Silke Paul

Mechanisms of B deactivation control by F co-implantation

Thermal annealing after preamorphization and solid-phase epitaxy of ultrashallow B implants leads to deactivation and diffusion driven by interstitials released from end-of-range defects. F inhibits these processes by forming small clusters that trap interstitials. A competing B–F interaction causes deactivation when F and B profiles overlap. Both pathways suppress B transient enhanced diffusion.

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.

Clusters formation in ultralow-energy high-dose boron-implanted silicon

The formation and evolution of small cluster defects in 500 eV, 1×1015 cm−2 boron-implanted silicon is investigated. These clusters are identified by high-resolution transmission electron microscopy (TEM) as small dislocation loops lying on {100} planes with an interstitial character. Weak-beam dark-field TEM analysis shows that, during annealing at 650 °C, they evolve following an Ostwald ripening mechanism. Spike anneals at high temperatures make them dissolve but an immobile boron peak is still detected in the secondary ion mass spectroscopy profiles. Upon oxidation, the average size of the clusters increases, while boron electrical deactivation occurs. These results strongly indicate that the observed clusters contain both boron interstitials and silicon self-interstitials atoms.

Millisecond Annealing: Past, Present and Future

The challenge of achieving maximal dopant activation with minimal diffusion has re-awakened interest in millisecond-duration annealing processes, almost two decades after the initial research in this field. Millisecond annealing with pulsed flash-lamps or scanned energy beams can create very shallow and abrupt junctions with high concentrations of electrically active carriers, but solutions for volume manufacturing must also meet formidable process control requirements and economic metrics. The repeatability and uniformity of the temperature cycle is the key for viable manufacturing technology, and the lessons from the development of commercial rapid thermal processing (RTP) tools are especially relevant. Advances in the process capability require a fuller understanding of the trade-off between dopant activation, defect annealing. diffusion and deactivation phenomena. There is a strong need for a significant expansion of materials science research into the fundamental physical processes that occur at the short time scales and high temperatures provided by millisecond annealing.

Fluorine-vacancy complexes in ultrashallow B-implanted Si

Shallow fluorine-vacancy (FV) complexes in Si have been directly observed using variable-energy positron annihilation spectroscopy and secondary ion mass spectrometry. The FV complexes, introduced to combat the deactivation and transient-enhanced diffusion of ultrashallow boron, were observed in preamorphized Si wafers implanted with 0.5keV B and 10keV F ions at a dose of 1015cm−2, and then annealed isothermally at 800°C for times ranging from 1to2700s. The results are in agreement with a model which predicts that the complexes are of the form F3nVn, with n most probably being 1 and/or 2.

Challenges for ultra-shallow junction formation technologies beyond the 90 nm node

The continuing scaling of MOS devices poses increasing challenges for the formation of ultra-shallow junctions (USJ). At the 90 nm device node USJ requirements for PMOS devices include junction depth below 25 nm and sheet resistance below 660 /spl Omega//square. Success in volume manufacturing also requires excellent repeatability and wafer uniformity, including optimization with respect to wafer pattern effects. This paper shows that sophisticated spike-annealing techniques combined with low-energy ion implantation can meet these requirements. For the 65 nm node, current methods will have to be augmented with optimized preamorphization and co-implantation techniques. The paper also examines the potential of new techniques such as millisecond annealing and solid-phase epitaxy (SPE). For millisecond annealing one of the major challenges arises from greatly magnified pattern effects combined with the very large thermal stresses induced by the enormous temperature gradients imposed on the wafer. SPE can provide the very shallow, highly activated junctions needed for advanced technologies but the issues of process integration and residual damage will require further development.

Distribution and segregation of arsenic at the SiO2/Si interface

The segregation and pile-up of arsenic atoms at the Si/SiO2 interface in steady state was investigated in detail by a combination of gracing incidence x-ray fluorescence spectroscopy (GI-XRF) measurements, electrical measurements, etching on the nanometer scale, and measurements of the step heights by interferometry. Using GI-XRF measurements and removal of the highly doped segregation layer by a sensitive etching process it was possible to distinguish clearly between the piled-up atoms and the arsenic atoms in the bulk over a large range of implantation doses, from 3×1012 to 1×1016 cm−2. The samples were annealed at different temperatures from 900 °C to 1200 °C for time periods long enough to make sure that the segregation reflects an equilibrium state. With additional step height measurements at line-space structures, the thickness of the layer with the piled-up arsenic and the shape of the segregation profile was determined. Electrical measurements indicated that the segregated arsenic atoms are deep d...

Detailed investigation of Ge–Si interdiffusion in the full range of Si1−xGex(0≤x≤1) composition

Based on the recently developed MCs2+ secondary ion mass spectrometry methodology, the Ge–Si interdiffusion has been investigated, using Ge(:B) solid sources, for Ge concentrations between 0 and 100 at. %. A strong dependence of the interdiffusion with the Ge content of SiGe alloys, formed during annealing, has been shown. The Boltzmann–Matano method was used to extract the interdiffusivity values for all the temperatures studied (750, 800, 850, and 900 °C) in the full range of SiGe compositions. Two regimes of interdiffusion have been identified, both exhibiting an exponential increase in the interdiffusion coefficient as a function of the Ge concentration. The high Ge content regime (>65 at. %) is in good agreement with the values known in the “extreme” cases of Ge diffusion in Si (0 at. %), Ge self-diffusion, and Si diffusion in Ge (100 at. %), while in the low Ge content regime (<50 at. %), the presence and evolution of misfit dislocation can explain the important values of interdiffusivity found in t...

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.

Mechanistic benefits of millisecond annealing for diffusion and activation of boron in silicon

Millisecond annealing techniques with flash lamps or lasers have become increasingly common for activating dopants and eliminating implantation-induced damage after ion implantation for transistor junction formation in silicon. Empirical data show that such techniques confer significant benefits, but key physical mechanisms underlying these benefits are not well understood. The present work employs numerical simulation and analytical modeling to show that for boron, millisecond annealing reduces unwanted dopant spreading by greatly reducing the time for diffusion, which more than compensates for an increased concentration of Si interstitials that promote dopant spreading. Millisecond annealing also favorably alters the relative balance of boron interstitial sequestration by the crystal lattice vs interstitial clusters, which leads to improved electrical activation at depths just short of the junction.