Cross-sectional Transmission Electron Microscopy Analysis Research Articles

Structural changes in the nano-oxide layer with annealing in specular spin valves

We investigated microstructural changes in a nano-oxide layer (NOL) with annealing in specular spin valves (SVs) by cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy analysis. In the SV annealed at high temperature of 400 °C, an increase in thickness and a local breakdown of the NOL were observed. This local coarsening of the NOL is closely related to the formation of Mn oxides in the oxide-rich part of the NOL through Mn diffusion. Thus, the chemical structure of the NOL changes to the structure with Mn oxide-rich content after annealing.

Formation of silicon nano-dots in luminescent silicon nitride

Strong room-temperature photoluminescence (PL) was observed in the hydrogenated silicon-rich silicon nitride (a-SiNx:H) thin films grown by plasma-enhanced chemical vapor deposition technique. After the thermal annealing process, silicon nano-dots were clearly observed in the Si-rich a-SiN0.56:H thin films. From the X-ray photoelectron spectroscopy (XPS), the Si 2p peak shows distinct SiSi4 bonds after thermal annealing indicated the existence of Si clusters. In addition, the existence of nano-crystallized (nc) Si dots was revealed from the image of high-resolution cross-section transmission electron microscopy (XTEM) analysis. The PL spectra exhibited extensive red-shift from 1.97 to 1.33eV along with the annealing temperature suggests that, the Si nano-dot related luminescence dominates in the luminescence centers of the a-SiN0.56:H layer. The reveal of Si nano-dots related luminescence and the high density of Si nano-dots suggest that the a-SiN0.56:H layer is suitable for the stable light-emitting device.

Local composition analysis of SiC microstructures formed by ion projection in silicon using energy filtered TEM in combination with FIB specimen preparation

Buried silicon carbide (SiC) microstructures with lateral dimensions in the μm range were formed by high-dose projection of 1.5 MeV C 2+ ions in Si(100) at different doses and temperatures and subsequent annealing for 10 h at 1250 °C. Sections of individual SiC microstructures were prepared for cross-sectional transmission electron microscopy (TEM) analysis using a focused ion beam (FIB). Besides the possibility to select an individual microstructure, the FIB technique has the advantage of producing specimen foils of uniform thickness. Therefore, it was possible to map the carbon concentration of microstructures by energy filtered TEM (EFTEM) using the C K absorption edge without the need of any sample thickness correction. Local overstoichiometric (>50%) carbon concentrations are shown to be correlated to the formation of an amorphous phase in the SiC and to significant swelling visible at the Si wafer surface 2 μm above.

Atomic-layer deposition of wear-resistant coatings for microelectromechanical devices

Friction and wear are major concerns in the performance and reliability of microelectromechanical systems (MEMS) devices employing sliding contacts. While many tribological coating materials are available, most traditional surface coating processes are unable to apply conformal coatings to the high aspect ratio (height/width) structures typical of MEMS devices. We demonstrate that thin, conformal, wear-resistant coatings can be applied to Si surface-micromachined structures by atomic-layer deposition (ALD). For this demonstration, we apply 10-nm-thick films of Al2O3 using a binary reaction sequence with precursors of trimethyl aluminum and water. Deposition is carried out in a viscous flow reactor at 1 Torr and 168 °C, with N2 as a carrier gas. Cross-section transmission electron microscopy analysis shows that films are uniform to within 5% on MEMS device structures with aspect ratio ranging from 0 to >100. Films are stoichiometric Al2O3, with no evidence of contamination from other species, and are amorphous. Preliminary friction and wear data show that ALD films have promising properties for application to MEMS devices.

Epitaxial cobalt silicide formation using a Co/TiSix bilayer on Si (1 0 0) by sputtering

Annealing a Co/Ti bilayer by sputtering on the Si substrate offers higher probability of epitaxial growth and less Si consumption than annealing of a single Co layer on the Si substrate. Nevertheless, the Co/Ti bilayer epitaxy method does not solve the Si consumption problem satisfactorily. In this communication, a new CoSi2 epitaxial growth technique of annealing a Co/TiSix bilayer on Si (100) is investigated for the first time. Cobalt silicide thin films obtained using the Co/TiSix bilayer have been analyzed using X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) techniques to identify the phases and to investigate the surface and interface morphologies and the chemical composition. The XRD spectra show the epitaxial growth of CoSi2 layer with (200) crystallographic orientation on the Si (100) substrate for a Co/TiSix bilayer while the Co–Ti–Si spinel phase is detected over the annealing temperature range of 400–600 °C. The AES analysis indicates that native oxides on the silicon substrates are removed by Ti at the beginning of RTA and Co diffuses inward so that an epitaxial CoSi2 layer could form. The AFM micrographs show smooth surface and the cross-sectional high-resolution TEM analysis reveals that the layer is composed of the CoSi2 epi-layer formed on the Si substrate. Also it is found that Si consumption during silicidation annealing for the Co/TiSix bilayer formed by sputtering has been significantly reduced compared with that for the Co/Ti bilayer formed by sputtering.

‘3-Dimensional’ TEM silicon-device analysis by combining plan-view and FIB sample preparation

Cross-sectional transmission electron microscopy (TEM) analysis has become routinely used in semiconductor industry to support failure and yield analysis. Plan-view transmission electron microscopy analysis however is much less frequently performed. In this paper it is illustrated that plan-view transmission electron microscopy analysis can add valuable information in yield analysis studies, especially when crystal defects are involved. ‘3-Dimensional’ information can be obtained by combining cross-sectional transmission electron microscopy analysis with plan-view analysis. If the available material is limited, it can become a difficult choice whether to go for a cross-sectional or a plan-view analysis. Therefore it was explored if a cross-sectional specimen could still be made out of a plan-view specimen, using the plan-view analysis to locate the failure site precisely. This has recently been successfully done using the in-situ lift-out technique in the focused ion beam machine.

The evolution of cavities in Si co-implanted with Si and He ions 1

Different levels of damage were first introduced into CZ p-type Si (100) by the implantation of 80 keV Si ions to different doses ranging from 10 14 to 5×10 15 cm −2. All the Si implanted samples together with virgin Si were then subjected to 1 MeV 3He ion implantation to the same dose of 5×10 16 cm −2. Cross-sectional transmission electron microscopy (XTEM) and nuclear reaction analysis (NRA) measurements were used to quantify the evolution of He-cavities and He desorption from the cavities after subsequent annealing, respectively. Our results show that the presence of high level of damage induced by Si implants tends to inhibit the growth of He-cavities and increase the rate of He desorption. The results are tentatively interpreted on the basis of the evolution of Si induced damage upon annealing and its interaction with He-cavities.

Si adatom diffusion on Si (100) surface in selective epitaxial growth of Si

The growth temperature dependence of Si adatom diffusion on Si (100) surface was systematically investigated in a cold wall ultrahigh vacuum chemical vapor deposition system. Si epitaxial layers were selectively grown on local oxidation of silicon patterned Si substrates. By cross-sectional transmission electron microscopy analysis, the increase in Si growth rate on the Si (100) surface near the edge of (311) facet was observed at various growth temperatures. This can be understood as a consequence of the mass transport from the sidewall (311) facet to the top (100) surface. Based on a simple diffusion model, the surface diffusion lengths of Si adatoms along the [110] direction were estimated to be about 70, 140, and 200 nm at 550, 600, and 650 °C, respectively. The calculated activation energy of 1.4 eV for diffusion of Si adatoms from the temperature dependence of the diffusion length was relatively higher than those in previous reports obtained under ultrahigh vacuum environment. This difference was discussed in terms of the discrepancy in the surface states by hydrogen adsorption on the Si surface.

Epitaxial Si1-xGex Films and Superlattice Structures Grown by CVD for Infrared Photodetectors

AbstractIntegration of photodetectors with high responsitivity in the near infrared (1.3-1.55 μm) on standard Si electronic circuits is important for a variety of applications in the field of on-chip, local area and long haul optical communications. In this work we report on a detailed structural and optical characterization of epitaxial Si1-xGex films and Si1-xGex /Si multilayers grown by chemical vapor deposition on (100) Si wafers. Cross-sectional transmission electron microscopy analyses show that metastable strained Si1-xGex films of few nanometer with x>40% can be deposited at low growth temperature and pressure. Absorption measurements on these films demonstrate the extension of the photo-response to 1.55 μm. Using these films as active layers Schottky integrated photodetectors have been fabricated.

Minimisation of spanning dislocations in the crystallisation of deep amorphous silicon wells through the alignment of volume edges with fast growth directions

Deep amorphous silicon wells were created in a crystalline substrate by MeV ion-implantation. The sides of the rectangular amorphous volume were aligned normal to fast growth directions. Upon heating at elevated temperatures crystallisation proceeded inwards at both lateral and vertical interfaces. The progress of the epitaxy and the number and nature of the secondary structures formed were investigated through both plan-view and cross-sectional transmission electron microscopy analyses. The number of spanning dislocations was significantly reduced in this aligned configuration compared with the situation where the sides of the well were not coincident with crystallographic directions. The reduction in the number of spanning dislocations allowed a more complete characterisation of other defects which arise uniquely from the crystallisation of volumes in this geometry.

Effect of Low Temperature Annealing Prior to Laser Annealing of an Ultrashallow n + / p Junction

The effect of low temperature annealing prior to laser annealing on junction characteristics was investigated. A sample annealed at 400°C for 10 min before laser annealing showed a significant reduction in defect density which, in turn, improved junction characteristics such as low resistance, low junction leakage current, and less phosphorus deactivation during subsequent high temperature annealing. Cross-sectional transmission electron microscopy analysis confirmed that defects induced by plasma doping were effectively removed by preannealing followed by laser annealing. A preannealing prior to a laser annealing process represents a promising technology for future ultrashallow junction applications. © 2002 The Electrochemical Society. All rights reserved.

Structural investigations in the formation of the epitaxial CoSi 2 layer using a Co/TiSi x bilayer on Si (1 0 0)

Epitaxial cobalt silicide layers were formed on the p-type Si (1 0 0) by co-sputtering of Ti and Si as the interlayer, using the Co/TiSi x bilayer structure and subsequent rapid thermal annealing (RTA) at high temperatures. The cobalt silicide films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and atomic emission spectrometry (AES) to identify the phases, surface and interface morphologies and the chemical compositions. The XRD analysis results show that the epitaxial CoSi 2 layer with a (2 0 0) crystallographic orientation has been successfully grown on the Si (1 0 0) substrate. Effects of the variation of the d.c. power of the sputtering process and the annealing temperature (up to 800 °C) during RTA were investigated. The presence of a Co–Ti–O spinel phase was detected during silicidation in the annealing temperature range 400–600 °C. The AFM micrographs of the surface of the annealed Co/TiSi x bilayer structure show that the RMS roughness increased sharply up to 600 °C and stabilized thereafter at a moderate value of 8.9 nm, implying the formation of a relatively smoother surface in spite of high-temperature annealing. The AES analysis results indicate that native oxide on the Si substrate are removed by Ti at the beginning of RTA and Co diffuses to the clean surface of the Si substrate so that an epitaxial CoSi 2 layer can form. The cross-sectional high-resolution transmission electron microscopy (HRTEM) analysis further reveals the epitaxial relationship between the CoSi 2 layer and the Si (1 0 0) substrate.

Effects of amorphizing species’ ion mass on the end-of-range damage formation in silicon

The effects of preamorphizing ion mass on the end-of-range (EOR) damage and subsequent enhanced diffusivity have been investigated. Amorphizing silicon with implants of 22 keV 28Si+, 32 keV 73Ge+, 40 keV 119Sn+, and 45 keV 207Pb+ provided the mass comparisons. Cross-sectional transmission electron microscopy analysis showed that the amorphous layer depths were approximately 400 Å. After postimplantation annealing at 750 °C for 30 min, plan-view transmission electron microscopy (PTEM) revealed that increasing the ion mass decreased the defect size and density. Quantitative analysis of PTEM results also showed that increasing ion mass decreased the population of interstitials trapped in the EOR. Secondary ion mass spectrometry depth profiles of grown-in boron marker layers showed that increasing the ion mass decreased the time average diffusivity enhancements of boron (〈DB〉/DB*).

High-energy (MeV) Al and B ion implantations into 4H-SiC and fabrication of pin diodes

High-energy (MeV) implantation of Al+ or B+ into 4H-SiC epilayers has been investigated. A 3 μm deep pn junction was formed by multiple-step Al+ or B+ implantation with implantation energies up to 6.2 or 3.4 MeV, respectively. Rutherford backscattering channeling and cross-sectional transmission electron microscopy analyses have revealed residual damages in the implanted layers even after high-temperature annealing at 1600–1800 °C. Nevertheless, high electrical activation ratios over 90% have been achieved for both Al+- and B+-implanted layers by annealing at 1800 °C. Mesa pin diodes with a 15-μm-thick i layer formed by MeV implantation have exhibited high breakdown voltages of 2860–3080 V. The reverse characteristics of diodes have been substantially improved by increasing annealing temperature up to 1800 °C. The diode performance is discussed with the results of deep level analyses near the junctions.

Interfacial reactions and failure mechanism of Cu/Ta/SiO 2/Si multilayer structure in thermal annealing

The integrity of Cu/Ta/SiO 2/Si multilayer structure under nitrogen thermal annealing has been examined by sheet resistance measurement, X-ray diffraction, scanning electron microscopy, secondary ion mass spectroscopy, Rutherford backscattering spectrometry and cross-section transmission electron microscopy analysis. According to electrical measurement it was found that Ta diffusion barrier could preserve the integrity of the Cu/Ta/SiO 2/Si structure up to 650 °C in N 2 for 35 min. There are two causes by which the Cu/Ta/SiO 2/Si structure became degraded. One is the out diffusion Ta atoms towards the Cu film. The other factor is the formation of Cu, Ta and Cu–Ta oxide. Hence, Cu penetration is not the only reason to cause the failure; oxidation, phase transformation and interfacial reactions are also associated problems during thermal annealing.

Stress-induced failure of Si3N4 metal-insulator-metal capacitors fabricated by plasma enhanced chemical vapor deposition

Microstructural and in turn functional failure of Si3N4 metal-insulator-metal (MIM) capacitors fabricated by plasma enhanced chemical vapor deposition was investigated using cross-sectional transmission electron microscopy and residual stress analysis. As a result it was manifested that the failure of the Si3N4 MIM capacitors was caused by microvoids formed over the Si3N4 dielectric and the TiN interlayer adopted for the use of diffusion barrier. The microvoid having occurred at the MIM capacitor with very thin Si3N4–less than 50 nm thick in the present article caused it to leak out much of the current to the extent of a few microamperes even at bias of 3 V. The microvoid, one of the important constraints in the fabrication of high capacitive Si3N4 MIM capacitors, was explained by the residual stress of the constituent layers. The stress analysis showed that the absolute stress normalized by the thickness of the Si3N4 layer should be less than 30 MPa/nm to avoid microvoiding. In this research we noted that the stress state of not only the dielectric but also the interlayer should be taken into account for the successful design of high capacitive Si3N4 MIM capacitors.

TEM and SEM studies of microstructural transformations of thin iron films during annealing

High-temperature induced transformations of the bulk structure as well as the surface and bulk morphology of thin polycrystalline iron films have been investigated using a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The polycrystalline Fe films were evaporated onto a quartz substrate at 78K under UHV conditions and then annealed in situ within a temperature range 330–1000K. The morphology of both the surface and bulk Fe films have been observed ex situ after successive annealing steps of the Fe film using SEM and cross-sectional TEM analysis, respectively. An anisotropic polycrystalline bulk morphology accompanied by a fine-grained surface and the formation of microvoids was observed after heating the Fe film at 330K. The iron films annealed at higher temperatures, exhibit large grain size surface morphology. Polycrystalline Fe film transformation occurred at an annealing temperature of 700–1000K, resulting in the formation of a columnar microstructure of the bulk phase. The crystallites formed as a result of annealing at 1000K revealed a monocrystalline structure characterised by low-index Fe bcc diffraction patterns.

The Influence of Low Temperature Pre-Annealing on the Defect Removal and the Reduction of Junction Depth in Excimer Laser Annealing

AbstractThe influence of low temperature pre-annealing on p+/n ultra-shallow junction was investigated. An ultra-shallow junction was formed by means of B2H6 plasma doping at an energy of 500V. The activation was performed by excimer laser annealing. To study the low temperature annealing prior to laser annealing, furnace annealing at 300°C∼500°C for 5min was performed. Compared with control samples with no pre-annealing, the low temperature preannealing significantly improves junction characteristics, resulting in a reduction of junction depth and a lower leakage current density. A cross-sectional transmission electron microscopy analysis confirmed the lower defect density, which explains the lower leakage current. By optimizing the process conditions, excellent electrical characteristics of the p+/n ultra-shallow junction such as a junction depth of 28nm and a sheet resistance of 250Δ/sq. can be obtained.

Microstructural characterization of the NdBa 2Cu 3O 7− δ islands fabricated by liquid phase epitaxy

NdBa 2Cu 3O 7− δ (NBCO) islands were grown on MgO substrate by liquid phase epitaxy (LPE). The microstructures of NBCO islands ranging from 4.5 to 48 μm in lateral length were investigated in detail by cross-sectional transmission electron microscopy and energy-dispersive X-ray analysis. Most islands exhibit epitaxial relationship, {0 0 1} NBCO //{0 0 1} MgO , which will lead to the growth of c-axis epitaxial NBCO film. It was revealed that the NBCO islands grow laterally and some Ba–Cu–O fluxes are entrapped between NBCO and MgO substrate. The growth mechanisms of the NBCO islands by LPE were discussed in terms of two growth modes. One is coarsening, which results in no grain boundary, the other is coalescence. Furthermore, the formation of flux-entrapping was discussed.

Defect formation due to the crystallization of deep amorphous volumes formed in silicon by mega electron volt (MeV) ion implantation

Solid-phase epitaxy was examined in deep amorphous volumes formed in silicon wafers by multi-energy self-implantation through a mask. Crystallization was effected at elevated temperatures with the amorphous volume being transformed at both lateral and vertical interfaces. Sample topology was mapped using an atomic force microscope. Details of the process were clarified with both plan-view and cross-sectional transmission electron microscopy analyses. Crystallization of the amorphous volumes resulted in the incorporation of a surprisingly large number of dislocations. These arose from a variety of sources. Some of the secondary structures were identified to occur uniquely from the crystallization of volumes in this particular geometry.