PARAMETRIC ANALYSIS OF IRRADIANCE DISTRIBUTION IN PROXIMITY PRINTING OF MICRO CIRCULAR AND ANNULUS APERTURES

摘要

Proximity printing is one of the lithography processes used in fabricating micro-scale components and systems to transfer mask pattern to the substrate. This paper investigates pattern distortion in the proximity printing process of circular arrays and annulus arrays in micro scale by dimensionless parameters. The effect is analyzed based on the Huygens-Fresnel diffraction theorem. The irradiance distribution exposed on the photoresist at different εx, the dimensionless parameter representing the ratio of the gap between the mask and the photoresist to the radius of the circular aperture, are investigated. Two dimensional (2D) and 3D irradiance distributions on the projected photoresist for single-aperture, dual-aperture and multi-aperture masks are analyzed and simulated. It showed that diffraction effect, which causes interactions among apertures, increases as ε,x decreases. This results in the distortion of the projected pattern in proximity printing. The boundaries between the exposed and shared areas are blurred when %x increases. The effect of annulus patterns is further investigated by introducing another parameter εa, the ratio between the radii of the inner and the outer circles. It is found that peaks appear at the center that is supposed no exposure. It also found that the intensity of exposition moves to the outer area when εa increases. Experiments to verify the simulated distortion is also conducted using a He-Ne laser. The results showed consistency with the simulation and verified that near-field diffraction is the major factor for the pattern distortion as the diffraction becomes stronger when ε,x decreases.