Constant precision volumetric dilution vessel

Information

  • Patent Grant
  • 6722779
  • Patent Number
    6,722,779
  • Date Filed
    Friday, October 26, 2001
    23 years ago
  • Date Issued
    Tuesday, April 20, 2004
    20 years ago
Abstract
A chemical delivery apparatus is provided. In one exemplary arrangement, the apparatus comprises a first vessel having a body and a neck extending upwardly from the body. The neck has a smaller cross-sectional area than the body. A fluid inlet is provided near a top of the neck. A fluid outlet is provided near a bottom of the body. A first sight tube port is provided near the top of the neck, and a second sight tube port is provided near the bottom of the body. A sight tube is connected between the first and second sight tube ports to indicate an amount of fluid in the first vessel. A first fluid source selectively communicates with the first vessel through the fluid inlet of the first vessel. A second vessel is also provided, comprising a fluid inlet and a fluid outlet. A second fluid source selectively communicates with the second vessel through the fluid inlet of the second vessel. A mix chamber selectively communicates with the first and second vessels through the fluid outlets of the first and second vessels.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates generally to methods and apparatus for mixing chemicals used in semiconductor manufacturing processes and, more particularly, to methods and apparatus for mixing chemicals for use in chemical mechanical polishing processes.




2. Description of the Related Art




Chemical mechanical polishing (CMP) planarization techniques are commonly used in the manufacture of layered semiconductor devices. In typical CMP processes, a workpiece or wafer to be polished is pressed against a polishing pad under controlled conditions in the presence of a chemical mixture. The chemical mixture typically comprises a slurry including small, abrasive particles that abrade the surface of the wafer, and chemicals that etch and/or oxidize the surface of the wafer. When the pad and the wafer are moved with respect to one another, material is chemically and mechanically removed from the surface of the wafer to produce a polished or planarized surface.




Chemical mixtures used in CMP processes vary depending on the material to be removed from the surface of the wafer. If a metal surface is to be polished, the mixture may comprise, for example, a slurry containing a suspension of electrically charged alumina or silica particles and an oxidizer comprising, for example, hydrogen peroxide. If a nonmetal surface is to be polished, the mixture may comprise, for example, a slurry containing a suspension of electrically charged silica particles and, for example, ammonia or ammonium hydroxide.




In order to ensure consistent process results between wafers, it is necessary to precisely control the composition of the chemical mixture used. Prior art CMP systems typically include volumetric pumps that pump the various components of the mixture from bulk sources to a mix chamber where the components are mixed together. While typically providing high throughput, such systems typically do not allow precise control of the mixture composition due to the limited precision of the volumetric pumps. Accordingly, a need exists for a CMP system in which the composition of the chemical mixture delivered to the wafer can be precisely controlled without adversely affecting throughput.




SUMMARY OF THE INVENTION




In accordance with one aspect of the present invention, a method of preparing a fluid mixture comprising predetermined amounts of two or more fluids is provided. The method comprises the steps of providing a first vessel having a body and a neck extending upwardly from the body. The neck has a smaller cross-sectional area than the body. A first fluid is delivered to the first vessel to fill the body and at least a portion of the neck. A sight tube indicating an amount of the first fluid in the first vessel is read, preferably by an optical sensor. The delivery of the first fluid is discontinued when the sight tube indicates that a predetermined amount of the first fluid is in the first vessel. A second vessel is also provided. A second fluid is delivered to the second vessel. A sight tube indicating an amount of the second fluid in the second vessel is read, also preferably by an optical sensor. The delivery of the second fluid is discontinued when the sight tube indicates that a predetermined amount of the second fluid is in the second vessel. The predetermined amounts of the first and second fluids are then delivered to a mix chamber and mixed.




In accordance with another aspect of the present invention, a chemical delivery apparatus is provided, comprising a first vessel having a body and a neck extending upwardly from the body. The neck has a smaller cross-sectional area than the body. A fluid inlet is provided near a top of the neck. A fluid outlet is provided near a bottom of the body. A first sight tube port is provided near the top of the neck, and a second sight tube port is provided near the bottom of the body. A sight tube is connected between the first and second sight tube ports to indicate an amount of fluid in the first vessel. A first fluid source selectively communicates with the first vessel through the fluid inlet of the first vessel. A second vessel is also provided, comprising a fluid inlet and a fluid outlet. A second fluid source selectively communicates with the second vessel through the fluid inlet of the second vessel. A mix chamber selectively communicates with the first and second vessels through the fluid outlets of the first and second vessels.




In accordance with another aspect of the present invention, a method of preparing a fluid mixture comprising predetermined amounts of two or more fluids is provided. The method comprises the steps of providing a vessel having a body and a neck extending downwardly from the body. The neck has a smaller cross-sectional area than the body. A first fluid is delivered to the vessel to fill a portion of the neck. A sight tube indicating an amount of the fluid in the vessel is read, preferably by an optical sensor. The delivery of the first fluid is discontinued when the sight tube indicates that a predetermined amount of the first fluid is in the vessel. A second fluid is then delivered to the vessel to fill a remaining portion of the neck and at least a portion of the body. The sight tube is read by the optical sensor, and the delivery of the second fluid is discontinued when the sight tube indicates that a predetermined amount of the second fluid is in the vessel. The predetermined amounts of the first and second fluids are then delivered to a storage chamber.




In accordance with another aspect of the present invention, a chemical delivery apparatus is provided, comprising a vessel having a body and a neck extending downwardly from the body. The neck has a smaller cross-sectional area than the body. First and second fluid inlets are provided near a top of the body. A fluid outlet is provided near a bottom of the neck. A first sight tube port is provided near the top of body, and a second sight tube port is provided near the bottom of the neck. A first fluid source selectively communicates with the vessel through the first fluid inlet. A second fluid source selectively communicates with the vessel through the second fluid inlet. A sight tube connected between the first and second sight tube ports indicates an amount of fluid in the vessel. A storage chamber selectively communicates with the vessel through the fluid outlet.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a simplified schematic view of a first exemplary apparatus for mixing chemical slurries for chemical mechanical polishing of a workpiece;





FIG. 2

is a front elevational view of one of the vessels of the apparatus of

FIG. 1

;





FIG. 3

is a right side elevational view of the vessel of

FIG. 2

;





FIG. 4

is a top plan view of the vessel of

FIG. 2

;





FIG. 5

is a simplified schematic view of a second exemplary apparatus for mixing chemical slurries for chemical mechanical polishing of a workpiece;





FIG. 6

is a rear elevational view of one of the vessels of the apparatus of

FIG. 5

;





FIG. 7

is a right side elevational view of the vessel of

FIG. 6

; and





FIG. 8

is a bottom plan view of the vessel of FIG.


6


.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




With reference to

FIG. 1

, an apparatus for preparing a chemical mixture for use in CMP processing of semiconductor wafers is illustrated and designated generally by the reference number


20


. In the illustrated embodiment, the apparatus


20


comprises a first fluid source


24


and a second fluid source


28


. Depending on the surface material to be polished, the first fluid source


24


may comprise, for example, a slurry containing a suspension of electrically charged alumina particles. The second fluid source


28


may comprise, for example, hydrogen peroxide.




In the apparatus of

FIG. 1

, the first fluid source


24


is connected by a first fluid line


32


to a first vessel


34


. The second fluid source


28


is connected by a second fluid line


40


to a second vessel


44


. In the illustrated embodiment, each of the first and second vessels


34


,


44


generally comprises a lower body portion


48


and a neck portion


50


that extends upwardly from the body


48


, preferably at one side of the body


48


, as best illustrated in

FIGS. 2-4

. A fluid inlet


54


is provided near a top of the neck


50


, and a fluid outlet


56


is provided near a bottom of the body portion


48


. The first and second fluid lines


32


,


40


are connected to the fluid inlets


54


.




Each of the vessels


34


,


44


preferably includes an upper sight tube port


60


near the top of the neck


50


, and a lower sight tube port


62


near the bottom of the body portion


48


. A sight tube


66


preferably is connected between the upper and lower sight tube ports


60


,


62


, as illustrated schematically in

FIG. 1. A

vent opening


70


(see

FIG. 4

) preferably is also provided near the top of the neck


50


.




In the illustrated embodiment, each of the sight tubes


66


comprises a tubular fluid conduit


74


having an upper end connected to the upper sight tube port


60


and a lower end connected to the lower sight tube port


62


. As is well known in the art, fluid flows out of the lower sight tube port


62


and into the conduit


74


as the vessel


34


,


44


is filled with fluid. The height of the fluid column in the sight tube


66


indicates the level of the fluid in the vessel


34


,


44


. Based on the dimensions of the vessel


34


,


44


, the volume of the fluid in the vessel


34


,


44


can then be determined.




Preferably, the height of the fluid column in the sight tube


66


is sensed by an optical sensor(s)


65


. The optical sensor


65


sends a signal to a programmable controller


75


, which communicates with various pumps and/or valves in the apparatus. In the simplified schematic of

FIG. 1

, a single pump


80


and a single valve


82


are provided in each of the first and second fluid lines


32


,


40


between the fluid sources


24


,


28


and the vessels


34


,


44


.




Optical sensors are well known in the art and can be purchased from a number of different suppliers, including Omron Electronics, Inc., of Schaumburg, Ill. The precision of a typical optical sensor in sensing the height of a fluid column in a sight tube (and, thus, the fluid level in a vessel to which the sight tube is attached) is about ±1 mm of fluid height at 99 percent confidence. Accordingly, given the limited precision of such sensors, as the volume of fluid per unit height in a vessel is decreased, the precision with which it is possible to measure the total volume of fluid in the vessel is increased.




In order to decrease the volume of fluid per unit height in a vessel, and thus increase the precision with which the total volume of fluid in the vessel can be determined, the cross-sectional area of the vessel must be decreased. As the cross-sectional area of the vessel is decreased, however, the height of the vessel must be increased to maintain the same total volume of the vessel. This can be problematic, because the maximum height of the vessel is typically constrained by the environment in which the vessel is located.




Each of the vessels


34


,


44


of the apparatus of

FIG. 1

comprises a body portion


48


having relatively large cross-sectional area and a neck portion


50


having a smaller cross-sectional area. Preferably, the cross-sectional area of the neck portion


50


of each of the vessels


34


,


44


is less than about one-third the cross-sectional area of the body portion


48


. In the illustrated embodiment, the cross-sectional area of the neck portion


50


of each vessel


34


,


44


is about 20 percent that of the body portion


48


.




When the fluid level in the vessel


34


,


44


is below the neck portion


50


thereof, the precision with which the total volume of fluid in the vessel


34


,


44


can be determined is relatively low, due to the relatively large cross-sectional area of the body portion


48


and the limited precision of the optical sensor


65


. As the vessel


34


,


44


is filled and the fluid level rises into the neck portion


50


, however, it is possible to more precisely determine the total volume of fluid in the vessel


34


,


44


, assuming the volume of the body portion


48


of the vessel


34


,


44


is known. Because the cross-sectional area of the neck


50


is relatively small, the fluid level in the neck


50


, and thus the height of the fluid column in the sight tube


66


, rises or falls significantly as the volume of fluid in the vessel


34


,


44


is increased or decreased. As a result, the volume of fluid in the vessel


34


,


44


can be sensed more precisely by the optical sensor


65


. At the same time, because of the relatively large cross-sectional area of the body


48


of the vessel


34


,


44


, the total volume of the vessel


34


,


44


can be substantial without requiring that the height of the vessel


34


,


44


be excessive.




With reference again to

FIG. 1

, in operation, the controller


75


opens the valve


82


and activates the pump


80


to pump the first fluid through the first fluid line


32


from the first fluid source


24


to the first vessel


34


. The fluid level in the vessel


34


rises through the body


48


of the vessel


34


and into the neck


50


. As the vessel


34


is filled, the fluid column in the sight tube


66


rises. The optical sensor


65


senses the height of the fluid column in the sight tube


66


. When the column reaches a predetermined height indicating that the desired amount of fluid is in the vessel


34


, the sensor sends a signal to the controller


75


to close the valve


82


and deactivate the pump


80


.




In a similar manner, the controller


75


opens the valve


82


and activates the pump


80


of the second fluid line


40


to pump the second fluid from the second fluid source


28


to the second vessel


44


. The fluid level in the second vessel


44


similarly rises through the body


48


of the vessel


44


and into the neck


50


. As the vessel


44


is filled, the fluid column in the sight tube


66


rises. The optical sensor


65


senses the height of the fluid column in the sight tube


66


. When the column reaches a predetermined height indicating that the desired amount of fluid is in the vessel


44


, the sensor


65


sends a signal to the controller


75


to close the valve


82


and deactivate the pump


80


.




In the arrangement of

FIG. 1

, each of the first and second vessels is connected to a mix chamber


100


or storage chamber by a fluid line


102


. The fluid lines


102


are connected to the fluid outlets


56


(see

FIGS. 2-3

) of the vessels


34


,


44


. When the vessels


34


,


44


are filled to the desired levels (taking into account the amount of fluid in the fluid lines


102


between the vessels


34


,


44


and the mix chamber


100


), the controller


75


opens a valve


108


in each of the fluid lines


102


and delivers the precisely measured contents of vessels


34


,


44


into the mix chamber


100


. Depending on the particular arrangement of the apparatus, additional pumps may be necessary to pump the fluids through the fluid lines


102


to the mix chamber.




The mix chamber


100


may include a mechanical mixer (not shown) to stir the contents of the mix chamber


100


and prevent the mixture from stagnating or separating. In the illustrated embodiment, a recirculation line


110


is provided for such purpose. The mixture exits the mix chamber


100


and is pumped through the recirculation line


110


and back into the mix chamber


100


. In the illustrated arrangement, a three-way valve


118


is provided in the recirculation line


110


so that a portion of the mixture can be diverted to the workpiece (not shown) for use in the CMP process.




It is to be understood that the apparatus


20


illustrated schematically in

FIG. 1

is merely exemplary. Those skilled in the art will recognize that, depending on the particular process to be carried out, alternative arrangements may include a greater or lesser number of vessels and accommodate additional or different fluids. In addition, depending on the precision with which it is necessary to measure the various components of the chemical mixture, only certain of the vessels may have the large cross-sectional body and smaller cross-sectional area neck configuration of the vessels of the apparatus of FIG.


1


.




With reference now to

FIG. 5

, a simplified schematic view of a second exemplary apparatus


200


for preparing chemical mixtures is illustrated. In the illustrated embodiment, the apparatus


200


comprises a first fluid source


210


and a second fluid source


212


. Again, depending on the surface material to be polished, the first fluid source


210


may comprise, for example, a slurry containing a suspension of electrically charged silica particles. The second fluid source


212


may comprise, for example, deionized water.




In the arrangement illustrated in

FIG. 5

, the first fluid source


210


is connected by a first fluid line


218


to a mix vessel


220


. The second fluid source


212


is connected by a second fluid line


222


to the mix vessel


220


. As best illustrated in

FIGS. 6-9

, the mix vessel


220


generally comprises a body portion


230


and a neck portion


232


that extends downwardly from the body


230


, preferably at one side of the body


230


. A pair of fluid inlets


236


are provided near a top of the body


230


. A fluid outlet


238


is provided near a bottom of the neck


232


. The first and second fluid lines


218


,


222


(

FIG. 5

) are connected to the fluid inlets


236


of the vessel


220


.




The vessel


220


preferably includes an upper sight tube port


244


near the top of the neck


232


, and a lower sight tube port


246


near the bottom of the body portion


230


. A sight tube


250


preferably is connected between the first and second sight tube ports


244


,


246


, as illustrated schematically in

FIG. 5. A

vent opening (not shown) and a recirculation inlet


256


preferably are also provided near the top of the body


230


.




Fluid flows out of the lower sight tube port


246


and into the sight tube


250


as the vessel


220


is filled with fluid. The height of the fluid column in the sight tube


250


indicates the level of the fluid in the vessel


220


. Preferably, the height of the fluid column in the sight tube


250


is sensed by an optical sensor


249


, which sends a signal to a programmable controller


251


. The controller


251


communicates with various pumps and/or valves in the apparatus. In the simplified schematic of

FIG. 5

, a single pump


262


and a single valve


264


are provided in each of the fluid lines


218


,


222


between the fluid sources


210


,


212


and the vessel


220


.




As illustrated in

FIGS. 6-8

, the body portion


230


of the vessel


220


has a relatively large cross-sectional area. The neck portion


232


has a smaller cross-sectional area. Preferably, the cross-sectional area of the neck portion


232


is less than about one-third that of the body portion


230


. In the illustrated embodiment, the cross-sectional area of the neck portion


232


of the vessel


220


is about 21 percent that of the body portion


230


.




The vessel


220


preferably includes a transitional region


270


between the body portion


230


and the neck


232


, as best illustrated in FIG.


6


. Preferably, the cross-sectional area of the transitional region


270


decreases progressively from the body portion


230


to the neck


232


to facilitate fluid drainage from the vessel


220


. In the vessel


220


of

FIGS. 6-8

, the cross-sectional area of the neck


232


similarly decreases from the transitional region


290


to the bottom of the neck


232


to facilitate drainage from the vessel


220


.




With reference to

FIG. 5

, in operation, the controller


251


opens the valve


264


and activates the pump


262


to the first fluid through the fluid line


218


from the first fluid source


210


to the vessel


220


. The fluid rises into the neck portion


232


of the vessel


220


. Because of the relatively small cross-sectional area of the neck portion


232


, the fluid level in the neck


232


, and thus the height of the fluid column in the sight tube


250


, rises significantly as the volume of fluid in the neck


232


is increased. The volume of the first fluid in the neck


232


can thus be precisely determined by the optical sensor


249


. When the fluid column reaches a predetermined height indicating that a desired volume of fluid is in the neck portion


232


, the sensor


249


sends a signal to the controller


251


to close the valve


264


and deactivate the pump


262


.




The controller


251


then opens the valve


264


and activates the pump


262


of the second fluid line


222


to pump the second fluid from the second fluid source


212


to the vessel


220


. The fluid level in the vessel


220


rises through the remaining part of the neck


232


and into the body portion


230


of the vessel


220


. As the vessel


220


is filled, the fluid column in the sight tube


250


rises. The optical sensor


249


senses the height of the fluid column in the sight


250


tube. When the column reaches a predetermined height, the sensor


249


sends a signal to the controller


251


to close the valve


264


and deactivate the pump


262


.




The vessel


220


illustrated in

FIGS. 5-8

is particularly advantageous when a desired mixture includes a substantially greater volume of one component than another component. The smaller volume component is first delivered to the vessel


220


to fill the neck


232


of the vessel


220


. Because of the smaller cross-sectional area of the neck


232


, the precise volume of the smaller volume component in the neck


232


can be precisely determined. The larger volume component, which need not be measured as precisely, can then be delivered to the vessel


220


to fill the body


230


of the vessel


220


.




In the arrangement of

FIG. 5

, a recirculation line


290


is provided to prevent the mixture from stagnating. The mixture exits the vessel


220


through the fluid outlet


238


and is pumped through the recirculation line


290


and back into the vessel


220


through the recirculation inlet


256


. In the illustrated arrangement, a three-way valve


294


is provided in the recirculation line


290


so that a portion of the mixture can be diverted to the workpiece (not shown) for use in the CMP process.




It is to be understood that the apparatus illustrated in

FIG. 5

, too, is merely exemplary. Those skilled in the art will recognize that, depending on the particular process to be carried out, alternative arrangements may include a greater of vessels and accommodate additional or different fluids. In addition, depending on the precision with which it is necessary to measure the various components of the chemical mixture, only certain of the vessels may have the large cross-sectional body and smaller cross-sectional area neck configuration of the vessel of the apparatus of FIG.


5


.




Although the invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.



Claims
  • 1. A method of preparing a fluid mixture comprising predetermined amounts of two or more fluids, the method comprising the steps of:providing a first vessel comprising a body and a neck extending upwardly from said body, said neck having a smaller cross-sectional area than said body; delivering a first fluid to said first vessel to fill said body and at least a portion of said neck; reading a sight tube connected to said first vessel, said sight tube indicating an amount of said first fluid in said first vessel; discontinuing said delivery of said first fluid when said sight tube indicates that a predetermined amount of said first fluid is in said first vessel; providing a second vessel; delivering a second fluid to said second vessel; reading a sight tube connected to said second vessel, said sight tube indicating an amount of said second fluid in said second vessel; discontinuing said delivery of said second fluid when said sight tube indicates that a predetermined amount of said second fluid is in said second vessel; delivering said predetermined amounts of said first and second fluids to a mix chamber; and mixing said predetermined amounts of said first and second fluids in said mix chamber.
  • 2. The method of claim 1, wherein said second vessel comprises a body and a neck extending upwardly from said body, said neck having a smaller cross-sectional area than said body, and said delivering of said second fluid to said second vessel comprises filling said body and at least a portion of said neck of said second vessel.
  • 3. A chemical delivery apparatus, comprising:a first vessel comprising a body and a neck extending upwardly from said body, said neck having a smaller cross-sectional area than said body, a fluid inlet near a top of said neck, a fluid outlet near a bottom of said body, a first sight tube port near the top of said neck, a second sight tube port near the bottom of said body, and a vent opening near the top of said neck; a first fluid source selectively communicating with said first vessel through said fluid inlet of said first vessel; a sight tube connected between said first and second sight tube ports of said first vessel, said sight tube indicating an amount of fluid in said first vessel; a second vessel comprising a fluid inlet and a fluid outlet; a second fluid source selectively communicating with said second vessel through said fluid inlet of said second vessel; and a mix chamber selectively communicating with said first and second vessels through said fluid outlets of said first and second vessels.
  • 4. The apparatus of claim 3, wherein a cross-sectional area of said neck is less than about one-third that of said body.
  • 5. The apparatus of claim 3, further comprising an optical sensor, said optical sensor sensing a height of a fluid column in said sight tube.
  • 6. The apparatus of claim 5, further comprising a programmable controller in communication with said optical sensor.
  • 7. A method of preparing a fluid mixture comprising predetermined amounts of two or more fluids, the method comprising the steps of:providing a vessel comprising a body and a neck extending downwardly from said body, said neck having a smaller cross-sectional area than said body; delivering a first fluid to said vessel to fill a portion of said neck; reading a sight tube connected to said vessel, said sight tube indicating an amount of said fluid in said vessel; discontinuing said delivery of said first fluid when said sight tube indicates that a predetermined amount of said first fluid is in said vessel; delivering a second fluid to said vessel to fill a remaining portion of said neck and at least a portion of said body; reading said sight tube; discontinuing said delivery of said second fluid when said sight tube indicates that a predetermined amount of said second fluid is in said vessel; and delivering said predetermined amounts of said first and second fluids to a storage chamber.
  • 8. The method of claim 7, wherein said reading comprises sensing a height of a fluid column in said sight tube with an optical sensor.
  • 9. A chemical delivery apparatus, comprising:a vessel comprising a body and a neck extending downwardly from said body, said neck having a smaller cross-sectional area than said body, a first fluid inlet near a top of said body, a second fluid inlet near a top of said body, a fluid outlet near a bottom of said neck, a first sight tube port near a top of body, a second sight tube port near a bottom of said neck, and a vent opening near a top of said body; a first fluid source selectively communicating with said vessel through said first fluid inlet; a second fluid source selectively communicating with said vessel through said second fluid inlet; a sight tube connected between said first and second sight tube ports, said sight tube indicating an amount of fluid in said first vessel; and a storage chamber selectively communicating with said vessel through said fluid outlet.
  • 10. The apparatus of claim 9, wherein a cross-sectional area of said neck is less than about one-third that of said body.
  • 11. The apparatus of claim 9, wherein said vessel further comprises a transitional region between said body and said neck, said transitional region having a cross-sectional area that decreases progressively from said body to said neck.
  • 12. The apparatus of claim 11, wherein a cross-sectional area of said neck decreases from said transitional region to the bottom of said neck.
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3976087 Bolton et al. Aug 1976 A
5484336 McConnell Jan 1996 A
5750440 Vanell et al. May 1998 A
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Number Date Country
0381894 Aug 1990 EP