Indirect laser annealing of PolySilicon for three-dimensional IC´s

A new laser annealing technique for producing single crystalline silicon islands on an amorphous insulating layer has been developed using a Si cap for three- -dimensional IC´s. This technique stably produces a desired temperature gradient in order to eliminate grain boundaries in re-- crystallized silicon islands; the interior of the Si islands is kept cooler than the periphery and crystal growth begins from the interior. This desired temperature gradient is realized because the Si islands are indirectly heated by an Ar ion laser beam. Laser power is absorbed in a Si cap and heat flow takes place to the Si islands laterally as well as vertically through a separation cap from the high- -temperature Si cap. Grain boundaries are eliminated completely in 30×60 µm²islands recrystallized by the indirect laser annealina. Field effect mobility of 460 cm²/v . s is obtained for SOI/MOSFET´s fabricated in the silicon islands. This technique is suitable for fabricating three-dimensional IC´s in which many MOSFET´s are stacked vertically, because the desired temperature gradient is produced by the cap structure and the same recrystallization sequence can be used frequently for SOI of all the layers, keeping the underlying layers at low temperature.