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The etch rate of silicon in CF4/O2 plasmas is a strong function of the masking material coated on the wafer to define etch patterns. Samples coated with several different metals (silver, copper, chromium, and aluminum) all exhibit a higher silicon etch rate compared to samples coated with a photoresist mask. For silver-masked samples, the silicon etch rate can be enhanced by as much as a factor of five relative to a photoresist mask. These results can be explained in terms of a catalytic reaction occurring on the mask surface which gives rise to a local enhancement of the fluorine radical concentration leading to an increased etch rate of silicon. The validity of this explanation was confirmed by actinometry.We recently reported on the observation that etch rates of silicon and silicon dioxide in CF4/O2 plasmas are dependent upon the material used as an etch mask (1). It was shown that aluminum-masked silicon etched about twice as fast as silicon masked by photoresist. Conversely, aluminum-masked oxide etched about 10% more slowly than silicon dioxide that was masked by photoresist. We subsequently extended this work to other fluorine containing etch gases, and showed that a similar effect was observed in the silicon etch rate with a variety of fluorocarbon and nonfluorocarbon gases (2). We have demonstrated that this enhancement is not restricted to aluminum, but that other metal masks, such as silver and copper, enhance the silicon etch rate, some even more dramatically than aluminum (3, 4). Most recently, we have shown that this effect is not restricted to silicon and silicon dioxide, but is also observed with four other important substrates used in microelectronics fabrication; specifically plasma-deposited and thermally grown polysilicon and plasma and thermal silicon nitride (5). A possibly related effect, arising from metal residues on silicon surfaces, has also been reported to enhance the plasma etch rate in F2 plasmas (6).We have suggested that the reason for the increase in the silicon etch rate was a catalytic production of fluorine radicals on the metal surface which had the result of locally increasing the fluorine radical concentration and hence the silicon etch rate. We have previously presented evidence for metal masks increasing the fluorine radical concentration in fluorine-based plasmas (4).We now wish to report a detailed study on the use of chromium, copper, and silver etch masks, and their effect on the plasma etch rate of silicon. We show that the effect of mask dependent etch rates is not restricted to aluminum, but is observed to different degrees with other metal masks. We also show that the metals can increase the relative concentration of fluorine radicals in the plasma, and that this increase in fluorine radical concentration is responsible for the increase in plasma etch rates. ExperimentalFive different wafers were used for these experiments: silicon masked with photoresist, silicon masked with aluminum, silicon masked with chromium, silicon masked with copper, and silicon masked w...

Improvement of dielectric breakdown characteristics and hot-electron-induced interface degradation of metal-oxide-semiconductor capacitors having fluorinated ultradry oxides has been demonstrated. The fluorine is introduced through HF surface treatment of Si prior to oxidation. Secondary-ion mass spectrometry data indicate that SiF distribution is peaked both at the surface of the oxide and at the SiO2/Si interface in the fluorinated ultradry oxide. The possible role of fluorine on the improvement of the dielectric characteristics will be discussed.