Patent Application
20250114903
The present technology relates to semiconductor systems, processes, and equipment. More specifically, the present technology relates to polishing film deposited on a substrate.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, and/or insulative layers on a silicon wafer. A variety of fabrication processes use the planarization of a layer on the substrate between processing steps. For example, for certain applications, e.g., polishing of a metal layer to form vias, plugs, and/or lines in the trenches of a patterned layer, an overlying layer is planarized until the top surface of a patterned layer is exposed. In other applications, e.g., planarization of a dielectric layer for photolithography, an overlying layer is polished until a desired thickness remains over the underlying layer.
Chemical mechanical polishing (CMP) is one common method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. Abrasive polishing slurry is typically supplied to the surface of the polishing pad.
One problem in CMP is uniformly polishing the entire surface of the substrate. Oftentimes, due to the design of CMP systems the regions of the polishing pad proximate the peripheral edges, and in particular proximate the leading and/or trailing edge, of the substrate may be subject to higher or lower polishing rates. For example, as the substrate and polishing pad are moved relative to one another, a trailing edge of the substrate may contact an inner retaining ring, which may generate a side load on the substrate. The side load may be concentrated at the contact point of the trailing edge, which may generate higher polishing rates at the trailing edge. As a result, film thickness may be uneven across one or more edge regions of the substrate. This film non-uniformity may cause lithography issues and may lead to a loss in die yield from a given substrate.
Thus, there is a need for improved systems and methods that can be used to polish substrates to generate a uniform film across an entire surface area of the substrate. These and other needs are addressed by the present technology.
Exemplary carrier heads for a chemical mechanical polishing apparatus may include a carrier body. The carrier heads may include a flexible membrane coupled with the carrier body. The flexible membrane may include a substrate-receiving surface that faces away from the carrier body. The substrate-receiving surface may include a plurality of gripping elements that protrude away from the substrate-receiving surface. Each of the plurality of gripping elements may have a maximum lateral dimension that is no greater than 2 mm.
In some embodiments, each of the plurality of gripping elements may include a wide base that tapers to a gripping surface. The gripping surface may be convex. The gripping surface may be concave. Each of the plurality of gripping elements may be substantially mushroom-shaped. The carrier heads may include a plurality of substrate retaining members coupled with the carrier body. Each of the plurality of substate retaining members may be disposed at a different angular position about a periphery of the substrate-receiving surface. The plurality of retaining members may collectively extend about less than 20% of the periphery of the substrate-receiving surface. An adhesive may be applied to a gripping surface of at least some of the plurality of gripping elements. Each of the plurality of gripping elements may have a maximum lateral dimension that is no greater than 0.1 mm. Each of the plurality of gripping elements may be flexible in a lateral direction.
Some embodiments of the present technology may encompass flexible membranes for a chemical mechanical polishing apparatus. The flexible membranes may include a flexible membrane body having a substrate-receiving surface. The substrate-receiving surface may include a plurality of gripping elements that protrude away from the substrate-receiving surface. Each of the plurality of gripping elements may have a maximum lateral dimension that is no greater than 2 mm.
In some embodiments, each of the plurality of gripping elements may include a wide base that tapers to a gripping surface. The gripping surface may be convex. The gripping surface may be concave. A height of each of the plurality of gripping elements may be no greater than 1 mm. An open area of the substrate-receiving surface may be less than 50%.
Some embodiments of the present technology may encompass methods of polishing a substrate. The methods may include engaging a substrate with a plurality of gripping elements of a substrate-receiving surface of a flexible membrane of a carrier head. The methods may include flowing a polishing slurry from a slurry source to a polishing pad. The methods may include moving the carrier head to polish the substrate atop the polishing pad.
In some embodiments, moving the carrier head may include one or both of rotating the carrier head and laterally translating the carrier head relative to the polishing pad. The carrier head may include a plurality of substrate retaining members that are disposed at different angular positions about a periphery of the substrate-receiving surface. Each of the plurality of substrate retaining members may include an inner portion that contacts a periphery of the substrate and that terminates prior to reaching the polishing pad and an outer region that contacts the polishing pad.
Such technology may provide numerous benefits over conventional systems and techniques. For example, the polishing heads described herein may help prevent excess polishing from occurring at the edge regions, and in particular at the trailing edge, of a substrate during polishing operations. This may enable the film thickness uniformity to be improved across the surface of the substrate, which may lead to increased die yield. These and other embodiments, along with many of their advantages and features, are described in more detail in conjunction with the below description and attached figures.
A further understanding of the nature and advantages of the disclosed technology may be realized by reference to the remaining portions of the specification and the drawings.
Several of the figures are included as schematics. It is to be understood that the figures are for illustrative purposes and are not to be considered of scale unless specifically stated to be of scale. Additionally, as schematics, the figures are provided to aid comprehension and may not include all aspects or information compared to realistic representations and may include exaggerated material for illustrative purposes.
In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a letter that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the letter.
In conventional chemical mechanical polishing (CMP) operations it is often difficult to uniformly polish the surface of a substrate. Conventional CMP polishing involves a substrate being positioned face down on a polishing pad, with a carrier that holds the substrate against a rotating polishing pad. As the substrate and polishing pad are moved relative to one another, the trailing edge of the substrate may be pushed against an inner surface of an inner retaining ring. In conventional CMP systems, the contact between the inner retaining ring and the trailing edge of the substrate generates a side load that increases stress on the substrate near the trailing edge. This increased substrate stress causes increased polishing/material removal rates at and/or proximate the trailing edge relative to the rest of the substrate. This may result in film non-uniformity issues that result in a lower die yield. Additionally, the use of the retaining ring may cause slurry to agglomerate against the inner surface of the retaining ring instead of reaching the surface of the substrate being polished, which may result in uneven polishing and/or waste of slurry.
The present technology overcomes these issues with conventional polishing systems by using a membrane that adheres to or otherwise grasps the substrate to replace or supplement the retaining ring. The membrane may include a number of small gripping elements that increase the surface contact between the substrate and the membrane, which may reduce or eliminate the need for a retaining ring. For example, the retaining ring may be replaced using a number of small retaining members that are positioned at different angular positions about an edge of the substrate. The retaining members may reduce the contact area with the substrate and may eliminate or reduce any pad deformation effects that are attributed to use of a retaining ring. Additionally, the elimination of the retaining ring may help prevent the agglomeration of slurry and may therefore reduce the use of slurry. These techniques may be used in conjunction with conventional CMP systems to produce substrates with improved film thickness uniformity.
Although the remaining disclosure will routinely identify specific film polishing processes utilizing the disclosed technology, it will be readily understood that the systems and methods are equally applicable to a variety of other semiconductor processing operations and systems. Accordingly, the technology should not be considered to be so limited as for use with the described polishing systems or processes alone. The disclosure will discuss one possible system that can be used with the present technology before describing systems and methods or operations of exemplary process sequences according to some embodiments of the present technology. It is to be understood that the technology is not limited to the equipment described, and processes discussed may be performed in any number of processing chambers and systems, along with any number of modifications, some of which will be noted below.
In some embodiments of performing a chemical-mechanical polishing process, the rotating and/or sweeping substrate carrier 108 may exert a downforce against a substrate 112, which is shown in phantom and may be disposed within or coupled with the substrate carrier. The downward force applied may depress a material surface of the substrate 112 against the polishing pad 110 as the polishing pad 110 rotates about a central axis of the platen assembly. The interaction of the substrate 112 against the polishing pad 110 may occur in the presence of one or more polishing fluids delivered by the fluid delivery arm 118. A typical polishing fluid may include a slurry formed of an aqueous solution in which abrasive particles may be suspended. Often, the polishing fluid contains a pH adjuster and other chemically active components, such as an oxidizing agent, which may enable chemical mechanical polishing of the material surface of the substrate 112.
The pad conditioning assembly 120 may be operated to apply a fixed abrasive conditioning disk 122 against the surface of the polishing pad 110, which may be rotated as previously noted. The conditioning disk may be operated against the pad prior to, subsequent, or during polishing of the substrate 112. Conditioning the polishing pad 110 with the conditioning disk 122 may maintain the polishing pad 110 in a desired condition by abrading, rejuvenating, and removing polish byproducts and other debris from the polishing surface of the polishing pad 110. Upper platen 106 may be disposed on a mounting surface of the lower platen 104, and may be coupled with the lower platen 104 using a plurality of fasteners 138, such as extending through an annular flange shaped portion of the lower platen 104.
The polishing platen assembly 102, and thus the upper platen 106, may be suitably sized for any desired polishing system, and may be sized for a substrate of any diameter, including 200 mm, 300 mm, 450 mm, or greater. For example, a polishing platen assembly configured to polish 300 mm diameter substrates, may be characterized by a diameter of more than about 300 mm, such as between about 500 mm and about 1000 mm, or more than about 500 mm. The platen may be adjusted in diameter to accommodate substrates characterized by a larger or smaller diameter, or for a polishing platen 106 sized for concurrent polishing of multiple substrates. The upper platen 106 may be characterized by a thickness of between about 20 mm and about 150 mm, and may be characterized by a thickness of less than or about 100 mm, such as less than or about 80 mm, less than or about 60 mm, less than or about 40 mm, or less. In some embodiments, a ratio of a diameter to a thickness of the polishing platen 106 may be greater than or about 3:1, greater than or about 5:1, greater than or about 10:1, greater than or about 15:1, greater than or about 20:1, greater than or about 25:1, greater than or about 30:1, greater than or about 40:1, greater than or about 50:1, or more.
The upper platen and/or the lower platen may be formed of a suitably rigid, light-weight, and polishing fluid corrosion-resistant material, such as aluminum, an aluminum alloy, or stainless steel, although any number of materials may be used. Polishing pad 110 may be formed of any number of materials, including polymeric materials, such as polyurethane, a polycarbonate, fluoropolymers, polytetrafluoroethylene polyphenylene sulfide, or combinations of any of these or other materials. Additional materials may be or include open or closed cell foamed polymers, elastomers, felt, impregnated felt, plastics, or any other materials that may be compatible with the processing chemistries. It is to be understood that polishing system 100 is included to provide suitable reference to components discussed below, which may be incorporated in system 100, although the description of polishing system 100 is not intended to limit the present technology in any way, as embodiments of the present technology may be incorporated in any number of polishing systems that may benefit from the components and/or capabilities as described further below.
The housing 202 may generally be circular in shape and may be connected to a drive shaft to rotate therewith during polishing. There may be passages (not illustrated) extending through the housing 202 for pneumatic control of the carrier head 200. The base assembly 204 may be a vertically movable assembly located beneath the housing 202. The gimbal mechanism 206 may permit the base assembly 204 to gimbal relative to the housing 202, while preventing lateral motion of the base assembly 204 relative to the housing 202. The loading chamber 208 may be located between the housing 202 and the base assembly 204 to apply a load, i.e., a downward pressure or weight, to the base assembly 204. The vertical position of the base assembly 204 relative to a polishing pad (such as polishing pad 110) may be also controlled by the loading chamber 208. The substrate backing assembly 210 may include a flexible membrane 250 with a lower surface 252 that may provide a mounting surface for a substrate 280.
The substrate 280 can be held by the inner ring assembly, which may be clamped to a base assembly 204. The inner ring assembly may be constructed from inner ring 240 and a flexible membrane 250 shaped to provide an annular chamber. The inner ring 240 may be positioned beneath the flexible membrane 250 and may be configured to be secured to the flexible membrane 250. While the inner ring 240 may be configured to retain substrate 280 and provide active edge process control, the outer ring 260 may provide positioning or referencing of the carrier head 200 to the surface of the polishing pad. In addition, the outer ring 260 may contact and provide lateral referencing of the inner ring 240. The outer ring 260 may circumferentially surround inner ring 240 and may include an inner surface that is disposed against the outer surface of the inner ring 240. Like the inner ring 240, a lower surface of the outer ring 260 may be brought into contact with the polishing pad. The lower surface of the outer ring 260 may be smooth and wearable surface and may be selected so as to not abrade the polishing pad. An upper surface of the outer ring 260 may be secured to the base 204, e.g., the outer ring 260 may not vertically movable relative to the base 204. In some embodiments, an upper portion of the outer ring 260 may be formed of a material that is more rigid than a lower portion of the outer ring 260. For example, the lower portion may be a plastic, e.g., polyetheretherketone (PEEK), carbon filled PEEK, Teflon® filled PEEK, polyamidimid (PAI), or a composite material, while the upper portion may be a metal, e.g., stainless steel, molybdenum, or aluminum, or a ceramic, e.g., alumina. A portion of the outer ring 260 that includes the lower surface may be formed of a more rigid material than the portion of the inner ring 240 that includes the second surface 246. This may result in the outer ring 260 wearing at a lower rate than the inner ring 240. For example, the lower portion of the outer ring 260 may be a plastic that is harder than the plastic of the inner ring 240.
The flexible membrane 250 may be configured to be clamped above to base assembly 204 and secured below to inner ring 240. Positioning the flexible membrane between the inner ring 240 and the carrier head 200 may reduce or eliminate the impact of carrier distortion on the inner ring 240 which occurs when the ring 240 is directly secured to the carrier head 200. The elimination of this carrier distortion may reduce the uneven wear on the inner ring 240, reduce process variability at the substrate edge, and enable lower polishing pressures to be used, increasing ring lifetime. The flexible membrane 250 may be formed of a material that is elastic, allowing the membrane to flex under pressure. The elastic material may include silicone and other exemplary materials.
Second surface 315 may form or define a substrate-receiving surface 320 that is sized and shaped to contact a backside of a substrate. As best illustrated in
Each gripping element 325 may have a substantially same (e.g., with a deviation of less than 10%, less than 5%, less than 3%, less than 1%, or less) height (e.g., protrusion distance) from a main surface of substrate-receiving surface 320. For example, each gripping element 325 may have a height that is no greater than 1 mm, no greater than 0.75 mm, no greater than 0.5 mm, no greater than 0.25 mm, no greater than 0.1 mm, no greater than 0.075 mm, no greater than 0.05 mm, no greater than 0.025 mm, no greater than 0.015 mm, or less. For example, each gripping element 325 may have a maximum height of between 0.015 mm and 1 mm. Gripping elements 325 and/or gripping surfaces 330 may all have a same lateral size and shape in some embodiments, while in other embodiments some or all of the gripping elements 325 and/or gripping surfaces 330 may have different lateral shapes and/or sizes. Each gripping element 325 and/or gripping surface 330 may have a maximum lateral dimension (e.g., diameter) of no greater than 2 mm, no greater than 1.75 mm, no greater than 1.5 mm, no greater than 1.25 mm, no greater than 1 mm, no greater than 0.75 mm, no greater than 0.5 mm, no greater than 0.25 mm, no greater than 0.1 mm, no greater than 0.075 mm, no greater than 0.05 mm, no greater than 0.025 mm, no greater than 0.01 mm, no greater than 0.005 or less. For example, each gripping element 325 may have a maximum lateral dimension of between 0.005 mm and 2 mm.
Gripping elements 325 may be formed on substrate-receiving surface 320 using various techniques. For example, in some embodiments gripping elements 325 may be microprinted and/or micro-molded onto substate-receiving surface 320. Gripping elements 325 may be formed from a same or different material as the rest of membrane body 305. For example, gripping elements 325 may be formed from rubber, silicone, and/or other elastomeric and/or polymeric material. In some embodiments, some or all of the gripping surfaces 330 may be formed from and/or be coated with an adhesive and/or high friction material that may better enhance the ability of the respective gripping surface 330 to grip a backside of a substrate. Suitable materials may include, without limitation, polymeric materials.
In some embodiments, base 405 may be wider than stem 415 such that gripping element 400 tapers from a wide base 405 to gripping surface 310. The degree of taper may be constant along a length of stem 415, such as with stem 415a in
Gripping surfaces 410 may be wider than stems 415 in some embodiments. In such embodiments, transitions between stem 415 and gripping surface 410 may take different forms. For example, as shown in
Gripping surface 410 may take various forms that may provide different gripping characteristics. For example, as shown in
While
The use of membranes having gripping elements as described herein may improve the contact and friction/grip between the membrane and the backside of a substrate in relation to conventional planar membranes. For example, due to manufacturing limitations, the planarity of a conventional planar membrane may be non-uniform at a microlevel, which may limit the contact area between the membrane and the backside of the substrate. The use of numerous small, flexible gripping elements may enable each gripping element to independently contact and/or deform against the backside of the substrate, which may increase the actual contact area between the membrane and the backside of the substrate. Additionally, the ability of the individual gripping elements to flex laterally and/or longitudinally may better enable membranes with the gripping elements to maintain secure contact with the backside of the substrate as the substrate is subjected to lateral and/or rotational forces during polishing operations. The enhanced gripping ability of such membranes may enable retaining rings of the carrier head to be removed and/or reduced in size, as the membrane may have sufficient contact force to prevent the substrate from slipping out of the carrier head during processing operations.
As noted above, the membranes and gripping elements described herein may reduce or eliminate the need for a retaining ring, such as inner ring 240, within a carrier head. In some embodiments, to supplement the gripping ability of the membrane, a carrier head may include a number of retaining members that are positioned to prevent the substrate from slipping out of the substrate-receiving surface during polishing operations.
Retaining members 505 may be formed from a material that is compatible with a polishing slurry and that is wear-resistant to prevent retaining members 505 from wearing due to abrasion from sliding against a polishing pad. In some embodiments, retaining members 505 may be formed from polyetheretherketone (PEEK), carbon filled PEEK, Teflon® filled PEEK, polyamidimid (PAI), or a composite material, although other materials are possible in various embodiments. Retaining members 505 may be positioned in carrier head 500 at similar radial positions as an inner ring, such as inner ring 240. For example, retaining members 505 may be positioned radially outward of membrane 510 such that at least a portion of an inner surface of each retaining member 505 is aligned with a peripheral edge of a substrate-receiving surface of membrane 510. Such positioning may enable the portion of the inner surface of each retaining member 505 to contact a peripheral edge of a substrate positioned against the substrate-receiving surface of membrane 510 to help maintain the substrate at least substantially centered with respect to the substrate-receiving surface of membrane 510. In some embodiments, the inner surface of each retaining member 505 may be arcuate, such as having a radius that matches a radius of the substrate-receiving surface of membrane 510, to provide greater contact area between each retaining member 505 and the peripheral edge of the substrate.
Any number of retaining members 505 may be used to retain the substrate in a desired position. In some embodiments, two larger retaining members may be used to collectively grasp a large portion (e.g., at least 25%) of the peripheral edge of the substrate. In other embodiments a greater number of retaining members 505 may be used. For example, carrier head 500 may include three or more retaining members, four or more retaining members, five or more retaining members, six or more retaining members, nine or more retaining members, twelve or more retaining members, fifteen or more retaining members, or more. Retaining members 505 may be positioned at regular and/or irregular intervals about a periphery of the substrate-receiving surface of membrane 510. Retaining members 505 may be the same size or different sizes. In some embodiments, retaining members 505 may collectively extend about less than 25% of a peripheral edge of the substrate-receiving surface, less than 20% of a peripheral edge of the substrate-receiving surface, less than 15% of a peripheral edge of the substrate-receiving surface, less than 10% of a peripheral edge of the substrate-receiving surface, less than 5% of a peripheral edge of the substrate-receiving surface, or less. The use of smaller retaining members 505 at discrete locations may effectively secure the substrate within carrier head 500 (e.g., due to the increased grip afforded by membrane 510) while providing sufficiently open edges to prevent polishing slurry from agglomerating against the inner surface of retaining members 505 as is often seen with conventional retaining rings.
Such designs may move a contact area between retaining member 505 and a polishing pad radially outward from substrate 550 and may help reduce or eliminate uneven polishing force that may occur due to pad deformation and/or rebounding as seen with conventional retaining rings. Additionally, the use of small, discrete retaining members 505 may help reduce such effects from pad deformation and/or rebounding since only small regions around the periphery of substrate 550 will be deformed by retaining members 505, with any lingering effects being mitigated by rotation of substrate 550 relative to the polishing pad.
Method 600 may include engaging a substrate with a plurality of gripping elements of a substrate-receiving surface of a flexible membrane of a carrier head at operation 605. For example, the substrate may be positioned against the substrate-receiving surface of the membrane and compressed against a polishing pad. Method 600 may include flowing a polishing slurry from a slurry source to the polishing pad at operation 610. The substrate may be polished atop the polishing pad at operation 615. For example, the carrier head may rotate and/or translate (or sweep) the substrate about the surface of the polishing pad such that abrasive particles within the polishing slurry may gradually remove material from a surface of the substrate in a desired pattern and/or to achieve a desired film thickness profile. In some embodiments, in addition to or alternatively to the carrier head rotating and/or translating, the polishing pad may rotate and/or translate. A back surface of the substrate may be positioned against the flexible membrane and pressure may be applied to the back surface of the substrate during polishing operations. The substrate may be retained in a desired position relative to the carrier head and flexible membrane using the gripping force (e.g., adhesion, friction, etc.) of the gripping elements and/or using a number of retaining members that are disposed radially outward of the substrate at a number of discrete locations.
In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.
Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the embodiments. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present technology. Accordingly, the above description should not be taken as limiting the scope of the technology.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly or conventionally understood. As used herein, the articles “a” and “an” refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. “About” and/or “approximately” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, encompasses variations of +20% or +10%, +5%, or +0.1% from the specified value, as such variations are appropriate to in the context of the systems, devices, circuits, methods, and other implementations described herein. “Substantially” as used herein when referring to a measurable value such as an amount, a temporal duration, a physical attribute (such as frequency), and the like, also encompasses variations of +20% or +10%, +5%, or +0.1% from the specified value, as such variations are appropriate to in the context of the systems, devices, circuits, methods, and other implementations described herein.
Where a range of values is provided, it is understood that each intervening value, to the smallest fraction of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Any narrower range between any stated values or unstated intervening values in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of those smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the technology, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a heater” includes a plurality of such heaters, and reference to “the protrusion” includes reference to one or more protrusions and equivalents thereof known to those skilled in the art, and so forth.
Also, the words “comprise(s)”, “comprising”, “contain(s)”, “containing”, “include(s)”, and “including”, when used in this specification and in the following claims, are intended to specify the presence of stated features, integers, components, or operations, but they do not preclude the presence or addition of one or more other features, integers, components, operations, acts, or groups.
