Bilayer resist schemes (thin, silicon containing image layer over thick, organic transfer layer) can mitigate lithographic limitations associated with the smaller wavelengths and higher NA values required for patterning shrinking feature sizes. State of the art transfer etch processes utilize an oxygen based chemistry to oxidize Si in the image layer while etching the transfer layer beneath. Undercutting of the image layer, poor CD control, and LER can result from the use of oxidizing chemistry, and are exacerbated by more sensitive ArF materials. Commonly used SO2 addition (for sidewall passivation) can form undesirable byproducts leading to both tool and line contamination. In the present study we present an oxygen-free ammonia based transfer etch process. In addition to NH@sub3@; N@sub2@, H@sub2@, and C@sub2@H@sub4@ were examined as additives. It is hypothesized that selectivity to the underlayer arises from nitridation of the silicon containing image layer which becomes resistant to etch. XPS analyses of the etched samples, optical emission and mass spectroscopic studies were performed to understand the mechanisms involved.