Introduction

Sputtering refers to a thin-film deposition method that has dramatically improved since its discovery in 1852. Its initial development was to deposit metals, which were not to be applied through thermal evaporation. Magnetron sputtering emerged as part of the advancement of this technology, controlled by magnetic fields used to manipulate electrons. It improves the process by increasing ionization, resulting in a denser plasma. There are two types of magnetron sputtering: balanced and unbalanced. Both differ in characteristics and applications, and the blog delves into the details of balanced and unbalanced magnetron sputtering.

Understanding Magnetron Sputtering

Magnetron sputtering is a technique for depositing thin films on different substrates. It involves bombarding a target material with high-energy ions, typically from an inert gas such as argon. The ions bombard the target, ejecting atoms from it and depositing them onto the substrate to form a thin film.

The key innovation in magnetron sputtering is the magnetic fields that trap the electrons near the target. This increases the gas’s ionization, creating a denser plasma and an efficient deposition process. The two classes of magnetron sputtering, balanced and unbalanced, vary in their influence on the film deposition process.

Balanced Magnetron Sputtering: Key Features

In balanced magnetron sputtering, magnetic field lines close on themselves around the target and confine electrons to regions near the target surface. Most of the plasma remains localized near the target; thus, ions that arrive at the substrate are relatively low energy.

This low ion energy makes the technique especially suitable for forming smooth, defect-free films, particularly in semiconductor fabrication industries. However, low ion energies may lead to poor film adhesion or lower film density.

If the substrate is set far from the target, it may not receive enough ion flux to alter its surface properties and thus modify the properties of the film. To mitigate this, an applied bias to the substrate would increase the ion energy but likely introduce stress or defects.

Unbalanced Magnetron Sputtering: Key Features

Unbalanced magnetron sputtering differs from balanced sputtering because the magnetic field does not form a closed trap, allowing more electrons to escape and enter the plasma. This increases the size of the plasma, further increasing ion bombardment on the substrate.

The film produced has stronger adhesion and is denser and harder. Increased ion bombardment increases the ions’ energy, enabling the coater to coat larger substrates and complex shapes.

There are two types of unbalanced magnetron sputtering.

Type I: The central magnet is weaker, allowing more electrons to reach the substrate. This is a good way to make hard, wear-resistant coatings.
Type II: The central magnet is stronger, resulting in fewer electrons reaching the substrate. This type of method is not frequently used.

This method is used for hard coatings, such as titanium nitride (TiN) or diamond-like carbon (DLC), in industries requiring high durability, such as automotive, aerospace, and tooling.

Balanced vs. Unbalanced Magnetron Sputtering: A Comparative Overview

The difference between balanced and unbalanced magnetron sputtering is the intensity and energy of the ion bombardment that impacts the substrate. This directly correlates with the resultant film properties and their applicability.

Feature	Balanced Magnetron Sputtering	Unbalanced Magnetron Sputtering
Ion Bombardment	Low energy, low ion bombardment	High energy, high ion bombardment
Plasma Distribution	Plasma remains near the target	Plasma extends beyond the target
Film Adhesion	Lower adhesion due to lower ion energy	Higher adhesion due to higher ion energy
Film Density	Lower density films	Higher density films
Deposition Rate	Slower deposition rate	Faster deposition rate
Best For	Uniform, low-defect coatings (e.g., semiconductors)	Durable, hard coatings (e.g., aerospace parts)

Balanced sputtering is best used in applications requiring smooth, defect-free, uniform coatings, like in the electronics and semiconductor industries. On the other hand, unbalanced sputtering is more suitable for applications that demand stronger, tougher films, like cutting tools and aerospace components.

Conclusion

In conclusion, the choice of magnetron sputtering depends on the project’s requirements. Balancing sputtering is chosen if the task is to obtain smooth, sharp coatings on delicate substrates. Yet, unbalanced sputtering performs better for rough and wear-resistant films on robust surfaces. With increasing industry demands for advanced coatings with improved durability, unbalanced magnetron sputtering is frequently used for high-performance applications. However, both techniques have different advantages and are thus essential tools in thin-film deposition.