Introduction to Low Pressure Glow Discharges for Semiconductor Manufacturing with special Emphasis on Plasma Etching

Plasma processing is one of the key technologies in the fabrication of modern silicon devices. It is applied to approximately one third of the several hundred fabrication steps. Plasma etching enables together with advanced lithography the high volume production of submicron structures. The significant difference to the formerly used wet etching in liquid chemicals is its ability to keep the mask dimensions much more accurately. Plasma assisted deposition reduces the necessary number of high temperature thermal treatments > 700◦C which might degrade the device performance, as it allows the deposition of several important materials in semiconductor manufacturing at below 500◦C. Finally plasma treatments are used to modify surfaces e. g. to increase wetability of chemicals, to clean organic residues and so on. This short summary on low pressure glow discharges used in IC manufacturing is intended to give an introduction to the basics of the plasma processing involved in the IC fabrication process. It is devoted to the physical and chemical concepts of plasma etching and a bit deposition, but addresses also the overall IC fabrication briefly, because many specific requirements can only be understood in the context of the total fabrication process. The script is mainly considered for young process engineers and technicians working in the wafer fab, giving them a rather practical introduction, but might be also interesting for all persons who want to get in touch with the subject. While reading, please be always aware that my main intention is to give you some feeling and conceptual knowledge, not detailed recipes for specific applications. I might have omitted expections, doesn’t have described all restrictions, so don’t take the given arguments to literally and seriously, but anyway the concepts introduced should be valid. Due to the complexity of our subject I try to explain all related terms shortly during the first chapter to have a good basis for the more detailed discussions following. Most of the given examples come from submicron CMOS technology as this is my current field of interest. Most of the basic material presented comes from four books of Chapmann [1], Liebermann [5], Chen [2] and Sugawara [7]. The first one of Chapmann is already more than twenty years old but is still a excellent first overview. The graduate textbook of Liebermann provides a rather complete coverage together with a rather strict quantitative analysis. Chens book is not devoted to plasma processing, it is about plasmas and controlled fusion and is my reference for questions to basic plasma physics. The final one edited by Sugawara is rather new from 1998 and contains therefore very actual material. I just selected, summarized and expanded everything in a way that is in my humble opinion useful for the actual practical application.