JPH0827396B2 - X-ray projection exposure apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray projection exposure apparatus in X-ray lithography, and more particularly to a uniform illumination system thereof.

B. Conventional Technology Conventionally, an optical transfer method has been generally used to form a resist pattern in the LSI manufacturing process. However, in the optical transfer method, it is said that the transfer of 0.5 μm pattern is the limit due to the resolution limit of the lens system, and even if it does not reach that limit, the formation of fine patterns of 1 μm or less, especially the step difference of aluminum wiring pattern etc. Since the influence of Fresnel diffraction and the depth of focus are small when printing on a certain pattern, necking occurs in a single-layer resist and a multi-layer resist method or a process technique such as CEL must be used. As a result, the process becomes complicated and the yield is reduced, and it is said that the limit will be reached in the near future. Then, electron beam direct writing and X-ray lithography are considered as alternative means. However, the electron beam direct writing method has a problem in that a multilayer resist or the like must be used to form a pattern with a high aspect ratio due to throughput, stage joining accuracy, and proximity effect, and the process becomes complicated. . On the other hand, X-ray lithography is particularly promising because it is suitable for mass production because it is a transfer process. Since it uses a wavelength of several A to several tens of A, the influence of diffraction is practically ignored. This is possible, and a resolution of up to about 0.1 μm can be expected. In addition, since X-rays pass through dust, it is possible to reduce the influence of dust in the exposure atmosphere such as scattering and transfer failure. Furthermore, since the depth of focus is deep, a sufficient effect can be expected with a single-layer resist even for pattern transfer onto steps. Therefore, it is not good at optical lithography such as pattern transfer onto steps without waiting for the theoretical limit of 0.5 μm of optical lithography. It is considered that the pattern transfer will be shifted to X-ray lithography.

X-ray lithography can be roughly classified into two methods. One is the so-called proximity method, in which the distance between the X-ray mask and the wafer is close to about 10 μm, X-rays are irradiated, and the mask pattern is transferred.
This is a projection exposure method in which a projection image of a mask is transferred using a line imaging element.

FIG. 2 shows the same-size proximity method. In the figure, the gap g is provided between the X-ray mask 2 having the mask pattern 3 and the wafer 4 on which the pattern is transferred in order to prevent the mask and the wafer from being scratched by contact.
In this configuration, when the X-ray source 1 irradiates the resist 5 on the wafer 4 with X-rays through the X-ray mask 2, the mask pattern 3 is transferred onto the resist 5. However, at the time of pattern transfer, even if there is no blur due to diffraction, the penumbra blur δ = g / L × φ due to the spread of the X-ray source 1 and the runout error r = g / due to the gap g between the X-ray mask 2 and the wafer 4. L × R occurred, and the merit of using X-rays was not fully utilized. There has been a strong demand for a method that solves this problem and sufficiently achieves the effect that the original X-ray diffraction is small. Further, since the exposure is the same size, when an X-ray mask is manufactured, electron beam writing is used to form a resist pattern, but as the pattern width decreases, the difficulty of mask manufacturing increases dramatically. There were technical difficulties.

In order to solve these difficulties, the X-ray reduction projection exposure method has been considered. As an illumination system of this system, as shown in FIG. 3, Bragg's condition 2d sin θ = λ (d: lattice constant,
The X-ray source 1 is placed on the Rowland circle 11 so as to satisfy θ: the angle between the incident X-ray and the lattice plane of the crystal, and λ: wavelength, and the lattice plane of the curved crystal 7 is 0 in the XY plane. −12
Bend along a circle centered on the center of curvature 12 with the radius as the radius, and polish the reflecting surface into a Roland circle 11, and in the XZ plane, X
Intersection 13 with a straight line 0-12 connecting the radiation source 1 and the X-ray focusing point 9
Use a toroidal type curved crystal whose lattice plane is curved along a circle centered at, that is, X-ray source 1, focusing point 9, curvature in all planes including the straight line 1-9 and cutting the dispersive crystal. The crystal 7 is always arranged on the Roland circle 11. With this configuration, the X-ray flux emitted from the X-ray source 1 can be focused on the focal point 9 without aberration. It is considered that the X-ray mask 2 is arranged between the crystal 7 and the focusing point 9 to reduce and project the mask image on the wafer 4 positioned near the focusing point 9. However, the curved crystal used at this time is quite difficult in that the crystal lattice plane is curved to a toroidal plane. Furthermore, this curved plane has a curvature of 1/2 of the lattice plane in the XY plane and a lattice in the YZ plane. It is also difficult to polish along the surface. Further, if the X-ray source 1 is not a point source, the image of the mask 2 transferred onto the wafer 4 will be blurred, which makes it difficult to use the X-ray source as a point source with high intensity.

C. DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention remarkably improves the difficulty in manufacturing the crystal of the illumination system of the X-ray mask as described above, and also shortens the time required for manufacturing and the manufacturing cost. Furthermore, the uniformity of the illumination is improved at the same time, and X with high resolution is provided.
By projecting a reduced image of an X-ray mask using a line imaging element, the feature of high resolution X-rays can be maintained and the contrast of the projected image can be made uniform. The objective is to commercialize a reduced projection batch exposure method suitable for production.

D. Means for Solving Problems In the illumination system of the X-ray projection exposure apparatus, a cylindrical Johan-type or Johansson-type curved crystal that connects the X-ray incident point on the Rowland circle and the X-ray converging point of the crystal is used. The X-ray mask is illuminated uniformly along the circumference of a circle whose radius is the distance between this axis and the center of the curved crystal, and the X-ray mask is illuminated as described above. An X-ray imaging element such as a Fresnel Zone plate or an X-ray multilayer mirror is provided at the position where the X-rays are focused, and an X-ray transmissive mask is placed on the optical axis between the crystal and the imaging element. As a result, the mask image is exposed on the X-ray resist arranged at the position of the image of the X-ray mask formed by the imaging element.

E. According to the present invention, in the illumination system of the X-ray projection exposure apparatus,
Place the X-ray source on the Roland circle in the curved crystal,
It suffices to bend the crystal in one direction by shaking the cylindrical curved crystal along a circumference whose radius is the distance between this axis and the center of the curved crystal arranged on the Rowland circle. Because it can be made smaller in the direction
The difficulty of manufacturing the crystals for the illumination system and the manufacturing time could be significantly reduced, and the price of the crystals was also considerably reduced. By shaking such a cylindrical crystal, X-rays from a point-like X-ray source cannot be completely focused on one point, but in the present invention using a zone plate as an imaging element, this is not a drawback. It is an advantage. That is, the original resolution cannot be obtained unless the entire surface of the imaging element is irradiated with X-rays. Therefore, it is ideal that the X-rays are wasted in a small amount, instead of completely focusing on one point as shown in FIG. For the same reason, even if the X-ray source has a spread, the amount of X-rays that can be used does not have to be wasted so much, so that resolution is obtained by the proximity method, that is, penumbra blur is reduced. Therefore, it is not necessary to make the X-ray source small and have high brightness. Since the X-ray source may have some spread, high brightness can be easily obtained. By illuminating an X-ray mask with such an irradiation system, reducing the image with an X-ray imaging element having high resolution, and baking it on a substrate coated with X-ray resist,
It has become possible to easily obtain highly precise fine patterns.

F. Embodiment FIG. 1 shows a block diagram of an embodiment of the present invention. Figure 1 shows a Fresnel zone plate (FZ
In the embodiment in which P) 9 is used, 1 is an X-ray source and emits a characteristic X-ray flux 6 of MoLα5.406Å. 2 is an X-ray mask provided with a mask pattern 3 to be transferred to the resist 5 on the wafer 4, 7 is a Johansson type curved crystal and has a 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 curved crystal 7.
This is the Roland Yen.

Since the X-ray flux is reflected by the curved crystal 7 when the Bragg condition 2d sin θ = λ is satisfied, in this configuration,
θ = 56 ° 16 ′, and the centers of the X-ray source 1 and the FZP 9 are arranged on the Rowland circle 11 in the XY plane so as to satisfy this Bragg condition. The crystal illuminator 7 bends the crystal lattice plane along the circumference centered on the intersection 12 of the normal in the XY plane and the Roland circle 11, and the reflecting surface is the Roland circle.
It was polished to match 11. In this YZ plane, this crystal element has a straight line connecting the X-ray source 1 and FZP9 as an axis, and for example, a motor 15 is attached to this axis and an arm connecting the axis and the crystal is attached to shake the crystal, or A crystal pedestal with a predetermined radius of curvature along the Z-axis is placed along a guide plate 14 having a radius of curvature equal to that of the crystal pedestal. Make a statue. For example, the same effect can be obtained by forming an X-ray flux 8 focused on a FZP using a toroidal curved crystal of 70 × 70 by shaking a cylindrical curved crystal of 70 × 5 in the Z-axis direction by ± 35 mm. There is. Moreover, the unevenness of the illuminance caused by the error in the minute area of the variation in the curvature due to the location of the individual, which is considered when using the toroidal curved crystal, can be reduced within the individual by shaking one cylindrical curved crystal. It is flattened even if there are variations in processing. Further, it goes without saying that the accuracy is improved by manufacturing a small cylindrical curved crystal rather than a large toroidal curved crystal. For these reasons, it is extremely convenient from the viewpoint of uniform illumination. In this way, a magnified image of the X-ray source 1 having a spread is formed on the FZP 9. Since the cylindrical curved crystal is swung in the Z direction, it deviates slightly from the ideal toroidal surface, and thus some aberration occurs.
At the X-ray focusing point where the FZP is placed, scattering of the X-ray focusing points occurs, which is rather effective in uniformly illuminating the FZP9.
When the X-ray mask 2 is arranged at a predetermined position between the crystal illuminating element 7 and the FZP 9, the X-ray flux reflected by the crystal illuminating element 7 becomes X.
The X-ray flux transmitted through the mask 2 by uniformly illuminating the line mask 2 is
Focus on FZR9. The effective surface of the X-ray mask 2 is 50 x 50 mm
Therefore, the mask pattern 3 is formed of Au on the BN (boron nitride) substrate. In such a region, X
When X-rays are radiated from the radiation source 1 to the crystal illuminating element 7, the mask pattern 3 is transferred as a 1/5 reduced image on the 10 × 10 mm field of the resist 5 by the FZP 9. In this case, since all the X-rays that have passed through the mask pattern 3 pass through the FZP9, there is no waste of X-rays.

The above method is an example in which almost aberration-free illumination is performed, but aberration occurs depending on the arrangement of the illumination system and the form of the crystal illumination element (for example, the number of crystal divisions is small).
Not all of the light that irradiates the line mask reaches the imaging element and is not necessarily involved in imaging. In this case, the shape of the effective focal point of the X-ray source is adjusted to the aberration image of the illumination system of the imaging element,
Alternatively, the X-ray flux related to the image formation may be selected so as not to cause any practical problem by making it sufficiently large. For example,
When the number of crystal divisions is small, the image of the point source becomes a line perpendicular to the plane of the Rowland circle, but by focusing the X-ray source in the direction parallel to the plane of the Rowland circle, the light is condensed. At the points, the X-rays are distributed in the rectangular area, and the entire surface of the imaging element can be effectively irradiated.

As described in the above embodiments, an X-ray projection reduction exposure apparatus can be constructed by combining the crystal illuminating element and the FZP, but it goes without saying that the method of shaking the crystals is not limited to the above embodiments. There is meaning in itself to reduce the difficulty and time for producing crystals by shaking. In order to obtain a reduced image of the X-ray mask, an X-ray element other than FZP, for example, a reflecting objective made of an X-ray mirror may be used. Further, it can be used not only for the reduced image but also for the same size projection exposure by the same method.

G. Effect According to the present invention, a crystal having a configuration in which a slender Johann-type or Johansson-type cylindrical curved crystal is shaken along the toroidal surface so as to focus X-rays from a common X-ray source at a common focusing point. It is possible to use a powerful X-ray light source by using the illumination element in the illumination system of the X-ray projection exposure type X-ray mask and combining it with an imaging element with high resolution such as FZP or X-ray mirror. Therefore, an unpleasant image with a high resolution and a depth of focus can be formed. Further, since it is an X-ray transfer, dusts and the like attached to the mask are not transferred, the mask has a long life because of the projection method, and it is easy to manufacture an X-ray mask when reduction exposure is performed. Therefore, it is possible to deal with LSI process with 100Mbit class integration up to the lithography process without using any special process technology and without reducing throughput.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a side view schematically showing a conventional equal-magnification proximity X-ray lithography, and FIG. 3 is a diagram showing a focusing principle of a toroidal curved crystal. Is. 1 ... X-ray source, 2 ... X-ray mask, 5 ... Resist, 7 ... Crystal illuminator (Johansson type curved crystal), 8 ... X-ray flux, 9 ...
… Fresnel zone plate (FZP), 10 …… Reduced image, 11…
… Roland circle, 12 …… Center of curvature of xy plane of lattice plane, 13…
… Centers of curvature of the xz plane of the lattice and reflection surfaces, 14 …… Guide plate, 15 …… Motor

Claims (1)

[Claims] 1. An X-ray incident point in which a Johan-type or Johansson-type cylindrical curved crystal is arranged on its Rowland circle, and an X-ray flux diverged from this incident point is focused on the Roland circle by the crystal. A straight line connecting the X-ray focusing points is used as an axis, and a desired amount is swung so that the crystal plane is along a circumference having a radius as a distance between the axis and the center of the curved crystal. Fresnel zone plate or X
An X-ray imaging element such as a line multilayer film mirror is arranged, an X-ray transmission mask is arranged on the optical axis between the X-ray imaging mirror and the same, and it is arranged at the position of the image of the mask by the imaging element. An X-ray projection exposure apparatus, which exposes the mask image onto an X-ray photoreceptor or an X-ray resist.