Fluorine effect on boron diffusion: chemical or damage?

Abstract

It is known that boron transient enhanced diffusion (TED) is influenced by the existence of fluorine. This paper further investigates this phenomenon by separating the damage effect of fluorine from the chemical effect of fluorine. To accomplish this goal, a u)Ne+ implant with equivalent energy and dose was selected to simulate the fluorine damage (F has an amu of 19). Three types of samples were investigated. First was a 5keV BF2 implant. The second sample created the same damage profile but the B and F implants were separated using a 1.94keV 2e15 Ft followed by 1.2keV le15 B+ implant. The third sample used a 2keV 1.8e15 Ne+ implant to create the amorphous layer followed by a 1.2keV le15 B+ implant. All three implant sets were then subjected to the same rapid thermal annealing conditions (RTA) between 950°C and 1050°C for lOsec in a controlled 300ppm 0 2 in N2 ambient. It was found that FF plus B+ resulted in the least amount of B diffusion with AXj=20a at 950°C and loo.& at 1050°C. BF2+ and Ne+ plus B+ implants showed AXj>lOOdi for all temperatures. Damage behavior was also studied by using transmission electron microscopy (TEM). The defect structure of F+B implant is similar to that of Ne+B implant and different from the BF2 implant. Results indicate that the chemical effect of fluorine on boron diffusion dominates over the implant damage effect.

Reduced boron diffusion under interstitial injection in fluorine implanted silicon

“…12 Although the effect of fluorine is well documented in the literature, its mechanism in suppressing boron diffusion is still under research. Initial work 5 suggested that the suppression of boron diffusion by fluorine was due to chemical effect of the fluorine. However, later work on fluorine implantation into crystalline silicon showed that the suppression of boron thermal diffusion by fluorine correlated with the presence of a shallow fluorine secondary ion mass spectroscopy ͑SIMS͒ peak at approximately half the range of the fluorine implant.…”

“…This interest has been motivated by the effect of fluorine in totally suppressing boron transient enhanced diffusion [1][2][3][4][5][6][7][8][9] ͑TED͒ and also in reducing boron thermal diffusion 7,8 in silicon. When applied to complementary MOS technology, fluorine implantation has been shown to improve the threshold voltage roll-off in p-channel transistors 10 and has been used to produce a supersharp halo profile in n-channel transistors.…”

Effect of fluorine implantation dose on boron thermal diffusion in silicon

“…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. 2 However, there have also been contradictory reports in the literature, which showed that fluorine implants had little or no effect on boron transient enhanced diffusion 10 and that fluorine enhanced boron diffusion in preamorphized silicon 6 using a silicon implant.…”

“…[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. 18 Finally the interaction of fluorine with silicon interstitials has been widely proposed as a mechanism of suppressing boron transient enhanced 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.…”