Ion implant method for forming trench isolation for integrated circuit

Abstract

A method is described for forming trench isolation for integrated circuits on silicon wafers by selectively doping the trench regions by ion implantation and then etching these areas with a wet chemical etch. A dopant such as boron, is implanted in a sequence of energies and doses to provide a desired trench profile of heavily doped silicon. The implanted silicon etches far more rapidly than the surrounding silicon and is readily etched out forming a trench. The concentration of dopant diminishes rapidly in the periphery of the implanted region. As the etch front approaches the periphery, the silicon etch rate, likewise diminishes and the etch can be quenched to leave a uniform surface layer of enhanced boron concentration which lines the resultant trench to form an effective channel stop. Wet etched trenches provide advantages over trenches formed by RIE including smooth rounded trench profiles which reduce stress. In addition, trenches having widths below 0.25 microns and essentially vertical walls can readily be formed.