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 Sisingle bondN groups, involving Si3N4, Hsingle bondSisingle bondN3, H2single bondSisingle bondN2, and Si3single bondSisingle bondN, in the a-SiNxHy films. Deposition at 300 °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 Sisingle bondN groups (Si3N4 or Hsingle bondSisingle bondN3) are distributed with one inter-buffer group (Si3single bondSisingle bondN). 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 Sisingle bondN 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.