Ultra-shallow Depths Research Articles

Shallow dopant pairs in silicon: An atomistic full configuration interaction study

The two-electron states and exchange couplings are investigated for a phosphorous donor pair in silicon using an atomistic full configuration interaction method for donor separations spanning from 0.4 to 15 nm. Three distinct donor separation regimes appear from our large basis calculations, from which the validity of simplified methods such as Heitler-London and Hartree-Fock type approaches can be assessed. For bulk donors, the exchange coupling saturates below 5 nm due to excited bonding orbital contributions to the wave functions. Ionic contributions to the two-electron state decrease between 5 and 14 nm, and a fully correlated Heitler-London-like state is reached from 14 nm onwards. Oscillations in exchange couplings can be strongly suppressed by placing the donors in the same $z$ plane and at a small depth, $D$, from the surface. This is a consequence of the $z$-valley terms becoming dominant within the dopant's wave function and of small changes with $x$ and $y$ separations no longer having much effect. We find the depth to be an important parameter in determining the exchange coupling for subsurface dopants, not only through valley repopulation ($D<10$ nm) but also through additional interface effects for ultrashallow depths ($D<2.5$ nm). Our full configuration interaction method provides insights in the exchange interaction for various regimes of donor separation and depths, from the Heitler-London limit at large distances to the 0.4--5 nm range relevant for scanning tunneling microscope based quantum state imaging and spectroscopy experiments. The precise control of electron-electron quantum correlations in such engineered atoms in the solid state is useful to design quantum logic gates and quantum simulators.

Methodology for Combining Data Acquired by Unmanned Surface and Aerial Vehicles to Create Digital Bathymetric Models in Shallow and Ultra-Shallow Waters

This paper presents a method for integrating data acquired by unmanned surface vehicles and unmanned aerial vehicles. The aim of this work was to create a uniform bathymetric surface extending to the shoreline. Such a body of water is usually characterized by ultra-shallow depths, which makes measurement impossible even with hydrographic autonomous vessels. Bathymetric data acquired by the photogrammetric method are, however, characterized by large errors with increasing depth. The presented method is based on processing of two data sets using a bathymetric reference surface and selection of points on the basis of generated masks. Numerical bathymetric models created by interpolation methods confirmed the usefulness of the concept adopted.

A Numerical Study: Transitional Hydrodynamic Behaviour of a Moored Barge in Different Ultra-shallow Water Depths of Malaysia

Background: Malaysia has most of its oil reservoirs in the South China sea. The water depth ranges from 50 m to 200 m. The effects of ultra-shallow water are of prime importance in the exploration of marginal oil fields. Hence, there is an increasing demand for understanding the hydrodynamic behavior of FPSO in ultra-shallow water depths. Objective: A simulation study in both frequency-domain and time-domain analyses has been performed to understand the dynamic responses of a moored barge in varying shallow water depths. The objective of this study was to observe the transitional hydrodynamic behavior of the moored barge under varying shallow water depths. Methods: The moored barge was administered under regular and irregular waves. Operating conditions for irregular waves in terms of significant wave height and peak time period were incorporated from PETRONAS Technical Standards (PTS). The wave-body interactions and mooring effects have been numerically modelled using a commercial Computational Fluid Dynamics (CFD) and simulation software (ANSYS AQWA) successfully. In order to gain confidence in the simulation software, additional experimental validation was performed for a FPSO model. Results: Though the barge was primarily free to rotate in all Degrees Of Freedom (DOF), however, only three DOFs were considered for our study; viz, heave, roll and yaw respectively. The force spectral density, cable RAO’s in addition to the time series of cable forces, along with the effect of significant motions on the mooring cables behavior have been discussed. Conclusion: In irregular beam sea state, the significant motions in ultra-shallow water were greater than that for deep waters, this was primarily the main reason for higher cable responses in ultra-shallow water.

Ultra-Shallow Doping B, Mg, Ni, Cu, Mn, Cr and Fe into SiC with Very High Surface Concentrations Based on Plasma Stimulated Room-Temperature Diffusion

Very recently, we reported a novel doping method called plasma doping without any external bias (PDWOEB) for the introduction of some impurities into Si and GaN at room temperature (RT). In this work, the RT doping of some impurities, including B, Mg, Ni, Cu, Mn, Cr and Fe, into SiC with ultra-shallow depths of tens of nanometer and very high surface concentrations, approaching or exceeding 1E20/cm3, by using PDWOEB is reported. It has been found for the first time that the doping depths and surface concentrations of these impurities doped into SiC by the PDWOEB increase drastically with increasing doping time and the ferromagnetism of SiC due to Ni doping is demonstrated. Moreover, the approximate diffusivities of B, Mg, Ni, Cu, Mn, Cr and Fe in SiC at RT under plasma stimulation are obtained. The physical mechanism of PDWOEB is further discussed, and some unclear viewpoints are clarified.

Experimental Study on the Nanoindentation of Thin Copper Films from Deep Submicron to Nano-Scale

AbstractThis study uses the nanoindentation technique to evaluate the mechanical properties of thin copper films at indentation depths measured in the order of nanometers. Copper films with various thicknesses are deposited on a single crystal silicon wafer with a (100) orientation and on a polymethylmethacrylate (PMMA) substrate, respectively. The experimental results show that for soft thin films on a hard substrate, the substrate effect is negligible when the indentation depth is less than 20% of the film thickness. However, the results suggest that hard films on a soft substrate should be treated as a composite system in indentation because the substrate effect is significant. Finally, the results reveal that a significant indentation size effect exists for thin films with a thickness of less than 100nm. A number of possible reasons for the depth dependence of the hardness properties at ultra-shallow indentation depths are proposed and discussed.

A correction to the nanoindentation technique for ultrashallow indenting depths

A correction to the nanoindentation technique taking into account the elastic recovery at extremely shallow contact depths was proposed. Using a high-sensitivity nanoindentation system with a sharp indenting tip, the magnitude of the elastic recovery could be obtained directly from very low-force load–unload curves, which was then used to correct the contact area used for hardness measurements. Nanoindentation experiments were performed on a standard fused quartz sample and, compared to standard nanoindentation techniques, the proposed method was found to be more accurate at ultrashallow indenting depths of <3 nm.

The effect of plasma exposure and annealing atmosphere on shallow junction formation using plasma source ion implantation

The effect of recoil-implantation and out-diffusion in plasma source ion implantation (PSII) on ultra-shallow p +/n junction formation has been studied. Because the wafer is directly exposed to plasma, diborane radicals in the plasma can be adsorbed on the wafer surface. The amount of recoil-implanted boron as an additive dose was measured. In the annealing process, increasing the nitrogen pressure from vacuum to 360 torr, decreased the boron out-diffusion. In addition, increasing the annealing time rendered the boron out- and in-diffusion severe. Considering recoil implantation, the wafers were implanted with a dose of 1.98×10 15 atoms/cm 2. The as-implanted wafers were subsequently spike-annealed at 1000 °C in nitrogen ambient. With implant energy of 0.5 and 1 keV, ultra-shallow junction depths of 360 and 380 Å, respectively, could be acquired. In addition, sheet resistance of 420 and 373 Ω/□ were obtained, respectively. This junction depth and sheet resistance prepared by PSII was found to satisfy next-generation memory-device doping technology.

Silicon Self-Interstitial Cluster Formation and Dissolution in SOI

AbstractSilicon-on-insulator (SOI) is a promising alternative to bulk silicon as ultra shallow junction depths have begun to shrink below 50 nm. This study examined the effect of the SOI surface silicon/buried oxide interface on {311} defect evolution after Si+ ion implantation. SOI wafers were produced such that the surface silicon thickness varied from 300Å to 1600Å. Non-amorphizing Si+ implants at 5 and 20 keV with a dose of 2x1014 cm-2 were performed into SOITEC SOI wafers. Furnace anneals were done at 750°C from 5 minutes to 4 hours and quantitative transmission electron microscopy (QTEM) was used to study the implant damage evolution. At 5 keV, the dissolution behavior of the SOI was very similar to that of the bulk. However, the extended defects in the 300 Å SOI did not nucleate the same as those observed in the bulk or thicker SOI. Similar results were seen at 20 keV for the 700 Å SOI, but a slight decrease in the concentration of trapped interstitials was observed due to interface recombination as a result of the increased projected range of the implant. It is concluded that the surface Si/BOX interface does not significantly affect recombination of interstitials trapped in extended defects unless the interstitial profile is close to or truncates the interface. However, the interface does appear to affect the stability of zig-zag {311} defects and dislocation loops in thin SOI at lower implant energies.

Plasma Source Ion Implantation for Ultrashallow Junctions: Low Energy and High Dose Rate

Ultrashallow p+/n junctions fabricated by plasma source ion implantation (PSII) were studied. After as-implanted samples were spike-annealed at 1000°C and annealed for 5 s at 1000°C, for samples with a background doping concentration of 6×1017 #/cm3, ultrashallow junction depths of 548 Å and 745 Å, respectively, could be obtained with an implant energy of 0.5 keV. Also, sheet resistances of 330 Ω/\\Box and 228 Ω/\\Box were acquired, respectively. These junction depths and sheet resistances obtained by the PSII process were found to satisfy 0.15 µm metal oxide semiconductor field effect transistor (MOSFET) applications.

The dependence of ultrashallow junction depths on impact dose rates

Ultrashallow junctions (∼60 nm) are obtained using low energy BF2 (5 keV) implants in crystalline Si. The variation of junction depth as a function of the dose rate is studied for doses of 1×1014 and 1×1015 cm−2. Boron diffusion is retarded in the tail region for the higher dose rates and consequently the junction depth decreases as compared to the lower dose rates. The residual defect density after a 950 °C, 10 s anneal for a dose of 1×1015 cm−2 is reduced for the higher dose rate as compared to the lower dose rate.