JPH0291600A - Fresnel zone plate for X-rays and X-ray reduction exposure optical system - Google Patents

Abstract

PURPOSE:To obtain an X-ray reduction projection exposure optical system whose image forming characteristic is satisfactory by forming the line width of a shielding part of a concentric ring for constituting a Fresnel zone plate larger than the line width of its adjacent opening part. CONSTITUTION:A line P of a shielding part of a concentric ring for constituting a Fresnel zone plate (FZP) is formed larger than its adjacent opening part. Accordingly, even the FZP in which an absorber does not reach sufficient thickness can optimize the contrast of intensity by controlling the line width of a pattern. In such a way, by using the optimized FZP for an image forming element of an optical system, the resolution of an X-ray reduced image can be improved, and also, the manufacture itself of the FZP is facilitated, and a large aperture can also be obtained. Also, by using other substance than gold for the absorber, the condensing intensity increases more than that of the FZP of a conventional type, and the throughput of exposure can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) This invention relates to a Fresnel zone plate and an X-ray reduction projection exposure optical system, which are necessary as imaging elements for X-ray lithography and X-ray microscopes.

BACKGROUND) Conventional technology The optical reduction exposure method conventionally used to form resin patterns in the LSI manufacturing process is approaching the theoretical resolution limit of red as patterns become finer. It is thought that it is quite difficult to transfer submicron patterns using light. One of the exposure methods that is currently considered to be a promising alternative to light is X-ray lithography. However, currently under development.

Rurui is the commercially available XJ1! All of the exposure apparatuses use the same-magnification projection exposure method, so although they can handle submicron patterns Ki, it is difficult to transfer quarter-micron patterns due to problems such as phantom-out errors, penumbra filling, and mask fabrication.

In order to overcome the problems of the X-ray equal-magnification projection exposure method, various reduction projection exposure methods are being considered. For example, JP-A No. 62-230021 (Japanese Patent Application No. 61-7
The X-ray reduction exposure method according to No. 4694) will be explained with reference to FIG. This is a Fresnel zone plate (hereinafter abbreviated as FZP) on the same circumference due to the divergence xmt Johansson curved crystal C emitted from a point light source on the Rowland circle.
This is to focus the light onto K and form a reduced image of X-ray 772M on wafer W using FZP. The X-ray PZP of the imaging element uses gold for the XM absorber (shiyahei part), and the FZP has a line width ratio of 1:1 between the adjacent shielding part and the transmitting (aperture) part. Usually used. XJil
! J41FZP is also FZP.

Ideally, the X-ray absorbers constituting the concentric ring zones should completely block Xls, but in some cases they cannot completely block Xls. However, as the wavelength used becomes shorter, the penetrating power of X-rays increases, making it more difficult to suppress. X-rays can be suppressed by increasing the thickness of the X-ray absorber, but patterning with a higher aspect ratio is required toward the ring zone at the end. It will be difficult to make it, and you cannot make it unnecessarily thick. However, if the thickness of the X-ray absorber is not sufficient, the intensity of the diffracted light at the imaging point will be weakened, and the tX-rays that have passed through the absorber will become zero-order noise, which is one of the causes of reducing the contrast of the image. Taji. As described above, in a gold FZP for X-rays, there is a trade-off between element productivity and performance as an imaging element.

FZP uses gold for the target and edge of the blade, and is capable of imaging with much higher contrast and stronger intensity than normal X-ray FZP, and has X-ray reduction with good imaging characteristics. First, the structure of the zero-order light suppressing type FZP for X-rays used in the present invention will be explained with reference to FIG. 1.

FIG. 1 is a sectional view of the FZP, and the shaded area represents the ring zone made of the X-ray absorber. The incident X-ray is a parallel ray of light that travels in the positive direction of the Hz axis and is focused at a focal point F by FZP.

The focal length is f, the total thickness of the X-ray absorber is t, and the wavelength used for the X-ray absorber is λ. Letting the refractive index at 7=1-δ+ik, the transmission coefficient '1'tr) of the FZP of the misfired invention at any distance r from the center can be expressed as follows.

■ Equation (2) is a Fourier expansion of the CIJ equation.

In a normal PZP, the blocking part completely blocks the light ((IJ, (corresponds to t-+■ in Equation 27), so the intensity at the focal point of the primary light reaches its maximum when 1 = π. In the above equation, the phase type zone plate (hereinafter abbreviated as PZP) corresponds to when →Ot -4/(2δ), but in this case, the focused light intensity is maximum when j = π. becomes.

However, in general, in the X-ray region, all substances have a finite value of δ, so it is theoretically impossible to create a perfect FZP or a perfect PZP.

7'jFZp1 with sufficient thickness due to microfabrication constraints
In view of this situation, the present invention optimizes the line width (corresponding to i) of the pattern to increase the contrast of the diffracted light.

Furthermore, a substance other than all is used for the X-ray absorber (ff.

(equivalent to changing kl) to create FZPt, which is closer to PZP, and increase the focused light intensity.

(e) Operation Next, a method of optimizing the line width in order to make the FZP function as a ThO-order light-suppressing type FZP with any pattern width described above will be explained.

When parallel light is incident on F'ZP in the optical system shown in FIG. 2, the intensity distribution of diffracted light produced on the imaging plane is examined.

optical axis? Select the Z-axis and make the direction of X-ray travel positive.

PZP with radius a is in a plane perpendicular to the Z axis, and the position in the F22 plane is ξ-η coordinate in orthogonal coordinates and r-θ in one rotation coordinate.
Expressed in coordinates. The imaging plane is also in a plane perpendicular to the Z axis, and the distance from point Q on 0FZP to point P on the imaging plane is represented by x-y coordinates in Cartesian coordinates, ρ-ψ coordinates in rotational coordinates, and @' line. ,
The amplitude of the X-ray at the center O of pzp or the point P on the plane [1(
PJ applies Fresnel approximation to t(rJ
(If you calculate using the 2J formula, the 3J formula will be as follows. However, B is a constant O IJ [P) = B CWI + IW2]
(4)...When μat>, x[cos (2nθ mountain value <;+',>, 袷ゝ)−
sin (-F nθ) <10+', >, position) 1°
When 1°101 μa > lv, xcos(±nθ> 7 pieces 2K < 11-10±
>, 2x.

2 λof S'λoS'+s
in (+nθ)s(<+”;:>, 9))(ωs'-i) where Jn(x) represents a Bessel function of the first kind.

From this, the intensity distribution of the diffracted light at the imaging plane I O') is I
(P)= +B+2(W1' +VI:) 11
It is given by 1. I (PJ is a function of only ρ on the imaging plane, but in the present invention, when the thickness t of the absorber is given,
Find the distribution of this I (P) with respect to ρ while changing θ, find the value 7 that maximizes the contrast of the condensed diffracted light, and find the FZP with the corresponding line width ratio as a result of the exposure optical system. Used for image elements.

Further, in the present invention, a substance other than gold is used for the absorber.

Strengthen the phase effect to 1 intensity I (strengthen PJ itself.

In order to strengthen the phase effect, it is sufficient to use a material that easily transmits X-rays and refracts them greatly, so in the present invention, nickel, copper, silver, and nuzu, which have a larger θ and a smaller k than gold, are used. When these materials are used, the focused light intensity will be higher than when gold is used even with the same thickness. = 54 people, the radius of FZP is a = Q
, lm.

First, regarding the FZP of the present invention, consider gold with a thickness of 1013.45 mm as the X-ray absorber of the FZP.

λ. = 5.4 The optical constant of gold in humans is δ = 2.52
23X10-', k = 3.0247X10-'.

FIG. 3 shows the intensity distribution of diffracted X-rays in the ρ direction when changing θ. The center intensity of the diffraction line itself reaches its maximum when θ=π, but the maximum intensity I0 at the center position and the first
Ratio work with minimal strength work ρ1. /■ρ1 is maximum when θ=0,6π as shown in FIG. θ is converted to the distance from the center of FZP, and γ = fλ. Since it corresponds to θ/π, the line width ratio OA1 between the opening and the barrier in FIG.
' If the ratio of AlA2 is set to 1.2:1, the contrast of the diffraction intensity of FZP with a thickness of 1013.45 mm will be maximized.

Next, a silver FZP is selected as an example of the FZP of the present invention.

λ. = 5.4 The optical constant of silver in humans is δ = 3.163
6X10, k=4.431]X10,
Compared to the optical constants of gold, δ is large and kfl is small.

When θ=π and the thickness is 6000 people, gold FZP and silver F
The diffraction intensity I (PJ'e) due to ZP is calculated and shown in Figure 5. In Figure 5, when comparing the two condensed intensities,
It can be seen that even with the same thickness of FZP, silver is about 2.3 times stronger than gold. Note that the procedure for making FZP from silver is almost the same as the procedure for making FZP'i from gold, and there is no difference in processing difficulty.

(Intensity contrast can be optimized by adjusting the line width of the pattern even in FZP where the thickness of the Toph effect absorber has not reached a sufficient thickness.
By using this in the imaging element of the optical system shown in Fig. 6, it is expected that the resolution of the reduced X-ray image will be improved.
It becomes easier to manufacture P itself, and it becomes possible to increase the diameter.

Furthermore, by using a substance other than gold for the g&amp;

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of FZP in which the patterning line width is set arbitrarily. Figure 2 depicts the geometrical arrangement of the imaging optical system when imaging by F'ZP, and Figure 3 depicts the intensity distribution on the imaging plane when the width of the FZPQ ring zone is changed. In the diagram shown, the vertical axis represents the intensity of X-rays. The horizontal axis represents the distance from the optical axis to a point on the image plane. Figure 4 shows the ratio between the maximum intensity and the first minimum intensity of X-rays when the width of the FZP annular zone is changed, where the vertical axis corresponds to the intensity ratio and the horizontal axis corresponds to the width of the annular zone. Figure 5 shows the intensity distribution on the imaging plane when gold and silver are used as the annular material of the FZP, where the vertical axis is the intensity and the horizontal axis is the intensity of the points on the imaging plane. Represents the distance from the optical axis. FIG. 6 shows an example of an X-ray reduction projection exposure optical system. C...X-ray condensing element such as a curved crystal or X-ray multilayer mirror D...X-ray source K...imaging element (FZP) M...X-ray manuk W...imaging surface (Wafer no O... Center of FZP F... Focus Al of FZP, A2... Points at both ends of the first ring zone, Q... FZ
Point P on P...Point θ on the image plane (X 几)

Claims (1)

[Scope of Claims] 1. A Fresnel zone plate for X-rays, characterized in that the line width of the narrow part of the concentric rings constituting the Fresnel zone plate is larger than the line width of adjacent opening parts. 2. In an X-ray exposure optical system in which an X-ray imaging element reduces and projects an image of an X-ray mask illuminated by a curved crystal or an X-ray multilayer mirror, the Fresnel zone according to claim 1 An X-ray reduction exposure optical system characterized by using a plate as an X-ray imaging element.