The minority carrier recombination related to grain boundaries is studied by the SEM/EBIC technique. The specimens investigated are silicon bicrystals obtained by the Czochralski pulling process. The specimens are heated for 2 hours at 750°C in a neutral atmosphere. Heterogeneous recombination of the grain boundaries is then observed.

X-Ray topography and Transmission Electron Microscopy (TEM) have been performed to determine the origin of the heterogeneous recombination. A direct relationship between the local recombination along the grain boundary and the precipitates localized at the interface has been established. The chemical origin of the precipitates is discussed.

The gettering effectiveness of various thin film structures on n-type CZ silicon wafers has been investigated using electron microscopy, synchrotron radiation topography and optical techniques. Polysilicon, silicon nitride, and poly/nitride films were deposited on etched wafer backsurfaces. The various materials characteristics were correlated with gate oxide breakdown voltage, minority carrier lifetime and yield of MOS capacitors. These studies show that the poly/nitride configuration is superior as a gettering technique.

Czochralski silicon with constant controlled oxygen level of 15+/-0.5 ppma (ASTM F121–80) and varying carbon content intentionally doped at five different levels from 0.1 ppma to 4.1 ppma (ASTM F123–81) was used to fabricate 16K dynamic random access memories, MOS test capacitors with guard rings, and pn junctions. The results of the experiment have been analyzed for relative yield to functional and refresh characteristics, MOS generation and bulk recombination lifetime, pn junction leakage, and both surface and bulk defect densities. Peak performance of the silicon did not occur at the lowest carbon level, but was dominated by the oxygen precipitate defect density and depth of the denuded zone near the active device regions. The results of the capacitor measurements, the DRAM yield measurements, the junction leakage measurements and the bulk and surface lifetime measurements are self-consistent and emphasize the need for control of the oxygen precipitation whether it is nucleated by carbon or other homogeneous and heterogeneous processes. There is no evidence that carbon has any impact on the device performance other than its impact on the precipitation kinetics of the interstitial oxygen.

A review is presented of some aspects on the interactions of light element impurities with dislocations in silicon crystals on the basis of the works done by the author's group. Topics taken up are gettering of impurities by dislocations, electrical and optical activities of impurity atoms accumulated at the dislocation core, immobilization of dislocations due to impurity gettering, and the mechanism of strengthening of silicon wafers due to doping of impurities such as oxygen and nitrogen.

The possible effects of oxygen on plastic flow of Si ribbons during growth by the, dendritic web process are described. Cooling rates preclude homogeneous nucleation and growth of detectable SiOx precipitates. Calculated resolved shear stresses on {111} <110> slip systems arising from thermoelastic strains exhibit periodic oscillations in sign and magnitude. The dwell times at elevated temperatures corresponding to zero or low stress periods accompanying such sign reversals are shown to be sufficiently long to permit decoration and locking of dislocations by oxygen atoms.

Quantitative measurements of the mechanical properties of Czochralski silicon were made. Samples were strained in tension to determine the yield characteristics (at 800°C) of silicon crystals which had been subjected to various heat treatments and which contained various concentrations of oxygen and carbon. The heat treatments included single step, two step (nucleation and growth) and three step (dissolution, nucleation and growth) annealing. Carbon concentration was found to affect both the rate of oxygen precipitation and the resulting precipitate morphology but did not have a direct effect on the yield stress of unprecipitated samples. There was a clear correlation between the amount of precipitated oxygen and the magnitude of the upper yield stress in samples with the same initial oxygen concentration. Precipitation caused a reduction in the upper yield stress for all precipitate morphologies, but the reduction was less severe (for a given amount of precipitation) where the precipitates were fine grains (<200Å) than where they were larger polyhedra or plates.

X-ray topography and minority carrier lifetime measurements were used to study the structural and electrical properties in silicon dendritic web ribbon. The effects of annealing on the material quality of high- and lowstressribbon were investigated.

Early measurements are reviewed relating to the solubility. the segregation coefficient, diffusion. Internal precipitation, the infrared absorption and the effect on the lattice parameter of silicon due to substitutional carbon. Interactions with oxygen and group III Impurities are mentioned. A survey is given of the effects of high energy irradiation and heat treatments on both FZ and CZ silicon containing carbon. A rich variety of defects can form, but in general atomic structures have not been determined. The process of site switching from substitutional to interstitial locations which occurs by the selective trapping of self-Interstitials is proving to be invaluable in elucidating the mechanisms of various defect reactions, particularly those Involving oxygen Impurities.

An overview of the behavior of intrinsic point defects in silicon and their interaction with carbon is given for temperatures above about 500° C. The diffusive mechanism of carbon in silicon, which involves silicon self-interstitials, is treated in some detail and compared with the diffusion mechanism of oxygen. The solubility of interstitial carbon is estimated. Co-precipitation of carbon and self-interstitials or oxygen are dealt with in terms of simple volume considerations. It is proposed that the contradicting results on the influence of intrinsic point defect supersaturations on oxygen nucleation and precipitation may possibly be explained in the frame-work of opposite effects depending on the carbon concentration. Finally the influence of carbon on the incorporation and diffusion of gold in silicon is discussed.

Oxygen and carbon aggregation in silicon after thermal processing can be characterized using SIMS profiles and SIMS imaging. Fluctuations in the oxygen SIMS signal during the profile have been correlated with the change in interstitial oxygen after thermal processing as measured by FTIR and the precipitate size as measured by TEM. In cases where precipitation is known to be the cause of impurity clustering, a computer program for simulating the profiling process allows semi-quantitative characterization of precipitates as a function of depth. The use of a Resistive Anode Encoder on a CAMECA IMS-3f coupled with image enhancement can be used to image oxygen and carbon related defects. Examples of this technique are given by imaging oxygen aggregation and the co-aggregation of oxygen and carbon in thermally-processed Czochralski-silicon.

The defects formed in carbon rich CZ and EFG silicon after a 900°C, 160 or 560 min long, phosphorous diffusion were studied with TEM. Besides misfit dislocations, numerous precipitates were observed in the junction region in both materials. However, no precipitates were found in the bulk. The precipitates in CZ had a larger strain field than those in EFG material. The difference in the extent of the strain field of precipitates in CZ and EFG silicon can be ascribed to the higher oxygen content in CZ silicon. It appears that oxygen is involved in the Si-self interstitial promoted precipitation of carbon.

Carbon diffusivity is reported for different ambient conditions imposed during annealing of silicon in the temperature range from 800 to 100°C, which produce varying levels of silicon self-interstitial supersaturation. The diffusivities are deduced from SIMS analysis of carbon out-diffusion profiles. Carbon diffusivity is increased by up to a factor of 70 in annealing with phosphorus in-diffusion, and by a factor of as much as seven in an oxidizing ambient, when compared to anneals in a nitrogen ambient. The enhancements tend to decrease above 11000C. This behavior can be explained by attributing the increase in carbon diffusivity to self-interstitial supersaturation which increases the concentration of highly mobile carbon selfinterstitial pairs. Significant time dependent effects were also observed for 800 and 9000C phosphorus in-diffusion conditions.

Polycrystalline Si crystals grown by gas-assistedsolidification have been characterized by chemical and physical techniques with particular emphasis on carbon determination. The life time of this material appears to be not correlated with [0] or [C].

The ability of hydrogen to migrate in crystalline Si at low temperatures (<400°C) and bond to a variety of both shallow and deep level impurities, passivating their electrical activity, is of fundamental and technological interest. Recent results on the deactivation of the shallow acceptors in Si are compared with similar experiments in other semiconductors, microscopic models are proposed, and the implications for the states of hydrogen in the Si lattice at a variety of temperatures, and the diffusivity of some of these different states, is discussed. New results on the migration of atomic hydrogen under electronic stimulation are also detailed, along with a compendium of the deep levels in Si passivated by reaction with hydrogen. Surface damage by hydrogen-containing plasmas, and the infrared and electrical properties of H-related defect complexes are also reviewed.

Transport of the hydrogen-related, acceptor-compensating defect has been observed in reverse-bias annealed Al-gate Schottky and n+-P diodes from hydrogenated, B-doped p-Si. Secondary ion mass spectroscopy (SIMS) profiling (deuterium substitution) confirmed field-aided migration. Significant differences in field transport (and thermal diffusion) between diodes from Hand D-treated p-Si(B) qualitatively indicates a monatomic species. The effect is interpreted as field drift of a positively charged species, possibly H+, with a donor charge state in the upper-half band gap, in conflict with long-held theory predicting very deep level activity. Acceptor compensation is unstable under minority (electron) carrier injection by forward bias or illumination at 25°C, supporting the acceptor-protonic trap pair model (A-H+) of Sah, Pan and Hsu [J. Appl. Phys. 57, 5148 (1985)].

The electrical activity of the oxygen-related thermal donors in heat-treated, P-doped, Czochralski grown Si is passivated by reaction with atomic hydrogen. Secondary ion mass spectrometry and spreading resistance profiles on deuterium plasma treated samples show a direct correlation between the deuterium incorporation depth and the distance over which the thermal donors are passivated. The donor activity is restored by annealing above 400°C, and comparison with other defect dehydrogenation data suggests that the thermal donors may contain Si dangling bonds. Results obtained from deep level transient spectroscopy measurements are used to illustrate the observed donor passivation and reactivation kinetics.

Cz-grown Si samples containing a high concentration of oxygen are investigated after various processing steps by DLTS. Heat treatments ranging from 500°C–1000°C are performed to study the formation and annihilation of the “New Oxygen Donor” (ND) traps. Hydrogenation at low temperature leads to a reduction of the ND trap states. The experimental results confirm the “SiOx Interface Model” which assumes two differing types of interfacerelated states.

The channeling technique has been used to study the lattice location of deuterium ion-implanted into silicon. Compared to earlier measurements by Picraux and Vook, the temperature range has been extended from 30 to 500 K, and the dose has been decreased down to ≃ 8 × 1014 D/cm2. The implantation was performed at 30 K gnd at an energy of 10 keV. The channeling analysis was done using the d(3 He,p)4 He nuclear reaction. Angular scans were measured along the <100>, <110>, <111> axis and the {100}, {110}, {111} planes, Experiments were carried out on the implanted sample (30K) and after annealing to 200 and 500 K. In the as-implanted sample, 80% of the deuterium is located close to the bond center, whereas the remaining 20% is placed at the tetrahedral site. The deuterium sites change after annealing to 200 and 50OK, and the nature of these annealings stages will be discussed.

The effect of implanted hydrogen on the resistivity of polycrystalline silicon films has been investigated. The observed reduction in resistivity due to hydrogen is most pronounced for lightly doped films, and is accentuated by a 450°C anneal. An increase in Hall mobility is also observed. The pre-implant resistivity is completely recovered by annealling at 600°C. Diffusion of hydrogen at low temperatures is monitored by local resistivity changes detected with spreading resistance measurements.

The near-surface hydrogen profile was measured using the 15N hydrogen profiling technique in silicon. By depositing an adlayer of Al on the surface we were able to observe the separation of the near-surface hydrogen profile in silicon from the surface contamination layer. The hydrogen profiling of the near-surface region revealed the existence of a subsurface hydrogen layer which acts as a barrier to the transfer of hydrogen into the bulk. The observed subsurface layer is saturated with molecular hydrogen and its profile drops off sharply with increasing depth. The structure of this molecular hydrogen barrier and its thermal stability were studied.