Molecular layer deposition (MLD) is an increasingly important thin film synthesis technique in areas such as sensors, microelectronics, protective coatings, and catalysis. However, new analytical approaches are needed to advance fundamental understanding of deposition reaction mechanisms. This work introduces ultrafast laser-based pump–probe picosecond acoustics analysis to characterize thickness-dependent properties of MLD films. Polyurea films are deposited on hydroxylated SiO2 substrates using 1,4-phenylene diisocyanate and a diamine reactant, either ethylenediamine (PDIC/ED polymer) or 1,6-hexanediamine (PDIC/HD), and the expected polymer structure is confirmed by Fourier transform infrared spectroscopy. During the first ∼20 nm of deposition, spectroscopic ellipsometry shows constant refractive index but decreasing growth rate before reaching steady state. X-ray reflectivity also shows approximately constant density during initial growth. However, the measured picosecond acoustics signatures demonstrate a marked increase in sound speed initially, indicating a transition in the physical film structure. The observed trends are ascribed to a transition in the kinetics of active site production and termination with increasing thickness, leading to changes in polymer and oligomer connectivity within the film. These findings provide a basis for better understanding MLD processes and reaction mechanisms that determine deposited film properties.
During TiO2 atomic layer deposition (ALD) using TiCl4 and H2O at ∼150 °C, nucleation proceeds rapidly on hydroxylated SiO2 but is inherently delayed on passivated surfaces such as H-terminated silicon (Si-H) and trimethylsilyl-passivated SiO2 (SiO2-TMS) formed using dimethylamino-trimethylsilane (DMA-TMS) as a small molecule inhibitor. In this work, we explore details of TiO2 nucleation on both Si-H and SiO2-TMS and show that the mechanisms leading to unwanted nuclei depend strongly on the passivation mechanism. Initial growth is observed as a function of ALD cycles using scanning electron microscopy to obtain average particle size, density, and overall surface coverage fraction. Also, average film thickness vs cycle is estimated using ellipsometry or Rutherford backscattering spectrometry. Data are compared to an analytical model that considers that either nucleation sites are present on the starting non-growth surface or sites are generated during the ALD process. On the Si-H surface, data and modeling indicate that nucleation occurs predominantly from a fixed number of nucleation sites present on the starting growth surface that start to immediately grow. However, on TMS-passivated SiO2, nucleation sites are predominantly generated during the growth process so that the density of nucleation sites increases as growth proceeds. Results indicate that nucleation sites are created when adsorbed ALD reactants become kinetically trapped on the SiO2-TMS surface. This demonstrates that mechanisms associated with unwanted nucleation during area-selective deposition (ASD) can depend on details of the surface passivation scheme, thereby providing insight to help to improve ASD strategies for advanced applications.
Background: Extreme ultraviolet (EUV) lithography is crucial to achieving smaller device sizes for next-generation technology, although organic resists face substantial challenges, such as low etch resistance, which limit the resolution of smaller features.Aim: Evaluate the potential for area-selective deposition (ASD) to improve EUV pattern resolution (e.g., by increasing etch resistance).Approach: We evaluate thermal compatibility, atomic layer deposition growth rate, and selectivity for TiO 2 ASD on various organic EUV resist materials using water contact angle, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy. The effects of photo-acid generator (PAG) and EUV exposure on polymer properties and selectivity are considered. Results:The organic resist materials studied demonstrate thermal compatibility with TiO 2 ALD (125°C for 60 min). The TiO 2 ALD process from TiCl 4 and H 2 O proceeds readily on poly(tert-butyl methacrylate), poly(p-hydroxystyrene), and poly(p-hydroxystyrene-randommethacrylic acid) polymers, with and without PAG incorporation, in either the as-formed or EUV exposed state. However, TiO 2 is inhibited on poly(cyclohexyl methacrylate). Conclusions:We demonstrate that as-formed EUV resists can serve as either the growth or nongrowth surface during TiO 2 ASD, thereby enabling resist hardening and tone inversion applications, respectively. These results serve as a basis for further ASD studies on EUV resist materials to improve pattern resolution in next-generation devices.
Extreme ultraviolet (EUV) lithography is crucial to achieving smaller device sizes for next-generation technology, although organic resists face substantial challenges, such as low etch resistance, which limit the resolution of smaller features. Area-selective deposition (ASD) is one potential avenue to improve pattern resolution from organic EUV resists by selectively depositing material on one region of the resist, while preventing material deposition on an adjacent region. We therefore evaluate the compatibility of various organic EUV resists with area-selective atomic layer deposition (ALD) processes, including considering the effects of photo-acid generator (PAG) and EUV exposure on polymer properties and selectivity. The thermal stability of thin resist materials at the TiO2 deposition temperature (125 o C for 60 minutes) is confirmed with water contact angle and atomic force microscopy. Upon TiO2 ALD from TiCl4 and H2O, Rutherford backscattering spectrometry reveals successful TiO2 deposition on poly(tert-butyl methacrylate), poly(p-hydroxystyrene), and poly(p-hydroxystyrene-random-methacrylic acid) polymers, regardless of PAG or EUV exposure. However, TiO2 inhibition is observed on poly(cyclohexyl methacrylate). Thus, we demonstrate that EUV polymers can serve as either the growth or non-growth surface during TiO2 ASD, an insight that can be used to enable resist hardening and tone inversion applications, respectively. These results serve as a basis for further ASD studies on EUV resist materials to improve pattern resolution in next-generation devices.
Organic thin films formed by molecular layer deposition (MLD) are important for next-generation electronics, energy storage, photoresists, protective barriers and other applications. This study uses in situ ellipsometry and quartz...
Area-selective atomic layer deposition (AS-ALD) is a coveted method for the fabrication of next-generation nano-electronic devices, as it can complement lithography and improve alignment through atomic scale control. Selective reactions of small molecule inhibitors (SMIs) can be used to deactivate growth on specific surface areas and as such enable AS-ALD. To investigate new applications of ASD, we need insight into the reactions of SMIs with a broad range of technology relevant materials. This paper investigates the reactions of aminosilane SMIs with a broad range of oxide surfaces and the impact on subsequent atomic layer deposition (ALD). We compare the reactions of two aminosilane SMIs, namely, dimethylamino-trimethylsilane (DMA-TMS) and hexamethyldisilazane (HMDS), with a hydroxylated SiO2 surface and the impact on subsequent ALD processes. The DMA-TMS reaction saturates faster than the HMDS reaction and forms a dense trimethylsilyl (TMS) layer with a higher TMS surface concentration. The higher TMS surface concentration yields better inhibition and higher selectivity during subsequent TiO2 ALD. We show that a wide range of surfaces, i.e., MgO, HfO2, ZrO2, Al2O3, TiO2 (TiN/TiOx), SiO2, SnO2, MoOx, and WO3 remain reactive after DMA-TMS exposure for conditions where SiO2 is passivated, indicating that DMA-TMS can enable AS-ALD on these surfaces with respect to SiO2. On these surfaces, DMA-TMS forms residual TMS and/or SiOxCyHz surface species that do not markedly inhibit ALD but may affect interface purity. Surfaces with lower, similar, and higher surface acidity than SiO2 all show less reactivity toward DMA-TMS, suggesting that surface acidity is not the only factor affecting the substrate-inhibitor interaction. Our study also compares a hybrid inorganic-organic SnOxCyHz and inorganic SnO2 material in view of their relevance as resist for extreme ultraviolet lithography. DMA-TMS can enable selective infiltration in SnOxCyHz, as opposed to selective deposition on SnO2, indicating tunable reactivity by bulk and surface composition. These insights into the reactivity of aminosilane SMIs may aid the design of new area-selective deposition processes, broaden the material space, and enable new applications.
Extreme ultraviolet (EUV) lithography is a critical enabler in nextgeneration technology, although the low etch resistance of conventional organic EUV resists results in low resolution pattern transfer, particularly for smaller features. In this work, we integrate area-selective deposition (ASD), a bottom-up nanopatterning technique, with EUV resists of industrially relevant thicknesses (<50 nm thick) to form resist hardening or tone inverting layers for improved resolution. We utilize TiO 2 ASD via atomic layer deposition on 25−35 nm thin photosensitive polymethacrylate-based EUV materials. By tuning the polymer structure and functionality, we enable different scenarios for selective deposition on top of the resist, infiltrated into the bulk resist, or selective to the resist. We find that a cyclohexyl protecting group causes TiO 2 inhibition, thus showing promise for tone inversion applications with oxide underlayers. In contrast, resist materials containing a tert-butyl protecting group are good candidates for resist hardening because they enable TiO 2 deposition on both EUV exposed and unexposed polymers. Furthermore, we report the integration of a dimethylamino-trimethylsilane inhibitor with the resists to inhibit TiO 2 surface nucleation and facilitate subsurface diffusion, thus further broadening potential applications. The results described here establish an important baseline for utilizing ASD on various organic resists to achieve tone inversion or resist hardening and hence improve EUV pattern resolution.
Area-selective deposition (ASD) is a technique to deposit material only on a defined area of a prepatterned surface, while no deposition occurs on adjacent surface areas. It is the subject of intense investigations by the scientific and engineering communities as it offers the prospect to simplify and improve patterning processes for fabrication of nanoelectronic devices as well as to reduce the manufacturing costs. Numerous efforts have been dedicated to identify process conditions for highly selective ASD processes. Still, the search for optimal conditions is often an empirical process due to the limited understanding of the mechanisms that take place at the atomic scale. Understanding the links between precursor reactivity, surface treatments, and the reactor operating conditions could greatly contribute to the development of highly selective ASD processes. In this paper, we therefore combine first-principles calculations with statistical thermodynamics to understand the role of the precursors in area-selective TiO2 atomic layer deposition (ALD). First, we investigate the selectivity loss mechanisms for TiCl4/H2O ALD on SiO2 nongrowth surfaces with different surface terminations (e.g., OH groups and trimethylsilyl groups). We link the resulting thermodynamic driving forces to experimental reports. Subsequently, we extend the investigation to a total of 26 commercially available titanium precursors and to three different oxygen sources and rank their potential for TiO2 ASD for the SiO2 surfaces with different surface terminations (OH groups and trimethylsilyl groups). We find that the combination of TiCl4 with H2O offers the best performance in terms of selectivity. The theoretical approach proposed here is expected to greatly assist and accelerate the design of precursors for different ASD approaches.
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