Kazuo Asaumi

Characterization of orientation-dependent etching properties of single-crystal silicon: effects of KOH concentration

Abstract We have evaluated the orientation dependence in chemical anisotropic etching of single-crystal silicon. Etch rates for a number of crystallographic orientations have been measured for a wide range of etching conditions, including KOH concentrations of 30 to 50% and temperatures of 40 to 90 °C. Though the etchants all consist of the same components KOH and water, the orientation dependence varies considerably with change in etchant temperature and concentration. The resulting etch-rate database allows numerical prediction of etch profiles of silicon, necessary for the process design of microstructures. Changing the KOH concentration yields different etch profiles both analytically and experimentally.

Anisotropic etching rates of single-crystal silicon for TMAH water solution as a function of crystallographic orientation

Abstract We evaluated orientation dependence in the etching rate of single-crystal silicon for tetramethyl-ammonium-hydroxide (TMAH) water solutions. Etching rates for a number of crystallographic orientations were measured for a wide range of etching conditions, including TMAH concentrations of 10–25% and temperatures of 70–90°C. We found significantly different characteristics from those for KOH water solutions. Firstly, different types of orientation dependence in etching rate were found around (111) between TMAH and KOH. This means the bonding energy of the silicon crystal lattice is not a single factor that dominates orientation dependence, and there exist different etching mechanisms for the two etchants. Secondly, effects of the circulation of etchants on the etching rates were not negligible in TMAH in contrast to KOH system.

Non-photolithographic pattern transfer for fabricating pen-shaped microneedle structures

We developed a new fabrication process for pen-shaped microneedle structures by using non-photolithographic pattern transfer. The process is a combination of anisotropic wet etching and a dicing technology that uses a saw. The process has an advantage, in which the needle diameter is easily changed by altering the groove profile formed in the dicing-saw process. We fabricated pen-shaped needle structures in a dense array for medical applications. The needle height was larger than 200 µm, and the pitch distance was about 200 µm in the experiments. The width of the needle ranged from 10 to 30 µm. The radius at the needle tip was less than 100 nm.

Anisotropic-etching process simulation system MICROCAD analyzing complete 3D etching profiles of single crystal silicon

We have developed an anisotropic-chemical-etching process simulation system, MICRO-CAD, which is equipped with a database of orientation dependent etching rates of single crystal silicon. When crystallographic orientation of the wafer, mask pattern, etching media and etching conditions such as its concentration and temperature are given, it calculates 3D etching profiles according to the etching time increments.

Development of an Orientation-Dependent Anisotropic Etching Simulation System MICROCAD

As a tool to support the fabrication process design of micromachine devices with complicated three-dimensional (3D) configurations, a crystal orientation-dependent aniso-tropic etching analysis system called MICROCAD has been developed. This system has the capability to analyze the time variations of the 3D etching profile for an arbitrary mask pattern, by preparing the etching rate of the single-crystal silicon to be processed in all directions as a database. The measurement method of the etching rate in all directions, the configuration of the analysis system, and the computational method for the 3D etching profile are described. As examples of the applications of this system, a design of a compensation mask pattern, an analysis of the etching shape while still in progress after etching through of the wafer, and the process design of a multistage etching process are presented so that the effectiveness of this system for the process design is discussed.

Characterization of anisotropic etching properties of single-crystal silicon: effects of KOH concentration on etching profiles

We have evaluated the orientation dependence in chemical anisotropic etching of single-crystal silicon. Etch rates for a number of crystallographic orientations were measured for a wide range of etching conditions, inducting KOH concentrations of 30 to 50% and temperatures of 40 to 90/spl deg/C. Though the etchants all consisted of the same components KOH and water, the orientation dependence varied considerably with change in etchant temperature and concentration. The resulting etch rate database allows numerical prediction of etch profiles of silicon, necessary for the process design of microstructures. Changing the KOH concentration yielded different etch profiles both analytically and experimentally.

Development of quartz etching database and 3-D micromachining simulation system

We have characterized anisotropic etching properties of single-crystal quartz by using a spherical specimen made of alpha-quartz. Spherical specimen allowed us to measure etching rates for a number of orientations with a single etching operation. Measured etching-rates further allowed us to perform complete 3-D etching simulation for arbitrary oriented quartz wafer.

Quartz tuning-fork type AFM probe operated in Anti-phase Vibration Mode

This paper presents that quartz tuning fork shows excellent properties as atomic force microscopy (AFM) probe. We used focused ion beam (FIB) system to monolithically form a sharp tip at the side end of one beam. The fabricated probe can vibrate and detect the deformation itself because of piezoelectric property of crystal quartz. We evaluated the vibration characteristic and the self-detection ability of tuning fork. The tuning fork probe is actuated in two different vibration mode; in-phase and anti-phase mode, and clarified that high Q-factor of 5247 was obtained in anti-phase mode. We further applied this mode for AFM observation and images were successfully with dynamic AFM system

Development of Self-Vibration and -Detection AFM Probe by using Quartz Tuning Fork

We developed a novel type of quartz tuning-fork probe that vibrates and detects its own probe deformation, for application to atomic force microscopy (AFM). This tuning-fork probe improves the AFM image resolution because of its high Q (quality) factor value. The tuning-fork probe has a sharp tip that was fabricated using anisotropic wet etching and a focused ion beam system. We evaluated the vibration properties of the tuning-fork in both the in-phase and anti-phase driving mode, and measured a Q factor value of 2808 in the anti-phase mode. We also confirmed that the tuning-fork probe is able to measure a 100 nm-step on a silicon surface by self-vibration and self-detection, without using external vibration and optical-detection mechanisms.

Estimation of Greenhouse Gas Emissions in Micro-fabrication of MEMS Devices

We study on estimation of greenhouse gas emissions in micro-fabrication of MEMS devices. The estimation is made on a test element groups of silicone-based sensors fabricated on an 8-inch SOI wafer at the green 8-inch MEMS prototype station. The estimation includes electric power, materials, and consumables used in fabrication equipments as well as contribution from usage of cleanroom’s facilities such as supply and waste disposal. The estimation is also made separately in each process steps. The result shows that electric power and purified nitrogen are major sources of greenhouse gas emissions. Our process-by-process approach for the estimation enables us to identify major sources in each process to reduce emissions.