Comparative study on the influence mechanism of He/Ar/N2 plasma treatments on the high tensile stress of a multilayer silicon nitride film

Abstract

Silicon nitride films with high tensile stress have great application potential in the strained silicon technology field. However, the current understanding of the mechanisms governing tensile stress development in films, particularly in multilayered structures, following diverse plasma treatments remains limited. Herein, the influence mechanism of He, Ar, and N₂ plasma bombardment on the development of stress in monolayer and multilayer films is investigated and compared in greater depth. The results of this research indicate that the observed increase in tensile stress is primarily attributed to the enhancement of the film's intrinsic stress induced by plasma bombardment. Following bombardment by N₂ or Ar plasma, the rupture of Si–H and N–H bonds, accompanied by the reconstruction of Si–N bonds, leads to densification through chemical bond reorganization in the treated surface layer. This structural evolution propagates stress coupling effects to non-treated regions, resulting in anisotropic lattice displacement along the normal and in-plane directions, thereby significantly enhancing the tensile stress of the film. Compared with the monolayer film, multilayer films treated with N₂ and Ar plasma exhibited 41.80% and 32.78% higher stress, respectively. In contrast, multilayer films treated with He plasma exhibited a gradual transition from tensile to compressive stress, which can be attributed to residual He formed during the plasma treatment process. At the initial stage of deposition, the residual He can increase the nitrogen content within the film by generating metastable reactive species. This reduces the cross-linking density of the Si–N network, leading to volumetric expansion and subsequent compression of the underlying structure. These findings can provide theoretical guidance for the preparation of high-tensile-stress multilayer SiN_x:H films.