CROSS-REFERENCE TO RELATED APPLICATION(S)
This application claims priority to Taiwan Patent Application No. 104112575 filed on Apr. 20, 2015, the disclosure of which is incorporated herein by reference.
BACKGROUND
1. Field of the Invention
The present invention relates to grinding tools used in chemical mechanical polishing techniques.
2. Description of the Related Art
Grinding and/or polishing techniques are generally applied to create a desirable surface roughness or planarity on a rigid part, such as metal, ceramic or glass parts, or semiconductor wafers. To this purpose, the grinding and/or polishing techniques use tools having abrasive elements that can wear the hard surface.
A well known polishing technique is the chemical mechanical polishing (CMP) technique employed in semiconductor fabrication processes. CMP uses corrosive chemical slurry in conjunction with a polishing pad to remove undesired residues and planarize a wafer surface, which can be made of ceramic, silicon, glass, sapphire or metal. CMP can be typically conducted multiple times to planarize wafers. For example, the fabrication process of semiconductor wafers having 28 nm-wide features may require up to 30 CMP steps. After the polishing pad is used over a period of time, the grinding action of the polishing pad may diminish. Accordingly, an additional grinding tool (also called “conditioner”) may be typically used to coarsen the surface of the polishing pad for maintaining an optimal grinding efficiency of the polishing pad.
Conventionally, a cutting rate of the grinding tool may be improved by increasing a distribution density of the abrasive elements provided thereon. This requires increasing the quantity of abrasive elements on the grinding tool, which makes the grinding tool more expensive to manufacture.
Therefore, there is a need for a grinding tool that can have an improved cutting rate, and can be fabricated in a cost-effective manner.
SUMMARY
The present application describes a grinding tool and methods of fabricating the grinding tool that can address at least the aforementioned problems. In one embodiment, the grinding tool includes a substrate having a working surface, and a plurality of abrasive particles distributed across the working surface and protruding outward from the working surface, wherein at least some of the abrasive particles are machined to form abrasive particles respectively having a pyramid shape, the pyramid shape being a right square pyramid or a right hexagonal pyramid.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a planar view illustrating an embodiment of a grinding tool;
FIG. 2 is a schematic cross-sectional view taken along section plane 2 of FIG. 1 illustrating support posts affixed in holes provided in the grinding tool;
FIG. 3A is a top view illustrating an abrasive particle having the shape of a right hexagonal pyramid;
FIG. 3B is a cross-sectional view of the right hexagonal pyramid of FIG. 3A taken along section plane 3;
FIG. 4A is a top view illustrating an abrasive particle having the shape of a right square pyramid;
FIG. 4B is a cross-sectional view of the right square pyramid of FIG. 4A taken along section plane 4;
FIG. 5 is a flowchart illustrating exemplary method steps of fabricating abrasive particles used in the grinding tool;
FIG. 6A is a schematic view illustrating one abrasive particle machined to form a right square pyramid; and
FIG. 6B is a schematic cross-sectional view of the abrasive particle of FIG. 6A taken along section plane 4′.
DETAILED DESCRIPTION OF THE EMBODIMENTS
FIG. 1 is a schematic planar view illustrating an embodiment of a grinding tool 1, and FIG. 2 is a schematic cross-sectional view taken along section plane 2 of FIG. 1 illustrating support posts 123 affixed in holes 112 of the grinding tool 1. In one example of implementation, the grinding tool 1 can be used as a conditioner for a polishing pad in chemical mechanical polishing (CMP) processes. Referring to FIGS. 1 and 2, the grinding tool 1 can include a substrate 11 and a plurality of abrasive particles 12. The substrate 11 can have a working surface 111 and a bottom surface 113 on two opposite sides, and a plurality of holes 112 respectively opening on the working surface 111 and the bottom surface 113. The abrasive particles 12 can be respectively affixed to a plurality of support posts 123, and the support posts 123 can be respectively attached in the holes 112 of the substrate 11 via bonding layers 14. The bonding layers 14 can be exposed outward on the bottom surface 113 of the substrate 11, and the abrasive particles 12 can project outward from the working surface 111 of the substrate 11. The working surface 111 of the substrate 11 thus can be used for uniformly grinding a desirable article. Examples of suitable materials for the substrate 11 can be stainless steel, polymer or ceramic.
Exemplary techniques for attaching the abrasive particles 12 to the support posts 123 can include brazing, sintering, electroplating and the like. The support posts 123 can have cylindrical shapes, parallelepiped shapes, or any other suitable shapes. Examples of suitable materials for the support posts 123 can include metallic materials.
The abrasive particles 12 can be made of any suitable materials having high hardness. Examples of suitable materials can include diamond, cubic boron nitride, aluminum oxide, and silicon carbide. The size of the abrasive particles 12 can exemplary be 20 to 30 US mesh, i.e., a mesh screen used to filter the abrasive particles can have 20 to 30 openings per square inch.
Referring again to FIG. 1, the abrasive particles 12 of the grinding tool 1 can include a plurality of first abrasive particles 121 and a plurality of second abrasive particles 122. The first abrasive particles 121 have specifically machined surfaces, and the second abrasive particles 122 have no machined surfaces. In FIG. 1, the first abrasive particles 121 are shown as hollow circles, and the second abrasive particles 122 are shown as solid circles. The first abrasive particles 121 can be distributed over the entire working surface 111, and the second abrasive particles 122 can be dispersed among the first abrasive particles 111.
The first abrasive particles 121 can be machined with an abrasive tool to obtain a desired shape. In one embodiment, the first abrasive particles 121 can be machined to have a pyramid shape with a sharp tip. More specifically, the pyramid shape of the first abrasive particles 121 can have a hexagonal base and an apex directly above a center of the base (called “right hexagonal pyramid”), or a square base and an apex directly above a center of the base (called “right square pyramid”).
FIG. 3A is a top view illustrating an abrasive particle having the shape of a right hexagonal pyramid 121a, and FIG. 3B is a cross-sectional view of the right hexagonal pyramid 121a taken along section plane 3 shown in FIG. 3A. As shown in FIGS. 3A and 3B, the abrasive particle having the shape of a right hexagonal pyramid 121a can have 8 side faces 301-308 and an apex 32. Any pair of opposite side faces (e.g., the side faces 302 and 306 shown in FIG. 3B) intersecting at the apex 32 can define a tip angle 34 between about 80 and about 100 degrees. When the abrasive particle having the shape of the right hexagonal pyramid 121a is used for grinding a desired article (e.g., a polishing pad), the sharp apex 32 can cut relatively deeper into the article, providing a higher cutting rate. In one embodiment, the tip angle 34 of the right hexagonal pyramid 121a is preferably about 90 degrees.
FIG. 4A is a top view illustrating an abrasive particle having the shape of a right square pyramid 121b, and FIG. 4B is a cross-sectional view of the right square pyramid 121b taken along section plane 4 shown in FIG. 4A. As shown in FIGS. 4A and 4B, the right square pyramid 121b of the abrasive particle can have 4 side faces 401-404 and an apex 42. Any pair of opposite side faces (e.g., the side faces 402 and 404 shown in FIG. 4B) intersecting at the apex 42 can define a tip angle 44 between about 70 and about 90 degrees. When the abrasive particle having the shape of the right square pyramid 121b is used for grinding a desired article (e.g., conditioning a polishing pad), the sharp apex 42 can cut relatively deeper into the article, providing a higher cutting rate. In one embodiment, the tip angle 44 of the right square pyramid 121b is preferably about 80 degrees.
In practice, it is observed that an abrasive particle having the shape of a right square pyramid may exhibit different grinding characteristics from an abrasive particle having the shape of a right hexagonal pyramid. For example, suppose that both types of abrasive particles (i.e., right hexagonal pyramid and right square pyramid) have a same tip angle and are used to condition a polishing pad. Compared to the abrasive particle having a right hexagonal pyramid shape, the abrasive particle having a right square pyramid shape can have a smaller contact surface with the polishing pad and form a narrower and deeper cutting groove. This may tend to show improved grinding action of abrasive particles having a right square pyramid shape compared to abrasive particles having a right hexagonal pyramid shape.
Generally, the higher cutting rate, the better grinding action. Through experiments, it is observed that that the cutting rate of abrasive particles with specifically machined surfaces (i.e., having right square pyramid or right hexagonal pyramid shapes) can be higher than conventional abrasive particles without specifically machined surfaces. Unlike conventional grinding tools having no abrasive particles with specifically machined surfaces (i.e., having only second abrasive particles 122 shown in FIG. 1), the grinding tool 1 described herein can have an improved cutting rate by incorporating first abrasive particles 121 having specifically machined surfaces and second abrasive particles 122 having no machined surfaces. As a result, a surface of a polishing pad subjected to conditioning treatment can be coarser when treated with the grinding tool 1 described herein (i.e., having abrasive particles with right square and/or right hexagonal pyramid shapes) than when treated with a conventional grinding tool having no abrasive particles with specifically machined surfaces.
FIG. 5 is a flowchart illustrating exemplary method steps of fabricating abrasive particles used in the grinding tool 1 described herein. In initial step 502, a plurality of abrasive particles are provided. The abrasive particles can be made of high hardness materials such as diamond, cubic boron nitride, aluminum oxide, and silicon carbide. The size of the abrasive particles can exemplary be 20 to 30 US mesh.
In next step 504, an abrasive tool is then used to machine at least some of the abrasive particles to form abrasive particles 121 having a pyramid shape with a sharp tip. The pyramid shape of the abrasive particles 121 can be a right square pyramid or a right hexagonal pyramid.
FIG. 6A is a schematic view illustrating one abrasive particle 121b machined to form a right square pyramid, and FIG. 6B is a schematic cross-sectional view of the abrasive particle 121b taken along section plane 4′ as shown in FIG. 6A. Referring to FIGS. 6A and 6B, an abrasive particle can be machined with the abrasive tool 9 to form the abrasive particle 121b having four side faces 411-414 and an apex 46. In order to form the side face 414 of the abrasive particle 121b, the abrasive tool 9 can be exemplary inclined to form an angle 48 between a grinding surface 91 of the abrasive tool 9 and a reference line 437 defined as an axis that is perpendicular to a horizontal plane and passes through the apex 46. For forming the side face 412 of the abrasive particle 121b opposite to the side face 414, the abrasive tool 9 can be inclined in a symmetrical manner to form an angle 49 between the grinding surface 91 of the abrasive tool 9 and the reference line 437, the angle 48 and 49 being substantially equal. A tip angle 47 defined by the two side faces 412 and 414 intersecting at the apex 46 can be between about 70 degrees and about 90 degrees, and the angles 48 and 49 can respectively range from about 35 degrees to about 45 degrees. In one embodiment, the tip angle 47 of the abrasive particle 121b can be equal to about 80 degrees. The other two side faces 411 and 413 of the abrasive particle 121b can be formed in a similar way.
It will be appreciated that abrasive particles can also be machined with the abrasive tool 9 to form a right hexagonal pyramid having 8 side faces and an apex.
Next referring to FIGS. 2 and 5, the abrasive particles 12 in step 506 can be respectively attached to the support posts 123. Exemplary techniques for attaching the abrasive particles 12 to the support posts 123 can include brazing, sintering, and electroplating.
Referring to FIGS. 1, 2 and 5, a substrate 11 is provided in step 508, the substrate 11 having a working surface 111 and a plurality of holes 112.
In next step 510, the support posts 123 can be respectively attached in the holes 112 of the substrate 11 with the abrasive particles 12 distributed across the working surface 111. In one embodiment, the support posts 123 can be respectively attached in the holes 112 of the substrate 11 via bonding layers 14. A grinding tool can be thereby fabricated with the abrasive particles 12 protruding outward on the side of the working surface 111.
Realizations of the grinding tool and its manufacture process have been described in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. These and other variations, modifications, additions, and improvements may fall within the scope of the inventions as defined in the claims that follow.
Patent Application
20160303704
