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 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.
摘要:
A split-gate flash memory cell having self-aligned source and floating gate self-aligned to control gate is disclosed as well as a method of forming the same. This is accomplished by depositing over a gate oxide layer on a silicon substrate a poly-1 layer to form a vertical control gate followed by depositing a poly-2 layer to form a spacer floating gate adjacent to the control gate with an intervening intergate oxide layer. The source is self-aligned and the floating gate is also formed to be self-aligned to the control gate, thus making it possible to reduce the cell size. The resulting self-aligned source alleviates punch-through from source to control gate while the self-aligned floating gate with respect to the control gate provides improved programmability. The method also replaces the conventional poly oxidation process thereby yielding improved sharp peak of floating gate for improved erasing and writing of the split-gate flash memory cell.
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 split gate P-channel flash memory cell and method of forming a split gate P-channel flash memory cell which avoids of high erasing voltage, reverse tunneling during programming, drain disturb and over erase problems, and permits shrinking the cell dimensions. The control gate has a concave top surface which intersects with the sidewalls to form a sharp edge. The cell is programmed by charging the floating gate with electrons by means of hot electron injection from the channel into the floating gate. The cell is erased by discharging the excess electrons from the floating gate into the control gate using Fowler-Nordheim tunneling. The sharp edge at the intersection of the concave top surface and the sidewalls of the floating gate produces a high electric field between the control gate and the floating gate to accomplish the Fowler-Nordheim tunneling with only moderate voltage differences between the floating gate and control gate. The P-channel flash memory cell has a higher impact ionization rage for creating hot electrons so that the distance between the source and drain junctions and the length of the floating gate can be kept small thereby permitting the dimensions of the flash memory cell to be shrunk.
摘要:
A novel method of forming a first polysilicon gate tip (poly-tip) for enhanced F-N tunneling in split-gate flash memory cells is disclosed. The poly-tip is formed in the absence of using a thick polysilicon layer as the floating gate. This is made possible by forming an oxide layer over the poly-gate and oxidizing the sidewalls of the polygate. Because the starting thickness of polysilicon of the floating gate is relatively thin, the resulting gate beak, or poly-tip, is also necessarily thin and sharp. This method, therefore, circumvents the problem of oxide thinning encountered in scaling down devices of the ultra large scale integration technology and the fast programmability and erasure performance of EEPROMs is improved.
摘要:
A method is disclosed for forming a split-gate flash memory cell having a protruding source in place of the conventional flat source. The vertically protruding source structure has a top portion and a bottom portion. The bottom portion is polysilicon while the top portion is poly-oxide. The vertical wall of the protruding structure over the source is used to form vertical floating gate and spacer control gate with an intervening inter-gate oxide. Because the coupling between the source and the floating gate is now provided through the vertical wall, the coupling area is much larger than with conventional flat source. Furthermore, there is no longer the problem of voltage punch-through between the source and the drain. The vertical floating gate is also made thin so that the resulting thin and sharp poly-tip enhances further the erasing and programming speed of the flash memory cell. The vertical orientation of the source structure and the floating gate and the self-alignment of the spacer control gate to the floating gate together makes it possible to reduce the memory cell substantially.
摘要:
A method is provided for forming a short and sharp gate bird's beak in order to increase the erase speed of a split-gate flash memory cell. This is accomplished by implanting nitrogen ions in the first polysilicon layer of the cell and removing them from the area where the floating gate is to be formed. Then, when the polysilicon layer is oxidized to form polyoxide, the floating gate region without the nitrogen ions oxidizes faster than the surrounding area still having the nitrogen ions. Consequently, the bird's beak that is formed at the edges of the polyoxide assumes a sharper shape with smaller size than that is found in prior art. This results in an increase in the erase speed of the memory cell.
摘要:
A method is provided for forming a split-gate flash memory cell having reduced size, partially buried source line, increased source coupling ratio, improved programmability, and overall enhanced performance. A split-gate cell is also provided with reduced size and improved performance. The source line is formed in a trench in the substrate over the source region. The trench walls provide increased source coupling and the absence of gate bird's beak with the trench together shrink the cell size. Programmability is also enhanced through more favorable hot electron injection though intergate oxide between the floating gate and the control gate.
摘要:
In this invention bit lines are ion implanted into a semiconductor substrate in columns beside floating gates of an array of flash memory cells. A control gate overlays each row floating gates and operates as a word lines for the rows of flash memory cells. Each bit line serves a dual purpose of providing a drain for one cell and a source for the adjacent cell. The flash memory cells are programmed, erased and read depending upon the voltages applied to the buried bit lines and the word line structured as a control gate that extends the length of each row. By implanting the bit lines into the semiconductor substrate the flash memory cell can be made smaller improving the density of the flash memory.