Classifications

• • 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
  • G11C16/0441—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10B—ELECTRONIC MEMORY DEVICES
  • H10B12/00—Dynamic random access memory [DRAM] devices
  • H10B12/30—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells
  • H10B12/37—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells the capacitor being at least partially in a trench in the substrate
• • 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
  • H10B41/40—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the peripheral circuit region
  • H10B41/42—Simultaneous manufacture of periphery and memory cells
• • 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
  • H10B41/70—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates the floating gate being an electrode shared by two or more components
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D1/00—Resistors, capacitors or inductors
  • H10D1/60—Capacitors
  • H10D1/68—Capacitors having no potential barriers
  • H10D1/692—Electrodes
  • H10D1/711—Electrodes having non-planar surfaces, e.g. formed by texturisation
  • H10D1/716—Electrodes having non-planar surfaces, e.g. formed by texturisation having vertical extensions
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D30/00—Field-effect transistors [FET]
  • H10D30/60—Insulated-gate field-effect transistors [IGFET]
  • H10D30/791—Arrangements for exerting mechanical stress on the crystal lattice of the channel regions
  • H10D30/795—Arrangements for exerting mechanical stress on the crystal lattice of the channel regions being in lateral device isolation regions, e.g. STI
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D84/00—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers
  • H10D84/80—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers characterised by the integration of at least one component covered by groups H10D12/00 or H10D30/00, e.g. integration of IGFETs
  • H10D84/811—Combinations of field-effect devices and one or more diodes, capacitors or resistors
  • H10D84/813—Combinations of field-effect devices and capacitor only
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D30/00—Field-effect transistors [FET]
  • H10D30/60—Insulated-gate field-effect transistors [IGFET]
  • H10D30/68—Floating-gate IGFETs
  • H10D30/6891—Floating-gate IGFETs characterised by the shapes, relative sizes or dispositions of the floating gate electrode
  • H10D30/6892—Floating-gate IGFETs characterised by the shapes, relative sizes or dispositions of the floating gate electrode having at least one additional gate other than the floating gate and the control gate, e.g. program gate, erase gate or select gate
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D84/00—Integrated devices formed in or on semiconductor substrates that comprise only semiconducting layers, e.g. on Si wafers or on GaAs-on-Si wafers
  • H10D84/90—Masterslice integrated circuits
  • H10D84/903—Masterslice integrated circuits comprising field effect technology
  • H10D84/907—CMOS gate arrays
  • H10D84/909—Microarchitecture
  • H10D84/929—Isolations
  • H10D84/931—FET isolation

Definitions

• a non-volatile-memory (NVM) bitcell is an electronic element that is configured to store information.
• the electrical state (e.g., threshold voltage) of a bitcell can be used to define a logic level, such as a logic low level (meaning digital low or 0) or a logic high level (meaning digital high or 1). This defined logic level may sometimes be referred to as information (or a bit) stored in the bitcell.
• an integrated circuit comprises a first plate, a second plate, and a dielectric layer disposed between the first and second plates, the first and second plates and the dielectric layer forming a vertical capacitor, wherein the first and second plates and the dielectric layer of the vertical capacitor are disposed on an isolation region of the integrated circuit.
• an integrated circuit comprises a floating gate flash bitcell comprising at least a control gate layer, a word line gate layer, and a dielectric layer.
• the integrated circuit also comprises a vertical capacitor disposed on a shallow trench isolation (STI) region, the vertical capacitor comprising the control gate layer, the word line gate layer, and the dielectric layer, the dielectric layer positioned between the control gate layer and the word line gate layer.
• STI shallow trench isolation
• a method of fabricating an integrated circuit having at least one vertical capacitor on a shallow trench isolation (STI) region on a substrate comprises depositing a first dielectric layer on the STI region; depositing a first polysilicon layer on the first dielectric layer; patterning the first polysilicon layer to form a first plate of the vertical capacitor having a sidewall; depositing a second dielectric layer such that the second dielectric layer contacts the sidewall; and depositing a second polysilicon layer such that the second polysilicon layer contacts the second dielectric layer, the second polysilicon layer forms a second plate of the vertical capacitor.
• STI shallow trench isolation
• FIG. 1(a) depicts a portion of an illustrative layout of a floating gate flash bitcell memory array, in accordance with various examples.
• FIG. 1(b) depicts a side-view cross-section of a pair of illustrative bitcells, in accordance with various examples.
• FIG. 1(c) depicts an illustrative layout of an array of vertical capacitors, in accordance with various examples.
• FIG. 1(d) depicts a side-view cross-section of illustrative vertical capacitors, in accordance with various examples.
• FIG. 2 depicts an illustrative method performed to fabricate vertical capacitors, in accordance with various examples.
• FIGS. 3(a) - 3(g) depict the fabrication of an illustrative bitcell, in accordance with various examples.
• FIGS. 4(a) - 4(g) depict the fabrication of at least one vertical capacitor, in accordance with various examples.
• Flash memory is a non-volatile storage medium that may store information in an array of bitcells. This stored information (or“bit”) can be electrically erased, programmed, and read.
• an array of floating-gate transistor bitcells may be used in flash memory.
• a floating- gate transistor bitcell resembles a standard metal-oxide-field-effect-transistor (MOSFET), except that the floating-gate transistor bitcell includes multiple gates, e.g., control gate and floating gate.
• MOSFET metal-oxide-field-effect-transistor
• an electrical state of a bitcell can be used to define a logic level, which can be referred to as a bit stored in the bitcell. This may be performed using changes in threshold voltages of the bitcells.
• the threshold voltage of a floating-gate type transistor bitcell may change because of the presence or absence of trapped charge in its floating gate, which further alters the threshold voltage (relative to the old threshold voltage) of the floating-gate transistor bitcell.
• the threshold voltage (or the electrical state of the floating-gate transistor bitcell) when electrons are trapped in the floating-gate type transistor bitcell can be characterized to as a digital low or“0” stored as a bit in the bitcell.
• the electrical state when electrons are depleted in the floating gate can be referred to as digital high or“1” stored as a bit in the bitcell.
• the characterization (e.g., digital high or low) of a bit stored in a floating-gate bitcell depends on the presence or absence of a charge in the floating gate.
• a charge is stored/depleted in a floating gate by applying a voltage potential (e.g., greater than or equal to 10V) at the control gate of the floating-gate transistor bitcell.
• a charge pump circuit is used to apply the voltage potential.
• An example charge pump circuit boosts the input charge to provide voltages higher than the voltage supplied to it.
• a charge pump circuit is capacitor-based, and usually, a capacitor-based charge pump circuit employs capacitors such as a metal-over-semiconductor (MOS).
• MOS metal-over-semiconductor
• a MOS capacitor usually includes a layer of metal (e.g., metal contact), a layer of insulating material (e.g., silicon dioxide), and a layer of semiconductor material (e.g., silicon). These layers are usually laterally fabricated, and the fabrication design of these capacitors results in a parasitic capacitance generated between the substrate (e.g. p-type silicon substrate) and the plates of the capacitors (e.g., nwell), which interferes with the capacitance of the MOS capacitor and degrades its performance. To avoid the parasitic capacitance interference, planar poly-to-poly capacitors or metal-to-poly capacitors are employed in the charge pumps. However, the fabrication of such capacitors requires extra masks, which increases the overall manufacturing cost. Therefore, an alternative design of capacitors that may be used in charge pump circuits and that mitigates the concerns described above is desired.
• metal e.g., metal contact
• insulating material e.g., silicon dioxide
• semiconductor material e.g., silicon
• the examples in this description are directed towards systems and methods for fabricating vertical capacitors that may be used in floating gate flash bitcell technology.
• vertical capacitors described herein are fabricated on the same die as the floating-gate flash bitcells, without using additional masks.
• the vertical capacitors in this description are positioned in isolation regions, such as the shallow trench isolation (STI) regions.
• the disposition of vertical capacitors on the STI regions prevents interference from the above-described parasitic capacitance (e.g., nwell to p-substrate).
• the vertical capacitors utilize the word line gate layers and the control gate layers of the flash bitcells as their capacitor plates.
• the control gate layers and the word line gate layers are separated by a dielectric layer, which may comprise a multi-layer structure.
• FIG. 1(a) shows a portion of an illustrative layout 100 of a floating gate flash bitcell memory array (or floating gate bitcells) in accordance with various examples.
• the layout 100 depicts at least some of the layers that form an array of floating gate bitcells.
• the layout 100 includes bit line (BL) layers 106, 108, 110, 112, 114, and 116, and a source line (SL) layer 124.
• the layout 100 also includes word line (WL) gate layers 118, 122, erase gate (EG) layer 120, and control gate (CG) layers 102, 104.
• the region occupied by the BL layers 106, 108, 110, 112, 114, and 116 is sometimes referred to as an active region.
• the layout 100 also depicts at least some of the layers that form the vertical capacitors to be utilized in the charge pump circuits (e.g., WL gate layers 118, 122, and CG layers 102, 104). This description is not limited to a floating gate bitcell array including the aforementioned gate layers. The description of vertical capacitors below is valid for other types of floating gate bitcells, including floating gate bitcells that do not employ an erase gate layer.
• FIG. 1(a) also illustrates a coordinate system 1, where the X-axis and the Y-axis of the coordinate system 1 each lie in the page of the drawing, and the Z-axis lies away from (outwards) the page of the drawing.
• a layout 100 perspective (as shown in Fig. 1(a))
• one or more bitcells are positioned on line 50 aligned with the Y-axis; however, from a fabrication perspective (as shown in Fig. 1(b)), a side-view of the cross-section of one or more bitcells may be observed in the Y-Z plane along the line 50.
• the layout 100 is used as a layout (or blueprint) to fabricate an array of floating gate bitcells and an array of vertical capacitors that are implemented along with a CMOS logic array (not expressly depicted).
• the layout 100 may be used to fabricate an array of bitcells that is implemented as a standalone memory device (e.g., implemented on its own semiconductor die, enclosed within its own chip package, etc.).
• the layout 100 may be used to fabricate an array of bitcells that is implemented in an integrated circuit (IC) (e.g., implemented on a semiconductor die that includes additional circuit(s)).
• IC integrated circuit
• FIG. 1(b) a side-view cross-section of a pair of illustrative bitcells 70, 80 may be observed in the Y-Z plane along the line 50 (FIG. 1(a)) through the bit line 112.
• Other bitcells may be observed in the Y-Z plane along other bit lines 106, 108, 110, 114, and 116 that are present on the Y-axis.
• the bitcells 70 and 80 are substantially similar in structure.
• the bitcell 70 includes a bit line layer 112 that is disposed in a substrate 126.
• the bitcell 70 also includes the word line (WL) gate layer 118, the control gate layer 102, the floating gate layer 132, and the erase gate layer 120 (that is also shared by the bitcell 80).
• the bitcell 70 further includes dielectric layers 138, 140. These dielectric layers are fabricated to provide isolation between the word line gate layer 118, the control gate layer 102, the floating gate layer 132, and the erase gate 120.
• the substrate 126 may include silicon.
• the dielectric layer 140 may include silicon dioxide
• the dielectric layer 138 may include silicon nitride.
• the bitcell 70 also includes a dielectric layer 111 that acts as the floating gate dielectric and provides isolation between the floating gate 132 and the substrate 126.
• the bitcell 70 forms a WL transistor that includes the WL gate layer 118 (analogous to a gate of a MOSFET), the bit line layer 112 (analogous to a drain of a MOSFET), and the source line layer 124 (analogous to a source of a MOSFET).
• the bitcell 70 also includes an implant layer 128 that is disposed below the word line gate layer 118 in the substrate 126. In some examples, the implant layer 128 may be used to alter the threshold voltage of the WL transistor.
• the substrate 126 also includes an additional implant layer, such as, the anti -punch through layer 136 that is formed by implanting dopants (e.g., boron) in the substrate 126.
• the bitcell 70 depicted in FIG. 1(b) includes the erase gate layer 120, the control gate layer 102, the word line gate layer 118, and the floating gate layer 132, this description is not limited to a floating gate bitcell 70 including the aforementioned gate layers. This description is valid for a floating gate bitcell array, where each of the floating gate bitcells includes the word line gate layer 118, the control gate layer 102, and the floating gate layer 132.
• the bitcell 80 includes the bit line 112, the source line layer 124, the erase gate layer 120, the floating gate layer 134, the control gate layer 104, and the word line gate layer 122.
• the bitcell 80 also includes dielectric layers 146, 148, which isolate the word line gate layer 122, the control gate layer 104, the floating gate layer 134, and the erase gate 120 from each other.
• the bitcell 80 also includes a dielectric layer 111 that acts as the floating gate 134 dielectric and provides isolation between the floating gate 132 and the substrate 126.
• the substrate 126 may include silicon.
• the dielectric layer 146 may include silicon dioxide
• the dielectric layer 148 may include silicon nitride.
• the word line gate layers 118, 122, and the control gate layers 102, 104 comprise polysilicon.
• bitcells 70, 80 may be fabricated in an integrated circuit (IC) (e.g., implemented on a semiconductor die that includes additional circuit(s)).
• IC integrated circuit
• vertical capacitors form using the word line gate layers and control gate layers on the same die as the array of floating gate bitcells. ETnlike the bitcells 70, 80 that are fabricated on the substrate 126, the vertical capacitors— to prevent parasitic capacitance interference— are fabricated on an isolation region (e.g., STI region). Although this description generally describes vertical capacitors on a single STI region, in some examples, multiple vertical capacitors are distributed among multiple isolation regions (e.g., STI regions).
• FIG. 1(c) depicts an illustrative layout 160 of an array of vertical capacitors that are formed using the control gate layers 167, 169, 171,... , 237 and the word line gate layers 166, 168, 170, ... , 236 of bitcells (not expressly shown) disposed in the same die as the vertical capacitors.
• the layout 160 includes the contact layer 162 that couples with each of the control gate layers 167,
• the layout 160 also includes the contact layer 164 that couples with each of the word line gate layers 166, 168, 170, ..., 236.
• control gate layers 167, 169, 171,... , 237 comprise polysilicon.
• the layout 160 may be used to fabricate an array of vertical capacitors and bitcells that are implemented in an integrated circuit (IC) (e.g., implemented on a semiconductor die that includes additional circuit(s)).
• IC integrated circuit
• FIG. 1(d) shows a side-view cross-section of vertical capacitors disposed along a portion of line 165 (FIG. 1(c)).
• FIG. 1(d) depicts vertical capacitors 251 - 260 that are disposed on the STI region 250, which is positioned on the substrate 126.
• the capacitors depicted in FIG. 1(d) comprise the word line gate layers 166, 168, 170, 172, 174, and 176 and the control gate layers 167, 169,
• the word line gate layer 166 acts as one of the plates and the control gate layer 167 acts as the other plate of the vertical capacitor 251.
• a dielectric layer 261 is disposed between the word line gate layer 166 and the control gate layer 167.
• this dielectric layer 261 may comprise a tri -layer structure.
• this tri -layer structure includes two dielectric layers 271 that are oxide layers and a dielectric layer 272 that is a nitride layer.
• the dielectric layers 271 comprise silicon dioxide
• the dielectric layer 272 comprises silicon nitride. Other materials may also be used.
• a vertical capacitor 252 forms between the control gate layer 167 and the word line gate layer 168, with the dielectric layer 262 disposed between them. Similar to the vertical capacitor 251, the vertical capacitor 252 is also disposed on the STI region 250.
• the dielectric layer 262 comprises a tri-layer structure. In some examples, this tri-layer structure includes two dielectric layers 296 that are oxide layers and a dielectric layer 297 that is a nitride layer. In examples where the substrate comprises silicon, the dielectric layers 296 comprise silicon dioxide, and the dielectric layer 297 comprises silicon nitride.
• each vertical capacitor 253 - 260 forms between word line gate layers 168, 170, 172, 174, and 176 and the control gate layers 169, 171, 173, and 175 on the STI region 250, with each vertical capacitor 253 - 260 including a dielectric layer, which, in turn, may comprise a tri-layer structure.
• an illustrative method 300 may be performed to fabricate the vertical capacitors that are positioned on the STI region.
• the method 300 is described in tandem with the illustrative fabrication flow diagrams depicted in FIGS. 3(a) - 3(g) and FIGS. 4(a) - 4(g).
• FIGS. 3(a) - 3(g) depict the fabrication of an illustrative bitcell including at least a control gate layer and a word line gate layer
• FIGS. 4(a) - 4(g) depict the fabrication of at least one vertical capacitor that employs the control gate layer and the word line gate layer of the above-referenced bitcell to form its parallel plates.
• FIGS. 3(a) - 3(g) may be observed along the line 50 (FIG. 1(a)), and the steps depicted in FIGS. 4(a) - 4(g) may be observed along the line 165 (FIG. 1(c)).
• the fabrication steps depicted in FIGS. 3(a) - 3(g) are of a single bitcell, and the steps depicted in FIGS. 4(a) - 4(g) are of at least one vertical capacitor that is formed using the control gate layer and the word line gate layer of the bitcell.
• the description may be adapted for the fabrication of a plurality of bitcells and vertical capacitors.
• the method 300 begins with obtaining the substrate 126 that comprises STI regions (step 310), such as the STI region 401 (FIG. 4(a)), which comprises silicon dioxide.
• STI regions are created early during the semiconductor device fabrication process, before other electronic elements (e.g., transistors, bitcells) are formed.
• the fabrication of STI regions involves etching a pattern of trenches (not expressly shown in FIGS. 3(a) - 3(g) and 4(a) - 4(g)) in the substrate, such as the substrate 126. Further steps in the fabrication of STI regions include depositing one or more dielectric materials (e.g., silicon dioxide) to fill the trenches, and then eliminating the excess dielectric material using planarization techniques (e.g., chemical-mechanical planarization).
• dielectric materials e.g., silicon dioxide
• additional steps may be performed.
• the additional steps may include depositing a floating dielectric layer 405 and a floating gate layer 410 to form a portion of the bitcell (FIG. 3(a), FIG. 3(b), respectively).
• the deposition of the gate layer 410 can be observed in FIG. 4(b); however, the deposition of the dielectric layer 405 is masked to contain it to the fabrication of the bitcell.
• the dielectric layer 405 may be fabricated such that the dielectric layer 405 is disposed on the STI region 410 (not expressly depicted in FIG. 4(b)).
• the floating gate layer 410 comprises polysilicon.
• the aforementioned deposition steps may be performed using chemical vapor deposition.
• the method 300 may also include removing the floating gate layer 410 from the STI region 401 (FIG. 4(c)).
• the floating gate layer 410 may be removed using masking techniques and the dry/wet etching technique such that the gate layer 410 is removed from the STI region 401 (FIG. 4(c)) and not from the dielectric layer 405 of FIG. 3(c).
• the chemical -mechanical polishing technique may be used to remove the floating gate layer 410 from STI region 401.
• the method 300 may proceed to step 320, which may include depositing the dielectric layer 413. From the vertical capacitor’s perspective, the dielectric layer 413 is deposited on the STI region 401 (FIG. 4(c)), and from bitcell’s perspective, the dielectric layer 413 is deposited on the floating gate layer 410 (FIG. 3(c)).
• the dielectric layer 413 may comprise a tri -layer structure. In some examples, this tri-layer structure includes two dielectric layers 412, 416 that comprise silicon dioxide and a dielectric layer 414 that comprises silicon nitride.
• the step 320 may also include implanting dopants (e.g., boron) in the substrate 126 to form an anti-punch through layer 136 (FIG. 3(c)).
• dopants e.g., boron
• step 330 includes depositing a control gate layer 420 on the dielectric layer 413.
• the control layer 420 can be observed from both the vertical capacitor’s (FIG. 4(c)) and bitcell’s (FIG. 3(c)) perspectives.
• the step 330 may also include depositing a dielectric layer 430 on the control gate layer 420. Again, the dielectric layer 430 can be observed from both the vertical capacitor’s (FIG. 4(c)) and bitcell’s (FIG. 3(c)) perspectives.
• the deposition of both the control gate layer 420 and the dielectric layer 430 may be performed using chemical vapor deposition.
• the control gate layer 420 includes poly silicon
• the dielectric layer 430 includes silicon nitride.
• the method 300 may then move to the step 340 that includes patterning the control gate layer 430 (FIGS. 3(d) and 4(d)).
• the patterning may be performed using photo lithography and dry plasma etching.
• FIGS. 3(a) - 3(g), and FIGS. 4(a) - 4(g) describe the formation of a single bitcell and at least one vertical capacitor.
• the patterning may be performed such that a plurality of bitcells and vertical capacitors may form.
• FIG. 4(d) shows the sidewalls 2, 3 of the patterned control gate layer 420.
• the method 300 may proceed to step 350, which includes depositing dielectric layers 417 on the sidewalls 2, 3 of the control gate layer 420 (FIG. 4(e)).
• the deposition of dielectric layers 417 can also be observed in FIG. 3(e).
• FIG. 4(e) depicts the dielectric layers 417 abutting the control gate layer 420 and the dielectric layer 430 (e.g., the deposition of the dielectric layers 417 may extend from the top of the dielectric layer 416 to the top of the dielectric layer 430), in some examples, the dielectric layers 417 abut only the control gate layer 420.
• a portion of the floating gate layer 410 may be etched/removed, which is further followed by implantation of dopants (such as boron) in the substrate 126.
• dopants such as boron
• the dielectric layers 417 assume a tri -layer structure, which includes the dielectric layers 418, 420, 422.
• the dielectric layers 418, 422 comprise silicon dioxide
• the dielectric layer 420 comprises silicon nitride.
• the method 300 may then proceed to step 360, which includes depositing a polysilicon layer 421 such that the polysilicon layer 421 is disposed on top of the dielectric layer 416, the dielectric layer 418, 420, 422, and 430 (FIGS. 3(f), 3(g), 4(f), and 4(g)).
• the step 360 may also include etching a portion of the poly silicon layer 421 to form two separate polysilicon layers 413 and 415 (FIGS. 3(g) and 4(g)), which are referred to as word line gate layer and erase gate layer, respectively.

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