Daniel F. Downey

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...

Advanced Thermal Processing of Ultrashallow Implanted Junctions Using Flash Lamp Annealing

The use of flash lamp annealing for ultrashallow junction formation in silicon has been described. Low energy boron and arsenic implants have been heat-treated in this way using peak temperatures in the range of 1100 to 1300°C and effective anneal times of 20 and 3 ms. Secondary ion mass spectrometry and four-point probe measurements have been undertaken to determine the junction depth and the sheet resistance, respectively. Optimum processing conditions have been identified, under which one can obtain combinations of junction depth and sheet resistance values that meet the 90 nm technology node requirements and beyond.

The Effect of Impurities on Diffusion and Activation of ion Implanted Boron in Silicon

The interaction between boron and silicon interstitials caused by ion implant damage is a physical process which hinders the formation of ultra-shallow, low resistivity junctions. The possibility of mitigating the effective interstitial point defect population via introduction of nonmetallic impurities in ion implanted silicon has been investigated. Amorphization of a n-type Czochralski wafer was achieved using a series of Si+ implants of 40 keV and 150 keV, each at a dose of 1×10 15 /cm 2 . The Si + implants produced a 2800A deep amorphous layer, which was then implanted with 8 keV 1×10 14 /cm 2 B + . The samples were then implanted with high doses of either carbon, oxygen, sulfur, chlorine, selenium, or bromine. The implant energies of the impurities were chosen such that the damage and ion profiles of the impurity were contained within the amorphous layer. This allowed for the chemical species effect to be studied independent of the implant damage caused by the impurity implant. Post-implantation anneals were performed in a tube furnace at 750° C. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Hall effect measurements were used to study the dopant activation. Transmission electron microscopy (TEM) was used to study the end-of-range defect evolution. The addition of carbon and chlorine appear to reduce the boron diffusion enhancement compared to the boron control. Carbon and chlorine also appear to prevent boron out-diffusion during annealing compared to the control, which exhibited 20% dose loss following annealing.

The Effects of Small Concentrations of Oxygen in RTP Annealing of Low Energy Boron, BF 2 and Arsenic Ion Implants

Ion implants of 1.0 keV 11 B + , 5 keV BF 2 + , and 2.0 keV As + at a dose of IeI5/cm 2 were rapid thermal annealed (RTA) in a STEAG AST-2800µ with varying percents of oxygen in N 2 , ranging from 0-lppm to 50,000 ppm to investigate the effects of low concentrations of oxygen during anneal. Sheet resistance (R s ), ellipsometry, SIMS, Tapered Groove Profilometry (TGP), and Scanning Force Microscopy (SFM) were employed to characterize these layers. For each of these implant cases, an optimal RTA condition is established which maximizes retained dose while still producing shallow junctions. As a function of O 2 content, anneal temperature and implant condition, three regimes are observed that affect after anneal retained dose. These regimes are: dopant loss to the ambient resulting from etching of Si, dopant loss by out-diffusion from evaporation/chemical reactions, a capping regime that minimizes out-diffusion. In this later regime the dopant loss results from consumption into the RTA grown oxide. In addition, this paper also discusses oxidation enhanced diffusion (OED) and identifies its extent as a function of temperature and O 2 content of the anneal for the three implant conditions investigated. For example, a 1.0 keV 11 B + wafer annealed at 1050°C lOs in a controlled 33 ppm of O 2 in N 2 yields a SIMS junction depth 320 A shallower than previously reported by others.

Metastable boron active concentrations in Si using flash assisted solid phase epitaxy

There has been considerable interest recently, in the formation of the source drain junctions of metal oxide semiconductor transistors using solid phase epitaxy (SPE) to activate the dopants rather than a traditional high temperature anneal. Previous studies have shown that this method results in high dopant activation as well as shallow junctions (due to the small thermal budget). In this we study the effect the temperature of SPE regrowth has on the boron activation. We find that boron activation has a monotonically increasing dependence on the temperature. Significantly, we show that by carrying out the SPE regrowth at temperatures above 1050°C, it is possible to obtain active concentrations well above the electrical solubility limits.

Dose-rate effects on the formation of ultra-shallow junctions with low-energy B+ and BF2+ ion implants

Abstract 11B+ and 49BF2+ implants on a Varian VIISion-80 PLUS Ion Implanter from 2.0 to 8.9 keV at a dose of 1E15/cm2, and at various controlled and measured (in situ) peak beam-current densities, ranging from 3 to 600 μA/cm2, were investigated to study the effects of dose rate on the formation of ultra-shallow junctions. The implants and annealing conditions were chosen to produce junction depths, as measured by secondary ion mass spectrometry (SIMS), of 40 to 150 nm. In addition, a comprehensive study of B vs. BF2 at a boron effective energy of 2.0 keV (i.e. B at 2.0 keV and BF2 at 8.9 keV) was undertaken. The results show that for the implant conditions investigated the dose rate does not have a significant effect (if any) on the junction depth and that there is a distinct advantage to BF2 implants in forming shallower junctions. This advantage is not dose-rate related, but is related to the presence of fluorine. This paper also addresses the effects of pre-amorphization with Ge on dopant activation and on transient enhanced diffusion, and annealing techniques to optimize sheet resistance while minimizing junction depths. The background concentration of O2 during anneal was found to have a dramatic impact on the annealed junction (from oxidation-enhanced diffusion). Reducing the O2 concentration to trace amounts, produced the shallowest junctions observed. By combining those techniques which reduce boron diffusion, junctions that were only 39 nm deep, having a sheet resistance of 361 Ω/sq., were fabricated with 5 keV BF2.

Characterizing implant behavior during flash RTP by means of backside diagnostics

A promising new technique for achieving ultra-fast rapid thermal annealing of shallow implants is Flash-assist RTP/spl trade/ (fRTP/spl trade/). The Vortek fRTP tool produces a unique time-temperature profile on the wafer surface by first rapidly heating the bulk of the wafer to an intermediate temperature and then exposing the implanted surface of the wafer to an intense flash of radiation. The sudden increase and decrease of the wafer surface temperature results in a more gradual variation in the wafer backside temperature, which can be easily monitored with a radiometer. This paper describes the thermal physics involved in this annealing technique and shows how the backside measurement can be used to estimate the front-side temperature. The annealing behaviour of various boron and BF/sub 2/ implant conditions is presented. These data are presented graphically, in a manner that clarifies the advantages of fRTP over conventional spike annealing.

Techniques and applications of secondary ion mass spectrometry and spreading resistance profiling to measure ultrashallow junction implants down to 0.5 keV B and BF2

Secondary ion mass spectrometry and spreading resistance profiling techniques have been used to measure dopant profiles and determine electrical activation in ion-implanted samples with effective ion energies as low as 112 eV (i.e., for 0.5 keV BF2). The analytical protocols will be discussed and used to compare the results for samples implanted with ion energies ranging from 0.5 keV (B and BF2) to 8.9 keV (BF2), with and without Ge preamorphization (with and without solid phase epitaxy anneals at 550 °C for 30 min), and finally annealed at 750–1050 °C for 10 s. Limitations of both analytical techniques for ultrashallow junction characterization and areas where improvements are required are discussed.

Deactivation of Solid Phase Epitaxy-Activated Boron Ultrashallow Junctions

The solid phase epitaxial growth technique appears to be a promising method for achieving junction depths and sheet resistance values low enough to meet the performance specifications of the 65 and 45 nm node for boron, BF 2 , and BF 3 doping profiles in amorphous silicon. Room-temperature implants of these three dopant species into Si(100) preamorphized by 7 4 Ge + (30 keV, 1.0 X 10 1 5 cm - 2 ) lead to boron concentration profiles that fulfill the technological requirements. It was found that even for ultrashallow junctions the time for the regrowth process at 650°C has to be optimized with regard to the implanted species in the range between 5 and 60 s, especially when fluorine is present. The thermal stability of the boron profile distribution that meets 65-nm-node requirements was evaluated by subsequent thermal anneals simulating the thermal effects expected for typical silicidation processes. For a more detailed investigation, the postannealing temperatures ranged from 250 to 1050°C with times from a few to several hundred seconds. All the junctions were analyzed by four-point probe and selected samples by secondary ion mass spectroscopy, transmission electron microscopy, and high-resolution electron microscopy.

Rapid Thermal Process Requirements for The Annealing of Ultra-Shallow Junctions

2. 0 keV 11 B + , 2.2 keV 49 BF 2 + ion implanted and 1.0 kV Plasma Doped (PLAD) wafers of a dose of 1E15/cm 2 were annealed at various times and temperatures in a variety of ambiente: 600 to 50,000 ppm O 2 in N 2 ; 5% NH 3 in N 2 ; N 2 O; N 2 or Ar, in order to investigate the effects of the annealing ambient on the formation of ultra-shallow junctions. RGA data was collected during some (if the anneals to assist in identifying the complex surface chemistry responsible for boron out-diffusion. Subsequent to the anneals, ellipsometric, XPS, four-point probe sheet resistance and SJJVIS measurements were performed to further elucidate the effects of the different ambients on the r etained boron dose, the sheet resistance value, the RTP grown oxide layer and the junction depth. In the cases where oxygen was present, e.g. N 2 O and O 2 in N 2 , an oxidation enhanced diffusion of the boron was observed. This was most dramatic for the N 2 O anneals, which at 1050°C 10s diffused the boron an additional 283 to 427 A, depending on the particular doping condition and species. For the case of BF 2 implants and PLAD, anneals in 5% NH 3 in N 2 reduced the junction depth by a nitridation reduced diffusion mechanism. RGA data indicated that the out-diffusion mechanisms for B and BF 2 implanted wafers are different, with the BF 2 exhibiting dopant loss mechanisms during the 950°C anneals, producing F containing compounds. B implants did not show doping loss mechanisms, ais observed by the RGA, until the 1050°C anneals and these signals did not contain F containing compounds. Equivalent effective energy boron implants of 8.9 keV BF 2 vs. 2.0 keV B, however, indicated that the overall effect of the F in the BF 2 implants is very beneficial in the creation of ultra-shallow junctions (compared to B implants): reducing the junction depth by 428 A, and increasing the electrical activation (determined by SRP) by 11.7%, even though the retained dose (resulting from an increased out-diffusion of B), was decreased by 5.4%.