 Solution

Projection lithography images a mask through reduction optics; its resolution scales approximately as $k_1\lambda /\mathrm{NA}$. It offers parallel exposure, high throughput and accurate repeat patterning, but small features demand short wavelengths, large numerical aperture, costly optics and high-quality masks, with a shrinking depth of focus.

Electron beam lithography directly writes a programmable pattern using a focused electron beam. Its much shorter wavelength and small probe permit nanometre-scale features without an optical mask, making it attractive for research prototypes, low-volume devices and mask fabrication. Its limitations are serial writing time, charging of insulating substrates, beam drift, field stitching and forward/backscattering proximity effects in electron-beam lithography. Electron wavelength alone does not set the resist resolution. E-beam is often preferable for a few very small custom structures; projection remains preferable for high-volume repeated manufacture.