Reduced boron diffusion under interstitial injection in fluorine implanted silicon

Abstract

Point defect injection studies are performed to investigate how fluorine implantation influences the diffusion of boron marker layers in both the vacancy-rich and interstitial-rich regions of the fluorine damage profile. A 185 keV, 2.3ϫ 10 15 cm −2 F + implant is made into silicon samples containing multiple boron marker layers and rapid thermal annealing is performed at 1000°C for times of 15-120 s. The boron and fluorine profiles are characterized by secondary ion mass spectroscopy and the defect structures by transmission electron microscopy ͑TEM͒. Fluorine implanted samples surprisingly show less boron diffusion under interstitial injection than those under inert anneal. This effect is particularly noticeable for boron marker layers located in the interstitial-rich region of the fluorine damage profile and for short anneal times ͑15 s͒. TEM images show a band of dislocation loops around the range of the fluorine implant and the density of dislocation loops is lower under interstitial injection than under inert anneal. It is proposed that interstitial injection accelerates the evolution of interstitial defects into dislocation loops, thereby giving transient enhanced boron diffusion over a shorter period of time. The effect of the fluorine implant on boron diffusion is found to be the opposite for boron marker layers in the interstitial-rich and vacancy-rich regions of the fluorine damage profile. For marker layers in the interstitial-rich region of the fluorine damage profile, the boron diffusion coefficient decreases with anneal time, as is typically seen for transient enhanced diffusion. The boron diffusion under interstitial injection is enhanced by the fluorine implant at short anneal times but suppressed at longer anneal times. It is proposed that this behavior is due to trapping of interstitials at the dislocation loops introduced by the fluorine implant. For boron marker layers in the vacancy-rich region of the fluorine damage profile, suppression of boron diffusion is seen for short anneals and then increased diffusion after a critical time, which is longer for inert anneal than interstitial injection. This behavior is explained by the annealing of vacancy-fluorine clusters, which anneal quicker under interstitial injection because the injected interstitials annihilate vacancies in the clusters.

Microscopic origins of dry-etching damages in silicon large-scaled integrated circuits revealed by electrically detected magnetic resonance

“…13 The F n V m defects prevent the diffusion of fluorine atoms and lead to a sharper depth profile of fluorine. 1,6,13 The SIMS profile in Fig. 1(b) shows such a behavior.…”

“…However, the signal intensity of G11 was much smaller than that of "Ci" (G12-type), despite the fact that our devices went through the high-temperature thermal processes (over-1000 C activation anneal for seconds as well as over-400 C anneal for hours). We suggest that a large amount of excess Si i in MOSFETs 1,2 causes the dominant formation of the G12-type centers [C þ Si] i rather than the G11 centers (C i þ C s ). Also strongly strained Si lattice by the surrounding structures 12 may affect the thermal stability of the defects.…”

“…They are intentionally introduced by co-implantation in order to form an abrupt junction profile of Si metal-oxide-semiconductor field effect transistors (MOSFETs). 1,2 In the implanted regions, carbon and fluorine atoms can trap excess interstitial Si atoms and strongly suppress the transient enhanced diffusion of boron and phosphorous dopants. 1,2 They are also unintentionally introduced by dry etching.…”

“…1,2 In the implanted regions, carbon and fluorine atoms can trap excess interstitial Si atoms and strongly suppress the transient enhanced diffusion of boron and phosphorous dopants. 1,2 They are also unintentionally introduced by dry etching. 3,4 Fluorocarbon containing fluorine and carbon is one of the most popular gases for reactive ion etching (RIE) of SiO 2 and SiN films.…”

Fluorine improvement of MOSFET interface as revealed by RTS measurements and HRTEM

“…This is attributed to a reduction in interface-state density as observed from increase in RTS on-off time constants, improvement in surface mobility [3], increase in immunity to hot-carrier degradation [4][5][6][7], and reduction in the negative-bias instability (NBTI) and plasmacharging induced shifts [8][9][10]. Fluorine near the silicon surface also reduces the transient enhanced diffusion (TED) of boron [11][12], and causes a slight increase in gate oxide thickness [4,13]. The incorporation of highdose fluorine into the gate oxide, however, enhances boron penetration into and through the oxide, causing severe instabilities in PMOS structures [14][15].…”