Patent Application
20250108477
This disclosure generally describes techniques for optimizing edge control during chemical mechanical polishing (CMP) procedures. More specifically, this disclosure describes CMP pad recesses to improve edge control during polishing operations.
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. The abrasive polishing slurry is typically supplied to the surface of the polishing pad.
In some embodiments, a chemical mechanical polishing (CMP) chamber for polishing semiconductor substrates may include a platen configured to rotate within the CMP chamber; a polishing pad that may be configured to be mounted on the platen and rotated with the platen, where the polishing pad may include one or more recesses around a periphery of the polishing pad; and a carrier head configured to hold a substrate and rotate the substrate against the polishing pad during a CMP process.
In some embodiments, a method of polishing semiconductor substrates may include rotating a platen within a CMP chamber, where a polishing pad may be mounted on the platen and rotated with the platen, and the polishing pad may include one or more channels around a periphery of the polishing pad. The method may also include rotating a carrier head configured to hold a substrate against the polishing pad during a CMP process. The method may additionally include providing a polishing slurry to the polishing pad, where the polishing slurry may be directed off of the polishing pad through the one or more channels during the CMP process.
In some embodiments, a polishing pad for CMP chambers may include a sub pad that includes a bottom side of the polishing pad that may be configured to be mounted to a platen in a CMP chamber. The polishing pad may also include a plurality of grooves on a top side of the polishing pad, and one or more recesses around a periphery of on the top side of the polishing pad.
In any embodiments, any and all of the following features may be implemented in any combination and without limitation. The polishing pad may also include one or more channels around the periphery of the polishing pad that are positioned relative to the one or more recesses to direct polishing slurry out of the one or more recesses and off of the polishing pad during a CMP process. The one or more channels may include at least eight channels that may be evenly spaced around the periphery of the polishing pad. A width of the one or more recesses may be tapered between the one or more channels to direct polishing slurry from the one or more recesses into the one or more channels. The one or more recesses may include at least one continuous circular recess having an inner radius and an outer radius around the periphery of the polishing pad. A width of the one or more recesses may be between about 4% and about 8% of a diameter of the substrate. The polishing slurry may be collected in a circular recess located around a periphery of the polishing pad, where the circular recess may direct the polishing slurry into the one or more channels to be directed off of the polishing pad during the CMP process. The one or more channels may have a length that is directed outward perpendicular to an edge of the polishing pad and perpendicular to a circular recess around a periphery of the polishing pad. The one or more channels may have a length that is between about 0.5 inches and about 3.0 inches. The one or more channels may have a width and a depth such that a flow rate at which the polishing slurry is provided to the polishing pad is less than or equal to a flow rate at which the polishing slurry exits the polishing pad through the one or more channels. The one or more channels may have a width between about 0.25 inches and about 1.0 inches. The one or more channels may include at least three channels that are evenly distributed around an edge of the polishing pad. The one or more recesses may have a width of between about 0.2 inches and about 1.0 inches. The one or more recesses may be offset from an edge of the polishing pad by between about 0.5 inches and about 3.0 inches. The one or more recesses may have a depth that is the same as a depth of the plurality of grooves. The one or more recesses may have a depth that extends down to a surface of a top pad beneath the plurality of grooves and on top of the sub pad. The polishing pad may also include one or more channels around the periphery of the polishing pad that may be positioned relative to the one or more recesses to direct polishing slurry out of the one or more recesses and off of the polishing pad during a CMP process.
A further understanding of the nature and advantages of various embodiments may be realized by reference to the remaining portions of the specification and the drawings, wherein like reference numerals are used throughout the several drawings to refer to similar components. In some instances, a sub-label is associated with a reference numeral to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sub-label, it is intended to refer to all such multiple similar components.
Existing CMP processes have difficulty controlling the removal rate of material on a substrate at the edge of the polishing pad. For example, the removal rate of material at the edge is generally higher than the removal rate of material towards the center of the polishing pad. This faster removal rate may lead to uneven surfaces on the substrate. The faster removal rate may also cause damage to underlying layers on the substrate that are below the target layer for removal. One cause of the faster removal rate at the edge of the substrate is the increased pressure and uneven stress that may be applied at the edge of the polishing pad.
These and other technical problems may be solved by alleviating the pressure applied to the substrate at the edge of the polishing pad. For example, one or more recesses may be formed on the surface of the processing pad near the outer edge of the processing pad. The recess(es) may include a number of geometries, including a continuous circular recess. The recess(es) may also include radial channels that direct polishing slurry and other byproducts away from the recess(es) to prevent buildup from occurring within the recess(es). For example, these radial channels may extend from a circular recess out to the edge of the polishing pad to direct material out of the radial channels and off the edge of the pad.
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 an upper 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 upper 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, lightweight, 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 polishing pad 200 may include one or more recesses in around a periphery 219 of the polishing pad 200. In order to alleviate the pressure of the polishing process when the substrate moves into the periphery 219, one or more recesses may be formed in the periphery 219 of the polishing pad 200. When the substrate moves over the one or more recesses, the recesses may relieve at least a portion of the higher pressure typically exerted on the substrate when in the periphery 219 of the polishing pad 200. Since the carrier head will move the substrate between the center of the polishing pad 200 and the edge 204 of the polishing pad 200, the effect of these one or more recesses may be evenly distributed across the surface of the substrate as it rotates and moves relative to the polishing pad 200. For example, the one or more recesses may create temporary low-pressure areas beneath the substrate that average out the high-pressure areas that are still in contact with the substrate around the periphery 219.
The periphery 219 of the polishing pad may be defined by an internal radius 217 that is a predetermined distance 215 from an edge 204 of the polishing pad 200. Any features located between the internal radius 217 and the edge 204 of the polishing pad 200 may be considered to be in the periphery 219 of the polishing pad 200. The distance 215 of the internal radius 217 from the edge 204 may be between about 10 mm and about 50 mm. For example, the periphery 219 may extend inwards from the edge 204 between about 10 mm and about 15 mm, between about 15 mm and about 20 mm, between about 20 mm and about 25 mm, between about 25 mm and about 30 mm, between about 30 mm and about 35 mm, between about 35 mm and about 40 mm, between about 40 mm and about 45 mm, and/or between about 45 mm and about 50 mm.
The distance 215 may also be any combination of any of these sub-ranges (e.g., between about 15 mm and about 25 mm). The distance 215 may also be any specific distance within these ranges (e.g., about 13 mm).
By way of example, the one or more recesses may include a circular recess 202 as illustrated in
The width 210 of the circular recess 202 may be tuned or adjusted based on the size of the semiconductor substrate being polished. For example, if the width 210 of the circular recess 202 is too narrow relative to the diameter of the substrate, the circular recess 202 may be insufficient to reduce the pressure on the substrate at the periphery 219 of the polishing pad 200. Alternatively, if the width 210 of the circular recess 202 is too wide relative to the diameter of the substrate, the circular recess 202 may cause damage to the substrate. For example, the substrate may “overhang” above the circular recess 202 without sufficient support if the width 210 of the circular recess 202 is too wide. This may cause the substrate to break or crack during the polishing process. For example, when using a 300 mm wafer, the width 210 may be optimized to be between about 0.2 inches and about 1.0 inches. Other embodiments may size the width 210 of the circular recess 202 based on the relative width of the substrate. For example, the width 210 may be between about 2% and about 4% of the diameter of the substrate, between about 4% and about 6% of the diameter of the substrate, between about 6% and about 8% of the diameter of the substrate, between about 8% and about 10% of the diameter of the substrate, and/or between about 10% and about 12% of the diameter of the substrate. The width 210 may also be any combination of any of these sub-ranges (e.g., between about 4% and about 8%). The width 210 may also be any specific value within these ranges (e.g., about 7%).
The one or more recesses may be offset from the edge 204 of the polishing pad 200 by an offset distance 221. This allows the polishing pad 200 to provide support at the periphery 219 while still allowing the one or more recesses to alleviate the pressure on the substrate. This also prevents polishing slurry from being directed off of the polishing pad 200 too quickly. In some embodiments, the circular recess 202 may be offset from the edge 204 by an offset distance 221 of between about 0.5 inches and about 4.0 inches. For example, the offset distance 221 may be between about 0.5 inches and about 1.0 inches, between about 1.0 inches and about 1.5 inches, between about 1.5 inches and about 2.0 inches, between about 2.0 inches and about 2.5 inches, between about 2.5 inches and about 3.0 inches, between about 3.0 inches and about 3.5 inches, and/or between about 3.5 inches and about 4.0 inches. The offset distance 221 may also be any combination of any of these sub-ranges (e.g., between about 0.5 inches and about 3.0 inches). The offset distance 221 may also be any specific value within these ranges (e.g., about 1.7 inches).
The circular recess 202 is provided as only one example of the one or more recesses that may be formed in the periphery 219 of the polishing pad 200. The circular recess 202 is not meant to be limiting. Although not shown explicitly, other embodiments may divide the circular recess 202 into a plurality of independent and isolated sectors that are distributed around the periphery 219. While the circular recess 202 forms a continuous recess around the periphery 219, other types of recesses may be subdivided into separate regions. For example, the polishing pad 200 may be divided into quadrants, and the circular recess 202 may be subdivided into four independent sectors to form the one or more recesses. Additionally, the circular inner radius and circular outer radius of the circular recess 202 are also provided only by way of example and are not meant to be limiting. Other embodiments may use a repeating pattern around the circular recess 202 as described in greater detail below in relation to the optional channels. In another example, the one or more recesses may include a plurality of concentric circular recesses within the periphery 219. Although not shown explicitly in
To solve this and other problems, some embodiments may optionally include a plurality of channels 308 that are distributed around the one or more recesses on the polishing pad 300. The channels 308 may be distinguished from the one or more recesses by function, by location, by number, by geometry, and/or by other factors. For example, the function of the channels 308 may be to direct the polishing slurry and other material out of the one or more recesses and off of the polishing pad 300 through the channels 308 during a CMP process. In the example of
The one or more channels 308 may have a width 314 and a length 312. The length 312 may be directed radially outward from a center of the polishing pad 300 as illustrated in
The one or more channels 308 may include a plurality of channels that are regularly or evenly spaced around the edge 304 of the polishing pad 300. For example, a distance 315 between the channels 308 may be uniform. In other embodiments, the distance 315 may be at least 1 inch, at least 2 inches, at least 3 inches, at least 4 inches, at least 5 inches, at least 6 inches, at least 7 inches, at least 8 inches, at least 9 inches, at least 10 inches, at least 12 inches, or at least 15 inches. In some embodiments, the circular recess 302 may be subdivided into individual sectors as described above. Each of the sectors may include one or more of the channels 308. In some embodiments, the channel 308 may be evenly spaced to include at least 2 channels, at least 3 channels, at least 4 channels, at least 5 channels, at least 6 channels, at least 8 channels, at least 10 channels, at least 12 channels, or at least 16 channels or more channels.
The channels 308 may have a length 312 that may correspond to the offset distance 221 described above in
The width 314 of the channel 308 may vary based on the operating parameters of the CMP process. For example, the total cross-sectional areas of the channels 308 may be designed to match a rate at which the polishing slurry is provided to the polishing pad during the CMP process. For example, the flow rate of the polishing slurry in an example CMP chamber may be approximately 200-300 ml/min. Therefore, the exit cross-sectional area of the channels 308 (e.g., the width 314 multiplied by the depth of the channels 308) may be multiplied by the number of channels 308 to ensure that a flow rate at which the polishing slurry is delivered to the polishing pad is less than or equal to the rate at which the polishing slurry can exit the polishing pad through the channels 308.
The width 314 may be increased until the flow rate of the polishing slurry flowing out of the channels 308 is great enough to clear the circular recess 302. In some embodiments, the width 314 may be increased so long as the space between the channels 308 can provide sufficient support for the substrate. As described above, if the circular recess 302 and/or the channels 308 become too large, the substrate may overhang these regions and crack or break. For example, the width 314 of the channels may be sized to be between about 0.25 inches and about 1.5 inches. The width 314 may be between about 0.25 inches and about 0.50 inches, between about 0.50 inches and about 0.75 inches, between about 0.75 inches and about 1.0 inches, between about 1.0 inches and about 1.25 inches, between about 1.25 inches and about 1.50 inches, between about 1.50 inches and about 1.75 inches, and/or between about 1.75 inches and about 2.00 inches. The width 314 may also be any combination of any of these sub-ranges (e.g., between about 0.5 inches and about 1.0 inches). The width 314 may also be any specific value within these ranges (e.g., about 0.80 inches).
The width of the channels 404 may be decreased as the number of channels is increased. As described above, the area of the exit for the polishing slurry provided by the channels 404 should be sufficient to expel the polishing slurry based on the rate at which the polishing slurry is provided to the polishing pad 400. This total exit area may be divided between the number of channels 404 to determine the width of each channel. For example, some embodiments may use two relatively wide channels space 180° apart. The example of
A recess 501 may have any shape, such as the circular recess discussed above. The view illustrated in
The recess 501 may be distinguished from the grooves 504 by geometry, size, and/or other factors. For example, as shown in
Although
The method may include rotating a platen within a CMP chamber (702). The polishing pad may be mounted on the platen and rotated with the platen as described above in
The method may further include directing the polishing slurry off of the polishing pad through the one or more channels during the CMP process (708). As described above, the slurry may collect in one or more recesses (e.g., a circular recess) located around the periphery of the polishing pad. The recess(es) may then direct the polishing slurry into the channels to be directed off of the polishing pad during the CMP process. Therefore, the one or more recesses may have a direction that runs in a circular direction around the polishing pad, while the channels may have a length that is directed outward away from the one or more recesses to the edge of the polishing pad. For example, the one or more channels may have a length that is directed outward to be perpendicular to an edge of the polishing pad and perpendicular to the one or more recesses.
It should be appreciated that the specific steps illustrated in
As used herein, the terms “about” or “approximately” or “substantially” may be interpreted as being within a range that would be expected by one having ordinary skill in the art in light of the specification.
In the foregoing description, for the purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of various embodiments. It will be apparent, however, that some embodiments may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form.
The foregoing description provides exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the foregoing description of various embodiments will provide an enabling disclosure for implementing at least one embodiment. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of some embodiments as set forth in the appended claims.
Specific details are given in the foregoing description to provide a thorough understanding of the embodiments. However, it will be understood that the embodiments may be practiced without these specific details. For example, circuits, systems, networks, processes, and other components may have been shown as components in block diagram form in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may have been shown without unnecessary detail in order to avoid obscuring the embodiments.
Also, it is noted that individual embodiments may have been described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may have described the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in a figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination can correspond to a return of the function to the calling function or the main function.
The term “computer-readable medium” includes, but is not limited to portable or fixed storage devices, optical storage devices, wireless channels and various other mediums capable of storing, containing, or carrying instruction(s) and/or data. A code segment or machine-executable instructions may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc., may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, etc.
Furthermore, embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine readable medium. A processor(s) may perform the necessary tasks.
In the foregoing specification, features are described with reference to specific embodiments thereof, but it should be recognized that not all embodiments are limited thereto. Various features and aspects of some embodiments may be used individually or jointly. Further, embodiments can be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. The specification and drawings are, accordingly, to be regarded as illustrative rather than restrictive.
Additionally, for the purposes of illustration, methods were described in a particular order. It should be appreciated that in alternate embodiments, the methods may be performed in a different order than that described. It should also be appreciated that the methods described above may be performed by hardware components or may be embodied in sequences of machine-executable instructions, which may be used to cause a machine, such as a general-purpose or special-purpose processor or logic circuits programmed with the instructions to perform the methods. These machine-executable instructions may be stored on one or more machine readable mediums, such as CD-ROMs or other type of optical disks, floppy diskettes, ROMs, RAMS, EPROMS, EEPROMs, magnetic or optical cards, flash memory, or other types of machine-readable mediums suitable for storing electronic instructions. Alternatively, the methods may be performed by a combination of hardware and software.
