Amorphous Phase Formation During Ion Mixing of Ti/Si Bilayers at Elevated Temperature
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AMORPHOUS PHASE FORMATION DURING ION MIXING OF Ti/Si BILAYERS AT ELEVATED TEMPERATURE K. MAEX, R.F. DE KEERSMAECKER, M. VAN ROSSUM and W.F. VAN DER WEG° Interuniversity Microelectronics Center (IMEC v.z.w.) Kapeldreef 75, B-3030 Leuven, Belgium. 0
Department of Technical Physics, State University Utrecht, PO Box 80000, 3508 TA Utrecht, The Netherlands. Abstract The amorphousphaseformationin Ti-Si bilayers upon ion mixing at elevated temperaturesand in Ti-Si multilayers upon thermal treatmentwas studied.In the case of ion mixing with 5x10 15 cm"2 Xe atoms at temperaturesaround2400C a lOOnm thick amorphousTi-Si alloy is formed with a very homogeneous Ti:Si=3:4 composition. Thermal treatment of the Ti-Si multilayer structure at similar temperatures also yields amorphous silicide layers. The results are interpretedaccording to the evolution in a planarbinary diffusion couple, where the Si and Ti concentrationsin the reactedlayer are dictatedby thermodynamicand kinetic arguments. Introduction Refractory metal silicides have become increasingly important because of their applications in integrated circuits. As a result, various techniques for their formation have been explored. The formation of TiSi2 by a solid-phase reaction between a deposited Ti film and the Si substrate is very attractive in advanced semiconductor processing, as it allows selective silicidation [1]. The reaction between the Ti film and the Si substrate under ion bombardment has received a lot of attention in recent years because of its technological implications [2]. Since the phase formation sequence of Ti/Si bilayers during solid state reaction is of interest both from a technological and theoretical viewpoint, it has been the subject of several investigations [3-51. In ion mixing the transient nature of the energy deposition associated with the ion irradiation opens interesting perspectives with respect to phase formation and meta-stable equilibrium phenomena. In this work experiments were carried out using both ion mixing and thermal treatments to induce the Ti/Si reaction. In this way more insight could be obtained in the underlying mechanisms responsible for the phase formation sequence. Experimental conditions Thin films of Ti (60nm) were deposited on Si, using DC magnetron sputtering at a rate of 0.5nm/s in a system with a base pressure of 10-7 Torr and an Ar working pressure of 3xl0-4 Torr. The native oxide on the Si was removed by a 2% HF dip immediately preceding the metal deposition. Ion irradiation was carried out mainly with 260keV Xe-ions with doses ranging from 1015 to 5x10 16 cm 2 with a constant current of about l2OnA/cm 2 in a vacuum better than 5xl0"6Torr. Other species like Sb, As and Kr were used as well. The implantation energy was chosen such that the projected range of the ions was approximately l0nm beyond the Ti/Si interface, so that the majority of the implanted ions passed the interface. During ion implantation the samples were held at fixed temperatures. Cooling rates after implantation were of the order of 100 0C/min.
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