WO2014179809A1 - Gallium nitride field effect transistor - Google Patents

Gallium nitride field effect transistor Download PDF

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Publication number
WO2014179809A1
WO2014179809A1 PCT/US2014/036842 US2014036842W WO2014179809A1 WO 2014179809 A1 WO2014179809 A1 WO 2014179809A1 US 2014036842 W US2014036842 W US 2014036842W WO 2014179809 A1 WO2014179809 A1 WO 2014179809A1
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WIPO (PCT)
Prior art keywords
metal
layer
gate
silicon
atomic percent
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PCT/US2014/036842
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French (fr)
Inventor
Asad Mahmood HAIDER
Jungwoo Joh
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Texas Instrument Incorporated
Texas Instruments Japan Limited
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Publication date
Application filed by Texas Instrument Incorporated, Texas Instruments Japan Limited filed Critical Texas Instrument Incorporated
Priority to JP2016512994A priority Critical patent/JP6562559B2/en
Priority to CN201480024438.1A priority patent/CN105164810B/en
Priority to EP14792233.0A priority patent/EP2992557A4/en
Publication of WO2014179809A1 publication Critical patent/WO2014179809A1/en

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    • H—ELECTRICITY
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    • 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
    • H01L29/778—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface
    • H01L29/7786—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface with direct single heterostructure, i.e. with wide bandgap layer formed on top of active layer, e.g. direct single heterostructure MIS-like HEMT
    • H01L29/7787—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface with direct single heterostructure, i.e. with wide bandgap layer formed on top of active layer, e.g. direct single heterostructure MIS-like HEMT with wide bandgap charge-carrier supplying layer, e.g. direct single heterostructure MODFET
    • 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
    • H01L21/02—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
    • H01L21/28264—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being a III-V compound
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    • 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
    • H01L21/283—Deposition of conductive or insulating materials for electrodes conducting electric current
    • H01L21/285—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation
    • H01L21/28506—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers
    • H01L21/28575—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers on semiconductor bodies comprising AIIIBV compounds
    • 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
    • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
    • H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/20—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds
    • H01L29/2003—Nitride compounds
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    • 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
    • H01L29/4966—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET the conductor material next to the insulator being a composite material, e.g. organic material, TiN, MoSi2
    • H01L29/4975—Metal-insulator-semiconductor electrodes, e.g. gates of MOSFET the conductor material next to the insulator being a composite material, e.g. organic material, TiN, MoSi2 being a silicide layer, e.g. TiSi2
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    • 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
    • H01L29/518—Insulating materials associated therewith the insulating material containing nitrogen, e.g. nitride, oxynitride, nitrogen-doped material
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    • 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
    • H01L29/66446—Unipolar field-effect transistors with an active layer made of a group 13/15 material, e.g. group 13/15 velocity modulation transistor [VMT], group 13/15 negative resistance FET [NERFET]
    • H01L29/66462—Unipolar field-effect transistors with an active layer made of a group 13/15 material, e.g. group 13/15 velocity modulation transistor [VMT], group 13/15 negative resistance FET [NERFET] with a heterojunction interface channel or gate, e.g. HFET, HIGFET, SISFET, HJFET, HEMT
    • 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
    • H01L29/42364—Gate electrodes for field effect devices for field-effect transistors with insulated gate characterised by the insulating layer, e.g. thickness or uniformity
    • H01L29/42368—Gate electrodes for field effect devices for field-effect transistors with insulated gate characterised by the insulating layer, e.g. thickness or uniformity the thickness being non-uniform
    • 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
    • H01L29/452—Ohmic electrodes on AIII-BV compounds

Definitions

  • This relates in general to semiconductor devices, and in particular to gallium nitride field effect transistors.
  • a gallium nitride field effect transistor may have an insulated metal gate and tunneling source and drain contacts. Forming reliable source and drain contacts may require annealing at a temperature which causes degradation of the gate dielectric layer.
  • a semiconductor device may be formed by forming a metal gate with 2 atomic percent to 10 atomic percent silicon.
  • the metal gate is formed over a gate dielectric layer containing silicon.
  • a subsequent contact anneal may include heating for at least 30 seconds at a temperature of at least 750 °C.
  • FIGS. 1A-1E are cross sections of a semiconductor device depicted in successive stages of fabrication.
  • FIGS. 2-4 depict exemplary processes for forming metal gates of GaN FETs with 2 atomic percent to 10 atomic percent silicon.
  • a semiconductor device may be formed by forming a silicon-containing gate dielectric layer, such as silicon nitride, over a semiconductor layer.
  • a gate metal layer is formed over the gate dielectric layer; the gate metal layer includes 2 atomic percent to 10 atomic percent silicon during formation.
  • the gate metal layer is patterned to form a metal gate.
  • Contact metal is formed and possibly patterned to form source and drain contacts.
  • a subsequent contact anneal heats the contact metal and gate for at least 30 seconds at a temperature of at least 750 °C.
  • Ill-Nitride (III-N) semiconductor materials are materials in which Group III (boron group) elements (boron, aluminum, gallium, indium) provide a portion of the atoms in the semiconductor material and nitrogen atoms provide the remainder.
  • Group III-N semiconductor materials are gallium nitride, boron gallium nitride, aluminum gallium nitride, indium nitride, and indium aluminum gallium nitride.
  • III-N materials may be written with variable subscripts to denote a range of possible stoichiometries.
  • aluminum gallium nitride may be written as Al x Gai_ x N and indium aluminum gallium nitride may be written as In x Al y Gai_ x _ y N.
  • GaN FET is an example of a field effect transistor that includes III-N semiconductor materials.
  • the sputtered aluminum also includes up to a few percent of copper, silicon, titanium and/or other elements, so as to improve the aluminum's electromigration properties.
  • FIGS. 1A-1E are cross sections of a semiconductor device depicted in successive stages of fabrication.
  • the semiconductor device 100 is formed on a substrate 102 which may have a low-defect layer of III-N semiconductor material at a top surface, for example, an unintentionally doped layer of gallium nitride.
  • a barrier layer 104 of III-N semiconductor material is formed on the top surface of the substrate 102.
  • the barrier layer 104 may include Al x Gai_ x N or In x Al y Gai_ x _ y N, 2 to 30 nanometers thick.
  • barrier layer 104 Forming the barrier layer 104 on the low-defect layer of III-N semiconductor material at the top surface of the substrate 102 generates a two-dimensional electron gas in the low-defect layer just below the barrier layer 104 with an electron density of, for example, l x lO 12 to 2> ⁇ 10 13 cm 2 .
  • An optional cap layer 106 of 2 to 5 nanometers of gallium nitride may be formed over the barrier layer 104.
  • a silicon-containing gate dielectric layer 108 is formed over the barrier layer 104, and over the cap layer 106 if present.
  • the gate dielectric layer 108 may be, for example, 10 to 20 nanometers of silicon nitride formed by low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD).
  • LPCVD low pressure chemical vapor deposition
  • PECVD plasma enhanced chemical vapor deposition
  • the gate dielectric layer 108 may include one or more layers of silicon nitride, silicon dioxide and/or silicon oxynitride.
  • a layer of field dielectric 110 is formed on the gate dielectric layer 108 and patterned to have sloped edges adjacent to a channel region of the semiconductor device 100.
  • the field dielectric 110 may include, for example, 100 to 300 nanometers of silicon nitride, formed by LPCVD or PECVD.
  • a metal gate 112 is formed on the gate dielectric layer 108 over the channel region and overlapping the sloped edge of the field dielectric 110.
  • the metal gate 112 may include at least 10 percent titanium, for example titanium tungsten alloy.
  • the metal gate 112 further includes 2 atomic percent to 10 atomic percent silicon.
  • the metal gate 112 may be formed, for example by an etch process or a liftoff process.
  • a passivation dielectric layer 114 is formed over the metal gate 112, the field dielectric 110 and the gate dielectric layer 108.
  • the passivation dielectric layer 114 may include, for example, 200 to 300 nanometers of silicon nitride, formed by PECVD.
  • Source and drain contact holes 116 are etched through the passivation dielectric layer 114, the gate dielectric layer 108 and the cap layer 106, and into the barrier layer 104 proximate to the two-dimensional electron gas.
  • the source and drain contact holes 116 may be 1 to 10 microns wide.
  • contact metal 118 is formed in the source and drain contact holes 116 and patterned.
  • the contact metal 118 may include, for example, a layer of titanium 120 40 to 100 nanometers thick sputtered in the source and drain contact holes 116, a layer of sputtered aluminum 122 50 to 200 nanometers thick formed on the titanium layer 120, and a layer of titanium nitride 124 30 to 80 nanometers thick formed on the sputtered aluminum layer 122 by reactive sputtering, also known as physical vapor deposition (PVD).
  • PVD physical vapor deposition
  • the contact metal 118 is formed so as to provide an open cavity in each of the source and drain contact holes 116.
  • Forming the metal gate 112 and the passivation dielectric layer 114 prior to forming the source and drain contact holes 116 and the contact metal 118 advantageously allows closer gate-source spacing and more fabrication process latitude, because the contact metal 118 may overlap a top surface of the passivation dielectric layer 114 without interfering with the metal gate 112.
  • formation of the source and drain contact holes 116 may be omitted so that the contact metal 118 is formed on an existing top surface of the III-N semiconductor material.
  • a contact anneal process 126 heats the contact metal 118 to at least 750 °C for at least 30 seconds.
  • the contact anneal process 126 improves an electrical connection between the contact metal 118 and the two-dimensional electron gas by reducing an impedance of the electrical connection and making the electrical connection more ohmic, that is, making a current voltage relationship of the electrical connection more linear. Increasing the temperature of the contact anneal process 126 further improves the electrical connection.
  • the contact anneal process 126 heats the contact metal 118 to at least 800 °C for at least 30 seconds.
  • the contact anneal process 126 heats the contact metal 118 to at least 850 °C for at least 30 seconds. In a further version, the contact anneal process 126 heats the contact metal 118 to at least 900 °C for at least 30 seconds.
  • the contact anneal process 126 may be performed, for example, in a rapid thermal processor (RTP) tool which heats the semiconductor device 100 using incandescent lamps.
  • RTP rapid thermal processor
  • a first metallization layer 128 is formed on the contact metal 118.
  • the first metallization layer 128 may include, for example, an adhesion layer 130 of 50 to 150 nanometers of sputtered titanium tungsten, a main metal layer 132 of 200 to 500 nanometers of sputtered aluminum formed on the adhesion layer 130, and an anti-refection layer 134 of 20 to 40 nanometers of titanium nitride formed on the main metal layer 132.
  • the first metallization layer 128 is patterned so as to overlap the source and drain contact holes 116.
  • FIGS. 2-4 depict exemplary processes for forming metal gates of GaN FETs with 2 atomic percent to 10 atomic percent silicon.
  • a substrate 202 of a semiconductor device 200 is positioned in a sputtering tool 236.
  • the sputtering tool 236 includes a metal target 238 which has silicon incorporated in the metal target 238.
  • Sputtering gas 240 such as argon is introduced into the sputtering tool 236 between the metal target 238 and the substrate 202.
  • a plasma is formed in the sputtering gas 240 and electrical bias is applied to the metal target 238 so that metal and silicon are sputtered from the metal target 238 onto the substrate 202 to form a metal gate layer 242 incorporating silicon on the substrate 202.
  • a concentration of silicon in the metal target 238 is selected so that the metal gate layer 242 has 2 atomic percent to 10 atomic percent silicon.
  • the metal gate layer 242 may be patterned to form a metal gate such as the metal gate 112 depicted in FIGS. 1A-1E.
  • a substrate 302 of a semiconductor device 300 is positioned in a sputtering tool 336.
  • the sputtering tool 336 includes a metal target 338 which has less than 1 atomic percent silicon.
  • Sputtering gas 340 which includes an inert gas such as argon and a silicon species 344 such as silane, is introduced into the sputtering tool 336 between the metal target 338 and the substrate 302.
  • a plasma is formed in the sputtering gas 340 and electrical bias is applied to the metal target 338 so that metal is sputtered from the metal target 338 onto the substrate 302 and silicon from the silicon species 344 is incorporated in the sputtered metal to form a metal gate layer 342 incorporating silicon on the substrate 302.
  • a pressure and a flow rate of the silicon species 344 is selected so that the metal gate layer 342 has 2 atomic percent to 10 atomic percent silicon.
  • the metal gate layer 342 may be patterned to form a metal gate such as the metal gate 112 depicted in FIGS. 1A-1E.
  • a substrate 402 of a semiconductor device 400 is positioned in a sputtering tool 436.
  • the sputtering tool 436 includes a metal target 438 and a separate silicon target 446.
  • Sputtering gas 440 such as argon is introduced into the sputtering tool 436 between the metal target 438 and the silicon target 446 and the substrate 402.
  • a plasma is formed in the sputtering gas 440 and electrical bias is applied to the metal target 438 and to the silicon target 446 so that metal and silicon are sputtered from the metal target 438 and the silicon target 446, respectively, onto the substrate 402 to form a metal gate layer 442 incorporating silicon on the substrate 402.
  • the substrate 402 may remain stationary with respect to the metal target 438 and the silicon target 446 during formation of the metal gate layer 442 while sputtering occurs concurrently at both targets 438 and 446.
  • the substrate 402 may move alternately between a first position under the metal target 438 in which predominantly metal is sputtered onto the substrate 402, and a second position under the silicon target 446 in which predominantly silicon is sputtered onto the substrate 402.
  • Process parameters such as sputter rates from the metal target 438 and the silicon target 446 are selected so that the metal gate layer 442 has 2 atomic percent to 10 atomic percent silicon.
  • the metal gate layer 442 may be patterned to form a metal gate such as the metal gate 112 depicted in FIGS. 1A-1E.

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Abstract

A semiconductor device (100) may be formed by forming a silicon-containing gate dielectric layer (108) over a semiconductor layer (104). A gate metal layer is formed over the gate dielectric layer (108); the gate metal layer includes 2 atomic percent to 10 atomic percent silicon during formation. The gate metal layer is patterned to form a metal gate (112). Source and drain contact holes (116) are subsequently formed, and contact metal (118) is formed and patterned in the contact holes (116). A subsequent contact anneal heats the contact metal (118) and gate (112) for at least 30 seconds at a temperature of at least 750 °C.

Description

GALLIUM NITRIDE FIELD EFFECT TRANSISTOR
[0001] This relates in general to semiconductor devices, and in particular to gallium nitride field effect transistors.
BACKGROUND
[0002] A gallium nitride field effect transistor (GaN FET) may have an insulated metal gate and tunneling source and drain contacts. Forming reliable source and drain contacts may require annealing at a temperature which causes degradation of the gate dielectric layer.
SUMMARY
[0003] A semiconductor device may be formed by forming a metal gate with 2 atomic percent to 10 atomic percent silicon. The metal gate is formed over a gate dielectric layer containing silicon. A subsequent contact anneal may include heating for at least 30 seconds at a temperature of at least 750 °C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIGS. 1A-1E are cross sections of a semiconductor device depicted in successive stages of fabrication.
[0005] FIGS. 2-4 depict exemplary processes for forming metal gates of GaN FETs with 2 atomic percent to 10 atomic percent silicon.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0001] The following describe related subject matter and are hereby incorporated by reference: Application No. US 13/886,378; US 2014/0042452 Al; Application No. US 13/886,429 (TI-71209WO corresponding PCT application filed simultaneously herewith); Application No. US 13/886,652 (TI-71492WO corresponding PCT application filed simultaneously herewith); Application No. US 13/886,709; and Application No. US 13/886,688 (TI-72417WO corresponding PCT application filed simultaneously herewith).
[0006] A semiconductor device may be formed by forming a silicon-containing gate dielectric layer, such as silicon nitride, over a semiconductor layer. A gate metal layer is formed over the gate dielectric layer; the gate metal layer includes 2 atomic percent to 10 atomic percent silicon during formation. The gate metal layer is patterned to form a metal gate. Contact metal is formed and possibly patterned to form source and drain contacts. A subsequent contact anneal heats the contact metal and gate for at least 30 seconds at a temperature of at least 750 °C.
[0002] Ill-Nitride (III-N) semiconductor materials are materials in which Group III (boron group) elements (boron, aluminum, gallium, indium) provide a portion of the atoms in the semiconductor material and nitrogen atoms provide the remainder. Examples of III-N semiconductor materials are gallium nitride, boron gallium nitride, aluminum gallium nitride, indium nitride, and indium aluminum gallium nitride. III-N materials may be written with variable subscripts to denote a range of possible stoichiometries. For example, aluminum gallium nitride may be written as AlxGai_xN and indium aluminum gallium nitride may be written as InxAlyGai_x_yN. GaN FET is an example of a field effect transistor that includes III-N semiconductor materials.
[0007] In one example of aluminum formed by sputtering ("sputtered aluminum"), the sputtered aluminum also includes up to a few percent of copper, silicon, titanium and/or other elements, so as to improve the aluminum's electromigration properties.
[0008] FIGS. 1A-1E are cross sections of a semiconductor device depicted in successive stages of fabrication. Referring to FIG. 1A, the semiconductor device 100 is formed on a substrate 102 which may have a low-defect layer of III-N semiconductor material at a top surface, for example, an unintentionally doped layer of gallium nitride. A barrier layer 104 of III-N semiconductor material is formed on the top surface of the substrate 102. The barrier layer 104 may include AlxGai_xN or InxAlyGai_x_yN, 2 to 30 nanometers thick. Forming the barrier layer 104 on the low-defect layer of III-N semiconductor material at the top surface of the substrate 102 generates a two-dimensional electron gas in the low-defect layer just below the barrier layer 104 with an electron density of, for example, l x lO12 to 2>< 1013 cm2. An optional cap layer 106 of 2 to 5 nanometers of gallium nitride may be formed over the barrier layer 104.
[0009] A silicon-containing gate dielectric layer 108 is formed over the barrier layer 104, and over the cap layer 106 if present. The gate dielectric layer 108 may be, for example, 10 to 20 nanometers of silicon nitride formed by low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD). In other version of the instant example, the gate dielectric layer 108 may include one or more layers of silicon nitride, silicon dioxide and/or silicon oxynitride.
[0010] A layer of field dielectric 110 is formed on the gate dielectric layer 108 and patterned to have sloped edges adjacent to a channel region of the semiconductor device 100. The field dielectric 110 may include, for example, 100 to 300 nanometers of silicon nitride, formed by LPCVD or PECVD. A metal gate 112 is formed on the gate dielectric layer 108 over the channel region and overlapping the sloped edge of the field dielectric 110. The metal gate 112 may include at least 10 percent titanium, for example titanium tungsten alloy. The metal gate 112 further includes 2 atomic percent to 10 atomic percent silicon. The metal gate 112 may be formed, for example by an etch process or a liftoff process.
[0011] Referring to FIG. IB, a passivation dielectric layer 114 is formed over the metal gate 112, the field dielectric 110 and the gate dielectric layer 108. The passivation dielectric layer 114 may include, for example, 200 to 300 nanometers of silicon nitride, formed by PECVD. Source and drain contact holes 116 are etched through the passivation dielectric layer 114, the gate dielectric layer 108 and the cap layer 106, and into the barrier layer 104 proximate to the two-dimensional electron gas. The source and drain contact holes 116 may be 1 to 10 microns wide.
[0012] Referring to FIG. 1C, contact metal 118 is formed in the source and drain contact holes 116 and patterned. The contact metal 118 may include, for example, a layer of titanium 120 40 to 100 nanometers thick sputtered in the source and drain contact holes 116, a layer of sputtered aluminum 122 50 to 200 nanometers thick formed on the titanium layer 120, and a layer of titanium nitride 124 30 to 80 nanometers thick formed on the sputtered aluminum layer 122 by reactive sputtering, also known as physical vapor deposition (PVD). In one version of the instant example, the contact metal 118 is formed so as to provide an open cavity in each of the source and drain contact holes 116. Forming the metal gate 112 and the passivation dielectric layer 114 prior to forming the source and drain contact holes 116 and the contact metal 118 advantageously allows closer gate-source spacing and more fabrication process latitude, because the contact metal 118 may overlap a top surface of the passivation dielectric layer 114 without interfering with the metal gate 112. In an alternate version of the instant example, formation of the source and drain contact holes 116 may be omitted so that the contact metal 118 is formed on an existing top surface of the III-N semiconductor material.
[0013] Referring to FIG. ID, a contact anneal process 126 heats the contact metal 118 to at least 750 °C for at least 30 seconds. The contact anneal process 126 improves an electrical connection between the contact metal 118 and the two-dimensional electron gas by reducing an impedance of the electrical connection and making the electrical connection more ohmic, that is, making a current voltage relationship of the electrical connection more linear. Increasing the temperature of the contact anneal process 126 further improves the electrical connection. In one version of the instant embodiment, the contact anneal process 126 heats the contact metal 118 to at least 800 °C for at least 30 seconds. In another version, the contact anneal process 126 heats the contact metal 118 to at least 850 °C for at least 30 seconds. In a further version, the contact anneal process 126 heats the contact metal 118 to at least 900 °C for at least 30 seconds. The contact anneal process 126 may be performed, for example, in a rapid thermal processor (RTP) tool which heats the semiconductor device 100 using incandescent lamps. Forming the metal gate 112 to have 2 atomic percent to 10 atomic percent silicon reduces a net flow of silicon from the silicon-containing gate dielectric layer 108 into the metal gate 1 12, thereby advantageously improving dielectric integrity of the gate dielectric layer 108.
[0014] Referring to FIG. IE, a first metallization layer 128 is formed on the contact metal 118. The first metallization layer 128 may include, for example, an adhesion layer 130 of 50 to 150 nanometers of sputtered titanium tungsten, a main metal layer 132 of 200 to 500 nanometers of sputtered aluminum formed on the adhesion layer 130, and an anti-refection layer 134 of 20 to 40 nanometers of titanium nitride formed on the main metal layer 132. The first metallization layer 128 is patterned so as to overlap the source and drain contact holes 116. [0015] FIGS. 2-4 depict exemplary processes for forming metal gates of GaN FETs with 2 atomic percent to 10 atomic percent silicon. Referring to FIG. 2, a substrate 202 of a semiconductor device 200 is positioned in a sputtering tool 236. The sputtering tool 236 includes a metal target 238 which has silicon incorporated in the metal target 238. Sputtering gas 240 such as argon is introduced into the sputtering tool 236 between the metal target 238 and the substrate 202. A plasma is formed in the sputtering gas 240 and electrical bias is applied to the metal target 238 so that metal and silicon are sputtered from the metal target 238 onto the substrate 202 to form a metal gate layer 242 incorporating silicon on the substrate 202. A concentration of silicon in the metal target 238 is selected so that the metal gate layer 242 has 2 atomic percent to 10 atomic percent silicon. After the metal gate layer 242 has been formed to a desired thickness, the metal gate layer 242 may be patterned to form a metal gate such as the metal gate 112 depicted in FIGS. 1A-1E.
[0016] Referring to FIG. 3, a substrate 302 of a semiconductor device 300 is positioned in a sputtering tool 336. The sputtering tool 336 includes a metal target 338 which has less than 1 atomic percent silicon. Sputtering gas 340, which includes an inert gas such as argon and a silicon species 344 such as silane, is introduced into the sputtering tool 336 between the metal target 338 and the substrate 302. A plasma is formed in the sputtering gas 340 and electrical bias is applied to the metal target 338 so that metal is sputtered from the metal target 338 onto the substrate 302 and silicon from the silicon species 344 is incorporated in the sputtered metal to form a metal gate layer 342 incorporating silicon on the substrate 302. A pressure and a flow rate of the silicon species 344 is selected so that the metal gate layer 342 has 2 atomic percent to 10 atomic percent silicon. After the metal gate layer 342 has been formed to a desired thickness, the metal gate layer 342 may be patterned to form a metal gate such as the metal gate 112 depicted in FIGS. 1A-1E.
[0017] Referring to FIG. 4, a substrate 402 of a semiconductor device 400 is positioned in a sputtering tool 436. The sputtering tool 436 includes a metal target 438 and a separate silicon target 446. Sputtering gas 440 such as argon is introduced into the sputtering tool 436 between the metal target 438 and the silicon target 446 and the substrate 402. A plasma is formed in the sputtering gas 440 and electrical bias is applied to the metal target 438 and to the silicon target 446 so that metal and silicon are sputtered from the metal target 438 and the silicon target 446, respectively, onto the substrate 402 to form a metal gate layer 442 incorporating silicon on the substrate 402. In one version of the instant embodiment, the substrate 402 may remain stationary with respect to the metal target 438 and the silicon target 446 during formation of the metal gate layer 442 while sputtering occurs concurrently at both targets 438 and 446. In another version, the substrate 402 may move alternately between a first position under the metal target 438 in which predominantly metal is sputtered onto the substrate 402, and a second position under the silicon target 446 in which predominantly silicon is sputtered onto the substrate 402. Process parameters such as sputter rates from the metal target 438 and the silicon target 446 are selected so that the metal gate layer 442 has 2 atomic percent to 10 atomic percent silicon. After the metal gate layer 442 has been formed to a desired thickness, the metal gate layer 442 may be patterned to form a metal gate such as the metal gate 112 depicted in FIGS. 1A-1E.
[0018] Those skilled in the art will appreciate that modifications may be made to the described embodiments, and also that many other embodiments are possible, within the scope of the claims.

Claims

CLAIMS What is claimed is:
1. A semiconductor device, comprising:
a substrate which has a semiconductor layer disposed over a top surface of the substrate;
a gate dielectric layer disposed over the semiconductor layer, the gate dielectric layer containing silicon;
a metal gate disposed over the gate dielectric layer, the metal gate including 2 atomic percent to 10 atomic percent silicon; and
contact metal disposed in source and drain contact holes proximate to the metal gate.
2. A semiconductor device, comprising:
a substrate which has a semiconductor layer including III-N semiconductor material disposed over a top surface of the substrate;
a gate dielectric layer disposed over the semiconductor layer, the gate dielectric layer containing silicon;
a metal gate disposed over the gate dielectric layer, the metal gate including 2 atomic percent to 10 atomic percent silicon; and
source and drain tunneling contacts disposed proximate to the metal gate, the source and drain tunneling contacts having contact metal disposed in source and drain contact holes which make tunneling connections to a two-dimensional electron gas disposed in the III-N semiconductor material.
3. The semiconductor device of claim 2, wherein the metal gate includes 4 atomic percent to 6 atomic percent silicon.
4. The semiconductor device of claim 2, wherein the gate dielectric layer includes silicon nitride.
5. The semiconductor device of claim 2, wherein the metal gate includes at least 10 percent titanium.
6. The semiconductor device of claim 2, wherein the metal gate includes titanium tungsten.
7. The semiconductor device of claim 2, wherein the contact metal includes a titanium layer contacting the semiconductor layer.
8. The semiconductor device of claim 7, wherein the contact metal includes a sputtered aluminum layer disposed on the titanium layer.
9. A process of forming a semiconductor device, comprising:
providing a substrate;
forming a semiconductor layer over a top surface of the substrate;
forming a gate dielectric layer over the semiconductor layer, the gate dielectric layer containing silicon;
forming a metal gate over the gate dielectric layer, the metal gate including 2 atomic percent to 10 atomic percent silicon;
subsequently forming contact metal on the substrate; and
annealing the contact metal for at least 30 seconds at a temperature of at least
750 °C.
10. The process of claim 9, wherein the metal gate includes 4 atomic percent to 6 atomic percent silicon.
11. The process of claim 9, wherein the gate dielectric layer includes silicon nitride.
12. The process of claim 9, wherein the semiconductor layer includes a III-N semiconductor material.
13. The process of claim 9, wherein the metal gate includes titanium tungsten.
14. The process of claim 9, wherein the contact metal includes a titanium layer contacting the semiconductor layer.
15. The process of claim 14, wherein the contact metal includes a sputtered aluminum layer disposed on the titanium layer.
16. The process of claim 9, wherein annealing includes heating the contact metal for at least 30 seconds at a temperature of at least 800 °C.
17. The process of claim 9, wherein annealing includes heating the contact metal for at least 30 seconds at a temperature of at least 850 °C.
18. The process of claim 9, wherein forming the metal gate includes sputtering a metal gate layer from a metal target which has silicon incorporated in the metal target.
19. The process of claim 9, wherein forming the metal gate includes sputtering a metal gate layer from a metal target which has less than 1 atomic percent silicon using a sputtering gas which includes an inert gas and a silicon species.
20. The process of claim 9, wherein forming the metal gate includes sputtering a metal gate layer from a metal target and a separate silicon target.
PCT/US2014/036842 2013-05-03 2014-05-05 Gallium nitride field effect transistor WO2014179809A1 (en)

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JP2016522991A (en) 2016-08-04
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EP2992557A4 (en) 2017-07-12
JP2019125802A (en) 2019-07-25
EP2992557A1 (en) 2016-03-09
US20140327047A1 (en) 2014-11-06
CN105164810A (en) 2015-12-16
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JP7000641B2 (en) 2022-01-19
JP6562559B2 (en) 2019-08-21

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