Patent Grant
9211628
Embodiments of the present invention are in the field of chemical mechanical polishing (CMP) and, in particular, polishing pads with concentric or approximately concentric polygon groove patterns.
Chemical-mechanical planarization or chemical-mechanical polishing, commonly abbreviated CMP, is a technique used in semiconductor fabrication for planarizing a semiconductor wafer or other substrate.
The process uses an abrasive and corrosive chemical slurry (commonly a colloid) in conjunction with a polishing pad and retaining ring, typically of a greater diameter than the wafer. The polishing pad and wafer are pressed together by a dynamic polishing head and held in place by a plastic retaining ring. The dynamic polishing head is rotated during polishing. This approach aids in removal of material and tends to even out any irregular topography, making the wafer flat or planar. This may be necessary in order to set up the wafer for the formation of additional circuit elements. For example, this might be necessary in order to bring the entire surface within the depth of field of a photolithography system, or to selectively remove material based on its position. Typical depth-of-field requirements are down to Angstrom levels for the latest sub-50 nanometer technology nodes.
The process of material removal is not simply that of abrasive scraping, like sandpaper on wood. The chemicals in the slurry also react with and/or weaken the material to be removed. The abrasive accelerates this weakening process and the polishing pad helps to wipe the reacted materials from the surface. In addition to advances in slurry technology, the polishing pad plays a significant role in increasingly complex CMP operations.
However, additional improvements are needed in the evolution of CMP pad technology.
Embodiments of the present invention include polishing pads with concentric or approximately concentric polygon groove patterns.
In an embodiment, a polishing pad for polishing a substrate includes a polishing body. The polishing body has a polishing surface and a back surface. The polishing surface has a pattern of grooves including concentric or approximately concentric polygons. The pattern of grooves has no radial groove continuous from the inner most polygon to the outer most polygon.
In another embodiment, a method of fabricating a polishing pad for polishing a substrate includes mixing a pre-polymer and a curative to form a mixture in the base of a formation mold. The lid of the formation mold is moved into the mixture. The lid has disposed thereon a pattern of protrusions including concentric or approximately concentric polygons. The pattern of protrusions has no radial protrusion continuous from the inner most polygon to the outer most polygon. With the lid placed in the mixture, the mixture is at least partially cured to form a molded homogeneous polishing body including a polishing surface having disposed therein a pattern of grooves corresponding to the pattern of protrusions of the lid.
In another embodiment, a polishing pad for polishing a substrate includes a polishing body. The polishing body has a polishing surface and a back surface. The polishing surface has a pattern of grooves including a plurality of discrete linear segments orthogonal to radii of the polishing surface and forming a portion of a, but not a complete, concentric or approximately concentric polygon arrangement.
In another embodiment, a polishing pad for polishing a substrate includes a polishing body. The polishing body has a polishing surface and a back surface. The polishing surface has a pattern of grooves including nested incomplete polygons having continuity there between.
Polishing pads with concentric or approximately concentric polygon groove patterns are described herein. In the following description, numerous specific details are set forth, such as specific polishing pad compositions and designs, in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known processing techniques, such as details concerning the combination of a slurry with a polishing pad to perform CMP of a semiconductor substrate, are not described in detail in order to not unnecessarily obscure embodiments of the present invention. Furthermore, it is to be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.
Polishing pads for polishing substrates in CMP operations typically include at least one surface with physical grooves formed therein. The grooves may be arranged to balance an appropriate amount of surface area for polishing the substrate while providing a reservoir for slurry used in the CMP operation. In accordance with embodiment of the present invention, groove patterns based on a series of concentric polygon shapes are described for polishing surfaces of polishing pads. As an example, a polishing pad with a diameter of approximately 20 inches has a polishing surface with a groove pattern based on concentric decagonal grooves.
Groove patterns described herein may provide benefits for, or may be advantageous over prior art polishing pads for, polishing substrates in a CMP operation using slurry. For example, advantages of groove patterns described herein may include (a) improved averaging of a slurry-based polish process across a polished substrate as the polishing pad rotates and the individual grooves translate radially inward and outward, (b) improved slurry retention on the polishing pad relative to pads with radial grooves. Both concepts are described in greater detail below, e.g., in association with
Basic embodiments of the present invention include groove patterns based on a series of grooves that form similar polygons, all with the same center point, and all aligned with an angle theta of zero so that their straight line segments are parallel and their angles are aligned in a radial fashion. Nested triangles, squares, pentagons, hexagons, etc., are all considered within the spirit and scope of the present invention. There may be a maximum number of straight line segments above which the polygons will become approximately circular. Preferred embodiments may include limiting the groove pattern to polygons with a number of sides less than such a number of straight line segments. One reason for this approach may be to improve averaging of the polish benefit, which might otherwise be diminished as the number of sides of each polygon increases and approaches a circular shape. Another embodiment includes groove patterns with concentric polygons having a center that is not in the same location as the polishing pad center.
More involved embodiments may include groove patterns with concentric polygons oriented to have a small angle, theta, relative to one another. This small angle theta can be positive or negative relative to the direction of rotation of the pad on the polishing tool. Such embodiments may provide a visual impression of the straight line angles forming a gentle spiral from the center to the edge of the polishing pad (see description of
Conventional polishing pads typically have concentric circular groove patterns. For example,
Referring to
Polishing pads having radial grooves may exacerbate slurry loss during polishing of a substrate. For example,
Referring to
In contrast to
In an aspect of the present invention, a polishing pad may be fabricated with a polishing surface having a concentric polygon pattern of grooves thereon. As an example,
Referring to
It is to be understood that the outer edges of the polishing pad 300 may not be able to accommodate complete polygons. However, there may be a need to include grooves at the outer most reaches of polishing pad 300. For example, in an embodiment, one or more broken polygons 320 is included near or at the edge of polishing pad 300, as is depicted in
In another aspect of the present invention, a polishing pad may be fabricated with a polishing surface having thereon a concentric polygon pattern of grooves and one or more radial groove that is not continuous from the inner most polygon to the outer most polygon of the concentric. Inclusion of such a radial groove may be included as a marking to indicate a feature of the polishing pad or may be included for very localized slurry transfer. Also, such a radial groove may be present as an artifact of a pad fabrication process.
For comparison,
Instead,
By including a pattern of concentric polygon grooves, versus concentric circles, improved averaging of a polish process may be achieved across a polished substrate as the polishing pad rotates and the individual grooves translate radially inward and outward. As an example,
Referring to
In another aspect of the present invention, the number of faces of each polygon in a concentric pattern of polygons may be varied depending on the specific application, as well as the size, of the polishing pad. As an example,
In an embodiment, the number of edges of each polygon is determined by the diameter of the polishing pad or by the diameter of the substrate to be polished by the polishing pad. For example, in one embodiment, the diameter of the polishing pad is approximately 30 inches, the diameter of the substrate is approximately 12 inches, and the concentric polygons are concentric hexadecagons. In another embodiment, the diameter of the polishing pad is approximately 20 inches, the diameter of the substrate is approximately 8 inches, and the concentric polygons are concentric decagons. In an embodiment, the length of each edge of the outer most polygon is approximately in the range of 50-60% of the length of the diameter of the substrate to be polished. In another embodiment, a polishing pad contemplated herein is used to polish a substrate having a diameter of approximately 450 millimeters.
A plurality of concentric polygons, if not offset from one another, may induce a rain gutter effect by inadvertently removing large amounts of slurry at locations where the edges of the polygons are aligned. Instead, in another aspect of the present invention, successive polygons may be rotated relative to one another. For example,
As a comparison to illustrate the above concept, referring again to
In another aspect, the center of the concentric polygons of a groove pattern need not be at the center of a polishing pad. For example,
As a comparison to illustrate the above concept, referring again to
It is to be understood that the outer edges of the polishing pad 800 may not be able to accommodate complete polygons. However, there may be a need to include grooves at the outer most reaches of polishing pad 800. For example, in an embodiment, one or more partial polygons 820 and/or one or more broken polygons 822 is included near or at the edge of polishing pad 800, as is depicted in
In another aspect, the concentric polygon pattern may be interrupted with non-polygon grooves. For example,
Referring to
In another aspect, the concentric polygon pattern need not include polygons all having the same number of edges. For example,
Referring to
In an embodiment, polishing pads described herein, such as polishing pad 300, 400B, 400C, 500B, 600A, 600B, 700A, 700B, 800, 900A or 900B, are suitable for polishing substrates. The substrate may be one used in the semiconductor manufacturing industry, such as a silicon substrate having device or other layers disposed thereon. However, the substrate may be one such as, but not limited to, a substrates for MEMS devices, reticles, or solar modules. Thus, reference to “a polishing pad for polishing a substrate,” as used herein, is intended to encompass these and related possibilities.
Polishing pads described herein, such as polishing pad 300, 400B, 400C, 500B, 600A, 600B, 700A, 700B, 800, 900A or 900B, may be composed of a homogeneous polishing body of a thermoset polyurethane material. In an embodiment, the homogeneous polishing body is composed of a thermoset, closed cell polyurethane material. In an embodiment, the term “homogeneous” is used to indicate that the composition of a thermoset, closed cell polyurethane material is consistent throughout the entire composition of the polishing body. For example, in an embodiment, the term “homogeneous” excludes polishing pads composed of, e.g., impregnated felt or a composition (composite) of multiple layers of differing material. In an embodiment, the term “thermoset” is used to indicate a polymer material that irreversibly cures, e.g., the precursor to the material changes irreversibly into an infusible, insoluble polymer network by curing. For example, in an embodiment, the term “thermoset” excludes polishing pads composed of, e.g., “thermoplast” materials or “thermoplastics”—those materials composed of a polymer that turns to a liquid when heated and returns to a very glassy state when cooled sufficiently. It is noted that polishing pads made from thermoset materials are typically fabricated from lower molecular weight precursors reacting to form a polymer in a chemical reaction, while pads made from thermoplastic materials are typically fabricated by heating a pre-existing polymer to cause a phase change so that a polishing pad is formed in a physical process. Polyurethane thermoset polymers may be selected for fabricating polishing pads described herein based on their stable thermal and mechanical properties, resistance to the chemical environment, and tendency for wear resistance.
In an embodiment, polishing pads described herein, such as polishing pad 300, 400B, 400C, 500B, 600A, 600B, 700A, 700B, 800, 900A or 900B, include a molded homogeneous polishing body. The term “molded” is used to indicate that a homogeneous polishing body is formed in a formation mold, as described in more detail below in association with
In an embodiment, polishing pads described herein, such as polishing pad 300, 400B, 400C, 500B, 600A, 600B, 700A, 700B, 800, 900A or 900B, include a polishing body having a plurality of closed cell pores therein. In one embodiment, the plurality of closed cell pores is a plurality of porogens. For example, the term “porogen” may be used to indicate micro- or nano-scale spherical or somewhat spherical particles with “hollow” centers. The hollow centers are not filled with solid material, but may rather include a gaseous or liquid core. In one embodiment, the plurality of closed cell pores is composed of pre-expanded and gas-filled EXPANCEL™ distributed throughout (e.g., as an additional component in) a homogeneous polishing body of the polishing pad. In a specific embodiment, the EXPANCEL™ is filled with pentane. In an embodiment, each of the plurality of closed cell pores has a diameter approximately in the range of 10-100 microns. In an embodiment, the plurality of closed cell pores includes pores that are discrete from one another. This is in contrast to open cell pores which may be connected to one another through tunnels, such as the case for the pores in a common sponge. In one embodiment, each of the closed cell pores includes a physical shell, such as a shell of a porogen, as described above. In another embodiment, however, each of the closed cell pores does not include a physical shell. In an embodiment, the plurality of closed cell pores is distributed essentially evenly throughout a thermoset polyurethane material of a homogeneous polishing body.
In an embodiment, the homogeneous polishing body is opaque. In one embodiment, the term “opaque” is used to indicate a material that allows approximately 10% or less visible light to pass. In one embodiment, the homogeneous polishing body is opaque in most part, or due entirely to, the inclusion of an opacifying lubricant throughout (e.g., as an additional component in) the homogeneous thermoset, closed cell polyurethane material of the homogeneous polishing body. In a specific embodiment, the opacifying lubricant is a material such as, but not limited to: boron nitride, cerium fluoride, graphite, graphite fluoride, molybdenum sulfide, niobium sulfide, talc, tantalum sulfide, tungsten disulfide, or Teflon.
The sizing of the homogeneous polishing body may be varied according to application. Nonetheless, certain parameters may be used to make polishing pads including such a homogeneous polishing body compatible with conventional processing equipment or even with conventional chemical mechanical processing operations. For example, in accordance with an embodiment of the present invention, the homogeneous polishing body has a thickness approximately in the range of 0.075 inches to 0.130 inches, e.g., approximately in the range of 1.9-3.3 millimeters. In one embodiment, the homogeneous polishing body has a diameter approximately in the range of 20 inches to 30.3 inches, e.g., approximately in the range of 50-77 centimeters, and possibly approximately in the range of 10 inches to 42 inches, e.g., approximately in the range of 25-107 centimeters. In one embodiment, the homogeneous polishing body has a pore density approximately in the range of 6%-36% total void volume, and possibly approximately in the range of 15%-35% total void volume. In one embodiment, the homogeneous polishing has a porosity of the closed cell type, as described above, due to inclusion of a plurality of pores. In one embodiment, the homogeneous polishing body has a compressibility of approximately 2.5%. In one embodiment, the homogeneous polishing body has a density approximately in the range of 0.70-1.05 grams per cubic centimeter.
In another embodiment of the present invention, a polishing pad with a polishing surface having a concentric polygon pattern of grooves thereon further includes a local area transparency (LAT) region disposed in the polishing pad. For example,
In another embodiment, a polishing pad with a polishing surface having a concentric polygon pattern of grooves thereon further includes a detection region for use with, e.g., an eddy current detection system. For example, referring again to
In another aspect of the present invention, polishing pads with concentric polygon groove patterns may be fabricated in a molding process. For example,
Referring to
In an embodiment, the polishing pad precursor mixture 1106 is used to ultimately form a molded homogeneous polishing body composed of a thermoset, closed cell polyurethane material. In one embodiment, the polishing pad precursor mixture 1106 is used to ultimately form a hard pad and only a single type of curative is used. In another embodiment, the polishing pad precursor mixture 1106 is used to ultimately form a soft pad and a combination of a primary and a secondary curative is used. For example, in a specific embodiment, the pre-polymer includes a polyurethane precursor, the primary curative includes an aromatic diamine compound, and the secondary curative includes a compound having an ether linkage. In a particular embodiment, the polyurethane precursor is an isocyanate, the primary curative is an aromatic diamine, and the secondary curative is a curative such as, but not limited to, polytetramethylene glycol, amino-functionalized glycol, or amino-functionalized polyoxypropylene. In an embodiment, the pre-polymer, a primary curative, and a secondary curative have an approximate molar ratio of 100 parts pre-polymer, 85 parts primary curative, and 15 parts secondary curative. It is to be understood that variations of the ratio may be used to provide polishing pads with varying hardness values, or based on the specific nature of the pre-polymer and the first and second curatives.
Referring to
It is to be understood that embodiments described herein that describe lowering the lid 1108 of a formation mold 1100 need only achieve a bringing together of the lid 1108 and a base of the formation mold 1100. That is, in some embodiments, a base of a formation mold 1100 is raised toward a lid 1108 of a formation mold, while in other embodiments a lid 1108 of a formation mold 1100 is lowered toward a base of the formation mold 1100 at the same time as the base is raised toward the lid 1108.
Referring to
Referring to
In an embodiment, referring again to
Thus, groove patterns contemplated in embodiment of the present invention may be formed in-situ. For example, as described above, a compression-molding process may be used to form polishing pads with a grooved polishing surface having a pattern of concentric polygons. By using a molding process, highly uniform groove dimensions within-pad may be achieved. Furthermore, extremely reproducible groove dimensions along with very smooth, clean groove surfaces may be produced. Other advantages may include reduced defects and micro-scratches and a greater usable groove depth.
Individual grooves of the concentric polygon groove patterns described herein may be from about 4 to about 100 mils deep at any given point on each groove. In some embodiments, the grooves are about 10 to about 50 mils deep at any given point on each groove. The grooves may be of uniform depth, variable depth, or any combinations thereof. In some embodiments, the grooves are all of uniform depth. For example, the grooves of a concentric polygon pattern may all have the same depth. In some embodiments, some of the grooves of a concentric polygon pattern may have a certain uniform depth while other grooves of the same pattern may have a different uniform depth. For example, groove depth may increase with increasing distance from the center of the polishing pad. In some embodiments, however, groove depth decreases with increasing distance from the center of the polishing pad. In some embodiments, grooves of uniform depth alternate with grooves of variable depth.
Individual grooves of the concentric polygon groove patterns described herein may be from about 2 to about 100 mils wide at any given point on each groove. In some embodiments, the grooves are about 15 to about 50 mils wide at any given point on each groove. The grooves may be of uniform width, variable width, or any combinations thereof. In some embodiments, the grooves of a concentric polygon pattern are all of uniform width. In some embodiments, however, some of the grooves of a concentric polygon pattern have a certain uniform width, while other grooves of the same pattern have a different uniform width. In some embodiments, groove width increases with increasing distance from the center of the polishing pad. In some embodiments, groove width decreases with increasing distance from the center of the polishing pad. In some embodiments, grooves of uniform width alternate with grooves of variable width.
In accordance with the previously described depth and width dimensions, individual grooves of the concentric polygon groove patterns described herein may be of uniform volume, variable volume, or any combinations thereof. In some embodiments, the grooves are all of uniform volume. In some embodiments, however, groove volume increases with increasing distance from the center of the polishing pad. In some other embodiments, groove volume decreases with increasing distance from the center of the polishing pad. In some embodiments, grooves of uniform volume alternate with grooves of variable volume.
Grooves of the concentric polygon groove patterns described herein may have a pitch from about 30 to about 1000 mils. In some embodiments, the grooves have a pitch of about 125 mils. For a circular polishing pad, groove pitch is measured along the radius of the circular polishing pad. In CMP belts, groove pitch is measured from the center of the CMP belt to an edge of the CMP belt. The grooves may be of uniform pitch, variable pitch, or in any combinations thereof. In some embodiments, the grooves are all of uniform pitch. In some embodiments, however, groove pitch increases with increasing distance from the center of the polishing pad. In some other embodiments, groove pitch decreases with increasing distance from the center of the polishing pad. In some embodiments, the pitch of the grooves in one sector varies with increasing distance from the center of the polishing pad while the pitch of the grooves in an adjacent sector remains uniform. In some embodiments, the pitch of the grooves in one sector increases with increasing distance from the center of the polishing pad while the pitch of the grooves in an adjacent sector increases at a different rate. In some embodiments, the pitch of the grooves in one sector increases with increasing distance from the center of the polishing pad while the pitch of the grooves in an adjacent sector decreases with increasing distance from the center of the polishing pad. In some embodiments, grooves of uniform pitch alternate with grooves of variable pitch. In some embodiments, sectors of grooves of uniform pitch alternate with sectors of grooves of variable pitch.
It is to be understood that embodiments of the present invention may also include groupings of polygons that are not precisely concentric. In such embodiments, increasingly larger polygons are provided, but the center for each individual polygon need not necessarily align exactly with the center of a preceding or successive polygon. Nonetheless, such near-concentric or approximately concentric polygons are considered to be within the spirit and scope of the present invention.
It is also to be understood that embodiments of the present invention may include polygons where, for an individual polygon, either the edge lengths are not all the same, the angles between edges are not all the same, or both. As an example,
Referring to
It is also to be understood that embodiments of the present invention may include groove patterns with continuity, e.g., with a spiral effect, of “open” or incomplete polygons that provide an overall feel or appearance of concentric polygons. For example,
Referring to
The polishing surface 1302 may, in an embodiment, include only incomplete polygons with continuity there between 1304. For example, the continuous pattern may begin at or near the center of the polishing surface 1302 and may end at or near the outer region of the polishing surface 1302. However, in another embodiment, only a portion of the polishing surface 1302 includes a groove pattern with incomplete polygons having continuity there between 1304. For example, referring again to
In an embodiment, the pattern of grooves including the pattern of nested incomplete polygons with continuity there between 1304 gives a general appearance of concentric dodecagons, as depicted in
Thus, referring again to
It is also to be understood that embodiments of the present invention may include groove patterns with groupings of discrete line segments that provide an overall feel or appearance of concentric polygons. For example,
Referring to
In another example,
Referring to
Thus, referring again to
It is to be understood that embodiments of the present invention may also include discrete linear segments that are not precisely orthogonal to radii of the polishing surface. In such embodiments, the discrete linear segments form a portion of a, but not a complete, concentric or approximately concentric polygon arrangement, but the relative association with the corresponding radius in not precisely 90 degrees but rather, perhaps a fraction of a degree to a few degrees off of 90 degrees. Nonetheless, such near-orthogonal or approximately orthogonal discrete linear segments are considered to be within the spirit and scope of the present invention.
Polishing pads described herein may be suitable for use with a variety of chemical mechanical polishing apparatuses. As an example,
Referring to
Thus, polishing pads with concentric or approximately concentric polygon groove patterns have been disclosed. In accordance with an embodiment of the present invention, a polishing pad for polishing a substrate includes a polishing body. The polishing body has a polishing surface and a back surface, the polishing surface having a pattern of grooves including concentric or approximately concentric polygons. The pattern of grooves has no radial groove continuous from the inner most polygon to the outer most polygon. In one embodiment, each of the polygons has the same number of edges, the number of edges determined by the diameter of the polishing pad or by the diameter of the substrate. In one embodiment, the pattern of grooves has no radial grooves.
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