How to form buried bitline in Flash EEPROM

摘要

The present invention comprises the steps of forming a field oxide film 6 on a predetermined portion of the semiconductor substrate 1, forming a photoresist film 5 'pattern, which is a mask for a buried bit line, and implanting cobalt ions into a wafer. Embedded implantation of a flash EEPROM comprising the steps of performing ion implantation so that ions reach under the field oxide film 6 while applying a temperature of 400 to 500 ° C., and annealing the wafer. The present invention relates to a formation method, which uses a single crystal CoSi ₂ layer as a bit line instead of an ion implanted BN ⁺ layer to greatly reduce bit line resistance. In addition, since the CoSi ₂ layer is formed after the field oxidation process, there is little lateral diffusion, thereby ensuring more space margin between bit lines, which improves punch through characteristics and reduces cell size, thereby contributing to the improvement of device quality. It works.