US20040026688A1 - Schottky barrier tunnel transistor using thin silicon layer on insulator and method for fabricating the same - Google Patents
Schottky barrier tunnel transistor using thin silicon layer on insulator and method for fabricating the same Download PDFInfo
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- US20040026688A1 US20040026688A1 US10/331,945 US33194502A US2004026688A1 US 20040026688 A1 US20040026688 A1 US 20040026688A1 US 33194502 A US33194502 A US 33194502A US 2004026688 A1 US2004026688 A1 US 2004026688A1
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- 230000004888 barrier function Effects 0.000 title claims abstract description 11
- 239000012212 insulator Substances 0.000 title claims abstract description 7
- 238000000034 method Methods 0.000 title claims description 25
- 229910052710 silicon Inorganic materials 0.000 title claims description 14
- 239000010703 silicon Substances 0.000 title claims description 14
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title description 14
- 229910021332 silicide Inorganic materials 0.000 claims abstract description 26
- FVBUAEGBCNSCDD-UHFFFAOYSA-N silicide(4-) Chemical compound [Si-4] FVBUAEGBCNSCDD-UHFFFAOYSA-N 0.000 claims abstract description 26
- 239000000758 substrate Substances 0.000 claims abstract description 21
- 238000004519 manufacturing process Methods 0.000 claims abstract description 14
- 239000004020 conductor Substances 0.000 claims description 17
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- 239000003870 refractory metal Substances 0.000 claims description 10
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- 238000000151 deposition Methods 0.000 claims description 6
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- 238000006243 chemical reaction Methods 0.000 description 5
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 238000005468 ion implantation Methods 0.000 description 4
- 238000004151 rapid thermal annealing Methods 0.000 description 4
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- 206010010144 Completed suicide Diseases 0.000 description 2
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- 229910017052 cobalt Inorganic materials 0.000 description 2
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- 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
- H01L27/12—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 other than a semiconductor body, e.g. an insulating body
-
- 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
- H01L29/42384—Gate electrodes for field effect devices for field-effect transistors with insulated gate for thin film field effect transistors, e.g. characterised by the thickness or the shape of the insulator or the dimensions, the shape or the lay-out of the conductor
-
- 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
- H01L29/45—Ohmic electrodes
- H01L29/456—Ohmic electrodes on silicon
- H01L29/458—Ohmic electrodes on silicon for thin film silicon, e.g. source or drain electrode
-
- 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
- H01L29/68—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
- H01L29/7839—Field effect transistors with field effect produced by an insulated gate with Schottky drain or source contact
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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
- H01L29/68—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
- H01L29/786—Thin film transistors, i.e. transistors with a channel being at least partly a thin film
- H01L29/78606—Thin film transistors, i.e. transistors with a channel being at least partly a thin film with supplementary region or layer in the thin film or in the insulated bulk substrate supporting it for controlling or increasing the safety of the device
- H01L29/78609—Thin film transistors, i.e. transistors with a channel being at least partly a thin film with supplementary region or layer in the thin film or in the insulated bulk substrate supporting it for controlling or increasing the safety of the device for preventing leakage current
-
- 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
- H01L29/68—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
- H01L29/786—Thin film transistors, i.e. transistors with a channel being at least partly a thin film
- H01L29/78696—Thin film transistors, i.e. transistors with a channel being at least partly a thin film characterised by the structure of the channel, e.g. multichannel, transverse or longitudinal shape, length or width, doping structure, or the overlap or alignment between the channel and the gate, the source or the drain, or the contacting structure of the channel
Definitions
- the present invention relates to a transistor and a method of fabricating the same, and more particularly, to a Schottky barrier tunnel transistor (hereinafter, referred to as “SBTT”) using a Schottky barrier formed between metal and a semiconductor, and a method of fabricating the same.
- SBTT Schottky barrier tunnel transistor
- junction depth of source and drain regions must be within the range from a quarter to one third of the channel length of a transistor.
- Extensive research is continuously conducted to reduce the junction depth of source and drain regions with low accelerating voltage, using a general ion implantation method, but it is almost impossible to regularly and shallowly form the junction depth to 30 nm or less. Meanwhile, a reduction in the junction depth results in an increase in parasitic resistance. For instance, if a doping concentration is 1E19 cm ⁇ 3 and junction depth is 10 nm, a sheet resistance value exceeds more than 500 ⁇ / ⁇ and a signal delay would be caused.
- a rare-earth oxide layer is used as a better alternative than a silicon oxide layer.
- the rare-earth oxide layer is thermally unstable and thus is not proper to be processed at a high temperature, unlike the silicon oxide layer.
- a process temperature is required to be remarkably reduced when fabricating a semiconductor device, but a great reduction in the process temperature will place a limit on the thermal treatment for doping activation and recovery of damaged crystals.
- a SBTT is known as a transistor that has shallow junction depth and enables a gate oxide layer with high permittivity. Shallow junction depth is considered the most important factor in scaling down a metal-oxide-semiconductor field effect transistor (MOSFET).
- MOSFET metal-oxide-semiconductor field effect transistor
- the SBTT is made by replacing source and drain regions of the MOSFET with metal or silicide, in which a sheet resistance value is reduced from one tenth to one fiftieth of that of a general transistor. Therefore, the operational speed of the SBTT is improved, and the channel length is reduced to 35 nm or less. Also, ion implantation is not carried out when fabricating the SBTT, and therefore the subsequent thermal treatment is not needed.
- the SBTT is compatible with fabricating a transistor adopting a gate oxide layer of high permittivity. Further, the SBTT is fabricated using a lower thermal process than a general transistor and thus fabrication of the SBTT is compatible with a process of fabricating a transistor having a metallic gate electrode.
- a bulk silicon substrate is mainly used in fabricating a SBTT or conducting research into the operational characteristics of the SBTT.
- the use of a bulk silicon substrate causes a great number of silicon atoms to diffuse into the silicide during the formation of silicide source and drain regions, thereby causing a lot of vacancies in the crystalline bulk silicon substrate.
- the vacancies are generally densely formed in a space charge region and act as interface impurities that generate leakage current.
- the SBTT be fabricated with a silicon-on-insulator (SOI) substrate.
- SOI silicon-on-insulator
- a Schottky barrier tunnel transistor including a buried oxide layer formed on a base substrate layer and having a groove at its upper surface; an ultra-thin silicon-on-insulator (SOI) layer formed across the groove; an insulating layer wrapping the SOI layer on the groove; a gate formed to be wider than the groove on the insulating layer; source and drain regions each positioned at both sides of the gate, the source and drain regions formed of silicide; and a conductive layer for filling the groove.
- SBTT Schottky barrier tunnel transistor
- the SOI layer is formed to a thickness of about 50 nm or less.
- the conductive layer and the gate may be formed of doped polysilicon. Otherwise, the conductive layer may be formed of doped polysilicon and the gate may be formed of silicide.
- An insulating spacer and a hard mask layer may be further formed on sidewalls of the gate and on the gate, respectively.
- the bottoms of the source and drain regions contact the buried oxide layer.
- the SBTT according to the present invention is fabricated using a Schottky barrier.
- the Schottky barrier is formed between metal and a semiconductor and is made by forming silicide source and drain regions on a thin SOI layer.
- the SOI layer is formed to an ultra-thin thickness to minimize leakage current, and a channel in the SOI layer below a gate is completely wrapped by the gate and a conductive layer, thereby improving the operational characteristics of the SBTT.
- a method of fabricating an SBTT including making a substrate on which a base substrate layer, a buried oxide layer, and an ultra-thin SOI layer are sequentially formed; patterning the SOI layer to define two wide regions, as source and drain regions, and a narrow channel region between the two wide regions; forming a groove by removing a portion of the buried oxide layer that contacts the channel region; thermally oxidizing the remaining SOI layer to form an insulating layer, the insulating layer wrapping the channel region; depositing a conductive material for a gate on the insulating layer while filling the groove with the conductive material; patterning the conductive material and the insulating layer to form a gate and a gate oxide layer across the channel region, the gate and the gate oxide layer being formed to be wider than the groove; and forming source and drain regions on the two wide regions using silicide.
- the SOI layer is formed to a thickness such that an electric field controlled by the gate can completely control the channel region.
- Forming a groove includes forming a photoresist on the remaining SOI layer; performing exposure and development on the photoresist to form an opening that is wider than the channel region; removing a predetermined thickness of the buried oxide layer exposed via the opening and having an etch selectivity with respect to the SOI layer; and removing the photoresist entirely.
- Forming the gate and the gate oxide layer includes forming a hard mask layer on the conductive material to be wider than the groove and across the channel region; and patterning the conductive material and the insulating layer using the hard mask layer.
- Forming the source and drain regions includes depositing a refractory metal layer on the resultant structure on which the gate is formed; and forming a self-aligned silicide layer by thermally treating the substrate and reacting silicon of the two wide regions.
- the SBTT according to the present invention has a silicon-on-insulator (SOI) layer of a wrap structure, in which a portion of a buried oxide layer underlying a channel region is selectively removed to form a groove and the groove is filled with a conductive material for a gate, thereby preventing leakage current from occurring in an SOI substrate via the buried oxide layer.
- SOI silicon-on-insulator
- FIG. 1 is a cross-sectional view of a Schottky barrier tunnel transistor (SBTT) according to a preferred embodiment of the present invention
- FIGS. 2A, 3A, 4 A, and 5 A are top views illustrating a method of fabricating an SBTT according to the present invention
- FIGS. 2B, 3B, 4 B, and 5 B are cross-sectional views of the SBTT shown in FIGS. 2A, 3A, 4 A, and 5 A, respectively, taken along the line b-b′;
- FIGS. 6 and 7 are cross-sectional views illustrating subsequent processes performed after a process explained with reference to FIG. 5A is performed.
- FIG. 1 is a cross-sectional view of a SBTT according to a preferred embodiment of the present invention.
- source and drain regions 160 are formed of suicide that is a composition of silicon and metal.
- the metal for the silicide may be cobalt (Co), tungsten (W), nickel (Ni), palladium (Pd), platinum (Pt), or titanium (Ti).
- a silicon-on-insulator (SOI) layer 130 which acts as a channel, has a wrap structure in which a portion of a buried oxide layer 120 contacting the SOI layer 130 is removed to a predetermined thickness to form a groove, and the groove is filled with a conductive layer 150 b .
- the conductive layer 150 b is formed of doped polysilicon, which is also a substance for a gate 150 a , and effectively prevents a leakage current from occurring at an interface between the buried oxide layer 120 and the SOI layer 130 .
- the SOI layer 130 which acts a channel, has a structure wrapped by first and second insulting layers 140 a and 140 b .
- the first insulating layer 140 a on the SOI layer 130 acts as a gate oxide layer
- the second insulating layer 140 b below the SOI layer 130 insulates the gate 150 a and the conductive layer 150 b.
- the SOI layer 130 is thinly formed to a thickness of 50 nm or less, the thickness of a channel, which is controlled by the gate 150 a , becomes reduced, and the formation of an inversion layer can be very easily controlled. As a result, a leakage current formed between source and drain regions of the SBTT is reduced. It is more preferable that the bottom of the source and drain regions 160 contacts the buried oxide layer 120 so as to reduce the leakage current.
- the SBTT of FIG. 1 is formed on a base substrate layer 110 that serves as a mechanical base frame of the SBTT:
- An insulating spacer 155 is formed on the sidewalls of the gate 150 a to prevent short circuiting between the gate 150 a and the source and drain regions 160 .
- the insulating spacer 155 is formed of nitride or oxide. If necessary, a hard mask layer (not shown) may be further formed on the gate 150 a to protect the gate 150 a.
- the conductive layer 150 b and the gate 150 a are described as being formed of doped polysilicon. However, to reduce the gate resistance more than in this embodiment, the gate 150 a may be formed of silicide.
- the SBTT according to the present invention is very advantageous.
- the SBTT according to the present invention uses a Schottky barrier formed between metal and a silicon semiconductor, the Schottky barrier is made by forming the source and drain regions 160 on thin SOI layer 130 using silicide.
- the SBTT has improved operational characteristics because the SOI layer 130 is formed to an ultra-thin thickness so as to minimize leakage current and a channel is completely wrapped with the gate 150 a and the conductive layer 150 b.
- the SBTT according to the present invention does not adopt a doping method using ion implantation, and thus several processes related to ion implantation can be omitted, thereby reducing manufacturing costs. Also, the operational principles of the SBTT are based on quantum mechanical physics, and thus the SBTT can be applicable as a quantum device.
- FIGS. 2A, 3A, 4 A, and 5 A are top views illustrating a method of fabricating an SBTT according to a preferred embodiment of the present invention.
- FIGS. 2B, 3B, 4 B, and 5 B are cross-sectional views of the SBTT shown in FIGS. 2A, 3B, 4 B, and 5 B, respectively, taken along the line b-b′.
- FIGS. 6 and 7 are cross-sectional views illustrating subsequent processes performed after a process explained with reference to FIG. 5A.
- a method of fabricating an SBTT according a preferred embodiment to the present invention will now be described with reference to the above drawings.
- the base substrate layer 110 serves as a mechanical base frame, and a buried oxide layer 120 , and an ultra-thin SOI layer 130 are sequentially formed on the substrate layer 110 .
- the buried oxide layer 120 is typically formed of silicon dioxide and the base substrate layer 110 is usually formed of silicon.
- the SOI layer 130 is formed to a thickness such that a channel can be completely controlled by an electric field that is controlled by a gate. For instance, the SOI layer 130 is formed to a thickness of 50 nm or less.
- the SOI layer 130 is patterned to form two wide regions, which are to be source and drain regions and a narrow channel region between the two wide regions.
- a portion of the buried oxide layer 120 which contacts the channel region of the SOI layer 130 , is removed to form a groove 135 .
- a photoresist 132 is applied onto the SOI layer 130 shown in FIG. 2A. Thereafter, exposure and development are performed on the photoresist 132 to form an opening that is broader than the channel region. In this case, the photoresist 132 is removed only from a portion of the channel region, and thus the two wide regions, which are to be the source and drain regions are still completely wrapped with the photoresist 132 .
- the opening caused by the removal of the photoresist 132 is defined to be narrower than a gate which is to be formed in the subsequent process.
- the buried oxide layer 120 is selectively removed to a predetermined thickness with respect to the SOI layer 130 , thereby forming the groove 135 .
- the buried oxide layer 120 may be wet etched using a buffered oxide etchant (BOE) or a hydrofluoric acid (HF) solution.
- BOE buffered oxide etchant
- HF hydrofluoric acid
- the SOI layer 130 which is formed of silicon, has a different etch selectivity from that of the buried oxide layer 120 which is formed of an oxide, and the SOI layer 130 is not etched during the wet etching.
- the photoresist 132 is applied over the entire two wide regions, which are to be the source and drain regions, prevent the removal of portions of the buried oxide layer 120 , which contacts bottoms of the two wide regions and on which silicide is to be formed, during the wet etching.
- the removal of the buried oxide layer 120 below the two wide regions makes it difficult to form silicide on the two wide regions.
- FIGS. 4A and 4B are a top view of and a cross-sectional view of an SBTT according to the present invention, and thus it appears that the insulating layers 140 a and 140 b are formed on and below the SOI layer 130 . However, all surfaces of the SOI layer 130 are substantially wrapped by the insulating layers 140 a and 140 b.
- a conductive material for a gate is deposited on the insulating layer 140 a and filled in the groove 135 , and the conductive material and the insulating layer 140 a are patterned.
- the gate 150 a and a gate oxide layer are formed across the channel region to be wider than the groove 135 .
- a hard mask layer (not shown) may be formed on the conductive material to run across the channel region and the conductive material, and the insulating layer 140 a may be patterned using the hard mask layer.
- the conductive material for a gate of doped polysilicon has such excellent step coverage that it is suitable for a material for filling the groove 135 .
- a conductive layer 150 b having a smooth surface is formed in the groove 135 .
- the insulating layer 140 b below the SOO layer 130 insulates the gate 150 a and the conductive layer 150 b .
- a leakage current between the source and drain regions is transmitted to an interface between an SOI layer and a buried oxide layer, which is positioned below a channel region.
- an SBTT according to the present invention has a wrap structure in which all of the surfaces of the channel region are wrapped by the gate 150 a and the conductive layer 150 b , thereby completely blocking every possible leakage current paths.
- the insulating spacer 155 is formed on the sidewalls of the gate 150 a .
- an insulating material is deposited on the resultant structure of FIG. 5B and anisotropically etched to leave the insulating material only along the sidewalls of the gate 150 a , thereby forming the insulating spacer 155 .
- the insulating spacer 155 prevents short-circuiting between the gate 150 a and the source and drain regions.
- the source and drain regions 160 are formed of silicide on the two wide regions.
- the source and drain regions 160 may be formed by depositing a refractory metal layer on the resultant structure of FIG. 6, on which the gate 150 a is formed, and thermally treating the refractory metal layer to react the refractory metal layer with the silicon of the two wide regions.
- the reaction of the refractory metal layer with the silicon of the two wide regions results in the formation of a self-aligned suicide layer.
- the refractory metal layer may be formed of cobalt, tungsten, nickel, palladium, platinum, or titanium, and the thermal treatment may be rapid thermal annealing (RTA).
- the RTA it is preferable to obtain sufficient silicide reaction by controlling deposition thickness, and reaction temperature and time of the refractory metal layer, until the bottom of the source and drain regions 160 reach the buried oxide layer 120 .
- a non-reacted portion of the refractory metal layer is cleansed and removed in the subsequent process.
- the non-reacted portion may be cleansed by performing argon (Ar) sputtering thereon in a chamber or by dipping said portion into a HF solution.
- Ar argon
- the gate 150 a since the gate 150 a is formed to be wider than the groove 135 , short-circuiting between the source and drain regions 160 and the conductive layer 150 b can be prevented. Due to the insulating spacer 155 along the sidewalls of the gate 150 a , short-circuiting between the gate 150 a and the source and drain regions 160 can also be prevented.
- Silicide reaction does not occur on the gate 150 a when the hard mask layer is formed on the gate 150 a , whereas silicon of the gate 150 a reacts with the refractory metal layer to become silicide when the hard mask layer is not formed on the gate 150 a .
- Silicide has a lower resistance than polysilicon, and therefore the operational speed of a transistor formed of silicide can be improved.
- the SBTT according to the present invention may be easily fabricated using either a general method of fabricating a silicon transistor or spontaneous silicide reaction.
- the SBTT according to the present invention is advantageous in that a fabrication method is simple and has a high practicability. In particular, a fine transistor on a nanometer scale can be easily fabricated using the above fabrication method.
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Abstract
Description
- This application claims the priority of Korean Patent Application No. 2002-47506, filed on Aug. 12, 2002 in the Korean Intellectual Property Office, which is incorporated herein in its entirety by reference.
- 1. Field of the Invention
- The present invention relates to a transistor and a method of fabricating the same, and more particularly, to a Schottky barrier tunnel transistor (hereinafter, referred to as “SBTT”) using a Schottky barrier formed between metal and a semiconductor, and a method of fabricating the same.
- 2. Description of the Related Art
- Advances in the techniques of fabricating semiconductor devices result in the development of a transistor having a short channel of 100 nm or less. Therefore, the characteristics of a semiconductor device, which operates according to the laws of classic electrodynamics, are now governed by quantum mechanics In this case, a leakage current, however, is extremely increased due to short channel effect in a transistor. Thus, there is a need to prevent a short channel effect from occurring in such a transistor.
- To suppress the occurrence of the short channel effect, junction depth of source and drain regions must be within the range from a quarter to one third of the channel length of a transistor. Extensive research is continuously conducted to reduce the junction depth of source and drain regions with low accelerating voltage, using a general ion implantation method, but it is almost impossible to regularly and shallowly form the junction depth to 30 nm or less. Meanwhile, a reduction in the junction depth results in an increase in parasitic resistance. For instance, if a doping concentration is 1E19 cm−3 and junction depth is 10 nm, a sheet resistance value exceeds more than 500 Ω/□ and a signal delay would be caused.
- Accordingly, an increase in the permittivity of a gate oxide layer, as well as a shallow junction depth, is required to suppress the occurrence of the short channel effect. To increase the permittivity of a gate oxide layer, a rare-earth oxide layer is used as a better alternative than a silicon oxide layer. However, the rare-earth oxide layer is thermally unstable and thus is not proper to be processed at a high temperature, unlike the silicon oxide layer. For the use of the rare-earth oxide layer, a process temperature is required to be remarkably reduced when fabricating a semiconductor device, but a great reduction in the process temperature will place a limit on the thermal treatment for doping activation and recovery of damaged crystals.
- A SBTT is known as a transistor that has shallow junction depth and enables a gate oxide layer with high permittivity. Shallow junction depth is considered the most important factor in scaling down a metal-oxide-semiconductor field effect transistor (MOSFET). The SBTT is made by replacing source and drain regions of the MOSFET with metal or silicide, in which a sheet resistance value is reduced from one tenth to one fiftieth of that of a general transistor. Therefore, the operational speed of the SBTT is improved, and the channel length is reduced to 35 nm or less. Also, ion implantation is not carried out when fabricating the SBTT, and therefore the subsequent thermal treatment is not needed. For this reason, the SBTT is compatible with fabricating a transistor adopting a gate oxide layer of high permittivity. Further, the SBTT is fabricated using a lower thermal process than a general transistor and thus fabrication of the SBTT is compatible with a process of fabricating a transistor having a metallic gate electrode.
- In general, a bulk silicon substrate is mainly used in fabricating a SBTT or conducting research into the operational characteristics of the SBTT. However, the use of a bulk silicon substrate causes a great number of silicon atoms to diffuse into the silicide during the formation of silicide source and drain regions, thereby causing a lot of vacancies in the crystalline bulk silicon substrate. The vacancies are generally densely formed in a space charge region and act as interface impurities that generate leakage current.
- To prevent the formation of vacancies, it is suggested that the SBTT be fabricated with a silicon-on-insulator (SOI) substrate. However, in the SBTT formed on the SOI substrate, an interface between a buried oxide layer and an SOI layer becomes a path through which a leakage current is generated.
- To solve the above problem, it is one aspect of the present invention to provide a SBTT in which generation of short channel effect and a leakage current are prevented.
- It is another aspect of the present invention to provide a method of fabricating such a SBTT.
- To achieve one aspect of the present invention, there is provided a Schottky barrier tunnel transistor (SBTT) including a buried oxide layer formed on a base substrate layer and having a groove at its upper surface; an ultra-thin silicon-on-insulator (SOI) layer formed across the groove; an insulating layer wrapping the SOI layer on the groove; a gate formed to be wider than the groove on the insulating layer; source and drain regions each positioned at both sides of the gate, the source and drain regions formed of silicide; and a conductive layer for filling the groove.
- Preferably, the SOI layer is formed to a thickness of about 50 nm or less.
- The conductive layer and the gate may be formed of doped polysilicon. Otherwise, the conductive layer may be formed of doped polysilicon and the gate may be formed of silicide.
- An insulating spacer and a hard mask layer may be further formed on sidewalls of the gate and on the gate, respectively.
- Preferably, the bottoms of the source and drain regions contact the buried oxide layer.
- As mentioned above, the SBTT according to the present invention is fabricated using a Schottky barrier. The Schottky barrier is formed between metal and a semiconductor and is made by forming silicide source and drain regions on a thin SOI layer. The SOI layer is formed to an ultra-thin thickness to minimize leakage current, and a channel in the SOI layer below a gate is completely wrapped by the gate and a conductive layer, thereby improving the operational characteristics of the SBTT.
- To achieve another aspect of the present invention, there is provided a method of fabricating an SBTT, including making a substrate on which a base substrate layer, a buried oxide layer, and an ultra-thin SOI layer are sequentially formed; patterning the SOI layer to define two wide regions, as source and drain regions, and a narrow channel region between the two wide regions; forming a groove by removing a portion of the buried oxide layer that contacts the channel region; thermally oxidizing the remaining SOI layer to form an insulating layer, the insulating layer wrapping the channel region; depositing a conductive material for a gate on the insulating layer while filling the groove with the conductive material; patterning the conductive material and the insulating layer to form a gate and a gate oxide layer across the channel region, the gate and the gate oxide layer being formed to be wider than the groove; and forming source and drain regions on the two wide regions using silicide.
- The SOI layer is formed to a thickness such that an electric field controlled by the gate can completely control the channel region.
- Forming a groove includes forming a photoresist on the remaining SOI layer; performing exposure and development on the photoresist to form an opening that is wider than the channel region; removing a predetermined thickness of the buried oxide layer exposed via the opening and having an etch selectivity with respect to the SOI layer; and removing the photoresist entirely.
- Forming the gate and the gate oxide layer includes forming a hard mask layer on the conductive material to be wider than the groove and across the channel region; and patterning the conductive material and the insulating layer using the hard mask layer.
- Forming the source and drain regions includes depositing a refractory metal layer on the resultant structure on which the gate is formed; and forming a self-aligned silicide layer by thermally treating the substrate and reacting silicon of the two wide regions.
- The SBTT according to the present invention has a silicon-on-insulator (SOI) layer of a wrap structure, in which a portion of a buried oxide layer underlying a channel region is selectively removed to form a groove and the groove is filled with a conductive material for a gate, thereby preventing leakage current from occurring in an SOI substrate via the buried oxide layer.
- The above aspects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:
- FIG. 1 is a cross-sectional view of a Schottky barrier tunnel transistor (SBTT) according to a preferred embodiment of the present invention;
- FIGS. 2A, 3A,4A, and 5A are top views illustrating a method of fabricating an SBTT according to the present invention;
- FIGS. 2B, 3B,4B, and 5B are cross-sectional views of the SBTT shown in FIGS. 2A, 3A, 4A, and 5A, respectively, taken along the line b-b′; and
- FIGS. 6 and 7 are cross-sectional views illustrating subsequent processes performed after a process explained with reference to FIG. 5A is performed.
- The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. The same reference numerals in different drawings represent the same element, and thus their descriptions will not be repeated.
- FIG. 1 is a cross-sectional view of a SBTT according to a preferred embodiment of the present invention. Referring to FIG. 1, source and drain
regions 160 are formed of suicide that is a composition of silicon and metal. The metal for the silicide may be cobalt (Co), tungsten (W), nickel (Ni), palladium (Pd), platinum (Pt), or titanium (Ti). A silicon-on-insulator (SOI)layer 130, which acts as a channel, has a wrap structure in which a portion of a buriedoxide layer 120 contacting theSOI layer 130 is removed to a predetermined thickness to form a groove, and the groove is filled with aconductive layer 150 b. Theconductive layer 150 b is formed of doped polysilicon, which is also a substance for agate 150 a, and effectively prevents a leakage current from occurring at an interface between the buriedoxide layer 120 and theSOI layer 130. - The
SOI layer 130, which acts a channel, has a structure wrapped by first and secondinsulting layers layer 140 a on theSOI layer 130 acts as a gate oxide layer, and the second insulatinglayer 140 b below theSOI layer 130 insulates thegate 150 a and theconductive layer 150 b. - If the
SOI layer 130 is thinly formed to a thickness of 50 nm or less, the thickness of a channel, which is controlled by thegate 150 a, becomes reduced, and the formation of an inversion layer can be very easily controlled. As a result, a leakage current formed between source and drain regions of the SBTT is reduced. It is more preferable that the bottom of the source and drainregions 160 contacts the buriedoxide layer 120 so as to reduce the leakage current. - The SBTT of FIG. 1 is formed on a
base substrate layer 110 that serves as a mechanical base frame of the SBTT: An insulatingspacer 155 is formed on the sidewalls of thegate 150 a to prevent short circuiting between thegate 150 a and the source and drainregions 160. The insulatingspacer 155 is formed of nitride or oxide. If necessary, a hard mask layer (not shown) may be further formed on thegate 150 a to protect thegate 150 a. - In this embodiment, the
conductive layer 150 b and thegate 150 a are described as being formed of doped polysilicon. However, to reduce the gate resistance more than in this embodiment, thegate 150 a may be formed of silicide. - The SBTT according to the present invention is very advantageous. First, the SBTT according to the present invention uses a Schottky barrier formed between metal and a silicon semiconductor, the Schottky barrier is made by forming the source and drain
regions 160 onthin SOI layer 130 using silicide. The SBTT has improved operational characteristics because theSOI layer 130 is formed to an ultra-thin thickness so as to minimize leakage current and a channel is completely wrapped with thegate 150 a and theconductive layer 150 b. - Second, the SBTT according to the present invention does not adopt a doping method using ion implantation, and thus several processes related to ion implantation can be omitted, thereby reducing manufacturing costs. Also, the operational principles of the SBTT are based on quantum mechanical physics, and thus the SBTT can be applicable as a quantum device.
- Third, it is possible to prevent the occurrence of a leakage current by forming source and drain
regions 160 on anultra-thin SOI substrate 130 using silicide and forming a channel region to be completely wrapped with a gate and a conductive layer. The occurrence of leakage current is regarded as being a factor that makes it the most difficult to secure the characteristics of an SBTT. Accordingly, in an SBTT using an SOI substrate and a wrap structure, according to the present invention, the occurrence of leakage current can be completely prevented, thereby increasing the practicability of the SBTT according to the present invention. - FIGS. 2A, 3A,4A, and 5A are top views illustrating a method of fabricating an SBTT according to a preferred embodiment of the present invention. FIGS. 2B, 3B, 4B, and 5B are cross-sectional views of the SBTT shown in FIGS. 2A, 3B, 4B, and 5B, respectively, taken along the line b-b′. FIGS. 6 and 7 are cross-sectional views illustrating subsequent processes performed after a process explained with reference to FIG. 5A. A method of fabricating an SBTT according a preferred embodiment to the present invention will now be described with reference to the above drawings.
- Referring to FIGS. 2A and 2B, the
base substrate layer 110 serves as a mechanical base frame, and a buriedoxide layer 120, and anultra-thin SOI layer 130 are sequentially formed on thesubstrate layer 110. The buriedoxide layer 120 is typically formed of silicon dioxide and thebase substrate layer 110 is usually formed of silicon. Preferably, theSOI layer 130 is formed to a thickness such that a channel can be completely controlled by an electric field that is controlled by a gate. For instance, theSOI layer 130 is formed to a thickness of 50 nm or less. Next, theSOI layer 130 is patterned to form two wide regions, which are to be source and drain regions and a narrow channel region between the two wide regions. - Next, as shown in FIGS. 3A and 3B, a portion of the buried
oxide layer 120, which contacts the channel region of theSOI layer 130, is removed to form agroove 135. For the formation of thegroove 135, aphotoresist 132 is applied onto theSOI layer 130 shown in FIG. 2A. Thereafter, exposure and development are performed on thephotoresist 132 to form an opening that is broader than the channel region. In this case, thephotoresist 132 is removed only from a portion of the channel region, and thus the two wide regions, which are to be the source and drain regions are still completely wrapped with thephotoresist 132. The opening caused by the removal of thephotoresist 132 is defined to be narrower than a gate which is to be formed in the subsequent process. - Next, a portion of the buried
oxide layer 120 exposed via the opening is selectively removed to a predetermined thickness with respect to theSOI layer 130, thereby forming thegroove 135. For instance, the buriedoxide layer 120 may be wet etched using a buffered oxide etchant (BOE) or a hydrofluoric acid (HF) solution. In this case, theSOI layer 130, which is formed of silicon, has a different etch selectivity from that of the buriedoxide layer 120 which is formed of an oxide, and theSOI layer 130 is not etched during the wet etching. Thephotoresist 132 is applied over the entire two wide regions, which are to be the source and drain regions, prevent the removal of portions of the buriedoxide layer 120, which contacts bottoms of the two wide regions and on which silicide is to be formed, during the wet etching. The removal of the buriedoxide layer 120 below the two wide regions makes it difficult to form silicide on the two wide regions. - Next, referring to FIGS. 4A and 4B, the
photoresist 132 is completely removed and the remainingSOI layer 130 is thermally oxidized to form the insulatinglayers SOI layer 130 is formed across thegroove 135, the thermal oxidation of theSOI layer 130 makes the exposed surfaces of theSOI layer 130 be completely wrapped by the insulatinglayers layers SOI layer 130. However, all surfaces of theSOI layer 130 are substantially wrapped by the insulatinglayers - Referring to FIGS. 5A and 5B, a conductive material for a gate is deposited on the insulating
layer 140 a and filled in thegroove 135, and the conductive material and the insulatinglayer 140 a are patterned. As a result, thegate 150 a and a gate oxide layer are formed across the channel region to be wider than thegroove 135. For the formation of thegate 150 a and the gate oxide layer, a hard mask layer (not shown) may be formed on the conductive material to run across the channel region and the conductive material, and the insulatinglayer 140 a may be patterned using the hard mask layer. - It is preferable to form the conductive material for a gate of doped polysilicon. The doped polysilicon has such excellent step coverage that it is suitable for a material for filling the
groove 135. Thus, if thegroove 135 is filled with the doped polysilicon, aconductive layer 150 b having a smooth surface is formed in thegroove 135. The insulatinglayer 140 b below theSOO layer 130 insulates thegate 150 a and theconductive layer 150 b. In a conventional SBTT, a leakage current between the source and drain regions is transmitted to an interface between an SOI layer and a buried oxide layer, which is positioned below a channel region. In contrast, an SBTT according to the present invention has a wrap structure in which all of the surfaces of the channel region are wrapped by thegate 150 a and theconductive layer 150 b, thereby completely blocking every possible leakage current paths. - Next, referring to FIG. 6, the insulating
spacer 155 is formed on the sidewalls of thegate 150 a. In detail, an insulating material is deposited on the resultant structure of FIG. 5B and anisotropically etched to leave the insulating material only along the sidewalls of thegate 150 a, thereby forming the insulatingspacer 155. The insulatingspacer 155 prevents short-circuiting between thegate 150 a and the source and drain regions. - Next, as shown in FIG. 7, the source and drain
regions 160 are formed of silicide on the two wide regions. The source and drainregions 160 may be formed by depositing a refractory metal layer on the resultant structure of FIG. 6, on which thegate 150 a is formed, and thermally treating the refractory metal layer to react the refractory metal layer with the silicon of the two wide regions. The reaction of the refractory metal layer with the silicon of the two wide regions results in the formation of a self-aligned suicide layer. For instance, the refractory metal layer may be formed of cobalt, tungsten, nickel, palladium, platinum, or titanium, and the thermal treatment may be rapid thermal annealing (RTA). During the RTA, it is preferable to obtain sufficient silicide reaction by controlling deposition thickness, and reaction temperature and time of the refractory metal layer, until the bottom of the source and drainregions 160 reach the buriedoxide layer 120. A non-reacted portion of the refractory metal layer is cleansed and removed in the subsequent process. For instance, the non-reacted portion may be cleansed by performing argon (Ar) sputtering thereon in a chamber or by dipping said portion into a HF solution. During the RTA, since thegate 150 a is formed to be wider than thegroove 135, short-circuiting between the source and drainregions 160 and theconductive layer 150 b can be prevented. Due to the insulatingspacer 155 along the sidewalls of thegate 150 a, short-circuiting between thegate 150 a and the source and drainregions 160 can also be prevented. - Silicide reaction does not occur on the
gate 150 a when the hard mask layer is formed on thegate 150 a, whereas silicon of thegate 150 a reacts with the refractory metal layer to become silicide when the hard mask layer is not formed on thegate 150 a. Silicide has a lower resistance than polysilicon, and therefore the operational speed of a transistor formed of silicide can be improved. - Using the above fabrication method, it is possible to make an SBTT according to the present invention in which the occurrence of a short channel effect and leakage current are suppressed. The SBTT according to the present invention may be easily fabricated using either a general method of fabricating a silicon transistor or spontaneous silicide reaction. The SBTT according to the present invention is advantageous in that a fabrication method is simple and has a high practicability. In particular, a fine transistor on a nanometer scale can be easily fabricated using the above fabrication method.
Claims (15)
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KR10-2002-0047506A KR100470832B1 (en) | 2002-08-12 | 2002-08-12 | Schottky barrier tunnel transistor using thin silicon layer on insulator and method for fabricating the same |
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Cited By (8)
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WO2004105086A2 (en) * | 2003-05-15 | 2004-12-02 | Wu Koucheng | Schotty-barrier tunneling transistor |
US20050167766A1 (en) * | 2004-01-21 | 2005-08-04 | Atsushi Yagishita | Semiconductor device and manufacturing method thereof |
WO2005081768A2 (en) * | 2004-02-18 | 2005-09-09 | Koucheng Wu | Schottky-barrier tunneling transistor |
US20060022280A1 (en) * | 2004-07-14 | 2006-02-02 | International Business Machines Corporation | Formation of fully silicided metal gate using dual self-aligned silicide process |
CN102832127A (en) * | 2011-06-15 | 2012-12-19 | 中国科学院微电子研究所 | metal source-drain SOI MOS transistor and forming method thereof |
WO2014207078A1 (en) * | 2013-06-26 | 2014-12-31 | Technische Universität Darmstadt | Field effect transistor arrangement |
US20150076493A1 (en) * | 2013-09-19 | 2015-03-19 | Semiconductor Energy Laboratory Co., Ltd. | Semiconductor device and manufacturing method thereof |
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US7504328B2 (en) * | 2004-05-11 | 2009-03-17 | National University Of Singapore | Schottky barrier source/drain n-mosfet using ytterbium silicide |
KR100592740B1 (en) | 2004-12-03 | 2006-06-26 | 한국전자통신연구원 | Schottky barrier tunnel single electron transistor and a method for fabricating the same |
FR2881273B1 (en) * | 2005-01-21 | 2007-05-04 | St Microelectronics Sa | METHOD FOR FORMING INTEGRATED CIRCUIT SEMICONDUCTOR SUBSTRATE |
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JPH02302044A (en) * | 1989-05-16 | 1990-12-14 | Fujitsu Ltd | Manufacture of semiconductor device |
JP2603886B2 (en) * | 1991-05-09 | 1997-04-23 | 日本電信電話株式会社 | Method for manufacturing thin SOI insulated gate field effect transistor |
JPH05343686A (en) * | 1992-06-04 | 1993-12-24 | Mitsubishi Electric Corp | Semiconductor device and manufacture thereof |
JPH06151854A (en) * | 1992-11-05 | 1994-05-31 | Nippon Steel Corp | Manufacture of soi mos transistor |
US6207530B1 (en) * | 1998-06-19 | 2001-03-27 | International Business Machines Corporation | Dual gate FET and process |
KR100434534B1 (en) | 1998-10-13 | 2004-07-16 | 삼성전자주식회사 | Single Electronic Transistor Using Schottky Tunnel Barrier and Manufacturing Method Thereof |
KR100555454B1 (en) * | 1998-10-29 | 2006-04-21 | 삼성전자주식회사 | Manufacturing Method of SOI Transistor |
US6198113B1 (en) * | 1999-04-22 | 2001-03-06 | Acorn Technologies, Inc. | Electrostatically operated tunneling transistor |
US6339005B1 (en) | 1999-10-22 | 2002-01-15 | International Business Machines Corporation | Disposable spacer for symmetric and asymmetric Schottky contact to SOI MOSFET |
JP3425603B2 (en) * | 2000-01-28 | 2003-07-14 | 独立行政法人産業技術総合研究所 | Method for manufacturing field effect transistor |
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2002
- 2002-08-12 KR KR10-2002-0047506A patent/KR100470832B1/en active IP Right Grant
- 2002-12-31 US US10/331,945 patent/US6693294B1/en not_active Expired - Fee Related
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US20060022280A1 (en) * | 2004-07-14 | 2006-02-02 | International Business Machines Corporation | Formation of fully silicided metal gate using dual self-aligned silicide process |
US7271455B2 (en) * | 2004-07-14 | 2007-09-18 | International Business Machines Corporation | Formation of fully silicided metal gate using dual self-aligned silicide process |
US20080026551A1 (en) * | 2004-07-14 | 2008-01-31 | International Business Machines Corporation | Formation of fully silicided metal gate using dual self-aligned silicide process |
US7785999B2 (en) | 2004-07-14 | 2010-08-31 | International Business Machines Corporation | Formation of fully silicided metal gate using dual self-aligned silicide process |
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WO2014207078A1 (en) * | 2013-06-26 | 2014-12-31 | Technische Universität Darmstadt | Field effect transistor arrangement |
US20150076493A1 (en) * | 2013-09-19 | 2015-03-19 | Semiconductor Energy Laboratory Co., Ltd. | Semiconductor device and manufacturing method thereof |
US9443934B2 (en) * | 2013-09-19 | 2016-09-13 | Semiconductor Energy Laboratory Co., Ltd. | Semiconductor device and manufacturing method thereof |
CN110120434A (en) * | 2019-06-18 | 2019-08-13 | 合肥晶澳太阳能科技有限公司 | Cell piece and preparation method thereof |
Also Published As
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KR20040015417A (en) | 2004-02-19 |
JP2004079986A (en) | 2004-03-11 |
US6693294B1 (en) | 2004-02-17 |
KR100470832B1 (en) | 2005-03-10 |
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