ON MECHANISMS OF OXYGEN INFLUENCE ON GAS-PHASE PARAMETERS AND SILICON REACTIVE-ION ETCHING KINETICS IN HBr + Cl2 + O2 PLASMA

Abstract

The effects of both HBr/O2 and Cl2/O2 mixing ratios in HBr+Cl2+O2 gas mixture on plasma parameters, steady-state densities of active species and Si etching kinetics were studied under the typical conditions of reactive ion etching process: total gas pressure (p = 10 mTorr), input power (W = 500 W), bias power (Wdc = 200 W). The data on internal plasma parameters and plasma chemistry were obtained using a combination of Langmuir probe diagnostics and 0-dimensional (global) plasma modeling. It was found that the variation in HBr/O2 mixing ratio at constant Cl2 fraction in a feed gas is characterized by the stronger impact on the steady-state plasma composition through both electron-impact and atom-molecular reaction kinetics as well as allows one to obtain the wider change in the total halogen atom density. It was shown that changes in both HBr/O2 and Cl2/O2 mixing ratios toward O2-rich plasmas lowers the Si etching rate that exhibits no evident correlations with total halogen atom flux and ion energy flux. The model-based analysis of Si etching kinetics allowed one to conclude that the effective reaction probability for Si + Cl/Br heterogeneous reaction depends on the flux of oxidative species – oxygen atoms and OH radicals. The reasons may be 1) the oxidation of silicon resulting in higher reaction threshold energy; and 2) the decreasing fraction of free adsorption sites for Cl/Br atoms due to the oxidation of reaction products into the lower volatile SiBrxOy and SiClxOy compounds.

ON THE COMPARISON OF REACTIVE-ION ETCHING MECHANISMS FOR SiO2 AND Si3N4 IN HBr + Ar PLASMA

“…At the same time, the decreasing tendency for the ion bombardment energy appears to be weaker compared with the growth of ion flux. As results, one can obtain an increase in the ion bombardment intensity toward Ar-rich plasmas, as it follows from the change of (Mii) 1/2 + [10,11,19] (Fig. 1(c)).…”

“…Therefore, the difference between corresponding sputtering yields seems to be lower than that for effective reaction probabilities. In earlier works, it was shown that the experimentally obtained RIE rate, R, represents the combination of two summands, such as the rate of physical sputtering Rphys (since under typical RIE conditions the ion bombardment energy exceeds the sputtering threshold for etched material) and the rate of ion-assisted chemical reaction Rchem [10,11,22]. In order to evaluate contributions of these etching pathways, we measured SiO2 and Si3N4 etching rates in pure Ar plasma Rphys,Ar, calculate corresponding sputtering yields as YS,Ar = = Rphys,Ar/+ ( 0.03 for both SiO2 and Si3N4 at ion energy of 230 eV) and then, determined actual sputtering yields for HBr + Ar plasma as YS = YS,Ar(mi/mAr) 1/2 .…”

“…Both plasma diagnostics and etching experiments were performed in the planar inductively coupled plasma (ICP) reactor known from our previous works [6,10,11]. Plasma in the HBr + Ar gas mixture was excited using the 13.56 MHz power supply while another 13.56 MHz rf generator was powered the bottom electrode (the substrate holder) to produce the negative bias potential, -Udc.…”

Mechanisms of Plasma Etching of Titanium, Indium, Tin, and Zinc Oxides in a Mixture of HBr + Ar

“…) [4,28,29]. Thus, reducing the etching rate with growth can take place with the dominance of both chemical and physical etching mechanisms.…”