Coefficient of thermal expansion and elastic modulus of thin films

The coefficient of thermal expansion (CTE), biaxial modulus, and stress of some amorphous semiconductors (a-Si:H, a-C:H, a-Ge:H, and a-GeCx:H) and met allic (Ag and Al) thin films were studied. The thermal expansion and the bi axial modulus were measured by the thermally induced bending technique. The stress of the metallic films, deposited by thermal evaporation (Ag and Al) , is tensile, while that of the amorphous films deposited by sputtering (a- Si:H, a-Ge:H, and a-GeCx:H) and by glow discharge (a-C:H) is compressive. W e observed that the coefficient of thermal expansion of the tetrahedral amo rphous thin films prepared in this work, as well as that of the films repor ted in literature, depend on the network strain. The CTE of tensile films i s smaller than that of their corresponding crystalline semiconductors, but it is higher for compressive films. On the other hand, we found out that th e elastic biaxial modulus of the amorphous and metallic films is systematic ally smaller than that of their crystalline counterparts. This behavior sta nds for other films reported in the literature that were prepared by differ ent techniques and deposition conditions. These differences were attributed to the reduction of the coordination number and to the presence of defects , such as voids and dangling bonds, in amorphous films. On the other hand, columnar structure and microcrystallinity account for the reduced elasticit y of the metallic films. (C) 1999 American Institute of Physics. [S0021- 89 79(99)01021-X].