Abstract:
Methods adapted to clean a chemical mechanical polishing (CMP) pad are disclosed. The methods include positioning an energized fluid delivery assembly over a CMP polishing pad; rotating the polishing pad on a platen; energizing a fluid within the energized fluid delivery assembly; applying the energized fluid to the polishing pad to dislodge slurry residue and debris; and removing the dislodged slurry residue and debris using a vacuum suction unit. Systems and apparatus for carrying out the methods are provided, as are numerous additional aspects.

Description:
FIELD 
       [0001]    The present invention generally relates to electronic device manufacturing, and more particularly is directed to using fluids to clean chemical mechanical planarization (CMP) polishing pads. 
       BACKGROUND 
       [0002]    The electronics industry currently spends in excess of one billion U.S. Dollars each year manufacturing silicon substrates that must exhibit very flat and smooth surfaces. Known techniques to manufacture smooth and even-surfaced silicon substrates are plentiful. The most common of these involves the process known as chemical mechanical polishing (CMP) which includes the use of a polishing pad in combination with abrasive slurry. Of central importance in CMP processes is the attainment of high performance levels in aspects such as uniformity of polished substrate, smoothness of the IC circuitry, removal rate for productivity, longevity of consumables for CMP economics, etc. Chemical mechanical polishing (sometimes known in the art as chemical mechanical planarization), or CMP, is thus a well-known process used in the fabrication of electronic devices. CMP combines mechanical polishing (using, for example, abrasive slurries) with selective chemical reactions to increase the mechanical removal rate of material. The chemical reactions particularly provide greater material removal selectivity than mechanical polishing alone. 
         [0003]    CMP is commonly used to flatten the surface of a substrate after etch and/or deposition steps, generally to such a degree that subsequent photolithography steps have a sufficient focus margin. In general, CMP is performed by using a polishing pad in combination with a slurry of water, abrasives, and reactive chemicals for the desired chemical reaction or reactions. The polishing pad is caused to be pressed against the substrate surface and relative motion between the substrate and the pad is imparted (that is, by moving one or both of the substrate and the pad). 
         [0004]    The polishing pad is conventionally a porous pliable material. Polyurethane foam is particularly common for use as a polishing pad. Surface asperities of the polishing pad are critical to the polishing process because they provide the mechanical polishing action. However, as the pad is used for polishing, it tends to become smoother as the asperities are rubbed away and/or as slurry residues build up in the pores. As a result, the polishing process is degraded. It is therefore conventionally known to condition the polishing pad to roughen the surface and increase the open porosity of the foam. 
         [0005]    Conventional conditioning methods however typically wear the polishing pad such that a given pad can only be conditioned a finite number of times before it must be discarded. Thus, what is needed are systems, methods, and apparatus that allow the useful life of CMP polishing pads to be extended, but still effectively remove slurry and debris from the pores and grooves of the pad without unnecessarily wearing the pad. 
       SUMMARY 
       [0006]    Inventive embodiments of methods and apparatus are provided for cleaning slurry and debris from CMP polishing pads by applying energized fluids to the polishing pads. Embodiments of the present invention use energized fluid (e.g., liquids and gases) to clean off slurry residues and pad debris between substrate polishing or during wafer polishing. During an energized fluid cleaning cycle, as the polishing pad is sprayed or otherwise applied with energized liquids or gases that loosen and dislodge slurry residue and pad debris, a vacuum pump is used to remove the dislodged material. In some embodiments, a scraper, beater, and/or a rotating bristle brush may selectively, continuously, or intermittently contact the polishing pad to further help loosen and dislodge residue and debris. In some embodiments, instead of merely pressurizing a fluid, the energized fluid can be acoustically energized (e.g., via acoustic cavitation), pneumatically assisted (e.g., using a liquid mixed with a pressurized gas), and/or thermally state changed (e.g., liquid heated to gas). Other methods and combinations of energizing fluids can be used. 
         [0007]    In some embodiments, a method for cleaning a chemical mechanical polishing (CMP) pad is provided. The method includes positioning an energized fluid delivery assembly over a CMP polishing pad; rotating the polishing pad on a platen; energizing a fluid within the energized fluid delivery assembly; applying the energized fluid to the polishing pad to dislodge slurry residue and debris; and removing the dislodged slurry residue and debris using a vacuum suction unit. 
         [0008]    In some other embodiments, a system for cleaning a chemical mechanical polishing (CMP) pad is embodiment. The system includes a processor; and a memory storing instructions executable by the processor, the instructions operative to: position an energized fluid delivery assembly over a CMP polishing pad; rotate the polishing pad on a platen; energize a fluid within the energized fluid delivery assembly; apply the energized fluid to the polishing pad to dislodge slurry residue and debris; and remove the dislodged slurry residue and debris using a vacuum suction unit. 
         [0009]    In yet other embodiments, an apparatus for cleaning a chemical mechanical polishing (CMP) pad is provided. The apparatus includes an energized fluid delivery assembly configured to energize a fluid and apply the energized fluid to a CMP polishing pad to dislodge slurry residue and debris from the polishing pad; and a vacuum suction unit configured to remove the dislodged slurry residue and debris. 
         [0010]    In still yet other embodiments, a system for cleaning a chemical mechanical polishing (CMP) pad is provided. The system includes a polishing pad configured to be rotated on a platen; a polishing head configured to hold a substrate against the polishing pad; and an energized fluid delivery assembly configured to apply an energized fluid to the polishing pad to dislodge slurry residue and debris from the polishing pad. 
         [0011]    Numerous other aspects are provided. Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a schematic side-view drawing depicting an example of a CMP system according to embodiments. 
           [0013]      FIGS. 2A to 2C  illustrates top, side, and front views respectively of a CMP polishing pad and an example of an energized fluid cleaning assembly according to a first embodiment. 
           [0014]      FIGS. 3A and 3B  illustrates top and side views respectively of a CMP polishing pad and an example of an energized fluid cleaning assembly according to a second embodiment. 
           [0015]      FIGS. 4A to 4C  illustrates top, side, and front views respectively of a CMP polishing pad and an example of an energized fluid cleaning assembly according to a third embodiment. 
           [0016]      FIG. 5  illustrates a flowchart depicting an example method of cleaning a CMP polishing pad using energized fluid according to some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Embodiments of the present invention provide improved systems, methods and apparatus configured to clean slurry and debris from CMP polishing pads by applying energized fluids to the polishing pads. During CMP, slurries and pad debris are accumulated and become trapped within pad grooves and pores, which can cause scratches on the substrate being polished. Current state-of-the-art technology uses a high-pressure (e.g., ˜40 PSI) de-ionized water (DIW) rinse and/or vacuum to pick up such residues from the pad. However, the high-pressure DIW rinse and vacuum have been shown not to be sufficient to dislodge slurry/debris residues from the pad grooves and pores. Therefore, conventional methods of using high-pressure DIW rinse and vacuum are not sufficient for pad cleaning. 
         [0018]    One or more embodiments of the present invention use energized fluid (e.g., liquids and gases) to clean off slurry residues and pad debris between wafer polishing or during wafer polishing. During an energized fluid cleaning cycle, as the polishing pad is sprayed or otherwise applied with energized liquids or gases that loosen and dislodge slurry residue and pad debris, a vacuum pump is used to remove the dislodged material. In some embodiments, a scraper, beater, and/or a rotating bristle brush may selectively, continuously, or intermittently contact the polishing pad to further help loosen and dislodge residue and debris. In some embodiments, instead of merely pressurizing a fluid, the energized fluid can be acoustically energized (e.g., via acoustic cavitation), pneumatically assisted (e.g., using a liquid mixed with a pressurized gas), and/or thermally state changed (e.g., liquid heated to gas). Other methods and combinations of energizing fluids can be used. In some embodiments, the present invention can be used for pad cleaning, pad conditioning, and brush break-in. 
         [0019]    Turning to  FIG. 1 , a side view of an example chemical-mechanical planarization (CMP) system  100  for polishing substrates is shown. The system  100  includes a polishing head assembly  102  supported by an polishing head arm  104  operative to position the polishing head assembly  102  over a polishing pad  106  supported by and rotated on a platen  108 . The platen  108  is driven to rotate by a motor  110 . In operation, the polishing head assembly  102  is operative to securely hold a substrate, to rotate the substrate, and to press the substrate against the rotating polishing pad  106  during CMP processing. In other words, as the polishing pad  106  is rotated on the platen  108 , the head  102  rotates and pushes the substrate down against the polishing pad  106 . 
         [0020]    The system  100  also includes an energized fluid delivery assembly  112  supported by fluid delivery arm  114 . The fluid delivery arm also supports a vacuum suction unit  116  operative to remove residue and debris dislodged by the application of the energized fluid to the CMP polishing pad  106 . 
         [0021]    Each of the components can be coupled to, and operated by, a controller  118  (e.g., a processor, programmable logic array, embedded controller, computer, etc.) operative to execute instructions (e.g., software, programs, commands, signals, etc.) to perform the methods of the present invention, and in particular, the methods described below with respect to the flowchart in  FIG. 5 . 
         [0022]    As indicated above, the energized fluid can be acoustically energized. Ultrasonically or megasoincally energized fluid (e.g., fluid that experiences acoustic cavitation) can dislodge residues from large areas like polishing pad grooves and also from smaller areas like polishing pad pores. This capability to dislodge particles from both larger and smaller areas provides for a higher cleaning efficiency of the polishing pad as compared to conventional methods. 
         [0023]      FIGS. 2A through 2C  depict top, side and front views respectively of an energized fluid delivery assembly  112  ( FIG. 1 ) that includes an acoustically energized fluid delivery unit  212  that is adapted to delivery acoustically energized fluid  214  to the polishing pad  106  while vacuum suction unit  116  removes dislodged residue and debris. In some embodiments, the acoustically energized fluid delivery unit  212  can include a piezoelectric transducer (PZT) operating in the frequency range from the lower ultrasonic range (approximately 20 KHz) to the upper megasonic range (approximately 2 MHz.) Other frequency ranges can be used. The shape of a suitable acoustic energy source generator (e.g., a PZT) can be rectangular with dimensions in the range of approximately 5 mm×50 mm to approximately 15 mm×1500 mm. Other sized PZTs can be used. For example, with a polishing pad radius of 15 inches, a PZT with a length of 15 inches may be used. Likewise, the vacuum suction unit  116  can be the same length. 
         [0024]    In some embodiments, shorter length PZTs can be used in the acoustically energized fluid delivery unit  212  where the acoustically energized fluid delivery unit  212  is adapted to be swept from the center of the pad  106  to the edge of the pad  106 . In such embodiments, the fluid delivery arm  114  ( FIG. 1 ), can be used to sweep the acoustically energized fluid delivery unit  212  across the pad  106  radially. Alternatively, a separate gantry can be used to sweep the acoustically energized fluid delivery unit  212  back and forth radially over the pad  106 . 
         [0025]    In some embodiments, the acoustically energized fluid delivery unit  212  can include a housing with an input channel to receive fluid, a PZT held within the housing to apply energy to the received fluid, and a slot or plurality of nozzles along the bottom length of the housing aimed at the polishing pad  106  to distribute the energized fluid  214  across the polishing pad  106 . In some embodiments, the housing or individual nozzles can be configured to rock back and forth as energized fluid  214  is being dispensed to further enhance the loosening action of the energized fluid  214  by continually altering the angle of impact of the energized fluid  214  on the pad  106 . 
         [0026]    As indicated by the ‘H’ dimension labeled in  FIGS. 2B and 2C , the acoustically energized fluid delivery unit  212  can be disposed from approximately 4 mm to approximately 10 mm above the polishing pad  106  during application of the acoustically energized fluid  214 . Likewise the vacuum suction unit can be similarly disposed from approximately 4 mm to approximately 10 mm above the polishing pad  106  during application of the acoustically energized fluid  214 . 
         [0027]    In some embodiments, the fluid that is energized can be deionized water (DIW) and/or cleaning chemistry. The temperature of the fluid can be from 20 C. to 90 C. Other temperatures can be used. The flow rate of the energized fluid  214  can be in the range of approximately 100 ml/min to approximately 10 L/min. Other flow rates can be used. In some embodiments, the cleaning chemistry can be, for example, diluted potassium hydroxide (KOH) when using, for example, SemiSperse® SS12 slurry manufactured by Cabot Microelectronics Corporation of Aurora, Ill. 
         [0028]    In some embodiments, a scraper, beater, and/or a rotating bristle brush may selectively, continuously, or intermittently contact the polishing pad  106  to further help loosen and dislodge residue and debris. The use of a scraper, beater, and/or a rotating bristle brush may be selectively applied by the controller  118 . An optical sensor can be used to inspect the pad  106  and provide information to the controller  118  as to the status of the pad  106 . Based on the status of the pad  106 , the controller  118  can determine if the pad should continue to be treated with energized fluid, if higher energy should be applied to the fluid (e.g., heat, pressure, acoustic energy, etc.), or of the pad should receive contact from a scraper, beater, and/or a rotating bristle brush. 
         [0029]    As indicated above, the energized fluid can alternatively be energized using pressurized gas. As with acoustically energized fluid, pressurized gas assisted liquid spray jets can be used to effectively dislodge residue and debris from large areas like polishing pad grooves and also from smaller areas like polishing pad pores. As noted, this capability provides for high cleaning efficiency of the polishing pad as compared to conventional pad cleaning methods. The pressurized gas assisted spray removes particles via fluid droplet momentum transfer. Because this method has a lower fluid flow rate, not only is DIW conserved, the amount of splash is drastically reduced and therefore, there is substantially less slurry residue build up within the system  100 . 
         [0030]      FIGS. 3A and 3B  depict top and side views respectively of an energized fluid delivery assembly  112  ( FIG. 1 ) that includes an pressurized gas energized fluid delivery unit  312  that is adapted to delivery pressurized gas energized fluid  314  to the polishing pad  106  while vacuum suction unit  116  removes dislodged residue and debris. In some embodiments, the pressurized gas energized fluid delivery unit  312  can include a pressurized gas supply such as filtered air or nitrogen (N 2 ). The mixing chamber within the pressurized gas energized fluid delivery unit  312  can be rectangular with dimensions in the range of approximately 5 mm×50 mm to approximately 15 mm×1500 mm. Other sized mixing chambers can be used. For example, with a polishing pad radius of 15 inches, a mixing chamber with a length of 15 inches may be used. Likewise, the vacuum suction unit  116  can be the same length. 
         [0031]    In some embodiments, shorter length mixing chambers can be used in the pressurized gas energized fluid delivery unit  312  where the delivery unit  312  is adapted to be swept from the center of the pad  106  to the edge of the pad  106  as indicated by the double ended arrow in  FIG. 3A . In such embodiments, the fluid delivery arm  114  ( FIG. 1 ), can be used to sweep the pressurized gas energized fluid delivery unit  312  across the pad  106  radially. Alternatively, a separate gantry can be used to sweep the pressurized gas energized fluid delivery unit  312  back and forth radially over the pad  106 . 
         [0032]    In some embodiments, the pressurized gas energized fluid delivery unit  312  can include a housing with a liquid input channel to receive the liquid and a gas input channel to receive the pressurized gas. The housing also includes the mixing chamber to apply the pressurized gas to the liquid and a slot or plurality of nozzles along the bottom length of the housing aimed at the polishing pad  106  to distribute the energized fluid  314  across the polishing pad  106 . In some embodiments, the housing or individual nozzles can be configured to rock back and forth as energized fluid  314  is being dispensed to further enhance the loosening action of the energized fluid  314  by continually altering the angle of impact of the energized fluid  314  on the pad  106 . 
         [0033]    As indicated by the ‘H’ dimension labeled in  FIG. 3B , the pressurized gas energized fluid delivery unit  312  can be disposed from approximately 10 mm to approximately 100 mm above the polishing pad  106  during application of the pressurized gas energized fluid  314 . The vacuum suction unit can be disposed from approximately 4 mm to approximately 10 mm above the polishing pad  106  during application of the pressurized gas energized fluid  314 . 
         [0034]    In some embodiments, the fluid that is energized can be deionized water (DIW) and/or cleaning chemistry. The temperature of the fluid can be from 20 C. to 90 C. Other temperatures can be used. In some embodiments, the air pressure applied to energize the fluid can be in the range from approximately 40 PSI to approximately 140 PSI. Other pressures can be used. The liquid flow rate can be in the range from approximately 100 ml/min to approximately 2 L/min. Other flow rates can be used. The droplet speed can be in the range from approximately 100 m/s to approximately 300 m/s. Other droplet speeds can be used. In some embodiments, the cleaning chemistry can be, for example, diluted potassium hydroxide (KOH) when using, for example, SemiSperse® SS12 slurry manufactured by Cabot Microelectronics Corporation of Aurora, Ill. 
         [0035]    In some embodiments, a scraper, beater, and/or a rotating bristle brush may selectively, continuously, or intermittently contact the polishing pad  106  to further help loosen and dislodge residue and debris. The use of a scraper, beater, and/or a rotating bristle brush may be selectively applied by the controller  118 . An optical sensor can be used to inspect the pad  106  and provide information to the controller  118  as to the status of the pad  106 . Based on the status of the pad  106 , the controller  118  can determine if the pad should continue to be treated with energized fluid, if higher energy should be applied to the fluid (e.g., heat, pressure, acoustic energy, etc.), or of the pad should receive contact from a scraper, beater, and/or a rotating bristle brush. 
         [0036]    As indicated above, the energized fluid can alternatively be thermally energized to change state. As with acoustically and pressurized gas energized fluid, thermally energized liquid forced to change into gas (e.g., using an ultra-pure DIW to steam generator) can be used to effectively dislodge residue and debris from large areas like polishing pad grooves and also from smaller areas like polishing pad pores. As noted, this capability provides for high cleaning efficiency of the polishing pad as compared to conventional pad cleaning methods. The thermally energized gas removes particles via heat transfer. Because this method has a lower fluid flow rate, not only is DIW conserved, the amount of splash is drastically reduced and therefore, there is substantially less slurry residue build up within the system  100 . 
         [0037]      FIGS. 4A through 4C  depict top, side, and front views respectively of an energized fluid delivery assembly  112  ( FIG. 1 ) that includes a thermally energized fluid delivery unit  412  that is adapted to delivery thermally energized fluid  414  to the polishing pad  106  while vacuum suction unit  116  removes dislodged residue and debris. In some embodiments, the thermally energized fluid delivery unit  412  can include a heater to vaporize cleaning fluid. The vaporizing chamber within the thermally energized fluid delivery unit  412  can be rectangular with dimensions in the range of approximately 5 mm×50 mm to approximately 15 mm×1500 mm. Other sized vaporizing chambers can be used. For example, with a polishing pad radius of 15 inches, a vaporizing chamber with a length of 15 inches may be used. Likewise, the vacuum suction unit  116  can be the same length. 
         [0038]    In some embodiments, shorter length vaporizing chambers can be used in the thermally energized fluid delivery unit  412  where the delivery unit  412  is adapted to be swept from the center of the pad  106  to the edge of the pad  106 . In such embodiments, the fluid delivery arm  114  ( FIG. 1 ), can be used to sweep the thermally energized fluid delivery unit  412  across the pad  106  radially. Alternatively, a separate gantry can be used to sweep the thermally energized fluid delivery unit  412  back and forth radially over the pad  106 . 
         [0039]    In some embodiments, the thermally energized fluid delivery unit  412  can include a housing with a liquid input channel to receive the liquid. The housing can hold a heating element that receives electrical energy to vaporize the liquid. The housing also includes the vaporizing chamber to apply the thermal energy to the liquid and a slot or plurality of nozzles along the bottom length of the housing aimed at the polishing pad  106  to distribute the energized fluid  414  across the polishing pad  106 . In some embodiments, the housing or individual nozzles can be configured to rock back and forth as energized fluid  414  is being dispensed to further enhance the loosening action of the energized fluid  414  by continually altering the angle of contact of the energized fluid  414  on the pad  106 . 
         [0040]    As indicated by the ‘H’ dimension labeled in  FIGS. 4B and 4C , the thermally energized fluid delivery unit  412  can be disposed from approximately 4 mm to approximately 10 mm above the polishing pad  106  during application of the thermally energized fluid  414 . The vacuum suction unit can be similarly disposed from approximately 4 mm to approximately 10 mm above the polishing pad  106  during application of the pressurized gas energized fluid  414 . 
         [0041]    In some embodiments, the fluid that is energized can be deionized water (DIW) and/or cleaning chemistry. The temperature of the fluid can be from 20 C. to 90 C. Other temperatures can be used. In some embodiments, the heat energy applied to energize the fluid can be in the range from approximately 2 Kcal (2 Cal) to approximately 2000 Kcal (2000 Cal). Other amounts of thermal energy can be used. The liquid flow rate can be in the range from approximately 100 ml/min to approximately 10 L/min. Other flow rates can be used. In some embodiments, the cleaning chemistry can be, for example, diluted potassium hydroxide (KOH) when using, for example, SemiSperse® SS12 slurry manufactured by Cabot Microelectronics Corporation of Aurora, Ill. 
         [0042]    In some embodiments, a scraper, beater, and/or a rotating bristle brush may selectively, continuously, or intermittently contact the polishing pad  106  to further help loosen and dislodge residue and debris. The use of a scraper, beater, and/or a rotating bristle brush may be selectively applied by the controller  118 . An optical sensor can be used to inspect the pad  106  and provide information to the controller  118  as to the status of the pad  106 . Based on the status of the pad  106 , the controller  118  can determine if the pad should continue to be treated with energized fluid, if higher energy should be applied to the fluid (e.g., heat, pressure, acoustic energy, etc.), or of the pad should receive contact from a scraper, beater, and/or a rotating bristle brush. 
         [0043]    Turning now to  FIG. 5 , a flowchart depicting an example method  500  of cleaning a CMP polishing pad is provided. Note that the steps listed can be implemented using the system  100  either manually by an operator or automatically by the controller  118  executing instructions or a program. In some embodiments, some steps may be performed manually while others are performed automatically. Also note that while four steps are listed to illustrate the method  500 , other sub-steps and compound or supra-steps can be included to increase or decrease the number of steps. 
         [0044]    After CMP processing has been performed on one or more substrates, an energized fluid delivery assembly  112  is positioned above the CMP polishing pad ( 502 ). In some embodiments, the energized fluid delivery assembly  112  may be positioned over the pad  106  while CMP processing is performed. In some embodiments, the method  500  may be performed while CMP processing is being performed. 
         [0045]    With the energized fluid delivery assembly  112  and the vacuum suction unit  116  in place, the CMP polishing pad  106  is rotated and the fluid in the energized fluid delivery assembly  112  is energized ( 504 ). In some embodiments, energizing the fluid can include applying acoustic energy, applying pressurized gas, applying thermal energy to change a liquid to a gas, or any combination of these methods. 
         [0046]    The energized fluid is applied to the polishing pad  106  while the pad  106  is monitored ( 506 ). The energized fluid can be applied directly to the pad  106  and in some embodiments, the energized fluid can be sprayed at the pad  106  from continuously changing angles by pivoting the energized fluid delivery assembly  112  or its output ports (e.g., slot or nozzles). The energized fluid delivery assembly  112  can also be oscillated in a radial direction relative to the pad  106  to cover the full radius to the pad  106 . 
         [0047]    In some embodiments, the energized fluid can be simply be applied for a fixed amount of time or a fixed amount of energized fluid can be applied. In some embodiments, an optical sensor can be used to monitor the pad  106 . In some embodiments, the vacuum suction unit  116  can include one or more sensors to determine if anything more than energized fluid is being removed from the pad  106  and thus, that the pad  106  is clean. Thus, cleaning completion can be determined based upon the pad  106  receiving a predefined amount of energized fluid, based on a predefined amount of time passing, or based upon feedback from one or more sensors providing status of the pad ( 508 ). 
         [0048]    Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.