| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系所 === 104 === As the feature size of VLSI devices scaling down, a lower dielectric constant both in the interlayer dielectric (ILD) and etch-stop/diffusion barrier (ES/DB) layer is necessitated to slow down the increasing trend of RC propagation delay in the backend interconnect. However the critical problem is the dilemma between dielectric constant and mechanical properties of such dielectrics. When the dielectric constant is much reduced, its mechanical properties may be too weak to survive processes such as chemical-mechanical polish and packaging due to chip-package interaction. To solve this problem, UV-assisted thermal annealing has been used to post-treat carbon-doped silicon (SiCOH) ILD for reduced k-value but enhanced mechanical strength. Yet, there is a lack in the understanding if UV-assisted thermal anneal can favorably affect the dielectric constant and mechanical strength on the low-k ES/DB materials.
This work investigates the effect of UV-assisted thermal annealing on the structure and properties of silicon carbonitride (SiCxNy) films for application in copper interconnects. In particular, SiCxNy films are deposited by plasma-enhanced chemical vapor deposition at substrate temperature 80 – 200 ℃ and 1 Torr using a single precursor, N-methyl-aza-2,2,4-trimethylsilacyclopentane (MTSCP). Comparative studies on post-treatment of SiCxNy films deposited at various temperatures are carried out using (1) thermal annealing at 400 ℃ for 5 minutes and (2) UV-assisted thermal annealing at 400 ℃ with 80 mW/cm2 UV light exposure for 5 minutes.
In this study, UV-assisted thermal annealing is found to remove the organic phase, break up the high-polarizability NH bonding, and enhance SiN backbone structure. Thus, UV-assisted thermal anneal can enhance the properties of SiCxNy film compared to conventional thermal annealing under same curing time, 5 min. The optimal result of low-k SiCxNy film using MTSCP precursor was obtained by deposition at 150 ℃,1 Torr, and under a plasma power density of 0.27 W/cm2. Under these conditions, the dielectric constant of low-k SiCxNy film drops 0.22 from 4.05 to 3.83, while the Young’s modulus maintains the same at about 20 GPa. As a result, UV-assisted thermal annealing can be a powerful post-treatment technique to enhance silicon carbonitride films for backend interconnect applications.
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