Laser Debonding Induces the Carbonization of Polyimide: Carbonization Mechanism and Wettability Change under High-Pressure Conditions

Laser debonding in advanced packaging has been developed to address the low mechanical strength of ultrathin wafers. However, the high-pressure laser field readily induces carbon cluster formation with complex wettability on the substrate surfaces during the debonding, and the causes of high pressure and the wettability law of carbon clusters remain controversial. Hence, this study integrated the molecular dynamics (MD) simulations of laser-carbonized polyimide (PI) and carbon clusters wetting with experimental investigations of the critical debonding parameters, including laser fluence (F) and spot overlap ratio (R), to investigate the mechanisms of high pressure and carbonization and the wettability law of carbon clusters. MD revealed the initial decomposition products of PI primarily consisted of carbon chains and small-molecular gases, with carbon monoxide (CO) significantly accelerating the decomposition ratio (from 1.21 to 4.72 units/ps) and increasing ambient pressure (from 31.43 to 82.96 MPa/ps). At 2.17 GPa, carbon chains were reformed into amorphous carbon clusters, which subsequently were transformed into graphene under prolonged laser irradiation, thereby improving wettability. The experiment demonstrated that increasing F significantly promoted the sparse distribution and vertical accumulation of carbon clusters with the graphene structure on the substrate surface. Further adjustments to the F and R thermally oxidized rather than reduced carbon clusters, thereby improving wettability. Overall, this study explores the mechanism of pressure transition and carbonization and the wettability law of carbon clusters, offering insights into controlling wettability in laser debonding and reducing residual carbon clusters in ultrathin wafer cleaning.