Laser-induced epitaxial growth for 3D-IC & 3D-memory devices

Abstract

Laser-induced epitaxial growth (Laser-induced Epitaxial Growth) process has been developed to obtain single crystalline silicon on insulator using a seed which is formed by selective epitaxial growth process. It was found that the lateral epitaxial growth of molten silicon occurs when the energy density of the laser beam is high enough to completely melt the deposited amorphous silicon on seeds and that on oxide films. The location and size of such single crystalline grain were precisely controlled due to the pre-patterned epitaxial seeds. Furthermore the problem caused by the edge area of the laser beam was thoroughly analyzed, and solutions to the problem were reasonably suggested. Consequently this proposed laser-induced epitaxial growth process enables the realization of location-controlled perfect single crystalline silicon layer on oxide films for monolithic three-dimensional integration. Novel isolation technology by using LEG process has been introduced to obtain monolithically stacked active silicon without any thermal budget. With the LEG process, the epitaxial behavior is completely understood by solidification modeling. It is shown that the characteristics of cell transistors with LEG-active silicon are the same as those with bulk-active Si, in terms of both performance and distribution using high density 512Mb DRAM devices. Thus LEG process is believed to be a promising device isolation technology for monolithic multi-stack device.