In this study Ni-Si and Co-Si films were deposited on fused quartz substrates by coevaporating the metal and silicon. The source separation and deposition rate were chosen to produce a composition range across the substrate. These films were then melted with a scanned cw argon laser beam. This results in a dramatic phase segregation that is readily observed in a light or scanning electron microscope. For the Ni-Si sample two phases separate into irregularly shaped regions up to ≈l10μm size. Electron microprobe measurements indicate that one phase is NiSi2 while the other is pure Si. With the Co-Si sample two phases segregate into narrow stripes that usually follow the temperature gradient produced by the scanned laser beam. The composition analysis indicates that these phases are CoSi and CoSi2. A possible cause for this morphology is discussed.

Epitaxial growth of Pd2Si films on Si(lll) substrates by scanning cw electron beam annealing is investigated theoretically and experimentally. First, the nonlinear heat conduction equation is solved in a substrate with finite thickness to estimate the surface temperature during annealing. Then, the optimum growth conditions are experimentally determined, in which annealing parameters such as the beam current intensity, the scan speed, and the overlap width are changed. It has been shown by Rutherford backscattering and channeling techniques that the crystalline quality of the e-beam annealed Pd2Si films is somewhat worse than that of the furnace-annealed films.

The use of Q-switched ruby laser and multiscanning electron beam annealing (MEBA) to produce the reaction of thin Ti and Ni films deposited onto single crystal Si has been studied. Laser annealing produces a reaction at the interface between the metal and the semiconductor; the reacted layers are not uniform in composition and more similar to a mixture than to a well-defined phase. The silicide layers produced by MEBA results from the solid state reaction of whole metal layer and have well-defined compositions and sharp interfaces between phases and the underlying crystal. The observed thicknesses of the silicides produced by MEBA cannot be accounted for by the parabolic volume diffusion mechanism operating in the standard furnace annealing. Post annealing treatments in furnace showed that e-beam produced silicides have the same thermal stability as those produced by conventional heat treatments. The presence of a critical temperature for silicide formation in Ti/Si MEBA annealed samples has been confirmed and studied in detail.

Patterns of sharp narrow vertical p-n junctions were produced by scanning a laser beam over the surface of a silicon wafer coated on the backsurface by either Au-Sb, Al or Ga. Formation of the junctions occurs by liquid zone migration along the thermal gradient induced by the laser beam. Nd-YAG as well as CO2 laser light was employed and the dependance of migration zone width, velocity, front stability and structure on the different laser wave lengths was studied. Structural investigations of the regrown layers included optical microscopy, SEM and TEM studies as well as spreading resistance measurements to ascertain the behaviour of the various p-n junctions produced. Annealing treatments of the migrated zones were performed to alleviate the stresses produced during the migration experiments.

The growth of device-worthy silicon crystals on insulating substrates would have a revolutionary impact upon microelectronics, and is consequently the object of intense effort. This article reviews recent progress in the application of laser and electron beams and incoherent light to this end. In every case, radiant energy is employed to melt a precursor material, from which device-worthy layers are produced during resolidification. Techniques include seeded and unseeded growth, partial and complete encapsulation of the liquid layer, and oscillation of the solid-liquid interface. Considerations of liquid zone stability, temperature gradient control, and interface morphological stability are central to each technique. Progress in this field has been rapid and several techniques have been successfully demonstrated.

Beam-recrystallized silicon-on-insulator is an attractive material for VLSI integrated circuit and flat panel display applications. This paper describes the electrical characteristics that are unique to MOSFETs fabricated in this material. The back-interface between the silicon and the insulator significantly affects the leakage current by acting as a possible leakage path, depending on the charge at the back interface and the doping concentration in the silicon close to the back interface. In addition, enhanced arsenic diffusion along grain boundaries can cause short circuits between the source and the drain of an n-channel MOSFET. Evidence of such enhanced diffusion are presented as well as means to reduce the impact of the problem. It is shown that molecular hydrogen can be used to passivate the grain-boundaries in the recrystallized silicon material, thereby increasing the carrier mobility. A profile of the carrier mobility as a function of depth from the surface of the silicon is presented, showing that the carrier mobility is not reduced significantly, even close to or at the back interface.

The optical properties of polysilicon on insulating SiO2 were measured by spectroscopic ellipsometry over the energy range 3.0 to 6.0 eV. Spectra were obtained for films as-deposited and after irradiation with an Ar ion laser (focused to a 50μm spot diameter) at 6.0, 7.0 or 7.5 watts. We observed monotonic changes in both ε1 and ε2 with increasing incident power even though the power density was high enough to completely melt the silicon surface in all cases. The changes observed are caused by changes in microstructure; with increasing power the amorphous component decreases and the density increases. Approximate values of the microstructural components are estimated by comparing measured spectra to those synthesized from constituent spectra in the Bruggeman effective medium approximation.

A thermal model is developed for cw laser annealing of multilayer structures. Each layer has arbitrary thickness, thermal conductivity and optical properties. Steady state conditions with no phase transition are assumed. A procedure is presented for obtaining the temperature distribution in any system and explicit integral expressions are developed for the two and three layer cases. Results are calculated for the Si/glass and Si/SiO2 /Si systems.

An analytic model is presented for laser beam induced solid-state crystal growth in silicon on sapphire. The model, which assumes a single activation energy, utilizes temperature profiles calculated from a Green's function solution to the heat equation. Calculated crystal growth in silicon on sapphire is compared to experimentally measured values.

Structural and electrical characterization of laser recrystallized LPCVD silicon films on amorphous substrates using a shaped cw laser beam have been performed. In comparing the results to data obtained using a circular beam, it was found that a significant increase in grain size can be achieved and that the surface morphology of the shaped beam recrystallized material was much smoother. It was also found that whereas circular beam recrystallized material has a random grain structure, shaped beam material is highly oriented with a <100> texture. Finally the electrical characteristics of the recrystallized film were very good when measured in directions parallel to the grain boundaries.

Seeded epitaxial growth of Si over SiO2 is demonstrated in two types of structures. In the first case, rectangular pads of deposited Si were recessed into a thick SiO2 film. Narrow (≃ 5μm) via holes in SiO2 linked the pads with the bulk Si substrates. In the second embodiment, SiO2 patterns were recessed into the Si wafers which were then covered with a continuous 0.5μm poly-Si layer. In both cases, nearly planar geometries were maintained by use of local oxidation and etching techniques. Silicon was recrystallized with a focused Ar+ laser beam. Depending on the scanning conditions and the Si pattern geometry, single crystal growth propagated between 30 and >500μm. The factors influencing the extent and quality of the crystallized regions are discussed.

We report the use of a swept line–source electron beam for liquid phase recrystallization of Si films on Si3N4 layers over Si substrates. For the case of 5000Å of Si on 1000Å of Si3N4 layers over Si Si3N4, we have demonstrated the growth of Si crystalline regions as large as 0.5 × 5 mm of predominately [100] orientation normal to the film and [010] in the sweep direction. The nucleation of grain growth for this case occurred at small defects in the nitride layer at the edge of the treated area, growing out as far as 500 μm over intact nitride. Thicker nitrides (2500Å) remained intact at power densities useful for treating the Si film. For this thicker nitride we demonstrate non–seeded growth for single and repetitively melted Si. In all cases the surface morphology of the regrown regions is suggestive of rapid growth along <100> directions.

Laser-annealing phenomena have typically been divided into two distinct realms. Pulsed lasers involved very short anneal times and small deposited energy densities. Slowly scanned cw lasers involved intermediate times (ms range) and larger energy densities. Repetitively scanned electron beams have extended the range of anneal time and energy density toward conventional thermal processing. This paper examines the regime between pulsed laser annealing and conventional cw laser annealing. By greatly increasing the scan speed of the laser, annealing times and deposited energy densities are reduced and approach those of pulsed laser annealing. Applications are discussed in the areas of silicon-on-insulator recrystallization, low resistivity poly, vertical integration, local lateral seeding, explosive crystallization, and line-source simulation.

A systematic investigation of the formation of large grained rings in polysilicon by Q-switched laser irradiation has been performed. Parameters varied in this study were polysilicon thickness, substrate temperature and underlying oxide thickness. Increasing ring widths were obtained for increasing substrate temperature, polysilicon film thickness and underlying oxide thickness. The width of these rings was found to be independent of incident laser power above a certain threshold value. Surface morphology and the occurrence of cracking and ablation in these films as a function of these parameters was also investigated.

A CO2 laser beam was used to heat bulk fused silica which had previously defined Si3N4 and Si02 encapsulated LPCVD polysilicon islands (25,μm × 100μm) on its surface. The recrystallization process produces single crystal islands under a wide variety of laser treatment parameters. Under certain conditions, the recrystallized islands exhibit a (100) plane parallel to the substrate. These results are the first demonstration of oriented single crystal thin film growth using island predefinition, which eliminates thermal stress induced microcracking resulting from the mismatch in expansion between silicon and bulk fused silica.

Explosive Crystallization occurs in cw laser annealing on a-Si films deposited on glass substrates at laser scan speeds higher than 30 cm/sec. Optical, structural and electrical properties of the crystallized films at various laser scan speeds confirm the existence of two kinds of explosive growth depending on the state of crystallinity of the starting material.

It has been found that careful control of the laser power and scan speed will convert deposited a­Si into continuous lines of uniformly crystallized silicon. Two solid phase “explosive” crystallization front velocities of 1000 cm/sec and 1400 cm/sec have been experimentally determined by matching the laser scan velocity with the runaway a–c phase boundary. If solid phase explosive crystallization is suppressed by pre-annealing, then a liquid assisted runaway crystallization velocity of 220 cm/sec is observed, as well as a continuous furnace-like crystallization process at 250 cm/sec.

Explosive crystallisation induced by an electron beam and by a CW Ar+ laser operating in fast scanning mode is observed for the first time on amorphized silicon layers created by implantation on either polycrystalline films deposited on Si02 or single crystal silicon substrates. The grain structure in the explosive crescents is studied by preferential chemical etching in conjunction with Nomarski optical microscopy, SEM and TEM. The results are similar to the so-called solid-phase explosive crystallization previously observed in a-Si films deposited on glass substrates.

Arsenic doped amorphous silicon layers have been deposited on silicon single crystals by R.F.cathodic sputtering of a silicon target in a reactive argon-hydrogen mixture, and annealed with a Q-switched Ruby laser. Topographic analysis of the irradiated layers has shown the formation of a crater, due to an evaporation effect of material which could be related to the presence of a high concentration of Ar in the amorphous layer. RBS and Raman Spectroscopy showed that the remaining layer is not recrystallised probably due to inhibition by the residual hydrogen. However, it was found that arsenic diffuses into the monocrystalline substrate by laser induced diffusion of dopant from the surface solid source, leading to the formation of good quality P-N junctions.

Intense, Q-switched Nd:YAG laser pulses were used to vaporize a silicon target. The pulsed atomic vapor generated produces amorphous silicon films at unusually fast accumulation speeds of 106 Å/s. Despite this speed, reactive deposition is made possible simply by evaporating in a reactive gas atmosphere. For instance, hydrogenated films have been produced by evaporating in hydrogen. Atomic hydrogen generated by thermal decomposition at a laserirradiated target spot is responsible for hydrogenation. Dynamics of this laser-induced deposition have been studied by a spectroscopic technique.