Measurements of effective thermal conductivity for advanced interconnect structures with various composite low-k dielectrics
ABSTRACT Accurate specification of design groundrules for interconnect systems requires knowledge of the thermal behavior of the systems. A key parameter that characterizes the thermal behavior is the thermal conductivity of the inter-level dielectric (ILD). In practical VLSI applications, the metal interconnects are fully embedded in a stacked, composite ILD media, which presents difficult challenges for the accurate determination of thermal conductivity. In this paper, we propose the concept of an "effective thermal conductivity" to model such complicated, composite media, and introduce a simple methodology to accurately measure effective and bulk thermal conductivities of various thin dielectric layers in integrated circuits. We present measured effective conductivities of several composite media, including various Cu/low-k dielectric configurations such as Cu/SiCOH, Cu/SiLK®, Cu/fluorinated silicate glass (FSG), and a hybrid stack with Cu lines in SiLK® and Cu vias in un-doped silicate glass (USG). Measurements were recorded in the temperature range from 30°C to 120°C using a unique combination of fully embedded Cu lines as heater/thermometers, wafer-level temperature vs. power (TVP) measurements, and the Harmon-Gill (H-G) quasi-analytical heat conduction model. The thermal conductivities of all the films studied here were observed to increase with rising substrate temperature.
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ABSTRACT: BRCA1/2 mutation carriers are offered gynaecological screening with the intention to reduce mortality by detecting ovarian cancer at an early stage. We examined compliance and efficacy of gynaecological screening in BRCA1/2 mutation carriers. In this multicentre, observational, follow-up study we examined medical record data of a consecutive series of 888 BRCA1/2 mutation carriers who started annual screening with transvaginal ultrasonography and serum CA125 between 1993 and 2005. The women were annually screened for 75% of their total period of follow-up. Compliance decreased with longer follow-up. Five of the 10 incident cancers were interval tumours, diagnosed in women with a normal screening result within 3-10 months before diagnosis. No difference in stage distribution between incident screen-detected and interval tumours was found. Eight of the 10 incident cancers were stage III/IV (80%). Cancers diagnosed in unscreened family members had a similar stage distribution (77% in stage III/IV). The observed number of cases detected during screening was not significantly higher than expected (Standardized Incidence Ratio (SIR): 1.5, 95% confidence interval: 0.7-2.8). For the subgroup that was fully compliant to annual screening, a similar SIR was found (1.6, 95% confidence interval: 0.5-3.6). Despite annual gynaecological screening, a high proportion of ovarian cancers in BRCA1/2 carriers are interval cancers and the large majority of all cancers are diagnosed in advanced stages. Therefore, it is unlikely that annual screening will reduce mortality from ovarian cancer in BRCA1/2 mutation carriers.British Journal of Cancer 05/2007; 96(9):1335-42. · 5.08 Impact Factor
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ABSTRACT: Thermal conductivities of hydrogen-silsesquioxane thin films—Dow Corning “flowable oxide” and nanoporous “extra-low-k” spin-on dielectrics—are measured in the temperature range 80–400 K using the 3ω method. Film thickness and atomic densities are characterized by the combination of Rutherford-backscattering spectrometry and variable-angle spectroscopic ellipsometry. Measurements of the longitudinal speeds of sound by picosecond ultrasonics and interferometry enable comparisons with the model of the minimum thermal conductivity of homogeneous materials. This model fails to capture the strong temperature dependence of the conductivity. Data for nanoporous silsesquioxane and SiO2 are compared to the predictions of effective medium theories of heterogeneous materials. Differential-effective-medium theory predicts a scaling of thermal conductivity Λ with atomic density n, Λ∝n3/2 in good agreement with experiment. The comparisons with effective-medium theories suggest that a greater control of pore microstructure may enable significant improvements in the thermal and mechanical properties of porous dielectrics.Physical Review B. 02/2002; 65(9).