Nonhalogen Dry Etching\nof Metal Carbide TiAlC by Low-Pressure N<sub>2</sub>/H<sub>2</sub> Plasma at Room Temperature

Ternary metal carbide TiAlC has been proposed as a metal\ngate material\nin logic semiconductor devices. It is a hard-to-etch material due\nto the low volatility of the etch byproducts. Here, a simple, highly\ncontrollable, and dry etching method for TiAlC has been first presented\nusing nonhalogen N<sub>2</sub>/H<sub>2</sub> plasmas at low pressure\n(several Pa) and 20 °C. A capacitively coupled plasma etcher\nwas used to generate N<sub>2</sub>/H<sub>2</sub> plasmas containing\nactive species, such as N, NH, and H to modify the metal carbide surface.\nThe etch rate of TiAlC was obtained at 3 nm/min by using the N<sub>2</sub>/H<sub>2</sub> plasma, whereas no etching occurred with pure\nN<sub>2</sub> plasma or pure H<sub>2</sub> plasma under the same conditions.\nThe surface roughness of the TiAlC film etched by N<sub>2</sub>/H<sub>2</sub> plasma was controlled at the atomic level. A smooth etched\nsurface was achieved with a root-mean-square roughness of 0.40 nm,\ncomparable to the initial roughness of 0.44 nm. The plasma properties\nof the N<sub>2</sub>/H<sub>2</sub> plasmas were diagnosed by using\na high-resolution optical emission spectrometer, detecting the NH\nmolecular line at 336 nm. The etching behavior and plasma–surface\nreaction between N<sub>2</sub>/H<sub>2</sub> plasma and TiAlC were\ninvestigated by using in situ spectroscopic ellipsometry, in situ\nattenuated total reflectance-Fourier transform infrared spectrometry,\nand X-ray photoelectron spectroscopy. The findings indicate that the\nN–H, C–N, and Ti(Al)–N bonds form on the TiAlC\nsurface etched by the N<sub>2</sub>/H<sub>2</sub> plasmas. The mechanism\nfor etching of TiAlC involving transformation reactions between inorganic\nmaterials (metal carbides) and inorganic etchants (N<sub>2</sub>/H<sub>2</sub> plasma) to form volatile organic compounds such as methylated,\nmethyl-aminated, and aminated metals is proposed. Nonhalogen or nonorganic\ncompound etchants were used during the etching process. The study\nprovides useful insights into microfabrication for large-scale integrated\ncircuits.