Abstract:
Systems and methods for the production of polysilicon or another material via chemical vapor deposition in a reactor are provided in which gas is distributed using a silicon standpipe. The silicon standpipe can be attached to the reactor system using a nozzle coupler such that precursor gases may be injected to various portions of the reaction chamber. As a result, gas flow can be improved throughout the reactor chamber, which can increase the yield of polysilicon, improve the quality of polysilicon, and reduce the consumption of energy.

Description:
This application is a national phase application filed under 35 USC §371 of PCT Application No. PCT/US2009/038393 with an International filing date of Mar. 26, 2009 which claims priority of U.S. Provisional Application Ser. No. 61/039,758 filed on Mar. 26, 2008. Each of these applications is herein incorporated by reference in their entirety for all purposes. 
    
    
     FIELD OF INVENTION 
     The subject invention is directed to systems and methods for the production of materials such as polysilicon via chemical vapor deposition in a reactor. More particularly, the subject invention relates to systems and methods for distributing gas to improve flow patterns in a chemical vapor deposition reactor using a silicon standpipe. 
     DESCRIPTION OF THE RELATED ART 
     Chemical vapor deposition (CVD) refers to reactions usually occurring in a reaction chamber that involve depositing a solid material from a gaseous phase. CVD can be used to produce high-purity, high-performance, solid materials such as polysilicon, silicon dioxide, and silicon nitride, for example. In the semiconductor and photovoltaic industries, CVD is often used to produce thin films and bulk semiconductor materials. For example, heated surfaces can be exposed to one or more gases. As the gases are delivered into the reaction chamber, they come into contact with heated surfaces. Once this occurs, reactions or decomposition of the gases then occurs forming a solid phase, which is deposited onto the substrate surface to produce the desired material. Critical to this process is the gas flow pattern which influences the rate at which these reactions will take place and the quality of the products. 
     In polysilicon chemical vapor deposition processes, for example, polycrystalline silicon can be deposited from silane (SiH 4 ), dichlorosilane (SiH 2 Cl 2 ), trichlorosilane (SiHCl 3 ), and tetrachlorosilane (SiCl 4 ) according to the respective reactions. These reactions are usually performed in a vacuum or a pressured CVD reactor, with either pure silicon-containing feedstock, or a mixture of silicon containing feedstock with other gases. The required temperatures for the reactions range from hundreds to over one thousand degrees Celsius. Polysilicon may also be grown directly with doping, if gases such as phosphine, arsine or diborane are added to the CVD chamber. 
     Gas flow pattern is therefore crucial not only to the growth of polysilicon and other materials, but it also impacts the production rate, product quality, and energy consumption of the overall CVD reactor system. 
     SUMMARY OF THE INVENTION 
     The subject invention relates to systems and methods for distributing gas in a chemical vapor deposition reactor, in particular, for improving gas flow in a CVD reactor. Thus, the subject invention can be used to increase efficiency of reactions within CVD reaction chambers, increase the output of solid deposit, improve product quality, and reduce overall operating costs. Also encompassed by the subject invention is that silicon deposited on standpipes in a CVD reactor can be used as additional polysilicon product. 
     In a reactor system and method according to the subject invention, in particular, a CVD reactor system and method, a standpipe is utilized. The standpipe can be used to inject various reactants into a reaction chamber. The standpipe preferably is made of silicon or other materials. These materials include, without limitation: metals, graphite, silicon carbide, and other suitable materials. The length of the standpipe can range from about 1-2 centimeters up to about a few meters depending on the application. The diameter of the pipe can range from about 1-2 millimeters up to tenths of centimeters depending on the gas flow rate. The thickness of the wall preferably is about 0.1 to about 5.0 millimeters. 
     The reactor system of the subject invention includes a reaction chamber having at least a base plate fixed within the reaction chamber and an enclosure operably connected to the base plate. One or more filaments are attached to the base plate within the chamber upon which various reactant gases are deposited during a chemical vapor deposition cycle. The filament may be a silicon filament or other desired solid to be fabricated. At least one gas inlet and one gas outlet are connected to the reaction chamber to allow gas flow through the reaction chamber. A window portion or viewing port for viewing an internal portion of the chamber also can be provided. An electrical current source preferably is connected to ends of the filament via electrical feedthroughs in the base plate for supplying a current to heat the filament directly during a CVD reaction cycle. A cooling system for lowering a temperature of the chemical vapor deposition system also can be employed having at least one fluid inlet and at least one fluid outlet. 
     The standpipe according to the subject invention preferably is operably connected to the at least one gas inlet for injecting gas flow to the reaction chamber. The standpipe preferably includes a nozzle coupler and a pipe body. The length and diameter of the pipe body can be selected based on at least a desired gas flow rate. The nozzle coupler further can include a sealing device such as a gasket for sealing the pipe body to the at least one gas inlet. The standpipe preferably has at least one injection tube within the chamber for distributing a process gas flow. The dimensions of the at least one injection tube are based on a desired flow rate. The injection tube material can be made of silicon or another material. 
     These and other aspects and advantages of the subject invention will become more readily apparent from the following description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the method and device of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a perspective view of a reaction chamber system of the subject invention; 
         FIG. 2  is an internal perspective view of the reaction chamber of  FIG. 1 ; 
         FIG. 3A  is an enlarged cutaway view of a standpipe according to the subject invention; 
         FIG. 3B  is a detailed view of a nozzle coupler attached to a pipe body of the standpipe of  FIG. 3A ; 
         FIG. 3C  is an enlarged view of a gasket of the nozzle coupler depicted in  FIG. 3B ; and 
         FIG. 4  is a partial cross-sectional view of the reaction chamber system of the subject invention incorporating multiple standpipes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the subject invention are described below with reference to the accompanying drawings, in which like reference numerals represent the same or similar elements. 
     The subject invention relates to systems and methods for distributing gas in a reactor, in particular, for improving gas flow in a chemical vapor deposition (CVD) reactor. In particular, the subject invention is directed to a system and method for distributing gas in a CVD reactor using a standpipe. The benefits and advantages of the subject invention include, but are not limited to, increased production rates of a solid deposit (e.g. polysilicon), decreased energy consumption, and reduced overall operating costs. While the disclosure of the subject invention is directed toward an exemplary polysilicon CVD reactor system, the system and methods of the subject invention can be applied to any CVD reactor system for which increased gas distribution and improved gas flow patterns are desired, or any reactor system generally. 
     In an exemplary application, trichlorosilane gas reacts on rods or silicon tube filaments within a reaction chamber to form polysilicon deposits on the thin rods or filaments. The subject invention is not restricted to CVD reactors using polysilicon deposition involving a reaction of trichlorosilane but can be used for reactions involving silane, dichlorosilane, silicon tetrachloride, or other derivatives or combinations of gases, for example, by using thin rods or filaments with large surface area geometries and similar electrical resistivity properties in accordance with the invention. Filaments of various shapes and configurations can be utilized, for example, those disclosed in U.S. Patent Application Publication US 2007/0251455, which is incorporated herein by reference. 
     Referring to  FIGS. 1 and 2 , a chemical vapor deposition (CVD) reactor is shown, in which polysilicon is deposited onto thin rods or filaments according to the subject invention. A reactor system  10  includes a reaction chamber  12  having a base plate  30 , a gas inlet nozzle  24  or process flange, a gas outlet nozzle  22  or exhaust flange, and electrical feedthroughs or conductors  20  for providing a current to directly heat one or more filaments  28  within the reaction chamber  12 , as shown in  FIG. 2 . A fluid inlet nozzle  18  and a fluid outlet nozzle  14  are connected to a cooling system for providing fluid to the reaction chamber  10 . In addition, a viewing port  16  or sight glass preferably allows visual inspection of the interior of the reaction chamber  12 , and can optionally be used to obtain temperature measurements inside the reaction chamber  12 . 
     According to a preferred embodiment of the subject invention as depicted in  FIGS. 1 and 2 , the reactor system  10  is configured for bulk production of polysilicon. The system includes the base plate  30  that may, for example, be a single plate or multiple opposing plates, preferably configured with filament supports, and an enclosure attachable to the base plate  30  so as to form a deposition chamber. As used herein, the term “enclosure” refers to an inside of the reaction chamber  12 , where a CVD process can occur. 
     One or more silicon filaments  28  preferably are disposed within the reaction chamber  12  on filament supports (not shown), and an electrical current source is connectible to both ends of the filaments  28  via electrical feedthroughs  20  in the base plate  30 , for supplying a current to directly heat the filaments. Further provided is at least one gas inlet nozzle  24  in the base plate  30  connectible to a source of silicon-containing gas, for example, and a gas outlet nozzle  22  in the base plate  30  whereby gas may be released from the reaction chamber  12 . 
     Referring to  FIG. 2 , an exemplary standpipe  42  structure is shown, in which a pipe body  44  preferably is operably connected to at least one gas inlet nozzle  24  for injecting various gases into the reaction chamber  12  in conjunction with a CVD reaction occurring in the reaction chamber  12  (see also  FIG. 3A ). Although a single injection tube  42  is depicted in  FIG. 2 , one or more standpipes can be included in a reaction chamber. For example, referring to  FIG. 4 , the single standpipe can be replaced by standpipes  42 . The dimensions of each standpipe or injection tube  42  may vary from about 1-2 cm in length up to a few meters, and about 1-2 mm in diameter to tenths of centimeters, depending upon a desired gas flow design. 
     The one or more standpipes  42  preferably are used to inject one or more gases to various parts of the reaction chamber  12 , depending upon a desired flow pattern. The standpipe(s)  42  can be attached to the reactor by any known installation mechanism, for example, by screwing a pipe body  44  into an inlet nozzle coupler  25  of the reaction chamber  12  (see  FIGS. 3A-3C , as described herein). Because gas flow patterns can be crucial to the growth, production rate, product quality, and energy consumption of polysilicon, the subject invention can be applied to polysilicon manufacturing processes and any other processes that involve silicon or silicon compound deposition. Specifically, it can also be applied to processes where corrosion, contamination, and deposition can occur on the pipe and other shapes of components. 
     Referring again to  FIGS. 3A-3C , various components of the standpipe  42  preferably are made of silicon pipe. Silicon is used as an alternative to non-silicon materials such as stainless steel or other metals that can cause corrosion, contamination, melting and unwanted silicon deposition within the pipe body  44 . At one end of the pipe body  44 , the material from which the pipe body  44  is made is fused with materials that can be machined. These materials include metals, graphite, silicon carbide, and any other suitable material. At the other end, as shown in  FIGS. 3A-3C , the pipe body  44  preferably is attached to the nozzle coupler  25  having an appropriate diameter. The nozzle coupler  25  preferably is formed with a gasket  26  for providing an airtight seal between the gas inlet nozzle  24  and a standpipe gas supply source. The length of the pipe body  44  can range from about a few centimeters to about a few meters depending on the application. The diameter of the pipe body  44  can range from about a few millimeters to tenths of centimeters depending on the gas flow rate. The thickness of the pipe body  44  wall preferably is on the order of about a few millimeters or less. The pipe body  44  preferably is made of silicon. 
     A method for depositing a material in a reactor can include steps of: providing a reaction chamber including at least a base plate fixed within the reaction chamber and an enclosure operably connected to the base plate; attaching at least one filament to the base plate; connecting an electrical current source to the reaction chamber for supplying a current to the filament; connecting a gas source to the reaction chamber to allow gas through the reaction chamber; connecting a standpipe to the gas source for distributing a gas flow within the reaction chamber; and operating the reactor to deposit the material on the at least one filament in the reaction chamber. 
     An additional benefit of a standpipe of the subject invention is that it can be reused or recycled. During the gas injection process, silicon is deposited on the pipe body  44 . Once the silicon builds up, the silicon can be removed from the pipe bases and used as silicon product. 
     Although the subject invention has been described with respect to preferred embodiments, those skilled in the art will readily appreciated that changes or modifications thereto may be made without departing from the spirit or scope of the subject invention as defined by the appended claims. 
     INCORPORATION BY REFERENCE 
     The entire contents of all patents, published patent applications and other references cited herein are hereby expressly incorporated herein in their entireties by reference.