Silicon carbide device with trench gate structure and method of manufacture

Abstract

Silicon carbide devices having trench gate structures and methods of manufacture are disclosed. A silicon carbide device (500) includes a silicon carbide body (100) having a trench gate structure (150) extending into the silicon carbide body (100) from a first surface (101). A body region (120) is in contact with an active sidewall (151) of the trench gate structure (150). A source region (110) is in contact with the active sidewall (151), wherein the source region (110) is between the body region (120) and the first surface (101). The body region (120) includes a first body portion (121) directly below the source region (110) and away from the active sidewall (151). In at least one horizontal plane parallel to the first surface (101), a dopant concentration in the first body portion (121) is at least 150% of a reference dopant concentration in the body region (120) in the horizontal plane at the active sidewall (151), and a horizontal extension (w1) of the first body portion (121) is at least 20% of a total horizontal extension (w0) of the body region (120).

Description

TECHNICAL FIELD

[0001] Examples of the present disclosure relate to silicon carbide devices, and in particular to silicon carbide devices having trench gate structures and methods of manufacturing silicon carbide devices having trench gate structures. BACKGROUND

[0002] Power semiconductor devices are typically used as switches and rectifiers in circuits for converting electrical energy, for example in DC / AC converters, AC / AC converters or AC / DC converters, and in circuits driving heavy inductive loads, for example in motor driver circuits. Since silicon carbide (SiC) has a high dielectric breakdown field strength compared to silicon, SiC devices can be significantly thinner and can show lower on-state resistance compared to their silicon counterparts. Typically, in SiC devices, the contribution of the channel resistance to the total on-state resistance is larger compared to the case of equivalent silicon devices.

[0003] There is a need for improving silicon carbide device parameters. SUMMARY

[0004] An embodiment of the present disclosure relates to a method of manufacturing a silicon carbide device. A silicon carbide body is provided. A trench gate structure is formed extending into the silicon carbide body from a first surface. A body region is formed in contact with an active sidewall of the trench gate structure. A source region is formed between the body region and the first surface in contact with the active sidewall. A dopant is implanted into a first body portion of the body region, wherein the first body portion is directly below the source region and away from the active sidewall. A dopant concentration in the first body portion in at least one horizontal plane is at least 150% of a reference dopant concentration in the body region in the horizontal plane at the active sidewall body region, and a horizontal extension of the first body portion is at least 20% of a total horizontal extension of the body region.

[0005] Another embodiment of the present disclosure relates to a silicon carbide device comprising a silicon carbide body. A trench gate structure extends into the silicon carbide body from a first surface. A body region is in contact with an active sidewall of the trench gate structure. A source region is in contact with the active sidewall between the body region and the first surface. The body region comprises a first body portion directly below the source region and away from the active sidewall. In at least one horizontal plane parallel to the first surface, a dopant concentration in the first body portion is at least 150% of a reference dopant concentration in the body region in the horizontal plane at the active sidewall, and a horizontal extension of the first body portion is at least 20% of a total horizontal extension of the body region.

[0006] Those skilled in the art will realize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0007] The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of silicon carbide devices and methods of manufacturing silicon carbide devices, and together with the description serve to explain principles of the embodiments. Further embodiments are described in the detailed description and claims.

[0008] Figures 1A-1B A schematic vertical cross-sectional view of a portion of a silicon carbide body is shown for illustrating a method of manufacturing a silicon carbide device with a heavily doped body portion according to an embodiment.

[0009] Figures 2A-2B A schematic vertical cross-sectional view of a portion of a silicon carbide body is shown for illustrating a method of manufacturing a silicon carbide device according to an embodiment using a tilted implant.

[0010] Figures 3A-3C A schematic vertical cross-sectional view of a portion of a silicon carbide body is shown for illustrating a method of manufacturing a silicon carbide device according to an embodiment using an implant mask that is recessed in the lateral direction.

[0011] Figures 4A-4D A schematic vertical cross-sectional view of a portion of a silicon carbide body is shown for illustrating a method of manufacturing a silicon carbide device according to an embodiment using more than one implant mask recess.

[0012] Figure 5A A schematic vertical cross-sectional view of a portion of a silicon carbide device with a heavily doped body portion according to another embodiment is shown.

[0013] Figure 5B A schematic diagram is shown for illustrating horizontal dopant gradients in the body region of Figure 5A .

[0014] Figures 6A-6B A vertical cross-sectional view of a silicon carbide device according to an embodiment and a vertical cross-sectional view of a comparison device are shown.

[0015] Figures 6C-6D A schematic diagram is shown for discussing effects of embodiments, which illustrates horizontal and vertical dopant gradients in a silicon carbide device of Figures 6A-6B and in a comparison device.

[0016] Figures 6E-6F A schematic diagram is shown for discussing effects of embodiments, which illustrates boundaries of depletion zone bands in the body region of a silicon carbide device of Figures 6A-6B and a comparison device in a blocking mode. DETAILED DESCRIPTION

[0017] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific embodiments in which a silicon carbide device can be practiced. It is to be understood that other embodiments can be utilized and structural or logical changes can be made without departing from the scope of the present disclosure. For example, features illustrated with respect to one embodiment can be used in alternate embodiments or in combination with other embodiments to produce yet other embodiments. It is intended that the present disclosure include these modifications and changes. Specific language is used herein to describe examples, but the use of such specific language is not intended to limit the scope of the claims. The drawings are not scaled, and are for illustrative purposes only. If not otherwise stated, corresponding elements in different drawings are denoted by the same reference numeral.

[0018] The terms "have", "comprise", "include", "contain", "comprising", "including", "containing", "comprise", "comprises", "include" and "includes" are open-ended, and the terms specify the presence of stated structures, elements or features but do not preclude the presence or addition of one or more other structures, elements, or features. The quantifiers and referring words "one", "a" and "the" are intended to include both the singular and the plural, unless the context clearly indicates otherwise.

[0019] The term "electrically connected" describes a permanent low-resistance connection between electrically connected elements, such as a direct contact between the elements or a low-resistance connection via a metal and / or a heavily doped semiconductor material. The term "electrically coupled" includes that one or more intermediate elements can be connected between the electrically coupled elements, such as elements that are controllable to temporarily provide a low-resistance connection in a first state and a high-resistance decoupling in a second state.

[0020] An ohmic contact is a non-rectifying electrical junction with linear or almost linear current-voltage characteristics. A Schottky contact is a metal-semiconductor junction with rectifying characteristics, wherein the work function of the metal and the dopant concentration in the semiconductor material are chosen such that a depletion zone forms in the semiconductor material along the metal-semiconductor junction without an externally applied electric field. In the case of a Schottky contact, the term "metal-semiconductor junction" can also refer to a junction between a metalloid semiconductor and a semiconductor, wherein the junction has the same characteristics as a metal-semiconductor junction. For example, it can be possible to form a Schottky contact between polysilicon and silicon carbide. If two components (e.g. two regions) form an ohmic contact or a Schottky contact, respectively, this can mean that there is an ohmic contact or a Schottky contact between said two components. In both cases, it can be possible for said two regions to directly abut each other. However, it can also be possible that further components are located between said two components.

[0021] The safe operating area (SOA) defines the voltage and current conditions under which a semiconductor device can be expected to operate without self-damage. The SOA is given by published maximum values for device parameters, such as maximum continuous load current, maximum gate voltage, and other parameters.

[0022] The figures illustrate relative doping concentrations by indicating "-" or "+" next to the doping type "n" or "p". For example, "n-" means a lower doping concentration than the doping concentration of the "n" doped region, while an "n+" doped region has a higher doping concentration than the "n" doped region. Doped regions of the same relative doping concentration do not necessarily have the same absolute doping concentration. For example, two different "n" doped regions can have the same or different absolute doping concentrations.

[0023] Two contiguous doped regions having the same conductivity type and having different dopant concentrations form a unipolar junction, e.g., an n / n+ or p / p+ junction along the boundary surface between the two doped regions. At the unipolar junction, the dopant concentration profile orthogonal to the unipolar junction can show a step or a turning point at which the dopant concentration profile changes from concave to convex, or vice versa.

[0024] Ranges given for physical sizes include the boundary values. For example, a range from a to b for a parameter y reads as a < y < b. The same applies to ranges having one boundary value, such as "at most" and "at least".

[0025] The main components of a layer or structure from a chemical compound or alloy are 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.

[0026] The term "on" should not be interpreted as meaning "directly on". Rather, if an element is located "on" another element (e.g., a layer "on" another layer or "on" a substrate), further components (e.g., further layers) can be located between these two elements (e.g., a further layer can be located between one layer and a substrate, if this layer is "on" said substrate).

[0027] With respect to structures and doped regions formed in a silicon carbide body, a second region is "under" a first region if the minimum distance between the second region and a first surface at a front side of the silicon carbide body is larger than the maximum distance between the first region and the first surface. The second region is directly "under" the first region, wherein the vertical projections of the first and second regions into the first surface overlap. The vertical projection is the projection orthogonal to the first surface. A "horizontal plane" is a plane parallel to the planar first surface or to a coplanar surface segment of the first surface.

[0028] According to an embodiment, a method of manufacturing a silicon carbide device can include providing a silicon carbide body. A trench gate structure can be formed extending into the silicon carbide body from a first surface. A body region and a source region zone can be formed in contact with an active sidewall of the trench gate structure, with the source region zone being between the body region and the first surface. A source region can be formed in the source region zone before or after forming the trench gate structure.

[0029] The body region and the source region are oppositely doped and form a pn junction. Here and in the following, the conductivity type of the source region is named the first conductivity type, and the conductivity type of the body region is named the second conductivity type. Dopants defining the body region and the source region can be introduced into the silicon carbide body before or after forming the trench gate structure, or after forming at least part of the trench gate structure, e.g. after forming the trench, after forming a sacrificial layer on the trench sidewall, or after forming a gate dielectric along at least part of the trench sidewall.

[0030] The trench gate structure includes a conductive gate electrode and a gate dielectric between at least the body region and the gate electrode.

[0031] Before or after forming the trench gate structure, dopants can be implanted into a first body portion of the body region, with the first body portion being directly below the source region zone and away from the active sidewall. The dopants have the second conductivity type, and a net dopant concentration is boosted in the first body portion relative to a second body portion between the first body portion and the active sidewall. As a result, in at least one horizontal plane parallel to the first surface, an average dopant concentration in the first body portion can be at least 150% of a reference dopant concentration, and a horizontal extension of the first body portion can be at least 20% of a total horizontal extension of the body region. The reference dopant concentration is a dopant concentration in the body region at the active sidewall in the same horizontal plane.

[0032] The dopant concentration within the first body portion and / or within the second body portion can be constant. In this case, "constant" can mean that the dopant concentration varies within the first body portion and / or the second body portion by at most ±10% of the average dopant concentration, respectively.

[0033] A transition region is between the first body portion and the second body portion. Within the transition region, a horizontal dopant gradient can show a drop from at least 90% of the average dopant concentration in the first body portion and / or from at least 130% of the reference dopant concentration to at most 110% of the reference dopant concentration. The transition region has a certain distance to the active sidewall, which means that the first body portion is away from the active sidewall.

[0034] Alternatively or in addition, the first body portion can extend across at least 50% of the total horizontal extension of the body region.

[0035] Along the active sidewalls, an inversion channel is formed in the on-state of the silicon carbide device. In operation, no inversion channel is formed along the non-active sidewalls within the SOA. Each trench gate structure can comprise one, two, three, four or six active sidewalls.

[0036] The first body portion and the second body portion form a unipolar junction. A minimum distance between the trench gate structure and the unipolar junction can be at least 100 nm, for example at least 200 nm.

[0037] In the blocking mode of the silicon carbide device with the field effect transistor structure, a space charge region (depletion region) can penetrate into the body region from the side opposite to the source region, for example from the drift structure. The depletion region can extend into the channel region of the silicon carbide device and thus can lower the potential barrier between the body region and the region opposite to the source region, for example the drift structure. This can lead to a lowering of the gate threshold voltage (so-called "barrier lowering"). This drain-induced barrier lowering (DIBL) can significantly influence the gate threshold voltage and can impair the electrical properties of the silicon carbide device.

[0038] By providing the first body portion with an increased doping concentration in the body region, the extension of the depletion region can be reduced. The difference of the first body portion to the channel region and / or the gate structure can be chosen such that, on the one hand, the difference is large enough to avoid a detrimental increase of the gate threshold voltage due to the increase of the doping concentration in the first body portion and, on the other hand, the difference is small enough to allow the depletion region to be deflected into the first body portion. Due to the sufficient distance of the first body portion to the trench gate structure with the gate dielectric, the higher dopant concentration in the first body portion has no or only marginal effect on the nominal gate threshold voltage. The formation of the first body portion leaves the lateral extension of the source region unaffected and does not impair or only marginally impairs the contact resistance of the source region.

[0039] According to embodiments, the dopant for forming the first body portion can be implanted into the first body portion before forming the trench gate structure. In this way, the first body portion can be formed without adverse effects on the structures in the trench gate structure, for example without adverse effects on the implanted ions on the gate dielectric.

[0040] According to embodiments, the injection axis for injecting dopants into the first body portion can be tilted with respect to the vertical direction of the silicon carbide body. The injection axis can be oriented such that the dopants for the first body portion are injected towards the active sidewalls of the trench gate structure. For example, the dopants can be injected from a side at which the body region directly adjoins the trench gate structure towards the trench gate structure. The injection axis runs parallel to the direction of the ion beam by which the dopants are injected.

[0041] The injection axis and the vertical direction enclose an injection angle above the first surface. Below the first surface, the injection axis and the vertical direction enclose a negative injection angle.

[0042] The active sidewalls of the gate trench structure can run along the vertical direction or can enclose a taper angle with the vertical direction at the first surface. In either case, the gate trench structure can comprise at least one active sidewall, in some cases at least two opposing active sidewalls or even more than two active sidewalls (e.g. four or six active sidewalls). For each active sidewall, the injection axis can be chosen in dependence on the orientation of the active sidewall. The active sidewall or at least one of the active sidewalls can run essentially (i.e. within a tolerance of ± 2° or ± 1°) along a main crystallographic plane of the silicon carbide body. The gate trench structure can further comprise at least one non-active sidewall at which no channel is formed.

[0043] In case of a silicon carbide body having a so-called off-axis angle, typically a tapered trench gate structure is used. The taper angle can differ by at most 2°, in particular at most 1° in absolute value from the off-axis angle. In other embodiments, the silicon carbide body can be provided with an off-axis angle, but the sidewalls can still run along the vertical direction.

[0044] For each active sidewall, the injection axis can be chosen such that the injection direction and the active sidewall of the silicon carbide body and / or one main crystallographic direction (e.g. the C-axis) have the same relative orientation, but differ in absolute value (e.g. by at least 1° or at most 2° and at most 10° or at most 8° or at most 5°). In some embodiments, the injection angle and the taper angle can have the same sign (i.e. can both be oriented clockwise or counter-clockwise), but can differ in absolute value. That is, the injection axis and the active sidewall and / or one main crystallographic direction can have the same relative orientation (e.g. the same tilt direction), but can differ in absolute value.

[0045] Generally (e.g. in the case of a conical shape and in the case of a gate trench structure with an active sidewall along the vertical direction), the implant angle can be chosen such that the implant axis is tilted away from the active sidewall. In other words: the implant can be directed towards the active sidewall. The acute angle between the implant axis and the first surface (i.e. the angle which is smaller than 90°) can be (in absolute value) smaller than the acute angle between the active sidewall and the first surface.

[0046] The implant angle can be chosen such that the implant axis is different from a main crystal plane (e.g. all main crystal planes) and / or a main crystal axis (e.g. all main crystal axes) of the silicon carbide body. Typically, the implant angle is chosen to be larger (in absolute value) than the conical angle and / or the off-axis angle. For example, the implant angle can be at least 2°, e.g. at least 3° or at least 4° larger (in absolute value) than the conical angle and / or the off-axis angle. In the case of a trench gate structure with vertical sidewalls, the conical angle is assumed to be 0° in the aforementioned relation.

[0047] In one embodiment, the conical angle and / or the off-axis angle can be at least 2° and at most 6°, e.g. 4° (in absolute value). The implant angle can then be at least 6° (e.g. at least 7°) and at most 14° (e.g. at most 12° or at most 11°) (in absolute value). However, in some embodiments, the implant angle can be smaller than 6° in the case of a conical trench gate structure. Generally, the conical angle of an active sidewall and the implant angle of an implant corresponding to said active sidewall can both be negative ("clockwise oriented") or positive ("counter clockwise").

[0048] By using a tilted implant, it can be possible to reduce or avoid channeling effects. Channeling typically occurs when the implant axis is essentially parallel to a main crystal direction along which the crystal lattice forms a continuous lattice channel. When channeling occurs, the implant depth can vary strongly in response to only slight changes of the implant angle. A sufficiently large preset angle between the implant axis and the main crystal direction can reduce the fluctuations of the implant depth to a high degree.

[0049] Additionally or alternatively, by using a tilted implant, lateral deviations can be reduced. Vertical implants into a semiconductor material (i.e. where the implant axis runs essentially parallel to the vertical direction) typically show lateral deviations such that in the case of a masked implant, a portion of the implanted ions becomes residing outside the vertical projection of the opening. In contrast thereto, a tilted implant from one side of the body region towards the active sidewall can reduce lateral deviations at the side of the mask which the tilted implant is directed away from (i.e. at the side which the tilted implant is directed away from).

[0050] The implantation mask masking the dopant implant for the first body portion can comprise relatively wide openings and relatively narrow mask strips between the openings. Further, each mask strip can be positioned asymmetrically with respect to the interface between the trench gate structure and the body region. In particular, a lateral distance between the gate dielectric and a first edge of the mask strip over the body region can be larger than a lateral distance between the gate dielectric and a second edge of the mask strip over the trench gate structure.

[0051] In case of a vertical implant, the lateral offset at the side of the second edge of the mask strip can increase the dopant concentration directly along the gate dielectric and thus the gate threshold voltage.

[0052] In case of an inclined implant, it can be possible that the lateral offset at the side of the second edge of the mask strip has no or only a negligible impact on the gate threshold voltage.

[0053] The implantation angle between the implantation axis and the vertical direction can be at least 3°, for example at least 7°, for example at least or exactly 11° in absolute value.

[0054] According to an embodiment, a body-enhanced implantation mask can be formed on the first surface and a dopant can be implanted into the first body portion through an opening in the body-enhanced implantation mask. The body-enhanced implantation mask can cover at least a first source portion of the source region zone. The opening in the body-enhanced implantation mask can expose at least a body contact region of the first surface. The body contact region laterally directly adjoins the source region zone. In the body contact region, a low-resistance ohmic contact between the body region and a first load electrode at the front side of the silicon carbide body can be formed at a later processing stage.

[0055] For example, the body-enhanced implantation mask can cover the entire source region zone and the opening in the body-enhanced implantation mask can only expose the body contact region. In this way, it can be possible that the body-enhanced implantation can also be used as a body contact implantation mask defining the heavily doped body contact region in the body contact region.

[0056] For example, the heavily doped body contact region can be formed by implanting a dopant through the opening in the body-enhanced implantation mask with a low implantation energy, wherein a range peak of the dopant is at a distance from the first surface and the distance is within a vertical extension of the source region zone.

[0057] Forming the first body portion can include at least one angled implant. The implant energy for the angled implant can be selected such that the range peak end is within the body region and at a distance from the source region strip. Implanting dopants into the first body portion can include one, two or more than two implants with different implant energies. The dose of the various implants can be the same or can be different. Using the same implant mask for the one or more angled implants defining the first body portion directly below the source region and for the implant defining the body contact portion directly adjacent to the source region facilitates forming the first body portion with low additional effort.

[0058] According to embodiments, the opening in the body enhancement implant mask can expose the body contact region and a second source portion of the source region strip, wherein the second source portion is located between the body contact region and the first source portion. In this way, the first body portion can be formed with a greater lateral extension with respect to the source region. The extension of the depleted portion of the body region in the off-state can be further reduced. As a result, the DIBL effect can be further reduced without reducing the lateral extension of the source region.

[0059] According to embodiments, a body contact implant mask can be formed on the first surface, wherein the body contact implant mask can cover the source region strip, and wherein an opening in the body contact implant mask exposes the body contact region. Dopants of the conductivity type of the body region, i.e. dopants of the second conductivity type, can be implanted through the opening in the body contact implant mask. The implanted dopants can form a heavily doped body contact region laterally adjacent to the source region strip. The implant dose can be high enough such that the body contact region forms a low resistance ohmic contact with a first load electrode that can be formed at a later stage.

[0060] After forming the body contact region, the body contact implant mask can be recessed laterally. The body contact implant mask can be exclusively recessed laterally, wherein only the opening becomes wider. Alternatively, the lateral recessing can also include a vertical recessing at the same or at a different recessing rate. For example, an isotropic etch can recess the body contact implant mask laterally as well as vertically, wherein the recessing also reduces the thickness of the body contact implant mask. The body contact implant mask that is at least recessed laterally can form the body enhancement implant mask.

[0061] In this way, the body enhancement implant mask can be formed in an efficient way without additional lithography processes. The first body portion and the body contact region can be formed in a self-aligned manner.

[0062] According to embodiments, a deep implantation mask can be formed on the first surface, wherein the deep implantation mask can cover the third source portion of the source zone. An opening in the deep implantation mask can expose the body contact region and the fourth source portion of the source zone. The fourth source portion is located between the body contact region and the third source portion. Dopants of the conductivity type of the body region, i.e. dopants of the second conductivity type, are implanted through the opening in the deep implantation mask, wherein a range peak end of the dopants is at a distance from the first surface, and the distance can be larger than a maximum distance between the body region and the first surface.

[0063] The dopants can form a deep shielding portion. Implanting the dopants into the deep shielding portion can include one, two or more than two implantations with different implantation energies. The doses of the various implantations can be the same or can be different.

[0064] After forming the deep shielding portion, the deep implantation mask can be recessed in the lateral direction. The deep implantation mask recessed in the lateral direction can form a body enhancement implantation mask. In this way, the body enhancement implantation mask can be formed in an efficient way without additional lithography processes. The first body portion can be formed self-aligned to the deep shielding portion of the same conductivity type, wherein the deep shielding portion can shield the trench gate structure from the drain electrode potential and / or can provide a body diode.

[0065] According to embodiments, a body contact implantation mask can be formed on the first surface, wherein the body contact implantation mask covers the source zone and an opening in the body contact implantation mask exposes the body contact region. Dopants of the second conductivity type can be implanted through the opening in the body contact implantation mask to form a heavily doped body contact portion. Then, the body contact implantation mask can be recessed in the lateral direction to provide a body contact implantation mask recessed in the lateral direction.

[0066] The body contact implantation mask recessed in the lateral direction can form a deep implantation mask. Dopants of the second conductivity type can be implanted through an opening in the deep implantation mask to form a deep shielding portion. Then, the deep implantation mask can be recessed in the lateral direction to provide a deep implantation mask recessed in the lateral direction. The deep implantation mask recessed in the lateral direction can form a body enhancement implantation mask for forming the first body portion.

[0067] In this way, the deep shielding portion, the body contact portion and the first body portion can be formed in an efficient way based on one single lithography process. The first body portion, the body contact portion and the deep shielding portion can be formed self-aligned to each other, i.e. without lithography overlay displacement.

[0068] According to embodiments, dopants of a conductivity type complementary to that of the body region, i.e. dopants of the first conductivity type, can be implanted into the source region zone to form a doped source region in the source region zone. The source region can be formed before or after the first body portion is formed.

[0069] According to embodiments, the horizontal extension of the first body portion in at least one horizontal plane is at least 20% of the total horizontal extension of the body region. The overlap of 20% of the first body portion with the source region results in a significant improvement against DIBL. According to further embodiments, the horizontal extension of the first body portion can be at least 40% or even 50% of the total horizontal extension of the body region, wherein the DIBL effect is further reduced without the presence of the first body portion affecting the nominal gate threshold voltage.

[0070] According to at least one further embodiment, the silicon carbide device can comprise a silicon carbide body having a trench gate structure extending into the silicon carbide body from a first surface of the silicon carbide body. The body region is in contact with an active sidewall of the trench gate structure. The source region is in contact with the active sidewall. The source region is located between the body region and the first surface. The body region can comprise a first body portion directly below the source region and at a distance from the active sidewall. In at least one horizontal plane parallel to the first surface, a dopant concentration in the first body portion is at least 150% of a reference dopant concentration in the horizontal plane at the active sidewall.

[0071] The silicon carbide device can be or can comprise an IGFET (insulated gate field effect transistor), e.g. a MOSFET (metal oxide semiconductor FET) or MCD (MOS controlled diode) in the general sense including FETs having a metal gate and FETs having a gate from a semiconductor material by way of example.

[0072] The additional dopants in the first body portion can contribute to reducing the influence of the depletion region on the barrier height. The first body portion can reduce the drain induced barrier lowering and can improve the stability of the electrical characteristics of the silicon carbide device.

[0073] According to embodiments, the horizontal extension of the first body portion in at least one horizontal plane is at least 20% of the total horizontal extension of the body region.

[0074] According to embodiments, the silicon carbide device can further comprise a shield region of the conductivity type of the body region, i.e. a shield region of the second conductivity type. The shield region can extend into the silicon carbide body from the first surface and can directly adjoin the source region and the body region laterally.

[0075] For example, a shield region can be formed between the source region and the body region at one side and the further trench gate structure at the other side. The shield region can separate the source region and the body region from the further trench gate structure. The vertical extension of the shield region can be larger than the vertical extension of the trench gate structure. The shield region can comprise a portion directly below the trench gate structure, wherein the shield region can shield the trench gate structure from the drain potential and can reduce the maximum electric field strength occurring along the edge of the trench gate structure.

[0076] According to an embodiment, in at least one horizontal plane, the lateral dopant profile in the portion of the shield region directly adjoining the first body portion can be equal to the dopant concentration in the first body portion. At least a vertical section of the shield region and the first body portion can result from these implants.

[0077] According to another embodiment, the shield region can be in contact with a second sidewall of the further trench gate structure.

[0078] According to an embodiment, the first body portion can result from an inclined implant. By way of example, the implant angle can have been chosen in the range from 3° to 11° in absolute value. The inclined implant can be visible, for example, from the shape of the first body portion in the device. Dopants in silicon carbide semiconductor material typically do not show diffusion. Thus, the asymmetric shape resulting from the inclined implant can still be visible in the first body portion even after activation of the dopants.

[0079] Figures 1A-4D A method of manufacturing a silicon carbide device is involved. The silicon carbide device can be manufactured from a silicon carbide substrate comprising at least one silicon carbide body 100. At least one semiconductor die (chip) of a silicon carbide device can be obtained from each silicon carbide body 100.

[0080] For example, the silicon carbide body 100 can comprise or consist of a silicon carbide layer grown by epitaxy on a suitable single crystalline substrate.

[0081] By way of example, the silicon carbide body 100 can be polytypic 15R-SiC, 2H-SiC, 4H-SiC or 6H-SiC. In addition to the main components silicon and carbon, the silicon carbide body 100 can comprise dopant atoms, for example nitrogen N, phosphorous P, beryllium Be, boron B, aluminum Al and / or gallium Ga. Further, the silicon carbide body 100 can comprise unwanted impurities, for example hydrogen and / or oxygen.

[0082] The silicon carbide body 100 comprises a first surface 101 at a front side and an opposite second surface 102 at a back side. The first surface 101 and the second surface 102 can be parallel to each other, wherein the first surface 101 can be flat or textured. In case of a textured first surface 101, for simplification, in the following, the average plane through the textured main surface 101 is considered to be the first surface 101.

[0083] The silicon carbide body 100 extends along a main extension plane in a horizontal direction, which is also referred to as lateral direction in the following. Perpendicularly to the horizontal direction, in a vertical direction 104, the silicon carbide body 100 has a small thickness compared to the extension of the silicon carbide body 100 along the main extension plane. The vertical direction can run along the lateral direction in the following.

[0084] The vertical direction 104 of the silicon carbide body 100 can coincide with a main lattice direction or can be tilted with respect to the main lattice direction by an off-axis angle, wherein the off-axis angle can be in a range from 2° to 8° in absolute value. At the back side of the silicon carbide body 100, the second surface 102 can extend parallel to the flat first surface 101 or parallel to the average plane of the textured first surface 101.

[0085] The total thickness of the silicon carbide body 100 between the first surface 101 and the second surface can be in a range from a few hundred nm to a few hundred pm and is related to the nominal blocking capability of the manufactured silicon carbide device.

[0086] The following embodiments relate to a silicon carbide device having an n-channel transistor cell with an n-doped source region and with a p-doped body region. Thus, the conductivity type of the source region - or the first conductivity type - is n-type and the conductivity type of the body region - or the second conductivity type - is p-type. By inverting the conductivity types of the source region and the body region, the disclosure with respect to the n-channel transistor cell can be applied to a p-channel transistor cell with the necessary modifications.

[0087] The silicon carbide body 100 comprises a drift structure 130 with a lightly n-doped drift zone 131. The drift structure 130 can optionally comprise an n-doped current spreading region 137 between the first surface 101 and the drift zone 131, wherein the current spreading region 137 can directly adjoin the drift zone 131. Between adjacent current spreading regions, a p-doped shielding region 140 can extend in the silicon carbide body 100 from a body contact region 126 into the drift structure 130, wherein the body contact region 126 is a section of the first surface 101.

[0088] The shielding region 140 and the current spreading region 137 may be stripe-shaped, with the horizontal longitudinal axes of the shielding region 140 and the current spreading region 137 extending orthogonally to the cross-sectional plane. However, other shapes may also be possible depending on the desired shape of the transistor cell (e.g., the shape of the gate trench).

[0089] The p-doped body region 120 between the first surface 101 and the current spreading region 137 may directly adjoin the current spreading region 137 in a vertical direction. The maximum dopant concentration in the body region 120 may be lower than the maximum dopant concentration in the shielding region 140.

[0090] The source zones 210 located between the first surface 101 and the body region 120 may directly adjoin the body region 120. Each source zone 210 includes a first source portion 211 in the center and a second source portion 212 between the first source portion 211 and the adjacent body contact region 126. In the source zones 210, heavily n-doped source regions 110 may be formed before or after the p-type implantation described below.

[0091] A body enhancement implantation mask 450 is formed on the first surface 101 , and p-type dopants are implanted through openings 455 in the body enhancement implantation mask 450 .

[0092] Figure 1A A body enhancement implant mask 450 is shown covering the first source portion 211. Openings 455 in the body enhancement implant mask 450 expose the body contact regions 126 and the second source portion 212. The openings 455 may be stripe-shaped with a longitudinal axis of the openings 455 extending orthogonally to the cross-sectional plane.

[0093] P-type dopant ions can be implanted through opening 455 at one or more different implant energies, wherein the implantations at the different implant energies can have the same implant dose or different implant doses. The implant axis can be vertical, i.e., parallel to vertical direction 104, or can be tilted at an implant angle β relative to vertical direction 104. Implant angle β is in a cross-sectional plane and is perpendicular to the longitudinal axis of opening 455. The implanted p-type dopant ions form a heavily doped first body portion 121 directly below second source portion 212.

[0094] The body enhancement implant mask 450 can be removed. An n-type dopant can be implanted into the source zone band 210 to form source regions 110 in the source zone band 210. A trench mask can be formed on the first surface 101. The trench mask can have openings of strip shape with a longitudinal axis orthogonal to the cross-sectional plane. Each opening in the trench mask can overlap in the lateral direction with one current spreading region 137 and with one shielding region 140. Using the trench mask as an etching mask, gate trenches can be etched into the silicon carbide body 100. A gate dielectric 159 can be formed lining at least portions of the gate trenches. One or more electrically conductive materials can be deposited. The electrically conductive materials form gate electrodes 155 in the gate trenches. Portions of the deposited electrically conductive materials deposited outside the gate trenches can be removed.

[0095] Figure 1B Trench gate structures 150 extending into the silicon carbide body 100 from the first surface 101 are shown. Each trench gate structure 150 comprises an electrically conductive gate electrode 155 and a gate dielectric 159 between the gate electrode 155 and the silicon carbide body 100. The sidewalls 151, 152 of the trench gate structure 150 can be orthogonal to the first surface 101. According to the illustrated embodiment, the trench gate structure 150 tapers as the distance to the first surface 101 increases, such that both sidewalls 151, 152 are inclined to the vertical direction 104.

[0096] At least one of the sidewalls 151, 152 can be an active sidewall parallel to a crystal plane with a high charge carrier mobility. In the on-state of the semiconductor device, an inversion channel is formed in the body region along the active sidewall 151. In case the semiconductor device is operated within an SOA, no inversion channel is formed in the body region along the non-active sidewall 152. While the following figures refer to trench gate structures 150 having only one active sidewall 151 at the left side of each trench gate structure 150, embodiments can also be applied to trench gate structures 150 having only one active sidewall 151 at the right side of each trench gate structure, or to trench gate structures 150 having two or more active sidewalls 151.

[0097] The source regions 110 and the body regions 120 are in contact with the active sidewalls 151 of the trench gate structures 150. The body regions 120 separate the source regions 110 from the current spreading regions 137. The current spreading regions 137 form a low resistance connection between the body regions 120 and the lightly doped drift zone band 131.

[0098] The heavily doped shielding regions 140 separate the source regions 110, the body regions 120 and the current spreading regions 137 from adjacent trench gate structures 150. The vertical extension of the shielding regions 140 can be greater than the vertical extension of the trench gate structures 150.

[0099] Each body region 120 is formed directly under one source region 110. A first body portion 121 of the body region 120 directly adjoins the shield region 140 and is spaced apart from the trench gate structure 150. A second body portion 122 of the body region 120 is located between the first body portion 121 and the trench gate structure 150. A maximum net dopant concentration pi in the first body portion 121 is greater than at least twice a maximum net dopant concentration po, for example, in the second body portion 122. For example, the maximum net dopant concentration pi in the first body portion 121 can be at least ten times greater than the maximum net dopant concentration po in the second body portion 122.

[0100] In Figure 2A and Figure 2B The angled implant forms at least a portion of the first body portion 121.

[0101] Figure 2A A body layer 720 is shown between the first surface 101 and the current spreading region 137. The body layer 720 can directly adjoin the current spreading region 137. The body layer 720 can also be formed between the body contact region 126 and the deep shield portion 148, which laterally separates adjacent current spreading regions 137. The body layer 720 can be formed as a laterally continuous layer. Forming the body layer 720 can include an unmasked implant, p-type epitaxy, or a combination of the two. Between adjacent body contact regions 126, a source region band 210 can be located between the first surface 101 and the body layer 720.

[0102] The body enhancement implant mask 450 includes openings 455 that exclusively expose the body contact regions 126. In other words, the body enhancement implant mask 450 completely covers the source region bands 210, where n-doped source regions can have already been formed or can be formed at a later stage.

[0103] The body enhancement implant mask 450 can mask one, two, or more implants at different implant energies, where the implants can be performed at different implant angles. For example, a first orthogonal implant at a first implant energy can form a doped first local region 141 proximate to the first surface 101. A second orthogonal implant at a second implant energy can form a doped second local region 142 at a greater distance from the first surface 101. The second local region 142 can be in contact with or can overlap the deep shield portion 148.

[0104] An oblique implant with an implant axis 451 tilted by an implant angle β to the vertical direction 104 and an implant energy greater than the first implant energy and less than the second implant energy can form a doped third local region 143 between the first local region 141 and the second local region 142. Due to the implant angle β, the third implant region 143 is formed asymmetrically with respect to the center of the opening 455 in the body-enhanced implant mask 450.

[0105] A deep implant can be used to mask a further implant of p-type dopants at a higher implant energy to form a deep screening portion 148, which can use an implant mask 450 that is an implant mask from which the body-enhanced implant mask 450 is derived, e.g., by lateral recessing, or an implant mask derived from the body-enhanced implant mask 450, e.g., by lateral recessing. The deep screening portion 148 can be formed before or after the first local region 141, the second local region 142, and the third local region 143 are formed. The body-enhanced implant mask 450 can be removed, and the trench gate structure 150 can be formed as described with respect to Figures 1A-1B

[0106] Figure 2B A body region 120 is shown in a case where a protrusion is formed in the first body region 121 that extends from the screening region 140 into the body region 120, where the maximum lateral extension of the protrusion can be positioned at a distance from the source region 110, at a distance from the drift structure 130, or spaced apart from both. Below the body contact region 126, the first local region 141, the second local region 142, and the third local region 143, as well as the deep screening portion 148 form a continuous screening region 140 as described above.

[0107] Figures 3A-3C A method is described that involves forming a body-enhanced implant mask by recessing a previously used implant mask in the lateral direction.

[0108] Figure 3A A silicon carbide body 100 is shown with a lightly n-doped drift zone 131 and a p-doped body layer 720. N-doped current spreading regions 137 can extend from the body layer 720 into the drift zone 131. P-doped deep screening portions 148 can separate adjacent current spreading regions 137 in the lateral direction. A heavily n-doped source layer 710 can be formed between the first surface 101 and the body layer 720. The source layer 710 and / or the deep screening portions 148 can also be formed at a later stage.

[0109] ​A body contact implantation mask 430 is formed on the first surface 101. The body contact implantation mask 430 includes a mask opening 435 having a first mask opening width mw1. The mask opening 435 has a longitudinal extension perpendicular to the cross-sectional plane and is formed above the deep shielding portion 148. P-type dopants are implanted with a relatively low implantation energy and a relatively high implantation dose to form doped first local regions 141 along the first surface 101, wherein the first local regions 141 will later form a contact region for the shielding region and / or the body region 120.

[0110] The implantation may be vertical or only slightly tilted to the vertical direction 104 , for example at an implantation angle of less than 3° in absolute value. At least one further orthogonal implantation or only slightly tilted implantation may be performed at a higher implantation energy to form the doped buried local region 145 .

[0111] The heavily doped first local region 141 directly adjoins the body contact region 126 of the first surface 101. The dopant concentration of the first local region 141 is high enough to form a low-resistance ohmic contact between the first local region 141 and a metal structure formed on the first surface 101 at a later stage.

[0112] A further orthogonal or only slightly tilted implant can form a buried local region 145 approximately in the vertical projection of the first local region 141. As shown, the buried local region 145 can be spaced apart from the first local region 141 or can be in contact with the first local region 141. The buried local region 145 can extend into the deep shield portion 148. Due to the lateral bias of the implanted ions, the lateral extension of the buried local region 145 can increase with increasing distance from the first surface 101. The portion of the source layer 710 covered by the body contact implantation mask 430 forms the source region 110.

[0113] Figure 3B Shown by Figure 3A The body contact implantation mask 430 is recessed in the lateral direction to form a body enhancement implantation mask 450, wherein the third mask opening width mw3 of the stripe-shaped opening 455 in the body enhancement implantation mask 450 is greater than Figure 3A The first mask opening width mw2.

[0114] For example, you can use Figure 3B The body contact implant mask 430 is laterally recessed by wet etching to form a body enhancement implant mask 450. In addition to the body contact region 126, the opening 455 also exposes the second source portion 212 of the source region 110, wherein the second source portion 212 directly adjoins the body contact region 126.

[0115] The body-enhanced implant mask 450 includes a mask strip 456 having a width w3. The mask strip 456 covers the first source portion 211 of the source region 110. The p-type dopant is implanted through the opening 455 along an implant axis that is tilted to the vertical direction 104 by an implant angle that is at least 3° or even at least 10° in absolute value. The p-type dopant can be implanted at one, two or more different implant energies that cause an implant peak at a distance from the first surface 101 and between the source region 110 and the current spreading region 137. The implanted dopant forms the first body portion 121 in the body layer 720. Figure 3A The section of the body layer 720 under the source region 110 and not affected by the tilted implant forms the second body portion 122 of the body region 120.

[0116] Under the body contact region 126, Figure 3A the first local region 141, Figure 3A the buried local region 145, Figure 3A the deep shield portion 148, and the dopant implanted directly under the body contact region 126 by the tilted implant form a continuous shield region 140. Along a vertical line, the dopant type of the shield region 140 is continuously p-type. The net dopant concentration along a vertical line can include several local maxima and minima.

[0117] The process can continue to form the trench gate structure 150 as described with reference to the previous figures.

[0118] As shown in Figure 3C the lateral extension of the first body portion 121 is defined by Figure 3B the width of the second source portion 212, the implant angle of the tilted implant(s), and the implant energy of the tilted implant(s).

[0119] Figures 4A-4D A method is illustrated that uses one single lithography process to define different doped regions of the same conductivity type at the front side of a silicon carbide device.

[0120] Figure 4A A silicon carbide body 100 is shown with a drift region zone 131 that is lightly n-doped. An n-doped current spreading layer 737 is located between the first surface 101 and the drift region zone 131 and in contact with the drift region zone 131. The body layer 720 between the first surface 101 and the current spreading layer 737 can be in direct contact with the current spreading layer 737. The source layer 710 between the first surface 101 and the body layer 720 can be in direct contact with the body layer 720 and the first surface 101.

[0121] A body contact implantation mask 430 is formed on the first surface 101. Figure 3A As depicted, p-type dopants are implanted through the mask opening 435 having the first mask opening width mw1.

[0122] Figure 4A A heavily doped first local region 141 in contact with the body contact region 126 and a doped buried local region 145 which may extend into the current spreading layer 737 are shown.

[0123] A deep implantation mask 440 may be formed on the first surface 101, wherein the second mask opening width mw2 of the stripe-shaped second mask opening 445 in the deep implantation mask 440 is greater than Figure 4A The first mask opening width mw1.

[0124] For example, you can use Figure 4A The body contact implant mask 430 is recessed at least laterally to form a deep implant mask 440. In addition to the body contact region 126, the second mask opening 445 also exposes the fourth source portion 214 of the source zone 210, wherein the fourth source portion 214 is directly adjacent to the body contact region 126. Sections of the deep implant mask 440 cover the third source portion 213 of the source zone 210. P-type dopants are implanted through the second mask opening 445 to form a heavily doped deep shielding portion 148 in the current spreading layer 737.

[0125] according to Figure 4B , each deep shield portion 148 may extend from the body layer 720 to the drift zone 131 . Figure 4A The portion of the current spreading layer 737 between adjacent deep shielding portions 148 forms an n-doped current spreading region 137. According to another example, the deep shielding portion 148 is kept spaced apart from the drift zone 131, and Figure 4B A remnant of the current spreading layer 737 may remain between the deep shield portion 148 and the drift zone 131 .

[0126] Figure 4B The deep implantation mask 440 can be used as a reference Figures 2A-2B Such a body enhancement implant mask 450 is described.

[0127] Alternatively, as in Figure 4C As shown in the figure, by using Figure 4B The deep implantation mask 440 is further recessed in the lateral direction to form a body enhancement implantation mask 450, wherein the third mask opening width mw3 of the stripe-shaped opening 455 in the body enhancement implantation mask 450 is greater than Figure 4B The second mask opening width mw2.

[0128] For example, you can useFigure 4B The deep implant mask 440 is at least recessed in lateral direction to form a body enhancement implant mask 450. The openings 455 expose the second source portion 212 in addition to the body contact region 126, wherein the second source portion 212 directly adjoins the body contact region 126 and is wider than the first source portion 211. Figure 4B The section of the body enhancement implant mask 450 covers the first source portion 211. The p-type dopants are implanted through the openings 435, wherein the implant axis is tilted with respect to the vertical direction 104. The p-type dopants can be implanted at one, two or more different implant energies.

[0129] below the body contact region 126, Figure 4C the first local region 141, Figure 4C the buried local region 145, Figure 4C the deep shield portion 148 of the shield region 140 and the dopants of the tilted implant directly implanted below the body contact region 126 form a continuous shield region 140 as described above. The process can continue to form the trench gate structure 150 as described with reference to the previous figures.

[0130] Figure 4D The body region 120 is shown with a first body region 121 forming a wide protrusion into the body region 120 from the shield region 140 over at least 50% of the lateral width of the source region 110 in direction towards the trench gate structure 150. The maximum lateral extension of the protrusion can be positioned at a distance from the source region 110, at a distance from the drift structure 130 or spaced apart from both.

[0131] The methods as described with any one of Figure 1A and Figure 1B , Figure 2A and Figure 2B , Figures 3A-3C and Figures 4A-4D may be used to form any silicon carbide device 500 as described with reference to Figure 5A and Figure 5B , Figure 6A and Figure 6B and Figure 6E and Figure 6F . Any silicon carbide device 500 described with reference to Figure 5A and Figure 5B , Figure 6A and Figure 6B , and Figure 6E and Figure 6F may be formed by reference to Figure 1A and Figure 1B , Figure 2A and Figure 2B , Figures 3A-3C , andFigures 4A-4D obtained by any of the methods described.

[0132] Figure 5A and Figure 5B relate to a silicon carbide device 500 comprising a transistor cell TC. The silicon carbide device 500 comprises a silicon carbide body 100 which can be embodied as described above with respect to Figures 1A-4D the silicon carbide body 100.

[0133] The transistor cell TC is formed along a trench gate structure 150 in a strip shape extending into the silicon carbide body 100 from the first surface 101. The trench gate structure 150 can be a long strip extending along a longitudinal direction through an active region of the silicon carbide device 500. In other embodiments, the trench gate structure 150 can be hexagonal or square, for example. The portions of the silicon carbide body 100 between adjacent trench gate structures 150 form SiC mesas.

[0134] The drift structure 130 can comprise a lightly doped drift zone 131 of the first conductivity type and a heavily doped contact portion 139 of the first conductivity type between the drift zone 131 and the second surface 102.

[0135] The heavily doped contact portion 139 can be or can comprise a substrate portion obtained from a crystal ingot or can comprise a heavily doped portion of a layer formed by epitaxy. Along the second surface 102, the dopant concentration in the contact portion 139 is sufficiently high to ensure a low resistance ohmic contact between the contact portion 139 and the second load electrode 320.

[0136] The drift zone 131 can be formed in a layer grown by epitaxy. The average net dopant concentration in the drift zone 131 can be in the range from 1E15 cm -3 to 5E16 cm -3 . The drift zone 131 can directly adjoin the contact portion 139. Alternatively, a buffer layer forming a unipolar junction with the drift zone 131 can be located between the drift zone 131 and the contact portion 139, wherein the vertical extension of the buffer layer can be about 1 pm and wherein the average dopant concentration in the buffer layer can be in the range from 3E17 cm -3 to 1E18 cm -3 by way of example.

[0137] The trench gate structure 150 extending into the silicon carbide body 100 from the first surface 101 comprises a conductive gate electrode 155 which can comprise or consist of a heavily doped polysilicon layer and / or a metal-containing layer. The gate electrode 155 can be electrically connected to a gate metallization forming a gate terminal or being electrically connected or coupled to a gate terminal.

[0138] The gate dielectric 159 separates the gate electrode 155 from the silicon carbide body 100 along at least one side of the trench gate structure 150. The gate dielectric 159 can comprise or consist of thermally grown or deposited silicon oxide, silicon nitride, silicon oxynitride, another deposited dielectric material, or any combination thereof. The thickness of the gate dielectric 159 can be chosen to obtain a transistor cell TC having a threshold voltage in the range from 1.0 V to 8 V. The trench gate structure 150 can exclusively comprise the gate electrode 155 and the gate dielectric 159, or can comprise further conductive and / or dielectric structures in addition to the gate electrode 155 and the gate dielectric 159.

[0139] The trench gate structure 150 is bar-shaped. That is: the length of the trench gate structure 150 along a first lateral direction is greater than the width of the trench gate structure 150 along a second lateral direction orthogonal to the first direction.

[0140] The trench gate structures 150 can be equally spaced, can have equal widths, and can form a regular bar pattern, wherein the center-to-center distance between the trench gate structures 150 can be in the range from 1 pm to 10 pm, for example in the range from 2 pm to 5 pm. The length of the trench gate structures 150 can amount to several millimeters. The vertical extension of the trench gate structures 150 can be in the range from 0.3 pm to 5 pm, for example in the range from 0.5 pm to 2 pm. At the bottom, the trench gate structures 150 can be rounded.

[0141] The opposite sidewalls of each trench gate structure 150 can essentially extend along the vertical direction 104, or can be tilted with respect to the vertical direction 104 by a tapering angle. In the latter case, the trench gate structure 150 can taper as the distance to the first surface 101 increases. The tapering angle between the sidewall and the vertical direction 104 at the first surface can be chosen according to the alignment of the crystal axis and / or according to the off-axis angle. For example, the absolute value of the tapering angle between the first sidewall and the vertical direction can deviate by no more than ±1° from the absolute value of the off-axis angle (for example, in the case of 4H-SiC, it can be in the range from at least 3° to at most 5°). However, the tapering angle can be oriented opposite to the off-axis angle. The tapering angle between the second sidewall opposite to the first sidewall and the vertical direction can be oriented opposite to the tapering angle of the first sidewall. The greater the tapering angle, the more the trench gate structure 150 narrows from the first surface.

[0142] Generally, at least the first sidewall of the trench gate structure 150 can run essentially along a crystal plane of the silicon carbide body where the charge carrier mobility is high, for example one of the {11-20} crystal plane or the {1-100} crystal plane. The first sidewall can be an active sidewall, that is, a channel region can run along the first sidewall. In some embodiments, the second sidewall can also be an active sidewall (for example, in case of a vertical trench gate structure 150). In other embodiments, the second sidewall can be a non-active sidewall.

[0143] Each SiC mesa between adjacent trench gate structures 150 comprises at least a portion of the source region 110, the body region 120 and the shield region 140. The source region 110 is between the first surface 100 and the body region 120 and in direct contact with the active sidewall 151 of the trench gate structure 150.

[0144] The body region 120 separates the source region 110 and the drift structure 130. 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. The body region 120 directly adjoins the active sidewall 151 of the first trench gate structure 150. The vertical extension of the body region 120 corresponds to the channel length of the transistor cell TC and can be in the range from 0.2 pm to 1.5 pm.

[0145] The first load electrode 310 at the front side of the silicon carbide body 100 is electrically connected with the source region 110 and the body region 120. A strip-shaped portion of the interlayer dielectric 250 separates the first load electrode 310 from the gate electrode 155 in the trench gate structure 150. The first load electrode 310 can form or can be electrically connected or coupled to a first load terminal, which can be an anode terminal of the MCD or a source terminal S of the MOSFET.

[0146] A second load electrode 320 forming a low-resistance ohmic contact with the contact portion 139 can form or can be electrically connected or coupled to a second load terminal, which can be a cathode terminal of the MCD or a drain terminal D of the MOSFET.

[0147] A first portion of the shield region 140 is arranged between the body region 120 and the non-active sidewall 152 of the trench gate structure 150. A second portion of the shield region 140 can vertically overlap with the second trench gate structure 150. In other words, the second portion of the shield region 140 is directly formed underneath the trench gate structure 150, for example, between the trench gate structure 150 and the second surface 102. The shield region 140 is electrically connected to or coupled to the first load electrode 310.

[0148] The maximum dopant concentration in the shielding region 140 can be higher than the maximum dopant concentration in the body region 120. The vertical dopant concentration profile in the shielding region 140 can have a local maximum at a location below the trench gate structure 150. Along the inactive sidewalls 152, the dopant concentration in the shielding region 140 can be higher, i.e., at least ten times higher, than the dopant concentration along the active sidewalls 151 in the body region 120.

[0149] The shielding region 140 and the drift structure 130 form a third pn junction pn3, which can provide an integrated freewheeling diode function for the silicon carbide device 500. In addition, in the blocking state of the silicon carbide device 500, the second portion of the shielding region 140 below the trench gate structure 150 can shield the active portion of the gate dielectric 159 along the active sidewall 151 from the potential applied to the second load electrode 320.

[0150] The illustrated silicon carbide device 500 is an n-channel SiC-TMOSFET, wherein the first load electrode 310 forms or is electrically connected to or coupled to the source terminal S, and wherein the second load electrode 320 forms or is electrically connected to or coupled to the drain terminal D. The silicon carbide device 500 includes a plurality of transistor cells TC and a plurality of trench gate structures 150, as shown in FIG. Figure 5A As shown in FIG, the trench gate structure 150 is in the shape of a bar, with a longitudinal axis orthogonal to the cross-sectional plane.

[0151] The body region 120 of the transistor cell TC includes a first body portion 121 and a second body portion 122 separating the first body portion 121 from the adjacent trench gate structure 150 .

[0152] Figure 5B Shown along the pass Figure 5A Figure 4 illustrates a horizontal dopant gradient 420 along line BB of the body region 120. On the abscissa, x1 denotes the location of the lateral pn junction between the source region 110 and the shield region 140. x2 indicates the location of the unipolar junction between the first and second body portions. x2 marks the location of the active sidewalls. w3 denotes the lateral extension of the transition region 423 between the first and second body portions.

[0153] The horizontal dopant gradient 420 through the bulk region 120 comprises a first section 421 in which the horizontal dopant gradient is approximately constant and a second section 422 in which the horizontal dopant gradient is approximately constant but significantly lower compared to the first section 421. The first section 421 corresponds to the first bulk portion 121 and directly adjoins the shield region 140. The second section 422 corresponds to the second bulk portion 122 and directly adjoins the trench gate structure 150. In a horizontal plane defined by the cross-sectional line B-B, the horizontal extension wl of the first bulk portion 121 is at least 20% of the total horizontal extension wO of the bulk region 120.

[0154] The average dopant concentration Nl in the first section 421 is at least ten times higher than the average dopant concentration N2 in the second section 422. Within a transition region 423 between the first bulk portion and the second bulk portion, the average dopant concentration Nl in the first section 421 is reduced to the average dopant concentration N2 in the second section 422. The transition region 423 can start at 90% of the average net dopant concentration of the first bulk portion and end at 110% of the reference dopant concentration and / or the average net dopant concentration of the second bulk portion. The reduction of the average dopant concentration within the transition region 423 can be relatively steep. The lateral extension w3 of the transition region can be significantly smaller than the lateral extension of the source region 110. The average dopant concentration Nl in the first bulk portion 121 can be equal or approximately equal to the dopant concentration in the directly adjoining portion of the shield region 140.

[0155] Figure 6A and Figure 6B Corresponding cross-sectional views of a portion of a silicon carbide bulk 900 according to a comparative example and a portion of a silicon carbide bulk 100 according to an embodiment are shown.

[0156] Figure 6A The comparative silicon carbide bulk 900 shows a bulk region 120 which is laterally almost uniformly doped under the source region 110. In Figure 6B In the silicon carbide bulk 100, the bulk region 120 comprises a significantly, relatively heavily doped first bulk portion 121 and a relatively lightly doped second bulk portion 122 between the first bulk portion 121 and the trench gate structure 150. The first bulk portion 121 extends over more than 50% of the lateral extension of the source region 110.

[0157] In Figure 6C The dashed line shows the horizontal dopant profile 601 along the line C-C of Figure 6A The solid line shows the horizontal dopant profile 602 along the line C-C of Figure 6B In the horizontal plane defined by the cross-sectional line B-B, xl designates the position of the lateral pn junction between the bulk contact region 126 and the source region 110, x12 isFigure 6A the junction between the shield region 140 and the body region 120 in Figure 6B the location of the unipolar junction between the first body portion 121 and the second body portion 122 in

[0158] The dopant concentration N1 along the interface to the shield region 140 can for example be in the range from 1 E+17 cm -3 to 1 E+19 cm -3 for example in the range from 1 E+18 cm -3 to 5 E+18 cm -3 The dopant concentration of the second body portion 122 along the trench gate structure 150 can be at least one order of magnitude lower compared to in the shield region 140. The region between the line 601 and the line 602 represents additional charge that can be used to compensate for the charge of the static charge carriers in the depletion region formed in the blocking mode.

[0159] In Figure 6D the dashed line shows the vertical dopant profile 611 along the line D-D of Figure 6A and the solid line shows the vertical dopant profile 612 along the line D-D of Figure 6B In the abscissa, y2 marks the location of the pn-junction between the source region 110 and the body region 120 in Figure 6A and y4 marks the location of the pn-junction between the body region 120 and the current spreading region 137 in Figure 6A y1 marks the location of the pn-junction between the source region 110 and the first body portion 121 in Figure 6B and y3 marks the location of the pn-junction between the first body portion 121 and the current spreading region 137 in Figure 6B

[0160] In the silicon carbide body 100 of Figure 6B a first body portion 121 is formed with a relatively constant vertical dopant profile 612 that shows a variation of the dopant from the maximum value of less than 50% across at least 60% of the vertical extension of the body region 120, using two implants at different implant energies. The average vertical extension of the first body portion 121 between y1 and y4 can be greater than the maximum vertical extension of the second body portion 122.

[0161] Figure 6E and Figure 6F show the boundaries 621, 622 of the depletion region formed in the blocking mode of the silicon carbide device 500 of Figure 6A and Figure 6B

[0162] ​​In Figure 6A the majority of the body region 120 depleted in the comparative example is not depleted in the silicon carbide body 100 of Figure 6B such that less static charge carriers need to be compensated by electrons that reduce the barrier height at the gate dielectric 159.

Claims

1. A method of manufacturing a silicon carbide device, the method comprising: providing a silicon carbide body, forming a trench gate structure extending into the silicon carbide body from a first surface, forming a body region and a source region zone, wherein after forming the trench gate structure, the body region and the source region zone are in contact with an active sidewall of the trench gate structure, wherein the source region zone is located between the body region and the first surface, forming a body boost implantation mask on the first surface, wherein the body boost implantation mask covers at least a first source portion of the source region zone, wherein an opening in the body boost implantation mask exposes at least a body contact region of the first surface, wherein the first source portion is adjacent to the active sidewall, implanting a dopant into a first body portion of the body region through the opening in the body boost implantation mask, wherein the first body portion is located directly below the source region zone and away from the active sidewall, wherein in at least one horizontal plane, a dopant concentration in the first body portion is at least 150% of a reference dopant concentration in the body region at the active sidewall, and a horizontal extension of the first body portion is at least 20% of a total horizontal extension of the body region, and forming a shield region of a conductivity type of the body region, and the shield region extending into the silicon carbide body from the first surface, wherein the shield region is directly adjacent to the source region and the body region in a lateral direction, and wherein the shield region is in contact with a non-active sidewall of a further trench gate structure, wherein a lateral dopant profile in a portion of the shield region directly adjacent to the first body portion deviates from the dopant concentration in the first body portion by no more than ±10% in the at least one horizontal plane.

2. The method according to claim 1, wherein implanting a dopant into the first body portion before forming the trench gate structure.

3. The method according to claim 1, wherein, an implantation axis for implanting the dopant into the first body portion is tilted with respect to a vertical direction of the first surface, and wherein the dopant is directed in a direction of the active sidewall of the trench gate structure.

4. The method according to claim 3, wherein: an implantation angle between the implantation axis and the vertical direction is at least 3° in absolute value.

5. The method according to claim 1, wherein the body contact region is directly adjacent to the source region zone in the lateral direction.

6. The method according to claim 1, wherein: the opening in the body boost implantation mask exposes a second source portion of the source region zone, and wherein the second source portion is located between the body contact region and the first source portion.

7. The method according to claim 1, further comprising: forming a body contact implantation mask on the first surface, wherein the body contact implantation mask covers the source region zone, wherein an opening in the body contact implantation mask exposes the body contact region, implanting a dopant of the conductivity type of the body region through the opening in the body contact implantation mask, and recessing the body contact implantation mask in the lateral direction, wherein the recessed body contact implantation mask forms the body boost implantation mask.

8. The method according to claim 1, further comprising: forming a deep implant mask on the first surface, wherein the deep implant mask covers the third source portion of the source zone, wherein an opening in the deep implant mask exposes the fourth source portion of the source zone, wherein the fourth source portion is located between the body contact region and the third source portion, and implanting dopants of the conductivity type of the body region through the opening in the deep implant mask.

9. The method of claim 8, further comprising: recessing the deep implant mask in the lateral direction, wherein the recessed deep implant mask forms a body boost implant mask.

10. The method of claim 8, further comprising: forming a body contact implant mask on the first surface, wherein the body contact implant mask covers the source zone, and wherein an opening in the body contact implant mask exposes the body contact region, implanting dopants of the conductivity type of the body region through the opening in the body contact implant mask, and recessing the body contact implant mask in the lateral direction to provide a recessed body contact implant mask, wherein the recessed body contact implant mask forms the deep implant mask.

11. The method of claim 1, further comprising: implanting dopants of a conductivity type complementary to the conductivity type of the body region into the source zone to form a doped source region in the source zone.

12. The method of claim 1, wherein in the at least one horizontal plane, a horizontal extension of the first body portion is at least 50% of a total horizontal extension of the body region.

13. A silicon carbide device, comprising: a silicon carbide body comprising: a trench gate structure extending from a first surface into the silicon carbide body; a body region in contact with an active sidewall of the trench gate structure; a source region in contact with the active sidewall, wherein the source region is located between the body region and the first surface; and a shield region of a conductivity type of the body region, wherein the shield region extends from the first surface into the silicon carbide body, wherein the shield region directly adjoins the source region and the body region in the lateral direction, and wherein the shield region is in contact with a non-active sidewall of a further trench gate structure, and wherein the body region comprises a first body portion directly below the source region and away from the active sidewall, and wherein in at least one horizontal plane parallel to the first surface, a dopant concentration in the first body portion is at least 150% of a reference dopant concentration in the body region in the horizontal plane at the active sidewall, and a horizontal extension of the first body portion is at least 20% of a total horizontal extension of the body region, wherein in the at least one horizontal plane, a lateral dopant profile in a portion of the shield region directly adjoining the first body portion deviates from the dopant concentration in the first body portion by no more than ±10%.

14. The silicon carbide device of claim 13, wherein in the at least one horizontal plane, a horizontal extension of the first body portion is at least 50% of a total horizontal extension of the body region.

15. The silicon carbide device of claim 13, wherein the first body portion is formed by a masked angled implant.

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