We propose a cross-layer self-alignment primitive for monolithic 3D semiconductor interconnect in which acoustic wavelength, rather than lithographic overlay, defines inter-tier via position. Standing surface acoustic waves (SSAWs) applied during the fluid phase of dielectric deposition create deterministic periodic surface topology — mountains, valleys, and saddle points — whose geometry is defined entirely by wave frequency. The mechanism requires a dielectric material with a transient fluid phase, such as hydrogen silsesquioxane (HSQ) spin-on flowable oxide; solid-phase deposition methods are outside its scope. This acoustic scaffolding serves two functions: first, as a structured base for standard subtractive lithography, where wave-defined topology replaces flat-surface multi-patterning for certain interconnect layers; second, and more significantly, as a cross-layer self-alignment primitive for monolithic 3D integration. Mountain peaks, being geometrically reproducible across deposition cycles via closed-loop resonant frequency feedback, define punch-through via targets that are layer-invariant by physical construction rather than by lithographic alignment. Copper-filled vias connecting successive acoustic-templated layers enable dense vertical interconnect at densities approaching intra-layer wiring pitch. We outline the mechanism, its physical constraints, a closed-loop deposition protocol, and experimental predictions. This architecture does not replace front-end lithography at advanced nodes but addresses the alignment tolerance and via density limitations that currently constrain back-end-of-line (BEOL) 3D integration. v2.0.0 (2026-03-23): Added Section 5.2 - Wafer-scale field uniformity: resonant chuck approach. Added Val Baker et al. 2024 reference. v3.0.0 (2026-03-23): Scoped topology formation mechanism to fluid-phase dielectrics; adopted HSQ spin-on flowable oxide as reference MVP material. Added topology amplitude estimate (eq. 2). Closed ALD spacer peak-centre registration argument. Updated Voigt feedback discussion and abstract for internal consistency. Added Penaud et al. 2006 reference.v4.0.0 (2026-03-23): Corrected three reference errors: SAW polymer topology DOI and article number (EML 101932 -> 101998, authors added); M3D via pitch paper corrected from Nature to Nature Nanotechnology with updated DOI (s41586-024-07660-9 -> s41565-024-01705-2, Pendurthi et al.); SAW layered dispersion paper corrected from Ultrasonics to Applied Surface Science with updated DOI and authors added (Assouar and Elmazria 2000). v5.0.0 (2026-03-25): Generalized alignment primitive in §2.1 to decouple from SSAW-specific implementation; revised abstract lede for clarity; removed internal revision notes from bibliography.
William Harold Whitty (Wed,) studied this question.