Power device having trenches of different vertical heights and method for producing a power device

Abstract

A power device (10) comprising a first electrode (1), a second electrode (2), a semiconductor body (3) and a plurality of trenches (4) having different vertical heights (H) is provided. The semiconductor body (3) is located between the first electrode (1) and the second electrode (2). The semiconductor body (3) comprises a first part (31) adjoining the first electrode (1) and a second part (32) adjoining the second electrode (2). Along a vertical direction from a rear side (10R) towards a front side (10F) of the power device (10), the trenches (4) extend from a rear side (10R) of the power device (10) throughout a layer of the second electrode (2) into different vertical regions of the second part (32). Moreover, a method for producing such a power device (10) is provided.

Description

[0001]P2024,0651 WO E / P240042WO01 September 6, 2024 - 1 - Description POWER DEVICE HAVING TRENCHES OF DIFFERENT VERTICAL HEIGHTS AND METHOD FOR PRODUCING A POWER DEVICE The present disclosure relates to a power device having trenches of different vertical heights and a method for producing a power device. It is a challenge for providing power devices having a controlled injection of charge carriers for achieving improved reverse recovery softness and improved dynamic ruggedness. For example, a controlled injection of holes to compensate electrons serves to limit a high electric field peak at a cathode side that power devices may experience during strong dynamic avalanche. This is of particular interest at low currents when the performance of a power device is limiting. Moreover, at extreme switching conditions, snap-off behaviors and high voltage oscillations are common but not desired. Embodiments of the present disclosure address the above shortcomings in whole or in part. The embodiments of a power device and of a method for producing a power device are subject matters of the independent and dependent claims. The present disclosure proposes a new engineered rear side design of a power device that targets the problem of how to avoid or reduce snap-off behaviors and high voltage oscillations as well as to achieve an improved reverse recovery softness and improved dynamic ruggedness. In an embodiment of a power device, the device comprises a first electrode, a second electrode, a semiconductor body and P2024,0651 WO E / P240042WO01 September 6, 2024 - 2 - a plurality of trenches having different vertical heights. The semiconductor body is located between the first electrode and the second electrode. The semiconductor body comprises a first part adjoining the first electrode and a second part adjoining the second electrode. Along a vertical direction from a rear side towards a front side of the power device, the trenches extend throughout a layer of the second electrode into different vertical regions of the second part. The layer of the second electrode, through which the trenches extend, can be electrically conductive layer, for instance a doped semiconductor layer, but is not necessarily restricted thereto. In virtue of the trenches having different vertical heights within the second part of the semiconductor body, a controlled injection of charge carriers can be achieved. This results in achieving an improved reverse recovery softness and improved dynamic ruggedness. Such a power device, for instance a high power diode device, can have a tailored backside or rear side with trenches of different vertical heights which can be formed for instance by using a common masking step resulting in reduction of cost and fabrication complexity. In particular, for a power device having a Bi-mode Insulated Gate Transistor, BIGT, structure, a smooth transition from a pilot Insulated-Gate Bipolar Transistor, IGBT, region to Reverse Conducting Insulated-Gate Bipolar Transistor, RC- IGBT, region / s can be achieved via using the trenches of different vertical heights for instance for the purpose of tuning mixed regions within the second part of the semiconductor body. Thus, it is possible to tailor the mixed regions in a third dimension to help ameliorate so-called P2024,0651 WO E / P240042WO01 September 6, 2024 - 3 - secondary snapback events. Using the trenches having different vertical heights, this disclosure can be targeted for low-voltage BIGT devices where low current snapback, diode softness and heat distribution can be particularly problematic as plasma uniformity can be difficult to achieve in such thin devices. According to a further embodiment of the device, the plurality of trenches having different vertical heights are configured to provide a controlled rear side injection, i.e. backside injection, of charge carriers, for instance of electrons or holes. A controlled injection of backside holes may lead to an improved reverse recovery softness and improved dynamic ruggedness. The power device can comprise diode structure / s or RC-IGBT / BIGTs structures with controlled backside injection of charge carriers like holes or electrons. According to a further embodiment of the device, for instance in plan view of the rear side of the power device, the trenches of different vertical heights comprise different lateral widths, wherein the wider the lateral width of one trench is, the larger is the vertical high of that one trench. Thus, the trenches of different vertical heights or depths can be fabricated using one single backside masking step which can take advantage for example of dry etch processes that yield different trench depths depending on the initial masking dimensions. According to a further embodiment of the device, for instance in plan view of the rear side of the power device, at least some of the trenches have different lateral lengths and / or orientations. An appropriate distribution of the trenches P2024,0651 WO E / P240042WO01 September 6, 2024 - 4 - regarding the lateral lengths and / or orientations may result in a controlled injection of charge carriers from the rear side. This may lead to a highly homogeneous distribution of charge carriers within the semiconductor body even at low currents. According to a further embodiment of the device, at least in places along one lateral direction, for instance from a central region of the rear side to an edge region of the rear side or from one edge region to an adjacent or opposite edge region of the rear side, the vertical heights of the different trenches monotonically change, for instance monotonically increase or monotonically decrease. It is possible that along a lateral direction from an edge of the rear side via a central region of the rear side to another edge, for instance to an opposite edge of the rear side, the vertical heights monotonically increase and then monotonically decrease, or vice versa. At the central region, the trenches may have the largest vertical heights or the smallest vertical heights, respectively. According to a further embodiment of the device, the power device is a Bi-mode Insulated Gate Transistor, BIGT. The device can comprise a pilot Insulated-Gate Bipolar Transistor, IGBT, region. The device can further comprise a Reverse Conducting Insulated-Gate Bipolar Transistor, RC- IGBT, region. The trenches can be formed in the RC-IGBT region, for instance only in the RC-IGBT region. In virtue of the trenches of different vertical heights, a smooth transition from a pilot Insulated-Gate Bipolar Transistor, IGBT, region to Reverse Conducting Insulated-Gate Bipolar Transistor, RC-IGBT, region / s can be achieved, since P2024,0651 WO E / P240042WO01 September 6, 2024 - 5 - the trenches of different vertical heights can be used for achieving a controlled injection of electrons or for the purpose of tuning mixed regions within the second part of the semiconductor body for achieving a controlled injection of holes. Using the trenches having different vertical heights, low-voltage BIGT devices having improved snapback behavior and enhanced diode softness as well as improved heat distribution properties can be achieved. According to a further embodiment of the device, the second electrode or the rear side comprises a centrally arranged pilot electrode for the pilot IGBT region. At least along one lateral direction from the RC-IGBT region towards the pilot IGBT region, the vertical heights of the different trenches can monotonically change. For instance, the vertical heights of the different trenches filled with an electrically conductive material monotonically decrease towards the pilot electrode. This may result in achieving a controlled injection of holes. It is also possible that the vertical heights of the different trenches filled with an electrically insulating material monotonically increase towards the pilot electrode. This may result in achieving a controlled injection of electrons. According to a further embodiment of the device, on the rear side or in a plan view of the rear side of the power device, the trenches are arranged in a symmetrical manner. A symmetrical arrangement of the trenches on the rear side, for instance around a pilot electrode may lead to soft transition between the pilot IGBT region and the RC-IGBT region / s which may result in an improved reverse recovery and improved softness for a diode structure or a BIGT structure. P2024,0651 WO E / P240042WO01 September 6, 2024 - 6 - According to a further embodiment of the device, the second part comprises a plurality of local mixed regions at different vertical depths of the second part. The trenches can extend into the local mixed regions. The trenches can be filled with an electrically conductive material. The local mixed regions may be p+ regions or n+ regions. The local mixed regions can be located completely within the second part of the semiconductor body. It is, however, possible for some of the local mixed regions to be located at boundary regions between the first part and the second part of the semiconductor body. Using the trenches of different heights, appropriate ion implantation can be performed through the trenches for forming a plurality of local mixed regions at different vertical depths. Thus, a power device with a tailored rear side with different p-doped or n-doped depths can be manufactured for instance by using the same masking step resulting in a reduction of cost and fabrication complexity. Although the replacement for instance of an n+ cathode region by for instance a p+ region may lead to decreased injection efficiency of the cathode and increased Vf, when properly adjusted for instance by increasing the cathode n+ doping concentration, the diode softness can be achieved without performance loss. According to a further embodiment of the device, the first electrode is an anode of the power device. The second electrode is a cathode of the power device. The local mixed regions are p+ doped regions. The trenches can form local p+ anode shorts. P2024,0651 WO E / P240042WO01 September 6, 2024 - 7 - Such a power device, for instance a power diode, can have a varied depth p+ doped backside design that can be processed with a single masking step as desired for tailored hole injection, softness and improved reverse recovery. Having varied depth p+ doped regions separated by a particular distance allow for hole injection in a controlled step-wise manner. In virtue of this, reverse recovery can be slowed down and the device snappiness can be avoided. According to a further embodiment of the device, the first electrode is a cathode of the power device. The second electrode is an anode of the power device. The local mixed regions are n+ doped regions. The trenches can form local n+ cathode shorts. Such a power device, for instance a power diode, can have a varied depth n+ doped backside design that can be processed with a single masking step as desired for tailored electron injection, softness and improved reverse recovery. Having varied depth n+ doped regions separated by a particular distance allow for electron injection in a controlled step- wise manner. The power device can be a BIGT device with a pilot / RC-IGBT structure. It is possible that the deepest trenches, i.e. trenches with largest vertical heights, with n+ cathode shorts, which can be connected to a rear side cathode metal, are located closest to a termination area. The vertical heights of the trenches can decrease monotonically towards the pilot region. The shortest trenches, i.e. trenches with smaller or smallest vertical heights, for instance with n+ cathode shorts, can be located next to the pilot region. Thus, electrons coming from a frontside channel can reach the P2024,0651 WO E / P240042WO01 September 6, 2024 - 8 - pilot region first so that the pilot area or the pilot electrode starts injecting holes already at low currents. According to a further embodiment of the device, the trenches are filled with an electrically insulating material, for instance with polysilicon, for instance with undoped polysilicon, or dielectric borophosphosilicate glass, BPSG. The trenches of different vertical heights can act as electron blocking barriers. This may result in a controlled injection of charge carriers for instance from the rear side of the power device. The first electrode can be a cathode of the power device. The second electrode comprises contact regions being for instance p+ anode regions of the power device. On the rear side or in plan view of the rear side, the power device can further comprise additional electrical contacts, wherein each of the additional electrical contacts can be arranged between two adjoining trenches. The additional electrical contacts can be electrically connected to the second part of the semiconductor body and form n+ cathode shorts. The power device can be BIGT device with a pilot / RC-IGBT structure. The trenches can be filled with an electrically insulating material, for instance with polysilicon or another dielectric like borophosphosilicate glass, BPSG. For such an embodiment, the trenches having varied depths can be fabricated in a single masking step and subsequently be filled with the electrically insulating material. In this case, the trenches would serve to trap electrons or hamper electron movement, for instance to increase electron path from a front side to find an n+ short, for example one of the n+ cathode shorts at the rear side, to make the pilot region P2024,0651 WO E / P240042WO01 September 6, 2024 - 9 - more efficient at low currents. It is possible that the shortest trenches, i.e. trenches with smallest vertical heights are located closest to a termination area. The vertical heights of the trenches can increase monotonically towards the pilot region. The deepest trenches, i.e. trenches with larger or largest vertical heights, can be located next to the pilot region. According to a further embodiment of the device, the second part comprises a plurality of local mixed regions. The local mixed regions can form additional electrical contacts. The local mixed regions or the additional electrical contacts can form n+ cathode shorts, for example at the rear side. It is possible that a separate masking step may be applied to define the n+ cathode shorts. In an embodiment of a method for producing a power device comprising a first electrode, a second electrode, a semiconductor body and a plurality of trenches having different vertical heights, the method comprises a step of providing the semiconductor body. The semiconductor body comprises a first part and a second part, wherein the first part adjoins the first electrode, and wherein the second electrode adjoins the second part. The semiconductor body is located between the first electrode and the second electrode. The method further comprises a step of forming the plurality of trenches in the second part of the semiconductor body using a single mask, wherein along a vertical direction from a rear side towards a front side of the power device, the plurality of trenches extend throughout a layer of the second electrode into different vertical regions of the second part. P2024,0651 WO E / P240042WO01 September 6, 2024 - 10 - According to a further embodiment of the method, for forming the plurality of trenches, the single mask has openings of different lateral widths and is provided for instance on the rear side of the power device or on the second electrode. The plurality of trenches having different vertical heights are formed by a common etching step. The different vertical heights of the trenches can depend on the different lateral widths of the openings of the mask. Thus, only one single masking step can be used for forming all trenches of different heights. This reduces the production cost and fabrication complexity. According to a further embodiment of the method, the common etching step is performed by a dry etching process, for instance by a BOSCH type process or by other anisotropic dry etching process. According to a further embodiment of the method, after forming the plurality of trenches, ion implantation is performed through the trenches for forming a plurality of local mixed regions at different vertical depths of the second part. The trenches can be subsequently filled with an electrically conductive material extending into the local mixed regions. In other words, the electrically conductive material can be adjacent to the local mixed regions. This disclosure suggests the production of a power device having a varied depth doping backside design which can be processed with a single masking step as desired for tailored charge carrier injection, softness and improved reverse recovery in a diode. The power device can have a general diode structure or a BIGT / RC-IGBT structure. In contrast to conventional methods, for achieving such varied depth doping P2024,0651 WO E / P240042WO01 September 6, 2024 - 11 - profiles, no expensive fabrication processes such as epitaxial layer deposition and proton implantation are needed. All trenches can be manufactured using a single masking step as the final depths or heights of the trenches depend on the initial mask opening dimensions. Here, a dry etching process can be used, for instance a BOSCH type process (C4F8 passivation step, O2 cleaning step and a SF6 isotropic etch step in consecutive pulsed cycles) or another anisotropic dry etching process using for example a mix of SF6 and C4F8. According to a further embodiment of the method, the trenches are filled with an electrically insulating material which can act as electron blocking barriers. According to a further embodiment of the method, the method is configured to produce any of the power devices described in this disclosure. The present disclosure comprises several embodiments of the power device and of the method for producing a power device. Every feature described with respect to one of the embodiments is also disclosed herein with respect to the other embodiments, even if the respective feature is not explicitly mentioned in the context of the specific embodiment. For example, the method described in this disclosure is directed to a method for producing the power device described in this disclosure. Thus, features and advantages described in connection with the power device can be used for the method, and vice versa. While the disclosure is amenable to various modifications and alternative forms, specifics thereof are shown by way of examples in the figures and will be described in detail. It P2024,0651 WO E / P240042WO01 September 6, 2024 - 12 - should be understood, however, that the intention is not to limit the disclosure to the particular described embodiments and examples. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure defined by the appended claims. The accompanying figures are included to provide further understanding of the disclosure. In the figures, elements of the same structure and / or functionality may be assigned to the same reference signs. It is to be understood that the examples shown in the figures are illustrative representations and are not necessarily true to scale. Figure 1 shows a general concept of a power device comprising a plurality of trenches having different vertical heights. Figure 2 shows a concrete example of a power device comprising a plurality of trenches having different vertical heights. Figures 3A, 3B and 3C show another example of a power device comprising a plurality of trenches having different vertical heights. Figures 4A, 4B, 4C and 5 show further examples of a power device comprising a plurality of trenches having different vertical heights. Figure 6 shows different expanding phases of charge carrier density in a BIGT. Figure 7A shows a distribution of charge carriers within one power device during a turn-off phase. P2024,0651 WO E / P240042WO01 September 6, 2024 - 13 - Figures 7B shows a turn-off behavior of one power device with contributions from pilot tail and RC tail. Figures 8A and 8B show turn-off behaviors of different power devices for having a comparison. Figures 9A, 9B and 9C show some method steps of an example of a method for producing a power device. Figures 10A, 10B and 10C show some method steps of another example of a method for producing a power device. Figures 11A, 11B and 11C show some method steps of a further example of a method for producing a power device. Figure 1 schematically shows a section of a power device 10. The power device 10 can be a diode, for instance high power diode or a Bi-mode Insulated Gate Transistor, BIGT. A device 10 being a BIGT can comprise a pilot Insulated-Gate Bipolar Transistor, IGBT, region and further comprises a Reverse Conducting Insulated-Gate Bipolar Transistor, RC-IGBT, region. The power device 10 comprises a first electrode 1, a second electrode 2 and a semiconductor body 3. The semiconductor body 3 comprises a first part 31 adjoining the first electrode 1 and a second part 32 adjoining the second electrode 2. Each of the first part 31 and of the second part 32 can be formed from a single semiconductor layer or from a sequence of semiconductor layers. The first electrode 1 can be in direct electrical contact to the first part 31. The second electrode 2 can be in direct electrical contact to the P2024,0651 WO E / P240042WO01 September 6, 2024 - 14 - second part 32. The semiconductor body 3 is located between the first electrode 1 and the second electrode 2. The first electrode 1 and / or the second electrode 2 can comprise a doped semiconductor layer and / or a metallization. As shown in Figure 1, the second electrode 2 can comprise at least one layer 30, through which trenches 4 extend. The second electrode 2 can comprise a metallization 20. The metallization 20 can be adjacent to the layer 30 and / or to the trenches 4. The trenches 4 can be filled with a material which can differ from a material of the metallization 20 or can be the same as the material of the metallization 20. It is possible that the metallization 20 partially or completely covers a rear side 10R of the power device 10. It is possible for power device 10 shown in subsequent Figures 2 to 5, 9C, 10C and 11C to comprise such a second electrode 2 including the layer 30 only or the layer 30 and the metallization 20. For the sake of clarity and for better illustrating the sizes and the arrangements of the trenches 4, in Figures 2 to 5, 9C, 10C and 11C, the second electrode 2 is shown in a simplified manner without explicitly showing the layer 30 and / or the metallization 20. It is possible that at least in places, a boundary region between the first part 31 and the second part 32 comprises a p-n-junction or several p-n-junctions. The second part 32 can form a buffer region. It is possible for the first part 31 and the second part 32 to be at least locally the p-side and the n-side of the power device 10, respectively, or vice versa. Thus, the first electrode 1 and the second electrode 2 can be anode and cathode, respectively, or vice versa. P2024,0651 WO E / P240042WO01 September 6, 2024 - 15 - As shown in Figure 1, a front side 10F of the power device 10 can comprise a surface of the first electrode 1. A rear side 10R of the power device 10 can comprise a surface or several surfaces of the second electrode 2. The rear side 10R can be formed by surface of a layer of the second electrode 2, for instance of a doped layer or of a metallization of the second electrode 2. Here, a lateral direction x or y can be understood to mean a direction which is parallel to the front side 10F and / or to the rear side 10R of the power device 10. Thus, a vertical direction z can be understood to mean a direction which is directed perpendicular to the front side 10F and / or to the rear side 10R of the power device 10. The vertical direction z and the lateral direction x or y are orthogonal to each other. Within a lateral plane, a first lateral direction x and a second lateral direction y can be orthogonal to each other. The power device 10 comprises a plurality of trenches 4 having different vertical heights H and / or different lateral widths W. Along the vertical direction z, the trenches 4 extend throughout a layer of the second electrode 2 into different vertical regions of the second part 32. The layer can be a doped layer, for instance a doped semiconductor layer formed as part of the electrode 2. For example, the trenches 4 extend towards the front side 10F only as far as the second part 32 of semiconductor body 3. In other words, it is possible that none of the trenches 4 extends into the first part 31 of the semiconductor body 3. A targeted distribution of the trenches 4 having different vertical heights H within the second part 32 of the semiconductor body 3 may result in a controlled injection of charge carriers from the rear side 10R of the power device P2024,0651 WO E / P240042WO01 September 6, 2024 - 16 - 10, for instance in a controlled injection of positively charged charge carriers or holes. This may lead to a highly homogeneous distribution of charge carriers within the semiconductor body 3. Depending on different applications, the trenches 4 may be filled with an electrically conductive material or with an electrically insulating material for having a controlled injection of backside charge carriers. For instance, the controlled injection of backside holes can result in an improved reverse recovery softness and improved dynamic ruggedness. The controlled injection of holes to compensate electrons, or vice versa, may serve to limit a high electric field peak that the power device may experience during strong dynamic avalanche. This is of particular importance at low currents where the performance of a power device is limiting. It is possible for the vertical heights H and / or for lateral width W of the different trenches 4 to monotonically change, for instance monotonically increase or monotonically decrease, at least in places along one lateral direction as shown in Figure 1. Here, from a left side towards a right side along the lateral direction y, the vertical heights H of the different trenches 4 can monotonically decrease. From the left side towards the right side along the lateral direction y, the lateral widths W of the different trenches 4 can monotonically decrease. The left side can be a central region of the rear side 10R and the right side can be an edge region of the rear side 10R, or vice versa. For example, there is a correspondence between the vertical height H and the lateral width W of the trench 4. It is possible that the wider the lateral width W the trench 4 is, the larger is the vertical high H of the trench 4. P2024,0651 WO E / P240042WO01 September 6, 2024 - 17 - Figure 2 shows a concrete example of a power device 10 comprising a plurality of trenches 4 having different vertical heights H. The example of a power device 10 shown in Figure 2 substantially corresponds to the example of a power device 10 shown in Figure 1. In deviation from Figure 1, the power device 10 shown in Figure 2 comprises a plurality of local mixed regions 32M at different vertical depths of the second part 32. The trenches 4 can be filled with an electrically conductive material 42, wherein the trenches 4 or material 42 of the trenches 4 can extend into the local mixed regions 32M. It is possible that the first electrode 1 is an anode of the power device 10. In this case, the second electrode 2 is a cathode of the power device 10. The second electrode 2 can be an n+ cathode. The local mixed regions 32M can be p+ doped regions. Thus, the trenches 4, which are filled with an electrically conductive material 42, can form local p+ anode shorts. It is possible that trenches 4 filled with the electrically conductive material 42 are in direct electrical contact with the second electrode 2. For producing such a power device 10, the second electrode 2 being for instance a cathode and / or the second part 32 being for instance a buffer area can be first produced by method steps like deep diffused buffer followed by ion implantation for instance of phosphorus plus laser annealing, or proton buffer followed by low temperature anneal, or ion implantation for instance of phosphorus plus laser annealing alone or thermal activation in a furnace. The trenches 4 of different depths or heights H and / or of different widths W and / or lengths L can be processed with a single masking step. The height H of one trench 4 depends for instance on initial P2024,0651 WO E / P240042WO01 September 6, 2024 - 18 - mask opening. The mixed regions 32M being p+ areas can be implanted and activated by a thermal step, for instance by laser anneal or by a high temperature step. As an alternative, it is possible that the first electrode 1 is a cathode of the power device 10. The second electrode 2 can be an anode of the power device 10, for instance a p+ anode. The local mixed regions 32M can be n+ doped regions. The trenches 4 can form local n+ cathode shorts. The power device 10 can be a diode, for instance a BIGT device as shown for instance in Figures 3A, 3B and 3C. Figures 3A, 3B and 3C show a further concrete example of a power device 10 comprising a plurality of trenches 4 having different vertical heights H. The example of a power device 10 shown in Figure 3A substantially corresponds to the example of a power device 10 shown in Figure 1. In deviation from Figure 1, the power device 10 shown in Figure 3A comprises a plurality of local mixed regions 32M at different vertical depths of the second part 32 as shown for example in Figure 2. The trenches 4 can be filled with an electrically conductive material 42, wherein the trenches 4 or material 42 of the trenches 4 can extend into the local mixed regions 32M. As further deviation from Figures 1 and 2, as an example in Figure 3A, the widths D and / or the heights H of the trenches 4 monotonically increase instead of decrease from the left to the right, for example along a lateral direction from the region 5 towards the region 6 shown in Figure 3A. Figure 3B shows a possible design of the trenches 4 on the rear side 10R. The power device 10 in this disclosure, however, is not limited thereto. P2024,0651 WO E / P240042WO01 September 6, 2024 - 19 - It is possible that the power device 10 comprises a pilot Insulated-Gate Bipolar Transistor, IGBT, region 5 and a Reverse Conducting Insulated-Gate Bipolar Transistor, RC- IGBT, region 6. In plan view of the rear side 10R, the pilot IGBT region 5 can be located in a central region on the rear side 10R. The pilot IGBT region 5 can be laterally surrounded by the RC-IGBT region / s 6. It is possible that the trenches 4 are formed in the RC-IGBT region 6, for instance only in the RC-IGBT region. From the centrally located pilot IGBT region 5, the trenches 4 can form a radial layout in the RC-IGBT region 6. Regarding the pilot IGBT region 5 and the trenches 4, the rear side 10R or the second electrode 2 can have a symmetrical design, for instance a one fold or multifold, for instance twofold or fourfold, mirror-symmetrical design, as shown in Figure 3B. Thus, in plan view of the rear side 10R, the trenches 4 are arranged in a symmetrical manner. The second electrode 2 can comprises a plurality of contact regions 62. On the lateral x-y-plane, each of the contact regions 62 can be arranged between two adjacent trenches 4. The second electrode 2 can further comprise a pilot electrode 52. The pilot electrode 52 can be electrically connected to the contact regions 62. The trenches 4 can be filled with an electrically conductive material 42 and can extend from the rear side 10R into the local mixed regions 32M. Thus, the trenches 4 filled with the electrically conductive material 42 may form a shorting design at the rear side 10R of the power device 10. Here, the shorts can be provided by the conductive material 42 of the trenches 4 which can be in electrical contact with the contact regions 62. It has been found that, at extreme switching conditions, for instance at low currents and high variations of currents in P2024,0651 WO E / P240042WO01 September 6, 2024 - 20 - time, a so-called diode snap-off or snap-back and high voltage oscillations are common. The diode turn-off behavior can be made softer by using a field charge extraction effect, FCE, structure in which for instance additional p+ regions are placed on a n+ cathode area. At the end of the reverse recovery phase, the high electric field towards the cathode area forces an injection of holes from the p-doped regions adding to the reverse recovery current resulting in a prevention of a snap-off behavior. Hence, the trenches 4 at the rear side 10R as shown in Figure 2 or 3A may provide a shorting design for providing a reduced snap-off or snap-back characteristics or even a snap-off- or snap-back-free characteristics of the power device 10, for instance at low operating voltages and / or currents. As shown in Figure 3B, at the rear side 10R of the power device 10, at least some of the trenches 4 can have different lateral lengths L and / or orientations. It is also possible that on the rear side 10R of the power device 10, at least some of the adjacent trenches 4 are oriented parallel to each other. The trenches 4 of the power device 10 shown in Figures 1 and 2 can also have such properties. The lateral length L of one trench 4 can be understood as the largest lateral extension of the trench 4 at the rear side 10R of the device 10. The lateral width D can be understood as an extension of the trench 4 along a lateral direction orthogonal to the lateral length L. As shown in Figure 3B, the trenches 4, for instance most or all trenches 4, are orientated parallel or orthogonal to either one of the diagonals the rear side 10R. In other words, a lateral expansion of such a trench 4 can intersect to adjoining edges of the rear side 10R. In deviation from P2024,0651 WO E / P240042WO01 September 6, 2024 - 21 - Figure 3B, it is possible for the trenches 4 to have other orientations, for example, parallel or orthogonal to either one the edges of the rear side 10R. In this case, a lateral expansion of such a trench 4 can intersect to opposite edges of the rear side 10R. Other orientations of the trenches 4 are also possible. A highly symmetrical arrangement of the trenches 4 around the pilot electrode 52 may lead to soft transition between the pilot IGBT region 5 and the RC-IGBT region 6 which may result in an improved reverse recovery and improved softness for a diode structure. Along a lateral direction, the lateral lengths L of the different trenches 4 can monotonically change, for instance monotonically increase in places and then monotonically decrease in places as shown for instance along the line PQ in Figure 3B. The power device 10 described here, however, is not restricted thereto. Along a lateral direction, the lateral widths W and / or the vertical heights H of the different trenches 4 can monotonically change, for example along the line PQ or MN shown in Figure 3B. Only as an example, Figure 3A shows a cross-sectional view of the power device 10 along the line MN shown in Figure 3B. It is possible that the first electrode 1 is a cathode of the power device 10. In this case, the second electrode 2 is an anode of the power device 10, for instance a p+ anode. The second electrode 2 can comprise contact regions 62 for instance for electrically contacting the RC-IGBT region 6. The contact regions 62 can be p+ anode regions 62. The second electrode 2 can comprise pilot electrode 52 for instance for electrically contacting the pilot IGBT region 5. The local mixed regions 32M can be n+ doped regions. Thus, the trenches 4, which are filled with an electrically conductive material P2024,0651 WO E / P240042WO01 September 6, 2024 - 22 - 42, can form local n+ cathode shorts. It is possible that trenches 4 filled with the electrically conductive material 42 are in direct electrical contact with the second electrode 2, for instance with the contact regions 62 and / or with the pilot electrode 52. Figure 3C shows a section of the power device 10 according to Figures 3A and 3B in three dimensions. At the rear side 10R, starting from the pilot electrode 52 towards an edge of the rear side 10R, the widths D and / or the heights H of the trenches 4 can change monotonically, for instance increase monotonically. For producing such a power device 10, which can have a pilot IGBT, RC-IGBT and / or BIGT structure, the second electrode 2 being for instance an anode and the second part 32 being for instance a buffer area can be first produced by at least one of the method steps like deep diffused buffer followed by ion implantation for instance of boron plus laser annealing, proton buffer followed by low temperature anneal, ion implantation for instance of phosphorus plus laser annealing for buffer and for instance boron implant plus laser annealing for the anode. The trenches of different depths, heights H and / or widths W can be processed with a single masking step. The height H of one trench 4 depends for instance on initial sizes of openings of a mask. The mixed regions 32M being n+ areas can be implanted for instance by ion implementation and activated by a thermal step, for instance by laser anneal or by a high temperature step. Figures 4A, 4B, and 4C show another example of a power device 10 which differs from the power device 10 shown in Figures 3A, 3B and 3C at least in that the trenches 4 are filled with P2024,0651 WO E / P240042WO01 September 6, 2024 - 23 - an electrically insulating material 41. Starting from the pilot electrode 52 and moving along a lateral direction for instance towards an edge of the rear side 10R, the widths D and / or the heights H of the trenches 4 can decrease monotonically. It is possible that the first electrode 1 is a cathode of the power device 10. The second electrode 2 can comprise contact regions 62 being for instance p+ anode regions 62 of the power device 10. At the rear side 10R, the power device 10 further comprises additional electrical contacts 61, wherein each of the additional electrical contacts 61 can be arranged between two adjoining trenches 4. The additional electrical contacts 61 can be electrically connected to the second part 32 of the semiconductor body 3 and can form n+ cathode shorts. The power device 10 shown in Figures 4A, 4B and 4C can have a BIGT structure which can comprise a RC-IGBT region 6 and a pilot IGBT region 5. For producing such a power device, the second electrode 2 being an anode and the second part 32 being for instance a buffer area can be produced by at least one of method steps like deep diffused buffer followed by ion implantation for instance of boron plus laser annealing, proton buffer followed by low temperature anneal, ion implantation for instance of phosphorus plus laser annealing for buffer and boron implantation plus laser annealing for the anode. The trenches 4 of different depths, heights H and / or widths W can be processed with a single masking step. The height H of the trench 4 depends for instance on the initial mask opening. The trenches 4 can be filled with an electrically insulating material 41 to act as electron blocking barriers. The electrically insulating material 41 P2024,0651 WO E / P240042WO01 September 6, 2024 - 24 - can be polysilicon or dielectric borophosphosilicate glass, BPSG. In a further masking step, n+ areas can be defined and activated by a thermal step, for instance by laser anneal or high temperature step. Such n+ areas and n+ cathode shorts are shown for instance in Figure 5 as the mixed regions 32M and / or as the additional contacts 61. Thus, the second part 32 can comprise a plurality of local mixed regions 32M which can be electrically connected to a rear side contact layer or with a metallization shown for instance in Figure 1. Each of the mixed regions 32M can be located between two adjacent trenches 4 filled with the electrically insulating material 41 as shown in Figure 5. Similarly to Figure 3B, Figure 4B shows a possible design of the trenches 4 and of the second electrode 2 at the rear side 10R. The rear side 10R or the second electrode can comprise a centrally arranged pilot electrode 52 for the pilot IGBT region 5. The pilot region 5 can be laterally surrounded by the RC-IGBT region 6. It is possible that the trenches 4 are formed mainly or only in the RC-IGBT region 6. Thus, in a plan view on the rear side 10R, the trenches 4 can be arranged around the pilot electrode 52, for instance in a symmetric manner. At least along one lateral direction from the RC-IGBT region 6 towards the pilot IGBT region 5, the vertical heights H of the different trenches 4 can monotonically change, for instance monotonically increase. Figure 4C shows a section of the power device 10 according to Figures 4A and 4B in three dimensions. At the rear side 10R, starting from the pilot electrode 52 towards an edge of the rear side 10R, the widths D and / or the heights H of the P2024,0651 WO E / P240042WO01 September 6, 2024 - 25 - trenches 4 can change monotonically, for instance decrease monotonically. The example of a power device 10 shown in Figure 5 substantially corresponds to the example of a power device 10 shown in Figure 4A. In deviation from Figure 4A, as shown in Figure 5, the second part 32 of the semiconductor body 3 comprises a plurality of local mixed regions 32M which can form additional electrical contacts 61 forming n+ cathode shorts as mentioned above. Figure 6 shows different expanding phases of charge carrier density, in particular of density of holes, in a power device during conduction which also illustrates the challenges to eliminate snap back / s. The power device 10 can be a diode, for instance a BIGT. Figure 6 shows a snap-back behavior of such the power device 10 at different currents I and voltage V. Figure 6 shows the distribution of holes within the power device 10, in particular in the pilot IGBT region 5 and in the RC-IGBT region / s 6. Different expanding phases of hole density, or of plasma distribution, during on-state conduction from the pilot 5 to the RC region 6 are shown with increasing current densities. Here, main and secondary snap-back effects are illustrated which can be reduced by using the ideas presented in this disclosure regarding tuning the trench depths and / or arranging the trenches 4 in a targeted manner. Figure 6 shows two phases P1 and P2. Phase P1 basically describes the conduction in the pilot IGBT region 5, wherein initial snap-back SB is effectively reduced with increasing current. Phase P2 basically describes the transition into RC- P2024,0651 WO E / P240042WO01 September 6, 2024 - 26 - IGBT which may require higher current and may suffer from snap-backs. For a power device 10 described here, due to the use of trenches 4 of different vertical heights H, a controlled injection of charge carriers from the rear side 10R can be achieved which leads to an especially homogeneous distribution of charge carriers within the semiconductor body. Thus snap-back effects can be reduced. Figure 7A shows hole density during turn-off in a power device, for instance in an IGBT. Here, the current is turned off in a forward direction. Comparing to the distribution of charge carriers even in phase P2 shown in Figure 6, the distribution of charge carriers shown in Figure 7A has a higher degree of homogeneity. For illustration purposes, Figure 7B shows a turn-off behavior of a power device 10 with contributions from a pilot tail PT and a RC tail RCT. Figure 7B shows a curve Cv describing the development of the voltage V as well as by a curve Ci describing the development of the current I as a function of time t after turn-off. As shown in Figure 7B, the curve Cv shows no voltage overshoot and no high voltage oscillations. The curve Ci shows a RC tail RCT and a pilot tail PT. This indicates that charge carriers, in particular holes, injected from the pilot region 5 create tail even at very low currents. Using the ideas presented in this disclosure regarding tuning the trench depths and / or arranging the trenches 4 in a targeted manner, both the RC tail RCT and the pilot tail PT can be made better, i.e. shorter. It is also possible to have full P2024,0651 WO E / P240042WO01 September 6, 2024 - 27 - removal of the pilot tail PT if the pilot region is not required to mitigate low current snapback which would result in less turnoff losses. In general, the turn-off behavior can be made softer by using a field charge extraction, FCE, effect. For example, additional p+ regions can be placed on an n+ cathode area. At the end of the reverse recovery phase, the high electric field towards the cathode area can force an injection of holes from an p-doped regions adding to the reverse recovery current and preventing snap-off. Thus, the FCE effect brings additional softness during BIGT turn-off phase. The FCE effect can be enhanced by using the trenches 4 having different vertical heights H in the semiconductor body. This can be shown for instance in connection with the illustrations in Figures 8A and 8B which do not show a RC tail RCT and a pilot tail PT at low currents. For a comparison, Figures 8A and 8B show some further curves Cv and Ci during a turn-off phase of power devices. While Figure 8A shows a behavior with smooth tail and without overshoot, Figure 8B shows a non-optimized version thereof. Moreover, Figure 8B shows stronger voltage oscillations and both Figures 8A and 8B do not show a RC tail RCT and a pilot tail PT at low currents. Using the ideas presented in this disclosure regarding tuning the trench depths and / or arranging the trenches 4 in a targeted manner, a behavior as shown in Figure 8A rather than a behavior ash shown in Figure 8B is expected. According to Figure 8A, the turn-off behavior has reduced high voltage oscillations as well as a reduced snap-off or snap-back P2024,0651 WO E / P240042WO01 September 6, 2024 - 28 - characteristics even at low operating voltages and / or currents. Thus, it has been found that possible performance limitations of RC-IGBT / BiGT / diode can be improved with the implementation of trenches having different vertical heights. In particular, the implementation of such trenches contributes to an improved reverse recovery and improved softness for a diode structure. Furthermore, it is possible to tune or tailor the mixed regions adjoining the trenches in different vertical heights to ameliorate secondary snapback events. Figures 9A, 9B and 9C illustrate some method steps of a method for producing a power device 10 shown for instance in Figure 2. Figures 10A, 10B and 10C illustrate some method steps of a method for producing a power device 10 shown for instance in Figures 3A to 3C. Figures 11A, 11B and 11C illustrate some method steps of a method for producing a power device 10 shown for instance in Figures 4A to 4C. In all cases, only one single common mask 7 having openings of different sizes, for instance of different widths W, is used for the forming of the trenches 4 having different vertical heights H. This can be performed by a dry etching process, wherein the different vertical heights H of the trenches are proportional to the different lateral widths W of the openings of the mask 7. As indicated in Figures 9B to 9C and 10B to 10C, after the trenches 4 have been formed, ion implantation can be performed for forming the mixed regions 32M. For instance, ion implantation of boron as p+ dopant, preferably at 0 degrees to avoid shadowing, can be carried out for forming P2024,0651 WO E / P240042WO01 September 6, 2024 - 29 - the mixed p+ regions 32M. As an example, phosphorous ion implantation can be performed for forming the mixed n+ regions 32M. The implantation of other appropriate ions for forming the n+ or p+ regions 32M are also possible. Only as an example for illustrating the production of the power device 10 shown in Figure 2 or 9C, in combination with Figures 9A to 9C, following steps may be performed: i. Blanket phosphorous ion implantation for forming the second electrode 2 being a cathode, for instance an n+ cathode; ii. Hard mask deposition, for instance using SiO2 or a nitride. Here, depending on the desired final depths of the trenches 4 and ion implantation conditions in step vii, this step might be optional; iii. Masking step comprising: Resist coating, exposure, development. The initial mask opening (i.e. trench width W) will determine the final trench depth or height H for instance using a BOSCH type process or other anisotropic dry etch process; iv. Dry etching of hard mask if present; v. Resist removal; vi. Dry etching for forming the trenches 4; vii. Ion implantation for forming the mixed regions 32M, for instance ion implantation of boron as p+ dopants; viii. Hard mask removal (for instance SiO2 with BOE or HF, nitride with hot phosphoric acid); ix. Laser annealing for the activation of the dopants and filling the trenches 4 with an electrically conductive material; P2024,0651 WO E / P240042WO01 September 6, 2024 - 30 - x. If necessary, a rear side metallization can be formed, for instance by sputtering to ensure conformality in the trench steps; and xi. Low temperature annealing. Here, step i mentioned above can be used for forming the layer 30 of the second electrode 2 shown in Figure 1. Step x can be used for forming the metallization 20 of the second electrode 2 shown in Figure 1. For the production of the power device 10 shown in Figures 3A to 3C or 4A to 4C, the method steps illustrated in Figures 10A to 10C or 11A to 11C can be adapted accordingly. When studying SEM cross-sectional views of the power device, it could be shown that the different trenches of different depths or vertical heights are created at the same time. The power device can also be treated chemically, for instance using HNO and HF, to decorate and highlight the different doped areas. The examples shown in the figures as stated represent examples of the power device and of the method for producing the power device; therefore, they do not constitute a complete list of all examples according to the improved power device and the improved method for producing the power device. Actual arrangements or implementations of the power device and of the method may vary from the examples described above. P2024,0651 WO E / P240042WO01 September 6, 2024 - 31 - Reference signs 10 power device 10F front side of the power device 10R rear side / backside of the power device 1 first electrode 2 second electrode 30 layer of the second electrode 20 metallization of the second electrode 3 semiconductor body 31 first part of the semiconductor body 32 second part of the semiconductor body 32M mixed region of the second part 4 trenches 41 electrically insulating material 42 electrically conductive material 5 pilot IGBT region 52 pilot electrode 6 Reverse Conducting IGBT region 61 additional electrical contact 62 contact regions of the second electrode 7 mask H vertical height of the trench W lateral width of the trench L lateral length of the trench

Claims

P2024,0651 WO E / P240042WO01 September 6, 2024 - 32 - Claims 1. A power device (10) comprising a first electrode (1), a second electrode (2), a semiconductor body (3) and a plurality of trenches (4) having different vertical heights (H), wherein − the semiconductor body (3) is located between the first electrode (1) and the second electrode (2), − the semiconductor body (3) comprises a first part (31) adjoining the first electrode (1) and a second part (32) adjoining the second electrode (2), and − along a vertical direction from a rear side (10R) towards a front side (10F) of the power device (10), the trenches (4) extend throughout a layer of the second electrode (2) into different vertical regions of the second part (32).

2. The power device (10) according to claim 1, wherein in plan view of the rear side (10R) of the power device (10), the trenches (4) of different vertical heights (H) comprise different lateral widths (W), wherein the wider the lateral width (W) of one of the trenches (4) is, the larger is the vertical high (H) of that one of the trenches (4).

3. The power device (10) according to one of the preceding claims, wherein in plan view of the rear side (10R) of the power device (10), at least some of the trenches (4) have different lateral lengths (L) and / or orientations.

4. The power device (10) according to one of the preceding claims, wherein in plan view of the rear side (10R) of theP2024,0651 WO E / P240042WO01 September 6, 2024 - 33 - power device (10), the trenches (4) are arranged in a symmetrical manner.

5. The power device (10) according to the preceding claim, wherein at least in places along one lateral direction, the vertical heights (H) of the different trenches (4) monotonically change.

6. The power device (10) according to one of the preceding claims, wherein the power device (10) is a Bi-mode Insulated Gate Transistor, BIGT, which comprises a pilot Insulated-Gate Bipolar Transistor, IGBT, region (5) and further comprises a Reverse Conducting Insulated-Gate Bipolar Transistor, RC- IGBT, region (6), and wherein the trenches (4) are formed in the RC-IGBT region (6).

7. The power device (10) according to the preceding claim, wherein − the second electrode (2) comprises a centrally arranged pilot electrode (52) for the pilot IGBT region (5), and − at least along one lateral direction from the RC-IGBT region (6) towards the pilot IGBT region (5), the vertical heights (H) of the different trenches (4) monotonically change.

8. The power device (10) according to one of the preceding claims, wherein − the second part (32) comprises a plurality of local mixed regions (32M) at different vertical depths of the second part (32), − the trenches (4) extend into the local mixed regions (32M), andP2024,0651 WO E / P240042WO01 September 6, 2024 - 34 - − the trenches (4) are filled with an electrically conductive material (42).

9. The power device (10) according to preceding claim, wherein − the first electrode (1) is an anode of the power device (10), − the second electrode (2) is a cathode of the power device (10), − the local mixed regions (32M) are p+ doped regions, and − the trenches (4) form local p+ anode shorts.

10. The power device (10) according to claim 8, wherein − the first electrode (1) is a cathode of the power device (10), − the second electrode (2) is an anode of the power device (10), − the local mixed regions (32M) are n+ doped regions, and − the trenches (4) form local n+ cathode shorts.

11. The power device (10) according to any of claims 1 to 7, wherein the trenches (4) are filled with an electrically insulating material (41).

12. The power device (10) according to preceding claim, wherein − the first electrode (1) is a cathode of the power device (10), − the second electrode (2) comprises contact regions (62) being p+ anode regions (62) of the power device (10), − in plan view of the rear side (10R), the power device (10) further comprises additional electrical contacts (61),P2024,0651 WO E / P240042WO01 September 6, 2024 - 35 - each of the additional electrical contacts (61) being arranged between two adjoining trenches (4), the additional electrical contacts (61) being electrically connected to the second part (32) of the semiconductor body (3) and forming n+ cathode shorts.

13. The power device (10) according to the preceding claim, wherein the second part (32) comprises a plurality of local mixed regions (32M) at least partially forming the additional electrical contacts (61).

14. A method for producing a power device (10) comprising a first electrode (1), a second electrode (2), a semiconductor body (3) and a plurality of trenches (4) having different vertical heights (H), wherein the method comprises: − providing the semiconductor body (3) comprising a first part (31) and a second part (32), the first part (31) adjoining the first electrode (1), the second electrode (2) adjoining the second part (32), and the semiconductor body (3) being located between the first electrode (1) and the second electrode (2), and − forming the plurality of trenches (4) in the second part (32) of the semiconductor body (3) using a single mask (7), along a vertical direction from a rear side (10R) towards a front side (10F) of the power device (10) the plurality of trenches (4) extending throughout a layer of the second electrode (2) into different vertical regions of the second part (32).

15. The method according to claim 14, wherein for forming the plurality of trenches (4), the single mask (7) having openings of different lateral widths (W) is provided, wherein the plurality of trenches (4) havingP2024,0651 WO E / P240042WO01 September 6, 2024 - 36 - different vertical heights (H) are formed by a common etching step, and wherein the different vertical heights (H) of the trenches (4) depend on the different lateral widths (W) of the openings of the mask (7).

16. The method according to claim 15, wherein the common etching step is performed by a dry etching process.

17. The method according to any of claims 14 to 16, wherein after forming the plurality of trenches (4), ion implantation is performed through the trenches (4) for forming a plurality of local mixed regions (32M) at different vertical depths of the second part (32), wherein the trenches (4) are subsequently filled with an electrically conductive material (42) extending into the local mixed regions (32M).

18. The method according to any of claims 14 to 16, wherein the trenches (4) are filled with an electrically insulating material (41) acting as electron blocking barriers.

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