Joost J. Vlassak

The use of thin films in integrated circuits has created a strong interest in the mechanical properties of thin-film materials and materials in small volumes. As the complexity of integrated circuits increases, the materials used in them have to meet more stringent requirements.

Until recently, integrated circuits consisted of relatively few materials: single and polycrystalline silicon, various aluminum alloys, silicon oxides and nitrides of varying composition, as well as barrier films and silicides (TiN, TiSi2, CoSi2, etc.). Recently, however, requirements for better electrical performance have led to the incorporation of a host of new materials such as Cu and dielectrics with low dielectric constants. Integration of these new materials into integrated circuits poses interesting challenges for engineers in research and development organizations.

A good understanding of the mechanical properties of these materials and of the interfaces between them is critical to the successful integration of these materials. Other applications in which mechanical properties of thin films play an important role include micro-electromechanical systems (MEMS), electronic packaging, and data storage (e.g., magnetic storage media).

Professor Vlassak has developed a variety of new experimental techniques for studying the mechanical behavior of thin films. He has investigated the effect of elastic anisotropy on stiffness measurements on small volumes of materials using low-load indentation techniques and has developed a technique for visualizing the plastic displacement field around indentations in multilayered thin films.

He has also developed a method for measuring stress-strain curves of freestanding thin films using silicon micro-machining techniques. His goal is to develop a better understanding of how microstructure controls the mechanical behavior of thin films.

Because adhesion is one of the critical properties that determine the performance of a thin film on a substrate, Professor Vlassak also studies the mechanical behavior of thin-film interfaces. He is currently planning to expand his research to fatigue and fracture toughness of thin films as well as time-dependent properties.