| Summary: | 博士 === 國立交通大學 === 材料科學與工程學系所 === 107 === C-rich SiCxNy films are fabricated using radio frequency (RF) plasma-enhanced chemical vapor deposition (PECVD) of single-precursor, silazanes, for use as low-k diffusion barrier and etch-stop layer for reducing the effective k (keff) of intra-metal dielectrics in the back-end-of-line (BEOL). The precursors in this work consist of linear and cyclic silazanes with different Si:N:C ratios, number of Si-N units, and alkyl/alkene groups, such as 1,3-divinyl-1,1,3,3-tetramethyl-disilazane (DVTMDS), 1,3,5-trimethyl-1,3,5-trivinyl-cyclotrisilazane (VSZ), 1,3,5,7-tetravinyltetra-methylcyclo-tetrasilazane (TVSZ), and n-methyl-aza-2,2,4- trimethylsilacyclo-pentane (MTSCP). Our first goal is to establish the correlation between silazane chemical structure and structure-property of low-k SiCxNy films with a dielectric constant, k ≤ 5 and a fairly good mechanical strength. Among these silazane precursors, a SiCxNy film of low k=3.5 is achieved by successful incorporation of ethylene bridge embedded within Si-N(-Cx) network by using the linear silazane precursor, DVTMDS. In addition, for these silazanes-deposited SiCxNy films at a fixed dielectric constant below 4.2, cyclic silazane, VSZ, produces films of higher film density and modulus, compared to those by linear silazane precursor, DVTMDS.
Next, MTSCP precursor with Si-C3-N rings of relatively high C/Si=7 ratio is examined and compared with DVTMDS for SiCxNy films with even higher carbon content or further reduced k-value. The alkyl groups in MTSCP are intact in SiCxNy films at Ts ≤ 100 °C, and then its matrix is changed to predominantly C-N crosslinked structure at Ts > 300 °C, leading to a wide optical band gap range, from 5.2 to 3.7 eV. The deposition using MTSCP yields a higher Si-N(-C) network than DVTMDS and provides wider tunable properties of SiCxNy films at Ts ≤ 400 °C. At 400 °C, the DVTMDS-deposited SiCxNy film with stable ethylene bridge shows excellent optical transmittance, 85% in the visible wavelengths. However, the mechanical strength of MTSCP-deposited SiCxNy film at 100 oC shows a mere 6.1 GPa, when a large carbon content is incorporated in the film to achieve low the dielectric constant down to 3.6.
Post-treatment such as UV and thermal annealing of silicon carbonitride films are then explored for enhancing its materials properties, preferably mechanical strength. The post-treatment of MTSCP-deposited SiCxNy films is carried out by a broadband UV-assisted thermal annealing (UV-Annealing) at 400 oC for 5 minutes. UV-Annealing can improve both dielectric and mechanical properties of low-k SiCxNy films. Upon UV-Annealing, most Si-H and N-H radicals are broken up, which induces more Si-N cross-linking and converts Si-C matrix into Si-N matrix. The ethylene bridges in Si-(CH2)2-Si also remain intact, but the unbridged hydrocarbons decompose completely during the UV-Annealing process. These account for the reduced dielectric constant to k=3.2 from 3.6 and a 21% enhancement of Young's modulus to 7.4 GPa in the SiCxNy films after UV-Annealing. Broadband UV-Annealing shows promise as a post-treatment method for enhancing the properties of the developed low-k dielectric barrier, SiCxNy films.
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