Plasma treatment method

A plasma treatment method (400) for etching a portion (112) of an isolating layer (106) present on a surface (110) of an opening in a semiconductor structure (100) is provided. The method (400) comprising: providing (402) a semiconductor structure (100) comprising an opening (102) in an external surface (104), wherein the external surface (104) of the semiconductor structure (100) and surfaces (108,110, 114) defining the opening (102) are at least partially covered by the isolating layer (106), introducing (404) a treatment gas to the semiconductor structure (100) and the isolating layer (106), the treatment gas comprising a first component providing forming of a protective polymer during plasma treatment and second component providing etching of the isolating layer (106) during plasma treatment, and treating (406) the semiconductor structure (100) and the isolating layer (106) by inducing a plasma in the treatment gas, such that a protective polymer layer (118) is formed on at least portions (1 06a) of the isolating layer (106) present on the external surface (104) of the semiconductor structure (100) and on at least portions (1 06b) of the isolating layer (106) present on upper portions of sidewalls (114) of the opening (102), thereby protecting the portions (106a, 1 06b) of the isolating layer (106) where the protective polymer layer (118) is being formed, from the plasma, wherein portions (112) of the isolating layer (106) being exposed to the plasma are etched.