Reactive Ion Etching in  SF 6 Gas Mixtures

Abstract

Reactive ion etching of crystalline silicon, polysilicon, SIO2, and Si3N4 has been studied in a parallel plate electrode configuration, with and without magnetic confinement, in SF6 gas diluted with varying proportions of 02, N2, H2, and Ar. In order to investigate the contamination from the RF cathode, RIE studies were done with RF cathode covered with aluminum disk as well as with 0.5 cm thick circular quartz plate. The RF frequency used is 13.56 MHz and RF power density varied from 0.1 to 0.4 Wcm -2. Experimental results indicate the following: (i) significant contamination occurs on the etched surface with the aluminum covered cathode, but no detectable contamination occurs with the quartz plate covered cathode, (ii) there are etch rate maxima both for silicon and polysilicon with 02 dilution in the range 10-20 volume percent for aluminum covered cathode; these maxima are more pronounced at higher power levels, (iii) etch rates of silicon and polysilicon are much reduced with O2, N2, and especially H~ dilution in volume proportions >30% at all power levels and irrespective of cathode covers; argon dilution has the least effect on the etch rates; (iv) due to loading effect the etch rates 0 20 40 60 80

The SF5Ox Radicals, x=0–3

“…The latter compound undergoes hydrolysis to form SO 2 F 2 , which is even more stable. Because hydrolysis requires significant water concentration, a downward diffusion of SF 4 O and/or SO 2 F 2 from the stratosphere into more humid air should be observable. Finally, SO 2 F 2 hydrolyzes very slowly (yields sulfuric acid and HF) which makes it suitable as a tracer for SF 6 or SF 5 CF 3 degradation in the atmosphere.…”

“…[2] Because SF 6 is an excellent source of fluorine atoms upon strong excitation and contains no carbon, it leaves no carbonaceous deposits in the plasma etching process. [3][4][5] An attractive feature of SF 6 is its nonflammability and chemical inertness. Surprisingly, the environmental concerns of the long-term usage of SF 6 have become an issue only recently as a result of its increasing abundance in the atmosphere.…”

“…[8] Recent studies of the environmental consequences of the decomposition of SF 6 have attempted to characterize the breakdown products that result from electrical discharges. [9][10][11][12] The main products observed under various spark arc and corona discharge conditions are SF 2 O, SF 2 O 2 , and SF 4 O. Detailed mechanisms to describe their formation remain unclear.…”

“…Six fundamentals were observed while for the missing modes the calculations predict either a low frequency (not yet measured) and/or a very low intensity. Photolysis of SF 5 O in a Ne matrix with full radiation of a xenon or mercury high-pressure lamp resulted in a slow decrease of its IR bands, yielding mainly SF 4 O and fluorine atoms, and as a minor channel SF 4 + OF (see Figure 1). Hence, SF 5 O is a weak UV absorber (for its Ne matrix UV spectrum, see the Supporting Information).…”

Optimization of Reactive-Ion Etching (RIE) parameters to maximize the lateral etch rate of silicon using SF6/N2 gas mixture: An alternative to etching Si in MEMS with Au components

“…Even though this method is a good option for Si isotropic etching, the XeF2 is expensive and rare [4]. Reactive-Ion Etching (RIE) based on the physical/chemical process using SF6 plasma is also an effective method for the isotropic etching of silicon due to a high density of radicals (SF5 * and F*) responsible for the Si lateral etching [5,6]. However, preliminary tests have shown that SF6 plasma causes damage to Au thin films as shown in Fig.…”