JPS6210840A - Ion source - Google Patents

Abstract

PURPOSE:To enable high intesity and current of an ion source to be obtained as large as that of a liquid metal source, by supplying helium from a liquid helium tank to the tip of an electric field radiation chip utilizing superfluidity of helium. CONSTITUTION:An ion source is composed of a chip 5 for electric field radiation, a lead electrode 6, a liquid helium reservoir 7, and a cooling cylinder 8. The reservoir 7 is kept below 2.1 deg.K by the cooling cylinder 8. And, the liquid helium moves from the reservoir 7 to the tip of the chip 5 through a capillary 11 due to superfluidity, and is taken out as helium ion owing to electrolysis caused by the voltage applied to the lead electrode 6. Thus, the emission efficiency of ion is improved to obtain high intensity and current as large as that of a liquid metal source.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a novel field emission type ion source.
By utilizing the superfluid phenomenon described below, we will improve the supply of helium from the helium reservoir to the tip of the field emission chip, and improve the emission of helium ions by field emission by more than two orders of magnitude compared to conventional technology. That is.

[Conventional technology] First, a conventional field emission type ion source will be explained.

A schematic cross-sectional diagram of a field emission type ion source according to the conventional technology is shown in Part 1.
As shown in the figure, a gas such as hydrogen is blown from the gas supply port 3 onto the field emission chip 2, which has been cooled to about 20°K by the cooler 1, and the gas is adsorbed onto the chip 2. A voltage of several 1.0 kV is applied between the extraction electrode 4 and the chip 2, and the adsorbed gas is ionized and extracted to obtain an ion beam. According to this method, the brightness of the ion beam can be reduced to 10 A.
l2-8r is an improvement of about 6 orders of magnitude compared to conventional ion sources, and about 2 orders of magnitude compared to liquid metal ion sources, which have been attracting attention in recent years as high-brightness ion sources.

[Problems to be Solved by the Invention] However, the biggest problem with this field emission ion source is that a sufficiently large current cannot be extracted. The reason for this is that the rate of gas adsorption to the tip of the field emission tip cannot be sufficiently increased, and the total amount of current obtained is at most μ8, which is about two orders of magnitude lower than that of a liquid metal ion source.

To summarize the problems of the prior art as described above, (1) Field emission type ion sources can obtain high brightness, but cannot obtain a sufficiently large current.

(2) With a liquid metal ion source, the brightness is two orders of magnitude lower, but the current can be two orders of magnitude higher. However, the ion source obtained mainly contains metal ions such as gallium and gold, and it is not possible to obtain light ions such as helium.

[Means for Solving the Problems] The present invention has been made to solve the following two problems of the prior art, and uses helium superfluid to move from the liquid helium tank to the tip of the field emission chip. It supplies helium.

[Function] By cooling liquid helium to a temperature below the temperature at which an electric current occurs, the ion emission efficiency is improved, allowing field effect ion sources to achieve the same high brightness as conventional sources and the same large size as liquid metal ion sources. It becomes possible to obtain electric current.

[Example] The present invention will be described in detail below based on examples.

Example 1 A high brightness, high current ion source according to the present invention is shown in FIG.

This ion source has a field emission chip5. Extraction electrode 6. It consists of a liquid helium reservoir 7 and a cooling cylinder 8. The cooling cylinder 8 keeps the reservoir 7 at a temperature below 2.1'K, and the tip of the chip 5 at a temperature below 2.1°K. Liquid helium passes from the reservoir 7 through the capillary 11 and reaches the tip of the chip 5 due to superfluidity, and is extracted as helium ions by an electric field caused by a voltage applied to the extraction electrode 6. The tip 5 was made of tungsten with a thickness of 100 μmφ, and the curvature of the tip was 0.1 μm or less. The cooling tube 8 was connected to the helium refrigerator 9 via a helium oxide plate 10 having a thickness of 3 mm in order to be in thermal contact with and electrically insulated.

Embodiment 2 FIG. 3 shows another embodiment of the present invention, in which the refrigerator 1
2. The periphery of the cooling cylinder 14 cooled by the insulating plate 13 and the end surface between the capillary 15 and the field emission chip 16 except for 20 are covered with a thermally insulating material 17, and the outer wall temperature of the thermally insulating material 17 is 2.7°K or higher. I will make it happen. The superfluid helium flowing out of the capillary 15 flows toward the field emission chip according to the temperature difference, but does not flow into the area covered with the heat edge material 17, so that the efficiency of using liquid helium can be greatly improved. Therefore, the size of the reservoir 18 can be reduced, and as a result, the size of the entire device can be reduced, so that efficiency can be improved.

Since it is thermally insulated from the extraction electrode 19, thermal efficiency can also be increased. Although alumina (aluminum oxide AQ2o3) is used as the heat insulating material in this embodiment, any material may be used as long as it is an insulator and can withstand ultra-high vacuum.

Embodiment 3 In the above embodiments, liquid helium was stored in a reservoir and ionized by field radiation, but in this embodiment, an ion source equipped with a liquid helium supply system will be described. FIG. 4 shows this embodiment. Freezer 21
．． Heat insulation board 22. Cooling cylinder 23. Reservoir 24. Capillary 25. Needle 26. Extracting electrode 27. Thermal insulation material 28
4 = In the ion source, capillary 2 for supplying liquid helium
It is characterized by having 9. In this ion source structure, the reservoir 24 is not necessarily required, and the liquid helium supply capillary 29 can be directly connected to the capillary 25. In this case, the temperature of the refrigerator 21 is
Setting the temperature lower than No. 3 is the same as in the other embodiments. In this embodiment, the extraction electrode 27 has a
kV was applied, the temperature of the refrigerator 21 was set to 2.1aK, and the cooling cylinder 2
3 By setting the temperature to 2.6'K, the ion source brightness 1
0 A/aJ-sr and a helium ion current of 13 μA could be obtained. When a fine ion beam with a diameter of 0.1 μm was created under these conditions, the output was 400 pA, which was about 40 pA compared to the conventional one.
I was able to obtain a current that was more than twice as large. In order to improve the writing speed, writing was performed using a rectangular shaped beam with an aperture of 0.5 μm. Accelerating voltage 100kV Refrigerator temperature 2.0aK
, needle temperature 2.7' K, ion source brightness 10 A/a#sr, ion current 20 μ
I got an A. We were able to obtain a shaping beam current of 10 μA. This value is a current sufficient to enable direct writing with an ion beam.

[Effect of the invention] So big.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an ion source according to the prior art, and FIGS. 2 to 4 are explanatory diagrams of ion sources according to embodiments of the present invention. 2.5, 16.26... field emission emitter needle,
4,6,1.9,27...Extraction electrode, 3,7A. 15.25...Gas supply capillary, 7,18°24.
...Reservoir, 1. ．． 8, 14, 23...Cooling cylinder, 1
．． 0, 13, 22... Insulating plate, 17, 28... Heat insulator.

Claims (1)

[Claims] 1. It is characterized by being equipped with a refrigerator cooled to 2.1°K or less, a needle that emits ions by electrosonic radiation, and a capillary with an opening near the needle through which superfluid helium flows. ion source.