X-ray imaging: applications to patterning and lithography

X-ray lithography (XRL) is a patterning technique for the fabrication of semiconductor devices with very small dimensions (⩽100 nm). In this process the device and circuit layout images are formed by exposing a thin layer of organic material, the photoresist. XRL is based on the idea that the short wavelength (≈1 nm) of the radiation allows a faithful reproduction of the desired pattern to very small dimensions. The physics of the interaction of the x-rays with matter dictates many aspects of the technique: the imaging process is controlled by Fresnel diffraction, and the recording process by the interaction of low-energy photoelectrons with the resist material. Phase shift effects play a key role in the image formation process, and are used to improve the sharpness of the image. To achieve high-resolution patterning it is necessary to carefully design the pattern itself, and optimize several exposure parameters. This paper presents a detailed discussion of the image formation process, and a brief review of other technical aspects of the technology.