Patent Publication Number: US-11387359-B2

Title: Ppower semiconductor device with anticorrosive edge termination structure

Description:
TECHNICAL FIELD 
     This specification refers to embodiments of a power semiconductor device. In particular, this specification relates to embodiments of a power semiconductor device having a hard passivation layer arranged at least in a portion of an edge termination region. 
     BACKGROUND 
     Many functions of modern devices in automotive, consumer and industrial applications, such as converting electrical energy and driving an electric motor or an electric machine, rely on power semiconductor devices. For example, insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOSFETs) and diodes, to name a few, have been used for various applications including, but not limited to switches in power supplies and power converters, e. g., in traction applications. 
     A power semiconductor device usually comprises a semiconductor body that is configured for conducting a load current along a load current path between two load terminals of the device. Further, in case the power semiconductor device has a transistor configuration, the load current path may be controlled by means of an insulated electrode, often referred to as gate electrode. For example, upon receiving a corresponding control signal from, e. g., a driver unit, the control electrode may set the power semiconductor device in one of a conducting state and a blocking state. 
     Further, for conducting the load current, the power semiconductor device may comprise one or more power cells, which may be arranged in a so-called active region of the power semiconductor device. The power semiconductor device may be laterally confined by an edge. Between the lateral edge and the active region that comprises the one or more power cells, there may be arranged an edge termination region, which may comprise an edge termination structure. Such an edge termination structure may serve for the purpose of influencing the course of an electric field within the semiconductor body, e. g., so as to ensure a reliable blocking capability of the power semiconductor device. The edge termination structure may comprise one or more components arranged within the semiconductor body, and also one or more components arranged above a surface of the semiconductor body. 
     A common example of such edge termination concepts is a combination of p-doped poly-silicon field rings with field plates, wherein the field plates may be configured for providing an effective screening of external charges. For example, the field plates may comprise a metal, such as aluminum. Alternatively, such field plates may be formed of polysilicon, e. g., in order to make the edge termination structure less susceptible to corrosion when exposed to humidity and electric fields. For example, in an edge termination structure combining p-doped field rings with n-doped poly-silicon field plates, metallic layers may still be present to provide an electric contact between a field plate and a field ring reducing the influence of an electric field on the outer edges of the metallic layers. 
     Usually, one or more passivation layers, such as a hard passivation comprising an oxide and a nitride, are provided in the edge termination region. For example, such a passivation layer may be arranged above an edge termination structure so as to protect the semiconductor surface including edge termination structure from electrical and chemical contaminants, such as ions. 
     It is generally desirable to provide edge termination and passivation concepts that are reliable even under harsh environmental conditions that are, for example, met in traction applications. To this end, it may be desirable to render edge termination structures less susceptible to corrosion under the combined influence of humidity and electric fields. Device performances under such conditions are usually tested by strongly accelerated reliability tests, such as, e. g., HV-H3TRB or H 2 S. 
     SUMMARY 
     According to an embodiment, a power semiconductor device has a power semiconductor transistor configuration and comprises: a semiconductor body having a front side coupled to a first load terminal structure, a backside coupled to a second load terminal structure, and a lateral chip edge; an active region configured for conducting a load current between the first load terminal structure and the second load terminal structure in a conducting state of the power semiconductor device; and an edge termination region separating the active region from the lateral chip edge. At the front-side, the edge termination region comprises a protection region, which does not comprise any metallic structure, unless the metallic structure is electrically shielded from below by a polysilicon layer that extends further towards the lateral chip edge than the metallic structure by a lateral distance of at least 20 μm. In a blocking state of the power semiconductor device, the protection region is configured to accommodate a voltage change of at least 90% of a blocking voltage inside the semiconductor body in a lateral direction from the active region towards the lateral chip edge. 
     According to an embodiment, a power semiconductor device has a power semiconductor transistor configuration and comprises: a semiconductor body having a front side coupled to a first load terminal structure, a backside coupled to a second load terminal structure, and a lateral chip edge; an active region configured for conducting a load current between the first load terminal structure and the second load terminal structure in a conducting state of the power semiconductor device; and an edge termination region separating the active region from the lateral chip edge. At the front-side, the edge termination region comprises a protection region, which does not comprise any metallic structure, unless the metallic structure is electrically shielded from below by a polysilicon layer that extends further towards the lateral chip edge than the metallic structure by a lateral distance of at least 20 μm. In a vertical cross-section, the protection region extends along the lateral direction from a starting point to the lateral chip edge, wherein the starting point is located at a distance of at most 30 μm from an outermost point where a doped semiconductor region is in contact with a metal layer that is electrically connected with the first load terminal structure. 
     According to another embodiment, a power semiconductor device, comprises: a semiconductor body having a front side coupled to a first load terminal structure, a backside coupled to a second load terminal structure, and a lateral chip edge; an active region configured for conducting a load current between the first load terminal structure and the second load terminal structure in a conducting state of the power semiconductor device; an edge termination region separating the active region from the lateral chip edge; an insulation layer being arranged at the front side, wherein a lateral edge of the insulation layer defines at least one contact hole, the contact hole being filled with a metal layer that is in contact with a doped semiconductor region of the semiconductor body; and a hard passivation layer being arranged at the front side at least in a portion of the edge termination region in such a way that the hard passivation layer does not extend above the lateral edge of the insulation layer. 
     According to a further embodiment, a power semiconductor device comprises: a semiconductor body having a front side coupled to a first load terminal structure, a backside coupled to a second load terminal structure, and a lateral chip edge; an active region configured for conducting a load current between the first load terminal structure and the second load terminal structure in a conducting state of the power semiconductor device; an edge termination region separating the active region from the lateral chip edge; a hard passivation layer being arranged at the front side at least in a portion of the edge termination region, the hard passivation layer comprising an oxide layer having an oxide layer thickness; and a metal layer being arranged at the front side at least in a portion of the edge termination region and having a lateral edge, wherein, in a cross-section along a vertical direction pointing from the front side to the backside, the cross-section being perpendicular to the lateral edge, a common lateral extension range of the hard passivation layer and the metal layer amounts to at most 10 times the oxide layer thickness. 
     According to a further embodiment, a method of processing a power semiconductor device comprises the following steps: providing a semiconductor body having a front side, a backside, and a lateral chip edge; creating an active region that is configured for conducting a load current between a first load terminal structure arranged at the front side and a second load terminal structure arranged at the backside in a conducting state of the power semiconductor device; and creating an edge termination region that separates the active region from the lateral chip edge, wherein, at the front-side, the edge termination region comprises a protection region, which does not comprise any metallic structure, unless the metallic structure is electrically shielded from below by a polysilicon layer that extends further towards the lateral chip edge than the metallic structure by a lateral distance of at least 20 μm, and wherein, in a blocking state of the power semiconductor device, the protection region is configured to accommodate a voltage change of at least 90% of a blocking voltage inside the semiconductor body in a lateral direction from the active region towards the lateral chip edge. 
     According to another embodiment, a method of processing a power semiconductor device comprises the following steps: providing a semiconductor body having a front side, a backside, and a lateral chip edge; creating an active region that is configured for conducting a load current between a first load terminal structure arranged at the front side and a second load terminal structure arranged at the backside in a conducting state of the power semiconductor device; and creating an edge termination region that separates the active region from the lateral chip edge, wherein, at the front-side, the edge termination region comprises a protection region, which does not comprise any metallic structure, unless the metallic structure is electrically shielded from below by a polysilicon layer that extends further towards the lateral chip edge than the metallic structure by a lateral distance of at least 20 μm. In a vertical cross-section, the protection region extends along the lateral direction from a starting point to the lateral chip edge, wherein the starting point is located at a distance of at most 30 μm from an outermost point where a doped semiconductor region is in contact with a metal layer that is electrically connected with the first load terminal structure. 
     According to a further embodiment, a method of processing a power semiconductor device comprises the following steps: providing a semiconductor body having a front side, a backside, and a lateral chip edge; creating an active region that is configured for conducting a load current between a first load terminal structure arranged at the front side and a second load terminal structure arranged at the backside in a conducting state of the power semiconductor device; creating an edge termination region that separates the active region from the lateral chip edge; creating an insulation layer at the front side, such that a lateral edge of the insulation layer defines at least one contact hole; filling the contact hole with a metal layer so as to establish contact with a doped semiconductor region of the semiconductor body; and creating a hard passivation layer at the front side at least in a portion of the edge termination region in such a way that the hard passivation layer does not extend above the lateral edge of the insulation layer. 
     According to another embodiment, a method of processing a power semiconductor device comprises the following steps: providing a semiconductor body having a front side, a backside, and a lateral chip edge; creating an active region that is configured for conducting a load current between a first load terminal structure arranged at the front side and a second load terminal structure arranged at the backside in a conducting state of the power semiconductor device; creating an edge termination region that separates the active region from the lateral chip edge; creating a hard passivation layer at the front side at least in a portion of the edge termination region, the hard passivation layer comprising an oxide layer having an oxide layer thickness; and creating a metal layer at the front side at least in a portion of the edge termination region, the metal layer having a lateral edge, wherein, in a cross-section along a vertical direction pointing from the front side to the backside, the cross-section being perpendicular to the lateral edge, a common lateral extension range of the hard passivation layer and the metal layer amounts to at most 10 times the oxide layer thickness. 
     Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The parts in the Figures are not necessarily to scale, emphasis being instead placed upon illustrating principles of the invention. Moreover, in the Figures, like reference numerals designate corresponding parts. In the drawings: 
         FIGS. 1A-1C  each schematically and exemplarily illustrate a section of a vertical projection of a power semiconductor device in accordance with one or more embodiments; 
         FIG. 2  schematically and exemplarily illustrates a section of a vertical cross-section of a power semiconductor device in accordance with one or more embodiments; 
         FIG. 3  schematically and exemplarily illustrates a section of a vertical cross-section of a power semiconductor device in accordance with one or more embodiments; 
         FIG. 4  schematically and exemplarily illustrates a section of a vertical cross-section of a power semiconductor device in accordance with one or more embodiments; 
         FIG. 5  schematically and exemplarily illustrates a section of a vertical cross-section of a power semiconductor device in accordance with one or more embodiments; and 
         FIG. 6  shows an enlarged view of a section of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof and in which are shown by way of illustration of specific embodiments in which the invention may be practiced. 
     In this regard, directional terminology, such as “top”, “bottom”, “below”, “front”, “behind”, “back”, “leading”, “trailing”, “below”, “above” etc., may be used with reference to the orientation of the Figures being described. Because parts of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     Reference will now be made in detail to various embodiments, one or more examples of which are illustrated in the Figures. Each example is provided by way of explanation and is not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present invention includes such modifications and variations. The examples are described using specific language which should not be construed as limiting the scope of the appended claims. The drawings are not scaled and are for illustrative purposes only. For clarity, the same elements or manufacturing steps have been designated by the same references in the different drawings if not stated otherwise. 
     The term “horizontal” as used in this specification intends to describe an orientation substantially parallel to a horizontal surface of a semiconductor substrate or of a semiconductor structure. This can be for instance the surface of a semiconductor wafer or a die. For example, both the first lateral direction X and the second lateral direction Y mentioned below can be horizontal directions, wherein the first lateral direction X and the second lateral direction Y may be perpendicular to each other. 
     The term “vertical” as used in this specification intends to describe an orientation which is substantially arranged perpendicular to the horizontal surface, i.e., parallel to the normal direction of the surface of the semiconductor wafer. For example, the vertical direction Z mentioned below may be a vertical direction that is perpendicular to both the first lateral direction X and the second lateral direction Y. 
     In this specification, n-doped is referred to as “first conductivity type” while p-doped is referred to as “second conductivity type”. Alternatively, opposite doping relations can be employed so that the first conductivity type can be p-doped, and the second conductivity type can be n-doped. 
     Further, within this specification, the term “dopant concentration” may refer to an average dopant concentration or, respectively, to a mean dopant concentration or to a sheet charge carrier concentration of a specific semiconductor region or semiconductor zone. Thus, e. g., a statement saying that a specific semiconductor region exhibits a certain dopant concentration that is higher or lower as compared to a dopant concentration of another semiconductor region may indicate that the respective mean dopant concentrations of the semiconductor regions differ from each other. 
     In the context of the present specification, the terms “in ohmic contact”, “in electric contact”, “in ohmic connection”, and “electrically connected” intend to describe that there is a low ohmic electric connection or low ohmic current path between two regions, sections, zones, portions or parts of a semiconductor device or between different terminals of one or more devices or between a terminal or a metallization or an electrode and a portion or part of a semiconductor device. Further, in the context of the present specification, the term “in contact” intends to describe that there is a direct physical connection between two elements of the respective semiconductor device; e. g., a transition between two elements being in contact with each other may not include a further intermediate element or the like. 
     In addition, in the context of the present specification, the term “electric insulation” is used, if not stated otherwise, in the context of its general valid understanding and thus intends to describe that two or more components are positioned separately from each other and that there is no ohmic connection connecting those components. However, components being electrically insulated from each other may nevertheless be coupled to each other, for example mechanically coupled and/or capacitively coupled and/or inductively coupled. To give an example, two electrodes of a capacitor may be electrically insulated from each other and, at the same time, mechanically and capacitively coupled to each other, e. g., by means of an insulation, e. g., a dielectric. 
     Specific embodiments described in this specification pertain to, without being limited thereto, a power semiconductor device exhibiting a stripe cell or needle cell configuration, such as a power semiconductor transistor, that may be used within a power converter or a power supply. Thus, in an embodiment, the semiconductor device is configured for carrying a load current that is to be fed to a load and/or, respectively, that is provided by a power source. For example, the semiconductor device may comprise one or more active power unit cells, such as a monolithically integrated diode cell, and/or a monolithically integrated transistor cell, and/or a monolithically integrated IGBT cell, and/or a monolithically integrated RC-IGBT cell, and/or a monolithically integrated MOS Gated Diode (MGD) cell, and/or a monolithically integrated MOSFET cell and/or derivatives thereof. Such diode cell and/or such transistor cells may be integrated in a power semiconductor module. A plurality of such cells may constitute a cell field that is arranged with an active region of the power semiconductor device. 
     The term “power semiconductor device” as used in this specification intends to describe a semiconductor device on a single chip with high voltage blocking and/or high current-carrying capabilities. In other words, such power semiconductor device is intended for high current, typically in the Ampere range, e. g., up to several ten or hundred Ampere or even up to some kA, and/or high voltages, typically above 100 V, more typically 500 V and above, e. g., up to at least 1 kV, up to at least 6 kV. For example, the semiconductor device described below may be a semiconductor device exhibiting a stripe cell configuration or a needle cell configuration and can be configured for being employed as a power component in a low-, medium- and/or high voltage application. 
     For example, the term “power semiconductor device” as used in this specification is not directed to logic semiconductor devices that are used for, e. g., storing data, computing data and/or other types of semiconductor-based data processing. 
       FIGS. 1A to 1C  each schematically and exemplarily illustrate a section of a vertical projection of a power semiconductor device  1  in accordance with some embodiments. The illustrated vertical projection is in each case in parallel to a plane defined by a first lateral direction X and a second lateral direction Y and orthogonal to a vertical direction Z. The power semiconductor device  1  comprises a semiconductor body  10  having a lateral chip edge  109 . Further, the power semiconductor device  1  exhibits an active region  16  that is configured for conducting a load current (e. g. substantially along the vertical direction Z) and an edge termination region  17  that is arranged laterally in between the chip edge  109  and the active region  16 . As can be seen in each of  FIGS. 1A to 1C , the active region  16  may be laterally surrounded by the edge termination region  17 . 
     For example, the active region  16  comprises one or more power cells  14  that each extend at least partially into the semiconductor body  10 . The present specification is not limited to a specific kind of configuration of the one or more power cells  14 . Rather, the power cells  14  can exhibit any configuration that is common for a power semiconductor device, e. g., at least one of a diode configuration, a thyristor configuration, a MOS gated diode (MGD) configuration, a transistor configuration, such as an IGBT configuration, an RC (reverse conducting) IGBT configuration, a MOSFET configuration, and any configuration derived there from. The skilled person is acquainted with these kinds of configurations. Accordingly, in  FIGS. 1A-C , the power cells  14  are only schematically illustrated, as the exact configuration is not a major subject of this specification. 
     For example, the configuration shown in  FIG. 1A  may correspond to a power diode configuration comprising a single power cell  14 . By contrast, the configurations illustrated in  FIGS. 1B and 1C  may, for instance, represent semiconductor switch configurations (such, e. g., a MOSFET and/or IGBT configuration), wherein the power cells  14  may be configured for controlling a load current by switching the power semiconductor device  1  into one of a conducting state and a blocking state. Such power cells  14  may, for example, comprise a control structure such as a MOS-control structure. As exemplarily illustrated in  FIG. 1B , the power cells  14  may exhibit a stripe configuration, which may extend, e. g., throughout the entire active region  16  along the second lateral direction Y. In another embodiment, as illustrated in  FIG. 1C , the power cells  14  may exhibit a cellular configuration, e. g., having a horizontal cross-section exhibiting one of a quadratic shape, a rectangular shape, a rectangular shape with rounded corners, a circular shape, and an ellipsoidal shape. 
     The one or more power cells  14  that may be included in the active region  16  of the power semiconductor device  1  may be configured for selectively conducting a load current and for blocking a blocking voltage depending, e. g., on a switching state of the power semiconductor device  1  and/or on a direction in which a current and/or voltage is fed or applied to the power semiconductor device  1 . 
     For example, the power semiconductor device  1 , by means of the at least one power cell  14 , may be configured for supporting a blocking voltage of at least 300 V, of at least 500 V, of at least 600 V, of at least 1000 V, of at least 1500 V, or of at least 3000 V, or of even more than 6000 V. Further, the at least one power cell  14  may exhibit a compensation structure which is also referred to as a “superjunction” structure. 
     For example, in order to control the one or more power cells  14 , a control terminal (not illustrated) may be provided that may be configured for forwarding a control signal to a control electrode structure of the one or more power cells  14 . For example, the control terminal can be a gate terminal. Thereby, the power semiconductor device  1  may be set into one of the conducting state and the blocking state. In an embodiment, such a control signal can be provided by means of applying a voltage between the control terminal and a first load terminal (not shown in  FIGS. 1A-C ). 
     In between the chip edge  109 , which may have come into being, e. g., by means of wafer dicing, and the active region  16 , there may be arranged an edge termination structure  171  (not shown in  FIGS. 1A-C , refer to  FIGS. 2 to 5 ). In other words, an edge termination structure  171  may be arranged in the edge termination region  17 . For example, the edge termination structure  171  may entirely surround the active region  16 . The edge termination structure  171  is not configured for conducting a load current, but rather configured for ensuring a reliable blocking capability of the power semiconductor device  1 , in accordance with an embodiment. For example, the edge termination structure  171  comprises a field ring/field plate termination structure. Additionally or alternatively, the edge termination structure may comprise at least one of a junction-termination-extension (JTE) structure and a variation-of-lateral-doping (VLD) structure. The person skilled in the art is acquainted with these kinds of edge termination structures. 
       FIGS. 2 to 6  each schematically and exemplarily illustrate a section of a vertical cross-section of the power semiconductor device  1  in accordance with some embodiments. The illustrated cross-sections are in parallel to a plane defined by the first lateral direction X and the vertical direction Z, wherein each of the illustrated components may also extend along the second lateral direction Y.  FIG. 6  shows an enlarged view of a section of  FIG. 5 . 
     The sections of the vertical cross-sections shown in  FIGS. 2 to 6  are in each case located close to the lateral chip edge  109  of the semiconductor body  10  and include a vertical cross-section of at least a portion of the edge termination region  17 . In addition, a peripheral portion of the active region  16  adjacent to the edge termination region  17  is illustrated in each of  FIGS. 2 to 5 . 
     The semiconductor body  10  is coupled to each of a first load terminal structure  11  and a second load terminal structure  12  of the power semiconductor device  1 . The first load terminal structure  11  may be, for example, an anode terminal, an emitter terminal, or a source terminal (depending on the type of power semiconductor device) being arranged on a front side  10 - 1  of the semiconductor body  10 . Correspondingly, the second load terminal  12  may be, for example, a cathode terminal, a collector terminal, or a drain terminal being arranged on a backside  10 - 2  of the semiconductor body  10 . For example, the first load terminal  11  and/or the second load terminal  12  may comprise respective front side or backside metalizations. The front side metallization may comprise a copper and/or an aluminum metallization. 
     The semiconductor body  10  comprises a drift region  100  of a first conductivity type (e. g., n-type). In an embodiment, the drift region  100  is an n − -doped region. As depicted in  FIGS. 2 to 5 , the drift region  100  may extend into each of the active region  16  and the edge termination region  17  of the power semiconductor device  1 . Each of the one or more power cells  14  that may be included in the active region  16  of the power semiconductor device  1  may comprise a part of said drift region  100 . Further, each of the one or more power cells  14  may be configured for conducting a load current via said drift region  100  between the load terminal structures  11  and  12 , and for blocking a blocking voltage applied between said load terminal structures  11  and  12 . 
     For example, in some embodiments in accordance with each of  FIGS. 1B to 6 , the power semiconductor device  1  may be a switching device, such as, e. g., an IGBT or a MOSFET. In this case, the active region  16  comprises a plurality of power cells  14 , wherein each power cell  14  may, e. g., comprise a trench-gate structure, as schematically depicted in  FIGS. 2 to 5 , which show in each case one outermost power cell  14  of the active region  16 . For example, the trench-gate structure may be arranged in one of a stripe configuration, as illustrated in  FIG. 1B , and a cellular configuration (e. g., exhibiting a quadratic or rectangular shape in a horizontal cross-section), as exemplarily illustrated in  FIG. 1C . For example, each of the power cells  14  may comprise a control electrode (not depicted in the Figures) arranged inside a trench  141 , wherein the control electrode may be configured for receiving a control signal, such as a gate voltage, from a control terminal of the power semiconductor device  1  (not illustrated). For example, within each power cell  14 , the control electrode may be electrically insulated from the first load terminal by means of an insulation structure, such as an oxide structure, as is well known to those skilled in the art. 
     Further, each of the cells  14  may comprise a body region  142  of the second conductivity type (e. g., p-type) and at least one source region  143  of the first conductivity type, the source region  143  being arranged in contact with the first load terminal  11 , wherein the body region  142  isolates the at least one source region  143  from the drift region  100 . As shown in each of  FIGS. 2 to 5 , a transition between the body region  102  and the drift region  100  may form a pn-junction  103  being configured for blocking a blocking voltage that is applied in forward direction between the first load terminal  11  and the second load terminal  12 . Inside each power cell  14 , the respective control electrode may be electrically insulated from each of the source region  143 , the body region  142 , and the drift region  100  by an insulation structure, such as a gate oxide (schematically indicated with a fat line in  FIGS. 2-6 ). For example, the control electrode may be configured for inducing a transport channel, such as, e. g., an n-channel, in the body region  142  between the source region  143  and the drift region  100  in dependence on the control signal, thereby enabling the conducting state of the power semiconductor device  1 . Instead of such trench cells  14 , the power semiconductor device  1  may be equipped with so called planar power switching cells, wherein the gate electrode is located vertically above the semiconductor body  10  (not shown in the Figures). The skilled person is acquainted with the principles and variants of configurations of such trench-based or planar power switching cells  14 , and they will therefore not be explained in further detail. 
     As is also well known to those skilled in the art, in case the power semiconductor device has an IGBT configuration, the semiconductor body  10  may further comprise a backside emitter region  108  of the second conductivity type (e. g., p-type) that is arranged at the backside  10 - 2  in contact with the second load terminal  12 . In another variant, wherein the power semiconductor device  1  is configured, e. g., as a MOSFET, such a backside emitter region  108  may be absent and may be replaced by a highly doped region (drain) of the first conductivity type. 
     It should be noted that the transistor power cell  14  depicted in each of  FIGS. 2 to 5  is just an exemplary realization of a power cell in the active region  16 . For example, in an alternative embodiment in accordance with  FIG. 1A , there may be provided a single large power cell  14 , which may be configured as a power diode cell. For example, the power diode cell  14  comprises an anode region of a second conductivity type (e. g., p-type), wherein the anode region is arranged in contact with the first load terminal  11 . Further, a transition between the anode region and the drift region  100  forms a pn-junction that is configured for blocking a blocking voltage between the first load terminal  11  and the second load terminal  12 . Thus, while the cross sections shown in  FIGS. 2 to 5  illustrate by way of example in each case an active region  16  comprising a power cell  14  having trench-gate structure, aspects related to the configuration of the edge termination region  17  that will be explained in the following may as well refer to embodiments of the power semiconductor device  1  having a diode configuration, e. g., in the form of a single large power cell  14  inside the active region  16 . 
     Turning now to the edge termination region  17 , in accordance with all embodiments illustrated in  FIGS. 1A to 6 , said edge termination region  17  may comprise an edge termination structure  171  that is not configured for conducting a load current, but rather configured for ensuring a reliable blocking capability of the power semiconductor device  1 . The edge termination structure  171  may be configured for laterally terminating an electric field that is present in the semiconductor body  10  in a blocking state of the power semiconductor device  1 . For example, such an edge termination structure  171  may comprise at least one of a junction-termination-extension (JTE) structure, a field ring/field plate termination structure, a variation-of-lateral-doping (VLD) structure, and a combined VLD-DLC edge termination structure. The skilled person is acquainted with these kinds of edge termination structures as such. 
     In the exemplary embodiments illustrated in  FIGS. 2 to 5 , the edge termination structure  171  comprises a doped semiconductor region  1711  of the second conductivity type. For example, the doped semiconductor region  1711  may exhibit a variation of lateral doping (VLD). Further, in the embodiments of  FIGS. 2 to 5 , the edge termination structure  171  may comprise an electrically active semi-insulating layer  1712  that is arranged above a portion of the doped semiconductor region  1711 . For example, the semi-insulating layer  1712  is electrically insulated from the doped semiconductor region  1711  by at least one insulation layer  15 , such as an oxide. The semi-insulating layer  1712  may, for example, comprise at least one of: amorphous silicon (a-Si), semi-insulating poly-crystalline silicon (SIPOS), and an electro-active material, such as diamond-like carbon (DLC) or hydrogenated amorphous carbon (a-C:H). For example, such an electrically active semi-insulating layer may have an electric resistivity in a range from 1E07 Ωcm to 1E15 Ωcm. It may thus be configured for ensuring a relatively high electric blocking capability. At the same time, the electric resistivity may be low enough to prevent the accumulation of electric charges, e. g., in a region of the semiconductor body  10  close to the hard passivation layer  18 . 
     In an embodiment in accordance with each of  FIGS. 2 to 6 , a hard passivation layer  18  is arranged at the front side  10 - 2  inside the edge termination region  17 . The hard passivation layer  18  may extend at least above a portion of an edge termination structure  171 , as illustrated in the Figures. For example, in an embodiment in accordance with  FIGS. 2 and 3 , the hard passivation layer  18  may cover the entire edge termination region  17  and may optionally also extend further into the active region  16 , as exemplarily illustrated in  FIG. 2 . In other embodiment, the hard passivation layer  18  may, for example, comprise several disconnected portions. 
     In an embodiment, the hard passivation layer  18  comprises an oxide layer  181 . For example, the oxide layer  181  may have an oxide layer thickness d 2 . The oxide layer thickness d 2  may be, e. g., in the range from 50 nm to 5000 nm, for example 2700 nm. In addition, in an embodiment, the hard passivation layer  18  may comprise a nitride layer  182  For example, the nitride layer  182  may be arranged above the oxide layer  181 , such as on top of the oxide layer  181 . Such a nitride layer  182  may have a nitride layer thickness d 3  that amounts to at least 100 nm, such as at least 400 nm, or even at least 800 nm. 
     Further, in an embodiment, the edge termination region  17  comprises a protection region  172 . The protection region  172  is arranged at the front side  10 - 1  of the semiconductor body  10  and does not comprise any metallic structure. This is exemplarily illustrated in  FIGS. 2 and 3 . It should be noted that in this context a structure consisting of polysilicon is not to be understood as a metallic structure. Further, in the present context, the statement that the protection region  172  does not comprise any metallic structure means that no metallic structure that has been created at wafer level, such as, e. g., a gate runner electrode or a metal-filled contact hole, is present inside the protection region  172 . In other words, a metallic structure that may have been arranged, for example, as part of a package of the power semiconductor device  1  in a later assembly step (e. g., bond wires) are not to be understood as “metallic structures” in the context of this specification. 
     In another embodiment, a protection region  172  may be provided in the edge termination region  17 , wherein the protection region  172  does not comprise any such metallic structure unless the metallic structure is electrically shielded from below by a polysilicon layer  178 . This is exemplarily illustrated in  FIG. 4 . In the exemplary embodiment shown in  FIG. 4 , a gate runner electrode GR is arranged at the front side  10 - 1  inside the edge termination region  17 . Such a gate runner electrode GR may be provided for distributing a control signal, which may stem, e. g., from a gate driver, to the control electrodes of a plurality of transistor cells  14  which may be arranged in different regions of the active region  16 . The function and design of such gate runner electrodes is well known to those skilled in the art and will therefore not be described in further detail. As exemplarily illustrated in  FIG. 4 , a polysilicon layer  178  extends below the gate runner electrode GR. The polysilicon layer  178  may be configured for shielding the gate runner electrode GR from below. This is to say that the polysilicon layer  178  may screen the gate runner electrode GR from an electric field that may be present in the semiconductor body  10  in the vicinity of the front side  10 - 1 , e. g., in the blocking state of the power semiconductor device  1 . For example, the polysilicon layer  178  may be embedded in an insulation structure, which may be formed, e. g., by oxide layers  1715 ,  15 , as exemplarily illustrated in  FIG. 4 . 
     In a variant embodiment, such a polysilicon layer  178  that screens a metallic structure inside the edge termination region  17  extends further towards the lateral chip edge  109  than the metallic structure by a lateral distance d 5  of at least 15 μm, such as at least 20 μm or even at least 50 μm. This is exemplarily depicted in  FIG. 4 , wherein the metallic structure is a gate runner electrode GR, as described above. 
     In accordance with the exemplary embodiments that are illustrated in each of  FIGS. 2 to 6 , it may be provided that, in a blocking state of the power semiconductor device  1 , the protection region  172  is configured to accommodate a voltage change of at least 90% of a blocking voltage inside the semiconductor body in a lateral direction from the active region  16  towards the lateral chip edge  109 . For example, the voltage may change by at least 90% along the lateral direction X inside the protection region  172 . For example, such a lateral voltage change at the front side  10 - 1  of the semiconductor body  10  may be achieved by means of an edge termination structure  171  as described above, wherein the edge termination structure  171  may be arranged at least partially inside the protection region  172 . 
     In an embodiment, in a vertical cross-section as exemplarily depicted in each of  FIGS. 2 to 6 , the protection region  172  extends along the lateral direction X from a starting point SP to the lateral chip edge  109 . The starting point SP may be located at a distance dsp of at most 5 μm, such as at most 10 μm or at most 30 μm from an outermost point P where a doped semiconductor region  1711  is in contact with a metal and/or polysilicon layer  111  that is electrically connected with the first load terminal structure  11 . For example, in this context, “outermost” is to be understood as being situated closest to the lateral chip edge  109  (as compared to all other points in the vertical cross-section where a doped semiconductor region is in contact with a metal layer that is electrically connected with the first load terminal structure). The doped semiconductor region  1711  may be of the second conductivity type. For example, the doped semiconductor region  1711  may form a part of an edge termination structure  171 , as is exemplarily illustrated in  FIGS. 2 to 4 . In the exemplary embodiments of  FIGS. 2 to 4 , the portion of the doped semiconductor region  1711  that is in contact with the metal and/or polysilicon layer  111  forms a part of a drainage cell D that is configured for draining holes from the semiconductor body  10  in certain operating states of the power semiconductor device  1 . In other embodiments (not illustrated) the doped semiconductor region that is in contact with the metal layer may be, e. g., a body region of an outermost power cell of the active region  16 . For example, the metal and/or polysilicon layer  111  may form a part of the first load terminal structure  11 . 
     In an embodiment, the hard passivation layer  18  does not extend further towards the active region  16  than the protection region  172  (not illustrated). More generally, in case the hard passivation layer  18  comprises an oxide layer  181  having an oxide layer thickness d 2 , it may be provided that the hard passivation layer  18  may extend further towards the active region  16  than the protection region  172  at most by a lateral distance of 10 times the oxide layer thickness d 2 . Such a situation is schematically and exemplarily depicted in  FIG. 3 . 
     Further, in an embodiment in accordance with each of  FIGS. 2 to 6 , a soft passivation layer  13  may arranged above at least a portion of the hard passivation layer  18 . For example, the soft passivation layer  13  comprises an organic material, such as polyimide and/or an epoxy compound. It should be understood that, in the context of this specification, the term “soft passivation layer” shall designate a dielectric layer that is or has been created at wafer level, such as by deposition on a semiconductor wafer. In other words, material layers that may have been arranged, for example, as a part of a package of the power semiconductor device  1  in a later assembly step (e. g., a molding compound) are not to be understood as “soft passivation layer”. 
     In an embodiment, the soft passivation layer  13  may cover the entire edge termination region  17  (cf., e. g.,  FIG. 2 ). Further, in an embodiment, the soft passivation layer  13  may also be arranged above the front-side  10 - 1  in a considerable portion of the active region  16 . 
     In another embodiment, as exemplarily illustrated in  FIG. 3 , the soft passivation layer  13  does not extend further towards the active region  16  than the protection region  172 . For example, in that case, the hard passivation layer  18  may laterally extend further towards the active region  16  than the soft passivation layer  13 . For example, the hard passivation layer  18  may extend further towards the active region  16  than the soft passivation layer  13  by at least 2 μm, such as by at least 5 μm, or even by at least 10 μm. 
     In an embodiment, in accordance with each of  FIGS. 2 to 6 , the power semiconductor device  1 , may comprise an insulation layer  15  being arranged at the front side  10 - 1 , wherein a lateral edge  151  of the insulation layer  15  defines at least one contact hole H. The contact hole H may be filled with a metal and/or polysilicon layer  111 . For example, the metal and/or polysilicon layer  111  is in contact with a doped semiconductor region  1711  of the semiconductor body  10 . In the exemplary embodiments of  FIGS. 2  to  6 , the metal and/or polysilicon layer  111  is electrically connected with the first load terminal structure  11  so as to establish an electrical connecting of a drainage cell D to the first load terminal structure  11 , as described earlier. It should be noted that the contact hole H may also be extended in a lateral direction (e. g. along the second lateral direction Y) so as to form an elongate contact groove. For example, the lateral edge  151  of the insulation layer  15  may define a pronounced step topography at the front side  10 - 1  of the semiconductor body  10 . 
     As exemplarily illustrated in more detail in  FIG. 6 , which provides an enlarged view of a section of  FIG. 5 , the hard passivation layer  18  may be arranged at the front side  10 - 2  at least in a portion of the edge termination region  17  in such a way that the hard passivation layer  18  does not laterally extend across a vertical projection V of the lateral edge  151  of the insulation layer  15 . In other words, the hard passivation layer  18  may be arranged in such a way that it does not extend in a region that is located above the lateral edge  151  of the insulation layer  15 . For example, in case the hard passivation layer  18  comprises an oxide layer  181  having an oxide layer thickness d 2 , as described earlier, it may be provided that the hard passivation layer  18  laterally terminates at a minimum distance d 4  of at least 1 times, such as at least 5 times, or even at least 10 times the oxide layer thickness d 2  from the vertical projection V of the lateral edge  151  of the insulation layer  15 . In a further development, it may be provided that the hard passivation layer  18  laterally terminates at a minimum distance d 4  of at least 1 μm from the lateral edge  151  of the insulation layer  15  in case the oxide layer thickness d 2  is equal to or smaller than 1 μm. 
     In an embodiment, the metal and/or polysilicon layer  111  that fills the contact hole H may be covered at least partially by a soft passivation layer  13 , such as, e. g., a polyimide layer  13  as described above. This is schematically illustrated in  FIG. 6 , wherein the dot-dashed line shall indicate that the soft passivation layer  13  may optionally extend further towards the active region  16 , thus covering the metal and/or polysilicon layer  111  in the contact hole H. 
     Further, as illustrated in  FIG. 6 , the power semiconductor device  1  may comprise one or more metal layers  111 ,  174  being arranged at the front side  10 - 1  at least in a portion of the edge termination region  17 . For example, such a metal layer  111  establishes an electrical connection between a drainage cell D and the first load terminal  11 , as described previously. Additionally or alternatively, a metal layer  174  may form at least a portion of a gate runner electrode GR, as has also been described above. 
     The metal layer  111 ,  174  in each case exhibits at least one lateral edge  111 - 1 ,  174 - 1 . For example, the lateral edge  111 - 1 ,  174 - 1  defines a step topography. Further, as mentioned above, the hard passivation layer  18 , which may comprise an oxide layer  181  having an oxide layer thickness d 2 , extends at least in a portion of the edge termination region  17 . 
     In an embodiment in accordance with  FIG. 6 , it may be provided that, in a cross-section along a vertical direction Z pointing from the front side  10 - 1  to the backside  10 - 2 , the cross-section being perpendicular to the respective lateral edge  111 - 1 ,  174 - 1 , a respective common lateral extension range LX 1 , LX 2 , LX 3  of the hard passivation layer  18  and the respective metal layer  111 ,  174  amounts to at most 10 times the oxide layer thickness d 2 . For example, the respective common lateral extension range LX 1 , LX 2 , LX 3  may start at the respective lateral edge  111 - 1 ,  174 - 1 . Additionally or alternatively, it may be provided that said common lateral extension range LX 1 , LX 2 , LX 3  amounts to at most 10 times a metal layer thickness d 6 , d 7  of the respective metal layer  111 ,  174  as measured at the respective lateral edge  111 - 1 ,  174 - 1 . 
     In a variant embodiment, it may be provided that at any such lateral edge of a metal layer that may be present inside the edge termination region  17  said common lateral extension range of the hard passivation layer  18  and the respective metal layer amounts to at most 10 times the oxide layer thickness and/or to at most 10 times a metal layer thickness of the respective metal layer at the respective lateral edge of the metal layer. 
     Further, a soft passivation layer  13  (comprising, e. g., polyimide) may be arranged above at least a portion of the hard passivation layer  18 , such as on top of the hard passivation layer  18 , as described above. The soft passivation layer  13  may also extend above a portion of the respective metal layer  111 ,  174  or above the entirety of the metal layer  111 ,  174 . This is schematically illustrated in each of  FIGS. 6 and 7 , wherein the dot-dashed line shall indicate that the soft passivation layer  13  may optionally extend further towards the active region  16 , thus covering the metal layer  111 ,  174 . 
     Embodiments of a method of processing a power semiconductor device correspond to the embodiments of the power semiconductor as described above with respect to the Figures. Hence, for example, the features of the embodiments of the power semiconductor device described above with reference to the Figures may be achieved by carrying out corresponding processing method steps. Embodiments of a method of processing a power semiconductor device may thus comprise providing a semiconductor body  10  and forming the respective structures being arranged in/on the semiconductor body  10 , e. g., by processes such as masked implantation of dopants and deposition of semiconductor and/or oxide layers. 
     The embodiments described above include the recognition that the reliability of a power semiconductor device, such as its ruggedness under high voltage and high humidity operating condition, may be improved significantly by respecting certain design rules with respect to the arrangement of metallic structures and/or passivation layers in an edge termination region of the power semiconductor device. 
     In accordance with one or more embodiments, a protection region may be provided inside an edge termination region at the front side of a power semiconductor device, wherein the protection region does not comprise any metallic structure, unless the metallic structure is electrically shielded from below by a polysilicon layer that extends further towards a lateral chip edge than the metallic structure by a lateral distance of at least 20 μm, and wherein, in a blocking state of the power semiconductor device, the protection region is configured to accommodate a voltage change of at least 90% of a blocking voltage inside the semiconductor body in a lateral direction from the active region towards the lateral chip edge. For example, by providing such a protection region it may be avoided from the outset that metallic structures, which may be covered by a hard passivation layer, are exposed to high electric field strengths during operation of the power semiconductor device. 
     Further, in accordance with one or more embodiments, an insulation layer is arranged at the front side of the power semiconductor device, wherein a lateral edge of the insulation layer defines at least one contact hole, the contact hole being filled with a metal layer that is in contact with a doped semiconductor region of the semiconductor body. A hard passivation layer is arranged at the front side at least in a portion of the edge termination region in such a way that the hard passivation layer does not extend above the lateral edge of the insulation layer. 
     Further, in accordance with one or more embodiments, a metal layer and a hard passivation layer comprising an oxide layer are arranged at the front side of a power semiconductor device at least in a portion of an edge termination region. The metal layer exhibits a lateral edge. In a cross-section along a vertical direction pointing from the front side to the backside of the power semiconductor device, the cross-section being perpendicular to the lateral edge, a common lateral extension range of the hard passivation layer and the metal layer amounts to at most 10 times the oxide layer thickness. 
     For example, by keeping the lateral edges of contact holes free from a hard passivation layer and/or by avoiding a tight encapsulation of a metal layer edge by a hard passivation layer, an exchange of ions with the environment may still possible, thus mitigating or preventing crevice corrosion of the metal layer. For example, instead of a crevice corrosion, the metal layer may undergo a moderate self-limiting corrosion which may not be detrimental to the reliability of the edge termination. 
     Features of further embodiments are defined in the dependent claims. The features of further embodiments and the features of the embodiments described above may be combined with each other for forming additional embodiments, as long as said features are not explicitly described as being alternative to each other. 
     In the above, embodiments pertaining to a power semiconductor device, such as a diode, a MOSFET, or an IGBT, and corresponding processing methods were explained. For example, these devices are based on silicon (Si). Accordingly, a monocrystalline semiconductor region or layer, e. g., the semiconductor body  10  and its regions/zones, such as regions  100 ,  108 ,  142 ,  143 ,  103 , and  1711 , can be a monocrystalline Si-region or Si-layer. In other embodiments, polycrystalline or amorphous silicon may be employed. 
     It should, however, be understood that the semiconductor body  10  and its doped regions/zones can be made of any semiconductor material suitable for manufacturing a semiconductor device. Examples of such materials include, without being limited thereto, elementary semiconductor materials such as silicon (Si) or germanium (Ge), group IV compound semiconductor materials such as silicon carbide (SiC) or silicon germanium (SiGe), binary, ternary or quaternary III-V semiconductor materials such as gallium nitride (GaN), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium gallium phosphide (InGaPa), aluminum gallium nitride (AlGaN), aluminum indium nitride (AlInN), indium gallium nitride (InGaN), aluminum gallium indium nitride (AlGaInN) or indium gallium arsenide phosphide (InGaAsP), and binary or ternary II-VI semiconductor materials such as cadmium telluride (CdTe) and mercury cadmium telluride (HgCdTe) to name few. The aforementioned semiconductor materials are also referred to as “homojunction semiconductor materials”. When combining two different semiconductor materials a heterojunction semiconductor material is formed. Examples of heterojunction semiconductor materials include, without being limited thereto, aluminum gallium nitride (AlGaN)-aluminum gallium indium nitride (AlGaInN), indium gallium nitride (InGaN)-aluminum gallium indium nitride (AlGaInN), indium gallium nitride (InGaN)-gallium nitride (GaN), aluminum gallium nitride (AlGaN)-gallium nitride (GaN), indium gallium nitride (InGaN)-aluminum gallium nitride (AlGaN), silicon-silicon carbide (SixC1-x) and silicon-SiGe heterojunction semiconductor materials. For power semiconductor device applications currently mainly Si, SiC, GaAs and GaN materials are used. 
     Spatially relative terms such as “under”, “below”, “above”, “lower”, “over”, “upper” and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the respective device in addition to different orientations than those depicted in the Figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
     As used herein, the terms “having”, “containing”, “including”, “comprising”, “exhibiting” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. 
     With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Power semiconductor device 
           10  Semiconductor body 
           10 - 1  Front side 
           10 - 2  Backside 
           100  Drift region 
           109  Chip edge 
           11  First load terminal structure 
           111  Metal and/or polysilicon layer 
           111 - 1  Lateral edge 
           12  Second load terminal structure 
           13  Soft passivation layer 
           14  Power cell(s) 
           141  Trench 
           142  Body region 
           143  Source region 
           15  Insulation layer 
           151  Lateral edge of the insulation layer 
           16  Active region 
           17  Edge termination region 
           171  Edge termination structure 
           1711  Doped semiconductor region 
           1712  Semi-insulating layer 
           1715  Oxide layer 
           172  Protection region 
           174  Metal layer 
           174 - 1  Lateral edge 
           178  Polysilicon layer 
           18  Hard passivation layer 
           181  Oxide layer 
           182  Nitride layer 
         D Drainage cell 
         d 2  Oxide layer thickness 
         d 3  Nitride layer thickness 
         d 4  Minimum distance 
         d 5  Lateral distance 
         d 6  Metal layer thickness 
         d 7  Metal layer thickness 
         GR Gate runner electrode 
         H Contact hole 
         LX 1  Lateral extension range 
         LX 2  Lateral extension range 
         LX 3  Lateral extension range 
         X First lateral direction 
         Y Second lateral direction 
         Z Vertical direction