Solid Phase Epitaxial Regrowth Research Articles

32-nm Multigate Si-nTFET With Microwave-Annealed Abrupt Junction

Microwave annealing (MWA) activates dopants through solid-phase epitaxial regrowth with low thermal budget. Optimizing the microwave power during MWA is capable of realizing low defect density at the junction, suppressing the dopant diffusion, and mitigating the straggle effect of ion implantation. These favorable features of MWA facilitate the formation of extremely abrupt junction profiles in tunnel FETs (TFETs). In conjunction with the improved gate-to-channel controllability of the multiple-gate (MG) structure, we demonstrate high-performance lateral n-type Si-TFETs using a CMOS-compatible process flow with excellent band-to-band tunneling efficiency and device scalability. The 32-nm MG Si-TFET shows promising characteristics, including a high ON-state current of 41.3 $\mu \text{A}/\mu \text{m}$ , a large current ON/OFF ratio of $> 5\times 10^{7}$ , and minimal short-channel effect using $V_{G}=2$ V and $V_{D}=1$ V.

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.

Solid phase epitaxial regrowth of (001) anatase titanium dioxide

The growing interest in metal oxide based semiconductor technologies has driven the need to produce high quality epitaxial films of one metal oxide upon another. Largely unrecognized in synthetic efforts is that some metal oxides offer strongly polar surfaces and interfaces that require electrostatic stabilization to avoid a physically implausible divergence in the potential. The present work examines these issues for epitaxial growth of anatase TiO2 on strontium titanate (001). Solid phase epitaxial regrowth yields only the (001) facet, while direct crystalline growth by atomic layer deposition yields both the (112) and (001). The presence of amorphous TiO2 during regrowth may provide preferential stabilization for formation of the (001) facet.

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.

Methodology for thermal budget reduction of SPER down to 450 °C for 3D sequential integration

3D sequential integration enables the full use of the third dimension thanks to its unique contact density far above the possibilities of 3D packaging solutions. However, as the transistors are sequentially stacked over each other, the thermal budget allowed for the fabrication of the top transistor is limited by the maximal temperature accepted by the already made bottom one. It was previously described that a thermal budget of T>500°C is enough to degrade the bottom transistors performance. So the technological challenge is to develop low temperature routines for the fabrication of the top devices. For that, different processes have to be adapted, mainly the dopant activation step, where the T>1000°C spike annealing must be replaced. In this contribution, we present the feasibility to dope by solid phase epitaxial regrowth (SPER) at 450°C thin Si films (22nm) containing high dopant concentration of 5×1020at/cm3. For n- and p-type dopants, the 450°C SPER rendered low sheet resistance values, as low as the ones obtained with the high temperature activation method.

Atomistic modeling of epitaxial growth of semiconductor materials

The epitaxial growth of semiconductors is a very important step for the processing of microelectronic devices. Solid Phase Epitaxial Regrowth (SPER) is involved in both the recrystallization of amorphous silicon and germanium areas. Selective epitaxial growth (SEG) is routinely used in manufacturing modern 3D devices like finFETs, raised source/drain transistors, gate-all-around transistors, etc. In this work, lattice kinetic Monte Carlo modeling is used as the main tool for the modeling and simulation of epitaxial growth in IV and III–V based materials. This is done by detecting particular local configurations at the interfaces, and assigning local growth rates depending on such configurations. This simple idea is used to identify recrystallization planes or to compute different formation energies for the trapping, detrapping and migration of atoms. Introduction of defects is also possible by allowing the formation of twins and small defective areas. We will show different cases where our model is used, namely: SPER and defect formation of Si, and we will explain how the models can be extended to simulate the epitaxial growth of III–V materials and to obtain the different facet formation and growth kinetics. All these cases are compared with relevant experimental results from the literature to provide an assessment of their current capabilities but also possible limitations.

Formation of multiple dislocations in Si solid-phase epitaxy regrowth process using stress memorization technique

This work investigates the formation mechanism of stress memorization technique (SMT)-induced edge dislocations and stacking faults during solid-phase epitaxy regrowth (SPER) using molecular dynamics (MD) simulation. During the SPER process of a patterned amorphous Si under a high-tensile capping film, growth fronts along the (110) and (001) planes collapse to form 5- and 7-rings which trigger the Frankel partial dislocation in the {111} plane. In addition, the line defects of stacking faults along {111} plane are generated with two symmetric boundaries of atomic structures which are confirmed as micro-twin defects. The MD simulation results are validated using high-resolution transmission electron microscopy and inverse fast Fourier transform images. The strain distribution obtained from the atomic structure reveals that the stress field is mainly caused by Frankel partial dislocations and the minor stress effect from the micro-twin defects.

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.

Study of millisecond laser annealing on recrystallization, activation, and mobility of laser annealed SOI doped via arsenic ion implantation

Millisecond anneal techniques have been demonstrated to achieve fully recrystallized, highly activated, shallow, and abrupt junctions in silicon with both p- and n-type dopants due to the technique's fast time scale and high temperature. To understand and model the effects of millisecond laser annealing, knowledge of the true thermal profile experienced by the active semiconductor region must be known. This work simulates the impacts of a scanning laser in a series of shallow implants, and compares those results to experimental results. Arsenic ion (As+) implant energies of 10, 19, and 25 keV at doses of 1.5 × 1015 and 3 × 1015 cm−2 into a silicon-on-insulator substrate are studied to achieve different doping levels and amorphization depths. The recrystallization, activation, and mobility of the laser annealed, ion implanted experimental cells are then analyzed. For each experiment, Sentaurus technology computer aided design is used to create a calibrated 2D laser model to approximate the thermal budget of the lasing recipes (850–1250 °C) then using that output as an input into lattice kinetic Monte Carlo (LKMC) to simulate the solid phase epitaxial regrowth (SPER) during anneal of the various implant conditions. Sheet resistance and Hall effect measurements were used to correlate dopant activation and mobility with the regrowth process during laser anneal, showing the onset of high conductivity associated with completion of SPER in the films. The LKMC model shows an excellent agreement with cross section transmission electron microscopy, correlating the increase of conductivity with completion of crystal regrowth, increased activation, and crystal quality at various temperatures. Shallow, lower dose implants are capable of single crystal regrowth, producing high levels of activation >1 × 1020 cm−2 and nominal mobilities for highly arsenic-doped silicon. However, higher energy implants that fully amorphize the film regrow polycrystalline silicon with low mobilities even at very high temperatures (1250 °C), unsuitable for source–drain formation in logic devices.

Multiscale modeling of defect formation during solid-phase epitaxy regrowth of silicon

This work presents a multiscale approach to understanding the defect formation during the evolution of solid-phase epitaxy regrowth in Si. A molecular dynamics (MD) simulation technique has been used to elucidate the defect formation mechanisms, as well as to determine their nature. A hybrid lattice kinetic Monte Carlo (LKMC)–finite element method (FEM) model fed by the outcome of MD was subsequently implemented. It scales up the simulation times and sizes, while reproducing the important features of the defected regrowth predicted previously. FEM calculations provide the strain pattern due to the density variation between the amorphous and crystalline phases, which is then taken into account by the LKMC model by including the effect of the strain in the rates of recrystallization. Overall, this multiscale modeling provides a physical explanation of the generation of defects and its relation with the presence of strain. The model also captures the character of formed defects. It distinguishes two types: twins formed at {111} planes and dislocations produced by the collapse of the two recrystallization fronts. Simulation results are validated by comparing them with significant experiments reported in the literature.

Invited: Direct Bonding: A Key Enabler for 3D Monolithic Integration

Monolithic 3D Integration (3DMI) consists in processing transistors on top of each other sequentially. This technology appears to be an alternative solution to scaling, from the 7nm node integration and below, as substantial gain in area and performance as compared to planar technology is expected without scaling the transistor technology node. 3DMI appears to be the most optimized way to take advantage of the vertical dimension as almost no alignment constraints remains. By using a standard lithography, the top transistors can be aligned directly onto their bottom counterparts with a high accuracy (see Fig. 1), contrary to TSV-based 3D technologies [2]. Furthermore, 3DMI is a highly versatile technology as the different transistor levels can be optimized independently, from the choice of the channel characteristics (e.g. material, orientation, strain) to the architecture itself (e.g. CMOS on CMOS, PMOS on NMOS, FinFET on BULK, LVT on RVT) [3]. Such sequential integration raises two main technological challenges: - Creating an active layer above a bottom transistor which will become the channel of the top transistor. In order to achieve similar performance for top FET than bottom FET, the substrate quality must be equivalent than commercial substrates. Thus, this layer must be monocristalline and defect free in order to optimize the mobility and to be consistent with high performance criteria. A precise thickness control is also necessary in order to avoid device performance dispersion. - Realizing a high performance top transistor level without degrading the bottom level as the stacked transistor levels are processed sequentially, i.e. at low temperature process –typically below 600°C. Recent results demonstrate some integration solutions, such as junction activation by Solid Phase Epitaxy Regrowth below 600°C [4].To tackle the first challenge, we transfer a thin silicon layer from a high quality Silicon On Insulator (SOI) wafer by direct bonding. It appears to be the most effective solution to obtain a defect free monocristalline active layer with a well-controlled thickness. This method is preferred to different techniques which have been developed to create large monocristal grains of silicon either by laser anneal of amorphous Poly-Silicon [5] or by µ-Czochralsky process [6]. However, in both cases, large “seed layers” are necessary to control the orientation and the size of these grains, which is not consistent with for high density circuits.For this layer transfer, a blanket SOI wafer on which a Si02 layer is either grown or deposited, is bonded on the classical pre-metal dielectric above the bottom transistor level. The SOI backside is then removed by grinding and chemical etching to keep only the silicon layer. While expert knowledge has been reached for full sheet wafer bonding, the situation on a patterned layer can be really challenging with the design rules of 3DMI. In order to face these challenges, the surface preparation, the direct bonding process and the thinning steps have been optimized to prevent any defect on the whole 300mm surface. Also TMAH bevel edge protection and silicide protection layer have been added.This work will give a general overview of 3D monolithic challenges. Also, a specific focus will be made on direct bonding which is a major enabler of this type of integration. Indeed among the other alternative techniques, it appears to be the best solution to meet the high performance and high density criteria.REFERENCES:[1] P. Batude et al., VLSI Technology, pp. 158 (2011) [1] P. Batude et al., ECS Spring meeting, (16) pp. 47 (2008) [2] P. Batude et al., IITC-AMC (2014) [3] P. Batude et al., IEDM, pp.731-734 (2011) [4] C-H. Shen et al., IEDM, pp. 931-934 (2013) [5] J. Derakhshandeh et al., TED vol.58, no. 11 (2011)Fig.1: 3DMI demonstration with ultra-high alignment between the stacked transistors [1] obtained with 248nm stepper.

High Performance 400 °C p+/n Ge Junctions Using Cryogenic Boron Implantation

We report high performance Ge p + /n junctions using a single, cryogenic (-100 °C) boron ion implantation process. High activation>4 × 10 20 cm -3 results in specific contact resistivity of 1.7 × 10 -8 Ω-cm 2 on p + -Ge, which is close to ITRS 15 nm specification (1 × 10 -8 Ω-cm 2 ) and nearly 4.5× lower than the state of the art (8 × 10 -8 Ω-cm 2 ). Cryogenic implantation is shown to enable solid-phase epitaxial regrowth and lower junction depth through amorphization of the surface Ge layer. These improvements in Ge p + /n junctions can pave the way for future high mobility Ge p-MOSFETs.

Modeling of junction formation in scaled Si devices

In this article, modeling of junction formation in scaled Si device is shown. An atomistic kinetic Monte Carlo (KMC) diffusion modeling is used for the analysis of dopant diffusion and defects during shallow junction formation processes. Dopant diffusion and defect evolution during sub-millisecond non-melt laser annealing (NLA) are studied in both experiments and an atomistic kMC diffusion modeling. Pre-amorphization implant is often used for ultra shallow junction formation. It is shown that Solid Phase Epitaxial Regrowth (SPER) annealing stage plays an important role for dopant diffusion in junction formation process. As Ge implant energy is increased, damage structure and IV composition of Amorphous Pockets are changed and this affects the dopant diffusion and activation behavior. KMC simulations show that B, As deactivation is induced by the formation of dopant-defect complexes, such as B n I m , As n V m , As n I m , As n , during millisecond annealing time range. Both experiments and KMC show that defect evolution during millisecond annealing time range. Fluorine, Carbon co-implant effects are also modeled using KMC.

Atomistic investigation of the impact of stress during solid phase epitaxial regrowth

AbstractAn atomistic model to account for the impact of stress during solid phase epitaxial regrowth (SPER) is proposed. This model is based on the lattice kinetic Monte Carlo method. It has been compared with experimental data of regrowth velocity as a function of hydrostatic and non‐hydrostatic stresses.In particular, it permits to provide a physical explanation of the observations upon in‐plane uniaxial stress based on the assumption that {100} events occur through a dual‐timescale atomistic mechanism. Our model also catches the fact that compressive normal uniaxial stress and hydrostatic pressure result in an enhancement of the regrowth velocity with a similar activation volume.(© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In situ high-resolution transmission electron microscopy of material reactions

Abstract

An atomistic investigation of the impact of in-plane uniaxial stress during solid phase epitaxial regrowth

We propose an atomistic comprehensive model based on a lattice kinetic Monte Carlo approach to analyse the impact of in-plane uniaxial stress during solid phase epitaxial regrowth. We observed no influence of tensile stress on the regrowth kinetics. In contrast, compressive stress leads to (i) a reduction of the macroscopic regrowth velocity, (ii) an enhancement of the amorphous/crystalline interface roughness, and (iii) defective Si formation. Our observations are in good agreement with experimental data from the literature. Our atomistic approach also clarifies the interpretation of the interface morphological instability based on the kinetics of microscopic events.

Comprehensive modeling of solid phase epitaxial growth using Lattice Kinetic Monte Carlo

Damage evolution of irradiated silicon is, and has been, a topic of interest for the last decades for its applications to the semiconductor industry. In particular, sometimes, the damage is heavy enough to collapse the lattice and to locally amorphize the silicon, while in other cases amorphization is introduced explicitly to improve other implanted profiles. Subsequent annealing of the implanted samples heals the amorphized regions through Solid Phase Epitaxial Regrowth (SPER). SPER is a complicated process. It is anisotropic, it generates defects in the recrystallized silicon, it has a different amorphous/crystalline (A/C) roughness for each orientation, leaving pits in Si(110), and in Si(111) it produces two modes of recrystallization with different rates.The recently developed code MMonCa has been used to introduce a physically-based comprehensive model using Lattice Kinetic Monte Carlo that explains all the above singularities of silicon SPER. The model operates by having, as building blocks, the silicon lattice microconfigurations and their four twins. It detects the local configurations, assigns microscopical growth rates, and reconstructs the positions of the lattice locally with one of those building blocks. The overall results reproduce the (a) anisotropy as a result of the different growth rates, (b) localization of SPER induced defects, (c) roughness trends of the A/C interface, (d) pits on Si(110) regrown surfaces, and (e) bimodal Si(111) growth. It also provides physical insights of the nature and shape of deposited defects and how they assist in the occurrence of all the above effects.

Role of the Ge surface during the end of range dissolution

We investigated the structure of end-of-range (EOR) defects in Ge and the role played by the surface during their dissolution caused by annealing. Ge samples were amorphized with Ge+ ions at two different energies (30 and 100 keV) in order to induce, after solid phase epitaxial regrowth, the formation of EOR band at different depths. High resolution x-ray diffraction and transmission electron microscopy showed that the EOR population consists mainly on small defects and few dislocation loops lying on 〈001〉 planes. The deepest EOR defects are more stable during thermal annealing demonstrating the role of the surface during their dissolution.

Microstructural changes in silicon induced by patterning with focused ion beams of Ga, Si and Au

We use focused beams of Ga(+), Au(+) and Si(++) ions to induce local microstructural changes in single crystal silicon. The ions were delivered as single spot pulses into thin Si membranes that could subsequently be imaged and annealed in situ in a transmission electron microscope. For each ion, the focused ion beam implantation created an array of amorphous regions in the crystalline membrane. Annealing causes solid phase epitaxial regrowth to take place, but we show that the resulting microstructure depends on the ion species. For Ga(+) and Au(+), precipitates remain after recrystallization, while for Si(++), dislocation loops form around the periphery of each implanted spot. We attribute these loops to defects formed during solid phase epitaxial regrowth, with controlled placement of the loops possible.

Deep-amorphization and solid-phase epitaxial regrowth processes for hybrid orientation technologies in SOI MOSFETs with thin body

Local Deep-Amorphization (DA) and subsequent Solid-Phase Epitaxial Regrowth (SPER) are envisioned for the co-integration of devices with hybrid surface orientation. The impact of these processes on the electrical characteristics of p-channel MOSFETs with 20nm thick film and HfO2 gate insulator/metal gate along the 〈110〉 direction on a (110) substrate is studied. No deterioration of transconductance and subthreshold swing at the front or back channels was induced by DA/SPER. The transconductance enhancement for the front and back channels on (110) substrates reaches +200% and +230% gain, respectively. For these transistors, we also discuss the variation of the external resistance and their operation in double-gate mode.