The triangular voltage sweep method as a performance metric for diffusion barrier evaluation in copper metallization

Increasing demands on computer chip technology require exploration of novel materials, deposition techniques and characterization methods. Copper-based interconnects have been implemented in advanced microprocessor designs owing to copper's low resistivity (1.7 μΩ-cm). Copper interconnects require a barrier layer to prevent diffusion into the dielectric layer.; Traditionally, a technique known as bias-thermal-stress-capacitance-voltage (BTS) has been used to quantify barrier reliability against Cu diffusion. Triangular voltage sweep (TVS) is a new method for quantifying barrier reliability against Cu diffusion, whose advantage lies in its ability to discriminate between various mobile charges based on their mobilities in an insulator.; In the first phase of this work, physical vapor deposited (PVD) tantalum nitride (TaN) was first used as a baseline barrier to establish and understand the performance metrics of TVS. The development and optimization of PVD TaN employed a design of experiment (DOE) approach. The optimization resulted in stoichiometric TaN films with a resistivity of 250 μΩ-cm for 50 nm thick films. The films were polycrystalline and exhibited a zone “T” type microstructure. TVS was used to characterize these films. Pertinent results, including possible failure mechanisms, are presented in the document.; As the device sizes shrink to 100 nm and below, diffusion barrier thickness is expected to fall to less than 10 nm. One potential material for the barrier layer in the sub-100 nm technology is tungsten nitride (WN_x) deposited by chemical vapor deposition (CVD). Tungsten nitride is expected to perform well as a barrier because of its refractory nature and excellent thermal, chemical, and mechanical properties. In addition, it can be deposited in amorphous form. Amorphous materials have no grain boundaries, thereby avoiding grain boundary diffusion, which is a fast path diffusion mechanism. Additionally, a low-dielectric constant material, such as SiLK, will be used in the sub-100 nm technology node. Accordingly, the second phase of this work employed TVS to characterize CVD grown WN_x films as a diffusion barrier in the Cu/SiLK technology node. Results from this study and proposed failure mechanisms for WN_x are also presented and discussed.