Patent Grant
9597769
Embodiments of the present invention are in the field of chemical mechanical polishing (CMP) and, in particular, polishing pads with a polishing surface layer having an aperture or opening above a transparent foundation layer.
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 a polishing surface layer having an aperture or opening above a transparent foundation layer.
In an embodiment, a polishing pad for polishing a substrate includes a foundation layer having a global top surface and a transparent region. A polishing surface layer is attached to the global top surface of the foundation layer. The polishing surface layer has a polishing surface and a back surface. An aperture is disposed in the polishing pad from the back surface through to the polishing surface of the polishing surface layer, and aligned with the transparent region of the foundation layer. The foundation layer provides an impermeable seal for the aperture at the back surface of the polishing surface layer.
In another embodiment, a polishing pad for polishing a substrate includes a foundation layer having a global top surface and a transparent region. A polishing surface layer is attached to the global top surface of the foundation layer. The polishing surface layer has a polishing surface and a back surface. An opening is disposed in the polishing pad from the polishing surface, but not through to the back surface, of the polishing surface layer. The opening is aligned with the transparent region of the foundation layer.
In another embodiment, a method of fabricating a polishing pad for polishing a substrate includes providing, in a formation mold, a foundation layer and a mixture formed from mixing a set of polymerizable materials. The foundation layer has a transparent region. A pattern of grooves of the formation mold is coupled with the mixture. With the pattern of grooves coupled with the mixture, the mixture is at least partially cured to form a molded homogeneous polishing surface layer directly on the foundation layer. The molded homogeneous polishing surface layer includes a pattern of protrusions corresponding to the pattern of grooves of the formation mold. An aperture or opening is formed in the polishing surface layer, aligned with the transparent region of the foundation layer.
Polishing pads with a polishing surface layer having an aperture or opening above a transparent foundation layer 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.
One or more embodiments described herein are directed to a detection system composed of an aperture or opening formed in a polishing layer of a polishing pad. The aperture or opening may be used in conjunction with an aperture-free transparent foundation layer having the polishing layer disposed thereon. Embodiments of polishing pads described herein may be used for end-point detection (EPD) in a chemical mechanical polishing process. As used herein, an aperture generally refers to a hole formed throughout an entirety of a layer or pad described as having the aperture therein. By contrast, an opening generally refers to an incomplete hole (e.g., a trench or partial aperture) formed at one surface of, but not throughout an entirety of, a layer or pad described as having the opening therein. Specific embodiments include, but are not limited to, a polishing pad having one or more of (1) an aperture disposed in a polishing surface layer and over an optically transparent foundation layer, (2) an aperture disposed in a polishing surface layer and over an opening or local slurry deflection system formed in a transparent foundation layer, (3) an opening or slurry defection system disposed in a polishing surface layer and over an optically transparent foundation layer, and (4) an opening or slurry defection system disposed in a polishing surface layer and over an opening or local slurry deflection system of an optically transparent foundation layer. It is to be understood that embodiments are not limited to a foundation layer that is entirely transparent. In an embodiment, reference to a transparent foundation layer indicates that at least a portion or region of the foundation layer is transparent. Openings or apertures in a polishing surface layer residing above the foundation layer do so (e.g., are aligned with) the transparent portion of the foundation layer.
For a more thorough understanding, in a first aspect, features may need to be introduced to polishing pads for advanced chemical mechanical polishing processing. For example, otherwise opaque polishing pads may have one or more “windows” included therein to allow a substantial transmission of visible light for various monitoring applications. One such monitoring application may involve use of an optical device mounted within or on a chemical mechanical polishing apparatus. The optical device is used to monitor a chemical mechanical polishing process by, e.g., reflectance changes in the substrate undergoing polishing. The process is monitored through the window of the polishing pad since the polishing occurs at a top polishing surface of the polishing pad. The window is typically formed by inserting a transparent plug into the pad or by molding a transparent region (e.g., a local area transparency region or LAT) into an otherwise opaque pad at the time of fabrication. In either case, the window is composed of a distinct material included in the pad.
In accordance with an embodiment of the present invention, a “windowless” polishing pad suitable for optical monitoring there through is provided. As an example, an aperture or opening is provided in a polishing surface layer of a polishing pad allowing for optical monitoring through the polishing pad. In one embodiment, the aperture or opening is a complete or incomplete hole made in the polishing surface layer that extends through the entire polishing surface layer. Thus, in contrast to a pad including a window composed of a material, the windowless polishing pad is characterized by the absence of material.
Conventionally, a mere hole formed in a polishing pad would have been unsuitable for monitoring a chemical mechanical process. For example, slurry would have been able to escape through the pad, possibly eroding an underlying optical monitoring device. In another example, a hole that fills with an opaque slurry may be unsuitable for allowing sufficient light transmission for optical detection. However, advanced slurries now being tested or in use are relatively, if not entirely, transparent.
As such, in an embodiment of the present invention, filling of an aperture or opening with a slurry does not detrimentally impact optical detection. Furthermore, in an embodiment, a transparent foundation layer is included below the polishing surface layer. In one such embodiment, the transparent foundation layer provides a seal to protect a platen and, e.g., a quartz laser site of a chemical mechanical polishing apparatus. As described in more detail below, various aperture or opening designs are provided. In some embodiments, the designs include provisions to keep a slurry flushing across the opening or aperture during a polishing process. In a specific such embodiment, an aperture designed for slurry flushing is used to prevent polishing debris from collecting, agglomerating, and potentially attenuating the laser or other optical signal.
Conventional “window” polishing pads typically have an insert or LAT region of a material suitably transparent included therein. For example,
Referring to
In a second aspect, polishing pads for CMP operations may have trade-offs in performance such as a trade-off between across-wafer polishing uniformity versus within die polishing uniformity. For example, hard polishing pads may exhibit good die-level planarization, but poor across-wafer uniformity. They may also scratch a substrate being polished. On the other hand, soft polishing pads may exhibit poor die-level planarization (e.g., they may cause dishing within die), but good wafer-level uniformity. An approach to mitigating the above performance trade-off may be to decouple within-wafer and within-die polishing effects.
Conventional approaches to fabricating and using soft pads may have limitations. For example, casted soft pads may offer low defect characteristics but compromised planarization performance. There may be a need for polishing pads that offer both low defect characteristics yet high planarization performance during polishing operations. Similarly, conventional approaches to fabricating and using hard pads may have limitations. For example, faster gelling speeds possibly inherent in harder urethane formulations may force process compromises that impact pad uniformity and limit formulation options. There may be a need for an approach suitable to produce and implement hard pads that avoid such compromises. Additionally, as noted above, it may be desirable to decouple the properties of the polishing surface of a pad from its bulk properties, such that the properties of each may be separately optimized.
In accordance with an embodiment of the present inventions, polishing pads with bulk or foundation material different from the material of the polishing surface are described herein. Such polishing pads may be fabricated or implemented in approaches suitable to address the above described compromises made for conventional pads. In one embodiment, a composite polishing pad includes a foundation or bulk layer fabricated from a stable, essentially non-compressible, inert material onto which a polishing surface layer is disposed. A harder foundation layer may provide support and strength for pad integrity while a softer polishing surface layer may reduce scratching, enabling decoupling of the material properties of the polishing layer and the remainder of the polishing pad.
In a specific embodiment elaborated in greater detail below, the planarization characteristics of a soft pad is made available by producing a soft polishing surface layer on a stiff backer material or foundation layer, such as a sheet of polycarbonate. Other possibilities include use of a polyethylene terephthalate (PET) material, a PETG material, glass, quartz, an acrylic material, MMA or polystyrene. In accordance with embodiments of the present invention, approaches to mitigating the above described performance trade-off include the formation of polishing pads having either a soft continuous polishing surface layer or a soft polishing surface layer composed of discrete protrusions bonded with a hard foundation layer. Although the foregoing may be preferred, it is to be understood that reverse arrangements, e.g., a hard polishing surface layer disposed on a soft underlying foundation layer, are also contemplated and described herein.
In an aspect of the present invention, a windowless polishing pad suitable for optical monitoring includes a polishing surface layer having an aperture there through or an opening therein. For example,
Referring to
An aperture or opening 208 is disposed in the polishing surface 202. In an embodiment, there is no material disposed in the aperture or opening 208, e.g., there is no plug, insert or LAT region in the location of aperture or opening 208. Variations of possible embodiments of the polishing pad of
A polishing pad may be provided with a continuous polishing surface layer having an aperture formed therein. For example,
Referring to
Referring to
In another aspect, a polishing pad may be provided with a discontinuous polishing surface layer having an aperture formed therein. For example,
Referring to
In an embodiment, the above described polishing pads are suitable for use with an end-point detection system. For example, end-point detection may be performed through the transparent foundation layer in conjunction with an aperture formed in an overlying polishing surface layer. Thus, in an embodiment, a transparent foundation layer is substantially transparent to light such as, but not limited to, visible light, ultra-violet light, infra-red light, or a combination thereof. However, it may be the case that the foundation layer cannot or need not be fabricated to be perfectly transparent, but may still be effective for transmission of light for end-point detection. In one such embodiment, a transparent foundation layer transmits as little as approximately 80% of incident light in the 700-710 nanometer range, but is still suitable to act as a portion of a detection region within a polishing pad. In another embodiment, however, a transparent foundation layer transmits as approximately 80% or more of incident light in the 700-710 nanometer range. In an embodiment, a transparent foundation layer is effectively transparent (e.g., ideally totally transparent) for transmission of light for end-point detection.
In another aspect, a polishing pad may be provided with a continuous polishing surface layer having an opening formed therein. For example,
Referring to
In an embodiment, the polishing surface layer 508 includes a continuous layer portion with a plurality of polishing features protruding there from, as depicted in
Referring again to
As described in greater detail below, the polishing surface layer 508 may be opaque. Nonetheless, the thickness T1 may be sufficiently thin to allow at least some transmission of light, e.g., for an end-point detection process. For example, in an embodiment, the combination of the transparent foundation layer 502 and the portion of the back surface 508A of the polishing surface layer 508 underneath the opening 510 (e.g., the region having thickness T1) is substantially transparent to light such as, but not limited to, visible light, ultra-violet light, infra-red light, or a combination thereof. In one such embodiment, the combination of the transparent foundation layer 502 and the portion of the back surface 508A of the polishing surface layer 508 underneath the opening 510 transmits approximately 80% or more of incident light in the 700-710 nanometer range. In an embodiment, the combination of the transparent foundation layer 502 and the portion of the back surface 508A of the polishing surface layer 508 underneath the opening 510 is effectively transparent for transmission of light for end-point detection.
In another aspect, a slurry deflection system is included in a transparent foundation layer or in a polishing surface layer disposed on a transparent foundation layer. In a first example,
Referring to
In a second example,
Referring to
In an embodiment, a slurry deflection system includes use of a geometry in a polishing surface layer, in a transparent foundation layer, or both, suitable to allow flushing of slurry from the aperture during a chemical mechanical polishing operation. Although only two examples of such deflections systems are illustrated in
The polishing surface layers of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 are described as being attached to the corresponding transparent foundation layer. In an embodiment, the polishing surface layers are “bonded with” the corresponding transparent foundation layers. In a first such embodiment, the polishing surface layers are bonded directly to the corresponding transparent foundation layers. That is, the polishing surface layers are in direct contact with the corresponding transparent foundation layers. In one embodiment, then, “bonded directly to” describes direct contact with no intervening layers (such as pressure sensitive adhesive layers) or otherwise glue-like or adhesive films. It may be preferable that the polishing surface layers are bonded directly to the corresponding transparent foundation layers so that only the polishing surface layer and corresponding transparent foundation layer dictate the polishing performance of a pad composed there of. In another embodiment, attached is used to mean the use of intervening layers (such as pressure sensitive adhesive layers) or otherwise glue-like or adhesive films. Other intervening films or layers may also be included.
In a specific such embodiment, a polishing surface layer is covalently bonded to the corresponding transparent foundation layer. In an embodiment, the term “covalently bonded” refers to arrangements where atoms from a first material (e.g., the material of a polishing surface layer) are cross-linked or share electrons with atoms from a second material (e.g., the material of a foundation layer) to effect actual chemical bonding. Covalent bonding is distinguished from mechanical bonding, such as bonding through screws, nails, glues, or other adhesives. In another specific embodiment, a polishing surface layer is not covalently bonded, but is rather only electrostatically bonded, to the corresponding transparent foundation layer. Such electrostatic bonding may involve van der Waals type interactions between the transparent foundation layer and the polishing surface layer.
Peel resistance may provide an indication of the strength and extent to which a polishing surface layer is bonded with a transparent foundation layer. In an embodiment, a transparent foundation layer and the corresponding polishing surface layer have a peel resistance sufficient to withstand a shear force applied during the useful lifetime of the polishing pad.
In an embodiment, a surface roughness is used at the interface of a polishing surface layer and a transparent foundation layer to enhance bond strength of these two portions of a polishing pad. In one such embodiment, the transparent foundation layer has a surface roughness greater than approximately 1 micrometer Ra (root mean square) where a corresponding polishing surface layer is bonded directly to the transparent foundation layer. In a specific such embodiment, the surface roughness is approximately in the range of 5-10 micrometers Ra (root mean square).
However, in another embodiment, substantial surface roughness is not included and the interface of a polishing surface layer and a transparent foundation layer is particularly smooth. The strength of such a smooth interface may be independent of surface roughness or may not need further strengthening by the inclusion of such surface roughness. In one such embodiment, a transparent foundation layer has a smooth surface with a surface roughness less than approximately 1 micrometer Ra (root mean square) where a corresponding polishing surface layer is bonded directly to the transparent foundation layer. The decision or need to include or exclude roughness at an interface of a transparent foundation layer and a polishing surface layer may depend on the pristine nature of the interface (e.g., exclusion of impurities such as oil films) or on the nature of the materials at the interface. For example, in a particular such embodiment, a polishing surface layer at a smooth interface is composed of a material formed from polyurethane.
The materials of the polishing surface layers and corresponding transparent foundation layer of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 may each have defined parameters suitable to provide desired polishing characteristics, either as individual components or collectively for the polishing pad as an entirety. For example, in one such embodiment a polishing surface layer and corresponding transparent foundation layer differ in their energy loss factor, or KEL. KEL is parameter for predicting polishing performance. ASTM D4092-90 (“Standard Terminology Relating to Dynamic Mechanical Measurements of Plastics”) defines this parameter as the energy per unit volume lost in each deformation cycle. In other words, it is a measure of the area within the stress-strain hysteresis loop. The Energy Loss Factor (KEL) is a function of both tan δ and the elastic storage modulus (E′) and may be defined by the following equation: KEL=tan δ*1012/[E′*(1+tan δ2)] where E′ is in Pascals. The ratio of elastic stress to strain is the storage (or elastic) modulus and the ratio of the viscous stress to strain is the loss (or viscous) modulus. When testing is performed in tension, flex, or compression, E′ and E″ designate the storage and loss modulus, respectively. The ratio of the loss modulus to the storage modulus is the tangent of the phase angle shift (δ) between the stress and the strain. Thus, E″/E′=tan δ and is a measure of the damping ability of the material. In an embodiment, a transparent foundation layer has an energy loss factor of less than approximately 100 KEL at 1/Pa at 40° C., e.g., of approximately 7. In an embodiment, a polishing surface layer has an energy loss factor of greater than approximately 1000 KEL at 1/Pa at 40° C., e.g., of approximately 8000. In an embodiment, a transparent foundation layer has an energy loss factor of less than approximately 100 KEL at 1/Pa at 40° C., the corresponding polishing surface layer has an energy loss factor of greater than approximately 1000 KEL at 1/Pa at 40° C., and the transparent foundation layer and the corresponding polishing surface layer together have an energy loss factor of less than approximately 100 KEL at 1/Pa at 40° C.
The materials of the polishing surface layer and corresponding transparent foundation layer of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 may each have defined compressibility of elasticity suitable to provide desired polishing characteristics, either as individual components or collectively for the polishing pad as an entirety. In an embodiment, a transparent foundation layer has a compressibility of less than approximately 1% under an applied pressure of 5 PSI. In an embodiment, a polishing surface layer has a compressibility of greater than approximately 0.1% under an applied pressure of 5 PSI. In an embodiment, a polishing surface layer has a first modulus of elasticity, and the corresponding transparent foundation layer has a second modulus of elasticity greater than approximately 5 times, and even 10 times, the first modulus of elasticity, e.g. for a relatively harder polishing surface on a hard foundation layer. In another embodiment, however, a polishing surface layer has a first modulus of elasticity, and the corresponding transparent foundation layer has a second modulus of elasticity greater than approximately 100 times the first modulus of elasticity, e.g. for a relatively softer polishing surface on a hard transparent foundation layer.
In another example, the materials of the polishing surface layer and corresponding transparent foundation layer of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 may each have defined hardness suitable to provide desired polishing characteristics, either as individual components or collectively for the polishing pad as an entirety. In an embodiment, a transparent foundation layer has a hardness greater than approximately 75 Shore D, e.g., approximately 84-85 Shore D for a polycarbonate transparent foundation layer. In an embodiment, a polishing surface layer has a hardness less than approximately 70 Shore D and, preferably, less than approximately 60 Shore D. In an embodiment, a transparent foundation layer has a hardness approximately in the range of 70-90 Shore D, and the corresponding polishing surface layer has a hardness approximately in the range of 50-60 Shore D, e.g., for a hard polyurethane polishing surface layer. In another embodiment, a transparent foundation layer has a hardness approximately in the range of 70-90 Shore D, and the corresponding polishing surface layer has a hardness approximately in the range of 20-50 Shore D, e.g., for a soft polyurethane polishing surface layer.
The materials of the polishing surface layers and corresponding transparent foundation layers of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 may each have defined composition suitable to provide desired polishing characteristics, either as individual components or collectively for the polishing pad as an entirety. In an embodiment, a transparent foundation layer is composed of a polycarbonate material. In one such embodiment, the polycarbonate material is composed of a stack of several discrete layers (sub layers) of polycarbonate or is composed of a single, continuous, layer of polycarbonate. In another embodiment, a transparent foundation layer is composed of a material such as, but not limited to, an epoxy board material.
In an embodiment, a polishing surface layer of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 is a homogeneous polishing surface layer. In one such embodiment, the homogeneous polishing surface layer is composed of a thermoset polyurethane material. For example, in a specific embodiment, the homogeneous 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 body. For example, in an embodiment, the term “homogeneous” excludes polishing pad bodies 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, although a polishing surface layer is composed of a thermoset material, the corresponding transparent foundation layer is composed of a thermoplastic material, such as a polycarbonate.
The materials of the polishing surface layers of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 may be molded. The term “molded” may be used to indicate that the polishing surface layer is formed in a formation mold, as described in more detail below in association with
The materials of a polishing surface layer of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 may include pore-forming features. In an embodiment, a polishing surface layer has a pore density of closed cell pores approximately in the range of 6%-50% total void volume. 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 polishing surface layer of a 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 surface layer. In an embodiment, although a polishing surface layer includes pore-forming features, the corresponding transparent foundation layer does not and is non-porous.
In an embodiment, polishing pads described herein, such as polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700, include a polishing surface layer that is opaque. In one embodiment, the term “opaque” is used to indicate a material that, in its bulk form, allows approximately 10% or less visible light to pass. In one embodiment, a polishing surface layer is opaque in most part, or due entirely to, the inclusion of an opacifying particle filler, such as a lubricant, throughout (e.g., as an additional component in) the polishing surface layer. In a specific embodiment, the opacifying particle filler 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®.
In another example, the materials of the polishing surface layers of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 and corresponding transparent foundation layers may each have defined dimensions suitable to provide desired polishing characteristics, either as individual components or collectively for the polishing pad as an entirety. In an embodiment, a polishing surface layer has a thickness (a′ in
In an embodiment, the thickness (b′) of the transparent foundation layer is greater than the thickness (a′) of the corresponding polishing surface layer. In an embodiment, the transparent foundation layer has a thickness (b′) and hardness relative to the thickness (a′) and hardness of the corresponding polishing surface layer sufficient to dictate the bulk polishing characteristics of the corresponding polishing pad. In an embodiment, the transparent foundation layer is sufficiently thick for the corresponding polishing pad to provide die-level polishing planarity, but sufficiently thin for the polishing pad to provide wafer-level polishing uniformity.
Although the above embodiments primarily focus on polishing pads with a polishing surface layer softer than a corresponding, underlying, transparent foundation layer, other arrangements are contemplated within the spirit and scope of embodiments of the present invention. For example, in an embodiment, a polishing pad for polishing a substrate includes a transparent foundation layer having a first hardness. A polishing surface layer is bonded with the transparent foundation layer. The polishing surface layer has a second hardness equal to or greater than the first hardness. In one embodiment, the polishing surface layer is directly bonded to, and is covalently bonded to, the transparent foundation layer. In one embodiment, the transparent foundation layer and the polishing surface layer have a peel resistance sufficient to withstand a shear force applied during the useful lifetime of the polishing pad. In one embodiment, the polishing surface layer is composed of a continuous layer portion with plurality of polishing features protruding there from, the continuous layer portion bonded directly to the transparent foundation layer. In one embodiment, the polishing surface layer is composed of a plurality of discrete polishing protrusions bonded directly to the transparent foundation layer.
In another example, in an embodiment, a polishing pad for polishing a substrate includes a transparent foundation layer having an energy loss factor of less than approximately 100 KEL at 1/Pa at 40° C. A polishing surface layer is bonded with the transparent foundation layer. The polishing surface layer has an energy loss factor of greater than approximately 1000 KEL at 1/Pa at 40° C. The transparent foundation layer and the polishing surface layer together have an energy loss factor of less than approximately 100 KEL at 1/Pa at 40° C. In one embodiment, the polishing surface layer is composed of a continuous layer portion with plurality of polishing features protruding there from, the continuous layer portion attached to the transparent foundation layer. In one embodiment, the polishing surface layer is composed of a plurality of discrete polishing protrusions attached to the transparent foundation layer. In one embodiment, the polishing surface layer is composed of a thermoset polyurethane material.
In another example, in an embodiment, a polishing pad for polishing a substrate includes a transparent foundation layer having a first hardness. A polishing surface layer is bonded with the transparent foundation layer. The polishing surface layer has a second hardness less than the first hardness and is composed of a thermoset material. In one embodiment, the polishing surface layer is a homogeneous polishing surface layer. In one embodiment, the thermoset material is polyurethane. In one embodiment, the transparent foundation layer has a hardness approximately in the range of 70-90 Shore D, and the polishing surface layer has a hardness approximately in the range of 50-60 Shore D. In one embodiment, the transparent foundation layer has a hardness approximately in the range of 70-90 Shore D, and the polishing surface layer has a hardness approximately in the range of 20-50 Shore D. In one embodiment, the polishing surface layer is composed of a continuous layer portion with plurality of polishing features protruding there from, the continuous layer portion attached to the transparent foundation layer. In one embodiment, the polishing surface layer is composed of a plurality of discrete polishing protrusions attached to the transparent foundation layer. In one embodiment, the polishing surface layer has a pore density of closed cell pores approximately in the range of 6%-50% total void volume.
In another example, in an embodiment, a polishing pad for polishing a substrate includes a nonporous transparent foundation layer. A polishing surface layer is bonded with the transparent foundation layer. The polishing surface layer has a pore density of closed cell pores. In one embodiment, the pore density of closed cell pores is approximately in the range of 6%-50% total void volume. In one embodiment, the polishing surface layer is composed of a continuous layer portion with plurality of polishing features protruding there from, the continuous layer portion bonded directly to the transparent foundation layer. In one embodiment, the polishing surface layer is composed of a plurality of discrete polishing protrusions bonded directly to the transparent foundation layer.
The polishing surface layer of the above described polishing pads 200, 300A, 300B, 300C, 400, 500, 600 and 700 may have a pattern suitable for polishing during a CMP operation. Examples are depicted in
In another general example, some embodiments of the present invention include a plurality of protrusions having a pattern of linear features. In a specific such example,
In another general example, some embodiments of the present invention include a plurality of protrusions having a pattern of discrete curved features. In a specific such example, discrete arc-shaped protrusions are included. Other specific such embodiments include, but are not limited to, a plurality of partial circumferential protrusions disposed on a substantially circular polishing pad.
In another general example, some embodiments of the present invention include a plurality of protrusions having a pattern of discrete tiles. In a specific such embodiment, discrete hexagonal tile protrusions are included. Other specific such embodiments include, but are not limited to, pluralities of circular tiles, oval tiles, square tiles, rectangular tiles, or a combination thereof.
Although the above general examples may be defined in terms of protrusions (e.g., the highest points of a patterned polishing surface layer), the polishing surface layers may also or alternatively be defined in terms of grooves (e.g., the lowest points of a patterned polishing surface layer). Individual grooves 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 groove pattern may all have the same depth. In some embodiments, some of the grooves of a groove 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 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 groove pattern are all of uniform width. In some embodiments, however, some of the grooves of a groove 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 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 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.
In another aspect, a polishing pad with a polishing surface layer and corresponding transparent foundation layer further includes a detection region for use with, e.g., an eddy current detection system. For example,
Referring to
In an embodiment, a polishing pad described above further includes a sub pad, e.g., a conventional sub pad as known in the CMP art. The foundation layer is disposed proximate to the sub pad. In one such embodiment, the sub pad has a hardness less than the hardness of the corresponding foundation layer. In one such embodiment, the sub pad is composed of a material such as, but not limited to, foam, rubber, fiber, felt or a highly porous material. In an embodiment, the sub pad has an aperture. The aperture of the sub pad is aligned with the transparent region of the foundation layer.
In another aspect, polishing pads with transparent foundation layers and corresponding polishing surface layers having an aperture or opening disposed therein may be fabricated in a molding process. For example, such multi-layer (e.g., surface polishing layer plus underlying transparent foundation layer) polishing pads as those described above may be fabricated with a molding process to facilitate direct bonding between a surface polishing layer and an underlying foundation layer.
Referring to
Referring again to
In an embodiment, the mixture 1006 is used to ultimately form a molded polishing surface layer composed of a thermoset, closed cell polyurethane material. In one embodiment, the mixture 1006 is used to ultimately form a hard polishing surface layer and only a single type of curative is used. In another embodiment, the mixture 1006 is used to ultimately form a soft polishing surface layer 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 a molded polishing surface layer with varying hardness values, or based on the specific nature of the pre-polymer and the first and second curatives. In an embodiment, mixing the pre-polymer and any curatives to form the mixture 1006 includes degassing the mixture 1006.
Referring to
It is to be understood that embodiments described herein that describe lowering the lid 1008 of a formation mold 1000 need only achieve a bringing together of the lid 1008 and a base of the formation mold 1000. That is, in some embodiments, a base of a formation mold 1000 is raised toward a lid 1008 of a formation mold, while in other embodiments a lid 1008 of a formation mold 1000 is lowered toward a base of the formation mold 1000 at the same time as the base is raised toward the lid 1008.
Referring to
In an embodiment, at least partially curing the mixture 1006 includes heating the base of the formation mold 1000. In an embodiment, at least partially curing the mixture 1006 includes heating both the mixture 1006 and the transparent foundation layer 1001. This approach may alleviate compression stress that may otherwise result upon cooling of a molded polishing surface layer if the transparent foundation layer 1001 is not heated. In an embodiment, at least partially curing the mixture 1006 forms the molded homogeneous polishing surface layer 1012 covalently bonded with the transparent foundation layer 1001.
Referring to
The molded homogeneous polishing surface layer 1012 includes an opening or aperture 1060 (aperture in the case of
By including a foundation layer in the molding process, efficiency may be built into the molding process with respect to timing of demolding a fabricated pad from the formation mold. For example, in an embodiment, removal of the coupled transparent foundation layer 1001 and molded polishing surface layer 1012 from the formation mold 1000 (e.g., removal of polishing pad 1050) is performed when the extent of curing is sufficient to maintain geometry of the molded homogeneous polishing surface layer 1012 but insufficient for the molded homogeneous polishing surface layer 1012 to withstand mechanical stress. That is, the removal is performed prior to removal of a solo molded homogeneous polishing surface layer could otherwise be performed in the absence of a foundation layer. In one such embodiment, the transparent foundation layer 1001 having the molded homogeneous polishing surface layer 1012 attached thereto is removed from the base of the formation mold 1000 less than approximately 4 minutes after coupling the pattern of grooves of the formation mold of lid 1008 with the mixture 1006. Such timing may reflect an approximately three-fold reduction in time for the molding process, enabling greater throughput in a given individual mold. In an embodiment, removal of the coupled transparent foundation layer 1001 and molded polishing surface layer 1012 from the formation mold 1000 is performed immediately after the material of the molded homogeneous polishing surface layer 1012 gels.
In addition to adding backing support, a transparent foundation layer may additionally be sized larger than the polishing surface layer 1012 to further enable an earlier demolding time. For example, in one embodiment (not shown), a foundation layer extends beyond a molded homogeneous polishing surface layer, and removing the transparent foundation layer having the molded homogeneous polishing surface layer formed thereon from the base of the formation mold includes taking hold of the transparent foundation layer but not the molded homogeneous polishing surface layer. In an embodiment, the portion of the foundation layer extending beyond the molded homogeneous polishing surface layer is removed, e.g., by cutting away the extended portion. In an alternative embodiment, the molded homogeneous polishing surface layer extends beyond the foundation layer. In one such embodiment, the polishing surface layer partially encapsulates the foundation layer to hinder delamination from the foundation layer.
It is noted that further curing of the polishing surface layer 1012 through heating may be desirable and may be performed by placing the polishing pad 1050 in an oven and heating. Thus, in one embodiment, curing the mixture 1006 includes first partially curing in the formation mold 1000 and then further curing in an oven. Either way, a polishing pad 1050 is ultimately provided, wherein a molded polishing surface layer 1012 is formed on a transparent foundation layer 1001. In an embodiment, the molded polishing surface layer 1012 is composed of a thermoset polyurethane material with a plurality of closed cell pores disposed in the thermoset polyurethane material.
By including a foundation layer in the molding process, further processing of a fabricated pad there from may be reduced or eliminated. For example, conventional molding may require subsequent back-side cutting of the body of a polishing pad. However, in an embodiment, a polishing pad (e.g., polishing pad 1050) including the transparent foundation layer 1001 having the molded homogeneous polishing surface layer 1012 formed thereon is suitable for performing a polishing process without performing a backside cut of the transparent foundation layer 1001, or of the polishing pad 1050 in general.
By including a transparent foundation layer in the molding process, recycling or reuse of materials may be made possible. For example, in an embodiment, the molded homogeneous polishing surface layer 1012 is removed from the transparent foundation layer 1001, and a second homogeneous polishing surface layer is formed on the transparent foundation layer. Such a reuse process of the transparent foundation layer 1001 may be performed after the life of the polishing surface layer and, thus, the life of the polishing pad is determined to have terminated in a CMP facility. In another such embodiment, providing the transparent foundation layer 1001 in the formation mold 1000 includes first removing a previously formed polishing surface layer from the transparent foundation layer 1001.
In an embodiment, referring again to
Thus, groove or protrusion patterns contemplated in embodiments of the present invention may be formed in-situ. Furthermore, openings or apertures in a polishing layer may also be formed simultaneously in the molding fabrication process. For example, as described above, a compression-molding process may be used to form polishing pads with a grooved polishing surface layer having an aperture or opening disposed therein. 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.
Also, since the fabricated aperture or opening is formed during the molding, the positioning of the resulting pad during formation of a pad in a mold can be determined after removal of the pad from the mold. That is, such an aperture or opening can provide traceability back to the molding process. Thus, in one embodiment, the polishing surface layer of a polishing pad is a molded polishing surface layer, and an aperture or opening included therein indicates a location of a region in a mold used for forming the molded polishing surface layer.
In an embodiment, polishing pads described herein, such as polishing pads 200, 300A, 300B, 300C, 400, 500, 600, 700, 800 or 900, 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. In an embodiment, a polishing pad 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.
Polishing pads described herein may be suitable for use with a variety of chemical mechanical polishing apparatuses. As an example,
Referring to
In accordance with an embodiment of the present invention, an aperture or opening in a polishing surface of a polishing pad disposed on a transparent foundation layer, such as an aperture or opening described in association with
As described above, in an embodiment, modern slurries are essentially transparent and will not attenuate or scatter a detection beam as early-generation slurries may otherwise have. Constant flow of slurry across an aperture opening may keep the opening free of debris. In one embodiment, a molding process is suitable for creating the opening during molding, so no extra manufacturing operations are needed. For windowless design features, in an embodiment, the purpose of each feature is to enable constant flushing of the opening with slurry during use. Features may be used individually or in combination. As described above, and in accordance with one or more embodiments of the present invention, one such feature may be a wedge or ramp shape of one or more edges of the opening. Another such feature may include one or more grooves connected with the opening. Radial grooves, circumferential grooves, or a combination thereof may be connected or continuous with the opening. The groove depth may be equal to the opening depth where they connect, with the groove floor ramping up to normal groove depth. Blocked or diverted flow of some grooves may be used so that they do not drain into the opening. A rounded shape of some or all of the corners of the opening may also be used.
In reference to polishing apparatus 1100 and one or more polishing pads described in association with 2, 3A-3C, 4, 5, 6, 7, 8 or 9, a method of polishing a substrate includes disposing a polishing pad above a platen of a chemical mechanical polishing apparatus. A chemical mechanical polishing slurry is dispensed on the polishing surface of the polishing pad. A substrate is polished with the chemical mechanical polishing slurry at the polishing surface of the polishing pad. The polishing of the substrate is monitored, through the aperture, with an optical monitoring device coupled with the platen. In an embodiment, polishing the substrate with the chemical mechanical polishing slurry includes dispensing a slurry of sufficient transparency for monitoring the polishing of the substrate with the optical monitoring device. In a specific such embodiment, dispensing the slurry of sufficient transparency includes dispensing a slurry having greater than approximately 80% transmission of a wavelength of light emitted from the optical monitoring device. In another specific such embodiment, dispensing the slurry of sufficient transparency includes dispensing a slurry having less than approximately 1% of opaque components.
Thus, polishing pads with a polishing surface layer having an aperture or opening above a transparent foundation layer have been disclosed. In accordance with an embodiment of the present invention, a polishing pad for polishing a substrate includes a transparent foundation layer having a global top surface. A polishing surface layer is attached to the global top surface of the transparent foundation layer. The polishing surface layer has a polishing surface and a back surface. An aperture is disposed in the polishing pad from the back surface through to the polishing surface of the polishing surface layer. The transparent foundation layer provides an impermeable seal for the aperture at the back surface of the polishing surface layer. In one embodiment, the aperture is disposed over the global top surface of the transparent foundation layer. In one embodiment, the aperture is disposed over an opening formed in the transparent foundation layer, and the bottom of the opening is below the global top surface of the transparent foundation layer. In one embodiment, the aperture is disposed over a protrusion formed from the transparent foundation layer, and the top of the protrusion is above the global top surface of the transparent foundation layer and located within the aperture.
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