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

Abstract Amorphous hydrogenated silicon nitride ( a -SiN x H y ) 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 Si 3 N 4 , H Si N 3 , H 2 Si N 2 , and Si 3 Si N, in the a -SiN x H y films. Deposition at 300 °C and flow ratio of SiH 4 /NH 3  = 30/30 sccm leads to the yield of special a -SiN x H y films, in which per two high-N-coordinated Si N groups (Si 3 N 4 or H Si N 3 ) are distributed with one inter-buffer group (Si 3 Si N). Such a -SiN x H y 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 -SiN x H y films were proposed, and the thermodynamic calculations indicate that the utilization ratio of NH 3 reagent in the chemical reactions increases significantly with the increase of SiH 4 flow, but the utilization ratio of Si N bonds in the a -SiN x H y formation decreases inversely. This work discloses valuable information on the chemical reactions and structures for a -SiN x H y films, and suggests a route to the preparation of a -SiN x H y films with high hardness and low stress by conventional PECVD.