Abstract:
Showerheads including a plate having a plurality of gas outlet holes extending therethrough and a head cover coupled to the plate to form a space between the plate and the head cover. A gas supply inlet member is configured to provide gas to the space directed toward the head cover. A gas distribution member on an inner face of the head cover facing the space is configured to partially suppress flow of the gas provided to the space in a direction along the gas distribution member to substantially uniformly distribute the gas in the space. The direction along the gas distribution member may be a horizontal direction and the gas provided to the space is directed in a substantially vertical upward direction. Apparatus and methods using the showerheads are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is related to and claims priority from Korean Patent Application No. 2004-12093 filed on Feb. 24, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a showerhead, an apparatus for processing a semiconductor substrate, and more particularly, to an apparatus having a showerhead and a method of distributing a gas using the same. 
   Semiconductor devices are provided for various data storage and processing applications having a high integration density and performance. To manufacture such high integration density and high performance semiconductor devices, it is generally important to use technology that will accurately form a thin film pattern on a semiconductor substrate. 
   The technology approaches for forming the thin film pattern on the semiconductor substrate may generally be divided into a physical vapor deposition (PVD) process and a chemical vapor deposition (CVD) process. In addition, it is known to form a thin film pattern by an atomic layer deposition (ALD) process that may more accurately form a thin layer. 
   The CVD and the ALD process may operate based on a chemical reaction between a source gas AX and a reaction gas BY. The chemical reaction process may be represented by the following chemical reaction equation:
 
AX(g)+BY(g)→AB(s)+XY(g)
 
   To facilitate the chemical reaction between the source gas and the reaction gas, the gases may be heated at a high temperature or may be exposed to a high voltage using a showerhead. The showerhead generally heats the source and reaction gases or exposes the gases to the high voltage as well as spraying the gases on the semiconductor substrate. 
   A conventional showerhead for converting a process gas into a plasma state is disclosed in U.S. Pat. No. 6,173,673 issued to Golovato, et al. The conventional showerhead typically has a cylindrical shape. The showerhead is generally disposed over a process chamber in which a semiconductor substrate is manufactured. The source and reaction gases may then be introduced into the process chamber through the showerhead. 
     FIG. 1  is a cross sectional view illustrating a conventional showerhead  100 . Referring now to  FIG. 1 , the showerhead  100  has a cylindrical shape including an inner space. The showerhead  100  includes a head cover  110 , and first and second plates  120  and  130  having holes shown as defining gas outlets  103 . The first plate  120  is coupled to a lower face of the head cover  110 . A diffusion space  102  is formed between the head cover  110  and the first plate  120  when they are coupled together. The second plate  130  is coupled to a lower face of the first plate  120 . 
   A gas inlet  101  is formed through the head cover  110 . The gas outlets  103  extend through the first and second plates  120  and  130 . The gas inlet  101  is in fluid communication with the diffusion space  102 . The diffusion space  102  is also in fluid communication with the gas outlets  103 . 
   A source gas or a reacting gas is introduced into the showerhead  100  through the gas inlet  101 . The gas flows downwardly from the gas inlet  101  and widely diffuses in the diffusion space  102 . The gas may then be distributed on a semiconductor substrate (not shown) through the gas outlet  103 . However, as the diffusion space  102  in the conventional showerhead  100  has a relatively small volume, gas distributions in the diffusion space  102  may vary significantly at different positions relative to the gas inlet  101  and with the number of gas inlets provided. 
   When a gas is introduced into the diffusion space  102  through a gas inlet  101  that is positioned at a central portion of the head cover  110 , as shown in  FIG. 1 , the gas may be concentrated in a central portion of the diffusion space  102 . The gas concentration in the central portion of the diffusion space  102  may cause the gas to be distributed preferentially on a central portion of the semiconductor substrate through the gas outlets  103  that are positioned at central portions of the first and second plates  120  and  130 . Thus, a more extensive gas deposition reaction may be generated at the central portion of the semiconductor substrate as compared to an edge portion of the semiconductor substrate. As a result, a layer on the semiconductor substrate formed by the deposition reaction may have an uneven thickness that is gradually thinned from the central portion to the edge portion of the semiconductor substrate. 
   A layer having an uneven thickness may cause failure problems for a semiconductor device, such as deteriorating characteristics of the semiconductor device. Although various conventional technologies have been developed that are addressed to the above-mentioned problems, these technologies have failed to overcome the problems. 
   For example, in accordance with one known conventional technology, the gas inlet  101  is blocked and a gas pipe is built in the first plate  120 . The gas is jetted out from the central portion of the first plate  120  to the head cover  110 . Thus, more gas may be provided to the edge portion of the diffusion space  102  as compared to the central portion of the diffusion space  102 . As a result, the gas distribution to the edge portion of the first and second plates  120  and  130  may be increased. 
   However, the gas distribution to the central portion of the first and second plates  120  and  130  may be decreased, whereas the gas distribution on the edge portion of the first and second plates  120  and  130  is increased. Therefore, the deposition reaction at the edge portion of the semiconductor substrate may exceed that at the central portion of the semiconductor substrate. As a result, a layer on the semiconductor substrate may have an uneven thickness that is gradually thickened from the central portion to the edge portion of the semiconductor substrate. 
   As described above, when the gas is not uniformly distributed on the semiconductor substrate from the conventional showerhead  100 , the layer on the semiconductor substrate may have an uneven surface. When other layers are formed on the uneven surface of the layer in following processes, errors may be generated in the following processes, which may deteriorate performance characteristics of a semiconductor device. 
   SUMMARY OF THE INVENTION 
   Embodiments of the present invention provide showerheads including a plate having a plurality of gas outlet holes extending therethrough and a head cover coupled to the plate to form a space between the plate and the head cover. A gas supply inlet member is configured to provide gas to the space directed toward the head cover. A gas distribution member on an inner face of the head cover facing the space is configured to partially suppress flow of the gas provided to the space in a direction along the gas distribution member to substantially uniformly distribute the gas in the space. The direction along the gas distribution member may be a horizontal direction and the gas provided to the space is directed in a substantially vertical upward direction. The showerhead may be a showerhead for a semiconductor substrate processing apparatus and the gas may be a source gas and/or a reaction gas for forming a film on the semiconductor substrate. 
   In some embodiments of the present invention, the gas distribution member is a stepped structure providing a height of the space that decreases from a position where the gas is provided to the space to a position in the space displaced therefrom. The position where the gas is provided may be in a central portion of the space and the stepped structure may be convex. Alternatively, the position where the gas is provided may be in an edge portion of the space and the stepped structure may be concave. The plurality of gas outlet holes may be arranged in concentric circles and the stepped structure may have a corresponding arrangement of steps aligned with the concentric circles of gas outlet holes. The stepped structure may be a plurality of stepped grooves formed in the inner face of the head cover. 
   In other embodiments of the present invention, the gas distribution member is concentrically arranged with respect to a position from which the gas is provided and is configured to partially suppress a horizontal flow of the gas in the space. The gas distribution member may be a stepped structure on an inner face of the head cover facing the plate. The stepped structure may include stepped portions. 
   In further embodiments of the present invention, the position corresponds to at least one position in a central portion of the space, and the stepped structure includes stepped grooves concentrically positioned on the inner face of the head cover. The position may correspond to a plurality of positions that are arranged on a substantially common plane at substantially identical angular intervals around a central axis of the space. In other embodiments, the position corresponds to a plurality of positions that are arranged at spaced apart locations along an edge portion of the space at substantially identical angular intervals around a central axis of the space, and the stepped structure includes stepped protrusions that are concentrically positioned on the inner face of the head cover. The position may correspond to a plurality of positions that are arranged at spaced apart locations from a central portion to an edge portion of the space at substantially identical intervals in the space, and the stepped structure may include annular grooves concentrically positioned on the inner face of the head cover. 
   In other embodiments of the present invention, the gas supply inlet member is inserted into the plate in a horizontal direction. The shower head may further include a sealing member enclosing a lower portion of the plate, a second plate coupled to the seating member to form a second space between the sealing member and the second plate and a second gas supply inlet member that is configured to provide a second gas to the second space in a direction toward the plate. The second gas supply inlet member may extend from an edge portion of the second space to a central portion of the second space. The second gas supply inlet member may be inserted into the second plate in a horizontal direction. 
   In yet further embodiments of the present invention, apparatus for processing a substrate include a process chamber configured to receive a substrate to be processed therein and a chuck in the process chamber that supports the substrate. A showerhead is positioned to provide a gas to the process chamber. The showerhead includes a plate having a plurality of gas outlet holes extending therethrough, a head cover coupled to the plate to form a space between the plate and the head cover, a gas supply inlet member configured to provide gas to the space directed toward the head cover and a gas distribution member on an inner face of the head cover facing the space that is configured to partially suppress flow of the gas provided to the space in a direction along the gas distribution member to substantially uniformly distribute the gas in the space. 
   In other embodiments of the present invention, the gas distribution member is concentrically arranged with respect to a position from which the gas is supplied, the gas distribution member partially suppressing a horizontal flow of the gas. The apparatus further includes a discharging member configured to discharge remaining gas and byproducts generated in a process for processing the substrate to control a pressure in the process chamber. 
   In further embodiments of the present invention, a high-frequency power source provides a high-frequency power to the showerhead to convert the gas in the process chamber into a plasma. A heating member and a cooling member may be provided that control a temperature of the gas. The heating member may enclose the showerhead, and the cooling member may be arranged on the showerhead. 
   In yet other embodiments of the present invention, methods of distributing a gas include providing a showerhead that includes a plate and a head cover coupled to the plate to form a space between the plate and the head cover A gas is provided to the space in a direction toward the head cover. A horizontal flow of the gas in the space is partially suppressed to substantially uniformly distribute the gas in the space. 
   In some embodiments of the present invention, partially suppressing the horizontal flow of the gas includes partially suppressing the horizontal flow with a stepped structure positioned on a face of the head cover facing the plate. The stepped structure may include stepped portions. The stepped structure may include concentric stepped grooves on the face of the head cover and the gas being may be sprayed from a central portion of the space to the stepped grooves. In other embodiments, the stepped structure includes concentric stepped protrusions on the face of the head cover and the gas is sprayed from a central portion of the space to the stepped protrusions. The stepped structure may include concentric annular grooves spaced apart from each other by substantially identical intervals and the gas may be sprayed from a central portion of the space to the annular grooves. 
   In yet further embodiments of the present invention, showerheads include a plate having a plurality of gas outlet holes extending therethrough. A head cover is coupled to the plate to form a space between the plate and the head cover. A gas supply inlet member is configured to provide gas to the space directed toward the head cover. A gas distribution member on an inner face of the head cover facing the space includes a stepped structure providing a height of the space that decreases from a position where the gas is provided to the space to a position in the space displaced therefrom. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a cross sectional view illustrating a conventional showerhead; 
       FIG. 2  is an exploded perspective view illustrating a showerhead in accordance with some embodiments of the present invention; 
       FIG. 3  is an enlarged cross sectional view illustrating diffusion of a gas generated in the showerhead of  FIG. 2  according to some embodiments of the present invention; 
       FIG. 4  is an enlarged plan view illustrating a plate and a gas supply member for the showerhead of  FIG. 2  in accordance with some embodiments of the present invention; 
       FIG. 5  is a cross sectional view illustrating a showerhead in accordance with other embodiments of the present invention; 
       FIG. 6  is a cross sectional view illustrating a showerhead in accordance with further embodiments of the present invention; 
       FIG. 7  is a cross sectional view illustrating an apparatus for processing a semiconductor substrate in accordance with some embodiments of the present invention; and 
       FIG. 8  is a flow chart illustrating methods of distributing a gas in accordance with some embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. 
   It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
   It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
   Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
   The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
   Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
   Various embodiments of the present invention will now be described with reference to  FIGS. 2-4 .  FIG. 2  is an exploded perspective view illustrating a showerhead,  FIG. 3  is an enlarged cross sectional view illustrating a diffusion of a gas generated in the showerhead in  FIG. 2  and  FIG. 4  is an enlarged plan view illustrating a plate and a gas supply member of the showerhead of  FIG. 2  in accordance with some embodiments of the present invention. 
   Referring to  FIGS. 2 to 4 , a showerhead  200  of the illustrated embodiments includes a head cover  210 , a first plate  220 , a sealing member  225 , a second plate  230 , a first gas supply line  226 , a second gas supply line  236 , and a gas distribution member  240  defined by the head cover  210 . 
   The head cover  210  may have a cylindrical shape, and may be formed of aluminum and/or steel. A stepped structure is formed in a lower face  215  of the head cover  210 . The stepped structure defines a first diffusion space  221  in the head cover  210 . 
   In particular, a cylindrical first groove  211  having a first diameter is vertically formed at the lower face  215  of the head cover  210 . A second groove  212  having a second diameter less than the first diameter is formed from an inner end of the first groove  211 . A third groove  213  having a third diameter less than the second diameter is formed from an inner end of the second groove  212 . A fourth groove  214  having a fourth diameter less than the third diameter is formed from an inner end of the third groove  213 . Thus, a first stepped portion  241  is formed between the first groove  211  and the lower face  215 . A second stepped portion  242  is formed between the first and second grooves  211  and  212 . A third stepped portion  243  is formed between the second and third grooves  212  and  213 . A fourth stepped portion  244  is formed between the third and the fourth grooves  213  and  214 . The four stepped portions  241 ,  242 ,  243 ,  244  of the illustrated embodiments comprise the gas distribution member  240 . The stepped structure is formed from the lower face  215  of the head cover  210  to define the first diffusion space  221  in the head cover  210 . 
   In the illustrated embodiments of  FIG. 2 , the first, the second, the third and the fourth stepped portions  241 ,  242 ,  243  and  244  are respectively formed from the lower face  215  of the head cover  210  by the first, the second, the third and the fourth grooves  211 ,  212 ,  213  and  214  that have different respective diameters. The first diffusion space  221  includes the first, the second, the third and the fourth grooves  211 ,  212 ,  213  and  214 . 
   The first diffusion space  221  has a diameter that is gradually stepwise decreased and a depth that is correspondingly gradually stepwise increased from the first stepped portion  241  to the fourth stepped portion  244 . In other words, the first diffusion space  221  has a stepped radial structure with respect to the first stepped portion  241 . When a gas is introduced into the first diffusion space  221 , the stepped structure substantially uniformly distributes the gas in the first diffusion space  221  from a central through an outer edge region thereof. As noted above, the stepped structure including the first, the second, the third and the fourth stepped portions  241 ,  242 ,  243  and  244  will be collectively referred to herein as the gas distribution member  240 . 
   In some embodiments of the present invention, an annular groove (not shown) having a diameter substantially equal to or greater than the first diameter of the first groove  211  may be formed at the lower face  215  of the head cover  210 . A detachable gas distribution member (not shown) having a stepped structure therein may be inserted into the annular groove. A stepped diffusion space (not shown) having a shape substantially identical to the first diffusion space may thereby be formed in the head cover  210  having the detachable gas distribution member. In other words, the one part structure  210  illustrated in  FIG. 2  may be a multi-part structure. 
   In addition, while four stepped portions are shown as defining the gas distribution member  240  in the illustrated embodiments of  FIGS. 2-4 , more or less stepped portions may be used and the number thereof may vary based on the number and pattern of arrays of first outlet holes  229  in the first plate  220 . 
   As shown in the embodiments of  FIGS. 2-4 , the first plate  220  is coupled to the lower face  215  of the head cover  210  to define the first diffusion space  221  between the first plate  220  and the head cover  210 . The first plate  220  may have an outer diameter substantially identical to that of the head cover  210 . As shown in  FIGS. 2 and 3 , vertical distances between the lower face  215  of the head cover and an upper face of the first plate  220  are gradually decreased from a central portion of the first plate  220  to an edge portion of the first plate  220 . 
   First holes  218 , which may be threaded or unthreaded, for attaching the first plate  220  are formed through an edge portion of the head cover  210  that makes contact with the first plate  220 . As seen in  FIG. 2 , a plurality of the first holes  218  may be disposed around the edge portion of the head cover  210 . Second holes  228 , which may be threaded or unthreaded, aligned with corresponding ones of the first holes  218  are formed through the edge portion of the first plate  220 . First screw(s)  227 , one of which is shown in  FIG. 2 , are inserted into the first and the second holes  218  and  228  to attach the first plate  220  to the head cover  210 . The first plate  220  may be formed from the same material as the head cover  210 , such as a metal. 
   The first plate  220  shown in the embodiments of  FIGS. 2-4  has a plurality of first outlet holes  229 . The first outlet holes  229  extend vertically through the first plate  220 . In the illustrated embodiments, there is a greater density of the first outlet holes  229  disposed within a region of the central portion of the first plate  220 . The higher density region may have a diameter substantially equal to or less than the first diameter of the first groove  211 . 
   A first horizontal hole  224  (or a plurality of radially displaced horizontal holes) is formed in a horizontal direction extending into the first plate  220 . The first horizontal hole  224  extends from a side face of the first plate  220  to the central portion of the first plate  220 . For the embodiments of  FIGS. 2-4 , the first horizontal hole  224  does not intersect any of the first outlet holes  229 . An inner end of the first horizontal hole  224  adjacent to the central portion of the first plate  220  is upwardly opened. In other words, the first horizontal hole  224  generally has an L shape. 
   A first gas supply line  226  (or lines as seen in  FIG. 4 ) having a tubular shape is inserted into the first horizontal hole  224 . The first gas supply line  226  has a diameter substantially equal to or less than that of the first horizontal hole  224  and also has a length longer than that of the first horizontal hole  224 . The first gas supply line  226  is connected to a gas reservoir (not shown) containing a supply of a gas or gases to be used in a manufacturing process. The gas is introduced into the first diffusion space  221  through the first gas supply line  226 . The first gas supply line  226  in the illustrated embodiments terminates at a position that is adjacent to the inner end of the first horizontal hole  224 . As a result, the gas may be readily provided to the inner end of the first horizontal hole  224  through the first gas supply line  226 . 
   The gas (hereinafter, referred to as a first gas) passing through the first gas supply line  226  is jetted from an opening formed at the central portion of the first plate  220 . That is, the opening is in fluid communication with the first horizontal hole  224 . The first gas is delivered from the first plate  220  into the first diffusion space  221 . 
   As shown in  FIG. 4 , to facilitate provision of the first gas into the first diffusion space  221 , four first horizontal holes  224  are formed through the first plate  220  rotationally offset by a substantially identical angle, shown as about 90° in  FIG. 4 . Four first gas supply lines  226  are provided to the respective four first horizontal holes  224 . 
   While four first gas supply lines  226  arranged by an offset angle of about 90° on a substantially identical plane are shown in  FIG. 4 , the present invention is not limited to such an arrangement. The numbers and intervals of the first gas supply line(s)  226  may vary in various embodiments of the present invention as will be understood by those skilled in the art. Further, although the first gas supply line  226  is received in the first plate  220  in the illustrated embodiments, the first gas supply line  226  may also be disposed over the first plate  220 . 
   The circular second plate  230  is disposed under the first plate  220 . The second plate  230  may have a diameter substantially identical to that of the first plate  220 . The sealing member  225 , having a ring shape, is interposed between the first and second plates  220  and  230  to define a second diffusion space  222  between the first plate  220  and the second plate  230 . A second gas may be introduced into the second diffusion space  222 . 
   The second plate  230  in the illustrated embodiments has a configuration substantially identical to that of the first plate  220 . Second outlet holes  239  corresponding to the first outlet holes  229  are formed extending through the second plate  230 . The second outlet holes  239  may be concentrated within a region in a central portion of the second plate  230  that corresponds to that of the first plate  220 . The second plate  230  may be formed of a material, such as a metal, substantially identical to that of the first plate  220 . 
   The sealing member  225  and the second plate  230  may be attached to the first plate  220  using a second screw  237  or screws (one shown in  FIG. 2 ). Attaching the sealing member  225  and the second plate  230  to the first plate  220  using the second screw  237  may be carried out in generally the same manners as described with reference to attaching the first plate  220  to the head cover  210  using the first screw(s)  227 . 
   Second horizontal holes  234  are formed in the second plate  230  in a horizontal direction. In the illustrated embodiments four second horizontal holes  234  are provided at rotationally displaced locations at substantially equal angular intervals. Second gas supply lines  236  are inserted into corresponding ones of the second horizontal holes  234 . Inserting the second gas supply lines  236  into the second horizontal holes  234  may be performed in substantially the same manner as described with reference to inserting the first gas supply lines  226  into the first horizontal lines  224 . 
   Operations related to generally uniformly distributing the first and second gases using the showerhead of  FIGS. 2-4  according to various embodiments of the present invention will now be described. The first plate  220 , the sealing member  225  and the second plate  230  are sequentially disposed under the head cover  210 . The first gas supply line  226  is installed in the first plate  220  and the second gas supply line  236  is installed in the second plate  230 . 
   The first gas passing through the first gas supply line  226  is jetted from the central portion of the first plate  220  to the central portion of the head cover  210 . The jetted first gas diffuses in a substantially spherical shaped pattern and then contacts the gas distribution member  240 . For example, after a portion of the first gas sprayed onto the fourth groove  214  diffuses horizontally and contacts the fourth stepped portion  244 , the portion of the first gas sprayed onto the fourth groove  214  drops downwardly (i.e., back towards the first plate  220 . After a portion of the first gas sprayed onto the third groove  213  diffuses horizontally and contacts against the third stepped portion  243 , the portion of the first gas sprayed onto the third groove  213  drops downwardly. After a portion of the first gas sprayed onto the second groove  212  diffuses horizontally and contacts the second stepped portion  242 , the portion of the first gas sprayed onto the second groove  212  drops downwardly. A portion of the first gas sprayed onto the first groove  211  diffuses horizontally and contacts the first stepped portion  241 , and then the portion of the first gas sprayed onto the first groove  211  drops downwardly. As a result, in some embodiments of the present invention, the first gas may be uniformly distributed onto the upper face of the first plate  220 . To uniformly distribute the first gas onto the first plate  220 , the first, the second, the third and the fourth stepped portions  241 ,  242 ,  243  and  244  may be provided as tapered structures inclined by a predetermined angle. 
   The fluid mechanics of flows of the first gas may be very complicated. Thus, completely analyzing the actual flows of the first gas may be very difficult. Accordingly, the flows of the first gas are schematically analyzed herein. For the illustrated embodiments of  FIGS. 2-4 , as horizontal diffusion of the first gas sprayed from the central portion of the first plate  220  may be partially suppressed due to the gas distribution member  240 , the first gas may be generally uniformly distributed in the first diffusion space  221 . 
   The first gas in the first diffusion space  221  may be uniformly distributed over the first plate  220 . Also, the first gas passing through the first plate  220  may thereby be uniformly distributed in the second diffusion space  222 . 
   The second gas is jetted into the second diffusion space  222  through the second gas supply line  236 . To substantially uniformly distribute the second gas in the second diffusion space  222 , the second diffusion space  222  may have stepped structures. However, particularly when the second gas has a low molecular weight, the second diffusion space may not have stepped structures. For example, when the second gas includes O 2  or N 2 O having a molecular weight less than that of Ti(tmhd) 2  or Zr(tmhd) 2 , the second gas including O 2  or N 2 O generally easily diffuses in a small space. Thus, the second gas may readily diffuse regardless of whether the second diffusion space  222  has the stepped structures. 
   As shown in  FIG. 3 , the second gas widely diffuses in the second diffusion space  222  and may also be readily mixed with the first gas passing through the first plate  220 . Accordingly, the first and the second gases may be uniformly distributed in the second diffusion space  222 . 
   Numbers of the stepped portions provided to the gas distribution member  240  may vary in accordance with the arrangement of arrays of the first outlet holes  229  in the first plate  220 . In particular, with reference to the embodiments in  FIGS. 3 and 4 , the first outlet holes  229  are disposed concentrically with respect to a central axis of the first plate  220 . The first gas supply lines  226  are disposed spaced apart from each other radially by an angle of about 90° and do not intersect with the first outlet holes  229 . 
   The gas distribution member  240  may have numbers of the stepped portions substantially identical to those of concentric circles of the first outlet holes  229 . Further, the concentric circles may have diameters substantially identical to those of the first, the second, the third and the fourth grooves  211 ,  212 ,  213  and  214 , respectively. 
   As described above, the horizontal diffusion of the first gas may be partially suppressed by the gas distribution member  240  so that the first gas drops downwardly from the stepped portions of the gas distribution member  240 . To increase an amount of the first gas passing through the first plate  220 , the first outlet holes  229  may be disposed at positions on which the first gas drops. In the embodiments of  FIGS. 2-4 , the gas distribution member  240  has four stepped portions and the first outlet holes  229  are disposed along four corresponding diameter concentric circles on the first plate  220 . The first outlet holes  229  may be arranged in accordance with the numbers of the stepped portions and the shape of the gas distribution member  240 . However, the arrangement of the first outlet holes  229  may vary in various embodiments of the present invention. 
   When the inner face of the head cover  210  has a stepped structure, the gas distribution in the first diffusion space  221  may be improved. Generally, a fluid jetted in a fountain shape drops on regions spaced apart from the position of the jet. Thus, an amount of the fluid dropping in regions adjacent to the jet position may be very small. When a gas having a high molecular weight is jetted, the gas distribution is typically poor. However, according to some embodiments of the present invention, the first gas is uniformly distributed in the first diffusion space  221  due to the gas distribution member  240 . Therefore, the amounts of the first gas returning to the central portion of the first plate  220  may be sufficient. 
   A gas distribution member  240  having a dome shape may have comparatively poor performance. When the gas distribution member  240  has a dome shape, the first gas generally diffuses along the inner face of the first diffusion space  221 , thereby concentrating the first gas on the edge portion of the first plate  220 . As a result, an amount of the first gas sprayed from the edge portion of the first plate  220  may be increased. 
   For the embodiments of  FIGS. 2-4 , the showerhead  200  has a first diffusion space  221  having a height that is gradually increased and a width that is gradually decreased moving from the edge portion of the head cover  210  to the central portion of the head cover  210  in a step-wise manner. Therefore, the first gas may rise upwardly and then widely diffuse. The first gas may horizontally diffuse along the inner face of the head cover  210  and then drop downwardly due to the gas distribution member  240 . As a result, the first gas may be uniformly distributed over the first plate  220 . 
   Further embodiments of the present invention will now be described with reference to  FIG. 5 .  FIG. 5  is a cross sectional view illustrating a showerhead according to some embodiments of the present invention. 
   In the embodiments of  FIG. 5 , a showerhead  300  includes a head cover  310 , a first plate  320 , a sealing member  325 , a second plate  330 , a first gas supply line(s)  326 , a second gas supply line(s)  336 , and a gas distribution member  340 . 
   The showerhead  300  includes various features that are substantially identical to those described with reference to  FIGS. 2-4 . However, the first gas supply line  326  and the gas distribution member  340  differ in  FIG. 5  as will now be further described. 
   The gas distribution member  340  has a stepped structure provided on a lower face  315  of the head cover  310 . The stepped structure of the gas distribution member  340  is a convex structure as contrasted with the concave structure of the gas distribution member  240 . In particular, a cylindrical first groove  311  is formed at the lower face  315  of the head cover  310 . The first groove  311  has a first outer diameter less than that of the head cover  310 , and a first inner diameter. A second groove  312  is formed from an inner end of the first groove  311 . The second groove  312  has a second outer diameter substantially identical to the first inner diameter, and a second inner diameter. A third groove  313  is formed from an inner end of the second groove  312 . The third groove  313  has a third outer diameter substantially identical to the second inner diameter, and a third inner diameter. A fourth groove  314  is formed from an inner end of the third groove  313 . The fourth groove  314  has a fourth outer diameter substantially identical to the third inner diameter, and a fourth inner diameter. Thus, a first stepped portion  341  is formed between the first groove  311  and the lower face  315 . A second stepped portion  342  is formed between the first and the second grooves  311  and  312 . In addition, a third stepped portion  343  is formed between the second and the third grooves  312  and  313 . A fourth stepped portion  344  is formed between the third and the fourth grooves  313  and  314 . As a result, a stepped structure is formed on the lower face  315  of the head cover  310  to define the first diffusion space  321  in the head cover  310 . As the first outer diameter is shorter than the outer diameter of the head cover  310 , the first diffusion space  321  is isolated from the outside by the head cover  310 . 
   Comparing the first diffusion space  321  of  FIG. 5  with the first diffusion space  221  of  FIG. 3 , the first diffusion space  321  has a convex shape, whereas the first diffusion space  221  has the concave shape. Thus, the gas distribution member  340  of  FIG. 5  has a configuration that may be described as symmetrical to the gas distribution member  240  of  FIG. 3 . The numbers of stepped portions included in the gas distribution member  340  may be substantially identical to those of circumferentially distributed sets of the first outlet holes  329  formed extending through the first plate  320 . 
   The first outlet holes  329  illustrated in  FIG. 5  are formed through the first plate  320  along four concentric circles of increasing diameters extending out from the central portion thereof. Thus, the illustrated number of concentric circles are substantially identical to those of the stepped portions of the gas distribution members  340 . However, the number of the concentric circles may vary in various embodiments of the present invention. 
   A first horizontal hole (or holes, two visible in the cross-section of  FIG. 5 )  324  is formed in a horizontal direction extending into the first plate  320 . The first horizontal hole  324  is formed extending from a side face of the first plate  320  towards central portion of the first plate  320 . The first horizontal hole  324  does not intersect with the first outlet holes  329 . An inner end (towards the central portion) of the first horizontal hole  324  is opened upwardly. Thus, the first horizontal hole  324  generally has an L shape. Four first horizontal holes  324  may be disposed at substantially identical radially offset angular locations, for example, about every 90°. In other embodiments, the first horizontal holes  324  may be arranged spaced apart from each other by an angle of more or less than 90°. 
   A first gas supply line  326  is inserted into the first horizontal hole  324  (or a line into each corresponding hole). A first gas is introduced into the first diffusion space  321  through the first gas supply line  326 . As compared with the embodiments of  FIG. 3 , the first gas is jetted from an opening formed at an edge portion of the first plate  320 . The first gas is sprayed from the edge portion of the first plate  320  towards the head cover  310 . 
   The first plate  320  is coupled to the lower face  315  of the head cover  310 . The sealing member  325 , having a ring shape, is coupled to a lower face of the first plate  320 . The second plate  330  is coupled to a lower face of the sealing member  325 . The first and second plates  320  and  330  and the sealing member  325  define a second diffusion space  322  into which a second gas is introduced. The sealing member  325  and the second plate  330  may be substantially identical to those of the embodiments of  FIGS. 2-4  and, therefore, need not be further described herein. 
   Operations for uniformly distributing the first and second gases using the showerhead of  FIG. 5  according to some embodiments of the present invention will now be described. The first gas passing through the first gas supply line  326  is jetted from the edge portion of the first plate  320  to the edge portion of the head cover  310 . The jetted first gas diffuses in a generally spherical shape, and then contacts against the gas distribution member  340 . In particular, a portion of the first gas sprayed to the first groove  311  diffuses horizontally and contacts the first stepped portion  341 , and then the portion of the first gas sprayed to the first groove  311  drops downwardly. After a portion of the first gas sprayed to the second groove  312  diffuses horizontally and contacts the second stepped portion  342 , the portion of the first gas sprayed to the second groove  312  drops downwardly. After a portion of the first gas sprayed to the third groove  313  diffuses horizontally and contacts the third stepped portion  343 , the portion of the first gas sprayed to the third groove  313  drops downwardly. A portion of the first gas sprayed to the fourth groove  314  diffuses horizontally and contacts the fourth stepped portion  344 , and then the portion of the first gas sprayed to the fourth groove  314  drops downwardly. Therefore, the first gas may be uniformly distributed over the first plate  320 . 
   For the embodiments of  FIG. 5 , as horizontal diffusion of the first gas sprayed from the edge portion of the first plate  320  is partially suppressed due to the gas distribution member  340 , the first gas may be uniformly distributed in the first diffusion space  321 . The first gas in the first diffusion space  321  may, therefore, be uniformly distributed over the first plate  320 . As such, the first gas passing through the first plate  320  may be uniformly distributed in the second diffusion space  322 . 
   The second gas may widely diffuse in the second diffusion space  322  and may thereby be readily mixed with the first gas passing through the first plate  320 . Accordingly, the first and second gases may be uniformly distributed in the second diffusion space  322 , thereby improving distributions of the first and second gases in the second diffusion space  322 . 
   The gas distribution member  340  may have stepped portions substantially corresponding to (i.e., radially aligned with) respective ones of the concentric circles of the first outlet holes  329 . 
   For the embodiments of  FIG. 5 , the horizontal diffusion of the first gas may be partially suppressed by the gas distribution member  340  having the convex structure so that the first gas may be more uniformly distributed in the first diffusion space  321 . The first gas in the first diffusion space  321  passes through the first plate  320 , and is then distributed in the second diffusion space  322 . The first gas is mixed with the second gas in the second diffusion space  322 . The mixed gas may be uniformly distributed on a semiconductor substrate through the second plate  330 . 
   Further embodiments of the present invention will now be described with reference to  FIG. 6 .  FIG. 6  is a cross sectional view illustrating a showerhead according to further embodiments of the present invention. As shown in  FIG. 6 , a showerhead  400  includes a head cover  410 , a first plate  420 , a sealing member  425 , a second plate  430 , a first gas supply line  426 , a second gas supply line  436 , a gas distribution member  440 , a heating member  450  and a cooling member  460 . 
   The showerhead  400  of the embodiments of  FIG. 6  includes aspects substantially identical to those in the previously described embodiments and also includes the heating member  450  and the cooling member  460 . The heating member  450  may surround and enclose the head cover  410 . The heating member  450  heats the head cover  410  to control a temperature of a gas in a first diffusion space  421 . Examples of the heating member  450  include a heating coil, a heating jacket, a lamp, etc. A heating jacket is shown as the heating member  450  in  FIG. 6 . 
   The heating member  450  transmits heat into the head cover  410  to heat the gas in the first diffusion space  421 . Additionally, a temperature sensor (not shown) for monitoring and controlling the temperature of the gas may be used. Examples of the temperature sensor include a thermocouple or the like. 
   To control the temperature in the first diffusion space  421 , the cooling member  460  as well as the heating member  450  may be used. The cooling member  460  cools the head cover  410  to control the temperature of the gas in the first diffusion space  421 . The cooling member  460  may include a cooling line through which a cooling media, such as water, flows and the like. 
   As described above, the showerhead  400  of  FIG. 6  includes the heating member  450  and the cooling member  460  for controlling the temperature of the gas in the first diffusion space  421 . Thus, a gas sensitive to variations of temperatures may be used in the showerhead  400  while controlling the temperature thereof. 
   Operations for controlling the temperature of the gas in the first diffusion space  421  according to some embodiments of the present invention will now be described. Generally, a deposition process for forming a layer on a semiconductor substrate may be performed at a high temperature of no less than about 600° C. Thus, the showerhead  400  may be exposed to an environment having a high temperature. When a gas sensitive to the variations of temperature is introduced into the first diffusion space  421 , cooling the head cover  410  may be used to prevent abnormal changes of the gas. The cooling member  460  absorbs heat in the head cover  410  to cool the gas in the first diffusion space  421 . On the contrary, to heat the gas in the first diffusion space  421 , the heating member  450  is used. The heating member  450  provides heat to the head cover  410  to heat the gas in the first diffusion space  421 . 
   Yet further embodiments of the present invention will now be described with reference to  FIG. 7 .  FIG. 7  is a cross sectional view illustrating an apparatus for processing a semiconductor substrate in accordance with some embodiments of the present invention. As shown in the embodiments of  FIG. 7 , an apparatus  500  for processing a semiconductor includes a process chamber  501 , a chuck  503 , a showerhead  505  and a high-frequency power source  507 . The showerhead  505  includes a head cover  510 , a first plate  520 , a sealing member  525 , a second plate  530 , a first gas supply line  526 , a second gas supply line  536 , a gas distribution member  540 , a heating member  550  and a cooling member  560 . The illustrated showerhead  505  includes various aspects substantially identical to those in the previously described embodiments, which aspects will not be further described herein. 
   The process chamber  501  in the illustrated embodiments has a cylindrical shape. The process chamber  501  has an internal space in which processes for processing a semiconductor substrate W, positioned on the chuck  503 , are carried out. The showerhead  505  is disposed in the internal space of the process chamber  501 . The chuck  503  is disposed under the showerhead  505  in the internal space. 
   The showerhead  505  provides gases used for processing the substrate W into the process chamber  501 . The high-frequency power source  507  is connected to the showerhead  505 . The high-frequency power source  507  provides a high-frequency voltage to the showerhead  505  to convert the gases into plasma. 
   The chuck  503  supports and fixes the substrate W. The chuck  503  fixes the substrate W, for example, using a vacuum or electrostatic power. 
   A discharge hole  509  is formed through a lower portion of the process chamber  501 . The discharge hole  509  is connected to a vacuum pump (not shown) to discharge the gases and byproducts in the process chamber  501 . Thus, an inner pressure of the process chamber  501  may be controlled by the discharge operations. 
   Operations for processing the substrate W in the process chamber  501  according to some embodiments of the present invention will now be described. Operations may include a deposition process, an etching process, etc. The deposition process is performed in the process chamber  501 . In particular, the substrate W loaded into the process chamber  501  is disposed on the chuck  503 . The process chamber is maintained under vacuum. A first gas is introduced into the first diffusion spacer  521  through the first gas supply line  526 . The first gas is jetted from a central portion of the first plate  520 . 
   The jetted first gas collides against the gas distribution member  540  and is substantially uniformly distributed in the first diffusion space  521 . The first gas in the first diffusion space  521  flows into the second diffusion space  522  through the first plate  520  as the pressure in the first diffusion space  521  increases. The first gas is distributed in the second diffusion space  522 . 
   The first gas is mixed with the second gas in the second diffusion space  522 . The mixed gas is substantially uniformly sprayed on the substrate W on the chuck  503  through the second plate  530 . 
   As the high-frequency power source  507  provides the high-frequency voltage to the process chamber  501 , a high electric field may be formed in the process chamber  501 . Thus, the mixed gas may be exposed to the high electric field to be converted into a plasma, which forms a layer on the substrate W. 
   Techniques for generating the high-frequency voltage in the process chamber  501  are well known. Additionally, to increase intensity of the high-frequency voltage in the process chamber  501 , a bias power may be connected to the chuck  503 . 
   As described above, a thickness of the layer formed on the substrate W may be significantly influenced by the distribution of the first and second gases over the substrate W. For example, when the first gas has a molecular weight less than that of the second gas, the first gas may concentrate on the central portion of the first plate  520  due to the gas distribution member  540  and the second gas may also concentrate on the central portion of the second plate  530 . As a result, the mixed gas may concentrate on the central portion of the substrate W. Thus, in some embodiments of the present invention, to substantially uniformly distribute the first and the second gases over the substrate W, the first gas has molecular weight greater than that of the second gas. 
   When the gases include a reaction gas and a source gas, the reaction gas generally corresponds to the first gas and the source gas generally corresponds to the second gas. Examples of the reaction gas include O 2 , N 2 O, O 3 , etc. Examples of the source gas include Pb(tmhd) 2 , Ti(tmhd) 2 , Zr(tmhd) 2 , etc. Further, the first gas may have a sensitivity with respect to variations of temperatures higher than that of the second gas. 
   The heating member  550  and/or the cooling member  560  may be provided (thermally contact) to the head cover  510  to control the temperature of the first gas in the first diffusion space  521 . Additionally, the heating member  550  and/or the cooling member  560  may be provided to the sealing member  525  and/or the second plate  530  to control the temperature of the second gas in the second diffusion space  522 . 
   As the reaction gas is typically more sensitive to the variations of the temperatures than the source gas, the reaction gas may be sprayed into the first diffusion space  521  and the source gas may be sprayed into the second diffusion space  522 . 
   The gas may be uniformly distributed on the substrate W using the showerhead  505  so that the substrate W is precisely processed. Therefore, characteristics of the semiconductor device may be improved and errors in subsequent processing operations may be reduced. 
   Further embodiments of the present invention will now be described with reference to  FIG. 8 .  FIG. 8  is a flow chart illustrating a method of distributing a gas in accordance with a fifth embodiment of the present invention. As shown in  FIG. 8 , at block ST 1 , a showerhead is prepared. The showerhead includes a plate having a plurality of holes, and a head cover combined with the plate to define a diffusion space between the plate and the head cover. 
   At block ST 2 , a gas is spayed into the diffusion space towards the head cover. The gas may, for example, be sprayed from a central portion of the plate to the head cover. In other embodiments, the gas may be sprayed from an edge portion of the plate to the head cover. Further, the gas may be sprayed from the edge portion of the plate along the central portion of plate. 
   An inner face of the head cover may have a shape that varies in accordance with spraying directions of the gas with respect to the plate. When the gas is sprayed from the central portion of the plate, the inner face of the head cover in some embodiments has a stepped structure that is gradually recessed (i.e, stepwise increase in height) from the edge portion of the head cover to the central portion of the head cover. When the gas is sprayed from the edge portion of the plate, the inner face of the head cover in some embodiments has a stepped structure that is gradually protruded (i.e., stepwise decreased height) from the edge portion of the head cover to the central portion of the head cover. Also, when the gas is sprayed from the edge portion of the plate along central portion of the plate, the inner face of the head cover may have an annular stepped structure. 
   At block ST 3 , the gas sprayed to the head cover collides against (contacts) a gas distribution member that partially suppresses horizontal diffusion of the gas. At block ST 4 , the gas drops downwardly to be substantially uniformly distributed on the plate. At block ST 5 , an additional gas is continuously introduced into the diffusion space to increase a pressure in the diffusion space. At block ST 6 , the gas passes through the plate from the diffusion space to be substantially uniformly distributed on an object, for example a semiconductor substrate. 
   For the embodiments of  FIG. 8 , the gas passing through the plate from the diffusion space may be uniformly distributed by use of the gas distribution member. Thus, for a process that is greatly influenced by the gas distribution, for example a process for processing a semiconductor substrate, efficiency of the process may be significantly improved and errors in following processes may be considerably reduced according to some embodiments of the present invention. 
   As described above, in some embodiments of the present invention, the gas is jetted into the diffusion space in the showerhead. The gas collides against the gas distribution member provided in the showerhead to substantially uniformly distribute over the plate. As a result, the gas may be uniformly distributed from the showerhead. 
   Also, the showerhead may be positioned in the process chamber so that the substrate may be accurately processed using the uniformly distributed gas. Thus, the characteristics of the semiconductor device may be improved and errors in following processes may be significantly reduced. 
   The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.