Nitrogen trifluoride (NF3) is a likely candidate to replace perfluorocompounds (PFCs) in stripping and reactor cleaning applications. In this article, the performance of NF3 for the etching of silicon, silicon dioxide (SiO2), and silicon nitride (Si3N4) is compared with that of CF4, C2F6, and C3F8. The performance measures emphasized in this article are the dissociation efficiency of the parent molecule in the discharge, the etch rate, and the gas utilization. The destruction efficiency of NF3 in the discharge as determined by mass spectrometry is typically 100%. The maximum destruction of the PFC gases for the parameters used in this investigation is approximately 75% for CF4, and can approach 100% for C2F6 and C3F8. The removal rates for NF3 obtained at optimum settings of O2 addition and microwave power are significantly higher than those for PFC gases. The gas utilization, which describes the degree of conversion of the parent molecules into etch products and is defined in this article, is also higher for NF3 than for the other gases investigated.

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A large solvent polarity effect on the rate of singlet to triplet intersystem crossing (ksT) has been observed in the carbenes, diphenylcarbene (DPC) and dicycloheptadienylidene (DCHD)-it is found that both ksT and the energy splitting (A&T) separtaing the singlet and triplet states decrease as the solvent polarity increases for the aromatic carbenes. This "inverse" gap effect, i.e. the time for intersystem crossing decreases with increasing energy gap, is esplained by an offresonance intersystem crossing from the singJet to a sparse triplet vibronic manifold characteristic of a smalJ energy gap. The trend in AEsT, which is proposed to be responsible for the variation in ~SJ-for DPC, DCHD and structurally related aromatic carbenes, is suggested to arise from the variation in the bond a&e of the central methylene carbon atom.

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