Emi Ishida

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

Ion implants of 1 keV 11B+ 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 A, any difference in damage between the typically amorphizing BF2 implants and the nonamorphizing B implants is eliminated because the entire profile (<800 A 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 annealin...

Shallow junction doping technologies for ULSI

Abstract The fabrication of thin, sub-40 nm doped layers in Si with high concentrations of electrically active dopants and box-like profiles is a major technological challenge. Making these regions without introducing residual defects in the material and without affecting the properties of other material regions in the device is even more difficult. The need to control these properties of doping profiles in ultra-large-scale integrated (ULSI) circuits has driven the study of low energy implantation, transient enhanced diffusion (TED), and focused the search fornew shallow junction doping techniques. In this article, wereview the motivation for shallowjunctions, specific requirements for shallow junctions used in deep sub-micron dimension metal-oxide-semiconductor field effect transistors (MOSFETs), current understanding of implant and diffusion processes, and the state-of-the-art in low energy implantation and a number of alternate doping technologies, including plasma implantation, gas-immersion laser (GILD) doping, rapid vapor-phase doping (RVD), ion shower doping, and decaborane (B10H14) implantation.

Fluorine effect on boron diffusion: chemical or damage?

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 /sup 20/Ne/sup +/ 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 5 keV BF/sub 2/ implant. The second sample created the same damage profile but the B and F implants were separated using a 1.94 keV 2e15 F/sup +/ followed by 1.2 keV 1e15 B/sup +/ implant. The third sample used a 2 keV 1.8e15 Ne/sup +/ implant to create the amorphous layer followed by a 1.2 keV 1e15 B/sup +/ implant. All three implant sets were then subjected to the same rapid thermal annealing conditions (RTA) between 950/spl deg/C and 1050/spl deg/C for 10 sec in a controlled 300 ppm O/sub 2/ in N/sub 2/ ambient. It was found that F/sup +/ plus B/sup +/ resulted in the least amount of B diffusion with /spl Delta/Xj=20 /spl Aring/ at 950/spl deg/C and 100 /spl Aring/ at 1050/spl deg/C, BF/sub 2//sup +/ and Ne/sup +/ plus B/sup +/ implants showed /spl Delta/Xj>100 /spl Aring/ 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 BF/sub 2/ implant. Results indicate that the chemical effect of fluorine on boron diffusion dominates over the implant damage effect.

The chemical effect of fluorine on boron transient enhanced diffusion

The role of fluorine in suppressing boron diffusion is studied by comparing the diffusion of boron from 5 keV BF/sub 2//sup +/ implants versus 1.1 keV /sup 11/B/sup +/ implants with varying 1.9 keV F/sup +/ implant doses. Prior to B/sup +/, F/sup +/ or BF/sub 2//sup +/ implantation, the surface was amorphized to a depth of 1450 /spl Aring/ using a 70 keV Si/sup +/ 1/spl times/10/sup 15//cm/sup 2/ implant. By implanting the boron, fluorine or BF/sub 2/ into pre-amorphized silicon, the differences in damage are factored out of the experiment. In addition, the pre-amorphizing implant provides a source of silicon interstitials for studying boron transient-enhanced diffusion (TED). Secondary Ion Mass Spectrometry (SIMS) profiles indicate negligible reduction in boron diffusion, even with higher fluorine doses corresponding to F:B ratios>that for BF/sub 2/. Transmission electron microscopy (TEM) analysis shows no effect of the presence of F on the evolution of the source of the interstitials, except at F doses>2/spl times/10/sup 14//cm/sup 2/. Earlier studies also using pre-amorphized substrates, but higher dose B implants, showed a significant effect of F on B TED. By comparing our results on lower dose B to these earlier results on higher dose B, a mechanism for the observed reduction in B TED at high B doses is proposed.