氮气对PECVD制备氮化硅薄膜结构与性质的影响

Influence of Nitrogen on Structures and Properties of Silicon Nitride Films Deposited by PECVD

采用等离子体增强化学气相沉积(PECVD)技术,以SiH_4、NH_3和N_2为反应气体,研究氮气对制备氮化硅薄膜及其结构与性质影响.研究结果表明,利用PECVD沉积非晶SiNx薄膜时,薄膜中含有大量以Si-H和N-H键存在的H+离子,当其键合断裂时,大量H从膜中扩散出来并与其他杂质和缺陷发生反应,在沉积SiNx薄膜的过程中形成H空位,H以氢-空位对方式迅速扩散,完成钝化过程,导致薄膜致密性降低.适当增加氮流量,导致薄膜中N/Si比增大,Si-Si键浓度减少,Si-N键浓度增加,并出现轻微的蓝移;继续增加氮流量,薄膜逐渐呈富N态,伴随缺陷态增多,辐射增强,导致光学带隙迅速展宽,带尾态能量逐渐减小;当氮流量较高时,薄膜中形成了包埋在非晶SiNx中的Si_3N_4晶粒,实现了从非晶SiNx薄膜向包含Si_3N_4小晶粒薄膜材料的演变过程.

The effects of nitrogen on the structure and properties of silicon nitride thin films were studied by plasma enhanced chemical vapor deposition （PECVD） te.chnique with SiH_4, NH_3 and N_2 as reac- tion gases. The results show that a large number of hydrogen ions in the form of Si-H bonds and N-H bonds exist in the amorphous SiN_x thin films by PECVD deposition. When the hydrogen bonds were broke, a large number of H＋ spilled from the films,and other impurities and defects produced chemical reaction, accordingly formed H vacancy in the process of depositing the SiN_x films. The hydrogen diffuse rapidly in the form of H-vacancy pair,finally the passivation process of the films were completed. The vacancy exist- ing in the films result in a reducing of the film compactness. Appropriate increasing of N_2 flow rate,result in increasing of N/Si ratio in the films, decreasing of the Si-Si bonds concentration, increasing of the Si-N bonds concentration,and accompanying with a slight blue shift. As further increasing of the N_2 flow ratess, the films gradually show nitrogen-rich state, along with increasing of the defect states, enhancing cf the radiation,broadening of the optical band gap rapidly, and decreasing of the band tail energy gradually. However,when N_2 flow rates reach a higher levels, the small Si_3 N_4 crystal grains embedded in the amor- phous SiN_x matrix were formed. Thus, the evolution process of the films have been achieved from amor- phous SiN_x to small Sis N_4 crystal grains embdede in the amorphous SiN_x films.