Downstream Microwave Plasma Research Articles

A plasma assisted in situ restoration process for sidewall damaged ULK dielectrics

This paper describes a novel in situ restoration process to repair damaged porous low-k materials by a plasma assisted approach. The main advantage is the enhanced repair efficiency due to the formation of small plasma activated multiple repairing fragments as well as the in situ handling to avoid a further k-value increase by water uptake. A liquid repair chemistry was evaporated and inserted into downstream microwave plasma to form activated species with repair character and to prevent the contact of porous low-k materials with UV irradiation and ion bombardment. In this study Octamethylcyclotetrasiloxane (OMCTS) and Bis(dimethylamino)dimethylsilane (DMADMS) were chosen for blanket samples with a k-value of 2.4. Furthermore OMCTS was investigated on patterned ULK trench structures of 62nm width. Besides the OMCTS flow rate, the addition of oxygen, methane or nitrogen was studied with regards to the formation of repair fragments and restoration efficiency.

Plasma-assisted simultaneous reduction and nitrogen doping of graphene oxide nanosheets

An environmentally benign and scalable route for the production of gram scale quantities of nitrogen-doped graphene using a downstream microwave plasma source is reported. Simultaneous reduction and doping of graphene oxide is achieved and the process negates the need for high temperatures and toxic solvents associated with existing methods. This gas-phase low temperature process is completely dry and, thus, minimises re-aggregation of graphene flakes which is typically associated with liquid phase reduction methods. The resulting material has many potential uses, particularly in electrochemical energy.

Surface oxidation of single-walled carbon nanotube paper with oxygen atoms

Single-walled carbon nanotube paper was surface oxidized with gaseous oxygen atoms produced by low-pressure: (1) vacuum UV (λ = 104.8 and 106.7 nm) photo-oxidation and (2) downstream microwave plasma discharge of an Ar–O2 mixture. X-ray photoelectron spectroscopy was used to detect the carbon- and oxygen-containing functional groups in the top 2–5 nm of the sample’s surface. Both methods produced a saturation level of ca. 12 at.% oxygen with the predominant formation of the epoxide/ether groups.

Structure Retention and Water Stability of Microwave Plasma Polymerized Films From Allylamine and Acrylic Acid

AbstractLow‐pressure downstream microwave plasma was used to deposit thin water resistant PPAAm and PPAAc films on titanium substrates. Film stability against dissolution was tested under sonication in ultrapure water. Variation of duty cycle on mean power was applied to evaluate the sensitivity of film properties on plasma conditions. Strong cross‐linked and therewith water resistant PPAAm and PPAAc films correlate with a relatively low but for biomedical applications sufficient density of functional groups. Furthermore, some similarity exists between process parameter and dissolution stability of deposited plasma polymer films prepared by microwave and reported for radio frequency plasmas.

Perspective on the Development of Microplasma Technology: The Role of Oxygen in Downstream Microwave Plasma

AbstractWe studied the role of a minor fraction of oxygen in nitrogen and argon downstream microwave plasma in view of plasma‐processing of ultrathin organic films ‐ self‐assembled monolayers (SAMs). As test systems we used SAMs of alkanethiolates on gold substrate. The plasma‐induced processes in the films, including their chemical modification, oxidation, and partial decomposition, were monitored in detail. These processes could be directly correlated with the presence of reactive, oxygen‐derived species in the plasma. The major plasma‐induced processes could be well described by the first order kinetics; the respective reaction rates were also derived. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fluorescent Plasma Nanocomposite Thin Films Containing Nonaggregated Rhodamine 6G Laser Dye Molecules

This letter reports a novel methodology for the synthesis of dye-containing nanocomposite thin films containing fluorescent rhodamine 6G (Rh6G) laser dye molecules. The nanocomposites are deposited in one step at room temperature in a downstream microwave plasma operating at low pressure and power. By controlling the plasma chemistry, it is possible to reduce the formation of dye dimers and higher aggregates that quench the fluorescence of the dye molecules. The films are intensely absorbent and fluorescent, insoluble in water, mechanically stable, and present good adhesion to the substrate. Besides, the method is compatible with the present silicon technology and therefore particularly interesting for the fabrication of integrated optoelectronic devices.

Modification of Monomolecular Self-Assembled Films by Nitrogen−Oxygen Plasma

The modification of octadecanethiolate self-assembled monolayers on Au and Ag by nitrogen-oxygen downstream microwave plasma with variable oxygen content (up to 1%) has been studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy. The primary processes were dehydrogenation, desorption of hydrocarbon and sulfur-containing species, and the oxidation of the alkyl matrix and headgroup-substrate interface. The exact character and the rates of the plasma-induced changes were found to be dependent on the substrate and plasma composition, with the processes in the aliphatic matrix and headgroup-substrate interface being mostly decoupled. In particular, the rates of all major plasma-induced processes were found to be directly proportional to the oxygen content in the plasma, which can be, thus, considered as a measure of the plasma reactivity. Along with the character of the observed changes, exhibiting a clear dominance of the oxidative processes, this suggests that the major effect of the oxygen-nitrogen downstream microwave plasma is provided by reactive oxygen-derived species in the downstream region, viz. long-living oxygen radicals and metastable species.

Modification of Aliphatic Self-Assembled Monolayers by Free-Radical-Dominant Plasma: The Role of the Plasma Composition

Modification of octadecanethiolate self-assembled monolayers on Au by nitrogen-oxygen or argon-oxygen downstream microwave plasma with a low oxygen content (estimated below several percent) has been studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy and water contact angle measurements. For both types of plasma, the primary processes were found to be the loss of conformational and orientational order and the oxidation of the alkyl matrix and headgroup-substrate interface. At the same time, the film modification occurred much faster and with different intermediates for the nitrogen plasma than for the argon plasma. The reasons for these differences are considered in terms of the different reactivities and different efficiencies of the energy transfer between the plasma constituents in these two types of plasma.

Modification of Aliphatic Monomolecular Films by Free Radical Dominant Plasma: The Effect of the Alkyl Chain Length and the Substrate

High-resolution photoelectron spectroscopy was applied to study the modification of alkanethiolate (AT) self-assembled monolayers (SAMs) on gold and silver substrates by nitrogen−oxygen downstream microwave plasma. The dominating plasma-induced processes are the oxidation of the alkyl matrix and the thiolate headgroups and the desorption of the alkylsulfonate species. The rates and extent of these processes and the mechanism of film modification depend on the substrate and the length of the alkyl chain. The films on Ag were found to be much more resistant to degradation by the reactive plasma, which is related to stronger thiolate−metal and sulfonate−metal bonds as compared to those on Au and to a partial polymerization of the alkyl matrix in AT/Ag at the initial stages of the plasma treatment. On a given substrate, the length of the aliphatic chain noticeably affects the rates and extent of the oxidation and desorption processes. The major effect stems from a two-step character of the thiolate−sulfonate ...

The Effect of the Substrate on Response of Thioaromatic Self-Assembled Monolayers to Free Radical-Dominant Plasma

Synchrotron-based high-resolution photoelectron spectroscopy was applied to study the modification of self-assembled monolayers (SAMs) of 4‘-methyl-1,1‘-biphenyl-4-thiols (BPT) on (111) gold and silver substrates by a nitrogen−oxygen downstream microwave plasma and the attachment of acrylic acid to the plasma-modified SAMs. The plasma treatment resulted in massive damage and disordering of the BPT films, with the extent and character being noticeably different for BPT/Au and BPT/Ag. Whereas for BPT/Au a profound desorption of the entire BPT moieties and a complete defragmentation of the residual hydrocarbon part occurred, only partial desorption and oxidation took place for BPT/Ag, where even a part of intact BPT moieties survived the plasma treatment. The differences in the response of BPT/Au and BPT/Ag to the plasma treatment are related to the stronger thiolate−substrate bonds for the latter system. Taking into account that an analogous difference was also observed in alkanethiolate films, one can consider it as a general property of thiol-derived SAMs. The extent of acrylic acid attachment to the plasma-treated BPT/Ag was found to be essentially larger than that to the hydrocarbon residues in the case of BPT/Au.

Modification of Alkanethiolate Self-Assembled Monolayers by Free Radical-Dominant Plasma

Synchrotron-based high-resolution photoelectron spectroscopy was applied to study the modification of the alkanethiol (AT) self-assembled monolayers on gold and silver substrates by nitrogen−oxygen downstream microwave plasma. Because of the low density and energy of the ionizing particles, the long-lived nitrogen and oxygen radicals provided the major impact of plasma treatment. The treatment resulted in massive damage and disordering of the initially well-ordered and chemically homogeneous AT films. The most pronounced processes are the complete (AT/Au) or partial (AT/Ag) oxidation of the pristine thiolate species, partial desorption of hydrogen and carbon-containing fragments with subsequent cross-linking within the residual hydrocarbon layer, and partial oxidation of this layer, and appearance of the nitrogen-containing entities. The plasma-treatment-induced changes in the alkyl matrix and at the S−substrate interface are only partly correlated. The rate and extent of the oxidation processes at this interface are noticeably larger for C18/Au than for C18/Ag, which suggests a stronger S−metal bond in the latter system. The results demonstrate that a smallest oxygen contamination should be avoided if one wants to perform a soft modification of thin organic layers or definite molecular entities attached to these layers through the exposure to plasma.

Plasma-Induced Surface Functionalization of Polymeric Biomaterials in Ammonia Plasma

Plasma-chemical modification is frequently used to improve the adaption of polymer surfaces to biological environments. In this regard amino functional groups play a key role. They provide an excellent basis for subsequent modifications with specific biomolecules. It would be of great value to get an amino functionalization independent of the specific material in use. The paper reports on an investigation concerning the feasibility of such an universal plasma functionalization procedure. Two different downstream microwave plasma sources were taken to apply a procedure, which was developed for high-grade modification of polystyrene (PS), to a number of other polymers including polyetheretherketone (PEEK), polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate (PC), polyethylene (PE), polymethylmethacrylate (PMMA) and fluorinated polymers. In many cases, very similar results were obtained. At maximum 5% of the surface were covered by nitrogen functional groups. In some cases, about 50% of total nitrogen functional groups were amino groups. The results suggest that a downstream ammonia plasma treatment indeed is a fairly universal method for high performance amino functionalization of polymeric biomaterials.

Plasma-Induced Surface Functionalization of Polymeric Biomaterials in Ammonia Plasma

Plasma-chemical modification is frequently used to improve the adaption of polymer surfaces to biological environments. In this regard amino functional groups play a key role. They provide an excellent basis for subsequent modifications with specific biomolecules. It would be of great value to get an amino functionalization independent of the specific material in use. The paper reports on an investigation concerning the feasibility of such an universal plasma functionalization procedure. Two different downstream microwave plasma sources were taken to apply a procedure, which was developed for high-grade modification of polystyrene (PS), to a number of other polymers including polyetheretherketone (PEEK), polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate (PC), polyethylene (PE), polymethylmethacrylate (PMMA) and fluorinated polymers. In many cases, very similar results were obtained. At maximum 5% of the surface were covered by nitrogen functional groups. In some cases, about 50% of total nitrogen functional groups were amino groups. The results suggest that a downstream ammonia plasma treatment indeed is a fairly universal method for high performance amino functionalization of polymeric biomaterials.

Chemical vapor deposition of fluoroalkylsilane monolayer films for adhesion control in microelectromechanical systems

We have developed a new process for applying a hydrophobic, low adhesion energy coating to microelectromechanical (MEMS) devices. Monolayer films are synthesized from tridecafluoro-1,1,2,2- tetrahydrooctyltrichlorosilane (FOTS) and water vapor in a low-pressure chemical vapor deposition process at room temperature. Film thickness is self-limiting by virtue of the inability of precursors to stick to the fluorocarbon surface of the film once it has formed. We have measured film densities of ∼3 molecules nm2 and film thickness of ∼1 nm. Films are hydrophobic, with a water contact angle >110°. We have also incorporated an in situ downstream microwave plasma cleaning process, which provides a clean, reproducible oxide surface prior to film deposition. Adhesion tests on coated and uncoated MEMS test structures demonstrate superior performance of the FOTS coatings. Cleaned, uncoated cantilever beam structures exhibit high adhesion energies in a high humidity environment. An adhesion energy of 100 mJ m−2 is observed after exposure to >90% relative humidity. Fluoroalkylsilane coated beams exhibit negligible adhesion at low humidity and ⩽20 μJ m−2 adhesion energy at >90% relative humidity. No obvious film degradation was observed for films exposed to >90% relative humidity at room temperature for ∼24 h.

Surface Kinetics of Polyphenylene Oxide Etching in a CF 4 / O 2 / Ar Downstream Microwave Plasma

A downstream microwave plasma etcher with in situ diagnostics has been constructed to elucidate the chemical mechanisms in plasma etching of polyphenylene oxide (PPO). reactant gases are used. Stable reaction products are investigated with mass spectrometry while reactive‐free radical information is obtained using optical emission spectroscopy. Additionally, the weight loss of PPO is measured to determine average etch rate. A linear correlation between weight loss measurements of PPO laminates and integration of CO and formation measured by mass spectrometry suggests that real‐time monitoring of polymer etching can be achieved. Etching dynamics are studied with gas compositions of varied from 6.6 to 30%. The etch process exhibits a dynamic reduction in rate with . spectra of X‐ray photoelectron spectroscopy show an increase in fluorination of the etched surface with . A kinetic model based on the dynamic change of the number of carbon sites that are fluorinated is proposed. © 2000 The Electrochemical Society. All rights reserved.

Chromatic monitoring of downstream microwave plasma source

The application of the chromatic sensing for monitoring of a microwave plasma source is described. The emitted radiation from the plasma excited in the argon, oxygen and CF4 mixture was measured with three PIN-diodes with integrated optical filters. The response of the chromatic signals on variation of power and gas composition was investigated. Whereas a good sensitivity of the integrated optical signal to the power was confirmed, only a limited sensitivity to the working gas mixture was found.

Nitrogen plasma annealing for low temperature Ta2O5 films

A low temperature oxygen/nitrogen plasma process is reported that substantially reduces leakage currents in chemical vapor deposited (CVD) and physical vapor deposited (PVD) films of tantalum oxide. We show that a combination of nitrogen and oxygen in a remote downstream microwave plasma source reduces leakage currents in CVD films of tantalum oxide and also reduces trap densities as measured by charge pumping. The as deposited CVD films show a high level of photoluminescence that is substantially lowered by the plasma anneal due to a reduction in the density of midgap states. For films deposited by PVD in the thickness range of 100 nm we find low leakage currents with a substantial improvement from the introduction of nitrogen into the plasma. However, PVD films in the thickness range of 20 nm show larger relative leakage currents and less of an improvement from the addition of nitrogen. The role of nitrogen in lowering leakage currents and charge trapping is thought to occur from a reduction in the density of bulk trap states in the oxide due to partial incorporation of nitrogen in the oxide. Both of these low temperature deposition and annealing processes are compatible with integration into the upper levels of metallization for high density circuits.

In Situ Infrared Studies of Polyvinyl Chloride Films Exposed to H 2 / O 2 / Ar Downstream Microwave Plasmas

The effects of Ar, , and downstream microwave plasmas on the surface structure and properties of polyvinyl chloride films are described. Plasma‐polymer surfaces interactions are monitored using in situ infrared reflection‐absorption spectroscopy. The influence of downstream microwave plasma conditions (e.g., pressure, gas composition, irradition time) on polymer surfaces are studied, in either the direct or the indirect exposure configuration. Indirect downstream microwave plasma exposures under appropriate conditions do not alter polymer surfaces to the detection limit of the infrared technique. Complementary results are provided by pressure changes in the plasma reactor system, water contact angle measurements, and surface morphology studies on polymer surfaces using atomic force microscopy. The results of similar plasma treatments on polyethylene surfaces are described briefly.

Resist preparation and removal techniques for high dose implantation on 200 mm wafers

Ion implanter manufacturers are providing high current batch systems consistent with the throughput demands of DRAM manufacturers as well as any manufacturers striving for the “lowest cost of ownership”. As beam currents increase above 20 mA in production, so do problems associated with the implant integrity; i.e., neutrals from collision with evolved gases from the resist, but also problems related to resist removal after the implant. This paper reviews simple, stable techniques useful for a wide variety of resist removal applications with emphasis on elimination or minimization of contamination or device damage during the resist removal process. Implants using As, B, P, BF 2 with high doses and various dose rates (beam currents up to 26 mA) were done on patterned 200 mm wafers. Using a downstream microwave plasma asher, the differences in ashing rates and resist removal of the two critical materials are compared for the various implant conditions. Special programs/recipes are selected to accommodate (a) the tough carbonized top layer of resist, and (b) the softer bulk resist at the bottom. The results of this joint effort, between a major implanter manufacturer and asher manufacturer, will help solve several potential or existing end user problems related to high dose implantation resist removal processes.

Ammonia plasma passivation of GaAs in downstream microwave and radio-frequency parallel plate plasma reactors

The poor electronic properties of the GaAs surface and GaAs–insulator interfaces, generally resulting from large density of surface/interface states, have limited GaAs device technology. Room-temperature ammonia plasma (dry) passivation of GaAs surfaces, which reduces the surface state density, is investigated as an alternative to wet passivation techniques. Plasma passivation is more compatible with clustered-dry processing which provides better control of the processing environment, and thus, improves interface integrity. Passivation was monitored in real-time and in situ using photoluminescence (PL). In addition, the passivated surfaces are inspected using x-ray photoelectron spectroscopy. Passivation with two different plasma excitation methods, downstream microwave (2.45 GHz) and rf (13.56 MHz) parallel plate, are compared, and effects of operating parameters such as pressure, flow rate, and power are examined. In both methods plasma-generated H atoms reduce the surface state density by removing excess As and As2O3 during the first few seconds of the plasma exposure. This step is followed by formation of Ga2O3 which takes place on a longer time scale (5–10 min). While the final passivation result appears to be similar for both methods, surface damage by ion bombardment competes with passivation in the parallel plate method, reduces the PL yield and adversely affects the long term stability of the passivated surface. Although it is common to heat the sample during passivation, we show that NH3 plasma passivation is possible at room temperature without heating. Low-temperature processing is important since passivation can be done at the end of device processing when it is undesirable to expose the device to elevated temperatures. The absence of ion bombardment damage combined with efficient generation of H atoms in the downstream microwave treatment, make this scheme a preferred dry passivation process, which could be easily and inexpensively clustered with existing GaAs processes.