Chao-Kun Hu

Electromigration and adhesion

It has been demonstrated that, in those instances where electromigration-induced mass transport is dominated by interfacial diffusion, the adhesion at the interface where mass transport is primarily taking place is related to the electromigration flux. Furthermore, it is shown that the cohesive energy of the interface is directly related to the activation energy for diffusion.

Copper contact metallization for 22 nm and beyond

We used Cu contact metallization to solve one of the critical challenges for 22 nm node technology. Cu contact metallization allowed us to demonstrate worlds smallest and fully functional 22 nm node 6T-SRAM [1]. Cu contact metallization was executed using CVD Ru-containing liner. We obtained early reliability data by thermally stressing bulk device. Bulk device parameters such as junction and gate leakage currents and overlap capacitance were stable after BEOL anneal stress. We also demonstrated the extendibility of Cu contact metallization using 15 nm contacts.

Line Resistance and Electromigration Variations Induced by Hydrogen-Based Plasma Modifications to the Silicon Carbonitride/Copper Interface

This paper reports a detailed study of several hydrogen-based plasma cleans prior to plasma-enhanced chemical vapor deposition of silicon carbonitride cap films, and it finds a tradeoff between improved electromigration and increased copper resistivity. Previously proposed mechanisms do not explain this tradeoff, and we propose an alternative mechanism for the cap/copper interface modification. Electromigration is improved by forming a copper silicide interfacial layer, but the copper resistivity is also increased by silicon diffusion into the copper from the cap/copper interface. Hydrogen-based plasmas generate silicon by reacting with the silicon nitride seasoning layer on the chamber surfaces and transporting the silicon to the copper surface. The transport of silicon can be prevented by adding nitrogen to the plasma or removing the seasoning layer.

Ruthenium interconnect resistivity and reliability at 48 nm pitch

48 nm pitch dual damascene interconnects are patterned and filled with ruthenium. Ru interconnect has comparable high yield for line and via macros. Electrical results show minimal impact for via resistance and around 2 times higher line resistance. Resistivity and cross section area of Ru interconnects are measured by temperature coefficient of resistivity method and the area was verified by TEM. Reliability results show non-failure in electromigration and longer time dependent dielectric breakdown. Based on the data collected, Ru could be a metallization contender at linewidth of 16 nm and below.

Electromigration: Void Dynamics

The detailed knowledge of the void evolution is helpful to understand and interpret traditional electromigration (EM) lifetime experiments. As void formation and subsequent evolution is highly dynamic, an in situ observation experiment was employed using an SEM allowing for void detection down to a few nanometers in diameter. For void nucleation, it has been suggested that due to the large anisotropy in modulus in Cu, incompatible grain boundaries can act as stress concentrators for both stress-induced and EM-induced voiding. In addition, during growth, the shape change and migration have been associated with the microstructure. To better understand void formation and evolution, we examined the Cu microstructure using EBSD during the experiment without interruption. We tested interconnects consisting of Cu-based damascene (M1) drift type structures, capped with SiCN. Void formation could be confirmed to be associated with features such as incompatible grain boundaries in some instances. In other cases, triple points and grain boundary/sidewall intersections were found as void nucleation sites. Void growth and migration is found strongly correlated with the driving current density. We show conditions under which void migration takes place or is suppressed. In particular, a critical current density of approximately 10 mA/μm2 is observed, below which no void migration occurs. At current densities of 15 mA/μm2 and above, all voids migrated at a net drift velocity proportional to the current density. Independent of migration, all voids are observed to grow at rates consistent with published data for a mixed near bamboo microstructure and interface diffusion.