Tetramethylammonium Hydroxide Concentration Research Articles

Performance and fouling characteristics in a pilot-scale reverse osmosis membrane system for microelectronic wastewater treatment

The microelectronic industry faces the significant challenge of managing vast volumes of wastewater containing toxic and harmful pollutants. While the Ultrafiltration-Reverse Osmosis (UF-RO) system has gained recognition as a potential solution for the reclamation and reuse of such wastewater, there is a lack of comprehensive understanding on its performance and membrane fouling conditions in the context of actual microelectronic wastewater. In this study, we continuously monitored the performance of a pilot-scale UF-RO system treating microelectronic wastewater. The RO membrane was subject to autopsy characterization at the end of its operation. The UF pretreatment performance remained consistent, with the UF-RO system showcasing high removal efficiency (>99.5 %) for tetramethylammonium hydroxide (TMAH), the primary pollutant in the microelectronic wastewater. Inorganic, organic, and biofouling were identified on the membrane surface, with the biofouling as the predominant form. A microbial community analysis showed that Proteobacteria and Bacteroidetes were the dominant bacteria on the membrane surface at the phylum level, while Alicycliphilus, Chryseobacterium, and Flavobacterium were predominant at the genus level. Fouling characteristics and degrees varied across the four stages, with the fouling in the 2nd stage being the most severe. Interestingly, an increased concentration of TMAH in the influent of the 4th stage seemed to inhibit the development of biofouling to some extent. This study offers valuable insights into the practical performance of the pilot-scale UF-RO technology when treating microelectronic wastewater and lays the groundwork for developing strategies to address membrane fouling concerns within the microelectronics industry.

Redox flow desalination for tetramethylammonium hydroxide removal and recovery from semiconductor wastewater

As part of humankind’s path towards more sustainable water technologies, redox flow desalination (RFD) has emerged as a promising technology due to its high energy efficiency and easy operation. So far, RFD research has focused on removing and recovering inorganic salts such as lithium-ions, heavy metal ions, or phosphate and nitrate ions. Thus, the potential of RFD in water desalination and resource recovery processes has not been fully demonstrated. Therefore, this study aimed to assess RFD for the valorization of tetramethylammonium hydroxide (TMAH) as value-added organic compounds from wastewater beyond inorganic elements, which is widely being used as an etching solvent, photoresist developer, and surfactant in semiconductor and display industries. By applying a low cell voltage (<1.2 V), a reversible redox reaction allowed a continuous removal of TMAH from the wastewater stream and a simultaneous recovery for reuse as a form of tetramethylammonium cation. The TMAH removal rate was approximately 4.3 mM/g/h with a 40% recovery ratio. With various operational conditions (i.e., TMAH concentration, cell voltage, and flow rate), our system exhibited a high potential for the valorization of TMAH with 60% reduction in capital cost compared to conventional desalination processes.

Extraction and quantification of metal-containing nanoparticles in marine shellfish based on single particle inductively coupled plasma-mass spectrometry technique

Quantitative characterization of nanoparticles (NPs) in marine shellfish is critical to understanding the risks of bio-accumulation. Based on single particle (sp)ICP-MS and electron microscopy, a standardized protocol was developed to extract Ag, Au, and indigenous Ti-containing NPs from mussels. The optimal parameters are: dry sample extraction with tetramethylammonium hydroxide (TMAH), 5% (v/v) final concentration of TMAH, extraction at 25 ℃ for 12 h, and separation by centrifugation (3000 rpm for 5 min). The particle number recoveries of spiked Ag and Au NPs were 88 ± 0.9% and 95 ± 1.1%, respectively, while Ti-containing NPs had a particle number concentration of 8.2 × 106 particles/mg and an average size of 70 nm in tested mussels. Furthermore, titanium oxide NPs, including rutile, anatase, and Magnéli phases (TixO2x-1) were found ubiquitously in 10 shellfish based on the optimal method. The particle number concentrations and average sizes of the Ti-containing NPs were 2.1 × 106–8.4 × 106 particles/mg and 70–80 nm, respectively. These Ti-containing NPs, such as TiO2, accounted for about half of the Ti mass in shellfish, indicating that marine shellfish may be a significant sink for Ti-containing NPs.

Analysis of dissolution kinetics of narrow polydispersity poly(4-hydroxystyrene) in alkaline aqueous solution using machine learning

Understanding the dissolution kinetics of resist materials is essential for their efficient development. In this study, we investigated the dissolution kinetics of poly(4-hydroxystyrene) (PHS) with a weight-average molecular weight (M w) of 8000–30 000 and a polydispersity index (M w /M n) of 1.07–1.20. The dissolution kinetics of PHS films was observed in tetramethylammonium hydroxide (TMAH) aqueous developers by a quartz crystal microbalance (QCM) method. The TMAH concentration was changed from 0 to 2.38 wt%. The formation of a thick transient swelling layer at these M w /M n values was suppressed compared with that at M w /M n > 2. QCM data were analyzed using the polynomial regression to clarify the effects of M w and M w /M n on the dissolution kinetics in a narrow polydispersity region. Both dissolving and swelling kinetics largely depended on M w/M n. M w had little effect in 2.38 wt% TMAH developer; however, it had a large effect on the swelling when 2.38 wt% TMAH developer was diluted.

Microbial properties of the granular sludge in a psychrophilic UASB reactor fed with electronics industry wastewater containing organic chemicals

In this study, a lab-scale upflow anaerobic sludge blanket (UASB) reactor was applied to the treatment of artificial electronics industry wastewater containing tetramethylammonium-hydroxide (TMAH), monoethanolamine (MEA), and isopropyl-alcohol (IPA) in order to evaluate process performance and degradation properties. During 800 days of operation, 96% efficiency of chemical oxygen demand (COD) removal was stably achieved at an organic loading rate of 8.5 kgCOD/m3/day at 18–19 °C. MEA degradation, carried out by acid-forming eubacteria, was confirmed within a week. The physical properties of the retained granular sludge were degraded by feeding with TMAH wastewater, but maintained by feeding with MEA wastewater due to an accumulation of species from the genus Methanosaeta and family Geobacteraceae. Analysis of the microbial community structure via SEM and 16S rRNA genes showed a proliferation of Methanomethylovorans-like cells and Methanosaeta-like cells at the surface and in the core of the granular sludge with TMAH, MEA and IPA acclimation. Furthermore, a batch degradation experiment confirmed that process inhibition due to increasing chemical concentration was relatively stronger for TMAH than for MEA or IPA. Thus, controlling the TMAH concentration of the influent to below 1 gCOD/L will be important for the stable treatment of electronics industry wastewater by UASB technology.

Reaction Kinetics of Poly-Si Etching in TMAH Solution

Tetramethylammonium hydroxide (TMAH) is a metal-free strong alkaline solution which can etch poly-Si. The concentration of dissolved gas as well as the concentration of TMAH affects etching rate of poly-Si. The detailed kinetics of poly-Si etching in TMAH solution is investigated in this study. The effect of water and TMAH concentration on the etching kinetics of poly-Si was investigated by using various concentrations of TMAH solution. It is found that H2O in TMAH solution plays an important role in etching poly-Si. Presence of dissolved CO2 and O2 in TMAH solution tends to inhibit etching of poly-Si. The concentration of dissolved CO2 and O2 in TMAH were reduced by Ar bubbling, thereby the poly-Si etching rate increased.

Enhancement of Enzymatic Hydrolysis of Lignocellulose by Tetrabutylammonium Hydroxide (TBAOH) and Tetramethylammonium Hydroxide (TMAOH) Aqueous Solution Pretreatment

AbstractBACKGROUNDLignocellulose is usually pretreated as a raw material, and then it undergoes hydrolysis, fermentation, and other processes to produce biofuels, which is conducive to improving the utilization of agricultural and forestry wastes. However, most pretreatments, such as acid–base, CO2 explosion, and microbial degradation, could enhance the yield of enzymatically hydrolyzed (EH) sugars, but the conditions are relatively harsh, environmentally unfriendly, and economically unfeasible. Ionic liquids, in view of their excellent physical and chemical properties and strong solubility, have been proven to be an effective green solvent for pretreating lignocellulose. The aim of this study was to exploit tetrabutylammonium hydroxide (TBAOH) and tetramethylammonium hydroxide (TMAOH) aqueous solutions to pretreat corn cob under relatively mild conditions.RESULTSThe optimal pretreatment conditions for the two solutions were 30 °C, TBAOH concentration of 20 wt%, 60 min, 5 wt/wt, and 20 °C, TMAOH concentration of 10 wt%, 60 min, 5 wt/wt, and the corresponding sugar yields were 88.9% and 92.2%, respectively. Compared with the unpretreated corn cob, the yield of EH sugar increased by about 2.7–2.8 times. Characterization results confirmed that hemicelluloses and lignin were removed from the raw material during the pretreatment process, and that the cellulose was purified. Furthermore, after 5 cycles of reuse of the TBAOH and TMAOH aqueous solutions, the pretreated corn cob could still achieve a sugar yield higher than 70%.CONCLUSIONThe pretreatment with TBAOH and TMAOH aqueous solutions significantly enhanced the enzymatic hydrolysis, which provided a green, simple, and economical new approach for the pretreatment of agricultural waste biomass. © 2021 Society of Chemical Industry

Aerobic degradation of high tetramethylammonium hydroxide (TMAH) and its impacts on nitrification and microbial community

Tetramethylammonium hydroxide (TMAH) was often used as developer in the high-tech industries. Information regarding biological treatment of high TMAH-containing wastewater is limited. This study investigated aerobic degradation of high TMAH, its impacts on nitrification, and microbial community in a sequencing batch reactor (SBR). The initial TMAH concentrations of SBR gradually increased from 200 to 4666 mg L−1 (equivalent to 31 to 718 mg-N L−1) to enrich microbial community for aerobic TMAH degradation and nitrification. The results indicated that the aerobic specific TMAH degradation rates followed the Monod-type kinetics with a maximum specific TMAH degradation rate of 2.184 mg N hour−1 g volatile suspended solid (VSS)−1 and the half-saturation coefficient of 175.1 mg N L−1. After TMAH degradation and ammonia release, the lag time for the onset of nitrification highly correlated with initial TMAH fed for the SBR. According to the microbial community analysis using next generation sequencing (NGS), potential aerobic TMAH-degraders including Mycobacterium sp. and Hypomicrobium sp. were enriched in the aerobic SBR. The results of real-time quantitative polymerase chain reaction (qPCR) and reverse transcript (RT)-qPCR indicated that Hyphomicrobium sp. may be able to utilize both TMAH and its degradation intermediates such as trimethylamine (TMA), while Thiobacillus sp. can only utilize TMAH. The qPCR and RT-qPCR results suggested that TMAH may inhibit nitrification by inactive expression of amoA gene and the intermediates of TMAH degradation may compete ammonia monooxygenase (AMO) enzyme with ammonia for nitrification inhibition.

Controlled synthesis of monodisperse core–shell γ‐Fe 2 O 3 @SiO 2 nanoparticles with well‐dispersed γ‐Fe 2 O 3 seeds

Fe2O3@SiO2 nanoparticles with well-dispersed γ-Fe2O3 seeds were prepared in aqueous solution using a simple one-step method. Transmission electron microscopy, X-ray diffraction analysis, and Raman spectrum were used to characterise the morphology and structure of γ-Fe2O3 and γ-Fe2O3@SiO2 nanoparticles. The concentration of tetramethylammonium hydroxide (TMAOH) was found to be very influential in the control of the morphology of γ-Fe2O3@SiO2 nanoparticles. Water-soluble monodisperse γ-Fe2O3@SiO2 nanoparticles with well-dispersed γ-Fe2O3 seeds were successfully synthesised when the concentration of TMAOH is 0.015 M.

Optimized Sample Preparation for Sulfur Determination in Animal Feed by Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES) with Correlation to the Total Protein Content

This work describes the optimization and development of a straightforward method for the determination of sulfur in animal food by inductively coupled plasma – optical emission spectrometry (ICP-OES) after sample preparation with tetramethylammonium hydroxide (TMAH). The domain of the factors, including the concentration of TMAH, time, and temperature, was optimized using a central composite design. The optimized condition was obtained at 80 °C, 13.5% (w/w) TMAH and 130 min for a sample mass of 200 mg. The analytical calibration using matrix matching standards was necessary. The limit of detection of the method was 0.02 mg g−1, and the accuracy was accessed by comparing the results of the analysis of a certified reference material and four pet food samples using the proposed method and microwave-assisted digestion in addition to recovery tests. The results demonstrated that both methods are in agreement using a paired sample t-test at the 95% confidence level. The recovery values ranged from 99 to 117%. Sixteen animal food samples were analyzed, and the concentration of sulfur ranged from 0.40 to 4.88 mg g−1 while the total protein content ranged from 174.1 to 324.8 mg g−1.

Dissolution kinetics of poly(4-hydroxystyrene) with different molecular weight distributions in alkaline aqueous solution

A poly(4-hydroxystyrene) (PHS) backbone polymer and a tetramethylammoniumhydroxide (TMAH) aqueous developer are typically combined to form a positive chemically amplified resist. We investigated the dissolution kinetics of PHS with different molecular weights and molecular weight dispersions and different concentrations of TMAH by quartz crystal microbalance (QCM) measurement. QCM graphs showed different dissolution rates and forms for different concentrations. We attempted to explain the dissolution kinetics by introducing a dissolution index calculated from swelling and dissolving factors. These factors were calculated using a penetrating factor (water or TMAH molecules) and a disentanglement factor. It is considered that the dissolution index depends on the molecular weight distribution because polymers with different molecular weight distributions have different voids in their bulk and different tendencies of disentanglement. Our results suggest that dissolution can be controlled by adjusting the molecular weight distribution, which will lead to reduced defect generation during the fabrication of fine structures.

Aerobic Treatment of Waste Process Solutions from the Semiconductor Industry: From Lab to Pilot Scale

Tetramethylammonium hydroxide (TMAH) is widely used as a solvent in the semiconductor industry. After the photo-impression process, it is necessary to remove the photoresist (PR) layer from the surface of the circuits; for this purpose, a TMAH solution is usually used. This chemical compound is highly toxic and corrosive and cannot be discharged into the environment. This study was carried out in collaboration with LFoundry (SMIC group), in order to prove the feasibility of biodegradation under aerobic conditions, using microorganisms coming from the LFoundry’s wastewater treatment plant (WWTP) at different operating conditions. The feed composition was modified in order to add a small but increasing amount of TMAH and PR. The aim was to verify if the increase of TMAH concentration was harmful to bacteria. The feed stream, containing TMAH and PR, was the only carbon source for the metabolism of the aerobic microorganisms. The results of this study demonstrated an effective biological degradation of TMAH and showed a total removal efficiency of more than 99.3%, with a final concentration of 7 mg/L. Moreover, the kinetic parameters of the Monod model were also calculated. The results obtained from the experimental campaign were used to design a pilot plant that will treat around 25 L/h of waste TMAH/PR solution.

Biological treatment of electronic industry wastewater containing TMAH, MEA and sulfate in an UASB reactor

This study investigated the feasibility of the methanogenic treatment of electronic industry wastewater containing tetramethylammonium hydroxide (TMAH), monoethanolamine (MEA) and sulfate in a lab-scale mesophilic up-flow anaerobic sludge blanket reactor. Feeding a mixture of electronic industry wastewater and co-substrate organics to the reactor for smooth acclimatization of sludge gave complete degradation of each organics within five days. When the reactor was fed only electronic industry wastewater, total COD removal, TMAH removal and MEA removal were achieved over 80, 99 and 99%, respectively, at an organic loading rate of 11.5 kg-COD m−3 day−1. 173 mg-S L−1 of influent sulfate was almost reduced simultaneously with the COD removal. In order to evaluate performance stability, the TMAH shock load event was performed under the conditions of 11,000 mg-COD L−1 for 24 h. Inflow of high TMAH concentration inhibited TMAH degradation and sulfate reduction for more than one month, however, not MEA. The batch feeding experiment and specific activity measurement revealed degradation pathways of each organics. TMAH was degraded via methanogenic pathway without sulfate reduction, MEA was degraded via methanogenic pathway with sulfate reduction. The results indicated that methanogenic treatment was applicable to electronic industry wastewater by appropriate reactor handling.

Ultrasound-assisted extraction of Pb, Cd, Cr, Mn, Fe, Cu, Zn from edible oils with tetramethylammonium hydroxide and EDTA followed by determination using graphite furnace atomic absorption spectrometer

A new method for extraction and determination of trace and ultratrace impurities from edible oils via an ultrasound-assisted extraction using tetramethylammonium hydroxide (TMAH) and ethylenediaminetetraacetic acid (EDTA) has been described. Method is simple and sensitive. Extraction variables like pH, concentrations of TMAH and EDTA, ultrasonication and centrifugation times were all optimised for analytes using engine-oil. Under optimised conditions, extraction of spiked analytes from all the edible oils into aqueous-medium were investigated and found to be quantitative (89–101%). Using this method, concentrations of impurities in edible-oils were determined by graphite furnace atomic absorption spectrometer (GFAAS) using standard-addition calibration method and validated with microwave-digestion method. The method was successfully applied to edible oils extracted from various seeds such as mustard oil, sun flower oil, sesame oil, ground nut oil, coconut oil, rice bran oil and corn oil containing ultratrace impurities. Accuracy of developed method for edible-oils was checked with corresponding results obtained by microwave digestion method.

Experimental investigation and techno-economic analysis of tetramethylammonium hydroxide removal from wastewater in nano-electronics manufacturing via membrane distillation

In nano-electronics manufacturing, tetramethylammonium hydroxide (TMAH) is extensively used in the photo-lithography and etching processes, leading to a waste disposal issue. The present study focuses on TMAH wastewater treatment in nano-electronics industries by using membrane distillation technology. Actual TMAH wastewater samples were collected at imec, Belgium. An air gap membrane distillation bench unit was employed to perform the experiments for different operating conditions i.e., feed temperatures and flow rates. High quality water is recovered after reducing the TMAH concentration to 1 ppm and lowering the TOC to 0.8 ppm from 8 ppm. For the industrial scale TMAH wastewater treatment, industrial waste heat driven and district heating driven membrane distillation systems are designed and analyzed. It is determined that 14 GWh thermal energy is required annually to treat 20,000 m3 of TMAH wastewater/year while considering 65 °C as the membrane distillation feed temperature. Expected unit water treatment cost is found as low as 16 $/m3 of TMAH wastewater, roughly 80% lower than current disposal costs.

Surface Texturing of Silicon {100} in an Extremely Low Concentration TMAH for Minimized Reflectivity

Micro-texturing of silicon front surface which consists of geometrical array of structures is needed to reduce the overall reflectance and to increase light trapping by multiple internal reflections of incident light for solar cell application. A wet anisotropic etching technique based on the alkaline solution is widely used to form micro-sized pyramidal structures on the silicon surface. In this work, an extremely low concentration tetramethylammonium hydroxide (TMAH) is employed for texturing the surface of {100} oriented monocrystalline silicon without adding any additive and agitation during etching to investigate the surface roughness and thereby reflectance. TMAH concentration is varied from 1.0-0.1 wt% in a step of 0.1 wt%. For each concentration, time of etching is also varied from 20–100 min with an interval of 20 min at a fixed temperature of 70°C. Surface morphology and surface roughness for as-textured silicon surfaces are analyzed by scanning electron microscope (SEM) and 3D laser scanning microscope, respectively. SEM images of etched silicon surface with 0.5 wt% TMAH confirm uniform and dense pyramidal structures. As measured by UV-Vis spectrometer using integrating sphere mode, we were able to achieve the lowest reflectance of 8.3% at 570 nm and solar weighted reflectance (RSW) of 9.7% in visible range after 80 min of etching in 0.5 wt% TMAH solution at 70°C.

Cost-effective synthesis of CHA zeolites with controllable morphology and size

Cost-effectively develop zeolites with controllable morphology and size is significant in design and optimization of the physical properties for CO2/CH4 adsorption separation. Herein, we report the synthesis of CHA zeolites with tunable morphology and size by a facile one-step dual template-directed strategy. A mixture of organic structure-directing agents (OSDA) composed of N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) and tetramethylammonium hydroxide (TMAOH) was employed and found to function cooperatively in directing the crystallization of CHA zeolites. Additionally, the dual template strategy reduced the consumption of expensive TMAdaOH to a great extent. The crystal morphology and size were remarkably dependent on TMAOH concentration in the dual template-directed synthesis system, regardless of TMAdaOH concentration. We demonstrate that the gradual decrease of TMAOH concentration in the batch composition enables a fine-tuning of the zeolite morphology from cubic to rough sphere crystals, accompanied by the size ranging from ca. 3 μm to 400 nm. We speculate that the two organic species work synergistically in the formation of CHA crystals, where TMAdaOH is the microporous structure director, and TMAOH plays a role in bridging neighboring particles via electrostatic interactions. The variation of crystal size is confirmed to have considerable influence on CO2/CH4 separation performances. Moreover, the ability to tailor the physical properties of CHA zeolite by dual template method makes it possible to optimize the performances in other commercial applications.

Effect of the Hydrodynamic Cavitation for the Treatment of Industrial Wastewater

In the present work, the degradation of tetramethyl ammonium hydroxide (TMAH) from synthetic liquid waste of electronic industry was investigated by using hydrodynamic cavitation process. The core of the experimenal apparatus was a Venturi tube having a diameter of 12 mm and a convergent of 2 mm. The experiments were performed using synthetic solutions with an initial TMAH concentration of 2 g/L. A factorial plant with 2 factors and 2 levels was planned to prove that the hydrodinamic cavitation was an effective method to degrade TMAH. The investigated factors were: solution pH (3 – 20) and time (5 -20 min). The experiments have been carried out at a fixed temperature of 20°C and a pressure of 4 bar. The inlet pressure of 4 bar was chosen as a result of preliminary experiments that showed as at this value the degradation yields were higher than those obtained at other pressure values. The experiments showed that pH solution was significant with a negative effect. The optimal performance (around 44%) of process for degradation of tetramethyl ammonium hydroxide was achieved at pH=3 after 20 minutes.

Purification of Diatomaceous Earth Using Leaching and Liquid-Liquid Extraction Processes to Produce High Purity Silica for Solar-Grade Silicon

Recently, the demand for solar-grade silicon (SOG-Si) with 6-7N (99.9999~9%) level of purity is dramatically increasing due to its popularity of photovoltaic power generation. The conventional process, Siemens method, is majorly used for SOG-Si production, which, however, consumes huge amount of energy and time. So, there is a need to develop an alternate production process for SOG-Si. As the cost-effective process, we are now focusing on a wet chemical process for purification of silica, followed by electrochemical reduction of silica to SOG-Si [1]. This purification process consists of two main steps: (i) acid leaching including dissolution & precipitation treatment of diatomaceous earth as an abundant Si source and (ii) liquid-liquid extraction for precise elimination of lighter element impurities that are possible to influence the semiconductor property of Si. Aim of the present work is to increase the extraction efficiency of each process to be optimized and combining them to complete the whole process. First, we optimized the acid leaching process. This process performs pH adjustments of strong alkaline solution with diatomaceous earth dissolved to separate impurity-rich phase and silica. It has been shown that more than 90% of the heavy element (Fe, Al, etc.) impurities precipitate by decreasing pH [2]. However, since NaOH was used in the preparation of initial alkaline solution, much amount of Na impurities turned out to be included in the final silica product. For this, we employed the mixture of NaOH and Tetramethylammonium hydroxide (TMAH) to lower the concentration of Na in the alkaline solution preparation. Experimental results suggested that some amount of Na ion was necessary to be included in the solution in order to provide sufficient dissolution rate of silica. This led us to the optimal concentration of NaOH and TMAH in the mixture: 0.05 M NaOH and 1.40 M TMAH. Further purification, experiment results concluded that this mixture effectively prevented the inclusion of Na impurity, resulting in 5N level of purity when the process was repeated 3 times. In spite of the achievement shown above, the lighter element, in particular, B is hard to be eliminated from the leaching process, because the pH dependence of solubility of B is similar to that of Si. To further eliminate this impurity, the liquid-liquid extraction process is employed. Since our previous results indicated that the effective mixing of aqueous and organic phase leads to the best efficiency of B elimination, we first designed flow type reactor with 3D printing technology. The reactor was designed to have 2 characteristic structures: a throat like structure that shows gradually diverging part after converging (converging/diverging structure) near Y shaped inlets and obstacles structure on downstream [3]. The high-speed camera demonstrated the reactor offered a fully dispersed flow regime, which leaded to the efficient solution mixing. Based upon these results, we carried out a model experiment, using silica powder of 99.9 % purity with trace amount of B was dissolved in NaOH solution (aqueous phase) and injected into one of the inlet of the liquid-liquid extraction reactor. The extractant, 2,2,4-trimethyl-1,3-pentanediol (TMPD) solution (organic phase) was injected into the other inlet. The extraction was repeated 5 times at 380 ml/min and the efficiency was found to be 99.7% leaving less than 0.1 ppm of B in silica (7N purity). From the above results, it is concluded that we have achieved efficient process to prepare 7N level silicon, by combining optimized leaching and liquid-liquid extraction with designed reactor. This could be a promising method to produce SOG-Si with lower cost than the present process at industries.

Silicon Anisotropic Etching in Ternary Solution Composed of TΜΑΗ+Triton+NH2ΟΗ

Present work reports the anisotropic etching characteristics of silicon in various concentrations of tetramethylammonium hydroxide (TMAH) without and with addition of 10% hydroxylamine (NH2OH) and Triton X-100 ranging from ppb to ppm. The etch rate, undercutting at convex corners, and etched surface morphology are investigated in pure TMAH, TMAH+NH2OH, and different compositions of TMAH+NH2OH+Triton (i.e. ternary solution). High etch rate and undercutting are achieved in NH2OH-added 15 wt% TMAH, while 25 wt% TMAH + 10% NH2OH + 1 ppm Triton provided significantly less corner undercutting with reasonably good etch rate of Si{100}. This work is very useful for engineering applications for the fabrication of microstructures using silicon wet bulk micromachining for MEMS-based devices.