Method of manufacturing a semiconductor device having signal line above main ground or main VDD line

A method of manufacturing a semiconductor device, comprising the process steps of:

• forming a lower-layer signal line in a lower layer on a semiconductor substrate via a first insulating film;
• forming a second insulating film with which the lower-layer signal line is covered;
• forming a first through hole which passes through he second insulating film and reaches the lower-layer signal line;
• embedding a first conductor in the first through hole;
• forming one of a main power-supply line and a ma n ground line on the second insulating film, which has a window for providing a space above the first conductor, and forming a conducting portion on the first conductor inside the window, where the conducting portion is isolated from said one of the main power-supply line and the main ground line;
• forming a third insulating film with which the conducting portion and said one of the main power-supply line and the main ground line are covered;
• forming a second through hole which passes through the third insulating film and reaches the conducting portion;
• embedding a second conductor in the second through hole;
• forming an upper-layer signal line in an upper layer on the second conductor, where the main power-supply line and the main ground line are wider than the upper-layer signal line.