KrF Excimer Laser Exposure Research Articles

Local growth of vertical aligned carbon nanotubes by laserinduced surface modification of coated silicon substrates

The stimulation of carbon nanotubes (CNT) growth in a thermal CVD process using an acetylene/nitrogen gas mixture by KrF-excimer laser exposure of iron nitrate coated silicon is described. At moderate laser fluences of ∼1 J/cm2 the growth of nanotube bundles up to 100 μm consisting of vertical aligned multi-walled carbon nanotubes (VA-MWCNT) is observed. AFM measurements show the formation of nanoparticles in the laser-exposed areas. At this catalytic sites the nanotubes grow and sustain one another and forming the well-defined bundles. Via the laser exposure the control of the catalytic sites formation and consequently the nanotube growth and properties can be achieved.

Etching microscopic defects in polycarbonate due to high dose ArF or KrF laser exposure

The ArF or KrF excimer laser exposure on the polycarbonate (PC) with corresponding doses higher than ϕ th 5.2 J / cm 2 , at 32 mJ / cm 2 fluence per pulse and 5 Hz pulse repetition rate (PRR), induces regular defects leading to self assembled defect structure following electrochemical etching (ECE). We have observed the conical-like structure for ϕ > ϕ th , whereas the polymer experiences hardening effect due to crosslinking when ϕ < ϕ th . Subsequently, conical-like, structure turns into track-like pits developing under ECE multiple treeing. Self assembled defect structure may be seen by naked eye as white spots, despite SEM illustrates a type of periodic pit formation-morphology. The exact explanation of the effect is not well understood yet. It looks like alpha tracks in the polymer surface, however the PC pieces were simply treated by excimer lasers at high doses, and they have not been exposed to the nuclear particles afterwards. We could not observe those effects at 308 nm (XeCl laser) or longer wavelengths at 351 nm (XeF laser) where UV photoablation does not occur. It indicates that UV ablation establishes surface degradation at shorter wavelengths, leading to laser micro etching. The mean track (defect) density is about one order of magnitude greater than the normal alpha tracks. Increasing UV doses, polymer undergoes a plateau, corresponding to etched defect saturation on PC.

Atomic Force Microscopy Study on the Dissolution Processes of Chemically Amplified Resists for KrF Excimer Laser Lithography

The surface images of chemically amplified KrF excimer laser resists after development were measured by atomic force microscopy (AFM). From the AFM images at various exposure doses, the dissolution behavior of the polyvinylphenol-based KrF resists differed from that of novolak-diazonaphthoquinone (DNQ) resists. An explanation for the different dissolution behavior has been proposed by considering the difference in the mechanisms of formation of soluble sites between chemically amplified resists and novolak-DNQ resists (non-chemically amplified resists). In addition, AFM topographic images of the resists dissolving layer by layer were observed clearly in the resist spin-coated on a Si wafer. The step heights of the layered structure observed by AFM are in good agreement with the computed value of the distance between two adjacent nodes of standing waves formed by KrF excimer laser exposure. The layered dissolution may be applied to the processing of thin polymer films.

Effect of Coherence Factor σ and Shifter Arrangement for the Levenson-Type Phase-Shifting Mask

To apply the Levenson-type phase-shifting mask to actual ULSI devices, we have investigated the resolution limit and the depth of focus (DOF) for several shifter arrangements experimentally. Resist patterns were printed using a KrF excimer laser stepper of 0.42 NA. It was suggested that the σ value should be decreased for the various shifter arrangements to obtain higher resolution. Moreover, it was found that resolution capabilities of irregular shifter patterns were higher than those of conventional mask patterns under the condition σ=0.3. In addition, it was found that arrangements where the optical phases for both side apertures are equal should be avoided in the fabrication of 0.30 µm rule devices by a KrF excimer laser exposure with the Levenson-type phase-shifting mask.

New portable conformable masking excimer laser lithography using water-soluble contrast enhanced material

A new portable conformable masking (PCM) using excimer laser lithography has been developed. This method is characterized by the combination of poly(dimethylglutarimide) and the water‐soluble contrast enhanced material developed here and the use of KrF excimer laser exposure. Using this lithography, we obtained good resist pattern profiles and submicron region resolution by a very simple process.

Recent Progress in Excimer Laser Lithography

ABSTRACTA KrF excimer laser exposure method has been developed for laboratory use, which employs 10 to 1 achromatic projection lens of 0.37 NA and 5x5 mm field size , and a TTL alignment system using the double diffraction method, which was realized by the use,of the achromatic lens. Novolak type mid-UV resists, such as AZ-5214 and PR-1024, were best suited for use in 248 nm exposure, considering the sensitivity and etching resistance from a practical viewpoint, and an additional post exposure baking process also improved the resist profile. The dependences of the exposure characteristics on the energy density per pulse and pulse frequency of these resists were not observed in the region of the practical exposure conditions. An alignment precision of x±30-= 0.2 μm was achieved for the alignment mark consisting of poly Si pattern. Thus, a 0.3 μm line and space pattern was realized by using tri-level resist process and a 0.2 μm gate pattern was successfully fabricated on the coplanar pattern with a 0.4 μm step.