Self-ion Implantation Research Articles

Kinetics of Intrinsic and Dopant-Enhanced Solid Phase Epitaxy in Buried Amorphous Si Layers

AbstractThe kinetics of intrinsic and dopant-enhanced solid phase epitaxy (SPE) have been measured in buried amorphous Si (a-Si) layers produced by ion implantation. Buried a-Si layers formed by self-ion implantation provide a suitable environment for studies of the intrinsic growth kinetics of amorphous Si, free from the rate-retarding effects of H. For the first time, dopant-enhanced SPE rates have been measured under these H-free conditions. Buried a-Si layers containing uniform As concentration profiles ranging from 1–16.1 × 1019 As.cm−3 were produced by multiple-energy ion implantation and time resolved reflectivity was used to measure SPE rates over the temperature range 480–660°C. In contrast to earlier studies, the dopant-enhanced SPE rate is found to depend linearly on the As concentration over the entire concentration range measured. The SPE rate can be expressed in the form, v/vi(T) = 1 + N/[No exp(-ΔE/kT)], where vi(T) is the intrinsic SPE rate, N is the dopant concentration and No = 1.2 × 1021 cm−3, ΔE = 0.21 eV.

Kinetics of Intrinsic and Dopant-Enhanced Solid Phase Epitaxy in Buried Amorphous Si Layers

AbstractThe kinetics of intrinsic and dopant-enhanced solid phase epitaxy (SPE) have been measured in buried amorphous Si (a-Si) layers produced by ion implantation. Buried a-Si layers formed by self-ion implantation provide a suitable environment for studies of the intrinsic growth kinetics of amorphous Si, free from the rate-retarding effects of H. For the first time, dopant-enhanced SPE rates have been measured under these H-free conditions. Buried a- Si layers containing uniform As concentration profiles ranging from 1–16.1 × 1019 As.cm-3 were produced by multiple-energy ion implantation and time resolved reflectivi[ty was used to measure SPE rates over the temperature range 480–660°C. In contrast to earlier studies, the dopant-enhanced SPE rate is found to depend linearly on the As concentration over the entire concentration range measured. The SPE rate can be expressed in the form, v/vi(T) = 1 + N/[No exp(−Λ E/kT)], where vi(T) is the intrinsic SPE rate, N is the dopant concentration and No = 1.2 × 1021 cm-3, ΔE = 0.21 eV.

Transient kinetics in solid phase epitaxy of Ni doped amorphous silicon

Solid phase epitaxy (SPE) of amorphous silicon layers doped with Ni in the concentration range 10 19–10 20 cm −3 has been studied. The amorphous layers were produced by self-ion implantation of Si(100) samples. Transient kinetics of the SPE process are observed, and the results imply that the regrowth changes from an initial impurity driven crystallization to the ‘ordinary’ thermally activated one. The initial enhancement of the SPE rate may be attributed to a difference in the density of trapping sites for Ni atoms at the initial (‘as-prepared’) amorphous-crystalline (a–c) interface compared to the advancing one. The role of the simultaneous process of Ni precipitation is also addressed. The results are consistent with those SPE models which treat rearrangements at the a–c interface as a critical stage in the crystallization process.

Surface Damage During Kev Ion Irradiation: Results of Computer Simulations

AbstractMD simulations have been employed to investigate damage processes near surfaces during keV bombardment of metal targets. For self-ion implantation of au, Cu, and Pt in the range of 5-20 keV, we have found that the proximity of the surface leads to significantly more damage and atomic mixing in comparison to recoil events occurring in the crystal interior. IN some cases, large craters are formed in a micro-explosive event, while in others a convective flow of atoms to the surface creates adatoms and leaves dislocations behind. Both the amount damage created in the surface and its morphology depend sensitively on the details of the energy deposition along individual ion trajectories. the results of these simulations will be summarized and compared to recent scanning tunneling microscopy studies of individual ion impacts in Pt and Ge.

Nanocrystal size modifications in porous silicon by preanodization ion implantation

A tuning of the nanocrystal sizes in porous silicon has been obtained by self-ion implantation in p-type silicon wafers before the anodization treatment. Sample porosity, luminescence spectra, Raman scattering, and transmission electron microscopy have been used to determine the structure of porous silicon samples. A porosity increase, a blue shift of the luminescence peak, a widening of the phonon resonance, and a decrease in the size features revealed by transmission electron microscopy (TEM) images are observed by increasing the ion implantation dose. It is suggested that this effect results from the increased resistivity of the Si wafer caused by the ion implantation damage.

Suppression of Self-Interstitials in Silicon During on Implantation via in-situ Photoexcitation

AbstractThe influence of in-situ photoexcitation during low temperature implantation on selfinterstitial agglomeration following annaealing has been investigated using transmission electron microscopy (TEM). A reduction in the level of as-implanted damage determined by RBS and TEM occurs athermally during 150 keV self-ion implantation. The damage reduction following a 300°C anneal suggests that it is mostly divacancy related. Subsequent thermal annealing at 800°C resulted in the formation of 13111 rod like defects or dislocation loops for samples with and without in-situ photoexcitation, respectively. Estimation of the number of self-interstitials bound by these defects in the sample without in-situ photoexcitation corresponds to the implanted dose; whereas for the insitu photoexcitation sample a suppression of ≈2 orders in magnitude is found. The kinetics of the athermal annealing process are discussed within the framework of either a recombination enhanced defect reaction mechanism, or a charge state enhanced defect migration and Coulomb interaction.

Damage formation in Si(100) induced by MeV self-ion implantation

Damage formation in Si(100) induced by MeV self-ion implantation was studied using the Rutherford backscattering and channeling technique. Damage accumulations were found to be produced mainly near the ions' end of range. Two distinct regions were observed for dose dependence upon damage. One is for low doses, in which the damage increases slowly with dose. The second region is for high-dose implantation, in which the damage increases rapidly as the dose increases. Beam self-annealing was found in MeV Si ion implanted Si(100). The effects of the energy depositions on the defect production are also discussed.

The effects of yttrium ion implantation on the oxidation of nickel-chromium alloys. I. The microstructures of yttrium implanted nickel-chromium alloys

Yttrium ions of 150 keV energy were implanted into the alloys Ni-20Cr, Ni-4Cr, and into nickel. The microstructures were then characterized using transmission electron microscopy, selected area channeling patterns and back-scattered electron images. Low yttrium fluences between 1×1014 and 5× 1015 Y+/cm2 did not alter the microstructures of Ni-20Cr. However, fluences of 1×1016, 5×1016, and 7.5×1016 caused the crystalline structures of the alloy to be replaced by an amorphous phase. Fluences of 7.5×1016 Y+/cm2 also rendered Ni-4Cr and nickel amorphous. Self-ion implantation experiments on Ni-20Cr did not cause the amorphous phase to form. The depth distribution of elements in Ni-20Cr following yttrium ion implantation (7.5× 1016 Y+/cm2) was determined by Auger electron spectroscopy. This showed in addition to the added yttrium a surface depletion in nickel concentration and a simultaneous enrichment in chromium concentration. At approximately 500 A, the chromium concentration is approximately 32 at.%. This depletion/enrichment zone extends throughout the implanted layer. Annealing the Ni-20Cr implanted with 7.5×1016 Y+/cm2 in vacuum for one hour at 600°C resulted in the recrystallization of Ni-Cr solid solution and the formation of very fine grains of Y2O3. Annealing at 800°C for 5 minutes showed recrystallized Ni-Cr, Y2O3, and an additional phase or phases.

The formation and annealing of dislocation damage from high-dose self-ion implantation of aluminum

Quantitative electron channeling and weak-beam transmission electron microscopy (TEM) measurements of dislocation density have been used to study the formation and annealing of the dislocation network in self-ion-implanted aluminum. The channeling linewidth is found to be proportional to the dislocation density. Several mathematical expressions for the dislocation network growth are examined. One by Igata et al. [in Effects of Radiation on Materials: Proceedings of the 10th International Symposium, edited by D. Kramer, H. R. Brager, and J. S. Perrin, STP 725 (ASTM, Philadelphia, 1980), p. 627] is found to describe the implantation data accurately. This model has a linear growth term and terms for dislocation loss due to surface effects and recovery. The fit is insensitive to the relative importance of the two loss terms. Annealing is found to occur in two stages; roughly one third of the dislocation density is gone by 300 °C, corresponding to typical recovery processes, while the remaining network is stable to about 500 °C.

Manipulation of nucleation sites in solid-state Si crystallization

Single grains of Si crystal are manipulated, for the first time, in solid-state crystallization of amorphous Si films. The artificial nucleation sites are introduced by employing the self-ion implantation. The nucleation and growth, during the subsequent thermal annealing strongly depends on the ion dose and energy. Preferential growth of the single nucleus takes place exclusively at each site and continues to propagate over them. Consequently, the location of grains is controlled, and the size distribution is remarkably shrunken in contrast to the films crystallized by random nucleation.

MeV, self-ion implantation in Si at liquid nitrogen temperature; a study of damage morphology and its anomalous annealing behavior

The damage formed by 1.25 MeV, self-ions in Si at liquid nitrogen temperature was studied. A dominant feature of the damage for moderate ion fluences is the presence of isolated amorphous regions over the range of the ions. The microstructure of this damage is detailed and formation mechanisms discussed. The amorphous regions are shown to give rise to strain in the surrounding crystal lattice which varies with ion dose in a complicated manner. The annealing behavior of the damage was studied and two distinct, low-temperature stages observed. Different mechanisms are shown to be responsible for each stage including a transient mechanism at 300 °C initiated by the release of defects from damage clusters, and enhanced crystallization of amorphous Si at 400 °C due to lattice stress.

New model for damage accumulation in Si during self-ion irradiation

The dependence of the damage produced by self-ion implantation in Si on dose is determined and is shown to exhibit two distinct behaviors: an initial sublinear increase of damage with dose, followed by a period of greatly accelerated growth. Ion backscattering analysis using both single- and double-alignment channeling measurements is used to determine the distribution of damage in the samples. The nature of the damage is determined from its thermal annealing behavior and differences in the spectra recorded in the two channeling configurations. Damage is found to consist predominantly of two components: simple defects, such as divacancies, and regions of amorphous Si. The behavior of these components is shown to be divergent at the fluence which separates the two different growth regimes. A model is proposed which considers the amorphization process in Si as a critical-point phenomenon, one in which the onset of amorphization leads to a cooperative behavior among the various types of damage resulting in a greatly accelerated transition.

Damage Growth in Si During Self-Ion Irradiation: a Study of Ion Effects Over an Extended Energy Range

AbstractDamage nucleation/growth in single-crystal Si during ion irradiation is discussed. For MeV ions, the rate of growth as was well as the damage morphology are shown to vary widely along the track of the ion. This is attributed to a change in the dominant, defect-related reactions as the ion penetrates the crystal. The nature of these reactions were elucidated by studying the interaction of MeV ions with different types of defects. The defects were introduced into the Si crystal prior to high-energy irradiation by self-ion implantation at a medium energy (100 keV). Varied damage morphologies were produced by implanting different ion fluences. Electron microscopy and ion-channeling measurements, in conjunction with annealing studies, were used to characterize the damage. Subtle changes in the predamage morphology are shown to result in markedly different responses to the high-energy irradiation, ranging from complete annealing of the damage to rapid growth. These divergent responses occur over a narrow range of dose (2–3 × 1014 cm-2) of the medium-energy ions; this range also marks a transition in the growth behavior of the damage during the predamaging implantation. A model is proposed which accounts for these observations and provides insight into ion-induced growth of amorphous layers in Si and the role of the amorphous/crystalline interface in this process.

Low-temperature oxidation of implanted TiSi2 films

The effect of implantation on the low-temperature oxidation behavior of TiSi2 films is investigated. Critical fluences of implanted impurities, such as As and Ga, are shown to alter the dominant oxidation mechanism in the films and greatly enhance oxidation. Different techniques, such as inert- and self-ion implantation, and implantation at elevated temperatures, were done so that ion-induced damage and chemical effects could be separately studied. These results, along with the dose dependency of the film’s behavior, will be presented. A model is proposed which accounts for these observations.

Damage Formation in Semiconductors During Mev Ion Implantation

ABSTRACTDamage produced by 1.0-2.5 MeV self-ion and O-ion implantation into Si and Ge single crystals has been characterized by cross-sectional electron microscopy and ion channeling. In Si, it is observed that the damage morphology varies substantially along the ion's track. Near the end-of-range of the ion, damage accumulation is very similar to that which occurs during medium- to low-energy implantation (i.e., damage increases monotonically with dose until the lattice is made completely amorphous). In front of this end-of-range region, however, damage saturates at a very low level for moderate implantation fluences. A model based on homogeneous damage nucleation in Si is discussed. For Ge, damage accumulation is very different; a monotonic increase of damage with dose is observed over the entire range of the ion. Possible mechanisms responsible for the differences between Si and Ge are discussed.

Dose rate dependence and time constant of the ion-beam-induced crystallization mechanism in silicon

The influence of dose rate on the ion-beam-induced crystallization of amorphous layers in silicon has been investigated. The amorphous layers were produced by self-ion implantation both in bulk silicon and in silicon on sapphire. Subsequent recrystallization was induced at 200 to 400 °C by Ne, Si, Ar, and Kr ion beams of 300 keV energy passing through the amorphous layers. Rutherford backscattering/channeling measurements showed that the regrowth rate decreased with increasing dose rate. This behavior was more pronounced for heavy ions where high dose rates and/or low temperatures could reverse the recrystallization and induce further amorphous growth of the layer. In this new solid-phase growth regime, the amorphous/crystalline interface moved inwards into the crystal in a manner similar to an epitaxial process. An intermittent beam experiment yielded a time constant for the ion beam induced crystallization mechanism of the order of 0.3 s. The time constant and a scaling law for different ions support a model where the planar growth is caused by the accumulation of divacancies in the interface region.

Al/Si Interface Characteristics Formed by Partially Ionized Beam Deposition at 2.5Kv

ABSTRACTPartially ionized beam (PIB) deposition technique was used to deposit Al thin film on Si(n) substrate. The fabricated Schottky diodes showed an anomalous C-V characteristics for the Al films deposited with a bias potential equal to 2.5kV. The 1/C2 vs. V plot showed a drastic decrease in the slope as compared to the diodes deposited without the bias potential. Further measurements showed a frequency dependence in the C-V characteristics. This anomalous C-V characteristics can be explained by the formation of a p-n junction diode underneath the Si surface. A model of self-ion implantation which explains the formation of this surface p-layer on the Si(n) substrate is proposed and tested.

Orientation and doping effects in ion beam annealing of α-silicon

The regrowth of amorphous layers in and Si substrates has been studied under irradiation with 600 keV Kr+ at target temperature in the 250–400°C range. The amorphous layers were obtained by P+ or Si+ implants. 2.0 MeV He+ backscattering in combination with channeling effect technique was adopted as the analytical technique. The regrown thickness increases linearly with fluence and with the energy density deposited into nuclear collisions at the amorphous-single crystal interface in all the investigated cases. The rate of regrowth for the orientation is two times that for the orientation. The measured activation energy of 0.22–0.05 eV is equal within the experimental accuracy for both orientations. The influence of impurities has been investigated in Si substrates preamorphized with P+ or Si+ ions. The regrowth is enhanced in the presence of phosphorus by a factor of ≈- 4 with respect to the Si self-ion implantation. The results are discussed in terms of the existing models of thermal and ion assisted epitaxial regrowth.

Dose Dependence of Ion Beam Mixing of Au on Amorphous and Single Crystalline Si and Ge

ABSTRACTThe rate of ion induced mixing of 700 Å Au layers vapor deposited on amorphous and single crystalline Si substrates held at room temperature was measured as a function of dose using 300 key Si, 350 keV Ar, and 525 keV Kr ion beams.Mixing profiles were measured at various fluences by Rutherford backscattering techniques and were found to be consistent with mixed layers whose thicknesses increased with ion dose. Mixing compositions, which were stoichiometric over the entire mixed region at Au-28.5 at.% Si, were found to be independent of ion species or implant fluence. For all ion species the dose dependence of mixing was closer to linear than the square root power law reported previously [1]. In addition, the mixing rate for Au on single crystalline substrates was significantly higher than Au n substrates amorphised by Si (self-ion) implantation at liquid nitrogen temperature. No difference was found between the mixing rates when the amorphous substrates were prepared by room temperature implantation. Preliminary results indicate similar behavior for the Au/Ge couple.

Ion implantation as a tool for studying the Kondo-systemZnMn

In the case ofZnMn alloys it is shown how low temperature ion implantation can be used for the production of dilute magnetic alloys. The Kondo effect in the resistivity ρ(T) was studied between 1.1K and 20 K. The phonon part of the resistivity was subtracted using ρ(T)-curves from Zn-Films with similar disorder produced by self-ion implantation. A logT-dependence with a slope proportional to the Mn-concentration was found below 200 ppm. The influence of disorder on the specific Kondo slope is discussed.