Fabrication of quantum dot array diffraction grating for soft x-ray spectroscopy

A novel diffractive optical element (DOE), quantu-dot-array diffraction grating(QDADG), used in soft X-ray spectroscopy has been fabricated for the first time. The QDADG, which consists of a large number of quantum dots distributed on a substrate as sinusoidal function, has many advantages in theory over conventional transmission grating (TG) in soft X-ray spectroscopy, such as doubtless diffraction efficiency, no higher-order diffraction and no subordination diffraction maximum, and so on. So, it can be predicted theoretically to improve the precision and Signal Noise Ratio of soft X-ray spectroscopy in laser plasma diagnosis. But, there are many difficulties in the fabrication of soft X-ray spectroscopy QDADG because of its much small dimension and complex pattern. In this paper, a combined lithography was proposed to fabricate QDADG including electron beam lithograph (EBL) and proximity X-ray lithograph(XRL). The diffraction property of QDADG has also been proved to be consistent with theoretical prediction from test experiment. In the process of fabrication, because of the thin film substrate of soft X-ray QDADG, the backscattering of incidence electrons can be effectively restrained in the electron beam lithograph, which can cause much higher resolution. Without proximity effect correction, QDADG with 250nm minimal unit has been successfully fabricated. In order to further increase the spectroscopy resolution and dispersion power of QDADG, it is necessary to carry out proximity effect correction in electron beam lithograph.