Digital Scanner (DS) is an optical maskless exposure tool with a SLM (Spatial Light Modulator) and a DUV solid-state laser with wavelength of 193 or 248 nm. There are two configurations of SLM: a tilt SLM, in which each micro-mirror pixel tilts to change the amplitude of reflected light; and a piston SLM in which each micro-mirror pixel moves along optical path to change the phase of reflected light. Both types are applicable for DS, but piston SLM has a better image contrast due to strong phase shift effect. A DS proof-of-concept tool (DS-POC) with piston SLM and exposure wavelength of 193 nm was developed, which has a similar imaging resolution with the DS248, a tool planned as the first DS product for lithography of 180 nm node or below. Exposure results of 180 nm node logic patterns by DS-POC are presented. Process window analysis of the logic patterns by simulation shows better performance of piston SLM than tilt SLM on exposure latitude. CD accuracy of less than 10% was experimentally demonstrated for resolution chart of L/S with CD from 150 nm through 300 nm using piston SLM at DS-POC.
Nikon has been developing the Digital Scanner, an optical maskless exposure tool with a DUV light source. The Digital Scanner uses a spatial light modulator and rasterized pattern data, instead of glass photomasks, to project an optical image. The modulator is a micromirror array and each micromirror takes one of two possible states, so the pattern data are essentially equivalent to a one bit per pixel bitmap image. In spite of the one-bit depth input similar to a black-and-white bitmap, the Digital Scanner can control projected patterns in subpixel resolution because the pixel size is chosen to be smaller than the resolution of the projection optics. Besides the projection hardware, we have also developed special pattern data preparation system for the Digital Scanner in order to realize the subpixel controllability. Polygons from GDSII or OASIS files are rasterized by dedicated pixel-based algorithms so that the optical image of the resulting pixel data becomes equivalent to that of input polygons. Another pattern data converter with optical proximity correction (OPC) capability is also being developed and available for large area conversion. We explain the exposure system of the Digital Scanner and report the progress of the pixel-based data preparation system including recent demonstration printing results of exposure data generated by the new converter that has OPC capability.
Digital scanner (DS), a deep ultraviolet optical maskless exposure tool is being developed. DS uses a micromirror-type spatial light modulator to create the “mask” pattern combined with a solid-state laser with a wavelength of 193 or 248 nm. The exposure concept of DS and advantage of solid-state laser as an exposure light source is described. DS proof-of-concept tool with resolution of half-pitch 80 nm L/S was developed. The exposure results of maskless unique application, such as large area printing and chip ID printing for security purposes, are shown.
The first planned Digital Scanner product, DS248, will have the optical resolution of 110 nm and overlay accuracy of less than 10 nm, the same level as a KrF mask scanner. In addition, DS248 has more application areas, such as individual chip customization and large-area printing up to wafer size, with KrF resolution, which are not possible with the current mask scanner but will be beneficial for performance enhancement of semiconductor devices in future. The latest exposure results of DS-POC, which has the similar imaging performance with DS248, are introduced including chip ID exposure on entire 200 mm wafer and exposure of wafer scale integration substrate. Simulation data of high aspect ratio patterning with high resolution by means of integration of multiple heads of solid-state laser is described. Development progress of DS’s pixel mask conversion software that directly generates pixel mask from target pattern with OPC is reported.
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