Hard and relaxed a-SiNxHy films prepared by PECVD: Structure analysis and formation mechanism

Amorphous hydrogenated silicon nitride (a-SiNxHy) films were prepared by plasma-enhanced chemical vapor deposition (PECVD). Their chemical structures and mechanical properties were investigated. Results reveal that there are four kinds of Si-N groups, involving Si3N4, H-Si-N-3, H-2-Si-N-2, and Si-3-Si-N, in the a-SiNxHy films. Deposition at 300 degrees C and flow ratio of SiH4/NH3 = 30/30 sccm leads to the yield of special a-SiNxHy films, in which per two high-N-coordinated Si-N groups (Si3N4 or H-Si-N-3) are distributed with one inter-buffer group (Si-3-Si-N). Such a-SiNxHy films exhibit ultralow residual stress (0.17 MPa), high elastic modulus (206.9 GPa) and high uniformity, holding great potential for device fabrications. The chemical reactions for the formation of a-SiNxHy films were proposed, and the thermodynamic calculations indicate that the utilization ratio of NH3 reagent in the chemical reactions increases significantly with the increase of SiH4 flow, but the utilization ratio of Si-N bonds in the a-SiNxHy formation decreases inversely. This work discloses valuable information on the chemical reactions and structures for a-SiNxHy films, and suggests a route to the preparation of a-SiNxHy films with high hardness and low stress by conventional PECVD. (C) 2012 Elsevier B. V. All rights reserved.