PULSED ION BEAM SURFACE MODIFICATION OF MATERIALS (SILICON, SILICIDES, METASTABLE).

摘要

Applications of pulsed ion beams to the surface modification of materials are presented. These applications include controlled metal/silicon interfacial reactions, the crystallization of amorphous silicon, and the formation of metastable alloys.; The technique of transient conductance was used to measure the melt depth of pulsed ion beam irradiated silicon as a function of time. It was found that melting was largely influenced by the ion species. For heavy ions, the penetration depth was less. This resulted in higher surface temperatures and steeper temperature gradients. For light ions (80 percent protons), the temperature was uniform over the top 1.5 (mu)m of silicon. This resulted in lower regrowth velocities. In addition, a higher incident energy density was needed to initiate melting. Melt depths greater than 1.0 (mu)m and regrowth velocities as low as 1.2 m/s were observed. Good agreement was found between computer simulations of the melt depth as a function of time and the experimental data.; Interfacial melting, at near eutectic compositions, was observed in four metal/silicon systems (Ni/Si, Co/Si, Pt/Si, and Au/Si). In all cases, the initial reaction occurred below the melting temperature of either the deposited metal layer or the silicon substrate. At high incident energy densities, the composition of the reacted layer became graded, and varied from the eutectic composition to the nearest silicon rich phase (Au/Si, Pt/Si, Ni/Si). Cross sectional transmission electron microscopy of the Ni/Si and Co/Si samples showed that the reacted layer formed a sharp interface with the silicon substrate.; Amorphous phase formation by pulsed ion beam melting was possible at non-congruent compositions. A critical factor in amorphous phase formation was the absence of nucleation sites in the sample or on the substrate. Ti-Au multilayers deposited on SiO(,2) substrates could be completely amorphized, providing that the alloy had an non-congruent composition and that complete melting occurred. Surface melting of Cu(,60)Zr(,40) metallic glass ribbons, without crystallization, was also observed.; Amorphous silicon layers, on silicon substrates, were crystallized by pulsed ion beam irradiation. At high incident energy densities (>0.8 J/cm('2)) crystallization occurred in the liquid phase. At energy densities above 0.9 J/cm('2), epitaxial regrowth was observed. At low incident energy densities (0.4 - 0.8 J/cm('2)), crystallization occurred without impurity diffusion. Results in this energy range indicated the occurrence of self-sustained crystallization.