Abstract:
The invention provides a polishing pad suitable for polishing or planarizing at least one of semiconductor, optical and magnetic substrates. The polishing pad includes a polishing layer having a polymeric matrix, a thickness and a polishing track representing a working region of the polishing layer for polishing or planarizing. Radial drainage grooves extend through the polishing track facilitate polishing debris removal through the polishing track and underneath the at least one of semiconductor, optical and magnetic substrates and then beyond the polishing track toward the perimeter of the polishing pad during rotation of the polishing pad.

Description:
BACKGROUND 
       [0001]    The present invention relates to grooves for chemical mechanical polishing pads. More particularly, the present invention relates to groove designs for reducing defects during chemical mechanical polishing. 
         [0002]    In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited onto and removed from a surface of a semiconductor wafer. Thin layers of conducting, semiconducting and dielectric materials may be deposited using a number of deposition techniques. Common deposition techniques in modern wafer processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) and electrochemical plating, among others. Common removal techniques include wet and dry isotropic and anisotropic etching, among others. 
         [0003]    As layers of materials are sequentially deposited and removed, the uppermost surface of the wafer becomes non-planar. Because subsequent semiconductor processing (e.g., metallization) requires the wafer to have a flat surface, the wafer needs to be planarized. Planarization is useful for removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches and contaminated layers or materials. 
         [0004]    Chemical mechanical planarization, or chemical mechanical polishing (CMP), is a common technique used to planarize or polish work pieces such as semiconductor wafers. In conventional CMP, a wafer carrier, or polishing head, is mounted on a carrier assembly. The polishing head holds the wafer and positions the wafer in contact with a polishing layer of a polishing pad that is mounted on a table or platen within a CMP apparatus. The carrier assembly provides a controllable pressure between the wafer and polishing pad. Simultaneously, a polishing medium (e.g., slurry) is dispensed onto the polishing pad and is drawn into the gap between the wafer and polishing layer. The polishing pad and wafer typically rotate relative to one another to polish a substrate. As the polishing pad rotates beneath the wafer, the wafer sweeps out a typically annular polishing track, or polishing region, wherein the wafer&#39;s surface directly confronts the polishing layer. The wafer surface is polished and made planar by chemical and mechanical action of the polishing layer and polishing medium on the surface. 
         [0005]    Reinhardt et al., U.S. Pat. No. 5,578,362 discloses the use of grooves to provide macrotexture to the pad. In particular, it discloses a variety of patterns, contours, grooves, spirals, radials, dots or other shapes. Specific examples included in Reinhardt are the concentric circular and the concentric circular superimposed with and X-Y groove. Because the concentric circular groove pattern provides no direct flow path to the edge of the pad, the concentric circular groove has proven the most popular groove pattern. 
         [0006]    Lin et al., in U.S. Pat. No. 6,120,366, at  FIG. 2 , disclose a combination of circular plus radial grooves. This example illustrates adding twenty-four radial grooves to a concentric circular groove pattern. The disadvantage of this groove pattern is that it provides limited improvement in polishing with a substantial increase in slurry usage. 
         [0007]    Notwithstanding, there is a continuing need for chemical mechanical polishing pads having better combination of polishing performance and slurry usage. Furthermore, there is a need for grooves that reduce defects and increase the useful polishing pad lifetime. 
       STATEMENT OF INVENTION 
       [0008]    An aspect of the invention provides a polishing pad suitable for polishing or planarizing at least one of semiconductor, optical and magnetic substrates with a polishing fluid and relative motion between the polishing pad and the at least one of semiconductor, optical and magnetic substrates, the polishing pad comprising the following: a polishing layer having a polymeric matrix and a thickness, the polishing layer including a center, a perimeter, a radius extending from the center to the perimeter and a polishing track that surrounds the center intersects the radius, the polishing track representing a working region of the polishing layer for polishing or planarizing the at least one of semiconductor, optical and magnetic substrates; a plurality of feeder grooves (δ) intersecting the radius, the feeder grooves (δ) having land areas between the feeder grooves (δ) for polishing or planarizing of the at least one of semiconductor, optical or magnetic substrates with the polishing pad and the polishing fluid, the plurality of feeder grooves (δ) having an average cross-sectional feeder area (δ a ), the average cross-sectional feeder area (δ a ) being total cross-sectional area of each feeder groove divided by total number of feeder grooves (δ); at least one radial drainage groove (ρ) in the polishing layer intersecting with the plurality of feeder grooves (δ) for allowing the polishing fluid to flow from the plurality of feeder grooves (δ) to the at least one radial drainage groove (ρ) and the at least one radial drainage groove (ρ) having an average drainage cross-sectional area (ρ a ), the average drainage cross-sectional area of the at least one radial drainage groove (ρ a ) being greater than the average cross-sectional feeder (δ a ) area as follows: 
         [0000]      2*δ a ≦ρ a ≦8*δ a  
 
         [0009]    wherein (n r ) represents number of radial grooves and (n f ) represents the number of feeder grooves and 
         [0000]      (0.15) n   f *δ a   ≦n   r *ρ a ≦(0.35) n   f *δ a  
 
         [0000]    and the at least one radial drainage groove (ρ) extending through the polishing track for facilitating polishing debris removal through the polishing track and underneath the at least one of semiconductor, optical and magnetic substrates and then beyond the polishing track toward the perimeter of the polishing pad during rotation of the polishing pad. 
         [0010]    An alternative aspect of the invention provides a polishing pad suitable for polishing or planarizing at least one of semiconductor, optical and magnetic substrates with a polishing fluid and relative motion between the polishing pad and the at least one of semiconductor, optical and magnetic substrates, the polishing pad comprising the following: a polishing layer having a polymeric matrix and a thickness, the polishing layer including a center, a perimeter, a radius extending from the center to the perimeter and a polishing track that surrounds the center intersects the radius, the polishing track representing a working region of the polishing layer for polishing or planarizing the at least one of semiconductor, optical and magnetic substrates; a plurality of feeder grooves (δ) intersecting the radius, the feeder grooves (δ) having land areas between the feeder grooves (δ) for polishing or planarizing of the at least one of semiconductor, optical or magnetic substrates with the polishing pad and the polishing fluid, the plurality of feeder grooves (δ) having an average cross-sectional feeder area (δ a ), the average cross-sectional feeder area (δ a ) being total cross-sectional area of each feeder groove divided by total number of feeder grooves (δ); at least one radial drainage groove (ρ) in the polishing layer intersecting with the plurality of feeder grooves (δ) for allowing the polishing fluid to flow from the plurality of feeder grooves (δ) to the at least one radial drainage groove (ρ) and the at least one radial drainage groove (ρ) having an average drainage cross-sectional area (ρ a ), the average drainage cross-sectional area of the at least one radial drainage groove (ρ a ) being greater than the average cross-sectional feeder (δ a ) area as follows: 
         [0000]      2*δ a ≦ρ a ≦8*δ a  
 
         [0011]    wherein (n r ) represents number of radial grooves and (n f ) represents the number of feeder grooves and 
         [0000]      (0.15) n   f *δ a   ≦n   r *ρ a ≦(0.35) n   f *δ a  
 
         [0012]    wherein n r  equals a number between 2 and 12 and the at least one radial drainage groove (ρ) extending through the polishing track for facilitating polishing debris removal through the polishing track and underneath the at least one of semiconductor, optical and magnetic substrates and then beyond the polishing track toward the perimeter of the polishing pad during rotation of the polishing pad. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a top view schematic of a prior art circular plus radial groove pattern. 
           [0014]      FIG. 2  is a partial broken away schematic top view of the debris removal groove of the invention. 
           [0015]      FIG. 2A  is a partial broken away schematic top view of the debris removal groove of the invention that includes a perimeter land area. 
           [0016]      FIG. 3  is a partial broken away schematic top view of the debris removal groove of the invention illustrating the flow through feeder and debris removal grooves. 
           [0017]      FIG. 3A  is a partial broken away schematic top view of the debris removal groove of the invention illustrating the flow through feeder and debris removal grooves that includes a perimeter land area. 
           [0018]      FIG. 4  is a top view schematic of a debris groove pattern of the invention having one debris removal channel and a wafer substrate. 
           [0019]      FIG. 5  is a top view schematic of a debris groove pattern of the invention having two debris removal channels and a wafer substrate. 
           [0020]      FIG. 6  is a top view schematic of a debris groove pattern of the invention having four debris removal channels. 
           [0021]      FIG. 6A  is a top view schematic of a debris groove pattern of the invention having four debris removal channels that includes a perimeter land area. 
           [0022]      FIG. 7  is a top view schematic of a debris groove pattern of the invention having eight debris removal channels. 
           [0023]      FIG. 8  is a top view schematic of a debris groove pattern of the invention having sixteen debris removal channels. 
           [0024]      FIG. 9  is a top view schematic of a debris groove pattern of the invention having eight tapered debris removal channels. 
           [0025]      FIG. 10  is plot of radial drainage groove ratio as a function of the number of drainage grooves deployed. 
           [0026]      FIG. 11  is a plot of total defects versus time that includes polishing pad groove patterns of the invention. 
           [0027]      FIG. 12  is a plot of total defects versus time for control pad versus 90 mil (0.23 cm) radial overlay samples of the invention. 
           [0028]      FIG. 13  is a plot of a post-HF etch defect summary that includes polishing pad groove patterns of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The removal process in closed cell pad materials occurs in a thin lubrication film that contains asperities on the pad side. In order for removal to occur, the asperities must come into direct, or semi-direct, contact with the substrate surface. This is affected by tailoring the surface texture to facilitate liquid transport and relief of hydrostatic pressure, and incorporating grooves or other sorts of macrotexture to facilitate drainage. Maintenance of well controlled contact is relatively sensitive to process conditions, maintenance of the texture in the land area between the grooves, and a variety of other variables. 
         [0030]    The local environment in the substrate contact zone in current pads has characteristics as follows: 
         [0031]    The surface/volume ratio (S/V) is quite high both on the wafer side and the pad side, likely &gt;200:1. This makes liquid transport within the lubrication film quite difficult. More particularly, given the mass removal rates during polishing, the lubrication film is significantly depleted in reactants and significantly enriched in reaction products. 
         [0032]    Liquid temperatures are well above ambient, with large depth and lateral gradients. This has been studied internally in significant detail at a macroscopic and microscopic level. The polishing process consumes a great deal of energy, not all of which results in removal. Contact or near-contact friction and viscous friction within the liquid gives rise to significant contact heating. Since the pad is an efficient insulator, the majority of the generated heat is dissipated through the liquid. Thus the local environment within the lubrication film, especially near asperities, is mildly hydrothermal. The temperature gradients, together with the high S/V provide a driving force for precipitation of reaction products within the textural volume, particularly at the pad surface. Since these are likely to be quite large, and are expected to grow in size over time, this may be one of the primary mechanisms for producing microscratch defects. Silica precipitation is a major concern, as the temperature effect on monomer solubility is quite steep. 
         [0033]    From the frame of reference of a point on the substrate surface, the thermal and reaction history undergoes extreme cyclic variation. A significant contribution to this cyclic variation is the need for grooves in the pad (to affect uniform contact with the wafer). The liquid environment in the groove is significantly different than in the land area. It is significantly cooler, significantly enriched in reactant, and significantly lower in reaction products. Thus, every point on the wafer sees rapid cycling between these two very different environments. This can provide a driving force for redeposition of polishing byproducts onto the wafer surface, particularly at the trailing edge of contact. 
         [0034]    The slurry transport onto the land areas during wafer contact occurs via the grooves. Unfortunately, the grooves serve two purposes; feeding in fresh slurry, and removing spent slurry. In all current pad designs, this must occur simultaneously in the same volume. Thus, the lands are not fed by fresh slurry but by a variable mixture. The location where variable mixing occurs is known as the backmixing zone. While it can be mitigated through groove design, it cannot be eliminated. This constitutes another significant source of large particles for both scratching and residual deposition. The largest concern is that if the slurry in the grooves is not continuously refreshed, formation and growth of large aggregated particles will occur continuously. Given the simultaneous introduction of fresh slurry, and undirected liquid transport, these large particles will eventually be washed onto the land surface in greater and greater numbers, giving rise to a progressive increase in scratch defects. This effect is commonly observed during the use of the pad, regardless of process conditions or mode of conditioning. Defectivity changes during the pad lifetime have three regimes as follows: (a) initial high defectivity when a new pad is introduced (break-in); (b) break-in defectivity decreases to a low steady state for the portion of its use; and (c) end of life state, where both defectivity and wafer non-uniformity rise to undesirably high levels. From the above, it is apparent that preventing or delaying regime (c) improves the useful polishing lifetime of the pad. 
         [0035]    The most commonly used feeder groove types are circular. When these circular grooves intersect radial drainage grooves they form arcs. Alternatively, the feeder grooves may be linear segments or sinusoidal waves. Many different feeder groove widths, depths, and pitches are commercially available. 
         [0036]    Prior art grooves are generally developed empirically to improve rate uniformity and pad lifetime by controlling the hydrodynamic response. This generally results in relatively thin grooves, especially for circular designs. The most widely employed circular groove is the 1010 groove manufactured to groove specifications as follows: 0.020 in. wide ×0.030 in. deep×0.120 in pitch (0.050 cm wide×0.076 cm deep×0.305 cm pitch). Even connected grooves of these dimensions are not efficient vehicles for transporting liquids due to the low cross-sectional area. An additional issue is the roughness of the exposed pad surfaces. A closed cell porous polymer, such as IC1000, typically has a surface roughness of ˜50 microns. For the 1010 groove, which has a surface area/liquid volume ratio of &gt;50:1, the fraction of liquid volume contained in the side-wall texture is quite high (˜11%). This leads to stagnation of flow at the side-walls. This is a source of aggregation of waste products, which grow over time into large and damaging point sources of scratches if re-introduced onto the pad surface. Since there is no directional flow out of the grooves, the addition of a means of removing slurry efficiently from the grooves by addition of at least one drainage groove prevents large particle agglomeration or growth, and, therefore, reduce scratches. While it is expected that improved groove drainage would have an immediate beneficial effect, the largest benefit is the increased working lifetime prior to the onset of the end of life effects. 
         [0037]    Referring to  FIG. 1 , polishing pad  10 includes a combination of circular grooves  12  and radial grooves  16 . Flat, typically porous land areas  14 , divide the circular grooves  12  and radial grooves  16 . During polishing, circular grooves  12  combine with radial grooves  16  to distribute polishing slurry or polishing solution to land areas  14  for interaction with a substrate, such as at least one of a semiconductor, optical or magnetic substrate. The circular grooves  12  and radial grooves  16  have a uniform cross section. The problem with these groove patterns is that over time polishing debris collects in the grooves  12  and  16  then periodically moves to land areas  14  where it imparts defects, such as scratch defects of the substrate. 
         [0038]    Referring to  FIG. 2 , polishing pad  200  includes feeder grooves  202 A,  204 A,  206 A,  208 A and  202 B,  204 B,  206 B,  208 B that can all flow into radial drainage groove  216 . In this embodiment, the radial drainage groove  216  has a depth “D” equal to the depth of the feeder grooves. During polishing, feeder grooves  202 A,  204 A,  206 A,  208 A and  202 B,  204 B,  206 B,  208 B and radial drainage groove  216  distribute polishing slurry or solution over land areas  214 . The arrows indicate the flow of the polishing slurry or solution to and past the polishing pad  200 &#39;s perimeter wall  234 . During clockwise polishing, flow from feeder grooves  202 A,  204 A,  206 A and  208 A is greater than flow from feeder grooves  202 B,  204 B,  206 B and  208 B. During counterclockwise polishing, flow from feeder grooves  202 B,  204 B,  206 B and  208 B is greater than flow from feeder grooves  202 A,  204 A,  206 A and  208 A. This optional embodiment allows all polishing debris an unencumbered exit from the polishing pad  200  through radial drainage groove  216 . 
         [0039]    Referring to  FIG. 2A , polishing pad  200  includes feeder grooves  202 A,  204 A,  206 A and  202 B,  204 B,  206 B that can all flow into radial drainage groove  216 . In this embodiment, the radial drainage groove  216  has a depth “D” equal to the depth of the feeder grooves or the height of side walls  232 . During polishing, feeder grooves  202 A,  204 A,  206 A and  202 B,  204 B,  206 B and radial drainage groove  216  distribute polishing slurry or solution over land areas  214 . From drainage groove  216  the polishing slurry or solution flows through perimeter grooves  210 A and  210 B. The polishing slurry or solution then exits perimeter grooves  210 A and  210 B over perimeter land area  220  and past perimeter wall  222 . The arrows indicate the flow of the polishing slurry or solution to the perimeter grooves  210 A and  210 B, over perimeter land area  220  and past the polishing pad  200 &#39;s perimeter wall  222 . During clockwise polishing, flow from feeder grooves  202 A,  204 A and  206 A is greater than flow from feeder grooves  202 B,  204 B and  206 B. During counterclockwise polishing, flow from feeder grooves  202 B,  204 B and  206 B is greater than flow from feeder grooves  202 A,  204 A and  206 A. This optional embodiment slows the exit of polishing slurry or solution and can increase polishing efficiency for some polishing combinations. 
         [0040]    Referring to  FIG. 3 , polishing pad  300  includes feeder grooves  302 A,  304 A,  306 A,  308 A and  302 B,  304 B,  306 B,  308 B that can all flow into radial drainage groove  316 . In this embodiment, the radial drainage groove  316  has a depth “D” greater than the depth D 1  of the feeder grooves  302 A,  304 A,  306 A,  308 A and  302 B,  304 B,  306 B,  308 B. In particular, drainage groove  316  extends additional depth D 2  below the depth D 1  of the feeder grooves  302 A,  304 A,  306 A,  308 A and  302 B,  304 B,  306 B,  308 B. The height of side walls  332  is equal to depth D 1 plus depth D 2 . During polishing, feeder grooves  302 A,  304 A,  306 A,  308 A and  302 B,  304 B,  306 B,  308 B and radial drainage groove  316  distribute polishing slurry or solution over land areas  314 . The arrows indicate the flow of the polishing slurry or solution to and past the polishing pad  300 &#39;s perimeter wall  334 . During clockwise polishing, flow from feeder grooves  302 A,  304 A,  306 A and  308 A is greater than flow from feeder grooves  302 B,  304 B,  306 B and  308 B. During counterclockwise polishing, flow from feeder grooves  302 B,  304 B,  306 B and  308 B is greater than flow from feeder grooves  302 A,  304 A,  306 A and  308 A. This optional embodiment allows all polishing debris an unencumbered exit from the polishing pad  300  through radial drainage groove  316 . 
         [0041]    Referring to  FIG. 3A , polishing pad  300  includes feeder grooves  302 A,  304 A,  306 A and  302 B,  304 B,  306 B that can all flow into radial drainage groove  316 . In this embodiment, the radial drainage groove  316  has a depth “D” greater than the depth D 1  of the feeder grooves  302 A,  304 A,  306 A,  308 A and  302 B,  304 B,  306 B,  308 B. In particular, drainage groove  316  extends additional depth D 2  below the depth D 1  of the feeder grooves  302 A,  304 A,  306 A,  308 A and  302 B,  304 B,  306 B,  308 B. This design facilitates the flow of high density polishing debris over perimeter land  320  area to the polishing pad  300 &#39;s perimeter wall  322 . During polishing, feeder grooves  302 A,  304 A,  306 A and  302 B,  304 B,  306 B and radial drainage groove  316  distribute polishing slurry or solution over land areas  314 . From drainage groove  316  the polishing slurry or solution flows through perimeter grooves  310 A and  310 B. The polishing slurry or solution then exits perimeter grooves  310 A and  310 B over perimeter land area  320  and past perimeter wall  322 . The arrows indicate the flow of the polishing slurry or solution to the perimeter grooves  310 A and  310 B, over perimeter land area  320  and past the polishing pad  300 &#39;s perimeter wall  322 . During clockwise polishing, flow from feeder grooves  302 A,  304 A and  306 A is greater than flow from feeder grooves  302 B,  304 B and  306 B. During counterclockwise polishing, flow from feeder grooves  302 B,  304 B and  306 B is greater than flow from feeder grooves  302 A,  304 A, and  306 A. This optional embodiment slows the exit of polishing slurry or solution and can increase polishing efficiency for some polishing combinations. 
         [0042]    Referring to  FIG. 4 , polishing pad  400  has center  401  and perimeter  405  where radius r extends from center  401  to perimeter  405 . In this embodiment, wafer  440  moves with respect to the polishing pad  400  around the wafer track marked with parallel lines and over a single radial drainage groove  416 .  FIG. 4  shows the wafer covering multiple feeder grooves  412  and land areas  414 . The radial drainage groove  416  drains all the feeder grooves in the wafer track and outside the wafer track. 
         [0043]    Referring to  FIG. 5 , polishing pad  500  illustrates wafer  540  that moves with respect to the polishing pad  500  around the wafer track marked with parallel lines and over a two radial drainage grooves  516 A and  516 B spaced 180° apart.  FIG. 5  shows the wafer covering multiple feeder grooves  512  and land areas  514 . In particular, the radial drainage grooves  516  extend through the polishing track for facilitating polishing debris removal through the polishing track and underneath the wafer and then beyond the polishing track toward the perimeter  505  of the polishing pad  500  during rotation of the polishing pad  500 . The radial drainage grooves  516 A and  516 B drain all the feeder grooves in the wafer track and outside the wafer track. 
         [0044]    Referring to  FIG. 6 , polishing pad  600  illustrates four radial drainage grooves  616 A to  616 D spaced 90° apart. Alternatively, the spacing of the radial drainage and feeder grooves could be uneven. During operation, polishing slurry or solution flows outward toward perimeter  605  over the land areas  614  and through the radial drainage grooves  616 A to  616 D. The radial drainage groove  616 A to  616 D drain all the feeder grooves  612  in the wafer track (not seen) and outside the wafer track. 
         [0045]    Referring to  FIG. 6A , polishing pad  600  illustrates four radial drainage grooves  616 A to  616 D spaced 90° apart. Alternatively, the spacing of the radial drainage and feeder grooves could be uneven. During operation, polishing slurry or solution flows outward toward perimeter  605  over the land areas  614  and through the radial drainage grooves  616 A to  616 D. Before reaching the perimeter  605 , the polishing slurry or solution flows into perimeter groove  610  and from perimeter groove  610  over perimeter land area  620 . The radial drainage groove  616 A to  616 D drain all the feeder grooves  612  in the wafer track (not seen) and outside the wafer track. 
         [0046]    Referring to  FIG. 7 , polishing pad  700  illustrates eight radial drainage grooves  716 A to  716 H spaced 45° apart. Alternatively, the spacing of the radial drainage and feeder grooves could be uneven. During operation, polishing slurry or solution flows outward toward perimeter  705  over the land areas  714  and through the radial drainage grooves  716 A to  716 H. The radial drainage grooves  716 A to  716 H drain all the feeder grooves  712  in the wafer track (not seen) and outside the wafer track. 
         [0047]    Referring to  FIG. 8 , polishing pad  800  illustrates sixteen radial drainage grooves  916 A to  916 P spaced 22.5° apart. Alternatively, the spacing of the radial drainage and feeder grooves could be uneven. During operation, polishing slurry or solution flows outward toward perimeter  805  over the land areas  814  and through the radial drainage grooves  816 A to  816 P. The radial drainage groove  816 A to  816 P drain all the feeder grooves  812  in the wafer track (not seen) and outside the wafer track. 
         [0048]    Referring to  FIG. 9 , polishing pad  900  illustrates eight tapered radial drainage grooves  916 A to  916 H spaced 45° apart. Alternatively, the spacing of the radial drainage and feeder grooves could be uneven. During operation, polishing slurry or solution flows outward toward perimeter  905  over the land areas  914  and through the tapered radial drainage grooves  916 A to  916 H. The tapered radial drainage grooves  916 A to  916 H all have a width greater toward the perimeter  905  than the center  901 . This taper allows the radial drainage groove to accommodate increased fluid and polishing debris loads. Alternatively to width, depth could increase toward the perimeter to increase flow. But for most circumstances, increased centrifical forces are sufficient to accommodate increased flow through the drainage groove as the polishing slurry or solution flows toward the pad&#39;s perimeter. 
         [0049]    For the invention, the feeder grooves (δ) have an average cross-sectional feeder area (δ a ) where the average cross-sectional feeder area (δ a ) is the total cross-sectional area of each feeder groove divided by the total number of feeder grooves (δ). The radial drainage groove (ρ) has an average drainage cross-sectional area (ρ a ) where the average drainage cross-sectional area of the radial drainage groove (ρ a ) is at least two times greater than the average cross-sectional feeder (δ a ) area but less than eight times greater than cross-sectional feeder (δ a ) as follows: 
         [0000]      2*δ a ≦ρ a ≦8*δ a  
 
         [0050]    wherein (n r ) represents number of radial grooves and (n f ) represents the number of feeder grooves representing a total summation from each side of the radial drainage groove as follows: 
         [0000]      (0.15) n   f *δ a   ≦n   r *ρ a ≦(0.35) n   f *δ a  
 
         [0051]    Typically, n r  is 1 to  16 . Most advantageously, n r  is 2 to 12. 
       EXAMPLE 1 
       [0052]    A series of polishing pads with increasing numbers of radial grooves (1, 2, 4, 8 and 16) created increased drainage capacity with a constant feed groove area. The polishing pads had groove dimensions as follows: 
         [0053]    Cross-sectional area of a single circular feeder groove: 0.0039 cm 2    
         [0054]    Number of feeder grooves bisected by a drainage groove: 80 
         [0055]    Total cross-sectional area of feeder grooves feeding into a single drainage groove: =0.0039*80*2=0.619354 cm 2    
         [0056]    Note: Feeder groove calculations used in this specification assume slurry flowing from both sides of each single intersection between a feeder groove and a drainage groove. For example, 80 circular feeder grooves form 160 groove intersections with a single drainage groove. 
         [0000]    Cross-sectional area of a single drainage groove: 0.01741932 cm 2    
         [0057]    Radial drainage groove to feeder groove cross sectional area ratio if a single drainage groove were applied: 0.04 
         [0058]    In the example shown, a single drainage groove was insufficient to effectively drain the set of feeder grooves. However, by addition of multiple feeder grooves, drainage efficiency can readily be increased to acceptable levels.  FIG. 10  graphically illustrates the improved drainage capacity increases with the number of grooves. 
         [0059]    A relative drainage area ratio of less than 0.15 is not efficacious. Because of the delivery of excess fresh slurry over the upper surface of the pad the number of radial grooves depends upon a number of variables, including the slurry delivery rate. If the drainage capacity is too high, then this results in insufficient slurry in the grooves available for use, and may result in pad drying. This is a detrimental source of defects, such as scratching defects. The drainage grooves of the invention reduce defects. Similarly, too low a drainage ratio will not remove sufficient polishing byproducts and not reduce defects. Too high a drainage ratio affects hydrodynamics (manifested by increased wafer non-uniformity) and increased defects over even the case where no drainage grooves are employed. 
       EXAMPLE 2 
       [0060]    In order to assess the optimal range, the following experiment was performed. Five different radial grooves were applied to a set of closed cell polyurethane polishing pads. These pads had circular grooves of 20 mil wide, 30 mil deep and 120 mil pitch (0.051 cm×0.076 cm×0.305 cm pitch). Designations and radial groove dimensions and number are shown in Table 1. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Pad Sample Set 
               
             
          
           
               
                   
                 Radial Groove width 
                 Radial Groove Depth 
                 Radial Groove 
               
             
          
           
               
                 Pad 
                 (mil) 
                 (mm) 
                 (mil) 
                 (mm) 
                 Number 
               
               
                   
               
             
          
           
               
                 A 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 1 
                 60 
                 1.52 
                 30 
                 0.76 
                 8 
               
               
                 2 
                 120 
                 3.05 
                 30 
                 0.76 
                 8 
               
               
                 3 
                 180 
                 4.57 
                 30 
                 0.76 
                 8 
               
               
                 4 
                 90 
                 2.29 
                 30 
                 0.76 
                 8 
               
               
                 5 
                 90 
                 2.29 
                 30 
                 0.76 
                 16 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Drainage Groove to Feeder Groove Area Ratio 
               
             
          
           
               
                 Pad 
                 No. Drainage Grooves 
                 Drainage/Feeder Area Ratio 
               
               
                   
               
             
          
           
               
                 A 
                 0 
                 Undefined 
               
               
                 1 
                 8 
                 0.15 
               
               
                 2 
                 8 
                 0.30 
               
               
                 3 
                 8 
                 0.45 
               
               
                 4 
                 0 
                 0.225 
               
               
                 5 
                 16 
                 0.45 
               
               
                   
               
             
          
         
       
     
         [0061]    Polishing conditions are summarized as follows:
       MDC Mirra, K1501-50 μm colloidal slurry   Saesol AK45(8031c1) diamond disk, pad break-in 30 min 7 psi (48 kPa), full insitu   condition at 7 psi (48 kPa),   Process: Pad Downforce 3 psi (20.7 kPa)
           Platen Speed 93 rpm   Carrier Speed 87 rpm   Slurry Flow 200 ml/m   
           Monitor wafer polished at wafer counts of 11, 37, 63, 89, 115, 141, 167 and 193.   Defect count was with a Surfscan SP1analyzer from KLA-Tencor.       
 
         [0071]    Each pad was broken-in to remove start-up effects, and polished for 200 wafers to assess rate and defectivity stability. There were no large differences in rate between pads. However, there were significant differences in defectivity, as shown in  FIGS. 11 and 12 . The pad samples with 90 mil (0.229 cm) width/8 radial grooves, and 120 mil (0.305 cm) width/8 radial grooves showed low and stable defect levels. All others, including the control showed higher defect levels that varied over the duration of the test, and increased with increasing polish time. This is particularly evident in  FIG. 11 , which compares the control pad behavior to the 90 mil (0.229 cm) groove pads. 
         [0072]    The doubling of the number of drainage grooves (drainage to feeder area ratio increased from 0.225 to 0.45) significantly increased defectivity overall, even relative to the control. This is taken as an indication that there is a critical range for the drainage efficiency ratio. This critical range can vary with the size and number of feeder groove and the size of the radial drainage groove. 
         [0073]    Defect data after HF etch was also examined to compare total defectivity to scratch density. HF etching is effective at removing particles, and increased the sensitivity to scratches, as the HF enlarges the scratch depth by removal of the strain region around the crack itself (decoration). As shown if  FIG. 13 , the same low and stable defect response was observed for the 90 mil (0.229 cm)/8 and the 120 mil (0.305 cm)/8 pads, although the 60 mil (0.152 cm)/8 pad response was more closely similar, indicating that a large fraction of the total defects in that pad sample were small particulates rather than large damaging aggregates. This is an indication that there is also a lower limit for the drainage efficiency ratio. Based on these results, the critical range for the radial drainage to feeder groove area ratio of 0.2 to 0.3 is most advantageous. 
         [0074]    From the above discussion, it becomes clear that the drainage efficiency expression can be used to determine drainage groove dimensions and numbers needed for achieving reduced defectivity over a wide variety of feeder groove dimensions and pitches. Some practical limitations may be imposed; for example, it is probably undesirable to deploy only one drainage groove, due to rotational eccentricity. It is also concluded that the drainage grooves be restricted to radial grooves, or variations thereof. The reasons for this are as follows: a.) they possess a single rotational symmetry; and b.) they provide minimal contribution to texture-induced nanotopography (undesirable). As regards to groove dimensions, it may also be desirable to further regulate transport by designing the radial drainage grooves to widen with radius, with the limitations of the range of drainage efficiency ratios cited above, as calculated at the periphery of the pad. 
         [0075]    The invention is efficacious for forming porous polishing pads for extended chemical mechanical planarization applications that maintain low defect levels. In addition, these pads can improve polishing rate, global uniformity and reduce polishing vibration.