Nitrogen incorporation in ultrathin gate dielectrics: A comparison of He/N2O and He/N-2 remote plasma processes

Ultrathin Si oxynitride films grown by low-temperature remote plasma proces sing were examined by on-line Auger electron spectroscopy and angle-resolve d x-ray photoelectron spectroscopy to determine the concentration, spatial distribution, and chemical bonding of nitrogen. The films were grown at 300 degreesC on Si(100) substrates using two radio-frequency remote plasma pro cesses: (i) He/N2O remote plasma-assisted oxidation (RPAO) and (ii) two-ste p remote plasma oxidation/nitridation. A 5 min He/N2O RPAO process produces a 2.5 nm oxynitride film incorporating approximately 1 monolayer of nitrog en at the Si-SiO2 interface. The interfacial nitrogen is bonded in a N-Si-3 configuration, as in silicon nitride (Si3N4). By comparison, a 90 s He/N-2 remote plasma exposure of a 1 nm oxide (grown by 10 s He/O-2 RPAO) consume s substrate Si atoms creating a 1 nm subcutaneous Si3N4 layer. The nitrogen areal density obtained via the two-step process depends on the initial oxi de thickness and the He/N-2 remote plasma exposure time. Moreover, as the o xide thickness is increased (by increasing the He/O-2 remote plasma exposur e), the nitrogen distribution shifts away from the Si-SiO2 interface and in to the oxide. More nitrogen with a tighter distribution is incorporated usi ng He versus Ar dilution. Insight into the remote plasma chemistry was prov ided by optical emission spectroscopy. Strong N-2 first positive and second positive emission bands were observed for He/N2O and He/N-2 remote plasmas indicating the presence of N-2 metastables and ground-state N atoms. (C) 2 001 American Institute of Physics.