Remote Hydrogen Plasma Research Articles

Integration of porous low-k dielectrics using post porosity pore protection

Post porosity pore protection is studied as a means for low damage integration of porous low-k dielectrics. Homogeneous low-k densification is achieved using poly(methyl methacrylate) (PMMA) as a sacrificial filler. The improvement in plasma-induced damage is investigated on a plasma-enhanced chemical vapor deposition 2.0 porous organo-silicate glass, including damage from radicals and vacuum ultraviolet photons. Open pores are sealed upon polymer protection; therefore the penetration of metal species during deposition of a metal diffusion barrier is avoided. Various solutions for post metallization polymer removal are investigated, such as hydrogen remote plasma and an ultraviolet cure. The PMMA removal process is studied in order to avoid Cu wire degradation. Finally, low-k damage and barrier continuity are investigated on patterned wafers with functional circuits. By means of transmission electron microscopy inspection and electrical measurement, effective integrated k-values are extracted, giving a value keff ~ 2.5–2.6 for the post metallization polymer removal option.

Effects of remote hydrogen plasma on chemical bonding features and electronic states of 4H-SiC(0001) surface

We have demonstrated a novel dry cleaning process for the 4H-SiC surface using remote hydrogen plasma (H2-RP). The effects of H2-RP exposure on the chemical structures and electronic states of the wet-cleaned 4H-SiC surface have been evaluated by X-ray photoelectron spectroscopy (XPS) and total photoelectron yield spectroscopy (PYS). XPS shows that H2-RP exposure is effective in removing contaminants from the 4H-SiC surface. PYS indicates that the defect states at the surface are generated after the H2-RP exposure and such generated defect states are drastically decreased by annealing at 850 °C. The combination of H2-RP exposure with the subsequent annealing is found to be effective in 4H-SiC surface cleaning.

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).

Activating basal-plane catalytic activity of two-dimensional MoS2 monolayer with remote hydrogen plasma

Two-dimensional layered transition metal dichalcogenide (TMD) materials such as Molybdenum disufide (MoS2) have been recognized as one of the low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER). The crystal edges that account for a small percentage of the surface area, rather than the basal planes, of MoS2 monolayer have been confirmed as their active catalytic sites. As a result, extensive efforts have been developing in activating the basal planes of MoS2 for enhancing their HER activity. Here, we report a simple and efficient approach—using a remote hydrogen-plasma process—to creating S-vacancies on the basal plane of monolayer crystalline MoS2; this process can generate high density of S-vacancies while mainly maintaining the morphology and structure of MoS2 monolayer. The density of S-vacancies (defects) on MoS2 monolayers resulted from the remote hydrogen-plasma process can be tuned and play a critical role in HER, as evidenced in the results of our spectroscopic and electrical measurements. The H2-plasma treated MoS2 also provides an excellent platform for systematic and fundamental study of defect-property relationships in TMDs, which provides insights for future applications including electrical, optical and magnetic devices.

Interface Characterization of HfO2/GaSb MOS Capacitors With Ultrathin Equivalent Oxide Thickness by Using Hydrogen Plasma Treatment

We investigate p-type GaSb MOS capacitors with various HfO2 thicknesses grown using an atomic layer deposition. GaSb surfaces treated with ex-situ chemical solution and in situ remote hydrogen plasma are inspected. After a series of etching steps, the GaSb surfaces exhibit smooth topography, indicating that this combination of treatments is capable of realizing ultrathin dielectric deposition. After etching processes, the ultrathin (approximately 3 nm) HfO2 layer deposited successfully on GaSb exhibit high-permittivity (approximately 21) properties as well as equivalent oxide thickness (EOT) of 0.75 nm, which can be attributed to the flat surface. To the best of our knowledge, the EOT of GaSb capacitor prepared using the exploited approach is record low. Furthermore, we find that the interlayer present after hydrogen plasma treatment and forming gas annealing could efficiently passivate interface state density and achieve high $C$ – $V$ modulation. Compared with the benchmark of gate leakage current versus EOT, the electrical performance with low gate leakage current of the GaSb MOS capacitors demonstrates the high feasibility of the proposed treatments.

High-Sulfur-Vacancy Amorphous Molybdenum Sulfide as a High Current Electrocatalyst in Hydrogen Evolution.

The remote hydrogen plasma is able to create abundant S-vacancies on amorphous molybdenum sulfide (a-MoSx ) as active sites for hydrogen evolution. The results demonstrate that the plasma-treated a-MoSx exhibits superior performance and higher stability than Pt in a proton exchange membrane based electrolyzers measurement as a proof-of-concept of industrial application.

Interactions of hydrogen with vanadium in crystalline silicon

In this work, we have investigated interactions of vanadium with hydrogen in n‐ and p‐type float zone grown silicon using deep level transient spectroscopy (DLTS), Laplace DLTS, capacitance‐voltage and secondary ion mass spectroscopy measurements (SIMS). Vanadium was introduced into Si wafers by ion implantation with subsequent heat treatments at 800 °C for removing the implantation induced lattice damage. In the DLTS spectra of the annealed samples, we have observed two deep level states due to interstitial vanadium (Vi) atoms in n‐type Si and one in p‐type Si. A comparison of concentration profiles of the Vi atoms with those for the total concentration of V measured by SIMS has shown that at the projected implantation depth the [Vi]/[Vtotal] ratio is less than 0.05 at chemical concentration of vanadium of 1 × 1015 cm−3, so the majority of V atoms are in electrically inactive states in this region. At lower chemical concentrations of vanadium, similar values of [Vi] and [Vtotal] are observed. After the treatment of the n‐type V‐doped samples in a remote hydrogen plasma at room temperature, we have found that the concentration of the Vi atoms decreases while additional electron traps emerge in the DLTS spectra. A trap with the highest concentration has been attributed to a vanadium–hydrogen complex. In the p‐type Si:V samples, no new levels have emerged in the DLTS spectra after the H‐plasma treatments. It is suggested that in p‐type Si:V an interaction of H atoms with the Vi atoms is suppressed because of the Coulombic repulsion of positively charged Vi and hydrogen defects. It is argued that no electrically active defects are formed in either the n‐ or p‐type Si:V samples due to possible interactions of hydrogen with electrically inactive V‐related defects. We present evidence that annealing of the n‐type Si:V samples in the temperature range 75–125 °C following the application of hydrogen plasma results in up to 20% decrease in the total concentration of electrically active V‐related defects, indicating the formation of some electrically inactive V–H complexes. Heat treatments at temperatures above 175 °C have resulted in the disappearance of all the V–H complexes and recovery of electrical activity of the Vi atoms.

Influence of post-hydrogenation upon electrical, optical and structural properties of hydrogen-less sputter-deposited amorphous silicon

Amorphous silicon (a-Si) is common in the production of technical devices and can be deposited by several techniques. In this study intrinsic and doped, hydrogen-less amorphous silicon films are RF magnetron sputter deposited and post-hydrogenated in a remote hydrogen plasma reactor at a temperature of 370°C. Secondary ion mass spectrometry of a boron doped (p) a-Si layer shows that the concentration of dopants in the sputtered layer becomes the same as present in the sputter-target. Improved surface passivation of phosphorous doped 5Ωcm, FZ, (n) c-Si can be achieved by post-hydrogenation yielding a minority carrier lifetime of ~360μs finding an optimum for ~40nm thin films, deposited at 325°C. This relatively low minority carrier lifetime indicates high disorder of the hydrogen-less sputter deposited amorphous network. Post-hydrogenation leads to a decrease of the number of localized states within the band gap. Optical band gaps (Taucs gab as well as E04) can be determined to ~1.88eV after post-hydrogenation. High resolution transmission electron microscopy and optical Raman investigations show that the sputtered layers are amorphous and stay like this during post-hydrogenation. As a consequence of the missing hydrogen during deposition, sputtered a-Si forms a rough surface compared to CVD a-Si. Atomic force microscopy points out that the roughness decreases by up to 25% during post-hydrogenation. Nuclear resonant reaction analysis permits the investigation of hydrogen depth profiles and allows determining the diffusion coefficients of several post-hydrogenated samples from of a model developed within this work. A dependency of diffusion coefficients on the duration of post-hydrogenation indicates trapping diffusion as the main diffusion mechanism. Additional Fourier transform infrared spectroscopy measurements show that hardly any interstitial hydrogen exists in the post-hydrogenated a-Si layers. The results of this study open the way for further hydrogen diffusion experiments which require an initially unhydrogenated drain layer.

Silicon Oxycarbide Films Produced by Remote Microwave Hydrogen Plasma CVD using a Tetramethyldisiloxane Precursor: Growth Kinetics, Structure, Surface Morphology, and Properties

Amorphous hydrogenated silicon oxycarbide (a‐SiCO:H) thin films are produced by remote microwave hydrogen plasma CVD using 1,1,3,3‐tetramethyldisiloxane precursor. The effect of substrate temperature (TS) on the chemical structure and some properties of resulting a‐SiCO:H films is reported. The examination performed by infrared spectroscopy revealed that the increase in TS involves the elimination of organic moieties from the film and its transformation from polymer‐like to ceramic‐like high‐crosslink‐density material. Due to their small surface roughness, high density, and good optical transparency, the a‐SiCO:H films seem to be useful coatings for optical and electronic devices.

Hydrogen desorption kinetics for aqueous hydrogen fluoride and remote hydrogen plasma processed silicon (001) surfaces

The desorption kinetics of molecular hydrogen (H2) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H2 desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH2/3), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H2 desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H2 evolved from subsurface states and 450 °C exposure leading to more H2 desorption from surface SiHx species. Additional surface desorption states were observed, which were attributed to H2 desorption from Si (111) facets formed as a result of surface etching by the remote hydrogen plasma or aqueous hydrogen fluoride treatment. The kinetics of surface H2 desorption were found to be in excellent agreement with prior investigations of silicon surfaces exposed to thermally generated atomic hydrogen.

Hydrogen desorption from hydrogen fluoride and remote hydrogen plasma cleaned silicon carbide (0001) surfaces

Due to the extreme chemical inertness of silicon carbide (SiC), in-situ thermal desorption is commonly utilized as a means to remove surface contamination prior to initiating critical semiconductor processing steps such as epitaxy, gate dielectric formation, and contact metallization. In-situ thermal desorption and silicon sublimation has also recently become a popular method for epitaxial growth of mono and few layer graphene. Accordingly, numerous thermal desorption experiments of various processed silicon carbide surfaces have been performed, but have ignored the presence of hydrogen, which is ubiquitous throughout semiconductor processing. In this regard, the authors have performed a combined temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) investigation of the desorption of molecular hydrogen (H2) and various other oxygen, carbon, and fluorine related species from ex-situ aqueous hydrogen fluoride (HF) and in-situ remote hydrogen plasma cleaned 6H-SiC (0001) surfaces. Using XPS, the authors observed that temperatures on the order of 700–1000 °C are needed to fully desorb C-H, C-O and Si-O species from these surfaces. However, using TPD, the authors observed H2 desorption at both lower temperatures (200–550 °C) as well as higher temperatures (>700 °C). The low temperature H2 desorption was deconvoluted into multiple desorption states that, based on similarities to H2 desorption from Si (111), were attributed to silicon mono, di, and trihydride surface species as well as hydrogen trapped by subsurface defects, steps, or dopants. The higher temperature H2 desorption was similarly attributed to H2 evolved from surface O-H groups at ∼750 °C as well as the liberation of H2 during Si-O desorption at temperatures >800 °C. These results indicate that while ex-situ aqueous HF processed 6H-SiC (0001) surfaces annealed at <700 °C remain terminated by some surface C–O and Si–O bonding, they may still exhibit significant chemical reactivity due to the creation of surface dangling bonds resulting from H2 desorption from previously undetected silicon hydride and surface hydroxide species.

Role of grain boundaries in tailoring electronic properties of polycrystalline graphene by chemical functionalization

Grain boundaries, inevitably present in chemical vapor deposited graphene, are expected to have considerable impact on the development of graphene-based hybrid materials with tailored material properties. We demonstrate here the critical role of polycrystallinity on the chemical functionalization of graphene comparing ozone-induced oxidation with remote plasma hydrogenation. We show that graphene oxidation and hydrogenation occur in two consecutive stages upon increasing defect density: an initial step in which surface-bound functional groups are generated, followed by the creation of vacancies. Remarkably, we find that hydrogenation yields homogeneously distributed defects while ozone-induced defects are preferentially accumulated at the grain boundaries eventually provoking local cracking of the structure. Supported by quantum simulations, our experimental findings reveal distinct electronic transport regimes depending on the density and distribution of induced defects on the polycrystalline graphene films. Our findings highlight the key role played by grain boundaries during graphene functionalization, and at the same time provide a novel perspective to tailor the properties of polycrystalline graphene.

High Density Formation of FePt Alloy Nanodots Induced by Remote Hydrogen Plasma and Characterization of their Magnetic Properties

High Density Formation of FePt Alloy Nanodots Induced by Remote Hydrogen Plasma and Characterization of their Magnetic Properties

High quality HfO2/p-GaSb(001) metal-oxide-semiconductor capacitors with 0.8 nm equivalent oxide thickness

We investigate in-situ cleaning of GaSb surfaces and its effect on the electrical performance of p-type GaSb metal-oxide-semiconductor capacitor (MOSCAP) using a remote hydrogen plasma. Ultrathin HfO2 films grown by atomic layer deposition were used as a high permittivity gate dielectric. Compared to conventional ex-situ chemical cleaning methods, the in-situ GaSb surface treatment resulted in a drastic improvement in the impedance characteristics of the MOSCAPs, directly evidencing a much lower interface trap density and enhanced Fermi level movement efficiency. We demonstrate that by using a combination of ex-situ and in-situ surface cleaning steps, aggressively scaled HfO2/p-GaSb MOSCAP structures with a low equivalent oxide thickness of 0.8 nm and efficient gate modulation of the surface potential are achieved, allowing to push the Fermi level far away from the valence band edge high up into the band gap of GaSb.

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.

Remote hydrogen microwave plasma chemical vapor deposition from methylsilane precursors. 1. Growth mechanism and chemical structure of deposited a-SiC:H films

Amorphous hydrogenated silicon carbide (a-SiC:H) thin films were produced by remote microwave hydrogen plasma chemical vapor deposition (RP-CVD) using dimethylsilane (DMS) and trimethylsilane (TrMS) as single-source precursors. The effect of substrate temperature on the rate of RP-CVD process, chemical composition and chemical structure of resulting a-SiC:H films is reported. The Arrhenius plots of substrate temperature dependencies of the thickness-based film growth rate imply that the investigated RP-CVD for DMS precursor is a non-thermally activated process, whereas for TrMS precursor is an adsorption-controlled process. The examination of the a-SiC:H films performed by means of Auger electron spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared absorption spectroscopy, revealed that the increase in the substrate temperature from 30°C to 400°C causes the elimination of organic moieties from the films and the formation of Si-carbidic network structures. On the basis of the results of structural study the elementary reactions involved in the formation of a-SiC:H films are proposed.

Remote hydrogen microwave plasma chemical vapor deposition from methylsilane precursors. 2. Surface morphology and properties of deposited a-SiC:H films

Amorphous hydrogenated silicon carbide (a-SiC:H) films produced by remote microwave hydrogen plasma chemical vapor deposition from dimethylsilane and trimethylsilane precursors were characterized in terms of their basic useful properties including surface morphology, conformality of coverage, density, refractive index, optical absorption (absorption coefficient and optical bandgap) adhesion to a substrate, and friction coefficient. The effect of substrate temperature (varied in the range TS=30–400°C) on the properties of a-SiC:H films is reported. In view of the scanning electron microscopy and atomic force microscopy examinations the films were found to be morphologically homogeneous materials exhibiting excellent conformality of coverage and small surface roughness, which drop with rising TS to a small value of 0.9nm at TS=400°C. The relationships between the film compositional and structural parameters, expressed, respectively, by the atomic ratio Si/C, and the relative integrated intensities of the absorption IR band from the SiC bonds (controlled by TS), were determined. Due to their good conformality of coverage, strong adhesion to a substrate, very low friction coefficient, and excellent optical transparency in a wide range of wavelength a-SiC:H films produced from trimethylsilane precursor at high substrate temperature regime (TS=300–400°C) seem to be useful as scratch-resistant protective coatings for optical glass elements and various metal surfaces.

On the effects of hydrogenation of thin film polycrystalline silicon: A key factor to improve heterojunction solar cells

The hydrogen plasma passivation of thin film polycrystalline silicon (pc-Si) was investigated in conjunction with plasma texturing process to make efficient heterojunction solar cells. The pc-Si layers were first treated using direct and remote hydrogen plasma technologies. The heterojunction solar cells were then fabricated by subsequent deposition of i/n+ a-Si:H. Hydrogenation at high temperature (610°C) results in enhanced dissolution and diffusion of hydrogen in pc-Si by a factor of about 3 and 4, respectively, in comparison with those at low temperature (420°C). The hydrogen atoms in the pc-Si layer mainly bond to the silicon dangling bonds and form complexes with dopant atoms. In addition, platelets defects are generated by the hydrogen plasma in the sub-surface region of pc-Si hydrogenated at 420°C and cause higher saturation current in the space charge region whilst they form in the region deeper than 1μm at 610°C. Removal of the platelets using SF6/N2O plasma post-texturing after low-temperature hydrogenation not only enhances the short circuit current but also improves the open circuit voltage and the fill factor simultaneously. Combining plasma pre-texturing with high-temperature hydrogenation, the best 2µm-thick pc-Si heterojunction solar cell reaches an efficiency of 8.54%.

High Density Formation of Iron Nanodots on SiO<sub>2</sub> Induced by Remote Hydrogen Plasma

We have successfully formed Fe-nanodots with an areal dot density as high as ~2.4×1011 cm-2 on thermally grown SiO2 by exposing a 3-nm-thick Fe layer to a remote plasma of pure H2 without external heating. During remote H2 plasma exposure, the surface temperature rising up to ~500 °C was caused by surface recombination of atomic H, which enhanced surface migration of Fe atoms and promoted self-assembling nanodots. Electrical separation among Fe-nanodots was also verified from the changes in surface potential after charge injection using an AFM/Kelvin probe technique. The magnetic characterization by using magnetic force microscopy suggests that Fe-nanodots act as not only charge storage nodes but also spin-dependent active elements.

Influence of boron doping and hydrogen passivation on recombination of photoexcited charge carriers in silicon nanocrystal/SiC multilayers

The influence of boron (B)-doping and remote plasma hydrogen passivation on the photoexcited charge carrier recombination in silicon nanocrystal/SiC multilayers was investigated in detail. The samples were prepared by high temperature annealing of amorphous (intrinsic and B-doped) Si1−xCx/SiC superlattices. The photoluminescence (PL) intensity of samples with B-doped silicon rich carbide layers was found to be up to two orders of magnitude larger and spectrally red shifted in comparison with that of the other samples. Hydrogen passivation leads to an additional increase in PL intensities. The PL decay can be described well by a mono-exponential function with a characteristic decay time of a few microseconds. This behavior agrees well with the picture of localized PL centers (surface states) together with the passivation of non-radiative defects by boron. The samples with B-doped SiC layers exhibit an additional PL band in the green spectral region that is quenched by hydrogen passivation. Its origin is attributed to defects due to suppression of crystallization of amorphous SiC layers as a result of B-doping. Measurement of ultrafast transient transmission allowed us to study the initial (picosecond) carrier dynamics. It was found to be dependent of pump intensity and interpreted in terms of multiparticle electron-hole recombination.