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.

Subsurface reactions of silicon nitride in a highly selective etching process of silicon oxide over silicon nitride High aspect ratio SiO 2 etching with high resist selectivity improved by addition of organosilane to tetrafluoroethyl trifluoromethyl ether Selective etching of SiO 2 over polycrystalline silicon using CHF 3 in an inductively coupled plasma reactor Use of 2H-heptafluoropropane, 1-iodoheptafluoropropane, and 2-iodoheptafluoropropane for a high aspect ratio via etch in a high density plasma etch tool A highly selective dry etching process for the removal of silicon nitride ͑Si 3 N 4 ) layers from silicon and silicon dioxide (SiO 2 ) is described and its mechanism examined. This new process employs a remote O 2 /N 2 discharge with much smaller flows of CF 4 or NF 3 as a fluorine source as compared to conventional Si 3 N 4 removal processes. Etch rates of Si 3 N 4 of more than 30 nm/min were achieved for CF 4 as a source of fluorine, while simultaneously the etch rate ratio of Si 3 N 4 to polycrystalline silicon was as high as 40, and SiO 2 was not etched at all. For NF 3 as a fluorine source, Si 3 N 4 etch rates of 50 nm/min were achieved, while the etch rate ratios to polycrystalline silicon and SiO 2 were approximately 100 and 70, respectively. In situ ellipsometry shows the formation of an approximately 10-nm-thick reactive layer on top of the polycrystalline silicon. This oxidized reactive layer suppresses etching reactions of the reactive gas phase species with the silicon.

The chemical dry etching of silicon nitride (Si 3 N 4)and silicon nitride (SiO 2) in a downstream plasma reactor using CF 4 , O 2 , and N 2 has been investigated. A comparison of the Si 3 N 4 and SiO 2 etch rates with that of polycrystalline silicon shows that the etch rates of Si 3 N 4 and SiO 2 are not limited by the amount of fluorine arriving on the surface only. Adding N 2 in small amounts to a CF 4 /O 2 microwave discharge increases the Si 3 N 4 etch rate by a factor of 7, but leaves the SiO 2 etch rate unchanged. This enables etch rate ratios of Si 3 N 4 over SiO 2 of 10 and greater. The Si 3 N 4 etch rate was investigated with respect to dependence of tube length, tube geometry, and lining materials. Argon actinometry has shown that the production of F atoms in the plasma is not influenced by the addition of N 2 to the discharge. Mass spectrometry shows a strong correlation between the Si 3 N 4 etch rate and the NO concentration. X-ray photoelectron spectra of the silicon nitride samples obtained immediately after the etching process show that F atoms are the dominant foreign species in the reaction layer, and that N 2 addition to the feed gas enhances the O atom incorporation. Based on these data, we propose a mechanism for the etch rate enhancement of N 2 addition to a CF 4 /O 2 discharge.

The etching of silicon nitride (Si 3 N 4) and silicon dioxide (SiO 2) in the afterglow of NF 3 and NF 3 /O 2 microwave discharges has been characterized. The etch rates of both materials increase approximately linearly with the flow of NF 3 due to the increased availability of F atoms. The etch rate of Si 3 N 4 is enhanced significantly upon O 2 injection into the NF 3 discharge for O 2 /NF 3 ratios of 0.3 and higher, whereas the SiO 2 etch rate is less influenced for the same flow ratios. X-ray photoelectron spectroscopy of processed Si 3 N 4 samples shows that the fluorine content of the reactive layer, which forms on the Si 3 N 4 surface during etching, decreases with the flow of O 2 , and instead oxidation and nitrogen depletion of the surface occur. The oxidation of the reactive layer follows the same dependence on the flow of O 2 as the etch rate. Argon actinometry and quadrupole mass spectrometry are used to identify reactive species in the etching of both materials. The atomic fluorine density decreases due to dilution as O 2 is added to the discharge. The mass spectrometer did not detect NF x species (xϭ1-3) at any discharge parameter setting, which indicates the near complete dissociation of NF 3. Nitric oxide ͑NO͒ was detected by mass spectrometry, and the NO density shows the same dependence on O 2 flow as the Si 3 N 4 etch rate and the surface oxidation. Based on this observation, we propose that the etch rate enhancement for Si 3 N 4 is due to the adsorption of the NO on the Si 3 N 4 surface, followed by the formation of N 2 with a N atom from the surface. The O atom can then attach to the same surface site, contributing to the oxidation.