fig2 f prevent ion implantation into the surfaces the substrate 11 below them the sidewalls of the trenches 18 in substrate 11 were ion implanted at an oblique angle with a dose of bf 2 dopant from about 1 e 12 ions cm 2 to about 7 e 13 ions cm 2 at an energy from about 15 kev to about 45 kev after annealing the concentration of the boron dopant in the sidewalls of the substrate 11 was from about 8 e 16 atoms cm 3 to about 8 e 17 atoms cm 3 as a result p type dopant has formed regions 24 in the substrate 11 where source regions s will be formed later with implanted n type dopant as shown in fig1 g and 2g referring to fig1 g and 2g source drain s d regions s and d are formed by ion implanting n type dopant in an anisotropic substantially vertical implant into the exposed surfaces of substrate 11 aside from the fox regions 16 again the fox regions 16 in fig2 g prevent ion implantation into the surfaces the substrate 11 below them the source drain regions s and d were ion implanted with a dose of arsenic phosphorus or antimony n type dopant from about 5 e 14 ions cm 2 to about 5 e 15 ions cm 2 at an energy from about 20 kev to about 45 kev after annealing the concentration of arsenic.