Abstract:
A brush core and the method for making a brush core for use in substrate scrubbing are provided. The substrate can be any substrate that may need to undergo a scrubbing operation to complete a cleaning operation, etching operation, or other preparation. For instance, the substrate can be a semiconductor wafer, a disk, or any other type of work piece that will benefit from a brush core that can deliver uniform controlled amounts of fluid through the brush along an entire length of the brush core. The brush core is defined by a tubular core having a length that extends between a first end and a second end. The first end has an opening into a bore that is defined through a middle of the tubular core and extends along an inner length of the tubular core. A first plurality of holes are oriented along a plurality of first lines that extend in the direction of the length of the tubular core, and each of the first plurality of holes define paths to the bore of the tubular core. A second plurality of holes are oriented along a plurality of second lines that extend in the direction of the length of the tubular core, and each of the second plurality of holes define paths to the core of the tubular core. The plurality of first lines and the plurality of second lines alternate and the holes of the first and second plurality of holes are equally spaced apart. The holes of the second plurality of holes are offset relative to the holes of the first plurality of holes.

Description:
This is a Continuation application Ser. No. 09/454,698 filed on Dec. 3, 1999, now U.S. Pat. No. 6,240,588. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to semiconductor wafer fabrication, and more particularly to semiconductor wafer scrubbing equipment. 
     2. Description of the Related Art 
     As is well known, semiconductor devices are fabricated from semiconductor wafers, which are subjected to numerous processing operations. These operations include, for example, impurity implants, gate oxide generation, inter-metal oxide depositions, metallization depositions, photolithography pattering, etching operations, chemical mechanical polishing (CMP), etc. Although these processes are performed in ultra clean environments, the very nature of many of the process operations is to blame for the generation of surface particles and residues. For instance, when CMP operations are performed, a film of particles and/or metal contaminants are commonly left behind. 
     Because surface particles can detrimentally impact the performance of an integrated circuit device, wafer cleaning operations have become a standard procedural requirement after certain process steps. Although cleaning operations are rather procedural, the equipment and chemicals implemented to perform the actual cleaning are highly specialized. This specialization is important because each wafer, being at different stages of fabrication, represents a significant investment in terms of raw materials, equipment fabrication time, and associated research and development. 
     To perform the cleaning operations in an automated manner, fabrication labs employ cleaning systems. The cleaning systems typically include one or more brush boxes in which wafers are scrubbed. Each brush box includes a pair of brushes, such that each brush scrubs a respective side of a wafer. To enhance the cleaning ability of such brush boxes, it is common practice to deliver cleaning fluids through the brush (TTB). TTB fluid delivery is accomplished by implementing brush cores that have a plurality of holes that allow fluids being fed into the brush core at a particular pressure to be released into an outer brush surface. The outer brush surface is made out of a very porous and soft material so that direct contact with the delicate surface of a wafer does not cause scratches or other damage. Typically, the outer brush surface is a made out of polyvinyl alcohol (PVA) foam. Although, other materials such as nylon, mohair or a mandrel wrapped with a polishing pad material can be used. 
     As semiconductor design and performance requirements continue increase, cleaning engineers are also challenged to improve their associated processes. To meet these demands, the same cleaning equipment is now being used to perform operations other than basic de-ionized (DI) water cleaning. Such operations include the application of sophisticated chemicals TTM to remove particulates and/or to etch precision amounts of materials from the surfaces of a wafer. Although much research and development goes into the design of cleaning and etching chemicals, the effectiveness of such chemicals is only as good as their delivery and application onto the surface of a wafer. 
     Recent research of conventional brush core technology has uncovered non-uniformities in the application of the chemicals onto the surface of wafers. The research indicates that although chemicals are being flushed out of the brush cores and onto the wafer surfaces, the applied chemicals do exit the holes of the brush core at the same rate over the length of a core. For instance, chemicals are generally supplied to an internal bore of a brush core from one end of the brush core at a given pressure. Ideally, the chemicals are expected to flow through the bore and drip or flow out of the core equally from all of the brush core holes (e.g., the same amount drips out each of holes all along the brush core). Unfortunately, research shows that chemicals are not dripping out of all of the holes at the same or substantially the same rate. In fact, much of the research indicates that the brush core holes near the chemical receiving end drip out chemicals at a substantially faster rate than holes at the opposite side of the chemical receiving end. 
     Because traditional cleaning typically only included the application of DI water and/or ammonia based chemicals, the uneven application of these fluids through the brush core did not in many cases detrimentally impact cleaning performance. However, because most cleaning systems are now required to also apply engineered chemicals, such as hydrofluoric acid (HF) containing etch chemicals, any uneven application will have a severe impact on the wafer being processed. For instance, if more HF is applied to one part of the wafer and less is applied to another part of the wafer, the surface of the processed wafer may exhibit performance impacting etch variations due to experienced chemical concentration variations. 
     FIG. 1A provides a simplified diagram  10  of a prior art brush core  12  having a plurality of holes  12   a . The brush core  12  has a center bore  12   b  which is configured to receive fluids from a fluid input  16  at one end of the brush core  12 . The brush core  12  is shown having a brush  14  mounted thereon to illustrate that fluid that enters the bore  12   b  exits the holes  12   a  soaks the brush  14  that is designed to contact a wafer. This simplistic diagram also illustrates fluid flow lines  18   a  and  18   b , in which fluid lines  18   a  illustrate that more fluid tends to flow out of holes  12   a  near the fluid input than at the opposite end. It is believed that this occurs because chemicals are either not applied to the brush core  12  at a sufficient pressure or the holes  12  are too large and/or are improperly arranged and thus allow gravity to pull more fluid out of the brush core  12  near the fluid input  16  than at the opposite end. 
     Some of these prior art brush cores  12  have a center bore  12   b  that is about 0.36 inch in diameter or larger and holes  12   a  that are about 0.13 inch in diameter or larger. To compensate for the larger size of these dimensions and to attempt to prevent the uneven delivery of fluids, cleaning systems need to deliver fluids to the brush cores  12  at higher pressures. These higher pressures range between 30 to 35 PSI or higher. However, the application of higher pressures require the cleaning system to have access to facilities and associated equipment that can deliver the desired controlled pressures at all times. However, cleaning systems are installed in clean rooms around the world having different facilities which may or may not be able to deliver the recommended pressures. Additionally, the holes  12   a  of most prior art brush cores  12  are arranged such that one hole  12   a ′ is directly opposite of another hole  12   a ′. This arrangement is also believed to contribute to the higher outflow of fluids near the fluid input  16  than at the opposite end. 
     In view of the foregoing, there is a need for improved brush core designs that enable controlled amounts of fluid to be evenly delivered and distributed over the surface areas of a brush core. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by providing a brush core for use in scrubbing substrates. The substrate can be any substrate that may need to undergo a scrubbing operation to complete a cleaning operation, etching operation, or other preparation. For instance, the substrate can be a semiconductor wafer, a disk, or any other type of work piece that will benefit from a brush core that can deliver uniform controlled amounts of fluid through the brush along an entire length of the brush core. 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, a brush core for use in substrate scrubbing is disclosed. The brush core is defined by a tubular core extending between a first end and a second end. A bore is defined through a middle of the tubular core. A first and second plurality of holes are provided. Each hole of the first and second plurality of holes is defined through the tubular core to define a path to the bore. The first plurality of holes is defined along a first line that extends between the first end and the second end and the second plurality of holes is defined along a second line that extends between the first end and the second end. The first line and the second line are repeated around the tubular core and the first line and the second line alternate around the tubular core, and the holes of the first plurality of holes are offset relative to the holes of the second plurality of holes. 
     In another embodiment, a brush core is disclosed. The brush core is defined by a tubular core having a length that extends between a first end and a second end. The first end has an opening into a bore that is defined through a middle of the tubular core and extends along an inner length of the tubular core. A first plurality of holes are oriented along a plurality of first lines that extend in the direction of the length of the tubular core, and each of the first plurality of holes define paths to the bore of the tubular core. A second plurality of holes are oriented along a plurality of second lines that extend in the direction of the length of the tubular core, and each of the second plurality of holes define paths to the core of the tubular core. The plurality of first lines and the plurality of second lines alternate and the holes of the first and second plurality of holes are equally spaced apart. The holes of the second plurality of holes are offset relative to the holes of the first plurality of holes. 
     In yet a further embodiment, a method of making a brush core is disclosed. The method includes providing a tubular core having a length that is configured to extend over a substrate. A bore is defined through a center of the tubular core. A first plurality of holes oriented along a plurality of first lines that extend in the direction of the length of the tubular core is defined. Each of the first plurality of holes is configured to establish paths to the bore of the tubular core. A second plurality of holes oriented along a plurality of second lines that extend in the direction of the length of the tubular core is defined. Each of the second plurality of holes is configured to establish paths to the core of the tubular core. The defined first plurality of holes are configured to be offset from the defined second plurality of holes. 
     Advantageously, the embodiments of the present invention provide brush cores for delivering a uniform fluid distribution throughout the core. The uniform fluid distribution is achieved by designing specially placed and sized holes into the brush core. The holes define paths to a specially designed center bore, which is configured and sized to quickly pressurize the bore such that the delivered fluid exits the plurality of holes at bout the same rate. Achieving this substantial even outflow of fluid from the core along the entire length of the brush core ensures that the outer brush receives equal amounts of fluids during an application process. As can be appreciated, even outflow of fluids is especially important when the fluids are engineered chemicals, such as etchants, that are designed to remove certain material particles, films, or layers. 
     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 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. 
     FIG. 1A provides a simplified diagram of a prior art brush core having a plurality of holes. 
     FIG. 1B shows a wafer cleaning station of the present invention that may be controlled in an automated way by a cleaning control station. 
     FIG. 1C shows a more detailed schematic of an exemplary wafer cleaning station, in accordance with one embodiment of the present invention. 
     FIG. 2A illustrates a simplified three-dimensional diagram of a pair of brushes scrubbing a top surface and a bottom surface of a wafer, in accordance with one embodiment of the present invention. 
     FIGS. 2B and 2C illustrate cross-sectional views of two different orientations for scrubbing a wafer, in accordance with one embodiment of the present invention. 
     FIG. 3 illustrates a three-dimensional view of a brush core, in accordance with one embodiment of the present invention. 
     FIGS. 4A through 4C illustrate alternative channel geometries for a tubular core, in accordance with one embodiment of the present invention. 
     FIG. 5A shows a cross-sectional view of the brush core, in accordance with one embodiment of the present invention. 
     FIGS. 5B and 5C illustrate cross-sectional views A—A and B—B along a brush core, in accordance with one embodiment of the present invention. 
     FIG. 6 illustrates a simplified diagram of a plurality of channels having a plurality of holes, in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An invention is described for a brush core for use in scrubbing substrates. The substrate can be any substrate that may need to undergo a scrubbing operation to complete a cleaning operation, etching operation, or other preparation. 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. 1B shows a wafer cleaning station  100  of the present invention that may be controlled in an automated way by a cleaning control station  102 . The wafer cleaning station  100  includes a sender station  104 , a cleaning stage  106 , a spin-rinse and dry (SRD) station  108 , and a receiver station  110 . As a broad overview of the cleaning process, semiconductor wafers are initially placed into the sender station  104 . The sender station  104  then delivers a wafer (one-at-a-time) to the cleaning stage  106 . In one embodiment, the cleaning stage  106  is divided into a first cleaning stage  106   a  and a second cleaning stage  106   b , although having just one cleaning stage  106  will also work. After passing through the cleaning stage  106 , the wafer is passed through an exit spray in order to remove the cleaning fluids and any contaminants. The SRD station  108  dries the wafer and then it is delivered to the receiver station  110  for temporary storage. FIG. 1C shows a more detailed schematic of an exemplary wafer cleaning station  100 . Both the sender station  104  and the receiving station  110  are preferably adapted to receive a cassette containing a number of wafers. The first and second leaning stages  106   a  and  106   b  preferably include a set of PVA brushes  120  that are very soft and porous. As will be described below, the brushes  120  are mounted on brush cores  200  of the present invention. As is well known, the brushes  120  are capable of scrubbing the wafer clean without damaging the delicate surface. 
     FIG. 2A illustrates a simplified three dimensional diagram of a pair of brushes  120   a  and  120   b  for scrubbing a top surface and a bottom surface, respectively, of a wafer  130 . Typically, the wafer  130  is caused to rotate in a particular direction while the brushes  120  rotate around an axis of rotation while the surface of the brushes  120  are in contact with the surfaces of the wafer  130 . The brushes  120   a  and  120   b  are mounted on brush cores  200   a  and  200   b . The brush cores  200  are configured to have at one end, a fluid inlet  201  which connects to tubing  202 . The tubing  202  will thus supply the desired fluids to a bore  270  within the brush core  200 . The brush core  200 , as will be described in greater detail below, will have a plurality of holes  260  that will allow the fluids provided into the bore  270  to uniformly exit the brush core  200  (i.e., therefore evenly supplying the desired fluid to the brushes  120 ). 
     FIGS. 2B and 2C illustrate cross-sectional views of two different orientations for scrubbing a wafer  130 , in accordance with one embodiment of the present invention. As shown in FIG. 2B, the wafer is held horizontally while a top brush  120   a  scrubs the top surface of the wafer  130 , and a bottom brush  120   b  scrubs the bottom surface of the wafer  130 . As mentioned above, the wafer  130  is configured to rotate (using rollers not shown) at the same time that the brushes  120  rotate to ensure that the entire surface area of the wafer is properly scrubbed to remove contaminants or etch the surface to a desired degree. Thus, FIG. 2B illustrates a horizontal wafer scrubber  100   b . In contrast, FIG. 2C illustrates a vertical wafer scrubber  100   c  in which the wafer  130  is scrubbed while in a vertical position. Typically, the wafer  130  sits on a pair of rollers of the scrubber  100   c . The brushes  120  are configured to rotate in a desired direction such that both sides of the wafer  130  are evenly scrubbed, using an equal and opposite pressure on each side of the wafer  130 . For more information on vertical wafer scrubbing, reference may be made to U.S. Pat. No. 5,875,507, having inventors Stephens et al., entitled “Wafer Cleaning Apparatus,” which is hereby incorporated reference. 
     FIG. 3 illustrates a three-dimensional view of a brush core  200 , in accordance with one embodiment of the present invention. The brush core  200  is defined by a tubular core  250  that extends between a first end  253  and a second end  251 . The tubular core is configured to include, in one embodiment, a plurality of channels  252  which are recessed into the surface of the tubular core  250 . One feature of the present invention is to ensure that an even distribution of fluid is provided throughout the brush core  200 . For instance, a fluid source  263  supplies fluid by way of tubing (not shown) into the bore  270  of the tubular core  250  such that the fluid is evenly distributed to each of the plurality of holes  260 . In a preferred orientation, the plurality of holes  260  of one channel  252  are arranged in an offset configuration relative to holes defined in an adjacent respective channel  252 . 
     For instance, one channel may include a first plurality of holes  260  aligned along a first line across the length of the tubular core  250 , and the next channel that is adjacent to the first channel will have its plurality of holes  260  defined along a second line across the length of the tubular core  250 . However, the holes  260  defined in the adjacent channel  252  will be offset relative to the holes of its respective adjacent channel  252 . In a preferred embodiment, the holes  260  will be evenly spaced apart and defined along the channel  252  that traverses the length of the tubular core  250 . As shown, the holes  260  of the adjacent channel are shifted by an amount that is equal to about half of the separation distance between the holes of the first channel. In one embodiment, the offset can be any amount so long as some offset is provided. In this manner, any fluid provided by the fluid source  263  into the bore that is defined through the tubular core  250  will evenly distribute into the bore and emanate out from all of the plurality of holes defined through the tubular core  250 . 
     In this example, the first end  253  of the brush core  200  includes a threaded insert  262  and an extension  264 . This threaded insert  262  and extension  264  are configured to provide a way to connect up to an appropriate fluid line which will deliver fluids (e.g., chemicals, DI water, or mixtures of fluids) to the bore  270  of the tubular core  250 . The second end  251  of the brush core  200  includes a connection hole  256  for holding the second end of the brush core  200  in place when it is installed into a suitable brush box mechanism. Also shown are a plurality of locking pin holes  254  for engaging the tubular core  250  and enabling the application of a torque rotation to the brush core when the brush box requires the brush core to rotate about a defined axis. 
     FIGS. 4A through 4C illustrate alternative channel geometries for the tubular core  250 , in accordance with one embodiment of the present invention. As shown in FIG. 4A, a radial channel  252  can be defined into the tubular core  250  so that when the brush  120  is mounted on the brush core  200 , any fluid provided through the plurality of holes  260  can be distributed along the channel and the length of the tubular core  250 . FIG. 4B illustrates an alternative embodiment of the channel  252   a  in which a slotted channel is provided to achieve the distribution of the fluids along the length of the tubular core  250 . In certain embodiments, it may be desired to eliminate the channel altogether as shown in FIG. 4C, and rely upon the very porous nature of the PVA brush which will absorb and evenly distribute the fluids throughout the brush. It should be understood that the actual shape or geometry of the channel can be varied or eliminated altogether if desired, for the particular application. 
     FIG. 5A shows a cross-sectional view of the brush core  200 , in accordance with one embodiment of the present invention. As shown in this example, the brush core  200  will include a bore  270  which is defined along an inner length of the tubular core  250 . The plurality of holes  260  illustrated along the top of the cross section are shown to be offset relative to the plurality of holes  260  defined along the bottom of the cross-sectional view. This offset design is configured to allow the even distribution of a fluid flow through the entire length of the bore  270 , and thus allow an equal outflow of the fluid flow through each of the plurality of holes  260 . That is, the present design is configured to allow a fluid flow having a reduced pressure to rapidly fill the bore  270  and reach equilibrium such that an equal flow of fluid will emanate from the plurality of holes  260  around the entire brush core  200 . Thus, holes such as  260   a  defined near the first end  253  of the brush core  200  will exhibit about the same outflow of fluids as holes such as  260   b  defined at the second end  251  of the brush core  200 . 
     FIGS. 5B and 5C illustrate cross-sectional views  5 B— 5 B and  5 C— 5 C along the brush core  200 , in accordance with one embodiment of the present invention. In this example, FIG. 5B illustrates the cross-sectional view of cross section  5 B— 5 B, and shows how the holes  260  are arranged around the tubular core  250 . In this example, holes are defined around the tubular core  250  at 12 o&#39;clock, 2 o&#39;clock, 4 o&#39;clock, 6 o&#39;clock, 8 o&#39;clock, and 10 o&#39;clock. However, at cross section  5 B— 5 B, only holes  260  at  12  o&#39;clock, 4 o&#39;clock, and 8 o&#39;clock, are exposed to the fluid flow that travels down the bore  270 . 
     Because of the offset nature of the plurality of holes  260  that are defined along lines of the tubular core  250 , a cross-sectional view at  5 C— 5 C shown in FIG. 5C, illustrates that the holes at 2 o&#39;clock, 6 o&#39;clock, and 10 o&#39;clock are now exposed to the fluid flow. In a preferred embodiment, the bore  270  will have a diameter ranging between about 0.060 inch and about 0.35 inch, and more preferably, between about 0.125 inch and about 0.30 inch, and most preferably at about 0.25 inch. It should be noted that the diameter of the bore  270  is substantially smaller than that typically used or suggested for brush cores of the prior art. By reducing the diameter of the bore  270  to such a reduced diameter, it has been tested that the fluid flow that enters the bore  270  will rapidly fill the volume of the bore  270  within the brush core  250 . 
     Because the volume within the bore  270  is rapidly filled, the bore  270  will be pressurized rapidly and the fluid will be ready to quickly outflow through the plurality of holes  260  all the way around the surface of the tubular core  250 . In this preferred embodiment, each of the plurality of holes  260  should have a diameter ranging between about 0.005 inch and about 0.092 inch, and most preferably, about 0.050 inch. It should be noted that the diameter of each of the plurality of holes  260  is also substantially reduced, which is configured in conjunction with the reduced bore  270  diameter to distribute any fluid flow delivered to the brush core  200  in a more even and distributed manner throughout the entire length of the brush core  200 . As discussed above, this is a substantial improvement in the art considering that the TTB fluid delivery is now being used to deliver sophisticated chemicals that are designed to alter the surface materials on a given substrate. For example, when chemistries including HF are applied to semiconductor wafer surfaces in an effort to etch certain material layers or films, an uneven application of such chemicals can cause surface damaging surface variations. 
     Continuing with the preferred design characteristics of a brush core  200 , when the brush core  200  is designed for a 300 mm wafer scrubbing application, the brush core may have six channels  252  around the tubular core  250 . Of course, more or less channels may be used (e.g., ranging between 2 and 12 channels). The total length L A  of the exemplary brush core  200  is about  14  inches, and the brush  120  will thus have a length L B  of about 13 inches. In this embodiment, the length L C  of the channel  252  will be about 11 inches. Again, it should be understood that the length of the brush core  200  can vary and the number of holes within the channels  252  can also vary. 
     FIG. 6 illustrates a simplified diagram of a plurality of channels  252  having a plurality of holes  260 , in accordance with one embodiment of the present invention. In the case where six channels are provided, a channel will be provided at 12 o&#39;clock, 2 o&#39;clock, 4 o&#39;clock, 6 o&#39;clock, 8 o&#39;clock, and 10 o&#39;clock. As shown, the orientation of the plurality of holes  260  along the channels for 12 o&#39;clock, 4 o&#39;clock, and 8 o&#39;clock begin at the same location of their respective channel  252 . Each of the plurality of holes  260  are separated by a separation distance S. In one embodiment, the separation distance is about 1.26 inch. 
     The separation distance S is selected such that an even spacing can be distributed along the distance of a selected channel. Thus, if the channel is longer or shorter, the separation S will be modified to meet the desired length of a given channel. In the exemplary embodiment of the present invention, the channel length is about 11 inches, and therefore the separation between each of the plurality of holes  260  is as described above about 1.26 inch. The holes in the adjacent channels  252  defined at 2 o&#39;clock, 6 o&#39;clock, and 10 o&#39;clock, are offset relative to the holes of the first plurality of channels defined at 12 o&#39;clock, 4 o&#39;clock, and 8 o&#39;clock. 
     This offset is preferably about half the distance of the separation parameter S. As pictorially illustrated, the offset between the channel of 12 o&#39;clock and 2 o&#39;clock is defined by an offset separation (OS) of about 0.63 inch. It should be understood that these parameters are only exemplary in nature and may be modified so long as some offset orientation is maintained to ensure even distribution of a fluid that may be provided into the bore  270 . 
     It is again noted that the brush core of the present invention can be modified for use in scrubbing any number of substrate types, for example, semiconductor wafers, hard drive discs, flat panel displays, and the like. Additionally, the brush core can be modified for substrate scrubbing applications of any size, for example, 100 mm wafers, 200 mm wafers, 300 mm wafers, larger wafers, small hard disks, etc. It should also be noted that any number of fluids can be delivered through the brush (TTB), for example, DI water, ammonia containing chemical mixtures, HF containing chemical mixtures, surfactant containing chemical mixtures, and many other variations. 
     For more information on wafer scrubbing brush technology, reference can be made to U.S. Pat. No. 5,806,126, having inventors de Larios et al., entitled “Apparatus For A Brush Assembly,” and U.S. patent application Ser. No. 09/112,666, having inventors Vail et al., entitled “Brush Interflow Distributor.” This U.S. Patent and U.S. Patent Application are hereby incorporated by reference. 
     For additional information on wafer preparing systems and techniques, reference may be made to commonly owned U.S. patent application Ser. No. (1) 08/792,093, filed Jan. 31, 1997, now U.S. Pat. No. 5,858,109, entitled “Method And Apparatus For Cleaning Of Semiconductor Substrates Using Standard Clean 1 (SC1),” (2) Ser. No. 08/542,531, filed Oct. 13, 1995, now U.S. Pat. No. 5,806,128, entitled “Method and Apparatus for Chemical Delivery Through the Brush,” and (3) Ser. No. 09/277,712, filed Mar. 26, 1999, entitled “Pressure Fluctuation Dampening System.” All three U.S. patent applications are hereby incorporated by reference. 
     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 may 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.