Electrical Properties of Schottky Contacts of TiW on RTCVD Si 1-x-y Ge x C y Films
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Rapid thermal CVD (RTCVD) has its further advantages. Low thermal budget is indispensable to the metastable alloys due to lattice relaxation and silicon carbide precipitation. The major issue of epitaxial growth of SiGeC on Si is to subsititutionally incorporate carbon into the alloy without introducing any defects. It is generally known that non-thermal-equilibrium growth, i.e. low temperature and high growth rate, is required [1,7]. For a particular growth method, the growth mechanism should be studied by taking into account the specific features of the growth process. Also, it would be useful to study the relationship between growth conditions and the electrical properties of the alloys. To this end, we have grown SiGeC on Si by RTCVD, and studied the crystal properties of SiGeC/Si heterostructures and electrical properties of TiW/SiGeC Schottky contacts. EXPERIMENTAL Silx.yGeCy/Si heterostructures were produced using a commercial RTCVD reactor (Jipelec, Jetlight 200), using hydrogen as a carrier gas and silane, germane, and methylsilane as source gases. The growth system and growth procedures were described in Ref 2 and 8. A Si layer of 200 nm thick as a buffer layer was first grown on a 4 in. (100)-Si substrate at 900'C, followed by the growth of a SiGeC layer at 560 or 600'C. The growth pressure was 1.5 Torr. The Si substrates were n-type, and have a resistivity of about I Qcm. All epitaxial layers were unintentionally doped. The process conditions for the samples used in this study are summarized 121 Mat. Res. Soc. Symp. Proc. Vol. 470 01997 Materials Research Society
in Table I. Also given in the Table are germanium and carbon concentrations. For defect-free alloy layers, substitutional carbon concentrations were obtained from x-ray diffraction (XRD), while total carbon concentrations of samples D and E, whose crystal quality is degraded, were determined from secondary ion mass spectroscopy (SIMS). Sample A,, is used as a reference SiGeC sample for Fourier transform infrared spectroscopy (FTIR) measurements. Schottky diodes with SiGeC alloy layers were fabricated using conventional silicon technology (see Fig. 1). Phosphorus was implanted into the back of the substrate to ensure good electrical contact, with the energy and dose being 40 keV and 5x 1013 cm"2, respectively. Donor activation was achieved with a furnace annealing in N2 ambient at 550'C for 30 min. A TiW (10%Ti) layer of 100 nm thick was deposited on SiGeC by sputtering to form the Schottky contact. Aluminum films of 11jm thick were deposited on both sides to form electrode contacts. Electrodes with areas of 2.83 x 10-3 cm 2 were formed on the front side using standard wet and plasma patterning. Both material and electrical characterizations were performed. XRD, FTIR, and transmission electron microscopy (TEM) were used to evaluate the crystal structures of the as-grown SiGeC/Si heterostructures. Current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed to investigate the electrical properties of TiW/SiGeC Schottky diodes
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