Effect of fluorine on characteristics of shallow trench isolation prepared using high-density plasma chemical vapor deposition including NF₃ chemistry

We investigated whether the fluorine of the field oxide affected gate oxide reliability and some isolation characteristics of metal-oxide semiconductor (MOS) transistors for high-density dynamic random-access memory (DRAM). Fluorine was incorporated during high density plasma (HDP) chemical vapor deposition (CVD) using NF₃ chemistry for better shallow trench isolation (STI) gap-filling ability. Considerable fluorine included in the field oxide during deposition diffused from the field oxide to the silicon surface of a shallow trench during the subsequent thermal processes. This fluorine of the field oxide did not degrade the gate oxide reliability such as SILC and charge-to-breakdown characteristics. Moreover, it could improve various transistor characteristics such as the junction leakage, isolation punch-through current and data retention time of a DRAM device. It was inferred that some improvement of the MOS transistor was obtained by the interaction of Si interface traps near the trench wall with fluorine and the reduction of the density of Si interface traps.