Formation of ultra-shallow junctions by ion implantation and RTA

Forming sub-100-nm junctions for source/drain designs in <180-nm devices requires optimized low-energy ion implantation and rapid thermal annealing to place dopants accurately and activate them without excessive diffusion. Boron ions were implanted at a range of low energies and implanted wafers were then annealed using various soak times, temperatures, and ramp rates. Junctions with depths of 30-70 nm (at 1 x 10(18) cm(-3)) can be formed with sheet resistance tunable between 200 and 900 Omega/square, using spike annealing at ramp rates up to 150 degrees C/sec. Oxygen content in the rapid thermal annealing ambient is also an important factor in controlling both sheet resistance and junction depth.