Germanium as a versatile material for low-temperature micromachining

Though germanium (Ge) shares many similar physical properties with silicon (Si), it also possesses unique characteristics that are complementary to those of Si. The advantages of Ge include its compatibility with Si microfabrication, its excellent gas and liquid phase etch selectivity to other materials commonly used in Si micromachining, and its low deposition temperature (<350°C) that potentially allows Ge to be used after the completion of a standard CMOS run. Wider applications of Ge as a structural, sacrificial, and sensor material require a more systematic investigation of its processing and properties. The results of such an undertaking are presently reported. The topics covered are the formation of Ge thin films and novel application of the selective deposition of Ge to etch hole filling, characterization of the effects of thermal treatment on the evolution of the residual stress in Ge thin films, etch selectivity for etch mask and sacrificial layer applications, and gas phase release technique for stiction elimination