Abstract: According to the present invention, there is provided a sample surface treating apparatus for processing a fine pattern by plasma etching, comprising: a stage provided in a chamber, on which a sample to be subjected to a surface treatment is placed; etching gas supplying means for continuously supplying an etching gas for plasma generation into the chamber; plasma generating means for generating a high-density plasma in the chamber; a bias power supply for applying a bias voltage of 100 kHz or higher to the stage independently of the plasma generation; and pulse modulating means for modulating the bias power supply at a frequency of 100 Hz to 10 kHz, wherein a surface treatment in which the minimum feature size is 1 &mgr;m or smaller is performed to the sample placed on the stand.