UV-assisted thermal annealing of PECVD Low-k Silicon Carbonitride Films

• Main Authors: Chung, Hau-ting, 鐘皓廷
• Other Authors: 呂志鵬
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/k23hdz

碩士 === 國立交通大學 === 材料科學與工程學系所 === 105 === Low-k silicon carbonitride films (SiCxNy) (k = 5.0–6.0) have been introduced as low-k etch-stop/dielectric barrier materials in CMOS backend interconnections. For 14 nm node and below, SiCxNy films (k < 5.0) with good mechanical strength are highly desirable. In this study, a single precursor, N-methyl-aza-2,2,4-trimethyl silacyclopentane (MTSCP) with high C/Si ratio (C:N:Si=7:1:1) was used to fabricate SiCxNy films at various substrate temperatures by PECVD. This thesis examines the effect of UV-assisted annealing at 400oC on the dielectric constant, structural change, and mechanical properties of SiCxNy films, compared to those by conventional thermal annealing. UV light is found to significantly alter the composition and structure of silicon carbonitride films. Upon UV irradiation onto SiCxNy film at 400oC, its Si-N peak intensity increased and stretching band blue-shifted according to Fourier transform infrared spectroscopy, indicating a denser and more cross-linked Si-N structure. In addition, UV radiation is effective in removing polar groups such as N-H and Si-H. For SiCxNy film as-deposited at low temperature, such as 100oC, UV-assisted thermal annealing reduced the k-value from 3.6 to 3.2, presumably due to the removal of polar groups, -NH and SiH and a decrease in density by breaking up hydrocarbon in carbon chain. Still, the enhanced crosslinking led to 23% improvement of mechanical strength from 6.0GPa to 7.4GPa. UV-assisted annealing of 300oC-deposited SiCxNy film showed an increase of Young’s modulus from 50GPa to 58GPa, while the dielectric constant increased slightly from 4.2 to 4.4 due to slight increase of film density by enhanced Si-N crosslinking. The film stress is also strongly affected by UV radiation as characterized by a wafer curvature method, i.e. bending beam. After UV-assisted annealing, the stress of 100oC-deposited SiCxNy film changed from +10 MPa (tensile) to +45 MPa. In contrast, SiCxNy films deposited at 300oC showed a compressive stress of -120 MPa, then increased to -58 MPa upon UV annealing. This can be attributed to the removal of Si-H combined with enhanced Si-N crosslinking by UV-assisted annealing. The applicability of UV-assisted thermal annealing as a post-treatment technique to improve silicon carbonitride films is also addressed.