Direct alpha Ta formation on TaN by resputtering for low resistive diffusion barriers.
Jung-Chih Tsao1, Chuan-Pu Liu, Ying-Lang Wang
1Department of Materials Science and Engineering and Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan, Taiwan.
Journal of Nanoscience and Nanotechnology
|June 25, 2008
Summary
This study enhances copper interconnects by controlling tantalum (Ta) phase formation. Argon ion bombardment of tantalum nitride (TaN) surfaces promotes the low-resistivity alpha-Ta phase, improving device performance.
Area of Science:
- Materials Science
- Electrical Engineering
- Semiconductor Device Fabrication
Background:
- Tantalum (Ta) and tantalum nitride (TaN) bilayers are crucial for copper (Cu) multilevel interconnects, offering good coherence with dielectric layers.
- The performance of Ta/TaN layers is highly dependent on the Ta phase; the body-centered cubic alpha-Ta phase (15-60 microOmega-cm) is preferred over the resistive tetragonal beta-Ta phase (150-250 microOmega-cm).
- Beta-Ta phase commonly forms on face-centered cubic (fcc) TaN, posing a challenge for achieving optimal performance in interconnects.
Purpose of the Study:
- To develop a method to bypass the formation of the high-resistivity beta-Ta phase during the deposition of Ta on TaN.
- To promote the direct formation of the desired alpha-Ta phase for improved performance in Cu interconnects.
Main Methods:
- A surface treatment scheme involving resputtering of TaN using argon ion bombardment prior to Ta deposition was employed.
- X-ray diffraction (XRD) and resistivity measurements were used to characterize the phase and electrical properties of the deposited Ta films.
- Auger electron spectroscopy (AES) depth profiling was utilized to analyze the elemental composition and surface chemistry changes.
Main Results:
- Sufficient argon ion bombardment treatment of the TaN surface directly induced the formation of the alpha-Ta phase, confirmed by XRD and resistivity data.
- AES analysis revealed that the surface treatment created a nitrogen-deficient layer on the TaN surface.
- This nitrogen deficiency facilitated phase transitions from fcc-TaN to hexagonal close-packed (hcp) Ta2N, then to body-centered cubic (bcc) Ta(N), providing a favorable lattice structure for alpha-Ta nucleation and growth.
Conclusions:
- The proposed surface treatment method effectively suppresses the formation of the undesirable beta-Ta phase.
- Direct formation of the low-resistivity alpha-Ta phase is achievable, leading to enhanced performance characteristics for Ta/TaN bilayers in Cu interconnects.
- This approach offers a simple yet effective strategy for optimizing barrier layer properties in advanced semiconductor manufacturing.
