Nonhalogen Dry Etching of Metal Carbide TiAlC by Low-Pressure N₂/H₂ Plasma at Room Temperature

Abstract

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 highresolution 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.