Shallow junction formation by polyatomic cluster ion implantation

Recent integrated circuits require shallow junctions which are less than 0.1 μm depth. This creates a strong demand for low energy ion beam techniques. Equivalent low-energy and high current ion beams can be realized quite easily with clusters, because the kinetic energy of the cluster is shared between the constituent atoms. Additionally, cluster-ion beams avoid damage due to excessive charge. We have used polyatomic clusters, decaborane (B₁₀H₁₄) as a kind of B cluster, in order to form a very shallow p⁺ junction. A B SIMS profile of B₁₀H₁₄ implanted into Si (100) at 20 keV was quite similar to that of B implanted at 2 keV. These SIMS measurements revealed that the cluster ion beam can realize equivalent low-energy implantation quite easily. The implantation efficiency achieved was about 90%. The damage induced by B₁₀H₁₄ implantation was completely removed by a 600°C furnace anneal for 30 min, and implanted B atoms were electrically activated. After rapid thermal annealing (RTA) at 900°C of a sample prepared with a dose of 5×10¹³ ion/cm² the sheet resistance decreased to about 600 W/sq. and the activation efficiency was about 50%. These results show that a polyatomic cluster ion beam is useful for shallow junction formation