Highly selective etching of SiNxover SiO2using ClF3/Cl2remote plasma.

Highly selective etching of silicon nitride over silicon oxide is one of the most important processes especially for the fabrication of vertical semiconductor devices including 3D NAND (Not And) devices. In this study, isotropic dry etching characteristics of SiNxand SiO2using ClF3/Cl2remote plasmas have been investigated. The increase of Cl2percent in ClF3/Cl2gas mixture increased etch selectivity of SiNxover SiO2while decreasing SiNxetch rate. By addition of 15% Cl to ClF3/Cl2, the etch selectivity higher than 500 could be obtained with the SiNxetch rate of ∼8 nm min-1, and the increase of Cl percent to 20% further increased the etch selectivity to higher than 1000. It was found that SiNxcan be etched through the reaction from Si-N to Si-F and Si-Cl (also from Si-Cl to Si-F) while SiO2can be etched only through the reaction from Si-O to Si-F, and which is also in extremely low reaction at room temperature. When SiNx/SiO2layer stack was etched using ClF3/Cl2(15%), extremely selective removal of SiNxlayer in the SiNx/SiO2layer stack could be obtained without noticeable etching of SiO2layer in the stack and without etch loading effect.

Microfluidic Airborne Metal Particle Sensor Using Oil Microcirculation for Real-Time and Continuous Monitoring of Metal Particle Emission.

Airborne metal particles (MPs; particle size > 10 µm) in workplaces result in a loss in production yield if not detected in time. The demand for compact and cost-efficient MP sensors to monitor airborne MP generation is increasing. However, contemporary instruments and laboratory-grade sensors exhibit certain limitations in real-time and on-site monitoring of airborne MPs. This paper presents a microfluidic MP detection chip to address these limitations. By combining the proposed system with microcirculation-based particle-to-liquid collection and a capacitive sensing method, the continuous detection of airborne MPs can be achieved. A few microfabrication processes were realized, resulting in a compact system, which can be easily replaced after contamination with a low-priced microfluidic chip. In our experiments, the frequency-dependent capacitive changes were characterized using MP (aluminum) samples (sizes ranging from 10 µm to 40 µm). Performance evaluation of the proposed system under test-bed conditions indicated that it is capable of real-time and continuous monitoring of airborne MPs (minimum size 10 µm) under an optimal frequency, with superior sensitivity and responsivity. Therefore, the proposed system can be used as an on-site MP sensor for unexpected airborne MP generation in precise manufacturing facilities where metal sources are used.

Microfluidic condensation nanoparticle counter using water as the condensing liquid for assessing individual exposure to airborne nanoparticles.

We present a compact and inexpensive detection system that can accurately measure the number concentration of nanoparticles (NPs; particles smaller than 100 nm) in real-time for assessing individual exposure to airborne NPs in various environments. Our system is based on the condensation nucleation light scattering technique and uses water as the condensing liquid, which solves the self-contamination issues that affect most portable NP detection systems. Our system comprises two units: a microfluidic condensation chip for growing NPs into water droplets and a miniature optical detector for singly counting grown droplets. To effectively minimize the size and cost of our system, droplets are grown on a single chip according to the semiconductor manufacturing process. To use water as the condensing liquid, a super-hydrophilic wick (i.e., Cu micropillar array coated with CuO nanowires) is monolithically integrated into the chip. Simulations were performed to verify the method of generating supersaturated water vapor. Quantitative experiments using NaCl and Ag NPs revealed that our system grew NPs larger than 9.3 nm into 2.25 µm diameter water droplets and could count individual droplets over an extremely wide concentration range (0.021-105 N cm-3) with high accuracy. This outstanding performance allowed our system to resolve the daily pattern of the NP concentration along a metropolitan commuting street with strong agreement compared to the reference instrument. Because our system uses water, it can accurately monitor individual exposure to NPs in various kinds of environments, including multiuse facilities such as elementary schools and hospitals.

MEMS-based condensation particle growth chip for optically measuring the airborne nanoparticle concentration.

To monitor airborne nanoparticles at a particular point of interest sensitively and accurately, we developed a compact and inexpensive but highly-precise nanoparticle detection system. The proposed system, based on nucleation light-scattering, consists of two components: a microelectromechanical system (MEMS)-based particle growth chip that grows nanoparticles to micro-sized droplets through condensation and a miniaturized optical particle counter (mini-OPC) that detects individual grown droplets using a light-scattering method. To minimize the dimensions and cost of this system, all elements of the particle growth chip were integrated onto a glass slide through simple photolithography and 3D printing. Moreover, a passive cooling technique was adopted, which eliminated the need for an active cooling system. Thus, our system was much more compact, inexpensive, and power-efficient than conventional nanoparticle detection instruments. Through quantitative experiments using Ag nanoparticles in the size range of 5 to 70 nm, it was found that our system could count extremely small nanoparticles (12.4 nm) by growing them to micrometer-sized droplets. Furthermore, our system could provide an accurate number concentration of nanoparticles (the maximum difference was within 15% compared to the reference instrument), regardless of high (3500 N cm-3) and low (0.05 N cm-3) concentration environments. These results indicate that our system can be applied successfully to the monitoring of nanoparticles in various kinds of fields including not only indoor and outdoor environments but also high-tech industries utilizing cleanrooms, air filtration systems, etc.

Particle size spectrometer using inertial classification and electrical measurement techniques for real-time monitoring of particle size distribution.

To achieve real-time monitoring of aerodynamic submicron particle size distributions at a point-of-interest, we developed a high-performance particle size spectrometer that is compact, low-cost, and portable. The present system consists of four key components: a unipolar mini-discharger for electrically charging particles, an inertial size-separator for classifying charged particles into five size fractions in terms of their aerodynamic sizes, a portable multi-channel electrometer for detecting femto-ampere currents carried by charged particles at each stage, and a retrieval algorithm for converting the current data into a smooth particle size distribution. The unipolar mini-discharger and inertial size separator were quantitatively characterised by using standard polystyrene latex (PSL) particles. The experimentally determined cut-off diameters at each stage in the inertial size separator were 1.17, 0.94, 0.71, 0.54, and 0.23 µm, respectively. Then, the system was compared with a commercial reference aerodynamic particle sizer (APS) in the environment where the number concentration and the average size of TiO2 particles were changing. The present system resolved peak size and geometric standard deviation of particles to within 11.2%, and 6.3%, respectively, indicating that the system can be used to accurately monitor submicron particle size distributions in real time.

Determination of furan levels in coffee using automated solid-phase microextraction and gas chromatography/mass spectrometry.

Furan is a 5-member ring chemical with high volatility. Because it is highly volatile, furan levels in foods are not easily determined with accuracy. In this study, an analytical method for furan analysis using an automated solid-phase microextraction system in combination with gas chromatography/mass spectroscopy is described. The performance of the method was demonstrated by the results obtained from a variety of coffees. Furan was detected at part-per-billion levels in coffee. The limit of detection was 0.3 ng/g and limit of quantitation, 0.8 ng/g. The percent recoveries were between 92 and 102.