Time-Resolved Studies of Rapid Solidification in Highly Undercooled Molten Silicon

1984 ◽  
Vol 35 ◽  
Author(s):  
D.H. Lowndes ◽  
G.E. Jellison ◽  
R.F. Wood ◽  
S.J. Pennycook ◽  
R.W. Carpenter
Keyword(s):  
Liquid Layer ◽  
Laser Energy ◽  
Surface Region ◽  
Experimental Information ◽  
Molten Silicon ◽  
Undercooled Liquid ◽  
Time Resolved ◽  
Model Calculations ◽  
Near Surface ◽  
Si Substrates

ABSTRACTA KrF (248 nm) pulsed laser was used to melt 90-, 190-, and 440-nm thick amorphous silicon layers produced by Si ion implantation into (100) crystalline Si substrates. Time-resolved reflectivity measurements at two different probe wavelengths (633 nm and 1.15 μm) and post-irradiation TEM measurements were used to study the formation of an undercooled liquid Si phase and the subsequent solidification processes. The time-resolved measurements provide new experimental information about the nucleation of fine-grained Si crystallites in undercooled liquid Si, at low laser energy densities (Eℓ), and about the growth of large-grained Si in the near-surface region at higher Eℓ. Measurements with the infrared probe beam reveal the presence of a buried, propagating liquid layer at low ??. Model calculations indicate that this liquid layer is generated in part by the release of latent heat associated with the nucleation and growth process.

Time-Resolved Reflectivity Measurements of Silicon And Germanium Using A Pulsed Excimer Laser

1985 ◽  
Vol 51 ◽  
Author(s):  
G. E. Jellison ◽  
D. H. Lowndes ◽  
D. N. Mashburn ◽  
R. F. Wood
Keyword(s):  
Excimer Laser ◽  
Surface Region ◽  
Finite Energy ◽  
Time Resolved ◽  
Model Calculations ◽  
Near Surface ◽  
Maximum Reflectivity ◽  
Liquid Phases ◽  
Silicon And Germanium ◽  
Melt Duration

ABSTRACTTime-resolved reflectivity measurements of silicon and germanium have been made during pulsed KrF excimer laser irradiation. The reflectivity was measured simultaneously at both 1152 and 632.8 nm wavelengths, and the energy density of each laser pulse was monitored. The melt duration and the time of the onset of melting were measured and compared with the results of melting model calculations. For energy densities just above the melting threshold, it was found that the melt duration was never less than 20 ns for Si and 25 ns for Ge, while the maximum reflectivity increased from the value of the hot solid to that of the liquid over a finite energy range. These results, along with a reinterpretation of earlier time-resolved ellipsometry measurements, indicate that, during the melt-in process, the near-surface region does not melt homogeneously, but rather consists of a mixture of solid and liquid phases. The reflectivity at the onset of melting and in the liquid phase have been measured at both 632.8 and 1152 nm, and are compared with the results found in the literature.

Time-Resolved and Nicrostructural Studies of Solidification in Undercooled Liquid Silicon

1988 ◽  
Vol 100 ◽  
Author(s):  
D. H. Lowndes ◽  
S. J. Pennycook ◽  
R. F. Wood ◽  
G. E. Jellison ◽  
S. P. Withrow
Keyword(s):  
Heat Flow ◽  
Near Infrared ◽  
Laser Energy ◽  
Solidification Process ◽  
Sample Surface ◽  
Undercooled Liquid ◽  
Time Resolved ◽  
Plan View ◽  
Model Calculations ◽  
Fine Grained

ABSTRACTNanosecond resolution visible (633 nm) and near-infrared (1152 nm) reflectivity measurements have been used, together with transmission electronmicroscopy (TEM), to study pulsed KrF (248 nm) laser melting and subsequent solidification of thick (190–410 nm) amorphous (a) silicon layers. The measurements cover the entire laser energy density (El) range between the onset of melting (∼ 0.12 J/cm2) and the completion of epitaxial crystallization (∼1.1 J/cm2). Four distinct El-regimes of melting and solidification are found for the 410-nm thick a-Si layers. For El > 0.25 J/cm2, the time of formation, velocity and final depth of “explosively” propagating undercooled liquid layers were measured in specimens that had been uniformly implanted with Si, Ge, or Cu. TEM shows that the “fine-grained polycrystalline Si” produced by explosive crystallization (XC) actually contains large numbers of disk-shaped Si flakes that have largely amorphous centers and are visible only in plan view. The optical and TEM measurements suggest (1) that flakes are the crystallization events that initiate XC, and (2) that lateral heat flow (parallel to the sample surface) must be taken into account in order to understand flake formation. Results of new two-dimensional (2-D) model calculations of heat flow and solidification are presented. These calculations confirm the importance of 2-D heat flow and crystallite growth early in the solidification process. For 0.3 4 < El > 1.0 J/cm2, pronounced changes in both the shape and the duration of the reflectivity signals provide information about the growth of polycrystalline grains; this information can be correlated with post-irradiation plan and cross-section view TEM microstructural measurements.

Time-resolved optical studies of oxide-encapsulated silicon during pulsed laser melting

1988 ◽  
Vol 3 (3) ◽  
pp. 498-505 ◽  
Author(s):  
G. E. Jellison ◽  
D. H. Lowndes ◽  
J. W. Sharp
Keyword(s):  
Laser Annealing ◽  
Laser Energy ◽  
Threshold Energy ◽  
Pulsed Laser ◽  
Silicon Layer ◽  
Oxide Thickness ◽  
Time Resolved ◽  
Model Calculations ◽  
Near Surface ◽  
Surface Profiling

Nanosecond time-resolved reflectivity and ellipsometry experiments have been performed on (100) Si wafers encapsulated by 5.5–76.2 nm thick thermal oxides, using pulsed KrF (248 nm) laser energy densities sufficient to melt the Si beneath the oxide. Post-irradiation nulling ellipsometry, optical microphotography, and surface profiling measurements were carried out. It was found that the threshold energy density required to melt the Si varies with oxide thickness; this is explained primarily by the reflective properties of the oxide overlayer. The time-resolved reflectivity and ellipsometry measurements show that rippling of the SiO2 layer occurs on the 20–40 ns timescale and results in a decrease in specular reflectivity of the rippled silicon surface beneath. Optical model calculations suggest that pulsed laser annealing through a thick oxide layer results in a damaged near-surface silicon layer (∼ 30 nm thick); this layer contains defects that are probably responsible for the degraded performance of devices.

Low Temperature Crystallization of Amorphous Silicon Films Using an Excimer Laser

1989 ◽  
Vol 149 ◽  
Author(s):  
S. E. Ready ◽  
J. B. Boyce ◽  
R. Z. Bachrach ◽  
R. I. Johnson ◽  
K. Winer ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Excimer Laser ◽  
Laser Energy ◽  
Amorphous Material ◽  
Surface Region ◽  
Silicon Films ◽  
Starting Material ◽  
Near Surface ◽  
Silicon Thin Films ◽  
Crystallite Sizes

ABSTRACTIn an effort to enhance the electrical properties of silicon thin films, we have performed recrystallization experiments on a variety of amorphous silicon films using an excimer laser. The intense, pulsed UV produced by the laser (308nm, using XeCl gas) is highly absorbed by the amorphous material and thus provides intense localized heating in the near surface region. Two types of starting films were studied: plasma CVD a-Si:H and LPCVD a-Si. The subsequent modification produces crystallites whose structure and electrical characteristics vary due to starting material and laser scan parameters. The treated films have been characterized using Raman, x-ray diffraction, TEM, SIMS and transport measurements. The results indicate that crystallites nucleate in the surface region. The degree of crystallization near the surface increases dramatically as a function of deposited laser energy density and less so as a function of laser shot density. The hall mobility of the highly crystallized samples exhibit an increase of 2 orders of magnitude over the amorphous starting material. In the PECVD material, the rapid diffusion of hydrogen causes voids to be formed at intermediate laser energy densities and removal of film at higher energy densities. The LPCVD material withstands the high laser energies to produce well crystallized films with crystallite sizes greater then 1000Å.

Time-Resolved and Post-Irradiation Studies of the Interaction of High-Power Pulsed Microwave Radiation with Silicon

1986 ◽  
Vol 74 ◽  
Author(s):  
R. B. James ◽  
P. R. Bolton ◽  
R. A. Alvarez ◽  
R. E. Valiga ◽  
W. H. Christie
Keyword(s):  
Mass Spectrometry ◽  
Secondary Ion Mass Spectrometry ◽  
Surface Region ◽  
Surface Damage ◽  
Threshold Value ◽  
Optical Measurements ◽  
Time Resolved ◽  
Near Surface ◽  
Reflected Power ◽  
Secondary Ion

AbstractWe have measured the microwave-induced damage to the near-surface region of silicon for 1.9-μs pulses at a frequency of 2.856 GHz and a pulse power of up to 7.2 MW. Rectangular samples were irradiated in a test section of WR-284 waveguide that was filled with freon to a pressure of 30 psig. Incident, transmitted and reflected powers were monitored with directional couplers and fast diodes. The results of the time-resolved optical measurements show that the onset of surface damage is accompanied by a large increase in the reflected power. Examination of the irradiated surfaces shows that the degree of damage is greatest near the edges of the samples. Using secondary ion mass spectrometry to profile the implanted As, we find that the microwave pulses can melt the near-surface region of the material for pulse powers exceeding a threshold value.

Excimer Laser Induced Crystallization of Amorphous Silicon-Germanium Films

1993 ◽  
Vol 321 ◽  
Author(s):  
A. Slaoui ◽  
C. Deng ◽  
S. Talwar ◽  
J. K. Kramer ◽  
B. Prevot ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Excimer Laser ◽  
Silicon Germanium ◽  
Laser Energy ◽  
Electron Gun ◽  
Laser Crystallization ◽  
Time Resolved ◽  
Si Substrates ◽  
Si Films ◽  
Amorphous Silicon Germanium

ABSTRACTApplication of excimer laser crystallization of Amorphous silicon (a-Si) has introduced a new, interesting potential technology for the fabrication of polycrystalline (poly-Si) thin film transistors. We are currently studying polycrystalline Si1−xGex thin films in order to determine whether this material can lead to improved electrical properties or to better processing requirements when compared with polycrystalline Si films. In this work we analyze by RBS, TEM, Raman spectroscopy and surface reflectance, the structure of thin Amorphous Si1−xGex films after irradiation with a XeCl excimer laser. The Amorphous SiGe films were prepared by evaporation of Si and Ge onto oxidized Si substrates using an electron gun in vaccum. The effects of laser energy fluence during irradiation are investigated. The Amorphous to crystalline transition is followed by in-situ measurement of time-resolved reflectivity.

Time Resolved Transmission and Reflectivity of Pulsed Ruby Laser Irradiated Silicon

1981 ◽  
Vol 4 ◽  
Author(s):  
Douglas H. Lowndes ◽  
G. E. Jellison ◽  
R. F. Wood
Keyword(s):  
Ruby Laser ◽  
Crystalline Silicon ◽  
Laser Energy ◽  
Pulsed Laser ◽  
Quantitative Agreement ◽  
Laser Wavelength ◽  
Time Resolved ◽  
Model Calculations ◽  
Thermal Melting ◽  
Apparent Disagreement

ABSTRACTThe time resolved optical transmission, T (atλ = 1152 nm), and reflectivity, R (at 633 nm and 1152 nm), have been measured for n-type single crystalline silicon (c-Si) during and immediately after pulsed ruby laser irradiation (λ = 693 nm, FWHM pulse duration 14 nsec), for a range of pulsed laser energy densities, El. The T is found to go to zero, and to remain at zero, for a period of time that increases with increasing El, in apparent disagreement with earlier measurements elsewhere that used semi-insulating Si and a different pulsed laser wavelength. Measured reflectivities during the high R phase agree within experimental error with reflectivities calculated from the optical constants of molten Si. Quantitative agreement is also found between both our T and R measurements and detailed time– and El-dependent results of thermal melting model calculations.

Rapid Heating of Ion-Implanted Silicon by High-Power Pulsed Microwave Radiation

1988 ◽  
Vol 124 ◽  
Author(s):  
R. B. James ◽  
P. R. Bolton ◽  
R. A. Alvarez ◽  
W. H. Christie
Keyword(s):  
Secondary Ion Mass Spectrometry ◽  
Light Emission ◽  
Electrical Breakdown ◽  
Rapid Heating ◽  
Surface Region ◽  
Time Resolved ◽  
Near Surface ◽  
Microwave Induced Plasma ◽  
Spatially Homogeneous ◽  
Secondary Ion

ABSTRACTWe have used 1.1-μs microwave pulses at a frequency of 2.856 GHz to rapidly heat the near-surface region of arsenic-implanted silicon. The samples were irradiated inside a WR-284 waveguide by single-pass TE10 traveling wave pulses. Post-irradiation studies show that surface melting occurs for incident pulse powers exceeding about 3 MW. Time-resolved measurements of the microwave reflectivity (R) show that there is an abrupt and large increase in R for microwave pulse powers greater than the melt threshold. Significant light emission was also observed from the test cell, which is most likely due to the relaxation of a microwave-induced plasma formed by electrical breakdown of gas. Using secondary ion mass spectrometry, we measured the depth profile of the implanted arsenic and found that the penetration of the melt front in the near-surface region is not spatially homogeneous over the silicon surface.

Monitoring of Dopant Activation in Sub-Surface P-Type Si Using the Surface Charge Profiling (SCP) Method

1996 ◽  
Vol 448 ◽  
Author(s):  
P. Roman ◽  
J. Staffa ◽  
S. Fakhouri ◽  
J. Ruzyllo ◽  
E. Kamieniecki
Keyword(s):  
Surface Charge ◽  
Boron Concentration ◽  
Surface Region ◽  
Ambient Air ◽  
Epitaxial Layers ◽  
Near Surface ◽  
Si Substrates ◽  
Boron Doped ◽  
Order Of Magnitude ◽  
P Type

AbstractIn this study the SCP (Surface Charge Profiling) method, based on non-contact, small-signal ac-SPV measurement is used to study thermal activation of boron in the near surface region of p-type Si wafers. Boron tends to form pairs with impurities such as hydrogen, iron and copper in the near surface region of Si substrates which render it inactive. During device processing, activation of boron may take place resulting in uncontrolled variations in active boron concentration in the near surface region.In this work, both boron doped, polished CZ wafers and wafers with boron doped epitaxial layers are studied. In the former case, the concentration of active boron in the near surface region was initially up to an order of magnitude less than the bulk concentration determined from four-probe measurements, but increased with the temperature of an anneal in ambient air and approached the bulk value. In contrast, the wafers with epitaxial layers showed no consistent variations of surface dopant concentration with temperature. These results confirmed previous findings that the near surface region of the polished wafers is contaminated with metals introduced during polishing operations. The SCP method was found to be very effective in monitoring variations in active boron concentration in the near-surface region.

Pulsed Microwave Irradiation of Graphite/Epoxy Composites

1988 ◽  
Vol 124 ◽  
Author(s):  
R. B. James ◽  
P. R. Bolton ◽  
R. A. Alvarez
Keyword(s):  
Light Emission ◽  
Electrical Breakdown ◽  
Surface Region ◽  
Surface Damage ◽  
Sample Surface ◽  
Optical Measurements ◽  
Time Resolved ◽  
Near Surface ◽  
Reflected Power ◽  
Surface Decomposition

ABSTRACTWe have measured the microwave-induced damage to the near-surface region of a graphite/epoxy composite material for 1.1-μs pulses at a frequency of 2.856 GHz and a pulse power of up to 8 MW. Rectangular samples were irradiated by single-pass TE10 traveling wave pulses inside a WR-284 waveguide, and in situ and post irradiation studies were performed to characterize the material modifications induced by the microwave pulses. The results of the time-resolved optical measurements in vacuo show that surface decomposition of the epoxy resin occurs for incident pulse powers exceeding 1.1 MW, and that the surface damage is accompanied by a large increase in the reflected microwave power. Simultaneous with the onset of surface decomposition, significant light emission from the sample and a large enhancement of the gas pressure in the test cell were observed. The large increments in both the reflected power and light emission are attributed to the formation of a plasma due to electrical breakdown of the gas at (or near) the sample surface.

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