NOVELTY - A patterned oxygen-containing plasma etchable layer is formed by incorporating boron trichloride in conjunction with an oxygen-containing plasma etchable layer to provide better linewidth control and a more uniform sidewall profile of the patterned oxygen-containing plasma etchable layer.    USE - For forming a patterned oxygen-containing plasma etchable layer in microelectronic fabrications, solar cell microelectronic fabrications, ceramic substrate microelectronics fabrications, and flat panel display microelectronics fabrications.    ADVANTAGE - The process forms a patterned oxygen-containing plasma etchable layer with enhanced linewidth control and uniform sidewall profile. It is readily commercially implemented, and does not discriminate w.r.t the nature of microelectronics fabrication and to the nature of an oxygen containing plasma etchable material. The second etchant gas composition provides attenuated surface etching of the patterned hard mask layer.    DETAILED DESCRIPTION - The formation of a patterned oxygen-containing plasma etchable layer involves forming a blanket oxygen-containing plasma etchable layer on a substrate (30), forming a blanket hard mask layer on the etchable layer, forming a patterned photoresist layer on the hard mask layer, etching the hard mask layer using a first plasma etch in conjunction with the patterned photoresist layer (40a, 40b) as a first etch mask layer to form a patterned hard mask layer, and etching the etchable layer using a second plasma etch with at least the patterned hard mask layer as a second etch mask layer (38) to form a patterned oxygen-containing plasma etchable layer. The second plasma etch employs a second etchant gas composition comprising an oxygen containing etchant gas which upon plasma activation provides an active oxygen etching species, and boron trichloride.    An INDEPENDENT CLAIM is included for the production of a patterned conductor layer comprising forming a patterned oxygen-containing plasma dielectric layer (36) defining an aperture using the above process, and forming a patterned conductor layer in the aperture while employing a damascene method.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional view of a step during the production.    Substrate (30)    Patterned oxygen-containing plasma dielectric layer (36)    Second etch mask layer (38)    Photoresist layer (40a, 40b)