Supercritical Fluid Deposition of Conformal SrTiO[sub 3] Films with Composition Uniformity in Nanocontact Holes

Abstract

SrTiO 3 with a high dielectric constant is considered a promising capacitor dielectric for dynamic random access memory. Until now, a SrTiO 3 deposition with compositional uniformity and perfect conformality inside high-aspect nanoscale holes has been difficult by chemical vapor deposition ͑CVD͒ and atomic layer deposition ͑ALD͒. In this study, we report a supercritical fluid deposition ͑SCFD͒ of SrTiO 3 . Compared to CVD SrTiO 3 , the SCFD SrTiO 3 showed perfect conformality and compositional uniformity inside nanosize holes. From these results, the SCFD is expected to be a solution for the stoichiometry and conformality issues of the CVD and ALD SrTiO 3 .SrTiO 3 ͑STO͒ is considered as a promising dielectric material for dynamic random access memory capacitors due to its high dielectric constant up to 300, low leakage current, and good chemical stability. 1-7 Moreover, complicated three-dimensional ͑3D͒ device structures with device downscaling to sub-40 nm have emerged to increase integration density. 8,9 Hereupon, a highly conformal deposition technique is an essential requirement for nanoscale device fabrications. One widely studied deposition technique for STO thin films is metallorganic chemical vapor deposition ͑MOCVD͒. 10-13 Although relatively good composition controllability can be achievable by MOCVD, it is difficult to obtain highly conformal deposition on nanoscale 3D structures. In addition, compositional variation in deep trenches or nanoholes is also a significant problem. For example, energy-dispersive spectroscopy ͑EDS͒ analysis exhibited that the Sr/Ti composition ratio of MOCVD STO films continuously decreases from top to bottom of the nanoholes. 10 The nonuniform Sr/Ti ratio of the MOCVD STO films inside nanoholes was attributed to the different deposition characteristics of Ti and Sr precursors, depending on arriving rates and sticking coefficients of the precursors during MOCVD. [10][11][12] Atomic layer deposition ͑ALD͒ was suggested as an alternative technique for MOCVD STO. 14-17 Generally, ALD enables a deposition with atomic thickness uniformity, high conformality in nanoscale holes and trenches, and large-area uniformity. 18 In spite of these promising aspects, previous studies on ALD of STO reported that various problems exist such as lack of volatile precursors and difficulty in controlling stoichiometry. 14-16 Although ALD STO showed better results in terms of thickness and chemical conformality than MOCVD STO, the Sr/Ti ratio along the 3D contact holes was not uniform and sensitive to growth parameters such as growth temperatures and precursor injection rates. 15,16 Recently, supercritical fluid deposition ͑SCFD͒ emerged as a promising thin-film deposition method for deposition on nanoscale 3D structures due to its excellent conformality and gap-filling properties. 19-21 Especially, SCFD has merits of chemical vapor deposition ͑CVD͒ and ALD such as large-area process for mass production, high deposition rate, and high conformality. 19-21 The supercritical fluid CO 2 has liquidlike...

Selective Cu filling of nanopores using supercritical carbon dioxide

“…Supercritical fluid chemical deposition, frequently abbreviated as SFCD or SCFD, is a technique used to deposit films= particles from a precursor dissolved in a supercritical fluid (SCF) through thermochemical reactions. The deposition of various metals [1][2][3][4][5][6][7][8][9][10] and oxides [11][12][13][14][15][16] has been reported. A typical overall reaction of metal deposition is described as ML 2 + H 2 → M + 2HL (M is a metal atom and L is a ligand).…”

Smooth and Conformal TiO2Thin-Film Formation Using Supercritical Fluid Deposition

“…2), such as tmhd-and acac-based chemicals, enabled lower process temperatures in SCFD than in vacuum technologies such as MOCVD. 18,22,25,26 For example, Momose et al obtained pure Cu films from Cu(tmhd) 2 at only 180 • C, 20 whereas CVD using the same precursor required 250 • C. 27 Peng et al found that the thermal decompositions of Al(acac) 3 and Ga(acac) 3 in scCO 2 were initialized at ∼150 • C and 160 • C, respectively, 18 which were lower than those in analogous vacuum-based processes (∼250 • C and 360 • C, respectively). Therefore, these three titanium precursors with tmhd or acac ligands were chosen as potential precursors for TiO 2 -SCFD at low process temperatures.…”

“…Although many papers have been published on metal SCFD, only a few papers have been published on metal-oxide SCFD, including Al 2 O 3 , Ga 2 O 3 , SrRuO 3 , TiO 2 , and SrTiO 2 SCFD. 18,[21][22][23] To date, no report has been published on precursor-concentration-independent growth by metal-oxide SCFD. Peng et al observed first-order reaction kinetics during Al 2 O 3 deposition, 18 but did not discuss the relation between the kinetics and step coverage on HAR features.…”

Cu Wiring Fabrication by Supercritical Fluid Deposition for MEMS Devices

“…Oxides can also be deposited in a similar manner through thermochemical reactions in the fluid that dissolve the precursors. RuOx [25], TiO 2 [26], SiO 2 [27], ZnO [28], Al 2 O 3 [29], Y 2 O 3 [30], Bi 2 O 3 [31], SrO [32], and other oxides and mixed oxides that are deposited by CVD can also be deposited by SFCD. Figure 5 illustrates the principles of SFCD for high-aspect-ratio feature filling, and this will be discussed below.…”