US20090086540A1 - Method of operating non-volatile memory array - Google Patents
Method of operating non-volatile memory array Download PDFInfo
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- US20090086540A1 US20090086540A1 US12/331,367 US33136708A US2009086540A1 US 20090086540 A1 US20090086540 A1 US 20090086540A1 US 33136708 A US33136708 A US 33136708A US 2009086540 A1 US2009086540 A1 US 2009086540A1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
- G11C16/0408—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors
- G11C16/0433—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors comprising cells containing a single floating gate transistor and one or more separate select transistors
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
- G11C16/0483—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells having several storage transistors connected in series
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C16/00—Erasable programmable read-only memories
- G11C16/02—Erasable programmable read-only memories electrically programmable
- G11C16/06—Auxiliary circuits, e.g. for writing into memory
- G11C16/10—Programming or data input circuits
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/401—Multistep manufacturing processes
- H01L29/4011—Multistep manufacturing processes for data storage electrodes
- H01L29/40114—Multistep manufacturing processes for data storage electrodes the electrodes comprising a conductor-insulator-conductor-insulator-semiconductor structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
- H01L29/78—Field effect transistors with field effect produced by an insulated gate
- H01L29/792—Field effect transistors with field effect produced by an insulated gate with charge trapping gate insulator, e.g. MNOS-memory transistors
- H01L29/7923—Programmable transistors with more than two possible different levels of programmation
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B41/00—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates
- H10B41/30—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the memory core region
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B41/00—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates
- H10B41/30—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the memory core region
- H10B41/35—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the memory core region with a cell select transistor, e.g. NAND
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B69/00—Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices
Definitions
- the present invention relates to a semiconductor device. More particularly, the present invention relates to a method of manufacturing a non-volatile memory and a method of operating a non-volatile memory array.
- EEPROM Electrically erasable programmable read only memory
- a typical EEPROM has a floating gate and a control gate fabricated using doped polysilicon.
- a select gate is set up above the substrate on the sidewall of the control gate and the floating gate forming a so-called split-gate structure.
- FIG. 1 is a schematic cross-sectional view of a portion of a conventional AG_AND memory cell structure.
- the AG-AND memory cell structure includes a substrate 100 , a well region 102 , an auxiliary gate transistor Qa 1 (Qa 2 ), a memory device Qm 1 (Qm 2 ) and source/drain regions 104 a , 104 b ( 104 c ) in the substrate 100 on one side of the auxiliary gate transistor Qa 1 (Qa 2 ) and the memory device Qm 1 (Qm 2 ) respectively.
- the auxiliary gate transistor Qa 1 (Qa 2 ) includes an auxiliary gate 106 a and the memory device Qm 1 (Qm 2 ) includes a floating gate 108 a ( 108 b ) and a word line 110 .
- the word line 110 serves as a control gate for the memory device Qm 1 (Qm 2 ).
- the auxiliary gate transistor Qa 1 (Qa 2 ) and the memory device Qm 1 (Qm 2 ) together form a memory cell Q 1 (Q 2 ).
- neighboring memory cells in the row direction use a common source/drain region.
- a 13V bias voltage is applied to the word line 110 , a 1V bias voltage is applied to the auxiliary gate 106 a , a 0V bias voltage is applied to the source/drain region 104 a and a 5V bias voltage is applied to the source/drain region 104 b .
- electrons are injected into the floating gate 108 a of the memory device Qm 1 to program the memory cell Q 1 . Because a bias voltage is not applied to the auxiliary gate 106 b , the memory cell Q 2 is not programmed.
- a source/drain region ( 104 a , 104 b or 104 c ) is formed in the substrate 100 on each side of the memory cell Q 1 (Q 2 ).
- the source/drain regions ( 104 a , 104 b or 104 c ) have to be separate from each other by a definite distance. This precludes any further miniaturization of the memory cell array.
- the present invention is directed to a non-volatile memory, a non-volatile memory array and a manufacturing method thereof capable of simplifying the fabrication of non-volatile memory array.
- the non-volatile memory is also programmed using a source-side injection (SSI) method so that the average programming speed of the memory cells is increased and overall performance of the memory is improved.
- SSI source-side injection
- the present invention is also directed to a non-volatile memory, a non-volatile memory array and a manufacturing method thereof capable of increasing the overlapping area between the floating gate and the control gate inside the memory. Hence, the coupling ratio of the gates inside the memory is increased and overall performance of the memory is improved.
- the present invention is also directed to a non-volatile memory, a non-volatile memory array and a manufacturing method thereof capable of miniaturizing the memory cells and increasing overall level of integration of devices.
- the non-volatile memory includes a substrate, a first row of memory cells, a first source/drain region and a second source/drain region.
- the first row of memory cells further includes a plurality of stacked gate structures, a plurality of spacers, a plurality of control gates, a plurality of floating gates, a plurality of inter-gate dielectric layers and a plurality of tunneling dielectric layers.
- the stacked gate structures are formed on the substrate and separated from each other by a gap.
- Each stacked gate structure includes, from the substrate surface upward, a select gate dielectric layer, a select gate and a cap layer.
- the spacers are disposed on the sidewalls of the stacked gate structures respectively.
- the control gates are disposed over the substrate filling the gap between every pair of neighboring stacked gate structures. Furthermore, the control gates are connected together through a control gate line.
- the floating gates are disposed between every pair of neighboring stacked gate structures between the control gate and the substrate respectively.
- the inter-gate dielectric layers are disposed between the control gates and the floating gates respectively.
- the tunneling dielectric layers are disposed between the floating gates and the substrate.
- the first source/drain region and the second source/drain region are disposed in the substrate on each side of the first row of memory cells.
- the aforementioned non-volatile memory further includes a second row of memory cells, a second source/drain region and a third source/drain region disposed on the substrate.
- the second row of memory cells is connected with the first row of memory cells by the second source/drain region, wherein the second row of memory cells have structures identical to the first row of memory cells.
- the third source/drain region is disposed in the substrate on the side of the second row of memory cells corresponding to the second source/drain region.
- the level of integration of the memory array is increased.
- the present invention is also directed to a non-volatile memory array including a substrate, a plurality of rows of memory cells, a plurality of control gate lines, a plurality of select gate lines, a plurality of source lines and a plurality of drain lines.
- the rows of memory cells are aligned to form a memory array.
- Each row of memory cells further includes a plurality of stacked gate structures disposed on the substrate and separated from each other by a gap.
- Each stacked gate structure includes, from the substrate surface upward, a select gate dielectric layer, a select gate and a cap layer.
- the spacers are disposed on the sidewalls of the stacked gate structures.
- the floating gates are disposed in the gaps between every pair of neighboring stacked gate structures.
- the tunneling dielectric layer is disposed between the floating gate and the substrate.
- the control gates are disposed between every pair of neighboring stacked gate structures above the floating gate.
- the inter-gate dielectric layers are disposed between the control gates and the floating gates.
- the source/drain regions are disposed in the substrate just outside the outermost two stacked gate structures.
- the control gate lines connect all the control gates in the same row of memory cells.
- the select gate lines connect all the select gates in the same column of memory cells.
- the source lines connect all the source regions in the same column.
- the drain lines connect all the drain regions in the same column.
- the memory array can be further divided into at least a first memory block and a second memory block.
- the drains of each row of memory cells within the first memory block are connected together through a first drain line.
- the drains of each row of memory cells within the second memory block are connected together through a second drain line.
- both the first memory block and the second memory block use a common source line.
- the aforementioned memory cell array may utilize source-side injection to inject electrons into the floating gate of a selected memory cell and program the selected memory cell. Furthermore, the Fowler-Nordheim tunneling effect is utilized to pull the electrons trapped within the floating gate of the memory cells into the substrate so that all the data within the memory array are erased.
- the present invention is also directed to a method of fabricating a non-volatile memory.
- a substrate is provided.
- a plurality of stacked gate structures is formed on the substrate.
- Each stacked gate structure includes a select gate dielectric layer, a select gate and a cap layer.
- a source region and a drain region are formed in the substrate.
- the source region and the drain region are separated from each other by at least two stacked gate structures.
- a tunneling dielectric layer is formed over the substrate and then a first conductive layer is formed over the tunneling dielectric layer.
- the first conductive layer is patterned to form a plurality of floating gate in the gaps between the stacked gate structures.
- a second conductive layer is formed over the substrate.
- the second conductive layer is patterned to form a plurality of mutually linked control gates in the gaps between neighboring stacked gate structures.
- the tunneling dielectric layer can be formed by performing a thermal oxidation process. Furthermore, an additional insulating layer may also be formed over the source/drain region.
- floating gates having concave opening is produced to increase the overlapping area between the floating gate and the control gate.
- the gate-coupling ratio of the memory cells is increased and the required operating voltage is lowered.
- the average operating speed of the memory cell is increased.
- a thick insulating layer is also formed over the source region and the drain region.
- the insulating layer isolates the floating gate and the control gate above the source region and the drain region so that their effects on the source and the drain region are minimized. Since there is no need to perform an extra processing operation to remove the floating gate and the control gate above the source and the drain, the process of fabricating the non-volatile memory is very much simplified.
- FIG. 1 is a schematic cross-sectional view of a portion of a conventional AG_AND memory cell structure.
- FIG. 2A is a top view of a non-volatile memory array according to an embodiment of the present invention.
- FIG. 2B is a schematic cross-sectional view along line A-A′ of FIG. 2A .
- FIGS. 3A through 3E are schematic cross-sectional views along a line A-A′ of FIG. 2A showing the steps for fabricating a non-volatile memory according to an embodiment of the present invention.
- FIG. 4 is a simplified circuit diagram of a non-volatile memory array according to an embodiment of the present invention.
- FIG. 2A is a top view of a non-volatile memory array according to an embodiment of the present invention.
- FIG. 2B is a schematic cross-sectional view along line A-A′ of FIG. 2A .
- the memory array can be divided into a first memory block 200 a and a second memory block 200 b .
- the first memory block 200 a and the second memory block 200 b use a common source region 220 (the source line S). In the following, only the row of memory cells 200 a is discussed.
- the non-volatile memory array of the present invention includes a substrate 200 , a plurality of rows of memory cells QL 1 ⁇ QL 4 , a plurality of control gate lines CG 1 ⁇ CG 4 , a plurality of select gate lines SG 1 ⁇ SG 5 , a source line S and a drain line D.
- the rows of memory cells QL 1 ⁇ QL 4 are aligned to form a memory array.
- the control gate lines CG 1 ⁇ GC 4 connects the control gates of the memory cells in the same row.
- the select gate lines SG 1 ⁇ SG 5 connects the select gates of the memory cells in the same column.
- the source line S connects all the source regions of the rows of memory cells in the same column.
- the drain line D connects all the drain regions of the rows of memory cells in the same column.
- the non-volatile memory structure of the present invention includes at least a substrate 200 , a plurality of stacked gate structures 202 a ⁇ 202 e (each of these stacked gate structures 202 a ⁇ 202 e includes, from the substrate surface upward, a select gate dielectric layer 204 , a select gate 206 and a cap layer 208 ), a plurality of spacers 210 , a plurality of tunneling dielectric layer 212 , a plurality of floating gates 214 a ⁇ 214 f , a plurality of control gates 216 a ⁇ 216 f , a plurality of inter-gate dielectric layers 218 , a plurality of source regions 210 and a plurality of drain regions 222 .
- the substrate 200 is a silicon substrate, for example.
- the stacked gate structures 202 a ⁇ 202 e are disposed on the substrate 200 .
- Each stacked gate structure is a linear strip having a thickness between 2000 ⁇ to 3500 ⁇ , for example.
- the select gate dielectric layer 204 having a thickness between 160 ⁇ ⁇ 170 ⁇ is formed by silicon oxide, for example.
- the select gate 206 having a thickness between 600 ⁇ to 1000 ⁇ is formed by doped polysilicon, for example.
- the cap layer 208 having a thickness between 1000 ⁇ to 1500 ⁇ is formed by silicon oxide, for example.
- the spacer is disposed on the sidewalls of the stacked gate structures 202 a ⁇ 202 e .
- the spacer is formed by silicon oxide or silicon nitride, for example.
- the control gates 216 a ⁇ 216 d are disposed on the substrate 200 filling the gap between every pair of neighboring stacked gate structures 202 a ⁇ 202 e . Furthermore, the control gates 216 a ⁇ 216 d are connected together through the control gate lines 216 .
- the control gates 216 a ⁇ 216 d and the control gate lines 216 are formed together as an integrative unit. In other words, the control gates 216 a ⁇ 216 d extend over the stacked gate structures and link with each other to form the control gate lines 216 .
- the control gate lines 216 is roughly perpendicular to the stacked gate structures 202 a ⁇ 202 e .
- the control gates 216 a ⁇ 216 d are formed by doped polysilicon, for example.
- the floating gates 214 a ⁇ 214 d are disposed in the gaps between every pair of neighboring stacked gates 202 a ⁇ 202 e and positioned between the control gates 216 a ⁇ 216 d and the substrate 200 .
- Each of the floating gates 214 a ⁇ 214 d has a concave opening 215 , for example.
- the upper surface of the floating gates 214 a ⁇ 214 d are located on one side of the stacked gate structure 202 a ⁇ 202 e between the upper surface of the select gate 206 and the upper surface of the cap layer 208 .
- the floating gates 214 a ⁇ 214 d are formed by doped polysilicon, for example.
- the tunneling dielectric layer 212 is disposed between the floating gates 214 a ⁇ 214 d and the substrate 200 .
- the tunneling dielectric layer is a silicon oxide layer having a thickness between 60 ⁇ ⁇ 90 ⁇ , for example.
- the inter-gate dielectric layer 218 is disposed between the control gates 216 a ⁇ 216 d and the floating gates 214 a ⁇ 214 d .
- the inter-gate dielectric layer 218 is a composite layer including a silicon oxide, silicon nitride and silicon oxide layer each having a thickness of about 70 A.
- the inter-gate dielectric layer 218 can be a composite layer including a silicon oxide and a silicon nitride layer.
- the inter-gate dielectric layer 218 also covers the upper surface of the stacked gate structures 202 a ⁇ 202 e.
- the stacked gate structures 202 a ⁇ 202 e , the spacers 210 , the tunneling dielectric layers 212 , the floating gates 214 a ⁇ 214 d , the control gates 216 a ⁇ 216 d and the inter-gate dielectric layer together constitute a row of memory cells 230 .
- the source region 222 and the drain region 220 are disposed in the substrate 200 on each side of the row of memory cells 230 .
- the drain region 220 is disposed in the substrate 200 on one side of the stacked gate structure 202 a while the source region 222 is disposed in the substrate 200 on one side of the stacked gate structure 202 e .
- the drain region 220 and the source region 222 are disposed in the substrate 200 just outside the two outermost stacked gate structures ( 202 a and 202 e ) of the row of connected memory cells 230 .
- the stacked structures including control gates 216 a ⁇ 216 d and floating gates 214 a 214 d respectively and the stacked gate structures 202 a ⁇ 202 d together form memory cell structures 226 a ⁇ 226 d .
- the stacked gate structure 202 e closest to the source region 222 also serves as a switching transistor. Because there is no gap between memory cell structures 226 a ⁇ 226 d and the stacked gate structure 202 e , the row of memory cells can have a higher level of integration.
- an insulating layer 224 is disposed over the drain region 220 and the source region 222 respectively.
- the insulating layer 224 is fabricated using silicon oxide, for example.
- the insulating layer 224 serves to isolate the stacked gate structure including the control gate 216 f and the floating gate 214 f and the drain region 220 as well as the stacked gate structure including the control gate 216 e and the floating gate 214 e and the source region 222 .
- the operation of the control gate 216 f and the floating gate 214 f above the drain region 220 and the control gate 216 e and the floating gate 214 e above the source region 222 have no effect on the drain region 220 and the source region 222 respectively.
- the floating gates 214 a ⁇ 214 d all have a concave opening 215 , overlapping area between various floating gates 214 a ⁇ 214 d and their corresponding control gates 216 a ⁇ 216 d is increased thereby increasing their gate-coupling ratio.
- the memory cells can have a lower operating voltage, a higher operating speed and a better overall performance.
- four memory cell structures 226 a ⁇ 226 d are serially connected together.
- the number of memory cells that are serially connected together may vary according to actual requirements.
- the same control gate line may link together 32 to 64 memory cell structures.
- FIGS. 3A through 3E are schematic cross-sectional views along a line A-A′ of FIG. 2A showing the steps of fabricating a non-volatile memory according to one embodiment of the present invention.
- a substrate 300 such as a silicon substrate is provided.
- a plurality of stacked gate structures 308 each including a dielectric layer 302 , a conductive layer 304 and a cap layer 306 is formed over the substrate 300 .
- the stacked gate structures 308 are formed, for example, by depositing dielectric material, conductive material and cap material in sequence over the substrate 300 and patterning the dielectric layer, the conductive layer and the cap layer in photolithographic and etching processes thereafter.
- the dielectric layer is a silicon oxide layer formed, for example, by performing a thermal oxidation process.
- the conductive layer is a doped polysilicon layer formed, for example, by performing a chemical vapor deposition process and implanting ions into the doped polysilicon layer thereafter.
- the cap layer is a silicon oxide layer formed, for example, by performing a chemical vapor deposition process using tetra-ethyl-ortho-silicate (TEOS)/ozone (O 3 ) as the gaseous reactants.
- TEOS tetra-ethyl-ortho-silicate
- O 3 ozone
- a spacer 310 is formed on the sidewall of the stacked gate structures 308 .
- the spacers 310 are silicon oxide or silicon nitride layers are formed, for example, by depositing insulating material over the substrate and performing an anisotropic ion etching process thereafter.
- a mask layer 312 is formed over the substrate 300 .
- the mask layer 312 has openings 314 that expose the areas on the substrate 300 for forming a source region 316 and a drain region 318 .
- the mask layer 312 is a photoresist layer.
- a source region 316 and a drain region 318 are formed in the substrate 300 by performing an ion implantation process, for example.
- the source region 316 and the drain region 318 are separated from each other by at least two stacked gate structures 308 .
- a tunneling dielectric layer 320 is formed over the substrate 300 and an insulating layer 322 is formed over the source region 316 and the drain region 318 .
- the tunneling dielectric layer 320 and the insulating layer 322 are silicon oxide layer formed by performing a thermal oxidation process, for example.
- the source region 316 and the drain region contain dopants, the oxidation rate is higher than other areas free of dopants since the insulating layer 322 is formed over the source region 316 and the drain region 318 . Consequently, the insulating layer 322 has a thickness greater than the tunneling dielectric layer 320 .
- the conductive layer is a doped polysilicon layer formed, for example, by depositing an undoped polysilicon layer over the substrate in a chemical vapor deposition and then performing an ion implantation process.
- the conductive layer 324 is a conformal layer over the substrate 300 such that the gap between neighboring stacked gate structures 308 is unfilled.
- the conductive layer 324 is patterned to form a plurality of floating gates 326 .
- the floating gates 326 are formed, for example, by depositing a material over the substrate 300 to form a material layer (not shown) that completely fills the gaps between the stacked gate structures 308 .
- the material layer has an upper surface lying between the upper surface of the cap layer 306 and the upper surface of the conductive layer 304 .
- the material layer is a photoresist layer or an anti-reflection coating formed, for example, by spin coating to form the material layer and then etching back the material layer. Thereafter, using the material layer as a mask, a portion of the conductive layer 324 is removed.
- the upper surface of the connective sections between the conductive layer 324 and the stacked gate structures 308 is located between the upper surface of the conductive layer 304 and the cap layer 306 .
- photolithographic and etching processes are carried out to remove a portion of the conductive layer 324 so that the conductive layer 324 is dissected into a plurality of blocks thereby forming floating gates 326 between the stacked gate structures 308 .
- Each floating gate 326 has a concave opening 327 for increasing the overlapping area with a subsequently formed control gate.
- a portion of the conductive layer 324 can be directly removed by performing an etching back process instead of using the material layer so that the conductive layer 324 has an upper surface between the conductive layer 304 and the cap layer 306 . Thereafter, a portion of the conductive layer 324 is removed to dissect the conductive layer 324 into separate blocks of floating gates 326 .
- the step of dissecting the conductive layer 324 into a plurality of blocks is skipped altogether. Instead, the conductive layer 324 is dissected to form a plurality of floating gates 326 later on in a subsequent process for fabricating the control gate by using the control gate as a mask.
- an inter-gate dielectric layer 328 is formed over the substrate 300 .
- the inter-gate dielectric layer 328 is a silicon oxide, silicon nitride, silicon oxide composite layer, for example.
- the inter-gate dielectric layer is formed, for example, by performing a thermal oxidation process to form a silicon oxide layer and then forming a silicon nitride layer and another silicon oxide layer in sequence in a chemical vapor deposition process.
- another conductive layer (not shown) is formed over the substrate 300 .
- the conductive layer completely fills the gaps between the stacked gate structures 308 .
- the conductive layer is formed, for example, by depositing conductive material over the substrate and performing a chemical-mechanical polishing or an etching back process to planarize the conductive material layer.
- the conductive layer is a doped polysilicon layer formed, for example, by depositing undoped polysilicon material to form an undoped polysilicon layer in a chemical vapor deposition process and then implanting ions to transform the undoped polysilicon layer into a doped polysilicon layer.
- the conductive layer is patterned to form a word line 330 such that the word line 330 fills the gaps between the stacked gate structures 308 .
- the control gate line 330 above the floating gate 326 serves as a control gate 330 a .
- the control gate 330 a extends into the surface of the stacked gate structure 308 to connect with each other.
- all floating gates 326 have a concave opening so that the overlapping area between the floating gate 326 and the control gate 330 a is increased. Hence, the gate-coupling ratio of the memory cells is increased and the required operating voltage is lowered. Ultimately, the average operating speed of the memory cell is increased.
- insulating layer 322 is also formed over the source region 316 and the drain region 318 .
- the insulating layer 322 isolates the floating gate 326 and the control gate 330 a above the source region 316 and the drain region 318 so that their effects on the source region 316 and the drain region 318 are minimized.
- four memory cell structures are serially connected together.
- the number of memory cells that are serially connected together in a row may vary according to actual requirements. For example, a single bit line may link together 32 to 64 memory cell structures.
- the method of fabricating a row of memory cells can be directly applied to manufacture an entire memory cell array.
- FIG. 4 is a simplified circuit diagram of a non-volatile memory array according to the present invention.
- the memory is divided into a first memory block BLOCK 1 and a second memory block BLOCK 2 .
- the memory block BLOCK 1 having altogether 16 memory cells is used as an example to illustrate the operation of a memory array in the present invention.
- each of the memory cells Q 11 ⁇ Q 44 has a select gate, a control gate and a floating gate.
- the source line S and the drain line extend in the column direction. In the column direction, the drain line D and the source line S link up a plurality of memory cells.
- Each row of memory cells includes four memory cells and a switching transistor serially connected together. For example, the memory cells Q 11 ⁇ Q 14 and the switching transistor T 1 are serially connected together.
- the memory cells Q 21 ⁇ Q 24 and the switching transistor T 2 are serially connected together, the memory cells Q 31 ⁇ Q 34 and the transistor T 3 are serially connected together and the memory cells Q 41 ⁇ Q 44 and the transistor T 4 are serially connected together.
- the control gate lines CG 1 ⁇ CG 4 connect all the control gates of the memory cells in various rows.
- the control gate line CG 1 connects the control gates of the memory cells Q 11 ⁇ Q 14 .
- the control gate line CG 2 connects the control gates of the memory cells Q 21 ⁇ Q 24
- the control gate line CG 3 connects the control gates of the memory cells Q 31 ⁇ Q 34
- the control gate line CG 4 connects the control gates of the memory cells Q 41 ⁇ Q 44 .
- the select gates SG 1 ⁇ SG 4 connect the select gates of the memory cells in various columns.
- the select gate SG 1 connect the select gates of the memory cells Q 1 ⁇ Q 41 .
- the select gate SG 2 connect the select gates of the memory cells Q 12 ⁇ Q 42
- the select gate SG 3 connect the select gates of the memory cells Q 13 ⁇ Q 43
- the select gate SG 4 connect the select gates of the memory cells Q 14 ⁇ Q 44 .
- the select gate SG 5 connects the gates of the switching transistors T 1 ⁇ T 4 in the same column.
- a 5V bias voltage is applied to the source line S
- a 1.5V bias voltage is applied to the selected gate line SG 2
- an 8V bias voltage is applied to the non-selected gate lines SG 1 , SG 3 and SG 4
- an 8V bias voltage is applied to the select gate line SG 5
- a 10 ⁇ 12V bias voltage is applied to the control gate line CG 1
- a 0 ⁇ 2V bias voltage is applied to the non-selected control gate lines CG 2 , CG 3 and CG 4 and the substrate and the drain line D is connected to a ground.
- SSI source-side injection
- a 0V bias voltage is applied to the source line S
- a 4.5V bias voltage is applied to the select gate lines SG 1 ⁇ SG 5
- a 3V bias voltage is applied to the control gate line CG 1
- a 2V bias is applied to the drain line D.
- a ⁇ 20V bias voltage is applied to the control gate line CG 1 and a 0V bias voltage is applied to the substrate so that the Fowler-Nordheim (F-N) tunneling effect can be utilized to pull trapped electrons within the floating gate of the memory cells into the substrate.
- F-N Fowler-Nordheim
- the hot carrier effect is utilized to program a single bit of data into a single memory cell but the F-N tunneling effect is utilized to erase the data in the entire memory cell array.
- the electron injection efficiency is relatively high. In other words, the operating memory cell current is lowered and the operating speed is increased. With a reduction in the memory cell current, the average power consumption of the memory chip is reduced.
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Abstract
A method of operating a non-volatile memory array is provided. The non-volatile memory array includes a substrate, a number of rows of memory cells, a number of control gate lines, a number of select gate lines, a number of source lines, and a number of drain lines. The operating method includes applying 5V voltage to a selected source line, 1.5V voltage to a selected select gate line, 8V voltage to non-selected select gate lines, 10-12V voltage to a selected control gate line and 0-−2V voltage to non-selected control gate lines and the substrate. The drain lines are grounded so that source-side injection (SSI) is triggered to inject electrons into a floating gate of the selected memory cell in a programming operation.
Description
- This is a divisional application of patent application Ser. No. 11/621,095, filed on Jan. 8, 2007, now allowed, which is a divisional application of patent application Ser. No. 10/904,478, filed on Nov. 12, 2004 and allowed as U.S. Pat. No. 7,180,128, granted on Feb. 20, 2007, which claims the priority benefit of Taiwan patent application serial no. 93113274, filed on May 12, 2004 and is now allowed. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.
- 1. Field of the Invention
- The present invention relates to a semiconductor device. More particularly, the present invention relates to a method of manufacturing a non-volatile memory and a method of operating a non-volatile memory array.
- 2. Description of Related Art
- Electrically erasable programmable read only memory (EEPROM) is a type of non-volatile memory that allows multiple data reading, writing and erasing operations. In addition, the stored data will be retained even after power to the device is removed. With these advantages, it has been broadly applied in personal computer and electronic equipment.
- A typical EEPROM has a floating gate and a control gate fabricated using doped polysilicon. To prevent erroneous reading resulting from the over-erasure of the EEPROM during an erasing operation, a select gate is set up above the substrate on the sidewall of the control gate and the floating gate forming a so-called split-gate structure.
- At present, the industry has developed an AG-AND memory cell array fabricated using a split-gate memory cells (refer to U.S. Pat. No. 6,567,315).
FIG. 1 is a schematic cross-sectional view of a portion of a conventional AG_AND memory cell structure. As shown inFIG. 1 , the AG-AND memory cell structure includes asubstrate 100, awell region 102, an auxiliary gate transistor Qa1 (Qa2), a memory device Qm1 (Qm2) and source/drain regions substrate 100 on one side of the auxiliary gate transistor Qa1 (Qa2) and the memory device Qm1 (Qm2) respectively. The auxiliary gate transistor Qa1 (Qa2) includes anauxiliary gate 106 a and the memory device Qm1 (Qm2) includes afloating gate 108 a (108 b) and a word line 110. The word line 110 serves as a control gate for the memory device Qm1 (Qm2). The auxiliary gate transistor Qa1 (Qa2) and the memory device Qm1 (Qm2) together form a memory cell Q1 (Q2). In an AG-AND array, neighboring memory cells in the row direction use a common source/drain region. - To program memory cell Q1 of the aforementioned AG-AND memory cell array, a 13V bias voltage is applied to the word line 110, a 1V bias voltage is applied to the
auxiliary gate 106 a, a 0V bias voltage is applied to the source/drain region 104 a and a 5V bias voltage is applied to the source/drain region 104 b. Thus, electrons are injected into thefloating gate 108 a of the memory device Qm1 to program the memory cell Q1. Because a bias voltage is not applied to theauxiliary gate 106 b, the memory cell Q2 is not programmed. - However, in the aforementioned AG-AND memory cell structure, a source/drain region (104 a, 104 b or 104 c) is formed in the
substrate 100 on each side of the memory cell Q1 (Q2). To prevent the source/drain region (104 a, 104 b or 104 c) from getting too close to the conductive channels underneath the memory cell, the source/drain regions (104 a, 104 b or 104 c) have to be separate from each other by a definite distance. This precludes any further miniaturization of the memory cell array. - Accordingly, the present invention is directed to a non-volatile memory, a non-volatile memory array and a manufacturing method thereof capable of simplifying the fabrication of non-volatile memory array. The non-volatile memory is also programmed using a source-side injection (SSI) method so that the average programming speed of the memory cells is increased and overall performance of the memory is improved.
- The present invention is also directed to a non-volatile memory, a non-volatile memory array and a manufacturing method thereof capable of increasing the overlapping area between the floating gate and the control gate inside the memory. Hence, the coupling ratio of the gates inside the memory is increased and overall performance of the memory is improved.
- The present invention is also directed to a non-volatile memory, a non-volatile memory array and a manufacturing method thereof capable of miniaturizing the memory cells and increasing overall level of integration of devices.
- According to an embodiment of the present invention, the non-volatile memory includes a substrate, a first row of memory cells, a first source/drain region and a second source/drain region. The first row of memory cells further includes a plurality of stacked gate structures, a plurality of spacers, a plurality of control gates, a plurality of floating gates, a plurality of inter-gate dielectric layers and a plurality of tunneling dielectric layers. The stacked gate structures are formed on the substrate and separated from each other by a gap. Each stacked gate structure includes, from the substrate surface upward, a select gate dielectric layer, a select gate and a cap layer. The spacers are disposed on the sidewalls of the stacked gate structures respectively. The control gates are disposed over the substrate filling the gap between every pair of neighboring stacked gate structures. Furthermore, the control gates are connected together through a control gate line. The floating gates are disposed between every pair of neighboring stacked gate structures between the control gate and the substrate respectively. The inter-gate dielectric layers are disposed between the control gates and the floating gates respectively. The tunneling dielectric layers are disposed between the floating gates and the substrate. The first source/drain region and the second source/drain region are disposed in the substrate on each side of the first row of memory cells.
- The aforementioned non-volatile memory further includes a second row of memory cells, a second source/drain region and a third source/drain region disposed on the substrate. The second row of memory cells is connected with the first row of memory cells by the second source/drain region, wherein the second row of memory cells have structures identical to the first row of memory cells. The third source/drain region is disposed in the substrate on the side of the second row of memory cells corresponding to the second source/drain region.
- Since no contacts and device isolation structures are formed between various rows of memory cells in the non-volatile memory according to an embodiment of the present invention, the level of integration of the memory array is increased.
- The present invention is also directed to a non-volatile memory array including a substrate, a plurality of rows of memory cells, a plurality of control gate lines, a plurality of select gate lines, a plurality of source lines and a plurality of drain lines. The rows of memory cells are aligned to form a memory array. Each row of memory cells further includes a plurality of stacked gate structures disposed on the substrate and separated from each other by a gap. Each stacked gate structure includes, from the substrate surface upward, a select gate dielectric layer, a select gate and a cap layer. The spacers are disposed on the sidewalls of the stacked gate structures. The floating gates are disposed in the gaps between every pair of neighboring stacked gate structures. The tunneling dielectric layer is disposed between the floating gate and the substrate. The control gates are disposed between every pair of neighboring stacked gate structures above the floating gate. The inter-gate dielectric layers are disposed between the control gates and the floating gates. The source/drain regions are disposed in the substrate just outside the outermost two stacked gate structures. The control gate lines connect all the control gates in the same row of memory cells. The select gate lines connect all the select gates in the same column of memory cells. The source lines connect all the source regions in the same column. The drain lines connect all the drain regions in the same column.
- In the aforementioned non-volatile memory array, the memory array can be further divided into at least a first memory block and a second memory block. The drains of each row of memory cells within the first memory block are connected together through a first drain line. Similarly, the drains of each row of memory cells within the second memory block are connected together through a second drain line. Furthermore, both the first memory block and the second memory block use a common source line.
- The aforementioned memory cell array may utilize source-side injection to inject electrons into the floating gate of a selected memory cell and program the selected memory cell. Furthermore, the Fowler-Nordheim tunneling effect is utilized to pull the electrons trapped within the floating gate of the memory cells into the substrate so that all the data within the memory array are erased.
- According to an embodiment of the present invention, there is no gap between the various memory cell structures in the non-volatile memory array. Hence, the level of integration of the memory cell array is increased.
- Since no contacts and device isolation structures are formed between various rows of memory cells in the non-volatile memory array of the present invention, the level of integration of the memory array is increased.
- The present invention is also directed to a method of fabricating a non-volatile memory. First, a substrate is provided. A plurality of stacked gate structures is formed on the substrate. Each stacked gate structure includes a select gate dielectric layer, a select gate and a cap layer. Thereafter, a source region and a drain region are formed in the substrate. The source region and the drain region are separated from each other by at least two stacked gate structures. A tunneling dielectric layer is formed over the substrate and then a first conductive layer is formed over the tunneling dielectric layer. The first conductive layer is patterned to form a plurality of floating gate in the gaps between the stacked gate structures. After forming an inter-gate dielectric layer over the substrate, a second conductive layer is formed over the substrate. The second conductive layer is patterned to form a plurality of mutually linked control gates in the gaps between neighboring stacked gate structures.
- According to an embodiment of the present invention, the tunneling dielectric layer can be formed by performing a thermal oxidation process. Furthermore, an additional insulating layer may also be formed over the source/drain region.
- According to an embodiment of the present invention, floating gates having concave opening is produced to increase the overlapping area between the floating gate and the control gate. Hence, the gate-coupling ratio of the memory cells is increased and the required operating voltage is lowered. Ultimately, the average operating speed of the memory cell is increased.
- Furthermore, a thick insulating layer is also formed over the source region and the drain region. The insulating layer isolates the floating gate and the control gate above the source region and the drain region so that their effects on the source and the drain region are minimized. Since there is no need to perform an extra processing operation to remove the floating gate and the control gate above the source and the drain, the process of fabricating the non-volatile memory is very much simplified.
- In addition, no device isolation structures are set up between various rows of memory cells. Hence, the number of processing steps can be reduced and the level of integration of the memory array can be increased.
- It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
- The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
-
FIG. 1 is a schematic cross-sectional view of a portion of a conventional AG_AND memory cell structure. -
FIG. 2A is a top view of a non-volatile memory array according to an embodiment of the present invention. -
FIG. 2B is a schematic cross-sectional view along line A-A′ ofFIG. 2A . -
FIGS. 3A through 3E are schematic cross-sectional views along a line A-A′ ofFIG. 2A showing the steps for fabricating a non-volatile memory according to an embodiment of the present invention. -
FIG. 4 is a simplified circuit diagram of a non-volatile memory array according to an embodiment of the present invention. - Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
-
FIG. 2A is a top view of a non-volatile memory array according to an embodiment of the present invention.FIG. 2B is a schematic cross-sectional view along line A-A′ ofFIG. 2A . As shown inFIGS. 2A and 2B , the memory array can be divided into afirst memory block 200 a and asecond memory block 200 b. Thefirst memory block 200 a and thesecond memory block 200 b use a common source region 220 (the source line S). In the following, only the row ofmemory cells 200 a is discussed. - As shown in
FIG. 2A , the non-volatile memory array of the present invention includes asubstrate 200, a plurality of rows of memory cells QL1˜QL4, a plurality of control gate lines CG1˜CG4, a plurality of select gate lines SG1˜SG5, a source line S and a drain line D. - The rows of memory cells QL1˜QL4 are aligned to form a memory array. The control gate lines CG1˜GC4 connects the control gates of the memory cells in the same row. The select gate lines SG1˜SG5 connects the select gates of the memory cells in the same column. The source line S connects all the source regions of the rows of memory cells in the same column. The drain line D connects all the drain regions of the rows of memory cells in the same column.
- In the following, the rows of non-volatile memory cell structure are explained using a single row of memory cells QL1 as an example.
- As shown in
FIGS. 2A and 2B , the non-volatile memory structure of the present invention includes at least asubstrate 200, a plurality of stacked gate structures 202 a˜202 e (each of these stacked gate structures 202 a˜202 e includes, from the substrate surface upward, a selectgate dielectric layer 204, aselect gate 206 and a cap layer 208), a plurality ofspacers 210, a plurality of tunnelingdielectric layer 212, a plurality of floating gates 214 a˜214 f, a plurality ofcontrol gates 216 a˜216 f, a plurality of inter-gatedielectric layers 218, a plurality ofsource regions 210 and a plurality of drain regions 222. - The
substrate 200 is a silicon substrate, for example. The stacked gate structures 202 a˜202 e are disposed on thesubstrate 200. Each stacked gate structure is a linear strip having a thickness between 2000 Å to 3500 Å, for example. The selectgate dielectric layer 204 having a thickness between 160 Ř170 Å is formed by silicon oxide, for example. Theselect gate 206 having a thickness between 600 Å to 1000 Å is formed by doped polysilicon, for example. Thecap layer 208 having a thickness between 1000 Å to 1500 Å is formed by silicon oxide, for example. The spacer is disposed on the sidewalls of the stacked gate structures 202 a˜202 e. The spacer is formed by silicon oxide or silicon nitride, for example. - The
control gates 216 a˜216 d are disposed on thesubstrate 200 filling the gap between every pair of neighboring stacked gate structures 202 a˜202 e. Furthermore, thecontrol gates 216 a˜216 d are connected together through the control gate lines 216. Thecontrol gates 216 a˜216 d and thecontrol gate lines 216 are formed together as an integrative unit. In other words, thecontrol gates 216 a˜216 d extend over the stacked gate structures and link with each other to form the control gate lines 216. Thecontrol gate lines 216 is roughly perpendicular to the stacked gate structures 202 a˜202 e. Thecontrol gates 216 a˜216 d are formed by doped polysilicon, for example. - The floating gates 214 a˜214 d are disposed in the gaps between every pair of neighboring stacked gates 202 a˜202 e and positioned between the
control gates 216 a˜216 d and thesubstrate 200. Each of the floating gates 214 a˜214 d has aconcave opening 215, for example. Furthermore, the upper surface of the floating gates 214 a˜214 d are located on one side of the stacked gate structure 202 a˜202 e between the upper surface of theselect gate 206 and the upper surface of thecap layer 208. Typically, the floating gates 214 a˜214 d are formed by doped polysilicon, for example. - The
tunneling dielectric layer 212 is disposed between the floating gates 214 a˜214 d and thesubstrate 200. Typically, the tunneling dielectric layer is a silicon oxide layer having a thickness between 60 Ř90 Å, for example. The inter-gatedielectric layer 218 is disposed between thecontrol gates 216 a˜216 d and the floating gates 214 a˜214 d. Typically, the inter-gatedielectric layer 218 is a composite layer including a silicon oxide, silicon nitride and silicon oxide layer each having a thickness of about 70A. Obviously, the inter-gatedielectric layer 218 can be a composite layer including a silicon oxide and a silicon nitride layer. The inter-gatedielectric layer 218 also covers the upper surface of the stacked gate structures 202 a˜202 e. - The stacked gate structures 202 a˜202 e, the
spacers 210, the tunnelingdielectric layers 212, the floating gates 214 a˜214 d, thecontrol gates 216 a˜216 d and the inter-gate dielectric layer together constitute a row ofmemory cells 230. The source region 222 and thedrain region 220 are disposed in thesubstrate 200 on each side of the row ofmemory cells 230. For example, thedrain region 220 is disposed in thesubstrate 200 on one side of the stacked gate structure 202 a while the source region 222 is disposed in thesubstrate 200 on one side of thestacked gate structure 202 e. In other words, thedrain region 220 and the source region 222 are disposed in thesubstrate 200 just outside the two outermost stacked gate structures (202 a and 202 e) of the row ofconnected memory cells 230. - In the aforementioned row-connected
memory cell structure 230, the stacked structures includingcontrol gates 216 a˜216 d and floating gates 214 a 214 d respectively and the stacked gate structures 202 a˜202 d together formmemory cell structures 226 a˜226 d. Thestacked gate structure 202 e closest to the source region 222 also serves as a switching transistor. Because there is no gap betweenmemory cell structures 226 a˜226 d and thestacked gate structure 202 e, the row of memory cells can have a higher level of integration. Furthermore, an insulating layer 224 is disposed over thedrain region 220 and the source region 222 respectively. The insulating layer 224 is fabricated using silicon oxide, for example. The insulating layer 224 serves to isolate the stacked gate structure including thecontrol gate 216 f and the floatinggate 214 f and thedrain region 220 as well as the stacked gate structure including thecontrol gate 216 e and the floatinggate 214 e and the source region 222. Hence, the operation of thecontrol gate 216 f and the floatinggate 214 f above thedrain region 220 and thecontrol gate 216 e and the floatinggate 214 e above the source region 222 have no effect on thedrain region 220 and the source region 222 respectively. - Furthermore, because the floating gates 214 a˜214 d all have a
concave opening 215, overlapping area between various floating gates 214 a˜214 d and theircorresponding control gates 216 a˜216 d is increased thereby increasing their gate-coupling ratio. In other words, the memory cells can have a lower operating voltage, a higher operating speed and a better overall performance. - In the aforementioned embodiment, four
memory cell structures 226 a˜226 d are serially connected together. Clearly, the number of memory cells that are serially connected together may vary according to actual requirements. For example, the same control gate line may link together 32 to 64 memory cell structures. - Furthermore, in the memory cell array shown in
FIG. 2A , no device isolation structures or contacts are fabricated between various rows of memory cells. Thus, the level of integration of the memory array is increased. -
FIGS. 3A through 3E are schematic cross-sectional views along a line A-A′ ofFIG. 2A showing the steps of fabricating a non-volatile memory according to one embodiment of the present invention. First, as shown inFIG. 3A , asubstrate 300 such as a silicon substrate is provided. A plurality of stackedgate structures 308 each including adielectric layer 302, aconductive layer 304 and acap layer 306 is formed over thesubstrate 300. Thestacked gate structures 308 are formed, for example, by depositing dielectric material, conductive material and cap material in sequence over thesubstrate 300 and patterning the dielectric layer, the conductive layer and the cap layer in photolithographic and etching processes thereafter. The dielectric layer is a silicon oxide layer formed, for example, by performing a thermal oxidation process. The conductive layer is a doped polysilicon layer formed, for example, by performing a chemical vapor deposition process and implanting ions into the doped polysilicon layer thereafter. The cap layer is a silicon oxide layer formed, for example, by performing a chemical vapor deposition process using tetra-ethyl-ortho-silicate (TEOS)/ozone (O3) as the gaseous reactants. Theconductive layer 304 serves as a select gate and thedielectric layer 302 serves as a select gate dielectric layer. - As shown in
FIG. 3B , aspacer 310 is formed on the sidewall of the stackedgate structures 308. Thespacers 310 are silicon oxide or silicon nitride layers are formed, for example, by depositing insulating material over the substrate and performing an anisotropic ion etching process thereafter. Amask layer 312 is formed over thesubstrate 300. Themask layer 312 hasopenings 314 that expose the areas on thesubstrate 300 for forming asource region 316 and adrain region 318. Typically, themask layer 312 is a photoresist layer. Thereafter, using themask layer 312 as a mask, asource region 316 and adrain region 318 are formed in thesubstrate 300 by performing an ion implantation process, for example. Thesource region 316 and thedrain region 318 are separated from each other by at least twostacked gate structures 308. - After removing the
mask layer 312, atunneling dielectric layer 320 is formed over thesubstrate 300 and an insulatinglayer 322 is formed over thesource region 316 and thedrain region 318. Thetunneling dielectric layer 320 and the insulatinglayer 322 are silicon oxide layer formed by performing a thermal oxidation process, for example. Thesource region 316 and the drain region contain dopants, the oxidation rate is higher than other areas free of dopants since the insulatinglayer 322 is formed over thesource region 316 and thedrain region 318. Consequently, the insulatinglayer 322 has a thickness greater than the tunnelingdielectric layer 320. - As shown in
FIG. 3C , anotherconductive layer 324 is formed over thesubstrate 300. The conductive layer is a doped polysilicon layer formed, for example, by depositing an undoped polysilicon layer over the substrate in a chemical vapor deposition and then performing an ion implantation process. Theconductive layer 324 is a conformal layer over thesubstrate 300 such that the gap between neighboringstacked gate structures 308 is unfilled. - As shown in
FIG. 3D , theconductive layer 324 is patterned to form a plurality of floatinggates 326. The floatinggates 326 are formed, for example, by depositing a material over thesubstrate 300 to form a material layer (not shown) that completely fills the gaps between thestacked gate structures 308. The material layer has an upper surface lying between the upper surface of thecap layer 306 and the upper surface of theconductive layer 304. The material layer is a photoresist layer or an anti-reflection coating formed, for example, by spin coating to form the material layer and then etching back the material layer. Thereafter, using the material layer as a mask, a portion of theconductive layer 324 is removed. Hence, the upper surface of the connective sections between theconductive layer 324 and thestacked gate structures 308 is located between the upper surface of theconductive layer 304 and thecap layer 306. After removing the material layer, photolithographic and etching processes are carried out to remove a portion of theconductive layer 324 so that theconductive layer 324 is dissected into a plurality of blocks thereby forming floatinggates 326 between thestacked gate structures 308. Each floatinggate 326 has aconcave opening 327 for increasing the overlapping area with a subsequently formed control gate. - In the process of forming the floating
gates 326 according to another embodiment, a portion of theconductive layer 324 can be directly removed by performing an etching back process instead of using the material layer so that theconductive layer 324 has an upper surface between theconductive layer 304 and thecap layer 306. Thereafter, a portion of theconductive layer 324 is removed to dissect theconductive layer 324 into separate blocks of floatinggates 326. - In the process of forming the floating
gates 326 according to yet another embodiment, the step of dissecting theconductive layer 324 into a plurality of blocks is skipped altogether. Instead, theconductive layer 324 is dissected to form a plurality of floatinggates 326 later on in a subsequent process for fabricating the control gate by using the control gate as a mask. - Thereafter, an inter-gate
dielectric layer 328 is formed over thesubstrate 300. The inter-gatedielectric layer 328 is a silicon oxide, silicon nitride, silicon oxide composite layer, for example. The inter-gate dielectric layer is formed, for example, by performing a thermal oxidation process to form a silicon oxide layer and then forming a silicon nitride layer and another silicon oxide layer in sequence in a chemical vapor deposition process. - As shown in
FIG. 3E , another conductive layer (not shown) is formed over thesubstrate 300. The conductive layer completely fills the gaps between thestacked gate structures 308. The conductive layer is formed, for example, by depositing conductive material over the substrate and performing a chemical-mechanical polishing or an etching back process to planarize the conductive material layer. The conductive layer is a doped polysilicon layer formed, for example, by depositing undoped polysilicon material to form an undoped polysilicon layer in a chemical vapor deposition process and then implanting ions to transform the undoped polysilicon layer into a doped polysilicon layer. Thereafter, the conductive layer is patterned to form aword line 330 such that theword line 330 fills the gaps between thestacked gate structures 308. Thecontrol gate line 330 above the floatinggate 326 serves as a control gate 330 a. In other words, the control gate 330 a extends into the surface of thestacked gate structure 308 to connect with each other. Thereafter, a few more steps are still required to complete the process of fabricating the memory array. Since these are conventional steps, detailed descriptions are omitted. - In the aforementioned embodiment, all floating
gates 326 have a concave opening so that the overlapping area between the floatinggate 326 and the control gate 330 a is increased. Hence, the gate-coupling ratio of the memory cells is increased and the required operating voltage is lowered. Ultimately, the average operating speed of the memory cell is increased. - Furthermore, a thick
insulating layer 322 is also formed over thesource region 316 and thedrain region 318. The insulatinglayer 322 isolates the floatinggate 326 and the control gate 330 a above thesource region 316 and thedrain region 318 so that their effects on thesource region 316 and thedrain region 318 are minimized. - Since there is no need to perform an extra processing operation to remove the floating
gate 326 and the control gate 330 a above thesource 316 and thedrain 318, the process of fabricating the non-volatile memory is simplified. - In addition, no device isolation structures are set up between various rows of memory cells. Hence, the number of processing steps can be reduced and the level of integration of the memory array can be increased.
- In the aforementioned embodiment, four memory cell structures are serially connected together. Clearly, the number of memory cells that are serially connected together in a row may vary according to actual requirements. For example, a single bit line may link together 32 to 64 memory cell structures. Furthermore, the method of fabricating a row of memory cells can be directly applied to manufacture an entire memory cell array.
-
FIG. 4 is a simplified circuit diagram of a non-volatile memory array according to the present invention. InFIG. 4 , the memory is divided into a first memory block BLOCK1 and a second memory block BLOCK2. In the following, the memory block BLOCK1 having altogether 16 memory cells is used as an example to illustrate the operation of a memory array in the present invention. - As shown in
FIG. 4 , there are 16 memory cells Q11˜Q44, four switching transistors T1˜T4, five select gate lines SG1˜SG5, four control gate lines CG1˜CG4, a source line S and a drain line D in the memory block BLOCK1. Each of the memory cells Q11˜Q44 has a select gate, a control gate and a floating gate. The source line S and the drain line extend in the column direction. In the column direction, the drain line D and the source line S link up a plurality of memory cells. Each row of memory cells includes four memory cells and a switching transistor serially connected together. For example, the memory cells Q11˜Q14 and the switching transistor T1 are serially connected together. Similarly, the memory cells Q21˜Q24 and the switching transistor T2 are serially connected together, the memory cells Q31˜Q34 and the transistor T3 are serially connected together and the memory cells Q41˜Q44 and the transistor T4 are serially connected together. - The control gate lines CG1˜CG4 connect all the control gates of the memory cells in various rows. For example, the control gate line CG1 connects the control gates of the memory cells Q11˜Q14. Similarly, the control gate line CG2 connects the control gates of the memory cells Q21˜Q24, the control gate line CG3 connects the control gates of the memory cells Q31˜Q34 and the control gate line CG4 connects the control gates of the memory cells Q41˜Q44.
- The select gates SG1˜SG4 connect the select gates of the memory cells in various columns. For example, the select gate SG1 connect the select gates of the memory cells Q1˜Q41. Similarly, the select gate SG2 connect the select gates of the memory cells Q12˜Q42, the select gate SG3 connect the select gates of the memory cells Q13˜Q43 and the select gate SG4 connect the select gates of the memory cells Q14˜Q44. In addition, the select gate SG5 connects the gates of the switching transistors T1˜T4 in the same column.
- To program the memory cells Qn2, for example, a 5V bias voltage is applied to the source line S, a 1.5V bias voltage is applied to the selected gate line SG2, an 8V bias voltage is applied to the non-selected gate lines SG1, SG3 and SG4, an 8V bias voltage is applied to the select gate line SG5, a 10˜12V bias voltage is applied to the control gate line CG1, a 0˜−2V bias voltage is applied to the non-selected control gate lines CG2, CG3 and CG4 and the substrate and the drain line D is connected to a ground. Hence, a source-side injection (SSI) is triggered to inject electrons into the floating gates of the memory cells thereby programming the memory cells Qn2.
- To read data from the memory, a 0V bias voltage is applied to the source line S, a 4.5V bias voltage is applied to the select gate lines SG1˜SG5, a 3V bias voltage is applied to the control gate line CG1 and a 2V bias is applied to the drain line D. Because the channel of memory cells with floating gate having a net negative charge will block the passage of a current and the channel of memory cells with floating gate having a net positive charge will facilitate the passage of a current, the channel on/off state or the size of the channel current can be used to determine the binary data ‘1’ or ‘0’ stored inside the memory cells.
- To erase data from the memory cells, a −20V bias voltage is applied to the control gate line CG1 and a 0V bias voltage is applied to the substrate so that the Fowler-Nordheim (F-N) tunneling effect can be utilized to pull trapped electrons within the floating gate of the memory cells into the substrate.
- In the operating mode of the memory cell array according to the present invention, the hot carrier effect is utilized to program a single bit of data into a single memory cell but the F-N tunneling effect is utilized to erase the data in the entire memory cell array. Hence, the electron injection efficiency is relatively high. In other words, the operating memory cell current is lowered and the operating speed is increased. With a reduction in the memory cell current, the average power consumption of the memory chip is reduced.
- It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Claims (3)
1. A method of operating a non-volatile memory array, the non-volatile memory array comprising:
a substrate;
a plurality of rows of memory cells, wherein each row of memory cells includes a plurality of stacked gate structures separated from each other by a gap, and each stacked gate structure includes a select gate, a plurality of floating gates disposed in the gap between every pair of neighboring stacked gate structures, a plurality of control gates disposed between every pair of neighboring stacked gate structures and positioned above the floating gate, and a pair of source/drain region disposed in the substrate on each outer side of the row of the memory cells;
a plurality of control gate lines connected with the control gates in the same row;
a plurality of select gate lines connected with the select gates in the same column;
a plurality of source lines connected with the source regions in the same column; and
a plurality of drain lines connected with the drain regions in the same column, the operating method comprising:
applying 5V voltage to a selected source line, 1.5V voltage to a selected select gate line, 8V voltage to non-selected select gate lines, 10-12V voltage to a selected control gate line and 0-−2V voltage to non-selected control gate lines and the substrate; and
grounding the drain lines so that source-side injection (SSI) is triggered to inject electrons into the floating gate of the selected memory cell in a programming operation.
2. The method of claim 1 , further comprising:
applying 0V voltage to the source lines, 4.5V voltage to the select gate lines, 3V voltage to the selected control gate line and 2V voltage to the drain lines to read data from the memory cells.
3. The method of claim 1 , further comprising:
applying −20V voltage to the control gate lines and 0V voltage to the substrate so that the Fowler-Nordheim (F-N) tunneling effect can be induced to erase all data within the memory array.
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US12/331,367 US20090086540A1 (en) | 2004-05-12 | 2008-12-09 | Method of operating non-volatile memory array |
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TW093113274A TWI233691B (en) | 2004-05-12 | 2004-05-12 | Nonvolatile memory, nonvolatile memory array and manufacturing method thereof |
US10/904,478 US7180128B2 (en) | 2004-05-12 | 2004-11-12 | Non-volatile memory, non-volatile memory array and manufacturing method thereof |
US11/621,095 US7485529B2 (en) | 2004-05-12 | 2007-01-08 | Method of fabricating non-volatile memory |
US12/331,367 US20090086540A1 (en) | 2004-05-12 | 2008-12-09 | Method of operating non-volatile memory array |
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Cited By (4)
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US20080081410A1 (en) * | 2006-10-02 | 2008-04-03 | Mammen Thomas | Multi-bit memory technology (MMT) and cells |
US8320191B2 (en) | 2007-08-30 | 2012-11-27 | Infineon Technologies Ag | Memory cell arrangement, method for controlling a memory cell, memory array and electronic device |
US20140001531A1 (en) * | 2012-06-28 | 2014-01-02 | Taiwan Semiconductor Manufacturing Co., Ltd. | Damascene non-volatile memory cells and methods for forming the same |
US20220293159A1 (en) * | 2018-05-02 | 2022-09-15 | Semiconductor Energy Laboratory Co., Ltd. | Semiconductor device |
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US20050253184A1 (en) * | 2004-05-12 | 2005-11-17 | Chih-Wei Hung | Nonvolatile memory, nonvolatile memory array and manufacturing method thereof |
US8482052B2 (en) * | 2005-01-03 | 2013-07-09 | Macronix International Co., Ltd. | Silicon on insulator and thin film transistor bandgap engineered split gate memory |
TWI296145B (en) * | 2005-03-09 | 2008-04-21 | Powerchip Semiconductor Corp | Non-volatile memory and fabricating method thereof |
US9330922B2 (en) | 2012-03-07 | 2016-05-03 | Silicon Storage Technology, Inc. | Self-aligned stack gate structure for use in a non-volatile memory array and a method of forming such structure |
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US20080081410A1 (en) * | 2006-10-02 | 2008-04-03 | Mammen Thomas | Multi-bit memory technology (MMT) and cells |
US7583530B2 (en) * | 2006-10-02 | 2009-09-01 | Mammen Thomas | Multi-bit memory technology (MMT) and cells |
US8320191B2 (en) | 2007-08-30 | 2012-11-27 | Infineon Technologies Ag | Memory cell arrangement, method for controlling a memory cell, memory array and electronic device |
US9030877B2 (en) | 2007-08-30 | 2015-05-12 | Infineon Technologies Ag | Memory cell arrangement, method for controlling a memory cell, memory array and electronic device |
US20140001531A1 (en) * | 2012-06-28 | 2014-01-02 | Taiwan Semiconductor Manufacturing Co., Ltd. | Damascene non-volatile memory cells and methods for forming the same |
US9076727B2 (en) * | 2012-06-28 | 2015-07-07 | Taiwan Semiconductor Manufacturing Co., Ltd. | Damascene non-volatile memory cells and methods for forming the same |
US20150270275A1 (en) * | 2012-06-28 | 2015-09-24 | Taiwan Semiconductor Manufacturing Co., Ltd. | Damascene non-volatile memory cells and methods for forming the same |
US9666588B2 (en) * | 2012-06-28 | 2017-05-30 | Taiwan Semiconductor Manufacturing Co., Ltd. | Damascene non-volatile memory cells and methods for forming the same |
US20220293159A1 (en) * | 2018-05-02 | 2022-09-15 | Semiconductor Energy Laboratory Co., Ltd. | Semiconductor device |
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US7180128B2 (en) | 2007-02-20 |
TWI233691B (en) | 2005-06-01 |
US7485529B2 (en) | 2009-02-03 |
US20050253182A1 (en) | 2005-11-17 |
US20070109851A1 (en) | 2007-05-17 |
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