Abstract:
A deposition method includes placing a substrate on a susceptor inside a chamber, the susceptor including a center pin passing through the susceptor for lifting the substrate, energizing an electrode to applying a uniform electric field to the substrate, electrically connecting a ground member extending along and attached to an entire axial length of the center pin to a ground voltage source, and forming a film on the substrate by chemical vapor deposition.

Description:
The present application is a Continuation of U.S. patent application Ser. No. 10/144,806 filed May 15, 2002, now U.S. Pat. No. 7,081,165 issued Jul. 25, 2006, which claims the benefit of Korean Patent Application No. P2001-27128 filed in Korea on May 18, 2001, both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chemical vapor deposition apparatus, and more particularly to a chemical vapor deposition apparatus for creating a uniform electric field. 
     2. Description of the Related Art 
     In general, a liquid crystal display (LCD) controls a light transmittance of liquid crystal cells that are arranged in a matrix array on a liquid crystal display panel. Accordingly, the liquid crystal cells receive data signals, thereby displaying an image (picture). The LCD includes electrodes for supplying an electric field to a liquid crystal layer, a thin film transistor (TFT) for switching the data signals provided to the liquid crystal cells, a lower substrate having signal wiring for supplying the data signals to the liquid crystal cells and signal wiring for supplying control signals of the TFT, an upper substrate having a color filter, a spacer formed between the upper substrate and the lower substrate for providing a predetermined cell gap, and liquid crystal molecules disposed within a space provided between the upper substrate and the lower substrate. 
     During fabrication of the liquid crystal display device, a channel portion in an active layer of the TFT and a protective layer protecting the TFT are formed during plasma enhanced chemical vapor deposition (PECVD) processing. During PECVD processing, a gas is injected into a vacuum chamber. Then, at a specific pressure and substrate temperature, the injected gas decomposes into a plasma by use of a radio frequency (RF) voltage, thereby depositing materials onto a surface of the substrate. A quality of the deposited material is dependent upon the deposition conditions, such as the vacuum, the RF voltage, the RF voltage frequency, substrate temperature, reaction gas, and reaction pressure, for example. In addition, the deposited materials includes insulating films, semiconductor films, gate insulating films, protective films, and etch stopper films. The semiconductor films include amorphous silicon (a-Si:H) that form an active layer, and doped amorphous silicon (n+a-Si:H) that form a contact protective layer. 
       FIG. 1  is a cross sectional view of a plasma enhanced chemical vapor deposition (PECVD) apparatus according to a related art. In  FIG. 1 , the PECVD apparatus includes a gas jet  9  for releasing a gas to be deposited onto a substrate  7 , and a chamber  1 . The chamber  1  includes a susceptor  5  for applying heat via a heating coil to the substrate  7 , an arrow pin  10  for securing the substrate  7 , and a center pin  12  for separating the susceptor  5  from the substrate  7 . 
     During processing, the substrate  7  is placed upon the susceptor  5  within the chamber  1 , and the susceptor  5  applies heat to the substrate  7  and functions as a lower electrode for generating a plasma. A temperature of the susceptor  5  averages about 370° C. In addition, the susceptor  5  includes various pins formed to penetrate the susceptor  5 . 
     The arrow pin  10  secures the substrate  7  within the chamber  1 , and the center pin  12  rises by a pin plate  16  to prevent any drooping of the substrate  7 . In addition, the center pin and pin plate  16  prevents formation of any scratches between a robot arm  14  and the substrate  7  during loading and unloading of the substrate  7 . The pin plate  16  includes a center pin-supporting portion  18  having the center pin  12  passing through it. 
       FIGS. 2A to 2D  show a process for loading a substrate into a chamber according to the related art. 
     In  FIG. 2A , the substrate  7  is loaded into the chamber  1  by the robot arm  14 , and the substrate  7 , the susceptor  5 , and the center pin  12  are not mutually contacting each other. 
     In  FIG. 2B , the pin plate  16  rises to mount the center pin-supporting portion  18  in center pin mount portions  20  and  21  equipped on a rear surface of the susceptor  5 , and each of corner pins  22  and  23  and the center pin  12  rise by a power driver (not shown) to lift the substrate  7 . 
     In  FIG. 2C , the robot arm  14  is separated from the substrate  7  by the power driver (not shown). 
     In  FIG. 2D , the susceptor  5  rises by a susceptor-lifting portion  24  to make the susceptor  5  lift the substrate  7  and the center pin  12 . Then, the susceptor  5  raises the substrate  7  close to the arrow pin  10 . Accordingly, the substrate  7  is safely placed into a deposition position. 
       FIG. 3  is a cross sectional view representing an inside of a chamber according to the related art. In  FIG. 3 , the chamber  1  includes the substrate  7  safely placed upon the susceptor  5 , and an upper electrode  30  that faces the substrate  7  with a predetermined gap therebetween. The center pin  12  raises the substrate  7  upon loading, and the susceptor  5  rises. Accordingly, the substrate  7  sustains a predetermined gap from the upper electrode  30 , and the center pin  12  lowers into a center pin hole  19  formed on the susceptor  5 . The center pin  12  is made of ceramic material that has a low coefficient of thermal expansion. 
       FIG. 4  is a cross sectional view of a center pin according to the related art as shown in  FIG. 3 . In  FIG. 4 , an insulating film Al 2 O 3  is formed upon a head portion  3  of the center pin  12 , thereby preventing electrical arcing during plasma processing. Accordingly, the center pin  12  is not ground to the susceptor  5 . However, the heating coil (not shown) formed inside the susceptor  5  is ground with an external ground voltage source GND. 
     In  FIG. 3 , a radio frequency (RF) voltage source  32  is connected to the upper electrode  30 . Accordingly, an electric field is generated between the upper electrode  30  and the substrate  7 , whereby an insulating film or a semiconductor film is deposited upon a surface of the substrate  7 . When depositing the insulating film or the semiconductor film on the substrate  7 , the electric field emanating from the upper electrode  30  is bowed in a region of the center pin  12 . Accordingly, an electric field density in a region of the center pin  12  is relatively low, thereby a thickness of the deposition film in the region of the center pin  12  will be thinner than surrounding regions. 
       FIG. 5  shows a defect resulting from the center pin according to the related art. In  FIG. 5 , a thickness of the deposition film in an area A of the substrate  7 , which corresponds to a region of the center pin  12  (in  FIG. 3 ), is different from a thickness of the deposition film in other regions. 
       FIG. 6  is a spectrum photograph showing the defect on a substrate illustrated in  FIG. 5  according to the related art. In  FIG. 6 , the thickness of the deposition film in the area A of the substrate  7 , which corresponds to the region of the center pin  12  (in  FIG. 3 ), is relatively thinner than the thickness of the deposition film in the other regions. 
       FIG. 7  is a graph showing thickness distribution of a deposition film of the substrate  7  (in  FIG. 5 ) taken along I-I′ of  FIG. 6 . In  FIG. 7 , the graphical distribution of deposition thickness of the deposition film on the substrate indicates that a defect is generated in a region corresponding to the center pin  12  (in  FIG. 3 ). Accordingly, the defect degrades image quality of the liquid crystal display device. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a chemical vapor deposition apparatus and method of using the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a chemical vapor deposition apparatus and method of using the same to generate a uniform electric field, thereby forming a deposition film having a uniform thickness. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a chemical vapor deposition method includes placing a substrate on a susceptor inside a chamber, the susceptor including a center pin passing through the susceptor for lifting the substrate, energizing an electrode to applying a uniform electric field to the substrate, electrically connecting a ground member extending along and attached to an entire axial length of the center pin to a ground voltage source, and forming a film on the substrate by chemical vapor deposition. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a cross sectional view of a chemical vapor deposition apparatus according to a related art; 
         FIGS. 2A to 2D  show a process for loading a substrate into a chamber according to the related art; 
         FIG. 3  is a cross sectional view of an inside of a chamber according to the related art; 
         FIG. 4  is a cross sectional view of a center pin according to the related art, as shown in  FIG. 3 ; 
         FIG. 5  shows a defect resulting from the center pin according to the related art; 
         FIG. 6  is a spectrum photograph showing the defect on a substrate illustrated in  FIG. 5  according to the related art; 
         FIG. 7  is a graph showing thickness distribution of a deposition film of the substrate taken along I-I′ of  FIG. 6 ; 
         FIG. 8  is a cross sectional view showing an exemplary chamber according to the present invention; 
         FIG. 9  is a cross sectional view of an exemplary center pin according to the present invention; and 
         FIG. 10  is a cross sectional view of another exemplary center pin according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 8  is a cross sectional view showing an exemplary chamber according to the present invention. In  FIG. 8 , a chemical vapor deposition apparatus may include a chamber  50  for performing a deposition process on a substrate  37 . The chamber  50  may include a susceptor  45  contacting the substrate  37 , a center pin  42  for lifting the substrate  37 , and an upper electrode  40  facing the substrate  37  and having a predetermined gap therebetween for generating an electric field. 
     The substrate  37  may be placed onto the susceptor  45  within the chamber  50 . A heating coil (not shown) may be formed within the susceptor  45  to supply heat to the substrate  37 . The susceptor  45  may also function as a lower electrode for generating a plasma discharge. During the deposition process, a temperature within the susceptor  45  may average about 370° C. The susceptor  45  may include various pins (not shown) that pass through the susceptor  45  for chemical vapor deposition. 
     The center pin  42  may be elevated by means of a pin plate  36  to prevent any drooping of the substrate  37 . The pin plate  36  prevents any of the substrate  37  by a robot arm (not shown) during loading and unloading of the substrate  37 . In addition, the pin plate  36  functions to raise the center pin  42  via a power driver (not shown). 
       FIG. 9  is a cross sectional view of an exemplary center pin according to the present invention. In  FIG. 9 , the center pin  42  may include a head portion  53 , a head supporter  54 , and a grounding terminal  52 . The head portion  53  may include a conductive segment  53   a  formed of aluminum (Al), for example, and an insulating segment  53   b  such as aluminum oxide (Al 2 O 3 ), for example. The insulating segment  53   b  may prevent electrical arcing between the substrate  37  and the susceptor  45  when the electrical field is applied between the susceptor  45  and the upper electrode  40  (in  FIG. 8 ). 
     The head supporter  54  may be formed of a ceramic material, for example, having a low coefficient of thermal expansion. A ground line  56  may be formed at one side of the head supporter  54 . The ground line  56  may be formed of an electrically conductive metal such as aluminum (Al), for example, inserted into a groove formed at one side of the head supporter  54  and electrically interconnected to the conductive segment  53   a  of the head portion  53 . 
     The ground terminal  52  may be electrically connected to the conductive segment  53   a  of the head portion  53  via the ground line  56 , thereby grounding the center pin  42  to an external ground voltage source GND. The grounding the center pin  42  may be accomplished by electrically connecting a lower part of the center pin  42  to the ground terminal  52  after removing a portion of the ground terminal  52  that has been coated with the insulating segment  43   b . Then, the ground terminal  52  may be connected to a metal line that extends from a lower part of the susceptor  45 , thereby electrically grounding the center pin  42  to the external ground voltage source GND. 
     In  FIG. 8 , the upper electrode  40  may receive a voltage from a radio frequency voltage source  38  to form a deposition film on the substrate  37 . Accordingly, since the center pin  42  is grounded to the ground voltage source GND via the ground line  56 , a uniform electric field is generated between the susceptor  45  and the upper electrode  40 . This uniform electric field results in a deposition film have a uniform thickness across a surface of the substrate  37 , and prevents formation of any defects within a region of the center pin  42 . 
       FIG. 10  is a cross sectional view of another exemplary center pin according to the present invention. In  FIG. 10 , the center pin  42  may include a head portion  53 , a head supporter  54 , and a grounding terminal  52 . The head portion  53  may include a conductive segment  53   a  formed of aluminum (Al), for example, and an insulating segment  53   b  such as aluminum oxide (Al 2 O 3 ). The insulating segment  53   b  may prevent electrical arcing between the substrate  37  and the susceptor  45  when the electrical field is applied between the susceptor  45  and the upper electrode  40  (in  FIG. 8 ). 
     The head supporter  54  may be formed of a ceramic material, for example, having a low coefficient of thermal expansion. A ground line  56  may be formed passing through a center part of the head supporter  54 , and may be formed of an electrically conductive metal, for example, and may electrically interconnect the conductive segment  53   a  of the head portion  53  to an external ground voltage source GND via the grounding terminal  52 . 
     The ground terminal  52  may be electrically connected to the conductive segment  53   a  of the head portion  53  via the ground line  56 , thereby grounding the center pin  42  to an external ground voltage source GND. The grounding the center pin  42  may be accomplished by electrically connecting a lower part of the center pin  42  to the ground terminal  52  after removing a portion of the ground terminal  52  that has been coated with the insulating segment  43   b . Then, the ground terminal  52  may be connected to a metal line that extends from a lower part of the susceptor  45 , thereby electrically grounding the center pin  42  to the external ground voltage source GND. 
     In  FIG. 8 , the upper electrode  40  may receive a voltage from a radio frequency voltage source  38  to form a deposition film on the substrate  37 . Accordingly, since the center pin  42  is grounded to the ground voltage source GND via the ground line  56 , a uniform electric field is generated between the susceptor  45  and the upper electrode  40 . This uniform electric field results in a deposition film have a uniform thickness across a surface of the substrate  37 , and prevents formation of any defects within a region of the center pin  42 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the chemical vapor deposition apparatus of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.