Abstract:
A chemical mechanical polishing apparatus includes a polishing pad. A pad conditioner includes a static conditioner head having a surface area configured to contact and condition the pad. The surface area has a first end proximate to an axis of rotation of the pad and a second end remote from the axis of rotation of the pad. The first end defines a first arc length, and the second end defines a second arc length, where the first arc length and the second arc length are substantially identical.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to the planarization of semiconductor substrates, and more particularly to the conditioning of polishing pads.  
           [0002]    Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes successively less planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to planarize the substrate surface to provide a planar surface. Planarization, in effect, polishes away a non-planar, outer surface, whether a conductive, semiconductive, or insulative layer, to form a relatively flat, smooth surface.  
           [0003]    Chemical mechanical polishing (“CMP”) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, with the surface of the substrate to be polished exposed. The substrate is then placed against a rotating polishing pad. The carrier head may also rotate and/or oscillate to provide additional motion between the substrate and polishing surface. Further, polishing slurry, including an abrasive and at least one chemically reactive agent, may be spread on the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate. In some specific applications the abrasive is entrained in, affixed to the surface of, the polishing pad.  
           [0004]    Important factors in the chemical mechanical polishing process are: substrate surface planarity and uniformity, and the polishing rate. Inadequate planarity and uniformity can produce substrate defects. The polishing rate sets the time needed to polish a layer. Thus, it sets the maximum throughput of the polishing apparatus.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    In one embodiment, a chemical mechanical polishing apparatus includes a polishing pad. The pad conditioner includes a static conditioner head having a surface area configured to contact and condition the pad. The surface area has a first end proximate to an axis of rotation of the pad and a second end remote from the axis of rotation of the pad. The first end defines a first arc length, and the second end defines a second arc length, where the first arc length and the second arc length are substantially identical.  
           [0006]    In another embodiment, a chemical mechanical polishing apparatus includes a polishing pad, a wafer carrier carrying a wafer to be polished, and a pad conditioner including a static conditioner head having a surface area configured to contact and condition the pad. The static conditioner head is held at a fixed position. The surface area has a first end proximate to an axis of rotation of the pad and a second end remote from the axis of rotation of the pad. The first end defines a first arc length S 1 =R 1 θ 1  and the second end defines a second arc length S 2 =R 2 θ 2 , where R is a radii from the axis of rotation and θ is an angle subtending an arc section corresponding to the R, wherein S 1  is substantially identical to S 2 .  
           [0007]    In another embodiment, a chemical mechanical polishing apparatus includes a polishing pad. The pad conditioner includes a static conditioner head having a surface area configured to contact and condition the pad. The surface area has a first end proximate to an axis of rotation of the pad and a second end remote from the axis of rotation of the pad. The first end defines a first width, and the second end defines a second width, where the first width is greater than the second width.  
           [0008]    In another embodiment, a pad conditioner includes a static conditioner head having a non-smooth surface area to contact and condition the pad The surface area has a first end proximate to an axis of rotation of the pad and a second end remote from the axis of rotation of the pad. The first end defines a first arc length, and the second end defines a second arc length, where the first arc length and the second arc length are substantially identical.  
           [0009]    In yet another embodiment, a method for operating a polishing apparatus includes polishing a wafer on a polishing pad rotating about an axis at a given speed. Slurry having a chemical agent and an abrasive agent to facilitate the wafer polishing is provided. A non-smooth area of a static conditioner head is contacted to the polishing pad to condition the polishing pad. The conditioner head is held at a fixed position. The non-smooth surface area has a first end proximate to the axis and a second end remote from the axis. The first end defines a first arc length, and the second end defines a second arc length, where the first arc length and the second arc length are substantially identical. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 illustrates a schematic view of a chemical mechanical polishing apparatus.  
         [0011]    [0011]FIG. 2 illustrates a schematic top view of a conditioner head and a polishing pad according to one embodiment of the present invention.  
         [0012]    [0012]FIG. 3 illustrates a schematic top view of a conditioner head according to one embodiment of the present invention.  
         [0013]    [0013]FIG. 4. illustrates a schematic cross-sectional view of the conditioner head taken along the arrow IV of FIG. 3 according to one embodiment of the present invention.  
         [0014]    [0014]FIG. 5 illustrates a schematic cross-sectional view of a conditioner head according to another embodiment of the present invention.  
         [0015]    [0015]FIG. 6 illustrates a schematic top view of a pad conditioner according to one embodiment of the present invention.  
         [0016]    [0016]FIG. 7 illustrates a schematic cross-sectional view of the pad conditioner taken along the arrow VII of FIG. 6 according to one embodiment of the present invention.  
         [0017]    [0017]FIG. 8 illustrates a schematic cross-sectional view of a pad conditioner according to another embodiment of the present invention.  
         [0018]    [0018]FIG. 9 illustrates a schematic, enlarged top view of a conditioner head and a polishing pad according to one embodiment of the present invention.  
         [0019]    [0019]FIG. 10 illustrates a graph showing a preferred shape of a conditioner head according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    [0020]FIG. 1 illustrates a schematic perspective view of a CMP polishing apparatus  100 . The apparatus  100  includes a rotatable platen  102  supporting a polishing pad  104  and a rotatable wafer carrier  106  carrying a wafer (not shown) using hydrodynamic forces. The platen is generally is rigid and may be temperature controlled. The polishing pad  104  is typically comprised of polyurethane or polyurethane impregnated fiber. The wafer carrier  106  has a retaining ring (not shown) to firmly hold the wafer therein during the polishing operation, at which time the wafer carrier oscillates back-and-forth and rotates against the polishing pad, as shown by the arrows in FIG. 1. The wafer carrier also applies a net downward force F 1  uniformly to various parts of the wafer, so that wafer is pressed against the pad during the polishing operation for uniform removal of material.  
         [0021]    The apparatus also includes a pad conditioner  110  having a conditioner head  110  that is directed onto the polishing pad and a slurry dispenser  112  to supply slurry onto the polishing. The slurry includes chemically active and abrasive materials to enhance the wafer planarization. Accordingly, this polishing operation is commonly referred to a chemical mechanical polishing (“CMP”) process.  
         [0022]    The pad conditioner  110  is used to refresh or condition the polishing pad  104  to counteract the pad decay resulting from repeated polishing operations, so that high polishing efficiency and consistency from substrate to substrate may be maintained. An example of such pad decay is the glazing phenomenon that is a complex combination of contamination, thermal, chemical and mechanical damage to the pad material. When the polishing apparatus  100  is in operation, the pad is subject to compression, shear and friction producing heat and wear. Slurry and abraded material from the wafer and pad are pressed into the pores of the pad material and the material itself becomes matted and even partially fused. These effects reduce the pad&#39;s roughness and its ability to apply fresh slurry to the substrate.  
         [0023]    Accordingly, the pad conditioner is used to continually condition the pad by removing trapped slurry, and unmatting or re-expanding the pad material. During conditioning, the conditioner head  110 , generally made of diamond-impregnated ring or disk tools, is pressed against the rotating polishing pad. The pressure and relative motion of the conditioner head  110  erodes a small amount of pad material. Pad erosion is required to keep the surface of the pad free of the material build-up associated with the reaction products of CMP, i.e., spent abrasives and removed dielectric material. Pad conditioning also maintains the micro-texture or roughness of the pad, which tends to smooth during CMP in response to heat-induced viscoelastic flow.  
         [0024]    A pad conditioning process whereby pad conditioning and wafer polishing occur simultaneously is referred to as “in-situ” conditioning. When pad conditioning occurs between the wafer polishing and the conditioning process, it is called “ex-situ” conditioning. The size of the conditioning tools depends on the CMP platform, but they are usually smaller in diameter than the polishing pad. Ring-conditioning tools are usually larger than the wafer diameter. In practice, ring-conditioning tools are positioned at a fixed radial distance (no oscillation) from the polishing pad&#39;s rotational axis. At this location the ring-conditioner rotates and provides the required erosion in the “wafer-track.” The wafer-track is an annular zone on the polishing pad where the oscillating wafer resides during CMP. Disk conditioners are typically smaller than the wafer, and their use requires that they oscillate across the pad surface to provide the necessary cover of the wafer-track. During pad conditioning, the location and rotation rate of the conditioning tools affect the uniformity of erosion in the wafer-track that influences the removal rate stability and polishing uniformity of the CMP process.  
         [0025]    [0025]FIG. 2 illustrates a schematic top view of a polishing apparatus  200  having a static pad conditioner  202  according to one embodiment of the present invention. The pad conditioner  202  is provided on a polishing pad  204  and has a conditioner head  206  for contacting the pad  204 . Other features of the pad conditioner  202  are not depicted in FIG. 2 but are illustrated subsequently in FIGS. 6-8. FIG. 2 is shown for illustrative purposes, as with other figures herein, and does not accurately depict the actual dimensions of the pad conditioner and the polishing pad. In one embodiment, the pad conditioner  110  consists essentially of the conditioner head, in which case the downward force F N  acting on the conditioner head is provided by its own weight.  
         [0026]    Referring to FIGS. 2 and 3, the conditioner head  206  is substantially planar and rigid and has a surface area  208  that is coated with a suitable abrasive material and is directed onto the rotating polishing pad  204  having a surface area  205 . In one embodiment, the conditioner head is constructed of polished glass or ceramic. The surface area  208  of the pad conditioner that contacts the polishing pad is coated preferably with a chemically inert abrasive material, e.g., Diamond, BCN, SIC, SIN, Al 2 O 3 , or the like. The conditioner head is pressed against the pad with a controlled and uniformly distributed force.  
         [0027]    [0027]FIG. 4 shows a cross-sectional view of the conditioner head  206  taken along the arrows IV of FIG. 3. The conditioner head  206  includes a main body  210  and an abrasive material  212  coated thereon. In one embodiment, the entire conditioner head  206  is made of abrasive material.  
         [0028]    [0028]FIG. 5 shows a cross-sectional view of a conditioner head  302  according to one embodiment of the present invention. The conditioner head  302  includes a main body  304  and a lower portion  306  that is removably joined to the main body. For example, the lower portion  306  may be screwed to the main body, adhesively coupled, clamped, or the like. The lower portion  306  includes an abrasive region  308  that is configured to contact and condition the polishing pad. The lower portion of the conditioner head  302  may be replaced with a new lower portion after it becomes worn after repeated conditioning.  
         [0029]    [0029]FIG. 6 shows a schematic top view of a pad conditioner  402  according to one embodiment of the present invention. The pad conditioner  402  includes a conditioner head  404 , a base  406  to support the conditioner head  404 , and a shaft  408  coupled to the conditioner head  404  at one end and the base at the other end.  
         [0030]    [0030]FIG. 7 shows a schematic cross-sectional view of the pad condition  402  taken along the arrows VII of FIG. 6. The pad conditioner  402  includes a connector  410  that couples the conditioner head  404  and the shaft  408 . In one embodiment, the connector  410  may removably couple or join the conditioner head  404  and the shaft  408 , so that the conditioner head  404  may be replaced with a new conditioner head after the former becomes worn upon repeated use.  
         [0031]    In one embodiment, the conditioner head  404  may include a lower portion  412  that is removably coupled or joined to the main body  414 , as in the conditioner head  302  of FIG. 5. The lower portion  412 , rather than the entire conditioner head  404 , is replaced after it becomes worn as in the conditioner head  302  of FIG. 5. The conditioner head  404  may be decoupled from the shaft  408  in order to replace the worn lower portion.  
         [0032]    In one embodiment, the shaft  408  includes a horizontal portion  416  and a vertical portion  418 . The horizontal portion is coupled to the connector  410  at one end and the vertical portion at the other end. The vertical portion, in turn, is coupled to the base  406 . The base includes a horizontal motor (not shown) and a vertical motor (not shown). The horizontal motor enables the vertical portion  418  of the shaft to rotate in a direction parallel to the polishing pad, i.e., in the direction of an arrow  420 , so that the conditioner head may be positioned above the polishing pad to prepare the pad conditioner  402  for a conditioning operation. The conditioner head may be rotated off or otherwise removed from the polishing pad once the conditioning operation has been completed or if the conditioner head  404  needs to be replaced. The conditioner head preferably is replaced away from the polishing pad to prevent the pad from being contaminated with falling debris. The vertical motor enables the vertical portion  418  of the shaft to move in a direction perpendicular to the polishing pad, i.e., in the direction of an arrow  422 , so that the conditioner head  404  may be pressed against the polishing pad to commence a conditioning operation.  
         [0033]    [0033]FIG. 8 shows a schematic cross-sectional view of the pad condition  502  according to one embodiment of the present invention. The pad conditioner  502  includes a conditioner head  504 , a vertical shaft  506 , and a base  508 . The base  508  includes a motor (not shown) that enables the vertical shaft  418  to move in a perpendicular direction to the polishing pad, i.e., in the direction of an arrow  510 , so that the conditioner head  404  may be pressed against the polishing pad to commence a conditioning operation.  
         [0034]    Referring back to FIGS. 2 and 4, in one embodiment, the surface area  208  of the conditioner head  206  is configured to have a shape such that the arc length S of any point on the pad  204  within the wafer tracks, e.g., tracks R 1  and R 2 , is independent of the radial distance of the point with respect to the pad&#39;s rotational axis (typically geometric center). Thus, as the pad rotates beneath the surface  208 , each point experiences a uniform relative displacement across the surface  208 . This conditioner head configuration enables uniform material removal or conditioning on these points and across all points within the wafer track.  
         [0035]    During pad conditioning, pad material is removed by mechanical abrasion via the abrasive material provided on the surface area  208 . Moving the polishing pad relative to the pad conditioner generates mechanical energy. The relative motion generates mechanical energy W as follows:  
           W=F   N μ s   ·ds   (1)  
         [0036]    where F N  is the total force normal to the pad surface, μ s  is the coefficient of sliding friction between the pad and the pad conditioner, and d s  is a differential element of length. In other words, mechanical work is defined by Force x Distance. Accordingly, assuming the conditioner head is applied to the polishing pad with a constant and uniform force, it follows from the above equation (1) that the material removal during pad conditioning is directly proportional to the displacement between the pad conditioner and the polishing pad.  
         [0037]    [0037]FIG. 9 shows an enlarged view of a relevant portion of FIG. 2 illustrating the surface  208  and two hypothetical arc paths on the polishing pad  204  that are traveling under the surface area  208 . The arc length S of a circular arc section subtended by an angle θ (expressed in radiant) can be expressed as follows:  
           S=R·θ   (2)  
         [0038]    Thus, the arc length for the outer radii R 2  is S 2 =R 2 ×θ 2 , and that for the inner radii R 1  is S 1 =R 1 ×θ 1 . According to the equation (1), if S 1 =S 2 , then the mechanical work, and therefore material removal, shall be equal at those points on the polishing pads located at a radius of R 1  and R 2 . Such a condition can be obtained by controlling the angle θ subtending the edges of the pad conditioners to satisfy the following relationship:  
         R 1 θ 1 =R 2 θ 2  or S 1 =S 2   (3)  
         [0039]    Based on the above, the dimension of the surface area  208  of a conditioner head is configured, so that as the radius increases linearly, the angle θ is decreased by a proportional amount according to one embodiment of the present invention. The shape of the conditioner head or surface  208  is determined using the above principle. The pad conditioner&#39;s length is determined preferably by the width of the wafer&#39; track since the length preferably is slightly longer than the wafer track to ensure that the pad is evenly applied over a length scale comparable or larger than the wafer track itself. The size of the annular wafer track includes the wafer diameter, retaining ring width, and an additional amount for wafer oscillation.  
         [0040]    Below is a Table and Graph (FIG. 10) illustrating a static pad conditioner according to one embodiment of the present invention. The pad conditioner is provided with a length of 10 inches to sufficiently cover the wafer-track for an 8-inch wafer, assuming the oscillation during CMP, plus twice the retaining ring width, is &lt;2″. As shown below, a constant arc length is maintained by varying the angle from 180 degrees (R n1 =1 inch) to 18 degrees (R n2 =10 inches).  
                                                                           Table of values for one embodiment of the static pad conditioner                (R) Inches   Radians   Degrees   (S) Inches                            1.00   3.141593   180.000000    3.141593           1.50   2.094395   120.000000    3.141593           2.00   1.570796   90.000000   3.141593           2.50   1.256637   72.000000   3.141593           3.00   1.047198   60.000000   3.141593           3.50   0.897598   51.428571   3.141593           4.00   0.785396   45.000000   3.141593           4.50   0.698132   40.000000   3.141593           5.00   0.628319   36.000000   3.141593           5.50   0.571199   32.727273   3.141593           6.00   0.523599   30.000000   3.141593           6.50   0.483322   27.692308   3.141593           7.00   0.448799   25.714286   3.141593           7.50   0.418879   24.000000   3.141593           8.00   0.392699   22,500000   3.141593           8.50   0.369599   21.176471   3.141593           9.00   0.349066   20.000000   3.141593           9.50   0.330694   18.947368   3.141593           10.00   0.314159   18.000000   3.141593                      
 
         [0041]    Referring to FIG. 10, the shape of a static conditioner head is nearly rectangular at large values of R but tapers off as R decreases. The X-axis represents the length of the pad conditioner, and the Y-axis represents the width of the pad conditioner. By inspection and referring to the equation (1), a simple rectangular conditioner head would wear the polishing pad faster towards the center of the pad, i.e., at R=0. FIG. 11 illustrates a schematic top view of a static pad conditioner  600  satisfying the dimensions disclosed in the Table and Graph provided above. FIG. 11 also illustrates top views of a polishing pad  602  and a wafer  604  being polished thereon.  
         [0042]    While the above embodiments describes the present invention fully, they are provided merely to illustrate the invention. Other modifications or alterations are within the scope of the present invention. For example, the force F N  may be provided by a gas or fluid-filled bladder coupled to the main body  304  and a mechanical assembly, which is firmly attached to the frame of the polishing apparatus. By controlling the pressure within the bladder, a uniform force could be applied to the area of the polishing pad that is contacting the surface area.  
         [0043]    In another embodiment, a non-uniform force F N  may be provided by any means to the main body  304  and a mechanical assembly, which is firmly attached to the frame of the polishing apparatus. By controlling the pressure distribution on the main body or mechanical assembly, a non-uniform pressure could be applied to the area of the polishing pad that is contacting the surface area thereby affecting un-even pad wear, which may be desirable in some specific applications.  
         [0044]    In another embodiment, the static pad conditioning concept described above could be extended to the design of a polishing machine where the object being polished is an annulus or a solid disk, where the area being polished is an annular region and the polishing pad shape is of the ideal shape as described herein.  
         [0045]    In addition, the concept described above is applicable to other systems where uniform translation, polishing, grinding, or any other form of mechanical, physical, or electrical contact is desirable in an annular region of a rotating disk and another contacting body. Examples includes, but not limited to, pad conditioning systems for other polishing systems, such as those in the disk drive industry, the lens/glass polish industry, or the broader semiconductor industry where lapping or polishing is required.  
         [0046]    Alternatively, embodiments of the present invention may be applied to disk brake systems or electrical brush contacts for effecting an electrical connection between the brush and a conductive rotating plate. Accordingly, the embodiments described above should not be used to limit the scope of the present invention. Rather, the scope of the present invention should be interpreted based on the appended claims.