Grain‐Growth Mechanisms in Polysilicon

Abstract

The electrical characteristics of polycrystalline silicon layers are closely related to their grain structure. This paper describes a comprehensive study of the grain growth of polysilicon under a wide range of doping and processing conditions. A grain‐growth model has been developed and implemented in the SUPREM process simulator, and the simulated results are compared to those obtained by transmission electron microscopy for As‐, P‐ and B‐doped polysilicon. These results indicate that n‐type dopants increase the growth rate whereas the p‐type dopant has a negligible effect.

Evaluation of Grain Surface Area in Heavily Arsenic‐doped Polysilicon

“…It is noted that the grain size is directly proportional to the square root of the annealing time as reported earlier (MEI et al;THOMSON et al;THOMSON, KALAINATHAN et al 1988). The surface area of the grain can be written as…”

“…This process is known as grain growth. Recently many researchers have been attracted by the mechanism of grain growth in various materials (KALAINATHAN et al 1988;MEI et al;SROLOVITZ et al;THOMSON et al;THOMSON;WADA et al). In the case of grain growth in metals, driving force for the grain growth exists from the reduction of grain boundary area during the thermal treatment.…”

Principal Ideas of Crystal Growth

“…For silicon, the most dramatic efIect was observed with phosphorus when its concentration reached (3)(4)(5) x 102(), cm -3 , i.e., approximately 1% relative to the silicon matrix. (178)(179)(180)(181)(182) The efIect is a significant increase of crystalline sizes when the film is annealed at temperatures in the range lOOO-1200°C, both primary and secondary recrystallization being afIected by the impurity. The efIect is in line with many other efIects in which doping with phosphorus (as weIl as with other group V elements) enhanced the kinetics of processes in silicon or germanium, including acceleration of self-difIusion in silicon (183) and crystallization of amorphous silicon.…”

Faceting of twin grain boundaries in polysilicon films

“…This is of practical importance since polysilicon films in electronic devices are usually doped. Numerous investigations 5, 25–29 have shown that grain growth in polysilicon films is greatly affected by electrically active dopants. The presence of impurities plays two roles: an increase of vacancy concentration caused by a shift of the Fermi level and the change of GB energy resulting from impurity segregation at the boundaries.…”

“…The presence of impurities plays two roles: an increase of vacancy concentration caused by a shift of the Fermi level and the change of GB energy resulting from impurity segregation at the boundaries. N‐type dopants, such as arsenic and phosphorus, significantly enhance grain growth, while p‐dopants including boron have only a minimal effect 5, 25–29. Both phosphorus and arsenic doping of polysilicon enhances the rate of abnormal grain growth (presumably through enhancement of the GB mobility).…”