摘要:
A split-gate flash memory cell having a three-dimensional source capable of three-dimensional coupling with the floating gate of the cell, as well as a method of forming the same are provided. This is accomplished by first forming an isolation trench, lining it with a conformal oxide, then filling with an isolation oxide and then etching the latter to form a three-dimensional coupling region in the upper portion of the trench. A floating gate is next formed by first filling the three-dimensional region of the trench with polysilicon and etching it. The control gate is formed over the floating gate with an intervening inter-poly oxide. The floating gate forms legs extending into the three-dimensional coupling region of the trench thereby providing a three-dimensional coupling with the source which also assumes a three-dimensional region. The leg or the side-wall of the floating gate forming the third dimension provides the extra area through which coupling between the source and the floating gate is increased. In this manner, a higher coupling ratio is achieved without an increase in the cell size while at the same time alleviating the punchthrough and junction break-down of source region by sharing gate voltage along the side-wall.
摘要:
A method is disclosed to form a split-gate flash memory cell having nitride spacers formed on a pad oxide and prior the forming of an inter-poly oxide layer thereover. In this manner, any damage that would normally occur to the inter-poly oxide during the etching of the nitride spacers subsequent to the forming of the inter-poly oxide is avoided. Consequently, the variation in the thickness of the inter-poly oxide due to the unpredictable damage to the underlying spacers is also avoided by reversing the order in which the spacers and the inter-poly oxide are formed, including the forming of the pad oxide first. As a result, variation in the erase speed of the inter-gate flash memory cell is prevented, both for cells fabricated on the same wafer as well as on different wafers on same or different production lines.
摘要:
A split-gate flash memory cell having a three-dimensional source capable of three-dimensional coupling with the floating gate of the cell, as well as a method of forming the same are provided. This is accomplished by first forming an isolation trench, lining it with a conformal oxide, then filling with an isolation oxide and then etching the latter to form a three-dimensional coupling region in the upper portion of the trench. A floating gate is next formed by first filling the three-dimensional region of the trench with polysilicon and etching it. The control gate is formed over the floating gate with an intervening inter-poly oxide. The floating gate forms legs extending into the three-dimensional coupling region of the trench thereby providing a three-dimensional coupling with the source which also assumes a three-dimensional region. The leg or the side-wall of the floating gate forming the third dimension provides the extra area through which coupling between the source and the floating gate is increased. In this manner, a higher coupling ratio is achieved without an increase in the cell size while at the same time alleviating the punchthrough and junction break-down of source region by sharing gate voltage along the side-wall.
摘要:
A method is provided to improve the control of bird's beak profile of poly in a split gate flash memory cell. The control of the bird's beak profile is achieved in a first embodiment where the polycrystalline layer of the floating gate is annealed at a high temperature. The annealing promotes small grain size and hence smoother surface in the polysilicon, which in turn promotes sharper poly tip. The smoother poly surface also results in thinner inter-poly between the floating gate and the control gate, which together with the sharp poly tip, enhances the erase speed of the split-gate flash memory cell. In a second embodiment, the performance is further enhanced by providing an amorphous silicon for the floating gate, because the amorphous nature of the silicon yields a very smooth surface. This smooth surface is transferred to the recrystallized state of the silicon layer through annealing. Thus, a good control for the bird's beak is achieved. A sharp and short poly tip then results from a well controlled and well-defined bird's beak. Hence, an enhanced split-gate flash memory cell follows.
摘要:
A method of programming split gate flash memory cells which avoids erroneously programming non selected cells and allows the cell size and the array size to be shrunk below previously realizable limits. For N channel cells with the control gates connected to word lines and drains connected to bit lines a negative voltage is supplied between the non selected word lines and ground potential. For P channel cells with the control gates connected to word lines and drains connected to bit lines a positive voltage is supplied between the non selected word lines and ground potential. This allows the minimum length of the control gate over the channel region to be reduced below previously allowable limits and still prevent programming of non selected cells. This also allows cell size and array size to be reduced.
摘要:
A split-gate flash memory cell having a three-dimensional source capable of three-dimensional coupling with the floating gate of the cell, as well as a method of forming the same are provided. This is accomplished by first forming an isolation trench, lining it with a conformal oxide, then filling with an isolation oxide and then etching the latter to form a three-dimensional coupling region in the upper portion of the trench. A floating gate is next formed by first filling the three-dimensional region of the trench with polysilicon and etching it. The control gate is formed over the floating gate with an intervening inter-poly oxide. The floating gate forms legs extending into the three-dimensional coupling region of the trench thereby providing a three-dimensional coupling with the source which also assumes a three-dimensional region. The leg or the side-wall of the floating gate forming the third dimension provides the extra area through which coupling between the source and the floating gate is increased. In this manner, a higher coupling ratio is achieved without an increase in the cell size while at the same time alleviating the punchthrough and junction break-down of source region by sharing gate voltage along the side-wall.
摘要:
There is presented an improved method of fabricating an EEPROM device with a split gate. In the method, a silicon substrate is provided having spaced and parallel recessed oxide regions that isolate component regions where the oxide regions project above the top surface of the substrate. A thin gate oxide is formed on the substrate, and a first conformal layer is deposited over the gate oxide and projecting oxide regions. The substrate is then chemical-mechanically polished to remove the projections of polysilicon over the oxide regions. A silicon nitride layer is deposited on the resultant planar surface of the polysilicon, and elongated openings formed that will define the position of the floating gates that are perpendicular to the oxide regions. The exposed polysilicon in the openings in the silicon nitride are oxidized down to at least the level of the underlying silicon oxide regions, and the silicon nitride layer removed. The polysilicon layer is then removed using the silicon oxide layer as an etch barrier, and the edge surfaces of the resulting polysilicon floating gates oxidized. A second polysilicon layer is deposited on the substrate and elongated word lines formed that are parallel and partially overlapping the floating gates. Source lines are formed in the substrate, and gate lines are formed that overlie the floating gates.
摘要:
A method is provided for forming a split-gate flash memory cell having reduced size, increased coupling ratio and improved program speed. A split-gate cell is also provided where the a first polysilicon layer forms the floating gate disposed over an intervening intergate oxide formed over a second polysilicon layer forming the control gate. However, the second polysilicon layer is also formed over the source region and overlying the other otherwise exposed portion of the floating gate such that this additional poly line now shares the voltage between the source and the floating gate, thereby reducing punch-through and junction breakdown voltages. In addition, the presence of another poly wall along the floating gate increases the coupling ratio between the source and the floating gate, which in turn improves program speed of the split-gate flash memory cell.
摘要:
A method is disclosed to form a split-gate flash memory cell having nitride spacers formed on a pad oxide and prior the forming of an inter-poly oxide layer thereover. In this manner, any damage that would normally occur to the inter-poly oxide during the etching of the nitride spacers subsequent to the forming of the inter-poly oxide is avoided. Consequently, the variation in the thickness of the inter-poly oxide due to the unpredictable damage to the underlying spacers is also avoided by reversing the order in which the spacers and the inter-poly oxide are formed, including the forming of the pad oxide first. As a result, variation in the erase speed of the inter-gate flash memory cell is prevented, both for cells fabricated on the same wafer as well as on different wafers on same or different production lines.
摘要:
A method is provided to form a sharp poly tip to improve the speed of a split-gate flash memory. The sharp poly tip is provided in place of the conventional gate bird's beak (GBB) because the latter requires the forming of thick poly-oxide which is more and more difficult in the miniaturized circuits of the ultra scale integrated technology. Furthermore, it is well known that GBB encroaches under the gate edge in a split-gate flash and degrades the programmability of submicron memory cells. The sharp poly tip of the invention is provided by forming a tapered floating gate through a high pressure etch such that the tip of the upper edge of the floating gate under the poly oxide is sharper and more robust, and, therefore, less susceptible to damage during the manufacture of the cell. The invention is also directed to a semiconductor device fabricated by the disclosed method.