Activation Of Boron In Silicon Research Articles

Effect of hydrogen implantation on low-temperature activation of boron in silicon

Understanding the behavior of dopant activation at low temperatures is necessary for three-dimensional integration of transistors. In this work, the impact of hydrogen coimplantation on boron activation was investigated at implantation doses below the amorphization threshold. The carrier depletion effect due to substrate doping was simulated to accurately characterize the initial activation behavior of boron. At temperatures higher than 400 °C, the boron activation level decreased as the hydrogen dose increased. The deactivation caused by hydrogen diminished after extended annealing at 500 °C. This indicated the passivation of boron by hydrogen. However, the boron activation in the sample implanted with hydrogen at a dose of 1 × 1015 cm−2 was first degraded and then enhanced during annealing at 300 °C. The time-dependent activation behavior suggested the elimination of isolated defects via reactions associated with hydrogen migration.

Full Activation of Boron in Silicon Doped by Self-Assembled Molecular Monolayers

Self-assembled molecular monolayer (SAMM) doping has great potential in state-of-the-art nanoelectronics with unique features of atomically precision and nondestructive doping on complex 3D surface...

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.

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.

Enhanced boron activation in silicon by high ramp-up rate solid phase epitaxial regrowth

We investigate the influence of thermal conditions during solid phase epitaxial regrowth (SPER) on the electrical activation level of boron in preamorphized silicon, both with respect to heating ramp rates and the use of low temperature preanneals. Enhancement of electrically active boron concentration by 36% is observed for activation with the fastest ramp rate (487°C∕s) compared to the slowest one (1°C∕s). An important clustering pathway occurs within the amorphous silicon phase (during low temperature preanneal) prior to completion of the SPER process. In these junctions boron deactivation during isochronal post-annealing is almost independent on the maximum boron activation level.

A technology oriented model for transient diffusion and activation of boron in silicon

We propose a model for point-defect-assisted transient diffusion and activation of high-dose boron implants in silicon. To model transient diffusion, a nonlinear equilibrium clustering model for point defects is used. The activation of boron is modeled as a Fermi-level-dependent transformation of inactive dopant clusters to substitutional atoms. Comparison with experimental data shows that this approach can provide a description of both rapid thermal annealing and long-time furnace annealing steps, with an excellent predictive capability for both chemical and electrically active profiles.

Shallow boron-doped junctions in silicon

Shallow boron-doped junctions in silicon have been investigated by means of secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, spreading resistance profiling, and four-point probe techniques. The junctions were formed by implanting BF+2 ions into n-type Si at the dose range of 1–5×1015 ions/cm2, through a thin (25-nm) screen layer of silicon dioxide. We have emphasized the higher dose range (3–5×1015 ions/cm2) as it is more relevant to processes in the current level of device integration. The use of BF+2 species and the screen oxide layer is necessary in order to form junctions whose depths xj≤0.4 μm, when conventional annealing techniques are employed. We have also examined junctions that were activated in a rapid thermal annealing system that utilizes an incoherent light source. One of the main objectives of this study is to compare conventional and rapid thermal annealing techniques. We thus evaluate the results obtained by these two methods of annealing for both the junction depth xj and the sheet resistivity Rs. Other relevant variables such as a low-temperature (77-K) implantation, surface amorphization by Si implantation, and preactivation annealing have also been examined and their effects are discussed. Based on the results of the present study, a mechanism for boron activation in silicon is discussed.