Fabrication of 3-dimensionally shaped Si diaphragm dynamic focusing mirror

To obtain a dynamic focusing mirror with optically ideal or parabolic deformation, a thin Si diaphragm with a 3-D specific thickness profile has been fabricated by a unique processing method. The specific thickness profile which allows optically ideal deformation is determined by the finite-element method (FEM). The mirror is approximately 10 mm in diameter and 9-μm in thickness. Its specific profile of the mirror is created by a dry-etching method. Photoresist on a Si substrate is first exposed to a specific energy profile through a mask made by the dither method. The photoresist is then developed to form a specific curved profile which complies with the optical energy profile. The curved profile is transcribed to the Si substrate by dry etching in CF₄ /O₂ plasma. The processed 3-D profile matches the design with less than 2% deviation