Soller slit using low density materials

Abstract

A Soller slit device is provided for collimation of high energy radiation, such as X-ray or EUV radiation, and has a low angle of divergence (less than 0.1°) and a high transmission efficiency (60 to 80% or greater). The Soller slit is made up of multiple blades of low-density material, such as glass, mica, or the like, which are treated to reduce reflectivity. The Soller slit device of the invention advantageously provides an increased peak intensity and decreased peak width in diffraction patterns produced in high energy diffractometry applications, such as X-ray diffractometry.

Description

FIELD OF THE INVENTION [0001] The present invention relates to X-ray metrology. Specifically, the present invention relates to an absorption element used to control the divergence of a beam of X-rays. BACKGROUND OF THE INVENTION [0002] In recent years, technology involving high energy radiation, such as X-ray and extreme ultraviolet (EUV) radiation has increased. However, because of the very nature of this type of radiation, it is often difficult to control its divergence. One common optical element used for controlling the divergence of an X-ray beam is called a Soller slit. Soller slits generally comprise a set of parallel, or nearly parallel, plates or blades that limit the divergence of an X-ray beam by simple blocking or absorption of divergent rays, which are not allowed to pass through an open section of the array. [0003] Typically, Soller slits have been made of materials of high density to allow for absorption of divergent X-rays. It has been generally thought that material...

AI Technical Summary

Benefits of technology

[0012] In accordance with the present invention, the foregoing objectives are achieved by way of an X-ray Soller slit collimating device that uses lightweight, low density materials that are relatively inexpensive. The density of the material used is less than 6 g / cm3. The Soller slit device of the present invention provides an increased transmission throughput efficiency of greater than 60%, while maintaining a low divergence of less than 0.1°.

[0014] Advantageously, by making Soller slits devices from such low density materials, the blades of the devices of the invention can be made much thinner than traditional Soller slit blades. For example, in accordance with an embodiment of the present invention, glass blades that measure approximately 50 μm in thickness may be used. Such a thin blade allows for great increases in the throughput efficiency of the Soller slit device. Additionally, the blades of the Soller slit device of the present invention may be spaced with wide spacings therebetween, which also contributes to an increased transmission efficiency.

[0015] Additionally, the blades of the Soller slit device of the present invention may be produced in longer lengths, which decreases the angle of divergence of the beam transmitted through the device. These longer lengths are available as the blades of the present invention do not bend like the metal blades of prior devices. In accordance with an embodiment of the present invention, the angle of divergence of the Soller slit device may be less than 0.1°.

[0016] Because of the longer length of the blades, lower density materials may be used to construct the blades. This is because a divergent beam, which exceeds the divergence angle of the Soller slit device of the present invention (e.g., greater than 0.1°) strikes the blades of the Soller slit device at an oblique angle that magnifies the absorption capability of each blade by a large factor. For example, in accordance with an embodiment of the present invention, each blade's absorption ability may be multiplied by a factor of about 600. Because of this large absorption factor, glass, mica, and other low density materials provide adequate absorption for divergent high energy radiation, including X-rays.

[0017] The present invention also provides for a diffractometer or system for X-ray, or other high radiation, diffractometry which makes use of the Soller slit described above. Specifically, the system for diffractometry provided by the present invention allows for the use of a Soller slit as a collimation element within the system. The Soller slit provides a greatly reduced divergence, and an advantageously increased transmission efficiency. Specifically, transmission efficiency of the Soller slit used by the system for diffractometry allows for a transmission efficiency of at least 60% and preferably approximately 80%, while maintaining a divergence of less than 0.1°. This is accomplished by using a Soller slit manufactured from relatively low density materials.

Problems solved by technology

However, because of the very nature of this type of radiation, it is often difficult to control its divergence.

Although these metal sheets can be made extremely thin, the mechanical stability of very thin sheets is not good enough for high precision X-ray work.

For example, any curling or rumpling of the sheets, which is common with metals, will result in poor transmission through the Soller slit device, and consequently unpredictable divergence.

These metal foil devices yield relatively low transmission efficiencies.

Moreover, the transmission efficiencies of such devices worsens as the required divergence is reduced (i.e., the quality of such devices' outputs becomes worse as their design constraints are made more restrictive).

However, the Soller slit described therein requires expensive ceramic materials processing to build, and is therefore less desirable for commercial applications.

One problem generally associated with Soller slit devices used for such commercial applications as X-ray diffractometry, however, is that they generally have relatively low transmission efficiencies and large divergence angles.

Thus, generally well over half of the X-ray radiation passing through the device is lost and unusable for measurements in the application in which the Soller slit is being employed.

This typical divergence angle is large, and negatively impacts the Soller slit's ability to effectively collimate x-ray radiation for many important commercial applications such as X-ray diffractometry.

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