Patent ID: 6849191

Claim:
A method of treating a surface of a sample having a film formed on a thin underlying film, which film is etched as a main part of etching, comprising the steps of: generating a plasma in a treatment chamber; applying an rf bias voltage of a frequency of at least 100 kHz so that ions of intermediate energy which promote etching reaction while providing poor directionality are reduced, and ions of high energy having a high directionality and ions of low energy which do not contribute to etching are increased, so as to have at least one peak point at a region of high ion energy and at least one peak point at a region of low ion energy for anisotropic etching, and the rf bias voltage to which a peak to peak voltage Vpp value larger than a Vpp value of a continuous rf bias voltage at which the same etch rate can be obtained is given, so as to have the high ion energy which is larger than a high ion energy of the continuous rf bias voltage, is applied to a stage on which a sample is placed independently of the generation of the plasma; and on-off modulating the rf bias voltage by effecting modulation of the rf bias voltage for one period of anisotropic etching treatment of the sample which is prior to another period of etching treatment of the surface of the sample in which selectivity is higher than selectivity at the one period and in which modulation of the rf bias voltage is not effected, wherein said one period of anisotropic etching treatment in which the modulation of the rf bias voltage is effected is applied to said film as a main part of etching, and said another period of etching treatment in which the modulation of the rf bias voltage is not effected and having a higher selectivity than the selectivity in said one period is applied to a small amount of said film which remains before said thin underlying film is exposed.