Patent Publication Number: US-2004040575-A1

Title: Brush for cleaning/scrubbing a substrate

Description:
BACKGROUND  
       [0001] 1. Technical Field  
       [0002] An embodiment of the present invention relates to a brush for cleaning and scrubbing a substrate. More particularly, an embodiment of the present invention relates to a brush for cleaning and scrubbing a planar object such as a silicon wafer or semiconductor substrate.  
       [0003] 2. Discussion of the Related Art  
       [0004] In the manufacture of integrated circuits (ICs), semiconductor wafer surface planarity is of utmost importance. To achieve the degree of planarity necessary to produce ultra-high density ICs, chemical-mechanical polishing/planarization (CMP) is often utilized. Generally, CMP involves holding a semiconductor wafer against a moving polishing surface that is wetted with a chemically-reactive slurry, which contains abrasive materials such as silica or alumina. The polishing surface is usually a planar pad made of relatively soft, porous material, such as brown polyurethane, and it is usually mounted on a planar platen. A major concern with the use of CMP is the efficient and complete removal of the polishing slurry to prevent problems in subsequent processing steps.  
       [0005] After CMP, a wafer rinse and some form of mechanical agitation of the wafer surface is usually employed to remove the slurry chemical and abrasive residue from the surface of the semiconductor wafer. Particle removal is greatly enhanced by the addition of mechanical shear forces. Accordingly, mechanical brush scrubbing is widely used as a method of post-CMP cleaning.  
       [0006] Typically, to scrub and clean a semiconductor wafer, a pair of brush rollers is utilized. Each brush is pressed against, respectively, the front and back surfaces of the semiconductor wafer. The purpose of the brushes being pressed against each surface is two-fold: to clean the wafer surfaces, and to support the semiconductor wafer to uniformly distribute the pressure placed onto the wafer during its scrubbing and cleaning.  
       [0007] In some instances, the semiconductor wafer, or other substrate, need be cleaned only on one side. In this particular case, contact between the brush and the other side of the wafer or substrate, which requires no cleaning, can be detrimental. Such a contact may cause contamination of the wafer or substrate surface with particles, scratch the surface, etc. In other words, conventional cleaning brushes do not allow for the elimination or reduction of the contact and contact area between the brush and the wafer/substrate surface while still providing brush support of the wafer/substrate during scrubbing and cleaning. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008]FIG. 1 illustrates a perspective view of a brush apparatus having a first brush and a second brush according to an embodiment of the present invention;  
     [0009]FIG. 2 illustrates a side view of a brush according to an embodiment of the present invention;  
     [0010]FIG. 3 illustrates a side view of a brush according to an embodiment of the present invention;  
     [0011]FIG. 4 illustrates a side view of a brush according to an embodiment of the present invention;  
     [0012]FIG. 5 illustrates a side view of a brush according to an embodiment of the present invention; and  
     [0013]FIG. 6 illustrates a flow chart diagram of scrubbing/cleaning a planar object utilizing a first brush and a second brush according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0014]FIG. 1 illustrates a perspective view of a brush apparatus having a first brush and a second brush according to an embodiment of the present invention. In the embodiment illustrated in FIG. 1, the first brush  101  of the brush apparatus  100  is in a top position while the second brush  150  of the brush apparatus  100  is in a bottom position. However, the brushes  101 ,  150  may be configured in a reverse orientation where the first brush  101  is in the bottom position and the second brush  150  is in the top position. In the configuration illustrated in FIG. 1, the brush apparatus  100  is adapted to scrub/clean the bottom surface of a wafer or substrate. A motor is provided with the brush apparatus  100  to drive and rotate at least one of the brushes  101 ,  150 .  
     [0015] The first brush  101  has a central portion  130  and end portions  110 ,  120 . The central portion  130  is recessed from the end portions  110 ,  120 . The second brush  150  has an outer surface and opposes the first brush  101 . The outer surface of the second brush  150  may be the same as the outer surfaces of the end portions  110 ,  120  of the first brush  101 , or they may be different. The first brush  101  and the second brush  150  are adapted to receive a planar object, such as a semiconductor wafer or substrate in between the first brush  101  and the second brush  150 . Due to the design of the first brush  101 , the outer surface of the second brush  150  and the end portions  110 ,  120  of the first brush  101  are in contact with the planar object when inserted in between the first brush  101  and the second brush  150 . Because of the recess within the central portion  130  of the first brush  101 , the central portion  130  avoids contact with the planar object as it is inserted in between the first brush  101  and the second brush  150 . Therefore, contact by the brush apparatus  100  of the top surface of a planar object to be scrubbed/cleaned is greatly minimized by utilizing the first brush  101  according to an embodiment of the present invention, and contamination and damage to the planar object during scrubbing/cleaning is also minimized.  
     [0016] In several steps of IC manufacturing, backside scrubbing of the wafer is utilized to remove and/or reduce the particles left on the backside of the wafer during IC manufacturing. Particles left on the wafer backside can distort subsequent lithographic processing. Flatness of the wafer (i.e., no particles on the backside) is extremely important in producing optimal focus for modern optical lithography employing wavelengths of 248 nanometers (nm) and less. The aim of backside scrubbing is to remove particles from only the backside of the wafer; however, a brush pair that is utilized in a conventional brush apparatus and in a scrubber is in contact with both back (bottom) and front (top) surfaces of the wafer. Contact from both sides of a wafer is required to provide the mechanical support and correct pressure on the wafer. However, while polishing of the back side of the wafer is beneficial, as it removes the particles from this side, the polishing of the front side can be detrimental because it tends to distribute the particles from the edges of the wafer over the entire surface of the front side of the wafer, which may cause defects in the wafer. By reducing the contact and contact area between the first brush  101  and the front side (top surface) of the planar object, contamination and distribution of particles from the edges of the wafer are greatly reduced.  
     [0017]FIG. 2 illustrates a side view of a brush according to an embodiment of the present invention. The brush  200  according to an embodiment of the present invention may be “dog bone” shaped or “dumb bell” shaped so that there are end portions  210 ,  220  and a central portion  230  that is recessed from the end portions  210 ,  220 . Although the “dog bone” or “dumb bell” shape is illustrated, any suitable configuration of a brush having a central portion  230  that is recessed from the end portions  210 ,  220  may be utilized. This configuration of the brush  200  reduces the contact area between the brush  200  and a planar object to be scrubbed/cleaned, such as a polished substrate or a silicon wafer, so as to preserve one side of the wafer from particle deposit contamination and scratching, while maintaining the efficiency of the backside scrubbing/cleaning of the substrate. The end portions  210 ,  220  provide support to the planar object, while the central portion  230  is not in contact with the planar object. The brush  200  illustrated in FIG. 2 is a “sharp” dog bone shape design, that is, the central portion  230  is cut away with a rectangular recess.  
     [0018] The brush  200  may be formed of an outer material  250  and a central core  240  onto which the outer material  250  is coupled. In the brush  200  illustrated in FIG. 2, the recess is cut away from the central portion  230  of the outer material  250  of the brush  200 . The brush  200  may be formed by utilizing a conventional cylindrical brush, or the like, such as the one utilized as the second brush  150  illustrated in FIG. 1. Because the brush  200  may be formed utilizing the same brush type as that of the second brush  150 , the outer surface of the end portions  210 ,  220  of the brush  200  may be the same as the outer surface of the second brush  150 . For example, the outer surface of the end portions  210 ,  220  of the brush  200  may be smooth, noduled (see FIG. 1), splined, or dented (or Swiss cheese-like). The noduled, splined, or dented outer surfaces further reduce the contact area between the brush and the surface of the planar object compared to a conventional smooth cylindrical brush, where the entire brush surface is in contact with the surface of the planar object. Conversely, the bottom brush  150  may have the same or different type of outer surface as that of the top brush  101 . However, because the central portion  230  of the brush  200  is recessed and does not make contact with the planar object to be scrubbed/cleaned, the type of surface (e.g., brush-type surface, smooth core surface, etc.) utilized for the central portion  230  is not critical.  
     [0019]FIG. 3 illustrates a side view of a brush according to an embodiment of the present invention. Similar to the brush  200  in FIG. 2, the brush  300  illustrated in FIG. 3 includes end portions  310 ,  320  and a central portion  330  having a curved recess (i.e., “curved” dog bone shaped). The brush  300  may be formed of an outer material  350  and a central core  340  onto which the outer material  350  is coupled. This configuration of the brush  300  also reduces the contact area between the brush  200  and a planar object. The end portions  310 ,  320  provide support to the planar object, while the central portion  330  is not in contact with the planar object.  
     [0020]FIG. 4 illustrates a side view of a brush according to an embodiment of the present invention. The brush  400  illustrated in FIG. 4 is similar to the “sharp” dog bone shaped brush illustrated in FIG. 2. The brush  400  includes end portions  410 ,  420  and a central portion  430  having a rectangular recess. The brush  400  is assembled from a brush core  440 , an intermediate outer material  452  coupled to the core  440 , and an exterior outer material  454 ,  456  coupled to the intermediate outer material  452  forming the end portions  410 ,  420 . The end portions  410 ,  420  provide support to a planar object, while the central portion  430  is not in contact with the planar object. Although these particular components are utilized to form the brush  400  in FIG. 4, any suitable combination and number of pieces, components, or parts may be utilized to construct the brushes according to embodiments of the present invention.  
     [0021]FIG. 5 illustrates a side view of a brush according to an embodiment of the present invention. The brush  500  illustrated in FIG. 5 is similar to the “sharp” dog bone shaped brushes illustrated in FIGS. 2 and 4. The brush  500  includes end portions  510 ,  520  and a central portion  530  having a rectangular recess. The brush  500  may be assembled from a brush core  540  and an outer material  552  coupled to the core  540  forming the end portions  510 ,  520 . The core  540  of the brush  500  in FIG. 5 serves as the outer surface within the recess of the central portion  530  of the brush  500 . The end portions  510 ,  520  provide support to a planar object, while the central portion  530  is not in contact with the planar object. Although these particular components are utilized to form the brush  500  in FIG. 5, any suitable combination and number of pieces, components, or parts may be utilized to construct the brushes according to embodiments of the present invention.  
     [0022]FIG. 6 illustrates a flow chart diagram of scrubbing/cleaning a planar object utilizing a first brush and a second brush according to an embodiment of the present invention. With reference to FIG. 1, a first brush  101  is rotated  610 . The first brush  101  has a central portion  130  and end portions  110 ,  120 . The central portion  130  of the first brush  101  is recessed from the end portions  110 ,  120  A second brush  150  is also rotated  620 . The second brush  150  has an outer surface and is opposed to the first brush  101 . The first brush  101  and the second brush  150  are adapted to receive a planar object therebetween. With the first brush  101  and the second brush  150  rotating, the planar object to be scrubbed/cleaned, such as a semiconductor wafer or substrate, is inserted in between the first brush  101  and the second brush  150 . The outer surface of the second brush  150  and the end portions  110 ,  120  of the first brush  101  make contact with the planar object as it is inserted in between the two brushes  101 ,  150 , and the central portion  130  of the first brush  101  avoids contact with the top surface of the planar object. The brush apparatus  100 , for example, as illustrated in FIG. 1 permits the elimination or reduction of the contact (and contact area) between the first brush  101  and the top surface of a planar object (the top surface of which does not require to be scrubbed/cleaned) while still providing mechanical (brush) support of the planar object and uniform pressure distribution as it goes through the brushes  101 ,  150  during the scrubbing and cleaning operation of the bottom surface of the planar object. Therefore, contact with the top surface of the planar object is minimized (to the sides only by the end portions  110 ,  120  of the first brush  101 ), therefore minimizing contamination as a result of contact with a brush.  
     [0023] The methods and apparatuses according to embodiments of the present invention may be utilized for backside (or one-side) scrubbing of bare wafers or wafers coated with poly-silicon, deposited silicon nitride, and deposited oxides (e.g., standard oxides plus Low k (dielectric constant) dielectrics), as well as utilized prior to lithography steps involving implanted layers including wells, tips, and source/drains. The applications of the methods and apparatuses of embodiments of the present invention are not limited only to those described herein and any other suitable applications may be utilized.  
     [0024] While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.