Segregation and Diffusion of Sb Compared to as for Ultra-Shallow Implantation Into Silicon
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SEGREGATION AND DIFFUSION OF Sb COMPARED TO As FOR ULTRA-SHALLOW IMPLANTATION INTO SILICON D. Krüger, P.Zaumseil, V. Melnik, R. Kurps, P. Formanek, and D. Bolze IHP, Frankfurt (Oder), Im Technologiepark 25, 15236 Frankfurt (Oder), Germany, email: [email protected] ABSTRACT We investigate diffusion and segregation of Sb and As after low energy implantation and annealing. Sb implantation profiles are significantly more stable against segregation for implantation energies higher than 5 keV compared to As. For ultra-shallow profiles and annealing temperatures above 850°C we demonstrate strong Sb and As segregation up to 1021 cm–3 in an interfacial layer less than 3 nm. In comparison to As antimony profiles show reduced tails mainly due to less sensitivity for excess Si self-interstitial effects generated both during implantation defect anneal and during deactivation of heavily n-doped regions by clustering. INTRODUCTION The formation of low resistive ultra-shallow junctions is one of the major challenges for scaling down sub-µm CMOS and BiCMOS technologies. Arsenic is the most widely used silicon dopant for n-type layers in the corresponding circuits. The successful fabrication of sub-0.1 µm MOSFETs using low energy As ion implantation has been reported several years ago (see, e.g.,[1,2]). Very high doping concentrations, in excess of 1 x 1020 cm–3 can be achieved metastably, through solid phase regrowth or laser activation. The subsequent deactivation of this arsenic has been the subject of ongoing research in order to maximize conductivity. Clustering of As is accepted as the phenomenon responsible for the electrically inactive non-precipitated dopant. Self interstitial injection during electrical deactivation of As can strongly enhance the diffusion of As itself or neighboring B profiles [3], even at low temperatures (e.g., 500°C) [4]. Enhanced dopant diffusion during electrical deactivation by clustering and transient enhanced diffusion (TED) due to implantation damage make it difficult to maintain the steepness of as-implanted As profiles after common processing steps [5]. Antimony has been suggested as an alternative for shallow source/drain areas and source/drain extensions [6-8] and is nowadays intensively under investigation. Several details of the segregation and the impact of typical process steps on shallow Sb junctions remains to be clarified. Here we investigate the diffusion and segregation of ultra-shallow Sb implants in comparison to As implants. We show that Sb can be used to eliminate enhanced diffusion effects due to deactivation of heavily n-doped regions. For implantation energies above 5 keV segregation of Sb is reduced compared to As . The observed reduction of enhanced diffusion makes Sb an interesting candidate for replacing As in ultra-shallow junction and S/D extension formation for sub - 100 nm CMOS and BiCMOS technologies.
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EXPERIMENTAL To produce as-implanted profiles with closely similar depth, As and Sb were implanted into (100) Si through an 2.5 nm screeni
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