阅读说明：本技术 圆盘的区段设计 (Sector design of a disc ) 是由 D·耶内尔 C·苏里亚加 J·索萨 L·厄乌尔 J·里韦尔斯 E·巴卢 于 2020-04-08 设计创作，主要内容包括：揭示一种用于化学机械平坦化(CMP)组合件的垫修整器及CMP垫修整器组合件。所述垫修整器包含衬底,所述衬底具有第一表面及与所述第一表面相对的第二表面。多个突起在垂直于所述第一表面的方向上远离所述第一表面突出。所述多个突起经布置成多个行。所述多个行中的第一行从所述多个行中的第二行偏移。(A pad conditioner and a Chemical Mechanical Planarization (CMP) pad conditioner assembly for a CMP assembly are disclosed. The pad conditioner includes a substrate having a first surface and a second surface opposite the first surface. A plurality of protrusions project away from the first surface in a direction perpendicular to the first surface. The plurality of protrusions are arranged in a plurality of rows. A first row of the plurality of rows is offset from a second row of the plurality of rows.)

1. A pad conditioner for a Chemical Mechanical Planarization (CMP) assembly, comprising:

a substrate having a first surface and a second surface opposite the first surface; and

a plurality of protrusions protruding away from the first surface in a direction perpendicular to the first surface, wherein the plurality of protrusions are arranged in a plurality of rows,

wherein a first row of the plurality of rows is offset from a second row of the plurality of rows.

2. The pad conditioner of claim 1, wherein said plurality of protrusions comprise a uniform geometry.

3. The pad conditioner of claim 2, wherein said plurality of protrusions comprise one of a conical shape and a frustoconical shape.

4. The pad conditioner of claim 1, wherein said plurality of protrusions are evenly spaced.

5. The pad conditioner of claim 1, wherein said plurality of protrusions are formed of silicon carbide having a diamond coated cutting surface.

6. The pad conditioner of claim 1, wherein a density of said plurality of protrusions is from 0.10/mm²Or about 0.10/mm²To 25/mm²Or about 25/mm²。

7. The pad conditioner of claim 1, wherein a protrusion distance from said substrate is from 15 μ ι η or about 15 μ ι η to 100 μ ι η or about 100 μ ι η.

8. The pad conditioner of claim 1, wherein said offset is from 10 ° or about 10 ° to 60 ° or about 60 °.

9. The pad conditioner of claim 1, wherein said offset is 45 ° or about 45 °.

10. The pad conditioner of claim 1, wherein a number of protrusions in said first row of said plurality of protrusions is different from a number of protrusions in said second row of said plurality of protrusions.

11. The pad conditioner of claim 1, wherein said plurality of rows includes a third row, said third row of said plurality of rows being offset from said second row of said plurality of rows.

12. A Chemical Mechanical Planarization (CMP) pad conditioner assembly, comprising:

a back plate having a first back plate surface; and

a plurality of pad conditioners secured to the first backing plate surface, each of the plurality of pad conditioners comprising:

a substrate having a first surface and a second surface opposite the first surface; and

a plurality of protrusions protruding away from the first surface in a direction perpendicular to the first surface, wherein the plurality of protrusions are arranged in a plurality of rows,

wherein a first row of the plurality of rows is offset from a second row of the plurality of rows.

13. The assembly of claim 12, wherein the plurality of pad conditioners are circumferentially spaced around the backing plate.

14. The assembly of claim 12, wherein each of the plurality of pad conditioners are the same.

15. The assembly of claim 12, wherein the plurality of protrusions include a uniform geometry.

16. The assembly of claim 15, wherein the plurality of protrusions include one of a conical shape and a frustoconical shape.

17. The assembly of claim 12, wherein the plurality of protrusions are evenly spaced.

18. The assembly of claim 12, wherein the plurality of protrusions are formed of silicon carbide having a diamond coated cutting surface formed by chemical vapor deposition.

19. The assembly of claim 12, wherein the density of the plurality of protrusions is from 0.10/mm²Or about 0.10/mm²To 25/mm²Or about 25/mm²。

20. The assembly of claim 12, wherein the offset is 45 ° or about 45 °.

Technical Field

The present invention generally relates to an apparatus for manufacturing semiconductors. More particularly, the present invention relates to a pad conditioner for Chemical Mechanical Planarization (CMP).

Background

Chemical mechanical planarization or Chemical Mechanical Polishing (CMP) can be part of a manufacturing process for semiconductor devices. During CMP, material is removed from the wafer substrate via the polishing pad and the polishing slurry. CMP may optionally comprise one or more chemical agents. Over time, the polishing pad can become tangled and become saturated with debris. The pad conditioner may be used to recondition the polishing pad.

Disclosure of Invention

The present invention generally relates to an apparatus for manufacturing semiconductors. More particularly, the present invention relates to a pad conditioner for Chemical Mechanical Planarization (CMP).

A pad conditioner for a Chemical Mechanical Planarization (CMP) assembly is disclosed. The pad conditioner includes a substrate having a first surface and a second surface opposite the first surface. A plurality of protrusions project away from the first surface in a direction perpendicular to the first surface. The plurality of protrusions are arranged in a plurality of rows. A first row of the plurality of rows is offset from a second row of the plurality of rows.

A Chemical Mechanical Planarization (CMP) pad conditioner assembly is also disclosed. The CMP pad conditioner assembly includes: a back plate having a first back plate surface; and a plurality of pad dressers secured to the first backing plate surface. Each of the plurality of pad conditioners includes a substrate having a first surface and a second surface opposite the first surface. A plurality of protrusions project away from the first surface in a direction perpendicular to the first surface. The plurality of protrusions are arranged in a plurality of rows. A first row of the plurality of rows is offset from a second row of the plurality of rows.

Drawings

Reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration embodiments in which the systems and methods described in this specification may be practiced.

Fig. 1A is a top view of a pad conditioner assembly according to an embodiment.

FIG. 1B is a cross-sectional view of the pad conditioner assembly of FIG. 1A taken along line 1B-1B, according to an embodiment.

Fig. 2 is a top view of one of the plurality of pad dressers of fig. 1A, according to an embodiment.

FIG. 3 is a top view of one of the plurality of pad dressers of FIG. 1A according to another embodiment.

Like reference numerals refer to like parts throughout.

Detailed Description

The present invention generally relates to an apparatus for manufacturing semiconductors. More particularly, the present invention relates to a pad conditioner for Chemical Mechanical Planarization (CMP).

Fig. 1A is a top view of a pad conditioner assembly 10, according to an embodiment. Fig. 1B is a cross-sectional view of the pad conditioner assembly 10 taken along line 1B-1B, according to an embodiment. The pad conditioner assembly 10 is generally useful for reconditioning polishing pads used in CMP.

The pad conditioner assembly 10 includes a backing plate 15 having a first backing plate surface 20. In an embodiment, the back plate 15 may have a disc shape. In an embodiment, the back plate 15 may alternatively be referred to as a disc-shaped holder 15 or the like. In an embodiment, the first backplate surface 20 may alternatively be referred to as the first backplate surface 20. The back plate 15 has a diameter D. In embodiments, the diameter D may be between 3 inches or about 3 inches to 13 inches or about 13 inches. It should be understood that this range is an example and that the actual diameter D may be outside the stated range in accordance with the principles in this specification. The back plate 15 may be made of stainless steel, plastic or the like.

The backplate 15 has a second backplate surface 25 (FIG. 1B) opposite the first backplate surface 20. The second backing plate surface 25 of the backing plate 15 can include one or more mounting structures (not shown) for securing the backing plate 15 of the pad conditioner assembly 10 to a CMP tool. In an embodiment, the second back plate surface 25 may alternatively be referred to as the mounting surface 25. The one or more mounting structures may be magnetic, snap fit, apertures (e.g., for screws, bolts, or the like), or the like. The backing plate 15 may be made of a material that is chemically compatible or chemically passivated with the CMP process chemicals and slurry.

A plurality of pad conditioners 30 are secured to the first backing plate surface 20. An embodiment of a plurality of pad dressers 30 is shown and described in more detail below with reference to fig. 2 and 3. It should be understood that the pad conditioner 30 is not drawn to scale in FIG. 1A.

The pad conditioner assembly 10 includes a pad conditioner 30 secured to the first backing plate surface 20 by an adhesive 35. In embodiments, suitable adhesives may include, but are not limited to, epoxies, tape adhesives, or the like.

The pad conditioner 30 can include a core 40 and one or more additional layers. In embodiments, the core 40 may be secured to the back plate surface 20 via an adhesive 35. The core 40 may be, for example, porous silicon carbide or the like. The surface layer 45 is disposed on the core 40. In an embodiment, the surface layer 45 may be a silicon carbide surface layer added to the core 40 via, for example, a chemical vapor deposition process. The surface layer 45 includes a hardened layer 55. The hardened layer 55 may be a diamond coating added to the surface layer 45, for example, via chemical vapor deposition. The surface layer 45 and the hardened layer 55 are etched (e.g., via a laser or the like) to create a plurality of surface features 50. A plurality of surface features 50 provide an abrasive surface on the pad conditioner 30. Thus, when reconditioning a polishing pad for a CMP tool, the surface features 50 contact the polishing pad. In embodiments, the core 40 and the surface layer 45 may be collectively referred to as a substrate.

Each of the plurality of pad conditioners 30 typically provides an abrasive region. When the pad conditioner assembly 10 is used to recondition a polishing pad used in CMP, the abrasive regions collectively contact the polishing pad. The polishing zone is typically defined by a plurality of contact surfaces.

Various features of the pad conditioner 30 can be configured depending on the application of the polishing pad reconditioned using the pad conditioner assembly 10. For example, the relative size of the pad conditioner 30; the number of pad conditioners 30; feature density on the pad conditioner 30; the depth of the features on the pad conditioner 30; a suitable combination thereof; or the like, may be selected based on the application of the polishing pad to be reconditioned.

The pad conditioners 30 each have a length L and a width W. In embodiments, the ratio of the length L to the width W may be from 0.2 or about 0.2 to 1 or about 1. The length L and width W may be 0.1 inches or about 0.1 inches to 3 inches or about 3 inches. It should be understood that these ranges are examples and that the actual length L, width W, and corresponding ratios may vary beyond the stated ranges in accordance with the principles of the present specification. In the illustrated embodiment, the pad conditioner 30 is substantially square when viewed from a top view. As used in this specification, "substantially square" means a square subject to manufacturing tolerances or the like. That is, the length L and width W of the pad conditioner 30 are substantially equally subject to manufacturing tolerances or the like. In another embodiment, the geometry of the pad conditioner 30 may be other than square. The pad conditioner 30 can include rounded corners and chamfered edges, for example, to minimize material accumulation and, for example, to reduce scratches resulting from this accumulation. In embodiments, the pad conditioner 30 may be rectangular or the like.

In the illustrated embodiment, four pad conditioners 30 are shown. The spacing between the four pad conditioners 30 can be maintained such that the arc length a around the backing plate 15 is equal among all of the pad conditioners 30. In an embodiment, the spacing between the four pad conditioners 30 can be selected such that the arc length a is not equal among all of the pad conditioners 30.

The number of pad conditioners 30 can vary. For example, in embodiments, more than four pad conditioners 30 may be included on the backing plate 15. Alternatively, according to embodiments, less than four pad conditioners 30 may be included on the backing plate 15. In an embodiment, the minimum number of pad conditioners 30 can be three. Even when the number of pad conditioners 30 varies beyond the illustrated example, the spacing between the pad conditioners 30 can be maintained so that the arc length a around the backing plate 15 remains equal among the pad conditioners 30. Alternatively, the arc length a around the backing plate 15 may vary among pad conditioners 30 such that at least one of the arc lengths a is not equal to another of the arc lengths a.

Each of the plurality of pad conditioners 30 includes a plurality of protrusions that project away from the first back-plate surface 20 in a direction perpendicular to the first back-plate surface 20. More details of the pad conditioner 30 are discussed below in relation to fig. 2 and 3.

The surface features 50 may be conical, frustoconical, a combination thereof, or the like. Other geometries of surface features 50 may be selected. In the illustrated embodiment, the surface features 50 extend from the backplate 15 in a direction perpendicular to the second backplate surface 25 by a distance P from the first backplate surface 20. In addition, each of the surface features 50 extends a distance H from the etched surface portion 60 in a direction away from the second backplane surface 25. The distance H and the distance P may vary. The distances H and P can be selected based on, for example, the application of the pad conditioner assembly 10 (e.g., the particular polishing pad to be reconditioned by the pad conditioner assembly 10). The distance H from the etched surface portion 60 may vary among the surface features 50. For example, a first one of the surface features 50 may extend a first distance H from the etched surface portion 60, while a second one of the surface features 50 may extend a second distance from the etched surface portion 60, the second distance being different from the first distance H. In embodiments, the distance H ranges from 15 μm or about 15 μm to 100 μm or about 100 μm. In an embodiment, the surface features 50 each extend the same distance H such that the contact surface 65 is substantially flat.

In embodiments in which the surface features 50 are frustoconical, the contact surface 65 may be substantially parallel to the first backplate surface 20 of the backplate 15. In an embodiment, the contact surface 65 may be a tip of the conical form of the surface feature 50. In this embodiment, the plane across the tips of the conical form of the surface features 50 may be substantially parallel to the first backplate surface 20 of the backplate 15. In embodiments where the distance H is non-uniform among the surface features 50, the contact surface 65 may not be flat and may not be parallel to the first backplane surface 20 of the backplane 15. Depending on the characteristic tip diameter and geometry, the contact surface 65 may be flat and parallel to the first backplane surface 20. The shape of contact surface 65 may be substantially circular if the feature tip diameter is relatively less than 50 μm or about 50 μm. When the pad conditioner assembly 10 is used to recondition a polishing pad, the contact surface 65 is the point of contact with the polishing pad. As used herein, substantially flat is flat subject to manufacturing tolerances or the like.

Fig. 2 is a schematic top view of one of a plurality of pad dressers 30, according to an embodiment. To simplify the present description, one of the plurality of pad dressers 30 will be referred to as a pad dresser 30A.

The pad conditioner 30A includes a plurality of surface features 50. In an embodiment, the plurality of surface features 50 have a uniform geometry. That is, each of the surface features 50 is geometrically identical. This may be subject to manufacturing tolerances or the like, for example. In another embodiment, the plurality of surface features 50 may be geometrically different (i.e., non-uniform geometry).

The plurality of surface features 50 are provided in a plurality of rows and a plurality of columns. Two of the plurality of rows are labeled R1, R2, and two of the plurality of columns are labeled C1, C2. The remaining rows and columns are not labeled in order to simplify the figure. In the illustrated embodiment, there are nine rows of surface features 50 and 19 columns of surface features 50. The number of rows and the number of columns of surface features 50 may vary. In the illustrated embodiment, the number of columns of surface features 50 is greater than the number of rows of surface features 50. In embodiments, this may be reversed such that the number of rows of surface features 50 is greater than the number of columns of surface features 50. In an embodiment, the number of rows of surface features 50 may be the same as the number of columns of surface features 50. Such an embodiment is shown and described below with reference to fig. 3.

The surface features 50 in row R1 are offset from the surface features 50 in row R2. In the illustrated embodiment, the offset is shown as a distance O. The distance O represents the spacing between columns. That is, the distance O is equal to the spacing between the columns C1 and C2 of surface features 50. The spacing between surface features 50 within a row is shown as distance S. In the illustrated embodiment, distance S represents the horizontal spacing and distance V represents the vertical spacing (relative to the page). The distance S and the distance V are the same in fig. 2. In embodiments, the distance S and the distance V may vary. In embodiments, the distance S and the distance V may be non-uniform across the entire surface of the pad conditioner 30A.

The distance O may be up to or about half the distance S. In the illustrated embodiment, the distance O may range from 0.1S to 0.5S. In an embodiment, the distance O is 0.5S.

An angle θ is shown representing the angle between surface features 50 in row R2 and row R1. The angle θ may vary as the offset between rows R1 and R2 varies. In embodiments, θ may range from 10 ° or about 10 ° to 60 ° or about 60 ° or more particularly, θ may range from 35 ° or about 35 ° to 55 ° or about 55 °. In embodiments, the angle θ is 45 ° or about 45 °. A smaller angle theta represents a larger offset between the surface features 50 in row R1 and the surface features 50 in row R2, while a relatively larger angle theta represents a smaller offset between the surface features 50 in row R1 and the surface features 50 in row R2.

The density of surface features 50 in the conditioner pad 30A may vary. For example, if the distance S, the distance V, or a combination thereof is decreased, the conditioner pad 30A may include additional surface features 50. Conversely, if the distance S, the distance V, or a combination thereof is increased, the conditioner pad 30A may include fewer surface features 50. In embodiments, the density of the surface features 50 may be from 0.10/mm²Or about 0.10/mm²To 25/mm²Or about 25/mm²Or more particularly, the density of the surface features 50 may be from 0.25/mm²Or about 0.25/mm²To 15/mm²Or about 15/mm²Within the range of (1).

The surface features 50 in a single row (e.g., Rl) are aligned in a horizontal direction with respect to the page. The rows of surface features 50 (e.g., R1 and R2) are substantially parallel to each other. As used herein, "substantially parallel" means parallel subject to manufacturing tolerances or the like. The surface features 50 in a single row (e.g., R1) are evenly spaced apart (distance S).

The surface features 50 in a single row (e.g., C1) are aligned in a vertical direction with respect to the page. The columns of surface features (e.g., C1 and C2) are substantially parallel to each other. In the illustrated embodiment, the spacing between rows (e.g., distance V) and the spacing between columns (e.g., distance O) is constant across the conditioner pad 30A. The surface features 50 in a single column (e.g., C1) are evenly spaced (distance V). In embodiments, the spacing between rows (e.g., distance V) and the spacing between columns (e.g., distance O) may be non-constant across the conditioner pad 30A. In an embodiment, the surface features 50 in a single column (e.g., C1) may have varying spacing (i.e., non-uniformly spaced (distance V)).

The columns, rows, or both columns and rows may have variable spacing. In embodiments, the ratio of the number of columns to the number of rows is from 0.2 or about 0.2 to 1 or about 1.

Fig. 3 is a schematic top view of one of a plurality of pad conditioners 30 according to another embodiment. To simplify the present description, one of the plurality of pad dressers 30 will be referred to as a pad dresser 30B. The pad conditioner 30B has a density of surface features 50 that is different from the density of surface features 50 in the pad conditioner 30A of fig. 2.

The pad conditioner 30B includes a plurality of surface features 50. In an embodiment, the plurality of surface features 50 have a uniform geometry. That is, each of the surface features 50 is geometrically identical. This may be subject to manufacturing tolerances or the like, for example. In another embodiment, the plurality of surface features 50 may be geometrically different (i.e., non-uniform geometry).

The plurality of surface features 50 are provided in a plurality of rows and a plurality of columns. Two of the plurality of rows are labeled R1, R2 and two of the plurality of columns are labeled C1, C2. The remaining rows and columns are not labeled in order to simplify the figure. In the illustrated embodiment, there are nine rows of surface features 50. The number of rows of surface features 50 may vary.

The surface features 50 in row R1 are offset from the surface features 50 in row R2. In the illustrated embodiment, the offset is shown as a distance O. The distance O represents the spacing between columns. That is, the distance O is equal to the spacing between the columns C1 and C2 of surface features 50. The spacing between surface features 50 within a row is shown as distance S. In the illustrated embodiment, distance S represents the horizontal spacing and distance V represents the vertical spacing (relative to the page). The distance S and the distance V are the same in fig. 3. In embodiments, the distance S and the distance V may vary. In embodiments, the distance S and the distance V may be non-uniform across the entire surface of the pad conditioner 30B.

The distance O may be up to or about half the distance S.

An angle θ is shown representing the angle between surface features 50 in row R2 and row R1. The angle θ may vary as the offset between rows R1 and R2 varies. In embodiments, θ may range from 10 ° or about 10 ° to 60 ° or about 60 ° or more particularly, θ may range from 35 ° or about 35 ° to 55 ° or about 55 °. In embodiments, the angle θ is 45 ° or about 45 °. A smaller angle theta represents a larger offset between the surface features 50 in row R1 and the surface features 50 in row R2, while a relatively larger angle theta represents a smaller offset between the surface features 50 in row R1 and the surface features 50 in row R2.

The density of surface features 50 in the conditioner pad 30B may vary. For example, if the distance S, the distance V, or a combination thereof is decreased, the conditioner pad 30B may include additional surface features 50. Conversely, if the distance S, the distance V, or a combination thereof is increased, the conditioner pad 30B may include fewer surface features 50. In embodiments, the density of the surface features 50 may be from 0.10/mm²Or about 0.10/mm²To 25/mm²Or about 25/mm²Or, more particularly, in a range of from 0.25/mm²Or about 0.25/mm²To 15/mm²Or about 15/mm²Within the range of (1).

In the illustrated embodiment, distance T and distance U: the surface features 50 in the first row are measured T to the surface features 50 in the second row (which are offset from the first surface features 50) and the surface features 50 in the third row are measured U to the surface features 50 in the second row. According to a further embodiment, the distances U and T are equal in the illustrated figure, but may vary such that the distances are not equal.

Aspect(s)

It should be noted that any of aspects 1-13 may be combined with any of aspects 14-22.

Aspect 1. a pad conditioner for a Chemical Mechanical Planarization (CMP) assembly, comprising: a substrate having a first surface and a second surface opposite the first surface; and a plurality of protrusions projecting away from the first surface in a direction perpendicular to the first surface, wherein the plurality of protrusions are arranged in a plurality of rows, wherein a first row of the plurality of rows is offset from a second row of the plurality of rows.

Aspect 2 the pad conditioner of aspect 1, wherein said plurality of protrusions comprise a uniform geometry.

Aspect 3 the pad conditioner of aspect 2, wherein the plurality of protrusions comprise one of a conical shape and a frustoconical shape.

Aspect 4 the pad conditioner of any of aspects 1-3, wherein said plurality of protrusions are evenly spaced.

Aspect 5 the pad conditioner of any of aspects 1-4, wherein the plurality of protrusions are formed of silicon carbide having a diamond coated cutting surface.

Aspect 6 the pad conditioner of any of aspects 1-5, wherein the density of the plurality of protrusions is from 0.10/mm²Or about 0.10/mm²To 25/mm²Or about 25/mm²Or from 0.25/mm²To 15/mm²Or about 15/mm²。

Aspect 7 the pad conditioner of any one of aspects 1-6, wherein a protrusion distance from the substrate is from 15 μ ι η or about 15 μ ι η to 100 μ ι η or about 100 μ ι η.

Aspect 8 the pad conditioner of any one of aspects 1-7, wherein said offset is from 10 ° or about 10 ° to 60 ° or about 60 °, or from 35 ° or about 35 ° to 55 ° or about 55 °.

Aspect 9 the pad conditioner of any one of aspects 1-8, wherein said offset is 45 ° or about 45 °.

Aspect 10 the pad conditioner of any of aspects 1-9, wherein a number of protrusions in the first row of the plurality of protrusions is different from a number of protrusions in the second row of the plurality of protrusions.

Aspect 11 the pad conditioner of any of aspects 1-10, wherein the number of rows in the plurality of rows is different from the number of protrusions in the rows.

Aspect 12 the pad conditioner of any of aspects 1-11, wherein the plurality of protrusions are integrally formed in the substrate.

Aspect 13 the pad conditioner of any of aspects 1-12, wherein said first one of said plurality of rows includes the same number of protrusions as the number of said plurality of columns.

Aspect 14. a Chemical Mechanical Planarization (CMP) pad conditioner assembly, comprising: a back plate having a first back plate surface; and a plurality of pad dressers secured to the first backing plate surface, each of the plurality of pad dressers comprising: a substrate having a first surface and a second surface opposite the first surface; and a plurality of protrusions projecting away from the first surface in a direction perpendicular to the first surface, wherein the plurality of protrusions are arranged in a plurality of rows, wherein a first row of the plurality of rows is offset from a second row of the plurality of rows.

The assembly of aspect 14, wherein the plurality of pad conditioners are circumferentially spaced around the backing plate.

Aspect 16 the assembly of aspect 14 or 15, wherein each of the plurality of pad conditioners are the same.

The assembly of any of aspects 14-16, wherein the plurality of protrusions include a uniform geometry.

Aspect 18 the assembly of aspect 15, wherein the plurality of protrusions are one of conical and frustoconical.

Aspect 19 the assembly of any of aspects 14-18, wherein the plurality of protrusions are evenly spaced.

Aspect 20 the assembly of any of aspects 14-19, wherein the plurality of protrusions are formed of silicon carbide having a diamond coated cutting surface formed by chemical vapor deposition.

Aspect 21. the assembly of any of aspects 14-20, wherein the density of the plurality of protrusions is from 0.10/mm²Or about 0.10/mm²To 25mm²Or about 25/mm²Or from 0.25/mm²Or about 0.25/mm²To 15/mm²Or about 15/mm²。

The assembly of any of aspects 14-21, wherein the offset is 45 ° or about 45 °.

The terminology used in the description is for the purpose of describing particular embodiments and is not intended to be limiting. The terms "a", "an" and "the" also include the plural forms unless specifically indicated otherwise. The terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components.

With regard to the foregoing description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size and arrangement of the parts without departing from the scope of the present invention. It is intended that the specification and described embodiments be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.