K. Park

Discontinuity of B‐diffusion profiles at the interface of polycrystalline Si and single crystal Si

Boron diffusion in polycrystalline Si‐on‐single crystal Si systems has been studied by secondary ion mass spectrometry. The extrapolated B‐diffusion profiles in polycrystalline Si and in the single crystal Si substrate reveal a discontinuity at the polycrystalline Si‐single crystal Si interface. The discontinuity in the B profiles is believed to occur due to the blockage of B‐defect complexes by the interfacial oxide between polycrystalline Si and the single‐crystal Si substrate, as well as the immobility of these defect complexes in single crystal Si. The B in the implant peak region above the B solid solubility limit is found to be immobile in single crystal Si during annealing due to the formation of electrically inactive B‐defect complexes. In polycrystalline Si, however, our results show that the B in the peak region spreads out more rapidly than in single crystal Si possibly due to the diffusion of B‐defect complexes along grain boundaries. The B‐defect complexes are electrically inactive as determi...

Analysis of ion‐implanted amorphous and polycrystalline silicon films as diffusion sources for ultrashallow junctions

This paper discusses the diffusion of As, P, and B in amorphous and polycrystalline silicon‐on‐single‐crystal silicon systems during rapid thermal annealing and furnace annealing. It is found that the changes of microstructure during annealing play a major role in determining the diffusion profiles in the substrate as well as in the polycrystalline silicon layer. For As or P doping, a drive‐in diffusion results in a much larger grain microstructure for as‐deposited amorphous silicon than for as‐deposited polycrystalline silicon, which leads to the formation of shallower junctions in the substrate for the first case. For B doping, there is little difference in the final microstructure and junction depth between the two cases. At high anneal temperatures, the native interfacial oxide breaks up, causing epitaxial realignment of the polycrystalline silicon film and subsequent enhanced diffusion in the substrate.

Quantitative scanning thermal microscopy of ErAs/GaAs superlattice structures grown by molecular beam epitaxy

A proximal probe-based quantitative measurement of thermal conductivity with ∼100–150 nm lateral and vertical spatial resolution has been implemented. Measurements on an ErAs/GaAs superlattice structure grown by molecular beam epitaxy with 3% volumetric ErAs content yielded thermal conductivity at room temperature of 9 ± 2 W/m K, approximately five times lower than that for GaAs. Numerical modeling of phonon scattering by ErAs nanoparticles yielded thermal conductivities in reasonable agreement with those measured experimentally and provides insight into the potential influence of nanoparticle shape on phonon scattering. Measurements of wedge-shaped samples created by focused ion beam milling provide direct confirmation of depth resolution achieved.

Analysis of lateral uniformity of ultrashallow junctions in polycrystalline silicon‐on‐single crystal silicon systems

The lateral uniformity of n+‐p junctions formed by indiffusion of As or P from an amorphous or polycrystalline silicon thin‐film source into the underlying silicon substrate has been investigated using a concentration‐dependent etch and transmission electron microscopy. Grain boundaries act as fast diffusant pipelines and also possibly inject point defects into the substrate, thereby enhancing bulk diffusivities locally in the substrate. Delineated ultrashallow junctions show significant doping lateral inhomogeneities in the substrate for as‐deposited amorphous silicon diffusion sources but not for as‐deposited polycrystalline silicon diffusion sources because of a larger final grain microstructure after annealing in the former case. However, the doping inhomogeneities are gradually smeared out as impurities diffuse deeper into the substrate.

Role of negatively charged vacancies in secondary grain growth in polycrystalline silicon during rapid thermal annealing

It has been reported that there is a drastic increase of grain size in polycrystalline silicon because of secondary grain growth in ultrathin, heavily n‐type doped films upon conventional furnace annealing. There has been very limited work on secondary grain growth during rapid thermal annealing (RTA). This letter presents for the first time extensive data on secondary grain growth in heavily n‐type, P‐doped amorphous silicon‐on‐oxide films during RTA. Grains as large as 16 μm in diameter have been obtained in 160‐nm‐thick films which represent the largest secondary grains and largest grain size to film thickness reported in the literature. The role of charged silicon vacancies is invoked in a new way to explain the observed lower activation energy for grain boundary mobility during secondary grain growth than during normal grain growth.

Ultra-shallow junctions in silicon using amorphous and polycrystalline silicon solid diffusion sources

The inter-dependence of diffusion behavior and grain microstructure in amorphous silicon/polysilicon-on-single crystal silicon systems has been studied for rapid thermal and furnace annealing for P and BF2 implants. It is found that the changes of microstructure during annealing play a major role in determining the diffusion profiles in the substrate as well as in the polysilicon layer. For P doping, a drive-in diffusion results in a much larger grain microstructure for as-deposited amorphous silicon than for as-deposited polysilicon, which leads to the formation of shallower junctions in the substrate for the first case. For B doping, there is little difference in the final microstructure and junction depth between the two cases. The P and B junctions formed in the substrate are found to be laterally very uniform in spite of expected doping inhomogeneities due to polysilicon grain boundaries both for as-deposited amorphous silicon diffusion sources and for as-deposited polysilicon diffusion sources.

Scanning capacitance microscopy of ErAs nanoparticles embedded in GaAs pn junctions

Scanning capacitance microscopy is used to characterize the electronic properties of ErAs nanoparticles embedded in GaAs pn junctions grown by molecular beam epitaxy. Voltage-dependent capacitance images reveal localized variations in subsurface electronic structure near buried ErAs nanoparticles at lateral length scales of 20-30 nm. Numerical modeling indicates that these variations arise from inhomogeneities in charge modulation due to Fermi level pinning behavior associated with the embedded ErAs nanoparticles. Statistical analysis of image data yields an average particle radius of 6-8 nm—well below the direct resolution limit in scanning capacitance microscopy but discernible via analysis of patterns in nanoscale capacitance images.

Rapid thermal hydrogen passivation of polysilicon MOSFETs

The effectiveness of rapid thermal annealing as a passivation technique using Si/sub 3/N/sub 4/ as a solid source of H is discussed. Polysilicon MOSFETs with an on/off ratio of 10/sup 7/ can be obtained through rapid thermal hydrogen passivation, compared to an on/off ratio of 10/sup 6/ after furnace passivation. The improvement of subthreshold slope, threshold voltage, and channel transconductance compared to unpassivated MOSFETs is greater for rapid thermal annealing (RTA) than for furnace passivation.<<ETX>>

Increased InAs quantum dot size and density using bismuth as a surfactant

We have investigated the growth of self-assembled InAs quantum dots using bismuth as a surfactant to control the dot size and density. We find that the bismuth surfactant increases the quantum dot density, size, and uniformity, enabling the extension of the emission wavelength with increasing InAs deposition without a concomitant reduction in dot density. We show that these effects are due to bismuth acting as a reactive surfactant to kinetically suppress the surface adatom mobility. This mechanism for controlling quantum dot density and size has the potential to extend the operating wavelength and enhance the performance of various optoelectronic devices.

Conductivity and structure of ErAs nanoparticles embedded in GaAs pn junctions analyzed via conductive atomic force microscopy

We have used conductive atomic force microscopy to investigate the influence of growth temperature on local current flow in GaAs pn junctions with embedded ErAs nanoparticles grown by molecular beam epitaxy. Three sets of samples, one with 1 ML ErAs deposited at different growth temperatures and two grown at 530 °C and 575 °C with varying ErAs depositions, were characterized. Statistical analysis of local current images suggests that the structures grown at 575 °C have about 3 times thicker ErAs nanoparticles than structures grown at 530 °C, resulting in degradation of conductivity due to reduced ErAs coverage. These findings explain previous studies of macroscopic tunnel junctions.