Non-volatile semiconductor memory and method of making same, and semiconductor device and method of making device
View Patent ↗A semiconductor device, which ensures device reliability especially in fine regions and enables great capacitance and high-speed operations, has memory cells including, in a first region of a main surface of a semiconductor substrate, a gate insulating film, a floating gate electrode, an interlayer insulating film, a control gate electrode, and source and drain regions of the second conduction type arranged in a matrix, with a shallow isolation structure for isolating the memory cells. When using a shallow structure buried with an insulating film for element isolation, the isolation withstand voltage in fine regions can be prevented from lowering and the variation in threshold level of selective transistors can be reduced. When the memory cells in a memory mat are divided by means of selective transistors, the disturb resistance of the memory cells can be improved.
1. A semiconductor device comprising:
first MISFETs constituting memory cells arranged in a first direction and in a second direction crossing to the first direction; and
selective MISFETs,
wherein each of the first MISFETs includes a floating gate formed on a main surface of a semiconductor substrate through a first gate insulating film, a control gate electrode formed over an upper portion of the floating gate electrode through a first interlayer insulating film, a first semiconductor region and a second semiconductor region formed in the substrate and serving as source/drain regions, and a channel-forming region formed between the first semiconductor region and the second semiconductor region,
wherein the first MISFETs adjoining in the second direction are isolated by a first insulating film filled in a groove formed in the semiconductor substrate,
wherein a selective MISFET, of the selective MISFETs, includes a first gate electrode formed with the same level layer as the floating gate electrode, a second interlayer insulating film formed with the same level layer as the first interlayer insulating film, a second gate electrode formed with the same level layer as the control gate electrode, and a pair of third semiconductor regions formed in the substrate and serving as source/drain regions,
wherein the selective MISFET is arranged in the first direction adjacent to a first MISFET, of the first MISFETs, such that the first semiconductor region of the first MISFET is electrically connected to one of the pair of the third semiconductor regions of the selective MISFET,
wherein the selective MISFET includes a first region and a second region such that the first region and the second region are arranged in the first direction and such that, at the first region, the second gate electrode is formed over an upper portion of the first gate electrode through the second interlayer insulating film, and
wherein, at the second region of the selective MISFET, the second interlayer insulating film is removed such that a bottom surface of the second gate electrode at the second region is lower than a bottom surface of the second gate electrode at the first region and such that a channel-forming region at the second region of the selective MISFET is in contact with the second semiconductor region.
2. A semiconductor device according to claim 1 , wherein the second gate electrode includes a first layer and a second layer formed over the first layer, and wherein, at the second region, a bottom surface of the second layer at the second region is lower than an upper surface of the first gate electrode at the first region.
3. A semiconductor device according to claim 2 , wherein the second layer includes a refractory metal as a component.
4. A semiconductor device according to claim 2 , wherein the groove is formed in self-alignment with the floating gate electrodes adjacent to adjacent first MISFETs in the second direction.
5. A semiconductor device according to claim 1 , wherein the groove is formed in self-alignment with the floating gate electrodes adjacent to adjacent first MISFETs in the second direction.
6. A semiconductor device according to claim 5 , wherein the floating gate electrode includes a first floating gate electrode and a second floating gate electrode formed over the first floating gate electrode, and wherein the second floating gate electrode extends over the first insulating film in the second direction.
7. A semiconductor device according to claim 1 , wherein the floating gate electrode includes a first floating gate electrode and a second floating gate electrode formed over the first floating gate electrode, and wherein the second floating gate electrode extends over the first insulating film in the second direction.
8. A semiconductor device according to claim 1 , wherein information of two bits or more is memorized in one memory cell.
9. A semiconductor device according to claim 1 , wherein the first semiconductor region extends under the first gate electrode at the first region.
10. A semiconductor device according to claim 1 , wherein the second interlayer insulating film includes a first silicon oxide film, a silicon nitride film formed over the first silicon oxide film and a second silicon oxide film formed over the silicon nitride film.
11. A semiconductor device according to claim 1 , wherein the first semiconductor region is integrally formed with the one of the pair of the third semiconductor regions of the selective MISFET.