Patent Publication Number: US-2022231125-A1

Title: Power Semiconductor Device Having a Control Cell for Controlling a Load Current

Description:
TECHNICAL FIELD 
     This specification refers to embodiments of a power semiconductor device and to embodiments of a method of processing a power semiconductor device. In particular, this specification refers to aspects of a power semiconductor device including a control cell that is configured to induce a conduction channel in a semiconductor mesa. 
     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. 
     A power semiconductor device usually comprises a semiconductor body configured to conduct a load current along a load current path between two load terminals of the device. 
     Further, in case of a controllable power semiconductor device, such as a transistor, the load current path may be controlled by means of an insulated control electrode, commonly 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 forward conducting state and a forward blocking state by inducing or cutting-off a conduction channel in a channel region of a semiconductor mesa. The mesa may be electrically connected with a metallic load terminal structure of the power semiconductor device, e.g., by means of a doped contact region of the mesa. 
     It is generally desirable to provide a reliable device having low power losses. To this end, it can be desirable to provide for a reliable and low-resistance electrical contact between a load terminal structure and a semiconductor mesa of the device. 
     Further, it can be desirable to provide for a reliable and cost-efficient processing method for such a power semiconductor device. 
     SUMMARY 
     Aspects described herein relate to a semiconductive contact plug being arranged at least partially between a load terminal structure and a semiconductor mesa. Creating such a contact plug may be achieved by means of a self-aligned process. 
     According to an embodiment, a power semiconductor device comprises a control cell for controlling a load current, the control cell being electrically connected to a first load terminal structure of the power semiconductor device on the one side and electrically connected to a drift region of the power semiconductor device on the other side, the drift region comprising dopants of a first conductivity type. The control cell comprises:
         a mesa extending along a vertical direction and including: a contact region having dopants of the first conductivity type or of a second conductivity type complementary to the first conductivity type and being electrically connected to the first load terminal structure, and a channel region being coupled to the drift region;   a control electrode being configured for inducing a conduction channel in the channel region; and   a contact plug comprising a doped semiconductive material, the contact plug being arranged in contact with the contact region,
 
wherein an electrical connection between the contact region and the first load terminal structure is established by means of the contact plug. For example, a portion of the contact plug may project beyond lateral boundaries of the mesa. The contact plug may be arranged at least partially between the contact region and the first load terminal structure. Further, for example, when viewed in a vertical cross-section, the contact plug may contact the mesa on more than one surface, such as, e.g., on the top of the mesa and on both (upper portions of the) sidewalls of the mesa.
       

     According to a further embodiment, a method of processing a power semiconductor device comprises:
         providing a semiconductor body;   recessing portions of the semiconductor body so as to create a plurality of mesas protruding from a remaining bulk portion of the semiconductor body;   forming a first insulation layer on the bulk portion in between the mesas;   forming a gate oxide layer on the mesas;   depositing a gate electrode layer on the first insulation layer and on the gate oxide layer;   forming a second insulation layer filling a space between neighboring mesas, wherein the second insulation layer is formed in such a way that portions of the gate electrode layer are exposed at a level above the mesas; and   recessing the exposed portions of the gate electrode layer down to a defined recess depth so as to create recesses adjacent to respective upper portions of the mesas.       

     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, instead emphasis is being 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 cross-section of a power semiconductor device in accordance with one or more embodiments; 
         FIGS. 2A-2B  each schematically and exemplarily illustrate a section of a vertical cross-section of a power semiconductor device in accordance with one or more embodiments; 
         FIGS. 3A-3H  schematically and exemplarily illustrate a series of processing steps of a method in accordance with one or more embodiments; 
         FIGS. 4A-4C  schematically and exemplarily illustrate further processing steps of a method in accordance with one or more embodiments; 
         FIGS. 5A-5B  each schematically and exemplarily illustrate a section of a horizontal cross-section of a power semiconductor device in accordance with one or more embodiments; and 
         FIGS. 6A-6D  each schematically and exemplarily illustrate a top view of a relative arrangement of a mesa and one or more contact plug in accordance with one or more embodiments. 
     
    
    
     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 specific embodiments in which the invention may be practiced. 
     In this regard, directional terminology, such as “top”, “bottom”, “below”, “front”, “behind”, “back”, “leading”, “trailing”, “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 or a chip. 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. Also, the radial direction R mentioned below can be a lateral, i.e., horizontal direction, e.g., formed by an arbitrary, e.g., linear, combination of the first lateral direction X and the second lateral direction Y. 
     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/chip/die. For example, the extension direction Z mentioned below may be an extension direction that is perpendicular to both the first lateral direction X and the second lateral direction Y. The extension direction Z is also referred to as “vertical direction Z” herein. 
     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. 
     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 single cell, a stripe cell, a cellular (also referred to as “needle” or “columnar”) cell or another cell configuration, e.g., a power semiconductor device that may be used within a power converter or a power supply. Thus, in an embodiment, the power semiconductor device described herein can be configured to carry a load current that is to be fed to a load and/or, respectively, that is provided by a power source. 
     For example, the power semiconductor device may comprise one or more active power semiconductor cells, such as a monolithically integrated diode cell, a derivative of a monolithically integrated diode cell (e.g., a monolithically integrated cell of two anti-serially connected diodes), a monolithically integrated transistor cell, e.g., a monolithically integrated IGBT cell, a monolithically integrated RC IGBT cell, a monolithically integrated MOSFET cell, a monolithically integrated thyristor cell, a monolithically integrated Gate turn-off thyristor (GTO) cell and/or derivatives thereof. Such diode/transistor cells may be integrated in a power semiconductor module. A plurality of such equally configured 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, the power semiconductor device described herein can be a single-chip power semiconductor device and can be intended for high currents, typically in the Ampere range, e.g., up to several ten or hundred Ampere, and/or high voltages, typically above 15 V, more typically 100 V and above, e.g., up to at least 400 V or even more, e.g., up to at least 3 kV, or even up to 10 kV or more. 
     For example, the power semiconductor device described herein may be a single semiconductor chip exhibiting a single cell configuration, a stripe cell configuration or a cellular cell configuration and can be configured to be 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. 
       FIG. 1A  schematically and exemplarily illustrates a section of a vertical cross-section of a power semiconductor device  1  in accordance with one or more embodiments. For example, the power semiconductor device  1  may have a vertical configuration and may be configured for conducting a load current between a first load terminal structure  11  arranged at a front side (the upper part shown in  FIG. 1A ) and a second load terminal structure (not illustrated) arranged at a backside. For example, the backside and the second load terminal structure may be situated below the section depicted in  FIG. 1A . Hence, the power semiconductor device  1  may be configured such that (in an on-state of the power semiconductor device  1 ) the load current flows mainly along the vertical direction Z. 
     It should be noted in this context that the section of the power semiconductor device  1  shown in  FIG. 1A  includes only a small portion of the first load terminal structure  11 , namely, a portion that is arranged inside a contact hole CH. For example, the contact hole CH may be filled with a metal that forms part of the first load terminal structure  11 . For example, the first load terminal structure  11  may further comprise a front side metallization layer. Such a front side metallization layer may in turn be electrically connected with a first external load terminal, such as an emitter terminal or a source terminal, of the power semiconductor device  1  (not illustrated). 
     Similarly, the second load terminal structure that may be arranged at the backside may comprise, e.g., a backside metallization that is electrically connected with a second external load terminal, such as a collector terminal or a drain terminal of the power semiconductor device  1  (not illustrated). 
     The section of the vertical cross-section of the power semiconductor device  1  depicted in  FIG. 1A  includes a control cell  141  that is configured for controlling the load current  15 . For example, a plurality of such control cells  1  may be provided in an active area of the power semiconductor device  1 . 
     The control cell  141  is electrically connected to the first load terminal structure  11  on one side (namely, the upper side). Further, the control cell  141  is electrically connected to a semiconductor drift region  100  of the power semiconductor device  1  on the other (lower) side. The drift region  100  forms a part of a semiconductor body  10  and comprises dopants of a first conductivity type, e.g., the n-type. 
     The control cell  141  comprises a semiconductor mesa  101  which forms a part of the semiconductor body  10 . The mesa  101  extends from a bulk portion of the semiconductor body  10  (which includes the drift region  100 ) in parallel to the vertical direction Z. In other words, in a vertical cross-section along the vertical direction Z, as depicted in  FIG. 1A , a main extension direction of the mesa  101  may be parallel to the vertical direction Z. 
     In  FIG. 1A , the cross-section is along each of the vertical direction Z and the first lateral direction X. Regarding a form of the mesa with respect to the second lateral direction Y (i.e., perpendicular to the cross-section), it should be noted that the mesa  101  may, for example, have fin shape with a substantial extension along this direction Y. For example, the mesa  101  may extend throughout an entire active region (or through a substantial part of the active region) of the power semiconductor device  1  along the second lateral direction Y. 
     Alternatively, the lateral extension of the mesa  101  along the second lateral direction Y may be, for example, equal to or similar to a lateral extension W 1  of the mesa  101  (also referred to as a horizontal mesa width W 1 ) along the first lateral direction X, as illustrated in  FIG. 1A . In the latter case, the mesa  101  may in fact have the form of a pillar exhibiting, e.g., a quadratic or circular shape in a lateral cross-section along the first and second lateral directions X, Y. This will be further elucidated below with reference to  FIG. 5B . 
     In an embodiment, the horizontal mesa width W 1  may be less than 100 nm, such as in a range from 20 nm to 60 nm. For example, as schematically illustrated in  FIG. 1A  the mesa  101  may be spatially confined, in the first lateral direction X (i.e., perpendicular to the current flow direction Z of the load current in the mesa  101 ) by an insulation structure  1331 ,  1332 ,  1334  comprising, e.g., one or more oxides. The mesa  101  may exhibit a total extension W 1  of less than 100 nm, such as in the range from 20 nm to 60 nm, in said direction X. 
     Regarding vertical dimensions, the mesa  101  may have a total mesa height H of at least 50 nm, such as in the range from 50 nm to 600 nm, for example. 
     The mesa  101  includes, at an upper end, a contact region  1011  having dopants of the first conductivity type (e.g., n-type) or of a second conductivity type (e.g., p-type) complementary to the first conductivity type. Further, the mesa  101  has a channel region  1012  extending vertically from the contact region  1011  to a lower end of the mesa  101  and being coupled to the drift region  100  at the lower end of the mesa  101 . For example, the horizontal mesa width W 1  mentioned above and in the following, may be a minimal horizontal extension of the channel region  1011 . 
     A control electrode  131  is provided in the vicinity of the channel region  1012 . The control electrode  131 , which may also be referred to as gate electrode, is configured for inducing a conduction channel in the channel region  1012 , e.g., in dependence on a control signal provided via an external control terminal (or gate terminal) to which it is electrically connected (not illustrated). 
     The control electrode  131  is formed by a conductive layer, which may, for example, comprise (or consist of) polysilicon or a metal. The conductive layer  131  may be formed by a conformal deposition step. For example, the conductive layer  131  may be a flat layer extending mainly along the first and second horizontal directions X, Y. In other words, the conductive layer  131  may have a larger extension in the horizontal direction X, Y than in the vertical direction Z. As illustrated in  FIG. 1A , the conductive layer  131  has a vertical layer thickness T 1 . For example, said vertical layer thickness T 1  may be a minimal vertical layer thickness T 1 . For example, the vertical layer thickness T 1  may be a layer thickness of the conductive layer  131  as measured in the middle between two neighboring mesas. 
     In an embodiment, the vertical layer thickness T 1  is equal to or smaller than half the mesa height H, such as equal to or smaller than one third of the mesa height H. For example, in case the mesa height is in the range from 50 nm to 600 nm, the vertical layer thickness T 1  may be in the range from 15 nm to 300 nm, for example. 
     Additionally or alternatively, the vertical layer thickness T 1  may be equal to or larger than the horizontal mesa width W 1 , such as larger than twice or even three times the horizontal mesa width W 1 . 
     In accordance with the embodiment of  FIG. 1A , a vertical sidewall of the conductive layer  131  may be separated from the channel region  1012  of the mesa  101  by means of a gate insulation structure, such as a gate oxide  1334 . Sometimes, such an arrangement is referred to as a “sidewall gate” configuration. 
     For example, a gate oxide layer thickness T 3  of the gate oxide  1334  between the conductive layer  131  and the channel region  1012  may be in the range from 5 nm to 50 nm, such as in the range from 5 nm to 20 nm. 
     The vertical extension of the conduction channel in the channel region  1012  is mainly defined by the vertical extension H 2  of a portion of the gate oxide  1334  separating the conductive layer  131  from the mesa  101 . For example, the vertical extension H 2  of the portion of the gate oxide  1334  separating the conductive layer  131  from the mesa  101  is equal to or smaller than half the mesa height H, such as equal to or smaller than one third of the mesa height H. In the present exemplary embodiment, said vertical extension H 2  may be equal to the minimal vertical layer thickness T 1 . However, in other embodiments, this need not be the case, i.e., it is generally possible that the vertical extension H 2  of the portion of the gate oxide  1334  separating the conductive layer  131  from the mesa  101  may be larger or smaller than the minimal vertical layer thickness T 1 . This will be explained further below, e.g., with reference to  FIGS. 3E (a) and  3 E(b). 
     Further, in accordance with the embodiment illustrated in  FIG. 1A , said portion of the gate oxide  1334  separating the conductive layer  131  from the mesa  101 ,  102  is equal to or larger than twice a horizontal width W 1  of the mesa  101 ,  102 , such as equal to or larger than three times the horizontal width W 1  of the mesa  101 ,  102 . 
     Further, as illustrated, a bottom oxide  1331  may be arranged below the conductive layer  131 , i.e., between the conductive layer  131  and a bulk of the semiconductor body  10 . For example, the bottom oxide  1331  may have a vertical extension H 1  that is equal to or smaller than one third of the mesa height H. Additionally or alternatively, the vertical extension H 1  of the bottom oxide  1331  may be equal to or larger than the horizontal width W 1  of the mesa  101 . 
     The power semiconductor device  1  according to the embodiment of  FIG. 1A  further comprises a top insulation structure  1332 . The top insulation structure  1332  is arranged above the conductive layer  131 , i.e., further away from the bulk of the semiconductor body  10  than the conductive layer  131 . 
     The top insulation structure  1332 , the gate oxide  1334 , and the bottom  1331  together may form the insulation structure  1331 ,  1332 ,  1334  referred to above. 
     The contact region  1001  is electrically connected to the first load terminal structure  11  by means of a contact plug  107 . The contact plug  107  is arranged in contact with the contact region  1011  and at least partially between the contact region  1011  of the mesa  101  and the first load terminal structure  11 , such that it separates the contact region  1011  from the first load terminal structure  11 . An electrical connection between the contact region  1011  and the first load terminal structure  11  is thus established by means of the contact plug  107 . 
     For example, the contact plug  107  comprises or consists of a doped semiconductive material, such as at least one of the following materials: polysilicon, single crystalline or amorphous silicon, epitaxially grown silicon, silicon carbide, or silicon-germanium. In another embodiment, the contact plug  107  may comprise (or consist of) a metal. 
     In an embodiment in accordance with  FIG. 1A , a portion of the contact plug  107  projects horizontally beyond lateral boundaries  101 - 1  of the mesa  101 . This is to say that, in a cross-section view like the one shown in  FIG. 1A , a portion of the contact plug  107  horizontally projects (on each side) further than the mesa  101 , namely, for example, further than a respective vertical sidewall of the mesa  101 . In other embodiments, this may not necessarily be the case (cf.  FIG. 6D  and the corresponding description below). 
     Further in accordance with  FIG. 1A , a horizontal width W 2  of the contact plug  107  (e.g., at the level of an upper end of the mesa  101 ) amounts at least to the sum of a horizontal mesa width W 1  and twice the vertical layer thickness T 1  of the conductive layer forming the control electrode  131 . For example, in a vertical cross-section as shown in  FIG. 1A  and at the level of an upper end of the mesa  101 , the contact plug  107  may project on each side beyond a respective lateral boundary  101 - 1  of the mesa  101  by a distance W 3  that is equal to or larger than the vertical thickness T 1  of the conductive layer  131 . In an embodiment, the bottom of the contact plug  107  projects on each side beyond the respective lateral boundary  101 - 1  of the mesa  101  by a distance that corresponds to a sum of the vertical thickness T 1  of the conductive layer  131  and the gate oxide layer thickness T 3 . 
     In an embodiment in accordance with  FIG. 1A , the top insulation structure  1332  has a vertical extension H 3  between the contact plug  107  and an upper end of the control electrode  131 , wherein said vertical extension H 3  is equal to or smaller than one third of the mesa height H. Additionally or alternatively, said vertical extension H 3  may be equal to or larger than the horizontal width W 1  of the mesa  101 , such as equal to or larger than twice the horizontal mesa width W 1 . For example, said vertical extension H 3  may be measured between a bottom of the contact plug  107  and the upper end of the control electrode  131 , as schematically indicated in  FIG. 1A . 
     For example, as illustrated in  FIG. 1A , a portion of the contact plug  107  may extend laterally adjacent to the mesa  101  so as to form a lateral contact C between the contact plug  107  and a sidewall of the mesa  101 . Correspondingly, the contact region  1011  of the mesa  101  may exhibit a vertical overlap H 4  (defining a vertical extension of said lateral contact C) with the contact plug  107 . For example, in an embodiment, the vertical overlap H 4  may amount to at least the horizontal mesa width W 1 . 
     In the exemplary embodiment shown in  FIG. 1A , such a lateral contact C is formed on each side of the mesa  101 , such that the contact plug  107  is arranged on the mesa  101  (and centered on the mesa  101 ) in what may be referred to as a “saddle configuration.” It should be noted, however, that in other embodiments, the contact plug  107  does not necessarily form such a lateral contact C with a sidewall of the mesa  101 . In other words, in these other embodiments, the vertical overlap H 4  referred to above may be zero. This will be further explained below with reference to  FIG. 1C . 
       FIG. 1B  shows another exemplary embodiment of a power semiconductor device  1 , which differs from the power semiconductor device  1  of  FIG. 1A  in that the contact plug  107  comprises a silicided contact portion  1071  that is arranged in contact with the first load terminal structure  11 . For example, an electrical contact between first load terminal structure  11  and the contact plug  107  may thus be improved. The contact region  1011  of the mesa  101  may be arranged in contact with the silicided contact portion, as illustrated in  FIG. 1B . However, this need not be the case in other embodiments. 
       FIG. 1C  shows yet another variant embodiment of a power semiconductor device  1 , which differs from the power semiconductor device  1  of  FIG. 1A  in that the contact plug  107  does not form a lateral contact C with a sidewall of the mesa  101 . Instead, the contact plug  107  is arranged only on top of the mesa  101 . In other words, in the variant according to  FIG. 1C , the contact plug  107  does not have a “saddle configuration” referred to above in connection with  FIG. 1A . 
     In an embodiment in accordance with  FIG. 2A , the power semiconductor device  1  comprises two or more control cells  141 ,  142 , which are in each case configured as described above with reference to  FIGS. 1A-C . For example, a plurality of such control cells  141 ,  142  may be provided, each of which are electrically connected to a common (i.e., a same) first load terminal structure  11  (not illustrated). 
     Further, in an embodiment, a (common) control terminal may be provided, which may be is electrically connected with each of the control electrodes  131  of the plurality of control cells  141 ,  142  (not illustrated). This is to say that each of the control electrodes  131  may be provided with a same external control signal, which is received by the common control terminal. 
     In an embodiment, a first control cell  141  and a second control cell  142  may be provided, wherein the above description of the first control cell  141  of the power semiconductor devices  1  of  FIGS. 1A-B  may generally also apply to each of a first control cell  141  and a second control cell  142  of the embodiment shown in  FIG. 2A . In turn, what will be described in the following with reference to  FIGS. 2A-B , may analogously apply to the embodiment of  FIGS. 1A-C . 
     Accordingly, the first control cell  141  of the power semiconductor device  1  shown in  FIG. 2A  comprises a first mesa  101  which includes a first contact region  1011  and a first channel region  1012 . The second control cell  142  comprises a second mesa  102  which includes a second contact region  1021  and a second channel region  1022 . 
     Regarding dimensions, what has been stated above with reference to  FIGS. 1A-B , may also apply to the embodiment of  FIG. 2A . Thus, for example, a respective horizontal mesa width W 1  of the first and second mesas  101 ,  102  may be less than 100 nm, such as in a range from 20 nm to 60 nm. For example, the mesas  101 ,  102  may be spatially confined in the direction X (i.e., perpendicular to the current flow direction Z of the load current in the mesa  101 ,  102 ) by an insulation structure  1331 ,  1332 ,  1334  comprising one or more oxides. The mesas  101 ,  102  may exhibit a total extension of less than 100 nm, such as in the range from 20 nm to 60 nm, in said direction X. 
     In an embodiment in accordance with  FIG. 2A , the first contact region  1011  of the first mesa  101  may have dopants of the first conductivity type (e.g., n-type), whereas the second contact region  1021  of the second mesa  102  may have dopants of a second conductivity type that is complementary to the first conductivity type (e.g., p-type). 
     Further, at a backside of the power semiconductor device  1 , the semiconductor body  10  may comprise a backside emitter region  103 , which may have dopants at a higher dopant concentration as compared to the drift region  100 . For example, the backside emitter region  103  may have dopants of the second conductivity type (e.g., p-type). In this case, the power semiconductor device  1  may have an IGBT configuration. 
     The backside emitter region  103  may be arranged in contact with a second load terminal structure  12 , e.g., in the form of a backside metallization that is arranged on the backside of the power semiconductor body  10 . 
     In addition, the drift region  100  may comprise a buffer region (also referred to as field stop region; not illustrated) of dopants of the first conductivity type, wherein the buffer region comprises dopants of the first conductivity type at a higher dopant concentration than the remaining portions of the drift region  100 . Modes of realization of such a buffer region are well known to those skilled in the art and will therefore not be explained in detail here. 
     In accordance with one or more embodiments, the power semiconductor device  1  may be configured as a power semiconductor device  1  (such as an IGBT) having fully depletable channel regions  1012 ,  1022 . Accordingly, each of the first channel region  1012  and the second channel region  1022  may be fully depletable of charge carriers of at least one charge carrier type in dependence on a control signal (i.e., a gate voltage) provided to the control electrode(s)  131 . 
     For example, by “fully depletable” it shall be understood that the dimensions and the doping of the channel regions  1012 ,  1022  (as well as the dimensions of the gate oxide layer  1334 ) are such that, depending on a gate voltage that is applied to the control electrode(s)  131 , a space charge region may be induced in a respective channel regions  1012 ,  1022  from each side, which extends further than half of the mesa width W 1 . Hence, at least a portion of the channel region  1012 ,  1022  extending in the vicinity of the control electrode(s)  131  may be depleted of charge carriers over its entire horizontal extension W 1 . 
     For example, the channel regions  1012 ,  1022  may be doped with dopants of the second conductivity type (e.g., p-doped). In another embodiment, the channel regions  1012 ,  1022  may have dopants of the first conductivity type (e.g., n-type). In another embodiment, the second channel region  1022  may comprise dopants of a conductivity type different from the first channel region  1012 . 
     For example, at least a central portion (with regard to the vertical extension) of each of the channel regions  1012 ,  1022  may have essentially the same dopant concentration of dopants of the first conductivity type as the drift region  100 , e.g., a basic doping of a semiconductor substrate. External of said central portion, the doping may differ from the one of the drift region  100 , e.g., as a result of diffusion of dopants from the semiconductor regions that are arranged above and below the channel region  1012 ,  1022 . For example, in this embodiment, the control electrode  131  may comprise a semiconductor material (e.g., polysilicon) having dopants of the second conductivity type (e.g., p-type). 
     In an embodiment, the first contact region(s)  1011  may have dopants of the first conductivity type, whereas the second contact region(s)  1012  may have dopants of the second conductivity type. 
     The first control cell(s)  141  may thus be configured for controlling a current of charge carriers of the first conductivity type (e.g., an electron current). The first control cell(s)  141  may be configured for nearly completely suppressing a flow of charge carriers of the second conductivity type (e.g., a hole current) through the fully depleted first channel region  1012  in an on-state of the power semiconductor device. The first control cell(s)  141  may be configured such that the current through the first mesa(s)  101  caused by charge carriers of the first conductivity type is at least 10 times larger than the current through the first mesa(s)  101  caused by charge carriers of the second conductivity type in an on-state (or forward conducting state) of the power semiconductor device  1 . The second control cell(s)  142  may be configured for suppressing a flow of charge carriers of the first and second conductivity type (e.g., a hole current) through the fully depleted second channel region  1022  in an on-state (or forward conducting state) of the power semiconductor device, but enable an outflow of charge carriers of the second conductivity type—and hence support a fast removal of an electron-hole plasma from the drift region  100 —during turn-off or in the forward blocking state of the device  1 . To this end, the first and second control cells  141 ,  142  may have different threshold voltages (e.g., gate-emitter threshold voltages) for the onset of a channel formation for electrons/holes in the first and second channel regions  1012 ,  1022 . 
     As schematically illustrated in  FIG. 2A , the semiconductor body  10  may further comprise a first plateau region  1013  and a second plateau region  1023 . The first plateau region  1013  may be in contact with the first channel region  1012  and may exhibit dopants of the first conductivity type. The second plateau region  1023  may exhibit dopants of the second conductivity type and may be coupled to the second channel region  1022  such that the second plateau region  1023  is electrically coupled to the second contact region  1021  in case the second channel region  1022  is in conduction mode for carriers of the second conductivity type. In an embodiment, the second plateau region  1023  may be in contact with the second channel region  1022 . 
     For further explanations of functional and structural features of power semiconductor devices having a fully depletable channel region, it is referred, for example, to the published German patent applications DE 10 2014 108 913 A1, DE 10 2016 112 017 A1, and DE 10 2016 112 016 A1. The power semiconductor device  1  of the present invention may be generally configured as described therein, wherein one or more contact plugs  107  as described in the present specification may be additionally provided. Further, power semiconductor devices as described in the aforementioned patent applications may be produced using one or more process steps according to the present specification. 
       FIG. 2B  shows another exemplary embodiment of a power semiconductor device  1 , which differs from the power semiconductor device  1  of  FIG. 2A  in that the control electrodes  131 , which are in the present example formed by polysilicon layers, comprise a silicided control electrode portion  1311 . The silicided control electrode portion  131  is arranged in contact with the top insulation structure  1332 . For example, a gate resistance of the power semiconductor device  1  may be reduced due to the silicided control electrode portion  1311 . 
     In what follows, processing steps of a method of processing a power semiconductor device  1  will be explained with reference to  FIGS. 3A-H . For example, a power semiconductor device  1  as described above with reference to  FIGS. 1A-2B  in various embodiments may be produced by means of such processing steps. Hence, what has been explained in the above regarding features of the power semiconductor device  1  of the present invention may apply analogously to the processing method that will be presented in the following, and vice versa. 
     Starting with  FIG. 3A , in a first step, a power semiconductor body  10  may be provided. For example, the power semiconductor body  10  may be provided in the form of a wafer of, e.g., silicon or silicon carbide. 
     Further with reference to  FIG. 3A , portions of the semiconductor body  10  may be recessed so as to create a plurality of mesas  101 ,  102  protruding from a remaining bulk portion  10 - 3  of the semiconductor body  10 . For example, this may be achieved by means of a lithography/etch sequence or by means of so-called double patterning process, as is in principle well known in the art. Also, an isotropic etch step for further thinning the mesas  101 ,  102  after initial mesa formation may be included. Generally, it should be noted that a horizontal mesa width W 1  of the mesas  101 ,  102  may be further reduced by one or more optional process steps after the initial formation of the mesas  101 ,  102 . The exemplary dimensions and dimension relations mentioned in the following may apply to the mesa width W 1  after the initial creation of the mesas  101 ,  102  (in the recessing step) and/or to a smaller mesa width W 1 , which may result from one or more of such further mesa thinning steps. 
     With regard to dimensions, it may be provided that the mesas  101 ,  102  exhibit a horizontal mesa width W 1 , which may be in the range from 20 nm to 100 nm, for example. A mesa height H (as measured between upper ends of the mesas  101 ,  102  and an upper surface of the recessed bulk portion  10 - 3  of the semiconductor body  10 ) may be in the range from 50 nm to 600 nm, for example. Further, a pitch P between neighboring mesas  101 ,  102  may be, e.g., in the range from 50 nm to 10 μm. 
     A part of said bulk portion  10 - 3  of the semiconductor body  10  may form the drift region  100  of the power semiconductor device  1  referred to above. 
     Turning now to  FIG. 3B , in a further step, a first insulation layer  1331  may be formed on the bulk portion  10 - 3  in between the mesas  101 ,  102 . The first insulation layer  1331  may form the bottom oxide  1331  of the power semiconductor device  1  referred to above. Accordingly, in an embodiment, the first insulation layer  1331  may have a vertical extension H 1  that is equal to or smaller than one third of the mesa height H. Additionally or alternatively, the vertical extension H 1  of the bottom oxide  1331  may be equal to or larger than the horizontal mesa width W 1 . 
     For example, the formation of the first insulation layer  1331  may comprise an oxide deposition, optionally combined with a back etch process, and further optionally combined with a CMP planarization step. For example, a resulting oxide thickness H 1  may be in the range from 10 nm to 150 nm. 
     As further illustrated in  FIG. 3B , a gate oxide layer  1334  may be formed on the mesas  101 ,  102 . For example, a thickness of the gate oxide layer  1334  may be in the range from 5 nm to 50 nm. 
     In accordance with  FIG. 3C , the processing method may further comprise a step of depositing a gate electrode layer  131  on the first insulation layer  1331  and on the gate oxide layer  1334 . For example, at least a part of the gate electrode layer  131  may form at least a part of the control electrode(s)  131  of the power semiconductor device  1  referred to above. For example, the gate electrode layer  131  may comprise or consist of a doped polysilicon or amorphous silicon. In an alternative embodiment, the gate electrode layer  131  may be a metal layer. 
     For example, a layer thickness T 1  of the deposited gate electrode layer  131  may be in the range from 50 nm to 500 nm. In an embodiment, the layer thickness T 1  of the deposited gate electrode layer  131  is equal to or smaller than one third of the mesa height H. In an embodiment, the layer thickness T 1  of the deposited gate electrode layer  131  is equal to or smaller than one third of the distance between two mesas in order to not completely fill the space. For example, the layer thickness T 1  may be a vertical layer thickness of the gate electrode layer  131  as measured in the middle between two neighboring mesas  101 ,  102 . 
     Next, referring to  FIG. 3D , the method may comprise a step of forming a second insulation layer  1332 - 1  which fills a space between neighboring mesas  101 ,  102 . The second insulation layer  1332 - 1  may be formed in such a way that portions of the gate electrode layer  131  are exposed at a level above the mesas  101 ,  102 , as illustrated in  FIG. 3D . This may be achieved, for example, by means of an oxide deposition, which may be combined with a CMP step for planarization and/or a back etch process to expose said portions of the gate electrode layer  131 . For example, at least a part of the second insulation layer  1332 - 1  may form at least a part of the top insulation structure  1332  of the power semiconductor device  1  mentioned above. 
     As schematically illustrated in  FIGS. 3E, 3E (a), and  3 E(b), the exposed portions of the gate electrode layer  131  may then be recessed down to a defined recess depth D 1  so as to create recesses R 1 , R 2  adjacent to respective upper portions of the mesas  101 ,  102  (and centered about the respective mesa  101 ,  102 ). This recessing step may be carried out by means of an etch process. 
     For example, such an etch process may be configured for etching silicon (in the case of a polysilicon gate electrode layer  131 ) while being selective to the insulation material of the second insulation layer  1332 - 1  and the gate oxide layer  1334 , such that these layers  1332 - 1 ,  1334  may not be affected by the recessing step. 
     It should be noted that the recesses R 1 , R 2  are thus created in a self-aligned manner with respect to the mesas  101 ,  102 , e.g., in the form of side trenches R 1 , R 2  on each side of the mesas  101 ,  102 . 
     The recess depth D 1  defines a vertical gate length of the gate electrode  131  of the power semiconductor device  1  to be produced. For example, the vertical gate length may be adjusted to be different from the gate electrode layer thickness T 1 , as required. 
     In one variant embodiment in accordance with  FIG. 3E , the recess depth D 1  is at the same level as a top edge of the gate electrode layer  131  within a variation of at most 10% of a thickness T 1  of the gate oxide layer  1334 . 
     In another variant embodiment, which is schematically illustrated in  FIG. 3E (a), the recess depth D 1  is located at a higher level than the top edge of the gate electrode layer  131  in the middle between two neighboring mesas  101 ,  102 . Hence, in this variant, the vertical gate length may exceed the gate electrode layer thickness T 1 . 
     In yet another variant, which is schematically illustrated in  FIG. 3E (b), the recess depth D 1  is located deeper than the top edge of the gate electrode layer  131  in the middle between two neighboring mesas  101 ,  102 . Hence, in this variant, the vertical gate length may be smaller than the gate electrode layer thickness T 1 . In other words, in this case, the recess R 1 , R 2  may define the minimal vertical extension of the gate electrode layer  131 . 
       FIG. 3F  schematically illustrates a further processing step, which consists in the formation of a third insulation layer  1333  on top of the gate electrode layer  131  inside the recesses R 1 , R 2 . The third insulation layer  1333  may also be referred to as an intermediate oxide. 
     In accordance with an embodiment, the third insulation layer  1333  may be formed by means of an oxide deposition having both sputtering and deposition components, such as by means of a so-called high density plasma deposition (HDP) process. The oxide deposition may be followed by a defined back etch process. For example, as a result, tilted sidewalls S of the recesses R 1 , R 2  may be formed, as illustrated in  FIG. 3F . 
     Alternatively, the recesses R 1 , R 2  may be first completely filled with an oxide or another insulating layer, followed by a CMP planarization and the application of a lithographical mask. Then, a contact etch process, e.g. in the form of a reaction ion etching (RIE) process, may be carried out to define a contact hole and the third insulation layer  1333 . 
     For example, the gate oxide layer  1334  may also be removed from upper ends of one of the mesas  101 ,  102  during an etch process as mentioned in the preceding paragraphs, or by means of a further (separate) etch process (see  FIG. 3G ). 
     As further illustrated in  FIG. 3G , the recesses R 1 , R 2  may then be filled with a semiconductive material so as to form a contact plug  107 . For example, this step may comprise a deposition of polysilicon, optionally followed by a CMP planarization step. Alternatively, for example, a selective epitaxy of silicon may be carried out, which may be followed by a back etch process. 
     After the filling step, the semiconductive material may be doped, e.g. by means of an implantation of dopants of the first conductivity or of the second conductivity type, as required. 
     In another embodiment, the recesses R 1 , R 2  may be filled with a metal instead of a semiconductive material. 
     Further, the method may comprise siliciding a surface portion of each of the contact plugs  107  so as to form silicided contact portions  1071  (see  FIG. 3H ). For example, the silicided contact portions  1071  may comprise at least one of titanium disilicide (TiSi2), cobalt disilicide (CoSi2), and nickel disilicide (NiSi2). The silicide formation may, for example, comprise a process sequence including a deposition of a suitable metal, a rapid thermal anneal (RTA), a wet etch, and another RTA. 
     For finishing the processing of the power semiconductor device  1 , further steps, such as another oxide deposition, a contact formation, structuring of a front side metallization, a deposition of a polyimide etc. may be carried out. Such steps are as such well known in the art and are therefore not illustrated or explained in detail here. 
     The formation of doped contact regions  1011 ,  1021  of the mesas  101 ,  102  (cf.  FIGS. 1A-2B ) is also not explicitly illustrated in  FIGS. 3A-H . The contact regions  1011 ,  1021  may be formed by methods which are as such well known, e.g., by means of ion implantation, plasma doping or solid phase outdiffusion using lithography masks. 
       FIGS. 4A-C  schematically illustrate steps of a process variant which allows for creating silicided control electrode portions  1311  of the kind that have been described above with reference to  FIG. 2B . In this case, the gate electrode layer  131  is a polysilicon layer. 
     For example, after the process step of forming the contact plugs  107 , which has been explained above with reference to  FIG. 3G , portions of the second insulation layer  1332 - 1  may be removed so as to expose portions of the polysilicon layer  131  (see  FIG. 4A ). This step may comprise an etch process, wherein the contact plugs  107  (which may consist, e.g., of polysilicon) are used as a hard mask. For example, remaining portions of the second insulation layer  1332 - 1  may form oxide spacers on each side of the contact plug  107  as a result of the etch process, which may hence also be referred to as a “spacer etch” process. 
     The exposed portions of the polysilicon layer  131  may then be silicided. This may be accomplished in a similar way as described above in connection with  FIG. 3H  and the polysilicon contact plugs  107 . Accordingly, the silicide formation may, for example, comprise a process sequence including a deposition of a suitable metal  4  (see  FIG. 4B ), a rapid thermal anneal (RTA), a wet etch, and another RTA. 
     As schematically illustrated in  FIGS. 4B-C , the siliciding of the surface portions of the contact plugs  107  and of the exposed portions of the polysilicon layer  131  may thus be carried out in one or more shared processing steps (such as the deposition of the metal layer  4 ). It should be noted that the silicide may be formed on exposed polysilicon surfaces, but not on oxides, such as the oxide spacers  1332 . 
     For example, as already mentioned in connection with  FIG. 3H , the resulting silicided portions  1071  of the contact plugs  107  and the silicided control electrode portions  1311  may comprise at least one of titanium disilicide (TiSi2), cobalt disilicide (CoSi2), and nickel disilicide (NiSi2). 
       FIGS. 5A-B  each schematically and exemplarily illustrate a section of a horizontal cross-section of a power semiconductor device  1  in accordance with one or more embodiments, such as the embodiments described above with reference to  FIGS. 1A-2B . For example,  FIGS. 5A-B  may show horizontal cross-sections through two different variant embodiments of the power semiconductor device  1  in accordance with  FIGS. 2A-B , wherein the cross-section is in each case at a (vertical) level of the control electrode  131 . 
     In the variant embodiment illustrated in  FIG. 5A , the mesas  101 ,  102  are formed as elongated fins having their main horizontal extension in the second lateral direction Y. For example, the mesas may have a length L in said direction, wherein the length L may be, e.g., in the range from 1 μm to 100 μm. The mesa width W 1  may be much smaller, such as in the range from 20 nm to 60 nm, as mentioned earlier. 
     By contrast, in the variant embodiment illustrated in  FIG. 5B , the mesas  101 ,  102  are formed as pillars having a quadratic cross-section. In other embodiments, which are not illustrated, such pillars may instead have a round cross-section, such as a circular cross-section. 
     In both variant embodiments according to  FIGS. 5A and 5B , the mesas  101 ,  102  are laterally surrounded by the gate oxide layers  1334  and the gate electrodes  131  from each side. In other words, the mesas  101 ,  102  are embedded in the respective gate electrode  131  while being separated from the gate electrode  131  by means of the gate oxide layers  1334 . 
     With regard to the spatial arrangement of first mesas  101  and second mesas  102 , it should be noted that  FIGS. 5A-B  are merely examples. Different relative arrangements of first mesas  101  and second mesas  102  are possible. 
       FIGS. 6A-D  each schematically and exemplarily illustrate a top view of a relative arrangement of an exemplary mesa  101  and a contact plug  107  in accordance with one or more embodiments. In each case, the mesa  101  has an elongated fin configuration and the contact plug(s)  107  is/are indicated by means of one or more dashed rectangles. 
     For example, in accordance with  FIG. 6A , the contact plug  107  may overlap the mesa  101  on all four sides (cf.  FIG. 1A  and the corresponding description referring, e.g., to the lateral contact C and the vertical overlap H 4 ). Here, one large contact plug  107  forms a single large contact with the mesa  101 . For example, with such a layout, a relatively small contact resistance may be achieved. 
     For example, the contact plug  107  may be centered precisely on the mesa  101  with respect to the first horizontal direction X. This centered arrangement may, for example, result automatically from a self-aligned processing method as described above with reference to  FIGS. 3A-4C . 
       FIG. 6B  show a variant wherein, again, one large contact plug  107  forms a single large contact with the mesa  101 . However, in contrast to  FIG. 6A , the contact plug  107  overlaps the mesa  101  only on two sides. 
     In the variant embodiment that is illustrated in  FIG. 6C , multiple smaller contact plugs  107  are provided, wherein each contact plug  107  overlaps the mesa  101  on two sides. 
     Finally, in the exemplary embodiment illustrated in  FIG. 6D , there is no vertical overlap of the contact plug  107  and the mesa  101  at all. 
     In the above, embodiments pertaining to power semiconductor devices and corresponding processing methods were explained. 
     For example, these semiconductor devices are based on silicon (Si). Accordingly, a monocrystalline semiconductor region or layer, e.g., the semiconductor body  10  and its regions/zones, e.g., regions etc. 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 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 switches applications currently mainly Si, SiC, GaAs and GaN materials are used. 
     Spatially relative terms such as “under”, “below”, “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. Uke 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.