ALD2018 Session AS-TuA: Area Selective Deposition II
Tuesday, July 31, 2018 1:30 PM in 113-115
AS-TuA-1 Integrated Isothermal Atomic Layer Deposition and Thermal Atomic Layer Etching: “Atomic-Level Processing” for Area-Selective Patterning of TiO2
Seung Keun Song (North Carolina State University); Paul C. Lemaire (Lam Research Corp.); Gregory N. Parsons (North Carolina State University)
Area-Selective Atomic Layer Deposition (AS-ALD) is attracting more attention from the semiconductor industry as a possible solution to alignment issues typically faced when scaling down transistor feature sizes. To address this challenge we show a new approach to AS-ALD, where self-limiting thermally-driven atomic layer etching (ALE) is chemically coupled with self-limiting thermal atomic layer deposition (ALD) to yield several nanometers of TiO2 thin film formation on receptive SiO2 surfaces at 170°C, with no measurable grown on adjacent areas of hydrogen-terminated silicon (100). When TiO2 ALD using TiCl4 and H2O is done 170°C on non-oxidized hydrogen-terminated silicon, we find an incubation time of ~30 cycles is required before substantial TiO2 nuclei appear. On SiO2 surfaces, however, TiO2 nucleation proceeds rapidly, allowing 10-20 Å of deposition before nucleation on Si-H. Using this inherent nucleation delay combined with a novel self-limiting thermal ALE procedure employing sequential doses of WF6 and BCl3, we create a new isothermal “Atomic-Level Process”, where the atomic-scale chemical control of ALD is intimately coupled with that of thermal ALE to build up on a prepared surface, precise nanoscale constructs with pre-selected location and dimension. Using the integrated ALD/ALE sequence, we achieve in excess of 200 TiO2 ALD cycles, yielding ~ 4 nm of TiO2 on SiO2, before visible nuclei form on Si-H, as determined by SEM, ellipsometry and TEM analysis. Process and materials analysis using in-situ QCM and ex-situ AFM and XPS further confirm our findings. To date, extending the ALD/ALE sequence to more than 500 ALD cycles leads to incomplete TiO2 etch removal from Si-H, ascribed to changes in Si-H during prolonged exposure to deposition and etch species. This demonstrated Atomic Level Process for improved control in selective deposition offers substantial opportunities for integrated area-selective ALD, and provides a viable pathway to explore other Atomic Level Processes for parallel and wafer-scale synthesis of nanoscale and sub-nanoscale constructs.View Supplemental Document
AS-TuA-2 Inherent Substrate Selectivity and Nucleation Enhancement during Ru ALD using the RuO4-Precursor and H2-gas.
Matthias Minjauw, Hannes Rijckaert, Isabel Van Driessche, Christophe Detavernier, Jolien Dendooven (Ghent University, Belgium)
Ruthenium is a candidate to replace copper in future sub-10 nm interconnects. At these dimensions the resistivity of Ru lines is expected to be lower compared to Cu due to the lower sensitivity to size effects.1 In addition, it is likely that Ru interconnects won’t require a diffusion barrier, and will show a better electromigration performance.2 At feature sizes below 10 nm it will be difficult to align subsequent lithography steps, and the conformality of the deposition method is increasingly important, such that area selective atomic layer deposition (ALD) of ruthenium is of high interest.3
We first report inherent area selective ALD of Ru on H-terminated Si (Si-H) versus SiO2, using the thermal RuO4 (ToRuSTM)/ H2-gas ALD process.4 In situ spectroscopic ellipsometry (SE) on blanket substrates shows that Ru growth initiation occurs from the first cycle on Si-H, while on SiO2 the growth is delayed, resulting in a substrate selectivity window of ~ 70 cycles (Figure 1, a). Area selective Ru ALD was evaluated using a patterned substrate of 1-10 µm wide Si-H lines separated by 10 µm wide SiO2 regions, and exposing it to 20 cycles of the RuO4 / H2-gas ALD process. Ex situ scanning electron microscopy (SEM) and cross section high resolution transmission electron microscopy (HRTEM) measurements show that a 4.5 nm Ru film could be deposited on the Si-H, with no Ru detected on the SiO2 (Fig. 2). In vacuo X-ray photoelectron spectroscopy (XPS) experiments showed that exposure of Si-H to a single RuO4 pulse leads to the oxidation of the Si surface, together with the deposition of RuO2. On SiO2 however, the surface is already oxidized, and in vacuo XPS shows that for the same exposure to RuO4 no Ru is deposited on the surface (Fig. 3). Therefore, we propose that the mechanism behind the inherent substrate selectivity is the oxidation of the Si-H surface by RuO4. Secondly, we report for a methodology to enhance the nucleation of the RuO4 / H2-gas process on oxide substrates. In vacuo XPS and in situ SE experiments show that a single exposure of SiO2 to trimethylaluminum (TMA) makes the surface reactive towards RuO4, which allows for Ru growth initiation from the first cycle (Fig. 1, b; Fig. 3). We propose that this is due to the combustion of surface CH3-groups by RuO4. As TMA is known to be reactive towards many oxide substrates, this methodology presents a way to achieve Ru metallization of virtually any surface.
1 S. Dutta et al. IEEE Elec. Dev. Lett. 2017, 38, 949.
2 O. V. Pedreira et al. 2017 IEEE IRPS, Monterey, CA, 6B-2.1.
3 P. C. Lemaire et al. J. Chem. Phys.2017, 146, 052811.
4 M. M. Minjauw et al. J. Mater. Chem. C. 2015, 3, 132.View Supplemental Document
AS-TuA-3 Surface Preparation and High Nucleation for Selective Deposition using Anhydrous Hydrogen Peroxide
Daniel Alvarez, Jeffrey Spiegelman, Keisuke Andachi (RASIRC)
Creative surface protecting agents are being used in efforts to explore novel methods for Area Selective Deposition (ASD). These agents include self-assembled monolayers, patterned photoresists, plasma deposited films and others. At the same time, fast nucleation and growth of metal oxide films require creation of fully covered reactive surfaces. Surface treatment ideally will:
Anhydrous hydrogen peroxide has been largely ignored as a potential novel reactive chemistry. There are several reasons for this. First, there is no precedent in the literature. Second, when delivered H2O2 is typically mixed with H2O, which dominates the reaction. Third, this material has only recently become available in a packaged form that could integrate into selective deposition process equipment.
Hydrogen Peroxide is an attractive chemistry for area selective deposition because of both its oxidation properties and proton transfer properties. The chemistry compares favorably to Ozone (oxidation potential = 2.1V versus 1.8V for H2O2). It also has slightly stronger proton transfer than water (water pKa = 7.0 versus 6.5 for H2O2). Most critically, H2O2 has a very weak O-O bond, with Bond Energy = 36 kcal/mole, suggesting more energetically favorable reactivity at reduced temperatures.
Results from our work show good correlation with selective deposition requirements:
Other testing shows that metal oxide film quality grown using anhydrous H2O2 are nearly identical to those grown with ozone methods. Metal oxide films include aluminum oxide, hafnium oxide, and zirconium oxide.
The presentation will discuss details of newly discovered reactivity of anhydrous H2O2 on several surfaces and will outline potential ASD pathways.
AS-TuA-4 An Inherently Selective Atomic Layer Deposition of MoSix on Si (001) in Preference to Silicon Nitride and Silicon Oxide
Jong Youn Choi, Christopher Ahles (University of California San Diego); Raymond Hung, Namsung Kim (Applied Materials); Andrew Kummel (University of California San Diego)
As metal-oxide-semiconductor field effect transistors (MOSFETs) shrink into the <10 nm regime, it becomes a significant challenge to minimize electrical loss with a decreasing pitch especially at the contact regions. To reduce resistance in a compact geometry, selective atomic layer deposition (ALD) of transition metal disilicides is of great interest. In previous studies, selective ALD of tungsten (W) via a fluorosilane elimination process was demonstrated using WF6 and SiH4 or Si2H6.1,2 Selectivity was achieved by an inherently favorable reactivity of the precursors on hydrogen-terminated Si versus OH-terminated SiO2. In this study, sub-stoichiometric MoSix (x= 0.7–1.4) was selectively deposited by ALD on H-terminated Si (001) in preference to SiO2 and SiN using MoF6 and Si2H6 at 120°C. In-situ, X-ray Photoelectron Spectroscopy (XPS) was used to investigate the chemical composition of MoSix ateach experimental step. To confirm selective deposition on the nanoscale, MoSix was deposited on a Si sample patterned with SiO2 and Si3N4 and cross-sectional Tunneling Electron Microscopy (TEM) was performed. It was observed that the Si-H surface termination allowed nucleation of MoSix on Si in contrast to the inherently chemically passive (non-reactive) SiOx and SiN surfaces. This substrate-dependent selectivity was retained for MoSix growth of up to 10 nm with a proper N2 purge gas to prevent any CVD components on SiO2 and SiN. Performing additional Si2H6 doses after the ALD cycles allowed the incorporation of more Si into the film and increased the stoichiometry to be closer to MoSi2. The MoSix catalyzes this self-limiting CVD of Si while retaining selectivity over SiO2 and SiN. In-situ Scanning Tunneling Microscopy (STM) showed that MoSix ALD on Si produced an atomically flat surface with a root mean square (RMS) roughness of 2.8 Å. Post-annealing in ultra-high vacuum at 500°C for 3 minutes further decreased the RMS roughness to 1.7 Å. A depth profiling XPS study revealed that the bulk of the MoSix film is close to stoichiometric MoSi2 with <10% oxygen and fluorine. The TEM imaging shows that the selectivity is retained on the nanoscale and that MoSix can be selectively deposited on Si without substrate consumption. This is enabled by just taking advantage of the selective ALD of substiochiometric MoSix combined with the ability of the substiochiometric MoSix films to selectivity induce self-limiting Si deposition from Si2H6.
1. Ph. Gouy-Pailler et al., Thin Solid Films, 241, 374 (1994)
2. B. Kalanyan et al., Chem. Mater., 28, 117-126 (2016).View Supplemental Document
AS-TuA-5 Investigating the Difference in Nucleation during Si-based ALD on Different Surfaces (Si, SiC, SiO2 and SiNx) for Future Area-Selective Deposition (AS-ALD)
Ekaterina A. Filatova (Tyndall National Institute, University College Cork, Ireland); Alfredo Mameli, Adrie Mackus (Eindhoven University of Technology, Netherlands); Fred Roozeboom (Eindhoven University of Technology and TNO, Netherlands); Wilhelmus Kessels (Eindhoven University of Technology, Netherlands); Dennis Hausmann (Lam Research Corp.); Simon D. Elliott (Schrödinger, Inc., Ireland)
Area-selective atomic layer deposition (AS-ALD) allows nanostructures of arbitrary composition and lateral shape to be built with atomic precision on pre-selected substrate locations. Most current approaches for AS-ALD are based on local inhibition (e.g. with self-assembled monolayers) or activation. However, for some applications of AS-ALD (e.g. in self-aligned fabrication) it is relevant to be able to exploit differences in chemical behavior of a pre-patterned substrate. For this reason, investigating inherent differences in nucleation on diverse substrates is of crucial importance for developing future AS-ALD processes. In this paper we are focussing on substrates of silicon and silicon-based dielectric materials (SiC, SiO2 and SiNx) used in electronics.
In order to investigate the possibility of area-selective deposition of Si-based materials using aminosilane precursors, nucleation on four different Si-based surfaces (Si:H, SiC:H, SiO2:OH and Si3N4:NH2/NH) was analyzed. First, we investigated the difference in precursor adsorption on these surfaces during the exposure of di(isopropylamino)silane (DIPAS), di(sec-butylamino)silane (DSBAS) and bis(t-butylamino)silane (BTBAS) precursors by calculating their adsorption energies using ab-initio modelling. From density functional theory (DFT) calculations, we found that DSBAS is thermodynamically favorable to react with Si3N4 and SiO2, but not with SiC and Si at 0K. To experimentally corroborate these results, SiNx was deposited using Plasma-Enhanced ALD from DSBAS precursor and N2 plasma on three different surfaces (H2 plasma-exposed SiC, HF-last c-Si and c-Si with native SiO2). In-situ spectroscopic ellipsometry (SE) measurements were performed after every half-cycle to analyze the DSBAS adsorption reaction on these surfaces. During the first DSBAS dosing cycle on the SiO2 surface a change in the SE signal was observed, suggesting initial DSBAS adsorption, while no changes were observed on the Si and SiC surfaces. The selective adsorption of DSBAS on SiO2 is in agreement with the DFT predictions. The subsequent N2 plasma half-cycle modifies the non-growth surface into SiNx, after which the selectivity is lost. These results illustrate that it is generally difficult to achieve area-selective ALD for nitrides, because of the nitridation of all the exposed substrate surfaces during the plasma step.
We conclude, that during ALD on Si-based substrate materials DSBAS reacts selectively with SiO2 and SiNx surfaces but not with Si and SiC surfaces. Our results highlight the role of DFT calculations in predicting possible routes towards AS-ALD process development.View Supplemental Document
AS-TuA-6 Strategies for Area Selective Atomic Layer Deposition and Applications in Catalysis
Rong Chen, Kun Cao, Xiao Liu, Jiaming Cai, Bin Shan, Jie Zhang (Huazhong University of Science and Technology, China)
Atomic layer deposition (ALD) is a mainstay technology for the semiconductor industry since it allows deposition of nanometer-thin layers of desired materials onto a substrate in a very controlled and uniform manner. Recently, ALD has been adapted to design and synthesize composite catalysts that allow them to promote multiple chemical reactions. In fabrication of composite catalysts, the selective approaches of ALD are of great importance to exert spatial control of deposition to fabricate three dimensional nanostructures.
In this talk, strategies for selective ALD and enabled nanostructures for catalytic applications will be discussed. Selective ALD allows directional and precise tailoring of the structural size, composition, interfaces, and active sites, that is of great importance for catalysis applications. Two major types of selective ALD approaches are introduced, template selective method via surface modification of self-assembled monolayers (SAMs) and reverse SAMs passivation, as well as inherently selective deposition. With these methods, core shell nanoparticles, oxide overcoating structures ranging from porous coating to ordered structures, and oxide surrounding structures could be fabricated controllably. Theoretical simulations, spectroscopic and microscopic analysis, and catalytic performance are carried out to verify the results. These strategies of selective ALD demonstrate unique advantages to design and fabricate highly stable and active catalysts on the atomic scale, providing unique opportunities to understand the structure–property relationship of catalysis.