Image Number 7 for United States Patent #6319797.
An HSQ film 4 is formed on a silicon oxide film 1 and the film 4 is subject to B.sub.2 H.sub.6 plasma irradiation, to form a boron-implanted region 5. After forming a plasma TEOS film 6 on the region, a concave 8 is formed with a hydrofluoric acid-containing etchant, while wet-etching is stopped on the boron-implanted region 5. Then, the exposed HSQ film 4 in the bottom of the concave 8 is dry-etched to form a contact hole 9 reaching an Al interconnection 2. Then, the contact hole 9 is filled with an upper interconnection material to provide a multilayered interconnection structure.