JP2008016209A - Focused ion beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focused ion beam device capable of reducing contamination of a blanking electrode. <P>SOLUTION: An ion collector 16 consists of a blanking plate 16A taking on a conical outer periphery with its vertex on an incident side of ion beams, and having an opening for the ion beams to pass through along a center axis at the time of non-blanking, a cover 16C arranged in opposition to the incident side of the ion beams of the blanking plate and having an opening larger than that of the blanking plate, a cylinder 16B supporting the blanking plate and the cover made of a non-magnetic conductive member, and a pair of coils 16E1, 16E2 oppositely arranged at an outer periphery side of the cylinder. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a focused ion beam apparatus that irradiates a sample with a finely focused ion beam to perform microfabrication of the sample, and more particularly to a focused ion beam apparatus having an ion collector.

  Conventionally, as a focused ion beam apparatus that performs fine processing of a sample by irradiating the sample with a finely focused ion beam, for example, the one described in Patent Document 1 is known. Here, in the focused ion beam apparatus, it is not always necessary for the beam to irradiate the sample in processing observation, and it is necessary to block the beam as appropriate. Therefore, an electrode (blanking electrode) for deflecting the beam in the vicinity of the beam and a stop on the optical axis of the beam are provided to block the beam. The beam is blocked by deflecting the beam off the optical axis with a deflector (blanking electrode) so that it cannot pass through the stop on the optical axis.

JP 10-162769 A

Here, when the beam is interrupted, ions are irradiated onto the diaphragm, so secondary electrons and sputter ions are generated from the diaphragm. In the case of an ion beam, the mass m is 10 ³ to 10 ⁴ times larger than that of electrons, and the deflection sensitivity of the magnetic field is proportional to 1 / √m, so that ions with heavy mass are difficult to bend, whereas the deflection sensitivity of the electric field is mass. Since it is proportional to the charge regardless of m, the ion beam is deflected by an electrostatic deflector. In the electrostatic deflector, since the deflection sensitivity is determined by the strength of the electric field, it is necessary to apply a positive or negative voltage to the electrode or to apply a positive or negative voltage. Further, in order to obtain effective deflection at a short distance, it is necessary to increase the voltage difference between the electrodes and reduce the distance between the electrodes facing each other. Therefore, when the beam is interrupted, either positive or negative voltage, or positive or negative voltage is applied to the blanking electrode, so secondary electrons generated in the diaphragm and leaking to free space. And sputtered ions are captured and accelerated by the electric field generated by the voltage applied to the blanking electrode, and collide with the blanking electrode. Thereby, molecules adhering to the blanking electrode are decomposed and solidified to form a film (contamination), thereby forming a film in which sputtered particles and adhering molecules are mixed, and the electrode becomes dirty. This coating is insulative and easily charged on the surface, and when charged, the beam diameter expands or the irradiation position shifts depending on the state of charging. That is, when the images are captured in an overlapping manner, an image shift occurs in which the positions of the first and second images are shifted, and the processing position accuracy is deteriorated in processing.

  Here, the performance of the focused ion device is better as the beam current density is higher. The high beam current density means that even with a large current, the beam diameter is small and processing with high accuracy can be performed with a large current.

In recent years, a beam having a maximum beam current of about 60 nA and a beam diameter of 1 μmφ or less, a current density of 7.6 A / cm ² or more, a beam current of 20 nA, a beam diameter of 0.25 μmφ, a current density of 60 A / cm ² or more, Development of an apparatus capable of obtaining a beam having a beam diameter of 0.12 μmφ and a current density of 88 A / cm ² at a beam current of 10 nA has progressed, and high-precision processing can be performed even with a beam current of 10 nA or more.

  For this reason, the appearance of a device with a high beam current density has made the blanking electrode easily soiled, and high-precision machining with a high-current beam has become possible. It can no longer be ignored. That is, since the beam current is large, a large amount of secondary electrons are generated while the beam is cut off, and the blanking electrode and the like are contaminated by contamination in a short time, and image shift is likely to occur. Further, the amount of charge on the contamination surface increases during processing, and the shift of the processing position increases.

High current density at the beam current 10nA beam diameter as the beam 0.12μmφ, 88A / cm ² of the high current density in the conventional beam as the beam diameter is the same 0.12Myuemufai, current density approximately half 44A / cm ² as a beam current Comparing processing with a positional accuracy of 0.2 μm at 5 nA, a beam current of 10 nA can be completed in half the time compared to processing with a precision of 0.2 μm with a conventional beam current of 5 nA. However, since the current density has doubled, there is a problem in that the contamination of the blanking electrode takes half the time of the conventional beam, and double contamination is likely to occur due to contamination of the contamination. If the beam position is shifted by 0.1 to 0.2 μm due to the influence, the accuracy falls to 0.28 μm. That is, even if the accuracy and the processing speed are increased, if the blanking electrode is contaminated, there is a problem that the processing position is shifted and the processing accuracy is lowered.

  The objective of this invention is providing the focused ion beam apparatus which can reduce the contamination of a blanking electrode.

  Further, by supporting the ion collector by an insulating support, it is possible to accurately measure the collected ions, and to provide an apparatus capable of accurate processing based on accurate monitor measurement of ion current. There is.

  According to the present invention, an ion collector includes a blanking plate having a conical outer periphery having an ion beam incident side as an apex, an opening through which the ion beam passes during non-blanking along the central axis, and a blanking A cover disposed opposite to the ion beam incident side of the plate and having an opening larger than the opening of the blanking plate, a blanket plate supporting the cover and a cylinder made of a non-magnetic conductive member, It consists of a pair of coils arranged facing the outer peripheral side of the cylinder.

  According to the present invention, the contamination of the blanking electrode can be reduced.

  In addition, accurate monitor measurement of ion current is possible.

Hereinafter, the configuration of a focused ion beam apparatus according to an embodiment of the present invention will be described with reference to FIGS.
First, the optical system of the focused ion beam apparatus according to the present embodiment will be described with reference to FIG.
FIG. 1 is an explanatory diagram of an optical system of a focused ion beam apparatus according to an embodiment of the present invention.

  First, in the ion beam micromachining method, it is possible to process with higher throughput by selecting the aperture diameter and lens operating conditions to be used in each process of sample positioning, roughing, intermediate processing, and finishing. The reason will be described. That is, there is a combination of an optimum aperture diameter and lens operating condition depending on the purpose of use of the beam.

  FIG. 1 shows how an ion beam is generated in an ion beam irradiation apparatus. A beam spot on the sample 10 by the ion beam 9 is created by a method of projecting an image of the ion source 1 onto the sample 10 using an optical system including the condenser lens 2 and the objective lens 8. Since the ion source 1 is projected onto a smaller image as the imaging magnification of the optical system is smaller, a smaller beam spot is given on the sample 10. A narrow beam with a small beam spot is suitable for following the process positioning process.

  On the other hand, for processing, it is necessary to use a beam with a large current in order to increase the throughput. Therefore, an aperture 3 having a large diameter is used. However, when the diameter of the aperture 3 is increased, the beam diameter is increased due to lens aberration, and an expanded beam spot 21 is formed on the sample 10. However, the size of the ion source image 20 projected on the sample 10 is not changed. As shown in FIG. 1, in this state, the aberration determines the size of the beam spot on the sample 10.

  According to the principle of the luminance conservation law in the optical system, a larger beam current is obtained as the imaging magnification is larger. According to this principle, a beam whose current amount is increased by using a large aperture has already increased its beam diameter due to aberration as described above, so that the ion source is projected at a slightly larger imaging magnification in FIG. Even if it is projected so as to have the size shown as 22, a large beam current should be obtained without increasing the beam diameter so much. When the imaging magnification is further increased, the amount of current further increases, but this time, the ion source image becomes larger than the aberration, and the beam spot diameter on the sample 10 becomes too large.

  An ion beam having a relatively small beam spot diameter and containing a large current, that is, a thin and high current density, is formed such that the beam expansion due to aberration balances the size of the ion image. An ion beam generated at a magnification. This optimum imaging magnification can be obtained by calculation from the size of the aperture and the size of the ion source. If the optimum magnification is determined, the lens operating condition (the applied voltage or excitation current of the lens) necessary for generating the ion beam at that magnification can also be obtained by calculation.

  In order to produce a beam with a larger amount of current, a larger aperture is used. In this case, since the aberration also increases, the optimum magnification of the optical system for this aperture is even larger. That is, in the ion beam processing apparatus, there are combinations of aperture diameter and imaging magnification that are optimal for each purpose for each of the processing positioning, rough processing, intermediate processing, and finishing processing. By performing the operation, the processing operation can be performed efficiently. That is, high-precision machining positioning can be performed with a narrower beam, and high-throughput machining can be performed with a beam having a high current density.

  In FIG. 1, reference numeral 13 denotes a partition wall between the ion gun and the lens.

Next, the configuration of the focused ion beam apparatus according to the present embodiment will be described with reference to FIG. Here, an example in which the focused ion beam apparatus is applied to an ion beam processing apparatus is shown.
FIG. 2 is a partial cross-sectional perspective view showing the configuration of the focused ion beam apparatus according to an embodiment of the present invention.

  The ion beam 9 irradiated from the ion source 1 receives a weak focusing action by the condenser lens 2 and irradiates the diaphragm device 3. The aperture device 3 has, for example, four apertures having diameters of 5 μm, 40 μm, 300 μm, and 650 μm, and is moved left and right by the aperture moving device, so that an arbitrary aperture can be brought on the central axis of the device. The beam that has passed through the aperture of the diaphragm 3 enters the objective lens 8 through the aligner / stigma 4, the blanker 5, the ion collector 16 having a blanking plate, and the beam scanner 7. The ion beam 9 is narrowed down by the objective lens 8 and irradiates the sample 10 placed on the sample stage 11. The ion beam irradiation position on the sample 10 is controlled by the beam scanner 7. A signal generated by irradiating the sample 10 with the ion beam 9 is detected by the detector 12, and an image is displayed on the screen in synchronization with the operation signal of the beam scanner 7.

The magnification of the beam 9 obtained by the aperture of the diaphragm 3 is controlled so that the maximum current density is obtained at each aperture. When the diameter is 5 μm, the beam current is 1 nA, the beam diameter is 6 nmφ, and when the diameter is 40 μm, the beam current is 0.2 μA. beam diameter 30Nmfai, the diameter 300 [mu] m, the beam current the current density of 60A / cm ² with a beam diameter 0.25μmφ at 20 nA, diameter 520 .mu.m, the beam diameter 1μmφ in beam current 60nA beam current density 7.6A / cm ² is obtained .

  In the focused ion beam apparatus, it is not always necessary to irradiate the sample 10 with the beam 9 in the processing observation, and it is necessary to interrupt the beam appropriately except during the processing. If the interruption is not possible, the sample 9 is always irradiated with the beam 9 and extra processing is performed. Therefore, the beam is deflected by the blanker 5 and collected by the ion collector 16 having a blanking plate.

Next, the configuration of the ion collector used in the focused ion beam apparatus according to the present embodiment will be described with reference to FIGS. 3 and 4.
FIG. 3 is a cross-sectional view showing a configuration of an ion collector used in the focused ion beam apparatus according to an embodiment of the present invention. FIG. 4 is a perspective view showing a configuration of a coil that constitutes a part of an ion collector used in the focused ion beam apparatus according to the embodiment of the present invention.

  As shown in FIG. 3, the ion collector 16 includes a blanking plate 16A, a tube 16B, a secondary electron cover 16C, a support plate 16D, and a pair of coils 16E1 and 16E2.

  The blanking plate 16A is a cylindrical aperture member having a conical outer periphery whose apex is the incident side of the ion beam, and the upper opening serves as a diaphragm. The blanking plate 16A is made of a conductive material. The opening at the top of the blanking plate 16A is, for example, 1 mmφ. The cylinder 16B is conductive and is formed of a nonmagnetic material and has a cylindrical shape. The lower part of the cylinder 16B is joined to the lower part of the blanking plate 16A. The secondary electron cover 16C has a disk shape, and an opening is formed in the center thereof.

  The secondary electron cover 16C is formed of a conductive material, and is joined to the inner peripheral side of the cylinder 16B. The diameter of the opening of the secondary electron cover 16C is larger than the diameter of the upper opening of the blanking plate 16A. The support plate 16D is joined to the outer periphery of the upper portion of the cylinder 16C. Here, as a material for the blanking plate 16A, the cylinder 16B, the secondary electron cover 16C, and the support plate 16D, here, phosphor bronze having conductivity and non-magnetism is used. The support plate 16 </ b> D is supported by the partition wall 17 </ b> A attached to the inner periphery of the lens barrel 17 via the insulating support 15.

As shown in FIG. 4, the coils 16E1 and 16E2 are saddle type deflector coils. When the cylinder 16C has an outer diameter of 8 mmφ and a length of 30 mm, the coils 16E1 and 16E2 have a number of turns of 10 and a length of 6 × 12 mm, and a current is always passed through the coils 16E1 and 16E2 to be perpendicular to the optical axis of the beam. A magnetic field B of about 5 × 10 ⁻⁸ T is generated in any direction. The coils 16E1 and 16E2 are disposed on the outer peripheral side of the cylinder 16C and substantially at the center in the optical axis direction.

  A blanking electrode (blanker) 5 for deflecting the beam 9 is provided on the upper part of the ion collector 16. When the beam is cut off, the beam 9 is deflected by 1 to 2 mm from the optical axis by the deflector (blanking electrode) 5 and removed so that it cannot pass through the diaphragm (blanking plate) 16A on the optical axis. For example, in order to obtain an effective deflection with the blanking electrode 5 having a length of 20 mm, the voltage difference between the electrodes 5 is 200 V, and the distance between the electrodes 5 facing each other is 2 mm. When the beam 9 is interrupted, ions (9) are irradiated to the diaphragm (blanking plate) 16A, and secondary electrons and sputter ions are generated from the diaphragm (blanking plate) 16A.

Here, in the present embodiment, the coils 16E1 and 16E2 are added to the ion collector 16. The current of the coils 16E1 and 16E2 is always passed to generate a magnetic field B of about 5 × 10 ⁻⁸ T in the direction perpendicular to the optical axis of the beam, so that the energy of secondary electrons is mostly 10 eV or less. Therefore, charged particles such as secondary electrons having a velocity of a component perpendicular to the magnetic field B receive a force perpendicular to the velocity and the magnetic field B and draw a spiral in the lateral direction inside the ion collector 16. Then, it is trapped on the wall of the ion collector 16. On the other hand, for ions, the deflection sensitivity by magnetic field is 1 / √m of mass m, and the mass of ions is 10 ³ to 10 ⁴ times larger than the mass of electrons, so the influence of ions by magnetic field B is about 1/100 of electrons. In addition, since the acceleration voltage of the main beam is several tens of kV, the magnetic field B of the collector 16 does not affect the main beam 9.

  Since charged particles such as secondary electrons are trapped by the ion collector 16 and can be prevented from adhering to the blanking electrode 5, contamination of the blanking electrode 5 can be reduced. Accordingly, it is possible to prevent the beam diameter from being expanded or the irradiation position from being shifted due to the charge-up due to the contamination of the blanking electrode, and the first and second image positions are shifted when the images are captured in a superimposed manner. Generation of shift can be prevented, and processing position accuracy can be improved in processing.

  Further, as described above, the support plate 16 </ b> D at the top of the ion collector 16 is supported by the partition wall 17 </ b> A attached to the inner periphery of the lens barrel 17 via the insulating support 15. On the other hand, the cylinder 16 </ b> C of the ion collector 16 is grounded via the ion monitor 18. Therefore, since the total amount of the charged particles collected by the ion collector 16 is measured by the ion monitor 18, the collected ions can be accurately measured. Accurate processing can be performed by measuring this accurate ion current.

  As described above, according to the present embodiment, the probability that all secondary electrons generated by scattering ions without affecting the incident ion beam are collected by the ion collector and leaked as secondary electrons. Becomes extremely low, and unnecessary contamination by leaked electrons can be prevented.

Further, by supporting the ion collector by the insulating support, the collected ions can be accurately measured, and accurate processing can be performed based on accurate monitor measurement of the ion beam current.

It is explanatory drawing of the optical system of the focused ion beam apparatus by one Embodiment of this invention. It is a perspective view of the partial cross section which shows the structure of the focused ion beam apparatus by one Embodiment of this invention. It is sectional drawing which shows the structure of the ion collector used for the focused ion beam apparatus by one Embodiment of this invention. It is a perspective view which shows the structure of the coil which comprises some ion collectors used for the focused ion beam apparatus by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ion source 2 ... Condenser lens 3 ... Aperture 4 ... Aligner / stigma 5 ... Blanker 7 ... Beam scanner 8 ... Objective lens 9 ... Ion beam 10 ... Sample 11 ... Stage 12 ... Signal detector 13 ... Partition 15 ... Insulation support Body 16 ... Ion collector 16A ... Blanking plate 16B ... Tube 16C ... Cover 16D ... Support plates 16E1, 16E2 ... Deflection coil 18 ... Current monitor

Claims (2)

A focused ion beam apparatus having a blanking deflection system for turning on / off an ion beam irradiated on a workpiece and an ion collector for collecting ions during blanking,
The ion collector is
A blanking plate having a conical outer periphery with the ion beam incident side as an apex, and having an opening through which the ion beam passes during non-blanking along a central axis;
A cover that is disposed opposite the ion beam incident side of the blanking plate and has an opening larger than the opening of the blanking plate;
While supporting the blanking plate and the cover, a cylinder made of a non-magnetic conductive member,
A focused ion beam device comprising a pair of coils arranged to face the outer peripheral side of the cylinder. The focused ion beam device according to claim 1.
The focused ion beam apparatus, wherein the ion collector is supported by a lens barrel of the focused ion beam apparatus by an insulating support.

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