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Summary form only given, as follows. A large plasma source using microwaves with a slotted antenna has been newly developed for the ashing and etching processes, which has a simple structure without magnetic field. The plasma source consists of two discharge regions, aiming at a large-size-substrate of more than 400 u-500 mm/sup 2/. In each discharge region, the microwaves emitted through a slotted antenna in rectangular waveguide propagate in the dielectric window and generate high-density surface wave plasma. The shape of the slotted antenna is determined based on the experiments and electromagnetic calculations. Two slotted antennas in 5-steps-stair shape, where the length of each step corresponds to half of the guide wavelength, are located in parallel along the long axis of the waveguide. The electron density is estimated to be more than 1011 cm/sup -3/ from the results obtained in a small-size experimental apparatus. The operating conditions such as gas ratio and microwave power are optimized using the slotted antenna plasma source. The ashing rate of more than 1000 nm/min and the uniformity of 9.8% are obtained under the conditions of gas ratio of O2/CF4=2200/165 SCCM, gas pressure of 35 Pa, and microwave power of 2.75 kWu/spl sim/2. Full ashing with a high selectivity of resist to Si and SiO2 for a large TFT-LCD process at room temperature, which is as about 3 times as high as in the case of a parallel plate electrode type, is attained using high-density plasma with O/sub 2/ while adding CF/sub 4/. The Al chamber of the plasma source which is coated with almite prevents rate fluctuation of the ashing rate, due to the suppression of the reactions between O/sub 2/ radicals and AlF on the chamber surface.