Abstract:
A neutral beam etching device for separating and accelerating a plasma is provided. The device includes a first chamber having a first opening formed at one side thereof; a second chamber having a second opening formed at one side thereof and being disposed inside the first chamber to form a plasma generation area; a first channel fluidly communicating the first opening with the plasma generation area; a second channel fluidly communicating the second opening with the plasma generation area; a coil disposed on an outer surface of the first chamber and which generates a magnetic field to generate a plasma in the plasma generation area; and an acceleration part disposed within the first and second chambers and configured to separate the plasma into a positive ion and an electron, accelerate the positive ion and the electron, and discharge the positive ion and electron through the first and the second channels.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from Korean Patent Application No. 2005-63433, filed on Jul. 13, 2005, in the Korean Intellectual Property Office, the entire contents of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a neutral beam etching device, and more particularly, to a neutral beam etching device which separates and accelerates a plasma using a grid. 
   2. Description of the Related Art 
   A neutral beam etching device uses a plasma state material to etch a wafer. In order to obtain energy sufficient to etch the wafer, the neutral beam etching device has to accelerate a plasma generated in a predetermined area thereof. 
   A method for accelerating a plasma has been developed for the purpose of studying an ion engine of a rocket for space travel and nuclear fusion, and has been recently used to etch a wafer in the process of manufacturing a semiconductor. 
   The plasma is a gas that is separated into an electron having negative charges and an ion having positive charges at high temperature. The plasma has high efficiency of charge separation and also is electrically neutral because the positive charge equals to the negative charges. Generally, the three states of matter include solids, liquids, and gases. The plasma is known as the fourth state of matter. Most types of matter are converted from the solid state to the liquid state and from the liquid state to the gaseous state as temperature increases. The gases are separated into electrons and atomic nuclei at tens of thousands of degrees Celsius (° C.) and thus enter a plasma state. Since the plasma state is neutral, an etching device using the plasma is called a neutral beam etching device. 
     FIG. 1  is a view illustrating a conventional neutral beam etching device. Referring to  FIG. 1 , the neutral beam etching device adopts a phase matching method and so it is called a ‘traveling wave engine’. Referring to  FIG. 1 , the neutral beam etching device comprises an external coil  10 , an inner coil  20 , a discharge coil  30 , an external cylinder  40 , an inner cylinder  50 , a cover  60  and a channel  70 . 
   The cover  60  bridges between the external cylinder  40  and the inner cylinder  50  such that the channel  70  is formed in a space between the external cylinder  40  and the inner cylinder  50 . The discharge coil  30  is formed on a top of the cover  60 . 
   The external coil  10  and the inner coil  20  comprise a plurality of coils. The coils coaxially wind around the channel  70  in parallel to one another. In  FIG. 1 , each of the external coil  10  and the inner coil  20  comprises three coils  1 ,  2 ,  3 . 
   When electric currents are applied to the external coil  10 , the inner coil  20  and the discharge coil  30 , a magnetic filed is generated inside the channel  70 . The generated magnetic field generates an induced current according to Maxwell&#39;s equations and the generated induced current converts the gases existing in the channel  70  into the plasma state. Accordingly, a plasma is generated in an upper portion of the channel  70 . 
   The plasma generated in the upper portion of the channel  70  is accelerated in the direction of outlet (marked by the arrow) by applying currents to the external and inner coils  10  and  20  winding from the upper portion of the channel  70  to the outlets in sequence. That is, the currents are applied in the order of a first coil  1 , a second coil  2  and a third coil  3 . By applying the currents in order to the first, second, and third coils  1 ,  2 ,  3 , a slope of magnetic field is generated at the channel  70  such that the plasma is accelerated. 
   However, the conventional neutral beam etching device cannot sufficiently accelerate the plasma generated in the upper portion of the channel  70  and thus does not have an energy sufficient to etch a wafer. Accordingly, a satisfactory etching performance cannot be achieved. 
   Also, phases of currents to be applied to the external and inner coils  10  and  20  have to be adjusted and matched so that the slopes of magnetic fields are generated in the channel  70  in sequence. However, if the plasma generated in the upper portion of the channel  70  has a low initial velocity, a difference between phases becomes larger and thus it is difficult to adopt the phase matching. If a small frequency of driving current is set for the initial velocity, the discharge coil  30  does not smoothly transmit energy to the plasma and thus plasma generation efficiency deteriorates. As a result, an etching efficiency deteriorates. 
   SUMMARY OF THE INVENTION 
   The present invention has been developed in order to address these and other problems in the related art. Accordingly, an aspect of the present invention is to provide a neutral beam etching device which arranges grids within a channel and separates and accelerates a plasma by using an electrostatic force, thereby obtaining an energy sufficient to etch a wafer and thus improve etching efficiency. 
   Another aspect of the present invention is to provide a neutral beam etching device which use a pyramid-shaped chamber to focus a plasma separated and accelerated by an electrostatic force on an area to be etched. 
   The above and other aspects are achieved by providing a neutral beam etching device comprising a first chamber having a first opening formed at one side thereof, a second chamber having a second opening formed at one side thereof and being disposed inside the first chamber to form a plasma generation area, a first channel fluidly communicating the first opening with the plasma generation area, a second channel fluidly communicating the second opening with the plasma generation area, a coil which is disposed on an outer surface of the first chamber and which generates a magnetic field to generate a plasma in the plasma generation area, and an acceleration part which is disposed within the first chamber and the second chamber and which is configured to separate the plasma into a positive ion and an electron, accelerate the positive ion and the electron, and discharge the positive ion and electron through the first and the second channels. 
   Preferably, but not necessarily, the acceleration part comprises a first grid which is disposed in the first channel and which accelerates and discharges one of the positive ion and the electron of the plasma through the first channel, and a second grid which is disposed in the second channel and which accelerates and discharges the remaining one of the positive ion and the electron through the second channel. 
   Preferably, but not necessarily, the neutral beam etching device further comprises a bridge part which is configured to bridge between the first and the second chambers. 
   Preferably, but not necessarily, the bridge part is arranged at intervals between the first chamber and the second chamber. 
   Preferably, but not necessarily, the first chamber is in the shape of a pyramid such that the first chamber has a closed surface which has a larger size than that of the first opening and is formed at an opposite side to the first opening, and a lateral surface drawn from the first opening to the closed surface. 
   Preferably, but not necessarily, the second chamber is in the shape of a pyramid such that the second chamber has a top surface which is formed at an opposite side to the second opening and has a larger size than that of the second opening, and a lateral surface drawn from the second opening to the top surface. 
   Preferably, but not necessarily, the first channel is formed between the lateral surface of the first chamber and the lateral surface of the second chamber. 
   Preferably, but not necessarily, the first grid is charged with a first polarity to thereby accelerate one of the positive ion and the electron existing in the plasma generation area that has an opposite polarity to the first polarity. 
   Preferably, but not necessarily, the second grid is charged with an opposite polarity to the first polarity to thereby accelerate one of the positive ion and the electrons exiting in the plasma generation area that has the first polarity. 
   Preferably, but not necessarily, the coil is formed on a top of the closed surface of the first chamber. 
   Preferably, but not necessarily, the neutral beam etching device further comprises a gas injection part which is disposed on the outer surface of the first chamber and which injects a gas into the plasma generation area. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects of the present invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a view illustrating a conventional neutral beam etching device; 
       FIG. 2  is a view illustrating a neutral beam etching device according to a first exemplary embodiment of the present invention; 
       FIG. 3  is a top view of the neutral beam etching device of  FIG. 2 ; 
       FIG. 4  is a bottom view of the neutral beam etching device of  FIG. 2 ; 
       FIG. 5  is a view illustrating a neutral beam etching device according to a second exemplary embodiment of the present invention; and 
       FIG. 6  is a view illustrating a neutral beam etching device according to a third exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Hereinafter, exemplary embodiments of the present invention will now be described in greater detail with reference to the accompanying drawings. 
     FIG. 2  is a view illustrating a neutral beam etching device according to a first exemplary embodiment of the present invention. Referring to  FIG. 2 , the neutral beam etching device comprises a first chamber  110 , a second chamber  120 , a first channel  130 , a second channel  140 , a coil  160  and an acceleration part  170 . 
   The first chamber  110  has an opening formed at one side thereof and a closed surface formed at the other side. 
   The second chamber  120  is disposed inside the first chamber  110 . The second chamber  120  has an opening formed at one side like the first chamber  110 . The first and the second chambers  110  and  120  share the same axis but have different diameters. Accordingly, the opening of the second chamber  120  is nested in the opening of the first chamber  110 . 
   The closed surface of the first chamber  110  is spaced away from the top of the second chamber  120  to form a plasma generation area  150 . Gas is injected into the plasma generation area  150 . In the conventional neutral beam etching device, a gas generation area is limited to the top of channel, which is insufficient to generate a plasma. However, the neutral beam etching device according to an exemplary embodiment of the present invention has the relatively large plasma generation area  150  because the first chamber  110  and the second chamber  120  are spaced away from each other. 
   The coil  160  is formed on the top of the closed surface of the first chamber  110 . When current is applied to the coil  160 , a magnetic field is generated in the plasma generation area  150 . The generated magnetic field generates an induced current according to Maxwell&#39;s equations. The generated induced current converts the gas in the plasma generation area  150  into a plasma state. 
   The first channel  130  is formed between the inside surface of the first chamber  110  and the outer surface of the second chamber  120 . 
   The second channel  140  is formed in the second chamber  120 . The second chamber  140  fluidly communicates the opening of the second chamber  120  to the plasma generation area  150 . 
   The acceleration part  170  separates the plasma generated in the plasma generation area  150  into positive ions and electrons, accelerates the positive ions and the electrons, and discharges them to the outside of the neutral beam etching device through the first and the second channels  130  and  140 . If the positive ions are accelerated through the first channel  130 , the electrons are accelerated through the second channel  140 . If the electrons are accelerated through the first channel  130 , the positive ions are accelerated through the second channel  140 . 
   More specifically, the acceleration part  170  comprises a first grid  171  arranged in the first channel  130  and a second grid  172  arranged in the second channel  140 . The first and the second grids  171  and  172  are lattice pattern nets formed of conductive material. The first and the second grids  171  and  172  are connected to power supplies having different polarities. Accordingly, the first and the second grids  171  and  172  are charged with different polarities. 
   If the first grid  171  is charged with positive polarity and the second grid  172  is charged with negative polarity, an electrostatic force is generated between the negative electrons of the plasma and the first grid  171 , and thus the electrostatic force accelerates the negative electrons in the direction of an outlet of the first channel  130 . Also, an electrostatic force is generated between the positive ions and the second grid  172 , and thus the electrostatic force accelerates the positive ions in the direction of an outlet of the second channel  140 . The arrows shown in  FIG. 2  indicate the directions of outlet. 
   If the first grid  171  is charged with negative polarity and the second grid  172  is charged with positive polarity, the positive ions are accelerated through the first channel  130  and the electrons are accelerated through the second channel  140 . 
     FIG. 3  is a top view illustrating the neutral beam etching device of  FIG. 2 . Referring to  FIG. 3 , the closed surface formed on the upper portion the first chamber  110  is formed in the shape of a circle. 
   The coil  160  comprises a plurality of coils that are formed on the closed surface of the first chamber  110  coaxially with the first chamber  110 . The coil  160  may be formed in a spiral pattern. 
     FIG. 4  is a bottom view of the neutral beam etching device of  FIG. 2 . Referring to  FIG. 4 , the outlet of the first channel  130  is formed in a ring shape having an empty space at center, and the outlet of the second channel  140  is in the form of a circle. Accordingly, the first and the second grids  171  and  172  are in the shapes of a ring and a circle, respectively. 
     FIG. 5  is a view illustrating a neutral beam etching device according to a second exemplary embodiment of the present invention. Referring to  FIG. 5 , the neutral beam etching device has a first chamber  210  and a second chamber  220  which are in the shape of a pyramid. That is, openings of the first and the second chambers  210  and  220  are formed towards a common vertex of the pyramid. The first and the second chambers  210  and  220  may be in the shape of a cone, quadrangular pyramid, or pentagonal pyramid. Accordingly, positive ions and electrons generated in a plasma generation area  250  are discharged towards outlets and focused onto an area that is to be etched. 
   According to the pyramid shape of the first and the second chambers  210  and  220 , a first grid  271  is of a different shape than in the first exemplary embodiment described above. The first grid  271  has an inside ring edge upwardly inclining. A second grid  272  is in the shape of a circle. Since a coil  260 , a first channel  230 , and a second channel  240  are similar to those of the first exemplary embodiment in terms of general shapes and functions, descriptions thereof are omitted. 
     FIG. 6  is a view illustrating a neutral beam etching device according to a third exemplary embodiment of the present invention. Referring to  FIG. 6 , the neutral beam etching device comprises a first chamber  310 , a second chamber  320 , a first channel  330 , a second channel  340 , a coil  360 , a first grid  371 , and a second grid  372 . The neutral beam etching device according to the third exemplary embodiment further comprises a gas injection part  365  and a bridge part  380 . 
   Positive ions and electrons accelerated in a plasma generation area  350  through the first and the second channels  330  and  340  are discharged towards a wafer  400  and used to etch an area formed on the wafer  400 . The area may be predetermined. 
   Since the first chamber  310 , the second chamber  320 , the first channel  330 , the second channel  340 , the coil  360 , the first grid  371 , and the second grid  372  are similar to those of the second exemplary embodiment in terms of general structure and function, descriptions thereof are omitted. 
   The gas injection part  365  injects gas into the plasma generation area  350 . The neutral beam etching device uses gas of Group 0 such as Ar, ionizable gas such as O 2  or O 2  compound, gas such as C 2 F 2 , or other similar gas known in the art. The gas injection part  365  injects the gas through a connection pipe connected to the plasma generation area  350 . 
   The bridge part  380  bridges between the first chamber  310  and the second chamber  320 . Although the first chamber  310  and the second chamber  320  are connected to each other by the first grid  371 , it is advantageous to form the bridge part  380  to bear the weight of the second chamber  320 . The location of the bridge part  380  is limited to a specific area so that positive ions and electrons generated in the plasma area  350  are smoothly discharged towards the first and the second channels  330  and  340 . If the first and the second chambers  310  and  320  are in the shape of a pyramid, the bridge part  380  is arranged at intervals of 90° to support the second chamber  320  without unduly obstructing positive ion and electron discharge. 
   The second chamber  320  has an empty portion  390  formed in the rest portion except the second channel  340 . Therefore, the weight of the second chamber  320  is reduced and thus a load exerted to the bridge part  380  is reduced. 
   According to exemplary embodiments of the present invention as described above, the plasma is separated into positive ions and electrons and accelerated by the electrostatic force. Accordingly, acceleration energy necessary for an etching process can be saved and thus etching efficiency is improved. Also, if the first and the second chambers  110 ,  120 ,  210 ,  220 , and  310 ,  320  of first, second, and third exemplary embodiments, respectively, are in the shape of a pyramid, the separated and accelerated positive ions and electrons are focused into the area that is to be etched. As a result, it is easier to perform the etching operation. 
   The foregoing embodiments and aspects are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of exemplary embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.