Size of critical features in an integrated circuit (IC) has continually decreased, and the need to perform high resolution lithography processes grows. As a consequence, the depth of focus of the radiation used for lithography has also decreased. There is a need to control the precision of planarization of wafers at atomic scale. For example, typical depth-of-field requirements for 28 nm, 22 nm, 16 nm and 10 nm technology are approaching angstrom levels. These are, of course, merely examples and are not intended to be limiting.
Chemical mechanical polishing (CMP) is most commonly used during wafer fabrication to provide an atomically flat surface at the beginning of the lithography process. In addition, as lithography has evolved and complexity of lithography increased, other areas of use for CMP have developed. For example, lately, CMP is used to planarize shallow trenches by polishing metal layers such as aluminum, copper and tungsten, etc.
A typical CMP tool includes a rotating flat plate covered by a pad facing up. The wafer to be polished is placed on a carrier with the surface to be polished facing down. A chemical slurry is disposed on the pad and the wafer (i.e., the surface to be polished) is contacted with the pad. The flat plate and the carrier are rotated, typically in opposite directions, while the carrier is additionally oscillated. The relative motion between the pad and the wafer surface results in polishing of the wafer surface. The pad is typically made of a porous polymeric material with a pore size in a range from about 30-50 μm. During the CMP process, the pads are consumed and need to be conditioned periodically.
The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus/device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. In addition, the term “made of” may mean either “comprising” or “consisting of.”
Apparatuses for polishing thin, flat semiconductor wafers are well known in the art. Such an apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semiconductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or a wafer load station.
Chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. The CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is “planarized” or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
The present disclosure generally relates to methods and apparatuses for monitoring and controlling the chemical mechanical polishing (CMP) process used in semiconductor manufacturing. Wafers are typically planarized using the CMP process which uses a polishing pad and a chemical slurry. The slurry is typically a colloid of a material that acts as a chemical etchant for etching the material at the top surface of the wafer. The polishing pad is rotated relative to the wafer while slurry is disposed so as to remove material and smooth any irregular topography. As the wafer is planarized, the polishing pad gets used, and needs to be conditioned periodically. The embodiments disclosed herein provide a device for conditioning the polishing pads.
In an embodiment, the polishing head assembly 120 includes a head 122 and a carrier 124. The head 122 holds the carrier 124 which holds the wafer 90 to be polished. In some embodiments, the polishing head assembly 120 includes a displacement mechanism (not shown) to oscillate the head 122 sideways 126. In some embodiments, the head 122 may include a motor for rotating the wafer 90 relative to the platen 110. In some embodiments, the wafer 90 and the platen 110 are rotated in an asynchronous non-concentric pattern to provide a non-uniform relative motion between the platen 110 and the wafer 90. The non-uniformity of the relative motion facilitates uniform removal of material from the wafer surface by avoiding a repeated removal from the same spot. The polishing head assembly 120 applies a controlled downward pressure to the wafer 90 to hold the wafer 90 against the platen 110.
The slurry supply system 130 introduces a chemical slurry 134 (interchangeably referred to herein as “the slurry”) of a suitable material to be used as an abrasive medium between the pad 112 and the wafer 90. In an embodiment, the slurry 134 is a colloid of abrasive particles dispersed in water with other chemicals such as rust inhibitors and bases to provide an alkaline pH. In some embodiments, the abrasive particles are of materials such as, for example, silica, ceria, and alumina. In an embodiment, the abrasive particles have a generally uniform shape and a narrow size distribution, with average particle size ranging from about 10 nm to about 100 nm or more depending on the application for which it is being used. In an embodiment, the slurry supply system 130 includes a storage system (not explicitly shown) and a conduit 132 for delivering the slurry 134 to the polishing pad 112 atop the platen 110. The rate of flow of the slurry 134 may be controlled based on the application.
In an embodiment, the pad conditioner 140 “conditions” the polishing pad 112 to provide uniform thickness and roughness across the entire area of the platen 110 by polishing the pad 112. Maintaining the thickness and roughness of the pad 112 prevents unwanted pressure points or warpage on the wafer 90 during the polishing process, and helps to maintain uniform thickness of the wafer 90.
A conditioning head 142 is mounted on the conditioning arm 141 which is extended over the top of the polishing pad 112 for making sweeping motion across the entire surface of the polishing pad 112. The polishing pad 112 is a consumable item used in a semiconductor wafer fabrication process. Under normal wafer fabrication conditions, the polishing pad is replaced after predetermined hours of usage. The polishing pad 112 may be hard, incompressible pad or soft pad. For oxide polishing, hard and stiffer pad is generally used to achieve planarity. Softer pad is generally used in other polishing processes to achieve improved uniformity and smooth surface. The hard pad and the soft pad may also be combined in an arrangement of stacked pads for customized applications.
A problem frequently encountered in the use of polishing pads in oxide planarization is the rapid deterioration in oxide polishing rates with successive wafers. The cause for the deterioration is known as “pad glazing” wherein the surface of a polishing pad becomes smooth such that the pad no longer holds slurry in-between the fibers. This is a physical phenomenon on the pad surface not caused by any chemical reactions between the pad and the slurry. To remedy the pad glazing effect, numerous techniques of pad conditioning or scrubbing have been proposed to regenerate and restore the pad surface and thereby, restoring the polishing rates of the pad. The pad conditioning techniques include the use of silicon carbide particles, diamond emery paper, blade or knife for scrapping the polishing pad surface. The goal of the conditioning process is to remove polishing debris from the pad surface, re-open the pores, and thus forms micro-scratches in the surface of the pad for improved life time. The pad conditioning process can be carried out either during a polishing process, i.e. known as concurrent conditioning, or after a polishing process.
Embodiments disclosed herein provide the conditioning device 200 used for conditioning the polishing pad used in a CMP process. The conditioning device disclosed herein reduces wastage and expense, and requires lesser storage space. A comparative conditioning disk for use in pad conditioning is shown in
The conditioning devices are not necessarily uniformly damaged, but rather only portions of the conditioning device are damaged or reduced in thickness. In other words, it may not be necessary to replace the entire conditioning device prior to a subsequent conditioning process. Therefore, any unnecessary waste and/or additional expense can be reduced by replacing only a portion of the conditioning device that need to be replaced. However, the conditioning device shown in
The conditioning portion 230 further includes a conditioning film 221 including such as, for example, diamond, on a conditioning surface 211 of the base 210. By way of example and without limitation, the conditioning film 221 can be formed by chemical vapor deposition (CVD) at a thickness of about 0.1 mm to about 30 mm (e.g., 30 mm). In some embodiments, the conditioning film 221 defines the “working area” of the conditioning disk 220. That is, the area of the conditioning disk 220 that contacts the pad and “activates” (conditions) the top surface of the pad. The conditioning film 221 can have a nanocrystalline or microcrystalline microstructure, according to some embodiments. By way of example and without limitation, the size of the diamond microcrystals or nanocrystals in conditioning film 221 can range from about 1 μm to about 1000 μm.
It will be understood that not all advantages have been necessarily discussed herein, no particular advantage is required for all embodiments or examples, and other embodiments or examples may offer different advantages.
According to one aspect of the present disclosure, a conditioning device for conditioning a polishing pad used in chemical mechanical polishing includes a base having an opening and a conditioning disk removably attached to the base. The conditioning disk includes a conditioning portion and a fitting portion. The conditioning portion is disposed on a conditioning surface of the base. The fitting portion is fitted into or through the opening of the base. The fitting portion is to prevent dislodging of the conditioning disk from the base during a conditioning process of the polishing pad for the chemical mechanical polishing. In some embodiments, the base further includes a plurality of openings to receive a portion of the fitting portion. In some embodiments, the base further includes a shaped opening with a profile selected from at least one of “I”-shaped cross-sectional profile, “T”-shaped cross-sectional profile, or “+” shaped cross-sectional profile. In some embodiments, the fitting portion of the conditioning disk further includes a fastener. In such embodiments, the fastener comprises at least one selected from a screw, a rivet, and a barb. In some embodiments, the fitting portion is fitted to the base by a snap-fitting mechanism. In such embodiments, the snap-fitting mechanism is made of an elastic material. In some embodiments, the fitting portion is fitted to the base by a magnet snap lock. In such embodiments, the magnet snap lock includes a protruding portion and a recessed portion. In some embodiments, the magnet snap lock includes magnetic portion and a corresponding ferromagnetic portion. In some embodiments, the fitting portion of the conditioning disk is configured to receive a mating fastener. In such embodiments, the mating fastener comprises at least one selected from a screw, a rivet, and a barb. In some embodiments, the conditioning disk further includes a replacement conditioning disk.
It should be understood that while term “conditioning disk” is used herein, the shape of the “disk” is not particularly limited and can be, for example, circular, quadrangular, triangular, hexagonal, or any other convex shape.
According to another aspect of the present disclosure, a method of conditioning a polishing pad for chemical mechanical polishing includes identifying a portion of the conditioning device that needs replacement. The conditioning device comprises a base having an opening, and a conditioning disk removably attached to the base. The conditioning disk comprises a conditioning portion disposed on a first surface of the base and a fitting portion removably fitted into or through the opening of the base. The fitting portion is fitted through or into the opening to base to prevent dislodging of the conditioning disk from the base during a process of conditioning a polishing pad for the chemical mechanical polishing process. After identifying the portion of the conditioning device that needs replacement, the method removes one or more conditioning disks from the base from the identified portion. Subsequently, the method provides replacement conditioning disks corresponding to the one or more removed conditioning disks in the base. In some embodiments, the method provides a reusable base assembly including the base and a reusable fastener. In some embodiments, the method provides a reusable base assembly including the base and a reusable fastener.
According to other aspects of the present disclosure, a conditioning assembly for conditioning a polishing pad used in chemical mechanical polishing includes a base, a conditioning disk, and a replacement conditioning disk. The base has an opening and the conditioning disk removably attached to the base. The conditioning disk includes a conditioning portion and a fitting portion. The conditioning portion is disposed on a conditioning surface of the base. The fitting portion is fitted into or through the opening of the base. The fitting portion is to prevent dislodging of the conditioning disk from the base during a conditioning process of the polishing pad for the chemical mechanical polishing. In some embodiments, the conditioning assembly further comprises a reusable base assembly including the base and a reusable fastener. In some embodiments, the replacement conditioning disk is stackable. In some embodiments, the base further includes a shaped opening with a profile selected from at least one of “I”-shaped cross-sectional profile, “T”-shaped cross-sectional profile, or “+” shaped cross-sectional profile.
The foregoing outlines features of several embodiments or examples so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments or examples introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
The present application claims priority to and incorporates by reference U.S. Provisional Application 62/753,916 filed on Oct. 31, 2018 in its entirety.
Number | Date | Country | |
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62753916 | Oct 2018 | US |