1. Field of the Invention
The present invention relates to an X-ray inspection apparatus, and specifically, to an X-ray microscopic inspection apparatus with ultra-high resolving power using an electron source for emitting a high brightness electron, to which new functions such as a CT (computerized tomography: X-ray tomography) function with high resolving power never before possible, an elemental analysis function utilizing a fluorescent X-rays, a target switching function capable of selecting a target depending on a purpose of inspection with a plurality of metal targets are added.
2. Description of the Related Art
As an inspection apparatus utilizing an X-ray, various kinds of industrial inspection apparatuses such as an X-ray microscope, a foreign body inspection apparatus, a fluorescent X-ray analyzing apparatus, and medical X-ray apparatuses such as an X-ray diagnostic apparatus are known. FIG. 1 shows a construction example of a conventional X-ray inspection apparatus. The X-ray inspection apparatus in this example is designed so as to obtain a micro X-ray point source 23a by accelerating electrons Re from an electron source 21b by applying a high voltage between a grid 21a and an anode 21c using a thermionic emission cathode 21b as the electron source, and then focusing the electrons Re on a target 23 formed of a thin plate of high-melting point metal such as tungsten by electron lenses 22. Subsequently, the inside of a sample (object to be inspected) 10 is projected in magnification mode by using the point-form X-ray Rx generated from the X-ray target 23a and the microstructure inside of the sample is subjected to non-destructive perspective inspection.
In the conventional X-ray microscopic inspection apparatus that the applicant has developed and commercialized, a two-stage reduction system using lenses having as small spherical aberration and chromatic aberration as possible for the focusing lens system and a LaB6 (lanthanum hexaboride) cathode having an advantageous character as a thermionic source are adopted, and further, an image intensifier with high sensitivity is used, and thereby the resolving power becomes less than 1 μm and achieves about 0.4 μm. This resolving power is the highest value on a global basis as a practical X-ray inspection apparatus at present (the degree of 0.1 μm is the highest value if the exposure time is neglected), and the value may be assumed as the technical limit under the present circumstances. Therefore, the resolving power better than 0.1 μm expected in the invention can not be implemented by the conventional technology (see the following description of the non-patent documents).
On the other hand, several companies have become to add a micro CT function to these X-ray inspection apparatuses, recently, and an arbitrary cross sectional CT images of a sample can be observed, and thereby, its utility has been very much increased. However, the resolving power of a CT image in the present circumstances is several times worse than that of the original projection image, and its development is being inhibited. This is caused by the technical limit of axial runout in the rotation of the sample, which is required to obtain the CT image and essential limit that the sample can not be rotated in the state in which the sample is close to the target.
Conventionally, in the X-ray inspection apparatus of projection type, the kind of sample is only estimated from the image contrast (i.e., difference of transmittance) and the need for the elemental analysis has been extremely great, however, the analysis has been never performed. This is caused by that, if the conventional detector for elemental analysis is disposed underneath the sample, the continuous X-rays directive from the target and the characteristic X-rays from the sample (in this case, fluorescent X-rays) are superposed and can not be distinguished. In addition, as shown in FIG. 1, this is also caused by that there is no space for the accommodation of the detector above the sample 10.
It is necessary to perform observation by changing the way of providing contrast according to the sample, and thus, it is desirable that the accelerating voltage and the kind of target are changed. Changing the accelerating voltage is often performed, however, since it is very difficult to change the target while keeping it in high vacuum and there is no choice but to lead a large scaled apparatus for interchangeable targets, it has never been performed in the conventional X-ray inspection apparatus on-line.
Hereinafter, the conventional technology concerning the resolving power of the X-ray inspection apparatus will be described.
The technology concerning the resolving power is disclosed in Non-patent Document 1, Nixon, “High-resolution X-ray projection microscopy”, 1960, A232: pp. 475–485, Non-patent Document 2, Keiji Yada & Hisashi Ishikawa, “Transmission X-ray Shadow Microscopy using SEM”, Bulletin of the Research Institute for Scientific Measurements, Tohoku University, 1980, Vol. 29, No. 1, pp. 25–42, Non-patent Document 3, Keiji Yada & Kunio Shinohara, “Development of Soft X-ray Microscopy”, 1980, Biophysics, Vol. 33, No. 4, pp. 8–16, Non-patent Document 4, Keiji Yada & Shoichi Takahashi, “High-Resolution Projection X-ray Microscopy”, 1994, Chap. 8, pp. 133–150, and Non-patent Document 5, Keiji Yada & Kunio Shinohara, “Development of Projection X-Ray Microscopy and Its Biological Applications” 1996, Bulletin of Aomori Public College, Vol. 1, pp. 2–13, for example. In Non-patent Document 1, there described that, regarding X-ray Shadow Microscopy, the limit of its resolving power has been 0.5 μm conventionally, however, the resolving power of 0.1 μm is achieved by using a high brightness electron emitter and a very thin metal film (0.1 μm in thickness) as the target at this time. In addition, there also described that the exposure time for obtaining a sheet of image is five minutes, and after Non-patent Document 1 is disclosed, studies for shortening the exposure time have been actively performed. Further, Non-patent Document 2 is a research report (bulletin of the research institute for scientific measurements, Tohoku University) on the projection X-ray shadow microscopy utilizing an irradiation system of an electron microscope, and there described that the resolving power of 0.1 μm is achieved. Additionally, theoretical analyses are performed regarding respective factors that affect the resolving power, and there derived the conclusion that the spot size of the X-ray source exerts the greatest effects on the resolving power. Furthermore, there described that, by utilizing the microscope as a SEM (scanning electron microscope), swinging the electron beam with a deflection coil is utilized for focusing.
Moreover, Non-patent Document 3 is for explaining the trend in the X-ray microscopy to the present, and there explained that the soft X-ray microscope of a relatively short wavelength (0.1 to 10 nm) by specifically referring to the observation of biological samples. The contents of Non-patent Document 4 are substantially the same as those of Non-patent Document 2, however, there shown a densitometry profile of an X-ray image having the resolving power of 0.1 μm (on 146 page in the main body). Non-patent Document 5 is for explaining the X-ray microscope in an easily understandable way, and there described that the image quality becomes better by changing the target in relation to the sample that is difficult to provide contrast as is the case with Non-patent Documents 2, 3, and 4.
The current semiconductor technology is ever being directed to miniaturization, and the X-ray microscopic apparatus of resolving power on the order of 0.1 μm is expected to become essential in the near future. The nano-technology extends across information, medical, environmental fields, and, for example, in a micromachine referred to in the medical field, the component constituting the machine becomes smaller than 1 μm and ready to enter nano order. In addition, the current semiconductor technology is ever being directed to miniaturization, and non-destructive inspection in the class of the resolving power equal to or better than 0.1 μm using the micro X-ray source never before possible becomes a challenge that is required by all means. Especially, in the information field, there is the great challenge that the line width in the next generation very large scale integrated circuit is to be made from 180–130 nm at present to 70–100 nm. Simultaneously, it is often the case where the microstructure consisted principally of a light element become an object to be observed, and, for providing contrast to the image, it becomes an important challenge that the high resolution power is held even in the case of using an X-ray having a long wavelength by the low accelerating voltage of 10 to 20 kV, which is difficult in the conventional X-ray inspection apparatus. Concurrently with that, many new functions never before possible would be desired.
In order to manufacture an X-ray inspection apparatus having high resolution never before possible, an electron source with higher brightness (greater electron current per unit area/unit solid angle) and greater emission current amount becomes required. Additionally, an electron lens system for assuring as a great electron probe current amount as possible becomes also required. Further, devices for increasing the heat release effect of the target become required so that the target may not melt or evaporate even if an electron probe having such high current density impinges thereon.
The first of new functions that are desired to be put into practical use in the X-ray inspection apparatus having ultra-high resolving power (here, resolving power of equal to or better than 0.1 μm is referred to) is a function (hereinafter, referred to as focal point adjustment function) capable of easily performing adjustment such as focus adjustment to the target (X-ray source) for X-ray generation of the electron probe and astigmatic correction of the electron probe while watching the image. Further, the second is a function (hereinafter, referred to as electron probe control function) of swinging the electron probe freely on the target surface so that the choice of suitable target may be enabled. The third is an electron axis alignment function capable of easily performing axis alignment of the electron beam allowed to impinge on the target for X-ray generation. The fourth is a CT function with high resolving power at high speed. The fifth is an elemental analysis function for analyzing the element of the desired part of the perspective image. For this, the elemental analysis with a fluorescent X-ray is utilized, and the X-ray target therefor is necessary. Therefore, the sixth function is, with a plurality of targets for short wavelengths and long wavelengths provided other than the target for analysis, a target switching function capable of choice of suitable target depending on the purpose of inspection.
The invention is achieved in light of the above described circumstances, and an object of the invention is to provide an X-ray microscopic inspection apparatus capable of largely contributing to the nano-technology fields. Specifically, the object of the invention is to provide an X-ray microscopic inspection apparatus capable of performing non-destructive inspection with high resolving power within a very short period, and equipped with advantageous functions such as the high precision electron probe control function, the CT function, the elemental analysis function, and the target switching function.