Effect of Deposition Conditions on the Structural and Mechanical Properties of Poly SiGe

Abstract

ABSTRACTMicroElectroMechanical Systems (MEMS) are used in a wide variety of applications such as accelerometers [1], gyroscopes [2], infrared detectors [3],…etc. For high volume applications, fabrication costs can be possibly reduced by monolithic integration of MEMS with the driving electronics. The easiest approach for monolithic integration is post processing MEMS on top of the driving electronics, as this does not introduce any change into standard fabrication processes used for realizing the driving electronics. On the other hand, post processing imposes an upper limit on the fabrication temperature of MEMS in order to avoid any damage or degradation in the performance of the driving electronics. Polycrystalline silicon (Poly Si) has been widely used for MEMS applications [4], but the main disadvantage of this material is that it requires a high processing temperature (higher than 800°C [5]) to achieve the desired physical properties. In particular, a low tensile stress is needed for MEMS. Polycrystalline silicon germanium (Poly SiGe) seems to be an attractive alternative to poly Si as it has similar properties, while the presence of germanium reduces its melting point. Hence, the desired physical properties are expected to be realized at lower temperature. Depending on the germanium concentration and the deposition pressure, the transition temperature from amorphous to polycrystalline can be reduced to 450°C [6], or even lower, compared to 580°C for LPCVD poly Si. Also, the residual mechanical stress in poly SiGe is lower than that in poly Si [7].