Abstract:
The present invention relates to a plasma apparatus comprising a reaction chamber having a reaction space which accommodates a substrate to be treated; a coil located on the outside of the reaction space; a power source applying alternating frequency power on the coil; and a conducting plate located between the coil and the reaction space and generating an induced current from the alternating frequency power applied on the coil. Thus, the present invention provides a plasma apparatus that induces a uniform electric field in an internal gas of the reaction chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 2004-0112123, filed on Dec. 24, 2004, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a plasma apparatus, and more particularly, to an inductively coupled plasma (ICP) apparatus.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, a plasma apparatus is used for etching, depositing or stripping certain materials on the surfaces of wafers to fabricate semiconductor devices, or on substrates to fabricate liquid crystal display (LCD) panels.  
         [0006]     The plasma apparatus requires that the plasma generated therein maintain a high uniformity as well as a high density.  
         [0007]     Various methods may be used to form plasma including, but not limited to, a capacitive coupled plasma (CCP) method and an inductively coupled plasma (ICP) method. The ICP method may generate plasma with a high density and high uniformity.  
         [0008]     An ICP type plasma apparatus comprises a reaction chamber including a reaction space for generating plasma, a coil and a power source disposed on the outside of the reaction chamber, and a dielectric plate between the reaction chamber and the coil. Generally, the dielectric plate comprises a quartz or ceramic material.  
         [0009]     If high frequency power is applied on the coil through a power source, an electric field will be induced on the internal gas of the reaction space through the dielectric plate.  
         [0010]     However, if the plasma process has been progressing for many hours, the polymer that has been accumulated as a byproduct during the plasma process will deposit on the surface of the dielectric plate facing the reaction space where the dielectric plate corresponds to the coil. The polymer may fall on the substrate inside of the reaction chamber to thereby cause a defect. Also, the surface of the dielectric plate corresponding to the coil will be etched. Thus, the dielectric plate may have a short life, and so will require frequent replacement.  
         [0011]     Basically, these problems stem from irregularity of the electric field that is applied to the internal gas of the reaction chamber through the dielectric plate.  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, it is an aspect of the present invention to provide a plasma apparatus that applies a uniform electric field upon an internal gas of the reaction chamber.  
         [0013]     A plasma apparatus is provided, comprising: a reaction chamber having a reaction space to accommodate a substrate to be treated, a coil located on the outside of the reaction space, a power source applying alternating frequency power on the coil, and a conducting plate located between the coil and the reaction space and generating an induced current from the alternating frequency power applied on the coil.  
         [0014]     According to another aspect of the invention, the high frequency power is below about 1 MHz.  
         [0015]     According to another aspect of the invention, the high frequency power is below about 500 KHz.  
         [0016]     According to another aspect of the invention, the conducting plate covers a substantial portion of the upper part of the reaction space.  
         [0017]     According to another aspect of the invention, further comprising an insulating part located between the reaction space and the conducting plate.  
         [0018]     According to another aspect of the invention, the insulating part comprises a ceramic material.  
         [0019]     According to another aspect of the invention, the size of the conducting plate is larger than about 1 m×1 m.  
         [0020]     According to another aspect of the invention, the thickness of the conducting plate is below about 3 cm.  
         [0021]     According to another aspect of the invention, the conducting plate is formed by a metal that comprises at least one of aluminum, iron, copper, silver, and nickel.  
         [0022]     According to another aspect of the invention, further comprising a lower electrode located in the reaction space and having a shape of a plate, and a lower power applying the high frequency power on the lower electrode.  
         [0023]     According to another aspect of the invention, the lower electrode is disposed parallel to the conducting plate.  
         [0024]     According to another aspect of the invention, the substrate is seated on the lower electrode.  
         [0025]     According to another aspect of the invention, the substrate is used to fabricate a liquid crystal display.  
         [0026]     According to another aspect of the invention, the coil covers a substantial portion of the conducting plate.  
         [0027]     According to another aspect of the present invention, a plasma apparatus comprises: a reaction chamber having a reaction space to accommodate a substrate to be treated, a coil located on the outside and in an upper part of the reaction space over the area thereof, a power source applying alternating frequency power on the coil, conducting plate located between the coil and the reaction space and which generates an induced current from the alternating frequency power applied on the coil, a gas inlet to allow an inlet gas to flow into the reaction space, and a gas outlet to allow an outlet gas to flow out of the reaction space.  
         [0028]     According to another aspect of the invention, the gas inlet allows a source gas to flow into the reaction space, and the gas outlet allows a reacted source gas and a by-product from an etching process to flow out of the reaction space.  
         [0029]     According to another aspect of the invention, further comprising a supporting member attached to the conducting plate to maintain the height level of the conducting plate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     These and other aspects of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0031]      FIG. 1  is a perspective view of a plasma apparatus according to a first embodiment of the present invention;  
         [0032]      FIG. 2  is a sectional view of the plasma apparatus according to the first embodiment of the present invention;  
         [0033]      FIG. 3  is a view explaining an induced current that is formed with a conducting plate according to an embodiment of the present invention;  
         [0034]      FIG. 4  is a view explaining an intensity change of the induced current according to a thickness of the conductive plate according to an embodiment of the present invention;  
         [0035]      FIG. 5  is a perspective view of a plasma apparatus according to a second embodiment of the present invention; and  
         [0036]      FIG. 6  is an expanded sectional view of the part A in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0038]      FIGS. 1 and 2  schematically show a plasma apparatus according to a first embodiment of the present invention.  
         [0039]     As shown in  FIGS. 1 and 2 , a plasma apparatus  1  comprises a reaction chamber  11 , a coil  21 , and a conducting plate  31 .  
         [0040]     The reaction chamber  11  is approximately a rectangular parallelepiped form and comprises a reaction space  12  for generating plasma. On an upper part of the reaction chamber  11  is formed an inlet  13  to flow in a source gas. If the use of the source gas is for etching, the source gas comprises at least one of sulfur fluoride (SF 6 ), chlorine (Cl 2 ), hydrochloric acid (HCl), carbon fluoride (CF 4 ), oxygen, nitrogen, helium, and argon. Also, if the use of the source gas is for depositing, the source gas comprises at least one of silane (SiH 4 ), methane (CH 4 ), ammonium (NH 3 ), and nitrogen.  
         [0041]     In another embodiment of the present invention, the inlet  13  may be provided in the upper part of the reaction space  12 , i.e., in the conducting plate  31 . Also, the inlet  13  may be provided in a plurality of conduits to provide the reaction space  12  with the source gas uniformly. On the lower part of the reaction chamber  11  is formed an outlet  14  to allow the reacted source gas and the by-product from the etching process to flow out of the reaction space  12 . The position and the number of the outlet  14  may be changed as needed. The outlet  14  is preferably, but not necessarily, connected to a pump (not shown).  
         [0042]     The pump makes the reacted source gas and the by-product flow out to the outside of the reaction space  12  effectively and maintains the vacuum level of the reaction space  12  efficiently.  
         [0043]     The coil  21  is located outside of the reaction space  12 . The coil  21  is located in the upper part of the reaction space  12  over the area thereof. The coil  21  is connected to a power source  22  that applies high frequency power (or RF power). An impedance matching unit  23  is provided between the coil  21  and the power source  22 .  
         [0044]     The conducting plate  31  is disposed between the reaction space  12  and the coil  21 . That is, the conducting plate  31  separates the reaction space  12  and the coil  21 . The coil  21  is provided at predetermined intervals that are parallel to the conducting plate  31 . The conducting plate  31  is formed by a metal plate that comprises at least one of aluminum, iron, copper, silver, and nickel. The conducting plate  31  is rectangular. The thickness of the conducting plate  31  is preferably but not necessarily less than about 3 cm. If the thickness of the conducting plate  31  is over about 3 cm, the induced current that is formed with the conducting plate  31  will not generate on the reaction space  12  sufficiently. The particular description of the conducting plate  31  will be described later. The length and width of the conducting plate  31  are each preferably equal to or larger than about 1 m, because the size of the substrate  61  that is to be treated increases.  
         [0045]     An insulating part  41  is provided between the reaction chamber  11  and the conducting plate  31 . The insulating part  41  is shaped like a quadrangular band and comprises an insulating material like ceramics. The insulating part  41  electrically separates the reaction chamber  11  and the conducting plate  31 . The conducting plate  31  is floating or held in suspension because it is not connected with the coil  21 . The distance of the connection between the conducting plate  31  and the insulating part  41  as well as the connection of the reaction chamber  11  to the insulating part  41  may close up to maintain a predetermined vacuum level.  
         [0046]     On the lower part of the reaction space  12  is provided a lower electrode  51 . The lower electrode  51  is shaped like a plate and disposed substantially in parallel to the conducting plate  31 . Also, the lower electrode  51  may be made of aluminum. The lower electrode  51  is preferably but not necessarily larger than the substrate  61  that is the object of treatment because the substrate  61  is seated thereon. The lower electrode  51  is connected with a lower power source  52  that applies alternating frequency power, and a lower impedance matching unit  53  is provided between the lower electrode  51  and the lower power source  52 . If high frequency power is applied on the lower electrode  51 , the plasma in the reaction space  12  will be more uniformed.  
         [0047]     The substrate  61  that is the object of treatment is seated on the lower electrode  51 . The substrate  61  may be a wafer for fabricating a semiconductor device, or a thin film transistor substrate or a color filter substrate for fabricating a liquid crystal display. According to an embodiment of the present invention, a larger reaction space  12  may correspond to greater uniformity. Further, the larger reaction space  12  having greater uniformity in the plasma facilitates processing a larger substrate  61  for fabricating a liquid crystal display.  
         [0048]     The principle of inducing an electric field on the reaction space  12  will be described as follows in the plasma apparatus  1  according to the first embodiment.  
         [0049]     Referring to  FIG. 3 , if the power source  22  applies high frequency power on the coil  21 , a current flows in the coil  21 . For example, current will flow in a counterclockwise direction as shown in  FIG. 2 . Also, the current of the coil  21  makes a magnetic field that pass through the conducting plate  31 . At this point, the conducting plate  31  forms an induced current that flows in a clockwise direction. The induced current flows in a direction exactly against the current of the coil  21 .  
         [0050]     A cause of forming an induced current will be described as follow. If alternating current flowing to the coil  21  is near a conductor, a magnetic field that is generated to the surroundings of the coil  21  acts on the conductor. At this point, the conductor has electromotive force that interrupts a change in the magnetic flux passing through it.  
         [0051]     This phenomenon is electromagnetic induction. The current that is formed with electromotive force is an induced current or an eddy current.  
         [0052]     Hence, the electric field of the induced current that is generated to the coil  21  is generated on the reaction space  12  to generate plasma.  
         [0053]     The conducting plate  31  according to an embodiment of the present invention generally forms a uniform electric potential. Therefore, the polymer will not deposit onto the surface of the conducting plate  31  locally. Also, the surface of the conducting plate  31  will not etch. Moreover, because the density of the plasma that exists in the inside of the reaction space  12  is uniform, the substrate  61  may be easily treated.  
         [0054]     The conducting plate  31  that forms the fitting density of the plasma will be described below with reference to  FIG. 4 .  
         [0055]     The strength of an induced current can weaken due to the thickness of the conducting plate  31 . As a result, the induced current is strongest at a position adjacent to the coil  21 , and the induced current weakens at a position closer to the reaction space  12 .  
         [0056]     The formula of the skip depth (δ) that the induced current diminishes at a rate of 1/e (where e=2.718) is described as follow. 
 
δ∝(2/ωμσ) 1/2  
 
         [0057]     ω is angular frequency, that is, 2πf (f is a frequency of an alternating frequency power). μ is the magnetic permeability of the conducting plate  31 . σ is the electric conductivity of the conducting plate  31 .  
         [0058]     Accordingly, if the frequency of the alternating frequency power decreases or the conducting plate  31  is formed with material of significant magnetic permeability and electric conductivity, the skip depth (δ) will increase. Therefore, the frequency of an alternating frequency power has a significant effect upon the skip depth (δ). Generally, the frequency of the alternating frequency power to form plasma is about 13.56 MHz. On the other hand, the frequency of the alternating frequency power according to a first embodiment of the present invention is below about 1 MHz, and preferably below about 500 KHz.  
         [0059]     Another method to increase the strength of an electric field generated on the reaction space  12  is to use a thinner conducting plate  31 . Accordingly, the thickness of the conducting plate  31  is preferably less than about 3 cm.  
         [0060]     Preferably, the thickness and material of the conducting plate  31  is determined in consideration with the intensity of an induced current as well as the size and shape of the conducting plate  31 .  
         [0061]     The plasma apparatus  1  according to the first embodiment of the present invention may be changed in accordance to different reaction conditions. For instance, the shape of the reaction chamber  11  is not limited to a hexahedron, but may be provided as a cylinder. At this point, the coil  21 , the conducting plate  31  and the insulating part  41  will be changed according to the shape of the reaction chamber  11 .  
         [0062]     The plasma apparatus  1  according to a second embodiment of the present invention will be described below with reference to  FIGS. 5 and 6 . Reference numerals identical to those of a first embodiment of the present invention denote identical elements, and detailed description of these identical elements will not be repeated.  
         [0063]      FIG. 5  is a perspective view of a plasma apparatus according to a second embodiment of the present invention, and  FIG. 6  is an expanded sectional view of the part A in  FIG. 5 .  
         [0064]     The plasma apparatus  1  according to the second embodiment of the present invention further comprises a couple of support members  70  that are parallel to each other and support the conducting plate  31  at the upper part of the coil  21 .  
         [0065]     The support member  70  comprises a pair of fixing parts  71 , and a supporting bar  72  connecting the pair of fixing parts  71  to each other. The fixing parts  71  are fixed by a screw at a side wall of the reaction chamber  11 . The supporting bar  72  traverses the conducting plate  31 . Also, it is preferable but not necessary that the fixing parts  71  and the supporting bar  72  are integrally formed with a strong metal.  
         [0066]     The surface of the supporting bar  72  facing the conducting plate  31  has ring fixing parts  73  at regular intervals. Each ring fixing part  73  is projected and connected with a ring  74 .  
         [0067]     The conducting plate  31  comprises a link  32  to be aligned with the ring fixing part  73 . The link  32  may be fixed by welding at the conducting plate  31 .  
         [0068]     The support member  70  supports the conducting plate  31  because the ring  74  of the support member  70  connects with the ring fixing part  73  and the link  32  respectively.  
         [0069]     If the substrate  61  to be treated is of a larger size, the conducting plate  31  may also be larger. The edge of the conducting plate  31  is supported by the insulating part  41  fixed on the reaction chamber  11 . However, the center portion of the conducting plate  31  is not supported. Therefore, the conducting plate  31  may be bent to the reaction space  12 .  
         [0070]     Particularly, to maintain the intensity of a fitting induced current, the thickness of the conducting plate  31  should remain thin. Further, the bending of the conducting plate  31  may be severe because the reaction space  12  is applied to a vacuum.  
         [0071]     Thus, it is preferred that the support member  70  according to the second embodiment of the present invention maintains the height level of the conducting plate  31 .  
         [0072]     The support member  70  is disposed at the upper part of the coil  21 , so that the distance between the coil  21  and the conducting plate  31  is not increased. Therefore, the intensity of an induced current formed by the conducting plate  31  is not substantially changed.  
         [0073]     The plasma apparatus  1  according to the second embodiment of the present invention may be changed in accordance to different reaction conditions. For instance, the number of the support member  70  and the establishment direction of the support member  70  may be changed as necessary. Also, it is possible that the supporting bar  72  connect with each other or the support member  70  further comprises an extra structure supporting the middle of the supporting bar  72 , thereby preventing the support member  70  from bending.  
         [0074]     Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.