Solid Phase Epitaxial Regrowth Rate Research Articles

Atomistic modeling of the Ge composition dependence of solid phase epitaxial regrowth in SiGe alloys

The solid phase epitaxial regrowth (SPER) of SiGe alloys has been studied using atomistic simulation techniques. Molecular Dynamics (MD) simulations reproduce the recrystallization process of amorphous structures created in two different ways: introducing atoms at random positions according to the crystalline density and carefully relaxing the structure; and using a bond switching algorithm by means of ab initio. Activation energies are confronted, and the first method is validated as an efficient way to generate amorphous-crystalline structures suitable to study SPER processes. The MD extracted results show that the SPER rate does not vary monotonically with the Ge composition; instead, activation energies reveal a non-linear behaviour with the addition of Ge, due to the two-part behaviour of the SPER rate: SPER rate itself and a hypothesized extra strain due to the bond length difference. Since SPER is a thermally activated process, nudged elastic band calculations are carried out in order to extend the previous assumption. The energy barrier for an atom to attach to the crystalline phase is computed. The extracted values confirm the presence of the mentioned strain contribution required for an atom to recrystallize when it is not as the same type of the bulk.

Hydrogen diffusion and segregation during solid phase epitaxial regrowth of preamorphized Si

The redistribution of hydrogen during solid phase epitaxial regrowth (SPER) of preamorphized silicon has been experimentally investigated, modeled, and simulated for different H concentrations and temperatures. H was introduced by H implantation and/or infiltration from the sample surface during partial thermal anneals in air in the 520–620 °C temperature range. We characterized the time evolution of the H redistribution by secondary ion mass spectrometry and time resolved reflectivity. The good agreement between all experimental data and the simulations by means of full rate equation numerical calculations allows the quantitative assessment of all the phenomena involved: in-diffusion from annealing atmosphere and the H effect on the SPER rate. We describe the temperature dependence of microscopic segregation of H at the amorphous/crystal (a-c) interface. Only a fraction of H atoms pushed by the a-c interface can be incorporated into the crystal bulk. We propose an energetic scheme of H redistribution in amorphous Si. The segregation of H at the a-c interface is also considered for (110) and (111) orientated substrates. Our description can also be applied to other material systems in which redistribution of impurities during a solid-solid phase transition occurs.

An atomistic investigation of the composition dependence in SiGe alloys during Solid Phase Epitaxial Regrowth

The germanium fraction dependence of the Solid Phase Epitaxial Regrowth (SPER) rate in SiGe alloys has been investigated using a lattice kinetic Monte Carlo (LKMC) approach. Experiments show that the SPER rate is monotonically increasing with the addition of germanium. However, the extracted activation energy exhibits a non-linear evolution with the increase of germanium content. To investigate the influence of germanium in SiGe alloys, a comprehensive atomistic model is presented. The model focuses on the chemical bond types between the amorphous and the crystalline phases. As several recrystallization configurations exist at the amorphous–crystalline interface, a competition between them arises during SPER. This competition, implemented into a LKMC simulator, is able to reproduce several phenomena observed during SPER experiments on SiGe alloys: the monotonically increasing SPER rate and the non linear activation energy behavior regarding the germanium content as well as the temperature dependence on the extracted activation energy. The presented model is in close agreement with experimental data from literature.

Revisiting the role of strain in solid-phase epitaxial regrowth of ion-implanted silicon

Solid-phase-epitaxial-regrowth (SPER) dynamics of ion-implanted silicon were studied through in situ time-resolved reflectivity measurements. The roles of strain induced by dopant and isovalent impurities with different atomic sizes were disentangled by considering the actual Fermi-level shifting and effective strain induced by partial impurities, as obtained from Hall measurements and high-resolution X-ray diffraction. Contrary to in the previous model, SPER rate retardation was found in the cases of both isovalent-impurity-induced tensile and compressive strain. We propose a modified model incorporating strain into generalized Fermi-level shifting to inclusively explain the SPER dynamics.

Molecular dynamics modeling of solid phase epitaxial regrowth

Solid phase epitaxial regrowth (SPER) is of great technological importance in semiconductor device fabrication. A better understanding and accurately modeling of its behavior are vital to the design of fabrication processes and the improvement of the device performance. In this paper, SPER was modeled by molecular dynamics (MD) with Tersoff potential. Extensive MD simulations were conducted to study the dependence of SPER rate on temperature, growth orientation, pressure, and uniaxial stress. The simulation data were fitted to empirical formula, and the results were compared with experimental data. It was concluded that MD with Tersoff potential can qualitatively describe the SPER process. For a more quantitatively accurate model, larger simulation systems and a better interatomic potential are needed.

Strain-doping coupling dynamics in phosphorus doped Si:C formed by solid phase epitaxial regrowth

We investigate the solid phase epitaxial regrowth (SPER) dynamics of phosphorus doped Si:C by time resolved reflectivity and high resolution x-ray diffraction. The effect of SPER kinetics on strain profile and dopant activation is analyzed. The accumulated tensile strain induced by both C and P during SPER synergistically determines the onset of SPER rate retardation and leads to lower strain and electrical conductance near surface. Physical origin for the observed SPER rate evolution is discussed and explained with a strain included solute trapping model. Possibility of tailoring strain and doping profiles is discussed.

Impact of the chemical concentration on the solid-phase epitaxial regrowth of phosphorus implanted preamorphized germanium

The impact of the phosphorus concentration [P] on the solid-phase epitaxial regrowth rate of preamorphized p-type germanium has been studied by a combination of Rutherford backscattering, secondary ion mass spectrometry, and transmission electron microscopy. It will be shown that for P concentrations in the 1018–5×1019 cm−3 range, the regrowth rate is significantly enhanced compared with undoped germanium, while the opposite holds for [P] above about 4–5×1020 cm−3. This regrowth retardation is shown associated with segregation across the crystalline/amorphous boundary and snow plow of P in excess of the metastable solid solubility in the recrystallized material.

Role of the strain in the epitaxial regrowth rate of heavily doped amorphous Si films

Solid phase epitaxial regrowth (SPER) of p-doped preamorphized Si was studied by time resolved reflectivity. Strain and dopant concentration were opportunely varied by implanting neutral (Ge) and isovalent (B, Ga) impurities in order to disentangle the two different effects on SPER. Larger SPER rate variations occurred in strained doped Si with respect to undoped samples. The generalized Fermi level shifting model was implemented to include the role of the strain and to fit the experimental data over a large range of temperature for p- and n-type doping. We introduced a charged defect, whose energy level is independent of the dopant species.

Solid phase epitaxial regrowth of amorphous layers in silicon created by low energy phosphorus implantation: A medium energy ion scattering study

Medium energy ion scattering (MEIS) has been used to study the kinetics of solid phase epitaxial regrowth (SPEG) of ultrathin amorphous layers created by room temperature implantation of 5keV energy phosphorus ions into Si(100). P ion fluences ranged from 5e14cm−2 up to 1e16cm−2, the associated a-Si thicknesses from 9.2nm to 20nm. Regrowth was driven by rapid thermal annealing for anneal temperatures 425°C⩽TA⩽600°C and for times up to 2500s. The Si(P) regrowth velocities exceed that of the intrinsic Si SPEG rate by an order of magnitude. Regrowth in the near surface is approximately 1.7 times slower than in the bulk. In Si implanted to high P fluence, Φ⩾5e15cm−2, regrowth is severely retarded when the recrystallization front intercepts P concentrations in excess of ∼1e21cm−3.

Solid-phase epitaxial regrowth of a shallow amorphised Si layer studied by X-ray and medium energy ion scattering

Solid-phase epitaxial regrowth (SPER) of Si amorphised by ion implantation is considered as a potential solution for the fabrication of ultra-shallow junctions for future technology nodes of Si CMOS devices. In the present work, a series of Epi-Si samples amorphised by ultra-low energy As implantation was investigated by monitoring the lattice recovery during SPER and the simultaneous evolution of implantation-induced defects using the combined capabilities of X-ray scattering methods and medium energy ion scattering. Annealing temperatures between 550 and 700 °C and times from 10 to 200 s were chosen to characterise different stages of the SPER as well as the onset of defect annealing. Small defect clusters were detected in the end-of-range damage region of the implanted samples and layer-by-layer regrowth of the amorphised region was clearly observed. The complementary nature of the information obtained by the two methods is demonstrated. This study confirms that the high dose As implant causes the slowing down of the SPER rate in Si.

Study of reverse annealing behaviors of p+/n ultrashallow junction formed using solid phase epitaxial annealing

Solid phase epitaxial (SPE) annealing at low temperature has the advantage of high dopant activation and very little dopant diffusion. However, due to the low thermal budget engaged in SPE, a large amount of defects can exist in the area beyond the original interface of the crystal and the pre-amorphized layer. These defects may cause severe junction leakage. They may also cause dopant diffusion and deactivation in a following higher temperature process. This work studies the reverse annealing behaviors during a second annealing step for SPE-formed p+/n junction using either 1 keV B+ or 5 keV BF2+ implants. Four-point probe, secondary-ion-mass spectroscopy, and transmission electron microscopy are used in this study. The results show that the boron deactivation after second-step annealing is not only correlated with the transmission electron diffraction (TED), but also correlated with the end of range defect evolution. The results also show that BF2 implanted wafer has slower boron deactivation, less TED and slower defect evolution than the B implanted wafer. In addition, the BF2 implanted wafer shows a much slower SPE regrowth rate at 550 °C than the B implanted wafer.

Silicon isotopic tracing with the 29Si(p, γ) narrow resonance near 415 keV

Atomic transport of silicon during the formation of modified surface layers on silicon single crystal wafers has often been evoked in processes such as SIMOX or thermal oxidation but has never been directly observed. Recently, observations of substantial oxygen exchange at the SiO 2/Si interface during dry thermal oxidation indicate diffusion of oxygen-containing species from the interface to the gas phase, one candidate being the molecule SiO. Silicon isotopic tracing studies could contribute decisive new information to help understand these and other processes. Preparation of single crystal Si enriched in one of the rare isotopes has so far proven to be difficult. In this paper we report on the preparation of about 400 Å thick epitaxial layers enriched in 29Si to over 30 at.% by ion implantation. After amorphisation and high dose implantation, the solid phase epitaxial regrowth rate is much reduced compared to low dose implants because of significant oxygen contamination due to recoil implantation of oxygen, but channeling in the enriched layer shows a χ min of a few percent, indicating good epitaxial regrowth. Our first application of silicon isotopic tracing is to the study of the dry thermal oxidation of silicon. We have found significant silicon loss during this process.

Kinetics of silicide-induced crystallization of polycrystalline thin-film transistors fabricated from amorphous chemical-vapor deposition silicon

Self-aligned, n-channel, polycrystalline silicon thin-film transistors with 15 μm channels were fabricated by recrystallizing amorphous silicon for 6 h at 500 °C. A thin nickel silicide at the source and drain was used to seed the crystallization. The channel mobility was initially 87 cm2/V s, and improved to 170 cm2/V s after hydrogenating the devices. The recrystallization velocity in the channel was measured optically and electrically, and found to be 3.5×10−8 cm/s; this value exceeds by two orders of magnitude the solid-phase epitaxial regrowth rate of amorphous silicon. This observation, together with the low activation energy of 0.3 eV measured for the silicide-assisted regrowth velocity as compared to 2.76 eV for epitaxial regrowth, suggest that the channel recrystallization is assisted by Ni diffusing to the recrystallization front.

Carbon incorporation for strain compensation during solid phase epitaxial recrystallization of SiGe on Si at 500–600 °C

Transmission electron microscopy has been combined with time-resolved reflectivity and ion channeling to study the effects of carbon doping on solid-phase epitaxial regrowth (SPER) of strained 2000 Å, Si0.88Ge0.12Si alloy layers grown by molecular-beam epitaxy (MBE). Relative to the undoped layers, carbon incorporation in the MBE grown SiGe layers prior to regrowth at moderate temperatures (500–700 °C) has three main effects on SPER. These include a reduction in SPER rate, a delay in the onset of strain-relieving defect formation, and a sharpening of the amorphous/crystalline (a/c) interface, i.e., promotion of a two-dimensional (planar) growth front. These results suggest that C incorporated during SPER reduces the lattice-mismatch strain.

The Effects of Rapid Recrystallization and Ion Implanted Carbon on The Solid Phase Epitaxial Regrowth of Si1−xGex Alloy Layers On Silicon

ABSTRACTTransmission electron microscopy has been combined with time-resolved reflectivity and ion channeling to study the effects of regrowth temperature and carbon introduction by ion implantation on the solid phase epitaxial regrowth (SPER) of strained 2000Å, Sio.88Ge0.12/Si alloy films grown by molecular-beam epitaxy (MBE). Relative to the undoped layers, carbon incorporation in the MBE grown SiGe layers prior to regrowth at moderate temperatures (500- 700°C) has three main effects on SPER; these include a reduction in SPER rate, a delay in the onset of strain-relieving defect formation, and a sharpening of the amorphous-crystalline (a/c) interface, i.e., promotion of a two-dimensional (planar) growth front.1 Recrystallization of amorphized SiGe layers at higher temperatures (1 100°C) substantially modifies the defect structure in samples both with and without carbon. At these elevated temperatures threading dislocations extend completely to the Si/SiGe interface. Stacking faults are eliminated in the high temperature regrowth, and the threading dislocation density is slightly higher with carbon implantation.

Kinetics of solid phase epitaxial regrowth in amorphized Si0.88Ge0.12 measured by time-resolved reflectivity

Time-resolved reflectivity has been used to measure the rate of solid phase epitaxial regrowth (SPER) in situ during annealing of strained Si0.88Ge0.12 epilayers on Si preamorphized by the implantation of Si. The SPER velocities were measured over more than two orders of magnitude at temperatures from 503 to 603 °C. The results confirm that the average SPER velocity in thin, strained Si0.88Ge0.12 layers is less than that in pure Si. Furthermore, these real-time measurements demonstrate that the SPER rate for strained Si0.88Ge0.12 alloys is not a constant during regrowth at a fixed temperature but varies systematically as a function of the position of the amorphous-crystalline interface. The activation energy barrier of SPER in strained Si0.88Ge0.12 is higher than that in pure Si and is also a function of interface position, ranging from 2.94 to 3.11 eV. Cross-section transmission electron microscopy shows that strain-relieving defects are introduced coincidentally with the minimum regrowth rate.

Interface Stability During Solid Phase Epitaxy Of Strained GexS1-x Films on Si (100)

ABSTRACTStrained solid phase epitaxial (SPE) regrowth of amorphous GexSi1-x on Si (100) substrates was studied using time-resolved reflectivity (TRR). Films of CVD-grown Ge0.13Si0.87 on Si were amorphized by Si ion implantation, and subsequently regrown at temperatures between 550°C and 610°. Information on regrowth dynamics and interface roughness evolution was obtained by accurately modeling the complicated TRR data for GexSi1-x regrowth using a Moving, statistically roughening interface. The SPE regrowth rate slowed as the interface crossed into the GexSi1-x layer and the originally planar interface roughened, as confirmed by transmission electron Microscopy. A Minimum in the regrowth velocity was observed after regrowing approximately 60 nm into the GexSi1-x layer; the SPE rate subsequently increased to a final, thickness-dependent velocity that was still below that for pure Si. Upon entering the GexSi1-x layer, the interface roughened quickly to a 15–20 nm amplitude, increasing only slightly more during the remainder of regrowth. The degree of roughening and velocity reduction was found to be dependent on the anneal temperature. In contrast, samples with low Ge concentrations (< 3 at.%) prepared by ion implantation exhibited minimal interface roughening and essentially identical SPE velocities as pure Si.

Annealing of Pb-Implanted SrTiO3 in The Presence of Water Vapour: A Study Using D218O Labelling

ABSTRACTWe report new measurements of the regrowth behaviour of Pb-implanted SrTiO3 crystals in the presence of water vapour. Doubly labelled water vapour, D218O, at greater than 95% enrichment in each isotope has been added to the annealing ambient and depth profiles of D and 18O have been obtained from the regrown crystals using secondary ion mass spectrometry (SIMS). The D and 18O content has also been measured by nuclear reaction analysis (NRA) using the reactions D(3He,p)4 He and 18O(p,α)15 N. The crystals were regrown in a conventional furnace under a controlled gas ambient and time-resolved optical reflectivity (TRR) was used to dynamically monitor the regrowth rate during the anneal. An enhancement of the solid-phase epitaxial regrowth rate is observed when water vapour is added to the annealing ambient. This rate increase is accompanied by incorporation of D throughout the regrown layer. 18O is incorporated into the lattice but does not appear to penetrate deep enough to influence the regrowth rate.

Time resolved reflectivity measurements in Pb-implanted SrTiO 3

Time resolved optical reflectivity (TRR) is a simple and elegant technique for dynamically monitoring the interface motion that occurs during crystallisation of thin films and amorphous layers on crystalline substrates. This in situ technique has enabled measurements of the solid-phase epitaxial regrowth rate of amorphous silicon layers produced by ion implantation to be extended by over five orders of magnitude to rates in excess of 10 6 Å/s [1]. TRR is also well suited to measurements of crystallisation kinetics in ion-implanted ceramic oxides. In the present work, the technique is used to directly monitor the regrowth during thermal annealing of amorphous layers produced by ion implantation in the crystalline ceramic oxide SrTiO 3. In particular, the effect of ambient water vapour on the epitaxial regrowth rate of amorphous layers in this material has been examined. This study provides new insight into the role of water in regrowth of materials of this nature and clearly illustrates the utility of TRR in measurements of crystallisation rates in ceramic oxides.

Ionization Enhanced Solid Phase Epitaxy of Amorphous Silicon with Aluminum Impurities

AbstractIn this work we measured the functional dependence of the solid phase epitaxial regrowth (SPER) of amorphous silicon on NAI, the concentration of implanted aluminum (p-type). The SPER rates of self-ion amorphized layers in silicon wafers with (100) substrate orientation were measured by in situ high precision, isothermal, cw laser interferometry for temperatures from 470 °C to 550 °C, and concentrations in the range 3×1018 cm−3 ≤NAI≤ 4.7×1020 cm−3 obtained from samples implanted with three different doses.In the concentration range 3×1018 cm−3 ≤NAI≤ 2.3×1019 cm−3, we observed a “compensation effect” in which, with increasing NAI, the SPER rate decreased below the regrowth rate in intrinsic silicon and the activation energy of SPER increased to 2.85 eV, compared to 2.72 eV for intrinsic silicon. In the range 3.3×1019 cm−3 ≤NAI≤ 5.6×1019 cm−3, the regrowth rate increased linearly with NAI as previously observed for SPER in boron, phosphorus, and arsenic implanted samples. However, due to the compensation effect, the aluminum data could not be fit to the normalized equation; V/Vi = 1 + N/Ni, as was done previously for data obtained for boron, phosphorus, and arsenic. The regrowth rate increased nonlinearly to the maximum implanted concentration of 4.7× 1020 cm−3 at which the regrowth rate was more than double the previously observed maximum rate in boron doped silicon. In the high concentration range, the SPER rate enhancement could be fit by a quadratic equation whose curvature was positive as was the case for boron. This contrasts with the negative curvature required to fit the nonlinear dependence of the SPER rate on the concentration of donor impurities such as phosphorus and arsenic.