gate cross section profile in fig3 b moreover the data shown by the examples in fig5 a and 5b is indicated by a dashed line as a comparative example as can be understood from fig3 a even when the total number of wafers being processed reaches 1000 the dimension shift value is suppressed below 1 nm and a stable etching process with high reproducibly is realized according to the method of the present embodiment further it also can be understood that even when the total number of wafers being processed reaches to 1000 the shape of the cross section of the metal gate becomes the favorable shape of nearly rectangular and not becoming as the over cut shape as in conventional method for that matter a favorable result also is obtained even when the total number of wafers being processed reaches to 7000 the dimension shift value is constantly suppressed below 1 nm and the interior angle a also maintained constantly at 89 0 degrees as described above according to the present embodiment when the etching process fig2 s 2 to s 4 is initiated the identical coating film is formed on the inner surface of the chamber 1 in other word the inner surface of the chamber 1 is constantly in the same condition when the etching process is initiated consequently the condition of plasma used for the etching process is also the same accordingly the dependence of the.