JPS62278744A - Ion gun for focusing ion beam device - Google Patents

Abstract

PURPOSE:To make possible to increase the current density of an ion beam, by connecting a heat radiation shield which encloses the ion beam generation part to a refrigerator and also, making the shield have a specified wall thickness so that it can cool the vicinity of the beam generation part. CONSTITUTION:Through a nozzle 2 Helium gas or the like is introduced to a space airtightly sealed by a heat radiation shield 4, and by applying a high voltage between a needle-shaped electrode mounted on a refrigerator 12 through an insulation sapphire 13 and a drawing electrode 3, an ion beam is drawn out. Thus an ion gun for a focusing ion beam device is constituted. In this case, the heat radiation shield 4 is formed with copper of about 5mm, and its top part is closely attached to the refrigerator 12 ranging a wide avea. Also, the relation between a radius R of the shield 4 and a radius of curvature r of a needle electrode holder 14 is made to be R > 10r. Thus, cooling effect of the shield 4 is increased and also, unnecessary discharge is avoided so that the ion current density can be increased.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a focused ion beam generator.
In particular, it relates to the structure of an ion gun that can obtain a large ion current density.

[Summary of the invention]

The present invention provides a focused ion beam generator using a gas ion source, in which a thermal radiation shield member surrounding an ion beam generating section and having a predetermined thickness is connected to a refrigerator, and the thermal radiation shield member is provided at least near the ion beam. By cooling the ion beam, it is possible to obtain an ion beam current with a high current density without causing problems such as discharge.

[Conventional technology]

As the development of VLSI advances to 4M DRAM, finer pattern forming technology becomes increasingly important.

About 1μm for optical methods, 0.5μm for electron beam exposure
There is a limit to the formation of patterns as fine as about m. There 0
．． Focused ion beam processing technology (Focused Ion BeamFa) enables pattern formation of approximately 2 μm.
brication Technology: FI
BT) suddenly started to attract attention. The idea is to use an ion beam focused to about 0.1 μm for ion implantation and etching.If this were realized, masks and photolithography would be unnecessary in the semiconductor manufacturing process, dramatically simplifying the process. This is because the drying process progresses and it is possible to respond to finer patterns. Considering phosphorography, it is also possible to improve the proximity effect and resist anger, which are current technical hurdles in electron beam exposure, for resist exposure.

Compared to electrons, ions have different properties, masses, and specific electric charges depending on the ion species, so they can be used in a much wider range of applications than ion beams. Semiconductor manufacturing technologies include resist exposure, maskless milling, maskless ion implantation, maskless deposition, and STM (Scanning Ion Micors).
It has the potential to be applied to almost all processes of semiconductor device manufacturing, such as photocopy.

This can further be said to have the potential to fully automatically manufacture semiconductor devices in a dry system, that is, in a vacuum, without using a resist. This means that there is a possibility that semiconductor devices can be manufactured at the laboratory level without requiring a large number of expensive equipment like current semiconductor manufacturing lines.

The advantages of FIBT can be roughly divided into the following two categories.

(1) Properties as a charged beam Similar to electron beams, since the ion beam can be focused and deflected by an electron optical system, it is possible to draw patterns under computer control, making it possible to form fine patterns. Furthermore, since a parallel beam can be easily obtained, penumbra blurring, which is a problem in X-ray exposure, does not occur even if a batch exposure is performed using a mask.

(2) Characteristics of atoms (elements) If patterns are drawn using an ion beam of B, As, or the like, an innovative process called maskless ion implantation can be realized. Also,
Since ions have an order of magnitude greater mass than electrons, there is little scattering in the resist and from the substrate during resist exposure, and there is very little so-called proximity effect that degrades the resolution of electron beam exposure. Furthermore, maskless etching can be realized by utilizing the substrate etching effect of an ion beam.

FIG. 3 shows a block diagram of an example of a focused ion beam device. The ion source is equipped with an electric field type separation liquid metal ion source that is a high-intensity ion source, and the ion beam is focused by two stages of electrostatic lenses. It has a beam alignment electrode and a beam deflection unit that use electrostatic deflection, and a built-in mass separator that allows only the necessary ions to be selected. A secondary electron detector is provided near the sample stage, and the sample can be observed and aligned by scanning the sample with an ion beam.

(Electronic Materials June 1984 issue p, p, 39-I),
p, 4 The configuration of the ion chamber of a conventional gas ion source type focused ion beam device is shown in FIG.

The tip of the emitter 1 (needle electrode) is sharpened to a sharp point with a radius of curvature of 500 to 1000 by electric field polishing. A gas such as He is introduced from the gas nozzle 2 into a space sealed with a thermal radiation shield 4, and the inside of the device is heated to about 10-7
When a DC high voltage of about 30 KV is applied between the emitter 1 and the extraction electrode 3 in a TorrO high vacuum state, a strong electric field is generated at the tip of the emitter 1, and gas molecules (atomic ) is ionized, and an ion beam of He or the like is obtained from the hole 4 of the extraction electrode 3.

A refrigerator tip 12 made of a copper plate cools the emitter 1 through an insulating sapphire 13 having good thermal conductivity and an emitter holder 14. A thermal radiation shield 4 that covers from the side wall of the refrigerator tip 12 to the emitter l
is made of a copper plate with a thickness of 0.5 to 1 mm, which cuts off heat radiation from the outside and keeps the temperature of the emitter 1 at a low temperature.

The thermal radiation shield 4 is kept at ground potential and the emitter l
is a lead wire inlet 15 provided in the thermal radiation shield 4.
A DC voltage of about 30 KV is applied by a lead wire introduced from the main body.

[Problem that the invention seeks to solve]

Usually, helium gas is used as an ion source, but
In this case, in order to increase the ion beam current, it is required that the emitter of the ion gun be frozen to about 5 to IOK at the tip. In the past, when bulk electrodes were used as emitters, cooling efficiency was not so much of an issue, but now that needle-like electrodes are being used as emitters, it is important to consider how to cool needle-like emitters, which have poor cooling efficiency. The big question was whether to do so. When the conventional ion gun structure for bulk electrodes is used as a needle electrode, the distance between the thermal radiation shield and the high potential part is narrow, and when a high voltage is applied to the emitter, a discharge occurs between the high potential part and the thermal radiation shield. There were drawbacks such as the emitter tip being damaged and the ion beam current stopping.

Also, when the high voltage applied to the emitter is lowered to 20KV, the ion beam current becomes
Like 1″7I, it falls to less than half. Therefore,
In order to maintain high throughput of the focused ion beam device, it is desirable to apply a voltage of 30 KV or more to the ion gun.

The heat radiation shield of the conventional structure has its own temperature of about 50℃, so it cuts off the heat radiation from the outside and emitter 1
temperature cannot be lowered sufficiently.

[Means for solving problems]

The present invention provides an ion beam generator of a gas ion source type in which an ion beam generating section is disposed in a refrigerator via an insulating material, in which a thermal radiation shield member surrounding the ion beam generating section is connected to the refrigerator. At the same time, the above-mentioned problem was solved by making the thermal radiation shielding member have a predetermined thickness and cooling at least the ion beam generating portion (bone portion) of the thermal radiation shielding member.

[Effect]

In the structure of the ion gun of the present invention, except for the extraction electrode 3 around the tip of the emitter 1, the distance between the high potential part and the thermal radiation shield 4 at the ground potential is set sufficiently large. No unnecessary discharge occurs even if a high potential of 30 KVO is applied to.

The hole of the lead wire inlet 15 through which the lead wire for supplying high potential to the emitter 1 is passed is sufficiently large so that no discharge occurs there. On the other hand, since the radius R of the heat radiation shield of the ion gun of the present invention shown in FIG. can be ignored.

Moreover, since the thickness of the thermal radiation shield 4 of the present invention is thicker than that of the conventional shield, the refrigeration efficiency is improved.

〔Example〕

FIG. 1 shows the ion gun of the present invention. A gas serving as an ion source, such as TL, is introduced from a gas nozzle 2 into a space surrounded by a thermal radiation shield 4. The thermal radiation shield 4 made of copper with a thickness of 5 mm is in close contact with the refrigerator tip 12 over a wide area at its leading edge, improving the cooling efficiency of the thermal radiation shield. The radius R of this thermal radiation shield 4 is 7.5
cm, height is 15 CIt+, and weight is 2 kg.

Its surface is mirror-finished and Ni-plated to better reflect external heat radiation. At its center, an extraction electrode 3 made of MO or the like, which does not easily generate secondary electrons, is attached. The radius of the lead wire inlet 15 is 1 cm, and the angle looking into it from the emitter 1 is a half-angle less than π15 rad.

The refrigerator tip 12 had an Ile temperature of 4.2K, the thermal radiation shield 4 had a temperature of 30K, and the emitter 1 had a temperature of 10K.

A high voltage of 30 KV is applied to the emitter holder 14 provided on the insulating sapphire 13 through an external lead wire. The 11e gas at 10-'Torr is ionized by the electric field between the extraction electrode 3 at ground potential and the emitter 1, and an ion beam is generated.

In order to prevent unnecessary discharge, in the present invention,
The radius of curvature r of the emitter holder 14 and the radius R of the thermal radiation shield 4 have a relationship of R>lor. In other words, the radius of curvature r of the emitter holder 14 is prevented from becoming too large compared to the radius R of the thermal radiation shield 4.

〔effect〕

In order to show the effects of the ion gun of the present invention, a plot of the relationship between applied potential and ion current is shown in Figure 2.
It can be seen that the ion gun of the present invention provides an ion current that is 20% or more higher than that of the conventional example. This is because the structure of the ion gun of the present invention does not cause unnecessary discharge even when a high potential of 30 KV is applied, and the fact that the ion gun near the emitter 1 is
This is due to the fact that it is cooled below 0.

In addition, in the present invention, the thickness of the thermal radiation shield 4 is set to 5 m.
1, the temperature of emitter 1 can be lowered to IOK in 3 hours after the start of operation.

[Brief explanation of drawings]

FIG. 1 shows the ion gun of the present invention. FIG. 2 shows the effect of the ion gun of the present invention. FIG. 3 shows a block diagram of a focused ion beam device. FIG. 4 shows a conventional ion gun. 1... Emitter 2... Gas nozzle 3
... Extracting electrode 4... Heat radiation shield 5... Accelerating electrode 6... Condensing lens 1
0... Objective lens 11... Deflection electrode 1
2... Refrigerator tip 13... Insulating sapphire 14... Emitter holder 15... Lead wire inlet

Claims (1)

[Claims] In a gas ion source type ion beam generation device in which an ion beam generation section is disposed in a refrigerator via an insulating material, a thermal radiation shield member surrounding the ion beam generation section is connected to the refrigerator and the thermal radiation An ion beam generation device characterized in that the shield member has a predetermined thickness, and at least a portion of the thermal radiation shield member near the ion beam generation portion is cooled.