Photolithographic mask exhibiting enhanced light transmission due to utilizing sub-wavelength aperture arrays for imaging patterns in nano-lithography
A nanophotolithography mask includes a layer of an electrically conductive optically opaque material deposited on a mask substrate in which regular arrays of sub-wavelength apertures are formed. The plasmonic excitation in the layer perforated with the sub-wavelength apertures arrays under the light incident on the mask produces high resolution far-field radiation patterns of sufficient intensity to expose a photoresist on a wafer when propagated to the same. The fill-factor of the mask, i.e., the ratio of the total apertures area to the total mask area, may lead to a significant increase in mask manufacturing throughput by FIB or electron beam “writing”. The mask demonstrates the defect resiliency and ability to imprint coherent clear features of nano dimensions and shapes on the wafers for integrated circuits design.
1. A method for fabricating a far-field photolithographic mask for imprinting at least one feature at a wafer in a nano-lithography, comprising the steps of:
forming a far-field photolithographic mask as a double-layer structure consisting of a first layer and a second layer by the steps of:
(a) forming said first layer from an electrically-conducting optically opaque material of a predetermined thickness of approximately 100 nm on said second layer, said second layer being a mask substrate;
(b) directing an energetic beam onto said first layer to mill an aperture of a predetermined diameter extending through said predetermined thickness of said first layer;
(c) moving said energetic beam a predetermined distance from said aperture to mill at least another aperture through said predetermined thickness of said first layer;
(d) repeating said step (c) to create at least one array of a plurality of said apertures, thereby defining at least one pattern area at said first layer, wherein said at least one pattern area filled with said array of said plurality of said apertures corresponds to the at least one feature to be created at the wafer, said apertures being spread within said at least one pattern area according to a predetermined order, wherein said at least one pattern area has a predetermined periphery including a plurality of corners; and
forming correctional structures outside said at least one pattern area and adjacent said plurality of corners along said periphery of said at least one pattern area, wherein each of said correctional structures is formed by mill on n×n matrix of correctional holes by said energetic beam through said predetermined thickness of said layer, wherein n is an integer and 1≦n≦3.
2. The method of claim 1 , wherein said apertures in said at least one pattern area are milled by a Focused Ion Beam (FIB) directed towards said layer of the electrically-conducting optically opaque material.
3. The method of claim 1 , wherein said predetermined distance between the apertures is in the range of 1.40 nm-320 nm, wherein said at least one array of apertures constitutes an A×B matrix of the apertures, wherein A=2, 3, . . . , 10, . . . , N, and wherein B=2, 3, . . . 10, . . . N, and wherein N is an integer.
4. The method of claim 1 , further comprising the step of:
optimizing said predetermined distance between said apertures and said predetermined diameter of said apertures in correlation with an exposure dose provided by an illumination light incident on the wafer though said mask in accordance with a desired size and quality of said at least one feature to be imprinted on the wafer.