Several liquid crystal (LC) modes, such as twisted nematic, vertical alignment (VA), and in-plane switching, have been
in competition with each other in the LC display market. Among them, the VA mode has been widely used because of
the high contrast ratio. Since the LC molecules are aligned perpendicular to the substrate in the initial state, an excellent
dark state can be obtained at normal viewing direction. However, effective phase retardation of LC layer at oblique
viewing direction differs greatly from that at normal viewing direction. Thus, gamma distortion phenomenon occurs at
oblique view direction. To reduce the gamma shift in the VA mode at oblique viewing direction, multi-domain VA
modes were proposed. Although gamma shifts of these modes are smaller than that of the single domain VA mode, the
problems still remain. Recently, several technologies for 8-domain alignment have been proposed to decrease the gamma
shift at off-axis. However, additional driving circuits are required to realize the eight-domain structure. In this paper we
report technologies for the multi-domain VA mode with no additional driving circuits. By using the proposed
technologies, we can obtain the dual threshold voltage in each sub-pixel to realize the multi-domain VA mode with no
decrease of contrast ratio.
Thinner absorber structure in EUVL mask is supposed to be applied in 2x HP node since it shows several
advantages including H-V bias reduction. Here, lithographic performances of EUVL masks as a function of absorber
stack height are investigated using ADT exposure experiments. Wafer SEM images show that minimum resolution is
almost identical at ~27.5 nm with absorber thickness ranging from 45 to 70 nm. Simulations also exhibit that NILS and
contrast become maximized and saturated in those ranges. However, thinner absorber structure using 50-nm-thick
absorber shows much lower H-V bias than conventional structure using 70-nm-thick absorber. MEEF, EL, DOF, and
LWR are also slightly improved with thinner absorber. One of the noticeable issues in thin absorber is low OD which
results in pattern damages and CD reduction at shot edges due to light leakage from the neighboring exposures. To
overcome these issues, appropriate light shielding process during mask fabrication as well as minimizing OoB radiation
in EUVL scanner are required. Another item to prepare for 2x HP node is to increase defect detection sensitivity with
19x nm inspection tools. Thus, absorber stacks with new ARC layer optimized for 19x nm inspection should be
developed and applied in EUVL mask blanks.
Phase-shifting EUVL masks applying thinner absorber are investigated to design optimum mask structure with less shadowing problems. Simulations using S-Litho show that H-V bias in Si capping structure is higher than that of Ru capping since the high n (= 0.999) of Si increases sensible absorber height. Phase differences obtained from the patterned masks using the EUV CSM are well-matched with the calculated values using the practical refractive index of absorber materials. Although the mask with 62.4-nm-thick absorber, among the in-house masks, shows the closest phase ΔΦ(= 176°) to the out-of-phase condition, higher NILS and contrast as well as lower H-V bias are obtained with 52.4-nm-thick absorber (ΔΦ = 151°) which has higher R/R0 ratio. MET results also show that lithography performances including MEEF, PW, and resist threshold (dose), are improved with thinner absorber structure. However, low OD in EUVL mask, especially in thinner absorber structure, results in light leakage from the neighboring exposure shots, and thus an appropriate light-shielding layer should be introduced.
Lifetime of EUVL masks which are intentionally contaminated with carbon is investigated by comparing Si and Ru
capping layer. Carbon deposition is observed not only on the multilayer, but also on the absorber sidewall of the mask.
Deposited carbon on the sidewall during EUV exposure gradually varies mask CD and also induces the changes in the
wafer printability and dose in the scanner. In addition, we compare the effects of carbon contamination between Si and
Ru capped blank. Ru capped blank shows longer mask mean time between cleaning (MTBC) than Si capped blank by 25% in our experiments.
This paper describes the simulation approach of the improvement of dispersion tolerance for an electrical-binary-signalbased duobinary transmitter. We can transmit the duobinary signals over 200 km of singe-mode fiber by optimizing the relative time delay and the driving voltage.
This paper presents several ways to implement cost-effective optical duobinary transmitters using low-cost optical modulators. We show that, compared to the conventional scheme, the proposed schemes can be used to implement cost-effective duobinary transmission systems without a significant sacrifice of system performance.
Differential phase-shift keying (DPSK) has recently attracted a great deal of attention especially for high-speed, long-haul transmission systems. The reason is that, compared to conventional on-off keying (OOK), this format offers ~3 dB better receiver sensitivity and higher tolerance to some fiber nonlinearities. To take full advantage of this modulation format, however, balanced reception should be provided for the receiver, which makes the system implementation complex and costly. This paper reviews the recent progress of DPSK format, with emphasis on system impairments by linear and nonlinear optical phenomena. We also compare the merits and demerits of DPSK with those of OOK format.
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