Fabrication of precision 3D microstructures by use of a combination of ultraprecision diamond turning and reactive ion etching process

A novel 3D microstructure fabrication process using a combination of an ultraprecision machining process and reactive ion etching technique is described. Compared to the lithographic process, the conventional microstructuring technique, this new process can produce continuous 3D features on wafer substrates instead of the multi-level profiles created using the lithography-based method. Using ultraprecision single point diamond turning and slow tool servo control, true 3D microstructures were fabricated first on a thin SU-8 photoresist layer, and then the patterned 3D structures on the photoresist layer were transferred to the silicon substrate by precisely controlling the etch depth using the timed reactive ion etching technique. Specifically, a diffractive optical element and a sine wave grating were fabricated using this method on silicon and fused silica wafer substrates. The machined wafers were measured by using an optical profilometer, a scanning electron microscope and an atomic force microscope. All measured profiles showed good agreement with the original design. Finally, a diffractive optical pattern that was fabricated using this technique was successfully transferred to a glass optical surface by use of the compression molding process as a demonstration of possible industrial applications.