E. J. H. Collart

Vacancy-engineering implants for high boron activation in silicon on insulator

The formation of boron interstitial clusters is a key limiting factor for the fabrication of highly conductive ultrashallow doped regions in future silicon-based device technology. Optimized vacancy engineering strongly reduces boron clustering, enabling low-temperature electrical activation to levels rivalling what can be achieved with conventional preamorphization and solid-phase epitaxial regrowth. An optimized 160keV silicon implant in a 55∕145nm silicon-on-insulator structure enables stable activation of a 500eV boron implant to a concentration ∼5×1020cm−3.

Diffusion and activation of ultrashallow B implants in silicon on insulator: End-of-range defect dissolution and the buried Si∕SiO2 interface

The fabrication of preamorphized p-type ultrashallow junctions in silicon-on-insulator (SOI) has been investigated. Electrical and structural measurements after annealing show that boron deactivation and transient enhanced diffusion are reduced in SOI compared to bulk wafers. The reduction is strongest when the end-of-range defects of the preamorphizing implant are located deep within the silicon overlayer of the SOI silicon substrate. Results reveal a very substantial increase in the dissolution rate of the end-of-range defect band. A key player in this effect is the buried Si∕SiO2 interface, which acts as an efficient sink for interstitials competing with the silicon surface.

Elemental B distributions and clustering in low-energy B+ ion-implanted Si

A detailed study is presented of characteristic elemental B distributions in Si produced by low-energy B+ ion implantation and annealing. Implant concentration profiles have been determined with approximately nanometer spatial resolution using energy-filtered imaging in the transmission electron microscope, for a B+ ion dose close to those relevant to electronic device processing. It is demonstrated that, for as-implanted Si, the near-surface B distribution shows a smooth concentration peak which correlates well with theoretical simulation and shows no anomalous surface buildup of the type generally indicated by secondary ion mass spectrometry measurements. After annealing of the layers, the present direct observations reveal that the final B distribution is characterized by residual nanometer-scale elemental clusters which comprise disordered zones within the restructured Si lattice.

Boron deactivation in preamorphized silicon on insulator: Efficiency of the buried oxide as an interstitial sink

Preamorphization of ultrashallow implanted boron in silicon on insulator is optimized to produce an abrupt boxlike doping profile with negligible electrical deactivation and significantly reduced transient enhanced diffusion. The effect is achieved by positioning the as-implanted amorphous/crystalline interface close to the buried oxide interface to minimize interstitials while leaving a single-crystal seed to support solid-phase epitaxy. Results support the idea that the interface between the Si overlayer and the buried oxide is an efficient interstitial sink.

Process interactions between low-energy ion implantation and rapid-thermal annealing for optimized ultrashallow junction formation

The shallow doping requirements for the next 2–3 device generations can be satisfied by a combination of low-energy ion implantation and rapid-thermal anneal. However, the differing requirements of distinct types of devices preclude the definition of a single optimized process. To tailor the junction properties according to device type and geometry, requires an understanding of the effects of process parameters in both implant and anneal steps. In describing the interactions and mechanisms behind this optimization, a number of tradeoffs are highlighted: (i) The choice of implant energy and dose may be traded off against the anneal time–temperature profile. (ii) The benefits of preamorphization to reduce ion channeling are offset by the detrimental increase in transient-enhanced diffusion and dopant segregation. (iii) The use of oxygen in the anneal ambient is discussed in terms of its effects on diffusion versus dopant loss at the surface.

Uphill diffusion of ultralow-energy boron implants in preamorphized silicon and silicon-on-insulator

Redistribution during annealing of low-energy boron (B) implants in silicon on insulator (SOI) structures and in bulk Si has been investigated by comparing secondary ion mass spectrometry (SIMS) and simulated profiles. All the samples have been preamorphized with Ge at different implantation energies in order to investigate the effects of the position of the damage on B diffusion. Different B doses in the range between 2×1013 and 2×1015u2002cm−2 and annealing temperatures between 700 and 1100u2009°C have been investigated. All SIMS profiles show a B pileup in the first few nanometers of the Si matrix in proximity of the Si surface. The results of our simulations, performed on samples implanted at different doses (below and above the solid solubility), indicate that the B redistribution upon annealing can be explained with a simple model which considers the presence of traps in the surface region, without considering any asymmetric behavior of the dopant diffusion. The sink region is a few monolayers (1–2 nm) for ...

Doping and Mobility Profiles in Defect-Engineered Ultra-Shallow Junctions: Bulk and SOI

Silicon on insulator (SOI - Smartcut(R)) wafers were implanted with 1MeV and 300keV silicon ions to doses of 3.8x10(15) cm(-2) and 3x10(14) cm(-2), respectively, in order to modify the vacancy concentration in a controlled way. Boron was then implanted at 2keV to a dose of 1x10(15) cm(-2) into the near-surface part of the vacancy-engineered region. Atomic profiles were determined using SIMS and electrical profiles were measured using a novel Differential Hall Effect (DHE) technique, which enables profiling of electrically active dopants with a nanometer depth resolution. The electrical profiles provide pairs of carrier concentration and mobility values as a function of depth. The buried oxide (BOX) is proven to restrict the back diffusing interstitials positioned below the BOX from entering the silicon top layer and interacting with the boron profile. Also an increase of similar to50% in boron activation is achieved when a co-implant is used. However, SOI shows a reduced degree of activation when compared to bulk silicon, with or without a co-implant.

Process Characterization Of Low Temperature Ion Implantation Using Ribbon Beam And Spot Beam On The AIBT iPulsar High Current

The damage and amorphous layer formation properties of a 6 keV 1×1015u2009cm−2 carbon implant were investigated using spot beam and ribbon beam and substrate temperature. The effects of wafer temperature on dopant activation and diffusion were further investigated for boron implants between 300 eV and 2 keV and arsenic implants between 2 keV and 20 keV. The carbon implant amorphization characteristics can be understood using the concept of critical dose for amorphization. B and As activation was found to be 15%–20% improved at the lowest implant temperature but with similar junction depths compared to higher implant temperatures. Higher energy implants showed less or no activation or junction depth improvement at lower implant temperatures.

Effect of buried Si/SiO2 interface on dopant and defect evolution in preamorphizing implant ultrashallow junction

P-type ultrashallow junctions are widely fabricated using Ge preamorphization prior to ultralow-energy boron implantation. However, for future technology nodes, issues arise when bulk silicon is supplanted by silicon-on-insulator (SOI). An understanding of the effect of the buried Si∕SiO2 interface on defect evolution, electrical activation, and diffusion is needed in order to optimize the preamorphization technique. In the present study, boron has been implanted in germanium preamorphized silicon and SOI wafers with different preamorphizing implant conditions. Subsequent to implantation an isothermal annealing study of the samples was carried out. Electrical and structural properties were measured by Hall-effect and secondary-ion-mass spectroscopy techniques. The results show a variety of interesting effects. For the case where the Ge preamorphization end-of-range defects are close to the buried oxide interface, there is less dopant deactivation and less transient-enhanced diffusion, due to a lower inter...

Understanding, modeling and optimizing vacancy engineering for stable highly boron-doped ultrashallow junctions

This work presents breakthrough results on the physics, modeling and application of ion-implanted vacancies for high-performance B-doped ultrashallow junctions. We demonstrate for the first time electrically active B concentrations approaching 1021/cm3, achieved by low-temperature annealing, without preamorphisation. Source/drain (S/D) junctions formed by advanced vacancy engineering implants (VEI) are activated far above solubility, are stable with respect to deactivation, and are practically diffusionless. Furthermore sheet resistance Rs is predicted to stay almost constant with decreasing junction depth Xj outperforming other S/D engineering approaches beyond the 45 nm node