The present invention relates to a method of
etching tungsten or
tungsten nitride in
semiconductor structures, and particularly to the
etching of gate electrodes which require precise control over the
etching process. We have discovered a method of etching
tungsten or
tungsten nitride which permits precise etch profile control while providing excellent selectivity, of at least 175:1, for example, in favor of etching tungsten or
tungsten nitride rather than an adjacent
oxide layer. Typically, the
oxide is selected from
silicon oxide,
silicon oxynitride,
tantalum pentoxide,
zirconium oxide, and combinations thereof. The method appears to be applicable to tungsten or
tungsten nitride, whether deposited by
physical vapor deposition (PVD) or
chemical vapor deposition (CVD). In particular, an initial etch
chemistry, used during the majority of the tungsten or tungsten
nitride etching process (the main etch), employs the use of a
plasma source gas where the chemically functional etchant species are generated from a combination of
sulfur hexafluoride (SF6) and
nitrogen (N2), or in the alternative, from a combination of
nitrogen trifluoride (NF3),
chlorine (Cl2), and carbon
tetrafluoride (CF4). Toward the end of the main etching process, a second
chemistry is used in which the chemically functional etchant species are generated from Cl2 and O2. This final portion of the etch process may be referred to as an "overetch" process, since etching is carried out to at least the surface underlying the tungsten or tungsten
nitride. However, this second etch
chemistry may optionally be divided into two steps, where the
plasma source gas
oxygen content and
plasma source power are increased in the second step.