Location-control of large Si grains by dual-beam excimer-laser and thick oxide portion

An array of large Si grains was placed at a predetermined position by dual excimer-laser irradiation of a multi-layer structure of silicon (Si), silic on dioxide (SiO2) with an array of bumps and metal on a glass substrate. We have investigated the effects of irradiating energy density and the topolo gy of the structure on the grain size and crystallographic structure by sca nning electron microscopy (SEM) and electron back-scattering pattern (EBSP) analysis. In the low-energy-density regime, numerous small grains and peta l shaped grains formed on top of the SiO2 bumps. The number of small grains on the bumps decreased with increasing irradiating energy density. At suff iciently high energy densities, one single Si grain as large as 3.5 mu m wa s positioned at the center of the bumps. Although most of the area of the l arge Si grain has a single crystallographic orientation, twins and low-angl e grain boundaries are often formed at the periphery of the grain. There wa s no preferred crystallographic orientation in the center of the location-c ontrolled Si grain. Numerical analysis of the temperature profile showed th at a temperature drop occurs at the center of the bump, during and immediat ely after laser irradiation. The diameter of the location-controlled Si gra in increased with total thickness of the intermediate SiO2 layer, and took the maximum value of 6.2 mu m.