Resistivity scaling in epitaxial MAX-phase Ti4SiC3(0001) layers

In situ transport measurements on 5.8-92.1nm thick epitaxial Ti4SiC3(0001) layers are used to experimentally verify the previously predicted low resistivity scaling. Magnetron co-sputtering from three elemental sources at 1000 degrees C onto 12-nm-thick TiC(111) nucleation layers on Al2O3(0001) substrates yields epitaxial growth with Ti4SiC3(0001) parallel to Al2O3(0001) and Ti4SiC3(10 (1) over bar0) parallel to Al2O3(2 (11) over bar0), a low and thickness-independent surface roughness of 0.6 +/- 0.2nm, and a measured stoichiometric composition. The room-temperature resistivity rho increases slightly with decreasing thickness, from rho=35.2 +/- 0.4 to 37.5 +/- 1.1 mu Omega cm for d=92.1-5.8nm, and similarly from 9.5 +/- 0.2 to 11.0 +/- 0.4 mu Omega cm at 77K, indicating only a minor effect of electron surface scattering on rho. Data analysis with the classical Fuchs-Sondheimer model yields a room-temperature bulk resistivity rho(o)=35.1 +/- 0.4 mu Omega cm in the basal plane and suggests effective mean free paths lambda=1.1 +/- 0.6 at 293K and lambda=3.0 +/- 2.0nm at 77K if assuming completely diffuse electron surface scattering. First-principles calculations predict an anisotropic Ti4SiC3 Fermi surface and a product rho(o)lambda=19.3x10(-16)Omega m(2) in the basal plane. This value is six times larger than that predicted previously and five times larger than the measured temperature-independent effective rho(o)lambda=(3.8 +/- 2.1)x10(-16)Omega m(2). This deviation can be explained by a high experimental electron scattering specularity of p=0.8 for Ti4SiC3(0001) surfaces. Air exposure causes a 4% room-temperature resistivity increase for d=5.8nm, indicating a decrease in the surface scattering specularity Delta p=-0.19. The overall results show that Ti4SiC3 is not directly applicable as an interconnect material due to its relatively large rho(o). However, the particularly small resistivity scaling with an effective lambda that is more than an order of magnitude smaller than that of Cu confirms the potential of MAX phase materials for high-conductivity narrow interconnects. Published under an exclusive license by AIP Publishing.

Automated summary

Experimental results show that the resistivity of Ti4SiC3 material increases slightly with decreasing thickness, with minimal impact from electron surface scattering. Exposure to air leads to an increase in resistivity and a decrease in surface scattering specularity for Ti4SiC3 material.