Patent Publication Number: US-2013240637-A1

Title: Showerhead for cvd depositions

Description:
This is a divisional of U.S. patent application Ser. No. 13/346,603, filed Jan. 9, 2012, which is a divisional of U.S. application Ser. No. 13/025,035, filed Feb. 10, 2011, which claims the benefit of U.S. Provisional Application 61/325,793, (Texas Instruments Docket Number TI-69353PS, filed Apr. 19, 2010), the contents of which are incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to single-wafer processes involving the production of semiconductor devices. More particularly this invention relates to chemical vapor deposition (CVD) processes and equipment. 
    
    
     
       DESCRIPTION OF THE VIEWS OF THE DRAWING 
         FIG. 1  (Prior art) is a cross-section of a CVD process chamber. 
         FIG. 2  (Prior art) is top down view of a showerhead. 
         FIG. 3  is a cross-section of a chamber showerhead. 
         FIG. 4  is a cross-section of a dual chamber showerhead. 
         FIG. 5  is a cross-section of a dual showerhead. 
         FIG. 6  is a cross-section of a dual split showerhead. 
         FIG. 7  is a cross-section of a separated dual showerhead. 
         FIG. 8  is a cross-section of a separated dual split showerhead. 
     
    
    
     DETAILED DESCRIPTION 
     The example embodiments are described with reference to the attached figures, wherein like reference numerals are used throughout the figures to designate similar or equivalent elements. The figures are not drawn to scale and they are provided merely to illustrate the example embodiments. Several aspects are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the example embodiments. One skilled in the relevant art, however, will readily recognize that the example embodiments can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the embodiment. The example embodiments are not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the example embodiments. 
     The term “non-reacting process gas mixture” refers to a mixture of at least more than one non-inert process gases that do not react with each other when mixed together. For example, a lead organometallic process gas may be mixed with a zirconium organometallic process gas—with no chemical reaction occurring. Likewise silane process gas may be mixed with dichlorosilane process gas—with no chemical reaction occurring. 
     Most single wafer deposition reactions, including CVD, are activated either thermally or using a plasma. Thin film uniformity depends upon mass transport of the reactants and reaction products over the wafer. As shown in  FIG. 1 , many single wafer CVD systems are structured to allow the process gasses to be introduced into the CVD chamber  1002  above the wafer  1004  through orifices  1006  in a showerhead  1010 . The process gases may enter the showerhead  1010  through gas delivery tube  1008 . As shown in  FIG. 2 , the showerhead orifices  2002  are typically arranged in a radial pattern (to mimic the shape of the wafer  1004 ). Returning to  FIG. 1 , the process gases typically flow from the wafer center to the wafer edge as indicated by the broken lines  1012 . The process gases are pumped out of the CVD chamber  1002  around the edges of the wafer  1004  through a vacuum port  1014 . 
     In a new embodiment, process gasses may be divided into non-reacting process gas mixtures. As illustrated in  FIG. 3 , a first of the non-reacting process gas mixtures may be introduced into the showerhead mixing chamber  3006  of the chamber showerhead  3002  through a first process gas delivery tube  3004 , and a second non-reacting process gas mixture may be introduced into the showerhead mixing chamber  3006  through a second process gas delivery tube  3010 . The first non-reacting gas mixture and the second non-reacting gas mixture may mix within the showerhead mixing chamber  3006  prior to exiting through showerhead orifices  3008  into the CVD deposition chamber. After the process gasses have exit through the showerhead orifices  3008 , they will react and deposit a thin film on the semiconductor wafer. In an example embodiment, the first non-reacting gas mixture contains a lead organometallic, a zirconium organometallic, and a titanium organometallic; plus a carrier gas such as helium or argon. The second non-reacting gas mixture may be oxygen plus a carrier gas, or oxygen only. These process gasses are designed to deposit a PZT (lead-zarconium-titaniate) thin film onto the wafer surface. (Note that in the case when the second non-reacting gas mixture is oxygen only, it is not a mixture of more than one gas.) 
     For some processes, the two non-reacting gas mixtures may begin to react as soon as they come in contact with each other inside the showerhead mixing chamber  3006  prior to exiting through the orifices  3008 . If that happens, a thin film deposition may occur within the showerhead mixing chamber  3006  and on the surfaces of the orifices  3008 —possibly causing a partial or full blockage of one or more orifices  3008 . In addition, unwanted particulates may form and then deposit onto the wafer—possibly causing wafer defects. This problem may be avoided by using a split showerhead as is illustrated in the embodiment in  FIG. 4 . A first non-reacting process gas mixture may be introduced into the first showerhead chamber  4006  of the dual chamber showerhead  4002  through a first process gas delivery tube  4004 , and a second non-reacting process gas mixture may be introduced into the second showerhead chamber  4012  through a second process gas delivery tube  4010 . The first non-reacting gas mixture exits through first showerhead orifices  4008  and the second non-reacting gas mixture exits through second showerhead orifices  4014  into the CVD deposition chamber where they mix, react, and deposit a thin film on the semiconductor wafer. In an example embodiment, the first non-reacting gas mixture contains a lead organometallic, a zirconium organometallic, and a titanium organometallic, plus a carrier gas such as helium or argon. The second non-reacting gas mixture contains oxygen plus a carrier gas, or oxygen only. The first non-reacting gas mixture reacts with the second non-reacting gas mixture to deposit a PZT (lead-zarconium-titaniate) thin film onto the wafer. (Again, note that in the case when the second non-reacting gas mixture is oxygen only, it is not a mixture of more than one gas.) 
     PZT thin films are often used within ferroelectric devices in integrated circuits. To achieve the desired lead content in the PZT thin film, an excess lead reactant is applied. In addition, a temperature tilt (i.e. a temperature gradient) of approximately 10° C. to 30° C. is imposed from wafer center to wafer edge in a typical 200 mm CVD deposition chamber. While this achieves the desired PZT composition and thickness uniformity in the center of the wafer, the lead that is deposited on the chamber walls may desorb. Plus, lead may also desorb from the edges of the wafer (because of the higher temperature at the edges of the wafer). That released lead may react with oxygen in the gaseous phase above the wafer to form unwanted particles. The unwanted lead oxide particles may then deposit on the wafer surface; forming defects in the PZT thin film. Therefore, it is very important, but may be very difficult, to achieve target thin film thickness and/or composition uniformity using conventional single wafer CVD equipment. 
     In an embodiment shown in  FIG. 5 , the showerhead is divided radially to form a dual showerhead  5002  that includes a circular inner showerhead  5006  and an outer ring showerhead  5004 . To avoid unwanted thin film deposition and particle formation in the process gas delivery tubes, the process gases may be separated into two groups of non-reacting process gas mixtures. For the outer ring showerhead  5004 , the first group of non-reacting process gas mixtures may be formed in first and second gas delivery systems,  5005  and  5015 . This first group of non-reacting process gas mixtures is delivered to the outer showerhead mixing manifold  5012  through separate first and second process gas delivery tubes  5008  and  5010 . For the circular inner showerhead  5006 , the second group of non-reacting process gas mixtures may be formed in third and fourth gas delivery systems,  5007  and  5017 . This second group of non-reacting process gas mixtures is delivered through separate third and fourth process gas delivery tubes  5014  and  5016  to the inner showerhead mixing manifold  5018 . The first group of non-reacting process gas mixtures and the second group of non-reacting process gas mixtures may combine in the outer and inner shower head mixing chambers,  5012  and  5018 , prior to exiting through the showerhead orifices. These process gasses then react in the CVD chamber to deposit a thin film on a semiconductor wafer. 
     In an example embodiment that utilizes the dual showerhead  5002 , the first group of non-reacting process gas mixtures includes a lead organometallic, a zirconium organometallic, and a titanium organometallic. In addition, a carrier gas such as helium or argon may be introduced into the inner showerhead mixing manifold  5018  through the third process gas delivery tube  5014  while oxygen (or oxygen plus inert gas mixture) may be delivered to the inner showerhead mixing manifold  5018  through the fourth process gas delivery tube  5016 . The second group of non-reacting process gas mixtures includes a lead organometallic, a zirconium organometallic, and a titanium organometallic. In addition, a carrier gas such as helium or argon may be introduced to the outer showerhead mixing manifold  5012  through the first process gas delivery tube  5008  while oxygen (or oxygen plus inert gas mixture) may be delivered to the outer showerhead mixing manifold  5012  through the second process gas delivery tube  5010 . The dual showerhead  5002  design enables an organometallic gas mixture with a lower concentration of lead to be introduced to outer showerhead mixing manifold  5012 . The lower concentration of lead in the outer showerhead mixing manifold enables a lower temperature tilt to be used from wafer center to wafer edge. This in turn reduces the likelihood of the formation of lead oxide particulates near the wafer edge and thus reduces wafer defects. 
     In a more detailed embodiment, a first gas mixture with a lead/(zirconium+titanium) ratio in the range of approximately 0.8 to 1.5, and more specifically a ratio of 1.2, may be delivered through the fourth process gas delivery tube  5016  to the circular inner showerhead  5006  while oxygen is provided through the third process gas delivery tube  5014 . A second gas mixture with a lead/(zirconium+titanium) also having a ratio in the range of approximately 0.8 to 1.5, and more specifically a ratio of  1 . 0 , may be delivered to the outer ring showerhead  5004  through the second process gas delivery tube  5010  while oxygen is provided through the first process gas delivery tube  5008 . This ratio difference facilitates a wafer center-to-edge temperature tilt of less than about 10° C.; therefore, it may deliver the desired center-to-edge composition uniformity and thickness uniformity (with reduced particle formation) across a 200 mm wafer. 
     Additional concentric showerheads (such as triple or quadruple showerheads) may be used if needed. The additional concentric showerheads may be useful for thin film deposition processes involving larger diameter wafers. Moreover, the additional showerheads may accommodate the use of more than two groups of non-reacting process gas mixtures. 
     An embodiment that may reduce the formation of particles inside the outer and inner showerhead mixing manifolds  5012  and  5018  (often caused by process gas reaction within the outer and inner showerheads  5004  and  5006 , respectively) is illustrated in  FIG. 6 . In this embodiment, a dual split showerhead  6002  separates the process gasses (that react with each other) until they are introduced into the CVD chamber through separate orifices. For example, a mixture of a lead organometallic process gas, a zirconium organometallic process gas, a titanium organometallic process gas, plus a carrier gas (such as helium or argon) may be provided by a first process gas delivery tube  6014  and flow into the CVD chamber through a first set of orifices  6030  in the circular inner showerhead  6006 . A separate second process gas delivery tube  6016  may provide oxygen to the CVD chamber through a separate second set of orifices  6028  in the same circular inner showerhead  6006 . 
     The first gas distribution manifold  6018  is separate from the second gas distribution manifold  6020 . (Areas  6020  are different regions of the same gas distribution manifold.) However, the two gas distribution manifolds  6018  and  6020  combine to form the circular inner showerhead  6006 . 
     A different mixture containing different concentrations of a lead organometallic process gas, a zirconium organometallic process gas, a titanium organometallic process gas, and a carrier gas may be introduced through a third process gas delivery tube  6008  to the CVD chamber through a third set of orifices  6024  in the outer ring showerhead  6004 . (Note that areas  6012  are different regions of the same third gas distribution manifold. Likewise, areas  6022  are different regions of the same fourth gas distribution manifold.) Together, the third and fourth gas distribution manifolds  6012  and  6022  form the outer ring showerhead  6004 . A separate fourth process gas delivery tube  6010  may provide oxygen to the CVD chamber through a separate fourth set of orifices  6026  in the same outer ring showerhead  6004  (at locations that are closer to the orifices for the mixture provided by the third process gas delivery tube  6008 ). 
     In the embodiments supra, gasses such as the lead, zirconium, and titanium organometallics may be mixed together prior to delivery to the showerheads because these organometallic reagents do not react with each other. This may reduce the cost of additional tubing and flow meters that are often required when process gases are delivered to the showerhead individually. Furthermore, the dual (or multiple) showerhead embodiments accommodate the delivery of a mixture of process gases to the circular inner showerhead (at the center of the wafer) that has different reactant concentrations than the mixture delivered to the outer ring showerhead (at the edge of the wafer). Moreover, because the process gases which react with each other may be kept separate until they exit through the orifices in the dual showerheads, the deposition of unwanted particles within the process gas delivery tubes, showerhead manifolds, and the orifices may be reduced. The dual split showerhead  6002  may also enable the deposition of a PZT thin film having uniform wafer center-to-edge composition and thickness with an across wafer temperature tilt of about 10° C. or less. For larger diameter wafers, more showerheads with more segments may be used, such as triple split showerheads or quadruple split showerheads. 
     Additional embodiments showing separated dual showerheads  7002  and separated split dual showerheads  8002  are illustrated in  FIG. 7  and  FIG. 8 , respectively. The outer ring and circular inner showerheads  7004 ,  7006  shown in  FIG. 7  may be similar to the showerheads  5004 ,  5006  shown in  FIG. 5 ; however the showerheads  7004 ,  7006  in  FIG. 7  are physically separated by spaces  7010 . Furthermore, the outer ring and circular inner showerheads  8004 ,  8006  shown in  FIG. 8  may be similar to the showerheads  6004 ,  6006  shown in  FIG. 6 ; however, the showerheads  8004 ,  8006  in  FIG. 8  are physically separated by spaces  8010 . In these embodiments, the outer ring showerheads  7004 ,  8004  are physically separated from the circular inner showerheads  7006 ,  8006 . The space  7010 ,  8010  between the outer and inner showerheads may be filled with a dielectric material so that outer and inner showerheads may be powered or biased separately for PECVD. Alternatively or additionally, the space  7010 ,  8010  may be filled with a thermally insulating material so that the outer and inner shower heads may be maintained at different temperatures. 
     Various additional modifications are within the scope of the above embodiments. As an example, the deposition of a PZT thin film is discussed supra; however, other thin films may be deposited (such as barium strontium titaniate). 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the embodiments. Thus, the breadth and scope of the embodiments should not be limited by any of the above described embodiments. Rather, the scope of the embodiments should be defined in accordance with the following claims and their equivalents.