CMOS compatible metal stacks for suppression of secondary grains in Sc0.125Al0.875N

The electromechanical response of AlN can be enhanced by alloying with Sc up to ∼44%, with challenges arising in deposition of high Sc-content films due to the presence of secondary grains. While templating ScxAl1−xN (ScAlN) from platinum has shown success in yielding highly-textured c-axis ScAlN without the presence of secondary grains, platinum is not compatible with complementary metal-oxide-semiconductor (CMOS) electronics. In this work, Sc0.125Al0.875N and AlN films were deposited on various CMOS compatible metal stacks, i.e., combinations of Ti, TiN, and AlCu (0.5 wt. %). Optimal film microstructure and texture was obtained for films deposited on highly-textured Ti, Ti/AlCu, and Ti/TiN/AlCu metal stacks. The lowest FWHM values for AlN and Sc0.125Al0.875N were 0.81° and 1.09°, respectively, for 750-nm-thick films deposited on Ti/TiN/AlCu. Secondary grains and film roughness were examined using atomic force microscopy and found to be significantly reduced in ScAlN films deposited on Ti, Ti/AlCu, and Ti/TiN/AlCu. The success of these bottom metal stacks is attributed to their lattice matching and texture quality, which can enable the deposition of higher Sc-alloyed films that outperform their AlN counterpart. Additionally, the CMOS compatibility of these metal stacks brings ScAlN one step closer to commercialization.