Use of a planarizing layer to improve multilayer performance in extreme ultra-violet masks

#1. Field of the Invention

#The present invention relates generally to a reticle or mask used in a lithography process, and, more particularly, to fabricating a reticle or mask for use in an extreme ultra-violet lithography process.

#2. State of the Art

#By way of example, particular embodiments of the invention will be described with reference to the accompanying drawing, in which:

#FIG. 1 shows an EUV reticle of the present invention.

#The present invention relates to the fabrication and use of a reticle or mask in an EUV lithography process. To achieve the desired surface flatness of a substrate, a planarizing layer is formed on the substrate. Ideally, the planarizing layer makes a surface of the substrate having raised surface perturbations or cupped lower areas into a planar surface. The planarizing layer changes the topography of the substrate from non planar to, ideally, perfectly planar. The planarizing layer is formed over, or in contact with, a surface of the substrate. The planarizing layer provides a flat surface upon which a reflective layer may be formed. By using the planarizing layer to cover and smooth surface defects in the substrate, the defects do not affect the reflectivity of the overlying reflective layer and are not propagated to the semiconductor wafer. The planarizing layer may remain a part of the reticle because the EUV radiation is not transmitted through the reticle. Therefore, the planarizing layer does not have to be removed from the reticle before patterning.

#As shown in FIG. 1, the EUV reticle 2 comprises, in ascending order, a substrate 4, a planarizing layer 6, and a reflective layer 8. Even though reflective layer 8 is shown as a single layer for the sake of clarity of description, reflective layer 8 is actually a multilayer structure, as known in the art. Reflective layer 8 comprises more than one layer, which is represented by the dashed line in FIG. 1. For example, reflective layer 8 comprises multiple layers of Mo/Si or Mo/Be, with individual layers of the reflective layer 8 alternating between Mo and Si or Be. The individual layers may exhibit substantial differences in their refractive indices, with reflective layer 8 comprising a low refractive index layer and a high refractive index layer. For example, a transition metal element exhibiting a high melting point may be used for the low refractive index layer while a semiconductor material may be used for the high refractive index layer. The individual layers of reflective layer 8 may be formed by sputtering, such as sputtering in a dual source RF or DC magnetron sputtering system, ion-beam sputtering, or other sputtering techniques known in the art. In addition, conventional deposition or formation techniques known in the art may be used, including, but not limited to, chemical vapor deposition (“CVD”).

#The substrate 4 provides physical support to the EUV reticle 2, upon which the remaining layers are formed. In addition, the substrate 4 may provide surface flatness and low thermal expansion characteristics. While the substrate 4 may be comprised of silicon, the substrate 4 may also comprise a material with a CTE of approximately 1.0 ppm/° C. or less. It is desirable that the substrate comprises a material with a CTE of approximately 0.5 ppm/° C. or less. More desirably, the substrate 4 comprises a material with a CTE of approximately 0.1 ppm/° C. or less. It is also desirable that the substrate 4 is an ultra-low thermal expansion glass material, such as ULE™ glass or ZERODUR™ glass ceramic (Corning, Inc., Corning, N.Y.). The optical properties of the substrate 4 are not critical to the invention because the reflective layer 8 reflects the EUV radiation before it reaches the substrate 4.