stress memorization technique (smt)

**Stress Memorization Technique (SMT)** is a **process integration method where stress is permanently "memorized" in the silicon channel** — by depositing a stressed film, performing a high-temperature anneal (which locks in the stress through crystal rearrangement), and then removing the stressed film. **How Does SMT Work?** - **Process**: 1. Deposit a highly stressed nitride film over the gate. 2. Anneal at high temperature (source/drain activation anneal). 3. During anneal, the channel recrystallizes under stress -> the strain is "memorized" in the new crystal structure. 4. Remove the nitride film. The stress remains. - **Benefit**: The channel retains tensile strain even after the stressor is gone. **Why It Matters** - **NMOS Boost**: Primarily benefits NMOS (tensile stress improves electron mobility). - **Process Simplicity**: The stressed film is only temporary — no permanent stressor needed in the final device. - **Complementary**: Can be combined with CESL and embedded SiGe for additional strain. **SMT** is **permanent muscle memory for silicon** — teaching the crystal to hold a strained posture even after the training force is removed.