Abstract:
An integrated circuit comprises a first poly-silicon region including a first poly-silicon layer, a second poly-silicon layer disposed over the first poly-silicon layer, a first poly-silicon finger associated with the first poly-silicon layer, and a second poly-silicon finger associated with the second poly-silicon layer. The first poly-silicon finger and the second poly-silicon finger are oriented in a substantially orthogonal manner relative to each other. The integrated circuit comprises a second poly-silicon gate region including the first poly-silicon layer. The first polysilicon gate region and the second polysilicon gate region each have different poly-silicon gate structures.

Description:
This application is a divisional of U.S. patent application Ser. No. 13/071,385 filed Mar. 24, 2011, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention is related to computer-readable memory, and in particular, but not exclusively, to a method of fabricating integrated devices. 
     BACKGROUND 
     Various types of electronic memory have been developed in recent years. Some exemplary memory types are electrically erasable programmable read only memory (EEPROM) and electrically programmable read only memory (EPROM). EEPROM is easily erasable but lacks density in storage capacity, whereas EPROM is inexpensive and denser but is not easily erased. “Flash” EEPROM, or Flash memory, however, combines the advantages of these two memory types. 
     For example, Flash memory may be utilized in both the electronics of larger products such as vehicles and industrial control systems, and within smaller electronic devices such as laptop computers, digital camera/camcorders, digital recording equipment, portable digital assistants (PDAs), portable music players, cell phones, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings, in which: 
         FIG. 1  illustrates a flow diagram of a fabrication process according to an embodiment of the present invention; 
         FIGS. 2A-2C  illustrate semiconductor structures at various stages of the fabrication process described in  FIG. 1  according to an embodiment of the present invention; 
         FIG. 3  illustrates a block diagram of an embodiment of a memory; 
         FIG. 4  shows a partial top plan view of an embodiment of core and peripheral sections of a memory that may be employed in the memory of  FIG. 3 . 
         FIG. 5  illustrates a block diagram of an embodiment of a NOR memory array; 
         FIG. 6  shows a cross-sectional side view of an embodiment of a core section of  FIG. 4 ; 
         FIG. 7  illustrates a flow diagram of a Flash memory fabrication process according to an embodiment of the present invention; 
         FIGS. 8A-8I  illustrate embodiments of portions of a Flash memory device at various stages of the fabrication process described in  FIG. 7  according to an embodiment of the present invention; and 
         FIG. 9  illustrates a block diagram of an embodiment of a system that includes the memory device of  FIG. 3 , in accordance with aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will be described in detail with reference to the drawings, where like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention. 
     Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of “a,” “an,” and “the” includes plural reference, and the meaning of “in” includes “in” and “on.” The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. Similarly, the phrase “in some embodiments,” as used herein, when used multiple times, does not necessarily refer to the same embodiments, although it may. As used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. The term “based, in part, on”, “based, at least in part, on”, or “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. The term “coupled” means at least either a direct electrical connection between the items connected or an indirect connection through one or more passive or active intermediary devices. The term “signal” means at least one current, voltage, charge, temperature, data, or other signal. 
     Briefly stated, embodiments are directed towards embedded Flash applications, which includes, among other things, the integration of advanced logic with Flash memory cell technologies. For example, this integration may include the fabrication, on a single die, of Flash core memory and high-voltage (HV) transistors for providing the Flash memory portion along with low-voltage (LV) transistors utilized for implementing the advanced logic functionality. In one embodiment, two different poly-silicon layers may be fabricated in order to produce height differences between the poly-silicon structures of the Flash and advanced logic portions that are produced on the same die. 
     General Operation 
       FIG. 1  illustrates a flow diagram of a fabrication process for generating poly-silicon layers of different heights according to an embodiment of the present invention. In one embodiment, process  134  may be employed during Flash memory fabrication. In some embodiments, process  134  may be preceded by other semiconductor die fabrication processes. For example, in one embodiment of a Flash memory fabrication process, process  134  may be preceded by fabrication processes to create shallow trench formations, well formations, tunnel oxide, a charge trap layer, ultra-high voltage gate oxidation, high-voltage gate oxidation, and low-voltage gate oxidation. 
     In any event, process  134  begins, after a start block, at step  130 , where a first poly-silicon layer is deposited over a first region and a second region. In one embodiment, the first poly-silicon layer may have a thickness of about 1000 Å (Angstroms). In another embodiment, the first poly-silicon layer may have a thickness of about 500-1000 Å. In yet another embodiment, the first poly-silicon layer may have any other suitable thickness. In some embodiments, the first region may refer to non-contiguous portions of a semiconductor die. For example, in some embodiments of a Flash memory environment, a first region may include high-voltage transistors and core memory transistors, where the high-voltage transistors may be noncontiguous to the core memory transistors. Similarly, in some embodiments, the first region may be noncontiguous to the second region on the die. 
     Process  134  then proceeds to step  131 , where an oxide layer is deposited over the first poly-silicon layer within the second region. In some embodiments, an oxide layer may be deposited over the first poly-silicon layer. In one embodiment, the oxide layer may have a thickness of between 50-200 Å. In some embodiments, the oxide layer may be an oxide-nitride-oxide (ONO) layer. Further, in one embodiment, an etch resist layer may be deposited over the oxide layer and lithographically patterned using a mask. As a result, a designated portion of the etch resist layer protects a portion of the oxide layer associated with the second region of the die from being etched away. Subsequently, in some embodiments, the oxide layer corresponding to the first region may be etched down to the upper-surface of the first poly-silicon layer. 
     Continuing to step  132 , a second poly-silicon layer is deposited over the first region and the second region, such that the second poly-silicon layer is deposited over the first poly-silicon layer and the oxide layer. In some embodiments, the second poly-silicon layer may have a thickness of about 1000 Å (Angstroms). In another embodiment, the second poly-silicon layer may have a thickness of about 500-1000 Å. In yet other embodiments, the second poly-silicon layer may have any other suitable thickness. 
     Process  134  then proceeds to step  133 , where a portion of the second poly-silicon layer over the oxide layer is stripped away, i.e. the second region. In some embodiments, the second poly-silicon layer may be etched away using a second mask and photolithography. Thus, in one embodiment, a portion of the second poly-silicon layer may be protected by a resist layer patterned during the second masking and photolithography stage. As a result, etching may be limited to removing a portion of the second poly-silicon layer, while leaving the oxide layer and first poly-silicon layer intact over the second region. 
       FIGS. 2A-2C  illustrate a cross-sectional view of an embodiment of semiconductor device  246  in fabrication, such as by implementing fabrication process  134  of  FIG. 1 . Although  FIGS. 2A-2C  illustrate the first region and the second region as contiguous, the invention is not so limited; rather, in some embodiments, the first region may be noncontiguous to the second region. Similarly, in some embodiments, the first region may refer to non-contiguous portions of a semiconductor die. For example, in some embodiments of a Flash memory environment, a first region may include high-voltage transistors and core memory transistors, where the high-voltage transistors may be noncontiguous to the core memory transistors. 
       FIG. 2A  illustrates a cross-sectional view of semiconductor device  246  after step  130  and step  131  of process  134  of  FIG. 1  have been performed. Semiconductor device  246  includes a first region, a second region, first poly-silicon layer  268 , resist  269 , and oxide layer  270 . 
       FIG. 2B  illustrates a cross-sectional view of semiconductor device  246  after step  132  of process  134  of  FIG. 1  has been performed. Semiconductor device  246  includes a first region, a second region, first poly-silicon layer  268 , second poly-silicon layer  272 , and oxide layer  270 . 
       FIG. 2C  illustrates a cross-sectional view of semiconductor device  246  after step  132  of process  134  of  FIG. 1  has been performed. Semiconductor device  246  includes a first region, a second region, first poly-silicon layer  268 , portions of second poly-silicon layer  274 , resist layer  275 , and oxide layer  270 . 
     Example Memory Environment 
       FIG. 3  shows a memory environment in which embodiments of the invention may be employed. Not all the components illustrated in the figures may be required to practice the invention, and variations in the arrangement and type of the components may be made without departing from the spirit or scope of the invention. For example, although some embodiments of the invention are described in the context of a MirrorBit™ NOR Flash memory, the fabrication described herein may be employed in manufacturing other types of microelectronic memories or devices such as other various types of Flash memory. 
     As shown, memory  347  includes arrayed memory  303  and memory controller  306 . Memory controller  306  is arranged to communicate addressing data and program data over signal path  302 . For example, signal path  302  can provide 8, 16, or more I/O lines of data. Memory controller  306  is also configured to access arrayed memory  303  over signal path  301 . For example, memory controller  306  can read, write, erase, and perform other operations at portions of arrayed memory  303  via signal path  301 . In addition, although shown as single lines, signal path  301  and/or signal path  302  may be distributed across a plurality of signal lines and/or bus lines. 
     Arrayed memory  303  includes memory sectors  304  (identified individually as sectors 1-i) that can be accessed via memory controller  306 . Memory sectors  304  can include, for example, 256, 512, 1024, 2048 or more sectors having memory cells that can be individually or collectively accessed. In other examples, the number and/or arrangement of memory sectors can be different. In one embodiment, for example, sectors  304  can be referred to more generally as memory blocks and/or can be configured to have a configuration that is different than a bit line, word line, and/or sector topology. 
     Memory controller  306  includes decoder component  307 , voltage generator component  308 , and controller component  309 . In some embodiments, memory controller  306  may be located on the same chip as arrayed memory  303 . In other examples, other implementations of memory controller  306  are possible. For example, memory controller  306  can include a programmable microcontroller. 
     Decoder component  307  is arranged to receive memory addresses via addressing signal path  302  and to select individual sectors, arrays, or cells according to the architecture of arrayed memory  303 . 
     Decoder component  307  includes, for example, multiplexer circuits, amplifier circuits, combinational logic, or the like for selecting sectors, arrays, and/or cells based on any of a variety of addressing schemes. For example, a portion of a memory address (or a grouping of bits) can identify a sector within arrayed memory  303  and another portion (or another grouping of bits) can identify a core cell array within a particular sector. 
     Voltage generator component  308  is arranged to receive one or more supply voltages (not shown) and to provide a variety of reference voltages required for reading, writing, erasing, pre-programming, soft programming, and/or under-erase verifying operations. For example, voltage generator component  308  can include one or more cascode circuits, amplifier circuits, regulator circuits, and/or switch circuits that can be controlled by controller component  309 . 
     Controller component  309  is arranged to coordinate reading, writing, erasing, and other operations of memory  347 . In one embodiment, controller component  309  is arranged to receive and transmit data from an upstream system controller (not shown). Such a system controller can include, for example, a processor and a static random access memory (SRAM) that can be loaded with executable processor instructions for communicating over signal path  302 . In another embodiment, controller component  109  as well as other portions of memory controller  306  may be embedded or otherwise incorporated into a system controller or a portion of a system controller. 
     Embodiments of controller component  309  can include a state machine and/or comparator circuits. State machine and comparator circuits can include any of a variety of circuits for invoking any of a myriad of algorithms for performing reading, writing, erasing, or other operations of memory  347 . State machines and comparator circuits can also include, for example, comparators, amplifier circuits, sense amplifiers, combinational logic, or the like. 
     In some embodiments, memory  347  is a Flash-based memory including Flash-based memory cells, such as Flash-based NOR cells, NAND cells, or hybrids of the two. In some embodiments, memory  347  is a MirrorBit™ Flash memory. 
       FIG. 4  shows a partial top plan view of separate sections of a memory. Core section  415 , for example, may be an embodiment of a portion of sector  304  of  FIG. 3  and may include arrayed core memory cells. Peripheral section  416 , for example, may be an embodiment of memory controller  306  of  FIG. 3  or a portion of memory controller  306  of  FIG. 3 . 
     Core section  415  includes core poly-silicon lines  418 , conductive regions  419 , and a portion of substrate  417 . Portions of core poly-silicon lines  418  are coupled to the gates of individual memory cells (not shown in  FIG. 4 ) and can be configured as a word line, a source select gate line, and/or a drain select gate line. Portions of conductive regions  419  can include, for example, p-type and/or n-type doped regions of substrate  417  for forming source/drain regions and/or conductive lines. For example, conductive regions  419  can form portions of bit lines and/or other signal lines. Also, in some embodiments, individual conductive regions  419  extend at least partially underneath individual core poly-silicon lines  418 . 
     In one embodiment, core section  415  is arranged in a NOR topology, and individual memory cells can be individually accessed via individual conductive regions  419 . In another embodiment, core section  415  is arranged in a NAND topology, and individual memory cells can be accessed though individual conductive regions  419  collectively but not individually. To other embodiments, hybrid architectures can be employed. For example, core section  415  can be configured to have a portion that is NAND-based and another portion that is NOR-based. Also, although not shown in  FIG. 4 , core section  415  may include any of a variety of interconnect and/or passivation layers, such as dielectric, conductive, or other layers. For example, conductive regions  419  can be positioned beneath a dielectric spacer layer. 
     Peripheral section  416  includes peripheral poly-silicon lines  420 , conductive regions  421 , and interconnects  422 . Portions of peripheral poly-silicon lines  420  are coupled to individual peripheral devices (not shown in  FIG. 4 ). 
     Portions of conductive regions  421  can include, for example, p-type and/or n-type doped regions of substrate  417  for forming conductive features, such as a source, a drain, or other type of well. Interconnects  422  can include conductive lines that electrically intercouple portions of peripheral section  416  and/or electrically couple core section  415  with peripheral section  416 . For example, interconnects  422  can include a combination of metal lines and vias. Also, although not shown  FIG. 4 , peripheral section  416  may also include any of a variety of other interconnect and/or passivation layers. 
       FIG. 5  illustrates a block diagram of an embodiment of memory device  567 , which may be employed as an embodiment of memory device  347  of  FIG. 3 . Memory device  567  includes memory array  526  and individual memory cells  527  located within memory array  526 . Memory cells  527  are arranged in N+1 rows and M+1 columns in memory array  526 . In one embodiment, each row of memory array  526  is accessed by two of the bit lines BL0 to BLN. Each column of memory array  526  is accessed by one of word lines WL0 to WLM. Accordingly, each of memory cells  527  can be accessed by activating the corresponding bit lines and a corresponding word line of the cell. In one embodiment, each column of memory array  526  defines a data word. If N+1 has a value of 8, for example, the cells in each column of memory array  526  define a byte of data. 
     Memory cells  527  may be Flash memory cells which store bits in different ways in different embodiments. In various embodiments, a single cell may store one or more bits. For example, some memory cells are single cell devices, some memory cells are dual cells devices, and in some embodiments, more than one distinct level of threshold voltage may be used to represent more than one bit per cells, as discussed in greater detail below. In some embodiments, Flash memory stores information in an array of memory cells made from floating-gate transistors. In, for example, a NOR gate Flash, the transistors resemble a standard metal-oxide-semiconductor field-effect transistor (“MOSFET”) except that the transistor has two gates, a floating gate and a control gate, instead of one. On top is the control gate (“CG”), as in other metal-oxide-semiconductor transistors, but below this there is a floating gate (“FG”) insulated all around by an oxide layer. The FG is interposed between the CG and the MOSFET channel. Because the FG is electrically isolated by an insulating layer, any electrons placed on it are trapped there and, under normal conditions, will not discharge for many years. When the FG holds a charge, it screens (partially cancels) the electric field from the CG, which modifies the threshold voltage (“VT”) of the cell. The threshold voltage of a MOSFET is usually defined as the gate voltage where an inversion layer forms at the interface between the insulating layer (oxide), and the substrate (body) of the transistor. During read-out, a voltage is applied to the CG, and the MOSFET channel will become conducting or remain insulating, depending on the VT of the cell, which is in turn controlled by the charge on the FG. The current flow through the MOSFET channel is sensed which permits a determination of the voltage threshold for the device, which in turn provides information about the binary data stored within the device. 
     In a single cell device, each control gate of a transistor stores a single charge amount that represents the stored information. In its default or “un-programmed” state, it is logically equivalent to a binary “1” value, because current will flow through the channel under application of an appropriate voltage to the control gate. 
     In a dual cell device, each control gate stores two charge amounts that represent the stored information. That is, two physically distinct quantities of charge are stored on opposite sides of the floating gate. Reading or writing data on one side of the floating gate occurs independently of the data that is stored on the opposite side of the floating gate. In this technology, the FG is split into two mirrored or complementary parts, each of which is formulated for storing independent information. Each dual cell, like a traditional cell, has a gate with a source and a drain. However, in the dual cell the connections to the source and drain may be reversed in operation to permit the storage of the two bits. Each of the memory cells is comprised of multi-layers. A charge-trapping dielectric layer is formed over a semiconductor substrate. The charge-trapping dielectric layer can generally be composed of three separate layers: a first insulating layer, a charge-trapping layer, and a second insulating layer. Word-lines are formed over the charge-trapping dielectric layer substantially perpendicular to the bit lines. Programming circuitry controls two bits per cell by applying a signal to the word-line which acts as a control gate, and changing bit line connections such that one bit is stored by the source and drain being connected in one arrangement and the complementary bit is stored by the source and drain being connected in another arrangement. 
     In a single-level cell (“SLC”) device, each cell stores only one bit of information, either the cell is “un-programmed” (has a “1” value) or “programmed” (has a “0” value). In contrast, multi-level cell (“MLC”) devices can store more than one bit per cell by choosing between multiple levels of electrical charge to apply to the floating gates of its cells. In these devices, the amount of current flow is sensed (rather than simply its presence or absence), to determine more precisely the level of charge on the FG. 
     As one example, a dual cell device may also be a MLC device that stores four-bits-per-cell so that one transistor equates to 16 different states. This enables greater capacity, smaller die sizes and lower costs for the Flash devices. 
     Memory device  567  further includes controller  509 , decoder  528 , decoder  529 , voltage regulator  523 , and voltage regulator  524 . 
     Decoder  528  and decoder  529  can each receive address bus information from controller  509  and can utilize such information to facilitate accessing or selecting the desired memory cell(s) (e.g., memory location(s)) associated with the command, and to provide the needed voltages to the bit lines (decoder  528 ) and the word lines (decoder  529 ) according to timing that is controlled by controller  509 . 
     Decoder  528  may also include a sector decoder in some embodiments. As such, decoder  509  may be arranged to facilitate accessing or selection particular column or grouping of columns within memory device  567 . For example, a grouping of columns may define a sector, and another grouping of columns may define another sector. In another embodiment, portion  501  may include an array decoder for to a particular memory array  525 . In addition, embodiments of array decoders can be configured to work separately or in conjunction with a sector decoder. 
     In some embodiments, decoders such as decoder  528  and decoder  529  may each receive a boosted voltage, which may be received at the gates of one of more transistors in the decoders. These transistors may be referred to as high-voltage (HV) transistors or HV devices due to the boosted voltage that the HV transistors receive at their respective gates. HV transistors may be used in bit line decoding, word line decoding, sector decoding, array decoding, and/or the like. In contrast, logic in the periphery section of the Flash memory includes transistors that have gates that receive voltages that are not boosted. These transistors may be referred to as low-voltage (LV) transistors or LV devices. For example, controller  509  may include high-performance logic that includes LV transistors. The HV devices, LV devices, and core memory cells have different requirements, including different poly heights. 
     Memory controller  509  is also configured to control the activation and de-activation of individual word lines WL0 to WLM for reading, writing, and/or erasing to memory array  526 . For example, memory controller  510  can provide a select signal to decoder  529  to select one of the columns WL1 to WLM to activate that column. Further, memory controller  536  can provide a select signal to decoder  528  for selecting particular rows BL0 to BLN (or sector) to be written to or read from. 
       FIG. 6  shows a cross-sectional side view of a memory cell in core section  648 . In one embodiment, core section  648  is an embodiment of core section  415  of  FIG. 4 . 
     Memory cell  636  includes a portion of substrate  605 , dielectric spacer layer  639 , channel region  640 , source/drain regions  638   a  and  638   b , and layered stack  641 , including charge trapping component  642  and a portion of core poly-silicon line  637 . Substrate  605  may be an embodiment of substrate  417  of  FIG. 4 . Source/drain regions  638   a  and  638   b  may be an embodiment of one or more conductive regions  419  of  FIG. 4 . Core poly-silicon line  637  may be an embodiment of an individual core poly-silicon line  418  of  FIG. 4 . 
     In operation, core poly-silicon line  637  and source/drain regions  638   a  and  638   b  are configured to provide electrical potential(s) to memory cell  636  for trapping charge at charge trapping component  642 . A bit is “programmed” when it is trapping a charge and “unprogrammed” when it is not trapping charge. To trap charge, charge trapping component  642  employs tunneling layer  643 , charge trapping layer  644 , and dielectric layer  645 . In general, tunneling layer  643  provides a tunneling barrier, charge trapping layer  644  is a layer that is configured to store charge, and dielectric layer  645  electrically isolates charge trapping layer  644  from core poly-silicon line  637 . In one embodiment, memory cell  636  is a one bit memory cell that is configured to store up to two logic states. In another embodiment, memory cell  636  can store more than two logic (or bit) states. 
     In some embodiments, charge trapping component  642  is an oxide-nitride-oxide (ONO) layer in which dielectric layer  645  is an oxide (such as silicon dioxide), charge trapping layer  644  is a nitride, and tunneling layer  643  is an oxide (such as silicon dioxide). In one embodiment in which charge trapping layer  644  is a nitride, charge trapping layer  644  may be a silicon-rich nitride (SiRN) or a stoichiometric silicon nitride. Dielectric spacer layer  639  may be a nitride spacer, an oxide-nitride spacer, other type of spacer composed of one or more dielectric materials, or the like. 
     Modern semiconductor devices are typically created as integrated circuits manufactured on the surface of a substrate of semiconductor material, which is typically a wafer formed by slicing a single crystal ingot growth by a Czochralski process. Various devices are formed on the wafer using a series of steps that include deposition, removal processes (such as etching), patterning, and doping. Few steps or many hundreds of such steps may be used in various designs. The patterning steps may be performed by photolithography or other lithographic methods. For example, the wafer may be coated with a photoresist, which is exposed, with a device that transmits light through a photomask, exposing portions of the wafer not blocked by the photomask to light. The exposed regions are removed so that the photoresist remains only in areas that were not exposed to light. This allows a layer to be etched according to the pattern on the photomask. After the devices have been formed on the wafer, various back-end processing and packaging is performed, including properly interconnecting the devices and bringing metal lines to the chip edge for attachment to wires. 
     A designer creates the device design in accordance with a set of design rules provided by the fabricator, and creates a series of design files based on the design, which may be stored in a machine-readable medium. Various design tools may be used by the designer in creating the design, simulating the design, and checking the design for layout rules violations. When completed, the design files are provided to the fabricator, which are used to generate photomasks for use in the fabricating the device. The design files may be communicated in different ways, including over a network. 
     Illustrative Embodiment 
       FIG. 7  illustrates a flow diagram of a fabrication process for generating poly-silicon layers of different heights according to an embodiment of the present invention. Various steps associated with process  749  of  FIG. 7  will be described with the aid of  FIGS. 8A-8I .  FIGS. 8A-8I  illustrate a cross-sectional view of portions of an embodiment of Flash memory device  800 , in fabrication that includes, for example, a first region (i.e. a Flash memory region) comprising at least one HV transistor and/or at least one core memory transistor, and a second region (i.e., an advanced and/or complex logic device region) comprising at least one LV transistor. 
     Process  749  may begin, after a start block, at step  750 , where a standard Flash fabrication process creates shallow trench formations, well formations, tunnel oxide, a charge trap layer, ultra-high voltage gate oxidation, high-voltage gate oxidation, and low-voltage gate oxidation on the same semiconductor die. 
     Process  749  then proceeds to steps  751 . Steps  751 ,  752 ,  754 , and  756  will now be described with the aid of  FIG. 8A . In one embodiment,  FIG. 8A  illustrates portions of Flash memory device  800  in fabrication. At step  751 , once these structural elements are fabricated (step  750 ), a first layer of poly-silicon  868  having a thickness of about 1000 Å (Angstroms) is deposited. Proceeding next to step  752 , an oxide layer of between 50-200 Å is deposited over the poly-silicon layer  868 . Process  749  then proceeds to step  754 , where an etch resist layer is then deposited over the oxide layer and lithographically patterned using a mask. As a result, a designated portion of the etch resist layer  869  protects a portion of the oxide layer  870  associated with the LV transistor region of the die from being etched away. Continuing to step  756 , the remaining portion of oxide layer corresponding to the HV and core memory transistor region, as designated by  871 , are etched down to the upper-surface of the first layer of poly-silicon  868 . Next, at step  758 , the bit-lines associated with the core memory transistors are formed. 
     Process  749  then proceeds to step  760 , where a second layer of poly-silicon  872  also having a thickness of about 1000 Å (Angstroms) is deposited over both the first layer of poly-silicon  868  and the oxide layer  870 , which is illustrated in  FIG. 8B . 
     Proceeding to step  762 , as illustrated in  FIG. 8C , the portion ( FIG. 8B ) of the second layer of poly-silicon  872  that is deposited over the LV transistor region  873  of the die is etched away using a second mask and photolithography. Thus, portion  874  of the second layer of poly-silicon  872  remains protected by the resist layer  875  patterned during the second masking and photolithography stage. As shown, the etching is limited to removing a portion  873  ( FIG. 8B ) of the second layer of poly-silicon  872 , while leaving the entire first layer of poly-silicon  868  intact. 
     Process  749  next proceeds to step  764 , where word-lines and gates are formed on the core memory, HV, and LV transistors, as illustrated in  FIGS. 8D-8I . Referring to  FIG. 8D , an oxide hard cover mask process is used to generate oxide regions  876   a - 876   d  over portion  874  of the second poly-silicon layer. A core memory/HV gate mask is then used to pattern (over the oxide regions) the gate structures for the transistor devices within the HV and core memory region  871  of the die. Therefore, as a result of this patterning, resist regions  877   a - 877   c  cover the generated oxide regions  876   a - 876   c  of the core memory gate structures, respectively, and deposited resist region  877   d  is deposited over the generated oxide region  876   d  of the HV transistor gate structure. In addition, resist region  877   e  covers the entire LV transistor region  873 . A hard mask etch process then strips away the resist regions  878  that were not patterned during the core memory/HV gate mask. As illustrated in  FIG. 8E , a hard mask etch is utilized to strip away the remaining resist regions  877   a - 877   e  shown in  FIG. 8D . 
     As shown in  FIG. 8F , an LV gate mask is used to pattern the gate structure for the LV transistor device within a portion of the LV region  871  of the die. Thus, as a result of this patterning, resist region  879  covers the HV and core memory region  871  and, in some embodiments, a relatively small interface (between the HV/core memory region and LV transistor region) portion  880  of the LV transistor region  873 . In addition, resist region  881  covers an oxide region  882  corresponding, to the gate structure of the LV transistor. Accordingly, upon a hard mask etching process, regions  883  of oxide region  870  ( FIG. 8E ) are stripped away, while the remaining HV and core memory structures are protected by resist region  879 . 
     As shown in  FIG. 8G , once the etch resist region  881  ( FIG. 8F ) is stripped away from the gate structure of the LV transistor, the oxide region  882  remains. A resist layer is then deposited over the entire device and patterned in order to remove portions of the first and second layers of poly-silicon  868 ,  874  ( FIG. 8F ). Accordingly, based on the patterning of the resist layer, during etching, regions  884  of the first and second layers of poly-silicon  868 ,  874  are stripped away from the HV and core memory region  871 . Thus, poly-silicon structures  886 ,  887 , and  888  form the gate and word-lines of the core memory transistors, while poly-silicon structure  889  forms the gate of the HV transistor. Also, during this etching process, resist region  885  protects the oxide region  882  within the LV transistor region  873 . 
     As shown in  FIG. 8H , once the etch resist region  885  ( FIG. 8G ) is stripped away from the LV transistor region  873 , another resist layer  890  is deposited over the entire device and patterned in order to now remove portions of the first and second layers of poly-silicon  868 ,  874  ( FIG. 8F ) associated with the LV transistor region  873 . After such patterning, resist layer  890  protects the HV and core memory region  871 , and the relatively small interface portion  880  of the LV transistor region  873 . However, within the remaining portion  891  of the LV transistor region  873 , regions  892  of the first layer of poly-silicon  868  are stripped away in order to create poly-silicon structure  893 , which forms an LV transistor gate. During the etching of regions  892  of the poly-silicon  868 , oxide  882  acts as a natural etch stop. As illustrated in  FIG. 8I , following the etching process, resist layer  890  is stripped away leaving a structure that includes a semiconductor device structure having poly-silicon gate structures of different heights, which depend on each particular transistor&#39;s functionality and structure. 
     As previously described, LV transistors may include short channels for facilitating high-speed operations. Thus, as a result of the short-channel construction, fabricating gate structures of an increased height may lead to several instabilities, such as gate collapse. As illustrated by portions of Flash memory device  800  in fabrication in  FIG. 8I , the poly-silicon structure  893  of the LV transistor gate is formed from a portion of a single poly-silicon layer such as layer  868 . In contrast to the LV transistor devices, the core memory and HV transistors include poly-silicon gate structures that are formed from multiple poly-silicon layers in order facilitate the application of higher voltages during operation. For example, as illustrated in  FIG. 8I , the poly-silicon structures  886 ,  887 ,  888 ,  889  forming the gate structures of both the core memory and HV transistors are formed from a portion of multiple poly-silicon layers such as layers  868  and  874 . 
     Poly-silicon structures  886 ,  887 , and  888  correspond to the gate regions of the core memory transistor devices and poly-silicon structure  889  forms the gate region of the HV transistor. As designated at  894 , a slightly blow-up plan view of poly-silicon structure  886  is shown. As illustrated, the gate region of device  886  includes poly-silicon fingers P1 and P2. Poly-silicon finger P2, which is fabricated from the second layer of poly-silicon  674  (e.g.,  FIG. 8C ), runs in an orthogonal direction (V) relative to poly-silicon finger P1 running horizontally in the direction of arrow (H). The gaps between adjacent poly-silicon fingers P1 and P′1 in the vertical (V) direction are filled with oxide  895  of the same thickness as the poly-silicon fingers P1. Thus, when poly-silicon finger P2 is laid over poly-silicon fingers P1 and P′1, the poly-silicon material corresponding to poly-silicon finger P2 does not fill the gaps between poly-silicon fingers P1 and P′1. Poly-silicon finger P1 is fabricated from the first layer of poly-silicon  868  (e.g.,  FIG. 8C ) and overlaps (at least partially) with poly-silicon finger P2, which is laid over poly-silicon finger P1. As further illustrated, some regions  896  of poly-silicon finger P1 are etched away during the etching of the second layer of poly-silicon  874 . In poly-silicon structures  886 ,  887 , and  888 , poly-silicon finger P1 may include a floating gate structure while poly-silicon finger P2 may form a word-line. 
     Regarding the poly-silicon structure  889  forming the gate region of the HV transistor, poly-silicon region  897  of the first layer of poly-silicon  868  and poly-silicon region  898  of the second layer of poly-silicon  874  are stacked on top of each other with no interface material between them. 
     Continuing with step  766  of  FIG. 7 , once the word-line and gates are formed (step  764 ), any remaining standard Flash processes are carded out. After step  766 , process  749  returns. Although  FIG. 7  and  FIG. 8  are described with reference to specific embodiments, the invention is not so limited; rather  FIG. 7  and  FIG. 8  show example embodiments and other suitable embodiments may be employed without departing from the scope and spirit of the invention. Thus, in some embodiments, other suitable semiconductor fabrication embodiments may be employed without departing from the scope and spirit of the invention, in one non-limiting and non-exhaustive example,  FIG. 8  describes oxide layer  870  as an oxide; however, in some embodiments, oxide layer  870  may include an oxide-nitride-oxide layer. In another non-limiting and non-exhaustive example,  FIG. 7  describes a first layer of poly-silicon having a thickness of about 1000 Å; however, in other embodiments, a first layer of poly-silicon may have another suitable thickness. 
     Embodiments of a memory device that employ embodiments of the present invention, such as portions of Flash memory device  800  in  FIGS. 8A-8I  in fabrication, can be incorporated into any of a variety of components and/or systems, including for example, a processor and other components or systems of such components.  FIG. 9  shows one embodiment of system  910 , which may incorporate memory  911 , which is an embodiment of memory device  347  of  FIG. 3 . Memory  911  can be directly or indirectly connected to any one of processor  912 , input devices  913 , and/or output devices  914 . In one embodiment, memory  911  may be configured such that it is removable from system  910 . In another embodiment, memory  911  may be permanently connected to the components or a portion of the components of system  910 . 
     In many embodiments, memory  911 , processor  912 , input devices  913 , and/or output devices  914  of system  910  are configured in combination to function as part of a larger system. For example, system  910  may be incorporated into a cell phone, a handheld device, a laptop computer, a personal computer, and/or a server device. In addition or alternatively, system  910  can perform any of a variety of processing, controller, and/or data storage functions, such as those associated with sensing, imaging, computing, or other functions. Accordingly, system  910  can be incorporated into any of a wide variety of devices that may employ such functions (e.g., a digital camera, an MP3 player, a GPS unit, and so on). 
     The above specification, examples and data provide a description of the fabrication processes and structure associated with core Flash memory, HV, and LV transistors integrated within a single die in accordance with the manufacture and use of the composition of the invention. However, it will be appreciated that the methods and structures illustrated and described above may apply to any semiconductor fabrication process involving forming poly-silicon structures of differing heights. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended