Uniformity study in large-area showerhead reactors

Large area plasma-enhanced chemical vapor deposition of thin films such as silicon nitride or amorphous silicon is widely used for thin film transistor fabrication in the flat panel display industry. A numerical three-dimensional model to calculate the deposition uniformity over the whole electrode surface for rf rectangular showerhead reactors powered at 13.56 MHz is presented. The simulation tool is a commercially available finite-volume software (CDF-ACE (R)) which solves the multispecies, multireaction chemistry in capacitively coupled rf plasma. In order to simplify the three-dimensional geometry,the injected gas flow distribution across the showerhead is calculated separately and introduced as volumetric source terms for the gas flow and species continuity equations. The model is applied to the particular case of silicon nitride deposition and the results are compared with uniformity profiles obtained in an industrial plasma enhanced chemical vapor deposition reactor. Perturbations due to reactor edges together with nonuniform distribution of voltage due to standing wave effect are investigated as possible sources of the inhomogeneity of the thin film. (c) 2005 American Vacuum Society

Triplet excitation transfer in triphenylene columnar phases

International audienceTriplet excitation transport occurring in the columnar liquid crystalline phase of a triphenylene derivative at room temperature is studied by transient absorption spectroscopy with nanosecond resolution. The properties of the triplet excitons are evidenced by doping the mesophase with different concentrations of 2,4,6-trinitrofluoren-9-one (TNF) which is inserted in the stacks of the triphenylene cores (T) and acts as energy trap. It is shown that triplet migration and trapping leads to the formation of the ion-pair 3(T+, TNF-), whose recombination rate constant is 5.5 × 105 s-1. The comparison of the experimentally determined time dependence of the ion-pair concentration with numerically simulated curves on the basis of an one-dimensional random walk model allows the determination of the hopping time (2 ± 1 ps). The latter value is close to that found, in a previous study, for the singlet excitation transport (1.2 ± 0.5 ps) in the same mesophase. This is in agreement with the finding that interactions due to intermolecular orbital overlap, responsible for energy transport in the triplet state, are also the main driving force for singlet excitation transport. The migration length of the triplet exciton is limited by structural defects to a few hundreds of triphenylene cores

Development of a numerical simulation tool to study uniformity of large area PECVD film processing

A numerical two dimensional model to calculate the deposition uniformity over the whole electrode surface in large area rectangular plasma enhanced chemical vapour deposition reactors is presented. In this model, the three dimensional mass and species continuity equations are averaged over the electrode gap, which is small compared to the lateral dimensions of the plasma reactor, to obtain the two dimensional averaged transport equations. The model was applied to the particular case of silicon nitride deposition by selecting a limited chemistry model, including 8 neutral species and nine gas phase reactions. The results are compared with uniformity profiles obtained in a UNAXIS KAI-I 800 Plasmabox(R) reactor. (C) 2002 Elsevier Science B.V. All rights reserved