Abstract:
Provided is a pyrolysis furnace having a gas flowing path controller with an improved structure. The pyrolysis furnace includes: a silicon substrate; a main body of the pyrolysis furnace; a heating unit that is formed around the main body and controls the temperature of the main body; at least one gas supplying tube through which a gas flows into the main body; and a gas flowing path controller that is installed inside the main body and controls the flow of the gas. As a result, controlling and manufacturing of small-sized nanoparticles with excellent characteristics is possible.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims the priority of Korean Patent Application No. 10-2004-0070818, filed on Sep. 6, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
         [0002]     1. Field of the Disclosure  
         [0003]     The present disclosure relates to a pyrolysis furnace having an improved gas flowing path controller, and more particularly, to a pyrolysis furnace which controls the flow speed of a gas such as a source gas, uniformly heats the source gas, and controls pyrolysis characteristics of the source gas, thereby manufacturing nanoparticles of uniform size.  
         [0004]     2. Description of the Related Art  
         [0005]     Methods of manufacturing nanoparticles are mainly divided into chemical wet process methods and vapor deposition methods. A vapor deposition method can be used to freely control the size of nanoparticles compared to other methods, and form nanoparticles at desired locations. Typical vapor deposition methods include a laser ablation method and a pyrolysis method.  
         [0006]     In the pyrolysis method, a precursor of a material that is to be processed is used. In more detail, by applying heat to a precursor, which is a source gas, the precursor is pyrolyzed, and monomers in an aerosol state are generated from the pyrolyzed precursor. The monomers are developed to form nanoparticles. Such a pyrolysis method is performed using a simple manufacturing apparatus and process, and the size of the nanoparticles can be easily controlled.  
         [0007]      FIGS. 1A and 1B  are views of conventional apparatuses for fabricating nanoparticles.  FIG. 1A  is a schematic view of a pyrolysis furnace  11 , an oxidation furnace  12 , and a deposition chamber  13  according to the prior art, and  FIG. 1B  is a cross section of a pyrolysis furnace disclosed in U.S. Pat. No. 6,586,785.  
         [0008]     Referring to  FIG. 1A , the pyrolysis furnace  11  is fed a source gas  11   a  of nanoparticles to be formed in the pyrolysis furnace  11  and a carrier gas  11   b.  The inside temperature of the pyrolysis furnace  11  is maintained at about 900° C. by a heating device (not shown), and thus the source gas  11   a  is pyrolyzed. When oxidation of the pyrolyzed source gas  11   a  is required, the source gas is oxidized at a high temperature of about 700° C. or higher inside the oxidation furnace  12 . Then, the pyrolyzed and oxidated source gas flows into the deposition chamber  13 , thereby depositing nanoparticles on a substrate  13   a.    
         [0009]     The pyrolysis furnace  11  may take the form of the pyrolysis furnace illustrated in  FIG. 1B . The pyrolysis furnace  11  is fed a source gas  11   a  and a carrier gas  11   b  via a source gas tube  15  and a carrier gas tube  14 , respectively. The source gas  11   a  and the carrier gas  11   b  are mixed and preheated in a ramping region  18   a  of the pyrolysis furnace  11 , and are pyrolyzed in a thermal decomposition region  18   b,  thereby changing into an aerosol state at a high temperature. Then, the aerosol flows in a direction indicated by an arrow  16   a  towards an exit  16   b  and into a deposition chamber (not shown) in which the nanoparticles forming process is performed.  
         [0010]     The basic characteristics such as the size, density, and dispersion of the nanoparticles are determined by the density of the source gas  11   a,  that is, a precursor. When fabricating nanoparticles with a high density, the density of the source gas  11   a  needs to be high. However, as the density of the precursor increases, the dispersion characteristics of the generated nanoparticles deteriorate.  
         [0011]     Such a disadvantage is known to be related to a reaction that occurs when the source gas  11   a  enters into the pyrolysis furnace  11  for the pyrolysis process. That is, the pyrolysis characteristics of the source gas  11   a  change according to the amount of time the source gas  11   a  remains in the ramping region  18   a  (i.e., a preheating region) after the source gas  11   a  enters the pyrolysis furnace  11  and before the pyrolysis occurs.  
         [0012]      FIG. 2  is a graph illustrating the temperature distribution of a gas injected into the pyrolysis furnace  11  illustrated in  FIG. 1B . In the graph, it can be seen that there is a great change in the temperature in the ramping region  18   a  when the source gas  11   a  and the carrier gas  11   b  are supplied to the pyrolysis furnace  11 . If the time the gas spends in the ramping region  18   a  increases due to the temperature change, the size of a precursor, which is the source gas  11   a,  changes, thereby deteriorating the dispersion characteristics of nanoparticles.  
         [0013]     To form nanoparticles of uniform size, the source gas  11   a  and the carrier gas  11   b  must be quickly and sufficiently mixed in uniform densities before pyrolysis occurs, and the mixed gases must have a uniform density distribution throughout the pyrolysis furnace  11 . However, a conventional pyrolysis apparatus and process does not satisfy these requirements.  
       SUMMARY OF THE INVENTION  
       [0014]     Embodiments of the present invention provide a pyrolysis furnace having a ramping region with an improved structure to minimize the time required to preheat a precursor, which is a source gas, thereby improving pyrolysis characteristics of the precursor when fabricating nanoparticles using a pyrolysis method.  
         [0015]     According to an aspect of the present invention, there is provided a pyrolysis furnace including: a main body of the pyrolysis furnace; a heating unit that is formed around the main body and controls the temperature of the main body; at least one gas supplying tube through which a gas flows into the main body; and a gas flowing path controller that is installed inside the main body and controls the flow of the gas.  
         [0016]     The main body can include a ramping region in which a supply gas is preheated; and a pyrolysis region in which the source gas is pyrolyzed.  
         [0017]     The gas flowing path controller can be installed in the ramping region.  
         [0018]     A gas flowing path can be formed between an outer wall of the gas flowing path controller and an inner wall of the main body so that the gas can flow into the pyrolysis region between the outer wall of the gas flowing path controller and the inner wall of the main body.  
         [0019]     The gas flowing path controller can be supported by a movable supporter connected to the gas flowing path controller and a side wall of the main body so that the location of the gas flowing path controller can be adjusted inside the main body.  
         [0020]     An outer wall of the gas flowing path controller can contact an inner wall of the main body, and at least one gas flowing path is formed inside the gas flowing path controller so that the gas can flow into the pyrolysis region.  
         [0021]     The gas flowing path can include through-holes passing through the gas flowing path controller.  
         [0022]     The diameters of the through-holes are greater near the inner wall of the main body.  
         [0023]     The gas flowing path controller can be formed of the same material as the main body.  
         [0024]     The gas flowing path controller can be formed of a material including quartz.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0026]      FIG. 1A  is a schematic view of a pyrolysis furnace, an oxidation furnace, and a deposition chamber according to the prior art;  
         [0027]      FIG. 1B  is a cross section of a pyrolysis furnace disclosed in U.S. Pat. No. 6,586,785;  
         [0028]      FIG. 2  is a graph illustrating the temperature distribution of a gas injected into a pyrolysis furnace illustrated in  FIG. 1B ;  
         [0029]      FIGS. 3A through 3C  are views of a pyrolysis furnace including a gas flowing path controller according to an embodiment of the present invention;  
         [0030]      FIGS. 4A and 4B  are views of a pyrolysis furnace including a gas flowing path controller according to another embodiment of the present invention; and  
         [0031]      FIG. 5  is a graph comparing sizes and densities of nanoparticles formed using a pyrolysis furnace with a gas flowing path controller and nanoparticles formed using a pyrolysis furnace without a gas flowing path controller. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     A pyrolysis furnace with a gas flowing path controller having an improved structure will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.  
         [0033]      FIG. 3A  is a cross sectional view of a pyrolysis furnace including a gas flowing path controller  34   a  according to an embodiment of the present invention. Referring to  FIG. 3A , a heating unit  33  formed around the outer circumference of a main body  31  of the pyrolysis furnace is composed of at least one gas supplying tube through which a source gas and a carrier gas pass. A ramping region  35   a  in which the source gas and the carrier gas are mixed and preheated, and a pyrolysis region  35   b  in which the source gas and the carrier gas are pyrolyzed exist in the main body  31 . The gas flowing path controller  34   a  is formed in the ramping region  35   a.    
         [0034]     Although the cylindrical-shaped gas flowing path controller  34   a  is illustrated in  FIG. 3A , the shape of the gas flowing path controller  34   a  need not be cylindrical. The gas flowing path controller  34   a  is formed inside the ramping region  35   a,  and may be made of a non-reactive material in which the pyrolysis furnace is typically made of, such as quartz.  
         [0035]     As illustrated in  FIG. 3A , for the supplied gas to propagate along the length of the pyrolysis furnace along a gas flowing path formed between the main body  31  and the gas flowing path controller  34   a,  the gas flowing path controller  34   a  must have a smaller diameter than the inner diameter of the main body  31 . That is, the gas flowing path of the supply gas in the ramping region  35   a  is between the outer wall of the gas flowing path controller  34   a  and the inner wall of the main body  31 .  
         [0036]      FIGS. 3B and 3C  are perspective views of the gas flowing path controller  34   a  illustrated in  FIG. 3A .  
         [0037]     Referring to  FIG. 3B , the gas flowing path controller  34   a  is fixed by a fixed supporter  36  connected to the inner wall of the main body  31 . The fixed supporter  36  is installed inside the main body  31  so as not to affect the gas flowing path of the supply gas supplied to the main body  31 .  
         [0038]     Referring to  FIG. 3C , the gas flowing path controller  34   a  is supported by a movable supporter  37 , and the length of the movable supporter  37  can be controlled from the outside of the main body  31 . Therefore, the location of the gas flowing path controller  34   a  can be controlled along the length of the movable supporter  37  inside the main body  31 .  
         [0039]      FIG. 4A  is a cross-sectional view of a pyrolysis furnace including a gas flowing path controller  34   b  according to another embodiment of the present invention. Referring to  FIG. 4A , a main body  31  of the pyrolysis furnace can be divided into a ramping region  35   a  in which a source gas and a carrier gas are mixed and a pyrolysis region  35   b  in which the source gas and the carrier gas are pyrolyzed. The gas flowing path controller  34   b  is formed in the ramping region  35   a,  to which gas supplied through a gas supplying tube  32  is injected, and is located inside the main body  31 . The structure of the pyrolysis furnace in  FIG. 4A  is similar to the structure of the pyrolysis furnace in  FIG. 3A .  
         [0040]     However, the gas flowing path controller  34   b  has a diameter similar to the inner diameter of the main body  31 , and through-holes  38  are formed on the gas flowing path controller  34   b  so that the source gas and the carrier gas can flow along the length of the main body  31 .  
         [0041]      FIG. 4B  is a perspective view of the pyrolysis furnace of  FIG. 4A , illustrating the through-holes  38  formed inside the gas flowing path controller  34   b  along the length of the main body  31 . The shapes and sizes of the through-holes  38  can be changed, but the size and diameter or distribution of the through-holes  38  increase further away from the center of the gas flowing path controller  34   b  in consideration of heat transfer since the source gas and the carrier gas need to be mixed and preheated considering the characteristics of the ramping region  35   a.    
         [0042]     The gas flowing path controller  34   b  is formed in the ramping region  35   a  as illustrated in  FIGS. 3A and 4A  for the following reasons.  
         [0043]     First, to maximize efficient preheating in the ramping region  35   a,  the source gas and the carrier gas flow through the main body  31  as closely as possible to the inner wall of the main body  31 , which has a relatively high temperature due to the heating unit, thereby increasing the temperature of the supply gas to the temperature at which pyrolysis occurs faster.  
         [0044]     Second, by reducing the area of the ramping region  35   a  to decrease the time that the supply gases such as the source gas and the carrier gas remains in the ramping region  35   a,  the size change of particularly a precursor, which is the source gas, is prevented, thereby preventing deterioration of dispersion characteristics of nanoparticles.  
         [0045]     Therefore, by forming the gas flowing path controllers  34  in the ramping regions  35   a  as in  FIGS. 3A and 4A , the source gas and the carrier gas flow into the ramping region  35   a  and mixes, and quickly pass through the ramping region  35   a,  and thus, most of the source gas is simultaneously pyrolyzed in the same region at the same temperature. The gas flowing path controller  34  has a cylindrical shape, symmetrical about the flow direction of the gases or has through-holes  38  formed inside the gas flowing path controller  34  as described above.  
         [0046]     The present inventor manufactured nanoparticles through a pyrolysis method using a pyrolysis furnace including a gas flowing path controller. A conventional pyrolysis furnace in which a cylindrical-shaped gas flowing path controller was installed in a ramping region and a conventional reaction chamber were used.  
         [0047]     To form Si nano particles on a substrate, SiH 4  was used as a source gas, and N 2  was used as a carrier gas. The cylindrical-shaped gas flowing path controller was installed in the ramping region of the pyrolysis furnace. Since SiH 4  starts to pyrolyze in the range of about 300-600° C., the temperature of the pyrolysis furnace was maintained greater than 300° C. using a heating unit. The pyrolyzed Si was deposited on the substrate, thereby forming nanoparticles. To compare to the prior art, other nanoparticles were formed under the same conditions except that the gas flowing path controller was not included in the pyrolysis furnace.  
         [0048]      FIG. 5  is a graph comparing the sizes and densities of nanoparticles formed using the pyrolysis furnace with the gas flowing path controller and nanoparticles formed using the pyrolysis furnace without the gas flowing path controller as described above. The x-axis represents the size of the nanoparticles, and the y-axis represents the distribution of nanoparticles according to the sizes of the nanoparticles.  
         [0049]     Referring to  FIG. 5 , Si nanoparticles with a diameter of about 8 nm were mostly formed while nanoparticles with a diameter greater than 15 nm were hardly formed when using the pyrolysis furnace according to an embodiment of the present invention. In other words, the nanoparticles were very uniform in size. However, Si nanoparticles with a diameter about 10 nm were mostly formed using the conventional technique and quite a few nanoparticles with a diameter greater than 15 nm were formed, and thus the distribution of the diameters of the nanoparticles were wide.  
         [0050]     The standard deviations of the size of Si nanoparticles formed using the present invention and Si nanoparticles formed using the conventional technique were measured. It was determined that the standard deviation of the size of the Si nanoparticles formed using the present invention was 1.31, while the standard deviation of the size of the Si nanoparticles formed using the conventional technique was 1.42. Therefore, the statistical data indicates that nanoparticles with improved characteristics can be formed when the gas flowing path controller is formed in the pyrolysis furnace as in the present invention.  
         [0051]     The present invention has the following advantages over the conventional method of manufacturing nanoparticles. Nanoparticles of uniform size can be manufactured by forming a gas flowing path controller in a ramping region to control pyrolysis characteristics and uniformly heat source gases. In particular, since deterioration of dispersion characteristics can be prevented when a source gas with a high concentration is used, it is possible to manufacture small-sized nanoparticles having excellent characteristics. Thus, the efficiency of the overall manufacturing process can be improved.  
         [0052]     The present invention has been particularly shown and described with reference to exemplary embodiments thereof. However, the gas flowing path controller can be formed in various shapes besides the cylindrical shape and can be structured to have a plurality of holes therein, and may have, for example, a mesh structure, a lattice structure, or a beehive structure. Therefore, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.