Quantum interference corrections to the magnetoresistance in one-sided modulation doped Si/SiGe quantum wells were investigated. From the weak localization effect, the temperature dependence of the phase coherence time is deduced and compared with the momentum relaxation time, It is found that electron-electron scattering is consistent with this observed behavior, but electron-phonon scattering is not. For magnetic fields above 0.5 T, the magnetoresistance is attributed to disorder-induced electron-electron interaction.