THE SELECTIVE EPITAXIAL GROWTH OF SILICON

Abstract

The SEG technique and its extension epitaxial lateral overgrowth (ELO) have already found many applications in device fabrication both in terms of process simplification and new device structures. The basic processes involve substrate preparation, ex-situ cleaning, in-situ surface oxide removal and SEG/ELO growth. Substrate preparation involves fabrication of the necessary seed-windows in, e.g. oxide or nitride layers down to the single crystal substrate : this is usually achieved using a reactive ion etch (RIE) process followed by the growth and subsequent etching of a sacrificial oxide (SO) for surface damage removal. Ex-situ cleaning usually consists of a wet chemical treatment, e.g. RCA, with the final RCA-2 step leaving the silicon surface coated with a reproducible thin oxide layer which also serves to remove various contaminants. The in-situ clean removes the latter oxide through a low pressure H2 prebake, using a temperature which effectively etches the oxide via the [MATH] disproportionation reaction, but which minimises the concomitant undercutting of the exposed SiO2/Si oxide - substrate interface by the same reaction. The growth process involves optimisation of the main parameters, i.e. temperature, pressure and gas flows, to obtain full control of selectivity (i.e. polysilicon nucleation on the field area), sidewall faceting, defect generation and autodoping. This paper will review the technique of selective silicon epitaxy and discuss the results obtained during the optimisation of the above parameters for device applications using a modified Applied Materials LPCVD vertical barrel epitaxial reactor system.