Nobukazu Ikeda

A high sensitivity compact gas concentration sensor using UV light and charge amplifier circuit

A high sensitivity compact gas concentration sensor based on the ultraviolet (UV) light absorption spectrophotometry employing charge amplifier circuit is developed in this work as inline gas concentration monitoring system for electronic device manufacturing lines. The developed sensor was verified to be useful for concentration monitoring of metal organic (MO) gases including Bis(cyclopentadienyl)magnesium(Cp2Mg) with a high accuracy and a high reproducibility for 10ppm to 0.036% concentration range, where there was no in-line gas concentration sensor sufficiently applicable to this gas before.

New Metal Organic Gas Supply System by Using an Advanced Flow Control System

Gas flow control is important factor that influence the concentration of process gas and the pressure of process chamber. In silicon semiconductor manufacturing process, the flow rate of process gas is controlled by flow controller, and gas concentration is controlled by adjusting with the ratio between process gas and dilution gas. However, tetraethoxysilane (TEOS) that often used as source gas for interlayer dielectric is liquid state at room temperature, and it is difficult to control the flow rate of TEOS for its low vapor pressure. Thus, the method to carry the vapor of TEOS by carrier gas such as bubbling method is the main stream at present. We developed gas flow control system based on pressure measurement (FCS) that provide greater performance in stability and response of flow control than mass flow controller (MFC) [1]. Fig. 1 shows the simplified schematic diagram of sectional view of FCS. FCS is constructed of control valve, pressure sensor and orifice plate from gas inlet. Here, upstream pressure of orifice plate is P1 and downstream pressure of orifice plate is P2. When the relationship between P1 and P2 become P1 2P2, the flow rate of gas through orifice is constant at sonic speed. FCS controls flow rate of gas using this law and the flow rate vary in direct proportion to P1. Moreover, we developed FCS for high temperature (HT-FCS) to control MO gases that are low vapor pressure at room temperature. HT-FCS can operate precisely in heating condition up to 250 . FCS and HTFCS control P1 with high speed control responsiveness at any time. So, the gas flow rate by controlled FCS and HTFCS don’t vary at all, when supply pressure varies rapidly. And we developed new vaporizer that takes advantage of this property of HT-FCS and liquid source supply system (LSCS) was developed by combining HT-FCS and this vaporizer. Fig.2 shows the simplified schematic diagram of sectional view of LSCS. The vaporizer has three chambers to heat MO gas effectively. The first chamber is entered liquid source and vaporization of the liquid source occurs. Gas vaporized in first chamber pass through second and third chambers and the flow rate of gas are controlled by HT-FCS placed in downstream of vaporizer. Supply of the liquid source to vaporizer is controlled by switching operation of valve (V1) and vaporizer pressure is measured by pressure sensor (P0). Fig.3 shows schematic diagram of control sequence of vaporizer pressure. When the liquid source is in the first chamber, vaporizer pressure indicates vapor pressure value corresponding to heating temperature of vaporizer (Point ). However, when the supply of gas is performed continuously, the liquid source in first chamber finally becomes empty. At the same moment, the vaporizer pressure starts decreasing (Point ). This decreasing of vaporizer pressure continuously occurs and the vaporizer pressure achieves threshold pressure that is preset. When vaporizer pressure decreases to threshold pressure, the liquid source is supplied into the vaporizer by opening V1 (Point ). And vaporizer pressure recovers the value corresponding to heating temperature (Point and ). Here, V1 opens at a preset time for adjust supply quantity of liquid source (Point ). By performing these control, the vaporizer pressure are kept higher than the threshold pressure. And as previously explained, HT-FCS can control gas flow rate stably, if vaporizer pressure vary widely by this sequence. Fig. 4 shows the flow control result of TEOS by using LSCS. The flow rate and vaporizer pressure were plotted in this figure. From the result, after the vaporizer pressure decreased to 40 kPa abs., the vaporizer pressure recovered to 47kPa abs.. The pressure value of 40kPa abs. was the threshold pressure that liquid TEOS was supplied in vaporizer. This recovery showed that liquid TEOS was supplied in vaporizer and vaporization of TEOS was occurred. As a result, the vaporizer pressure could be kept at 40kPa abs. and the flow rate of TEOS was kept constant by set up the threshold pressure above control pressure. The result shows that the developed system can supply the controlled flow rate stably by vaporizing MO material with the quantity need at each time. [1] M.Nagase et al., Jpn. J.Appl. Phys., 40, 5168 (2001).

Highly reliable fitting for gas delivery systems

After confirming the basic characteristics of two types of metal gasket fittings, which are used in construction of ultrapure gas delivery systems for semiconductor manufacturing, it is noticed that the pipe usually twists at the time the fitting is tightened. This may be the possible cause of an external leak, therefore a twist leak test was undertaken to confirm the reliability of the seal during assembly. As a result, it was found that one type of fitting leaked and another type of fitting did not leak. This later type did not leak (leak rate is less than 2.98×10−16 Pa m3/s) even after 70° of twisting.