Patent ID: 6902979

Claim:
A method for manufacturing a mask ROM of flat cell structure comprising the steps of: providing a semiconductor substrate having a flat cell array region and a peripheral circuit region; forming a first and a second mask patterns exposing the substrate portions corresponding to a diffusion layer formation region of the flat cell array region and a device isolation layer of the peripheral circuit region; ion-implanting an impurity in the exposed substrate portions; forming a trench by etching the exposed substrate portion of the peripheral circuit region; forming a linear oxide layer on the first and the second mask patterns and the surface of the trench, a diffusion layer on the flat cell array region, and a barrier oxide layer on the surface of diffusion layer in accordance with a thermal oxidation process; depositing an oxide layer on the linear oxide layer to fill up the trench; polishing the oxide layer to expose the surface of the first and second mask patterns; and forming a diffusion layer on the flat cell array region and a trench type isolation layer on the peripheral circuit region by removing the fist and the second mask patters.