AVS 59th Annual International Symposium and Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS1-ThM

Paper PS1-ThM5
Etching Reaction Analysis of CoFeB by Carbon Monoxide / Methyl Alcohol Based Plasmas

Thursday, November 1, 2012, 9:20 am, Room 24

Session: Plasma Processing for Disruptive Technologies (NVM, TSV, etc.)
Presenter: K. Karahashi, Osaka University, Japan
Authors: K. Karahashi, Osaka University, Japan
T. Ito, Osaka University, Japan
S. Hamaguchi, Osaka University, Japan
Correspondent: Click to Email
Magneticrandom access memory (MRAM)devices,which are composed of magnetic-tunnel-junction (MTJ) stacks, have potential to replace static random access memory, dynamic access memory, and flash memory devices because they can provide high speed operation, low operating voltage, and nonvolatile storage. For the realization of high-density MRAM devices, dry etching of magnetic thin films must be developed.Argon ion milling seems to be almost the only etching technique available in the current manufacturing processes for MRAM devices. However, capabilities of Argonion milling for anisotropic and selective etching of magnetic films are severely limited and therefore new technologies of reactive ion etching (RIE) for magnetic films are now seriously sought.RIE processes based on CO/NH3 and CH3OH are candidates for selective etching processes of magnetic thin films. In this study, we have focused on etching processes of CoFeB alloy thin films and examined etching reactionscaused by energetic CO+ or O+ ions, which are considered to be the major etchants of CO/NH3 or CH3OH plasmas. We have determined the etching yields and analyzed surface reactions, using a mass-selected ion beam system. The ion beam system is designed to inject mono-energetic single-species ions into a sample surface in ultra-high vacuum conditions. The reaction chamber is equipped with an X-ray photoelectron spectroscopy (XPS) for in-situ chemical analyses of irradiated surfaces. The ion beam energy used in this study is in the range of 300-1000eV. The etching rates are determined from measured depth profiles of irradiated surfaces and ion fluxes. It has been found that the etching rates of CoFeB by Ar+ ions are smaller than those of CoFe. Thereforephysical sputtering yields of such magnetic thin films are affected byboron atoms contained in them.The etching rates of CoFeB by CO+ ions are found to belower than those by Ar+and increasewiththe cobalt content. From XPS analysis ofCO+ irradiated CoFeB surfaces, it has been found that, although cobalt does not oxidize,iron of CoFeBoxidizes and inhibits the etching reactions. Therefore, the etching rates of CoFeB by CO+ irradiation are dependent on the atomic compositions of CoFeB films. The results suggest that design of the atomic composition of CoFeBfilms is important also for the etching process development.This work was supported by the Semiconductor Technology Academic Research Center (STARC).