Takuya Takeuchi

Impacts of CF+, CF2+, CF3+, and Ar Ion Beam Bombardment with Energies of 100 and 400 eV on Surface Modification of Photoresist

Photoresists used in advanced ArF-excimer laser lithography are not tolerant enough for plasma etching processes. Degradation of photoresists during etching processes might cause not only low selectivity, but also line edge roughness (LER) on the sidewalls of etched patterns. For a highly accurate processing, it is necessary to understand the mechanisms of etching photoresists and to construct a new plasma chemistry that realizes a nano scale precise pattern definition. In this study, the modified layers formed on the surface of a photoresist by the bombardment of fluorocarbon ions of CF+, CF2+, and CF3+, and argon (Ar) ions were analyzed by X-ray photoelectron spectroscopy (XPS). The etching yield of the modified steady-state surface was almost dependent on the mass of incident ion species. The surface composition was modified with increasing dosage of each ion species, and reached a specific steady state that was dependent on the ion species. The bombardment of F-rich ion species such as CF2+ and CF3+ resulted in the formation of not only fluorocarbon layers, but also graphite like structures on the surface. On the basis of these results, the surface reaction for the ion-beam-induced modification was discussed.

Development of the sputtering yields of ArF photoresist after the onset of argon ion bombardment

Modification of an advanced ArF excimer lithographic photoresist by 400 eV Ar ion irradiation was observed in situ in real time using both infrared spectroscopy and a quartz microbalance sensor. The photoresist sputtering yields had a characteristic behavior; the sputtering yields were higher than unity at the beginning, until an ion dose of 2 × 1016 ions cm−2. Thereafter, the yields decreased immediately to almost zero and remained constant with the yield at zero until a dose of approximately 4 × 1016 ions cm−2 was reached. At larger doses, the yields increased again and reached a steady-state value of approximately 0.6. This development of the sputtering yield after the onset of ion bombardment is explained by an ion-induced modification of the photoresist that includes preferential sputtering of individual groups, argon ion implantation and the generation of voids. All these effects must be taken into account to assess line-edge-roughness on a photoresist subjected to highly energetic ion irradiation.

Surface roughening of photoresist after change of the photon/radical and ion treatment sequence

The formation of surface roughness during ion irradiation was suppressed by photon/radical pretreatment of a photoresist with HBr or H2 plasmas. The opposite sequence of treatment after ion irradiation enhanced the surface roughness. The enhancement of roughness after post-treatment was not correlated with a decrease in the film thickness, reactions of Br radicals at the surface, or with the presence of the amorphous carbon-like layer generated by ion irradiation because similar modification was observed for the pretreatment. Fourier transform infrared spectroscopy analysis revealed that the intensities of peaks originated from the C=O absorption of methacrylic acid and methacrylate groups were decreased by irradiation with vacuum ultraviolet light at wavelengths in the range between 115 and 170 nm emitted from HBr or H2 plasmas. The removal of the C=O groups possibly generated dangling bonds and induced crosslinking reactions of the photoresist polymers. The nonuniformity of crosslinking reactions on the roughened photoresist intensively increased the surface roughness.The formation of surface roughness during ion irradiation was suppressed by photon/radical pretreatment of a photoresist with HBr or H2 plasmas. The opposite sequence of treatment after ion irradiation enhanced the surface roughness. The enhancement of roughness after post-treatment was not correlated with a decrease in the film thickness, reactions of Br radicals at the surface, or with the presence of the amorphous carbon-like layer generated by ion irradiation because similar modification was observed for the pretreatment. Fourier transform infrared spectroscopy analysis revealed that the intensities of peaks originated from the C=O absorption of methacrylic acid and methacrylate groups were decreased by irradiation with vacuum ultraviolet light at wavelengths in the range between 115 and 170 nm emitted from HBr or H2 plasmas. The removal of the C=O groups possibly generated dangling bonds and induced crosslinking reactions of the photoresist polymers. The nonuniformity of crosslinking reactions on the...

Dependence of absolute photon flux on infrared absorbance alteration and surface roughness on photoresist polymers irradiated with vacuum ultraviolet photons emitted from HBr plasma

The absolute fluxes of vacuum ultraviolet (VUV) photons emitted from HBr plasma were analyzed and the effects of VUV photons on a photoresist polymer in ArF-excimer-laser (193 nm) lithography were quantitatively investigated on the basis of the infrared spectra attributed to the C=O region. The spectral peak intensity assigned to the methacrylic acid (MAA) in the photoresist drastically decreased owing to the loss of this monomer caused by the irradiation of VUV photons at dosages below 16 × 1016 photons/cm2. X-ray photoelectron spectroscopy observation showed that the removed monomer moved to the surface and generated volatile products that induced a decrease in film thickness. As a consequence, the surface became rough during the early-stage irradiation at dosages lower than 16 × 1016 photons/cm2 owing to the monomer loss of MAA with volatile product formation and subsequent cross-linking reactions.

A novel fast and flexible technique of radical kinetic behaviour investigation based on pallet for plasma evaluation structure and numerical analysis

This paper describes a new, fast, and case-independent technique for sticking coefficient (SC) estimation based on pallet for plasma evaluation (PAPE) structure and numerical analysis. Our approach does not require complicated structure, apparatus, or time-consuming measurements but offers high reliability of data and high flexibility. Thermal analysis is also possible. This technique has been successfully applied to estimation of very low value of SC of hydrogen radicals on chemically amplified ArF 193 nm photoresist (the main goal of this study). Upper bound of our technique has been determined by investigation of SC of fluorine radical on polysilicon (in elevated temperature). Sources of estimation error and ways of its reduction have been also discussed. Results of this study give an insight into the process kinetics, and not only they are helpful in better process understanding but additionally they may serve as parameters in a phenomenological model development for predictive modelling of etching for ultimate CMOS topography simulation.

Anaysis of photoresist surface modified by fluorocarbon ions and radicals

Summary form only given. Photoresist is indispensable material for the pattern formation using lithography and subsequent etching processes. It is well known that the photoresist for ArF (193 nm) excimer laser lithography have poor tolerability against etching plasmas and they may often be deformed and some roughness on the and surface and sidewall of the photoresist patterns are developed. This roughness will cause the hindrance of exact nano fabrication. In order to improve process condition and resist materials toreduce such roughness, it is indispensable to understand the reaction mechanism of photoresist and reactive species. We investigated the reaction of ArF photoresist with the mass-separated fluorocarbon ions, CF x + (x=1∼3)1.

Sticking coefficient of hydrogen radicals on ArF photoresist estimated by parallel plate structure in conjunction with numerical analysis

Investigation of radicals kinetic behavior and estimation of radical sticking coefficient become indispensable for establishing plasma processing control by its internal parameters. This approach is required for plasma processing of single-nanometer gate length field effect transistors and 3-diemnsional gates in particular. In our works we have developed new technique for radicals kinetic behavior investigation and its sticking coefficient estimation. Our approach is based on application of parallel plate structure in conjunction with numerical analysis. This approach allows for radicals behavior investigation apart from ions and ultraviolet photons. Moreover this approach allows for analysis role of radical direct and indirect fluxes. By comparison of measured profile thickness and simulated stuck radicals profile we were able to estimate hydrogen radical sticking probability to ArF photoresist.