Thickness effect on the structural and electrical properties of poly-SiGe films

As lateral dimensions of electromechanical devices are scaled down to length scales comparable to electron mean free paths, the influence of thickness effect on their properties becomes sine qua non. This paper presents a detailed study of thickness effect on the Young's modulus, residual stress, resistivity and Hall mobility of ultrathin poly-Si11Ge89 films deposited by low pressure chemical vapour deposition. The Young's moduli for the films thicker than about 40 nm are close to the bulk value (135 GPa) while those of the thinner films are much lower. The reduction in resistivity and subsequent improved Hall mobility as thickness increases are discussed in light of surface morphology which is evident from atomic microscopy images. The near constant values of Young's modulus, resistivity and Hall mobility for the films thicker than about 40 nm are attributed to the columnar grain structure as confirmed by the transmission electron microscopy images.