氢流量对富硅-氮化硅薄膜键结构及光学性质的影响

Influence of Hydrogen Flow Rates on Bond Structures and Optical Properties of Silicon-rich Nitride Films

采用等离子体增强化学气相沉积法,以SiH_4、NH_3和H_2为反应气体,通过改变氢流量来制备富硅-氮化硅薄膜。利用傅里叶变换红外吸收光谱、紫外-可见光透射光谱、X射线衍射谱和光致发光谱对薄膜的结构与性质进行表征。实验发现,适当地增加H2流量,可以提高反应过程中H离子与Si、N悬挂键的键合几率,从而起到钝化薄膜悬键的作用。当H_2流量从10 sccm变化到20 sccm时,H主要起到钝化薄膜悬挂键作用,因而缺陷态减少,缺陷态发光减弱,薄膜的光学带隙缓慢展宽。继续增加H_2流量,薄膜中的氮原子持续增加,伴随着缺陷态再次增多,辐射加强,并导致光学带隙迅速展宽。当H_2流量达到30 sccm时,薄膜中的氮化硅晶粒增大,数目增多,缺陷态发光消失,出现了氮化硅中由非晶硅量子点团簇引起的发光现象,说明薄膜中出现了非晶硅量子点团簇。因此,适量的增加氢流量能够对薄膜起到钝化的作用,并实现从富硅-氮化硅向Si_3N_4相转变的过程中形成氮化硅基质包埋的非晶硅量子点团簇结构。

Silicon-rich silicon nitride thin films were deposited by plasma enhanced chemical vapor deposition method using SiH_4,NH_3 and H_2 as reaction gas source with changing of H_2 flow rates. The structures and properties of the materials were characterized by Fourier transform infrared absorption spectroscopy,ultraviolet-visible transmission spectra,XRD and photoluminescence spectra,respectively.The results show that,properly increasing hydrogen flow rate helps to improve the bonding probability between hydrogen ion and Si and N dangling bonds in deposition process. Thus hydrogen plays an important role in passivation of dangling bonds. When hydrogen flow rates change from 10 sccm to 20 sccm,hydrogen ions mainly play a role of dangling bond passivation. which resulting in the reduction of defect states and weakening of defect state photoluminescence effect,so that bandgap of the film widening slowly. When hydrogen flow rates increase,the amounts of nitrogen atoms grow up continuously,with the increase of defect states again,enhancement radiation,and leading to the optical bandgap rapidlybroadening. When the hydrogen flow rates is 30 sccm,silicon nitride grain size and numbers increase in the films,photoluminescence effects of defect states disappear,the luminescence effects caused by amorphous silicon cluster quantum dots in the silicon nitride matrix appear. It indicated that amorphous silicon cluster quantum dots create in the films. Therefore,properly increasing hydrogen flow rate helps to passivate films and grow out of the structures of amorphous silicon cluster quantum dots embedded amorphous silicon nitride matrix in the process of structure transition from rich silicon nitride to Si_3N_4 phase.