Method for fabricating high-density semiconductor read-only memory device

Abstract

A semiconductor read-only memory (ROM) device is provided and includes an array of diode-based memory cells for storing binary data. Whether a memory cell of the ROM device is set to a permanently-ON or OFF state, depends upon whether the memory cell is formed with a junction diode, wherein the presence of a junction diode in the memory cell causes the memory cell to be set to a permanently-ON state. Formation of the junction diode includes the step of forming a plurality of parallel-spaced first diffusion regions of a semiconductor type, to serve as a plurality of bit lines. An insulating layer is then formed to cover the first diffusion regions. A plurality of contact windows are formed at predefined locations of the insulating layer where a first group of memory cells, set to a permanently-ON state, are formed. The unexposed portions of the first diffusion regions are associated with a second group of memory cells that are set to a permanently-OFF state. The method further includes the step of doping the exposed portions of the first diffusion regions with impurities to form a plurality of second diffusion regions of another semiconductor type within the first diffusion regions, and thus, forming the junction diode. A plurality of conductive layers serving as word lines are then formed over the insulating layer to intersect with the bit lines.