Length Effects on the Reliability of Dual-Damascene Cu Interconnects

The effects of interconnect length on the reliability of dual-damascene Cu metallization have been investigated. As in Al-based interconnects, the lifetimes of Cu lines increase with decreasing length. However, unlike Al-based interconnects, no critical length exists, below which all Cu lines are âimmortal’. Furthermore, we found multi-modal failure statistics for long lines, suggesting multiple failure mechanisms. Some long Cu interconnect segments have very large lifetimes, whereas in Al segments, lifetimes decrease continuously with increasing line length. It is postulated that the large lifetimes observed in long Cu lines result from liner rupture at the bottom of the vias, which allows continuous flow of Cu between the two bond pads. As a consequence, the average lifetimes of short lines and long lines can be higher than those of lines with intermediate lengths.Singapore-MIT Alliance (SMA

Investigation of the Fundamental Reliability Unit for Cu Dual-Damascene Metallization

An investigation has been carried out to determine the fundamental reliability unit of copper dual-damascene metallization. Electromigration experiments have been carried out on straight via-to-via interconnects in the lower metal (M1) and the upper metal (M2), and in a simple interconnect tree structure consisting of straight via-to-via line with an extra via in the middle of the line (a "dotted-I"). Multiple failure mechanisms have been observed during electromigration testing of via-to-via Cu interconnects. The failure times of the M2 test structures are significantly longer than that of identical M1 structures. It is proposed that this asymmetry is the result of a difference in the location of void formation and growth, which is believed to be related to the ease of electromigration-induced void nucleation and growth at the Cu/Si₃N₄ interface. However, voids were also detected in the vias instead of in the Cu lines for some cases of early failure of the test lines. These early failures are suspected to be related to the integrity and reliability of the Cu via. Different magnitudes and directions of electrical current were applied independently in two segments of the interconnect tree structure. As with Al-based interconnects, the reliability of a segment in this tree strongly depends on the stress conditions of the connected segment. Beyond this, there are important differences in the results obtained under similar test conditions for Al-based and Cu-based interconnect trees. These differences are thought to be associated with variations in the architectural schemes of the two metallizations. The absence of a conducting electromigration-resistant overlayer in Cu technology allows smaller voids to cause failure in Cu compared to Al. Moreover, the Si₃N₄ overlayer that serves as an interlevel diffusion barrier provides sites for easy nucleation of voids and also provides a high diffusivity path for electromigration. The results reported here suggest that while segments are not the fundamental reliability unit for circuit-level reliability assessments for Al or Cu, vias, rather than trees, might be the appropriate fundamental units for the assessment of Cu reliability.Singapore-MIT Alliance (SMA

Experimental characterization of the reliability of 3-terminal dual-damascene copper interconnect trees

Materials Research Society Symposium - Proceedings716431-438MRSP

Operating the LCLS Gas Attenuator and Gas Detector System with Apertures of 6mm Diameter

The possibility of increasing the apertures of the LCLS gas attenuator/gas detector system is considered. It is shown that increase of the apertures from 3 to 6 mm, together with 4-fold reduction of the operation pressure does not adversely affect the vacuum conditions upstream or downstream. No change of the pump speed and the lengths of the differential pumping cells is required. One minor modification is the use of 1.5 cm long tubular apertures in the end cells of the differential pumping system. Reduction of the pressure does not affect performance of the gas attenuator/gas detector system at the FEL energies below, roughly, 2 keV. Some minor performance degradation occurs at higher energies

Damage in Mo/Si multilayer optics irradiated by intense short-wavelength FELs

Multilayer coated optics are promising candidates for optical schemes at XUV & X-ray Free Electron Lasers. They can fulfill the extreme requirements in terms of figure and roughness errors, wavefront preservation, and stability. Such optics enable deflection angles much larger than those reasonably achieved with single material mirrors. In addition, due to their good wavelength selectivity, they can be used as narrow bandpass filters. However, since damage of the optical surface is a possible limitation, resistivity studies of MoSi multilayers were carried out at the XUV Free Electron Laser FLASH in Hamburg. The results, reported in [1], show that the leading damage mechanism is melting of the amorphous silicon layer, followed by Mo atoms diffusion into Si, leading to molybdenum-silicide formation. These studies have been extended to the soft X-ray part of the spectrum at the LCLS FEL facility. Although a similar final state of damage was observed, the damage threshold appeared to be strongly wavelength dependent. A possible explanation will be discussed during the presentation. The results are important for the design and further development of the optical coatings for the new generation of the short wavelength light sources, not only for the multilayers but for the single metallic layer coatings as well

Amorphous to crystalline phase transition in carbon induced by intense femtosecond x-ray free-electron laser pulses

We present the results of an experiment where amorphous carbon undergoes a phase transition induced by femtosecond 830 eV x-ray free-electron laser pulses. The phase transition threshold fluence is found to be 282 +/- 11 mJ/cm(2). Atomic force microscopy, photoelectron microscopy, and micro-Raman spectroscopy give experimental evidence for the phase transition in terms of a volume expansion, graphitization, and change of local order of the irradiated sample area. The interaction is modeled by an accurate time-dependent treatment of the ionization dynamics coupled to a two-temperature model. At the phase transition fluence threshold the free-electron density N-e is found to be at maximum 9 x 10(20) cm(-3) while the ion (atom) temperature is found to be 1050 K, e.g., above the crystallization activation temperature reported in the literature. This low ionization rate and high atom temperature suggest a thermally activated phase transition