PROCESS FOR MANUFACTURING A VERTICAL CONDUCTION SILICON CARBIDE ELECTRONIC DEVICE AND VERTICAL CONDUCTION SILICON CARBIDE ELECTRONIC DEVICE

Abstract

A metal layer is deposited on a wafer that has silicon carbide, wherein the metal layer forms a contact face. A laser annealing is performed at the contact face using a laser beam application that causes the metal layer to react with the wafer and form a silicide layer. The laser beam has a footprint having a size. To laser anneal the contact face, a first portion of the contact face is irradiated, the footprint of the laser beam is moved by a step smaller than the size of the footprint, and a second portion of the contact face is irradiated, thereby causing the first portion and the second portion of the contact face to overlap.

Claims

1. A process for manufacturing a vertical conduction silicon carbide electronic device, comprising: depositing a metal layer on a wafer comprising silicon carbide, wherein the metal layer forms a contact face; and laser annealing the contact face with a laser beam to cause the metal layer to react with the wafer and form a silicide layer, wherein the laser beam has a footprint on the contact face having a size; wherein laser annealing the contact face comprises irradiating a first portion of the contact face, moving the footprint of the laser beam by a step smaller than the size of the footprint and irradiating a second portion of the contact face, wherein the first portion and the second portion of the contact face at least partially overlap.

2. The process according to claim 1, wherein the footprint forms, on the contact face, a gradient region having a spatially varying energy, wherein the gradient region causes the formation of a rough region of the silicide layer.

3. The process according to claim 2, wherein the rough region comprises a plurality of irregularly arranged protrusions, each protrusion having a diameter in the range 0.5 μm-2 μm.

4. The process according to claim 2, wherein the gradient region has a size smaller than the size of the footprint.

5. The process according to claim 4, wherein the size of the gradient region is comprised between 0.5% and 5% of the size of the footprint.

6. The process according to claim 1, wherein the step is comprised between one tenth and one half of the size of the footprint.

7. The process according to claim 1, wherein the footprint has a polygonal shape having a side comprised between 8 mm and 36 mm.

8. The process according to claim 1, wherein the laser beam has an energy density comprised between 3.4 J/cm.sup.2 and 4.8 J/cm.sup.2.

9. The process according to claim 1, wherein laser annealing comprises pulsing the laser beam with a pulse duration comprised between 100 ns and 300 ns.

10. The process according to claim 1, wherein the laser beam has a wavelength comprised between 290 nm and 370 nm.

11. The process according to claim 1, wherein laser annealing comprises scanning the entire contact face with the laser beam using a step-and-repeat type of scanning.

12. The process according to claim 1, further comprising depositing a metallization layer on the silicide layer.

13. The process according to claim 1, wherein the silicide layer is formed on a first conduction terminal surface of the wafer, the wafer also having a second conduction terminal surface and comprising a device layer that forms the second conduction terminal surface, the process further comprising forming electrically conductive device regions in the device layer, and forming a connection structure layer on the second conduction terminal surface.

14. A vertical conduction silicon carbide electronic device formed in a die, comprising: a body of silicon carbide; and a contact region of silicide extending on the body and forming a connection surface; wherein the contact region comprises a first rough portion and a second rough portion, the first rough portion extending at a distance from the second rough portion, the first rough portion and the second rough portion including a plurality of irregularly arranged protrusions of silicide.

15. The device according to claim 14, wherein the first rough portion and the second rough portion each have a width comprised between 50 μm and 500 μm, and wherein the distance between the first rough portion and the second rough portion is smaller than 2.5 mm.

16. The device according to claim 15, wherein each protrusion has a diameter comprised between 0.5 μm and 2 μm.

17. The device according to claim 14, wherein the contact region extends on a first conduction terminal surface of the body and the body also has a second conduction terminal surface, the device further comprising a device region extending in the body and forming the second conduction terminal surface, and a connection structure region extending on the second conduction terminal surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] For a better understanding of the present invention, a non-limiting embodiment is now described, with reference to the attached drawings, wherein:

[0015] FIG. 1 shows a cross-section of a work body comprising a silicon carbide wafer, according to the present manufacturing process;

[0016] FIG. 2 is a top plan view of the work body of FIG. 1;

[0017] FIG. 3 is a cross-section of the work body of FIG. 1 in a subsequent manufacturing step;

[0018] FIG. 4 is a cross-section of the work body of FIG. 3 in a subsequent manufacturing step comprising a laser annealing step;

[0019] FIGS. 5 and 6 show an energy profile of a footprint of a laser beam along two different directions;

[0020] FIG. 7 shows a perspective view of the energy profile of the footprint of FIGS. 5 and 6;

[0021] FIG. 8 shows a top-plan view of the footprint of the laser beam of FIGS. 5-7 formed on the work body, during the laser annealing step of FIG. 4;

[0022] FIGS. 9 and 10 are schematic representations of a scanning method of the laser annealing step of FIG. 4;

[0023] FIGS. 11 and 12 are respectively a cross-section and a top plan view of the work body of FIG. 4 after the laser annealing step;

[0024] FIG. 13 shows a cross-section of the work body of FIGS. 11 and 12 in a subsequent manufacturing step;

[0025] FIG. 14 is a cross-section of the present electronic device; and

[0026] FIG. 15 is an exemplificative micrograph of a surface of the present electronic device.

DETAILED DESCRIPTION

[0027] FIGS. 1 and 2 show a work body 1 in a Cartesian reference system XYZ comprising a first axis X, a second axis Y and a third axis Z.

[0028] The work body 1 has already been subject to first manufacturing steps.

[0029] The work body 1 is formed by a wafer 5 of silicon carbide (SiC) in one of its polytypes, such as 3C-SiC, 4H-SiC and 6H-SiC, having a first surface 5A and a second surface 5B, and by a connection structure layer 8 extending on the first surface 5A of the wafer 5.

[0030] The wafer 5 comprises a work substrate 12, which forms the second surface 5B of the wafer 5, and a device layer 15, which forms the first surface 5A of the wafer 5 and extends directly on the work substrate 12.

[0031] The device layer 15 may be a portion of the work substrate 12 or may be an epitaxial layer grown on the work substrate 12.

[0032] The device layer 15 comprises current conduction zones, here not shown, whose structure, number and configuration depend on the specific application.

[0033] For example, the device layer 15 may comprise a drift layer and one or more implanted regions which may form, for example, source regions and body regions, depending on the specific application, examples whereof are shown for illustrative purposes in FIG. 14.

[0034] In an embodiment, the device layer 15 may also comprise gate structures. In another embodiment, the device layer 15 may be a multilayer, with different device structures integrated in the various layers.

[0035] The connection structure layer 8 comprises one or more metal layers that form an electrical interconnect structure for the device layer 15.

[0036] According to an embodiment, the connection structure layer 8 may also comprise one or more layers of insulating materials, forming passivation structures.

[0037] The device layer 15 and the connection structure layer 8 form at least one die portion, here a plurality of die portions 18.

[0038] Each die portion 18 is intended to form a respective electronic device, after dicing the work body 1.

[0039] Each die portion 18 has a die area, which occupies a respective portion of the area of the first surface 5A of the wafer 5.

[0040] In FIG. 2, for simplicity, the die portions 18 are schematically indicated by dashed lines.

[0041] In detail, in this embodiment, each die portion 18 has a rectangular shape in top plan view. By way of example only, the die area may be approximately of few millimeters squared, for example approximately 4 mm by 5 mm.

[0042] Subsequently, FIG. 3, the work body 1 is flipped upside down and a contact layer 20 is deposited on the second surface 5B of the wafer 5, forming a contact surface 22 of the work body 1.

[0043] The contact layer 20 is a metal material such as nickel, titanium or an alloy of nickel and silicon, and has a thickness, measured parallel to the third axis Z, comprised for example between 20 nm and 150 nm, in particular of about 100 nm.

[0044] Then, as shown in FIG. 4, the work body 1, in particular the contact layer 20, undergoes a laser annealing step.

[0045] In detail, a laser source 30 is used to generate a light beam 33 and focus the light beam 33 on the contact surface 22.

[0046] The light beam 33 has an energy density higher than 3 J/cm.sup.2, for example comprised between 3.4 J/cm.sup.2 and 4.8 J/cm.sup.2, in particular of 4.0 J/cm.sup.2.

[0047] The light beam 33 has a wavelength comprised, for example, between 290 nm and 370 nm, in particular of 310 nm.

[0048] The light beam 33 may be a pulsed light beam having a duration comprised, for example, between 100 ns and 300 ns, in particular of 160 ns.

[0049] The light beam 33 has a beam footprint 35 on the contact surface 22.

[0050] FIGS. 5 and 6 show an energy profile of the beam footprint 35, parallel to the first axis X and, respectively, to the second axis Y.

[0051] In detail (FIG. 5), the beam footprint 35 has a first width W.sub.X parallel to the first axis X and comprises a first plateau region 36 having a first energy E.sub.max,X and a first plateau length L.sub.p,X, and two first sloped regions 37, each having a first slope length L.sub.s,X, wherein the beam energy decreases from the first energy E.sub.max,X to zero.

[0052] In particular, the beam energy may decrease linearly in the first sloped regions 37, from the first energy E.sub.max,X to zero.

[0053] Moreover, in this embodiment, the first energy E.sub.max,X is constant.

[0054] The first width W.sub.X may be comprised, for example, between 8 mm and 36 mm, in particular may be about 10 mm.

[0055] In this embodiment, the first slope length L.sub.s,X is much smaller than the first plateau length L.sub.p,X. For example, the first slope length L.sub.s,X is comprised between 0.5% and 5% of the first plateau length L.sub.p,X, in particular about 3% of the first plateau length L.sub.p,X.

[0056] For example, the first slope length L.sub.s,X may be comprised between 50 μm and 500 μm, in particular may be 300 μm.

[0057] Accordingly, in a first approximation, the first plateau length L.sub.p,X is about the same as the first width W.sub.X of the beam footprint 35.

[0058] In addition (FIG. 6), the beam footprint 35 has a second width W.sub.Y parallel to the second axis Y and comprises a second plateau region 38 having a second energy E.sub.max,Y and a second plateau length L.sub.p,Y, and two second sloped regions 39, each having a second slope length L.sub.s,Y, wherein the beam energy decreases from the second energy E.sub.max,Y to zero.

[0059] In particular, here, the beam energy may decrease linearly in the second sloped regions 39, from the second energy E.sub.max,Y to zero.

[0060] Moreover, in this embodiment, the second energy E.sub.max,Y is constant and equal to the first energy E.sub.max,X.

[0061] The second width W.sub.Y may be comprised, for example, between 8 mm and 36 mm, in particular may be about 10 mm.

[0062] In this embodiment, also the second slope length L.sub.s,Y is much smaller than the second plateau length L.sub.p,Y. For example, the second slope length L.sub.s,Y is comprised between 0.5% and 5% of the second plateau length L.sub.p,Y, in particular about 3% of the second plateau length L.sub.p,Y.

[0063] For example, the second slope length L.sub.s,Y may be comprised between 50 μm and 500 μm, in particular may be 300 μm.

[0064] Accordingly, in a first approximation, the second plateau length L.sub.p,Y is about the same as the second width W.sub.Y of the beam footprint 35.

[0065] In this embodiment, the beam footprint 35 has the same energy profile as the ones shown in FIGS. 5 and 6 for every section parallel to the first axis X and, respectively, to the second axis Y.

[0066] Moreover, in this embodiment, the energy profile of the beam footprint 35 along any direction parallel to the first axis X is equal to the energy profile along any direction parallel to the second axis Y. Therefore, a 3-dimesional representation of the energy profile of the beam footprint 35 is a truncated pyramid, as shown in the perspective view of FIG. 7.

[0067] The footprint 35 may be obtained for example using the laser LT-3100 manufactured by SCREEN Semiconductor Solutions Co., Ltd.

[0068] The beam footprint 35 forms a polygonal shape on the contact surface 22, in particular a squared shape, as shown in FIG. 8, whose sides have the first width W.sub.X along the first axis X and the second width W.sub.Y along the second axis Y.

[0069] In practice, for each portion of the contact surface 22 that is exposed by the laser beam 33, the beam footprint 35 forms a central region 42, which is irradiated with a constant energy and corresponds to the first plateau region 36 and the second plateau region 38, and a gradient region 44, which is irradiated with a non-constant energy and corresponds to the first sloped regions 37 and the second sloped regions 39, wherein the gradient region 44 surrounds the central region 42.

[0070] In FIGS. 8-10, for clarity, the gradient region 44 is indicated with oblique lines.

[0071] During the annealing step of FIG. 4, the laser source 30 focuses the laser beam 33 on a first portion 47 of the contact surface 22 (FIG. 8).

[0072] The laser beam 33 is absorbed by the contact layer 20 and by part of the work substrate 12. The absorbed light generates heat locally (i.e., immediately under the first portion 47 of the contact surface 22), for example to a depth of few microns from the contact surface 22.

[0073] The generated heat causes the contact layer 20 and the work substrate 12 to react locally, at a respective portion of the second surface 5B of the wafer 5, forming a silicide, for example nickel silicide or titanium silicide.

[0074] In order to cause the reaction of the entire contact layer 20 with the work substrate 12, the contact surface 22 is scanned using a step-and-repeat approach.

[0075] In detail, the work body 1 is moved with respect to the laser beam 33 so that the laser beam 33 is focused on a second portion 48 of the contact surface 22 (FIG. 9).

[0076] For clarity, in FIG. 9, the second portion 48 of the contact surface 22 is drawn by a dashed line.

[0077] The second portion 48 of the contact surface 22 partially overlaps the first portion 47 of the contact surface 22 and partially extends next to the first portion 47 of the contact surface 22 along a first scanning line A parallel to the first axis X.

[0078] In detail, the relative movement of the work body 1 with respect to the laser source 30 causes the beam footprint 35 to move by a first shift step D.sub.X along the first scanning line A. Therefore, also the second portion 48 of the contact surface 22 is shifted with respect to the first portion 47 of the contact surface 22 along the first scanning line A, on the right in FIG. 9, by the first shift step D.sub.X.

[0079] The first shift step D.sub.X is smaller than the first width W.sub.X of the beam footprint 35.

[0080] In detail, the first shift step D.sub.X is a fraction of the first width W.sub.X, for example comprised between one tenth and one half of the first width W.sub.X, in particular about one fourth of the first width W.sub.X.

[0081] For example, in one embodiment, the first width W.sub.X may be 10 mm and the first shift step D.sub.X may be smaller than 2.5 mm.

[0082] Subsequently, the laser source 30 focuses the laser beam 33 on subsequent portions of the contact surface 22 along the first scanning line A throughout the entire length of the contact surface 22 along the first scanning line A.

[0083] Subsequently, the laser beam 33 scans the contact surface 22 along a second scanning line, here not shown, parallel to the first scanning line A and shifted along the second axis Y to expose a third portion 49 of the contact surface 22, as shown for example in FIG. 10, where the third portion 49 of the contact surface 22, for clarity, is drawn with a dashed line.

[0084] The third portion 49 of the contact surface 22 partially overlaps the first portion 47 of the contact surface 22 and partially extends next to the first portion 47 of the contact surface 22 along a direction parallel to the second axis Y.

[0085] In detail, the relative movement of the work body 1 with respect to the laser source 30 causes the beam footprint to move by a second shift step D.sub.Y in a direction parallel to the second axis Y with respect to the position of the first portion 47 (FIG. 10). Therefore, the third portion 49 of the contact surface 22 is shifted by the second shift step D.sub.Y, parallel to the second axis Y, from the first portion 47.

[0086] The second shift step D.sub.Y is smaller than the second width W.sub.Y. In detail, the second shift step D.sub.Y is a fraction of the second width W.sub.Y, for example comprised between one tenth and one half of the second width W.sub.Y, in particular about one fourth of the second width W.sub.Y.

[0087] For example, in one embodiment, the second width W.sub.Y may be 10 mm and the second shift step D.sub.Y may be smaller than 2.5 mm.

[0088] By repeating the steps discussed above, the entire contact surface 22 is scanned by the laser beam 33.

[0089] In general, adjacent irradiated portions of the contact surface 22 may be shifted by steps different from the first shift step D.sub.X and the second shift step D.sub.Y.

[0090] For example, the first shift step D.sub.X may be different from the second shift step D.sub.Y. In addition, the first shift step D.sub.X or the second shift step D.sub.Y may be varied along a same scan line or among different scan lines. This may allow to tune the distance between adjacent gradient regions 44, for example to increase (or decrease) the density of gradient regions 44 in specific portions of the contact surface 22.

[0091] FIG. 11 shows the work body 1 after the contact surface 22 has been completely exposed by the laser beam 33, thereby causing the complete reaction of the contact layer 20 with the work substrate 12 and formation of an ohmic layer 50.

[0092] The ohmic layer 50 is of silicide and extends between a first surface 50A, which corresponds to the second surface 5B of the wafer 5, and a second surface 50B, which corresponds to the contact surface 22.

[0093] Generally, the ohmic layer 50 is thicker than the contact layer 20, since also part of the work substrate 12 has reacted to form the ohmic layer 50.

[0094] FIG. 12 shows a top plan view of the second surface 50B of the ohmic layer 50, according to an idealized representation. By virtue of the laser annealing step of FIG. 4, the ohmic layer 50 comprises a rough region 55 and a plurality of smooth regions 57.

[0095] The smooth regions 57 correspond to the portions of the contact surface 22 that have been exposed only to the first plateau region 36 and the second plateau region 38 of the beam footprint 35 (i.e., that have received a spatially uniform energy).

[0096] The rough region 55 corresponds to the gradient portions 44 of the contact surface 22 (i.e., to the portions of the contact surface 22 that have received a spatially non-uniform energy).

[0097] The gradient of energy of the gradient regions 44 generates in fact also a thermal gradient during the laser annealing step of FIG. 4, which in turn causes the rough region to have an increased roughness with respect to the smooth regions 57, as also discussed below with reference to FIG. 15.

[0098] Again, with reference to FIG. 12, in this embodiment, the rough region 55 is a grid formed by a plurality of horizontal stripes 58, parallel to the first axis X, and a plurality of vertical stripes 59, parallel to the second axis Y.

[0099] Each horizontal stripe 58 has a width Lx, parallel to the first axis X, which approximately corresponds to the first slope length L.sub.s,X of the beam footprint 35 and extends at a distance from an adjacent horizontal stripe 58 that is approximately equal to the first shift step D.sub.X.

[0100] Each vertical stripe 59 has a width L.sub.Y, parallel to the second axis Y, which approximately corresponds to the second slope length L.sub.s,Y of the beam footprint 35 and extends at a distance from an adjacent vertical stripe 59 that is approximately equal to the second shift step D.sub.Y.

[0101] By changing the first shift step D.sub.X and the second shift step D.sub.Y, the number of horizontal stripes 58 and vertical stripes 59 may be changed.

[0102] In this embodiment, as visible in FIG. 12, the first shift step D.sub.X and the second shift step D.sub.Y have been chosen so that each die portion 18 has two horizontal stripes 58 and two vertical stripes 59.

[0103] In FIG. 13, a metallization layer 60 is deposited on the second surface 50B of the ohmic layer 50. The metallization layer 60 may be a single metal layer or a stack of different metal layers, for example Ti/NiV/Ag.

[0104] The metallization layer 60 is useful for subsequent manufacturing steps, for example assembling processes such as sintering and diffusion soldering.

[0105] The work body 1 is then subject to known final manufacturing steps, such as dicing, thereby forming an electronic device 100 (FIG. 14) for each die portion 18.

[0106] The electronic device 100 comprises a die 103 including a body 105 having a first surface 105A, which corresponds to the first surface 5A of the wafer 5, and a second surface 105B, which corresponds to the first surface 50A of the ohmic layer 50.

[0107] The body 105 comprises a substrate 107 (corresponding to the work substrate 12 and forming the second surface 105B) and a device region 109 (corresponding to the device layer 15 and forming the first surface 105A).

[0108] The device region 109, as discussed above for the device layer 15, accommodates functional regions of various kind and dimensions, according to the specific type of the electronic device 100 and the specific application.

[0109] By way of example, the electronic device 100 may be a JBS or an MPS diode. In this case, as shown in FIG. 14 by way of example, the device region 109 forms a drift region 111 of a first conductivity type (e.g., N-type) accommodating two implanted regions 113 of a second conductivity type (e.g., P-type).

[0110] As an alternative, as also shown as an example in FIG. 14, the electronic device 100 may be a MOSFET device. In this case, the drift region 111 accommodates body regions 115 of the second conductivity type, source regions 117 of the first conductivity type and insulated gate regions 120 of dielectric material (represented with dashed lines in FIG. 14).

[0111] The die 103 comprises an ohmic connection region 123, corresponding to the ohmic layer 50, extending on the second surface 105B of the body 105 and forming a metallization contact surface, which corresponds to the second surface 50B of the ohmic layer 50 and therefore it is indicated by the same reference number.

[0112] The die 103 also comprises a back metallization region 125 corresponding to the metallization layer 60 and extending on the metallization contact surface 50B.

[0113] The die 103 further comprises a connection structure region 127 corresponding to the connection structure layer 8, extending on the first surface 105A of the body 105.

[0114] In detail, the device region 109 and the connection structure region 127 correspond to a respective die portion 18 (FIG. 2).

[0115] In use, the electronic device 100 has a current path 128, schematically represented by a dashed arrow in FIG. 14, which extends between the connection structure region 111 and the back metallization region 125, through the body 105.

[0116] In use, a current may flow through the current path 128, depending on the specific structure of the device region 109 (i.e., on the type of the electronic device 100).

[0117] The ohmic connection region 123 shows a high mechanical stability.

[0118] The ohmic connection region 123 comprises a rough region and one or more smooth regions. The rough region and the smooth regions correspond to the portion of the rough region 55 and, respectively, to the smooth regions 57 within the respective die portion 18 of FIG. 12. Therefore, hereinafter, the rough region of the ohmic connection region 123 is indicated by the same reference number as the rough region 55 of FIG. 12 and the smooth regions of the ohmic connection region 123 are indicated by the same reference number as the smooth regions 57 of FIG. 12.

[0119] The shape of the rough region 55 of the ohmic connection region 123 depends on the first and the second shift step D.sub.X, D.sub.Y, and on the first width W.sub.X, the second width W.sub.Y, the first slope length L.sub.s,X and the second slope length L.sub.s,Y of the beam footprint 35. Accordingly, the rough region 55 of the ohmic connection region 123 is formed by portions of the horizontal stripes 58 and portions of the vertical stripes 59.

[0120] In detail, in this embodiment, the rough region 55 of the ohmic connection region 123 is formed by portions of two adjacent horizontal stripes 58 and portions of two adjacent vertical stripes 59.

[0121] Depending on the first and the second shift step D.sub.X, D.sub.Y, and on the first width W.sub.X, the second width W.sub.Y, the first slope length L.sub.s,X and the second slope length L.sub.s,Y of the beam footprint 35, the percentage of the ohmic connection region 123 that is formed by the smooth regions 57 (and accordingly by the rough region 55) may be varied.

[0122] The rough region 55 of the ohmic connection region 123 has a non-uniform thickness along the third axis Z.

[0123] The rough region 55 of the ohmic connection region 123 has, at the second surface 105B of the body 105 and at the second surface 50B of the ohmic connection region 123, a higher roughness than the smooth regions 57 of the ohmic connection region 123.

[0124] FIG. 15 is an exemplificative zoomed-in micrograph of a portion of the second surface 50B of the ohmic connection region 123, showing the effect of the gradient regions 44 during the laser annealing of FIG. 4.

[0125] The micrograph of FIG. 15 shows a portion 130 of the rough region 55 of the ohmic connection region and two portions 135 of the smooth region 57. The portion 130 of the rough region 55, which corresponds for example to a portion of a horizontal stripe 58 or of a vertical stripe 59, is formed by a plurality of protrusions 140 of silicide, each having a diameter comprised for example between 0.5 μm and 2 μm.

[0126] The inventors have verified that the protrusions 140 increase the mechanical robustness of the ohmic connection region 123. The electronic device 100 is therefore less subject to mechanical defects such as fracture and delamination of the ohmic connection region 123.

[0127] In particular, a shear test of the electronic device 100, performed by the inventors after subjecting test devices to one hundred thermal cycles, shows an average increase of the shear strength of the electronic device 100 even up to 156% with respect to a case wherein the electronic device 100 has no overlap portions.

[0128] At the same time, the ohmic connection region 123 ensures a good electrical contact, in particular an ohmic contact, with the substrate 107. Therefore, the electronic device 100 also maintains good electrical properties.

[0129] It is clear that the present manufacturing method and the corresponding electronic device may be subject to modifications and variations without departing the scope of the present invention, as defined in the attached claims.

[0130] For example, the beam footprint 35 may have a different shape such as rectangular, circular or any other shape.

[0131] In addition, the energy profile along the first axis may be different from the energy profile along the second axis Y. For example, the spatial trend of the first and the second sloped regions 37, 39 may be different, such as non-linear.

[0132] Moreover, a higher number of laser shots or pulses may be used to expose each irradiated portion of the contact surface 22. For example, two to five laser shots or pulses may be used.

[0133] In the annealing step of FIG. 4, the step-and-repeat type of scanning may be achieved either by moving the work body 1, by moving the laser source 30, by deflecting the laser beam 33 or a combination thereof, depending on the specific application.

[0134] Moreover, the shape of the rough region 55 of FIG. 12 (and accordingly also of the rough region 55 of the ohmic connection layer 123 of the electronic device 100) may be different. A different number of horizontal and vertical stripes 58, 59 may be comprised in a die portion 18. For example, the density of horizontal and vertical stripes 58, 59 may be so high that the ohmic layer 50 (and therefore also the ohmic connection region 123 of the electronic device 100) is approximately entirely formed by a rough region.

[0135] Alternatively, the rough region 55 may have a shape different from a grid, for example the rough region 55 may form a non-regular pattern such as a plurality of separated portions with increased roughness.