JP5269706B2 - Production method of liquid metal ion gun - Google Patents

Description

  The present invention relates to a liquid metal ion source (LMIS), and more particularly to a technique for stably and long-lasting ion emission (emission) of a Ga liquid metal ion source.

  The liquid metal ion gun has a vacuum vessel in which a liquid metal ion source is disposed, and a liquid metal ion source that is electrically insulated from the vacuum vessel. The liquid metal ion gun is connected with a high voltage cable capable of flowing a current between both terminals of the liquid metal ion source, whereby a high voltage is supplied to the liquid metal ion source, and the liquid metal ion source is appropriately selected. A high voltage can be applied to (heated).

  The ion emission amount (emission current) can be adjusted by the voltage between the liquid metal ion source and the extraction electrode. The emitted ions are received by a beam limiting aperture.

  Although it is important to stably maintain the ion emission of the Ga liquid metal ion source, gallium (hereinafter referred to as “Ga”) consumed by the ion emission is stably supplied from the reservoir. There is a need to. The state where the emission current is stable is a state where the consumption of Ga and the supply of Ga are balanced, that is, an equilibrium state where Ga corresponding to the ion emission is supplied.

  However, when foreign matter is mixed in Ga, the supply of Ga may be hindered, and when the purity of Ga changes, physical properties change, and the balance between consumption and supply of Ga is lost. For this reason, the stability of the emission deteriorates.

  In order to obtain stable emission, conventionally, the extraction electrode has been structured not to be directly irradiated with a radiated ion beam so that foreign matters are not mixed into Ga. In addition, even if the sputtered particles of the electrode that is irradiated with the radiation ion beam adhere to the Ga of the liquid metal ion source and become contaminated, the Ga compound metal, that is, the melting point of Ga, is raised. An electrode (beam limiting aperture) that receives the beam irradiation is made of a metal (Sn, In) that is not allowed to be irradiated.

  Also, since the number of sputtered particles (particles that cause contamination) resorbed on the LMIS decreases in proportion to the square of the distance between the emitter and the beam limiting aperture, the emitter and beam limiting (GUN) aperture Was away.

  For example, Patent Document 1 describes a technique in which a portion irradiated with an ion beam is configured by a sintered body infiltrated with a low melting point metal. Patent Document 2 describes a technique in which the same kind of Ga is used as a protective diaphragm material when general Ga is used as a liquid metal ion source. Further, Patent Document 3 describes that the surface of the emitter electrode or the entire surface thereof is composed of one or more kinds of metals constituting a molten metal or alloy provided at the tip of the emitter electrode.

Japanese Patent No. 3190395 JP 2001-160369 A JP-A-4-14455

  However, in each of the above prior arts, there is no mention regarding the limitation of the constituent material (base material) of the aperture. Therefore, when the constituent material (base material) of the beam limiting aperture is exposed to the ion irradiation, a change in emission stability due to the base material being sputtered and mixed into the liquid metal source is not considered.

  Even with the above technique, in a liquid metal ion source that is desired to be used for several hundred hours or more, it is difficult to maintain the emission stably for a long time and return the unstable emission to a stable state. That is, the difficulty of recovery when the emission becomes unstable is not considered.

  In addition, in order to realize a focused ion beam apparatus for a processing beam having a high current and a high current density, it is not preferable to make the distance between the emitter and the beam limiting aperture too long. However, considering the lifetime of contamination and the beam limiting aperture, it is better to increase the distance between the emitter and the beam limiting aperture, improve the performance of the focused ion beam device, and reduce the contamination of the emitter. It can be seen that there is a conflicting relationship.

  Since the beam limiting aperture is configured to receive the total emission current (2 to 3 μA) of the ion source, as the ion irradiation time (emission current × usage time) increases, the beam limiting aperture is sputtered to become thin and the opening begins to expand. When the aperture starts to expand, the lower electrode is exposed together with the increase of the beam current downstream of the beam limiting aperture, and particles from the lower electrode other than the beam limiting aperture are included in the sputtered particles. The lower electrode generally has a different material from that of the beam limiting aperture. When the sputtered particles adhere to the emitter, the sputtered particles from the lower electrode do not dissolve in Ga, and the melting point increases even if dissolved. Ga supply is inhibited.

  Further, even when the beam limiting aperture is made of a metal such as In or Sn, there is a problem that the purity of Ga drops due to sputtered particles adhering to the emitter. Even if a metal such as In or Sn is mixed, if it is up to about 10 wt%, the melting point of Ga is lowered. However, as a result of accumulation of Sn and In after being used for a long time, the purity of Ga decreases and physical characteristics. Changes, the supply state of Ga changes, and the emission current changes.

  Hereinafter, the problems of a general liquid metal ion gun will be described more specifically with reference to FIG. As shown in FIG. 3, the ion gun has a Ga liquid metal ion source 2-1, an extraction electrode 2-2 for emitting ions, and a beam limiting aperture 2-3. -2 is made of SUS, has an opening φ3 mm, an opening side wall thickness of 1 mm, a distance from the emitter tip to the extraction electrode 2-2 of 0.8 mm, and the radiation ion beam 7 from the liquid metal ion source 2-1 is the extraction electrode. It has a structure that does not directly irradiate 2-2. The extraction electrode 2-2 has a built-in beam limiting (GUN) aperture 2-3 formed with an opening 2-31 having a diameter of 0.3 mm, and an Sn-made aperture having a thickness of 3 mm is connected to the extraction electrode 2-2. It is located 5 mm below the top surface.

  The beam limiting aperture 2-3 functions as a diaphragm for limiting beam irradiation. The extraction electrode 2-2 has a function of radiating ions by applying a voltage between the emitter and the extraction electrode (space between the emitter and the upper surface of the extraction electrode). It has a structure in which a beam limiting aperture 2-3 is incorporated in the extraction electrode 2-2. Both have the same potential but have different roles.

  When a voltage difference of about 7 kV is applied between the Ga liquid metal ion source 2-1 and the extraction electrode 2-2, Ga + ions are emitted from the Ga liquid metal ion source 2-1, and a Sn beam limiting (GUN) aperture 2 is formed. -3. The Sn beam limiting aperture 2-3 is sputtered with Ga + ions and Sn atoms (sputtered particles 11) are scattered around, and a part thereof is scattered and adsorbed on the Ga liquid metal ion source 2-1.

  Further, the beam limiting aperture 2-3 has a lifetime because the thickness of the beam limiting (GUN) aperture 2-3 decreases as the sputtering with Ga + ions progresses, and the aperture diameter increases. When used beyond the lifetime of the beam limiting aperture 2-3, the lower electrode of the beam limiting aperture 2-3 is exposed, and the constituent atoms of the electrode material are scattered around by sputtering with Ga + ions, and a part thereof is Ga liquid. Adsorbed to the metal ion source 2-1. This adsorbed substance raises the melting point of Ga, or directly obstructs the Ga supply flow path and makes the emission unstable. When the beam limiting aperture is Sn, the sputtered Sn particles form a compound with Ga and dissolve in Ga, and the melting point is 30 ° C. or less up to about 10 wt%. Therefore, Sn adsorbed on the Ga liquid metal ion source is Ga The physical properties such as the surface tension and melting point of Ga change depending on the concentration of the solute.

  For stable ion emission, Ga corresponding to the radiation is supplied and it is desirable that this does not change with time, but if the physical characteristics of Ga change, the equilibrium point changes, so the emission current also changes. The emission current also changes when the Ga flow path is blocked or when the Ga supply amount changes. Therefore, in the general configuration example shown in FIG. 3, it is difficult to obtain a stable emission for a long time, for example, several hundred hours.

  In view of the problems described above, the object of the present invention is as follows. In other words, even if the distance between the emitter and the beam limiting aperture is short, the emission should be stable for a long time. In addition, extending the life of the beam limiting aperture when subjected to sputtering by beam irradiation. Furthermore, when the emission of the liquid metal ion source becomes unstable, the emission is restored to a stable state with good reproducibility, and the life is extended by using the liquid metal ion source for a long time. Another object of the present invention is to provide a stable liquid metal ion gun that does not require beam adjustment of a focused ion beam apparatus.

The present invention provides a method of producing liquid metal ion gun equipped with a beam limiting aperture for receiving the irradiation of the radiation ions from a liquid metal ion source and the liquid metal ion source, said beam limiting aperture, W of (tungsten) Formed with a metal material, put a Ga lump on the non-oxidized W surface, irradiate the beam limiting aperture with Ga ions, dissolve the Ga lump in the irradiation region, and in the irradiation region of the beam limiting aperture The present invention relates to a method for producing a liquid metal ion gun, characterized by diffusing Ga on the surface.

In this case, the beam limiting aperture may be immersed in a sodium hypochlorite solution to obtain a non-oxidized W surface. Further, the beam limiting aperture to the electrolytic polishing, the beam limiting aperture surface dirt fell to ultrasonic cleaning with pure water, may be obtained without oxidation W surface.

  According to the present invention, in processing by a large current beam such as a focused ion beam apparatus provided with a liquid metal ion source, processing without damage due to ion irradiation can be performed around the processing. According to the liquid metal gun of the present invention, in a liquid metal ion source intended for use for several hundred hours or more, the point of maintaining stable emission for a long time and the unstable emission in a stable state are ensured. The return point, that is, the ease and reproducibility of recovery of emission stability is excellent.

It is a figure which shows the structural example of the ion beam apparatus by one embodiment of this invention. It is a figure which shows the structure of Ga liquid metal ion source. It is a figure which shows the structure of a general liquid metal ion gun. FIGS. 4A and 4B are diagrams showing a configuration example of a liquid metal ion gun according to an embodiment of the present invention, in which a Ga reservoir is provided. FIGS. 5A to 5C are diagrams showing a configuration example of a beam limiting aperture according to an embodiment of the present invention. It is a figure which shows the example of the incident angle dependence of the sputtering yield of a monoatomic solid-state imaging device. FIGS. 7A to 7C are diagrams showing a configuration example of the beam limiting aperture according to the embodiment of the present invention.

  A liquid metal ion gun according to an embodiment of the present invention will be described with reference to the drawings. The liquid ion gun according to the present invention relates to a liquid metal ion gun equipped with a liquid metal ion source and a beam limiting aperture that receives irradiation of radiation ions from the ion source.

  First, an overall configuration of an apparatus equipped with an ion gun according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an ion beam apparatus using a Ga liquid metal ion gun according to an embodiment of the present invention. In FIG. Reference numeral 1 denotes an ion beam device, and reference numeral 2 denotes an ion gun. Among these, reference numeral 2-1 denotes an ion source, 2-2 denotes an extraction electrode, 2-3 denotes a beam limiting aperture, and 2-4 denotes a ground electrode. Reference numeral 3 is a vacuum vessel, 4 is an evacuation device, 5 is an ion pump, 6 is a high-voltage power supply unit, and 6-1 is a high-voltage power supply for accelerating ions, 6-1a, 6 -2a is a high-voltage connection, 6-2 is a high-voltage power supply for ion extraction, 6-3a and 6-3b are high-voltage cables, 6-6 is a heating power source for the ion source, and 7 is irradiated ions. A beam 8 is a gate valve provided between the vacuum vessel 3 and the vacuum exhaust device 4.

  The main operation (action) of this apparatus will be described. The ion beam generated by being extracted from the ion source (emitter) 2-1 by the extraction electrode 2-2 passes through the beam limiting aperture 2-3 while restricting the beam expansion, and the passed beam passes through the earth electrode 2. -4 is accelerated and irradiated downstream. In addition to the above configuration, a processing observation device is formed by adding a signal detection system for detecting a signal from an ion beam irradiated sample and a function of irradiating the sample by narrowing the irradiation ion beam with a lens and controlling the beam deflection. be able to.

  Next, the configuration and principle of LMIS will be described. FIG. 2 is a diagram showing the configuration of the liquid metal ion source. As shown in FIG. 2, a liquid metal ion source, for example, a Ga liquid metal ion source 2-1, includes a needle-like emitter 2-11 having a conical tip, a reservoir 2-12 for storing Ga, and a reservoir 2-12. It has a filament 2-13 for energizing and heating the inner Ga and the needle-like emitter 2-11, and an insulator base 2-15 for fixing a terminal 2-14 for energizing the filament 2-13.

  The material of the needle-shaped emitter 2-11, the reservoir 2-12, and the filament 2-13 is tungsten (W), and the reservoir 2-12 is filled with Ga. Thus, the constituent materials of a general Ga liquid metal ion source are W, Ga, and insulator.

  The principle of operation related to ion emission is that the tip of the needle-like emitter has a conical shape, and the electric field gradient in the axial direction becomes stronger toward the tip. Ga near the tip of the needle-like emitter is supplied to the tip of the emitter having a strong electric field due to the electric field stress, and becomes a conical shape with a point apex. As a result, the peak of the liquid metal becomes a strong electric field of about V / Å, so that the ionization potential is lowered and electric field evaporation occurs, or electrons are lost and it becomes easy to ionize. Therefore, in a strong electric field of about V / Å, ions jump out into the vacuum and an ion flow is generated.

  Along with the ion emission, it is necessary to supply Ga corresponding to the emission amount of Ga ions. However, since Ga behaves fluidically, a pressure gradient is generated and a continuous fluid surface layer flow is generated. Since this flow is a Poiseuille flow caused by surface tension, the flow rate changes due to changes in surface tension and viscosity.

  In general, pure Ga has good wettability with respect to clean tungsten. For example, if tungsten has a thin groove, it diffuses through the groove by capillary action due to surface tension. In general, needle-shaped emitters are made of a W material with a thin vertical groove in the axial direction. This causes Ga in the reservoir to diffuse through the groove by capillary action of surface tension and supply it to the vicinity of the tip of the emitter. can do. The stable emission is supplied with Ga corresponding to the ion emission, but when the surface tension changes, the supply amount changes and the emission changes.

  In the liquid metal ion gun according to the present embodiment, a Ga reservoir (if the reservoir is a first Ga supply source, this can also be referred to as a second Ga supply source) is provided as described below. This configuration will be described with reference to FIG. As shown in FIG. 4A, the emitter 2-11 of the Ga liquid metal ion source 2-1 includes a base material W12 as a constituent material and an ion source material Ga9 covering the surface. Here, even when the sputtered particles 11 are attached to the Ga liquid metal ion source 2-1, by making the sputtered particles 11 become a constituent material (W, Ga) of the Ga liquid metal ion source 2-1, Contamination that changes physical properties does not occur.

  In other words, a W aperture was used as the beam limiting (GUN) aperture 2-3, and about 25 mg of Ga (melting point: 30 ° C.) was placed on the surface of the portion applied to the beam irradiation region 7-1 (Ga reservoir 10). When this beam limiting (GUN) aperture 2-3 is irradiated with ions, Ga in the irradiation region 7-1 is melted and Ga diffuses on the surface of the beam irradiation region of the W aperture (see FIG. 4B). Therefore, Ga melting and diffusion to the irradiation region occur spontaneously with ion irradiation, and therefore it is not necessary to apply Ga to the W aperture in advance. When the beam limiting aperture according to the present embodiment was replaced with the above-mentioned beam limiting aperture from a general Sn beam limiting aperture, a stable emission state could be obtained over 1200 hours (h).

Next, the opening of the liquid metal ion gun will be described. In the case of using general gallium as the liquid metal ion source, the distance L (7 mm) between the emitter tip of the Ga liquid metal ion gun and the beam limiting aperture, the Ga mass m (25 mg) of the Ga reservoir, and the Ga density Assuming that ρ (5.93 g / cm ³ ) and ion emission angle α (20 °), the aperture diameter (radius) r of the W beam limiting aperture with Ga reservoir is
r ≧ m / ρπ (Lα) ²
In this case, the opening diameter (radius) r is 0.23 mm.

  In the above formula, when the cross section of the thickness of Ga is blocked by the opening (see FIG. 5A), Ga protrudes from the opening onto a semicircle having a diameter of the thickness and contacts at the opposing portion (FIG. 5 ( It is known that, under the above conditions, the opening is actually clogged when the diameter is φ0.3, but it is difficult to clog when φ0.6 (see FIG. 5C). Therefore, a W beam limiting aperture with a Ga pool with an aperture of φ0.6 mm was used.

Next, the angle dependency of the liquid metal ion gun will be described. The ion processing speed (sputtering yield) depends on the incident angle. FIG. 6 shows a characteristic example related to the incident angle dependence of the sputtering yield. As shown in FIG. 6, when the incident angle θ is increased, the cascade is generated on the surface side, so that it increases at cos ^−f θ (f = 1 to 2) as indicated by the Zigmund theory. When the incident angle θ increases, the collision coefficient is limited due to the shielding effect of adjacent atoms on the surface, making it difficult to pass through the surface. Finally, all incident ions are reflected with almost no energy applied to the solid, yielding Decreases rapidly.

  In addition, since the sputtering phenomenon varies depending on the crystal orientation of the crystal grains, the sputtering phenomenon can be uneven with the crystal grains as the starting point. The unevenness of the surface is increasingly promoted due to the dependency of the unevenness and the ion processing speed on the incident angle, and the lifetime of the beam limiting aperture is shortened because the processing speed is increased. However, the crystal grain size of W is about 1 μm, and the crystal grain size of Sn is 6 to 10 μm. For this reason, W cannot be uneven as compared with Sn, and the sputtering yield is small. Further, when the W beam limiting aperture with Ga reservoir of the present invention is used, even when unevenness of about 1 μm is formed, the surface becomes mirror-like because the surface is wetted with Ga, and even if the beam limiting aperture is used, the sputtering rate is reduced. There is little change.

  In addition, since the surface is covered with Ga, sputtering of W hardly occurs even when Ga sputtering occurs. Since the beam limiting aperture does not receive sputtering if the Ga does not wither, a desired life can be obtained even if the W aperture is thin.

  Next, the mounting state of the liquid metal ion gun will be described. The Ga reservoir 10d is obtained by placing a Ga lump on the surface of the W beam limiting aperture 2-3 having the opening 2-31, melting the Ga lump, and solidifying the W beam limiting aperture in a heating and cooling atmosphere of −20 ° C. (See FIG. 7A). Also, Ga10e is applied to a ring-shaped W material or W sintered body 9 arranged so as not to be applied to the ion irradiation region, and placed on the beam limiting aperture 2-3, or Ga is formed in a ring shape. A structure sandwiched between the W material or the W sintered body 9 and the W beam limiting aperture 2-3 may be used (FIG. 7B). Alternatively, by forming a recess or a groove 2-3-1 on the surface of the W beam limiting aperture 2-3 in a region away from the opening 2-31, so that the Ga reservoir 10f is easily formed, Even when melted and fluid, liquid Ga can be stored at a predetermined position.

W and Ga have good wettability, but are difficult to wet when W is oxidized. In order to obtain a clean W surface without oxidation, a W beam limiting aperture was immersed in a sodium hypochlorite solution for 1 hour. Alternatively, subjected to ultrasonic cleaning with pure water from Clean the surface with electrolyte solution electrolytic polishing using such NaOH.

When a Ga liquid metal ion gun using a W-beam limiting aperture with a Ga reservoir is installed in the apparatus, the ultimate vacuum of the ion gun is operated at 10 ⁻⁷ Pa. As a result, the extraction voltage is 7 kV and the emission is 2.4 μA. The state could be continuously maintained for 120 hours, and during that time, changes in the beam focus state could be suppressed without performing maintenance such as flushing and emission control.

  As described above, when the W beam limiting aperture according to the present embodiment is used, even if Ga or W particles sputtered from the beam limiting aperture adhere to the emitter, the Ga of the liquid metal ion source is contaminated. Therefore, even when a beam limiting aperture is placed near the Ga liquid metal ion source, a stable emission state can be maintained for a long time.

  Further, according to the W beam limiting aperture according to the present embodiment, since the ion irradiation region is wet with Ga as a basic operation, there is no exposure of W, and sputtering by ion irradiation is mainly Ga, and liquid metal ions Even if the sputtered particles are adsorbed to the source, no change in emission is suppressed because no contamination occurs. Further, when the constituent material (W base material) of the beam limiting aperture is exposed after being irradiated with ions for a long time, the W base material may be sputtered. In this case, even if W is sputtered and adheres to the Ga liquid metal source, the emission is reduced. However, because W and Ga wettability is good, W is covered with Ga by flushing (temporarily heating the emitter). Easy to recover.

In addition to this, the oxide of Ga can be considered as a contamination of the Ga liquid metal ion source. However, if the operating vacuum is 10 ⁻⁶ Pa, the emission is stable for several days, and at the same time, the oxidation of Ga is also possible. As it progresses, the emission decreases as the oxidation progresses. However, Ga oxide can be recovered with good reproducibility (emission current, necessary extraction voltage and stability) by performing flushing (heating) at about 700 ° C. for about 30 seconds.

Also, if the operating vacuum is on the order of 10 ⁻⁷ Pa, the emission is stable without changing the radiation conditions such as the extraction voltage over several days, so that the lens action of the ion optical system does not change. For this reason, ion processing can be performed without performing focus adjustment for several days, and the stability of the apparatus and the simplicity of operability are greatly improved.

  If even a part of the Ga irradiation area of the beam limiting aperture has Ga accumulation, Ga spontaneously diffuses and gets wet in the beam irradiation area of the beam limiting aperture. For this reason, the beam irradiation region of the beam limiting aperture is a Ga mirror surface having no irregularities, so that the angle dependency of sputtering is minimized and the life is extended. Further, Ga is mainly sputtered on the surface of the beam limiting aperture, and almost no sputtering of W occurs. Therefore, even if the beam limiting aperture is thin, the lifetime can be increased.

  Further, when the thickness is reduced, the number of beams scattered on the side wall of the beam limiting aperture is reduced, so that a beam having a uniform energy and direction can be passed downstream of the beam limiting aperture. Therefore, in the processing with a large current beam of the focused ion beam apparatus, processing without damage due to ion irradiation can be performed around the processing. In particular, according to the liquid metal ion gun using the W beam limiting aperture according to the present embodiment, in a liquid metal ion source intended for use for several hundred hours or more, the point of maintaining stable emission for a long time and instability It is excellent in the point of reliably returning the emitted emission to a stable state, that is, the ease of recovering the emission stability and the reproducibility.

  The present invention is particularly effective when long-time processing is required. In addition, since it is easy to maintain, it is highly usable in large-scale production lines.

  DESCRIPTION OF SYMBOLS 1 ... Ion beam apparatus, 2 ... Ion gun, 2-1 ... Ga liquid metal ion source, 2-11 ... Emitter base material, 2-12 ... Reservoir, 2-13 ... Filament, 2-14 ... Terminal, 2-15 ... Base, 2-2 ... Extraction electrode, 2-21 ... Opening, 2-3 ... Beam limiting aperture, 2-31 ... Opening, 2-4 ... Ground electrode, 3 ... Vacuum container, 4 ... Vacuum exhaust device, 5 ... Ion pump, 6 ... high voltage power supply, 6-1 ... acceleration power supply, 6-1a ... high voltage connection, 6-2 ... drawing power supply, 6-2a ... high voltage connection, 6-3a ... high voltage cable, 6 -4 ... Heating power source, 7 ... Irradiated ion beam, 7-1 ... Beam irradiation region, 8 ... Gate valve, 9 ... Ga covering emitter surface, 10 ... Ga reservoir, 11 ... Sputtered particles.

Claims (3)

A method for producing a liquid metal ion gun equipped with a liquid metal ion source and a beam limiting aperture that is irradiated with radiation ions from the liquid metal ion source,
The beam limiting aperture is formed of a metal material of W (tungsten),
Place a mass of Ga on the W surface without oxidation,
Irradiating the beam limiting aperture with Ga ions, dissolving the Ga mass in the irradiation region, and diffusing Ga on the surface in the irradiation region of the beam limiting aperture;
A method for producing a liquid metal ion gun. A method for producing a liquid metal ion gun according to claim 1,
A method for producing a liquid metal ion gun, wherein the beam limiting aperture is immersed in a sodium hypochlorite solution to obtain a non-oxidized W surface. A method for producing a liquid metal ion gun according to claim 1,
It said beam limiting aperture and the electrolytic polishing, the beam limiting aperture surface dirt fell to ultrasonic cleaning with pure water, a method of producing liquid metal ion gun, characterized in that to obtain an oxidant W surface.

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