Integrated Cleanroom Process for the Vapor-Phase Deposition of Large-Area Zeolitic Imidazolate Framework Thin Films

Abstract

Robust and scalable thin film deposition methods are key to realize the potential of metal-organic frameworks (MOFs) in electronic devices. Here, we report the first integration of the chemical vapor deposition (CVD) of MOF coatings in a custom reactor within a cleanroom setting. As a test case, the MOF-CVD conditions for ZIF-8 are optimized to enable smooth, pinhole-free, and uniform thin films on full 200 mm wafers under mild conditions. The single-chamber MOF-CVD process and the impact of the deposition parameters are elucidated via a combination of in situ monitoring and ex situ characterization. The resulting process guidelines will pave the way for new MOF-CVD formulations and a plethora of MOF-based devices. Apart from their applications in catalysis, 1 gas storage, 2 and separation processes, 3 metal-organic frameworks (MOFs), with their unprecedented specific surface areas and chemical modularity, show tremendous potential for integration in microelectronics. 4,5 As sensor coatings, their tunable composition and crystalline structure can be exploited for the selective adsorption of target molecules. 6-9 The low dielectric constant resulting from their porosity makes MOFs prime candidates for high-performance insulators in future logic processors. 10,11 To capitalize on the 10-6 cm 2 , were estimated using a CCD camera. All instruments were controlled using custom software. The generated current density (J) histograms were fitted using Gaussian functions for determining the peak center and width.

Solvent‐Free Powder Synthesis and Thin Film Chemical Vapor Deposition of a Zinc Bipyridyl‐Triazolate Framework

“…At the same time, larger crystallites are formed by ripening (Figures and S4.4). A similar growth process was observed for ZIF‐8 CVD …”

“…For this study, MAF‐252 thin films were deposited within an hour in a simple glass reactor kept at 200 °C to ensure a high enough vapor pressure of this low‐volatility linker (Figures S3.1 and S3.2). MAF‐252 CVD is a very simple and robust film deposition process, while ZIF‐8 and MAF‐6 CVD require precise control over the atmosphere composition (e.g., relative humidity), as well as the temperature gradient between substrate and reactor to achieve reproducible film morphology …”

Advanced technologies for the fabrication of MOF thin films

“…10a). 63,64 The authors used a sacrificial ZnO thin film obtained by ALD to template the synthesis of MOFs. Thus, the ZnO film was subsequently converted to ZIF-8 through a vapor-solid reaction 65,66 with 2-methylimidazole in a relatively short time ( Fig.…”

“…Nevertheless, for microelectronic applications, the MOF-CVD approach must be optimized to be compatible with automated cleanroom facilities. 64 In all the gas phase approaches reviewed above, the main characteristic has been the absence of solvents during the synthesis procedure. As previously stated, this can be advantageous because it could avoid surface-tension phenomena or eventual corrosion of the final device, and could also lead to a reduction of costs from a scale-up perspective.…”

Hierarchical Metal‐Organic Framework Films with Controllable Meso/Macroporosity

“…Only for ZnO FNNs with an extrinsic porosity ≥97%, full conversion into crack-free ZIF-8 films was observed ( Figures S5-9, Supporting Information). For lower porosity fractions, the volume expansion that occurs during the oxide-to-MOF conversion (10-17 times, depending on the ZnO crystallinity) [17,24] limits the diffusion of the ligand, resulting in a partial conversion, residual stress, and cracks within the final MOF films ( Figure S5, Equation 1, Supporting Information). The full conversion to ZIF-8 was confirmed by the absence of ZnO diffraction peaks ( Figures S6,7,10a, Supporting Information) and FTIR spectroscopy ( Figure S10b, Supporting Information).…”