Helicon wave plasma excited by a single-loop antenna and etching characteristic of Si and SiO2 is studied on a basis of plasma parameters and wave patterns measurements. A wide variety of wavelength with space is observed in the single-loop antenna, and because of no external boundary for the wavelength, the best match of the rf source with plasma is possible. This fact is ascribable to the density enhancement rather than in the conventional double-loop antenna. A condition that the magnetic field is lowered in the antenna portion is also effective on the density enhancement. This is explained by a longer time in resonance of the electron. The etching uniformity is also improved by using a larger diameter one-loop antenna, with a great usefulness.