| Summary: | 博士 === 國立中興大學 === 精密工程學系所 === 102 === This study presents the results of four-point bending tests investigating the effects of substrate strain on the growth of interfacial Cu-Sn inter-metallic compounds (IMCs). Test specimens were cut into strips, 27 mm in length and 5 mm in width, from 4 inch double polished silicon wafers. A very thin adhesion layer (Ta) was deposited on the silicon substrate by sputtering followed by a 10 μm thick layer of copper using electroplating. Finally, a 30 μm tin layer was deposited over the copper film also by electroplating. Samples were then placed in a furnace at 200 ℃ to undergo bending in order to introduce in-plane strain under tension or compression. Control samples also underwent the same treatment without applied strain. Our aim was to investigate the influence of substrate strain and aging time on the formation of IMCs (1.54 x 10-4, 2.3 x 10-4 and 3.46 x 10-4). The thickness and separation of each phase (Cu3Sn) and (Cu6Sn5) are clearly visible in scanning electron microscope images. Compressive strain and tensile strain both increased the thickness of the IMC layer during the aging process; however, the effects of compressive strain were more pronounced than those of tensile strain. We hypothesize that the increase in IMC thickness is related to the strain enhanced out-diffusion of Cu towards the solder as well as strain in the underlying lattice at the diffusion interface.
We also investigate the internal friction in nanocrystalline silver and gold thin films (40 – 170 nm thick) deposited on silicon substrate. Paddle-like samples were designed to present uniform stress and all measurements were performed under high vacuum to eliminate the effects of air damping. Annealed thin films presented far less internal friction than as-deposited films. Annealing reduced the internal friction in Ag films by 3 – 28 times lower than those obtained from as-deposited films. Annealing reduced internal friction in Au films to 17 %, 29 %, and 42 % in 41 nm, 90 nm, and 170 nm samples, respectively. With the exception of the thinnest Au film, the internal friction in all thin metal films was dependent on film thickness. In all cases, internal friction was affected by grain size and grain boundary.
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