Abstract:
An optical monitoring system includes a ring-shaped object suspended by and engaged with a plurality of vertical plunger shafts. Normally, the vertical plunger shafts move upward and downward reciprocally and coherently, but independently, such that the ring-shaped object ascends or descends horizontally. A light transceiver device is affixed to one vertical plunger shaft. A plurality optical reflector elements are affixed to respective other plunger shafts. A light beam emanated from said light transceiver is reflected by the optical reflector elements and is eventually re-directed back to the light transceiver device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to an apparatus for manufacturing a semiconductor device and, more particularly, to a dry etching apparatus capable of monitoring the motion of the wafer area pressure (WAP) ring and the plunger shafts that actuate the WAP ring.  
         [0003]     2. Description of the Prior Art  
         [0004]     Plasma etching has become the preferred technique for etching patterns in the various layers utilized in the manufacture of integrated circuit devices. The apparatus for such etching typically includes a chamber housing a pair of essentially planar electrodes that are spaced apart in a parallel relationship to define an interaction space therebetween. On a lower electrode is positioned a semiconductor wafer being processed. For such processing, an appropriate gaseous medium is introduced into the chamber and then one or more suitable high radio-frequency voltages are impressed across the pair of electrodes to generate discharge and form plasma that etches suitably exposed regions of the wafer.  
         [0005]     It has become of increasing importance both for efficiency and for uniformity to confine the plasma essentially to the interaction space between the two electrodes. To this end, it has been proposed to include a ring-shaped element (a plasma confinement ring) at the periphery of one or both of the electrodes to confine the discharge to the interaction space. Such plasma confinement ring is also known as a wafer area pressure (WAP) ring, which is provided to confine the plasma stream to the area of the wafer.  
         [0006]      FIG. 1  is a schematic, cross-sectional diagram illustrating the arrangement of a top electrode and WAP ring of a conventional plasma etching apparatus. As shown in  FIG. 1 , the plasma etching apparatus  10  comprises a lower assembly  12  and an upper portion  13 . The lower assembly  12  generally includes a disk-shaped electrostatic chuck (ESC)  12   a , a focus ring  12   b , and a ground ring  12   c . The ESC  12   a  is capable of holding a wafer  20  and is typically serves as a bottom electrode or anode. The focus ring  12   b  extends around a peripheral portion of the ESC  12   a . The upper portion  13  generally includes a top electrode or cathode  14  and a WAP ring  16 . The WAP ring  16  encircles the top electrode  14 . Typically, the WAP ring  16  includes a thicker twist ring  16   a  and three thinner lower rings  16   b ,  16   c  and  16   d . Both the lower assembly  12  and the upper portion  13  are installed in a chamber housing  25 .  
         [0007]     Generally, the WAP ring  16  is connected to three plunger shafts  32  (only one of the three shafts is shown). One end of each of the three plunger shafts  32  is further connected with a movable lower roller  34 . The lower roller  34  is bonded to a corresponding fixed upper roller  36  with a resilient means such as spring (not shown). An annular cam  40  reciprocally moves along the direction  42  between the lower roller  34  and the upper roller  36  such that the WAP ring  16  descends and ascends between the “home position” as shown in  FIG. 1  and the “work position” as shown in  FIG. 2 .  
         [0008]     One drawback of the above-described prior art is that a gap  18  between the top electrode  14  and the WAP ring  16  is very small, which is typically about 0.02 inch or less. During the descending and ascending of the WAP ring  16 , even very small discrepancy between the three plunger shafts  32  results in oblique WAP ring and undesired rubbing or scratching of the top electrode  14  and the WAP ring  16 , thus causing particle contamination of the chamber or wafer. The discrepancy between the three plunger shafts  32  may result from fatigue of the spring or worn rollers or parts.  
         [0009]     It is desirable to precisely control the descending and ascending of the WAP ring  16  in a horizontal manner and to provide a system to monitor the abnormal motion of each of the three plunger shafts  32  during descending and ascending of the WAP ring  16 , thereby preventing particle contamination of the chamber or wafer.  
       SUMMARY OF THE INVENTION  
       [0010]     It is one object of the present invention to provide an alarm and monitor system to detect the abnormal motion of each of the plunger shafts during descending and ascending of the WAP ring, thereby preventing particle contamination of the chamber or wafer.  
         [0011]     From one aspect, the present invention provides a dry etching apparatus capable of monitoring motion of a wafer-area-pressure (WAP) ring. The dry etching apparatus includes a chamber housing encompassing an upper portion and a lower assembly, the upper portion further comprising the WAP ring encircling a top electrode; plunger shafts engaging with the WAP ring, wherein the plunger shafts are connected to respective movable lower rollers that are bonded to corresponding fixed upper rollers by using a resilient means; an annular cam reciprocally moves between the lower roller and the upper roller along a predetermined direction to protrude the WAP ring downward from the top electrode; and an optical monitoring system comprising a light transceiver device and optical reflector elements affixed to respective the lower rollers or the plunger shafts, wherein a light beam emanated from the light transceiver is reflected by the optical reflector elements and is re-directed back to the light transceiver device.  
         [0012]     From another aspect, the present invention provides an optical monitoring system for monitoring horizontal ascending or descending of a suspended ring-shaped or disk-shaped object. The optical monitoring system includes a ring-shaped or disk-shaped object suspended by and engaged with a plurality vertical plunger shafts, wherein, normally, the vertical plunger shafts move upward and downward reciprocally and coherently, but independently, such that the ring-shaped or disk-shaped object ascends or descends horizontally; a light transceiver device affixed to one of the vertical plunger shafts; and a plurality of optical reflector elements affixed to respective other the plunger shafts, wherein a light beam emanated from the light transceiver is reflected by the optical reflector elements and is eventually re-directed back to the light transceiver device.  
         [0013]     From still another aspect, the present invention provides an optical monitoring system for monitoring deformation of an object. The optical monitoring system includes a light transceiver device affixed to one position of the object; and a plurality optical reflector elements affixed to respective other positions of the object, wherein a light beam emanated from the light transceiver is reflected by the optical reflector elements and is eventually re-directed back to the light transceiver device.  
         [0014]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:  
         [0016]      FIG. 1  is a schematic, cross-sectional diagram illustrating the arrangement of a top electrode and WAP ring of a conventional plasma etching apparatus;  
         [0017]      FIG. 2  is a schematic, cross-sectional diagram illustrating the WAP ring in “work position” according to the prior art;  
         [0018]      FIG. 3  is a schematic, cross-sectional diagram illustrating the arrangement of WAP ring, plunger shaft and optical monitoring system of a dry etching apparatus in accordance with one preferred embodiment of this invention;  
         [0019]      FIG. 4  is a schematic plan view illustrating the optical monitoring system, the annular cam and the upper rollers of an upper portion of a dry etching apparatus in accordance with one preferred embodiment of this invention;  
         [0020]      FIG. 5  is a schematic, sectional view demonstrating the optical monitoring system, the annular cam, plunger shafts and the upper portion of a dry etching apparatus in accordance with one preferred embodiment of this invention; and  
         [0021]      FIG. 6  is a schematic diagram illustrating an optical monitoring system for monitoring or detecting deformation of an object in a three-dimensional fashion according to this invention. 
     
    
     DETAILED DESCRIPTION  
       [0022]     The present invention will now be described in more detail hereinafter with reference to the accompanying drawings. In the drawings, the size and relative position of the elements of the dry etching apparatus are exaggerated for the sake of clarity. Furthermore, like numeral numbers refer to like elements throughout the drawings.  
         [0023]     Please refer to  FIG. 3 .  FIG. 3  is a schematic, cross-sectional diagram illustrating the arrangement of WAP ring, plunger shaft and optical monitoring system of a dry etching apparatus in accordance with one preferred embodiment of this invention. The dry etching apparatus  100  comprises a lower assembly  12  and an upper portion  13 . Both the lower assembly  12  and the upper portion  13  are installed in a chamber housing  25 .  
         [0024]     The lower assembly  12  generally includes a disk-shaped electrostatic chuck (ESC)  12   a , a focus ring  12   b , and a ground ring  12   c . The ESC  12   a  is capable of holding a wafer  20  and is typically serves as a bottom electrode or anode. The focus ring  12   b  extends around a peripheral portion of the ESC  12   a  and is provided to enhance the uniformity of the plasma density. The focus ring  12   b  may be made of pure aluminum, anodized aluminum or stainless steel, among others.  
         [0025]     Likewise, the upper portion  13  generally includes a top electrode or cathode  14  and a WAP ring  16 . The WAP ring  16  encircles the top electrode  14 . Typically, the WAP ring  16  includes a thicker twist ring  16   a  and three thinner lower rings  16   b ,  16   c  and  16   d , but not limited thereto. During a plasma etching process, the WAP ring  16  descends, and touches the ground ring  12   c , to confine the plasma generated between the two parallel electrodes to an area corresponding to the projected area of the wafer  20 .  
         [0026]     The WAP ring  16  may be made of quartz, ceramic, or materials, which are not damaged by plasma. During a plasma etching process, reaction gas flows into the chamber through the gas inlet conduits disposed at the center of the top electrode  14 . A baffle (not shown) may be installed atop the top electrode  14 . The reacted gas is exhausted from the chamber by using a vacuum pump (not shown).  
         [0027]     The WAP ring  16  is engaged with three plunger shafts  32  (only one of the three shafts is shown in  FIG. 3 ). One end of each of the three plunger shafts  32  is further connected with a movable lower roller  34 . The lower roller  34  is bonded to a corresponding fixed upper roller  36  with a resilient means such as spring (not shown). An annular cam  40  reciprocally moves between the lower roller  34  and the upper roller  36  such that the WAP ring  16  can descend or ascend during the etching processing.  
         [0028]     When the reaction gas is injected into the chamber and the power is applied to the cathode and the anode by the RF power supply, an RF electrical field is formed between the cathode and the anode and the reaction gas is converted to plasma by the RF electrical field. The plasma impinges the wafer  20  supported on the anode, thereby dry etching the wafer.  
         [0029]     As previously mentioned, the gap  18  between the top electrode  14  and the WAP ring  16  is small. Slight discrepancy between the three plunger shafts  32  results in oblique WAP ring and undesired scratching of the top electrode  14  and the WAP ring  16 , thus causing particle contamination of the chamber or wafer. The discrepancy between the three plunger shafts  32  may result from fatigue of the spring or worn rollers or parts.  
         [0030]     To prevent this, referring to  FIGS. 4-5  and briefly to  FIG. 3 , an optical monitor system  60  comprising three optical elements  60   a ,  60   b  and  60   c  disposed at a 120-degree position are provided along the outer perimeter of the annular cam  40 . The optical element  60   a  comprises a laser diode transmitter and receiver  62   a  affixed to one end of a supporting member  64   a . The optical element  60   b  comprises an optical reflector element  62   b  affixed to one end of a supporting member  64   b . The optical element  60   c  comprises an optical reflector element  62   c  affixed to one end of a supporting member  64   c.    
         [0031]     The laser diode transmitter and receiver  62   a , the optical reflector  62   b  and  62   c  are substantially coplanar. The laser diode transmitter and receiver  62   a  is aimed to direct a laser light beam  72  toward optical reflector element  62   b . During the descending or ascending of the WAP ring  16 , in a normal situation, the laser light beam  72  is reflected by the optical reflector element  62   b  and is re-directed toward the optical reflector element  62   c , and is again reflected by the optical reflector element  62   c  and re-directed back toward the laser diode transmitter and receiver  62   a  and received by the detector thereof.  
         [0032]     In an abnormal situation, for example, one of the three plunger shafts  32  does not ascend or descend as the other two normally do because of fatigue of the spring, worn rollers or other causes, then the laser diode transmitter and receiver  62   a  will not receive and detect any reflected light beam. In such case, as shown in  FIG. 5 , the laser diode transmitter and receiver  62   a  triggers an alarm device  80  such as sound or light to notify the operators, and/or sends a signal to a control unit  90  that can immediately stop the motion of the annular cam  40  and the plunger shafts  32 , thereby avoiding rubbing or scratching of the WAP ring  16  and the top electrode  14 .  
         [0033]     According to the preferred embodiment, as shown in  FIG. 3 , the laser diode transmitter and receiver  62   a , the optical reflector elements  62   b  and  62   c  protrude from the top of the upper roller for a height H, which is equal to or greater than the distance between the “home position” and “work position” of the WAP ring  16 . In any case, the upper roller  36  should not obstruct the light path between the coplanar laser diode transmitter and receiver  62   a , the optical reflector elements  62   b  and  62   c.    
         [0034]     The other end of each of the supporting members  64   a ,  64   b  and  64   c  is affixed to the respective movable lower roller  34  or plunger shaft  32 , such that the optical element  60   a ,  60   b  and  60   c  descend and ascend together with the corresponding lower roller  34  and plunger shaft  32 . Preferably, the supporting members  64   a ,  64   b  and  64   c  are made of rigid materials such as stainless steel or metals, but not limited thereto.  
         [0035]     The optical reflector elements  62   b  and  62   c  may be a mirror or retro-reflective surface such as an adhesive-backed retro-reflective tape. In other cases, the optical reflector elements  62   b  and  62   c  may be optical fiber through which light can be transmitted by successive internal reflections. Other light sources and detectors could be used to replace the laser diode transmitter and receiver  62   a , for example, infrared light or light emitting diode (LED), though external optic elements might be required to provide a suitable small beam spot size or light intensity at the reflective surface. The accuracy and precision of the optical monitor system  60  may be adjusted by altering the dimension of the optical reflector elements  62   b  and  62   c.    
         [0036]     The present invention is also applicable to the field of monitoring deviation of position or deformation of shape due to fatigue of an object such as fuselage in a three-dimensional fashion.  FIG. 6  is a schematic diagram demonstrating such application. The monitoring system  120  includes a laser diode transceiver  102  and a plurality of optical reflector elements  104 ,  106 ,  108  and  110  disposed at positions A, B, C and D, respectively. The number of the optical reflector elements depends on the light source power. The laser diode transceiver  102  is electrically connected to an alarm  140  such as light or sound. Each of the optical reflector elements  104 ,  106 ,  108  and  110  is arranged to reflect the laser light beam  132  originally emanated from the laser diode transceiver  102  and the last optical reflector element  110  directs the reflected light beam back to the laser diode transceiver  102 . Once the monitored object (not explicitly shown) deforms and the laser diode transceiver  102  receives no light signal from the last optical reflector element  110  (optical path is changed due to displacement of the positions A, B, C or D), the laser diode transceiver  102  triggers the alarm to notify or warn someone.  
         [0037]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.