Polysilicon thin film transistor EEPROMs using ECR $N_2O$-plasma thin oxide as tunnel oxide and interpoly dielectric

Abstract

Electron cyclotron resonance (ECR) nitrous oxide ($N_2O$)-plasma thin oxide is investigated fot a tunnel oxide and interpoly dielectric (IPD) of polycrystalline silicon thin-film transistor EEPROMs (poly-Si TFT EEPROMs), and high-performance poly-Si TFT EEPROMs with the ECR $N_2O$-plasma oxide is demonstrated. ECR $N_2O$-plasma oxide has self-limited growth characteristics due to nitrogen pile-up of 4~5 a.t. % at oxide/poly-Si interface and strong bonds of Si≡N are formed even at low temperature. Furthermore, ECR $N_2O$-plasma oxide exhibits lower leakage current, higher breakdown field of 10MV/cm, larger barrier height of 2.72eV, which is much better electrical properties than oxide thermally grown on poly-Si film. On the other hand, poly-Si film crystallized by excimer laser annealing (ELA) has excellent crystallinity and larger grain size compared to solid-phase crystallized (SPC) poly-Si films. Therefore, ECR $N_2O$-plasma oxide grown on ELA poly-Si film has slightly higher breakdown field, much smaller gate voltage shifts, and higher charge-to- breakdown (Qbd) up to 4C/㎠ than that on SPC poly-Si film. $POCl_3$ doped poly-Si film has larger surface roughness than in-situ doped poly-Si film and thus it seriously degrades the reliability of polyoxide on $POCl_3$ doped poly-Si film. However, ECR $N_2O$-plasma polyoxide on in-situ doped poly-Si film has lower leakage current and higher breakdown field, furthermore, lower electron trapping rate and larger Qbd up to 10 C/㎠, which is comparable to the electrical properties of ONO IPD. Especially, although polysilicon films are heavily doped with phosphorus of $1×10^{22}cm^{-3}$, ECR $N_2O$-plasma polyoxide exhibits significantly high breakdown field of 10MV/cm and low electron trapping rate of 0.5V, which are independent of phosphorus concentration. This is mainly attributed to the smooth polyoxide/poly-Si interface, low phosphorus concentration, and nitrogen-rich layer with strong Si-N bonds at the polyoxide/po...