US20110256705A1 - Method for forming a split gate device - Google Patents
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- US20110256705A1 US20110256705A1 US12/760,313 US76031310A US2011256705A1 US 20110256705 A1 US20110256705 A1 US 20110256705A1 US 76031310 A US76031310 A US 76031310A US 2011256705 A1 US2011256705 A1 US 2011256705A1
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/772—Field effect transistors
- H01L29/78—Field effect transistors with field effect produced by an insulated gate
- H01L29/788—Field effect transistors with field effect produced by an insulated gate with floating gate
- H01L29/7881—Programmable transistors with only two possible levels of programmation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/401—Multistep manufacturing processes
- H01L29/4011—Multistep manufacturing processes for data storage electrodes
- H01L29/40114—Multistep manufacturing processes for data storage electrodes the electrodes comprising a conductor-insulator-conductor-insulator-semiconductor structure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
- H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
- H01L29/42312—Gate electrodes for field effect devices
- H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
- H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
- H01L29/42324—Gate electrodes for transistors with a floating gate
- H01L29/42328—Gate electrodes for transistors with a floating gate with at least one additional gate other than the floating gate and the control gate, e.g. program gate, erase gate or select gate
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
- H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
- H01L29/42312—Gate electrodes for field effect devices
- H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
- H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
- H01L29/42324—Gate electrodes for transistors with a floating gate
- H01L29/42332—Gate electrodes for transistors with a floating gate with the floating gate formed by two or more non connected parts, e.g. multi-particles flating gate
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/66007—Multistep manufacturing processes
- H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
- H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
- H01L29/66409—Unipolar field-effect transistors
- H01L29/66477—Unipolar field-effect transistors with an insulated gate, i.e. MISFET
- H01L29/66825—Unipolar field-effect transistors with an insulated gate, i.e. MISFET with a floating gate
Definitions
- This disclosure relates generally to semiconductor processing, and more specifically, to split gate devices.
- Split gate devices which include both a select gate and a control gate, are typically used as bitcell storage devices within nonvolatile memory arrays.
- the use of a separate select gate for the bitcells in such arrays allows for improved isolation and reduced bitcell disturb during programming and reading of the bitcells. For example, program disturb is reduced for memory cells that are unselected but are either on the selected row or, in the alternative, on the selected column. Normally, cells on the selected row or the selected column are the most likely to be a problem for disturb regardless of the operation that is being performed on a selected cell. With the split gate memory cell having substantially solved the program disturb problem for cells on the selected rows or columns, a disturb problem with cells on unselected rows and unselected columns has become significant.
- FIGS. 1-8 illustrate a method for forming a split gate semiconductor device having a shallow recess in accordance with one embodiment of the present invention.
- FIGS. 9-14 illustrate a method for forming a split gate transistor device having a deep recess in accordance with one embodiment of the present invention.
- split gate devices are useful as bitcells in a memory.
- One embodiment described herein includes a method for forming a split gate device which may allow for improved performance.
- a split gate device includes a shallow recessed region adjacent a sidewall of the select gate in which portions of the charge storage layer and the control gate are formed.
- a split gate device includes a shallow recessed region adjacent a sidewall of the select gate in which portions of the charge storage layer and the control gate are formed.
- FIG. 1 illustrates a semiconductor structure 10 having a semiconductor substrate 12 .
- Semiconductor substrate 12 described herein can be any semiconductor material or combinations of materials, such as gallium arsenide, silicon germanium, silicon-on-insulator (SOI), silicon, monocrystalline silicon, the like, and combinations of the above.
- Semiconductor substrate 12 may also be referred to as a semiconductor layer.
- Semiconductor structure 10 includes a gate dielectric layer 14 over substrate 12 , a select gate layer 16 over the gate dielectric layer 14 , and an anti-reflective coating (ARC) layer 18 over select gate layer 16 .
- Gate dielectric layer 14 may be any appropriate gate dielectric layer, such as, for example, a gate oxide layer.
- Select gate layer 16 may be a polysilicon gate layer.
- select gate layer 16 may also be a metal, titanium nitride, or a combination of materials.
- semiconductor structure 10 also includes a patterned masking layer 20 over ARC layer 18 which defines the gate electrode to be formed from select gate layer 16 and ARC layer 18 .
- patterned masking layer 20 can be formed using any known method.
- a dry etch 22 is then performed on semiconductor structure 10 .
- dry etch 22 includes multiple etch steps, such as a first etch step (i.e. a breakthrough etch) to etch through ARC layer 18 followed by a second etch step (i.e. a main etch step) to etch through most of select gate layer 16 .
- the etch chemistry may differ between the breakthrough etch and the main etch.
- the main etch step of dry etch 22 in addition to including an etch chemistry which etches through the material of select gate layer 16 (such as, for example, carbon fluoride, in the case that select gate layer 16 is polysilicon), the etch chemistry may also include an oxidizing agent.
- the oxidizing agent may include for example, oxygen (O 2 ) or helium oxide (HeO 2 ).
- FIG. 2 illustrates semiconductor structure 10 after completion of dry etch 22 in which exposed areas of ARC layer 18 have been removed and exposed portions of select gate layer 16 have been removed, thus defining recess regions 30 .
- portions 26 of select gate layer 16 in regions 30 remain after dry etch 22 , covering gate dielectric layer 14 .
- dry etch 22 contained an oxidizing agent in its main etch step, dry etch 22 results in oxygen penetrating through portions 26 and gate dielectric 14 into semiconductor substrate 12 , thus forming oxidized regions 24 under gate dielectric layer 14 .
- a dry etch 28 is performed on semiconductor structure 10 , as illustrated by the arrows in FIG. 2 .
- dry etch 28 may be referred to as a third step of the dry etch 22 (which occurs subsequent to the second step of dry etch 22 ).
- This third step may also be referred to as a soft etch step.
- the soft etch step is performed using a lower etch power such that a lower etch rate results.
- dry etch 28 is more delicate as compared to dry etch 22 and is able to more carefully land or stop within gate dielectric layer 14 , as will be seen in FIG. 3 .
- a same etch chemistry may be used in both the main etch step and the soft etch step, with the exception that soft etch step may not include the oxidizing agent.
- one or more etch parameters may be changed between the main etch step and the soft etch step, such as, for example, etch chemistry, RF power, etch bias, etc., or combinations thereof.
- FIG. 3 illustrates semiconductor structure 10 after completion of dry etch 28 in which portions 26 of select gate layer 26 have been removed from regions 30 , and exposed portions (i.e. a top portion) of gate dielectric layer 14 in regions 30 have been removed. However, note that portions of gate dielectric layer 14 in regions 30 remain after dry etch 28 , covering and thus protecting oxidized regions 24 and substrate 12 . Note also that, due to the lower etch rate of dry etch 28 as compared to the main etch step of dry etch 22 , foot portions 32 of select gate layer 16 remain in regions 30 after dry etch 28 . After dry etch 28 is performed, a dry etch 34 is performed on semiconductor structure 10 , as illustrated by the arrows in FIG. 3 .
- dry etch 34 may be referred to as a fourth step of dry etch 22 (which occurs subsequent to the third etch step of dry etch 22 , i.e. subsequent to the soft etch step of dry etch 28 ).
- the fourth etch step may also be referred to as an overetch step.
- the overetch step is performed using a greater etch power than the third etch rate such that foot portions 32 can be removed, as well as all of gate dielectric layer 14 in regions 30 and portions of oxidized regions 24 .
- one or more etch parameters may be changed between the soft etch step and the overetch step, such as, for example, etch chemistry, RF power, etch bias, etc., or combinations thereof.
- FIG. 4 illustrates semiconductor structure 10 after completion of dry etch 34 , in which all exposed portions of gate dielectric layer 14 in regions 30 , foot portions 32 , and portions of oxidized regions 24 have been removed.
- the remaining portion of select gate layer 16 under patterned masking layer 20 can be referred to as the select gate electrode (or the select gate), and the remaining portion of gate dielectric layer 14 under patterned masking layer 20 can be referred to as the gate dielectric. Therefore, after removal of the portions of oxidized regions 24 , recesses 35 are formed in substrate 12 in regions 30 , adjacent the select gate electrode, where an oxide layer 36 remains in recesses 35 (representing the remaining portions of oxidized regions 24 ).
- recesses 35 result in substrate 12 having a recessed top surface as compared to the top surface of substrate 12 located under gate dielectric 14 and select gate electrode 16 .
- recesses 35 may be referred to as shallow recesses and have a depth of approximately 15 Angstroms from the top surface of substrate 12 located under gate dielectric 14 .
- FIG. 5 illustrates semiconductor structure 10 after removal of patterned masking layer 20 and oxide layer 36 .
- a first wet etch may be performed to remove patterned masking layer 20 and second wet etch, having a different etch chemistry, may be performed to remove oxide layer 36 .
- oxide layer 36 may not be removed.
- FIG. 6 illustrates semiconductor structure 10 after forming a charge storage layer 44 over substrate 12 in recesses 35 and over select gate electrode 16 .
- formation of charge storage layer 44 begins with growing an oxide 38 on exposed portions of substrate 12 in recesses 35 and along sidewalls of select gate electrode 16 . (Note that, in the case that oxide layer 36 is not removed, oxide 38 is grown on oxide layer 36 in recesses 35 where oxide layer 36 becomes part of oxide 38 .) In one embodiment, oxide 38 is grown to a thickness in a range of approximately 4 to 10 nanometers. After formation of oxide 38 , nanocrystals 40 and an insulating layer 42 surrounding nanocrystals 40 are formed over oxide layer 36 and select gate electrode 16 (e.g. over ARC layer 18 of gate electrode 16 ).
- nanocrystals 40 have diameters in a range of approximately 3 to 20 nanometers. Conventional processing may be used to form nanocrystals 40 .
- Nanocrystals 40 may include any type of conductive material, such as, for example, silicon, germanium, a metal, or the like.
- Insulating layer 42 is formed over and surrounding nanocrystals 40 , and, in one embodiment, is an oxide layer. Alternatively, insulating layer 42 may include hafnium oxide, aluminum oxide, etc. In one embodiment, insulating layer 42 has a thickness in a range of 8 to 20 nanometers. Therefore, note that oxide 38 (over substrate 12 ), nanocrystals 40 , and insulating layer 42 form charge storage layer 44 .
- charge storage layer 44 has a total thickness in a range of approximately 12 to 30 nanometers. Therefore, in one embodiment, charge storage layer 44 may be referred to as a thin storage layer which has a thickness of at most approximately 30 nanometers. Note that a portion of charge storage layer 44 is formed in recesses 35 and another portion of charge storage layer 44 is formed along a first sidewall of select gate electrode 16 . In alternate embodiments, any type of charge storage layer may be used. For example, charge storage layer 44 may include a single nitride layer, a trap oxide layer, or may include a stack of different layers.
- FIG. 7 illustrates semiconductor structure 10 after formation of a control gate electrode 50 (also referred to as control gate 50 ) over a portion of select gate electrode 16 and over substrate 12 within recess 35 adjacent a first sidewall of select gate electrode 16 . That is, note that control gate electrode 50 is formed such that it overlies a portion of select gate electrode 16 and extends over a sidewall of select gate electrode 16 onto substrate 12 within recess 35 adjacent the sidewall of select gate electrode 16 . In one embodiment, control gate electrode 50 is formed using conventional deposition and etching techniques. Note that during the etch to form control gate electrode 50 , portions of charge storage layer 44 are also etched, such that charge storage layer 44 remains between control gate electrode 50 and select gate electrode 16 and between control gate electrode 50 and substrate 12 . In one embodiment, control gate electrode 50 may include polysilicon, a metal, titanium nitride, etc., or combinations thereof.
- FIG. 8 illustrates semiconductor structure 10 after formation of spacers 48 and formation of source/drain regions 46 and 47 in substrate 12 to form a substantially completed split gate device.
- a first spacer of spacers 48 is formed along a sidewall of select gate electrode 16
- a second and third spacer of spacers 48 are formed along sidewalls of charge storage layer 44 and control gate electrode 50 .
- Conventional processing and materials may be used to form spacers 48 .
- Conventional processing may be used to form source/drain regions 46 and 47 .
- source/drain region 46 includes an extension region which extends under gate dielectric layer 14 and source/drain region 47 includes an extension region which extends under charge storage layer 44 .
- source/drain region 47 may be referred to as a source region which is adjacent a first sidewall of select gate electrode 16 where a portion of control gate electrode 50 is between the first sidewall of select gate electrode 16 and the source region, and source/drain region 46 may be referred to as a drain region which is adjacent a second sidewall of select gate electrode 16 .
- a substantially completed nanocrystal split gate device (also referred to as a split gate bitcell) is illustrated in FIG. 8 .
- rounded corner 52 allows for a thicker oxide in these corners underlying nanocrystals 40 . This may allow for an increased breakdown voltage and thus helps improve program and erase operation. Also, the thicker oxide may also allow for different polarities of an erase operation of the device and may also reduce any gap nanocrystal effect.
- the recessed regions in which charge storage layer 44 is formed may also allow for improved program operation due to improved ballistic injection and improved current drive.
- FIG. 9 illustrates a semiconductor structure 100 which may correspond to semiconductor structure 10 after dry etch 22 in accordance with another embodiment of the present invention. Therefore, prior to FIG. 9 , semiconductor structure 100 is the same as semiconductor structure 10 in FIG. 1 .
- dry etch 22 of FIG. 1 includes a first step (i.e. a main etch step) which etches through exposed portions of ARC layer 18 and select gate layer 16 , and etches into gate dielectric layer 14 , removing portions of gate dielectric layer 14 .
- the remaining portion of select gate layer 16 under patterned masking layer 20 may be referred to as select gate electrode 16 (or select gate 16 ).
- recess regions 60 are defined on either side of select gate electrode 16 .
- the main etch step includes an etch chemistry which etches through the material of select gate layer 16 (such as, for example, carbon fluoride, in the case that select gate layer 16 is polysilicon), and does not include an oxidizing agent.
- dry etch 22 is performed, dry etch 62 is performed on semiconductor structure 100 , as illustrated by the arrows of FIG. 9 .
- dry etch 62 may be referred to as a second step of dry etch 22 (which occurs subsequent to the first etch step), and may be referred to as a breakthrough etch step.
- the breakthrough etch etches through gate dielectric 14 to substrate 12 , thus removing all exposed portions of gate dielectric 14 in regions 60 .
- FIG. 10 illustrates semiconductor structure 100 after completion of dry etch 62 (i.e. after the breakthrough etch) in which substrate 12 is exposed in regions 60 .
- a dry etch 64 is performed on semiconductor structure 100 , as illustrated by the arrows of FIG. 10 .
- dry etch 64 may be referred to as a third etch step of dry etch 22 and may be referred to as a soft etch step.
- the soft etch step is performed using a lower etch power as compared to the main etch step such that a lower etch rate results. In this manner, dry etch 64 is more delicate as compared to dry etch 22 .
- a same etch chemistry may be used in both the main etch step and the soft etch step, with the exception that the soft etch step may include an oxidizing agent.
- the oxidizing agent may include for example, oxygen (O 2 ) or helium oxide (HeO 2 ).
- one or more etch parameters may be changed between the main etch step and the soft etch step, such as, for example, etch chemistry, RF power, etch bias, etc., or combinations thereof.
- FIG. 11 illustrates semiconductor structure 100 after completion of dry etch 64 in which deep recesses 68 are formed in substrate 12 in regions 60 , adjacent select gate electrode 16 .
- the soft etch step includes an oxidizing agent which allows for thin oxides to be formed on exposed portions of substrate 12 which are removed during the soft etch process. For example, these thin oxides may be iteratively formed and removed during the soft etch process. The use of the oxidizing agent may help the quality of the surface of substrate 12 being etched, such as by preventing pitting. In this manner, the surface of recesses 68 may allow for an improved interface with subsequent layers.
- recesses 68 have a depth of approximately 200 Angstroms from the top surface of substrate 12 located under patterned masking layer 20 . Note that after formation of recesses 68 , a wet etch may be used to remove patterned masking layer 20 .
- FIG. 12 illustrates semiconductor structure 100 after forming a charge storage layer 76 over substrate 12 in recesses 68 and over select gate electrode 16 .
- charge storage layer 76 includes an oxide 70 grown on exposed portions of substrate 12 in recesses 68 and along sidewalls of select gate electrode 16 , nanocrystals 72 formed over oxide 70 and select gate electrode 16 (e.g. over ARC layer 18 of gate electrode 16 ), and an insulating layer 74 surrounding nanocrystals 72 .
- charge storage layer 76 is analogous to charge storage layer 44 , and therefore, the descriptions provided above with respect to charge storage layer 44 , oxide 38 , nanocrystals 40 , and insulating layer 42 also apply to charge storage layer 76 , oxide 70 , nanocrystals 72 , and insulating layer 74 , respectively. Therefore, in one embodiment, as with charge storage layer 44 , charge storage layer 76 may be referred to as a thin storage layer which has a thickness of at most approximately 30 nanometers. Note that a portion of charge storage layer 76 is formed in recesses 68 and another portion of charge storage layer 76 is formed along a first sidewall of select gate electrode 16 . In alternate embodiments, any type of charge storage layer may be used. For example, charge storage layer 76 may include a single nitride layer, a trap oxide layer, or may include a stack of different layers.
- FIG. 13 illustrates semiconductor structure 100 after formation of a control gate electrode 78 (also referred to as a control gate) over a portion of select gate electrode 16 and over substrate 12 within recess 68 adjacent a first sidewall of select gate electrode 16 . That is, note that control gate electrode 78 is formed such that it overlies a portion of select gate electrode 16 and extends over a sidewall of select gate electrode 16 onto substrate 12 within recess 68 adjacent the sidewall of select gate electrode 16 . In one embodiment, control gate electrode 78 is formed using conventional deposition and etching techniques.
- control gate electrode 78 may include polysilicon, a metal, titanium nitride, etc., or combinations thereof.
- FIG. 14 illustrates semiconductor structure 100 after formation of spacers 80 and formation source/drain regions 82 and 81 in substrate 12 to form a substantially completed split gate device.
- a first spacer of spacers 80 is formed along a sidewall of select gate electrode 16
- a second and third spacer of spacers 80 are formed along sidewalls of charge storage layer 76 and control gate electrode 78 .
- Conventional processing and materials may be used to form spacers 80 .
- Conventional processing may be used to form source/drain regions 82 and 81 .
- source/drain region 82 includes an extension region which extends under gate dielectric layer 14
- source/drain region 81 includes an extension region which extends under charge storage layer 76 .
- source/drain region 81 may be referred to as a source region which is adjacent a first sidewall of select gate electrode 16 where a portion of control gate electrode 78 is between the first sidewall of select gate electrode 16 and the source region, and source/drain region 82 may be referred to as a drain region which is adjacent a second sidewall of select gate electrode 16 .
- FIG. 14 a substantially completed nanocrystal split gate device (also referred to as a split gate bitcell) is illustrated in FIG. 14 .
- recess 68 may allow for an increased breakdown voltage and thus helps improve program and erase operation.
- the thicker oxide at the corner of recess 68 may also allow for different polarities of an erase operation of the device and may also reduce any gap nanocrystal effect.
- the recessed regions in which charge storage layer 76 is formed may also allow for improved program operation due to improved ballistic injection and improved current drive. Note that vertical wall 66 of recess 68 is substantially vertical as it extends into substrate 12 .
- This vertical wall may reduce program disturb for cells on unselected row and unselected columns by reducing the peak electric field in substrate 12 between the select gate and control gate (gap region), typically near the surface of substrate 12 , adjacent to the select gate.
- a sufficiently high peak electric field in the gap region leads to generation of carriers by band-to-band tunneling. Carriers generated in the gap may subsequently lead to disturb of erased bits.
- Item 1 includes a method for forming a semiconductor device including forming a dielectric layer over a substrate; forming a select gate layer over the dielectric layer; etching the select gate layer at a first etch rate to form a first portion of a sidewall of a select gate, wherein the step of etching the select gate layer at the first etch rate includes using an oxidizing agent to oxidize at least a top portion of the substrate underlying the dielectric layer to form an oxide layer below the dielectric layer; and etching the select gate layer at a second etch rate lower than the first etch rate to form a second portion of the sidewall of the select gate, wherein the step of etching the select gate layer at the second etch rate includes removing only a top portion of the dielectric layer.
- Item 2 includes the method of item 1, wherein the oxidizing agent is selected from a group consisting of oxygen and helium oxide.
- Item 3 includes the method of item 1, and further includes removing the oxide layer and any remaining portion of the dielectric layer to expose a portion of the substrate; forming a charge storage layer overlying exposed portion of the substrate and the sidewall of the select gate; forming a control gate layer overlying the charge storage layer; and forming a control gate by patterning the control gate layer and the charge storage layer.
- Item 4 includes the method of item 3, wherein the step of forming the charge storage layer comprises forming a layer of one of a group consisting of nanocrystals, nitride, and oxide.
- Item 5 includes the method of item 1, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch power and the step of etching the select gate layer at the second etch rate comprises using the RF plasma at a second etch power lower than the first etch power.
- Item 6 includes the method of item 1, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch bias and the step of etching the select gate layer at the second etch rate comprises using the RF plasma at a second etch bias lower than the first etch bias.
- Item 7 includes the method of item 1, wherein the step of etching the select gate layer at the first etch rate comprises using a first etch chemistry and the step of etching the select gate layer at the second etch rate comprises using a second etch chemistry, wherein the second etch chemistry is different from the first etch chemistry.
- Item 8 includes the method of item 1 and further includes removing the oxide layer and any remaining portion of the dielectric layer to form a recess in the substrate adjacent to the sidewall of the select gate.
- Item 9 includes a method for forming a semiconductor device including forming a dielectric layer over a substrate; forming a select gate layer over the dielectric layer; using a first etch chemistry etching the select gate layer at a first etch rate to form a sidewall of a select gate; using a second etch chemistry different from the first etch chemistry, selectively etching the dielectric layer; and etching the substrate at a second etch rate lower than the first etch rate to form a recess in the substrate adjacent to the sidewall of the select gate, wherein the step of etching the substrate at the second etch rate includes using an oxidizing agent.
- Item 10 includes the method of item 9, wherein the oxidizing agent is selected from a group consisting of oxygen and helium oxide.
- Item 11 includes the method of item 9 and further includes forming a charge storage layer overlying any exposed portion of the substrate and the sidewall of the select gate; forming a control gate layer overlying the charge storage layer; and forming a control gate by patterning the control gate layer and the charge storage layer.
- Item 12 includes the method of item 11, wherein the step of forming the charge storage layer comprises forming a layer of one of a group consisting of nanocrystals, nitride, and oxide.
- Item 12 includes the method of item 9, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch power and the step of etching the substrate at the second etch rate comprises using the RF plasma at a second etch power lower than the first etch power.
- Item 14 includes the method of item 9, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch bias and the step of etching the substrate at the second etch rate comprises using the RF plasma at a second etch bias lower than the first etch bias.
- Item 15 includes the method of item 9, wherein the step of etching the substrate at the second etch rate comprises using a third etch chemistry, wherein the third etch chemistry is different from the first etch chemistry.
- Item 16 includes the method of item 9, wherein the step of etching the substrate at a second etch rate lower than the first etch rate to form the recess in the substrate comprises forming a substantially vertical recess.
- Item 17 includes a method for forming a semiconductor device including forming a dielectric layer over a substrate; forming a select gate layer over the dielectric layer; etching the select gate layer at a first etch rate to form a first portion of a sidewall of a select gate, wherein the step of etching the select gate layer at the first etch rate includes using an oxidizing agent to oxidize at least a top portion of the substrate underlying the dielectric layer to form an oxide layer below the dielectric layer; etching the select gate layer at a second etch rate lower than the first etch rate to form a second portion of the sidewall of the select gate, wherein the step of etching the select gate layer at the second etch rate includes removing only a top portion of the dielectric layer; using a wet etch removing the oxide layer and any remaining portion of the dielectric layer to expose a portion of the substrate; forming a charge storage layer overlying exposed portion of the substrate and the sidewall of the select gate; forming a control gate
- Item 18 includes the method of item 17, wherein the oxidizing agent is selected from a group consisting of oxygen and helium oxide.
- Item 19 includes the method of item 18, wherein the step of forming the charge storage layer comprises forming a layer of one of a group consisting of nanocrystals, nitride, and oxide.
- Item 20 includes the method of item 19, wherein the second etch rate is lower than the first etch rate as a result of a variation in at least one of an etch power, an etch bias, and an etch chemistry associated with a respective etching step.
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Abstract
Description
- 1. Field
- This disclosure relates generally to semiconductor processing, and more specifically, to split gate devices.
- 2. Related Art
- Split gate devices, which include both a select gate and a control gate, are typically used as bitcell storage devices within nonvolatile memory arrays. The use of a separate select gate for the bitcells in such arrays allows for improved isolation and reduced bitcell disturb during programming and reading of the bitcells. For example, program disturb is reduced for memory cells that are unselected but are either on the selected row or, in the alternative, on the selected column. Normally, cells on the selected row or the selected column are the most likely to be a problem for disturb regardless of the operation that is being performed on a selected cell. With the split gate memory cell having substantially solved the program disturb problem for cells on the selected rows or columns, a disturb problem with cells on unselected rows and unselected columns has become significant. One of the reasons is that the particular stress that is applied for cells on unselected rows and columns is applied for many more cycles than for a stress that is applied for cells on a selected row or column. Also, due to the length of the select gates and control gates, reduced drive current is obtained which degrades reading performance.
- The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.
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FIGS. 1-8 illustrate a method for forming a split gate semiconductor device having a shallow recess in accordance with one embodiment of the present invention. -
FIGS. 9-14 illustrate a method for forming a split gate transistor device having a deep recess in accordance with one embodiment of the present invention. - As described above, split gate devices are useful as bitcells in a memory. One embodiment described herein includes a method for forming a split gate device which may allow for improved performance. For example, in one embodiment, a split gate device includes a shallow recessed region adjacent a sidewall of the select gate in which portions of the charge storage layer and the control gate are formed. Also, in one embodiment, a split gate device includes a shallow recessed region adjacent a sidewall of the select gate in which portions of the charge storage layer and the control gate are formed.
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FIG. 1 illustrates asemiconductor structure 10 having asemiconductor substrate 12.Semiconductor substrate 12 described herein can be any semiconductor material or combinations of materials, such as gallium arsenide, silicon germanium, silicon-on-insulator (SOI), silicon, monocrystalline silicon, the like, and combinations of the above.Semiconductor substrate 12 may also be referred to as a semiconductor layer.Semiconductor structure 10 includes a gatedielectric layer 14 oversubstrate 12, aselect gate layer 16 over the gatedielectric layer 14, and an anti-reflective coating (ARC)layer 18 overselect gate layer 16. Gatedielectric layer 14 may be any appropriate gate dielectric layer, such as, for example, a gate oxide layer. Selectgate layer 16 may be a polysilicon gate layer. Alternatively,select gate layer 16 may also be a metal, titanium nitride, or a combination of materials. InFIG. 1 ,semiconductor structure 10 also includes a patternedmasking layer 20 overARC layer 18 which defines the gate electrode to be formed fromselect gate layer 16 andARC layer 18. Note that patternedmasking layer 20 can be formed using any known method. As indicated by the arrows inFIG. 1 , adry etch 22 is then performed onsemiconductor structure 10. In one embodiment,dry etch 22 includes multiple etch steps, such as a first etch step (i.e. a breakthrough etch) to etch throughARC layer 18 followed by a second etch step (i.e. a main etch step) to etch through most ofselect gate layer 16. Therefore, the etch chemistry may differ between the breakthrough etch and the main etch. In one embodiment, the main etch step ofdry etch 22, in addition to including an etch chemistry which etches through the material of select gate layer 16 (such as, for example, carbon fluoride, in the case that selectgate layer 16 is polysilicon), the etch chemistry may also include an oxidizing agent. The oxidizing agent may include for example, oxygen (O2) or helium oxide (HeO2). -
FIG. 2 illustratessemiconductor structure 10 after completion ofdry etch 22 in which exposed areas ofARC layer 18 have been removed and exposed portions ofselect gate layer 16 have been removed, thus definingrecess regions 30. Note thatportions 26 ofselect gate layer 16 inregions 30 remain afterdry etch 22, covering gatedielectric layer 14. Also, sincedry etch 22 contained an oxidizing agent in its main etch step,dry etch 22 results in oxygen penetrating throughportions 26 and gate dielectric 14 intosemiconductor substrate 12, thus forming oxidizedregions 24 under gatedielectric layer 14. Afterdry etch 22 is performed, adry etch 28 is performed onsemiconductor structure 10, as illustrated by the arrows inFIG. 2 . In one embodiment,dry etch 28 may be referred to as a third step of the dry etch 22 (which occurs subsequent to the second step of dry etch 22). This third step may also be referred to as a soft etch step. In one embodiment, the soft etch step is performed using a lower etch power such that a lower etch rate results. In this manner,dry etch 28 is more delicate as compared todry etch 22 and is able to more carefully land or stop within gatedielectric layer 14, as will be seen inFIG. 3 . In one embodiment, a same etch chemistry may be used in both the main etch step and the soft etch step, with the exception that soft etch step may not include the oxidizing agent. In one embodiment, to result in a lower etch rate, one or more etch parameters may be changed between the main etch step and the soft etch step, such as, for example, etch chemistry, RF power, etch bias, etc., or combinations thereof. -
FIG. 3 illustratessemiconductor structure 10 after completion ofdry etch 28 in whichportions 26 ofselect gate layer 26 have been removed fromregions 30, and exposed portions (i.e. a top portion) of gatedielectric layer 14 inregions 30 have been removed. However, note that portions of gatedielectric layer 14 inregions 30 remain afterdry etch 28, covering and thus protecting oxidizedregions 24 andsubstrate 12. Note also that, due to the lower etch rate ofdry etch 28 as compared to the main etch step ofdry etch 22,foot portions 32 ofselect gate layer 16 remain inregions 30 afterdry etch 28. Afterdry etch 28 is performed, adry etch 34 is performed onsemiconductor structure 10, as illustrated by the arrows inFIG. 3 . In one embodiment,dry etch 34 may be referred to as a fourth step of dry etch 22 (which occurs subsequent to the third etch step ofdry etch 22, i.e. subsequent to the soft etch step of dry etch 28). The fourth etch step may also be referred to as an overetch step. In one embodiment, the overetch step is performed using a greater etch power than the third etch rate such thatfoot portions 32 can be removed, as well as all of gatedielectric layer 14 inregions 30 and portions of oxidizedregions 24. In one embodiment, one or more etch parameters may be changed between the soft etch step and the overetch step, such as, for example, etch chemistry, RF power, etch bias, etc., or combinations thereof. -
FIG. 4 illustratessemiconductor structure 10 after completion ofdry etch 34, in which all exposed portions of gatedielectric layer 14 inregions 30,foot portions 32, and portions of oxidizedregions 24 have been removed. Note that the remaining portion ofselect gate layer 16 under patternedmasking layer 20 can be referred to as the select gate electrode (or the select gate), and the remaining portion of gatedielectric layer 14 under patternedmasking layer 20 can be referred to as the gate dielectric. Therefore, after removal of the portions of oxidizedregions 24,recesses 35 are formed insubstrate 12 inregions 30, adjacent the select gate electrode, where anoxide layer 36 remains in recesses 35 (representing the remaining portions of oxidized regions 24). Therefore,recesses 35 result insubstrate 12 having a recessed top surface as compared to the top surface ofsubstrate 12 located under gate dielectric 14 andselect gate electrode 16. In one embodiment,recesses 35 may be referred to as shallow recesses and have a depth of approximately 15 Angstroms from the top surface ofsubstrate 12 located under gate dielectric 14. -
FIG. 5 illustratessemiconductor structure 10 after removal of patternedmasking layer 20 andoxide layer 36. In one embodiment, a first wet etch may be performed to remove patternedmasking layer 20 and second wet etch, having a different etch chemistry, may be performed to removeoxide layer 36. In an alternate embodiment,oxide layer 36 may not be removed. -
FIG. 6 illustratessemiconductor structure 10 after forming acharge storage layer 44 oversubstrate 12 inrecesses 35 and overselect gate electrode 16. In one embodiment, formation ofcharge storage layer 44 begins with growing anoxide 38 on exposed portions ofsubstrate 12 inrecesses 35 and along sidewalls ofselect gate electrode 16. (Note that, in the case thatoxide layer 36 is not removed,oxide 38 is grown onoxide layer 36 inrecesses 35 whereoxide layer 36 becomes part ofoxide 38.) In one embodiment,oxide 38 is grown to a thickness in a range of approximately 4 to 10 nanometers. After formation ofoxide 38, nanocrystals 40 and an insulatinglayer 42 surroundingnanocrystals 40 are formed overoxide layer 36 and select gate electrode 16 (e.g. overARC layer 18 of gate electrode 16). In one embodiment, nanocrystals 40 have diameters in a range of approximately 3 to 20 nanometers. Conventional processing may be used to formnanocrystals 40.Nanocrystals 40 may include any type of conductive material, such as, for example, silicon, germanium, a metal, or the like. Insulatinglayer 42 is formed over and surroundingnanocrystals 40, and, in one embodiment, is an oxide layer. Alternatively, insulatinglayer 42 may include hafnium oxide, aluminum oxide, etc. In one embodiment, insulatinglayer 42 has a thickness in a range of 8 to 20 nanometers. Therefore, note that oxide 38 (over substrate 12), nanocrystals 40, and insulatinglayer 42 formcharge storage layer 44. In one embodiment,charge storage layer 44 has a total thickness in a range of approximately 12 to 30 nanometers. Therefore, in one embodiment,charge storage layer 44 may be referred to as a thin storage layer which has a thickness of at most approximately 30 nanometers. Note that a portion ofcharge storage layer 44 is formed inrecesses 35 and another portion ofcharge storage layer 44 is formed along a first sidewall ofselect gate electrode 16. In alternate embodiments, any type of charge storage layer may be used. For example,charge storage layer 44 may include a single nitride layer, a trap oxide layer, or may include a stack of different layers. -
FIG. 7 illustratessemiconductor structure 10 after formation of a control gate electrode 50 (also referred to as control gate 50) over a portion ofselect gate electrode 16 and oversubstrate 12 withinrecess 35 adjacent a first sidewall ofselect gate electrode 16. That is, note that control gate electrode 50 is formed such that it overlies a portion ofselect gate electrode 16 and extends over a sidewall ofselect gate electrode 16 ontosubstrate 12 withinrecess 35 adjacent the sidewall ofselect gate electrode 16. In one embodiment, control gate electrode 50 is formed using conventional deposition and etching techniques. Note that during the etch to form control gate electrode 50, portions ofcharge storage layer 44 are also etched, such thatcharge storage layer 44 remains between control gate electrode 50 andselect gate electrode 16 and between control gate electrode 50 andsubstrate 12. In one embodiment, control gate electrode 50 may include polysilicon, a metal, titanium nitride, etc., or combinations thereof. -
FIG. 8 illustratessemiconductor structure 10 after formation of spacers 48 and formation of source/drain regions 46 and 47 insubstrate 12 to form a substantially completed split gate device. A first spacer of spacers 48 is formed along a sidewall ofselect gate electrode 16, and a second and third spacer of spacers 48 are formed along sidewalls ofcharge storage layer 44 and control gate electrode 50. Conventional processing and materials may be used to form spacers 48. Conventional processing may be used to form source/drain regions 46 and 47. In one embodiment, source/drain region 46 includes an extension region which extends undergate dielectric layer 14 and source/drain region 47 includes an extension region which extends undercharge storage layer 44. In one embodiment, source/drain region 47 may be referred to as a source region which is adjacent a first sidewall ofselect gate electrode 16 where a portion of control gate electrode 50 is between the first sidewall ofselect gate electrode 16 and the source region, and source/drain region 46 may be referred to as a drain region which is adjacent a second sidewall ofselect gate electrode 16. - Therefore, a substantially completed nanocrystal split gate device (also referred to as a split gate bitcell) is illustrated in
FIG. 8 . Note that rounded corner 52 allows for a thicker oxide in thesecorners underlying nanocrystals 40. This may allow for an increased breakdown voltage and thus helps improve program and erase operation. Also, the thicker oxide may also allow for different polarities of an erase operation of the device and may also reduce any gap nanocrystal effect. The recessed regions in whichcharge storage layer 44 is formed may also allow for improved program operation due to improved ballistic injection and improved current drive. -
FIG. 9 illustrates asemiconductor structure 100 which may correspond tosemiconductor structure 10 afterdry etch 22 in accordance with another embodiment of the present invention. Therefore, prior toFIG. 9 ,semiconductor structure 100 is the same assemiconductor structure 10 inFIG. 1 . In the current example,dry etch 22 ofFIG. 1 includes a first step (i.e. a main etch step) which etches through exposed portions ofARC layer 18 andselect gate layer 16, and etches intogate dielectric layer 14, removing portions ofgate dielectric layer 14. Referring tosemiconductor structure 100 ofFIG. 9 , the remaining portion ofselect gate layer 16 under patternedmasking layer 20 may be referred to as select gate electrode 16 (or select gate 16). Therefore,recess regions 60 are defined on either side ofselect gate electrode 16. Note that not all ofgate dielectric layer 14 inregions 60 is removed, such that a portion ofgate dielectric layer 14 inregions 60remains covering substrate 12. In the current example, the main etch step includes an etch chemistry which etches through the material of select gate layer 16 (such as, for example, carbon fluoride, in the case that selectgate layer 16 is polysilicon), and does not include an oxidizing agent. Afterdry etch 22 is performed,dry etch 62 is performed onsemiconductor structure 100, as illustrated by the arrows ofFIG. 9 . In one embodiment,dry etch 62 may be referred to as a second step of dry etch 22 (which occurs subsequent to the first etch step), and may be referred to as a breakthrough etch step. In one embodiment, the breakthrough etch etches through gate dielectric 14 tosubstrate 12, thus removing all exposed portions of gate dielectric 14 inregions 60. -
FIG. 10 illustratessemiconductor structure 100 after completion of dry etch 62 (i.e. after the breakthrough etch) in whichsubstrate 12 is exposed inregions 60. Afterdry etch 62 is performed, a dry etch 64 is performed onsemiconductor structure 100, as illustrated by the arrows ofFIG. 10 . In one embodiment, dry etch 64 may be referred to as a third etch step ofdry etch 22 and may be referred to as a soft etch step. In one embodiment, the soft etch step is performed using a lower etch power as compared to the main etch step such that a lower etch rate results. In this manner, dry etch 64 is more delicate as compared todry etch 22. In one embodiment, a same etch chemistry may be used in both the main etch step and the soft etch step, with the exception that the soft etch step may include an oxidizing agent. The oxidizing agent may include for example, oxygen (O2) or helium oxide (HeO2). In one embodiment, to result in a lower etch rate, one or more etch parameters may be changed between the main etch step and the soft etch step, such as, for example, etch chemistry, RF power, etch bias, etc., or combinations thereof. -
FIG. 11 illustratessemiconductor structure 100 after completion of dry etch 64 in which deep recesses 68 are formed insubstrate 12 inregions 60, adjacentselect gate electrode 16. As described above, the soft etch step includes an oxidizing agent which allows for thin oxides to be formed on exposed portions ofsubstrate 12 which are removed during the soft etch process. For example, these thin oxides may be iteratively formed and removed during the soft etch process. The use of the oxidizing agent may help the quality of the surface ofsubstrate 12 being etched, such as by preventing pitting. In this manner, the surface ofrecesses 68 may allow for an improved interface with subsequent layers. In one embodiment, recesses 68 have a depth of approximately 200 Angstroms from the top surface ofsubstrate 12 located under patternedmasking layer 20. Note that after formation ofrecesses 68, a wet etch may be used to remove patternedmasking layer 20. -
FIG. 12 illustratessemiconductor structure 100 after forming acharge storage layer 76 oversubstrate 12 inrecesses 68 and overselect gate electrode 16. In one embodiment,charge storage layer 76 includes anoxide 70 grown on exposed portions ofsubstrate 12 inrecesses 68 and along sidewalls ofselect gate electrode 16, nanocrystals 72 formed overoxide 70 and select gate electrode 16 (e.g. overARC layer 18 of gate electrode 16), and an insulatinglayer 74 surroundingnanocrystals 72. Note that thecharge storage layer 76 is analogous to chargestorage layer 44, and therefore, the descriptions provided above with respect to chargestorage layer 44,oxide 38, nanocrystals 40, and insulatinglayer 42 also apply to chargestorage layer 76,oxide 70, nanocrystals 72, and insulatinglayer 74, respectively. Therefore, in one embodiment, as withcharge storage layer 44,charge storage layer 76 may be referred to as a thin storage layer which has a thickness of at most approximately 30 nanometers. Note that a portion ofcharge storage layer 76 is formed inrecesses 68 and another portion ofcharge storage layer 76 is formed along a first sidewall ofselect gate electrode 16. In alternate embodiments, any type of charge storage layer may be used. For example,charge storage layer 76 may include a single nitride layer, a trap oxide layer, or may include a stack of different layers. -
FIG. 13 illustratessemiconductor structure 100 after formation of a control gate electrode 78 (also referred to as a control gate) over a portion ofselect gate electrode 16 and oversubstrate 12 withinrecess 68 adjacent a first sidewall ofselect gate electrode 16. That is, note thatcontrol gate electrode 78 is formed such that it overlies a portion ofselect gate electrode 16 and extends over a sidewall ofselect gate electrode 16 ontosubstrate 12 withinrecess 68 adjacent the sidewall ofselect gate electrode 16. In one embodiment,control gate electrode 78 is formed using conventional deposition and etching techniques. Note that during the etch to formcontrol gate electrode 78, portions ofcharge storage layer 76 are also etched, such thatcharge storage layer 76 remains betweencontrol gate electrode 78 andselect gate electrode 16 and betweencontrol gate electrode 78 andsubstrate 12. In one embodiment,control gate electrode 78 may include polysilicon, a metal, titanium nitride, etc., or combinations thereof. -
FIG. 14 illustratessemiconductor structure 100 after formation ofspacers 80 and formation source/drain regions substrate 12 to form a substantially completed split gate device. A first spacer ofspacers 80 is formed along a sidewall ofselect gate electrode 16, and a second and third spacer ofspacers 80 are formed along sidewalls ofcharge storage layer 76 andcontrol gate electrode 78. Conventional processing and materials may be used to formspacers 80. Conventional processing may be used to form source/drain regions drain region 82 includes an extension region which extends undergate dielectric layer 14 and source/drain region 81 includes an extension region which extends undercharge storage layer 76. In one embodiment, source/drain region 81 may be referred to as a source region which is adjacent a first sidewall ofselect gate electrode 16 where a portion ofcontrol gate electrode 78 is between the first sidewall ofselect gate electrode 16 and the source region, and source/drain region 82 may be referred to as a drain region which is adjacent a second sidewall ofselect gate electrode 16. - Therefore, a substantially completed nanocrystal split gate device (also referred to as a split gate bitcell) is illustrated in
FIG. 14 . As described above with respect toFIG. 8 andrecess 35,recess 68 may allow for an increased breakdown voltage and thus helps improve program and erase operation. Also, the thicker oxide at the corner ofrecess 68 may also allow for different polarities of an erase operation of the device and may also reduce any gap nanocrystal effect. The recessed regions in whichcharge storage layer 76 is formed may also allow for improved program operation due to improved ballistic injection and improved current drive. Note thatvertical wall 66 ofrecess 68 is substantially vertical as it extends intosubstrate 12. This vertical wall may reduce program disturb for cells on unselected row and unselected columns by reducing the peak electric field insubstrate 12 between the select gate and control gate (gap region), typically near the surface ofsubstrate 12, adjacent to the select gate. A sufficiently high peak electric field in the gap region leads to generation of carriers by band-to-band tunneling. Carriers generated in the gap may subsequently lead to disturb of erased bits. - By now it should be appreciated that there has been provided a method for forming a nanocrystal split gate device useful as a bitcell in a memory. Through the use of shallow or deep recessed regions which may allow for rounded corners and for a thicker oxide beneath the nanocrystals, an improved split gate device may be achieved.
- Although the invention has been described with respect to specific conductivity types or polarity of potentials, skilled artisans appreciated that conductivity types and polarities of potentials may be reversed.
- Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
- Although the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For example, different thin charge storage layers may be used, spacers (such as spacer 22) may be left within the final device, or two devices which share a source/drain region may be formed. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.
- Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles.
- Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements.
- The following are various embodiments of the present invention.
-
Item 1 includes a method for forming a semiconductor device including forming a dielectric layer over a substrate; forming a select gate layer over the dielectric layer; etching the select gate layer at a first etch rate to form a first portion of a sidewall of a select gate, wherein the step of etching the select gate layer at the first etch rate includes using an oxidizing agent to oxidize at least a top portion of the substrate underlying the dielectric layer to form an oxide layer below the dielectric layer; and etching the select gate layer at a second etch rate lower than the first etch rate to form a second portion of the sidewall of the select gate, wherein the step of etching the select gate layer at the second etch rate includes removing only a top portion of the dielectric layer. Item 2 includes the method ofitem 1, wherein the oxidizing agent is selected from a group consisting of oxygen and helium oxide. Item 3 includes the method ofitem 1, and further includes removing the oxide layer and any remaining portion of the dielectric layer to expose a portion of the substrate; forming a charge storage layer overlying exposed portion of the substrate and the sidewall of the select gate; forming a control gate layer overlying the charge storage layer; and forming a control gate by patterning the control gate layer and the charge storage layer. Item 4 includes the method of item 3, wherein the step of forming the charge storage layer comprises forming a layer of one of a group consisting of nanocrystals, nitride, and oxide. Item 5 includes the method ofitem 1, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch power and the step of etching the select gate layer at the second etch rate comprises using the RF plasma at a second etch power lower than the first etch power. Item 6 includes the method ofitem 1, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch bias and the step of etching the select gate layer at the second etch rate comprises using the RF plasma at a second etch bias lower than the first etch bias. Item 7 includes the method ofitem 1, wherein the step of etching the select gate layer at the first etch rate comprises using a first etch chemistry and the step of etching the select gate layer at the second etch rate comprises using a second etch chemistry, wherein the second etch chemistry is different from the first etch chemistry. Item 8 includes the method ofitem 1 and further includes removing the oxide layer and any remaining portion of the dielectric layer to form a recess in the substrate adjacent to the sidewall of the select gate. - Item 9 includes a method for forming a semiconductor device including forming a dielectric layer over a substrate; forming a select gate layer over the dielectric layer; using a first etch chemistry etching the select gate layer at a first etch rate to form a sidewall of a select gate; using a second etch chemistry different from the first etch chemistry, selectively etching the dielectric layer; and etching the substrate at a second etch rate lower than the first etch rate to form a recess in the substrate adjacent to the sidewall of the select gate, wherein the step of etching the substrate at the second etch rate includes using an oxidizing agent.
Item 10 includes the method of item 9, wherein the oxidizing agent is selected from a group consisting of oxygen and helium oxide.Item 11 includes the method of item 9 and further includes forming a charge storage layer overlying any exposed portion of the substrate and the sidewall of the select gate; forming a control gate layer overlying the charge storage layer; and forming a control gate by patterning the control gate layer and the charge storage layer.Item 12 includes the method ofitem 11, wherein the step of forming the charge storage layer comprises forming a layer of one of a group consisting of nanocrystals, nitride, and oxide.Item 12 includes the method of item 9, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch power and the step of etching the substrate at the second etch rate comprises using the RF plasma at a second etch power lower than the first etch power.Item 14 includes the method of item 9, wherein the step of etching the select gate layer at the first etch rate comprises using a RF plasma at a first etch bias and the step of etching the substrate at the second etch rate comprises using the RF plasma at a second etch bias lower than the first etch bias. Item 15 includes the method of item 9, wherein the step of etching the substrate at the second etch rate comprises using a third etch chemistry, wherein the third etch chemistry is different from the first etch chemistry.Item 16 includes the method of item 9, wherein the step of etching the substrate at a second etch rate lower than the first etch rate to form the recess in the substrate comprises forming a substantially vertical recess. - Item 17 includes a method for forming a semiconductor device including forming a dielectric layer over a substrate; forming a select gate layer over the dielectric layer; etching the select gate layer at a first etch rate to form a first portion of a sidewall of a select gate, wherein the step of etching the select gate layer at the first etch rate includes using an oxidizing agent to oxidize at least a top portion of the substrate underlying the dielectric layer to form an oxide layer below the dielectric layer; etching the select gate layer at a second etch rate lower than the first etch rate to form a second portion of the sidewall of the select gate, wherein the step of etching the select gate layer at the second etch rate includes removing only a top portion of the dielectric layer; using a wet etch removing the oxide layer and any remaining portion of the dielectric layer to expose a portion of the substrate; forming a charge storage layer overlying exposed portion of the substrate and the sidewall of the select gate; forming a control gate layer overlying the charge storage layer; and forming a control gate by patterning the control gate layer and the charge storage layer.
Item 18 includes the method of item 17, wherein the oxidizing agent is selected from a group consisting of oxygen and helium oxide. Item 19 includes the method ofitem 18, wherein the step of forming the charge storage layer comprises forming a layer of one of a group consisting of nanocrystals, nitride, and oxide.Item 20 includes the method of item 19, wherein the second etch rate is lower than the first etch rate as a result of a variation in at least one of an etch power, an etch bias, and an etch chemistry associated with a respective etching step.
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US20150287737A1 (en) * | 2013-08-23 | 2015-10-08 | Taiwan Semiconductor Manufacturing Co., Ltd. | Silicon dot formation by self-assembly method and selective silicon growth for flash memory |
US9257445B2 (en) * | 2014-05-30 | 2016-02-09 | Freescale Semiconductor, Inc. | Method of making a split gate non-volatile memory (NVM) cell and a logic transistor |
US9281203B2 (en) | 2013-08-23 | 2016-03-08 | Taiwan Semiconductor Manufacturing Co., Ltd. | Silicon dot formation by direct self-assembly method for flash memory |
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US8530950B1 (en) * | 2012-05-31 | 2013-09-10 | Freescale Semiconductor, Inc. | Methods and structures for split gate memory |
US9590058B2 (en) | 2013-06-28 | 2017-03-07 | Nxp Usa, Inc. | Methods and structures for a split gate memory cell structure |
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US6232185B1 (en) | 2000-05-15 | 2001-05-15 | Integrated Memory Technologies, Inc. | Method of making a floating gate memory cell |
US6706601B1 (en) * | 2003-03-19 | 2004-03-16 | Taiwan Semiconductor Manufacturing Company | Method of forming tiny silicon nitride spacer for flash EPROM by using dry+wet etching technology |
US7202170B2 (en) * | 2004-01-20 | 2007-04-10 | Taiwan Semiconductor Manufacturing Co., Ltd. | Method of improving etching profile of floating gates for flash memory devices |
US7274068B2 (en) | 2004-05-06 | 2007-09-25 | Micron Technology, Inc. | Ballistic direct injection NROM cell on strained silicon structures |
US20050259467A1 (en) | 2004-05-18 | 2005-11-24 | Micron Technology, Inc. | Split gate flash memory cell with ballistic injection |
US7105889B2 (en) * | 2004-06-04 | 2006-09-12 | International Business Machines Corporation | Selective implementation of barrier layers to achieve threshold voltage control in CMOS device fabrication with high k dielectrics |
US7544610B2 (en) * | 2004-09-07 | 2009-06-09 | International Business Machines Corporation | Method and process for forming a self-aligned silicide contact |
KR100654341B1 (en) | 2004-12-08 | 2006-12-08 | 삼성전자주식회사 | Nonvolatile memory device and method for fabricating the same |
KR100674958B1 (en) * | 2005-02-23 | 2007-01-26 | 삼성전자주식회사 | Split type flash memory device having self aligned control gate and method for manufacturing the same |
DE102006015090B4 (en) | 2006-03-31 | 2008-03-13 | Advanced Micro Devices, Inc., Sunnyvale | Method for producing different embedded deformation layers in transistors |
US8178406B2 (en) * | 2007-10-29 | 2012-05-15 | Freescale Semiconductor, Inc. | Split gate device and method for forming |
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US20150287737A1 (en) * | 2013-08-23 | 2015-10-08 | Taiwan Semiconductor Manufacturing Co., Ltd. | Silicon dot formation by self-assembly method and selective silicon growth for flash memory |
US9281203B2 (en) | 2013-08-23 | 2016-03-08 | Taiwan Semiconductor Manufacturing Co., Ltd. | Silicon dot formation by direct self-assembly method for flash memory |
US9385136B2 (en) * | 2013-08-23 | 2016-07-05 | Taiwan Semiconductor Manufacturing Co., Ltd. | Silicon dot formation by self-assembly method and selective silicon growth for flash memory |
US9257445B2 (en) * | 2014-05-30 | 2016-02-09 | Freescale Semiconductor, Inc. | Method of making a split gate non-volatile memory (NVM) cell and a logic transistor |
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