text: as noted above , it is believed that large agglomerated particulates cause defects to be formed on the semiconductor wafer during the polishing process . thus , the goal of the present invention is to prevent the formation of these particulates in the slurry . although extremely fine mesh physical filters may be used to filter the agglomerate particles , because the particles can be extremely small , the filtering may be ineffective , or may be cost - prohibitive . therefore , the present invention provides a method for reducing or eliminating the amount of agglomerate particles in the slurry delivered to the cmp apparatus . specifically , the present invention relates to the agglomeration of particles caused by ph shock , or the change in ph level of the slurry due to outside influences . as is known in the art , deionized water is used by cmp machines for various purposes . for example , for concentrated slurries , deionized water is used to dilute the slurry in the slurry distribution system . deionized water is also used to flush and clean the piping in the slurry distribution system and the cmp machines during routine preventive maintenance . deionized water is also commonly used to rinse and wash the polishing pad of the cmp machine between wafers and between runs . finally , deionized water is also used to condition the polishing pad . thus , it can be seen that deionized water is used in very important aspects of the cmp process . typically , the deionized water is neutral , i . e ., has a ph of 7 . in contrast , the slurries used in the cmp process may have a ph of 10 for a dielectric cmp slurry down to a ph below 4 for a metal cmp slurry . inevitably , the slurry will be in contact with deionized water . it has been found that a highly acid or base slurry coming in contact with the neutral deionized water will suffer &# 34 ; ph shock &# 34 ;. the ph shock will cause agglomeration of the particles , which as noted above , will lead to increased defects during the cmp process . the present invention attempts to eliminate the ph shock by adjusting the ph of the deionized water to match that of the slurry being currently used by the cmp machine . turning to fig1 a cmp polishing system 101 in accordance with the present invention is shown . the system 101 includes a cmp tool 103 that receives slurry from a day tank 105 . the day tank 105 is a reservoir that holds the slurry that will be used for that day or other predetermined period of time . after the slurry has been used by the cmp tool 103 , the slurry is disposed of through a drain system . feeding the day tank 105 is a slurry tank 107 and a deionized water tank 107 . the slurry tank 107 contains a reservoir of slurry , typically in concentrated form . the deionized water tank 107 contains deionized water that is used for mixing with the slurry from the slurry tank 107 in order to dilute the slurry . also , a system flush line between the deionized water tank 107 and the cmp tool 103 is provided . this flush line provides water to the cmp tool for pad or wafer rinsing and system flush . the foregoing elements of the system 101 are of conventional design . the present invention modifies this design by adding a system for monitoring and adjusting the ph of the deionized water to match that of the slurry . in particular , a slurry ph monitor 113 is provided for monitoring the ph of the slurry being delivered from the day tank 105 to the cmp tool 103 . the slurry ph monitor 113 is of conventional design and can rapidly determine the ph of the slurry . the ph information for the slurry is provided to a ph controller 115 . similarly , a deionized water ph monitor 111 is provided for monitoring the ph of the deionized water being delivered from the deionized water tank 107 to the day tank 105 . the deionized water ph monitor 111 is of conventional design and can rapidly determine the ph of the water . the ph information for the deionized water is provided to the ph controller 115 . in the preferred embodiment , the ph controller 115 is a commercially available microprocessor . the ph controller is operative to compare the ph of the deionized water with the ph of the slurry . this procedure can be seen in fig2 which is a flow diagram of the logic contained in the ph controller 115 . first at a step 201 , the ph for the slurry and the ph for the water is received by the ph controller 115 . next , at step 203 , a determination is made to determine if the ph of the two fluids are within a predetermined range from each other . if yes , then the ph controller 115 takes no action and returns to monitoring the ph levels at step 201 . for example , if the ph of the slurry is 5 . 3 and the ph of the water is 5 . 4 , and the predetermined range is 0 . 2 , then no action is taken . however , if the ph controller 115 finds that a large difference in ph between the slurry and the water exists , then at step 205 , a determination is made as to whether the ph of the slurry is greater than the ph of the water . if the ph of the slurry is greater than the ph of the water , then this indicates that the slurry is more base - like than the water . thus , at step 207 , a valve 117 is directed to add base from a base tank 121 to the deionized water tank 107 . the base may be koh ( inorganic ) or nh 4 oh ( inorganic ) or organic bases such as amines . however , if the ph of the slurry is not greater than the ph of the water , then this indicates that the slurry is more acid - like than the water . thus , at step 209 , the valve 117 is directed to add acid from an acid tank 119 to the deionized water tank 107 . the acid may be hno 3 ( inorganic acid ) or citric acid ( organic acid ) or any other acid . the goal of this closed loop system is to ensure that the ph of the deionized water is closely matched with the ph of the slurry being delivered to the cmp tool 103 . because the cmp polishing system is kept in a near constant ph environment , the ph shock is reduced , resulting in lower particle agglomeration . this in turn lowers the amount of defects during the cmp process . moreover , because of the reduced gelling and agglomeration , the frequency of preventive maintenance of the slurry delivery system can be lowered . while the preferred embodiment of the invention has been illustrated and described , it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention .