N2 Plasma Treatment Research Articles

Thermal plasma treatment of titanium carbide powders: Part II. In-flight formation of carbon-site vacancies and subsequent nitridation in titanium carbide powders during induction plasma treatment

The in-flight modification of titanium carbide powders was carried out in radio-frequency (rf) inductively coupled plasmas. The powders were partially melted and evaporated, and then subjected to modifications in morphology, size, and chemical composition. Both the Ar–H2and Ar–N2plasma treatments induced the formation of carbon-site vacancies in titanium carbide. The mixing of NH3to Ar–H2plasma at the plasma tail, and the Ar–N2plasma treatment resulted in the partial substitution of carbon by nitrogen. The variation in physical and chemical modification was discussed compared with the predictions by the thermochemical analysis, and the numerically obtained heat transfer of our preceding paper.

Enhanced Metalorganic Chemical Vapor Deposition Titanium Nitride Film Fabricated Using Tetrakis-Dimethylamino-Titanium for Barrier Metal Application in Sub-Half-Micron Technology

Enhanced metalorganic chemical vapor deposition (MOCVD) titanium nitride (TiN:C) film with low resistivity (<700 µ Ω· cm) has been fabricated by thermal decomposition of tetrakis-dimethylamino-titanium (TDMAT; Ti[N(CH3)2]4). Enhancement is carried out by in-situ N2 plasma treatment of as-deposited TiN:C film and the enhanced TiN:C film has good stability: less than 4% increase in film resistivity after exposure to air for 24 days. The amount of oxygen absorbed in this enhanced TiN:C film after air exposure, determined by Auger electron spectroscopy (AES) was significantly reduced. This enhanced MOCVD TiN:C film has been successfully applied to sub-half-micron devices. A void-tree tungsten plug (W plug) for sub-half-micron holes can be achieved. Good barrier performance and low contact/via resistance have also been demonstrated.

Plasma Chemical Modification of Polycarbonate Surfaces for Electroless Plating

Abstract The preliminary steps of the “electroless” metallization of polycarbonate are investigated by XPS. They consist of the chemisorption of a catalyst (Pd) on the surface to be metallized. The corresponding surface can be activated either by chemical etching or by reactive or non-reactive gas plasma treatment. Therefore, the surface treatment of polycarbonate determines the palladium adsorption. It is shown here that a surface carrying oxygenated functions adsorbs palladium through Sn2+ ions which are themselves bonded to oxygen atoms. On the other hand, a surface on which nitrogenated groups have been grafted (by NH3 or N2 plasma treatment) chemisorbs palladium directly on these nitrogen atoms. Reaction mechanisms are proposed in both cases and a new and simplified process for making the surfaces catalytic is proposed.

Suppression of Resistance Increase in Annealed Al/W Interconnects by Capacitively Coupled Plasma Nitridation on W Surface

The suppression of the resistance increase in annealed Al/chemical vapor deposition (CVD)-W interconnects has been achieved by exposing the W surface to N2 plasma before Al deposition. The N2 plasma was generated in a capacitively coupled parallel-plate reactor. This process forms a thin WNx layer at the interface between the Al and the W layer. The WNx layer prevents Al-W alloy formation during annealing at 450°C. With this N2 plasma treatment, the resistance increase after annealing at 450°C is suppressed to only 10% compared to 140–180% in samples without the N2 plasma treatment. The N/W ratio and the thickness of the WNx layer are about 1.1 and 4 nm, respectively. The WNx layer formed in our experiment is found to be thicker and have a higher N concentration than the WNx layer formed by electron cyclotron resonance (ECR) plasma nitridation. This is probably due to the large self-bias voltage of the N2 plasma generated in a capacitively coupled parallel-plate reactor.

An Efficient Improvement for Barrier Effect of W-filled Contact

A post chemical vapor deposition of tungsten (CVD-W) treatment by N2 plasma is proposed to suppress the WAl12 formation during subsequent thermal annealing, which improves the thermal stability of W-filled contact. Selective CVD-W is employed to fill the contact hole. Following W deposition, in situ N2 plasma treatment is performed prior to Al alloy metallization. It is shown that this post CVD-W treatment efficiently suppresses the formation of WAl12, resulting in an improvement of the barrier capability of W-filled contact.

Fomation of a novel Al2O3surface (Al–O*) by plasma-excited nitrogen: O2production by water treatment of the Al–O* surface

An uphill reaction (N2+3H2O → 2NH3+ 3/2O2) takes place on the Al2O3 surface by means of N2 plasma treatment followed by water treatment at room temprature.

Adhesion mechanisms of silica layers on plasma-treated polymers. Part II. Polypropylene

We have investigated the influence of plasma pretreatment in various gases (Ar, NH3, N2) on the adhesion of plasma-deposited silica layers to polypropylene (PP). UV-visible ellipsometry measurements enabled us to detect crosslinking at the polymer surface. All treatments, and especially the Ar-diluted N2 treatment, induced crosslinking in the surface layer. The adhesion of silica to PP, as measured by the micro-scratch test, was improved by every treatment. In the case of Ar, the adhesion improvement is attributed to crosslinking, and possibly to surface activation by radical formation. In addition, surface functionalization was studied by in situ IR ellipsometry, X-ray photoelectron spectroscopy, and contact angle measurements. N2 plasma treatments induced a significant nitrogen grafting (17.5 at.% concentration after dilute N2 treatment, in the form of amines and imines), leading to an increase in both the electron-acceptor and the electron-donor components of the surface free energy. In contrast, dilute NH3 plasma treatment seemed to result in weak bonding of the nitrogen atoms to the surface, as deduced from a comparison of measurements performed in situ after this treatment, after aging, and after an additional SiH4 plasma treatment. The dilute NH3 treatment, performed after Ar treatment, did not further improve the adhesion of silica to PP, while an additional improvement was obtained with dilute and pure N2 treatments. This may be attributed to C-N-Si bond formation or to acid-base interactions between the nitrogenated polymer surface and silica.

Adhesion study of SiOx / PET films: comparison between scratch test and fragmentation test

Scratch and fragmentation tests were performed on 100 nm thick SiOx, coatings (1.1 x 2) deposited on PET substrates with and without prior N2-plasma treatment. A correlation was found between the critical normal forces measured during scratching and crack densities at fragmentation saturation. Quantification of the works of adhesion, and a comparison of their values for the scratch and fragmentation tests were possible by a comparison of the model developed by Bull, Burnett and Rickerby for the former, and Kelly and Tyson's model combined with the approach from Nardin and Schultz for the latter.

Interface Characterization and Delamination Mechanism of c-BN Film

ABSTRACTCubic boron nitride films were prepared by helicon wave plasma CVD process on (100) Si. The growth and delamination mechanism of c-BN film was investigated with FT-IR spectroscopy and transmission electron microscopy. The film deposited under the intense impact of energetic ions is usually delaminated from the substrate after deposition. It is found that moisture in the air, surface roughness of the film and substrate, as well as severe compressive stresses in the film are the primary contributors to film delamination. An aqueous oxidation was verified by EDXS analysis, which generate local stress by volume expansion at the crack region in the c-BN layer. From the experimental results and ??? observation a model for the delamination mechanism of c-BN film is suggested. Based on the delamination mechanism, several kinds of remedies such as post annealing and post N2plasma treatment were carried out for improving the adhesion.

Surface biomedical effects of plasma on polyetherurethane

Surface biomedical effects of plasma treatment and plasma polymerization on medical-grade polyetherurethane were studied. N2 and Ar plasma treatments and hexamethyldisiloxane (HMDS) plasma polymerization were performed at a power of 100 W with exposure times ranging from 1 to 15 min. The results showed that the contact angle of water was decreased from 79° to 62° by N2 and Ar plasma treatments, and N2 plasma treatment caused a slight enhancement in anti-coagulability and anti-calcific behavior. HMDS polymerization resulted in a decrease from 79° to 43° in the contact angle and an increase from 30.5 to 37.4 s in the recalcification time. At the same time, the anti-coagulability of polymerized samples for the exposure time of 2-5 min was 2.5 times that of the untreated sample. Results of XPS and ESR analyses showed that HMDS deposited onto the polyetherurethane surface and formed new Si-N bonds, and increased the number of radicals in the sample. XPS analysis also showed that N2 and Ar plasma treatments bro...

Characteristics of hydrogenated amorphous silicon thin-film transistor

The effects of N2 plasma interface treatment and atmospheric pressure chemical vapor deposition (APCVD) silicon dioxide (SiO2) gate insulator were investigated for the performance and the stability of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs). To improve an a-Si:H/SiO2 interface, the N2 plasma treatment was carried out on the SiO2 surface. As a result, both the threshold voltage and subthreshold voltage swing were decreased remarkably. The high performance of a-Si:H TFTs was achieved with a field-effect mobility of 1.27 cm2/V s, threshold voltage of 3.5 V, and subthreshold voltage swing of 0.4 V/decade. For both positive and negative gate bias stresses, the threshold voltage was shifted in the positive direction and was dominated by the defect creation near the a-Si:H/SiO2 interface. There was little charge trapping into the APCVD SiO2 gate insulator. For the positive gate bias and time stress, the threshold voltage shifts were smaller than those of the conventional a-Si:H TFTs with the a-Si:H/SiNX interface.

Phenyl alanine, tryptophan immobilized chitosan beads as adsorbents for selective removal of immunoproteins.

The use of adsorbents for the treatment of patients suffering from various immune diseases is still in its infancy. Therefore, the development of selective absorbents for the removal or decrease of immunoproteins from plasma is of great importance. In this study, chitosan, a natural polysaccharide having structural characteristics similar to glycosamino glycans, which is non-toxic and biocompatible, has been used for protein adsorption studies. Amino acids like phenyl alanine and tryptophan in different ratios are bonded to these polymers to observe immunoadsorption. Several layers of phenyl alanine or tryptophan have been coated covalently on chitosan beads using N2-plasma, carbodiimide or glutaraldehyde treatments. Scanning electron micrographs have revealed the surface morphological changes after such modifications. The surface modified chitosan beads have exhibited high binding affinity for gamma-globulin compared to bare beads. It is also observed that the amount of fibrinogen adsorption is reduced on modified substrate. A selective removal of IgG and IgM has also been observed with these modified matrix when tested with human plasma, using immuno diffusion methods. The modified chitosan membranes have demonstrated a reduction in platelet attachment, showing that these substrates have become more blood compatible. Hence, it appears that modified chitosan surfaces may be an excellent sorbent system for haemoperfusion due to their high binding affinity for immunoproteins and blood compatibility. Further studies are needed to determine the behaviour under clinical conditions.

Performance improvement of amorphous silicon thin-film transistors with SiO2 gate insulator by N2 plasma treatment

We studied the performance improvement of hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) using atmospheric pressure chemical vapor deposition (APCVD) SiO2 as a gate insulator. The threshold voltage and the subthreshold swing decrease remarkably by N2 plasma treatment on the APCVD SiO2 surface even though the field effect mobility changes little, indicating that the interface state density around the Fermi level is reduced significantly by N2 plasma treatment. We obtained the high performance a-Si:H TFT with the field effect mobility of 1.25 cm2/V s, the threshold voltage of 3.5 V and the subthreshold swing of 0.45 V/dec.

Stability of a-Si:H TFTs Employing APCVD SiO2 with N2 Plasma Treatment as a Gate Dielectric

ABSTRACTWe have investigated the stability of the hydogenated amorphous silicon thin film transistors (a-Si:H TFTs) employing silicon dioxide (SiO2) with N2 plasma treatment as a gate dielectric, where SiO2 was deposited by atmospheric pressure chemical vapor deposition (APCVD). Their stability was compared with those of a-Si:H TFTs whose gate dielectric was silicon nitride (SiNx) deposited by plasma enhanced chemical vapor deposition (PECVD). Two kinds of stresses, gate bias and light illumination, were applied. The threshold voltage shin (AVu,) and the inverse subthreshold slope shift (ΔVth) were measured as a function of the bias voltage and the light stress time. For the positive bias stress, the ΔVth, of the a-Si:H TFTs with the N2 plasma treated SiO2 dielectric is smaller than that with the PECVD SiNx gate dielectric. For the negative bias stress and light stress, however, the ΔVth of TFT with N2 plasma treated SiO2 dielectric is larger than that with the SiNx dielectric

Enhancement of the sticking coefficient of Mg on polypropylene by in situ ECR-RF Ar and N2 plasma treatments

A study of the sticking coefficient of Mg vapour on in situ Ar and N2 plasma-treated polypropylene (PP) is presented. After exposure of the pretreated sample to a determined amount of Mg vapour, X-ray photoelectron spectroscopy (XPS) allows measurement of the adhered Mg amount at the polymer surface and the chemical nature of the interface. The sticking coefficient on an as-received sample is zero and is increased to several tenths depending on the pretreatment conditions, namely the nature and the pressure of the neutral gas, the treatment time, and the applied RF-bias. Relations between the plasma parameters, the XPS measured surface state before the metallization, and the sticking coefficient are investigated.

Plasma treatment of polymers: the effect of the plasma parameters on the chemical, physical, and morphological states of the polymer surface and on the metal-polymer interface

The results of the characterization of plasma-treated polypropylene (PP) and polymethylmethacrylate (PMMA) by X-ray photoelectron spectroscopic, atomic force microscopic (AFM), and surface resistivity measurements are presented. Chemical, physical, and morphological modifications of the polymer surface were investigated. The importance of the neutral gas of the electron cyclotron resonance-radio frequency (ECR-RF) plasma treatment is principally demonstrated. Large differences between the effects of noble and reactive gas plasmas were observed by AFM and surface resistivity measurements. However, the maximum sticking coefficient of evaporated Mg on PP is similar for both Ar and N2 plasma treatments.

Effects of N2 Plasma Treatment on SiO2 Gate Insulator in a-Si:H Thin Film Transistor

AbstractWe fabricated the high performance a-Si:H TFT using the N2 plasma treated APCVD SiO2 as a gate insulator. The effects of N2 plasma treatment on the APCVD SiO2 were investigated by XPS and SIMS measurements. And the formation of the oxynitride interface layer between a-Si:H and APCVD SiO2 was found in the a-Si:H TFT. From our experimental results, It may be concluded that most nitrogen atoms, which were incorporated by the exposure of SiO2 layer to N2 plasma, exist, not bonded to other atoms, near the surface of the SiO2 layer and during the sequential deposition of a-Si:H on the N2 plasma treated APCVD SiO2 layer Si-N bonds are formed, resulting in the oxynitride layer in the interface region. This explains the high performance a-Si:H TFT with the N2 plasma treated APCVD SiO2 gate insulator.

Effects of N2 Plasma Treatment on SiO2 Gate Insulator in a-Si:H Thin Film Transistor

ABSTRACTWe fabricated the high performance a-Si:H TFT using the N2 plasma treated APCVD SiO2 as a gate insulator. The effects of N2 plasma treatment on the APCVD SiO2 were investigated by XPS and SIMS Measurements. And the formation of the oxynitride interface layer between a-Si:H and APCVD SiO2 was found in the a-Si:H TFT. From our experimental results, It May be concluded that most nitrogen atoms, which were incorporated by the exposure of SiO2 layer to N2 plasma, exist, not bonded to other atoms, near the surface of the SiO2 layer and during the sequential deposition of a-Si:H on the N2 plasma treated APCVD SiO2 layer Si-N bonds are formed, resulting in the oxynitride layer in the interface region. This explains the high performance a-Si:H TFT with the N2 plasma treated APCVD SiO2 gate insulator.

Polylysine-immobilized chitosan beads as adsorbents for bilirubin.

Hyperbilirubinemia generally relates to an elevated bilirubin level in the blood and is usually an indication of a disease of the blood, liver, or biliary tract. Hemoperfusion using synthetic resins as sorbents has been one of the ways to reduce bilirubin. In this study, chitosan, a natural polysaccharide having structural characteristics similar to glycosaminoglycans and which is nontoxic and biocompatible, has been used for bilirubin binding. Several layers of poly-L-lysine have been coated covalently onto chitosan beads, using N2 plasma and carbodiimide treatments. Such surface-modified chitosan beads exhibited high binding affinities for bilirubin (1.13 +/- 0.18 mg/g beads) in aqueous phosphate buffer solutions at 4 degrees C in relation to activated charcoal (0.74 +/- 0.2 mg/g). The polylysine-coated resins have been reported to have an improved binding affinity for bilirubin over cholestyramine. It seems that the surface-immobilized polylysine has an increased bilirubin binding affinity and is highly stable. The binding capacity is proportional to the amount of polylysine bonded to the chitosan beads. The hemolytic potential of all modified beads is compatible with polystyrene control tubes. Studies were also performed against albumin as proof of specificity toward bilirubin binding. The albumin-coated beads have shown the highest blood compatibility and selectivity over the other modified beads. However, it appears that polylysine-modified chitosan may be an excellent sorbent system for hemoperfusion due to its high binding affinity, capacity, and blood compatibility. Further studies are needed to determine its behavior under clinical conditions.

WNx Schottky diodes on plasma treated GaAs

The influence of the GaAs surface condition on the properties and thermal stability of WNx Schottky diodes on GaAs has been studied by performing in situ H2 and N2 plasma treatments just before the WNx sputter deposition. The WNx/GaAs contacts have been investigated by x-ray photoelectron spectroscopy, Rutherford backscattering, nuclear reaction analysis, secondary ion-mass spectroscopy, x-ray diffraction, and transmission electron microscope and correlated to electrical current-voltage and capacitance-voltage measurements. A strong correlation was found between the diode properties and the surface conditions, both for the as-deposited samples and for samples annealed in the range 700–850 °C. Poor rectifying properties were obtained for the plasma-cleaned diodes due to the cumulative effects of plasma cleaning and sputter deposition. After annealing, improved characteristics were generally found. The highest Schottky barrier height values φI-V=0.76 V, which were found for the H2 plasma treated diodes annealed at 800 °C, were almost independent of the WNx composition and sputtering conditions. The H2 treated samples also showed the smoothest WNx/GaAs interface. HCl cleaned and N2 treated surface also showed high-barrier height and small interfacial reactions after high-temperature annealing.