Research On Characteristics And Fabrication Method Of Large-area High-quality Thick Al Films For Echelle Gratings

Large-area echelle grating has large aperture and extreme high diffraction orders, which lead to a high spectral resolution of 106. Owing to the advantages of wide spectral range and high dispersion, it is widely used in spectroscopy detection and field analysis, and gradually becomes the main component of key optical devices in high-power lasers and astronomical observation. Generally, large-size echelle grating is ruled on a thick aluminum film with the process of diamond knife extrusion and polishing deposition. Nano-scale periodic microstructure is made on the aluminum surface. Thus, the thick Al film is the key factor in the preparation process of echelle grating. Its structural and optical properties directly influence the performance of the grating.Firstly, analysis was made to present that the uniformity of the film is closely related to the position of the evaporation source and the fixture height. Results of theoretical calculation show that the optimal parameters were L = 500 mm and H = 1050 mm, with which, an experimental test was carried out and a high quality thick aluminum film with the uniformity error less than ±1% was obtained. By adjusting the position of the evaporation source and fixture height, we obtained a high quality Al film with thickness larger than 12 μm and the uniformity error less than ±1%, which was made on the neoceramic glass substrate with diameter of 700 mm.Secondly, we measured the surface and internal morphology of Al, the surface roughness and film hardness, by the means of scanning electron microscope(SEM, JSM-6510 of JEOL), atomic force microscopy(AFM, EDG of Bruker) and nano indentation instrument(Nano Indenter G200 of Agilent) respectively. The influence of the deposition angle, substrate temperature and speed on the film forming quality of thick aluminum film was studied. We found that with the increase of deposition angel and substrate temperature, the film quality degraded. With the increase of deposition speed, the quality was improved at first and then degraded. Conclusions are that the temperature has great influence on the film quality and therefore leads to the coating process innovation.Thirdly, a novel multi-step deposition theory of high-quality large area thick aluminum was presented. The quality difference of thick Al film with single step and multi-step deposition was compared, the improvement of the surface roughness and the grain size of the thick aluminum film was analyzed.Finally, a high-quality thick-Al film was made on the neoceramic glass substrate of 520 mm × 420 mm, which met the requirements successfully.