| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Poster Session |
| Presenter: | Woongkyu Lee, Seoul National University, Republic of Korea |
| Authors: | W. Lee, Seoul National University, Republic of Korea W. Jeon, Seoul National University, Republic of Korea Y.W. Yoo, Seoul National University, Republic of Korea C.H. An, Seoul National University, Republic of Korea M.J. Chung, Seoul National University, Republic of Korea T.-M. Chung, Korea Research Institute of Chemical Technology B.K. Park, Korea Research Institute of Chemical Technology S.M. George, Korea Research Institute of Chemical Technology C.G. Kim, Korea Research Institute of Chemical Technology C.S. Hwang, Seoul National University, Republic of Korea |
| Correspondent: | Click to Email |
Strontium titanate(SrTiO3, STO) has been attracting a great deal of attention as the capacitor dielectric material for DRAM with design rule < 20 nm due to its much higher dielectric constant (k > 100) compared with those of presently adopted dielectrics based on ZrO2 (k ~30 – 40). Because of the severe three-dimensional geometry of DRAM capacitors, atomic layer deposition (ALD), which provides the ultimate step coverage, is indispensable. The conformality of film is generally induced by self-limited growth mechanism of the ALD. However, in previous studies, non-ideal excess growth was observed during the early stage of STO deposition on Ru electrode, the most promising electrode material. The excessive growth was more dominant for the incorporation of Sr into the film compared with Ti. This was mainly attributed to the reduction of in-situ oxidized Ru substrate during the O3 pulses in the previous ALD steps.[1, 2] Such adverse effect was further aggravated by the high growth temperature (370 oC), which was adopted for the in-situ crystallization of the STO film. Also, the weak chemical bonding between the cyclopentadienyl(Cp)-based ligands and Sr ions in the conventional Cp-based Sr-precursor induced such problem.
In this study, therefore, [Sr(demamp)(tmhd)]2, developed by Korea Research Institute of Chemical Technology,[3] which is supposed to have a chemical properties in medium of the Cp-based Sr-precursor and tmhd-based homoleptic Sr-precursor, was adopted as the new Sr-precursor and attempted ALD process of STO film. A high density (250 g/m3) O3 was employed as the oxygen source for SrO deposition and sputtered Ru was used as the substrate with its temperature of 370 oC. Ti(Me5Cp)(O Me)3 was employed as the Ti-precursor which is also reacted with O3. With this novel heteroleptic Sr-precursor, good ALD-specific saturation growth behaviors were observed with respect to the precursor injection, Ar purge, O3 injection, and Ar purge step times. Most importantly, the unwanted overgrowth of Sr element in initial stage of film growth decreased substantially, and the linear growth behavior of both Sr and Ti were achieved. Meanwhile, the growth rate was decreased to 0.50 Å /cycle, which was lower than the previous case with Cp-based Sr-precursor (1.23 Å /cycle) but assisted to have a denser as-deposited film. With more ideal-like ALD process, the deposited film showed excellent film properties including high purity, high crystallinity, high electrical properties, and excellent step coverage.
[1] S. W. Lee, et al., Chem. Mater. 23, 2227, 2011.
[2] W. Lee, et al., Chem. Mater. 25, 953, 2013.
[3] S. M. George, et al., Eur. J. Inorg. Chem. 2014, 2002, 2014.