Berc Kalanyan

An absorption imaging technique was described for visualizing molybdenum pentachloride (MoCl ₅ ) flow during an atomic layer deposition/pulsed chemical vapor deposition process. The imaging system was composed of a telecentric lens and a commercial 7.1-megapixels (MP) complementary metal oxide semiconductor (CMOS) camera. The light source was a fiber-coupled light emitting diode operating at a peak emission wavelength of 443 nm. Flow images of MoCl ₅ vapor entrained in a carrier gas were recorded at approximately 93 frames per second in a research-grade vapor deposition chamber. The utility of this technique was illustrated by comparing the MoCl ₅ flow patterns for two precursor injection conditions, conditions consisting of different argon carrier gas flow rate and chamber pressure. For a low flow rate and chamber pressure, the flow images showed a gradual expansion of the MoCl ₅ concentration front through the field of view with a relatively short MoCl ₅ residence time. These flow patterns result in a relatively uniform precursor concentration front impinging on the wafer surface with the precursor being efficiently exhausted from the chamber, making these conditions desirable for thin film deposition in this chamber. For a high carrier gas flow rate and elevated chamber pressure, the flow images showed a high gas velocity jet impinging on the wafer chuck surface and the formation of gas recirculation zones, resulting in a relatively long residence time. These flow conditions would make it difficult to reproducibly deposit uniform thin films in this chamber. This comparison demonstrated the utility of this technique for qualitative characterization of precursor flow fields with minimal data processing. However, the two-dimensional data obtained from this technique can also provide the basis for training and validating computational fluid dynamics models. Furthermore, the addition of duplicate optical systems would provide the basis for determining the three-dimensional precursor distribution through tomographic analysis.

This letter reports on pilot tests of microfabricated nanocalorimeters as a metrology platform for rapid (<40 ms response time) and sensitive (in the range of 1020 m−2 s−1–1017 m−3 for radicals’ flux and density, respectively) detection of neutral radicals generated by reactive cold plasmas. The setup consists of a nanocalorimeter resistive sensor coated with a catalyst alongside an inert reference sensor with identical thermal masses. By measuring the temperature increase in the active sensor caused by radical surface recombination reactions and comparing it to the reference sensor, parasitic stimuli such as IR/visible/UV irradiation and ion- and/or electron-induced heat fluxes can effectively be isolated. The system was successfully tested in a hydrogen plasma environment, and critical performance metrics such as sensitivity and response time were evaluated and benchmarked against the existing plasma radical diagnostic techniques.

This article describes time-resolved optical measurements of H2S partial pressure and mass flow in a pulsed gas delivery system approximating injection conditions encountered during atomic layer deposition. A high-speed nondispersive ultraviolet (NDUV) gas analyzer design is employed for in-line H2S detection in a gas delivery line with flowing carrier gas. An in-place analyzer calibration performed in a reference cell yields an H2S detection limit of ≈1.4 Pa (at 22 °C) at a sampling rate of 1 kHz. Flow measurements performed on the delivery line are used to evaluate the effects of adjustable delivery parameters on the time-dependent injection system output. Short pulse widths exhibit partial pressure transients attributed to flow development within the different volumes of the delivery system. After ≈1.0 s of injection, steady-state flow is established across flow elements. A partial pressure of H2S in the delivery line is found to vary linearly with upstream H2S pressure, consistent with choked flow. A stronger scaling of partial pressure is evident when the flow coefficient of the downstream metering valve is adjusted. Estimated steady-state H2S flow rates in the range of 0.05–0.21 mg/s are observed within a limited range of valve flow coefficients. However, further increases in the flow coefficient do not result in increased flow, likely due to conductance limitations in downstream flow system components. The utility of NDUV absorption measurements for high-pressure pulsed gas delivery systems is discussed.

Nondispersive ultraviolet visible gas analyzer designs were evaluated for monitoring molybdenum-containing chloride and oxychloride precursor delivery during microelectronics vapor deposition processes. The performances of three analyzer designs, which differed only in the bandpass filter employed for wavelength selection, were compared for measuring the partial pressure of molybdenum pentachloride, molybdenum oxytetrachloride (MoOCl ₄ ), and molybdenum dioxydichloride (MoO ₂ Cl ₂ ). The analyzer's optical response with a 369 nm center wavelength filter for molybdenum pentachloride was determined by measuring the molybdenum pentachloride absorbance as a function of vapor molar density. The calibrated analyzer was transferred to a process line on a deposition chamber and used to measure the molybdenum pentachloride partial pressure during delivery in a flowing carrier gas. The molybdenum pentachloride minimum detectable density was determined to be 1 × 10 ^–4 mol m ^–3 (0.35 Pa for a cell temperature of 145 °C), for data collected at 1 kHz and referenced to a 0.2 s duration background. The analyzer optical response for molybdenum pentachloride with the two other filters and the response for MoOCl ₄ and MoO ₂ Cl ₂ with all three filters were simulated with a simple model. These data were used to evaluate the sensitivity and selectivity of analyzers incorporating the different filters to some likely combinations of analytes and interferents.

This article reports quantitative absorption spectra for MoCl5, MoOCl4, and MoO2Cl2 in the vapor phase from 45,500 to 15,500 cm(-1) (645 to 220 nm). Spectra are obtained in an ultrahigh purity stainless steel vacuum system by rapidly sampling a range of analyte partial pressures. The short measurement times and the differential absorbance method employed here minimize effects from uncontrolled transients such as window deposits. A detailed analysis of replicate measurements and time-resolved spectra shows generally reproducible spectral response from MoCl5 vapors at 120 degrees C. The presence of HCl and MoOCl4 impurities in the MoCl5 vapor samples is determined to be unlikely based on the analysis of absorbance-pressure curves and spectral peak fitting. Comparison with MoOCl4 and MoO2Cl2 spectra shows a unique spectral fingerprint for MoCl5 at 28,500 cm(-1) providing a convenient means of discriminating between MoCl5 and its oxychlorides in the visible wavelengths. Adsorption behavior of MoCl5 on surfaces is also discussed with particular emphasis on the use of MoCl5 as a reactant in vapor phase thin film deposition processes.

This study demonstrates that commonly used consumer products such as single-use food grade nylon bags and hot beverage cups lined with low-density polyethylene release nanometer-sized plastic particles at number densities >10¹² L^-1 when exposed to water. The number of particles released was a function of the initial water temperature (high temperature vs ambient) for each of the tested materials. Mean particle diameters were between 30 and 80 nm with few particles >200 nm. The number of particles released into hot water from food grade nylon was 7 times higher when compared to single-use beverage cups. On a particle number density basis, particles released into water from a single 300 mL hot beverage cup equate to one particle for every seven cells in the human body in a size range available for cellular uptake.

Potential commercial applications for transition metal dichalcogenide (TMD) semiconductors such as MoS2 rely on unique material properties that are only accessible at monolayer to few-layer thickness regimes. Therefore, production methods that lend themselves to the scalable and controllable formation of TMD films on surfaces are desirable for high volume manufacturing of devices based on these materials. The authors have developed a new thermal atomic layer deposition process using bis(tert-butylimido)-bis(dimethylamido)molybdenum and 1-propanethiol to produce MoS2-containing amorphous films. They observe a self-limiting reaction behavior with respect to both the Mo and S precursors at a substrate temperature of 350 °C. Film thickness scales linearly with precursor cycling, with growth per cycle values of ≈0.1 nm/cycle. As-deposited films are smooth and contain nitrogen and carbon impurities attributed to poor ligand elimination from the Mo source. Upon high-temperature annealing, a large portion of the impurities are removed, and the authors obtain few-layer crystalline 2H-MoS2 films.

In situ chemical measurements of solution/surface reactions during metal–organic framework (MOF) thin film growth can provide valuable information about the mechanistic and kinetic aspects of key reaction steps and allow control over crystal quality and material properties. Here, we report a new approach to studying the growth of MOF thin films in a flow cell using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Real-time spectra recorded during continuous-flow synthesis were used to investigate the mechanism and kinetics that govern the formation of (Zn,Cu) hydroxy double salts (HDSs) from ZnO thin films and the subsequent conversion of HDS to HKUST-1. We found that both reactions follow pseudo-first-order kinetics. Real-time measurements also revealed that the limited mass transport of reactants may lead to partial conversion of ZnO to HDS and therefore leaves an interfacial ZnO layer beneath the HDS film, providing strong adhesion of the HKUST-1 coating to the substrate. This in situ flow-cell ATR-FTIR method is generalizable for studying the dynamic processes of MOF thin film growth and could be used for other solid/liquid reaction systems involving thin films.

High-volume manufacturing of devices based on transition metal dichalcogenide (TMD) ultrathin films will require deposition techniques that are capable of reproducible wafer-scale growth with monolayer control. To date, TMD growth efforts have largely relied upon sublimation and transport of solid precursors with minimal control over vapor-phase flux and gas-phase chemistry, which are critical for scaling up laboratory processes to manufacturing settings. To address these issues, we report a new pulsed metal–organic chemical vapor deposition (MOCVD) route for MoS₂ film growth in a research-grade single-wafer reactor. Using bis(tert-butylimido)bis(dimethylamido)molybdenum and diethyl disulfide, we deposit MoS₂ films from ∼1 nm to ∼25 nm in thickness on SiO₂/Si substrates. We show that layered 2H-MoS₂ can be produced at comparatively low reaction temperatures of 591 °C at short deposition times, approximately 90 s for few-layer films. In addition to the growth studies performed on SiO₂/Si, films with wafer-level uniformity are demonstrated on 50 mm quartz wafers. Process chemistry and impurity incorporation from precursors are also discussed. This low-temperature and fast process highlights the opportunities presented by metal–organic reagents in the controlled synthesis of TMDs.