US20230147486A1 - Integrated freewheeling diode and extraction device - Google Patents

Integrated freewheeling diode and extraction device Download PDF

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US20230147486A1
US20230147486A1 US18/090,835 US202218090835A US2023147486A1 US 20230147486 A1 US20230147486 A1 US 20230147486A1 US 202218090835 A US202218090835 A US 202218090835A US 2023147486 A1 US2023147486 A1 US 2023147486A1
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extraction
extraction device
main switch
igbt
fwd
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US18/090,835
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Dumitru G. Sdrulla
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MW RF Semiconductors LLC
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MW RF Semiconductors LLC
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Definitions

  • This disclosure relates to semiconductor devices, and, more particularly, to a semiconductor structure that includes a Freewheeling Diode coupled to a forced carrier Extraction Device that improves the switching speed of a Main Switch for which the turn-off process depends on the recombination speed of charge carriers.
  • IGBTs Insulated Gate Bi-Polar Transistors
  • IGBTs include a built-in diode, but the built-in diode cannot be used as a FWD because of the P-type injector layer, which causes the built-in diode of the IGBT on the backside of the IGBT to have an orientation opposite that of a Mosfet.
  • the diode in an IGBT is formed at the intersection of the P-wells and N-type drift layer, for instance, or at the intersection of an N-well for a P-type IGBT.
  • the injector layer of the IGBT provides the conductivity modulation of the drift region while the IGBT is conducting, which makes the IGBT such a well-performing device from an on-conduction point of view. But this same injector layer prevents the built-in diode in an IGBT from acting as an FWD, which is why nearly all IGBTs are equipped with a separate FWD in most power applications.
  • SiC SBDs Silicon Carbide Schottky Barrier Diodes
  • Extraction Plugs which are described in detail in the incorporated '832 application, may be formed or placed inside the Main Switch, such as an IGBT, such that the electrical performance of the Main Switch is not degraded in any way. Although such Extraction Plugs may speed up a power semiconductor switch when coupled to an Extraction Device to remove charge in the drift region during the turn-off process of the switch, forming the Extraction Device itself may involve extra process steps compared to forming the IGBT itself.
  • Embodiments of the disclosure address these and other limitations of the prior art.
  • FIG. 1 is a conceptual schematic diagram of a switch having an Extraction terminal, connected to a voltage-controlled Extraction Device, according to embodiments of this disclosure.
  • FIG. 2 is a schematic diagram of a complementary IGBT having an injecting PNP transistor, as well as a P-channel MOSFET, and an N-channel MOSFET coupled in series, according to embodiments of the disclosure.
  • FIG. 3 is a simplified schematic diagram illustrating an IGBT switching device, having emitter, collector, and gate terminals, and further illustrating an Extraction Plug connection, to which an Extraction Device may be connected, according to embodiments of the disclosure.
  • FIG. 4 is a schematic of a known voltage-controlled Main Switch, such as an IGBT, having a free-wheeling diode connected in parallel to the switch.
  • FIG. 5 is a schematic diagram illustrating a Main Switch, a Freewheeling Diode, and an Extraction Device, according to embodiments of the invention.
  • FIG. 6 is a cross-sectional diagram of a Freewheeling Diode and an Extraction Device, according to embodiments of the invention.
  • FIG. 7 is a cross-sectional diagram illustrating a Freewheeling Diode, high-voltage termination, and a multi-cell PMOS formed on a semiconductor substrate, according to embodiments of the invention.
  • FIG. 8 is a cross-sectional diagram of a lateral PMOS Extraction Device and a high voltage capacitor according to embodiments of the invention.
  • FIG. 9 is a cross-sectional diagram of a vertical PMOS Extraction Device and a high voltage capacitor according to embodiments of the invention.
  • FIG. 10 is a top layout view of an integrated FWD with an Extraction Device, placed outside of the high voltage termination of the FWD, according to embodiments of the invention.
  • FIG. 11 is a top layout view of an integrated FWD with an Extraction Device, interspaced in the active area of the die, according to embodiments of the invention.
  • FIG. 12 is a top layout view of a voltage controlled Main Switch having an output on the backside of the die, according to embodiments of the invention.
  • FIG. 13 is a top assembly view of a voltage controlled Main Switch having Extraction Plugs formed around an edge of the die, according to embodiments of the invention.
  • the present disclosure relates to the field of power semiconductors with conductivity modulation, like IGBTs and its variants, which are structured or used to switch inductive loads.
  • a Freewheeling Diode is commonly used when the switching device, like the IGBT, has to commutate On and Off current through an inductance.
  • IGBTs remain an excellent choice for those semiconductor devices carrying relatively large amounts of current, so called power devices, the slow switching speeds caused by the slow recombination of minority carriers in conductivity-modulation bipolar devices after switching off continues to inhibit their performance.
  • Including Extraction Plugs and an Extraction Device in a three terminal device that uses conductivity modulation can greatly improve its switching speed, as described below.
  • Benefits of including an Extraction Device in conjunction with a power semiconductor device are described with reference to FIGS. 1 - 3 .
  • Benefits of including FWDs with power semiconductor devices that also include an Extraction Device are described with reference to FIGS. 4 - 13 .
  • FIG. 1 is a conceptual schematic diagram of a combined device 100 that generally includes a Main Switch 110 coupled to an Extraction Device 120 .
  • the device 100 further includes one or more Extraction Plugs 130 formed in the drift layer of the Main Switch 110 .
  • Extraction Plugs are fully described in the previously incorporated U.S. patent application Ser. No. 17/339,832.
  • Extraction Plugs may be formed in devices that use conductivity modulation to provide access to a drift layer of the device.
  • the Extraction Plugs 130 are formed and placed so that they do not degrade, in any way, the performance of the structure 100 , especially its blocking voltage.
  • An Extraction Device 120 also described in the '832 application, turns on when the Main Switch 110 turns off.
  • the Extraction Device 120 works to remove charge carriers left over in the bulk region when the Main Switch 110 turns off through the Extraction Plug 130 of the Main Switch.
  • the forced Extraction Device 120 is preferably voltage controlled, and its blocking voltage between terminals is generally the same or higher than the blocking voltage of the Main Switch 110 .
  • the structure 100 of FIG. 1 may be structured as a three-terminal device.
  • the structure 100 includes an input terminal coupled to an input 112 of the Main Switch 110 and to an input 122 of the Extraction Device 120 , and an output terminal 126 coupled to an output of the Extraction Device 120 .
  • the structure 100 further includes a ground terminal 114 coupled to the Main Switch 110 . Because the inputs 112 , 122 of the Main Switch 110 and Extraction Device 120 are tied together, the input signal driving the input 112 of the Main Switch 110 also drives the input 122 of the Extraction Device 120 .
  • the Extraction Device 120 may be integrated on the same die as the Main Switch 110 , or it may be a discrete device formed on a separate semiconductor substrate that is electrically coupled to the Main Switch. In some embodiments the semiconductor substrate for the Main Switch and a semiconductor substrate for the Extraction Device 120 may be separate substrates but assembled together in a single module or even in a single package.
  • the structure 100 of FIG. 1 conceptually operates as indicated as in Table 1:
  • the Extraction Device 120 In operation, when the Main Switch 110 is ON, the Extraction Device 120 is OFF, and vice-versa. In device operation, i.e., when the Main Switch 110 is conducting, the Extraction Device 120 does not interfere or affect the operation of the Main Switch 110 .
  • the operating parameters of a Main Switch 110 coupled to the Extraction Device 120 are the same or similar as a Main Switch that is not coupled to an Extraction Device.
  • the Main Switch 110 has a low breakdown voltage between the input and ground terminals, but a relatively high breakdown voltage between the output and ground terminals.
  • the Extraction Device 120 has a high breakdown voltage between its input and ground terminals, and a relatively low breakdown voltage between the ground and the output terminals.
  • FIG. 2 is a schematic diagram of a circuit 200 including components that may be used to form an example embodiment 200 that functions as the structure 100 of FIG. 1 .
  • the circuit 200 includes an IGBT Main Switch, which is formed of a PNP transistor 250 as an injector and an N-channel Mosfet 270 that drives the PNP transistor.
  • a P-channel Mosfet 260 functions as the Extraction Device 120 of FIG. 1 .
  • the Mosfets 260 and 270 are coupled in series.
  • the device 200 may be integrated on a single semiconductor die.
  • the P-Channel Mosfet 260 may be formed on a separate semiconductor die and electrically connected to the N-Channel Mosfet 270 .
  • the IGBT Main Switch further include a collector 216 , and an emitter 214 .
  • the P-Channel Mosfet 260 which operates as the Extraction Device, includes a source 224 and a drain 226 . Since the output terminal of the device 200 , in this configuration, is coupled to both the collector 216 of the IGBT and the drain 226 of the P-Channel Mosfet 260 , it is labeled as Output/Drain/Collector. Similarly, the ground terminal is coupled to the emitter 214 of the IGBT and the source of the N-Channel Mosfet 270 , the ground terminal is labeled Ground/Source/Emitter.
  • the input terminal of the device 200 is coupled to the gates of both the N-Channel Mosfet 270 and the P-Channel Mosfet 260 , the input terminal is labeled Input/Gate.
  • an Extraction Plug for the IGBT would be coupled to the base of the PNP transistor 250 , which is in the drift region of the IGBT, and is labeled as reference 280 .
  • the Extraction Plug, or reference 280 is electrically coupled to a source of the P-Channel Mosfet 260 .
  • the base of the PNP 250 transistor is connected to a ground at the source of the MOSFET 270 , while the device 200 is conducting. Then, when the Input/gate voltage goes LOW, to turn off the device 200 , the N-channel MOSFET 270 turns OFF, while the P-channel MOSFET 260 turns ON.
  • the P-Channel MOSFET 260 turning ON provides a path for excess charge to be removed from the drift region 280 from the source of the P-Channel Mosfet 260 to the drain of the P-Channel Mosfet, which is coupled to the output of the device 200 .
  • the P-Channel MOSFET 260 is formed so that, when the gate voltage is HIGH, the P-Channel MOSFET 260 is OFF, and turns on when the gate voltage goes LOW.
  • the P-Channel MOSFET 260 operates similar to that of a resistor, with its drain coupled to the positively bias on the collector 216 of the PNP 250 . Therefore, electrons are pulled toward the positively biased drain electrode of the P-Channel MOSFET 260 , and charge is removed from the drift region 280 at a relatively constant rate.
  • the P-Channel MOSFET 260 provides a path for the charge, carried by electrons, to be removed from the drift layer 280 through the positively charged drain.
  • the Extraction Device which here is the P-channel MOSFET 260 , extracts excess carriers relatively quickly from the bulk drift area 280 of the IGBT by conducting them to the collector through the P-channel MOSFET 260 . This action of removing the excess charge carriers when the IGBT turns off significantly decreases the turn-off time of the IGBT.
  • Extraction Plugs are used to provide access to areas of the bulk semiconductor in conductivity modulation devices. These Extraction Plugs, in turn, may be coupled to the source (i.e, the input or extraction terminal) of an Extraction Device to remove the excess carriers from the conductivity modulation device when the conductivity modulation device is being turned off. This greatly reduces the turn-off time of the conductivity modulation device. Further details of the structure of the Extraction Plugs may be obtained from the '832 application, although embodiments of the invention are applicable to other forms of Extraction Plugs providing the same function as that described herein.
  • FIG. 3 is a simple schematic diagram illustrating an IGBT switching device 300 , having emitter, collector, and gate terminals, and further illustrating an Extraction Plug terminal, also called an Extraction Terminal, to which an Extraction Device may be connected.
  • This schematic diagram neatly illustrates the concepts of including one or more Extraction Plugs in the drift region of an IGBT, which, as described above, facilitates the removal of carriers during forced carrier extraction from the drift region through the Extraction Plugs and further through the Extraction Device during turn-off of the Main Switch.
  • the Extraction Plug terminal is electrically connected to the Extraction Plug or Plugs in the IGBT.
  • the Extraction Plug terminal of the IGBT switching device 300 may be further coupled to an Extraction Device, as detailed below.
  • the Extraction Plug and Extraction Device are formed on the same semiconductor substrate, it is not strictly necessary that the Extraction Plug be coupled to an output terminal.
  • the Extraction Plug may be coupled to an Extraction Plug Terminal, which, in turn, may be coupled to an Extraction Device located on a different substrate. In this way, the process steps for forming an IGBT having an Extraction Plugs may be optimized separately from the process steps for forming an IGBT.
  • FIG. 4 is a schematic of a known voltage-controlled Main Switch 10 , such as an IGBT, having an FWD 12 connected in parallel to the switch.
  • FWD Freewheeling Diode
  • FIG. 4 is a schematic of a known voltage-controlled Main Switch 10 , such as an IGBT, having an FWD 12 connected in parallel to the switch.
  • some power semiconductor devices that carry relatively large amounts of current include an FWD, especially those that operate on inductive loads.
  • the FWD is connected in parallel to the main semiconductor switch.
  • the IGBT 10 is a bipolar semiconductor device used for carrying relatively large current loads.
  • the IGBT 10 includes emitter, collector, and gate terminals, which function as the input, output, and gate terminals of the switch.
  • the FWD 12 is coupled in parallel to the IGBT, with one terminal of the FWD coupled to the collector and the other terminal coupled to the emitter.
  • the FWD 12 shunts current from the inductive load across the IGBT 10 as the IGBT turns off, and also limits voltage across the IGBT. Otherwise, the current generated by the collapse of the magnetic field around the inductor would be applied directly to the IGBT 10 , which would likely cause damage. In this way the FWD 12 acts as a protection device for the switch 10 .
  • the FWD 12 is designed and fabricated to withstand the full rated voltage of the Main Switch 10 , including the avalanche rating, or it has to be implemented with a higher blocking voltage than the Main Switch.
  • FIG. 5 is a schematic diagram illustrating a system 500 that includes a Main Switch 510 having an Extraction Plug electrode 512 , an FWD 520 , and an Extraction Device 530 , according to embodiments of the invention.
  • a Main Switch 510 having an Extraction Plug electrode 512 , an FWD 520 , and an Extraction Device 530 , according to embodiments of the invention.
  • the FWD 520 and an Extraction Device 530 are packaged in a separate device 550 , which is electrically connected to the Main Switch 510 .
  • the Main Switch 510 may be a one semiconductor die, and the separate device 550 , including the FWD 520 and an Extraction Device 530 , is formed on another semiconductor die, but both the semiconductor dies are together in a single semiconductor module or package. More details and discussion of possible layouts is given below.
  • System 500 illustrates a three-terminal device capable of driving inductive loads, since the IGBT Main Switch 510 is electrically coupled to the FWD 520 , even though the diode 520 may be formed on a substrate separate from the IGBT Main Switch 510 . Further, since the turn-off time of an IGBT is shortened by coupling an Extraction Device 530 to the Extraction Plug 512 of the IGBT 510 , including an Extraction Device 530 in the system 500 provides the extraction function when the IGBT 510 turns off. Therefore, it may be convenient to produce the IGBT Main Switch 510 with an Extraction Plug terminal 512 separately from a device that includes both an FWD as well as an Extraction Device, such as the device 530 .
  • the system 500 may form a single package or module including one component having the IGBT Main Switch 510 and having another component 550 , which includes the FWD 520 and the Extraction Device 530 . Electrical connections are made within the system 500 as illustrated in FIG. 5 .
  • a gate of the IGBT Main Switch 510 is electrically coupled to an input of the Extraction Device 530 .
  • the Extraction Plug terminal 512 of the IGBT Main Switch 510 is electrically coupled to an extraction input 532 of the Extraction Device 530 .
  • a collector of the IGBT Main Switch 510 is coupled to an output of the Extraction Device 530 .
  • a cathode of the FWD 520 is coupled to a collector of the IGBT Main Switch 510
  • the anode of the FWD 520 is coupled to an emitter of the IGBT Main Switch 510 .
  • the system 500 is created in a discrete package 560 , it could be a three-terminal device with an input control terminal 562 , a ground terminal 564 , and an output terminal 566 .
  • a package 560 includes an IGBT 510 or Main Switch having an Extraction Plug terminal 512 that is coupled to a component 550 .
  • the component 550 includes an FWD 520 and an Extraction Device 530 .
  • This package 560 includes all of the components for a power device for driving an inductive load having a shortened turn-off time compared to typical IGBTs.
  • the FWD 520 is effectively mandatory for any power switch operating with an inductive load.
  • Embodiments of the invention further include the Extraction Device 530 to shorten the turn-off time of the voltage-controlled switch device with conductivity modulation 510 .
  • the Main Switch 510 is illustrated as being an IGBT, embodiments of the invention extend to any voltage-controlled switch device with conductivity modulation.
  • FIG. 6 is a cross-sectional diagram of an integrated device 600 including an FWD 610 and an Extraction Device 620 produced on a same semiconductor substrate, according to embodiments of the invention.
  • the FWD 610 is a merged PN-Schottky structure.
  • the FWD 610 may be any of several different types of FWDs.
  • the FWD 610 may be a PIN (p-type and n-type materials separated by an insulator) diode, and may or may not include materials for shortening carrier lifetimes, such as gold or platinum diffusions, electron or proton irradiations, etc.
  • the FWD 610 may also be a Fast Recovery Diode, for example.
  • the FWD 610 and the Extraction Device 620 of the integrated device 600 are formed on the same semiconductor die, they may be separated by a deep trench 640 , which may be formed using standard fabrication techniques.
  • the deep trench 640 separates the cathode of the FWD 520 ( FIG. 5 ) from the substrate of the lateral PMOS in the Extraction Device 530 . Such separation allows each device to operate virtually independent from one another. It is not necessary that the FWD 610 and the Extraction Device 620 be formed on the same die. In other embodiments the FWD 610 and the Extraction Device 620 may be electrically coupled to one another but formed on separate semiconductor dies.
  • the lateral PMOS Extraction Device 620 includes a thick gate oxide 105 .
  • the Extraction Device 620 is also “counter doped” at the surface of the semiconductor to create conditions for a suitable turn-on voltage, Vth. As represented in this cross section of FIG. 6 , the FWD 610 and the PMOS Extraction Device 620 structures could be formed and interspaced in the active area of the die.
  • the device 600 is an example of the type of structure that could make the component 550 part of the device 500 of FIG. 5 .
  • a polysilicon gate 103 front metal 106 , passivation layer 108 , substrate 150 , such as SiC or other wide bandgap material, N-type drift region 151 , P-Wells 160 , Schottky Metal 165 , and counter-doped region 170 .
  • FIG. 7 is a cross-sectional diagram of a device 700 illustrating an FWD 710 , high-voltage termination 750 , and a multi-cell PMOS Extraction Device 720 formed on any type of semiconductor, such as Silicon, SiC, wide-bandgap material, etc., according to embodiments of the invention.
  • the placement of the Extraction Device 720 in the illustrated embodiment of FIG. 7 is outside of the High Voltage Termination 750 of the FWD 710 , but this placement is not mandatory.
  • the P-Wells 101 of the FWD 710 and Extraction Device 720 can very well operate together to provide a blocking voltage needed for the FWD.
  • Other conventional components of the device 700 not referred to above include a gate 202 , source 203 , and drain 204 of the PMOS transistors in the Extraction Device 720 .
  • FIG. 8 is a cross-sectional diagram of a lateral PMOS Extraction Device 800 that includes a PMOS transistor 810 coupled to a high voltage capacitor 820 , according to embodiments of the invention.
  • the capacitor 820 includes electrodes 822 separated by an insulating or dielectric layer 824 .
  • the PMOS transistor 810 includes a thin gate oxide 812 . In some instances the thin gate oxide 812 is easier to produce than a thick gate oxide, used in previous examples, so the thin gate oxide may be preferable.
  • the high voltage capacitor 820 is series coupled to the built-in capacitance of the thin gate oxide 812 .
  • the Extraction Device does not have any substantive function during the DC operation of the Main Switch, i.e., while the Main Switch is fully off or fully on.
  • an external capacitor with a relatively high voltage rating it is possible for an external capacitor with a relatively high voltage rating to be used to seamlessly protect the gate oxide of the PMOS Extraction Device, even when, such as in the Extraction Device 800 , it has a thin gate oxide.
  • This series circuit configuration is possible because the PMOS Extraction Device 800 operates only during the switching on and off of the Main Device (not illustrated in FIG.
  • the switching control signals also cause the turn-on and turn-off of the PMOS transistor 810 in a seamless way.
  • the total capacitance of the series connection of these two capacitances can be tailored to adjust the voltage spikes of the gate signal. This protection is important, especially in the case when the Main Switch is made on wide bandgap semiconductors, for which the gate oxides are very thin and therefore very sensitive to voltage spikes.
  • the capacitance of the series connection of the capacitance of the gate oxide 812 of the PMOS 810 and the capacitor 820 itself may range from 1 pF to 800 pF, and more preferably from 1 pF to 100 pF. Of course, the specific values of the capacitance of the series connection will be implementation specific.
  • the Extraction Device 800 is an example type of device that may be present in the device 550 and used for the Extraction Device 530 of FIG. 5 .
  • FIG. 9 is a cross-sectional diagram of a vertical PMOS Extraction Device 900 , including a vertical PMOS transistor 910 .
  • the PMOS transistor 910 may be made on any type of semiconductor material.
  • the PMOS transistor 910 in this embodiment has a thick gate oxide 105 , which provides a high voltage rating for the PMOS transistor 910 , exceeding that of a Main Switch to which it is connected.
  • the Extraction Device 900 includes a high-voltage rated capacitor 920 that is connected in series with the Gate-Drain capacitance of the vertical PMOS transistor 910 .
  • the capacitor 920 is formed of conductive plates 922 separated by an insulator 924 .
  • the high voltage capacitor 920 has similar dimensions as does the PMOS transistor 910 , such as the Poly Gate Width of the vertical PMOS 910 , in actuality, the high voltage capacitor 920 can be placed anywhere on the top of the PMOS die, or outside of it and properly wire-bonded to the control electrode of the Extraction Device.
  • FIGS. 8 and 9 illustrate various options that may be used in implementing the Extraction Device, such as the Extraction Device 530 of FIG. 5 .
  • FIG. 10 is a top layout view of a device 1000 that includes an FWD 1010 integrated with an Extraction Device 1030 on a single semiconductor substrate.
  • the FWD 1010 may be one of the FWDs described above.
  • the FWD 1010 is surrounded by a high voltage termination 1020 .
  • An Extraction Device 1030 is placed outside the high voltage termination 1020 of the FWD 1010 .
  • the Extraction Device 1030 includes an input electrode 1032 for extraction, an output electrode 1034 , and a control electrode 1036 .
  • This device 1030 is an example layout of the device 550 of FIG. 5 .
  • the control electrode 1036 would be coupled to a gate of the IGBT
  • the input (for extraction) electrode 1032 would be coupled to the Extraction Plug terminal of the IGBT
  • the output electrode 1034 would be coupled to both a collector of the IGBT and to a cathode (not illustrated) of the FWD 1010 .
  • the anode (not illustrated) of the FWD 1010 would be coupled to the emitter of the IGBT.
  • FIG. 11 is a top layout view of a device 1100 including one or more FWDs 1110 and one or more Extraction Devices 1130 as described above.
  • the FWDs 1110 are interleaved with the Extraction Devices 1130 in the active area of the die.
  • the electrodes of the Extraction Devices 1130 are not illustrated as they may be implementation specific, and may be placed as the design dictates.
  • the FWDs 1110 illustrated in the device 1100 may be coupled together to make one or more FWDs. In other words, FWDs 1110 A and 1110 B may be coupled to one another to make a single, larger FWD.
  • all of the FWDs 1110 A, 1110 B, 1110 C, and 1110 D maybe be coupled together to make a single FWD for the entire device 1100 .
  • FIG. 11 illustrates the cellular or tessellated nature of the design in which multiple FWDs 1110 and Extraction Devices 1130 may be produced without affecting the functionality of the device.
  • the FWD 1110 and Extraction Device 1130 may be coupled to a one or more IGBTs as described above with reference to FIG. 10 .
  • FIG. 12 is a top layout view of a complete device 1200 that includes a voltage controlled Main Switch 1210 formed on a first semiconductor die coupled to an assisting device 1220 formed on a second semiconductor die.
  • the Main Switch 1210 includes Extraction Plugs 700 placed inside an active area 1250 .
  • the active area 1250 of a semiconductor device is the area within which the main electrical function of the power semiconductor device is performed.
  • Metallizations 107 connect the Extraction Plugs 700 to each other.
  • a gate terminal 1212 of the Main Switch 1210 is also illustrated within the active area 1250 .
  • the Main Switch 1210 has its output on the backside of the die.
  • the assisting device 1220 includes an FWD 1230 and a PMOS transistor 1240 , which functions as an Extraction Device, as described above.
  • the Extraction Device 1240 includes an input terminal 1242 for extraction, an output terminal 1244 , and a control terminal 1246 .
  • the Extraction Plugs 700 of the Main Switch 1210 are connected to one another through the metalizations 107 and also to the extraction input 1242 of the Extraction Device 1240 through a wire bond 1260 .
  • a wire bond electrically connects devices that are produced on two different substrates, where die metallizations cannot be used.
  • Another wire bond 1282 couples the gate terminal 1212 of the Main Switch 1210 to the control electrode 1246 of the Extraction Device 1240 .
  • the FWD 1230 has its anode coupled to an emitter of the Main Switch 1210 through a wire bond 1264 .
  • the output of the Extraction Device 1240 is coupled by a wire bond 1266 to a collector of the Main Switch 1210 , which, as described above, is located on the back side of the Main Switch 1210 , and is therefore not visible in FIG. 12 .
  • the output of the Extraction Device 1240 is also coupled to the cathode of the FWD 1230 .
  • This connection between the output of the Extraction Device 1240 and the cathode of the FWD 1230 may be an internal metallization within the assisting device 1220 , and is therefore not separately illustrated in FIG. 12 .
  • FIG. 12 is an example of a physical manifestation of the device 560 described above with reference to FIG. 5 , which includes both a Main Switch 510 and assisting device 550 .
  • the wire bond 1264 would be coupled to the ground terminal of the device, the wire bond 1266 would be coupled to the output terminal of the device, and the wire bond 1262 would be coupled to the control input terminal of the device.
  • the wire bond 1260 would not need to be connected to a terminal of the complete device 1200 because the connection between the Extraction Plug terminal of the Main Switch 1210 and the input terminal 1242 of the Extraction Device 1240 need only be an internal connection.
  • FIG. 13 is a top assembly view of a device 1300 that is similar to the device 1200 of FIG. 12 .
  • the same or similar features that were described with reference to FIG. 12 will not be repeated in the description of FIG. 13 , for brevity.
  • the main difference between devices 1200 and 1300 is that the extraction plugs 700 of the device 1300 are formed outside of the high voltage termination 1250 , whereas the Extraction Plugs 700 of the device 1300 are formed within the high voltage termination 1250 .
  • location of the Extraction Plugs 700 has little or no effect on their function to provide an access to the drift area of the semiconductor Main Switch through which the Extraction Device 1240 can expediently remove charge from while the Main Switch is turning off.
  • Power semiconductor switches having Extraction Plugs may be developed as a hybrid of the devices 1200 and 1300 , with some Extraction Plugs 700 located inside the high voltage termination area 1250 and some Extraction Plugs 700 located outside the high voltage termination area within the same device itself.
  • an IGBT or other semiconductor device may take the following forms, along with their equivalents.
  • Example 1 is a Freewheeling diode integrated with a Forced Extraction Device.
  • the Freewheeling diode may be of any kind, such as PIN, Schottky, etc.
  • Example 2 is a Freewheeling Diode coupled to an Extraction Device, which, in turn, is connected to a Main Switch that includes an Extraction Electrode or Extraction Plugs.
  • Example 3 is a Freewheeling Diode integrated with an Extraction Device, in which both the Diode and Extraction Device are made on Silicon.
  • Example 4 is a Freewheeling Diode integrated with an Extraction Device, in which both the Diode and Extraction Device are made on Wide Bandgap semiconductors.
  • Example 5 is a Freewheeling Diode integrated with a lateral PMOS Extraction Device, which, in turn, is connected to a Main Switch.
  • the lateral PMOS Extraction Device has a thick gate oxide that withstands at least the blocking voltage of the Main Switch (IGBT).
  • Example 6 is a Freewheeling Diode integrated with a lateral PMOS Extraction Device.
  • the lateral PMOS has a thin gate oxide and a high voltage rating capacitor that is connected in series with the capacitor of the controlling electrode of the Extraction Device.
  • Example 7 is a Freewheeling Diode integrated with a vertical PMOS Extraction Device which, in turn, is connected to a Main Switch.
  • the vertical PMOS Extraction Device has a thick gate oxide that withstands at least the blocking voltage of the Main Switch (IGBT).
  • Example 8 is a Freewheeling Diode integrated with a vertical PMOS Extraction Device.
  • the vertical PMOS has a thin gate oxide and a high voltage rating capacitor that is connected in series with the capacitor of the controlling electrode of the Extraction Device
  • Example 9 is a High Voltage Capacitor connected in series with the capacitor of the controlling electrode of the Extraction Device.

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Abstract

A Freewheeling Diode of any kind (Fast Recovery Diode, Schottky Barrier Diode or other variants) is integrated with a Forced Extraction Device and in this way two entirely different functions—the Free-Wheeling function and the Forced Extraction function are combined in one device, simplifying the circuit and reducing the number of components. The FWD part of the integrated device is standard in the industry, but the Forced Extraction Device is made using a lateral or vertical PMOS with a votage capability between a control input and the output terminals that is as high or higher than the rating voltage of the Main Switch that will be used together with the FWD.

Description

    CROSS-REFERENCE TO RELATED APPLICATIONS
  • This application is a continuation of U.S. application Ser. No. 17/496,658, filed Oct. 7, 2021, which is a non-provisional of and claims benefit to U.S. provisional patent application No. 63/093,701, filed Oct. 19, 2020, entitled SEMICONDUCTOR STRUCTURE HAVING A FORCED EXTRACTION DEVICE, the disclosure of which is incorporated herein by reference in its entirety. This application is also related to U.S. patent application Ser. No. 17/339,832, filed Jun. 4, 2021, entitled POWER SEMICONDUCTOR DEVICE WITH FORCED CARRIER EXTRACTION AND METHOD OF MANUFACTURE, which is incorporated herein by reference in its entirety.
    • TECHNICAL FIELD
  • This disclosure relates to semiconductor devices, and, more particularly, to a semiconductor structure that includes a Freewheeling Diode coupled to a forced carrier Extraction Device that improves the switching speed of a Main Switch for which the turn-off process depends on the recombination speed of charge carriers.
    • BACKGROUND
  • The previously incorporated U.S. patent application Ser. No. 17/339,832 describes problems with long turn-off times in power semiconductor switches and a solution that uses a forced carrier Extraction Device. Some power semiconductor devices that carry relatively large amounts of current include a Freewheeling Diode (FWD), especially those that operate on inductive loads. In power circuits like push-pull, half-bridge or full-bridge modules, the Freewheeling Diode is connected in parallel to the main semiconductor switch. Some power switches, like Mosfets, have a “built in” diode, which can be used as a Freewheeling Diode. In such cases, special process steps are used to shorten the reverse recovery time and lower the reverse recovery charge of the FWD, as this charge contributes to the turn-on switching energy of the Main Switch.
  • Insulated Gate Bi-Polar Transistors (IGBTs) are widely used for a broad range of power semiconductors since their features are well suited for such roles. IGBTs include a built-in diode, but the built-in diode cannot be used as a FWD because of the P-type injector layer, which causes the built-in diode of the IGBT on the backside of the IGBT to have an orientation opposite that of a Mosfet. The diode in an IGBT is formed at the intersection of the P-wells and N-type drift layer, for instance, or at the intersection of an N-well for a P-type IGBT. The injector layer of the IGBT provides the conductivity modulation of the drift region while the IGBT is conducting, which makes the IGBT such a well-performing device from an on-conduction point of view. But this same injector layer prevents the built-in diode in an IGBT from acting as an FWD, which is why nearly all IGBTs are equipped with a separate FWD in most power applications.
  • Recently, Silicon Carbide Schottky Barrier Diodes (SiC SBDs) have been replacing Silicon FWDs in commercial products. An SBD formed on SiC has a lower forward voltage and no reverse recovery charge, and therefore its contribution to the turn-on energy loss of the Main Switch, such as when an IGBT is used for the Main Switch, is due only to the charge stored in the depletion region of the SBD.
  • Another effect of the existence of the injector layer opposite to the Mosfet makes the turn-off process of a Main Switch that employs conductivity modulation, such as an IGBT, very slow, due to the need of the injected carriers to “disappear” through recombination when the IGBT turns off.
  • Special process steps that control the level of injection or the recombination rate are widely used to speed up the turn-off time of power semiconductors that use conductivity modulation. Providing such a switch, such as an IGBT, with an ability or structure to remove excess charge in the drift region and therefore lower the turn-off energy of the power semiconductor, is a worthwhile goal.
  • State-of-the-art IGBTs lack the means to access the region where the carriers contributing to the conductivity modulation recombine. Extraction Plugs, which are described in detail in the incorporated '832 application, may be formed or placed inside the Main Switch, such as an IGBT, such that the electrical performance of the Main Switch is not degraded in any way. Although such Extraction Plugs may speed up a power semiconductor switch when coupled to an Extraction Device to remove charge in the drift region during the turn-off process of the switch, forming the Extraction Device itself may involve extra process steps compared to forming the IGBT itself.
  • Embodiments of the disclosure address these and other limitations of the prior art.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a conceptual schematic diagram of a switch having an Extraction terminal, connected to a voltage-controlled Extraction Device, according to embodiments of this disclosure.
  • FIG. 2 is a schematic diagram of a complementary IGBT having an injecting PNP transistor, as well as a P-channel MOSFET, and an N-channel MOSFET coupled in series, according to embodiments of the disclosure.
  • FIG. 3 is a simplified schematic diagram illustrating an IGBT switching device, having emitter, collector, and gate terminals, and further illustrating an Extraction Plug connection, to which an Extraction Device may be connected, according to embodiments of the disclosure.
  • FIG. 4 is a schematic of a known voltage-controlled Main Switch, such as an IGBT, having a free-wheeling diode connected in parallel to the switch.
  • FIG. 5 is a schematic diagram illustrating a Main Switch, a Freewheeling Diode, and an Extraction Device, according to embodiments of the invention.
  • FIG. 6 is a cross-sectional diagram of a Freewheeling Diode and an Extraction Device, according to embodiments of the invention.
  • FIG. 7 is a cross-sectional diagram illustrating a Freewheeling Diode, high-voltage termination, and a multi-cell PMOS formed on a semiconductor substrate, according to embodiments of the invention.
  • FIG. 8 is a cross-sectional diagram of a lateral PMOS Extraction Device and a high voltage capacitor according to embodiments of the invention.
  • FIG. 9 is a cross-sectional diagram of a vertical PMOS Extraction Device and a high voltage capacitor according to embodiments of the invention.
  • FIG. 10 is a top layout view of an integrated FWD with an Extraction Device, placed outside of the high voltage termination of the FWD, according to embodiments of the invention.
  • FIG. 11 is a top layout view of an integrated FWD with an Extraction Device, interspaced in the active area of the die, according to embodiments of the invention.
  • FIG. 12 is a top layout view of a voltage controlled Main Switch having an output on the backside of the die, according to embodiments of the invention.
  • FIG. 13 is a top assembly view of a voltage controlled Main Switch having Extraction Plugs formed around an edge of the die, according to embodiments of the invention.
    •  DETAILED DESCRIPTION OF THE DRAWINGS
  • The present disclosure relates to the field of power semiconductors with conductivity modulation, like IGBTs and its variants, which are structured or used to switch inductive loads. When switching inductive loads, a Freewheeling Diode is commonly used when the switching device, like the IGBT, has to commutate On and Off current through an inductance. Thus, although IGBTs remain an excellent choice for those semiconductor devices carrying relatively large amounts of current, so called power devices, the slow switching speeds caused by the slow recombination of minority carriers in conductivity-modulation bipolar devices after switching off continues to inhibit their performance. Including Extraction Plugs and an Extraction Device in a three terminal device that uses conductivity modulation can greatly improve its switching speed, as described below.
  • Benefits of including an Extraction Device in conjunction with a power semiconductor device are described with reference to FIGS. 1-3 . Benefits of including FWDs with power semiconductor devices that also include an Extraction Device are described with reference to FIGS. 4-13 .
  • FIG. 1 is a conceptual schematic diagram of a combined device 100 that generally includes a Main Switch 110 coupled to an Extraction Device 120. The device 100 further includes one or more Extraction Plugs 130 formed in the drift layer of the Main Switch 110. Extraction Plugs are fully described in the previously incorporated U.S. patent application Ser. No. 17/339,832. In general, Extraction Plugs may be formed in devices that use conductivity modulation to provide access to a drift layer of the device. The Extraction Plugs 130 are formed and placed so that they do not degrade, in any way, the performance of the structure 100, especially its blocking voltage. An Extraction Device 120, also described in the '832 application, turns on when the Main Switch 110 turns off. If the Main Switch is embodied by a device that uses conductivity modulation, such as an IGBT, the Extraction Device 120 works to remove charge carriers left over in the bulk region when the Main Switch 110 turns off through the Extraction Plug 130 of the Main Switch. The forced Extraction Device 120 is preferably voltage controlled, and its blocking voltage between terminals is generally the same or higher than the blocking voltage of the Main Switch 110.
  • The structure 100 of FIG. 1 may be structured as a three-terminal device. The structure 100 includes an input terminal coupled to an input 112 of the Main Switch 110 and to an input 122 of the Extraction Device 120, and an output terminal 126 coupled to an output of the Extraction Device 120. The structure 100 further includes a ground terminal 114 coupled to the Main Switch 110. Because the inputs 112, 122 of the Main Switch 110 and Extraction Device 120 are tied together, the input signal driving the input 112 of the Main Switch 110 also drives the input 122 of the Extraction Device 120.
  • The Extraction Device 120 may be integrated on the same die as the Main Switch 110, or it may be a discrete device formed on a separate semiconductor substrate that is electrically coupled to the Main Switch. In some embodiments the semiconductor substrate for the Main Switch and a semiconductor substrate for the Extraction Device 120 may be separate substrates but assembled together in a single module or even in a single package.
  • The structure 100 of FIG. 1 conceptually operates as indicated as in Table 1:
  • TABLE 1
    Operational States of Main Device and Extraction Device
    Turn Turn Input-Ground Output-Ground
    Device/State On Off Voltage Voltage
    Main Device On Off Low High
    Extraction Device OFF On High Low
  • In operation, when the Main Switch 110 is ON, the Extraction Device 120 is OFF, and vice-versa. In device operation, i.e., when the Main Switch 110 is conducting, the Extraction Device 120 does not interfere or affect the operation of the Main Switch 110. In other words, the operating parameters of a Main Switch 110 coupled to the Extraction Device 120 are the same or similar as a Main Switch that is not coupled to an Extraction Device. The Main Switch 110 has a low breakdown voltage between the input and ground terminals, but a relatively high breakdown voltage between the output and ground terminals. Conversely, the Extraction Device 120 has a high breakdown voltage between its input and ground terminals, and a relatively low breakdown voltage between the ground and the output terminals.
  • FIG. 2 is a schematic diagram of a circuit 200 including components that may be used to form an example embodiment 200 that functions as the structure 100 of FIG. 1 . The circuit 200 includes an IGBT Main Switch, which is formed of a PNP transistor 250 as an injector and an N-channel Mosfet 270 that drives the PNP transistor. A P-channel Mosfet 260 functions as the Extraction Device 120 of FIG. 1 . The Mosfets 260 and 270 are coupled in series. The device 200 may be integrated on a single semiconductor die. In other embodiments, as described above, the P-Channel Mosfet 260 may be formed on a separate semiconductor die and electrically connected to the N-Channel Mosfet 270. Internal components of the IGBT Main Switch further include a collector 216, and an emitter 214. The P-Channel Mosfet 260, which operates as the Extraction Device, includes a source 224 and a drain 226. Since the output terminal of the device 200, in this configuration, is coupled to both the collector 216 of the IGBT and the drain 226 of the P-Channel Mosfet 260, it is labeled as Output/Drain/Collector. Similarly, the ground terminal is coupled to the emitter 214 of the IGBT and the source of the N-Channel Mosfet 270, the ground terminal is labeled Ground/Source/Emitter. Finally, since the input terminal of the device 200 is coupled to the gates of both the N-Channel Mosfet 270 and the P-Channel Mosfet 260, the input terminal is labeled Input/Gate. Although it is not separately shown on the schematic diagram of the circuit 200, an Extraction Plug for the IGBT would be coupled to the base of the PNP transistor 250, which is in the drift region of the IGBT, and is labeled as reference 280. Importantly, the Extraction Plug, or reference 280, is electrically coupled to a source of the P-Channel Mosfet 260.
  • In operation of the device 200, when the Input/gate voltage is HIGH, the base of the PNP 250 transistor is connected to a ground at the source of the MOSFET 270, while the device 200 is conducting. Then, when the Input/gate voltage goes LOW, to turn off the device 200, the N-channel MOSFET 270 turns OFF, while the P-channel MOSFET 260 turns ON. The P-Channel MOSFET 260 turning ON provides a path for excess charge to be removed from the drift region 280 from the source of the P-Channel Mosfet 260 to the drain of the P-Channel Mosfet, which is coupled to the output of the device 200. The P-Channel MOSFET 260 is formed so that, when the gate voltage is HIGH, the P-Channel MOSFET 260 is OFF, and turns on when the gate voltage goes LOW. At low Vgs voltages of the N-Channel Mosfet 270, when the Main Switch (IGBT) turns OFF, the P-Channel MOSFET 260 operates similar to that of a resistor, with its drain coupled to the positively bias on the collector 216 of the PNP 250. Therefore, electrons are pulled toward the positively biased drain electrode of the P-Channel MOSFET 260, and charge is removed from the drift region 280 at a relatively constant rate. The P-Channel MOSFET 260 provides a path for the charge, carried by electrons, to be removed from the drift layer 280 through the positively charged drain. Recall that one of the main problems for conventional IGBT devices to switch off quickly is that there is no access to the drain of the Mosfet. Instead, the Extraction Device, which here is the P-channel MOSFET 260, extracts excess carriers relatively quickly from the bulk drift area 280 of the IGBT by conducting them to the collector through the P-channel MOSFET 260. This action of removing the excess charge carriers when the IGBT turns off significantly decreases the turn-off time of the IGBT.
  • The aforementioned Extraction Plugs, or merely plugs, are used to provide access to areas of the bulk semiconductor in conductivity modulation devices. These Extraction Plugs, in turn, may be coupled to the source (i.e, the input or extraction terminal) of an Extraction Device to remove the excess carriers from the conductivity modulation device when the conductivity modulation device is being turned off. This greatly reduces the turn-off time of the conductivity modulation device. Further details of the structure of the Extraction Plugs may be obtained from the '832 application, although embodiments of the invention are applicable to other forms of Extraction Plugs providing the same function as that described herein.
  • FIG. 3 is a simple schematic diagram illustrating an IGBT switching device 300, having emitter, collector, and gate terminals, and further illustrating an Extraction Plug terminal, also called an Extraction Terminal, to which an Extraction Device may be connected. This schematic diagram neatly illustrates the concepts of including one or more Extraction Plugs in the drift region of an IGBT, which, as described above, facilitates the removal of carriers during forced carrier extraction from the drift region through the Extraction Plugs and further through the Extraction Device during turn-off of the Main Switch. The Extraction Plug terminal is electrically connected to the Extraction Plug or Plugs in the IGBT. In application, the Extraction Plug terminal of the IGBT switching device 300 may be further coupled to an Extraction Device, as detailed below. In embodiments where the Extraction Plug and Extraction Device are formed on the same semiconductor substrate, it is not strictly necessary that the Extraction Plug be coupled to an output terminal. In other embodiments, where the Extraction Plug and Extraction Device are formed on different substrates, the Extraction Plug may be coupled to an Extraction Plug Terminal, which, in turn, may be coupled to an Extraction Device located on a different substrate. In this way, the process steps for forming an IGBT having an Extraction Plugs may be optimized separately from the process steps for forming an IGBT.
  • Further, recall from above that power switching devices that drive inductive loads nearly always include a Freewheeling Diode (FWD) to protect the switch from over voltage as the switch turns off and the magnetic field around the inductive load collapses. To protect against damage caused by the inductor, a protective FWD is coupled in parallel to the switch. FIG. 4 is a schematic of a known voltage-controlled Main Switch 10, such as an IGBT, having an FWD 12 connected in parallel to the switch. As described above, some power semiconductor devices that carry relatively large amounts of current include an FWD, especially those that operate on inductive loads. In power circuits like push pull, half-bridge or full-bridge modules, the FWD is connected in parallel to the main semiconductor switch. With reference to FIG. 4 , the IGBT 10 is a bipolar semiconductor device used for carrying relatively large current loads. The IGBT 10 includes emitter, collector, and gate terminals, which function as the input, output, and gate terminals of the switch. The FWD 12 is coupled in parallel to the IGBT, with one terminal of the FWD coupled to the collector and the other terminal coupled to the emitter. In circuits that drive inductive loads, the FWD 12 shunts current from the inductive load across the IGBT 10 as the IGBT turns off, and also limits voltage across the IGBT. Otherwise, the current generated by the collapse of the magnetic field around the inductor would be applied directly to the IGBT 10, which would likely cause damage. In this way the FWD 12 acts as a protection device for the switch 10. Also, the FWD 12 is designed and fabricated to withstand the full rated voltage of the Main Switch 10, including the avalanche rating, or it has to be implemented with a higher blocking voltage than the Main Switch.
  • FIG. 5 is a schematic diagram illustrating a system 500 that includes a Main Switch 510 having an Extraction Plug electrode 512, an FWD 520, and an Extraction Device 530, according to embodiments of the invention. Although all of the components illustrated in FIG. 5 may be integrated on a single die, it is possible, and perhaps preferable, that the FWD 520 and an Extraction Device 530 are packaged in a separate device 550, which is electrically connected to the Main Switch 510. Also, the Main Switch 510 may be a one semiconductor die, and the separate device 550, including the FWD 520 and an Extraction Device 530, is formed on another semiconductor die, but both the semiconductor dies are together in a single semiconductor module or package. More details and discussion of possible layouts is given below.
  • System 500 illustrates a three-terminal device capable of driving inductive loads, since the IGBT Main Switch 510 is electrically coupled to the FWD 520, even though the diode 520 may be formed on a substrate separate from the IGBT Main Switch 510. Further, since the turn-off time of an IGBT is shortened by coupling an Extraction Device 530 to the Extraction Plug 512 of the IGBT 510, including an Extraction Device 530 in the system 500 provides the extraction function when the IGBT 510 turns off. Therefore, it may be convenient to produce the IGBT Main Switch 510 with an Extraction Plug terminal 512 separately from a device that includes both an FWD as well as an Extraction Device, such as the device 530. Thus the system 500 may form a single package or module including one component having the IGBT Main Switch 510 and having another component 550, which includes the FWD 520 and the Extraction Device 530. Electrical connections are made within the system 500 as illustrated in FIG. 5 . For instance, a gate of the IGBT Main Switch 510 is electrically coupled to an input of the Extraction Device 530. The Extraction Plug terminal 512 of the IGBT Main Switch 510 is electrically coupled to an extraction input 532 of the Extraction Device 530. A collector of the IGBT Main Switch 510 is coupled to an output of the Extraction Device 530. To finish the connections, a cathode of the FWD 520 is coupled to a collector of the IGBT Main Switch 510, and the anode of the FWD 520 is coupled to an emitter of the IGBT Main Switch 510.
  • If the system 500 is created in a discrete package 560, it could be a three-terminal device with an input control terminal 562, a ground terminal 564, and an output terminal 566. Such a package 560 includes an IGBT 510 or Main Switch having an Extraction Plug terminal 512 that is coupled to a component 550. The component 550 includes an FWD 520 and an Extraction Device 530. This package 560 includes all of the components for a power device for driving an inductive load having a shortened turn-off time compared to typical IGBTs. In detail, the FWD 520 is effectively mandatory for any power switch operating with an inductive load. Embodiments of the invention further include the Extraction Device 530 to shorten the turn-off time of the voltage-controlled switch device with conductivity modulation 510. Although the Main Switch 510 is illustrated as being an IGBT, embodiments of the invention extend to any voltage-controlled switch device with conductivity modulation.
  • FIG. 6 is a cross-sectional diagram of an integrated device 600 including an FWD 610 and an Extraction Device 620 produced on a same semiconductor substrate, according to embodiments of the invention. In this example, the FWD 610 is a merged PN-Schottky structure. But, the FWD 610 may be any of several different types of FWDs. For example, the FWD 610 may be a PIN (p-type and n-type materials separated by an insulator) diode, and may or may not include materials for shortening carrier lifetimes, such as gold or platinum diffusions, electron or proton irradiations, etc. The FWD 610 may also be a Fast Recovery Diode, for example. Although the FWD 610 and the Extraction Device 620 of the integrated device 600 are formed on the same semiconductor die, they may be separated by a deep trench 640, which may be formed using standard fabrication techniques. The deep trench 640 separates the cathode of the FWD 520 (FIG. 5 ) from the substrate of the lateral PMOS in the Extraction Device 530. Such separation allows each device to operate virtually independent from one another. It is not necessary that the FWD 610 and the Extraction Device 620 be formed on the same die. In other embodiments the FWD 610 and the Extraction Device 620 may be electrically coupled to one another but formed on separate semiconductor dies. In the illustrated embodiment, the lateral PMOS Extraction Device 620 includes a thick gate oxide 105. The Extraction Device 620 is also “counter doped” at the surface of the semiconductor to create conditions for a suitable turn-on voltage, Vth. As represented in this cross section of FIG. 6 , the FWD 610 and the PMOS Extraction Device 620 structures could be formed and interspaced in the active area of the die. The device 600 is an example of the type of structure that could make the component 550 part of the device 500 of FIG. 5 .
  • Other structures in the integrated device 600 are conventional, such as a polysilicon gate 103, front metal 106, passivation layer 108, substrate 150, such as SiC or other wide bandgap material, N-type drift region 151, P-Wells 160, Schottky Metal 165, and counter-doped region 170.
  • FIG. 7 is a cross-sectional diagram of a device 700 illustrating an FWD 710, high-voltage termination 750, and a multi-cell PMOS Extraction Device 720 formed on any type of semiconductor, such as Silicon, SiC, wide-bandgap material, etc., according to embodiments of the invention. The placement of the Extraction Device 720 in the illustrated embodiment of FIG. 7 is outside of the High Voltage Termination 750 of the FWD 710, but this placement is not mandatory. The P-Wells 101 of the FWD 710 and Extraction Device 720 can very well operate together to provide a blocking voltage needed for the FWD. Other conventional components of the device 700 not referred to above include a gate 202, source 203, and drain 204 of the PMOS transistors in the Extraction Device 720.
  • FIG. 8 is a cross-sectional diagram of a lateral PMOS Extraction Device 800 that includes a PMOS transistor 810 coupled to a high voltage capacitor 820, according to embodiments of the invention. The capacitor 820 includes electrodes 822 separated by an insulating or dielectric layer 824. The PMOS transistor 810 includes a thin gate oxide 812. In some instances the thin gate oxide 812 is easier to produce than a thick gate oxide, used in previous examples, so the thin gate oxide may be preferable. The high voltage capacitor 820 is series coupled to the built-in capacitance of the thin gate oxide 812. As described above, when a PMOS transistor is used as the Extraction Device, the Extraction Device does not have any substantive function during the DC operation of the Main Switch, i.e., while the Main Switch is fully off or fully on. This means the Extraction Device 800 is OFF when the Main Switch is turned ON and it is ON when the Main Switch gets turned OFF. Given these characteristics, it is possible for an external capacitor with a relatively high voltage rating to be used to seamlessly protect the gate oxide of the PMOS Extraction Device, even when, such as in the Extraction Device 800, it has a thin gate oxide. This series circuit configuration is possible because the PMOS Extraction Device 800 operates only during the switching on and off of the Main Device (not illustrated in FIG. 8 ) to which it is coupled, and the switching control signals also cause the turn-on and turn-off of the PMOS transistor 810 in a seamless way. Further, by using a high-voltage external capacitor 820 in series with the capacitor formed by a polysilicon gate and the gate oxide 812 of the lateral PMOS 810, the total capacitance of the series connection of these two capacitances can be tailored to adjust the voltage spikes of the gate signal. This protection is important, especially in the case when the Main Switch is made on wide bandgap semiconductors, for which the gate oxides are very thin and therefore very sensitive to voltage spikes. The capacitance of the series connection of the capacitance of the gate oxide 812 of the PMOS 810 and the capacitor 820 itself may range from 1 pF to 800 pF, and more preferably from 1 pF to 100 pF. Of course, the specific values of the capacitance of the series connection will be implementation specific. The Extraction Device 800 is an example type of device that may be present in the device 550 and used for the Extraction Device 530 of FIG. 5 .
  • FIG. 9 is a cross-sectional diagram of a vertical PMOS Extraction Device 900, including a vertical PMOS transistor 910. The PMOS transistor 910 may be made on any type of semiconductor material. The PMOS transistor 910 in this embodiment has a thick gate oxide 105, which provides a high voltage rating for the PMOS transistor 910, exceeding that of a Main Switch to which it is connected. Also, the Extraction Device 900 includes a high-voltage rated capacitor 920 that is connected in series with the Gate-Drain capacitance of the vertical PMOS transistor 910. The capacitor 920 is formed of conductive plates 922 separated by an insulator 924. Even though in this illustration the high voltage capacitor 920 has similar dimensions as does the PMOS transistor 910, such as the Poly Gate Width of the vertical PMOS 910, in actuality, the high voltage capacitor 920 can be placed anywhere on the top of the PMOS die, or outside of it and properly wire-bonded to the control electrode of the Extraction Device.
  • Thus, the embodiments of the Extraction Devices illustrated in FIGS. 8 and 9 illustrate various options that may be used in implementing the Extraction Device, such as the Extraction Device 530 of FIG. 5 .
  • FIG. 10 is a top layout view of a device 1000 that includes an FWD 1010 integrated with an Extraction Device 1030 on a single semiconductor substrate. The FWD 1010 may be one of the FWDs described above. The FWD 1010 is surrounded by a high voltage termination 1020. An Extraction Device 1030 is placed outside the high voltage termination 1020 of the FWD 1010. The Extraction Device 1030 includes an input electrode 1032 for extraction, an output electrode 1034, and a control electrode 1036. This device 1030 is an example layout of the device 550 of FIG. 5 . If the device 1000 were coupled to a Main Switch, such as an IGBT having an Extraction Plug terminal, the control electrode 1036 would be coupled to a gate of the IGBT, the input (for extraction) electrode 1032 would be coupled to the Extraction Plug terminal of the IGBT, and the output electrode 1034 would be coupled to both a collector of the IGBT and to a cathode (not illustrated) of the FWD 1010. Finally, the anode (not illustrated) of the FWD 1010 would be coupled to the emitter of the IGBT. When so connected, the FWD 1010 of the device 1000 provides high voltage protection to the IGBT during turn-off while the Extraction Device 1030 substantially increases the turn-off speed of the IGBT.
  • FIG. 11 is a top layout view of a device 1100 including one or more FWDs 1110 and one or more Extraction Devices 1130 as described above. In this layout, the FWDs 1110 are interleaved with the Extraction Devices 1130 in the active area of the die. The electrodes of the Extraction Devices 1130 are not illustrated as they may be implementation specific, and may be placed as the design dictates. Also, the FWDs 1110 illustrated in the device 1100 may be coupled together to make one or more FWDs. In other words, FWDs 1110A and 1110B may be coupled to one another to make a single, larger FWD. In another embodiment, all of the FWDs 1110A, 1110B, 1110C, and 1110D, maybe be coupled together to make a single FWD for the entire device 1100. The same is true for the Extraction Devices 1130A, 1130B, and 1130C, which may be variously connected to one another to make one, two, or three separate Extraction Devices 1130. FIG. 11 illustrates the cellular or tessellated nature of the design in which multiple FWDs 1110 and Extraction Devices 1130 may be produced without affecting the functionality of the device. Further, the FWD 1110 and Extraction Device 1130 may be coupled to a one or more IGBTs as described above with reference to FIG. 10 .
  • FIG. 12 is a top layout view of a complete device 1200 that includes a voltage controlled Main Switch 1210 formed on a first semiconductor die coupled to an assisting device 1220 formed on a second semiconductor die. The Main Switch 1210 includes Extraction Plugs 700 placed inside an active area 1250. The active area 1250 of a semiconductor device is the area within which the main electrical function of the power semiconductor device is performed. Metallizations 107 connect the Extraction Plugs 700 to each other. A gate terminal 1212 of the Main Switch 1210 is also illustrated within the active area 1250. The Main Switch 1210 has its output on the backside of the die. The assisting device 1220 includes an FWD 1230 and a PMOS transistor 1240, which functions as an Extraction Device, as described above. The Extraction Device 1240 includes an input terminal 1242 for extraction, an output terminal 1244, and a control terminal 1246.
  • The Extraction Plugs 700 of the Main Switch 1210 are connected to one another through the metalizations 107 and also to the extraction input 1242 of the Extraction Device 1240 through a wire bond 1260. A wire bond electrically connects devices that are produced on two different substrates, where die metallizations cannot be used. Another wire bond 1282 couples the gate terminal 1212 of the Main Switch 1210 to the control electrode 1246 of the Extraction Device 1240. With reference to FIG. 5 , the FWD 1230 has its anode coupled to an emitter of the Main Switch 1210 through a wire bond 1264. The output of the Extraction Device 1240 is coupled by a wire bond 1266 to a collector of the Main Switch 1210, which, as described above, is located on the back side of the Main Switch 1210, and is therefore not visible in FIG. 12 . The output of the Extraction Device 1240 is also coupled to the cathode of the FWD 1230. This connection between the output of the Extraction Device 1240 and the cathode of the FWD 1230 may be an internal metallization within the assisting device 1220, and is therefore not separately illustrated in FIG. 12 . Thus, FIG. 12 is an example of a physical manifestation of the device 560 described above with reference to FIG. 5 , which includes both a Main Switch 510 and assisting device 550. If the complete device 1200 is a three terminal device, then the wire bond 1264 would be coupled to the ground terminal of the device, the wire bond 1266 would be coupled to the output terminal of the device, and the wire bond 1262 would be coupled to the control input terminal of the device. The wire bond 1260 would not need to be connected to a terminal of the complete device 1200 because the connection between the Extraction Plug terminal of the Main Switch 1210 and the input terminal 1242 of the Extraction Device 1240 need only be an internal connection.
  • FIG. 13 is a top assembly view of a device 1300 that is similar to the device 1200 of FIG. 12 . The same or similar features that were described with reference to FIG. 12 will not be repeated in the description of FIG. 13 , for brevity. The main difference between devices 1200 and 1300 is that the extraction plugs 700 of the device 1300 are formed outside of the high voltage termination 1250, whereas the Extraction Plugs 700 of the device 1300 are formed within the high voltage termination 1250. As described above, location of the Extraction Plugs 700 has little or no effect on their function to provide an access to the drift area of the semiconductor Main Switch through which the Extraction Device 1240 can expediently remove charge from while the Main Switch is turning off.
  • Power semiconductor switches having Extraction Plugs may be developed as a hybrid of the devices 1200 and 1300, with some Extraction Plugs 700 located inside the high voltage termination area 1250 and some Extraction Plugs 700 located outside the high voltage termination area within the same device itself.
    • Example Embodiments
  • In accordance to the present disclosure, an IGBT or other semiconductor device may take the following forms, along with their equivalents.
  • Example 1 is a Freewheeling diode integrated with a Forced Extraction Device. The Freewheeling diode may be of any kind, such as PIN, Schottky, etc.
  • Example 2 is a Freewheeling Diode coupled to an Extraction Device, which, in turn, is connected to a Main Switch that includes an Extraction Electrode or Extraction Plugs.
  • Example 3 is a Freewheeling Diode integrated with an Extraction Device, in which both the Diode and Extraction Device are made on Silicon.
  • Example 4 is a Freewheeling Diode integrated with an Extraction Device, in which both the Diode and Extraction Device are made on Wide Bandgap semiconductors.
  • Example 5 is a Freewheeling Diode integrated with a lateral PMOS Extraction Device, which, in turn, is connected to a Main Switch. The lateral PMOS Extraction Device has a thick gate oxide that withstands at least the blocking voltage of the Main Switch (IGBT).
  • Example 6 is a Freewheeling Diode integrated with a lateral PMOS Extraction Device. The lateral PMOS has a thin gate oxide and a high voltage rating capacitor that is connected in series with the capacitor of the controlling electrode of the Extraction Device.
  • Example 7 is a Freewheeling Diode integrated with a vertical PMOS Extraction Device which, in turn, is connected to a Main Switch. The vertical PMOS Extraction Device has a thick gate oxide that withstands at least the blocking voltage of the Main Switch (IGBT).
  • Example 8 is a Freewheeling Diode integrated with a vertical PMOS Extraction Device. The vertical PMOS has a thin gate oxide and a high voltage rating capacitor that is connected in series with the capacitor of the controlling electrode of the Extraction Device
  • Example 9 is a High Voltage Capacitor connected in series with the capacitor of the controlling electrode of the Extraction Device.
  • The above description of illustrated implementations of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific implementations of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
  • These modifications may be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific implementations disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims (1)

What is claimed is:
1. A semiconductor device formed on a semiconductor substrate, the semiconductor having a first, second, third, and fourth terminals, the semiconductor device comprising:
a freewheeling diode coupled between the first and second terminals; and
an Extraction Device structured to be coupled to a conductivity modulation switch device through the third terminal, the Extraction Device further coupled to the second terminal and the fourth terminal.
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