A systematic study of the thermally induced reaction of 20 transition metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, and Cu) with Ge substrates was carried out in order to identify appropriate contact materials in Ge-based microelectronic circuits. Thin metal films, nominally 30nm thick, were sputter deposited on both amorphous Ge and crystalline Ge(001). Metal-Ge reactions were monitored in situ during ramp anneals at 3°Cs−1 in an atmosphere of purified He using time-resolved x-ray diffraction, diffuse light scattering, and resistance measurements. These analyses allowed the determination of the phase formation sequence for each metal-Ge system and the identification of the most promising candidates—in terms of sheet resistance and surface roughness—for their use as first level interconnections in microelectronic circuits. A first group of metals (Ti, Zr, Hf, V, Nb, and Ta) reacted with Ge only at temperatures well above 450°C and was prone to oxidation. Another set (Cr, Mo, Mn, Re, Rh, Ru, and Ir) did not form low resistivity phases (<130μΩcm) whereas no reaction was observed in the case of W even after annealing at up to 1000°C. We found that Fe, Co, Ni, Pd, Pt, and Cu were the most interesting candidates for microelectronic applications as they reacted at relatively low temperatures (150–360°C) to form low resistivity phases (22–129μΩcm). Among those, two monogermanides, NiGe and PdGe, exhibited the lowest resistivity values (22–30μΩcm) and were stable over the widest temperature window during ramp anneals. In passing, we note that Cu, Ni, and Pd were the most effective in lowering the crystallization temperature of amorphous Ge, by up to 290°C for our typical ramp anneals at 3°Cs−1.

Metal induced crystallization (MIC) is a technique that lowers the crystallization temperature of amorphous semiconductors. The process has mainly been used to influence the crystallization of amorphous silicon (a-Si) and multiple studies on this subject have already been performed. The research of the MIC of amorphous Ge (a-Ge) has been mostly limited to the use of a Ni or Al film. This paper focuses on the characterization of the crystallization behavior of a-Ge films in the presence of 20 transition metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, and Al). The kinetics of the crystallization process are also systematically studied for the seven metals that lower the initial crystallization temperature the most. In addition, the influence of the thickness of the metal film was determined for the case of a Au and Al film. A comparison of the influence of the various metals on a-Ge and a-Si is made and the similarities and differences are discussed using existing models for the MIC process

The solid-state reaction between a 30-nm-thick Ni film and Ge substrates was investigated using in situ x-ray diffraction, diffuse light scattering, and four-point probe electrical measurements. Our results reveal that Ni5Ge3 and NiGe appear consecutively on Ge(111) while they grow simultaneously on amorphous Ge(α-Ge) and Ge(001). Furthermore, phase formation temperatures depend strongly on the nature of the substrate being the lowest on α-Ge and the highest on Ge(111). X-ray pole figure measurements of the NiGe phase obtained from the reaction with an amorphous substrate indicate a completely random texture while several epitaxial and axiotaxial texture components are observed on both Ge(001) and Ge(111). The texturing for the NiGe film on Ge(111), which showed a sequential phase formation, is an order of magnitude more pronounced than for the film on Ge(001) which showed a simultaneous growth.