Why Automatic Sputter Coating Delivers More Uniform SEM Coatings than Manual Processes

The fundamental principles and parameters of sputter coating have been utilized to advance the LUXOR A² technology, which serves as the core of the latest series of LUXOR metal sputter coaters. How this innovative technology is manifested in the design and automation, as well as the benefits it provides to the operator, is detailed here.

Previously, the essential workflow of a manual sputter coating process that employs gold as the sputter material and argon as the inert process gas was examined.

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It fundamentally comprises the subsequent steps:

1. Once the air has been evacuated and the chamber is filled with argon, the vacuum pump achieves the predetermined target vacuum.
2. Upon reaching the vacuum level, the high voltage is activated, and the operator adjusts the argon flow to establish a sputtering current.
3. The sputtering process commences with the specified argon flow for a designated duration.
4. When the designated time elapses, the sputter coating process ceases, and the chamber is replenished with air.

This description leads to the conclusion that precise regulation of the vacuum and sputtering current is crucial for effective control of a sputter coating process. Furthermore, it is evident that maintaining a lower sputtering current will yield a finer sputtering outcome.

However, lower currents lead to increased instability in plasma behavior. A consistent low sputtering current combined with a stable vacuum yields a high-quality coating characterized by homogeneity, coverage, density, and grain size.

Other factors, such as the dimensions and configuration of the coating chamber and the target material, are fixed and considered.

The fundamental process flow of a manual sputter coating system, as previously described, has a significant drawback: it lacks an automated mechanism to regulate and balance the vacuum level and the amount of process gas introduced. Consequently, the sputtering current, which is influenced by the volume of process gas injected, cannot be adjusted during the coating operation.

As a result, manual and semi-automatic sputtering systems are compelled to function at relatively high sputtering currents to avoid instability or failure of the plasma during the coating process.

This elevated sputtering current also results in coatings that are less homogeneous and exhibit larger grain sizes.

What Does an Automatic Sputter Coating Process Look Like?

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1. The air within the sputtering chamber is removed by the vacuum pump, and the chamber is subsequently filled or flushed with argon.
2. The vacuum pump, along with the vacuum valve that introduces the argon, establishes the necessary target vacuum in the chamber.
3. Once the target vacuum is achieved, the high voltage is activated. The interplay of vacuum and voltage ignites the plasma, resulting in a flow of current.
4. The sputtering process commences, and a continuous flow of argon is introduced into the sputtering chamber to maintain a steady coating current.
5. Upon reaching the predetermined end criterion, the sputter coating process ceases.
6. Finally, the chamber is replenished with air and can be safely opened.

A² Technology: What is it All About?

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In a LUXOR sputter coater featuring A² technology, once the initial target vacuum is achieved, a tuning process commences that maintains the target vacuum at a constant level by rapidly dosing micro quantities of the process gas, which is usually argon or air.

The A² algorithm regulates the vacuum control valve to ensure a balance between the discharge through the vacuum pump and the input through the vacuum valve (step 2 in the process graph). The initial target vacuum is determined in such a manner that, upon the application of voltage, the argon dosage will produce the desired coating current.

Image Credit: Luxor

When the target vacuum remains within the established tolerance for a specified duration, voltage is applied, resulting in current flow, plasma generation, and initiation of the sputtering process. In the initial phase of sputtering, fluctuations in voltage and current are observed. At this point, the A² algorithm activates and regulates the vacuum valve to quickly stabilize the target current.

During this stage, the sputter current becomes the key parameter, and the vacuum level may begin to fluctuate to maintain a constant value (step 3 in the process graph).

Maintaining a constant vacuum level during this phase would adversely affect the sputter current, leading to an uneven accumulation of the metal coating. A² Technology keeps the current very low and stable, thereby avoiding issues caused by an unstable plasma.

This information has been sourced, reviewed and adapted from materials provided by Luxor.

For more information on this source, please visit Luxor.