Exposure characteristics of alternate aperture phase-shifting masks fabricated using a subtractive process

Abstract

Exposure characteristics of an alternate aperture phase-shifting mask fabricated using a subtractive process will be discussed. The subtractive process, where the phase-shifted regions are etched into a layer below the chromium, is attractive because it allows for the use of conventional chromium-an-quartz blanks, as well as providing more processing flexibility, However, recent results using a subtractive fabrication process have determined that a linewidth variation of -0.05 f..lm exists between features imaged with etched and nonetched regions of the alternate aperture pattern. This article examines some of the potential causes for this linewidth variation, including mask linewidth control, surface roughness, contamination during phase-shift forming etch step, and sidewall profile and position. Results indicate that the sidewall profile and position are critical parameters in defining the wafer feature size. The impact of phase is also investigated. The wafer feature size depends on the depth of the quartz etch and accurate endpointing of the phase-shift depth is essential for maintaining critical dimension uniformity across an features imaged with a phase-shifting mask.

Level-specific lithography optimization for 1-Gb DRAM

“…Thus alternating PSM's are sometimes classified as strong PSM's whereas attenuated PSM's are classified as 4 Other types of PSM's such as rim [8] and chromeless [9] are not considered because of design and practicality issues. 5 In an actual alternating PSM, mask topography effects cause transmittance imbalance [25] which can be partially or, in some cases, totally corrected [26], [27]. weak PSM's.…”

Transmission and phase balancing of alternating phase-shifting masks (5x): theoretical and experimental results

“…A first approach to this issue is to investigate the influence of the phase etch-depth PS on the printing behavior of the different options. A suitable measure for this influence is the phase index of Equation (2). An increased phase index indicates a worse printing behavior due to the offset of the Bossung-plots of the deep and shallow etched areas.…”

Through-focus image balancing of alternating phase-shifting masks

“…Image imbalance was first reported by Kostelak et al [2] on alternating aperture masks in 1992. From a image formation stand point of view, the phenomenon can be attributed to the presence of a finite 0-th diffraction order that propagates through the stepper imaging lens.…”

“…Several important characteristics of image imbalance can be learned from the model. Several methods have been proposed to reduce or eliminate image imbalance [2][3][4]7,8J. The etchback approach involves wet etch quartz substrate in both the 0 and 180-degree openings.…”