Die Stack Assembly Using An Edge Separation Structure For Connectivity Through A Die Of The Stack

Abstract

A die stack assembly includes first and second power semiconductor device dice. The first die has a P type peripheral edge separation structure that extends from the top planar semiconductor surface of the first die all the way to the bottom planar semiconductor surface of the die, and that is doped at least in part with aluminum. The backside of the first die is mounted to the backside of the second die. A metal feature that is not covered with passivation, and that can serve as a bonding pad, is disposed on part of the peripheral edge separation structure. A metal member (for example, a bond wire or metal clip) contacts the metal feature such that an electrical connection is established from the metal member, through the metal feature, through the peripheral edge separation structure of the first die, and to an electrode of the second die.

Claims

1-14. (canceled)

15. A method comprising: (a) wafer bonding a backside of a first wafer to a backside of a second wafer thereby obtaining a bonded wafer structure; and (b) dicing the bonded wafer structure thereby obtaining a power semiconductor device die assembly, wherein the power semiconductor device die assembly comprises a first power semiconductor device die and a second power semiconductor device die, wherein the first power semiconductor device die comprises a peripheral edge separation structure that extends from a first substantially planar semiconductor surface of the first power semiconductor device die to a second substantially planar semiconductor surface of the first power semiconductor device die along a side edge of the first power semiconductor device die, wherein the second power semiconductor device die comprises a peripheral edge separation structure that extends from a first substantially planar semiconductor surface of the second power semiconductor device die to a second substantially planar semiconductor surface of the second power semiconductor device die along a side edge of the second power semiconductor device die, and wherein the peripheral edge separation structure of the first power semiconductor device die is electrically coupled within the assembly to the peripheral edge separation structure of the second power semiconductor device die.

16. The method of claim 15, further comprising: (c) attaching a bond wire to a bond pad, wherein the bond pad is disposed on a surface area of the peripheral edge separation structure of the first power semiconductor device die.

17. The method of claim 15, further comprising: (c) attaching a wafer interface member to a topside of the second wafer prior to the dicing of (b) such that when the dicing of (b) occurs the wafer interface member is diced along with the first and second wafers, wherein the power semiconductor device die assembly comprises the first power semiconductor device die, the second power semiconductor device die, and a die-sized interface member cut from the wafer interface member, wherein the die-sized interface member comprises a first metal feature and a second metal feature, wherein the first metal feature is in electrical contact with a first metal electrode of the second power semiconductor device die, and wherein the second metal feature is in electrical contact with a second metal electrode of the second power semiconductor device die.

18-19. (canceled)

20. An apparatus comprising: a first power semiconductor device die that comprises a peripheral edge separation structure and a metal feature disposed on a surface of the peripheral edge separation structure, wherein the peripheral edge separation structure of the first power semiconductor device die is at least in part doped with aluminum; a metal member that is bonded to the metal feature; and a second power semiconductor device die, wherein a surface of the second power semiconductor device die is bonded to a backside surface of the first power semiconductor device die such that an electrode of the second power semiconductor device die is electrically coupled via the peripheral edge separation structure of the first power semiconductor device die and the metal feature to the metal member, wherein the peripheral edge separation structure of the first power semiconductor device die comprises a contiguous amount of P type semiconductor material that extends from a topside substantially planar semiconductor surface of the first power semiconductor device die to a bottomside substantially planar semiconductor surface of the first power semiconductor device die, wherein the first power semiconductor device has a reverse breakdown voltage greater than three thousand volts, and wherein some of the contiguous amount of P type semiconductor material of the peripheral edge separation structure of the first power semiconductor device die is an amount of P type semiconductor material disposed in a trench.

21. (canceled)

22. The apparatus of claim 20, wherein the peripheral edge separation structure extends from the topside substantially planar semiconductor surface of the first power semiconductor device die to the bottomside substantially planar semiconductor surface of the first power semiconductor device die along a side edge of the first power semiconductor device die, and wherein no part of the side edge of the first power semiconductor device die is N type semiconductor material.

23. The method of claim 15, wherein the first power semiconductor device die further comprises a metal layer disposed on the second substantially planar semiconductor surface of the first power semiconductor device die, wherein the second power semiconductor device die further comprises a metal layer disposed on the second substantially planar semiconductor surface of the second power semiconductor device die, and wherein the metal layer of the first power semiconductor device die is bonded to the metal layer of the second power semiconductor device die.

24. The method of claim 23, wherein a layer comprising silver bonds the metal layer disposed on the second substantially planar semiconductor surface of the first power semiconductor device die to the metal layer disposed on the second substantially planar semiconductor surface of the second power semiconductor device die.

25. The method of claim 23, wherein the wafer bonding of (a) involves sintering the layer comprising silver.

26. The method of claim 15, wherein the peripheral edge separation structure of the first power semiconductor device die is a region of P type semiconductor material, and wherein no part of the side edge of the first power semiconductor device die is N type semiconductor material.

27. The method of claim 15, wherein a metal feature covers and makes electrical contact with the peripheral edge separation structure at the first substantially planar semiconductor surface of the first power semiconductor device die, and wherein the metal feature is electrically coupled within the assembly through the peripheral edge separation structure of the first power semiconductor device die to the peripheral edge separation structure of the second power semiconductor device die.

28. The method of claim 15, wherein the first power semiconductor device die has a control electrode disposed on the first substantially planar semiconductor surface of the first power semiconductor device die, and wherein the second power semiconductor device die has a control electrode disposed on the first substantially planar semiconductor surface of the second power semiconductor device die.

29. A method comprising: wafer bonding a backside of a first wafer to a backside of a second wafer thereby obtaining a bonded wafer structure; and dicing the bonded wafer structure to obtain a die assembly, wherein the die assembly comprises a first die and a second die, wherein the first die comprises a peripheral edge separation structure that extends from a first substantially planar semiconductor surface of the first die to a second substantially planar semiconductor surface of the first die along a side edge of the first die, wherein the second die comprises a peripheral edge separation structure that extends from a first substantially planar semiconductor surface of the second die to a second substantially planar semiconductor surface of the second die along a side edge of the second die, wherein the peripheral edge separation structure of the first die is a region of P type semiconductor material, and wherein no part of the side edge of the first die is N type semiconductor material, and wherein the peripheral edge separation structure of the first power semiconductor device die is electrically coupled within the die assembly to the peripheral edge separation structure of the second die.

30. The method of claim 29, further comprising: attaching a bond wire to a bond pad, wherein the bond pad is disposed on a surface area of the peripheral edge separation structure of the first die.

31. The method of claim 29, further comprising: attaching a wafer interface member to a topside of the second wafer prior to the dicing such that the wafer interface member is diced along with the first and second wafers, wherein the die assembly comprises the first die, the second die, and a die-sized interface member cut from the wafer interface member, wherein the die-sized interface member comprises a first metal feature and a second metal feature, wherein the first metal feature is in electrical contact with a first metal electrode of the second die, and wherein the second metal feature is in electrical contact with a second metal electrode of the second die.

32. The method of claim 29, wherein the first die further comprises a metal layer disposed on the second substantially planar semiconductor surface of the first die, wherein the second die further comprises a metal layer disposed on the second substantially planar semiconductor surface of the second die, and wherein the metal layer of the first die is bonded to the metal layer of the second die.

33. The method of claim 32, further comprising: a layer comprising silver, wherein the layer comprising silver bonds the metal layer disposed on the second substantially planar semiconductor surface of the first die to the metal layer disposed on the second substantially planar semiconductor surface of the second die.

34. The method of claim 28, wherein the peripheral edge separation structure of the first die is a region of P type semiconductor material, and wherein no part of the side edge of the first die is N type semiconductor material.

35. The method of claim 28, wherein a metal feature covers and makes electrical contact with the peripheral edge separation structure at the first substantially planar semiconductor surface of the first die, and wherein the metal feature is electrically coupled within the die assembly through the peripheral edge separation structure of the first die to the peripheral edge separation structure of the second die.

36. The method of claim 28, wherein the first die has a control electrode disposed on the first substantially planar semiconductor surface of the first die, and wherein the second die has a control electrode disposed on the first substantially planar semiconductor surface of the second die.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.

[0007] FIG. 1 is a cross-sectional side view of a stacked power semiconductor device die assembly in accordance with one novel aspect.

[0008] FIG. 2 is a circuit diagram of the assembly of FIG. 1.

[0009] FIG. 3 is a perspective diagram of a die stack assembly involving a first power semiconductor device die, a second power semiconductor device die, and a die-sized interface member, where the die stack assembly is mounted to the top of a substrate.

[0010] FIG. 4 is a cross-sectional diagram of the assembly of FIG. 3.

[0011] FIG. 5 is a flowchart of a method of fabricating a packaged power semiconductor device in accordance with another novel aspect.

[0012] FIG. 6 is a cross-sectional diagram of a peripheral edge separation structure that may be employed in the structures of FIG. 1, FIG. 3 and FIG. 4.

DETAILED DESCRIPTION

[0013] Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the description and claims below, when a first object is referred to as being disposed over or on or covering a second object, it is to be understood that the first object can be directly on the second object, or an intervening object may be present between the first and second objects. Similarly, terms such as top, bottom, side, up, upward, down, downward, vertically, horizontally, laterally, lower and underneath describe relative orientations between different parts of the structure being described, and it is to be understood that the overall structure being described can actually be oriented in any way in three-dimensional space.

[0014] FIG. 1 is a cross-sectional side view diagram of a power semiconductor device assembly 1. Assembly 1 includes a first power semiconductor device die 2 and a second power semiconductor device die 3. The backside of the first die 2 is bonded to the backside of the second die 3 by a conductive metal layer 4. In one example, conductive metal layer 4 is a layer of sintered silver. The first and second dice 2 and 3 are shown in simplified fashion. Each of the first and second dice 2 and 3 may, for example, include additional peripheral guard rings (not shown) and a metal field plate (not shown) as is known in the power semiconductor device arts.

[0015] The first die 2 is a thyristor die (also called a SCR or Silicon Controlled Rectifier). The first die 2 has a P type semiconductor region 5, an N type semiconductor region 6, a P type semiconductor region 7, and an N type semiconductor region 8. The N type semiconductor region 8 is referred to as the N-emitter region. The P type semiconductor region 7 is referred to as the P-base region. The P type semiconductor region 5 comprises a planar P type layer portion 5A that extends across the entire backside of the die as well as a peripheral edge separation P type diffusion region 5B. The two regions 5A and 5B merge together to form the larger P type semiconductor region 5. Region 5A is also referred to as the P-emitter region. The peripheral edge separation diffusion region 5B is an amount of P type semiconductor material that extends all the way from a first substantially planar semiconductor surface 2A of the die to a second substantially planar surface 2B of the die along a side edge 9 of the die. No part of any side edge of the first die 2 is N type semiconductor material. At least a part of the P type semiconductor region 5 is doped with aluminum. The first die 2 has a reverse breakdown voltage in excess of 3000 volts. A metal anode electrode 10 makes contact with the bottom surface of the P-emitter region 5. It is to this metal anode electrode 10 that the conductive layer 4 bonds. At the top of the die 2, a metal feature 11 makes contact with the N type region 8. Region 8 is also referred to as the N-emitter region. Metal feature 11 is the metal cathode electrode of the device. A metal feature 12 is disposed on the top semiconductor surface 2A and makes contact the P type P-base region 7. This metal feature 12 is the metal gate electrode (a control electrode) of the device. A metal feature 13 is disposed on the top surface of the P type peripheral edge separation diffusion region 5B. This metal feature 13 is the metal anode electrode of the device. Metal feature 13, when the die is considered from the top-down perspective, appears as a four-sided peripheral ring of metal that extends along the four peripheral edges of the die 2. This ring of metal is not entirely covered with passivation, but rather is at least in part exposed from the top of die 2 so that an electrode connection can be made down to the ring by one or more bond wires. Reference numeral 14 identifies areas of passivation that are disposed on the top semiconductor surface 2A.

[0016] The second die 3 is an Anode-Gated Thyristor (an AGT) die. Second die 3 has a P type semiconductor region 15, an N type semiconductor region 16, a P type semiconductor region 17, and an N type semiconductor region 18. N type region 19 is also referred to as the N-emitter region. The P type semiconductor region 15 is also referred to as the P-emitter region. The N type semiconductor region 18 is also referred to as the N-emitter region. The P type semiconductor region 17A is also referred to as the P-base region. P type semiconductor region 17 comprises a planar P type layer portion 17A that extends across the entire backside of the die as well as a peripheral edge separation P type diffusion region 17B. The two regions 17A and 17B merge together to form the larger P type semiconductor region 17. The peripheral edge separation diffusion region 17B is an amount of P type semiconductor material that extends all the way from a first substantially planar semiconductor surface 20A of the die to a second substantially planar surface 20B of the die along a side edge 21 of the die. At least a part of the P type semiconductor region 17 is doped with aluminum. A metal cathode electrode 22 makes contact with the N-emitter region 18. It is to this metal cathode electrode 22 that the conductive layer 4 bonds. A metal feature 23 makes contact with the P type P-emitter region 15. This metal feature 23 is the metal anode electrode of the device. A metal feature 24 is disposed on semiconductor surface 2A and makes contact to the N type region 19 and to the P type P-emitter region 15. This metal feature 24 is the metal gate electrode (a control electrode) of the device of the second die. Reference numeral 25 identifies an area of passivation that is disposed on the semiconductor surface 20A.

[0017] FIG. 2 is a circuit diagram of the circuit of FIG. 1. The metal anode electrode 10 of the first die 2 is mounted to, and is electrically coupled to, the metal cathode electrode 22 of the second die 3. The metal anode electrode 10 of the first die 2 is mounted to the metal cathode electrode 22 of the second die 3 by sintered silver metal layer 4. Metal feature 12 provides a gate electrode bond pad for the first die 2. Metal feature 11 provides a cathode electrode bond pad for the first die 2. Metal feature 13 provides an anode electrode bond pad for first die 2, and simultaneously provides a bond pad for the cathode electrode of the second die 3 due to the fact that the P emitter region 5 of the first die is mounted to the N-emitter region 18 of the second die. Metal feature 23 provides the anode electrode bond pad of the second die 3. Metal feature 24 provides the gate electrode bond pad of the second die 3.

[0018] FIG. 3 is a perspective view of an assembly 30. The assembly 30 includes the assembly 1 of FIG. 1, as well as a die-sized interface member 31, a substrate 32, and bond wires 33-37. Bond wire 35 physically connects at one end to a patterned metal feature 38 of the substrate 32. Substrate 32, which in one example is a Direct-Bonded Metal (DBM) or a Direct-Bonded Copper (DBC) or a Direct-Copper Bonded (DCB) structure, includes an insulative body layer 47, and several patterned metal features 38, 39, 40, 44 and 46 disposed on the insulative body layer 47. Through this bond wire 35, an electrical connection is established from the patterned metal feature 38, through the bond wire 35, to a bond pad portion 41 of the ring metal feature 13, and then through the peripheral edge separation diffusion region 5B of the first die 2, and through the metal layers 10, 4, and 22, to the N type semiconductor region 18 of the second die 3. Metal layer 22 is an electrode of the second die 3. In addition, bond wire 34 couples patterned metal feature 39 of the substrate 32 to a bond pad portion 42 of the metal cathode electrode 11 of the first die 2. Bond wire 33 couples patterned metal feature 40 to metal feature 12 (gate electrode bond pad 12) of first die 2. Each of the bond pad portions 41 and 42 and 12 on the top of the first die is at least one hundred microns wide by one hundred microns long so that there is enough square surface area of exposed metal provided for wirebonding. Bond pad portion 41 is preferably disposed less than one hundred microns from the side edge 9 of the first die 2. Metal gate electrode 24 on the bottom of assembly 1 is coupled through a metal portion 43 of the die-sized interface member 31 to a patterned metal feature 44 on the top of substrate 32. Metal anode electrode 23 on the bottom of assembly 1 is coupled through a metal portion 45 of die-sized interface member 31 to a patterned metal feature 46 on the top of substrate 32. Bond wire 37 couples the patterned metal feature 44 of the substrate 32 to another object such as, for example, a first bonding pad (not shown) of a first lead of a lead frame. Bond wire 36 couples the patterned metal feature 46 of the substrate 32 to another object such as, for example, a second bonding pad (not shown) of a second lead of the lead frame.

[0019] FIG. 4 is a cross-sectional diagram that shows the assembly 30 of FIG. 3 in more detail. The cross-sectional view of FIG. 4 is taken along sectional line A-A of FIG. 3. Die-sized interface member 31 includes an insulative layer 56 as well as number of metal portions. Although not illustrated this way in FIG. 4, insulative layer 56 may be a composite sandwich structure of multiple insulative layers and each metal portion may also be a composite sandwich structure of multiple metal layers. Each metal portion of the die-sized interface member 31 provides electrical contact from the top side of insulative layer 56, through the insulative layer 56, and to the bottom side of insulative layer 56. Two of the metal portions are identified in FIG. 4 by reference numerals 43 and 45. Passivation layer 25 on the downward facing surface of the second die 3 is substantially thicker than metal features 23 and 24. The metal portions 43 and 45 of the die-sized interface member 31 extend upward from the top surface of insulative layer 56 by enough so that the metal portion 43 makes physical and electrical contact with metal feature 24, and so that metal portion 45 makes physical and electrical contact with metal feature 23. Die-sized interface member 31 is fabricated so that the metal portions of the die-sized interface member 31 register with, and can make electrical contact with, proper corresponding metal features on the downward facing surface of the second die 3. The metal portions 43 and 45 of the die-sized interface member 31 also register with, and make electrical contact with, corresponding metal features on the top side of substrate 32. Reference numeral 57 identifies amounts of adhesive disposed between the die-sized interface member 31 and the bottom of the second die 3. Reference numeral 58 identifies an amount of sintered silver that bonds and electrically couples metal portion 43 of the die-sized interface member 31 to the corresponding metal feature 24 on the bottom of the second die 3. Reference numeral 59 identifies an amount of sintered silver that bonds and electrically couples metal portion 45 of the die-sized interface member 31 to the corresponding metal feature 23 on the bottom of the second die 3.

[0020] After the assembly structure of FIG. 3 has been fabricated, it is packaged and is thereby incorporated into a semiconductor device package. In one example, the assembly structure of FIG. 3 is wire bonded and/or attached as appropriate to a stamped metal lead frame (not shown). The assembly structure of FIG. 3 is then overmolded with a volume of an encapsulant in an injection molding process. The metal leads of the lead frame that extend from the volume of encapsulant are then trimmed and lead formed to make a standard leaded plastic semiconductor device package.

[0021] FIG. 5 is a flowchart of a method 100 in accordance with one novel aspect. A first wafer of power semiconductor devices is fabricated (step 101). Each of what will be individual dice of the first wafer has a peripheral edge separation structure. A second wafer of power semiconductor devices is fabricated (step 102). The backside of the first wafer is wafer bonded (step 103) to the backside of the second wafer, thereby obtaining a bonded wafer structure. The backside of a wafer is the side of the wafer that does not have any gate electrodes. In one example, the wafer bonding is done by sandwiching a foil of sinterable material between the two wafers, and then under pressure heating the sandwich such that the silver of the sinter foil sinters, and in so bonds the two wafers together. A suitable sinter foil can be obtained from Alpha Sintered Metals, 95 Mason Run Road, Ridgway, Pa. 15853. With adequate pressure, the sintering temperature and duration of the sintering operation are reduced to the point that the semiconductor structures within the two wafers are not damaged in this high temperature step.

[0022] Next, a wafer-shaped interface member is attached (step 104) to the second wafer side of the bonded wafer structure. In one example, the wafer-shaped interface member is a flexible wafer-shaped interface member available from Mektec International Corporation, 1731 Technology Drive, Suite 840, San Jose, Calif. 95110. The flexible wafer-shaped interface member includes an insulative layer that has patterned metal portions. The insulative layer has holes through it such that each of the patterned metal portions of the wafer-shaped interface member provides an electrical connection from one side of the wafer-shaped interface member, through the insulative layer, and to the other side of the wafer-shaped interface member. The insulative layer of the wafer-shaped interface member may, for example, be a flexible layer of insulative material such as mylar or polyimide. In another example, the insulative layer is a rigid layer of insulative material such as FR4 fiberglass and epoxy. Prior to attaching the wafer-shaped interface member to the bottom of the second wafer, regions of sintered or sinterable silver may be formed or otherwise placed on the metal features on the bottom side of the second wafer. An adhesive can be applied to selected parts of the bottom of the prepared second wafer. The wafer-shaped interface member is then placed onto the adhesive. The entire sandwich structure is then heated under appropriate pressure and temperature so that discrete amounts of sinterable silver form good electrical contacts between the metal features on the bottom of the second wafer and corresponding metal portions on top of the wafer-shaped interface member.

[0023] After attachment of the wafer-shaped interface member to the second wafer of the bonded wafer structure, the bonded wafer structure is diced (step 105) so that a plurality of identical power semiconductor device die assemblies is obtained. Each power semiconductor device die assembly includes a first power semiconductor device die, a second power semiconductor device die, and a die-sized interface member. The peripheral edge separation structure of the first die is electrically coupled to an electrode of the second die. Because the first power semiconductor device die, the second power semiconductor device die, and the die-sized interface member are all cut at the same time from the same bonded wafer structure, the periphery of the first die, the periphery of the second die, and the periphery of the die-sized interface member are all identical. The cross-section of the power semiconductor device die assembly is as shown in FIG. 4.

[0024] Next, bond wires are attached (step 106) to bond pads on the top surface of the power semiconductor device assembly. In one example, the bottom of the power semiconductor device assembly is mounted to the top of a substrate, and certain of the bond pads on the top of the power semiconductor device die assembly are wire bonded to patterned metal features on the top of the substrate as shown in FIG. 3. The bottom of the resulting structure is placed on a device support portion of a lead frame, and more wire bonding is performed to connect appropriate parts of the assembly and/or substrate to corresponding bonding pads of leads of the lead frame. After the wire bonding, a wire bond is left attached to a bond pad on the top surface of the die assembly such that an electrical connection exists from the bond wire, through the bond pad, through the peripheral edge separation structure of the first die, and to an electrode of the second die. Typically, several bond wires will be attached to the same four-sided ring-shaped metal feature 13. These several bond wires provide separate parallel current paths to/from the four-sided ring-shaped metal feature 13. Accordingly, the novel ring-shaped metal feature 13 may have a ring of bond pad areas for engaging multiple separate bond wires. After the assembly and the substrate have been mounted and wirebonded as appropriate to the leadframe, a semiconductor device package is formed (step 108) that contains the assembly. The forming of the semiconductor device package may, for example, include the step of injection molding an amount of molding compound over the assembly, then step of lead forming, and the step of lead trimming.

[0025] In a first example of the method of FIG. 5, the peripheral edge separation structure of the first wafer is formed by providing a first strip of aluminum on the top of the N-type wafer so that the strip extends along what will be the ultimate side edges of the device die. A second strip of aluminum is provided on the opposite side of the wafer, directly underneath the first strip. The two aluminum strips act as a diffusion sources. The aluminum strips are first converted into aluminum oxide by heating the first wafer in a nitrogen-oxygen atmosphere at a temperature of about 500 degrees Celsius, which is a temperature below the 660 degree Celsius melting point of aluminum. Once the aluminum has been oxidized, the first wafer is heated to a higher temperature of about 1250 degrees Celsius. Under this higher temperature condition, aluminum from the aluminum oxide strips diffuses into the first wafer, thereby forming a downward extending P type region that extends downward from the top semiconductor surface of the wafer, and thereby forming an upward extending P type region that extends upward from the bottom semiconductor surface of the wafer. The two diffusion fronts of aluminum meet, thereby forming a peripheral P type region that extends all the way from the top semiconductor surface of the wafer, through the wafer, and to the bottom semiconductor surface of the wafer. The entire backside of the first wafer is doped with boron to form a P type layer. In each device area of the wafer, this boron-doped P type layer merges with a P type peripheral edge separation diffusion region to form an overall P type anode region. This P type region separates the active area of the device in the center of what will be the die (after singulation) from what will be the side edges of the die (after singulation). The peripheral edge separation structure keeps the high electric fields of the reverse biased depletion region in the active area from reaching the side edges of the die. For additional information on peripheral edge separation structures and techniques suitable for use in making the first die 2, see: 1) U.S. patent application Ser. No. 14/948,156, entitled Trench Separation Diffusion For High Voltage Device, filed Nov. 20, 2015, by Wisotzki et al.; 2) U.S. Pat. No. 7,442,630, entitled Method For Fabricating Forward And Reverse Blocking Devices, filed Aug. 30, 2005, by Kelberlau et al.; and 3) U.S. Pat. No. 5,698,454, entitled Method Of Making A Reverse Blocking IGBT, filed Jul. 31, 1995, by N. Zommer (the entire subject matter of each of these patent documents is incorporated by reference herein).

[0026] In a second example of the method, the peripheral edge separation structure of the first wafer is the structure shown in cross-section in FIG. 6. As in the case of the peripheral edge separation structure of FIG. 1, a region of P type semiconductor material extends all the way from the top substantially planar semiconductor surface of the wafer to the bottom substantially planar semiconductor surface of the wafer. In the case of the peripheral edge separation structure of FIG. 6, this P type semiconductor material includes an amount of P type polysilicon 61 disposed on a sidewall of a peripheral trench 48, and also includes a region of P type semiconductor material 49 that extends upward from semiconductor surface 2B. After deposition of P type polysilicon 61 in the trench, the remainder of the trench is filled, for example with oxide 50. A peripheral four-sided ring-shaped metal feature 51 extends along the peripheral side edges of the die of FIG. 6 at surface 2A in the same way that the four-sided ring-shaped metal feature 13 extends along the peripheral side edges of the first die of FIG. 1. P type layer 60 of FIG. 6 corresponds to P type layer 5A of FIG. 1. Metal layer 52 of FIG. 6 corresponds to metal layer 10 of FIG. 1. Passivation layer 53 of FIG. 6 corresponds to passivation layer 14 of FIG. 1. N type region 54 of FIG. 6 corresponds to N type region 6 of FIG. 1. Side edge 55 of FIG. 6 corresponds to side edge 9 of FIG. 1. For additional information on the peripheral edge separation structure of FIG. 6, see: U.S. patent application Ser. No. 14/948,156, entitled Trench Separation Diffusion For High Voltage Device, filed Nov. 20, 2015, by Wisotzki et al. (the entire subject matter of which is incorporated by reference herein).

[0027] Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.