Bamboo-like Grain Research Articles

Comparison of Cu electromigration lifetime in Cu interconnects coated with various caps

Electromigration in Cu Damascene lines with bamboo-like grain structures, either capped with Ta/TaN, SiNx, SiCxNyHz layers, or without any cap, was investigated. A thin Ta/TaN cap on top of the Cu line surface significantly improves electromigration lifetime when compared with lines without a cap and with lines capped with SiNx or SiCxNyHz. The activation energy for electromigration increased from 0.87 eV for lines without a cap to 1.0–1.1 eV for samples with SiNx or SiCxNyHz caps and to 1.4 eV for Ta/TaN capped samples.

Microstructure and He Bubble Effects on Al-Cu Thin Films

ABSTRACTThe effects of film morphology (mosaic- or bamboo-like grain structures) and of He bubbles on the redistribution of Cu, as well as on the formation of Al-Cu precipitates in 200 nm thick Al/SiO2 films similar to microelectronic device interconnects, are investigated using Rutherford backscattering spectrometry, elastic recoil detection analysis and transmission electron microscopy. As-deposited and pre-annealed Al films were implanted with Cu and/or He ions forming concentration profiles located 100 nm below the surface and with peak concentrations of about 3 at.%. It is shown that grain boundaries and/or He bubbles can affect the vacancy fluxes inside the grains and reduce or even inhibit the Cu redistribution as well as the nucleation and growth of θ and θ′ Al-Cu precipitates during post-implantation annealings at temperatures from 473 to 553 K. It is also shown that mosaic-like grain structures allow the control of grain size distribution within the 25 to 1500 nm size range, thus providing an additional microstructure engineering tool to improve device reliability against electromigration failures.

Electromigration of Aluminium through Quasi Bamboo-Like Grain Blocked Silicide Interconnects

MoSi 2 interconneets between electrical aluminium contact pads were exposed to a high direct current density of 1 MA cm -2 during 2000 hours. Thermal annealing of the interconnects prior to the experiment generated grains of almost the width of the line, providing for bamboo-like grain blocked polycrystalline clusters along the line acting as migration stopping sites. Aluminium migration out of the cathode contact pad is observed with pronounced precipitations on the interconnect side walls. SEM and EDX are applied to identify sites and nature of the electromigration product.

Electromigration of Aluminium through Quasi Bamboo-Like Grain Blocked Silicide Interconnects

Electromigration of Aluminium through Quasi Bamboo-Like Grain Blocked Silicide Interconnects

Linear analysis of electromigration-induced void instability in Al-based interconnects

Void shape changes induced by electromigration pose reliability problems in Al-based interconnects. Recent observations have shown that a rounded void sometimes collapses to a transverse slit in an interconnect with bamboo-like grain structure. This article provides a linear stability analysis for a circular void that is only partially conductive in an otherwise infinite conductive medium. The relation between the inner conductivity (i.e., the conductivity of the medium in the void) and the critical remote electric field intensity, Ecr, for the linear stability of the void is established. It is proven that when the inner conductivity becomes zero, Ecr goes to infinity, and we can look upon the inner conductivity of a vacuum void as zero. That is why the vacuum circular void is linearly stable. It is also shown that when the inner conductivity is very small, the stability of a void is sensitive to it. From the computational results, we know that if the inner conductivity is 0.1% of that outside the void, the Ecr is only twenty times of that for the dislocation loop case.

Internal friction of powder metallurgy (P/M) and ingot metallurgy (I/M) Al-Fe alloys at elevated temperature

Low-frequency internal friction measurements have been carried out on the powder metallurgy (P/M) and ingot metallurgy (I/M) Al–Fe alloy. Internal friction peaks can be seen at about 820–830 K and 530–620 K in the I/M alloys, but not in the P/M alloys. The former is probably due to the grain-boundary relaxation and the latter to recrystallization. Activation energies for the grain-boundary relaxation are estimated to be in two ranges: one is between 100 and 130 kJ mol−1 and the other is between 200 and 210 kJ mol−1, according to the iron content and fabrication processes. The high activation energy is given by the low iron content I/M alloys having a bamboo-like grain. It is suggested that such a difference in the activation energy is due to whether or not the solute iron diffuses into the grain boundary to lower the grain boundary energy.

Electromigration in 0.25 μm wide Cu line on W

Electromigration in isolated 0.25–1. 0 μm wide pure Cu fine lines has been investigated using both resistance and edge displacement techniques in the sample temperatures range 221–394°C. The Cu lines, sandwiched with a top and bottom Ta layer, were 200 μm long and were connected to underlying W bars on each end of the Cu line. Transmission electron microscopy revealed that the microstructures of the 1 and 0.25 μm wide lines were polycrystalline and bamboo-like grain structures, respectively. During electromigration, voids formed at the cathode end while hillocks grew at the anode end. The failure lifetimes were correlated to the sizes of voids formed in the vicinity of the cathode end of the line, and a distribution of multiple failure modes was found. A low value of electromigration activation energy, 0.81±0.05 eV, and a linear relationship between failure lifetime and metal linewidth were found, despite the fact that these narrow lines were close to a perfect bamboo-like grained structure. These results suggest that the mass transport of Cu during electromigration primarily occurs along the sidewall surfaces of the lines.

EuBa 2Cu 3O 7-δ Thin Films Grown on Sapphires with Epitaxial CeO 2 Buffer Layers

Epitaxial growth of CeO2 films on Al2O3 (11̄02) substrates and the effect of CeO2 buffer layers on the growth orientation and superconducting properties of EuBa2Cu3O7-δ (EBCO) were investigated. CeO2 and EBCO films were prepared by rf and dc magnetron sputtering, respectively, and were characterized by X-ray diffraction (θ-2θ scan and ϕ scan), atomic force microscopy (AFM) and high resolution scanning electron microscopy. Epitaxial (001) CeO2 films were obtained at an off-center distance (D on-off) of 3.5 cm and a substrate temperature of 660°C. The structural and superconducting properties of EBCO films deposited at 650°C depended on the thickness of the CeO2 buffer layer. The EBCO films deposited on CeO2 50-400-Å-thick buffer layers had T ce's of 90 K or above. The high-T c EBCO films had in-plane epitaxial orientation relationships of Al2O3 [112̄0]\\varparallelCeO2 [100]\\varparallelEBCO[110]. The EBCO films on the thin CeO2 buffer layers had rectangular grains similar to those on MgO(001) substrates. The critical current density of the EBCO films with T ce=90 K was about 6 ×105 A/cm2 in zero field at 77.3 K. The T ce varied largely and decreased with increasing CeO2 buffer layer thickness above 500 Å. AFM observation of a 1000-Å-thick CeO2 film showed growth of bamboo-like crystal grains 1700 Å long and 300 Å wide along the direction of CeO2 [110]. The ravine depths were about 100 Å. The EBCO films on the thick CeO2 buffer layer (>500 Å) exhibited poor superconducting behavior and gave (103) or (110) diffraction peaks.

Tem Observations of AG-TI Bilayers After Thermal Aging Treatment in a Reducing Ambient

ABSTRACTTransmission electron microscopy (TEM) in both cross sectional and plan view is used to study the effect of annealing Ag-Ti bilayers deposited on SiO2/Si substrates in an NH3 ambient. The resulting structure, texture and grain size are investigated. Comparisons are made between films annealed at 400, 500 and 600 °C. Silver films show increasingly strong <111> texture with annealing temperature while exhibiting a bamboo-like grain structure at 600 °C. Considerable grain growth with lateral grain sizes of up to 5 times the thickness of the Ag film is observed at 600 °C. The grains typically extend through the Ag film thickness. The Ti/SiO2 interface uniformity and the absence of voids at the substrate surface are positive indicators of the role of titanium as a good adhesion promoter. At 600 °C, a uniform TiN encapsulation layer is observed on the Ag surface.

Using Principle of Virtual Motion and Galerkin Approximation to Analyze Surface Diffusion

AbstractThis paper outlines the use of the Principle of Virtual Motion and the Galerkin approximation to analyze surface diffusion phenomena. Various ideas are illustrated with an analysis of the evolution of a fiber of bamboo-like grain structure.

Electromigration-induced dislocation climb and multiplication in conducting lines

Electromigration along dislocation cores is considered as a mass-transport mechanism, in conducting lines of bamboo-like grains, below one half of the melting temperature. Given that the dislocation density in annealed metals may be insufficient to account for the observed mass-transport rate, this paper focused on electromigration-induced dislocation motion and multiplication. A prismatic loop climbs like a rigid ring, as electromigration relocates atoms along the core, from one portion of the loop to the other. Each loop is therefore a mass carrier: a vacancy loop migrates towards the cathode and an interstitial loop towards the anode. Furthermore, a thread of an edge dislocation multiplies prismatic loops under a sufficiently high electric field. A bamboo grain-boundary catches loops on one side and emits on the other. Available empirical facts are discussed according to this picture, including lifetime, linewidth, stress gradient and alloying.

The bamboo boundary peak in an AlZr alloy

An inverted torsion pendulum is used to study the high temperature internal friction of Al-0.073 wt% Zr alloy. Two internal friction peaks well separated from each other, the bamboo boundary peak and the conventional grain boundary peak, are observed in the original internal friction curve when the size of some grains is larger than the diameter of the specimen. The height of the bamboo boundary peak increases while that of the grain boundary peak decreases with increasing number of bamboo-like grains. The bamboo boundary peak in the completely bamboo-structured specimen decreases linearly in height with increasing size of bamboo grains, until the peak is completely absent in the single crystal specimen. The peak temperature of the bamboo boundary peak and the associated activation energy are 690 K (fp = 0.29 Hz) and 3.20 eV when bamboo grains coexist with fine grains, and 635 K (fp = 0.31 Hz) and 2.74 eV when the complete bamboo structure is formed, respectively. Combining the electron microscopic observation of the second phase particles in boundaries, it is suggested that the bamboo boundary peak is originated by the stress relaxation of the particle-bearing boundary.

Precipitate Drifting and Coarsening Caused by Interface Electromigration

ABSTRACTA mechanism is proposed to explain electromigration-enhanced precipitate coarsening in Al-Cu alloy interconnects. The interface between the α-phase matrix and a θ-phase Al2Cu precipitate is incoherent, along which both Al and Cu atoms diffuse under an applied electric field. Depending on the relative mobility of Al and Cu, the diffusion causes the precipitate to migrate towards either the positive or the negative electrode. The velocity of a spherical precipitate is proportional to the electric field and the mobilities and inversely proportional to its radius. A critical electric field or precipitate radius exists, above which the precipitate can penetrate a grain boundary. Consequently, the precipitates agglomerate by the synergism between the surface tension-induced ripening and the current-induced migration. The resulting particles are distantly separated, depleting Cu atoms from the rest of the interconnect. The mechanism appears to limit the lifetime of interconnects having bamboo-like grains, tested below 300°C, less than half of the melting temperature of Al.

Alloying design of oxide dispersion strengthened ferritic steel for long life FBRs core materials

Oxide dispersion strengthened (ODS) ferritic steels with excellent swelling resistance and superior high temperature strength are prospective cladding materials for advanced fast breeder reactors. The addition of Ti in 13Cr-3W ODS ferritic steels improved the high temperature strength remarkably by the formation of uniformly distributed ultra-fine oxide particles. ODS ferritic steels have a bamboo-like grain structure and a strong deformation texture. The decrease of creep rupture strength in the bi-axial direction compared to the uni-axial direction is attributed mainly to this unique bamboo grain structure. Nearly equivalent creep rupture strength for both bi-axial and uni-axial direction was successfully attained by introducing the α to γ transformation in ODS martensitic steel.

Stress-induced grain boundary fractures in Al–Si interconnects

This paper presents a study on grain boundary fracture failures found in Al–Si interconnects during aging tests without electric current flow. Failure rate analysis and microscopic observation by transmission electron microscopy and scanning electron microscopy indicate that failures are caused by slitlike voids formed at grain boundaries during the relaxation process in Al–Si conductors stressed by temperature cycling under the volume constraint of passivation films. Conductors are seen to fail in two modes; an open mode at bamboolike grain boundaries and a high-resistance mode at grain boundaries having large silicon precipitates.