Abstract:
A polishing head assembly for single side polishing of silicon wafers includes a polishing head and a cap. The polishing head includes a top surface and a bottom surface and defines a longitudinal axis extending therethrough. The cap is positioned coaxially with the polishing head and includes an upper surface and a lower surface. The upper surface is spaced from the bottom surface of the polishing head to form a chamber that allows the cap to deflect toward the polishing head.

Description:
CROSS REFERENCE 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/829,685 filed May 31, 2013, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    This disclosure relates generally to polishing of semiconductor or solar wafers and more particularly to single side polishing apparatus and methods for controlling flatness of the wafer. 
       BACKGROUND 
       [0003]    Semiconductor wafers are commonly used in the production of integrated circuit (IC) chips on which circuitry are printed. The circuitry is first printed in miniaturized form onto surfaces of the wafers. The wafers are then broken into circuit chips. This miniaturized circuitry requires that front and back surfaces of each wafer be extremely flat and parallel to ensure that the circuitry can be properly printed over the entire surface of the wafer. To accomplish this, grinding and polishing processes are commonly used to improve flatness and parallelism of the front and back surfaces of the wafer after the wafer is cut from an ingot. A particularly good finish is required when polishing the wafer in preparation for printing the miniaturized circuits on the wafer by an electron beam-lithographic or photolithographic process (hereinafter “lithography”). The wafer surface on which the miniaturized circuits are to be printed must be flat. Similarly, flatness and finish are also important for solar applications. 
         [0004]    The construction and operation of conventional polishing machines contribute to the unacceptable flatness parameters. Polishing machines typically include a circular or annular polishing pad mounted on a turntable or platen for driven rotation about a vertical axis passing through the center of the pad and a mechanism for holding the wafer and forcing it into the polishing pad. The wafer is typically mounted to the polishing head using for example, liquid surface tension or a vacuum/suction. A polishing slurry, typically including chemical polishing agents and abrasive particles, is applied to the pad for greater polishing interaction between the polishing pad and the surface of the wafer. This type of polishing operation is typically referred to as chemical-mechanical polishing (CMP). 
         [0005]    During operation, the pad is rotated and the wafer is brought into contact with and forced against the pad by the polishing head. As the pad wears, e.g., after a few hundred wafers, wafer flatness parameters degrade because the pad is no longer flat, but instead has a worn annular band forming a depression along the polishing surface of the pad. Such pad wear impacts wafer flatness, and may cause “dishing” or “doming” or a combination thereof resulting in a “w-shape”. 
         [0006]    When the flatness of the wafers becomes unacceptable, the worn polishing pad has to be replaced with a new one. Frequent pad replacement adds significant costs to the operation of the polishing apparatus not only because of the number of pads that need to be purchased, stored, and disposed of, but also because of the substantial amount of down time required to change the polishing pad. 
         [0007]    Accordingly, there is a need for a polishing apparatus that has the ability to optimize flatness parameters by modulating the wafer thickness shape in the polishing process for doming, dishing, and +/−w-shape. 
         [0008]    This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
       SUMMARY 
       [0009]    A first aspect is a polishing head assembly for single side polishing of silicon wafers. The polishing head assembly includes a polishing head and a cap. The polishing head includes a top surface and a bottom surface and defines a longitudinal axis extending therethrough. The cap is positioned coaxially with the polishing head and includes an upper surface and a lower surface. The upper surface is spaced from the bottom surface of the polishing head to form a chamber that allows the cap to deflect toward the polishing head. The wafer carrier is disposed adjacent to the cap. 
         [0010]    Another aspect is a single side polishing apparatus for single side polishing of silicon wafers. The single side polishing apparatus includes a polishing head for rotating the wafer in relation to a polishing pad, a cap, and a movable stopper. The polishing head has a polishing side facing a location of the wafer. The cap is mounted in spaced relation from the polishing side of the polishing head and is capable of deflecting under a polishing pressure. The movable stopper is located between the polishing head and the cap to limit movement of the cap with respect to the polishing head along a direction that is perpendicular to the polishing side of the polishing head. 
         [0011]    Another aspect is a method for the polishing of silicon wafers. The method includes providing a polishing apparatus that includes a wafer carrier for retaining a wafer placed therein and a polishing head assembly. The polishing head assembly has a polishing head and a cap attached to a polishing side of the polishing head for rotating the wafer in relation to a polishing pad. The polishing head is moved with respect to the wafer carrier to cause the cap to react against the wafer resulting in a polishing pressure. The cap is deflected with respect to the polishing head. A surface of the wafer is polished by causing rotational movement between the wafer and the polishing pad to form a polished surface on the wafer. The polishing pressure is adjusted to regulate the deflection of the cap for improving flatness of the polished surface. 
         [0012]    Various refinements exist of the features noted in relation to the above-mentioned aspects. Further features may also be incorporated in the above-mentioned aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments may be incorporated into any of the above-described aspects, alone or in any combination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a partially schematic elevation of a single side polisher; 
           [0014]      FIG. 2  is a cross section of a single side polishing head with a domed plate in accordance with one embodiment, the shape of the domed plated being exaggerated for illustration purposes; 
           [0015]      FIG. 3  is a cross section of the single side polishing head of  FIG. 3  under polishing pressure; 
           [0016]      FIG. 4  is a cross section of the single side polishing head of  FIG. 3  under polishing pressure 0.9 P; 
           [0017]      FIG. 5  is a cross section of the single side polishing head of  FIG. 3  under polishing pressure 1.1 P; 
           [0018]      FIG. 6  is a pressure profile graph plotting the correlation of the contact pressure and wafer radius; 
           [0019]      FIG. 7  is a cross section of a single side polishing head with a flat plate in accordance with another embodiment; 
           [0020]      FIG. 8  is a cross section of the single side polishing head of  FIG. 7  with a pressurized section under no polishing pressure; 
           [0021]      FIG. 9  is a cross section of the single side polishing head of  FIG. 7  with a pressurized section under polishing pressure; 
           [0022]      FIG. 10  is a cross section of the single side polishing head of  FIG. 7  with a pressurized section under polishing pressure 0.9 P; 
           [0023]      FIG. 11  is a cross section of the single side polishing head of  FIG. 7  with a pressurized section under polishing pressure 1.1 P; 
           [0024]      FIG. 12  is a cross section of a single side polishing head with a flat plate and two adjustable stoppers in accordance with another embodiment; 
           [0025]      FIG. 13  is a cross section of the single side polishing head of  FIG. 12  with a pressurized section under no polishing pressure; 
           [0026]      FIG. 14  is a cross section of the single side polishing head of  FIG. 12  with a pressurized section under polishing pressure; 
           [0027]      FIG. 15  is a cross section of the single side polishing head of  FIG. 12  with a pressurized section under polishing pressure 0.9 P; 
           [0028]      FIG. 16  is a cross section of the single side polishing head of  FIG. 12  with a center stopper retracted and a pressurized section under polishing pressure 1.3 P; 
           [0029]      FIG. 17  is a cross section of the single side polishing head of  FIG. 12  with stopper ring retracted and a pressurized section under polishing pressure 1.3 P; 
           [0030]      FIG. 18  is a cross section of the single side polishing head of  FIG. 12  with both stoppers retracted and a pressurized section under polishing pressure 1.1 P; 
           [0031]      FIG. 19  is a Doming Correction graph plotting the correlation of the contact pressure and the radius; 
           [0032]      FIG. 20  is a Negative W-factor Correction graph plotting the correlation of the contact pressure and the radius; and 
           [0033]      FIG. 21  is a cross section of a single side polishing head with a flat plate and an inflatable bellow attached to a center stopper in accordance with another embodiment. 
       
    
    
       [0034]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0035]    Generally, and in one embodiment of the present disclosure, a wafer that has previously been rough polished so that it has rough front and back surfaces is first subjected to an intermediate polishing operation in which the front surface of the wafer, but not the back surface, is polished to improve flatness parameters or to smooth the front surface and remove handling scratches. To carry out this operation, the wafer is placed against the polishing head. In this embodiment, the wafer is retained in position against the polishing head by surface tension. The wafer also is placed on a turntable of a machine with the front surface of the wafer contacting the polishing surface of a polishing pad. 
         [0036]    A polishing head mounted on the machine is capable of vertical movement along an axis extending through the wafer. While the turntable rotates, the polishing head is moved against the wafer to urge the wafer toward the turntable, thereby pressing the front surface of the wafer into polishing engagement with the polishing surface of the polishing pad. 
         [0037]    A conventional polishing slurry containing abrasive particles and a chemical etchant is applied to the polishing pad. The polishing pad works the slurry against the surface of the wafer to remove material from the front surface of the wafer, resulting in a surface of improved smoothness. As an example, the intermediate polishing operation preferably removes less than about 1 micron of material from the front side of the wafer. 
         [0038]    The wafer is then subjected to a finish polishing operation in which the front surface of the wafer is finish polished to remove fine or “micro” scratches caused by large size colloidal silica, such as Syton® from DuPont Air Products Nanomaterials, LLC, in the intermediate step and to produce a highly reflective, damage-free front surface of the wafer. The intermediate polishing operation generally removes more of the wafer than the finishing polishing operation. The wafer may be finish polished in the same single-side polishing machine used to intermediate polish the wafer as described above. However, a separate single-side polishing machine may also be used for the finish polishing operation. A finish polishing slurry typically has an ammonia base and a reduced concentration of colloidal silica is injected between the polishing pad and the wafer. The polishing pad works the finish polishing slurry against the front surface of the wafer to remove any remaining scratches and haze so that the front surface of the wafer is generally highly-reflective and damage free. 
         [0039]    Referring to  FIG. 1 , a portion of a single side polishing apparatus is shown schematically and indicated generally at  100 . The single side polisher  100  may be used to polish a front surface of semiconductor wafers W. It is contemplated that other types of single side polishing apparatus may be used. 
         [0040]    The polishing apparatus  100  includes a wafer holding mechanism, e.g., a backing film  110 , a retaining ring  120 , a polishing head assembly  130 , and a turntable  140  having a polishing pad  150 . The backing film  110  is located between a polishing head assembly  130  and the retaining ring  120 , which receives a wafer W. The retaining ring  120  has at least one circular opening to receive the wafer W to be polished therein. The wafer W of this embodiment is retained against the polishing head assembly  130  by surface tension. 
         [0041]    The polishing apparatus  100  applies a force to the polishing head assembly  130  to move the polishing head assembly vertically to raise and lower the polishing head assembly  130  with respect to the wafer W and the turntable  140 . An upward force raises the polishing head assembly  130 , and a downward force lowers the polishing head assembly. As discussed above, the downward vertical movement of the polishing head assembly  130  against the wafer W provides the polishing pressure to the wafer to urge the wafer into the polishing pad  150  of the turntable  140 . As the polishing apparatus  100  increases the downward force, the polishing head assembly  130  moves vertically lower to increase the polishing pressure. 
         [0042]    A portion of the polishing head assembly  130  and polishing pad  150  and turntable  140  are rotated at selected rotation speeds by a suitable drive mechanism (not shown) as is known in the art. The rotational speeds of the polishing pad and the turntable may be the same or different. In some embodiments, the apparatus  100  includes a controller (not shown) that allows the operator to select rotation speeds for both the polishing head assembly  130  and the turntable  140 , and the downward force applied to the polishing head assembly. 
         [0043]    With reference to  FIG. 2 , the polishing head assembly  130  includes a polishing head  160  and a cap  170 . The cap is suitably made of plastic, aluminum, steel, ceramic, such as alumina or silicon carbide, or any suitable material with sufficient stiffness, including coated silicon. 
         [0044]    The cap  170  includes a plate or floor  172  surrounded by an annular wall  174  extending upward therefrom. In a natural or un-deflected state, the floor  172  has a concave shape (relative to the chamber), such that the center of the floor is lower than the perimeter. The floor  172  is capable of temporarily deflecting without permanently deforming. The floor  172  is about 0.118 to about 0.275 inches (3-7 mm) thick, or about 0.625 inches (16 mm) thick for plastic, and has a diameter of about 5.905 to about 6.496 inches (150-165 mm). 
         [0045]    The annular wall  174  is rigidly attached to and extends downward from an edge  162  of the polishing head  160 . Together the polishing head  160  and the cap  170  form a downwardly domed structure. The cap  170  may be attached to the polishing head  160  with bolts or other suitable fasteners. In other embodiments, an adhesive, such as an epoxy, is used to attach the cap  170  to the edge  162  of the polishing head  160 . 
         [0046]    Downward movement of the polishing head assembly  130  causes the cap  170  to contact the wafer W, and deflects the floor  172  upward toward the polishing head  160 . The direction of deflection is perpendicular to the top surface of the wafer W. 
         [0047]    As the polishing pressure of the cap  170  against the wafer W increases, the magnitude of deflection also increases. Regulation of the polishing pressure allows the deflection of the floor  172  to be increased or decreased. As the deflection of the floor  172  is changed, the shape of the floor is also changed. 
         [0048]    Changing the shape of the floor  172  causes a resulting change in the force distribution of the polishing pressure across the wafer W and thereby causes the wafer to bend in response. The change in force distribution also causes a change in the rate of removal of material from the wafer W. Generally, the rate of removal is increased at portions of the wafer W that transfer relatively greater force to the polishing pad  150 . 
         [0049]    As a result, the downward force of the polishing head assembly  130  may be controlled to increase or decrease the deflection of the floor  172  of the cap  170  and thereby adjust the amount of doming or dishing of the wafer. As the polishing pressure is increased, the floor  172  transitions from a natural, un-deflected or downwardly curved shape to a flat shape that is substantially parallel with a bottom surface of the polishing head  160 , and finally to an upwardly curved or convex shape. 
         [0050]    As shown in  FIG. 3 , under a given or predetermined polishing pressure P the floor  172  is deflected to be substantially flat, resulting in a removal profile that is also substantially flat. As shown in  FIG. 4 , lowering the polishing pressure 0.9 P causes both the floor  172  and the removal profile to become downwardly curved. As shown in  FIG. 5 , increasing the polishing pressure 1.1 P causes both the shape of the floor  172  and the removal profile to become dished. Suitably, the change in polishing pressure may range from about 0.7 P to about 1.3 P. Thus, a change in polishing pressure P provides an operator with a control variable and the ability to adjust the polished shape of the wafer W. In some embodiments, the predetermined polishing pressure may range from 1.0 psi to 4.0 psi. In other embodiments, the predetermined polishing pressure may be less than 6.0 psi. 
         [0051]    In some embodiments, the domed shaped plate may be attached to an existing polishing head so as to change the polishing properties of the polisher without extensively reworking the machine or buying a new machine. 
         [0052]    With reference to  FIG. 6 , a plot of a finite element simulation showing the correlation between the contact pressure and the radius are shown. This plot illustrates the ability of this embodiment to modulate the contact pressure profile by increasing or decreasing the standard polishing pressure P resulting in an adjustment of the removal profile. 
         [0053]    With reference to  FIG. 7 , another embodiment of the polishing head assembly  230  has a polishing head  260  and a cap  270 . The cap  270  includes a floor  272  surrounded by an annular wall  274 . The floor  272  is substantially flat in an initial or un-deflected state. The annular wall  274  is rigidly attached to and extends downward from an edge  262  of the polishing head  260  to form a chamber  232  between the floor  272  and the polishing head  260 . The chamber  232  may be connected with a pressurizing source (not shown) to provide a pressurizing media or fluid to the chamber  232 . 
         [0054]    As shown in  FIG. 8 , the chamber  232  may be pressurized causing the floor  272  to deflect into a downward dome shape, similar to floor  172 . The pressure within the chamber  232  does not need to be changed frequently. Therefore, it may be adjusted manually when the polishing head assembly  230  is mounted on the polishing apparatus  100 . In some embodiments, the cap  270  may be used to retrofit an existing polishing head without the need to drill holes through the existing head or spindle for passage of air or fluid through the spindle and rotary unions. 
         [0055]    Similar to the floor  172 , the floor  272  of the cap  270  is adapted to temporarily deflect in a direction that is perpendicular to the polishing surface as the polishing pressure is increased. The cap is not permanently deflected or deformed by the pressure. The floor  272  transitions from a pressurized deflected or downwardly curved shape to a flat shape that is substantially parallel with a bottom surface of the polishing head  260 , and finally to a upwardly curved or convex shape as the polishing pressure is increased. 
         [0056]    As shown in  FIG. 9 , under a given or predetermined polishing pressure P the floor  272  is deflected to be substantially flat, resulting in a removal profile that is also substantially flat. As shown in  FIG. 10 , lowering the polishing pressure 0.9 P causes both the floor  272  and the removal profile to become downwardly curved. As shown in  FIG. 11 , increasing the polishing pressure 1.1 P causes both the shape of the floor  272  and the removal profile to become dished. Thus, a change in polishing pressure P provides an operator the ability to adjust the polished shape of the wafer W. 
         [0057]    As described above, the polishing system is capable of adjusting pressure distribution to control the shape of a polished wafer, e.g., for minimizing doming and dishing of the wafer after polishing. 
         [0058]    With reference to  FIG. 12 , another embodiment of the polishing head assembly  330  is adapted to adjust pressure distribution to a wafer during the polishing process for controlling or minimizing doming, dishing, and w-shape cross section of the wafer. 
         [0059]    The polishing head assembly  330  has a polishing head  360 , a cap  370 , a stopper ring  380 , and a center stopper  382 . The cap  370  includes a floor  372  surrounded by an annular wall  374 . The floor  372  is substantially flat in an initial or un-deflected state. The annular wall  374  is rigidly attached to and extends downward from an edge  362  of the polishing head  360  to form a chamber  332  between the floor  372  and the polishing head  360 . The chamber  332  may be connected with a pressurizing source (not shown) to provide a pressurizing fluid to the chamber  332 . 
         [0060]    As shown in  FIG. 13 , the chamber  332  may be pressurized causing the floor  372  to deflect into a downward dome shape, similar to floors  172  and  272 . The pressure within the chamber  332  does not need to be changed frequently. Therefore, it may be adjusted manually when the polishing head assembly  330  is mounted on the polishing apparatus  100 . In some embodiments, the cap  370  may be used to retrofit an existing polishing head without the need to drill holes through the existing head for passage of air or fluid through the spindle and rotary unions. 
         [0061]    Similar to the floors  172  and  272 , the floor  372  of the cap  370  is adapted to temporarily deflect in a direction that is perpendicular to the polishing surface as the polishing pressure P is increased. The cap is not permanently deflected or deformed by the pressure. The floor  372  transitions from a pressurized deflected or downwardly curved shape to a flat shape that is substantially parallel with a bottom surface of the polishing head  360 , and finally to a upwardly curved or convex shape. 
         [0062]    As shown in  FIG. 14 , under a given or predetermined polishing pressure P, the floor  372  is deflected to be substantially flat, resulting in a removal profile that is also substantially flat. As shown in  FIG. 15 , reducing the polishing pressure 0.9 P causes both the floor  372  and the removal profile to become downwardly curved. 
         [0063]    Stopper ring  380  and center stopper  382  limit the upward deflection of the floor  372 . The stopper ring  380  is spaced inward from the outer circumference and is annular in shape. The center stopper  382  is co-axially aligned with the polishing head  360 , the cap  370 , and the stopper ring  380 . With additional reference to  FIG. 12 , the stopper ring  380  and the center stopper  382  extends from the bottom surface of the polishing head  360  to an inner or top surface of the floor  372 . The height of the stopper ring  380  and the center stopper  382  are substantially equivalent to the between the polishing head  360  and the floor  372 . 
         [0064]    With reference to  FIGS. 15-18 , the height of each the stopper ring  380  and the center stopper  382  may be adjusted to vary the deflection shape of the floor  372 . 
         [0065]    As shown in  FIG. 16 , reducing the height of the center stopper  382  and increasing the polishing pressure 1.3 P causes both the shape of the floor  372  and the removal profile to become w-shaped. As shown in  FIG. 17 , reducing the height of the stopper ring  380  and increasing the polishing pressure 1.3 P causes both the shape of the floor  372  and the removal profile to become m-shaped. As shown in  FIG. 18 , reducing the height of both the stopper ring  380  and the center stopper  382 , and increasing the polishing pressure 1.1 P causes both the shape of the floor  372  and the removal profile to become domed. Thus, a change in polishing pressure provides the operator with the ability to adjust the polished shape of the wafer W. 
         [0066]    Finite element simulation results illustrating this embodiment&#39;s ability to modulate contact pressure profiles for adjusting doming and w-shape wafer profiles are shown in  FIGS. 19 and 20 .  FIG. 19  is a doming correction graph that plots the correlation of the contact pressure and the radius in accordance with the embodiment above is shown.  FIG. 20  is a negative w-factor correction graph that plots the correlation of contact pressure and the radius in accordance with the embodiment above is shown. 
         [0067]    With reference to  FIG. 21 , another embodiment of the polishing head assembly  430  is adapted to adjust pressure distribution to a wafer during the polishing process for controlling or minimizing doming, dishing, and w-shape cross section of the wafer. 
         [0068]    The polishing head assembly  430  has a polishing head  460 , a cap  470 , and a center stopper  480 . The cap  470  includes a floor  472  that is rigidly attached to edges  462  of the polishing head  460  with screws  464  and extends across the edges to form a chamber  432  between the floor and the polishing head. In other embodiments, an adhesive is used to attach the floor  472  to the edges  462  of the polishing head  460 , instead of screws  464 . The floor  472  is substantially flat in an initial or un-deflected state. The chamber  432  is connected with a first pressurizing source FS through a chamber passageway  466  and connector  486  to provide a pressurizing fluid to the chamber  432  that may cause the floor  472  to deflect into a downward dome shape, similar to floors  172 ,  272 , and  372 . 
         [0069]    Similar to the floors  172 ,  272 , and  372 , the floor  472  of the cap  470  is adapted to temporarily deflect in a direction that is perpendicular to the polishing surface as the polishing pressure is increased. The cap  470  is not permanently deflected or deformed by the pressure. The floor  472  has the ability to transition from a pressurized deflected or downwardly curved shape to a flat shape that is substantially parallel with a bottom surface of the polishing head  460 , and finally to an upwardly curved or convex shape based on the amount of pressurizing fluid supplied to the chamber  432 . 
         [0070]    Under a given or predetermined polishing pressure P, the floor  472  is deflected to be substantially flat, resulting in a removal profile that is also substantially flat. Reducing the polishing pressure 0.9 P causes both the floor  472  and the removal profile to become downwardly curved. 
         [0071]    The center stopper  480  includes a stop  482  connected with inflatable bellows  484 . The bellow  484  is connected with and extends into the chamber  432  from the polishing head  460 . The height of the stop  482  is adjusted by increasing or decreasing the pressure within the bellows  484 , which is connected with a second pressurizing source SS through a center passageway  468  and a connector  488 . Adjustment of the pressure within the bellows  484  may either limit the upward deflection of the floor  472  or to deflect the floor  472  outward. The first and second pressurizing sources FS and SS may be connected through a controller  490  to respective connectors  486  and  488 . In some embodiments, first and second pressurizing sources FS and SS are the same pressurizing source and are connected with the respective connectors  486  and  488  through the controller  490 , which may include a divider and control valves (not shown). In some embodiments, the polishing head assembly  430  does not include a center stopper  480 . In these embodiments, the first pressurizing source FS may be supplied to the chamber  432  through the center of the polishing head  460 . 
         [0072]    The center stopper  480  is co-axially aligned with both the polishing head  460  and the cap  470 . During operation, the center stopper  482  may extend from the bottom surface of the polishing head  460  to an inner or top surface of the floor  472 , such that the height of the center stopper  480  is substantially equivalent to the chamber between the polishing head  460  and the floor  472 . 
         [0073]    In a method of one embodiment, a polishing process of a wafer is controlled by adjustment of the polishing pressure used in the polishing apparatus  100  to change the shape of a polishing head assembly to regulate the polished shape of a wafer W. In some embodiments, the polishing apparatus is a single side polisher. In another embodiment, the polishing pressure is regulated by a controller before or during the polishing process. 
         [0074]    The method includes providing a polishing apparatus with a turntable for rotating a polishing pad in relation to the wafer and a polishing head assembly with a cap attached to a polishing side of a polishing head. The cap is moved with respect to the wafer to cause a polishing pressure from the wafer to react against the cap. The cap is deflected with respect to the polishing head. A liquid may be applied to the cap to wet it, such that the wafer is held in place, against the cap, by surface tension when the wafer is placed against it. The liquid on the lower surface of the cap can be squeezed to almost zero film thickness to retain the wafer by surface tension. 
         [0075]    The polishing pressure reacting against the cap is adjusted to regulate the deflection of the cap for improving flatness of the polished surface. A surface of the wafer is polished by causing movement between the wafer and the polishing pad to form a polished surface on the wafer. An internal pressure within a chamber between the polishing head and the cap may be adjusted to regulate deflection of the cap with respect to the wafer for improving flatness of the polished surface. 
         [0076]    Changing the shape of the cap from dish to dome or vice versa changes the material removal profile of the wafer and thus, changes the shape of the polished wafer. A domed head will cause more material removal in the center and thus make the wafer thickness profile dished relative to its thickness profile before polishing. While a dished head will remove more material on the edges of the wafer making the wafer domed relative to its thickness profile before polishing. In some embodiments, the shape of the polishing head may be changed by adding a low stiffness cap to the bottom of the existing head and then regulating the polishing pressure to deflect the cap to change its shape. 
         [0077]    The embodiments described herein provide the ability to modulate the polishing head for doming, dishing, and +/−w-shape to enable an efficient and economical polishing method of processing semiconductor wafers. The method improves wafer yield and process capability, while reducing product tolerances and the time needed for maintenance associated with the replacement of the polishing pads and templates mounted on the single side polishing head. 
         [0078]    When introducing elements of the present invention or the embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., “top”, “bottom”, “side”, “down”, “up”, etc.) is for convenience of description and does not require any particular orientation of the item described. 
         [0079]    As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawing[s] shall be interpreted as illustrative and not in a limiting sense.