A mechanism of field-oxide-ungrowth phenomenon in recessed isolation process and practical solution

Abstract

Field-oxide-ungrowth (FOU) phenomenon in recessed local oxidation of silicon (R-LOCOS) isolation process has been studied. Field oxidation temperature has been revealed to play a decisive role in the occurrence of FOU and nitrogen-containing polymers originated from the etching process are believed to be converted into oxidation barrier materials at a certain temperature and above. This transition temperature lies between 1000 and 1050°C, independent of the ambient in the furnace. Although field oxidation below the transition temperature can eliminate the FOU, it causes severe thinning of the field oxide at a small isolation spacing. In order to remove the FOU and at the same time to minimize the field oxide thinning, we propose a new field oxidation method which is a combination of a breakthrough field oxidation at below the transition temperature and a high temperature field oxidation.