Abstract:
A chemical collection assembly and a method for using the assembly such that a chemical-mechanical polishing (CMP) pad used in the manufacture of semiconductor wafers can be assessed for cleanliness. The method involves delivering solvent from the assembly&#39;s reservoir to an enclosed volume over the CMP pad. The solvent then brings contaminants imbedded on the CMP pad into solution. This solution is then drawn back up from the enclosed volume wherefrom a sample of the solution can be taken. That sample is then analyzed for the level of contaminants present therein, and the analysis is compared to a pre-determined level of cleanliness to determine whether the CMP pad should or should not continue to be used for semiconductor wafer manufacturing.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to semiconductor processing and, in particular, concerns a method of conditioning and measuring pads used in planarizing surfaces of a wafer using chemical-mechanical polishing.  
           [0003]    2. Description of the Related Art  
           [0004]    Chemical-mechanical polishing (CMP) is a technique whereby surfaces are planarized by the simultaneous application of both an etching and a polishing process. Semiconductor wafers are often globally planarized using CMP processing. In a typical CMP process, the semiconductor wafer is placed on a carriage, and a pad is positioned over the wafer to contact the upper surface of the semiconductor wafer. The carriage and the pad are further rotated in opposite directions, and a slurry containing an etchant and abrasive particles flows between the upper surface of the semiconductor wafer and the pad. The combination of the mechanical polishing of the pad and the chemical etching action involved in this process serves to remove exposed surfaces of the wafer thereby planarizing the upper surface of the semiconductor wafer.  
           [0005]    In one implementation, the CMP process is used for demascene processing in which excess layers of copper compounds are removed from the semiconductor wafer surface, leaving only the necessary copper conduit. After a time, newly removed copper compounds, such as Cu(OH) 2  and Cu(OH), clog and contaminate the CMP pad, thereby degrading its planarization effectiveness. More specifically, as the CMP pad is used, contaminants build up within the pores or grooves of the CMP pad, thereby inhibiting an even distribution of slurry. This could cause uneven planarization of the wafer and necessary wafer materials might be removed.  
           [0006]    To address these problems, methods have been developed to determine the level of contaminants on the CMP pad so as to indicate when the pad is no longer acceptable for use. One such method involves pouring a solvent, such as a solution of 1% nitric acid (HNO 3 ), onto the pad whereby the solvent draws the contaminants from the pad. Then, a sample of this solvent and contaminant mixture is taken from the pad using a pipette, and this sample is tested for the level of contaminants present in the solution using spectrometer technology, such as ion coupled plasma analysis.  
           [0007]    This method has several problems. For example, pouring the solution on the pad in an uncontrolled manner may actually wash away contaminants from the area that will ultimately serve as the collection point. As a result, the sample taken may not be a representative sample of the level of contaminants actually on the rest of the pad.  
           [0008]    Also, as stated above, the contaminants often reside in the grooves and pores of the CMP pad, so in order to get samples of solvent that contain a representative amount of contaminants, the sample should be taken from within the grooves or pores. However, the pipette tips are generally too large to fit down into the narrow grooves on the CMP pad. As a result, the sample taken may be inaccurate, and the user will likely make an inappropriate assessment of the CMP pad cleanliness. Another problem is that the solvent may absorb into the CMP pad after it is poured. As a result, it may be difficult to collect the required amount of solvent for testing.  
           [0009]    Hence from the foregoing, it will be appreciated that there is a need for a device and method that will simply and accurately measure the amounts of contaminants deposited on a CMP pad in order to determine its level of cleanliness.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention satisfies the aforementioned needs. The disclosed method and apparatus permit easier, more accurate, and more controlled sampling of the contaminants on a CMP pad.  
           [0011]    One aspect of the present invention comprises a method of determining the cleanliness of a CMP pad. First, the user selects a solution that will dissolve contaminants on the CMP pad. Then, the user positions a retaining structure on a first surface of the CMP pad so as to define a controlled space and injects a controlled volume of solution onto the CMP within the controlled space. Next, the solution with dissolved contaminants is extracted from the controlled space adjacent the CMP pad. Finally, the extracted solution is sampled to determine the quantity of dissolved contaminants in the CMP pad, and it is determined, based on this sampling of the extracted solution, whether the CMP pad meets a pre-selected cleanliness threshold.  
           [0012]    Another aspect of the present invention is an assembly for obtaining a sample indicative of the cleanliness of a CMP pad having a first surface. The assembly comprises a retaining structure that is positionable adjacent the first surface so as to define an enclosed volume adjacent the first surface of the CMP pad. The assembly also comprises a reservoir containing a sampling solution and a delivery mechanism for delivering the sampling solution to the enclosed volume such that the sampling solution absorbs contaminants on the first surface of the CMP pad. Furthermore, the assembly comprises an extraction mechanism that extracts the sampling solution from the enclosed volume such that the extracted sampling solution contains contaminants of the first surface of the CMP pad. The sampling solution can then be evaluated to determine the cleanliness of the first surface of the CMP pad.  
           [0013]    Most of the solution will remain inside the enclosed space in the retaining structure after it is injected therein. Advantageously, the solution is easy to collect for subsequent sampling. Also, the enlarged area of the enclosed space allows sampling of contaminants that may be present in multiple grooves, where there may be different levels of contaminants. As a result, the present invention advantageously allows the user to take a more representative sample of the level of contaminants present on the CMP pad.  
           [0014]    Another aspect of the present invention comprises a retaining structure that is adapted to be positioned adjacent a surface of the CMP pad, and the retaining structure defines an enclosed volume that retains fluid within the enclosed volume adjacent the surface of the pad. In this embodiment, a pipette is used to inject cleaning solution onto the surface of the CMP pad within the enclosed volume. The pipette is also used to extract cleaning solution from the enclosed volume for subsequent analysis. The analysis determines the level of contaminants to thereby ascertain whether the CMP pad is suitable for continued use. Advantageously, use of this embodiment of the chemical collection assembly allows for easy set up and break down because the components involved are preferably light and portable.  
           [0015]    A different aspect of the present invention comprises a delivery system for delivering cleaning solution to the surface of the CMP pad. This embodiment also comprises a retaining structure that is positionable with respect to the surface of the CMP pad so as to define an area on the surface of the CMP pad into which the delivery system positions the cleaning solution. Additionally, a recovery system that recovers cleaning solution from the area on the CMP pad is used. A controller sends signals to the delivery system and the recovery system so as to induce delivery and recovery of the cleaning solution.  
           [0016]    Advantageously, use of this embodiment of the present invention allows for easy assessment of the CMP pad cleanliness because it is substantially automated. Also, the correlation between pad use and pad cleanliness can be discerned more quickly and with more confidence because human error is unlikely to affect the data collected from the cleanliness testing.  
           [0017]    These and other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a schematic illustration representing one embodiment of a chemical-mechanical polishing (CMP) system;  
         [0019]    [0019]FIG. 2 is a perspective view of one embodiment of a chemical collection assembly of the present invention;  
         [0020]    [0020]FIG. 3 is a top view of various embodiments of chemical retaining structures of the present invention;  
         [0021]    [0021]FIG. 4 is a flow chart illustrating the general process steps of the chemical collection and measurement method of the present invention;  
         [0022]    [0022]FIG. 5 is a perspective view of another embodiment of the chemical collection assembly of the present invention; and  
         [0023]    [0023]FIG. 6 is a schematic view of another embodiment of the chemical collection assembly of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]    Reference will now be made to the drawings wherein like numerals refer to like parts throughout. Referring initially to FIG. 1, an exemplary CMP system  100  is illustrated. In particular, the CMP system  100  includes a platen  102  that is rotated about a shaft  106  by a motor (not shown). The platen  102  retains a polishing pad  104 , and the CMP system  100  also includes a carriage  110  that has a wafer receiving surface  112  which is adapted to retain a wafer  116  within the carriage  110 . The carriage  110  is also adapted to be rotated about a shaft  114  by a motor (not shown).  
         [0025]    The operation of the CMP system  100  is similar to the operation of similar CMP systems of the prior art. Basically, the platen  102  is rotated and the carriage  110  is rotated such that rotational movement between the silicon wafer  116  and the polishing pad  104  is imposed. The platen  102  and the carriage  110  are then moved together such that an exposed surface  118  of the wafer  116  is brought into contact with an outer surface  105  of the polishing pad  104 . A wetting solution or slurry  120  is provided to the outer surface  105  of the polishing pad  104  so as to wet the interface  122  between the outer surface  105  of the polishing pad  104  and the exposed surface  118  of the wafer  116  to thereby enhance the polishing and removal of the surface  118  of the wafer  116 . It will be appreciated that the CMP system  100  illustrated in FIG. 1 is simply exemplary of any of a number of well known CMP systems currently used in semiconductor fabrication and processing. The single platen  102  could be one of a number of platens in a more sophisticated system without departing from the spirit of the present invention.  
         [0026]    As is understood in the art, the combined effects of the pad  104  frictionally engaging with the exposed surface  118  of the wafer  116  and the existence of etchants in the wetting solution or slurry  120  results in the systematic removal of layers of the exposed surface  118  of the wafer  116 . As the layers of material are removed from the exposed surface  118  of the wafer  116 , contaminants, such as Cu(OH) 2  or Cu(OH) in demascene processing, deposit onto the outer surface  105  of the pad  104 . As the CMP process continues, more and more material collects on this outer surface  105  and especially the grooves of the pad  104  thereby degrading the planarization properties of the pad  105 . This problem is compounded if the pad  105  is used repeatedly for multiple wafers  116 .  
         [0027]    [0027]FIG. 2 illustrates one embodiment of a chemical collection assembly  130 . As shown, the chemical collection assembly  130  generally comprises a reservoir  134 , a stem section  136 , and a retaining structure  132 . As shown, the chemical collection assembly  130  is placed adjacent the exposed surface  105  of the CMP pad  104 . The reservoir  134 , the stem section  136 , and the retaining structure  132  are hollow so that a solvent  138  can flow through them. The solvent  138  is preferably selected to dissolve contaminants present on the exposed surface  105  of the CMP pad  104 . As will be discussed in greater detail below, the solvent  138  is injected from the reservoir  134  through the stem section  136  to the retaining structure  132  and vice versa in order to measure the cleanliness of the exposed surface  105  of the pad  104 .  
         [0028]    As shown in FIG. 2, one embodiment of the reservoir  134  comprises a cylinder  140  comprising a first end  141  and a second end  142 . The reservoir  134  further comprises an inner surface  139  which defines a first volume  146 . As will be described below, when the solvent  138  is in the reservoir  134  of the chemical collection assembly  130 , the solvent  138  resides in the first volume  146 . Furthermore, FIG. 2 shows that at the first end  141  of the cylinder  140  is a first surface  143 , which substantially closes off the first end  141  of the cylinder  140  except for an aperture  144 . Through the aperture  144  passes a plunger assembly  145 .  
         [0029]    [0029]FIG. 2 shows that the plunger assembly  145  comprises a plunger  148 , which is cylindrically shaped and has an outer second surface  150 . Preferably, the second surface  150  of the plunger  148  is positioned sufficiently close to the inner surface  139  of the reservoir  134  such that it creates a loose seal therebetween. At a third surface  151  of the plunger  148  is a shaft  149 , which passes through the aperture  144  in the first surface  143  of the cylinder  140 . Connected to the shaft  149  is a handle  147 , both of which can take on a variety of shapes and sizes. As will be described below, the plunger assembly  145  functions in a manner such that when force is applied to the handle  147  in order to depress it, the force is transferred to the shaft  149  and ultimately to the plunger  148 . As stated, the geometry of the plunger  148  preferably creates a seal between the plunger  148  and the inner surface  139  of the reservoir  134 . This seal ensures that solvent  138  is forced from the cylinder  140  when the handle  147  is depressed, and solvent  138  is drawn up into the cylinder  140  when the handle  147  is lifted both due to vacuum suction.  
         [0030]    [0030]FIG. 2 also illustrates that the reservoir  138  further comprises a funnel  153 . The funnel comprises a large diameter first end  154  and a small diameter second end  155  with a wall  137  connecting both. More specifically, the first end  154  of the funnel  153  lies adjacent to the second end  142  of the cylinder  140 . The funnel  153  acts to channel the solvent  138  from the cylinder  140  into the stem section  136 .  
         [0031]    As stated, the chemical collection assembly  130  also comprises the stem section  136 . As shown in FIG. 2, the stem section  136  generally comprises a main shaft  159 , a sampling shaft  160 , and a plurality of delivery shafts  161 . As will be described in greater detail below, the stem section  136  provides a means for delivering solvent  138  to and from the reservoir  134 .  
         [0032]    [0032]FIG. 2 further shows that the main shaft  159  has a first end  157  and a second end  158  wherein the first end  157  of the main shaft  159  lies adjacent to the second end  155  of the funnel  153 . The second end  158  of the main shaft  159  splits off into the plurality of the delivery shafts  161 . In the embodiment shown, there are three delivery shafts  161 , and the axes of the delivery shafts  161  extend at an obtuse angle with respect to the axis of the main shaft  159 , and the delivery shafts  161  extend to the retaining structure  132 . Preferably, the individual delivery shafts  161  are evenly spaced around the main shaft  159 . As will be described below, the use of a plurality of evenly-spaced delivery shafts  161  ensures that the solvent  138  will be applied evenly over a specified area of the CMP polishing pad  104 .  
         [0033]    Furthermore, according to the embodiment shown in FIG. 2, the sampling shaft  160  extends from a midpoint in the main shaft  159 . Connected to the sampling shaft  160  is a flexible hose  162 . As will be described in greater detail below, the sampling shaft  160  and flexible hose  162  allow samples of solvent  138  to be drawn from the chemical collection assembly  130  so as to measure the cleanliness of the CMP polishing pad  104 .  
         [0034]    Both the main shaft  159  and the sampling shaft  160  comprise a valve  164 ,  165  respectively. The valves  164 ,  165  are standard in the art, and as will be described below, the valves  164 ,  165  control the flow of solvent  138  through their respective shafts  159 ,  160  of the chemical collection assembly  130 .  
         [0035]    As stated, the chemical collection assembly  130  also comprises the retaining structure  132 . In the embodiment shown in FIG. 2, the retaining structure  132  comprises a wall  167 , which defines a first upper aperture  166  and a second lower aperture  169 . In the embodiment shown, the retaining structure  132  comprises a ring shape. In one embodiment, the diameter of the retaining structure  132  is 1.5 to 2.0 inches.  
         [0036]    As will be described in greater detail below, in order to evaluate the cleanliness of a polishing pad  104 , the chemical collection assembly  130  is placed over the outer surface  105  of the polishing pad  104  such that a section of the outer surface  105  covers the second lower aperture  169  of the retaining structure  132 . In this manner, the retaining structure  132  and CMP pad  104  combination defines a volume  152  wherein solvent  138  can dissolve contaminants located on the outer surface  105  of the pad  104 . As will be discussed below, placement of the retaining structure  132  in this manner retains the majority of solvent  138  injected onto the surface  105  of the pad  104 . Advantageously, collection of a sample of this solvent  138  with dissolved contaminants contained therein is facilitated because the solvent  138  will not run out from the volume  152  or excessively soak into the CMP pad  104 .  
         [0037]    [0037]FIG. 3 illustrates different embodiments of the retaining structure  132  mounted atop a CMP pad  104 . As shown, the retaining structure  132  can take on a variety of shapes and sizes depending upon the type of CMP pad  104  that is being tested. A CMP pad  104  often has a plurality of protrusions  124  with corresponding grooves  128  between the protrusions  124 . One embodiment of the retaining chamber  132  is sized so as to lie substantially in the groove  128  and enclose a plurality of protrusions  124 . The shape of the retaining structure  132  allows solvent  138  to flow over an enlarged area of the CMP pad  104  and coat a multitude of surfaces. Thus, samples taken from the retaining structure are more representative of the overall pad  104  cleanliness because different areas of the pad can contain different amounts of contaminants.  
         [0038]    Another embodiment of the retaining chamber  132  comprises two walls  114   a,    114   b  that are set substantially inside the groove  128  and extend between the nearby protrusions  124   a,    124   b  so as to define a first volume  108 . When solvent  138  is injected between the walls  114   a,    114   b,  the solvent  138  is retained by the walls  114   a,    114   b  and the protrusions  124   a,    124   b  and pools within the first volume  108 . Advantageously, this embodiment of the retaining structure  132  allows the user to target specific areas of the CMP pad  104  for testing without having to form several different retaining chamber  132  shapes.  
         [0039]    Advantageously, the use of the retaining structure  132  defines an area in which the solution can be contained. As illustrated above, the retaining structure  132  can comprise an enclosed shape that is positioned on an exposed surface  105  of the CMP pad  104  or the retaining structure  132  can comprise a shape that is positionable within one of the grooves  128 . Moreover, the retaining structure  132  can also be defined by a combination of structures, including protrusions on the pad  104  that result in an enclosed volume without departing from the spirit of the present invention.  
         [0040]    [0040]FIG. 4 illustrates a method  170  of evaluating the cleanliness of a CMP pad  104  using a chemical collection assembly  130  similar to the assembly  130  shown in FIG. 2. As shown, a first step  172  of the method  170  involves loading the empty chemical collection assembly  130  with solvent  138 . In one embodiment, this can be accomplished by first opening the valve  164  on the main shaft  159  and closing the valve  165  on the sampling shaft  160 . Next, the handle  147  of the plunger assembly  145  is depressed toward the first end  141  of the cylinder  140  until the handle  147  stops. Then, the retaining structure  132  is positioned into a pool of solvent  138  such that the lower aperture  169  of the retaining structure  132  lies underneath the surface of the pool of solvent  138 . Next, the handle  147  of the plunger assembly  145  is raised away from the first end  141  of the cylinder  140 , and solvent is drawn into the chemical collection assembly  130 . More specifically, the plunger  148  of the plunger assembly  145  is designed to create vacuum suction when the handle  147  is raised in this manner. Special attention is given during the first step  172  to ensure that the lower aperture  169  of the retaining structure  132  remains underneath the surface of the pool of solvent  138  such that the vacuum suction draws only solvent  138  and not air into the chemical collection assembly  130 . The handle  147  is lifted until the desired amount of solvent  138  is drawn up into the chemical collection assembly  130 . In one embodiment, the desired amount of solvent  138  for testing is approximately 300 milliliters.  
         [0041]    At this point, as shown on FIG. 4, a second step  174  of the method  170  involves positioning the chemical collection assembly  130  over the exposed surface  105  of the CMP pad  104 . More specifically, the chemical collection assembly  130  is positioned such that the wall  167  of the retaining structure  132  creates a seal between the retaining structure  132  and the exposed surface  105  of the CMP pad  104 . As will be described below, the chemical collection assembly  130  is most effective when solvent  138  does not leak from the retaining structure  132  into the CMP pad  104 .  
         [0042]    [0042]FIG. 4 shows that a third step  176  of the method  170  entails injecting solvent  138  through the first upper aperture  166  and into the retaining structure  132  to thereby coat one area of the CMP pad  104 . First, the valve  164  of the main shaft  159  is opened if it is not already. Then, the handle  147  of the plunger assembly  145  is depressed until a desired amount of solvent  138  is delivered into the retaining structure  132 . As stated, depressing the handle  147  of the plunger assembly  145  forces the solvent  138  to flow from the reservoir  134  through the stem section  136  and into the retaining structure  132 . Next, the solvent  138  dissolves and draws up contaminants from the exposed surface  105  of the CMP pad  104 .  
         [0043]    As stated above, the retaining structure  132  on top of the CMP pad  104  defines an enclosed volume  152  within which the solvent  138  dissolves contaminants present on the CMP pad  104 . Preferably, the retaining structure  132  holds the majority of the solvent  138  within its wall  167 . As such, the contaminants on the pad  104  will not be washed away from the retaining structure  132 , and the level of contaminants in the sample of solvent  138  subsequently taken from the retaining structure  132  will be representative of the level of the contaminants that were on the pad  104  prior to testing. Advantageously, this allows for more accurate cleanliness testing.  
         [0044]    As mentioned above, contaminants in the pad  104  often reside in the grooves of the CMP pad. It is understood that the amount of contaminants may vary along a single groove, and different grooves may have different amounts of contaminants contained therein. Due to the enlarged area of the second lower aperture  169  of the retaining structure  132 , the solvent  138  can spread out over the CMP pad  104  and dissolve contaminants along the length of a groove and affect multiple grooves simultaneously. As a result, the sample of solvent  138  with contaminants contained therein is more likely to be an average measurement of contaminants contained on the CMP pad  104 . Advantageously, this results in a more accurate assessment of the cleanliness of the entire CMP pad  104 .  
         [0045]    As shown on FIG. 4, the method  170  includes a fourth step  178 . In this step  178 , the solvent  138  is drawn back through the stem section  136  and into the reservoir  134 . This is achieved by lifting the handle  147  of the plunger assembly  145  until a required amount of solvent  138  with dissolved contaminants is drawn into the stem section  136  and reservoir  134 . The valve  164  on the main shaft  159  of the stem section  136  is then closed.  
         [0046]    A fifth step  180  of the method  170  shown on FIG. 4 involves sampling the solvent  138  containing contaminants. First, the valve  165  on the sampling shaft  160  is opened, and then the handle  147  of the plunger assembly  145  is depressed. This causes solvent  138  with contaminants dissolved therein to move from the reservoir  134  through the stem section  138  and then out the sampling shaft  160  and into a sampling receptacle (not shown). The handle  147  of the plunger assembly  145  is depressed until a required amount of solvent  138  with contaminants dissolved therein is delivered into the sampling receptacle. In one embodiment, an adequate amount of sample is approximately five to ten milliliters.  
         [0047]    The solvent  138  with contaminants dissolved therein is then moved to testing equipment in a sixth and final step  182  of the method  170  as shown in FIG. 4. Testing preferably involves using equipment known in the art to test the presence of substances in liquid media. In one embodiment, spectrometer technology, such as ion coupled plasma analysis, is used to measure the amount of contaminants. The results from the testing equipment can be compared to a pre-selected level of CMP pad  104  cleanliness in order to determine whether the CMP pad  104  should be used further, cleaned and re-conditioned with a diamond wheel, or discarded.  
         [0048]    Advantageously, this method  170  allows for easy collection of the solvent  138  because the solvent  138  is pooled within the retaining chamber  132 , allowing the delivery shafts  161  to simply draw up solvent  138  therefrom with vacuum suction. Also, the enlarged area of the retaining structure  132  allows for sampling of contaminants that may be present across a single or multiple grooves. As a result, the method  170  allows the user to take a more representative sample of the level of contaminants present on the CMP pad because different locations on the pad  104  might contain different levels of contaminants. Finally, frequent and repeated utilization of this method  170  will likely lead to an increased understanding of the correlation between CMP pad use and cleanliness because testing data can be compiled and studied. Advantageously, the CMP process will likely become more efficient because the user will have a good approximation as to when the CMP pad  104  is too contaminated for further use.  
         [0049]    [0049]FIG. 5 illustrates another embodiment of a chemical collection assembly  330 . As shown the chemical collection assembly  330  comprises a pipette  332 , and a retaining structure  334 . The pipette  332  is an instrument well known in the art used for injecting fluid to a desired location or sucking up fluid therefrom. The retaining structure  334  is similar to the retaining structure  134  described above, and as shown, the retaining structure  334  is placed atop an exposed surface  305  of a CMP pad  304 . Similar to the chemical collection assembly  130  described above, testing the CMP pad  304  cleanliness involves positioning the retaining structure  334  over the CMP pad  304  in order to define a volume  352  into which a solvent  338  can be introduced and substantially retained. Upon introduction into the volume  352 , the solvent  338  dissolves contaminants located on the CMP pad  104 . Then, the pipette  332  is used to draw solvent  338  with dissolved contaminants from the retaining structure  334  for subsequent testing. Advantageously, a user of this embodiment of the chemical collection assembly  330  can easily set up and remove the necessary equipment because the pipette  332  and retaining structure  334  are easily portable.  
         [0050]    [0050]FIG. 6 illustrates a substantially automated embodiment of the chemical collection assembly  430 . As shown, the chemical collection assembly  430  comprises a reservoir  434 , a stem section  436 , and a retaining structure  432 , all of which are substantially similar to the reservoir  134 , the stem section  136 , and the retaining structure  132  described above. As shown, the stem section  436  also comprises a controllable valve  424 , which controls the flow of solvent  438  through the stem section  436 . Also, the chemical collection assembly  430  comprises a sample tank  426 , which in one embodiment, comprises a cylindrical shape. The reservoir  434  holds a solvent  438 , and as will be described in more detail below, the solvent  438  is delivered to and from the retaining structure  432  or to the sample tank  426  through the stem section  436  with the aid of a variety of components.  
         [0051]    The chemical collection assembly  430  also comprises a vacuum source  422 , used to generate a suction force. As shown in FIG. 6, the vacuum  422  is connected to the sample tank  426  by way of a vacuum hose  414 . As will be described in greater detail below, the vacuum source  422  forces the solvent  438  to move through the chemical collection assembly  430 .  
         [0052]    [0052]FIG. 6 also illustrates that the chemical collection assembly  430  can include an actuator  416  that is connected to the retaining structure  432  in order to move the retaining structure  432  onto and off of an exposed surface  405  of a CMP pad  404 . This operation will be described in greater detail below.  
         [0053]    The chemical collection assembly  430  also comprises a controller  410  that is equipped with a timer  418  that regulates when control signals are sent, and the controller  410  regulates where the control signals are sent. As shown, the controller  410  is connected to the vacuum source  422 , the actuator  416 , and the valve  424  by way of signal lines  420 . At desired time intervals determined by the timer  418 , the controller  410  sends control signals to individually control the vacuum source  422 , the valve  424 , and the actuator  416  as will be described in greater detail below.  
         [0054]    When cleanliness of the CMP pad  404  needs evaluating, the controller  410  sends a control signal to the actuator  416 . The control signal is translated into movement of the actuator  416 , which moves the retaining structure  432  onto the surface  405  of the CMP pad  404 . Then, the controller  410  sends a signal to the valve  424 , which opens the valve  424  into a first position such that solvent  438  flows from the reservoir  434  to the retaining structure  432  through the stem section  436 . The controller  410  sends a signal to close the valve  424  when the desired amount of solvent  438  is delivered to the retaining structure  432 . Next, the controller  410  sends a signal to shift the valve  424  into a second position such that solvent can flow from the retaining structure  432  to the sample tank  426  through the stem section  436 . After a predetermined period of time, the controller  410  sends a signal to turn on the vacuum source  422 , and the resulting vacuum pressure in the vacuum hose  414  causes solvent  438  to be drawn from the retaining structure  432  to the sample tank  424 . Solvent  438  is then obtained from the sample tank  424  for subsequent testing in an analysis system  442  such as ion plasma analysis equipment.  
         [0055]    In one embodiment, the solvent  438  in the sample tank  424  is automatically directed to the analysis system  442 . After solvent  438  is delivered into the sample tank  424 , the controller  410  sends a signal to turn on the vacuum source  422 , thereby moving solvent  438  from the sample tank  424  into the analysis system  442 . If the level of contaminants in the solvent  438  is too high, then the analysis system  442  sends a signal to the controller  410 . In one embodiment, this signal turns on an audible alarm which notifies the user that the CMP pad  404  can no longer be used in its current condition.  
         [0056]    Less human interaction is necessary when using the chemical collection assembly  430  because of the automation described above. The controller  410  will control, with a high degree of accuracy, the amount of solvent  438  delivered into the retaining structure  432  and the time interval between delivery to and delivery from the retaining structure  432 . Advantageously, it is easy to assess the cleanliness of the pad  404  because the chemical collection assembly  430  requires lesser human interaction.  
         [0057]    Also, it is understood that significant amounts of data will be generated from such testing. Test data would likely include the amount of time the pad was used, the visual appearance of the pad, and the amount of contaminants contained in the solvent. Collection of such data, after time would reveal the correlation between pad cleanliness, processing time, and pad appearance. Discovery of these correlations would eventually allow the user to run the CMP process more efficiently. This automated system, reduces the effect that human error would have on such test data. Advantageously, the user would be able to discern such correlations more quickly.  
         [0058]    In one embodiment, the entire chemical collection assembly  430  is compact enough to be attached to a single fixture (not shown). In this embodiment, the fixture is permanently attached to the CMP system described above in relation to FIG. 1, and the fixture is pivoted out of position from above the CMP pad  404  during normal CMP processing. With this embodiment, the user can simply pivot the fixture into position above the CMP pad  404  and start the automated chemical collection assembly  430 . Advantageously, this embodiment allows for a quick transition between ordinary CMP processing and testing the CMP pad cleanliness.  
         [0059]    Although the foregoing description of the preferred embodiment of the present invention has shown, described, and pointed out the fundamental novel features of the invention, it will be understood that various omissions, substitutions, and changes in the form of the detail of the apparatus as illustrated as well as the uses thereof, may be made by those skilled in the art, without departing from the spirit of the invention. Consequently, the scope of the invention should not be limited to the foregoing discussions, but should be defined by the appended claims.