MeV Si Implantation Research Articles

Identification by photoluminescence and positron annihilation of vacancy and interstitial intrinsic defects in ion-implanted silicon

Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching, annealing studies, and the dependence on impurities. The broad 935meV photoluminescence band occurs at intrinsic interstitial complexes, the 835meV band at small vacancy clusters, and the 1062meV line at a low concentration of vacancy clusters which are possibly formed by aggregation of the 835meV centers.

Ion implantation and electron irradiation damage in unstrained germanium and silicon–germanium alloys

The possibility of making devices which use the high hole mobility of Ge and Ge-rich SiGe alloys in mainstream semiconductor technology has drawn attention to the very limited knowledge base regarding ion implantation damage and its removal in germanium. In this paper we present measurements of point defects using deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS on Ge irradiated with γ-rays from a 60Co source or MeV electrons and the ensuing defect reactions which occur during annealing. This is compared with damage induced by MeV Si implantation into Ge at low and high doses and its subsequent removal by furnace annealing. The focus of this work has been on vacancy related defects because of their technological importance. It is well known that the diffusion of both acceptors and donors is vacancy mediated in Ge and so vacancy clusters rather than interstitial clusters are expected to be the technologically significant defects in enhanced diffusion.

Effect of substrate temperature on the radiation damage from MeV Si implantation in Si

We have investigated the radiation damage by MeV implantation of Si in Si and its evolution under thermal annealing. Si wafers were implanted with MeV Si at various substrate temperatures. Damages were characterized by Rutherford-backscattering (RBS) channeling and by transmission electron microscopy (TEM). Defect formation after post-implantation annealing is very sensitive to the substrate temperatures during implantation. When the substrate temperature was decreased to 200K, TEM revealed two distinct bands of damage after annealing: one around the mean projected ion range and another at half the projected range. Our study indicates that the formation of defects at half range results from the solid phase epitaxy growth of initial buried amorphous layers.

The point defect engineering approaches for ultra-shallow boron junction formation in silicon

When high energy heavy ions bombard a single crystal, such as MeV Si implantation in Si, the surface region becomes vacancy-rich, while interstitials are mostly distributed near the range of the implants. We have demonstrated that vacancy retards while interstitial enhances boron thermal diffusion in silicon. In this paper we will show experimental results on the modification of boron diffusivity by point defect engineering, and its application in ultra-shallow junction (10 nm) formation. In this paper, we will also show cluster ion, such as GeB and SiB, implantation in silicon, and two-stage annealing in forming ultra shallow junction in Si. RBS, channeling, nuclear reaction, and secondary ion mass spectrometry are used for this studies.

Transmission electron microscopy characterization of secondary defects created by MeV Si, Ge, and Sn implantation in silicon

Extended defects created in Si by ion implantation to doses below the amorphization threshold have been studied after annealing at 800 °C for 15 min. The implant species were the group IV elements Si, Ge, and Sn, and structural defects created by similar damage distribution were compared. The mass of the implanted ion influences the type of defect observed. For all three implant species, rod-like {311} planar defects were observed. Additionally, in Ge and Sn implanted samples, small {111} interstitial faulted dislocation loops were observed.

High-energy x-ray diffraction study of pure amorphous silicon

Medium and high-energy x-ray diffraction has been used to study the atomic structure of pure amorphous Si prepared by MeV Si implantation into crystalline silicon. Both as-implanted and annealed samples were studied. The inelastically scattered x rays were removed by fitting the energy spectrum for the scattered x rays. The atomic scattering factor of silicon, previously known reliably up to 20 ${\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}$, has been extended to 55 ${\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}$. The radial distribution function of amorphous Si, before and after annealing, has been determined through an unbiased Fourier transformation of the normalized scattering data. Gaussian fits to the first neighbor peak in these functions shows that scattering data out to at least 40 ${\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}$ is required to reliably determine the radial distribution function. The first-shell coordination number increases from 3.79 to 3.88 upon thermal annealing at 600 \ifmmode^\circ\else\textdegree\fi{}C, whereas that of crystalline Si determined from similar measurements on a Si powder analyzed using the same technique is 4.0. Amorphous Si is therefore under coordinated relative to crystalline Si. Noise in the distribution function, caused by statistical variations in the scattering data at high-momentum transfer, has been reduced without affecting the experimental resolution through filtering of the interference function after subtracting the contribution of the first-neighbor peak. The difference induced by thermal annealing in the remainder of the radial distribution functions, thus revealed, is much smaller than previously believed.

Annealing and recrystallization of amorphous silicon carbide produced by ion implantation

The annealing behavior of amorphous SiC layers produced by MeV Si-implantation into 6H–SiC has been investigated systematically by means of step height measurements and X-ray diffraction analysis. Two annealing stages are found. Each of them causes a specific densification of the amorphous layer. At temperatures below 700°C defect annealing processes are responsible for densification. Amorphous states with continuously varying densities can be produced in this first stage of annealing. Annealing at temperatures above 700°C is characterized by a combination of defect annealing and recrystallization. It is shown that the crystallization mode changes with increasing temperature from nucleated growth at 800°C to epitaxial regrowth at 1000°C.

The effect of stoichiometric disturbance on activation of MeV Si implantation in GaAs

MeV Si implantation into semi-insulating (SI) GaAs is a common technique used to create a deep doping layer. It is observed that the maximum of the carrier concentration is at a shallower depth than that of the implanted atom concentration. This unexpected phenomenon has previously been explained as depth measurement error. Based on our theoretical calculations and experiments, the phenomenon can be attributed to the effect of non-uniform stoichiometric disturbances (NSD) on the activation of implanted atoms. The effect of NSD in GaAs substrate is caused by MeV implantation. After implantation, an excess concentration of the heavier element As exists at shallower depth, while an excess concentration of the lighter element Ga is seen at greater depth. It is likely that Si atoms move more easily to Ga sites when they are heated in an As-rich environment. Excess lattice interstitials build up around the depth of the peak in the implanted Si+ concentration and prevent Si atoms from becoming activated there.

Depth profiling of vacancy clusters in MeV-implanted Si using Au labeling

A technique for profiling the clustered-vacancy region produced by high-energy ion implantation into silicon is described and tested. This technique takes advantage of the fact that metal impurities, such as Au, are trapped in the region of excess vacancies produced by MeV Si implants into silicon. In this work, the clustered-vacancy regions produced by 1-, 2-, and 8-MeV Si implants into silicon have been labeled with Au diffused in from the front surface at 750 °C. The trapped Au was profiled with Rutherford backscattering spectrometry. The dynamics of the clustered-vacancy region were monitored for isochronal annealing at 750–1000 °C, and for isothermal annealing at 950 °C, for 10–600 s. Cross-sectional transmission electron microscopy analysis revealed that after the drive-in anneal, the Au in the region of vacancy clusters is in the form of precipitates. The results demonstrate that the Au-labeling technique offers a convenient and potentially quantitative tool for depth profiling vacancies in clusters.

Annealing and recrystallization of amorphous silicon carbide produced by ion implantation

The annealing behavior of amorphous SiC layers produced by MeV Si implantation into 6H–SiC has been investigated systematically by means of step height measurements, x-ray diffraction, and optical microscopy. Two annealing stages are found. Each of them causes a specific densification of the amorphous layer. At temperatures between 250 and 700 °C both the rapidity and the low activation energy (184 meV) of the densification suggest that defect annealing processes are responsible for densification. Partial crystallization and changes of the amorphous network structure can be excluded as a possible reason for low temperature densification. Annealing at temperatures above 700 °C is characterized by a combination of defect annealing and recrystallization. The crystallization kinetics is analyzed in terms of the Johnson–Mehl–Avrami theory. It is shown that the crystallization mode changes with increasing temperature from nucleated growth at 800 °C to epitaxial growth at 1000 °C. The recrystallization generates stress in the layer which leads to surface cracking if the layer exceeds a critical thickness.

Evolution of interstitial- and vacancy-type defects upon thermal annealing in ion-implanted Si

We have quantitatively analyzed the structure and the annealing behavior of the point defects introduced by ion implantation in Si. We used deep-level transient spectroscopy to monitor and count interstitial-type (e.g., carbon–oxygen complexes) and vacancy-type (e.g., divacancies) defects introduced by MeV Si implants in crystalline Si and to monitor their annealing behavior for temperatures up to 400 °C. A small fraction (∼4%) of the initial interstitial–vacancy pairs generated by the ions escapes recombination and forms equal concentrations of interstitial- and vacancy-type room-temperature stable defect pairs. At T⩽300 °C, vacancy-type defects dissociate, releasing free vacancies, which recombine with interstitial-type defects, producing their dissolution. This defect annihilation occurs preferentially in the bulk. At temperatures above 300 °C, all vacancy-type defects are annealed and the residual damage contains only ∼3 interstitial-type defects per implanted ion. This imbalance between vacancies and interstitials is not observed in electron-irradiated samples, demonstrating that it is the direct consequence of the extra ion introduced by the implantation process.

Enhanced Diffusion of Dopants in Vacancy Supersaturation Produced by MeV Implantation

ABSTRACTThe 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.

The Effect of Impurity Content and Ion Mass on the Depth Profiles of Vacancy-Type Defects in MeV Implanted Si

AbstractWe used deep level transient spectroscopy to determine the concentration and depth profile of the defects introduced by MeV He and Si implants in n-type crystalline Si. We have found that only ∼ 16% of the Frenkel pairs generated by the ion escapes recombination and is stored into room temperature stable defects such as divacancies and oxygen vacancy complexes. For a light ion (He), the depth distribution of these defect complexes is strongly dependent on the O content of the substrate: it mirrors the initial distribution of I-V pairs, as calculated by TRIM (a Monte Carlo Code) when the O content is high (∼ 1018/cm3) while it can be much wider (up to 2 μm) in a highly pure (low O content) epitaxial substrate. This effect is due to a long range migration of vacancies before clustering or trapping at impurities. This migration is strongly inhibited for an ion of higher mass (such as Si) since in a denser collision cascade direct clustering is strongly favoured with respect to agglomeration of migrating defects.

The Effect of Impurity Content and Ion Mass on the Depth Profiles of Vacancy-Type Defects in MeV Implanted Si

AbstractWe used deep level transient spectroscopy to determine the concentration and depth profile of the defects introduced by MeV He and Si implants in n-type crystalline Si. We have found that only ˜ 16% of the Frenkel pairs generated by the ion escapes recombination and is stored into room temperature stable defects such as divacancies and oxygen vacancy complexes. For a light ion (He), the depth distribution of these defect complexes is strongly dependent on the O content of the substrate: it mirrors the initial distribution of I–V pairs, as calculated by TRIM (a Monte Carlo Code) when the O content is high (˜1018/cm3) while it can be much wider (up to 2 μm) in a highly pure (low O content) epitaxial substrate. This effect is due to a long range migration of vacancies before clustering or trapping at impurities. This migration is strongly inhibited for an ion of higher mass (such as Si) since in a denser collision cascade direct clustering is strongly favoured with respect to agglomeration of migrating defects.

Electrical characteristics of MeV Si-implanted and annealed GaAs

The effects of MeV Si implantation followed by RTA (rapid thermal annealing) on the electrical characteristics of GaAs are reported. MeV Si implantation and RTA generates active buried layers in GaAs. The buried layer quality is found to be at least comparable to a similarly processed keV Si-implanted active GaAs layer. The deep traps in MeV-implanted GaAs are identified and explained in terms of their probable origins. The deep level behavior of MeV Si-implanted and RTA GaAs is distinctly different from keV Si-implanted and RTA GaAs. This difference is attributed to the dynamic annealing occurring during MeV implantation.

10–20 MeV energy range Si implantations into InP:Fe

Si implantations in the energy range 10–20 MeV were performed into InP:Fe with a dose of 4×1014 cm−2. The secondary-ion mass spectrometry profiles for the as-implanted samples were used to calculate the first four statistical moments of the Si implant distribution. Either 875 °C/10 s rapid thermal annealing or 735 °C/10 min furnace annealing was used to activate the Si implants. No redistribution of Si was observed after annealing. Electrochemical capacitance-voltage profiling was performed on the annealed samples to obtain the carrier concentration depth profiles. Activations of 90%–100% and peak carrier concentrations of 3–4×1018 cm−3 were measured for 10–20 MeV Si implants after 875 °C/10 s rapid thermal annealing.

Impurity trapping and gettering in amorphous silicon

Palladium atoms have been gettered from the bulk of an amorphous Si (a-Si) layer to an ion-implanted surface region. The 2.2-μm-thick a-Si layers, formed by MeV Si implantation, were implanted with 500 keV Pd and then annealed at 500 °C. This produces a complete redistribution of Pd within the layer and relaxation or substantial defect annihilation in the a-Si. Subsequently, defects were introduced into the surface region (∼4000 Å) by 200 keV Si implantation at various doses. After low-temperature diffusion at 250 °C, Pd atoms are gettered in the Si-implanted region. At low Si fluences, Pd decorates the Gaussian depth distribution of the ion-induced damage, while at higher a saturation is reached in the gettering profile. The ion damage is calculated to saturate when 2% of the target Si atoms are displaced by atomic recoils. Below saturation, the displacement of two Si atoms is calculated to produce one Pd trapping site.

Defect states of amorphous Si probed by the diffusion and solubility of Cu

The diffusivity and solubility of Cu impurities have been measured in different structural states of amorphous Si (a-Si) formed by MeV Si implantation. The 2.2-μm-thick a-Si layers were first annealed (structurally relaxed) at 500 °C and then implanted with 200 keV Cu ions, returning a 300-nm-thick surface layer to the as-implanted state. After diffusion at temperatures in the range 150–270 °C, we observe solute partitioning at a sharp phase boundary between the annealed and Cu-implanted layers, the partition coefficient being as large as 8.2±1.3. The diffusion coefficient in annealed a-Si is 2–5 times larger than in as-implanted a-Si, with activation energies of 1.39±0.15 and 1.25±0.04 eV, respectively. The data show quite strikingly the role which defects can play in the a-Si structure.

Homogeneous and interfacial heat releases in amorphous silicon

Amorphous Si layers prepared by MeV Si implantation of (100) wafers have been studied by scanning and isothermal calorimetry. A homogeneous heat release of 5.1±1.2 kJ/mole and an interfacial heat release, due to crystallization, of 13.4±0.7 kJ/mole have been measured. Isothermal measurements unambiguously demonstrate the occurrence of the homogeneous release. The heat released isothermally at each temperature is between 6% and 8.5% of the total homogeneous release, and the time constants are only very weakly temperature dependent.

Electrical measurement of implantation damage profiles in InP

Depth profiles of ion implantation damage resulting from high-energy implantations into InP were measured with an electrochemical capacitance-voltage technique. The evolution of these profiles during annealing at temperatures up to 500 ° C was investigated. The experimental profiles of unannealed implantations were compared with simulation results from the TRIM program to obtain information about the type of defect being measured. The computed vacancy/interstitial concentration profile showed a strong similarity with experimental profiles for 2 MeV Si implants and 800 keV C implants. The simulations are discussed in detail with respect to replacement collisions and antisite formation.