X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-09-14
2002-05-07
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
Reexamination Certificate
active
06385290
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an a x-ray device, and more particularly, to an x-ray apparatus such as an x-ray exposure apparatus, an x-ray microscope, or an x-ray analysis device.
The present invention also relates to an x-ray generating apparatus for use as an x-ray source in an x-ray apparatus such as an x-ray exposure apparatus, an x-ray microscope, or an x-ray analysis device.
2. Description of the Related Art
An apparatus, which uses a reduction and projection type exposure by light technique, is currently widely used for the manufacture of semiconductor integrated circuits that have fine semiconductor integrated circuit patterns. Examples of such an apparatus include an x-ray exposure apparatus, an x-ray microscope, and an x-ray analysis device. This apparatus also includes an x-ray generating apparatus as an x-ray source, and a plurality of optical elements.
The wavelength of the light used in such an apparatus has become progressively shorter as patterns have become finer. As a result, attempts have been made to use soft x-rays for the formation of fine patterns, which are, in principle, impossible to achieve using visible or ultraviolet light. However, in the soft x-ray region that includes wavelengths of 1 to 100 nm, all substances show a strong absorption. Accordingly, transmission type optical elements that utilize refraction in the visible light region are not used. Instead, extremely thin-film filters or reflective mirrors, which have multi-layer films formed on them, are used as optical elements. In particular, multi-layer film mirrors have been manufactured in which a direct-incidence reflectivity of approximately 70% is obtained in the vicinity of wavelengths of 11 nm and 13 nm, and the reduction and projection type exposure apparatus with reflective optical systems using such multi-layer films has been proposed.
In cases where thin-film filters or multi-layer films are used, contaminants adhering to the surfaces of such elements are a serious problem. Furthermore, all substances show a strong absorption in the soft x-ray region. Moreover, if a device contains sliding parts such as sample stages, fine particles are generated, and these particles might adhere to the surfaces of soft x-ray optical elements. Soft x-rays are also absorbed by air, and therefore, the light path must be evacuated to a vacuum state. However, there is a slight back flow of oil from ordinary evacuation systems. Under such conditions, when soft x-ray irradiation is performed, carbon contaminants adhere to the surfaces of soft x-ray optical elements. In addition, in an x-ray exposure apparatus, wafers coated with light sensitive polymer known as resists are conveyed into the vacuum vessel during exposure, and such resists generate small amounts of gases that may also cause carbon contamination. These contaminants cause a drop in soft x-ray transmissivity and reflectivity.
Moreover, the x-ray generating apparatus that is used as the x-ray source in an x-ray apparatus also generates particles that adhere to optical elements of the apparatus. An example of an x-ray source is a laser plasma x-ray source or an LPX. In all LPX, pulsed laser light (one example of an exciting energy beam) is focused and directed onto a target material placed in a vacuum vessel under reduced pressure. The target material is rapidly converted into plasma, and x-rays with an extremely high brightness are emitted from this plasma. In particular, such x-ray apparatus are compact, but have a brightness comparable to that of undulators.
Furthermore, an LPX differs from synchrotron radiation light since a high degree of vacuum, such as approximately 10
−9
torr, is not required. It is only necessary for the degree of vacuum to be high enough to prevent gas discharge due to residual gas before the laser light reaches the surface of the target; or to prevent strong absorption of the x-rays generated from the plasma before these x-rays reach the object of irradiation. In particular, a pressure from several tens of torr to 0.1 torr is sufficient. Accordingly, an inexpensive vacuum evacuation device such as a rotary pump is sufficient, and can easily be used. Thus, such an LPX has attracted attention in recent years for use as an x-ray source in x-ray exposure apparatus, x-ray microscopes, or x-ray analysis devices.
In an LPX, particles such as high-velocity ions and electrons, and particles of materials from the target material such as gasified materials, ionized materials, and material fragments are emitted from the plasma along with the x-rays. These particles scatter throughout the interior of the vacuum vessel. In an x-ray apparatus, which uses an LPX as an x-ray source, such scattered particles adhere to the surfaces of soft x-ray optical elements and cause problems, such as reduction in reflectivity and transmissivity. Accordingly, it is necessary to reduce the quantities of such particles that are generated, and to remove scattered particles that adhere to the optical elements.
Various methods are used to reduce and remove contamination. A wet cleaning method is the most commonly used method to clean the surfaces of contaminated substances. This method consists of treatment by a chemical agent and rinsing by pure water. This cleaning method is very widely used in semiconductor integrated circuit manufacturing processes, and is capable of removing fine adhering substances if the purity of the chemical solution and pure water is increased. However, the wet cleaning method has various problems including consumption of large quantities of cleaning solution and pure water. As a result, in recent years, other cleaning methods, such as the blowing of fine water droplets onto the objects being cleaned at super-high velocities and irradiation with pulsed light, have been proposed.
The latter method of irradiation with pulsed light is effective if a light of a wavelength that can be strongly absorbed by the adhering matter or the substrate is used. When the pulsed light abruptly heats a slight surface portion of the substance, then this surface portion expands. However, when heating occurs in a short time by pulsed light, the displacement acceleration is extremely large, and as a result, the fine particles adhering to the surface can be removed. Furthermore, even in cases where adhering matter is formed in a thin-film configuration on the surface, instantaneous peeling occurs during irradiation with pulsed light. In such cases, the adhering matter is removed, as in the case of fine particles, due to a result of differences in the physical characteristics such as the thermal expansion rate of the underlying material.
Moreover, if the adhering matter is organic matter consisting chiefly of carbon, the removal can be achieved by irradiation with ultraviolet light in an appropriate oxygen atmosphere. In particular, the bonds between carbon atoms in the adhering matter are cleaved by the ultraviolet light. As a result, the carbon bonds with oxygen and is removed in the form of carbon dioxide.
The possibility of some type of substance adhering to the surfaces of soft x-ray optical elements placed in a vacuum cannot be completely eliminated. However, the soft x-ray optical systems are extremely sensitive to surface contamination, and it is necessary to remove substances adhering to such soft x-ray optical elements. However, cleaning in a vacuum using wet cleaning methods, which are currently the most common methods in use, is undesirable because in order to perform cleaning in such cases, it is necessary to remove the soft x-ray optical elements from the vacuum vessel. Moreover, it is necessary to perform a strict alignment when re-installing the soft x-ray optical elements in the vacuum vessel after cleaning. Such a procedure requires considerable time, and is therefore undesirable. As a result, a technique is needed that makes it possible for removing substances adhering to the surfaces of soft x-ray optical elements with the elements left in place without removing the
Kandaka Noriaki
Kondo Hiroyuki
Kim Robert H.
Morgan & Lewis & Bockius, LLP
Nikon Corporation
Yun Jurie
LandOfFree
X-ray apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2848192