Surface Stabilization of Polycrystalline‐Silicon Films during Laser Recrystallization

Abstract

In the past several years numerous In i t ia l work by the Stanford group (5) attempts have been made to recrystal l ize ut i l ized an llO0 ~ furnace anneal in thin films of fine-grain CVD polycrystalline a nitrogen atmosphere for one hour to sil icon into large-grain material in order to reduce the influence of the grain boundaries. Recrystallization with a scanned CW laser has been found to increase the average grain size to several microns (1). The con-sequent reduction in defect concen-tration makes possible the fabrication of active devices, such as MOSFETs with their active channels within the layer of laser-recrystall ized polysilicon (2,3). Such devices can be used in monolithic si l icon integrated circuits to improve packing density or perfor-mance or can be constructed in sil icon films deposited on inexpensive sub-strates for applications such as f la t-panel displays. In the in i t ia l work, recrystal l iza-tion was found to occur more satis-factor i ly when the polysilicon was deposited on sil icon-nitride-coated sil icon wafers, rather than on oxidized wafers. In the latter case, at the high laser powers needed to melt the entire thickness of the polysil icon, the sil icon tends to agglomerate or delaminate, leaving regions of the underlying oxide exposed. Although the recrystal l ization proceeds more controllably on sil icon nitr ide, the electrical properties of an under-lying polysi l icon/si l icon-dioxide interface are far superior to those of a polys i l icon/s i l icon-ni t r ide inter-face (4). Consequently, attempts were made to improve the contro l lab i l i ty of the recrystal l izat ion process on s i l i-con dioxide.