ANOMALOUS FIELD-OXIDE-UNGROWTH PHENOMENON IN RECESSED LOCAL OXIDATIONOF SILICON ISOLATION STRUCTURE

An anomalous field-oxide-growth phenomenon in a recessed local oxidati on of silicon (LOGOS) structure with a nitride spacer (R-LOCOS), in wh ich the field oxide growth at the center of the opening area is suppre ssed when isolation spacing is small, is reported. The field-oxide-ung rowth (FOU) phenomenon was found to have strong structural dependence, on the aspect ratio of the opening area, active pattern density, and silicon recess depth. By changing process conditions, such as dry etch ing and wet cleaning conditions, however, the FOU was not affected. Si nce the tendency of the FOU occurrence was coincident with that of the microloading effect in reactive ion etching, the FOU was believed to originate from a residue on the exposed silicon surface after the etch ing process. When silicon was not recessed, the FOU was not observed a t any of the structural variations. From a two-dimensional simulation of field oxidation, it has been found that in a nonrecessed LOGOS stru cture, a residue on the silicon surface does not significantly affect field oxide growth, but in the recessed LOGOS structure, field oxide g rowth is very sensitive to the existence of a residue on the recessed surface. Thus, to successfully use the recessed LOGOS structure with a subquarter micron design rule avoiding the occurrence of the FOU, str uctural factors that include an active pattern layout should be carefu lly chosen.