Electronically programmable read-only memory device - with increased integration density and data retaining property

摘要

Semiconductor memory device has a persistent memory element with a first layer for trapping charges and a second layer, on this, to which a random voltage can be applied for trapping the charges in the first layer. The novelty is that the first and second layer are covered with a Si nitride film or a polycrystalline Si film. The first and second layers pref. consist of polycrystalline Si. The memory is surrounded by a matrix with a transparent window. A section contg. a persistent memory cell is covered with a Si oxide film and a contact window is formed in this on a semiconductor zone. A Si nitride film and phosphosilicate glass film are formed consecutively, overlapping the Si oxide film and covering the cell section. Pt. of the glass film is etched away to form a contact window and expose pt. of the Si nitride film, which is also etched away, then the Si oxide film is etched away using the Si nitride film as mask. Alternatively, a poly-Si film is formed, overlapping the Si oxide film and covering the cell section, then pt. of this and the underlying Si oxide film are etched away consecutively and the poly-Si film is oxidised to form an oxide film covering this. The device is used as electronically programmable read-only memory (EPROM). The integration density and data retaining properties are improved.