CMP platen with patterned surface

Information

  • Patent Grant
  • 6220942
  • Patent Number
    6,220,942
  • Date Filed
    Friday, April 2, 1999
    25 years ago
  • Date Issued
    Tuesday, April 24, 2001
    23 years ago
Abstract
A chemical mechanical polishing system is provided having one more polishing stations. The polishing stations include a platen and pad mounted to an upper surface of the platen. The upper surface of the platen is patterned to define a raised area and a recessed area. The raised area provides a rigid mounting surface for the pad and the recessed area provides the pad a desired degree of flexibility and compliance of the pad when brought into contact with a substrate.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to an apparatus for polishing substrates. More particularly, the invention relates to a platen/polishing pad assembly having a compliant surface to improve polishing uniformity of substrates.




2. Background of the Related Art




In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited and removed from a substrate during the fabrication process. Often it is necessary to polish a surface of a substrate to remove high topography, surface defects, scratches or embedded particles. The polishing process is often referred to as chemical mechanical polishing (CMP) and is used to improve the quality and reliability of the electronic devices formed on the substrate.




Typically, the polishing process involves the introduction of a chemical slurry during the polishing process to facilitate higher removal rates and selectivity between films on the substrate surface. In general, the polishing process involves holding a substrate against a polishing pad under controlled pressure, temperature and rotational speed (velocity) of the pad in the presence of the slurry or other fluid medium. One polishing system that is used to perform CMP is the Mirra® CMP System available from Applied Materials, Inc., and shown and described in U.S. Pat. No. 5,738,574, entitled, “Continuous Processing System for Chemical Mechanical Polishing,” the entirety of which is incorporated herein by reference.




An important goal of CMP is achieving uniform planarity of the substrate surface. Uniform planarity includes the uniform removal of material deposited on the surface of substrates as well as removing non-uniform layers which have been deposited on the substrate. Successful CMP also requires repeatability from one substrate to the next. Thus, uniformity must be achieved not only for a single substrate, but also for a series of substrates processed in a batch.




Substrate planarity is dictated, to a large extent, by the construction of the CMP apparatus and the consumables such as slurry and pads. In particular, a preferred construction allows for a proper balance between rigidity (or stiffness) and compliance (or flexibility) of the polishing device, and in particular to the stiffness and compliance of the polishing pad. In general, stiffness is needed to ensure within-die uniformity while sufficient compliance provides within-substrate uniformity. Within-substrate uniformity refers to the ability of the CMP apparatus to remove features across the diameter of the substrate regardless of substrate shape and/or topography across its surface. Within-die uniformity refers to the ability of the CMP apparatus to remove features within a die, regardless of size and feature density.




Conventional polishing systems include a platen having a polishing pad disposed thereon. Current state of the art strongly suggests the use of more than one polishing pad to provide compliance to the pad for improved results both withinsubstrate and within-die. For example, two pads are typically assembled together into a stack, which may be termed a “composite polishing pad.” A typical polishing apparatus


10


comprising a metal platen


12


having a composite polishing pad


14


mounted thereto is shown in FIG.


1


. Both the composite polishing pad


14


and the platen


12


are generally disc-shaped and of equal diameters. The top (upper) pad


16


, is brought into contact with a substrate to perform the polishing process, while the bottom (lower) pad


18


is secured to a smooth upper mounting surface of the rotatable platen


12


to provide a seating surface for the top pad


16


. An adhesive


20


, such as a pressure sensitive adhesive (PSA) is provided on the back face of the pads


16


,


18


to bond the pads to one another and to the platen


12


. The top pad


16


is typically made of cast polyurethane while the bottom pad


18


is typically made of polyester felt stiffened with polyurethane resin. Other pads having different material composition are also available and known in the industry.




Generally, it is preferable that the top pad


16


be stiffer than the more compliant bottom pad


18


to provide a sufficiently rigid polishing surface. Typically, stiffness provides better within-die uniformity, while some compliance is needed to ensure within-substrate uniformity. The combination of pads having the proper proportions of stiffness and flexibility can achieve good planarity and uniformity over the surface of the substrate. In addition, the polishing profile on a substrate can be changed or modified by changing the thickness of either or both of the upper and lower pads. The change in thickness without a change in composition can change the properties of the composite pad in terms of stiffness and compliance.




However, a number of problems are associated with the conventional composite, or stacked, pad construction. In particular, each additional layer, i.e., pad and adhesive layer, in the stack acts as a source of variation affecting the overall stiffness and/or compliance of the stack. The greater the number of layers or even variations in the thickness of pads, the greater the potential for variation. As a result, a polishing device utilizing a composite polishing pad is often unable to achieve desired polishing results over a number of substrates. Specifically, variations in compressibility, loss of within-substrate uniformity, uncontrolled wetting of the lower pad, and variation from pad to pad result due to multiple process variables. In addition, the planarity changes as the top pad is worn away by a process known as conditioning the pad, and planarity may decrease with increasing number of substrates polished on the pad.




One solution has been to minimize the number of layers in the composite polishing pad. Thus, the goal in CMP would be to remove the bottom pad and secure the top pad directly to the upper surface of the platen. Removal of bottom pad also eliminates the need for one layer of the adhesive. However, it has been discovered that elimination of the bottom pad and mounting the polishing pad directly on the platen results in an overly rigid pad/platen assembly which compromises the compliance of the assembly. The rigidity is a consequence of directly interfacing the top pad with the non-compliant platen surface, typically made of aluminum or other metal.




Therefore, there is a need for a platen/pad assembly which eliminates the need for a sub-pad while providing sufficient compliance during polishing.




SUMMARY




The present invention generally provides an apparatus for polishing a substrate which enhances polishing pad compliance and maintains or improves substrate and die uniformity. The apparatus is preferably adapted for incorporation into a chemical mechanical polishing system.




In one aspect of the invention, a platen is provided having a patterned upper surface to define a raised area and a recessed area. The raised area provides a rigid mounting surface for a polishing pad, while the recessed area allows for a desired degree of compliance of the pad.




In another aspect of the invention, a platen is provided having a pad disposed thereon. The upper surface of the platen is patterned to define a raised pad seating area and a recessed area. The raised area provides a rigid mounting surface for the pad and the recessed area provides a desired degree of flexibility and compliance of the pad when brought into contact with a substrate. Preferably, a portion of the recessed area extends to the perimeter of the platen thereby forming pathways between the platen and the pad that communicate with the platen's environment.




In another aspect of the invention, a patterned surface is provided and is adapted to be disposed on the upper surface of a platen to support a polishing pad thereon. The patterned surface is preferably a hard rubber-like material defining an upper polishing pad supporting surface having channels or other recesses formed therein to provide pad compliance.




In another aspect of the invention, a platen having a patterned upper surface is provided and is coated with a rubber-like or compliant upper surface. The patterned surface includes both an upper pad supporting surface and a lower grooved portion for providing some compliance to the pad.











BRIEF DESCRIPTION OF THE DRAWINGS




So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.




It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.





FIG. 1

is a schematic side view of a platen and composite polishing pad assembly.





FIG. 2

is a schematic view of a CMP system.





FIG. 3

is a schematic view of a polishing station.





FIG. 4

is a top view of the platen.





FIG. 5

is a schematic side view of the platen in

FIG. 4

having a pad disposed thereon.





FIG. 6

is a top view of the platen showing an alternative embodiment.





FIG. 7

is an exploded perspective view of a platen assembly including a patterned mat disposed between a polishing pad and a platen.





FIG. 8

is a partial cross sectional view of a platen having a coating disposed thereon.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




The present invention generally relates to a platen having a patterned surface for mounting a pad, such as a polishing pad, thereto. The patterned surface includes a raised pad supporting portion and a recessed pad displacement portion. The raised portion defines a mounting surface for a polishing pad. The recessed portion provides a deflection area and is preferably vented to allow communication with the platen environment.




For clarity and ease of description, the following description refers primarily to a CMP system. However, the invention is equally applicable to other types of processes that utilize a platen and pad assembly for polishing or cleaning a substrate.





FIG. 2

is a schematic view of a CMP system


30


, such as a Mirra® CMP System available from Applied Materials, Inc., located in Santa Clara, Calif. The system shown includes three polishing stations


32


and a loading station


34


. Four polishing heads


36


are rotatably mounted to a polishing head displacement mechanism


37


disposed above the polishing stations


32


and the loading station


34


. A front-end substrate transfer region


38


is disposed adjacent to the CMP system and is considered a part of the CMP system, though the transfer region


38


may be a separate component. A substrate inspection station


40


is disposed on or near the substrate transfer region


38


to enable pre and/or post process inspection of substrates introduced into the system


30


.




Typically, a substrate is loaded on a polishing head


36


at the loading station


34


and is then rotated through the three polishing stations


32


. The polishing stations


32


each comprise a rotating platen


41


having polishing or cleaning pads mounted thereon described in detail below with reference to FIG.


3


. One process sequence includes a polishing pad at the first two stations and a cleaning pad at the third station to facilitate substrate cleaning at the end of the polishing process. At the end of the cycle the substrate is returned to the front-end substrate transfer region


38


and another substrate is retrieved from the loading station


34


for processing.





FIG. 3

is a schematic view of a polishing station


32


and polishing head


36


used to advantage with the present invention. The polishing station


32


comprises a pad


44


secured to an upper surface of the rotatable platen


41


. The pad


44


may be any commercially available pad supplied by manufacturers such as Rodel and preferably comprises a plastic or foam such as polyurethane. The platen


41


is coupled to a motor


46


or other suitable drive mechanism to impart rotational movement to the platen


41


. During operation, the platen


41


is rotated at a velocity V


p


about a center axis X. The platen


12


can be rotated in either a clockwise or counterclockwise direction.

FIG. 3

also shows the polishing head


36


mounted above the polishing station


32


. The polishing head


36


supports a substrate


42


for polishing. The polishing head


36


may comprise a vacuum-type mechanism to chuck the substrate


42


against the polishing head


36


. During operation, the vacuum chuck generates a negative vacuum force behind the surface of the substrate


42


to attract and hold the substrate


42


. The polishing head


36


typically includes a pocket (not shown) in which the substrate


42


is supported, at least initially, under vacuum. Once the substrate


42


is secured in the pocket and positioned on the pad


44


, the vacuum can be removed. The polishing head


36


then applies a controlled pressure behind the substrate, indicated by the arrow


48


, to the backside of the substrate


42


urging the substrate


42


against the pad


44


to facilitate polishing of the substrate surface. The polishing head displacement mechanism


37


rotates the polishing head


36


and the substrate


42


at a velocity V


s


in a clockwise or counterclockwise direction, preferably the same direction as the platen


41


. The polishing head displacement mechanism


37


also preferably moves the polishing head


36


radially across the platen


41


in a direction indicated by arrows


50


and


52


.




With reference to

FIG. 3

, the CMP system also includes a chemical supply system


54


for introducing a chemical slurry of a desired composition to the pad. The slurry provides an abrasive material which facilitates the polishing of the substrate surface, and is preferably a composition formed of solid alumina or silica. During operation, the chemical supply system


54


introduces the slurry as indicated by arrow


56


on the pad


44


at a selected rate.





FIG. 4

shows a preferred embodiment of a platen


41


of the invention. The platen


41


comprises a patterned surface whereon a polishing pad may be disposed. Generally, the patterned surface has features formed therein defining a raised area and a recessed area. In the embodiment shown in

FIG. 4

, the raised area consists of a plurality of protrusions


60


while the recessed area is a plurality of intersecting grooves


62


defined by the protrusions


60


. More specifically, the recessed area consists of two parallel sets of equally spaced orthogonally intersecting grooves


62


in a checkerboard pattern. Each groove


62


traverses the upper surface of the platen


41


from one perimeter to the another. Thus, the grooves


62


are not contained, or blocked, at either end. However, the present invention also contemplates an embodiment having blocked grooves.




The raised area of the platen


41


, or protrusions


60


, defines a pad mounting surface. Preferably, the protrusions


60


cooperate to provide a substantially planar mounting surface


64


along a common plane A for supporting a polishing pad


44


as shown in FIG.


5


. The pad


44


is attached using a commercially available pressure sensitive adhesive (PSA). Thus, the present invention eliminates the bottom pad of prior art as discussed with reference to FIG.


1


. Further, the necessary pad compliance, previously achieved by using a bottom pad, is now provided by the cooperation of the recessed and raised areas, or grooves


62


and protrusions


60


, respectively. The protrusions


60


ensure sufficient rigidity (or stiffness) while the grooves


62


allow the proper proportion of pad compliance to accommodate a substrate's varying topography.




As noted above, the grooves


62


are preferably open at some point along their length to prevent vacuum adherence of the pad to the surface. Thus, the grooves


62


provide pathways between the platen


41


and the pad


44


which vent to the environment of the platen


41


as shown in FIG.


5


. Such a construction anticipates the use of perforated pads such as those available from Rodel. The perforations in the pad allow fluid flow therethrough. Where the grooves


62


are isolated from the environment, such as where the grooves


62


comprise concentric circles enclosed at the top by a perforated pad, a partial vacuum condition may be created in the grooves


62


as a substrate is urged against the pad. In such a case, the substrate remains chucked to the pad after the polishing cycle making it difficult to remove. By constructing the grooves


62


as shown in

FIGS. 4 and 5

, the grooves


62


remain at equal pressure to the ambient environment allowing easy dechucking of the substrate. Where a concentric pattern is desired, a vent channel or channels extending to the perimeter of the platen


41


can be provided to eliminate adhesion between the substrate and platen


41


. Such an embodiment is shown in FIG.


6


and described in detail below.




Preferably, the protrusions


60


and the grooves


62


shown in

FIGS. 4 and 5

are defined by machining away a portion of the upper surface of the platen


41


which comprises a metal such as aluminum. However, the present invention also contemplates alternative embodiments. For example, the plurality of protrusions


60


may be constructed separately from the platen


41


. The protrusions


60


may then be secured to the platen


41


surface by conventional methods such as brazing or welding. In another alternative, the platen


41


may comprise two separable plates with a lower plate secured to the motor


46


(shown in

FIG. 3

) and an upper plate comprising the patterned surface for mounting the pad


44


. The plates may be permanently coupled by such methods as welding, or they may be detachably coupled by temporary fasteners or clamps. The latter embodiment provides a versatile platen assembly having an exchangeable mounting surface.




The dimensions of the patterned surface may be varied to achieve the desired proportions of compliance and rigidity. In general, the mounting surface


64


makes up to between about 20 to 95% of the total upper surface area but may be varied according to the pad thickness and modulus, as well as the applied polishing pressure. In a specific embodiment shown in

FIG. 4

having a diameter of about twenty (20) inches, the groove depth is about 0.250 inches and the groove width is about 0.062 inches. Thus, the total surface area of the mounting area


64


is preferably about 20-95% of the total area of the platen. The diameter of the platen


41


may be varied to accommodate any substrate size such as 100 mm, 200 mm or 300 mm substrates. As a result, relative sizes of the grooves and protrusions will vary accordingly.




It is to be understood that the present invention allows for virtually limitless design variations.

FIG. 4 and 5

show only one possible embodiment according to the invention. Another embodiment is shown in FIG.


6


. In general, the embodiment of

FIG. 6

provides a raised area and recessed area of the platen


41


. Specifically, the platen


41


comprises a plurality of “broken” concentric grooves


65


intersected by radial grooves


66


. The radial grooves


66


originate at a central hub


67


thereby communicating all of the features of the recessed area. The embodiments described above are merely illustrative and a person skilled in the art will recognize other embodiments within the scope of the present invention.




In addition to patterning the upper surface of the platen, a patterned mat, liner or other coating could be applied to or disposed over a typical platen as shown in

FIGS. 7 and 8

. A hard rubber-like coating could be molded or otherwise formed to provide one of the patterned surfaces described above. Thus,

FIG. 7

shows a patterned mat


100


disposed on a platen


102


and having a polishing pad


103


disposed on an upper patterned mounting surface


104


. In the specific embodiment shown, the patterned mat


100


has a surface profile similar to that of the platen


41


shown in FIG.


4


and described above, however, any pattern may be used to advantage. In such an embodiment, the platen


102


preferably comprises an untextured mounting surface (as shown in

FIG. 7

) for securing the patterned mat


100


thereto but may also comprise a patterned surface to cooperate with the patterned mat


100


in providing additional flexibility and compliance. The polishing pad


103


, patterned mat


100


, and platen


102


are secured to one another by any conventional methods such as by an adhesive.





FIG. 8

is a partial cross sectional view of an alternative embodiment comprising a coating


110


disposed on a patterned platen


112


. The particular surface profile of the platen


112


shown in

FIG. 8

is similar to that of the platen


41


shown in

FIG. 4

but it is to be understood that any pattern may be used to advantage, such as those shown in

FIGS. 4-7

. The coating


110


may be secured to the platen


112


by conventional methods such as by an adhesive. A polishing pad (not shown) may then be secured to the upper mounting surface


114


defined by the coating


110


and platen


112


.




The material used for the patterned mat


100


and coating


110


is preferably determined according to the material of the platen. In general, the patterned mat


100


and coating


110


comprise a material more compliant than the platen. For example, where the platen is made of a metal, such as aluminum or stainless steel, the patterned mat


100


and coating


110


may comprise an elastomer such as rubber. Other materials which are known and unknown could be used to advantage.




It is to be understood that terms such as top, bottom, below, above, backside and the like are relative terms and are not intended to be limiting. Other configurations are contemplated where a substrate can be handled in different orientations.




While foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.



Claims
  • 1. An apparatus for polishing a substrate, comprising:(a) a rotatable platen having a mounting surface, at least one groove formed in the mounting surface; and (b) a pad disposed on the mounting surface and bridging the at least one groove.
  • 2. The apparatus of claim 1, further comprising a coating disposed on the mounting surface.
  • 3. The apparatus of claim 1, wherein the pad comprises polyurethane.
  • 4. The apparatus of claim 1, wherein the pad comprises a plastic foam.
  • 5. The apparatus of claim 1, wherein the mounting surface is rigid.
  • 6. The apparatus of claim 1, wherein the at least one groove extends to a perimeter of the rotatable platen.
  • 7. The apparatus of claim 1, wherein the at least one groove and the pad define a plurality of pathways.
  • 8. The apparatus of claim 7, wherein at least a portion of the plurality of pathways extend to a perimeter of the rotatable platen to allow fluid communication between a backside of the pad and an environment of the rotatable platen.
  • 9. The apparatus of claim 1, wherein said the rotatable platen defines a plurality of grooves that define a patterned mounting surface.
  • 10. The apparatus of claim 1, wherein the rotatable platen is part of a chemical mechanical polishing system.
  • 11. The apparatus of claim 1, wherein the rotatable platen comprises aluminum.
  • 12. The apparatus of claim 1, wherein the at least one groove are disposed in a grid pattern.
  • 13. The apparatus of claim 1, wherein the at least one groove further comprise:a plurality of concentric grooves; and at least one radial groove.
  • 14. A substrate polishing apparatus, comprising:(a) one or more polishing stations each including a rotatable platen wherein at least one of the rotatable platens has a mounting surface, at least one groove formed in the mounting surface; and (b) one or more polishing heads rotatably mounted above the rotatable platens; and (c) a polishing pad disposed on the mounting surface and bridging said groove.
  • 15. The apparatus of claim 14, further comprising a coating disposed on the mounting surface.
  • 16. The apparatus of claim 14, further comprising a motor coupled to the rotatable platen to selectively impart rotation.
  • 17. The apparatus of claim 14, wherein the mounting surface is rigid.
  • 18. The apparatus of claim 14, wherein the at least one groove and the pad define a plurality of pathways.
  • 19. The apparatus of claim 18, wherein at least a portion of the plurality of pathways extend to a perimeter of the rotatable platen to allow fluid communication between a backside of the pad and an environment of the rotatable platen.
  • 20. The apparatus of claim 14, wherein the rotatable platen defines a plurality of grooves that define a patterned mounting surface.
  • 21. A rotatable platen assembly for a polishing apparatus, comprising:(a) a mat having a mounting surface; at least one groove formed in the mounting surface; and (b) a pad disposed on the mounting surface and bridging the groove.
  • 22. The rotatable platen assembly of claim 21, wherein the mounted surface is rigid.
  • 23. The rotatable platen assembly of claim 21, wherein the at least one groove extends to a perimeter of the mat.
  • 24. The rotatable platen assembly of claim 21, wherein the mat comprises aluminum.
  • 25. The rotatable platen assembly of claim 21, wherein the pad comprises a plastic foam.
  • 26. The rotatable platen assembly of claim 21, wherein the mat defines a plurality of grooves that define a patterned mounting surface.
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