Polishing solution feeder

Information

  • Patent Grant
  • 6406364
  • Patent Number
    6,406,364
  • Date Filed
    Monday, October 25, 1999
    25 years ago
  • Date Issued
    Tuesday, June 18, 2002
    22 years ago
Abstract
The object of the present invention is to provide a polishing apparatus that can supply a polishing solution having a non-varying distribution of abrading particles sizes at a steady rate. An apparatus (20) for delivering a polishing solution to a polishing apparatus (22) is disclosed. The apparatus (20) comprises: a solution passage for transporting the polishing solution; and an ultrasonic vibrator (72) being provided in at least one location of the solution passage.
Description




TECHNICAL FIELD




This invention relates to an apparatus for supplying a polishing solution for use in polishing, for example, a semiconductor substrate, and relates in particular to an apparatus for steadily supplying a polishing solution having a constant dispersion of abrading particles in the liquid.




BACKGROUND ART




Recent advances in circuit integration in semiconductor devices have produced micro-sized circuit patterns with narrow line widths. As a result, circuit pattern printing by optical lithography requires extremely shallow depth of focus, so that the substrate surface needs to be precisely flat in the focal plane of the stepper apparatus.




A method of obtaining a flat surface on a semiconductor substrate is to polish the wafer using a polishing tool (for example, polishing table with a polishing cloth), and a wafer holding member for holding and pressing the surface to be polished of the wafer against the polishing table, and moving the surface to be polished relative to the polishing tool while supplying a polishing solution at the contact interface between the polishing tool and the surface to be polished. Such a polishing apparatus can perform not only mechanical polishing using a polishing solution containing abrasive particles, but can also perform chemical polishing using an alkaline or acidic polishing solution. For example, a slurry for polishing an oxidized surface of the wafer is based on a KOH or NH


4


OH solution with a dispersion of silica particles.




To produce a good substrate using such a polishing apparatus, it is required that the polishing solution of a constant concentration be steadily supplied at a constant rate. A system for supplying a polishing solution has an undiluted solution tank to store a mixed solution of KOH, NH


4


OH and silica powder; a dilution tank to dilute the undiluted solution with pure water and others; and a supply piping to deliver the solution from the dilution tank to the nozzle of the polishing apparatus.




However, to meet the demand of cost reduction for equipment and operation, it is desired to supply the polishing solution from one tank to a plurality of polishing apparatuses, so that there is a tendency for long lengths of delivery piping. As a result, the polishing solution becomes stagnant inside the piping and tends to cause aggregation of abrasive particles so that the abrasive particles tend to cluster, thereby causing damage (scratch) to the substrate surface, thereby changing the amount of polishing as a result of changes in solution concentration, or thereby plugging the piping.




DISCLOSURE OF INVENTION




This invention is presented in view of the problems outlined above, and it is an object of the present invention to provide a polishing apparatus that can supply a polishing solution, having a non-varying distribution of abrading particle sizes, at a steady rate.




The invention includes an apparatus for delivering a polishing solution to a polishing apparatus, with the apparatus comprising: a solution passage for transporting the polishing solution; and an ultrasonic vibrator being provided in at least one location of the solution passage. Accordingly, clustered powder particles are dispersed by the ultrasonic vibration, so that a polishing solution, having a constant size distribution of fine powder particles in a given size range, can be delivered to the polishing apparatus. The dispersion effect of the treatment is retained for some time after applying the ultrasonic vibration, so that the particles are prevented from clustering while the solution is being delivered through the solution passage to reach the polishing apparatus.




The ultrasonic vibrator can be provided in a stock tank for storing an undiluted solution. The stock tank may be a storage tank for storing an undiluted solution delivered from an external source, or a tank to prepare a polishing solution by mixing powder particles and a solution to produce an undiluted solution or a polishing solution.




The solution passage may have a circulation passage for circulating the polishing solution and a delivery passage extending from the circulation passage to a polishing apparatus, and the ultrasonic vibrator can be provided on the circulation passage. Accordingly, non-stopping circulation of the polishing solution inside the solution passage prevents changes in the concentration of the solution or plugging in the passage caused by precipitated solid clusters of powder particles inside the passage. Also, one solution supply apparatus can deliver a polishing solution from one supply source to a number of polishing apparatuses, so that the apparatus cost can be lowered.




The ultrasonic vibrator can also be provided on the delivery passage. Also, the polishing solution may contain powder particles in a range of particle sizes between 0.1 to 0.2 μm.




The ultrasonic vibrator can be provided in a mixing section for mixing an undiluted solution and a dilution solution for adjusting a solution concentration.




The invention also includes a polishing apparatus which comprises a holding device for holding an object to be polished, a polishing tool opposing the holding device and a spray nozzle for introducing a polishing solution at an interface between the object to be polished and the polishing tool, wherein an ultrasonic vibrator is provided on those parts of the holding device and/or the polishing tool that retain the polishing solution.











BRIEF DESCRIPTION OF DRAWINGS





FIG. 1

is a diagram showing the overall configuration of the polishing solution supply apparatus of the present invention; FIGS.


2





2


C are graphs showing the effects of ultrasonic processing; FIGS.


3





3


C are similar graphs showing the effects of ultrasonic processing;

FIG. 4

is also a graph showing the effects of ultrasonic processing;

FIG. 5

shows another embodiment of the polishing solution supply apparatus; FIGS.


6





6


C are various views of the structures of the ultrasonic vibration device shown in

FIG. 5

; and

FIG. 7

is a schematic view of another embodiment of the polishing solution supply apparatus.











BEST MODE FOR CARRYING OUT THE INVENTION




In the following, a first embodiment will be presented with reference to FIG.


1


. This apparatus for delivering a polishing solution comprises: two stock tanks


10


for storing an undiluted solution; a dilution tank


12


for delivering a dilution solution to dilute the undiluted solution to a given concentration; a mixing section


18


for mixing the solutions supplied from the tanks through pipes


14


,


16


to produce a polishing solution of a given concentration; a circulation passage


20


for circulating the polishing solution; and a delivery pipe


24


to supply the polishing solution from the circulation passage


20


to the polishing unit


22


. Each stock tank


10


has a stirrer


70


inside, and a ultrasonic vibrator


72


is attached to a bottom section thereof. And, each stock tank


10


has a liquid level sensor


73


, a temperature sensor


75


and others.




There are two stock tanks


10


, and when one tank becomes empty, a valve


11


is opened to switch to the undiluted solution supply line


14


. Each of the supply line


14


and the dilution liquid supply line


16


is connected to a buffer tube


18


, which is a mixing section, through a respective shutoff valve


26


and flow adjusting valve


28


, thereby producing a polishing solution of a given ratio inside the buffer tube


18


.




The buffer tube


18


acting as the mixing section, in this embodiment, is disposed in a path of the circulation pipe


20


that supplies a polishing solution to a plurality of polishing units


22


. The buffer tube


18


is a cylindrical container


30


of a diameter larger than that for the circulation pipe


20


, is disposed vertically, and has a discharge opening


32


at the bottom section thereof, with a top section being covered by a lid


36


provided with an O-ring


34


. A return pipe for the circulation pipe


20


and supply pipes


14


,


16


for the undiluted solution and the dilution solution are connected to the buffer tube


18


at its top.




Container


30


is provided with liquid level sensors


40




a,




40




b


and


40




c


for detecting upper, lower and lowermost levels, for example, and outputting respective signals to a controller (not shown). The controller outputs control signals to a shutoff valve


26


and a flow adjusting pump


28


, so that the undiluted solution and the dilution solution will be supplied when the liquid level drops or the supply will be stopped when the liquid level reaches the upper level. If the liquid level should reach the lowermost level, the controller generates a warning signal or a stop signal for the polishing unit


22


.




Circulation pipe


20


is constructed such that the solution exits from the discharge opening


32


at the bottom of the buffer tube


18


, circulates near one or more polishing unit


22


for supplying polishing solution thereto, and then returns to the buffer tube


18


through the return pipe. Circulation pipe


20


is provided with a circulation pump


46


for circulating the polishing solution, a one-way valve(check valve)


48


for preventing a reverse flow, and a pressure sensor


50


and the like. An output signal from the pressure sensor is input to the controller, and the controller controls the operation of the circulation pump


46


according to the output signal of the pressure sensor so as to maintain the internal pressure in the circulation pipe


20


at a constant value. Circulation pipe


20


is branched into delivery pipes


24


near each polishing unit


22


to deliver the polishing solution thereto, and each delivery pipe


24


is connected, through a shutoff valve


52


and an adjustable flow pump


54


, to a spray nozzle


56


directed at a certain location of each polishing unit


22


.




Accordingly, by circulating the polishing solution at all times inside the piping to guide the solution to the neighborhood of the polishing unit


22


, changes in solution concentration and line plugging caused by precipitated solid clusters from a stagnating polishing solution can be eliminated. Also, because the arrangement of the supply device permits the use of a long length of circulation piping, one supply source (mixing section)


18


can be used to supply a polishing solution, in a stable condition, and the cost of the overall facility can be reduced. Because each polishing unit


22


has its own working schedule, the polishing solution may become stagnant in some delivery pipes


24


in which the flow is stopped, but any adverse effects of stagnation can be eliminated by flowing a sufficient quantity of polishing solution to replace the stagnant liquid in the delivery pipes at the beginning of each operation.




Next, the effect that ultrasonic vibration applied to the solution has on the abrading particles or polishing qualities will be described with reference to

FIGS. 2A through 4

.





FIGS. 2A through 2C

show an example of changes in the particle size distribution when vibrations are applied over a period of time. The stirrer


70


was operated for 30 minutes to produce a distribution of average particle size 51.7 μm, and a standard deviation 49.7 μm, as shown in FIG.


2


A. After 10 minutes of ultrasonic vibration applied to the solution, an average particle size of 0.29 μm and a standard deviation 2.73 μm were obtained, as shown in FIG.


2


B. After ultrasonic vibration applied to the solution for


60


minutes, an average particle size 0.15 μm and a standard deviation 0.029 μm were obtained, as shown in FIG.


2


C. When vibration was applied longer than 60 minutes, further changes beyond those shown in

FIG. 2C

were not observed.





FIGS. 3A through 3C

show changes in a particle size distribution observed when the vibrated solution was left standing.

FIG. 3A

shows the change after 120 minutes of standing,

FIG. 3B

shows the change after one day of standing, and

FIG. 3C

shows the change after six days of standing. The results indicated that the solution retains a fine particle size distribution for a considerable length of time after ultrasonic vibration is applied.





FIG. 4

shows a comparison of polishing performance of the solutions treated without ultrasonic vibrations and with ultrasonic vibrations, and a comparison with a commercial polishing solution containing silica powder. The results show that the polishing rate is increased when ultrasonic vibrations are applied because the particles become finely dispersed. The results also show that the polishing rates of a test slurry subjected to vibrations are about the same for a commercial polishing slurry. The results observed in

FIGS. 2A through 4

regarding the effects of ultrasonic vibration treatment on the particle size distribution and polishing capability, were applied to the polishing solution supply apparatus in this embodiment.




The operation of the polishing solution supply apparatus will be explained below. The stock tank


10


is opened by lifting a lid, and a silica powder and given quantities of polishing liquids such as KOH, NH


4


OH are added and stirred with the stirrer


70


to disperse the abrading (silica) particles. Concurrently with stirring or after stirring for a given time, the ultrasonic vibrator


72


is operated for a given interval. This step disperses clustered powder particles that exhibited a relatively wide range of particle sizes, and produces a particle size distribution centered about a narrow range of fine particle sizes. The processing interval and frequency of the application of ultrasonic vibration are governed by the size of the tanks


10


. For example, ultrasonic vibration may be carried out in a regular pattern, for example, for two minutes continuously over a period of sixty minutes or five minutes continuously over a period of thirty minutes.




Next, by operating the pumps


28


an a polishing solution of a given mixture ratio is produced. The control device controls the circulation pump


46


so that the downstream pressure is maintained above a certain value, and a steady circulating flow of polishing solution in the circulation passage


20


is generated.




When the individual polishing units


22


are operated, a portion of the polishing solution is delivered through the respective delivery pipes


24


into the nozzles


56


of the respective polishing units


22


. When the solution level inside the buffer tube


18


becomes lower than the lower limit, the level sensor


40




b


sends a signal to the control device to open the valves


26


, whereby the undiluted solution and pure water, whose flow rates are controlled by the flow control valves


26


, are supplied to the buffer tube


18


at a constant mixing ratio, until the liquid level reaches the upper limit. In this step, because the undiluted solution has been treated by ultrasonic vibration for a given length of time in the stock tank


10


, silica is less likely to aggregate.





FIG. 5

shows another embodiment of this invention, in which the ultrasonic vibrators are provided at various locations in the supply passage. For example, vibrators


72




a,




72




b,




72




c,




72




d


of suitable sizes and shapes are applied at one or more locations including the mixing section (buffer tube)


18


for the undiluted solution and dilution solution, circulation pipe


20


, near the nozzle


56


, and on the turntable


23


.





FIGS. 6A through 6C

show details of attaching the vibrators


72




a,




72




b,




72




c,




72




d.


As shown in each diagram, the vibrators


72




a


through


72




d


comprise ultrasonic elements


74




a


through


74




d


and ultrasonic oscillators


76




a


through


76




d.



FIG. 6A

shows an installation of the vibrator


72




a


on the bottom section of the buffer tube


18


. Vibrator


72




b


is similarly disposed about the circulation pipe


20


.

FIG. 6B

shows the vibrator


72




c


installed near the tip of the nozzle


56


which directs polishing solution onto the turntable


23


. Vibrators


72




a


through


72




c


can be installed in any suitable place on the buffer tube


18


and each piping.





FIG. 6C

shows a cross sectional view of the ultrasonic vibrator


72




d


imbedded in the turntable


23


. The vibrator


72




d


is imbedded near the center of the abrading surface of the turntable underneath a polishing pad


78


. In this embodiment, the vibrator is imbedded near the center, but the location of the vibrator


72




d


may be underneath and off-center near the location of supply of solution on the turntable, or near the pressing point for polishing the wafer.




In these embodiments, the solution can be supplied on the turntable


23


in a well dispersed state, because the point of solution delivery is a downstream location of the solution flow, or close to the location where the solution is actually being applied to the wafer. Also, even when the polishing units


22


are stopped and the solution flow rate drops or the solution becomes stagnant, particle clustering is less likely to occur. In this embodiment, additional ultrasonic vibrations are applied to locations other than the stock tank, so that, compared with the case of applying the ultrasonic vibrations only at the stock tank, clustering can be prevented even if the size of the apparatus for supplying the polishing solution is increased.





FIG. 7

shows an arrangement when there are not enough polishing units


22


to justify a circulation pipe


20


, so that the buffer tube may be replaced with a supply bottle


80


.




The supply bottle


80


is held in a water tank


84


by virtue of a support


82


, and the water tank


84


is provided with a water supply pipe


86


to constantly supply water and a discharge pipe


88


to maintain the water level constant so as to keep the bottom of the supply bottle


80


always under water. An immersion type ultrasonic vibrator


72




e


is immersed in the water tank


84


located directly below the water bottle


80


. The vibrator


72




e


is controlled by a controller


77


located outside of the water tank


84


. An opening section


83


is cut out of the support


82


between the supply bottle


80


and the vibrator


72




e,


so that ultrasonic waves generated from the vibrator


72




e


impact the bottom of the supply bottle


80


through the opening section


83


. A stirrer


90


is introduced into the supply bottle


80


from a top opening thereby and attached to the supply bottle


80


, so as to enable stirring of the solution while the bottom of the supply bottle


80


is subjected to ultrasonic vibrations. The material for making the supply bottle


80


, water tank


84


, and support


82


includes resins, quartz glass, stainless steels and resin coated metals. Although not shown in the drawing, it is preferable that the supply bottle


80


is provided with a lid so as to prevent solution evaporation and reaction with the environment.




In this embodiment, the undiluted solution and the dilution solution are pumped individually to the supply bottle


80


from respective supply sources


10


,


12


by pumps


28


. A polishing solution prepared at a certain concentration in the supply bottle


80


is stirred and ultrasonically vibrated as necessary to generate a dispersion of the powder in the solution as previously described. The solution is delivered to polishing units through one or more delivery pipes


92


by a slurry pump


94


.




As explained above, according to this invention, a polishing solution having a constant distribution of polishing particle size can be delivered to polishing units by dispersing the agglomerated powder particles by subjecting the solution to go ultrasonic vibration. It follows that polishing can be performed in a stable manner by preventing surface scratches caused by aggregated power particles, or by preventing changes of polishing rate caused by changes in the particle concentration.




Industrial Applicability




This invention is useful as an apparatus for delivering a polishing solution to a polishing apparatus for manufacturing, for example, semiconductor devices which are highly integrated.



Claims
  • 1. An apparatus for delivering a polishing solution to a polishing device, comprising:a solution passage for transporting a polishing solution, with said solution passage including a circulation passage for circulating the polishing solution and a delivery passage extending from said circulation passage to a polishing device; and an ultrasonic vibrator provided at at least one of said circulation passage and said delivery passage.
  • 2. An apparatus for delivering a polishing solution to a polishing device, comprising:a solution passage for transporting a polishing solution, with said solution passage including a mixing section for mixing an undiluted solution and a dilution solution to adjust a polishing solution concentration; and an ultrasonic vibrator provided at said mixing section.
  • 3. A polishing apparatus comprising:a solution passage for transporting a polishing solution, with said solution passage including a stock tank for stocking an undiluted solution; an ultrasonic vibrator provided at said stock tank; a holding device for holding an object to be polished; a polishing tool to be opposed to said holding device; a nozzle for supplying the polishing solution onto said polishing tool; and a vibrator positioned in said polishing tool.
  • 4. The apparatus according to claim 3 wherein said vibrator positioned in said polishing tool comprises an ultrasonic vibrator positioned in said polishing tool.
  • 5. The apparatus according to claim 4, wherein said polishing tool includes an abrading surface, and wherein said polishing tool is to be opposed to said holding device by having said abrading surface be opposed to said holding device.
  • 6. The apparatus according to claim 5, wherein said ultrasonic vibrator is positioned in said polishing tool by being positioned beneath said abrading surface.
  • 7. The apparatus according to claim 6, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said ultrasonic vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
  • 8. The apparatus according to claim 3, wherein said polishing tool includes an abrading surface, and wherein said polishing tool is to be opposed to said holding device by having said abrading surface be opposed to said holding device.
  • 9. The apparatus according to claim 8, wherein said vibrator is positioned in said polishing tool by being positioned beneath said abrading surface.
  • 10. The apparatus according to claim 9, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
  • 11. A polishing apparatus comprising:a solution passage for transporting a polishing solution, with said solution passage including a circulation passage for circulating the polishing solution and a delivery passage extending from said circulation passage to a polishing device; and an ultrasonic vibrator provided at at least one of said circulation passage and said delivery passage, wherein said polishing device includes a holding device for holding an object to be polished, a polishing tool to be opposed to said holding device, a nozzle for supplying the polishing solution onto said polishing tool, and a vibrator positioned in said polishing tool.
  • 12. The apparatus according to claim 11, wherein said vibrator positioned in said polishing tool comprises an ultrasonic vibrator positioned in said polishing tool.
  • 13. The apparatus according to claim 12, wherein said polishing tool includes an abrading surface, and wherein said polishing tool is to be opposed to said holding device by having said abrading surface be opposed to said holding device.
  • 14. The apparatus according to claim 13, wherein said ultrasonic vibrator is positioned in said polishing tool by being positioned beneath said abrading surface.
  • 15. The apparatus according to claim 14, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said ultrasonic vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
  • 16. The apparatus according to claim 11, wherein said polishing tool includes an abrading surface, and wherein said polishing tool is to be opposed to said holding device by having said abrading surface be opposed to said holding device.
  • 17. The apparatus according to claim 16, wherein said vibrator is positioned in said polishing tool by being positioned beneath, said abrading surface.
  • 18. The apparatus according to claim 17, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
  • 19. A polishing apparatus comprising:a solution passage for transporting a polishing solution, with said solution passage including a mixing section for mixing an undiluted solution and a dilution solution to adjust a polishing solution concentration; an ultrasonic vibrator provided at said mixing section; a holding device for holding an object to be polished; a polishing tool to be opposed to said holding device; a nozzle for supplying a polishing solution onto said polishing tool; and a vibrator positioned in said polishing tool.
  • 20. The apparatus according to claim 19, wherein said vibrator positioned in said polishing tool comprises an ultrasonic vibrator positioned in said polishing tool.
  • 21. The apparatus according to claim 20, wherein said polishing tool includes an abrading surface and wherein said polishing tool is to be opposed to said holding device by having said abrading surface be opposed to said holding device.
  • 22. The apparatus according to claim 21, wherein said ultrasonic vibrator is positioned in said polishing tool by being positioned beneath said abrading surface.
  • 23. The apparatus according to claim 22, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said ultrasonic vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
  • 24. The apparatus according to claim 19, wherein said polishing tool includes an abrading surface, and wherein said polishing tool is to be opposed to said holding device by having said abrading surface be opposed to said holding device.
  • 25. The apparatus according to claim 24, wherein said vibrator is positioned in said polishing tool by being positioned beneath said abrading surface.
  • 26. The apparatus according to claim 25, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
  • 27. A polishing apparatus comprising:a polishing device including a holding device for holding an object to be polished, a polishing tool to be opposed to said holding device, a nozzle for supplying a polishing solution onto said polishing tool, and a vibrator positioned in said polishing tool; a store section for storing a solution, said store section including at least one of a stock section for storing an undiluted solution and a mixing section for mixing an undiluted solution and a dilution solution to adjust a polishing solution concentration; a solution passage for transporting a polishing solution from said store section to said dishing device; and a vibrator positioned at said store section.
  • 28. The apparatus according to claim 27, wherein said vibrator positioned in said polishing tool comprises an ultrasonic vibrator positioned in said polishing tool, and said vibrator positioned at said store section comprises an ultrasonic vibrator positioned at said store section.
  • 29. The apparatus according to claim 28, wherein said polishing tool includes an abrading surface, and wherein said polishing tool is to be opposed to said holding device by having said abrading surface be opposed to said holding device.
  • 30. The apparatus according to claim 29, wherein said ultrasonic vibrator is positioned in said polishing tool by being positioned beneath salty abrading surface.
  • 31. The apparatus according to claim 30, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said ultrasonic vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
  • 32. The apparatus according to claim 27, wherein said polishing tool includes an abrading surface, and wherein said polishing tool is to be opposed to said holding device by having said abrading, surface be opposed to said holding device.
  • 33. The apparatus according to claim 32, wherein said vibrator is positioned in said polishing tool by being positioned beneath said abrading surface.
  • 34. The apparatus according to claim 33, wherein said abrading surface includes a polishing pad provided on an upper surface of said polishing tool, and wherein said vibrator is positioned beneath said abrading surface by being positioned beneath said polishing pad.
Priority Claims (1)
Number Date Country Kind
9-354134 Aug 1997 JP
PCT Information
Filing Document Filing Date Country Kind
PCT/JP98/05541 WO 00
Publishing Document Publishing Date Country Kind
WO99/29505 6/17/1999 WO A
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