Release of As from SiO sub 2 by a temperature gradient and formation of buried n sup + conductive layers in Si-on-SiO sub 2 structures.

We demonstrate the utility of a temperature gradient, DELTA T, in transporting dopants, such as As, undirectionally through SiO sub 2 and into Si. The transport, based on thermomigration of dopant-rich precipitates toward the heat source, turns oxide into an efficient diffusion source. It also provides the only possible method of forming buried n sup + conductive layers in recrystallized, thick Si-on-SiO sub 2 structures. To build such structures, arsenic is implanted into the oxide, where it remains trapped during deposition of polycrystalline Si and its recrystallization from the melt, but is subsequently released into the Si film by a directional drift in the DELTA T. In the future, controlling dopant transport with two independent parameters (temperature and DELTA T), instead of the temperature alone may allow processing of 3-dimensional circuits at higher temperatures than would be otherwise possible.