Investigation of Gate Oxide Wear out Using Polysilazane-base Inorganic as Shallow Trench Filling

The floating gate (FG) crystallization and extrinsic gate oxide breakdown (Vbd )using polysilazane-base inorganic material SOD (Spin-On-Dielectric) as shallow trench isolation (STI) filling is investigated. The pinholes are found along the FG grain boundary in wide active regions because of tensile stress induced by SOD material in STI process, thus gate oxide wears out by following wet cleaning steps. The chemical oxide formation during FG deposition can effectively inhibit gate oxide early breakdown. Moreover, FG sheet resistance (Rs) in 550 /air °C deposition condition can significantly reduce about 20% in comparison with 520 / °C O2 and 400 /N °C 2 conditions The FG1 phase transformation combined with FG2 deposition which used 400C boat-in temperature in N2 ambient; is no interface found in the floating gate. Unfortunately, the tensile stress that comes from SOD material will induce FG pinholes on a large active area by top-view SEM check In order to circumvent chemical solvent flow into pinholes along the FG grain boundary and inducing the gate oxide Vbd problem, the discontinuous poly grain between FG1 and FG 2 is investigated by various FG2 furnace boat-in conditions and verify by accumulated probability of breakdown voltage in Pwell and Nwell capacitors. The results elucidate that either 550°C boat-in in air ambiance or 520°C boat-in in oxygen ambiance in FG 2 deposition can absolutely improve early Vbd except for 400°C boat-in in nitrogen ambiance due to oxygen ambience and formed discontinuous poly grain between FG 1 and FG 2. The cumulative probability of FG Rs by various FG2 deposition conditions, it is realized that 520°C boat-in in O2 has higher Rs because of the chemical oxide between FGs. Moreover, 550°C boat-in in air condition reduces 20% of Rs compared with 400°C boat-in in nitrogen We propose a recovery process to inhibit gate oxide early breakdown by means of optimal FG2 deposition condition. The chemical oxide and discontinuous grain boundary formation within a floating gate can prevent solvent flow through the grain boundary and keep gate oxide from being directly damaged. Cumulative probability of floating gate Rs by higher temperature boat-in with air or oxygen ambience show acceptable Rs for memory cell operation.