Diode-based semiconductor read-only memory device and method of fabricating the same

A method for fabricating a diode-based ROM device, comprising the steps of:

• (1) preparing a semiconductor substrate of a first semiconductor type, and then forming a plurality of substantially parallel-spaced trenches on a surface of the substrate in a first direction;
• (2) forming a first insulating layer over the substrate, the first insulating layer filling up all of the trenches on the substrate;
• (3) removing a thickness of the first insulating layer other than the portions in the trenches;
• (4) performing a first ion-implantation process so as to dope a first impurity material of a second semiconductor type into those portions of the substrate that are located between the trenches to form a plurality of substantially parallel-spaced first diffusion regions of the second semiconductor type between the trenches, the first diffusion regions serving as a plurality of bit lines for the ROM device on which a plurality of memory cells are defined;
• (5) forming a second insulating layer which covers all of the first diffusion regions and all of the remaining portions of the first insulating layer in the trenches;
• (6) forming a plurality of contact windows in the second insulating layer so as to expose a selected group of the first diffusion regions that are associated with a first selected group of the memory cells of the ROM device that are to be set to a permanently-ON state;
• (7) by using the second insulating layer as a mask, performing a second ion-implantation process so as to dope a second impurity material of the first semiconductor type into an upper portion of each of the exposed first diffusion regions so as to form a plurality of second diffusion regions of the first semiconductor type respectively in the upper portion of each of the exposed first diffusion regions;
• each of the second diffusion regions and the associated one of the first diffusion regions in combination constituting a junction diode;
• (8) forming a conductive layer over the second insulating layer, which fills up all of the contact windows in the second insulating layer to come in electrical contact with all of the second diffusion regions;
• and
• (9) removing selected portions of the conductive layer so as to form a plurality of substantially parallel-spaced word lines in a second direction.