In leading edge technologies, Optical Proximity Correction (OPC) plays a critical role in the total imaging flow. Large
investments in terms of time and engineering resources are made to obtain the required models and recipes to get the OPC
job done. In the model building area, the metrology component is becoming more and more critical. Questions like which
structures to put in a calibration pattern, how to measure, where to measure them, and how often has a serious impact on
the calibration dataset, and thus on the final model.
Corner rounding starts to become an increasingly important factor in imaging and device performance. Because of
this, the model 2D behavior needs to be verified as the least, using reliable metric. In this paper two techniques are
described.
Finally the cost of model building is discussed. When the number of measurements for a model calibration is
considered, available machine time almost always plays a key role. In this paper, a slightly different approach is made on
this problem by looking at the cost of the different components of model calibration, and how that is going to progress in
the process generations to come.
We have investigated the requirements for resist materials in via-first dual damascene copper processes. We first patterned vias on a dielectric stack, and then, after via etching and stripping, we formed metal trench patterns using KrF/ArF lithography. A bottom anti-reflective coating (BARC) was used to fill the vias prior to the resist coating in order to protect the bottom of the vias during the trench etching. Trench patterns were formed on the BARC using chemically amplified resists. We found that resists with lower transparency and a lower maximum development rate (Rmax) were not developed in the vias on the partially filled BARC. When the trench patterns were etched with resist residue in the vias, severe fence defects were observed around the via openings at the bottom of the trenches. These defects cannot be removed by dry or wet stripping. Complete removal of the resists in the vias prevented the formation of fences. Simulation of the resist profile showed the use of resists with high transparency and a high Rmax prevented the accumulation of resist residue in the vias. A KrF resist formulated with higher transparency and a higher Rmax was completely developed even in the vias, so that trench patterns without the fences were formed after trench etching.
To improve the CD controllability of isolated lines, we have developed a new method using multiple-focus exposure in alternating phase-shift lithography. In this paper, the imaging performance such as DOF, exposure latitude, mask linearity, and CD controllability is discussed through both experiments and simulation. Multiple-focus exposure experiments were performed using a KrF scanner by giving a tilt offset between the image focal plane and the wafer leveling plane. For the conventional alternating phase-shift method, the CD-focus curve showed a strong concave shape and thus the DOF was rather small. By applying multiple-focus exposure, the shape of the CD-focus curve changed from concave to flat, and therefore the DOF was much improved. We have also found that the CD controllability considering focus errors can be improved by our method.
To enhance the depth-of-focus (DOF) of isolated lines, we have developed a new method using multiple-focus exposure in the negative-tone resist process. Experiments were performed using a KrF scanner by giving a tilt offset between the image focal plane and the wafer leveling plane along the scan direction. Using this new method, we obtained 0.75- micrometers DOF for a 180-nm isolate line, which was much larger than that in the conventional exposure. Furthermore, we evaluated the common DOF for 180-nm lines having five different pitches. Our method improved the DOF of not only isolated lines but also lines having various pitches.
The stage vibration effect on imaging performance, such as DOF and CD uniformity is evaluated experimentally and compared with simulation analysis. Various kinds of 0.25 - 0.18 micrometer patterns are investigated by using KrF excimer scanner with 0.6 NA and 0.75 partial coherency and two types of chemically amplified positive resists. In the case of a standard resist for 0.25 micrometer level patterning, the CD at the best focus changed and the DOF decreased rapidly with increasing moving standard deviation (MSD) in 0.18 micrometer level pattern formation. Allowable MSD value of L&S pattern was estimated to be around 25 nm. To improve the stage synchronous error margin, the application of a high resolution resist was effective on L&S and isolated space patterns (about 40 nm), but showed little improvement for isolated line and hole patterns. Therefore, totally allowable MSD value was still about 30 nm. In particular it was found that both isolated line and hole patterns were very sensitive to stage vibration effect. Strict stage control has to be required for 0.18 micrometer patterns even if the high resolution resist is used.
To enhance depth of focus (DOF) for isolated line patterns, we have developed a new assistant pattern method. In this method, opaque additional patterns are placed beside the attenuated phase-shift main pattern. DOF enhancement effects of this and conventional assistant pattern method were evaluated by means of a KrF excimer exposure tool with variable NA (0.45, 0.50 and 0.55). Using the new method with off-axis illumination, we obtained 1.5 micrometers DOF for 0.25 micrometers isolated line pattern, much wider than that achieved in the conventional method (0.9 micrometers ). Furthermore, we confirmed that this new method was effective not only for improving the exposure dose latitude but also for reducing the optical proximity effect.
In this study, the optical proximity effect (OPE) of positive and negative tone line patterns is compared under a variety of exposure conditions. 0.25 micrometers lines with various pitch sizes were printed by a KrF stepper, and the CD variation as a function of pitch was evaluated. We found that the OPE was suppressed significantly in negative patterns under various conditions. The effect of resolution enhancement techniques on the OPE is also investigated. We found that negative patterning with the combination of off- axis illumination and attenuated phase-shift masks not only improved DOF but also gave a small OPE.
The dissolution kinetics of a 3-component chemically amplified DUV positive resist (base resin; t-BOC protected polyhydroxystyrene, PAG; benzenesulfonic acid derivative, dissolution inhibitor; t-BOC protected bisphenol A;) was investigated under various conditions. Particularly, the effects of the dissolution inhibitor on the dissolution rate characteristics together with the effect of the t-BOC protection ratio of the base resin were studied. Moreover, in order to obtain ideal dissolution characteristics, a resist profile simulation analysis was carried out. The dissolution rate contrast as well as the slope N of log(dissolution rate)-log(exposure dose) plots increased with increasing inhibitor concentrations. However, a very high inhibitor concentration induced a severe standing wave effect and T-topping profile, resulting in the deterioration of resist performance. Therefore, it was discovered that inhibitor concentration has an optimum value in this resist system. These results are similar to those of t-BOC protection ratio in base resin. According to resist simulation, the slope N was closely related to resist performance, but the dissolution rate contrast was not. A slope value of more than 15 was necessary for 0.25 micrometers patterning (focus margin > 1.3 micrometers ). In addition, the acid diffusion length was one of the key factors: suitable diffusion length was essential for achieving a good resist profile; short diffusion length induces a severe standing wave profile and a long diffusion length deteriorates resolution capability. Based on the analysis of the dissolution characteristics and resist profile simulation, it was concluded that the optimization of the base resin structure and inhibitor concentration is effective for modifying the dissolution parameter. Moreover, it was also found that a steep slope (> 15), moderate dissolution contrast (approximately 10,000) and adequate acid diffusion length (approximately 35) can bring about ideal dissolution characteristics leading to 0.25 micrometers pattern formation.
Dissolution kinetics of a 3-component chemically amplified positive resist, which consists of t-BOC protected phenolic resin, benzenesulfonic acid derivative as a PAG and an additional dissolution inhibitor, have been investigated under various conditions. Especially, the effects of t-BOC protection ratio and molecular weight of the base resin have been studied. In a previous paper, we reported that the dissolution rate R of a 2- component positive resist was determined by one rate determining step, i.e., developer penetration into hydrophobic t-BOC protected phenolic resin. Rapid formation of surface insoluble layer which induced T-toping profiles deteriorated its original resist performance. In this paper, we evaluated both t-BOC protection ratio and the molecular weight dependencies of the dissolution characteristics. The 3-component resist evaluated did not produce distinct T-topping profile when time duration between exposure and PEB was within 30 minutes.
KEYWORDS: Lithography, Carbon, Diffusion, Excimer lasers, Absorption, Chemically amplified resists, Catalysis, Scanning electron microscopy, Deep ultraviolet, Chemical species
The chemically amplified negative resist, composed of polyvinylphenol derivative as a base resin, melamine derivative as a crosslinker and alkyl sulfonic acid derivative which has several number of carbon atoms (n equals 3, 4 and 8) as a photoacid generator PAG, has been investigated. The absorbance of this resist system remains constant even in the introduction of different alkyl sulfonic acid type PAG materials. The resolution, as well as the depth of focus, was not so different from each other within the carbon number from n equals 3 (n- and iso-propyl) to n equals 4 (n-butyl). In the case of n equals 8 (n-octyl), however, the resolution capability was degraded drastically and the depth of focus was also reduced. Furthermore, the carbon number of alkyl sulfonic acid affected the resist profile, that is, rounded profile (n equals 3) became rectangular (n equals 4) or overhang (n equals 8) profile. Especially, very heavy overhang profile was observed in the case of n equals 8, therefore, good resolution could not be achieved. And, the standing wave effect at the side wall increased with increasing carbon number. Relationship between lithographic performance and acid size was investigated by evaluating the dissolution rate characteristics. The fact that the dissolution kinetics were almost the same in the cases of n equals 3 and n equals 4 but degraded in the n equals 8, was consistent with lithographic performance as mentioned above. Based on these results, the most suitable acid size for this chemically amplified negative resist could be determined.
PbTiO3 films having a perovskite structure have been successfully grown on sapphire, MgO, and Si substrates by the photo-MOCVD technique using tetraethyl lead, titanium tetraisopropoxide, oxygen, and nitrogen dioxide. When O2 was used as an oxidizing gas, polycrystalline perovskite PbTiO3 films were grown at substrate temperatures higher than 600 degree(s)C. UV light irradiation affected the growth rate and crystalline structure. Only when films were grown using the photo-MOCVD method, highly (111) oriented PbTiO3 films were obtained on (0001) sapphire at 600 degree(s)C. When NO2 was used, perovskite PbTiO3 films were grown at a substrate temperature of 530 degree(s)C using the photo- MOCVD method. The use of NO2 in the photo-MOCVD process significantly reduced growth temperature due to its wide absorption wavelength. The electrical properties of films were also measured. The step coverage of films obtained using the photo-MOCVD method was fairly good.
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