Patent Publication Number: US-2023133331-A1

Title: Single bodied platen housing a detection module for cmp systems

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     This application is a continuation of U.S. patent application Ser. No. 16/672,099, filed Nov. 1, 2019 which claims the benefit and priority to U.S. Application No. 62/772,600, filed Nov. 28, 2018, the entirety of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Chemical mechanical polishing or chemical mechanical planarization (CMP) is an important step in semiconductor manufacturing. The CMP utilizes the combined effects of chemical and mechanical interactions for polishing and planarizing surfaces. That is, the CMP is used to achieve a substantially planar and smooth surface of a material layer or layers, such as semiconductor, dielectric and metallization layers on a workpiece, such as a semiconductor wafer. When the purpose is to remove surface materials, it is referred to as chemical mechanical polishing. On the other hand, when the purpose is to flatten a surface, it is referred to as chemical mechanical planarization. This manufacturing process is used to fabricate, for example, integrated circuits, microprocessors, memory chips or the like. 
     One step of the CMP process for polishing and planarizing the material layers on a workpiece is dispensing chemical slurry between the workpiece and a pad where the workpiece contacts the pad with an applied downforce. Slurry is typically a colloid having abrasive and corrosive features. After the slurry is applied and the CMP process is complete, the pad and a platen supporting the pad are cleaned of the slurry residue for later use. 
    
    
     
       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    schematically illustrates a perspective view of a portion of a CMP device according to one embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view of a general CMP device of the related art. 
         FIG.  3    is a perspective view of an unused lower platen in the related art. 
         FIG.  4    is a cross-sectional view of a CMP device having a platen according to one embodiment of the present disclosure. 
         FIG.  5    is a cross-sectional view of a CMP device having a platen with sealing means and fasteners according to the present disclosure. 
         FIG.  6    is a cross-sectional view of a CMP device having a platen according to one embodiment of the present disclosure. 
         FIG.  7 A  is a top view of a detector cover of the CMP device according to one embodiment of the present disclosure. 
         FIG.  7 B  is a cross-sectional view of a platen according to another 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 device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     The present disclosure is directed to a single-body or unitary platen for use in chemical mechanical polishing/planarization (CMP) devices and CMP systems. A platen structure according to the related art uses an upper platen which is separate and distinct from a lower platen structure. In such platen structures of the related art, the upper platen is overlaid on the lower platen and an end point detector, for example, is mounted on the lower platen and within a portion of the upper platen. In such platen structures according to the related art, a space or gap exists between the upper platen and the lower platen. However, when a fluid, such as slurries or deionized water (DIW), is applied during the rotation of the platen structure, the fluid permeates into the gap between the upper platen and the lower platen. The slurries, which have corrosive characteristics, may damage components placed on the lower platen as well as components disposed between the lower platen and the upper platen. Further, the slurries can also affect other components of the CMP device they come in contact with, e.g., bearings beneath the lower platen for supporting the rotation of the lower platen during a polishing or planarization process. 
       FIG.  3    is a perspective view of a normal unused lower platen. However, when the lower platen is used numerous times the surface of the lower platen deteriorates as well as the surface of the other components that come in contact with the surface of the lower platen. For example, when fluid leaks into a gap between the upper and lower platen of the two-part platen structure, undesirable damage to the upper and lower platens can occur, as well as damage to components associated with the upper platen and the lower platen, e.g., an end point detector or a bearing. 
     One aspect of the present disclosure provides a unitary platen that has a structure that avoids the problem of damage to the platen caused by fluids leaking into a gap between an upper and a lower platen. The single-body platen in accordance with embodiments of the present disclosure may house an end point detector inside a recess of the platen. Platen assemblies in accordance with the present disclosure do not include a gap between an upper and a lower platen into which fluids, such as slurries and/or DIW, can flow and access interior portions of the platen and components housed within the platen. Platen structures in accordance with embodiments of the present disclosure exhibit substantially reduced or no damage as a result of fluids, such as slurries or DIW, causing deterioration of interior portions of the platen and/or components, such as an end point detector or bearing, contained within or connected to the platen. 
     Another aspect of the present disclosure relates to a platen including a seal ring adjacent to a periphery or contour of a recess within the platen or adjacent a periphery or contour of a component contained within the platen, such as an end point detector. The seal ring provides a barrier to fluids, such as slurries and/or DIW, which gain access to internal locations of the platen. The shape of the seal ring can be any suitable shape that can surround the recess or component and serve as a barrier to fluids entering the recess or coming in contact with the component, such as an end point detector. The seal ring can have any cross-sectional shape. For example the seal ring can have a cross-section that is an O-shape, or a rectangular shape or any other suitable shape that enables the seal ring to provide the desired barrier to fluids. In some cases, the shape and size of the seal ring will depend on the shape and size of the recess and/or component contained in the recess, such as an end point detector and any additional electronic components adjacent to and/or associated with the end point detector. 
     A further aspect of the present disclosure relates to providing a platen having fasteners around a periphery or contour of a recess in the platen which can receive a peripheral component of the platen, such as an end point detector. The fasteners attach a recess cover positioned to cover a recess formed in the platen. In some embodiments, such recess receives an end point detector, and the recess cover is positioned over the end point detector. In some embodiments, the recess cover includes an optically transparent portion. The optically transparent portion serves as a viewing window for an end point detector capable of detecting and determining the polishing or planarization end point of, for example, a workpiece by interrogating the workpiece with a laser or other suitable light source. When the recess cover is secured to the platen with the fasteners, the seal ring is compressed between the recess cover and the platen and creates a barrier to fluid that comes in contact with the seal ring. This barrier prevents the fluid from coming in contact with components of the platen that are on the side of the seal ring opposite from the side of the seal ring the fluid contacts. In certain embodiments, the fasteners are received by the platen at a location that is on the same side of the seal ring that may be contacted by the fluid. 
     By employing a platen according to embodiments of the present disclosure, the significant hours required to clean slurries off the platen can be substantially decreased. Moreover, use of a platen in accordance with embodiments of the present disclosure reduces the frequency with which components contained in the platen, such as an end point detector, must be replaced or serviced, thereby lowering the manufacturing cost. 
     Further aspects of the present disclosure will be now detailed in connection with the Figures. 
       FIG.  1    schematically illustrates a perspective view of a portion of a CMP device or system  100  according to one embodiment of the present disclosure. As shown in  FIG.  1   , the CMP system  100  includes a platen  170 , a polishing pad  120 , a polishing head  130 , a slurry dispenser  140 , and a pad conditioner  155  having a disk  150 . The polishing pad  120  is arranged on the platen  170 . The slurry dispenser  140 , the polishing head  130 , and the pad conditioner  155  are present above the polishing pad  120 . The platen  170  includes a circular upper portion  110  and a circular lower portion  115  which are collectively referred to as a platen  170 . In one embodiment, the platen  170  according to the present disclosure has a single, seamless, and unitary structure. That is, the platen  170  is a single-body or integral structure with recesses formed therein (see  FIG.  4   ). The single-body or integral structure of a platen  170  formed in accordance with the embodiments described herein is distinct from platen assemblies that include an upper portion that is separate and distinct from a lower portion, which requires the upper and lower portions to be secured to each other, e.g., using fasteners or other means for securing the upper portion to the lower portion. The circular upper portion  110  forms an upper portion of the platen  170  and the circular lower portion  115  forms a lower portion of the platen  170  and as explained, the circular upper portion  110  and the circular lower portion  115  are not a separate pieces, but rather refer to sections or portions of the integral, unitary platen of embodiments of the present disclosure. In some embodiments, the circular upper portion  110  and the circular lower portion  115  are made of different materials. In such embodiments, the circular upper portion and the circular lower portion may be formed separately and fused together to form an integral, unitary platen. An integral, unitary plan in accordance with embodiments of the present disclosure are characterized by an absence of a gap or void space when the circular upper portion is fused to the circular lower portion of the platen. Welding or soldering techniques can be used to fuse the circular upper portion to the circular lower portion provided the welding or soldering does not leave any gaps or void space between the circular upper portion and the circular lower portion of the platen. In other embodiments, the circular upper portion  110  and the circular lower portion  115  are made of the same material. In such embodiments, the platen can be formed by casting or forging the material that will form the platen. Further, in some embodiments, the circular upper portion  110  has different size and shape from the circular lower portion  115 . For example, in some embodiments the circular upper portion  110  has a diameter (or a radius) greater than a diameter (or a radius) of the circular lower portion  115 . The specific structure of the platen  170  will be explained in detail below. The unitary platen  170  may be formed by cutting a metal using CNC (Computerized Numerical Control Lathe) method. Further, the unitary platen  170  may be coated using a PFA (Perfluoroalkoxy) coating method to form an acid and alkali resistant surface. The present disclosure is not limited to the above forming methods and coating methods and other suitable methods may be employed for forming the unitary platen  170 . 
     The polishing pad  120  is formed of a material that is hard enough to allow the abrasive particles in the slurry  142  to mechanically polish a workpiece  160 , such as a wafer, which is between the polishing head  130  and the polishing pad  120 . The following description refers to a wafer as one example of workpiece  160 ; however, the present disclosure is not limited to workpieces that are wafers. On the other hand, polishing pad  120  is soft enough so that it does not substantially scratch or otherwise damage the wafer  160  during the polishing process. 
     During the CMP process, the platen  170  is supported by a bearing (not shown) that is located beneath the platen  170 . The platen  170  and the bearing connected together, cooperate with a mechanism, such as a motor or a drive (not shown), and rotate the polishing pad  120  in a direction D 1  around an axis. As the platen  170  and polishing pad  120  are rotating, the polishing head  130  biases the wafer  160  in a direction D 2  so that a surface of the wafer is pushed against the polishing pad  120 , such that the surface of the wafer  160  in contact with the polishing pad  120  is polished by the slurry  142 . 
     In accordance with embodiments of the present disclosure, the polishing head  130  rotates (e.g., in the direction D 1 , as shown or the reverse direction), causing the wafer  160  to rotate around an axis of the polishing head  130 , and move on the polishing pad  120  at the same time; however, various embodiments of the present disclosure are not limited in this way. In some embodiments of the present disclosure, as shown in  FIG.  1   , the polishing head  130  and the polishing pad  120  rotate in the same direction (e.g., clockwise or counter-clockwise). In alternative embodiments, the polishing head  130  and the polishing pad  120  rotate in opposite directions. 
     While the CMP system  100  is in operation, the slurry  142  flows between the wafer  160  and the polishing pad  120 . The slurry dispenser  140 , which has an outlet over the polishing pad  120 , is used to dispense slurry  142  onto the polishing pad  120 . In some embodiments, the slurry dispenser  140  may dispense other chemical materials suitable for polishing or planarizing the wafer  160 . The material dispensed by the slurry dispenser is not limited to slurries. The slurry  142  includes reactive chemical(s) that react with the surface layer of the wafer  160  and abrasive particles for mechanically polishing the surface of the wafer  160 . Through the chemical reaction between the reactive chemical(s) in the slurry  142 , the surface layer of wafer  160 , and the mechanical polishing, the surface layer of wafer  160  is removed. 
     As the polishing pad  120  is used, the polishing surface of the polishing pad tends to glaze, reducing the removal rate and overall efficiency. The disk  150  of the pad conditioner  155  is arranged over the polishing pad  120 , and is configured to be used to condition the polishing pad  120 , e.g., by removing undesirable by-products generated during the CMP process. The disk  150  generally has protrusions or cutting edges that can be used to polish and re-texturize the surface of the polishing pad  120  during a dressing or conditioning process. In some embodiments of the present disclosure, the disk  150  contacts the top surface of the polishing pad  120  when the polishing pad  120  is to be conditioned. During the conditioning process, the polishing pad  120  and the disk  150  are rotated, so that the protrusions or cutting edges of the disk  150  move relative to the surface of the polishing pad  120 , thereby polishing and re-texturizing the surface of the polishing pad  120 . 
       FIG.  2    is a cross-sectional view of a CMP device  200  of the related art. The CMP device  200  illustrated in  FIG.  2    includes an upper platen  210 , a lower platen  220 , a bearing  230 , a seal O-ring  240 , an end point detector  250  and a view port  260 . In  FIG.  2   , a wafer  160  is in contact with the upper surface of the upper platen  210 . 
     The upper platen  210  and the lower platen  220  of the CMP device  200  illustrated in  FIG.  2    are two separate structures or pieces that are attached together. The CMP device illustrated in  FIG.  2    includes a gap or void between the upper platen  210  and lower platen  220 . The end point detector  250  is housed at least partially within the gap or space between the upper platen  210  and the lower platen  220  and at least partially within the upper platen  210 . The view port  260  is housed within the upper platen  210 . The upper platen  210  includes a recess where the end point detector  250  is placed in a selected location of the upper platen  210 . The upper platen  210  and the lower platen  220  are reversibly detachable and attachable to each other so they can be separated from each other when it is necessary to periodically clean the upper platen  210  and the lower platen  220 , e.g., when slurry  142  enters the gap or void space between the upper platen  210  and the lower platen  220 . 
     The end point detector  250  is an example of a sensor which forms a part of CMP device  200  and is used to assess the progress of the CMP process and determine when the CMP processing of the wafer  160  should be stopped. In  FIG.  2    the wafer  160  is illustrated as being above the upper platen  210 . Though not illustrated in  FIG.  2   , as described above with reference to  FIG.  1   , in actual use, a polishing pad is provided between upper platen  210  and wafer  160 . In  FIG.  2   , the slurry and DIW  142  used for polishing the wafer  160  during the CMP process is shown in the gap or void between upper platen  210  and lower platen  220 . This slurry and DIW  142  in the gap or void flows from between the wafer  160  and the upper platen  210  to the side surface of the upper platen  210 , from the side surface of the upper platen  2  can to the bottom surface of the upper platen  210 , and then into the gap or void between the upper platen  210  and the lower platen  220 . 
     A seal O-ring  240  is located near the outer periphery of the lower platen  220  between the upper platen  210  and the lower platen  220 . The of seal O-ring  240  is to block or resist the flow of slurry and DIW  142  into the gap or void between the upper platen  210  and the lower platen  220 . However, as shown in  FIG.  2   , it has been observed that the flow of slurry and DIW  142  are not completely blocked by seal O-ring  240  and the slurry and DIW  142  collect in the gap or void between the upper platen  210  and lower platen  220 . The slurry and DIW  142  that collects in the gap or void between the upper platen  210  and lower platen  220  contacts end point detector  250 . Even though the drive assembly rotates the upper platen  210  and lower platen  220 , the centrifugal force applied to the slurry and DIW  142  on the upper surface of the upper platen  210  is insufficient to prevent the slurry and DIW  142  from flowing around the side and bottom of the upper platen  210  and into the gap between the upper platen  210  and the lower platen  220 . In the CMP device illustrated in  FIG.  2   , the slurry and DIW  142  in the gap between the upper platen  210  and the lower platen  220  flows into a conduit provided in a center portion of the lower platen  220 . 
       FIG.  3    is a perspective view  300  of an unused lower platen  220  in the related art.  FIG.  3    illustrates the appearance of a lower platen  220  that has not been corroded by a combination of slurry and DIW  142 . 
     When the slurry and DIW  142  come in contact with the end point detector  250 , the bearing  230 , the upper platen  210 , and/or the lower platen  220 , these components of CMP device  200  can be damaged, for example by corrosion caused by the slurry and DIW  142 . For example, the dual-platen structure of the related art which includes an upper platen  210  and lower platen  220  is susceptible to the slurry and DIW  142  collecting in the gap between the upper platen  210  and lower platen  220 . The slurry and DIW  142 , over time, will deteriorate, e.g., corrode, the lower platen  220  as well as components associated with the lower platen  220  that come in contact with the slurry and DIW  142 . One or more deteriorated portions may be present on the surface of the platen  220  in  FIG.  3    after multiple uses. When such deterioration or corrosion becomes too extensive, it is necessary to replace the end point detector  250 , the bearing  230 , and/or the platens, which is expensive and time consuming. Even when the corrosion is not so extensive so as to damage the end point detector  250 , the bearing  230  or the platens, frequent disassembly and cleaning of the platens, end point detector and/or bearing is necessary and involves significant amount of time (e.g., typically totaling more than about 650 hours per year for a CMP device) which significantly decreases the productivity and the efficiency of the overall CMP process and the semiconductor device manufacturing process. 
       FIG.  4    is a cross-sectional view  400  of a portion of a CMP system  100  including a unitary platen  170  according to embodiments of the present disclosure. As shown in  FIG.  4   , the CMP device  100  includes a platen  170  having a circular upper portion  110  and a circular lower portion  115 . The CMP device  100  also includes a bearing  230  for supporting the platen  170 . The bearing  230  cooperates with a rotating mechanism such as a drive assembly (not shown) to allow the platen  170  to rotate around an axis. For the sake of simplicity, other known components of the CMP device  100  have been omitted. 
     The circular upper portion  110  comprises the upper portion of the platen  170  and the circular lower portion  115  comprises the lower portion of the platen  170 . Unlike the platen structure of the related art, the platen  170  in accordance with some embodiments described herein, is a single, seamless, unitary structure. That is, the platen  170  is made of a single-body structure, e.g., without any gaps or voids between the upper portion and the lower portion of the platen  170  or without any gaps or voids between the upper portion and lower portion of platen  170  which are accessible by fluids, e.g., liquids that come in contact with the platen  170 . In other words, in some embodiments of the present disclosure, the circular upper portion  110  and the circular lower portion  115  are not separate structures or pieces. For example, the circular upper portion  110  and the circular lower portion  115  are formed from the same body of materials and are formed as a single unitary structure. In other embodiments, the circular upper portion  110  and the circular lower portion  115  are separate structures or pieces. In such embodiments, these separate structures or pieces are attached to each such that no gaps or voids exist between the circular upper portion  110  and the circular lower portion  115 . Alternatively, in such embodiments, these separate structures or pieces are attached to each other in a way that prevents fluids that come in contact with the platen  170  from gaining access to or collecting in gaps or voids between the circular upper portion  110  in the circular lower portion  115 . 
     In one or more embodiments, the circular upper portion  110  has a different size and shape compared to the size and/or shape of the circular lower portion  115 . For example, as shown in  FIG.  4   , the circular upper portion  110  is larger in size than the circular lower portion  115  (e.g., the circular upper portion  110  has a larger radius or diameter compared to the radius or diameter of the circular lower portion  115 ). However, in other examples, the circular lower portion  115  is larger in size than the circular upper portion  110  (e.g., the circular lower portion  115  has a greater radius or diameter compared to the radius or diameter of the circular upper portion  110 ). In one embodiment, the circular upper portion  110  is thinner than the circular lower portion  115 . In another embodiment, the circular upper portion  110  is thicker than the circular lower portion  115 . 
     In  FIG.  4   , a first recess  410  is formed in both a portion of the circular upper portion  110  and a portion of the circular lower portion  115 . However, in other embodiments, the first recess  410  is formed in the circular upper portion  110  and the first recess  410  does not protrude into the circular lower portion  115 . In some embodiments, a second recess  420  extends into a portion of the circular upper portion  110  but does not extend into the circular lower portion  115  of the platen  170 . In other embodiments, the second recess  420  extends through the circular upper portion  100  and partially into the circular lower portion  115 . The circular upper portion  110  includes an upper surface  172  on one face of the platen  170  and the circular lower portion  115  includes a lower surface  173  on a face of the platen  170  opposite from the upper surface  172 . In some embodiments the lower surface  173  contacts a bearing  230 . The second recess  420  extends downward from the upper surface  172  of the platen  170  towards the lower surface  173 . The second recess portion  420  has a selected depth D 1  extending into the platen  170  from the upper surface  172  and a lateral dimension parallel to the upper surface  172 . In some embodiments, the depth D 1  of the second recess  420  is less than the depth D 2  of the first recess  410 . In other embodiments, the depth D 1  of the second recess  420  is greater than the depth D 2  of the first recess  410 . The first recess portion  410  extends from a bottom of the second recess portion  420  towards the lower surface  173  of platen  170 . The first recess portion  410  has a lateral dimension parallel to the upper surface  172 . The lateral dimension of the first recess is different from or equal to the lateral dimension of the second recess. For example, in some embodiments the lateral dimension of the second recess is greater than the lateral dimension of the first recess. In other embodiments, the lateral dimension of the second recess is less than the lateral dimension of the first recess. In one or more embodiments, the first recess portion  410  and the second recess portion  420  are circular and concentric. In other embodiments, the first recess portion  410  and the second recess portion  420  are not circular or concentric, e.g., see  FIG.  7 B  embodiments. In one or more embodiments, an axis of the first recess  410  and an axis of the second recess  420  are coaxial and spaced apart from the axis of the platen  170 . As shown in  FIG.  4   , the axis of the platen  170  and the axis of the bearing  230  are coaxial such that the platen  170  and the bearing  230  are able to rotate together around the common axis. 
     In one or more embodiments, a sensor, such as an end point detector ( 340 ; shown in  FIG.  5   ) is positioned in the first recess  410 . The following description refers to an end point detector  340 ; however, the present disclosure is not limited to sensors that are end point detectors. The size and shape of the first recess  410  depends on the size and shape of the end point detector  340 . For example, the end point detector  340  may have substantially the same depth and lateral dimension of the first recess  410 . In other embodiments, any other suitable components, other than an endpoint detector, can be incorporated in the platen  170  and these components can be fit inside various recesses in the platen  170 . For example, to incorporate additional components within the platen  170 , will include additional recesses with various sizes and shapes. 
     The second recess  420  is formed above the first recess  410 . In some embodiments, since the first recess  410  is already formed in the platen  170 , a subsequent second recess  420  may be formed by forming a recess that is wider than the first recess  410 . In other embodiments, the second recess  420  being a wider and less deep recess (e.g., greater lateral dimension and less deep compared to the first recess  410 ) can be formed first and thereafter the first recess  410  being a narrower and deeper recess can be formed. The order of forming the first and second recesses  410 ,  420  may vary depending on the manufacturing process or the design needs. 
     In some embodiments, a ratio of a diameter of the circular upper portion  110  and a diameter of the circular lower portion  115  may vary based on the manufacturing process or the design needs, as well as the size and shape of the components (e.g., end point detector, detector cover which is described in connection to  FIG.  5   ) embedded in the unitary platen  170 . For example, the diameter of the circular upper portion  110  may be greater than the diameter of the circular lower portion  115 , and thus the ratio between the two diameters may be greater than 1. 
     However, in other embodiments, the ratio between the two diameters may be 1. That is, the circular upper portion  110  and the circular lower portion  115  may have the same diameter. 
     In further embodiments, the circular lower portion  115  may be designed to have a diameter slightly greater than the diameter of the circular upper portion  110 , and thus the ratio between the two diameters may be less than 1. 
     In yet some embodiments, the platen  170  may be designed to have a tapered sidewall shape as well. By having the tapered sidewall shape for the platen  170  may allow the slurries  142  to smoothly slide and fall off to the bottom of the platen  170 . The shape of the sidewall of the platen  170  is not limited to the aforementioned shapes and may employ other sidewall shapes as well. For example, when the diameter of the circular upper portion  110  is greater than the diameter of the circular lower portion  115 , the sidewall of the circular lower portion  115  may have a circular or a semi-circular sidewall shape. That is, the sidewall of the circular lower portion  115  may extend from the protruded part of the circular upper portion  110  in a curvature. With this sidewall shape, it may also prevent the slurries  142  from permeating inside the platen  170  during operation. 
     Referring to  FIG.  5   , in one embodiment, the end point detector  340  is placed in the first recess  410  and thereafter a detector cover  350  (not shown in  FIG.  4   ) is placed above the end point detector  340  and in the second recess  420 . In some embodiments, the detector cover  350  includes a view port  360 . 
       FIG.  5    is a cross-sectional view  500  of a CMP device  500  including a platen  170  with fasteners  320  and sealing means  330  according to embodiments of the present disclosure. As shown in  FIG.  5   , the CMP device  500  includes a platen  170 , an end point detector  340  placed in a first recess  410 , a detector cover  350  placed in a second recess  420 , fasteners  320  for securing detector cover  350  to circular upper portion  110  and sealing means  330 . 
     The sealing means  330  include any suitable structure for creating a fluid-tight seal at the interface between the circular upper portion  110  of platen  170  and the detector cover  350 . In one embodiment, the sealing means  330  include a gasket or a seal ring. The gasket or seal ring can be of any type of material, any suitable lateral shape and any suitable cross-sectional shape. In one embodiment, the gasket will have a lateral shape that is the same as the shape of the end point detector  340  and or the first recess  410  allowing it to be placed around the end point detector  340  or first recess  410 . For example, in some embodiments, the gasket defines a lateral shape that is circular or rectangular-shaped or some other shape. The gasket can be made of synthetic rubbers, thermoset, plastic, thermoplastics or any other material that meets the chemical compatibility, sealing pressure, application temperature, lubrication requirements, or other property for creating a fluid-tight seal between the circular upper portion  110  of platen  170  and the underside of detector cover  350 . Such fluid-tight seal serves to isolate the end point detector  340  from the slurry and DIW  142  that reaches sealing means  350 . 
     The end point detector  340  interrogates the surface of the workpiece as the CMP process progresses. Signals from the end point detector are used to identify a CMP processing end point for a workpiece, e.g., the wafer  160 . For example, the end point detector  340  provides signals that are used by a controller to determine when to stop the CMP process or when to change polishing conditions, such as slurry composition or operating parameters, such as rotation rate of the polishing pad or workpiece. In one embodiment, the signals generated by the end point detector  340  are based on a change in reflection intensity of light from the surface of the wafer  160 . That is, the end point detector  340  transmits an incident light onto a the surface of the wafer  160  and measures an intensity of the incident light that is reflected back to the end point detector  340  by the surface of the wafer. In one embodiment, the end point detector  340  emits light and senses the reflected light using a sensor. The emitted light may be a laser. In particular, the laser is applied from the sensor to a surface of the wafer  160  during polishing of the surface and based on the intensity of the laser reflected by the surface, the end point detector  340  generates a signal that is used to assess the progress of the CMP process and ultimately to determine when the CMP processing should come to an end. 
     In one or more embodiments, the end point detector  340  is used to control the timing to end the polishing. The timing of the end of the polishing can be based on a number of factors, including obtaining uniform thickness of certain layers on the wafer  160  surface and/or to obtain a target thickness of layers on the wafer  160  surface. 
     In some embodiments, the end point detector  340  has an upper surface  342 . In the embodiment illustrated in  FIG.  5   , the upper surface  342  of the end point detector  340  is substantially coplanar with the top of the first recess  410 . In the embodiment of  FIG.  5   , the top of the first recess  410  is coplanar and partially coincides with a bottom surface of the second recess  420 . In other embodiments, the upper surface  342  of the end point detector  340  is not substantially coplanar with the top of the first recess  410 . For example, in such other embodiments, the upper surface  342  of the end point detector  340  is below the top of the first recess  410  and below the bottom surface of the second recess  420 . In yet other embodiments, the upper surface  342  of end point detector  340  is above the top of the first recess  410  and above the bottom surface of the second recess  420 . In these latter embodiments, the lower surface of detector cover  350  includes a recess to accommodate the portion of end point detector  340  that is above the top of first recess  410  and above the bottom surface of the second recess  420 . 
     In  FIG.  5   , the sealing means  330  is placed in a selected location that is spaced apart from a first surface  342  of the end point detector  340 . The selected location may be along a second surface  332  that defines a bottom surface of the second recess  420 . In one embodiment, the first surface  342  and the second surface  332  are coplanar. In another embodiment, the sealing means  330  is located at a bottom of the second recess  420  and extends around the first recess  410 . In other embodiments, the first surface  342  and the second surface  332  may not be in the same plane and one of the surfaces may be lower or higher than the other surface. Second surface  332  includes a seal seat, e.g., a groove or indention in second surface  332 , for receiving the sealing means  350 . The seal seat typically has a cross-sectional shape that mates with the cross-sectional shape of the sealing means  350 . 
     The detector cover  350  is received in second recess  420  where it overlies end point detector  340 . When the detector cover  350  is placed in the second recess  420  and secured in place by fasteners  320 , the gasket or the sealing means  330  is compressed between the underside of detector cover  350  and the platen  170  and provides a barrier to fluids that come in contact with sealing means  330 . The detector cover  350  includes a viewing window  360  which passes through detector cover  350 . The viewing window  360  is provided so that light emitted by the sensor of the end point detector  340  can pass through detector cover  350  via viewing window  360  for purposes of inspecting the workpiece  160  (e.g., wafer  160 ). In one embodiment, the viewing window  360  is made of a transparent material so that light emitted by end point detector  340  passes through the viewing window  360 , is reflected by workpiece  160  and passes back through the viewing window  360  to the sensor of the end point detector  340 . Viewing window  360 , is transparent to light or other electromagnetic energy emitted by end point detector  340  and reflected by wafer  160 . In some embodiments, the viewing window  360  is encircled by a structural portion  365  that may not be transparent (see  FIG.  7 A ). In further embodiments, the transparent viewing window  360  of the detector cover  350  is substantially aligned with the optical axis of the light emitting sensor of the end point detector  340 . 
     The fasteners  320  are used to attach the detector cover  350  to the platen  170  in the second recess  420 . In embodiments in accordance with  FIG.  5   , fasteners  320  are received into the second surface  332  of the platen  170 . In one embodiment, the fasteners  320  pass through the detector cover  350  and reach the second surface  332 . Second surface  332  includes threaded bores for receiving threaded ends of fastener&#39;s  320 . The fasteners  320  are received at a selected location of the second surface  332  that are spaced apart from the end point detector  340  and spaced apart from the selected location of sealing means  330 . In embodiments in accordance with  FIG.  5   . Fasteners  320  are received at a location of the second surface  332 , such that sealing means  330  is positioned between fasteners  320  and end point detector  340 . In one or more embodiments, the fasteners  320  are configured so that slurries and DIW  142  that come in contact with fasteners  320  are prevented from seeping into detector cover  350 . For example, a rubber seal ring or gasket is provided between fasteners  320  and detector cover  350  and/or a thread sealing compound is applied to the threads of fasteners  320 . Preventing slurries and DIW from seeping into detector cover  350  reduces the risk that slurries and DIW  142  comes in contact with the end point detector  340 . In  FIG.  5   , the fasteners  320  are shown as passing through the detector cover  350  at two locations. However, more fasteners  320  can be employed to perform both fixating the detector cover  350  to the platen  170  and preventing infiltration of slurries and DIW  142  into the platen  170 . 
     The fasteners  320  include any suitable means for coupling the detector cover  350  with the platen  170 . In addition, the fasteners  320  include any suitable means that prevents the infiltration of slurries and DIW  142  into the platen  170 . In one embodiment, the fasteners  320  include any type of fastener, mechanical joint, or the like. The fasteners  320  can be of any type and shape. In one embodiment, the fasteners  320  include a hardware device that mechanically joins or affixes two or more objects together. These fasteners  320  can be removed or dismantled without damaging the joining component. For example, the fasteners  320  can include bolts, screws, clips, pins, or the like. In other examples, the fasteners  320  do not necessarily have to have hardware, mechanical characteristics. That is, synthetic rubbers, or plastics or any other material that is capable of fixating the detector cover  350  to the platen  170  and preventing the slurry and DIW  142  from penetrating into the platen  170 , where the slurry and DIW may contact end point detector  340 , may be used. 
     In accordance with some embodiments of the present disclosure, when the fasteners  320  affix the detector cover  350  to the upper portion of the platen (i.e., circular upper portion  110 ), the top surface  352  of the detector cover  350  is coplanar, i.e., lies in the same plane, with the top surface  172  of the circular upper portion  110 . In one or more embodiments, the tops of fasteners  320  are embedded, recessed or countersunk into the surface  352  of the detector cover  350 . 
     In some embodiments, the depth D 1  of the second recess  420  may be based on the thickness of the detector cover  350 , and the depth D 2  of the first recess  410  may be based on the thickness of the end point detector  340 . However, in other embodiments, the depth D 1  of the second recess and the depth D 2  of the first recess may not be necessarily dependent upon the thickness of these components. Various dimensions of the first and second recess may be utilized. For example, the size and depth of the recess may increase or decrease based on additional components that may be embedded inside the recess. 
       FIG.  6    is a cross-sectional view  600  of a CMP device  100  having a platen  170  according to embodiments of the present disclosure. As shown in  FIG.  6   , a wafer  160  is overlain on the area of platen  170  that includes end point detector  340 . In  FIG.  6   , the polishing pad  120  between the circular upper portion  110  and wafer  160  and the polishing head  130  have been omitted for simplicity. 
     Unlike the non-unitary dual-platen structure in the related art, the unitary platen  170  in accordance with embodiments according to the present disclosure does not include a seam or gap between its circular upper portion  110  and its circular lower portion  115  that is exposed on an exterior surface of platen  170  where slurries and DIW  142  can penetrate into platen  170 , e.g., into a space between the circular upper portion  110  and the circular lower portion  115 . As illustrated in  FIG.  6   , in accordance with some embodiments of the present disclosure, when a seam or gap between an upper platen  210  in  FIG.  2    and a lower platen  220  in  FIG.  2    is absent, yes you are you and the slurries and DIW  142  can flow from the top surface  172  of the platen  170 , to a vertical side surface of the platen  170  and to the underside of the circular upper portion  110 , where the slurries and DIW drip off of the underside of the circular upper portion  110 . 
     In some cases, should slurry and DIW  142  infiltrate into a space  610  between the circular upper portion  110  of the platen  170  and the detector cover  350  or into the portion of detector cover  350  which receives fasteners  320 , and find come in contact with the sealing means  330 , the infiltration of the slurries and DIW  142  to the end point detector  340  is effectively reduced or prevented by seal means  330 . For example, the fasteners  320  and seals or thread sealing compounds associated with fasteners  320  formulate a first blockade against the slurries and DIW  142 . Further, even if some slurry and DIW  142  pass the fasteners  320  or seep into a space between detector cover  350  and platen  170 , the sealing means  330  formulates a second blockade against the slurry and DIW  142 , effectively preventing the slurry and DIW  142  from coming in contact with the end point detector  340 . 
       FIG.  7 A  is a top view  700  of an example detector cover  350  of a CMP device  100  according to embodiments of the present disclosure. In  FIG.  7 A , for purpose of illustration, the location of the sealing means  330  is described. In one embodiment, the sealing means  330  is located between the platen  170  and the detector cover  350 . In some embodiments, an outer portion  370  surrounds the detector cover  350 . In the outer portion  370 , the fasteners  320  are arranged. In this embodiment, the fasteners  320  are located outside of the location where the sealing means  330  is located. However, in other embodiments, the fasteners  320  can be arranged within the contour of the location where sealing means  330  are placed. Any numbers of fasteners  320  can be used to fix the detector cover  350  to the platen  170 . 
       FIG.  7 B  is a cross-sectional view  750  of a platen  170  according to another embodiment of the present disclosure. In  FIG.  7 B , a third recess  430  is formed below the first recess  410  and the second recess  420 . The third recess  430  may be provided as a space for other suitable components needed to perform and/or monitor the CMP process. 
     In this embodiment, the circular upper portion  110  and the circular lower portion  115  of the platen  170  have common outer side surfaces. That is, different from the embodiments shown in  FIG.  5   , e.g., the circular upper portion  110  does not have a larger lateral dimension, e.g., diameter, than the circular lower portion  115 . That is, according to embodiments of  FIG.  7 B , the size and shape of the circular upper portion  110  and the size and shape of the circular lower portion  115  are identical. The thickness/depth of the second recess  420  is denoted as D 1 ; the thickness of the first recess  410  is denoted as D 2 ; and the thickness of the third recess  430  is denoted as D 3 . The thickness of the recesses D 1 , D 2 , D 3  may vary based on the depth of components that are to be placed in each second, first, and third recess, respectively. In some embodiments, additional recesses can be formed in the platen  170  for placing other suitable components for the CMP process. Various relationships between the thickness of the recesses D 1 , D 2 , D 3  may be employed based on various needs. 
     The surface  332  in the second recess  420  includes a seal seat  334 . The sealing means  330  is placed in the seal seat  334 . 
     A view  336  in  FIG.  7 B  shows an enlarged view of the seal seat  334  according to the present disclosure. In one embodiment, the seal seat  334  for the sealing means  330  has a depth O 1  and a lateral dimension O 2 . The depth O 1  and the lateral dimension O 2  may differ based on the size and dimension of the sealing means  330 . In some embodiments, the depth O 1  and the lateral dimension O 2  will substantially match the size of the sealing means  330  so that no slurry or DIW  142  can pass by the sealing means  330  and come in contact with the end point detector  340 . 
     Platen assemblies according to the present disclosure are less susceptible to failure of sensitive electrical or optical components contained within the platen due to damage caused by slurry and DIW coming in contact with the sensitive components. The seamless, unitary platen structure in accordance with presently disclosed embodiments effectively isolates sensitive components, such as an end point detector housed inside the platen, from foreign and external materials (e.g., slurry, DIW, or any other materials) that could damage the sensitive components. Further aspects of the present disclosure provide a platen having sealing means and fasteners around the periphery or the contour of a end point detector. The sealing means and fasteners are configured to provide additional protection for preventing the slurries from penetrating into the internal locations of the platen. By employing a CMP device or system including a platen according to the present disclosure, damage to sensitive components, housed within the platen, resulting from the sensitive component coming in contact with slurry and/or DIW that leaks in the platen is reduced. Reducing damage to such sensitive components, reduces the time required for engineers to clean slurries off a platen and to repair or replace damaged components. Such reduction in time for maintenance or repair translates into a lower cost of manufacturing. 
     In one embodiment of the present disclosure, a platen for a chemical mechanical polishing system includes a unitary platen including an upper surface on one face of the platen and a lower surface on an opposite face of the platen. The platen, in operation, rotates around an axis. The first recess portion in the upper surface of the platen has a depth extending into the platen from the upper surface and a lateral dimension parallel to the upper surface. 
     The platen includes a second recess portion in the platen. The second recess portion has a depth and extending from a bottom of the first recess portion into the platen towards the lower surface of the platen. The second recess portion has a lateral dimension parallel to the upper surface. The lateral dimension of the second recess portion is different than the lateral dimension of the first recess portion. 
     Another aspect of the present disclosure provides a chemical mechanical polishing system including a platen and a drive assembly. The drive assembly is coupled to the platen. The drive assembly is configured to rotate the platen in a selected direction. 
     In one embodiment, the platen includes a unitary platen including a pad surface on one face of the platen, a drive assembly surface on an opposite face of the platen and an axis, around which, in operation, the platen rotates. 
     In one embodiment, the platen further includes a first recess portion extending from the pad surface of the unitary platen towards the drive assembly surface. 
     In one embodiment, the platen further includes a second recess portion extending from a bottom of the first recess portion into the platen towards the drive assembly surface. A distance between the bottom of the first recess portion and a bottom of the second recess portion is greater than a distance between the pad surface and the bottom of the first recess portion. 
     Yet another aspect of the present disclosure provides a chemical mechanical polishing system including a platen configured for mounting a substrate. The platen includes: a unitary platen including a first surface on one face of the platen, a second surface on an opposite face of the platen, and an axis adjacent to the second surface, around which, in operation, the unitary platen rotates; a first recess portion extending from the first surface of the unitary platen towards the second surface; a second recess portion extending from a bottom of the first recess portion into the unitary platen towards the second surface, a distance between the bottom of the first recess portion and a bottom of the second recess portion being greater than a distance between the pad surface and the bottom of the first recess portion; and a third recess portion extending from a bottom of the second recess portion towards the second surface of the unitary platen. 
     In one embodiment, the second recess portion includes a lateral dimension parallel to the first surface that is less than a lateral dimension of the first recess portion parallel to the first surface. 
     In one embodiment, the third recess portion includes a lateral dimension parallel to the first surface that is less than a lateral dimension of the second recess portion parallel to the first surface. 
     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.