Mechanisms in the Ion-Assisted Etching of TiSi 2
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MECHANISMS IN THE ION-ASSISTED ETCHING OF TiSi 2 W.L. O'BRIEN*, T.N. RttODIN* AND L.C. RATHBUN** *School of Applied and Engineering Physics, Cornell University, Ithaca NY 14853 "**NationalNanofabrication Facility, Cornell University, Ithaca NY 14853
ABSTRACT A detailed investigation into the mechanisms of the ion-assisted etching of TiSi 2 using 1000 eV argon ions and chlorine gas is reported. X-ray photoelectron spectroscopy (XPS) was used to investigate surface product distributions and modulated ion beam mass spectroscopy (MIBMS) was used to investigate gas phase product distributions. Identical experiments were performed on silicon and titanium single crystal substrates. Information on chemical mechanisms during ion-assisted etching was obtained by comparing the product distributions of the three substrates. For each substrate, the di and tetrachlorides were the major gas phase products. These products were emitted with high thermal velocities following a surface residence process. TiC1 and TiC12 products were found on the titanium surface after simultaneous exposure to chlorine and argon ions, but not on the TiSi 2 surface. These observations are discussed in terms of specific chemical mechanisms which are critical during ion-assisted etching. I. INTRODUCTION The mechanisms of ion-assisted etching have been the subject of extensive research during the past decade. Typically, these mechanisms are interpreted in terms of physical processes associated with ion bombardment and/or ion-induced surface chemistry. Silicon, etched with chlorine and argon ions, is the most widely studied system[I,2,3]. This is due to the importance of silicon etching to the microprocessing industry. Other systems which have received detailed investigations are Si/XeF 2 /Ar[4], GaAs/C12 /Ar[5,6], W/XeF 2 /Ar[7] and Ti/C12 /Ar[8]. In this paper we present new experimental results on the ion-assisted etching of TiSi 2 using chlorine gas and argon ions. Comparison of these results is made to results obtained for the Si/Cl 2 /Ar+ and Ti/Cl2 /Ar+ systems using identical experimental conditions. These results are interpreted in terms of specific chemical mechanisms involved in ion-assisted etching. It is appropriate to discuss the present day knowledge of ion-assisted etching and then to discuss the specific systems Si/C12 /Ar+ and Ti/C12 /Ar+ to provide a background to understanding the new work on the TiSi2 /C1 2 /Ar+ system. When an energetic ion strikes a surface it induces a collisional-cascade. The depth of this cascade is ;20-30 A for the ion energies and substrates discussed in this paper. During the duration of this cascade physical (collisional-cascade) sputtering takes place. If an ion strikes a surface in the presence of a reactive adsorbate, "ion-mixing" occurs. These ion-mixing processes have been discussed in detail by Dieleman et. al.[1] and have been investigated using Rutherford backscattering by Mayer et. al.[2]. Briefly, the incident ion implants adsorbed species by direct momentum transfer, or induces the adsorbate and su
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