March 05th, 2021
Plasma spraying is an advanced surface coating technique used to generate extremely high quality, uniform coatings on a wide range of substrate types. It is among the most versatile thermal spraying processes due to the high temperature range of plasma spray guns and the growing variety of plasma torch configurations.
This article will introduce some of the basics of plasma spray technology, with a brief introduction to its importance in semiconductor manufacturing.
Plasma Spraying: Solutions for Modern Technical Challenges
The study of plasma—initially described as radiant matter—is a relatively young field of research. It was first identified little over a hundred years ago, and was not properly described until the late 1920s. However, our understanding of plasma technology has grown at a commensurate rate; partially motivated by key technological challenges of the day.
For instance: How to decouple the bulk properties of engineering materials from those at the surface where exposed to extremely harsh conditions?
This is a cross-disciplinary challenge spanning industries ranging from aerospace to semiconductor manufacturing. But the sheer versatility of plasma spraying technology provides solutions across the board.
The Basics of Thermal Plasma Spraying
Thermal plasmas for coating applications are generated by ionising inert gas with electrodes and either an alternating current (AC), direct current (DC), or radiofrequencies (RF). Higher stability plasmas with minimal fluctuation, greater process control and overall extended electrode service are expected with DC plasma torches.
These spray guns can be further sub-divided into transferred and non-transferred torches—we will explore the concept of plasma transfer arcs (PTA) in a future article.
Thermal spray feedstocks vary from ceramic rods to wires, and plasma spray uses exclusively powders. At Saint-Gobain Coating Solutions, we specialise in thermal spray powders engineered to optimise the functional performance of materials through surface modification.
When plasma spraying with ceramic powders, an injector feeds a stream of particles into the jet which creates a high velocity flow of molten/semi-molten particles. The torch accelerates the spraying particles onto a relatively cool substrate, which promotes rapid cooling and clamping of the surface roughness leading to greater substrate-coating bond strength.
Why is This Important for Semiconductors?
Semiconductor and flat-panel-display (FPD) production equipment is subjected to extremely harsh working conditions. Dry etching via ionisation is a now standard method of microfabrication. However, high concentrations of radicals generated during the wafer etching process—such as CF4/O2 plasma—can erode components within the chamber.
Plasma sprayed coatings composed of high-purity oxide ceramics promote greater surface erosion resistance in plasma chambers. It is important to note that the efficiency of semiconductor coatings depends on the configuration of the plasma gun plus the quality and composition of the feedstock. We explored the importance of surface coating chemistry in semiconductor production in our recent article.
Key takeaways from the use of plasma sprayed coatings in plasma chambers are enhanced process quality, extended component service lives, and long-term savings through reduction of maintenance. If you would like to learn more, why not contact a member of the Saint-Gobain Coating Solutions team today?