The present disclosure relates generally to conditioning of chemical-mechanical planarization (CMP) polishing pads and, more particularly, to CMP pad conditioners having brush bristles and abrasive regions.
Manufacture of high-performance solid state devices requires an extremely precise and clean completion of a series of unit operations. One series of unit operations refines surfaces created and manipulated in the manufacture of solid state devices. Surfaces created in the manufacture of solid state devices must meet rigid quality control criteria that include a minimizing of irregularities from one point on the surface to another. Irregularities are characterized by deviations in topography over the surfaces or by transient chemical reactions, such as an undesirable oxidation reaction on a surface. Polishing the surfaces having the irregularities is one operation used to remove the irregularities.
One polishing operation is a CMP, also called chemical-mechanical polishing. This polishing (or planarizing) operation produces a desired surface topography by simultaneous performance of chemical etching with an etchant and mechanical buffing with an abrasive. In other words, it is a hybrid of chemical etching and free abrasive polishing.
The CMP operation is used to treat a surface of a silicon wafer. Specifically, wafers are mounted on rotating holders and lowered onto a pad surface that is rotated in an opposite direction to the rotating holders. A slurry of a silica abrasive suspended in a chemical etchant such as potassium hydroxide or ammonium hydroxide is applied to the pad. Polishing action of the pad mechanically removes the oxide or metal layers continuously, until the set thickness of the layer, as determined by process parameters, is reached. The goal of the process is to achieve local and global wafer planarization without creating any surface defects.
The CMP operation is also usable in the manufacture of an integrated circuit or a circuit section such as a metallized layer that is supported by a silicon wafer. Complex integrated circuits include multi-level metallized layers or patterns. These metallized layers are part of a dense circuit design, with a variable topography and a material mix. This type of dense design is enhanced by planarization of the metallic components, which allows precise imaging on the layers by photolithography, and which reduces thinning.
Initially, the following terminology is used in this disclosure to describe types of conditioning of a CMP pad: preparation and restoration. Pad preparation, which is also referred to as pad pre-conditioning or simply pre-conditioning, means using a conditioner on a CMP pad preparatory to (i.e., before) a CMP polishing process so as to normalize a new CMP pad's morphology and surface and thereby establish a baseline condition suitable for a workpiece. Pad restoration means to remove debris formed during the polish and thereby rejuvenate the pad surface. Restoration may be performed between cycles (or sequential stages) of a wafer CMP polishing process, or it may be performed simultaneously with the wafer CMP polishing. When performed with the wafer CMP polish, the restoration is referred to as in situ pad conditioning or simply in situ conditioning.
CMP pad conditioners are referred to as conditioner tools or simply conditioners. Such conditioners are usually shaped as disks including brush bristles, one or more abrasive ceramic regions or regions of another rigid abrasive material, or some combination of bristles and abrasives. Generally, the abrasive-type conditioner tools are referred to as conditioner disks or simply disks, whereas brush-type conditioner tools are referred to as conditioner brushes (not to be confused with post-CMP brushes to clean wafers after the CMP process).
A typical conditioner brush design contains a polymer or plastic composite base with elastic or flexible (usually a kind of polymeric material, i.e., nylon) bristles that perform conditioning across uneven pad topography. A typical conditioner disk design contains a ceramic base with the pedestals mounted on the base. Outer surfaces of the pedestals are covered with abrasive diamond films, available in various degrees of roughness, deposited in various ways. Conditioning begins when a diamond film is in contact with a pad surface, as shown in
Carrier 23 holds the backside of substrate 25 in contact with the bottom of carrier 23 by a vacuum or simply by wet surface tension. An insert pad 27 cushions substrate 25 from carrier 23. A retaining ring 26 is employed to prevent substrate 25 from slipping laterally from beneath carrier 23 during processing.
Pad 21 may comprise a relatively hard polyurethane, or similar material, capable of transporting abrasive particulate matter such as silica particles. The pressure of F1 is used to facilitate the abrasive polishing of a surface of the thin film. In this manner, the thin film to be polished is placed in direct contact with the upper surface of pad 21. Shaft 22 may also rotate to impart rotational movement to substrate 25 as a dispenser 28 applies a slurry to pad 21. The slurry, as well as rotational movement, enhances the polishing process.
Additionally, a pad conditioning assembly 30 is provided for conditioning pad 21. Pad conditioning assembly 30 comprises a conditioner arm 32 in which one end of arm 32 is coupled by a joint 34 to an end effector 36. End effector 36 helps to ensure that a bottom surface 37 of a conditioner brush-and-abrasive hybrid 50 is uniformly in contact with pad 21 when undulations in pad 21 are present. The weight of pad conditioning assembly 30, as well pressure applied by mechanical means such as motors or other actuators, provides a downward force F2 of a predetermined process-specific PSI discussed subsequently in this disclosure.
Conditioners are available in different levels of aggressiveness in which the desired level of aggressiveness depends on the type of design (e.g., brushes are typically less aggressive than ceramics) intended for a specific CMP process. For example, conditioner disks of various degrees of aggressiveness are typically used for conditioning solid polymeric polishing pads, such as a IC1000υ pad available from The Dow Chemical Company of Midland, Mich., whereas conditioner brushes are typically used for conditioning highly porous poromeric pads, such as a POLITEX™ pad, also available from Dow.
Some CMP processes perform pre-conditioning using the same conditioner tool that is also used for in situ conditioning. But under such processes, pre-conditioning entails significant tool time because a less abrasive conditioner (e.g., one that is suitable for restoration) is also being used to achieve a suitable pre-conditioned state after a prolonged pre-conditioning treatment. On the other hand, using a more aggressive conditioner for pre-conditioning reduces overall conditioning time, but it may be too aggressive for later restoration. Accordingly, some CMP processes include a change of conditioner from more to less aggressive abrasiveness between, for example, the steps of pad preparation and restoration.
Changing conditioner tools entails stopping a polishing tool, removing a previously installed tool, replacing it with a new tool, and continuing the CMP process with the new tool. Thus, manual tool changes by the technician include retooling and technician delays. Tool-time loss can be as high as 30 to 60 minutes. And that time lost may actually offset any time saved by using different tools for the different steps of a CMP process. In other words, change of aggressiveness from one application to another entails physical replacement of the conditioner of one type with the conditioner of another type on the polishing tool. Physical replacement of the conditioner disks or conditioner brush on the polishing tool entails stopping of the tool and manual operations, such as unscrewing/screwing multiple screws to and from a conditioner holder or end effector.
This disclosure contemplates enhancements of a multi-step conditioning process including an initial step of preparation (i.e., pre-conditioning) and a subsequent step of restoration (i.e., intermittently conditioning and polishing, in situ conditioning, or combinations thereof). One example enhancement is achieved using a CMP pad conditioner brush-and-abrasive hybrid that has a combination of brush bristles and abrasive elements. The abrasive elements are readily deployed for pre-conditioning as the brush bristles are pressed (or otherwise flexed) such that they are not in use on a pad. But the brush bristles are still readily deployed for conditioning during pad restoration when they are not pressed out of use as less downforce is applied to the conditioner. Thus, a universal hybrid conditioner is capable of alteration of its aggressiveness without physically changing a conditioner on a polisher tool.
This disclosure describes a conditioner of a hybrid design that allows changing conditioner aggressiveness during a multi-step CMP-pad conditioning process without replacing the conditioner between steps. In one embodiment, aggressiveness can also be modulated during the process, e.g., during in situ conditioning. This feature of the hybrid conditioner saves significant tool time otherwise wasted during physical replacement of the conditioner of one type with the conditioner of another type and provides additional flexibility of the CMP conditioning process. Physical replacement of the currently used conditioner, e.g., to change conditioner aggressiveness, is not needed because a hybrid conditioner allows changing aggressiveness in situ or with a simple operation by the operator. Thus, the combination of the functions of a conditioner disk and conditioner brush in one conditioner provides significant saving of tool time and increase of tool availability. This capability of the hybrid conditioner also accelerates the CMP process, increases the useful life of CMP conditioner consumables, and provides for fine-tuning for various CMP processes.
To demonstrate advantages of a conditioner hybrid used for pre-conditioning, experiments were performed showing how a pad preparation process could use abrasives to speed up processes formerly using only brushes for pre-conditioning. The concept was verified using a proprietary polishing process, as well as a research-grade CMP tool for polishing 300 mm wafers. Experiments were performed both at an Intel factory using a high volume manufacturing (HVM) polisher and metrology tools, and in a CMP lab using the research-grade 300 mm wafer polisher. Under the factory tests, accelerated break-in (i.e., pre-conditioning) of a poromeric pad was performed using a conditioner disk, which was found to save approximately six hours per pad change, or 36 hours of tool time per week. Removal rate and wafer defects (defects determined during wafer polishing using the pad, pre-conditioned per the described process) were, mostly, within the process control limits. Pad roughness was measured using a white light spectrometer.
In an HVM standard procedure, both pre-conditioning and in situ conditioning of a poromeric Fujibo pad, available from Fujibo Holdings, Inc. of Tokyo, Japan, were performed using a conditioner brush. Pre-conditioning using a conditioner brush may take many minutes or hours. To establish target values for Fujibo pad conditioning, pad roughness was measured after the pad was conditioned for a process-specific duration using the HVM tool. Then, to accelerate the pre-conditioning process, the tests used a Morgan conditioner disk available from Morgan Advanced Materials of Windsor, U.K., and measured Fujibo pad roughness after pre-conditioning for 5, 10, and 15 minutes at downforce of two, four, and six PSI. Additionally, fixed zone and regular HVM sweep conditioning were compared, as were conditioning in deionized water (DIW) and HVM slurry. In all of the above experiments, after the conditioning by the Morgan conditioner disk, Fujibo pad roughness was measured using a non-contact tool white light spectrometer. Table 1 summarizes consumables and criteria used during testing.
GRC HVM tests demonstrated saving time on pre-conditioning process/increase tool availability time by 36 hours per week, while wafer removal rate and wafer defects were, mostly, within control limits of the process. Pre-conditioning using a conditioner disk instead of a POR conditioner brush significantly reduces pre-conditioning time, as compared to the POR process based on using the conditioner brush. Time to achieve target values decreases with increase of conditioning downforce.
1. A chemical-mechanical planarization (CMP) pad conditioner, comprising: a base having a major surface; an abrasive portion depending from the major surface and having an abrasive surface parallel to the major surface; and a brush portion affixed to the major surface so as to substantially encompass the abrasive portion, the brush portion having brush bristles depending away from the major surface to define a brush surface, in which, in a CMP pad pre-conditioning configuration, the brush surface is compressible so as to be at a first height that is substantially similar to that of the abrasive surface, and, in a CMP pad restoration configuration, the brush surface is substantially uncompressed so as to be at a height that extends past that of the abrasive surface.
2. The CMP pad conditioner of example 1, in which the brush bristles comprise angled bristles.
3. The CMP pad conditioner of example 1, in which the brush bristles comprise straight bristles.
4. The CMP pad conditioner of any of examples 1-3, in which the brush bristles comprise nylon bristles.
5. The CMP pad conditioner of example 1, in which the abrasive surface is configured to contact a polishing pad in response to a force applied to flex the brush bristles.
6. The CMP pad conditioner of example 5, in which the force that configures the abrasive surface to contact the polishing pad is between about two pounds-force per square inch (PSI), 13789.5 Pascal (Pa) and about six PSI, 34473.8 Pa.
7. The CMP pad conditioner of example 5 or 6, in which the force is about six PSI, 34473.8 Pa.
8. The CMP pad conditioner of example 1, in which the base comprises a ceramic base.
9. A system for polishing a surface of a workpiece, the system comprising:
a chemical-mechanical planarization (CMP) polishing pad having a pad surface; a pad conditioning assembly; and a CMP pad conditioner brush-and-abrasive hybrid tool comprising: an abrasive portion depending toward the pad surface and having an abrasive surface parallel to the pad surface; and a brush portion in a region of the CMP pad conditioner brush-and-abrasive hybrid tool adjacent the abrasive portion, the brush portion having brush bristles depending toward the pad surface to define a brush surface, in which, in a CMP pad pre-conditioning configuration, the brush surface is under a first force to press the abrasive surface against the pad surface such that the brush bristles flex to move the brush surface to be at a first height that is substantially similar to that of the abrasive surface, and, in a CMP pad restoration configuration, the brush surface is under a second force less than the first force to maintain the abrasive portion in a recessed position relative to the brush portion, and the brush surface is at a second height that extends past that of the abrasive surface.
10. The system of example 9, in which the brush bristles comprise angled bristles.
11. The system of example 9, in which the brush bristles comprise straight bristles.
12. The system of any of examples 9-11, in which the brush bristles comprise nylon bristles configured to flex under downforce applied by the pad conditioning assembly.
13. The system of example 9, in which the abrasive surface is configured to contact the pad surface in response to a force applied to flex the brush bristles.
14. The system of example 13, in which the force that configures the abrasive surface to contact the pad surface is between about two pounds-force per square inch (PSI), 13789.5 Pascal (Pa) and about six PSI, 34473.8 Pa.
15. The system of example 13 or 14, in which the force is about six PSI, 34473.8 Pa.
16. The system of example 9, in which the abrasive portion comprises a plurality of ceramic disks.
17. A method of reducing tool time by preparing and restoring a chemical-mechanical planarization (CMP) pad using a CMP pad conditioner brush-and-abrasive hybrid tool, the method comprising: preparing the CMP pad using a disk portion of the CMP pad conditioner brush-and-abrasive hybrid tool by applying a first downforce to the CMP pad conditioner brush-and-abrasive hybrid tool; and restoring the CMP pad using a brush portion of the CMP pad conditioner brush-and-abrasive hybrid tool by applying a second downforce to the CMP pad conditioner brush-and-abrasive hybrid tool, the second downforce being less than the first downforce such that the disk portion does not contact the CMP pad during the restoring.
18. The method of example 17, further comprising restoring the CMP pad by conditioning in situ during a polishing process.
19. The method of example 17, further comprising restoring the CMP pad by conditioning intermittently between conditioning and polishing steps of a polishing process.
20. The method of any of examples 17-19, further comprising preparing the CMP pad by pre-conditioning for a duration of about 12 to about 35 minutes under about two pounds-force per square inch (PSI) 13789.5, Pascal (Pa) to about six PSI, 34473.8 Pa.
21. The method of example 17, in which the first downforce is about two pounds-force per square inch (PSI), 13789.5 Pascal (Pa) to about six PSI, 34473.8 Pa.
22. The method of example 17, in which the brush portion includes non-straight bristles.
23. The method of example 17, in which the brush portion includes substantially straight bristles.
24. An apparatus for reducing tool time during a multi-step process of conditioning a chemical-mechanical planarization (CMP) pad, the apparatus comprising: means for pre-conditioning the CMP pad using an abrasive portion of a CMP pad conditioner; and means for restoring the CMP pad using a brush portion of the CMP pad conditioner.
25. The apparatus of example 24, further comprising means for restoring the CMP pad by conditioning in situ during a polishing process.
26. The apparatus of example 24, further comprising means for restoring the CMP pad by conditioning intermittently between conditioning and polishing steps of a polishing process.
27. The apparatus of any of examples 24-26, further comprising means for preparing the CMP pad by pre-conditioning for a duration of about 12 to about 35 minutes under about two pounds-force per square inch (PSI) 13789.5, Pascal (Pa) to about six PSI, 34473.8 Pa.
28. The apparatus of example 17, in which the brush portion includes non-straight bristles.
29. The apparatus of example 17, in which the brush portion includes substantially straight bristles.
Skilled persons will understand that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the disclosure. The scope of the present invention should, therefore, be determined according to claims.
Filing Document | Filing Date | Country | Kind |
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PCT/US2016/054427 | 9/29/2016 | WO | 00 |