US20030207508A1 - Double recessed transistor - Google Patents
Double recessed transistor Download PDFInfo
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- US20030207508A1 US20030207508A1 US10/430,649 US43064903A US2003207508A1 US 20030207508 A1 US20030207508 A1 US 20030207508A1 US 43064903 A US43064903 A US 43064903A US 2003207508 A1 US2003207508 A1 US 2003207508A1
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- 239000000758 substrate Substances 0.000 claims abstract description 6
- KDYFGRWQOYBRFD-UHFFFAOYSA-N succinic acid group Chemical group C(CCC(=O)O)(=O)O KDYFGRWQOYBRFD-UHFFFAOYSA-N 0.000 claims description 24
- 229910052782 aluminium Inorganic materials 0.000 claims description 21
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 21
- 238000000034 method Methods 0.000 claims description 15
- 239000004065 semiconductor Substances 0.000 claims description 13
- 239000001384 succinic acid Substances 0.000 claims description 11
- 150000001732 carboxylic acid derivatives Chemical class 0.000 claims 1
- 239000010410 layer Substances 0.000 description 152
- 125000006850 spacer group Chemical group 0.000 description 12
- 238000005530 etching Methods 0.000 description 8
- 230000015556 catabolic process Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 238000001451 molecular beam epitaxy Methods 0.000 description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 3
- 150000001735 carboxylic acids Chemical class 0.000 description 3
- GPXJNWSHGFTCBW-UHFFFAOYSA-N Indium phosphide Chemical compound [In]#P GPXJNWSHGFTCBW-UHFFFAOYSA-N 0.000 description 2
- KDYFGRWQOYBRFD-NUQCWPJISA-N butanedioic acid Chemical compound O[14C](=O)CC[14C](O)=O KDYFGRWQOYBRFD-NUQCWPJISA-N 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 1
- 229910000530 Gallium indium arsenide Inorganic materials 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 238000000609 electron-beam lithography Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 238000001039 wet etching Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/66007—Multistep manufacturing processes
- H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
- H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
- H01L29/66409—Unipolar field-effect transistors
- H01L29/66446—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
- 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
- H01L21/28512—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 elements of Group IV of the Periodic Table
- H01L21/28537—Deposition of Schottky electrodes
-
- 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
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
- H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
- H01L21/30604—Chemical etching
-
- 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
- H01L29/47—Schottky barrier electrodes
-
- 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
- H01L29/778—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface
- H01L29/7782—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 confinement of carriers by at least two heterojunctions, e.g. DHHEMT, quantum well HEMT, DHMODFET
- H01L29/7783—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 confinement of carriers by at least two heterojunctions, e.g. DHHEMT, quantum well HEMT, DHMODFET using III-V semiconductor material
- H01L29/7785—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 confinement of carriers by at least two heterojunctions, e.g. DHHEMT, quantum well HEMT, DHMODFET using III-V semiconductor material with more than one donor layer
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/10—Details of semiconductor or other solid state devices to be connected
- H01L2924/102—Material of the semiconductor or solid state bodies
- H01L2924/1025—Semiconducting materials
- H01L2924/1026—Compound semiconductors
- H01L2924/1032—III-V
- H01L2924/10337—Indium gallium arsenide [InGaAs]
Definitions
- This invention relates generally to high electron mobility transistors (HEMTs) and more particularly to transistors of such type which are fabricated with a double recess.
- HEMTs high electron mobility transistors
- HEMT high electron mobility transistor
- GaAs gallium arsenide
- InP indium phosphide
- a doped donor/undoped spacer layer of one material and an undoped channel layer of a different material.
- a heterojunction is formed between the doped donor/undoped spacer layer and the undoped channel layer.
- One device which has been found to provide good device characteristics such as breakdown voltage, output currents, and pinch-off voltage is a double recessed HEMT.
- Such a device is fabricated with two aligned recesses in which the gate is formed.
- the recesses are typically formed by wet etching the device.
- the etching process is periodically interrupted and the device is tested for certain characteristics, e.g., current. If the characteristics meet the desired criteria, then etching for that recess is terminated. Otherwise, the etching continues. This process continues until both recesses meet the established criteria. This process takes time and money to repeatedly stop the etching and test the device. Also, the etching is not uniform across the wafer, resulting in inconsistent device characteristics across the wafer and low yield of acceptable devices on the wafer.
- a transistor structure has a source electrode and a drain electrode.
- a doped cap layer of Ga x In 1-x As is disposed below and in ohmic contact with the source electrode and the drain electrode and provides a cap layer opening.
- An undoped resistive layer of Ga x In 1-x As is disposed below the cap layer and provides a resistive layer opening in registration with the cap layer opening and having a first width.
- a Schottky layer of Al y In 1 ⁇ y As is disposed below the resistive layer.
- An undoped channel layer is disposed below the Schottky layer.
- a semi-insulating substrate is disposed below the channel layer.
- a top surface of the Schottky layer beneath the resistive layer opening provides a recess having a second width smaller than the first width.
- a gate electrode is in contact with a bottom surface of the recess provided by the Schottky layer.
- a semiconductor structure having a Schottky layer adapted to be etched at a first etch rate by an etchant.
- the semiconductor structure also has a contact layer disposed above the Schottky layer and adapted to be etched by the etchant at a second etch rate that is substantially faster than the first etch rate.
- the contact layer provides an opening exposing a region of a top surface of the Schottky layer, the region having a first width.
- the region of the top surface of the Schottky layer provides a recess of a second width smaller than the first width.
- the Schottky layer contains aluminum, with an etch rate of about 0.1 ⁇ /second relative to a succinic acid etchant, while the contact layer is substantially free of aluminum, having an etch rate of about 5 ⁇ /second relative to succinic acid etchant.
- Such composition allows the transistor's contact layer to be selectively etched with succinic acid to form the opening while leaving the Schottky layer substantially intact.
- uniform device characteristics such as breakdown voltage, output currents, and pinch-off voltage can be achieved and a high yield of acceptable devices produced.
- a transistor structure having a Schottky layer adapted to be etched at a first etch rate by an etchant and a contact layer disposed above the Schottky layer and adapted to be etched by the etchant at a second etch rate that is substantially faster than the Schottky layer's first etch rate.
- a region above a portion of a top surface of the Schottky layer is substantially free of the contact layer.
- the portion of the top surface of the Schottky layer has a first width and provides a recess having a second width smaller than the first width and adapted to receive a gate electrode.
- the Schottky layer comprises at least about 35 percent Aluminum and the contact layer comprises less than about ten percent Aluminum.
- a method of forming a semiconductor includes forming a Schottky layer adapted to be etched by a first etchant at a first etch rate and forming a contact layer above the Schottky layer adapted to be etched by the first etchant at a second etch rate that is substantially faster than the first etch rate.
- the first etchant is o applied to etch the contact layer to expose a portion of the Schottky layer.
- a second etchant is applied to etch the portion of the Schottky layer exposed by the first etchant.
- the Schottky layer contains Aluminum while the contact layer is substantially free of Aluminum.
- the first etchant includes a carboxylic-acid based wet etchant.
- Embodiments of the invention may provide one or more of the following advantages.
- the invention saves time and money in manufacturing HEMTs. It also eliminates or decreases the need to etch a device and periodically test the device for certain characteristics. Uniformity of device characteristics on a wafer can be improved.
- FIG. 1 is a cross sectional diagrammatical sketch of a double recessed HEMT according to the invention.
- FIGS. 2 - 4 are cross sectional diagrammatical sketches of the double recessed HEMT of FIG. 1 in various stages of manufacture.
- transistor 10 has a source electrode 12 and a drain electrode 14 .
- the electrodes 12 and 14 are in ohmic contact with a cap layer 16 .
- the cap layer 16 here is Ga 0.47 In 0.53 As, about 70 ⁇ thick, and has a doping concentration of about 5 ⁇ 10 18 cm ⁇ 3 .
- Disposed below the cap layer 16 is a recess or resistive layer 18 .
- the resistive layer 18 here is Ga 0.47 In 0.53 As, about 300 ⁇ thick, and undoped.
- the cap and resistive layers 16 and 18 form a contact layer 50 .
- a Schottky layer 20 Disposed below the resistive layer 18 is a Schottky layer 20 , here undoped Al 0.60 In 0.40 As about 200 ⁇ thick.
- the cap and resistive layers 16 , 18 provide an opening 38 from a surface 56 to a top surface 42 of the Schottky layer 20 .
- the top surface 42 of the Schottky layer 20 provides a recess 44 with a bottom surface 48 .
- a gate electrode 22 In Schottky contact with the Schottky layer 20 at the bottom surface 48 is a gate electrode 22 .
- a doped pulse layer 24 is disposed below the Schottky layer 20 .
- the pulse layer 24 is silicon and has a doping concentration of about 2 ⁇ 10 12 cm ⁇ 2 .
- Disposed below the pulse layer 24 is a spacer layer 26 .
- the spacer layer 26 here is Al 0.48 In 0.52 As, about 30 ⁇ thick, and undoped.
- a channel layer 28 Disposed below the spacer layer 26 is a channel layer 28 .
- the channel layer 28 here is Ga 0.47 In 0.53 As, about 200 ⁇ thick, and undoped.
- a second spacer layer 30 is disposed below the channel layer 28 .
- the spacer layer 30 is Al 0.48 In 0.52 As, about 50 ⁇ thick, and undoped.
- Disposed below the spacer layer 30 is a second pulse layer 32 .
- the pulse layer 32 is silicon and has a doping concentration of 1 ⁇ 10 2 cm ⁇ 2 , providing a silicon pulse ratio of 2:1 between the first pulse layer 24 and the second pulse layer 32 to help linearize the performance of the transistor 10 .
- a buffer layer 34 Disposed below the pulse layer 32 is a buffer layer 34 .
- the buffer layer 34 here is Al 0.48 In 0.52 As, about 2000 ⁇ thick, and undoped.
- the Schottky layer 20 can be undoped, as shown, or doped.
- An undoped Schottky layer provides a higher breakdown voltage than with a doped Schottky layer 20 .
- a doped Schottky layer 20 reduces resistance which lowers the breakdown voltage and increases conduction compared to an undoped Schottky layer 20 .
- transistor 10 has a double recess structure including a first recess 39 , formed by the opening 38 and the top surface 42 of the schottky layer 20 , and the second recess 44 .
- the first recess 39 is provided by the cap layer 16 and the resistive layer 18 .
- Side walls 40 of the first recess 39 are provided by the cap and resistive layers 16 , 18 from the surface 56 to the top surface 42 of the Schottky layer 20 .
- the first recess 39 exposes a first width W1 of the Schottky layer 20 at a top level 43 of the Schottky layer 20 .
- the second recess 44 has a second width W2 at the bottom surface 48 , the width W2 being smaller than the width W1.
- the second recess 44 is provided by the top surface 42 of the Schottky layer 20 and has side walls 46 extending from the top 43 of the Schottky layer 20 to the bottom surface 48 .
- the cap and resistive layers 16 , 18 have a different etch rate than the Schottky layer 20 to provide etch selectivity.
- the Schottky layer 20 is adapted to be etched at a first etch rate by an etchant.
- the Al 0.60 In 0.40 As Schottky layer 20 shown has an etch rate of about 0.1 ⁇ /second when exposed to an etchant of succinic acid, which is a carboxylic-acid based wet etchant.
- the cap and resistive layers 16 , 18 are adapted to be etched by the etchant at a second etch rate that is substantially faster than the first etch rate.
- the Ga 0.47 In 0.53 As layers 16 , 18 have etch rates of about 5 ⁇ /second when etched by succinic acid.
- FIG. 2 shows the forming of layers 16 , 18 , and 20 .
- FIGS. 3 and 4 show the etching of layers 16 , 18 , and 20 .
- FIG. 1 shows the finished transistor 10 .
- the substrate 36 is provided and the buffer layer grown on the substrate 36 by molecular beam epitaxy (MBE).
- MBE molecular beam epitaxy
- the pulse layer 32 is grown by MBE and doped by silicon.
- the spacer layer 30 is grown by MBE and doped by silicon.
- the Schottky layer 20 is grown by MBE.
- the contact layer 50 including the cap layer 16 and the resistive layer 18 , is formed by MBE on the Schottky layer 20 to complete the formation of an intermediate structure 54 .
- a wet etch process for mesa isolation is performed by applying 1:8:160 H 2 SO 4 :H 2 O 2 :H 2 O for about 20 seconds to define the mesa.
- 6:1 succinic acid:H 2 O 2 is applied for about 90 seconds to selectively etch back the InGaAs channel layer 28 . This forms a channel notch (not shown) to help prevent shorting of the channel layer 28 to the gate electrode 22 via a conductor (not shown) running up the side of the mesa.
- a first etchant here a carboxylic-acid based wet etchant, specifically 6:1 succinic acid:H 2 O 2 is applied to the top surface 56 of the cap layer 16 .
- Electron beam lithography is used with the succinic acid and the succinic acid is applied for enough time, e.g., about 60 seconds, to etch the contact layer 50 at the second etch rate to form the opening 38 .
- the contact layer 50 can be a single layer, doped or undoped.
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Abstract
A transistor structure is provided. This structure has a source electrode and a drain electrode. A doped cap layer of GaxIn1-xAs is disposed below the source electrode and the drain electrode and provides a cap layer opening. An undoped resistive layer of GaxIn1−xAs is disposed below the cap layer and defines a resistive layer opening in registration with the cap layer opening and having a first width. A Schottky layer of AlyIn1−yAs is disposed below the resistive layer. An undoped channel layer is disposed below the Schottky layer. A semi-insulating substrate is disposed below the channel layer. A top surface of the Schottky layer beneath the resistive layer opening provides a recess having a second width smaller than the first width. A gate electrode is in contact with a bottom surface of the recess provided by the Schottky layer.
Description
- This invention relates generally to high electron mobility transistors (HEMTs) and more particularly to transistors of such type which are fabricated with a double recess.
- As is known in the art, there are several types of active devices used at microwave and millimeter frequencies to provide amplification of radio frequency signals. In general, one of the more common semiconductor devices used at these frequencies is the high electron mobility transistor (HEMT). Typically, HEMTs are formed from Group III-V materials such as gallium arsenide (GaAs) or indium phosphide (InP). In a HEMT there is a doped donor/undoped spacer layer of one material and an undoped channel layer of a different material. A heterojunction is formed between the doped donor/undoped spacer layer and the undoped channel layer. Due to the conduction band discontinuity at the heterojunction, electrons are injected from the doped donor/undoped spacer layer into the undoped channel layer. Thus, electrons from the large bandgap donor layer are transferred into the narrow bandgap channel layer where they are confined to move only in a plane parallel to the heterojunction. Consequently, there is spacial separation between the donor atoms in the donor layer and the electrons in the channel layer resulting in low impurity scattering and good electron mobility.
- One device which has been found to provide good device characteristics such as breakdown voltage, output currents, and pinch-off voltage is a double recessed HEMT. Such a device is fabricated with two aligned recesses in which the gate is formed. The recesses are typically formed by wet etching the device. The etching process is periodically interrupted and the device is tested for certain characteristics, e.g., current. If the characteristics meet the desired criteria, then etching for that recess is terminated. Otherwise, the etching continues. This process continues until both recesses meet the established criteria. This process takes time and money to repeatedly stop the etching and test the device. Also, the etching is not uniform across the wafer, resulting in inconsistent device characteristics across the wafer and low yield of acceptable devices on the wafer.
- In accordance with the present invention, a transistor structure is provided. This structure has a source electrode and a drain electrode. A doped cap layer of GaxIn1-xAs is disposed below and in ohmic contact with the source electrode and the drain electrode and provides a cap layer opening. An undoped resistive layer of GaxIn1-xAs is disposed below the cap layer and provides a resistive layer opening in registration with the cap layer opening and having a first width. A Schottky layer of AlyIn1−yAs is disposed below the resistive layer. An undoped channel layer is disposed below the Schottky layer. A semi-insulating substrate is disposed below the channel layer. A top surface of the Schottky layer beneath the resistive layer opening provides a recess having a second width smaller than the first width. A gate electrode is in contact with a bottom surface of the recess provided by the Schottky layer.
- With such structure, uniform device characteristics such as breakdown voltage, output currents, and pinch-off voltage are achievable, as is a high yield of acceptable devices.
- In accordance with another feature of the invention, a semiconductor structure is provided having a Schottky layer adapted to be etched at a first etch rate by an etchant. The semiconductor structure also has a contact layer disposed above the Schottky layer and adapted to be etched by the etchant at a second etch rate that is substantially faster than the first etch rate. The contact layer provides an opening exposing a region of a top surface of the Schottky layer, the region having a first width. The region of the top surface of the Schottky layer provides a recess of a second width smaller than the first width.
- In a preferred embodiment of the invention, the Schottky layer contains aluminum, with an etch rate of about 0.1 Å/second relative to a succinic acid etchant, while the contact layer is substantially free of aluminum, having an etch rate of about 5 Å/second relative to succinic acid etchant. Such composition allows the transistor's contact layer to be selectively etched with succinic acid to form the opening while leaving the Schottky layer substantially intact. Thus, uniform device characteristics such as breakdown voltage, output currents, and pinch-off voltage can be achieved and a high yield of acceptable devices produced.
- In accordance with another feature of the invention, a transistor structure is provided having a Schottky layer adapted to be etched at a first etch rate by an etchant and a contact layer disposed above the Schottky layer and adapted to be etched by the etchant at a second etch rate that is substantially faster than the Schottky layer's first etch rate. In this structure, a region above a portion of a top surface of the Schottky layer is substantially free of the contact layer. The portion of the top surface of the Schottky layer has a first width and provides a recess having a second width smaller than the first width and adapted to receive a gate electrode.
- In a preferred embodiment of the invention, the Schottky layer comprises at least about 35 percent Aluminum and the contact layer comprises less than about ten percent Aluminum.
- In accordance with another feature of the invention, a method of forming a semiconductor is provided. The method includes forming a Schottky layer adapted to be etched by a first etchant at a first etch rate and forming a contact layer above the Schottky layer adapted to be etched by the first etchant at a second etch rate that is substantially faster than the first etch rate. The first etchant is o applied to etch the contact layer to expose a portion of the Schottky layer. A second etchant is applied to etch the portion of the Schottky layer exposed by the first etchant.
- In a preferred embodiment of the invention, the Schottky layer contains Aluminum while the contact layer is substantially free of Aluminum. Further, the first etchant includes a carboxylic-acid based wet etchant.
- Embodiments of the invention may provide one or more of the following advantages. The invention saves time and money in manufacturing HEMTs. It also eliminates or decreases the need to etch a device and periodically test the device for certain characteristics. Uniformity of device characteristics on a wafer can be improved.
- Other advantages will be apparent from the following description and from the claims.
- FIG. 1 is a cross sectional diagrammatical sketch of a double recessed HEMT according to the invention; and
- FIGS.2-4 are cross sectional diagrammatical sketches of the double recessed HEMT of FIG. 1 in various stages of manufacture.
- Referring now to FIG. 1, a high electron mobility transistor (HEMT)10 is shown. Here,
transistor 10 has asource electrode 12 and adrain electrode 14. Theelectrodes cap layer 16. Thecap layer 16 here is Ga0.47In0.53As, about 70 Å thick, and has a doping concentration of about 5×1018 cm−3. Disposed below thecap layer 16 is a recess orresistive layer 18. Theresistive layer 18 here is Ga0.47In0.53As, about 300 Å thick, and undoped. The cap andresistive layers contact layer 50. Disposed below theresistive layer 18 is a Schottkylayer 20, here undoped Al0.60In0.40As about 200 Å thick. The cap andresistive layers opening 38 from asurface 56 to atop surface 42 of the Schottkylayer 20. Thetop surface 42 of theSchottky layer 20 provides arecess 44 with abottom surface 48. In Schottky contact with theSchottky layer 20 at thebottom surface 48 is a gate electrode 22. A dopedpulse layer 24 is disposed below theSchottky layer 20. Here thepulse layer 24 is silicon and has a doping concentration of about 2×1012 cm−2. Disposed below thepulse layer 24 is aspacer layer 26. Thespacer layer 26 here is Al0.48In0.52As, about 30 Å thick, and undoped. Disposed below thespacer layer 26 is achannel layer 28. Thechannel layer 28 here is Ga0.47In0.53As, about 200 Å thick, and undoped. Asecond spacer layer 30 is disposed below thechannel layer 28. Here thespacer layer 30 is Al0.48In0.52As, about 50 Å thick, and undoped. Disposed below thespacer layer 30 is asecond pulse layer 32. Here thepulse layer 32 is silicon and has a doping concentration of 1×102 cm−2, providing a silicon pulse ratio of 2:1 between thefirst pulse layer 24 and thesecond pulse layer 32 to help linearize the performance of thetransistor 10. Disposed below thepulse layer 32 is abuffer layer 34. Thebuffer layer 34 here is Al0.48In0.52As, about 2000 Å thick, and undoped. Disposed below thebuffer layer 34 is asemi-insulating InP substrate 36. - The
Schottky layer 20 can be undoped, as shown, or doped. An undoped Schottky layer provides a higher breakdown voltage than with a dopedSchottky layer 20. A dopedSchottky layer 20 reduces resistance which lowers the breakdown voltage and increases conduction compared to anundoped Schottky layer 20. - As shown,
transistor 10 has a double recess structure including afirst recess 39, formed by theopening 38 and thetop surface 42 of theschottky layer 20, and thesecond recess 44. Thefirst recess 39 is provided by thecap layer 16 and theresistive layer 18.Side walls 40 of thefirst recess 39 are provided by the cap andresistive layers surface 56 to thetop surface 42 of theSchottky layer 20. Thefirst recess 39 exposes a first width W1 of theSchottky layer 20 at atop level 43 of theSchottky layer 20. Thesecond recess 44 has a second width W2 at thebottom surface 48, the width W2 being smaller than the width W1. Thesecond recess 44 is provided by thetop surface 42 of theSchottky layer 20 and hasside walls 46 extending from the top 43 of theSchottky layer 20 to thebottom surface 48. - The cap and
resistive layers Schottky layer 20. TheSchottky layer 20 includes Group III-V material, here aluminum and indium. Sixty percent of the Group III-V material in theSchottky layer 20 is aluminum and forty percent is indium. To provide desirable device characteristics, there is preferably at least 35 percent aluminum in theSchottky layer 20, and less than about ten percent aluminum in the cap andresistive layers resistive layers - The cap and
resistive layers Schottky layer 20 to provide etch selectivity. TheSchottky layer 20 is adapted to be etched at a first etch rate by an etchant. The Al0.60In0.40AsSchottky layer 20 shown has an etch rate of about 0.1 Å/second when exposed to an etchant of succinic acid, which is a carboxylic-acid based wet etchant. The cap andresistive layers layers - A method of forming a semiconductor device such as
transistor 10 is now described, referring to FIGS. 1-4. FIG. 2 shows the forming oflayers layers finished transistor 10. - The method of forming
transistor 10 in FIG. 1 includes forming theSchottky layer 20 and the cap andresistive layers Schottky layer 20. An etchant is applied to the cap andresistive layers top surface 42 of theSchottky layer 20. Another etchant is applied to etch the exposedtop surface 42 of theSchottky layer 20 to produce therecess 44. - Referring to FIG. 2, forming the semiconductor layers16, 18, and 20 is now described. As shown in FIG. 2, the
substrate 36 is provided and the buffer layer grown on thesubstrate 36 by molecular beam epitaxy (MBE). Over thebuffer layer 34 thepulse layer 32 is grown by MBE and doped by silicon. Over thepulse layer 32 thespacer layer 30, thechannel layer 28, and thespacer layer 26 grown by MBE. Over thespacer layer 26 thepulse layer 24 is grown by MBE and doped by silicon. Over thepulse layer 24 theSchottky layer 20 is grown by MBE. Referring now to FIG. 3, thecontact layer 50, including thecap layer 16 and theresistive layer 18, is formed by MBE on theSchottky layer 20 to complete the formation of anintermediate structure 54. A wet etch process for mesa isolation is performed by applying 1:8:160 H2SO4:H2O2:H2O for about 20 seconds to define the mesa. Then, 6:1 succinic acid:H2O2 is applied for about 90 seconds to selectively etch back theInGaAs channel layer 28. This forms a channel notch (not shown) to help prevent shorting of thechannel layer 28 to the gate electrode 22 via a conductor (not shown) running up the side of the mesa. - Referring to FIGS. 3 and 4, etching the
intermediate structure 54 is now described. As shown in FIG. 3, a first etchant, here a carboxylic-acid based wet etchant, specifically 6:1 succinic acid:H2O2 is applied to thetop surface 56 of thecap layer 16. Electron beam lithography is used with the succinic acid and the succinic acid is applied for enough time, e.g., about 60 seconds, to etch thecontact layer 50 at the second etch rate to form theopening 38. This exposes thetop surface 42 of theSchottky layer 20, selectively forms thefirst recess 39, and completes the formation of anintermediate structure 58. Because the first etch rate of theSchottky layer 20 is substantially slower than the second etch rate of thecontact layer 50 in response to the succinic acid, the succinic acid essentially does not etch theSchottky layer 20. The first etch is a selective etch. - Now referring to FIG. 4,
intermediate structure 58 is etched. A second etchant, e.g., 1:1:100 H3PO4:H2O2:H2O is applied to a portion of thetop surface 42 of theSchottky layer 20 exposed by the succinic acid for enough time to etch theSchottky layer 20, e.g., 10 seconds. This etching forms thesecond recess 44, and completes the formation ofintermediate structure 60. - Referring to FIG. 1,
electrodes intermediate structure 60 to complete thetransistor 10. The source and drainelectrodes top surface 56 of thecap layer 16. These ohmic contacts for the source and drainelectrodes bottom surface 48 of theSchottky layer 20. The gate electrode is formed by depositing a resist layer, not shown, exposing therecess 44. Schottky metal of 500 Å Ti-500 Å Pt-4000 Å Au is deposited over the resist layer on therecess 44. The resist layer is lifted off to remove unwanted metal, leaving the gate electrode 22. - The
transistor 10 shown in FIG. 1 has been fabricated and tested. Thetransistor 10 had a typical carrier sheet density of about 3×1012 cm−2, Hall mobility of 8300 cm2/V-sec at room temperature, maximum output current in the range 590-640 mA/mm, and breakdown voltage in the range 12.3-14.4 V. - Other embodiments are within the spirit and scope of the appended claims. For example, the
contact layer 50 can be a single layer, doped or undoped.
Claims (17)
1. A semiconductor structure comprising:
a Schottky layer adapted to be etched at a first etch rate by an etchant; and
a contact layer disposed above the Schottky layer and adapted to be etched by the etchant at a second etch rate that is substantially faster than the first etch rate;
wherein the contact layer provides an opening through the contact layer exposing a region of a top surface of the Schottky layer, the region having a first width; and
wherein the region of the top surface of the Schottky layer provides a recess of a second width smaller than the first width.
2. The semiconductor recited in claim 1 wherein the Schottky layer contains Aluminum.
3. The semiconductor recited in claim 2 wherein the Schottky layer comprises at least about 35 percent Aluminum.
4. The semiconductor recited in claim 3 wherein the Schottky layer is Al0.6In0.4As.
5. The semiconductor recited in claim 1 wherein the contact layer comprises less than about ten percent Aluminum.
6. The semiconductor recited in claim 1 wherein the contact layer is substantially free of Aluminum.
7. A transistor structure comprising:
a Schottky layer adapted to be etched at a first etch rate by an etchant; and
a contact layer disposed above the Schottky layer and adapted to be etched by the etchant at a second etch rate that is substantially faster than the first etch rate;
wherein a region above a portion of a top surface of the Schottky layer is substantially free of the contact layer, the portion having a first width;
wherein the portion of the top surface of the Schottky layer provides a recess of a second width smaller than the first width; and
wherein the recess of the second width is adapted to receive a gate electrode.
8. The transistor recited in claim 7 wherein the Schottky layer comprises at least about 35 percent Aluminum and the contact layer comprises less than about ten percent Aluminum.
9. A method of forming a semiconductor comprising:
forming a Schottky layer adapted to be etched by a first etchant at a first etch rate;
forming a contact layer above the Schottky layer adapted to be etched by the first etchant at a second etch rate;
applying the first etchant to etch the contact layer to expose a portion of the Schottky layer; and
applying a second etchant to etch the portion of the Schottky layer exposed by the first etchant;
wherein second etch rate is substantially faster than the first etch rate when using the first etchant.
10. The method recited in claim 9 wherein the Schottky layer contains Aluminum.
11. The method recited in claim 10 wherein the Schottky layer comprises about 35 percent Aluminum.
12. The method recited in claim 11 wherein the contact layer is substantially free of Aluminum.
13. The method recited in claim 11 wherein the first etchant includes a carboxylic-acid based wet etchant.
14. The method recited in claim 13 wherein the first etchant is succinic acid.
15. The method recited in claim 11 wherein the second etchant is applied for a predetermined time.
16. A transistor structure comprising:
a source electrode;
a drain electrode;
a doped cap layer of GaxIn1-xAs disposed below and in ohmic contact with the source electrode and the drain electrode and providing a cap layer opening;
an undoped resistive layer of GaxIn1-xAs disposed below the cap layer and providing a resistive layer opening in registration with the cap layer opening and having a first width;
a Schottky layer of AlyIn1−yAs disposed below the resistive layer;
an undoped channel layer disposed below the Schottky layer; and
a semi-insulating substrate disposed below the channel layer;
wherein a top surface of the Schottky layer beneath the resistive layer opening provides a recess having a second width smaller than the first width; and
wherein a gate electrode is in contact with a bottom surface of the recess provided by the Schottky layer.
17. The transistor recited in claim 16 wherein the Schottky layer is doped.
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US10/430,649 US20030207508A1 (en) | 1999-08-06 | 2003-05-06 | Double recessed transistor |
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US09/369,954 US6271547B1 (en) | 1999-08-06 | 1999-08-06 | Double recessed transistor with resistive layer |
US09/872,286 US6573129B2 (en) | 1999-08-06 | 2001-05-31 | Gate electrode formation in double-recessed transistor by two-step etching |
US10/430,649 US20030207508A1 (en) | 1999-08-06 | 2003-05-06 | Double recessed transistor |
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US09/872,286 Division US6573129B2 (en) | 1999-08-06 | 2001-05-31 | Gate electrode formation in double-recessed transistor by two-step etching |
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US09/872,286 Expired - Lifetime US6573129B2 (en) | 1999-08-06 | 2001-05-31 | Gate electrode formation in double-recessed transistor by two-step etching |
US10/430,649 Abandoned US20030207508A1 (en) | 1999-08-06 | 2003-05-06 | Double recessed transistor |
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US09/369,954 Expired - Lifetime US6271547B1 (en) | 1999-08-06 | 1999-08-06 | Double recessed transistor with resistive layer |
US09/872,286 Expired - Lifetime US6573129B2 (en) | 1999-08-06 | 2001-05-31 | Gate electrode formation in double-recessed transistor by two-step etching |
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EP (1) | EP1210736B1 (en) |
JP (2) | JP2003531470A (en) |
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US6144048A (en) * | 1998-01-13 | 2000-11-07 | Nippon Telegraph And Telephone Corporation | Heterojunction field effect transistor and method of fabricating the same |
US6258639B1 (en) * | 1999-05-21 | 2001-07-10 | Agilent Technologies, Inc. | Sintered gate schottky barrier fet passivated by a degradation-stop layer |
US6271547B1 (en) | 1999-08-06 | 2001-08-07 | Raytheon Company | Double recessed transistor with resistive layer |
US6797994B1 (en) * | 2000-02-14 | 2004-09-28 | Raytheon Company | Double recessed transistor |
-
1999
- 1999-08-06 US US09/369,954 patent/US6271547B1/en not_active Expired - Lifetime
-
2000
- 2000-08-07 WO PCT/US2000/021470 patent/WO2001011695A1/en active IP Right Grant
- 2000-08-07 JP JP2001516254A patent/JP2003531470A/en active Pending
- 2000-08-07 DE DE60045447T patent/DE60045447D1/en not_active Expired - Lifetime
- 2000-08-07 KR KR10-2002-7000977A patent/KR100483376B1/en active IP Right Grant
- 2000-08-07 EP EP00952580A patent/EP1210736B1/en not_active Expired - Lifetime
-
2001
- 2001-05-31 US US09/872,286 patent/US6573129B2/en not_active Expired - Lifetime
-
2003
- 2003-05-06 US US10/430,649 patent/US20030207508A1/en not_active Abandoned
-
2009
- 2009-04-16 JP JP2009100021A patent/JP2009200511A/en active Pending
Also Published As
Publication number | Publication date |
---|---|
US20010029073A1 (en) | 2001-10-11 |
US6573129B2 (en) | 2003-06-03 |
EP1210736B1 (en) | 2010-12-29 |
KR100483376B1 (en) | 2005-04-15 |
DE60045447D1 (en) | 2011-02-10 |
JP2009200511A (en) | 2009-09-03 |
EP1210736A1 (en) | 2002-06-05 |
WO2001011695A1 (en) | 2001-02-15 |
US6271547B1 (en) | 2001-08-07 |
EP1210736A4 (en) | 2005-03-16 |
JP2003531470A (en) | 2003-10-21 |
KR20020033739A (en) | 2002-05-07 |
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Legal Events
Date | Code | Title | Description |
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AS | Assignment |
Owner name: UNITED STATES AIR FORCE, MASSACHUSETTS Free format text: CONFIRMATORY LICENSE;ASSIGNOR:RAYTHEON COMPANY;REEL/FRAME:014463/0129 Effective date: 20030820 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |