Abstract:
In order to uniformly neutralize a large current and a large diameter ion beam so as to irradiate an ion beam having a reduced beam divergence on a process target, an ion beam processing apparatus comprises an ion source for producing a processing plasma, a processing chamber as a vacuum chamber for accommodating a process target, an extract electrode for extracting an ion beam so as to irradiate on said process target, an annular electrode disposed in said processing chamber for forming an annular magnetic field therein, through which said ion beam is irradiated on said process, and a wave guide for introducing microwave through an opening provided on a wall forming said processing chamber, into said annular magnetic field.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is related to an ion beam processing apparatus, and in particular, to an ion beam processing apparatus which is suitable for processing a work piece by etching with a large current and a large diameter ion beam. 
     As a prior art ion beam processing apparatus, there is known, for example, an etching apparatus for etching a work piece using an ion beam as disclosed in JPA Laid-Open No. 63-157887. In this apparatus, in order to prevent for the work piece charged by the ion beam irradiated thereon from being damaged due to its charging, an ion beam neutralizing method is employed, wherein a plasma is generated by a microwave discharge in a neutralizing unit disposed near to the ion beam, and electrons are supplied from the plasma through a small opening to the ion beam so as to neutralize the ion beam. This method assures a longer time of operation compared to an ion beam neutralizing method which uses a hollow cathode containing a filament for emitting thermoelectrons, and thus is suitable for neutralizing a reactive ion beam. Further, because no filament such as tungsten is used, contamination of the work piece by heavy metals constituting the filament can be prevented, thereby providing for a clean ion beam processing. 
     However, the conventional neutralizing method has a limitation in providing for a large current and large diameter ion beam because of the following reasons to be described below. 
     When providing for a large current ion beam, it becomes necessary also to increase a flow of electrons to be supplied from the neutralizing unit in order to effectively neutralize the large current ion beam thus increased. However, according to the conventional method whereby electrons are supplied from the plasma produced within the neutralizing unit, a same quantity of ion current as an increase in the large current ion beam must be collected within the neutralizing unit. That is, an increase in the flow of electrons to be supplied means that the ion current to be collected also increases. In addition, in order for a higher density plasma to be generated within the neutralizing unit, it becomes necessary to increase the power of a microwave to be input into the neutralizing unit, consequently increasing a plasma potential in the neutralizing unit. This means an increase in collision energy of ions to be collected in the neutralizing unit. According to the conventional method as described above, with increases in the ion current colliding on the internal wall of the neutralizing unit and in the ion energy, conducting particles sputtered from the internal wall of the neutralizing unit by ion bombardment are caused easily to deposit on a microwave inlet window of the neutralizing unit, thereby substantially limiting a service life of the neutralizing unit. 
     Further, in order to extract a large quantity of electrons into the processing chamber, it becomes necessary to decrease a potential of the neutralizing device itself to a negative potential which is far below compared to that of the processing chamber. Consequently, the energy of electrons having been extracted from the neutralizing device becomes greater, thereby distorting a distribution of potentials in the ion beam, and thereby causing to diverge the ion beam which inherently must be parallel. Still further, because the site of supply of electrons to the ion beam is localized according to the conventional method, its spatial uniformity effect of neutralization is deteriorated with an increasing diameter of the ion beam. 
     From the reasons described above, it has been difficult according to the conventional methods to obtain a large current, large diameter ion beam with a minimized divergence, which is in excess of 300 mA and 200 mm in diameter, and which is uniformly neutralized. 
     Hence, in order to solve these problems, there has been proposed a microwave neutralizing device for use in an ion beam processing apparatus as disclosed in JPA No. 8-296069, which utilizes a multi-cusp magnetic field formed between electron cyclotron resonance magnetic fields, and into which a microwave is introduced through a wave guide to form a plasma therein. This plasma is used as a source of low energy electrons. 
     SUMMARY OF THE INVENTION 
     When using the microwave neutralizing device as disclosed in JPA No. 8-296069, it becomes possible to provide an ion beam processing apparatus to uniformly neutralize a large current and a large diameter ion beam so as to irradiate an ion beam having a reduced beam divergence on a process target. 
     However, in such ion beam processing apparatus, an annular electrode  8  is disposed between a plasma generating chamber  1  and a processing chamber  23  and the processing chamber  23  is connected to the plasma generating chamber  1  through the annular electrode  8 . 
     Therefore, the annular electrode  8  forms a portion of the vacuum chamber providing the vacuum of the vacuum chamber, and needs to be constructed with a thick metal to be strong in order to prevent the vacuum chamber from an atmospheric pressure. 
     Here, many permanent magnets  9  for forming an annular magnetic field inside of the vacuum chamber are arranged outside of the vacuum chamber. 
     Therefore, the thick metal of the annular electrode  8  make the annular magnetic field generated by the many permanent magnets  9 , difficult sufficiently to be formed inside of the vacuum chamber through the thick metal. 
     The present invention is provided referring to this problem. 
     An ion beam processing apparatus in the present invention comprises an ion source for producing a processing plasma, a processing chamber provided as a vacuum chamber for accommodating a process target being disposed adjacent to said ion source, an extract electrode for extracting an ion beam from said processing plasma into the processing chamber so as to irradiate on said process target, an annular electrode disposed in said processing chamber for forming an annular magnetic field therein, through which said ion beam being irradiated on said process, and a wave guide for introducing microwave through an opening provided on a wall forming said processing chamber, into said annular magnetic field. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of an ion beam processing apparatus according to one embodiment of the invention; 
     FIG. 2 is a cross-sectional view of a wave-guide for introducing a microwave; 
     FIG. 3A is a schematic diagram indicating a method of generating a neutralizing plasma according to the invention; 
     FIG. 3B is a characteristic diagram indicating a distribution of spatial potentials along line a-b; 
     FIG. 4 is a cross-sectional view of the ion beam processing apparatus of FIG. 1, cut out along line X—X; 
     FIG. 5 is a schematic cross-section of a wave-guide according to a second embodiment of the invention; 
     FIG. 6 is a schematic cross-section of a wave-guide according to a third embodiment of the invention; 
     FIG. 7 is a schematic cross-section of a wave-guide according to a fourth embodiment of the invention; 
     FIG. 8 is a cross-section of an ion beam processing apparatus according to a second embodiment of the invention; FIG. 9A is a cross-section of a wave guide according to a fifth embodiment of the invention; and 
     FIG. 9B is a cross-section of a wave-guide according to a sixth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A first preferred embodiment of the invention will be described with reference to the accompanying drawings in the following. 
     FIG. 1 is a schematic cross-sectional view of an ion beam processing apparatus according to a first embodiment of the invention. FIG. 2 is a schematic cross-sectional view of a main part of a guide wave indicative of its structure for introducing the microwave according to the invention The ion beam processing apparatus of FIGS. 1 and 2 is comprised of ion source  1 , acceleration electrode  6 , deceleration electrode  9 , protection electrode (third electrode)  11 , microwave neutralizer  14 , and processing chamber  13 . The processing chamber  13 , which constitutes a vacuum container, is disposed in juxtaposition with the ion source  1 , and is connected thereto via insulation spacer  12 . Regarding the microwave neutralizer  14 , a part of which that does not constitute the vacuum container, is disposed outside the processing chamber  13 , and a main part thereof is disposed inside the processing chamber  13 . 
     The ion source  1  which is composed as a container for generating a processing plasma has a plasma gas inlet pipe  3  connected at its upper side, a plasma generation filament  4  disposed therein, and an opening portion  46  formed at its bottom side. Plasma gas  2  which is introduced into the ion source  1  through gas inlet tube  3  is heated by conduction of filament  4  so as to obtain a sufficient energy to become a plasma  5 . Acceleration electrode  6  is disposed in the opening portion  46  of the ion source  1  and firmly connected thereto. This acceleration electrode  6  is connected to an acceleration power supply  7  via ion source  1 . Both the acceleration electrode  6  and ion source  1  are applied a positive voltage from the acceleration power supply  7 . A deceleration electrode  9  is mounted on the acceleration electrode  6  via an electrode insulation spacer  8 . The deceleration electrode  9  is supplied with a negative voltage from a deceleration power supply  10 . Namely, the acceleration electrode  6  and the deceleration electrode  9  are disposed in juxtaposition with the ion source  1 , and are composed as an extraction electrode for extracting a processing ion beam  36  from plasma  5  within the ion source  1  into processing chamber  13  and irradiating the same on a wafer (process target)  27  placed on a holder  26 . Protection electrode (third electrode)  11  is mounted on the deceleration electrode  9  via insulation spacer  8 , and the protection electrode  11  is further connected to microwave neutralizer  14  via conductor  45 . Microwave neutralizer  14  is connected to neutralizing power supply  25 . According to this embodiment of the invention, because that a potential of processing chamber  13  is set at the earth potential, a potential of the protection electrode  11  and microwave neutralizer  14  is maintained at a negative potential relative to a potential of the processing chamber  13 . Namely, by setting the potential of the protection electrode  11  at a negative potential relative to the potential of processing chamber  13 , the ions in the neutralizing plasma generated by the microwave neutralizer  14  are collected by protection electrode  11  before they collide on the deceleration electrode  9 , thereby preventing for the deceleration electrode  9  to be damaged by ion bombardment. 
     The microwave neutralizer  14  of the invention, which functions as the neutralizing plasma generation means and the ion collection means, is comprised of external (atmospheric side) wave guide  24 , quartz plate  23 , internal (vacuum side) wave guide  21 , a plurality of permanent magnets  16 , annular electrode  47 , and deposition prevention plate  28 , and wherein the annular electrode  47  is disposed inside the processing chamber  13  aligned with the center line of ion source  1  and is firmly fixed thereto via insulation spacer  15 . The external (atmospheric side) wave guide  24  disposed outside the processing chamber  13  and with interposition of quartz plate (microwave transparent plate)  23  which hermetically seals the opening  22  formed in the processing chamber  13  for introducing the microwave thereinto is firmly fixed on an outer wall of processing chamber  13  as an external portion of the wave guide for guiding microwave  34  generated in a microwave generator (not shown) to the opening  22 . A recess portion  31  and O-ring groove  32  are formed on the outer surface of processing chamber  13  and in the vicinity of the opening  22 . O-ring  33  is mounted in the O-ring groove  32 , and quartz plate  23  is disposed on the O-ring  33 . The quartz plate  23  is coupled to the opening  22  as supported by an end portion of the wave-guide  24 . The end portion of the wave guide  24  is firmly fixed to the outer wall of processing chamber  13  by means of fixtures such as insulated screws, insulated bolts and the like (not shown). Namely, by connecting firmly the wave guide  24  outside the opening  22  of processing chamber  13  via O-ring  33  and quartz plate  23 , vacuum in processing chamber  13  is maintained. 
     Internal wave guide (on vacuum side)  21  provided for guiding the microwave passing through quartz plate  23  is firmly fixed at its one end to an inner wall of processing chamber  13  via insulation spacer  15 , and at the other end thereof coupled to annular electrode  47  formed into a straight tube integral therewith. Further, the wave guide  21  is provided with a deflection portion  20  for reflecting microwave  34  passing through quartz plate  23  toward a direction of annular electrode  47  on its way so as to prevent for high energy conducting particles from depositing on quartz plate  23  which serves as the microwave introduction window. 
     Annular electrode  47 , which is formed approximately into a cylindrical shape as an annular member which surrounds a periphery of a propagation region of processing ion beam  36 , is provided with an opening  19  for introducing microwave  34  into a region inside the annular member  47 . Further, the annular electrode  47 , likewise the protection electrode  11 , is connected to neutralizing power supply  27 , and the annular electrode  47  is applied with a voltage which is negative relative to that of the processing chamber  13 . A pair of permanent magnets  16  having their magnetic poles counterposed is disposed in plural numbers at a predetermined space along an external periphery of annular electrode  47 . Namely, arrays of plural permanent magnets (magnetic substances)  16  which constitute the magnetic field forming members of the invention are arranged with their magnetic polarities counterposed along the outer periphery of the annular electrode  47 . Each pair of permanent magnets  16  disposed in opposite polarities produces a line of magnetic force  17 , and a magnetic field  18  is allowed to be formed, on the internal side of annular electrode  47 , having a flux density of electron cyclotron resonance corresponding to a frequency of microwave  34 . Magnetic field  18  is allowed to form a multi ring cusp magnetic field as will be described later. Further, annular electrode  47  is connected to a deposition prevention plate  28  via insulation spacer  29 . 
     This deposition prevention plate  28  is provided for preventing a sputter from wafer  27  placed on holder  26  from depositing on microwave neutralizer  14 . This deposition prevention plate  28  is maintained at the same potential as that of the processing chamber  13  (which is normally at the earth potential). Further, an exhaust opening  30  is formed in the processing chamber  13  so as to allow for the inside of the processing chamber  13  to be vacuum deaerated as required by an exhaust system connected to the opening  30 . By way of example, when connecting respective portions via insulation spacers, electric connection structures using insulation screws or the like are employed. 
     Now, operation of the ion beam processing apparatus of FIG. 1 will be described in the following with reference to FIGS. 3 and 4. When microwave  34  of 2.45 GHz is introduced from the microwave generator into the atmospheric side wave guide  24 , microwave  34  guided through wave guide  24  is allowed to pass through quartz plate  23  to enter vacuum side wave guide  21 . When this microwave  34  is reflected on the deflector  20  and is introduced into the inner region of annular electrode  47  through opening  19 , this microwave  34  is absorbed by electrons by resonance absorption in the magnetic field  18  with an electron cyclotron resonance flux density of 875 gauss, thereby generating high energy electrons. This high energy electrons move along the line of magnetic force  17  reciprocating in the multi ring cusp magnetic field formed between the juxtaposed magnets and on the inner surface of annular electrode  47 . As a macro movement, the high energy electrons revolve in a circumferential direction by a magnetic field grading drift action as indicated in FIG. 4 along annular (band) electrode  47  so as to ionize the gas and generate a neutralizing plasma in an uniform ring shape. Then, a portion of the neutralizing plasma having a good containment of the plasma is represented as a high-density plasma portion  35 . This plasma portion  35  is in contact with the annular electrode  47  and the ion beam  36 . At this instant, because the neutralizing plasma is generated in front of the opening  18 , microwave  34  introduced from the wave guide  21  is deflected outwardly in the directions of electron cyclotron resonance magnetic fields  18  so as to facilitate its arrival thereto, thereby ensuring an efficient absorption of microwave  34 . 
     Still further, when the neutralizing plasma is formed, because that annular electrode  47  is set at the negative potential relative to the potential of processing chamber  13 , ions  37  in the neutralizing plasma are captured by the annular electrode  47 , thereby allowing electrons  38  having a same quantity of opposite charge as that of ions  37  to be supplied uniformly toward the ion beam  36 . In addition, because that the protection electrode  11  is maintained likewise the annular electrode  47  at the negative potential relative to the potential of processing chamber  13 , it becomes possible to reduce a probability of direct collision of the ions  37  of the neutralizing plasma with deceleration electrode  9 , to increase an efficiency of capture of ions  37  from the neutralizing plasma, and improve a quantity of supply of electrons  38  into ion beam  36  as well. By way of example, even if the potential of protection electrode  11  is set at the same potential as that of processing chamber  13 , the probability of direct collision by ions  37  of the neutralizing plasma on the deceleration electrode  9  can be reduced as well. 
     In the above-mentioned embodiment of the invention, because that the vacuum side wave guide  21  and annular electrode  47  are disposed inside of the processing chamber  13 , no additional machining is required for maintaining wave guide  21  and annular electrode  47  in vacuum, and further because that a thickness of walls of the portions through which the line of magnetic force  17  passes can be made thinner, there is another advantage that a magnetic strength of each permanent magnet can be made relatively smaller. In addition, because that the insulation of wave guide  21  can be provided on the side of the internal wall of processing chamber  13 , it is not necessary to provide for an insulation structure for the wave guide exposed to the atmosphere. 
     Still more, in the above-mentioned embodiment of the invention, because that deflector  20  is provided in the vacuum side wave guide  21  after quartz plate  23  for introducing microwave  34  into processing chamber  13 , a sputtering from wafer  27  under etching can be prevented from directly flying toward quart plate  23  to deposit thereon, thereby preventing formation of a film on quartz plate  23  which hinders transmission of microwave  34 , and allowing a more prolonged time of operation for ion beam processing. 
     Although the above-mentioned embodiment of the invention has been described by way of example, which has a single opening  22  for introducing the microwave for generating the neutralizing plasma, it is not limited thereto, and other modifications having a plurality of openings  22  formed in processing chamber  13  can be contemplated within the scope of the invention, wherein each opening connected to each of a plurality of vacuum side wave guides  21  allows for a plurality of microwaves  34  to be introduced therein through the plurality of vacuum side wave guides  21 , thereby capable of neutralizing a larger current, broader diameter ion beam  36 . 
     Although the above-mentioned embodiment of the invention has been described by way of example using an integral assembly of wave guide  21  and annular electrode  47 , wherein the wave guide  21  and annular electrode  47  are formed integral, but it is not limited thereto, and other modifications allowing their insert-connection can be contemplated within the scope of the invention wherein one end of wave guide  21  is formed into a straight pipe opening type wave guide  40  which can be inserted into an opening  19  which is formed in annular electrode  47  at its wave guide connection port  39 , thereby allowing for a more simplified process of manufacture. 
     With reference to FIG. 6, as for the structure of wave-guide  21 , one end of wave-guide  21  can be formed into a tapered opening type wave-guide  41 , which can be connected integral with annular electrode  41 . 
     When the wave guide  21  having tapered opening type wave guide  41  at its one end is provided, because its microwave is caused to propagate in wider radial directions, it becomes possible to irradiate microwave  34  more efficiently into electron cyclotron resonance magnetic field  18 , ensuring for microwave  34  to reach the electron cyclotron resonance magnetic field  18  more easily. 
     With reference to FIG. 7, another structure of wave guide  21  allowing for an insertion fit-in connection method can be provided wherein one end of wave guide  21  is formed into a tapered opening type wave guide  41 , which can be inserted into the opening  19  for connection therebetween. 
     A schematic block diagram indicating a second embodiment of the invention is shown in FIG. 8. A feature of the second embodiment of the invention different from the preceding embodiment resides in that although the negative voltage is applied to annular electrode  47  by connecting the same to neutralizing power supply  25  in the preceding embodiment, its negative voltage is applied from neutralizing power supply  25  to a band electrode  43  which is fixed via electrode insulation spacer  42  on the internal side of annular electrode  47 , and through opening  48  formed in annular electrode  47  for internal connection therebetween. Other elements for construction thereof are the same as those in the preceding embodiment of the invention of FIG.  1 . 
     The band electrode  43  provided as a second annular electrode is formed into a cylindrical shape, and allows microwave  34  to be introduced through opening  49 . The same is further connected to protection electrode  11  via conductor  45 . 
     According to the second embodiment of the invention, because that its neutralizing plasma can be generated in a region which is inside of band electrode  43 , the same effect as the preceding embodiment of the invention can be achieved, and because that annular electrode  47  as well as wave guide  21  can be maintained at the same potential as that of processing chamber  13 , wave guide  21  and annular electrode  47  can be coupled firmly with processing chamber  13  without use of insulation spacer  15  and deposition prevention plate insulation spacer  29 , thereby eliminating use of insulation structure screws for these spacers. 
     Further, according to the second embodiment of the invention, wave guide  21  can be formed integral with annular electrode  47 , otherwise as indicated in FIG.  9 ( a ) the one end of wave guide  21  can be formed into tapered opening type wave guide  41  having spacer  44  mounted on its end, which can be inserted into opening  19 . Alternatively, as indicated in FIG.  9 ( b ), one end of wave guide  21  can be formed into a straight tube opening type wave guide  40  having spacer  44  mounted to this end, which can be inserted into opening  19  for connection therebetween. 
     Further, according to this method whereby insulation spacer  44  is mounted on the end of wave guide  40 ,  41 , the provision of insulation spacer  15  is not required for connection of wave guide  21  to processing chamber  13 , thereby eliminating the use of the insulation construction screws corresponding to these spacers. 
     The aforementioned embodiments  1  and  2  have been described by way of examples in which annular electrode  47  and protection electrode  11  are connected via conductor  45 , or in which band electrode  43  is connected to protection electrode  11  via conductor  45 , however, it is not limited thereto, and another modification within the scope of the invention can be adopted in which protection electrode  11  is connected to a power supply having the same potential as the potential of processing chamber  13 , instead of its connection to neutralizing power supply  25 .