RADIATION-DAMAGE TO THERMAL SILICON DIOXIDE FILMS IN RADIO-FREQUENCY AND MICROWAVE DOWNSTREAM PHOTORESIST STRIPPING SYSTEMS

Radio-frequency (13.56 MHz) and microwave (2.45 GHz) downstream plasma photoresist stripping configurations were compared with regard to electrical damage to 26 nm thick thermal SiO2 films. The plasma systems were identical except for the excitation source. High frequency and quasi-static capacitance-voltage (CV) techniques established that SiO2 exposure in the radio-frequency (RF) system produced a greater increase in effective oxide charge and interface trap densities than the microwave system. Vacuum ultraviolet (VUV) emission and relative downstream positive ion density were higher in the rf system. In addition, the visible emission spectrum of the rf plasma showed more intense oxygen ion peaks than the microwave plasma. The differences in VUV emission and positive ion density correlated with the measured electrical damage in the oxide films. All damage observed in this study was removed by a 400-degrees-C anneal in forming gas.