Dry Etching of SiO 2 Thin Films with Perfluoropropenoxide–O 2 and Perfluoropropene–O 2 Plasmas Francesco FRACASSI, Riccardo D’AGOSTINO, Antonella FORNELLI and Tatsuru SHIRAFUJI 1  CNR, Centro di Studio per la Chimica dei Plasmi, c/o Dipartimento di Chimica, Universita ` di Bari, Via Orabona, 4-70126, Bari, Italy 1 International Innovation Center, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501, Japan (Received February 7, 2002; revised manuscript received June 20, 2002; accepted for publication July 1, 2002) In this work, the plasma etching characteristics of SiO 2 thin films have been investigated using RF glow discharges fed with C 3 F 6 O and C 3 F 6 mixted with oxygen. The results have been compared with performances obtained with CF 4 –CHF 3 gases. The research was aimed at studying the utilization of new fluorocarbons in SiO 2 plasma etching with a low impact on global warming. The following features have been investigated: SiO 2 etch rate, SiO 2 /Si selectivity, contamination of silicon surfaces exposed to the plasma, and greenhouse gas emission. [DOI: 10.1143/JJAP.41.6287] KEYWORDS: C 3 F 6 O, C 3 F 6 , CF 4 , CHF 3 , global warming, plasma, etching 1. Introduction SiO 2 dry etching is an important step in microelectronics manufacturing. In order to achieve acceptable performance levels, mixtures of perfluorocompounds (PFC’s) and hydro- fluorocompounds (HFC’s) are generally utilized since this chemistry leads to high etch rates, good selectivity to silicon and photoresist, low contamination and acceptable surface damage, through ion assisted reactions of SiO 2 with CF x radicals. The processes, however, are undergoing continuous evolution, due to the requirement of reduced feature sizes, the increase of device complexity, and the reduction of the associated environmental impact. In fact, PFCs and many HFCs are strong greenhouse gases with high global warming potentials (GWPs) 1) and though their effect is much lower than those of other pollutants emitted in the atmosphere in much higher amounts (CO 2 ,H 2 O, NO x ), according to the Kyoto Conference of Parties held in December 1997, 2) their utilization and emission must be reduced. Several alternative compounds have been examined in the last few years, such as different hydrofluorocarbons, 3–6) unsaturate fluorocarbons (UFC), 7) oxalyl fluoride, 8) perfluor- oethers, 9) iodofluorocarbons, 4–6) and others, 10) alone or in mixture form with additives. The new compounds have often been tested both for oxide patterning and for the cleaning of deposition chambers. We have already contributed to this literature 6,11–13) by studying the etching behaviors of CF 3 I, CH 2 F 2 ,C 2 H 2 F 4 and trifluoracetic anhydride among others. In some cases, the results have been compared with those obtained with the conventional chemistry of CF 4 –CHF 3 mixtures. The present paper deals with the utilization of perfluoropropenoxide (C 3 F 6 O) and perfluoropropene (C 3 F 6 ) in mixtures with oxygen in SiO 2 etching. Since the GWPs of C 3 F 6 O and C 3 F 6 are expected to be very low, 7) their utilization should reduce the impact of oxide etching on global warming at least during the steps of flow and pressure stabilization, i.e. before the plasma is turned on and the gas feed is completely released unchanged into the atmosphere. These compounds have already been utilized for oxide etching by other authors but under different experimental conditions. In particular, the production of greenhouse compounds from C 3 F 6 O has been evaluated in pulsed plasmas 3) and it has been reported that in high-density inductively-coupled plasmas, pure C 3 F 6 shows acceptable SiO 2 -resist selectivity, good process anisotropy, as well as a 70% reduction of greenhouse gas emission with respect to conventional feeds. 7) The results reported in this paper have been obtained with a dual-frequency triode reactor by mixing the fluorocom- pounds with oxygen with the aim of following the SiO 2 etch rate, SiO 2 /Si selectivity, surface contamination and atmo- spheric greenhouse gas emission as process parameters. Even though the experiments were performed under the optimal conditions available for the experimental reactor utilized, the values of etch rate and Si-SiO 2 selectivity are lower than those obtained with industrial apparatuses. 2. Experimental The triode reactor utilized is similar to the commercial LAM Rainbow 4520 XL etching system (Fig. 1). It is a symmetrical parallel-plate reactor equipped with two inter- nal (6 inches) electrodes; the substrate is positioned on the lower electrode while the feed gas enters through a silicon shower which also works as an upper electrode. As in a typical dual-frequency triode configuration, the lower electrode is connected to a 400 kHz generator to drive the ion bombardment on the substrate, the upper electrode is connected to a 13.56MHz power supply for plasma Fig. 1. Schematic drawing of experimental apparatus.  E-mail: fracassi@chimica.uniba.it Jpn. J. Appl. Phys. Vol. 41 (2002) pp. 6287–6290 Part 1, No. 10, October 2002 #2002 The Japan Society of Applied Physics 6287