A method for forming etch features in an etch layer over a substrate and below an organic ARC layer, which is below an immersion lithography photoresist mask is provided. The substrate with the etch layer, organic ARC layer, and immersion lithography photoresist mask is placed into a processing chamber. The organic ARC layer is opened. The organic ARC layer opening comprises flowing an organic ARC open gas mixture into the processing chamber, wherein the organic ARC open gas mixture comprises an etchant gas and a polymerization gas comprising CO, forming an organic ARC open plasma from the organic ARC open gas mixture, etching the organic ARC layer with the organic ARC open plasma until the organic ARC layer is opened, and stopping the flow of organic ARC open gas mixture into the processing chamber before the etch layer is completely etched.