(A) study on performance, short-channel effects, and stability of polycrystalline silicon thin-film transistors using ECR $N_2O$-plasma gate oxide

Abstract

Electron cyclotron resonance (ECR) nitrous oxide ($N_2O$) plasma gate oxide and its application to the gate insulator of polycrystalline silicon thin-film transistors (poly-Si TFT``s have been investigated systematically. ECR $N_2O$-plasma oxidation was investigated as a thin oxide process to grow on polycrystalline silicon and (100), (111), and (110) oriented crystalline silicon. It was found that in spite of a low thermal budget, ECR $N_2O$-plasma oxidation incorporates nitrogen atoms at the silicon/silicon dioxide interface and forms a nitrogen-rich layer. The incorporated nitrogen atoms are tightly bound to silicon atoms at the interface with N(1s) electron energy of 397.8 eV and form Si≡N bonds. Oxidation rate in $N_2O$-plasma is very small and less dependent on crystalline orientation in comparison with thermal $O_2$, and therefore nearly identical in poly- and single crystalline-Si. Polysilicon oxide grown by ECR $N_2O$-plasma oxidation exhibits very high breakdown field of 10 MV/cm and large charge-to-breakdown up to 10 C/㎠, which is much better electrical properties than thermally grown oxides and comparable to those of oxide on crystalline silicon. The improvements are attributed to the smooth interface between polyoxide and poly-Si film. Poly-Si TFT``s fabricated with ECR $N_2O$-plasma oxide ($N_2O$-TFT``s) show improved performance in comparison with those with thermal oxide, which is attributed not only to the smooth interface but also to oxygen- and nitrogen-plasma passivation. It was found that the incorporation of nitrogen accompanied by formation of Si≡N bonding mainly passivates the defect states in upper half band gap and turns the dangling bond midgap defect states into metastable tail states, which behave like donor states. Short-channel effects of poly-Si TFT``s were investigated. With the ECR $N_2O$-plasma oxide of 12 nm thickness, short-channel effects can be almost eliminated for n-channel (p-channel) transistors of 3 ㎛ (1 ㎛) gate le...