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Evolution of microsctructures on silicon substrates by surface diffusion

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Evolution of Microsctructures on Silicon Substrates by Surface Diffusion Koichi Sudoh The Institute of Scientific and Industrial Research, Osaka University Recently, spontaneous shape transformation of microstructures fabricated on silicon substrates by high temperature annealing has attracted attention because of the potentiality for development of novel microstructure fabrication techniques [1]. We have studied the mechanism of the spontaneous shape transformation of high-aspect-ratio microstructures, such as one-dimensional (1D) gratings [2,3] and two-dimensional (2D) hole arrays [4], on Si(001) substrates. The conventional fabrication technique using reactive ion etching (RIE) with SiO2 mask is employed to fabricate high-aspect-ratio microstructures on n-type Si(001) substrates. High temperature annealing of the sample is conducted under hydrogen gas ambient using a ramp furnace or under ultrahigh vacuum (UHV). The structures of the samples were observed by scanning electron microscopy (SEM). For evaluation of cross-sectional profiles, the samples were cleaved parallel to (001) plane. When 1D grating structures are annealed above ~ 1000 °C, rounding of the trench corners occurs. In Fig. 1, the evolution of a trench corner is shown with the dependence of the corner curvature on annealing time. According to the time scaling property of shape transformation presented by Herring, the characteristic length scale of a steady state profile evolves as t1/2 and t1/4 as the shape transformation occurs by evaporation-condensation and surface diffusion, respectively [5]. Thus, the decrease in the curvature as t-1/4 shown in Fig.1 is the evidence suggesting that the dominant mass transport mechanism responsible for the shape transformation is surface diffusion, although sublimation may be possible at such high temperature. We have performed numerical simulations of the shape transformation of one-dimensional tren

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