Monolithic

3D IC: go vertical — bond two wafers, or build the second tier in placeParallel 3D bonds finished wafers via TSV or Cu-Cu; monolithic 3D grows a new transistor tier on top, in place1 · Two ways to go verticalParallel — bonddie 2die 1TSV / Cu-Cu bondMonolithic — in placetier 2tier 1inter-tier via (nm)Parallel bonds two finishedwafers; monolithic grows tier 2directly on tier 1 — no bond.Inter-tier vias are far denserthan any bonded connection —that is the whole point.2 · Vertical pitch laddermicrobump~30–40 µmTSV~5–10 µmCu-Cu hybrid bond< 1 µmmonolithic inter-tier via~50–100 nmFiner vertical pitch = finer 3Dpartitioning: whole chips, thenblocks, then individual gates.Bonding buys density; monolithicbuys another 100x on top.3 · Thermal budget & payoffsPayoffsShorter global wiresMemory directly over logicCFET: nFET over pFET, tiny cellsNew floorplans across tiersThe thermal wallTier-2 built cold (<~500 °C) sotier-1 devices surviveBuried tiers are hard to coolYield multiplies across tiersHeat removal and low-temp devicequality are the real limits.Bond or build-in-placeStack and bond two finished wafers,or grow a second transistor tiersequentially on the first.Density sets the payoffFrom TSV µm to monolithic-via nm,finer vertical pitch moves you fromchip-level to gate-level 3D.Heat & thermal budget biteBuried tiers are hard to cool, andmonolithic's top tier must be builtcold enough to spare the bottom.

Monolithic 3D VLSI Integration is stacking multiple device layers on silicon via sequential processing for extreme integration density — achieves 3-4x density gain. Monolithic 3D transcends 2D planar limits. Sequential Processing grow first layer, insulate, pattern vias, repeat for next layer. Layer-by-layer construction enables vertical integration. Thermal Budget second layer processing limited by first layer (interconnects stable to ~500°C for copper). Requires lower-temperature processes for upper layers. Channel Material Quality regrown silicon via solid-phase crystallization or transfer maintains crystallinity. Device Stacking stack transistors vertically. Significant footprint reduction. Interlayer Connections vias through dielectric connect layers. Contact/via resistance critical. 3D Density theoretical 3x improvement; practical 2-2.5x accounting for overhead. Prototype Status demonstrated by MIT, Samsung on research circuits. Not yet production volume. Power Efficiency shorter interconnects reduce capacitance, power dissipation. Thermal Management lower tiers' heat dissipates through upper layers, challenging. Stress Control CTE mismatch between materials; engineering mitigates via films. Gate Engineering gate-last compatible with sequential processing. Yield Challenges first-tier defects propagate; yield lower than 2D. Monolithic 3D achieves maximum density through stacked sequential processing.

Take monolithic further

Ask the copilot about this term, or have our engineers assess it against your process.

Ask CFSGPT about this → Request a technical assessment → Open the CFS app