Process for the formation of contact holes in semiconductor integrated circuit

A method of forming contact holes in a semiconductor integrated circuit comprising:

• providing a semiconductor substrate;
• forming a field insulating film on selected areas of a surface of said semiconductor substrate thereby isolating a first element forming region and a second element forming region;
• forming a gate insulating film on the surface of said semiconductor substrate;
• forming a first conductive film over said field insulating film and said gate insulating film;
• forming a buffer insulating film over said first conductive film;
• patterning the buffer insulating film, the first conductive film, and the gate insulating film thereby forming:
• a first opening extending from an area on the semiconductor substrate of the second element forming region to an area on the field insulating film, and
• a second opening extending from an area on the semiconductor substrate of the first element forming region to an area on the field insulating film;
• etching to remove insulating material on the semiconductor substrate in the first and second openings along with the buffer insulating film on the first conductive film thereby exposing:
• the surface of said semiconductor substrate in the first and second openings, and
• the surface of the first conductive film;
• forming a second conductive film over the area of said semiconductor substrate;
• patterning said first and second conductive film thereby forming:
• a first gate electrode in the first element forming region,
• a first interconnection layer to connect the first gate electrode and the semiconductor substrate in the first opening,
• a second gate electrode in the second element forming region, and
• a second interconnection layer to connect the second gate electrode and the semiconductor substrate in the second opening;
• and
• introducing impurities into the semiconductor substrate to form source/drain regions in the semiconductor substrate on both sides of the first gate electrode and on both sides of the second gate electrode.