| AVS 60th International Symposium and Exhibition | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM+AS+PS+TF-ThM |
| Session: | Materials and Process for Advanced Interconnects I |
| Presenter: | D. Yang, University of Delaware |
| Authors: | D. Yang, University of Delaware R. Opila, University of Delaware V. Pallem, Air Liquide D. Dutta, University of Michigan D. Gidley, University of Michigan N. Bhargava, University of Delaware |
| Correspondent: | Click to Email |
As transistor density on integrated circuits doubles as driven by Moore’s Law, propagation delays from interconnections at the back-end-of-line (BEOL) have begun to contribute significantly. Low dielectric constant (k) materials, e.g. organosilicate glasses (SiCOH), have been introduced to replace silicon oxide to reduce power consumption and capacitive signal delay. It has been generally agreed that decreasing material density by incorporating porosity is the most feasible means to achieve ultra low k. However, when a higher portion of porogen is introduced, pores tend to aggregate and interconnect, especially when porosity is above percolation threshold. The pore interconnectivity may lead to degradation of mechanical and thermal properties and permit intrusion of moisture, chemical species and sequestering of cleans byproducts. Therefore, characterization and understanding of porosity and pore interconnectivity are important tooptimize porous low-k materials. In this work, three non-destructive porosimetry techniques, Positron Annihilation Lifetime Spectroscopy (PALS), Ellipsometric Porosimetry (EP) and X-ray Reflectivity (XRR), are applied to characterize porous SiCOH low-k dielectric thin films of different porosity and pore interconnection, results will be analyzed and compared to highlight each technique’s advantage and limitation for characterizing porous low-k materials. This study will provide valuable guidance for future porosity characterization, data comprehension, porosity understanding and further structural optimization of porous low-k materials.
The results showed that ellipsometric porosimetry (EP) provides information on open meso-pores accessible to organic solvents but may underestimate porosity without probing pores smaller than the probing organic molecule3; Positron Annihilation Lifetime Spectroscopy (PALS), which probes the amount of free surface and is able to detect micropores but with limitations on analyzing multiple pore size distribution within pore interconnection length ; PALS also has unique feature to quantify pore interconnection length by depth-profiling; X-ray Reflectivity(XRR) gives absolute overall porosity in terms of film density but tends to overestimate porosity and provides few details on pore size distribution.
After comparison, we conclude that each porosimetry technique shows their strengths and limitations due to different physical principles. Information derived from any single porosimetry technique is not sufficient to reveal comprehensive pore information without bias. Therefore, metrology must be carefully selected and complementary techniques are required in order to acquire a full picture of pores.