Initial void formation in bamboo Al-Cu(1%) two-level structure AIP Conf. Electromigration in Cu thin films is studied in a cross-strip configuration. Cu lines with isolated areas of Cu͑Al͒ or Cu͑Sn͒ 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 Al 2 O 3 layer at all temperatures, indicating the likelihood that Cu migrates faster through the Cu free surface than the interface between the surface layer of Al 2 O 3 and Cu͑Al͒. 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.
This paper presents experimental evidence suggesting that electromigration (EM) can be a serious reliability threat when the dimension of Cu interconnects approaches the nanoscale range. To understand the failure mechanism prevailing in nanoscale Cu interconnects, single-level, 400-µm long interconnects with various effective widths, ranging from 750 nm to 80 nm, were made, EM tested, and characterized in this investigation. The results indicate that interface EM (Cu/barrier) may be the predominant EM mechanism in all line widths. The evidence supporting the active Cu/barrier interface EM includes the fact that the EM lifetime is inversely proportional to the interface area fraction. Microscopic analysis of the failure sites also supports the conclusion of interface EM because voids and hillocks are found at the ends of the test strip, which is not possible if lines fail by grain-boundary EM in the test structure used in this study. In addition, our study finds evidence that failure is assisted by a secondary mechanism. The influence of this factor is particularly significant when the feature size is small, resulting in more uniform distribution of failure time in narrower lines. Although limited, evidence suggests that the secondary factor is probably attributed to pre-existing defects or grain boundaries.
The electrochemical mechanism behind voltammograms produced by defective barriers in low-k/Cu interconnect structures is investigated using simulation cells which mimic various barrier conditions. The findings reveal that the Cu reaction peak current used as an indicator for barrier defects represents oxidation of Cu at the anodic electrode. When both electrodes have similar defect (Cu) fraction, the voltammogram is symmetric, but when the electrodes have different Cu fraction, the voltammogram is asymmetric and changes during repeated cycling until a stable form is reached.
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.
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