Tetramethylammonium Hydroxide Solution Research Articles

Effect of Dissolved Oxygen on the Removal of BTA from Cu By Tetra Methyl Ammonium Hydroxide

In the fabrication of copper interconnects, chemical mechanical polishing (CMP) is used to remove excess copper and barrier layers. Because of its ability to form a protective layer, Benzotriazole (BTA) is used as Cu corrosion inhibitor during CMP as well as post-CMP cleaning [1, 2]. It is desirable to remove this protective layer between multiple copper deposition and CMP steps. Investigations on the removal of chemisorbed BTA by tetra methyl ammonium hydroxide (TMAH), hydroxylamine and organic acid have been reported [2-4]. These studies have used 0.1 wt % and lower concentration of BTA at natural pH ( < 7) or alkaline pH (11) to form adsorbed layers [3-5]. The effect of dissolved oxygen content on the adsorption of BTA and subsequent removal by TMAH is not yet reported. In this work, removal of BTA adsorbed on Cu at a pH value of ~10, which is close to the conditions that exist during barrier CMP, using a quartz crystal microbalance (QCM) technique. Since the study focussed only on the BTA removal, particles were not included in the test solution. A thin layer of Cu was first electrodeposited on Au electrodes of a quartz crystal in an electrolyte containing 10 mM CuSO4 and 100 mM H2SO4. The electrodeposition was carried out at – 150 mV vs. Ag/AgCl for 300 s. An SRS QCM-200 model quartz crystal microbalance (QCM) was used to monitor the changes in mass of the Cu coated crystal, during BTA adsorption and removal. A freshly prepared surface was used for each run. The dissolved oxygen level was controlled by bubbling either nitrogen or air before and during the experiments. During the adsorption and removal experiments, the temperature was maintained at 30 ± 0.1 °C using a circulating bath. After the completion of each experimental run, the Cu layer was stripped by maintaining the electrode at +600 mV vs.Ag/AgCl in the same solution. In the first part of investigation, a Cu sample was immersed in KOH solution of pH 10 without BTA for 200 s. After this conditioning time, the solution was switched to 1 wt% TMAH. The changes in the crystal resonance frequency were converted to changes in mass per unit area, using Sauerbrey equation as Δm = -17.67(ng/cm2/Hz) Δf and reported in Figure 1. Figure 1(a) shows that when air is bubbled in the KOH solution, the mass increases over time and this is probably due to the formation of oxides and hydroxides of Cu. Upon switching the solution to TMAH, the mass decreases and goes below the original value. This indicates that TMAH removes Cu oxides, hydroxides and Cu. When the sample is immersed in KOH solution with nitrogen bubbling, the mass remains relatively constant, but switching the solution to TMAH causes a reduction in mass. This confirms that TMAH etches bare Cu. In the second part of the investigation, a Cu sample was immersed in KOH solution of same pH but containing 0.1 wt% BTA for 200 sec. The results are presented in Figure 1 (b). The mass increases to roughly the same extent regardless of whether air or nitrogen is bubbled in the solution. When the solution was switched to aerated TMAH solution, the mass decreases rapidly indicating that BTA and possibly the oxides of Cu are removed. On the other hand, when nitrogen deaerated (nitrogen saturated) TMAH was used, the mass continues to increase suggesting that BTA is not removed. These results indicate that BTA adsorbed on oxide free Cu surface is not attacked by TMAH to the same extent as that adsorbed on oxide free surface.

Study of Cu Bimetallic Corrosion and Its Inhibition Strategy for Cu Interconnect Application Using Micro-Pattern Corrosion Screening

Ru and other noble metals have been actively investigated for use as seedless liner/barrier materials for advanced Cu interconnect applications. Due to the lack of volatile byproducts in the reactive ion etching of Cu, the Cu interconnects are fabricated by dual damascene patterning process that involves etching a trench/via pattern into a dielectric, the blanket deposition of a diffusion barrier followed by Cu electroplating, and finally removal of Cu overburden by chemical-mechanical planarization (CMP). Since the CMP process exposes the Cu interconnect and metal barrier to the continual presence of corrosive chemicals, the resulting bimetallic corrosion between Cu and diffusion barrier metal can be detrimental to the overall production yields of integrated circuit devices. In this paper, we will present findings from a new corrosion screening metrology utilizing micro-corrosion test patterns (Cu dots, D≈130µm) to provide rapid in-situ corrosion evaluations in manufacture relevant chemical environments used to produce Cu interconnect structure. The results from Cu micro-pattern corrosion screening corroborate well with XPS and electrochemical techniques to reveal the detailed bimetallic corrosion mechanisms in specific chemical environments. For most of the CMP solutions studied to date, the Cu corrosion was found to be accelerated through an oxygen reduction reaction catalyzed by Ru. The new insights obtained from mechanistic investigation on Cu/Ru bimetallic corrosion not only help to unveil the real functions of each chemical previously masked by the complex matrix of CMP formulation, it also significantly expands the chemistry tool set that enables better corrosion inhibition strategy to protect detrimental corrosion defects of Cu interconnect with minute nanometer dimension used in advanced IC device. For example, micro-pattern corrosion screening results and electrochemical analyses revealed that 1mM pyrazole in 8 wt.% tetramethyl ammonium hydroxide (TMAH) solution could inhibit Cu corrosion more effectively than 10mM benzotriazole (BTA) in the same solution. Overall Cu corrosion rate in TMAH based highly alkaline post CMP cleaning solution is shown to be considerably reduced to <1Å/min by addition of pyrazole as corrosion inhibitor.

Effects of sidewall MOS channel on performance of AlGaN/GaN FinFET

AlGaN/GaN FinFETs with various fin widths (Wfin), which have both a 2DEG channel and two sidewall MOS channels, have been fabricated by using electron-beam lithography and subsequent sidewall wet etch in tetramethyl ammonium hydroxide (TMAH) solution. The devices with wide Wfin of 150nm showed normally-on operation with threshold voltage (Vth) of −2.5 and −5.0V, respectively. The devices also exhibited broad transconductance (gm), and excellent off-state performance with very low subthreshold swing (SS). On the other hand, narrow device with Wfin of 50nm exhibited normally-off operation with Vth of 3.0V, but degraded SS due to trapping effect at the sidewall of fin.

Micro and nanofabrication of SiGe/Ge bridges and membranes by wet-anisotropic etching

Germanium bridges and membranes have been fabricated by lithography and wet-anisotropic chemical etching from SiGe/Ge heterostructures epitaxially deposited on Si substrates. The goal of this work is to remove completely the Si under the structures without damaging the Si material present in the SiGe alloys by using a suitable etchant. Etching by potassium hydroxide and by tetramethylammonium hydroxide solutions have been optimized in order to etch only the pure silicon underneath the structures. All the fabrication processes, to achieve free-standing structures with different shape and size, have been systematically characterized by scanning electron microscopy and μRaman spectroscopy.

Analysis of iodine and its species in animal tissues

A method allowing the determination of the total iodine content and iodine species in samples of animal tissues using inductively coupled plasma mass spectrometry (ICP-MS) as an element-specific detector was developed. The total iodine content was determined after microwave digestion with 25% (w/w) water solution of tetramethylammonium hydroxide. The detection limit was 26.9 μg kg−1 I, and the accuracy of the determination was proven through the analysis of SRM “Non-Fat Milk Powder,” porcine liver, and Atlantic Cod muscle samples using standard addition methods. The extracts for the speciation analysis were prepared through sample dispersion in water using an Ultra-Turrax® T10. The extraction yields ranged from 46 to 84% for different types of tissues. The determination of the inorganic iodine species was performed using ion-exchange chromatography (PRP X100, mobile phase 100 mmol L−1 ammonium nitrate, pH 7.4) coupled to ICP-MS. A detection limit of 1.1 μg kg−1 I was obtained for both species. The organic iodine species were separated using size-exclusion chromatography (Superdex 75 column, mobile phase 20 mmol L−1 Tris–HCl, pH 7.5) and also detected using ICP-MS. Samples of porcine muscle, liver, kidney and thyroid gland, chicken muscle and liver and Atlantic Cod muscle were analyzed. The porcine thyroid gland and Atlantic Cod muscle samples were the richest in iodine (a more than 10× greater content of iodine than the other samples). With respect to the inorganic species, only iodide was found in the sample extracts. Conversely, many organic iodine species were found in the extracts.

Time-varying wetting behavior on copper wafer treated by wet-etching

The wet cleaning process in semiconductor fabrication often involves the immersion of the copper wafer into etching solutions and thereby its surface properties are significantly altered. The wetting behavior of a copper film deposited on silicon wafer is investigated after a short dip in various etching solutions. The etchants include glacial acetic acid and dilute solutions of nitric acid, hydrofluoric acid, and tetramethylammonium hydroxide. It was found that in most cases a thin oxide layer still remains on the surface of as-received Cu wafers when they are subject to etching treatments. However, a pure Cu wafer can be obtained by the glacial acetic acid treatment and its water contact angle (CA) is about 45°. As the pure Cu wafer is placed in the ambient condition, the oxide thickness grows rapidly to the range of 10–20Å within 3h and the CA on the hydrophilic surface also rises. In the vacuum, it is surprising to find that the CA and surface roughness of the pure Cu wafer can grow significantly. These interesting results may be attributed to the rearrangement of surface Cu atoms to reduce the surface free energy.

Simultaneous determination of bromine and iodine in milk powder for adult and infant nutrition by plasma based techniques after digestion using microwave-induced combustion

In this work, bromine and iodine determination in milk powder for adult and infant nutrition was performed by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES) after digestion by microwave-induced combustion (MIC). Contrarily to previous works using MIC, a higher sample mass was digested (700 mg). Water and ammonium hydroxide (10 to 100mmolL−1) were investigated as absorbing solutions and accurate results were achieved using a 25mmolL−1 NH4OH solution. Moreover, the high stability of analytes after digestion (up to 30 days) using this solution was observed. The accuracy of the proposed MIC method was evaluated using certified and reference materials of milk powder (NIST 1549 and NIST 8435). No statistical difference was observed between results obtained by MIC-ICP-MS and reference values. Results for samples were also compared with those obtained by ICP-OES and no statistical difference was observed. Microwave-assisted alkaline extraction (MW-AE) was also evaluated for milk powder using NH4OH and tetramethylammonium hydroxide solutions. Solutions obtained after digestion by MIC (whole milk powder) presented low carbon content in digests (<25mgL−1) while solutions obtained after alkaline extraction presented up to 10,000mgL−1 of C. MIC method was preferable in view of the possibility of obtaining solutions with low carbon content even using a relatively high sample mass (up to 700mg) avoiding additional dilution prior to ICP-MS analysis, thus allowing better detection limits. Limits of detection obtained by MIC-ICP-MS were 0.007 and 0.003μgg−1 for Br and I, respectively, while for MW-AE were 0.1 and 0.05μgg−1 respectively for Br and I. Among the main advantages of the proposed method are the use of diluted alkaline solutions that is in agreement with green analytical chemistry recommendations, the high stability of analytes in solution and the suitability of digests for analysis by ICP-MS and also ICP-OES, minimizing memory effects and being advantageous for routine analysis.

Robust ultrasound assisted extraction approach using dilute TMAH solutions for the speciation of mercury in fish and plant materials by cold vapour atomic absorption spectrometry (CVAAS)

A simple and robust ultrasound assisted extraction (UAE) protocol with dilute solutions of tetramethyl ammonium hydroxide (TMAH) for the speciation of mercury in fish and plant tissues was developed by CVAAS as an alternative to conventional methods.

The formation and microstructural properties of uniform α-GaOOH particles and their calcination products

Uniform α-GaOOH submicron particles of different shapes (spindles, rhombic rods, rhombic prisms, hierarchical particles) were synthesized by simple low-temperature (at 60°C) or hydrothermal (at 160°C) precipitation from the mixture of aqueous solutions of gallium(III) chloride and organic alkali tetramethylammonium hydroxide (TMAH) at various pH values (5, 7 or 9). The growth mechanism of these particles was discussed. Crystallographic directions and crystal planes in α-GaOOH particles were identified. Differences in crystallite size, thermal and infrared properties of α-GaOOH particles were observed and discussed. Uniform α-Ga2O3 and β-Ga2O3 particles of the same or similar shapes, containing holes due to dehydroxylation, were obtained by calcination of the corresponding α-GaOOH particles at 500 or 900°C, respectively. Differences in crystallite size and infrared properties of obtained gallium oxide samples, as well as differences in photoluminescence properties of β-Ga2O3 samples were observed and discussed.

Fast Si (100) etching with a smooth surface near the boiling temperature in surfactant‐modified tetramethylammonium hydroxide solutions

The etching characteristics of the commonly utilised Si (100) facet at high temperatures near the boiling point in surfactant-modified tetramethylammonium hydroxide (TMAH) solutions are investigated. Solutions of 25 wt% TMAH are selected because of the etching stability and the rate of addition of the surfactant Triton-X-100 [C14H22O(C2H4O)n, n = 9–10] ranges from 0.01 to 1% v/v. The etching rates of Si (100) facets close to the boiling point are three to four times higher than those at 80°C in the surfactant-modified 25 wt% TMAH solutions. In particular, at 115°C, the very near temperature of the boiling point, the silicon sample possessing a high etching rate of 1.45 μm/min and the smooth etched Si (100) surface with an average roughness of about 1 nm is obtained. Moreover, the samples do not demonstrate much undercut difference at the etched convex corners near the boiling point. These results are useful for the fabrication of microelectromechanical systems and indeed provide an efficient etching method for industry products.

Advanced Monitoring of TMAH Solution

Tetramethyl ammonium hydroxide (TMAH) has wide applications in semiconductor industry, including photoresist development, silica etching (especially Sigma etching), and wafer cleaning, etc. One of the critical areas of the photolithography process is the development of unexposed (negative) or exposed (positive) photoresists without pattern distortion. As a metal free, basic aqueous solution, TMAH is the most common positive photoresist developer providing no metal contaminations. The bath composition, especially the concentration of TMAH, is strictly controlled within the process specifications (~2.2 to 2.4 % (w/w)), since it greatly affects the developing rate and contrast [1]. Traditional monitoring of TMAH concentration does not suffice for the modern needs of a sub-20 nm IC fabrication process. Additional critical parameters include dissolved carbonate and proprietary surfactants.

A fabrication process based on structural layer formation using Au–Au thermocompression bonding for RF MEMS capacitive switches and their performance

This paper presents a radio frequency micro-electro-mechanical-systems (RF MEMS) fabrication process based on a stacked structural layer and Au–Au thermocompression bonding, and reports on the performance of a sample RF MEMS switch design implemented with this process. The structural layer consists of 0.1 µm SiO2/0.2 µm SixNy/1 µm Cr–Au layers with a tensile stress less than 50 MPa deposited on a silicon handle wafer. The stacked layer is bonded to a base wafer where the transmission lines and the isolation dielectric of the capacitive switch are patterned. The process flow does not include a sacrificial layer; a recess etched in the base wafer provides the air gap instead. The switches are released by thinning and complete etching of the silicon handle wafer by deep reactive ion etching (DRIE) and tetramethylammonium hydroxide (TMAH) solution, respectively. Millimeter-wave measurements of the fabricated RF MEMS switches demonstrate satisfactory up-state performance with the worst-case return and insertion losses of 13.7 and 0.38 dB, respectively; but the limited isolation at the down-state indicates a systematic problem with these first-generation devices. Optical profile inspections and retrospective electromechanical analyses not only confirm those measurement results; but also identify the problem as the curling of the MEMS bridges along their width, which can be alleviated in the later fabrication runs through proper mechanical design.

Oxidative degradation of TMAH solution with UV persulfate activation

Abstract Tetramethylammonium hydroxide (TMAH) is an alkaline, neuronal toxic, and chemically stable compound; furthermore, it is widely used in the high-tech industry as a developing agent. Disposal of TMAH wastewater from an industrial plant is a difficult and costly problem. Ultraviolet light (UV) activated persulfate (S2O82−) is an advanced oxidation process proven to be effective in destroying a variety of organic pollutants. This bench-scale study investigated the feasibility of using the UV/S2O82− process to treat TMAH. The effects of various operational parameters, including pH conditions, dosages of persulfate, UV intensities, and system temperatures were evaluated. The results revealed that pH 2 exhibited higher decay rate of TMAH (kobs = 0.0331 ± 0.0031 min−1) than other pH conditions (pH 7 and 11) at 20 °C. In general, the TMAH decay increased with increasing persulfate dosage; however, the highest TMAH degradation rate was observed with a persulfate concentration of 50 mM. Also, higher reaction temperature and stronger UV irradiation can increase the degradation of TMAH. TMAH degradation byproducts were identified and finally transformed to nitrate and ammonium, which suggested that the demethylation mechanism was the main degradation pathway.

Determination of total iodine in serum and urine samples by ion chromatography with pulsed amperometric detection - studies on analyte loss, optimization of sample preparation procedures, and validation of analytical method.

A fast, accurate and precise ion chromatography method with pulsed amperometric detection was applied to evaluate a variety of parameters affecting the determination of total iodine in serum and urine of 81 subjects, including 56 obese and 25 healthy Polish children. The sample pretreatment methods were carried out in a closed system and with the assistance of microwaves. Both alkaline and acidic digestion procedures were developed and optimized to find the simplest combination of reagents and the appropriate parameters for digestion that would allow for the fastest, least time consuming and most cost-effective way of analysis. A good correlation between the certified and the measured concentrations was achieved. The best recoveries (96.8% for urine and 98.8% for serum samples) were achieved using 1ml of 25% tetramethylammonium hydroxide solution within 6min for 0.1ml of serum/urine samples. Using 0.5ml of 65% nitric acid solution the best recovery (95.3%) was obtained when 7min of effective digestion time was used. Freeze-thaw stability and long-term stability were checked. After 24 weeks 14.7% loss of iodine in urine, and 10.9% in serum samples occurred. For urine samples, better correlation (R(2)=0.9891) of various sample preparation procedures (alkaline digestion and application of OnGuard RP cartidges) was obtained. Significantly lower iodide content was found in samples taken from obese children. Serum iodine content in obese children was markedly variable in comparison with the healthy group, whereas the difference was less evident when urine samples were analyzed. The mean content in serum was 59.12±8.86μg/L, and in urine 98.26±25.93 for obese children when samples were prepared by the use of optimized alkaline digestion reinforced by microwaves. In healthy children the mean content in serum was 82.58±6.01μg/L, and in urine 145.76±31.44μg/L.

Corrosion of porous silicon in tetramethylammonium hydroxide solution

Corrosion of porous silicon in tetramethylammonium hydroxide (TMAH) solution was studied using weight loss measurements and scanning electron microscope. The effects of temperature, concentration of TMAH and volume ratio of ethanol in 1.0M TMAH on corrosion rate and corrosion time were elaborately investigated. The residue of corrosion products were characterized as a mixture of [(CH3)4N]2SiO3 and SiO2. A comparative test among TMAH, KOH and NaOH illustrated that the 1.0M TMAH could act as an applicable and novel corrosion solution to remove porous silicon layer for determining the porosity of porous silicon.

Determination of total iodine in samples with an organic matrix by solid-phase spectrophotometry

A solid-phase spectrophotometry method is proposed for determining total iodine in samples with an organic matrix. The method involves the sorption of I2 formed in oxidation of iodide with oxone (active ingredient potassium peroxomonosulfate) by polyurethane foams, followed by the registration of the adsorbent absorbance at 360 nm. Sample preparation includes treatment with an aqueous methanolic solution of tetramethylammonium hydroxide followed by thermostation at 90 ± 2°C for 3 h. The detection limit for iodine calculated using the 3s-test is 0.03 μg in a sample aliquot portion of ≤8 cm3. The relative standard deviation is 8–12% for iodine concentration in the range 0.3–5.0 μg/g.

Simple and Fast Sample Preparation Procedure Prior to Multi-element Analysis of Slim Teas by ICP OES

The knowledge about mineral content of slim teas is of great importance since the consumption of these beverages has rapidly increased for the past several years. An increasing popularity of these tea products is mainly attributed to their nutritional properties, flavor, taste and health effects. Therefore, the main goal of the present work was to develop a precise and accurate method of the multi-element analysis of slim teas by inductively coupled plasma optical emission spectrometry (ICP OES) without the need for a laborious and tedious sample treatment preceding spectrometric measurements. Five sample preparation procedures, i.e., the total decomposition in a mixture of HNO3 and H2O2 solutions using closed vessel microwave-assisted or open vessel hot-plate systems, the solubilisation in aqua regia or a tetramethyl ammonium hydroxide solution and the extraction in a diluted HNO3 solution, were compared. The performance of the compared procedures was determined in terms of the precision and the accuracy of results achieved and limits of detection of elements. It was found that the solubilisation in aqua regia gave the best results, i.e., limits of detection between 0.15 and 98.4 ng l−1, the precision within 0.6−3.0 % and the accuracy better than 5 %. The developed method of the analysis, being a useful alternative to time-consuming wet digestion procedures, was successfully applied to the analysis of five slim tea products.

Research on increasing silicon etch rate in deep wet etching with tetramethyl ammonium hydroxide etchant

The etching characteristics of Si (1 0 0) in silicon deep wet etching with tetramethyl ammonium hydroxide solution, containing silicic acid and ammonium persulfate, were studied in this article. The phenomena associated with the addition of ammonium persulfate at intervals in tetramethyl ammonium hydroxide solution were analyzed, and the mechanism of interplay between ammonium persulfate and silicic acid for increasing etch rate was proposed. The influence of these phenomena on the etch rate and roughness of Si (1 0 0) was discussed. The addition of ammonium persulfate at a periodic interval of time to a tetramethyl ammonium hydroxide solution, especially at the temperature of 80 °C, resulted in remarkable ascending of silicon etch rate. The etch rate of Si (1 0 0) in tetramethyl ammonium hydroxide solution with adding ammonium persulfate at intervals was superior to the etch rate in tetramethyl ammonium hydroxide solution without adding ammonium persulfate at intervals. The highest etch rate of Si (1 0 0) (0.83 µm/min), calculated with the help of profiler, was achieved after etching in tetramethyl ammonium hydroxide solution with adding ammonium persulfate at an interval of 120 min. This method appears to be a good candidate in applications where high and stable etch rate is required in long-time etching.

Selective dual-side functionalization of hollow SiO2 micropillar arrays for biotechnological applications

We report a method for the fabrication and selective functionalization of the internal and external surfaces of high-aspect-ratio hollow silicon dioxide (SiO2) micropillar arrays. The strategy enables independent surface reactions with no cross-contamination. The dual-functionalization is carried out during the fabrication of the micropillars in four steps. First, a sample of macroporous silicon is prepared by electrochemical etching and then it is thermally oxidized to create a thin layer of silicon dioxide on the internal surface of the macropores. Next, the internal surface is functionalized with mercaptopropyl trimethoxysilane (MPTMS). Subsequently, the micropillars are released by etching the back side of silicon wafers using a solution of tetramethylammonium hydroxide (TMAH). Finally, the external surface of the micropillars is chemically modified in a multi-step biofunctionalization with aminopropyl triethoxysilane (APTES), glutaraldehyde (GTA) and bovine serum albumin (BSA). The resulting structures were characterized by scanning electron microscopy and the surface reactions were confirmed by Fourier-transform infrared spectroscopy. The internal and external sides were photolabeled with tetramethyl rhodamine-5-maleimide and fluorescein isothiocyanate (FITC), respectively, and analyzed using fluorescence confocal microscopy. The peculiar three-dimensional (3D) geometry of the micropillars allows these double-active surfaces to be imaged at the same time. Results demonstrated the successful dual-side chemical modification and the feasibility of imaging both internal and external sides. Due to its remarkable architecture and chemical versatility, these micropillar arrays are a promising engineered platform for a range of applications such as biosensing, 3D cell culture and drug delivery.

Study on Corrosion Behaviour of n-Type Porous Silicon Layer in Tetramethylammonium Hydroxide Solution

Study on Corrosion Behaviour of n-Type Porous Silicon Layer in Tetramethylammonium Hydroxide Solution