Abstract:
A supply of a germanium precursor such as germanium n-butylamidinate is provided in close proximity to a microelectronic device substrate to be contacted therewith for deposition of germanium-containing material on the substrate. Specific arrangements are described, including tray and reservoir structures from which solid, liquid, suspended or dissolved germanium precursor can be volatilized for transport to the substrate surface together with other precursors, carrier gases, co-reactants or the like. In such manner, the germanium precursor can be activated independently of the activation of other precursors, within the deposition chamber, to achieve highly efficient formation of germanium-containing material on the substrate, e.g., a GST film of a phase change memory device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The benefit of priority of U.S. Provisional Patent Application No. 61/263,052 filed Nov. 20, 2009 in the name of Jun-Fei Zheng for “SYSTEM FOR THE DELIVERY OF GERMANIUM-BASED PRECURSOR” is hereby claimed under the provisions of 35 USC 119(e). The disclosure of U.S. Provisional Patent Application No. 61/263,052 is hereby incorporated herein by reference in its entirety, for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is directed to a system for the delivery of germanium from germanium-based precursors to wafers for use in semiconductor applications. 
       BACKGROUND 
       [0003]    In prior art systems employing low vapor pressure germanium-based precursors such as germanium n-butylamidinate for the delivery of germanium to target wafers, there is oftentimes an insufficient delivery of germanium to the target wafers. This is typically due to the difficulty of maintaining sufficient vapor flux in batch processing of the wafers. One reason for this difficulty in maintaining sufficient vapor flux is that the flux is often consumed prior to coming into contact with the target wafers or specific target portions of the wafers during the process, thereby resulting in non-uniform deposition. 
         [0004]    Additionally, the germanium is often delivered to the wafer surface using a chemical vapor deposition (CVD) process in the batch process. In using CVD to deposit the germanium in a batch process, the germanium from the precursor may be deposited in undesirable locations in the process chamber. For example, particles of the deposited germanium may clog a shower head or other device through which the precursors are introduced into the chamber, thereby bringing about the need for frequent maintenance of the chamber. 
       SUMMARY 
       [0005]    The systems described herein provide for an efficient and substantially uniform delivery of germanium from a germanium-based precursor to a plurality of target wafers in a process chamber via a CVD process. The germanium is deposited to the device sides of each of the wafers, thereby allowing the flux to be sufficiently consumed in the desired deposition process before errant particles are deposited elsewhere in the process chamber. The system also is applicable to a single wafer process. 
         [0006]    In one aspect, the present disclosure relates to a system for the delivery of germanium n-butylamidinate precursor flux to a wafer in a batch process. This system comprises a process chamber or furnace and at least one inlet port through which germanium n-butylamidinate precursor can be delivered to an interior portion of the furnace. During delivery, the germanium n-butylamidinate is vaporized in the interior portion of the furnace. Also, in the batch process, each wafer is positioned adjacent to an internal reservoir of germanium n-butylamidinate precursor in a tray that delivers the identical and uniform flux of germanium n-butylamidinate vapor toward the wafer to achieve uniform germanium deposition. Many trays or a large tray with surface area equal to or larger than that of the total wafer surface on which devices are to be mounted will allow sufficient flux of germanium n-butylamidinate vapor. 
         [0007]    In another aspect, the present disclosure relates to a chemical vapor deposition system for the delivery of germanium n-butylamidinate precursor to a wafer, the system comprising: 
         [0008]    at least one tray for retaining liquid germanium n-butylamidinate precursor, the tray being heatable inside a deposition chamber of the system at a temperature above the melting point of germanium n-butylamidinate suitable to provide germanium n-butylamidinate precursor vapor, the tray comprising a plurality of tubes extending from a bottom surface of the tray and being in communication with holes uniformly distributed in the trays such that the holes allow other precursors and co-reactants to pass through; 
         [0009]    wherein said at least one tray is arranged inside the deposition chamber such that a device side of a wafer faces the tray in parallel relationship; and wherein all the wafers when in a batch process carried out in said system will face respective trays containing germanium n-butylamidinate in a corresponding fashion so that the device side of each wafer will receive substantially uniform doses of germanium n-butylamidinate precursor flux. 
         [0010]    In another aspect, the disclosure relates to a method of depositing germanium on a substrate in a vapor deposition chamber, comprising providing germanium n-butylamidinate in a receptacle in said vapor deposition chamber, heating the germanium n-butylamidinate in said receptacle to volatilize same to form germanium n-butylamidinate vapor, and flowing said germanium n-butylamidinate vapor to said substrate for contacting therewith. 
         [0011]    Other aspects and features of the invention will be more fully apparent from the ensuing description and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic representation of a chemical vapor deposition apparatus in which germanium n-butylamidinate is stored in the chemical vapor deposition chamber and vaporized in the chamber for contacting with a semiconductor substrate. 
           [0013]      FIG. 2  is a schematic perspective view of a tray structure for holding germanium n-butylamidinate for vaporization in a vapor deposition chamber. 
           [0014]      FIG. 3  is a photographic perspective view of the tray structure of  FIG. 2 . 
           [0015]      FIG. 4  is a top plan view of a batch process arrangement in which multiple wafers are mounted in a spaced array, above a foraminous tray holding germanium n-butylamidinate in receptacle portions of the tray, while allowing passage of vapor of other precursors as well as other fluid co-reactants or carrier gases to flow through openings of the tray. 
           [0016]      FIG. 5  is an elevation view of the central wafer and associated tray structure of  FIG. 4 , taken along line A-A of  FIG. 4 . 
           [0017]      FIG. 6  is a perspective schematic view of a vapor deposition chamber in which multiple wafers are mounted above respective trays that are coextensive in areal extent with the wafers. 
           [0018]      FIG. 7  is a schematic elevation view of the multiple wafer and tray structure shown in 
           [0019]      FIG. 6 , taken along line A′-A′ of  FIG. 6 . 
           [0020]      FIG. 8  is a schematic elevation view of a tube furnace containing multiple wafers, each mounted above a tray containing openings for flow of fluid therethrough, and receptacle portions adapted to hold germanium precursor for volatilization in the furnace to generate precursor vapor for contacting with the wafer surface. 
           [0021]      FIG. 9  is a schematic elevation view of a microelectronic device substrate mounted below a tray including receptacle portions for holding germanium precursor and openings for allowing downflow of antimony and tellurium precursor vapors, arranged so that the germanium precursor vapor produced by volatilization of the germanium precursor in the heated chamber, is co-flowed with the antimony and tellurium precursor vapors for contacting the microelectronic device substrate. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Germanium n-butylamidinate has a low vapor pressure that makes it difficult to deliver to a substrate wafer using a delivery system such as a chemical vapor deposition (CVD) system. In the delivery system of the present disclosure using a source comprising germanium butylamidinate, diterbutyltelluride, and tris(dimethylamido)antimony, the deposition of Ge, GeTe, or GeSbTe is typically at very low rate such that a film formed on the substrate wafer is desirably and suitably conformal and amorphous. 
         [0023]    The germanium n-butylamidinate compound is preferably a compound of the formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    i.e., [{nBuC(iPrN) 2 } 2 Ge], or bis(2-butyl-N,N′-diisopropylamidinato)germanium, and is also referred to herein as GeM. The system and method of the disclosure are also applicable to other germanium amidinate compounds, of the general formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein:
 
each R is independently selected from among H, C 1 -C 6  alkyl, C 5 -C 10  cycloalkyl, C 6 -C 10  aryl, and) —Si(R 0 ) 3  wherein each R 0  is independently selected from C 1 -C 6  alkyl; and each X is independently selected from among C 1 -C 6  alkyl, C 1 -C 6  alkoxy, —NR 1 R 2 , and —C(R 3 ) 3 , wherein each of R 1 , R 2  and R 3  is independently selected from H, C 1 -C 6  alkyl, C 5 -C 10  cycloalkyl, C 6 -C 10  aryl, and —Si(R 4 ) 3  wherein each R 4  is independently selected from C 1 -C 6  alkyl.
 
         [0024]    A batch process in which multiple wafers are treated simultaneously is desired for efficient wafer throughput. In such a batch process, wafers may be (1) stacked side-by-side on a platform or stage, or (2) stacked with suitable spacing in a tube furnace. In either configuration, sufficient delivery of the low vapor pressure germanium n-butylamidinate precursor to the individual wafer surface while maintaining a uniform flux over the wafer surface is desired. 
         [0025]      FIG. 1  is a schematic representation of a chemical vapor deposition apparatus  10  in which germanium n-butylamidinate  38  is stored in the chemical vapor deposition chamber and vaporized in the chamber for contacting with a semiconductor substrate. As shown, the chemical vapor deposition apparatus  10  includes a chamber wall  12 , within which is provided a circumscribing heating shield  14 , which may be formed of sheet-metal or other thermally conductive material. The chamber wall  12  and heating shield  14  thus, our coaxially arranged with respect to one another, and form an annular volume  16  therebetween. 
         [0026]    At the upper end of the heating shield  14  is mounted a showerhead plate member  18 , having openings  20  therein for downward flow through the plate member of various fluid species, including (i) the germanium precursor, bis(2-butyl-N,N-diisopropylamidinato)germanium, designated GeM, (ii) the antimony precursor, tetrakis(dimethylamido)antimony, designated SbTDMA, (iii) the tellurium precursor, di-t-butyl-tellurium, Te(tBu) 2 , and (iv) the co-flow gas mixture of ammonia and hydrogen, NH 3 /H 2 . By such arrangement, the precursor vapors and co-reactants are flowed downwardly through the showerhead plate member. Located below such showerhead plate member is a conductive metal mesh member  22 , arranged to be heated by the coil heater  24  to suitable temperature, such as a temperature in a range of from 180 to 400° C. 
         [0027]    Positioned at a lower portion of the CVD chamber is a stage  26 , arranged with a heating coil  28  so that the stage is heated to suitable temperature, e.g., temperature in a range of from 110 to 250° C., for corresponding heating of the wafer  30  mounted on the stage. The wafer may for example have a size of 2.5 cm×2.5 cm, and the spacing S between the wafer and the heating coil  24 /conductive metal mesh member  22  may be on the order of 1.2 to 2.5 cm. The CVD chamber includes an observation port in the form of a laterally projecting extension  32  closed at its outer end by an observation window  34  suitably sealed to the extension by means of a coupling including gasket  36 . 
         [0028]    Between the gasket  36  and the window  34 , condensed germanium precursor may be trapped as a deposit 38. When this deposit is heated, as for example to it, temperature on the order of 70° C., the precursor is re-volatilized, and resulting GeM vapor flows to the wafer  30  and is contacted therewith, to deposit germanium on such substrate. 
         [0029]      FIG. 1  provides a schematic illustration of one exemplary embodiment of a process with internal germanium n-butylamidinate precursor delivery. The germanium n-butylamidinate precursor is heated to 130° C. in a stainless steel vessel and vaporized. For such purpose, a vaporizer vessel of a type that is commercially available from ATMI, Inc. (Danbury, Conn., USA) under the trademark ProE-Vap® can be advantageously used. Upon delivery to a CVD chamber, the vaporized precursor condenses in a cold spot at about 70° C. to form the condensate  38 , which is at the window  34  of the chemical vapor deposition apparatus  10 , and is stored in the CVD chamber. The condensed and stored germanium n-butylamidinate precursor is then heated to a higher temperature around 100° C., thereby causing it to vaporize and flowed to the substrate, as previously described. 
         [0030]    By such arrangement, the precursor vapor, and co-reactants flowed downwardly through the chamber and are discharged at a lower end thereof in the direction indicated by arrows B, by action of a pump or other motive fluid driver (not shown), to remove reacted, partially reacted, and unreacted precursors and co-reactants from the chamber. 
         [0031]    Table 1 below lists some experimental results of Ge x Sb y Te z  deposition from the precursor source materials described above, in a CVD chamber of the type described above and shown in  FIG. 1 , with the germanium n-butylamidinate precursor heated to about 100° C. as indicated above. The Te(tBu) 2  and SbTDMA were heated separately to increase the activation of these two precursors. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Deposition Results with the Internal GeM Source from the GeM 
               
               
                 Near the window and possibly other places inside the chamber 
               
             
          
           
               
                 Run 
                 Ge % 
                 Sb % 
                 Te % 
                 Thickness (A) 
                 Detailed Experimental Conditions 
               
               
                   
               
             
          
           
               
                 #3031 
                 24.7 
                 22.3 
                 53.0 
                 101.8 
                 Substrate 150 C., precursor activation 
               
               
                   
                   
                   
                   
                   
                 heating coil at 0.5″ above the substrate at 
               
               
                   
                   
                   
                   
                   
                 220 C. 
               
               
                 3032 
                 29.6 
                 11.2 
                 59.2 
                 67 
                 Substrate 150 C., precursor activation zone 
               
               
                   
                   
                   
                   
                   
                 heating coil is 220 C. 
               
               
                 3033 
                 35.0 
                 9.25 
                 55.8 
                 42.7 
                 Substrate 130 C., precursor activation 
               
               
                   
                   
                   
                   
                   
                 heating coil is 220 C. 
               
               
                 3034 
                 30.1 
                 28.5 
                 41.4 
                 56.6 
                 Substrate 125 C., precursor activation 
               
               
                   
                   
                   
                   
                   
                 heating coil is at 186 degree C. 
               
               
                 3035 
                 18.0 
                 31.7 
                 50.3 
                 79.7 
                 Substrate 200 C., precursor activation 
               
               
                   
                   
                   
                   
                   
                 heating coil is at 200 degree C. 
               
               
                 3036 
                 30.1 
                 28.0 
                 41.9 
                 58.8 
                 Substrate 110 C., precursor activation 
               
               
                   
                   
                   
                   
                   
                 heating coil is at 186 degree C. 
               
               
                   
               
             
          
         
       
     
         [0032]      FIG. 2  is a schematic perspective view of a tray structure  50  for holding germanium n-butylamidinate for vaporization in a vapor deposition chamber.  FIG. 3  is a photographic perspective view of the tray structure of  FIG. 2 . 
         [0033]    As shown in  FIG. 2 , a configuration of a delivery system of the present disclosure for use in a CVD process is shown. In this configuration, germanium n-butylamidinate precursor is introduced into a tray of the type shown in  FIG. 2 . This tray includes a circumscribing sidewall  52  joined at its lower end to a bottom surface of floor member  56  having holes therein. Tubes  62  extend from the holes in the tray and define passages  64  to allow other precursors and co-reactants to pass from one side of the tray to the other. In the center of the floor member is a collar  58 . Defining a central passage  60  through which one or more fluid components can be passed downwardly for subsequent upflow through the passages  64  of the tubes  62 . 
         [0034]    Germanium n-butylamidinate precursor is charged into the tray  50  in solid or liquid form or as a solid dissolved in solvent. The germanium n-butylamidinate precursor in liquid form will be at a temperature higher than 40° C. If the germanium n-butylamidinate precursor is charged into the tray in solvent, the solvent will be boiled off, thereby causing the germanium n-butylamidinate in liquid form to stay in the tray. The germanium n-butylamidinate precursor can be recharged to tray(s) of such type by injection of germanium n-butylamidinate melted at greater than the melting point, i.e., in a liquid form, or germanium n-butylamidinate can be introduced as dissolved in solvent, via a tube from a source external to the process chamber or tube furnace. As an internal germanium n-butylamidinate source, the solvent is boiled off after a charge of the germanium n-butylamidinate precursor in a solvent medium. 
         [0035]    Thus, the tray structure shown in  FIGS. 2 and 3  employs tubes  62  that allow gas/vapor to pass through, while the floor member and circumscribing sidewall of the tray cooperate to retain the germanium precursor in liquid or solid form. A tray of such type may be relatively small in size, e.g., about 10 cm in diameter, or alternatively, the tray may be constructed with a very large size, to enable the tray to be placed under many wafers mounted in side-by-side relationship to one another in a batch chemical vapor deposition chamber. Alternatively, a tray of appropriate size, e.g., 30 cm diameter, may be placed under each individual wafer in the CVD chamber, with the wafer being of a same or alternatively a different size than the tray. 
         [0036]      FIG. 4  is a top plan view of a batch process arrangement in which multiple wafers  84  are mounted in a spaced array, above a foraminous tray  80  holding germanium n-butylamidinate in receptacle portions of the tray, while allowing passage of vapor of other precursors as well as other fluid co-reactants or carrier gases, e.g., Te(tBu) 2 , SbTDMA, carrier gas, co-reactants, etc., to flow through openings  82  of the tray. Such other precursors may be heated to a suitable temperature, e.g., in a range of from 180 to 400° C., for pre-activation thereof. 
         [0037]    In this arrangement, the single tray  80  is mounted beneath multiple wafers in the array. The receptacle portions of the tray  80  contain germanium n-butylamidinate, which is heated to a temperature in a range of from 40 to 150° C. to volatilize the germanium precursor and form a germanium precursor vapor. Thus, the holes  82  in the tray  80  permit precursors, other than germanium n-butylamidinate, along with carrier gases, co-reactants, etc., to flow through the tray openings, while the germanium precursor is stored, with the tray functioning as a pan in which the germanium precursor is retained, and to which additional germanium precursor can be added by injection or in other suitable manner. 
         [0038]    For example, the germanium precursor can be added in a solution or suspension, in a suitable solvent, so that subsequent to introduction to the tray, the solvent will evaporate upon heating and/or pump-down to vacuum level in the vapor deposition chamber, leaving the germanium precursor in the pan structure of the tray, so that the germanium precursor can thereafter be volatilized to form precursor vapor for contacting with the microelectronic device substrate. 
         [0039]      FIG. 5  is an elevation view of the central wafer  84  and associated tray structure  80  of  FIG. 4 , taken along line A-A of  FIG. 4 . As illustrated in  FIG. 4 , many wafers can be arranged to have their device surface (the surfaces of the wafers on which devices are located) facing the direction of germanium n-butylamidinate vapor flux from the tray. The Sb, Te, and any co-reactants involved will pass through the openings in the tray, schematically represented as holes  82 . The germanium precursor retained in the receptacle portion of the tray between the tube openings will then volatilize and form a vapor flux that contacts the device side  86  of the microelectronic device substrate, so that the germanium precursor vapor co-flows with the other precursors being flowed in the direction indicated by arrows E toward the substrate. 
         [0040]      FIG. 6  is a perspective schematic view of a vapor deposition chamber  100  defining an interior chamber volume  102  in which multiple wafers  106  are mounted above respective trays  104  that are coextensive in areal extent with the respective wafers with which they are associated. Thus, in this arrangement, there are as many trays as wafers, with the size of the trays being the same as the size of the wafers in diameter and area, and both being circular or disk-like in shape. 
         [0041]      FIG. 7  is a schematic elevation view of the multiple wafer and tray structure shown in  FIG. 6 , taken along line A′-A′ of  FIG. 6 . As illustrated, the microelectronic device substrate, wafer  106 , is oriented with its device side  108  facing the tray  104 . In this manner, the germanium precursor held in the receptacle portion of the tray is volatilized and flows with the precursor vapor of other precursors (passing through openings of the tray, in the direction indicated by arrows) for contacting with the device side  108  of the substrate  106 . 
         [0042]    The delivery of the germanium n-butylamidinate precursor from a tray is a proportional function of the inner surface area of that tray. By using the tray specified in  FIGS. 2 ,  3 ,  6 , and  7 , the inner surface area of the trays is as large as that of the wafer surface, which will lead to sufficient delivery of GeM to the wafer. Also, the wafers are positioned such that the device side of each faces the tray, with the surfaces of the device sides parallel to the trays containing germanium n-butylamidinate. A plurality of trays may be alternatingly stacked with the wafers such that precursor flux is in the direction of the device side of each wafer, to enable substantially uniform delivery of germanium n-butylamidinate precursor flux to the device side of each wafer. 
         [0043]      FIG. 8  is a schematic elevation view of a tube furnace  120  including a furnace housing  122  defining an enclosed interior volume  124  containing multiple wafers  126 ,  128  and  130 , each mounted above a tray  140 ,  142  and  144 , respectively, with the trays containing openings for flow of fluid therethrough in the direction indicated by arrows M. The trays also include receptacle portions adapted to hold germanium precursor for volatilization in the furnace to generate precursor vapor for contacting with the wafer surface. In this orientation, the wafers are arranged with their device sides  132 ,  134  and  136  in facing relationship to the tray retaining the germanium precursor, and generating a germanium precursor vapor flux for contacting with the device side of the corresponding wafer. 
         [0044]    In the  FIG. 8  arrangement, wafers are stacked vertically inside a tube furnace with the device side facing the vaporization of the precursors in the tray. There are as many trays as there are wafers, with each tray under a corresponding wafer. The tray can be loaded into the tube furnace in a similar fashion as the wafer, after the tray is loaded with precursor for each run. 
         [0045]    In the configurations shown in  FIGS. 4-8 , the trays can be stationed inside the deposition chamber under continuous vacuum without the interference of loading and unloading the wafers via a vacuum load lock. In the configurations in  FIGS. 6-8 , however, the trays can be removed from the chamber or the tube furnace and put back as desired in a similar fashion of taking wafers in and out using a robotic transfer mechanism, provided such transfers keep the trays containing germanium n-butylamidinate under vacuum. The configurations in  FIGS. 6-8  allow for the easy maintenance of the trays, such as cleaning the trays. 
         [0046]    Although  FIGS. 4-8  show that the device sides of the wafers are facing down to receive the germanium n-butylamidinate from the trays and Sb and Te precursors flowing upwardly through the holes of the trays, the wafers can also be placed with the device sides facing upward and with the trays containing germanium n-butylamidinate above the wafer. In this case, the vaporized germinanium n-butylamidinate will pass toward the wafer device side surfaces through the holes, together with the Sb and Te precursor. This is shown in  FIG. 9 . 
         [0047]      FIG. 9  is a schematic elevation view of a vapor deposition chamber arrangement  150  including a microelectronic device substrate  154  oriented with its device side  156  on top, and mounted below a tray  152  including receptacle portions  158  for holding germanium precursor  172  and openings  160  for allowing downflow of antimony and tellurium precursor vapors in the direction indicated by corresponding arrows. By this arrangement, the germanium precursor vapor produced by volatilization of the germianium precursor in the heated chamber is co-flowed with the antimony and tellurium precursor vapors for contacting the device side  156  of the microelectronic device substrate  154 . 
         [0048]    In operation, the vaporized germanium n-butylamidinate precursor is carried toward the device side of the wafer surface via holes  160  after vaporizing and leaving the surface of the tray  152 . Other precursors such as Te(tBu) 2  and SbTDMA, carrier gas, co-reactants, etc. pass through the holes. One or more of the precursors can be heated by a hot zone, e.g., to temperature in a range of from 180° C. to 400° C., in the precursor passage during its flow toward the wafer device side surface  156 , for pre-activation of such precursors. 
         [0049]    Although this disclosure has been set forth and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed in the above detailed description, but that the disclosure will include all embodiments falling within the scope of the foregoing description, the drawings, and the appended claims hereof.