Clean Silicon Wafers Research Articles

Electronic structure and chemical reaction of Ca deposition on regioregular poly(3-hexylthiophene) surfaces

Conjugated polymer, regioregular poly(3-hexylthiophene) (rr-P3HT), films were prepared by spin-coating the rr-P3HT chloroform solution onto clean silicon wafer surfaces. The chemical reaction and electronic structure of Ca deposition on rr-P3HT surfaces were in situ investigated by synchrotron radiation photoemission spectroscopy (SRPES) and X-ray photoemission spectroscopy (XPS). Upon Ca deposition, Ca-induced band bending of rr-P3HT is observed. In addition, Ca atoms preferentially react with S atoms of rr-P3HT. No obvious reaction between Ca and C atoms can be found. Through the investigation of the evolution of valence band spectra and secondary electron cut-off of rr-P3HT during the process of Ca deposition, an energy level alignment diagram at the Ca/rr-P3HT interface is derived.

Quantitative XPS depth profiling of codeine loaded poly( l-lactic acid) films using a coronene ion sputter source

The controlled release of active pharmaceutical ingredients from polymers over prolonged periods of time is vital for the function of drug eluting stents and other drug loaded delivery devices. Characterisation of the drug distribution in polymers allows the in vitro and in vivo performance to be rationalised. We present the first X-ray photoelectron spectroscopy (XPS) depth profiling study of such a drug eluting stent system for which we employ a novel coronene ion sputter source. The rationale for this is to ascertain quantitative atomic concentration data through the thickness of flat films containing codeine and poly( l-lactic acid) (PLA) as a model of a drug loaded polymer device. A range of films of thickness of up to 96 nm are spun cast from chloroform onto Piranha cleaned silicon wafers. Ellipsometry of the films is undertaken prior to depth profiling to determine the total film thickness and provide a measure of the relative loading of drug within the PLA matrix through spectroscopic analysis. Progressive XPS analysis of the bottom of the sputter crater with sputter time indicated codeine to be depleted from the surface and segregated to the bulk of the polymer films by comparison with a uniform distribution calculated from the bulk loading. This serves to illustrate that surface depletion of drug occurs, which poses important implications for drug loaded polymer delivery systems.

Megasonic Sweeping and Silicon Wafer Cleaning

Megasonic Sweeping and Silicon Wafer Cleaning

Teflon is Hydrophilic. Comments on Definitions of Hydrophobic, Shear versus Tensile Hydrophobicity, and Wettability Characterization

Comments are made concerning the recent use of adjectives to describe solid surfaces that exhibit anomalously high water contact angle values. We suggest that the meaning of the word hydrophobic be resolved before it is modified, for example, to superhydrophobic and further modified, for example, to sticky superhydrophobic and before the definitions of these new words become issues of contention. The case is made that the first statement in the title is appropriate with experiments that demonstrate significant attractive interaction between liquid water and the surface of solid Teflon. Four types of experiments are described: the interaction of a silicon-supported covalently attached perfluoroalkyl monolayer (a model Teflon surface) with a sessile water drop (1) and with a thin film of water on a clean silicon wafer surface (2), the interaction of 1 and 12 microm diameter solid Teflon particles with a water droplet surface (3), and the interaction of a thin (<5 microm) Teflon film with a water droplet (4). The concepts of shear and tensile hydrophobicity are introduced, and the recommendation that two numbers, advancing and receding contact angle values, should be considered necessary data to characterize the wettability of a surface. That the words hydrophobic, hydrophilic, and their derivatives can and should only be considered qualitative or relative terms is emphasized.

Effect of porous silicon layer on the performance of Si/oxide photovoltaic and photoelectrochemical cells

Abstract Photovoltaic and photoelectrochemical systems were prepared by the formation of a thin porous film on silicon. The porous silicon layer was formed on the top of a clean oxide free silicon wafer surface by anodic etching in HF/H2O/C2H5OH mixture (2:1:1). The silicon was then covered by an oxide film (tin oxide, ITO or titanium oxide). The oxide films were prepared by the spray/pyrolysis technique which enables doping of the oxide film by different atoms like In, Ru or Sb during the spray process. Doping of SnO2 or TiO2 films with Ru atoms improves the surface characteristics of the oxide film which improves the solar conversion efficiency. The prepared solar cells are stable against environmental attack due to the presence of the stable oxide film. It gives relatively high short circuit currents (Isc), due to the presence of the porous silicon layer, which leads to the recorded high conversion efficiency. Although the open-circuit potential (Voc) and fill factor (FF) were not affected by the thickness of the porous silicon film, the short circuit current was found to be sensitive to this thickness. An optimum thickness of the porous film and also the oxide layer is required to optimize the solar cell efficiency. The results represent a promising system for the application of porous silicon layers in solar energy converters. The use of porous silicon instead of silicon single crystals in solar cell fabrication and the optimization of the solar conversion efficiency will lead to the reduction of the cost as an important factor and also the increase of the solar cell efficiency making use of the large area of the porous structures.

Immobilization of Tris-(8-hydroxyquinoline) aluminum onto P4VP polymer thin films by UV irradiation cross-linking

We report a novel method for the immobilization of Tris-(8-hydroxyquinoline) aluminum (Alq 3) onto poly(4-vinylpyridine) (P4VP) thin polymer films by UV irradiation cross-linking. The polymer films were prepared by spin-coating of P4VP onto cleaned silicon wafer surface followed by UV irradiation. The thicknesses of the polymer thin films were measured by ellipsometry with different irradiation times. The immobilization of Alq 3, orientation and the surface activity were followed using photoluminescence and UV–visible spectroscopy. The surface morphology was investigated by using field emission scanning electron microscopy and atomic force microscopy. Patterning of Alq 3 on P4VP film was obtained using photolithography technique. Our experimental results show that the cross-linked P4VP thin film is a universal surface modifier.

Novel low-cost approach for removal of surface contamination before texturization of commercial monocrystalline silicon solar cells

This paper reports a novel approach on the surface treatment of monocrystalline silicon solar cells using an inorganic chemical, sodium hypochlorite (NaOCl) that has some remarkable properties. The treatment of contaminated crystalline silicon wafer with hot NaOCl helps the removal of organic contaminants due to its oxidizing properties. The objective of this paper is to establish the effectiveness of this treatment using hot NaOCl solution before the saw damage removal step of the conventional NaOH texturing approach. A comparative study of surface morphology and FTIR analyses of textured monocrystalline silicon surfaces with and without NaOCl pre-treatment is also reported. The process could result in a significant low cost approach viable for cleaning silicon wafers on a mass production scale.

Detection of 30–40-nm Particles on Bulk-Silicon and SOI Wafers Using Deep UV Laser Scattering

As semiconductor devices continue to get smaller, and thus the size of yield-limiting particles decreases, a need has arisen for detecting smaller particles on silicon surfaces. The current minimum detectable diameter of wafer-surface particle-detection systems employing 488-nm wavelength Ar+ gas lasers widely used in semiconductor production lines is, under optimized conditions, 50-60 nm on bulk-silicon surfaces. The sensitivity for SOI wafers, however, is considerably lower than this level due not only to the additional optical reflections from Si/SiO2/Si interfaces within the SOI stack but also to the undesirable light scattering at the rough interfaces. The challenges in meeting the requirement to detect smaller particles specified in the ITRS will be presented. Using a 266-nm solid-state laser, we have developed for semiconductor manufacturing a high sensitivity system capable of detecting particles as small as 30 and 40 nm on unpatterned bulk-silicon wafers and SOI wafers, respectively. Our technique of single-wafer spin cleaning with repetitive use of ozonated water and dilute HF cleaning of silicon wafers can reduce surface microroughness, thus reducing background noise in this system, and providing higher particle-detection sensitivity than conventional RCA cleaning. Defect classification using this system integrated with a review scanning electron microscope will also be discussed

Post Sliced Cleaning of Silicon Wafers using Ozone and Ultrasound

【The effect of ozone and/or ultrasound treatments on the efficiency of slurry removal in post sliced cleaning (PSC) of silicon ingot was studied. Efficiency of slurry removal was evaluated as functions of time, temperature and surfactant with DOE (Design of Experiment) method. Residual slurries were observed on the wafer surface in case of cleaning by ozone or ultrasound separately. However, a clean wafer surface was appeared when cleaned with ozone and ultrasound simultaneously. It has found that cleaning time was the main effect among temperature, time and surfactant. Elevated temperature, addition of surfactant and high ozone concentration helped to accelerate efficient removal of slurry. The improvement of removal efficiency seems to be related to the formation of more active OH radicals. The highly cleaned surface was achieved at 10 wt% ozone, 1 min and 10 vol% surfactant with ultrasound. Application of ozone and ultrasound might be a useful method for PSC process in wafer cleaning.】

Damage-Free Ultradiluted HF / Nitrogen Jet Spray Cleaning for Particle Removal with Minimal Silicon and Oxide Loss

There has been a trade-off between efficient particle removal and damage minimization to fragile device structures when using mixed-liquid/gas jet spray cleaning of silicon wafers. We have developed an ultradiluted HF/nitrogen jet spray cleaning procedure for single-wafer spin-cleaning, which can efficiently remove particles on both silicon and silicon-dioxide surfaces even at a low nitrogen flow rate without causing damage to fragile 45-nm polysilicon gate structures in a short period. The use of ultradiluted HF can make silicon and oxide loss negligible, below 0.003 nm and 0.03 nm, respectively. This very simple single-step cleaning procedure drastically reduces chemical consumption.

Durable ultraviolet sensors using highly oriented diamond films

We fabricated vacuum ultraviolet (VUV) sensors using highly oriented diamond (HOD) films and studied their long-term stability to evaluate the feasibility of the sensors for practical use. The sensors are composed of a pair of interdigitated Pt electrodes on the HOD film surfaces, and sealed in the industrially standard can packages. Xenon (Xe) excimer lamps ( λ = 172 nm) and low-pressure mercury (Hg) lamps ( λ = 185 nm) were used as the radiation sources. It was demonstrated that the output signal of the sensors is reproducible and stable over 700 h under the intense VUV irradiation from Xe excimer lamps. The results of low-pressure Hg lamp measurements showed that the sensors were sensitive only to the 185-nm radiation irrespective of the presence of the 254-nm radiation that is five to ten times more intense than the 185-nm radiation. It is thus concluded that the present HOD film sensors make possible a continuous monitoring of the intense VUV radiation sources, and can be applicable to dry cleaning of silicon wafers or glass substrates in semiconductor industry and flat panel display manufacturing processes, respectively.

Synthesis, Langmuir and Langmuir–Blodgett film behaviour of new dendritic amphiphiles

New amphiphilic compounds 1–9 that feature a construction with dendronized hydrophilic and hydrophobic segment groups connected to a specific aromatic or aliphatic spacer unit have been synthesized, following a modular building block strategy. The hydrophilic dendrons are typically branched elements with peripheral carboxylic groups, unlike the hydrophobic dendrons that contain peripheral alkyl chains as part of respective amide functions. The hydrophilic dendrons are in different generations of branching, while the hydrophobic dendrons are all in the first generation of branching (three terminal branching), but differ in the length of the alkyl chains, thus giving rise to designed structure and amphiphilic properties in the new compounds. The resulting surfactants are capable of forming well-defined Langmuir films of remarkable stability when spread from a solution onto an aqueous subphase. Nevertheless, specific packing behaviour and orientation of the amphiphilic molecules were found, depending on the molecular structure, as determined using analysis of the surface pressure–area (π–A) isotherms. Langmuir–Blodgett transfer of the first monolayer from a pure water subphase to a clean silicon wafer proved possible for the amphiphiles of peripheral alkyl chain length C12, while the amphiphiles with the longer alkyl chains failed, possibly due to the more rigid monolayers they form, impeding the transfer.

Acoustic emission monitoring during laser shock cleaning of silicon wafers

A laser shock cleaning is a new dry cleaning methodology for the effective removal of submicron sized particles from solid surfaces. This technique uses a plasma shock wave produced by laser-induced air breakdown, which has applied to remove nano-scale silica particles from silicon wafer surfaces in this work. In order to characterize the laser shock cleaning process, acoustic waves generated during the shock process are measured in real time by a wide-band microphone and analyzed in the change of process parameters such as laser power density and gas species. It was found that the acoustic intensity is closely correlated with the shock wave intensity. From acoustic analysis, it is seen that acoustic intensity became stronger as incident laser power density increased. In addition, Ar gas has been found to be more effective to enhance the acoustic intensity, which allows higher cleaning performance compared with air or N 2 gas.

Water Motion in Carrierless Wet Station

Water flow in an overflow rinse bath of the carrierless wet station for cleaning silicon wafers of 300 mm diam was studied, from the view point of the transport phenomena. Both the experiment of flow visualization and the numerical calculation using the transport equations show that the direction and the velocity distribution of the water from the water nozzle can be optimized by adjusting the wall thickness of the water nozzle. Additionally, this direction is shown to influence the water motion in the entire rinse bath and that between the wafers. Theoretical calculations taking the entire geometry and the detail of the water nozzle into account are shown to be applicable to predict and design the water flow in the wet cleaning bath. © 2004 The Electrochemical Society. All rights reserved.

Ablative thresholds in laser cleaning of substrates from particulates

‘Laser cleaning’ thresholds based on the local ablation of substrate material are studied theoretically. Results are compared with the experimental data on the cleaning of silicon wafers from spherical silica particles using laser wavelengths at 248, 532 and 1064 nm. Calculations take into account local enhancement in the laser-light intensity and are based on analytical solutions for the temperature distribution. Influence of vapor atmosphere on cleaning thresholds is studied experimentally and theoretically. Here cleaning is assisted by explosive vaporization of capillary condensed water. A possibility to increase the window for damage-free cleaning by varying the pulse duration and laser wavelength is also discussed.

Non-contact removal of 60-nm latex particles from silicon wafers with laser-induced plasma

In micro- and nano-manufacturing particles are created and circulated as by-products of the processes utilized. The removal of micro- and nano-particles during manufacturing processes is of great importance in many industries, including semiconductors, optics, photonics and microelectromechanical systems (MEMS). One specific application is in the cleaning of silicon wafers. According to the 2002 update of the International Technology Roadmap for Semiconductors, by the year 2006, techniques for the removal of polystyrene latex (PSL)-equivalent particles with size less than 35 nm will be required and currently, according to the roadmap update, there is no known method to remove PSL-equivalent particles smaller than diameter D = 40 nm. The current study reports and demonstrates a non-contact laser-induced plasma method for removal of particles with D = 60 nm. Non-contact techniques are desired to reduce the risk of substrate damage. Chemical usage in traditional cleaning methods is also a serious concern for process cost, workplace safety and environmental conservation. The development of dry, rapid, non-contact and non-damaging nanoparticle removal methods is, therefore, a critical need for various applications. Using a scanning mechanism, the process discussed can be automated for rapid cleaning of large silicon wafers.

Post-chemical mechanical polishing cleaning of silicon wafers with laser-induced plasma

During chemical-mechanical polishing (CMP), wafers are subjected to various particle sources such as slurry, polishing pads and polishing machines. Consequently, wafer post-CMP cleaning is crucial in micro- and nano-manufacturing to improve yield. In conventional cleaning process, the wafer is subjected to forces whose magnitudes are large enough to potentially cause substrate damage. This damage concern is becoming more severe as the characteristic feature size shrinks to sub-100-nm region. The development of dry, rapid, non-contact and non-destructive particle removal methods has been emerging as a critical requirement for post-CMP cleaning. In recent years a novel technique for particle removal using the pressure field generated by pulsed laser-induced plasma (LIP) has been introduced for cleaning surfaces and trenches. In the current study, it is demonstrated that the LIP removal technique is capable of removing ceria CMP particles with size of 100 nm and above without any substrate damage. The results reported in this study prove that LIP can also be applied over extended areas for post-CMP cleaning. It is possible to remove smaller particles at lower gap distances but the minimum particle size that can be removed is limited by the risk of substrate damage. Results reported in this study indicate that the LIP particle removal technique has significant potential for post-CMP cleaning in the near future.

Development of Chemical Processes for Preparation of Bonding Substrates

Modified methods for preparing surfaces when obtaining silicon structures on an insulator by bonding substrates are developed. The surfaces of silicon wafers and the device layer of silicon structures on an insulator which are synthesized by bonding methods are obtained and investigated. The investigations of the parameters of the samples obtained show that the technological process chosen for cleaning silicon wafers are promising and such work is best done at microelectronics companies.

Near field induced defects and influence of the liquid layer thickness in Steam Laser Cleaning of silicon wafers

The removal of particles from commercial silicon wafers by Steam Laser Cleaning was examined. Polystyrene colloids were used as model contaminants due to their well defined size and shape. In contrast to previous studies, where the experimental conditions on the surface were only roughly determined, special care was taken to control the amount of liquid applied to the surface. We report measurements of the cleaning threshold for different particle sizes. The comparability of the results was ensured by the reproducible conditions on the surface. Moreover, we studied the influence of different liquid film thicknesses on the cleaning process. Investigations of laser induced liquid evaporation showed that the cleaning threshold coincides with the fluence necessary for the onset of explosive vaporization. After particle removal, the surface was examined with an atomic force microscope. These investigations demonstrated that near field enhancement may cause defects on the nm-scale, but also showed that Steam Laser Cleaning possesses the capability of achieving damage-free removal for a large range of different particle sizes.

Efficiency studies of particle removal with pulsed-laser induced plasma

The detachment and removal of micro- and nanoparticles from surfaces is of importance in many industries. The cleaning of silicon wafers is of great interest in the semiconductor, microelectronics, and optics industries. The development and adoption of dry, rapid, non-contact, and non-damaging particle removal technologies is a critical process. The proposed laser-induced plasma (LIP) removal technique is a novel method for detaching and removing fine particles from substrates. The current technique is a dry, non-contact method that takes advantage of the strong shock wavefront from expanding plasma, created by focusing a laser pulse in air above the substrate. The transient pressure field acts on the target particles to produce a rotational moment and a rolling mode of detachment from the substrate. In the current study, the LIP removal technique is employed repeatedly to remove particles over an area of a silicon wafer, and a systematic efficiency study for the removal effectiveness is performed. A Q-switched Nd:YAG pulsed laser operating at 1064 nm with a 370 mJ pulse energy and 5 ns pulse length is used in experiments. 0.99 μm diameter silica spheres and 3.063 μm diameter polystyrene spheres were successfully detached and removed with no substrate damage. The removal efficiency at various gap distances between plasma core and substrate is determined and reported. This work is the first laboratory demonstration of the LIP technique over an extended area. The reported results substantiate the LIP removal technique as a serious option for particle detachment and removal from extended areas.