Chim Seng Seet

Via Resistance Reduction using “Cool” PVD-Ta Processing

Different processes, including cool physical vapor deposition (PVD), of Ta barrier and Cu seed deposition were compared in Cu interconnect development. In the cool Ta process, the substrate temperature was 100°C in the standard process. With the cool process, via resistance (0.19 μm in via size) was reduced by about 25%, although 40% thicker Ta was measured at the via bottom. This was not in agreement with the common understanding that the thicker the Ta film is, the higher the via resistance. Blank film studies suggested that a mixed texture of α- and β-Ta was formed at via bottom in the new Ta/Cu process. X-ray diffraction spectra clearly exhibited the existence of α-Ta in addition to the β-Ta, where the latter is usually observed in the standard process. Electron diffraction spectra further supported the claim of mixed α-/β-Ta formation at via bottom. Moreover, Rutherford backscattering data suggested that the mixed α-/β-Ta had even higher thermal stability.

Bias-temperature stressing analysis on the stability of an ultrathin Ta diffusion barrier

Proper electrical functionality of devices is dependent on the proper insulation between active/passive areas and metal interconnect. Although low-k materials are gradually replacing SiO2 to achieve lower parasitic capacitance, they are still SiO2-based. With the introduction of Cu as back-end metallization, the need for a barrier between insulator and metal arises, regardless of insulating materials. Ta has been established as a mainstream diffusion barrier in Cu interconnects. As device feature size shrinks, thickness of the Ta barrier also decreases. This raises a big concern on the effectiveness of thin, columnar Ta barriers in stopping the diffusion of Cu into SiO2, especially under simultaneous application of bias and thermal stresses. As the integrity of SiO2 is reliant on Ta to prevent Cu diffusion, bias-temperature stressing (BTS) would be a very suitable test to indirectly evaluate the Ta barrier through SiO2 integrity. In this study, the stability of a 5 nm Ta barrier is investigated under vari...

Four-Point Bending Methodology development for 40nm technology Cu/Nblk interface adhesion measurement

A sample preparation methodology was developed for Four-Point Bending test (4PB) of Cu/Nblk (Nitrogen-doped Barrier for Low-k, SiCN) bi-material in order to overcome interfacial delamination zero yielding issue, possibly caused by the change in carbon content of Nblk film. The methodology involving (i) chemical de-processing (HNO3:BOE mixture) and (ii) film thickness optimization was instrumental in achieving greater than 50% delamination yield.