Regrowth Kinetics Research Articles

Stripe width dependence of oxidation-enhanced diffusion in submicron local oxidation of silicon structures

Oxidation enhanced diffusion (OED) of phosphorus under very narrow oxidized region is investigated. The OED effect is found to depend on the oxidized region width for below 4–5 μm, i.e., the enhancement of phosphorus diffusivity decreases with decreasing the oxidized region width. In order to clarify the mechanism, two dimensional numerical simulations are carried out using various models for silicon self-interstitial generation at the Si/SiO2 interface during thermal oxidation. A series of OED observations is well simulated by using the new model in which the self-interstitial concentration at the oxidized interface is determined by the balance of (a) the interstitial generation due to oxidation reaction at the interface, (b) the kinetics of surface regrowth, and (c) the flux of interstitials into previously formed oxide. Effective surface regrowth rate constants for self-interstitials at the nonoxidized interface are then extracted. It is found that the surface regrowth rate constants in local oxidation of silicon structures are considerably large compared with those extracted from back side oxidation experiments.

Microstructural and chemical effects in Al2O3 implanted with iron at 77 K and annealed in oxidizing or reducing atmospheres

Implantation of Fe (160 keV) into α–Al2O3 at 77 K produces an amorphous surface layer for fluences in the range of 1016 to 1017 Fe/cm2. Measurements of short-range order were made by extended energy loss fine structure analysis (EXELFS). The structure of amorphous Al2O3 produced by implantation of iron at 77 K exhibits short-range order that differs from that produced by stoichiometric (Al + O) implants. This difference is manifested by changes in the Al–O near-neighbor bond length. The local environments of implanted iron were determined from conversion electron Mössbauer spectroscopy (CEMS). The iron resides in several different local environments consistent with the electronic states of Fe2+, Fe4+, and Fe0. The relative amount of each environment depends upon the concentration (fluence) of the implanted iron ions. Regrowth of the amorphous zone during annealing occurs in the sequence amorphous → γ–Al2O3 ↠ α–Al2O3. The kinetics of regrowth and phase separation vary with implanted fluence and with annealing atmosphere. The higher the concentration of implanted iron, the slower the formation of iron-aluminum oxide precipitate phases in oxidizing atmospheres and α–Fe precipitates in reducing atmospheres.

Amorphisation and solid phase epitaxial regrowth of the silicon overlayer in SIMOX structures

In order to study the kinetics of amorphisation and regrowth m SIMOX material, device grade SIMOX wafers were implanted with 80 and 150 keV 28Si + ions at room temperature over the dose range 1 × 10 14 to 5 × 10 15 cm −2. Bulk silicon control samples ((100), 17 Ω cm) were implanted at the same time under similar conditions. Subsequently these samples were annealed at temperatures of up to 550° C. The regrowth kinetics were studied using 1.5 MeV H + Rutherford backscattering and channeling and in this paper a comparison of the regrowth in bulk silicon and in SIMOX is reported.

Regrowth Kinetics of Dactylis glomerata Following Defoliation

This study describes and analyses the regrowth kinetics of vegetative plants of Dactylis glomerata L. following defoliation. Plants were grown hydroponically in growth chambers at two constant temperatures, 17 and 25 °C. The variations with time of shoot and root f. wts after the cutting were measured using a non-destructive method. During regrowth, the shoots were found to grow almost exponentially with time, whereas the growth rate of roots slowed markedly. A decrease in root f. wt was observed under the severest level of cutting. The regrowth kinetics were analyzed on an energetical basis. Shoot and root growth were calculated as the difference between the input of the carbon substrates supplied by photosynthesis and the loss of carbon associated with respiratory processes. A satisfactory description of the experimental kinetics was obtained under the main assumption that during regrowth the net photosynthetic production is partitioned between shoots and roots according to a constant ratio. From this analysis, the effect of defoliation can be interpreted in terms of a perturbation of the internal energetical equilibrium which, in roots, modifies the proportion of carbon substrates utilized for growth and maintenance requirements.

Invited review Multicell spheroids as a model for cell kinetic studies

Cells growing in tissue culture as three-dimensional, multicellular aggregates called 'spheroids' typically show a decreasing growth fraction and development of quiescent subpopulations as the spheroids enlarge. Kinetic studies in a number of spheroid systems have indicated that the primary reason for the tumour-like growth is a progressive decrease in growth fraction, with only a modest elongation of cell cycle time in larger spheroids. In this paper, the cellular growth kinetics for spheroids of V79 Chinese hamster lung cells are reviewed, and the regrowth kinetics of cells resuming growth after recovery from quiescent regions of the spheroids are described. Further, the role of regrowth/repopulation in determining the spheroid response to anti-tumour cytotoxics is explored, with particular emphasis on treatment with cisplatin and etoposide. By separating the effects of cytotoxicity and regrowth in the overall spheroid response to anti-neoplastic drugs, it is suggested that 'drug resistance' in tumours can be a kinetic as well as a genetic problem.

Molecular dynamics simulation of displacement cascades in Cu and Ni: Thermal spike behavior

Molecular dynamics simulations of energetic displacement cascades in Cu and Ni were performed with primary-knock-on-atom (PKA) energies up to 5 keV. The interatomic forces were represented by the Gibson II (Cu) and the Johnson-Erginsoy (Ni) potentials. Our results indicate that the primary state of damage produced by displacement cascades is controlled basically by two phenomena: replacement collision sequences during the ballistic phase, and melting and resolidification during the thermal spike. The thermal-spike phase is of longer duration and has a more marked effect in Cu than in Ni. Results for atomic mixing, defect production, and defect clustering are presented and compared with experiment. Simulations of “heat spikes” in these metals suggest a model for “cascade collapse” based on the regrowth kinetics of the molten cascade core.

Epitaxial crystallisation of tin implanted silicon

Time resolved reflectivity, Rutherford backscattering and channeling, and transmission electron microscopy have been used to examine the epitaxy of amorphous layers formed by Si + and Sn + ion implantation into both 〈100〉 and 〈111〉 silicon. Although Sn at concentrations less than about 1 at.% does not have any influence on the regrowth kinetics of (100) silicon, it has a beneficial effect on the growth of (111) silicon. At high concentrations Sn retards epitaxy and can lead to a polycrystalline phase transformation.

Amorphization and Annealing of 6H SiC Implanted with N-Type, P-Type or Isovalent Dopants

Abstractlons of boron, phosphorous, titanium and neon were implanted into (0001) oriented 6H SiC crystals at 300 K. Implantation energies and fluences were chosen to produce equal (calculated) displacements per atom at similar peak damage depths and a randomized (metaminct or amorphous) zone extending to the front surface. RBS/channeling was used to test the amorphization criteria. Dopant effects on regrowth kinetics and microhardness have been determined by isochronal annealing.

Ion implantation and annealing of crystalline oxides

The technique of ion implantation is being investigated as a general method for altering the near-surface properties of insulating materials. The primary motivation behind these investigations is to develop ion implantation as a practical means of controlling and improving the near-surface mechanical, optical, or electronic properties of insulators. Changes in these properties depend on the microstructures and compositions developed in the material during the ion implantation process and subsequent thermal treatments. In many cases, structures and compositions can be produced by implantation and thermal annealing that cannot be achieved by conventional techniques. In this work, the response of a wide range of crystalline oxides to ion implantation and subsequent thermal processing will be reviewed. The materials treated here include Al 2 O 3 , LiNbO 3 , CaTiO 3 , SrTiO 3 , ZnO, and MgO, as well as the non-oxide materials Si 3 N 4 and SiC. The response of these insulators to ion implantation varies widely and depends on the specific material, the implantation species and dose, and the implantation temperature. Ion implantation produces displacement and other damage in the near-surface region, and in many cases, the surfaces of originally crystalline insulators are turned amorphous. Thermal annealing can often be used to restore crystallinity to the damaged near-surface region, and additionally, metastable solid solutions can be produced. For a number of oxide materials, the annealing behavior has been studied in detail using both Rutherford backscattering-ion channeling techniques and transmission electron microscopy. These studies show that, in some materials, the annealing behavior is quite simple and takes place by solid-phase epitaxial crystallization where the amorphous-to-crystalline transformation occurs at an interface that moves toward the free surface during the annealing process. In such materials, the regrowth kinetics have been measured, and the associated activation energies for crystallization have been determined. The formation of metastable solid solutions during crystallization of the amorphous phase will also be discussed.

Automated selective dissociation of cells from different regions of multicellular spheroids.

In this report we describe a new apparatus which has been developed for the automated selective dissociation of multicellular spheroids into fractions of viable cells from different locations in the spheroid. This device is based on the exposure of spheroids to a 0.25% solution of trypsin under carefully controlled conditions, such that the cells are released from the outer spheroid surface in successive layers. Study of the spheroid size, number of cells per spheroid, and sections through the spheroid with increasing exposure to trypsin demonstrate the effectiveness of this technique. The technique has been successfully used on spheroids from five different cell lines over a wide range of spheroid diameters. We also present data detailing the effect of varying the dissociation temperature, the mixing speed, the trypsin concentration, and the number of spheroids being dissociated. The new apparatus has several advantages over previous selective dissociation methods and other techniques for isolating cells from different regions in spheroids, including: a) precise control over dissociation conditions, improving reproducibility; b) short time to recover cell fractions; c) ability to isolate large numbers of cells from many different spheroid locations; d) use of common, inexpensive laboratory equipment; and e) easy adaptability to new cell lines or various spheroid sizes. Applications of this method are demonstrated, including the measurement of nutrient consumption rates, regrowth kinetics, and radiation survivals of cells from different spheroid regions.

Solid phase epitaxy of laser amorphized silicon

The solid phase epitaxial regrowth kinetics of laser amorphized [100] silicon-on-sapphire was studied using in situ time-resolved optical transmission. Regrowth rates for ≤20-nm-thick amorphous silicon films were observed to increase from 1.7×10−10 cm/s at 750 K to 1.9×10−7 cm/s at 900 K. The recrystallization velocity followed an Arrhenius behavior with an activation enthalpy of 2.71 eV. These results provide strong confirmation that the metastable phase quenched following laser irradiation is structurally equivalent to amorphous silicon produced by ion implantation or ultrahigh vacuum deposition, and is not stabilized by impurities.

Dose effects during solid phase epitaxial regrowth of boron-implanted, germanium-amorphized silicon induced by rapid thermal annealing

The effect of implanted boron concentration on the solid phase epitaxial regrowth (SPER) kinetics during rapid thermal annealing (RTA) of 73Ge+-amorphized 〈100〉 silicon in the temperature range 500–575 °C has been studied using Rutherford backscattering and channeling measurements. Relatively flat 11B+ profiles at 5×1019, 1020, and 3×1020 cm−3 were implanted up to a depth ≂0.18 μm into different 73Ge+-preamorphized 75-cm-diam wafers. Following a RTA anneal at 800 °C/10 s (in order to recrystallize the amorphized layer and activate the implanted boron), the wafers were reamorphized with 73Ge+ ions (constant concentration ≂3×1020 cm−3 up to a depth ≂0.2 μm) and the SPER kinetics studied as indicated above. This procedure ensured that the defect densities in the wafers were the same in spite of their different boron doses. Our results clearly show an activation energy reduction from 2.86 eV at 5×1019 atoms/cm3 to 2.6 eV at 3×1020 cm−3 (in spite of the constant defect concentration in the wafers), with a linear relation between the growth rate and the implanted dose throughout the temperature range of study.

On the kinetics of solid phase regrowth and dopant activation during rapid thermal annealing of implantation amorphized silicon

We have studied the solid phase epitaxial regrowth (SPER) of implantation [31P+,11B+(73Ge+ preamorphized)] amorphized silicon in the temperature range 500–600 °C induced by rapid thermal annealing (RTA), using Rutherford backscattering (RBS) and channeling measurements. Our results show rate enhancements (≂3.5–6.5) of the velocities of regrowth in all cases studied with respect to values reported in the literature for furnace-induced epitaxy. The measured SPER activation energies (2.7 and 2.6 eV for 31P+ and 11B+ implantations, respectively) while being comparable to literature reported values, were nevertheless higher than the energy required for the activation of these dopants, ≂1.55–2.45 eV. Also, the ratio VB/VP (velocity of regrowth in the presence of boron with respect to phosphorus) gives a value of approximately 3 in both RTA and furnace-induced kinetics. These results are explained by a model which takes into account the role of electrically active interfacial defect sites during SPER.

High-pressure study of solid phase epitaxial regrowth in implanted amorphous GaAs

A new in situ technique for determination of solid phase epitaxial regrowth kinetics under high-pressure conditions is described. It is applied to the study of pressure effects on recrystallization kinetics of amorphous implanted GaAs. The results show that the epitaxial growth rate is enhanced with pressure. An empirical formalism is developed describing the effect of pressure as a softening of the acoustic modes and a consequent decrease of the activation energies. Good agreement is obtained with the experimental data.

Rapid thermal annealing-induced epitaxy of ion-implanted amorphous layers on 〈100〉 silicon

A high-resolution Rutherford backscattering-channeling experiment was used to investigate the regrowth kinetics of Ge+- and As+-implanted amorphous layers on 〈100〉 silicon during a rapid thermal (lamp) annealing (RTA). Our results are compared to the well-known recrystallization behavior obtained in a standard furnace. A substantial enhancement of the growth rate with no variation of activation energy is shown. The accuracy of the temperature reading is first discussed. It is also shown that incident radiations (light) play no significant role in this enhancement. It is further concluded that there is actually no difference between RTA and furnace annealing, the epitaxy velocity increase being time limited to a few minutes. This transient effect is explained similarly to the increased diffusivity observed at higher temperature.

Recrystallization kinetics pattern in III-V implanted semiconductors

Solid phase epitaxial regrowth has been studied for a variety of ion-implanted compound semiconductors. The time-resolved reflectivity technique is used to determine growth kinetics. It is shown that the growth rate follows a thermal activation law whose activation energy and pre-exponential factor are measured. In all III-V compounds and alloys, a common regrowth kinetics behavior is found, with the activation energy proportional to a characteristic vibrational relaxation energy which also intervenes in the description of point defect migration. Differences with the case of column IV semiconductors are discussed.

Interface structure evolution and impurity effects during solid-phase-epitaxial growth in GaAs

The time-resolved reflectivity technique is shown to be able to characterize interface structure during solid-phase epitaxy in GaAs. A detailed study of interface structure during regrowth and recrystallization kinetics is made for different implanted impurities and implantation parameters in GaAs. It is shown that the interface roughens on a macroscopic scale during the regrowth process and that this evolution has an intrinsic character in the implanted material. Activation energy is shown to be independent of implantation conditions. Substitutional impurity implantation does not produce variations in regrowth kinetics whereas argon implantation drastically decreases the growth rate. Results are interpreted in terms of interface roughening due to nonrelaxing atomic configurations in the disordered phase. The evolution of the interface has been related to an increase of disorder in the regrown layers.

Stability and formation of NiAl3 under ion irradiation

Compound samples of NiAl3 as well as Ni23Al77 multilayered samples have been irradiated by either Xe or Ne ions to doses of 2 × 1015 Xe ions/cm2 and 1.3 × 106 Ne ions/cm2 at temperatures of 100 K, 300 K, and 373 K. In the case of compound irradiation, NiAl3 stability appears to be determined by regrowth kinetics and increased with lighter irradiating ion mass and higher irradiation temperature. The formation of NiAl3 by ion mixing Ni/Al multilayers was not affected by irradiating ion mass and appears to be limited by nucleation.

Regrowth of Implanted–Amorphous Si

AbstractA two dimensional model of nucleation and growth is described which is consistent with the following experimental phenomena observed in the regrowth of ion-implanted silicon: (1) Substrate orientation effect on regrowth kinetics. (2) Impurity effects on regrowth kinetics. (3) The activation energy dependence of regrowth rate. (4) Impurity redistribution and supersaturation effect.

An immunological approach to analyse the kinetics of minimal residual disease in acute leukemia

The quantity and kinetic behaviour of “residual disease” in human acute leukemia are still largely unknown entities. The number of leukemic cells present during the phase of “complete remission” may vary from 0 to 1010. More knowledge on these entities will obviously have clinical implications in terms of (a) evaluating the efficacy of a given treatment regimen (remission-induction-, consolidation- and maintenance chemotherapy), (b) choosing the optimal — combination of — cytostatic drugs, e.g., phase-specific versus alkylating agents, dependent on the kinetics of regrowth of leukemia, (c) early detection of drug resistance, (d) predicting an early relapse with subsequent resumption of intensive treatment of a relatively low tumor mass, (e) quantification of the number of “contaminating” leukemic cells in autologous marrow grafts including the evaluation of the efficacy of in vitro elimination procedures, etc.