Fabrication of high-efficiency ultraviolet blazed gratings by use of direct Ar_2-CHF_3 ion-beam etching through a rectangular photoresist mask

摘要

In ultraviolet spectroscopy, there is a constant need to improve the diffraction efficiency. A blazed grating can concentrate most of the light intensity into a desired diffraction order, so it is the optimum choice among gratings of different kinds of profile. As the operating wavelength of most UV spectral applications is less than 200 nm, the required blaze angle is small; groove irregularity and surface roughness of nanometer magnitude can cause a significant loss of diffraction efficiency. Therefore, it is important to control the groove shape precisely, especially the blaze angle and the apical angle. We have presented a direct shaping method to fabricate EUV blazed gratings by using an ion-beam mixture of Ar~+ and CHF_2~+ to etch K9 glass with a rectangular photoresist mask. With this method, we have succeeded in fabricating well-shaped UV blazed gratings with a 1200 line/mm groove density and 8.54° blaze angles and 1200 line/mm groove density and 11.68° blaze angles, and the metrical efficiency is about 81% and 78%. The good performance of the gratings was verified by diffraction efficiency measurements. When one uses the etching model, the conditions on the ion-beam grazing incident angle and the CHF_3partial pressure should be noted. Besides, since the etched groove shape depends on the aspect ratio of the photoresist mask ridge, if we wish to fabricate larger gratings with this method, we must improve the uniformity of the photoresist mask before ion-beam etching.