Abstract:
The present invention is a bubbler having a diptube inlet ending in a bubble size reducing outlet and at least one baffle disc positioned between the outlet of the diptube and the outlet of the bubbler to provide a narrow annular space between the baffle disc and the wall of the bubbler to prevent liquid droplets from entering the outlet to the bubbler. The bubble size reducing outlet is an elongated cylindrical porous metal frit situated in a sump of approximately the same dimensions. A metal frit is placed at the inlet of the outlet of the bubbler. The present invention is also a process of delivering a chemical precursor from a bubbler vessel having the above structure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 11/939,109, filed on Nov. 13, 2007, which claims the benefit of priority under 35 U.S.C. §119(e) to U.S. provisional patent applications 60/875,200 filed Dec. 15, 2006 and 60/908,376 filed Mar. 27, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The electronics fabrication industry uses chemical precursor containers that convert liquid chemicals into chemical vapor for delivery to electronics fabrication reactors, i.e. tools, for conducting chemical vapor deposition (“CVD”). CVD is a favored technique for forming layers, films and other depositions in the construction of electronic fabrications such as integrated circuits or computer chips. Liquids or solids are preferred as sources of supply because of the efficiency of transport and storage of a volume of chemical precursor, but the industry frequently prefers to actually deliver the chemical precursor at the site of the tool in the form of a vapor, i.e. CVD. Alternatively, some fabrications are conducted using direct liquid injection (“DLI”), although even then, the liquid is vaporized in the tool after delivery. 
         [0003]    When using vapor delivery for CVD, the containers typically have an inert carrier gas passed through them or bubbled, i.e., bubbler, to carry entrained chemical precursor vapor in the inert carrier gas to the tool. Bubblers typically have a downtube inlet where the carrier gas is introduced into the container under the surface of the liquid chemical precursor wherein the carrier gas bubbles up through the liquid chemical precursor, entraining the chemical precursor as the carrier gas surfaces the liquid as a bubble and exits the container or bubbler by an outlet set above the liquid level of the chemical precursor. 
         [0004]    It is undesirable to have the chemical precursor leave the container through the outlet in the liquid form, even as small droplets. A homogenous vapor is preferred as the dispensed product of such bubblers. This avoids corrosion, cleanup, and uneven flow, especially through mass flow controllers which control the flow of chemical precursor from the bubbler to the tool in a precisely metered fashion. 
         [0005]    The industry has attempted various forms of splashguards for bubblers to address this issue, such as in: U.S. Pat. No. 6,520,218; EP 1 329 540; US 2004/0013577; EP 0 420 596; U.S. Pat. No. 5,589,110; U.S. Pat. No. 7,077,388; US 2003/0042630; U.S. Pat. No. 5,776,255; and U.S. Pat. No. 4,450,118. Each of these attempts to provide splashguard function has had less than desired performance, but the present invention as disclosed below successfully provides high levels of splashguard function, while still allowing high flows of chemical precursor or flows under high vacuum or high pressure differential conditions as will be described and illustrated below. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a bubbler for storing a volatile liquid chemical and delivering vapor of the volatile liquid chemical to a vapor deposition process when under vacuum, the bubbler comprising a cylindrical inside wall having a diameter, a floor, a diptube inlet ending in an outlet proximate the floor and at least one baffle disc positioned between the outlet of the diptube and an outlet of the bubbler, wherein the at least one baffle disc has a circumferential edge and a diameter slightly less than the diameter of the inside wall such that the space between the circumferential edge of the baffle disc and the cylindrical inside wall is sufficient to allow the vapor of the volatile liquid to pass through the space with minimum pressure drop, but sufficiently narrow to minimize the passage of liquid that may be ejected from a volatile liquid content under vacuum conditions and high flow rates of a carrier gas through the diptube, wherein the at least one baffle disc is solid and has a concave downward shape to collect condensed volatile liquid chemical for return by coalesced droplets that fall back into the stored volatile liquid chemical, wherein in operation under vacuum conditions, the bubbler is capable of preventing liquid droplets from entering the outlet of the bubbler. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic side view of a first embodiment of the present invention. 
           [0008]      FIG. 2  is a schematic side view of a second embodiment of the present invention. 
           [0009]      FIG. 3  is a detailed schematic side view of the second embodiment of the present invention of  FIG. 2 . 
           [0010]      FIG. 4  is a detailed schematic side view of the inner function structures of the second embodiment of the present invention of  FIG. 3 . 
           [0011]      FIG. 5  is a detailed schematic side view of the inner function structures of the second embodiment of the present invention of  FIG. 2  showing a diffuser in a sump configured to the approximate shape of the diffuser. 
           [0012]      FIG. 6  is a detailed schematic side view of the inner function structures of  FIG. 5  showing an alternate elbow outlet  34 . 
           [0013]      FIG. 7  is a detailed schematic side view of the inner function structures of  FIG. 5  showing an alternate “Tee” outlet  36 . 
           [0014]      FIG. 8  is a detailed schematic side view of the inner function structures of  FIG. 4  showing an alternate embodiment where baffle disc  22  has perforations  38 . 
           [0015]      FIG. 9  is a detailed schematic side view of the inner function structures of  FIG. 4  showing an alternate embodiment where baffle disc  24  is constructed of a porous metal frit material. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The present invention is a vapor generation bubbler designed for service in high vacuum or high flowrate conditions. The design prevents splashing and transport of aerosol droplets into the outlet delivery line that would result in erratic chemical mass flow delivery. 
         [0017]    Semiconductor manufacturers are turning to the use of high value chemicals that are increasingly difficult to transport for deposition onto a wafer in a vacuum chamber or tool. The vessel or bubbler of the present invention allows liquid chemical to be delivered from the container or bubbler as a vapor at high vacuum, without the splashing and the formation of aerosol droplets in the outlet of the vessel or bubbler that result in erratic chemical mass delivery rate. The present invention has a lower surface design that enables a constant saturation of a carrier gas with chemical vapor down to very low levels of the residual chemical. Yet, the present invention prevents splashing and the formation of aerosol droplets into the outlet of the bubbler, that would result in erratic chemical mass delivery rate, even when the chemical level in the container is high. Previously, bubblers used for high vacuum service or high flowrate service had to be used with only a partial charge of chemical (i.e.: 50% full). This required the semiconductor manufacturer to change the vessel or bubbler more often (taking down the tool), and added to the cost of the chemical, because of the increased container processing fees. This invention enables use of the bubbler from a full liquid chemical level down to a very low level and reduces semiconductor tool downtime. Also, since it is effective at limiting the chemical aerosol particles in the outlet, it can reduce particulate generation that might result from degradation of the aerosol droplets that deposit in the outlet and all of the delivery piping to the processing chamber or tool. 
         [0018]    Previous bubbler designs addressed the problem of splashing by installing at the bottom of the dip tube, piping, perpendicular to the diptube, with holes drilled along its length. This resulted in smaller bubbles generated over a larger area of the bubbler, which resulted in a less turbulent bubbling action, and therefore, less splashing, but these inventions are impossible to effectively clean for reuse by the chemical supplier. 
         [0019]    The present invention uses porous masses of material, such as porous metal frits, at the outlet of the inlet diptube to break down the size of the bubbles of inert carrier gas entering the liquid chemical precursor in conjunction with one or more baffle discs at the upper part of the vessel or bubbler that requires the carrier gas entrained with chemical precursor to pass indirectly to the outlet of the container or bubbler by flowing tortuously to the outside of the baffle discs in a narrow annular space between the inner diameter of the bubbler inside wall and the outer diameter or circumferential or perimeter edge of the baffle discs. This will be illustrated with reference to several preferred embodiments of the present invention. 
         [0020]      FIG. 1  shows a bubbler  10  of the present invention having a cylindrical bubbler sidewall  12  with a diptube inlet  14  terminating at its inlet end with a porous mass or block outlet, such as a stainless steel frit  18  that operates as a gas diffuser to generate small microbubbles of the inert carrier gas below the surface of the liquid chemical precursor (not illustrated). This reduces the chance of violent bubbling or the splattering of liquid above the headspace or freeboard of the bubbler. The outlet  18  of the bubbler diptube inlet  14  is proximate the floor of the bubbler in a sump  21 , shown in  FIG. 5 . 
         [0021]    In addition, the diptube  14  has a baffle disc  20 , having a circular and concave downward configuration like a shallow cone opening downward, affixed, as by welding, to the upper end of the diptube  14 , to further avoid liquid splattering or large scale liquid entrainment of the carrier gas flowing to the outlet  16 , which is undesired, but which has a greater probability under high flow or high vacuum conditions. 
         [0022]      FIG. 2  shows a second embodiment of the present invention where similar parts have similar part numbers. Here the splash guard comprises two baffle discs, a lower baffle disc  22  and an upper baffle disc  24  having a circular outer edge shape and being concave downward, such as a shallow downwardly open cone, that act in cooperation to make an even more tortuous path for chemical precursor leaving the bubbler  10 . The baffle discs are concave downward to further frustrate direct flow of chemical precursor to the outlet  16  and to collect condensed chemical precursor for return by coalesced droplets falling back into the stored chemical precursor (not illustrated). The baffle discs have a diameter slightly less than the inside diameter of the cylindrical inside wall of the bubbler. The space between the circumferential or perimeter edge of the baffle disc and the inside wall of the bubbler is sufficient to allow gas to pass through the space with minimal pressure drop, but sufficiently narrow to minimize the passage of liquid that may be ejected from the liquid content of the bubbler under high flow rates of carrier gas through the diptube or significant pressure fluctuations. 
         [0023]      FIG. 3  shows a more detailed illustration of the second embodiment of the present invention. Bubbler  10  is shown in cut away with an angled diptube  14  ending in a stainless steel frit outlet  18 , such as a Mott porous stainless steel cup Series 1200, catalog no 1200-A-B-L-Media grade. The two baffle discs  22  and  24  occupy different inside diameter locations in the container sidewall  12  so that the lower baffle disc  22  allows greater annular space from the cylindrical inside surface of the bubbler sidewall  12  for carrier gas and chemical precursor to pass toward the outlet, while upper baffle disc  24  provides less annular space to further avoid liquid entrainment in the outlet and downstream piping from the outlet. 
         [0024]      FIG. 4  shows an isolation of the internal structure of the bubbler of the second embodiment without the sidewall  12  being illustrated. In  FIG. 4 , the diptube inlet  14  and its outlet frit  18  are easily seen and the splash guard comprising baffle disc  22  and  24  are also readily seen with their concave downward shape. 
         [0025]      FIG. 5  shows a specific configuration of the second embodiment of  FIG. 2  in which the gas diffuser outlet  18  is shown as an horizontally disposed elongated cylindrical porous metal frit having a hollow gas passage interior and a porous metal frit outer shell, such as those made by Mott Corporation, Farmington, Conn. 06032, USA. Preferably, the porous metal frit gas diffuser outlet  18  has a media grade rating to filter out particles of 1 micron or larger, preferably filtering out at least 90% of particles 1 micron or larger. 
         [0026]    The gas diffuser outlet  18  of  FIG. 5  is situated in a sump  21  in the base, floor or bottom of the bubbler container  12 . The preferred diffuser  18  is an horizontally disposed elongated cylinder and the sump is thus a partial elongated cylinder open at its upper side to the inside of the bubbler and being of a dimension slightly larger than the elongated cylinder of the diffuser outlet  18 , sufficient to allow gas bubbles of carrier gas to escape the outside of the diffuser outlet  18  and to allow liquid chemical precursor stored in the bubbler or vessel  10  to reside in the sump  21  substantially or completely surrounding the diffuser outlet  18 . Preferably, the diffuser outlet  18  resides entirely with the sump  21 , such that the upper surface of the diffuser is no more than even with the upper edge of the sump wall. The level sensor  28  measures the liquid product level. Inlet  14  is controlled by inlet valve  30 , and outlet  16  is controlled by valve  26 . The goal of  FIG. 5  is to provide adequate flow of gas to entrain liquid product without creating bubbles of such size as to create splashing or violent spitting of the liquid getting to the outlet and downstream of the bubbler. This could contaminate the outlet or create flow problems in any downstream mass flow controller. To further avoid liquid escape from the bubbler, a metal frit  32  can be positioned at an inlet to the outlet  16 . 
         [0027]      FIG. 6  shows the embodiment of  FIG. 5  in which an elbow configuration or shape  34  of the inlet to the outlet  16  is used in place of metal frit  32 . The end of elbow  34  is directed radially inward away from the outer circumferential or perimeter edge of the baffle discs  22  and  24  and toward the axial center of the cylinder formed by the sidewall  12  of the vessel or bubbler  10  to minimize possible liquid introduction into the outlet  16 . 
         [0028]    Similarly,  FIG. 7  shows an alternate to  FIG. 6  wherein the elbow outlet  34  is replaced with a “Tee” shaped or configured inlet  36  to the outlet, again to minimize the possible introduction of liquid into the outlet  16  from the annular space between the baffle discs  22  and  24  and the inside wall of the sidewall  12  of the vessel or bubbler  10 . 
         [0029]    To avoid liquid introduction into the outlet  16 , it is further possible to change the construction of the baffle discs.  FIG. 8  shows lower baffle disc  22  with a plurality of perforations  38  to trap liquid spitting between baffle discs  22  and  24  and return it to the sump of the vessel.  FIG. 9  shows that upper baffle disc  24  is fabricated from porous metal frit material, to again minimize liquid introduction into the outlet  16 . 
         [0030]    The present invention provides superior minimization of liquid entrainment of droplets in the outlet and downstream piping of a bubbler connected to a CVD tool of an electronics fabrication system. Using either a single baffle disc or multiples of the baffle disc, alone or in combination with a diffuser or frit at an outlet to the diptube inlet provides the desired minimization of liquid droplet entrainment in the outlet  16  of the bubbler. 
         [0031]    Although the baffle discs have been shown as circular discs with a concavity where the disc is slightly smaller than the inside diameter of the cylindrical vessel or bubbler sidewall, it is understood that any baffle of any shape which provides only a narrow annular space at the inner sidewall of the vessel or bubbler is within the scope of the present invention. Likewise, any form of device with an array of small passages can be used as the frit or outlet of the diptube of the present invention. 
         [0032]    Although, it is preferred to use stainless steel, it is envisioned that any inert material of rigid form can be used for the splash guard or frit. Plastics, metal alloys, powdered metals, fabrics, textiles and ceramics are all contemplated. 
         [0033]    The vessel  10  can also be used for product flow in the opposite direction where outlet  16  functions as a pressurizing gas inlet to form a pressure head on liquid contained in the vessel  10  and force the liquid in liquid form through the frit  18  and out the diptube  14  for liquid delivery from the vessel using a pressurizing gas, in contrast to the vapor delivery described above.