JP4982161B2 - Gas field ion source and scanning charged particle microscope - Google Patents

Description

  The present invention relates to a gas field ion source for generating ions and a charged particle microscope for observing the surface of a sample such as a semiconductor device or a new material.

Non-Patent Document 1 is equipped with a gas field ionization ion source (abbreviated as GFIS) and focused using gas ions such as hydrogen (H ₂ ), helium (He), neon (Ne), etc. An ion beam (FIB) apparatus is described. These gases FIB do not cause Ga contamination in the sample, like gallium (Ga: FI) FIB from Liquid Metal IonSource (abbreviated as LMIS), which is currently used frequently. Further, it is described that GFIS can form a beam finer than Ga-FIB because the energy width of gas ions extracted therefrom is narrow and the ion source size is small. In particular, in GFIS, ion source characteristics such as increasing the radiation angle current density of the ion source when the tip of the ion emitter is provided with a minute protrusion (or the tip is not rounded but protruded to several atomic levels). It is disclosed to improve. It is also disclosed in Patent Documents 1 and 3 that the minute protrusion at the tip of the ion emitter increases the ion emission angular current density. The use of a second metal different from the emitter material of the first metal as the minute protrusion is disclosed in Patent Document 1, Non-Patent Documents 3 and 4, where the first metal and the second metal are respectively W and noble metal (Pt or Pd), and Ne ions are released. However, there is no disclosed literature on how to select the first and second metals to obtain He and hydrogen ions.

Non-Patent Document 2 and Patent Document 3 disclose a scanning charged particle microscope equipped with a GFIS that emits light element He ions. He ions are about 7000 times heavier than electrons and about 1/17 lighter than Ga ions from the viewpoint of the weight of irradiated particles. Therefore, the sample damage related to the magnitude of the momentum transferred by the irradiated He ions to the sample atoms is slightly more than that of the electrons, but very small compared to the Ga ions. In addition, since the excitation region of secondary electrons due to penetration of irradiated particles into the sample surface is localized on the sample surface compared to electron irradiation, the scanning ion microscope (Scanning Ion
Scanning Electron (Microscope, SIM for short)
A feature that is more sensitive to information on the surface of the extreme sample than Microscope (SEM for short) is expected. Further, from the viewpoint of a microscope, ions are heavier than electrons, and therefore, the diffraction effect can be ignored in the beam focusing, and an image having a very deep depth of focus can be obtained.

Published Patent Publication No. 58-85242 Published Patent Publication No. 2006-134638 Published Patent Publication No. Hei 7-192669 K. Edinger, V. Yun, J. Melngailis, J. Orloff, and G. Magera, J. Vac. Sci. Technol. A 15 (No. 6) (1997) 2365 J. Morgan, J. Notte, R. Hill, and B. Ward, Microscopy Today July 14 (2006) 24 H.-S. Kuo, I.-S. Hwang, T.-Y. Fu, YC. Lin, C.-C. Chang, and T. T. Tsong, 16th Int. Microscopy Congress (IMC16), Sapporo (2006 1120 H.-S. Kuo, I.-S. Hwang, T.-Y. Fu, J.-Y. Wu, C.-C. Chang, and T. T. Tsong, Nano Letters 4 (2004) 2379.

  In GFIS, an ion emitter having a fine protrusion at the tip is an important component, but a manufacturing method and structure with a high manufacturing yield have not yet been established. In addition, this protrusion may be destroyed by an unexpected small discharge, and there is a need from the viewpoint that the emitter structure can be repaired by a simple method.

The present invention is particularly intended for the ionization of light element He and hydrogen (H ₂ ), and is equipped with a GFIS that employs an ion emitter that can be manufactured at a high yield and can be easily repaired at the time of tip destruction. An object of the present invention is to provide a scanning charged particle microscope having a high resolution and a large focal depth.

  The present invention relates to forming an ion emitter with a needle-shaped first metal base and a second metal covering the tip. The second metal is a metal whose evaporation electrolysis strength is higher than the optimum electric field strength of field ionization imaging in the gas species of the desired ions, and which easily moves on the surface of the first metal atom by applying electric field / thermal energy to the covering portion. And

  According to the present invention, an ion emitter having a fine protrusion by coating at its tip can be manufactured with a high yield. As another aspect, when the coating is peeled off, many peelings can be repaired by applying an electric field / thermal energy thereto. As another aspect, since the evaporation electrolysis strength of the second metal is higher than the optimum field strength of the gas field ionization imaging, the emitter tip can be emitted for a long time without being rapidly consumed by the field evaporation. It is. As another aspect, by adopting this ion emitter in GFIS, a high-intensity ion source of a desired gas species can be provided. Further, as another aspect, by mounting this GFIS on a scanning charged particle microscope, it is possible to provide high resolution and large focal depth microscope characteristics at a high apparatus operating rate.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of the GFIS used in the first embodiment. The emitter 7 is fixed to the filament 6, and both ends thereof are fixed to the support portion 5. An electric wire 14 is connected to the support portion 5 so that the temperature can be increased using heat conduction by applying a voltage Vo to the emitter 7 and energizing and heating the filament 6. An extraction electrode 9 having a small hole for extracting ions 8 is placed opposite to the emitter 7, and the extraction electrode is attached to the tip of the cap 10. The extraction electrode 9 is an electrode that forms an electric field for ionizing a gas in the vicinity of the tip of the emitter. An electric wire 12 is connected to the cap 10, and an extraction voltage Ve (where the emitter voltage Vo is a reference) can be applied to the extraction electrode 9. The electric field at the tip of the emitter 7 is determined by the radius of curvature of the tip of the emitter and the voltage Ve. The ionizing gas 1 is sent to the tip of the emitter 7 using a glass thin tube 2 which is a gas supply means for supplying gas in the vicinity of the tip of the emitter. The glass container 3 that fixes the support portion 5, the cap 10, and the glass thin tube 2 is also a cooling means 13 that cools the emitter 7. By putting a coolant (for example, liquid nitrogen) 4 in the container, not only the emitter 7 but also the cap 10, the extraction electrode 9, the electric wire 12, and the gas 1 can be cooled. The glass container 3 is fixed to a flange 11 and is fixed to the flange surface when the GFIS is mounted as an ion source in a scanning charged particle microscope described later.

An enlarged schematic view of the tip of the emitter 7 is shown in FIG. The emitter 7 is composed of a first metal needle-like base body 20 and a second metal covering the tip of the needle. The first metal is a refractory metal such as single crystal tungsten (W) or molybdenum (Mo), and the second metal is easy to move on the atomic surface of the first metal at a high temperature, and For example, platinum (Pt), iridium (Ir), rhenium (Re), osmium (Os), palladium (Pd), and rhodium (Rh) having a high evaporation electrolytic strength.

Here, an emitter manufacturing method will be described. A needle-like substrate having a tip curvature radius of about 100 to 400 nm is produced by electropolishing a thin wire (axis direction is <111>) having a diameter of 200 to 400 μm of the first metal. The needle-like substrate 20 is put into an emitter manufacturing apparatus and evacuated to a vacuum. A schematic diagram of the emitter fabrication apparatus is shown in FIG. In the emitter manufacturing chamber 30, the needle-like substrate 20 is finished to an emitter 7 having a tip curvature radius of several tens of nm by high-temperature heating and electric field evaporation. Thereafter, the second metal set in the vacuum deposition source 35 is coated from the side surface (or front surface) of the emitter by vacuum deposition. Reference numeral 21 in FIG. 1 represents the partially covering atoms. Thereafter, the second metal atoms are moved to the tip of the emitter by high-temperature heating (yaku), and a part thereof forms a facet at the tip of the emitter, and a pyramidal projection 22 is formed. Liquid nitrogen 4 as a refrigerant is put in the cooling means, and gas 1 is introduced in the vicinity of the emitter 7. The pressure in the vicinity of the emitter 7 is an estimated 1 Pa order. The sample chamber has a field ion microscope (FIM for short) image and field emission microscope field for monitoring the radius of curvature of the emitter tip and the formation of protrusions.
Emission Microscopy (abbreviated as FEM) or Field Electron Microscope (Field Electron)
Microscopy (abbreviated as FEM) image fluorescent plate 33 is placed opposite the emitter. In addition, a microchannel plate (MCP) 32 is placed immediately before the emitter side of the fluorescent plate 33 in order to increase the sensitivity of the FIM image. In FIM / FEM image observation, in order to cause the fluorescent plate 33 to emit light, electron irradiation is more efficient than ions, and in the case of FEM image observation, the MCP 32 is not necessary. In FIG. 3, the FIM or FEM image can be observed through the observation window 34. Observation of the FIM image or the FEM image is performed by making the polarity of the voltage applied to the emitter 7 positive and negative, respectively. The electric field intensity in FIM and FEM image observation is about one digit higher in the former.

  When the protrusion of the emitter is damaged due to unexpected micro-discharge or the like, the protrusion can be formed again by moving the surface of the second metal by holding the emitter (about 1000 ° C.) and holding it for 3 to 30 minutes. . The heating temperature and holding time depend on the combination of the first metal and the second metal, the crystal orientation (111), (110) of the first metal viewed from the emitter axis direction, and the like. From the viewpoint of reproducibility of the formation of the protrusion, the crystal orientation (111) is superior. As described above, the repair can be performed by a simple method. The emitter fabrication chamber 30 is connected to a vacuum pump for evacuation, but is not shown in FIG. In addition, when the second metal is placed on the emitter base of the first metal, it is placed by a vacuum deposition method in this example, but it may be placed by a plating method after the needle-like base is produced by electrolytic polishing.

The desired emitted ion species in the present ion source is He or H ₂ ions. When an appropriate voltage is applied to the emitter 7 and the extraction electrode 9 to create a strong electric field at the tip of the emitter, most of the ionized gas atoms (or molecules) 23 are pulled to the emitter surface by the strong electric field, and jump orbits 25 on the emitter surface. , And reaches the vicinity of the tip of the projection 22 having the strongest electric field. The gas atoms (or molecules) 23 are preferentially ionized there and emitted as ions 24. The emitted ions from there narrow the ion emission angle to several degrees, and the ion emission angle current density is improved by about an order of magnitude compared to the conventional emitter without fine projections. The emitted ions are He ⁺ in He gas, and H ⁺ and H ₂ ⁺ are mixed in H ₂ gas.

Next, the combination of the emitted ion species and the second metal that forms the protrusion will be described. Table 1 shows the evaporation field strength F _n of the first metal and the second metal of the emitter base material. Here, n is the valence of field evaporation ions, and is an integer of 1, 2,. Minimum value F _n of F _n, n of _min varies depending on the material, F _n, are underlined _min value. Table 2 shows the optimum electric field strength F _{best_image} of the field ionization imaging of the emitted ion gas species He and H ₂ together with Ne and Ar. In the emitter from which ions are being emitted, the portion having the strongest electric field strength is a protrusion relating to ion emission. From the viewpoint of suppressing the electric field evaporation of the protrusion, the second metal forming the protrusion should satisfy the inequality condition of F _{n, min} > F _{best_image} . Therefore, in the He gas, the second metal is Pt, Ir, Re, or Os. Although an example of adopting Pd as the second metal is disclosed in Non-Patent Document 4, Pd is not suitable for field ionization of He gas. On the other hand, in the H ₂ gas, Pd, Pt, Ir, Rh, Re, or Os is suitable for the second metal.
In both the He gas and H ₂ gas ionization, Os as the second metal has the largest F _{n, min} in Table 1, and the most excellent damage resistance of the protrusion due to an unexpected excessive electric field.

In the first metal of the emitter substrate in He ion emission, W satisfies the inequality condition of F _{n, min} > F _{best_image} and has a large margin until electric field evaporation due to an over electric field is large. More preferable than Mo. In the emitter fabrication, H ₂ , Ne, or Ar gas whose F _{best_image} is lower than He can be used in addition to He as the gas species for FIM image observation of the emitter protrusion atomic arrangement. If the radius of curvature of the tip of the emitter is still large before the process of producing the protrusion, an FEM image that requires a low extraction voltage (absolute value) is useful. The radius of curvature of the tip can also be estimated from the dependency of the FE emission current on the extraction voltage.

  An embodiment of a scanning charged particle microscope equipped with the GFIS will be described. FIG. 4 is a schematic configuration diagram of a scanning charged particle microscope. The emitted ion beam 55 emitted from the GFIF 40 is accelerated by the acceleration electrode 41 and focused on the sample 49 by the focusing lens 42 and the objective lens 48. The acceleration electrode 41 may be incorporated as one electrode of the focusing lens 42 configuration. Between both lenses are a beam deflector / aligner 43, a movable beam limiting aperture 44, a blanking electrode 45, a blank beam stop plate 46, and a beam deflector 47. Secondary electrons 50 emitted from the sample 49 are detected by a secondary electron detector 51. The beam control unit 52 controls the GFIS 40, the focusing lens 42, the objective lens 48, the upper beam deflector / aligner 43, the lower beam deflector 47, the secondary electron detector 51, and the like. The PC 53 controls the beam controller 52 and processes and stores various data. The image display means 54 displays a SIM image and a control screen on the PC 53. The emission angle of the ion beam emitted from the protrusion 22 of the emitter 7 is as narrow as several degrees, but of these, it is less than several degrees to be used as a beam that leads to the sample 49. Adjustment selection of the beam emission axis to be used is a problem specific to a scanning charged particle microscope equipped with GFIS, and is performed as follows.

The movable beam limiting stop 44 is irradiated with a beam having a diameter larger than that of the stop hole, and only the beam that has passed through the stop hole reaches the adjustment sample 49. The beam is scanned on the movable beam limiting aperture 44 by the deflection action of the upper stage beam deflector / aligner 43, and a SIM image is created with the signal synchronized with this scanning signal as the XY signal and the secondary electron detection intensity as the Z (luminance) signal. The image is displayed on the image display means 54. Further, the movable beam limiting diaphragm 44 can be finely adjusted in the XY direction in a plane perpendicular to the optical axis for adjusting the optical axis. The objective lens 48 adjusts the lens action so that the deflection fulcrum of the upper beam deflector / aligner 43 is projected onto the sample 49. When this adjustment is completed, even if the beam is deflected by the upper beam deflector / aligner 43, the beam on the sample is not scanned, and the beam intensity changes to reflect the emission angle distribution of the emitted ion intensity from the emitter 7. Therefore, the SIM image on the monitor screen has an emitted ion intensity distribution with the XY axis as the ion emission angle. Since the FIM image has a resolution obtained by projecting the ion emission part of the emitter at the atomic level, this SIM image is equivalent to the FIM image convoluted with the solid angle of ion emission corresponding to the aperture of the movable beam limiting aperture 44. An image is obtained. In this monitor SIM image, if the deflection signal of the upper stage beam deflector / aligner 43 is aligned and fixed at the brightest point, the beam deflector / aligner 43 aligns the optical axis to the emission axis with the highest emitted ion intensity ( Adjusted). For the subsequent use of the focused ion beam, this aligned beam is used. The ion emission axis adjustment by the set of the beam deflector / aligner 43 and the movable beam limiting aperture 44 is a problem specific to a scanning charged particle microscope equipped with a GFIS. That is, the number of ion emission sites from the emitter protrusion of the GFIS is usually one atom or three atoms, which is usually several atoms or less. The direction of ion emission from these atoms is localized for each atom with a small solid angle (α = 1−2 degrees of πα ² ). Therefore, it is necessary to select which atom is selected as the ion emission site to be used as the focused ion beam, and which ion emission direction is selected as the optimum ion emission axis among the selected atoms and to adjust it with the ion optical axis. That's it.

An embodiment of a scanning charged particle microscope in which the GFIS is operated as a field emission electron source and either the GFIS or the field emission electron source is selected and used will be described. Since the schematic configuration diagram of this microscope is similar to FIG. However, GFIS 40 is read as GFIS / field emission electron source, and emitted ion beam 55 is read as emitted ion beam / emitted electron beam. The radius of curvature of the tip of the emitter of the GFIS is small, and electrons can be emitted by reversing the polarity of the electric field at the tip of the emitter. That is, GFIS can be operated as a field emission electron source. However, the electric field intensity of electron emission may be about one digit lower than in the case of field ion emission. Further, in the operation of the field emission electron source, gas introduction is stopped and the periphery of the emitter is kept in an ultrahigh vacuum. Further, the emitter is not required to be cooled to room temperature. In FIG. 4, all of the optical components such as the lens and the deflector / aligner are electrostatic systems (not magnetic field systems). By making them reverse polarity, a focused electron beam similar to the case of ions can be obtained. It is done. However, in field electron emission, the absolute value of the extraction voltage Ve is made lower than that in the case of ion emission. Therefore, it is necessary to change the lens potential even with the same emitter potential Vo (however, absolute value). The optical conditions of the focused ion beam and focused electron ion beam formation are stored in the memory of the PC 53. In response to the selection of one of the beam formations, the optical conditions for the selected beam formation are called from the memory, and the beam control unit 52 controls the optical system.

The schematic block diagram of a gas field ionization ion source (GFIS). The enlarged schematic diagram of the emitter tip. Schematic of an emitter manufacturing apparatus. The schematic block diagram of the scanning charged particle microscope which mounts GFIS.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas 2 Capillary tube 3 Glass container 4 Liquid nitrogen 5 Support part 6 Filament 7 Emitter 8 Ion 9 Extraction electrode 10 Cap 11 Flange 12, 14 Electric wire 13 Cooling means 20 Needle-like base 21 The 2nd metal atom which coats the needle-like base 22 Projection 23 Gas atom (or molecule)
24 Ion 30 Emitter production chamber 31 Emission ion 32 MCP
33 Fluorescent screen 34 Observation window 35 Deposition source 40 Gas field ionization ion source (GFIS)
41 Accelerating electrode 42 Focusing lens 43 Beam deflector / aligner 44 Movable beam limiting aperture 45 Blanking electrode 46 Blank beam stop plate 47 Beam deflector 48 Objective lens 49 Sample 50 Secondary electron 51 Secondary electron detector 52 Beam control unit 53 PC
54 Image display means 55 Emitted ion beam

Claims (4)

An emitter composed of a needle-shaped first metal and a second metal covering the tip of the first metal;
Gas supply means for supplying a gas in the vicinity of the tip of the emitter;
An extraction electrode for forming an electric field for ionizing the gas in the vicinity of the tip of the emitter;
A gas field ion source comprising: cooling means for cooling the emitter;
The first metal is tungsten or molybdenum;
The second metal is platinum, iridium, rhenium, or osmium whose evaporation electric field intensity is higher than the optimum electric field intensity of the gas field ionization imaging ;
It said gas, the gas field ion source, which is a helium. An emitter comprising a needle-shaped first metal and a second metal covering the tip of the first metal;
Gas supply means for supplying gas in the vicinity of the tip of the emitter, and an electric field for ionizing the gas at the tip of the emitter
A gas field ionization electrode including an extraction electrode formed in the vicinity and a cooling means for cooling the emitter.
On source,
A lens system for focusing ions extracted from a gas field ion source;
A beam deflector that scans the ion beam;
A secondary particle detector for detecting secondary particles;
A scanning charged particle microscope including an image display means for representing a scanning ion microscope image,
The first metal is tungsten or molybdenum;
The second metal is platinum, iridium, rhenium, or osmium whose evaporation electric field intensity is higher than the optimum electric field intensity of the gas field ionization imaging;
A scanning charged particle microscope, wherein the gas is helium. A scanning charged particle microscope according to claim 2,
A deflector that deflects and scans an ion beam closer to the emitter than the beam deflector;
A beam limiting aperture having a hole through which a portion of the deflection scanned beam passes;
A traveling device characterized in that the deflector can also function as an aligner while being fixed to a specific deflection.
Inspection particle microscope. An emitter comprising a needle-shaped first metal and a second metal covering the tip of the first metal;
Gas supply means for supplying gas in the vicinity of the tip of the emitter, and an electric field for ionizing the gas at the tip of the emitter
A charged particle source including an extraction electrode formed in the vicinity and a cooling means for cooling the emitter;
A lens system for focusing charged particles extracted from a charged particle source;
A beam deflector for scanning the focused charged particles;
A secondary particle detector for detecting secondary particles;
A scanning charged particle microscope including an image display means for displaying a scanning charged particle microscope image,
The first metal is tungsten or molybdenum;
The second metal is platinum, iridium, rhenium, or osmium whose evaporation electric field intensity is higher than the optimum electric field intensity of the gas field ionization imaging;
The gas is helium;
By changing the polarity of the electric field in the vicinity of the emitter tip, the charged particle source is
Scanning charged particles characterized by being used as either a field ion source or a field emission electron source
Child microscope.

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