Effect of Ge Pre-amorphization on Junction Characteristics for Low Energy B Implants

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Effect of Ge Pre-amorphization on Junction Characteristics for Low Energy B Implants Jinning Liu and Sandeep Mehta Varian Semiconductor Equipment Associates Gloucester, MA 01930 Abstract The drive towards developing deep sub-micron CMOS devices places more challenges on semiconductor processing. From the standpoint of doping technology, the challenge is to achieve ultra-shallow p+/n source/drain extension junctions for PMOS. Among the various approaches being pursued to meet this challenge, pre-amorphization was used to curtail channeling of the as-implanted Boron. The effect of pre-amorphization on junction depth and junction sheet resistance in the ultra-low implant energy regime is investigated in this study. Pre-amorphization was achieved with Ge implant. B was implanted at energies of 250eV to 5keV and at a dose of 1x1015cm-2 into crystalline and pre-amorphized wafers. Both spike anneal at 1050°C and furnace anneal at 500°C to 750°C were performed after B implants. In all spike anneal cases, the pre-amorphized wafers exhibit higher sheet resistance and shallower junction depth than crystalline wafers. In all furnace anneal cases, shallower junction depth as well as lower sheet resistance can be achieved with pre-amorphized wafers. Higher pre-amorphization energy induces lower sheet resistance after both furnace and rapid thermal anneal (RTA). Introduction Aggressive gate length scaling to sub-100nm is now being actively pursued. The challenge related to ion implantation is mainly to achieve ultra-shallow p+/n junctions. Pre-amorphization prior to Boron implant has been investigated to meet this challenge. The conventional purpose of pre-amorphization is to tailor boron profile tail to minimize channeling.1 In addition, preamorphization may, if positioned right, serve as barrier to the back-flow of free interstitials to reduce boron transient enhanced diffusion (TED).2 There has also been interest in the area of solid phase epitaxy (SPE) during low temperature annealing of amorphized wafer. The migration of Boron atoms to the substitutional sites during SPE improves activation of Boron in Silicon. n this paper, we investigate the effect of Ge pre-amorphization on low energy B implants. Junction characteristics after both high temperature RTA and low temperature SPE anneal have been studied. Comparisons have been made between pre-amorphized and crystalline wafers. Experimental N-type 200mm Silicon (100) wafers were used in this experiment. Some of the wafers were preamorphized with Ge. The implant conditions were 3keV 1x1015cm-2, 5keV 1x1015cm-2 and 50keV 5x1014cm-2. B was implanted at a dose of 1x1015cm-2 and energies of 250eV, 500eV, 1keV and 5keV. The implant tilt/twist angles for Ge implants were 7°/35° and for B implants were 0°/0°. Post-implant anneals were performed in a nitrogen ambient. Furnace anneals were done at 500°C to 750°C for 30min. RTA was done at 1050°C for 0 sec (spike anneal) with ramp up and down rate at 50°C/sec.

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SIMS analysis was performed using a PHI Quadrupole SIMS instrument a

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