As EUV approaches high volume manufacturing, reticle defectivity becomes an even more relevant topic for further investigation. Current baseline strategy for EUV defectivity management is to design, build and maintain a clean system without pellicle. In order to secure reticle front side particle adders to an acceptable level for high volume manufacturing, EUV pellicle is being actively investigated. Last year ASML reported on our initial EUV pellicle feasibility. In this paper, we will update on our progress since then. We will also provide an update to pellicle requirements published last year. Further, we present experimental results showing the viability and challenges of potential EUV pellicle materials, including, material properties, imaging capability, scalability and manufacturability.
Electron-beam array lithography (EBAL) uses array optics to expose 108 to 1010 resolution elements without mechanical motion. The array optics are based on the use of a first stage of deflection (coarse deflection) which selects one of an array of lenslets. The lenslet array is followed by a second stage of deflection (fine deflection) which selects the final spot position. In order to maximize exposure rate and also minimize mechanical motion, it is proposed to use a 3×3 array of array optics channels to expose a 100 mm wafer. As a numerical example of the projected throughput of such a system consider a 20 MHz stepping rate per channel and 0.5 μm pixels. Then (3×1010 pixels)/(9×2×107 pixels per s) ≊170 s. Now if variable spot sizes and vector writing are used such that only 10% of the pattern is exposed using the smallest feature (pixel), the exposure time is reduced to ∠20 s. Consistent with these calculations, EBAL systems are presently under development with engineering goals of 0.5 μm smallest features, 100 mm wafers, and throughputs of 50 wafers/h. The electron optics of these systems are all electrostatic, and use either thermionic (e.g., LaB6) or field-emission (e.g., W/Zr) cathodes. EBAL systems require that patterns be ’’stitched’’ across the boundaries of the lenslet fields in the array lens. This can be accomplished by the use of a standard calibration plate having fiducial marks at the corners and sides of lenslets. Measurement of the positions of these fiducials provides data from which to calculate a set of stitching constants for each lenslet of each electron-beam channel. Overlay between different pattern levels on a wafer is accomplished by a similar process using data from fiducial marks at the corners of each chip which is being written on a wafer. By these means any pattern level on any wafer can be exposed in any EBAL exposure station.
Methods are described for reducing shot-noise in magnetic-film memories which are to be read magneto-optically with the auxiliary aid of an electron beam. In such memories the principal source of shot noise is from the light which is used to illuminate the memory array. The following methods of reducing array shot noise are considered: (1) selective background, (2) magneto-optical balance, (3) temperature control of magneto-optical spectra in rare-earth iron garnets (REIG). It is concluded that the use of REIG spectra appears to offer not only the best, but also a satisfactory solution to the array shot-noise problem.
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