A plasma treatment method for etching a portion of an isolating layer present on a surface of an opening in a semiconductor structure, the method comprising: providing a semiconductor structure comprising an opening in an external surface, wherein the external surface of the semiconductor structure and surfaces (108,110, 114) defining the opening are at least partially covered by the isolating layer, introducing a treatment gas to the semiconductor structure and the isolating layer, the treatment gas comprising a first component providing forming of a protective polymer during plasma treatment and a second component providing etching of the isolating layer during plasma treatment, and treating the semiconductor structure and the isolating layer by inducing a plasma in the treatment gas, such that a protective polymer layer is formed on at least portions of the isolating layer present on the external surface of the semiconductor structure and on at least portions of the isolating layer present on upper portions of sidewalls of the opening, thereby protecting the portions (106a, 106b) of the isolating layer where the protective polymer layer is being formed, from the plasma, wherein portions of the isolating layer being exposed to the plasma are etched, wherein the treatment gas comprises C 4 F 6, CH 4, C 2 H 4 and/or CH 3 F providing forming of the protective polymer during the plasma treatment, CF 4, C 4 F 8, CHF 3 and/or SF 6 providing etching of the isolating layer during the plasma treatment, and Ar, O 2, N 2 and/or CO, and wherein the plasma is induced by radio frequency power, wherein the radio frequency power comprises a low frequency component providing acceleration of ions in the plasma and a high frequency component sustaining the plasma and controlling a density of the plasma, wherein the low frequency component refers to any frequency component in the range of 100 kHz to 4 MHz, and the high frequency component refers to any frequency component in the range of 10 MHz to 100 MHz. providing a semiconductor structure comprising an opening in an external surface, wherein the external surface of the semiconductor structure and surfaces (108,110, 114) defining the opening are at least partially covered by the isolating layer, introducing a treatment gas to the semiconductor structure and the isolating layer, the treatment gas comprising a first component providing forming of a protective polymer during plasma treatment and a second component providing etching of the isolating layer during plasma treatment, and treating the semiconductor structure and the isolating layer by inducing a plasma in the treatment gas, such that a protective polymer layer is formed on at least portions of the isolating layer present on the external surface of the semiconductor structure and on at least portions of the isolating layer present on upper portions of sidewalls of the opening, thereby protecting the portions (106a, 106b) of the isolating layer where the protective polymer layer is being formed, from the plasma, wherein portions of the isolating layer being exposed to the plasma are etched, wherein the treatment gas comprises C 4 F 6, CH 4, C 2 H 4 and/or CH 3 F providing forming of the protective polymer during the plasma treatment, CF 4, C 4 F 8, CHF 3 and/or SF 6 providing etching of the isolating layer during the plasma treatment, and Ar, O 2, N 2 and/or CO, and wherein the plasma is induced by radio frequency power, wherein the radio frequency power comprises a low frequency component providing acceleration of ions in the plasma and a high frequency component sustaining the plasma and controlling a density of the plasma, wherein the low frequency component refers to any frequency component in the range of 100 kHz to 4 MHz, and the high frequency component refers to any frequency component in the range of 10 MHz to 100 MHz.