Remote plasma reactors are being developed for treating surfaces between layers in MOS (metal-oxide-semiconductor) stacks, and for depositing (or growing) the SiO₂ layer. Systemmatic differences in the properties of oxide layers produced in remote plasma reactors have been observed when using different source gases for the oxygen precursors, presumably resulting from variations in the deposition precursors.

In remote plasma enhanced chemical vapor deposition (RPECVD) of SiO₂, it has been found that the fluxes of SiH₂O, SiH₃, and SiH_n, directly scale in the same manner as the experimental precursor rates. The production and uniformity of these precursors largely depends on the rate of oxidation of SiH₄. Reactions of O(³P) with SiH₄ proceed by a series of H abstraction and elimination reactions. Since the fluxes of O(³P) atoms are large , and not rate limiting, this scaling supports the proposal that the surface catalyzed reactions between atomic/molecular oxygen and SiH_n are deposition precursors. To investigate the reaction pathways and to identify depostion precursors, a model has been developed to simulate production and transport of such precusors.

Figure 1 Schematic of RPECVD tool used for deposition.

In this work the two-dimensional Hybrid Plasma Equipment Model (HPEM) has been applied to investigating remote plasma reactors operating in Ar/O₂ and Ar/N₂O mixtures. A statistical design of experiments is used to analyze reactant fluxes (ions, oxygen radicals and molecular excited states) to the substrate over a large parameter space in pressure (10s to 100s mTorr) and power deposition (a few to 100 W). Comparison to experimental measurements are used to correlate reactant fluxes with film properties.

Figure 2 Average Density of Atomic Oxygen.	Figure 3 Electron Temperature Distribution.

Figure 4 Neutral fluxes to the wafer.

Figure 5 Design of experiment results for flux of atomic Oxygen.

Conclusions

RPECVD provides high selectivity in generating and controlling the transport of precursors within the reactor.

The majority of chemical reactions occur within the throat of the reactor, but diffusion of metastables products still induce reactions downstream.

The flux of precursors to the substrate is sensitive to pressure and gas flow rates, and highly depends on the chemical kinetics that occur close to the substrate.

For the simulations shown, it was seen that the flux of atomic oxygen has high correlation to the local density of metastable products.

Research supported by ARPA/NCSU, SRC, and NSF.