A novel, in-situ plasma treatment method for eliminating or reducing striations caused by standing waves in a photoresist mask, is disclosed. The method includes providing a photoresist mask on a BARC (bottom anti-reflective coating) layer that is deposited on a feature layer to be etched, etching the BARC layer and the underlying feature layer according to the pattern defined by the photoresist mask, and subjecting the photoresist mask to a typically argon or hydrogen bromide plasma before, after, or both before and after etching of the BARC layer prior to etching of the feature layer. Preferably, the photoresist mask is subjected to the plasma both before and after etching of the BARC layer.