Nonhalogen Dry Etching of Metal Carbide TiAlC by Low-Pressure N<sub>2</sub>/H<sub>2</sub> Plasma at Room Temperature
Thi‐Thuy‐Nga Nguyen, Kazunori Shinoda, Shih‐Nan Hsiao, Kenji Maeda, Ken’etsu Yokogawa, Masaru Izawa, Kenji Ishikawa, Masaru Hori
Abstract
High Resolution Image Download MS PowerPoint Slide Ternary metal carbide TiAlC has been proposed as a metal gate material in logic semiconductor devices. It is a hard-to-etch material due to the low volatility of the etch byproducts. Here, a simple, highly controllable, and dry etching method for TiAlC has been first presented using nonhalogen N 2 /H 2 plasmas at low pressure (several Pa) and 20 °C. A capacitively coupled plasma etcher was used to generate N 2 /H 2 plasmas containing active species, such as N, NH, and H to modify the metal carbide surface. The etch rate of TiAlC was obtained at 3 nm/min by using the N 2 /H 2 plasma, whereas no etching occurred with pure N 2 plasma or pure H 2 plasma under the same conditions. The surface roughness of the TiAlC film etched by N 2 /H 2 plasma was controlled at the atomic level. A smooth etched surface was achieved with a root-mean-square roughness of 0.40 nm, comparable to the initial roughness of 0.44 nm. The plasma properties of the N 2 /H 2 plasmas were diagnosed by using a high-resolution optical emission spectrometer, detecting the NH molecular line at 336 nm. The etching behavior and plasma–surface reaction between N 2 /H 2 plasma and TiAlC were investigated by using in situ spectroscopic ellipsometry, in situ attenuated total reflectance-Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. The findings indicate that the N–H, C–N, and Ti(Al)–N bonds form on the TiAlC surface etched by the N 2 /H 2 plasmas. The mechanism for etching of TiAlC involving transformation reactions between inorganic materials (metal carbides) and inorganic etchants (N 2 /H 2 plasma) to form volatile organic compounds such as methylated, methyl-aminated, and aminated metals is proposed. Nonhalogen or nonorganic compound etchants were used during the etching process. The study provides useful insights into microfabrication for large-scale integrated circuits.