Mechanism of hemispherical-grained Si formation for dynamic random access memory cells by rapid thermal chemical vapor deposition

Abstract

An uneven coating made of hemispherical-grained Si (HSG) was formed on an amorphous Si layer by a rapid thermal chemical vapor deposition (CVD) (RTCVD) process. The uneven coating increases the effective surface area of a capacitor electrode in dynamic random access memory (DRAM) cells. The formation of the HSG consists of “seeding” and subsequent isothermal annealing stages. During the seeding stage, nanometer size Si single crystals are formed on the surface of the amorphous Si layer. During rapid thermal annealing at 665°C, under high vacuum, the Si grains grow linearly with increasing temperature and reach an average size of 95 nm after 20 sec. The nucleation and growth of the HSG occurs within a narrow range of temperature and time, which is sufficient for a short diffusion path of Si atoms on the surface of the amorphous Si layer, but insufficient for crystallization of the amorphous Si layer: The HSG coating increases the capacitance of a memory cell by a factor of 2.