An inductively coupled plasma source with an internal straight antenna was developed. By inserting an antenna into plasma, the induction of a strong electric field in the plasma and the efficient transmissions of power to plasma is enabled. However, there was a practical problem in that antenna sputtering occurred. Suppression of antenna sputtering and methods of insulating the antenna were studied. Consequently, it was found that sputtering impurities were reduced by covering the straight antenna with a quartz pipe. Furthermore, the amount of quartz pipe etching could be reduced to as little as 1/10th the original value. As a result of fabricating and evaluating the plasma source in which four straight antennas were arranged in parallel, electron density was determined to be as high as 1011 cm-3 even at a pressure as low as 4 mTorr. When the processing performance of the plasma source was evaluated, the ashing rate of the photoresist and the etching rate of the poly-Si were, respectively, 4.8 µm/min and 450 nm/min. These values are at practically applicable levels.