According to the disclosed method, there is provided a structure consisting of a
silicon substrate coated with a bottom thin SiO2 layer, a doped polysilicon layer, a
refractory metal layer and a top Si3N4 capping layer. Said
refractory metal and doped polysilicon
layers will form a
polycide layer under subsequent thermal treatments. First, a sacrificial layer of a
dielectric material such as oxynitride is deposited onto the structure. Oxynitride is impervious to UV
radiation and has excellent conformal properties. Then, a layer of a
photoresist material is deposited onto the structure and patterned to form a
mask. Now the
dielectric and top Si3N4
layers are anisotropically etched using the
photoresist mask. The
mask is stripped and the
refractory metal and doped polysilicon
layers are anisotropically dry etched down to the SiO2 layer using the patterned
dielectric layer as an in-situ
hard mask. A conformal layer of Si3N4 is deposited onto the structure, then anisotropically dry etched until the thin SiO2 layer is exposed to form the Si3N4 spacers.
Diffusion regions are formed in the substrate by
ion implantation. A layer of BPSG is deposited onto the structure and planarized. Contact holes are formed to
expose said
diffusion regions and filled with a metal to create borderless metal contacts therewith.