Polishing pad conditioner

Information

  • Patent Grant
  • 6540597
  • Patent Number
    6,540,597
  • Date Filed
    Tuesday, August 22, 2000
    24 years ago
  • Date Issued
    Tuesday, April 1, 2003
    21 years ago
Abstract
The polishing pad conditioner incorporates a plurality of diamond prisms 12 arranged regularly and protruding towards a surface to be processed, and a conducting bonding member 14 that fixes the diamond prisms into a single body. The conducting bonding member 14 is provided with a conducting metal plate 15 with a plurality of holes 15a for embedding the diamond prisms 12, and a conducting sintered metal 16 that is filled into the spaces between the holes and the diamond prisms and sintered. The conducting bonding member can be dressed electrolytically by passing a flow of conducting liquid 24 through the gap between the member and an electrode placed opposite. Thus, the surface of a polishing pad can be reprocessed (reconditioned) to an appropriate roughness, so the conditioner can continue to operate under even, stable conditions for a very long time, with a rather low manufacturing cost and without contaminating the silicon wafers.
Description




BACKGROUND OF THE INVENTION




1. Technical Field of the Invention




The present invention relates to a polishing pad conditioner that conditions a polishing pad.




2. Prior Art





FIG. 1

is a schematic view showing a CMP apparatus (Chemical Mechanical Polishing Apparatus) used in a final process for producing deviced/bare silicon wafers. The CMP apparatus is composed of a rotating base plate


3


with a polishing pad


2


mounted thereon, and a rotating plate


4


on the lower surface of which a silicon wafer


1


is fixed; while the rotating base plate


3


and the rotating spindle


4


are rotated around their respective axes, a slurry


5


containing colloidal silica is fed between the plate


3


and spindle


4


, and super-fine particles of SiO


2


(with grain diameters of several nanometers to several tens of nanometers) in the colloidal silica react with the silicon wafer (Si) and this softens the particles, and at the same time, the lower surface of the silicon wafer


1


is polished by the SiO


2


in the colloidal silica retained on the polishing pad.




The upper surface of the polishing pad


2


used in the CMP apparatus should have an appropriate roughness so that a preferred amount of slurry


5


is held in the space between the pad and the silicon wafer


1


and a suitable amount of friction is produced between the pad and the silicon wafer


1


. However, when the CMP apparatus is used continuously, the roughness of the upper surface of the polishing pad is gradually lost, and the surface becomes slippery like a mirror, and eventually the polishing rate is greatly reduced and efficient polishing can no longer be performed.




Therefore, the surface of the polishing pad must be reprocessed (in a process called conditioning) to restore the appropriate roughness, and a polishing pad conditioner, an example of which is shown in

FIGS. 2A and 2B

, has conventionally been used.





FIG. 2A

shows an electrodeposition grindstone in which the abrasive grains


8


(for instance, diamond abrasive grains with a grain diameter of several tens of microns) are fixed to the lower surface of a base metal


6


by a plated layer


7


of Ni etc. However, this polishing pad conditioner used to suffer from the fact that the abrasive grains


8


could be attached by only one layer of plating and the strength with which they were held by the metal plating was low. Consequently, because some of the abrasive grains


8


come off, the life is short and the operation can only be repeated a few times. And moreover, the detached abrasive grains are left on and become embedded in the polishing pad (which is for instance, made of a plastic material), with the problem that the silicon wafer


1


is damaged. Another problem was that due to the residue of heavy metal remaining after the plating process, the high-purity silicon wafer


1


was contaminated.





FIG. 2B

shows another polishing pad conditioner in which the lower surface of the base metal


6


is formed with an appropriate roughness in advance, and then its surface is coated with a thin diamond film


9


by CVD (Chemical Vapor Deposition). Although the thin film


9


of this polishing pad conditioner provides a high adhesive force, the time taken to grow the film is so long that the manufacturing cost is extremely high and this is a practical problem. In addition, there are other problems with this conditioner including the difficulty in obtaining a uniform film thickness and the short life due to the extremely thin film (several tens of microns).




SUMMARY OF THE INVENTION




The present invention aims at solving the various problems described above. More explicitly, the objects of the present invention are to provide a polishing pad conditioner that can reprocess (condition) the surface of a polishing pad so as to give it an extremely long life, that is capable of maintaining an even conditioning power, with a rather low manufacturing cost, and without the risk of contaminating the silicon wafer.




As modern science and technology have made great advances, the requirements for ultra-high-precision processing have rapidly become more and more rigorous, and for example, the Electrolytic In-process Dressing (ELID) process was developed by the applicants of the present invention and has been disclosed (Institute of Physical and Chemical Research, Symposium “Trends in Advanced Technologies for Mirror Surface Polishing,” held Mar. 5, 1991).




According to this ELID method, a conducting grindstone is used in place of the electrode used in conventional electrolytic grinding, and an electrode is provided opposite the grindstone with a gap between them, and while a conducting liquid flows between the grindstone and the electrode, a voltage is applied between the grindstone and the electrode, and by dressing the grindstone with the electrolyte, the workpiece is ground by the grindstone. With this ELID grinding method, even if the abrasive grains are fine, loading of the grindstone is prevented due to the electrolytic dressing, therefore by using the abrasive grains finer, a very excellent processed surface such as a mirror surface can be produced by the ELID grinding process. Consequently, it is expected that the ELID method will be applied to various grinding processes, because with this method, the sharpness of the grindstone can be maintained from high-efficiency grinding to mirror-surface grinding, and a highly accurate surface that could not be produced by conventional technologies can be created in a short time.




The present invention is aimed at greatly improving the performance of a polishing pad conditioner using the principles of this ELID method. In detail, in the present invention, a plurality of diamond prisms (


12


) are arranged so as to project towards a surface to be processed, and a conducting bonding material (


14


) fixes the aforementioned diamond prisms into a single body; the above-mentioned conducting bonding material can be dressed electrolytically by making a conducting liquid (


24


) flow in the gap between the bonding material and an electrode (


22


) opposite the bonding material.




According to the aforementioned configuration of the present invention, because the conducting bonding material (


14


) that fixes the diamond prisms into a single body can be dressed electrolytically with the flow of conducting liquid (


24


) to the electrode (


22


) placed opposite the body, when the tips of the diamond prisms (


12


) wear resulting in a reduced protrusion thereof from the conducting bonding material and a deterioration in the conditioning capability, an amount of the material is removed from the surface thereof by electrolytic dressing, thereby increasing the amount by which the diamond prisms protrude from the surface. Accordingly, the amount of protrusion can be optimized at all times, so the tips of the diamond prisms can always function as cutting edges, therefore a polishing pad (made of a plastic material, for instance) can be reconditioned to an appropriate roughness, hence the conditioning performance can be maintained at a stable, uniform level. In addition, since artificial prismatic diamonds with a length of about 2 mm can be used as the diamond prisms, the life is several tens of times as long as those of conventional abrasive grains or thin-film conditioners.




According to a preferred embodiment of the present invention, the above-mentioned conducting bonding material (


14


) is composed of a conducting metal sheet (


15


) with a plurality of holes (


15




a


) in which the diamond prisms (


12


) are embedded, and a conducting sintered metal (


16


) is filled into the gap between the aforementioned holes and the diamond prisms and sintered.




According to this configuration, the diamond prisms (


12


) are inserted into the holes (


15




a


), and a conducting metal powder is placed in the gaps and sintered, thus a conducting sintered metal (


16


) that firmly holds the diamond prisms (


12


) can be formed, so compared to the slow-growing, expensive CVD method, the manufacturing cost can drastically be reduced. In addition, because the metal powder can be sintered while being maintained at a high temperature in an inert gas environment, there is no risk of impurities getting mixed in, therefore the silicon wafer can be protected from contamination.




The above-mentioned conducting bonding material (


14


) is shaped as a circular disk, and tips of the aforementioned plurality of diamond prisms are located on the bottom surface of the disk. The material in this configuration can be used as a circular-disk-type polishing pad conditioner.




Other objects and advantages of the present invention are revealed in the following description referring to the attached drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a diagram showing a conventional CMP apparatus.





FIGS. 2A and 2B

are diagrams showing conventional pad conditioners.





FIGS. 3A and 3B

are diagrams of a polishing pad conditioner according to the present invention.





FIGS. 4A and 4B

show parts of the polishing pad conditioner related to

FIGS. 3A and 3B

.





FIG. 5

is a diagram showing a CMP apparatus using a polishing pad conditioner according to the present invention.





FIG. 6

is a diagram showing principle of the present invention.











DESCRIPTION OF PREFERRED EMBODIMENTS




Preferred embodiments of the present invention are described below referring to the drawings. The same part numbers are used in all the drawings to indicate the same parts, and no duplicate description is given.





FIGS. 3A and 3B

are diagrams showing the polishing pad conditioner according to the present invention.

FIG. 3A

is a section through the conditioner, and

FIG. 3B

a view of the bottom. As shown in these figures, the polishing pad conditioner


10


according to the present invention is composed of a plurality of diamond prisms


12


arranged regularly, protruding towards a surface to be processed (bottom surface in the figures), and the conducting bonding member


14


that fixes the diamond prisms


12


into a single body. The conducting bonding member


14


is a circular disk in shape according to this embodiment, and the plurality of diamond prisms


12


are distributed evenly on the lower surface of the circular disk. In this embodiment, about 2,000 prisms are embedded, the tips of which are positioned on the bottom surface of the disk.





FIGS. 4A and 4B

show component parts of the polishing pad conditioner shown in

FIGS. 3A and 3B

.

FIG. 4A

is an enlarged view of a diamond prism


12


in

FIG. 3B

, and

FIG. 4B

is an isometric view of a single diamond prism


12


.




The diamond prism


12


in

FIG. 4B

, used in this embodiment, is an artificial prismatic diamond with a square form with sides of about 0.2 mm and about 2 to 2.5 mm in length. Such artificial prismatic diamonds are presently being mass produced at relatively low costs.




As shown in

FIGS. 3A

,


3


B and


4


A, the conducting bonding member


14


is composed of a conducting metal sheet


15


with a plurality of holes


15




a


in which the diamond prisms


12


are embedded, and a conducting sintered metal


16


is filled into the gaps between the holes


15




a


and the diamond prisms


12


and sintered.




The polishing pad conditioner shown in

FIGS. 3A and 3B

is manufactured as described below.




With the embodiment in

FIGS. 3A and 3B

, a Ni metal sheet of about 2 mm in thickness is used as the conducting metal sheet


15


, and about 2,000 penetrating holes


15




a,


0.5 mm in diameter, are bored in this metal sheet, and a diamond prism


12


is embedded in each hole.




Next, conducting metal powder is filled into the gaps between the penetrating holes


15




a


and the diamond prisms


12


, and while the entire conducting metal sheet


15


is held at a high temperature in an inert gas environment, the metal powder is sintered, and a conducting sintered metal


16


that firmly holds the diamond prisms


12


is formed.




In this embodiment, the conducting metal sheet


15


is joined to a base metal


18


by soldering into one body. However, other means of joining, for instance diffusion joining can also be applied.





FIG. 5

is a drawing that shows a CMP apparatus using the polishing pad conditioner according to the present invention. In this figure, the CMP apparatus, like the conventional CMP apparatus shown in

FIG. 1

, is provided with a rotating base plate disk


3


with a polishing pad mounted on the top surface thereof, and a rotating plate


4


with a silicon wafer


1


fixed on the lower surface of the plate, and while the disk


3


and the plate


4


are rotated around their respective axes, a slurry


5


containing colloidal silica is supplied between them, thus ultra-fine particles (with grains of several to several tens of nanometers in diameter) in the colloidal silica are made to react with the silicon wafer (Si), and at the same time, SiO


2


contained in the colloidal silica is retained on the polishing pad and polishes the lower surface of the silicon wafer


1


.




The CMP apparatus in

FIG. 5

is further provided with a second rotating spindle


21


with the polishing pad conditioner


10


of the present invention mounted on the lower surface thereof. The second rotating spindle


21


is arranged to be capable of moving in the vertical and horizontal directions while rotating around its axis. Furthermore, the apparatus is provided with an electrode


22


separate and opposite the conducting bonding member


14


(composed of the plate


15


and the sintered metal


16


) of the polishing pad conditioner


10


at a location to which the second rotating spindle


21


can be moved in a horizontal direction (shown by the double chain line in FIG.


5


), a conducting liquid feeder that feeds a conducting liquid


24


therebetween, and a power supply


26


that charges the member


14


and the electrode


22


, positively and negatively, respectively.




Using this configuration, the polishing pad conditioner


10


is lowered and rotated while being pressed against the upper surface of the polishing pad


2


, thereby the surface of the polishing pad is reprocessed (reconditioned) to an appropriate roughness, and whenever required, the second rotating spindle is offset in the horizontal direction, and the surface of the polishing pad can be dressed electrolytically by making the conducting liquid


24


flow between the conducting bonding member and the electrode


22


that is located opposite the member with a gap between them.





FIG. 6

explains principles of the present invention. In this figure, (A) shows a section through the surface of the tool in the preferred condition for use as a polishing pad conditioner, wherein each diamond prism


12


protrudes evenly from the conducting bonding member


14


(composed of component parts


15


and


16


). (B) shows the surface of the tool after the diamond prisms


12


have become worn, and (C) shows the protrusions of the diamond prisms


12


after being dressed electrolytically.




As the polishing pad is conditioned continuously using the polishing pad conditioner


10


shown in (A), the tips of the diamond prisms


12


wear. As shown in (B), when the protrusion of the diamond prisms


12


from the conducting bonding member


14


becomes insufficient, the conditioner becomes overloaded due to friction in the machining process, so that conditioning can no longer continue in a stable manner. To avoid this situation, some of the conducting bonding member


14


is removed electrolytically, so that the tip of each diamond prism


12


is again protruding from the conducting bonding member


14


while the surface of the tool is restored to the good condition of (A), as shown in (C).




By repeating operations (A) to (C), the surface of the tool can be maintained in the preferred state for a polishing pad conditioner at all times.




According to the aforementioned configuration of the present invention, because the conducting bonding member


14


that fixes the diamond prisms into a single body can be electrolytically dressed by passing a flow of conducting liquid


24


through the gap between it and the electrode


22


placed opposite, when the tips of the diamond prisms


12


become worn and the protrusions of the prisms from the conducting bonding member become so small that the conditioning capabilities are adversely affected, some of the surface of the conducting bonding member can be removed by the electrolytic dressing, and the protrusions of the diamond prisms can be increased. As a result, the amount of the protrusions can be optimized at all times so that the tips of the diamond prisms can function as cutting edges, the polishing pad (a plastic material, for example) can be reprocessed (reconditioned) to an appropriate roughness, and appropriate conditions can be maintained in a stable and even manner. Moreover, because artificial diamond prisms with a length of about 2 mm, for instance, can be used, the life can be made several tens of times longer than the thickness of conventional abrasive grains or thin films.




In addition, the conducting bonding member


14


is composed of the conducting metal plate


15


with a plurality of holes


15




a,


and the conducting sintered metal


16


filling the gaps between the holes and diamond prisms and sintered, and the conducting sintered metal


16


that firmly holds the diamond prisms


12


can be formed by inserting the diamond prisms


12


into the holes


15




a


and charging conducting metal powder into the spaces therebetween and sintering the powder. Therefore, the manufacturing cost can be greatly reduced compared to that of the slow-growing, expensive CVD systems. Furthermore, since the metal powder can be sintered by holding it at a high temperature in an inert gas environment, no impurities can be mixed in so that the silicon wafer can be protected from contamination.




However, the present invention shall not be limited only to the above-mentioned embodiments, instead, the present invention can be modified in various ways as long as the scope of the present invention is not exceeded. For instance, although the CMP apparatus (Chemical Mechanical Polishing Apparatus) for devices/bare silicon wafers was detailed above, the principles of the present invention can be directly applied also to other polishing apparatus.




As described above, the polishing pad conditioner according to the present invention can provide various advantages and effects such as the capability of reprocessing (reconditioning) the surface of a polishing pad to an appropriate roughness, providing a very long life maintaining stable, even conditioning, relatively low manufacturing costs and no risk of contaminating the silicon wafers.




Although the present invention has been described referring to several preferred embodiments, it is understood that the scope of rights included in the present invention should not be limited only to these embodiments. Instead, the scope of rights of the present invention shall include all modifications, corrections and equivalent entities contained in the scope of the attached claims.



Claims
  • 1. A polishing pad conditioner comprising:a plurality of diamond prisms arranged regularly in such a manner that tips thereof protrude towards a surface to be processed; and a conducting bonding member that fixes the diamond prisms into a single body, wherein the conducting bonding member can be dressed electrolytically by passing of a flow of conductive fluid through a gap between the member and an electrode placed opposite thereto, and wherein each diamond prism is constructed to have a square form.
  • 2. The polishing pad conditioner specified in claim 1, in which the conducting bonding member comprises a conducting metal plate with a plurality of holes for embedding the diamond prisms, and a conducting sintered metal filled into a spaces between the holes and the diamond prisms and sintered therein.
  • 3. The polishing pad conditioner specified in claim 1, wherein the conducting bonding member has the shape of a circular disk, and tips of the plurality of diamond prisms are positioned on a bottom surface of the circular disk.
  • 4. A polishing pad conditioner comprising:a plurality of diamond prisms arranged regularly in such a manner that tips thereof protrude towards a surface to be processed; and a conducting bonding member that fixes the diamond prisms into a single body, wherein the conducting bonding member comprises a conducting metal plate with a plurality of holes for embedding the diamond prisms, and a conducting sintered metal filled into a spaces between the holes and the diamond prisms and sintered therein, wherein the conducting bonding member can be dressed electrolytically by passing of a flow of conductive fluid through a gap between the member and an electrode placed opposite thereto.
Priority Claims (1)
Number Date Country Kind
11-237745 Aug 1999 JP
US Referenced Citations (2)
Number Name Date Kind
6293854 Kimura et al. Sep 2001 B1
6306025 Torii Nov 2001 B1
Foreign Referenced Citations (1)
Number Date Country
WO9855265 Dec 1998 WO