Abstract:
A cleaning system for removing contaminants on a surface of a patterned substrate for defining integrated circuit devices is provided. The system includes a substrate carrier for supporting edges of the patterned substrate, and a cleaning head positioned over the patterned substrate. The cleaning head includes a plurality of dispensing holes to dispense a cleaning material on the surface the patterned substrate for defining integrated circuit devices, wherein the cleaning material includes polymers of a polymeric compound. The cleaning head is coupled to a storage of the cleaning material, which is coupled to the cleaning material preparation system. A support structure holds the cleaning head in proximity to the surface of the patterned substrate.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority as a divisional of U.S. patent application Ser. No. 12/131,667, filed Jun. 2, 2008, entitled “Apparatus for Particle Removal by Single-Phase and Two-Phase Media,” which claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/013,950, filed Dec. 14, 2007, entitled “Materials and Methods for Particle Removal by Single-Phase and Two-Phase Media.” These applications are incorporated herein by reference. 
       CROSS REFERENCE TO RELATED APPLICATIONS 
       [0002]    This application is related to U.S. patent application Ser. No. 12/131,654, filed Jun. 2, 2008, entitled “Apparatus for Particle Removal by Single-Phase and Two-Phase Media.” This application is related to U.S. patent application Ser. No. 12/131,660, filed Jun. 2, 2008, entitled “Methods for Particle Removal by Single-Phase and Two-Phase Media.” This application is also related to U.S. patent application Ser. No. 11/532,491, filed on Sep. 15, 2006, entitled “Method and Material for Cleaning a Substrate,” U.S. patent application Ser. No. 11/532,493, filed on Sep. 15, 2006, entitled “Apparatus and System for Cleaning a Substrate,” and U.S. patent application Ser. No. 11/641,362, filed on Dec. 18, 2006, entitled “Substrate Preparation Using Stabilized Fluid Solutions and Methods for Making Stable Fluid Solutions.” The disclosure of each of the above-identified related applications is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0003]    In the fabrication of semiconductor devices such as integrated circuits, memory cells, and the like, a series of manufacturing operations are performed to define features on semiconductor wafers (“wafers”). The wafers (or substrates) include integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Also, patterned conductive layers are insulated from other conductive layers by dielectric materials. 
         [0004]    During the series of manufacturing operations, the wafer surface is exposed to various types of contaminants. Essentially any material present in a manufacturing operation is a potential source of contamination. For example, sources of contamination may include process gases, chemicals, deposition materials, and liquids, among others. The various contaminants may deposit on the wafer surface in particulate form. If the particulate contamination is not removed, the devices within the vicinity of the contamination will likely be inoperable. Thus, it is necessary to clean contaminants from the wafer surface in a substantially complete manner without damaging the features defined on the wafer. However, the size of particulate contamination is often on the order of the critical dimension size of features fabricated on the wafer. Removal of such small particulate contamination without adversely affecting the features on the wafer can be quite difficult. 
         [0005]    Conventional wafer cleaning methods have relied heavily on mechanical force to remove particulate contamination from the wafer surface. As feature sizes continue to decrease and become more fragile, the probability of feature damage due to application of mechanical forces on the wafer surface increases. For example, features having high aspect ratios are vulnerable to toppling or breaking when impacted by a sufficient mechanical force. To further complicate the cleaning problem, the move toward reduced feature sizes also causes a reduction in the size of particulate contamination. Particulate contamination of sufficiently small size can find its way into difficult to reach areas on the wafer surface, such as in a trench surrounded by high aspect ratio features. Thus, efficient and non-damaging removal of contaminants during modern semiconductor fabrication represents a continuing challenge to be met by continuing advances in wafer cleaning technology. It should be appreciated that the manufacturing operations for flat panel displays suffer from the same shortcomings of the integrated circuit manufacturing discussed above. 
         [0006]    In view of the forgoing, there is a need for apparatus and methods of cleaning patterned wafers that are effective in removing contaminants and do not damage the features on the patterned wafers. 
       SUMMARY 
       [0007]    Broadly speaking, the embodiments of the present invention provide improved materials, apparatus, and methods for cleaning wafer surfaces, especially surfaces of patterned wafers (or substrates). The cleaning materials, apparatus, and methods discussed above have advantages in cleaning patterned substrates with fine features without substantially damaging the features. The cleaning materials are fluid, either in liquid phase, or in liquid/gas dual phase, and deform around device features; therefore, the cleaning materials do not substantially damage the device features or reduce damage all together. The cleaning materials, containing polymers of one or more polymeric compounds with large molecular weight, capture the contaminants on the substrate. For polymers made from one monomer, the polymers contain one polymeric compound. For polymers made from more than one monomers, such as copolymers or a mixture of polymers, the polymers contain more than one polymeric compounds. 
         [0008]    In addition, the cleaning materials entrap the contaminants and do not return the contaminants to the substrate surface. The polymers of a polymeric compound with large molecular weight form long polymer chains, which can also be cross-linked to form a network (or polymeric network). The length of the polymer chains for polymers that are not substantially cross-linked or almost not cross-linked can be estimated by dividing the molecular weight of the polymers by the molecular weight of the monomeric species (length˜(molecular weight of polymer)/(weight of monomer)). The long polymer chains and/or polymer network show superior capabilities of capturing and entrapping contaminants, in comparison to conventional cleaning materials. As a result, cleaning materials, in fluid form, including such polymers show excellent particle removal performance. The captured or entrapped contaminants are then removed from the surface of the substrate. 
         [0009]    As discussed above, the polymers can be cross-linked. However, the extent of cross-link is relatively limited to avoid making the polymers too hard or rigid, which would prevent the polymers from being soluble in a solvent and being deformed around device features on the substrate surface. 
         [0010]    It should be appreciated that the present invention can be implemented in numerous ways, including as a system, a method and a chamber. Several inventive embodiments of the present invention are described below. 
         [0011]    In one embodiment, a cleaning system for removing contaminants on a surface of a patterned substrate for defining integrated circuit devices is provided. The cleaning system includes a substrate carrier for supporting edges of the patterned substrate. The cleaning system also includes a cleaning head positioned over the patterned substrate held by the substrate carrier, the cleaning head having a plurality of dispensing holes to dispense a cleaning material on the surface the patterned substrate for defining integrated circuit devices. The cleaning material includes polymers of the polymeric compound with a molecular weight greater than 10,000 g/mol. The polymers are soluble in a solvent to form the cleaning material. The cleaning material has less than 1 part per billion (ppb) of metallic contaminants before being applied on the surface of the patterned substrate. 
         [0012]    The solubilized polymers have long polymer chains to capture and entrap the contaminants from the surface of the patterned substrate. The cleaning material deforms around device features on the patterned substrate when a force is applied on the cleaning material applied on the surface of the patterned substrate to remove the contaminants without substantially damaging the device features on the surface. The cleaning material is substantially free of abrasive particles before the cleaning material being applied on the surface of the patterned substrate. The cleaning head being coupled to a storage of the cleaning material, which is coupled to the cleaning material preparation system. Further, the cleaning system includes a support structure for holding the cleaning head in proximity to the surface of the patterned substrate. 
         [0013]    In another embodiment, a cleaning system for dispensing a cleaning material to remove contaminants on a surface of a patterned substrate for defining integrated circuit devices is provided. The cleaning system includes a substrate support for supporting the patterned substrate. The substrate support rotates during a cleaning process to remove contaminants from the surface of the patterned substrate. The cleaning system also includes a dispensing nozzle positioned over the patterned substrate for dispensing the cleaning material on the patterned substrate for defining integrated circuit devices. The cleaning material includes polymers of the polymeric compound with a molecular weight greater than 10,000 g/mol. The polymers are soluble in a solvent to form the cleaning material. The cleaning material has less than 1 ppb metallic contaminants before being applied on the surface of the patterned substrate. 
         [0014]    The solubilized polymers have long polymer chains to capture and entrap the contaminants from the surface of the patterned substrate. The cleaning material deforms around device features on the patterned substrate when a force is applied on the cleaning material applied on the surface of the patterned substrate to remove the contaminants without substantially damaging the device features on the surface. The cleaning material is substantially free of abrasive particles before the cleaning material being applied on the surface of the patterned substrate. The dispensing head is coupled to a storage of the cleaning material, which is coupled to the cleaning material preparation system. 
         [0015]    In another embodiment, a cleaning system for removing contaminants on a surface of a patterned substrate for defining integrated circuit devices is provided. The cleaning system includes a substrate carrier for supporting the patterned substrate. The cleaning material also includes a cleaning tank containing the cleaning material for removing contaminants from the surface of the patterned substrate for defining integrated circuit devices. the cleaning material includes polymers of the polymeric compound with a molecular weight greater than 10,000 g/mol. The polymers is soluble in a solvent to form the cleaning material. The cleaning material has less than 1 ppb metallic contaminants before being applied on the surface of the patterned substrate. 
         [0016]    The solubilized polymers have long polymer chains to capture and entrap the contaminants from the surface of the patterned substrate. The cleaning material deforms around device features on the patterned substrate when a force is applied on the cleaning material applied on the surface of the patterned substrate to remove the contaminants without substantially damaging the device features on the surface. The cleaning material is substantially free of abrasive particles before the cleaning material being applied on the surface of the patterned substrate. The dispensing head is coupled to a storage of the cleaning material. Further, the cleaning system has a mechanical mechanism for lowering the patterned substrate into the cleaning tank. 
         [0017]    In another embodiment, a cleaning material preparation system is provided. The cleaning material preparation system includes a polymer container, which contains polymers, and a solvent container, which contains a solvent. The cleaning material preparation system also includes a container for buffering agent, which contains a buffering agent. The cleaning material preparation system further includes a mixing container for mixing the polymers, the solvent, and the buffering agent to prepare the cleaning material. The mixing container is coupled to the polymer container, the solvent container, and the container for the buffering agent. The cleaning material is for removing contaminants on a surface of a patterned substrate for defining integrated circuit devices. The cleaning material includes polymers of the polymeric compound with a molecular weight greater than 10,000 g/mol, the polymers being soluble in a solvent to form the cleaning material. The cleaning material has less than 1 part per billion (ppb) of metallic contaminants before being applied on the surface of the patterned substrate. 
         [0018]    The solubilized polymers have long polymer chains to capture and entrap the contaminants from the surface of the patterned substrate. The cleaning material deforms around device features on the patterned substrate when a force is applied on the cleaning material applied on the surface of the patterned substrate to remove the contaminants without substantially damaging the device features on the surface. The cleaning material is substantially free of abrasive particles before the cleaning material being applied on the surface of the patterned substrate. The mixing container is coupled to a storage of the cleaning material, which is coupled to the cleaning material preparation system. 
         [0019]    In yet another embodiment, a cleaning material preparation system is provided. The cleaning material preparation system includes a polymer container, which contains polymers, and a solvent container, which contains a solvent. The cleaning material preparation system also includes a container for buffering agent and additives, which contains a buffer agent and additives for making the cleaning material. The cleaning material preparation system further includes a first mixing container for preparing a first mixture of the polymers, the solvent, the buffer agent, and the additives to make the cleaning material. The mixing container is coupled to the polymer container, the solvent container, and the container for buffering agent and additives. In addition, the cleaning material preparation system includes a purifier, which is a system that purifies the first mixture from the first mixing container. The purifier is coupled to the first mixing container. 
         [0020]    Additionally, the cleaning material preparation system includes an adjustment container for preparing the cleaning material by mixing the first mixture with additional buffering agent and additives. The adjustment container is coupled to the purifier. The cleaning material is for removing contaminants on a surface of a patterned substrate for defining integrated circuit devices. The cleaning material includes polymers of the polymeric compound with a molecular weight greater than 10,000 g/mol. The polymers are soluble in a solvent to form the cleaning material. The cleaning material has less than 1 part per billion (ppb) of metallic contaminants before being applied on the surface of the patterned substrate. The solubilized polymers have long polymer chains to capture and entrap the contaminants from the surface of the patterned substrate. The cleaning material deforms around device features on the patterned substrate when a force is applied on the cleaning material applied on the surface of the patterned substrate to remove the contaminants without substantially damaging the device features on the surface. The cleaning material is substantially free of abrasive particles before the cleaning material being applied on the surface of the patterned substrate. The adjustment container is coupled to a storage of the cleaning material, which is coupled to the cleaning material preparation system 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements. 
           [0022]      FIG. 1  shows a defect and device feature on a substrate, in accordance with one embodiment of the present invention. 
           [0023]      FIG. 2A  shows a diagram of 3 response curves related to applying a cleaning material on a patterned substrate, in accordance with one embodiment of the present invention. 
           [0024]      FIG. 2B  shows a diagram of 3 response curves related to applying a cleaning material on a patterned substrate. 
           [0025]      FIG. 2C  shows a diagram of 3 damage curves for different technology nodes and a force intensity curve of a cleaning material, in accordance with one embodiment of the present invention. 
           [0026]      FIG. 3A  shows a cleaning material containing polymers of a polymeric compound with large molecular weight dissolved in the cleaning solution, in accordance with one embodiment of the present invention. 
           [0027]      FIG. 3B  shows the cleaning material of  FIG. 3A  entrapping contaminants, in accordance with one embodiment of the present invention. 
           [0028]      FIG. 3C  shows the cleaning material of  FIG. 3A  dispensed on a patterned wafer to clean contaminants from the substrate surface, in accordance with one embodiment of the present invention. 
           [0029]      FIG. 3D  shows the cleaning material of  FIG. 3A  dispensed on a patterned wafer to clean contaminants from the substrate surface, in accordance with one embodiment of the present invention. 
           [0030]      FIG. 3E  shows the cleaning material of  FIG. 3A  dispensed on a patterned wafer with trenches and vias to clean contaminants from the substrate surface, in accordance with one embodiment of the present invention. 
           [0031]      FIG. 3F  shows a cleaning material with gel-like polymer droplets emulsified in the cleaning solution, in accordance with one embodiment of the present invention. 
           [0032]      FIG. 3G  shows a cleaning material with gel-like polymer lumps suspended in the cleaning solution, in accordance with one embodiment of the present invention. 
           [0033]      FIG. 3H  shows a foam cleaning material, in accordance with one embodiment of the present invention. 
           [0034]      FIG. 4A  shows a simplified schematic diagram of a top view of a system for cleaning a substrate in accordance with one embodiment of the invention. 
           [0035]      FIG. 4B  shows a bottom view of the cleaning head with a number of dispensing holes to dispense the cleaning material, in accordance with one embodiment of the present invention. 
           [0036]      FIG. 4C  shows a side view of the cleaning head dispensing a cleaning body of cleaning material under the cleaning head on a substrate surface, in accordance with one embodiment of the present invention. 
           [0037]      FIG. 4D  shows a cross-sectional view of a cleaning head over a substrate, in accordance with one embodiment of the present invention. 
           [0038]      FIG. 4E  shows a substrate cleaning system, in accordance with one embodiment of the present invention. 
           [0039]      FIG. 4F  shows a cleaning apparatus using the cleaning material containing polymers of a polymeric compound with large molecular weight to clean substrates and a rinsing apparatus to rinse off the cleaning material, in accordance with one embodiment of the present invention. 
           [0040]      FIG. 4G  shows a cleaning and rinsing apparatus using the cleaning material containing polymers of a polymeric compound with large molecular weight to clean substrates, in accordance with one embodiment of the present invention. 
           [0041]      FIG. 4H  shows a cleaning system, in accordance with one embodiment of the present invention. 
           [0042]      FIG. 4I  shows a simplified schematic diagram of a top view of a system for cleaning a substrate in accordance with one embodiment of the invention. 
           [0043]      FIG. 4J  shows a bottom view of the cleaning head and the rinse head of  FIG. 4I , in accordance with one embodiment of the present invention. 
           [0044]      FIG. 4K  shows a system for clean material preparation, in accordance with one embodiment of the present invention. 
           [0045]      FIG. 5A  shows particle removal efficiency (PRE) as a function of molecular weight for polyacrylic acid (PAA) and hydroxyethyl cellulose (HEC), in accordance with one embodiment of the present invention. 
           [0046]      FIG. 5B  shows PRE as a function of molecular weight for polyacrylamide (PAM), in accordance with one embodiment of the present invention. 
           [0047]      FIG. 5C  shows experimental results of using ammonium chloride to reduce viscosity of cleaning material made with polyacrylamide (PAM) polymers, in accordance with one embodiment of the present invention. 
           [0048]      FIG. 6A  shows a process flow of using the cleaning material containing polymers of a polymeric compound with high molecular weight to clean patterned substrates, in accordance with one embodiment of the present invention. 
           [0049]      FIG. 6B  shows a process flow of purifying cleaning material, in accordance with one embodiment of the present invention. 
           [0050]      FIG. 6C  shows a process flow of purifying cleaning material, in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0051]    Embodiments of materials, methods and apparatus for cleaning wafer surfaces without damaging surface features are described. The cleaning materials, apparatus, and methods discussed herein have advantages in cleaning patterned substrates with fine features without damaging the features. The cleaning materials are fluid, either in liquid phase, or in liquid/gas phase, and deform around device features; therefore, the cleaning materials do not damage the device features. The cleaning materials, containing polymers of a polymeric compound with large molecular weight, capture the contaminants on the substrate. In addition, the cleaning materials entrap the contaminants and do not return the contaminants to the substrate surface. The polymers of a polymeric compound with large molecular weight form long polymer chains, which can also be cross-linked to form a network (or polymeric network). The long polymer chains and/or polymer network show superior capabilities of capturing and entrapping contaminants, in comparison to conventional cleaning materials. 
         [0052]    It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
         [0053]    The embodiments described herein provide cleaning materials and cleaning methods that are effective in removing contaminants and do not damage the features on the patterned wafers, some of which may contain high aspect ratio features. While the embodiments provide specific examples related to semiconductor cleaning applications, these cleaning applications might be extended to any technology requiring the removal of contaminants from a substrate. 
         [0054]      FIG. 1  shows a substrate  100  with a substrate body  101 , in accordance with one embodiment of the present invention. On substrate  101  there is a device structure  102  and a particle  103  in the vicinity of surface  105 . Particle  103  has an approximate diameter  107 , which can be in the same order of magnitude as the width  104  of device structure  102 . 
         [0055]    For advanced technologies, such as 65 nm, 45 nm, 32 nm, 22 nm, and, 16 nm technology nodes, the width  104  of the device structure  102  is equal to or less than 65 nm. The widths of device structures, such as width  104  of device structure  102 , are scaled continuously down with each technology node to fit more devices on the limited surface area of chips. The heights of the device structures, such as height  106  of device structure  102 , in general do not scale down proportionally with the width of the device features due to concern of resistivities. For conductive structures, such as polysilicon lines and metal interconnect, narrowing the widths and heights of structures would increase the resistivities too high to cause significant RC delay and generate too much heat for the conductive structures. As a result, device structures, such as structure  102 , would have high aspect ratio, which make them prone to damage by force  111  applied on the structure. In one embodiment, the aspect ratio of the device structure can be in the range of about 2 or greater. Force  112  is applied on particle  103  to assist in removing particle  103 . Forces  111  and  112  are applied by cleaning material (not shown) on the substrate surface near device structure  102  to remove surface particulates, such as particle  103 . In one embodiment, forces  111  and  112  are very close in magnitude, since they are in the vicinity of each other. Forces  111 ,  112  applied on the substrate surface could be from any relative motion between the cleaning material and the substrate surface. For example, it can be from dispensing of cleaning material or rinsing of the cleaning material. 
         [0056]    The decreased width  104  of device structure  102  and the relatively high aspect ratio of device structure  102  make the device structure  102  prone to breakage under applied force  111  or accumulated energy under applied force  111 . The damaged device structure  102  becomes a particle source to reduce yield. In addition, the damage device structure  102  also can become inoperable due to the damage. 
         [0057]      FIG. 2A  shows a diagram of 3 response curves related to applying a cleaning material on a patterned substrate, in accordance with one embodiment of the present invention. Curve  201  shows intensity versus energy (as a result of force) exerted by a cleaning material on the substrate surface. The intensity of cleaning energy exerted by the cleaning material peaks at E P . Curve  202  shows particle removal efficiency as a function of energy applied on the substrate by the cleaning material. The particle removal rate peaks at near E R . When the energy exerted by the cleaning material reaches E R , the cleaning material is most efficient at removing particles from the substrate surface. Curve  203  shows the amount of damages of device structures caused by the cleaning material as a function of energy applied on the substrate surface by the cleaning material. The device structures become damaged at E S , which is higher than the higher end, E N , of energy exerted by the cleaning material on the substrate. Since the device structure damage curve  203  is outside the energy distribution  201  of the cleaning material exerts on the pattern substrate, the device structures on the pattern substrate would not be damaged. The particle removal curve  202  shows that the cleaning material can remove particles (or contacts) from the substrate surface without damaging structures on the substrate. 
         [0058]      FIG. 2B  shows a diagram of 3 response curves related to applying a cleaning material on a patterned substrate. Curve  201 ′ shows intensity versus energy exerted by a cleaning material on a patterned substrate. The intensity exerted by the cleaning material peaks at E P ′. Curve  202 ′ shows particle removal rate versus energy applied on the substrate. The particle removal rate peaks at near E R ′. When the energy exerted by the cleaning material reaches E R ′, the cleaning material is most efficient at removing particles from the substrate surface. Curve  203 ′ shows the amount of damages of device structures caused by the cleaning material as a function of energy applied on the substrate surface by the cleaning material. The device structures on the substrate become damaged at E S ′, which is lower than the higher end, E N ′, of energy distribution of energy exerted by the cleaning material. Since the device structure damage curve  203 ′ is within the energy distribution  201 ′ of the cleaning material exerts on the pattern substrate, the device structures on the pattern substrate would be damaged by the cleaning material to add particles (or defects). 
         [0059]    As mentioned above, damaging device structures during a cleaning process could render the device inoperable and damaged device structures could stay on the substrate surface to reduce device yield. Therefore, the relationship between the cleaning curve  201 ′ and damage curve  203 ′ of  FIG. 2B  is undesirable. In contrast, the relationship between the cleaning curve  201  and damage curve  203  of  FIG. 2A  is desirable. 
         [0060]    Conventional substrate cleaning apparatus and methods include brushes and pads utilizing mechanical forces in removing particulates from the substrate surface. For advanced technologies with device structures with narrow widths and high aspect ratios, the mechanical forces applied by the brushes and pads can damage the device structures. In addition, the harsh brushes and pads may also cause scratches on the substrate surface. Cleaning techniques, such as megasonic cleaning and ultrasonic cleaning, utilizing cavitation bubbles and acoustic streaming to clean substrate can also damage fragile structures. Cleaning techniques using jets and sprays can cause erosion of films and can also damage fragile structures. 
         [0061]      FIG. 2C  shows a cleaning curve  201 ″ for a conventional cleaning material applied by a conventional method, such as megasonic clean, in accordance with one embodiment of the present invention. There are damage curves  203   I ,  203   II , and  203   III  for three technology nodes, 90 nm, 65 nm, and 45 nm, respectively. The onset of damage starts at energy E SI  for curve  203   I  for patterned wafers for 90 nm technology node. E SI  is larger than the upper end E N ″ of energy distribution of the cleaning material on the patterned substrate. Therefore, there is no damage to the device structures. The conventional cleaning material of  FIG. 2C  still works for 65 nm technology node, since the onset of damage starts at E SII , which is higher than E N ″. As technology moves into narrower width, the onset of damage starts at lower energy level. When the technology node becomes 45 nm or lower, the conventional cleaning material and method of curve  201 ″ would cause damage to device structures. The onset of damage for 45 nm technology node, E SIII , is lower than the E N ″.  FIG. 2C  shows that although some cleaning materials and methods work for conventional technologies, they no longer work for advanced technologies with narrower feature widths. Therefore, there is a need to find a cleaning mechanism using a cleaning material that is gentle to the device structure and is effective in removing particles from the substrate surface for advanced technologies. 
         [0062]      FIG. 3A  shows a liquid cleaning material  300 , which contains a cleaning solution  305  containing polymers  310  with large molecular weight dissolved in the cleaning solution  305 , in accordance with one embodiment of the present invention. In one embodiment, the liquid cleaning material  300  is a gel. In another embodiment, the liquid cleaning material  300  is a sol. In yet another embodiment, the liquid cleaning material  300  is a liquid solution. The liquid cleaning material  300 , when applied on a substrate with particles on the substrate surface, can remove particles on the substrate surface. In one embodiment, the removed particles  320  are attached to the polymers  310 , as shown in  FIG. 3B . The polymers of a polymeric compound with large molecular weight, such as greater than 10,000 g/mol or 100,000 g/mol, form long polymer chains and polymeric network to capture and trap the removed particles to prevent the particles from returning back to the substrate surface. The polymers dissolve in a cleaning solution, which contains elements that affect the pH value, and enhance the solubility of the polymers. The polymers dissolved in the cleaning solution can be a soft gel or become gel-like droplets suspended in the cleaning solution. In one embodiment, the contaminants on the substrate surface attach to the solvated polymers by ionic force, van der Waals force, electrostatic force, hydrophobic interaction, steric interaction, or chemical bonding when the polymer molecules come in vicinity of the contaminants. The polymers capture and entrap the contaminants. 
         [0063]    In one embodiment, the polymers of a polymeric compound with large molecular weight forms a network in the cleaning solution  305 . In addition, the polymers of a polymeric compound with large molecular weight are dispersed in the liquid cleaning solution  305 . The liquid cleaning material  300  is gentle on the device structures on the substrate during cleaning process. The polymers  310  in the cleaning material  300  can slide around the device structures, such as structure  302 , as shown in cleaning volume  330  of  FIG. 3C , without making a forceful impact on the device structure  302 . In contrast, hard brushes, and pads mentioned above would make unyielding contacts with the device structures and damage the device structures. Forces (or energy) generated by cavitation in megasonic cleaning and high-speed impact by liquid during jet spray can also damage the structure. Alternatively, more than one type of polymer can be dissolved in the cleaning solution to formulate the cleaning material. For examples the polymers in the cleaning material can include an “A” polymeric compound and a “B” polymeric compound. 
         [0064]    The polymers of a polymeric compound with high molecular weight form long chains of polymers, with or without cross-linking to from a polymeric network. As shown in  FIG. 3C , the polymers  310  come in contact with the contaminants, such as contaminants  320   I ,  320   II ,  320   III ,  320   IV  on the patterned (or un-patterned) substrate surface and capture contaminants. After the contaminants are captured by the polymers, the contaminants become attached to the polymers and are suspended in the cleaning material.  FIG. 3C  shows that contaminants  320   III , and  320   IV , which are attached to the polymer chain(s)  311   I , and  311   II , respectively. Contaminants  320   I  and  320   II  are attached to other polymer chains. Alternatively, contaminants,  320   I ,  320   II ,  320   III , and  320   IV , can each be attached to multiple polymer chains, or be attached to a polymeric network. When the polymers in the cleaning material  300  are removed from the substrate surface, such as by rinsing, the contaminants attached to the polymers chains are removed from the substrate surface along with the polymer chains. 
         [0065]    The embodiment shown in  FIG. 3C  shows only one device structure  302 . On a substrate, such as substrate  301 , a number of device structures, such as  302   I ,  302   II ,  302   III , and  302   IV , can be clustered to be next to one another as shown in  FIG. 3D , in accordance with one embodiment of the present invention. Similar to  FIG. 3C , the liquid cleaning material  300 , in the cleaning volume  330 ′, is gentle on the device structures on the substrate during cleaning process. The polymers  310  in the cleaning material  300  slides around the device structures,  302   I ,  302   II ,  302   III , and  302   IV , without making a forceful impact on the device structures. Similar to the contaminants,  320   I ,  320   II ,  320   III , and  320   IV , of  FIG. 3C  being attached to polymer chains, contaminants,  325   I ,  325   II ,  325   III , and  325   IV , are also attached to polymers chains. 
         [0066]    In addition to cleaning substrate with lines features, such as the ones in  FIGS. 3C and 3D , substrates with other patterned features can also be cleaned by the materials and methods described in the current invention.  FIG. 3E  shows a substrate  301 ′ with structures  302 ′ that forms vias  315  and trenches  316 , in accordance with one embodiment of the present invention. Contaminants  326   I ,  326   II ,  326   III , and  326   IV  can also be removed by cleaning material  300  by mechanisms discussed above in  FIGS. 3C and 3D . In one embodiment, the polymers act as a flocculant that cause the particles (or contaminates) from the substrate surface to become floc, which is a mass formed by aggregation of fine suspended particles. In another embodiment, the polymers do not act as a flocculant. 
         [0067]    As described above, the polymers of a polymeric compound with large molecular weight are dispersed in the cleaning solution. Examples of the polymeric compound with large molecular weight include, but not limited to, acrylic polymers such as polyacrylamide (PAM), and polyacrylic acid (PAA), such as Carbopol 940™ and Carbopol 941™, poly-(N,N-dimethyl-acrylamide) (PDMAAm), poly-(N-isopropyl-acrylamide) (PIPAAm), polymethacrylic acid (PMAA), polymethacrylamide (PMAAm); polyimines and oxides, such as polyethylene imine (PEI), polyethylene oxide (PEO), polypropylene oxide (PPO) etc; Vinyl polymers such as Polyvinyl alcohol (PVA), polyethylene sulphonic acid (PESA), polyvinylamine (PVAm), polyvinyl-pyrrolidone (PVP), poly-4-vinyl pyridine (P4VP), etc; cellulose derivatives such as methyl cellulose (MC), ethyl-cellulose (EC), hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), etc; polysaccharides such as acacia (Gum Arabic), agar and agarose, heparin, guar gum, xanthan gum, etc; proteins such as albumen, collagen, gluten, etc. To illustrate a few examples of the polymer structure, polyacrylamide is an acrylate polymer (—CH 2 CHCONH 2 —)n formed from acrylamide subunits. Polyvinyl alcohol is a polymer (—CH 2 CHOH—)m formed from vinyl alcohol subunits. Polyacrylic acid is a polymer (—CH 2 ═CH_COOH—)o formed from acrylic acid subunits. “n”, “m”, and “o” are integers. The polymers of a polymeric compound with large molecular weight either is soluble in an aqueous solution or is highly water-absorbent to form a soft gel in an aqueous solution. In one embodiment, the molecular weight of the polymeric compound is greater than 100,000 g/mol. In another embodiment, the molecular weight of the polymeric compound is between about 0.1M g/mol to about 100M g/mol. In another embodiment, the molecular weight of the polymeric compound is between about 1M g/mol to about 20 M g/mol. In yet another embodiment, the molecular weight of the polymeric compound is between about 15M g/mol to about 20M g/mol. The weight percentage of the polymers in the cleaning material is between about 0.001% to about 20%, in one embodiment. In another embodiment, the weight percentage is between about 0.001% to about 10%. In another embodiment, the weight percentage is between about 0.01% to about 10%. In yet another embodiment, the weight percentage is between about 0.05% to about 5%. The polymers can dissolve in the cleaning solution, be dispersed completely in the cleaning solution, form liquid droplets (emulsified) in the cleaning solution, or form lumps in the cleaning solution. 
         [0068]    Alternatively, the polymers can be copolymers, which are derived from two or more monomeric species. For example, the copolymers can include 90% of PAM and 10% of PAA and are made of monomers for PAM and PAA. In addition, the polymers can be a mixture of two or more types of polymers. For example, the polymers can be made by mixing two types of polymers, such as 90% of PAM and 10% of PAA, in the solvent. 
         [0069]    In the embodiments shown in  FIG. 3A-3C , polymers of a polymeric compound with large molecular weight are dissolved uniformly in the cleaning solution. The base liquid, or solvent, of the cleaning solution can be a non-polar liquid, such as turpentine, or a polar liquid such as water (H 2 O). Other examples of solvent include isopropyl alcohol (IPA), dimethyl sulfoxide (DMSO), and dimethyl formamide (DMF). In one embodiment, the solvent includes more than one liquid and is a mixture of two or more liquid. For polymers with polarity, such as PAM, PAA, or PVA, the suitable solvent for the cleaning solution is a polar liquid, such as water (H 2 O). 
         [0070]    In another embodiment, the cleaning solution includes compounds other than the solvent, such as water, to modify the property of the cleaning material, which is formed by mixing the polymers in the cleaning solution. For example, the cleaning solution can include a buffering agent, which can be a weak acid or a weak base, to adjust the potential of hydrogen (pH) value of the cleaning solution and cleaning material formed by the cleaning solution. One example of the weak acid is citric acid. One example of the weak base is ammonium (NH 4 OH). The pH values of the cleaning materials are between about 1 to about 12. In one embodiment, for front-end applications (before the deposition of copper and inter-metal dielectric), the cleaning material is basic. The pH values for front-end applications are between about 7 to about 12, in one embodiment. In another embodiment, the pH values for front-end applications are between about 8 to about 11. In yet another embodiment, the pH values for front-end applications are between about 8 to about 10. For backend processing (after deposition of copper and inter-metal dielectric), the cleaning solution is slightly basic, neutral, or acidic, in one embodiment. Copper in the backend interconnect is not compatible with basic solution with ammonium, which attacks copper. The pH values for backend applications are between about 1 to about 7, in one embodiment. In another embodiment, the pH values for backend applications are between about 1 to about 5. In yet another embodiment, the pH values for backend applications are between about 1 to about 2. In another embodiment, the cleaning solution includes a surfactant, such as ammonium dodecyl sulfate (ADS) to assist dispersing the polymers in the cleaning solution. In one embodiment, the surfactant also assist wetting of the cleaning material on the substrate surface. Wetting of the cleaning material on the substrate surface allows the cleaning material to come in close contact with the substrate surface and the particles on the substrate surface. Wetting improves cleaning efficiency. Other additives can also be added to improve surface wetting, substrate cleaning, rinsing, and other related properties. 
         [0071]    Examples of buffered cleaning solution (or cleaning solution) include a buffered ammonium solution (BAS), which include basic and acidic buffering agents, such as 0.44 wt % of NH 4 OH and 0.4 wt % of citric acid, in the solution. Alternatively, the buffered solution, such as BAS, includes some amount of a surfactant, such as 1 wt % of ADS, to help suspend and disperse the polymers in the cleaning solution. A solution that contains 1 wt % of ADS, 0.44 wt % of NH3, and 0.4 wt % of citric acid is called solution “100”. Both solution “100” and BAS have a pH value of about 10. 
         [0072]    The embodiments shown in  FIGS. 3A-3E  provide a liquid cleaning material  300  that has the polymers  310  with large molecular weight dispersed (or dissolved) uniformly in the cleaning solution  305 . As described above, polymers with large molecular weight for this application are completely dissolved in the cleaning solution, which can be aqueous. The polymers are highly water-absorbent to form soft gel in an aqueous solution.  FIG. 3F  shows an embodiment of a liquid cleaning material  300 ′ with gel-like polymer droplets  340  emulsified in the cleaning solution  305 ′. The cleaning solution  305 ′ also contains small and isolated polymer  306 . A surfactant, such as ADS, could be added to the cleaning solution to help the gel-like polymer droplets  340  being dispersed uniformly in the cleaning solution  305 ′. In the embodiment shown in  FIG. 3F , there is a boundary  341  between the cleaning solution  305 ′ and the gel-like polymer droplets  340 . The gel-like polymer droplets  340  are soft and deform around device features on the substrate surface. Since the gel-like polymer droplets  340  deform around device features, they do not exert large energy (or force) on the device features to damage them. In one embodiment, the diameters of the droplets are between about 0.1 μm to about 100 μm. 
         [0073]    In another embodiment, the polymers of a polymeric compound with large molecular weight dissolve in the cleaning solution to form gel-like polymer lumps  350 , which do not establish a distinct boundary with the cleaning solution  305 ″, as shown in  FIG. 3G . The cleaning solution  305 ″ also contains small and isolated polymer  306 . The gel-like polymer lumps  350  are soft and deform around device features on the substrate surface, and do not exert large amount of energy (or force) on the device features on the substrate surface to damage them. In one embodiment, the diameters of the polymer lumps are between about 0.1 μm to about 100 μm. 
         [0074]    The cleaning materials discussed above are all in liquid phase. In yet another embodiment, the cleaning material, such as liquid cleaning materials  300 ,  300 ′, and  300 ″ discussed above, can be agitated to add a gas, such as N 2 , an inert gas, or a mixture of gases, such as air, to make the cleaning material into a foam, as shown in  FIG. 3H . In  FIG. 3H , the cleaning material  300 * has air bubbles  360  dispersed in the cleaning solution  305 . Polymers 310, is also dispersed in the cleaning solution  305 . In other embodiments, the polymers  310  in  FIG. 3H  can be polymer droplets  340  or polymer lumps  350 , described in  FIGS. 3F and 3G . The cleaning material  300 * has a gas phase and a liquid phase. 
         [0075]    The cleaning material described above can be dispensed by many mechanisms on the substrate surface. As discussed above in  FIGS. 2A and 2B , to avoid damaging device features on the patterned substrates, the energy applied by the cleaning material on the patterned surface needs to be below the minimum force E S  or E S ′ to avoid damaging the device features. The cleaning materials, such as cleaning materials  300 ,  300 ′,  300 ″, and  300 *, discussed above are either in liquid phase or in gas/liquid phases. Liquid and foam can flow on the substrate surface and deform (or flow) around the device features on the substrate surface. Therefore, the cleaning material can be applied on the patterned substrate without exerting large energy on the device features on the substrate surface. 
         [0076]      FIG. 4A  shows a simplified schematic diagram of a top view of a system  400  for cleaning a substrate in accordance with one embodiment of the invention. Wafer (or substrate)  420  moves in a linear direction toward a cleaning head  410  (or clean proximity head). The cleaning head is held by a support structure  450 , which can be an arm. The cleaning head  410  provides (or dispenses) the cleaning material described above. In one embodiment, the length  440  of the cleaning head  410  is longer than the diameter  451  of the wafer  420 . Wafer  420  is moved under the cleaning head only once. In another embodiment, the length  440  of the cleaning head  410  is shorter than the diameter  451  of the wafer  420 . Wafer  420  is moved under the cleaning head  410  multiple times to ensure the entire wafer  420  has been cleaned. 
         [0077]    In one embodiment, the cleaning material is delivered from a reservoir  470 , which may be pressurized, through a supply line  460 . Alternatively, the cleaning head  410  may move over wafer  420  while the wafer  420  is stationary or also moving. As described above, the cleaning material may be in the form of a liquid solution, a foam or an emulsion. If the reservoir  470  is pressurized, a cleaning solution or emulsion may be aerated and develop into a foam prior to being delivered to the cleaning head. Where the reservoir is not pressurized, the cleaning solution may be pumped or delivered through other commonly known means. 
         [0078]    In one embodiment, the cleaning head is also coupled to a container  423  for used cleaning material vacuumed from the substrate surface and a vacuum pump  425  that provides the vacuum. 
         [0079]      FIG. 4B  shows an exemplary bottom view of the cleaning head  410  with a number of dispensing holes  411  to dispense the cleaning material, in accordance with one embodiment of the present invention. Alternatively, the dispensing holes  411  are replaced with a long and narrow dispensing slot. In one embodiment, the (row of) dispensing holes  411  are surrounded by vacuum holes  414 , which removes cleaning material from the substrate surface. 
         [0080]      FIG. 4C  shows an embodiment of a side view of the cleaning head  410  dispensing a cleaning body  430  of cleaning material under the cleaning head  410  on a surface  421  of the wafer  420  to clean the surface  421 . The cleaning material is supplied by supply line  460 . The cleaning material is removed from the substrate surface by vacuum supplied by vacuum lines  465 . The wafer  420  moves under the cleaning head  410  in a direction illustrated by the arrow  422 . The cleaning body  430  of cleaning material forms a “meniscus.” The term, “meniscus,” as used herein, refers to the cleaning body (or volume)  430  of liquid bounded and contained in part by surface tension of the liquid. The meniscus is also controllable and can be moved over a surface in the contained shape. In specific embodiments, the meniscus is maintained by the delivery of fluids to a surface while also removing the fluids so that the meniscus remains controllable. Furthermore, the meniscus shape can be controlled by precision fluid delivery and removal systems that are in part interfaced with a controller a computing system, which may be networked. Details of a dispensing head forming a meniscus on the surface of a substrate is discussed in U.S. patent application Ser. No. 11/641,362 (Atty. Docket No. LAM2P581), filed on Dec. 18, 2006, entitled “Substrate Preparation Using Stabilized Fluid Solutions and Methods for Making Stable Fluid Solutions.” The disclosure of the above-identified related application is incorporated herein by reference. 
         [0081]    In one embodiment, the cleaning body  430  leaves behind a thin layer of cleaning material (not shown) on the surface  421  as the wafer  420  moves under the cleaning head  410 . The thin layer of cleaning material is a result of cleaning material not completely removed by the vacuum. The cleaning head  410  is held in proximity to the surface  421  of wafer  420  by an arm  450 . Therefore, the cleaning head  410  is called a proximity head. In one embodiment, the cleaning material dispensed from the cleaning head  410  exerts a shear force  432  on the surface  421  of the substrate under the cleaning body  430 . 
         [0082]    In another embodiment, the cleaning material dispensed from the cleaning head  410  also exerts a downward force (not shown) on the surface  421  of the substrate under the cleaning body  430 . In one embodiment, the downward force and the shear force assist bringing the polymers in contact with the contaminants to allow the contaminants to be attached to the polymer chains and/or network. In one embodiment, the contaminants are attached to the polymers by van der Waals force. In another embodiment, the contaminants are entrapped by the polymeric network. In another embodiment, neither a downward force nor a shear force is needed in bringing the polymers in the cleaning solution to be in contact with the contaminants. When the cleaning material is dispersed on the substrate surface, polymers dispersed in the cleaning material would come in contact with contaminants on the substrate surface. During the rinsing step to remove cleaning material from the substrate surface, the contaminants attached and/or entrapped by the polymers are removed from the substrate surface along with the cleaning material. 
         [0083]      FIG. 4D  shows a cross-sectional view of a cleaning head  410 ″ dispensing a cleaning material on a substrate  420 . The cleaning material is dispensed through dispensing holes coupled to cleaning material supply line  460  and removed from the surface of substrate  420  by vacuum holes coupled to the vacuum lines  465 . The cleaning material forms a meniscus  430 ′ between the cleaning head  420  and the substrate  420 . In addition, there are dispensing holes (not shown) of a surface tension reducing gas coupled to a supply line  467  of the surface tension reducing gas, which is used to reduce surface tension of the surface of substrate  420 . In one embodiment, the surface tension reducing gas include a mixture of isopropyl alcohol (IPA) and nitrogen (N 2 ). 
         [0084]      FIG. 4E  shows an embodiment of a cleaning system  400 ′ with a cleaning material dispensing assembly  418 , which include an upper cleaning head (or proximity head)  410 , a lower cleaning head (or proximity head)  410 ′, and a support structure  419 . The upper cleaning head  410 ′ is a minor image of the lower cleaning head  410 ′. The cleaning material dispensing assembly  418  is controlled by a controller  416 . A substrate  420 , being held by a substrate holder  424 , passes between the upper and lower cleaning heads  410 ,  410 ′ in the direction of  466 . With the upper and the lower cleaning heads  410 ,  410 ′, both the front and the back sides of the substrate are cleaned simultaneously. 
         [0085]    Each cleaning head includes a plurality of dispensing holes (or nozzle) through which the cleaning material is supplied that forms meniscus  200 . The liquid may be de-ionized water, a cleaning solution, or other liquid designed to process, clean, or rinse substrate  160 . A plurality of vacuum ports  114  apply a vacuum at a perimeter of meniscus  200 . Vacuum ports  114  aspirate liquid from meniscus  200  and surrounding fluid, such as air or other gas supplied by nozzles  112 . In certain embodiments, nozzles  112  surround vacuum ports  114  and supply isopropyl alcohol vapor, nitrogen, a mixture thereof, or other gas or two-phase gas/liquid fluid. The nozzles  112  and fluid supplied therefrom aid in maintaining a coherent liquid/gas interface at the surface of meniscus  200 . More details relating to proximity head structure and operation are incorporated by reference in the Cross Reference to Related Art section above. In particular, U.S. patent application Ser. Nos. 10/261,839, 10/330,843, and 10/330,897 are referenced for additional details relating to proximity head structure and operation. 
         [0086]    Details of cleaning apparatus using a proximity head to dispense cleaning materials are described in U.S. patent application Ser. No. 11/532,491 (Atty. Docket No. LAM2P548B), filed on Sep. 15, 2006, entitled “Method and Material for Cleaning a Substrate,” U.S. patent application Ser. No. 11/532,493 (Atty. Docket No. LAM2P548C), filed on Sep. 15, 2006, entitled “Apparatus and System for Cleaning a Substrate,” and U.S. patent application Ser. No 11/641,362 (Atty. Docket No. LAM2P581), filed on Dec. 18, 2006, entitled “Substrate Preparation Using Stabilized Fluid Solutions and Methods for Making Stable Fluid Solutions.” The disclosure of each of the above-identified related applications is incorporated herein by reference. 
         [0087]    The embodiments described above are merely examples. Other embodiments of cleaning heads for dispensing cleaning material on the substrate surface and for removing cleaning material from the substrate surface are also possible.  FIG. 4F  shows a cleaning tank  480  containing cleaning material  481  and a rinsing tank  490  containing rinse liquid  491 , in accordance with one embodiment of the present invention. Substrate  420 ′, held by a substrate carrier  426   a , is first dipped into the cleaning material  481  of tank  480  to allow the cleaning material to be in contact with the contaminants on the substrate surface. Substrate  420 ′ is lowered into and raised out of the cleaning material  481  in cleaning tank  480  by a mechanical mechanism (not shown). Afterwards, the substrate  420 ′, held by a substrate carrier  426   b , is then dipped into the rinse liquid  491  of rinsing tank  490  to rinse off the cleaning material. A mechanical mechanism (not shown) is used to lower and raise the substrate into and out of the rinse tank  490 . When the cleaning material leaves the surface of substrate  420 ′ in rinse tank (or rinsing tank)  490 , the contaminants are removed from the substrate surface along with the cleaning material. Substrate  420 ′ is lowered into the rinse liquid  491  in rinse tank  490  by a mechanical mechanism (not shown). Although the orientation of the substrate shown in  FIG. 4F  is vertical, other orientation is also possible. For example, the substrate can be submerged in the cleaning tank and/or the rinse tank in a horizontal orientation. 
         [0088]      FIG. 4G  shows another embodiment of a cleaning apparatus  499  for cleaning contaminants from the surface of the substrates. The cleaning apparatus has a cleaning tank  485  with a substrate support  483 . Substrate  420 * is placed on the substrate support  483 , which rotates during the cleaning process. The cleaning apparatus  499  has a cleaning material dispensing head  497 , which dispenses cleaning material on the surface of substrate  420 *. The cleaning material dispensing head  497  (or a dispensing nozzle) is coupled to a storage tank  470  of cleaning material. The cleaning apparatus  499  also has a rinse liquid dispensing head  498  (or a dispensing nozzle), which sprays rinse liquid on the surface of the substrate  420 ″. The rinse liquid dispensing head  498  is coupled to a storage tank  496  of the rinse liquid. The rotating substrate  420 * allows the cleaning material and the rinse liquid to cover the entire substrate surface. The cleaning material is dispensed on the substrate surface before the rinse liquid is dispensed to remove the cleaning material from the substrate surface. 
         [0089]    After the cleaning material is rinsed off the surface of the patterned substrate, the patterned substrate is dried by spinning (or rotating) the substrate at a relatively high speed. During the spinning, the substrate is secured by a device (or mechanism), which is not shown in  FIG. 4G . In one embodiment, a surface tension reducing gas is applied on the surface of the patterned substrate to assist in removing the rinse and possibly residual cleaning material. In one embodiment, the surface tension reducing gas includes a mixture of isopropyl alcohol (IPA) and nitrogen (N 2 ). Other surface tension reducing gas can also be used. 
         [0090]    The cleaning tank  485  can receive waste of the cleaning process. The waste of the cleaning process includes waste cleaning material and waste rinse liquid. In one embodiment, the cleaning tank  485  has a drainage hold  403 , which is connected to a waste line  404 . Waste line  404  is coupled to a valve  405 , which controls the draining of cleaning waste from the cleaning tank  485 . The cleaning waste can be directed to a recycling processor  406  or a waste processor  407 . 
         [0091]    The cleaning materials described above have special advantages in cleaning substrates with fine features (or topologies), such as polysilicon lines or metallic interconnects (with trenches and/or vias), on the substrate surface. The smallest width (or critical dimension) of these fine features can be 45 nm, 32 nm, 25 nm, or less. For advanced cleaning using cleaning materials described above, the cleaning materials need to come with as little metallic and/or particulate contaminants as possible. The metallic contaminants in the prepared cleaning material, before it is applied on the substrate surface, are specified to be less than 100 ppb (parts per billion) for all metallic contaminants, in one embodiment. In another embodiment, the metallic contaminants in the prepared cleaning material are specified to be less than 10 ppb (parts per billion). In yet another embodiment, the metallic contaminants in the prepared cleaning material are specified to be less than 1 ppb for advance cleaning. The particle specification for the prepared cleaning material, before it is applied on the substrate surface, is less than 50 for particle size grater than 65 nm, in one embodiment. In another embodiment, the particle specification is less than 20 for particle size greater than 65 nm. In another embodiment, the particle specification is less than 10 for particle size greater than 50 nm In yet another embodiment, the particle specification is less than 5 for particle size greater than 30 nm. The specification for metallic contaminants and particles is more strict for more advanced technology with finer (or smaller) feature sizes. 
         [0092]    A number of methods and systems can be used in making (or purifying) the cleaning material meet the metallic contamination specification. For example, metallic contaminants in the cleaning material can be removed (or cleaning material can be purified) by fractionation. In one embodiment, an alcohol is added to the aqueous solution of polymer. Since the polymer is much less soluble in the alcohol than in water, purer polymer would precipitate. In addition to the alcohol, acid can be added to the aqueous solution of polymer to assist in separating metal from the polymer. Acid can provide H +  to replace metal ions, such as Na + , attached to the polymer, which would assist in separating the metal from the polymer. Another method of removing metallic contaminants is by using ion exchange. The cleaning material is passed through a column packed with small particles of resin to exchange metal ions in the cleaning material with hydrogen ion provided by the column. The column if filled with acid, which provide hydrogen ions to replace metal ions, such as Na + . Na +  is only used as an example. Other metal ions can be removed by such methods and systems. Other methods can also be used to purify cleaning materials. 
         [0093]      FIG. 4H  shows a schematic diagram of a system  475  for cleaning a substrate in accordance with one embodiment of the invention. The cleaning head  410  (or clean proximity head) is similar to the one shown in  FIG. 4A . The substrate  420 ″ is held by a substrate holder (or substrate carrier)  424 . The cleaning head  410  is coupled to a reservoir  470  of cleaning material, such as cleaning material  300  discussed above. The cleaning head  410  is also coupled to a container  423  for used cleaning material, which is further coupled to a vacuum pump  425 . In one embodiment, system  475  has a rinse head  417 , which dispenses a rinse liquid to remove cleaning material from the surface of substrate  420 ″. The rinse head  417  is coupled to a reservoir  471  of the rinse liquid. In one embodiment, the rinse head  417  is structured similarly to the cleaning head with rinse liquid dispensing holes and vacuum holes. The rinse head  417  is coupled to a container  408  of used rinse liquid, which is further coupled to a vacuum pump  425 ′. In another embodiment, system  475  has a vacuum head  412 , which removes any remaining cleaning material and/or rinse liquid left on the substrate surface. The vacuum head is coupled to a waste container  409  of used cleaning material and rinse liquid. The waste container  409  is further coupled to a vacuum pump  425 ″. 
         [0094]      FIG. 4I  shows a top view of another cleaning system  400 *, in accordance with one embodiment of the present invention. Wafer (or substrate)  420  moves in a linear direction toward a cleaning head  410 * (or clean proximity head). The cleaning head is held by a support structure  450 , which can be an arm. The cleaning head  410  is coupled to a reservoir  470  of cleaning material. The cleaning head  410 * provides (or dispenses) the cleaning material described above. In one embodiment, the length  440  of the cleaning head  410 * is longer than the diameter  451  of the wafer  420 . Wafer  420  is moved under the cleaning head only once. In another embodiment, the length  440  of the cleaning head  410 * is shorter than the diameter  451  of the wafer  420 . Wafer  420  is moved under the cleaning head  410 * multiple times to ensure the entire wafer  420  has been cleaned. 
         [0095]    In the embodiment of  FIG. 4I , there is a rinsing head  417 * next to the cleaning head  410 *. Similar to cleaning head  410 *, the length  440 ′ of the rinse head  417 * can be longer or shorter than the diameter  451  of the wafer. Wafer  420  moves under cleaning head  410 * first and subsequently moves under rinsing head  417 *. The cleaning head  410 * includes a slit  411 * to dispense cleaning material.  FIG. 4J  includes a bottom view of the cleaning head  410 * with the slit  411 *. The rinsing head  417 * is coupled to a reservoir  471  of the rinse liquid. In one embodiment, the rinse head  417 * is structured similarly to the cleaning head  410  of  FIGS. 4A and 4B , with rinse liquid dispensing holes  401  and vacuum holes  402 .  FIG. 4J  includes a bottom view of rinse head  417 * with a number of rinse liquid dispensing holes  401 , which are surrounded by a number of vacuum holes  402 . The rinse head  417  is coupled to a container  408  of used rinse liquid, which is further coupled to a vacuum pump  425 ′. 
         [0096]    When wafer  420  moves under cleaning head  410 * and rinse head  417 *, the cleaning head  410 * dispenses cleaning material on the substrate surface and the rinse head  417 * rinses the cleaning material off the surface of wafer  420 . The rinse head  417 * also removes the cleaning waste, which include particles and contaminants on the surface of wafer  420 , cleaning material, and rinse liquid. 
         [0097]      FIG. 4K  shows a cleaning material preparation system  482 , in accordance with one embodiment of the present invention. System  482  has a polymer container  484 , which stores polymers used in the cleaning material. The polymer container  484  is further coupled to a dispense controller  488  that controls the amount of polymers being dispensed into a pre-mix container  493  in system  482 . System  482  also has a solvent container  486 , which stores solvent used in the cleaning material. The solvent container  486  is further coupled to a dispense controller  489  that controls the amount of solvent being dispensed into a pre-mix container  493  and to a cleaning material adjustment container  495  (will be further described below). In addition, system  482  has a buffering agent and additive container  487 , which stores buffering agent and additive(s), such as a surfactant, used in the cleaning material. The buffering agent and additive container  487  is coupled to a dispense controller  492 , which controls the amount of buffering agent and additive(s) being dispensed into the pre-mix container  493  and to the cleaning material adjustment container  495 . In another embodiment, no additive is needed in the cleaning material and there is no additive in the buffering agent and additive container  487 . In yet another embodiment, the buffering agent and the additive(s) are in separate containers and being controlled by separate controllers. 
         [0098]    In one embodiment, the polymers, solvent, buffering agent, and additive(s) are first mixed in the pre-mix container  493 . Afterwards, the mixture from container  493  is supplied to a purifier (or purifying system)  494  to remove metallic contaminants and other contaminants from the mixture. In one embodiment, the purifier  494  also has the function of filtering to filter out any particles (soft or abrasive) from the mixture. In another embodiment, only the polymers and the solvent are mixed in the pre-mix container  493 . The buffering agent and the additives are not mixed in the pre-mixed container  493  with the polymers and the solvent. 
         [0099]    After metallic contaminants have been removed, the mixture is moved to the adjustment container  495  for to add additional solvent, buffering agent, and additive(s) needed to make the final mixture of the cleaning material. The prepared cleaning material is stored in a container  427  for use in cleaning substrates. Alternatively, the mixture coming out of the purifier  494  is ready for use and does not need to be further processed in the adjustment container  495  for the cleaning material. Under such circumstances, the mixture coming out of the purifier  494  is the final cleaning material and is supplied to storage  427  of cleaning material. In another embodiment, the mixture from the pre-mix container  493  is ready to use and does not need to go through the purifier  494 . Under such as circumstance, the mixture, which is the cleaning material, is supplied to the storage  427 . 
         [0100]    System  482  does not have the purifier  494  and the adjustment container  495 , and the pre-mix container is a mixing container. Under such circumstance, the mixed cleaning material is supplied directly to the storage  427 . In one embodiment, the cleaning material in cleaning material reservoir  470  of  FIGS. 4A ,  4 E,  4 G,  4 H, and  4 I is from storage  427  of cleaning material. 
         [0101]    Table I compares the viscosity, rinse time, and particle removal efficiency (PRE) of different weight percent of Carbopol 941™ PAA in BAS. The viscosity is measured at strain rate of 500 s −1 . The rinse time measures the time it takes to rinse the cleaning material off the substrate surface. The PRE is measured by using particle monitor substrates, which are purposely deposited with silicon nitride particles with varying sizes. In this study, only particle sizes between 90 nm and 1 μm are measured. PRE is calculated by equation (1) listed below: 
         [0000]      PRE=(Pre-clean counts−Post-clean counts)/Pre-clean counts  (1)
 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Comparison of cleaning material with different concentration 
               
               
                 of Carbopol 941 ™ PAA polymers 
               
             
          
           
               
                   
                 Polymer 
                 Viscosity @ 
                   
                   
               
               
                 Concentration 
                 molecular weight 
                 500 s −1   
                 Rinse Time 
               
               
                 (wt %) 
                 (g/mol) 
                 (cP) 
                 (seconds) 
                 PRE 
               
               
                   
               
             
          
           
               
                 0.2% 
                 1.25M 
                 26 
                 &lt;5 
                 74% 
               
               
                 0.5% 
                 1.25M 
                 198 
                 5-10 
                 89% 
               
               
                     1% 
                 1.25M 
                 560 
                 8-10 
                 87% 
               
               
                   
               
             
          
         
       
     
         [0102]    The cleaning material of Table I is made by mixing Carbopol 941™ PAA, which is commercially available, in the BAS described above. The Carbopol 941™ PAA used has a molecular weight of 1,250,000 (or 1.25M) g/mol. The results in Table I show that PRE increases with weight % of Carbopol 941™ PAA until about 0.5%. There is no significant difference in PRE between 0.5% and 1% of polymers. The results also show that the viscosity of the cleaning material increases with the weight percentage of the polymers. In addition, the rinse time it takes to rinse off the cleaning material increases with the viscosity of the cleaning material. Water is used to rinse the substrate. 
         [0103]    Table II compares the ability of different cleaning materials in entrapping or suspending particles in the cleaning materials. Silicon nitride particles are purposely added into the cleaning materials. After being added with silicon nitride particles, the cleaning materials are dispensed on clean substrates. The cleaning materials are then rinse off of the substrate, which is then measured for the number of particles (silicon nitride) on the surface. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Comparison of particle counts with different cleaning 
               
               
                 materials added with silicon nitride particles. 
               
             
          
           
               
                 Cleaning Material 
                 Particle 
                 Cleaning Material 
                 Particle 
               
               
                 w/1X SiN 
                 counts after 
                 w/50X SiN 
                 counts after 
               
               
                 particles 
                 rinsing 
                 particles 
                 rinsing 
               
               
                   
               
               
                 DIW 
                 Saturated 
                 DIW 
                 Saturated 
               
               
                 DIW + ammonium 
                 6002 
                 DIW + ammonium 
                 Saturated 
               
               
                 (pH &gt;10) 
                   
                 (pH &gt;10) 
               
               
                 “100” 
                 4238 
                 “100” 
                 Saturated 
               
               
                 0.2% Carbopol 
                 1137 
                 0.2% Carbopol 
                 15689 
               
               
                 940 ™ in “100” 
                   
                 940 ™ in “100” 
               
               
                 0.5% PAM 
                 53 
                 0.5% PAM 
                 104 
               
               
                 in “100” 
                   
                 in “100” 
               
               
                   
               
             
          
         
       
     
         [0104]    Five types of solutions are used as cleaning materials. The first type of cleaning material, “DIW”, is de-ionized water. The second type of cleaning material is DIW added with ammonium to adjust the pH value to be greater than 10. The third type is solution “100”, which is BAS added with 1 wt % of ADS. As mentioned above, the pH value of solution “100” is 10. The fourth type of cleaning material is 0.2 wt % of Carbopol 940™ PAA dissolved in “100” solution. The molecular weight of Carbopol 940™ PAA is 4M (or 4 million) g/mol. The fifth type is 0.5 wt % of PAM dissolved in solution “100”. The molecular weight of PAM is 18M g/mol. The pH value of the fifth cleaning material is about 10. The five types of cleaning materials are mixed with two quantities of silicon nitride particles, 1×, and 50×. The number of silicon nitride particles of 50× is fifty times the number of particles of 1×. 1× nitride particles represent the nitride particle weight % is 0.00048%, while 50× nitride particle represent the nitride particle weight % is 0.024%. 
         [0105]    The results show that DIW is not very good at suspending and keeping silicon nitride particle in DIW. Large amount of silicon nitride particles (saturated) are left on the substrate surface. The description of “saturated” used in Table II describes particle (or defects) counts of greater than 75,000. In contrast, 0.2% Carbopol 940™ PAA in “100” and 0.5% PAM in “100” are much better at suspending silicon nitride particles in the cleaning material. 0.5% PAM in “100” is especially good at entrapping or suspending silicon nitride particles added in the cleaning material. Only small numbers, 53 for 1× silicon nitride particles, and 104 for 50× silicon nitride particles, of silicon nitride (or Si 3 N 4 ) particles in the cleaning material are left on the substrate surface. 
         [0106]    The molecular weight of polymers used in the cleaning material can affect the particle removal efficiency (PRE).  FIG. 5A  shows a graph of PRE of greater than 90 nm Silicon nitride particles on a substrate by cleaning materials with 1% (weight %) of PAA in “100” and 1% (weight %) of hydroxyethyl cellulose (HEC) in “100” as a function of the molecular weight of these two polymers (PAA and HEC). The data in  FIG. 5A  show that PRE increases with molecular weight of HEC between 100,000 g/mol to 1M (or 1,000,000) g/mol. Data in  FIG. 5A  also show that PRE increases with molecular weight for PAA between 500,000 g/mol and 1M g/mol. However, PRE does not change much between 1M g/mol and 1.25M g/mol for PAA.  FIG. 5B  shows a graph of PRE of greater than 90 nm Silicon nitride particles on a substrate by cleaning materials with 1% (weight %) of PAM in “100” as a function of the molecular weight of PAM. The data in  FIG. 5B  show that increasing the PRE increases with molecular weight of PAM between 500,000 g/mol to 18M g/mol. Data in both graphs show the effects of molecular weight on PRE. 
         [0107]    As mentioned above, the viscosity of the cleaning material would affect the rinsing time to remove the cleaning material from the substrate surface.  FIG. 5C  shows the results of adding ammonium chloride (NH 4 Cl) to cleaning material with 0.2 wt %-1 wt % of PAM dissolved in de-ionized (DI) water. The PAM has a molecular weight of 18M g/mol. The added ammonium chloride ionizes in the cleaning solution to provide additional ions to the cleaning material to increase the ionic strength of the cleaning material. The increased ionic strength reduces viscosity of the cleaning material. For example, 1.5 wt % of ammonium chloride is able to reduce the viscosity from about 100 cP to 60 cp for cleaning material with 1 wt % PAM. 1.5 wt % of ammonium chloride is also able to reduce the viscosity for cleaning material with 0.5 wt % PAM from about 50 cP to about 25 cP. Lowering the viscosity would lower the amount of time it takes to rinse the cleaning material from the substrate surface. In one embodiment, the viscosity of the cleaning material is dept below 500 cP to ensure substrate cleaning can be achieved within a reasonable time frame to achieve manufacturing goal. 
         [0108]      FIG. 6A  shows a process flow  600  of cleaning a patterned substrate using a cleaning material containing polymers of a polymeric compound with large molecular weight, in accordance with one embodiment of the present invention. The cleaning material is described above. At step  601 , the patterned substrate is place in a cleaning apparatus. At step  602 , the cleaning material is dispensed on the surface of the patterned substrate. At step  603 , a rinse liquid is dispensed on the surface of the patterned substrate to rinse off the cleaning material. The rinse liquid is described above. In one embodiment, after the rinse liquid is applied on the substrate surface, the rinse liquid, the cleaning material, and the contaminants on the substrate surface can be removed from the surface of the patterned substrate by vacuum. 
         [0109]      FIG. 6B  shows a process flow  650  of preparing a cleaning material to clean a patterned substrate, in accordance with one embodiment of the present invention. The cleaning material containing polymers of a polymeric compound with large molecular weight as described above. At step  651 , the materials, such as polymers, solvent, and additives (such as buffer agent, and/or surfactant), are mixed together to form the cleaning material, or a pre-mix of the cleaning material. At step  653 , the cleaning material (or the pre-mix) is purified to have less than 1 ppb metallic contaminants. It is possible that after the purification process, some additive(s), solvent, and/or buffer agent need to be added to restore the cleaning material to the desired formula. Under such circumstance, the additives, solvent, and/or buffer agent are added to make the final product of cleaning material. 
         [0110]    As discussed above, there are a number of methods for purifying the cleaning material to rid the cleaning material of metallic contamination. Alternatively, the purification can be performed during the cleaning material preparation process.  FIG. 6C  shows a process flow  670  of preparing a cleaning material to clean a patterned substrate, in accordance with another embodiment of the present invention. At step  671 , the polymeric compound and some solvent is mixed together to form a mixture. At step  672 , the mixture of polymer and solvent is purified to have less than 1 ppb metallic contaminants. At step  673 , the mixture of polymer and solvent are mixed with the remaining ingredients to form the cleaning material. Other embodiments of purifying the cleaning material are also possible. 
         [0111]    The cleaning materials, apparatus, and methods discussed above have advantages in cleaning patterned substrates with fine features without damaging the features. The cleaning materials are fluidic, either in liquid phase, or in liquid/gas phase (foam), and deform around device features; therefore, the cleaning materials do not damage the device features. The cleaning materials in liquid phase can be in the form of a liquid, a sol, or a gel. The cleaning materials containing polymers of a polymeric compound with large molecular weight capture the contaminants on the substrate. In addition, the cleaning materials entrap the contaminants and do not return the contaminants to the substrate surface. The polymers of a polymeric compound with large molecular weight form long polymer chains, which can also be cross-linked to form a network of polymers. The long polymer chains and/or polymer network show superior capabilities of capturing and entrapping contaminants, in comparison to conventional cleaning materials. 
         [0112]    The cleaning material is substantially free of non-deformable particles (or abrasive particles), before it is applied on the substrate surface to remove contaminants or particles from the substrate surface. Non-deformable particles are hard particles, such as particles in a slurry or sand, and can damage fine device features on the patterned substrate. During the substrate cleaning process, the cleaning material would collect contaminants or particles from the substrate surface. However, no non-deformable particles have been intentionally mixed in the cleaning material before the cleaning material is applied on the substrate surface for substrate cleaning. 
         [0113]    Although the embodiments above describe materials, methods, and systems for cleaning patterned substrates, the materials, methods, and systems can also be used to clean un-patterned (or blank) substrates. 
         [0114]    Although the discussion above is centered on cleaning contaminants from patterned wafers, the cleaning apparatus and methods can also be used to clean contaminants from un-patterned wafers. In addition, the exemplary patterns on the patterned wafers discussed above are protruding lines, such as polysilicon lines or metal lines. However, the concept of the present invention can apply to substrates with recessed features. For example, recess vias after CMP can form a pattern on the wafer and a most suitable design of channels can be used to achieve best contaminant removal efficiency. 
         [0115]    A substrate, as an example used herein, denotes without limitation, semiconductor wafers, hard drive disks, optical discs, glass substrates, and flat panel display surfaces, liquid crystal display surfaces, etc., which may become contaminated during manufacturing or handling operations. Depending on the actual substrate, a surface may become contaminated in different ways, and the acceptable level of contamination is defined in the particular industry in which the substrate is handled. 
         [0116]    Although a few embodiments of the present invention have been described in detail herein, it should be understood, by those of ordinary skill, that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details provided therein, but may be modified and practiced within the scope of the appended claims.