A set of interaction potentials for vacancy-assisted As diffusion in silicon have been provided via first-principles pseudo-potential calculations. Some important reactions such as As+V ⇌ AsV, AsV + As ⇌ As2V, AsV + V ⇌ V2, as well as V + V ⇌ V2 are considered. The results demonstrate that the existence of another As atom greatly reduces the migration barrier of vacancy moving between the two As atoms and speeds up the diffusion of As. The AsV pair can attract another nearby vacancy. The binding force mainly comes from the binding between two vacancies, rather than from the AsV pair. The obtained potential energy diagrams provide input information for atomistic diffusion simulations.

Boron segregation to {311} defects and transient enhanced diffusion (TED) of boron atoms during thermal annealing were investigated in detail using implanted superlattice and Si bulk wafers. We observed that (1)boron atoms segregate to {311} defects during low temperature annealing, (2){311} defects were formed in the area where the self-interstitial concentration exceeds 3×1017cm3, (3)free self-interstitials in the region beyond the implanted range causes initial rapid enhanced diffusion prior to the onset of normal TED.

The ripening of ion-beam generated point defects into extended defects has been investigated in detail. The interstitial supersaturation has been extracted from boron marker-layer diffusion after annealing under non-equilibrium defect conditions. We measured a very high initial supersaturation followed by a decrease over many orders of magnitude with a characteristic “plateau” related to the presence of {113} defects. A continuum inverse model has been used to properly describe the ripening of point defects into clusters and their evolution in the presence of a remote sink, e.g. the surface. It evidences that a nonconservative Ostwald ripening process takes place inside the defect band during the annealing and sustains the interstitial supersaturation. The model reveals moreover an oscillatory behaviour of dissociation energies of the nanometer-sized defects which are responsible for the initial high supersaturation. These defects are believed to be {113} precursors.

CVD grown boron marker layers were used to monitor the release of silicon interstitials from an arsenic doped surface region that was subsequently implanted with silicon. These structures were annealed for various times at 750°C in a nitrogen ambient. A comparison of boron spike enhancement and defect dissolution is made. It is shown that enhancement values from the Si+ implant were reduced at short times for samples containing arsenic compared to samples implanted with Si+ alone or As− alone. The TEM results showed that defect densities were dramatically reduced for the samples containing As. These results imply that the previously reported reduction in {311} formation observed in As doped wells is most likely not a Fermi level effect and is consistent with the formation of As interstitial clusters (AsIC's). The data shows that AsIC's form and control extended defect formation and slow the enhanced diffusion.

Continuous scaling of device dimensions requires better understanding of non-equilibrium diffusion phenomena such as transient enhanced diffusion (TED). To this end, it is important to understand the relationship of the defect evolution with TED. Defect evolution in P+ implanted Si has been investigated by transmission electron microscopy (TEM). Secondary ion mass spectroscopy (SIMS) has been used to study phosphorus TED. These studies show that another type of defect, i.e. dot defects are present in P+implanted Si (100 keV, 1.OX104/cm2). The evolution of defects in P+ implants is compared with that in Si+ implants. P+ implants give rise to small dot defects mixed with {311} defects while Si+ implants give rise to only {311} defects. The dot defects and {311} defects in P+ implants dissolve faster than the {311} defects from Si+ implants. The interstitial concentration trapped in the dot defects and the {311} defects from P+ implants is slight lower than that from Si+ implants. Dot defects seem to have only a small role in phosphorus TED. Interaction of silicon interstitials emitted from the dissolution of {311} defects with phosphorus dopant atoms is believed to be the dominant driving force for the TED. There may also be a contribution from dissolution of non-visible phosphorus interstitial clusters (PIC's). Correlation of defect evolution and TED has been addressed.

Complete suppression of transient enhanced boron diffusion (TED) and oxidation enhanced boron diffusion (OED) in silicon have been achieved using substitutional carbon to reduce the excess point defect concentration in the dopant region [1]. Recent efforts have focused on removing the carbon from the active regions of the device [2,3] to avoid device degradation due to electrically active carbon defects [4] and exploring remote carbon's effect on boron TED and OED, while using the boron diffusion to probe point defect concentrations.

In this paper we measure quantitatively the effect of remotely located carbon on phosphorus and boron diffusion above a buried SiGeC layer at 850°C in oxygen or nitrogen ambients. Remote carbon, located 1250 A below the phosphorus edge, is found to reduce the phosphorus diffusion enhancement factor due to OED from 8 to 2. The effect of the remotely located SiGeC buried layer on the excess interstitial concentration profile, which is responsible for the enhanced dopant diffusion, is probed by measuring boron and phosphorus diffusivites of in-situ doped boron and phosphorus layers above a buried SiGe(C) layer after oxidation or nitrogen anneals at 850°C. The enhanced boron diffusivity during oxidation is found to have a near linear dependence on depth ranging from 5–1.25. Finally, using x-ray diffraction and photoluminescence measurements of as-grown, buried, strained SiGe(C) structures and annealed SiGe(C) structures in oxygen or nitrogen ambient at 850°C the number of substitutional carbon atoms effectively consumed by oxidation is unambiguously correlated to the absolute number of injected interstitials using published values for the interstitial injection rate during oxidation [5].

The formation of vacancy-related defects in n-type silicon has been studied immediately after implantation of He, Si, or Ge ions at 85 K using in-situ DLTS. A-center concentrations in He-implanted samples reach a maximum immediately after implantation, whereas, with Si or Ge ion implanted samples they continuously increase during subsequent anneals. It is proposed that defect clusters, which emit vacancies during anneals, are generated in the collision cascades of Si or Ge ions. An illumination-induced suppression of A-center formation is seen immediately after implantation of He ions at 85 K. This effect is also observed with Si or Ge ions, but only after annealing. The suppression of vacancy complex formation via photoexcitation is believed to occur due to an enhanced recombination of defects during ion implantation, and results in reduced number of vacancies remaining in the defect clusters. In p-type silicon, a reduction in K-center formation and an enhanced migration of defects are concurrently observed in the illuminated sample implanted with Si ions. These observations are consistent with a model where the injection of excess carriers modifies the defect charge state and impacts their diffusion.

In this work we investigate the influence of defects injected by ions of different mass and energy on the diffusion of B and Sb markers in bulk Si. MeV (Si or As) ions induce Sb transient enhanced diffusion, whose amount increases with increasing the near-surface vacancy supersaturation generated by the knock-on recoil mechanism. The enhancement effect lasts less than 2 h at 800 °C and less than 10 min at 900 °C. At higher (1000 °C) annealing temperature it appears that the influence of extra-interstitials introduced by the implants comes into play, inducing a retardation in Sb diffusion which is larger for the higher close implant. The effect of vacancy supersaturation observed in medium-energy implanted samples is considerably weaker than the one found in high-energy implanted ones. In the case of B marker high-energy implantation induces moderate enhanced diffusion, much smaller than the one observed -after medium-energy implants.

Extended defects resulting from ion implantation are believed to act in some cases as a driving force behind transient enhanced diffusion (TED). We use secondary ion mass spectrometry (SIMS) to study the diffusion enhancements of an underlying boron doped spike after creating implant damage in the near surface region. Diffusion enhancements are compared for silicon implants and phosphorus implants to distinguish between factors related to chemical species interactions versus those related to ion beam damage. Transmission electron microscopy (TEM) is used to investigate the existence and dissolution of extended defects. {311} extended defects are clearly visible in self-implanted samples but absent in phosphorus doped samples. The extended defects resulting from phosphorus implantation are small (20Å to 60Å diameter) “dot” defects barely resolvable by conventional TEM. methods. Despite the marked differences in defect morphology, diffusion enhancements in the boron marker layer are observable for both species. Results comparing the TED of a buried marker layer after P+ and Si+ show a larger overall effective diffusion length results after high dose (1x1014 cm−2) phosphorus implants. Visible defects in phosphorus implanted silicon are not the only source of TED, suggesting the existence of sub-microscopic phosphorus interstitial clusters (PIC). This provides important insight into the affect of phosphorus on TED.

The dose loss and transient enhanced diffusion of indium in silicon were studied as a function of dose. Indium was implanted into silicon through a 90 A oxide at 50 keV for doses ranging from 3x 1012 to 2x14 cm−2. These conditions provide peak concentrations that approximately range from 1x1018-1x1020 cm−3. After an RTA anneal at 1000°C for 5s, indium exhibits substantial motion at both the tail and peak regions for high doses. The enhanced diffusion is mostly over within 5s. There was not any observable enhanced diffusion in the tail region at the lowest dose although there was significant movement at the peak region. The dose loss correlates very well with the enhancement in the diffusivity. TEM images show that the amorphization dose lies between 3x1013 and 8x1013 cm−2. In spite of the amorphization, diffusion enhancement in the tail region still keeps increasing with dose, which is contrary to a model of “+1” interstitials and complete removal of interstitials in the regrown layer. The 550°C lh anneals show that the dose loss can partially be attributed to the sweeping of the dopant by the growing a/c interface. Previously, the solubility of indium has been estimated to be around 1–2×1018 cm−3. At high doses, significant movement is observed at the peak of the indium profile although the peak concentration exceeds the solubility level by at least an order of magnitude. This shows that indium is not precipitating into an immobile phase like antimony or boron.

Experiment shows that the reverse short channel effect (RSCE) in nMOS devices is critically impacted by the inclusion of nitrogen in the gate oxide. A higher concentration of nitrogen results in a lessened RSCE, i.e. more threshold voltage rolloff for smaller gate lengths. We propose that the additional nitrogen reduces the interstitial recombination rate at the interface, resulting in a smaller interstitial flux and therefore less transient enhanced diffusion (TED) of boron to that interface. To test this hypothesis, we simulate boron redistribution in one and two dimensional MOS capacitor structures, as well as full nMOS devices. We then present simulations calibrated to a 0.2 pim technology currently in production.

We have studied by TEM the thermal evolution of a population of extrinsic defects composed of a mixture of both perfect and faulted dislocation loops (PDL's and FDL's respectively). It is shown that, when isolated from an external sink, the FDL's trap the Si interstitial atoms emitted by PDL's. When a highly recombining surface is located close to the defects, it preferably « pumps » the PDL's. On the contrary, injecting Si(int)'s from the surface helps stabilizing the PDL's while the FDL's grow. These experiments clearly show that FDL's are more stable, i.e. have higher binding energies than PDL's.

We have studied the influence of an epitaxial silicide layer on the diffusion of B and Sb in silicon. B and Sb doping superlattices have been grown by molecular beam epitaxy. They were then covered with a 20 nm thick CoSi2 layer. Test samples were also grown without silicide. Samples were oxidized at various temperatures ranging from 800°C to 1200°C for times that ensured sufficient broadening of the spikes. Another set of samples was annealed at the same times and temperatures in N2. Dopant depth profiles were measured before and after diffusion by secondary ion mass spectrometry (SIMS). At the test samples we observed thermal diffusion of B and Sb, oxidation enhanced diffusion of B and oxidation retarded diffusion of Sb, all in accordance with the literature. In contrast to this, oxidized silicide capped samples showed a retardation of B diffusion by a factor of 2 - 10 as compared to thermal diffusivity and an enhancement of Sb diffusion by a factor of 1 - 2.

The results of a two-dimensional dopant diffusion study using two new sample preparation techniques and a database-driven deconvolution technique are presented. These techniques are applied to real devices to justify complex implantation and diffusion models. It will be shown that the dose loss behavior is not uniform along the silicon/oxide interface from the source/drain region to the channel region. A new non-uniform dose loss model is proposed and used to explain the experimental results.

Controlling the profile of shallow doped layers is critical for obtaining desired performance from deep sub-micron devices. An especially difficult challenge is measuring depth uniformity of the activated implant over the full area of a wafer.

This paper demonstrates the capabilities of a new rapid, non-contact optical technique for measuring active doping depth of shallow implants. Employing a 2 Pim spot size, it provides a measurement of fine-scale spatial uniformity in dimensions approaching those of individual devices. By measuring multiple sites, it can rapidly characterize uniformity over large areas and edge-to-edge, without an edge exclusion zone.

Data will be presented showing performance on layers varying in depth from 200 to 1200 Å. Edge-to-edge diameter scans on 8” wafers with le15, B11 implants at energies in the range of 200 to 2,000 eV and various RTA temperatures show radially symmetric uniformity patterns of depth and edge effects in the outermost centimeter. Measurements are validated based on correlation to spreading resistance profiles for a number of samples.

method for characterizing the mechanical stress induced in silicon technology is described. Analysis by scanning Kelvin probe force microscopy (SKPM) coupled with finite-element (FE) mechanical strain simulations is performed. The SKPM technique detects variations in the semiconductor work function due to strain influences on the band gap. This technique is then used to analyze the strain induced by shallow trench isolation processes for electrical isolation. The SKPM measurements agree with the FE simulations qualitatively.

Interest in diffusion processes in SiGe alloys arises from their potential in HBT's, HFET's, and optoelectronics devices, where migration over distances as small as a few nanometres can be significant. Successful modelling of these processes requires a much improved understanding of the mechanisms of self- and dopant diffusion in the alloy, although recent progress has been made. It is the purpose of this review to set this in the context of diffusion processes in elemental silicon and germanium, and to identify how this can help to elucidate behaviour in the alloy. Firstly, self diffusion processes are reviewed, from general agreement that self-diffusion in germanium is dominated by neutral and acceptor vacancies, to the position in silicon which is still uncertain. Germanium diffusion in silicon, however, appears to be via both vacancy and interstitial processes, and in the bulk alloy there is evidence for a change in dominant mechanism at around 35 percent germanium. Next, a review of dopant diffusion begins with Sb, which appears to diffuse in germanium by a mechanism similar to self-diffusion, and in silicon via monovacancies also, from marker layer evidence. In SiGe, the effects of composition and strain in epitaxial layers on Si substrates are also consistent with diffusion via vacancies, but questions still remain on the role of charged defects. The use of Sb to monitor vacancy effects such as grown-in defects by low temperature MBE, are discussed. Lastly, progress in assessing the role of vacancies and interstitials in the diffusion of boron is reviewed, which is dominated by interstitials in silicon-rich alloys, but appears to change to domination by vacancies at around 40 percent germanium, although studies in pure germanium are greatly needed.

Phosphorus diffusion from in-situ doped Si1−xGex epitaxial films into Si at 800°C was investigated using secondary ion mass spectroscopy and differential resistance measurements. The surface P concentration in the diffused layer in Si was higher than the P concentration in the Si1−xGex, film in the present conditions, which signifies the segregation of P from the Si1−xGex, film into Si. The segregation coefficient, defined as the ratio of the active P concentration in the Si to that in the Si1−xGex, film, was about 2.5 in the case of the Si0.75Ge0.25 film as a diffusion source and increased with increasing Ge fraction. The P diffusion profiles in Si were normalized by x/√, even though the segregation of P occurred. The high concentration diffusion characteristics of P in Si were similar to those reported by using conventional diffusion sources.

Phosphorus diffusion in a biaxially compressed Si0.87Ge0.13 film has been investigated in the temperature range of 810–900°C. A significant enhancement of the P diffusion in the biaxially compressed Si0.87Ge0.13 in comparison with P diffusion in Si is observed. Injection of Si self-interstitials (I) during oxidation of a Si-cap in Si/Si0.87Ge0.13/Si heterostructures is used to characterize the atomic mechanism of P diffusion in Si0.87Ge0.13. It is found that the upper limit of the interstitial fraction of the P diffusion in Si0.87Ge0.13 is 0.87 of that in Si. A comparison between B and P diffusivities in SiGe supports the hypothesis of the pairing-controlled mechanism for the diffusion of B in SiGe.

Nitrogen implantation can be used to control gate oxide thicknesses [1,2]. This study aims at studying the fundamental behavior of nitrogen diffusion in silicon. Nitrogen at sub-amorphizing doses has been implanted as N2+ at 40 keV and 200 keV into Czochralski silicon wafers. Furnace anneals have been performed at a range of temperatures from 650°C through 1050°C. The resulting annealed profiles show anomalous diffusion behavior. For the 40 keV implants, nitrogen diffuses very rapidly and segregates at the silicon/ silicon-oxide interface. Modeling of this behavior is based on the theory that the diffusion is limited by the time to create a mobile nitrogen interstitial.