Role of Hydrogen in Ultrananocrystalline Diamond Deposition From Argon-Rich Microwave Plasmas

A two-step process consisting of an initial nucleation stage with hydrogen followed by a growth stage without hydrogen is used to examine the role of hydrogen in ultrananocrystalline diamond deposition in Ar-rich microwave plasmas. An addition of 5% of H
₂
to Ar-rich/CH
₄
in the initial stage increases the nucleation density (up to 10
⁹
cm
^-2
) and the mean grain size (around 10 nm), accompanied by some improvement of crystallinity. However, an addition of H
₂
above 10% suppresses nucleation by the etching of nucleation sites. The introduction of hydrogen atoms promotes the termination and stabilization of diamond grain surfaces toward sp
³
configuration, which are responsible for enhancing nucleation and crystallization. In contrast, Ar promotes renucleation by increasing the production of C
₂
radicals in the plasma, which causes the degradation of the stabilization on the growing surfaces.