Abstract:
A wafer preparation method is provided for producing a wet region and then a corresponding dry region on the wafer. Brushing produces the wet region on the wafer. As the brushing moves in a selected scan operation across the wafer, a generating operation forms a meniscus that follows the brushing and dries the wet region. The generating operation produces the meniscus at least partially surrounding the wet region scrubbed by the scrubbing. The controlled meniscus is formed by applying fluid to the surface of the wafer and simultaneously removing the fluid. The scan operations may be selected so the brushing scrubs the wet region and then the meniscus forms the dry region where the scrubbing took place. The scan operations include a radial scan, a linear scan, a spiral scan and a raster scan.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This Application is a Divisional of application Ser. No. 10/742,303, filed on Dec. 18, 2003 now U.S. Pat. No. 7,353,560 (the “prior application”), from which priority under 35 U.S.C. § 120 is claimed. The disclosure of the prior application is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to semiconductor wafer processing, and more specifically to optimizing semiconductor wafer cleaning and drying in an integrated unit. 
     2. Description of the Related Art 
     Typically, semiconductor wafer fabrication entails multiple processing operations. For example, the processing operations can include many repeated steps, such as implantation, photolithography, material deposition, planarization, and related etching. In between the multiple processing operations, cleaning must be performed to ensure the removal of particulates and unwanted material that adhere to the wafer. Exemplary particulates that can adhere to the surface of the wafer can include silicon dust, silica, slurry residue, polymeric residue, metal flakes, atmospheric dust, plastic particles, and silicate particles. 
     Cleaning the wafer typically includes the use of deionized water (DIW), chemicals, and chemicals with DIW applied to wafer surfaces using mechanical contact, such as brush scrubbing. The application of the chemicals can also occur by completely immersing the wafer in a chemical or spraying the chemical on the wafer. However, while chemical processing removes most particulates and unwanted material, there may be times when not all particulates or material are removed to the desired degree. 
     Following the chemical cleaning process, the wafer may be subjected to a spin, rinse and dry (SRD) cycle to further remove chemical residues or particulates. The wafer then exits the SRD cycle in a dry state and ready for the next processing step. This cycle then repeats for any number of layers needed to fabricate a desired integrated circuit device being made from the wafer. 
       FIG. 1  is a diagram illustrating a wafer cleaning system with brushes. The wafer cleaning system shows a wafer  100  rotating with a wafer spin  110  while disposed between a first brush  120  and a second brush  130 , both brushes having multiple nodules  160 . First brush  120  has a first through the brush (TTB) conduit  140  and is shown having a first brush rotation  125 . Correspondingly, second brush  130  has a second TTB conduit  150  having a second brush rotation  135 . While the brushes rotate in the directions shown, thus mechanically assisting in the removal of unwanted material, a chemical can be applied via first TTB conduit  140  and second TTB conduit  150  to chemically remove unwanted material. 
     The wafer cleaning system is typically housed within a containment chamber to prevent unwanted contamination of the semiconductor wafer fabrication environment. However, by design, brush cleaning will spray processing chemicals and water all over the containment chamber. This spraying, although common in brush scrubbing systems, can have the downside of introducing contaminants from prior scrub brush operations onto later processed wafers. Unfortunately, common prior art brush scrubbing will necessarily spray the process chemicals or water throughout the containment chamber during a brush scrubbing step. 
     In some processing configurations, brush scrubbing may only be done on one side of the wafer, such as the bottom side. In such cases, either no processing or application of another processing technology is used on the other side of the wafer. Although this is may be done, it is a common objective to not contaminate one side of the wafer with processing being done on the other side. That is, if brush scrubbing is being done on the bottom of the wafer, then it is generally undesirable to allow spraying or dripping of brush fluids on the top side. Although undesirable, such cross-contamination of backside to front side may necessarily occur due to the nature of the rotating brush. 
     Further, although this process can achieve the intended purpose of removing most unwanted material, the wafer cleaning system can leave residual chemicals or water on the wafer even after the SRD cycle. For example, residual chemicals can remain on the wafer, causing imperfections similar to water spots. These imperfections may then remain under subsequent deposition and etching processes. Cumulatively, the imperfections may, in some situations, cause faults in the electrical connections of circuits being formed in the wafer. Of course, this may result in lower yields from the resulting wafer. 
     Accordingly, what is needed is an apparatus and method to remove imperfections introduced by the wafer cleaning system while continuing to remove unwanted material from the wafer. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention is a proximity brush unit for optimizing semiconductor wafer cleaning and drying. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below. 
     In one embodiment, an apparatus has a head proximate to a surface of a wafer, a plurality of ports disposed on a surface of the head, such that the plurality of ports is capable of interfacing a first plurality of fluids to the surface of the wafer. Further, the brush disposed within the head is capable of being placed in contact with the surface of the wafer with the brush being partially contained by adjacent ones of the plurality of ports. 
     In another embodiment, a proximity brush unit has a plurality of ports capable of interfacing a first fluid, a second fluid and a third fluid on a surface of a substrate, to create a meniscus. Thereafter, the proximity brush unit has a rotatable brush adjacent to the plurality of ports, the rotatable brush being capable of delivering a fourth fluid to the surface of the substrate, the meniscus at least partially containing the rotatable brush and the fourth fluid. 
     The proximity brush unit can also be used in a method with the operations of providing a brush, partially surrounding the brush with a plurality of meniscus forming conduits, and applying the plurality of meniscus forming conduits proximate to a wafer surface. The operations also include scrubbing the wafer surface using the brush and activating the plurality of meniscus forming conduits to contain fluids at least partially around the brush, and scanning the wafer. 
     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagram illustrating a wafer cleaning system with brushes; 
         FIG. 2A  is a diagram illustrating a proximity brush unit with mechanical gears, in accordance with an embodiment of the invention; 
         FIG. 2B  is a diagram illustrating a proximity brush unit with a levitating brush, in accordance with an embodiment of the invention; 
         FIG. 2C  is a diagram illustrating a cross section of a proximity brush unit with nozzles, in accordance with an embodiment of the invention; 
         FIG. 3  is a diagram illustrating a top view of a proximity brush unit with a plurality of ports, in accordance with an embodiment of the invention; 
         FIG. 4A  is a diagram illustrating a proximity brush unit moving in a linear scan, in accordance with an embodiment of the invention; 
         FIG. 4B  is a diagram illustrating a proximity brush unit moving in a radial scan, in accordance with an embodiment of the invention; 
         FIG. 5  is a diagram illustrating a top view of a proximity brush unit, in accordance with an embodiment of the invention; 
         FIG. 6  is a diagram illustrating a side view of a proximity brush unit, in accordance with an embodiment of the invention; 
         FIG. 7  is a diagram illustrating a proximity brush unit moving in a linear scan to produce a wet region and a dry region on a wafer, in accordance with an embodiment of the invention; 
         FIG. 8A  is a diagram of a method for applying a proximity brush unit, in accordance with an embodiment of the invention; and 
         FIG. 8B  is a diagram of a method for scanning a wafer with a proximity brush unit to produce a wet region and a dry region on the wafer, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An apparatus and method for an optimal semiconductor wafer cleaning system is disclosed. Specifically, by using a partially enclosed brush that is proximate to a wafer surface in combination with a meniscus for drying the wafer surface, the wafer surface can be cleaned and dried while drastically reducing spraying and the propagation of impurities. The meniscus is as disclosed in U.S. Pat. No. 7,234,477 issued on Jun. 26, 2007 and entitled “Method and Apparatus for Drying Semiconductor Wafer Surfaces Using a Plurality of Inlets and Outlets Held In Close Proximity to the Wafer Surfaces”, which patent is incorporated herein by reference in its entirety. 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. 
       FIG. 2A  is a diagram illustrating a proximity brush unit with mechanical gears, in accordance with an embodiment of the invention. Wafer  100  spins in a direction shown by a wafer rotation  280 . Wafer  100  can be viewed as a substrate that is processed during processing operations. In some instances, the substrate can take on different shapes, such as square or rectangular shapes, as are used in flat panel substrates. For simplicity, reference will be made to a circular wafer, such as wafer  100 . The actual diameter of a wafer can vary, and current technology examples include 200 mm wafers, 300 mm wafers, or larger. Disposed proximately beneath wafer  100  is a proximity brush unit (PBU)  200  attached to a single arm  260 . Single arm  260  moves PBU  200  using various scanning methods to cover the entire surface of wafer  100 , as later shown in  FIGS. 4A and 4B . 
     PBU  200  includes a brush  210  having a plurality of nodules  220 . Although shown with circular geometric shapes having an even distribution on brush  210 , plurality of nodules  220  can take on any shape. All the shapes can be densely populated with an even distribution across brush  210  or can be sparsely populated with an uneven distribution. Any combination of distributing the shapes is possible, as long as the combination facilitates cleaning. In another embodiment, as later shown in  FIG. 6 , brush  210  can touch wafer  100  without using plurality of nodules  220 , as long as enough contact exists between brush  210  and wafer  100  to facilitate mechanical cleaning. 
     Further, although brush  210  is shown having a cylindrical, roller-pin type shape, brush  210  can be any geometric shape such as a circular, pancake-style shape. Brush  210  also includes a through the brush (TTB) mechanism  240  disposed through the center of brush  210 . TTB mechanism  240  can apply a plurality of fluids, such as a cleaning chemistry, through brush  210 . The cleaning chemistry can include SC1, hydrofluoric acid (HF), ESC 784, a surfactant, deionized water (DIW), DIW with a surfactant, or some other chemical capable of chemically cleaning wafer  100 . 
     Attached to TTB mechanism  240  is a mechanical gear  230 . An opposing mechanical gear  230  (not shown) is also attached to TTB mechanism  240  on the opposite end of brush  210 . Mechanical gears  230  can rotate brush  210  in a brush rotation  270  or keep brush  210  fixed. Further, mechanical gears  230  can move brush  210  up and down within PBU  200 , permitting more or less contact with wafer  100 . Ultimately, mechanical gears  230  can move brush  210  away from wafer  100 , thus permitting no contact with wafer  100 . 
     PBU  200  also includes a plurality of ports  250  disposed on the surface of PBU  200 , permitting fluids produced from plurality of ports  250  to contact wafer  100  while partially enclosing brush  210 . The fluids dry wafer  100  in conjunction with the wetting and scrubbing motion of brush  210 . Further, controlling the fluids produces a stable fluid meniscus, as later shown in  FIG. 3 . Although shown with an approximate L-shaped configuration, plurality of ports  250  can have other shapes, such as an approximate U-shape or approximate O-shape. Further, plurality of ports  250  can have other shapes and configurations, as discussed in later figures. 
     Although disposed proximately beneath wafer  100 , PBU  200  can also be disposed proximately above wafer  100 . Further, one PBU  200  can be proximately disposed on each side of wafer  100 , thus simultaneously permitting cleaning and drying of opposing surfaces on wafer  100 . Alternatively, PBU  200  can be disposed between two wafers  100  if PBU  200  includes the configuration as shown in  FIG. 2A  on the underside of PBU  200 . 
     Alternatively,  FIG. 2B  is a diagram illustrating a proximity brush unit with a levitating brush, in accordance with an embodiment of the invention. Disposed beneath wafer  100  is PBU  200  with a dual arm  295 . Dual arm  295  includes an electro-magnetic motor  290  located near each opposing end of brush  210 . Along the length of each arm of dual arm  295  is a gear drive  297 , permitting electro-magnetic motor  290  to levitate and rotate brush  210 . Dual arm  295  moves PBU  200  with a scanning method, to cover the entire surface of wafer  100  as wafer  100  spins with wafer rotation  280 . An advantage of using a levitating brush instead of a fixed motorized brush, as shown in  FIG. 2A , is that levitating the brush  210  may produce a cleaner environment. Specifically, if brush  210  rotates via levitation, then mechanical gears  230  do not generate particulates that may contaminate wafer  100 . 
     In one embodiment, PBU  200  has plurality of ports  250  in an approximate U-shaped configuration. Of course, other orientations, such as the approximate L-shape may be used. Although shown with two rows of plurality of ports  250  intersecting at 90-degree angles at two points, other embodiments of PBU  200  can have plurality of ports  250  intersecting at angles between 0 and 180 degrees. Thus, plurality of ports  250  can be a straight line having a 0/180 degree angle, can be a shape having an acute angle of 25-degrees, or can be a circular shape on PBU  200 . Further, although plurality of ports  250  is shown having rows that extend along the full length of an edge of PBU  200 , the rows can be any length. 
     As wafer  100  spins in the direction of wafer rotation  280 , electro-magnetic motor  290  engages and levitates brush  210  out of the center of PBU  210 , causing brush  210  contact with wafer  100 . Then, brush  210  rotates with brush rotation  270  during the application of the cleaning chemistry to chemically and mechanically clean wafer  100 . Subsequently, the stable fluid meniscus formed from the plurality of ports  250  dries the wet region created by brush  210 . 
       FIG. 2C  is a diagram illustrating a cross section of a proximity brush unit with nozzles, in accordance with an embodiment of the invention. PBU  200  contains brush  210  within a containment chamber  205 . In one embodiment, a cleaning fluid  285  partially encloses brush  210 , thus wetting brush  210  during brush rotation  270 . Cleaning fluid  285  can be one of the plurality of fluids, such as the cleaning chemistry, as described in relation to  FIG. 2A . At least one nozzle  275 , located anywhere within containment chamber  205 , provides cleaning fluid  285 . In an alternative embodiment, containment chamber  205  can be dry and nozzle  275  can provide cleaning fluid  285  to brush  210 . 
       FIG. 3  is a diagram illustrating a top view of a proximity brush unit with a plurality of ports, in accordance with an embodiment of the invention. Plurality of ports  250  is shown with rows of multiple ports including a first port  310 , a second port  320 , and a third port  330 . All the ports can produce controllable fluids that form a stable fluid meniscus. Alternatively, some of the ports can produce fluids, as long as some of the ports produce the stable fluid meniscus. First port  310  produces isopropyl alcohol (IPA) vapor, second port  320  produces deionized water (DIW), and third port  330  produces a vacuum. Alternatively, second port  320  can produce a chemical or a chemical and DIW. The chemical can be cleaning fluid  285  or some other chemical solution used to form the stable fluid meniscus. A row of second ports  320  is completely surrounded by rows of third ports  330 . Accordingly, as second ports  320  produce fluid, the vacuum created by third ports  330  removes fluid. Further, a row of first ports  310  trails the row of third ports  330  to help form the stable fluid meniscus. Accordingly, as PBU  200  moves across wafer  100 , the stable fluid meniscus dries wafer  100  after brush  210  performs a cleaning operation. 
       FIG. 4A  is a diagram illustrating a proximity brush unit moving in a linear scan, in accordance with an embodiment of the invention. As plurality of ports  250  produces the stable fluid meniscus, PBU  200  moves in the direction of a linear scan  430 . During linear scan  430 , brush  210  cleans wafer  100 . Specifically, as wafer  100  rotates with wafer rotation  280 , PBU  200  moves from the center of wafer  100  to a first linear scan location  410  followed by movement to a second linear scan location  420 . Consequently, the stable fluid meniscus dries the wet region formed on wafer  100  by brush  210 . 
     Alternatively,  FIG. 4B  is a diagram illustrating a proximity brush unit moving in a radial scan, in accordance with an embodiment of the invention. PBU  200  starts in the center of wafer  100  and moves to an edge of wafer  100  using a radial scan  440 . Radial scan  440  can have an arc from about 30 degrees to about 45 degrees. Further, as PBU  200  radially scans  440 , brush  210  cleans wafer  100  followed by the stable fluid meniscus formed by plurality of ports  250 . In alternative embodiments, PBU  200  can scan wafer  100  in a spiral scan, in a raster scan, or other scanning method ensuring full coverage of wafer  100  during wafer rotation  280 . 
       FIG. 5  is a diagram illustrating a top view of a proximity brush unit, in accordance with an embodiment of the invention. A full diameter proximity brush unit  500  (FPBU) contains a full diameter brush  510 . Full diameter brush  510  rotates with brush rotation  270  and cleans wafer  100 . As FPBU  500  moves in the direction of a full linear scan  590 , a linear plurality of ports  550  produces the stable fluid meniscus for drying the trailing edge of wafer  100 . Alternatively, wafer  100  can move in the direction of full linear scan  590  while FPBU  500  remains stationary. In another embodiment, a combination of movement from wafer  100  and FPBU  500  is possible without departing from the intended purpose of cleaning and drying wafer  100 . 
       FIG. 6  is a diagram illustrating a side view of a proximity brush unit, in accordance with an embodiment of the invention. PBU  200  applies a meniscus  620  from a plurality of conduits  630 . To form meniscus  620 , plurality of conduits  630  receives fluids from a fluid supply  640 . Some or all of the plurality of conduits  630  can receive fluids, as long as PBU  200  applies meniscus  620  to the surface of wafer  100 . Further, while wafer  100  rotates between two rollers  610 , meniscus  620  has a height as shown by a proximate distance  650 . Proximate distance  650  can be about 1.3 mm, but can also be any value in the range from about 0.5 mm to about 2.0 mm. However, as long as plurality of conduits  630  supplies controllable fluids proximate to the surface of wafer  100 , any distance is appropriate without departing from the intended purpose of creating the stable fluid meniscus. 
       FIG. 7  is a diagram illustrating a proximity brush unit moving in a linear scan to produce a wet region and a dry region on a wafer, in accordance with an embodiment of the invention. As PBU  200  moves in a linear scan under wafer  100 , the combined brush  210  and cleaning fluid  285  produces a wet region  730 . Correspondingly, plurality of ports  250  produces meniscus  620  to produce a dry region  740 . Specifically, PBU  200  produces dry region  740  when a PBU  200  trailing edge  720  moves past a wafer trailing edge  710 . As previously disclosed, other scanning methods are possible, as long as PBU  200  first produces wet region  730  followed by dry region  740 . In another embodiment (not shown), the wet region is formed on a leading edge of wafer  100  and the dry region is formed on a trailing edge of wafer  100 . 
       FIG. 8A  is a diagram of a method  800  for applying a proximity brush unit, in accordance with an embodiment of the invention. Method  800  begins by the proximity brush unit providing the brush to the wafer  100 , in operation  810 . Next in operation  820 , meniscus  620  partially surrounds the brush with meniscus forming conduits  630 . Then, in operation  830 , the proximity brush unit applies the brush to the wafer surface. In a subsequent operation  840 , the proximity brush unit applies the meniscus forming conduits  630  proximate to the wafer surface. The proximate brush unit then scrubs the wafer  100  using the brush and activates the meniscus forming conduits  630  to contain fluids at least partially around the brush, in operation  850 . Finally, the proximity brush unit scans wafer  100  in operation  860 , which ends method  800 . In alternative embodiments, the proximity brush unit can be one of many embodiments previously described and can include other proximity brush unit shapes such as a cylinder or other polygonal shape. 
       FIG. 8B  is a diagram of a method, shown in operation  860 , for scanning a wafer with a proximity brush unit to produce a wet region and a dry region on the wafer, in accordance with an embodiment of the invention. Operation  860  begins by selecting a scan method. In operation  875 , if the selected scan method is a radial scan, then proceed to operation  880 , which causes the movement of the proximity brush unit in an arc. Alternatively, in operation  885 , the proximity brush unit moves linearly. In operation  890 , upon the completed move of the proximity brush unit, the method ends. For other embodiments, any type of scanning method can replace the radial scan in operation  875 . For example, the scanning methods can include linear scanning, spiral scanning or raster scanning. Accordingly, corresponding operations to move the proximity brush unit in the selected scan method follow operation  875 . 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.