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加工技術

Anisotropic diamond etching through thermochemical reaction between Ni and diamond in high temperature water vapor

 Kanazawa University and National Institute of Advanced Industrial Science and Technology (AIST) announced on 27th April 2018, that the research group led by associate professor Norio Tokuda at Graduate School of Natural Science and Technology of the university succeeded in developing non-plasma process for anisotropic diamond etching. The results were published in Sientific Reports.

 Although diamond is supposed to be a promising material for high-power devices, device fabrication has met difficulties because of its high chemical stability. Instead of wet etching, plasma process is currently employed for etching diamond, but it is not selective and may cause damage to devices. In this study, the group utilized thermochemical reaction between Ni and diamond in high-temperature water vapor and successfully realized anisotropic etching of diamond without plasma, as follows.

 Ni film is deposited on diamond (100) substrate and patterned for selective etching. When exposed to high temperature water vapor condition, around 1000℃, the surface of the Ni film is oxidized to make NiO thin layer. On the other side of the Ni film, C atoms from diamond dissolve into the Ni then diffuse toward NiO surface layer. Arriving at the NiO layer, C atoms reduce NiO to oxidize themselves into CO2 and CO gas to be released from the Ni film. This reaction continues as cycles, and only the C atoms in the region of diamond covered by Ni film are removed, resulting in selective and high rate etching of diamond. Dissolution of C atoms into Ni film depends on the crystal orientation, thus the etching is anisotropic.

 The group fabricated the micro trench with the side wall angle approximately 55°on the diamond (100) surface. 55°corresponds to the angle between the (100) surface and the {111} surface of diamond.

* M. Nagai,K. Nakanishi,H. Takahashi, H. Kato,T. Makino,S. Yamasaki,T. Matsumoto,T.  Inokuma, and N. Tokuda, "Anisotropic diamond etching through thermochemical reaction between Ni and diamond in high-temperature water vapour", Scientific Reports, Vol. 8, Article number: 6687 (2018), doi: 10.1038/s41598-018-25193-2; Published online: 27 April 2018