Patent Application
20150212427
1. Field of the Invention
The present invention relates to mirror structures, and, more particularly, to a multilayer mirror structure having an enhanced reflectivity.
2. Description of Related Art
In recent years, along with fine-pitch designs of semiconductor integrated circuits, projection exposure equipment has been developed. In order to improve the resolution of an optical system that is limited by light diffraction, light with a wavelength less than ultraviolet, such as extreme ultraviolet (EUV) light with a wavelength in the range of 11 to 14 nm or deep extreme ultraviolet (DEUV) light with a wavelength in the range of 5 to 8 nm, is usually used.
Generally, a multilayer film structure is provided by alternately forming molybdenum (Mo) and silicon (Si) or niobium (Nb) and silicon (Si) on a substrate through deposition or evaporation. When the Bragg condition is satisfied, reflection waves undergo constructive interferences, thus leading to a high reflectivity. Therefore, such a structure can be used as a mirror.
The wavelength of EUV light is much less than that of visible light and very close to that of X-ray. Since EUV radiation can be absorbed by almost every material, conventional systems having transmission covers and transmission optical elements such as lenses cannot be used. Instead, EUV radiation is reflected or focused by a mirror optical element having a high reflectivity. The mirror optical element is further shaped to guide EUV radiation to a wafer to be patterned.
Therefore, an EUV mirror is required to have a surface with a high reflectivity and be capable of keeping its shape under high heat. To meet the requirements, a multilayer system is applied to a substrate having very low thermal expansion. Generally, 40 molybdenum layers and 40 silicon layers are alternately deposited on a substrate. Each of the molybdenum layers and the silicon layers has a thickness in nano-scale. At the interface between adjacent molybdenum and silicon layers, a portion of radiation is reflected. Theoretically, more than 70% of the incident radiation is reflected. However, since EUV radiation can be absorbed by almost every material, the reflectivity of 70% is only a theoretical value and cannot be reached in reality.
Therefore, how to overcome the above-described drawbacks has become critical.
In view of the above-described drawbacks, the present invention provides a multilayer mirror structure for reflecting EUV (Extreme Ultraviolet) light, which comprises: a substrate; and a plurality of first material layers and a plurality of second material layers alternately stacked on the substrate, wherein each of the first material layers has a plurality of low loss regions each having a low loss member for reducing the loss of the EUV light when the low loss regions are irradiated with the EUV light. In an embodiment, the low loss member is in a form of a through hole penetrating the corresponding first material layer.
In another embodiment, the low loss member is embedded in the corresponding first material layer.
According to the present invention, since each of the first material layers has a plurality of low loss regions each having a low loss member, when the first material layers are irradiated with the EUV light, the low loss members can effectively reduce the loss of the EUV light so as to enhance the reflectivity of the first material layers.
The following illustrative embodiments are provided to illustrate the disclosure of the present invention, these and other advantages and effects can be apparent to those in the art after reading this specification.
It should be noted that all the drawings are not intended to limit the present invention. Various modifications and variations can be made without departing from the spirit of the present invention. Further, terms such as “on”, “a” etc. are merely for illustrative purposes and should not be construed to limit the scope of the present invention.
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It should be noted that a plurality of dashed lines shown in
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In the present embodiment, the gas-state material is embedded in the first material layers 11 to form bubbles, i.e., the low loss members 111. Compared with the first material layers 11 made of silicon, the low loss members 111 have a lower EUV absorption rate and therefore achieve a better reflection effect, thereby enhancing the EUV reflectivity of the first material layers 11.
In the present embodiment, the gas-state material can be, but not limited to, helium, neon, argon, krypton, xenon, radon, fluorine, chlorine, hydrogen, oxygen or nitrogen. For example, the gas-state material can also be air or other gaseous substances.
In addition, the low loss members 111 can be made of a solid-state material such as strontium or beryllium, which is embedded in the first material layers 11 to enhance the EUV reflectivity of the first material layers 11.
Referring to
In the present embodiment, the through holes are of a circular shape and regularly arranged. In other embodiments, the through holes can be of a rectangular shape or a hexagonal shape. Further, the through holes can be regularly or irregularly arranged.
It should be noted that the shape, size and arrangement of the low loss members 111, 111a are not limited to the above-described embodiments. For example, the size or number of the low loss members 111, 111a can be increased as long as they do not adversely affect the structural strength of the first material layers 11.
According to the present invention, a plurality of low loss members 111, 111a are embedded in the first material layers 11 or in the form of through holes penetrating the first material layers 11 so as to reduce the EUV absorption rate of the first material layers 11, thereby enhancing the reflection effect.
The above-described descriptions of the detailed embodiments are only to illustrate the preferred implementation according to the present invention, and it is not to limit the scope of the present invention. Accordingly, all modifications and variations completed by those with ordinary skill in the art should fall within the scope of present invention defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103103092 | Jan 2014 | TW | national |
