ECR $N_2O$-plasma oxidation method has been investigated to grow thin gate dielectric on polycrystalline silicon. The growth and physico-chemical characteristics of ECR $N_2O$-plasma oxide are studied on crystalline silicon as well as polycrystalline silicon.
ECR $N_2O$-plasma oxidation shows good thickness controllability with its low oxidation rate on crystalline silicon. In spite of low process temperature, ECR $N_2O$-plasma oxidation successfully incorporates nitrogen atoms at the Si/$SiO_2$ interface, consequently, forms a nitrogen-rich layer. X-ray Photoelecton Spectroscopy(XPS) study shows that ECR $N_2O$-plasma oxidation generates Si≡ N bonds for oxide grown on crystalline silicon, while generates $Si_2$=N-O bonds as well as Si-N-$H_2$ bonds for oxide grown on polycrystalline silicon.
ECR $N_2O$plasma oxidation can improve the characteristics of thermal oxide. The ECR $N_2O$-plasma nitrided thermal oxide shows higher breakdown field, lower charge trapping, higher time-to-breakdown and higher charge-to-breakdown values in comparison with those of without ECR $N_2O$-plasma nitridation. Nitrogen-rich layer is responsible for the improved characteristics of nitrided thermal oxide, which replace stained Si-O bonds to Si-N bonds.
ECR $N_2O$-plasma oxidation does not degrade micro-roughness of polycrystalline silicon, which leads higher breakdown fields of ECR $N_2O$-plasma oxide on polycrystalline silicon. In addition, during ECR $N_2O$-plasma oxidation, defects in oxide and dangling bonds at the grain boundary are passivated by oxygen and nitrogen plasma. ECR $N_2O$-plasma oxidation process is used as a thin gate oxide growing process for the improvement of both uniformity and reliability in polycrystalline silicon thin-film transistor.
ECR $N_2O$-plasma oxide grown on polysilicon films exhibits good electrical characteristics and a smooth and uniform interface by a nitrogen-rich layer at the interface. Poly-Si TFTs with ECR $N_2O$-plasma oxide and no hydrogenation also shows better performance than with thermal oxide and with ECR $O_2$-plasma oxide, which is attributed to the smooth interface and oxygen plasma and nitrogen plasma passivation.
ECR $N_2O$-plasma oxidation process is directly applicable to poly-Si TFT, EEPROM on polycrystalline silicon substrate, and various applications where the thin oxide on polycrystalline silicon is needed.
