Toru Oizumi

Temperature compensation of ball surface acoustic wave sensor by two-frequency measurement using undersampling

To realize a practical two-frequency measurement (TFM) system for precise temperature compensation in a ball surface acoustic wave (SAW) sensor, the application of undersampling (US) was investigated. The subtraction coefficient for the temperature compensation in US was theoretically explained. The principle of the TFM system using US was simulated by the decimation of the oversampling (OS) waveform after applying a narrow band-pass filter, and the delay time was measured using a wavelet transform. In the application of the method to trace moisture measurement, the delay time response due to US matched that due to OS with a correlation coefficient higher than 0.9999. Although rms noise was increased by US, the response to the concentration change of 4?17 nmol/mol was measured with a signal-to-noise ratio higher than 20. From these results, it was shown that the precise output of the ball SAW sensor could be obtained even when using US, which was equivalent to that using OS.

Highly sensitive trace moisture ball surface acoustic wave sensor using SiOx film

Regarding the gases for the manufacturing process of semiconductor devices, fast and sensitive sensors are needed to control trace moisture to less than 1 ?mol/mol. A ball surface acoustic wave (SAW) sensor is promising technology for this purpose. In this study, we verify the response of a sol?gel SiOx film-coated ball SAW sensor to extremely low-concentration moisture using a cavity ring down spectroscopy (CRDS), the most sensitive commercially available moisture sensor, as a reference sensor. We clearly measured 17 nmol/mol moisture by developing a sensor cell using metal O-rings reducing the leakage of moisture. The response time from 390 to 790 nmol/mol was one tenth of that for the CRDS, and the detection limit was estimated to be as low as 0.2 nmol/mol.

Moisture adsorption desorption characteristics of stainless steel tubing measured by ball surface acoustic wave trace moisture analyzer

A ball surface acoustic wave (SAW) trace moisture analyzer (TMA) was applied to measuring the adsorption and desorption (AD) characteristics of a stainless steel tube. For the first time, two-frequency measurement for precise temperature compensation was attempted at intervals of 3 s using a burst waveform undersampling circuit. We succeeded in measuring the variations of moisture transit time and dry-down dynamics caused by inner surface treatments such as bright annealing (BA), electropolishing (EP), and electrochemical buffing (ECB) using a sample-tube length of only 100 mm at a flow rate of 0.1 L/min. Net moisture adsorption was evaluated from the measured adsorption subtracted by the background adsorption. As a result, it was found that the adsorption on the ECB tube was smaller than those on EP and BA tubes by 1/3 and 1/4, respectively, at a baseline concentration of 13 ppbv. From these results, it was demonstrated that the ball SAW TMA could be used for measuring the AD characteristics of stainless steel tubes with various surface treatments.

Doping Technology for Silicon Thin Films Grown by Temperature-Modulation Molecular Layer Epitaxy

Layer-by-layer growth of single-crystalline Si with doping was achieved by a temperature-modulation (TM) method combined with an intermittent supply of Si 2 H 6 and dopant precursor B 2 H 6 for p-type growth on Si(100). B 2 H 6 was introduced at a predetermined timing of supply in several doping modes. This TM Si molecular layer epitaxy enabled the growth of a flat surface with layer-by-layer growth in a self-limiting manner on Si(100) and with an outstanding high carrier concentration of over 5 X 10 20 cm -3 while maintaining selective epitaxy at the maximum temperature of 470°C. Based on the results of doping in several modes of growth, the incorporation mechanism of dopant on the growing surface is discussed with respect to the TM process.

A Novel Method and an Equipment for Generating the Standard Moisture in Gas Flowing through a Pipe

When inert gas containing water molecules flows into a metal pipe, the water molecules cannot exit instantaneously from the outlet of the pipe but are captured at adsorption sites on the inner surface of the pipe until most of the sites are occupied. A theoretical model and a subsequent experiment in this article show that the delay time depends on the amount of moisture level; the higher the moisture-level, the shorter the delay time. Based on the result, we propose a new method and its implementation to the validation of a standard moisture generation to be used in the field measurement such as in factories and pipe lines.

Development of ball surface acoustic wave trace moisture analyzer using burst waveform undersampling circuit

The measurement and control of trace moisture, where the water concentration is lower than 1 ppmv [-76.2 °C for the frost point (°CFP)], are essential for improving the yield rate of semiconductor devices and for ensuring their reliability. A ball surface acoustic wave (SAW) sensor with a sol-gel silica coating exhibited useful characteristics for a trace moisture analyzer (TMA) when the temperature drift of the delay time output was precisely compensated using two-frequency measurement (TFM), where the temperature-compensated relative delay time change (RDTC) was obtained by subtracting the RDTC at the fundamental frequency from that at the third harmonic frequency on an identical propagation path. However, the cost of the measurement circuit was a problem. In this study, a burst waveform undersampling (BUS) circuit based on the theory of undersampling measurement was developed as a practical means. The BUS circuit was useful for precise temperature compensation of the RDTC, and the ball SAW TMA was prototyped by calibrating the RDTC using a TMA based on cavity ring-down spectroscopy (CRDS), which is the most reliable method for trace moisture measurement. The ball SAW TMA outputted a similar concentration to that obtained by the CRDS TMA, and its response time at a set concentration in N2 with a flow rate of 1 l/min was about half that of the CRDS TMA, suggesting that moisture of -80 °CFP was measured within only 1 min. The detection limit at a signal-to-noise ratio of 3 was estimated to be 0.05 ppbv, comparable with that of the CRDS TMA. From these results, it was demonstrated that a practical ball SAW TMA can be realized using the developed BUS circuit.

Method for Thin-Film Technology of Si with Doping

Layer-by-layer growth of single crystalline Si was examined with a doping method that applied a low-temperature process. Si 2 H 6 (99.99%) and dopant precursor, PH 3 (or B 2 H 6 ), were injected intermittently on the Si(100) surface, and an atomically smooth surface was obtained with atomic-scale layer controllability of the growth thickness. At a process temperature of 525°C, an n-type layer doped with phosphorus was obtained up to the carrier concentration of 2.8 X 10 1 9 cm - 3 , and a smooth surface of the film was obtained under 2 X 10 1 9 cm - 3 . The carrier concentration of the p-type layer doped with boron reached 5 × 10 2 0 cm - 3 while maintaining an atomically smooth surface at a growth temperature of 510°C. Nanometer-scale multilayer structures using doping were fabricated, and the doping nrofile was sufficiently sharp and on the order of nanometers.