Growth of giant magnetoresistance multilayers: Effects of processing conditions during radio-frequency diode deposition

The magnetotransport properties of giant magnetoresistance multilayers are significantly effected by the atomic-scale structure of the interfaces betw een the nonferromagnetic conducting and ferromagnetic (FM) metal layers. Th e interfacial roughness and the extent of intermixing at these interfaces a re both known to be important. A combination of experimental and multiscale modeling studies have been used to investigate control of interface struct ure during multilayer growth by rf diode deposition and, the consequences o f such control for magnetotransport. Experiments were conducted to evaluate the dependence of the magnetotransport properties of NiFeCo/CoFe/CuAgAu mu ltilayers upon the growth conditions (background pressure, input power), an d to link the roughness of vapor-deposited copper layers to the same proces s parameters. These experimental studies reveal the existence of intermedia te background pressure (20 mTorr) and plasma power (175 W) that resulted in the highest magnetoresistance and a strong sensitivity of copper layer sur face roughness to both the power and pressure at,which deposition was condu cted. By using a combination of modeling technologies, the deposition proce ss conditions have been linked to the atomic fluxes incident upon the sampl e surface. This was then used to determine the atomic-scale roughness of th e film. Energetic metal atoms (and inert gas ions) were found to have very strong effects upon interfacial structure. The models revealed an increase in interfacial roughness when metal (or inert gas ion) translational energy was decreased by either reducing the plasma power and/or increasing the ba ckground pressure. Because high-energy metal impacts activated atomic jumpi ng near the impact sites, high plasma power, low background pressure proces s conditions resulted in the smoothest interface films. However, these cond itions were also conducive to more energetic Ar+ ion bombardment, which was shown by molecular dynamics modeling to induce mixing of the FM on,the cop per interface. Intermediate plasma powers/background pressures result in th e most perfect interfaces and best magnetotransport. The insights gained by the modeling approach indicate a need to avoid any energetic ion bombardme nt during the earl growth stages of each new layer. This could be accomplis hed by operating at low power and/or high pressure for the first few monola yers of each layer growth and may provide a growth strategy for further imp rovement in magnetotransport performance. (C) 2001 American Vacuum Society.