Chlorine Plasma Research Articles

Spatially resolved electron temperatures, species concentrations, and electron energy distributions in inductively coupled chlorine plasmas, measured by trace-rare gases optical emission spectroscopy

Determining the spatial dependence of charged and neutral species concentrations and energies in inductively coupled plasmas (ICP) is important for understanding basic plasma chemistry and physics, as well as for optimizing the placement of the wafer with respect to the ICP source to maximize properties such as etching rate uniformity, while minimizing charging-induced damage and feature profile anomalies. We have determined the line-integrated electron temperature (Te) and Cl-atom number density (nCl) as a function of the axial distance (z) from the wafer in a chlorine ICP, using trace rare gases optical emission spectroscopy (TRG-OES). By selecting rare gas lines that are either (a) excited mostly from the ground states, or (b) excited mainly from the metastable states we were also able to obtain approximate electron energy distributions functions (EEDFs). The gap between the wafer and the window adjacent to the flat coil inductive source was fixed at 15 cm. The pressure was 2, 10, or 20 mTorr (95% Cl2, 1% each of He, Ne, Ar, Kr, Xe) and the inductive mode source power was 340 or 900 W. Te measured by TRG-OES, mostly characteristic of the high-energy (>10 eV) part of the EEDF, peaked near the source under all conditions except 2 mTorr and 900 W, where a maximum Te of 5.5 eV was observed at midgap. The falloff in this high-electron-energy Te away from the source is mainly due to a preferential loss of high-energy electrons, which can be explained by an increasingly depleted (with increasing energy) EEDF, combined with the nonlocal effect: electrons lose kinetic energy as they approach the higher potential energy regions of lower electron density near the wafer. At 20 mTorr and 340 W, the mean free path for inelastic scattering by high-energy electrons becomes comparable to the reactor dimensions, causing added cooling of the EEDF near the wafer. TRG-OES EEDFs measured at a distance of 3 cm from the wafer and 900 W are in excellent agreement with previous Langmuir probe measurements. nCl increased with power and was highest at 900 W in the region between midgap and the ICP window, reaching a level corresponding to a high degree of dissociation of Cl2.

A coupled plasma and sheath model for high density reactors

We present a coupled plasma and collisionless sheath model for the simulation of high-density plasma processing reactors. Due to inefficiencies in numerical schemes and the resulting computational burden, a coupled multidimensional plasma and sheath simulation has not been possible for gas mixtures and high-density reactors of practical interest. In this work, we demonstrate that with a fully implicit algorithm and a refined computational mesh, a self-consistent simulation of a reactor including both the plasma and sheath is feasible. We discuss the details of the model equations, the importance of ion inertia, and the resulting sheath profiles for argon and chlorine plasmas. We find that at low operating pressures (10-30 mtorr), the charge separation occurs only within a 0.5-mm layer near the surface in a 300 mm inductively coupled plasma etch reactor. A unified simulation eliminates the use of offline or loosely coupled and oversimplified sheath models which generally leads to uncertainties in ion flux and sheath electrical properties.

Plasma Chloriding of Thin-Film Silver: A Novel Process in Silver-Silver Chloride Reference Electrode Fabrication

Silver thin films were modified using a novel plasma modification process for the development of thin-film silver-silver chloride reference electrodes. The surface, physical, and electrochemical properties of these electrodes were investigated by atomic force microscopy, thickness and resistivity measurement techniques, as well as impedance spectroscopy and potentiometry. After plasma treatment, thin-film growth was observed and the electrodes, in general, exhibited low interface impedance and a roughened surface. Evidence of a complex surface reorganization was found. Correlating plasma conditions with film properties suggested that increasing pressure and exposure duration increased species availability, therefore governing the reaction rates, while input power appeared to influence the type of surface chemical reactions. Results also indicated that mixtures should be employed rather than pure chlorine plasmas. © 2002 The Electrochemical Society. All rights reserved.

Electron temperatures of inductively coupled Cl2–Ar plasmas

Trace rare gases optical emission spectroscopy has been used to measure the electron temperature, Te, in a high-density inductively coupled Cl2–Ar plasma at 18 mTorr as function of the 13.56 MHz radio frequency power and Ar fraction. Only the Kr and Xe emission lines were used to determine Te, because of evidence of radiation trapping when the Ar emission lines were also used for larger Ar fractions. At 600 W (10.6 W cm−2), Te increases from ∼4.0±0.5 eV to ∼6.0±2.0 eV as the Ar fraction increases from 1% to 96%. In the H (inductive, bright) mode, Te, for a “neat” chlorine plasma (including 1% of each He/Ne/Ar/Kr/Xe) increases only slightly from ∼3.8 to 4.0 eV as power increases from 450 to 750 W. This increase is much larger for larger Ar fractions, such as from ∼4.0 to 7.3 eV for 78% Ar. Most of these effects can be understood using the fundamental particle balance equation.

Pulsed inductively coupled chlorine plasmas in the presence of a substrate bias

Pulsed inductively coupled plasmas (ICPs) sustained in electronegative gas mixtures using a substrate bias are being investigated to achieve improved etching characteristics in microelectronics fabrication. Experiments have shown that electron temperatures in pulsed ICPs without a substrate bias monotonically decrease during the afterglow. Under select conditions with a substrate bias, electron temperatures increase in the late afterglow. These trends suggest a transition in power deposition from inductive to capacitive. To investigate these processes, a two-dimensional, computationally parallel model was developed for pulsed ICPs. Results for Cl2 plasmas indicate that with a substrate bias the sheath thickness and speed, and hence electron heating, increase during the afterglow as the electron density decays. When the sheath reaches a critical thickness, capacitive electron heating begins.

Modelling of inductively coupled plasma processing reactors

A comprehensive model has been developed to study low-pressure,high-density plasma processing reactors. The model couples plasma generation andtransport self-consistently to fluid flow and gas energy equations. The modeland the simulation software have been used to analyse chlorine plasmas used inmetal etching. The effect of the inductive coil frequency on the plasmacharacteristics has been examined and found to influence plasma uniformityonly moderately. Model predictions for a CF4 plasma have been found to agreewell with experimental results.

Fabrication of nanohole array on Si using self-organized porous alumina mask

Formation of the ordered array of nanoholes on Si was investigated by the use of the self-organized porous alumina nanoholes array etching mask that is directly formed on the Si substrate by sputtering and subsequent anodic oxidation. Reactive ion etching using chlorine plasma against a porous alumina/thin-SiO2(10 nm)/Si substrate with a high self-bias of rf plasma was revealed to be very effective for pattern transfer to Si. After pattern transference a significant reduction of hole size was observed. In fact, the initial porous alumina hole size of 45 nm is reduced to 13 nm Si holes when the higher aspect ratio of porous alumina nanoholes mask is used. The etching characteristics strongly suggest that not only chemical etching but sputtering occurred, and that redeposition of nonvolatile materials in nanoholes plays an essential role in the reduction of the hole size.

Diagnostics of inductively coupled chlorine plasmas: Measurement of electron and total positive ion densities

This work is part of a broader study that creates a set of experimentally measured chlorine plasma parameters (electron and gas temperatures, electron energy distribution function, electron density, densities of ion fractions, and total ion density). This set is obtained over a broad range of operating conditions (1–20 mTorr, 5–1000 W) of an inductively coupled plasma. In this part, we present the electron (ne) and total positive ion (ni+=nCl2++nCl+) densities. ne and ni+ were measured with a Langmuir probe across the diameter or in the middle of the reactor. Line integrated values of ne were independently obtained with microwave interferometry, and converted into the spatially resolved data using the Langmuir probe ne profiles. Finally, a method is presented for measuring relative positive ion densities, based on optical emission at 7504 Å from trace amounts of Ar.

P‐48: Pattering of OLED Cathodes by Metal Dry Etching

AbstractA method to pattern the metal cathode of OLEDs by conventional photolithography and dry etching in a chlorine plasma is introduced. Sharp lines are obtained with feature sizes down to 20 μm. The performance of polymer LED fabricated this way is discussed. In addition, the growth of the non‐emissive region at the edge of the cathodes is analyzed in the context of this patterning technology.

The influence of He addition on Cl-etching procedure for Si-nanoscale structure fabrication using reactive ion etching system

Chlorine-based plasma have been often used to etch several semiconducting materials including Si and III–V materials. The chlorine plasma etching is well suited for fabrication of Si-nanoscale structures due to its good control of undercutting and etch profile. Due to some drawbacks such as trenches and damages on the etch mask from physical ion assisted etching, the Cl 2/He gas mixture using a conventional reactive ion etching system was utilized and the optimization procedures were performed. Therefore, the influence of the He flow rate was examined. As the He flow increases over 30% of the total inlet gas flow, the plasma state become stable and the etch rate starts to increase. For high flow rate over 60%, the relationship between the etch depth and the etch time was observed to be nearly linear. In addition, the etch rate has been turned out to be linearly increasing with the He flow rate. With this result, the Cl 2/He mixture plasma has been utilized and tested for fabrication of the deep Si sidewall and nanosize Si pillar array.

Polymer Masks on Semiconductors: A Novel Way to Nanostructures

We have successfully used self-assembling diblock copolymers on semiconductors as nanolithographic masks in dry etching processes. Quantum structures in the range of only a few nanometers have been fabricated, far beyond the limits of conventional optical lithography processes. In a first step, diblock-copolymers in solution are used to generate micelles. These micelles are loaded by a noble metal salt. After dipping of a semiconductor wafer into this solution, a monolayer of ordered micelles is generated over an area of up to 3 x 3 cm 2 . Exposure of the surface to a hydrogen plasma removes all the organic components and only the small metal clusters remain, each 15 nm in diameter and 50-130 nm apart. These clusters can be used as a direct mask for dry etching of semiconductor quantum wells to fabricate quantum dots. With the anisotropic etching of these structures in a reactive ion-beam chlorine plasma, it is possible to create cylinders in GaAs of up to 80 nm height. After annealing and overgrowing these structures by molecular beam epitaxy it should be possible to create quantum dots embedded in barrier material with higher energy gap and to detect photoluminescece light from these quantum structures at low temperatures.

Room-temperature copper etching based on a plasma–copper reaction

A promising room-temperature copper etching process is described. The copper thin film can be etched into a vertical profile at a high rate using a parallel-plate reactor under mild conditions. The key factor for the success of this process is a copper swelling phenomenon from the plasma–copper reaction. The reaction product has been identified as a crystalline copper chloride. Key parameters that influence the reaction process and the final copper profile have been studied. In addition to the plasma phase chemistry, ion bombardment plays a critical role in the process. Although results reported in this letter are based on the chlorine plasma, similar results can be obtained with other halogen gases. This process is potentially important to the fabrication of advanced microelectronic, storage, display, and optical devices.

Formation of GaN Self-Organized Nanotips by Nanomasking Effect

ABSTRACTWe have successfully fabricated self-organized GaN nanotips by reactive ion etching using chlorine plasma, and have revealed the formation mechanism. Nanotips with a high density and a high aspect ratio have been formed after the etching. We deduce from X-ray photoelectron spectroscopy (XPS) analysis that the nanotip formation is attributed to nanometer-scale masks of SiO2 on GaN. The structures calculated by Monte Carlo simulation of our formation mechanism are very similar to the experimental nanotip structures.

Formation of GaN Self-Organized Nanotips by Nanomasking Effect

AbstractWe have successfully fabricated self-organized GaN nanotips by reactive ion etching using chlorine plasma, and have revealed the formation mechanism. Nanotips with a high density and a high aspect ratio have been formed after the etching. We deduce from X-ray photoelectron spectroscopy (XPS) analysis that the nanotip formation is attributed to nanometer-scale masks of SiO2 on GaN. The structures calculated by Monte Carlo simulation of our formation mechanism are very similar to the experimental nanotip structures.

107 塩素プラズマによるシリコンエッチングの基板バイアス効果(O.S.1-2 プラズマ(1))(O.S.1 電子・イオン・分子の流れ)

107 塩素プラズマによるシリコンエッチングの基板バイアス効果(O.S.1-2 プラズマ(1))(O.S.1 電子・イオン・分子の流れ)

Etching Characteristics of Fine Ta Patterns with Electron Cyclotron Resonance Chlorine Plasma

In this research, the etching characteristics of a Ta thin film with chlorine plasma was studied using an electron cyclotron resonance plasma etching system. The native Ta oxide on the surface was removed by a sputtering mechanism, and then ion-assisted Ta etching, desorption of Ta chloride assisted by ion bombardment, proceeded. The atomic chlorine, which is believed to be the most active species responsible for etching, could be used as an indicator of the Ta etching process. By double step etching, an accelerated formation of Ta chloride by a chemical-reaction-dominant process in the second step, following the sputtering-dominant process step, successfully protected side walls, resulting in the suppression of the microloading effect.

Dominance of Cl2+ or Cl+ Ions in Time-Modulated Inductively Coupled Cl2 Plasma Investigated with Laser-Induced Fluorescence Technique and Probe Measurements

Relative densities of chlorine molecular ions Cl2+ and metastable chlorine atomic ions Cl+* were measured by a laser-induced fluorescence technique in cw and time-modulated inductively coupled chlorine plasma. In the discharge-off period of the time-modulated plasma, a considerable amount of Cl2+ persisted. Under the modulation frequency of 100 kHz, the decrease of the Cl2+ density in the discharge-off period was less than 30% and the decay time constant of Cl2+ density was longer than that of Cl+*. In order to investigate the dominance between Cl2+ and chlorine atomic ions Cl+, the relative densities of Cl2+ and Cl+* were calibrated as absolute densities along with the Langmuir probe measurements. The dominant ions in the cw plasma were Cl+, however, the Cl2+ density became comparable to the Cl+ density in the time-modulated plasma.

Diagnostics of inductively coupled chlorine plasmas: Measurement of Cl2 and Cl number densities

This article presents measurements of absolute Cl2 and Cl number densities in a chlorine transformer-coupled plasma. It is part of a series of reports on measurements of densities and energy distributions of all charged and neutral species in the same plasma system over an extensive range of pressure and power. Cl2 and Cl number densities were determined from optical emission spectroscopy and advanced actinometry. Number densities relative to the Xe actinometry gas are reported as a function of pressure (1–20 mTorr) and power (10–1000 W) during slow etching of SiO2-covered Si wafers. A detailed treatment of the effects of gas temperature on the conversion of these ratios into absolute number densities is also included. Cl2 is largely (∼90%) dissociated at the highest powers, with a somewhat higher degree of dissociation at low pressure. The Cl number density becomes nearly independent of power at high powers (especially at lower pressure) due to the combination of a higher degree of dissociation of Cl2 and an overall drop in number density due to heating of the gas. A zero-dimensional (global) model is used to compute Cl2 and Cl number densities. It gives a Cl wall recombination coefficient of 0.04 on the plasma-seasoned stainless steel walls.

Etching chemistry of benzocyclobutene (BCB) low-kdielectric films in F2+O2 and Cl2+O2 high density plasmas

The etching chemistry of benzocyclobutene (BCB) low-k dielectric films was studied in a high density plasma etcher using F2+O2 and Cl2+O2 plasmas. The etching rate in F2+O2 plasmas exceeded 1.2 μm/min with selectivity over oxide and nitride of 16 and 32, respectively. The etching rate in Cl2+O2 plasmas exceeded 0.6 μm/min with selectivity over oxide and nitride of 40 and 80, respectively. BCB films do not etch in pure Cl2 or pure O2 plasmas without ion bombardment, but etching rates of 1000 Å/min were observed using F2 plasmas without ion bombardment. The ion flux in F2+O2 plasmas is primarily O2+ and O+, whereas in Cl2+O2 the dominant ion is ClO+. BCB etching yields in F2+O2 plasmas were measured with a plasma beam/quartz crystal microbalance system. The etching yields suggest that the neutral fluxes and surface chemistry control the etching rates under these conditions, not the ion flux. Using x-ray photoelectron spectroscopy, it was determined that oxygen plasmas preferentially remove the carbon content of BCB, leaving behind a silicon oxide surface. Chlorine plasmas preferentially remove the silicon, leaving behind a carbon surface. F2+O2 plasmas etch BCB through a fluorocarbon film layer, the thickness of which increases with increasing fluorine concentration in the plasma.

Precise Chrome Etching in Downstream Chlorine Plasmas with Electron Depletion Through Negative Ion Production

In micropatterning down to 0.1 μm class devices, photolithography requires highly accurate microfabrication of chrome (Cr) reticle masks. In this paper we report the vertical chrome etching using electron beam (EB) resist masks in downstream chlorine plasmas, where the resist damage during etching can be suppressed because of the reduced electron density through negative ion production. Though the Cr etch rate in pure downstream plasmas was only 15 Å/min, slight oxygen addition of 1% resulted in a great increase of Cr etch rates as large as 20 times, while resist etch rates increased only twice. Though isotropic Cr etching reactions with chlorine and oxygen radicals caused undercut features, appropriate substrate biasing allows vertical patterning of 0.2 μm wide lines and spaces due to sidewall protection by redeposition of by‐products from etched Cr and resists. © 2000 The Electrochemical Society. All rights reserved.