Conventionally, in the field of the semiconductor device, a hole forming method using a mask including a fine opening pattern has been studied. Japanese Patent Laid-Open No. 2009-238998 discloses the hole forming method. In this method, a film, a metal film, and a resist mask are formed on base material. Then, the metal film is subjected to dry etching using the resist mask, and, at the same time, the retreat amount of the resist mask by the dry etching is controlled, resulting in forming opening with side surface which has first and second tilt angles.
Japanese Patent Laid-Open No. 2008-198991 discloses the hole forming method. This method comprises forming a first pattern, forming spacers on a side wall of the first pattern, forming a second pattern by filling with an insulating film into a gap between the spacers, removing the spacer in a contact hole region, and forming a contact hole by etching using the first and second patterns and the spacer.
Japanese Patent Laid-Open No. 2007-335628 discloses the method for forming the contact hole. In this method, a first resist film is formed on an insulating film, and, then, a second resist film is formed on the first resist film. Next, a first opening is formed in the second resist film using a first photolithography method and a second opening is formed in the first resist film using a second photolithography method, resulting in forming an overhang portion in the second resist film. Thereafter, a mortar-shape contact hole is formed in the insulating film by selectively removing the insulating film using a reactive ion etching method.