Semiconductor device and manufacturing method of the same

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

• forming first and second impurity diffusion regions at an interval from each other in a surface layer of a semiconductor substrate;
• forming a first insulating film over said semiconductor substrate;
• forming first and second holes in said first insulating film above said first and second impurity diffusion regions respectively by pattering said first insulating film;
• forming first and second conductive plugs electrically connected to said first and second impurity diffusion regions respectively in said first and second holes;
• forming an oxidation preventing insulating film on said first insulating film and on said first and second conductive plugs;
• forming a first opening in said oxidation preventing insulating film above said first conductive plug by removing said oxidation preventing insulating film from above said first conductive plug;
• forming a conductive film on said oxidation preventing insulating film and in said first opening above said first conductive plug;
• polishing said conductive film to remove said conductive film from said oxidation preventing insulating film, while leaving said conductive film in said first opening as an auxiliary conductive plug;
• forming a capacitor by stacking a lower electrode, a capacitor dielectric film and an upper electrode in this order on said auxiliary conductive plug and on said oxidation preventing insulating film located around said first opening;
• forming a second insulating film covering said capacitor;
• forming a third hole in said second insulating film above said upper electrode by patterning said second insulating film;
• forming a fourth hole in said second insulating film above said second hole by patterning said second insulating film, and further forming a second opening in said oxidation preventing insulating film under said fourth hole;
• forming a third conductive plug electrically connected to said upper electrode in said third hole;
• and
• forming a fourth conductive plug in said fourth hole and said second opening to electrically connected to said second conductive plug.