Bulk Stacking Faults Research Articles

Two-dimensional BMD, BSF, ring-OISF and COP distributions in a dislocation-free ingot grown by the NOC method

The noncontact crucible (NOC) method has a large and deep low-temperature region in Si melt to grow a uniform large Si single ingot. The theoretical simulation pointed out that the lowest vacancy or interstitial Si atom area appears in the region with the smaller ratio between temperature gradients at melt surface and growing interface. The growth condition to obtain this region is suitable for the NOC method. The quality of a NOC ingot was first evaluated by determining the distribution of bulk micro defect (BMD), bulk stacking fault (BSF), oxidation induced stacking fault (OISF) and crystal originated particle (COP) in the cross section of the dislocation-free ingot. A ring-OISF or BSF can be clearly observed on the cross section cut from the middle and tail parts of the ingot. BMD can be observed inside and outside the ring-OISF. By estimated comparison to the none-doping case, CV (=CI) at cross point clearly has a trend to increase for the high B-doing case (5 × 1019 cm−3), where CV and CI are concentration of vacancy and interstitial Si atom, respectively. Nevertheless, in comparison with the distribution of COP in Cz and NOC ingots, COP cannot be detected inside the ring-OISF in the NOC wafer under the same etching process as many COP can be observed in the Cz wafer. This may be a unique feature for NOC growth.

Defect and structural imperfection effects on the electronic properties of BiTeI surfaces

The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ∼100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability.

Electronic states of Ag thin films with a laterally periodic insertion of stacking faults

Electronic states of Ag thin films containing stacking faults periodically in a direction parallel to the surface are studied theoretically. Such Ag stacking-fault superlattice thin films were recently fabricated on the $\text{Si}(111)4\ifmmode\times\else\texttimes\fi{}1\text{-In}$ surface, and the formation mechanism of the one-dimensional electronic states observed in photoemission experiments has not been clarified. These systems are suitable for studying stacking faults on nanometer scales in well-defined conditions. Main results obtained in the present study are threefold. One is that the double stacking-fault model proposed in this paper reproduces better the observed dispersions than the originally proposed model. In addition the fact that the stacking-fault thin films have the (111) surface is the origin of the strong deformation near the bottom of the quantized subbands. Second is that the tilt of the stacking-fault plane with respect to the normal of the surface causes mixing of states in different subbands, which is an important factor to form the flat band structures observed. Third is the discussion on the mechanism of the anomalous perfect transmission through the bulk stacking faults of noble metals. In contrast to usual potential scattering, stacking faults change only the phase of orbitals. The condition for perfect transmission is that the effects of scattering are canceled out by renormalization using single phase factor, which is excellently satisfied in the case of noble metals. In addition the symmetry in atomic positions between regular and stacking-fault structures with respect to an axis is the origin of the directional dependence of transmission property.

Effect of oxygen precipitation on voids in bulk silicon

The effect of oxygen precipitation on flow pattern defects (FPDs) relative to voids in bulk silicon was investigated. FPDs and voids were measured after different annealing time, and with various interstitial oxygen contents and bulk stacking faults (BSFs). It was found that, during annealing, interstitial oxygen in bulk silicon precipitated, however the FPDs density remained constant. The density of BSFs increased with annealing time at 1100 °C. After annealing, the morphology of voids was found to be octahedral with the oxide films inside them, the same as as-grown samples. Therefore, it is concluded that the interstitial silicon atoms released during oxygen precipitation did not enter the voids because of the resistance of the oxide films inside the voids, but condensed into stacking faults. The dissolution of the oxide films is believed to be the principal cause for the annihilation of voids.

Etching pits and dislocations in Si{111}

The nature of etch pits that arise during anisotropic etching in KOH on Si{111} surfaces was investigated. It was verified that bulk stacking faults in the crystal lattice give rise to deep etching pits. Other types of dislocations, of which the nature is still unclear, were also found to be present, but these do not give rise to etching pits.

Assessment of Silicon Wafer Material for the Fabrication of Integrated Circuit Sensors

The influence of process induced defects on the surface quality of wet anisotropically etched cavities in silicon wafers is investigated. Localized thinning of silicon substrates using cavities of this kind is a common method for fabricating, e.g., diaphragms for silicon pressure sensors. Wafers with four different concentrations of interstitial oxygen varying from to were exposed to a thermally simulated complementary metal oxide semiconductor process and subsequently anisotropically etched with potassium hydroxide or tetramethylammonium hydroxide solution. Crystal defects caused by oxygen precipitation, such as stacking faults, punching systems, and dislocations, were found to be the origin of large craterlike defects in the sidewalls of the cavities. Wafer material with an initial concentration of interstitial oxygen between and exhibits a very low density of small precipitate‐dislocation complexes and, thus, etched cavities of good surface quality are obtained. In wafers with interstitial oxygen concentrations higher than bulk stacking faults were observed and the surface quality of the cavity sidewalls diminishes. The microscopic morphology of the craterlike defects in the {111} sidewalls of the etched cavities is explained using a computer simulation of the etching process. An influence of process induced defects on the surface quality of wet anisotropically etched {100} surfaces was not found. © 2000 The Electrochemical Society. All rights reserved.

Phase stability in Al/Ti multilayers

Structural stabilities in thin-film Al/Ti multilayers have been studied using transmission electron microscopy. It is shown that models based on interface-induced modifications to bulk stacking fault energies, and/or coherency-strain energy may not be used to explain the various phase transitions observed. Rather, phase stability may be rationalized by reference to a new model based on classical thermodynamics, involving the competition between bulk and interfacial energies. Thus, these phase transitions are shown to be driven by reductions in the overall interfacial energies. A biphase diagram (reciprocal of bilayer thickness vs composition) has been developed for the multilayers produced by magnetron sputtering. The influence of impurities possibly introduced during thin-foil preparation is considered and rationalized by reference to the biphase diagram for this system.

Gettering of Fe impurities by bulk stacking faults in Czochralski-grown silicon

Gettering of Fe impurities by bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron-beam-induced-current technique and transmission electron microscopy. It is found that Fe impurities only precipitate on Frank partial dislocations bounding stacking faults when the specimen is cooled slowly; however, both Frank partials and fault planes are decorated by Fe impurities when the specimen is cooled rapidly. It is explained that small oxygen precipitates on fault planes serve as the gettering centers for Fe impurities in the fast cooled specimen.

Ebic Study of Fe Precipitation on Bulk Stacking Fault in Czochralski-Grown Silicon

ABSTRACTFe precipitation on bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron-beam-induced-current (EBIC) technique and other techniques. It is found that Fe impurities only precipitate on Frank partial dislocations bounding stacking faults when the specimen is cooled slowly; however, they precipitate on both Frank partials and fault planes when the specimen is cooled fast. It is explained that small oxygen precipitates on fault planes, together with Frank partials, serve as the gettering centers for Fe impurities in the fast cooled specimen.

Iron precipitation at oxygen related bulk defects in Czochralski silicon

Behavior of iron atoms in silicon during a simulated integrated circuit device fabrication process was examined. The results from the electron microscopic and deep-level transient spectroscopic analysis indicate that iron at concentrations below the solubility limit precipitates at a bulk stacking fault containing an oxide precipitate. Based upon the defect morphology and the eutectoid temperature of the α-FeSi2 phase, it is suggested that iron precipitation occurs during the cooling down period after a high-temperature treatment. The result shows that iron may react with oxygen atoms in the oxide precipitate via a Fe2O3 phase transformation which in turn causes a change in the precipitate morphology. In this study, it is suggested that iron precipitation at the bulk defects is fundamentally different from that of other transition metals such as nickel and copper where the precipitation occurs either along the Frank partial dislocations of the bulk stacking fault or at the punch-out dislocation loops originating at the oxide precipitate interface.

Effect of Fe Impurities on the Generation of Process-Induced Microdefects in Czochralski Silicon Crystals

The enhancement effect of Fe impurities on the generation of surface and bulk microdefects, such as oxidation-induced stacking faults, oxide precipitates, precipitate-dislocation complexes and bulk stacking faults, has been observed in annealed silicon wafers prepared from Czochralski grown crystals intentionally contaminated with iron. The effect remains significant even for an Fe concentration as low as 1012 atoms/cm3. It has been found that Fe facilitates the nucleation of oxide precipitates in silicon. The mechanism of Fe-assisted nucleation of oxide precipitates is discussed. The effect of Fe on the generation of oxidation-induced stacking faults is explained, assuming that both oxide precipitates and Fe:Si precipitates formed near the wafer surface serve as active nucleation sites of these microdefects.

Precipitation behaviors of Cu and Fe on Frank-type partial dislocations in Czochralski-grown silicon

Precipitation behaviors of Cu and Fe on Frank-type partial dislocations bounding bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron beam-induced-current (EBIC) technique and transmission electron microscopy (TEM). Frank partials in a Cu-contaminated specimen do not exhibit an EBIC contrast at room temperature when the specimen is cooled slowly; however, in the Fe-contaminated specimen, they exhibit EBIC contrast at room temperature due to their Fe contamination. The TEM micrograph shows that Cu develops precipitate colonies in the region away from stacking faults and does not precipitate on Frank partials in the specimen. The results indicate that Fe impurity decorates Frank partials more easily than Cu impurity in Si.

A model for oxygen precipitation in silicon including bulk stacking fault growth

This paper describes a model that simulates the precipitation kinetics of oxygen and the evolution of the precipitate density in annealed Czochralski-silicon wafers. A discrete rate equation representation combined with Fokker-Planck equations are used to treat precipitation of oxygen and simultaneous formation of bulk stacking faults. This approach allows one to describe both statistical clustering during nucleation and diffusional transport during growth. The model considers explicitly influences of self interstitials and stress on precipitation of oxygen and thus is able to accurately predict the experimental observations published previously. In particular, we compare simulation results of precipitated oxygen concentration in 2-step, 3-step, complementary metal oxide semiconductor type multi-step, and rapid thermal anneals with experimental results taken from the literature and discuss them.

Gettering of Interstitial Iron in P/P+ Epitaxial Silicon Wafers

AbstractGettering of interstitial iron in p/p+ epitaxial silicon wafers during an integrated circuit device simulation annealing was examined. The results from the deep level transient spectroscopy and optical microscope examination suggest no correlation between the interstitial iron concentration in the epitaxial layer and the bulk microdefect density. An electron microscopic analysis revealed that gettering of interstitial iron took place at an oxide polyhedral precipitate located at the center of a bulk stacking fault. By comparing the results of iron implanted to non-implanted samples, it is concluded that iron gettering occurs via a phase transformation of Si02 to an α FeSi2 iron disilicide. In this study, it is suggested that gettering of iron atoms is fundamentally different from that of other transition metals where the silicide formation occurs predominantly along the Frank partial dislocations of the bulk stacking fault.

Gettering of copper by bulk stacking faults and punched-out dislocations in Czochralski-grown silicon

The characteristics of Cu precipitation on various types of defects associated with oxygen precipitation in Czochralski-grown silicon are investigated by transmission electron microscopy and the electron-beam-induced-current technique. Specimens containing dominantly either punched-out dislocations or bulk stacking faults were intentionally contaminated with Cu at various temperatures and cooled at three different rates. Colonies of Cu precipitates developed irrespective of cooling rate, apparently originating from punched-out dislocations developed around oxygen precipitates. In heavily contaminated specimens cooled fast from the contamination temperature, Cu also precipitates on Frank partial dislocations bounding stacking faults. During slow cooling, precipitation of Cu takes place on Frank partials only in lightly contaminated specimens but never in heavily contaminated specimens. Cu precipitates in colonies are thermally more stable than those formed on Frank partials. It is concluded that punched-out dislocations are more favorable precipitation sites for Cu than Frank partials.

Aggregations of silicon interstitials and interstitial defect species in Czochralski silicon degenerately doped with boron during low temperature processing

The generation mechanism of crystallographic defects in Czochralski silicon degenerately doped with boron during low temperature processing was studied. After an extended annealing at 900 °C, the primary defects were identified as the a/2〈110〉-type elongated hexagonal- and a/6〈211〉-type rhombus-shaped dislocation loops using the transmission electron microscope. A low density of bulk stacking faults of the type a/3〈111〉 was also observed. No oxide precipitates were detected. After subsequent high temperature annealing, no significant change in the morphology or density of the interstitial-type defects was observed. Based upon the present results, it is hypothesized that aggregations of silicon interstitials and interstitial defect species during low temperature annealing could be one of the generation mechanisms of crystallographic defects in degenerately doped silicon.

Computer simulation of Czochralski silicon thermal history and its effect on bulk stacking fault nuclei generation

A heat transfer finite element analysis is performed to simuaate the whole Czochralski process thermal history of a silicon ingot 150 mm in diameter pulled from an initial nutrient melt of 60 kg. The computed crystal cooling rates are carefully examined to highlight the most meaningful temperature range (1073–1273 K) and its upper dwell-time threshold (150 min), which is critical for stacking fault microdefects generation.

Thermally induced stacking faults distributed inhomogeneously in Czochralski silicon crystals

Inhomogeneous but symmetrical distribution of bulk stacking faults in Czochralski silicon crystals has been attributed to the corresponding distribution of self-interstitials, which greatly depends on the crystal growth conditions. The inhomogeneous distribution of self-interstitials is not affected by the shape of the solid-melt interface, which greatly affects growth striations. Consequently, it has been proved that silicon self-interstitials depress oxygen precipitation and the growth of surface oxide layer in silicon.

Improvement to Bulk Oxygen Precipitate Density Necessary for Internal Gettering in Antimony Doped N/N+ Epitaxial Wafers Using the 3‐Step Technique and Ramped Nucleation

The addition of a ramped nucleation cycle, just after an initial oxidation, is shown to greatly increase the precipitation of interstitial oxygen during simulated processing on N/N+ antimony doped epitaxial wafers. When used with fully processed wafers, the ramped nucleation improves internal gettering. Oxygen precipitate density and bulk stacking fault density achieved are about a factor of 100 higher when using ramped nucleation. These results indicate that N/N+ antimony doped epitaxial wafers have an intrinsic gettering capability as good as that of lightly doped material when using an activation cycle (initial oxidation) and subsequent ramped nucleation. A method for calculating bulk stacking fault density is presented. It is shown that, at high concentration (above 107 cm−3), the square of the bulk stacking fault length is inversely proportional to their density. This finding indicates that the growth of bulk stacking faults is limited by the supply of interstitial silicon generated in the bulk during oxygen precipitate growth.

The Gettering of Transition Metals by Oxygen‐Related Defects in Silicon

A study has been made of the gettering efficiency of a variety of transition metals (Ni, Cu, Co, Fe, and Pd) by a range of oxygen‐related defect distributions generated in Czochralski‐grown silicon wafers of various initial oxygen concentrations at two stages of a simulated CMOS process. An extension and variation of the palladium getter test was used to monitor gettering efficiencies. Cu and Ni were found to be the easiest to getter with Co and Pd progressively more difficult. Co was found to interact with the other metals and affect their ability to be gettered. A gettering threshold (for the amount of precipitated oxygen) was observed which varies from metal to metal but is in all cases very low and very steep. Complete gettering of all metals tested was observed in a wafer with an initial of after a portion of the CMOS simulation was complete. The amount of oxygen precipitated under these conditions is well below the level at which oxygen precipitates are visible by etching techniques or x‐ray topography and not reliably measurable by FTIR. No indication was found that bulk stacking faults are necessary for effective gettering. Some indication of a decrease in gettering efficiency with increasing precipitation or processing time was found. X‐ray topography and further etching experiments were performed to help shed light on the mechanisms of gettering in the variety of cases investigated.