WO2008135335A1 - Cmos circuits with high-k gate dielectric - Google Patents

Cmos circuits with high-k gate dielectric Download PDF

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Publication number
WO2008135335A1
WO2008135335A1 PCT/EP2008/054270 EP2008054270W WO2008135335A1 WO 2008135335 A1 WO2008135335 A1 WO 2008135335A1 EP 2008054270 W EP2008054270 W EP 2008054270W WO 2008135335 A1 WO2008135335 A1 WO 2008135335A1
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Prior art keywords
type fet
liner
fet device
gate
dielectric
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PCT/EP2008/054270
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French (fr)
Inventor
Charlotte Dewan Adams
Eduard Albert Cartier
Bruce Bennett Doris
Vijay Narayanan
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International Business Machines Corporation
Ibm United Kingdom Limited
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Publication date
Application filed by International Business Machines Corporation, Ibm United Kingdom Limited filed Critical International Business Machines Corporation
Priority to EP08735996A priority Critical patent/EP2150977A1/en
Priority to JP2010504612A priority patent/JP2010525591A/en
Publication of WO2008135335A1 publication Critical patent/WO2008135335A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H01L21/82—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components
    • H01L21/822—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components the substrate being a semiconductor, using silicon technology
    • H01L21/8232—Field-effect technology
    • H01L21/8234—MIS technology, i.e. integration processes of field effect transistors of the conductor-insulator-semiconductor type
    • H01L21/8238—Complementary field-effect transistors, e.g. CMOS
    • 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
    • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
    • H01L29/4983—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET with a lateral structure, e.g. a Polysilicon gate with a lateral doping variation or with a lateral composition variation or characterised by the sidewalls being composed of conductive, resistive or dielectric material
    • H—ELECTRICITY
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    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
    • H01L21/28008—Making conductor-insulator-semiconductor electrodes
    • H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
    • H01L21/28158—Making the insulator
    • H01L21/28167—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation
    • H01L21/28176—Making the insulator on single crystalline silicon, e.g. using a liquid, i.e. chemical oxidation with a treatment, e.g. annealing, after the formation of the definitive gate conductor
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    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H01L21/82—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components
    • H01L21/822—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components the substrate being a semiconductor, using silicon technology
    • H01L21/8232—Field-effect technology
    • H01L21/8234—MIS technology, i.e. integration processes of field effect transistors of the conductor-insulator-semiconductor type
    • H01L21/8238—Complementary field-effect transistors, e.g. CMOS
    • H01L21/823857—Complementary field-effect transistors, e.g. CMOS with a particular manufacturing method of the gate insulating layers, e.g. different gate insulating layer thicknesses, particular gate insulator materials or particular gate insulator implants
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    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • H01L21/82—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components
    • H01L21/822—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices to produce devices, e.g. integrated circuits, each consisting of a plurality of components the substrate being a semiconductor, using silicon technology
    • H01L21/8232—Field-effect technology
    • H01L21/8234—MIS technology, i.e. integration processes of field effect transistors of the conductor-insulator-semiconductor type
    • H01L21/8238—Complementary field-effect transistors, e.g. CMOS
    • H01L21/823864—Complementary field-effect transistors, e.g. CMOS with a particular manufacturing method of the gate sidewall spacers, e.g. double spacers, particular spacer material or shape
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    • H01L27/02—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers
    • H01L27/04—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body
    • H01L27/08—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body including only semiconductor components of a single kind
    • H01L27/085—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body including only semiconductor components of a single kind including field-effect components only
    • H01L27/088—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body including only semiconductor components of a single kind including field-effect components only the components being field-effect transistors with insulated gate
    • H01L27/092—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body including only semiconductor components of a single kind including field-effect components only the components being field-effect transistors with insulated gate complementary MIS field-effect transistors
    • 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
    • H01L29/6653—Unipolar field-effect transistors with an insulated gate, i.e. MISFET using the removal of at least part of spacer, e.g. disposable spacer
    • 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
    • H01L29/6656—Unipolar field-effect transistors with an insulated gate, i.e. MISFET using multiple spacer layers, e.g. multiple sidewall spacers
    • H—ELECTRICITY
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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
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/49—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET
    • H01L29/51—Insulating materials associated therewith
    • H01L29/517—Insulating materials associated therewith the insulating material comprising a metallic compound, e.g. metal oxide, metal silicate

Definitions

  • the present invention relates to electronic devices.
  • it relates to CMOS structures having high-k containing gate dielectrics, and to ways to adjust threshold voltages by exposing the gate dielectrics to oxygen.
  • the mainstay material of microelectronics is silicon (Si), or more broadly, Si based materials.
  • Si based material of importance for microelectronics is the silicon-germanium (SiGe) alloy.
  • the devices in the embodiments of the present disclosure are typically part of the art of single crystal Si based material device technology.
  • EOT equivalent oxide thickness
  • High performance small FET devices are also in need of precise threshold voltage control. As operating voltage decreases, to 2 V and below, threshold voltages also have to decrease, and threshold variation becomes less tolerable. Every new element, such as a different gate dielectric, or a different gate material, influences the threshold voltage. Sometimes such influences are detrimental for achieving the desired threshold voltage values. Any technique which can affect the threshold voltage, without other effects on the devices is a useful one.
  • CMOS structure which contains at least one first type FET device and at least one second type FET device.
  • the first type FET contains a first gate insulator which has a first high-k dielectric.
  • the first type FET also contains a first liner, which first liner has oxide and nitride portions. The nitride portions are forming the edge segments of the first liner, and these the nitride portions are capable of preventing oxygen from reaching the first high-k dielectric.
  • the second type FET device contains a second gate insulator which has a second high-k dielectric, a second liner which is of oxide without nitride portions. As a result, oxygen is capable to reach the second high-k dielectric and shift the threshold voltage of the second type of FET device.
  • the invention further discloses a method for producing a CMOS structure.
  • the method includes the fabricating in a first type FET device including a first gate insulator containing a first high-k dielectric, and a first liner consisting essentially of oxide. Fabricating a second type FET device having a second gate insulator containing a second high-k dielectric, and a second liner also consisting essentially of oxide.
  • the method further encompasses etching the first liner until edge portions of the first liner are replaced by empty grooves. Depositing nitride conformally, in such a manner that the nitride fills the previously produced empty grooves. This results in nitride edge segment portions for the first liner.
  • the method further includes exposing the first type FET device and the second type FET device to oxygen.
  • the oxygen penetrates through the second liner reaching the second high-k dielectric of the second gate insulator, and causes a predetermined shift in the threshold voltage of the second type FET device, while, due to the nitride edge segment portions of the first liner, oxygen is not penetrating to the first high-k dielectric of the first gate insulator, and the threshold voltage of the first type FET device remains unchanged.
  • FIG. 1 shows a schematic cross section of a CMOS structure with the liner of one device having nitride portions forming the liner edge segments, according to an embodiment of the present invention
  • FIG. 2 shows a schematic cross section of an initial stage in the processing of a CMOS structure according to an embodiment of the present invention
  • FIG. 3 shows a schematic cross section of a following stage in the processing of a CMOS structure according to an embodiment of the present invention
  • FIG. 4 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where empty grooves have been created at the edges of a liner
  • FIG.5 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where nitride has been deposited to fill the previously created grooves
  • FIG. 6 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where oxygen exposure shifts the threshold of one type of device
  • FIG. 7 shows a symbolic view of a processor containing at least one CMOS circuit according to an embodiment of the present invention.
  • FET Field Effect Transistor-s
  • Standard components of a FET are the source, the drain, the body in-between the source and the drain, and the gate.
  • the body is usually part of a substrate, and it is often called substrate.
  • the gate is overlaying the body and is capable to induce a conducting channel in the body between the source and the drain. In the usual nomenclature, the channel is hosted by the body.
  • the gate is separated from the body by the gate insulator.
  • PFET hole conduction type
  • NFET electron conduction type
  • an electrical attribute is the threshold voltage.
  • the threshold voltage When the voltage between the gate and the source exceeds the threshold voltage, the devices are capable to carry current between the source and the drain.
  • NFET threshold voltages are positive, and PFET threshold voltages are negative.
  • the threshold is an inherent attribute.
  • exposing a gate dielectric which comprises a high-k material to oxygen can result in shifting device thresholds in a direction which is the same as if one moved the gate workfunction toward a p + silicon workfunction. This results in lowering the PFET threshold, namely, making it a smaller negative voltage, and raising the NFET threshold, namely making it a larger positive voltage. It is preferable to carry out such oxygen exposure at relatively low temperatures. Accordingly, such a threshold shifting operation should occur late in the device fabrication, typically after the source and the drain have been activated.
  • threshold shifts due to oxygen diffusion through liners are known in the art, for instance as in the report: "2005 Symposium on VLSI Technology Digest of Technical Papers, Pg. 230, by E. Cartier". It would be preferable, however, if the thresholds of the different types of devices could be adjusted individually. Meaning, one would desire to use threshold tuning techniques, such as oxygen exposure, which alter the threshold of one type device, without affecting the threshold of the other type of device.
  • Embodiments of the present invention teach such a selective adjusting of a device threshold by having a liner allowing oxygen diffusion for one type of FET, while modifying the liner of the other type of FET in such a manner that it becomes impenetrable to oxygen.
  • FIG. 1 shows a schematic cross section of a CMOS structure with the liner of one device having nitride portions forming the liner edge segments.
  • the CMOS structure is adapted for being exposed to a low temperature oxidation, which may result in a threshold shift for one of the FETs.
  • the threshold shift is such that depending on which type of device allows oxygen diffusion to the gate insulator, the threshold of the PFET would be lowered, while the threshold of the NFET would be raised.
  • FIG. 1 depicts two devices, an NFET and a PFET, of the at least one NFET and PFET devices that make up a CMOS structure.
  • FIG. 1 it is not specified which of the two devices is an NFET and which one is a PFET.
  • Embodiments of the invention cover both cases, as to which type of device, NFET or PFET, is the one whose threshold can be adjusted. Accordingly, a first type and a second type device will be discussed, with the understanding that if the first type is an NFET than the second type is a PFET, and the other way around, if the first type is a PFET than the second type is an NFET.
  • the device bodies 50 are typically of a single crystal Si based material.
  • the Si based material bodies 50 are essentially single crystal Si.
  • the device bodies 50 are part of a substrate.
  • the substrate may be any type known in the electronic art, such as bulk, or semiconductor on insulator (SOI), fully depleted, or partially depleted, FIN type, or any other kind.
  • SOI semiconductor on insulator
  • substrates may have various wells of various conductivity types, in various nested positioning enclosing device bodies.
  • the figure shows what typically may be only a small fraction of an electronic chip, for instance a processor, as indicated by the wavy dashed line boundaries.
  • the devices may be isolated from one another by any method known in the art.
  • the figure shows a shallow trench 99 isolation scheme, as this is a typical advanced isolation technique available in the art.
  • the devices have source/drain extensions 40, and suicided sources and drains 41, as well as have suicide 42 on the top of the gates 55, 56.
  • these elements all have their individual characteristics. Accordingly, when the common indicators numbers are used in the figures of the present disclosure, it is because from the point of view of embodiments of the present invention the individual characteristics of such elements are not important.
  • FIG. 1 shows that the sources and drains of the devices have already been fabricated.
  • CMOS processing typically the highest temperature-budgets, meaning temperature and time exposure combinations, are reached during source/drain fabrication.
  • CMOS structure of FIG. 1 since the sources and drains have already been fabricated, such high temperature fabrication steps have already been performed, and it will not have to be exposed to further high temperature treatment.
  • exposure to a high temperature-budget means a comparable heat treatment as one used in source/drain fabrication.
  • the devices have standard sidewall spacers 60.
  • the spacer material is significant only to the extent that it is preferably impenetrable to oxygen.
  • the typical material used in the art for such spacers is nitride (SiN), which is an exemplary oxygen blocking material.
  • the gate 55 of the first type FET device and of the gate 56 of the second type FET device usually have their own internal structures, typically in layers.
  • the gates, also referred to as gate stacks, 55, 56 of the two types of devices may be processed independently of one another or together, and they typically, but not necessarily, have differing structures.
  • the first type FET device has a first gate insulator 10 and the second type FET device has a second gate insulator 11.
  • Both gate insulators comprise a high-k dielectrics.
  • Such high-k dielectrics may be AI2O3, ZrO 2 , HfO 2 , HfSiO and others known in the art, and/or their admixtures.
  • their common property is the possession of a larger dielectric constant than that of the standard oxide (SiO 2 ) gate insulator material, which has a value of approximately 3.9.
  • the gate insulator of the first type FET device 10 and the gate insulator of the second type FET device 11 may comprise the same high-k material, or they may have differing high-k materials. Each gate insulator 10, 11 apart of the high-k dielectric may have other components as well. Typically in embodiments of the present invention a very thin, less than about lnm, chemically deposited oxide may be present between the high-k dielectric layer and the device body 50. However, any and all inner structure, or the lack of any structure beyond simply containing a high-k dielectric, for either the first or second gate insulators 10, 11 is within the scope of the embodiments of the present invention. In exemplary embodiments of the present invention HfO 2 covering a thin chemical SiO 2 would be used as gate insulator, with an equivalent oxide thickness of about between 0.6 nm and 1.2 nm.
  • the second type FET device has a second liner 21.
  • Liners are known in the art, and regularly used in standard CMOS processing.
  • the typical material of such liners is an oxide, usually silicon-dioxide (SiO 2 ).
  • the traditional role for the liners is in the protection of the gate during various processing steps, particularly during etching steps.
  • Such liners typically have selective etching properties relative to nitride and silicon.
  • the material of the second liner 21, typically SiO 2 allows oxygen to diffuse through it, and allows oxygen to reach the gate dielectric.
  • the spacer 60 which spacer blocks oxygen, at the edges of the liner 21, underneath the spacers, and next to the top of the gate, oxygen may enter the liner 21, reach the gate insulator 11, and shift the threshold voltage of the second FET by a desired, predetermined amount.
  • FIG. 1 is only a schematic representation. As known in the art, there may be many more elements in the structures than present in the figures, but these would not effect the scope of the embodiments of the present invention. Such an element, as an example, may be any further layers between a liner and a gate. One type of such often used layer is called offset, or source/drain, spacer, which serve in source/drain fabrication.
  • the first type FET device has a first liner 20.
  • the first liner 20 consist of multiple portions. It has oxide portions, which are similar, and may be, but not necessarily, identical to the second liner 21. The oxide portions, typically of SiO 2 , would allow oxygen to diffuse.
  • the first liner 20 also has nitride portions 20', which are forming the edge segments of the first liner 20. Nitride, SiN, prevents oxygen penetration. Since the nitride segments 20' are positioned as edge segments, they block those paths, which for the second liner 21 were available for the oxygen to enter the liner. Due to the nitride portion edge segments 20', and the nitride spacer 60, the first gate dielectric 10 is completely surrounded by nitride material. Accordingly, with oxygen exposure one is capable to shift the threshold of the second type FET device, while not affecting the threshold of the first type FET device.
  • nitride portions 20' of the first liner 20 were deposited as a nitride layer 30, and parts of this layer, even after steps in which this layer was etched, may remain over the spacers 60, as shown in FIG. 1.
  • FIG. 2 shows a schematic cross section of an initial stage in the processing of a CMOS structure according to an embodiment of the present invention.
  • a first gate insulator 10 has been implemented in a manner that this first gate insulator includes a first high-k dielectric.
  • the first gate insulator 10 may essentially be of a high-k dielectric in itself, or may be implemented in combination with further dielectrics, such as, for instance, silicon dioxide, or others.
  • the first liner 20 has been deposited conformally essentially over all of the first type FET device, in particular over the gate 55 and over the source/drain 40 regions.
  • the first liner 20 consists essentially of an oxide material, typically SiO 2 .
  • FIG. 1 shows a schematic cross section of an initial stage in the processing of a CMOS structure according to an embodiment of the present invention.
  • the second gate insulator 11 has been implemented in a manner that this second gate insulator includes a second high-k dielectric.
  • the second gate insulator 11, may essentially be of a high-k dielectric in itself, or may be implemented in combination with further dielectrics, such as, for instance silicon dioxide, or others.
  • the second liner 21 has been deposited conformally essentially over all of the second type FET device, in particular over the gate 56 and over the source/drain 40 regions.
  • the second liner 21 consists essentially of an oxide material, typically SiO 2 . Many possible pathways of fabrication, all leading to a structure as in FIG. 2, are known in the art. Particular details given in the description herein are not intended to be interpreted in a limiting fashion.
  • the first and second liners 20, 21 are being deposited during a single processing event, and thus have essentially identical properties.
  • the liners 20, 21 could also be deposited during differing steps in the fabrication, and they may not have identical characteristics, such as, for instance, thickness, or exact composition. Similar considerations hold for the high-k materials in the first and second gate insulators 10, 11.
  • they may be deposited during differing processing steps, and may, or may not, be of the same material.
  • the gate insulators as well may be deposited in the same processing steps.
  • the high-k materials in the first and second gate insulators 10, 11 are of a same material, such as, for instance Of HfO 2 .
  • the gate 55 of the first type FET device and the gate 56 of the second type FET device may be composite structures themselves. Since the threshold of the first type FET device is selected not to be adjusted during an oxygen exposure, the composition of the gate 55 of the first type FET device has to be properly selected in order for the threshold voltage of the first type FET device to end up with the desired value. For this reason the first type FET device gate 55, may include a carefully selected, so called cap layer 55". Such cap layers are known in art, presented for instance by V. Narayanan et al, IEEE VLSI Symposium p. 224, (2006). The cap layer 55" may contain lanthanum (La), which under proper treatment may yield the desired threshold value.
  • La lanthanum
  • the first type FET device gate 55 my also contain a metal 55', such as, for instance, W, Ta, or others known in the art.
  • the gate 56 of the second type FET device also may have internal structure, for instance a metal layer 56'. This metal layer 56' may be in direct contact with the second gate insulator 11.
  • a metal for the second type FET device gate 56' may also be selected to be W, Ta, or other metals known to be suitable for gate fabrication.
  • metals deemed suitable for being parts of the gates, besides W, and Ta may include Mo, Mn, TaN, TiN, WN, Ru, Cr, Ta, Nb, V, Mn, Re, and their combinations.
  • the metal layers 55', 56' of the first and second type FET device gates 55, 56 may be fabricated of the same material.
  • the possible internal structures of the gates will not be indicated, but it is understood that if such structure was present at the stage of processing shown on FIG. 2, then that internal structure of the gates does not change, and it will be present all through further fabrication, and in the completed devices, as well.
  • further materials present in both gates 55, 56 may be polysilicon and amorphous silicon.
  • the figure also shows that by this stage usually the source/drain extensions 40 have also completed processing.
  • FIG. 3 shows a schematic cross section of a following stage in the processing of a CMOS structure according to an embodiment of the present invention.
  • the spacers 60 for both devices have been processed.
  • the property of interest for the spacers 60 is that they should not be penetrable by oxygen, since the spacers are to block oxygen entrance where they interface with the liners 20, 21.
  • the usual material used for spacers 60 is nitride (SiN), which efficiently blocks oxygen.
  • FIG. 4 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where empty grooves have been created at the edges of one of the liners.
  • the first liner 20 of the first type FET device is etched by a selective etch.
  • the selective etch removes the liner material, typically oxide, but it does not attack other exposed materials, such as the spacer 60 material, typically nitride, or the top material of the gate 55, typically polysilicon.
  • This etch in representative embodiments of the present invention, is a wet etch, such as dilute or buffered hydrofluoric acid (HF).
  • This selective etch removes substantially all of the exposed parts of the first liner 20, and penetrates under the spacers 60, and into between the spacers 60 and the gate 55, removing edge portions of the liner 20, such that empty grooves 25 replace the edge portions of the first liner.
  • FIG. 5 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where nitride has been deposited to fill the previously created grooves 25.
  • a nitride layer 30 is deposited, typically over all structures, in a conformal manner, meaning it deposits independently of the orientation of a surface. Due to the conformal nature of this deposition the grooves 25 at the edge sections of the first liner 20 are filled in with nitride.
  • the nitride layer 30 deposits on most surfaces such as over the spacers 60.
  • the spacers 60 and the groove filling layer 30, are of the same material, namely nitride (SiN).
  • a series of standard steps known in the art may follow.
  • the nitride layer is etched back, essentially removing it from most exposed surfaces, such as from the spacers 60, isolation 99, from source/drain regions, and others; the sources and drains are fabricated, and activated; suicide is formed over sources/drains 41 and gates 42.
  • FIG. 6 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where oxygen exposure shifts the threshold of one type of device.
  • the oxygen exposure 101 may occur at low temperature at about 200°C to 350°C by furnace or rapid thermal anneal.
  • the duration of the oxygen exposure 101 may vary broadly from approximately 2 minutes to about 150 minutes.
  • the oxygen is blocked from penetrating to the first gate insulator 10 by the nitride portions 20 'of the first liner 20, but it is capable of doing so to the second gate insulator 11.
  • the amount of threshold shift depends on the oxygen exposure parameters, primarily on the temperature and duration of the procedure. Threshold shifts up to the range of 250 mV to 300 mV may be achieved in embodiments of the present invention.
  • the oxygen exposure does not have to affect all second type FET devices for a given chip, or processor.
  • the one does not necessarily have to implement the nitride portions 20' in the liners on all of the first type of FET devices on a given chip, or processor. Accordingly, on a given chip or processor and one may have at least two different threshold values for the first type of FET devices, as well.
  • the threshold values may differ up to about 250 mV - 300 mV, but often threshold differences of about 50 mV - 100 mV are already of great value for some circuits. Examples of circuits that may find multiple threshold devices useful include circuits in signal processing and communication processors, and others. After the oxygen exposure, the CMOS structure, and the wiring into circuits may be completed with standard steps known to one skilled in the art.
  • FIG. 7 shows a symbolic view of a processor containing at least one CMOS structure incorporating an embodiment of the present invention.
  • a processor 900 has at least one chip 901, which contains at least one CMOS structure 100, with a FET having a liner with nitride portions, where the nitride portions are forming the edge segments of the liner.
  • the processor 900 may be any processor which can benefit from embodiments of the present invention.
  • Representative embodiments of processors manufactured with embodiments of the disclosed structure are digital processors, typically found in the central processing complex of computers; mixed digital/analog processors, typically found in signal processing and communication equipment; and others.

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Abstract

A CMOS structure is disclosed in which a first type FET contains a liner, which liner has oxide (20) and nitride (20') portions. The nitride portions are forming the edge segments of the liner. These nitride portions are capable of preventing oxygen from reaching the high-k dielectric gate insulator (10) of the first type FET. A second type FET device of the CMOS structure has a liner without nitride portions (21). As a result, an oxygen exposure is capable to shift the threshold voltage of the second type of FET, without affecting the threshold value of the first type FET. The disclosure also teaches methods for producing the CMOS structure in which differing type of FET devices have their threshold values set independently from one another.

Description

CMOS CIRCUITS WITH HIGH-K GATE DIELECTRIC
FIELD OF THE INVENTION
The present invention relates to electronic devices. In particular, it relates to CMOS structures having high-k containing gate dielectrics, and to ways to adjust threshold voltages by exposing the gate dielectrics to oxygen.
BACKGROUND OF THE INVENTION
Today's integrated circuits include a vast number of devices. Smaller devices and shrinking ground rules are the key to enhance performance and to reduce cost. As FET (Field- Effect- Transistor) devices are being scaled down, the technology becomes more complex, and changes in device structures and new fabrication methods are needed to maintain the expected performance enhancement from one generation of devices to the next. The mainstay material of microelectronics is silicon (Si), or more broadly, Si based materials. One such Si based material of importance for microelectronics is the silicon-germanium (SiGe) alloy. The devices in the embodiments of the present disclosure are typically part of the art of single crystal Si based material device technology.
There is a great difficulty in maintaining performance improvements in devices of deeply sub micron generations. Therefore, methods for improving performance without scaling down have become of interest. There is a promising avenue toward higher gate dielectric capacitance without having to make the gate dielectric actually thinner. This approach involves the use of so called high-k materials. The dielectric constant of such materials is significantly higher than that of SiO2, which is about 3.9. A high-k material may physically be significantly thicker than oxide, and still have a lower equivalent oxide thickness (EOT) value. The EOT, a concept known in the art, refers to the thickness of such an SiO2 layer which has the same capacitance per unit area as the insulator layer in question. In today state of the art FET devices, one is aiming at an EOT of below 2nm, and preferably below lnm. Device performance is also enhanced by the use of metal gates. The depletion region in the poly-Si next to the gate insulator can become an obstacle in increasing gate-to-channel capacitance, or equivalently to decrease the EOT. The solution is to use a metal gate. Metal gates also assure good conductivity along the width direction of the gates, reducing the danger of possible RC delays of the gate.
High performance small FET devices are also in need of precise threshold voltage control. As operating voltage decreases, to 2 V and below, threshold voltages also have to decrease, and threshold variation becomes less tolerable. Every new element, such as a different gate dielectric, or a different gate material, influences the threshold voltage. Sometimes such influences are detrimental for achieving the desired threshold voltage values. Any technique which can affect the threshold voltage, without other effects on the devices is a useful one. One such technique, available when high-k dielectrics are present in a gate insulator, is the exposure of the gate dielectric to oxygen. A high-k material upon exposure to oxygen lowers the PFET threshold and increases the NFET threshold. Such an effect has been known and used before. Unfortunately, shifting the threshold of both PFET and NFET devices simultaneously, may not easily lead to threshold values in an acceptable tight range for CMOS circuits. There is great need for a structure and a technique in which the threshold of one type of device can be independently adjusted without altering the threshold of the other type of device. To date, such structure and technique has not been taught.
SUMMARY OF THE INVENTION
In view of the discussed difficulties, embodiments of the present invention discloses a CMOS structure, which contains at least one first type FET device and at least one second type FET device. The first type FET contains a first gate insulator which has a first high-k dielectric. The first type FET also contains a first liner, which first liner has oxide and nitride portions. The nitride portions are forming the edge segments of the first liner, and these the nitride portions are capable of preventing oxygen from reaching the first high-k dielectric. The second type FET device contains a second gate insulator which has a second high-k dielectric, a second liner which is of oxide without nitride portions. As a result, oxygen is capable to reach the second high-k dielectric and shift the threshold voltage of the second type of FET device.
The invention further discloses a method for producing a CMOS structure. The method includes the fabricating in a first type FET device including a first gate insulator containing a first high-k dielectric, and a first liner consisting essentially of oxide. Fabricating a second type FET device having a second gate insulator containing a second high-k dielectric, and a second liner also consisting essentially of oxide. The method further encompasses etching the first liner until edge portions of the first liner are replaced by empty grooves. Depositing nitride conformally, in such a manner that the nitride fills the previously produced empty grooves. This results in nitride edge segment portions for the first liner. The method further includes exposing the first type FET device and the second type FET device to oxygen. The oxygen penetrates through the second liner reaching the second high-k dielectric of the second gate insulator, and causes a predetermined shift in the threshold voltage of the second type FET device, while, due to the nitride edge segment portions of the first liner, oxygen is not penetrating to the first high-k dielectric of the first gate insulator, and the threshold voltage of the first type FET device remains unchanged.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the present invention will become apparent from the accompanying detailed description and drawings, wherein:
FIG. 1 shows a schematic cross section of a CMOS structure with the liner of one device having nitride portions forming the liner edge segments, according to an embodiment of the present invention;
FIG. 2 shows a schematic cross section of an initial stage in the processing of a CMOS structure according to an embodiment of the present invention;
FIG. 3 shows a schematic cross section of a following stage in the processing of a CMOS structure according to an embodiment of the present invention;
FIG. 4 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where empty grooves have been created at the edges of a liner; FIG.5 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where nitride has been deposited to fill the previously created grooves;
FIG. 6 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where oxygen exposure shifts the threshold of one type of device; and
FIG. 7 shows a symbolic view of a processor containing at least one CMOS circuit according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
It is understood that Field Effect Transistor-s (FET) are well known in the electronic arts. Standard components of a FET are the source, the drain, the body in-between the source and the drain, and the gate. The body is usually part of a substrate, and it is often called substrate. The gate is overlaying the body and is capable to induce a conducting channel in the body between the source and the drain. In the usual nomenclature, the channel is hosted by the body. The gate is separated from the body by the gate insulator. There are two type of FET devices: a hole conduction type, called PFET, and an electron conduction type, called NFET. Often, but exclusively, PFET and NFET devices on the same chip are wired into CMOS circuits. A CMOS circuit contains at least one PFET and at least one NFET device. In manufacturing, or processing, when NFET and PFET devices are fabricated together on the same chip, one is dealing with CMOS processing and the fabrication of CMOS structures.
In FET operation, an electrical attribute is the threshold voltage. When the voltage between the gate and the source exceeds the threshold voltage, the devices are capable to carry current between the source and the drain. In general, NFET threshold voltages are positive, and PFET threshold voltages are negative. However, it is customary in the art to refer to the thresholds of both type of devices only by their absolute values. For FET devices the threshold is an inherent attribute.
As FET devices are scaled to smaller size, typically with gate lengths less than 100 nm, the traditional way of setting threshold voltage, namely by adjusting body and channel doping, looses effectiveness. The effective workfunction of the gate material, and gate insulator properties are becoming important factors in determining the threshold of small FETs, which FETs usually operate in a range of less than about 2 V. The direction of performance driven technology is toward the use of metallic gates and high-k dielectrics for gate insulator. However, the optimal combination of a particular metal gate and a particular high-k dielectric in the gate insulator, might not lead to optimal threshold values for both NFET and PFET devices from a performance, or processing point of view.
It is know that exposing a gate dielectric which comprises a high-k material to oxygen, can result in shifting device thresholds in a direction which is the same as if one moved the gate workfunction toward a p+ silicon workfunction. This results in lowering the PFET threshold, namely, making it a smaller negative voltage, and raising the NFET threshold, namely making it a larger positive voltage. It is preferable to carry out such oxygen exposure at relatively low temperatures. Accordingly, such a threshold shifting operation should occur late in the device fabrication, typically after the source and the drain have been activated. This requirement means that one has to expose the high-k material in the gate dielectric at a point in the fabrication process when substantially most of the processing has already been carried out, for instance, the gate and gate sidewalls are all in place, and the gate insulator is shielded under several layers of various materials. However, there may be a path for the oxygen to reach from the environs to the gate insulator. This path may be inside a liner. The use of liners, thin insulating layers which are deposited conformally essentially over all of the structures, in particular over the gates and the source/drain regions, is standard practice in CMOS processing. For adjusting the threshold of devices the property of interest is that the liner should be penetrable by oxygen. Indeed, such threshold shifts due to oxygen diffusion through liners, are known in the art, for instance as in the report: "2005 Symposium on VLSI Technology Digest of Technical Papers, Pg. 230, by E. Cartier". It would be preferable, however, if the thresholds of the different types of devices could be adjusted individually. Meaning, one would desire to use threshold tuning techniques, such as oxygen exposure, which alter the threshold of one type device, without affecting the threshold of the other type of device. Embodiments of the present invention teach such a selective adjusting of a device threshold by having a liner allowing oxygen diffusion for one type of FET, while modifying the liner of the other type of FET in such a manner that it becomes impenetrable to oxygen.
FIG. 1 shows a schematic cross section of a CMOS structure with the liner of one device having nitride portions forming the liner edge segments. At this stage of the fabrication the CMOS structure is adapted for being exposed to a low temperature oxidation, which may result in a threshold shift for one of the FETs. The threshold shift is such that depending on which type of device allows oxygen diffusion to the gate insulator, the threshold of the PFET would be lowered, while the threshold of the NFET would be raised.
FIG. 1 depicts two devices, an NFET and a PFET, of the at least one NFET and PFET devices that make up a CMOS structure. In FIG. 1 it is not specified which of the two devices is an NFET and which one is a PFET. Embodiments of the invention cover both cases, as to which type of device, NFET or PFET, is the one whose threshold can be adjusted. Accordingly, a first type and a second type device will be discussed, with the understanding that if the first type is an NFET than the second type is a PFET, and the other way around, if the first type is a PFET than the second type is an NFET.
It is understood that in addition to the elements of the embodiments of the invention, the figures show several other elements, since they are standard components of FET devices, as known in the art. The device bodies 50 are typically of a single crystal Si based material. In a representative embodiment of the invention the Si based material bodies 50 are essentially single crystal Si. In exemplary embodiments of the invention the device bodies 50 are part of a substrate. The substrate may be any type known in the electronic art, such as bulk, or semiconductor on insulator (SOI), fully depleted, or partially depleted, FIN type, or any other kind. Also, substrates may have various wells of various conductivity types, in various nested positioning enclosing device bodies. The figure shows what typically may be only a small fraction of an electronic chip, for instance a processor, as indicated by the wavy dashed line boundaries. The devices may be isolated from one another by any method known in the art. The figure shows a shallow trench 99 isolation scheme, as this is a typical advanced isolation technique available in the art. The devices have source/drain extensions 40, and suicided sources and drains 41, as well as have suicide 42 on the top of the gates 55, 56. As one skilled in the art would know, these elements all have their individual characteristics. Accordingly, when the common indicators numbers are used in the figures of the present disclosure, it is because from the point of view of embodiments of the present invention the individual characteristics of such elements are not important. FIG. 1 shows that the sources and drains of the devices have already been fabricated. In CMOS processing, typically the highest temperature-budgets, meaning temperature and time exposure combinations, are reached during source/drain fabrication. For the CMOS structure of FIG. 1 , since the sources and drains have already been fabricated, such high temperature fabrication steps have already been performed, and it will not have to be exposed to further high temperature treatment. For the intentions of embodiments of the present invention, exposure to a high temperature-budget means a comparable heat treatment as one used in source/drain fabrication.
The devices have standard sidewall spacers 60. For the embodiments of the present invention the spacer material is significant only to the extent that it is preferably impenetrable to oxygen. The typical material used in the art for such spacers is nitride (SiN), which is an exemplary oxygen blocking material. The gate 55 of the first type FET device and of the gate 56 of the second type FET device usually have their own internal structures, typically in layers. The gates, also referred to as gate stacks, 55, 56 of the two types of devices may be processed independently of one another or together, and they typically, but not necessarily, have differing structures.
The first type FET device has a first gate insulator 10 and the second type FET device has a second gate insulator 11. Both gate insulators comprise a high-k dielectrics. Such high-k dielectrics may be AI2O3, ZrO2, HfO2 , HfSiO and others known in the art, and/or their admixtures. As known in the art, their common property is the possession of a larger dielectric constant than that of the standard oxide (SiO2) gate insulator material, which has a value of approximately 3.9. In embodiments of the present invention the gate insulator of the first type FET device 10 and the gate insulator of the second type FET device 11 may comprise the same high-k material, or they may have differing high-k materials. Each gate insulator 10, 11 apart of the high-k dielectric may have other components as well. Typically in embodiments of the present invention a very thin, less than about lnm, chemically deposited oxide may be present between the high-k dielectric layer and the device body 50. However, any and all inner structure, or the lack of any structure beyond simply containing a high-k dielectric, for either the first or second gate insulators 10, 11 is within the scope of the embodiments of the present invention. In exemplary embodiments of the present invention HfO2 covering a thin chemical SiO2 would be used as gate insulator, with an equivalent oxide thickness of about between 0.6 nm and 1.2 nm.
The second type FET device has a second liner 21. Liners are known in the art, and regularly used in standard CMOS processing. The typical material of such liners is an oxide, usually silicon-dioxide (SiO2). The traditional role for the liners is in the protection of the gate during various processing steps, particularly during etching steps. Such liners typically have selective etching properties relative to nitride and silicon. The material of the second liner 21, typically SiO2, allows oxygen to diffuse through it, and allows oxygen to reach the gate dielectric. Although a large surface region of the liner is covered by the spacer 60, which spacer blocks oxygen, at the edges of the liner 21, underneath the spacers, and next to the top of the gate, oxygen may enter the liner 21, reach the gate insulator 11, and shift the threshold voltage of the second FET by a desired, predetermined amount.
It is understood that, as all figures, FIG. 1 is only a schematic representation. As known in the art, there may be many more elements in the structures than present in the figures, but these would not effect the scope of the embodiments of the present invention. Such an element, as an example, may be any further layers between a liner and a gate. One type of such often used layer is called offset, or source/drain, spacer, which serve in source/drain fabrication.
The first type FET device has a first liner 20. The first liner 20 consist of multiple portions. It has oxide portions, which are similar, and may be, but not necessarily, identical to the second liner 21. The oxide portions, typically of SiO2, would allow oxygen to diffuse. The first liner 20 also has nitride portions 20', which are forming the edge segments of the first liner 20. Nitride, SiN, prevents oxygen penetration. Since the nitride segments 20' are positioned as edge segments, they block those paths, which for the second liner 21 were available for the oxygen to enter the liner. Due to the nitride portion edge segments 20', and the nitride spacer 60, the first gate dielectric 10 is completely surrounded by nitride material. Accordingly, with oxygen exposure one is capable to shift the threshold of the second type FET device, while not affecting the threshold of the first type FET device.
At one point in the processing the nitride portions 20' of the first liner 20 were deposited as a nitride layer 30, and parts of this layer, even after steps in which this layer was etched, may remain over the spacers 60, as shown in FIG. 1.
Further discussion and figures may present only those processing steps which are relevant to yield the structure of FIG. 1. Manufacturing of NFET, PFET, and CMOS is very well established in the art. It is understood that there are a large number of steps involved in such processing, and each step might have practically endless variations known to those skilled in the art. It is further understood that the whole range of known processing techniques are available for fabricating the disclosed device structures, and only those process steps will be detailed that are related to embodiments of the present invention.
FIG. 2 shows a schematic cross section of an initial stage in the processing of a CMOS structure according to an embodiment of the present invention. In a first type FET device a first gate insulator 10 has been implemented in a manner that this first gate insulator includes a first high-k dielectric. The first gate insulator 10, may essentially be of a high-k dielectric in itself, or may be implemented in combination with further dielectrics, such as, for instance, silicon dioxide, or others. The first liner 20 has been deposited conformally essentially over all of the first type FET device, in particular over the gate 55 and over the source/drain 40 regions. The first liner 20 consists essentially of an oxide material, typically SiO2. Furthermore, FIG. 2 shows that in a second type FET device a second gate insulator 11 has been implemented in a manner that this second gate insulator includes a second high-k dielectric. The second gate insulator 11, may essentially be of a high-k dielectric in itself, or may be implemented in combination with further dielectrics, such as, for instance silicon dioxide, or others. The second liner 21 has been deposited conformally essentially over all of the second type FET device, in particular over the gate 56 and over the source/drain 40 regions. The second liner 21 consists essentially of an oxide material, typically SiO2. Many possible pathways of fabrication, all leading to a structure as in FIG. 2, are known in the art. Particular details given in the description herein are not intended to be interpreted in a limiting fashion. In representative embodiments of the invention the first and second liners 20, 21 are being deposited during a single processing event, and thus have essentially identical properties. The liners 20, 21 could also be deposited during differing steps in the fabrication, and they may not have identical characteristics, such as, for instance, thickness, or exact composition. Similar considerations hold for the high-k materials in the first and second gate insulators 10, 11. In representative embodiments of the invention they may be deposited during differing processing steps, and may, or may not, be of the same material. However, the gate insulators as well may be deposited in the same processing steps. In exemplary embodiments of the present invention the high-k materials in the first and second gate insulators 10, 11 are of a same material, such as, for instance Of HfO2.
The gate 55 of the first type FET device and the gate 56 of the second type FET device may be composite structures themselves. Since the threshold of the first type FET device is selected not to be adjusted during an oxygen exposure, the composition of the gate 55 of the first type FET device has to be properly selected in order for the threshold voltage of the first type FET device to end up with the desired value. For this reason the first type FET device gate 55, may include a carefully selected, so called cap layer 55". Such cap layers are known in art, presented for instance by V. Narayanan et al, IEEE VLSI Symposium p. 224, (2006). The cap layer 55" may contain lanthanum (La), which under proper treatment may yield the desired threshold value. In typical embodiments of the present invention the first type FET device gate 55 my also contain a metal 55', such as, for instance, W, Ta, or others known in the art. Similarly, the gate 56 of the second type FET device also may have internal structure, for instance a metal layer 56'. This metal layer 56' may be in direct contact with the second gate insulator 11. A metal for the second type FET device gate 56' may also be selected to be W, Ta, or other metals known to be suitable for gate fabrication. Typically metals deemed suitable for being parts of the gates, besides W, and Ta, may include Mo, Mn, TaN, TiN, WN, Ru, Cr, Ta, Nb, V, Mn, Re, and their combinations. The metal layers 55', 56' of the first and second type FET device gates 55, 56 may be fabricated of the same material. In subsequent figures, the possible internal structures of the gates will not be indicated, but it is understood that if such structure was present at the stage of processing shown on FIG. 2, then that internal structure of the gates does not change, and it will be present all through further fabrication, and in the completed devices, as well. In typical embodiments of the present invention further materials present in both gates 55, 56 may be polysilicon and amorphous silicon. The figure also shows that by this stage usually the source/drain extensions 40 have also completed processing.
FIG. 3 shows a schematic cross section of a following stage in the processing of a CMOS structure according to an embodiment of the present invention. At this stage, the spacers 60 for both devices have been processed. From the point of view of embodiments of the present invention the property of interest for the spacers 60 is that they should not be penetrable by oxygen, since the spacers are to block oxygen entrance where they interface with the liners 20, 21. The usual material used for spacers 60 is nitride (SiN), which efficiently blocks oxygen.
FIG. 4 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where empty grooves have been created at the edges of one of the liners. After proper masking, which protects the second type FET device, the first liner 20 of the first type FET device is etched by a selective etch. The selective etch removes the liner material, typically oxide, but it does not attack other exposed materials, such as the spacer 60 material, typically nitride, or the top material of the gate 55, typically polysilicon. This etch, in representative embodiments of the present invention, is a wet etch, such as dilute or buffered hydrofluoric acid (HF). This selective etch removes substantially all of the exposed parts of the first liner 20, and penetrates under the spacers 60, and into between the spacers 60 and the gate 55, removing edge portions of the liner 20, such that empty grooves 25 replace the edge portions of the first liner.
FIG. 5 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where nitride has been deposited to fill the previously created grooves 25. A nitride layer 30 is deposited, typically over all structures, in a conformal manner, meaning it deposits independently of the orientation of a surface. Due to the conformal nature of this deposition the grooves 25 at the edge sections of the first liner 20 are filled in with nitride. The nitride layer 30 deposits on most surfaces such as over the spacers 60. In typical embodiments of the present invention the spacers 60 and the groove filling layer 30, are of the same material, namely nitride (SiN).
Following the processing shown in FIG. 5, a series of standard steps known in the art may follow. By executing these steps the nitride layer is etched back, essentially removing it from most exposed surfaces, such as from the spacers 60, isolation 99, from source/drain regions, and others; the sources and drains are fabricated, and activated; suicide is formed over sources/drains 41 and gates 42. With these steps completed, one arrives to the desired structure depicted in FIG. 1, and discussed previously in reference to FIG. 1.
FIG. 6 shows a schematic cross section of a stage in the processing of a CMOS structure according to an embodiment of the present invention where oxygen exposure shifts the threshold of one type of device. The oxygen exposure 101 may occur at low temperature at about 200°C to 350°C by furnace or rapid thermal anneal. The duration of the oxygen exposure 101 may vary broadly from approximately 2 minutes to about 150 minutes. The oxygen is blocked from penetrating to the first gate insulator 10 by the nitride portions 20 'of the first liner 20, but it is capable of doing so to the second gate insulator 11. The amount of threshold shift depends on the oxygen exposure parameters, primarily on the temperature and duration of the procedure. Threshold shifts up to the range of 250 mV to 300 mV may be achieved in embodiments of the present invention.
The oxygen exposure does not have to affect all second type FET devices for a given chip, or processor. One may use global nitride masking to shield oxygen penetration for a portion of second type FET devices. In this manner one may fabricate chips, and processors, with second type FET devices of at least two different threshold values. Furthermore, the one does not necessarily have to implement the nitride portions 20' in the liners on all of the first type of FET devices on a given chip, or processor. Accordingly, on a given chip or processor and one may have at least two different threshold values for the first type of FET devices, as well. The threshold values may differ up to about 250 mV - 300 mV, but often threshold differences of about 50 mV - 100 mV are already of great value for some circuits. Examples of circuits that may find multiple threshold devices useful include circuits in signal processing and communication processors, and others. After the oxygen exposure, the CMOS structure, and the wiring into circuits may be completed with standard steps known to one skilled in the art.
FIG. 7 shows a symbolic view of a processor containing at least one CMOS structure incorporating an embodiment of the present invention. Such a processor 900 has at least one chip 901, which contains at least one CMOS structure 100, with a FET having a liner with nitride portions, where the nitride portions are forming the edge segments of the liner. The processor 900 may be any processor which can benefit from embodiments of the present invention. Representative embodiments of processors manufactured with embodiments of the disclosed structure are digital processors, typically found in the central processing complex of computers; mixed digital/analog processors, typically found in signal processing and communication equipment; and others.
Many modifications and variations of the present invention are possible in light of the above teachings, and could be apparent for those skilled in the art. The scope of the invention is defined by the appended claims.

Claims

CLAIM
1. A CMOS structure, comprising: at least one first type FET device, said first type FET comprises: a first gate insulator comprising a first high-k dielectric; a first liner, wherein said first liner comprises oxide and nitride portions, wherein said nitride portions are forming edge segments of said first liner, and wherein said nitride portions are capable of preventing oxygen from reaching said first high-k dielectric; and at least one second type FET device, said second type FET comprises: a second gate insulator comprising a second high-k dielectric; a second liner, wherein said second liner is comprised of oxide and is free of nitride portions, wherein oxygen is capable to reach said second high-k dielectric.
2. The CMOS structure of claim 1, wherein said first type FET device is a PFET device, and said second type FET device is an NFET device.
3. The CMOS structure of claim 1, wherein said first type FET device is an NFET device, and said second type FET device is a PFET device.
4. The CMOS structure of claim 1, wherein said first high-k dielectric and said second high-k dielectric are of a same material.
5. The CMOS structure of claim 4, wherein said same material is HfO2.
6. The CMOS structure of claim 1, wherein said first type FET device comprises a first gate, wherein said first gate comprises a first metal.
7. The CMOS structure of claim 6, wherein said first metal is in direct contact with said first gate insulator.
8. The CMOS structure of claim 6, wherein a cap layer is sandwiched inbetween said first metal and said first gate insulator.
9. The CMOS structure of claim 1, wherein said second type FET device comprises a second gate, wherein said second gate comprises a second metal, wherein said second metal is in direct contact with said second gate insulator.
10. A method for processing a CMOS structure, comprising: in a first type FET device, implementing a first gate insulator and a first liner, wherein said first gate insulator comprises a first high-k dielectric, and said first liner consists essentially of oxide; in a second type FET device, implementing a second gate insulator and a second liner, wherein said second gate insulator comprises a second high-k dielectric, and said second liner consists essentially of oxide; in said first type FET device, etching said first liner until edge portions of said first liner are replaced by empty grooves; depositing nitride conformally, wherein said nitride is filling said grooves, and forms nitride edge segment portions of said first liner; and exposing said first type FET device and said second type FET device to oxygen, wherein oxygen penetrates through said second liner reaching said second high-k dielectric of said second gate insulator, and causing a predetermined shift in the threshold voltage of said second type FET device, while due to said nitride edge segment portions of said first liner, oxygen is not capable to penetrate to said first high-k dielectric of said first gate insulator, whereby the threshold voltage of said first type FET device stays unchanged.
11. The method of claim 10, wherein said first type FET device is selected to be a PFET device, and said second type FET device is selected to be an NFET device.
12. The method of claim 10, wherein said first type FET device is selected to be an NFET device, and said second type FET device is selected to be a PFET device.
13. The method of claim 10, further comprising: depositing a single layer of oxide over said first type FET device and said second type FET device, and fabricating said first liner and said second liner from said single layer of oxide.
14. The method of claim 10, wherein said first high-k dielectric and said second high-k dielectric are selected to be of a same material.
15. The method of claim 14, wherein said same material is selected to be HfO2.
16. The method of claim 10, further comprising: in said first type FET device, implementing a first gate comprising a first metal; in a second type FET device, implementing a second gate comprising a second metal.
17. The method of claim 16, wherein for said first gate, processing a cap layer to be sandwiched inbetween said first gate insulator and said first metal.
18. The method of claim 16, wherein for said second gate, processing said second metal in such manner to be in direct contact with said second insulator.
19. A processor, comprising: a plurality of CMOS circuits, wherein at least one CMOS circuit of said plurality of CMOS circuits further comprises: at least one first type FET device with a first gate insulator comprising a first high-k dielectric, and with a first liner, wherein said first liner comprises oxide and nitride portions, wherein said nitride portions are forming edge segments of said first liner; and at least one second type FET device with a second gate insulator comprising a second high-k dielectric, and with a second liner, wherein said second liner is comprised of oxide and is free of nitride portions.
20. The processor of claim 19, wherein said processor has a plurality of said second type FET devices, wherein thresholds of said plurality of second type FET devices have at least two differing values, wherein said differing values are separated by at least 50 mV.
PCT/EP2008/054270 2007-05-02 2008-04-09 Cmos circuits with high-k gate dielectric WO2008135335A1 (en)

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