N. R. Rueger

Role of steady state fluorocarbon films in the etching of silicon dioxide using CHF3 in an inductively coupled plasma reactor

It has been found that in the etching of SiO2 using CHF3 in an inductively coupled plasma reactor of the planarized coil design, a thin steady state fluorocarbon film can play an important role in determining the rate of etching. This etching is encountered as the amount of bias power used in the SiO2 etching process is increased, and a transition from fluorocarbon film growth on the SiO2 to an oxide etching rate which is consistent with reactive sputtering theory is made. The observed presence of an intermediate region where etching occurs, although a steady state fluorocarbon film suppresses the etch rate from that expected for a reactive sputtering process, has been referred to as the fluorocarbon suppression regime. This work demonstrates the role of the steady state fluorocarbon film present on silicon dioxide during etching within the fluorocarbon suppression regime. X-ray photoelectron spectroscopy studies of the surfaces of partially etched SiO2 have shown a thinning of this film with increasing r...

High density fluorocarbon etching of silicon in an inductively coupled plasma: Mechanism of etching through a thick steady state fluorocarbon layer

For various fluorocarbon processing chemistries in an inductively coupled plasma reactor, we have observed relatively thick (2–7 nm) fluorocarbon layers that exist on the surface during steady state etching of silicon. In steady state, the etch rate and the surface modifications of silicon do not change as a function of time. The surface modifications were characterized by in situ ellipsometry and x-ray photoelectron spectroscopy. The contribution of direct ion impact on the silicon substrate to the etching mechanism is reduced with increasing fluorocarbon layer thickness. Therefore, we consider that the silicon etch rate is controlled by a neutral etchant flux through the layer. Our experimental data show, however, that ions play an import role in the transport of silicon etching precursors through the layer. A model is developed that describes the etch kinetics through a fluorocarbon layer based on a fluorine diffusion transport mechanism. The model is consistent with the data when one or two of the fol...

Study of the SiO2-to-Si3N4 etch selectivity mechanism in inductively coupled fluorocarbon plasmas and a comparison with the SiO2-to-Si mechanism

The mechanisms underlying selective etching of a SiO2 layer over a Si or Si3N4 underlayer, a process of vital importance to modern integrated circuit fabrication technology, has been studied. Selective etching of SiO2-to-Si3N4 in various inductively coupled fluorocarbon plasmas (CHF3, C2F6/C3F6, and C3F6/H2) was performed, and the results compared to selective SiO2-to-Si etching. A fluorocarbon film is present on the surfaces of all investigated substrate materials during steady state etching conditions. A general trend is that the substrate etch rate is inversely proportional to the thickness of this fluorocarbon film. Oxide substrates are covered with a thin fluorocarbon film (<1.5 nm) during steady-state etching and at sufficiently high self-bias voltages, the oxide etch rates are found to be roughly independent of the feedgas chemistry. The fluorocarbon film thicknesses on silicon, on the other hand, are strongly dependent on the feedgas chemistry and range from ∼2 to ∼7 nm in the investigated process...

Selective etching of SiO2 over polycrystalline silicon using CHF3 in an inductively coupled plasma reactor

Selective etching of SiO2 over polycrystalline silicon has been studied using CHF3 in an inductively coupled plasma reactor (ICP). Inductive powers between 200 and 1400 W, as well as pressures of 6, 10, and 20 mTorr were used in this study of the etch rate and selectivity behaviors for silicon dioxide, silicon, and passively deposited fluorocarbon films. Using in situ ellipsometry, the etch rates for all three of these materials were obtained for a self-bias voltage of −85 V, as well as passive deposition rates of fluorocarbon films. X-ray photoelectron spectroscopy has been used to examine the composition of steady-state fluorocarbon films present on the surfaces of polycrystalline silicon, and silicon dioxide during etching at high and low inductive powers. The dependence of the silicon etching behavior is shown to be clearly linked to the fluorocarbon polymerization and etching behavior. Thus, the polymerization and etching behavior of the fluorocarbon is the overwhelming parameter that governs the etc...

Surface science issues in plasma etching

Pattern transfer by plasma-based etching is one of several key processes required for fabricating silicon-based integrated circuits. We present a brief review of elementary plasma-etching processes on surfaces and within integrated-circuit microstructures-and an overview of recent work in our laboratory on plasma-etching aspects of the formation of self-aligned contacts to a polysilicon layer through a SiO 2 layer and a Si 3 N 4 etch-stop layer. The work illustrates the richness of associated surface science issues that must be understood and controlled in order to most effectively achieve plasma-based pattern transfer.

Observation of inverse reactive ion etching lag for silicon dioxide etching in inductively coupled plasmas

The slowdown of the oxide etch rate with width of submicrometer structures is known as reactive ion etching (RIE) lag and has been explained by ion shadowing and differential charging of the sidewalls, among other effects [R. A. Gottscho and co‐workers, J. Vac. Sci. Technol. B 10, 2133 (1992)]. Here we show for an inductively coupled high density plasma reactor working in the pressure regime from 6 to 20 mTorr that inverse RIE lag is primarily observed, i.e., the etch rates increase as the width of the microstructures decrease. Inverse RIE lag, which was first discussed by Vitkavage et al. [Tegal Plasma Proceedings Symposium, San Francisco, 1991 (unpublished)], may be explained by considering the neutral flux distribution at the structure bottom. The neutral flux has a stronger dependence on the aspect ratio than the ion flux due to its isotropic velocity distribution. The neutral flux distribution has been modeled and is consistent with etching profiles observed at high pressure.

Photoresist erosion studied in an inductively coupled plasma reactor employing CHF3

The evolution of integrated circuits into the ultralarge scale integrated regime takes today’s 0.35 μm circuit design rules to even smaller values of 0.18 μm and beyond. As a consequence, photoresist masks are becoming thinner and even more prone to erosion by etching. For this work an I-line novolak resist was used. Etch rates for various process conditions using in situ ellipsometry were obtained. Also the fluorocarbon surface layer, present on top of the photoresist during steady state etching was examined with x-ray photoelectron spectroscopy. The investigated pressure range was 6 to 20 mTorr and the inductive power range was 300 to 1400 W. It was found that there are two distinct regimes of etching behavior. At inductive powers below 600 W the etching is energy flux limited, at higher inductive powers the etching is ion energy limited.

Effect of capacitive coupling on inductively coupled fluorocarbon plasma processing

This article describes results obtained using various plasma and surface diagnostics in a study of inductively coupled fluorocarbon plasmas in which the amount of capacitive coupling was systematically varied. It is found that the plasma density decreases while the electron temperature increases as the amount of capacitive coupling is increased at a constant source power level. The rate at which the dielectric coupling window is eroded is found to scale with both the peak-to-peak rf voltage and the ion current density, and the dielectric window erosion is found to influence the resulting plasma gas-phase chemistry. The changes in plasma electrical and chemical characteristics have a large impact on the surface processes occurring in inductively coupled fluorocarbon plasmas such as fluorocarbon deposition, fluorocarbon etching, SiO2 etching and Si etching. Further, we show how the selective SiO2-to-Si etch process changes with varying capacitive coupling.

Study of plasma-surface interactions : chemical dry etching and high-density plasma etching

We report results of the characterization of the plasma - surface interactions of silicon and silicon dioxide in fluorocarbon discharges using real-time ellipsometry and post-plasma multi-technique surface analysis for chemical dry etching (CDE) and high-density plasma etching (HDPE). We show that changes of the gas composition in CDE causes major changes in silicon surface chemistry and etching behaviour. For low-pressure HDPE we investigate the influence of power deposition into the discharge and bias voltage and bias power at the wafer on the surface chemical changes of silicon and .

Using a quartz crystal microbalance for low energy ion beam etching studies

A quartz crystal microbalance (QCM) has been used for etching yield measurements in a low energy ion beam system. The goal is to obtain etching yields for ion energies below 150 eV for various ion chemistries and target materials. Typical beam currents are about 0.5 μA, and the mass change per unit time on the QCM is much smaller than that for typical QCM applications. A number of problems with the application of a QCM were encountered and a description of how they were overcome is presented in this article. Quantitative etch yield results for the etching of two different photoresists and SiO2 down to 25 eV ion energy are presented.