Liquid Phase Epitaxial Regrowth Research Articles

Impact of Nanosecond Laser Annealing on the Electrical Properties of Highly Boron-Doped Ultrathin Strained Si0.7Ge0.3 Layers

The CMOS scaling beyond 10 nm technology node requires high active dopant concentrations in source/drain modules to minimize contact resistance. Pulsed laser annealing has been targeted by chip manufacturers as a future option to enhance the activation level inside highly doped SiGe:B and Si:P regions, mostly used in PMOS and NMOS transistor fabrication, respectively. Indeed, this annealing process allows reaching high temperatures (above melt threshold), locally (~100nm below the surface) and with extremely fast temperature ramp rates (>109 °C/s), so that high doping levels have been demonstrated both in pure Si and Ge [1]. In a recent study, structural investigations allowed identifying the best conditions to obtain fully strained and defect-free undoped SiGe layers by liquid phase epitaxial regrowth (LPER) [2]. In this work, we report an analysis on the activation of boron dopants in similar layers. In-situ boron-doped 30 nm thick pseudomorphic Si0.7Ge0.3 layers were grown on p-type bulk Si (100) by CVD. Three different boron concentrations were incorporated inside these layers: 7.8x1019 (A), 1.4x1020 (B) and 2.3x1020 cm-3 (C). By combining the boron chemical profiles with the corresponding Hall effect measurements (Hall scattering factor: 0.35), it was possible to estimate the activation rate inside the as-grown strained SiGe layers and the impact of the possible inactive dopants on the transport properties. From the lowest to the highest boron chemical concentration, we found activation rates of ~100%, ~80% and ~60%, with no significant carrier mobility degradation, even in the sample with the highest fraction of inactive dopants.The SiGe layers were subsequently laser annealed in a SCREEN-LT3100 platform operating at 308 nm (XeCl laser) with a pulse duration around 160 ns. The laser energy densities (ED) ranged from 1.20 to 2.40 J/cm2 in order to investigate all the various annealing regimes. Results obtained using several characterization techniques were combined to determine the laser annealing regimes, quantify surface roughness and assess the layers’ composition, strain and crystalline quality. These results were compared to electrical measurements performed to analyse the evolution of the electrical parameters as a function of the laser anneal conditions, particularly the activation rate.For the lowly-doped and fully activated layer (A), the sheet resistance increases rapidly at the melt threshold (1.5 J/cm2, cf. Fig. 1, red curve), concomitantly with the appearance of a partial relaxation inside the layer (Fig. 2) and the formation of extended defects. The defects may induce a local dopant deactivation, while strain relaxation can result in a modification of the transport properties of the material (modified Hall scattering factor). Both phenomena can be therefore responsible for the observed increase of the sheet resistance. In contrast, for laser EDs allowing complete melt of the layer (i.e. beyond 2.0 J/cm2), the sheet resistance decreases with increasing ED and full activation is achieved (Fig. 3, red curve) together with strain recovery (Fig. 2) and no observable defects.For the highly-doped and partially activated layer (C), partial relaxation also occurs at the melt threshold (Fig. 2). However, thanks to the strain compensation effect of the small boron atoms, the relaxation level is lower compared to the lowly-doped sample and more quickly recovered when increasing the ED (no defects observed at 1.95 J/cm2, Fig. 4). In addition, the sheet resistance is found to continuously decrease as a function of the ED (Fig. 1, blue curve) independently of the strain state of the structure. This suggests that, in addition to the previously described phenomena, the initially inactive dopants are progressively incorporated into substitutional positions by LPER. Indeed, when full melt and strain recovery is achieved, a 100% dopant activation is also observed (Fig. 3, blue curve). Characterizations made on sample B suggest a similar behaviour to that of sample C.Finally, further results will be reported from additional experiments aiming at (i) better understanding the impact of strain relaxation on dopant activation and (ii) optimizing the laser annealing process to avoid relaxation. These experiments include the use of a shorter laser pulse for the annealing of the strained SiGe layers, as well as the comparison with results obtained from fully-relaxed boron-doped SiGe annealed under similar laser conditions.Acknowledgements:This work was supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 871813 MUNDFAB.

Boosting Ge-Epi P-Well Mobility & Crystal Quality with Si or Sn Implantation and Melt Annealing

We investigated the effects of Sn, Si and C7 implantation into both P-well and N-well doped regions of Ge-epi on Si wafers after RTA and laser annealing, on crystal quality using XRD analysis and mobility using ALPro profiler of Active Layer Parametrics , which provides mobility and carrier concentration profiles at sub-nm resolution. SIMS analysis was also used for chemical depth analysis. XRD analysis shows improved Ge-epi crystallinity after >1.5J/cm2 laser melt annealing (liquid phase epitaxial regrowth). Since µ=1/ρqN where µ=mobility (cm2/volt-sec), ρ=resistivity (ohm-cm), q=charge of an electron and N=dopant concentration (cm3), if we assume qN=K a constant for these low dopant well regions then we can estimate change in mobility based on change in P-well or N-well resistance then compare to mobility measured by ALPro profiler. For the P-well cases doped with B=5keV at 1E13/cm2 dose for a retrograde P-well ~1E18/cm3 the Ge-epi Rs decreased to 1,600Ω/□ compared to Si at 3,400Ω/□ suggesting a hole mobility increase of 2.1x from 150cm2/V-s to 315cm2/V-s based on literature with actual measured Hall mobility of 465.2cm2/V-s, an increase of 3.1x. The 1.8J/cm2 laser melt anneal boosted P-well Hall mobility by 22% to 567cm2/V-s to a depth of 80nm and adding Sn implant improved mobility 91% to 889cm2/V-s and at a depth beyond 80nm mobility increases to 3,000cm2/V-sec. Si implant improved mobility by 43% to 667cm2/V-s to a depth of >100nm. For the N-well cases doped with P=40keV at 1E13/cm2 dose for a retrograde N-well ~1E18/cm3 the Ge-epi Rs increased to 2,000Ω/□ compared to Si at 1,600Ω/□ suggesting an electron mobility decrease of 0.8x to 216cm2/V-s rather than the expected increase of 3.3x from 270cm2/V-s for Si to 900cm2/V-s for Ge reported in the literature and expected N-well Rs of 485Ω/□. The actual Ge-epi N-well Hall mobility measured was 449cm2/V-s so only a 1.7x increase and nearly identical to the P-well mobility of 465cm2/V-s but the mobility drops off beyond a depth of 40nm. The 1.8J/cm2 laser melt anneal reduces N-well mobility to 191cm2/V-s but is uniform to a depth of 70nm. Adding Si implant had a slight decrease in mobility to 183cm2/V-s while Sn implant increases mobility to 280cm2/V-s uniformly to a depth >100nm. C7 (cluster-C) implant reduced N-well surface mobility to 50.3cm2/V-s to a depth of 30nm but then mobility increases 10x up to ~500cm2/V-s to a depth of 80nm and then drops to ~100cm2/V-s in the non-carbon N-well region as revealed by C-SIMS analysis to a depth of 110nm, therefore measuring mobility versus depth can be very critical in engineering surface and bulk mobility improvements based on chemical compositional changes in the Ge-epilayer. B-SIMS analysis shows retrograde P-well profile with 2E18/cm3 Rp at 50nm and Xj at 150nm also the Ge/Si epilayer interface. The laser melt flattens the B P-well profile to ~1E18/cm3 with a B pile-up at ~2E18/cm3 at the Ge/Si interface. C-SIMS analysis revealed only slight to no C diffusion even in the liquid Ge-melt phase while we observe 2-5% Si intermixing in the Ge-melt but no B nor P diffusion when C was present. Additional results for RTA anneals will be presented.

Boosting Ge-Epi P-Well Mobility & Crystal Quality with Si or Sn Implantation and Melt Annealing

We investigated the effects of Si, Sn and cluster-C implantation into both P-well and N-well doped regions of Ge-epi on Si wafers after laser annealing. XRD analysis shows improved Ge-epi crystallinity after >1.5J/cm2 laser melt annealing (liquid phase epitaxial regrowth) compared to sub-melt annealing (solid phase epitaxial regrowth). For the P-well case the Ge-epi Rs decreased to 1,600Ω/□ compared to Si at 3,400Ω/□ suggesting a hole mobility increase of 2.1x from 150cm2/V-s to 315cm2/V-s but actual measured Hall mobility was 650cm2/V-s to a depth of 60nm, an increase of 4.3x. The 1.8J/cm2 laser melt anneal with Si implant improved mobility uniformly to 700cm2/V-s to a depth of 100nm while Sn implant improved mobility to 900cm2/V-s from the Ge-epi surface to a depth of 70nm then increases to 3000cm2/V-s at a depth of 100nm. Measuring mobility depth profiles can be very critical in engineering surface and bulk mobility improvements which can be determined by chemical compositional changes in the Ge-epilayer especially for C where no liquid phase diffusion or movement could be detected.

(Invited) Smartphones: Driving Technology to More than Moore 3-D Stacked Devices/Chips and More Moore FinFET 3-D Doping with High Mobility Channel Materials from 20/22nm Production to 5/7nm Exploratory Research

Today smartphone ICs are driving technology to More Moore 3-D device scaling and More Than Moore 3-D stacked devices with >1.24B smartphones sold in 2014 accounting for >27% of all ICs. The expected increase in smartphone application processor (AP) demand in 2015 (Samsung Exynos 7 for Galaxy S6 and Apple A9 for iPhone 6s/7) is driving the rapid ramp to 14/16nm technology node 3-D FinFET devices at foundries, 3-D memory devices such as 128Gb NAND Flash memory devices with 32-layers and 3-D stacked chips for form factor with >40% package area saving. Intel was first to production with 3-D bulk-FinFET devices at the 22nm technology node in 2011 and reported their SOC version for Chinese low-end smartphone market. Intel’s 2nd generation bulk-FinFET devices at 14nm node was introduced in Aug 2014 with their SOC version to follow. In Sept 2012 iPhone 5 was first to incorporate Sony’s 8M pixel 3-D stacked backside CMOS image sensor for rear-facing camera. In April 2015 Samsung Galaxy S6 incorporated 14nm technology node 3-D FinFET devices in the Exynos 7 Octa application processor and first 3-D ePOP (embedded package on package) which stacks AP+DRAM (3Gb LPDDR3)+Flash(128/64/32Gb)+eMMC (embedded multi-media card)+controller saving 40% area and use Sony’s 16M pixel 3-D stacked back-side CMOS image sensor for rear-facing camera and 5M pixel RWB image sensor for front-facing camera. Apple will introduce the iPhone 6s/7 in Sept 2015 with A9 application processor using 3-D FinFET devices with Samsung/Foundry 14nm technology node and TSMC 16FF+. 10nm technology node is expected in 2016 with higher mobility SiGe or Ge channel material then 7nm node in 2018 and gate-all-around nano-wire by 5nm node in 2020. To understand 3-D FinFET doping and high mobility channel material this paper will first review the current doping and Fin/channel mobility enhancement techniques used for 22nm FinFET production by Intel for both high performance logic and SOC devices and the changes they made for their 2nd generation 14nm FinFET. 3-D 8o tapered FinFET S/D extension conformal doping was achieved with high tilt ion implantation at >45 degree. Highest retained dose and improved Fin sidewall line-edge-roughness (LER) on the atomic level can be realized with Hydrogen annealing surface passivation. High dopant activation is also achieved with advanced annealing SPE techniques of amorphous implanted junctions. Other 3-D dopant methods such as plasma implantation, knock-in dopant and deposition doping with diffusion including monolayer doping were not successful due to poor dopant activation and severe surface dopant loss. FinFET channel mobility enhancement at 22nm node used (511) plane taper Fin with 55% eSiGe S/D compressive strain for PMOS and amorphous implant SPE residual stacking fault defect S/D tensile stressor for NMOS. For 14nm node taller vertical Fins without the (511) taper and still 55% eSiGe S/D for PMOS and now eS/D for NMOS which is full of stacking fault defects. At the 10nm or 7nm node direct higher mobility Fin/channel material (SiGe, Ge or III-V) is expected to be introduced followed by exploratory research of gate-all-around nanowire for 5nm technology node. 25% SiGe to 100% Ge high mobility Fin-channel material on Si wafers will be realized by traditional gas/vapor phase epitaxial growth techniques by chemical vapor deposition (CVD) in blanket, selective growth including aspect ratio trapping, Ge condensation or an alternative liquid phase epitaxial (LPE) regrowth of an amorphous material layer by melt solidification. At 5nm node Si, SiGe or Ge nano-wire gate-all-around devices. Finally a discussion on dopant activation in high mobility Ge and SiGe material with low junction leakage.

III–V semiconductor nanocrystal formation in silicon nanowires via liquid-phase epitaxy

Direct integration of high-mobility III–V compound semiconductors with existing Si-based complementary metal-oxide-semiconductor (CMOS) processing platforms presents the main challenge to increasing the CMOS performance and the scaling trend. Silicon hetero-nanowires with integrated III–V segments are one of the most promising candidates for advanced nano-optoelectronics, as first demonstrated using molecular beam epitaxy techniques. Here we demonstrate a novel route for InAs/Si hybrid nanowire fabrication via millisecond range liquid-phase epitaxy regrowth using sequential ion beam implantation and flash-lamp annealing. We show that such highly mismatched systems can be monolithically integrated within a single nanowire. Optical and microstructural investigations confirm the high quality hetero-nanowire fabrication coupled with the formation of atomically sharp interfaces between Si and InAs segments. Such hybrid systems open new routes for future high-speed and multifunctional nanoelectronic devices on a single chip. Open image in new window

A low-cost method of forming epitaxy SiGe on Si substrate by laser annealing

In this letter, a low-cost alternative for forming high grade silicon germanium (SiGe) by a laser-induced crystallization of an amorphous Ge layer deposited directly on Si+ preamorphized implantation Si substrate is demonstrated. The results show that a fully strained epitaxial SiGe layer on the Si (100) substrate can be obtained at laser fluence above the epitaxial threshold. This is due to a liquid-phase epitaxial regrowth process of the laser annealing induced melted layer. Below the epitaxial threshold, polycrystalline SiGe is formed due to explosive recrystallization process. Simultaneous boron activation is achieved with the SiGe formation, a result due to the high temperature induced by the laser annealing.

Depth distribution of B implanted in Si after excimer laser irradiation

Liquid phase epitaxial regrowth following laser melting significantly modifies the concentration of point defects in Si, such that peculiar depth distribution of subsequently implanted B arises. At room temperature, a large fraction of B atoms, ∼15%, implanted in laser preirradiated Si, migrate up to the original melt depth. During high temperature annealing, the nonequilibrium diffusion of B is reduced to ∼25% of that measured in unirradiated Si. Both these phenomena are conclusively attributed to an excess of vacancies, induced in the lattice during solidification and to their interaction with impurities and dopant.

Study of AlGaInP multiquantum-well/double heterostructure light-emitting diodes with In-added GaP window layer regrown by antimony-based liquid phase epitaxy

The characteristics of surface-emitting AlGaInP multiquantum-well (MQW) and double heterostructure (DH) light-emitting diodes (LEDs) with a GaP window layer regrown by a GaP source melt with the addition of indium in the liquid phase epitaxy (LPE) system are studied. Using antimony in the source melt instead of gallium eliminates the phenomenon of melt back at the top layer of the LED during the LPE regrowth process. Meanwhile, adding In and Zn to the source melt significantly increases the GaP growth rate and effectively reduces residual melt during the regrowth process. Thus, the AlGaInP LED with a Zn-doped GaP window layer regrown by In being added, Sb-based LPE exhibits a lower turn-on voltage and higher light output power than that without the regrown GaP window layer. However, the emission peak wavelength of the MQW LED shifts a little after the LPE regrowth process. The DH LED does not shift. Thus, the DH structure is more suitable than the MQW structure for the LPE regrowth process of GaP.

The Comparisons between GaP Window Layers of Double-Heterojunction Light-Emitting Diodes using Various Dopants and Source Melts Regrown by Indium-Addition Liquid Phase Epitaxy

The p-GaP window layer of surface-emitting InGaAlP/InGaP double heterojunction (DH) light-emitting diodes (LEDs) regrown using Ga and Sb source melts by In-addition liquid phase epitaxy (LPE) system is studied in this work. The Sb metal is introduced into the source melt in order to eliminate the phenomenon of melt back at dice edges, which occurs when using a Ga source melt during the LPE regrowth process. The GaP window layers regrown from pure Sb or Sb–In melt are free from antimony and are characterized by energy dispersive analysis of X-ray (EDAX). The solubility of GaP at different source melts is also investigated by the weight loss method. The GaP window layer with Zn doping is adopted in view of the ohmic contact of the device whose top layer must have a high concentration, and the p-type impurity of Zn with a high distribution coefficient is more suitable than Mg for doping atoms. The incorporation of In enormously enhances the growth rate during the regrowth process. By using the GaP window layer grown by In-addition LPE using a Sb source melt, the LEDs have a high breakdown voltage and maintain the same order cut-in voltages as the original LED (without a GaP window layer). The LEDs with a GaP window layer have better light output power performances than those without a GaP window layer.

Effect of Laser Thermal Processing on Defect Evolution in Silicon

AbstractLaser Thermal Processing (LTP) involves laser melting of an implantation induced preamorphized layer to form highly doped ultra shallow junctions in silicon. In theory, a large number of interstitials remain in the end of range (EOR) just below the laser-formed junction. There is also the possibility of quenching in point defects during the liquid phase epitaxial regrowth of the melt region. Since post processing anneals are inevitable, it is necessary to understand both the behavior of these interstitials and the nature of point defects in the recrystallized-melt region since they can directly affect deactivation and enhanced diffusion. In this study, an amorphizing 15 keV 1 x 1015/cm2 Si+ implant was done followed by a 1 keV 1 x 1014/cm2 B+ implant. The surface was then laser melted at energy densities between 0.74 and 0.9 J/cm2 using a 308 nm excimer-laser. It was found that laser energy densities above 0.81 J/cm2 melted past the amorphous-crystalline interface. Post-LTP furnace anneals were performed at 750°C for 2 and 4 hours. Transmission electron microscopy was used to analyze the defect formation after LTP and following furnace anneals. Secondary ion mass spectrometry measured the initial and final boron profiles. It was observed that increasing the laser energy density led to increased dislocation loop formation and increased diffusion after the furnace anneal. A maximum loop density and diffusion was observed at the end of the process window, suggesting a correlation between the crystallization defects and the interstitial evolution.

Threshold reduction in strained-layer InGaAs/GaAs quantum well lasers by liquid phase epitaxy regrowth

When liquid phase epitaxy regrowth at 780°C for 2 h is applied to the samples after molecular beam epitaxy, a decrease of the threshold current density in strained InGaAs/GaAs quantum well lasers by a factor of 3 to 4 is obtained. We suggest that this improvement is attributed to the reduction of nonradiative centers associated with deep levels at the three regions of the active region, the graded layer and the cladding layer. Indeed, a significant reduction of deep center densities has been observed by using minority and majority carrier injection deep level transient spectroscopy measurements.

Strain compensation in Si 1− x− yGe xC y layers prepared by ion implantation and excimer laser annealing

Si 1− x Ge x , Si 1− y C y and Si 1− x− y Ge x C y layers, about 200 nm thick, with x≈0.1 and y≈0.01, have been synthesized by multiple energy ion implantation and liquid-phase epitaxy regrowth using excimer laser pulses around 1 J cm −2. Secondary ion mass spectrometry and Rutherford backscattering depth profilings and Fourier transform infrared (FTIR) absorption show that, using selected conditions, both SiC precipitation and carbon diffusion can be avoided, while germanium is uniformly redistributed over the molten layer. Raman spectroscopy and FTIR confirm that C atoms are located in substitutional lattice sites. However, estimations of the tetragonal expansion using Raman scattering and channeling angular scans in oblique incidence, reveal an incomplete incorporation of carbon in substitutional positions and, consequently, a partial strain compensation in the ternary alloy.

Buried heterostructure AlGaAs photonic devices fabricated by low temperature mesa melt etching and regrowth

Low temperature melt-etching and liquid phase epitaxial regrowth was used to fabricate buried heterostructure laser diode arrays, optical amplifiers and active waveguide branches. 12 element laser diode arrays emitted 1 W total optical power at 1.2 A (room temperature, continuous wave) at 980 nm. 6 dB fiber to fiber optical gain was obtained in buried heterostructure optical amplifiers operating at 830 nm. Active branching waveguides are shown to allow the compensation of 3 db branching losses.

Transmission Electron Microscopy Studies of Kr+-Implanted Silicon

The structure and the depth distribution of radiation damage caused in (111) Si by high-dose krypton implantations (E; = 150 keV, T; = RT, D1 = 5 x 1015 , D2 = 1 x 1016 and D3 = 5 x 1016 cm z ) have been investigated using techniques of transmission electron microscopy. Formation of secondary defects (Kr bubbles and microtwins) on subsequent different annealing procedures, i.e. during solid phase epitaxial regrowth of damaged layers by conventional furnace heating and liquid phase epitaxial regrowth by applying laser pulses is compared and discussed. PACS numbers: 61.16.Bg, 61.72.Ff, 61.72.Qq, 61.72.Tt, 68.35.Fx, 81.40.Gh

Liquid phase epitaxial regrowth on sulfide-passivated Ga1−xAlxAs

We demonstrate that Na2S passivation allows liquid phase epitaxial regrowth of Ga0.5Al0.5As upon Ga1−xAlxAs (0.3≤x≤0.8) after air exposure. Large aluminum concentrations require concentrated (2.4 M) sulfide solutions. We have also studied the Ga1−xAlxAs etching rate by Na2S. For large sulfide concentrations or small aluminum concentrations, the etching process stops after some time. These two phenomena are correlated because both of them require the presence on the surface of a stable protective layer. This can be understood by assuming the existence at the surface of two competing mechanisms: etching and passivation.

A Low-Threshold 1.3 µm GaInAsP/InP Flat-Surface Circular Buried Heterostructure Surface Emitting Laser

The liquid phase epitaxy regrowth process of the GaInAsP/InP flat-surface circular buried heterostructure (FCBH) has been improved and a perfectly buried microsize active region of 8 µm in diameter and 1.2 µm in depth was realized with good reproduclbility. Low-threshold (Ith=52 mA) lasing operation of a 1.3-µm-range FCBH surface emitting laser with a pair of dielectric micromirrors was achieved in a pulsed condition at 0°C.

High speed operation of very low threshold strained InGaAs/GaAs double quantum well lasers

Very low threshold current strained In0.2Ga0.8As/GaAs double quantum well buried-heterostructure lasers have been fabricated by a hybrid metalorganic chemical vapor phase deposition and liquid phase epitaxy regrowth technique. The modulation bandwidths were compared in lasers of different active strip widths, cavity lengths, and facet reflectivities in order to achieve modest high-modulation bandwidth at low operating current. A 5 GHz 3 dB modulation bandwidth is demonstrated at a current of 2.1 mA in a laser with a threshold current of 0.5 mA.

Transverse Mode Characteristics of a DBR-Surface Emitting Laser with Buried Heterostructure

Distributed Bragg reflector (DBR)-surface emitting lasers (SELs) with buried heterostructure (BH) are fabricated with the combination of metal-organic chemical vapor deposition (MOCVD), electron cyclotron resonance (ECR) dry-etching and liquid phase epitaxial (LPE) regrowth techniques. Low threshold and stable fundamental lateral-mode characteristics are realized by the optimum design of the cavity diameter and refractive indices. Other important characteristics such as polarization characteristics, series resistance and thermal resistance are also discussed.

Resonant tunneling of two-dimensional electrons into one-dimensional subbands of a quantum wire

Liquid phase epitaxy regrowth on the edge of in situ cleaved substrates is employed to create a vertical two-dimensional electron gas in a double-barrier tunneling potential. Resonant tunneling of two-dimensional electrons through one-dimensional quantum wire subbands is unambiguously identified by negative differential resistance features in the transport characteristics. The bias positions of these features agree with simple tunneling theory estimates based on conservation laws and the calculated band alignment in the structure under bias.

Liquid phase epitaxy regrowth of two-dimensional electron gas on GaAs patterned by in situ meltback

Selective in situ meltback of V-groove channels followed by liquid phase epitaxial regrowth of a modulation-doping AlGaAs layer is used to produce a two-dimensional electron gas on a patterned GaAs substrate. The in situ meltback patterning of the substrate forms channels made up of definite crystallographic planes. Characterization of the two-dimensional electron gas by magnetotransport measurements in a tilted magnetic field at 4.2 K confirms that the electron gas exists on all the planes that comprise the channels. Since the regrowth surface is exposed neither to air nor chemical etchants, this technique holds promise of producing high quality interfaces on patterned GaAs.