Highly selective etching of a silicon dioxide layer using a very thin physical-vapor-deposited amorphous carbon layer (PVD-ACL) was investigated in a dual-frequency superimposed capacitively coupled plasma etcher. The following process parameters of the normalC4normalF8/CH2normalF2/normalO2 /Ar plasmas were manipulated: CH2normalF2/(CH2normalF2+normalO2) flow ratio, high frequency (HF) power (PHF) , and low frequency power (PLF) . A wide processing window existed to produce the ultrahigh etch selectivities of a SiO2 layer using the patterned PVD-ACL mask. The etch gas flow ratio played a critical role in determining the process window for ultrahigh silicon oxide/ ACL etch selectivity due to the disproportionate change in the degree of polymerization on the SiO2 and ACL surfaces. Etching of the ArF photoresist/bottom antireflective coating (BARC)/ SiOx /ACL/silicon-oxide-stacked structure allows the use of a very thin PVD-ACL as an etch mask layer for the etching of high aspect ratio silicon dioxide patterns.

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We investigated the processing window for the etch selectivity of silicon oxynitride ͑SiON͒ layers to extreme ultraviolet ͑EUV͒ resists and the variation in line edge roughness of EUV resists during etching of SiON/EUV resist structures in a dual-frequency superimposed capacitively coupled plasma etcher. We varied the processing parameters of the CH 2 F 2 /͑CH 2 F 2 + N 2 ͒ gas flow ratio and low frequency source power ͑ P LF ͒ in CH 2 F 2 /N 2 /Ar plasma and the O 2 flow rate in CH 2 F 2 /N 2 /O 2 /Ar plasma. The CH 2 F 2 /N 2 flow ratio was found to play a critical role in determining the processing window for infinite etch selectivity of SiON/EUV resists due to disproportionate changes in the degrees of polymerization on SiON and EUV resist surfaces. The preferential chemical reaction between hydrogen and carbon in the hydrofluorocarbon ͑CH x F y ͒ polymer layer, and the nitrogen and oxygen in the SiON layer, presumably led to the formation of HCN, CO, and CO 2 etch by-products and resulted in smaller steady-state hydrofluorocarbon thicknesses on SiON. As a result, continuous SiON etching due to enhanced SiF 4 formation occurred while the CH x F y layer was deposited on the EUV resist surface. The critical dimension and line edge roughness increased with increasing CH 2 F 2 /͑CH 2 F 2 + N 2 ͒ flow ratio due to an increased degree of polymerization.As device integration continuously increases for the fabrication of Si semiconductor devices, shorter wavelengths, such as 13.5 nm extreme ultraviolet ͑EUV͒ light, are needed to resolve nanoscale features. Double patterning technology using immersion ArF lithography with a light wavelength of 193 nm is currently being developed for patterning down to 32 nm nodes. Extreme ultraviolet lithography ͑EUVL͒ is also a leading candidate with the potential for resolving features smaller than 20 nm.Dielectric etch processes incorporating silicon oxide ͑SiO 2 ͒, silicon nitride ͑Si 3 N 4 ͒, or silicon oxynitride ͑SiON͒ hard-mask layers using EUV resists are expected to become a critical step for the patterning of future-generation multilayer resist structures with amorphous carbon ͑a-C͒ etch masks due to the fact that they require continuously decreasing resist thicknesses. 1-9 Therefore, the development of appropriate resists is a critical issue for next-generation EUVL. EUV resists must have different chemical structures than ArF resists and must also satisfy requirements for sensitivity, resolution, linewidth roughness, and line edge roughness ͑LER͒. Current chemically amplified resists ͑CARs͒ are widely applied as 193 nm ArF resists. CAR-type EUV resists provide the advantages of high sensitivity and resolution for EUVL, 10 but disadvantages include large LER, pattern collapse, and absorption of EUV light. 10 Variation in the LER during plasma etching has also become an important issue in patterning for nanoscale features because the LER of resists is transferred to the underlayer during dry etching. 11,12 Decreasing resist layers for high resolution at a sub-32 nm scale re...