An etching method includes applying a photoresist over a substrate, forming an opening in the photoresist, and etching the substrate under the opening using a plasma generated with a gas composition containing argon and an amount of higher atomic mass inert gas. The amount may be effective to increase photoresist stability compared to otherwise identical etching lacking any of the higher atomic mass inert gas. The photoresist may have a composition sensitized to an actinic energy wavelength of 248 nm or less. A method of increasing the stability of 248 nm or less photoresist during RIE includes providing a means for reducing electron temperature of a plasma and etching a substrate exposed through photoresist openings without substantially destabilizing the photoresist.