The precise and high-speed alteration of various gas species is important for realizing precise and well-controlled multiprocesses in a single plasma process chamber with high throughput. The gas replacement times in the replacement of N 2 by Ar and that of H 2 by Ar are measured in a microwave excited high-density and low electron-temperature plasma process chamber at various working pressures and gas flow rates, incorporating a new gas flow control system, which can avoid overshoot of the gas pressure in the chamber immediately after the valve operation, and a gradational lead screw booster pump, which can maintain excellent pumping capability for various gas species including lightweight gases such as H 2 in a wide pressure region from 10 À1 to 10 4 Pa. Furthermore, to control the gas flow pattern in the chamber, upper ceramic shower plates, which have thousands of very fine gas injection holes (numbers of 1200 and 2400) formed with optimized allocation on the plates, are adopted, while the conventional gas supply method in the microwave-excited plasma chamber uses many holes only opened at the sidewall of the chamber (gas ring). It has been confirmed that, in the replacement of N 2 by Ar, a short replacement time of approximately 1 s in the cases of 133 and 13.3 Pa and approximately 3 s in the case of 4 Pa can be achieved when the upper shower plate has 2400 holes, while a replacement time longer than approximately 10 s is required for all pressure cases where the gas ring is used. In addition, thanks to the excellent pumping capability of the gradational lead screw booster pump for lightweight gases, it has also been confirmed that the replacement time of H 2 by Ar is almost the same as that of N 2 by Ar.

A new screw pump has been developed as a useful backing pump for high-gas-flow semiconductor processing. The characteristic features of the screws are unequal lead and unequal slant angle, which realize higher pumping speed and smaller volume of the pumping system. This pump has a very wide dynamic range of 10−3–760 Torr with a high pumping speed and low electric power consumption by gradational lead screw structure and check valve at outlet. Furthermore, this pump is free from byproduct deposition, corrosion of inner surface and oil degradation. The backdiffusion of oils can be suppressed by admitting the N2 purge gas flow larger than 10 sccm to the inlet side of the pump.

Because the semiconductor industry is moving to a larger wafer size and higher process speed, a vacuum pump will be required to have higher pumping speed in both the viscous and molecular flow ranges. The “gradational lead screw (GLS) pump” unlike these conventional pumps demonstrated the ultimate pressure of 0.0004 Torr and a pumping speed of 8000 L/min over the viscous and molecular flow ranges. The improved performance is attributable to the GLS rotor design. The pump utilizes a small amount of oil. Mass analyzer testing (maximum mass number 120) revealed that there is no evidence of reverse diffusion in the pressure range above 0.002 Torr with a small amount of N2 gas injected. In summary, the GLS pump has high pumping speed because of its large intake volume. Electric power consumption is low as a result of its small exhaust volume. By-product is transferred and ejected from the exhaust port through the operation mechanism. The by-product deposition is minimized if the case temperature is maintained above 150 °C. Although manufacturing this pump requires a high level of skill, the pump structure is rather simple and the maintenance is easy. Hence it will increase the mean time between overhaul and reduce maintenance cost. A detailed report will be prepared on the characteristics of the GLS, the pump structure, and the performance attributes.

No abstract

Design and operation of scroll-type dry primary vacuum pumps