ION BEAM IMPLANTATION PROCEDURE

Abstract

Ion beam implantation method, comprising: orienting a substrate (700) to a target axis (706), wherein a remaining angular misalignment (Δθ) between the target axis (706) and a preselected crystal channel direction (707) in the substrate (700) lies within an angular tolerance interval (Rg), and wherein lattice guiding and / or channeling effects predominate over large-angle scattering effects along the crystal channel direction (707); implanting dopant ions into the substrate (700) through a substrate main surface (701) using an ion beam (800) propagating along an ion beam axis (801), wherein the dopant ions are implanted at different implantation angles (θ) between the ion beam axis (801) and the target axis (706), wherein the implantation angles (θ) lie within an implantation angle range (Rw) and wherein for the different implantation angles (θ) the ion beam (800) impinges on the same sub-area of ​​the substrate main surface (701), wherein a channel acceptance width (Rk) is effective for the preselected crystal channel direction (707), wherein the implantation angle range (Rw) is greater than 80% of a sum of the channel acceptance width (Rk) and twice the angle tolerance interval (Rg) and where the implantation angle range (Rw) is less than 500% of the sum of the channel acceptance width (Rk) and twice the angle tolerance interval (Rg).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an ion beam implantation method, a method of manufacturing a semiconductor device, and a semiconductor device including a doped region. BACKGROUND

[0002] If the direction of dopant ions incident on the surface of a monocrystalline substrate is sufficiently inclined to principal crystal directions in the substrate, the dopant ions are predominantly subject to large-angle scattering, which determines the final mean penetration depth of the dopant ions. If the direction of the dopant ions is approximately parallel to a principal crystal direction, the dopant ions are largely subject to only small-angle scattering, while the dopant ions pass through the crystal lattice. The dopant ions remain in the same crystal channel (“lattice guiding effect” or “channeling”) and can penetrate deeper into the crystal substrate than in the case of large-angle scattering.Therefore, ion beam implantation utilizing the channeling effect has the potential to form doped regions with end-of-range peaks located deeper below the main surface of a crystalline substrate than the end-of-range peaks of doped regions formed without channeling and using the same acceleration energy for the dopant ions. For dopant ions subject to lattice-guiding or tunneling, the distance between the end-of-range peak and the main surface can strongly depend on slight deviations between the crystal channel direction and the implantation beam axis.

[0003] The document DE 10 2016 102 865 A1 describes a method for implanting ions by means of a target implantation and a test implantation preceding the target implantation. For the test implantation, a semiconductor substrate is guided through an ion beam in a linear direction, wherein the angle of inclination of the semiconductor substrate to the ion beam is continuously varied from minus 3 degrees to plus 3 degrees, so that during a single linear pass of the ion beam, the ion beam strikes the semiconductor substrate at different positions and at different angles. The crystal defect or charge carrier density at the surface is lower where the implanted ions are implanted under channeling conditions. From the position of a local minimum of the crystal defect or charge carrier density,The charge carrier density on the semiconductor substrate can be used to determine the actual tilt angle at which the channeling condition is met. The information about the actual tilt angle is used in the subsequent target implantation to reliably align the ion beam parallel to the relevant channeling direction. US 2006 / 0 138 357 A1 describes the successive execution of several implantations at different tilt angles and the characterization of the completed implantations using thermal wave values ​​and sheet resistance values. US 2008 / 0 142 899 A1 shows vertical dopant profiles in CMOS logic components with high-dose buried guard ring (HBGR) layers.

[0004] The publication DE 10 2017 117 999 A1 describes an ion beam implantation process for forming doped regions with a vertical dopant distribution that is as homogeneous as possible over the largest possible vertical extent. For this purpose, the ion beam is aligned at a different angle to the surface normal for each individual ion beam implantation. Each ion beam implantation creates a characteristic distribution, with the projected range of the ions decreasing with increasing deviation of the ion beam from the surface normal. During the process, the ion beam covers an angular range of 45 degrees and more. The irradiation angles of the ion beam differ by several degrees. The implantation dose increases with increasing deviation from the surface normal.The superposition of the dopant distributions resulting from the individual ion beam implantations results in a pronounced plateau in the overall vertical dopant distribution.

[0005] There is a need for an improved ion implantation process. SUMMARY

[0006] One embodiment of the present disclosure relates to an ion beam implantation method. A substrate is oriented to a target axis, with a remaining angular misalignment between the target axis and a preselected crystal channel direction in the substrate within an angular tolerance interval. Dopant ions are implanted into the substrate using an ion beam propagating along an ion beam axis. The dopant ions are implanted at various implantation angles between the ion beam axis and the target axis.

[0007] The implantation angles lie within an implantation angle range. A channel acceptance width is effective for the preselected crystal channel direction. The implantation angle range is greater than 80% of the sum of the channel acceptance width and twice the angle tolerance interval. The implantation angle range is less than 500% of the sum of the channel acceptance width and twice the angle tolerance interval.

[0008] Another embodiment of the present disclosure relates to a semiconductor device. The semiconductor device includes a semiconductor body having a first surface and a doped region. The doped region comprises a first local dopant concentration maximum at a first distance from the first surface, a second local dopant concentration maximum at a second distance from the first surface, and a local dopant concentration minimum between the first distance and the second distance. The first distance is greater than the second distance. A difference between the first distance and the second distance is in a range from 200 nm to 1500 nm. A ratio between the first local dopant concentration maximum and the second local dopant concentration maximum is in a range from 0.5 to 2.A ratio between the sum of the first local dopant concentration maximum and the second local dopant concentration maximum and the local dopant concentration minimum is in a range of 2 to 10.

[0009] Another embodiment of the present disclosure relates to a further semiconductor device. A semiconductor body includes a first surface and a doped region. The semiconductor body includes silicon carbide. The doped region includes a first local dopant concentration maximum at a first distance from the first surface, a second local dopant concentration maximum at a second distance from the first surface, and a local dopant concentration minimum between the first distance and the second distance. Starting from the first distance, a dopant concentration in the doped region decreases by 90% of the first local dopant concentration maximum with increasing distance from the first surface within at most 2 µm. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of an ion beam implantation method and a semiconductor device and, together with the description, serve to explain principles of the embodiments. Further embodiments are described in the following detailed description and claims. Fig. 1A-1F contain schematic side and top views of a substrate to illustrate an ion beam implantation method according to one embodiment, including substrate alignment and ion beam implantation at various implantation angles. Fig. 2A-2B are schematic diagrams illustrating vertical dopant concentration profiles in semiconductor devices according to embodiments and illustrating effects of an ion beam implantation process according to another embodiment. Fig. 2C-2D are schematic diagrams to illustrate effects of an ion beam implantation method according to an embodiment. Fig. 3 illustrates a schematic vertical cross-sectional view of a portion of a semiconductor device having one or more doped regions including vertical dopant concentration profiles with a channeling tip, according to embodiments. Fig. 4A-4C are schematic diagrams showing vertical doping profiles along a line IV-IV' of the Fig. 3 illustrated semiconductor device. Fig. Figure 5 is a schematic diagram showing a vertical doping profile along a line VV' of the Fig. 3 illustrated semiconductor device. Fig. 6 is a schematic diagram illustrating a vertical dopant profile according to an embodiment including multiple ion implantation processes. Fig. Fig. 7 is a schematic diagram showing another vertical dopant profile along a line VI-VI in the semiconductor device of Fig. 3 according to another embodiment with multiple ion implantation processes. DETAILED DESCRIPTION

[0011] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which an ion beam implantation method and semiconductor device may be practiced. 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 disclosure. For example, features illustrated or described for one embodiment may be used in or in connection with other embodiments to achieve yet another embodiment. It is intended that the present disclosure encompass such modifications and changes.The examples are described using specific language, which should not be construed as limiting the scope of the appended claims. The drawings are not to scale and are for illustrative purposes only. Corresponding elements are designated by the same reference numerals throughout the various drawings unless otherwise noted.

[0012] The terms "have," "contain," "comprise," "have," and the like are open-ended terms. These terms indicate the presence of the identified structures, elements, or characteristics, but do not preclude the presence of additional elements or characteristics. The indefinite and definite articles are intended to include both the plural and the singular, unless the context clearly indicates otherwise.

[0013] The term "electrically connected" describes a permanent, low-resistance ohmic connection between electrically connected elements, for example, a direct contact between the elements in question or a low-resistance connection via a metal and / or a highly doped semiconductor material. The term "electrically coupled" encompasses the possibility that one or more intermediate elements suitable for signal and / or power transmission may be connected between the electrically coupled elements, for example, elements that can be controlled to temporarily provide a low-resistance connection in a first state and a high-resistance electrical decoupling in a second state. An ohmic contact is a non-rectifying electrical junction with a linear or nearly linear current-voltage characteristic.

[0014] The figures illustrate relative doping concentrations by indicating “¯” or “ + ” next to the doping type “n” or “p”. For example, “n - ” a doping concentration that is lower than the doping concentration of an “n” doping region, while an “n + "-doping region has a higher doping concentration than an "n"-doping region. Doping regions of the same relative doping concentration do not necessarily have the same absolute doping concentration. For example, two different "n"-doping regions can have the same or different absolute doping concentrations.

[0015] Ranges specified for physical dimensions include the boundary values. For example, a range for a parameter y from a to b is read as a ≤ y ≤ b. The same applies to ranges with a boundary value such as "at most" and "at least."

[0016] The main components of a layer or structure made of a chemical compound or alloy are those elements whose atoms form the chemical compound or alloy. For example, nickel and silicon are the main components of a nickel silicide layer, and copper and aluminum are the main components of a copper-aluminum alloy.

[0017] The term "over" should not be construed to mean only "directly over." Rather, if an element is positioned "over" another element (e.g., a layer is "over" another layer or "over" a substrate), another component (e.g., another layer) may be positioned between the two elements (e.g., another layer may be positioned between a layer and a substrate if the layer is "over" the substrate).

[0018] With regard to structures and doped regions formed in a substrate, a second region lies "below" a first region if a minimum distance between the second region and a first substrate main surface at the front side of the substrate is greater than a maximum distance between the first region and the first substrate main surface. The second region lies "directly below" the first region where the vertical projections of the first and second regions into the first substrate main surface overlap. The vertical projection is a projection orthogonal to the first substrate main surface.

[0019] Regions and / or structures may be laterally separated from each other within the same horizontal slice. Laterally separated regions and / or structures may also be vertically separated (i.e., positioned in different horizontal slices). In the latter case, orthogonal projections of the separated regions and / or structures into a horizontal projection plane are laterally separated. Regions and / or structures in different horizontal slices overlap laterally where orthogonal projections of the respective regions and / or structures into a horizontal projection plane overlap laterally.

[0020] The term “power semiconductor device” refers to semiconductor devices having a high voltage blocking capability of at least 30 V, for example 100 V, 600 V, 3.3 kV or higher and having a nominal forward current of at least 1 A, for example 10 A or higher.

[0021] Power semiconductor switches include IGBTs (insulated-gate bipolar transistors), JFETs (junction field-effect transistors), and IGFETs (insulated-gate field-effect transistors). IGFETs are voltage-controlled devices that include MOSFETs (metal-oxide-semiconductor FETs) and other FETs with gate electrodes based on a doped semiconductor material and / or with gate dielectrics that are not, or not exclusively, based on an oxide.

[0022] According to one embodiment, an ion beam implantation method may include orienting a substrate to a target axis, wherein a remaining angular misalignment between the target axis and a preselected crystal channel direction in the substrate may be within an angular tolerance interval.

[0023] The substrate may be a wafer-sized disc containing a single-crystal material (e.g., a wafer) or may contain a layer of a single-crystal material formed on a non-crystalline base substrate. The disc or layer of a single-crystal material may contain exclusively a single-crystal material or may contain structures of other materials, e.g., conductive structures and / or insulating structures, in addition to the single-crystal material.

[0024] The single-crystal material can be a ceramic, e.g., α-Al2O3 (sapphire), or a semiconductor material. The semiconductor material can be, for example, any Group IV element semiconductor, e.g., silicon (Si) or germanium (Ge), any Group IV compound semiconductor, e.g., silicon carbide (SiC) or silicon germanium (SiGe), or any Group III / V compound semiconductor, such as gallium arsenide (GaAs) or gallium nitride (GaN).

[0025] The single-crystal material can be, for example, 15R-SiC (silicon carbide of the 15R polytype) or, for example, silicon carbide with a hexagonal polytype, for example, 2H-SiC, 4H-SiC, or 6H-SiC. In addition to the main components of silicon and carbon, the single-crystal material can contain dopant atoms, for example, nitrogen (N), phosphorus (P), beryllium (Be), boron (B), aluminum (Al), and / or gallium (Ga). The single-crystal material can contain further impurities caused by a process imperfection and / or precursor impurities, for example, hydrogen, fluorine, and / or oxygen.

[0026] The substrate may have two substantially parallel main surfaces of the same shape and size and a lateral outer surface connecting the edges of the two substrate main surfaces. The substrate may extend laterally in a plane spanned by lateral directions. Accordingly, the substrate may have a surface extension along two lateral directions (hereinafter also referred to as horizontal directions). The substrate may have a thickness along a vertical direction perpendicular to the lateral directions. A first substrate main surface on the front side and a second substrate main surface on the back side may have the shape of a polygon (e.g., a rectangle or a hexagon) with or without rounded edges, a circle, or a circle with a notch or with a flat along the circumference.

[0027] Any crystal direction along which lattice guidance or channeling effects outweigh the effect of large-angle scattering can represent a crystal channel direction. For example, for a hexagonal crystal lattice, the crystal channel direction can be a principal crystal direction, e.g., the <0001> -lattice direction (“c-axis”), the <11-20> lattice directions (“a-axes”), the <1-100> lattice directions (“m-axes”), or the <11-23> lattice directions. For a cubic crystal lattice, the crystal channel direction can, for example, be a principal crystal direction, e.g., the <001> -Grid direction, the <001> -Grid direction, the <111> -Grid direction, the <112> -lattice direction, directions parallel to (111) planes and directions parallel to (022) planes.

[0028] A user can preselect one of the available crystal channel directions as the crystal channel direction that defines the position of the tip at the end of the range of tunneling dopant ions under predetermined process conditions.

[0029] The aiming axis can be identical to an idle ion beam axis. The idle ion beam axis can be the standard ion beam axis along which an ion beam propagates in idle mode. In idle mode, the ion beam implantation device uses a constant implantation angle.

[0030] The remaining angular misalignment (total incidence angle variation) between the target axis and the previously selected crystal channel direction may result from process imperfections in the process that orients the substrate to the target axis.

[0031] Imperfections in the processes can arise from mechanical limitations of the ion beam implantation device. For example, the ion beam implantation device may include a substrate tilt mechanism. The substrate tilt mechanism can rotate the substrate about a horizontal axis of rotation parallel to the first main substrate surface. Alternatively, the substrate tilt mechanism can successively rotate the substrate about two differently oriented, e.g., orthogonal horizontal, axes of rotation parallel to the first main substrate surface. The substrate tilt mechanism can align the preselected crystal channel direction with the target axis only with limited accuracy.

[0032] Alternatively or additionally, the ion beam implantation device may include an ion beam projection device with a controllable ion beam axis. The ion beam projection device may deflect the ion beam axis in an incident beam plane inclined to the first main substrate surface. Alternatively, the ion beam projection device may be adapted to deflect the ion beam axis in two differently oriented, e.g., orthogonal, incident beam planes. The ion beam projection device can align the ion beam axis to the preselected channel direction only with limited accuracy.

[0033] Alternatively or additionally, the ion beam implantation device may include a substrate rotation mechanism. The substrate rotation mechanism may rotate the substrate about a vertical axis through a lateral center of the first substrate main surface. The substrate rotation mechanism may align the preselected crystal channel direction to an incidence plane spanned by a surface normal and the ion beam axis only with limited accuracy.

[0034] Typically, a total angular tolerance window of the device, including tolerances for the substrate tilt mechanism and for the ion beam projection device, can be in a range from -0.5 degrees to +0.5 degrees, for example from -0.2 degrees to +0.2 degrees or from -0.1 degrees to +0.1 degrees.

[0035] Additionally or alternatively, the process imperfections may involve an off-axis cut, which defines the orientation of the first substrate main surface with respect to the main crystal directions, including the preselected crystal channel direction. Typically, the angular tolerance window for the off-axis cut may be in a range from -0.5 degrees to +0.5 degrees, for example, from -0.2 degrees to +0.2 degrees for silicon carbide (SiC) and silicon (Si), or from -0.1 degrees to +0.1 degrees for silicon (Si), for example.

[0036] Additionally or alternatively, the process imperfections may involve an angular deviation between an orientation indicator for a principal lattice plane and an actual orientation of the same principal lattice plane. For example, the surface of a flat or the direction of a notch on the outer perimeter of the substrate may indicate the orientation of a predefined principal lattice plane. Process imperfections may result in an angular deviation between the actual orientation of the predefined principal lattice plane and the surface of the flat, or between the actual orientation of the predefined principal lattice plane and the direction indicated by the notch.

[0037] The total angular tolerance interval can be the sum of the total angular tolerance window of the device and the angular tolerance windows for the off-axis cut and the orientation indicator. For example, the angular tolerance interval can be in a range from -1 degree to +1 degree, for example, from -0.4 degrees to +0.4 degrees, or from -0.2 degrees to +0.2 degrees.

[0038] The remaining angular misalignment can be described by a first angular component and a second angular component, wherein the first and second angular components are defined in orthogonal directions. For example, the first angular component describes the angular deviation of the preselected crystal channel direction from the target axis in a vertical plane orthogonal to a horizontal rotation direction of the substrate tilt mechanism.

[0039] A second angle component can describe the angular deviation of the vertical projection of the preselected crystal channel direction onto the first substrate main surface from the vertical projection of the target axis onto the first substrate main surface.

[0040] Dopant ions can be implanted into the substrate using a directed ion beam. The ion beam propagates along an ion beam axis. In a collimated ion beam, the dopant ions move parallel to the ion beam axis. In a diverging ion beam, the ion beam axis is the ion beam's axis of symmetry.

[0041] The dopant ions can be implanted at different implantation angles. The respective implantation angle is the angle between the ion beam axis and the target axis.

[0042] For example, the substrate tilt mechanism can tilt the substrate at various angles about a horizontal rotation axis parallel to the first main substrate surface. Alternatively, the ion beam projection device can deflect the ion beam axis at various deflection angles in the plane of incidence. Alternatively, the substrate rotation mechanism can rotate the substrate at various twist angles.

[0043] The implantation angle can change continuously during the ion implantation process. Alternatively, the implantation angle can change in discrete steps.

[0044] The implantation angles can lie within an implantation angle range. The implantation angle range can be symmetrical with respect to the target axis. Alternatively, the implantation angle range can be slightly asymmetrical with respect to the target axis. For example, a first partial range of the implantation angle on a first side of the target axis can cover 40% to 50% of the entire implantation angle range.

[0045] Each crystal channel direction can have a specific channel acceptance width. The channel acceptance width (or channeling probability distribution) is a measure of the angle dependence of the channeling efficiency. The angle-dependent channeling efficiency can be symmetric with respect to the crystal channel direction and can exhibit a global maximum at the respective crystal channel direction. The channel acceptance width can be defined by the FWHM (full-width-half-maximum) value. Typically, the angle-dependent channeling efficiency can be approximated by a Gaussian angular distribution. The channel acceptance width can, for example, be a function of an ion type, an ion energy, and an ion dose.

[0046] The implantation angle range can be greater than 80%, e.g., greater than 90%, or greater than 100%, of the sum of the channel acceptance width of the preselected crystal channel direction and twice the angular tolerance interval. Furthermore, the implantation angle range can be less than 500%, e.g., less than 400%, or less than 250%, of the sum of the channel acceptance width of the preselected crystal channel direction and twice the angular tolerance interval. The implantation angle range can be less than five times, e.g., less than four times, or less than 2.5 times, the sum of the channel acceptance width of the preselected crystal channel direction and twice the angular tolerance interval. If these preconditions are met, a lattice-guiding effect, or channeling, can be effective for the same or approximately the same amount of ion dopants, regardless of the actual angular misalignment between the target axis and the preselected crystal channel direction.For a given channeling acceptance width, for example, the implantation angle can be selected as small as possible to achieve a high channeling fraction with sufficient process stability.

[0047] An implantation pass may include a complete pass through the implantation angle range. For example, the implantation pass may include tilting the substrate about a horizontal rotation axis parallel to the first substrate main surface by the implantation angle range. According to another example, the implantation pass may include twisting the substrate about a vertical rotation axis by a rotation angle range. The rotation angle range may be derived from the implantation angle range and depend on characteristics of the preselected crystal channel direction.

[0048] The step of implanting the dopant ions into the substrate may include one or more implantation passes along a single rotation axis. For example, implanting the dopant ions may include one or more implantation passes orthogonal to a first horizontal rotation axis of a substrate tilt mechanism. Alternatively, implanting the dopant ions may include one or more rotation passes ("twists") about a vertical rotation axis.

[0049] Alternatively, implanting the dopant ions may include successive implantation passes along two or more rotation axes. For example, implanting the dopant ions may include at least one implantation pass orthogonal to a first horizontal rotation axis of a substrate tilt mechanism and at least one implantation pass orthogonal to a second horizontal rotation axis of the substrate tilt mechanism, where the second horizontal axis may be perpendicular to the first horizontal axis. Alternatively, implanting the dopant ions may include at least one implantation pass orthogonal to a horizontal rotation axis of a substrate tilt mechanism and at least one rotation pass about a vertical rotation axis.

[0050] In this way, the amount of tunneling dopant ions can be largely decoupled from the exact value of the angular misalignment between the crystal channel direction and the target axis. As a consequence, the distance between the tip at the end of the range of the tunneling dopant ions (the "channeling tip") and the first main substrate surface is the same or approximately the same, regardless of the actual angular misalignment between the target axis and the preselected channel crystal direction. Furthermore, the maximum dopant concentration at the channeling tip can be largely independent of the actual angular misalignment between the target axis and the preselected crystal channel direction.

[0051] The method can facilitate the practical and productive use of tunneling dopant ions for a wide variety of applications using substrates with typical angular deviations for off-axis cutting and / or using ion beam implanters with a substrate tilt mechanism with typical orientation accuracy.

[0052] Tunneling dopant ions can facilitate the formation of dopant regions with local dopant maxima at a comparatively large vertical distance from a substrate main surface and / or can contribute to a reduction in the maximum implantation energy. Ion implantation at lower implantation energies can reduce negative side effects such as damage to existing structures and damage to the semiconductor crystal lattice, and / or can enable the use of thinner implantation masks.

[0053] Furthermore, the non-tunneling dopant ions are distributed in the substrate between the first main substrate surface and the channeling tip. The distribution of the non-tunneling dopant ions can be tuned for each partial implantation using process parameters such as the implantation angle range, the distribution of implantation angles within the implantation angle range, implantation energy, implantation temperature, and / or implantation dose. For example, the process parameters can be selected such that the distribution of non-tunneling dopant ions includes another peak at the end of the range ("primary peak") between the main substrate surface and the channeling tip.

[0054] The primary peak and the channeling peak can be defined such that the vertical dopant concentration profile of the implanted dopant ions approximates a desired profile, e.g., a broad, plateau-like dopant profile with a less pronounced minimum or a dopant profile with two pronounced peaks. In this way, the method can enable the formation of an enormous variety of vertical dopant profiles with a single implantation process. In particular, the ratio between the dopant concentrations at the channeling peak and at the primary peak can be adjusted by selecting a suitable angular magnitude for the implantation angle range and / or by selecting suitable implantation angles, i.e., a suitable distribution of implantation angles, within the implantation angle range.

[0055] According to one embodiment, the implantation angle can continuously sweep through the implantation angle range at least once during an implantation of the dopant ions. In this context, "continuously" can mean that two directly consecutive angles can differ by at most 1° (or at most 0.1°) and / or by at most 10% (or at most 1%) from at least one of the consecutive angles. During a single implantation process about a rotation axis, for example, the implantation beam can sweep across the entire implantation angle range once, twice, or more often. During each angular sweep, the implantation beam can impinge on the same or approximately the same sub-region of the first substrate main surface. For example, the first substrate main surface can lie entirely within the implantation beam cone.The implantation beam cone can consist of a wide single beam or a fast, 2D-scanned spot beam. Fast 2D scanning can, for example, be electrostatic or magnetic scanning in the X and Y directions at frequencies in the range of a few Hz or a few kHz, respectively.

[0056] During each sweep, the average dopant ion current in the ion beam can be constant or nearly constant. The ratio between the dopant concentrations at the channeling tip and the primary tip can be adjusted by adjusting the angular velocity of the angular sweep. Varying the angular velocity as a function of the implantation angle can enable further variations of the vertical dopant profile without changing the dopant ion current in the ion beam.

[0057] The continuous sweep can be accomplished by a continuous rotation about a horizontal rotation axis of a substrate tilting mechanism, by a continuous reduction or increase of a deflection of the ion beam axis in a beam plane of an ion beam projection device with a controllable ion beam axis, or by a continuous rotation about the vertical rotation axis of a substrate rotation mechanism.

[0058] According to another embodiment, implanting the dopant ions may include nmax implant sub-processes at nmax different implantation angles between the ion beam axis and the target axis. Nmax may be at least 2, for example, at least 7, at least 15, or at least 16. Each implantation sub-process may be effective for a constant implantation angle. The method may be performed on ion beam implantation devices that provide the functionality to change the implantation angle between successive ion implantation sub-processes ("shots"). The ion implantation sub-processes may follow one another directly without intermediate calibration and / or tuning processes.Alternatively, a retuning and / or recalibration process may be performed once between at least two consecutive ion implantation sub-processes, between some of the ion implantation sub-processes, or between each pair of consecutive ion implantation sub-processes.

[0059] The different implantation angles can be achieved by stepping the tilt angle around a horizontal rotation axis of a substrate tilt mechanism, by stepping the deflection angle of the ion beam axis in an ion beam projection device with a controllable ion beam axis, or by stepping the rotation around the vertical rotation axis of a substrate rotation mechanism. For a rotation sweep, the range of the rotation sweep around the vertical rotation axis can be a function of the implantation angle range and can depend on the preselected crystal channel direction and / or the substrate material.

[0060] For each implantation sub-process, the total dopant ion current in the ion beam can be constant or approximately constant. In other words, each implantation sub-process can implant approximately the same amount of dopant ions, i.e., the same dopant ion dose. If the ion beam implantation equipment allows nmax implantation sub-processes within the same recipe and without further tuning and / or calibration of the ion beam, it is possible that splitting the implantation process into nmax implantation sub-processes may have no or only a marginal impact on the overall process time.

[0061] Alternatively, at least one implantation sub-process may implant an amount of dopant ions that differs from the amount of dopant ions implanted by at least one of the other implantation sub-processes.

[0062] For each implantation sub-process, the acceleration voltage used to accelerate the dopant ions can be identical or nearly identical. Alternatively, at least one implantation sub-process can use an acceleration voltage that differs from the acceleration voltage used in at least one of the other implantation sub-processes.

[0063] According to one embodiment, the nmax implantation angles of a multi-stage implantation process comprising a plurality of implantation sub-processes can be equally spaced. In other words, each implantation angle can have the same angular distance from its neighboring angular distance. In this way, it is possible for the position of the channeling tip and the dopant concentration at the channeling tip to be highly independent of the actual remaining misalignment angle between the target axis and the preselected crystal channel direction. According to other embodiments, the angular distance between neighboring implantation angles can be a function of the distance of the respective implantation angles from the angular center of the implantation angle range. For example, the angular distance between neighboring implantation angles can decrease or increase monotonically or strictly monotonically.Other distributions of implantation angles may also be possible. For example, the nmax implantation angles can result from equiangular distances (rotation angles) between adjacent implantation positions of a substrate rotation mechanism.

[0064] According to one embodiment, the nmax implantation sub-processes may include pairs of implantation sub-processes, wherein the implantation angles of each pair of implantation sub-processes are symmetrical with respect to an angular center of the implantation angle range. In this way, it may be possible for the resulting doping profiles to be highly independent of the angular direction of an angular deviation of the off-axis cut and / or the angular direction of a tilt error angle of a substrate tilt mechanism.

[0065] According to one embodiment, at least one of the implantation angles can be 0 degrees or deviate from 0 degrees by a maximum of 0.3 degrees. In other words, an implantation sub-process can be performed with the ion beam axis parallel to the target axis, i.e., along the idle ion beam axis. The target axis is as close as possible to the selected channel direction.

[0066] For example, in the case of a silicon carbide substrate with an off-axis cut of 4 degrees, with an implantation angle of 0 degrees between the target axis and the ion beam axis, the ion beam axis can have a tilt angle of about 4 degrees against the surface normal, provided that the <0001> -Grid direction is the selected channel direction. If the <11-23> lattice direction is the selected channel direction, the ion beam axis can have a tilt angle of 21 degrees or 13 degrees relative to the surface normal for an implantation angle of 0 degrees.

[0067] In the case of a single-crystalline silicon substrate with (001) lattice planes parallel to the main surfaces, at an implantation angle of 0 degrees between the target axis and the ion beam axis, the ion beam axis is almost perpendicular to the first surface if the <001> -Grid direction is the selected channel direction.

[0068] According to one embodiment, adjacent implantation angles may differ by a maximum of 0.5 degrees, for example, by a maximum of 0.2 degrees or by a maximum of 0.1 degrees. Starting from a first limit angle of the implantation angle range, the implantation angles of the implantation sub-processes may, for example, change in regular angular increments of 0.5 degrees until the second limit angle of the implantation angle range is reached. According to another example, the angular increment may be 0.2 degrees or 0.1 degrees.

[0069] For a rotational pass around a vertical rotation axis, the angular spacing between adjacent implantation positions may depend on the overall range of the rotational pass, which in turn may depend on the selected crystal channel direction. For example, the average angular spacing between adjacent implantation positions may range from 3% to 10% of the range of a rotational pass. According to another example, the angular spacing between adjacent implantation positions may range from 0.1 degree to 1 degree, e.g., 0.1 degree to 0.5 degree.

[0070] For example, in a combination of fifteen implantation sub-processes, it is possible to highly decouple the position of the channeling tip and the dopant concentration at the channeling tip from the actual angular misalignment between the target axis and the preselected crystal channel direction for a channel acceptance width of approximately 0.6 degrees or less. A channel acceptance width of approximately 0.6 degrees, for example, may be a reasonable approximation for the c-axis of a hexagonal silicon carbide lattice.

[0071] According to one embodiment, the implantation angle range is at most 6 degrees, for example, at most 5 degrees or at most 4 degrees. According to other examples, the implantation angle range may be at most 3 degrees, 2 degrees, 1 degree, or 0.2 degrees. For example, the implantation angle range may be the channel acceptance width increased by 0.8 degrees. The 0.8 degrees may represent a typical upper limit for the sum of the angle tolerance windows for the substrate tilt mechanism and the off-axis cut. A comparatively small—but sufficiently large—implantation angle range can sufficiently define the dopant concentration around the channeling tip with little additional effort.

[0072] According to one embodiment, an angular deviation between a lateral target direction and a lateral main crystal direction in the substrate can be determined prior to implantation.

[0073] The ion beam axes and the target axis define an implantation angle plane. The lateral target direction can have any—but predefined—orientation with respect to the implantation angle plane. For example, the implantation angle plane can be orthogonal or parallel to the lateral target direction. For substrates with a hexagonal crystal lattice and an off-axis cut, the lateral principal crystal direction can depend on the direction of the off-axis cut. For example, the lateral principal crystal direction can be a <11-20> lattice direction or a <1-100> lattice direction.

[0074] The angular deviation can be determined using a measuring unit, for example, optical means that detect the orientation of ribs on the first substrate main surface. The ribs can result from the off-axis cut and can, for example, extend orthogonally or parallel to the lateral main crystal direction. Alternatively, data indicating the angular deviation with respect to a notch or with respect to a flat on the outer perimeter of the substrate can be received and analyzed.

[0075] Furthermore, before implanting the dopant ions, the lateral main crystal axis can be aligned with the lateral target direction. The alignment process can include a rotational movement of the substrate ("twisting"). The remaining rotational misalignment between the lateral target direction and the lateral main crystal axis can be at most 0.5 degrees, e.g., at most 0.2 degrees, or at most 0.1 degrees.

[0076] As a consequence, the implantation angle plane can have a predefined orientation with respect to the crystal lattice for the entire implantation process. The implantation conditions for different substrates of the same type can be closely aligned. The additional alignment process can improve the reproducibility of the implantation results across a variety of substrates of the same type. The rotational alignment can follow or precede a beam tilt alignment using a substrate tilt mechanism and / or an ion beam projection device with a controllable ion beam axis as described above.

[0077] Rotational alignment can replace a rotational pass. Alternatively, rotational alignment can be combined with a rotational pass. For example, the angular position achieved by rotational alignment can be used as the angular center of at least one rotational pass. The pass area can be symmetrical or asymmetrical with respect to the angular center.

[0078] For example, with the angular center at 0 degrees for a rotational pass around a vertical rotational axis, the total range of a rotational pass for the implantation positions can be, for example, in a range from -14 degrees to +14 degrees, from -4.9 degrees to +4.9 degrees, from -2.1 degrees to +2.1 degrees, from -1.4 degrees to +1.4 degrees or from -0.7 degrees to +0.7 degrees.

[0079] According to a further embodiment, a semiconductor device may include a semiconductor body having a first surface and having a doped region.

[0080] The semiconductor device may be a power semiconductor device, e.g., a power semiconductor switch or a power semiconductor diode. The semiconductor body may contain a semiconductor material. The semiconductor material may contain silicon carbide, e.g., silicon carbide with a hexagonal crystal lattice. A second surface of the semiconductor body may be parallel or at least approximately parallel to the first main surface. The first and second main surfaces may extend along lateral directions and may have the same shape and size.

[0081] The doped region may include a first local dopant concentration maximum at a first distance from the first surface, a second local dopant concentration maximum at a second distance from the first surface, and a local dopant concentration minimum between the first distance and the second distance. The first distance may be greater than the second distance.

[0082] One of the first and second local dopant concentration maxima may be the global local dopant concentration maximum. Alternatively, none of the first and second local dopant concentration maxima is the global local dopant concentration maximum.

[0083] A difference between the first distance and the second distance may be in a range from 200 nm to 1500 nm, e.g., from 300 nm to 1000 nm. According to one embodiment, the difference between the first distance and the second distance may be in a range from 400 nm to 550 nm. A ratio between the first local dopant concentration maximum and the second local dopant concentration maximum may be in a range from 0.5 to 2. According to one embodiment, the ratio between the first local dopant concentration maximum and the second local dopant concentration maximum may be in a range from 0.9 to 1.1. A ratio between the sum of the first local dopant concentration maximum and the second local dopant concentration maximum on the one hand and the local dopant concentration minimum on the other hand may be in a range from 2 to 10.According to one embodiment, the ratio between the sum of the first local dopant concentration maximum and the second local dopant concentration maximum on the one hand and the local dopant concentration minimum on the other hand may be in a range of 5 to 7.

[0084] A vertical dopant concentration profile reflects the dopant distribution along a vertical direction orthogonal to the first surface. The vertical dopant concentration profile with the above-mentioned characteristics can sufficiently approximate box-shaped vertical dopant profiles for some applications and can be formed with comparatively little effort. To further smooth the resulting dopant profile, the implantation energy and / or the implantation dose can be varied for implantations at different angles.

[0085] According to one embodiment, a vertical dopant concentration profile of the doped region may include a first falling edge and a second falling edge. The first falling edge may lie between the second local dopant concentration maximum and the local dopant concentration minimum. The second falling edge may lie between the first local dopant concentration maximum and a second surface of the semiconductor body. The second falling edge may be steeper than the first falling edge.

[0086] The second surface may be opposite the first surface. The vertical dopant concentration profile with double peaks and a steeper slope at the deeper peak at the end of the range can be effectively formed using tunneling dopant ions. The tunneling dopant ions can enable a doped region with a lower edge at a comparatively large distance from the first surface.

[0087] According to one embodiment, forming the doped region may include implanting dopant ions into the semiconductor body using an ion beam implantation method as described above. The doped region may be formed efficiently using a comparatively small number of implantation steps.

[0088] According to one embodiment, the semiconductor device may include a gate structure. The gate structure may extend from the first surface into the semiconductor body. The gate structure may be in contact with the doped region. The doped region may form at least part of a source region, a body region, or a current spreading region of a transistor cell of a power semiconductor switch or an MCD (MOS-controlled diode). A source region, a body region, and / or a current spreading region containing the above-mentioned characteristics of the doped region may improve device characteristics of the semiconductor device with comparatively little additional effort and / or may contribute to a simplification of the manufacturing process, e.g., by reducing the number of implantation steps and / or by reducing the maximum acceleration energy.

[0089] According to one embodiment, the semiconductor device may include a body region in contact with the doped region and in contact with the gate structure. The doped region and the body region may form a pn junction. The doped region may be formed between the first surface and the body region. For example, the doped region may form a source region of a vertical transistor cell with a vertical load current flowing through the body region.

[0090] In a source region of a vertical transistor cell, a vertical dopant concentration profile containing at least two peaks as described above may enable adjustment of an overall bulk resistance of the source region with only minor adverse side effects on the ohmic contact resistance between a source metallization and the source region and on the characteristics of the pn junction between the source region and the body region.

[0091] The bulk resistance can be adjusted to provide a voltage drop during a short-circuit condition. This voltage drop allows for counteracting current filaments and can reduce the effective gate overvoltage. When adjusting the bulk resistance of the source region, a trade-off can also be considered, for example, between i) counteracting current filaments and / or reducing the effective gate overvoltage during a short-circuit current load by increasing the bulk resistance of the source region and ii) reducing the on-resistance of the device by decreasing the bulk resistance of the source region.

[0092] According to one embodiment, the semiconductor device may include a source region in contact with the doped region and in contact with the gate structure. The doped region and the source region may form a pn junction. The source region may be formed between the first surface and the doped region. For example, the doped region may form a body region of a vertical transistor cell.

[0093] The semiconductor material may contain silicon carbide, for example, and the dopant ions may contain aluminum ions. Due to the channeling effect, the acceleration energy for a given vertical extension of the body region can be comparatively low. The lower acceleration energy can reduce the defect density in the body region after ion beam implantation and / or can reduce ripple in the vertical dopant concentration profile. The channeling region of the vertical dopant concentration profile can increase the conductivity at the drain side of the body region without affecting the threshold voltage. In SiC IGBTs, a higher transverse conductivity at the drain end of the body region can improve latch-up robustness. Furthermore, the adverse effect of drain-induced barrier lowering can be reduced by such doping profiles.According to another example, the semiconductor material may comprise single-crystal silicon and the dopant ions may comprise boron ions.

[0094] According to one embodiment, the semiconductor device may include a body region in contact with the doped region and in contact with the gate structure. The doped region and the body region may form a pn junction. The body region may be formed between the first surface and the doped region. For example, the doped region may form a current spreading region of a vertical transistor cell. Due to the channeling effect used to define the first dopant concentration maximum, the current spreading region may extend relatively deep into the semiconductor body.

[0095] A current spreading region with a channeling peak as the local dopant concentration maximum with the greatest distance from the first surface and with a steeply sloping edge toward a lightly doped drift zone can combine high lateral conductivity with a small vertical extension of the highly conductive thin-film region. In other words, the current spreading region can effectively spread the forward current laterally with comparatively little adverse impact on the blocking capability and / or on-resistance.

[0096] According to one embodiment, the vertical dopant concentration profile of the doped region may include at least one further local dopant concentration maximum between the first surface and the second surface. Further local dopant concentration maxima may result from further ion beam implantation processes. The further ion beam implantation processes may exclusively include ion beam implantation without tunneling dopant ions. Alternatively, the further ion beam implantation processes may include at least one further ion beam implantation process that utilizes varying implantation angles around a target axis and utilizes tunneling dopant ions, as described above.

[0097] The additional local dopant concentration maxima can contribute to improving the flatness of the vertical dopant concentration profile of the doped region. For example, the additional local dopant concentration maxima can improve the flatness of the vertical dopant concentration profile of a body region and / or a current spreading region.

[0098] According to a further embodiment, a semiconductor device may include a semiconductor body having a first surface and a doped region. The doped region may include a first local dopant concentration maximum at a first distance from the first surface, a second local dopant concentration maximum at a second distance from the first surface, and a local dopant concentration minimum between the first distance and the second distance. The semiconductor body may include silicon carbide. Starting from the first distance, a dopant concentration in the doped region may decrease by 10% of the first local dopant concentration maximum with increasing distance from the first surface within a maximum of 2 µm, e.g., a maximum of 1.8 µm.

[0099] According to one embodiment, the semiconductor device may include a gate structure, wherein the gate structure may extend from the first surface into the semiconductor body. The doped region may be in contact with the gate structure. A body region may be in contact with the doped region and with the gate structure. A source region may be in contact with the body region and the gate structure. The body region may separate the source region and the doped region. A vertical dopant concentration profile of the doped region may include at least one further local dopant concentration maximum between the first surface and the second distance and at least one further local dopant concentration maximum between the second distance and the first distance.

[0100] Embodiments of the ion beam implantation method described herein may be used for a method of manufacturing embodiments of the semiconductor device as described herein. In at least some embodiments of the semiconductor device manufacturing method and / or the semiconductor device, the following features apply (if applicable), alone or in combination: (i) The doped region may form a shielding region for a gate structure of a vertical transistor cell, wherein the shielding region has the conductivity type of the body region, wherein a portion of the shielding region may be formed between the gate structure and the second surface of the semiconductor body, wherein a channeling tip may be located between a bottom of the gate structure and the second surface, wherein the shielding region and a source metallization may form a low-resistance ohmic contact, and wherein the semiconductor device may be a power semiconductor switch. The tunneling dopant ions may enable a larger vertical extension of the shielding region and / or improved shielding efficiency with little additional effort. (ii) The doped region may form at least a portion of a junction termination region, wherein the junction termination region may be p-doped, wherein the junction termination region may be formed in an edge region of the semiconductor body, wherein the edge region may laterally surround a central region containing functional transistor cells or a main pn junction of a power semiconductor diode, wherein the junction termination region may surround the central region, and wherein the semiconductor device may be a power semiconductor diode or a power semiconductor switch. The tunneling dopant ions may enable a larger vertical extent and / or a higher efficiency of the junction termination region with little additional effort. (iii) The doped region may form a field ring, wherein the field ring may be p-doped, wherein the field ring may be formed in an edge region of the semiconductor body, wherein the edge region may laterally surround a central region containing functional transistor cells or a main pn junction of a power semiconductor diode, wherein the field ring may surround the central region, and wherein the semiconductor device may be a power semiconductor diode or a power semiconductor switch. The tunneling dopant ions may enable a larger vertical extension and / or a higher efficiency of the field ring with little additional effort. (iv) The doped region may further form a channel stop zone, wherein the channel stop zone may be n-doped, wherein the channel stop zone may be formed in an edge region of the semiconductor body, wherein the edge region may laterally surround a central region containing functional transistor cells or a main pn junction of a power semiconductor diode, wherein the channel stop zone may surround the central region, wherein the channel stop zone may be in contact with the lateral outer surface of the semiconductor body, and wherein the semiconductor device may be a power semiconductor diode or a power semiconductor switch. The tunneling dopant ions may enable a larger vertical extension and / or a higher efficiency of the channel stop zone with little additional effort. (v) The ion beam implantation process may form a field stop or buffer zone, wherein the field stop or buffer zone may have the conductivity type of the source region of a transistor cell, wherein the field stop or buffer zone may be formed between a voltage-holding layer and a highly doped contact layer, wherein the voltage-holding layer may comprise a lightly doped drift zone of the conductivity type of the source region and / or a compensation structure, e.g.a superjunction structure, wherein the contact layer and a rear-side metallization form a low-resistance ohmic contact, wherein the rear-side metallization can be in contact with the second surface of the semiconductor body, wherein a dopant concentration in the field stop or buffer zone can decrease continuously with increasing distance from the second surface, and wherein the semiconductor device can be a power semiconductor diode or a power semiconductor switch. The dopant ions can be implanted through the second surface. The dopant ions can contain protons. If the semiconductor material contains SiC, the dopant ions can contain phosphorus ions and / or nitrogen ions. The tunneling dopant ions can enable a larger vertical extension of the field stop or buffer zone with little additional effort.

[0101] For the realization of the drift zone of the buffer / field stop zone using epitaxial techniques, the epitaxial process can be interrupted after reaching a well-defined thickness to implant the buffer layer by the process described above, thereby implementing the implantation into the surface defined by the epitaxial deposition; thereafter, the epitaxial deposition of the drift zone is performed.

[0102] (vi) The ion beam implantation method can form an emitter layer in the semiconductor body, wherein the emitter layer can have the conductivity type of the body region, wherein the emitter layer and a backside metallization form a low-resistance ohmic contact, wherein the backside metallization can be in contact with the second surface of the semiconductor body, wherein the emitter layer is formed between the backside metallization and a field stop zone, and wherein the semiconductor device can be an IGBT, e.g., a reverse-blocking IGBT. The dopant ions can be implanted through the second surface. The dopant ions can contain protons for creating a field stop zone. If the semiconductor material contains SiC, the dopant ions can contain phosphorus ions and / or nitrogen ions for creating the buffer layer / field stop zone.The tunneling dopant ions can, with little additional effort, enable a comparatively small distance between the emitter layer and a dopant concentration maximum, e.g., a proton density maximum, in the field-stop zone. Reducing the distance between the emitter layer and the dopant concentration maximum in the field-stop zone can contribute to improved short-circuit robustness and / or a reduction in leakage current.

[0103] (vii) The ion beam implantation process can form a doped column or a region of a doped column of a superjunction structure, wherein the superjunction structure can be formed in a voltage-holding layer of the semiconductor body, and wherein the semiconductor device can be a power semiconductor switch or a power semiconductor diode. The tunneling dopant ions can contribute to an increase in the vertical extent of the superjunction structure with comparatively little additional effort. In a multi-epitaxy / multi-implantation process, the utilization of tunneling dopant ions can contribute to a reduction in the total number of epitaxial sublayers.

[0104] (viii) A method for manufacturing semiconductor devices may comprise forming a scattering layer on the first main substrate surface of a semiconductor substrate, patterning the scattering layer, and implanting dopant ions through the patterned scattering layer using an ion beam implantation method with varying implantation angles around a target axis and utilizing tunneling dopant ions as described above. The patterned scattering layer may comprise a main region having a first thickness and at least one further region wherein the scattering layer is absent or wherein the scattering layer has a thickness that deviates significantly from the first thickness. The patterned scattering layer may enable the formation of laterally varying dopant profiles with little additional effort.

[0105] Fig. 1A-1F relate to the alignment of a substrate 700 and the implantation of dopant ions into the substrate 700 at various implantation angles. The substrate 700 may contain silicon carbide of a hexagonal polytype. A preselected crystal channel direction 707 for tunneling dopant ions may be the c-axis.

[0106] Fig. 1A shows the substrate 700 with a first substrate main surface 701 on a front side, a second substrate main surface 702 on a back side, and a lateral outer surface 703 connecting the edges of the two substrate main surfaces 701, 702. In the illustrated embodiment, the preselected crystal channel direction 707 for channeling is the c-axis, which is inclined by an off-axis cut angle α to the normal 704 to the first substrate main surface 701. The off-axis cut angle α may, for example, be in a range of 3 degrees to 5 degrees, e.g., about 4 degrees. According to another (not illustrated) embodiment, the preselected crystal channel direction may be the <11-23> lattice direction.

[0107] The substrate 700 is placed on a substrate holder of an ion beam implantation device. The ion beam implantation device is suitable for ion implantation at different implantation angles, wherein the ion beam changes the implantation angle in an implantation angle plane that is orthogonal to the first substrate main surface 701. The ion beam has a default or standard direction (idle ion beam axis). For ion beam implantation at changing implantation angles, a deflection unit of the ion beam implantation device deflects the ion beam with respect to the standard orientation. The deflection is effective in an implantation angle plane. In other words, for each implantation angle, the ion beam axis and the target axis span the same plane.

[0108] Before ion implantation, the substrate 700 can be aligned to the implantation angle plane and to the idle ion beam axis. Alignment to the implantation angle plane involves a rotational movement ("twisting"). Alignment to the idle ion beam axis involves tilting the substrate 700. Alignment by beam tilt can precede or follow the rotational alignment.

[0109] Fig. 1B shows a top view of the substrate 700. The substrate 700 has a nearly circular horizontal cross-section with a flat 903 forming a portion of the outer lateral surface 703. The flat 903 roughly indicates the orientation of a principal crystal plane parallel to the c-axis, e.g., the (1-100) crystal plane or the (11-20) crystal plane. Alternatively, the substrate 700 may include a notch in the outer lateral surface, wherein the notch roughly indicates a principal crystal direction. For example, an angular deviation φ between the flat 903 and the specified principal crystal plane may range from -3 degrees to +3 degrees.

[0110] The rotational alignment brings the specified main crystal plane into closer alignment with the implantation angle plane. In other words, the rotational alignment brings a lateral main crystal direction 708 in the corresponding main crystal plane into closer alignment with a lateral target direction 709 in the implantation angle plane.

[0111] For example, the rotational alignment may utilize an image recognition system that analyzes the orientation of ribs 905 resulting from the off-axis cut on the first substrate main surface 701. Alternatively or additionally, the rotational alignment may utilize data that can individually indicate the angular deviation between the orientation of the flat 903 and the specified main crystal plane for each individual substrate 700.

[0112] Imperfections in the rotational alignment may result in a residual rotational misalignment ψ between the lateral main crystal direction 708 and the lateral target direction 709. The residual rotational misalignment ψ may range from -0.2 degrees to +0.2 degrees.

[0113] Fig. 1C-1F relate to alignment by beam tilt. In the ion beam implantation device, the substrate 700 is oriented so that the preselected crystal channel direction 707 is aligned as closely as possible with the target axis 706. The target axis 706 can be the standard ion beam axis along which the dopant ions propagate in an idle mode, providing ion implantation at a constant implantation angle. The dopant ions are implanted after rotational alignment and beam tilt alignment.

[0114] Fig. 1C shows the sweep of the ion beam axis 801 between a minimum value 8011 and a maximum value 801 nmax in the case where the preselected crystal channel direction 707 is perfectly aligned with the target axis 706. The remaining angular misalignment Δθ is 0 degrees, and the preselected crystal channel direction 707 lies in the angular center of the implantation angle range Rw.

[0115] For example, implantation may begin at an implantation angle closest to the channeling direction and progress to implantation angles with greater angular separation from the channeling direction. In this way, it may be possible to avoid or minimize any potential adverse influence of previous implantations on the channel acceptance width. According to an embodiment with a symmetrical implantation angle range and with an odd number nmax, implantation may begin with an implantation angle corresponding to the idle beam axis for (nmax+1) / 2 and progress alternately to the two limit values: (nmax+1) / 2, (nmax+1) / 2 + 1, (nmax+1) / 2 - 1, (nmax+1) / 2 + 2, (nmax+1) / 2 - 2, ..., nmax, 1.

[0116] Due to technical imperfections in both the angle of the off-axis cut and the mechanism that orients the substrate 700 to the target axis 706, at the end of beam tilt alignment, the preselected crystal channel direction 707 is typically not perfectly aligned with the target axis 706.

[0117] Fig. Figure 1D shows the substrate 700 at the end of a beam tilt alignment with a remaining angular misalignment Δθ of about 2 degrees between the aiming axis 706 and the preselected crystal channel direction 707.

[0118] As in Fig. 1E, even with a remaining angular misalignment Δθ of about 2 degrees, the preselected crystal channel direction 707 can still be within the implantation angle range Rw. Provided that half the channel acceptance width is smaller than the angular separation between the preselected crystal channel direction 707 and the closer one of the critical angles of the implantation angle range Rw, the same (or approximately the same) amount of ion dopants will be delivered through the channel as for the Fig. Implanted in the case illustrated in Figure 1C.

[0119] Fig. 1F schematically shows a substrate 100 placed in an ion beam implantation device. The substrate 100 may be fixed to a substrate holder 750, e.g., by means of electrostatic force and / or by means of negative pressure. The substrate holder 750 may be adapted to perform a rotational movement about a first horizontal rotation axis 610. The substrate holder 750 may or may not be configured to perform a rotational movement about a second horizontal rotation axis 620. The second horizontal rotation axis 620 and the first horizontal rotation axis 610 may be perpendicular to each other. The first and second horizontal axes 610, 620 may lie in the same horizontal plane or may be vertically spaced. Additionally or alternatively, the substrate holder 750 may be adapted to perform a rotational movement (twisting) about a vertical rotation axis 630.The vertical axis of rotation 630 may pass through the lateral center of the substrate 100.

[0120] The ion beam implantation device may include an ion beam projection device 740 adapted to variably deflect an ion beam axis 801 at different angles within a first incident beam plane parallel to the first horizontal rotation axis 610. The ion beam projection device 740 may or may not be adapted to deflect the ion beam axis 801 at different angles within a second incident beam plane parallel to the second horizontal rotation axis 620.

[0121] Fig. 2A-2B show vertical dopant concentration profiles (hereinafter: vertical dopant profiles) that can be obtained in a silicon carbide substrate with a horizontal crystal lattice by applying the ion beam implantation method as described with reference to Fig. 1A-1F. The vertical dopant profiles may correspond to regions of vertical dopant profiles of doped regions in the semiconductor body of a semiconductor device.

[0122] Fig. Figure 2A shows the vertical dopant profiles of dopant ions, e.g., nitrogen ions, implanted with an ion beam at an acceleration energy of 2.5 MeV and an implantation angle sweep from -7 degrees to +7 degrees in 1-degree steps symmetrically around the standard ion beam direction. The preselected crystal channel direction is the c-axis of a 4H-SiC substrate. Line 401 represents the vertical dopant profile for an implantation with the c-axis perfectly aligned with the target axis. Line 402 illustrates the resulting dopant profile if the remaining angular misalignment Δθ between the target axis and the c-axis is 0.5 degrees. Line 403 illustrates the resulting dopant profile if the remaining angular misalignment Δθ between the target axis and the c-axis is 1 degree.Reference numeral 404 represents the end-of-range peak of the randomly implanted dopant ions (primary peak). Reference numeral 405 indicates the end-of-range peak for the tunneling dopant ions (channeling peak).

[0123] Position and maximum dopant concentration Nch of the channeling tip 405 show no or only a small dependence on the remaining angular misalignment Δθ.

[0124] Furthermore, the angular misalignment Δθ has only a minor impact on the rest of the dopant ion distribution. Consequently, the process can enable highly predictable and highly reproducible vertical dopant profiles for tunneling dopant ions, while simultaneously allowing alignment imperfections within the typical range for ion beam implantation devices and for typical off-axis cut tolerances.

[0125] To predict the vertical dopant profile, it is sufficient to know that the remaining angular misalignment between the target axis and the preselected crystal channel direction lies within a certain range. Knowledge of the exact remaining angular distribution between the target axis and the selected crystal channel direction is not necessarily required to predict the vertical dopant profile with sufficient reliability.

[0126] At the channeling tip 405, the vertical dopant profiles have a first local dopant concentration maximum Nch at a first distance dch from a first surface on a front side of a semiconductor body or from a first substrate main surface on the front side of a semiconductor substrate. At the primary tip 404, the vertical dopant profiles have a second local dopant concentration maximum Npr at a second distance dpr. Between the first distance dch and the second distance dpr, the vertical dopant profiles have a local dopant concentration minimum Nmin. The first distance dch is greater than the second distance dpr.

[0127] A difference between the first distance dch and the second distance dpr may be in a range from 400 nm to 550 nm. A ratio between the first local dopant concentration maximum Nch and the second local dopant concentration maximum Npr may be in a range from 0.9 to 1.1. A ratio between the sum of the first local dopant concentration maximum Nch and the second local dopant concentration maximum Npr on the one hand and the local dopant concentration minimum Nmin on the other hand may be in a range from 5 to 7.

[0128] Fig. 2B, an implantation angle sweep ranges from -0.7 degrees to +0.7 degrees in steps of 0.1 degrees. The influence of angular misalignment on the position and maximum dopant concentration in the channeling tip 405 is still small. The primary tip 404 is significantly lower than in the example of Fig. 2A. But both the channeling tip 405 and the primary tip 404 are to a large extent independent of the remaining angular misalignment between the target axis and the preselected crystal channel direction.

[0129] With knowledge of the accuracy of an angular alignment of the ion implantation device, the tolerance window for the angle α of an off-axis cut of the substrate and the width of the channel acceptance, the number of implantations and the implantation angle range can be selected to obtain a desired dopant distribution between two tips 404, 405 at the end of the reach.

[0130] The vertical dopant profiles of Fig. 2A and Fig. 2B benefit from the channeling effect. The implantation process therefore enables the formation of doped regions with a comparatively large vertical extent at comparatively low energy. Combined with the peak at the end of the range of the randomly implanted dopant ions, the process enables the approximation of plateau-like vertical dopant profiles, where the dopant concentration changes by a comparatively small amount over a comparatively large vertical range.

[0131] The diagrams of the Fig. 2C-2D illustrate further details regarding the vertical dopant profiles 401, 402, 403 of Fig. 2A. For simplicity, the ion beam divergence is assumed to be Gaussian and time-invariant. Likewise, the channel acceptance function 421 for tunneling of a specific dopant ion is approximated as a time-invariant Gaussian distribution. The channel acceptance function 421 can be obtained, for example, by simulation or using RBS (Rutherford backscattering spectrometry).

[0132] In Fig. In Figure 2C, the c-axis is exactly 4 degrees, and the first main substrate surface is tilted by exactly 4 degrees with respect to the standard ion beam axis. The channeling direction (e.g., the c-axis) is perfectly aligned with the idle beam axis. An inclined implantation comprises 15 individual shots, one of them at an implantation angle parallel to the channeling direction and the others symmetrical with respect to the channeling direction and equally spaced. The dotted line 422 represents the summed profile with an integrated dose of 1.5 × 10 13 cm -2 of 15 individual shots separated by 0.3 degrees. Each individual shot has an integrated dose of 1.0 × 10 12 cm -2The summed profile is constant from approximately -2 degrees to approximately +2 degrees. The summed profile is multiplied by the channel acceptance function 421 in angular space, yielding a function illustrated by the dashed line 423. The resulting hatched area 423 below the dashed line 423 corresponds to the integrated dose in the channeling tip.

[0133] In Fig. In 2D, the standard incident ion beam axis is misaligned by 1 degree to the channeling direction. In other words, the center of incidence of multiple shots is still at 0 degrees, but the c-axis is at 1 degree. The result of multiplying the summed profile (dotted line 422) by the channel acceptance function 421 in angular space and the resulting hatched area 424, which corresponds to the integrated dose in the channeling tip, are approximately the same as for Fig. 2C.

[0134] The Fig. The semiconductor device 500 shown in Figure 3 may be an IGBT (Insulated Gate Bipolar Transistor), an MCD (MOS Controlled Diode), or an IGFET (Insulated Gate Field Effect Transistor), for example, a MOSFET (Metal Oxide Semiconductor FET).

[0135] The semiconductor device 500 includes a semiconductor body 100, which may include a silicon carbide crystal with the main components silicon and carbon. The silicon carbide crystal may contain impurities such as hydrogen and oxygen and / or dopant atoms.

[0136] A first surface 101 on a front side of the semiconductor body 100 can be planar or ribbed. A surface normal 104 orthogonal to a planar first surface 101 or orthogonal to a mid-plane of a ribbed first surface 101 defines a vertical direction. Directions orthogonal to the surface normal 104 are horizontal and lateral directions. A second surface 102 on the back side of the semiconductor body can extend parallel to the first surface 101.

[0137] The semiconductor device 500 may include a transistor cell TC with a gate structure 150 extending from the first surface 101 into the semiconductor body 100. The gate structure 150 includes a gate dielectric 159 and a conductive gate electrode 155. The gate electrode 155 is electrically separated from the semiconductor body 100. For example, the gate dielectric 159 may completely separate the gate electrode 155 and the semiconductor body 100.

[0138] Furthermore, the transistor cell TC includes a source region 110, a body region 120, and a shielding region 140. The source region 110 and the body region 120 directly border a first sidewall of the gate structure 150. The source region 110 lies between the body region 120 and the first surface 101. The body region 120 separates the source region 110 from a drift structure 130.

[0139] The drift structure 130 is formed between the body region 120 and the second surface 102. The body region 120 and the drift structure 130 form a first pn junction pn1. The body region 120 and the source region 110 form a second pn junction pn2.

[0140] The shielding region 140 may extend along a second sidewall of the gate structure 150. A dopant concentration in the shielding region 140 along the second sidewall may be higher, e.g., at least ten times higher, than a dopant concentration in the body region 120 along the first sidewall. A vertical extent of the shielding region 140 may be greater than a vertical extent of the gate structure 150. For example, a local dopant concentration maximum in the shielding region 140 may have a greater distance from the first surface 101 than from a bottom of the gate structures 150.

[0141] The drift structure 130 includes a voltage-holding layer. For example, the voltage-holding layer may include a drift zone 131. A vertical extension and dopant concentration in the drift zone 131 are selected such that the semiconductor device 500 achieves its nominal blocking voltage capability. The drift zone 131 may be formed in an epitaxially grown layer. An average net dopant concentration in the drift zone 131 may be in the range of 1.0 × 10 15 cm -3 up to 5.0 × 10 16 cm -3 The vertical extent of the drift zone 131 is related to the nominal blocking capability of the semiconductor device 500. The vertical extent of the drift zone 131 can be in the range of approximately 1 µm to several tens of µm.

[0142] The drift structure 130 further includes a highly doped contact layer 139, which directly borders the second surface 102. The highly doped contact layer 139 is in contact with a backside metallization 320, which directly borders the second main surface 102. Along the second surface 102, a dopant concentration in the contact layer 139 is sufficiently high such that the contact layer 139 and the backside metallization 320 form a low-resistance ohmic contact. If the semiconductor device 500 is an MCD or an IGFET, or contains one or both, the contact layer 139 has the same conductivity type as the drift zone 131. If the semiconductor device 500 is an IGBT, the contact layer 139 has the complementary conductivity type of the drift zone 131 or contains zones of both conductivity types.

[0143] The drift zone 131 may directly border the contact layer 139, or a field stop or buffer zone 135 may be formed between the drift zone 131 and the contact layer 139. The field stop or buffer zone 135 forms a unipolar junction with the drift zone 131. A vertical extension of the field stop or buffer zone 135 may be approximately in a range from 1 µm to 10 µm. An average dopant concentration in the field stop or buffer zone 135 may, for example, be in a range from 1.0 × 10 17 cm -3 up to 1.0 × 10 18 cm -3 The field stop or buffer zone 135 can relieve mechanical stress in the semiconductor body 100 and / or can contribute to shaping the electric field in the drift structure 130.

[0144] The drift structure 130 may contain further doped regions, for example, barrier zones and / or current spreading regions 137 of the conductivity type of the drift zone 131 or counter-doped regions. Each current spreading region 137 may directly border a body region 120 and may extend between adjacent shielding regions 140. An average net dopant concentration in the current spreading regions 137 is higher than in the drift zone 131.

[0145] A front-side electrode 310 is electrically connected to the source region 110, the body region 120, and the shield region 140. An interlayer dielectric 210 electrically separates the front-side electrode 310 and the gate electrode 155.

[0146] According to one embodiment, the transistor cells TC are n-channel FET cells with p-doped body regions 120, n-doped source regions 110, and an n-doped drift zone 131. According to another embodiment, the transistor cells TC are p-channel FET cells with n-doped body regions 120, p-doped source regions 110, and a p-doped drift zone 131.

[0147] The source region 110, the body region 120, the current spreading region 137, the shielding region 140, the contact layer 139 and / or the field stop or buffer zone 135 can be formed using an ion beam implantation method with varying implantation angles and tunneling dopant ions as described above, e.g. with reference to Fig. 1A to 1F. For example, the semiconductor device 500 may have one, two or more of the vertical doping profiles as described with reference to Fig. 4A-4C, Fig. 5, Fig. 6 and Fig. 7. The method also applies to other layouts and designs for the transistor cell TC, e.g., transistor cells with a double-sided channel.

[0148] Fig. 4A shows a possible vertical source doping profile 430 of the source region 110 of Fig. 3. The vertical source doping profile 430 shows the dopant concentration ND as a function of a distance d from the first surface 101. The vertical source doping profile may include a primary peak 434 in a first source sub-region 111, a local doping concentration minimum 436 or valley in a second source sub-region 112, and a channeling peak 435 in a third source sub-region 113. The doping concentration value at the local doping concentration minimum 436 may, for example, be adjusted with respect to a desired total bulk resistance of the source region 110.

[0149] Fig. 4B refers to second source subregions 112 with more than one local doping concentration minimum 436. In the Fig. 4B, the second source subregion 112 includes two local doping concentration minima 436 and one local doping concentration maximum 437. The number of doping minima and doping maxima may also be greater than in Fig. 4B can be illustrated.

[0150] In Fig. 4C, the doping in the source region 110 includes an n-type component and a p-type component. The n-type component may have a vertical source dopant profile 430 similar to that shown in Fig. 4A. The p-type component may also include a channeling tip and a primary tip. The p-type primary tip may be formed between the n-type primary tip and the n-type channeling tip and may be used to tune the effective ohmic resistance of the source region between the first surface 110 and the body region 120. The p-type channeling tip may define a portion of the body region 120 and may define the pn junction between the third source sub-region 113 and the body region 120.

[0151] Fig. 5 shows a possible vertical body doping profile 440 of the body region 120 of Fig. 3. The vertical body doping profile 440 shows the dopant concentration ND in the body region 120 of Fig. 3 as a function of the distance d to the first surface 101. The vertical body doping profile 440 may include a primary peak 444 in a first body subregion 121, a local doping concentration minimum 446 or valley in a second body subregion 122, and a channeling peak 445 in a third body subregion 123.

[0152] In Fig. 6 shows a vertical current spread doping profile 460 a dopant concentration ND in the current spread region 137 of Fig. 3 as a function of the distance d to the first surface 101. The vertical current spreading doping profile 460 may include a first pair of a primary peak 4641 and a channeling peak 4651 resulting from an ion beam implantation with an acceleration energy of 2.5 MeV. The vertical current spreading doping profile 460 may include a second pair of a primary peak 4642 and a channeling peak 4652 resulting from an ion beam implantation with an acceleration energy of 2.1 MeV. The channeling peak and the primary peak of each pair have a specific distance from each other. The vertical current spreading doping profile 460 may include further peaks 467 resulting from further implantations, which may or may not utilize a channeling effect.

[0153] In Fig. 7 shows another vertical doping profile 470, the dopant concentration ND in a doped region as a function of a distance d to one of the main surfaces of a semiconductor body. The vertical doping profile 470 may be a vertical current spread doping profile of the Fig. 3, where d indicates the distance to the first surface 101 on the front side. Alternatively, the vertical doping profile 470 may be the vertical doping profile in the p-doped columns or in the n-doped columns of a superjunction structure.

[0154] The doped region contains a first local dopant concentration maximum at a first distance dch1 from the first surface (d=0), a second local dopant concentration maximum at a second distance dpr1 from the first surface, and at least one local dopant concentration minimum between the first distance dch1 and the second distance dpr1. Starting from the first distance dch1, the dopant concentration in the doped region decreases by 90% of the first local dopant concentration maximum with increasing distance from the first surface within a first distance d1. For example, the semiconductor body contains or consists of 4H-SiC, and the first distance d1 is at most 2 µm.

[0155] Fig.7 further shows a vertical reference doping profile 450 formed without utilizing the channeling effect. Compared to the vertical reference doping profile 450, the vertical body doping profile 470 exhibits a steeper slope on the side opposite the first surface. By exploiting the ability to define two peaks with an ion implantation process that utilizes varying implantation angles, the vertical doping profile 470 can be formed using a smaller number of ion beam implantations than the vertical reference doping profile 450.

[0156] The doping profile 470 may include at least two primary peaks 4741, 4742 and two channeling peaks 4751, 4752. A first peak pair comprising a primary peak 4741 and a channeling peak 4751 results from an ion beam implantation with a first acceleration voltage. A second peak pair comprising a different primary peak 4742 and a different channeling peak 4752 results from an ion beam implantation with a second, lower acceleration voltage. The channeling peak 4752 of the second peak pair may be located between the primary peak 4741 and the channeling peak 4751 of the first peak pair. The channeling peak and the primary peak of each peak pair have a specific distance from each other. The vertical body doping profile may contain further peaks 477 resulting from further implantations, which may or may not utilize a channeling effect.

[0157] Another ion beam implantation method may include orienting a substrate to a lateral target direction of an ion beam implantation device, wherein a remaining angular misalignment between the lateral target direction and the lateral main crystal direction lies within a lateral angle tolerance interval. Furthermore, the method may include implanting dopant ions into the substrate using an ion beam propagating in an incident beam plane parallel to an ion beam axis spanned, for example, by the ion beam axis and a substrate normal, wherein the dopant ions are implanted at different twist angles between the incident beam plane and the lateral target direction, as described above. The different twist angles lie within a twist angle range (total rotation sweep range).The twist angle range may be greater than the lateral angle tolerance interval, for example, at least twice or at least three times the angle tolerance interval. The twist angle range may be less than ten times the lateral angle tolerance interval, for example, at most five times or at most three times the angle tolerance interval. The lateral main crystal direction may be a horizontal main crystal direction or may be an orthogonal projection of any main crystal direction into the horizontal plane. The lateral target direction may be an orthogonal projection of a target direction as described above into the horizontal plane.

[0158] The ion beam propagates along an ion beam axis, as described above. The incident beam plane can be spanned by the ion beam axis and a vertical direction, as described above. For example, with the lateral aiming direction at 0 degrees, the total rotational sweep range for the implantation positions can be -14 degrees to +14 degrees, -4.9 degrees to +4.9 degrees, -2.1 degrees to +2.1 degrees, -1.4 degrees to +1.4 degrees, or -0.7 degrees to +0.7 degrees.

[0159] The lateral angle tolerance interval between the lateral target direction and the lateral main crystal axis can be a maximum of 3 degrees, e.g., a maximum of 1.6 degrees, a maximum of 1 degree, a maximum of 0.5 degrees, a maximum of 0.2 degrees, or a maximum of 0.1 degrees. The total rotation range for the implantation positions can be a maximum of 10 times, e.g., a maximum of 5 times, the lateral angle tolerance interval.

Claims

[1] Ion beam implantation method, comprising: orienting a substrate (700) to a target axis (706), wherein a remaining angular misalignment (Δθ) between the target axis (706) and a preselected crystal channel direction (707) in the substrate (700) lies within an angular tolerance interval (Rg), and wherein lattice guiding and / or channeling effects predominate over large-angle scattering effects along the crystal channel direction (707); implanting dopant ions into the substrate (700) through a substrate main surface (701) using an ion beam (800) propagating along an ion beam axis (801), wherein the dopant ions are implanted at different implantation angles (θ) between the ion beam axis (801) and the target axis (706), wherein the implantation angles (θ) lie within an implantation angle range (Rw) and wherein for the different implantation angles (θ) the ion beam (800) impinges on the same sub-area of ​​the substrate main surface (701), wherein a channel acceptance width (Rk) is effective for the preselected crystal channel direction (707), wherein the implantation angle range (Rw) is greater than 80% of a sum of the channel acceptance width (Rk) and twice the angle tolerance interval (Rg) and where the implantation angle range (Rw) is less than 500% of the sum of the channel acceptance width (Rk) and twice the angle tolerance interval (Rg). [2] Method according to the preceding claim, wherein the implantation angle (θ) continuously passes through the implantation angle range (Rw) at least once. [3] Method according to claim 1, where implantation of the dopant ions nmax implantation sub-processes at nmax different implantation angles (θ1,..., θ max ) and where nmax is at least 2. [4] Method according to the preceding claim, wherein the nmax implantation angles (θ1, ..., θ max ) are equally spaced. [5] Method according to one of the two preceding claims, wherein the nmax implantation sub-processes comprise pairs of implantation sub-processes and wherein the implantation angles (θ1) of each pair of implantation sub-processes are symmetrical with respect to the target axis (706). [6] Method according to one of the three preceding claims, wherein at least one of the implantation angles (θ1, ..., θ max ) deviates from 0 degrees by no more than 0.3 degrees. [7] Method according to one of the four preceding claims, wherein adjacent implantation angles (θ1, ..., θ max) by a maximum of 0.5 degrees. [8] Method according to one of the preceding claims, wherein the implantation angle range (Rw) is at most 6 degrees. [9] Method according to one of the preceding claims, further comprising: determining an angular deviation between a lateral target direction (709) and a lateral main crystal direction (708) in the substrate (700); and aligning, prior to implantation, the lateral main crystal direction (708) to the lateral target direction (709). [10] A method of manufacturing a semiconductor device, the semiconductor device comprising: a semiconductor body (100) having a first surface (101) and a doped region (180), wherein the doped region (180) has a first local dopant concentration maximum at a first distance (dch) from the first surface (101), a second local dopant concentration maximum at a second distance (dpr) from the first surface (101), and a local dopant concentration minimum between the first distance (dch) and the second distance (dpr), wherein the first distance (dch) is greater than the second distance (dpr); wherein a difference between the first distance (dch) and the second distance (dpr) is in a range of 200 nm to 1500 nm; wherein a ratio between the first local dopant concentration maximum and the second local dopant concentration maximum is in a range from 0.5 to 2; and wherein a ratio between the sum of the first local dopant concentration maximum and the second local dopant concentration maximum and the local dopant concentration minimum is in a range of 2 to 10, wherein forming the doped region (180) comprises implanting dopant ions into the doped region (180) using the ion beam implantation method of any one of claims 1 to 9. [11] The method according to the preceding claim, wherein a vertical dopant concentration profile of the doped region (180) has a first falling edge between the second local dopant concentration maximum and the local dopant concentration minimum and a second falling edge between the first local dopant concentration maximum and a second surface (102) of the semiconductor body (100), and wherein the second falling edge is steeper than the first falling edge. [12] A method according to any one of the two preceding claims, wherein the semiconductor device comprises: a gate structure (150) extending from the first surface (101) into the semiconductor body (100). [13] The method according to the preceding claim, wherein the semiconductor device further comprises: a body region (120) in contact with the doped region (180) and the gate structure (150), wherein the doped region (180) and the body region (120) form a pn junction (pn) and wherein the doped region (180) is formed between the first surface (101) and the body region (120). [14] The method of claim 12, wherein the semiconductor device further comprises: a source region (110) in contact with the doped region (180) and the gate structure (150), wherein the doped region (180) and the source region (110) form a pn junction (pn) and wherein the source region (110) is formed between the first surface (101) and the doped region (180). [15] The method of claim 12, wherein the semiconductor device further comprises: a body region (120) in contact with the doped region (180) and the gate structure (150), wherein the doped region (180) and the body region (120) form a pn junction (pn) and wherein the body region (120) is formed between the first surface (101) and the doped region (180). [16] Method according to one of the five preceding claims, wherein the vertical dopant concentration profile of the doped region (180) has at least one further local dopant concentration maximum between the first surface (101) and the second distance (dpr). [17] A method of manufacturing a semiconductor device, the semiconductor device comprising: a semiconductor body (100) having a first surface (101) and a doped region (180), the semiconductor body (100) comprising silicon carbide; wherein the doped region (180) has a first local dopant concentration maximum at a first distance (dch) from the first surface (101), a second local dopant concentration maximum at a second distance (dpr) from the first surface (101), and a local dopant concentration minimum between the first distance (dch) and the second distance (dpr), wherein, starting from the first distance (dch), a dopant concentration in the doped region (180) decreases with increasing distance from the first surface (101) within a maximum of 2 µm by 90% of the first local dopant concentration maximum, wherein forming the doped region (180) comprises implanting dopant ions into the doped region (180) using the ion beam implantation method of any one of claims 1 to 9. [18] The method according to the preceding claim, wherein the semiconductor device further comprises: a gate structure (150) extending from the first surface (101) into the semiconductor body (100), wherein the doped region (180) is in contact with the gate structure (150); a body region (120) in contact with the doped region (180) and the gate structure (150); and a source region (110) in contact with the body region (120) and the gate structure (150), wherein the body region (120) separates the source region (110) and the doped region (180), wherein a vertical dopant concentration profile of the doped region (180) has at least one further local dopant concentration maximum between the first surface (101) and the second distance (dpr) and at least one further local dopant concentration maximum between the second distance (dpr) and the first distance (dch).

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