Patent Publication Number: US-2012037491-A1

Title: Antenna for inductively coupled plasma generation, inductively coupled plasma generator, and method of driving the same

Description:
TECHNICAL FIELD 
     The described technology relates generally to an antenna for inductively coupled plasma generation, an inductively coupled plasma generator, and a method of driving the same, and more particularly, to an inductively coupled plasma generating antenna having at least one sub-antenna coil, a plasma generator having the inductively-coupled plasma generating antenna, and a method of driving the plasma generator. 
     BACKGROUND ART 
     Plasma generators are used to perform various surface treatment processes, such as etching, chemical vapor deposition (CVD), sputtering, oxidation and nitridation, in technical fields for semiconductor wafers or flat panel displays (FPDs) in which micropatterns should be formed. Lately, wafers for semiconductor device and substrates for FPDs have increased in size to, for example, 450 mm or more to reduce cost and improve throughput, and demand for a plasma generator for processing large wafers or substrates is increasing. 
     In general, plasma generators are classified into inductively coupled plasma generators, capacitively coupled plasma generators, and so on. In a method of driving inductively coupled plasma generators, antennas for plasma generation are disposed around a chamber, and high frequency or radio frequency (RF) power is applied to the antennas to form a magnetic field that varies according to time in a space surrounding the chamber. The magnetic field varying according to time forms an induced electric field inside the chamber, and the induced electric field generates plasma by accelerating free electrons in the chamber to collide with a neighboring neutral gas. On the other hand, in a method of driving capacitively coupled plasma generators, two electrodes are installed in a chamber, and RF power is applied between the two electrodes to form an electric field that varies according to time in a space between the two electrodes. The formed electric field generates plasma by efficiently accelerating free electrons in the chamber to collide with a neighboring neutral gas. 
     In inductively coupled plasma generators, an antenna can be disposed outside a chamber, and an electric field induced by the antenna has a circular shape. Thus, in comparison with capacitively coupled plasma generators, free electrons can be accelerated regardless of the position of an electrode, and high density plasma can be ensured. Therefore, research on such inductively coupled plasma generators is attracting attention. For example, Korean Patent Registration No. 488363 discloses an antenna structure of an inductively coupled plasma generator in which at least two loop antennas are installed electrically in parallel, and Korean Patent Registration No. 800369 discloses an inductively coupled plasma antenna that includes at least two spiral segments wound around a cylindrical plasma generation unit and a switching unit respectively formed in the spiral segments and switching the power of a high-frequency power supply to the spiral segments. 
     DISCLOSURE OF INVENTION 
     Solution to Problem 
     In one embodiment, an antenna for inductively coupled plasma generation is provided. The antenna for inductively coupled plasma generation includes: a first end connected to an alternating current (AC) power supply; a second end connected to a ground terminal; and an antenna coil connected to the first end and the second end, and configured to receive power of the AC power supply and generate an induced electric field. The antenna coil includes one or more sub-coil units configured to generate a magnetic field in a region adjacent to the antenna coil unit in response to the power of the AC power supply. 
     In another embodiment, an inductively coupled plasma generator is provided. The inductively coupled plasma generator includes: a chamber; an AC power supply and a ground terminal which are disposed outside the chamber; and a loop antenna including a first end connected to the AC power supply, a second end connected to the ground terminal, and an antenna coil unit. The antenna coil unit includes one or more sub-coil units arranged along the antenna coil. 
     In yet another embodiment, a method of driving an inductively coupled plasma generator is provided. The method of driving an inductively coupled plasma generator includes a process of introducing a gas for forming plasma into a chamber, and also a process of supplying power of an AC power supply to one end of a coil of a loop antenna disposed on an outer wall of the chamber. The loop antenna includes one or more sub-coil units arranged along the loop antenna. The loop antenna generates an induced electric field in an inner region of the loop antenna in response to the power of the AC power supply. The one or more sub-coil units generate a magnetic field in a region adjacent to the loop antenna. 
     The Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. The Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art by describing in detail example embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  schematically illustrates an antenna for inductively coupled plasma generation according to an embodiment of the present disclosure; 
         FIG. 2  schematically illustrates an antenna for inductively coupled plasma generation according to another embodiment; 
         FIG. 3  schematically illustrates an antenna for inductively coupled plasma generation according to yet another embodiment; 
         FIG. 4  is a perspective view schematically illustrating arrangement of an antenna for inductively coupled plasma generation according to an embodiment; 
         FIG. 5  is a top view schematically illustrating arrangement of an antenna for inductively coupled plasma generation according to another embodiment; 
         FIG. 6  is a perspective view schematically illustrating arrangement of an antenna for inductively coupled plasma generation according to yet another embodiment; 
         FIG. 7  is a schematic view of an inductively coupled plasma generator according to an embodiment; 
         FIG. 8  is a schematic view of an inductively coupled plasma generator according to another embodiment; 
         FIG. 9  is a schematic view of an inductively coupled plasma generator according to yet another embodiment; 
         FIG. 10  is a cross-sectional view of an inductively coupled plasma generator according to still another embodiment; 
         FIG. 11  is a cross-sectional view of an inductively coupled plasma generator according to still another embodiment; 
         FIG. 12  is a schematic top view of an antenna for inductively coupled plasma generation according to still another embodiment; 
         FIG. 13  is a schematic top view of an antenna for inductively coupled plasma generation according to still another embodiment; 
         FIG. 14  illustrates a chamber constituted to measure plasma density according to an embodiment; and 
         FIG. 15  shows results of measuring density of plasma generated by various antennas according to an embodiment. 
     
    
    
     MODE FOR THE INVENTION 
     It will be readily understood that the components of the present disclosure, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of apparatus and methods in accordance with the present disclosure, as represented in the Figures, is not intended to limit the scope of the disclosure, as claimed, but is merely representative of certain examples of embodiments in accordance with the disclosure. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. Moreover, the drawings are not necessarily to scale, and the size and relative sizes of layers and regions may have been exaggerated for clarity. 
     It will also be understood that when an element or layer is referred to as being “on, another element or layer, the element or layer may be directly on the other element or layer or intervening elements or layers may be present. 
     As described above, conventional antennas for inductively coupled plasma generation generally include a spiral type coil or a separate electrode type coil, and it may be still difficult to control plasma formed in a chamber to have uniform distribution. To be specific, in an antenna having a spiral type coil, inductive coils constituting the antenna are connected in series, and an alternating current(AC) flowing through each of the inductive coils is controlled to have the same value. Accordingly, the AC induces a magnetic field that varies according to time and the magnetic field generates an induced electric field around the antenna. Although the AC is controlled to have the same value, it is difficult to control density distribution of plasma caused by the induced electric field in the chamber. That is, due to ion and electron loss on the inner wall of the chamber, plasma density may be high in the center of the chamber and low in a portion adjacent to the inner wall of the chamber. Furthermore, since the inductive coils of the antenna are connected in series, voltage drop due to the antenna is great, which increases the influence of capacitive coupling between plasma and the inductive coils. Thus, power efficiency decreases, and it may be difficult to keep uniformity in the density distribution of plasma in the entire inner space of the chamber. 
     In an antenna having a separate electrode type coil, an antenna coil of the antenna may have, for example, three separate electrodes respectively connected to three high-frequency power supplies of different phases, At this time, plasma density generated by the antenna is high at a position adjacent to the respective separate electrodes but decreases from the respective separate electrodes to the center of the chamber. Thus, it may be difficult to ensure the uniformity in the density distribution of plasma. 
       FIG. 1  schematically illustrates an antenna for inductively coupled plasma generation according to an embodiment of the present disclosure. Part (a) Of  FIG. 1  shows a top view of an antenna for inductively coupled plasma generation according to an embodiment, and Parts (b) and (c) of  FIG. 1  show top views of a sub-coil unit of the antenna for inductively coupled plasma generation according to an embodiment. 
     Referring to part (a) of  FIG. 1 , an antenna  100  for inductively coupled plasma generation includes a first end  101 , a second end  102 , and an antenna coil unit  103 . The first end  101  may be connected to an AC power supply (not shown) such as a high frequency power supply or a radio frequency (RF) power supply, and the second end  102  may be connected to a ground terminal (not shown). Alternatively, the first end  101  may be connected to the ground terminal, and the second end  102  may be connected to the AC power supply. 
     The antenna coil unit  103  is connected to the first end  101  and the second end  102 , receives the power of the AC power supply, and generates an induced electric field. According to Ampere s law, a magnetic field is formed around the antenna coil unit  103  when current is applied to the antenna coil unit  103 . When power from the AC power supply is applied, a magnetic field varying according to time is generated around the antenna coil unit  103 , and an induced electromotive force is generated around the antenna coil unit  103  according to Faraday s law of electromagnetic induction. The induced electromagnetic force forms an induced electric field around the antenna coil unit  103  in the opposite direction to the power applied from the AC power supply. According to an embodiment, the antenna  100  for inductively coupled plasma generation may be disposed to have the form of a loop as shown in  FIGS. 4 to 6 . In this case, the antenna  100  may receive the power applied from the AC power supply and form an induced electric field having a circular shape through the loop. 
     The antenna coil unit  103  includes one or more sub-coil units  104 . The sub-coil units  104  may be formed in one body with the antenna coil unit  103  by shaping an antenna coil along the longitudinal direction (i.e., the X-axis direction in part (a) of  FIG. 1 ). For example, the sub-coil units  104  may be arranged in the same shape as each other along the longitudinal direction of the antenna coil unit  103 . 
     Parts (b) and (c) of  FIG. 1  show one of the sub-coil units  104  according to an embodiment. As shown in the drawings, the sub-coil unit  104  may have a substantially symmetrical shape with respect to line A-A′. For example, in the sub-coil unit  104 , a lower triangle coil  107  and an upper triangle coil  108  may be symmetric to each other with respect to line A-A′. 
     Referring to part (b) of  FIG. 1 , when current that flows from a left end  105  to a right end  106  is supplied from the AC power supply to the sub-coil unit  104 , a magnetic field may be formed around the sub-coil unit  104  according to Ampere s law. In this case, the direction of lines of magnetic force may be different according to a portion of the sub-coil unit  104  such as the lower triangle coil  107  or the upper triangle coil  108 . From the lower triangle coil  107 , a line of magnetic force may be generated to have a direction that is from the inside of the lower triangle coil  107  to the outside of the lower triangle coil  107 . On the other hand, from the upper triangle coil  108 , a line of magnetic force may be generated to have a direction that is from the outside of the upper triangle coil  108  to the inside of the upper triangle coil  108 . In this specification, the magnetic field polarity of a part in which a line of magnetic force is emitted is indicated by N pole, and the magnetic field polarity of a part in which a line of magnetic force is gathered is indicated by S pole. As shown in part (b) of  FIG. 1 , when current flows from the left end  105  to the right end  106 , a magnetic field may be locally formed to have the polarity of the N pole inside the lower triangle coil  107  and the polarity of the S pole outside the lower triangle coil  107 . Also, a magnetic field may be locally formed to have the polarity of the S pole inside the upper triangle coil  108  and the polarity of the N pole outside the upper triangle coil  108 . Thus, a magnetic field in the sub-coil unit  104  may be formed to have the polarity of the N pole inside the lower triangle coil  107  and the polarity of the S pole inside the upper triangle coil  108 . 
     Referring to part (c) of  FIG. 1 , when current that flows from the right end  106  to the left end  105  is supplied from the AC power supply to the sub-coil unit  104 , a magnetic field may be likewise formed around the sub-coil unit  104  according to Ampere s law. As shown in part (c) of  FIG. 1 , a magnetic field having the polarity of the S pole inside the lower triangle coil  107  and the polarity of the N pole outside the lower triangle coil  107  may be locally formed. Also, a magnetic field having the polarity of the N pole inside the upper triangle coil  108  and the polarity of the S pole outside the upper triangle coil  108  may be locally formed. Thus, a magnetic field in the sub-coil unit  104  may be formed to have the polarity of the N pole inside the upper triangle coil  108  and the polarity of the S pole inside the lower triangle coil  107 . 
     Referring back to part (a) of  FIG. 1 , when power is applied from the AC power supply to the antenna  100  for inductively coupled plasma generation, an induced electric field is generated around the antenna coil unit  103 , and also a new magnetic field caused by the sub-coil units  104  may be locally formed in a region adjacent to the sub-coil units  104 . According to an embodiment, because the direction of current supplied from the AC power supply to the antenna  100  varies according to time, a magnetic field having lines of magnetic force shown in part (b) of  FIG. 1  and a magnetic field having lines of magnetic force shown in part (c) of  FIG. 1  may be alternated according to time. 
     As shown in part (a) of  FIG. 1 , the N pole and S pole of the sub-coil units  104  are arranged in turn along the longitudinal direction of the antenna coil unit  103  (i.e., the X-axis direction) with respect to power applied from the outside, and the sub-coil units  104  may be disposed to form a local magnetic field whose polarity varies according to time. Also, the sub-coil units  104  may be disposed to form a magnetic field whose N pole and S pole are symmetrically arranged in a direction (i.e., the Y-axis direction of part (a) of  FIG. 1 ) substantially perpendicular to the longitudinal direction of the antenna coil unit  103  with respect to line A-A′. According to an embodiment, the sub-coil units  104  may be manufactured that the N pole and S pole of the sub-coil units  104  have lines of magnetic force of substantially the same magnitude with each other. 
       FIG. 2  schematically illustrates an antenna for inductively coupled plasma generation according to another embodiment. Part (a) of  FIG. 2  shows a top view of an antenna for inductively coupled plasma generation according to another embodiment, and part (b) of  FIG. 2  shows a top view of sub-coil units of the antenna for inductively coupled plasma generation shown in part (a) of  FIG. 2 . 
     Referring to part (a) of  FIG. 2 , an antenna  200  for inductively coupled plasma generation includes a first end  201 , a second end  202 , and an antenna coil unit  203 . The antenna coil unit  203  includes one or more sub-coil units  204 . The sub-coil units  204  may be formed in one body with the antenna coil unit  203  by shaping an antenna coil along the longitudinal direction (i.e., the X-axis direction). 
     Referring to part (b) of  FIG. 2 , the sub-coil units  204  may have a substantially symmetrical shape with respect to line B-B′. For example, in the sub-coil units  204 , a lower diamond-shaped coil  207  and an upper diamond-shaped coil  208  may be symmetric to each other with respect to line B-B′. As described with reference to parts (a) to (c) of  FIG. 1 , when current flows from a left end  205  to a right end  206 , a magnetic field may be locally formed to have the polarity of the N pole inside the lower diamond-shaped coil  207  and the polarity of the S pole outside the lower diamond-shaped coil  207 . Also, a magnetic field may be locally formed to have the polarity of the S pole inside the upper diamond-shaped coil  208  and the polarity of the N pole outside the upper diamond-shaped coil  208 . Thus, a magnetic field in the sub-coil units  204  may be formed to have the polarity of the N pole inside the lower diamond-shaped coil  207  and the polarity of the S pole inside the upper diamond-shaped coil  208 . 
     Although not shown in the drawings, when current flows from the right end  206  to the left end  205 , a magnetic field having polarities opposite to those of the case where the current flows from the left end  205  to the right end  206  may be locally formed in a region adjacent to the sub-coil units  204 . 
     According to other embodiments, the sub-coil units  204  may have any structure satisfying the requirement of a substantially symmetrical shape with respect to line B-B′. For example, the structure may include polygonal and circular upper and lower coils symmetric to each other. 
     According to an embodiment, the antenna  200  for inductively coupled plasma generation may be disposed to have the form of a loop as shown in  FIGS. 4 to 6 . In this case, the antenna  200  may receive the power applied from the AC power supply and form an induced electric field having a circular shape through the loop. 
       FIG. 3  schematically illustrates an antenna for inductively coupled plasma generation according to yet another embodiment. Part (a) of  FIG. 3  shows a top view of an antenna for inductively coupled plasma generation according to yet another embodiment, and part (b) of  FIG. 3  shows a top view of a sub-coil unit of the antenna for inductively coupled plasma generation according to yet another embodiment. 
     Referring to part (a) of  FIG. 3 , an antenna  300  for inductively coupled plasma generation includes a first end  301 , a second end  302 , and an antenna coil unit  303 . The antenna coil unit  303  includes one or more sub-coil units  304 . The sub-coil units  304  may be formed in one body with the antenna coil unit  303  by shaping an antenna coil along the longitudinal direction (i.e., the X-axis direction of part (a) of  FIG. 3 ). 
     Referring to part (b) of  FIG. 3 , the sub-coil units  304  may have a substantially symmetrical shape with respect to a direction forming a predetermined angle, e.g., 0 to 180, with respect to the X-axis direction. For example, in the sub-coil units  304 , a lower diamond-shaped coil  307  and an upper diamond-shaped coil  308  may be symmetric to each other with respect to line C-C′. When current flows from a left end  305  to a right end  306 , a magnetic field may be locally formed to have the polarity of the N pole inside the lower diamond-shaped coil  307  and the polarity of the S pole outside the lower diamond-shaped coil  307 . Also, a magnetic field may be locally formed to have the polarity of the S pole inside the upper diamond-shaped coil  308  and the polarity of the N pole outside the upper diamond-shaped coil  308 . Thus, a magnetic field in the sub-coil units  304  may be formed to have the polarity of the N pole inside the lower diamond-shaped coil  307  and the polarity of the S pole inside the upper diamond-shaped coil  308 . Although not shown in the drawings, when current flows from the right end  306  to the left end  305 , a magnetic field having polarities opposite to those of the case where the current flows from the left end  305  to the right end  306  may be locally formed in a region adjacent to the sub-coil units  304 . 
     According to other embodiments, the sub-coil units  304  may have any structure satisfying the requirement of a substantially symmetrical shape with respect to line C-C′ forming a predetermined angle, e.g., 0 to 180, with respect to the X-axis. For example, the structure may include polygonal and circular upper and lower coils symmetric to each other. 
     According to an embodiment, the antenna  300  for inductively coupled plasma generation may be disposed to have the form of a loop as shown in  FIGS. 4 to 6 . In this case, the antenna  300  may receive the power applied from the AC power supply and form an induced electric field having a circular shape through the loop. 
       FIG. 4  is a perspective view schematically illustrating arrangement of an antenna for inductively coupled plasma generation according to an embodiment. Referring to FIG.  4 , an antenna  400  for inductively coupled plasma generation includes a first end  410 , a second end  420 , and an antenna coil unit  450 . The antenna coil unit  450  includes one or more sub-coil units  460 . The sub-coil units  460  may be formed in one of the shapes of the sub-coil units  104 ,  204  and  304  of the embodiments described with reference to  FIGS. 1 to 3 . 
     As shown in the drawing, the antenna coil unit  450  is arranged in the form of a loop, the first end  410  is connected to an AC power supply  430 , and a second end  420  is connected to a ground terminal  440 . The AC power supply  430  may be, for example, a high frequency power supply or a radio frequency (RF) power supply. As one example, the RF power supply may provide frequencies of 2 MHz to 2.45 GHz for the antenna coil unit  450 . As another example, the RF power supply may provide frequency of 13.56 MHz for the antenna coil unit  450 . Planes constituted by lower coils  470  and upper coils  480  of the sub-coil units  460  may be different from a bottom plane on which the antenna coil unit  450  in the form of the loop is disposed. For example, the planes constituted by the lower coils  470  and upper coils  480  may be substantially perpendicular to the bottom plane on which the antenna coil unit  450  in the form of the loop is disposed. In this specification, an antenna having substantially the same shape as that of the antenna  400  is referred to as a vertical antenna. In the vertical antenna, planes where sub-coil units constitute are substantially perpendicular to a bottom plane where an antenna coil unit in the form of a loop is disposed. According to some embodiments, the vertical antenna may be arranged to have one or more loop turns. Also, the vertical antenna may be arranged to surround the outer wall of a chamber. 
       FIG. 5  is a top view schematically illustrating arrangement of an antenna for inductively coupled plasma generation according to another embodiment. Referring to  FIG. 5 , an antenna  500  for inductively coupled plasma generation includes a first end  510 , a second end  520 , and an antenna coil unit  550 . The antenna coil unit  550  includes one or more sub-coil units  560 . The sub-coil units  560  may be formed in one of the shapes of the sub-coil units  104 ,  204  and  304  of the embodiments described with reference to  FIGS. 1 to 3 . 
     As shown in the drawing, the antenna coil unit  550  is arranged in the form of a loop, the first end  510  is connected to an AC power supply  530 , and a second end  520  is connected to a ground terminal  540 . The AC power supply  530  may be, for example, a high frequency power supply or a radio frequency (RF) power supply. As one example, the RF power supply may provide frequencies of 2 MHz to 2.45 GHz for the antenna coil unit  550 . As another example, the RF power supply may provide frequency of 13.56 MHz for the antenna coil unit  550 . Planes constituted by lower coils  570  and upper coils  580  of the sub-coil units  560  may be substantially the same as a bottom plane on which the antenna coil unit  550  in the form of the loop is disposed. In this specification, an antenna having substantially the same shape as that of the antenna  500  is referred to as a horizontal antenna. In the horizontal antenna, planes where sub-coil units constitute are substantially the same as a bottom plane where an antenna coil unit in the form of a loop is disposed. According to some embodiments, the horizontal antenna may be arranged to have one or more loop turns. Also, the horizontal antenna may be arranged on the outer wall of a chamber. 
       FIG. 6  is a perspective view schematically illustrating arrangement of an antenna for inductively coupled plasma generation according to yet another embodiment. Referring to  FIG. 6 , an antenna  600  for inductively coupled plasma generation includes a first segment  610  and a second segment  620  that are physically separated from each other, and is arranged in the form of a loop. The first segment  610  and the second segment  620  are substantially the same as the antennas  100 ,  200  and  300  for inductively coupled plasma generation of the embodiments described with reference to  FIGS. 1 to 3 . 
     The first segment  610  and the second segment  620  may be vertical antennas, and connected to an AC power supply  630  and a ground terminal  640  in parallel. Alternatively, each of the first segment  610  and the second segment  620  may be a horizontal antenna, or a combination of the vertical antenna and the horizontal antenna. According to other embodiments, the antenna  600  for inductively coupled plasma generation may include three or more segments. The AC power supply  630  may be, for example, a high frequency power supply or a radio frequency (RF) power supply. As one example, the RF power supply may provide frequencies of 2 MHz to 2.45 GHz for the first segment  610  and the second segment  620 . As another example, the RF power supply may provide frequency of  13 . 56  MHz for the first segment  610  and the second segment  620 . 
       FIG. 7  is a schematic view of an inductively coupled plasma generator according to an embodiment. Part (a) of  FIG. 7  shows a cross-sectional view of an inductively coupled plasma generator according to an embodiment, and part (b) of  FIG. 7  shows a top view of a loop antenna shown in part (a) of  FIG. 7 . Referring to parts (a) and (b) of  FIG. 7 , an inductively coupled plasma generator  700  includes a chamber  710 , an AC power supply  720 , a ground terminal  730 , and a loop antenna  740 . 
     The chamber  710  may include a wafer  750  and a chuck  760  that supports the wafer  750 . Although not shown in the drawing, the chamber  710  may further include a gas inlet for supplying a gas for plasma generation and reaction, a gas outlet and pump system for discharging a gas in the chamber  710 . 
     The AC power supply  720  and the ground terminal  730  may be disposed outside the chamber  710  and supply the loop antenna  740  with power for inductively coupled plasma generation. The AC power supply  720  may be, for example, a high frequency power supply or a radio frequency (RF) power supply. As one example, the RF power supply may provide frequencies of 2 MHz to 2.45 GHz for the loop antenna  740 . As another example, the RF power supply may provide frequency of 13.56 MHz for the loop antenna  740 . 
     The antennas  100 ,  200  and  300  for inductively coupled plasma generation described with reference to  FIGS. 1 to 3  can be applied to the loop antenna  740 . Referring to  FIG. 7 , the loop antenna  740  is disposed on a flat surface of the outer wall of the chamber and connected to the AC power supply  720  and the ground terminal  730 . The loop antenna  740  has one or more sub-coil units  746  including an upper coil  742  and a lower coil  744 , and is arranged as a horizontal antenna described with reference to  FIG. 5 . 
     A gas, e.g., a non-reactive gas such as helium, hydrogen, argon or nitrogen, for plasma generation is introduced into the chamber  710 , and a pressure in the chamber  710  can be kept constant using the pump system. And, the AC power supply  720  disposed outside the chamber  710  supplies power to one end of the loop antenna  740 . 
     When power varying according to time is supplied from the AC power supply  720 , a magnetic field having magnetic flux that varies according to time is formed in the loop of the loop antenna  740  according to Ampere s law. The magnetic field having the magnetic flux varying according to time generates an induced electric field in the loop inside the chamber  710  according to Faraday s law. Free electrons accelerated along the induced electric field collide with a neutral gas and ionize the neutral gas, thereby generating plasma. At this time, the ions and electrons accelerated by the induced electric field collide with the inner wall of the chamber  710  and are lost, so that plasma density may be higher in the center of the chamber  710  and lower in a portion adjacent to the inner wall of the chamber  710 . In this embodiment, the antenna coil of the loop antenna  740  includes the one or more sub-coil units  746 , thus generating a local magnetic field around the antenna coil separately from the induced electric field. The magnetic field locally formed around the antenna coil applies Lorentz force to electrons or ions having a charge, thereby preventing the electrons or ions from approaching the inner wall of the chamber  710  and capturing and confining the electrons or ions in a predetermined region near the inner wall of the chamber  710 . Thus, a sheath region in which no electrons exist between plasma and the inner wall of the chamber  710  may be reduced around a region in which the sub-coil units  746  exist. The captured and confined electrons or ions near the inner wall of the chamber  710  can increase the ionization rate of the gas. As a result, plasma density around the inner wall of the chamber  710  on which the sub-coil units  746  are disposed can increase. Also, the local magnetic field effectively prevents collision between ions in plasma and the inner wall of the chamber  710 , so that generation of particles that pollute the chamber  710  can be inhibited. 
     As shown in  FIG. 7 , when the loop antenna  740  is disposed on the flat surface of the outer wall of the chamber  710  and is supplied with power varying according to time from the AC power supply  720 , a magnetic field varying according to time is generated in a direction penetrating the loop of the loop antenna  740  in the chamber  710 . In succession, the magnetic field varying according to time generates an induced electric field  780  having a direction opposite to that of the power supplied from the AC power supply  720  according to Faraday s law. Also, a local magnetic field  790  may be generated around the loop antenna  740  by the sub-coil units  746 . The local magnetic field  790  may serve to increase plasma density near the inner wall of the chamber  710 . 
       FIG. 8  is a schematic view of an inductively coupled plasma generator according to another embodiment. Part (a) of  FIG. 8  shows a cross-sectional view of an inductively coupled plasma generator according to another embodiment, and part (b) of  FIG. 8  shows a top view of a loop antenna shown in part (a) of  FIG. 8 . Referring to parts (a) and (b) of  FIG. 8 , an inductively coupled plasma generator  800  includes a chamber  710 , an AC power supply  720 , a ground terminal  730 , and a loop antenna  840 . Components denoted by the same reference numerals as in the embodiment described with reference to  FIG. 7  will not be described again in detail. 
     The loop antenna  840  is substantially the same as the loop antenna  740  described with reference to  FIG. 7  except that the loop antenna  840  is in the form of a spiral loop having a plurality of turns. As a result, when the loop antenna  840  is in the form of a spiral loop having a plurality of turns, the loop antenna  840  can effectively reduce a sheath region on the inner wall of the chamber  710  adjacent to the loop antenna  840  and effectively increase plasma density that is lower than that of the center of the chamber  710 . 
       FIG. 9  is a schematic view of an inductively coupled plasma generator according to yet another embodiment. Part (a) of  FIG. 9  shows a cross-sectional view of an inductively coupled plasma generator according to yet another embodiment, and part (b) of  FIG. 9  shows a top view of loop antennas shown in part (a) of  FIG. 9 . Referring to parts (a) and (b) of  FIG. 9 , an inductively coupled plasma generator  900  includes a chamber  710 , an AC power supply  720 , a ground terminal  730 , and loop antennas  940  and  950 . Components denoted by the same reference numerals as in the embodiment described with reference to  FIG. 7  will not be described again in detail. 
     The loop antennas  940  and  950  are substantially the same as the loop antenna  740  described with reference to  FIG. 7  except that the loop antennas  940  and  950  are physically separated from each other. The loop antennas  940  and  950  are connected to the AC power supply  720  and the ground terminal  730  in parallel. Alternatively, the loop antennas  940  and  950  may be connected to the AC power supply  720  and the ground terminal  730  in series. Referring to the drawings, the loop antenna  940  forms an outer loop, and the loop antenna  950  forms an inner loop. In some embodiments, three or more physically separated loop antennas may exist, and each of the loop antennas may be connected to the AC power supply  720  and the ground terminal  730 . 
     In this embodiment, a plurality of physically separated loop antennas can be disposed on a flat surface of the outer wall of a chamber, and can effectively reduce a sheath region on the inner wall of the chamber  710  adjacent to the loop antennas  940  and  950  and effectively increase plasma density that is lower than that of the center of the chamber  710 . 
       FIG. 10  is a cross-sectional view of an inductively coupled plasma generator according to still another embodiment. Referring to  FIG. 10 , an inductively coupled plasma generator  1000  includes a chamber  710 , an AC power supply  720 , a ground terminal  730 , and loop antennas  1040  and  1050 . Components denoted by the same reference numerals as in the embodiment described with reference to  FIG. 7  will not be described again in detail. 
     Each of the loop antennas  1040  and  1050  may be arranged in substantially the same way as in the embodiment described with reference to  FIG. 4  or  6 . Each of the loop antennas  1040  and  1050  may be the vertical antenna arranged to surround a curved surface of the outer wall of the chamber  710 . The vertical antenna operates in the same way as the horizontal antenna described with reference to  FIGS. 7 to 9 , and can form a local magnetic field  790  in a region adjacent to the vertical antenna while forming an induced electric field  780  inside the chamber  710 . 
     As shown in the drawing, the loop antennas  1040  and  1050  are connected to the AC power supply  720  and the ground terminal  730  in parallel. Alternatively, the loop antennas  1040  and  1050  may be connected to the AC power supply  720  and the ground terminal  730  in series. 
     As a result, the loop antennas  1040  and  1050  can effectively reduce a sheath region on the inner wall of the chamber  710  adjacent to the loop antennas  1040  and  1050  and effectively increase plasma density that is lower than that of the center of the chamber  710 . 
       FIG. 11  is a cross-sectional view of an inductively coupled plasma generator according to still another embodiment. Referring to  FIG. 11 , an inductively coupled plasma generator  1100  includes a chamber  710 , an AC power supply  720 , a ground terminal  730 , and loop antennas  1140 ,  1150  and  1160 . Components denoted by the same reference numerals as in the embodiment described with reference to  FIG. 7  will not be described again in detail. 
     The loop antennas  1140  and  1160  may be arranged in substantially the same way as in the embodiment described with reference to  FIG. 10 . The loop antenna  1150  may be arranged in substantially the same way as in the embodiment described with reference to  FIG. 7 . Each of the loop antennas  1140  and  1160  is arranged to surround a curved surface of the outer wall of the chamber  710 , and the loop antenna  1150  is arranged on a flat surface of the outer wall of the chamber  710 . 
     As a result, the loop antennas  1140 ,  1150  and  1160  can effectively reduce a sheath region on the inner wall of the chamber  710  adjacent to the loop antennas  1140 ,  1150  and  1160  and effectively increase plasma density that is lower than that of the center of the chamber  710 . 
       FIG. 12  is a schematic top view of an antenna for inductively coupled plasma generation according to still another embodiment. Referring to  FIG. 12 , an antenna  1200  for inductively coupled plasma generation includes a first end  1201 , a second end  1202 , and an antenna coil unit  1203 . The antenna coil unit  1203  ,may be formed by shaping an antenna coil along X- and Y-axis directions. The antenna coil unit  1203  includes one or more sub-coil units  1204  arranged along the X- and Y-axis directions. When power is applied to the first end  1201  and the second end  1202 , the antenna coil unit  1203  forms an induced electric field in response to the power applied from the outside in substantially the same way as the antenna coil units  103 ,  203  and  303  described with reference to  FIGS. 1 to 3 . The sub-coil units  1204  form a local magnetic field around the sub-coil units  1204  themselves in substantially the same way as the sub-coil units  104 ,  204  and  304  described with reference to  FIGS. 1 to 3 . The antenna  1200  for inductively coupled plasma generation may be arranged in the form of a loop to surround a curved surface of the outer wall of a chamber in a similar way to the antenna  400  for inductively coupled plasma generation of the embodiment described with reference to  FIG. 4 . 
     According to an embodiment, a height H of the antenna  1200  for inductively coupled plasma generation may be adjusted on the basis of the height of the outer wall of the chamber. For example, the height H of the antenna  1200  for inductively coupled plasma generation may be substantially the same as the height of the outer wall of the chamber. Thus, the antenna  1200  for inductively coupled plasma generation can surround most of the outer wall of the chamber. 
       FIG. 13  is a schematic top view of an antenna for inductively coupled plasma generation according to still another embodiment. Referring to  FIG. 13 , an antenna  1300  for inductively coupled plasma generation includes a first end  1301 , a second end  1302 , and an antenna coil unit  1303 . The antenna coil unit  1303  includes one or more sub-coil units  1304  arranged along X- and Y-axis directions. The antenna coil unit  1303  is arranged in a similar way to the antenna coil unit  1203  of  FIG. 12  except for the shape of the sub-coil units  1304 . 
     When power is applied to the first end  1301  and the second end  1302 , the antenna coil unit  1303  forms an induced electric field in response to the power applied from the outside in substantially the same way as the antenna coil units  103 ,  203  and  303  described with reference to  FIGS. 1 to 3 . The sub-coil units  1304  form a local magnetic field around the sub-coil units  1304  themselves in substantially the same way as the sub-coil units  104 ,  204  and  304  described with reference to  FIGS. 1 to 3 . The antenna  1300  for inductively coupled plasma generation may be arranged in the form of a loop to surround a curved surface of the outer wall of a chamber in a similar way to the antenna  400  for inductively coupled plasma generation of the embodiment described with reference to  FIG. 4 . According to this embodiment, a height H of the antenna  1300  for inductively coupled plasma generation can be adjusted in proportion to the height of the outer wall of the chamber, and the antenna  1300  for inductively coupled plasma generation can surround most of the outer wall of the chamber. 
     Thus far, embodiments of some aspects of the present disclosure have been described. However, the scope of the present disclosure is not limited to the above-described embodiments and, needless to say, includes various modifications that those skilled in the art can infer. To be specific, in some embodiments, arrangement of the loop antennas can be diversified according to the form of a chamber. 
     Hereinafter, a constitution and effect of the present disclosure will be described in detail with reference to detailed embodiments and comparative embodiments. However, the embodiments are not intended to limit the scope of the disclosure, but merely to aid in understanding of the disclosure. 
     Embodiment 
     A parallel double spiral antenna obtained by combining two single coils each having two turns, a single coil antenna having two turns, and a vertical antenna having one turn were arranged to surround the outer wall of a cylindrical chamber, and plasma density and distribution were observed. The vertical antenna is substantially the same as the antenna  400  for inductively coupled plasma generation shown in  FIG. 4 , and surrounds the outer wall of the cylindrical chamber. 
     Argon gas was introduced into the chamber at 400 sccm, and the chamber was maintained at a pressure of 800 mTorr. A wafer was disposed inside the chamber, and plasma density was measured at predetermined intervals from one end on the wafer to the other end using Langmuir probe to observe distribution of plasma density in the chamber. 
       FIG. 14  illustrates a chamber constituted to measure plasma density according to an embodiment of the present disclosure. As shown in the drawing, plasma density was measured at nine points on a wafer while power supplied to each antenna was changed. 
     &lt;Evaluation&gt; 
       FIG. 15  shows results of measuring density of plasma generated by various antennas according to an embodiment. Part (a) of  FIG. 15  shows density of plasma generated by various antennas according to supplied power and position on the wafer. Triangular indicators denote experimental results of the parallel double spiral antenna, square indicators denote results of the single coil antenna, and the diamond-shaped indicators denote results of the vertical antenna. Part (b) of  FIG. 15  shows temperature of electrons in plasma generated by the various antennas according to supplied power and position on the wafer. 
     Referring to part (a) of  FIG. 15 , density of plasma generated by the vertical antenna is higher than that generated by the other two antennas in all the cases of 200 W, 400 W and 600 W. Also, plasma distribution of the vertical antenna has a small deviation and is uniform between the center and outer portions of the wafer in comparison with the other two antennas. 
     Referring to part (b) of  FIG. 15 , electron temperature in plasma generated by the vertical antenna disclosed in this specification is lower than that in plasma generated by the other two antennas and is stable. Also, electron temperature in plasma generated by the vertical antenna has a small deviation and is uniform between the center and outer portion of the wafer. 
     Consequently, it can be seen that plasma generated by the vertical antenna has relatively high density and is uniformly distributed between the center and inner wall of a chamber. 
     The foregoing is illustrative of the present disclosure and is not to be construed as limiting thereof. Although numerous embodiments of the present disclosure have been described, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present disclosure and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The present disclosure is defined by the following claims, with equivalents of the claims to be included therein.