Effect of fluorine on the diffusion of boron in ion implanted Si

Abstract

Ion implants of 1 keV B+11 and 5 keV BF2+, to a dose of 1×1015/cm2 at a tilt angle of 0°, were implanted into preamorphized (Si+,70 keV, 1×1015/cm2) wafers. These samples were rapid thermal annealed in an ambient of 33 ppm of oxygen in N2 at very short times (<0.1 s spike anneals) at 1000 and 1050 °C to investigate the effects of the fluorine in BF2 implants on transient enhanced diffusion (TED). By using a relatively deep preamorphization of 1450 Å, any difference in damage between the typically amorphizing BF2 implants and the nonamorphizing B implants is eliminated because the entire profile (<800 Å after annealing) is well contained within the amorphous layer. Upon annealing, the backflow of interstitials from the end-of-range damage from the preamorphization implant produces TED of the B in the regrown layer. This allows the chemical effect of the fluorine on the TED of the B in the regrown Si to be studied independent of the damage. The secondary ion mass spectroscopy results show that upon annealing, the presence of fluorine reduces the amount of B diffusion by 30% for the 1000 °C spike anneal, and by 44% for the 1050 °C spike anneal. This clearly illustrates there is a dramatic effect of F on TED of B independent of the effects of implant damage. Analysis of the temperature dependence of the enhancement factors point to transient enhanced diffusion not boridation as the source of the interstitials.

Si interstitial contribution of F+ implants in crystalline Si

“…3 Some authors suggested the modification of Si self-interstitial defect stability, 14 while others indicated that F did not have an effect on defect evolution. 15 In any case, a change in defect stability or the temporary trapping of Si I's would alter B diffusion during the transient period ͑while defects or complexes exist͒, but once defects had been completely annealed out and all Si I's were released, the overall B diffusion should correspond to the excess Si I's generated independently of the stability of defects or complexes where they may have been temporarily stored. 16 An additional contribution of F could be attributed to its transport capability of point defects.…”

Effect of fluorine implantation dose on boron thermal diffusion in silicon

“…18 Finally the interaction of fluorine with silicon interstitials has been widely proposed as a mechanism of suppressing boron transient enhanced diffusion. 2, [4][5][6][7][8][9][10]18 In this paper, experiments are performed to investigate how the fluorine implantation dose influences the thermal diffusion of boron marker layers in silicon. Boron secondary ion mass spectroscopy (SIMS) profiles are studied for different fluorine implantation doses and compared with the corresponding fluorine profiles.…”

“…22 Work on the effects of fluorine from a BF 2 + implant showed that shallower junctions could be obtained when BF 2 + was implanted instead of B + . 1,7,8 In later work 2-6,9-15,17,18 fluorine was implanted separately to the boron to characterize the effect of the fluorine on boron diffusion. This work showed that the fluorine implant reduced boron transient enhanced diffusion [2][3][4][5]9,11,13,14,[16][17][18] and increased boron activity.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] A chemical interaction between boron and fluorine has been proposed to explain the suppression of boron transient enhanced diffusion by fluorine, 4,9,11,14,16 in which the fluorine combines with interstitial boron reducing its mobility 4,11,14,16 or reduces the probability of formation of a boron interstitial pair. 9,11 Alternatively, the formation of vacancy-fluorine complexes has been proposed, 13,17,18,[23][24][25][26] which act as a barrier for boron diffusion, 13 or suppress the interstitial concentration and hence reduce boron transient enhanced diffusion 17 and thermal diffusion.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] This research has been motivated by the requirement in advanced CMOS technologies to minimize boron diffusion for the formation of shallow source/drain junctions and sharply defined halo profiles. 19,20 The minimization of boron diffusion is also important in bipolar transistors, where boron diffusion limits the achievable base width and hence the value of cutoff frequency that can be obtained.…”