The influence of the Ar sputter pressure and sputter power on the growth of MgO tunnel barriers is investigated. It is found that radio frequency (RF) sputtering of MgO onto amorphous SiO2 from a target-facing-target (TFT) gun results in smooth films with a poor (0 0 1) texture when the Ar sputter is less than 1.3×10-3 mbar, whereas the use of a high-sputter pressure of 13×10-3 mbar gives rougher but better oriented MgO films. The transfer of these deposition parameters to the growth of Co80Fe10B10/MgO/Co80Fe10B10 magnetic tunnel junctions (MTJs) reveals a clear dependence of the tunneling magnetoresistance (TMR) on barrier roughness and texture perfection. A maximum TMR value of 72% is measured after annealing MTJs with MgO barriers grown under high Ar sputter pressures. In addition, the resistance-area (RA) product of the MTJs increases by two orders of magnitude if the sputter pressure is increased from 1.3×10-3 to 13×10-3 mbar. Contrary to these effects, the properties of the MTJs are nearly independent of magnetron sputter power.