JP4177645B2 - Microcapillary Ga liquid metal ion source - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the structure of a Ga liquid metal ion source used in a scanning ion microscope or a focused ion beam apparatus.
[0002]
[Prior art]
An ion source using a liquid metal gallium Ga is often used for an ion source such as a focused ion beam apparatus. As shown in FIG. 3, the conventional Ga liquid metal ion source has a structure in which a reservoir for containing gallium as an ionic material in a molten state is held by a stem which is an insulator, and the reservoir has a mortar-shaped bottom portion. There is a small opening, and a needle with a tip protruding from the center of the opening is disposed. A disc-shaped extraction electrode having a hole in the center is disposed near the tip of the needle. In addition, a heater for heating is installed around the reservoir so that the gallium stored in the reservoir is in a molten state, and the tip of the needle is encased in liquid gallium. In this state, when a high voltage is applied between the needle tip and the extraction electrode, the liquid gallium at the needle tip is ionized and extracted, and is focused on an ion beam by an ion optical system (not shown). In order for the phenomenon of ion emission to be always stably maintained, it is important to stably supply a liquid metal in an amount commensurate with the amount released as ions to the needle tip.
[0003]
By the way, in order to stably supply the liquid metal to the tip of the needle, a state in which a liquid metal film is uniformly formed on the needle surface, that is, a good wet state as shown in FIG. Is important. On the other hand, in the poor wet state as shown in FIG. 4B, the liquid metal cannot be stably supplied to the tip of the needle. Further, when a discharge is generated between the needle-shaped emitter and the extraction electrode, the tip shape may be lost as shown in FIG. 5 and the needle shape may be deformed. If the tip portion is missing in this way, ions cannot be extracted unless the extraction voltage is further increased, and the use becomes impossible. In this case, there is a problem that the ion source must be replaced.
Patent Document 1 has a structure that makes it easy to control the flow rate of molten ion material and improve the wetting of the emitter tip (needle) in a liquid metal ion source. It is presented as an ion source capable of stable ion emission over a long period of time without a shortage of supply. The present invention shown in FIG. 6 is provided in the reservoir on the reservoir side of an axially movable emitter installed through a hole provided in the reservoir or a capillary provided at the tip of the reservoir. A hole or a convex portion (see A in FIG. 6) having an outer diameter larger than the inner diameter of the capillary is provided, and the emitter is movable in the axial direction. Therefore, when the emitter is moved to the extraction electrode side, the emitter It is possible to adjust the gap between the convex portion provided on the bottom of the reservoir and the bottom of the reservoir or the upper end of the capillary, and to function as a valve for adjusting the supply amount of ion material to the tip of the emitter. A completely closed state is shown in FIG. Further, by making the emitter movable in the axial direction, it is also intended to contact the ionic material which is a liquid by pulling the tip portion into the capillary or reservoir when the wet state is poor. However, even with this technique, the wetting of the tip in the capillary may not be recovered. Furthermore, since this is also a needle-shaped emitter, the problem of defects due to discharge is not different from the conventional one. Further, the present invention has not been put into practical use due to the fact that the operation of moving the emitter is complicated and the structure is complicated.
[0004]
Accordingly, the present inventor has developed an ion source that can stably supply liquid gallium with a structure of only a capillary without using a needle-shaped emitter having a problem of wetting and a problem of a tip end defect. As an ion source for supplying liquid gallium with a structure having only a capillary, there is one disclosed in Non-Patent Document 1 as a conventional technique. FIG. 6 is a schematic diagram of the cluster ion source introduced in the literature. A solution having a specific resistance of 10 ⁶ and 10 ¹⁰ Ωcm is introduced into a vacuum from a nozzle of a metal capillary with an inner diameter of 20 μm, and a voltage of about 10 kV is applied. It is explained that it can be taken out as cluster ions when applied. This phenomenon is also called electrospray, and it is considered that ions having a mass / charge ratio determined by the Rayleigh limit are released. Acetone from the measurement of the mass / charge ratio by the time-of-flight method with sample, has been shown to be the cluster ions having a molecular weight of 10 approximately ⁴ has occurred, about nA is drawn as total ion current. In a focused cluster ion beam deposition experiment using a triisobutylaluminum solution while heating the substrate to 400 ° C., an aluminum thin film with a width of about 100 μm was successfully deposited. It has been reported that it aims at selective crystal growth. Although this non-patent document 1 shows a cryster ion source using a capillary, the material thereof is a metal, and the ion species is not assumed to be gallium which is widely used for a focused ion beam. There is no recognition of the problem of trying to provide a stable supply of ionic material to maintain the stability of ion emission.
[0005]
[Patent Document 1]
FIG. 4 [Non-patent Document 1]
Furumuro Masanori, “Current Status of Focused Ion Beam Device”, Surface Science, published by the Surface Science Society of Japan, 1995, Vol. 729-734
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a novel emitter in place of a needle-shaped emitter that can stably supply liquid gallium as an ion source of a focused ion beam and ensure stable ion emission.
[0007]
[Means for Solving the Problems]
The ion source of the focused ion beam apparatus according to the present invention includes a glass capillary that contains gallium as an ion material, a tip portion of the capillary is formed in a mortar shape, and a fine opening is provided in the central portion. The structure is such that gallium ions are extracted from the portion. Further, the glass microcapillary was provided with a temperature control means so as not to exceed 750 ° C.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Conventionally, an ion source placed in a focused ion beam device has a structure in which gallium liquid metal is supplied through a needle and ions are emitted from the tip, but it is difficult to always maintain a good wet state. In addition, in consideration of problems such as the fatal loss of the tip due to discharge when a high voltage is applied, the present invention has conceived an emitter structure using a microcapillary without using a needle-shaped emitter. Is. In order to maintain stable ion emission, it is necessary to develop a mechanism that can stably supply liquid gallium contained in the tip of the emitter without excess or deficiency, and not only the structure but also the wetting of the emitter and liquid gallium. The physical properties such as the surface tension of both materials, the viscosity of liquid gallium, and the static pressure corresponding to the filling amount of liquid gallium at the tip of the emitter are affected. First, compatibility with liquid gallium, wetting problems, chemical stability without reaction or compound formation, and ease of processing, glass is used as the material, and the tip of the microcapillary with a smaller diameter is made finer. A structure to provide an opening has been developed. A glass tube having a diameter of about several millimeters is heated, and a tip opening is formed to have a diameter of 5 to 50 μm by a micropipette puller technique. When the opening at the tip is opposed to the extraction electrode and a high voltage is applied, the liquid gallium exposed to the space at the opening is pulled in a cone shape as shown in FIG. It is done from the tip. Incidentally, when no high voltage is applied, it is spherical as shown. The supply of liquid gallium to the opening of the tip is analyzed to be mainly due to the capillary phenomenon, since the capillary is sufficiently thin and thus the influence of the viscosity is large and there is almost no influence of the static pressure. An opening with a diameter of 5 to 50 μm was processed at the tip of a φ2 mm glass capillary, and it was confirmed that liquid gallium in an amount commensurate with the amount of released ions was supplied from the glass microcapillary to the tip opening. . The diameter of the opening at the tip of the capillary is preferably 5 to 50 μm. When the value is larger than this value, the amount of gallium forming the cone tends to increase, the position of the cone tip portion moves, and the ion emission position tends to be uncertain.
[0009]
In the present invention, a matter to be noted is a temperature management problem. In general, in a gallium liquid metal ion source, an oxide film or a sputtered member of the diaphragm member adheres to the gallium surface due to secondary electrons from the counter electrode or the diaphragm member accompanying ion emission. In order to maintain the state of pure liquid gallium, it is sometimes necessary to heat to about 700 ° C., but the melting point and softening point of glass are low, and heating beyond that causes deformation of the capillary. . In general, in order to keep liquid gallium in a good state, it is necessary to heat it every 40 to 100 hours. Since the glass capillary may be deformed during the heating, it is important in the present invention to provide a heating means and to control the temperature so as not to exceed 750 ° C.
[0010]
[Example 1]
An embodiment of the present invention will be described with reference to FIG. Instead of using a needle, a glass microcapillary is used instead to form a gallium liquid metal ion source. First, the manufacturing method uses a quartz glass glass tube with an inner diameter of φ2 mm as a material for the capillary 2, and a supporting substrate. The stem 1 is welded. The stem is made of an insulating material, and in addition to the glass tube, two pins 3 serving as heater terminals are also fixedly arranged. With the tip of the glass capillary 2 heated and softened, the opening 20 is processed to have a diameter of about 5 to 50 μm using a processing method such as a micropipette puller. Since the opening is important, processing is performed with care so that the hole is not blocked. A heater 4 is attached so that a crow microcapillary 2 is wound around the circumference, and both ends are spot-welded to the two pins 3. Thereafter, the glass capillary 2 is filled with gallium 5.
[0011]
Since glass and gallium do not react with each other to form a compound or alloy, the initial liquid state can be maintained without becoming a solid and blocking the opening 20 and without changing the quality of gallium. Further, since glass has good wettability with gallium, the consumed liquid gallium is squeezed out and supplied to the opening of the capillary tip by capillary action. Since the structure of the present invention basically has no needle, the above-mentioned problems caused by a poor wet state or deformation of the needle shape are not relevant in the present invention.
[0012]
FIG. 2 shows an enlarged end portion of the capillary 2. When no high voltage is applied to the extraction electrode, the gallium surface exposed to the outer space at the capillary tip opening 20 has a substantially spherical shape. However, when a high voltage is applied and an attractive force is applied, the exposed surface of gallium is It becomes a cone shape. Then, ions are released from the formed cone tip. Since the cone is formed of liquid gallium itself, even if the tip shape is temporarily deformed by discharge or the like, it is naturally restored by supplying liquid gallium.
As for temperature management, the temperature change due to the energization time in which the heater current is determined is measured by means such as a radiation thermometer, the data is stored in a computer, and the temperature is controlled based on the stored data under the control of the computer. Specifically, in order to maintain the liquid gallium flow state, heating is performed every predetermined time, and in this embodiment, every 72 hours. The procedure is as follows.
(1) Stop emission.
(2) Data related to the heating current and energization time under environmental conditions such as temperature are stored in the computer, and the heating current and energization time corresponding to the situation at the time of execution are determined based on the data, Implement under supervision.
(3) When the predetermined time has passed, the heating is stopped and the zero value of the heater current is confirmed.
(4) Start emission.
[0013]
【The invention's effect】
The Ga liquid metal ion source of the present invention has a structure in which a microcapillary made of glass that contains gallium as an ion material and a fine opening at the center of the tip of the microcapillary, and gallium ions are introduced from the opening. Since it is drawn out, there is nothing equivalent to the needle of the conventional ion source, there is no problem of wetting or tip end defect due to discharge, and there is no consumption of the needle, so that it can be used for a long life. Since liquid gallium consumed by ion emission is supplied to the emitter without excess or deficiency by capillary action due to the mutual physical properties of liquid gallium and glass, stable ion beam irradiation is possible.
[0014]
In addition, the Ga liquid metal ion source of the present invention adopts a configuration in which a temperature control means is provided in a glass microcapillary so as not to exceed 750 ° C., thereby deforming the shape of the microcapillary formed of a glass material. Stable operation can be maintained without any problems. Incidentally, the conventional needle type Ga liquid metal ion source has a life of 1000 to 2000 hours, but the microcapillary type of the present invention has a long life of 5000 hours or more.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is an enlarged view of a tip opening of a microcapillary used in the present invention.
FIG. 3 is a diagram showing a general configuration of a conventional Ga liquid metal ion source.
FIG. 4 is a diagram for explaining a wet state of a liquid metal in a conventional needle emitter.
FIG. 5 is a diagram for explaining a state of discharge deficiency in a conventional needle emitter.
FIG. 6 is a diagram showing a special configuration of a conventional Ga liquid metal ion source.
FIG. 7 is a diagram showing a special configuration of a conventional crystal ion source.
[Explanation of symbols]
1 Stem 3 Pin 2 Microcapillary 4 Heater
20 Tip opening 5 Gallium

Claims (3)

  A liquid microcapillary made of glass that contains gallium as an ionic material, and a structure in which an opening is provided in the center of the tip of the microcapillary, and gallium ions are extracted from the opening. Ion source.   The Ga liquid metal ion source according to claim 1, wherein the glass microcapillary is provided with temperature control means so as not to exceed 750 ° C. 3. The Ga liquid metal ion source according to claim 1, wherein the size of the opening is φ5 to 50 μm.

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