Gradient area-selective deposition for seamless gap-filling in 3D nanostructures through surface chemical reactivity control

Abstract

The integration of bottom-up fabrication techniques and top-down methods can overcome current limits in nanofabrication. For such integration, we propose a gradient area-selective deposition using atomic layer deposition to overcome the inherent limitation of 3D nanofabrication and demonstrate the applicability of the proposed method toward large-scale production of materials. Cp(CH₃)₅Ti(OMe)₃ is used as a molecular surface inhibitor to prevent the growth of TiO₂ film in the next atomic layer deposition process. Cp(CH₃)₅Ti(OMe)₃ adsorption was controlled gradually in a 3D nanoscale hole to achieve gradient TiO₂ growth. This resulted in the formation of perfectly seamless TiO₂ films with a high-aspect-ratio hole structure. The experimental results were consistent with theoretical calculations based on density functional theory, Monte Carlo simulation, and the Johnson-Mehl-Avrami-Kolmogorov model. Since the gradient area-selective deposition TiO₂ film formation is based on the fundamentals of molecular chemical and physical behaviours, this approach can be applied to other material systems in atomic layer deposition.

Fig. 1. Schematic illustrations of ASD processes for seamless gap-filling.

a Typical ALD process. b ALD process for V-shaped growth. c The proposed gradient ASD process using an inhibitor.

Fig. 2. Adsorption behaviour and blocking property of TMPMCT inhibitor.

a Surface reaction energy diagram of TMPMCT molecules on the TiO₂ surface calculated by DFT. The structures below correspond to the Path 1. The dotted lines represent the reactions, where TS (transition states) structures were not calculated. Colours: Ti_surf (light blue), Ti_TMPMCT (yellow green), O_surf (red), O_TMPMCT (purple), C (brown), H (white pink). The corresponding chemical equations: Phy.: Cp(CH₃)₅Ti(OMe)₃, Ads.: *-Cp(CH₃)₅Ti(OMe)₃, 1OMe disso.: *-Cp(CH₃)₅Ti(OMe)₂ + *-(OMe), 2OMe disso.: *-Cp(CH₃)₅Ti(OMe) + 2·*-(OMe), 3OMe disso.: *-Cp(CH₃)₅Ti + 3·*-(OMe). Phy. (Physisorption), Ads. (Adsorption), disso. (dissociation), surf (surface), * refers to adsorbed species. b WCA measurement with various exposure times of TMPMCT on the TiO₂ surface. Fitting of the JMAK model (dashed lines) to the data (points with error bars) obtained from c the growth of subsequent TiO₂ ALD on the TMPMCT inhibitor layer (20, 40 and 60 s), and d selectivity calculated from the thickness measured by ellipsometry. e Areal coverage of TMPMCT on the TiO₂ surface (10 nm × 10 nm) using various impingement numbers calculated by MC simulation and the coverage of TDMAT on the TMPMCT-inhibited surface. f Adsorption mechanism of TMPMCT inhibitor. Unoccupied sites serve as starting points for the nucleation sites of TiO₂ in subsequent ALD cycles. Source data are provided as a Source data file.

Fig. 3. Blocking property of TMPMCT with an additional H₂O pulse.

a Schematic of TMPMCT exposure with an additional H₂O pulse to improve coverage. b Adsorption energy of hydrolysed TMPMCT species, Cp(CH₃)₅Ti(OMe)_3-x(OH)_x (x = 0, 1, 2 and 3), calculated by DFT. c MC simulation results for the adsorption of Cp(CH₃)₅Ti(OMe)_3-x(OH)_x with steric hindrance in cases x = 1, 2 and 3. Fitting of the JMAK model to data (points with error bars) obtained from d growth and e selectivity in the case of 20 s TMPMCT with and without additional H₂O pulse samples. Fitting of the JMAK model to data (points with error bars) obtained from f growth and g selectivity in the case of 40 s TMPMCT with and without additional H₂O pulse samples. Source data are provided as a Source data file.

Fig. 4. Hole pattern with a depth of 1600 nm, an opening diameter of 100 nm and a bottom diameter of 50 nm used for gap-filling.

a TEM images of the subsequent 40 nm thick TiO₂ ALD film on the 0, 40 and 60 s TMPMCT inhibitors and 40 s TMPMCT with an additional H₂O/10 nm TiO₂/SiO₂ hole. b Growth and c selectivity calculated from the TEM results. d Relative coverage of various TMPMCT pulses, as calculated from the equation described in Supplementary Note 3 and depicted in illustrations e 40 s TMPMCT pulse, f 60 s TMPMCT pulse. Source data are provided as a Source data file.

Fig. 5. 100 nm TiO₂ ALD deposited in holes with and without TMPMCT inhibitor.

a Cross-sectional TEM images of the hole pattern (depth = 1600 nm) for 100 nm TiO₂ ALD without TMPMCT. Unfilled zones are observed at the bottom (zone 4), and seam formation occurs along the centreline of the hole (zones 2 and 3). b Cross-sectional TEM images of the 100 nm TiO₂ ALD/60 s TMPMCT/SiO₂ hole and top-down TEM images at different depths, demonstrating hole filling without any seam formation.