Conventional Low Pressure Research Articles

(Invited) Plasma Processes for Emerging Silicon-Based MEMS, NEMS and Packaging Applications

Plasma processes are important for emerging silicon-based micro-electro-mechanical systems (MEMS), nano-electro-mechanical systems (NEMS) and packaging applications. Typically every device has a customised process flow but synergies can be found as most are produced using a 2.5D approach comprising sequential deposition, lithography and etch cycles. Plasma processes are critical in enabling reproducible dry deposition and etch steps during manufacture. Increasingly they are also being adopted in lithography (nanoimprint) and bonding process steps. Plasma processes can be divided into the following broad families: Chemical vapour deposition (CVD)Atomic layer deposition (ALD)Physical vapour deposition (PVD)Etch (physically-driven)Etch (chemically-driven)Surface functionalisation The merits of each plasma technique and their application to emerging devices are discussed. Plasma-enhanced chemical vapour deposition (PECVD) of dielectrics and silicon is widely used to enable lower temperature processes than conventional low pressure CVD. Adjustment of deposition parameters can tune stress, chemical resistance, optical properties and wear characteristics for different application requirements. At higher temperatures, plasma-assisted nanogrowth of carbon nanotubes and 2D materials (e.g. graphene) are emerging technologies. Conversely, inductively coupled plasma CVD (ICP-CVD) is attracting interest to enable high quality films at lower temperatures. Plasma-assisted ALD enables thin and uniform layers to be grown in a wider range of materials and, similarly, high quality films at lower processing temperatures. Plasma-based PVD processes include sputtering and ion beam deposition. The former is a standard technique for metallisation. Al-based schemes are typical in the silicon IC industry but different metallisations (e.g. Au or Pt-based) may be required for sensors to give HF resistance or long lifetime contacts. Ion beam deposition is often used for complex multilayer stacks. Physically-driven etch processes require ions to provide enough energy to enable a chemical reaction or to physically break bonds at the wafer surface. Conversely, chemically-driven etch processes spontaneously react but require passivation species to obtain directionality (anisotropy). Ion beam etch processes enable non-volatile materials to be physically etched, such as Vanadium Oxide for uncooled infra red detectors. If the substrate is tilted then non-vertical structures, such as blazed gratings, may be realised. Plasmas may be used to clean surfaces or to create specific surface conditions for subsequent steps. This may be to passivate them, increase bond strengths at low temperatures or to subsequently functionalise them – e.g. adding hydrophobic self-assembled monolayers (SAMs) in MEMS microphones or for bio-probes in medical devices. The process step common to the majority of MEMS devices today is the Bosch silicon etch. This uses a repeating sequence of PECVD deposition, physical etch for directional passivation removal and chemical etch that results in a high rate, highly vertical and highly selective silicon etch - although the cyclic nature results in a characteristic sidewall roughness (scalloping). High aspect ratio structures may be realised and the process is not sensitive to crystal orientation (which limits geometries with anisotropic wet etchants). The majority of physical sensing devices are based on sub-70μm depth features. Trends are towards higher aspect ratios for enhanced performance and smaller footprint whilst maintaining throughput. Increasingly, large cavities are also being etched for subsequent chip or wafer scale packaging and sensor structures may comprise multi-wafer stacks with one of more having through wafer etches (300-750μm). With the move to multi-wafer structures interconnect becomes more challenging. Monolithically integrated devices are key to some high volume MEMS applications; however, the most common approach is to use hybrid integration – allowing separate optimisation of readout IC and MEMS devices. Increasingly solutions are moving towards system-in-a-package (SiP) and system-on-a-chip (SoC) solutions. Through silicon vias (TSVs) are emerging as a key technology for this in both the MEMS and IC industries. Aspect ratios are generally limited to 10-15:1 using the Bosch process in production. This is typically followed by dielectric isolation (e.g. TEOS) and barrier / seed metal layers (e.g. by ALD) prior to electroplating for a low via resistance. At the nanoscale, etching becomes more challenging. The Bosch process is less well suited due to finite sidewall scallop size and reduced rate / selectivity. Typically it is not used below 500nm feature sizes although 100nm features have been demonstrated. A continuously passivating process has smooth sidewalls but a lower rate, selectivity and aspect ratio capability at room temperature. Moving to cryogenic temperatures enables the highest rate, selectivity and aspect ratios to be achieved and can realise trench features down to 10nm. Emerging applications in silicon-based MEMS, NEMS and packaging require a diverse range of plasma processes. With no standardised process flow, individual tools need the flexibility to address multiple different process requirements and enable unit cost reductions by running multiple products to achieve higher volumes. Figure 1

Room Temperature Photoluminescence Characterization of Interface Quality of SiN/SiO2/Si Prepared under Various Deposition Techniques and Conditions

Various types of stacked dielectric films are used in complimentary metal-oxide-semiconductor (CMOS) devices in gates, capacitors and device isolation structures. They are also used as insulating materials between conductors, as inter-metal dielectrics (IMD) and inter-layer dielectrics (ILD). The preparation technique, structure and properties of dielectrics strongly influence the quality of the dielectrics/Si interface. Nominally, similar dielectrics/Si structures, even prepared by the same technique, often show different electrical properties depending on subtle differences in process conditions (hidden variables). Monitoring of physical dimensions and chemical compositions of dielectrics often miss unexpected variations in electrical properties. Non-contact electrical property characterization techniques lack lateral resolution and often results in impairment of the dielectrics/Si interface due to strong external electric fields from the measurement process. Alternative dielectrics/Si interface characterization techniques, which can provide insights into electrical properties without external electric field, would be very useful as a complimentary process and material quality monitoring technique. In this study, we have investigated the effect of SiN film deposition techniques on the interface quality of the resulting SiN/SiO2/Si using spectroscopic room temperature photoluminescence (RTPL) under multiwavelength excitation. The sample preparation procedures are as follows. First, ultra thin (~2.2 nm thick), gate oxide quality, thermal oxide films were grown on 300 mm Si(100) wafers. Nominally 5.0 nm thick SiN films were grown on ~2.0 nm thick SiO2/Si wafers using conventional low pressure chemical vapor deposition (LPCVD) and atomic layer deposition (ALD) under various nitrogen source flow conditions. The film thickness was measured (after SiO2 film deposition) before and after SiN deposition using ellipsometry. Figure 1 (a) and (b) show RTPL spectra measured at the center of seven different SiN/SiO2/Si wafers under 650 nm excitation and showing maximum RTPL intensity under 650 nm and 827 nm excitation. Significantly large RTPL intensity variations were measured among the seven SiN/SiO2/Si wafers. The SiN film deposition conditions have modified the underlying SiO2/Si interface characteristics. Non-contact RTPL measurements are very sensitive to the thin film deposition techniques and conditions. It is effective as a complimentary dielectrics/Si process and interface characterization and monitoring technique. Figure 1

Evaluation of pore size spectrum of gas shale reservoirs using low pressure nitrogen adsorption, gas expansion and mercury porosimetry: A case study from the Perth and Canning Basins, Western Australia

Abstract Gas shales have a complex pore structure. Mechanisms of gas storage in the gas shale pore system are in two ways, free gas and sorbed gas. The nanometer scaled pore systems of gas shale reservoirs have a prominent contribution for gas storage, especially for adsorbing gas onto their surfaces. In this study three different methods of low pressure nitrogen adsorption, mercury porosimetry and gas expansion were used for pore structure characterization of gas shales. Mercury porosimetry and gas expansion methods have been used for a long time in characterization of conventional reservoirs but low pressure nitrogen adsorption has been considered recently as a tool for gas shale evaluation. The studied gas shale samples are coming from the Perth and Canning Basins, Western Australia. Analyzing the results of case study shows that the Canning shale samples have the specific surface area and micro/mesopore volume around 13 m2/g and 1.4 cc/100 g, respectively, which are relatively higher than the same values for the Perth shale samples. Quantitative analysis of the obtained results clarifies the shape, size and pore volume of the studied gas shale samples. However analyzing the results shows that there is not any consistency between similar parameters like effective porosity or pore size distribution (PSD) extracted from these techniques; several explanations have been proposed for justification of this inconsistency. As well as the results of this study make it clear that each of the usual techniques applied for characterization of gas shale pore systems has some deficiencies and cannot be used alone for this purpose. Whereas, by combining the results of these methodologies pore size spectrum of gas shales can be determined in a more accurate way.

Growth of Hexagonal Columnar Nanograin Structured SiC Thin Films on Silicon Substrates with Graphene-Graphitic Carbon Nanoflakes Templates from Solid Carbon Sources.

We report a new method for growing hexagonal columnar nanograin structured silicon carbide (SiC) thin films on silicon substrates by using graphene–graphitic carbon nanoflakes (GGNs) templates from solid carbon sources. The growth was carried out in a conventional low pressure chemical vapor deposition system (LPCVD). The GGNs are small plates with lateral sizes of around 100 nm and overlap each other, and are made up of nanosized multilayer graphene and graphitic carbon matrix (GCM). Long and straight SiC nanograins with hexagonal shapes, and with lateral sizes of around 200–400 nm are synthesized on the GGNs, which form compact SiC thin films.

Effects of wavelength and water quality on photodegradation of N-Nitrosodimethylamine (NDMA)

N-Nitrosodimethylamine (NDMA) is a potent carcinogen that yields a cancer risk of 10−6 at concentrations as low as 0.7ngL−1. Tentative guideline values are set at 3ngL−1 in California, USA; 9ngL−1 in Ontario, Canada; 40ngL−1 nationwide in Canada; and 100ngL−1 by the World Health Organization. NDMA is a great concern in treating reclaimed water as well as drinking water. UV degradation can be considered effective degradation method. A 1-log reduction of NDMA is achieved by 1000mJcm−2 of a 254-nm low pressure (LP) mercury UV lamp. However, a higher degradation efficiency than that provided by LP lamps is desired in practical treatment. In this study, the effects of wavelength and water quality were investigated to achieve higher degradation efficiency. The effects of wavelength were examined by comparing three UV lamps: a 222-nm Kr Cl Excimer UV lamp, a 254-nm LP mercury UV lamp, and a 230- to 270-nm filtered medium pressure (FMP) mercury UV lamp. The 222-nm lamp and FMP lamp achieved 4 times and 2.8 times higher degradation efficiency, respectively, than the conventional 254-nm LP lamp. Effects on water quality were also simulated by using absorption spectrum data of nitrate solutions and process water from a drinking-water treatment plant. In the simulation, the 222-nm lamp was affected by UV-absorbing compounds in the water, whereas the FMP lamp showed more stable degradation efficiency. Appropriate use of these three types of lamps could enhance the efficiency of degradation of NDMA.

Temperatures in fine grinding with minimum quantity lubrication (MQL)

Minimum quantity lubrication (MQL) is a promising new fluid delivery technique in grinding. However, the thermal behaviour of the process under such cooling conditions remains unclear. This work reports on the results of a recent investigation of MQL in fine-cut plane surface grinding. The experimental study considered three conditions: conventional low pressure fluid delivery, dry grinding and MQL delivery. Common steels EN8, M2 and EN31 were ground with a general purpose alumina wheel. Conventional fluid used was a general purpose 5% by volume emulsion; MQL fluid was a general purpose machining oil. Grinding temperatures were measured using the single-pole thermocouple method. Grinding temperatures obtained from experiment are compared with those predicted from theory. Results obtained demonstrate that MQL can deliver a comparable thermal performance to conventional flood delivery under the conditions investigated. Grinding kinematics are discussed to explain the outcomes and to improve understanding of MQL grinding performance.

Plasma Spray-PVD: A New Thermal Spray Process to Deposit Out of the Vapor Phase

Plasma spray-physical vapor deposition (PS-PVD) is a low pressure plasma spray technology recently developed by Sulzer Metco AG (Switzerland). Even though it is a thermal spray process, it can deposit coatings out of the vapor phase. The basis of PS-PVD is the low pressure plasma spraying (LPPS) technology that has been well established in industry for several years. In comparison to conventional vacuum plasma spraying (VPS) or low pressure plasma spraying (LPPS), the new proposed process uses a high energy plasma gun operated at a reduced work pressure of 0.1 kPa (1 mbar). Owing to the high energy plasma and further reduced work pressure, PS-PVD is able to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and electron beam-physical vapor deposition (EB-PVD) coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Owing to the forced gas stream of the plasma jet, complex shaped parts such as multi-airfoil turbine vanes can be coated with columnar thermal barrier coatings using PS-PVD. Even shadowed areas and areas which are not in the line of sight of the coating source can be coated homogeneously. This article reports on the progress made by Sulzer Metco in developing a thermal spray process to produce coatings out of the vapor phase. Columnar thermal barrier coatings made of Yttria-stabilized Zircona (YSZ) are optimized to serve in a turbine engine. This process includes not only preferable coating properties such as strain tolerance and erosion resistance but also the simultaneous coverage of multiple air foils.

Vapor Phase Deposition Using a Plasma Spray Process

Plasma spray-physical vapor deposition (PS-PVD) is a low pressure plasma spray technology recently developed by Sulzer Metco AG (Switzerland) to deposit coatings out of the vapor phase. PS-PVD is developed on the basis of the well established low pressure plasma spraying technology. In comparison to conventional vacuum plasma spraying and low pressure plasma spraying, these new processes use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics, which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material, which builds up a layer from liquid splats, but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional PVD technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and electron beam-physical vapor deposition (EB-PVD) coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated with columnar thermal barrier coatings using PS-PVD. Even shadowed areas and areas, which are not in the line-of-sight to the coating source, can be coated homogeneously. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase. Columnar thermal barrier coatings made of yttria stabilized zircona are optimized to serve in a turbine engine. This includes coating properties like strain tolerance and erosion resistance but also the coverage of multiple air foils.

Atmospheric Pressure-Ion Drift Chemical Ionization Mass Spectrometry for Detection of Trace Gas Species

This paper describes atmospheric pressure-ion drift chemical ionization mass spectrometry (AP-ID-CIMS) for monitoring of ambient trace species. Operation of the drift tube at atmospheric pressure allows a significantly longer ion-molecule reaction time and eliminates dilution of the ambient samples, while a well-defined electric field inside the drift tube provides the benefits to confine the flight path and velocity of reagent/product ions, to break down ion clusters, and to control the ion-molecule reaction time. The AP-ID-CIMS exhibits advantages over the conventional low pressure ID-CIMS and flow tube AP-CIMS, improving the detection sensitivity by 3 orders of magnitude and a factor of 3, respectively. We demonstrate that the AP-ID-CIMS allows quantification of sulfuric acid concentrations and is capable of detecting gaseous sulfuric acid with a detection limit of less than 10(5) molecules cm(-3), on the basis of 3sigma of the baseline noise and an integration time of 12 s. A field evaluation of the AP-ID-CIMS is presented for ambient H(2)SO(4) measurements.

Solid on liquid deposition

A process for the deposition of a solid layer onto a liquid is presented. The polymer poly-di-chloro-para-xylylene, also known as Parylene C, was grown on low vapour pressure liquids using the conventional low pressure chemical vapour deposition process. A reactor was built and a process developed to enable the deposition of Parylene C at atmospheric pressure over high vapour pressure liquids. It was used to deposit Parylene C over water among others. In all cases Parylene C encapsulated the liquid without influencing its initial shape. The results presented here show also that the Parylene C properties are not affected by its growth on liquid templates and the roughness of the Parylene C surface in contact with the liquid during the deposition is extremely low.

CVD of Pure Copper Films from a Novel Amidinate Precursor

This paper reports on the use of a novel copper(I) amidinate compound [Cu(i-Pr-MeAMD)]2 to produce copper films in conventional low pressure CVD using hydrogen as reducing gas-reagent. Copper films were deposited on steel, silicon and SiO2/Si substrates. Their composition, morphology, conductivity and growth rate were investigated in the temperature range 200 - 350 oC at total pressure of 10 Torr. XRD and EPMA confirmed that the films are composed of polycrystalline copper metal without carbon and nitrogen impurities.

Iron nitride thin films deposited by chloride assisted plasma enhanced chemical vapour deposition: facile stoichiometry control and mechanism study

A facile method for iron nitride thin film preparation by the plasma enhanced chemical vapour deposition technique using FeCl2, N2 and H2 as starting materials was developed. Iron nitride thin films with different phase structures, including three stoichiometric phases (γ′-Fe4N, ε-Fe3N and ζ-Fe2N) and solid solutions in between could be prepared by this method. Variation of N2 or H2 flow, plasma power or FeCl2 evaporation temperature allowed continuous adjustment of the film stoichiometry. Typical deposition rates of 10–20 nm min−1 was achieved in typical conditions, much faster than that in most conventional low pressure thin film fabrication methods. This method was also successfully applied to prepare the nitrides of Mn, Co and Ni by simply replacing FeCl2 with the corresponding metal chlorides. The mechanisms determining film stoichiometry and deposition rate were interpreted by a simple chemical model together with optical emission spectroscopy diagnostics of plasma.

Co–CoO nanoparticles prepared by reactive gas-phase aggregation

The technique of gas-phase aggregation has been used to prepare partially oxidized Co nanoparticles films by allowing a controlled flow of oxygen gas into the aggregation zone. This method differs from those previously reported, that is, the passivation of a beam of preformed particles in a secondary chamber and the conventional (low Ar pressure) reactive sputtering of Co to produce Co-CoO composite films. Transmission electron microscopy shows that the mean size of the particles is about 6 nm. For sufficiently high oxygen pressures, the nanoparticles films become super-paramagnetic at room temperature. X-ray diffraction patterns display reflections corresponding to fcc Co and fcc CoO phases, with an increasing dominance of the latter upon increasing the oxygen pressure in the aggrega- tion zone, which is consistent with the observed reduction in saturation magnetization. The cluster films assembled with particles grown under oxygen in the condensation zone exhibit exchange-bias fields (about 8 kOe at 20 K) systematically higher than those measured for Co-CoO core-shell nanoparticles prepared by oxidizing preformed particles in the deposition chamber, which we attribute, in the light of results from annealing experiments, to a higher ferromagnetic-antiferromagnetic (Co-CoO) interface density.

Use of cyclohexanedimethanol as a nonflammable organic solvent for industrial scale reversed phase chromatography

This work demonstrates that cyclohexanedimethanol is an effective nonflammable organic solvent for the pilot scale reversed phase chromatography of recombinant apolipoprotein A-I Milano. Cyclohexanedimethanol has low viscosity in water, enabling the use of conventional low pressure process scale chromatography columns and hardware. Results from pilot scale manufacturing using a 30 cm diameter CG71M packed column indicate that a 5.7 log reduction in E. coli host cell protein with >80% yield can be obtained for the purification of apolipoprotein A-I Milano.

Needle cricothyroidotomy

Needle cricothyroidotomy

大気圧プラズマ表面処理した銅線および銅撚線のフラックス無し鉛フリーはんだメッキ

There has been an intensive effort in the industries in recent years to replace leaded solder with lead-free process in order to minimize the emission of toxic materials. However, leaded solder is still used in many cases where no alternative lead-free process is currently available. Leaded soldering of the wire terminals is one of the worst examples as it causes cross contamination of lead into the lead-free solder bath during the successive process. To avoid this problem, it is important to develop a new process of successfully removing polymer film coated on a copper wire. We have investigated the use of atmospheric pressure plasma as a solution for the polymer removal in conjunction with lead-free solder plating. The atmospheric plasma technology has some unique advantages compared with the conventional low pressure plasma processes such as low cost operation and high speed processing as the chemical reaction tends to be more enhanced at higher pressure. An atmospheric micro-plasma source was thus developed for this purpose and its high etching rate of more than 100 μm/min with fluorine gas mixture was demonstrated. Furthermore, it was found that the copper wires processed by this plasma could be readily plated with lead-free solder at low temperature of 250°C without any use of fluxes even at 168 hours after removing the polymer film.

Investigation of the effect of the total pressure and methane concentration on the growth rate and quality of diamond thin films grown by MPCVD

The influence of total gas pressure (50–125 Torr) and methane concentration (0.75%–10%) on diamond growth by microwave plasma chemical vapor deposition (MPCVD) was investigated. Within the regimes studied, the growth rate was proportional to the methane concentration in the source gas while it exhibited a super-linear dependence on total pressure. For a fixed methane concentration, characterization by Raman spectroscopy, scanning electron microscopy and X-ray diffraction indicated there was a minimum pressure required for the growth of large grain diamond, and conversely, for a fixed pressure, there was a maximum methane concentration that yielded diamond deposition. Higher pressures and higher carbon concentrations yielded diamond growth rates more than 10 times higher than achieved by the conventional low pressure MPCVD process.

SUPERHEATED STEAM‐DRYING OF MATE LEAVES AND EFFECT OF DRYING CONDITIONS ON THE PHENOL CONTENT

ABSTRACT Four drying experiments of mate leaves (Ilex paraguariensis St. Hilaire) were carried out in a packed bed superheated steam dryer by varying outlet steam temperature from 120 to 140C and equivalent particle diameter from 4.7 × 10−3 to 6.95 × 10−3 m. The influence of these variables on the drying coefficient calculated by assuming a simplified drying kinetic model was investigated. A classical statistical approach revealed the significant effect of both factors on this parameter. Two additional drying runs were performed at identical conditions with conventional hot air and low pressure superheated steam, respectively. The influence of drying atmosphere on the total content of phenols was evaluated. A conventional process of extraction by using an aqueous methanol solution was adopted. Analyses for total phenols were performed by spectrophotometry at 715 nm by applying Folin‐Denis assay. The leaves dried with superheated steam had approximately 47% higher retention of these compounds.

Atmospheric Pressure Plasma Treatment and Non-Flux Lead-Free-Soldering of Cu Wire and Strand

There has been an intensive effort in the industries in recent years to replace leaded solder with lead-free process in order to minimize the emission of toxic materials. However, leaded solder is still used in many cases where no alternative lead-free process is currently available. Leaded soldering of the wire terminals is one of the worst examples as it causes cross contamination of lead into the lead-free solder bath during the successive process. To avoid this problem, it is important to develop a new process of successfully removing polymer film coated on a copper wire. We have investigated the use of atmospheric pressure plasma as a solution for the polymer removal in conjunction with lead-free solder plating. The atmospheric plasma technology has some unique advantages compared with the conventional low pressure plasma processes such as low cost operation and high speed processing as the chemical reaction tends to be more enhanced at higher pressure. An atmospheric microplasma source was thus developed for this purpose and its high etching rate of more than 100 mm/min with fluorine gas mixture was demonstrated. Furthermore, it was found that the copper wires processed by this plasma could be readily plated with lead-free solder at low temperature of 250 � C without any use of fluxes even at 168 h after removing the polymer film.

Ｔｉ合金製骨内インプラントのＨＡ膜の骨固定効果に関する考察

In 1995, the author reported the development of unique cementless total hip joints applying hydroxyapatite (HA) flame coating onto a porous titanium surface which is arc-sprayed with pure titanium material in argon gas at atmospheric pressure. The surface roughness of the porous layer was 360 microm Rmax, and the layer was more resistant to blast erosion than the conventional low pressure plasma sprayed porous layers. The thickness of the HA layer was between 20 and 40 microns considering the balance of bone conduction effect of HA and the risk of mechanical detachment of the layers from the porous titanium. Short-term animal tests showed excellent results. At that time a specific question was raised as to whether or not the coated HA layers would remain in the living bone for a long time. The results obtained from observation of retrieved specimens show that the thickness of the HA coating layer is sufficient for new bone formation after implantation, and HA would be absorbed in the body within a few years, after contributing to the new bone formation.