Simulation parameter effects on critical dimension and sensitivity of 193 nm Chemically Amplified Resist
It is helpful in lithography process and developing resist to know the relationship between the critical dimension variation and simulation parameters such as aerial image parameters, the Dill exposure parameters, PEB (Post Exposure Bake) parameters, and development parameters. In this paper the profiles of a 193 nm CAR (Chemically Amplified Resist) were simulated with those various parameter, and those results were analyzed by the response surface methodology (RSM) approach to know the influence of independent factors on a dependent response and to optimize each process. Both the parameter effects of each process and the simulation process effects of the whole process were described about critical dimension and side wall angle so that the sensitivity of lithography process could be assumed. The development parameters were modified with those of flood exposure experiment according to the pattern density and pattern size for more accurate lithography simulation. Also those effects on critical dimension and side wall angle were analyzed. For the validity of our results the quantitative comparison between our results and those of a commercial tool was shown.
Effective exposure-dose measurement in optical microlithography
An accurate measurement technique for effective exposure dose in optical microlithography has been developed. The effective exposure dose can be obtained by a dose monitor mark in a photomask named effective dose-meter, consisting of plural segments including grating patterns with a pitch below the resolution limit and different duty ratios gradually. Since the effective dose-meter does not resolve on a wafer but it makes flood exposure with the dose as a function of the duty ratio, residual thickness of the photoresist after development changes according to the duty ratio. Therefore, the effective exposure dose can be obtained by grasping the duty ratio of the grating patterns in the effective dose-meter corresponding to the position that the photoresist had cleared completely. A calibration technique utilizing an aerial image measurement system also has been proposed to avoid the influence of intra- wafer process variation. The advantages of this method are (1) completely focus-free, (2) the effective dose-meter is small enough to ignore the influence of the intra-wafer process variation on the accuracy, and (3) highly dose resolution of less than 0.5%. It was found that this technique function effectively. The variation of the effective exposure dose in a wafer in the current krypton-fluoride-excimer-laser lithography process was measured as a demonstration of this technology.
Level-specific strategy of KrF microlithography for 130 nm DRAMs
This paper reports technologies that enable KrF microlithography to be extended to 130 nm generation devices. Firstly, focus and dose budget analyses are carried out carefully to estimate their total deviations. Secondly, level specific cell-array patterns and exposure conditions are optimized for obtaining more process windows than the deviations by experiment and simulation. Optical proximity effect (OPE) and process proximity effect (PPE) for each level are investigated for core and peripheral circuit patterns. The key technologies for KrF microlithography, i.e. resolution enhancement technologies (RET) and process proximity correction (PPC), are discussed with a view to realizing 130 nm DRAMs.