JPH04106850A - Ion beam apparatus and cleaning method for the apparatus - Google Patents

Abstract

PURPOSE:To make a long time operation possible by installing a heating means to heat an ion optical part such as a convergent lens, etc., in a vacuum container and putting a valve as well as a cooling means between a sub-vacuum pump and the vacuum container. CONSTITUTION:An ion beam apparatus is composed of a heating means 7 to heat an ion optical part and valves 14, 14' and a cooling means 13 put between a sub-vacuum pump 11 and a vacuum container 2. At the time of not operating an ion source 3, the ion source is prevented from becoming high temperature as much as possible and only the ion optical part such as a convergent lens 4, etc., and an insulator are heated to degas positively and the generated gas are positively adsorbed on the cooling surface of the cooling means 13. After that, the sub-vacuum pump 11 and the vacuum container 2 are shut and the vacuum degree of the vacuum container 2 having the ion source 3 is maintained. Consequently, a long time operation is made possible.

Description

[Detailed description of the invention]

[Industrial Application Field 1] The present invention relates to an ion beam device that controls an ion beam emitted from an ion source to irradiate a sample, and is particularly used to clean ion optical system components from dirt caused by ions and ionized substance vapor. This invention relates to an ion beam device and its cleaning method. [Prior Art] An ion beam device emits ions from an ion source,
This is a device that irradiates a target sample with an ion beam. For example, semiconductor device manufacturing equipment that implants ions into a sample by irradiating it with an ion beam or performs sputter etching on the sample, and focused ion beams that focus an ion beam very narrowly and irradiate the sample. Device. Refers to various devices such as a secondary ion mass spectrometer that performs compositional elemental analysis of a sample by irradiating an ion beam and mass spectrometry the secondary ions emitted from the sample. These ion beam devices include ion sources such as liquid metal ion sources and surface ionization sources. Ion optical system components such as focusing lenses, deflectors, and mass separators for transporting and irradiating ion beams to desired locations;
It also consists of insulators to provide electrical insulation. Materials to be ionized in these ion beam devices (
The ionic material (ionic material) varies depending on the type of ion source and may be gaseous, liquid, or solid. Even if the ionization method and the state of the ion material are different, the common specifications required for ion beam equipment are how accurately (positionally and electrically) the ion beam can be irradiated to the target part of the sample. be. In order to achieve this, the electrodes are processed with high precision and a voltage is stably supplied using a high precision power source to control the beam with high precision. When a liquid or solid is used as an ion material in an ion beam device, if the vapor pressure of the material is very high, the degree of vacuum in the container will deteriorate due to evaporation of the ion material itself. Furthermore, if the ionic material is a gas and unionized ionic material flows out from the ion emitting section or other locations, the degree of vacuum in the container will also deteriorate. Regardless of the type of ion source, when the ion source is operated for a long period of time, there is a problem in that thermally evaporated ion material adheres to metal parts such as electrodes and insulators. In other words, the evaporated ionic material adheres to metal parts and obstructs their electrical conductivity, or conversely, adheres to insulators and deteriorates their electrical insulation. This means that due to the reduced electrical conductivity of metal parts, voltage is not supplied to the desired location, reducing the focusing and deflection ability of the ion beam, and deterioration of the withstand voltage of the insulator may cause the voltage balance of the desired electrode to deteriorate. It will destroy the In any case, adhesion of evaporated or flowed ion material to the ion optical system is undesirable and must be avoided from the viewpoint of highly accurate control of the ion beam. For example, in order to remove ionic materials attached to the inside of the device, as described in Japanese Patent Application Laid-Open No. 61-32940,
Ion accelerating electrodes, lens systems, walls of ion source containers, etc.
Devices equipped with a heating mechanism are known. [Problems to be Solved by the Invention] When comparing gallium and cesium, which are used as ion materials for liquid metal ion sources, in terms of vapor pressure at their melting points, the melting points of both elements are 29.8°C and 28.5°C, respectively. While they are almost the same, the vapor pressure at that time is approximately 3 x 10
-311. The vapor pressure of cesium is about 34 orders of magnitude higher, at 3 x 10-' (Pa). Therefore, if an ion beam device is equipped with an ion source using cesium and operated for a long time,
Due to the cesium vapor evaporated from the ion emitting section and the ion material holding section, cesium particles adhere not only to metal surfaces such as lens systems but also to insulators, causing problems such as deterioration of withstand voltage. Further, when cesium ions are generated from a surface ionization type ion source, compounds such as cesium chloride and cesium iodide are often used as ion materials. In the surface ionization type ion source, the ion emitting part is heated to a high temperature of nearly 100°C, so in addition to surface ionization ions, many compound particles are generated that are not ionized and evaporate. When such thermally evaporated compound particles adhere to metal parts such as lenses, they form an insulating film, which interferes with the stable supply of voltage. For example, when applying a high voltage to a lens electrode, the voltage supply terminal is often brought into point contact with the lens, but if an insulating film is formed on the contact area between such a terminal and the electrode, the voltage This causes the problem that the ion beam cannot be stably supplied and desired ion beam control cannot be performed. Regarding conventional equipment, from the above-mentioned point of view, metal parts,
There are improvements in the shape of parts that make it difficult for evaporated substances such as ionic materials to adhere to insulating parts. For example, if particles are flying in a straight line, providing a barrier near the insulator can prevent the flying particles from contaminating the insulator, and is commonly used. On the other hand, particles floating non-linearly in a vacuum container cannot be prevented from adhering to the insulator by the barrier described above. In addition, the reservoir in which the ionic material is stored in the liquid gold ion source must be as tightly sealed as possible, and structural measures must be taken to suppress its evaporation and scattering. To deal with this, attempts have been made to make the reservoir airtight by putting a lid on it, but the tip of the emitter, which is the ion emitting part, has a small exposed area, but the liquid/ion material is exposed in the vacuum and evaporates. ing. Therefore, even if the above-mentioned ionic materials adhere to the ion optical components, it is necessary to take measures to periodically remove them, but conventional devices have not taken this into consideration. There wasn't. In particular, such measures have been taken while maintaining the degree of vacuum without interrupting the scheduled operation of the device, and the operating conditions such as applied voltage and obtained ion current value can be reproduced and maintained during ion beam operation, achieving high accuracy. It was desired that ion beam control could be sustained. The present invention has been made in view of the above-mentioned problems. 1. An object of the present invention is to remove excess evaporated matter from the ion optical system when the ion source is not in operation, and to remove it when the ion source is not in operation. It is an object of the present invention to provide an ion beam device and a cleaning method therefor that enable long-term operation of an ion source and maintain highly accurate ion beam control by reducing deterioration.

[Means to solve the problem]

In an ion source device comprising an ion source housed in a vacuum container equipped with main and sub vacuum pumps, ion optical parts such as a focusing lens, etc., a heating means for heating the ion optical parts, the sub vacuum pump and the above The above problem can be solved by constructing the ion beam device from a valve and a cooling means installed between the vacuum vessels. Further, in these ion beam apparatuses, particularly when the ion source is a liquid metal ion source 1 surface ionization type ion source, the effect is particularly seen. Furthermore, the above object is achieved even if the material to be ionized used in these ion sources is an alkali metal, in particular cesium. In addition, using the ion beam device consisting of these components, there is a process of heating ion optical components such as a focusing lens when the ion source is not operating, and a process of opening a valve installed between the sub-vacuum pump and the vacuum vessel. After proceeding with the step of operating the cooling means and the step of evacuating the degas in the vacuum container with the sub-vacuum pump, the valve installed between the sub-vacuum pump and the vacuum container is closed and the inside of the vacuum container is removed. The above problem can be solved by a cleaning method for an ion beam device that includes a step of maintaining a vacuum.

[Function] Heating to clean the ion optical system cannot be performed because it lowers the degree of vacuum in the vacuum chamber, making the beam unstable during ion source operation, or introducing impurities into the beam. . Another option is to heat the entire vacuum container, but if the vapor pressure of the ionic material is high even when heated to about 100°C, it will not only further pollute the inside of the vacuum container, but may
It also leads to depletion of ionic materials. Therefore, the main focus of the ion beam device cleaning method according to the present invention is to prevent the ion source from heating up as much as possible when the ion source is not in operation, and to actively heat only the ion optical parts such as the focusing lens and the insulator. The generated degas is actively adsorbed on the cooling surface of the cooling means. Thereafter, the sub-vacuum pump and the vacuum container are shut off to maintain the degree of vacuum in the vacuum container containing the ion source. With such a device configuration and method,
Contamination inside the vacuum chamber, especially on ion optical parts such as a focusing lens and on the insulator surface, is improved. In addition, by using automatic operation instructions that preset these steps, the interior of the ion beam apparatus can be cleaned during periods when the ion beam apparatus is stopped, such as at night, so that highly accurate ion beam control can be reproduced and maintained during the first operation. [Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 1 shows an ion beam apparatus according to an embodiment of the present invention. The apparatus 1 of this embodiment is a so-called focused ion beam apparatus, and is equipped with an ion optical system such as an ion source 3, lens systems 4 and 5, and a deflector (not shown) in a vacuum container 2. The emitted ions 6 pass through an ion optical system including focusing lenses 4 and 5, a deflector (not shown), a blanker (not shown), and an aligner (not shown) to reduce the beam diameter to 1 micron or less. This is a device that irradiates the sample 8 with a very narrow ion beam. The vacuum container 2 is evacuated by main vacuum pumps 9, 10, sub vacuum pump 11, roughing vacuum pump 12, and the like. The ionic material used in this example was simple cesium. Cesium is an ion that must be present together with oxygen ions as a -order ion beam when performing secondary ion mass spectrometry of a sample. Surface ionization type ion sources and liquid metal ion sources are often used as ion sources for emitting cesium ions. Here, liquid metal ion source 3
(30) was used. A detailed explanation of the principle and structure of the liquid metal ion source 30 will be omitted here, but as shown in FIG. This is an ion source in which a high electric field is formed by an extraction electrode 33 at the tip of the ion source, and the ion material 32 is ionized by the high electric field. The material 32 to be ionized is held in a reservoir called a reservoir 34, and the ions 35 can be released for a long period of time. Cesium is emitted from the liquid metal ion source having such a structure, and the sample is irradiated with a focused cesium ion beam using the ion optical system as described above. After operating the cesium liquid metal ion source for a long time, the ion optical system components are heated and cleaned. At this time, in order to clean the inside of the vacuum container 2, for example,
It is also possible to heat the entire vacuum container from outside the vacuum container (so-called bakeout) as in Japanese Patent No. 32940, but baking out the entire vacuum container would also increase the ion source temperature. On the contrary, it results in active evaporation of cesium. Therefore, it is not a good idea to bake out the entire vacuum vessel, and we used a method of periodically baking out only the ion optical system, which is the most important for ion beam control. To bake out the lens system 4, as shown in FIG. 3(a), a ceramic heater 42 as the heating means 7 is embedded in the insulator 41 which is close to the ground potential, or a heater 42 is inserted into the insulator 41 (not shown). It was fixed in contact with the When the ion source is not operating, the ceramic heater 42
Raise the temperature of the electrodes to about 150°C. Insulator 41
is made of alumina and the electrodes are made of stainless steel, and their thermal conductivity is almost the same, so the electrode group (lens system) 4 is heated almost uniformly by thermal conduction without locally becoming high temperature. . Further, since the lens system 4 and the ions g3 are spatially separated, there is no need to worry about the temperature of the ion source 3 rising or excessive evaporation of the ion material 32 even when the lens system 4 is baked out. In addition, in order to prevent the heated heat from being taken away by the vacuum container with a large heat capacity, a thermal insulator 43 is inserted between the lens system 4 and the vacuum container that supports it, as shown in FIG. 3(b). The heating effect will be better. As described above, now that the basic idea of actively heating only the ion optical system components has been disclosed, other means and improvements similar to this can be easily conceived. In order to actively adsorb degassed gas produced by baking out the lens system 4, a cooling means 13 was installed immediately before the sub-vacuum pump 11. Specifically, the sub-vacuum pump 11 is a turbo-molecular pump, and the cooling means 13 is a liquid nitrogen trap. Further, a valve (gate valve) 14 is provided between the cooling means 13 and the vacuum vessel 2, and the sub-vacuum pump 11 is normally operated and opened when the lens system 4 is baked out, and is closed when the ion source is operated. The cooling means 13 is operated only when printing out the lens system 4,
When the valve 14 is closed, the temperature is raised to room temperature or higher, the adsorbed gas particles are released, and the sub-vacuum pump 11 exhausts the air to activate the gas adsorption surface of the cooling means 13. By this operation, the lens system 4 can be cleaned and the degree of vacuum can be maintained without causing the gas once adsorbed during baking to flow back into the vacuum container 2. The above-mentioned cleaning operation is performed at night when the ion beam device is not in operation, and involves starting the operation of the sub-vacuum pump 11 and the roughing vacuum pump 12, charging liquid nitrogen to the cooling means 13, opening the valve 14, and cleaning the ceramic. Start and end of heating of heater 42, closing of valve 14, cooling means 13
A series of operations such as stopping the supply of liquid nitrogen to the tank, stopping the operation of the sub-vacuum pump 11 and the roughing vacuum pump 12, etc. are all computer-controlled, and there is no need for an operator to perform each operation. Further, for setting the completion of baking, two methods were used: one method was to finish baking when a preset temperature was reached, and the other method was to finish baking by monitoring the degree of vacuum in the vacuum container. The latter method will be specifically explained below. The degree of vacuum before starting the baking operation is approximately I x 10-g Tor.
However, when the bakeout operation is started, the deposits attached to the ion optical components such as the insulators evaporate, and the degree of vacuum inside the vacuum container begins to decrease. For example, set the baking temperature to 18
If the temperature is fixed at 0°C and left for a long time, the amount of deposits will decrease and the degree of vacuum will start to rise again. In the example, the set temperature for baking out was 180°C, and the baking out was completed when the set vacuum level at the time of recovery of the vacuum level reached I x 10-'Torr. This lean operation was performed every 100 hours of cumulative operating time of the ion beam device. As a result, when the lean method was not used, it was 150 to 2
After 00 hours of operation, the withstand voltage of the insulator between the electrodes deteriorates,
Although the desired ion beam control could not be achieved due to the inability to supply the specified voltage, by using the above-mentioned method, no problem like the conventional one would occur even after a cumulative time of over 1000 hours.
The effectiveness of this method was demonstrated. Effects of the Invention According to the present invention, the ion beam apparatus can be operated for a long period of time by preventing excessive adhesion of evaporated matter to the ion optical system and reducing deterioration of withstand voltage of insulators and the like.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing an ion source device according to an embodiment of the present invention, FIG. 2 is a longitudinal cross-sectional view showing a schematic configuration of a liquid metal ion source, and FIG. 3 is a longitudinal cross-sectional view of main parts of an embodiment of the present invention. It is a front view. Explanation of symbols 1... Ion beam device, 2... Vacuum vessel, 3...
- Ion source, 4... Focusing lens system, 5... Focusing lens system, 6... Ion beam, 7... Heating means, 8...
...Sample, 9.. Main vacuum pump, 10.. Main vacuum pump, 11.. Sub vacuum pump, 12.. Roughing vacuum pump, 13.. Cooling means, 14.14'.
... Valve, 30... Liquid metal ion source, 31... Emitter, 32... Ionic material, 33... Extraction electrode, 34... Reservoir, 35... Ion, 41... Insulator, 42... Ceramic heater, 43... Thermal insulator

Claims (1)

[Scope of Claims] 1. In an ion beam device consisting of an ion source, ion optical parts such as a focusing lens, etc. housed in a vacuum container equipped with main and sub vacuum pumps, the focusing lens, etc. are placed in the vacuum container. heating means for heating the ion optical component of the
An ion beam device comprising a valve and cooling means installed between the sub-vacuum pump and the vacuum container. 2. The ion beam device according to claim 1, characterized in that a ceramic heater is built into a high voltage insulator installed in the ion optical system. 3. The ion beam device according to claim 1, wherein the heating source is brought into contact with a metal component at ground potential installed within the ion source optical system. 4. The ion beam according to claim 1 or 2, characterized in that a thermally insulating material is interposed between the ion optical component and the support for the ion optical component connected to the vacuum vessel. Device. 5. An ion beam device according to claim 1, characterized in that the ion source is, in particular, a liquid metal ion source. 6. An ion beam device according to claim 1, wherein the ion source is particularly a surface ionization type ion source. 7. The ion beam device according to any one of claims 1 to 6, wherein the material to be ionized used in the ion source is particularly an alkali metal or a compound thereof. 8. An ion beam device according to claim 7, wherein the alkali metal or compound thereof to be ionized is particularly composed of simple cesium or a cesium compound. 9. Claims 1 to 8, characterized in that the ion beam device is particularly a secondary ion mass spectrometer.
The ion beam device according to any one of paragraphs. 10. The ion beam device according to any one of claims 1 to 8, characterized in that the ion beam device is particularly a focused ion beam device. 11. When the ion source is not in operation, a step of heating ion optical components such as a focusing lens; a step of opening a valve installed between the sub-vacuum pump and the vacuum container and operating a cooling means; and a step of operating the cooling means; A method for cleaning an ion beam device, comprising a step of evacuating the degassed inside with a sub-vacuum pump, and a step of closing a valve installed between the sub-vacuum pump and the vacuum container after a certain period of time. 12. In the above method for cleaning an ion beam device, the heating start time, end time, heating temperature, and operation start time of the sub-vacuum pump in the heating step of the ion optical component;
A method for cleaning an ion beam device, characterized in that these steps are automatically performed by setting valve opening time, cooling start time, etc. in advance in a computer. 13. The ion device according to claim 11 or 12, wherein the degree of vacuum in the vacuum container is detected, and when a preset degree of vacuum is reached, the heating process of the ion optical component is terminated. How to clean the beam device.