Infrared Semiconductor Laser Annealing Used for Formation of Shallow Junction

Abstract

ABSTRACTWe report continuous-wave (CW) infrared-semiconductor laser annealing of silicon implanted with boron atoms with assistance of diamond-like carbon (DLC) films as optical absorption layer in order to form shallow junctions. BF2 ions were implanted at 10 keV at doses of 1.5×1015 cm−2 thorough an 8-nm thick SiO2 layer. The effective boron dose implanted into silicon was 7.5c1015 cm−2 a half of the implantation dose. The initial boron distribution had a peak concentration of 6×1020 cm−3 at the silicon surface and a concentration of 1×1019 cm−3 at a depth of 27 nm. The samples were coated with 200-nm-thick DLC films. The samples were annealed by irradiation with a 940 nm continuous wave laser at 80 kW/cm2 with a beam diameter of 180 μm for 2.6 ms. Heat flow analysis estimated that the sample surface was heated to 1350°C for 1.5 ms by laser annealing. Laser annealing markedly reduced the sheet resistance to 531 Ω/sq. Boron atoms were almost completely activated with a carrier density close to the effective boron dose of 7.5×1014 cm−2. The in-depth profile of boron concentration hardly changed within 3 nm for laser annealing for 2.6 ms. The intermediate SiO2 layer effectively blocked carbon incorporation to a level below 1017 cm−3. These results show that the present laser annealing method is suitable to form shallow junction of a high dopant activation ratio. We will report low energy implantation of boron-cluster ions followed by the present infrared-semiconductor laser annealing in order to form a shallow junction with a depth less than 15 nm.