(12) United States Patent
`Ogawa et a].
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 7,151,027 B1
`Dec. 19, 2006
`
`US00715 l027Bl
`
`METHOD AND DEVICE FOR REDUCING
`INTERFACE AREA OF A MEMORY DEVICE
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`(54)
`
`(75)
`
`Inventors: Hiroyuki OgaWa, Sunnyvale, CA (US);
`Yider Wu, Campbell, CA (US);
`Kuo-Tung Chang, Saratoga, CA (US);
`Yu Sun, Saratoga, CA (US)
`
`(73)
`
`Assignee: Spansion LLC, Sunnyvale, CA (US)
`
`5,303,185 A *
`
`4/1994 HaZani ................ .. 365/l85.26
`
`9/1997 Chang . . . . . . . . . . .
`. . . .. 365/l85.03
`5,666,307 A *
`9/1999 Pourkeramati ....... .. 365/l85.26
`5,953,254 A *
`3/2000 Huang et a1. ............. .. 438/257
`6,037,222 A *
`6,808,985 B1 * 10/2004
`438/257
`2005/0127428 Al* 6/2005 Mokhlesi et a1. ......... .. 257/315
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 29 days.
`
`* cited by examiner
`
`Primary ExamineriDavid Nhu
`
`(21)
`
`(22)
`
`(51)
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`(52)
`
`(58)
`
`Appl. N0.: 10/859,369
`
`Filed:
`
`Jun. 1, 2004
`
`Int. Cl.
`(2006.01)
`H01L 21/336
`US. Cl. .................... .. 438/257; 438/238; 438/381;
`257/E2l; 257/613; 257/694; 257/645
`Field of Classi?cation Search .............. .. 438/257,
`438/258, 238, 381, 647, 657, 734, 735, 954
`See application ?le for complete search history.
`
`(57)
`
`ABSTRACT
`
`A method and device for reducing interface area of a
`memory device. A poly-2 layer is formed above a substrate
`at an interface between a memory array and a periphery of
`the memory device. The poly-2 layer is etched proximate to
`the memory array. The poly-2 layer is etched proximate to
`the periphery such that a portion of the poly-2 layer remains
`at the interface.
`
`14 Claims, 6 Drawing Sheets
`
`3
`
`

`

`U.S. Patent
`
`Dec. 19, 2006
`
`Sheet 1 0f 6
`
`US 7,151,027 B1
`
`/ 1/ \/
`
`7/////
`
`Figure 1
`(Prior Art)
`
`IPR2014-00108
`Exhibit MX027-1001, p. 2
`
`

`

`U.S. Patent
`
`Dec. 19, 2006
`
`Sheet 2 0f 6
`
`US 7,151,027 B1
`
`Periphery Components
`_2_1g
`
`2;;0
`
`Memory Array
`ggg
`
`Figure 2
`
`IPR2014-00108
`Exhibit MX027-1001, p. 3
`
`

`

`U.S. Patent
`
`Dec. 19, 2006
`
`Sheet 3 0f 6
`
`US 7,151,027 B1
`
`core I
`‘
`I
`
`I
`ml
`I
`
`3.15 I
`
`interface
`
`Ipen‘phery
`I
`’
`
`I
`
`I
`
`I
`3.192 I
`I
`
`I
`
`————————4——_—_______I________
`300
`
`.
`
`FIgure 3A
`
`304
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`:
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`I
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`Iperiphery
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`my I
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`Figure 3B
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`\ 302
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`I
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`I L55
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`4.63
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`I
`
`305
`
`cor
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`e
`
`
`
`|PR2014-00108
`Exhibit MX027-1001, p. 4
`
`IPR2014-00108
`Exhibit MX027-1001, p. 4
`
`

`

`U.S. Patent
`
`Dec. 19, 2006
`
`Sheet 4 0f 6
`
`US 7,151,027 B1
`
`core
`
`-
`
`eri he
`P W
`
`P
`
`core
`<——|
`
`315
`
`periphery
`,__)
`
`3%
`
`w
`
`Figure 3E
`
`I
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`I
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`core
`‘-—[
`
`315
`
`@
`Interface
`Structure
`
`periphery
`[———>
`
`
`
`|PR2014-00108
`Exhibit MX027-1001, p. 5
`
`IPR2014-00108
`Exhibit MX027-1001, p. 5
`
`

`

`U.S. Patent
`U.S. Patent
`
`Dec. 19, 2006
`Dec. 19, 2006
`
`Sheet 5 0f 6
`Sheet 5 0f 6
`
`US 7,151,027 B1
`US 7,151,027 B1
`
`
`\
`J§I<
`
`I ___/
`
`CA) a
`
`|PR2014-00108
`Exhibit MX027-1001, p. 6
`
`IPR2014-00108
`Exhibit MX027-1001, p. 6
`
`

`

`U.S. Patent
`
`Dec. 19, 2006
`
`Sheet 6 6f 6
`
`US 7,151,027 B1
`
`00
`
`m
`Form a poly-1 layer on a substrate in an interface area
`between a memory array and a periphery of a memory
`device
`l
`4_20
`Apply a dielectric layer over the poly-t layer
`l
`9.129
`Form a poly-1 layer over the dielectric layer
`l
`5.49
`Etch the poly-t layer and poly-2 layer proximate to the
`memory array
`l
`9.59
`Etch the poly-2 layer proximate to the periphery
`l
`él?g
`Form spacers proximate to the memory array and to the
`periphery
`
`Figure 4
`
`IPR2014-00108
`Exhibit MX027-1001, p. 7
`
`

`

`US 7,151,027 B1
`
`1
`METHOD AND DEVICE FOR REDUCING
`INTERFACE AREA OF A MEMORY DEVICE
`
`TECHNICAL FIELD
`
`The present invention relates to the ?eld of ?oating gate
`devices. Speci?cally, the present invention relates to reduc
`ing the interface area betWeen a memory array and a
`periphery of a memory device.
`
`BACKGROUND ART
`
`A modern integrated circuit (IC), for example a ?ash
`memory device, may have millions to hundreds of millions
`of devices made up of complex, multi-layered structures that
`are fabricated through hundreds of processing steps. Those
`structures are formed by repeated deposition and patterning
`of thin ?lms on a silicon substrate, also knoWn as a Wafer.
`One important goal of the semiconductor industry is to
`reduce the siZe of memory devices. In reducing the siZe of
`operational components (e.g., a memory array) and periph
`ery components, an important consideration is the interface
`betWeen the operational components and periphery compo
`nents. Current fabrication processes for forming memory
`devices typically form the operational components and the
`periphery components using separate processes. For
`example, When the periphery components are formed only
`the periphery is etched, and When the memory array is
`formed, only the memory array is etched. By forming the
`periphery components and the memory array using different
`processes, a number of steps in the interface area are created.
`A step exists Where tWo adjacent structures have a different
`height, as shoWn in FIG. 1.
`FIG. 1 is a diagram of a side vieW of a portion of an
`interface area of an exemplary memory device 100, in
`accordance With the prior art. By using different processes to
`form the memory array and the periphery components,
`respectively, steps are created. Substrate 110 has been etched
`Wherein tWo structures 115 and 120 remain. As can be seen,
`structure 120 is higher than structure 115. In particular, the
`height of the step is hard to control because the different
`heights are created using different processes.
`SideWall spacers are commonly formed after the indi
`vidual transistors of the memory array have been formed.
`When the sideWall spacers are formed, stringer spacers (e.g.,
`stringer spacers 130 of FIG. 1) are formed in the interface
`area at the steps. A stringer spacer is a small component that
`is easily peeled or removed from the memory device. If
`removed, the debris may be displaced to the memory array
`or periphery componentry. This debris may result in a yield
`loss of performance by the memory array. Furthermore,
`because it is di?icult to control the height of the steps, it is
`also hard to control the height of the stringer spacers.
`In order to eliminate the risks caused by stringer spacer
`debris, current memory devices include a salicide block
`fabricated over the interface area (e.g., salicide layer 140 of
`FIG. 1). After transistor formation, a salicide block is formed
`over the interface, requiring an additional mask, adding
`costs to the fabrication process. Moreover, the salicide block
`requires additional area of the interface. In particular, the
`area required by the salicide block considerably limits the
`ability to reduce the siZe of the interface area.
`
`DISCLOSURE OF INVENTION
`
`Various embodiments of the present invention, a method
`and device for reducing interface area of a memory device,
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`are described. In one embodiment, a memory device is
`fabricated, in Which a poly-2 layer is formed above a
`substrate at an interface betWeen a memory array and a
`periphery of the memory device. The poly-2 layer is etched
`proximate to the memory array. The poly-2 layer is etched
`proximate to the periphery such that a portion of the poly-2
`layer remains at the interface. In one embodiment, the
`portion of the poly-2 layer remaining at the interface is the
`same height as the memory array proximate to the memory
`array and the same height as the periphery proximate to the
`periphery, such that step siZe is smoothed out reducing the
`occurrence of stringers from spacer etching.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`The accompanying draWings, Which are incorporated in
`and form a part of this speci?cation, illustrate embodiments
`of the invention and, together With the description, serve to
`explain the principles of the invention.
`FIG. 1 is a diagram of a side vieW of a portion of an
`interface area of an exemplary memory device, in accor
`dance With the prior art.
`FIG. 2 is a block diagram of a memory device in accor
`dance With an embodiment of the present invention.
`FIGS. 3A through 3G are diagrams of the side vieW ofan
`exemplary interface area of a memory device illustrating
`steps in a process for forming an interface structure, in
`accordance With an embodiment of the present invention.
`FIG. 4 is a ?owchart illustrating steps in a process for
`fabricating a memory device, in accordance With an embodi
`ment of the present invention.
`The draWings referred to in this description should be
`understood as not being draWn to scale except if speci?cally
`noted.
`
`MODE(S) FOR CARRYING OUT THE
`INVENTION
`
`Reference Will noW be made in detail to embodiments of
`the invention, examples of Which are illustrated in the
`accompanying draWings. While the invention Will be
`described in conjunction With the described embodiments, it
`Will be understood that they are not intended to limit the
`invention to these embodiments. On the contrary, the inven
`tion is intended to cover alternatives, modi?cations and
`equivalents, Which may be included Within the spirit and
`scope of the invention as de?ned by the appended claims.
`Furthermore, in the folloWing detailed description of the
`present invention, numerous speci?c details are set forth in
`order to provide a thorough understanding of the present
`invention. HoWever, the present invention may be practiced
`Without these speci?c details. In other instances, Well-knoWn
`methods, procedures, components, and circuits have not
`been described in detail as not to unnecessarily obscure
`aspects of the present invention.
`The present invention provides a method and structure for
`reducing interface area betWeen the memory array and the
`periphery of a memory device. In one embodiment, the
`boundaries of the various masks used to form a polysilicon
`layer are adjusted such that a polysilicon interface structure
`remains in the interface. The polysilicon interface structure
`is operable to smooth out any steps caused by the etching.
`In particular, the height of the polysilicon interface structure
`is easy to control, eliminating the creation of stringer spac
`ers. Furthermore, embodiments of the present invention do
`not require a salicide layer, thereby reducing the number of
`
`IPR2014-00108
`Exhibit MX027-1001, p. 8
`
`

`

`US 7,151,027 B1
`
`20
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`3
`masks needed to fabricate the memory device and to allow
`for a reduction in interface area.
`FIG. 2 is a block diagram of a memory device in accor
`dance With an embodiment of the present invention.
`Memory device 200 includes a periphery components por
`tion 210 and a memory array portion 220. In one embodi
`ment, memory device 200 is a ?ash memory device.
`Although only one memory array 220 is shoWn in memory
`device 200, it is completely viable for there to be more than
`one memory array 220 being formed on memory device 200.
`In one embodiment, memory array 220 is manufactured in
`a ?ash memory process that is Well knoWn in the art.
`Included in the manufacture of memory array 220 may be
`source-drain portions, poly one and poly-2 layers, tunnel
`oxide, silicon, ?eld oxide, and the like. In addition, interface
`area 230 of FIG. 2, Which is better illustrated in FIGS. 3A
`through 3G, includes poly-1 and poly-2 layers.
`FIGS. 3A through 3G are diagrams of the side vieW of an
`exemplary interface area of a memory device illustrating
`steps in a process for forming an interface structure 360
`(FIG. 3G), in accordance With an embodiment of the present
`invention. Speci?cally, FIGS. 3A, 3B, 3C, 3D, 3E, 3F and
`3G illustrate a process for fabricating an interface structure
`360 according to one embodiment of the present invention.
`In one embodiment, interface structure 360 includes poly
`silicon. In one such embodiment, interface structure 360
`includes a poly-1 layer and a poly-2 layer.
`It is understood that FIGS. 3A through 3G are not draWn
`to scale and that only portions of the substrate 300 and other
`layers are shoWn. For simplicity of discussion and illustra
`tion, the process is described for a single interface structure
`360, although in actuality multiple interface structures may
`be formed.
`Furthermore, although the device being formed is referred
`to as a an interface structure, it is appreciated that FIGS. 3A
`35
`through 3G only shoW an interface structure in the process
`of being formed, and not necessarily a completely formed
`interface structure. It is appreciated that other processes and
`steps associated With the fabrication of an interface structure
`may be performed along With the process illustrated by
`FIGS. 3A through 3G; that is, there may be a number of
`process steps before and after the steps shoWn and described
`by FIGS. 3A through 3G. Importantly, embodiments of the
`present invention can be implemented in conjunction With
`these other (conventional) processes and steps Without sig
`ni?cantly perturbing them. Generally speaking, the various
`embodiments of the present invention can replace a conven
`tional process Without signi?cantly affecting the peripheral
`processes and steps.
`Referring ?rst to FIG. 3A, in the present embodiment,
`substrate 300, isolation area 305 (e.g., a shalloW trenched
`area), and gate polysilicon (“poly-1”) 310a and 31019 are
`shoWn in cross section. In one embodiment, isolation area
`305 is ?lled With SiO2. Line 302 indicates the approximate
`border betWeen the memory array (e.g., care) and the
`interface area. Similarly, line 304 indicates the approximate
`border betWeen the interface area and the periphery. The
`portion of substrate 300 of the memory array is typically
`doped With n-type and p-type materials to form a number of
`regions in the memory array. For example, in an n-channel
`transistoriin particular, in a high voltage n-channel tran
`sistorithe substrate 300 may include silicon doped With a
`p-type material, a deep n-Well, a high voltage p-Well, and
`high voltage n-Wells. It should be appreciated that the
`portion of poly-1 31019 that resides in the interface and
`periphery regions may not be needed to form active tran
`sistors, and is therefore optional.
`
`55
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`4
`Referring noW to FIG. 3B, in the present embodiment, a
`?lm of dielectric material 315 is applied over substrate 300
`and poly-1 310a and 310b, essentially coating the exposed
`(upper) surfaces of substrate 300 and poly-1 310a and 3101).
`Different dielectric materials may be used; in one embodi
`ment, the dielectric material includes SiO2, and in another
`embodiment the dielectric material includes Si3N4. In one
`embodiment a oxide-nitride-oxide (ONO) dielectric layer is
`applied.
`Referring next to FIG. 3C, in the present embodiment, a
`knoWn process (such as an etch back process) is used to
`remove selectively the dielectric material 315 and poly-1
`310b. Signi?cantly, a portion of the dielectric material 315
`overlying poly-1 31019 and a portion of substrate 300 is
`deposited and then selectively removed. In one embodiment,
`the deposition and removal is necessary for the fabrication
`of transistors of the memory array. In one embodiment,
`notch 312 is etched into isolation area 305. It should be
`appreciated that notch 312 is a small trench that is etched as
`a result of the process used to remove dielectric material 315
`and poly-1 31019.
`With reference to FIG. 3D, in the present embodiment, a
`second polysilicon layer (poly-2) 320 is deposited above
`dielectric material 315 and substrate 300. In one embodi
`ment, poly-2 layer 320 is used to form a Word line for use
`in the active transistor of the memory array.
`With reference next to FIG. 3E, in the present embodi
`ment, a knoWn process (such as a stacked gate etch) is used
`to etch a portion of poly-1 310a, dielectric material 315, and
`poly-2 320 proximate to the memory array. The etch is used
`to form individual transistors of from the polysilicon layers.
`In one embodiment, the stacked gate edge uses a stacked
`gate mask above the interface region and the periphery. The
`etch creates a distinct boundary betWeen the memory array
`and the interface region. By locating the stacked gate mask
`close to the core region, poly-1 310a and poly-2 320 remain
`in the interface region.
`With reference next to FIG. 3F, in the present embodi
`ment, a knoWn process (such as a second gate etch) is used
`to etch a portion of poly-2 320 proximate to the periphery.
`The etch is used to form interface structure 360. In one
`embodiment, the second gate edge uses a second gate mask
`above the interface region and the memory array. The
`second gate etch creates a distinct boundary betWeen the
`memory array and the interface region. By locating the
`second gate etch close to the periphery region, only part of
`the poly-2 320 in the interface region is etched, keeping
`interface structure 360, including poly-1 310a and poly-2
`320, in the interface region. In one embodiment, interface
`structure 360 is the same height as the memory array
`proximate to the memory array and the same height as the
`periphery proximate to the periphery, such that step siZe is
`smoothed out reducing the occurrence of stringers from
`spacer etching.
`Referring noW to FIG. 3G, the memory device noW
`includes interface structure 360 as Well as transistor 330 and
`periphery poly-2 340. It should be appreciated that transistor
`330 is the last active transistor of the memory array next to
`the interface area. A ?lm of dielectric material 345 is applied
`over substrate 300, interface structure 360, transistor 330
`and periphery poly-2 340, essentially coating the exposed
`(upper) surfaces of substrate interface structure 360, tran
`sistor 330 and periphery poly-2 340. Different dielectric
`materials may be used; in one embodiment, the dielectric
`material includes SiO2, and in another embodiment the
`dielectric material includes Si3N4. AknoWn process (such as
`an etch back process) is used to remove selectively the
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`IPR2014-00108
`Exhibit MX027-1001, p. 9
`
`

`

`US 7,151,027 B1
`
`5
`dielectric material to form a ?rst set of spacers 350 along the
`side Walls of interface structure 360, transistor 330 and
`periphery poly-2 340. In one embodiment, a second set of
`spacers are formed adjacent to the ?rst spacers 350.
`FIG. 4 is a ?owchart illustrating steps in a process 400 for
`fabricating a memory device, in accordance With an embodi
`ment of the present invention. Although speci?c steps are
`disclosed in process 400, such steps are exemplary. That is,
`the present invention is Well suited to performing various
`other steps or variations of the steps recited in process 400.
`At step 410, a ?rst polysilicon layer (e.g., poly-l) is
`formed on a substrate in an interface area betWeen a memory
`array and a periphery of the memory device. In one embodi
`ment, a gate oxide is groWn on the substrate. At step 420, in
`one embodiment, a dielectric layer is applied over the ?rst
`polysilicon layer. In one embodiment, the dielectric layer is
`an ONO layer. At step 430, a second polysilicon layer (e.g.,
`poly-2) is formed over the dielectric layer. In one embodi
`ment, a gate or gate poly is formed over the gate oxide).
`At step 440, the poly-1 layer and the poly-2 layer are
`etched proximate to the memory array. In one embodiment,
`the etching is accomplished by performing a stacked gate
`etch. At step 450, the poly-2 layer is etched proximate to the
`periphery, such that an interface structure including a portion
`of the poly-1 layer and a portion of the poly-2 layer remains
`at the interface. In one embodiment, the etching is accom
`plished by performing a second gate etch.
`Thus, according to the various embodiments of the
`present invention, the interface structure is the same height
`as the memory array proximate to the memory array and the
`same height as the periphery proximate to the periphery,
`such that step siZe is smoothed out reducing the occurrence
`of stringers from spacer etching. At step 460, spacers are
`formed proximate to the memory array and proximate to the
`periphery. In one embodiment, the spacers are nitride spac
`ers.
`To summarize, the described embodiments provide a
`method and structure for reducing interface area betWeen the
`memory array and the periphery of a memory device. In one
`embodiment, the boundaries of the various masks used to
`form a polysilicon layer are adjusted such that a polysilicon
`interface structure remains in the interface. The polysilicon
`interface structure is operable to smooth out any steps
`caused by the etching. In particular, the height of the
`polysilicon interface structure is easy to control, eliminating
`the creation of stringer spacers. Furthermore, embodiments
`of the present invention do not require a salicide layer,
`thereby reducing the number of masks needed to fabricate
`the memory device and to alloW for a reduction in interface
`area.
`The foregoing descriptions of speci?c embodiments of the
`present invention have been presented for purposes of
`illustration and description. They are not intended to be
`exhaustive or to limit the invention to the precise forms
`disclosed, and obviously many modi?cations and variations
`are possible in light of the above teaching. The embodiments
`Were chosen and described in order to best explain the
`principles of the invention and its practical application, to
`thereby enable others skilled in the art to best utiliZe the
`invention and various embodiments With various modi?ca
`tions as are suited to the particular use contemplated. It is
`intended that the scope of the invention be de?ned by the
`Claims appended hereto and their equivalents.
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`What is claimed is:
`1. A method for fabricating a memory device, said method
`comprising:
`forming a poly-2 layer above a substrate at an interface
`betWeen a memory array and a periphery of said
`memory device;
`etching said poly-2 layer proximate to said memory array;
`and
`etching said poly-2 layer proximate to said periphery such
`that a portion of said poly-2 layer remains at said
`interface.
`2. The method as recited in claim 1 further comprising:
`forming a poly-1 layer above said substrate at said inter
`face, such that said poly-1 layer is above said substrate
`and beneath said poly-2 layer;
`etching said poly-1 layer proximate to said memory array;
`and
`etching said poly-1 layer proximate to said periphery such
`that a portion of said poly-1 layer remains at said
`interface.
`3. The method as recited in claim 1 Wherein said etching
`said poly-2 layer proximate to said memory array is accom
`plished by performing a stacked gate etch.
`4. The method as recited in claim 1 Wherein said etching
`said poly-2 layer proximate to said periphery is accom
`plished by performing a second gate etch.
`5. The method as recited in claim 1 further comprising:
`forming spacers proximate to said memory array; and
`forming spacers proximate to said periphery.
`6. The method as recited in claim 2 further comprising
`forming an ONO layer above said poly-1 layer such that said
`ONO layer is above said poly-1 layer and beneath said
`poly-2 layer.
`7. The method as recited in claim 1 Wherein said portion
`of said poly-2 layer remaining at said interface is a same
`height as said memory array proximate to said memory array
`a same height as said periphery proximate to said periphery,
`such that step siZe is smoothed out reducing an occurrence
`of stringers from spacer etching.
`8. A method for fabricating a memory device, said method
`comprising:
`forming a poly-1 layer above a substrate at an interface
`betWeen a memory array and a periphery of said
`memory device;
`forming a poly-2 layer above said poly-1 layer at said
`interface;
`etching said poly-1 layer and said poly-2 layer proximate
`to said memory array; and
`etching said poly-2 layer proximate to said periphery,
`such that an interface structure including a portion of
`said poly-1 layer and a portion of said poly-2 layer
`remains at said interface.
`9. The method as recited in claim 8 Wherein said etching
`said poly-1 layer and said poly-2 layer proximate to said
`memory array is accomplished by performing a stacked gate
`etch.
`10. The method as recited in claim 8 Wherein said etching
`said poly-2 layer proximate to said periphery is accom
`plished by performing a second gate etch.
`11. The method as recited in claim 8 further comprising:
`forming spacers proximate to said memory array; and
`forming spacers proximate to said periphery.
`12. The method as recited in claim 11 Wherein said
`spacers are nitride spacers.
`
`IPR2014-00108
`Exhibit MX027-1001, p. 10
`
`

`

`US 7,151,027 B1
`
`7
`13. The method as recited in claim 8 further comprising
`forming an ONO layer above said poly-1 layer such that said
`ONO layer is above said poly-1 layer and beneath said
`poly-2 layer.
`14. The method as recited in claim 8 Wherein said 5
`interface structure is a same height as said memory array
`
`8
`proximate to said memory array and a same height as said
`periphery proximate to said periphery, such that step siZe is
`smoothed out reducing an occurrence of stringers from
`spacer etching.
`
`IPR2014-00108
`Exhibit MX027-1001, p. 11
`
`