Patent Publication Number: US-2022234165-A1

Title: Chemical mechanical polishing apparatus using a magnetically coupled pad conditioning disk

Description:
BACKGROUND 
     Chemical mechanical polishing apparatuses are used to provide a planarization process during semiconductor manufacturing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a schematic perspective view of a chemical mechanical polishing apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a vertical cross-sectional view of a pad conditioning unit according to an embodiment of the present disclosure. 
         FIG. 3  is a perspective view of the pad conditioning unit while the pad conditioning disk is detached from the conditioning head according to an embodiment of the present disclosure. 
         FIG. 4  is a process flow diagram illustrating an exemplary manufacturing process for forming a CMP apparatus according to an embodiment of the present disclosure. 
         FIG. 5  is a process flow diagram illustrating an exemplary process for operating a CMP apparatus according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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&#39;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 may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Chemical mechanical polishing (CMP) is used in semiconductor manufacturing to enable an abrasive planarization process that provides a highly planar surface. A CMP apparatus includes a rotating platen with a polishing pad thereupon, a wafer carrier configured to hold and press a wafer against a top surface of the polishing pad, and a slurry dispenser. A CMP apparatus may optionally include a pad conditioning unit containing a pad conditioning disk. Pad conditioning disks are configured to be attached to a conditioning head of the pad conditioning unit by multiple mechanical fasteners, for example screws. However, in conventional pad conditioning disks, such screws tend to loosen during operation of a CMP apparatus. As a consequence, the loosened screws may cause degradation in the quality of the pad surface. Further, repair of a loose screw or dislodged screw requires a significant tool down time and reduces availability of a CMP apparatus. In addition, the mechanical fasteners may be susceptible to rust and corrosion. The rust may cause unwanted scratching of the wafer surfaces that are intended for CMP processing. 
     Various embodiments are disclosed herein which eliminate the need for a mechanical fastener to affix the pad conditioning disk in place. Various embodiments use a magnetically coupled pad conditioning disk to eliminate the use of any screw of any other mechanical fixture elements that may become loose or dislodged during operation. Such elimination of a mechanical fastener may reduce the tool down time and increase the availability of a CMP apparatus for production. The various aspects of the present disclosure are described in detail herebelow. 
       FIG. 1  is a schematic perspective view of a chemical mechanical polishing apparatus according to an embodiment of the present disclosure. Referring to  FIG. 1 , a chemical mechanical polishing (CMP) apparatus according to an embodiment of the present disclosure includes a polishing pad  12  located on a top surface of a platen  10 , a wafer carrier  40  configured to hold a substrate  41  upside down, a slurry dispenser  20  configured to dispense slurry  22  over the top surface of the polishing pad  12 , and a pad conditioning unit ( 30 ,  32 ) that is used to condition the top surface of the polishing pad  12 . 
     The platen  10  may have a generally cylindrical shape, and may have a circular top surface that is large enough to accommodate the polishing pad  12 . The polishing pad  12  may have a circular shape with a diameter that is at least twice the diameter of the substrate  41 . For example, if the diameter of the substrate  41  is 300 mm, the diameter of the polishing pad  12  may be at least 600 mm. If the diameter of the substrate  41  is 450 mm, the diameter of the polishing pad  12  may be at least 900 mm. Generally, the ratio of the diameter of the polishing pad  12  to the diameter of the substrate  41  may be in a range from 2 to 6, such as from 2.5 to 4. The polishing pad  12  includes asperities and pores that define the pad texture. The asperities and pores may be arranged into unit cells that are repeated across the polishing pad and to provide uniform pressure across the substrate  41  during polishing. 
     The platen  10  may be configured to rotate around a vertical axis passing through the geometrical center of the platen  10 . For example, a platen motor assembly  8  may be provided underneath the platen  10  to provide a rotational motion to the platen  10  around the vertical axis passing through the geometrical center of the platen  10 . The platen  10  may be configured to provide a rotational speed in a range from 10 revolutions per minute to 240 revolutions per minute. 
     The wafer carrier  40  may be configured to hold the substrate  41  on a bottom surface thereof, and to press the substrate  41  onto the top surface of the polishing pad  12 . In one embodiment, the wafer carrier  40  may include a vacuum chuck configured to provide suction to the backside of the substrate  41 . In one embodiment, differential suction pressures may be applied across different backside areas of the substrate  41 . For example, the suction pressure applied to the center portion of the substrate  41  may be different from the suction pressure applied to the peripheral portion of the substrate  41  to provide uniform polishing rate across the entire area of the front side of the substrate  41  that contacts the polishing pad  12 . In one embodiment, the wafer carrier  40  may include a retaining ring having an annular shape and configured to hold the substrate  41  therein so that the substrate  41  does not slide out from underneath the wafer carrier  40 . 
     A polishing head  42  may be provided over the wafer carrier  40 . The polishing head  42  may comprise a rotation mechanism that provides rotation to the wafer carrier  40 . In some embodiments, a gimbal mechanism may be provided between the rotation mechanism and the wafer carrier  40  so that the wafer carrier  40  tilts in a manner that provides maximum physical contact between the entire front surface of the substrate  41  and the polishing pad  12 . The combination of the polishing head  42  and the wafer carrier  40  constitutes a wafer polishing unit ( 40 ,  42 ) that positions and rotates the substrate  41  in a manner that induces polishing of material portions on the front side of the substrate  41  through abrasion caused by sliding contact with the top surface of the polishing pad  12 . 
     In one embodiment, the substrate  41  and the wafer carrier  40  may rotate around the vertical axis passing through the geometrical center of the wafer carrier  40 . A polishing pivot pillar structure  44  may be affixed to a frame (not shown) of the CMP apparatus such that the polishing pivot pillar structure  44  may rotate around a vertical axis passing through the geometrical center of the polishing pivot pillar structure  44 . The vertical axis passing through the geometrical center of the polishing pivot pillar structure  44  is stationary relative to the frame of the CMP apparatus. 
     A polishing arm  46  mechanically connects the polishing head  42  to the polishing pivot pillar structure  44 . Thus, upon rotation of the polishing pivot pillar structure  44  around the vertical axis passing through the geometrical center of the polishing pivot pillar structure  44 , the polishing arm  46  may rotate around the vertical axis passing through the geometrical center of the polishing pivot pillar structure  44 . The polishing head  42  may move around the vertical axis passing through the geometrical center of the polishing pivot pillar structure  44  over the polishing pad  12 . Lateral movement of the wafer polishing unit ( 40 ,  42 ) over the polishing pad  12  may enhance uniformity of polish rate across the substrate  41  during the chemical mechanical polishing process. 
     The slurry dispenser  20  is configured to dispense the slurry  22  over the top surface of the polishing pad  12 . The slurry  22  may include any slurry known in the art, such as commercially available slurries for chemical mechanical polishing processes. 
     The pad conditioning unit ( 30 ,  32 ) may be used to precondition the polishing pad  12  prior to, and/or during, the chemical mechanical polishing process that is used to polish material portions from the front surface of the substrate  41  that contacts the top surface of the polishing pad  12 . In one embodiment, the pad conditioning unit ( 30 ,  32 ) may include a pad conditioning disk  30  and a conditioning head  32  that is configured to hold the pad conditioning disk  30 . The pad conditioning disk  30  includes an abrasive bottom surface that can precondition the top surface of the polishing pad  12 . Typically, the abrasive bottom surface of the pad conditioning disk  30  embeds abrasive particles such as diamond particles. The pad conditioning disk  30  may be attached to the conditioning head  32  in a manner that enables rotation of the pad conditioning disk around a vertical axis passing through the geometrical center of the pad conditioning disk  30  without falling out from the conditioning head  32 . 
     A conditioner pivot pillar structure  34  may be affixed to a frame (not shown) of the CMP apparatus such that the conditioner pivot pillar structure  34  may rotate around a vertical axis passing through the geometrical center of the conditioner pivot pillar structure  34 . The vertical axis passing through the geometrical center of the conditioner pivot pillar structure  34  is stationary relative to the frame of the CMP apparatus. 
     A pad conditioner arm  36  mechanically connects the conditioning head  32  to the conditioner pivot pillar structure  34 . Thus, upon rotation of the conditioner pivot pillar structure  34  around the vertical axis passing through the geometrical center of the conditioner pivot pillar structure  34 , the pad conditioner arm  36  may rotate around the vertical axis passing through the geometrical center of the conditioner pivot pillar structure  34 . The conditioning head  32  may move around the vertical axis passing through the geometrical center of the conditioner pivot pillar structure  34  over the polishing pad  12 . Lateral movement of the pad conditioning unit ( 30 ,  32 ) over the polishing pad  12  may enhance uniformity of the surface condition of the polishing pad  12  after the pad preconditioning process. 
     Embodiments of the CMP apparatus may include a process controller  50  electrically connected to electrical components that control movement of various mechanical parts of the CMP apparatus. For example, the process controller  50  may be electrically connected to, and may be configured to control operation of, each of the platen motor assembly  8 , the polishing pivot pillar structure  44 , the wafer polishing unit ( 40 ,  42 ), the conditioner pivot pillar structure  34 , the pad conditioning unit ( 30 ,  32 ), and the slurry dispenser  20 . For example, the process controller  50  may control the rotational speed of the platen  10 , the polishing pivot pillar structure  44 , the wafer carrier  40 , the conditioner pivot pillar structure  34 , and the pad conditioning disk  30 , and may control the location of the slurry dispensation point and the rate of slurry dispensation. 
       FIG. 2  is a vertical cross-sectional view of a pad conditioning unit ( 30 ,  32 ) according to an embodiment of the present disclosure.  FIG. 3  is a perspective view of the pad conditioning unit ( 30 ,  32 ) while the pad conditioning disk  30  is detached from the conditioning head  32  according to an embodiment of the present disclosure. Referring collectively to  FIGS. 1-3  and according to an aspect of the present disclosure, the pad conditioning disk  30  may be attached to the conditioning head  32  with the assistance of a magnetic force. In one embodiment, the conditioning head  32  comprises an electromagnet, and the pad conditioning disk  30  comprises a first ferromagnetic material portion  308  configured to be attracted to the electromagnet when the electromagnet is energized. When it becomes necessary to detach the pad conditioning disk  30  from the conditioning head  32 , the electromagnetic in the conditioning head  32  may be deactivated, and the pad conditioning disk  30  may be removed from the conditioning head  32  without application of excessive force. 
     The pad conditioning disk  30  may include a disk frame  302  containing the first ferromagnetic material portion  308 , an abrasive plate  304  that is permanently attached to the distal surface of the disk frame  302 , an optional annular protrusion structure  305  that may be attached to the proximal surface of the disk frame  302 , and a screw thread that is herein referred to as an inner screw thread  306 . The inner screw thread  306  may be configured to fit a matching screw thread that is provided on a cylindrical inner sidewall of a cylindrical cavity  329  (shown in  FIG. 3 ) located in a bottom portion of the conditioning head  32 . The first ferromagnetic material portion  308  may comprise a permanent magnet having a shape of a cylindrical disk. The diameter of the cylindrical disk may be in a range from 30% to 90% of the maximum lateral dimension of the pad conditioning disk. The height of the cylindrical disk of the ferromagnetic material portion  308  may be in a range from 1 mm to 10 mm, although lesser and greater heights may also be used. The first ferromagnetic material portion  308  may have remanence in a range from 0.3 T to 1.5 T. In an illustrative example, the first ferromagnetic material portion  308  may include a ferrite magnet, a samarium-cobalt magnet, an Al—Ni—Co magnet, a neodymium magnet, or a magnet including an alloy of at least one rare earth element and at least one of Fe, Co, and Ni. 
     The conditioning head  32  comprises a stator unit ( 322 ,  323 ,  328 ,  338 ) that is attached to a pad conditioner arm  36  and configured to be stationary relative to the pad conditioner arm  36 . Further, the conditioning head  32  comprises a rotor unit ( 324 ,  325 ,  326 ) that is configured to rotate relative to the stator unit ( 322 ,  323 ,  328 ,  338 ), and is attached to the pad conditioning disk  30 . The stator unit ( 322 ,  323 ,  328 ,  338 ) comprises a stator housing  322  that contains a motor  323  and an electromagnet ( 328 ,  338 ). The rotor unit ( 324 ,  325 ,  326 ) includes a rotor frame  324  and a helical screw thread that is attached to an inner sidewall of a cylindrical cavity  329  of the rotor frame  324  and is configured to fit the inner screw thread  306 . The helical screw thread is herein referred to as an outer screw thread  326 . In one embodiment, the stator housing  322  may have a configuration of a cylinder within a vertically extending axial cavity therein, and the rotor frame  324  may include a shaft that vertically extends through the axial cavity within the stator housing  322 . The motor  323  may rotate the shaft of the rotor frame  324  so that the pad conditioning disk  30  may rotate during a pad conditioning process. A set of bearings  327  may be provided within an annular groove between the stator housing  322  and the rotor frame  324  to minimize friction during rotation between the stator housing  322  and the rotor frame  324 . 
     According to an aspect of the present disclosure, the rotor frame  324  of the conditioning head  32  may include a cylindrical cavity  329  at a bottom portion thereof. An upper portion of the pad conditioning disk  30  may be configured to fit into the cylindrical cavity  329  of the rotor frame  324  of the conditioning head  32 . In one embodiment, the conditioning head  32  comprises an outer screw thread  326  located at a periphery of the cylindrical cavity  329 , and the pad conditioning disk  30  comprises an inner screw thread  306  configured to fit the outer screw thread  326 . An upper portion of the pad conditioning disk  30  may fit into the cylindrical cavity  329  of the rotor frame  324  of the conditioning head  32  by screwing the inner screw thread  306  into the outer screw thread  326 . 
     In one embodiment, a contact switch  325  may be attached to the rotor unit ( 324 ,  325 ,  326 ). The contact switch  325  can be located at a top portion of the cylindrical cavity  329  and can be embedded within the rotor frame  324 . The contact switch  325  may be configured to detect physical contact with a top surface of the pad conditioning disk  30 . In one embodiment, the pad conditioning disk  30  may comprise an annular protrusion structure  305  that faces the contact switch  325 . In one embodiment, the process controller  50  may be electrically connected to the contact switch  325 , and may be configured to generate an alarm when the contact switch  325  detects absence of physical contact between the contact switch  325  and the top surface of the pad conditioning disk  30 , which may be an annular top surface of the annular protrusion structure  305 . In other words, the CMP apparatus may be configured to generate an alarm when the pad conditioning disk  30  does not make physical contact with the contact switch  325 . Thus, if the pad conditioning disk  30  becomes loose within the cylindrical cavity  329 , an alarm may be generated by the process controller  50 . 
     The stator unit ( 322 ,  328 ,  338 ) may be attached to a pad conditioner arm  36 , and is configured to be stationary relative to the pad conditioner arm  36 . The pad conditioner arm  36  may be attached to the pad conditioning unit ( 30 ,  32 ), and the conditioner pivot pillar structure  34  may be attached to the pad conditioner arm  36 . The pad conditioning unit ( 30 ,  32 ) and the pad conditioner arm  36  may be configured to rotate around a vertical axis passing through the conditioner pivot pillar structure  34 . 
     The stator unit ( 322 ,  328 ,  338 ) includes the electromagnet ( 328 ,  338 ), which includes a ferromagnetic core  338  comprising a second ferromagnetic material, and a conductive coil  328  that may be wound around the ferromagnetic core  338 . The second ferromagnetic material of the ferromagnetic core  338  may include a soft magnetic material. Soft ferromagnetic materials refer to a ferromagnetic material that has high permeability and small coercivity, and thus, has a narrow hysteresis loop. Commercial magnetically soft materials are usually made from alloys of iron and nickel with compositions around Ni 80 Fe 20 . The coercivity of the soft magnetic material of the ferromagnetic core  338  may be, for example, in a range from 0.1 μT to 10 μT, although lesser and greater coercivities may also be used. Generally, the coercivity of the first hard ferromagnetic material of the first ferromagnetic material portion  308  may be greater than the coercivity of the soft ferromagnetic material of the ferromagnetic core  338  by a factor in a range from 1,000 to 1,000,000. 
     The ferromagnetic core  338  may guide the magnetic field generated by the conductive coil  328  while the electromagnet ( 328 ,  338 ) may be energized so that the magnetic attraction between the electromagnet ( 328 ,  338 ) and the first ferromagnetic material portion  308  is strong. The low coercivity of the soft ferromagnetic material of the ferromagnetic core  338  minimizes the magnetic force between the between the electromagnet ( 328 ,  338 ) and the first ferromagnetic material portion  308  while the electromagnet ( 328 ,  338 ) is not energized, and facilitates removal of the pad conditioning disk  30  for replacement or repair. 
     In one embodiment, a direct current power supply unit configured to provide direct current may be provided within the CMP apparatus. The direct current power supply unit may be electrically connected to the conductive coil  338  by electrical wires connected to ends of the conductive coil  338  and extending through the pad conditioner arm  36 . In one embodiment, the direct current power supply unit may be located within the conditioner pivot pillar structure  34 , or may be located outside the conditioner pivot pillar structure  34  as an external device. Generally, the direct current power supply unit is configured to provide the direct current to the conductive coil  328  to energize the electromagnet ( 328 ,  338 ). The switching of the electromagnet ( 328 ,  338 ) may be controlled by the process controller  50 . 
     Generally, the chemical mechanical polishing (CMP) apparatus according to an embodiment of the present disclosure includes a polishing pad  12  located on a top surface of a platen  10  configured to rotate around a vertical axis passing through the platen  10 ; a wafer carrier  40  configured to hold a substrate  41  on a bottom surface thereof and to press the substrate  41  on a top surface of the polishing pad  12 ; a slurry dispenser  20  configured to dispense slurry  22  over the top surface of the polishing pad  12 ; and a pad conditioning unit ( 30 ,  32 ) comprising a pad conditioning disk  30  and a conditioning head  32  configured to hold the pad conditioning disk  30 , wherein the conditioning head  32  comprises an electromagnet ( 328 ,  338 ) and the pad conditioning disk  30  comprises a first ferromagnetic material portion  308  configured to be attracted to the electromagnet ( 328 ,  338 ) when the electromagnet ( 328 ,  338 ) is energized. 
     In one embodiment, the CMP apparatus may include the electromagnet ( 328 ,  338 ) which includes: a ferromagnetic core  338  comprising a second ferromagnetic material; and a conductive coil  328  that is wound around the ferromagnetic core  338 . In another embodiment, the CMP apparatus may include pad conditioner arm  36  attached to the pad conditioning unit ( 30 ,  32 ); and a conditioner pivot pillar structure  34  attached to the pad conditioner arm  36 , wherein the pad conditioning unit ( 30 ,  32 ) and the pad conditioner arm  36  are configured to rotate around a vertical axis passing through the conditioner pivot pillar structure  34 . In another embodiment, the CMP apparatus may include a direct current power supply unit configured to provide a direct current to the conductive coil  328  to energize the electromagnet ( 328 ,  338 ). In another embodiment, the first ferromagnetic material portion  308  includes a permanent magnet having a shape of a cylindrical disk. In another embodiment, the conditioning head  32  includes a cylindrical cavity  329 ; and an upper portion of the pad conditioning disk  30  is configured to fit into the cylindrical cavity  329 . In another embodiment, the CMP apparatus may include a contact switch  325  located at a top portion of the cylindrical cavity  329  and configured to detect physical contact with a top surface of the pad conditioning disk  30 . In another embodiment, the CMP apparatus may include a process controller  50  electrically connected to the contact switch  325  and configured to generate an alarm when the contact switch  325  detects absence of physical contact between the contact switch  325  and the top surface of the pad conditioning disk  30 . In another embodiment, the conditioning head  32  includes: an outer screw thread  326  located at a periphery of the cylindrical cavity  329 ; and the pad conditioning disk  30  comprises an inner screw thread  306  configured to fit the outer screw thread  326 . In another embodiment, the conditioning head  32  may include: a stator unit ( 322 ,  323 ,  328 ,  338 ) that is attached to a pad conditioner arm  36  and configured to be stationary relative to the pad conditioner arm  36  and including the electromagnet ( 328 ,  338 ); and a rotor unit ( 324 ,  325 ,  326 ) that is configured to rotate relative to the stator unit ( 322 ,  323 ,  328 ,  338 ) and attached to the pad conditioning disk  30 . 
       FIG. 4  is a process flow diagram illustrating an exemplary method for manufacturing a CMP apparatus illustrated in  FIGS. 1-3  according to an embodiment method of the present disclosure. Referring to step  410 , a polishing pad  12  may be disposed on a top surface of a platen  10  that is configured to rotate around a vertical axis passing through the platen  10 . Referring to step  420 , a wafer carrier  40  may be disposed over the top surface of the platen  10 . The wafer carrier  40  is configured to hold a substrate  41  on a bottom surface thereof and to press the substrate  41  onto the top surface of the polishing pad  12 . Referring to step  430 , a slurry dispenser  20  configured to dispense slurry  22  may be disposed over the top surface of the polishing pad  12 . Referring to step  440 , a pad conditioning disk  30  is attached to a conditioning head  32 . The pad conditioning disk  30  comprises a first ferromagnetic material portion  308  and the conditioning head  32  comprises an electromagnet ( 328 ,  338 ) configured to generate a magnetic field that attracts the first ferromagnetic material portion  308 , whereby a pad conditioning unit ( 30 ,  32 ) including the conditioning head  32  and the pad conditioning disk  30  is formed. Referring to step  450 , the pad conditioning unit ( 30 ,  32 ) may be disposed over the top surface of the platen  10 . 
     In one embodiment, a pad conditioner arm  36  may be attached to the pad conditioning unit ( 30 ,  32 ), and a conditioner pivot pillar structure  34  may be attached to the pad conditioner arm  36 . The pad conditioning unit ( 30 ,  32 ) and the pad conditioner arm  36  may be configured to rotate around a vertical axis passing through the conditioner pivot pillar structure  34 . 
     In one embodiment, the conditioning head  32  comprises a cylindrical cavity  329 , and the conditioning head  32  comprises a contact switch  325  located at a top portion of the cylindrical cavity  329  and configured to detect physical contact with the pad conditioning disk  30 . In this embodiment, an upper portion of the pad conditioning disk  30  may be fitted into the cylindrical cavity  329 . The pad conditioning disk  30  may be moved upward until the contact switch  325  detects physical contact with the pad conditioning disk  30 . 
     In one embodiment, the conditioning head  32  comprises an outer screw thread  326  located at a periphery of the cylindrical cavity  329 , and the pad conditioning disk  30  comprises an inner screw thread  306  configured to fit the outer screw thread  326 . In this embodiment, the pad conditioning disk  30  may be turned until the pad conditioning disk  30  contacts the contact switch  325 . The electromagnet ( 328 ,  338 ) may be turned off during maintenance, such as during turning the pad conditioning disk  30  until the pad conditioning disk  30  contacts the contact switch  325 . 
     In one embodiment, the conditioning head  32  comprises a stator unit ( 322 ,  323 ,  328 ,  338 ) that is attached to a pad conditioner arm  36  and is configured to be stationary relative to the pad conditioner arm  36  and including the electromagnet ( 328 ,  338 ), and a rotor unit ( 324 ,  325 ,  326 ) that is configured to rotate relative to the stator unit ( 322 ,  323 ,  328 ,  338 ). The pad conditioning disk  30  is attached to the rotor unit ( 324 ,  325 ,  326 ). 
       FIG. 5  is a process flow diagram illustrating an exemplary process for operating a CMP apparatus according to an embodiment of the present disclosure. Referring to step  510 , a CMP apparatus of the present disclosure may be provided. The CMP apparatus may comprise: a polishing pad  12  located on a top surface of a platen  10  configured to rotate around a vertical axis passing through the platen  10 , a wafer carrier  40  facing a top surface of the polishing pad  12 , a slurry dispenser  20  configured to dispense slurry  22  over the top surface of the polishing pad  12 , and a conditioning head  32  comprising an electromagnet ( 328 ,  338 ). Referring to step  520 , a pad conditioning disk  30  may be attached to the conditioning head  32 . The pad conditioning disk  30  comprises a first ferromagnetic material portion  308  configured to be attracted to the electromagnet ( 328 ,  338 ) when the electromagnet ( 328 ,  338 ) is energized. The wafer carrier  40  may be configured to hold the substrate  41  on a bottom surface thereof and to press the substrate  41  on the top surface of the polishing pad  12 , 
     In one embodiment, a substrate  41  may be attached upside down on a bottom surface of the wafer carrier  40  such that a front side of the substrate  41  faces the top surface of the polishing pad  12 . The front side of the substrate  41  may be polished by rotating the wafer carrier  40  and the substrate  41  while the platen  10  rotates and while the slurry  22  is present on the top surface of the polishing pad  12 . 
     In one embodiment, the conditioning head  32  comprises a cylindrical cavity  329 . An upper portion of the pad conditioning disk  30  may be fitted into the cylindrical cavity  329 . In one embodiment, the conditioning head  32  comprises a contact switch  325  located at a top portion of the cylindrical cavity  329 . The pad conditioning disk  30  may be moved up the cylindrical cavity  329  until the contact switch  325  detects physical contact with a top surface of the pad conditioning disk  30 . 
     In one embodiment, the electromagnet ( 328 ,  338 ) may be energized by passing electrical current through a conductive coil  328  of the electromagnet ( 328 ,  338 ). The polishing pad  12  may be conditioned by inducing contact between the pad conditioning disk  30  and the polishing pad  12  while the polishing pad  12  rotates around the vertical axis passing through the platen  10  and while the electromagnet ( 328 ,  338 ) is energized. 
     The embodiments of the present disclosure may be used to provide a CMP apparatus in which a pad conditioning disk  30  is attached to a conditioning head  32  by magnetic force that may be turned on during operation and may be turned off during maintenance. The magnetic coupling between the pad conditioning disk  30  and the conditioning head  32  prevents loosening or dislodging of the pad conditioning disk  30  from the cylindrical cavity  329  of the conditioning head  32 , and may increase the tool availability of the CMP apparatus, and may reduce the tool maintenance time of the CMP apparatus of the present disclosure. 
     The foregoing outlines features of several embodiments 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 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.