rapid thermal anneal

**Rapid Thermal Anneal (RTA)** — heating a wafer to high temperature (900-1100C) for very short durations (seconds) to activate dopants while minimizing unwanted thermal diffusion. **Why RTA?** - Traditional furnace anneals (30-60 minutes) caused excessive dopant diffusion at advanced nodes - RTA achieves activation in 1-10 seconds — dopants don't have time to spread - Enables ultra-shallow junctions needed for scaled transistors **Variants** - **Spike Anneal**: Ramp to peak temperature and immediately cool. No dwell time. Minimizes diffusion - **Flash Anneal**: Millisecond heating using lamp arrays. Even less diffusion - **Laser Spike Anneal (LSA)**: Microsecond heating of just the surface. Maximum activation with virtually zero diffusion - **Microwave Anneal**: Lower temperature activation being explored **Applications** - Dopant activation after ion implantation (primary use) - Silicide formation (controlled reaction temperature) - Oxide densification - Stress memorization technique (SMT) **Key Metrics** - Peak temperature and ramp rate (50-300C/second) - Temperature uniformity across wafer - Sheet resistance (measures activation quality) **Thermal budget management** — controlling the total heat exposure — is critical at every step of CMOS fabrication.