Silicon Interstitials Research Articles

Effect of point defects on the recombination activity of copper precipitates in p-type Czochralski silicon

The effect of point defects on the recombination activity of copper (Cu) precipitates in p-type Czochralski (CZ) silicon has been investigated by means of microwave photoconductivity decay and electron beam induced current (EBIC). It was found that the value of the reciprocal of effective minority carrier lifetime and EBIC contrast of the samples with pre-annealing in Ar, without pre-annealing and with pre-annealing in O2, related to the recombination activity of Cu precipitates, decreased in turn. It was considered that the highest recombination activity of Cu precipitates in the sample with pre-annealing in Ar was mainly attributed to the relative higher minority carrier capture cross section of Cu precipitates, which was affected by the induced vacancies. While the weakest recombination activity of Cu precipitates in the sample with pre-annealing in O2 was ascribed to the relative lower density of Cu precipitates, which was influenced by the induced silicon interstitials.

Theoretical study of small silicon clusters in4H−SiC

We have studied the small clusters of silicon and carbon interstitials by ab initio supercell calculations in 4H-SiC. We found that silicon interstitials can form stable and electrically active complexes with each other or with a carbon interstitial. Local vibration modes and ionization energies were also calculated in order to help the identification of the defects. We propose that silicon interstitials can emit from these clusters at relatively high temperatures, which may play an important role in the formation of the DI center. © 2007 The American Physical Society.

Effect of point defects on copper-related deep levels in p-type Czochralski silicon

The effect of point defects on the copper (Cu)-related deep levels in p-type Czochralski (Cz) silicon has been investigated. It was found that generally five deep levels Ev+0.14eV, Ev+0.17eV, Ev+0.32eV, Ev+0.35eV, and Ev+0.46eV were related to Cu in the p-type Cz silicon. Among them, the newly found levels Ev+0.35eV and Ev+0.32eV can be influenced by the point defects introduced during rapid thermal process. The intensity of level Ev+0.35eV increased with the introduced vacancies, while that of level Ev+0.32eV was dependent on the silicon interstitials. Moreover, the electronic states of those two levels were ascribed to be localized states. Based on the experimental facts, it is believed that the origins of levels Ev+0.35eV and Ev+0.32eV are the complex of Cu and vacancy and that of Cu and silicon interstitials, respectively.

First-principles studies of di-arsenic interstitial and its implications for arsenic-interstitial diffusion in crystalline silicon

We propose new structural configurations and novel diffusion mechanisms for neutral di-arsenic interstitial (As 2I 2) in silicon with a first-principle density functional theory simulation within the generalized gradient approximation. With an assumption of excess silicon interstitials and high arsenic concentrations, neutral As 2I 2 is expected to be favorable and mobile with low-migration barrier. Moreover, because the diffusion barrier of arsenic interstitial pairs (AsI) is very low (< 0.2 eV) under the same conditions, As 2I 2 can be easily formed and likely intermediate stage of larger arsenic interstitial clusters.

Molecular dynamics study of glancing angle gas cluster irradiation on irregular-structured surfaces

Surface modification processes resulting from glancing angle gas cluster ion irradiation were studied by molecular dynamics (MD) simulations. Large Ar2000 gas clusters accelerated with 20keV were irradiated onto Si(100) substrates to which were attached small Si block-shaped (size of 4096, 16384 or 65536 atoms) structures. The MD simulations revealed that when an Ar cluster is irradiated at 80° of incident angle, the cluster slides on the substrate surface without damage and impacts on the wall of the block structures causing multiple collisions, and dynamic deformation of the blocks. Especially, in the case of the impact on the small surface block (Si4096), a large part of the block was sputtered as a large chunk, and the target substrate was smoothed with only one cluster impact. The evaluation of the damage distribution showed that silicon interstitials, caused by the multiple collision mechanism, reside within 15Å from the surface, which suggests that low-damage and high-performance surface modification processing would be realized by utilizing a glancing angle gas cluster ion beam irradiation technique.

On the recombination of intrinsic point defects in dislocation-free silicon single crystals

The recombination of intrinsic point defects in dislocation-free silicon single crystals is investigated. It is established experimentally and confirmed by thermodynamic calculations that this process in the vicinity of the crystallization front is hindered by the recombination barrier. The recombination parameters (such as the recombination barrier height, the recombination time, and the recombination factor) for the model describing the dynamics of point defects at low and high temperatures are evaluated in terms of the heterogeneous mechanism of nucleation and transformation of grown-in microdefects. It is confirmed that the decomposition of a supersaturated solid solution of point defects can occur according to two mechanisms, namely, the vacancy and interstitial mechanisms. Vacancies and intrinsic interstitial silicon atoms find sinks in the form of oxygen and carbon background impurities. It is demonstrated that the formation of “intrinsic-point-defect-impurity” pairs is a dominant process in the vicinity of the melting temperature.

Structure and stability of irradiation-induced Frenkel pairs in 3C-SiC using first principles calculations

We have performed first principles calculations of intrinsic point defects and Frenkel pairs in cubic silicon carbide, using generalized gradient approximation. The considered Frenkel pairs have been obtained from a previous work on the determination of threshold displacement energies [G. Lucas, L. Pizzagalli, Phys. Rev. B 72 (2005) 161202]. Structures and formation energies of the defects are described. We found that our GGA results are in very good agreement with previous LDA studies. We found that Frenkel pairs are more stable than isolated single defects, especially for silicon interstitials, pointing to an attractive interaction between vacancies and interstitials as expected.

Modelling of Gettering by Mechanical Damage of MetallicImpurities in Silicon

Reducing the concentration of the metallic impurities present insilicon-based electronic components plays a vital role in manufactures.Gettering by induced mechanical damage is one of the methods used inneutralizing these impurities. To simulate this type of gettering, weexplicitly include the role of the traps due to mechanical damage,based on the mechanism of kick-out. In our model, we choose theessential parameters including concentration of impurities, thickness,temperature, time, etc. The diffusion coefficient and equilibriumconcentration of the silicon interstitials estimated from the literaturehave been adjusted to be in good agreement with the experimental data.

Suppressing Layout-Induced Threshold Variations by Halo Engineering

When creating source/drain regions of a MOSFET transistor, the implants introduce crystal damage. During subsequent activation annealing, the implant damage serves as a source of silicon interstitials that create dopant transient-enhanced diffusion (TED). The amount of TED is determined by the source/drain area and by the proximity of STI boundary, where interstitials recombine. Different amount of TED, experienced by transistors with different shapes and sizes of their source/drain area, lead to the difference in dopant diffusion in the channel/halo, and the corresponding variation of the threshold voltage. Depending on specific combination of layout and process flow, the MOSFET threshold voltages can either increase or stay flat or decrease with the distance from the channel to the STI. For each set of design rules/technology node, it is possible to design the halo implants such that the threshold sensitivity is close to flat and therefore eliminate layout sensitivity of the threshold voltage.

Structure of the interface between ultrathinSiO2films and4H−SiC(0001)

The interface between ultrathin ${\mathrm{SiO}}_{2}$ films and $4H\text{\ensuremath{-}}\mathrm{SiC}(0001)$ has been studied by x-ray photoelectron spectroscopy (XPS) and photoelectron diffraction. The investigation was performed for two different films. An ordered silicate layer showed a clear $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ reconstruction, whereas a second film showed no long-range order. The comparison of the photoelectron diffraction data from these two films reveals that the local atomic environments of the Si atoms at the interface are very similar in both films. Further, a comparison of the experimental data with simulation calculations within a comprehensive $R$-factor analysis shows that also the local environments around near-interface Si atoms inside the ${\mathrm{SiO}}_{2}$ film are similar, but some modifications to the model are necessary. The use of the cluster radius as a fitting parameter in the simulation allowed to estimate the size of locally ordered regions in the film without long-range order to be about 4.5 to $5.0\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. It turns out that the transition from $\mathrm{SiC}$ to ${\mathrm{SiO}}_{2}$ is abrupt and therefore the occurrence of defects in the ${\mathrm{SiO}}_{2}$ film near the interface is probable. These defects may be oxygen vacancies, oxygen dangling bonds or silicon interstitials.

New development of self-interaction corrected DFT for extended systems applied to the calculation of native defects in 3C–SiC

We recently developed a framework for implementing a scaled self-interaction corrected density functional theory (DFT-SIC) into pseudo-potential plane-wave DFT. The technique implements the original method of Perdew and Zunger by direct minimization of the DFT-SIC total energy functional. By using maximally localized Wannier functions, DFT-SIC calculation can be carried out efficiently even for extended systems. Using this new development, the formation energies of defects in 3C–SiC (silicon carbide) were calculated and compared to more standard DFT calculations. Differences of up to 1 eV were seen between DFT and DFT-SIC calculations of the formation energies. When compared to DFT, DFT-SIC produced less-stable vacancies and silicon interstitials, and more stable antisites and carbon interstitials. The most favourable interstitials were found to be C interstitials in a C+–C⟨100⟩ dumbbell configuration, with the formation energy of 5.91 eV with DFT and 5.65 eV with DFT-SIC. Si interstitials were not as stable as C interstitials. The most favourable Si interstitial was found to be Si tetrahedral surrounded by four C atoms, with a formation energy of 7.65 eV with DFT and 8.71 eV with DFT-SIC.

Enhancement of oxygen precipitation in Czochralski silicon wafers by high-temperature anneals

The effect of the prior conventional furnace anneal at 1250 °C with different cooling rates on oxygen precipitation in Czochralski silicon during the subsequent low–high two-step heat treatment was investigated. In comparison with oxygen precipitation in the as-received sample, that in the samples with the prior 1250 °C anneal with fast or slow cooling rate was significantly enhanced. It is believed that the prior 1250 °C anneal with fast cooling rate introduced a considerable amount of vacancies, thus enhancing oxygen precipitation in the subsequent anneal; while, that with slow cooling rate substantially removed the silicon interstitials generated during the formation of grow-in oxygen precipitates, thus eliminating the retard effect on oxygen precipitation in the subsequent anneal.

Mechanisms for Interstitial-Mediated Transient Enhanced Diffusion of N-type Dopants

AbstractAs silicon transistor dimensions scale down, transient enhanced diffusion of n-type dopants has become a major barrier toward achieving required junction depths for transistors. In this paper, we use density functional calculations to identify a pathway by which silicon interstitials can mediate As and P diffusion. We show that As-silicon interstitial and P-silicon interstitial pairs in the neutral and negative charge states diffuse via a mechanism in which the dopant is bond-centered at energy minima and threefold coordinated at the high energy saddle point during dopant migration. For both As-silicon interstitial and P-silicon interstitial pairs, we conclude that the neutral pairs will dominate under intrinsic conditions while the neutral and negatively charged pairs will both contribute under heavily doped extrinsic conditions.

Boron pocket and channel deactivation in nMOS transistors with SPER junctions

In this paper, we demonstrate the consequences of extension junction formation by low-temperature solid-phase-epitaxial-regrowth in nMOS transistors. Atomistic simulations, experimental device results, sheet resistance, and scanning spreading resistance microscopy data indicate that the high concentration of silicon interstitials associated with the end-of-range defect band promote the local formation of boron-interstitial clusters, and thus deactivate boron in the pocket and channel. These inactive clusters will dissolve after the high concentration silicon interstitial region of the end-of-range defect band has been annihilated. This nMOS requirement is in direct opposition to the pMOS case where avoidance of defect band dissolution is desired, to prevent deactivation of the high concentration boron extension profile.

Stress - Dependent Out - Annealing of Defects in Self - Implanted Silicon

Effect of hydrostatic pressure (HP) on out – annealing of defects in self – implanted silicon (Si:Si, Si+ doses 5x1016 cm-2 and 1x1017 cm-2, energies 50 keV and 160 keV), treated for 1 – 10 h at up to 1400 K (HT) under HP ≤ 1.4 GPa, has been investigated by photoluminescence, X-ray and related methods. Applied at 720 – 1270 K enhanced pressure does not affect or affects adversely Si:Si structure while at 1400 K assists in its improvement. HP – dependent transformations in Si:Si at HT are related to effect of HP on diffusion of point defects, such as silicon interstitials and vacancies produced at implantation. Out - annealing of defects in self - implanted silicon is dependent also on spatial position of damaged areas in Si substrate.

Influence of Neutron Irradiation on Stress - Induced Oxygen Precipitation in Cz-Si

Oxygen precipitation and creation of defects in Czochralski grown silicon with interstitial oxygen concentration 9.4·1017 cm-3, subjected to irradiation with neutrons (5 MeV, dose 1x1017 cm-2) and subsequently treated for 5 h under atmospheric and high hydrostatic pressures (HP, up to 1.1 GPa) at 1270 / 1400 K, were investigated by spectroscopic and X - Ray methods. Point defects created by neutron irradiation stimulate oxygen precipitation and creation of dislocations under HP, especially at 1270 K. The effect of pressure treatment is related to changed concentration and mobility of silicon interstitials and vacancies as well as of the VnOm – type defects.

The Role of Silicon Interstitials in the Formation of Boron-Oxygen Defects in Crystalline Silicon

Oxygen-rich crystalline silicon materials doped with boron are plagued by the presence of a well-known carrier-induced defect, usually triggered by illumination. Despite its importance in photovoltaic materials, the chemical make-up of the defect remains unclear. In this paper we examine whether the presence of excess silicon self-interstitials, introduced by ion-implantation, affects the formation of the defects under illumination. The results reveal that there is no discernible change in the carrier-induced defect concentration, although there is evidence for other defects caused by interactions between interstitials and oxygen. The insensitivity of the carrier-induced defect formation to the presence of silicon interstitials suggests that neither interstitials themselves, nor species heavily affected by their presence (such as interstitial boron), are likely to be involved in the defect structure, consistent with recent theoretical modelling.

The Role of Silicon Interstitials in Arsenic-Doped Ultrashallow Junction Formation

The 2005 F. M. Becket Summer Research Fellowship Summary Report

Observation of substitutional and interstitial phosphorus on cleanSi(100)−(2×1)with scanning tunneling microscopy

We have used scanning tunneling microscopy to identify phosphorus that is present at the clean silicon $(100)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface as a result of the thermal cycling necessary for preparation of samples cut from heavily doped wafers. Substitutional phosphorus is observed in top layer sites as buckled $\mathrm{Si}\text{\ensuremath{-}}\mathrm{P}$ heterodimers. We also observe a second type of feature that appears as a single depressed dimer site. Within this site, the atoms appear as a pair of protrusions in the empty states and a single protrusion in the filled states. These properties are not consistent with known adsorbate signatures or previously reported observations of $\mathrm{P}\text{\ensuremath{-}}\mathrm{P}$ dimers on the $(100)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface. The lack of other impurity sources suggests that they are due to either phosphorus or silicon. The symmetry of the features and their magnitude are consistent with one of those elements residing in an interstitial site just below the top layer of atoms. To identify the type of interstitial, we performed density functional theory calculations for both phosphorus and silicon located below a surface dimer. The resulting charge density plots and simulated STM images are consistent with interstitial phosphorus and not interstitial silicon.

Defect suppression of indium end-of-range during solid phase epitaxy annealing using Si 1− yC y in silicon

We report on the elimination of defect formation which is associated with high dose indium implantations under solid phase epitaxial regrowth (SPER) annealing conditions of 650–800 °C. This is achieved by incorporating a layer of epitaxially grown Si 1− y C y layer, strategically located at the end-of-range (EOR) of the implant profile. An indium implant of 115 keV at 1 × 10 14 cm − 2 was performed followed by annealing at temperature ranges of 650–800 °C. Samples with the Si 1− y C y layer revealed the elimination of secondary EOR defects with effectively suppressed indium transient enhanced diffusion (TED), indicating the function of carbon as an efficient sink for silicon interstitials at reduced annealing temperatures, in the SPER dopant activation regime.