Patent Publication Number: US-7214123-B2

Title: Retainer ring, Polishing head, and chemical mechanical polishing apparatus

Description:
PRIORITY STATEMENT 
   This application claims priority from Korean Patent Application No. 10-2005-0080923 filed on Aug. 31, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
   BACKGROUND 
   1. Field 
   Example embodiments relate to a retainer ring, a polishing head, and a chemical mechanical polishing apparatus. For example, example embodiments relate to a retainer ring having a thermoelectric element and a polishing head and a chemical mechanical polishing apparatus, having the retainer ring. 
   2. Description of the Conventional Art 
   Chemical mechanical polishing (CMP) is a semiconductor manufacturing processes that may use a CMP apparatus having a polishing pad to polish a wafer. A chemical solution including a slurry may be used in a manner such that a chemical reaction is induced on a wafer, and mechanical force produced by the polishing pad may be transmitted to the wafer so as to planarize the surface of the wafer. 
   A CMP apparatus may include a platen, a polishing pad, and/or a polishing head, which may be composed of a retainer ring and a wafer carrier. When polishing the wafer surface by rotating the polishing head, the temperature may rise due to friction between the polishing pad and the retainer ring, friction between the retainer ring and the wafer, and/or friction between the wafer and the polishing pad. The increase in temperature may lower the yield of the CMP process. For example, erosion and dishing may occur to a greater extent at the edge of the wafer than at the center of the wafer. Erosion is a phenomenon in which a portion of a spacer on a relatively fine pattern is concavely removed during the polishing process. Dishing is a phenomenon in which a top portion of a layer deposited in a trench becomes concave, like a dish, during the polishing process. 
   In the conventional art, a cooling device may be arranged in a platen to lower the heat during a CMP process. However, because the polishing pad is formed of polyurethane having a low thermal conductivity, it may be difficult to effectively reduce the heat. 
   SUMMARY 
   Example embodiments of may permit temperatures of a polishing pad, an edge of a wafer, and slurry to be reduced, may prevent/reduce erosion and/or dishing of an edge portion of the wafer, and may prevent/reduce a non-uniform surface polishing rate. 
   In an example embodiment, a retainer ring may include a heat absorbing element configured to surround a wafer therein, a thermoelectric element disposed in the heat absorbing element, and a heat dissipating element disposed on the thermoelectric element to dissipate heat absorbed by the heat absorbing element. 
   In another example embodiment, a polishing head may include a wafer carrier configured to hold and position a wafer, a retainer ring configured to reduce heat during a polishing process, and a cooling element disposed over the retainer ring and configured to dissipate the heat. 
   In another example embodiment, a chemical mechanical polishing apparatus may include a retainer ring and/or a polishing head. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Example embodiments of the present invention may be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
       FIG. 1A  is a perspective view illustrating a chemical mechanical polishing apparatus in accordance with an example embodiment; 
       FIG. 1B  is an example of longitudinal cross-sectional view taken along the line B–B′ of  FIG. 1A ; 
       FIG. 2A  is a perspective view illustrating a retainer ring in a chemical mechanical polishing apparatus in accordance with an example embodiment; 
       FIG. 2B  is an example of partially enlarged perspective view illustrating the lower surface of the heat absorbing element of the retainer ring; 
       FIG. 2C  is an example of longitudinal cross-sectional view of the retainer ring, taken along the line C–C′ of  FIG. 2A ; 
       FIG. 2D  is an example of transverse cross-sectional view of the retainer ring, taken along the line D–D′ of  FIG. 2A ; 
       FIG. 2E  is an example of plan view illustrating a stacked heat absorbing element, lower electrodes and thermoelectric semiconductors; 
       FIG. 2F  is an example of bottom view illustrating a stacked thermoelectric semiconductors, upper electrodes, and a heat dissipating element; 
       FIG. 3  is an example of longitudinal cross-sectional view illustrating a polishing head in a chemical mechanical polishing apparatus in accordance with another example embodiment of the present invention; 
       FIG. 4  is a perspective view illustrating a retainer ring in accordance with another example embodiment; 
       FIG. 5  is a perspective view illustrating a retainer ring in accordance with still another example embodiment; 
       FIG. 6A  is a perspective view illustrating a retainer ring in accordance with a yet another example embodiment; 
       FIG. 6B  is an example of longitudinal cross-sectional view taken along the line B–B′ of  FIG. 6A ; and 
       FIG. 7  is an example of flow chart illustrating the operation of the chemical mechanical polishing apparatus according to example embodiments. 
   

   DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
   Reference will now be made in greater detail to example embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like elements. 
   It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it may be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
   It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings. 
   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. It will be understood that the spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
   The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting global. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
   Example embodiments are described herein with reference to cross-section illustrations that may be schematic illustrations of idealized embodiments (and intermediate structures) of the present invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention. 
   Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     FIG. 1A  is a perspective view illustrating a chemical mechanical polishing apparatus in accordance with an example embodiment, and  FIG. 1B  is a longitudinal cross-sectional view taken along the line B–B′ of  FIG. 1A . 
   Referring to  FIGS. 1A and 1B , the chemical mechanical polishing apparatus  100  in accordance with an example embodiment may include a platen rotation shaft  101 , a platen  102 , a polishing pad  103 , a pad conditioner  104 , a slurry dispensing device  105 , and/or a polishing head  200 . The polishing head  200  may include a retainer ring  300  and/or a wafer carrier  210 . 
   The platen  102  may rotate the polishing pad  103  at a desired speed in order to polish a wafer W. The platen  102  may be positioned underneath the polishing pad  103 . The platen  102  may be connected to a platen driving motor (not shown) through the platen rotation shaft  101 . The platen  102  may be formed of an aluminum plate or a stainless steel plate. The platen  102  may have a disc shape, and may be rotated at various speeds. Through the rotation of the platen  102  at various speeds, it may be possible to precisely polish the wafer W. 
   The polishing pad  103  may be rotated to polish the wafer W in cooperation with abrasive particles formed thereon. The polishing pad  103  may be made of polyurethane, which may be formed with fine protuberances, for example, a kind of elastomeric material having a rough surface. The polishing pad  103  may be positioned on the platen  102 . The polishing pad  103  may also be rotated by the platen  102 . 
   The pad conditioner  104  may be provided to reduce the abrasion of the polishing pad  103 . After a period of use, the protuberances on the polishing pad  103  may be worn by friction between the polishing pad  103  and the wafer W. The wear to the protuberances may make it difficult to appropriately polish the wafer W. The pad conditioner  104  may be used with the polishing pad  103 , so that the polishing pad  103  may be used for an extended time without being replaced. 
   The slurry dispensing device  105  may dispense slurry solution  106  onto the polishing pad  103 . The slurry solution  106  may be used to conduct the chemical polishing process. The slurry solution  106  may be used to chemically planarize the wafer W. Abrasive particles contained in the slurry solution  106  may polish the wafer W as the polishing pad  103  is rotated. The abrasive particles may be formed of fine grains to reduce scratches on the surface of the wafer W. 
   The polishing head  200  may include the wafer carrier  210  and the retainer ring  300 . The polishing head  200  may polish the wafer W when the wafer W is fastened to the lower surface of the polishing head  200 . The polishing head  200  may be positioned to face the platen  102 . To rotate the wafer W, a motor may be mounted inside or outside the polishing head  200 . In addition to rotating, the polishing head  200  may move in the x, y, and z axes. Accordingly, the wafer may be polished. 
   The wafer carrier  210  may hold the wafer W, and also position the wafer W above the polishing pad  103 . The wafer carrier  210  may include wafer suction  220 , a head body  230 , a head rotation shaft  240 , and/or cooling global element  250 . 
   The vacuum suction element  220  may hold the wafer W with vacuum. A thin film (not shown), for example, a membrane, may be applied to the lower end of the wafer suction  220 . The membrane may be brought into contact with the surface side not to be polished on the wafer W. In other words, a first surface side to be polished on the wafer W may be positioned to face the polishing pad  103 , and a second surface side to be polished on the wafer W may be brought into contact with the wafer carrier  210 . 
   The head body  230  may support the vacuum suction element  220 , the head rotation shaft  240 , and the cooling element  250 . 
   The cooling element  250  may cool the heat dissipating element  330  of the retainer ring  300 . The cooling element  250  may be a water cooling-type cooling device. By placing the cooling element  250  in the polishing head  200 , it may be possible to manufacture the retainer ring  300  to be compact in size. 
   The water cooling-type cooling device may include a water jacket  251 , a temperature adjustor  252 , a radiator  253 , a water tank  254 , and a water pump  255 . The water jacket  251  may be positioned to be connected with the heat dissipating element  330  of the retainer ring  300  to reduce the heat of the heat dissipating element  330 . 
   The retainer ring  300  may prevent the wafer W from being unintentionally released from the wafer carrier  210  during the polishing process. The retainer ring  300  may be positioned below the wafer carrier  210  to surround the side surface of the wafer W. The retainer ring  300  may have a flat lower surface. 
   The retainer ring  300  may have a desired thickness to prevent/reduce an edge rebounding phenomenon. The edge rebounding phenomenon is when an edge portion of the polishing pad  103  is concavely worn, and an edge portion of a wafer W is concavely polished due to the elasticity of the polishing pad  103 . The edge rebounding phenomenon may be mitigated by pressing the polishing pad  103  with appropriate force around the edge of the wafer W using the retainer ring  300 . 
   While not shown in the drawings, the retainer ring  300  may have a plurality of purge holes to vacuum hold the wafer W. 
   The retainer ring  300  may include a heat absorbing element  310 , a thermoelectric element  320 , and/or the heat dissipating element  330 . 
   The heat absorbing element  310  may be brought into contact with the wafer W, the polishing pad  103 , and the slurry solution  106  to reduce the temperatures thereof. The heat absorbing element  310  may absorb heat generated due to friction between the polishing pad  103  and the retainer ring  300 , between the retainer ring  300  and the side surface of the wafer W, and/or between the lower surface of the wafer W and the polishing pad  103  during the polishing process on the wafer W. 
   The heat absorbing element  310  may be formed of ceramic. If the heat absorbing element  310  is formed of ceramic, abrasion resistance of the heat absorbing element  310  may be improved, and heat transfer may be promoted. The heat absorbing element  310  may be formed to be in direct contact with the side surface of the wafer W, the polishing pad  103 , and/or the slurry solution  106 . 
   The heat absorbing element  310  may be formed in a ring-shape. Therefore, because the heat absorbing element  310  may be disposed over the entire lower surface of the retainer ring  300 , the heat generated from the edge portion of the wafer W may be efficiently absorbed. 
   Temperature of portions of the polishing pad  103  adjacent to the edge of the wafer W, and the slurry solution  106  may be decreased by the presence of the heat absorbing element  310 . Therefore, it may be possible to reduce and/or prevent erosion and/or dishing phenomena and a non-uniform surface polishing rate. 
   The thermoelectric element  320  may transfer the heat absorbed by the heat absorbing element  310  to the heat dissipating element  330 . The thermoelectric element  320  may be formed on the heat absorbing element  310 , and may have a ring-shape, similar to the heat absorbing element  310 . 
   The thermoelectric element  320  may control the temperature depending upon a power supply level. When power is supplied to the thermoelectric element  320 , the thermoelectric element  320  may be more rapidly cooled. The thermoelectric element  320  may be a solid-state device producing lower noise and low vibration. Also, the thermoelectric element  320  may also be used for local cooling. Further, the thermoelectric element  320  may be manufactured to have a smaller size and/or lighter weight. Moreover, the thermoelectric element  320  may operate at any position and/or any direction. 
   Accordingly, in example embodiments, the temperature, for example, excess heat, generated during a chemical mechanical polishing process may be controlled using the thermoelectric element  320 . 
   The heat absorbed by the heat absorbing element  310  may be transferred to the heat dissipating element  330  by way of the thermoelectric element  320 . The heat dissipating element  330  may be formed on the thermoelectric element  320 . The heat dissipating element  330  may be formed of ceramic. The heat absorbing element  310  and the thermoelectric element  320  may also be formed of ceramic. A locking element (not shown) to connect the retainer ring  300  to the wafer carrier  210  may be disposed on the upper end of the heat dissipating element  330 . 
   The retainer ring  300  of the chemical mechanical polishing apparatus in accordance with the example embodiment will be described in more detail with reference to  FIGS. 2A through 2F . 
   Referring to  FIGS. 2A through 2F , the retainer ring  300  may include the heat absorbing element  310 , the thermoelectric element  320 , and/or the heat dissipating element  330 . The thermoelectric element  320  may include an insulator  321 , electrodes, and/or thermoelectric semiconductors. The thermoelectric semiconductors may include a first P-type pellet  324 , a second P-type pellet  328 , a first N-type pellet  325 , and/or a second N-type pellet  327 . The electrodes may include a first lower electrode  322 , a second lower electrode  323 , an upper electrode  326 , and/or a power electrode  329 . 
   Grooves  311  may be defined on a first surface of the heat absorbing element  310 . A slurry solution  106  may freely discharge to the outside through the grooves  311  during the polishing. Accordingly, the first surface of the heat absorbing element  310  may be constructed of a separate ceramic plate. 
   The insulator  321  may be formed around the thermoelectric semiconductors to insulate the thermoelectric semiconductors. The insulator  321  may also serve as heat insulation material between the heat absorbing element  310  and the heat dissipating element  330 . 
   The electrodes may electrically connect the thermoelectric semiconductors in series. The first lower electrode  322  and the second lower electrode  323  may be positioned on a first portion of the thermoelectric semiconductors, and the upper electrode  326  may be positioned on a second portion of the thermoelectric semiconductors. The power electrode  329  may supply power to the thermoelectric semiconductors. 
   The thermoelectric semiconductors may transfer the heat, absorbed by the heat absorbing element  310 , to the heat dissipating element  330 . The thermoelectric semiconductors may include the plurality of pellets  324 ,  325 ,  327 ,  328 , which may be formed of a column-shape. The thermoelectric semiconductors may be composed of the P-type pellets  324 ,  328 , and the N-type pellets  325 ,  327 . The P-type pellets  324 ,  328  and the N-type pellets  325 ,  327  may be alternately connected with each other by the upper electrode  326 . The P-type pellets  324 ,  328  may be formed of Bi x Te y Se z , and the N-type pellets  325 ,  327  may be formed of Bi x Te y Sb z . 
   If a positive potential difference is applied to the first P-type pellet  324 , which may be positioned between the first lower electrode  322  and the upper electrode  326 , holes in the first lower electrode  322  may migrate to the upper electrode  326 . The migration of the holes may transfer heat away from the first lower electrode  322 . 
   Also, if a positive potential difference is applied to the first N-type pellet  325 , which may be positioned between the second lower electrode  323  and the upper electrode  326 , electrons in the second lower electrode  323  may migrate to the upper electrode  326 . The migration of electrons may transfer heat away from the second lower electrode  323 . Accordingly, the temperature of the heat absorbing element  310  may decrease, and the temperature of the heat dissipating element  330  may increase. 
   The first P-type pellet  324  and the first N-type pellet  325  may be disposed to be parallel to each other. By connecting the respective upper portions of the first P-type pellet  324  and the first N-type pellet  325  to the upper electrode  326 , electrical connections may be formed in series. The lower portion of the second P-type pellet  328  may be connected in series with the lower portion of the first N-type pellet  325  through the second lower electrode  323 , and the lower portion of the second N-type pellet  327  may be connected in series with the lower portion of the first P-type pellet  324  through the first lower electrode  322 . 
   Although  FIGS. 2A–2F  illustrate that the thermoelectric semiconductors may be arranged in two circular loops electrically connected in series, it is understood by a person of ordinary skill that the thermoelectric semiconductors may be arranged in a single circular loop or multiple circular loops electrically connected in series. Also, the overall thermoelectric semiconductors may not necessarily be connected in series in one circular loop, but instead, may form several loops such that the thermoelectric semiconductors in each loop are connected in series and the loops are connected in parallel. 
   A chemical mechanical polishing apparatus in accordance with another example embodiment will be described with reference to  FIG. 3 .  FIG. 3  is a longitudinal cross-sectional view illustrating a polishing head in a chemical mechanical polishing apparatus in accordance with another example embodiment. 
   Referring to  FIG. 3 , the polishing head  201  in accordance with another example embodiment of the present invention is different from the polishing head  200  illustrated in  FIGS. 1–2F  in terms of the construction of the cooling element. The polishing head  201  may include an air cooling-type cooling device  256  as the cooling element. 
   The air cooling-type cooling device  256  may include a heat radiating plate  257  and a cooling fan  258 . The heat radiating plate  257  may be disposed to be in contact with a heat dissipating element  330  of a retainer ring  300 . The cooling fan  258  may be positioned on the heat radiating plate  257 . 
   A retainer ring in accordance with another example embodiment of the present invention will be described below with reference to  FIG. 4 . 
   Referring to  FIG. 4 , the retainer ring in accordance with another example embodiment may include a heat radiating plate  341  as a cooling element for lowering the temperature of a heat dissipating element  330 . The heat radiating plate  341  may be brought into direct contact with the heat dissipating element  330 . In order to increase the air contact area of the heat radiating plate  341 , a plurality of fins  345  extending upward may be formed on the heat radiating plate  341 . A cooling fan (not shown) may be located on the plurality of fins  345 . The cooling element may be formed on a retainer ring rather than on a polishing head. 
   A retainer ring in accordance with another example embodiment will be described below with reference to  FIG. 5 . 
   Referring to  FIG. 5 , a water jacket  342  may be disposed on a heat dissipating element  330 . The water jacket  342  may have a cooling water inlet port  343  and a cooling water outlet port  344 . Components (not shown) constituting the water cooling-type cooling device may be disposed outside the retainer ring. For example, a temperature adjustor, a radiator, a water tank, and/or a water pump may be located on the polishing head. 
   In the case that the cooling element does not operate properly, a heat absorbing element  310  may over heat a heat dissipating element  330 . Accordingly, if the cooling element is not properly operating, it may be necessary to inform operators of the current situation by means of an alarm sound, flashing light, etc. Accordingly, a control section may be configured to monitor whether the cooling element is properly operating. 
   A retainer ring in accordance with a still another example embodiment of the present invention will be described below with reference to  FIGS. 6A and 6B . 
   The retainer ring in accordance with still another example embodiment of the present invention may include thermoelectric element protection layers  350 . A thermoelectric element protection layer  350  may be formed of polyurethane to prevent/reduce an insulator  321 , a first lower electrode  322 , a second lower electrode  323 , an upper electrode  326 , a first P-type pellet  324 , and a first N-type pellet  325  from corrosion. 
     FIG. 7  is a flow chart illustrating an operation of a chemical mechanical polishing apparatus according to example embodiments of the present invention. 
   Referring to  FIG. 7 , a wafer held by a wafer carrier by vacuum may be polished by a polishing pad and slurry solution. During the polishing process, heat may be generated due to friction between the wafer and a retainer ring, between the retainer ring and the polishing pad, and between the polishing pad and the wafer (S 1 ). Protecting layers may absorb the heat generated during the polishing process (S 2 ). The heat absorbed by the heat absorbing element may be transferred to a heat dissipating element by the thermoelectric element (S 3 ). A cooling element may cool the heat dissipating element (S 4 ). 
   A retainer ring having a thermoelectric element may directly cool a polishing pad and a wafer, therefore, heat generated during the CMP process may be continually cooled. Accordingly, the temperature of the CMP process may be appropriately maintained, erosion and dishing phenomena occurring around the edge portion of the wafer may be reduced. 
   Temperatures of a polishing pad, an edge of a wafer, and slurry may be quickly reduced, and it may be possible to prevent/reduce the erosion and dishing of the edge portion of the wafer, and to prevent/reduce a non-uniform surface polishing rate due to the thermoelectric element provided to a retainer ring. 
   A cooling element may be disposed on a heat dissipating element of a retainer ring to effectively cool the heat dissipating element of the retainer ring. 
   Grooves may be defined on a first surface of a heat absorbing element of the retainer ring so that slurry solution may be more easily discharged. 
   The heat absorbing element of the retainer ring may be formed of ceramic to reduce or minimize abrasion of the heat absorbing element. 
   A cooling element may be arranged in the polishing head to reduce or minimize the size of the retainer ring. 
   Protective cover layers may be formed on sides of a thermoelectric element to reduce/prevent corrosion of the thermoelectric element. 
   Although example embodiments have been described, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without limiting the scope of example embodiments, as disclosed in the accompanying claims.