Method of manufacturing silicon carbide devices and wafer composite comprising laser modified zones in a handle substrate

Abstract

A method for manufacturing a silicon carbide device and a wafer complex including a laser modification zone in a handle substrate are disclosed. The wafer complex (900) includes a handle substrate (100), an auxiliary layer (200) formed on a first main surface (101) of the handle substrate (100), and a silicon carbide structure (320) formed on the auxiliary layer (200). The handle substrate (100) is subjected to laser irradiation, wherein the laser irradiation modifies the crystalline material along a focal plane (105) in the handle substrate (100). The focal plane (105) is parallel to the first main surface (101). The auxiliary layer (200) is adapted to prevent the propagation of microcracks (156) that may be generated in the handle substrate (100) by the laser irradiation.

Description

Technical Field

[0001] Examples of the present disclosure relate to a method of manufacturing a silicon carbide device, wherein the method includes laser irradiating a handle substrate. Further examples relate to a wafer composite having modification zones in separation zones of the handle substrate. Background Art

[0002] Semiconductor wafer preparation typically involves forming an ingot by vertical zone melting or by pulling a seed crystal rod from a crucible filled with molten semiconductor material. The ingot is sliced, for example, by sawing. Other processes produce epitaxial semiconductor wafers by forming a thin release layer on or near the top of a reusable handle wafer, epitaxially growing a semiconductor layer on the release layer, and then mechanically separating the epitaxially grown semiconductor layer from the handle wafer along the release layer.

[0003] There is a need for improved methods of providing substrates for silicon carbide devices in an economical manner. Summary of the Invention

[0004] Embodiments of the present disclosure relate to a method for manufacturing a silicon carbide device. The method includes providing a wafer composite comprising a handle substrate, an auxiliary layer, and a silicon carbide structure. The auxiliary layer is formed on a first main surface of the handle substrate. The silicon carbide structure is formed on the auxiliary layer. The handle substrate is subjected to laser irradiation. The laser irradiation modifies crystalline material in the handle substrate along a focal plane. The focal plane is parallel to the main surface. The auxiliary layer is adapted to prevent the propagation of microcracks generated in the handle substrate by the laser irradiation.

[0005] Another embodiment of the present disclosure relates to a wafer composite comprising a handling substrate, an auxiliary layer, and a silicon carbide structure. The handling substrate comprises a modification zone embedded in crystalline silicon carbide. The modification zone is arranged in a separation zone, wherein the separation zone extends parallel to a first major surface of the handling substrate. The auxiliary layer is formed on the first surface of the handling substrate. In the handling substrate, microcracks extend from the modification zone to the auxiliary layer and terminate at the auxiliary layer. The silicon carbide structure is formed on the auxiliary layer.

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

[0007] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated into and constitute a part of this specification. The drawings illustrate embodiments of a wafer composite and an embodiment of a method of manufacturing a silicon carbide device and, together with the description, serve to explain the principles of the embodiments. Further embodiments are described in the following detailed description and claims.

[0008] Figures 1A to 1C A schematic vertical cross-sectional view of a wafer composite is shown for illustrating a silicon carbide device manufacturing method according to an embodiment, the method comprising laser processing in a focal plane close to a first main surface of a handle substrate.

[0009] Figure 2A A schematic vertical cross-sectional view showing a portion of a silicon carbide substrate having modified zones formed by laser irradiation for discussing the effects of the embodiment is shown.

[0010] Figure 2B A schematic vertical cross-sectional view of a portion of a wafer composite having an auxiliary layer in a handle substrate and having modification zones is shown for discussing the effects of embodiments.

[0011] Figures 3A to 3F A schematic vertical cross-sectional view of a donor substrate, a handle substrate, and a wafer composite is shown for illustrating a silicon carbide device manufacturing method according to an embodiment using an auxiliary layer for bonding.

[0012] Figures 4A to 4E A schematic vertical cross-sectional view of a donor substrate, a handle substrate, and a wafer composite is shown for illustrating a silicon carbide device manufacturing method according to an embodiment using an intermediate layer.

[0013] Figure 5 It is used for discussion Figures 4A to 4E Schematic vertical cross-sectional view of a portion of a wafer complex illustrating the effects of an embodiment. DETAILED DESCRIPTION

[0014] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and in which are shown by way of illustration specific embodiments in which the wafer composite and the method of manufacturing a silicon carbide 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 with respect to one embodiment may be used on or in conjunction with other embodiments to produce still further embodiments. It is intended that the present disclosure include such modifications and variations. 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. Unless otherwise stated, corresponding elements are represented by the same reference numerals in different drawings.

[0015] The terms "having," "comprising," "including," and "comprising" are open ended and indicate the presence of stated structures, elements, or features, but do not preclude the presence of additional elements or features. The quantifiers "a," "an," and the pronoun "the" are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

[0016] Ranges given for physical dimensions include the bounding values. For example, a range from a to b for parameter y is read as a≤y≤b. The same applies to ranges with a bounding value such as "at most" and "at least."

[0017] The main components of a layer or structure from a chemical composition or alloy are such elements, the atoms of which form the chemical composition or alloy.For example, silicon (Si) and carbon (C) are the main components of a silicon carbide (SiC) layer.

[0018] The term “on” should not be interpreted as meaning only “directly on.” Rather, if an element is “on” another element (e.g., one layer is “on” another layer or is “on” a substrate), a further component (e.g., a further layer) may be located between the two elements (e.g., a further layer may be located between a layer and the substrate if the further layer is “on” the substrate).

[0019] According to an embodiment, a method of manufacturing a silicon carbide device includes providing a wafer composite, wherein the wafer composite may include a handle substrate, an auxiliary layer formed on the handle substrate, and a silicon carbide structure formed over the auxiliary layer.

[0020] The handling substrate may be a crystalline silicon carbide substrate, or may include a crystalline silicon carbide substrate. For example, the silicon carbide crystal of the handling substrate may have a hexagonal polytype, such as 4H or 6H. The handling substrate may be uniformly doped, or may include differently doped SiC layer portions. The handling substrate may include one or more layers of another material having a melting point close to or higher than that of the crystalline silicon carbide. For example, the layer of another material may be embedded in the crystalline silicon carbide substrate.

[0021] The handling substrate can have two substantially parallel major surfaces of identical shape and size, and a lateral surface area connecting the edges of the two major surfaces. For example, the handling substrate can be a rectangular prism with or without rounded edges, or a right circular cylinder or a slightly skewed cylinder (e.g., wherein the side surfaces are inclined at an angle of at most 8°, at most 5°, or at most 3°), with or without one or more flat surfaces or indentations along the outer circumference.

[0022] The handle substrate and / or wafer composite structure may extend laterally in a plane spanned by a transverse direction (also referred to as a "horizontal direction"). Perpendicular to the transverse direction, in a vertical direction, the handle substrate and / or wafer composite structure may have a thickness that is smaller than the corresponding extension of the handle substrate and / or wafer composite structure in the transverse direction. The transverse direction may run parallel to the main surfaces or may enclose an angle of at most 10°, at most 8°, or at most 5° with at least one of the main surfaces.

[0023] The auxiliary layer may be formed directly on the first major surface of the disposal substrate. The auxiliary layer may be adapted to prevent the propagation of microcracks in the disposal substrate. To this end, the auxiliary layer and the disposal substrate may have different crystal properties. For example, the auxiliary layer and the disposal substrate may be crystalline materials with different lattice constants. In other embodiments, the auxiliary layer and the disposal substrate may comprise or consist of different polytypes of the same semiconductor material, or may even comprise or consist of different materials. For example, the auxiliary layer and the disposal substrate may differ in at least one major component.

[0024] The silicon carbide structure may be formed on (e.g., directly on) a surface of the auxiliary layer on a side opposite to the handle substrate. The horizontal cross-sectional area of ​​the auxiliary layer and the silicon carbide structure may be equal to or approximately equal to the horizontal cross-sectional area of ​​the handle substrate in size and shape.

[0025] The silicon carbide structure may include one or more differently doped single-crystal SiC sub-layers. In the one or more SiC sub-layers, doped regions of functional elements such as diodes and / or transistors may be formed.

[0026] The handle substrate is subjected to laser irradiation. The laser irradiation can modify the crystalline SiC material along a focal plane in the handle substrate. The focal plane is parallel to the first major surface. The modified single-crystalline material can form laterally separated modified zones embedded in unmodified crystalline SiC material, for example, in unmodified single-crystalline SiC material.

[0027] The modified zone may include silicon carbide in a different crystalline phase than the unmodified SiC material, the modified zone may include silicon carbide having a different polytype than the unmodified SiC material, and / or the modified zone may include decomposed silicon and carbon.

[0028] The formation of modified zones may exert mechanical stress on the surrounding crystalline SiC material. For example, the partial decomposition of SiC presenting silicon and carbon may cause a temporary volume expansion of the decomposed components. The resulting mechanical stress may generate crystal lattice defects (so-called microcracks or cracks). At least some of the lattice defects may propagate along the main crystal planes, such as along the lattice planes in 4H-SiC. <0001> Crystalline plane (c-plane) propagation.

[0029] The c-plane can be tilted relative to the focal plane by an off-axis angle α, for example, in the range of 2° to 8°, for example, by approximately 4°. By applying a moderate mechanical or thermomechanical stress, microcracks extending along parallel c-planes can be promoted to facilitate cleavage of the wafer composite along a jagged fracture surface around the focal plane, wherein the fracture surface includes a section of the c-plane having microcracks.

[0030] Typically, cracks and microcracks propagate much deeper into the surrounding single-crystal material than is required for a reliable and reproducible separation process along the fracture surface. The maximum length of a microcrack along the c-plane multiplied by the sine of the off-axis angle α between the c-plane and the horizontal plane determines the vertical extension of the separation zone. The separation zone includes the vertical section of the treated substrate that includes the microcrack.

[0031] The auxiliary layer can be adapted to prevent the propagation of microcracks. To this end, the distance between the focal plane and the auxiliary layer can be sufficiently small so that microcracks generated in the focal plane and / or close to the focal plane due to laser irradiation can reach the auxiliary layer. The auxiliary layer can prevent the propagation of cracks and microcracks in the direction of the silicon carbide portion. The auxiliary layer can protect the silicon carbide portion from lattice defects caused by laser irradiation and can reduce the portion of crystalline silicon carbide affected by laser irradiation.

[0032] According to an embodiment, the wafer complex can be split along a focal plane. The splitting process can include applying moderate mechanical shear stresses, thermomechanical stresses and / or sound waves, such as ultrasound, to the wafer complex. The splitting does not follow exactly the focal plane, but rather follows a fracture surface having segments on both sides of the focal plane. The focal plane approximates a flat average plane of the fracture surface. The fracture surface can be serrated (also called saw-toothed or ribbed). Parallel surface segments that are offset relative to each other can construct the serrated shape. The main part of the surface segments of the fracture surface can be c-planes, wherein the surface segments are inclined with respect to the horizontal focal plane.

[0033] The cleaving process can separate the epitaxial wafer from the recovered portion of the treated substrate. The epitaxial wafer can include the silicon carbide structure, the auxiliary layer, and a first residue layer of the separation zone. The recovered portion of the treated substrate can include a second residue layer of the separation zone.

[0034] The second residue layer can be removed from the recovered portion of the disposal substrate. By way of example, the removal of the second residue layer can include CMP, lapping and / or grinding. Other polishing and / or surface smoothing methods can also be used. After removing the second residue layer, the reprocessed disposal substrate can have no or almost no crystal cracks and fissures originating from the laser treatment. The reprocessed disposal substrate can be used as a disposal substrate for further wafer complexes.

[0035] Since the auxiliary layer prevents cracks from propagating from the handle substrate to the silicon carbide structure, the silicon carbide structure can be free of crystal defects resulting from laser separation even when the focal plane is provided in close proximity to the first main surface of the handle substrate. This allows for more efficient use of the handle substrate than without the auxiliary layer.

[0036] According to an embodiment, the portion of the handle substrate extending from the first surface of the handle substrate to the focal plane may include single-crystalline silicon carbide. For example, the portion of the handle substrate extending from the first surface of the handle substrate to the focal plane may be composed of single-crystalline silicon carbide. The auxiliary layer can effectively constrain the vertical extension of microcracks in the silicon carbide to the minimum necessary for subsequent wafer splitting.

[0037] According to an embodiment, the laser irradiation may form the modification zones along parallel laser scan lines. Adjacent laser scan lines may have a center-to-center distance, in particular the same center-to-center distance.

[0038] For example, for a modified zone formed in 4H-SiC and at an off-axis angle α between the c-plane and the horizontal plane of approximately 4°, the distance between the focal plane and the auxiliary layer can be in a range of 3.2% to 14.3% of the center-to-center distance from the laser scan line. For example, the distance between the focal plane and the auxiliary layer can be in a range of 3.2% to 7.15% or 6.4% to 14.3% of the center-to-center distance from the laser scan line.

[0039] As a result, the distance between the focal plane and the auxiliary layer is large enough so that cracks initiated by adjacent laser scan lines are close enough to each other to ensure a reliable separation process. On the other hand, the distance between the focal plane and the auxiliary layer is small enough to facilitate a highly material-efficient separation process, which can result in very little loss of crystalline SiC material.

[0040] According to an embodiment, the auxiliary layer may include at least one layer subjected to compressive stress. For example, the auxiliary layer may include a single layer subjected to compressive stress. According to another example, the auxiliary layer may include a plurality of sublayers subjected to compressive stress and sublayers under tensile stress, wherein the sublayers under tensile stress and the sublayers under compressive stress alternate along the vertical direction. The layer under compressive stress may prevent the propagation of cracks and / or lattice defects. The sublayers subjected to compressive stress and the sublayers under tensile stress may be single crystal SiC layers having different average dopant concentrations and may be formed in an efficient manner by epitaxy using in-situ doping.

[0041] According to an embodiment, the auxiliary layer may have a melting point above 1800° C. The auxiliary layer having high temperature stability makes it possible to form a silicon carbide structure on the auxiliary layer at least partially by epitaxy. For example, the auxiliary layer may include a silicon nitride layer and / or a carbon layer and / or polycrystalline SiC. The auxiliary layer may consist of one of these layers or a combination of these layers.

[0042] According to an embodiment, the auxiliary layer may include at least one silicon carbide layer having a significantly higher dopant concentration than in the directly adjacent layer portion of the handle substrate. The auxiliary layer may be formed from a portion of the handle substrate, for example by introducing a dopant or by in-situ doping during epitaxial growth. For example, the average dopant concentration in the auxiliary layer may be at least ten times higher than in the directly adjacent layer portion of the handle substrate.

[0043] According to an embodiment, providing the wafer composite may include forming an auxiliary layer on at least one of the first main surface of the handle substrate and the processed surface of the SiC donor substrate. For example, the auxiliary layer may be formed exclusively on the handle substrate, may be formed exclusively on the donor substrate, or may include two sublayers, wherein a first sublayer is formed on the first main surface of the handle substrate and a second sublayer is formed on the processed surface of the SiC donor substrate.

[0044] The handle substrate and the SiC donor substrate may then be connected, for example, by bonding, wherein the auxiliary layer is arranged between the handle substrate and the SiC donor substrate.

[0045] For example, the handle substrate and the SiC donor substrate may be connected by direct bonding or by reaction bonding.The adhesion between the directly bonded layer and the substrate may be based on chemical bonding, hydrogen bonding, metallic bonding, ionic bonding and / or covalent bonding.

[0046] Direct bonding can include applying a physical force to press the SiC donor substrate and the handle substrate against each other, thermally treating at least one of the bonding surfaces at a moderate temperature, or a combination of the two (fusion bonding, thermal compression bonding, bonding by atomic rearrangement). Direct bonding can include the absence of any additional intermediate layers (e.g., adhesive layers). Firmly connecting the SiC donor substrate to the handle substrate can facilitate transfer of the transfer layer from the SiC donor substrate to the wafer composite.

[0047] According to an embodiment, the recovered portion of the SiC donor substrate can be separated from the transferred portion of the SiC donor substrate after the disposal substrate is physically connected to the SiC donor substrate. For example, the SiC donor substrate can include a release layer between the recovered portion and the transferred portion. The SiC donor substrate can be split along the release layer, wherein the recovered portion is separated from the transferred layer. The release layer may include crystal defects or voids generated by implanting light ions such as hydrogen and / or helium through the processed surface of the SiC donor substrate. The separation process can include a heat treatment to recombine silicon atoms and carbide atoms in the release layer.

[0048] According to an embodiment, an epitaxial silicon carbide layer can be formed on the transferred portion after the recovered portion is removed. For example, the silicon carbide can be deposited by a chemical vapor deposition method, wherein silicon atoms and carbon atoms grow in register with the single crystal lattice of the transferred portion. In the epitaxial silicon carbide layer, a semiconductor die for an integrated circuit (e.g., for a power semiconductor device) can be formed. In particular, silicon carbide devices can be formed exclusively in the epitaxially grown silicon carbide with minimal loss of crystalline silicon carbide from the disposed substrate.

[0049] According to an embodiment, the handle substrate may include a main portion, a separation layer formed on the main portion (e.g., directly on the main portion), and an intermediate layer on the separation layer (e.g., directly on the separation layer). The laser irradiation may be performed using a focal plane within the intermediate layer.

[0050] The major portion may be or may include crystalline silicon carbide, such as single crystal carbide.

[0051] The separation layer may be or include a layer subjected to compressive stress, such as a silicon carbide layer, having a dopant concentration that is higher than the average concentration in the intermediate layer and in the portion of the layer directly adjacent to the separation layer. According to another example, the separation layer may include at least one main component other than silicon and carbon. For example, the separation layer may include a silicon nitride layer.

[0052] The separation layer can be a single, uniform layer. According to another example, the separation layer can include multiple compressively stressed sublayers and multiple tensilely stressed sublayers, wherein the tensilely stressed sublayers and the compressively stressed sublayers alternate vertically. The compressively stressed layer can prevent the propagation of cracks and / or lattice defects. The compressively stressed sublayers and the tensilely stressed sublayers can be single crystal SiC layers with different average dopant concentrations and can be formed in an efficient manner by epitaxy.

[0053] The intermediate layer can be provided by a single-crystal or polycrystalline material having a melting point above 1800°C, exhibiting sufficient adhesion to the separation layer and being easily modified by laser irradiation. For example, the intermediate layer can be a silicon carbide layer having a hexagonal lattice type, such as a 4H-SiC layer having an off-axis angle α between the c-plane and the horizontal plane of approximately 4°. For example, the intermediate layer can be a layer under tensile stress.

[0054] The separation layer in the handle substrate may prevent crack propagation from the modified zone in the intermediate layer in the direction of the handle substrate and further reduce the loss of single crystal silicon carbide material.

[0055] According to an embodiment, the intermediate layer can be formed by layer transfer from a SiC donor substrate or from an alternative donor substrate. Layer transfer is advantageous for providing the intermediate layer from a material that might not otherwise form on the separation layer (e.g., a single crystal material, or a material that might only form on the separation layer under high forces).

[0056] For example, the intermediate layer can be a single-crystal silicon carbide layer. The average dopant concentration in the intermediate layer can be relatively high, for example, greater than the average dopant concentration in the main portion. The higher dopant concentration can improve the formation of microcracks along the c-plane. The thickness of the intermediate layer can be at least 6.4% and at most 14.5% of the center-to-center distance between the laser scan lines.

[0057] By providing the intermediate layer from a material other than single-crystal silicon carbide, a silicon carbide device can be obtained without sacrificing any single-crystal silicon carbide. In the case where the intermediate layer is provided from single-crystal silicon carbide, the intermediate layer can be formed from an alternative SiC donor substrate of lower crystal quality or can be formed from another polytype other than the silicon carbide donor substrate that provides the seed layer for epitaxial growth.

[0058] According to another embodiment, the wafer complex may include a handling substrate, an auxiliary layer, and a silicon carbide structure. The handling substrate may include a modification zone of a modification material embedded in single-crystal silicon carbide. The modification zone is formed in a separation zone. The separation zone is parallel to the first main surface of the handling substrate. The auxiliary layer may be formed (e.g., directly) on the first main surface of the handling substrate. The silicon carbide structure may be formed (e.g., directly) on the auxiliary layer. In the handling substrate, microcracks may extend from the modification zone to the auxiliary layer and may terminate at the auxiliary layer, for example, at an interface between the auxiliary layer and the handling substrate.

[0059] The auxiliary layer facilitates the formation of the modification zone at a relatively small distance from the first main surface of the handle substrate and restricts the length of cracks propagating from the modification zone along a crystal plane tilted relative to the main surface into the silicon carbide structure.

[0060] According to an embodiment, the modification zones may be formed in parallel laser scan lines having a center-to-center distance relative to each other. The distance between the auxiliary layer and the focal plane passing through the center of the modification zone may be in the range of 3.2% to 7.25% of the center-to-center distance from the laser scan lines.

[0061] At distances of the modified zone to the auxiliary layer within a given range, it is possible that only a small portion of the single-crystalline silicon carbide is lost in the cleavage process while reliable cleavage of the separate zones around the focal plane is still possible.

[0062] According to an embodiment, the auxiliary layer may be subjected to compressive stress. A layer subjected to compressive stress may prevent cracks from propagating along the main crystal plane with sufficient reliability.

[0063] According to an embodiment, the auxiliary layer may have a melting point higher than 1800° C. At least a portion of the silicon carbide structure may be formed by epitaxy at a temperature up to 1800° C. For example, the auxiliary layer may include a silicon nitride layer or a silicon carbide layer.

[0064] According to an embodiment, the silicon carbide structure may include an epitaxial layer. The epitaxial layer may include a wafer-shaped complex comprising a plurality of laterally connected semiconductor dies for an integrated circuit (e.g., for a power semiconductor device) at any processing stage. For example, the epitaxial layer may include a doped region of the integrated circuit, or a doped region of the integrated circuit and further dielectric structures and conductive structures from a non-single semiconductor material.

[0065] According to an embodiment, the handling substrate may include a main portion, a separation layer formed (e.g., directly formed) on the main portion, and an intermediate layer formed (e.g., directly formed) on the separation layer. The modification zone may be formed in the intermediate layer. The intermediate layer and the handling substrate may be made of materials other than nearly defect-free single-crystal silicon carbide. After separation along the focal plane and after removal of residues of the intermediate layer, the main portion of the handling substrate and the separation layer are not consumed and can be reused for the same purpose.

[0066] According to an embodiment, the intermediate layer may be a single-crystal silicon carbide layer under tensile stress. For example, the average dopant concentration in the intermediate layer may be relatively high, for example, greater than the average dopant concentration in the main portion. The tensile stress may improve the formation of microcracks along the c-plane.

[0067] The thermomechanical behavior of the intermediate layer matches the properties of the silicon carbide structure. Since the intermediate layer is not used as a seed crystal for epitaxy, the intermediate layer can be a silicon carbide layer of poor crystal quality.

[0068] Figures 1A to 1C A method is shown that facilitates fabricating a silicon carbide device from an epitaxial silicon carbide wafer 910 .

[0069] Figure 1A A wafer composite 900 is shown having a handle substrate 100 , an auxiliary layer 200 and a silicon carbide structure 320 stacked vertically one above the other.

[0070] The handling substrate 100 may be a flat plate having two parallel main surfaces 101, 102. A horizontal cross-section of the handling substrate 100 parallel to the first main surface 101 at the front side of the handling substrate 100 may be a polygon with or without rounded corners or may be an ellipse, such as a circle, wherein the handling substrate 100 may have a notch and / or a flat surface formed along the circumference. For example, the cross-section of the handling substrate 100 may be a circle with a notch or a flat surface along the circumference or a circle without a flat surface and a notch, wherein the diameter of the circle corresponds to the diameter of a standard wafer size. For example, the diameter may be 2 inches (51 mm), 3 inches (76 mm), 4 inches (100 mm), 125 mm (5 inches), 150 mm (6 inches) or 200 mm (8 inches).

[0071] The disposal substrate 100 can be completely from a silicon carbide crystal including silicon and carbon as main components, or can include at least a crystalline silicon carbide portion. In addition to silicon and carbon, the silicon carbide crystal can also include further materials, such as unintended impurities as a result of material and processing defects and / or unintended additives. Unintended impurities can include oxygen (O) and fluorine (F). The intended additives can include hydrogen (H) and / or dopant atoms, such as nitrogen (N), phosphorus (P), beryllium (Be), boron (B), aluminum (Al) and / or gallium (Ga). The surface normal 104 of the first main surface 101 can be defined and / or advance along the vertical direction. The direction orthogonal to the vertical direction is the lateral direction (also referred to as the horizontal direction).

[0072] The thickness v1 of the handle substrate 100 between the two main surfaces 101, 102 can be equal to, less than, or greater than the thickness of a standard silicon carbide wafer of the same diameter. For example, the handle substrate 100 can be 4 inches in diameter and the handle substrate thickness v1 can be equal to, less than, or greater than 525 μm.

[0073] The auxiliary layer 200 may be formed in contact with the first main surface 101 of the handle substrate 100. The auxiliary layer 200 may be subjected to compressive stress. The melting point of the auxiliary layer 200 may be higher than 1800°C. The thickness v2 of the auxiliary layer 200 may be in a range from 5 nm to 5 μm (e.g., from 20 nm to 0.5 μm). For example, the auxiliary layer 200 may be or include a silicon carbide layer having a higher dopant concentration than in the directly adjacent layer portion of the handle substrate 100. According to another example, the auxiliary layer 200 may be or include a silicon nitride layer.

[0074] The silicon carbide structure 320 may be in contact with the layer surface 201 of the auxiliary layer 200, wherein the layer surface 201 is opposite the handle substrate 100. The silicon carbide structure 320 may be formed at least partially by epitaxy. The silicon carbide structure 320 may be a composite of a plurality of identical, laterally connected semiconductor dies, wherein each semiconductor die includes a semiconductor body of an integrated circuit, such as a semiconductor body of a power semiconductor device. The thickness v3 of the silicon carbide structure 320 may be in a range from 20 μm to several hundred μm.

[0075] The handle substrate 100 comprises a modification zone 155. The modification zone 155 is formed from the material of the handle substrate 100 by laser irradiation applied in the handle substrate 100 and focused in the focal plane 105.

[0076] The focal plane 105 is close to the first major surface 101. For example, in a handled substrate 100 having a hexagonal crystal lattice and having an off-axis angle α between a horizontal plane and a major crystal plane (e.g., a c-plane) of approximately 4°, the distance d2 between the major surface 101 and the focal plane 105 may be in the range of 100 nm to 800 μm, typically in the range of 500 nm to 40 μm, in the range of 200 nm to 20 μm, or in the range of 1 μm to 20 μm.

[0077] The modification zones 155 may be arranged in the laser scan lines 151. The laser scan lines may extend orthogonally to the cross-sectional plane or obliquely to the cross-sectional plane. The center-to-center distance d1 between adjacent laser scan lines 151 may be in the range of 10 μm to 200 μm, for example, in the range of 40 μm to 100 μm.

[0078] From the modification zone 155, the microcrack 156 may extend primarily along a c-plane intersecting or closely approaching the modification zone 155. The vertical section of the handled substrate 100 defined by the length of the microcrack 156 forms a separation zone 160.

[0079] The laser irradiation may be applied from the front side, for example, after the epitaxial process of forming at least a portion of the silicon carbide structure 320 and before forming the metallization of the semiconductor die. Alternatively, the laser irradiation may be applied from the back side, for example, after the epitaxial process of forming at least a portion of the silicon carbide structure 320, for example after completing the front side processing of the silicon carbide structure, in particular after forming the front side metallization of the semiconductor die.

[0080] Wafer composite 900 can be cleaved along focal plane 105. For example, mechanical shear stress can be applied between silicon carbide structure 320 and handle substrate 100. Applying mechanical shear stress can be combined with further processing to support cleavage. For example, thermomechanical stress can be applied by cooling. Alternatively or in addition, acoustic waves, such as ultrasonic waves, can be directed toward separation zone 160.

[0081] The focal plane 105 determines the vertical position of the split. The split does not follow directly the focal plane 105. Instead, the split mainly follows parallel segments of the c-plane in the separation zone 160.

[0082] Figure 1B The epitaxial wafer 910 is shown cleaved from the handle substrate 100. The epitaxial wafer 910 includes the silicon carbide structure 320, the auxiliary layer 200 and the Figure 1A The first residue layer 161 of the separation zone 160 is formed. The processing substrate 100 includes Figure 1A A second residue layer 162 of the separation zone 160 is formed.

[0083] The fracture surfaces 157 of the epitaxial wafer 910 and the handle substrate 100 are mainly composed of parallel surface segments in the c-plane. From the surface segments in the c-plane, microcracks 156 may extend into the first residue layer 161 and the second residue layer 162.

[0084] The epitaxial wafer 910 is further processed. For example, the first residue layer 161 is removed and, if applicable, the auxiliary layer 200 can be removed. During cleavage and during further processing, an auxiliary carrier can be temporarily attached to the front side surface 911 of the epitaxial wafer 910.

[0085] The handled substrate 100 may be reprocessed. For example, the second residue layer 162 may be removed from the front side of the handled substrate 100. By way of example, the removal of the second residue layer 162 may include chemical mechanical polishing, lapping, and / or grinding.

[0086] Figure 1C Shown are a reworked handle substrate 100 and a further processed epitaxial wafer 910. The thickness v4 of the reworked handle substrate 100 is smaller than the vertical extension v1 of the handle substrate 100 before cleaving.

[0087] Figure 2A and Figure 2B Graphic Figures 1A to 1C The auxiliary layer 200 has the following effects.

[0088] Figure 2A A single-crystal 4H-SiC substrate having an off-axis angle α of 4° between the horizontal plane and the c-plane is mentioned. Modification zones 155 are formed by laser irradiation along laser scan lines 151 extending orthogonally to the cross-sectional plane. The center-to-center distance d1 between adjacent laser scan lines 151 is in the range of several microns. At the focal position and directly around the focal position, the laser beam can transform the single-crystal material of the treated substrate 100 into a different polytype (e.g., from 4H-SiC to 3C-SiC) and / or into a structure with a different degree of crystallinity.

[0089] For example, the laser wafer length can be within the silicon carbide absorption gap, where multi-phonon interactions can cause a local decomposition of the silicon carbide crystal into silicon and carbon. The decomposition can be accompanied by a volume expansion of the modified material. The volume expansion can induce mechanical stresses in the surrounding portion of the silicon carbide crystal. The stresses cause lattice defects, cracks, and / or microcracks 156 that propagate primarily along the c-plane 108. The microcracks 156 weaken the mechanical stability of the silicon carbide crystal in the separation zone 160. By applying appropriate mechanical stresses, the treated substrate 100 is split along a separation surface 157 consisting primarily of parallel surface segments in the c-plane 108.

[0090] The microcracks 156 along the c-plane 108 can be quite long. The maximum length of the microcracks 156 determines the vertical extension v5 of the separation zone 160. Microcracks 156 are almost absent outside the separation zone 160. Due to the high lattice defect density and / or microcracks 156, the separation zone 160 is typically not usable for further processing.

[0091] For further processing, the vertical section of the treated substrate 100 with the vertical extension v5 is lost. The vertical extension v5 is typically greater than 25% of the center-to-center distance d1 between adjacent laser scan lines 151. In addition, there is a certain risk that some microcracks 156 may extend beyond the assumed extension of the separation zone 160.

[0092] exist Figure 2B In the embodiment of the present invention, the auxiliary layer 200 limits the propagation of microcracks 156 toward the silicon carbide structure 320 and protects the silicon carbide structure 320 from cracks and lattice defects generated by laser irradiation. The distance d2 between the auxiliary layer 200 and the focal plane 105 can be selected so that reliable cleavage is just possible. Figure 2B The vertical extension v5 of the separation zone 160 in the can be significantly smaller than Figure 2A The vertical extension v5 of the separation zone 160 in.

[0093] Figures 3A to 3F Laser-assisted separation of the epitaxial wafer 910 from the handle substrate 100 is combined with layer transfer from the SiC donor substrate 300 .

[0094] Light ions may be implanted through the processed surface 301 of the single crystal SiC donor substrate 300. The light ions may include helium (He) and / or hydrogen (H). The light ions may damage the crystal lattice of the SiC donor substrate 300 in the release layer 310.

[0095] Figure 3A The release layer 310 is shown extending to the machined surface 301 at a uniform distance across the entire cross-sectional area of ​​the silicon carbide donor substrate 300 .

[0096] The SiC donor substrate 300 is physically connected to the handle substrate 100, for example, by bonding. For this purpose, the auxiliary layer 200 may be formed on the main surface 101 of the handle substrate 100, and the processed surface 301 of the SiC donor substrate 300 may be bonded to the exposed layer surface 201 of the auxiliary layer 200. Alternatively, the auxiliary layer 200 may be formed on the processed surface 301 of the SiC donor substrate 300, and the main surface 101 of the handle substrate 100 may be bonded to the auxiliary layer 200. Alternatively, a first sublayer of the auxiliary layer 200 may be formed on the processed surface 301 of the SiC donor substrate 300, and a second sublayer may be formed on the main surface 101 of the handle substrate 100, and the two sublayers may be bonded together.

[0097] Figure 3B A wafer composite 900 is shown, which includes a SiC donor substrate 300 physically connected to a handle substrate 100 via an auxiliary layer 200 .

[0098] The recovered portion 321 of the SiC donor substrate 300 can be separated, e.g., cleaved, from the transferred portion 322 of the SiC donor substrate 300. For example, the thermal treatment can cause a recombination of atoms in the release layer 310, wherein the recovered portion 321 can be cleaved by applying a moderate mechanical force.

[0099] The residue of the release layer 310 on the recovered portion 321 may be removed, and the processed surface 301 of the recovered portion 321 may be planarized. The recovered portion 321 may be used as a SiC donor substrate 300 in the next processing cycle.

[0100] Residues of the release layer 310 on the wafer composite 900 may be removed, and the exposed surface of the transferred portion 322 may be planarized.

[0101] Figure 3C Wafer composite 900 is shown including a transferred portion 322 on auxiliary layer 200. Transferred portion 322 can be used as a seed layer for an epitaxial process. For example, a chemical vapor deposition process can deposit silicon and carbon atoms that are deposited on the seed layer in a manner aligned with the single crystal lattice of transferred layer 322. The deposited silicon and carbon atoms form epitaxial layer 324.

[0102] As in Figure 3D As shown in FIG, the transferred layer 322 and the epitaxial layer 324 form a silicon carbide structure 320, in which semiconductor dies for multiple identical integrated circuits (e.g., power semiconductor devices) can be formed. At an appropriate processing stage, laser irradiation forms a separation zone 160 including a modified zone 155 arranged along the focal plane 105.

[0103] Figure 3E A semiconductor die 500 formed in at least a portion of a silicon carbide structure 320 and a modification zone 155 arranged along the focal plane 105 in the separation zone 160 are schematically illustrated.

[0104] The auxiliary carrier 600 can be attached to the exposed surface of the silicon carbide structure 320. For example, the adhesive layer 611 can mechanically connect the auxiliary carrier 600 and the silicon carbide structure 320. The silicon carbide structure 320 can then be separated from the handle substrate 100 by applying a moderate mechanical stress. If applicable, applying the mechanical stress can be combined with further treatment, such as by cooling the wafer composite 900 and / or by applying acoustic waves to locally increase the mechanical stress in the separation zone 160.

[0105] Figures 4A to 4E A method is shown that helps to further reduce the vertical extension of the separation zone 160 by providing the handle substrate 100 with a separation layer 120 prior to layer transfer from the donor substrate.

[0106] Figure 4A An alternative donor substrate 400 is shown, which may be derived from or include single-crystal silicon carbide, or may be derived from another material other than single-crystal 4H-SiC. For example, the alternative donor substrate 400 may be formed from single-crystal SiC having a polytype other than 4H-SiC, or from single-crystal SiC having a relatively high crystal defect density and / or having a relatively high content of unintended impurities.

[0107] Light ions may be implanted into the replacement donor substrate 400 through the machined surface 401 to form a release layer 420. The replacement donor substrate 400 is firmly connected to the substrate structure 190 including the main portion 110 and the separation layer 120.

[0108] Figure 4B An alternative donor substrate 400 is shown mechanically connected (eg, bonded) to the exposed surface of the separation layer 120 of the substrate structure 190 .

[0109] The main portion 110 of the substrate structure 190 may be single-crystal silicon carbide of any polytype. For example, the main portion 110 may have a relatively high defect density and / or a high content of unwanted impurities.

[0110] The separation layer 120 may be a layer having a high melting point, for example, a layer having a melting point exceeding 1800° C. The separation layer 120 may be or include a layer subjected to compressive stress. For example, the separation layer 120 may be or include a silicon nitride layer and / or a lightly doped silicon carbide layer.

[0111] The recovered portion 421 of the replaced donor substrate 400 is removed by cleaving the replaced donor substrate 400 along the release layer 420. The exposed surface of the remaining transferred portion 422 may be planarized.

[0112] Figure 4C The handling substrate 100 in the embodiment includes the main portion 110 of the substrate structure 190 and the separation layer 120, as well as an intermediate layer 130 formed by a planarized transferred portion 422 of the replaced donor substrate 400 on the separation layer 120 (e.g., directly on the separation layer 120). The exposed surface of the intermediate layer 130 forms the main surface 101 of the handling substrate 100.

[0113] A release layer 320 is formed in the SiC donor substrate 300. The SiC donor substrate 300 is connected (eg, bonded) to the main surface 101 of the handle substrate 100 via the auxiliary layer 200.

[0114] Figure 4D A SiC donor substrate 300 is shown which is physically connected to the handle substrate 100 via the auxiliary layer 200 .

[0115] The recovered portion 321 of the SiC donor substrate 300 can be split apart. The remaining transferred portion 322 can be flattened. An epitaxial layer can be formed on (e.g., directly on) the flattened transferred portion 322. The epitaxial layer and the transferred portion 322 form a silicon carbide structure 320. The semiconductor die 500 can be formed in the silicon carbide structure 320. Laser irradiation forms a modified zone 155 in a focal plane, wherein the focal plane 105 is in the intermediate layer 130 of the handle substrate 100. The modified zone 155 can be formed at any stage after the transferred portion 322 is transferred to the handle substrate 100.

[0116] Figure 4E A modified zone 155 is shown formed in the intermediate layer 130. The vertical extension of the separation zone 160 is constrained to the intermediate layer 130. The epitaxial wafer comprising the silicon carbide structure 320 can be separated from the handle substrate 100 by cleaving along the separation zone 160.

[0117] like Figure 5 As shown in FIG, separation layer 120 limits the propagation of microcracks 156 toward main portion 110 of handled substrate 100 and protects main portion 110 from cracks and lattice defects generated by laser irradiation. Auxiliary layer 200 limits the propagation of microcracks 156 toward silicon carbide structure 320 and protects silicon carbide structure 320 from cracks and lattice defects generated by laser irradiation. The length of microcracks 156 is constrained by the thickness of intermediate layer 130.

[0118] Figure 5The vertical extension v5 of the separation zone 160 in the can be significantly smaller than Figure 2B The vertical extension v5 of the separation zone 160 in.

Claims

1. A method for manufacturing a silicon carbide device, the method comprising: Providing a wafer composite (900), the wafer composite (900) including a handle substrate (100), an auxiliary layer (200) formed on a first surface (101) of the handle substrate (100), and a silicon carbide structure (320) formed on the auxiliary layer (200); and subjecting the handle substrate (100) to laser irradiation, wherein the laser irradiation modifies the crystalline material along a focal plane (105) in the handle substrate (100), wherein the focal plane (105) is parallel to the first major surface (101), The auxiliary layer (200) is adapted to prevent the propagation of microcracks (156) generated in the handle substrate (100) by laser irradiation.

2. The method of the preceding claim, further comprising: The wafer composite (900) is cleaved along the focal plane (105).

3. A method as claimed in any one of the preceding claims, wherein A portion of the handle substrate (100) extending from a first surface (101) of the handle substrate (100) to a focal plane (105) comprises single crystal silicon carbide.

4. The method according to any one of claims 1 to 2, wherein: Laser irradiation forms modification zones (155) along parallel laser scan lines (151), wherein adjacent laser scan lines (151) have a center-to-center distance (d1), and wherein a distance (d2) between the focal plane (105) and the auxiliary layer (200) is in the range of 3.2% to 7.25% of the center-to-center distance (d1).

5. The method according to any one of claims 1 to 2, wherein: The auxiliary layer (200) includes at least one layer subjected to compressive stress.

6. The method according to any one of claims 1 to 2, wherein: The auxiliary layer (200) has a melting point higher than 1800°C.

7. The method according to any one of claims 1 to 2, wherein: The auxiliary layer (200) comprises single-crystal silicon carbide, and wherein the average dopant concentration in the auxiliary layer (200) is higher than the average dopant concentration in at least one layer portion of the handle substrate (100) along the first main surface (101).

8. The method of any one of claims 1-2, wherein providing the wafer composite (900) comprises: forming an auxiliary layer (200) on at least one of a main surface (101) of a handle substrate (100) and a machined surface (301) of a silicon carbide donor substrate (300); as well as A handle substrate (100) and a silicon carbide donor substrate (300) are connected, wherein the auxiliary layer (200) is arranged between the handle substrate (100) and the silicon carbide donor substrate (300).

9. The method according to any one of claims 1 to 2, further comprising: After joining, the recovered portion (321) of the silicon carbide donor substrate (300) is separated from the transferred portion (322) of the silicon carbide donor substrate (300), wherein the transferred portion (322) forms at least a portion of the silicon carbide structure (320).

10. The method according to any one of claims 1 to 2, further comprising: An epitaxial layer (324) is formed on the transferred portion (322).

11. The method according to any one of claims 1 to 2, wherein: The handling substrate (100) includes a main portion (110), a separation layer (120) formed on the main portion (110), and an intermediate layer (130) on the separation layer (120), and wherein a focal plane (105) of laser adjustment is in the intermediate layer (130).

12. The method according to any one of claims 1 to 2, wherein: The intermediate layer (130) is formed by layer transfer from a silicon carbide donor substrate (300) or from an alternative donor substrate (400).

13. A wafer composite (900) comprising: a handle substrate (100), wherein the handle substrate (100) comprises a modification zone (155) of modification material embedded in crystalline silicon carbide, wherein the modification zone (155) is formed in a separation zone (160), and wherein the separation zone (160) extends parallel to the first main surface (101) of the handle substrate (100); an auxiliary layer (200) formed on the first main surface (101) of the handle substrate (100), wherein in the handle substrate (100), the microcracks (156) extend from the modification zone (155) to the auxiliary layer (200) and terminate at the auxiliary layer (200); as well as A silicon carbide structure (320) is formed on the auxiliary layer (200).

14. The wafer composite as claimed in the preceding claim, wherein The modification zone (155) is formed in a laser scan line (151) having a center-to-center distance (d1), and wherein a distance (d2) between the auxiliary layer (200) and a focal plane (105) passing through the center of the modification zone (155) is in the range of 3.2% to 7.25% of the center-to-center distance (d1).

15. The wafer composite according to any one of the two preceding claims, wherein The auxiliary layer (200) includes at least one layer subjected to compressive stress.

16. The wafer composite according to any one of claims 13 to 14, wherein The auxiliary layer (200) has a melting point higher than 1800°C.

17. The wafer composite of any one of claims 13-14, wherein The silicon carbide structure (320) includes an epitaxial layer.

18. The wafer composite of any one of claims 13-14, wherein The handling substrate (100) includes a main portion (110), a separation layer (120) formed on the main portion (110), and an intermediate layer (130) formed on the separation layer (120), and wherein the modification zone (155) is formed in the intermediate layer (130).

19. The wafer composite of any one of claims 13-14, wherein: The intermediate layer (130) is a single crystal silicon carbide layer.

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