Abstract:
A slurry delivery system for a chemical mechanical polisher, comprising a bag housing fitted with a slurry intake conduit and a slurry outlet conduit. An expandible and collapsible pump bag is provided in fluid communication with the conduits inside the bag housing, and the interior of the pump bag is sealed from the bag housing. As an air/vacuum controller withdraws air from the housing, the pump bag enlarges and slurry is drawn into the pump bag. As the air/vacuum controller subsequently introduces air into the housing, the pump bag collapses and the slurry is expelled from the pump bag through the slurry outlet conduit. A purge valve is provided upstream of the pump bag to remove air bubbles from the slurry and vent the air to the atmosphere.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to chemical mechanical polishers used for polishing semiconductor wafers in the semiconductor fabrication industry. More particularly, the present invention relates to a new and improved slurry delivery system for delivering slurry to a chemical mechanical polisher for the polishing of semiconductor wafers.  
         BACKGROUND OF THE INVENTION  
         [0002]    Apparatus for polishing thin, flat semiconductor wafers are well-known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semiconductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head, a wafer unload station, or a wafer load station.  
           [0003]    More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically-actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is “planarized” or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in deionized water.  
           [0004]    CMP polishing results from a combination of chemical and mechanical effects. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An altered layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide may be formed and removed separately. The chemical mechanical polishing method can be used to provide a planar surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films.  
           [0005]    Referring next to FIG. 1, a conventional CMP apparatus  50  includes a conditioning head  52 , a polishing pad  56 , and a slurry delivery arm  54  positioned over the polishing pad. The conditioning head  52  is mounted on a conditioning arm  58  which is extended over the top of the polishing pad  56  for making a sweeping motion across the entire surface of the polishing pad  56 . The slurry delivery arm  54  is equipped with slurry dispensing nozzles  62  which are used for dispensing a slurry solution on the top surface  60  of the polishing pad  56 . Surface grooves  64  are further provided in the top surface  60  to facilitate even distribution of the slurry solution and to help entrapping undesirable particles that are generated by coagulated slurry solution or any other foreign particles which have fallen on top of the polishing pad  56  during a polishing process. The surface grooves  64 , while serving an important function of distributing the slurry, also presents a processing problem when the pad surface  60  gradually wears out after prolonged use.  
           [0006]    The slurry solution is typically distributed to the slurry dispensing nozzles  62  through tubing (not illustrated), by operation of a pump (not illustrated). The force generated by the pump forcing the slurry through the tubing tends to crack the tubing, and this causes premature drying of some of the slurry in the tubing and formation of particles in the tubing before the slurry is dispensed onto the wafer. These slurry particles tend to scratch the wafer during the CMP process. Additionally, air enters the slurry through the cracked tubing, forming air bubbles which tend to adversely affect the CMP operation.  
           [0007]    Accordingly, a slurry delivery system is needed for removing particles and air bubbles from a CMP slurry as the slurry is transported from a slurry source to a CMP dispensing nozzle or nozzles.  
           [0008]    An object of the present invention is to provide a slurry delivery system for delivering a polishing slurry to a slurry dispensing nozzle of a chemical mechanical polisher, wherein the slurry is devoid of air bubbles when dispensed onto a wafer for polishing.  
           [0009]    Another object of the present invention is to provide a slurry delivery system for delivering a polishing slurry to a slurry dispensing nozzle of a chemical mechanical polisher, wherein the slurry is devoid of particles when dispensed onto a wafer for polishing.  
           [0010]    Still another object of the present invention is to provide a slurry delivery system which is capable of removing air bubbles and particles from a polishing slurry before the slurry is deposited onto a semiconductor wafer for chemical mechanical polishing of the wafer.  
           [0011]    Yet another object of the present invention is to provide a slurry delivery system which facilitates a substantial reduction in wafer scratching during chemical mechanical polishing of the wafer.  
           [0012]    A still further object of the present invention is to provide a slurry delivery system which optimizes the performance of a chemical mechanical polisher in the polishing of semiconductor wafers.  
           [0013]    Another object of the present invention is to provide a slurry delivery system which may be programmed to deliver selected quantities of slurry to a chemical mechanical polisher.  
           [0014]    Yet another object of the present invention is to provide a slurry delivery system which may be operably connected to a chemical mechanical polisher in pairs in order to provide a continuous supply of slurry to the chemical mechanical polisher.  
         SUMMARY OF THE INVENTION  
         [0015]    In accordance with these and other objects and advantages, the present invention comprises a slurry delivery system which removes air bubbles and particles from a polishing slurry and delivers the slurry to a CMP apparatus for the chemical mechanical polishing of semiconductor wafers. The slurry delivery system of the present invention comprises a bag housing fitted with a slurry intake conduit and a slurry outlet conduit. An expandible and collapsible pump bag is provided in fluid communication with the conduits inside the bag housing, and the interior of the pump bag is sealed from the bag housing. As an air/vacuum controller withdraws air from the housing, the pump bag enlarges due to the negative pressure in the housing, and slurry is drawn into the pump bag through the slurry intake conduit. As the air/vacuum controller subsequently introduces air into the housing, the pump bag collapses and the slurry is expelled from the pump bag through the slurry outlet conduit. A purge valve is provided upstream of the pump bag to remove air bubbles from the slurry and vent the air to the atmosphere. A filter is provided typically in the slurry intake conduit to filter particles from the slurry before entry into the pump bag.  
           [0016]    A pair of the slurry delivery systems of the present invention may be connected to the chemical mechanical polisher in parallel with each other, in order to provide a continuous supply of the polishing slurry to the CMP apparatus. Accordingly, as the first system undergoes the suction phase to draw slurry from the intake conduit into the pump bag, the second system undergoes the output phase to expel the slurry from the pump bag and outlet conduit to the CMP apparatus, and vice-versa. The systems may be programmed to deliver selected quantities of the slurry to the CMP apparatus.  
           [0017]    The purge valve is located at a higher level than and upstream of the bag housing, typically at the junction between the slurry intake conduit and the bag housing, to facilitate the destruction of air bubbles in the slurry as the air bubbles rise in the slurry from the intake conduit into the purge valve. In a preferred embodiment of the invention, the purge valve includes a rotation floater which is rotatably mounted in a purge valve housing. A spring-loaded valve ball is slidably disposed in the purge valve housing above the rotation floater. During the suction phase of the pump bag, the rotation floater engages a floater support and the valve ball engages a ball stop shoulder in the purge valve housing to prevent flow of slurry out of the slurry intake conduit and into the purge valve. During the output phase of the pump bag, the rotation floater disengages the floater support and the valve ball disengages the ball stop shoulder. Accordingly, as slurry flows into the purge valve housing and past the rotation floater, the rotation floater rotates and destroys air bubbles in the slurry. The air from the broken air bubbles rises beyond the valve stop shoulder and valve ball and is vented from the system through the vent port. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0019]    [0019]FIG. 1 illustrates a typical conventional chemical mechanical polishing (CMP) apparatus;  
         [0020]    [0020]FIG. 2 is a schematic view of a slurry delivery system of the present invention, with the pump bag of the system shown in the suction phase of operation;  
         [0021]    [0021]FIG. 3 is a schematic view of the slurry delivery system of the present invention, with the pump bag of the system shown in the output phase of operation;  
         [0022]    [0022]FIG. 4 is a schematic view of the purge valve element of the slurry delivery system of the present invention, with the rotation floater and valve ball components in the closed positions during the suction phase of the pump bag;  
         [0023]    [0023]FIG. 5 is a schematic view of the purge valve element of the slurry delivery system of the present invention, with the rotation floater and valve ball components in the open positions during the output phase of the pump bag;  
         [0024]    [0024]FIG. 6 is a top view of the rotation floater of the purge valve;  
         [0025]    [0025]FIG. 7 illustrates utilization of a pair of slurry delivery systems of the present invention in parallel with each other to provide a continuous flow of slurry to a CMP apparatus (not shown);  
         [0026]    [0026]FIG. 8 is a graph illustrating staggered or alternate operation of a pair of slurry delivery systems to provide a continuous flow of slurry to a CMP apparatus; and  
         [0027]    [0027]FIG. 9 is a schematic illustrating a piping configuration for multiple slurry delivery systems connected to each other in parallel. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    The present invention has particularly beneficial utility in removing air bubbles and particles from a polishing slurry and delivering the slurry to a chemical mechanical polishing (CMP) apparatus used in the polishing of semiconductor wafers. However, the invention is not so limited in application and while references may be made to such polishing slurry and CMP apparatus, the invention is more generally applicable to removing air bubbles and particles from liquids and transporting the liquids in a variety of industrial and mechanical applications.  
         [0029]    Referring initially to FIGS. 2 and 3, an illustrative embodiment of the slurry delivery system of the present invention is generally indicated by reference numeral  10 . The slurry delivery system  10  is designed to remove particulate impurities and air bubbles from a polishing slurry as it pumps the slurry from a slurry supply reservoir  17  to a CMP apparatus  68 . The slurry delivery system  10  includes a slurry intake conduit  16  which leads from the slurry supply reservoir  17 . A downward bend  16   a  in the slurry intake conduit  16  defines a sloped segment  16   b  of the slurry intake conduit  16 . A particle filter  20  of selected design and pore size is provided in the slurry intake conduit  16 , typically in the sloped segment  16   b . An intake check valve  18  is provided in the slurry intake conduit  16 , typically between the slurry supply reservoir  17  and the bend  16   a . The sloped segment  16   b  of the slurry intake conduit  16  enlarges to define a purge housing  22 , which extends into the upper end of a sloped bag housing  12  and includes a discharge end  23  that terminates in the housing interior  14  of the bag housing  12 . A purge valve  24 , the details of which will be hereinafter further described, is confluently connected to the upper end of the purge housing  22 .  
         [0030]    The sloped segment  40   b  of a slurry outlet conduit  40  angles downwardly and exits from the lower end of the sloped bag housing  12 , with the intake end  41  of the slurry outlet conduit  40  extending into the housing interior  14  of the bag housing  12 . The sloped segment  40   b  of the slurry outlet conduit  40  angles at a bend  40   a  to define the remaining straight segment of the slurry outlet conduit  40 , which is confluent with the slurry dispensing arm (not illustrated) of the CMP apparatus  68 , according to the knowledge of those skilled in the art. An output check valve  42  is provided in the slurry outlet conduit  40 .  
         [0031]    A resilient pump bag  46 , which may be constructed from a Teflon sheet, includes an upper open end which is connected in gas-tight communication to the discharge end  23  of the purge housing  22 , inside the housing interior  14 . The opposite, lower open end of the pump bag  46  is, in like manner, connected in gas-tight communication to the intake end  41  of the slurry outlet conduit  40 , inside the housing interior  14 . Accordingly, the junctions between the pump bag  46  and the discharge end  23  of the purge housing  22  and between the pump bag  46  and the intake end  41  of the slurry outlet conduit  40  provide a gas-tight seal between the bag interior  48  of the pump bag  46  and the housing interior  14  of the bag housing  12 . An air/vacuum controller  44  is confluently connected to the housing interior  14  of the bag housing  12  for alternately introducing air into the housing interior  14  and withdrawing air from the housing interior  14 . Because the bag housing  12  forms a gas-tight seal with the purge housing  22  and with the sloped segment  40   b  of the slurry outlet conduit  40 , the air introduced into the housing interior  14  by operation of the air/vacuum controller  44  is incapable of escaping from the housing interior  14  except back through the air/vacuum controller  44 . The air/vacuum controller  44  may be actuated through a tool PC (not shown) for the CMP apparatus  68  or a system PC (not shown).  
         [0032]    Referring next to FIGS. 4 and 5, the purge valve  24  includes a valve housing  25  which is confluently attached to the upper end of the purge housing  22  (FIGS. 2 and 3). A rotational floater  26 , which may be constructed of Teflon, is vertically displaceably mounted in the valve housing  25 . The rotational floater  26  includes a floater body  27  from which extend multiple floater vanes  28 . The floater vanes  28  extend from the floater body  27  at an angle, typically toward a counterclockwise direction when the rotational floater  26  is viewed from above, as shown in FIG. 6. Alternatively, the floater vanes  28  may extend from the floater body  27  at an angle in a clockwise direction when the rotational floater  26  is viewed from above. A circumferential floater seal  29  extends from the floater body  27 , and a tapered or cone-shaped floater base  30  extends downwardly from the floater body  27 . The floater base  30  extends through a flow opening  32  which extends through the center of a floater support  31  that spans the interior of the valve housing  25 . Accordingly, the rotational floater  26  is capable of movement between a lower position in which the floater seal  29  disengages the valve housing  25  and the floater base  30  is seated in the flow opening  32 , as shown in FIG. 4, and an upper position in which the floater seal  29  engages the valve housing  25  and the floater base  30  withdraws from the flow opening  32 , as shown in FIG. 5. When the rotational floater  26  is positioned in the lower configuration of FIG. 4, a spring  35  biases a valve ball  34  against a ball stop shoulder  36  above the rotational floater  26  and blocks flow of air or liquid from the valve housing  25  through a vent port  37  in the upper end of the valve housing  25 . When the rotational floater  26  is positioned in the upper configuration of FIG. 5, the valve ball  34  is pushed against the spring  35  and disengages the ball stop shoulder  36  to facilitate flow of air from the valve housing  25  through the vent port  37 , as hereinafter further described.  
         [0033]    In operation of the slurry delivery system  10 , and referring again to FIGS. 2 and 3, a supply of polishing slurry  19  is pumped from the slurry supply reservoir  17  to the CMP apparatus  68  and simultaneously, particles and air bubbles are removed from the slurry  19  before the slurry  19  reaches the CMP apparatus  68 . Accordingly, with the intake check valve  18  in the open configuration and the output check valve  42  in the closed configuration, the pump bag  46  is initially operated in a suction phase, illustrated in FIG. 2, to draw slurry  19  from the slurry supply reservoir  17  into the bag interior  48  of the pump bag  46 . This is accomplished by causing the air/vacuum controller  44  to withdraw air from the housing interior  14  of the bag housing  12 . The resulting negative air pressure in the housing interior  14  (typically about −1 psi) causes the pump bag  46  to expand therein, such that slurry  19  is drawn from the slurry supply reservoir  17 , through the slurry intake conduit  16 , the open intake check valve  18  and particle filter  20 , and into the purge housing  22  and bag interior  48 , respectively. Simultaneously, the purge valve  24  assumes the closed configuration of FIG. 4, wherein the floater seal  29  of the rotational floater  26  disengages the valve housing  25  and the floater base  30  is inserted in the flow opening  32 , and the valve ball  34 , under actuation by the spring  35 , is biased against the ball stop shoulder  36  to prevent fluids or air from exiting the purge valve  24  through the vent port  37 . The particle filter  20  removes from the slurry  19  particles exceeding a selected size depending on the pore size of the particle filter  20 .  
         [0034]    After the suction phase is completed, the pump bag  46  is operated in an output phase, shown in FIG. 3, to expel the slurry from the bag interior  48 , through the slurry output conduit  40  and open output check valve  42  and ultimately, to the CMP apparatus  68 . Accordingly, with the intake check valve  18  in the closed configuration and the output check valve  42  in the open configuration, the air/vacuum controller  44  is operated to inject air into the housing interior  14  until the air pressure in the housing interior  14  reaches a pressure of typically about 1 psi. The air in the housing interior  14  compresses or collapses the pump bag  46 , which expels the slurry  19  from the bag interior  48 , through the slurry outlet conduit  40  and open output check valve  42  and ultimately, to the CMP apparatus  68 .  
         [0035]    As the pump bag  46  begins the output phase, any air bubbles (not shown) in the slurry  19  are forced upwardly through the slurry  19  in the bag interior  48  and purge housing  22 . Some of the slurry  19  flows upwardly into the valve housing  25 , first through the flow opening  32  and then between the floater seal  29  and valve housing  25 . This upward flow of the slurry  19  causes the rotational floater  26  to rotate in the clockwise direction when viewed from the top, as shown in FIG. 6, as the flowing slurry  19  impinges on the floater vanes  28 . The rotating action of the rotational floater  26  causes the floater vanes  28  to rupture and destroy any air bubbles rising through the slurry  19 . The slurry  19  typically rises to the top of the rotational floater  26  in the valve housing  25 , as indicated by the slurry level  38  in FIG. 5, at which time the rotational floater  26  rises in the slurry and engages the valve housing  25 . Air in the valve housing  25 , including air released from the ruptured air bubbles, impinges on the valve ball  34  due to the upward pressure of the air imparted by the contracting pump bag  46 . Accordingly, the air flows beyond the ball stop shoulder  36  and escapes the valve housing  25  through the vent port  37 . When the pump bag  46  subsequently begins a second suction phase and enlarges due to the negative pressure induced in the housing interior  14 , the rotational floater  26  and valve ball  34  again assume the closed positions of FIG. 4 as the slurry  19  is drawn from the valve housing  25  and into the bag interior  48  due to the negative pressure generated in the bag interior  48 .  
         [0036]    The quantity of slurry  19  drawn into the bag interior  48  from the slurry supply reservoir  17 , and thus, pumped to the CMP apparatus  68  may be varied by controlling the expansion volume of the pump bag  46  during the suction phase thereof. This is, in turn, determined by the volume of air withdrawn from the housing interior  14  by operation of the air/vacuum controller  44 . The lower the pressure induced in the housing interior  14  by operation of the air/vacuum controller  44 , the larger the expansion volume of the pump bag  46  and the larger the quantity of slurry  19  drawn into the bag interior  48  for subsequent pumping to the CMP apparatus  68 . Conversely, the higher the pressure induced in the housing interior  14  by operation of the air/vacuum controller  44 , the smaller the expansion volume of the pump bag  46  and the smaller the quantity of slurry drawn into the bag interior  48 .  
         [0037]    Referring next to FIGS. 7 and 8, in typical application two slurry delivery systems, indicated by reference numerals  10   a  and lob, respectively, are connected to each other in parallel as illustrated in FIG. 7. Accordingly, a pump controller  76  operates the air/vacuum controller  44 , the intake check valve  18  and the output check valve  42  (FIGS. 2 and 3) components of each slurry delivery system  10   a  and lob in conjunction with a shuttle valve  74  to alternately shuttle flow of slurry through the system  10   a  and system lob (designated “pump A” and “pump B”, respectively, in FIG. 8). Such alternating operation of the systems  10   a  and  10   b  provides a continuous flow or output of particle and air bubble free slurry  19  from a slurry supply reservoir  70  to a CMP apparatus  72 , as indicated by the graph in FIG. 8.  
         [0038]    [0038]FIG. 9 schematically illustrates a piping configuration for a selected number (n) of multiple slurry delivery systems connected to each other in parallel. Three of the slurry delivery systems  78  are designated by the reference numerals  78   a ,  78   b  and  78   c , respectively, and the nth slurry delivery system  78  is designated by the reference numeral  78   n . The slurry delivery systems  78  are connected through a slurry intake conduit  80 , slurry intake valve  82 , service conduit  84  and respective branch conduits  86  to a slurry supply reservoir  96  which contains a supply of polishing slurry  98 . Each of the slurry delivery systems  78  is operated in conjunction with the slurry intake valve  82  by a central controller (not illustrated). An auto stop valve  100  is provided in each branch conduit  86 , between the corresponding slurry delivery system  78  and a slurry output line  92 . Typically, each pair of branch conduits  86  serviced by adjacent slurry delivery systems  78  is connected to the same CMP apparatus (not shown), which continuously receives some of the slurry  98  by alternate operation of the paired slurry delivery systems  78 . Each of the branch conduits  86  is further connected to a slurry output conduit  92  which distributes the remaining slurry  98  back to the slurry supply reservoir  96  through a slurry return conduit  94 . One or multiple operator positions  88  may be provided for each system  78 . An auto stop valve  100  is typically included in each branch conduit  86  for automatically terminating flow of the slurry  98  through a branch conduit  86  in the event of a leakage or blockage in the branch conduit  86 . For example, in the event of a blockage or leakage in the branch conduit  86   a , the auto stop valve  10   a  terminates flow of the slurry  98  through the branch conduit  86   a  to continue supply of the slurry  98  to the slurry delivery systems  78   a ,  78   b ,  78   c  and  78   n , respectively. Typically at least about 10% of the total volume of the slurry  98  is continuously distributed back to the slurry supply reservoir  96  in order to prevent crystallization of the slurry  98  during circulation.  
         [0039]    While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.