Roughness Reduction of Large-Area High-Quality Thick Al Coatings for Large-Size Echelle Gratings by Chemical Mechanical Polishing

Large-area high-quality thick Al coating is one of the most important factor which always acts as a ruling substrate in realizing high-performance large-size echelle grating ruling process. Based on our previous work, we proposed use of precise mechanical polishing methods to further reduce surface roughness of thick Al films. Surface roughness Rq of 12 mu m-thick Al film can be effectively controlled under 25 nm by early reported multi-step deposition process. The chemical mechanical polishing method was chosen in this study to improve the surface quality of thick Al coating. Rq of Al film was significantly reduced to 5.26 nm as a consequence. The surface morphology, cross section and film hardness of the polished samples were also investigated in detail. Finally, the echelle grating was fabricated on the polishing sample and the diffraction efficiency was 50% at 632.8 nm laser and 36th order. This work has great potential for both high-quality thick Al film research and large-size echelle grating performance enhancement.