Invited Paper PS-ThA3
Around the World of RF-Plasma Generation: A Brief Tour in 80 (half) Minutes

Thursday, October 22, 2015, 3:00 pm, Room 210A

This paper starts with a review of historical progress to reach the present day, when it is virtually universal to use RF excited plasmas to process semiconductor materials. This may extend to hundreds of process steps as Deposition, Etching, Stripping, Cleaning and Surface treatments are all in the RF-plasma repertoire. In order to do so, multiple factors and timelines have had to converge, including:

I. Electronics development, specifically RF technology and devices.

II. Plasma Technology A.K.A. Gaseous Electronics, specifically Dry Processing as applied to: Semiconductors, Flat panel displays, P-V solar panels, MEMs devices etc.

It is less than 70 years since the invention of active solid state electronics in 1947, but the semiconductor industry is now mature and consolidated while continuing to advance according to Moore’s law. In the same period RF delivery systems have also progressed from high power vacuum tubes/valves to solid state devices in the 1980s. Most such RF systems use 50Ω transmission lines (for I.S.M.) so that matching networks are used to optimize power transfer to the antenna load impedance. Plasma technology use for semiconductor production did not start until the late 1960s / early 70s. In particular, despite the engineering complications of dealing with RF excitation, RF plasmas became popular because of their suitability for use with dielectric materials, and ameliorating the potential for damage caused by passing DC currents through delicate devices during manufacture.

In the second half of the paper we consider that while the technology involved in plasma processing has remained basically the same for nigh on 50 years, the demands on RF performance, control and consistency have escalated beyond all recognition. I will address some typical RF-plasma issues with examples taken from the current state of the art that continue to challenge us. These include igniting and delivering RF into the changing load impedance of a transient plasma, whether due to instability or by design. Another is dealing with the problem of stable and consistent excitation when there are multiple frequencies present either due to multiple source frequencies or due to the plasma generation of harmonics and mixing products. I will discuss how we achieve stable performance in terms of both uniformity and tool matching, in part by using sensor based control schemes. The question we must answer going forward is whether we can maintain or indeed improve this level of precision and performance, but do so ever more cost effectively.