Atmosphere-Regulated Conversion of Perhydropolysilazane (PHPS): Controlling Si–O–N Composition and Unveiling Atomistic Mechanisms

Perhydropolysilazane (PHPS) is an important polymeric precursor for producing silica-related inorganic materials through versatile solution-based processing, and has found broad applications in semiconductor manufacturing and microelectronic encapsulation. However, owing to its complex linear and branched architecture, high sensitivity to H₂O and O₂, and the inherently amorphous nature of the resulting silica or silicon oxynitride, the conversion mechanism of PHPS to SiOx/SiOxNy remains poorly understood. This knowledge gap significantly hampers the rational design and optimization of this promising methodology for the development of high-performance inorganic functional materials. Here, we developed a new Si/N/O/H ReaxFF parameter set capable of accurately describing the thermal conversion of PHPS under various O₂/H₂O atmospheres. ReaxFF molecular dynamics (MD) simulations reveal distinct atomistic pathways for O₂ and H₂O: O₂ accelerates Si-O bond formation but promotes the growth of a SiOx surface layer that impedes further O₂ diffusion, whereas H₂O facilitates NH₃ release and Si-N bond cleavage. Coordination analysis shows that Si-N tetrahedra are highly sensitive to the atmosphere, with higher O₂ levels favoring Si atoms bonded to four N atoms. These findings demonstrate that the Si-O-N composition of PHPS-derived SiOx/SiOxNy can be tuned by controlling the atmosphere during thermal conversion, offering practical guidance for processing optimization and material performance enhancement.