Abstract:
A system for cleaning a substrate with a foam performs a method for generating a cleaning foam. In the first operation of the method, the system pumps a fluid into a premix chamber. The premix chamber is a component of a male plug which fits into a female housing in the system. Then the system injects a gas into the premix chamber to initiate generation of the foam from the fluid. The foam flows from the premix chamber into a sealed helical channel formed by a helical indentation on an outside surface of the male plug and an inner surface of the female housing to allow the foam to reach a desired state along a length of the sealed helical channel. In the last operation of the method, the foam outputs from an exit end of the helical channel through the male plug to a component of the system.

Description:
CLAIM OF PRIORITY 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 12/185,780, entitled “Generator for Foam to Clean Substrate,” which was filed on Aug. 4, 2008, and was published on Feb. 4, 2010, as U.S. Published Patent Application No. 2010/0024842, whose disclosure is hereby incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    As described in numerous published patent applications, a system has been developed for cleaning particles from a semiconductor wafer with a high viscosity, non-Newtonian fluid deposited at a low velocity. See e.g., U.S. Published Patent Application No. 2006/0283486 entitled “Method and Apparatus for Cleaning a Substrate Using Non-Newtonian Fluids,” filed on Jun. 15, 2005, U.S. Published Patent Application No. 2006/0128590 entitled “Method for Removing Contamination from a Substrate and for Making a Cleaning Solution,” filed on Feb. 3, 2006, and U.S. Published Patent Application No. 2006/0128600 entitled “Cleaning Compound and Method and System for Using the Cleaning Compound,” filed on Feb. 3, 2006, all of which are hereby incorporated by reference. 
         [0003]    In particular implementations, the high viscosity, non-Newtonian fluid is a foam created by mechanically mixing a gas (such as nitrogen) and a fluid (an aqueous solution with a surfactant such as a fatty acid capable of forming micelles) in the microchannels formed by a packet of thousands of sapphire beads (e.g., approximately 1 mm in diameter). 
         [0004]    There are considerable drawbacks to such implementations. Sapphire beads are relatively expensive and react with the foam. Moreover, bead packets tend to clog fairly frequently and take considerable time and expense to clean. 
         [0005]    As a result of these drawbacks, there is a need to provide an inexpensive, readily maintainable apparatus, method, and system for mechanically generating a foam to clean a substrate (e.g., a semiconductor wafer). 
       SUMMARY 
       [0006]    Example embodiments include apparatuses, systems, and methods directed to mechanically generating a foam to clean a substrate. In one example embodiment, a device includes a female housing and a male plug. The plug includes an aperture into which a fluid flows from another part of the cleaning system. The plug includes a premix chamber which receives the fluid from the aperture and into which a gas such as nitrogen is injected to form an initial foam. In one particular example embodiment, the chamber is a hollow cylinder and the gas is injected into the cylinder through channels which are tangential to the cylinder. Additionally, the plug includes a solid cylinder with a continuous helical indentation on the outside of the solid cylinder. When the male plug is inserted into the female housing, the continuous helical indentation and the inner surface of the housing form a sealed helical channel through which the initial foam flows and is further mixed as the foam makes its way to another aperture which connects the plug to another component of the cleaning system, e.g., a proximity head where the final foam is applied to a semiconductor wafer. In one particular example embodiment, the plug and the housing are proximate to the proximity head where the final foam is applied to the semiconductor wafer, e.g., the plug and housing are located at the point of use of the final foam. In another example embodiment, the plug and housing are located away from the point of use of the final foam in another part of the cleaning system (e.g., in an onboard fluid delivery system). 
         [0007]    The advantages of the present invention will become apparent from the following detailed description, which taken in conjunction with the accompanying drawings, illustrates by way of example the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a diagram illustrating a perspective view of a male plug, in accordance with an example embodiment. 
           [0009]      FIG. 2  is a diagram illustrating a sectional view of a male plug, in accordance with an example embodiment. 
           [0010]      FIG. 3  is a diagram illustrating a cross-sectional view of a premix chamber in a male plug, in accordance with an example embodiment. 
           [0011]      FIG. 4  is a diagram illustrating a sectional view of a male plug and female housing, in accordance with an example embodiment. 
           [0012]      FIG. 5  is a diagram illustrating a sectional view of a male plug and female housing in a point-of-use system, in accordance with an example embodiment. 
           [0013]      FIG. 6A  is a diagram illustrating a perspective view of a male plug and female housing in a point-of-use system, in accordance with an example embodiment. 
           [0014]      FIG. 6B  is a simplified schematic diagram showing a pair of male plugs in a point-of-use system, in accordance with an example embodiment. 
           [0015]      FIG. 6C  is a simplified schematic diagram showing a processing station, in accordance with an example embodiment. 
           [0016]      FIG. 7  is a diagram illustrating a perspective view of a male plug and female housing in an onboard fluid delivery system, in accordance with an example embodiment. 
           [0017]      FIG. 8  is a diagram illustrating two independent variables, channel cross section and channel length, which were tested in example embodiments. 
           [0018]      FIG. 9  is a table showing the results of the tests with respect to channel cross section and channel length, for example embodiments. 
           [0019]      FIG. 10  is a table showing a comparison of the foam generator with a plug and housing and a foam generator with a long bead pack. 
           [0020]      FIG. 11  is a plot of a time series showing back pressure for an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the example embodiments. However, it will be apparent to one skilled in the art that the example embodiments may be practiced without some of these specific details. In other instances, implementation details and process operations have not been described in detail, if already well known. 
         [0022]      FIG. 1  is a diagram illustrating a perspective view of a male plug, in accordance with an example embodiment. In  FIG. 1 , the male plug  101  includes an aperture  102  into which a fluid (e.g., P2) is input or pumped by a system for cleaning a substrate (e.g., a semiconductor wafer). In particular example embodiments, the flow rate for the fluid might be 5 mL/m to 50 mL/m. From the aperture  102 , the fluid flows into a premix chamber  103 , where the fluid is injected with a gas (e.g., N2 or nitrogen) to form an initial foam. In particular example embodiments, the flow rate for the injected gas might be 50 sccm to 500 sccm. From the premix chamber  103 , the initial foam flows through the continuous helical indentation  104  on an outer surface of the plug to the aperture  105 , which outputs a final foam (e.g., P3) to the cleaning system. In this figure, the term “P2” refers to the two phases of matter that are present in the input fluid, e.g., liquid water and solid surfactant. The term “P3” refers to the three phases of matter that are present in the output foam, e.g., liquid water, solid surfactant, and gaseous nitrogen. It will be appreciated that P3 is a high viscosity, non-Newtonian fluid. 
         [0023]    In particular example embodiments, the male plug might be made from a highly nonreactive thermoplastic such as polyvinylidene chloride (PVDF) or KYNAR (also called HYLAR or SYGEF). In other alternative example embodiments, the plug might be made of ethylene chlorotrifluoroethlyene (ECTFE) or halar. It will be appreciated that it might be beneficial to match the material used to make the male plug with the material used to make the female housing (e.g., the male plug and the female housing would then have the same coefficient of thermal expansion). 
         [0024]      FIG. 2  is a diagram illustrating a sectional view of a male plug, in accordance with an example embodiment. In  FIG. 2 , the male plug  101  includes a premix chamber  103  which has a hollow core and which contains numerous perforations  106  on the outside surface of the premix chamber  103 , which permit the input of a gas (e.g., nitrogen), as described further below. The male plug  101  also includes an aperture  102  into which a fluid (e.g., P2) enters the premix chamber  103  and an aperture  107  from which an initial foam (e.g., nitrogen and P2) exits the premix chamber  103 . After exiting the premix chamber, the initial foam passes through the continuous helical indentation  104  on an outer surface of the plug. As depicted in  FIG. 2 , the plug beneath the continuous helical indentation is solid, to provide structural support. However, in other example embodiments, the plug beneath the continuous helical indentation might also have a hollow core. Once the initial foam traverses the channel formed by the continuous helical indentation, the initial foam emerges as a final foam (e.g., P3) which enters the aperture  105  and proceeds to another component of the cleaning system, e.g., a proximity head where the foam is delivered at low velocity to a substrate. 
         [0025]    In particular example embodiments, such a proximity head is proximate to the male plug  101  and the housing for the plug. That is, the plug  101  and the housing generate a foam at the point of use of the foam. However, in particular example embodiments, the final foam (e.g., P3) will maintain its mixture (e.g., its bubbles) for a relatively long period of time when confined in a sealed passageway (e.g., a tube) and the foam might be transported through such a passageway to a proximity head which is relatively distant from the plug  101  and housing (e.g., in an onboard fluid delivery system). 
         [0026]      FIG. 3  is a diagram illustrating a cross-sectional view of a premix chamber in a male plug, in accordance with an example embodiment. In  FIG. 3 , the male plug  101  includes aperture  102  which allows entry of a fluid (e.g., P2) to a premix chamber  103 . As depicted in  FIG. 3 , the premix chamber  103  has numerous small perforations which are channels for the injection of a gas (e.g., nitrogen) and which follow a specific pattern. As indicated in the annotation on the right side of  FIG. 3 , the pattern is created by rotating by 15 degrees a set of eight equidistant channels (e.g., with each channel 45 degrees from its two neighboring channels) which are coplanar in a cross-sectional plane. The rotation is shown pictorially in the cross-sections  108  and  109  on the left side of  FIG. 3 . Cross-section  108  (e.g., B-B from  103 ) shows eight equidistant channels prior to the rotation by 15 degrees. Cross-section  109  (e.g., C-C from  103 ) shows eight equidistant channels after rotation by 15 degrees. Cross-sections  108  and  109  also illustrate the hollow core of the premix chamber  103 . It will be appreciated that the fluid (e.g., P2) flows through this hollow core. It will further be appreciated that the eight equidistant channels are located tangential to this hollow core, e.g., the arrangement between the hollow core and the channels is not akin to a hub and spokes. In particular example embodiments, the tangential location of the channels and the pattern (e.g., rotation by 15 degrees) facilitate the creation of a vortex within the premix chamber  103  and the vortex facilitates mixing of the fluid (e.g., P2) and gas (e.g., nitrogen). 
         [0027]    In an alternative example embodiment, the pattern for the perforations might be created by rotating by 15 degrees a set of 6 or 10 equidistant channels, rather than 8. Similarly, in an alternative example embodiment, the rotation might be more (e.g., 20-25 degrees) or less (e.g., 5-10 degrees) than 15 degrees. 
         [0028]      FIG. 4  is a diagram illustrating a sectional view of a male plug and female housing, in accordance with an example embodiment. In  FIG. 4 , the male plug  101  fits tightly into the female housing  112 , creating a sealed helical channel  113  which facilitates further mixing of the initial foam into a final foam (e.g., P3). In particular example embodiments, the cross-sectional dimensions of the sealed helical channel might be approximately 0.06 inch×0.04 inch per section. In alternative example embodiments, the cross-sectional dimensions of the sealed helical channel might be approximately 0.06 inch×0.06 inch per section. It will be appreciated that a sealed helical channel with larger cross-sectional dimensions is more difficult to clog. Also depicted in  FIG. 4  is a tube  110  through which a fluid (e.g., P2) enters into the plug  101  and a tube  111  through which a gas (e.g., nitrogen) enters the premix chamber of the plug  101 . A final foam (e.g., P3) leaves the plug  101  through another tube  114 . 
         [0029]    It will be appreciated that final foams (e.g., P3) of different qualities are useful for different purposes, where quality might be defined as the volume of gas divided by the volume of gas and liquid on a scale that goes from 0% (no N2 and all P2) to 98% (100 sccm N2 and 2.5 mL/m P2). Further, as described below, for a given quality of foam (e.g., 80%), the surface and bulk size of bubbles in the foam and the surface and bulk spacing of bubbles in the foam is a function of the length (or distance) of the helical channel, where a longer length tends to produce bubbles that are smaller in surface and bulk size and smaller in surface and bulk spacing (e.g., closer together) for a given quality. 
         [0030]      FIG. 5  is a diagram illustrating a sectional view of a male plug and female housing in a point-of-use system, in accordance with an example embodiment. In  FIG. 5 , the male plug  101  fits tightly into female housing  112 , from which the male plug  101  can be readily removed for cleaning (e.g., with deionized water) or other maintenance.  FIG. 5  shows a premix chamber  103  with an inlet  115  for P2 and an inlet  116  for nitrogen, which are alternative inlets to the inlets depicted in  FIG. 4 .  FIG. 5  also shows the aperture  105  through which the final foam (e.g., P3) flows toward the proximity head which will be used to deposit the P3 on a substrate (e.g., a semiconductor wafer). In particular example embodiments which generate the final foam (e.g., P3) at the point of use of the foam, the proximity head might be located immediately to the left of  FIG. 5 , as described further below. 
         [0031]      FIG. 6A  is a diagram illustrating a perspective view of a manifold with two male plugs in a point-of-use system, in accordance with an example embodiment. In  FIG. 6A , manifold  117  includes two male plugs  101  which provide final foam (e.g., P3) to a proximity head which is to the upper right outside of  FIG. 6A .  FIG. 6A  also shows the transmission pipe  118  for the P2 fluid and the transmission pipe  119  for the nitrogen for the male plugs  101 . It will be appreciated that this perspective view does not show the female housings for the male plugs  101 , for purposes of exposition. However, the arrangement of components in  FIG. 6A  is similar to the arrangement of components in  FIG. 5 . 
         [0032]      FIG. 6B  is a simplified schematic diagram showing a pair of male plugs in a point-of-use system, in accordance with an example embodiment. In  FIG. 6B , the pair of male plugs  101  (the female housings are not shown) generate and transmit foam to upper and lower proximity heads  121 , which are located nearby in a processing station  120 . The proximity heads  121  then deposit the foam, through the use of a meniscus  124 , at a low velocity on a semiconductor wafer  122  carried by a wafer carrier  123 . It will be appreciated that by generating the foam close to the foam&#39;s point of use in the meniscus  124 , the system transmits the foam only a short distance, which is advantageous since the foam might be a highly viscous, non-Newtonian fluid, in a particular example embodiment. 
         [0033]      FIG. 6C  is a simplified schematic diagram showing a processing station, in accordance with an example embodiment. In  FIG. 6C , a male plug  101  is connected to a proximity head  121  (the female housing is not shown) in a processing station  120 . The male plug  101  is also connected to a fluid supply  125  and a gas supply  126 , which are located in facilities which might be some distance away from the processing station  120 , in a particular example embodiment. It will be appreciated that the male plug  101  in  FIG. 6C  is nonetheless a component in a point-of-use system, since it is located close to proximity head  121 , where the foam generated by the male plug  101  will be delivered at low velocity to a semiconductor wafer. 
         [0034]      FIG. 7  is a diagram illustrating a perspective view of a male plug and female housing in an onboard fluid delivery system, in accordance with an example embodiment. As shown in  FIG. 7 , the onboard fluid delivery system  127  includes numerous components, including two male plugs  101 . In particular example embodiments, the onboard fluid delivery system might be located in a cabinet beneath the proximity head that delivers the final foam (e.g., P3) to the substrate. It will be appreciated that in such a system the final foam (e.g., P3) is not generated at the point of use of the foam, though, as described above, the foam could still have small surface and bulk bubble size and small surface and bulk bubble spacing, if so desired. 
         [0035]      FIG. 8  is a diagram illustrating two independent variables, channel cross section and channel length, which were tested in example embodiments. In  FIG. 8 , test male plug  801  has a sealed helical channel with a cross section of 0.07 inch×0.06 inch, whereas test male plug  802  has a sealed helical channel with a cross section of 0.07 inch by 0.07 inch. In  FIG. 8 , test male plug  803  has a sealed helical channel which is 1 inch longer than test male plug  804  (e.g., 2.25 inch of “non-helical tubing”−1.25 inch of “non-helical tubing”). 
         [0036]      FIG. 9  is a table showing the results of the tests with respect to channel cross section and channel length, for example embodiments. In this table, the column labeled “Generator, one inch shorter” corresponds to  FIG. 803  in  FIG. 8  and the column labeled “Generator, two inch shorter” corresponds to  FIG. 804  in  FIG. 8 ; that is, the column labeled “Generator, one inch shorter” corresponds to a sealed helical channel which is one inch longer. It will be appreciated that the table demonstrates that longer channel length (or distance) produces bubbles of smaller size (e.g., surface and bulk) and spacing (e.g., surface and bulk) through the forces (e.g., friction, pressure, etc.) acting upon the foam (e.g., water, surfactant, and nitrogen). For a given foam quality (e.g., 80%), a generator whose sealed helical channel is one-inch longer tends to make bubbles with smaller surface bubble size (e.g., 134 versus 171 micrometers) and bulk bubble size (e.g., 189 versus 193 micrometers). Also, for the same foam quality (e.g., 80%), a generator whose sealed helical channel is one-inch longer tends to make bubbles with smaller surface bubble spacing (e.g., 316 versus 525 micrometers) and bulk bubble spacing (e.g., 209 versus 234 micrometers). 
         [0037]      FIG. 10  is a table showing a comparison of the foam generator with a plug and housing and a foam generator with a long bead pack. For a given foam quality (e.g., 91%) and given amounts of gas and fluid (e.g., 400 sccm of N2 and 40 mL/m of P2), the foam generator with the plug and housing tends to make bubbles with an average surface bubble size that is comparable to the long bead pack (134 versus 131 micrometers). For the same foam quality and amounts of gas and fluid, the foam generator with a plug and housing tends to make bubbles with an average surface bubble spacing that is comparable to the long bead pack (318 versus 265 micrometers). 
         [0038]      FIG. 11  is a plot of a time series showing back pressure for an example embodiment. As shown by this plot, the foam generator with a plug and housing tends to have a constant back pressure (e.g., PSI) as time progresses, which, in turn, tends to show that the foam generator has constant flow, e.g., the foam generator is not clogging. It will be recalled that clogging was a problem with the foam generator employing a bead pack. 
         [0039]    Although the foregoing example embodiments have 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. For example, the continuous helical indentation might be located on the female housing rather than the male plug, in alternative example embodiments. Furthermore, the invention as described herein might be used in other applications involving mechanical foam generation (e.g., in applications involving foams for oil and gas well drilling, culinary foams, and cosmetic foams). Accordingly, the example 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.