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This work demonstrates that photochemical doping of CVD-grown graphene can be easily achieved using photoacid (PAG) and photobase (PBG) generators such as triphenylsulfonium perfl uoro-1-butanesufonate (TPS-Nf ) and 2-nitrobenzyl N -cyclohexylcarbamate (NBC). The TPS-Nf ionic onium salt photoacid generator does not noticeably dope or alter the electrical properties of graphene when coated onto the graphene surface, but is very effective at inducing p-doping of graphene upon exposure of the PAG-coated graphene sample. Likewise, the neutral NBC photobase generator does not signifi cantly affect the electrical properties of graphene when coated, but upon exposure to ultraviolet light produces a free amine, which induces n-doping of the graphene. Electrical measurements show that the doping concentration can be modulated by controlling the deep ultraviolet (DUV) light exposure dose delivered to the sample. The interaction between both dopants and graphene is also investigated. The photochemical doping process is able to tune the work function of the single-layer graphene samples used in this work from 3.4 eV to 5.3 eV. Finally, a p-n junction is fabricated and analyzed, showing that it is possible to control the position of the two current minima (two Dirac points) in the ambipolar p-n junction.

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Top-down critical dimension scanning electron microscopy ͑SEM͒ is still the workhorse metrology tool used for nanoscale structure analysis, such as measurement of photoresist features, during integrated circuit manufacturing. However, the degree to which top-down SEM imaging can accurately be used to quantitatively determine the size, shape, and roughness characteristics of three-dimensional structures such as photoresist features has not been carefully characterized. A rigorous Monte Carlo simulation of scanning electron microscopy has been developed to probe the relationship between the roughness of a three-dimensional feature and the line edge roughness ͑LER͒ as measured by SEM. The model uses the differential Mott cross section to compute elastic scattering, while inelastic scattering and secondary electron generation are handled using dielectric function theory. The model can calculate the electron scattering for any arbitrary three-dimensional geometry. Experimental SEM measurements of photoresist nanostructures show good agreement with the simulation output. The critical dimension of the resist determined from SEM best matches the true resist feature width when the line edge is defined using a high image threshold because the roughness on the outer edge of the resist tends to cause an increase in SEM signal that is nonproportional to the amount of material on the outer edge of the feature. LER determined from SEM was found to be significantly smaller than the true resist feature sidewall roughness. The measured LER is typically greater than 50% smaller than the actual sidewall roughness.

A series of nonionic photoacid generators ͑PAGs͒ are synthesized and their acid generation efficiency measured under deep ultraviolet ͑DUV͒ and electron beam exposures. The acid generation efficiency is determined with an on-wafer method that uses spectroscopic ellipsometry to measure the absorbance of an acid sensitive dye ͑Coumarin 6͒. Under DUV exposures, common ionic onium salt PAGs show excellent photoacid generation efficiency, superior to most nonionic PAGs tested in this work. In contrast, when under 100-keV high energy e-beam exposures, almost all of the nonionic PAGs show significantly better acid generation performance than the ionic onium salt PAGs tested. In particular, one nonionic PAG shows almost an order of magnitude improvement in the Dill C acid generation rate constant compared to a triarylsulfonium PAG. The high energy acid generation efficiency is found to correlate well with the electron affinity of the PAGs, suggesting that improvements in PAG design can be predicted. Nonionic PAGs merit further investigation as a means for producing higher sensitivity resists under high energy exposure sources.