@article{khandelwal_niimi_lucovsky_lamb_2002, title={Low-temperature Ar/N-2 remote plasma nitridation of SiO2 thin films}, volume={20}, ISSN={["0734-2101"]}, DOI={10.1116/1.1513635}, abstractNote={Low-temperature nitridation of SiO2 thin films by Ar/N2 remote plasma processing was investigated using on-line Auger electron spectroscopy, angle-resolved x-ray photoelectron spectroscopy (ARXPS), and optical emission spectroscopy (OES). Nitridation experiments were performed at 300 °C using 30 W Ar/N2 remote plasmas at 0.1 and 0.3 Torr. Ar/N2 remote plasma exposure of 5 nm SiO2 films for 30 min results in nitrogen incorporation throughout the films, independent of process pressure and plasma reactor configuration (i.e., upstream versus downstream N2 injection). ARXPS indicates a N–Si3 local bonding configuration with second nearest neighbor oxygen atoms. Ar/N2 remote plasma exposure at 0.1 Torr results in higher nitrogen concentrations (8–10 at. %). Reactor configuration has a negligible effect at 0.1 Torr; conversely, downstream N2 injection results in higher nitrogen concentrations (5–6 at. %) than upstream injection (3–4 at. %) at 0.3 Torr. OES indicates that the Ar/N2 remote plasmas contain N2 triplet excited states and ground-state N atoms. The Ar emission intensities and the saturation N concentrations in the resultant films follow similar trends with processing pressure and reactor configuration; the N2 first positive emission intensities run counter to these trends. We infer that low-temperature SiO2 nitridation by Ar/N2 remote plasmas is a two-step process: O removal by Ar+ ion bombardment and N insertion by plasma-generated active N species. Moreover, the first step appears to be rate limiting under the conditions employed in this study. Annealing the oxynitride films in N2 at 900 °C decreases the N concentration and results in a more uniform nitrogen distribution.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Khandelwal, A and Niimi, H and Lucovsky, G and Lamb, HH}, year={2002}, pages={1989–1996} }
 @article{niimi_khandelwal_lamb_lucovsky_2002, title={Reaction pathways in remote plasma nitridation of ultrathin SiO2 films}, volume={91}, ISSN={["1089-7550"]}, DOI={10.1063/1.1419208}, abstractNote={Low-temperature nitridation of 3 nm SiO2 films using He/N2 and N2 remote radio frequency (rf) plasmas was investigated. On-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy (ARXPS) were employed to determine the concentration, spatial distribution, and local chemical bonding of nitrogen in the resultant films. Experiments were performed using a substrate temperature of 300 °C and 30 W rf power. Nitridation using an upstream He/N2 remote plasma at 0.1 Torr incorporates nitrogen at the top surface of the SiO2 film. In contrast, a lower concentration of nitrogen distributed throughout the film is obtained when the process pressure is increased to 0.3 Torr. ARXPS indicates a N–Si3 local bonding configuration, irrespective of the spatial distribution of N atoms. Slightly more nitrogen is incorporated using a downstream He/N2 plasma at each process pressure. By comparison, nitridation of SiO2 films using a N2 remote plasma at 0.1 Torr is very slow. Optical emission spectroscopy indicates that He dilution enhances the generation of N2+(B 2Σu+) species by altering the plasma electron energy distribution and by providing an additional kinetic pathway (Penning ionization). Changing the He/N2 remote plasma configuration from upstream to downstream (at 0.1 and 0.3 Torr) also enhances N2+(B 2Σu+) generation. For upstream He/N2 remote plasmas, the intensity of N2 first positive emission from N2(B 3Πg) states increases with pressure, whereas the N2+ first negative emission from N2+(B 2Σu+) states decreases. We infer from these observations that N2+ species are primarily responsible for top surface nitridation at 0.1 Torr, and that neutral species [N2(A 3Σu+) metastables and N atoms] are associated with sub-surface nitrogen incorporation.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Niimi, H and Khandelwal, A and Lamb, HH and Lucovsky, G}, year={2002}, month={Jan}, pages={48–55} }
 @article{khandelwal_smith_lamb_2001, title={Nitrogen incorporation in ultrathin gate dielectrics: A comparison of He/N2O and He/N-2 remote plasma processes}, volume={90}, ISSN={["0021-8979"]}, DOI={10.1063/1.1397286}, abstractNote={Ultrathin Si oxynitride films grown by low-temperature remote plasma processing were examined by on-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy to determine the concentration, spatial distribution, and chemical bonding of nitrogen. The films were grown at 300 °C on Si(100) substrates using two radio-frequency remote plasma processes: (i) He/N2O remote plasma-assisted oxidation (RPAO) and (ii) two-step remote plasma oxidation/nitridation. A 5 min He/N2O RPAO process produces a 2.5 nm oxynitride film incorporating approximately 1 monolayer of nitrogen at the Si–SiO2 interface. The interfacial nitrogen is bonded in a N–Si3 configuration, as in silicon nitride (Si3N4). By comparison, a 90 s He/N2 remote plasma exposure of a 1 nm oxide (grown by 10 s He/O2 RPAO) consumes substrate Si atoms creating a 1 nm subcutaneous Si3N4 layer. The nitrogen areal density obtained via the two-step process depends on the initial oxide thickness and the He/N2 remote plasma exposure time. Moreover, as the oxide thickness is increased (by increasing the He/O2 remote plasma exposure), the nitrogen distribution shifts away from the Si–SiO2 interface and into the oxide. More nitrogen with a tighter distribution is incorporated using He versus Ar dilution. Insight into the remote plasma chemistry was provided by optical emission spectroscopy. Strong N2 first positive and second positive emission bands were observed for He/N2O and He/N2 remote plasmas indicating the presence of N2 metastables and ground-state N atoms.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Khandelwal, A and Smith, BC and Lamb, HH}, year={2001}, month={Sep}, pages={3100–3108} }
 @article{smith_khandelwal_lamb_2000, title={Ar/N2O remote plasma-assisted oxidation of Si(100): Plasma chemistry, growth kinetics, and interfacial reactions}, volume={18}, ISSN={["1071-1023"]}, DOI={10.1116/1.591467}, abstractNote={The kinetics of Ar/N2O remote plasma-assisted oxidation of Si(100) and the mechanism of nitrogen incorporation at the Si–SiO2 interface were investigated using mass spectrometry, optical emission spectroscopy, and on-line Auger electron spectroscopy. N2, O2, and NO are the stable products of N2O dissociation in the plasma. The maximum NO partial pressure occurs at 10 W applied rf power; N2 and O2 are the predominant products for applied powers greater than 50 W. Ar/N2O remote plasmas are prolific sources of atomic O; in contrast, atomic N is not produced in significant concentrations. Ar/N2O remote plasma-assisted oxidation was investigated at 300 °C for applied rf powers of 5, 20, and 50 W. The oxide growth kinetics are slower than expected for a purely diffusionally controlled process. A diffusion-reaction model that incorporates first-order loss of the oxidizing species as it diffuses through the growing oxide layer fits the data very well. The initial oxidation rate increases linearly with plasma density, suggesting that the near-surface concentration of oxidizing species scales with the surface flux of plasma electrons. Nitrogen is incorporated at the Si–SiO2 interface in direct proportion to the N2 partial pressure in the Ar/N2O remote plasma. Molecular NO does not react at the Si–SiO2 interface at 300 °C, its role in Si thermal oxynitridation notwithstanding. Nitrogen incorporation at the Si–SiO2 interface was also achieved by exposure of ultrathin Ar/O2 plasma oxides to a remote 20 W Ar/N2 plasma.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Smith, BC and Khandelwal, A and Lamb, HH}, year={2000}, pages={1757–1763} }