Spike annealing is an ultra-short rapid thermal processing (RTP) technique where the wafer is heated to peak temperature (typically 1000-1100°C) with zero hold time—the temperature ramps up at 150-300°C/s, reaches the target, and immediately ramps down, creating a sharp temperature spike profile that maximizes dopant activation while minimizing thermal diffusion. Process characteristics: ramp rate 150-300°C/s up, peak temperatures 1000-1100°C (process dependent), soak time effectively zero (< 1 second at peak), cool-down rate 50-100°C/s (limited by wafer thermal mass and lamp power reduction). The thermal budget is characterized by the time-temperature integral, which directly determines dopant diffusion distance. Spike anneal vs. soak anneal: a conventional RTP soak at 1050°C for 10 seconds allows significant dopant diffusion (boron diffuses ~5-10nm), while a spike to 1075°C with zero soak limits diffusion to ~2-3nm while achieving comparable dopant activation (> 80% for arsenic, > 60% for boron). Applications: (1) source/drain activation (primary application—activate implanted dopants to achieve low sheet resistance while preserving shallow junction depth), (2) silicide formation (NiSi formation at 400-500°C spike), (3) stress memorization (spike anneal with stress liner to lock in channel strain). Spike anneal is performed in single-wafer RTP chambers using tungsten-halogen lamp arrays with pyrometric temperature control. The key challenge is temperature uniformity across the wafer during the rapid transient—edge vs. center temperature differences cause non-uniform activation and potential slip-line defects in the crystal. At advanced nodes below 7nm, even spike anneal provides too much thermal budget, driving adoption of millisecond-scale flash and laser annealing for the most diffusion-sensitive implant steps.