Semiconductor field region implant methodology

Abstract

An MOS device is provided having a channel-stop implant placed between active regions and beneath field oxides. The channel-stop dopant material is a p-type material of atomic weight greater than boron, and preferably utilizes solely indium ions. The indium ions, once implanted, have a greater tendency to remain in their position than boron ions. Subsequent temperature cycles caused by, for example, field oxide growth do not significantly change the initial implant position. Thus, NMOS devices utilizing indium channel-stop dopant can achieve higher pn junction breakdown voltages and lower parasitic source/drain-to-substrate capacitances. Furthermore, the heavier indium ions can be more accurately placed than lighter boron ions to a region just below the silicon layer which is to be consumed by subsequent field oxide growth. By fixing the peak concentration density of indium at a depth just below the field oxide lower surface, channel-stop implant region is very shallow. Small dispersions in range allow for more precise control of the indium atoms just below the field oxide, further from the inner bulk material of the underlying substrate.