Abstract:
Methods and apparatus for delivery of high purity reactive liquids using gaseous assist are described, the apparatus comprising a container body, the container body having fluidly connected thereto a gas inlet and a reactive liquid outlet, the gas inlet fitted with a means adapted to hold a gas filter media, and a gas filter media positioned within said means adapted to hold a gas filter media, the gas inlet having a gas inlet valve, the liquid outlet having a liquid outlet valve.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to containers and methods for delivering liquid chemicals to a point of use. Mores specifically, to containers and methods wherein a gaseous media is used to push the liquid chemical out of the container. 
     2. Related Art 
     In certain chemical processes, such as chemical vapor deposition with organometallic precursors (MOCVD), there is often the need to pressurize supply reagent containers with inert gas in order to provide sufficient pressure in the container to deliver the chemical to the chemical vapor deposition tool. The vapor pressure of the liquid chemical at use temperature alone is frequently not sufficient to deliver the chemical to the chemical vapor deposition tool. Heating the chemical to raise its vapor pressure in these cases is not practical and often leads to premature degradation of the precursor chemical. Mechanical pumps may also lead to contamination. 
     It is known practice to introduce inert gas under pressure into a container in order to force chemical out of the container and down a process line. Indeed, certain suppliers advertise integral internal filters for gas delivery cylinders. However, unlike other applications, in MOCVD, the precursor such as pentaethoxy tantalum, zirconium t-butoxide, titanium tetrachloride, and the like, are extremely reactive to air contaminants, particularly moisture, to form metal oxide solids and various other hazardous materials (depending on the compound) often along with large releases of energy. For this reason, even minute traces of air contaminants cannot be tolerated in delivery equipment for such precursor chemicals. Furthermore, there is need to periodically change out supply containers as chemicals are consumed during processing of semiconductors. It is mainly in the change-out of containers where there is greatest potential to contaminate the delivery system and therefore the precursor chemical. For this reason good purge out sequences for delivery systems are required to be carried out as stipulated by semiconductor equipment manufacturers. 
     The need for good purging techniques are required for all air-sensitive compounds, even those with high vapor pressure precursors. However, in the case of low vapor pressure chemicals, the air contaminant issue is much more severe because such contaminants are introduced into the container and hence contaminate the entire container of product after which these contaminants cannot be simply flushed out using a purging manifold. Such contamination can be quite costly to the user since the cost of chemicals involved can reach several thousands of dollars per kilogram. Further, contamination by-products that form are much harder to remove and can leave solid residue on the seals of valves and other components downstream of the container leading to component failure, and possibly to serious health and costly down time risks. 
     To improve the purging operation during container change-outs, better manifolds have been designed over the years (for example, see U.S. Pat. Nos. 5,590,695 and 5,964,254). However, even though better manifold design indeed leads to improved purging efficiency, operationally mishaps can occur from human error, computer controller errors, and component failures. Many compounds can lead to solid residues on valve seals, for example, which in turn leads to valve malfunctions. When such problems occur at chemical container filling locations, the degraded product will be detected in the routine product quality control procedures; however, when it occurs at a user&#39;s site location the problem exhibits itself only after it causes down time and hazardous shut-down scenario. 
     An alternate means of preventing air contamination from entering the container is the use of breakseals (for example, see U.S. Pat. Nos. 4,134,514; 4,140,735; 4,298,037; 4,851,821; 4,966,207; and 4,979,643). As indicated in many previous patents, use of breakseals is indeed quite common in the handling of air-sensitive compounds and does effectively prevent direct contact of air into the container. However, in the case of inefficient purge sequences, component failure, computer control problem or human error, such breakseals will not prevent air contaminants from entering the container. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, containers for delivery of high purity reactive liquids using gaseous assist are presented, as well as methods of use of same. In one embodiment, the container comprises a container body, the container body having fluidly connected thereto a gas inlet and a reactive liquid outlet, the gas inlet fitted with a means adapted to hold a gas filter media, preferably internally in the container, and a gas filter media positioned within the means adapted to hold a gas filter media, the gas inlet having a gas inlet valve, the liquid outlet having a liquid outlet valve. Preferred containers are those wherein the gas filter media is selected from a group consisting of silica, alumina, aluminosilicates; and containers wherein the liquid outlet is fitted with a means adapted to hold a liquid filter media, and a liquid filter media is positioned within the means adapted to hold a liquid filter media. Preferably, the liquid filter media is selected from a group consisting of silica, alumina, aluminosilicates. Other preferred containers are those wherein the means adapted to hold a gas filter media, and the gas filtered media, are integral to the container, and containers wherein the means adapted to hold a gas filter media comprises a conduit having a conduit inlet end positioned in said gas inlet of the container, the conduit having a conduit outlet end. Preferably, the conduit outlet end is internal to the container body. Preferably, the gas filter media is positioned between first and second gas filter media holders, both of the gas filter media holders being porous to gas used in gaseous assist delivery of liquid chemical adapted to be delivered from the container. Yet other preferred containers of the invention include those wherein the body has fluidly connected therewith a degas unit, the degas unit preferably integral with the liquid outlet and internal to the container body. Particularly preferred are containers of the invention wherein the reactive liquid does not make physical contact with the liquid filter media. This may be accomplished by use of means such as check valves, fine porous filter media, or even an elongated or coiled tube, as discussed herein. Also, the gaseous and liquid filter media may be external to the container in certain embodiments, positioned in close proximity to the container top. 
     Another aspect of the invention is a method of delivery of a high purity reactive liquid chemical to a point of use using gaseous assist, the method comprising the steps of: 
     (a) connecting the gas inlet of the inventive container to a source of gas, the container having liquid chemical therein; 
     (b) connecting the liquid outlet of the container to means able to accept the liquid chemical; 
     (c) initiating flow of gas by opening the gas inlet valve; and 
     (d) preventing impurities from entering the container through the gas inlet means. Preferred methods of the invention are those including preventing impurities from leaving the container through the liquid outlet, preferably methods wherein step (d) comprises passing the gas through the gas filter media, the gas filter media selected from a group consisting of silica, alumina, aluminosilicates, and the like. Still other preferred methods are those wherein the step of preventing impurities from leaving the container comprises passing the liquid chemical through a liquid filter media, the liquid filter media preferably selected from the same group of filter media that the gas filter media is selected from. 
     A second method embodiment of delivery of a high purity reactive liquid chemical to a point of use using gaseous assist comprises the steps of: 
     (a) connecting the gas inlet of the inventive container to a source of gas, the container having liquid chemical therein; 
     (b) connecting the liquid outlet of the container to means able to accept the liquid chemical; 
     (c) initiating flow of gas by opening the gas inlet valve; 
     (d) preventing impurities from entering the container through the gas inlet means; and 
     (e) degassing the liquid chemical before the liquid chemical exits the container. Preferred methods within this aspect of the invention are those wherein the method includes preventing impurities from leaving the container through the liquid outlet; methods wherein step (d) comprises passing the gas through the gas filter media, the gas filter media selected from the group consisting of alumina, silica, and aluminosilicates; and methods wherein the step of preventing impurities from leaving the container comprises passing liquid chemical through a liquid filter media. Other preferred methods include those wherein the liquid filter media is selected from the group consisting of silica, alumina, and aluminosilicates. 
     As used herein, the term “integral” means that a component is unable to be removed from the container body without great difficulty by an enduser. In this sense, “integral” does not mean that the component cannot be moved at all, but merely that the component cannot be removed during the normal course of use of the container. 
     As used herein the term “high purity” means that the liquid chemical is susceptible to contamination by contact with atmospheric air and its contaminants. Similarly, the term “reactive” means that the liquid chemical may decompose upon contact with air and its contaminants. 
     Chemicals such as organometallic precursors used in chemical vapor deposition need to be delivered at higher pressure than that of their own vapor pressure. A non-comprehensive list of chemicals which may benefit from the invention are listed in Table 1. This is easily done by pressurizing the container with inert gas to force the liquid out of the container. However, in such operations, such liquid chemicals run the risk of being contaminated with air impurities. These impurities, particularly moisture, react with many organometallic compounds to form other hazardous materials from the container. To prevent this from occurring, the container of the present invention has a design with an appropriate purifier to remove atmospheric contaminants before entering the container in the event of residual air being present in connecting lines which was not removed due to improper purge from operator handling, computer controller errors, or equipment component failures. Thus, better safety of chemical storage and improved assurance of chemical purity is attained which is often needed for critical processes such as that in the semiconductor industry. A particularly preferred method in accordance with the invention of preventing air contaminants from entering the container of the invention is to incorporate a purifying medium integral to the container itself and downstream of any line fittings that are disconnected for container change-outs. In accordance with the present invention, such purifier is preferably placed inside the container on the gas inlet port. Alternatively, such purifiers can be installed on both gas inlet and liquid outlet ports of the container. By making them an integral part of the container, no operator maintenance or intervention is required and the user is guaranteed the appropriate size and media to use for a particular chemical. 
     Thus, by incorporating a purifier on the gas inlet port of the container the inert gas used to pressurize the container will not contribute contaminants to the chemical. By making such purifier an integral part of the container, rather than fastening the purifier to the gas inlet line exterior to the container, there is far more certainty that all gas entering the container goes through the purifying media, thereby more effectively preventing error of contamination. Furthermore, preferably changing the filter media with every container change prevents over use of the filter media, and a human operator does not have to closely track usage of the filter media. The filter media is preferably economically sized for just one container volume of chemical, and preferably the filter media can be regenerated for use with another container. 
     As far as known to the inventor, no such container is available which incorporates purifiers directly into the container itself. Further, while it may be obvious that using gas purifies upstream of the gas flow can help assure purity of the gas itself, today, gas purity is rarely the problem since very high purities are usually attainable and commercially available. More frequently, the difficulty is in providing the user of liquid chemicals the assurance of reliable operations in purging out air contaminants sufficiently that result from installing new or replacement container by chemical delivery system. 
     The invention will be better understood with reference to the drawing figures and description of preferred embodiments which follows. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Chemicals That May Benefit From the Invention 
               
             
          
           
               
                   
                 Chemical 
                   
                   
                   
               
               
                 Name 
                 Structure 
                 Chemical Name 
                 Application 
                 Film 
               
               
                   
               
               
                 PET 
                 Ta(Oet)5 
                 Pentaethoxytantalum 
                 High-k Capacitor, 
                 Ta2O5 
               
               
                   
                   
                   
                 High-k Gate Oxide 
               
               
                 Zr(t-OBu)4 
                 Zr(O(CH3)3)4 
                 Zirconium tertiary butoxide 
                 High-k Gate Oxide 
                 ZrO/ZrSiO 
               
               
                 MS 
                 (CH3)SiH3 
                 Monomethylsilane 
                 Low-k 
                 SiOC 
               
               
                 4MS 
                 Si(CH3)4 
                 Tetramethylsilane 
                 Barrier Low-k 
                 SiC 
               
               
                 TiCl4 
                 TiCl4 
                 Tetrachlorotitanium 
                 Barrier Metal 
                 TiN 
               
               
                 TDMAT 
                 Ti(Nme2)4 
                 Tetrakisdimethylaminotitanium 
                 Barrier Metal 
                 TiN, TiSiN 
               
               
                 TDEAT 
                 Ti(NEt2)4 
                 Tetrakisdiethylaminotitanium 
                 Barrier Metal 
                 TiN, TiSiN 
               
               
                 EtCp2Ru 
                   
                 BisEthyl Cyclo PentaDienyl 
                 Electrode 
                 Ru/RuO 
               
               
                   
                   
                 Ruthenium 
               
               
                 DMDMOS 
                 (CH3)2Si(OCH3)2 
                 Dimethyldimethoxysilane 
                 Low-k 
                 SiOC 
               
               
                 HCDS 
                 Si2Cl6 
                 Hexachlorodisilane 
                 Etch Stopper, Cap 
                 SiN 
               
               
                   
                   
                   
                 Layer, Spacer 
               
               
                 Zr(NEt2)4 
                   
                 Tetrakisdiethylaminozirconium 
                 High-k Gate Oxide 
                 ZrO/ZrSiO 
               
               
                 Hf(NEt2)4 
                   
                 Tetrakisdiethylaminohafnium 
                 High-k Gate Oxide 
                 HfO/HfSiO 
               
               
                 Si(Nme2)4 
                 Si(N(CH3)2)4 
                 Tetrakisdimethylaminosilane 
                 High-k Gate Oxide 
                 HfSiO/ZrSiO 
               
               
                 Zr(Nme2)4 
                 Zr(N(CH3)2)4 
                 Tetrakisdimethylaminozirconium 
                 High-k Gate Oxide 
                 ZrO/ZrSiO 
               
               
                 HSi(Net2)3 
                 HSi(N(C2H5)2)3 
                 Trisdiethylaminosilane 
                 High-k Gate Oxide 
                 HfSiO/ZrSiO 
               
               
                 Hf(t-OBu)4 
                 Hf(O(CH3)3)4 
                 Hafniumtertiarybutoxide 
                 High-k Gate Oxide 
                 HfO/HfSiO 
               
               
                 Si(i-Opr)4 
                 Si(O(CH(CH3)2)4 
                 Silicon iso propoxide 
                 High-k Gate Oxide 
                 HfSiO/ZrSiO 
               
               
                 Si(NEt2)4 
                 Si(N(C2H5)2)4 
                 Tetrakisdiethylaminosilane 
                 High-k Gate Oxide 
                 HfSiO/ZrSiO 
               
               
                 3MS 
                 (CH3)3SiH 
                 Trimethylsilane 
                 Low-k, Barrier Low-k 
                 SiOC, SiC 
               
               
                 TMCTS 
                 C4H16O4Si4 ?? 
                 Tetramethylcyclotetrasiloxane 
                 Low-k 
                 SiOC 
               
               
                 HSi(NMe2)3 
                 HSi(N(CH3)2)3 
                 Trisdimethylaminosilane 
                 High-k Gate Oxide 
                 HfSiO/ZrSiO 
               
               
                 TATDMAE 
                 Ta(OC2H5)4(C4H10NO 
                 Tantalumtetraehoxydimethyl- 
                 High-k Capacitor, 
                 Ta2O5 
               
               
                   
                   
                 aminoethoxide 
                 High-k Gate Oxide 
               
               
                 ZrCl4 
                 ZrCl4 
                 TetraChlorozirconium 
                 High-k Gate Oxide 
                 ZrO/ZrSiO 
               
               
                 Pt(hfa)2 
                   
                 Bis Hexa Fluoro Acetyl 
                 Electrode 
                 Pt/PtO 
               
               
                   
                   
                 Acetonato Platinum 
               
               
                 Ir(acac)3 
                   
                 Tris Acetyl Acetonato 
                 Electrode 
                 Ir/IrO 
               
               
                   
                   
                 Iridium 
               
               
                 PbDPM2 
                   
                 Bis Di Pivaloyl Methanato 
                 Ferro Electric (PZT) 
                 PZT 
               
               
                   
                   
                 Lead 
               
               
                 ZrDPM 
                   
                 Tetra Di Pivaloyl Methanato 
                 Ferro Electric (PZT) 
                 PZT 
               
               
                   
                   
                 Zirconium 
               
               
                 Ti(DPM)2(i-OPr)2 
                   
                   
                 Ferro Electric (PZT) 
                 PZT 
               
               
                 Sr(DPM)2 
                   
                 Bis Di Pivaloyl Methanato 
                 Ferro Electric (SBT) 
                 SBT 
               
               
                   
                   
                 strontium 
               
               
                   
               
             
          
         
       
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates schematically, in side-sectional view, a first container embodiment of the invention; 
     FIG. 2 illustrates schematically, in side-sectional view, a second container embodiment of the invention; and 
     FIG. 3 illustrates schematically, in side-sectional view, a third container embodiment of the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the Figures, FIG. 1 illustrates a first embodiment  100  of a container of the invention. Container  100  includes a container body  2  having a top  4  and a gas inlet line  6 , through which gas is controlled using the gas inlet valve  8 . Gas inlet tube  6  traverses through top  4  of container  2  and preferably enters first porous media disc  10 . Disc  10  is held in place by a tube  12 , and tube  12  in turn holds in place a gas filter media cartridge  14  along with a second force disc  16 . Completing the gas inlet is a gas exit tube  18  which may or may not be present in all embodiments. Tube  18  prevents backsplash of liquid chemical into porous media  16 . Again, porous media  10 ,  16  and gas outlet tube  18  are only preferred and not necessary to the practice of the invention. The dotted portion  19  illustrates that tube  18  May be extended in an “S” shape, to help preclude liquid from entering the gas filter media  14 . Completing the first embodiment is a liquid exit tube  20  and a liquid control valve  22 . Liquid exit tube  20  extends through top  4  of container body  2  and into the liquid chemical, and preferentially extends near the bottom of container body  2  so that the chemical may be withdrawn even when the liquid level is low. It may be seen by this embodiment that any air impurities that may seek to enter container body  2  through the gas inlet will be caught by the filter media  14  and hence not enter into the container. 
     FIG. 2 illustrates a second embodiment 200 of the container of the invention, which is similar to the embodiment 100 of FIG. 1, however, container  200  of FIG. 2 includes a liquid filter media  26  held within a liquid filter media cartridge  24  both of which are attached to the end of liquid exit tube  20 . Although impurities are prevented from entering container body  2  through the inert gas inlet tube  6 , there could be occasion for impurities to generate within container  2  itself, for example, if the liquid chemical is exposed to higher than normal temperatures for prolonged time. Liquid filter  26  will filter out any developed impurities which happen to be generated within the container  2  and will not exit with liquid chemical out liquid exit tube  20 . 
     Another embodiment of the liquid delivery container of the invention is illustrated in FIG. 3 as embodiment 300. Embodiment 300 of FIG. 3 has all of the features of embodiment 200 of FIG. 2 on the gas inlet, but includes a pipe-in-pipe dip tube  28 . Dip tube  28  also includes a gas exit tube  30  which allows extraneous gas developed from impurities which may be generated within container body  2  to exit the system. These units are sometimes referred to as permeable degas units. Typically, gas exit  30  is attached to a suitable negative pressure device, such as a hood, exhaust manifold, or to a source of vacuum. In this embodiment, tube  20  preferably comprises a gas permeable material, having the function allowing gas to escape from liquid flowing therein. Also included in this embodiment is a liquid filter media  27 . 
     As illustrated in FIG. 1, in one of the simplest embodiments, the purifying media is enclosed in a small tube extending from the gas inlet port of the container. Preferably, the both ends of the purifying media have fitted therewith a fitted metal disc or other fine filtering substrate that can be welded in place in order to contain the gas filtering media. In this particular application, a proper choice of gas filtration media is important since it not only must remove trace air contaminants but also must be compatible with the liquid chemical itself. In this application, silica, alumina, and aluminosilicate materials are preferred since they are chemically inert and yet have the capability to remove moisture to very low levels. Furthermore, prewashing the purifying material itself with the liquid chemical to be delivered from container  2  will help assure compatibility. The volume of gas required to pass through the gas filter media is not very large, typically only two to three times that of the container volume itself, more preferably 3 or 4 times, so that there is no large capacity requirement for the gas purifying media. This allows a large range of materials to be used. The only critical requirement is that the gas filtering media be chemically compatible with the liquid chemical itself. The liquid contact with the gas purifying media can easily be eliminated by means of use of very fine porous filter substrates, a check valve, or by extending tube  18 , as illustrated in FIG. 1, below the downstream gas purifying media so as to maintain an inert gas pocket between gas filter media and the liquid itself. An alternative “S”-shaped tubing embodiment  19  is illustrated in FIG.  1 . 
     Alternatively, and as illustrated in FIGS. 2 and 3, purification media can be placed on both gas inlet and liquid outlet, provided the purifying media is fully compatible with the liquid chemical being delivered and the design can accommodate liquid flow rates required by the user. Since some liquid chemicals can degrade over time during storage to form solid particulates, the use of an appropriate filter on the outlet port can be very desirable. Again, as with the integral gas inlet filter media having a liquid particulate filter on the outlet port integral to the container itself is advantageous to the user in that the liquid filtration media has been properly pre-selected by the supplier and it “automatically” undergoes replacement with every container change-out. In an alternative embodiment, purifying media, whether for gas or liquid, are preferably contained in the gas and liquid valve ports. This may have advantages for assembly and disassembly. 
     As with the gaseous and liquid filtration media, if a permeable degas cartridge is used it is preferably integral to the container. This assures proper selection of the components compatible with the liquid chemical being delivered and the user does not have to worry that the appropriate permeable degas cartridge is installed in containers delivering appropriate chemical to the end use. It becomes an automatic replacement as the containers are changed out. 
     Methods of use of the containers of the invention are now described. As in most chemical usage situations, the procedures are cyclical. Assuming an empty container situation, the end user may prefer to simply purge container body  2  by keeping valves  8  and  22  open for a time, either controlled by human or computer control. After a sufficient purge time, valves  8  and  22  are closed and the container is disconnected from the user system through connections upstream of valve  8  and downstream of valve  22  (not shown). A new container  100  is then attached to the system. If the user desires flow of liquid, valve  22  is opened and valve  8  is opened, allowing gas to flow into container body  2 , thereby pushing liquid chemical out through liquid exit tube  20  and liquid exit valve  22 . As with the purge out sequence, this may be human controlled or computer controlled. 
     As gas enters the system through valve  8  and tube  6  the gas will be purified, or at least air contaminants will be removed, through filter media  14 . If the container embodiment 200 of FIG. 2 is used, furthermore, any impurities which are generated inside the container after the container itself has been installed, will be removed by liquid filter media  26  as liquid chemical is being delivered out of container  200 . Finally, as a further assurance of purity, a gas permeable pipe-in-pipe dip tube  28  with filter media  27  may be installed integrally as in the embodiment 300 of FIG. 3, thereby comprising the greatest assurance of purity for the end user. In embodiment 300, as inert gas enters through valve  8  and tube  6 , and is maintained clean by gas filter media  14 , liquid filter media  27  maintains liquid of high purity, while any gas that is developed from the liquid chemical is removed by the permeable unit  28 , through tube  30  which is connected to a negative pressure source. 
     Although not a feature of the present invention, it is preferable for containers of the invention to be equipped with liquid level sensing. This may either be accomplished through known means, such as float sensors, or through novel methods such as liquid level sensing via gas volume expansion monitoring. The containers of the invention my also be equipped with quick-purge canister change-out connections, thermally heated degas units, and delivery manifolds with liquid recovery (solvent or process chemical flushing) recovery canisters. Containers of the invention may also be supplied with mechanical pressurization (piston type) or bag (canisters). Solvent purge cleaning may also be equipped with the containers of the invention. All of these components are preferably “modular” add-on design, which can be installed and uninstalled in quick fashion by the user. For example, a modular design might include in one module all utilities such as gas pressurization flow, vacuum and solvent flow, while another module may consist of liquid output functions such as flow accumulation, flow meters, pressure sensors, filters, and degas units. Another module may contain purging and pressurizing sequences of valves. 
     Another module may include a scale to weigh the containers of the invention as they are being emptied, the scale may have variable height supports. Containers of the invention may include wheels, a weight scale, a bypass line, sight glasses for level sensing, UV/VIS level sensing and chemical purity monitoring, gas inlet purifies and degassing dip tubes. Specially preferred are UV/VIS probe sensors for level and purity monitoring as more fully explained in Applicant&#39;s copending application Ser. No. 09/905,598, filed on even date herewith, and incorporated by reference herein. 
     Preferred methods and apparatus for practicing the present invention have been described. It will be understood and readily apparent to the skilled artisan that many changes and modifications may be made to the above-described embodiments without departing from the scope of the present invention. The foregoing is illustrative only and other embodiments of the methods and apparatus may be employed without departing from the scope of the invention defined by the following claims.