A ruthenium film deposition method is disclosed. Briefly stated, in embodiments the invention operates by receiving an EM signal and recursively operating on approximate half cycles of the carrier signal. The external bus controller 2 includes a wait register 20 set with a wait number for accessing the external bus 3, and OR circuits 23a and 23b for externally outputting the external bus write signal 123 and the external bus read signal 124 from each CPU. The solution in principle according to the invention which is presented has, in contrast to other known methods, the advantage that the actuation of the corresponding controllers is comparatively simple with very good control results.