Remote H2 Research Articles

Stepwise Growth of Crystalline MoS2 in Atomic Layer Deposition

Transition metal dichalcogenides (TMDCs) are layered materials in which each layer is weakly bound by van der Waals forces. TMDCs have interesting intrinsic properties, including high mobility and excellent electrostatic controllability, even at monolayer thickness. Hence, they have emerged as promising materials for widespread applications in nanoelectronics, optoelectronics, gas sensors, etc. The aforementioned properties of TMDCs are significantly affected by the structuralquality and crystallinity. Accordingly, scalable techniques have been sought for synthesizing well-crystallized TMDCs.Atomic layer deposition (ALD) is considered a promising growth technique for transition metal dichalcogenides (TMDCs) because it ensures uniformity and homogeneity of the TMDC grains. However, the poor crystallinity of ALD-grown TMDCs remains a critical challenge. Although crystallinity depends on the growth mechanism, the growth behavior of crystalline TMDCs in ALD is unclear. We investigated the growth behavior of highly crystallized molybdenum disulfide (MoS2) by ALD at 650 oC with an extra pulse of remote H2 plasma. Growth at high temperatures using the activated species aided surface diffusion of the adsorbates. The ALD process facilitates repeated growth and saturation of MoS2, unlike the normal ALD of 3D bulk materials, where the film thickness monotonically increases with the number of ALD cycles. This unique behavior resulted from the evolution of the basal plane without dangling bonds. On the basal plane, MoS2 lateral growth dominates vertical growth, and prolonged incubation is required for nucleation on the basal plane. The grain size is small (up to two monolayers) because of the limited mobility on SiO2, and the grains of the third layer grow to a few hundred nanometers. These findings provide insights into the development of ALD technology for application to high-quality TMDCs.

Comparison of AlF3 thin films grown by thermal and plasma enhanced atomic layer deposition

Films of aluminum fluoride (AlF3) deposited by thermal and plasma enhanced atomic layer deposition (PEALD) have been compared using in situ multiwavelength ellipsometry (MWE) and monochromatic x-ray photoelectron spectroscopy (XPS). The AlF3 films were grown using cyclic exposures of trimethylaluminum, hydrogen fluoride, and H radicals from a remote H2 inductively coupled plasma. Films were characterized in situ using MWE and XPS for growth rate, film composition, and impurity incorporation. The MWE showed a growth rate of 1.1 and 0.7 Å per cycle, at 100 °C, for thermal and plasma enhanced ALD AlF3 films, respectively. Carbon incorporation was below the XPS detection limit. The plasma enhanced ALD AlF3 film showed the presence of Al-Al chemical states, in the Al 2p scans, suggesting the presence of Al-rich clusters with a concentration of 14%. The Al-rich clusters are thought to originate during the hydrogen plasma step of the PEALD process. The Al-rich clusters were not detected in thermal ALD AlF3 films using the same precursors and substrate temperature.

Effect of substrate temperature on plasma-enhanced self-assembling formation of high-density FePt nanodots

We formed FePt magnetic nanodots (NDs) by exposing an ultrathin bilayer metal stack on ∼3.0 nm SiO2/Si(100) substrates to a remote H2 plasma (H2-RP) and studied the effect of external heating during the exposure to H2-RP on the formation and magnetic properties of NDs. The ultrathin bilayer with a uniform surface coverage drastically changed to NDs with an areal density as high as ∼3.5 × 1011 cm−2 by exposing to H2-RP with external heating. We also found that NDs formed by the exposure to H2-RP at 400 °C exhibited a perpendicular anisotropy with a perpendicular coercivity of ∼1.5 kOe, reflecting the magneto-crystalline anisotropy of (001)-oriented L10 phase FePt.

Detection of hydrogen concentration based on an all-fiber fluorescence intensity ratio optical thermometer with Er3+/Yb3+ codoped NaBi(WO4)2 phosphors

The detection of hydrogen concentration was realized by measurement the change of local environmental temperature using an all-fiber fluorescence intensity ratio (FIR) optical thermometer. The temperature sensing optical material Er3+/Yb3+ codoped NaBi(WO4)2 phosphors were synthesized and used for the development of temperature sensing probe. Intense green upconversion luminescence was observed at an excitation power of 1.5 mW at room temperature and the dependence of FIR on the environmental temperature was obtained at the temperature range of 298.15–373.15 K. The maximum absolute temperature sensitivity reached the maximum value of 0.0127 K−1 at 373.15 K and the absolute error was 0.4 K to 0.3 K at 303.15 K, which laid the foundation for further research on real-time and remote H2 concentration detection. The local temperature change ∆T was measured due to the heat release from the reaction of H2 embedded with Pt-loaded WO3/SiO2 film. The relationship between ∆T and H2 concentration was established, which may be used to detect the leakiness of H2 gas during the traffic and storage process.

Characterization of Magnetic-Field Dependent Electron Transport of Fe3Si Nanodots by Using a Magnetic AFM Probe

The application of group-IV based ferromagnetic-nanodots (NDs) such as Fe3-silicide NDs to a floating gate in MOS memories has been attracting much attention from the view point of new functionality to control charging and discharging properties in NDs floating gate by the tunnel magnetoresistance effect between ferromagnetic NDs and gate electrodes [1-2]. In our previous work, we demonstrated the formation of high density Fe3Si-NDs on ultrathin SiO2 by exposing ultrathin Fe films deposited on Si-NDs, which were self-assembled on OH-terminated SiO2 layers by controlling the early stages of low-pressure chemical vapor deposition (LPCVD) using SiH4, to remote H2 plasma (H2-RP) [3]. In this work, we extend our research to the characterization of their local electron transport properties measured with a magnetic probe under external magnetic field.An atomic force microscope (AFM) image taken after the SiH4-LPCVD, and subsequent ultrathin Fe-film deposition and H2-RP exposure confirmed the formation of NDs with an areal density as high as ~2.7×1011 cm-2 and with an average height of ~5.9 nm which were evaluated from a size distribution of NDs obtained from the AFM image. In addition, from in-plane and perpendicular magnetization curves (M–H curves) measurements, a coercivities of 180 and 220 Oe were obtained for the in-plane and perpendicular directions, respectively. To evaluate local electron transport properties, a CoPtCr-coated AFM probe was scanned on the sample surface under application of an external magnetic field to take topographic and current images simultaneously where a DC bias of -2.0 V was applied to the AFM probe with respected to an Al bottom-electrode of the sample. The magnetization of the tip was initially set along the upward direction, and upward (positive) or downward (negative) external magnetic fields were applied to the NDs by placing the NdFeB magnet under the sample. When a positive field of 1.5 kOe was applied to the sample in the same direction as the initial tip magnetization, a clear correlation between the topographic images and current images was observed, namely the clear current image with a high contrast among dots and SiO2 (Fig. 1 (a) and (b)). However, a distinct decrease in the current level was detected when a negative field of 0.35 kOe was applied. Notice that, when a positive field of 1.5 kOe was applied to the sample in the same direction as the first magnetization, an almost complete recovery of the resistive state was observed. We also confirmed a reversal of the tip magnetization at a magnetic field of 1.5 kOe from the observation of the reversed contrast in a magnetic force microscope image of a floppy disk taken with the tip exposed to a field of 1.5 kOe. Based on these results, the increase in the resistance by the application of the magnetic field of 0.35 kOe in the opposite direction to the tip magnetization direction can be interpreted in terms of the reversal of the magnetization direction of the dots because the perpendicular coercivity of the dots is 220 Oe. After the re-magnetization at 1.5 kOe, the magnetization direction of the dots and tip can be aligned in parallel. These results indicate that with the application of a magnetic field of 0.35 kOe, the resistive state can be changed by controlling the magnetization directions of the dots. In conclusion, we evaluated the local electron transport properties of Fe3Si-NDs with the areal density as high as ~1011 cm-2 on an ultrathin SiO2/n-Si(100) by using the magnetic cantilever under the external magnetic field. We confirmed at room temperatures that there is a clear change in the contrast of the current images in which current through the NDs depends on the relative directions of magnetization between the NDs and the magnetic cantilever.Reference[1] Y. Nakamura, et al., Jpn. J. Appl. Phys. 50, 015501 (2011).[2] S. H. Sun, et al., Science 287, 1989 (2000).[3] J. Wu et al., 8th ISCSI, WP2-18 (Sendai, 2019). Figure 1

Impact of surface pre-treatment on Pt-nanodot formation induced by remote H2-plasma exposure

We evaluated the influence of the surface modification of ultrathin Pt films with remote plasma treatment using pure N2 or pure NH3 on the formation of Pt nanodots (NDs), which was induced by exposing Pt films on ultrathin SiO2 layers to remote H2 plasma. Well-defined Pt NDs were formed from pre-treated Pt films and, at a remote H2 plasma exposure time of 5 min, areal dot density was increased by factors of ∼2.3 for the remote NH3 plasma pre-treatment (5 min) and ∼3.5 for the N2 plasma pre-treatment (3 min), while the areal density of Pt NDs formed by remote H2 plasma for 5 min without the pre-treatment was 1.5 × 1011 cm−2. The results can be interpreted in terms of the surface migration length of Pt atoms being effectively reduced due to the chemisorption of N atoms on the Pt film surface. In addition, we also demonstrated the formation of high-density Pt NDs with an areal density as high as ∼9.0 × 1011 cm−2 by exposing the Pt film pre-treated with SiH4 to the remote H2 plasma.

High Density Formation and Magnetoelectronic Transport Properties of Fe3Si Nanodots

The application of group-IV based metallic-nanodots (NDs) such as silicide- and germanide-NDs to a floating gate in MOS memories has been attracting much attention as charge retention characteristics can be improved and they can be compatible with Si-based semiconductor devices [1]. By replacing nonmagnetic NDs with ferromagnetic NDs, floating gate MOS memories can have the new functionality to control charging and discharging properties in NDs floating gate and to improve retention characteristics by the tunnel magnetoresistance effect between NDs and ferromagnetic gate electorodes [2]. Recently, Fe3Si-NDs have received much attention as the promising materials for application to the Si-based spintronics and/or magnetic memory devices such as magnetoresistive random access memory [3]. Previously, we demonstrated the self-assembling formation of metal (Ni, Pt, Pd, Co and Fe) NDs on thermally grown SiO2 with an areal density as high as ~1012 cm-2 by simply exposing ultrathin metal films to remote H2 plasma (H2-RP) without external heating [4]. In this work, we extended our research to form high density Fe3Si-NDs and to study their magnetization and local I-V characteristics measured with a magnetic probe under external magnetic field application. After conventional wet-chemical cleaning steps for p-type Si(100) wafers, a ~3.6nm-thick SiO2 layer was grown at 850 ˚C. After that, a ~2.0nm-thick Fe layer was first deposited uniformly on the SiO2 layer by electron beam evaporation, and then uniformly with a ~2.0nm-thick amorphous Si (a-Si) layer was covered without air exposure. Subsequently, a ~1.5nm-thick Fe layer was deposited, where the film thicknesses were designed with stoichiometric ratio of Fe:Si=3:1. The Fe/a-Si/Fe trilayer stack was exposed to a H2-RP without external heating. By exposing the trilayer stack to the H2-RP, the formation of NDs with an areal density as high as ~5×1011 cm-2 and with an average height of ~10 nm was observed. Considering the fact that the temperature was raised up to ~480 ˚C in the case of a Fe foil during H2-RP exposure, this result suggests that Fe-Si alloying was promoted with agglomeration by cohesive action of Fe and Si atoms on the SiO2 surface during the H2-RP exposure. In addition, by X-ray diffraction and magnetization measurements, the formation of DO3-orderd NDs was confirmed. To evaluate the local electron transport properties of the DO3-orderd Fe3Si-NDs, a CoPtCr-coated Si cantilever was contacted with the sample surface and kept at the same position, and the I-V characteristics were measured at room temperature, where electrons are injected from the tip. Without any external magnetic field application, the current level was slightly increased with tip bias over ~-3.5 V. When applying a magnetic field of 0.5 kOe in the same direction as the tip magnetization, a distinct increase in the current level was detected, namely, the threshold voltage which is defined as a bias voltage at 0.1 nA was decreased from -4.0 to -0.3 V. With an increase in the magnetic field over 0.6 kOe, no further changes in the I-V curve were observable, which means that the resistance was kept at a significantly decreased level under magnetic fields of 0.5k Oe and over. When the CoPtCr-coated tip was replaced by a Rh-coated tip, almost no change was detected in the I-V curve by the application of a magnetic field of 4.5 kOe, irrespective of the field direction. We also confirmed a remarkable decrease in the current level and an almost complete recovery to the initial current level by applying a magnetic field of 0.5 kOe in the opposite direction to the first magnetization at 0.5kOe. Noted that, when the magnetic field of 0.5 kOe was applied in the same direction again, remarkable increase in the current level was observed. Here, the magnetization direction of the CoPtCr-coated tip is not affected by the magnetic field of 0.5 kOe. Therefore, the observed increase and decrease in the current level, namely, the change in the magnetoresistance can be interpreted in terms that the magnetization of the Fe3Si-NDs was aligned in parallel or antiparallel to that of the CoPtCr-coated tip by the external magnetic field.

High Density Formation and Magnetoelectronic Transport Properties of Fe3Si Nanodots

We fabricated DO3-orderd Fe3Si-nanodots (NDs) on ultrathin SiO2 and evaluated local I-V characteristics through individual dots under magnetic field application by using atomic force microscopy (AFM) with a magnetic cantilever. High-density Fe-silicide NDs with an areal density as high as ~1011 cm-2 were formed on thermally grown SiO2 by exposing ultrathin Fe/amorphous-Si/Fe tri-layer stacked structures to a remote H2 plasma without external heating. The formation of DO3-orderd NDs was confirmed by X-ray diffraction and magnetization measurements. From local electron transport properties, a clear change in resistance depending on the magnetization direction of Fe3Si-NDs with respect to the CoPtCr-coated AFM tip was confirmed at room temperature.

Formation of Mn-germanide nanodots on ultrathin SiO2 induced by remote hydrogen plasma

High-density Mn-germanide nanodots [MnxGe1−x (x = 0.8) NDs] with an areal dot density as high as ∼1012 cm−2 were formed on thermally grown SiO2 by exposing ∼1.0-nm-thick Mn/∼1.0-nm-thick amorphous Ge (a-Ge) bilayer stacked structures to a remote H2 plasma (H2-RP) without external heating. The germanidation reaction of the Mn/a-Ge bilayer was observed through high resolution X-ray photoelectron spectroscopy measurements. Electrical isolation among the MnxGe1−x (x = 0.8) NDs was verified from the changes in surface potential after charge injection using an atomic force microscope/Kelvin probe technique. As seen from the VHF input power and exposure time dependence of the ultrathin bilayer stacked structures, control of thickness and H-radical flux are important parameters for the high-density formation of MnGe alloy NDs induced by H2-RP.

(Invited) Processing and Characterization of High Density Si/Ge Quantum Dots for Electroluminescent Devices

Light emission from Si-based nanostructures including Si- and Ge-QDs has stimulated considerable interest in the field of silicon-based photonics because of its potential to combine photonic processing with electronic processing on a single chip. Much effort to improve light emission efficiency and its stability has been devoted with deliberate approaches which include not only the confinement of injected carriers but also the use of strained structures and impurity doping. So far, we have reported the formation of Si-QDs with Ge core on ultrathin SiO2 by controlling the thermal decomposition of pure SiH4 and 5% GeH4 diluted with He alternately, and demonstrated fairly broad photoluminescence (PL) spectra in the region of 0.6–0.8 eV originating from radiative recombination of photo-generated carriers through quantized states of Ge core. In this paper, our recent achievements on the formation of double-stacked high density Si-QDs with Ge core on thermally-grown SiO2 by highly-selective CVD, and characterization results of their electroluminescence (EL) under pulsed bias applications are reviewed. Si-QDs with Ge core with an areal density as high as ~1×1011cm-2, of which the average height was ~7nm including a Ge core with a height of ~2.5nm, were formed on thermally-grown SiO2/c-Si (100) by controlling the early stages of LPCVD using pure SiH4 for the pre-growth of Si-QDs, and the subsequent thermal decomposition of 5% GeH4 diluted with H2 and of pure SiH4 with keeping a gas pressure as low as 2.7Pa for highly selective depositions of Ge core and Si cap on the pre-grown Si-QDs, respectively. For the surface passivation of the QDs so prepared, ~2nm-thick SiO2 was formed by exposing the dot surface to remote O2 plasma at 500˚C. In stacking a layer of QDs, the process steps above mentioned was followed by remote H2 plasma exposure of SiO2 to terminate the oxide surface with OH bonds and repeated sequentially. With excitation by 979 nm laser light, humped–shape PL signals in the energy region from 0.64 to 0.8eV were observed even at room temperature. Notice that, in the energy region over ~1.0eV, no PL signals were detectable even with excitation by 690 nm laser light although PL signals from coreless Si QDs were observed in the energy region of 1.0-1.6eV. In addition, as a result of encapsulation of QDs with SiO2 having an expansion coefficient smaller than bulk Si and Ge, temperature dependence of PL is markedly weak and very different from phonon-assisted PL from bulk Si and Ge. We also confirm that, with double stacking of a QDs layer, PL intensity just about doubles with keeping the spectral shape and emission energy. From the spectral analysis using a Gaussian curve fitting method, it is revealed that the observed PL spectra can be deconvoluted into mainly four components peaked at 0.68, 0.71, 0.74 and 0.78eV in the double stacked QDs as in the case of single layer of Si-QDs with Ge core. Taking into account the fact that, with Si capping after Ge selective deposition on pre-grown Si QDs, PL signals above ~1.0eV are efficiently eliminated and the signals below ~0.8eV are enhanced significantly, the observed PL is interpreted in terms of recombination through quantized states of the Si-QDs with Ge core reflecting the type II energy band discontinuity between Si clad and Ge core. In fact, with decreasing Ge core size, a distinct blue shift of PL was observed. Based on these results, EL was characterized from the backside through the c-Si substrate after the formation of Al top and bottom electrodes. Current-voltage characteristics show clear rectification properties reflecting work function difference between the Al top electrode and p-Si(100) substrate. With application of pulsed biases in the forward direction, EL signals peaked at ~0.83eV was observed even at room temperature. The EL peak energy was higher than the PL peak energies. No EL was detected under reverse bias conditions. Notice that, with increasing the applied bias, the EL intensity was increased with no significant change in the spectral shape. The result indicates that the observed EL can be explained by radiative recombination between higher order quantized states in Ge core caused by hole injection from the p-Si(100) and electron injection from the top Al-electrode, in which direct bandgap transition might contribute to EL because the emission width of EL was narrower than that of PL. These results imply that Si-QDs with Ge core is greatly promising for their optoelectronic device applications. Acknowledgement: This work was supported in part by Grant-in Aid for Scientific Research (S) No. 15H05762 of MEXT, Japan.

Magnetoelectronic transport of double stack FePt nanodots

We designed and fabricated double stack FePt-nanodots (FePt-NDs) with different coercivities between the lower and upper NDs, in which the FePt-NDs were formed by exposing Pt/Fe bilayer stacks of different thicknesses to a remote H2 plasma. The double-stacked NDs show a clear change in their resistive state depending on the relative directions of magnetization between the upper and lower dots. From the high on/off current ratio between the high and low resistive states observed in the current-voltage characteristics, the FePt-NDs can be regarded as a spin-diode gate.

High-density formation of Ta nanodot induced by remote hydrogen plasma

We have studied the formation of Ta nanodots (NDs) on thermally grown SiO2/Si by exposing a thin metal layer to a remote H2 plasma (H2-RP) without external heating. Atomic force microscopy (AFM) analyses show that a combination of a Ge (∼30.0 nm)/Ta (∼2.0 nm) bilayer stack with subsequent H2-RP exposure is effective for forming electrically isolated Ta NDs with an areal dot density as high as ∼1011 cm−2, where the Ge layer plays an important role as a barrier layer against the oxidation of the ultrathin Ta layer surface. The change in the chemical structure of the Ge/Ta bilayer stack on SiO2/Si upon Ta ND formation by H2-RP exposure is investigated by hard X-ray photoemission spectroscopy (HAXPES) and X-ray photoelectron spectroscopy (XPS).

Nano spin-diodes using FePt-NDs with huge on/off current ratio at room temperature.

Spin transistors have attracted tremendous interest as new functional devices. However, few studies have investigated enhancements of the ON/OFF current ratio as a function of the electron spin behavior. Here, we found a significantly high spin-dependent current ratio—more than 102 at 1.5 V—when changing the relative direction of the magnetizations between FePt nanodots (NDs) and the CoPtCr-coated atomic force microscope (AFM) probe at room temperature. This means that ON and OFF states were achieved by switching the magnetization of the FePt NDs, which can be regarded as spin-diodes. The FePt magnetic NDs were fabricated by exposing a bi-layer metal stack to a remote H2 plasma (H2-RP) on ~1.7 nm SiO2/Si(100) substrates. The ultrathin bi-layers with a uniform surface coverage are changed drastically to NDs with an areal density as high as ~5 × 1011 cm−2. The FePt NDs exhibit a large perpendicular anisotropy with an out-of-plane coercivity of ~4.8 kOe, reflecting the magneto-crystalline anisotropy of (001) oriented L10 phase FePt. We also designed and fabricated double-stacked FePt-NDs with low and high coercivities sandwiched between an ultra-thin Si-oxide interlayer, and confirmed a high ON/OFF current ratio when switching the relative magnetization directions of the low and high coercivity FePt NDs.

Impact of embedded Mn nanodots on resistive switching characteristics of Si-rich oxides as measured in Ni-electrode metal–insulator–metal diodes

We studied the formation of high-density Mn nanodots (NDs) by remote H2 plasma (H2-RP) treatment and investigated how the embedding of Mn NDs affects the resistive switching properties of Si-rich oxides (SiOx) because it is expected that NDs will trigger the formation of the conductive filament path in SiOx. We fabricated Mn NDs with different ND areal densities by exposing an ultrathin Mn layer on the SiOx/Ni bottom electrode to H2-RP without external heating. After the deposition of SiOx as a resistive switching layer and the fabrication of Ni top electrodes, resistive switching behaviors of metal–insulator–metal (MIM) diodes were characterized from current–voltage (I–V) curves and compared with the results obtained from samples of SiOx without Mn NDs and with an ultrathin Mn layer instead. The embedding of Mn NDs in SiOx was found to be effective in increasing the ON/OFF ratio in resistance and reducing the variation in operation voltage.

Formation and characterization of high-density FeSi nanodots on SiO2 induced by remote H2 plasma

We demonstrated the formation of high-density iron silicide nanodots (NDs) on thermally grown SiO2 by exposing an electron-beam-evaporated Fe/amorphous-Si/Fe (Fe/a-Si/Fe) trilayer stack to remote H2 plasma without any external heating and characterized their silicidation state and crystalline phase. After the remote H2 plasma exposure, the formation of NDs with an areal density of ∼4.3 × 1011 cm−2 and an average height of ∼7.1 nm was confirmed. X-ray photoelectron spectroscopy (XPS) analyses indicate silicidation reaction induced by the remote H2 plasma exposure, which was accompanied by the agglomeration of Fe and Si atoms on the SiO2 surface. The formation of a crystalline β-FeSi2 phase was confirmed by Raman scattering spectroscopy and XRD pattern measurements. The electrical separation among the β-FeSi2 NDs was confirmed from changes in surface potential due to charging of the dots. The surface potential of the NDs changed in a stepwise manner with respect to the tip voltage because of multistep electron injection into and extraction from the semiconductor β-FeSi2 NDs.

H2 and N2 Remote Plasma Processing of Wurtzite‐Like Oxides: Implications for Energy Applications

Remote plasma processing is one of the most effective methods for the manipulation of intrinsic defects, doping, stoichiometry, and morphology of a large variety of oxides. Here, we discuss the interaction of polar ZnO and of LiGaO2 and LiAlO2 with atomic hydrogen and nitrogen produced by remote H2 and N2 plasmas. We show that the various crystallographic faces of those wurtzite‐like oxides are characterized by a different reactivity to hydrogen and nitrogen. Specifically, we demonstrate that the O‐polar ZnO is the most stable surface to hydrogen and, therefore, it should be the one of interest to preserve electrode stability in all those applications involving hydrogen. Conversely, we found that H2 remote plasma processing does not significantly alter Li‐based oxides LiGaO2 and LiAlO2, while their nitridation can be exploited to alter the Li composition and mobility.

Azoksimetan model of carcinogenesis in the pancreas in rats

Hydrogen (H2) plasma treatment at the interface between 4H-SiC substrate and Al2O3 dielectric prepared by the atomic layer deposition (ALD) was performed and its effects on capacitance–voltage characteristics as well as the interface state density (Dit) was evaluated with metal oxide semiconductor devices. The atomic force microscopy result indicates that the remote H2 plasma treatment reduces surface roughness. Compared with the non-passivated devices, lower leakage current, lower hysteresis and higher breakdown voltage are attained with remotely hydrogen plasma-treated devices. Without post metallization annealing (PMA), Dit value more than 1014 eV−1 cm−2 is attained with hydrogen plasma passivated devices, indicating plasma-induced damage on the surface. However, using PMA, Dit of the H2 plasma treated device is significantly reduced to as low as 1.00 × 1012 eV−1 cm−2 at Ec − Et = 0.4 eV and is about five times lower than that of sample without H2 plasma passivation (Dit = 4.84 × 1012 eV−1 cm−2).

Remote plasma atomic layer deposited Al2O3 4H SiC MOS capacitor with remote H2 plasma passivation and post metallization annealing

Hydrogen (H2) plasma treatment at the interface between 4H-SiC substrate and Al2O3 dielectric prepared by the atomic layer deposition (ALD) was performed and its effects on capacitance–voltage characteristics as well as the interface state density (Dit) was evaluated with metal oxide semiconductor devices. The atomic force microscopy result indicates that the remote H2 plasma treatment reduces surface roughness. Compared with the non-passivated devices, lower leakage current, lower hysteresis and higher breakdown voltage are attained with remotely hydrogen plasma-treated devices. Without post metallization annealing (PMA), Dit value more than 1014eV−1cm−2 is attained with hydrogen plasma passivated devices, indicating plasma-induced damage on the surface. However, using PMA, Dit of the H2 plasma treated device is significantly reduced to as low as 1.00×1012eV−1cm−2 at Ec−Et=0.4eV and is about five times lower than that of sample without H2 plasma passivation (Dit=4.84×1012eV−1cm−2).

Application of remote hydrogen plasma to selective processing for Ge-based devices: Crystallization, etching, and metallization

We demonstrated a novel technique for crystallizing ∼80-nm-thick hydrogenated amorphous Ge films (a-Ge:H) covered with Pt patterns with ∼2-nm-thick SiO2 interlayers on quartz substrates by exposing them to remote H2 plasma (H2-RP) without any external heating. After the samples were exposed to the H2-RP for 5 min, the crystallization of the whole film was confirmed in Raman scattering spectra, which implies that the exothermic recombination of hydrogen radicals generated in H2 plasma on a Pt film surface plays an important role in improving the crystallinity caused by energy transfer through the SiO2 interlayer. In the case without Pt coating and a SiO2 interlayer, the a-Ge:H film was completely removed at an etching rate as high as ∼56 nm/min. We also studied the impact of H2-RP exposure of a-Ge:H directly covered with Pt on the germanidation reaction without any external heating. Raman scattering signals attributable to the Pt–Ge phase were observable within the first 1 min of H2-RP exposure. After exposure for 20 min, full germanidation of ∼80-nm-thick a-Ge:H was achieved, and its resultant sheet resistance was as low as ∼4.5 Ω/sq. The driving force of such a germanidation reaction is attributed to heat transfer caused by the efficient recombination of atomic hydrogen on the Pt surface.

Low temperature hydrogen plasma-assisted atomic layer deposition of copper studied using in situ infrared reflection absorption spectroscopy

Atomic layer deposition (ALD) is an ideal technique to deposit ultrathin, conformal, and continuous metal thin films. However, compared to the ALD of binary materials such as metal oxides and metal nitrides, the surface reaction mechanisms during metal ALD are not well understood. In this study, the authors have designed and implemented an in situ reflection-absorption infrared spectroscopy (IRAS) setup to study the surface reactions during the ALD of Cu on Al2O3 using Cu hexafluoroacetylacetonate [Cu(hfac)2] and a remote H2 plasma. Our infrared data show that complete ligand-exchange reactions occur at a substrate temperature of 80 °C in the absence of surface hydroxyl groups. Based on infrared data and previous studies, the authors propose that Cu(hfac)2 dissociatively chemisorbs on the Al2O3 surface, where the Al-O-Al bridge acts as the surface reactive site, leading to surface O-Cu-hfac and O-Al-hfac species. Surface saturation during the Cu(hfac)2 half-cycle occurs through blocking of the available chemisorption sites. In the next half-reaction cycle, H radicals from an H2 plasma completely remove these surface hfac ligands. Through this study, the authors have demonstrated the capability of in situ IRAS as a tool to study surface reactions during ALD of metals. While transmission and internal reflection infrared spectroscopy are limited to the first few ALD cycles, IRAS can be used to probe all stages of metal ALD starting from initial nucleation to the formation of a continuous film.