the top electrode 7 is set to approximately 600 to 1000 w and the rf power applied to the chuck 13 is set to approximately 150 to 300 w which are preferred settings for transformer coupled plasma tcp tools the radio frequency employed is 13 56 mhz as the inventors of the present invention found out the addition of argon to the echant source gas additionally decreases the cd since reaction products are carried off more quickly this is also the case if an etchant source gas of a fluorine containing gas without oxygen is used in particular a flow rate of argon which is greater than that of the fluorine containing gas for example a ratio of 1 5 between argon gas flow rate and fluorine containing gas flow rate has provided excellent results after the hard mask opening step various gas rinsing steps can be performed in which inert gases such as argon or n 2 nitrogen are fed so as to remove residual gases from the former etching process from the plasma processing chamber moreover or alternatively stabilization steps as described above can be performed if necessary breakthrough steps are also performed in which the oxidized surface of a metal layer to be etched is removed by an anisotropic etching step thereafter another plasma etching process is performed so as to etch the metal layer stack the term u201c another plasma etching process u201d.