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 H 2 O and O 2, and the inherently amorphous nature of the resulting silica or silicon oxynitride, the conversion mechanism of PHPS to SiO x /SiO x N y 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 O 2 /H 2 O atmospheres. ReaxFF molecular dynamics (MD) simulations reveal distinct atomistic pathways for O 2 and H 2 O: O 2 accelerates Si–O bond formation but promotes the growth of a SiO x surface layer that impedes further O 2 diffusion, whereas H 2 O facilitates NH 3 release and Si–N bond cleavage. Coordination analysis shows that Si–N tetrahedra are highly sensitive to the atmosphere, with higher O 2 levels favoring Si atoms bonded to four N atoms. These findings demonstrate that the Si–O–N composition of PHPS-derived SiO x /SiO x N y can be tuned by controlling the atmosphere during thermal conversion, offering practical guidance for processing optimization and material performance enhancement.