Investigation and Modeling of Fluorine Co-Implantation Effects on Dopant Redistribution

Abstract

A comprehensive model is developed from ab-initio calculations to understand the effects of co-implanted fluorine (F) on boron (B) and phosphorus (P) under sub-amorphizing and amorphizing conditions. The depth of the amorphous-crystalline interface and the implant depth of F are the key parameters to understand the interactions. Under sub-amorphizing conditions, B and P diffusion are enhanced, in contrast to amorphized regions where the model predicts retarded diffusion. This analysis predicts the F effect on B and P to be entirely due to interactions of F with point-defects.

Effect of fluorine implantation dose on boron thermal diffusion in silicon

“…13,17,[23][24][25] For example, Shano et al 13 proposed the presence F-V 6 clusters on the basis of ab initio calculations and Diebel et al 17,25 proposed the presence of F-V 3 clusters. 17,25 Positron annihilation spectroscopy has also been used to directly show the presence of fluorine vacancy complexes close to the surface. 23 Our results are consistent with this work, and hence we propose that the shallow fluorine peak is due to the trapping of fluorine at vacancy-fluorine clusters.…”

“…As discussed in the introduction, several alternative mechanisms have been proposed to explain the effect of fluorine in suppressing the transient enhanced diffusion of boron, including a chemical interaction between boron and fluorine, 4,9,11,14,16 the presence of vacancy-fluorine cluster 13,17,18,25 and the interaction of fluorine with interstitials. 2,4-10, 18 The possibility of a chemical interaction between boron and fluorine can be discounted, since the shallow fluorine peak is seen whether or not a boron marker layer is present, as shown in Figs.…”

“…[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.…”

“…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.…”