N. L. Michael

Mechanism of reliability failure in Cu interconnects with ultralow-κ materials

This letter presents evidence of an oxidation-driven failure mechanism in Cu interconnects integrated with ultralow-κ materials. It is found that the open pore structure of ultralow-κ materials allows oxidants in the ambient to reach the interconnect structure and induce oxidation of Cu. In contrast to a normal oxidation process where Cu is in contact with the oxidant, oxidation is controlled by the outdiffusion of Cu through the barrier layers, Ta and SiCN, to form Cu oxide in the pores of the dielectric material. The loss of Cu by outdiffusion induces extensive voiding and subsequent failure in Cu interconnects.

Electromigration in Cu thin films with Sn and Al cross strips

Electromigration in Cu thin films is studied in a cross-strip configuration. Cu lines with isolated areas of Cu(Al) or Cu(Sn) are tested between 250 and 390 °C with the following results. The hillock and void marker motion indicates that Sn moves in the direction of electron flow. The marker polarity indicates that it decreases the grain boundary electromigration of Cu, in agreement with previous studies. This study also finds evidence of active surface migration in Cu. During tests in forming gas, hillocks and voids form adjacent to a native Al2O3 layer at all temperatures, indicating the likelihood that Cu migrates faster through the Cu free surface than the interface between the surface layer of Al2O3 and Cu(Al). Active surface migration in Cu thin films is also evidenced by the growth of hillocks with highly developed facets, most of which are attached to the underlying film by narrow necks.

Study of pore structure and stability in porous low-k interconnects using electrolyte voltammetry

This letter presents a step-mode voltammetry method which uses ion diffusivity to characterize pore structure in both dense and porous low dielectric constant materials (low k) in patterned interconnect structures. Findings reveal that the intramolecular space in dense low k acts like a small physical pore network. It is determined that electrolyte ions can migrate through such space in dense low k, but with higher activation energy than in porous low k or the bulk solution, 0.31eV vs 0.18–0.19eV. Also, this study finds that the pores in ultralow k are not stable but can either coalesce or collapse depending on stress conditions.

Mechanism of electromigration in Au/Al wirebond and its effects

This paper presents findings evidencing that electromigration(EM) imparts significant influence on the kinetics of contact failure of Au wire bonded to an Al pad. Contact resistance between Au wire and Al pad at moderately accelerated test conditions (T=150–175°C; j=5×104A/cm2) revealed that the failure rate depends highly on the direction of electron flow across the contact: electron flow from Au to Al resulted in far faster failure rate than the opposite direction. Microscopic inspection of the contact interface indicated that the wirebond contact failure is related to the growth of Au-Al intermetallic compounds (IMC). EM was found to influence the failure kinetics because it accelerates or decelerates the growth rate of the IMC.

Efficient electromigration testing with a single current source

This article introduces a simple and effective technique for conducting electromigration testing of a number of samples using a single current source. It is based on a configuration where all samples are serially connected to a single current source, allowing them to be subjected to identical current conditions. In this design, each sample has a current bypass circuit, consisting essentially of a computer controlled shunt relay and a Zener diode, to enable continuation of testing without any interruption in the test current when samples fail. With this technique, a large number of samples can be tested with the same current and excellent current stability, making it suitable for both reliability assessment and scientific investigation of electromigration mechanisms. Initial results show high correlation with industry standard testing systems.

New Electrochemical Cell Designs and Test Methods for Corrosion Testing of the Components in Integrated Circuit Liquid Cooling Systems

This paper introduces new electrochemical cells and testing methods that are ideal for characterizing corrosion risk assessment of the components used for liquid cooling system with high surface to liquid volume ratio. Two cell configurations are described in this paper and they use three electrode and two electrode cells. These cells have the identical structure except for the number of electrodes. These cells are made by sandwiching the working electrode plate (sample) and the counter electrode plate (graphite) with a spacer (gasket), and by filling the cavity with the liquid under interest. In case of the three-electrode cell, the reference electrode is inserted through the hole in the graphite. The three-electrode cell is ideal for the quantitative characterization of the corrosion rate by utilizing conventional electrochemical techniques such as a Tafel method. The use of the two-electrode cell is similar to the case of the galvanic corrosion characterization as it measures the cell current that flows between the dissimilar metals that are in contact with the liquid. When coupled with computer assisted data acquisition, the two-electrode cell configuration allows the characterization of long-term corrosion reliability of a component with a variation in a large number of test variables. It is particularly useful in finding corrosion inhibitors.Copyright

Development of Quantum Dot-Embedded Nanoparticles for Biothermal Imaging

Recent surgical management of cancer tends toward minimally invasive surgical techniques since tumors can be detected smaller than ever due to the advance of cancer diagnostic technologies. Many of these surgical procedures are thermal therapies where a localized freezing or heating zone (i.e. thermal lesion) is created to destroy tumors without damaging adjacent normal tissues. The outcomes of these innovative and less invasive surgeries, however, are significantly impaired by the limited image-guidance of the thermal lesion during the procedures. Since the primary clinical objective of these surgeries is to eradicate diseased tissues while sparing the adjacent normal tissue, accurate intra-operative monitoring of the thermal lesion is critical. Moreover, in many surgical situations, sparing adjacent tissue is not only desired, but imperative since major blood vessels, nerve bundles and surrounding organs are susceptible to thermal injury. However, currently available monitoring techniques have limited accuracy or accessibility, and/or are not capable of monitoring the lesion in real-time during the procedure. In our recent study [1], we demonstrated the feasibility of non-invasive thermometry using quantum dot (QD) as temperature probe. Although its feasibility was demonstrated, several limitations should be addressed before more rigorous clinical applications. Especially the lower quantum yield of core/shell QDs should be significantly improved for deeper tissue imaging. In the present study, QD-embedded nano-composite particles were developed for deeper tissue imaging and its temperature dependent fluorescence was characterized.© 2007 ASME