Paper TF-ThP20
Deposition and Etching of Hexagonal and Cubic Boron Nitride

Thursday, October 23, 2008, 6:00 pm, Room Hall D

Boron nitride is a material presenting a high thermal conductivity, a low dielectric constant and a high young modulus. Those properties make it a good material to be used in integrated circuits technologies. We present here a process to deposit cubic or hexagonal boron nitride from a high density plasma. The deposition is performed using an ultima high density plasma chamber from Applied Materials. We also present the etching properties of both phases of Boron Nitride using halogenated plasmas. The etching is performed in a DPS chamber from Applied Materials, using a 20 mTorr plasma, with 500W of source power and 100W of bias power. During the deposition, phase formation is found to be critically dependant on diborane, nitrogen and argon gas ratios and the bias utilized during deposition. Cubic boron nitride formation is found to be favored at the deposition/sputtering regime. A density of 2.9 g/cm³ for cubic boron nitride and of 1.8 g/cm³for hexagonal boron nitride is measured by XRR. The etch rate of hexagonal boron nitride is measured by ellipsometry. HBr/Ar plasmas present a very low etch rate (21nm/min). Addition of 25 sccm of Cl₂ into the plasma doubles the etch rate. Fluorine-based plasmas etch much faster boron nitride than Bromine- or Chlorine-based plasmas. An eth rate of 146 nm/min is obtained using CF₄/Ar, and the etch rate increases up to 511 nm/min with SF₆/Ar plasma. The substitution of CF₄ by a polymerizing gas such as CH₂F₂ leads to a decrease of boron nitride etch rate. The etch rate of cubic boron nitride is also measured. A ratio of 1.2 between hexagonal and cubic boron nitride etch rates is always obtained. Since the density ratio is 1.6, we can say that the structure of cubic boron nitride enhances its etch yield compared to hexagonal boron nitride. Thanks to the deposition and etching processes presented here, the integration of boron nitride in microelectronics technologies can be considered.