Solid Phase Epitaxy Rate Research Articles

Dopant effects on solid phase epitaxy in silicon and germanium

The kinetics of dopant-enhanced solid phase epitaxy (SPE) are studied in amorphous silicon (a-Si) and germanium (a-Ge) layers formed by ion implantation. Implanted Sb dopants into a-Ge up to a concentration of 1 × 1020 cm−3 are considered and compared to As implanted layers at similar concentrations. Although an active Sb concentration above the solubility limit is achieved, a significant portion of the implanted atoms are not. P, As, and B enhanced SPE rates in Si from the literature are also considered. The relative velocities of P and As in Si is similar to that of As and Sb in Ge. Theoretical predictions using a simple form of the generalized Fermi level shifting model, which incorporates both dopant and dopant-induced stress effects, is shown to agree well with the data. A single set of two parameters are determined, which describe the dopant enhanced SPE data well independent of dopant species and concentration.

Fluorine in Ge: Segregation and EOR-defects stabilization

In this paper we investigate the F behavior in Ge during solid phase epitaxy (SPE) and post-SPE annealing. Fluorine implanted with a fluence of 1 × 1015F/cm2 and an energy of 35keV induced the formation of an amorphous Ge layer. Detailed chemical and structural characterizations of the as implanted and annealed samples evidenced a strong segregation of F at the moving amorphous/crystalline interface, leading to a remarkable SPE rate retardation. In addition, we observed that F accumulates in correspondence of the end of range (EOR) defects. The comparison between the thermal evolution of damage produced by self-implantation and F implantation in Ge suggests that F increases significantly the stability of EOR. Such behavior clarifies the role of F in modifying the As diffusion in Ge recently reported in literature.

Hydrogen refinement during solid phase epitaxy of buried amorphous silicon layers

The effect of hydrogen on the kinetics of solid phase epitaxy (SPE) have been studied in buried amorphous Si layers. The crystallization rate of the front amorphous/crystalline (a/c) interface is monitored with time resolved reflectivity. Secondary ion mass spectrometry (SIMS) is used to examine H implanted profiles at selected stages of the anneals. The H retardation of the SPE rate is determined up to a H concentration of 2.3×1020 cm−3 where the SPE rate decreases by 80%. Numerical simulations are performed to model the H diffusion, the moving a/c interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. The segregation coefficient is estimated to be 0.07 at 575 °C. A significant fraction of the H escapes from the a-Si layer during SPE especially once the two a/c interfaces meet which is signified by the lack of H-related voids after a subsequent high temperature anneal.

Hydrogen in amorphous Si and Ge during solid phase epitaxy

Studies into the effect of hydrogen on the kinetics of solid phase epitaxy (SPE) in amorphous Si (a-Si) and Ge (a-Ge) are presented. During SPE, H diffuses into surface amorphous layers from the surface and segregates at the crystalline–amorphous interface. Some of the H crosses the interface and diffuses into the crystalline material where it either leaves the sample or is trapped by defects. H segregation at concentrations up to 2.3 × 10 20 H/cm 3 is observed in buried pha-Si layers with the SPE rate decreasing by up to 20%. H also results in a reduction of dopant-enhanced SPE rates and is used to explain the asymmetry effects between the SPE velocity profile and the dopant concentration profile observed with shallow dopant implants. Conversely, H diffusion is enhanced by dopants in a-Si. These studies suggest that H diffusion and SPE may be mediated by the same defect. The extent of H in-diffusion into a-Ge surface layers during SPE is about one order of magnitude less that that observed for a-Si layers. This is thought to be due to the lack of a stable surface oxide on a-Ge. However, a considerably greater retarding effect on the SPE rate in a-Ge of up to 70% is observed. A single unifying model is applied to both dopant-enhanced SPE and H diffusion processes.

Intrinsic and dopant-enhanced solid-phase epitaxy in amorphous germanium

The kinetics of intrinsic and dopant-enhanced solid-phase epitaxy (SPE) is studied in amorphous germanium $(a\text{-Ge})$ layers formed by ion implantation on $⟨100⟩$ Ge substrates. The SPE rates were measured with a time-resolved reflectivity (TRR) system between 300 and $540\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and found to have an activation energy of $(2.15\ifmmode\pm\else\textpm\fi{}0.04)\text{ }\text{eV}$. To interpret the TRR measurements the refractive indices of the $a\text{-Ge}$ layers were measured at the two wavelengths used, 1.152 and $1.532\text{ }\ensuremath{\mu}\text{m}$. For the first time, SPE rate measurements on thick $a\text{-Ge}$ layers $(>3\text{ }\ensuremath{\mu}\text{m})$ have also been performed to distinguish between bulk and near-surface SPE growth rate behavior. Possible effects of explosive crystallization on thick $a\text{-Ge}$ layers are considered. When H is present in $a\text{-Ge}$ it is found to have a considerably greater retarding effect on the SPE rate than for similar concentrations in $a\text{-Si}$ layers. Hydrogen is found to reduce the preexponential SPE velocity factor but not the activation energy of SPE. However, the extent of H indiffusion into $a\text{-Ge}$ surface layers during SPE is about one order of magnitude less than that observed for $a\text{-Si}$ layers. This is thought to be due to the lack of a stable surface oxide on $a\text{-Ge}$. Dopant-enhanced kinetics was measured in $a\text{-Ge}$ layers containing uniform concentration profiles of implanted As or Al spanning the concentration regime $1--10\ifmmode\times\else\texttimes\fi{}{10}^{19}/{\text{cm}}^{\ensuremath{-}3}$. Dopant compensation effects are also observed in $a\text{-Ge}$ layers containing equal concentrations of As and Al, where the SPE rate is similar to the intrinsic rate. Various SPE models are considered in light of these data.

Effects of patterned, stressed SiN overlayers on Si solid phase epitaxy

Striking nonuniformities are observed in the solid phase epitaxy (SPE) of blanket amorphized Si layers recrystallized in the presence of stress distributions induced by a patterned SiN overlayer. Measurements conducted for a range of SiN feature sizes and intrinsic stress values allowed us to isolate the effects of stress on the crystallization front. It is concluded that SiN-induced variations in SPE rates arise both from line-edge stresses, which scale with feature stress and increase SPE rates where the hydrostatic stress is compressive, and a SiN body effect, which suppresses SPE rates under the SiN features, independent of SiN stress state.

Intrinsic and Dopant-Enhanced Solid Phase Epitaxy in Amorphous Germanium

ABSTRACTThe kinetics of intrinsic and dopant-enhanced solid phase epitaxy (SPE) are studied in thick amorphous germanium (a-Ge) layers formed by ion implantation on <100> Ge substrates. The SPE rates for H-free Ge were measured with a time-resolved reflectivity (TRR) system in the temperature range 300 – 540 °C and found to have an activation energy of (2.15 ± 0.04) eV. Dopant enhanced SPE was measured in a-Ge layers containing a uniform concentration profile of implanted As spanning the concentration regime 1 – 10 × 1019 cm3. The generalized Fermi level shifting model shows excellent fits to the data.

Dopant-enhanced solid-phase epitaxy in buried amorphous silicon layers

The kinetics of intrinsic and dopant-enhanced solid-phase epitaxy (SPE) is studied in buried amorphous Si layers in which SPE is not retarded by H. As, P, B, and Al profiles were formed by multiple energy ion implantation over a concentration range of $(1--30)\ifmmode\times\else\texttimes\fi{}{10}^{19}∕{\mathrm{cm}}^{3}$. Samples were annealed in air at temperatures in the range $460--660\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and the rate of interface motion was monitored using time-resolved reflectivity. The dopant-enhanced SPE rates were modeled with the generalized Fermi level shifting model using degenerate semiconductor statistics. The effect of band bending between the crystalline and amorphous sides of the interface is also considered.

Point defect engineering in preamorphized silicon enriched with fluorine

Fluorine is known to have a beneficial role for the B diffusion reduction in preamorphized Si, and is promising for the realization of ultra-shallow junctions. Thus, we studied the F incorporation in Si during the solid phase epitaxy (SPE) process, pointing out the effects of the implanted F energy and fluence and the role played by the possible presence of dopants. The incorporation of fluorine proceeds by F segregation at the amorphous–crystalline interface, with a kinetics driven by the SPE rate. In fact, the quicker the SPE rate, the higher is the F fluence retained. Moreover, we demonstrated that F incorporated in Si layers does not appreciably affect the Is emission from spatially separated end-of-range (EOR) defects. The modification, induced by the presence of F, of the point defect density (Is and Vs) was also studied by means of B and Sb spike layers, used as local markers for Is and Vs, respectively. We showed that F is not only able to completely suppress the boron transient enhanced diffusion (TED), but can enhance the antimony diffusion. These experimental data demonstrate the ability of F in inducing an Is undersaturation or a Vs supersaturation, ruling out the hypothesis of a chemical bonding between F and the dopants. These results improve the engineering of F-enriched Si, for the realization of ultra-shallow junctions.

Fluorine incorporation in preamorphized silicon

We studied the effect of implanted fluorine on B-doped silicon formed by Si preamorphization, solid phase epitaxy (SPE) regrowth and post-SPE thermal treatments. We showed that the fluorine is an efficient diffusion inhibitor for boron, revealing the crucial importance of F implementation in the future generation devices. In samples doped with B we observed an anomalous F accumulation at the dopant implantation peak. Since the physical mechanisms driving these phenomena are not yet well understood, we investigated the effect of the presence of B and/or As on the F incorporation during the SPE process at 580°C. By using As coimplantation (thus modifying the SPE rate) we demonstrated that the above mentioned increased F incorporation is due to a kinetic effect, related to the SPE rate modification by doping, while a F–B chemical bonding is refused. These data shade new light upon the mechanism responsible for B diffusion reduction by F.

シリコンの固形成長速度へのヒ素原子の影響に関する分子動力学解析

Solid phase epitaxy (SPE) of Si is one of the most fundamental processes in semiconductor fabrication techniques. Many experimental studies have been carried out for understanding the growth mechanism. However microscopic mechanism is not well understood. In this study, we investigated the effect of arsenic atoms on the rate of Si SPE by using molecular dynamics simulation. In the case of non-doped Si, an activation energy of SPE is found to be 2.1±0.5eV, which shows good agreement with the experimental result (2.7eV). It is also found that the energy barrier of crystallization in a/c interface amounts to be about 0.6eV, which corresponds to defect migration process. It indicates other processes such as defect formation also control the SPE process. The SPE rate increases by 2 times for 3 at% As doping and 100 times for 5 at% As doping and an activation energy remains to be constant. The increase in SPE rate would be enhanced by defect formation process in amorphous silicon, which reflects the increase in self-diffusion of silicon atoms caused by active As atoms.

Fluorine segregation and incorporation during solid-phase epitaxy of Si

We report on the F incorporation into Si during solid-phase epitaxy (SPE) at 580°C and with the presence of B and∕or As, clarifying the F incorporation mechanism into Si. A strong segregation of F at the moving amorphous–crystalline interface has been characterized, leading to a SPE rate retardation and to a significant loss of F atoms through the surface. In B- or As-doped samples, an enhanced, local F incorporation is observed, whereas in the case of B and As co-implantation (leading to compensating dopant effect), a much lower F incorporation is achieved at the dopant peak. The F enhanced incorporation with the presence of B or As is shown to be a kinetic effect related to the SPE rate modification by doping, whereas the hypothesis of a F–B or F–As chemical bonding is refused. These results shed new light on the application of F in the fabrication of ultrashallow junctions in future generation devices.

Modeling the effect of hydrogen infiltration on the asymmetry in arsenic-enhanced solid phase epitaxy in silicon

The kinetics of solid phase epitaxy (SPE) in surface amorphous silicon layers doped with a single arsenic profile have been examined in relation to the generalized Fermi level shifting model of the SPE growth process. The model has been extended to include passivation by hydrogen of the defects responsible for SPE and∕or passivation of dopant atoms. A previous study has suggested that the asymmetry between the dopant-enhanced SPE rate and the arsenic concentration profile is due to the infiltration of hydrogen from the surface oxide. Theoretical calculations of the dopant-enhanced SPE rate compare well with experiment if it is assumed that the indiffusing hydrogen passivates some of the SPE defects and∕or some of the dopant atoms.

Kinetics of arsenic-enhanced solid phase epitaxy in silicon

The kinetics of intrinsic and arsenic-enhanced solid phase epitaxy (SPE) have been measured in buried amorphous Si (a-Si) layers in which crystallization occurs free from the rate retarding effects of hydrogen. Surface a-Si layers, where H infiltration can occur during crystallization, have also been studied. A single 1.45×1016 As/cm2 implant at 1200 keV was used to form an As concentration profile with a peak concentration of 3×1020 As/cm3 centered at 8000 Å beneath the crystal surface, allowing many different enhanced SPE rates to be examined simultaneously. The SPE rate through this profile and its intrinsic counterpart were measured using time-resolved reflectivity. The effects of hydrogen on the SPE rate can be determined by a comparison between the buried and surface a-Si layers. For the surface a-Si layers, it was found that the As-enhanced SPE rate versus depth curve is offset with respect to the concentration profile. We attribute this offset to the H infiltration in the case of the surface a-Si layer.

Defective Crystal Recovered from the Crystallization of Potassium-Doped Amorphous Silicon Films

The quality of a crystallized potassium-doped amorphous silicon film was investigated using transmission electron microscopy. It was discovered that the planar epitaxial growth of the amorphous layer was upset after a certain concentration of potassium was encountered by the interface. The crystal recovered subsequent to this point was twinned. The twins lie on {111} planes. The results from the transmission electron microscope analyses were correlated with the rate of solid-phase epitaxy as deduced using time resolved reflectivity and the potassium distribution measured using secondary ion mass spectroscopy. The roughening of the interface due to the growth of twins was determined as a function of depth from the extinction of reflectivity amplitude in the time resolved reflectivity trace. © 2003 The Electrochemical Society. All rights reserved.

The effect of potassium on the rate of solid phase epitaxy in silicon

Rutherford backscattering spectroscopy and ion channeling and secondary ion mass spectroscopy have been used to study the evolution of a potassium profile in amorphous silicon during solid phase epitaxial crystallisation. The potassium profile exhibits some propensity for refinement in front of the crystallising interface for the concentrations used in this experiment. Also, the potassium is partially substitutional in the crystallised layer. Preliminary studies on the influence of potassium on the rate of solid phase epitaxy (SPE) in silicon are presented. Surface amorphous films doped with potassium were crystallised and the rate of epitaxy was monitored using time resolved reflectivity. The inclusion of potassium was found to retard the rate of SPE. These results indicate that potassium doped amorphous films may be helpful in efforts to further refine present models of SPE in silicon.

Epitaxial growth of a low-density framework form of crystalline silicon: a molecular-dynamics study.

Crystal growth processes of low-density framework forms of crystalline silicon, named Si clathrates ( Si34 and Si46), during solid phase epitaxy (SPE) have been successfully observed in molecular-dynamics simulations using the Tersoff potential. The activation energy of SPE for Si34 has been found to correspond with the experimental value ( approximately 2.7 eV) for the cubic diamond phase, while the SPE rates of Si46 are much lower than that of Si34. The structural transition from Si46 to Si34 can be also observed during the Si46-[001] SPE. The present results suggest that new wide-gap Si semiconductors with clathrate structures can be prepared using epitaxial growth techniques.

Molecular-dynamics studies on solid phase epitaxy of guest-free silicon clathrates

ABSTRACTDynamical phenomena during the solid phase epitaxy (SPE) of guest-free Si clathrates (Si34 and Si46) via molecular-dynamics (MD) simulations using the Tersoff potential have been reported. The activation energy of SPE for Si34 has been found to correspond with the experimental value for the cubic diamond phase (c-Si; approximately 2.7eV), while the SPE rates of Si46 are much lower than that of c-Si. The structural transition from Si46 (type-I) to Si34 (type-II) can be also observed during the Si46 [001] SPE. The present results suggest that it is worthwhile to intensify experimental studies concerning crystal growth techniques of clathrate materials and these interesting Si forms may open up a new field in “silicon technologies”.

Large-grained polycrystalline Si films obtained by selective nucleation and solid phase epitaxy

We investigated the formation of large-grain polycrystalline silicon films on glass substrates for application in low-cost thin film crystalline silicon solar cells. Since the use of glass substrates constrains process temperatures, our chosen approach to form large-grain polycrystalline silicon templates is selective nucleation and solid phase epitaxy (SNSPE). In this process, selective crystallization of an initially amorphous silicon film, at lithographically predetermined sites, enables grain sizes larger than those observed via random crystallization. Selective heterogeneous nucleation centers were created for both P-doped, B-doped and undoped, 100 nm thick amorphous silicon films, by masked implantation of In or Ni islands, followed by annealing at temperatures below 600°C. Seeded crystallization begins at the metal islands and continues via lateral solid phase epitaxy (SPE), thus obtaining crystallized regions of several tens of square microns. The maximum achievable grain size depends on the product of the SPE rate and the incubation time for the spontaneous nucleation. We have studied the dependence of the SPE rate and the incubation time on the type of metal (In and Ni) inducing the nucleation and on the electronic dopant (e.g. P and B) concentration in the 10 19–10 21 cm −3 range.

Study of Vacancy and Impurity Complexes in Si Solid-Phase Epitaxial Crystallization with Positron Annihilation Spectroscopy

AbstractWe investigate the residual vacancy defect species after crystallization of amorphous Si (a-Si) by solid phase epitaxy (SPE). To this end, we correlate the total and electronically-active doping concentrations measured by secondary mass spectrometry and spreading resistance analysis, and data from positron annihilation spectroscopy (PAS), which is sensitive to openvolume defects. Float-zone silicon substrates were implanted with boron, phosphorus and both phosphorus and boron ions to create nonuniform doping profiles at degenerate doping levels, after an amorphization step by 29Si+ ions. Samples were vacuum annealed at 600°C to induce SPE, and the SPE rate was measured by time-resolved reflectivity. PAS was used for identification of the impurity-defect complexes. Momentum-resolved PAS measurements enable the detection of phosphorus-vacancy (P-V) and oxygen-vacancy (O-V) complexes.