G. A. Rozgonyi

Microstructure, growth, resistivity, and stresses in thin tungsten films deposited by rf sputtering

The growth process and the microstructure of very thin W films (80–500 A) deposited by rf sputtering on SiO2 and Si substrates have been observed by transmission electron microscopy (TEM). The resistivity and stress in these films have been related to the film microstructure, composition, and to the deposition conditions (substrate bias and rf deposition power). Thin W films deposited on silicon dioxide substrates under zero or positive bias have been found to grow in two distinct growth stages. Stage I corresponds to the formation of a thin continuous film (80–100 A thick) of β‐W. The β‐W phase has the A‐15 crystal structure and has been identified as a faulted W3W compound. A small grain size (50–100 A) is characteristic of the β‐W film. Stage II corresponds to the transformation of the β‐W film into a pure α‐W film with the bcc crystal structure. This thermally activated phase transformation takes place in the temperature range 100–200 °C. It is characterized by the growth of α‐W nuclei until complete ...

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.

Control of lattice parameters and dislocations in the system Ga1−xAlxAs1−yPy/GaAs

Since stress and dislocations are known to affect the performance of GaAs injection lasers, a systematic evaluation of these parameters has been carried out for LPE layers of Ga 1− x Al x As 1− y P y on GaAs substrates. Using an X-ray topographic camera which is also equipped to plot substrate lattice curvature it has been possible to measure room temperature stresses for various values of x with y =0, and for 0 y ≤0.05 with x =0.34. Stress limits at the growth temperature are estimated based on the detection of misfit dislocations. As a result of this study the conditions for room temperature stress-compensated layers can be determined. Also, because of the asymmetric nature of interfacial misfit dislocations, it is possible to simultaneously eliminate those segments of substrate dislocations which have propagated into the LPE layer. The dependence of this phenomenon on layer thickness is specified as well as measurements of asymmetric bending and misfit dislocation arrays.

A model for the formation of stacking faults in silicon

A model for the evolution of stacking faults in silicon during oxidation and during aging of silicon containing oxygen is proposed. Based on the proposed mechanism, the observed role of dislocations, point‐defect clusters constituting the swirl pattern, and abrasion‐induced strain in the generation of stacking faults can be accounted for in a unified manner.

Substrate and doping effects upon laser‐induced epitaxy of amorphous silicon

UHV‐deposited amorphous silicon was recrystallized on (100) single‐crystal substrates using pulsed Nd : YAG laser irradiation. Prior to deposition, substrates were prepared with either atomically clean surfaces, residual argon ion sputter damage, or from one to three monolayers of residual oxide. Epitaxial regrowth of bulk crystalline quality occurred regardless of substrate preparation. Annealing energy densities were significantly higher, however, for substrates retaining residual impurities. Certain layers were doped with Ga. At moderate doping levels recrystallization behavior was unaffected. At a 2% doping level, the annealing energy threshold dropped by one‐half and Ga atoms were displaced toward the epitaxial surface. It is shown that the decrease in energy threshold is due to an impurity‐induced increase in light absorption within the amorphous layer. Layers were crystallized with substitutional Ga concentrations of up to 10 times the equilibrium solid solubility limit.

Epitaxial laser crystallization of thin‐film amorphous silicon

Vapor‐deposited amorphous silicon films of 4000 A thickness have been epitaxially crystallized on (100) silicon substrates by pulsed Nd : YAG laser radiation of 125‐nsec duration at power levels of 90–120 MW/cm2. The epitaxial layers were found to be defect free when examined by transmission electron microscopy and Rutherford backscattering. Patterned arrays of epitaxial crystal were produced by overlapping individual 39‐μm laser pulse spots.

Threshold reduction by the addition of phosphorus to the ternary layers of double‐heterostructure GaAs lasers

By the addition of phosphorus to the ternary layers of standard double‐heterostructure GaAs injection lasers, significant reductions in lasing current threshold and increases in differential quantum efficiency have been obtained. Additional measurements suggest that the improvements are connected with a reduction in optical scattering loss.

Gettering of surface and bulk impurities in Czochralski silicon wafers

The ability of SiO2 precipitates to act as a source of process‐induced defects which can either beneficially getter unwanted impurities, or deleteriously interact with surface devices, has led to some confusion in interpreting the role of wafer oxygen content in device processing. This report presents a composite model which explains the many variables involved in oxygen precipitation and gettering phenomena.

Stress compensation in Ga1−xAlxAs1−yPy LPE layers on GaAs substrates

Epitaxial layers of Ga0.66Al0.34As1−yPy with y ≤ ≈ 0.04 have been grown in order to demonstrate that it is possible to adjust the lattice parameter of a mixed III‐V layer such that it is matched with the GaAs substrate at room temperature. The amount of stress compensation has been determined as a function of y, as well as estimates of the layer thicknesses required to suppress the formation of misfit dislocations.

Sources of oxidation‐induced stacking faults in Czochralski silicon wafers

Using optical microscopy/etch pit techniques for the delineation of defects in {100} Czochralski silicon wafers we have made a one‐to‐one correlation between bulk stacking faults in oxidized wafers and etch hillocks identified at the same sites before oxidation. Transmission electron microscopy of the hillock defects shows them to be clusters of precipitates ranging in size from 0.01 to 0.3 μm. A discussion of these stacking‐fault nucleation sites in light of previous work on ’’swirl’’ defects in float‐zone wafers and attempts at preoxidation gettering are also presented along with a model for the formation of the extrinsic stacking faults.