JPS63244002A - Fresnel zone plate - Google Patents

Abstract

PURPOSE:To permit formation of a large-diameter FZP by dividing diffraction rings to plural groups successively from the inner side and setting the positions of two light sources at the time of exposing in such a manner that the ring radii applying prescribed condensing characteristics at the use wavelengths of the representative diffraction rings and the radii of the interference ring is of the same sequence from the center at the time of exposing coincide with each other for each of the respective groups. CONSTITUTION:The Fresnel zone plate (FZP) patterns are divided to the diffraction ring groups on the inside L1, middle side L2, outside L3, etc. The representative rings are respectively selected with the respective groups. The ring radii are calculated from the conditions for using the FZP and the positions of the two light sources which give the same diffraction ring radii as the radii calculated with the diffraction rings of the same number at the time of exposing are counted back and determined. The interference pattern at the time of exposing and the diffraction ring pattern required at the time of use can be made identical with each other respectively at sufficient approximations for each of the respective groups, so that the FZP corrected in aberration is obtd. Since the aberrations are thereby removed in the prepn. of the FZP by a holographic exposing method, the formation of the larger-diameter FZP is permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a Fresnel zone plate used as an X-ray imaging element.

Conventional technology In recent years, light sources in the soft X-ray region have been significantly developed, including SOR light.
Powerful soft X-ray sources such as laser plasma X-ray sources have become relatively easy to use, opening up new fields such as spectroscopy in the soft X-ray region, X-ray lithography in the semiconductor industry, and X-ray microscopy in the biological and medical fields. Various applications are being attempted to open up new possibilities.

However, in the X-ray region, collimation and imaging cannot be performed as easily as with normal visible light, and both require ultra-precision machining. It is attracting attention as a line optical element. Therefore, repeated development of these X-ray optical elements is an important key to putting a device using soft X-rays into practical use.

The present invention relates to this FZP pattern.

FZP has traditionally been fabricated using two main methods, one of which is direct t! The other method is the holographic exposure method, which records interference fringes using two spherical light waves.

The light focusing principle of FZP will be explained with reference to FIG. In Fig. 3, 1 is the X-ray source, 2 is the FZP, 3 is the focal point, a is the distance from the X-ray source 1 to FZP2, b is the distance from FZP2 to the focal point 3, ^8 is the X-ray wavelength used, rl represents the radius of the n-th ring, and d represents the width of the n-th ring.

In order for the X-rays emitted from the X-ray source 1 to be diffracted by the FZP 2 and focused on the focusing point 3, - Next time when using a valve,
The optical path difference between the optical path length to the focal point of the X-ray diffracted by each ring and the optical path length between 1 and 3 on the optical axis is 0 times the wavelength λ8 (n is an integer and the ring number counted from the inside). For example, the optical path 1-4 of the nth ring in FIG.
-3 and the optical path 1-2-3 is nλ8, and the ring width d is the optical path difference between 1-4-3 and 1-5-3 is λ, /
2, the direct writing method using an electron beam can only produce small-diameter rings due to the limit of the ring width that can be manufactured, and the holographic exposure method has a smaller diameter than the direct writing method using an electron beam. Since the possible ring width is narrow, it is possible to create an FZP with a relatively large diameter, but this also requires that the aberration due to the wavelength difference between the exposure wavelength and the wavelength used during FZP production be within the allowable range (tolerable aberration). There was a problem in that the size of the aperture was limited in order to accommodate the X-rays, and the amount of X-rays that could be used was limited.

C1 Problems to be Solved by the Invention The present invention aims to increase the aperture of the FZP because aberrations occur due to the wavelength difference between the exposure wavelength and the used wavelength when producing a Fresnel zone plate for X-rays using holographic exposure. The purpose is to solve the problem of not being able to produce large-diameter FZPs.

20 Means for Solving Problems A Fresnel zone plate uses an interference ring formed by a holographic exposure method as a diffraction ring.The diffraction ring is divided into a plurality of groups sequentially from the inside, and a representative diffraction ring is appropriately selected for each group. Diffraction rings for each group are formed by setting the two light source positions during exposure so that the ring radius that provides a predetermined light condensing characteristic at the wavelength used matches the radius of the interference ring in the same order from the center during exposure. did.

One of the limiting factors for the size of the FZP produced by the Holographic holographic exposure method is the influence of aberrations caused by the wavelength difference between the used wavelength and the exposure wavelength. That is, when only the paraxial region is considered, the rings of FZP at wavelength λ and FZP with the light source and focal point distance doubled at wavelength λ/ are the same, but as the aperture increases, the rings of the same A shift occurs, and the wavelength λ
If the FZP for wavelength λ/ is used for other purposes, aberrations will occur.

Therefore, even if the diffraction ring group is of the same order, it is desirable that the exposure conditions (light source arrangement) when printing the diffraction pattern be slightly different between the inside and outside of the FZP pattern. Two light sources and FZP when exposing
The light source distance when exposing the outer diffraction ring group is approximately equal to the above reference distance, but
It is necessary to modify this approximate position due to the above-mentioned points.In reality, the FZP pattern is divided into diffraction ring groups such as inner, middle, and outer, and a representative ring is selected for each group, and the ring is adjusted based on the FZP usage conditions. By calculating the radius and back calculating the positions of the two light sources that give the same diffraction ring radius as the radius calculated above for the diffraction ring with the same number at the time of exposure, the interference pattern at the time of exposure and the required during use are determined for each group. The diffraction ring patterns can be matched with each other with sufficient approximation, and an aberration-corrected FZP can be obtained.

Embodiment FIG. 1 shows an embodiment of the present invention. In Figure 1, 1
is the light source, 2 is the FZP, 3 is the focal point, L.

(i=1.2...) is a ring group formed by exposure at the same light source position, a is the distance from the X-ray source 1 to FZP2, b is the distance from FZP2 to the focal point 3, and λ. indicates the X-ray wavelength used.

In this configuration, the wavelength used is λ = 5.4, the exposure wavelength is λH-4416 of He-Cd laser, and the light source distance a = 150 mm when used as an X-ray focusing element.
, the focal point distance b=680 mm. With the AZ series of positive resists, it is possible to create line widths of up to about 0.1 μm depending on development conditions. In FIG. 2, the allowable value of aberration is set to C□)l=0.181111.

In Figure 2, the focal point distance ξ of two spherical waves for exposure to form the k-th ring ρk (k is a serial number from the center ring) is ηk, and the radius of that ring is rk.
Now, when ξ is set to = η5, the ring radius r is given by the above-mentioned equation (2) from the above usage conditions.

As shown in FIG. 1, the spherical waves from the exposure positions 11 and 12 obtained in this way cause the first outer ring of the inner diffraction ring group Lkl to be ! 2, allowable aberration C,,8
formed to the extent that it does not exceed. At this time, the ring, 12k
For the 0th order, which is masked outside l, the light source position is adjusted according to equation (4) to form an intermediate diffraction ring group L2, and then an outer diffraction ring group L+ is successively formed.

In this way, without changing the masks on both sides of the substrate, the inner, middle, and outer diffraction ring groups and each diffraction ring group are printed in sequence.
Although the light sources were set at equal distances from the FZP substrate, one light source may be fixed and only the other one may be moved as the inner, middle, and outer diffraction ring groups are exposed.

G. Effects According to the present invention, FZP by holographic exposure method
Since aberrations are removed in the production of FZPs, it becomes possible to create FZPs with large apertures, which greatly improves the light-gathering ability of FZPs and widens the range of applications.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention, FIG. 2 is an explanatory diagram of the second embodiment, and FIG. 3 is an explanatory diagram of the principle of condensing FZP. 1...Radiation source, 2...Fresnel zone plate (FZ
P), 3... Focus point, Ll... Diffraction ring group.

Claims (1)

[Claims] This is a Fresnel zone plate whose diffraction ring is an interference ring formed by holographic exposure.The diffraction ring is divided into a plurality of groups from the inside, and each group has a predetermined light focusing characteristic at the wavelength used by the representative diffraction ring. A Fresnel zone plate characterized in that two light source positions during exposure are set so that the given ring radius matches the radius of an interference ring in the same order from the center during exposure to form each group of diffraction rings. .