Potential Step Coverage for Supercritical Fluid Deposition of TiO2 by Numerical Simulation and Microcavity Analysis

Abstract

The potential step coverage for supercritical fluid deposition of TiO 2 (TiO 2 -SCFD) was evaluated using numerical simulation based on kinetic parameters. A required parameter, the ratio of the surface reaction rate constant to the diffusivity, ks D , was retrieved experimentally. The simulations revealed that a step coverage of 0.97 was possible on deep trenches (6.75-μm depth, 125-nm width) without compromising the growth rate. Conformal deposition by TiO 2 −SCFD is possible on narrow trenches having the same aspect ratio. The simulations were validated experimentally. Our methodology for evaluating the potential step coverage is also equally applicable to SCFD of other metal oxides.Supercritical fluid deposition (SCFD) is a promising technology that enables conformal deposition on high-aspect-ratio features at low temperature. 1,2 In SCFD, metal-organic precursors and oxidants/reductants that are dissolved in supercritical CO 2 (scCO 2 ) react on the surface of a heated substrate and deposit. A lower process temperature compared with conventional dry processes such as chemical vapor deposition (CVD) is possible because of the solvent effect of the SCF. 3,4 A precursor molecule is surrounded by solvent molecules to form a cluster, which decreases the potential barrier for pyrolysis. Conformal deposition on high-aspect-ratio features is also helped by a high precursor concentration, which is possible because of the liquidlike solubility and high mass transfer because of gas-like diffusivity. 5 Despite several reports concerning low temperature oxide−SCFD, the feasibility of conformal deposition on high-aspect-ratio features remains uncertain. We selected TiO 2 to represent oxide materials because of successful reports of TiO 2 −SCFD, 6-8 and evaluated the potential step coverage of TiO 2 −SCFD on the basis of a kinetic study via the following steps: (1) deposition of TiO 2 in high-aspect-ratio trenches (aspect ratios of 50, 80, and 100), (2) extraction of kinetic parameters from the film thickness profile within the trenches using microcavity analysis, and (3) estimating the possible step coverage on various trenches by solving a mass balance equation of the filmforming species. Conformal TiO 2 films could be formed with similar quality as those from atomic layer deposition (ALD) using SCFD on ultra-narrow and high-aspect-ratio trenches. Our simulations reproduced all of the experimental results, validating our methodology.TiO 2 films were deposited by pyrolyzing a source precursor in 15 MPa scCO 2 on a substrate at 250 • C in a flow-type reactor. 9 Ti(Oi-C 3 H 7 ) 2 (C 11 H 19 O 2 ) 2 [Ti(O−iPr) 2 (tmhd) 2 ] was used as the source precursor. 10,11 High purity CO 2 (> 99.99%) was employed as the supercritical solvent. Si trenches with three different aspect ratios were used: (A) 50 (2-μm width, 100-μm depth), (B) 80 (1-μm width, 80-μm depth), and (C) 100 (0.6-μm width, 60-μm depth). Each trench was coated with thermal SiO 2 . A substrate was placed on the bottom of the reactor and heated to 250 • C by the pedes...

Conformal Bismuth Titanate Formation Using Supercritical Fluid Deposition

“…Conformal deposition has been reported for various materials including Cu, Ni, Ru, Ag, Pt, HfO 2 , ZrO 2 , and RuO 2 on trenches having ARs ranging from 10 to 100. [33][34][35][36][37] Concerning materials related to BIT, we demonstrated conformal TiO 2 deposition by SCFD on trenches having an AR of 100, 26 while step coverage of TiO 2 by CVD was as much as 0.6 on shallow trenches having an AR of 0.5. 38 Conformal deposition of multi-component films has also been achieved.…”

“…For example, the maximum concentration of the Ti precursor used in this study was five orders of magnitude higher for SCFD compared with CVD. 24,26,37 Using SCFD with its elevated precursor concentration enables conformal deposition on high-AR trenches without compromising the deposition rate. Furthermore, there is the possibility of significantly enhancing the growth rate by increasing the precursor concentration with some entrainers.…”

“…Supercritical fluid deposition (SCFD) is an emerging deposition technology involving the oxidation/reduction of metal organic compounds in supercritical CO 2 (scCO 2 ). [25][26][27][28][29][30][31][32] Because scCO 2 exhibits physical properties intermediate between those of a gas and liquid, e.g., it has the gaseous properties of high diffusivity, low viscosity and surface tension, and the liquid-like properties of high density and good dissolution capability, 28 scCO 2 works as an ideal reaction medium combining the respective advantages of liquid and gas. Compared with the traditional MOCVD, SCFD generally provides better step coverage on high aspect ratio (AR) features at a moderate deposition rate.…”

A Review of Three‐Dimensional Resistive Switching Cross‐Bar Array Memories from the Integration and Materials Property Points of View

“…Another promising deposition method for oxide films is the supercritical fluid deposition. Jung et al reported the TiO 2 film deposition using the supercritical fluid deposition method with a step coverage of >97% on a contact hole with an aspect ratio of 50 …”

Supercritical fluid deposition for conformal Cu film formation on sub-millimeter-scale structures used to fabricate terahertz waveguides

“…Studies regarding SCFD have focused on the Cu interconnections of ultra-large scale integrations (ULSIs), [17][18][19] where conformal Cu film formation has been achieved on nanometer-scale structures with high aspect ratios (ARs) of 100, as well as overhanging structures. [20][21][22] To evaluate the applicability of SCFD for sub-millimeter-scale THz wave devices, Cu film thickness profiles in THz waveguides prepared via SCFD have been simulated using the mass balance equation of the precursor (bis (2,2,6,6-tetramethyl-3,5-heptanedionato)-copper [Cu(tmhd) 2 ]), which is a β-diketone compound. 23) The results indicated that conformal deposition via the conventional SCFD method was difficult because of insufficient precursor concentration (to be discussed later).…”