Hiroki Ootera

Profile evolution during polysilicon gate etching with low-pressure high-density Cl2/HBr/O2 plasma chemistries

Profile evolution during polysilicon gate etching has been investigated with low-pressure high-density Cl2/HBr/O2 plasma chemistries. Etching was performed in electron cyclotron resonance Cl2/HBr/O2 plasmas as a function of HBr percentage in a Cl2/HBr mixture, using oxide-masked poly-Si gate structures. The linewidth was nominally 0.18 μm, and the spacing between the two neighboring poly-Si lines was varied in the range ∼0.2–10 μm. In addition, the macroscopic open space of the oxide-masked sample was also varied over a wide range from ≈28% to ≈76%. As the HBr percentage in Cl2/HBr is increased from 0 to 100%, the linewidth shift ΔL of poly-Si relative to the mask width (or the degree of sidewall tapering of poly-Si lines) first decreased linearly, passed through a minimum, and then increased considerably at above ∼80%. In Cl2/O2 plasmas without HBr addition, ΔL was almost independent of the microscopic and macroscopic poly-Si open spaces although its value was relatively large; on the contrary, in HBr/O2...

Simulation of Ion Trajectories near Submicron-Patterned Surface Including Effects of Local Charging and Ion Drift Velocity toward Wafer

Ion trajectories near a submicron-patterned surface were investigated using numerical simulations including the effects of local charging on the patterned surface and ion drift velocity toward the wafer. The simulation results were also discussed relative to the etched profile characteristics in electron cyclotron resonance (ECR) plasmas with a divergent magnetic field. Since the pattern size was much smaller than the Debye length, charge neutrality was not satisfied on the submicron-patterned surface. The simulated ion trajectories were largely deflected at the inside of the outermost lines of line-and-space patterns. Moreover, the ion trajectory deflection was reduced with increasing ion drift velocity. These simulation results showed a similar tendency as the etching characteristics.

Large-diameter microwave plasma source excited by azimuthally symmetric surface waves

This article describes a large-diameter, surface-wave excited plasma (SWP) source designed for materials processing. The plasma reactor employs a launcher of 2.45 GHz azimuthally symmetric surface waves in the field-free region of 24-pole line-cusp magnetic fields, generated by a set of permanent magnets surrounding the reactor chamber walls; the magnets also provide an electron cyclotron resonance (ECR) magnetic field of 875 G near the chamber wall surfaces. Langmuir probe and optical emission measurements were made for characterizing the plasma produced in Ar. After the microwave power was turned on, the discharge was observed to start near the ECR region and then propagate toward the field-free region in the central area of the chamber. Moreover, the discharge was also observed to be excited by ECR at low microwave-power levels, and by surface waves in the field-free region at above a critical power strongly depending on the gas pressure. Such a transition of plasma excitation from ECR to SWP was found...

Electrical and optical measurements of electron cyclotron resonance discharges in Cl2 and Ar

Electron cyclotron resonance (ECR) discharge plasmas in Cl2 and Ar have been investigated over a pressure range of 0.2–10 mTorr, using microwave interferometry, optical emission spectroscopy, electrostatic probes, and charge collectors. The plasma parameters measured were spatially nonuniform along the magnetic field. The plasma electron density and the plasma potential had their maxima around the ECR region and decreased in going forward the position of the substrate, giving rise to a broadened energy distribution of positive ions incident on the substrate. The plasma density in Ar increased monotonously with increasing pressure, while the density in Cl2 had its maximum around 0.3–0.4 mTorr.

ELECTRON CYCLOTRON RESONANCE PLASMA ETCHING OF SI WITH CL2 : PLASMA CHEMISTRY AND MECHANISMS

Electron cyclotron resonance (ECR) plasma etching of Si with C1, has been investigated from the viewpoint of plasma chemistry. Experiments were performed over a wide pressure range (0.2-10 mTorr), using a divergent magnetic- field ECR plasma reactor supplied with 2.45-GHz microwave input powers; a floating electrode or substrate holder was located -30 cm downstream (B=150 G) from the 875-G ECR resonance region, and samples of polycrystalline Si were etched with no additional wafer biasing. Several diagnostics were employed to characterize the plasma around the wafer position: two-photon laser-induced fluorescence (LIF), optical emission spectroscopy, microwave interferometry, and electrical measurements with Langmuir probes and a retarding grid analyzer. Moreover, chemical kinetics in C1, plasmas were modeled to gain an insight into the LIF and optical emission measurements, and to know chemical compositions in ECR C1, plasmas. Attention was then focused on neutral C1 atom fluxes and ion energies and fluxes onto the substrate, and on their correlations with the etching characteristics such as etch rates and profiles. The etch rate behavior is interpreted in terms of a modified adsorption-reaction-ion stimulated desorption process, and some lateral etching after an overetch step in terms of the incoming ion trajectories.

Transport mechanisms of ions and neutrals in low-pressure, high-density plasma etching of high aspect ratio contact holes

Transport mechanisms of ions and neutrals in high aspect ratio contact holes during low-pressure, high-density plasma etching were investigated by both experiments and numerical simulations. Etching experiments were performed in electron cyclotron resonance plasmas with a C4F8/O2 gas mixture, together with measurements of plasma parameters. The SiO2 etch rate decreased, and the deposition rate of polymer film during over-etching increased with decreasing hole diameter. The trajectories of ions and neutrals were investigated by numerical simulations that took into account the local charging effect for ions and Knudsen transport for neutrals. The etch rate distribution on the hole bottom was estimated by an etching model that included ion sputtering and ion-assisted etching. A sub-trench profile of the etch rate was obtained for a low aspect ratio hole, while a flat profile was observed for a high aspect ratio hole. This numerical result was in good agreement with the experimental results. Moreover, the dependence of polymer film thickness on over-etch duration was explained by a deposition model that included both the polymer formation by ion-assisted deposition and polymer removal by oxygen atoms.

Etching for 0.15-μm-level patterns with low microloading effect using beam plasmas generated by gas puff plasma sources

Microloading effects in high-density plasmas, which typically appear as a difference in the etch rates between the outermost space and the inner space in a line-and-space (L&S) pattern, were investigated using numerical simulations of ion trajectories and ion fluxes incident on the patterned surfaces, taking into account the effects of electrical properties of the materials, plasmas flowing to a wafer and local charging on the patterned surface. The simulation results showed that decrease of the incident ion flux densities were particularly enhanced in the area around the outermost space in the L&S pattern. Moreover, the difference in the incident ion fluxes among the patterns was reduced with increase of the drift velocities of the plasmas. Moreover, experiments on etching of fine patterns on the scale of around 0.15 µ m were also performed using chlorine beam plasmas with high drift velocities generated by gas puff plasma sources. The etch rate of poly-Si stayed nearly constant with decrease of pattern sizes from 1.0 to 0.15 µ m for time-averaged pressure of =0.2 m Torr in the specimen chamber.

A New Cleaning Technique for X-Ray Masks in Alkaline Solutions by Direct Control of Electrochemical Potential

This paper describes an electrochemical surface cleaning (ECSC) technique newly developed for removal of particulate contamination on X-ray masks employing WNx absorbers. In this technique, the electrochemical potential of absorber films is precisely controlled for preventing corrosion or etching of the films during their immersion in alkaline solutions. The particle removal efficiency and the stress change of WNx absorbers were examined and compared with those after the conventional cleaning operated under electrically floating condition. The etched depth (and thus etch rate) of WNx films in alkaline solutions was measured using an in-situ quartz-crystal-microbalance technique. Furthermore, X-ray photoelectron spectroscopy and atomic force microscopy were employed to characterize WNx film surfaces. Mechanisms responsible for a large stress change observed in the case of conventional cleaning are discussed. Moreover, it is demonstrated that the ECSC operated at cathodic potentials yields high removal efficiencies for a variety of particulates without change in film thickness and stress between before and after cleaning.

Anisotropic Etching of n+-Polysilicon Using Beam Plasmas Generated by Gas Puff Plasma Sources

Generation of pulsed chlorine beam plasmas using a nozzle beam system generated from an electron cyclotron resonance (ECR) discharge plasma source with a high-speed gas puff valve (gas puff plasma source) has been studied. Simulations of gas flow, and measurements of plasma parameters and their etching properties have also been discussed, comparing the experimental results with those of conventional ECR plasmas using an almost identical reactor. The time-averaged electron temperatures around a wafer were lower than those in the ECR plasmas for time-averaged pressure of 0.1-2 mTorr. The instantaneous ion energy distributions of the beam plasmas incident on the wafer had wider high-energy tails than those in the ECR plasmas. Thus, anisotropic etching profiles of n + -polysilicon were obtained at the position of the wafer (8 z ∼200 G) where notching phenomena were observed in the ECR plasmas.