Thermal warpage of a glass substrate during Xe-arc flash lamp crystallization of amorphous silicon thin-film

Abstract

Thermal warpage of a glass substrate after a flash lamp annealing process for crystallization of amorphous silicon thin-film is critical to subsequent fabrication processes for manufacturing large-scale displays. This phenomenon is understood through the structural mismatching of hypothetical two-layers in a homogeneous glass structure: thermally softened and uninfluenced, and is mechanistically different from that induced by the mismatch in coefficients of thermal expansions among heterogeneous thin-film structures. Thin subsurface region experiencing the intensified heating is softened, the stress in the region is relaxed, and finally the softened region is shrunk laterally, while uninfluenced part of the substrate remains as it is. The model assumes that the shrunk subsurface layer, of which the thickness is proportional to the thermal penetration, is bonded to the uninfluenced part completely. Due to structural mismatching the substrate is deformed considerably and warped towards the light source (the flash lamp) according to the curvature-flash duration relationship, γ = C 2 η(1 - C 1 η ½ ). This relationship is confirmed by numerical simulation results based on a viscoelastic model and by experimental observations.