While many studies have been made of liquid phase epitaxy impurity trapping and segregation in Si little is known about the equivalent processes in Ge. In this paper we have laser annealed Ge <100> and <111> crystals implanted, at liquid nitrogen temperature, with 200 keV 210Bi ions to doses of 2 × 1015 and 1016 ions cm−2. The samples were annealed with Q-switched ruby lasers and an XeCl excimer laser. We have observed 1) velocity and orientation dependence of the Bi segregation coefficient 2) interface instability and cell formation resulting from constitutional supercooling and 3) amorphization and defect production at high velocities. The phenomena are shown to be analogous to those seen in Si.

A model for laser induced diffusion is proposed, assuming the melting of Si surface under pulsed laser irradiation and the diffusion ,in liquid phase, of a thin filmof impurity deposited according to the “limited source” conditions. Depending on the thickness of the film, it results in a dopant distribution profile with a surface disordered layer induced either by segregation effects or precipitation of the dopant in excess of the solubility limit achieved by laser annealing. Experimental results, obtained for a ruby laser irradiation of thin films of different impurities of group III and V, like antimony, bismuth, gallium and indium deposited on silicon substrates are in good agreement with the model. Their effective segregation coefficients have been deduced by fitting the experimental amount of dopant precipitated in the disordered surface layer with the numerical calculations. A cellular structure is seen on surface.

The surface regions of semiconductor single crystals have been examined following laserannealing in an ultrahigh vacuum environment with the output of a pulsed ruby laser. Atomically clean surfaces with impurity levels below 0.1% of a monolayer can be produced by multiple pulse irradiation. Ordered surface structures are produced on low index oriented crystals as well as crystals slightly misoriented. Metastable surface structures exhibiting (l×1) LEED patterns have been produced on (111) orientations and are believed to be a consequence of the rapid cooling rates of 109 degs/sec achieved with the laser irradiation process. The surface and subsurface regions of ion-implanted Si crystals have been examined both before and after laser irradiation and results obtained from Si samples implanted with As are discussed.

The influence of pulsed laser processing (PLP) on the structure and composition of Si, GaAs, Inp and au surfaces has been investigated as a function of the laser fluence. Above a threshold fluence, all initial structures turn into a (1×1) structure and the V-element content of the compound surfaces is decreased. The structure change is shown to be related to the existence of a number of atomic steps on the Plp surface (up to 10114 /cm2 equivalent broken bonds). These defects can be eliminated by further annealings. On the other hand, the stoechiometry defects, which are less numerous (1012−1013/cm2) cannot be eliminated. A model for the mechanisms of defect creation and annihilation during PLP is outlined. The incidence of PLP-induced defects on device technology is evaluated.

Laser annealing is discussed in the context of potential applications in the fabrication of advanced solid state components and integrated circuits. General aspects of the uniquetemporal and spatial heating distributions that can be obtained with laser heating are presented, and selected examples are given which illustrate the advantage of special time/temperature heating cycles in the processing of specific semiconductor device structures. The performance of silicon and Hgcdte diodes, polysilicon resistors, multiple stacked polysilicon/oxide capacitors, Al/Si ohmic contacts and MOS/SOS transistors fabricated using laser annealing is significantly improved relative to devices fabricatedusing conventional furnace annealing.

Rapid Thermal Annealing (RTA) with tungsten halogen lamps provides excellent regrowth of silicon layers damaged by ion implantation. In addition to minimizing dopant redistribution, the inherent advantage of this technique is good control of temperature gradients. The latter is instrumental in reducing the density of extended defects in the annealed samples. In contrast, solid phase laser annealing, which involves steep temperature gradients, always leaves interstitial dislocation loops and point defect clusters. We present a comparative study of crystal quality following laser processing and incoherent light annealing as well as furnace annealing of As, P and B ion implanted Si wafers.

We have used an ultrahigh power, 100kW vortex cooled arc lamp to anneal As+ implant damage in <100> silicon wafers. When the wafer temperature was held above 1100°C for ∼1sec, TEM analysis indicated that the material was free of extended defects.The dopant diffused much more rapidly than would be expected from the usual models. However, preliminary results indicate that defect free material can be produced with dopant movement limited to ∼100Å.

We have investigated flame annealing of ion implantation damage (consisting of amorphous layers and dislocation loops) in (100) and (111) silicon substrates. The temperature of a hydrogen flame was varied from 1050 to 1200°C and the interaction time from 5 to 10 seconds. Detailed TEM results showed that a “defect-free” annealing of amorphous layers by solid-phase-epitaxial growth could be achieved up to a certain concentration. However, dislocation loops in the region below the amorphous layer exhibited coarsening,i.e., the average loop size increased while the number density of loops decreased. Above a critical loop density, which was found to be a function of ion implantation variables and substrate temperature, formations of 90° dislocations (a cross-grid of dislocation in (100) and a triangular grid in (111) specimens) were observed. Electrical (Van der Pauw) measurements indicated nearly a complete electrical activation of dopants with mobility comparable to pulsed laser annealed specimens. The characteristics of p-n junction diodes showed a good diode perfection factor of 1.20–1.25 and low reverse bias currents.

Both (100) and (111) Si wafers were implanted with As, P or B to doses from 1013 to 1016/cm2 and annealed with a Varian IA-200 isothermal annealer. The anneal occurs in a vacuum using infrared radiation for exposure times of 5 to 30 sec. Sheet resistance (Rs), Hall effect, RBS and SIMS were used to analyze the wafers. For each dopant a decreasing Rs occurs with increasing exposure time until a minimum value is reached. Longer anneals produce increased dopant diffusion, and the Rs for As and P implanted wafers increased unless the wafer was capped with 0.05 μm of SiO2 which prevents a loss of dopant. The results for (100) wafers are better than for (111) with As doses ≤1015/cm2, however at doses >1015/cm2 the (100) and (111) results are comparable. The As implanted, isothermally annealed layers were thermally stable for As concentrations ≤2E 20/cm3.

The application of electrochemically formed porous silicon to getter Cu and Au atoms in silicon crystals during incoherent light annealing for 4 to 20 sec is reported. Exposure light power density of 30 W/cm2 was used to heat the samples up to 950 °C. Improvement of lifetime related to Au and Cu gettering with porous silicon has been observed. Excess impurity interstitials and their enhanced diffusion are supposed to be responsible for the gettering effect.

A brief history and present state of beam processing techniques and applications to silicon integrated circuit technology are given. The viability of incorporating pulse-laser controlled doping profiles into the emitter-base structure of an advanced bipolar transistor is discussed. The areas of present I.C. technology which will constrain future device development are identified, and the contribution that beam processing can make in removing these constraints is discussed. The beam processing techniques most likely to be found in future I.C. technologies are described.

We present results which highlight applications of a continuous wave incoherent light source in the processing of semiconductor devices. In particular, damage removal and activation of ion implanted gallium arsenide is demonstrated for both capless and capped annealing of low dose implants at temperatures of > 800°C for times < 10 s. For gallium arsenide FET applications, we demonstrate that it is possible to simultaneously carry out activation, contacting and interconnection steps by utilizing thermomigration processes which are not available with conventional furnace processing. In silicon we demonstrate that shallow multi layer bipolar structures can be successfully fabricated with anneal cycles that lead to supersaturation effects and negligible diffusion.

The advantages of pulsed excimer lasers for semiconductor processing are reviewed. Studies of XeCl excimer laser annealing with pulses of 25 and 70 nsec duration and energy densities in the range from 0.5–3.0 J/cm2 are discussed. The annealing characteristics are described in terms of the results of melt depth, dopant profile spreading, and electrical properties (sheet resistivity, diode characteristics) measurements. Solar cells with efficiencies as high as 16.7% AMI have been fabricated using glow discharge implantation and XeCl laser annealing.

A pulsed ultraviolet excimer laser (XeCl, 308 nm wavelength, 40 nsec FWHM pulse duration) has been successfully used for laser annealing of both boron- and arsenic-implanted silicon. TEM, SIMS, and sheet electrical measurements are used to characterize specimens. C-V and I-V measurements demonstrate that near-ideal p-n junctions are formed (diode perfection factor A = 1.2). Electrical activation of implanted ions by single laser pulses is essentially complete for energy densities Eℓ≥ 1.4 J/cm2 , far below the threshold for substantial surface damage ∽4.5 J/cm2. Melting model calculations are in good agreement with observed thresholds for dopant redistribution and for epitaxial regrowth. Changes in annealing behavior resulting from multiple (1,2,5) laser pulses are also reported. Finally, we demonstrate the use of scanned overlapping excimer laser pulses for fabrication of large area (2 cm2 ) solar cells with good performance characteristics. In contrast to pulsed ruby laser annealing, high open circuit voltages can be obtained without the use of substrate heating.

The destruction of the oxygen donor complex in Czochralski silicon has been studied using scanning electron beam annealing in the range 550°C to 1050° C for 5s to 1000s. A two stage annealing schedule ensured a rapid rise to the target temperature and overscanning provided a uniform, non-distorting heating field. Four point probe and spreading resistance measurements showed a very rapid donor destruction rate above 650° C; between 550° C and 650°C the lower donor destruction rate allowed a study of the annealing behaviour.

In this work Pulsed Electron Beam Annealing has been used to Sctivaye As implanted in (100) and (111) silicon (140 keV- 1015 cm−2 ). With a selected electron beam energy deposition profile excellent regrowth layer quality and As activation has been obtained in the 1.2–1.4 J/cm2 fluence range. As redistribution is conistent with the melting model assuming a diffusivity of 10−4 cm2/s in liquid silicon. As losses might slightly reduce the carrier concentration near the surface in the case of (100) silicon. However a shallow and highly active N+ layer have been achieved with optimized PEBA conditions.

Recent interest in finding an efficient method for transient annealing of ion-implanted silicon has led to studies of various rapid annealing schemes such as graphite heaters and high intensity incoherent light sources as alternative methods to laser annealing. In this paper, we describe a recent study of transient annealing of ion-implanted silicon using a scanning IR line source created by a single tungsten filament enclosed in a quartz envelope. Various dopants (B+, P+ and As+) with fluences of 1014 to 1016 ions/cm2 were implanted and annealed under both transient and steady-state thermal conditions. Dopant depth distributions were analyzed using the SIMS technique. Sheet resistance measurements indicated that almost 100% activations of the implanted dopants were achieved. Sensitivities of dopant activation to transient annealing conditions were studied as a function of dopant concentrations, and high-dose As- and B-implanted samples were found to be sensitive to transient thermal cycle, particularly to the peak temperature. Recrystallization was studied with Rutherford backscattering spectroscopy using 2 Mev He+ ions.

We present a general theory of conduction in polysilicon. The theoretical framework reconciles two apparently divergent approaches for modeling conduction processes in polysilicon and provides a physical basis to correctly interpret and to point out the deficiencies of previously reported thermionic and thermionic field emission theory. This model is based on an extended state mobility in the disordered grain boundary and the thermionic emission-diffusion theory for conduction of current. The attractive features of our theory are (a) it can explain the experimental data without the use of an artificial factor, f, (b) the conduction process is characterized explicitly by the inherent material properties of the grain and the grain boundary. Our model is particularly suited for describing the electrical properties of laser restructured polysilicon, where because of large grain size the diffusion process is expected to be dominant.

The multiple-scan method of electron beam annealing has been used to activate shallow (Rp<150Å), highly doped silicon layers produced by ion implantation of arsenic at 10keV. Beam conditions have been optimised (600Wcm−2 for 100ms) to produce essentially undiffused layers, as determined by high resolution SIMS, containing high concentrations of electrically active arsenic impurities. Computer modelling of diffusion effects in such layers has been used to identify optimum beam conditions and the calculations have been compared with experimental results. Hot electron device structures, which depend on negligible diffusion and high electrical activity, have been fabricated using the multiplescan method with a peak annealing temperature of 900°C.

Selective laser crystallization of undoped polysilicon films has been achieved through the use of a patterned Si3N4 anti-reflection (AR) coating. The recrystallized poly-Si beneath the AR cap exhibits an etch rate 50–90% lower than the surrounding uncapped material, allowing anisotropic etching of poly-Si for the fabrication of MOSFET gates. Undercut is reduced by at least a factor of two from unannealed material. Annealed edge profiles are uniform within ±0.03μm for plasma etching (±0.05 for wet etching) compared to ±0.1μm (± 0.25μm for wet etching) for unannealed regions. The sheet resistivity of 0.5μm films doped by phosphorus diffusion was reduced from an initial value of 82±5 Ω/□ to 40±8 Ω/□ when the dopant was diffused into recrystallized poly-Si and to a final value of 10.2 ± 0.2 Ω/□; after a further laser activation step. Potential applications in VLSIC processing are discussed.