JPS63236244A - Liquid metal ion source - Google Patents

Abstract

PURPOSE:To improve both breakage of an ionized material and adhesion of an oxide and to enable the drawing of beams stably for long hours by forming a means in which a tip of a needle is cleaned and a needle up-and-down mechanism for drawing the needle into a capillary. CONSTITUTION:When a liquid metal ion source is operated for long hours, both breakage 10 of an ionized material and adhesion of an oxide 11 to the ionized material occur to make beam emission be instable and the emission is stopped at last. Accordingly, thermions 8 generated from a filament 7 are first made to impinge on a tip of a needle 4 by an electric field and so the tip is cleaned. The needle 4 is further drawn into the ionized material inside a capillary 1 and protruded again, and next the surface of the needle is coated with the ionized material again. A clean film of the ionized material, in which no impurities are contained, can be formed on the surface of the needle, so that beams can be drawn stably again. Thus, beams made instable can be stabilized, and besides the beams can be drawn stably again even if beam emission is completely stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid metal ion source, and particularly to a liquid metal ion source that has a long life and is suitable for stably extracting ions over a long period of time.

[Conventional technology]

Most liquid metal ion sources conventionally used in focused ion beam devices are needle-type ion sources shown in FIG. Also, in some cases, a medium-sized laser needle type ion source shown in Fig. 5 is used. In any of these conventional ion sources, the emitter needle is fixed. The ionized substance melted at the top is supplied to the tip of the needle by capillary action, and is drawn out as ions by application of a high voltage. At this time, in order to extract the ion beam stably for a long time, it is necessary to stably supply the ionized substance to the needle tip. In this regard, conventional ion sources have had the problem shown in FIG. 4. In other words, a break 10 of the ionized substance occurs in the middle of the needle, or an oxide 11 of the ionized substance forms at the tip of the needle, resulting in insufficient supply of the ionized substance and unstable ion release. Ta. Figure @5 shows typical changes in the 5-beam current as the emission time elapses when using a conventional ion source. Immediately after the start of emission, the beam is stable for a while, but gradually the above problems occur and the beam becomes unstable.
K suddenly stopped emitting completely. Conventional ion sources have fixed needles, and have no effective means to correct the occurrence of discontinuities in the ionized material or build-up of oxide layers and to stabilize the beam again.

On the other hand, as an ion source provided with a mechanism for moving the needle up and down, there is an ion source described in Japanese Patent Application Laid-Open No. 156344/1983. However, although countermeasures against discontinuation of the ionized substance have been taken in this ion source (-JIfW), no consideration has been given to the addition of an oxide layer.

[Problem that the invention seeks to solve]

Conventional ion sources with a fixed needle temperature do not have a means to improve the problem when discontinuities in ionized substances or adhesion of oxides occur. It was impossible to draw out the beam stably.

The ion source described in Japanese Patent Publication No. 58-156544 has an up-and-down mechanism that costs 121 dollars, and consideration has been given to improving the discontinuity of ionization. However, in case 1 shown in Figure 6, by pulling the needle into the ionized material reservoir and pushing it out again, the discontinuity of the ionized material can be improved, but the oxide layered at the tip cannot be improved. .

On the other hand, as a result of detailed observation of the needle light weight of ion sources where the beam became unstable or the beam emission stopped, we found that
They found that in most cases, there are several layers of oxides of ionized substances at the tip of the "smell" C=-dol. Therefore, in order to extract the beam stably for a long time, it is essential to improve the oxide layer, which is the main cause of beam instability.

An object of the present invention is to provide a liquid metal ion source that has a function of improving both the discontinuity of ionized substances and the formation of oxide layers, and can stably extract a beam for a long period of time.

[Means for solving problems]

The above objectives are achieved by cleaning the oxide deposited on the needle tip and recoating the needle with ionized material. Therefore, the present invention is characterized by providing means for cleaning the tip of the needle and a needle up and down mechanism for drawing the needle into the capillary.

[Effect]

The tip of the needle to which the oxide of the ionized substance has adhered is cleaned, for example, by electron beam bombardment to expose a clean surface of the needle member. The cleaned needle is then drawn into the ionized substance in the capillary and extruded again. This K coats the surface of the needle with a clean ionized substance free of oxides, making it possible to stably extract the beam again.

〔Example〕

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

<Example 1> FIG. 1 shows the basic principle of an embodiment of the present invention.

This embodiment uses electron beam impact as the needle tip cleaning mechanism. Now, when a liquid metal ion source is operated for a long time, as shown in FIG. 1 (α), fragments 10'P of the ionized substance and adhesion of oxide 11 of the ionized substance occur, making beam emission unstable. Eventually the emission stops. First, thermionic electrons 8 generated from the filament 7 are caused to collide with the tip of the 21 dollar using an electric field to clean the tip. Furthermore, the needle is drawn into the ionized material within the capillary and ejected again to recoat the needle surface with the ionized material. This makes it possible to form a clean film of ionized material on the needle surface without any impurities, making it possible to stably extract the beam again. According to the present invention, it is possible to stabilize a beam that has become unstable, and even when beam emission has completely stopped, it is possible to stably extract the beam again.

Figure N7 shows a configuration diagram of this embodiment. The needle 4 is connected to a micrometer 14 via a coupling 13 vacuum-sealed with an O-ring 12, and can be moved up and down from outside the vacuum. The needle height is controlled by controlling the number of pulses sent to a pulse motor 15 connected to a micrometer 14 by a needle position controller 20. Further, the needle 4 is bombarded with thermoelectrons from the filament 7 provided under the extraction electrode 6, thereby cleaning the tip of the needle 4. Now, when extracting ions under normal operating conditions, the ion accelerating power supply 25 first applies energy to the ejected ions. Heater power supply 21 in high voltage insulation box 27
, the ion extraction power source 23, and the filament power source 24 further output respective voltages based on the ion energy potential given by the ion accelerating power source 25. A current is passed from the heater power supply 21 to the heater 17 through the current introduction terminal 18 to melt the ionized substance in the evacuation unit 1.

Furthermore, a voltage is applied to the extraction electrode 6 by the ion extraction power source 25, and an ion beam is extracted from the tip of the needle 4. Ions are continuously ejected in this state, but if ion ejection continues for a long time, the ion ejection becomes unstable as described above. Therefore, first, a current is applied to the filament 7 by the filament power source 24, and the tip of the needle 4 is bombarded with thermoelectrons generated by the filament 7 to perform cleaning. Then, using the needle position controller 20, the needle 4 is drawn into the molten ionized material in the capillary 1 and ejected again to recoat the ionized material.

This makes it possible to stably release ions again. Note that the operation for stabilizing the beam can be completed within a few minutes. FIG. 8 shows measurement results that actually confirmed the effect of the present invention using this ion source. The horizontal axis shows the elapsed time after the start of ion ejection, and the beam current became unstable after 3 hours. Therefore, when 3 hours and 30 minutes had elapsed after the start of emission, a beam stabilization operation according to the present invention was performed, and a stable beam could be obtained again. In this experiment, the beam stabilization operation was performed manually, but with the power supply and controller configured as shown in FIG. 7, it can be automatically controlled by the CPU. in this case.

Since the inside of the high-voltage insulating box 27 is floating at a high voltage, data transfer between each device in the high-voltage insulating box and the CPU is performed via the original data link 26. Further, the beam current of ions emitted from the needle 4 is measured through the heater power source 21 using a beam ammeter 22 provided between the output potential of the ion accelerating power source 25 and the heater power source 21 . The measured value of the beam current by the beam current meter 22 is transferred to the CPU, and when the stability of the monitored beam current value falls below a certain value, the beam stabilization operation according to the present invention is controlled using the KCPU. do. With this trap, it is possible to continue emitting ion beams while always maintaining stability above a certain value.

On the other hand, in experiments to confirm the effects of the present invention, it was discovered that by performing a beam stabilization operation in advance before the beam becomes unstable, the beam can be stably extracted continuously for a considerable period of time. FIG. 9 shows an example of the measurement results.

This has nothing to do with the stability of the beam;
This is an example in which the beam stabilization operation was performed a total of three times, and the beam was drawn out continuously for more than 10 hours. The beam stability for 10 hours is within a certain range, which is a sufficiently practical value for a focused ion beam device.

In this way, it is possible to operate the ion source stably for a long time by repeating the beam stabilization operation before the beam becomes unstable. On the other hand, the present experiment revealed that in order to constantly stabilize the beam, it is necessary to perform the beam stabilization operation once every 5 hours.

Here, as a typical LSI wiring processing, 5μm x 5P
Assuming machining to a depth of 6 μm, the machining time will be 5 minutes.

Therefore, the beam stabilization operation is required approximately once every 50 processing operations, which is sufficiently practical.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to improve both the discontinuity of the ionized substance and the adhesion of oxides, etc. of the ionized substance in the liquid metal ion source, so that an ion beam can be extracted stably for a long time.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the principle of the present invention, Figure 2 is a schematic diagram of a conventional needle type ion source, Figure 3 is a schematic diagram of a conventional capillary needle type ion source, and Figure 4 is a problem with the conventional ion source. 5 is an explanatory diagram of changes in the emitted beam current of a conventional ion source, FIG. 6 is an explanatory diagram of problems in the known example, FIG. 7 is a configuration diagram of an embodiment of the present invention, and FIG. FIG. 9 is a diagram showing the effects of the present invention. 1... Capillary 2... Ionized substance 4.
...Needle 6...Extraction electrode 7...
Filament 8... Thermionic electron 10... Interruption of ionized substance 11... Oxide of ionized substance 12
...O-ring 15...Coupling 14
... Micrometer 15 ... Pulse motor 16
...Insulating material 17...Heater 1B...
Current introduction terminal 19... CPU 20... Needle position controller 21... Heater power supply 22... Beam electric R meter 23... Ion extraction power supply 24... Filament power supply 25... Ion acceleration power supply 26. ...Optical data link 27...High voltage insulation box 1 diagram Oo O. Figure 2 Figure J Figure 4 sl! l s Mo 6 Figure 7 Figure 8 Figure 9 Aeon Narita time (1r)

Claims (1)

[Claims] 1. In a capillary needle type liquid metal ion source having a capillary having a needle as an emitter and an ionized substance reservoir, a means for moving the needle up and down to draw the needle into the capillary, and a tip of the needle are provided. A liquid metal ion source characterized in that it is provided with means for cleaning and removing impurities such as oxides of ionized substances. 2. As a means of cleaning the needle tip,
The liquid metal ion source according to claim 1, which is an electron beam bombardment means. 3. As a means of cleaning the needle tip,
The liquid metal ion source according to claim 1, which is a condensed light irradiation means. 4. As a means of cleaning the needle tip,
The liquid metal ion source according to claim 1, characterized in that it is an ion bombardment means using plasma. 5. In a capillary needle type liquid metal ion source having a capillary with a needle as an emitter and an ionized substance reservoir, there is a means for moving the needle up and down to draw the needle into the capillary, and a means for cleaning the tip of the needle and oxidizing the ionized substance. A liquid metal ion source characterized in that it is provided with means for removing impurities such as substances and means for measuring emitted ion current.