Etching characteristics of TiN used as hard mask in dielectric etch process

This study focuses on the etching characteristics of a TiN hard mask in terms of etch rate and faceting when using a dielectric etch process. The etching experiments have been performed on blanket wafers and patterned structures in an inductively coupled plasma using a conventional CF4∕Ar based plasma. The etch rate and faceting of TiN have been measured as a function of the plasma parameters (bias power and pressure) and also plasma chemistries (Ar dilution and CH2F2 addition). The TiN etch rate is about 30nmmin−1 using the base line process conditions (70SCCM CF4, source power of 500W, bias power of 100W, and pressure of 4mTorr). Lower etch rate is observed at lower pressure and bias power and with higher Ar dilution and CH2F2 addition. The faceting is strongly reduced at lower bias power and higher pressure whereas higher Ar dilution and CH2F2 addition have no clear effect on the facet formation. Surface analysis using x-ray photoelectrons spectroscopy reveal that the top surface of TiN is mainly fluorinated in the steady state etching regime whatever the plasma conditions. Plasma diagnostics have been also performed thanks to an optical emission spectrometer, an ion mass spectrometer, and a capacitive probe to determine the fluorine concentration and the ion flux composition and density, respectively. The whole results show that the etching of TiN is mainly controlled by the fluorine concentration and the ions energy dissipated on the surface. The etch rate and faceting evolution will be discussed and interpreted in terms of plasma surface interaction.