Effect of N doping on the microstructure and dry etch properties of amorphous carbon deposited with a DC sputtering system

The importance of developing a hardmask with excellent performance, and physical and chemical properties to utilize in long-term etching is spotlighted due to the acceleration of development in high-density semiconductors. To develop such a hardmask, amorphous carbon hardmasks doped with various concentrations of N were fabricated with a DC magnetron sputtering system using varying inert gas (Ar to N-2) ratios. In contrast to the expectation that doped nitrogen would block the permeation of fluorine and improve the etch resistance, as the nitrogen concentration increased, the selectivity of the doped amorphous carbon films decreased. To understand this degradation with increasing nitrogen concentration, systematic X-ray photoelectron spectroscopy (XPS), radial distribution function (RDF), and X-ray reflectometry (XRR) analyses were conducted. In this study, we found that as the amount of nitrogen increased, the density of the film decreased, and the amount of pyridinic and pyrrolic nitrogen bonds with low formation energy increased. In contrast, based on time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of etched nitrogen-doped amorphous carbon films, the penetration depth of fluorine ions from the etchant decreased as the amount of nitrogen increased. Therefore, in order to develop an excellent hardmask using amorphous carbon, it is important to increase the density of the film and the nitrogen concentration in the film while lowering the ratio of pyrrolic N to pyridinic N, i.e., increasing the ratio of graphitic N.

Automated summary

The importance of developing a hardmask with excellent performance and physical and chemical properties for long-term etching in high-density semiconductors is highlighted. Amorphous carbon hardmasks doped with different concentrations of nitrogen were fabricated, and their properties were analyzed using various techniques. It was found that increasing the nitrogen concentration in the film decreased the selectivity of the doped amorphous carbon films but reduced the penetration depth of fluorine ions during etching. To develop an excellent hardmask, it is crucial to increase the film density, nitrogen concentration, and the ratio of graphitic nitrogen to pyrrolic nitrogen.