Plasma-Reactor Wall Interactions: Bromine-Fluorine Chemistry Duality in an Industrial Dry Etch Process
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Plasma-Reactor Wall Interactions: Bromine-Fluorine Chemistry Duality in an Industrial Dry Etch Process M.Rizquez1,2, A.Roussy1, B.Bortoloti2, J.Pinaton2 Y.Goasduff2 1 EMSE-CMP, 880 Avenue de Mimet, 13541, Gardanne, FRANCE. 2 STMicroelectronics, 190 av. Celestin Coq ZI Rousset-Peynier, 13106, Rousset, FRANCE. ABSTRACT The purpose of the present paper is to investigate the composition of the coating formed on the plasma reactor walls after an industrial process which is divided into two steps, where the chemistries used are CF4/CH2F2 followed by HBr/O2. Since Fluorine traces have been detected through the plasma and over the wafer even during the second chemistry, investigations of the Br-F chemistry duality for a new silicon etching process have been performed in order to see the reactions which are taking place inside of the reactor. The understanding of these formations is really important to avoid process instabilities and get better performance of the transistors. The coating on the walls after the process and after the cleaning between wafers has been characterized in order to figure out the level of F traces after each step and to understand the reminiscence of this element over time. This study is the starting point to propose a modification on the Waferless AutoClean (WAC) used nowadays in an industrial process. INTRODUCTION Plasma etching, used to fabricate integrated circuits, is one of the most critical process steps to maintain the uniformity of the critical dimension (CD). During the process, the plasma will generate volatile etch products from the chemical reactions and these products will be deposited on the reactor walls. Furthermore, the mix of the products and the complexity of the process recipes induce process instabilities due to the recombination of these species and the possible redeposition over the wafer surface. Since the process stability is very important in order to maintain the product quality, cleanings between processes are needed. The WAC is the dry cleaning strategy used as precondition step in this study. It takes place between processes as a process run after every wafer and it is focused on reducing the different by-products generated after each process to keep the same process conditions each time. However, the selection of the WAC parameters is highly important to improve the productivity by reducing particles and minimizing drifts associated to chamber conditioning as the first wafer effect. In view of foregoing, what is needed and it is object of this study, is the understanding of the reactions during the process and the characterization of polymers deposited on the reactor walls. The Floating sample method allows to show the effect of the plasma-reactor walls interactions. This information, together with the plasma-surface interaction by analyzing the wafer surface composition and the state of the plasma during the etching process, it will be the key to optimize and improve the dry cleaning and thus the process stability. This study is focused on the understanding of the Br-
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