US20050184312A1 - Double HBT base metal micro-bridge - Google Patents
Double HBT base metal micro-bridge Download PDFInfo
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- US20050184312A1 US20050184312A1 US11/116,745 US11674505A US2005184312A1 US 20050184312 A1 US20050184312 A1 US 20050184312A1 US 11674505 A US11674505 A US 11674505A US 2005184312 A1 US2005184312 A1 US 2005184312A1
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Images
Classifications
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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
- H01L29/66234—Bipolar junction transistors [BJT]
- H01L29/6631—Bipolar junction transistors [BJT] with an active layer made of a group 13/15 material
- H01L29/66318—Heterojunction transistors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—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
-
- 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
- H01L29/42304—Base electrodes for bipolar transistors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—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
- H01L29/70—Bipolar devices
- H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
- H01L29/73—Bipolar junction transistors
- H01L29/737—Hetero-junction transistors
- H01L29/7371—Vertical transistors
Definitions
- the present invention relates generally to electrical circuits, and more particularly to fabrication of heterojunction bipolar transistors.
- Heterojunction bipolar transistors are widely used in high speed and high frequency applications.
- the heterojunction bipolar transistor offers much higher speeds of operation than the more prevalent metal-oxide-semiconductor field-effect transistors (MOSFETS) or even conventional homojunction bipolar transistors, such as npn or pnp silicon transistors.
- MOSFETS metal-oxide-semiconductor field-effect transistors
- the HBT offers an alternative technology to metal semiconductor field effect transistors (MESFETs) and high electron mobility transistors (HEMTs) when a high degree of linearity is desirable.
- MESFETs metal semiconductor field effect transistors
- HEMTs high electron mobility transistors
- the use of different materials of differing bandgaps for the collector, base and emitter provides for additional design flexibility.
- the HBT is a layered structure that includes a semiconductor substrate, a subcollector, a collector, a base and an emitter stacked one on top the other in an integral assembly. Metal contacts are formed to connect power and other circuitry to the emitter, the base and the subcollector.
- the largest limitation to the operational frequency and speed of the HBT is the base-collector capacitance.
- the base-collector capacitance is largely due to the collector-base interface area. Reduction of the base area can introduce higher base resistance due to the reduction of the area of the base contact.
- a common HBT technology is based on Gallium Arsenide (GaAs)/Gallium Aluminum Arsenide (GaAlAs) based family.
- the GaAs based HBT suffers from base-collector capacitance due to the area of the interface between the base and collector layers.
- One method of reducing the base collector capacitance of a GaAs based HBT is to implant protons into an area of the collector surrounding the emitter so as to electrically insulate the implanted area.
- Another HBT technology is based on the Indium Phosphide (InP)/Indium Gallium Arsenide (InGaAs) material family.
- the InP/InGaAs HBT also suffers from base-collector capacitance.
- proton implantation has proved ineffective in rendering InP to be sufficiently insulating or semi-insulating.
- Miyamoto et al. addresses this problem by performing a selective etchant to substantially etch the collector layer under the base layer so as to undercut the edges of the base layer of InP-based HBTs in “Reduction of Base-Collector Capacitance by Undercutting the Collector and Subcollector in GaInAsInP DHBT's,” IEEE Electron Device Letters, vol. 17, March 1996, pp. 97-99.
- the undercuts are then backfilled with polyimide to provide mechanical integrity.
- the reduced size of the collector, together with the lower dielectric constant of the polyimide reduces the base-collector capacitance.
- this approach does not reduce the base-collector capacitance component from under the base contact.
- Other methods to reduce base-collector capacitance include using an electrically insulating region of iron (Fe) doped InP replacing part of the collector to reduce the base-collector area.
- Another method of reducing the base-collector capacitance has been to reduce the base area and form a base metal micro-bridge to a base contact disposed away from the active portion of the HBT.
- the base metal micro-bridge is typically formed by depositing the base metal and then etching away the semiconductor from underneath a portion of the base metal.
- the present invention relates to a HBT device structure which facilitates mitigation of base-collector capacitance and a method for making the same.
- the HBT device structure of the present invention employs a phosphorous based collector material. During removal of the phosphorous based collector material, for example, using a wet etch, only facets or geometric surfaces that are part of a convex side of the HBT, and are oriented at about a +/ ⁇ 45° (010 or 001 direction) or about a +/ ⁇ 135° (00 ⁇ overscore (1) ⁇ or 0 ⁇ overscore (1) ⁇ 0 direction) from the major flat of the wafer will be undercut (major flat is in the 00 ⁇ overscore (1) ⁇ crystal plane).
- the base-collector capacitance is decreased by reducing the base mesa area and fabricating a base connecting bridge or micro-bridge that electrically connects a base contact to the base mesa.
- the base connecting bridge is positioned along a 45° angle to a major flat of the wafer.
- the base layer is undercut forming the connecting bridge, successfully removing the collector and sub-collector material below the bridge. The removal of collector and sub-collector material will reduce the base-collector junction area, and therefore reduce the base-collector junction capacitance.
- a base undercut cantilever base contact structure further reduces the base-collector capacitance.
- the base undercut cantilever base contact structure is provided by aligning the orientation of the intrinsic HBT portion and base contact portions along a 45° angle to the major flat. Therefore, undercutting portions of the collector and subcollector that have a convex geometric surface under the base mesas during the etching process a cantilever base contact structure.
- FIG. 1 illustrates a schematic cross-sectional view of a HBT device structure in accordance with an aspect of the present invention.
- FIG. 2 illustrates a top representative view of a layout of a HBT device structure having a 45° angle bridge orientation in accordance with an aspect of the present invention.
- FIG. 3 illustrates a top representative view of a layout of a plurality of HBT device structures on an integrated circuit in accordance with an aspect of the present invention.
- FIG. 4 is a schematic cross-sectional illustration of a plurality of stacked layers for forming a HBT device structure in accordance with an aspect of the present invention.
- FIG. 5 is a schematic cross-sectional illustration of the structure of FIG. 4 undergoing an etch to form an emitter in accordance with an aspect of the present invention.
- FIG. 6 is a schematic cross-sectional illustration of the structure of FIG. 5 after the etch to form the emitter is substantially complete in accordance with an aspect of the present invention.
- FIG. 7 is a schematic cross-sectional illustration of the structure of FIG. 6 after undergoing a deposition process to form a base contact, a connecting bridge and a contact to a base mesa on the emitter portion of the HBT device structure in accordance with an aspect of the present invention.
- FIG. 8 is a schematic cross-sectional illustration of the structure of FIG. 7 after a photoresist layer has been formed on the structure in accordance with an aspect of the present invention.
- FIG. 9 is a schematic cross-sectional illustration of the structure of FIG. 8 undergoing patterning of the photoresist layer in accordance with an aspect of the present invention.
- FIG. 10 illustrates a top representative view of the structure of FIG. 9 in accordance with an aspect of the present invention.
- FIG. 11 is a schematic cross-sectional illustration of the structure of FIG. 10 undergoing an etch to form base mesas in accordance with an aspect of the present invention.
- FIG. 12 is a schematic cross-sectional illustration of the structure of FIG. 11 after the etch to form the base mesas is substantially complete in accordance with an aspect of the present invention.
- FIG. 13 is a schematic cross-sectional illustration of the structure of FIG. 12 undergoing an etch to form the collector regions and to remove collector material from underneath the connecting bridge in accordance with an aspect of the present invention.
- FIG. 14 is a schematic cross-sectional illustration of the structure of FIG. 13 after the etch to form the collector regions and to remove collector material from underneath the connecting bridge is substantially complete in accordance with an aspect of the present invention.
- FIG. 15 is a schematic cross-sectional illustration of the structure of FIG. 14 after undergoing a strip of excess photoresist in accordance with an aspect of the present invention.
- FIG. 16 is a schematic cross-sectional illustration of the structure of FIG. 15 after providing a second patterned photoresist layer and undergoing an etch to form the subcollector regions to remove subcollector material from under the connecting bridge in accordance with an aspect of the present invention.
- FIG. 17 is a schematic cross-sectional illustration of the structure of FIG. 16 after the etch to form the subcollector regions after undergoing a strip of excess photoresist and to remove subcollector material from underneath the connecting bridge and in accordance with an aspect of the present invention.
- FIG. 18 illustrates a top representative view of the structure of FIG. 17 in accordance with an aspect of the present invention.
- the present invention relates to a HBT device structure which facilitates mitigation of base-collector capacitance and a method for making the same.
- the HBT device of the present invention exhibits faster performance at higher frequencies than many conventional HBT devices.
- the HBT device of the present invention employs a phosphorous (e.g., Indium Phosphide (InP), Indium Gallium Phosphide (InGaP)) based collector material.
- a phosphorous e.g., Indium Phosphide (InP), Indium Gallium Phosphide (InGaP)
- the base-collector capacitance is decreased by fabricating a base micro-bridge on an InP-based HBT or double HBT (DHBT) by positioning the base micro-bridge along about a +/ ⁇ 45° or about a +/ ⁇ 135° angle to a major flat of the wafer.
- the HBT has one material for the emitter with another material for the collector, while the DHBT has three different materials for the emitter, base and collector.
- the collector layer is undercut forming the micro-bridge, successfully removing the collector and sub-collector material below the bridge. The removal of collector and sub-collector material will reduce the base-collector junction area, and therefore reduce the base-collector junction capacitance.
- a base undercut cantilever base contact structure further reduces the base-collector capacitance.
- FIG. 1 illustrates a schematic cross-sectional illustration of a HBT device structure 10 (e.g., double HBT device) in accordance with the present invention.
- the device structure 10 includes an InP substrate wafer 12 .
- the InP substrate 12 provides mechanical support for the device structure 10 , and is of a thickness suitable for providing such support.
- the device structure 10 includes a base contact portion 11 and an intrinsic HBT portion 13 .
- the base contact portion 11 includes a first subcollector region 14 , a first collector region 16 residing over the first subcollector region 14 , a first base mesa 22 residing over the first collector region 16 and a base contact 28 residing over the first base mesa 22 .
- the first subcollector region 14 , the first collector region 16 and the first base mesa 22 are provided for mechanical support of the base contact 28 and are not provided to form electrically active components of the HBT device structure 10 .
- the intrinsic HBT portion 13 includes a second subcollector region 15 residing over the InP substrate 12 , a second collector region 20 residing over the second subcollector region 15 , a second base mesa 26 residing over the second collector region 20 and an emitter 32 residing over the second base mesa 26 .
- the second subcollector region 15 , the second collector region 20 , the second base mesa 26 , and the emitter 32 form the electrically active components of the total HBT device structure 10 .
- the base material that forms the first and second base mesas 22 and 26 is comprised of an arsenic based material (e.g., Indium Gallium Arsenide (InGaAs), Indium Aluminum Arsenide (InAlAs), Indium Aluminum Gallium Arsenide (InAlGaAs), Gallium Arsenide Antimonide (GaAsSb), Gallium Arsenide (GaAs)).
- the collector material that forms the collector regions 16 and 20 and the subcollector regions are comprised of a phosphorous based material (e.g., Indium Phosphide (InP), Indium Gallium Phosphide (InGaP)).
- the present invention provides a mechanism to undercut a phosphorous layer by orienting a conductive bridge 30 (e.g., metal bridge) that connects the second base mesa 26 to a base contact 28 along about a +/ ⁇ 45° or about a +/ ⁇ 135° angle to the major flat of the substrate 12 .
- the conductive bridge 30 can be formed from a variety of conductive materials (e.g., metal).
- An open area 18 resides below a conductive bridge 30 and a remaining base material portion 24 .
- the remaining base material portion 24 can be removed during fabrication.
- the conductive bridge 30 forms an electrical connection from the base mesa 26 to the base contact 28 . Therefore, the base mesa area 26 can be reduced in area mitigating the effects of the base-collector capacitance of the HBT device structure 10 .
- the conductive bridge 30 is oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° angle from the major flat of the substrate 12 . Therefore, during the etching of the collector and the subcollector material, the portion of the collector and the subcollector underneath the base material portion 24 and the conductive bridge 30 is undercut on any convex geometric side or facet of the HBT device structure 10 .
- FIG. 2 illustrates a top representative view of a layout of a HBT 40 having a 45° angle bridge orientation in accordance with an aspect of the present invention.
- the HBT 40 includes a base contact portion 41 having a first longitudinal axis B-B and an intrinsic HBT portion 43 having a second longitudinal axis A-A substantially normal to the first longitudinal axis.
- the base contact portion 41 and the intrinsic HBT portion 43 are coupled to one another by a conductive bridge 48 oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° angle with respect to the major flat of the wafer.
- the base contact portion 41 includes a base contact 42 and a first base/collector mesa 46 illustrated in dashed lines.
- the intrinsic HBT portion 43 includes an emitter 52 and a second base/collector mesa 56 illustrated in dashed lines.
- a photoresist or nitride hardmask 44 is employed during formation of the first and second base/collector mesas 46 and 56 .
- a conductive contact portion 50 couples a base mesa portion of the second base/collector mesa 56 to the base contact 42 via the conductive bridge 48 .
- a collector contact 60 is coupled to a subcollector region 68 of the HBT 40 .
- the collector material is removed and undercuts underneath the base material below the bridge in the direction of the arrows 58 . Since the collector material is formed from a phosphorous based material, the collector etch process only undercuts facets that are oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° to a major flat of the wafer. This is referred to as the [010] family of planes. Additionally, the collector etch only undercuts planes that are convex (i.e., greater or equal to 180°) not concave planes (i.e., less than 180°).
- a collector etch process e.g., selective collector wet etch
- the collector etch will undercut the convex planes 62 in the direction of arrows 58 , but not the concave planes 64 .
- the subcollector material is also formed from a phosphorous based material.
- a sub-collector etch is then performed to form the subcollector region 68 , and remove the subcollector material from underneath the conductive bridge 48 .
- FIG. 3 illustrates a top representative view of a layout of a plurality of HBTs on an integrated circuit 80 disposed on a wafer with each HBT having about a +/ ⁇ 45° or about a +/ ⁇ 135° angle bridge orientation in accordance with another aspect of the present invention.
- the HBTs have a base undercut cantilever base contact structure that further reduces the base-collector capacitance.
- the base undercut cantilever base contact structure is provided due to alignment of the orientation of the intrinsic HBT portions and base contact portions along about a +/45° or about +/ ⁇ 135° angle to a major flat. Therefore, portions of the collector and subcollector that have a convex geometric surface under the base mesas will undercut during the etching process.
- a first HBT device 82 resides next to a second HBT device 110 .
- the second HBT device 110 illustrates an alternate geometry from the first HBT device 82 .
- the components of the first HBT device 82 and the second HBT device 110 are identical, therefore, a general discussion of the second HBT device 110 will be omitted.
- the first HBT device 82 includes a base contact portion 81 and an intrinsic HBT portion 83 aligned along about a +/ ⁇ 45° or about a +/ ⁇ 135° angle with respect to a major flat of the wafer.
- the base contact portion 81 and the intrinsic HBT portion 83 are coupled to one another by a conductive bridge 90 oriented at about a +/ 450 or about +/ ⁇ 135° angle with respect to the major flat of the wafer, and aligned with the base contact portion 81 and the intrinsic HBT portion 83 .
- the base contact portion 81 includes a base contact 86 and a first collector mesa 84 illustrated in dashed lines.
- the intrinsic HBT portion 83 includes an emitter 94 and a second collector mesa 98 illustrated in dashed lines.
- a photoresist or dielectric hardmask 88 is employed during formation of the first and second collector mesas 84 and 98 .
- a first base mesa 87 and a second mesa 89 reside underneath the dielectric hardmask 88 .
- a conductive contact portion 92 couples the second base mesa 89 to the base contact 86 via the conductive bridge 90 .
- a collector contact 104 is coupled to a subcollector region 102 of the HBT 82 .
- the collector material is removed and undercuts the base material below the bridge in the direction of the arrows 100 . Since the collector material is formed from a phosphorous based material, the collector etch process only undercuts facets that are oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° to a major flat of the wafer. Additionally, the collector etch only undercuts planes that are convex (i.e., greater or equal to 180°) not concave planes (i.e., less than 180°).
- a collector etch process e.g., selective collector wet etch
- the collector etch will undercut the convex planes 104 in the direction of the arrows 100 , but not the concave planes 106 .
- the collector material will also be removed from underneath the bridge of the second HBT 110 in the direction of the arrows 112 . It is to be appreciated that any number of HBTs can be fabricated concurrently, only limited by the size of the HBTs, the integrated circuits and the wafer on which the integrated circuits reside.
- a substrate 120 e.g., InP substrate, GaAs substrate
- a subcollector layer 122 resides over the substrate 120
- a collector layer 124 overlays the subcollector layer 122
- a base layer 126 overlays the collector layer 124
- an emitter layer 128 overlays the base layer 126 .
- the subcollector layer 122 , the collector layer 124 , the base layer 126 and the emitter layer 128 can be formed by epitaxial growth of each layer.
- any suitable technique for forming the various layers can be employed such as Molecular Beam Epitaxy (MBE), Metal Organic Chemical Vapor Deposition (MOCVD) and Chemical Beam Epitaxy (CBE). It is to be appreciated that other layers can be added such as emitter caps, etch stops and grading layers without appreciably modifying the fabrication of the HBT device.
- MBE Molecular Beam Epitaxy
- MOCVD Metal Organic Chemical Vapor Deposition
- CBE Chemical Beam Epitaxy
- other layers can be added such as emitter caps, etch stops and grading layers without appreciably modifying the fabrication of the HBT device.
- the base layer 126 is formed from an arsenic based material (e.g., InGaAs, InAlAs, InAlGaAs, GaAsSb, GaAs).
- the collector layer 124 and the subcollector layer 122 are formed from a phosphorous based material (e.g., InP, InGaP).
- the subcollector can be formed from an arsenic based material.
- arsenic based materials undercut easily during a selective etching process, while the phoshphorous based materials do not readily undercut many geometric structures. Therefore, to perform and undercut operation to remove the collector material and subcollector material beneath a conductive bridge connecting a base contact portion with an intrinsic HBT portion, the conductive bridge will be oriented along a 45° angle to a major flat of the substrate 120 .
- An etch 200 (e.g., anisotropic reactive ion etching (RIE), wet etch) ( FIG. 5 ) is performed to remove the emitter material layer 128 employing a photoresist or metal mask 129 to form an emitter 130 ( FIG. 6 ). Any suitable etch technique may be used to etch the emitter material layer 128 .
- RIE reactive ion etching
- the emitter material layer 128 can be anisotropically etched with a plasma gas(es), herein carbon tetrafloride (CF 4 ) containing fluorine ions, in a commercially available etcher, such as a parallel plate RIE apparatus or, alternatively, an electron cyclotron resonance (ECR) plasma reactor by a wet etch or a by a combination of these techniques to form the emitter 130 .
- a plasma gas(es) herein carbon tetrafloride (CF 4 ) containing fluorine ions
- CF 4 carbon tetrafloride
- ECR electron cyclotron resonance
- the deposition includes depositing a base metal (e.g., aluminum, titanium, gold, tungsten, platinum) to provide a connection between the base mesa on the intrinsic HBT portion and the base contact on the base contact portion.
- the metal layer forms a base contact 131 , a connecting bridge 132 between the intrinsic HBT portion and a contact 133 on the base mesa on the intrinsic HBT portion.
- Gaps 135 separate the emitter 130 from the contact 133 . It is to be appreciated that a plurality of conductive materials can be employed to provide the functionality associated with the base metal.
- the resultant structure is illustrated in FIG. 7 .
- a photoresist layer 134 is formed on the base layer 126 as illustrated in FIG. 8 .
- the photoresist layer 134 has a thickness suitable for functioning as a mask for etching the underlying base layer 126 .
- the photoresist layer 134 is then patterned by a performing selective irradiation 210 ( FIG. 9 ) to define a base mesa etch mask.
- the irradiated or nonirradiated portions are removed by applying a developer material. Any suitable photolithographic techniques can be performed to form a patterned photoresist material layer.
- the base mesa etch mask can be formed employing a dielectric hard mask.
- FIG. 10 illustrates a top view of a portion of the resultant structure including the base contact 131 , the connecting bridge 132 , the contact 133 , the emitter 130 , and the base mesa etch mask 134 .
- An etch 220 ( FIG. 11 ) is performed to form base mesa regions 142 , 144 and 146 ( FIG. 12 ) from the arsenic based base layer 126 .
- the etch 220 can be a wet etch using an acid base wet etchant, such as a mixture of Phosphoric Acid (H 3 PO 4 ) and Hydrogen Peroxide (H 2 O 2 ).
- an acid base wet etchant such as a mixture of Phosphoric Acid (H 3 PO 4 ) and Hydrogen Peroxide (H 2 O 2 ).
- the wet etch is an isotropic etch that undercuts the base mesa etch mask in all direction. However, by employing a short etch, the base mesa etch mask will not undercut substantially.
- a selective etch technique is used to etch the arsenic based base layer at a relatively greater rate as compared to patterned photoresist layer 134 , the base metal layer 132 and the underlying phosphorous based collector layer 124 .
- the collector layer 124 acts as a stop layer to the etch 220 , so that the etching 220 does not gouge into the collector layer 124 .
- the base mesas 142 and 146 are formed as a result of the etch 220 .
- a remaining portion 144 of the base layer 126 remains underneath the bridge 140 .
- An etch 230 ( FIG. 13 ) is performed to remove the phosphorous based collector material to form collector regions 148 and 152 ( FIG. 14 ).
- the etch 230 employs the base mesa regions as a mask.
- the etch 230 is a wet etch using an acid base wet etchant, such as an HCl wet etch.
- an acid base wet etchant such as an HCl wet etch.
- phosphorous based materials have unusual etching properties.
- the collector only undercuts facets that are both oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° to a major flat of the wafer and that have convex (i.e., greater or equal to 180°) geometric surfaces.
- the collector material is removed underneath the bridge, since the bridge is oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° to a major flat of the wafer, and has a side that is convex.
- the etch 230 forms both the collector regions 148 and 152 and an open region 150 ( FIG. 14 ) under the remaining base material 144 and the connecting bridge 132 .
- FIG. 15 illustrates a partially complete HBT device after a stripping step (e.g., ashing in an O 2 plasma) is substantially complete to remove remaining portions of the patterned photoresist layer 134 .
- a second photoresist layer 136 is formed on the resultant structure and patterned to form a subcollector mask.
- an etch 240 ( FIG. 16 ) is performed to remove the phosphorous based subcollector material to form subcollector regions 154 and 156 ( FIG. 17 ).
- the etch 240 is a wet etch using an acid base wet etchant, such as an HCl wet etch.
- phosphorous based materials have unusual etching properties.
- the subcollector etch only undercuts facets that are both oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° to a major flat of the wafer and that are convex (i.e., greater or equal to 180°). Therefore, during the etch 240 , the subcollector material is removed underneath the remaining base material 144 and the connecting bridge 132 , since the connecting bridge 132 is oriented at about a +/ ⁇ 45° or about a +/ ⁇ 135° to a major flat of the wafer, and has a side that is convex.
- the etch 240 forms both the subcollector regions 154 and 156 and extends the open region 150 under the base material 144 and the bridge 132 to the InP substrate 120 .
- FIG. 18 illustrates a top view of the resultant HBT structure.
- An additional process is performed to provide a collector contact 158 , which is coupled to the subcollector region 156 completing the formation of the HBT structure.
- the HBT structure includes the base contact 131 , the connecting bridge 132 , the base 133 , the emitter 130 , and the subcollector region 156 .
- the first collector mesa 148 and the second collector mesa 152 are illustrated with dashed lines.
- the first base mesa 142 resides under the base contact 131
- the second base mesa 146 resides under the base 133
- the remaining base material 144 resides under the conducting bridge 132 .
- FIG. 18 illustrates a top view of the resultant HBT structure.
- the HBT device has a base undercut cantilever base contact structure that further reduces the base-collector capacitance.
- the result is provided due alignment of the orientation of the intrinsic HBT base contact along about a +/ ⁇ 45° or about a +/ ⁇ 135° angle to the major flat. Therefore, undercutting portions of the collector and subcollector that have a convex geometric surface during the etching process.
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Abstract
A heterojunction bipolar transistor (HBT) device structure is provided which facilitates the reduction of the base-collector capacitance and a method for making the same. The base-collector capacitance is decreased by fabricating a base micro-bridge connecting a base contact to a base mesa on the HBT. The base micro-bridge is oriented along about one of 001, 010, 00{overscore (1)}, and 0{overscore (1)}0 direction to a major flat of the wafer. The HBT device employs a phosphorous based collector material. During removal of the phosphorous based collector material, the base layer is undercut forming the micro-bridge, successfully removing the collector and sub-collector material below the bridge due to the orientation of the micro-bridge. The removal of collector and sub-collector material reduces the base-collector junction area, and therefore reduce the base-collector junction capacitance.
Description
- The present invention relates generally to electrical circuits, and more particularly to fabrication of heterojunction bipolar transistors.
- Heterojunction bipolar transistors (HBTs) are widely used in high speed and high frequency applications. The heterojunction bipolar transistor (HBT) offers much higher speeds of operation than the more prevalent metal-oxide-semiconductor field-effect transistors (MOSFETS) or even conventional homojunction bipolar transistors, such as npn or pnp silicon transistors. The HBT offers an alternative technology to metal semiconductor field effect transistors (MESFETs) and high electron mobility transistors (HEMTs) when a high degree of linearity is desirable. The use of different materials of differing bandgaps for the collector, base and emitter provides for additional design flexibility. The HBT is a layered structure that includes a semiconductor substrate, a subcollector, a collector, a base and an emitter stacked one on top the other in an integral assembly. Metal contacts are formed to connect power and other circuitry to the emitter, the base and the subcollector. The largest limitation to the operational frequency and speed of the HBT is the base-collector capacitance. The base-collector capacitance is largely due to the collector-base interface area. Reduction of the base area can introduce higher base resistance due to the reduction of the area of the base contact.
- A common HBT technology is based on Gallium Arsenide (GaAs)/Gallium Aluminum Arsenide (GaAlAs) based family. The GaAs based HBT suffers from base-collector capacitance due to the area of the interface between the base and collector layers. One method of reducing the base collector capacitance of a GaAs based HBT is to implant protons into an area of the collector surrounding the emitter so as to electrically insulate the implanted area. Another HBT technology is based on the Indium Phosphide (InP)/Indium Gallium Arsenide (InGaAs) material family. The InP/InGaAs HBT also suffers from base-collector capacitance. However, proton implantation has proved ineffective in rendering InP to be sufficiently insulating or semi-insulating.
- Miyamoto et al. addresses this problem by performing a selective etchant to substantially etch the collector layer under the base layer so as to undercut the edges of the base layer of InP-based HBTs in “Reduction of Base-Collector Capacitance by Undercutting the Collector and Subcollector in GaInAsInP DHBT's,” IEEE Electron Device Letters, vol. 17, March 1996, pp. 97-99. The undercuts are then backfilled with polyimide to provide mechanical integrity. The reduced size of the collector, together with the lower dielectric constant of the polyimide, reduces the base-collector capacitance. However, this approach does not reduce the base-collector capacitance component from under the base contact. Other methods to reduce base-collector capacitance include using an electrically insulating region of iron (Fe) doped InP replacing part of the collector to reduce the base-collector area.
- Another method of reducing the base-collector capacitance has been to reduce the base area and form a base metal micro-bridge to a base contact disposed away from the active portion of the HBT. The base metal micro-bridge is typically formed by depositing the base metal and then etching away the semiconductor from underneath a portion of the base metal. Song et al. demonstrate this technique for an HBT with an InGaAs collector layer in “Reduction of Extrinsic Base-Collector Capacitance in InP/InGaAs SHBTs Using a New Base Pad Design, INP and Related Materials Conference, 2002, pp. 165-168.” However, it is difficult to fabricate the base metal micro-bridge for HBTs that have phosphorus based collector layers and arsenic based base layers due to the unusual etching characteristics of phosphorous based materials. A similar technique is demonstrated for removing InP subcollector layers (but not the collector layer) using a cumbersome double base contact pad by Ida et al. in “InP/InGaAs DHBTs with 341-GHz for a big current density over 800 kA/cm2, IEEE Electron Device Meeting, 2001, pp. 35.4.1-35.4.4.”
- The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended neither to identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
- The present invention relates to a HBT device structure which facilitates mitigation of base-collector capacitance and a method for making the same. The HBT device structure of the present invention employs a phosphorous based collector material. During removal of the phosphorous based collector material, for example, using a wet etch, only facets or geometric surfaces that are part of a convex side of the HBT, and are oriented at about a +/−45° (010 or 001 direction) or about a +/−135° (00{overscore (1)} or 0{overscore (1)}0 direction) from the major flat of the wafer will be undercut (major flat is in the 00{overscore (1)} crystal plane). The base-collector capacitance is decreased by reducing the base mesa area and fabricating a base connecting bridge or micro-bridge that electrically connects a base contact to the base mesa. The base connecting bridge is positioned along a 45° angle to a major flat of the wafer. During collector removal, the base layer is undercut forming the connecting bridge, successfully removing the collector and sub-collector material below the bridge. The removal of collector and sub-collector material will reduce the base-collector junction area, and therefore reduce the base-collector junction capacitance.
- Additionally, a base undercut cantilever base contact structure further reduces the base-collector capacitance. The base undercut cantilever base contact structure is provided by aligning the orientation of the intrinsic HBT portion and base contact portions along a 45° angle to the major flat. Therefore, undercutting portions of the collector and subcollector that have a convex geometric surface under the base mesas during the etching process a cantilever base contact structure.
- To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
-
FIG. 1 illustrates a schematic cross-sectional view of a HBT device structure in accordance with an aspect of the present invention. -
FIG. 2 illustrates a top representative view of a layout of a HBT device structure having a 45° angle bridge orientation in accordance with an aspect of the present invention. -
FIG. 3 illustrates a top representative view of a layout of a plurality of HBT device structures on an integrated circuit in accordance with an aspect of the present invention. -
FIG. 4 is a schematic cross-sectional illustration of a plurality of stacked layers for forming a HBT device structure in accordance with an aspect of the present invention. -
FIG. 5 is a schematic cross-sectional illustration of the structure ofFIG. 4 undergoing an etch to form an emitter in accordance with an aspect of the present invention. -
FIG. 6 is a schematic cross-sectional illustration of the structure ofFIG. 5 after the etch to form the emitter is substantially complete in accordance with an aspect of the present invention. -
FIG. 7 is a schematic cross-sectional illustration of the structure ofFIG. 6 after undergoing a deposition process to form a base contact, a connecting bridge and a contact to a base mesa on the emitter portion of the HBT device structure in accordance with an aspect of the present invention. -
FIG. 8 is a schematic cross-sectional illustration of the structure ofFIG. 7 after a photoresist layer has been formed on the structure in accordance with an aspect of the present invention. -
FIG. 9 is a schematic cross-sectional illustration of the structure ofFIG. 8 undergoing patterning of the photoresist layer in accordance with an aspect of the present invention. -
FIG. 10 illustrates a top representative view of the structure ofFIG. 9 in accordance with an aspect of the present invention. -
FIG. 11 is a schematic cross-sectional illustration of the structure ofFIG. 10 undergoing an etch to form base mesas in accordance with an aspect of the present invention. -
FIG. 12 is a schematic cross-sectional illustration of the structure ofFIG. 11 after the etch to form the base mesas is substantially complete in accordance with an aspect of the present invention. -
FIG. 13 is a schematic cross-sectional illustration of the structure ofFIG. 12 undergoing an etch to form the collector regions and to remove collector material from underneath the connecting bridge in accordance with an aspect of the present invention. -
FIG. 14 is a schematic cross-sectional illustration of the structure ofFIG. 13 after the etch to form the collector regions and to remove collector material from underneath the connecting bridge is substantially complete in accordance with an aspect of the present invention. -
FIG. 15 is a schematic cross-sectional illustration of the structure ofFIG. 14 after undergoing a strip of excess photoresist in accordance with an aspect of the present invention. -
FIG. 16 is a schematic cross-sectional illustration of the structure ofFIG. 15 after providing a second patterned photoresist layer and undergoing an etch to form the subcollector regions to remove subcollector material from under the connecting bridge in accordance with an aspect of the present invention. -
FIG. 17 is a schematic cross-sectional illustration of the structure ofFIG. 16 after the etch to form the subcollector regions after undergoing a strip of excess photoresist and to remove subcollector material from underneath the connecting bridge and in accordance with an aspect of the present invention. -
FIG. 18 illustrates a top representative view of the structure ofFIG. 17 in accordance with an aspect of the present invention. - The present invention relates to a HBT device structure which facilitates mitigation of base-collector capacitance and a method for making the same. The HBT device of the present invention exhibits faster performance at higher frequencies than many conventional HBT devices. The HBT device of the present invention employs a phosphorous (e.g., Indium Phosphide (InP), Indium Gallium Phosphide (InGaP)) based collector material. During removal of the phosphorous based collector material, for example, by using a wet etch, only facets that are part of a convex side of the HBT, and are oriented about a +/−45° (010 or 001 direction) or about a +/−135° (00{overscore (1)} or 0{overscore (1)}0 direction) from the major flat of the wafer will be undercut (major flat is in the 00{overscore (1)} crystal plane). The base-collector capacitance is decreased by fabricating a base micro-bridge on an InP-based HBT or double HBT (DHBT) by positioning the base micro-bridge along about a +/−45° or about a +/−135° angle to a major flat of the wafer. The HBT has one material for the emitter with another material for the collector, while the DHBT has three different materials for the emitter, base and collector. During collector removal, the collector layer is undercut forming the micro-bridge, successfully removing the collector and sub-collector material below the bridge. The removal of collector and sub-collector material will reduce the base-collector junction area, and therefore reduce the base-collector junction capacitance. Additionally, a base undercut cantilever base contact structure further reduces the base-collector capacitance.
-
FIG. 1 illustrates a schematic cross-sectional illustration of a HBT device structure 10 (e.g., double HBT device) in accordance with the present invention. Thedevice structure 10 includes anInP substrate wafer 12. TheInP substrate 12 provides mechanical support for thedevice structure 10, and is of a thickness suitable for providing such support. Thedevice structure 10 includes abase contact portion 11 and anintrinsic HBT portion 13. Thebase contact portion 11 includes afirst subcollector region 14, afirst collector region 16 residing over thefirst subcollector region 14, afirst base mesa 22 residing over thefirst collector region 16 and abase contact 28 residing over thefirst base mesa 22. Thefirst subcollector region 14, thefirst collector region 16 and thefirst base mesa 22 are provided for mechanical support of thebase contact 28 and are not provided to form electrically active components of theHBT device structure 10. Theintrinsic HBT portion 13 includes asecond subcollector region 15 residing over theInP substrate 12, asecond collector region 20 residing over thesecond subcollector region 15, asecond base mesa 26 residing over thesecond collector region 20 and anemitter 32 residing over thesecond base mesa 26. Thesecond subcollector region 15, thesecond collector region 20, thesecond base mesa 26, and theemitter 32 form the electrically active components of the totalHBT device structure 10. - The base material that forms the first and
second base mesas collector regions second base mesa 26 to abase contact 28 along about a +/−45° or about a +/−135° angle to the major flat of thesubstrate 12. Theconductive bridge 30 can be formed from a variety of conductive materials (e.g., metal). - An
open area 18 resides below aconductive bridge 30 and a remainingbase material portion 24. Alternatively, the remainingbase material portion 24 can be removed during fabrication. Theconductive bridge 30 forms an electrical connection from thebase mesa 26 to thebase contact 28. Therefore, thebase mesa area 26 can be reduced in area mitigating the effects of the base-collector capacitance of theHBT device structure 10. Theconductive bridge 30 is oriented at about a +/−45° or about a +/−135° angle from the major flat of thesubstrate 12. Therefore, during the etching of the collector and the subcollector material, the portion of the collector and the subcollector underneath thebase material portion 24 and theconductive bridge 30 is undercut on any convex geometric side or facet of theHBT device structure 10. -
FIG. 2 illustrates a top representative view of a layout of aHBT 40 having a 45° angle bridge orientation in accordance with an aspect of the present invention. TheHBT 40 includes abase contact portion 41 having a first longitudinal axis B-B and anintrinsic HBT portion 43 having a second longitudinal axis A-A substantially normal to the first longitudinal axis. Thebase contact portion 41 and theintrinsic HBT portion 43 are coupled to one another by aconductive bridge 48 oriented at about a +/−45° or about a +/−135° angle with respect to the major flat of the wafer. Thebase contact portion 41 includes abase contact 42 and a first base/collector mesa 46 illustrated in dashed lines. Theintrinsic HBT portion 43 includes anemitter 52 and a second base/collector mesa 56 illustrated in dashed lines. A photoresist ornitride hardmask 44 is employed during formation of the first and second base/collector mesas conductive contact portion 50 couples a base mesa portion of the second base/collector mesa 56 to thebase contact 42 via theconductive bridge 48. Acollector contact 60 is coupled to asubcollector region 68 of theHBT 40. - During a collector etch process (e.g., selective collector wet etch), the collector material is removed and undercuts underneath the base material below the bridge in the direction of the
arrows 58. Since the collector material is formed from a phosphorous based material, the collector etch process only undercuts facets that are oriented at about a +/−45° or about a +/−135° to a major flat of the wafer. This is referred to as the [010] family of planes. Additionally, the collector etch only undercuts planes that are convex (i.e., greater or equal to 180°) not concave planes (i.e., less than 180°). Therefore, the collector etch will undercut theconvex planes 62 in the direction ofarrows 58, but not the concave planes 64. The subcollector material is also formed from a phosphorous based material. A sub-collector etch is then performed to form thesubcollector region 68, and remove the subcollector material from underneath theconductive bridge 48. -
FIG. 3 illustrates a top representative view of a layout of a plurality of HBTs on anintegrated circuit 80 disposed on a wafer with each HBT having about a +/−45° or about a +/−135° angle bridge orientation in accordance with another aspect of the present invention. The HBTs have a base undercut cantilever base contact structure that further reduces the base-collector capacitance. The base undercut cantilever base contact structure is provided due to alignment of the orientation of the intrinsic HBT portions and base contact portions along about a +/45° or about +/−135° angle to a major flat. Therefore, portions of the collector and subcollector that have a convex geometric surface under the base mesas will undercut during the etching process. Additionally, aligning the intrinsic HBT portions and base contact portions in this manner facilitates improved density packing of the HBT devices on theintegrated circuit 80. In the illustration ofFIG. 3 , afirst HBT device 82 resides next to asecond HBT device 110. Thesecond HBT device 110 illustrates an alternate geometry from thefirst HBT device 82. However, the components of thefirst HBT device 82 and thesecond HBT device 110 are identical, therefore, a general discussion of thesecond HBT device 110 will be omitted. - The
first HBT device 82 includes abase contact portion 81 and anintrinsic HBT portion 83 aligned along about a +/−45° or about a +/−135° angle with respect to a major flat of the wafer. Thebase contact portion 81 and theintrinsic HBT portion 83 are coupled to one another by aconductive bridge 90 oriented at about a +/450 or about +/−135° angle with respect to the major flat of the wafer, and aligned with thebase contact portion 81 and theintrinsic HBT portion 83. Thebase contact portion 81 includes abase contact 86 and afirst collector mesa 84 illustrated in dashed lines. Theintrinsic HBT portion 83 includes anemitter 94 and asecond collector mesa 98 illustrated in dashed lines. A photoresist ordielectric hardmask 88 is employed during formation of the first and second collector mesas 84 and 98. Afirst base mesa 87 and asecond mesa 89 reside underneath thedielectric hardmask 88. Aconductive contact portion 92 couples thesecond base mesa 89 to thebase contact 86 via theconductive bridge 90. Acollector contact 104 is coupled to asubcollector region 102 of theHBT 82. - During a collector etch process (e.g., selective collector wet etch), the collector material is removed and undercuts the base material below the bridge in the direction of the
arrows 100. Since the collector material is formed from a phosphorous based material, the collector etch process only undercuts facets that are oriented at about a +/−45° or about a +/−135° to a major flat of the wafer. Additionally, the collector etch only undercuts planes that are convex (i.e., greater or equal to 180°) not concave planes (i.e., less than 180°). Therefore, the collector etch will undercut theconvex planes 104 in the direction of thearrows 100, but not theconcave planes 106. During the collector etch process, the collector material will also be removed from underneath the bridge of thesecond HBT 110 in the direction of thearrows 112. It is to be appreciated that any number of HBTs can be fabricated concurrently, only limited by the size of the HBTs, the integrated circuits and the wafer on which the integrated circuits reside. - Turning now to
FIGS. 4-18 , process blocks in connection with fabrication of the HBT device in accordance with an aspect of the present invention are described. A substrate 120 (e.g., InP substrate, GaAs substrate) or wafer is provided with several stacked layers disposed above thesubstrate 120. Asubcollector layer 122 resides over thesubstrate 120, acollector layer 124 overlays thesubcollector layer 122, abase layer 126 overlays thecollector layer 124 and anemitter layer 128 overlays thebase layer 126. Thesubcollector layer 122, thecollector layer 124, thebase layer 126 and theemitter layer 128 can be formed by epitaxial growth of each layer. It is to be appreciated that any suitable technique for forming the various layers can be employed such as Molecular Beam Epitaxy (MBE), Metal Organic Chemical Vapor Deposition (MOCVD) and Chemical Beam Epitaxy (CBE). It is to be appreciated that other layers can be added such as emitter caps, etch stops and grading layers without appreciably modifying the fabrication of the HBT device. - The
base layer 126 is formed from an arsenic based material (e.g., InGaAs, InAlAs, InAlGaAs, GaAsSb, GaAs). Thecollector layer 124 and thesubcollector layer 122 are formed from a phosphorous based material (e.g., InP, InGaP). Alternatively, the subcollector can be formed from an arsenic based material. As previously discussed, arsenic based materials undercut easily during a selective etching process, while the phoshphorous based materials do not readily undercut many geometric structures. Therefore, to perform and undercut operation to remove the collector material and subcollector material beneath a conductive bridge connecting a base contact portion with an intrinsic HBT portion, the conductive bridge will be oriented along a 45° angle to a major flat of thesubstrate 120. - An etch 200 (e.g., anisotropic reactive ion etching (RIE), wet etch) (
FIG. 5 ) is performed to remove theemitter material layer 128 employing a photoresist ormetal mask 129 to form an emitter 130 (FIG. 6 ). Any suitable etch technique may be used to etch theemitter material layer 128. For example, theemitter material layer 128 can be anisotropically etched with a plasma gas(es), herein carbon tetrafloride (CF4) containing fluorine ions, in a commercially available etcher, such as a parallel plate RIE apparatus or, alternatively, an electron cyclotron resonance (ECR) plasma reactor by a wet etch or a by a combination of these techniques to form theemitter 130. - Next, a deposition is performed on the structure of
FIG. 6 . The deposition includes depositing a base metal (e.g., aluminum, titanium, gold, tungsten, platinum) to provide a connection between the base mesa on the intrinsic HBT portion and the base contact on the base contact portion. The metal layer forms abase contact 131, a connectingbridge 132 between the intrinsic HBT portion and acontact 133 on the base mesa on the intrinsic HBT portion.Gaps 135 separate theemitter 130 from thecontact 133. It is to be appreciated that a plurality of conductive materials can be employed to provide the functionality associated with the base metal. The resultant structure is illustrated inFIG. 7 . - A
photoresist layer 134 is formed on thebase layer 126 as illustrated inFIG. 8 . Thephotoresist layer 134 has a thickness suitable for functioning as a mask for etching theunderlying base layer 126. Thephotoresist layer 134 is then patterned by a performing selective irradiation 210 (FIG. 9 ) to define a base mesa etch mask. The irradiated or nonirradiated portions are removed by applying a developer material. Any suitable photolithographic techniques can be performed to form a patterned photoresist material layer. Alternatively, the base mesa etch mask can be formed employing a dielectric hard mask.FIG. 10 illustrates a top view of a portion of the resultant structure including thebase contact 131, the connectingbridge 132, thecontact 133, theemitter 130, and the basemesa etch mask 134. - An etch 220 (
FIG. 11 ) is performed to formbase mesa regions FIG. 12 ) from the arsenic basedbase layer 126. Theetch 220 can be a wet etch using an acid base wet etchant, such as a mixture of Phosphoric Acid (H3PO4) and Hydrogen Peroxide (H2O2). Typically, the wet etch is an isotropic etch that undercuts the base mesa etch mask in all direction. However, by employing a short etch, the base mesa etch mask will not undercut substantially. A selective etch technique is used to etch the arsenic based base layer at a relatively greater rate as compared to patternedphotoresist layer 134, thebase metal layer 132 and the underlying phosphorous basedcollector layer 124. Thecollector layer 124 acts as a stop layer to theetch 220, so that theetching 220 does not gouge into thecollector layer 124. The base mesas 142 and 146 are formed as a result of theetch 220. A remainingportion 144 of thebase layer 126 remains underneath the bridge 140. - An etch 230 (
FIG. 13 ) is performed to remove the phosphorous based collector material to formcollector regions 148 and 152 (FIG. 14 ). Theetch 230 employs the base mesa regions as a mask. Theetch 230 is a wet etch using an acid base wet etchant, such as an HCl wet etch. As previously discussed, phosphorous based materials have unusual etching properties. The collector etch only undercuts facets that are both oriented at about a +/−45° or about a +/−135° to a major flat of the wafer and that have convex (i.e., greater or equal to 180°) geometric surfaces. Therefore, during theetch 230, the collector material is removed underneath the bridge, since the bridge is oriented at about a +/−45° or about a +/−135° to a major flat of the wafer, and has a side that is convex. Theetch 230 forms both thecollector regions FIG. 14 ) under the remainingbase material 144 and the connectingbridge 132. -
FIG. 15 illustrates a partially complete HBT device after a stripping step (e.g., ashing in an O2 plasma) is substantially complete to remove remaining portions of the patternedphotoresist layer 134. Asecond photoresist layer 136 is formed on the resultant structure and patterned to form a subcollector mask. Next, an etch 240 (FIG. 16 ) is performed to remove the phosphorous based subcollector material to formsubcollector regions 154 and 156 (FIG. 17 ). Theetch 240 is a wet etch using an acid base wet etchant, such as an HCl wet etch. As previously discussed, phosphorous based materials have unusual etching properties. If a phosphorous based subcollector is employed, the subcollector etch only undercuts facets that are both oriented at about a +/−45° or about a +/−135° to a major flat of the wafer and that are convex (i.e., greater or equal to 180°). Therefore, during theetch 240, the subcollector material is removed underneath the remainingbase material 144 and the connectingbridge 132, since the connectingbridge 132 is oriented at about a +/−45° or about a +/−135° to a major flat of the wafer, and has a side that is convex. Theetch 240 forms both thesubcollector regions open region 150 under thebase material 144 and thebridge 132 to theInP substrate 120. -
FIG. 18 illustrates a top view of the resultant HBT structure. An additional process is performed to provide acollector contact 158, which is coupled to thesubcollector region 156 completing the formation of the HBT structure. The HBT structure includes thebase contact 131, the connectingbridge 132, thebase 133, theemitter 130, and thesubcollector region 156. Thefirst collector mesa 148 and thesecond collector mesa 152 are illustrated with dashed lines. Thefirst base mesa 142 resides under thebase contact 131, thesecond base mesa 146 resides under thebase 133, and the remainingbase material 144 resides under the conductingbridge 132. As illustrated inFIG. 18 , the HBT device has a base undercut cantilever base contact structure that further reduces the base-collector capacitance. The result is provided due alignment of the orientation of the intrinsic HBT base contact along about a +/−45° or about a +/−135° angle to the major flat. Therefore, undercutting portions of the collector and subcollector that have a convex geometric surface during the etching process. - What has been described above includes exemplary implementations of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.
Claims (19)
1. A heterojunction bipolar transistor (HBT) device comprising:
an intrinsic HBT portion formed from a stacked layer having a subcollector region, a collector region disposed above the subcollector region, a base mesa disposed above the collector region and an emitter disposed above the base mesa;
a base contact portion having a base contact disposed away from the intrinsic HBT portion; and
a conductive bridge that connects the base mesa with the base contact, the conductive bridge oriented at about one of a 001, 010, 00{overscore (1)}, and 0{overscore (1)}0 direction with respect to a major flat of the wafer, the conductive bridge exposing convex edges along at least a portion of one side of the HBT device.
2. The HBT device of claim 1 , the collector region formed from a phosphorous based material.
3. The HBT device of claim 2 , the phosphorous based material being one of Indium Phosphide (InP) and Indium Gallium Phosphide (InGaP).
4. The HBT device of claim 2 , the base mesa formed from an arsenic based material.
5. The HBT device of claim 4 , the arsenic based material being one of Indium Gallium Arsenide (InGaAs), Indium Aluminum Arsenide (InAlAs), Indium Gallium Aluminum Arsenide (InAlGaAs), Gallium Arsenide Antimonide (GaAsSb) and Gallium Arsenide (GaAs).
6. The HBT device of claim 1 , the base contact portion formed from a stacked layer having a subcollector region, a collector region disposed above the subcollector region, a base mesa disposed above the collector region and the base contact disposed above the base mesa.
7. The HBT device of claim 1 , further comprising an opening below the conductive bridge between the collector regions of the base contact portion and the intrinsic HBT portion.
8. The HBT device of claim 1 , the opening extends between the subcollector regions of the base contact portion and the intrinsic HBT portion below the conductive bridge.
9. An integrated circuit comprising the HBT device of claim 1 .
10. The HBT device of claim 1 , the conductive bridge oriented at about one of 001, 010, 00{overscore (1)}, and 0{overscore (1)}0 direction with respect to a major flat of a wafer during fabrication of the HBT device.
11. A heterojunction bipolar transistor (HBT) device fabricated on a semiconductor wafer having a major flat, the HBT device comprising:
an intrinsic HBT portion formed from a stacked layer having a subcollector region, a phosphorous based collector region disposed above the subcollector region, an arsenic based base mesa disposed above the phosphorous based collector region and an emitter disposed above the arsenic based base mesa;
a base contact portion having a base contact disposed away from the intrinsic HBT portion; and
a connecting bridge that electrical connects the base mesa with the base contact, the connecting bridge oriented at about one of 001, 010, 00{overscore (1)}, and 0{overscore (1)}0 direction with respect to the major flat of the wafer during fabrication.
12. The HBT device of claim 11 , the intrinsic HBT portion, the base contact portion and the connecting bridge aligned at about one of 001, 010, 00{overscore (1)}, and 0{overscore (1)}0 direction with respect to the major flat of the wafer during fabrication.
13. The HBT device of claim 11 , the connecting bridge having at least one side with a convex geometric surface, such that the connecting bridge is undercut during at least one of a collector etch and a subcollector etch.
14. The HBT device of claim 11 , the phosphorous based material being one of Indium Phosphide (InP) and Indium Gallium Phosphide (InGaP).
15. The HBT device of claim 14 , the arsenic based material being one of Indium Gallium Arsenide (InGaAs), Indium Aluminum Arsenide (InAlAs), Indium Gallium Aluminum Arsenide (InAlGaAs), Gallium Arsenide Antimonide (GaAsSb) and Gallium Arsenide (GaAs).
16. The HBT device of claim 15 , the subcollector formed from one of a phosphorous based material or an arsenic based material.
17. The HBT device of claim 11 , the base contact portion formed from a stacked layer having a subcollector region, a collector region disposed above the subcollector region, a base mesa disposed above the collector region and the base contact disposed above the base mesa and an opening below the connecting bridge between the collector regions of the base contact portion and the intrinsic HBT portion, the opening formed during at least one of a collector etch and a subcollector etch that undercuts the connecting bridge.
18. The HBT device of claim 11 , the intrinsic HBT portion having a cantilever base contact structure.
19-27. (canceled)
Priority Applications (1)
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US11/116,745 US20050184312A1 (en) | 2003-05-27 | 2005-04-28 | Double HBT base metal micro-bridge |
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US10/445,612 US6924203B2 (en) | 2003-05-27 | 2003-05-27 | Double HBT base metal micro-bridge |
US11/116,745 US20050184312A1 (en) | 2003-05-27 | 2005-04-28 | Double HBT base metal micro-bridge |
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US10/445,612 Division US6924203B2 (en) | 2003-05-27 | 2003-05-27 | Double HBT base metal micro-bridge |
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US20050184312A1 true US20050184312A1 (en) | 2005-08-25 |
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US10/445,612 Expired - Lifetime US6924203B2 (en) | 2003-05-27 | 2003-05-27 | Double HBT base metal micro-bridge |
US11/116,745 Abandoned US20050184312A1 (en) | 2003-05-27 | 2005-04-28 | Double HBT base metal micro-bridge |
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US10/445,612 Expired - Lifetime US6924203B2 (en) | 2003-05-27 | 2003-05-27 | Double HBT base metal micro-bridge |
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US (2) | US6924203B2 (en) |
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Cited By (1)
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US20080173874A1 (en) * | 2007-01-18 | 2008-07-24 | National Central University | Heterojunction bipolar transistor having (In) (Al) GaAsSb/InGaAs base-collector structure |
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JP2004327717A (en) * | 2003-04-24 | 2004-11-18 | Sony Corp | Semiconductor device and manufacturing method therefor |
US7038250B2 (en) * | 2003-05-28 | 2006-05-02 | Kabushiki Kaisha Toshiba | Semiconductor device suited for a high frequency amplifier |
JP4089662B2 (en) * | 2004-07-21 | 2008-05-28 | ソニー株式会社 | Bipolar transistor and manufacturing method thereof |
RU2469438C1 (en) * | 2011-06-16 | 2012-12-10 | Федеральное государственное бюджетное учреждение науки Физико-технический институт им. А.Ф. Иоффе Российской академии наук | Semiconductor photodiode for infrared radiation |
US10998420B2 (en) * | 2018-04-04 | 2021-05-04 | International Business Machines Corporation | Direct growth of lateral III-V bipolar transistor on silicon substrate |
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Also Published As
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JP2004356613A (en) | 2004-12-16 |
US6924203B2 (en) | 2005-08-02 |
EP1482542A1 (en) | 2004-12-01 |
US20040238843A1 (en) | 2004-12-02 |
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