Method for Fabrication of a Suspended Elongated Structure by Etching or Dissolution Through Openings in a Layer

Abstract

In an embodiment a device includes a base layer, a support structure formed on the base layer, a side structure formed on the base layer and an elongated structure extending in a length direction in a device layer, wherein the elongated structure has a width in the device layer in a direction perpendicular to a length direction and a height in a direction out of the device layer and perpendicular to the length direction, wherein the elongated structure is delimited by two side surfaces and is supported on the support structure, and wherein at least a part of the side structure is arranged at a distance from the elongated structure in a width direction.

Claims

1.-47. (canceled)

48. A method for fabricating a device with an elongated structure extending in a length direction in a device layer, wherein the elongated structure has a width in the device layer in a direction perpendicular to the length direction and a height in a direction out of the device layer and perpendicular to the length direction, and wherein the elongated structure is delimited by two side surfaces and supported on a planar first layer by a support structure, the method comprising: providing the planar first layer on which the device layer is supported; removing a material in the device layer to provide a first set of openings through the device layer; removing a material by etching or dissolution from the planar first layer under the elongated structure through the first set of openings, wherein an arrangement of the first set of openings is such that the support structure is formed on which the elongated structure is supported; and removing the material from the device layer to form the elongated structure delimited by the side surfaces.

49. The method according to claim 48, further comprising arranging an additional layer between the device layer and the planar first layer, wherein the openings of the first set of openings are also arranged in the additional layer, and wherein the additional layer is a protective layer while removing the material from the planar first layer under the elongated structure.

50. The method according to claim 48, further comprising removing the material in the device layer to provide a second set of openings, wherein the first set of openings and the second set of openings are arranged on opposite sides of the elongated structure.

51. The method according to claim 48, wherein the planar first layer comprises a base layer and an intermediate layer, and wherein the support structure is formed in the intermediate layer.

52. The method according to claim 48, wherein the elongated structure is a waveguide for guiding an electromagnetic wave.

53. The method according to claim 52, wherein a thickness of the device layer is smaller than a wavelength to be guided.

54. The method according to claim 48, wherein the arrangement of the first set of openings is such that the support structure is formed as a number of support pillars being spaced apart so that the elongated structure is free-hanging between the support pillars.

55. A device comprising: a base layer; a support structure formed on the base layer; a side structure formed on the base layer; and an elongated structure extending in a length direction in a device layer, wherein the elongated structure has a width in the device layer in a direction perpendicular to the length direction and a height in a direction out of the device layer and perpendicular to the length direction, wherein the elongated structure is delimited by two side surfaces and is supported on the support structure, and wherein at least a part of the side structure is arranged at a distance from the elongated structure in a width direction.

56. The device according to claim 55, wherein a width of the support structure at a contact with the elongated structure is smaller than the width of the elongated structure at least along a part in the length direction.

57. The device according to claim 55, wherein a minimum distance between the side structure and the elongated structure in the width direction is more than a maximum distance, perpendicularly to the base layer, between the elongated structure and the base layer.

58. The device according to claim 55, wherein a minimum distance between the side structure and the elongated structure in the width direction is more than a maximum distance, perpendicularly to the base layer, in a height direction between the elongated structure and any other material.

59. The device according to claim 55, wherein a thickness of the side structure is at least 1/100 of a thickness of the support structure.

60. The device according to claim 55, wherein the side structure is physically separated from the support structure.

61. The device according to claim 55, further comprising a connection layer located on the base layer between the support structure and the side structure.

62. The device according to claim 61, wherein the connection layer is of the same material as the support structure or the side structure.

63. The device according to claim 61, wherein the connection layer is connected to at least one of the support structure or the side structure.

64. The device according to claim 61, wherein the connection layer is positioned under one of the side surfaces.

65. The device according to claim 61, wherein a thickness of the connection layer is smaller than a thickness of the support structure.

66. The device according to claim 61, wherein a thickness of the connection layer is smaller than a thickness of the side structure.

67. The device according to claim 61, wherein an edge of the elongated structure and an edge of the support structure are at least partially nonparallel in a plan view.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] In the following embodiments of the invention will be described with reference to the appended drawings.

[0086] FIG. 1 shows the starting material for fabrication of a device of a method according to an embodiment;

[0087] FIG. 2 shows the starting material with a first set of openings formed through the device layer;

[0088] FIG. 3 shows the device after material has been removed from the planar first layer and after the elongated structure has been separated from the device layer;

[0089] FIGS. 4a and 4b illustrate a device fabricated with a method according to an alternative embodiment;

[0090] FIGS. 5-8 illustrate a method according to an alternative embodiment;

[0091] FIG. 9 is a cross-sectional view of the elongated structure and the support structure;

[0092] FIG. 10a shows schematically in cross section a structure in which the first set of openings and the second set of openings have been sealed;

[0093] FIG. 10b shows schematically in cross section a structure after the void under the elongated structure has been partly filled;

[0094] FIG. 11a shows a structure with an additional layer between the planar first layer and the device layer after material has been removed from the planar first layer;

[0095] FIG. 11b shows a structure with an additional layer between the intermediate layer and the device layer after material has been removed from the intermediate layer;

[0096] FIG. 12a shows in cross section the structure of FIG. 11a in which parts of the additional layer have been removed;

[0097] FIG. 12b shows in cross section the structure of FIG. 11b in which parts of the additional layer have been removed;

[0098] FIG. 13 shows, in a top view, a first set of openings and a second set of openings, according to an alternative embodiment;

[0099] FIG. 14 is a flow diagram of a method according to an embodiment; and

[0100] FIG. 15 is a cross-sectional view of the elongated structure and the support structure according to an alternative to the cross section shown in FIG. 9.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0101] In the following description of embodiments the same reference numerals will be used for similar features in the different drawings. The drawings are not drawn to scale.

[0102] FIGS. 1-3 illustrate a method according to an embodiment for fabrication of a device with an elongated structure. The method is directed to the fabrication of a device 100 with an elongated structure 5 as is shown in part in FIG. 3. The elongated structure 5 extends in a length direction L in a device layer 2. The elongated structure 5 has a width w (FIG. 3) in the device layer 2 in a direction perpendicular to the length direction L, and a height h (FIG. 3) in a direction out of the device layer 2 and perpendicular to the length direction L. The elongated structure 5 is delimited by two side surfaces 6 and is supported on a first layer 1 by a support structure 4.

[0103] The starting material for the method is in the form of a planar first layer 1 on which a device layer 2 is arranged, as shown in FIG. 1. The planar first layer 1 comprises a base layer 7 and an intermediate layer 8.

[0104] In a first step material in the device layer 2 is removed to provide a first set of openings 3 through the device layer 2. FIG. 2 shows the planar first layer 1, comprising the base layer 7 and the intermediate layer 8, with a first set of openings 3 formed through the device layer 2. Depending on the material in the device layer 2 the first set of openings 3 may be formed using etching or dissolution.

[0105] In a second step material from the planar first layer 1 under the elongated structure 5 is removed through the first set of openings 3. The arrangement of the first set of openings 3 is such that a support structure 4 is formed. The removal of the material from the first layer 1 is performed using etching or dissolution depending on the material in the first layer. The different materials that may be used will be discussed in more detail below. In a third step material in the device layer 2 is removed to form the elongated structure 5 delimited by the side surfaces 6, as is shown in FIG. 3. The elongated structure 5 extends in the length direction L.

[0106] The step of removing material from the planar first layer 1 under the elongated structure 5 is made by etching or dissolution. A number of different etching techniques exist such as wet etching, dry etching and plasma etching. The step of removing material from the planar first layer 1 under the elongated structure 5 is performed during a predetermined time period. The predetermined time period is dependent on the etch rate/dissolution rate of the etchant/solvent or the process parameters in plasma etching, and the arrangement of the openings 3 in the device layer 2.

[0107] FIGS. 4a and 4b illustrate the fabrication of a device 100 with a method according to an alternative embodiment. FIG. 4a shows schematically the device 5 before the elongated structure 5 has been separated from the device layer 2. As can be seen in FIG. 4 the elongated structure 5 is formed as a closed loop in a double spiral. The arrangement of the elongated structure 5 as a closed loop enables the elongated structure 5 to be long in a small space. A first set of openings 3 and a second set of openings 3′ have been formed through the device layer 2 on opposite sides of the elongated structure 5. The first set of openings 3 comprises circular openings 11 and elongated openings 10. Similarly, the second set of openings 3 comprises circular openings H and elongated openings 10′. The cavity formed by removal of material from the intermediate layer 8 (FIGS. 1-3) is shown with the dotted lines 17. FIG. 4b shows the device 100 after the elongated structure 5 has been separated from the device layer 2 (FIGS. 1-3). If made by a suitable material the elongated structure 5 can be a waveguide. Coupling of light into and out of the elongated structure 5 can be performed with gratings (not shown) arranged on the surface of the elongated structure.

[0108] FIGS. 5-8 illustrate a method according to an alternative embodiment. FIG. 5 shows in a perspective view in cross section a planar first layer 1 on which a device layer 2 is arranged. The planar first layer 1 comprises a base layer 7 and an intermediate layer 8. In FIGS. 5-8 the base layer 7 is shown to be equally thick as the intermediate layer 8 for illustrative reasons. However, normally the base layer 7 is considerably thicker than the intermediate layer 8. In a first step two trenches 9, 9′, are formed in the device layer 2. In a second step material is removed from the device layer 2 to provide a first set of openings 3 and a second set of openings 3′. The resulting structure after the first step and the second step is shown in FIG. 6. The first set of openings 3 and the second set of openings 3′ are arranged on opposite sides of the elongated structure (not shown in FIG. 6). As can be seen in FIG. 6 the first set of openings 3 comprises a first elongated opening 10. The first elongated opening 10 is slightly V-formed with the tip of the V pointing away from the support structure 4 to be formed. Correspondingly, the second set of openings 3′ comprises a second elongated opening 10′ which is slightly V-formed with the tip of the V pointing away from the support structure 4 to be formed. The openings 11, 11′, as shown in FIG. 6 have circular shape. This increases the stability of the device layer 2 by preventing corners with high stress in the device layer 2. The openings 10, 10, ′11, 11′, must be sufficiently large to allow the etchant/solvent/radicals (in case of plasma etching) to penetrate through the device layer 2. The openings 10, 10′, 11, 11′, do not have to be very large. In fact, even openings 10, 10′, 11, 11′, with a diameter of a few tens or a few hundreds of nanometers can be used. Decreased hole size might allow easier processing in the following steps. The other openings in the first set of openings 3 and the second set of openings 3′ are circular openings 11, 11′. The size of the elongated openings 10, 10′, and the circular openings 11, 11′, is chosen so that an efficient removal of material may be performed through the openings 10, 10′, 11, 11′. The elongated openings 10, 10′, and the circular openings 11, 11′, have a smallest extension of no less than 10 nm and preferably no less than 100 nm. In some cases, it might be beneficial that the elongated openings 10, 10′, and the circular openings 11, 11′, in the device layer 2 also define the edge of the elongated structure 5 to be formed. Meaning, the distance between an opening 10, 10′, 11, 11′, and the elongated structure 5 can decrease to zero.

[0109] After formation of the first set of openings 3 and the second set of openings 3′ material is removed from the intermediate layer 8. Depending on the material in the intermediate layer 8 the removal of material from the intermediate layer is performed in different ways. The material may be removed through etching or dissolution using a solvent. There are a number of different etching techniques, known per se to a person skilled in the art, that may be used for removing material from the intermediate layer. These etch techniques can have an isotropic or anisotropic etch profile. After the step of removing material from the intermediate layer 8 under the elongated structure 5 additional processing steps including, photolithography and/or material deposition and/or thermal processing and/or surface functionalization and/or layer transfer processes and/or wet/dry etching processes are performed before the elongated structure 5 is separated from the device. The elongated structure 5 extends in the length direction L and is delimited on the sides by the side surfaces 6. FIG. 7 shows the resulting structure after removal of material from intermediate layer 8. The ratio of the removed area in the intermediate layer 8 to the total area of the openings 10, 10′, 11, 11′, through the device layer 2 is at least 2, preferably 5. In this way, the openings 10, 10′, 11, 11′, may have a limited size which is advantageous for mechanical stability of the device layer 2, as the material in the device layer 2 between the openings 10, 10′, 11, 11′, may be wider with smaller openings 10, 10′, 11, 11′. As can be seen in FIG. 7 a metal rib 12 in the form of a metal electrode has been formed on top of the device layer 2 between the trenches 9, 9′. Also, a first metal layer 13 and a second metal layer 13′ have been formed as electrodes on opposite sides of the trenches 9, 9′. Finally, a stack 14 of a two-dimensional material e.g. graphene and a passivation layer are transferred on top of the first metal layer 13, the second metal layer 13′, the trenches 9, 9′ and the metal rib 12. A rib waveguide is formed by the elongated structure 5 between the trenches 9, 9′, and the metal rib 12.

[0110] In a final step material is removed from the device layer 2 to form the elongated structure 5 delimited by side surfaces 6. The resulting structure can be seen in FIG. 8. The elongated structure 5 in the device 100 in FIG. 8 is a waveguide. In FIG. 8 it is seen that the elongated structure 5 in the form of a waveguide transits into a rib waveguide formed by the elongated 5 structure 5 between the trenches 9, 9. In the transition portion the thinned portion of the

device layer 2 widens. These thinned portions of the device layer 2 were formed as the trenches 9, 9′, in FIG. 6. In FIG. 8 the support structure 4 is in the form of a support pillar 18. As can be seen in FIG. 8 the support pillar 18 has a diamond shape which reflects the shape of the first elongated opening 10 and the second elongated opening 10′. The removal of material in the intermediate layer 8 takes place through the openings 10, 10′, 11, 11′. The void grows over time as the etching/dissolution continues. The size of the void depends on the etch rate/dissolution rate of the etchant/solvent step and the time of etching/dissolution. Thus, in order to control the removal of material from the intermediate layer 8 it is necessary to control the etch/dissolution rate as well as the time of etching/dissolution. The etching/dissolution is performed during a predetermined time period, wherein the predetermined time period is dependent and the arrangement of the openings 10, 10′, 11, 11′, in the device layer 2. The final edges of the void in the intermediate layer 8 is the etching front which is at a specific distance from the closest opening in the first set of openings 3 and the second set of openings 3′. If the etching/dissolution would have been allowed to continue the support pillar 18 would have become increasingly shorter. Simultaneously, the support structure would have become narrower.

[0111] In FIG. 8 only one support pillar 18 is shown but naturally the device fabricated with the method according an embodiment may comprise a number of support pillars 18 with the elongated structure 5 free-hanging between the support pillars 18. The shortest distance between the elongated structure 5 and the openings 10, 11, in the first set of openings 3 varies along the length of the elongated structure 5 and said distance has a maximum at the support pillars 18. Naturally, the distance between the elongated structure 5 and the openings 10, 11, in the first set of openings 3 is not clearly visible as the elongated structure 5 is not clearly visible until the elongated structure 5 has been separated from the surrounding device 30 layer 2.

[0112] When the elongated structure 5 is a waveguide the refractive index of the intermediate layer 8 is arranged to be different from the refractive index of the device layer 2. In FIGS. 5-8 the base layer 7 is a silicon layer, and the intermediate layer 8 is a silicon dioxide layer. Alternatively, the intermediate layer may be a sapphire layer, or a polymer layer. Additionally, the intermediate layer can be of chalcogenide glass (ChGs), germanium, silicon germanium, silicon nitride and, diamond. In case the intermediate layer is a polymer layer the removal of material from the intermediate layer may be performed by dissolution using a solvent. It is also possible to remove material from the intermediate layer by plasma etching using an oxygen plasma.

[0113] The device layer 2 may be a silicon layer. It is preferable to use a structure of silicon as base layer 7, silicon dioxide as intermediate layer 8 and silicon as device layer 2 as such substrates are readily available from a number of manufacturers. This makes the price on the starting material low. Such substrates are usually marketed under the abbreviation SOI (silicon on insulator).

[0114] It is of course also possible to choose other materials for the device layer 2, the first layer and the intermediate layer such as, e.g., a material from the group of materials consisting of chalcogenide glass (ChGs), germanium, silicon germanium, silicon nitride, sapphire and, diamond.

[0115] It is possible to use a polymer in the intermediate layer 8. In such a case, it is possible to use a solvent to remove material from the intermediate layer 8. Solvents used to dissolve polymers are considerably less aggressive than etchants used to remove silicon. Thus, metals can be deposited before removing a polymer below the device layer 2. Similarly, a deposited layer of silicon is not attacked when removing SiO.sub.2 below the device layer 2 with hydrofluoric acid. It is also possible to remove material from the intermediate layer 8 by plasma etching using an oxygen plasma.

[0116] When the elongated structure 5 is used as a waveguide the thickness of the device layer 2 is arranged to be smaller than the wavelength to be guided. Furthermore, the width of the waveguide in the device layer 2 is arranged to be at least 5 times the thickness of the device layer 2. It is favorable to have the width of the waveguide at least 5 times the thickness as the side surfaces 6 cannot be made with the same quality as the top and bottom surfaces. Thus, by making the waveguide wide the effect of the side surfaces 6 on the wave guiding properties is minimized.

[0117] The wavelength of the electromagnetic wave is within the range of 0.4-100 μm, preferably 1.2-20 μm, most preferred within 3-12 m. Silicon is a suitable material for the wavelength range from 1.1-10 μm while other materials from the materials mentioned above may be more suitable for wavelengths below 1.1 μm and above 10 μm. A support structure 4 made from silicon dioxide has very little effect on an electromagnetic wave propagating in the waveguide.

[0118] In order to minimize the effect of the support pillar 18 on the electromagnetic wave propagating in the waveguide it is desirable to have the width of the support pillar 18 smaller than the width of the elongated structure 5 at the point of support of the elongated structure. This is clearly shown in the cross-sectional view of the elongated structure 5 with side surfaces 6 and the support structure 4 of FIG. 9. In FIG. 9 it is clearly shown that the width Ws of the support pillar 18 is considerably smaller than the width w of the elongated structure 5. The cross section in FIG. 9 is taken at the center of the support pillar 18 in FIG. 8. The features in the background, behind the plane of the cross section, are not shown in FIG. 9.

[0119] As described above the material in the intermediate layer 8 may be removed before any additional process steps for forming, e.g., additional layers on the device layer 2. In order to optimize such later processes it is favorable to seal the openings 10, 11, in the first set of openings 3 and the second set of openings 3′, before performing said additional process steps. In FIG. 10a the openings 3, 3′, have been sealed by application of a sealing layer 19 on the device layer 2. Such a structure with sealed openings 10, 11, in the first set of openings 3 and the second set of openings 3′ is shown schematically in FIG. 10a. In case an easily removable material such as, e.g., a polymer is used, the material in the intermediate layer 8 may be removed after additional process steps.

[0120] In order to increase the stability of the device layer 2 after removing material from the intermediate layer 8 under the elongated structure 5, the void under the elongated structure 5 can be filled at least partly as is shown in FIG. 10b. The filling material 20 is preferably an easily dissolved/removable material such as a polymer or a photoresist. FIG. 10b is split to show to different variants of the filling. In the left part of FIG. 10b the filling supports the entire device layer 2 under which the intermediate layer 8 has been removed.

[0121] In some cases, it might be desirable to have the same material in the device layer 2 and the intermediate layer 8 or the planar first layer. Naturally this is very difficult to achieve without an additional layer. Thus, in order to allow the device layer 2 and the intermediate layer 8 to be of the same material an additional layer 15 may be added between the device layer 2 and the intermediate layer 8/planar first layer 1. The openings 10, 10′, 11, 11′, of the first set of openings 3 and the second set of openings 3 are arranged also through the additional layer 15. Before starting etching/dissolution of the intermediate layer 8/planar first layer 1, a protective layer 16 is arranged on the upper side of the device layer 2. FIG. 11a shows the structure after material has been removed from the planar first layer 1. The additional layer 15 is almost unaffected by the etching/dissolution and covers the underside of the elongated structure 5. The removal of material from the additional layer 15 must be sufficiently slower than the removal of material from the planar first layer 1 so that the device layer 2 is protected during etching. Similarly, the protective layer 16 is almost unaffected by the etching/dissolution and is intact on the upper side of the elongated structure. The protective layer 16 and the additional layer 15 may be of the same material such as, e.g., a polymer. The thickness of the additional layer 15 is 100 nm-50 μm. The addition of an additional layer 15 in the form of a polymer layer can reduce optical losses in the waveguide further. In FIG. 11a the support structure 4 is formed in the planar first layer. In FIG. 11b the planar first layer 1 comprises a base layer 7 and an intermediate layer 8. Another example of a structure with the same material in the device layer 2 and the intermediate layer 8 is a SOI (silicon on insulator) structure. An SOI wafer is then used as starting material so that the base layer 7 is a silicon layer, the intermediate layer 8 is a silicon dioxide layer and the device layer 2 is a silicon layer. Such a structure would result in a device with the same structure as is shown in FIGS. 11a and 12a.

[0122] When material has been removed from the intermediate layer 8/planar first layer 1, the protective layer 16 and parts of the additional layer 15 may be removed. In this case the protective layer 16 and parts of the additional layer 15 are polymer layers and are removed with a suitable solvent or plasma etching. The thickness of the polymer layer is 100 nm-50 μm, preferably 200 nm-1μ. The resulting structures are shown in in cross section in FIGS. 12a and 12b with the same reference numerals as in FIGS. 11a and 11b. In FIGS. 12a and 12b it can be clearly seen that the width Wa of the additional layer 15 is smaller than the width of the support structure 4 Ws at the top of the support structure 4.

[0123] With this method it is also possible to fabricate a device where Ws is larger than the width w of the elongated structure 5. However, to reduce optical losses through the support, it is beneficial to minimize the size of the support structure.

[0124] FIG. 13 shows, in a top view, a first set of openings 3 and a second set of openings 3′, according to an alternative embodiment. In FIG. 13 the elongated openings 10, 10′ have a straight shape but are arranged at an angle to the elongated structure 5. The resulting support pillar 18 is shown with dashed lines in FIG. 13. The arrangement of the elongated openings 10, 10′, is reflected in the shape of the support pillar 18 which is wedge shaped in FIG. 13. The elongated structure 5 is free-hanging on both sides of the support pillar 18.

[0125] It would of course be possible to replace the elongated openings 10, 10′, with a number of closely spaced circular openings 11, 11′. However, elongated openings 10, 10′, give smoother walls on the support structure 4. Abrupt edges on the support structure 4 may cause reflections in case the elongated structure 5 is a waveguide.

[0126] The shortest distance between the elongated structure 5 and the openings 10, 11, in the first set of openings 3 varies along the length of the elongated structure 5 and said distance has a maximum Dmax where the width of the support pillar 18 is at its maximum.

[0127] FIG. 14 is a flow diagram of a method according to an embodiment. In a first step 101 a planar first layer 1 is provided on which first layer 1 a device layer 2 is supported. In a second step 102 material is removed from the device layer 2 to provide a first set of openings 3 through the device layer 2. In a third step 103 material is removed from the planar first layer 1 under the elongated structure 5 through the first set of openings 3, wherein the arrangement of the first set of openings 3 is such that a support structure 4 is formed on which the elongated structure 5 is supported. In a fourth step 104 material is removed from the device layer 2 to form the elongated structure 5 delimited by the side surfaces 6.

[0128] FIG. 15 is a cross-sectional view of the elongated structure and the support structure according to an alternative to the cross section shown in FIG. 9. The difference between FIG. 15 and FIG. 9 is that the device comprises a connection layer 21 which is in contact with the base layer 7 and extends between the support structure 4 and the side structure 28.

[0129] The material of the side structure 28 may be different from the material of the base layer 7 and also different from the material of the device layer 2. However, in order to facilitate the production of the device the material of the connection layer is preferably the same as the material of the side structure. The side structure 28 is physically separated from the support structure 4.

[0130] As can be seen in FIG. 15 the side 29 of the side structure 28 facing away from the base layer 7 is free from contact with the device layer 2.

[0131] It can also be seen in FIG. 15 that the width of the support structure 4 at the contact with the elongated structure 5 is smaller than the width of the elongated structure 5 at least along a part in the length direction.

[0132] The minimum distance 31 between the side structure 28 and the elongated structure 5 in the width direction is more than the maximum distance 30, perpendicularly to the base layer, between the elongated structure 5 and the base layer 7, and also more than the maximum distance 32 between the elongated structure 5 and any material.

[0133] The thickness 31 of the side structure 28 is about the same as the thickness 30 of the support structure 4. This allows easy arrangement of a capping substrate on the side structure 28.

[0134] The thickness of the side structure 28 is larger than the maximum thickness of the connection layer 21.

[0135] As can be seen in FIG. 8 the edge of the elongated structure 5 and the edge of the support structure 4 are at least partially nonparallel in a plan view.

[0136] The embodiments described above may be amended in many ways without departing from the scope of the present invention.