Abstract:
A focused ion beam apparatus having two pieces of probers brought into contact with two points of a surface of a sample, a voltage source for applying a constant voltage between the two points with which the probers are brought into contact, and an ammeter for measuring a current flowing between the two points, in which a conductive film is formed to narrow a gap thereof between the two points by operating a deflection electrode and a gas gun and the current flowing between the two points is monitored, and when the current becomes a predetermined value, a focused charged particle beam irradiated to the surface of the sample is made OFF by the blanking electrode.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to an apparatus of forming an electrode with gas assist deposition using a charged particle beam and a method of using the same.  
         [0002]     In recent years, a technology of fabricating an integrated circuit is remarkable, and an integration degree is significantly promoted. Further, in order to realize more highly integrated formation, basic researches on molecule elements and single electron elements have been promoted.  
         [0003]     In developing the molecule element, in order to grasp properties of the molecule, it is necessary to measure a conduction property thereof. Hence, electrodes having a gap of a molecule size (about 1 nm) therebetween are fabricated, a molecule is interposed in the gap, and various properties are measured.  
         [0004]     As a method of fabricating a narrow gap, for example, there is a method of using a sputtering etching technology of a focused ion beam. According thereto, an electric wire comprising a conductive substance formed on an insulating film is etched by using a focused ion beam and an argon ion beam to form electrodes having a width of a gap of 5 nm therebetween (refer to Nonpatent Reference 1).  
         [0005]     [Nonpatent Reference 1] “Fabrication of nano-gap electrodes for measuring electrical properties of organic molecules using a focused ion beam”, Solid Thin Film 438-439 (2003) 374-377  
         [0006]     However, according to the method of fabricating a narrow gap by using a sputtering etching of a focused ion beam, there poses a problem that a lower limit of a width of the gap formed is rectified by a beam diameter of the focused ion beam.  
         [0007]     It is a problem of the invention to resolve the above-described problem to form a pair of electrodes having an extremely narrow gap width equal to or smaller than a beam diameter of a focused ion beam.  
       SUMMARY OF THE INVENTION  
       [0008]     In order to resolve the above-described problem, a charged particle beam apparatus according to the invention is constituted by a charged particle source, a focusing lens system for focusing a charged particle beam drawn out from the charged particle source, a blanking electrode for making the focused charged particle beam ON/OFF on a sample, a deflection electrode for deflecting to scan the focused charged particle beam, a movable sample stage mounted with the sample irradiated with the focused charged particle beam, a gas gun for locally blowing a gas to a position of irradiating the focused charged particle beam on a surface of the sample, a secondary charged particle detector for detecting a secondary charged particle generated by irradiating the focused charged particle beam to the sample, two pieces of probers brought into contact with two points on the surface of the sample, a voltage source for applying a constant voltage between the two points with which the probers are brought into contact, and an ammeter for measuring a current flowing between the two points.  
         [0009]     As operation of principal means having the above-described constitution, the electrodes having the extremely narrow gap therebetween can be formed without depending on a size of a beam diameter of the focused charged particle beam by forming a deposition film between the two points of the surface of the sample with which the probers are brought into contact by scanning to irradiate the focused charged particle beam while blowing a gas to the surface of the sample from the gas gun, applying the constant voltage between the two points with which the probers are brought into contact, measuring the current flowing between the two points, detecting that the current value becomes larger than a predetermined value, and making the focused charged particle beam irradiated to the surface of the sample OFF by the blanking electrode based on a signal thereof.  
         [0010]     As described above, according to the apparatus and the method of the invention, when the electrodes are formed by CVD using the charged particle beam, the conductive film is formed to narrow the interval between the electrodes, the interval is controlled by measuring the current flowing between the electrodes at this occasion and therefore, the electrodes having the gap therebetween equal to or smaller than 1 nm can be fabricated for evaluating electric properties of an extremely small substance of a molecule, a gene or the like. Thereby, researches and industrialization of a molecule element or biotechnology are promoted. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows a constitution example of an apparatus according to the invention.  
         [0012]      FIGS. 2A-2C  show an example of a method of fabricating a sample used in the invention.  
         [0013]      FIG. 3  shows an example of a method of fabricating an electrode according to the invention.  
         [0014]      FIGS. 4A-4B  show examples of scanning an ion beam in fabricating the electrode according to the invention.  
         [0015]      FIGS. 5A-5B  show a sectional shape of a sample used in the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     An embodiment of the invention will be explained in details in reference to the drawings as follows.  
         [0017]      FIG. 1  shows an example of a focused ion beam apparatus according to the invention.  
         [0018]     A focused ion beam lens-barrel mainly comprises an ion source portion  11 , a condenser lens  12 , a blanking electrode  13 , a movable diaphragm  14 , a deflection electrode  15 , an object lens  16 , and an optical axis correcting electrode, an astigmatism correcting electrode and the like, not illustrated.  
         [0019]     It is general to use liquid metal gallium for the ion source. Liquid metal gallium stored in a holding portion is supplied to an emitter in a needle-like shape by a surface tension. Further, a gallium reservoir, the emitter are made to be able to be heated by a filament. The emitter portion is applied with an electric field by a single or a plurality of electrodes, and gallium stored in the emitter portion is drawn out as an ion beam. Since the emitter is applied with a high voltage of about +30 kV relative to the ground potential, the ion beam is accelerated by the electric field.  
         [0020]     The ion beam is focused by the condenser lens  12 , and focused on a surface of a sample  20  by the object lens  16 . The blanking electrode  13  is made to be able to generate a large electric field between two sheets of electrodes opposed to each other. When the respective electrodes are applied with the same potential, normally, the ground potential, the ion beam reaches the sample  20 . However, when a large electric field is generated by applying signals having a large potential difference therebetween to the respective electrodes of the blanking electrode  13 , the ion beam is considerably deflected to impinge on a blocking member of the movable diaphragm  14  or the like and the ion beam does not reach the surface of the sample  20 .  
         [0021]     The deflection electrode  15  is constituted by at least two sets of electrodes comprising two electrodes opposed to each other, and a trajectory of the ion beam is two-dimensionally controlled by electric fields generated between the respective electrodes.  
         [0022]     Respective power sources for generating signals applied to the respective electrodes, the movable diaphragm are controlled by an apparatus control computer.  
         [0023]     Further, a detector  17  detects secondary charge particles generated when the ion beam is irradiated to the surface of the sample  20  to convert to an electric signal. An output signal thereof is inputted to the apparatus control computer, and by storing the output signal along with a position of irradiating the ion beam, the surface of the sample  20  can be observed.  
         [0024]     A sample stage  19  is movable at least in three axes of horizontal X, Y and vertical Z. The horizontal direction X-Y axes are used for observing the sample and determining a machining position. Further, the Z axis is used such that a height of the surface of the sample is always disposed at a position optimum for irradiating the focused ion beam. Otherwise, an inclining T axis, a rotating R axis or the like can also be provided.  
         [0025]     A thin film is fabricated by a beam assisted CVD method by a compound vapor blowing apparatus  18  mounted to the focused ion beam apparatus. In the beam assisted CVD method, there is used compound vapor including a material of the thin film deposited on the surface of the sample  20 . The compound vapor is blown to the surface of the sample  20  by the compound vapor blowing apparatus  18 . The compound vapor blown to the surface of the sample  20  is adsorbed by the surface of the sample  20 . When the focused ion beam is irradiated under the state, the compound vapor is decomposed by kinetic energy thereof or energy of second electrons generated in accordance with irradiation of the focused ion beam. A decomposed gas component is exhausted to outside of a sample chamber  22  by a vacuum pump  21 , and a solid component thereof remains on the surface of the sample by constituting the thin film. At this occasion, the focused ion beam executes also sputter etching simultaneously with deposition. Therefore, it is necessary to control an amount of introducing the compound vapor and an amount of irradiating the focused ion beam such that a rate of fabricating the thin film by deposition becomes higher than a rate of machining by sputter etching.  
         [0026]     Further, although a single one of the compound vapor blowing apparatus  18  is illustrated in the drawing, a plurality of compound vapor blowing apparatus may be used such that gasses can properly be used in accordance with objects.  
         [0027]     The sample chamber  22  and the focused ion beam lens-barrel are vacuumed by the vacuum pump  21 . Further, although not illustrated, there can also be provided a load/lock chamber for putting in and out a sample to and from the sample chamber without exposing the sample chamber to the atmosphere.  
         [0028]     Further, there is mounted a manipulator  23  capable of being brought into contact with two portions of the surface of the sample  20 . A voltage source  24  and an ammeter  25  are connected between two electrodes, and a resistance between two points is made to be able to be measured. When a value of the ammeter  25  becomes larger than a predetermined value, an input signal to the blanking electrode  13  is controlled based on the signal to thereby prevent the focused ion beam from reaching the surface of the sample  20 .  
         [0029]     Successively, the sample will be explained in reference to  FIGS. 2A-2C .  
         [0030]     As a material of a board, a silicon plate having face orientation of &lt;100&gt; is used. However, the face orientation is not particularly limited to &lt;100&gt;. A groove is formed in the silicon board  31  by using an MEMS technology. As shown by  FIG. 2A , for example, a silicon oxide film or a silicon nitride film is formed as a mask member  32  to cover the silicon board  31 , further, a window  33  is formed by using a photolithography technology.  
         [0031]     Further, as shown by  FIG. 2B , a membrane  34  is formed by anisotropic etching based on the face orientation by dipping the board into an alkali solution of potassium hydroxide solution or the like. At this occasion, although a thickness of the membrane is preferably as thin as possible, the thickness is preferably, for example, equal to or smaller than several micrometers.  
         [0032]     Successively, as shown by  FIG. 2C , a through hole  35  is formed at the membrane portion by using the focused ion beam. The through hole is preferably a long hole having a width equal to or smaller than 1 micrometer and a length of several micrometers. Further, a total of the board is covered with an insulating film and electrodes  36  are formed by interposing the through hole.  
         [0033]     The electrodes having a narrow gap are formed by using the sample.  
         [0034]     Although in  FIGS. 2A-2C , a penetrated hole is used at the groove, a hole which is not penetrated can also be used. In this case, as shown by  FIGS. 5A-5B , an inner wall of the hole becomes wider than an inlet thereof and in fabricating the electrodes, the inner wall is prevented from being formed with a deposition film.  
         [0035]     The sample  20  is mounted to the focused ion beam apparatus shown in  FIG. 1 .  
         [0036]     Needles of the manipulator  23  are brought into contact with the electrodes  36  of the sample. Under the state, as shown by  FIG. 3 , a machining frame  37  is set to ride over the through hole  35  and connect the electrodes  36 , and the focused ion beam is irradiated simultaneously with blowing a gas of hexacarbonyltungsten constituting a raw material of tungsten deposition to the surface of the sample  20  by using the gas introducing apparatus  18 . At this occasion, the focused ion beam may be scanned in one direction in the machining frame as shown by  FIG. 4A , or may be scanned while reciprocating in the machining frame as shown by  FIG. 4B .  
         [0037]     A tungsten film is formed to ride over the through hole by scanning to irradiate the focused ion beam. The tungsten film is formed from both sides of the through hole. At this occasion, a potential difference is provided to the respective electrodes  36  by the voltage source  25 . Further, when the gap between the electrodes becomes a nanometer order in accordance with growth of the tungsten film, a tunnel current is made to flow. For example, when the focused ion beam is prevented from reaching the surface of the sample  20  by controlling a control signal of the blanking electrode  13  when the potential difference becomes 2 mV and the tunnel current becomes 2 nA, the gap between the electrodes can be controlled to be equal to or smaller than 1 nm.  
         [0038]     The tungsten film is formed by irradiating the focused ion beam while monitoring the ammeter by control means  41 , and when the tunnel current becomes 2 nA, the focused ion beam is stopped to irradiate by the control signal from the controlling means  41 .  
         [0039]     Further, an arbitrary gap can reproducibly fabricated by controlling the applied voltage and the control current value.