the current rapidly to prevent charge buildup.
- Advantages: Versatility in sputtering a wide range of materials, including insulators and dielectrics. The alternating current prevents arcing and allows for uniform sputtering.
- Limitations: More complex and expensive than DC power supplies, with potentially lower sputter rates for conductive materials compared to DC.
Target Considerations
- Choice of Material: Depends on the desired coating. Common materials include metals (e.g., aluminium, titanium), alloys, and compounds.
- Target Thickness: Should be sufficient to avoid frequent replacements, but not too thick to cause issues with heat dissipation.
- Some thin or brittle targets may need a backing to provide support and prevent accidental cracking during use.
Substrate Preparation
- Cleanliness: Substrates must be clean and free from contaminants to ensure good adhesion and uniformity.
- Some PVD systems offer a substrate pre-clean using an in-chamber or load lock etch station.
- Temperature: Some processes require heating of the substrate to improve film quality and adhesion.
