Bombardment-Induced Mixing of Mo Films on Si
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A.H. VAN OMMEN. M.F.C. WILLEMSEN. P.R. BOUDEWIJN AND A. H. READER Philips Research Laboratories P.O.B. 80 000. 5600 JA Eindhoven. The Netherlands
ABSTRACT We studied ion beam mixing of thin Mo films on monocrystalline Si by As implantation at room temperature. The results differ significantly from those obtained for implantation at elevated temperature (T > 200"C), where ion beam mixing results in hexagonal MoSi, formation. Room temperature implantation results in the formation of an amorphous mixed layer. The composition of this layer varies with depth from Mo-rich to Sirich. The mixed layer thickness increases linearly with implanted dose and energy. An increase of the implantation temperature with 100TC gives rise to a factor of 2 larger mixed layer thickness and to the formation of amorphous MoSi, near the interface with Si. These phenomena indicate that at elevated temperature ion beam mixing is controlled by radiationenhanced diffusion whereas, at room temperature ballistic mixing is the dominant mechanism.
INTRODUCTION Bombardment of a thin metal film on a silicon substrate with energetic ions. having a range comparable to the film thickness. results in compositional and structural changes at the interface. This process is indicated by the term "ion beam mixing" and can be attributed to a variety of complex ionsolid interaction effects such as recoil implantation. cascade mixing and radiation enhanced diffusion. A detailed description of these effects vvas given in the review papers of Mayer and Lau I l1 and of Appleton 121. In silicide forming systems ion beam mixing generally results in a silicide layer with a definite composition rather than in uniform mixing of the elements. The composition of these layers is in general the same as the first phase formed bNthermal annealing. For nearnoble metal layers these ion beam induced reactions result in crystalline phases at room temperature. For refractory' metals such as Mo crystalline phases have only been observed with bombardment at elevated temperatures (200 0 C - 400 0 C 13.4.51. At room temperature. howvcexr, the mixed layer
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Ficlure Cross-sectional TEM picture a antd at S SIMS depth profile oin a structure of 30 inn Mo on (100)-Si afier implantation with 101 A.N/cm-I ith/i150 ke V at room temperatufre.
Mat. Res. Soc. Symp. Proc, Vol. 54. c 1986 Materials Research Society
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is amorphous 161. The thickness of the mixed layer has also been found to be dependent on implantation temperature [5]. Since ballistic mixing is a temperature independent effect, this shows that radiation-enhanced diffusion plays an important role in ion beam-induced silicide formation. In this paper we present some results of the intermixing of Mo and Si by ion bombardment at room temperature. Since at room temperature the structure of the mixed layer is found to be amorphous, it will be interesting to determine the mechanism of ion beam mixing that is operative at this temperature. Hung and Mayer [6] suggest that the process is determined by balli
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