Measurements have been made of ion energies in an electron cyclotron resonance plasma, under conditions typically employed for semiconductor materials processing. Both ion energies along magnetic field lines and ion energy distributions generated by a radio frequency (rf) sheath are characterized. Ion impact energies are found to vary between 10 and 35 eV under the conditions studied, with corresponding distribution widths from 3 to 8 eV. Ion energy distributions through an rf sheath are found to be highly dependent on bias frequency, with narrower distributions occurring at higher frequencies. Consequences of measured ion energies for processing results are discussed.