| Popis: |
The comment that typical clean room 'soft' defects (i.e., airborne, carbon-based particles) are transparent to x-rays is stated as a fundamental attribute of x-ray lithography. However, data showing lithographic conditions which result in a reduction in defect density have not yet been widely published. This paper reports an analysis of defect printability for soft x-ray lithography at wavelengths of 0.6 to 2.2nm and denotes exposure and resist development conditions under which representative soft and 'hard' reticle defects did not print. Resolution reticles with features down to 0.5pm were produced using Hampshire's baseline process which consists of electroplated gold absorber on a silicon support membrane. Latex spheres ranging in diameter from 0.36 to l.Opm were applied by VLSI Standards, Inc. to simulate soft defects. The large exposure latitude for x-ray lithography allows using an overexposure to reduce the impact of lower contrast defects without appreciable CD change. The printability of soft defects and defect-induced wall angle perturbations in resist patterns were also investigated through simulations using a modified version of SAMPLE and the results agreed with the observations. Identification of what constitutes a printable reticle defect for x-ray lithography is not as straightforward as that for optical lithography. |
