ICP Process Research Articles

Fabrication of microcoil/microsprings for novel chemical and biological sensing

This paper reports the fabrication of a novel microsensor structure using inductively coupled plasma source (ICP) dry etching process. The novel sensor is based on a SiO 2/Si/SU-8 trilayered microcoil/microspring structure. The diameter of the microcoil was approximately 600 μm. The ICP process and SU-8 exposing time are discussed. The SiO 2 layer can be conveniently modified according to typical silica surface modification procedures. The microcoils could expand or contract upon interaction of specific species in the environment with receptors on the SiO 2 surface due to the surface stress or energy applied on the SiO 2 surface of the microcoil. This microcoil device may be widely used in biomedical and chemical sensing applications.

Single-Run Single-Mask Inductively-Coupled-Plasma Reactive-Ion-Etching Process for Fabricating Suspended High-Aspect-Ratio Microstructures

In this work, we present a single-run single-mask (SRM) process for fabricating suspended high-aspect-ratio structures on standard silicon wafers using an inductively coupled plasma-reactive ion etching (ICP-RIE) etcher. This process eliminates extra fabrication steps which are required for structure release after trench etching. Released microstructures with 120 µm thickness are obtained by this process. The corresponding maximum aspect ratio of the trench is 28. The SRM process is an extended version of the standard process proposed by BOSCH GmbH (BOSCH process). The first step of the SRM process is a standard BOSCH process for trench etching, then a polymer layer is deposited on trench sidewalls as a protective layer for the subsequent structure-releasing step. The structure is released by dry isotropic etching after the polymer layer on the trench floor is removed. All the steps can be integrated into a single-run ICP process. Also, only one mask is required. Therefore, the process complexity and fabrication cost can be effectively reduced. Discussions on each SRM step and considerations for avoiding undesired etching of the silicon structures during the release process are also presented.

SiC Materials and Technologies for Sensors Development

Silicon Carbide has proven its strong interest for power and high frequency devices but it also has superior characteristics for application in the sensors and MEMS fields. The characteristic requirements of the starting material are different from that of power devices since the level of defects is not so critical while the layer stress is important especially in 3C-SiC on Si. The keyprocess for MEMS fabrication is the etching, which is progressing thanks to ICP process improvements. A perfect control of the etching step could allow the obtention of nano-resonators in SiC with fairly superior characteristics to the Si ones. Other electrical sensors for high temperature application such as gas sensors or Hall sensors have been also successfully developed taking profit of the deep etching process improvement and high temperature contact developments.

A novel out-of-plane MEMS tunneling accelerometer

A novel out-of-plane MEMS tunneling accelerometer is designed, fabricated and characterized. ICP process, which can generate large proof mass, is used for the first time to fabricate an out-of-plane tunneling accelerometer. To reduce the high Hooke's constant in out-of-plane direction of the ICP etching structure, the beams and the proof mass are dry-etched by double mask ICP process, which reduce the Hooke's constant, thereby enhance the sensitivity of the device. The tunneling current of open loop is tested in the air by HP4145B semiconductor analyzer, which verifies the presence of tunneling current and shows the needed driving voltage. The close-loop test shows sensitivity of 811 mV/g for feedback voltage (the sensitivity of actuate voltage is about 200 mV/g) and nonlinearity of 1% in the measurement range of 0 to +1 g. The spectrum measurement is performed in general environment and the resolution of the device is 0.5 mg/rtHz (1.25–100 Hz), which shows better low frequency property.

Effect of particle size distribution on ICP-induced elemental fractionation in laser ablation-inductively coupled plasma-mass spectrometry

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has become one of the well-accepted analytical techniques for in situ trace element analysis and a large number of successful applications have shown its potential. Each commonly employed laser wavelength (1064, 266, 213, 193, 157 nm) leads to some degree of non-stoichiometric ablation, which makes quantification using non-matrix-matched calibration standards difficult for some elements. Time-dependent changes in elemental ratios (so-called elemental fractionation) have been ascribed mostly to processes occurring at the ablation site. Therefore, wavelengths and related irradiance are the major variables that have been used to study this phenomenon in detail. However, there are a large number of parameters that influence the ablation process, aerosol transport, and the excitation process within the ICP. Each process can contribute to elemental fractionation, making the effects of each difficult to separate and to study in detail. The influence of the ICP as one possible source has not been studied thoroughly. The aim of this study was the determination of the source of elemental fractionation using a 266 nm Nd∶YAG laser ablation system. The sample transport system was designed to keep gas flows and plasma conditions constant. Various ablation procedures (single hole drilling and scanning) were tested to investigate the influence of the particle size on the excitation process within the ICP. Mineral wool was used to filter various fractions of the laser-induced aerosol to study signal behaviour as a function of the mass load of the ICP. Uranium and thorium, two elements with very similar properties (ionisation potential and concentration) in the NIST 600 Glass standard series, were used in particular to study ICP processes. It is shown that the particle size distribution is dependent on the wavelength of the laser and the absorption behaviour of the sample. The 266 nm Nd∶YAG laser produces a particle size distribution which is significantly larger in comparison with aerosols produced using a laser wavelength of 193 nm. Signals related to the ablated volume show that the larger particle fractions are not completely vaporised and ionised in the ICP. Filtering certain particle fractions allows final stoichiometric excitation and ionisation, but is accompanied by a loss of 50–80% of the total signal. For single hole ablation, the particle size distribution becomes smaller with increasing depth of the crater. Therefore, scanning mode ablation (which takes place always at the surface) produces a constant supply of larger particles, which results in significantly higher matrix effects within the ICP, as shown by significant changes in the elemental ratio of U∶Th. These studies indicate that the secondary effect of incomplete aerosol or particle excitation within the ICP is the dominant process influencing elemental fractionation during LA-ICP-MS. The effect was observed to be different for individual ICP sources and, therefore, the requirement for matrix-matched quantification in LA-ICP-MS remains instrument-dependent.