Method for manufacturing a semiconductor ROM device

A method for manufacturing a semiconductor memory device comprising the steps of:

• determining a device isolation region and an active region by forming a device isolation film on a semiconductor substrate;
• implanting ions of a first conductivity type on a whole surface of said semiconductor substrate where said device isolation film is formed, in order to initialize a cell transistor to be a depletion type;
• sequentially forming a first gate dielectric film and a first gate electrode having an upper portion capped with a first insulating layer on the whole surface of said semiconductor substrate where the ions of the first conductive type are implanted;
• forming a source/drain region which is self-aligned on said first gate electrode on said active region of said substrate;
• implanting ions of a second conductivity type for programming a first cell transistor which uses said first gate electrode;
• programming said device isolation region between a region where a second gate electrode is to be formed and said first gate electrode;
• and
• sequentially forming a second gate dielectric film and said second gate electrode which uses said programmed device isolation region as a channel on a resultant structure, where said device isolation region is formed.