Arsenic Doped Layers Research Articles

Annealing effect on grain boundary width of polycrystalline silicon for photovoltaic application

Nowadays, LPCVD (Low Pressure Chemical Vapor Deposition) and highly doped polycrystalline silicon films have numerous applications in microelectronic component manufacturing technologies, integrated circuits and solar cells. The complexity of the circuits, and the increasing degree of integration of the components, constantly require improvement and mastery of the properties of this type of material. As part of this work, we are interested in the study of the effect of doping and annealing Effect on grain boundary width of polycrystalline silicon thin films deposited by LPCVD. The results obtained showed, on the one hand, that arsenic doped layers are more resistive than boron doped ones, and on the other hand, and that the diffusion of dopants is generally much greater in grain boundaries than in grains; and considering the importance of the average grain size in the polycrystalline silicon material, which is an important parameter, on which the physical and electrical properties of this material depend.

Enhanced Antimony Activation for Ultra-Shallow Junctions in Strained Silicon

AbstractSheet resistance (Rs) reductions are presented for antimony and arsenic doped layers produced in strained Si. Results re-emphasise the Rs reduction for As comes purely as a result of mobility improvement whereas for Sb, a superior lowering is observed from improvements in both mobility and activation. For the first time, strain is shown to enhance the activation of dopant atoms whilst Sb is seen to create stable ultra-shallow junctions. Our results propose Sb as a viable alternative to As for the creation of highly activated, low resistance ultra-shallow junctions for use with strain-engineered CMOS devices.

Application of Arsenic Plasma Doping in Three-Dimensional MOS Transistors and the Doping Profile Evaluation

The application of plasma doping in three-dimensional (3-D) metal oxide semiconductor (MOS) transistors is proposed. One of the key steps in for fabricating 3-D MOS transistors with high-aspect-ratio channels is 3-D doping. Thus, plasma doping is analyzed and its profile is evaluated. Since conventional evaluation methods are not very effective for impurity concentration profiling along the sidewall of a vertical structure, a new method utilizing impurity-enhanced oxidation is proposed. By this method, an arsenic-doped layer of approximately 1×1020 cm-3 in concentration has been formed uniformly for a beam of 1 µm height and 0.2-1 µm width.

As- or P-Doped Si Layers Grown by RPCVD for Emitter Application in SiGeC HBTs

A new module for the emitter formation in a bipolar transistor is presented. Arsenic- or phosphorus-doped polycrystalline silicon layer for the emitter formation is deposited in a reduced pressure chemical vapor deposition reactor using silane as the silicon source gas. Characteristics such as the carrier concentration, conductivity, surface morphology, and thermal stability of the polycrystalline-silicon layer as well as the influence this layer has on a SiGeC transistor structure during the drive-in step area studied. The active carrier concentration of the as-grown sample is strongly dependent on the deposition temperature, especially arsenic doped layers which exhibit more than one order of magnitude difference. However, the carrier concentration for the As- or P-doped layer were comparable to that of a standard in-situ doped poly-crystalline layer after a dopant activation at 925°C for 10s.

TEM investigation of defects in arsenic doped layers grown in-situ by MBE

A study concerning the effect of growth condition on As incorporation and formation of defects using transmission electron microscopy (TEM) is presented. It is well known that devices in a narrow bandgap HgCdTe material system could suffer from tunneling currents and generation recombination processes, especially at cryogenic temperatures, due to material defects. For in-situ As doped p-on-n device structures grown by molecular beam epitaxy (MBE), extended defects and in particular twinning in a p-type layer grown under Hg-rich conditions is believed to reduce the zero bias dynamic impedance of devices and significantly impact recombination of carriers in the space charge region. Using TEM we have studied defects formed in As-doped layers grown under Hg- and Te-rich conditions. Samples grown under high II/VI flux ratio at growth temperature of 170 C have a high density of columnar twin defects, whereas no twin defects were seen for layers grown under optimal growth conditions at 190 C. A very high flux of As, however, was required to incorporate As into the layers at growth temperature of 190 C.

Focused ion beam written lateral field-effect transistors on standard silicon wafers

Lateral field effect devices can be produced by focused ion-beam implantation of 100 keV gallium into an arsenic doped layer on standard silicon wafers. The lateral electric field-effect across an implanted line controls the current through a small channel, leading to a gate voltage controlled source-drain current. In-plane gate transistors prepared this way are presented here. With typical geometrical channel widths around 2 μm, they show a drain saturation current of 35 μA and a transconductance of 28 μS. The threshold gallium dose, required to form lateral npn barriers after rapid thermal annealing is about 10 times the carrier density of the n-doped layer. Though the lateral electric field-effect is expected to be sensitive to the sample surface, the unpassivated transistors showed no significant aging over several weeks.

Critical review of the epitaxial growth of semiconductors by rapid thermal chemical vapor deposition

Rapid thermal processing, which was originally developed for implant annealing, has been extended to the epitaxial growth of semiconductors. Early work in this field featured the homoepitaxial growth of silicon. Abrupt doping profiles have been demonstrated for both boron and arsenic doped layers using conventional dichloro silane (DCS)/hydrogen chemistries. Minimum doping concentrations approaching 10 12 cm −3 have been demonstrated when growing over lightly doped substrates. Gas phase autodoping limits the minimum dopant concentration over more heavily doped substrates. Due to the temperature difference between the wafer and the walls, rapid thermal epitaxy has also been used to demonstrate the in-situ production of integrated device structures such as MOSFETs. Numerous authors have demonstrated the heteroepitaxial growth of strained layers of GeSi on Si, normally from the DCS/germane/hydrogen chemistry. The presence of germane dramatically increases the growth rate. This may be related to the ability of germane to produce reactive sites on the epi surface. The presence of arsine in the growth ambient shifts the growth activation energy back toward that of pure silicon. Numerous devices have been demonstrated with these films. Most common are the NPN heterojunction bipolar transistor and enhanced mobility p-channel FETs. These devices are natural applications of the technology because of the large valence band discontinuity. Growth of layers on strain relieved GeSi have led to the demonstration of PNP and n-channel devices. Optoelectronic devices have also been demonstrated, but the devices are not direct gap. Finally carbon incorporation can be used to reduce the strain. To some extent this provides the ability of decoupling strain and germanium mole fraction. The addition of small amounts of carbon dramatically increases the critical layer thickness.

Rapid Formation of Arsenic-Doped Layer More Than 1.0 µm Deep in Si Using Two KrF Excimer Lasers

Sequential irradiation by two KrF excimer lasers (λ=248 nm) has been used to activate arsenic atoms implanted into Si substrates. The 1st laser pulse having 34 ns pulse width followed by the 2nd laser pulse of 23 ns after a time delay was irradiated to the sample. Laser fluences of the 1st laser pulse and the 2nd laser pulse were set at 2.4 J/cm2 and 0.5 J/cm2, respectively. The substrate was heated to 700° C. From Rutherford backscattering spectroscopy (RBS) analysis, the depth of the doped layer is confirmed to be 1.0 µ m. Severely rippled surface was observed by atomic force microscope (AFM) for the sample irradiated without the 2nd laser pulse, but the surface morphology can be improved by the sequential irradiation of two pulses. For a time delay of 150 ns, the minimum values of χmin (4.61%) and sheet resistance (41.43 Ω/\\Box) were obtained.

Hydrogen-acceptor pairing in CdTe epitaxial layers grown by OMVPE

It is shown that the incorporation of unintentional hydrogen, during the growth by organometallic vapour phase epitaxy of cadmium telluride layers, is higher in arsenic doped layers than in undoped ones. Arsenic-hydrogen pairs are directly evidenced through the observation of the arsenic-hydrogen stretching local vibrational mode.

High-angle annular dark-field STEM imaging of doped semiconductor layers

With the development of crystal growth techniques such as molecular beam epitaxy (MBE), it is now possible to fabricate modulation-doped superlattices consisting of alternating ultrathin layers of n-and/or p-type material abruptly separated by undoped material. At sufficiently high dopant concentrations these abrupt layers may be imaged in cross section by electron microscopy. Pennycook et al. and Treacy et al. have used high angle annular dark-field (HAAD) imaging in the scanning transmission electron microscope (STEM) to image low levels of dopants (∼1 at. %) in semiconductors. This work is concerned with imaging boron and arsenic doped layers in silicon at levels « 1 at.%.Fig. 1 shows a HAAD image of a B-Si superlattice at the <110> zone-axis orientation taken at 100 kV using a VG HB501UX STEM. The bright vertical layers are the B-doped regions, containing ∼4 x 1020 B/cm3. The horizontal lines are due to beam instability while the image was recorded. Fig.2 shows a line scan across the same superlattice, recorded by scanning the beam across the specimen in a direction perpendicular to the layers.

Electron Microscope contrast mechanisms of doped semiconductor layers

With the development of crystal growth techniques such as molecular beam epitaxy, it is now possible to fabricate modulation-doped superlattices consisting of alternating, ultra-thin layers of n- and/or p-type material abruptly separated by undoped material. At sufficiently high dopant concentrations it has been found that these atomically abrupt layers can be readily imaged in the transmission electron microscope. This study is concerned with the visibility of boron and arsenic-doped layers in silicon from which a generalized interpretation of the TEM contrast of doped layers can be obtained.Fig.l is a cross-sectional, two-beam dark field image of a B-doped superlattice consisting of five three-layer sets. Each three-layer set was grown using a different substrate temperature in the range 600 to 800 °C; the boron occupies substitutional positions in the Si lattice at the lower temperatures while at the higher temperatures the boron has precipitated in stable clusters (∽3nm) as observed by direct lattice imaging. The maximum concentration of boron in all layers is ≈ 0.7 at.% which is well above the solid solubility limit at these temperatures. There are several important contrast features to note in Fig. 1. First, in the thicker areas of the foil where anomalous absorption effects are dominant, the B-doped layers appear dark relative to the Si matrix; the same is true in bright field.

Tunnel measurement of density of states of ultrathin arsenic-doped layers in silicon

The properties of 5.5 nm thick As doped layers in molecular beam epitaxy grown silicon were measured using a tunneling structure. The measurements reveal a large conductance minimum at zero bias at low temperature. The data agrees well with theory predicting a depression of the density of states at the Fermi level due to electron-electron interactions in a disordered system.

Structural properties of ultrathin arsenic-doped layers in silicon

We have grown δ-doped layers in Si by low-energy As-ion implantation during molecular beam epitaxy. The layers were investigated using cross-sectional transmission electron microscopy, secondary-ion mass spectrometry, Rutherford backscattering, and electrical measurements. The δ-doped layers were between 3.5 and 5.5 nm thick, and showed perfect epitaxy with 50–80% of the incorporated As on substitutional sites. Layers doped at concentrations from 1×1013 cm−2 to 8×1013 cm−2 had bulk-like mobilities and spanned the metal to insulator transition.

Boron and indium ion-implanted junctions in HgCdTe grown on CdTe and CdTe/Al2O3

This paper discusses the results of junction formation in p-type HgCdTe material which has been converted into n type by ion implantation processes. In was chosen as the candidate donor impurity because it has been observed to diffuse from the implanted source and to activate electrically in a Hg-vacancy doped material under certain anneal conditions. Our results indicate that In diffuses and activates in both Hg-vacancy doped and As-doped HgCdTe layers in both capped and uncapped with saturated Hg overpressure regardless of the background defect structure of the layer. Several apparently different diffusion mechanisms appear in In profiles giving fast, anomalous high concentration components and slow components with low concentration levels. However, under high temperature (400 °C) capped anneals, a single limited source diffusion mechanism appears to dominate (Deff=8×10−13 cm2/s). This mechanism is attributed to vacancies present in the background. Characteristics of indium implantation into arsenic-doped layers were observed in which n-type electrical activity is indium related and controllable by implant/anneal conditions. p-type electrical activity is due to arsenic and it could be controlled by adjusting the arsenic doping level during epitaxy.

Oxygen Precipitation Studies for N-Type and Epitaxial Silicon Substrates During Simulated Cmos Cycles by Synchrotron Section Topography

AbstractSynchrotron section topography is applied to the study of silicon wafers pulled out froma simulated advanced CMOS twin-tub process. Substrates are heavily doped with antimony and phosphorus. For comparison also high-resistivity samples are studied. Prior to epi deposition of arsenic doped layers some wafers are subjected to a three-step intrinsic gettering cycle.Section topographs show that in the lightly doped samples a denuded zone is formed by the CMOS process itself in contrast with the heavily doped ones in which the intrinsic gettering is needed.

Properties of CdTe films grown on InSb by molecular beam epitaxy

The optical and electrical properties of molecular beam epitaxial layers of CdTe grown on InSb(001) substrates at 200–225 °C and either doped with copper, arsenic, antimony or indium or undoped were investigated. Non-intentionally doped layers are found to be n type and to contain indium and antimony atoms out diffused from the substrates. For copper- and arsenic-doped layers, acceptor-bound exciton annihilation lines become dominant in the exciton region of the photoluminescence spectra at 6 K, whereas for antimony-doped layers the acceptor-bound exciton line remains weaker than the donor exciton line even at antimony concentrations of up to 1.2 × 10 18 cm -3. P-type conduction was observed only in heavily copper-doped samples.