Cathryn Christiansen

Thermal characterization and challenges of advanced interconnects (Invited)

Technology scaling and driving to high performance have led to more joule heating in both devices and interconnects. Since temperature is one of the most sensitive factors impacting interconnect reliability, this paper focuses on the thermal characteristics of metal lines with different geometries and surroundings to accurately assess local temperature of different circuit designs. The experimental results reported can be used as basic input parameters and calibration baseline for thermal model development and simulations.

Field acceleration factor extraction in MOL and BEOL TDDB

Recently a BEOL (Back End Of Line) and MOL (Middle Of Line) Time-dependent dielectric breakdown (TDDB) reliability test and fail rate projection methodology based on large data analysis was proposed and studied. However the extraction of one of the key model parameters, the field acceleration factor Ye was ambiguously defined. If no enough caution is taken, a systematically lower γE will be obtained which leads to a pessimistic projection. In this work, the fundamental differences with two different extraction methods are systematically studied by both experiments and Monte Carlo simulations. A more realistic and robust method is then proposed, for a more accurate reliability projection.

Correlation between the variation in the initial current at stress and the variation in the failure time during TDDB testing of BEOL structures

A novel approach for estimating variation in the TDDB failure time is reported. The results for structures with Dual Damascene copper-based metallization and a low-k dielectric material demonstrate that variation in the initial current at stress reasonably predicts variation in the TDDB failure time. Moreover, the method does not cause failure in the structures and is more efficient compared to other methods since only a current measurement is required. The approach represents an ideal way to monitor the expected TDDB lifetime behavior during manufacturing of an established process.

Time-dependent series resistance and implications for voltage acceleration models in BEOL TDDB

A continuous down-scaling of BEOL pitch for advanced process technologies has drastically increased the resistance of Cu interconnects, which brings up a concern of a series resistance effect or IR drop within metal electrode during high voltage TDDB stresses. For accurate TDDB lifetime projections at operating voltages, it is of a critical importance to understand the iR drop in BEoL devices under typically applied high voltage stresses to accurately estimate effective stress voltages and the voltage acceleration parameter of a chosen TDDB model. In this work, we present transient behavior of IV characteristics of BEoL dielectric material (k=2.55, SiCOH), a method of accurately calculating effective stress voltages resulting from time-dependent IR drop, successive breakdown characteristics of comb-serp device to explain the IR drop effect and comparison of breakdown characteristics of various devices possibly with and without IR drop to show that the impact of the IR drop on voltage acceleration parameter is negligible. Finally, our long-term TDDB results (> 2 years) of 64-pitch interconnect made of Cu/ULK (k=2.55, SiCOH) with IR drop corrections on high stress voltages show that the power law model best describes the voltage acceleration behavior of the ULK dielectric material used for our studies.