Patent Application
20150367478
Embodiments of the present invention are in the field of chemical mechanical polishing (CMP) and, in particular, polishing pads having porogens with liquid filler and methods of fabricating polishing pads having porogens with liquid filler.
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 involves use of 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 having porogens with liquid filler and methods of fabricating polishing pads having porogens with liquid filler.
In an embodiment, a polishing pad for polishing a substrate includes a polishing body having a polymer matrix and a plurality of porogens dispersed throughout the polymer matrix. Each of the plurality of porogens has a shell with a liquid filler. The liquid filler has a boiling point less than 100 degrees Celsius at a pressure of 1 atm.
In another embodiment, a polishing pad for polishing a substrate includes a polishing body having a polymer matrix and a plurality of porogens dispersed throughout the polymer matrix. Each of the plurality of porogens has a shell with a liquid filler. The liquid filler has a density less than water.
In another embodiment, a method of polishing a substrate involves providing a polishing pad on a platen. The polishing pad includes a plurality of porogens dispersed throughout a polymer matrix of a polishing body of the polishing pad. Each of the plurality of porogens includes a shell with a liquid filler, the liquid filler having a boiling point less than 100 degrees Celsius at a pressure of 1 atm or having a density less than water, or both. The method also involves conditioning the polishing pad. The conditioning involves breaking an uppermost portion of the plurality of porogens of the polishing body of the polishing pad to provide a polishing surface of the polishing pad. The method also involves applying a slurry on the polishing surface of the polishing pad. The method also involves polishing a substrate with the slurry on the polishing surface of the polishing pad.
In another embodiment, a method of fabricating a polishing pad involves mixing a pre-polymer and a curative with a plurality of porogens to form a mixture. Each of the plurality of porogens has a shell with a liquid filler, the liquid filler having a boiling point less than 100 degrees Celsius at a pressure of 1 atm or having a density less than water, or both. The method also involves curing the mixture to provide a polishing pad having a polishing body with the plurality of porogens dispersed throughout a polymer matrix of the polishing body. The curing does not substantially expand each of the plurality of porogens.
Polishing pads having porogens with liquid filler and methods of fabricating polishing pads having porogens with liquid filler are described herein. In the following description, numerous specific details are set forth, such as specific polishing pad designs and compositions, 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 chemical mechanical planarization (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 CMP polishing pads having liquid-filled porogens or microelements dispersed throughout the matrix of the polishing pad. In use, at the pad surface, the liquid-filled porogens are broken, e.g., by a pad disk conditioner. The liquid filler is volatilized and/or pushed out by slurry from the broken porogens to provide available pores at the pad surface. The liquid-filled porogens that remain embedded in the pad, below the pad surface, provide for a high density pad bulk that is desirable for planarization performance. At the pad surface, the material is transformed to a low density porous layer that is needed for slurry transport.
To provide context, attempts have been made to incorporate water-soluble particles in a CMP pad. The water-soluble particles would dissolve upon contact with an aqueous slurry. However, the inclusion of such water-soluble material in a CMP pad can result in undesired and or uncontrolled reaction with the slurry chemicals, particularly in cases where the water-soluble material is chemically active. In one embodiment, addressing the above issues, a polyurethane matrix of a CMP polishing pad is fabricated to include liquid-filled porogens, such as unexpanded EXPANCEL™ porogens. The pad manufacturing process is performed at a temperature lower than the EXPANCEL™ expansion temperature. The filler in the EXPANCEL™ porogens or microelements remains in the liquid phase during the pad manufacturing process. The result is a CMP polishing pad which, in use, can be made to have a bulk portion of that is as solid or dense as possible for planarization. Meanwhile, the pad surface can be rendered as soft as possible for defect reduction.
More generally, one or more embodiments described herein are directed to the fabrication of polishing pads having a high bulk density of greater than approximately 0.8 grams/cubic centimeter (g/cc) and, more particularly, a high density of greater than approximately 1 g/cc. The resulting pads may be based on a polyurethane material having a closed cell porosity which provides for the high density.
In an exemplary embodiment,
In an embodiment, the liquid filler 108 of the porogens 104 is a filler contained in the shell 106, a majority of which is in the liquid phase. In one such embodiment, for one or more of the porogens 104, the liquid filler 108 completely fills the shell 106 and, as such, is entirely in the liquid phase. However, in another embodiment, for one or more porogens 104, the liquid filler 108 only partially fills the shell 106. In that embodiment, the liquid filler may be in equilibrium with the gas phase of the liquid filler. Nonetheless, a majority (by mass) of the liquid filler 108 is in the liquid phase. It is to be appreciated that the liquid filer 108, as contained in the shell 106, is effectively in a closed system while contained in the body of the polishing pad 100.
In an embodiment, the liquid filler 108 has a boiling point less than that of water, i.e., a boiling point less than 100 degrees Celsius at a pressure of 1 atm. In an embodiment, the liquid filler has a density less than water, i.e., a density less than 1 g/cm3 (as defined for water at 4 degrees Celsius) and, in a particular embodiment, the liquid filler 108 has a density less than approximately 0.7 g/cm3. In one embodiment, the liquid filler 108 is a hydrocarbon such as, but not limited to, n-pentane, iso-pentane, butane, or iso-butane (e.g., hydrocarbons having a boiling point less than 40 degrees Celsius at a pressure of 1 atm). However, in other embodiments, heavier hydrocarbons such as toluene or light mineral may be used. In one such embodiment, the liquid filler 108 is a hydrocarbon molecule having seven or more carbon atoms.
In an embodiment, the shell 106 of each liquid-filled porogen 104 is a polymeric shell. In one such embodiment, the polymeric shell is composed of a material such as, but not limited to, a block-co-polymer, polyvinylidine chloride, an acrylic material, or acrylonitrile. In an embodiment, the liquid-filler 108/shell 106 pairings can be described as an Unexpanded Porogen Filler or Underexpanded Porogen Filler (both referred to as UPF) that would otherwise expand during polishing pad fabrication at some raised temperature. However, the UPF remains a liquid-filled non-expanded porogen if the polishing pad fabrication process is maintained below an expansion temperature, as is described in greater detail below. In one such embodiment, a large quantity of UPF is included in a polyurethane-forming mixture. The UPF does not expand during the pad casting process and creates a high density pad with liquid-filled porogens.
In an embodiment, at least some of the plurality of porogens 104 have a collapsed-sphere shape. That is, the porogens 104 may approximate a shape of a deflated sphere that could otherwise be inflated to a spherical shape. The collapsed-shape may be completely collapsed to provide a crescent-like shape, or may be partially spherical or even mostly spherical.
In an example,
It is to be appreciated that the liquid-filled porogens may also take on irregular shapes. In an example,
Regardless of actual shape, the liquid-filled porogens 104 may be described as having an average diameter. Different from a sphere where the diameter is the same in any direction, the liquid-filled porogens 104 can be sized by the average diameter achieved when the size of the porogen is measured in all directions. For example, a crescent-shaped porogen will have a short diameter in the crescent view and a long diameter in the bottom view. An average diameter for the porogen may be described as an average of such diameters. In a particular embodiment, each porogen 104, e.g., a collapsed-sphere shaped porogen, has an average diameter approximately in the range of 6-40 microns.
In an embodiment, the polymer matrix 102 of the polishing body of the polishing pad 100 is or includes a thermoset polyurethane material. In one such embodiment, the polishing body including the polymer matrix 102 and the plurality of porogens 104 has a total volume, with the plurality of porogens contributing approximately 20% to approximately 50% of the total volume. In an embodiment, the polishing body including the polymer matrix 102 and the plurality of porogens 104 has a total density greater than approximately 0.8 g/cm3 and, more particularly, a total density greater than approximately 1 g/cm3. Thus, in some embodiments, the polishing pad 100 is a high density polishing pad since other known polishing pads typically have a density between 0.65 and 0.8 g/cm3.
In another aspect, the polishing pad 100 described in association with
In an embodiment, prior to and/or during the CMP process, the polishing pad 100 is conditioned. Referring to
Referring to
In an embodiment, breaking the uppermost portion of the plurality of porogens 104 leads to the releasing of the liquid filler of the broken, uppermost portion, of the porogens. In one such embodiment, the liquid filler is released, at least to some extent, by volatilization of the liquid filler upon exposure to ambient conditions outside of the pad. In such cases, a liquid filler having a high vapor pressure can be released in this manner. In another embodiment, at least to some extent, the liquid filler is displaced by a liquid or slurry applied to the surface of the polishing pad. In such cases, a low viscosity liquid filler can be released or displaced in this manner.
Referring to
In an embodiment, referring again to
As an example of a polishing cross-section that is representative of surface 110 generated upon breaking of liquid-filled porogens,
In another aspect, polishing pads having liquid-filled porogens may be fabricated in a molding process. For example,
Referring to
Referring to
Referring again to
In an embodiment, the curing does not substantially expand each of the plurality of porogens 406. In an embodiment, substantial expansion of each of the plurality of porogens 406 would be greater than 50% increase in size by volume. For example, expansion of unexpanded EXPANCEL™ can be as much as 1000% to 4000% by volume. Accordingly, in an embodiment, an unexpanded porogen 406 essentially does not expand during curing. If there is any expansion at all, in one embodiment, the expansion is less than 50% by volume.
In one embodiment, curing the mixture 410 involves heating the mixture 410, but to a temperature less than an expansion temperature of the plurality of liquid-filled porogens 406. In one embodiment, each of the plurality of porogens 406 has a collapsed-sphere shape, and the curing does not substantially modify the collapsed-sphere shape of each of the plurality of porogens 406. In one embodiment, each of the plurality of porogens 406 has an average diameter approximately in the range of 6-40 microns, and the curing does not substantially increase the average diameter of each of the plurality of porogens 406. In one embodiment, each of the plurality of porogens 406 has an initial shell thickness, and the curing does not substantially decrease the shell thickness of each of the plurality of porogens 406.
Referring to
In an embodiment, as mentioned as a possibility above, the mixture 410 is only partially cured in the mold 400 and, in one embodiment, is further cured in an oven subsequent to removal from the formation mold 420. However, in that embodiment, the heating does not substantially expand each of the plurality of porogens 406.
In an embodiment, the pre-polymer 402 is an isocyanate and the curative 404 is an aromatic diamine compound, and the polishing pad 422 is composed of a thermoset polyurethane material 220. In one such embodiment, forming mixture 410 further involves adding an opacifying filler to the pre-polymer 402 and the curative 404 to ultimately provide an opaque molded polishing body 422. In a specific such embodiment, the opacifying 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 an embodiment, the polishing pad precursor mixture 410 is used to ultimately form a molded homogeneous polishing body 422 composed of a thermoset polyurethane material. In one such embodiment, the polishing pad precursor mixture 410 is used to ultimately form a hard pad and only a single type of curative 404 is used. In another embodiment, however, the polishing pad precursor mixture 410 is used to ultimately form a soft pad and a combination of a primary and a secondary curative (together providing 404) is used. For example, in a specific embodiment, the pre-polymer 402 includes a polyurethane precursor, the primary curative includes an aromatic diamine compound, and the secondary curative includes 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, a pre-polymer 402, a primary curative, and a secondary curative (together 404) have an approximate molar ratio of 106 parts pre-polymer, 85 parts primary curative, and 15 parts secondary curative, i.e., to provide a stoichiometry of approximately 1:0.96 pre-polymer:curative. It is to be appreciated 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 again to
Although several examples above refer to the fabrication of high density pads, polishing pads with liquid-filled porogens may be fabricated to include additional porosity and, thus, reduced density. For example, in an embodiment, in addition to a plurality of liquid-filled porogens, a polishing pad further includes a second plurality of porogens dispersed throughout the polymer matrix. The second plurality of porogens may be added as an additional component to forming the mixture 410 described in association with
As an example,
In an embodiment, each of the second plurality of microelements 599 is composed of pre-expanded and gas-filled EXPANCEL™ distributed throughout (e.g., as an additional component in) the polishing pad. That is, any significant expansion that could occur for the microelements 599 is carried our prior to their inclusion in a polishing pad formation, e.g., before being included in mixture 410. In a specific embodiment, the pre-expanded EXPANCEL™ is filled with pentane, a majority of which is in the gas phase.
In another embodiment, in addition to a plurality of liquid-filled porogens, a polishing pad further includes a plurality of shell-less porogens dispersed throughout the polymer matrix. The plurality of shell-less porogens may have a gas filler and may be formed as an additional component during or after forming the mixture 410 described in association with
In another aspect, a distribution of liquid-filled porogen average diameters in a polishing pad can have a bell curve or mono-modal distribution. The mono-modal distribution may be relatively broad or may be narrow, but is mono-modal, nonetheless. That is, for either a narrow distribution or a broad distribution, only one maximum average diameter population of liquid-filled porogens is provided in the polishing pad. Alternatively, a high density polishing pad may instead be fabricated with a bimodal distribution of porogen average diameters. As an example,
Referring to
In an embodiment, the plurality of liquid-filled porogens 602 includes porogens that are discrete from one another, as is depicted in
In an embodiment, the bimodal distribution of porogen average diameters of the plurality of liquid-filled porogens 602 may be approximately 1:1, as is depicted in
Referring to plot 620 of
In an embodiment, polishing pads described herein, such as polishing pad 100, 200A, 200B, 300, 422, 500 or 600, or the above described variations thereof, 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 100, 200A, 200B, 300, 422, 500 or 600, or the above described variations thereof, 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 polyurethane material. In an embodiment, the term “homogeneous” is used to indicate that the composition of a thermoset polyurethane material is consistent throughout the entire composition of the polishing body, regardless of the porogen distribution. 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, the homogeneous polishing body, upon conditioning and/or polishing, has a polishing surface roughness approximately in the range of 1-5 microns root mean square. In one embodiment, the homogeneous polishing body, upon conditioning and/or polishing, has a polishing surface roughness of approximately 2.35 microns root mean square. In an embodiment, the homogeneous polishing body has a storage modulus at 25 degrees Celsius approximately in the range of 30-120 megaPascals (MPa). In another embodiment, the homogeneous polishing body has a storage modulus at 25 degrees Celsius approximately less than 30 megaPascals (MPa). In one embodiment, the homogeneous polishing body has a compressibility of approximately 2.5%.
In an embodiment, polishing pads described herein, such as polishing pad 100, 200A, 200B, 300, 422, 500 or 600, or the above described variations thereof, 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 above in association with
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 filler throughout (e.g., as an additional component in) the homogeneous thermoset polyurethane material of the homogeneous polishing body. In a specific embodiment, the opacifying 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.
The sizing of the polishing pads, such as pads 100, 200A, 200B, 300, 422, 500 or 600, may be varied according to application. Nonetheless, certain parameters may be used to fabricate polishing pads compatible with conventional processing equipment or even with conventional chemical mechanical processing operations. For example, in accordance with an embodiment of the present invention, a polishing pad 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, 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.
In another embodiment of the present invention, a polishing pad described herein further includes a local area transparency (LAT) region disposed in the polishing pad. In an embodiment, the LAT region is disposed in, and covalently bonded with, the polishing pad. Examples of suitable LAT regions are described in U.S. patent application Ser. No. 12/657,135 filed on Jan. 13, 2010, assigned to NexPlanar Corporation, and U.S. patent application Ser. No. 12/895,465 filed on Sep. 30, 2010, assigned to NexPlanar Corporation.
In an alternative or additional embodiment, a polishing pad further includes an aperture disposed in the polishing surface and polishing body. The aperture can accommodate, e.g., a detection device included in a platen of a polishing tool. An adhesive sheet is disposed on the back surface of the polishing body. The adhesive sheet provides an impermeable seal for the aperture at the back surface of the polishing body. Examples of suitable apertures are described in U.S. patent application Ser. No. 13/184,395 filed on Jul. 15, 2011, assigned to NexPlanar Corporation.
In another embodiment, a polishing pad further includes a detection region for use with, e.g., an eddy current detection system. Examples of suitable eddy current detection regions are described in U.S. patent application Ser. No. 12/895,465 filed on Sep. 30, 2010, assigned to NexPlanar Corporation.
Polishing pads described herein, such as polishing pad 100, 200A, 200B, 300, 422, 500 or 600, or the above described variations thereof, may further include a foundation layer disposed on the back surface of the polishing body. In one such embodiment, the result is a polishing pad with bulk or foundation material different from the material of the polishing surface. 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. Examples of suitable foundation layers are described in U.S. patent application Ser. No. 13/306,845 filed on Nov. 29, 2011, assigned to NexPlanar Corporation.
Polishing pads described herein, such as polishing pad 100, 200A, 200B, 300, 422, 500 or 600, or the above described variations thereof, may further include a sub pad disposed on the back surface of the polishing body, e.g., a conventional sub pad as known in the CMP art. 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.
Referring again to
Individual grooves of a groove pattern formed in a polishing pad such as those 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 are all of uniform width. In some embodiments, however, some of the grooves of a concentric 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 groove patterns described herein, including grooves at or near a location of an aperture in a polishing pad, 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.
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 having porogens with liquid filler and methods of fabricating polishing pads having porogens with liquid filler have been disclosed. In accordance with an embodiment of the present invention, a polishing pad for polishing a substrate includes a polishing body having a polymer matrix and a plurality of porogens dispersed throughout the polymer matrix. Each of the plurality of porogens has a shell with a liquid filler. The liquid filler has a boiling point less than 100 degrees Celsius at a pressure of 1 atm, a density less than water, or both.
