Diffusion of gold in silicon has been studied by means of the spreading-resistance technique on dislocation-free, moderately dislocated and highly dislocated Si crystals. The penetration profiles not only show the general tendency that Au diffusion increases as a function of dislocation density, but also reveal qualitative differences between these three classes of specimens. It is demonstrated how within the framework of the kick-out model from the experimental data detailed information on both Au diffusion and Si self-diffusion can be obtained. In turn, the observed influence of dislocations on the diffusion of Au in Si represents a convincing confirmation of the kick-out mechanism.

The annealing and diffusion behaviour of ion implanted boron over a wide range of doses in as-received and pre-amorphised silicon (180 keV 5 × 1015 cm−2 silicon implants) has been studied using conventional furnace annealing and multiple scan electron beam heating in the rapid isothermal annealing mode. The layers obtained have been characterised using spreading resistance profiling (SRP), SIMS and TEM.

For furnace annealing the silicon implantation produces improved electrical activation for boron doses in excess of 1015 cm−2. SIMS and SRP data indicate that a higher level of peak activation has been achieved, whilst the overall amount of redistribution has been restricted. The reduction in diffusion achieved (∼0.2 μm) is greater than the maximum difference attributable to the effect of lower ion channelling for the silicon implanted samples. Cross-sectional TEM has been used to determine the resulting defect structure and provides insight into the details of the stable precipitated boron surface peak observed. A numerical diffusion model has been developed to allow interpretation of these experimental findings.

Similar samples have been annealed using multiple scan electron beam heating (peak temperatures up to 1100°C for times up to 300 s). For silicon implanted with boron alone, where cooling commenced once the peak temperature of 1100°C had been reached, diffusion was restricted to 0.05 μm while the sheet resistance (32 Ω/square) was reduced by ∼25% compared to furnace anneals at 950°C. Identical annealing of silicon implanted samples produced improved activation with a sheet resistance of 26 Ω/square. Results from SIMS, SRP and TEM analysis of these experiments are reported.

We have studied in detail the transient enhanced diffusion observed during furnace or rapid-thermal-annealing of ion-implanted Si. We show that the effect originates in the trapping of Si atoms by dopant atoms during implantation, which are retained during solid-phase-epitaxial (SPE) growth but released by subsequent annealing to cause a transient dopant precipitation or profile broadening. The interstitials condense to form a band of dislocation loops located at the peak of the dopant profile, which may be distinct from the band formed at the original amorphous/crystalline interface. The band can develop into a network and effectively getter the dopant. We discuss the conditions under which the various effects may or may not be observed, and discuss preliminary observations on As+ implanted Si.

A review of the use of oxygen precipitation for the purposes of internal gettering in silicon is given. The review considers current ideas about oxygen precipitation mechanisms and the relationships between different precipitate morphologies. Two different paths for oxygen precipitation are considered, the first path being 450C thermal donor - coesite defects and the second being <100> oriented platelets. A summary of the uses of oxygen precipitation gettering in integrated circuit fabrication and a simple model for optimization of internal gettering follows the precipitation discussion.

We found that the intrinsic gettering can be effectively realized in oxygen-lean Czochralski silicon grown in a magnetic field as well as in oxygen-free float-zone silicon. The intrinsic gettering has been observed thus far only in oxygen-rich Czochralski silicon and it has been believed to be intimately related to oxygen. We present experimental characteristics of the new intrinsic gettering process, and we propose a model involving outdiffusion and precipitation of silicon interstitials rather than oxygen which is involved in the standard intrinsic gettering.

The efficiency of solar cells fabricated from low-oxygen, high-carbon, EFG silicon ribbon can be improved by pre-annealing the ribbon at 1200°C prior to processing. TEM analysis shows that the increased efficiency is not related to a relaxation of the defect structure. Rather, EBIC investigations demonstrate a continuous reduction of the recombination activity of in-grown crystal defects (dislocations, grain boundaries) with increasing duration of the anneal. Since C is the only element in supersaturation at the annealing temperature, a model is suggested in which metallic contaminants are gettered at small carbon clusters.

The formation and annealing of buried damage layers in hydrogen implanted N-type float zone <111> silicon has been studied by Rutherford Backscattering/ion channeling and cross-section transmission electron microscopy. Implantation with 50 keV or 75 keV H+ ions was conducted at temperatures of 95K, 300K and 800K at fluences of 2×1017 H+/cm2, 8×1017 H+/cm2 and 1×1018 H+/cm2. Post implantation annealing was conducted at temperatures up to 800K. The results show a temperature dependent transition from a highly hydrogen doped amorphous zone bounded by strongly diffracting (TEM) 2–5 nm diameter defects for implantation at 95K to a crystalline microstructure containing small dislocation loops and ∼40% of the implanted hydrogen for implantation at 300K. Defect production and annealing and hydrogen trapping in the damage zone are shown to depend on the relative implantation and post implantation annealing temperatures.

Different techniques are presented for the characterization of the two-layered system consisting of a precipitate-free zone and a precipitated zone, generated in CZ-grown silicon wafers by thermal processing. The diffusion length profile can be determined by surface photovoltage characteristics; measurements of the collection efficiency for excess carriers generated by alpha particles gives relevant information about the soft error performance. Finally, oxygen depth profiling by SIMS is discussed. Results are shown and compared with damage patterns obtained from cleavage face etching.

It is found that the recombination activities of dislocation complexes and structural defects decorating twin boundaries in as-grown, p-type cast polycrystalline silicon have no observable temperature dependence in the range of 100–300 K, but the activities of these defects in phosphorusdiffused samples decrease with the increase of temperature in the same range. The results suggest that the phosphorus diffusion can cause a significant shift of energy levels of these defects toward the valence band from the middle of the band gap.

Some of the key issues involving the chemistry of oxygen in silicon crystals are presented in this paper. The incorporation of oxygen into Czochralski-grown ingots from melt contact with silica crucibles is described in the context of the Si-SiO2 phase diagram. The techniques for characterizing oxygen in silicon are reviewed, with an emphasis on the use of secondary ion mass spectrometry (SIMS) and 18O isotope substitution. The intrinsic diffusivity and solubility of oxygen in silicon derived from these SIMS measurements are compared to similar results from other techniques as well as related extrinsic behavior of oxygen. Aggregation phenomena involving oxygen, including thermal donor formation and precipitation are discussed. Finally, the recent progress in understanding internal gettering and shear stress are summarized.

A model has been developed that simulates oxygen precipitation in silicon wafers during high temperature device processing. The approach used to calculate the nucleation and growth of oxygen precipitates is radically different from other approaches presented in the literature. A discrete rate equation representation of nucleation and growth has been transformed into a continuum representation in the form of a partial differential equation. This partial differential equation describing both the statistical clustering of oxygen during nucleation and the diffusion driven transport during precipitate growth is solved continuously starting from crystal growth through any arbitrary time-dependent temperature process.

We report some results of an experiment designed to study the interaction of extrinsic-gettering (EG) and intrinsic-gettering (IG) schemes. We found that mechanical abrasion introduces interstitial type dislocations into the wafer backside, and produces a concave wafer frontside. The EG dislocation network enhances SiO2 precipitation which is responsible for the IG activity. The enhancement is most significant near the wafer backside. The interaction arises most probably because the dislocation network serves as a very efficient source/sink for point defects.

The effect of heavily doping silicon3with boron (up to 9.0×19/cm3) or antimony and arsenic (up to 1.0×19/cm3) on the nucleation and growth of bulk stacking faults (BSF) was investigated by the use of three-step heat treatment; 700°C-24 hrs., 900 °C 24 hrs., and 1050 °C up to 48 hrs.

The length and density of BSF were determined by optical microscopy after a Secco or Schimmel etch of cleaved specimens. From the effect of heavy doping on the density of BSF we imply the nucleation rate is doping level dependant. The effect of the low temperature (700°C) heat treatment time on the relationship between the density and the length of BSF indicates that the growth of BSF may be a supply-limited process. The effect of a high temperature (1300°C) oxygen dispersion treatment was also investigated. The results are analyzed in terms of a vacancy model.

In this study, nucleation time has been found to play an important role in the three-step (Hi-Lo-Hi) intrinsic gettering process. The longer the nucleation time, the higher the density of oxygen precipitates and oxidation induced stacking faults. The size of oxidation induced stacking faults, however, shrinks as the nucleation time increases. The reduction of junction leakage current indicates that gettering efficiency improves with increasing nucleation time. Oxidation induced stacking faults appear to be the dominant gettering sites.

Impurity gettering at defects/damage in Si is discussed. Details of intrinsic and extrinsic gettering in Si are presented. The utility of gettering is demonstrated by comparing the results from gettered and non-gettered test devices.

The application of denuding, nucleation, and intrinsic gettering in CMOS integrated circuit processes is described. Specifically, it will be demonstrated that an initial oxidizing step, as many manufacturers are using, seriously retards the effectiveness of any subsequent nucleation step or procedure. The results of a large number of one-step, two-step, and three-step heat treatments are summarized and design criteria for controlled oxygen precipitation in integrated circuit fabrication are described. Two-step heat treatments, without denuding and with the nucleation step first, have been used to induce precipitates close to the surface of CMOS wafers and DLTS measurements made to deduce the effectiveness of intrinsic gettering and the electrical characteristics of precipitation induced microdefects.

The dependences of dopant species and concentrations on the growth of oxide precipitates have been studied using transmission electron microscopy. Doping species are phosphorus, antimony and boron. Samples were annealed at 800°C and 850°C for 24∼384hr in dry nitrogen. In phosphorus-doped silicon, the precipitate density is independent of doping concentration and the growth of precipitate obeys the three-quarter power law. The enhancement of the precipitate growth is observed in antimony-doped silicon. On the other hand, the precipitate growth is suppressed in heavily boron-doped silicon as compared with that of lightly boron-doped silicon. This indicates the generation of excess silicon interstitials in heavily boron-doped silicon.

The morphology of micro-defects located in the bulk of Cz-grown silicon wafers was observed to be dependent on wafer thermal history, wafer dopant species and concentration, and wafer position in the grown silicon ingot (seed, center or tail section). Intrinsic gettering effectiveness and durability due to SiOx precipitates and/or stacking faults formed during various gettering sequences were investigated. Based on preliminary results, stacking fault micro-defects combined with SiOx micro-defects are preferred for maximum durability of the intrinsic gettering mechanism.

A new method for the nucleation of oxygen precipitates in Czochralski silicon is described. The temperature is ramped at approximately 100°C/hr from a very low value, near 400°C, to the highest temperature used for subsequent process steps. The technique generates a larger precipitate number density and a greater volume fraction of precipitated oxygen than standard isothermal nucleation anneals. The morphology of the precipitates changes from 0.lum sizéd (100) platelets to small particles unresovable by TEM. The new temperature ramping technique can reduce the time needed for precipitate nucleation by at least a factor of three. The details of oxygen precipitation can be totally controlled by adjusting the temperature ramp rate as a function of time.