We have studied the polycrystalline growth of Si prepared by a reactive gas flow of SiH4 and F2. In a very early stage of the film growth on the amorphous substrates, a thin layer of the amorphous phase was deposited even in the favorable condition for the crystal growth, whose thickness was determined by the growth condition and reached to 200–300nm in a certain condition. The crystalline phase consisted of closely packed small grains perpendicular to the substrate, 200–500nm in diameter, each of which displayed a tooth-like shape with fine structures, indicating a formation of the crystal nuclei in the amorphous phase and their growth to the grains. The generation probability of the nuclei was not uniform in the amorphous phase, high at the region far from the substrate, and very sensitive to the growth temperature, judging from cross sectional TEM micrographs of the films. These suggest that the network propagation of Si in which fluorine, participates the chemical process in the vicinity of the growing surface enhances a formation of the long range ordering in the network, resulting in the generation of the crystal nuclei.

This work describes an elegant way to control suicide integrity and the quality of the silicide/polySi or amorphous (α) Si interface by a multilayered deposition process. Structurally superior polySi/or-Si layer resulting from this process allows one to reduce the stack height of the polySi/α-Si layer without compromising suicide integrity and silicide/Si interfacial qualities.

Impact of layering during polySi/α-Si deposition on the suicided structure were evaluated from XRD, RBS, cross-sectional TEM, sheet resistance, and SIMS analysis.

In the present study we have modeled the diffusion of boron in single crystal silicon from an ion-implanted polysilicon film deposited on a single crystal silicon substrate. Modeling has been done for both BF2 and boron implants in the polysilicon layer. A new phenomenological model for a diffusivity has been implemented in the PEPPER simulation program using an effective concentration-dependent diffusivity approach. The effective diffusivities of boron in single crystal silicon have been extracted using Boltzmann-Matano analysis. The modeling has been implemented for a wide range of furnace anneal conditions (800°C to 950°C, from 30 min. to 6 hours), and implant conditions (BF2 doses varied from 5×1015 to 2×10'16 cm-2 at 70 keV, boron dose of 5×1015 cm-2 at 20 keV).

Polycrystalline silicon films have been grown using high frequency (110 MHz) rf plasma enhanced chemical vapor deposition with a hydrogen diluted silane gas. Polycrystalline growth was obtained when the silane fraction was less than 10% of the total gas mixture for all rf powers, in marked contrast to growth at 13.56 MHz where high power and more dilution are typically required for microcrystalline growth. Grains with [111] and [220] orientations were observed to have grain sizes up to 900 Angstroms. Room temperature free carrier concentrations as low as 5 × 1015 cm-3 for undoped films were determined by capacitance voltage measurements. Boron doped microcrystalline films were grown with conductivity as high as 8 (Ωcm) V

Extremely heavily doped polycrystalline silicon films were prepared by multiple-pulse XeCl excimer laser annealing of hydrogenated amorphous silicon films. The as-grown films used here included five types: intrinsic, boron-doped, phosphorous-doped, and carbon alloyed with and without boron doping. Raman studies reveal that the annealed films prepared from the boron or phosphorous doped a-Si:H have high carrier activation and display the interference lineshape (Breit-Wigner-Fano) of the discrete phonons (Si-Si and Si-B modes) interacting with the continuum of the single particle electronic Raman scattering. The Raman lineshapes indicate concentrations of ∼1 × 1021 cm3. This is confirmed by dark conductivities exceeding 100 S/cm in the annealed boron-doped and phosphorous-doped layers.

A method is described for the deposition of large-grain polysilicon films at low substrate temperatures. This technique uses precipitation from a thin molten prelayer of Si-Au or Si-Au which is supersaturated with Si from a DC magnetron sputter gun. Typical growth temperatures are 600° C for the Si-Al layer, and 500° C for the Si-Au layer. Growth rates of 6 μm/hr have been achieved, though higher rates seem possible. Films of 20 μm thickness and grain size up to several hundred μm have been grown on SiO2 and sheet Mo substrates using Au and Al as the “solvent” metals. The proposed model for film growth was confirmed by cross-section EDS studies of the film/substrate interface. Film crystallinity was confirmed by etching studies, X-ray diffraction, and selected area diffraction. Preferential nucleation has been achieved using a patterned suicide forming metal (Cr,Ni) on RuO2, coated oxidized wafer. A loss mechanism of the solvent metal during growth was observed.

Phase transition between crystalline and amorphous states was studied through 30ns-pulsed XeCl laser induced melting of silicon films. Crystallization occurs through interface controlled growth for laser energy above surface melting threshold. Grain size is smaller than lOOnm because of short melt duration (<80ns). Amorphization is observed in silicon films thinner than 40nm when the silicon films are completely melted then solidified homogeneously. The amorphized films have a large defect density (∼1020cm-3eV-1), which is remarkably reduced by hydrogen plasma treatment for 1 minute. This paper also discusses the application to fabrication of thin film transistors with a high carrier mobility (>100cm2/Vs) at a low temperature of 250°C.

In this work, we report on the electronic properties of polysilicon thin films and devices realised via furnace crystallisation of undoped a-Si: H. The onset of crystallisation, degree of amorphisation and average grain size are determined by UV reflectivity and electron microscopy. Grain size is found to increase with decreasing a-Si:H substrate temperature, and a maximum areal grain size of 0.4μm2 is obtained. Optical absorption, DC conductivity and transient photoconductivity measurements are employed to examine carrier transport mechanisms. We observe a Meyer-Neldel relationship between the DC conductivity prefactor σ0 and activation energy Eσ. A plasma hydrogenation treatment of the as-crystallised films results in an order of magnitude increase in the DC conductivity and a similar increase in photoconductivity. This is consistent with a shift of the Fermi level position 0.06 eV towards the conduction band. Additionally, analysis of the transient photoconductivity infers a reduced density of states. We discuss the implications of our results for polysilicon TFT optimisation.

Using planar view transmission electron microscope (TEM) and transient reflectance (TR) analyses, we have investigated the excimer laser crystallization of amorphous silicon (a-Si) films on SiO2. Emphasis was placed on characterizing the microstructures of the single-shot irradiated materials, as a function of the energy density of the laser pulse and the temperature of the substrate. The dependence of the grain size and melt duration as a function of energy density revealed two major crystallization regimes. In the low energy density regime, the average grain size first increases gradually with increases in the laser energy density. In the high energy density regime, on the other hand, a very fine grained microstructure, which is relatively insensitive to variations in the laser energy density, is obtained. In addition, we have discovered that at the transition between these two regimes an extremely small experimental window exists, within which an exceedingly large grain-sized polycrystalline film is obtained. We suggest a liquid phase growth model for this phenomenon, which is based on the regrowth of crystals from the residual solid islands at the oxide interface.

The grain size of phosphorous (P)-doped poly-Si film has been enlarged to about 5000 Å by controlling the solidification velocity of molten Si during ArF excimer laser annealing. The drastically enlarged grain has few defects inside the grain. It has been confirmed that control of the solidification velocity is effective for P-doped poly-Si similar to the case of non-doped poly-Si films. In addition, a sheet resistance of 80 Ω/□ (ρ = 4 × 10-4 Ω · cm) has been achieved for very thin (500 Å) films by recrystallizing PECVD P-doped a-Si films.

Excimer laser crystallization of hydrogenated amorphous silicon has been investigated as a function of substrate temperature. At low substrate temperatures hydrogen out-diffusion strongly influences the film morphology, while at 420 °C homogeneous recrystallized films are obtained, as a result of the reduced solidification velocity. This process has been successfully tested by fabricating with the recrystalllized material thin-film transistors according to the bottom-gate configuration.

In this paper we report on the ability of rapid thermal annealing (1050C, 45s) and furnace annealing (900C, 30min) to partially break up the interfacial oxide in bipolar transistors with different oxide thicknesses at the polysilicon/silicon interface. We have obtained the different oxide thicknesses either by performing different ex situ cleans (RCA clean or RCA clean + HF dip) before Low Pressure Chemical Vapor Deposition (LPCVD) of polysilicon, or by using a cluster tool for polysilicon deposition with the ability to perform an in situ clean and then allowing the growth of different oxide thicknesses at the interface prior to polysilicon deposition. For the in situ cleaned devices, it is observed that after the interface anneal, the current gain increases with increasing oxide thicknesses, but with little penalty in terms of higher emitter resistance, Re. This indicates that by controllably increasing the interfacial oxide thickness and by subsequent annealing to partially break up the interfacial oxide, higher current gains can be obtained with little sacrifice in terms of higher Re.

The relationship between the grain size of poly-Si after SPC and the structure of a-Si before SPC was studied. The structure of a-Si was characterized by TA/TO: the Raman intensity ratio of the Transverse Acoustic (TA) like band and the Transverse Optical (TO) like band. A good positive correlation between the grain size and TS/TO was revealed for the first time. The nucleation and growth kinetics were speculated by using a thermodynamic model. The grain size could be enlarged up to 6 μ m by applying textured substrates to a-Si with a large structural disorder. This film was applied to the active layer of solar cells, and a collection efficiency of 51% at 900 nm was obtained.

Al was deposited on the both sides of p-type Si by the sputtering, and the pulsed KrF excimer laser was irradiated on the one side and both sides of Al dot contacts. Due to the thin-high doping recrystallized layer, the transitions from the Schottky diodes to the ohmic contacts via backward diodes were observed in I-V measurement. Good N-shape negative resistances and notches were observed in the diodes, and ohmic contacts. Possible interpretations of the orgin of these phenomena are discussed. And, the simple model of the effective barrier height reduction under the thermionic field emission was developed using WKB approximation, and tunneling theory. By the depth Auger analysis, Al, and Si profiles near Al-Si interface after the laser irradiation were observed.

We show that the use of phosphorus doped spin-on glasses as diffusion source is an attractive approach for the formation of shallow junctions in polycrystalline silicon materials. Moreover, this very simple doping process using a glass film can be fruitfully associated to rapid thermal annealing.

A new annealing method, a combination of rapid thermal annealing (RTA) and furnace annealing, has been developed to obtain a high quality poly-Si from a-Si deposited by LPCVD. This method produces a large grain poly-Si with good uniformity, which may result from the growth of relatively defect-free nucleus generated at a high temperature by RTA. Poly-Si thin film transistors fabricated by this new annealing method have higher field effect mobility and better uniformity compared with those by the conventional furnace annealing.

Results of experiments on crystallization of thin (50 to 200 nm) amorphous Si films initially deposited onto glass substrates by different techniques (PECVD, LPCVD) and treated by different lasers (argon, excimer, or Cu-vapor) are given. The films treated are characterized by in-plane and cross-sectional TEM, and by microdiffraction. Some conclusions about mechanisms of the crystallization are made.

New GaAs quantum dots called tetrahedral quantum dots (TQDs) were fabricated using selective area metalorganic chemical vapor deposition (MOCVD). GaAs sub-micron crystals were completely buried in AlGaAs with single growth run without any processing damage at heterojunction interface. The substrates were SiO2 masked (111)B GaAs, which are partially etched free of SiO2 over triangular area using electron beam lithograpy and reactive ion etching techniques. First, truncated tetrahedral AlGaAs buffer layers with {110} facet sidewalls were grown in triangular area. Next, GaAs TQDs were sequentially grown on the top of AlGaAs. Finally, AlGaAs layers were overgrown on the resulting tetrahedral structures. The shape of GaAs tetrahedron was measured by an atomic force microscope(AFM). The size of bottom triangle of GaAs TQDs were estimated to be 20 nm. The size fluctuation was about 2%, which means that uniformity of selective area growth is excellent. Photoluminescence of GaAs TQDs buried in AlGaAs was measured at 8.5K. A clear emission peak from GaAs TQDs was observed at 810 nm. The energy shift from the GaAs emission peak is 19meV, which agrees well with the calculation. The results suggest that the selective area MOCVD method is very promising to fabricate GaAs quantum dots.

A selective growth of GaAs microcrystals was demonstrated on a Se-terminated GaAlAs surface. Ga molecules were supplied to the Se-terminated GaAlAs surface at first. The surface consisted of Ga droplets and bared Se-terminated GaAlAs surface. After the following As molecule supply to the surface, a selective GaAs microcrystal growth from Ga droplets was observed. The cross sectional investigations by the high resolution electron microscope revealed epitaxial growth of GaAs microcrystals with (111) facets and a possibility of (GaAl)2Se3, layer formation at the GaAs/Se-terminated GaAlAs interface.

We report recent results on the homogeneous nucleation of GaAs quantum dots from organometallic precursors and subsequent heterogeneous nucleation of epitaxial regrowth of GaAs on the clusters. We find that clusters onto which we have regrown GaAs exhibit a much higher degree of faceting, whereas particles subject to che same thermal cycles but onto which no new GaAs has been grown, though crystalline, have highly irregular shapes. These results suggest that epitaxial regrowth exhibits selectivity in the growth rates on the various crystal facets akin to that found in bulk samples.