科研之友
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摘要
Porous silicon films were fabricated from p(+)-Si (0.001-0.005 Omega cm) wafers and characterized for their applicability to wafer bonding and layer transfer schemes. Conditions for producing porous silicon films compatible with both (i) wafer bonding surface smoothness requirements and (ii) layer transfer mechanical requirements were investigated. Nanoindentation of various films showed the quadratic dependence of Young's modulus on relative density. High porosity films (>90%) exhibited prohibitively high surface roughness values for wafer bonding applications, while wafers with lower porosity produced surfaces that were sufficiently smooth; films with midrange Young's modulus were selected for layer transfer applications. Demonstration of wafer bonding of porous silicon surfaces using silicon nitride interlayers was shown without the use of a high temperature anneal step to densify the porous surface or chemical mechanical polishing. Coarsening of the porous structure was observed at temperatures as low as 300 degrees C, and the porous films remained pseudomorphic after annealing at all temperatures, as high as 900 degrees C. Strong bonds were formed at the silicon nitride interfaces after low temperature annealing. After higher temperature annealing, mechanical fracture of the bonded stack occurred in the porous film parallel to the wafer bond interface. A fracture mechanism for these structures is proposed.
- 出版日期2010
