JPS62229836A - Reflection type x-ray mask - Google Patents

Abstract

PURPOSE:To obtain a strong and unbreakable reflection type X-ray mask by a method wherein an X-ray absorbing thin film is patterned on a curved crystal substrate manufactured in such a way that the direction of the diffracted X-rays in the center of the substrate coincides with the normal of the center of the substrate. CONSTITUTION:On the surface of a substrate K cut out in a plane plate form from a curved crystal curved in such a way that a lattice plane C, which is involved in an X-ray diffraction in the crystal, has a focusing action to the diffracted X-rays, an X-ray absorbing thin film is patterned on the crystal substrate manufactured in such a way that the inclination of the substrate surface to the crystal lattice plane becomes such an inclination that the Bragg reflection (diffraction) X-rays in the center of the surface of the substrate cut out coincide with the normal of the substrate in the center and an X-ray reflection type mask is provided. After striking on the X-ray mask M, X-rays emitted from an X-ray source S are diffracted by the crystal lattice of the mask substrate and the image of the X-ray mask is formed on a wafer W by an X-ray image-forming element F.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an X-ray reflective mask used in projection exposure methods such as X-ray lithography.

2. Description of the Related Art In the conventional LSI manufacturing process, a phototransfer method has generally been used to form a resist pattern. However, the optical transfer method is said to have a limit of 0.5 μm, and due to the influence of Fresnel diffraction and the small depth of focus, in order to form fine patterns of 1 μm or less, multilayer resist methods and CE
A process technology such as the L method must be used. For this purpose, electron beam direct writing and X-ray lithography are being considered as processes. However, the electron beam direct writing method has drawbacks such as the need to use multilayer resist in order to achieve throughput, stage joint accuracy, and high aspect ratio. On the other hand, X-ray lithography is considered particularly promising because it is a transfer process and is suitable for mass production, and because it uses X-rays with wavelengths ranging from several to several tens of wavelengths, the effect of diffraction is ignored in practical use. It is possible to achieve a resolution of up to about 0.1 μm.

X-ray lithography can be roughly divided into two methods. One is the currently used method, in which X-rays are irradiated with the X-ray mask and wafer placed close to each other at a distance of about 10 μm.
One is the so-called proximity method, in which a pattern on a mask is transferred, and the other is a projection exposure method, in which a projected image of the mask is transferred using an X-ray imaging element.

The present invention relates to an X-ray mask necessary for the latter projection exposure, but all conventional masks are transmission masks, and the wavelength of the X-rays used in X-ray lithography ranges from several decades to several dozen. X-rays in the so-called soft X-ray region are easily absorbed by substances, so the substrate of the X-ray mask is made of an X-ray transparent material such as BN (boron nitride). An extremely thin film of approximately several micrometers is used, and an X-ray absorbing thin film such as Au is patterned on the same layer. For this reason, it is mechanically very fragile and extremely difficult to handle, and it has many problems such as strength, distortion due to heat, flatness, etc., and the manufacturing process is complicated.

C9 Problems to be Solved by the Invention The present invention solves the problems of conventional transmission masks by providing a reflective X-ray mask patterned on an X-ray reflective substrate with an X-ray focusing function. The purpose is to solve the problem.

21 Means for Solving Problems In a substrate surface cut into a flat plate from a curved crystal that is curved so that the lattice plane involved in X-ray diffraction in the crystal has a focusing function for diffracted X-rays, The first layer is manufactured so that the inclination between the substrate surface and the crystal lattice plane is such that the Bragg reflection (diffraction) X-ray at the center of the cut out substrate surface coincides with the normal line of the substrate at the same center. An X-ray reflective mask was provided by patterning an X-ray absorbing thin film on the crystal substrate.

E. Function The present invention utilizes X-ray diffraction using a curved crystal, and as shown in FIG. 2, the X-rays emitted from the X-ray source S are
After hitting M, only the X-rays irradiated onto the part of the mask where there is no patterned X-ray absorbing thin film are diffracted by the crystal lattice of the mask substrate and focused on the X-ray drifting element F. The image of the X-ray mask is formed on the wafer W by the X-ray imaging element F.

At this time, in order for the image formed on the wafer to be a reduction of the X-ray mask, the mask surface must be perpendicular to the optical axis A of the imaging optical system, and the X-ray source S must be It should not be on top.

Although this is an important part of the present invention, such conditions,
That is, in order to make it possible to match the diffracted X-rays at the center of the mask with the optical axis A of the X-ray imaging element F, the lattice plane C of the curved crystal is aligned with the normal to the substrate as shown in FIG. The X-ray absorbing thin film M is patterned on the same crystal substrate, and the X-ray absorbing thin film M is patterned on the same crystal substrate. A line-reflection mask was created, and therefore, by using such an X-ray mask, it became possible to place it perpendicular to the optical axis of the imaging optical system.

To, Example FIG. 1 shows an embodiment of the X-ray mask of the present invention.

In FIG. 1, K is a substrate cut out from a curved crystal with a lattice constant d, which is a flat plate cut obliquely from a curved crystal in which the lattice plane C is curved with the center of curvature at the Ro point. An X-ray reflective mask M is created by patterning (Au, etc.). O is the center point of the mask, C is the lattice plane of the curved crystal, R is its radius of curvature, and i is X
The angle of incidence of the ray, S is the X-ray source, F is the Fresnel zone.
Corresponds to the plate. Consider an X-ray with wavelength λ. Q.

U is the point where the X-ray that satisfies Bragg's condition at point -L of the mask passes through point 0 and intersects with the central X-ray that satisfies Bragg's condition; The point where an X-ray that satisfies the condition passes through point 0 and intersects with the central X-ray (optical axis A) that satisfies Bragg's condition, R is the center of curvature of the curved crystal, and J and N are straight lines from the point -L. Assuming that the foot of the perpendicular line is ORo, 00, the X-ray incident angle and reflection angle at the ±L point and the 0 point are all equal, so the point 0. -L, U
, Ro, and Q are on the same circumference r and are points.

0, T, Ro, and P are also on the same circumference r'.

Normal OR to crystal lattice plane C with lattice constant d.

X-rays of wavelength ^ that are incident at an angle i to Since they weaken each other, the light appears to be reflected only in the direction of the reflection angle i.

Considering the case where the cutting plane (substrate surface) is cut out, the normal line at the center of the cutting plane (substrate surface) makes an angle i with the normal line of the lattice plane, so the ! OR.

If it is placed on a line symmetrical to the normal line at the center of the cutting plane, the normal line at the center of the substrate plane will be in the X-ray diffraction direction of the wavelength ^ that satisfies the above Bragg's conditional expression (■), that is, the light of the imaging optical system. Coincides with axis A. , in the ray flux on the paper, if α is the angle between the diffracted X-ray that satisfies the Bragg stripe 1'4- at a point 1L at a distance w'r;a from the center of the substrate surface and the optical axis, then α is the angle between the normal to the lattice C at the -L point and the normal to the lattice C at the 0 point, so tan cz=LJ/Rg J=w-cos i/ (R-w-sin i>■O
Q=w/Lana=(R-w-sin i)/cos i
■0U=UN+NO=UL cos a+w-sin2i=QLco
s 2 i −cos a +w −sin
2 iHowever, QL=OQ/cos a,', 0U=cos 2 i (R-w-sin
i) /cos i+w Hsin 2 1 = (2Rcos”i+w-sin i −R)/co
st・・・・・・・・・■Similarly, OP= (R+w −sin i) / cos i
・・・・・・・・・■0T=eos 2 L (R+w-
sin L) /cos i)-w-sin 2
1 = (2Rcos”1-w-5in 1-R)/cos
t・・・・・・・・・・・・■, and X that satisfies Bragg's condition at points ±L from the center 0 of the board surface
Considering the aberration based on the midpoint between the point where the line intersects with the X-ray that satisfies Bragg's condition at the 0 point, the value is the same on both the object point and image point sides, ±w-tani...・・・・・・・・・・・・
...becomes ■. Therefore, the X-ray imaging element is separated from the substrate by R/
cost・・・・・・・・・・・・・・・・・・
... Place the X-ray source S on the optical axis at a distance of ■, on a line symmetrical with respect to the optical axis and the normal to the lattice plane at the center 0 of the substrate, and (2acos'1-R)/cos from the center point of the substrate. i・・---・・
It should be installed at a distance of ■.

As an example, Ge with X-ray wavelength λ=5.406A, curved crystal, lattice constant d=3.25A, and 1=33.76
Using the (111) plane of
Consider the case where the distance from the center of the substrate surface to the imaging element F is 600+i+s.

The radius of curvature R of the curved crystal is R/cos3 from the above formula (■)
3.7°=600,', R=600Xcos 33.7°=499.
2 (mm), and if the source is placed in the middle of the longitudinal aberration, then
The position Y of the radiation source is calculated from the above formula (■) as follows: Y= (2Reos
'1-R) /cos 1=277.2 (m garden) Maximum aberration 2w-taoi is 2w-tan i =2X25Xtan 33.7=3
3.3 (+sm), but since this degree of aberration is not a problem in practice, it is possible to focus X-rays using such a curved crystal, and the X-rays can be focused on the surface of the curved crystal. It is possible to project onto a board.

FIG. 2 shows a configuration diagram of a specific example using the X-ray reflective mask of the present invention, where S is an X-ray source, K is an X-ray reflective mask substrate,
M is a mask patterned on the substrate, C is a lattice plane, N is a normal to the lattice plane at the center point of the mask M, F is a Fresnel zone plate which is an X-ray coupling element, and W is a plane that forms an image of the mask. It is a wafer that can be imaged.

In this configuration, the X-rays irradiated from the X-edge source S are
Only the X-rays that hit the ridge of the ray mask, the part of the mask M that is battened on the mask substrate, that is, the part where there is no X-ray absorbing thin film, are diffracted by the crystal lattice of the mask substrate, and are transmitted to the X-ray imaging element. The light is focused on F, and
An image of the ray mask is formed onto the wafer W by an X-ray imaging element F. At this time, since the optical axis is set perpendicular to the surface of the mask M, the X-ray imaging optical system is rotationally symmetrical with respect to the optical axis, and the image formed on the wafer is
The size of the X-ray mask will be reduced.

G. Effects According to the present invention, the mask is held on an X-ray reflective substrate, and a durable and unbreakable reflective X-ray mask can be provided, thereby making it possible to transfer a mask pattern by projection exposure.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a configuration diagram of a specific example using the X-ray reflective mask of the present invention. Figure 1

Claims (1)

[Claims] In a substrate surface cut out into a flat plate from a curved crystal in which the lattice plane involved in X-ray diffraction within the crystal is curved, the inclination of the substrate surface and the crystal lattice plane causes Bragg reflection ( An X-ray reflective mask characterized in that an X-ray absorbing thin film is patterned on the above-mentioned crystal substrate manufactured so that the inclination of the X-rays (diffraction) coincides with the normal line of the substrate at the same center.