TaN is a potential candidate for metal gates. BCl3-based plasma is used to pattern metal gates because it has a high selectivity over Si substrate and capable of etching metal oxides (native oxides on metal gates and high-k dielectrics). During metal gate etch in inductively coupled plasma reactor, the authors found that the TaN metal gate profile depends on the composition of BCl3-based plasma. Pure BCl3 results in an undercut of TaN. The undercut can be avoided by addition of 5% O-2, further increase in O-2 concentration (until 10%) does not change the TaN profile. When N-2 is added to BCl3 plasma, first the undercut disappears (at about 6% of N-2) and then a slope appears as N-2 concentration increases further (toward 10%). It was found that the profile is controlled by a film deposited from BCl3-based plasma. In the case of pure BCl3 plasma, the film consists of B (50%), Cl (30%), and O (20%). When 5% of O-2 is added, no film is observed, but strong BO and BO2 peaks appear in the plasma emission spectra. When 5% N-2 is added to the BCl3 plasma, again a film is deposited, but it contains less Cl (18%). Based on our research, the authors propose the following etch mechanism to explain the observed profile notching/footing. In pure BCl3 plasma, a B- and Cl-containing film is deposited on the sidewalls of the gate. Cl from this film will react with TaN producing an undercut. When O-2 is added, no film is formed and the TaN profile is straight as B apparently reacts with O in the gas phase, forming volatile BOx species. Further increase of O-2 content does not change the profile as no film is formed. When N-2 is added to BCl3, a film is formed but in this case N replaces Cl and the film becomes passivating leading to a straight TaN profile. As more N-2 is added, the film passivates TaN more efficiently leading to a sloped profile. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3280170]