Integrated structure comprising neighboring transistors

Abstract

An integrated structure includes a first MOS transistor with a first controllable gate region overlying a first gate dielectric and a second MOS transistor neighboring the first MOS transistor and having a second controllable gate region overlying the first gate dielectric. A common conductive region overlies the first and second gate regions and is separated therefrom by a second gate dielectric. The common conductive region includes a continuous element located over a portion of the first and second gate regions and a branch extending downward from the continuous element toward the substrate as far as the first gate dielectric. The branch located between the first and second gate regions.

Claims

1. A method of making a semiconductor device, the method comprising: forming a first gate dielectric over a substrate; forming a first layer of gate material over the first gate dielectric; forming a first gate region and a second gate region by etching the first layer so as to form a slot in the first layer extending in a first direction between two ends; forming a second gate dielectric over the etched first layer and on sidewalls of the slot; forming a second layer of the gate material over the second gate dielectric; forming a continuous element extending along a second direction by patterning the second layer of the gate material, the second gate dielectric, the first layer of gate material and the first gate dielectric, the second direction being substantially orthogonal to the first direction; and forming electrically conductive contact pads for contacting the first, the second gate regions and the continuous element.

2. The method according to claim 1, wherein the first gate region forms a controllable gate of a first MOS transistor and the second gate region forms a controllable gate of a second MOS transistor, the controllable gates overlying the first gate dielectric.

3. The method according to claim 1, wherein forming a second layer of the gate material comprises forming a branch extending downward from the continuous element toward the substrate as far as the first gate dielectric, wherein the branch is located between the first and second gate regions and spaced from both first and second gate regions.

4. The method according to claim 1, further comprising: etching end portions of the continuous element and an underlying portion of the second gate dielectric so as to expose a portion of each of the first and the second gate regions, wherein the electrically conductive contact pads are formed on the exposed portions of the first and second gate regions.

5. A method of making a semiconductor device, the method comprising: forming a first gate dielectric over a substrate; forming a first controllable gate region and a second controllable gate region over the first gate dielectric, the first controllable gate region and the first gate dielectric forming a part of a first MOS transistor of an SRAM elementary cell, the second controllable gate region and the first gate dielectric forming a part of a second MOS transistor of the SRAM elementary cell; forming a second gate dielectric over the first controllable gate region and the second controllable gate region; forming a common conductive region overlying the first and second gate regions and separated therefrom by the second gate dielectric, the common conductive region being part of the SRAM elementary cell, the common conductive region comprising a continuous element located over a portion of the first and second controllable gate regions and a branch extending downward from the continuous element toward the substrate as far as the first gate dielectric, the branch located between the first and second controllable gate regions and spaced from both the first and second controllable gate regions, wherein the first controllable gate region laterally extends beyond the continuous element of the common conductive region, wherein the second controllable gate region laterally extends beyond the continuous element of the common conductive region; forming a first contact pad in the first controllable gate region for coupling to a first metal track portion disposed over the first controllable gate region; and forming a second contact pad in the second controllable gate region for coupling to a second metal track portion disposed over the second controllable gate region.

6. The method of claim 5, wherein the first and second gate controllable regions are aligned.

7. The method of claim 5, wherein orthogonal projections onto the substrate of two facing profiles of the first and second controllable gate regions are free from rounded portions.

8. The method of claim 5, wherein forming the second gate dielectric comprises forming a silicon nitride layer sandwiched between two silicon dioxide layers.

9. The method of claim 5, further comprising: forming a first electrically conductive contact electrically contacting the first contact pad; and forming a second electrically conductive contact electrically contacting the second contact pad, the common conductive region located between the first and second electrically conductive contacts.

10. The method of claim 5, further comprising: forming an additional electrically conductive contact in electrical contact with the common conductive region.

11. A method of making a semiconductor device, the method comprising: forming a plurality of memory cells arranged in rows and columns, wherein forming each memory cell comprises forming an SRAM elementary memory cell and a floating-gate transistor cell coupled together; and wherein forming the SRAM elementary memory cell comprises: forming a first source/drain region and a second source/drain region in a substrate and a first gate dielectric over the substrate, forming a first controllable gate region overlying the first gate dielectric and the first source/drain region, wherein the first controllable gate region, the first gate dielectric, and the first source/drain region are part of a first MOS transistor, forming a second controllable gate region overlying the first gate dielectric and a second source/drain region, wherein the second controllable gate region, the first gate dielectric, and the second source/drain region are part of a second MOS transistor, wherein the first controllable gate region is coupled to the second source/drain region and the second controllable gate region is coupled to the first source/drain region, forming a second gate dielectric over the first and the second controllable gate regions, forming a common conductive region overlying the first and the second controllable gate regions and capacitively coupled to the first and the second controllable gate regions through the second gate dielectric, the common conductive region comprising a continuous element located over a portion of the first and the second controllable gate regions and a branch extending downward from the continuous element as far as the first gate dielectric; and forming a first electrically conductive contact pad electrically contacting the first controllable gate region, and a second electrically conductive contact pad electrically contacting the second controllable gate region.

12. The method according to claim 11, wherein the branch is located between the first and second gate controllable regions and spaced from both the first and second controllable gate regions.

13. The method according to claim 11, wherein forming the SRAM elementary memory cell comprises forming two cross-coupled inverters comprising two pMOS transistors, wherein the first and second MOS transistors are the two pMOS transistors of the cross-coupled inverters.

14. The method according to claim 11, wherein forming the common conductive region comprises exposing a portion of the first and the second controllable gate regions laterally beyond the continuous element of the common conductive region.

15. The method according to claim 11, further comprising forming a third electrically conductive contact pad electrical contacting the common conductive region, wherein the common conductive region is located between the first and second electrically conductive contact pads.

16. The method of claim 11, wherein forming the second gate dielectric comprises forming a silicon nitride layer sandwiched between two silicon dioxide layers.

17. The method according to claim 1, wherein forming the electrically conductive contact pads comprises forming a first via contacting a portion of an outer surface of the first gate region, a second via contacting a portion of an outer surface of the second gate region, and a third via contacting a portion of an outer surface of the continuous element.

18. The method according to claim 17, wherein the third via is spaced substantially equidistant from the first via and the second via.

19. The method according to claim 1, further comprising: forming a first source region and a first drain region, the first source region and the first drain region are formed on opposite sides of the first gate region; and forming a second source region and a second drain region, the second source region and the second drain region are formed on opposite sides of the second gate region.

20. The method according to claim 19, further comprising: forming a first source contact to the first source region and a first drain contact to the first drain region; and forming a second source contact to the second source region and a second drain contact to the second drain region.

21. The method according to claim 11, wherein forming the SRAM elementary memory cell comprises forming two cross-coupled inverters comprising two nMOS transistors, wherein the first and second MOS transistors are the two nMOS transistors of the cross-coupled inverters.

22. The method according to claim 11, wherein forming the first and the second electrically conductive contact pads comprises forming a first via contacting a portion of an outer surface of the first controllable gate region, a second via contacting a portion of an outer surface of the second controllable gate region, and a third via contacting a portion of an outer surface of the common conductive region.

23. The method according to claim 22, wherein the third via is spaced substantially equidistant from the first via and the second via.

24. The method according to claim 11, further comprising: forming a first source region and a first drain region, the first source region and the first drain region are formed on opposite sides of the first controllable gate region; forming a second source region and a second drain region, the second source region and the second drain region are formed on opposite sides of the second controllable gate region; forming a first source contact to the first source region and a first drain contact to the first drain region; and forming a second source contact to the second source region and a second drain contact to the second drain region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages and features of the invention will become apparent on examining in detail completely nonlimiting implementations and embodiments thereof, and the appended drawings in which:

(2) FIGS. 1 to 15 schematically illustrate various implementations and embodiments of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(3) In FIG. 1, the reference STR designates the equivalent circuit of an integrated structure, one embodiment of which in an integrated circuit is schematically illustrated in FIGS. 2 to 5.

(4) In this respect, FIG. 3 is a cross section along the line III-III in FIG. 2, FIG. 4 is a cross section along the line IV-IV in FIG. 2 and FIG. 5 is a partial cross section along the line V-V in FIG. 3.

(5) With reference to FIGS. 1 to 5, it may be seen that the integrated structure STR here comprises a pair of MOS transistors TR1, TR2. Each transistor TR1, TR2 comprises a gate region RG1, RG2 separated from an underlying substrate 1 by a first gate dielectric OX1 for example comprising silicon dioxide.

(6) Located in the semiconductor substrate 1, which is for example made of silicon, are located the active zones ZA1 and ZA2 of the two transistors TR1 and TR2, which zones are bounded, in the conventional way, by isolating regions RIS, STIs (shallow trench isolations) for example.

(7) The structure STR moreover comprises an additional region RG3 comprising a gate material that may, just like the gate regions RG1, contain polysilicon.

(8) This additional region RG3 is separated from the two gate regions by a second gate dielectric OX12 that, as illustrated in FIG. 3, may advantageously comprise a stack formed of a layer OX120 of silicon nitride Si.sub.3N.sub.4 sandwiched between two layers OX121 and OX122 of silicon dioxide SiO.sub.2.

(9) The additional region RG3 possesses a continuous element RG30 located on top of a portion of the two gate regions RG1 and a branch RG31 united with a zone of the lower face of the element RG30 and extending between them and at distance from the two gate regions RG1 as far as the first gate dielectric OX1.

(10) Here, the gate regions RG1, RG2 project beyond the continuous element RG30, thereby are providing a simple way of applying a control potential or voltage to control these gate regions.

(11) In this respect, the structure STR for example comprises, on either side of the additional region RG3, two electrically conductive contact pads CNL1, CNL2 making contact with the two gate regions RG1, RG2, respectively. These contact pads, bearing against the projecting portions of the gate regions, allow the two gate regions RG1 and RG2 to be biased and here comprise contacts V1, V2 and metal track portions PST1, PST2 that here are located in the first metallization level of the integrated circuit.

(12) The structure STR also furthermore comprises, in this embodiment, an additional electrically conductive contact pad CNL3 making contact with the additional region RG3 and allowing, here again, this additional region RG3 to be optionally biased with a potential that may be the supply voltage or ground.

(13) This being so, this additional contact pad could be left floating. As a variant, the contact pad CNL3 could even optionally be omitted if the additional region RG3 were in fact to be left floating.

(14) Here again, the contact pad CNL3 comprises a contact V3 and a metal track PST3 that here is also located in the first metallization level of the integrated circuit.

(15) It may therefore be seen, especially in FIGS. 1 and 3, that the additional region RG3, the two gate regions RG1 and RG2 and the second gate dielectric OX12 form two capacitors C1 and C2 that are connected in parallel to the gates of the transistors TR1 and TR2. The first electrode of a capacitor is formed by the corresponding gate region of the transistor and the second electrode of each capacitor is formed by the additional region RG3.

(16) The contact pads CNL1, CNL2 and CNL3 allow different biases to be applied to the electrodes of the two capacitors.

(17) In FIG. 4, the zones ZSS1 and ZSD1 designate the source and drain zones of the transistor TR1, respectively. Contact pads CNLS1, CNLS2, CNLD1 and CNLD2 allow the source and drain zones of the two transistors TR1 and TR2 to be biased.

(18) It may be seen, especially in FIG. 5 (in which the branch RG31 has not been shown for the sake of simplicity) that, in this embodiment, the two gate regions RG1 and RG2 are aligned and separated by a slot FNT. Moreover, the orthogonal projections onto the substrate of the two profiles PRF1 and PRF2 of the two facing gate regions are free from rounded portions and have square edges.

(19) Reference is now more particularly made to FIGS. 6 to 9 to describe one implementation of a process for producing such an integrated structure STR in a semiconductor wafer.

(20) After isolation zones RIS have been formed in the substrate 1 of the wafer in a conventional way, the first gate dielectric OX1 is formed over all of the semiconductor wafer in a conventional way known per se. Next, again on the wafer scale, a first layer CHM1 of gate material, for example of polysilicon, is formed on top of the first gate dielectric OX1.

(21) Next, the first layer CHM1 is etched locally using a conventional photolithography step employing a mask containing a rectangular slot FNM1 extending in a first direction DR1 between two ends EX1 and EX2, so as to form in this first layer CHM1 a rectangular slot FNG corresponding to the slot FNM1.

(22) Next, as illustrated in FIG. 8, again on the wafer scale, the second gate dielectric OX12 is formed on the etched first layer and on the sidewalls of the slot FNG.

(23) Next, again on the wafer scale, a second layer CHM2 of gate material is formed on the second gate dielectric OX12, the second layer CHM2 especially, as illustrated in FIG. 8, filling the rest of the slot FNG between the gate dielectric OX12.

(24) Next, as illustrated in FIG. 9, the second layer CHM2 of gate material, the second dielectric OX12, the first layer CHM1 of gate material and the first dielectric OX1 are etched with a profile FNM2 possessing a rectilinear portion overlapping the slot FNG between its two ends EX1, EX2, this rectilinear, here rectangular, portion extending in a second direction DR2 substantially orthogonal to the first direction.

(25) The double-level gate structure illustrated in FIGS. 2 to 5 is thus obtained (after the ends of the region RG3 and of the second gate dielectric OX12 have been etched locally to allow contact to be made to contact pads CNL1 and CNL2).

(26) The fact that two orthogonal geometries FNG and FNM2 were used when etching the layers CHM1 and CHM2 has made it possible to prevent rounding of the facing profiles of the two gate regions, as illustrated in FIG. 5. Moreover, the first mask, comprising the slot FNM1 is associated with a narrower lithography than that associated with the mask comprising the profile FNM2. As a result, the gap between the two transistors is substantially decreased. Thus, a decrease of more than 50% may be obtained in the space between the active regions of the two transistors.

(27) Reference is now more particularly made to FIGS. 10 to 15 to illustrate an example application of such an integrated structure in a memory device DIS incorporated in an integrated circuit CI.

(28) As schematically illustrated in FIG. 10, the memory device DIS may in practice comprise a memory plane PM comprising a matrix of cells CELij organized into rows and columns, the plane being associated, in the conventional way, with a processor (MTR) configured to manage the memory plane PM and especially comprising a column decoder DCDX and a row decoder DCDY.

(29) The row decoders and column decoders may comprise integrated structures STR such as described above, thereby saving space.

(30) Such structures STR may also be incorporated into the memory cells CEL.sub.i,j of the device DIS, as will now be described with reference to FIGS. 11 to 15.

(31) In FIG. 11, the reference CEL designates a memory cell of a memory plane, comprising an SRAM elementary memory cell CELSR and at least one nonvolatile elementary memory cell CELNV, these two elementary memory cells being coupled together.

(32) The elementary memory cell CELSR has a conventional structure and comprises a flip-flop BSC formed from two cross-connected CMOS inverters, and two access transistors N1 and N8.

(33) The two inverters INV1, INV2 are connected between a supply terminal, which is intended to be connected to the supply voltage Vdd, and ground GND.

(34) The two access transistors N1 and N8 are respectively connected between the outputs of the two inverters and two bit lines BL and BL, BL designating the complementary bit line of the line BL.

(35) The gates of the access transistors N1 and N8 are connected to a word line WL.

(36) The operations for reading and writing a datum to the elementary memory cell CELSR are conventional operations known per se.

(37) When the power is cut or on an external signal, the datum contained in the elementary memory cell CELSR is transferred and stored in the nonvolatile elementary memory cell CELNV. This is what is referred to as a “nonvolatile transfer”. Next, when power returns, the elementary memory cell CELSR is reloaded with the content of the nonvolatile elementary memory cell CELNV.

(38) Furthermore, depending on the configurations chosen during this operation for reloading the cell CELSR, the datum may or may not be inverted relative to that initially stored in the memory cell CELSR before the nonvolatile transfer to the nonvolatile elementary memory cell CELNV.

(39) The elementary memory cell CELSR of the cell in Figure ii is configured to lower the risk of accidental flipping of logic states present at the output nodes of the two inverters, for example when hit by cosmic rays or even during a laser-beam attack.

(40) In this respect, the cell CELSR comprises a structure STR of the type of those illustrated in FIGS. 1 to 5 and forming the two pMOS transistors P1 and P2 of the two inverters INV1 and INV2.

(41) Moreover, whereas, as indicated above, the first electrodes ELC1 of these two capacitors C1 and C2 are formed by the gates of the transistors P1 and P2, respectively, the second electrodes ELC2 of these two capacitors C1 and C2 are here connected to the sources of these two transistors P1 and P2, and therefore to the supply voltage Vdd.

(42) As a variant, it would be possible, as illustrated in FIG. 12, to connect the two electrodes ELC2 of the two capacitors C1 and C2 to ground GND.

(43) These two capacitors C1 and C2 allow the total capacitance of the flip-flop BSC to be increased, thereby increasing the energy required to accidentally flip the flip-flop BSC.

(44) The thickness of the first gate dielectric OX1 (FIG. 3) is typically comprised between 20 Å and 250 Å whereas the thickness of the second gate dielectric OX12 is typically comprised between 100 Å and 200 Å. The fact that the dielectric OX12 consists of an SiO.sub.2/Si.sub.3N.sub.4/SiO.sub.2 sandwich allows a well-controlled capacitance to be obtained.

(45) It should be noted that using a structure STR to produce the pMOS transistors of the inverters saves space and that the region RG3 is either left floating or connected to a potential.

(46) It would also have been possible to produce the two nMOS transistors M3 and M6 of the two inverters using another structure STR. This being so, given that these two transistors M3 and M6 are offset in the layout, it was preferable, for the sake of simplicity of implementation, not to use a structure STR for these nMOS transistors.

(47) The invention is applicable to any type of nonvolatile memory cell comprising one or more floating-gate transistors, such as EEPROM cells for example.

(48) FIG. 13 illustrates one embodiment of a memory cell CEL comprising the SRAM elementary memory cell CELSR and two nonvolatile EEPROM elementary cells CELNV1 and CELNV2 here comprising two floating-gate transistors E1 and E2.

(49) Such a cell has been described in the French patent application numbered 1356720. Certain of its features will now be recalled.

(50) The nonvolatile EEPROM cells of the cell CEL are conventional cells, i.e. in which the selection transistor has been removed and having a tunnel injection zone between their floating gate and drain.

(51) The sources of these two transistors E1 and E2 are connected to a supply terminal BAL that here is connected to ground.

(52) As for the control electrodes of the two floating-gate transistors E1 and E2, they are connected to a first control line CGL.

(53) The drains of the two floating-gate transistors E1 and E2 are connected to the inputs and outputs of two inverters of the cell CELSR by an interconnect stage that here comprises two nMOS interconnect transistors, reference N2 and N7.

(54) More precisely, the two interconnect transistors N2 and N7 are connected between the drains of the two floating-gate transistors E1 and E2 and the two outputs of the two inverters P1, N3 and P2, N6, respectively. Moreover, the control electrodes (gates) of these two interconnect transistors N2 and N7 are connected to a second control line PRL.

(55) During an operation of writing to the elementary memory cell CELSR, this being a conventional write operation, the control line PRL is grounded, turning off the interconnect stage. Likewise, the first control line CGL is also grounded.

(56) As is well known by those skilled in the art, a nonvolatile transfer or write operation is made up of an erase cycle followed by a differential programming cycle as two nonvolatile elementary memory cells are present.

(57) For the erase cycle, the line PRL is grounded, turning off the interconnect transistors N2 and N7. Next, an erase voltage is delivered via the first control line CGL.

(58) During the differential programming cycle, the second control line PRL passes to the supply voltage, turning on the transistors N2 and N7. A programming voltage is then delivered via the first control line CGL.

(59) To reload the cell CELSR, the first control line CGL passes to a reference read voltage, typically 1 volt, while the second control line PRL is at a voltage of 2 volts, for example so as to turn on the transistors N2 and N7.

(60) FIG. 14 illustrates another embodiment of a memory cell CEL, here again incorporating two nonvolatile EEPROM memory cells CELNV1 and CELNV2 here comprising two floating-gate transistors E1 and E2.

(61) Such a cell has been described in the patent application numbered 1355439. Certain of its features will now be recalled.

(62) Here again, the nonvolatile EEPROM cells of the CEL cell are conventional cells, that is to say in which the selection transistor has been removed and having a tunnel injection zone between their floating gate and drain.

(63) The sources of these two transistors E1 and E2 are connected to a supply terminal BAL that here is connected to ground.

(64) As for the control electrodes of the two floating-gate transistors E1 and E2, they are connected to a first control line CGL.

(65) The drains of the two floating-gate transistors E1 and E2 are connected to the inputs and outputs of the two inverters by an interconnect stage that here comprises two first nMOS interconnect transistors, reference N2 and N7, and two second nMOS interconnect transistors, reference N4 and N5.

(66) More precisely, the two first interconnect transistors N2 and N7 are connected between the drains of the two floating-gate transistors E1 and E2 and the two outputs of the two inverters P1, N3 and P2, N6, respectively. Moreover, the control electrodes (gates) of these two interconnect transistors N2 and N7 are connected to a second control line PRL.

(67) As for the two second interconnect transistors N4 and N5, they are connected between the drains of the two floating-gate transistors E1 and E2 and the two inputs of the two inverters P1, N3 and P2, N6, respectively.

(68) The control electrodes of these two second interconnect transistors N4 and N5 are connected to a third control line RLL.

(69) Although the two second interconnect transistors N4 and N5 are not essential, they are particularly advantageous as they make it possible to prevent data being inverted when the contents of the two nonvolatile cells E1 and E2 are reloaded into the SRAM elementary memory cell CELSR, even when the supply terminal BAL is grounded.

(70) The operation used to write to the elementary memory cell CELSR is a conventional write operation.

(71) Thus, the control lines PRL, RLL are grounded, turning off the interconnect stage. Likewise, the first control line CGL is also grounded.

(72) The operation used to read a datum from the cell CELSR is also a conventional read operation.

(73) For the erase cycle, the lines PRL and PLL are grounded, turning off the interconnect transistors N2, N4, N5 and N7. Next, an erase voltage is delivered via the first control line CGL.

(74) For the differential programming cycle, the second control line PRL passes to the supply voltage Vdd while the third control line RLL remains grounded.

(75) Therefore, the interconnect transistors N2 and N7 are turned on while the interconnect transistors N4 and N5 are turned off.

(76) A programming voltage is then delivered via the first control line CGL.

(77) The floating-gate transistors E1 and E2 are all turned off during this differential programming operation.

(78) In order to reload the cell CELSR, the first control line CGL passes to a reference read voltage, typically 1 volt, while the second control line PRL is grounded and the third control line RLL is at a voltage of 2 volts, for example, so as to turn on the transistors N4 and N5 while the transistors N2 and N7 are turned off.

(79) The voltage on the word line WL is zero.

(80) FIG. 15 illustrates yet another embodiment of a memory cell CEL.

(81) Such a cell has been described in the aforementioned French patent application numbered 1355440.

(82) Certain of its features will now be recalled.

(83) This memory cell CEL comprises a single nonvolatile EEPROM elementary cell CELNV here comprising a controllable floating-gate transistor E1 that is turned off during an operation for programming a datum stored in the SRAM elementary memory cell into the nonvolatile elementary memory cell.

(84) Here again, the nonvolatile EEPROM cell of the cell CEL is a conventional cell, that is to say in which the selection transistor has been removed and having a tunnel injection zone between its floating gate and drain.

(85) The source of the transistor E1 is connected to a supply terminal BAL that here is grounded.

(86) As for the control electrode of the floating-gate transistor E1, it is connected to a first control line CGL.

(87) The drain of the floating-gate transistor E1 is here connected to the output (node ND) of the first inverter P1, N3 of the elementary memory cell CELSR by way of an interconnect stage, here comprising a first interconnect transistor N2. This single interconnect transistor N2 is here an nMOS transistor.

(88) The control electrode (gate) of this first interconnect transistor N2 is connected to a second control line PRL. Therefore, the interconnect stage is controlled by a signal originating from outside the memory cell CEL, i.e. by the control voltage present on the second control line PRL.

(89) The operation used to write to the elementary memory cell CELSR is here again a conventional write operation.

(90) Thus, the control line PRL is grounded, turning off the interconnect stage. Likewise, the first control line CGL is also grounded.

(91) For the erase cycle, the line PRL is grounded, turning off the interconnect transistor N2. Next, an erase voltage is delivered via the first control line CGL.

(92) In the programming cycle, the second control line PRL passes to the supply voltage Vdd.

(93) Therefore, the interconnect transistor N2 is turned on.

(94) A programming voltage is then delivered via the first control line CGL.

(95) Before it is reloaded, the SRAM elementary memory cell CELSR is initialized (or reset) so as to initialize it to a known state and to prevent it from entering into a metastable state.

(96) This initialisation may for example be obtained by writing a “1” to the SRAM cell using the conventional write procedure.

(97) For the reloading operation, the first control line CGL passes to a reference read voltage, typically 1 volt, while the second control line PRL is at a voltage of 2 volts, for example so as to turn on the interconnect transistor N2.

(98) The voltage on the word line WL is zero.