Characterization of Plasma-Enhanced Chemical Vapor Deposition of Ta2O5 Dielectric Thin Films

• Main Authors: Yi-Sheng Lai, 賴宜生
• Other Authors: J. S. Chen
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/72469685385441734247

碩士 === 國立成功大學 === 材料科學及工程學系 === 87 === The material properties as well as electrical behaviors of tantalum pentoxide (Ta2O5) thin films deposited by plasma-enhanced and low pressure chemical vapor deposition on Si and Pt substrates were investigated. The effectiveness of furnace annealing and plasma annealing on the dielectric and leakage characteristics of Ta2O5 film was also studied for the possible integration into high density dynamics random access memory (DRAM). Ta2O5 films were prepared by chemical reaction of O2 with Ta(OC2H5)5 vapor. Ta(OC2H5)5 liquid was heated at 120℃ and the vapor was carried to the chamber by N2 gas. Ethanol vapor was added to the reaction chamber to help facilitating the hydrolysis of Ta(OC2H5)5 and boosted the reaction. The deposition rates decreased as the plasma power increased. SEM micrographs show that the surface morphology become rough under plasma deposition. As deposited Ta2O5 films were amorphous and transformed to crystallized orthorhombic Ta2O5 after furnace annealing at 800℃ for 1h. Heat treatments in a tube furnace generally improved the electrical properties of the Ta2O5 capacitors. However, the annealing process also introduced interfacial reactions between Ta2O5 and the bottom electrode. Plasma-activated oxygen at 350℃ reduced the capacitor leakage without producing interfacial reactions. Lowering the process temperature is thus an advantage of this method. The C-V measurement indicates that MIM(Al/Ta2O5/Pt) capacitor structure exhibited a higher dielectric constant than that of the MIS(Al/Ta2O5/Si) capacitor. The MIS structure which has a lower dielectric constant may be attributed to the formation of interface SiO2 on between Ta2O5 and Si. PECVD deposited Ta2O5 thin films(35nm) on Pt substrate has higher dielectric constant of 23.5 than other parameters. After plasma annealing at 350℃, the dielectric constant raised to 25.4. Leakage current characteristic also showed better property than without plasma assisted. So it is worthy to further investigate the applications of dielectric materials deposited by PECVD for future DRAMs.