Reactive Ion Etching of Copper with SiCl 4 and CCl 2 F 2
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REACTIVE ION ETCHING OF COPPER WITH SiCI 4 AND CC12 F 2 B. J. HOWARD, S. K. WOLTERMAN, W. J. YOO, B. GITTLEMAN, and CH. STEINBR.UCHEL Center for Integrated Electronics Rensselaer Polytechnic Institute, Troy, New York 12180-3590 ABSTRACT Copper may become an alternative to aluminum as an interconnect material in future multilevel metallization schemes if it is possible to pattern Cu by dry etching in a manufacturable process. Here we report results on the reactive ion etching of Cu in SiCI 4 /Ar, SiCI 4/N 2 , and CC1 2 F 2/Ar plasmas. Etch rates have been investigated as a function of various plasma parameters, such as gas composition, pressure, etc., and substrate temperature. We have obtained etch rates as high as 850 A /min with SiCl 4/N 2 and a substrate temperature of - 200 ° C. Also, it appears feasible to pattern Cu anisotropically using either polyimide or amorphous carbon as a high-temperature etch mask. INTRODUCTION In current silicon VLSI integrated circuits, aluminum is the primary metal used as an interconnect material [1]. However, copper has a higher conductivity than aluminum, which gives copper an important advantage in multilevel metallization schemes requiring longer interconnect spans. In order for copper to be useful as an interconnect material, it will be necessary to produce fine patterns in the copper using a dry etch technique. To our knowledge, only one paper has been published investigating the reactive ion etching (RIE of copper thin films. Schwartz and Schaible were able to achieve an etch2 rate of 5000 A/min with a CC14 /Ar plasma using an input power density of 1.3 W/cm and a cathode temperature of 2250 C [2]. They found that the etch rate for Cu increased with increasing power density, cathode temperature and reactant partial pressure. In order to withstand these harsh conditions, magnesium oxide with a molybdenum adhesion layer was used as a mask. Etching was generally anisotropic, but occasional lateral attack of the vertical sidewalls did occur. The above results indicate that RIE of copper involves reaction of Cu with chlorine species. Studies of the copper-chlorine system have been performed by several investigators [3-11]. Sesselmann and Chuang [3,4] found that upon exposure to dry C12 at room temperature, a thick [several thousand angstroms] surface layer with average stoichiometry of CuCl, (0 < x < 2) is formed on the surface of the copper, depending on the gas exposure. These observations were supported by Winters [5,6]. Park et al [7] observed the formation of a passivating film, when Cu was exposed to 012, which slowed the sputtering rate of Cu with 2 keV Ar+ ions. Because of the fairly uniform composition of the CuCl. film, Sesselmann and Chuang postulated that the copper-chlorine reaction is probably controlled by the diffusion of Cu through the CuClI, film, similar to the Cabrera-Mott mechanism of oxidation. When the copper reaches the surface of the film, it is available to react with the chlorine species [3]. Several researchers have studied the thermal desorption from
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