Korvus Technology

What Is Pulsed DC Sputtering? 

Pulsed direct current (DC) magnetron sputtering is a physical vapour deposition technique for depositing metallic coatings with precise mechanical, electrical, and optical properties. This technique is especially beneficial for depositing dielectric materials, which are coatings made from non-conducting textiles, enabling them to conduct a charge. 

Pulsed DC sputtering offers one main advantage over traditional DC sputtering: arc suppression. This process significantly reduces or even eliminates the occurrence of undesired arcs, which could otherwise damage the thin film quality. 

This article explains the pulsed DC sputtering process, the equipment necessary to achieve this effect, and both the advantages and disadvantages of pulsed DC sputtering to keep in mind. 

The Pulsed DC Sputtering Process

Pulsed DC sputtering was a novel physical vapour deposition technique in the early 2000s that today is commonly used to deposit smooth, ultra-dense metallic coatings [1]

Pulsed DC sputtering involves placing a target material in a vacuum chamber, removing H2O, air, and H2, and then backfilling it with a high-purity inert process gas to create kinetic energy. Then, a pulsed DC electrical current is applied to the target coating material while a positive charge accumulation is applied to the coating material. Both unipolar pulsed sputtering (with one pulse) and bipolar pulsed sputtering (with two pulses) are common. 

Applying a strong negative pulse to the target initiates sputtering, colliding the target material with the coating material and creating an ionised gas. Then, a low-voltage short-duration cycle reversal occurs, “scrubbing” the target surface to prepare it for the next pulse sputtering process.

What Is the Frequency of Pulsed DC Sputtering?

The pulsed DC sputtering process is usually carried out through a negative bias with pulsing frequencies between 10 and 350 kHz. [2]. This variable frequency range suppresses the arc formation at the target.

However, researchers are also learning the benefits of applying mid-frequency (100 to 350 kHz) pulses [3]. This technique could allow for better control over the ion current. 

Equipment Used in Pulsed DC Sputtering 

Using the right equipment can prevent arc formation during the pulsed DC sputtering process and ensure a strong bond between the coating and the target material. The equipment must deliver the correct variable pulses and power supplies to maintain stability and precision without overwhelming your budget. 

The Fission DC and RF Sputtering Source is the premier choice for numerous technical applications globally. This system allows for a quick transition between DC and RF (radio frequency) sputtering that minimises downtime.

You can initiate the reactive sputtering process by introducing reactive gas directly into the vacuum chamber or through a separate gas feed — whichever makes the most sense for your manufacturing process. 

Industry Applications

Pulsed DC sputtering is widely used in the optical and industrial coating industries. Its primary use is within the sputtering process of metals and dielectric coatings. 

Dielectric coatings consist of thin layers of transparent dielectric materials. Their purpose is to alter the reflective properties of the target surface, often to make the surface more reflective. This technique is useful in applications like:

     

      • Highly reflecting laser mirrors

      • Dichroic mirrors

      • Optical filters

      • Beam splitters

      • Heat reflectors

      • Solar cell covers

      • Thin-film polarisers

    In these applications, the coating substrate is often a type of glass. 

    Pulsed DC sputtering also has practical applications like:

       

        • Tool coatings, especially titanium nitride coatings that provide long-lasting durability through harsh applications

        • Photovoltaic cells such as solar cells that need to be highly reflective and last for decades through strong weather conditions 

        • Decorative coatings, as they can easily create colour uniformity in a large area

      What Are the Advantages of Pulsed DC Sputtering? 

      When choosing between evaporation and sputtering, pulsed DC sputtering poses several advantages, such as:

         

          • Adhesion of coatings: DC sputtering processes create a strong adhesion of coatings to target materials, essential for applications ranging from metal tools to photovoltaic cells [1]

          • Arc suppression: Pulsed DC sputtering creates a deposition without arcing [2] by using high-negative pulses rather than small-positive pulses [4]

          • High deposition rates: By reducing the challenges associated with charge buildups and arcs, manufacturers can achieve higher deposition rates of the dielectric materials. 

          • Better plasma formation: Pulsing the current increases the plasma density.

        What Are the Disadvantages of Pulsed DC Sputtering? 

        Pulsed DC sputtering eliminates many of the most frequent issues within the sputtering process, such as low deposition rates and ionisation. However, it does present a few disadvantages. 

        While pulsed DC sputtering can significantly reduce arc discharge damage compared to traditional DC sputtering, this benefit is not foolproof. Arcs can still form, and they can lead to a serious quality control breakdown that requires researchers to restart the entire sputtering process. 

        Reactive sputtering in general sometimes experiences hysteresis phenomena, which presents as a dynamic lag between the input and output in magnetisation processes. 

        Final Thoughts 

        Pulsed DC sputtering proves a reliable thin film deposition method that minimises arc formation and produces high-adhesion coatings. If you’re looking to incorporate pulsed DC sputtering into your manufacturing processes, Korvus Technology can provide you with the user-friendly, efficient technology you need. 

        Explore our HEX Series to learn about our physical vapour deposition equipment, then get in touch with us today.

         

        References

        [1] Alami, J. et al. (2009). “High power pulsed magnetron sputtering: Fundamentals and applications.Journal of Alloys and Compounds, 483:1-2. 

        [2] A Belkind et al. (2003). “Characterization of pulsed DC magnetron sputtering plasmas.New Journal of Physics, 7:90. 

        [3] Arnell, R.D. et al. (2004). “Recent developments in pulsed magnetron sputtering.Surface and Coatings Technology, 188-189. 

        [4] Jonsson, L.B. et al. (2000). “Frequency response in pulsed DC reactive sputtering processes.Thin Film Solids, 365:1. 

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