Method of making multi-stage ROM structure

Claim 1

A method of forming a multi-stage read only memory, comprising the steps of: a. providing a substrate of a first conductivity-type having an upper surface, and having a pad oxide layer thereon; b. forming a plurality of first trenches on the substrate, wherein the first trenches are substantially parallel to each other and extend in a first direction; c. forming an insulating layer over the substrate and the first trenches; d. forming a first conductive layer of a second conductivity-type over the insulating layer and filling up the first trenches; e. removing a portion of the first conductive layer above the upper surface of the substrate and in the first trenches and leaving a remaining portion of the first conductive layer in the first trenches such that an upper surface of the remaining portion is below an upper surface of the substrate; f. removing a portion of the insulating layer from the first trenches until the upper surface of the insulating layer is lower than the upper surface of the remaining portion of the first conductive layer; g. forming a second conductive layer of the second conductivity-type over the substrate and filling up the first trenches over the remaining portion of the first conductive layer; h. etching back the second conductive layer until the upper surface of the second conductive layer has substantially the same level as the upper surface of the substrate, wherein the etched back second conductive layer and the remaining portion of the first conductive layer are formed a source/drain pole; i. removing the pad oxide layer; j. forming a plurality of second trenches on the substrate, wherein the second trenches are substantially parallel to each other and extend in a second direction; k. forming a first photoresist layer over the substrate, and exposing the periphery of a portion of the second trenches; l. doping the exposed second trenches, forming a plurality of impurity diffusion regions and stripping the first photoresist layer; m. forming a second insulating layer over the upper surface of the substrate and the surface of the second trenches, and removing a portion of the second insulating layer and leaving a remaining portion of the second insulating layer at the opposite side-walls of each of the second trenches so as to form a plurality of spacers; n. forming a second photoresist layer over the substrate and exposing a portion of the spacers; o. removing the exposed spacers and removing the second photoresist layer; p. forming a gate oxide layer over the substrate; q. forming a third conductive layer over the substrate so as to fill the second trenches; and r. defining the third conductive layer so as to form a plurality of gates.

Claim 2

A method of forming a multi-stage read only memory, comprising the steps of: a. providing a substrate of a first conductivity-type having an upper surface, and having a pad oxide layer thereon; b. forming a plurality of first trenches on the substrate, wherein the first trenches are substantially parallel to each other and extend in a first direction; c. forming an insulating layer over the substrate and the first trenches; d. forming a first conductive layer of a second conductivity-type over the insulating layer and filling up the first trenches; e. removing a portion of the first conductive layer above the upper surface of the substrate and in the first trenches and leaving a remaining portion of the first conductive layer in the first trenches such that an upper surface of the remaining portion is below an upper surface of the substrate; f. removing a portion of the insulating layer from the first trenches until the upper surface of the insulating layer is lower than the upper surface of the remaining portion of the first conductive layer; g. forming a second conductive layer of the second conductivity-type over the substrate and filling up the first trenches over the remaining portion of the first conductive layer; h. etching back the second conductive layer until the upper surface of the second conductive layer has substantially the same level as the upper surface of the substrate, wherein the etched back second conductive layer and the remaining portion of the first conductive layer are formed a source/drain pole; i. removing the pad oxide layer; j. forming a plurality of second trenches on the substrate, wherein the second trenches are substantially parallel to each other and extend in a second direction; k. forming a first photoresist layer over the substrate, and exposing the periphery of a portion of the second trenches; l. doping the exposed second trenches, forming a plurality of impurity diffusion regions and stripping the first photoresist layer; m. forming a second insulating layer over the upper surface of the substrate and the surface of the second trenches, and removing a portion of the second insulating layer and leaving a remaining portion of the second insulating layer at the opposite side-walls of each of the second trenches so as to form a plurality of spacers; n. forming a second photoresist layer over the substrate and exposing a portion of the spacers; o. removing the exposed spacers and removing the second photoresist layer; p. forming a gate oxide layer over the substrate; q. forming a third conductive layer over the substrate so as to fill the second trenches; and r. defining the third conductive layer so as to form a plurality of gates.