Composite dielectric structures for semiconductor die assemblies and associated systems and methods

Composite dielectric structures for semiconductor die assemblies, and associated systems and methods are disclosed. In some embodiments, the composite dielectric structure includes a flexible dielectric layer configured to conform to irregularities (e.g., particles, defects) at a bonding interface of directly bonded semiconductor dies (or wafers). The flexible dielectric layer may include a polymer material configured to deform in response to localized pressure generated by the irregularities during bonding process steps. The composite dielectric structure includes additional dielectric layers sandwiching the flexible dielectric layer such that the composite dielectric structure can provide robust bonding strength to other dielectric layers through the additional dielectric layers. In some embodiments, a chemical vapor deposition process may be used to form the composite dielectric structure utilizing siloxane derivatives as a precursor.