Optimization of Reactive Ion Etching of Polycrystalline Diamond for MEMS Applications

It has been found that diamond columns can be formed unintentionally in reactive ion etching (RIE) with O₂ plasma even without a precoated metal layer. The experimental results indicate that the existence of these diamond columns prevents the effective removal of polycrystalline diamond (poly-C), also known as microcrystalline diamond. A three-step sequential RIE of poly-C thin film in CF₄ (or CF₄/Ar), O₂, and H₂ plasmas is developed using lithographically patterned Al acting as a hard mask to achieve a smooth-etched surface after the removal of poly-C. This etching technique can remove a thick poly-C layer very effectively. For the first time, this letter eliminates RIE-related damage to underlying substrate (specific to RIE of poly-C) to optimize the technology for single- and multi-material MEMS made from poly-C.