JPH0577286B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to uniform illumination technology for X-ray projection exposure in X-ray lithography.

B. Prior 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, processes such as the multilayer resist method and CEL method are required to form fine patterns of 1 μm or less. We have to use technology. This complicates the process and causes a decrease in yield, and it is thought that it will reach its limit in the near future. Electron beam direct writing and X-ray lithography are being considered as alternative means. However, the electron beam direct writing method has drawbacks such as the need to use multilayer resist in order to achieve high 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 since it uses light with a wavelength of several Å to several hundred Å, the effect of diffraction can be ignored in practical use. It is possible to expect a resolution of up to about 0.1 μm.

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

Figure 3 shows the same size proximity method. In the figure, an X-ray mask 2 having a mask pattern 3
are provided close to the wafer 4 to which the pattern is to be transferred at a distance g. In this configuration, when X-rays from the X-ray source 1 are irradiated onto the resist 5 on the wafer 4 through the X-ray mask 2, the mask pattern 3 is transferred onto the resist 5. However, during pattern transfer, the penumbra blur δ=g/L due to the spread of the X-ray source 1
A runout error r=g/L×R occurs due to xψ and the distance g between the X-ray mask 2 and the wafer 4, and the advantage of using X-rays is not fully utilized. In addition, since it is a same-magnification exposure, when manufacturing an X-ray mask, the resist pattern is formed by electron beam drawing.
As the pattern width decreased, technical difficulties such as the difficulty of mask manufacturing increased dramatically.

C. Problems to be Solved by the Invention In order to solve the above-mentioned technical difficulties, the present invention uses a curved crystal in the projection exposure illumination system to uniformly irradiate the X-ray mask. The purpose is to utilize the feature of X-rays, such as resolution, and to achieve uniform contrast of projected images.

D. Means for solving the problem In the illumination system for the X-ray projection exposure method, a curved crystal with focusing ability and a Fresnel zone plate or X-ray multilayer provided at the position where the X-rays are focused by the crystal are used. An X-ray transmission mask was provided on the optical axis between an X-ray imaging element such as a membrane mirror, and the crystal and the imaging element.

According to the present invention, in an illumination system for an X-ray projection exposure method, if an X-ray source is placed on the Rowland circle of a curved crystal and the crystal is irradiated with X-rays, the crystal will emit X-rays. is focused at another point on the Rowland circle. Therefore, an X-ray imaging element such as a Fresnel zone plate or an X-ray multilayer mirror is installed at the same position, and an X-ray transmission mask is installed on the optical axis between the crystal and the imaging element. By installing a wafer coated with X-ray resist to project the mask pattern behind the image element, the reduced pattern of the X-ray mask was projected onto the wafer, making it possible to easily obtain highly precise patterns. .

F. Embodiment FIG. 1 shows a configuration diagram of an embodiment of the present invention. FIG. 1 shows an example in which a Fresnel zone plate (FZP) 9 is used as a projection imaging element. In the figure, 1 is an X-ray source which emits a characteristic X-ray flux 6 of MoLα5.406 Å. 2 is an X-ray mask provided with a mask pattern 3 to be transferred to a resist 5 on a wafer 4;
7 is a Johansson-type curved crystal with lattice constant d=3.25Å
Ge(111) is used. 10 is a reduced image of the mask pattern 3 formed on the resist 5, and 11 is a Rowland circle of the curved crystal 7.

When the X-ray flux satisfies Black's condition 2dsinθ=λ, it is reflected at the curved crystal 7, so in this configuration, θ=56°16', and the The lattice plane of the crystal is bent to a circumference centered on the intersection point 12 of the normal line at the center of the curved crystal and the Rowland circle 11, and the reflective surface is polished to match the Rowland circle 11. do. at the same time yz
In a plane, a so-called curved crystal is used, in which the lattice plane and the reflective plane coincide on the circumference centered on the point 13 where the straight line connecting the X-ray source 1 and the FZP 9 intersects the x-axis.
A uniform X-ray flux 8 converging on the FZP is formed. This prevents the image of the X-ray source 1 from being transferred onto the resist 5. Curved crystal 7 and FZP9
An X-ray mask 2 is placed at a predetermined position, and the X-ray mask 2 is uniformly illuminated. The effective surface of X-ray mask 2 is 50 x 50 mm, and it is made of BN (Boron Nitrite).
A mask pattern 3 is formed on the substrate using Au.
In such a configuration, when the X-ray source 1 emits radiation onto the curved crystal 7, the mask pattern 3 is transferred by the FZP 9 onto a 10×10 mm field of the resist 5 as a 1/5 reduced image.

FIG. 2 shows an explanatory diagram of the light focusing principle of a curved crystal.
According to Bragg's condition, when the angle θ between the incident direction of the X-ray and the crystal lattice plane satisfies 2dsinθ=λ, the lattice plane and θ are in the plane containing the incident ray and the normal to the crystal lattice plane. reflected from the corners. If the Bragg condition is not met, no reflection will occur. In the xy plane, the lattice plane 14 is made to coincide with a circle centered on the point 12, and draws a circle having the points 0 and 12 as both ends of its diameter. This circle is called the Roland circle 11.
A ray of light that is incident at point 0 at an angle of θ with the lattice plane so as to satisfy the Bragg condition is reflected at an angle of θ with the lattice plane. If the lattice plane at point 15 is a circle centered on point 12, and the reflective surface is on the Rowland circle 11, the circumferential angle α of arc 1-12 is 90°-θ, so the incidence with the lattice plane is The angle is θ. Also, arc 1
Since the circumferential angle of 2-16 is also 90°-θ, the reflection angle with the lattice plane is θ. In other words, if the reflective surface is on the Rowland circle and the lattice surface is on a circle centered on point 12, then the light emitted from a point on the Rowland circle 11 that satisfies the Bragg condition will be reflected again at another point on the Rowland circle 11. The light is focused on a point 16. On the other hand, in the xz plane, if the grating surface 14 and the reflecting surface 17 are on a circle centered on the point 13, the X-rays emitted from the X-ray source 1
The line can be focused at point 16. For this reason, the imaging element is arranged at 16 positions.

The above method is an example in which completely aberration-free illumination is possible, but aberrations may occur depending on the arrangement of the illumination system and the shape of the curved crystal, and not all of the light emitted by the X-ray mask may be condensed. It does not necessarily reach the image element and be involved in image formation. In this case, the shape of the effective focal point of the X-ray source should be matched to the aberration image caused by the illumination system of the imaging element, or be made sufficiently large, so that the X-ray flux related to imaging can be selected so as to cause no practical problems. good.

As explained in the above example, curved crystal and FZP
By combining these, an X-ray projection reduction exposure apparatus can be constructed. However, the form of the curved crystal is not limited to the above embodiment, and in order to obtain a reduced image of the X-ray mask, For example, a reflective objective made of an X-ray mirror may be used. Furthermore, it can be used not only for reducing images but also for performing same-magnification projection exposure using a similar method. In short, X
Uniform illumination of an X-ray mask, which is essential for performing line projection exposure, is achieved by utilizing the fact that a curved crystal reflects X-rays when it satisfies the Bragg condition.

G. Effects According to the present invention, a curved crystal is used in the illumination system of an X-ray mask using an X-ray projection exposure method, and by combining it with an imaging element having high resolution such as an FZP or an X-ray mirror reflection objective, high resolution can be achieved. Its resolving power allows it to form images with a deep depth of focus. In addition, since it is an X-ray transfer method, dust attached to the mask is not transferred, and since it is a projection method, the mask life is longer, and when performing reduction exposure, it is easier to manufacture an X-ray mask. Therefore, it has become possible to handle the lithography process of LSIs with 100 Mbit class integration without using any special process technology or reducing throughput.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is an explanatory drawing showing the principle of focusing X-rays with a curved crystal, and Fig. 3 is a diagram showing the conventional X-ray lithography using the same-magnification proximity method. FIG. 2 is a schematic side view.

Claims (1)

[Claims] 1. Between a curved crystal, an X-ray imaging element such as a Fresnel zone plate or an X-ray multilayer mirror provided at a position where the X-rays are focused by the crystal, and the crystal and the imaging element. An illumination system for an X-ray projection exposure method, characterized in that an X-ray transmission mask is provided on the optical axis of the illumination system.