1. EUV light sources & pellicles
Extreme ultraviolet lithography depends on tin plasma sources and fragile pellicles. Capacity and yield at this layer gate every advanced node — far upstream of the fab brand names investors quote.
2. High-bandwidth memory packaging
HBM stacks and advanced substrates (CoWoS-class packaging) are capacity-constrained. GPU and AI ASIC shipments often wait on packaging slots, not wafer starts.
3. Ultra-pure specialty gases
Neon, helium, and process gases for etch and deposition have concentrated supply. Geopolitical shocks or plant outages ripple through many fabs that look diversified on paper.
4. Photoresist & ancillary chemicals
Advanced photoresists and developers have few qualified recipes per node. Switching suppliers can take quarters of requalification — a soft chokepoint invisible in commodity chemical indexes.
5. Substrate & ABF film supply
Ajinomoto Build-up Film and similar substrates bottleneck substrate makers. Without them, advanced packages cannot ship even if silicon is ready.