Selective area chemical vapor deposition of epitaxial silicon-germanium thin films by the alternating cyclic method

The last few years have seen considerable advancement in SiGe technology due to the potential for achieving greater device speed than silicon alone. Si_1–xGe_x heterostructures have found applications in fabricating heterojunction bipolar transistors (HBTs), and in channel engineering, as gate material and in contact resistance applications in Insulated Gate Field Effect Transistors, IGFETs. In order to fabricate such devices, excellent control over the morphology and composition of epitaxial Si_1–xGe_x films is mandatory. Within this dissertation, the development of a process for selectively depositing epitaxial Si _1–xGe_x thin films by the Alternating Cyclic (A.C.) Method has been accomplished. The effect of various processing conditions, such as deposition temperature, input gas phase composition, and deposition time on the resulting Si_1–xGe_x film composition, morphology and crystalline perfection has been studied.; In order to study the applicability of the A.C. technique for selective area deposition of Si_1–xGe_x thin films, an extensive thermodynamic analysis has been performed over extensive temperature, pressure, input gas ratio and deposited solid composition ranges, for the Si-Ge-Cl-H and Si-Ge-Cl-H-Ar systems. These calculations have indicated that selective Si_1–xGe_x deposition by the A.C. technique is feasible. It was observed that, in order to deposit Si-Ge films with a low Ge content (which is the case in most practical applications) at a low deposition temperature, one needs to use the lowest practical total system pressure, the highest practical input SiCl₄/(SiCl₄ + GeCl₄) mole fraction and the highest practical input H/Cl ratio. Furthermore, it was found that the use of argon as an inert carrier gas has the potential to lower the temperature of deposition of the alloy, increase the efficiency of deposition at a given temperature and lower the temperature for onset of deposition composition plateaus.; Selective Si_1–xGe_x thin films have been deposited in a hot wall, low pressure chemical vapor deposition system, using oxide masked silicon wafers. It has been found that various experimental conditions influenced, to varying degrees, the tendency for formation of spurious nuclei on the oxide surface. However, under all conditions, the A.C. technique was found capable of preventing the formation of spurious nuclei on the oxide, guaranteeing essentially 100% selectivity control, for both non-implanted wafers and ion-implanted wafers.