US20130137199A1 - Systems and methods for monitoring heterojunction bipolar transistor processes - Google Patents

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  • H10D84/611—Combinations of BJTs and one or more of diodes, resistors or capacitors
  • H10D84/613—Combinations of vertical BJTs and one or more of diodes, resistors or capacitors
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  • H10D62/80—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials
  • H10D62/82—Heterojunctions
  • H10D62/824—Heterojunctions comprising only Group III-V materials heterojunctions, e.g. GaN/AlGaN heterojunctions
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  • H10D64/23—Electrodes carrying the current to be rectified, amplified, oscillated or switched, e.g. sources, drains, anodes or cathodes
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  • H01L2224/02—Bonding areas; Manufacturing methods related thereto
  • H01L2224/04—Structure, shape, material or disposition of the bonding areas prior to the connecting process
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  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
  • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
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  • H01L2224/4805—Shape
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  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
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  • H01L2224/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
  • H01L2224/491—Disposition
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  • H01L2924/10—Details of semiconductor or other solid state devices to be connected
  • H01L2924/11—Device type
  • H01L2924/12—Passive devices, e.g. 2 terminal devices
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  • H01L2924/11—Device type
  • H01L2924/13—Discrete devices, e.g. 3 terminal devices
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Definitions

• the present disclosure generally relates to structures and fabrication processes associated with bipolar transistors.
• a bipolar junction transistor typically includes two back-to-back p-n junctions formed by a base region disposed between an emitter region and a collector region. Such junctions can include a PNP configuration or an NPN configuration. The bipolar functionality results from its operation involving both electrons and holes.
• a heterojunction bipolar transistor is a type of BJT, where different semiconductor materials are utilized for the emitter and base regions to yield a heterojunction.
• HBTs can be particularly useful in radio-frequency (RF) applications, including high-efficiency RF power amplifiers.
• the present disclosure relates to a metallization structure that includes a selected semiconductor layer and a tantalum nitride (TaN) layer formed over the selected semiconductor layer.
• the selected semiconductor includes wide bandgap semiconductor lattice-matched to gallium arsenide (GaAs).
• the structure further includes a metal layer formed over the TaN layer, such that the TaN layer forms a barrier between the metal layer and the selected semiconductor layer.
• the selected semiconductor layer can include indium gallium phosphide (InGaP).
• the TaN layer can be configured to reduce the likelihood of the metal layer contacting the InGaP layer and behaving in an ohmic manner.
• the structure can further include a first gallium arsenide (GaAs) layer underneath the InGaP layer.
• the structure can further include a metal contact disposed relative to the first GaAs layer so as to facilitate electrical connection with the first GaAs layer.
• the InGaP layer can be dimensioned such that the metallization structure provides a capacitance density of at least 2.0 fF/ ⁇ m 2 when capacitance is measured between the metal layer and the metal contact.
• the first GaAs layer can be part of a base of a heterojunction bipolar transistor (HBT) and the InGaP layer can be part of an emitter of the HBT.
• the structure can further include a second GaAs layer configured as a collector of the HBT, and a semi-insulating GaAs substrate.
• the HBT can be configured as an NPN or PNP transistor.
• the present disclosure relates to a packaged module having a packaging substrate configured to receive a plurality of components.
• the module further includes a gallium arsenide (GaAs) die mounted on the packaging substrate and has an integrated circuit (IC).
• the die includes a GaAs substrate and a selected semiconductor layer formed over the GaAs substrate.
• the selected semiconductor includes wide bandgap semiconductor lattice-matched to GaAs.
• the die further includes a metallization assembly having a tantalum nitride (TaN) layer formed over the selected semiconductor layer, and a metal layer formed over the TaN layer.
• the TaN layer forms a barrier between the metal layer and the selected semiconductor layer.
• the selected semiconductor layer can include indium gallium phosphide (InGaP).
• the metallization assembly, the InGaP layer, and the GaAs substrate can form an on-die high-value capacitance element.
• Such an on-die capacitance element can be part of, for example, a power amplifier circuit, a tuning network circuit, or a power supply bypass circuit.
• the InGaP layer can be configured as an emitter of a heterojunction bipolar transistor (HBT).
• HBT heterojunction bipolar transistor
• Such an HBT can be part of, for example, a power amplifier circuit configured to amplify a radio-frequency (RF) signal.
• the module can be a power amplifier module.
• the present disclosure relates to a radio-frequency (RF) device having an antenna and a transceiver coupled to the antenna and configured to process a radio-frequency (RF) signal.
• the RF device also has an integrated circuit (IC) that is coupled to or is part of the transceiver and configured to facilitate the processing of the RF signal.
• the IC is implemented on a gallium arsenide (GaAs) die.
• the die includes a GaAs substrate and a selected semiconductor layer formed over the GaAs substrate.
• the selected semiconductor includes wide bandgap semiconductor lattice-matched to GaAs.
• the die further includes a metallization assembly having a tantalum nitride (TaN) layer formed over the selected semiconductor layer, and a metal layer formed over the TaN layer.
• TaN tantalum nitride
• the TaN layer forms a barrier between the metal layer and the selected semiconductor layer.
• the RF device can be a wireless device.
• the IC can be part of a power amplifier configured to amplify the RF signal.
• the present disclosure relates to a method for fabricating a metallization structure.
• the method includes providing or forming an underlying semiconductor layer, and forming a selected semiconductor layer over the underlying semiconductor layer.
• the method further includes forming a tantalum nitride (TaN) layer over the selected semiconductor layer, and forming a metal layer over the TaN layer.
• TaN tantalum nitride
• the present disclosure relates to a gallium arsenide (GaAs) die that includes a GaAs substrate and a selected semiconductor layer formed over the GaAs substrate.
• the selected semiconductor includes wide bandgap semiconductor lattice-matched to GaAs.
• the die further includes a metallization assembly having a tantalum nitride (TaN) layer formed over the selected semiconductor layer, and a metal layer formed over the TaN layer.
• TaN tantalum nitride
• the TaN layer forms a barrier between the metal layer and the selected semiconductor layer.
• the selected semiconductor layer can include indium gallium phosphide (InGaP).
• the metallization assembly, the selected semiconductor layer, and the GaAs substrate can form a high-value capacitance element.
• the selected semiconductor layer can be configured as an emitter of a heterojunction bipolar transistor (HBT).
• the GaAs substrate can include a first GaAs layer configured as a base and a second GaAs layer configured as a collector of the HBT.
• the present disclosure relates to a method for fabricating a heterojunction bipolar transistor (HBT).
• the method includes providing or forming a gallium arsenide (GaAs) substrate, and forming a collector layer, a base layer, and an emitter layer over the GaAs substrate.
• the method further includes forming a barrier layer over the emitter layer, forming a metal layer over the barrier layer, and measuring capacitance between the metal layer and the base layer, with the capacitance being representative of a thickness of the emitter layer.
• GaAs gallium arsenide
• the emitter layer can include indium gallium phosphide (InGaP). In some embodiments, the emitter layer can include a ledge. In some embodiments, the collector layer, the base layer, and the emitter layer can be configured as an NPN transistor. In some embodiments, the barrier layer can include tantalum nitride (TaN). In some embodiments, the method can further include forming a metal contact on the base layer. In some embodiments, the method can further include adjusting a process parameter so that the capacitance is within a selected range.
• the present disclosure relates to a system for monitoring a heterojunction bipolar transistor (HBT) fabrication process.
• the system includes a process assembly configured to form an emitter layer over a base layer, a barrier layer over the emitter layer, and a metal layer over the barrier layer.
• the system further includes a monitoring assembly configured to measure capacitance between the metal layer and the base layer, with the measured capacitance being representative of a thickness of the emitter layer.
• the emitter layer can include indium gallium phosphide (InGaP). In some embodiments, the emitter layer can include a ledge. In some embodiments, the barrier layer can include tantalum nitride (TaN).
• the process assembly can be further configured to form a metal contact on the base layer.
• the system can further include a process control assembly configured to adjust a process parameter so that the capacitance is within a selected range.
• the present disclosure relates to a method for monitoring a semiconductor fabrication process.
• the method includes providing or forming an underlying semiconductor layer, and forming a selected semiconductor layer over the underlying semiconductor layer.
• the selected semiconductor includes wide bandgap semiconductor lattice-matched to gallium arsenide (GaAs).
• the method further includes forming a tantalum nitride (TaN) layer over the selected semiconductor layer, and forming a metal layer over the TaN layer.
• the method further includes measuring capacitance between the metal layer and the underlying semiconductor layer to obtain an estimate of a thickness of the selected semiconductor layer.
• the method can further include adjusting a process parameter if the measured capacitance is outside of a selected range.
• the thickness of the selected semiconductor layer can be calculated from the measured capacitance based on an approximation that the metal layer behaves as a portion of a parallel-plate capacitor.
• the selected semiconductor layer can include indium gallium phosphide (InGaP).
• the underlying semiconductor layer can include gallium arsenide (GaAs).
• the InGaP layer and the GaAs layer can be emitter and base, respectively, of a heterojunction bipolar transistor (HBT).
• the metal layer, the TaN layer, the InGaP layer, and the GaAs layer form a high-value capacitor having a capacitance density is at least 2.0 fF/ ⁇ m 2 .
• the present disclosure relates to a metallization structure that includes a first-type gallium arsenide (GaAs) layer and a second-type indium gallium phosphide (InGaP) layer disposed over the GaAs layer, with the second-type being different than the first type.
• the metallization structure further includes a tantalum nitride (TaN) layer disposed over the InGaP layer, and a metal layer disposed over the TaN layer.
• the TaN layer can be configured as a barrier layer between the metal layer and the InGaP layer to reduce the likelihood of the metallization structure behaving in an ohmic manner.
• the first-type GaAs layer can include a p-type GaAs layer; and the second-type InGaP layer can include an n-type InGaP layer.
• the metal layer includes an M1 metal layer.
• the metallization structure can further include a metal contact disposed relative to the GaAs layer so as to facilitate electrical connection with the GaAs layer.
• the InGaP layer can be dimensioned such that the structure provides a capacitance density greater than or equal to a selected value when capacitance is measured between the metal layer and the metal contact.
• a selected value of capacitance density can be at least 2.0 fF/ ⁇ m 2 .
• the first-type GaAs layer can be part of a base of a heterojunction bipolar transistor (HBT), and the second-type InGaP layer can be part of an emitter of the HBT.
• the emitter can have a ledge.
• the present disclosure relates to a heterojunction bipolar transistor (HBT) having a semi-insulating gallium arsenide (GaAs) substrate, a collector layer disposed over the substrate, a first-type GaAs base layer disposed over the collector, and a second-type indium gallium phosphide (InGaP) emitter layer disposed over the base layer, with the second-type being different than the first type.
• the HBT further includes a tantalum nitride (TaN) layer disposed over the emitter layer, and a metal layer disposed over the TaN layer.
• the HBT can further include a sub-collector layer disposed between the collector layer and the GaAs substrate.
• the sub-collector layer can include n+ GaAs
• the collector layer can include n ⁇ GaAs
• the base layer can include p+ GaAs
• the emitter layer can include n ⁇ InGaP.
• the present disclosure relates to a gallium arsenide (GaAs) die having an integrated circuit (IC).
• the die includes a metallization structure that includes a first-type GaAs layer; a second-type indium gallium phosphide (InGaP) layer disposed over the GaAs layer, with the second-type being different than the first type; a tantalum nitride (TaN) layer disposed over the InGaP layer; and a metal layer disposed over the TaN layer.
• the metallization structure can be part of a capacitor. In some embodiments, the metallization structure can be part of a heterojunction bipolar transistor.
• the present disclosure relates to a packaged module that includes a packaging substrate and a gallium arsenide (GaAs) die mounted on the packaging substrate and having an integrated circuit (IC).
• the die includes a metallization structure that includes a first-type GaAs layer; a second-type indium gallium phosphide (InGaP) layer disposed over the GaAs layer, with the second-type being different than the first type; a tantalum nitride (TaN) layer disposed over the InGaP layer; and a metal layer disposed over the TaN layer.
• the present disclosure relates to a radio-frequency (RF) device that includes an antenna and a transceiver coupled to the antenna and configured to process RF signals.
• the RF device further includes an integrated circuit (IC) that is coupled to or is part of the transceiver.
• IC integrated circuit
• the IC is implemented on a gallium arsenide (GaAs) die, and IC includes a metallization structure that includes a first-type GaAs layer; a second-type indium gallium phosphide (InGaP) layer disposed over the GaAs layer, with the second-type different than the first type; a tantalum nitride (TaN) layer disposed over the InGaP layer; and a metal layer disposed over the TaN layer.
• GaAs gallium arsenide
• IC includes a metallization structure that includes a first-type GaAs layer; a second-type indium gallium phosphide (InGaP) layer disposed over the GaAs layer, with the second-type different than the first type; a tantalum nitride (TaN) layer disposed over the InGaP layer; and a metal layer disposed over the TaN layer.
• a metallization structure that includes a first-type Ga
• the present disclosure relates to a method for fabricating a metalized semiconductor structure.
• the method includes forming or providing a first-type gallium arsenide (GaAs) layer, and forming a second-type indium gallium phosphide (InGaP) layer over the GaAs layer, with the second-type being different than the first type.
• the method further includes forming a tantalum nitride (TaN) layer over the InGaP layer, and forming a metal layer over the TaN layer.
• TaN tantalum nitride
• the present disclosure relates to a method for fabricating a heterojunction bipolar transistor (HBT).
• the method includes providing or forming a semi-insulating gallium arsenide (GaAs) substrate, forming a collector layer over the substrate, forming a first-type GaAs base layer over the collector, and forming a second-type indium gallium phosphide (InGaP) emitter layer over the base layer, with the second-type being different than the first type.
• the method further includes forming a tantalum nitride (TaN) layer over the emitter layer, and forming a metal layer over the TaN layer.
• such an HBT can include an NPN HBT.
• the present disclosure relates to a system for monitoring a heterojunction bipolar transistor (HBT) fabrication process.
• the system includes a component configured to metalize an emitter with a ledge that includes indium gallium phosphide (InGaP).
• the system further includes a monitoring component configured to measure capacitance associated with the metalized emitter, where the measured capacitance is representative of thickness of the emitter.
• the thickness of the emitter can be calculated from the measured capacitance based on an approximation that the metalized emitter behaves as a parallel-plate capacitor.
• the system can further include a process control component configured to adjust at least a part of the HBT fabrication process if the measured capacitance or the calculated emitter thickness is outside of a desired range.
• the present disclosure relates to a method for monitoring a heterojunction bipolar transistor (HBT) fabrication process.
• the method includes metalizing an emitter by providing or forming an indium gallium phosphide (InGaP) emitter; forming a tantalum nitride (TaN) layer and a metal layer so that the TaN layer acts as a barrier layer between the metal layer and the emitter.
• the method further includes measuring capacitance associated with the metalized emitter to obtain an estimate of a thickness of the emitter.
• the present disclosure relates to a metallization structure that includes a selected semiconductor layer, a metal layer, and a tantalum nitride (TaN) layer disposed between the metal layer and the selected semiconductor layer so as to act as a barrier layer.
• the selected semiconductor includes wide bandgap semiconductor lattice-matched to gallium arsenide (GaAs).
• the selected semiconductor layer can include an indium gallium phosphide (InGaP) layer.
• FIGS. 1A and 1B schematically depict a capacitor such as a high-value capacitor and a heterojunction bipolar transistor (HBT) having one or more features as described herein.
• HBT heterojunction bipolar transistor
• FIG. 2 shows that in some implementations, an integrated circuit (IC) can include the capacitor and/or the HBT of FIG. 1 .
• IC integrated circuit
• FIG. 3 shows that one or more ICs of FIG. 2 can be implemented on a semiconductor die.
• FIG. 4A schematically shows that in some implementations, a packaged module can include one or more ICs of FIG. 2 .
• FIGS. 4B and 4C show different views of a more specific example of the packaged module of FIG. 4A .
• FIG. 5A schematically shows that in some implementations, a radio-frequency (RF) device such as a wireless device can include the module of FIG. 4 .
• RF radio-frequency
• FIG. 5B shows a more specific example of a wireless device.
• FIG. 6 shows an example configuration of an HBT having a barrier layer such as a tantalum nitride (TaN) layer disposed between an emitter having a ledge and an M1 conductor.
• a barrier layer such as a tantalum nitride (TaN) layer disposed between an emitter having a ledge and an M1 conductor.
• FIG. 7 shows a portion of the example HBT of FIG. 6 that can function as a high-value capacitor.
• FIGS. 8A and 8B show layout and side sectional views of the example capacitor of FIG. 7 .
• FIG. 9 shows that the example metallization structure of FIGS. 7 and 8 can behave as a diode and not in an ohmic manner.
• FIG. 10 shows examples of capacitance values measured for the metallization structure of FIGS. 7 and 8 having different areas for the TaN layer.
• FIGS. 11 and 12 shows additional details of the capacitance values, where active and implanted configurations can extend ranges of voltages having desired capacitance.
• FIG. 13 shows a process that can be implemented to fabricate the example metallization structure of FIGS. 7 and 8 .
• FIG. 14 shows a process that can be implemented to fabricate the example HBT structure of FIG. 6 .
• FIG. 15 shows a process that can be implemented as a more specific example of the process of FIG. 14 .
• FIG. 16 schematically depicts an HBT process monitoring system capable of monitoring formation of an InGaP emitter with a ledge.
• FIG. 17 shows a process that can be implemented to fabricate the InGaP emitter and metallization thereon, test the wafer to determine thickness of the emitter, and perform process control based on the test.
• FIG. 18 shows an example distribution of measured capacitance density (fF/ ⁇ m 2 ) across an example wafer being tested.
• FIG. 19 shows an example distribution of ledge thickness (angstrom) calculated from the measured capacitance.
• FIG. 20 shows an example of averaged ledge thickness variation across the example wafer.
• InGaP (indium gallium phosphide)/GaAs (gallium arsenide) heterojunction bipolar transistors (HBT) are widely used for wireless applications since they have excellent features such as high power density and high efficiency.
• InGaP emitter structures can offer significant performance advantages over AlGaAs emitter structures. For example, InGaP emitter HBTs can exhibit improvements in temperature and bias stability, as well as significantly enhanced reliability. Further InGaP emitter HBTs can also be easier to fabricate.
• Performance and reliability of an HBT can be greatly influenced by an emitter and the effectiveness of its ledge.
• a ledge typically reduces the recombination current to thereby provide better device scaling and improved reliability.
• Such effectiveness in desirable functionality can be based on the thickness of the emitter/ledge.
• an emitter of an HBT includes a ledge feature. Such a combination is sometimes referred to as an “emitter/ledge” or simply as an “emitter.” It will be understood, however, that one or more features of the present disclosure can also be implemented in HBTs where an emitter does not include a ledge.
• a ledge monitor can be achieved by using a first interconnect metal (M1) layer as a top electrode.
• the metal layer such as a Ti/Pt/Au stack, can be deposited directly on the AlGaAs passivation ledge to form a MIS (metal-insulator-semiconductor) capacitor between M1 and the HBT base (e.g., p+ base).
• MIS metal-insulator-semiconductor
• Described herein are devices and methodologies related to a metallization structure that allows effective way of monitoring of InGaP ledges.
• an InGaP ledge can be part of a GaAs HBT, and/or a high-value capacitor.
• TaN tantalum nitride
• M1 first metal
• M1 first metal
• a TaN barrier layer between M1 and InGaP layer can be formed using deposition methods such as physical vapor deposition (PVD) such as sputtering, evaporation, chemical vapor deposition (CVD), metal organic CVD (MOCVD), plasma assisted CVD (PACVD), and metal organic atomic layer deposition (MOALD).
• PVD physical vapor deposition
• CVD chemical vapor deposition
• MOCVD metal organic CVD
• PCVD plasma assisted CVD
• MOALD metal organic atomic layer deposition
• Such a TaN barrier layer can have a thickness in a range of, for example, 10 nm to 200 nm, 20 nm to 100 nm, 30 nm to 70 nm, or 40 nm to 60 nm. In the various examples described herein, the TaN barrier layer has a thickness of about 50 nm.
• InGaP InGaP is an example of wide bandgap semiconductor lattice-matched to gallium arsenide (GaAs). Accordingly, selected semiconductors can include wide bandgap semiconductors that are lattice-matched, substantially lattice-matched, or capable of being lattice-matched to GaAs.
• FIG. 1A schematically shows that one or more features related to metallization of InGaP (such as an InGaP emitter) with a barrier (such as a TaN layer) can be implemented in a capacitor 10 .
• a capacitor can have a relatively high-value capacitance density of about 3 fF/ ⁇ m 2 at about zero volt, which is about twice as much as that of a similarly sized stack capacitor.
• a capacitor having metalized InGaP with a TaN barrier as described herein can have a capacitance density that is at least 2.8 fF/ ⁇ m 2 , 2.5 fF/ ⁇ m 2 , or 2.0 fF/ ⁇ m 2 .
• FIG. 1B schematically shows that one or more features related to the metallization of InGaP as described herein can be implemented in an HBT 12 .
• an HBT can have an InGaP emitter whose quality (such as thickness) can be monitored during fabrication. Examples of such ledge monitoring are described herein in greater detail.
• FIG. 2 shows that in some embodiments, a capacitor 10 and/or an HBT 12 having one or more features as described herein can be implemented in an integrated circuit (IC) 20 .
• the IC 20 can include circuits that utilize HBTs.
• the IC 20 can include radio-frequency (RF) related circuits where high power efficiency is desired. More specifically, the IC 20 can include circuits for RF power amplifiers configured for wireless devices.
• the IC 20 can include circuits where high capacitance density is desired. More specifically, power amplifiers, tuning networks, and power supply bypass circuits are examples where one or more of such capacitors can provide beneficial functionalities.
• FIG. 3 shows that in some embodiments, one or more ICs of FIG. 2 can be implemented as part of a semiconductor die 30 .
• a first IC 20 is depicted as including a high-value capacitor 10 ; and a second IC 20 is depicted as including an HBT 12 .
• each of the example ICs can include either or both of the capacitor 10 and the HBT 12 .
• the die 30 can include a GaAs die. In some embodiments, the die 30 can be configured for mounting onto a substrate such as a laminate to accommodate wirebond or flip-chip connections.
• FIG. 4A schematically shows that in some embodiments, an IC 20 having a capacitor 10 and/or an HBT 12 as described herein can be implemented in a packaged module 40 .
• an IC can be implemented on a die (e.g., die 30 of FIG. 3 ).
• the module 40 can further include one or more packaging structures 44 that provide, for example, a mounting substrate and protection for the IC 20 of the die 30 .
• the module 40 can further include connection features 42 such as connectors and terminals configured to provide electrical connections to and from the IC 20 .
• FIGS. 4B and 4C show a plan view and a side view of a module 40 that can be a more specific example of the module 40 of FIG. 4A .
• the example module 40 can include a packaging substrate 44 that is configured to receive a plurality of components.
• such components can include an HBT die 20 having one or more featured as described herein.
• the die 20 can include an HBT and/or a capacitor having one or more features described herein.
• such an HBT and/or a capacitor can be part of a power amplifier 12 .
• a plurality of connection pads 45 formed on the die 20 can facilitate electrical connections such as wirebonds 42 to connection pads 46 on the substrate 44 to facilitate passing of various signals to and from the die 20 .
• the components mounted on the packaging substrate 44 or formed on or in the packaging substrate 44 can further include, for example, one or more surface mount devices (SMDs) (e.g., 47 ) and one or more matching networks (not shown).
• the packaging substrate 44 can include a laminate substrate.
• the module 40 can also include one or more packaging structures to, for example, provide protection and facilitate easier handling of the module 40 .
• a packaging structure can include an overmold 43 formed over the packaging substrate 44 and dimensioned to substantially encapsulate the various circuits and components thereon.
• module 40 is described in the context of wirebond-based electrical connections, one or more features of the present disclosure can also be implemented in other packaging configurations, including flip-chip configurations.
• FIG. 5A schematically shows that in some embodiments, a component such as the module 40 of FIG. 4 can be included in an RF device 50 .
• an RF device can include a wireless device such as a cellular phone, smart phone, tablet, or any other portable device configured for voice and/or data communication.
• the module 40 is depicted as including a capacitor 10 and/or an HBT 12 as described herein.
• the RF device 50 is depicted as including other common components such an antenna 54 , and also configured to receive or facilitate a power supply 52 such as a battery.
• FIG. 5B shows a more specific example of how the wireless device 50 of FIG. 5A can be implemented.
• an example wireless device 50 is shown to include a module 40 (e.g., a PA module) having one or more features as described herein.
• the PA module 40 can include a plurality of HBT power amplifiers 12 configured to provide amplifications for RF signals associated with different bands and/or modes.
• the PA module 40 can provide an amplified RF signal to the switch 66 (via a duplexer 64 ), and the switch 66 can route the amplified RF signal to an antenna 54 .
• the PA module 40 can receive an unamplified RF signal from a transceiver 65 that can be configured and operated in known manners.
• the transceiver 65 can also be configured to process received signals.
• the transceiver 65 is shown to interact with a baseband sub-system 63 that is configured to provide conversion between data and/or voice signals suitable for a user and RF signals suitable for the transceiver 65 .
• the transceiver 65 is also shown to be connected to a power management component 62 that is configured to manage power for the operation of the wireless device 50 .
• a power management component can also control operations of the baseband sub-system 63 and other components of the wireless device 50 .
• the baseband sub-system 63 is shown to be connected to a user interface 60 to facilitate various input and output of voice and/or data provided to and received from the user.
• the baseband sub-system 63 can also be connected to a memory 61 that is configured to store data and/or instructions to facilitate the operation of the wireless device, and/or to provide storage of information for the user.
• the duplexer 64 can allow transmit and receive operations to be performed simultaneously using a common antenna (e.g., 54 ).
• a common antenna e.g., 54
• received signals are shown to be routed to “Rx” paths (not shown) that can include, for example, a low-noise amplifier (LNA).
• LNA low-noise amplifier
• the example duplexer 64 is typically utilized for frequency-division duplexing (FDD) operation. It will be understood that other types of duplexing configurations can also be implemented.
• a wireless device having a time-division duplexing (TDD) configuration can include respective low-pass filters (LPF) instead of the duplexers, and the switch (e.g., 66 in FIG. 5B ) can be configured to provide band selection functionality, as well as Tx/Rx (TR) switching functionality.
• TDD time-division duplexing
• LPF low-pass filters
• TR Tx/Rx
• a wireless device does not need to be a multi-band device.
• a wireless device can include additional antennas such as diversity antenna, and additional connectivity features such as Wi-Fi, Bluetooth, and GPS.
• FIG. 6 shows an example of an HBT 12 structure having an InGaP emitter (with a ledge) 122 (such as an n ⁇ InGaP) metalized with a conductor 130 (such as an M1 layer) over a barrier layer 126 (such as a TaN layer).
• a metalized emitter is shown to be disposed over a base layer 120 (such as a p+ GaAs layer).
• Base contacts 124 are shown to be disposed over the base layer 120 so as to facilitate electrical connection with the base layer 120 .
• an assembly that includes the M1 layer 130 , the TaN barrier layer 126 , the InGaP emitter 122 , the base layer 120 , and the base contacts 124 can be considered to be a high-value capacitor 10 . Additional details concerning such a capacitor are described herein.
• FIG. 6 further shows that the foregoing assembly that can act as the capacitor 10 can be disposed over a collector layer 118 (such as an n ⁇ GaAs layer).
• the collector layer 118 can, in turn, be disposed over a sub-collector layer 114 (such as an n+ GaAs layer).
• Collector contacts 116 can also be disposed over the sub-collector layer 114 .
• the sub-collector layer 114 can, in return, be disposed over a semi-insulating substrate 110 (such as a semi-insulating GaAs substrate).
• FIG. 6 further shows that a passivation structure 128 can be formed about the emitter 122 and the base 120 . Access to the base contacts 124 is shown to be provided by openings 132 defined by the passivation structure 128 .
• the HBT 12 can further include isolation structures 112 configured to provide isolation for the HBT 12 .
• example HBT structure 12 is described in the context of an NPN GaAs configuration, other configurations such as PNP GaAs can also benefit from one or more features as described herein. Further, a concept of metalizing an emitter layer of an HBT with a barrier layer such as a TaN layer can also be implemented in other types of HBTs.
• FIG. 7 shows an enlarged view of the capacitor structure 10 described in reference to FIG. 6 .
• a TaN layer can be used as the barrier layer 126
• an M1 metal layer can be used as the conductor 130 .
• An assembly formed in the foregoing manner can yield a diode configuration 150 having a Schottky behavior (depicted as 152 ) for the M1 electrode 130 , leading to a desired MIS capacitor formation.
• the junction between the base layer 120 and the emitter layer 122 can behave as a diode 154 as shown.
• the capacitor structure 10 can be a part of an HBT ( 12 ) structure. In some embodiments, the capacitor structure 10 can be utilized as a high-value capacitor without being associated with an HBT.
• FIGS. 8A and 8B show layout and side sectional views of an example capacitor structure 10 that can be implemented based on the examples of FIGS. 6 and 7 .
• a base layer 120 is depicted as being a rectangular shaped region formed over an underlying layer 202 .
• An emitter (with a ledge) 122 is depicted as being a rectangular region formed over and within the area of the base layer 120 .
• An opening 132 for providing electrical connections to base contacts 124 (not shown in FIG. 8A ) is depicted as a via having a footprint in an inverted-U shape.
• the base contacts 124 are shown to be connected to an M1 metal layer 204 through conductors 206 .
• the example M1 metal layer 204 is depicted as also having an inverted-U shaped footprint.
• FIGS. 8A and 8B further show that a TaN barrier layer 126 can be formed over the emitter 122 and have a rectangular shaped footprint. Such a rectangle can be dimensioned (length L and width W) so as to be nested within the inverted-U shape of the M1 metal layer 204 .
• the TaN barrier layer 126 is also depicted as having a thickness ( 208 in FIG. 8B ).
• An M1 metal layer 130 is shown to be formed over the TaN barrier layer 126 and have an inverted-T shaped footprint.
• the TaN layer 126 can be dimensioned so that the leg portion of the T-shape covers the TaN barrier 126 and also be nested within the inverted-U shape of the M1 metal layer 204 .
• FIG. 9 shows I-V curves for the capacitor structure 10 ( FIGS. 7 and 8 ) having different values of the TaN layer area.
• the measured (between the emitter terminal 130 and the base terminal 204 ) I-V curves show that the devices tested have a desired Schottky behavior indicative of desired InGaP ledge thicknesses and quality. If the InGaP ledge is too thin, such an I-V curve can behave almost like a tunnel diode (with very low turn-on voltage due to the thin InGaP layer) between the TaN layer and the p-type base layer.
• FIG. 10 shows capacitance curves (measured between the emitter terminal 130 and the base terminal 204 ) as a function of voltage for the capacitor structure 10 ( FIGS. 7 and 8 ) having different values of the TaN layer area. Since the capacitor structure 10 can be approximated as a parallel-plate capacitor (where capacitance C is proportional to area), the measured capacitance values increase as the area increases, as expected. Since the parallel-plate capacitance C is also inversely proportional to the gap distance between the electrodes, a measured capacitance value will be approximately inversely proportional to the thickness of the emitter for a given TaN layer area. Accordingly, such capacitance measurement can provide information about the emitter thickness. An example application of such thickness determination is described herein in greater detail.
• FIG. 10 further shows that one or more layers of the capacitor structure 10 can be configured to adjust its operating voltage range.
• data points include those belonging to “active” and “implanted” configurations.
• the “implanted” data points generally start from the left side (less than ⁇ 2V), and the “active” data points generally start from about ⁇ 1.5V.
• an active configuration refers to epitaxial layers as grown; and an implant configuration refers to a damage implant in a process meant to disrupt the crystal lattice and thus provide electrical isolation between devices.
• the implant may damage both the emitter and the base, although its target is much deeper.
• the active cases are shown to have a desirable operating range (where capacitance is generally flat) between about ⁇ 1V to about +4V, while the implanted cases generally operate between about ⁇ 2V to about +3V.
• FIGS. 11 and 12 show more pronounced deviations from the desired flatness response.
• FIG. 11 shows a plot of area capacitance density (F/ ⁇ m 2 ) for active and implanted cases; and
• FIG. 12 shows a plot of fringe (peripheral) capacitance (F/ ⁇ m) of the emitter.
• F/ ⁇ m 2 area capacitance density
• FIG. 12 shows a plot of fringe (peripheral) capacitance (F/ ⁇ m) of the emitter.
• the implanted case's deviation at about +3V is readily apparent, while the active case extends out to about +4V.
• the active case's deviation at about ⁇ 1V is also readily apparent, while the implanted case extends out to about ⁇ 2V.
• the examples in FIGS. 10-12 show that the operating voltage range can be adjusted as needed or desired. For example, if it is desired to have an extended range in the negative voltage side, implantation can provide such an extension. In another example, if it is desired to have an extended range in the positive voltage side, maintaining an active configuration can provide such an extension.
• FIG. 13 shows a process 300 that can be implemented to fabricate a capacitor structure having one or more features as described herein.
• an active layer can be formed or provided.
• such an active layer can include a p+ GaAs layer.
• an InGaP layer can be formed over the active layer.
• a TaN layer can be formed over the InGaP layer.
• a metal layer can be formed over the TaN layer, such that the TaN layer acts as a barrier layer between the metal layer and the InGaP layer.
• an electrical contact for the active layer can be formed. In some implementations, the metal layer and the electrical contact can act as electrodes if the capacitor structure is utilized as a capacitor element.
• FIG. 14 shows a process 320 that can be implemented to fabricate an HBT structure having one or more features as described herein.
• a substrate can be formed or provided.
• such a substrate can include a semi-insulating GaAs substrate.
• a collector can be formed over the substrate.
• such a collector can include an n+ GaAs sub-collector layer formed over the substrate, and an n ⁇ GaAs collector layer formed over the sub-collector layer.
• a base can be formed over the collector.
• such a base can include a p+ GaAs base layer formed over the collector layer.
• an emitter having a ledge can be formed over the base.
• such an emitter can include an n ⁇ InGaP emitter layer formed over the base layer.
• a barrier can be formed over the emitter.
• such a barrier can include a TaN barrier layer formed over the emitter layer.
• a metal structure can be formed over the barrier so that the barrier is between the metal structure and the emitter.
• such a metal structure can include an M1 metal layer formed over the barrier layer.
• Other structures such as contacts for the base and the collector can also be formed at appropriate stages.
• FIG. 15 shows a process 340 that can be implemented as a more specific example of the process 320 of FIG. 14 .
• a semi-insulating GaAs substrate can be provided.
• an n+ GaAs sub-collector layer can be formed over the substrate.
• an n ⁇ GaAs collector layer can be formed over the sub-collector layer.
• a p+ GaAs base layer can be formed over the collector layer.
• an n ⁇ InGaP emitter layer can be formed over the base layer.
• a TaN barrier layer can be formed over the emitter layer.
• an M1 metal layer can be formed so that the TaN barrier layer is between the M1 layer and the InGaP emitter layer.
• FIG. 16 shows that in some implementations, one or more features described herein can be utilized in an HBT process monitoring system 400 .
• a system can include, for example, a component 402 configured to form InGaP emitters. In some implementations, such emitters can be formed on a wafer so as to facilitate fabrication of a plurality of HBT devices.
• the system 400 can also include a component 404 configured to perform capacitance measurements. Such a component can perform measurements of capacitance of a capacitor structure described herein, where the thickness of the emitter can influence capacitance.
• the system 400 can also include a component 406 configured to perform process control. Such a component can monitor the thickness of emitters being formed based on the capacitance measurements, and perform maintenance or adjustment to the emitter-formation process so as to yield emitters having desired properties such as a desired thickness.
• FIG. 17 shows a process 410 that can be performed by, or to facilitate, the HBT process monitoring system 400 of FIG. 16 .
• the process 410 can generally include a sub-process (e.g., 412 to 420 ) for partial fabrication of an HBT device, a sub-process (e.g., 430 and 432 ) for measurement of such a device, and a sub-process (e.g., 450 ) for process control based on such a measurement.
• a sub-process e.g., 412 to 420
• a sub-process e.g., 430 and 432
• a sub-process e.g., 450
• a base layer (e.g., p+ GaAs) can be formed on a wafer. In some implementations, such a wafer can already include other HBT components (e.g., sub-collector and collector layers).
• an InGaP emitter can be formed over the base layer.
• an electrical connection can be formed for the base layer. In some implementations such an electrical connection can include base contacts (e.g., 124 in FIG. 6 ).
• a TaN layer can be formed over the InGaP emitter.
• a metal layer (e.g., M1 metal layer) can be formed over the TaN layer.
• capacitance can be measured between the metal layer associated with the InGaP emitter and the electrical connection associated with the base layer.
• thickness of the InGaP emitter can be calculated based on the measured capacitance. An example of how such thickness can be calculated is described herein in greater detail.
• process control can be performed based on the calculated thickness of the InGaP emitter.
• Such process control can include, for example, maintenance or adjustment to the InGaP emitter formation process so as to yield emitters having a thickness within a desire range.
• FIGS. 18-20 show examples of measurements and calculated values associated with InGaP emitters formed at various locations on a sample wafer.
• FIG. 18 shows a normal quantile plot of capacitance density measurements as well as a distribution of the capacitance density values. As shown, the average capacitance density is about 3.00 fF/ ⁇ m 2 .
• FIG. 19 shows a normal quantile plot of emitter ledge thickness values calculated from the capacitance measurements as well as a distribution of the thickness values.
• various capacitor structures described herein can be approximated as a parallel-plate capacitor. Accordingly, capacitance C can be expressed as
• ⁇ r represents relative permittivity or dielectric constant (about 11.75 for InGaP)
• ⁇ 0 represents electric constant (approximately 8.854 ⁇ 10 ⁇ 12 F/m)
• A represents area
• d represents thickness.
• thickness (d) values can be calculated from capacitance density (C/A) values.
• a distribution of emitter thickness values across the sample wafer is depicted as a contour plot in FIG. 20 .
• the center area has smaller thickness values (e.g., about 330 angstroms); and the edge portions have larger thickness values (e.g., about 350 angstroms).
• a number of process verifications and/or adjustments can be achieved. For example, suppose that an acceptable range of emitter thickness includes all of the monitored thickness values. Then, the monitoring process has verified that at least the emitter formation portion is being achieved in a desirable manner. In another example, suppose that substantially all of the monitored thickness values are outside of the acceptable range. Then, there may be some systematic problem that needs to be identified and fixed. In yet another example, suppose that thickness values are too small at one location of the wafer and/or too large at another location. Then, it may be possible to refine the emitter deposition technique to obtain a more uniform distribution of thickness values across the wafer.
• the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.”
• the word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively.

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