JPH02179500A - Fresnel zone plate for soft x-ray - Google Patents

Abstract

PURPOSE:To enable a further strong image formation than that gotten by usage of a gold by using a nickel and the like other than gold as a material of a shielding part located side by side to a cocentric rings which constitutes a Fresnel zone plate Fzp. CONSTITUTION:Hatched parts in the figure show ring bands made of an X-ray absorber. An incident X-ray which is regarded as a beam parallel along to an positive direction of an Z axis, is focused to a focusing point F by a Fzp. Assuming that a focusing distance is f, a thickness of the X-ray absorber is t and a refraction index of the X-ray absorber at a wave length lambda0 in use, is n=1-delta+ik, a transmissivity t(r) of the Fzp at an arbitrary distance r from a center can be expressed as the equation showed in the figure. The first term of the right side of the equation is the 0 order diffraction which transmits as it is without being affected by any diffraction, and the second term shows the first stage to (2n-1) order diffraction beams according to a value of m. If thicknesses are same, k becomes small, and for a material having larger delta, a greater phase effect can be expected and therefore, when a Fzp having enough thickness are not available by a limitation derived from a fine processing, a Fzp close to a phase-typed one can be manufactured by using a nickel and the like, for example, other than a gold, as an X-ray absorber.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a Fresnel zone plate necessary as an imaging element for X-ray lithography and X-ray microscopes.

Prior Art and Its Problems In the LSI manufacturing process, the optical reduction exposure method conventionally used to form resist patterns is approaching its theoretical resolution limit as patterns become finer. It is thought that it is quite difficult to transfer submicron patterns using light.

2゜ 3゜ l.

) One of the exposure methods that is currently considered to be a promising alternative to light is X-ray lithography. However, all currently developed or commercially available X-ray exposure systems use the same-magnification projection exposure method using close-up exposure, so although they can handle submicron patterns, they cannot handle quarter-micron transfer due to run-out errors, penumbra blur, and mask production. Problems such as these arise and become difficult.

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, one example of the X-ray reduction exposure method will be explained with reference to FIG. This involves focusing divergent X-rays emitted from a point light source on the Rowland circle onto a Fresnel zone plate on the same circumference using a Johansson curved crystal C, and placing a reduced image of the X-ray mask M on the wafer W using Ezp. This is to form an image. By the way, in the X-ray Fzp of the imaging element, gold is used for the X-ray absorber (shielding part), and the line width ratio of the adjacent shielding part and the transmitting part is 1:1. It will be done. Since the Fzp for X-rays is also Fzp, it would be ideal for the X-ray absorbers that make up the concentric ring zones to completely shield X-rays, but in reality they cannot completely shield them. (As the X-ray absorber becomes thicker, the X-ray penetrating power increases, so it becomes more difficult to block the X-rays.) Since a high degree of patterning is required, it becomes difficult to create a large-diameter Fzp due to microfabrication constraints, and the thickness of the X-ray absorber cannot be increased unnecessarily.

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, which is one of the causes of reduced image contrast. In this way, X-rays using gold as an X-ray absorber
In line Fzp.

There is a trade-off relationship between the productivity of the device and the performance as an imaging device.

(c) Purpose The object of the present invention is to provide an Fzp that uses gold in its shielding part and is capable of forming an image with much stronger intensity than a normal Fzp for X-rays.

2) Configuration First, the configuration of the phase-type X-ray Fzp used in the present invention will be explained with reference to FIG.

FIG. 1 is a cross-sectional view of Fzp, and the shaded area represents the annular zone made of the X-ray absorber. Incident X-rays are a parallel light source that travels in the positive direction of the Z axis (rightward in the figure) and are focused at a focal point F by Fzp.

The focal length is f, the thickness of the X-ray absorber is t, and the refractive index at the used wavelength λ0 of the X-ray absorber is n.
Then, the transmission coefficient t(r) of Fzp at an arbitrary distance r from the center can be expressed as follows.

t('')■ In equation (1), the first term on the right side is transmitted as is without undergoing diffraction (represents 0th order diffracted light, and the second term is 1st order, 3rd order, etc. depending on the value of m, respectively).・・・・・・－・・・・・・(
2m-1) order...represents diffracted light.

For example, in the complete phase type Fzp that can be realized in the visible light region, etc., the above equation can be written as k→0゜t→λG/(2δ), so the 0th order light completely disappears, and instead the 1st order light has the maximum intensity. come to have.

However, since δ and k of any material generally take finite values in the region, it is not possible to create a perfect phase type Fzp.

However, if the thickness is the same, a material with a small k (and a large δ) can be expected to have a phase effect.

When it is not possible to create an Fzp with sufficient thickness due to microfabrication constraints, the present invention uses a substance other than metal for the X-ray absorber to create an Fzp that is closer to the phase type and increases the focused light intensity. Reinforce.

At the same time, it is intended to remove zero-order light that becomes noise.

(E) Effect In the optical system shown in FIG. 2, the intensity distribution of diffracted light produced on the imaging plane when parallel light is incident on Fzp is investigated. The optical axis is chosen to be the Z-axis, and the traveling direction of the X-rays is set to be positive. Fzp of radius a
and the imaging plane are perpendicular to the Z-axis, and the origin of the Fzp plane is O1, and the origin of the imaging plane is F. The point P on the imaging plane that we are currently focusing on is at a distance of ρ from F, and the distance between P and O is S'
shall be.

The intensity of the X-ray at point P is calculated as the first order by calculating the Fresnel-Kirchhoff diffraction integral considering the transmittance of Fzp under Fresnel approximation + (P) = l B 1
2 (W,!+ W, 2) ・・・・・・・・・■However,
B is a constant.

W,m C (II, v) Tomi S(u,v)■ ...When lμat>lvl W announcement- ・・・・・・・・・・・・・・・■ ...When 1μml>lvl Here, Jn(x) represents a Bessel function of the first kind.

S'-ft-7 ・・・・・・・・・・・・・・・■ In the phase-type Fzp of the present invention, a substance other than gold is used for the absorber to enhance the phase effect and strengthen the intensity at the focal point. . In order to strengthen the phase effect, it is sufficient to use a material that transmits X-rays easily (and refracts them greatly), so δ is larger than that of gold.
Nickel, copper, silver, and tin with small k are used.

(to) The wavelength of Example Xn is λo = 5.4 people, and the radius of Fzp is a =
We choose Fzp of silver as an example, which is 0.1-. λo
=5.The optical constant of silver in 4 people is.

δ=3.1636X10-4. k-4,4311X1
There is 0-i-te.

Optical constant of gold 6=2.5223X10-4. k=3.
The diffraction intensity 1 (P) due to gold Fzp and silver Fzp was calculated and shown in FIG. 3 when δ is large and δ is small compared to 0247xlO-4 and the thickness is 6000 mm.

Comparing the condensed light intensities of the two in FIG. 3, it can be seen that even with the same thickness of FZp, the intensity of silver is approximately 2.3 times stronger than that of gold.

The procedure for making FZP from silver is almost the same as the procedure for making FZP from gold, and there is no difference in processing difficulty.

(g) Effect By using a substance other than gold for the absorber, the focused light intensity is increased compared to the conventional Fzp, and the exposure throughput can be improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of Fzp. FIG. 2 is a diagram depicting the geometrical arrangement of the imaging optical system when imaging by Fzp. Figure 3 shows the intensity distribution on the imaging plane when gold and silver are used as the annular material of Fzp, where the vertical axis is the intensity and the horizontal axis is the point on the imaging plane. represents the distance from the optical axis. FIG. 4 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 mask W... 0...・ F... Q... P... Imaging surface (wafer) Center of Fzp Point on focal point Fzp of Fzp Point on the flawed surface

Claims (1)

[Claims] (1) Fresnel zone for soft X-rays, characterized in that the material of the shielding part of the adjacent opening and shielding part of the concentric rings constituting the Fresnel zone plate is nickel, copper, silver, or tin. plate.