Controlled Epitaxial Growth of Body-Centered Cubic and Face-Centered Cubic Cu on MgO for Integration on Si

The Cu/MgO interface plays a crucial role in applications. Face-centered-cubic (fcc) Cu has been reported to grow on MgO substrate (rock salt structure). However, no body-centered-cubic/tetragonal (bcc(t)) Cu has been stabilized on MgO. The special atomic structure of the bcc(t)/rock salt interface contributes to superior thermal, mechanical, and electrical properties. We report, for the first time, the epitaxial growth of bcc(t) and fcc Cu on Si(100) and Si(111) substrates using MgO(100)/TiN(100) and MgO(111)/TiN(111) buffer layers by pulsed laser deposition. We find that the deposition temperature determines the structure of Cu. At high temperature, only fcc Cu grows on both MgO/TiN(100) and MgO/TiN(111) templates. At room temperature, an epitaxial layer of bcc(t) Cu grows pseudomorphically on a MgO(100) template up to the critical thickness, while on a MgO/TiN(111) template, the majority of Cu is fcc, and bcc(t) Cu exists occasionally in a three-dimensional island shape. The growth of these heterostructures involves epitaxy across the misfit scale by matching MgO{200} planes with bcc(t) Cu{110} planes. The integration of Cu/MgO on the technologically important Si substrate holds tremendous promise, because the novel bcc(t) Cu/MgO structure can be integrated with present-day microelectronic or nanoelectronic devices.