Microstructure of nitrogen-rich a-Si xN yH z films

Abstract

The optical dielectric function ϵ (1.5 to 6.5 eV), IR absorption (400–4000 cm −1), and film density have been measured for a series of a-Si xN yH z films deposited at 400°C via rf plasma-enhanced CVD for varying NH 3/SiH 4 ratios. A proposed microstructural model based on a random mixture of Si-centered tetrahedra containing only SiN and NH bonds, i.e. SiN 4−i(NH) i with i=0 to 4, is consistent with the IR and density results for a nitrogen-rich film with N/Si=1.9. In order to explain the measured ϵ of this film, however, it has been necessary to include SiSi bonds in the model, thus demonstrating that careful measurements of ϵ 1 and ϵ 2 can serve as a sensitive probe of the local atomic bonding in these alloys.