As the wires connecting devices became smaller and smaller over the decades - to about 1/1,000th the width of a human hair today - the existing silicon dioxide material used to insulate chip wiring and keep circuits from shorting resulted in unacceptably slow circuits that consumed excessive power in several key applications. A new material called low-k dielectric (LKD) replaced silicon dioxide films in these applications and is now widely used in the industry. While LKDs were implemented to solve the performance and power issues, they created a new problem - the resulting devices had much shorter life spans than devices based on traditional silicon dioxide insulating films.

The Columbia University researchers, supported by SRC and working closely with industry partners, have incorporated optical excitation techniques in their investigation of LKDs to determine electron barrier heights, trap levels and trap densities in LKD thin films and the interfaces between other materials, with new, insightful results. The researchers now have a better understanding of the role of these parameters in defining electrical properties that can help to predict degradation and control leakage of currents contributing to potential breakdown.

"These data will help meet an industry-wide need to understand conduction mechanisms in low-k films, particularly those leading to leakage, time dependent dielectric breakdown (TDDB) and reliability concerns," said Dr. Scott List, director of Interconnect and Packaging Sciences at SRC. "The problems associated with traps in LKD films are expected to increase in importance as the push to even smaller circuitry and lower dielectric constants continue, and these measurements provide us the best insight available to help solve these problems", said Dr. Robert B. Laibowitz, senior research scientist at Columbia University.

The research focuses on optical and electrical studies of charge transport and trapping in LKD. The samples used in this study consist of both blanket LKD films on silicon and metal substrates, as well as more complex test structures used in industry reliability studies.

Using photo-induced current, laser second harmonic generation and capacitance-voltage measurements, Columbia University graduate student Joanna Atkin was able to determine the density of traps in LKD thin films and their generation dynamics with application of applied field for the first time. The work will be extended to an array of films and structures of varying dielectric constant and thickness, varying contact metallurgy and process history.

"As semiconductors migrate to new manufacturing technology nodes and smaller circuitry, further materials analysis will be needed," said Laibowitz. Columbia University and SRC plan to continue this work and extend both the techniques and LKD film advances for future generations.