The ab initio pseudopotential method is used to study transient-enhanced-diffusion (TED) related processes. The electronic degrees of freedom are included explicitly, together with the fully self-consistent treatment of the electron charge density. A large supercell and a fine k-point mesh are used to ensure numerical convergence. Such method has been demonstrated to give quantitative description of defect energetics. We will show that boron diffusion is significantly enhanced in the presence of the Si interstitial due to the substantial lowering of the migrational barrier through a kick-out mechanism. The resulting mobile boron can also be trapped by another substitutional boron, forming an immobile and electrically inactive two-boron pair. Similarly, carbon diffusion is also enhanced significantly due to the pairing with Si interstitiels. However, carbon binds to Si interstitials much more strongly than boron does, taking away most Si interstitials from boron at sufficiently large carbon concentration, which causes the suppression of the boron TED. We will also show that Fermi level effect plays an important role in both Si intersititial and boron diffusion.

Our recent work on the room temperature migration and trapping phenomena of self-interstitials and vacancies in crystalline Si is reviewed. Spreading resistance profiling and deep level transient spectroscopy measurements were used to monitor the interaction of ion beam generated defects with dopant atoms, intrinsic impurities (i.e. O and C), pre-existing defect marker layers and sample surface. We have found that both interstitials and vacancies undergo fast long range migration which is interrupted by trapping at impurities and by recombination at defects or at the surface. Effective defect migration lengths as large as 5 μm at room temperature have been observed in highly pure, defect free epitaxial Si samples. A lower limit of 1×10−10 cm2/sec for the room temperature diffusivity of self-interstitials has been determined. Furthermore, by monitoring the migration and interaction processes of point defects injected through a mask, we have established that surface acts as an effective sink for the migrating Si self interstitials.

Differently doped Si-wafers were irradiated with 2.5MeV electrons and subsequently investigated by X-ray diffraction methods. We show that a high concentration of defects (>1016 cm−3) can be frozen in at 4K and that a large fraction of the defects is stabilized in the form of close Frenkel pairs. These Frenkel pairs are characterized by the nearly perfect cancellation of the long-range displacement fields of the interstitial atom and the vacancy. We discuss the absolute size of these displacements as well as the introduction rate of the defects, which is of the order of Σ = 1cm−1. Similar results are obtained for weakly doped Cz-Si or FZ-Si and for degenerate p-type Si(B) and n-type Si(As), i.e., the results are independent of the oxygen content of the samples and of the position of the Fermi level. The high defect introduction rates are at variance with the results of electrical and EPR investigations and indicate that these methods detect only a few percent of the total defect concentration which is produced and frozen in at 4K. The consequences for the understanding of the defect production in Si and for the assumption of an athermal migration of interstitial atoms are discussed. In addition we compare the defect patterns observed after 4K irradiation to those observed after room-temperature irradiations and discuss the thermally activated defect reactions up to the final annealing at 1000K.

We have investigated the defect structure of ion-implanted and electron irradiated crystalline Si using deep level transient spectroscopy measurements to characterize both vacancy-(V) and interstitial- (I) type defects and to monitor their evolution upon annealing at temperatures ≤ 600 °C. It is found that only 4% of the Frenkel pairs generated by the energetic particles escape direct recombination and are stored into an equal number of room temperature stable V- and I-type defect complexes. No difference is found in the defect structure and annealing kinetics of ion implanted (1.2 MeV Si to fluences between 1×109 to 1010/cm2) and electron irradiated (9.2 MeV to fluences between 1 and 3×1015/cm2) samples in spite of the fact that denser collision cascades are produced by the ions. Annealing treatments result in a concomitant reduction in the concentration of I and V-type defects, demonstrating that defect recombination occurs preferentially in the bulk and not at the sample surface. Finally, at temperature above 300 °C, when most of the vacancy-type defects have been recombined, a residual concentration of I-type defects is found in ion implanted samples. This interstitial excess, not detected in electron irradiated samples, provides a direct evidence of the imbalance between I and V concentration produced by the extra incorporated ion.

We have investigated the properties of Si interstitial clusters in ion implanted crystalline Si. Deep Level Transient Spectroscopy measurements have been used to characterize the residual damage in Si samples implanted with Si ions at fluence in the range 1×109-1×1012/cm2 and annealed at temperatures of 100–700 °C. We have found that, in the fluence and annealing temperature range where extended defects are not formed, the residual damage is dominated by Si interstitial clusters which introduce deep levels at Ev+0.36 eV and at Ev+O-53 eV. By using Si substrates with a different impurity and dopant content, we have found that C, O and B play a role in determining the defect growth kinetics but are not the main constituents of these clusters. We estimate that 40 to 125 Si self intersti-tials are stored in these clusters and believe that they are the main source of Si self-inter-stitials in transient enhanced diffusion phenomena occurring in the absence of {311} or extended defects.

Diffuse X-ray scattering is a useful method for studying defects in silicon and metals. Although the traditional approaches of analyzing experimental diffuse X-ray scattering data have given much information about the size of defects and defect clusters, they are not very well suited for determining the atomic configuration. We present a fully atomistic computational method to calculate the diffuse X-ray scattering line profile of an arbitrary atomic configuration, and compare line profiles of point defects and Frenkel pair configurations with experiment.

We critically readdress the problem of vacancy clustering in silicon by perform large-scale tight-binding molecular dynamics simulations. We also compare the results of this quantum-mechanical approach to the widely used model-potential molecular dynamics scheme based on the Tersoff and Stillinger-Weber interatomic potentials.

A number of corrections must be made to a first-principles defect supercell calculation if the results are to be of use in calculating properties of isolated defects. These are illustrated for a tetrahedral self-interstitial in silicon, which places two electrons in the conduction band. One correction arises from the familiar Coulomb enhancement of the gap relative to local-density-approximation (LDA) calculations. The second is for the capture of these electrons in a double donor state. The third arises from the extra kinetic energy of the electrons due to their partial filling of the conduction band for a finite-sized supercell. The fourth is the partial occupation of the defect resonance, lowering the kinetic energy but increasing the Coulomb energy. A model is introduced which allows estimates of each of these corrections, with parameters which can be tuned to LDA supercell calculations. It allows then prediction of a wide range of properties dependent upon the defect in question.

We present a new empirical potential for silicon which is a considerable improvement over existing models in describing structures away from equilibrium, such as bulk defects. The interatomic interaction is described by two- and three-body terms using theoretically motivated functional forms which emphasize chemical and physical trends. The numerical parameters in the functional forms are obtained by fitting to several ab initio calculations, which include bulk phases and defect structures. The model is tested to core properties of partial dislocations in the glide set {111}, which are not included in the database, and gives results in very good agreement with ab initio calculations. This is the only known potential capable of describing the structure of both the 30°- and 90°-partial dislocations.

Ab initio Hartree-Fock calculations have been performed on a hydrogen molecule in silicon crystal using a cluster model of Si10H16. The hydrogen molecule is stable at a tetrahedral site of silicon. A calculated vibrational frequency of the hydrogen molecule is in reasonable agreement with the experimentally determined frequency of H2 in the silicon crystal.

The Vacancy-Oxygen (VO) centre is one of the most prominent defects appearing in silicon after irradiation with energetic particles and gamma rays. It is formed when migrating vacancies are trapped by interstitial oxygen atoms. It gives rise to a deep level in the upper part of the silicon bandgap at 0.164 eV below the conduction band edge that can be conveniently studied by deep level transient spectroscopy (DLTS). It is furthermore a very important defect from a technological point of view since it normally controls the charge carrier lifetimes in silicon power devices at high injection levels.

Various doped n-type float zone Si samples have been irradiated with MeV ions at low doses. DLTS measurements of the charge carrier capture kinetics reveal lower capture rates if heavier ions, i.e. larger collision cascades, have been used to generate the defects. This effect can be interpreted as a local lowering of the Fermi level following lattice disorder in regions with a high elastic energy deposition. It will be shown that the VO is also very sensitive to lattice disorder in a similar way as previously reported for the divacancy centre.

In the DLTS spectra another defect, originating from an interstitial-carbon—substitutional-carbon pair (Cj-Cs), overlaps with the VO-peak. The Ci-Cs pair has been observed to posses bistable properties and in this paper we will further elucidate the various contributions from the two defects to the Ec-0.164 eV peak. In particular, the temperature dependence of the electron capture cross section of the Cj-Cs level will be discussed.

The temperature dependence of the so-called reverse dose rate effect for generation of vacancy-type defects in silicon has been investigated using samples implanted with 1.3 MeV protons at temperatures between 70 and 300 K. The effect is found to involve a thermally controlled process which exhibits an activation energy of ∼0.065 eV, possibly associated with rapid migration of Si self-interstitials (I). Further, using a concept of dual Si ion-implants long range migration of I:s at room temperature has been studied. Annihilation of vacancy-type defects at a depth of ∼3 μm is obtained by injection of I:s from a shallow implant with sufficiently high dose.

Effect of increased pressure (up to 1.5GPa) during annealing of Cz-Si on creation of thermal donors (at 720 - 1000K) and visible luminescence (peaking at 1.7- 2.2eV for samples annealed at up to 1420K) is reported. The observed phenomena are related to stress - stimulated oxygen clustering / precipitation in Cz-Si resulting in creation of specific defects.

Despite more than 20 years of effort, detailed understanding of defect-coupled dopant diffusion in silicon still falls short of what is practically required to support state-of-the-art silicon technology development. The challenge for modeling in industry is to combine the best of our physical understanding with measurements of dopant profiles for technology-relevant conditions to provide models which are as predictive and efficient as possible. This paper presents experimental results which provide insight into damage generation and annealing processes and discusses practical modeling approaches to support technology development despite our incomplete understanding of the physical processes involved.

Low energy implantation is currently the most promising option for shallow junction formation in the next generations of silicon CMOS technology. Of the dopants that have to be implanted, boron is the most problematic because of its low stopping power (large penetration depth) and its tendency to undergo transient enhanced diffusion and clustering during thermal activation. This paper reports recent advances in our understanding of low energy B implants in crystalline silicon. In general, satisfactory source-drain junction depths and sheet resistances are achievable down to 0.18 micron CMOS technology without the need for implantation of molecular species such as BF2. With the help of defect engineering it may be possible to reach smaller device dimensions. However, there are some major surprises in the physical mechanisms involved in implant profile formation, transient enhanced diffusion and electrical activation of these implants, which may influence further progress with this technology. Some initial attempts to understand and model these effects will be described.

Understanding has advanced significantly in the interpretation of the thermal release of self interstitials into a silicon lattice from a region, e.g. ion implanted, which is rich in point defects. Progress has been accelerated through the use of delta doped layer structures, especially of boron doping type, where the transient enhanced diffusion (TED) of the dopant marks the arrival of the self interstitial species from a physically separate damage region. Frequently observed in such TED experiments is an immobile, electrically inactive, boron peak on top of the spreading diffusion profile. This signature boron peak has been attributed to the Si-interstitial driven clustering of boron. It has been observed that this feature occurs for high boron concentrations and implant fluences; however, a complete understanding of the clustering mechanism has remained elusive.

We present new data from experiments where the self implant fluence has been varied to allow the intensity of the transient flux to be adjusted and where repeat distances in the MBE structure have been adjusted to test for trapping. This has led to some clarifications to the current picture of boron clustering during TED. These results seem to be important in the context of the search for engineering control over dopant redistribution in Si during post-implantation annealing.

Recent studies on the relationship between defect evolution and transient enhanced diffusion (TED) have lead to the discovery that, for sub-amorphous Si+ implants, atoms released by extended defects (i.e. {311}'s) are a primary source of interstitials for TED. In this paper, the effect of implant energy on the interstitials stored in {311} defects is reported. Silicon wafers were implanted with Si+ at fluences of 1×1014/cm2 and 2×1014/cm2 and energies of 30, 50 and 100 keV. Rapid thermal anneals (RTA) and furnace anneals were performed at times ranging from a few minutes to several hours, at temperatures of 700°, 750° and 800°C. Cross-sectional and plan-view TEM was used to obtain microstructural information. The extended defects observed upon annealing consisted of both {311} defects and dislocation loops. It was found that the ratio of the interstitials bound by extended defects and the implant dose was 0.3. Changing the implant energy did not change the total number of interstitials trapped in both types of defects combined. There was a noticeable variation in the type of defect that dominated each implant regime, despite the constant value of the trapped interstitial to dose ratio. For an RTA of 5 min. at 750°C, the ratio of {311} “rod-like” defects to dislocation loops in the 2×1014/cm2 sample unexpectedly increased as the energy increased from 30 to 50 keV.

Longer furnace anneals were employed to determine the activation energy of {311} dissolution. Our data suggests a slightly higher activation energy for {311} dissolution of approximately 4.2 eV versus the previously reported 3.6 eV, however, this difference may be within experimental error.

Transient enhanced diffusion (TED) and electrical activation (EA) of ion-implanted boron during rapid thermal annealing has been investigated using three types of boron doped p-type Si (100) substrates: (a) Cz 20 Ωcm, (b) 3 μm thick 20 Ωcm epitaxial Si layer (epi-layer) grown on a 20 Ωcm Cz substrate, and (c) 3 μm thick 20 Ωcm epi-layer grown on a 5 mΩcin Fz substrate. The level of oxygen is known to decrease from material type (a) to (c). The samples were implanted with 20 keV, 5×1013 cm−2 boron and subjected to rapid thermal annealing (RTA) at various temperatures and times. The EA and TED were studied using spreading resistance profiling (SRP) and secondary ion mass spectrometry (SIMS), respectively. Although the amount of TED is almost identical for the three substrates, the EA is found to be significantly higher in the epi-layers compared to Cz substrates. It is speculated that the trapping of vacancies by oxygen in the ion-damaged region leads to an increase in the interstitial supersaturation during annealing, which then results in enhanced boron clustering and reduced electrical activation in the peak of the implanted profile.

In this paper we demonstrate, using both SIMS and transistor electrical characteristics, that substitutional carbon fractions of 0.5% in heavily doped Si0.8Ge0.2 base heterojunction bipolar transistors (HBTs) reduce both thermal diffusion and transient enhanced diffusion (TED) of boron. Furthermore we show that carbon suppresses TED of boron in carbon-free regions that surround the carbon layers.

The diffusion of Sb and B markers has been studied in vacancy supersaturations produced by MeV Si implantation in float zone (FZ) silicon and bonded etch-back silicon-on-insulator (BESOI) substrates. MeV Si implantation produces a vacancy supersaturated near-surface region and an interstitial-rich region at the projected ion range. Transient enhanced diffusion (TED) of Sb in the near surface layer was observed as a result of a 2 MeV Si+, 1×1016/cm2, implant. A 4× larger TED of Sb was observed in BESOI than in FZ silicon, demonstrating that the vacancy supersaturation persists longer in BESOI than in FZ. B markers in samples with MeV Si implant showed a factor of 10× smaller diffusion relative to markers without the MeV Si+ implant. This data demonstrates that a 2 MeV Si+ implant injects vacancies into the near surface region.