Lateral growth control in excimer laser crystallized polysilicon

The control of the structural properties of polysilicon obtained by excimer laser crystallization has become of great importance to further develop the polysilicon thin-®lm transistors technology. The most attractive crystallization regime is the so-called super lateral growth (SLG), characterized, however, by a very narrow energy density window and a strongly non-uniform grain size distribution. In this work we have investigated several approaches to achieve a control of the lateral growth mechanism through lateral thermal gradients, established by the opportune spatial modulation of the heating. To this purpose, three different patterned capping layers have been used: anti-reflective (SiO2), heat-sink (silicon nitride) and reflective (metal) overlayers. For all three types of overlayers, when the conditions to trigger the lateral growth mechanism are achieved, a band of oriented grains (1±2 um wide) appears at the boundary between capped and uncapped region and extending in the more heated region. Among the different approach the use of re¯ective overlayers appears promising and further engineering of this process is in progress.