Photospeed requirements for 193 nm and EUV lithography are approximately 10 mJ/cm2. As wavelengths are scaled, photon energy is increased, and the discrete photon events may become a fundamental contributor to resist edge roughness. A theoretical analysis of the shot noise impact on line edge roughness was performed. Based on the results, we estimate 1 nm of shot noise induced roughness at 10 mJ/cm2 resist sensitivity for 193 nm lithography. Therefore, discrete photon events are not expected to be a significant contributor to local CD control in 193 nm lithography. We conclude that edge roughness typically observed in 193 nm resists is therefore a process related effect.e However, at EUV, we are approaching a shot noise limit and edge roughness may be enhanced by photon counting effects. Without taking photo-acid diffusion into account, we estimate 8 nm of shot noise induced edge roughness at the EUVB wavelength and 10 mJ/cm2 sensitivity. Hence, local CD control may be compromised by the stringent 10 mJ/cm2 photospeed requirement. Edge roughness is improved by relaxing the resist sensitivity requirement. In addition, most resist technologies are likely to be chemically amplified, and thermally driven diffusion will improve local CD control but at the expense of image contrast and cross- wafer CD control.