B-doped Layers Research Articles

Kinetic Model of SiGe Selective Epitaxial Growth Using RPCVD Technique

Recently, selective epitaxial growth (SEG) of B-doped SiGe layers has been used in recessed source/drain (S/D) of pMOSFETs. The uniaxial induced strain enhances the carrier mobility in the channel. In this work, a detailed model for SEG of SiGe has been developed to predict the growth rate and Ge content of layers in dichlorosilane(DCS)-based epitaxy using a reduced-pressure CVD reactor. The model considers each gas precursor contributions from the gas-phase and the surface. The gas flow and temperature distribution were simulated in the CVD reactor and the results were exerted as input parameters for Maxwell energy distribution. The diffusion of molecules from the gas boundaries was calculated by Fick's law and Langmuir isotherm theory (in non-equilibrium case) was applied to analyze the surface. The pattern dependency of the selective growth was also modeled through an interaction theory between different subdivisions of the chips. Overall, a good agreement between the kinetic model and the experimental data were obtained.

Improvement in low-voltage performance of surface-electrode soft-X-ray detectors composed of undoped homoepitaxial CVD/HPHT Ib diamond layers

We have successfully fabricated diamond soft-X-ray (SXR) detectors with interdigitated surface electrodes that significantly improve the low-voltage performance using high-quality chemical-vapour-deposited (CVD) diamond films homoepitaxially grown on high-pressure/high-temperature-synthesised (HPHT) diamond Ib substrates. In the present study, the collection efficiencies of photon-excited carriers were evaluated using monochromatised SXRs at applied voltages ≤12V for two types of diamond detectors with different stacking structures of the CVD layers. We found that the diamond detectors with an electrically floating B-doped layer sandwiched between two undoped CVD layers yield significantly larger carrier collection efficiencies compared to those without an inserted B-doped layer, even under the no-applied-voltage condition; moreover, the carrier collection efficiencies only slightly increase with increases in applied voltages below 12V. This result indicates that the inserted B-doped layer can work independently (without electrical connection to any external circuit) as a potential barrier against carrier diffusions to a HPHT diamond substrate with much poorer quality than CVD diamond film of a photon absorption layer. The detector performances are discussed relative to the potential distribution formed in the active undoped diamond layer and the crystalline quality, which is based on the cathodoluminescence intensity of exciton emissions at room temperature.

Cross-sectional TEM study and film thickness dependence of Tc in heavily boron-doped superconducting diamond

The film thickness dependence of Tc in heavily B-doped diamond (111) and (001) films was investigated and cross-sectional transmission electron microscope observation was employed to investigate the crystalline structure of heavily B-doped diamond. (111) films with 5nm or more and (001) films with 40nm or more show superconducting transition. Few dislocations are observed in 500nm from the interface between the substrate and B-doped homoepitaxial layer in (111) film and defective structure observed in (001) film.

Boron-Induced Strain Relaxation in Hydrogen-Implanted SiGe/Si Heterostructures

The strain relaxation behavior of H-implanted heterostructures containing a B-doped Si buffer layer was investigated. The annealed H-implanted SiGe/Si samples with a B-doped Si buffer layer exhibit an additional relaxation compared to those with an undoped Si buffer layer. At an annealing temperature of 900°C, relaxation ratios of the H-implanted samples with and without a B-doped Si buffer layer were determined to be 79 and 53%, respectively. The increased relaxation can be attributed to the formation of the larger H-filled bubbles along the interface on both sides of the B-doped Si region. Such an annealed H-implanted SiGe/B-doped Si heterostructure was further demonstrated to have a threading dislocation density of with a root-mean-square roughness of only 0.48 nm. This work offers an effective approach to fabricate high quality strain-relaxed thin SiGe epilayers for high mobility device applications.

Enhancement Mechanism of Electrochemical Capacitance in Nitrogen-/Boron-Doped Carbons with Uniform Straight Nanochannels

Anodic aluminum oxide (AAO) with uniform straight nanochannels was completely coated with pure, N-doped, or B-doped carbon layer. Their electric double layer capacitances are measured in aqueous (1 M sulfuric acid) and organic (1 M Et4NBF4/polypropylene carbonate) electrolyte solutions in order to investigate the capacitance enhancement mechanisms caused by N- or B-doping. Since the three types of carbon-coated AAOs (pure, N-doped, or B-doped) have exactly the same pore structure, the observed capacitance enhancement was ascribable to only the following factors: (i) better wettability, (ii) the decrease of equivalent series resistance, (iii) the contribution of space-charge-layer capacitance, and (iv) the occurrence of pseudocapacitance. From the measurements of the wettability and the electrical resistance of the coated AAOs together with the electrochemical investigation (the cyclic voltammetry, the galvanostatic charge/discharge cycling, and the impedance analysis), it is concluded that the pseudocapacitance through faradic charge transfer (factor iv) is the most important factor to enhance the capacitance by N- or B-doping. This can be applied to not only the present carbon-coated AAOs but also any other porous carbons.

Characterization of diamond ultraviolet detectors fabricated with high-quality single-crystalline chemical vapor deposition films

We have fabricated high-performance ultraviolet (UV) detectors with high-quality undoped and B-doped homoepitaxial diamond layers which were sequentially grown on a high-pressure/high-temperature-synthesized (HPHT) type-Ib (100) substrate by means of a high-power microwave-plasma chemical vapor deposition method. The detector performance measured had large quantum efficiencies due to an effective built-in current amplification function, fast temporal responses, and high UV/visible sensing ratios although the HPHT substrate used had considerable amounts of various defects inducing visible light absorptions and slow detector responses. The usefulness of the bilayer detector structure employed is discussed.

Comprehensive Evaluation and Study of Pattern Dependency Behavior in Selective Epitaxial Growth of B-Doped SiGe Layers

The influence of chip layout and architecture on the pattern dependency of selective epitaxy of B-doped SiGe layers has been studied. The variations of Ge-, B-content, and growth rate have been investigated locally within a wafer and globally from wafer to wafer. The results are described by the gas depletion theory. Methods to control the variation of layer profile are suggested.

Selective epitaxial growth of B-doped SiGe and HCl etch of Si for the formation of SiGe:B recessed source and drain (pMOS transistors)

HCl chemical vapor etching and selective epitaxial growth of B-doped SiGe layers for recessed source/drain application for pMOSFET structure have been presented. The pattern dependency of the etch and epitaxy process were studied and the data correlated to the Si coverage of the chip.

Characterization of soft-X-ray detectors fabricated with high-quality CVD diamond thin films

We have characterized the performance of soft-X-ray detectors fabricated with undoped and B-doped homoepitaxial diamond layers of high quality which were grown on a commercially available type Ib (1 0 0) substrate by means of a high-power microwave-plasma chemical-vapor-deposition (CVD) method. The signal currents of the diamond-based detectors with thin TiN electrodes formed vertically (along the homoepitaxial growth direction) were measured at room temperature as a function of the applied voltage, V a, for irradiations of 500–1200 eV soft-X-ray beams ranging from ≈6 × 10 9 to ≈1 × 10 11 photons/s. The deduced apparent quantum efficiencies increased with the increasing V a and reached to 2.5 × 10 3 at V a = 60 V. As expected from the device structure, the detector performance depended only very slightly on the applied magnetic field up to 10 T. The excellently high sensitivities attained for soft-X-ray photons are discussed in relation to carrier amplification mechanisms which invested the above diamond detectors.

Pattern dependency in selective epitaxy of B-doped SiGe layers for advanced metal oxide semiconductor field effect transistors

This study presents investigations about the physical mechanisms, origin, and methods to control the pattern dependency in selective epitaxial growth of Si1−xGex (x=0.14–0.32) layers. It is shown with a comprehensive experimental study that the local Si coverage of individual chips on patterned wafers is the main parameter for the layer profile in the epitaxial growth. This was explained by the gas depletion of the growth species in the low velocity boundary layer over the wafer. The gas depletion radius around each oxide opening was in the centimeter range which is related to the boundary layer thickness. The results from these experiments were applied to grow Si0.75Ge0.25 layers with B concentration of 4×1020cm−3 selectively for elevated source and drains in fully depleted ultrathin body silicon on insulator p metal oxide semiconductor field effect transistor (p-MOSFET) devices. The epitaxy control was maintained over a wide range of device sizes by optimized process parameters in combination with a wafer pattern design consisting of dummy features causing a uniform gas depletion over the chips on the wafer.

Abnormal Out-Diffusion of Epitaxially Doped Boron in 4H–SiC Caused by Implantation and Annealing

The effects of postimplantation annealing on the homogeneous depth profiles of epitaxially doped B and Al in 4H–SiC were investigated after the ion implantation of various species. We found a marked decrease in the atomic B concentration close to the surface in epitaxially B-doped layers after the implantation of Al, N, or P ions followed by annealing at 1700 °C. On the other hand, the Al profiles in epitaxially Al-doped layers were preserved after the same processes.

Formation of germanium shallow junction by flash annealing

We have investigated flash-lamp annealing (FLA) of germanium wafers doped with phosphorous and boron introduced in the crystal by ion implantation. Annealing was performed by using pre-heating at 400–450°C in a conventional rapid thermal processing (RTP) unit and a fast (3–20ms) FLA annealing at 800°C or 900°C. Diffusion of P is suppressed during the 800°C–20ms FLA annealing, while concentration-enhanced diffusion occurs upon 900°C FLA anneals. Importantly, in both cases P activation seems to be enhanced by the FLA process. However, junction stability following the FLA process and possible deactivation are a concern.In contrast, the FLA process applied to B-doped pre-amorphized Ge layers does not show advantages as compared to a RTP conventional annealing combined with a solid phase epitaxial regrowth, in terms of B activation level.

Integration of HCl chemical vapour etching and SiGe:B selective epitaxy for source/drain application in MOSFETs

The integration of HCl chemical vapour etching and selective epitaxy by chemical vapour deposition of B-doped SiGe layers for recessed source/drain junction application has been studied. A temperature range of 850–900 °C is proposed to be suitable for the etch process in order to obtain a smooth Si surface. This point is crucial for the epitaxial quality of grown SiGe:B layers. The selectivity of the epitaxy was not as good for high B partial pressure. However, Si0.76Ge0.24 layers with a B concentration of 6 × 1020 cm−3 were selectively grown. The pattern dependence of the etch and epitaxy process was studied and a calibration of this versus Si coverage of the chip was performed.

Lattice strain of B–B pairs formed by He irradiation in crystalline Si1−xBx/Si

This work reports on the lattice strain induced by small B clusters in Si produced by He irradiation of an epitaxial layer uniformly doped with substitutional B. By means of high resolution X-ray diffraction measurements and nuclear reaction analysis, lattice strain profiles and B lattice location of the sample before and after He irradiation were extracted, respectively. We found that, as a consequence of He irradiation, all B atoms form B–B pairs, and the tensile strain status of the as-grown B-doped layer lowers by a factor of about 2. Moreover, the volume lattice expansion ΔV per clustered B atom was found to be (−(10.0±0.6)Å3). This negative value of ΔV is very different from the positive one (+(3.7±0.6)Å3) found for B clusters created as a consequence of the B interaction with self-interstitials produced by Si implantation and subsequent annealing [G. Bisognin, D. De Salvador, E. Napolitani, A. Carnera, E. Bruno, S. Mirabella, F. Priolo, A. Mattoni, Semicond. Sci. Technol. 21 (2006) L41]. The opposite sign of this volume lattice expansion suggests that a strong correlation exists between the atomistic structures associated with these two types of complexes and the lattice strain that they induce in the Si lattice.

Kick-Out Phenomena in Epitaxially Boron- and Aluminum-Doped 4H-SiC during Implantation and Annealing Processes

It is investigated whether the homogeneous depth profiles of epitaxially doped B or Al are changed or preserved by implantation of various implanted species and annealing processes. We have found a strong decrease in the atomic B concentration in epitaxially B-doped layers after implantation of N+, Al+, and P+ and subsequent annealing at 1700 °C. On the other hand, the Al profiles in epitaxially Al-doped layers are preserved after the same processes.

Role of Heavily B-doped Layer on Low-Temperature Fe Gettering in Bifacial Si Solar Cell Fabrication

The gettering behaviors of Fe into Si with and without a p+ layer are investigated by deep-level transient spectroscopy. The samples contaminated with Fe in a wide concentration range were annealed at 600 °C to induce gettering. The surface-layer gettering behaviors of Fe for the sample without the p+ layer strongly depend on the Fe contamination level, in which the surface-layer gettering is not effective for the sample with low-level contamination at a concentration of less than 1 ×1013 cm-3 but effective for the sample with middle-level contamination at a concentration of (1–5) ×1013 cm-3. In contrast, the samples with the p+ layer show effective gettering for low- and middle-level contaminations. The gettering mechanisms of Fe in Si without and with the p+ layer are discussed in detail.

H-induced platelet and crack formation in hydrogenated epitaxial Si∕Si0.98B0.02∕Si structures

An approach to transfer a high-quality Si layer for the fabrication of silicon-on-insulator wafers has been proposed based on the investigation of platelet and crack formation in hydrogenated epitaxial Si∕Si0.98B0.02∕Si structures grown by molecular-beam epitaxy. H-related defect formation during hydrogenation was found to be very sensitive to the thickness of the buried Si0.98B0.02 layer. For hydrogenated Si containing a 130nm thick Si0.98B0.02 layer, no platelets or cracking were observed in the B-doped region. Upon reducing the thickness of the buried Si0.98B0.02 layer to 3nm, localized continuous cracking was observed along the interface between the Si and the B-doped layers. In the latter case, the strains at the interface are believed to facilitate the (100)-oriented platelet formation and (100)-oriented crack propagation.

Characterization of ultralow-energy implants and towards the analysis of three-dimensional dopant distributions using three-dimensional atom-probe tomography

The addition of a local electrode geometry has transformed the conventional atom probe into a high-speed, high sensitivity tool capable of mapping three-dimensional (3D) dopant atom distributions in nanoscale volumes of Si. Fields of view exceeding 100nm in diameter and collection rates exceeding 18×106at.∕h are possible with the local electrode geometry. The 3D evolution of dopants, specifically dopant clustering, grain-boundary segregation, shallow-doped B layers, Ni–Si layers, and preamorphization regions, was analyzed. A 200eV B11 implant in Ge-amorphized Si was mapped. The native surface oxide, 8-nm-deep B-doped layer, and Ge distribution were simultaneously mapped in 3D space. A subsequent Ni silicide process was analyzed to show Ni penetration through the doped layer. In a heavily doped poly-Si sample, a cluster of dimensions 2×7×8nm3 and containing 264 B atoms was identified at the intersection of three grains. This shows that annealing highly overdoped thin poly-Si layers does not facilitate uniformly doped and highly conductive gate contact layers for nanoscale complementary metal-oxide semiconductor transistors.

Scanning capacitance microscopy: Quantitative carrier profiling down to nanostructures

We addressed the issues related to quantitative carrier profiling by scanning capacitance microscopy (SCM) on doped layers with different dimensions, starting from thick (∼5μm) uniformly B-doped Si layers, down to Si∕Si1−xGex∕Si quantum wells with nanometric width. We preliminarly discussed the influence of the SCM hardware on the quantification, by comparing the analyses performed on Si calibration standards with two different atomic force microscopes, i.e., DI3100 by Veeco and XE-100 by PSIA, equipped with different SCM sensors. Furthermore, both concentration and spatial resolution are demonstrated by measurements on specially designed samples containing B-doped quantum wells of Si0.75Ge0.25 layers strained between Si films. Measurements were taken both on cross-sectioned samples and on beveled ones. A SCM spatial resolution of 1nm with a concentration sensitivity from 5% to 10% was demonstrated by quantitative majority carrier profiling on the B-doped Si∕Si0.75Ge0.25∕Si heterostructures.

Dual Raman Features of Double Coaxial Carbon Nanotubes with N-Doped and B-Doped Multiwalls

Double coaxial carbon nanotubes with nitrogen (N)-doped and boron (B)-doped multiwalls possess composite Raman characteristics, originating not only from the outer N-doped but also from inner B-doped layers. Both N and B dopings result in substantial shifts of the characteristic D band and G band of sp(2) carbon constituting nanotube walls but in different ways. The downshift of the G band is correlated with the decreases of electrical resistivity of carbon nanotubes regardless of N or B doping.