A photoresist trimming gas compound is provided which will selectively remove a resist foot or scum from the lower portions of sidewalls of a photoresist. Additionally, the trimmer compound hardens or toughens an upper surface of the photoresist thereby strengthening the photoresist. The trimmer compound includes O.sub.2 and at least one other gaseous oxide and is typically utilized in a dry etching process after a trench has been formed in a photoresist The other oxide gases, in addition to the O.sub.2 may include CO.sub.2, SO.sub.2 and NO.sub.2.