Enhanced silicon grind using chemical additives in fluid during grinding process

Abstract

A method and apparatus for grinding a surface of a substrate is presented. The method includes positioning a substrate proximate a grinding surface using a carrier head, providing a pressure on the substrate to press an unpolished surface of the substrate to the grinding surface, flowing a grinding fluid onto the unpolished surface, the grinding fluid comprising a pH adjuster, viscosity additives, a surfactant, or combinations thereof, and grinding the unpolished surface using the grinding surface to create a polished surface on the substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation application of U.S. provisional patent application Ser. No. 63 / 666,530, filed Jul. 1, 2024, which is incorporated herein by reference.BACKGROUNDField

[0002] Embodiments of the present disclosure generally relate to systems and methods for semiconductor manufacturing and, more particularly, systems and methods to grind or planarize a semiconductor substrate during fabrication.Description of the Related Art

[0003] During manufacturing of semiconductor integrated circuits (ICs), various material layers and structures are formed over previously-formed layers and structures. However, the prior formations often leave the top surface topography of an in-process substrate highly irregular, with bumps, areas of unequal elevation, troughs, trenches and / or other surface irregularities. Such irregularities cause problems when forming the next layer. Additionally, if the irregularities are not leveled at each major processing step, the surface topography of the substrate can become even more irregular, causing further problems as the layers stack up during further processing. As such, it is necessary to planarize, or level, the IC structures.

[0004] One technique for planarizing the surface of a substrate is grinding. Grinding processes use a hard grinding surface to remove from the substrate surface all materials in substantially an absolute geometrical reference plane. Therefore, because of the front surface topography of the substrate, it is difficult to use a grinding process to planarize a substrate having one or more previously-formed layers without removing an excessive amount of underlying materials on at least some parts of the substrate.

[0005] Another process for planarizing the surface of a substrate is chemical mechanical polishing (CMP). In contrast to grinding processes, CMP involves holding a thin flat semiconductor substrate against a rotating wetted polishing surface, such as a compliant polishing pad, under a controlled downward pressure. During the CMP process, a slurry is provided to remove and flush away unwanted film material. In one exemplary implementation, a CMP process is used to remove an oxide coating to the level of previously-formed IC structures. In such processes, it is important to remove a sufficient amount of material to provide a smooth surface without removing an excessive amount of underlying materials. However, the particle removal rate of CMP processes is low, limiting throughput.

[0006] Accordingly, there is a need for improved grinding methods to remove excess material to produce a planar surface on a substrate without damaging or scratching the surface.SUMMARY

[0007] In one embodiment, a polishing station comprising a platen, a polishing pad having a grinding surface and disposed on the platen, a supply-rinse arm configured to flow a grinding fluid, the grinding fluid comprising a pH adjuster, viscosity additives, a surfactant, or combinations thereof, and a carrier head configured to hold a substrate is disclosed.

[0008] In another embodiment, a grinding system comprising a carrier head configured to hold a substrate and a grinding station is disclosed. The grinding station comprises a grinding pad having a grinding surface and a fluid bearing surface having openings configured to flow a grinding fluid, wherein the grinding fluid comprises a pH adjuster, viscosity additives, a surfactant, or combinations thereof.

[0009] In yet another embodiment, a method of grinding a substrate comprising positioning a substrate proximate a grinding surface using a carrier head, providing a pressure on the substrate to press an unpolished surface of the substrate to the grinding surface, flowing a grinding fluid onto the unpolished surface, the grinding fluid comprising a pH adjuster, viscosity additives, a surfactant, or combinations thereof, and grinding the unpolished surface using the grinding surface to create a polished surface on the substrate is presented.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of the present disclosure and are therefore not to be considered limiting of its scope, and the present disclosure may admit to other equally effective embodiments.

[0011] FIG. 1A is a schematic, cross-sectional view of a system for grinding a surface of a substrate, according to certain embodiments.

[0012] FIG. 1B is a top view of a grinding station of the system of FIG. 1A, according to certain embodiments.

[0013] FIG. 2 is a schematic cross-sectional side view of a polishing station, according to certain embodiments.

[0014] FIG. 3 illustrates a flow chart of a method for grinding a surface of a substrate, according to certain embodiments.

[0015] FIGS. 4A, 4B, 4C, 4D, and 4E illustrate schematic, cross-sectional view of a portion of a substrate undergoing the method of FIG. 3, according to certain embodiments.

[0016] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0017] Embodiments of the present disclosure generally relate to systems and methods for semiconductor manufacturing and, more particularly, systems and methods to grind or planarize a semiconductor substrate during fabrication.

[0018] The grinding process for a silicon substrate involves several stages. It begins with coarse grinding, which employs a mechanical grinding pad with large diamond grains to coarsely grind the substrate and eliminate the majority of the excess substrate thickness. The result is a substrate reduced to a preliminary thickness. Following coarse grinding, the process moves to fine grinding where a finer grit is used to precisely grind the substrate down to the required thickness. This step utilizes grinding pads with smaller diamond grains. Finally, the substrate undergoes a polishing step. This step aims to achieve smooth substrate surfaces by removing the damage induced by the previous grinding steps and enhancing the flatness of the substrate. The objective of the grinding process is to thin the substrate down to the desired thickness, for example, from 725 micrometers to 50 micrometers, while achieving a smooth, planar processing surface.

[0019] Each of these steps, however, must be executed with care to prevent damage to the substrate, such as the formation of a pinwheel patterned damage. Pinwheel damage, characterized by elongated grind lines from the center to the edge of the substrate, results from the movement of the grinding pad across the substrate surface. Pinwheel damage leads to inherent stress in the substrate, creating weak points that can result in cracking and negatively impact the quality of the final product.

[0020] Polishing alone, though gentler on the surface of the substrate, has a lower throughput and higher cost than grinding and may not be a feasible replacement. Polishing, however, can help mitigate the pinwheel damage caused by the grinding process. By removing a small amount of silicon from the substrate surface, the polishing process can reduce the valley micro-damage and micro-sized peaks caused by grinding. However, polishing may not completely eliminate all the damage, especially if the damage is deep. Thus, while polishing can improve the surface quality and reduce the pinwheel pattern damage, it may not completely eliminate all the damage.

[0021] The present disclosure provides a method of planarization for a bare substrate, such as an in-process substrate, to create a planar surface so that the substrate may be used for further processes. In particular, the present disclosure provides a grinding method using a grinding liquid with high pH or low pH in combination with a diamond impregnated polishing pad in a chemical mechanical polishing (CMP) system or diamond based fixed abrasive pads in a grinding system. Additionally, the grinding fluid may include a surfactant, viscosity additives, or both. The addition of a surfactant or high viscosity fluid enhances particle removal rate, enabling a process more like CMP with lower pressures, less damage, better control, and more easily-corrected concentric variation. The use of the grinding fluid may enable a more CMP-like process and results in a final substrate with less variation.

[0022] FIG. 1A is a schematic, cross-sectional view of a grinding system for grinding a surface of a substrate, according to certain embodiments. FIG. 1B is a top view of a grinding station of the grinding system of FIG. 1A, according to certain embodiments.

[0023] As shown in FIGS. 1A and 1B, a grinding system 100 for planarizing a surface of a semiconductor substrate 112 includes a carrier head 114 and a grinding station 140. The carrier head 114 performs several mechanical functions. Generally, the carrier head 114 holds the substrate 112 and can position the substrate proximate to a fluid bearing surface 120. The carrier head 114 evenly distributes a substantially uniform downward pressure across the entire back surface of the substrate 112. A carrier drive shaft 122 connects a carrier head motor 124 to the carrier head 114 allowing the carrier head to be moved by translation and / or rotation. A grinding disk or grinding pad 116 is at least partially disposed in a gap 108 formed at the upper surface of the fluid bearing surface 120.

[0024] The fluid bearing surface 120 can be implemented, for example, as a metal, ceramic or other plate with multiple openings 126 such as openings in its upper surface through which a fluid, such as a grinding fluid, can flow. The openings 126 preferably are spaced apart by about 1 cm or less, and the fluid exiting the openings provides an upward force against the front surface 136 of the substrate 112. Preferably the fluid providing the upward pressure is deionized water, although other liquids or gases can be used. Instead of circular openings as shown, the openings can take the form of grooves or slots. During the grinding process, the upward pressure of the fluid against the substrate 112 is balanced by the downward pressure from the carrier head 114 to maintain the entire front surface 136 of the substrate 112 at a substantially uniform height. In order to maintain the backpressure on the system, the carrier head 114 covers all the openings 126 in the fluid bearing surface 120. Alternatively, computer-controlled valves can be provided so that, during the grinding process, the fluid flows only through the openings 126 that are covered by the carrier head 114 and / or the substrate 112.

[0025] The fluid bearing formed by the grinding fluid exiting from the openings 126 acts like a tight spring having a relatively high stiffness, whereas the membrane of the carrier head 114 acts like a weak spring which is relatively compliant, in other words, which has relatively low stiffness. Therefore, when the carrier head 114 lowers the substrate 112 and brings it to a predetermined height proximate to the surface of the fluid bearing surface 120, the front surface 136 of the substrate is pressed against the fluid bearing and made substantially flat. In other words, any unevenness in the flatness of the substrate 112 appears on the back (top) side of the substrate. The relatively stiff fluid bearing presented to the front surface 136 of the substrate 112, together with the flat and stiff fluid bearing surface 120, allows the entire front surface of the substrate to be maintained at a substantially uniform height with respect to a grinding surface 128 of the grinding pad 116 during the grinding process. The effects of substrate warpage and variations in thickness across the substrate can, therefore, be reduced.

[0026] The materials which form the grinding surface 128 of the grinding pad 116 generally depends on the particular application. However, exemplary materials include diamond, cerium oxide, aluminum oxide, silicon dioxide and silicon carbide in a polymer matrix. Other materials can also be used.

[0027] As shown in FIGS. 1A and 1B, the grinding surface 128 of the grinding pad 116 encircles part of the fluid bearing and is secured to the top of a grinding pad shaft 130. The grinding pad shaft 130 is connected to a motor 132 for rotating the grinding pad 116 and is connected to a lifting mechanism 134 for raising and lowering the grinding pad. The lifting mechanism 134 can be pneumatically actuated to allow the grinding pad 116 to be raised and pressed into contact with the front surface 136 of the substrate 112. Rotating the grinding pad 116 while it is in contact with the substrate 112 causes the front surface 136 of the substrate to be ground. The lifting mechanism 134 allows the grinding pad to be advanced as the face of the grinding pad is worn away.

[0028] In one implementation, for a 200 mm diameter substrate 112, the gap 108 in the fluid bearing surface is on the order of about one centimeter (cm) with the grinding surface 128 having a radial thickness on the order of about 0.5 cm or less. As shown in FIG. 1B, one side 121 of the fluid bearing surface 120 that is adjacent the grinding pad 116 can be convex-shaped to conform to the circular shape of the grinding pad. In general, the particular dimensions can vary depending on the application. As also can be seen in FIG. 1B, the contact area between the substrate 112 and the grinding pad forms an arc across the substrate. As the grinding pad 116 rotates at a relatively high speed, for example at about 10,000 to 30,000 revolutions per minute, the substrate 112 is rotated by the carrier head 114 at a relatively low speed, for example at about sixty revolutions per minute. More generally, however, both the substrate 112 and the grinding pad 116 can be rotated at different speeds from the foregoing speeds. In this manner, the entire front surface 136 of the substrate 112 can be ground with the front surface of the substrate at a substantially uniform height during the grinding process.

[0029] In the illustrated implementation, the fluid bearing surface 120 can either be suspended from above or can be supported by a base from below.

[0030] The operation and control of the grinding system 100 are automated through the use of a controller 138. The controller 138 controls the vertical positioning and rotational speed of the carrier head 114 holding the substrate 112. The controller 138 also controls pressurization of the carrier head 114 to establish the downward pressure on the backside of the substrate 112. Additionally, the controller 138 controls the vertical positioning and rotational speed of the grinding pad 116. The controller 138 also can control the amount of grinding fluid flowing through the openings 126 in the fluid bearing surface 120 to establish a particular upward pressure against the front surface 136 of the substrate 112. To account for non-uniformities in the height of the upper surfaces of the fluid bearing surface 120, the controller 138 can use closed-loop feedback to control the local upward pressure generated by the grinding fluid flowing through the openings 126. In particular, using fluid control valves (not shown), the controller 138 can independently control the amount of grinding fluid flowing through each hole or group of openings 126 in the fluid bearing surface 120. To facilitate such closed-loop feedback, sensors (not shown) can be provided between the openings 126 to sense the proximity of the front surface 136 of the substrate at different points. The controller 138 can then adjust the flow of grinding fluid through the openings 126 to obtain a more uniform distance between the upper surface of the fluid bearing surface 120 and front of the substrate.

[0031] FIG. 2 is a schematic cross-sectional side view of a polishing station 200, according to certain embodiments. Specifically, FIG. 2 provides a schematic cross-sectional side view of a polishing station 200.

[0032] As shown in FIG. 2, the polishing station 200 of a CMP apparatus includes a rotatable, disk-shaped platen 202, which supports a polishing pad 204 disposed on the platen 202, a carrier head 210 to hold a substrate 212 against the polishing pad 204, and a pad conditioner 240. As discussed herein, the CMP apparatus can include multiple polishing stations. In some embodiments, the polishing station 200 may be used to perform a grinding operation.

[0033] In embodiments of the present disclosure, the polishing pad 204 can be a two-layer polishing pad with an outer layer 206 and a softer backing layer 208. In some cases, the polishing pad 204 can be a soft polishing pad or a 3D printed polishing pad. That is, the construction materials of the polishing pad 204 can include soft materials or 3D printing materials, which can include polymeric materials. The polishing pad can have a hardness of 204 to 230 Shore D scale. The polishing pad 204 may include abrasive additives embedded within the soft pad. For example, the polishing pad 204 may include diamond abrasive particles, such as a diamond-impregnated polishing pad. The addition of the abrasive particles allows for improved grinding effectiveness, such as a higher particle removal rate, while maintaining a generally soft surface to prevent surface damage, e.g., scratches, from occurring on the substrate surface.

[0034] The platen 202 is operable to rotate about an axis 214. For example, a motor 216 can turn a drive shaft 218 to rotate the platen 202 and polishing pad 204. The carrier head 210 is suspended from a support structure 220, e.g., a carousel or a track, and is connected by a drive shaft 222 to a carrier head rotation motor 224 so that the carrier head 210 can rotate about an axis 226. Optionally, the carrier head 210 can oscillate laterally, e.g., on sliders on the support structure 220, or by rotational oscillation of the support structure 220 itself. In operation, the platen 202 is rotated about its central axis 214, and the carrier head 210 is rotated about its central axis 226 and translated laterally across the top surface of the polishing pad 204.

[0035] The carrier head 210 can include a flexible membrane 230 having a substrate mounting surface to contact the back side of the substrate 212, and a plurality of pressurizable chambers 232 to apply different pressures to different zones, e.g., different radial zones, on the substrate 212. The carrier head 210 can also include a retaining ring (not shown) to hold the substrate.

[0036] The polishing station 200 can include a supply port or a combined supply-rinse arm 234 to dispense a grinding fluid 236 onto the polishing pad 204.

[0037] The polishing station 200 can also include a cleaning station (not shown), which contains one or more nozzles that are configured to deliver a cleaning and / or rinsing liquid to a conditioning head 242 of the pad conditioner 240. The cleaning station may also include one or more brushes of abrasive disks that are configured to engage with the conditioning surface of the conditioning head 242. The conditioning arm 244 can move the conditioning head 242 out of the cleaning station and place the conditioning head 242 atop the polishing pad 204.

[0038] The conditioning head 242 includes a conditioning disk 246 that can be brought into contact with the polishing pad 204. The conditioning disk 246 is generally positioned at a bottom of the conditioning head 242 and can rotate around a respective axis 248. In some embodiments, as shown in FIG. 2, the axis 248 is disposed in a first direction that extends along the length of the conditioning arm 244. A bottom surface of the conditioning disk 246 includes abrasive regions that contact the surface of the polishing pad 204 during the conditioning process. During conditioning, both the polishing pad 204 and the conditioning disk 246 may rotate, so that these abrasive regions move relative to the surface of the polishing pad 204, thereby abrading and retexturizing the surface of the polishing pad 204.

[0039] The conditioning head 242 includes mechanisms to attach the conditioning disk 246 to the conditioning head 242 (such as mechanical attachment systems, e.g., bolts or screws, or magnetic attachment systems) and mechanisms to rotate the conditioning disk 246 around the axis 248 (such as drive belts through the arm or rotors inside the conditioner head). In embodiments of the present disclosure the conditioning head 242 and the conditioning disk 246 are driven by a single motor to cause each conditioning head 242 rotate at the same revolutions-per-minute (RPM). In one example, the conditioning head 242 is rotated at substantially the same RPM, or similar RPM (+ / −20%), as the RPM of the polishing platen. In alternate embodiments, the conditioning disk 246 may be rotated at different RPMs through use of differing motors, different gearing, or other rotational control.

[0040] The polishing station 200 includes a controller 250. The controller 250 generally includes a central processing unit (CPU) 252, memory 254, and support circuits 256. The CPU 252 may be one of any form of a general purpose processor that can be used in an industrial setting. The memory 254, or non-transitory computer-readable medium, is accessible by the CPU 252 and may be one or more of memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits 256 are coupled to the CPU 252 and may include cache, clock circuits, input / output subsystems, power supplies, and the like. The various methods disclosed herein may generally be implemented under the control of the CPU 252 by the CPU 252 executing computer instruction code stored in the memory 254 (or in memory of a particular processing chamber) as, for example, a software routine. When the computer instruction code is executed by the CPU 252, the CPU 252 controls the processing chambers to perform processes in accordance with the various methods.

[0041] FIG. 3 illustrates a flow chart of a method 300 for grinding a surface of a substrate, according to certain embodiments. FIGS. 4A, 4B, 4C, 4D, and 4E illustrate schematic, cross-sectional views of a portion 400 of a substrate 402 undergoing the method 300 of FIG. 3, according to certain embodiments. The method 300 may be implemented by a controller in a grinding system, such as controller 138 of the grinding system 100 shown in FIGS. 1A and 1B or a controller of a CMP system, such as controller 250 of the polishing station 200 shown in FIG. 2.

[0042] In some embodiments the method 300 can be repeated. For example method 300 can be performed by the grinding system 100 (FIGS. 1A and 1B) and then method 300 can be performed by the polishing station 200 shown in FIG. 2.

[0043] As shown in FIG. 4A, the substrate 402 includes an unpolished surface 404 that may be rough or uneven. The substrate 402 may be a bonded substrate and the unpolished surface 404 may be a non-device side of the substrate 402. In some embodiments, the substrate 402 is a pure Si substrate having devices disposed on the substrate 402 opposite the unpolished surface 404. In some embodiments, the substrate 402 is a bonded substrate, a pure silicon substrate, a substrate with a stop film, or a silicon oxide (SiO) substrate. In operation 302, the substrate 402 is positioned proximate to a grinding surface 406 using a carrier head (such as the carrier head 114 or the carrier head 210). The grinding surface 406 may be a grinding surface of a grinding pad (such as the grinding pad 116) or a polishing surface of a polishing pad (such as the polishing pad 204). In operation 304, a downward force 416 is provided on the substrate 402 using the carrier head, e.g., the carrier head 114 or the carrier head 210, to press the unpolished surface 404 onto the grinding surface 406. The downward force 416 is about 1 psi to about 5 psi.

[0044] In operation 306, a grinding fluid 408 is flowed onto the unpolished surface 404 of the substrate 402. The grinding fluid 408 may be flowed onto the substrate 402 using a supply port or dispensing arm, e.g., supply-rinse arm 234, or other ports, such as the openings 126 of FIG. 1A. The grinding fluid 408 includes a pH adjuster 410, viscosity additives 412, a surfactant 414, or a combination thereof. In some embodiments, the grinding fluid 408 is a water based fluid that is supplied to the grinding surface 406, free of grinding particulate. In some embodiments, the grinding fluid 408 is a self-generating grinding fluid that generates particles during the grinding from one or more of the grinding surface 406 and the unpolished surface 404. The grinding fluid 408 is supplied to the substrate 402 at a rate of about 50 milliliters per minute to about 10,000 milliliters per minute, for example about 0.5 liters per minute to about 1.5 liters per minute. In some embodiments, about 100 milliliters to about 20,000 milliliters of grinding fluid 408 is supplied during a grinding operation. in some embodiments, a higher flow rate of grinding fluid 408 supplied to the substrate 402 increases removal rates and provides increased cooling capabilities.

[0045] The pH adjuster 410 may include materials to adjust the pH level of the grinding fluid 408 to improve the effectiveness of the grinding fluid 408. For example, the pH adjuster 410 may increase the pH of the grinding fluid 408 such that the pH of the grinding fluid 408 is, for example, basic having a pH level of about 7 to about 12. Alternatively, the pH adjuster 410 may decrease the pH of the grinding fluid 408, for example, to a pH of about 3 to about 7. The pH adjuster 410 further adjusts the pH of the grinding fluid 408 to prevent damage to the substrate 402, e.g., from being too acidic or too basic. The pH adjuster may include suitable materials, such as hydroxides, for example, tetramethylammonium hydroxide, potassium hydroxide, ammonium hydroxide, or a combination thereof, and acids, for example, citric acid, phosphoric acid, carbonic acid, or combinations thereof. In one example, the grinding fluid 408 includes the pH adjuster 410 without the viscosity additives 412 or the surfactant 414. Similarly, in another example, the grinding fluid 408 includes the viscosity additives 412 without the pH adjuster or the surfactant 414. In yet another example, the grinding fluid 408 includes the surfactant 414 without the pH adjuster 410 or the viscosity additives 412.

[0046] In some embodiments the pH adjuster 410 hydrolyzes the substrate 402 and is inert to the grinding surface 406. For example, the pH adjuster 410 is inert to the grinding pad 116 or the polishing surface of a polishing pad 204 (FIG. 1 and FIG. 2).

[0047] The viscosity additives 412 may include a suspension lapping gel, such as water-based gels with abrasive grains suspended therein. The viscosity additives 412 may also include organic thickeners, such as cellulosic thickeners, polysaccharide thickeners, and polypropylene thickeners. Examples of these thickeners include hydroxyethyl cellulose, xanthan gum, and polypropylene glycol. In addition to organic thickeners, the viscosity additives 412 may also include inorganic thickeners, such as inorganic salt thickeners and inorganic gel thickeners like fumed silica.

[0048] The concentration of the viscosity additives 412 as a weight percentage may be from about 1 wt % to about 20 wt %, such as about 3 wt % to about 5 wt %. The viscosity additives may be added to the grinding fluid 408 to increase the viscosity of the grinding fluid 408 such that, among other things, less of the grinding fluid 408 is lost during grinding or polishing. For example, the viscosity additives 412 thicken the grinding fluid 408 so that when the grinding fluid 408 is disposed on a rotating object, e.g., the polishing pad 204 or the grinding pad 116, less grinding fluid 408 loss is seen due to centripetal forces acted on the grinding fluid 408 by the rotation.

[0049] The surfactant 414 may be a single surfactant or a combination of surfactants. For example, the surfactant 414 may be one of three types: anionic, nonionic, and cationic. Anionic surfactants carry a negative charge and include substances like sodium laureth sulfate (SLES), sodium lauryl sulfate (SLS), ammonium lauryl sulfate (ALS), ammonium laureth sulfate (ALES), sodium stearate, and potassium cocoate. Nonionic surfactants, which do not carry a charge, include ethoxylates, alkoxylates, and cocamides. Lastly, cationic surfactants carry a positive charge and include substances like quaternary ammonium salts, cetyltrimethylammonium bromide (CTAB), benzalkonium chloride (BAC), and dodecylbenzene sulfonic acid.

[0050] The concentration of the surfactant 414 as a weight percentage may be from about 0.01 wt % to about 5 wt %, such as about 0.05 wt % to about 2 wt %. The factors that determine the concentration of surfactants needed include the Critical Micelle Concentration (CMC), the temperature of the CMP process, and pH of the polishing liquid. The CMC is the surfactant concentration at which micelles, e.g., aggregate surfactant molecules, start to form. Below this concentration, surfactant molecules remain soluble in water, while above it, micelles are present throughout the solution. Prior to reaching the CMC, the surface tension varies significantly with surfactant concentration. Upon reaching the CMC, the surface tension either remains relatively stable or changes at a reduced rate. The CMC value for a specific surfactant in a particular medium is influenced by temperature, pressure, and occasionally, the presence and concentration of other surface-active substances and electrolytes.

[0051] The pH of the grinding fluid 408 can also affect the properties of surfactants. Changes in pH alter the inter-molecular interactions of surfactants in the interfacial layers, thereby affecting interfacial network formation and dilatational visco-elasticity. The most pronounced negative effect on the effectiveness of the surfactant 414 in the grinding fluid 408 occurs at low pH levels, where the polymer charge density is the highest. As such, the pH adjuster 410 may be selected to improve the performance of the surfactant 414. The addition of a surfactant 414 and viscosity additives 412 enhance the removal rate enabling the grinding process, e.g., using a grinding pad, to be more like CMP with lower pressures, less damage, better control, and more easily-corrected concentric variation.

[0052] In operation 308, the unpolished surface 404 is ground using the carrier head and the grinding surface 406 while the grinding fluid 408 is flowing on the substrate 402. For example, the substrate 402 is rotated using the carrier head while the grinding fluid 408 is flowed onto the unpolished surface 404 of the substrate 402. The substrate 402 is rotated at about 30 rpm to about 150 rpm. Additionally, the grinding surface 406 is rotated to grind the unpolished surface 404 of the substrate 402 while the grinding fluid 408 is flowing. The removal rate is about 100 microns per minute to about 700 microns per minute. For example, about 250 microns per minute to about 350 microns per minute from the unpolished surface 404. In some embodiments, the unpolished surface 404 is ground using the carrier head and the grinding surface 406 for about two minutes or less per platen.

[0053] In some embodiments, the grinding surface 406 includes diamonds. The diamonds are about 1 microns to about 35 microns, for example about 18 microns to about 21 microns, for example 5 microns to about 10 microns. The diamonds are impregnated into the grinding surface 406 with a resin. In some embodiments, the diamonds have an orientation within the resin of the grinding surface 406. For example, the grinding surface 406 is formed of diamonds in resin pillar. exposed diamonds remove material during grinding and as resin wears, additional diamonds are exposed.

[0054] In operation 310, a substrate particle suspension is generated. As shown in FIG. 4B, while the grinding surface 406 rotates, substrate particles 418 of the unpolished surface 404 are loosened from the unpolished surface 404. As the grinding fluid 408 flows, the surfactant 414 binds to the substrate particles 418 to form a micelle layer 420 on the outer surfaces of the substrate particles 418 as shown in FIG. 4C. These micelle layers 420 allow for the substrate particles 418 to form a substrate particle suspension 422. The substrate particle suspension 422 includes substrate particles released from the unpolished surface 404.

[0055] The substrate particle suspension 422 is not cleared from the surface of the substrate 402, but rather used to exert a grinding force 424 in operation 312 as the grinding surface 406 continues to rotate against the unpolished surface 404 as shown in FIG. 4D. The grinding force 424 generated by the substrate particle suspension 422 act as abrasive particles to enhance polishing efficiency of the method 300. The addition of the viscosity additives 412 increases the viscosity of the grinding fluid 408, allowing for greater retention of the substrate particles 418 on the unpolished surface 404 of the substrate 402, increasing the density of the substrate particle suspension 422. In some embodiments the viscosity of the grinding fluid 408 with the viscosity additives 412 is about 0.2 centipoise (cP) to about 30 cP. With a higher particle density, the substrate particle suspension 422 may provide additional grinding force 424. As such, the viscosity additives 412 and the surfactant 414 allow for tuning of the resulting abrasiveness of the substrate particle suspension 422 generated. At the end of polishing, the substrate particle suspension 422 is rinsed away from the substrate 402, leaving the substrate 402 with a planar surface 426, as shown in FIG. 4E.

[0056] The grinding of the unpolished surface 404 occurs for a period of time. The period of time the unpolished surface 404 is ground is about 3 minutes or less. For example, the grinding of the unpolished surface 404 during operations 308, 310 and 312 occurs in about 2 minutes or less per platen.

[0057] In some embodiments, the substrate 402 has a thickness of about 750 microns to about 900 microns and the grinding of the unpolished surface 404 reduces the substrate by about 700 to 800 microns. After the grinding of the unpolished surface 404, the planar surface 426 has a surface roughness of about 0.5 microns to about 2 microns.Example 1

[0058] In some embodiments, method 300 is performed as a first grinding operation where a substrate with a first thickness of about 780 microns and is then ground for about 2 minutes to second thickness of about 30 microns. The first grinding operation uses a first pad having a 20 micron diamond abrasives to remove about 720 microns of material at a rate of 6 um / sec.

[0059] Method 300 is then performed again as a second grinding operation using a second pad different than the first pad. The second pad is a 6-9 micron diamond abrasive pad. The substrate is ground further from the second thickness for about 2 minutes to a third thickness of about 5 microns. Once the substrate is ground to the third thickness subsequent polishing operations.

[0060] The first grinding operation and second grinding operation both occur with a downforce of about 4.5 psi applied to the substrate by the carrier head. The first pad and the second pad are rotated during operation at about 135 RPM.

[0061] The present disclosure provides for methods and apparatus for grinding a substrate. The grinding method of the present disclosure is accomplished using a high or low pH grinding fluid to improve removal rate and to enable better control due the hydroxylated passivation. For other polishing steps, a high viscosity additive or surfactant can enhance removal rate. Application of the grinding fluid, e.g., the high or low pH and high viscosity, enables a polishing tool to reach the rates and costs of traditional silicon grind while eliminating the pinwheel variation and damage observed with grinding pads. The grinding fluid may also improve pinwheel damage when using grinding pads.

[0062] When introducing elements of the present disclosure or exemplary aspects or embodiments thereof, the articles “a,”“an,”“the” and “said” are intended to mean that there are one or more of the elements.

[0063] The terms “including,”“including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0064] The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B and object B touches object C, the objects A and C may still be considered coupled to one another-even if objects A and C do not directly physically touch each other. For instance, a first object may be coupled to a second object even though the first object is never directly in physical contact with the second object.

[0065] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A polishing station, comprising:a platen;a grinding pad having a grinding surface and disposed on the platen;a supply-rinse arm configured to flow a grinding fluid, the grinding fluid comprising a pH adjuster, viscosity additives, a surfactant, or combinations thereof; anda carrier head configured to hold a substrate.

2. The polishing station of claim 1, further comprising a controller, wherein the controller is configured to cause the polishing station to:position a substrate proximate the grinding surface using the carrier head;provide a pressure on the substrate to press an unpolished surface of the substrate to the grinding surface;flow a grinding fluid onto the unpolished surface using the supply-rinse arm; andgrinding the unpolished surface using the grinding surface of the grinding pad to create a polished surface on the substrate.

3. The polishing station of claim 1, wherein the grinding fluid has a pH level of about 7 to about 12.

4. The polishing station of claim 1, wherein the grinding fluid is configured to create a substrate particle suspension using a surfactant and substrate particles released from an unpolished surface of the substrate.

5. The polishing station of claim 4, wherein the surfactant forms a micelle layer on outer surfaces of the substrate particles.

6. The polishing station of claim 4, wherein the substrate particle suspension exerts a grinding force on an unpolished surface of the substrate.

7. The polishing station of claim 1, wherein the grinding pad comprises abrasive additives, the abrasive additives including diamond abrasive particles.

8. A grinding system, comprising:a carrier head configured to hold a substrate;a grinding station comprising:a grinding pad having a grinding surface; anda fluid bearing surface having openings configured to flow a grinding fluid, the grinding fluid comprising a pH adjuster, viscosity additives, a surfactant, or combinations thereof.

9. The grinding system of claim 8, further comprising a controller, wherein the controller is configured to cause the grinding system to:position a substrate proximate the grinding surface using the carrier head;provide a pressure on the substrate to press an unpolished surface of the substrate to the grinding surface;flow a grinding fluid onto the unpolished surface using the openings of the fluid bearing surface; andgrind, using the grinding surface, the unpolished surface to create a polished surface on the substrate.

10. The grinding system of claim 8, wherein the grinding fluid has a pH level of about 7 to about 12.

11. The grinding system of claim 8, wherein the grinding fluid is configured to create a substrate particle suspension using a surfactant and substrate particles released from an unpolished surface of the substrate.

12. The grinding system of claim 11, wherein the surfactant forms a micelle layer on outer surfaces of the substrate particles.

13. The grinding system of claim 11, wherein the substrate particle suspension exerts a grinding force on an unpolished surface of the substrate.

14. The grinding system of claim 8, wherein the grinding surface of the grinding pad comprises diamond abrasives.

15. A method of grinding a substrate, comprising:positioning a substrate proximate a grinding surface using a carrier head;providing a pressure on the substrate to press an unpolished surface of the substrate to the grinding surface;flowing a grinding fluid onto the unpolished surface, the grinding fluid comprising a pH adjuster, viscosity additives, a surfactant, or combinations thereof; andgrinding the unpolished surface using the grinding surface to create a polished surface on the substrate.

16. The method of claim 15, wherein the grinding surface comprises diamond abrasives.

17. The method of claim 15, wherein the grinding fluid has a pH level of about 7 to about 12.

18. The method of claim 15, further comprising:after flowing the grinding fluid, generating a substrate particle suspension using a surfactant and substrate particles released from the unpolished surface during grinding.

19. The method of claim 18, wherein the surfactant forms a micelle layer on outer surfaces of the substrate particles.

20. The method of claim 18, wherein the substrate particle suspension exerts a grinding force on the unpolished surface.

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