H. J. Leamy

Charge collection scanning electron microscopy

This review encompasses the application of the scanning electron microscope to the study and characterization of semiconductor materials and devices by the Electron Beam Induced Conductivity (EBIC) method. In this technique, the charge carriers generated by the electron beam of the microscope are collected by an electric field within the material and sensed as a current in an external circuit. When employed as the video signal of the SEM, this collected current image reveals inhomogeneities in the electrical properties of the material. The technique has been used to determine carrier lifetime, diffusion length, defect energy levels, and surface recombination velocities. Charge collection images reveal the location of p‐n junctions, recombination sites such as dislocations and precipitates, and the presence of doping level inhomogeneities. Both the theoretical foundation and the practical aspects of these effects are discussed in a tutorial fashion in this review.

Periodic regrowth phenomena produced by laser annealing of ion‐implanted silicon

We have discovered that interference effects extant during pulsed laser irradiation annealing of ion‐implanted silicon produce periodic property variations in the annealed material that mimic the interference pattern. These are manifest at near‐annealing threshold power densities as surface ripple and at higher power densities may be revealed by etching. The surface ripple observed at low power densities is correlated with the occurrence of polycrystalline silicon regions in the annealed material. Our observations suggest that surface melting and epitaxial regrowth are responsible for the annealing effect.

Conversion of Si to epitaxial SiC by reaction with C2H2

The growth of β‐SiC films on Si by reaction of a Si single crystal with C2H2 has been studied for the conditions 10−7 ≤PC2H2≤5×10−4 Torr, 800≤T≤1100°C, in both high‐ and ultrahigh‐vacuum chambers. At C2H2 pressures below approximately 10−5 Torr, linear growth kinetics were observed over the temperature range investigated and the reaction probability was determined as 0.02–0.03. In this pressure range growth occurs by the diffusion of Si through porous defects incorporated in the growing film. We have studied in detail the structure of defected films formed under various growth conditions by scanning electron microscopy, scanning transmission electron microscopy, and transmission electron microscopy. We conclude that the occurrence of defects is intrinsic to the mechanism of film growth. The predominant defect type consists of a shallow (∼ 2000 A) pit in the Si substrate, over which the growing SiC assumes a porous polycrystalline morphology. The number and areal densities of these defects are proportional...

Hydrogen passivation of point defects in silicon

Laser melting of crystalline silicon introduces electrically active defects which are observed by capacitance transient spectroscopy. The electrical activity of these point defects is neutralized by reaction with atomic hydrogen at 200 °C.

Reduction of GaAs surface recombination velocity by chemical treatment

Chemisorbed ruthenium ions on the surface of n‐GaAs decrease the surface recombination velocity of electrons and holes from 5×105 to 3.5×104 cm/sec. It is shown that the ions, in a one‐third monolayer thickness, are confined to the surface and do not form a new junction by diffusing into the GaAs. This use of Ru appears to be the first observation of the reduction of the surface recombination velocity for GaAs by the simple chemisorption of ions.

Laser‐induced reactions of platinum and other metal films with silicon

We have reacted thin Pt, Pd, and Ni films with single‐crystal Si using Q‐switched Nd : YAG laser pulses of 100‐nsec duration in the power range 18–50 MW cm−2. The layers are laterally very uniform in thickness but are not single phase. Average composition of the reaction product layer can be changed over a wide range by varying film thickness and laser power. The microstructure of the reacted layers indicates that reaction occurs via surface melting, mixing, and rapid resolidification.

The equilibrium properties of crystal surface steps

The equilibrium structure of [100] oriented steps on the (100) surface of a simple cubic crystal has been examined by Monte Carlo simulation methods. The structures of four surfaces (20,1,0), (10,1,0), (5,1,0) and (100), were simulated and the results combined to determine the properties of an isolated step. The step edge (ledge) energy/length first increases with temperature and then decreases continuously until, at a temperature TR, it vanishes. This temperature, TR, corresponds to the critical temperature for surface roughening, at which the structural and thermodynamic properties of the stepless surface exhibit singularities. These results indicate that TR may be regarded as the temperature above which surface steps may form without increasing the surface free energy. Alternatively, these results show that TR also corresponds to the temperature above which the cusp in a polar plot of surface free energy disappears and the surface becomes nonsingular. e/kTR as determined in this simulation is ∼ 1.57, where e is the strength of the first neighbor bond.

Explosive crystallization of amorphous germanium

We have obtained experimental confirmation of the prediction that explosive crystallization of amorphous germanium proceeds via an intermediate melting step.

Roughness of the Crystal‐Vapor Interface

The equilibrium structure of the interface between a Kossel crystal and its vapor has been investigated by Monte Carlo simulation techniques, and by statistical mechanical analysis in zeroth‐ and first‐order approximation. The interface structure depends on L/kTe, where L is the latent heat, k is the Boltzmann constant, and Te is the equilibrium temperature. The results differ significantly from earlier calculations based on single level models of the interface or on simpler statistical models of the interface. The roughness of the surface R, which is defined as the energy of the surface relative to the energy of a smooth boundary, was found to increase with kTe/L and to be almost the same for each model. The extent of the surface S defined as the number of surface molecules per unit area also increases with kTe/L and is also almost independent of the model. The distribution of atoms amongst the various energy levels has been calculated, and again is similar for the three models. The interface profile is ...

Effects of grain boundaries on laser crystallized poly-Si MOSFET's

Data are reported for n-MOSFETs fabricated in laser crystallized poly-Si on amorphous insulating substrates. The dependence of electrical characteristics on the effective channel length in the range of 100 to 0.3 µm and on channel width from 120 to 20 µm is presented. The electron surface mobility is found to increase as the channel length is reduced, approaching that of devices in single-crystalline silicon. The source-to-drain leakage current, negligible for long channels, rapidly increases for channels shorter than ≃ 3 µm. This excessive current results from grain boundary diffusion of As from source and drain during high temperature fabrication steps.