Abstract:
A pneumatic testing system or kit for testing the downstroke or reciprocating resistance and the presence of air leaks in an air-actuated, piston-type pad conditioning head of a pad conditioning system used in the conditioning of polishing pads for polishing semiconductor wafer substrates. The pneumatic testing system is pneumatically connected to the air-actuated piston in the conditioning head. The system is operated to drive the piston downwardly in the conditioning head while measuring the resistance imparted against the piston by the O-rings and other components in the conditioning head. A pair of switch timers connected to the circuit are capable of timing reciprocation of the piston in the conditioning head. In another application, the system is used to detect the presence of air leakages in the conditioning head.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to disks used in the conditioning of polishing pads on chemical mechanical polishers for semiconductor wafers. More particularly, the present invention relates to a pneumatic off-line testing kit or system for testing the downstroke or reciprocating resistance of a piston in a piston-actuated pad conditioning head and detecting the presence of air leakages from the pad conditioning head.  
         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]    A schematic of a typical CMP apparatus is shown in FIGS. 1A and 1B. The apparatus  20  for chemical mechanical polishing consists of a rotating wafer holder  14  that holds the wafer  10 , the appropriate slurry  24 , and a polishing pad  12  which is normally mounted to a rotating table  26  by adhesive means. The polishing pad  12  is applied to the wafer surface  22  at a specific pressure. 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]    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.  
           [0006]    A polishing pad is typically constructed in two layers overlying a platen with the resilient layer as the outer layer of the pad. The layers are typically made of polyurethane and may include a filler for controlling the dimensional stability of the layers. The polishing pad is usually several times the diameter of a wafer and the wafer is kept off-center on the pad to prevent polishing a non-planar surface onto the wafer. The wafer is also rotated to prevent polishing a taper into the wafer. Although the axis of rotation of the wafer and the axis of rotation of the pad are not collinear, the axes must be parallel.  
           [0007]    In a CMP head, large variations in the removal rate, or polishing rate, across the whole wafer area are frequently observed. A thickness variation across the wafer is therefore produced as a major cause for wafer non-uniformity. In the improved CMP head design, even though a pneumatic system for forcing the wafer surface onto a polishing pad is used, the system cannot selectively apply different pressures at different locations on the surface of the wafer. This effect is shown in FIG. 1C, i.e. in a profilometer trace obtained on an 8-inch wafer. The thickness difference between the highest point and the lowest point on the wafer is almost 2,000 angstroms, resulting in a standard deviation of 472 angstroms, or 6.26%. The curve shown in FIG. 1C is plotted with the removal rates in the vertical axis and the distance from the center of the wafer in the horizontal axis. It is seen that the removal rates obtained at the edge portions of the wafer are substantially higher than the removal rates at or near the center of the wafer. The thickness uniformity on the resulting wafer after the CMP process is poor.  
           [0008]    The polishing pad  12  is a consumable item used in a semiconductor wafer fabrication process. Under normal wafer fabrication conditions, the polishing pad is replaced after about  12  hours of usage. Polishing pads may be hard, incompressible pads or soft pads. For oxide polishing, hard and stiffer pads are generally used to achieve planarity. Softer pads are generally used in other polishing processes to achieve improved uniformity and smooth surfaces. The hard pads and the soft pads may also be combined in an arrangement of stacked pads for customized applications.  
           [0009]    A problem frequently encountered in the use of polishing pads in oxide planarization is the rapid deterioration in oxide polishing rates with successive wafers. The cause for the deterioration is known as “pad glazing”, wherein the surface of a polishing pad becomes smooth such that slurry is no longer held in between the fibers of the pad. This physical phenomenon on the pad surface is not caused by any chemical reactions between the pad and the slurry.  
           [0010]    To remedy the pad glazing effect, numerous techniques of pad conditioning or scrubbing have been proposed to regenerate and restore the pad surface and thereby restore the polishing rates of the pad. The pad conditioning techniques include the use of silicon carbide particles, diamond emery paper, blade or knife for scraping or scoring the polishing pad surface. The goal of the conditioning process is to remove polishing debris from the pad surface and re-open pores in the pad by forming micro-scratches in the surface of the pad for improved pad lifetime. The pad conditioning process can be carried out either during a polishing process, i.e. known as concurrent conditioning, or after a polishing process.  
           [0011]    Referring next to FIG. 2, a conventional CMP apparatus  50  includes a conditioning head  52  fitted with a conditioning disk  68 , which is formed by embedding or encapsulating diamond particles in nickel coated on the surface of the conditioning disk  68 ; a polishing pad  56 ; and a slurry delivery arm  54  positioned over the polishing pad  56 . 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.  
           [0012]    Recently, a pad conditioning arm  102  having a new type of pad conditioning head  101 , shown in FIGS. 3 and 4, has been designed for existing Mirra-type polishing pad conditioning systems. The pad conditioning head  101  includes a housing  103  which is typically mounted on a head support arm  130 . A cylindrical core wall  104  is mounted inside the housing  103 , and a cylindrical piston  107  is vertically slidably mounted between the inner surface of the housing  103  and the outer surface of the core wall  104 . An upper air cavity  108  is defined above the piston  107 , and a lower air cavity  111  is defined beneath the piston  107 . At least one upper cavity air opening  128  communicates with the upper air cavity  108  for the introduction of air into the upper air cavity  108  and moving the piston  107  downwardly in the housing  103 . Similarly, at least one lower cavity air opening (not shown) communicates with the lower air cavity  111  for the introduction of air into the lower air cavity  111  and moving the piston  107  upwardly in the housing  103 . An outside O-ring  110  is interposed between the piston  107  and the housing  103 . A magnetic ring  109  encircles the piston  107  and is disposed in contact with the inner surface of the housing  103 . A position-sensing proximity switch  112  is provided in the housing  103 , in magnetic contact with the magnetic ring  109 , for sensing the vertical position of the piston  107  in the housing  103 , as hereinafter further described. An inside O-ring  113  is typically interposed between the inner surface of the piston  107  and the outer surface of the core wall  104 .  
           [0013]    A cylindrical hub  115  having a central hub bore  116  is mounted inside the core wall  104 , with a ball bearing  118  and a needle bearing  121  typically interposed between the outer surface of the hub  115  and the inner surface of the core wall  104 . A belt gear  117 , which receives a drive belt  123  engaged by a driving mechanism (not shown), is mounted on the upper end of the hub  115 . A shaft  120  extends downwardly through the hub bore  116 , and a cylindrical bearing  119  is interposed between the shaft  120  and the hub  115 . A travel housing  122  is mounted on the bottom end of the shaft  120 . A conditioning disk holder  125  is attached to the travel housing  122  for supporting a conditioning disk  126  on the pad conditioning head  101 . The conditioning disk  126  typically threads into the conditioning disk holder  125 , in conventional fashion. A travel housing bearing  124  is interposed between the piston  107  and the travel housing  122 .  
           [0014]    In operation of the pad conditioning head  101 , the conditioning disk  126  is typically threadably attached to the conditioning disk holder  125  preparatory to conditioning a CMP pad  132 . Rotation is transmitted from the belt gear  117  to the conditioning disk  126  through the hub  115 , the cylindrical bearing  119 , the shaft  120 , the travel housing  122  and the conditioning disk holder  125 , respectively. Upon introduction of pressurized air into the upper air cavity  108 , the piston  107  slides downwardly in the housing  103  and pushes the travel housing bearing  124 , the travel housing  122 , the conditioning disk holder  125  and the conditioning disk  126  downwardly, such that the conditioning disk  126  is simultaneously rotated and pressed against the CMP pad  132  to be conditioned. Pressure of the conditioning disk  126  against the CMP pad  132  may be decreased or terminated by introducing pressurized air into the lower air cavity  111 , such that the piston  107  moves upwardly in the housing  103  and raises the conditioning disk  126  through the housing bearing  124 , the travel housing  122  and the conditioning disk holder  125 . The proximity switch  112  continually senses the position of the magnetic ring  109  on the piston  107  and feeds this information back to a timer control box  134 , as shown in FIG. 10, to vary the pressure exerted against the CMP pad  132  by the conditioning disk  126  as a function of time according to the conditioning needs of the CMP pad  132 .  
           [0015]    Typically, the cylinder-type pad conditioning head  101  is used to replace the diaphragm-type pad conditioning head which is currently in widespread usage to polish semiconductor wafers, since the latter tends toward frequent breakdown and other problems which must be fixed often. After installation, and during routine periodic maintenance, it is beneficial to test the cylinder-type pad conditioning head  101  as to both resistance imparted by the outside O-ring  110  and the inside O-ring  113  to the downstroke and reciprocating action of the piston  107  inside the housing  103 , as well as leakage of air from the upper air cavity  108 , the lower air cavity  111  or both, since both resistance and air leakage can adversely affect the magnitude of pressure that the pad conditioning head  101  is capable of applying to a wafer substrate for sufficient polishing of the substrate. Accordingly, a testing system or kit is needed for the post-installation and periodic maintenance (PM) testing of the cylinder-type Mirra pad conditioning head  101 .  
           [0016]    An object of the present invention is to provide a system or kit for testing a cylinder-type pad conditioning head for conditioning a polishing pad used in the conditioning of semiconductor wafer substrates.  
           [0017]    Another object of the present invention is to provide a system or kit for testing a cylinder-type pad conditioning head as to resistance imparted against the conditioning head piston during downstroke of the piston inside the head housing.  
           [0018]    Still another object of the present invention is to provide a system or kit for testing a cylinder-type pad conditioning head as to the presence of air leaks in the pneumatic pressure application system of the pad conditioning head.  
           [0019]    Yet another object of the present invention is to provide a system or kit for testing a Mirra cylinder-type pad conditioning head as to both the resistance imparted against the conditioning head piston during downstroke of the piston inside the head housing and as to the presence of air leaks in the pneumatic pressure application system of the pad conditioning head.  
           [0020]    A still further object of the present invention is to provide a pad conditioning head testing system or kit which includes at least one arm mount platform for receiving a pad conditioning arm having a piston-type pad conditioning head and is adapted for testing the downstroke resistance and/or presence of air leakages in the conditioning head.  
         SUMMARY OF THE INVENTION  
         [0021]    In accordance with these and other objects and advantages, the present invention is generally directed to a pneumatic testing system or kit for testing the downstroke or reciprocating resistance and the presence of air leaks in an air-actuated, piston-type pad conditioning head of a pad conditioning system used in the conditioning of polishing pads for polishing semiconductor wafer substrates. The pneumatic testing system is pneumatically connected to the air-actuated piston in the conditioning head. The system is operated to drive the piston downwardly in the conditioning head while measuring the resistance imparted against the piston by the O-rings and other components in the conditioning head. A pair of switch timers connected to the circuit are capable of timing reciprocation of the piston in the conditioning head. In another application, the system is used to detect the presence of air leakages in the conditioning head. At least one pad conditioning arm having the conditioning head may be placed typically in a maintenance tool which is equipped with the pneumatic testing system for testing and maintenance of the conditioning head. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0023]    [0023]FIG. 1A is a cross-sectional view of a conventional chemical mechanical polishing apparatus;  
         [0024]    [0024]FIG. 1B is an enlarged, cross-sectional view of a section of a wafer and polishing pad with a slurry solution therein between, in a conventional disk polishing operation;  
         [0025]    [0025]FIG. 1C is a graph illustrating the changes in removal rates as a function of distance on a wafer after a polishing pad is repeatedly used;  
         [0026]    [0026]FIG. 2 is a perspective view of a conventional CMP polishing pad with a slurry dispensing arm and a conditioning disk positioned on top;  
         [0027]    [0027]FIG. 3 is a cross-sectional view of a cylinder-type pad conditioning head suitable for implementation of the present invention;  
         [0028]    [0028]FIG. 4 is a schematic view of a pad conditioning arm having the cylinder-type pad conditioning head shown in FIG. 3;  
         [0029]    [0029]FIG. 5 is a schematic diagram of a pneumatic testing system of the present invention;  
         [0030]    [0030]FIG. 6 is an electrical diagram for the switch timers and solenoid valve components of the pneumatic testing system of FIG. 5;  
         [0031]    [0031]FIG. 7 is a front view of a pad conditioning arm maintenance tool of the present invention;  
         [0032]    [0032]FIG. 8 is a side view of the pad conditioning arm maintenance tool of FIG. 7;  
         [0033]    [0033]FIG. 9 is a top view of the pad conditioning arm maintenance tool; and  
         [0034]    [0034]FIG. 10 is a side view of a pad conditioning arm, mounted on the pad conditioning arm maintenance tool of FIGS.  7 - 9 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    Referring initially to FIG. 5, a pneumatic testing kit or system  30  in accordance with the present invention includes an air inlet line  31  which receives a stream of clean, dry air (CDA) from a standard CDA source in the semiconductor fabrication facility. A system pressure adjustment valve  32 , fitted with a main pressure gauge  32   a , is provided in the air inlet line  31 . A piston “down” line  33  and a piston “up” line  40  branch from the air inlet line  31 .  
         [0036]    A “down” speed adjustment valve  34  is provided in the piston “down’ line  33 , and a manual valve  35  is provided in the piston “down” line  33  downstream of the “down” speed adjustment valve  34 . A “down” air pressure gauge  36  is provided downstream of the manual valve  34 . A “down” solenoid valve  38 , having a pressure vent  39 , is provided downstream of the “down” air pressure gauge  36 . The downstream segment  33   a  of the piston  37  down” line  33 , extending from the outlet of the “down” solenoid valve  38 , is provided in pneumatic communication with the upper air cavity  108  (FIG. 3) of the pad conditioning head  101 . Assuming that the pad conditioning head  101  is a part of a first pad conditioning unit  45 , the pad conditioning head  101  of a second pad conditioning unit  46  may be pneumatically connected, via a piston “down” line  47 , to the downstream segment  33   a  in parallel with the pad conditioning head  101  of the first pad conditioning unit  45 .  
         [0037]    As further shown in FIG. 5, an “up” speed adjustment valve  41 , fitted with an “up” air pressure gauge  42 , is provided in the piston “up” line  40 . An “up” solenoid valve  43 , having a pressure vent  44 , is provided in the piston “up” line  40 , downstream of the “up” speed adjustment valve  41 . A downstream segment  40   a  of the piston “up” line  40  extends from the outlet of the “up” solenoid valve  43  and is provided in pneumatic communication with the lower air cavity  111  (FIG. 3) of the pad conditioning head  101 . Assuming that the pad conditioning head  101  is a part of the first pad conditioning unit  45 , the pad conditioning head  101  of the second pad conditioning unit  46  may be pneumatically connected, via a piston “up” line  48 , to the downstream segment  40   a  in parallel with the pad conditioning head  101  of the first pad conditioning unit  45 .  
         [0038]    Referring next to FIG. 6, an electrical schematic  70  for the pneumatic testing system  30  includes an on/off switch  71  that is applied across an AC electrical potential of typically  110  volts. The electrical schematic  70  further includes a switch timer  72  that is electrically connected to an SV (solenoid valve) switch  73  which controls the “down” solenoid valve  38  and the “up” solenoid valve  43 .  
         [0039]    Referring next to FIGS.  7 - 10 , the pneumatic testing system  30  may be provided on a maintenance tool  76  for testing and maintenance of the pad conditioning heads  101  of the respective first pad conditioning unit  45  and second pad conditioning unit  46 . The maintenance tool  76  includes a base  77 , which may contain an extendible drawer  78 . A back panel  82  extends from the base  77 , and an instrument panel  79  is provided in front of the rear panel  82 . As shown in FIG. 9, a pair of spaced-apart platform rotation collars  84 , each having a platform opening  85 , is provided on each side of the base  77 . An elongated arm mount platform  90  extends through the registering platform openings  85  of the corresponding pair of platform rotation collars  84 , and rotatably engages the platform rotation collars  84  according to the knowledge of those skilled in the art. Each arm mount platform  90  typically includes a body portion  91  and a head portion  92  extending from the body portion  91 . Each arm mount platform  90  is capable of rotating longitudinally in the platform openings  85  of the platform rotation collars  84 . As shown in FIG. 8, a pair of arm lock bolts  87  is typically provided in the body portion  91  of each arm mount platform  90  for removably mounting each pad conditioning arm  102  to the corresponding arm mount platform  90 . A rotation lock bolt  86  extends through at least one of the platform rotation collars  84  for engaging the pad conditioning arm  102  mounted on the corresponding arm mount platform  90  and preventing rotation of the arm mount platform  90  during testing or maintenance of the pad conditioning head  101 , as desired and hereinafter further described.  
         [0040]    The various control and indicator components of the pneumatic testing system  30  heretofore described with respect to FIG. 5 are typically provided on the maintenance tool  76 . Accordingly, the air inlet line  31  and the system pressure adjust valve  32 , having the main pressure gauge  32   a , are typically mounted on the back panel  82 . The “down” speed adjustment valve  34  and the “up” speed adjustment valve  41  are typically mounted on the horizontal portion of the instrument panel  79 . The “down” air pressure gauge  36  and the “up” air pressure gauge  42  may be provided in adjacent relationship to each other on the vertical portion of the instrument panel  79 , and the switch timer  72  may be provided on the instrument panel  79 , beneath the “down” air pressure gauge  36 . However, it is understood that these control and indicator components of the pneumatic testing system  30  may be provided in alternative locations on the maintenance tool  76 , as desired.  
         [0041]    Referring again to FIGS.  5 - 10 , in typical operation of the pneumatic testing system  30 , the pad conditioning arm  102  of the first pad conditioning unit  45  and the pad conditioning arm  102  of the second pad conditioning unit  46  may be removably mounted on the respective arm mount platforms  90  of the maintenance tool  76 , and alternately tested as to downstroke or reciprocating resistance and air leakage. This is accomplished typically by initially positioning the pad conditioning arms  102  on the respective arm mount platforms  90  and then threading the arm lock bolts  87  (FIG. 8) of each arm mount platform  90  into respective threaded lock bolt openings (not shown) provided in the head support arm  130  of the pad conditioning arm  102 . Next, the rotation lock bolts  86  may be threaded against the respective pad conditioning arms  102  in order to prevent longitudinal rotation of the arm mount platforms  90  and pad conditioning arms  102  in the respective pairs of platform rotation collars  84 , as desired.  
         [0042]    Referring again to FIGS. 3 and 4, the pneumatic testing system  30  is used to both measure the downstroke resistance of the piston  107  inside the housing  103  of the pad conditioning head  101  and detect and measure leakage of air from the upper air cavity  108  or lower air cavity  111  during reciprocation of the piston  107  inside the housing  103 . Both of these parameters tend to affect the magnitude of pressure that the conditioning disk  126  is capable of applying to the CMP pad  132  to achieve optimum polishing of the CMP pad  132 . Excessive downstroke resistance of the piston  107  with respect to the housing  103  may indicate excessive grinding of the O-rings  110  and  113 , respectively, for example, and enable facility personnel to replace the O-rings  110  and  113  in order to reduce the downstroke resistance. Likewise, leakage of air from the upper air cavity  108  reduces the magnitude of pressure that the conditioning disk  126  is capable of applying to the CMP pad  132 .  
         [0043]    The downstroke resistance of the piston  107  with respect to the housing  103  is measured, as follows. First, the system pressure adjust valve  32  is used to set the system air pressure, such as 5 psi, as indicated by the main pressure gauge  32   a . Next, the switch timer  72  is set to control the timing for reciprocation of the piston  107  in the housing  103 . The reciprocation speed of the piston  107  may be adjusted using the “down” speed adjustment valve  34  and the “up” speed adjustment valve  41 . Accordingly, the switch timer  72  initially triggers the SV switch  73  to actuate the “up” solenoid valve  43 , which facilitates the passage of air from the piston “up” line  40  to the downstroke segment  40   a  and into the lower air cavity  111  (FIG. 3) of the pad conditioning head  101 . The increased air pressure in the lower air cavity  111  drives the piston  107  upwardly in the housing  103 , as the piston  107  drives air from the upper air cavity  108 , through the downstream segment  33   a  and out the pressure vent  39  of the “down” solenoid valve  38 . Next, the switch timer  72  triggers the SV switch  73  to actuate the “down” solenoid valve  38 , which facilitates the passage of air from the piston “down” line  33  to the downstroke segment  33   a  and into the upper air cavity  108  of the pad conditioning head  101 . The increased air pressure in the upper air cavity  108  drives the piston  107  downwardly in the housing  103 , as the piston  107  drives air from the lower air cavity  111 , through the downstream segment  40   a  and out the pressure vent  44  of the “down” solenoid valve  43 . The “down” air pressure gauge  36  indicates the downstroke resistance, in psi, of the piston  107  in the housing  103 . Accordingly, in the event that the downstroke resistance exceeds the system air pressure, as indicated on the main pressure gauge  32   a , by a specified value, such as by about 50%, for example, then corrective measures may be taken to replace either or both of the O-rings  110 ,  113 , and/or other components in the pad conditioning head  101 , in order to reduce the downstroke resistance and optimize the down pressure applied by the conditioning disk  126  against the CMP pad  132 .  
         [0044]    The pad conditioning head  101  is tested as to the presence of air leakages, in the following manner. First, the switch timer  72  is set according to the desired leakage rate parameters for the leakage test. For example, if the rate of air leakage is to be measured in psi/minute, then the switch timer  72  is set to reciprocate the piston  107  in the housing  103  every two minutes (downwardly one minute and upwardly the next minute) Next, the system pressure adjust valve  32  is used to set the system air pressure, such as 5 psi, as indicated by the main pressure gauge  32   a . After the switch timer  72  causes the “down” solenoid valve  38  to move the piston  107  downwardly in the housing  103 , the manual valve  35  is closed, after which the switch timer  72  causes the “up” solenoid valve  43  to move the piston  107  upwardly in the housing  103 . In the event that none of the pressurized air leaks from the upper air cavity  108  or lower air cavity  111  of the pad conditioning head  101 , the air pressure as indicated by the “up” air pressure gauge  42  equals the system air pressure as indicated by the main pressure gauge  32   a , which is, in this case, 5 psi. On the other hand, in the event that air leaks from the upper air cavity  108  and/or the lower air cavity  111 , the air pressure as indicated by the “up” air pressure gauge  42  is lower than the system air pressure as indicated by the main pressure gauge  32   a . In that case, corrective repair measures may be taken to adequately seal the upper air cavity  108  and/or the lower air cavity  111  prior to beginning or resuming use of the pad conditioning arm  102 . Referring again to FIG. 9, it will be appreciated by those skilled in the art that the facility for longitudinally rotating the arm mount platforms  90  and the respective attached pad conditioning arms  102  on the maintenance tool  76  provides versatility in the repair and maintenance of the pad conditioning arms  102 .  
         [0045]    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.