Abstract

A new laser-based soft x-ray lithographic technology is described that was developed to utilize conventional resists. It is well recognized that x rays offer better resolution, larger depth of field, larger process latitude, better critical dimension control, and immunity to typical clean room defects when compared to existing or emerging ultraviolet lithographic technologies. Previous x-ray technologies utilized low-yield electron impact tubes that produced hard x rays which were inefficiently absorbed in Novolak resists. This required special hypersensitive resist materials to achieve modest wafer throughputs at the expense of process latitude and process tolerance. Soft x rays (i.e., photon energies <1 keV) are efficiently absorbed in Novolak resist producing exposure sensitivities comparable with that achievable with ultraviolet photons (i.e., E₀ of 50–100 mJ/cm²). The high brightness Hampshire laser-based source is capable of producing 10–20 mW/cm² yielding throughputs of twenty to forty wafers per hour depending on the resist's sensitivity. The source produces x rays from 0.8 to 2.0 nm with ~75% of the incident energy at wavelengths of 1.2-1.6 nm.

© 1988 Optical Society of America