Hydrogen Plasma Pretreatment Research Articles

Effect of the on/off Cycling Modulation Time Ratio of C2H2/SF6 Flows on the Formation of Geometrically Controlled Carbon Coils

Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under thermal chemical vapor deposition system. Nickel catalyst layer deposition and then hydrogen plasma pretreatment were performed prior to the carbon coils deposition reaction. To obtain the geometrically controlled carbon coils, the cycling on/off modulation process for C2H2/SF6 flows was introduced during the initial reaction. According to the different reaction processes, the different cycling on/off ratio and the different cycling numbers for C2H2/SF6 flows were carried out. The characteristics (formation density, morphology, and geometry) of the deposited carbon coils on the substrate were investigated. Microsized coils as well as nanosized coils could be existed under the higher growing/etching time ratio (180/30 s) condition. On the other hand, the formation of nanosized coils could be mainly observed under the lower growing/etching time ratio (30/180 s) condition. With increasing the numbers of cycles, the diameters of carbon nanofilaments composed the coils decreased. The enhanced etching ability by the fluorine species was considered the main cause to control the geometry of carbon coils according to the growing/etching time ratio of the cycling on/off modulation process for C2H2/SF6 flows.

Effect of an in-Situ H2 Plasma Pretreatment on the Minority Carrier lifetime of a-Si:H(i) Passivated Crystalline Silicon

In the future, thin (<100um) crystalline silicon (c-Si) solar cells based on amorphous heterostructures (a-Si:H/c-Si) are likely to become an essential branch of wafer-based photovoltaic industry. Within this thin technology, the surface passivation will have a larger influence on effective minority charge carrier lifetime, therefore an accurate analysis of the a-Si:H/c-Si interface is paramount to achieve high efficiencies. In this paper we studied an in-situ hydrogen (H2) plasma pretreatment before a-Si:H deposition, obtaining a surface recombination velocity (Srec) of 3.8±1.0cm/s at 1x1015 minority charge carriers/cm3 on moderately-doped n-type <100> silicon wafers and, therefore, we show a significant drop compared to the reference value (6.9±1.4cm/s). The trend is related to a change in surface hydrogen configuration toward lower hydrides (from SiH3 to SiH2 and SiH) and, thus, it indicates an atomic reconstruction more suited for the growth of a-Si:H(i) passivating layer. However, if the treatment is extended above an optimum time, the Srec increases abruptly above 10cm/s which suggests the introduction of defects. These effects are explained by hydrogen-induced reactions on the c-Si surface during the H2 pretreatment. The exposure to H2 plasma improves surface passivation without relevant modifications in the a-Si:H deposition process itself: hence, it represents an interesting option to be implemented in future heterojunction solar cells.

The influence of hydrogen plasma pre-treatment on the structure of BDND electrode surface applied for phenol detection

The surface properties of boron-doped nanocrystalline diamond films treated with H2 plasma was investigated in regard to their electrochemical response for phenol oxidation. The surface of these films is relatively flat formed by crystallites with sizes of about 40 nm. X-ray photoelectron spectroscopy analyses showed that electrode surface has a high amount of C–H bonds. This behavior is in agreement with Mott-Schottky plot measurements concerning the flat band potential that presented a value as expected for hydrogenated diamond surface. This electrode presented the phenol detection limit of 0.08 mg L−1 for low phenol concentrations from 40 to 250 μmol L−1.

Use of plasma treatment to grow carbon nanotube forests on TiN substrate

Hydrogen plasma pretreatment is used to enforce the growth of vertically-aligned carbon nanotube forests on TiN substrates. The evolution of the substrate, catalyst, and nanotubes are studied by in situ and ex-situ photoemission and X-ray diffraction in order to understand the growth mechanism. We find that TiN retains its crystallographic structure and its conductivity during plasma pretreatment and nanotube growth, which is confirmed by electrical measurements. Plasma pretreatment is found to favor the growth of nanotube forests by root growth, as it binds the catalyst nanoparticles more strongly to the substrate than thermal pretreatment. We find that plasma pretreatment time should be limited, otherwise poor or no growth is found.

Reduction of the phosphorus contamination for plasma deposition of p—i—n microcrystalline silicon solar cells in a single chamber

This paper investigates several pretreatment techniques used to reduce the phosphorus contamination between solar cells. They include hydrogen plasma pretreatment, deposition of a p-type doped layer, i-a-Si:H or μc-Si:H covering layer between solar cells. Their effectiveness for the pretreatment is evaluated by means of phosphorus concentration in films, the dark conductivity of p-layer properties and cell performance.

Surface passivation of crystalline silicon wafer via hydrogen plasma pre-treatment for solar cells

The carrier lifetime of crystalline silicon wafers that were passivated with hydrogenated silicon nitride (SiN x :H) films using plasma enhanced chemical vapor deposition was investigated in order to study the effects of hydrogen plasma pre-treatment on passivation. The decrease in the native oxide, the dangling bonds and the contamination on the silicon wafer led to an increase in the minority carrier lifetime. The silicon wafer was treated using a wet process, and the SiN x :H film was deposited on the back surface. Hydrogen plasma was applied to the front surface of the wafer, and the SiN x :H film was deposited on the hydrogen plasma treated surface using an in-situ process. The SiN x :H film deposition was carried out at a low temperature (<350 °C) in a direct plasma reactor operated at 13.6 MHz. The surface recombination velocity measurement after the hydrogen plasma pre-treatment and the comparison with the ammonia plasma pre-treatment were made using Fourier transform infrared spectroscopy and secondary ion mass spectrometry measurements. The passivation qualities were measured using quasi-steady-state photoconductance. The hydrogen atom concentration increased at the SiN x :H/Si interface, and the minority carrier lifetime increased from 36.6 to 75.2 μs. The carbon concentration decreased at the SiN x :H/Si interfacial region after the hydrogen plasma pre-treatment.

Threshold voltage shift under electrical stress in amorphous, polymorphous, and microcrystalline silicon bottom gate thin‐film transistors

AbstractThe crucial influence of the interface between the gate dielectric and intrinsic layer has been studied in detail for amorphous silicon, polymorphous silicon and microcrystalline silicon bottom gate thin‐film transistors. We show that the electrical parameters of the TFTs depend directly on the quality of this interface, which can be strongly degraded by a vacuum break. A hydrogen plasma pretreatment of this interface greatly improves the electrical characterstics of polymorphous silicon TFTs, the mobility increases from 0.4 to 0.75 cm2/V s while their subthreshold slope decreases from 1 to 0.7 V/dec. Moreover, we show that these improvements also translate into more stable TFT characteristics. Finally, microcrystalline silicon TFTs show the best stability and a nitrogen‐plasma treatment of the dielectric improves their stability.

Effects of hydrogen pretreatment on physical-vapor-deposited nickel catalyst for multi-walled carbon nanotube growth

Physical vapor deposited nickel catalyst layers of 10, 50, 100, 200, 350, and 500  were granulated using hydrogen plasma for varying times to determine an effective carbon nanotube (CNT) growth process using microwave plasma enhanced CVD (MPECVD). Nickel was deposited via sputtering or evaporation. The catalyst granule size, density, and resulting CNTs were analyzed. Sputtered nickel of 50  with 5 minutes of hydrogen plasma pretreatment resulted in the most effective CNT growth.

Effects of pretreatment and post-annealing on the field emission property of diamond-like carbon grown on a titanium/silicon substrate

Diamond-like carbon (DLC) films were deposited on titanium/silicon substrates with the help of the microwave plasma chemical vapor deposition (CVD) method with Ar, H 2, and CH 4 as a mixed gas source. Titanium/silicon substrates were polished by diamond powder and etched by hydrogen (H 2) plasma, prior to deposition. After deposition, rapid thermal annealing (RTA) was used as a post-treatment. The effects of hydrogen plasma pretreatment and RTA post-treatment on the electron field emission characteristics of the DLC films was examined and correlated by Raman scattering, average surface roughness, and surface morphology. It is found that both treatments can improve the field emission characteristics of DLC films. However, RTA post-treatment demonstrates a more pronounced effect on the enhancement of field emission than does the hydrogen plasma pretreatment. This improvement is attributed in part to the increase in surface roughness resulting from sp 2 clustering formed during the RTA. The tips of these sp 2 clusters provide plenty of efficient emission sites on the surface of the DLC films. Another reason for this improvement is the graphene-like layers formed during the RTA, which provide efficient conduction paths for electrons to move through the DLC films. The field emission characteristics of CVD deposited on DLC films can be greatly enhanced by appropriate pretreatment and post-treatment, leading to promising applications for cold cathodes.

The effects of hydrogen plasma pretreatment on the formation of vertically aligned carbon nanotubes

The effects of H 2 plasma pretreatment on the growth of vertically aligned carbon nanotubes (CNTs) by varying the flow rate of the precursor gas mixture during microwave plasma chemical vapor deposition (MPCVD) have been investigated in this study. Gas mixture of H 2 and CH 4 with a ratio of 9:1 was used as the precursor for synthesizing CNTs on Ni-coated TiN/Si(1 0 0) substrates. The structure and composition of Ni catalyst nanoparticles were investigated by using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). Results indicated that, by manipulating the morphology and density of the Ni catalyst nanoparticles via changing the flow rate of the precursor gas mixture, the vertically aligned CNTs could be effectively controlled. The Raman results also indicated that the intensity ratio of the G and D bands ( I D/ I G) is decreased with increasing gas flow rate. TEM results suggest H 2 plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles and, thus, is playing a crucial role in modifying the obtained CNTs structures.

Pretreatment of the TaSiN Substrate Surface for Copper-MOCVD

Effects of plasma pretreatments to the TaSiN film surface on Cu nucleation were investigated. Scanning electron microscopy (SEM) was used to measure the Cu nucleation density and to observe the morphology of the Cu film. X-ray spectroscopy (XPS) and Auger depth profiling analyses were used to investigate the bonding state of atoms and the concentrations of oxygen and nitrogen at the TaSiN film surface, respectively. Cu nucleation in Cu MOCVD is effectively enhanced by treating the underlying Ta-Si-N film surface with hydrogen plasma prior to Cu MOCVD. The Cu nucleation density in Cu MOCVD increases as the rf-power and the plasma exposure time increase in the hydrogen plasma pretreatment, but it is saturated at the rf-power of 40W and the plasma exposure time of 2min. To increase the rf-power and the plasma exposure time further would increase the plasma radiation damage for the Si substrate. Therefore, 40W and 2min are the optimal process conditions for the hydrogen pretreatment. Copper nucleation is enhanced by hydrogen plasma pretreatment because the plasma treatment removes the nitrogen and oxygen atoms from the Ta-Si-N film surface. Since Ta-Si is a substrate more favorable for Cu nucleation than Ta-Si-N(O), Cu nucleation on the Ta-Si-N film is enhanced by hydrogen plasma pretreatment of the Ta-Si-N film surface.

Growth and profile modification of carbon nanotubes designed for field emission applications by hydrogen plasma pretreatment

In chemical vapor deposition (CVD) of carbon nanotubes (CNTs), formation and density control of nano-sized catalysts is critical in obtaining vertically aligned nanotubes. Two commonly adopted methods of achieving catalytic nanoparticles are heat-treatment and plasma pretreatment of a catalytic thin film. In this study, the CNTs were grown inside silicon trench arrays utilizing microwave plasma CVD. The effects of hydrogen plasma pretreatment of the nickel catalysts on the growth of CNTs and their subsequent field emission characteristics were investigated. Without plasma pretreatment, randomly oriented, short CNTs with low tube density grew. With plasma pretreatment, vertically aligned and highly dense CNTs were observed to grow but longer pretreatment resulted in shorter CNTs. The plasma pretreatment technique was successfully employed to achieve gated CNT microcathodes with a convex-shape surface profile, having quasi-uniform electric field distribution on the CNT tips. CNT sample with 1-min pretreatment exhibited the lowest turn-on field of ∼5 V/μm and achieved a current density of 1.0 mA/cm 2 at a threshold field of 8.0 V/μm. Overall, the hydrogen plasma pretreatment has been demonstrated to be a useful technique for the synthesis of vertically aligned CNTs and surface profile tweaking in gated structures.

Influence of hydrogen plasma surface treatment of Si substrate on nickel silicide formation

Nickel silicide (NiSi) offers the advantages of lower processing temperature, reduced silicon consumption in silicide formation, and absence of bridging failures and is hence expected to replace Ti and Co silicides as contact material in Si microelectronics. In this article, we report on our work involving the study of hydrogen plasma pretreatment of the Si substrate on the properties of subsequently formed NiSi. We observe the sheet resistance of the silicide film to decrease with hydrogenation at the expected lower processing temperatures of 400 and 500°C. Transmission electron microscopy studies do reveal that defects are introduced near the silicide-silicon interface in the hydrogenated wafers at lower processing temperatures. But these defects are annealed out at higher processing temperatures. Secondary ion mass spectroscopy profiles show an enhanced diffusion of Ni into the Si substrate at 500 and 600°C, apparently due to the defects introduced in the substrate by the hydrogen treatment.

Effect of hydrogen plasma pretreatment on growth of carbon nanotubes by MPECVD

We have grown carbon nanotubes (CNTs) with a microwave (μW) plasma enhanced chemical vapor deposition (MPECVD) method, which has been regarded as one of the most promising candidates for the synthesis of CNTs due to the vertical alignment, the low temperature and the large area growth. We use methane (CH 4) and hydrogen (H 2) gas for the growth of CNTs. Ni catalytic layer (10 nm thick) were deposited on the Ti-coated Si substrate by RF magnetron sputtering method. In this work, we report the effects of pretreatment μW power on the growth of CNTs. We have pretreated the Ni catalytic layer in different μW power (600, 700, and 800 W) and grown same μW power (800 W). Scanning electron microscopy (SEM) images show Ni catalytic layer diameter and density are varied dependent with their pretreatment conditions. Raman spectroscopy of CNTs shows that I D/ I G ratios and G-peak positions vary with pretreatment conditions.

Optimization of field emission properties of carbon nanotubes by Taguchi method

It is the purpose of this study to evaluate the field emission property of carbon nanotubes (CNTs) prepared by microwave plasma-enhanced chemical vapor deposition (MPCVD) method. Nickel layer of 5 nm in thickness on 20-nm thickness titanium nitride film was transformed into discrete islands after hydrogen plasma pretreatment. CNTs were then grown up on Ni-coated areas by MPCVD. Through the practice of Taguchi method, superior CNT films with very low emission onset electric field, about 0.7 V/μm (at J = 10 μA/cm 2), are attained without post-deposition treatment. It is found that microwave power has the most important influence on the field emission characteristics of CNT films. The increase of methane flow ratio will downgrade the degree of graphitization of CNT and thus its field emission characteristics. Scanning electron microscope and transmission electron microscopy (TEM) observation and energy dispersive X-ray spectrometer analysis reveal that CNT growth by MPCVD is based on tip-growth mechanism. TEM micrographs validate the hollow, bamboo-like structure of the multi-walled CNTs.

Interfacial modification of amorphous substrates for microcrystalline silicon growth with in situ hydrogen plasma pretreatment

AbstractMicrocrystalline silicon (µc‐Si:H) films have been deposited onto hydrogenated and amorphous Si‐rich silicon nitride and thermal oxide substrates with silane (SiH4)–hydrogen (H2) in remote plasma‐enhanced chemical vapor deposition (RPECVD) at 250 °C, and these films have been investigated. It is found that in situ hydrogen plasma pretreatment of the amorphous substrates prior to µc‐Si:H deposition is effective in reducing the interfacial amorphous transition region. It is believed that this hydrogen plasma pretreatment gives adsorption and nucleation sites by breaking weak Si–N and Si–Si bonds and also removes native Si–O x and hydrocarbon impurities. In the case of SiNx:H surface, surface roughening from atomic hydrogen etching and surface cleaning effects are greater than those for stable thermal oxide. Surface crystallization at the initial stage of the growth can be obtained on amorphous substrate at low temperature without an a‐Si transition layer. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Influence of Applying Bias Voltage on Diamond Nucleation while Changing the Experimental Condition

It is necessary to achieve uniform, high-density and large-area nucleation to form a large-area diamond thin film. It was reported that the low-pressure bias-enhanced nucleation method with hydrogen plasma pretreatment was useful for increasing the nucleation density and expanding the nucleation area. To realize the high-density nucleation and reproducibility, the influence of applying bias voltage on diamond nucleation was examined while changing the experimental condition from treatment to successive treatment.

Hydrogen Plasma Pretreatment on Field Emission Properties of MultiWalled Carbon Nanotubes Grown by Microwave PECVD

The morphology and electron emission characteristics of multiwalled carbon nanotubes (CNTs) fabricated by microwave plasma-enhanced chemical vapor deposition (PECVD) were examined. Prior to the growth of CNTs, TiN and Ni were deposited in succession as a diffusion barrier and a catalyst layer, respectively, and hydrogen plasma pretreatment was carried out to form Ni nanoclusters. The growth of CNTs was performed using the mixture gas of and at low temperature of 500°C. The impact of hydrogen plasma pretreatment on the structure and emission properties of the CNTs was investigated. It was confirmed that the average diameter of CNTs could be easily controlled by hydrogen plasma pretreatment, and diameters were varied from 36 to 26 nm as pretreatment times were changed from 5 to 15 min. However, further increase of the pretreatment time gave rise to rapid decrease in CNT growth. After 25 min of plasma pretreatment time, scanning electron microscopy observation exhibited destruction of the CNTs. In addition, variation of CNT diameter due to the plasma pretreatment caused a drastic change in emission properties. The turn-on voltages of CNT emitters in a diode-type electron emission configuration were varied from 3.5 to 9 V/μm according to the hydrogen plasma pretreatment conditions. The close relationship between electron emission characteristics and pretreatment time indicates that pretreatment condition can be a key process parameter in CNT growth for field emission displays and should be optimized. © 2004 The Electrochemical Society. All rights reserved.

Effects of Hydrogen Plasma Treatment of the Underlying TaSiN Film Surface on the Copper Nucleation in Copper MOCVD

MOCVD is one of the major deposition techniques for Cu thin films and Ta-Si-N is one of promising barrier metal candidates for Cu with high thermal stability. Effects of hydrogen plasma pretreatment of the underlying Ta-Si-N film surface on the Cu nucleation in Cu MOCVD were investigated using scanning electron microscopy, X-ray photoelectron spectroscopy and Auger electron emission spectrometry analyses. Cu nucleation in MOCVD is enhanced as the rf-power and the plasma exposure time are increased in the hydrogen plasma pretreatment. The optimal plasma treatment process condition is the rf-power of 40W and the plasma exposure time of 2min. The hydrogen gas flow rate in the hydrogen plasma pretreatment process does not affect Cu nucleation much. The mechanism through which Cu nucleation is enhanced by the hydrogen plasma pretreatment of the Ta-Si-N film surface is that the nitrogen and oxygen atoms at the Ta-Si-N film surface are effectively removed by the plasma treatment. Consequently the chemical composition was changed from Ta-Si-N(O) into Ta-Si at the Ta-Si-N film surface, which is favorable for Cu nucleation.

Effect of Plasma Pre-Treatment on Dewetting Properties of CVD Cu on CVDW2N Barrier Layer

AbstractThe effect of different plasma pre-treatments of chemical vapor deposited (CVD) tungsten nitride (W2N) surfaces on the dewetting behavior of subsequently grown CVD Cu films was investigated by annealing the resulting film stacks in high purity argon. It was found that a hydrogen plasma pre-treatment significantly improved the resistance to Cu dewetting from the W2N surfaces while ammonia and nitrogen plasma pretreatment slightly accelerated the dewetting process. The proposed mechanisms and ramifications of these findings were discussed.