Patent Publication Number: US-2007114903-A1

Title: Multi-channel plasma accelerator

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority from Korean Patent Application No. 10-2005-0052615 filed Jun. 17, 2005, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a plasma accelerator, and more particularly, to a multi-channel plasma accelerator including a plurality of channels.  
      2. Description of the Related Art  
      Plasma accelerators accelerate flows of plasmas generated or existing in predetermined spaces using electric and magnetic energies.  
      Plasma accelerators have been developed with research on ion engines and nuclear fusion of long distance space travel rockets and are now used for etching wafers in semiconductor manufacturing processes.  
      Plasma is a gas state divided into negatively charged electrons and positively charged ions at a high temperature. In other words, the plasma is a neutral gas due to a considerably high charge division and the same number of negative and positive charges. The plasma is strictly called a fourth material state flowing solid, liquid, and gas (three kinds of states of a material). If temperature is gradually increased, almost all objects are changed from solid to liquid states into gas states. Gas is divided into electrons and atomic nuclei at tens of thousands of ° C. to be a plasma state.  
       FIG. 1  is a cut perspective view of a conventional plasma accelerator. Referring to  FIG. 1 , the conventional plasma accelerator includes inner and outer circular loop coils  10  and  20 , an outer cylinder  30 , an inner cylinder  60 , a channel  40  formed between the outer and inner cylinders  30  and  60 , and a discharge coil  50  installed at a bottom of the channel  40 .  
      The inner and outer circular loop coils  10  and  20  are coaxially disposed and apply a current in a direction along which the inner and outer circular loop coils  10  and  20  enclose the channel  40 . A current is applied to the inner and outer circular loop coils  10  and  20  clockwise or counterclockwise to generate a magnetic field crossing an inside of the channel  40 . The inner and outer circular loop coils  10  and  20  reduce a current flowing in coils wound in an axis direction to reduce the magnetic field induced inside the channel  40  in the axis direction. The magnetic field is perpendicular to the axis direction to cross the channel  40  so as to gradually decrease in the axis direction. The magnetic field formed inside the channel  40  induces a secondary current according to Maxwell&#39;s equations. Plasma formed inside the channel  40  by the discharge coil  50  is accelerated toward an exit  70  in the axis direction due to the magnetic field crossing the channel  40  and the secondary current.  
      The conventional plasma accelerator uses a B-field modulation method in which a great current is applied to coils wound toward an entrance  80  and a small current is applied to coils wound toward the exit  70  to produce a difference in a magnetic pressure so as to accelerate plasma. The conventional plasma accelerator using the B-field modulation method causes radiative non-uniformity of plasma and ions.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present general inventive concept has been made to address the above-mentioned and other problems, and an aspect of the present general inventive concept is to provide a multi-channel plasma accelerator including a plurality of channels so as to produce a uniform density of plasma.  
      Another aspect of the present general inventive concept is to provide an etching apparatus for etching a wafer used for manufacturing a semiconductor chip using the multi-channel plasma accelerator.  
      According to an aspect of the present invention, there is provided a multi-channel plasma accelerator including a central cylinder formed along a surface comprising a blocked upper surface so as to form a first channel inside the cylinder; and first and second outer cylinders formed along the surface, each having an identical coaxial shaft to the central cylinder, and a diameter of the first outer cylinder being larger than a diameter of the central cylinder and a diameter of the second outer cylinder being larger than the diameter of the first outer cylinder so as to form a second channel as a space between the first and second outer cylinders.  
      The multi-channel plasma accelerator may further include a first connector connecting the central cylinder to the first outer cylinder; and a second connector connecting the first outer cylinder to the second outer cylinder.  
      The multi-channel plasma accelerator may further include a plurality of upper coils independently supplied with radio frequency power to induce an electromagnetic field so as to form a plasma; and a plurality of side coils offsetting a portion of the electromagnetic field in an axis direction so as to accelerate the plasma in the axis direction.  
      The plurality of upper coils may include first and second upper coils formed along upper surfaces of the central cylinder and of the second connector, respectively, the first and second upper coils generating a ponderomotive force toward exits of the first and second channels to accelerate the plasma toward the exits.  
      The plurality of side coils may include first and second side coils formed along an inner side of the first outer cylinder and an outer side of the second outer cylinder, respectively, the first and second side coils operating to move waves of the electromagnetic field formed inside the first and second channels, and to accelerate the plasma inside the first and second channels.  
      At least one of heights and widths of the first and second channels and heights of exits of the first and second channels may be changed to uniformly adjust a density of the plasma formed inside the first and second channels.  
      The central cylinder and the first and second outer cylinders may be dielectrics.  
      According to another aspect of the present invention, there is provided a multi-channel plasma accelerator including a central cylinder formed along a surface of a cylinder comprising a blocked upper surface so as to form a first channel inside the cylinder; and first through fourth outer cylinders formed along the surface of the cylinder, each having an identical coaxial shaft to the central cylinder, and each having a diameter d 1 , d 2 , d 3 , and d 4 , respectively, wherein d 1  is greater than a diameter of the central cylinder, and d 2 &gt;d 1 , d 3 &gt;d 2 , and d 4 &gt;d 3 , and wherein a second channel is formed between the first and second outer cylinders, and a third channel is formed between the third and fourth outer cylinders.  
      The multi-channel plasma accelerator may further include a first connector connecting the central cylinder to the first outer cylinder; a second connector connecting the first outer cylinder to the second outer cylinder; a third connector connecting the second outer cylinder to the third outer cylinder; and a fourth connector connecting the third outer cylinder to the fourth outer cylinder.  
      The multi-channel plasma accelerator may further include a plurality of upper coils independently supplied with radio frequency power to induce an electromagnetic field so as to form a plasma; and a plurality of side coils offsetting a portion of the electromagnetic field in an axis direction so as to accelerate the plasma in the axis direction.  
      The plurality of upper coils may include first, second, and third upper coils formed along upper surfaces of the central cylinder, the second connector, and the fourth connector, respectively, and generating a ponderomotive force toward exits of the first, second, and third channels so as to accelerate the plasma toward the exits.  
      The plurality of side coils may include first, second, and third side coils formed along an inner side of the first outer cylinder, an inner side of the third outer cylinder, and an outer side of the fourth outer cylinder, respectively, the plurality of side coils operating to move waves of the electromagnetic field formed inside the first, second, and third channels, and to accelerate the plasma inside the first, second, and third channels.  
      At least one of height and widths of the first, second, and third channels and heights of exits of the first, second, and third channels may be changed so as to uniformly adjust a density of the plasma formed inside the first, second, and third channels.  
      The central cylinder and the first, second, and third outer cylinders may be dielectric.  
      According to still another aspect of the present invention, there is provided an etching apparatus etching a wafer used for manufacturing a semiconductor chip using the multi-channel plasma accelerator of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other aspects of the present invention will be more apparent by describing certain exemplary embodiments of the present invention with reference to the accompanying drawings, in which:  
       FIG. 1  is a cut perspective view of a conventional plasma accelerator;  
       FIG. 2  is a cut perspective view of a multi-channel plasma accelerator including two channels according to an exemplary embodiment of the present invention;  
       FIG. 3  is a view illustrating a wave of a magnetic pressure moving inside a plurality of channels at a period of time t (=0.025 μsec);  
       FIG. 4  is a cut perspective view of a multi-channel plasma accelerator including three channels according to another exemplary embodiment of the present invention;  
       FIG. 5  is a cross-sectional view illustrating a right side of the multi-channel plasma accelerator including three channels of  FIG. 4  based on a central axis of a central cylinder according to an exemplary embodiment of the present invention; and  
       FIG. 6  is a cross-sectional view illustrating a right side of the multi-channel plasma accelerator including three channels based on a central axis of a central cylinder according to another exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION  
      Certain exemplary embodiments of the present invention will be described in greater detail with reference to the accompanying drawings.  
      In the following description, same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description such as a detailed construction and elements are nothing but the ones provided to assist in a comprehensive understanding of the invention. Thus, it is apparent that the present invention can be carried out without those defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
       FIG. 2  is a cut perspective view of a multi-channel plasma accelerator including two channels according to an exemplary embodiment of the present invention. Referring  FIG. 2 , a multi-channel plasma accelerator  200  including two channels according to an exemplary embodiment of the present invention includes a central cylinder  205 , first and second outer cylinders  230  and  250 , first, second, and third connectors  220 ,  240 , and  255 , and a plurality of coils  260 A,  260 B,  270 , and  280 .  
      The plurality of coils  260 A,  260 B,  270 , and  280  are greatly classified into upper coils  260 A and  260 B and side coils  270  and  280 . The upper coils  260 A and  260 B are re-classified into first and second upper coils  260 A and  260 B, and the side coils  270  and  280  are re-classified into first and second side coils  280  and  270 .  
      The central cylinder  205  includes a side part  210  and an upper part  215  forming a first channel CH 1  having a circular cross-section. The first coil  260 A is wound along an upper surface of the upper part  215  so that a diameter of the first coil  260 A is reduced.  
      The central cylinder  205  is connected to the first outer cylinder  230  via the first connector  220 , and the first outer cylinder  230  is connected to the second outer cylinder  250  via the second connector  240  so as to form a second channel CH 2  having a ring-shaped cross-section. The first and second channels CH 1  and CH 2  are formed toward an axis direction in a space in which plasma is generated and moved and include channel upper portions as upper portions of the first and second channels CH 1  and CH 2  and exits as lower portions of the first and second channels CH 1  and CH 2 .  
      The first side coil  280  spirally wound along an inner side of the first outer cylinder  220  and the second side coil  270  spirally wound along an outer side of the second outer cylinder  250  offset a magnetic field of magnetic fields in the axis direction so as to accelerate plasma toward the axis direction. Also, the second upper coil  260 B is wound along an upper surface of the second connector  240  so that a diameter of the second upper coil  260 B is reduced.  
      The plurality of coils  260 A,  260 B,  270 , and  280  apply a radio frequency (RF) power to the multi-channel plasma accelerator  200  to generate the plasma and form an inclination of a magnetic pressure inside the first and second channels CH 1  and CH 2  so as to accelerate the plasma from the channel upper portions toward the exits (in a direction indicated by an arrow shown in  FIG. 2 )  
      In more detail, the first and second upper coils  260 A and  260 B generate a ponderomotive force toward the exits so as to accelerate ions in an initial stage. The first and second upper coils  260 A and  260 B operate independently.  
      The first and second side coils  280  and  270  move waves of an electromagnetic field and further accelerate the ions inside the first and second channels CH 1  and CH 2  so as to synchronize the accelerations of the ions. Also, one of the first and second side coils  280  and  270  is commonly used by the first and second channels CH 1  and CH 2 .  
      The first and second side coils  280  and  270  are wound one time as shown in  FIG. 2  but may be wound several times. The numbers of turns of the first and second side coils  280  and  270  may vary. The first and second side coils  280  and  270  may be independently fed by a separate RF generator (not shown). The separate RF generator synchronizes currents flowing in the first and second side coils  280  and  270  so that a phase shift is controlled between the currents.  
      The RF power applied to the first and second channels CH 1  and CH 2  is relatively adjusted to uniformly adjust fluxes of the plasma and the ions. The currents flowing in the first ands second side coils  280  and  270  may be adjusted, or widths, depths, and diameters of the first and second channels CH 1  and CH 2  may be changed to uniformly adjust densities of the fluxes of the plasma and the ions.  
      The multi-channel plasma accelerator  200  shown in  FIG. 2  includes two channels, but the multi-channel plasma accelerator  200  is not limited to only two channels. Moreover, the multi-channel plasma accelerator  200  may additionally include ring-shaped channels having large diameters so as to treat a larger substrate.  
       FIG. 3  is a view illustrating waves of a magnetic pressure moving inside a plurality of channels at every predetermined period of time t (=0.025 μsec). Referring to  FIG. 3 , a magnetic pressure inside the first and second channels CH 1  and CH 2  is expressed as in Equation 1:  
             MP   =       B   2       2   ⁢     μ   0                 (   1   )               
      wherein MP denotes the magnetic pressure, B denotes an intensity of a magnetic field, and μ 0  denotes a dielectric constant of a free space. The term “magnetic pressure” is used to compute an acceleration of plasma in electromagnetic fluid mechanics.  
               P   +       B   2       2   ⁢     μ   0           =   const           (   2   )             
 
      wherein P denotes a pressure produced by plasma particles,  
         B   2       2   ⁢     μ   0           
 
 denotes the magnetic pressure, and const denotes a constant. Equation 2 2,means that a sum of the pressure produced by the plasma particles and the magnetic pressure must be uniform. Thus, an inclination of the magnetic pressure generates a force applied to the plasma, and thus the plasma is accelerated along a direction toward which the magnetic pressure moves. The moving waves of the magnetic pressure are driven by the first and second side coils  280  and  270 . The first and second side coils  280  and  270  are independently fed by a sine wave RF current having a phase shift of 90° between neighboring coils. 
 
       FIG. 4  is a cut perspective view of a multi-channel plasma accelerator including three channels according to another exemplary embodiment of the present invention.  
      Referring to  FIG. 4 , a multi-channel plasma accelerator  400  including three channels according to an exemplary embodiment of the present invention includes a central cylinder  405 ; first, second, third, and fourth outer cylinders  430 ,  450 ,  460 , and  470 ; first, second, third, fourth, and fifth connectors  420 ,  440 ,  455 ,  465 , and  475 ; and a plurality of coils  480 A,  480 B,  480 C,  490 ,  495 , and  500 . The plurality of coils  480 A,  480 B,  480 C,  490 ,  495 , and  500  are classified into upper coils  480 A,  480 B, and  480 C and side coils  490 ,  495 , and  500 . The upper coils  480 A,  480 B, and  480 C are re-classified into first, second, and third upper coils  480 A,  480 B, and  480 C, and the side coils  490 ,  495 , and  500  are re-classified into first, second, and third side coils  490 ,  495 , and  500 .  
      The central cylinder  405  includes a side part  410  and an upper part  415  forming a first channel CH 1  having a circular cross-section. The first upper coil  480 A is wound along an upper surface of the upper part  415  so that a diameter of the first upper coil  480 A is reduced.  
      The central cylinder  405  is connected to the first outer cylinder  430  via the first connector  420 , and the first outer cylinder  430  is connected to the second outer cylinder  450  via the second connector  440 , so as to form a second channel CH 2  having a ring-shaped cross-section. The second outer cylinder  450  is connected to the third outer cylinder  460  via the third connector  455 , and the third outer cylinder  460  is connected to the fourth outer cylinder  470  via the fourth connector  465 , so as to form a third channel CH 3  having a ring-shaped cross-section.  
      The first side coil  490  spirally wound along an inner side of the first outer cylinder  430 , the second side coil  495  spirally wound along an inner side of the third outer cylinder  460 , and the third side coil  500  spirally wound along an outer side of the fourth outer cylinder  470  offset a portion of a magnetic field in an axis direction so as to accelerate plasma toward the axis direction.  
      The second upper coil  480 B is wound along an upper surface of the second connector  440  so that a diameter of the second upper coil  480 B is reduced, and the third upper coil  480 C is wound along an upper surface of the fourth connector  465  so that a diameter of the third upper coil  480 C is reduced.  
      The plurality of coils  480 A,  480 B,  480 C,  490 ,  495 , and  500  apply an RF power to the multi-channel plasma accelerator  400  to generate plasma and form an inclination of a magnetic pressure inside the first, second, and third channels CH 1 , CH 2 , and CH 3  so as to accelerate the plasma from upper portions of the first, second, and third channels CH 1 , CH 2 , and CH 3  toward exits of the first, second, and third channels CH 1 , CH 2 , and CH 3  (in a direction indicated by an arrow shown in  FIG. 4 )  
      In more detail, the first, second, and third upper coils  480 A,  480 B, and  480 C generate a ponderomotive force toward the exits so as to accelerate ions in an initial stage. The first, second, and third upper coils  480 A,  480 B, and  480 C operate independently.  
      The first, second, and third side coils  490 ,  495 , and  500  move waves of an electromagnetic field, further accelerate ions inside the first, second, and third channels CH 1 , CH 2 , and CH 3 , and synchronize the acceleration of the ions. The first, second, and third side coils  490 ,  495 , and  500  are each wound one time as shown in  FIG. 4  but may be wound several times. The numbers of turns of the first, second, and third side coils  490 ,  495 , and  500  may vary. The first, second, and third side coils  490 ,  495 , and  500  may be independently fed by an additional RF generator (not shown). The additional RF generator synchronizes the first, second, and third side coils  490 ,  495 , and  500  so as to control a phase shift among currents flowing in the first, second, and third side coils  490 ,  405 , and  500 . An RF power applied to the first, second, and third channels CH 1 , CH 2 , and CH 3  may be relatively adjusted to uniformly adjust fluxes of plasma and the ions. The currents flowing in the first, second, and third side coils  490 ,  495 , and  500  may be adjusted, or widths, depths, and diameters of the first, second, and third channels CH 1 , CH 2 , and CH 3  may be changed to uniformly adjust the fluxes of the plasma and the ions.  
      The multi-channel plasma accelerator  400  shown in  FIG. 4  has three channels and thus can treat a greater substrate than the multi-channel plasma accelerator  200  having the two channels shown in  FIG. 2 . The multi-channel plasma accelerators  200  and  400  shown in  FIGS. 2 and 4  may be used in an etching apparatus to be used for etching a wafer for manufacturing a semiconductor chip.  
       FIG. 5  is a cross-sectional view illustrating a right side of the multi-channel plasma accelerator  400  including three channels shown in  FIG. 4  based on a central axis of a central cylinder to show a distribution of a magnetic pressure inside the channels. A left boundary line of  FIG. 5  denotes a central axis of the central cylinder  405 . Referring to  FIG. 5 , heights of the first, second, and third channels CH 1 , CH 2 , and CH 3  are the same, and heights of exits of the first, second, and third channels CH 1 , CH 2 , and CH 3  are the same. Distances from the exits of the first, second, and third channels CH 1 , CH 2 , and CH 3  to a wafer  1000  may be changed to uniformly control fluxes of plasma and ions. This is because the ions flow out through the exits of the first, second, and third channels CH 1 , CH 2 , and CH 3  and then are radiated to the wafer  1000 .  
       FIG. 6  is a view illustrating a multi-channel plasma accelerator including three channels according to another exemplary embodiment of the present invention. Referring to  FIG. 6 , heights Y 1  of first and second channels CH 1  and CH 2  are different from a height Y 2  of a third channel CH 3 . Also, a height H 1  of an exit  1  of the first and second channels CH 1  and CH 2  is different from a height H 2  of an exit  2  of the third channel CH 3 , and a gap G 1  between the first and second channels CH 1  and CH 2  is different from a gap G 2  between the second and third channels CH 2  and CH 3 . As described above, a gap between channels or diameters of channels, heights of exits of the channels, heights of the channels, and the like can be adjusted so that a density of a plasma and a density of an ion current are uniform on a lower surface of a plasma accelerator.  
      If a ratio v/s of a surface area s of a channel to a volume v of the channel is large, a density of charge particles may be higher. Diameters of the cylinders forming the channels can be changed to control widths of the channels and a gap between the channels. Thus, a ratio of a surface area of each of the channels to a volume of each of the channels and a density of a plasma can be controlled.  
      As described above, a multi-channel plasma accelerator according to exemplary embodiments of the present invention can include a plurality of channels and uniform densities of plasma and fluxes of ions inside the channels. Thus, a substrate having a large area can be treated with a uniform etching ratio.  
      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.