Pure Cl2 Research Articles

Effects of inductively coupled plasma conditions on the etch properties of GaN and ohmic contact formations

In this study, n-GaN was etched using inductively coupled Cl 2/H 2 plasmas and the effects of plasma conditions on the etch properties, surface composition and ohmic contact formation were investigated as a function of gas composition using OES (optical emission spectroscopy), SEM (scanning electron microscope), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) and TLM (transmission line method). The addition of hydrogen to Cl 2 plasma decreased GaN etch rate and changed the surface composition from Ga-rich to N-rich. Etched profiles were near vertical with a smooth sidewall, however, the pure Cl 2 case showed the most anisotropic etch profile. Specific contact resistivity was increased with increasing hydrogen percent in Cl 2/H 2, however, most of contact resistivities of the contacts fabricated on the GaN etched with Cl 2/H 2 (≤75% H 2) were less than those fabricated on the non-etched GaN.

Reactive Ion Etching of Co–Zr–Nb Thin Film Using BCl3

Chlorine-based reactive ion etching (RIE) of a high-permeability Co–Zr–Nb film has been carried out. The etching rate was only about 10 nm/min in pure Cl2 in the temperature range in which anisotropic ion etching was dominant. Addition of BCl3 to the Cl2 resulted in an increase in the etching rate at low temperature. The activation energy in BCl3–Cl2 RIE was about 0.5 eV, whereas that in pure Cl2 RIE was 1.0 eV. The optimum BCl3 content was around 30 vol.%. The etching rate reached 750 nm/min at 1.2 W/cm2 RF power density and 300° C etching temperature. This improvement is due to the heavier mass and the higher ionization rate of BCl3 than those of Cl2. The ratio of the side etching rate to the depth-etching rate was about 30%, when the RF power density was 1.2 W/cm2 in BCl3–Cl2 RIE. The side etching was suppressed by both an increase in the RF power and addition of SiCl4 or SiCl4–O2 to the BCl3–Cl2. Anisotropy was promoted by both an increase in the ion energy and sidewall protection by Si or Si-oxide. An etching rate of 200 nm/min at 150° C and 2 W/cm2 RF power density in BCl3–Cl2–SiCl4 RIE has been achieved. The etching selectivity vs SiO2 was 20 and the side-etching rate was only 2% of the depth-etching rate.

Negative ion densities in chlorine- and boron trichloride-containing inductively coupled plasmas

The chlorine negative ion density and the electron density in chlorine- and boron trichloride-containing inductively coupled plasmas were investigated experimentally. Measurements were performed in a GEC reference cell operated in the inductively coupled mode. The chlorine negative ion density was measured as an excess electron density produced by photodetachment of electrons from the negative ions by 266 nm radiation from a frequency-quadrupled Nd:YAG laser. Both the excess electron density and the steady-state electron density were measured using a microwave interferometer. Various gas mixtures were investigated including pure Cl2, pure BCl3, combinations of the two, and combinations of these gases with N2 and Ar. Cl− densities up to 4×1011 cm−3 were measured depending on the gas mixture. The ratio of electron density to Cl− density was as high as 3 in Cl2 mixtures, and up to 5 in BCl3 mixtures. The plasma was probed at lower photon energy (355 nm) to photodetach electrons from other potential negative ions present in the plasma: to within the sensitivity of the measurement (1.3×108 cm−3), no other negative ions such as BClx− or Cl2− ions were detected. Significant interactions between Cl2 and Ar were observed as determined by changes in the Cl− density. The Cl− density also changed when BCl3 was added to Cl2 discharges. Addition of Ar or N2 to Cl2 plasmas had little effect on Cl− density, but nitrogen addition had very dramatic effects when added to BCl3, causing a factor of 2 increase in the Cl− density.

Study of shallow silicon trench etch process using planar inductively coupled plasmas

Silicon shallow trenches applied to the shallow trench isolation of integrated circuits were etched using planar inductively coupled Cl2 and HBr/Cl2 plasmas and the effects of process parameters such as gas combination, inductive power, and bias voltage on etch rates, selectivities, and etch profiles of silicon trenches were investigated. Also, the physical damages on the trench bottom and sidewall in Cl2 and HBr/Cl2 plasmas were studied using cross-sectional high resolution transmission electron microscopy (HRTEM). The increase of inductive power and bias voltage in Cl2 and HBr/Cl2 plasmas increased polysilicon etch rates in general, but reduced the etch selectivity over nitride. In case of Cl2 plasmas, low inductive power and high bias voltage showed an anisotropic trench etch profile, and the addition of oxygen or nitrogen to chlorine also increased the etch anisotropy. The use of pure HBr plasmas showed a positively angled etch profile and the addition of Cl2 to HBr improved the etch profile more vertically. HRTEM study showed defects formed near the sidewall, bottom, and bottom edge of the silicon trenches etched in Cl2/N2 plasmas, and more dense defects in HBr/Cl2 plasmas possibly due to the penetration of hydrogen in HBr. No defects were found for the trenches etched in pure Cl2 or Cl2/O2 plasmas.

Pattern profile control of polysilicon in magnetron reactive ion etching

The effects of adding H2 or CBrF3 to Cl2 plasma to control the pattern profile in polysilicon etching are studied using a magnetron reactive ion etching system. It is found that the sidewalls of patterns etched with pure Cl2 plasma at the pressure of 12 Pa are vertical or sloped depending on whether a radio frequency (rf) power of 600 W (0.77 W/cm2) or 700 W (0.9 W/cm2) is applied. By increasing the content of H2, the angle of the sidewall taper of the pattern etched at 600 W rf power reaches 70°. Adding CBrF3 makes it possible to adjust the slope of the sidewall over a range from 77° to 65° at a rf power of 700 W. These observed results are attributed to plasma polymerization.

Quantitative chemical topography of polycrystalline Si anisotropically etched in Cl2/O2 high density plasmas

The spatially resolved surface chemical composition or ‘‘chemical topography’’ of submicron features [polycrystalline silicon (poly-Si) masked with photoresist (PR) lines] etched in high density, low pressure helical resonator Cl2/O2 plasmas has been quantitatively determined using angle resolved x-ray photoelectron spectroscopy (XPS). The chemical topography of plasma etched microelectronic materials is important in understanding how impinging ions and neutrals interact with surfaces to influence etched profiles. The spatial origin of XPS signals was determined from a combination of geometric shadowing of photoelectrons by adjacent features, electrostatic charging of insulating surfaces, XPS signal calibration versus take-off angle, x-ray attenuation, and geometric modeling. Equal line and space width (0.75–2.0 μm) features, unmasked poly-Si, and unpatterned PR surfaces were examined following plasma etching and vacuum sample transfer. For pure Cl2 plasmas, Cl surface concentration was found to be similar for horizontal and vertical surfaces of the poly-Si and PR. Only a small amount of Si was found on the PR sidewall, and similarly, little C or O was observed on the side of the poly-Si features, indicating that sidewall passivation is not occurring. O coverage on all surfaces increased with O2 addition to the plasma. For Cl2/5% O2 plasmas, a small amount of O was found on the poly-Si trench bottom, and more (but still submonolayer) on the poly-Si sidewall. Also, more Cl, O, and Si were found on the PR sidewall with 5% O2. For Cl2/10% O2 plasmas, rough surfaces were observed by scanning electron microscopy (SEM). On poly-Si trench bottoms, O coverage is comparable to Cl at roughly a monolayer. On poly-Si sidewalls, O and Cl coverages are again comparable, but the O coverage is about double that found on the trench bottoms. The most dramatic effect by far at 10% added O2 is the formation of a thick SiOx Cly layer (where x≊y≊1) on the side of the PR, detected by both XPS and SEM. The quantitative analysis method developed in this study is readily applicable to other etching gases and materials.

Global model of Ar, O2, Cl2, and Ar/O2 high-density plasma discharges

We develop a global (volume averaged) model of high-density plasma discharges in molecular gases. For a specified discharge length and diameter, absorbed power, pressure, and feed gas composition, as well as the appropriate reaction rate coefficients and surface recombination constants, we solve the energy and particle balance equations to determine all species densities and the electron temperature. We use an expression for charged particle diffusive loss that is valid for low and high pressures and for electropositive and electronegative plasmas. We apply the model to Ar, O2, Cl2, and Ar/O2 discharges and compare with available experimental data. In Ar, we find that the ion density increases monotonically with increasing pressure, while for O2 and Cl2, the total positive ion density increases initially, then decreases as pressure is further increased. For a pure Cl2 discharge, we find that surface recombination processes are important in affecting the degree of dissociation and the negative-ion density of the system. For mixtures of Ar and O2, we find that at a fixed ratio of Ar to O2 flowrates, the dominant ionic species changes from Ar+ to O+ as pressure is increased. When a small amount of Ar is added to a pure O2 discharge, the overall positive-ion density increases, whereas the ratio of negative ion to electron density decreases.

High-Temperature Etching of PZT/Pt/TiN Structure by High-Density ECR Plasma

Submicron patterning technologies for the PZT/Pt/Ti/TiN/Ti structure with a spin on glass (SOG) mask were demonstrated using a high-density ECR plasma and a high substrate temperature above 300° C. A 30%-Cl2/Ar gas was used to etch a lead zirconate titanate (PZT) film. No deposits remained, which resulted in an etched profile of more than 80°. A 40%-O2/Cl2 gas was used to etch a Pt film. The etching was completely stopped at the Ti layer. 30-nm-thick deposits remained on the sidewall. They were removed after dipping in hydrochloric acid. The etched profile of a Pt film was more than 80°. The Ti/TiN/Ti layer was etched with pure Cl2 gas. The size shift from the SOG mask was less than 0.1 µ m. Interdiffusion between SOG and PZT was not detected by transmission electron microscopy and energy dispersive X-ray spectroscopy (TEM-EDX) analysis.

Lateral carrier diffusion and surface recombination in InGaAs/AlGaAs quantum-well ridge-waveguide lasers

We measured the increase in threshold currents due to lateral carrier diffusion in InGaAs/AlGaAs quantum-well ridge-waveguide laser diodes. The ridge stripes were fabricated by using both in situ monitored pure Cl2 reactive ion etching and selective wet etching to completely eliminate the spreading current in the conductive upper cladding layer while keeping the ridge sidewalls straight. After comparing the threshold data with a theoretical model, the ambipolar diffusion coefficient is found to be 22 cm2/s in the population-inverted InGaAs layer. This model is based on the calculated optical gain curve and the ambipolar carrier transport in the quantum-well and waveguiding layers. The dependence of carrier lifetime on the local carrier concentration is included in the calculation. Moreover, from another set of devices with the portions of the active layer outside the ridge stripes etched away, the surface recombination velocity is found to be around 1–2×105 cm/s.

Purification of anticardiolipin and lupus anticoagulant activities by using cardiolipin immobilized on agarose beads

We describe a novel method for the purification of aPL, in which pure CL is immobilized on octyl-sepharose beads by hydrophobic interaction. No lipid contamination was present in eluates, and the system could be reutilized three times without loosing extracting capacity. Four patients with antiphospholipid syndrome were studied. A marked decrease in aCL and LA activities was found in all patient plasmas after the passage through a CL-octyl-sepharose column. Both activities were recovered in eluates which contained β 2-GP-I and IgGs. β 2-GP-I was also present in normal plasma eluates, which showed no aCL and slight LA activity. This method represents an improvement in the purification of aPL, and could be useful in explaining the mechanism of action of antibodies that are obtained using pure phospholipid as extracting matrix.

Magnetically selected beams of atomic chlorine: measurement of long-range features of the chlorine–hydrogen and chlorine–methane potential-energy surfaces

An atomic beam of Cl (2PJ) atoms produced in a microwave discharge source in pure Cl2, after velocity and magnetic selection, has been used for absolute total cross-section measurements in collisions with the hydrogen and methane molecules. The data were obtained in the beam velocity range 0.4–2.3 km s–1(corresponding to 10–300 meV centre-of-mass energy) and under different populations of magnetic sublevels of Cl atoms. The analysis of the data, using an adiabatic decoupling scheme, permitted an accurate characterization of the long-range features for entrance valleys of the ground state and of the two lowest excited potential-energy surfaces. Non-adiabatic coupling matrix elements and other general features of the relevant interactions are also presented.

Chemical Topography of Si Etching in a Cl2 Plasma, Studied by X-RAY Photoelectron Spectroscopy and Laser-Induced Thermal Desorption

AbstractThis paper describes x-ray photoelectron spectroscopy (XPS) studies of etching of Si in high-density Cl2 plasmas. Polycrystalline Si films, masked with photoresist stripes, are etched and then transferred in vacuum to the XPS analysis chamber. Shadowing of photoelectrons by adjacent stripes and differential charging of the photoresist and poly-Si were used to separate contributions from the top of the mask, the side of the mask, the etched poly-Si sidewall, and the bottom of the etched trench. In pure Cl2 plasmas, surfaces are covered with about one monolayer of Cl. If oxygen is introduced into the plasma, either by addition of O2 or by erosion of the glass discharge tube, then a thin Si-oxide layer forms on the sides of both the poly-Si and the photoresist. Laser-induced thermal desorption (LITD) was used to study etching in real time. LITD of SiCI was detected by laser-induced fluorescence. These studies show that the Si-chloride layer formed during plasma etching is stable after the plasma is extinguished, so the XPS measurements are representative of the surface during etching. LITD measurements as a function of pressure and discharge power show that the etching rate is limited by the positive ion flux to the surface, and not by the supply of Cl2, at pressures above 0.5 mTorr and for ion fluxes of σ4× 1016cm−2 s−1.

New Etching System with a Large Diameter Using Electron Beam Excited Plasma

A new etching system using electron-beam-excited plasma (EBEP) has been developed. This EBEP system is able to steadily produce a high-density plasma with a large diameter by introducing a high-current low electron beam into the etching chamber. The nonuniformity of plasma density and floating potential in an 8-inch wafer are improved up to ±2.5% and ±2 V, respectively. Anisotropic etching of n+-poly-Si in a pure Cl2 plasma is achieved with a high etch rate of 360 nm/min. The etching selectivity is 40 for poly-Si/photoresist and 150 for poly-Si/SiO2. These experimental results show that the EBEP etching system is suitable for manufacturing advanced ULSI.

Pattern profile control in magnetron reactive ion etching of poly-Si

The effect of adding SF6 or C2H6 to Cl2 plasma to control the pattern profile in poly‐Si etching has been studied using a magnetron reactive ion etching system. It is found that the sidewalls of patterns etched with pure Cl2 plasma are either sloped or vertical depending on whether a radio‐frequency (rf) power of 700 W (0.9 W/cm2) or 600 W(0.77 W/cm2) is applied. By increasing the content of SF6 the angle of the sidewall taper of the pattern etched at 700 W rf power reaches 90°. Adding C2H6 makes it possible to adjust the slope of the sidewall over a range from 77° to 90° at a rf power of 600 W. These observed results are attributed to plasma polymerization.

Characterization of a new electron cyclotron resonance source working with permanent magnets

Most electron cyclotron resonance (ECR) sources available today are working with electromagnets. A new source, developed for etch applications, is supplied with permanent magnets. This leads to strong short-range magnetic fields and the ECR condition is fulfilled on a ring near the chamber wall. Having the maximum electric field strength of the 2.45 GHz along this ring in the microwave radiator leads to efficient plasma production. The principle source characteristics are demonstrated with oxygen plasmas. At low pressure (some 10−4—some 10−3 mbar) and moderate microwave power (100–500 W) the plasma burns as a ring plasma. Increasing pressure and/or microwave power over the above mentioned values leads to a ‘‘bulk’’-type plasma. The change from ‘‘ring’’-type to bulk-type plasma occurs discontinuously and is connected (a) with a discontinuity in the run of the reflected power and (b) with a sudden change in the relative ion flux densities of different ionic fragments measured by mass spectrometry. Absolute ion densities up to 5×1010 cm−3 have been found by Langmuir probe measurements in a bulk plasma at a pressure of 1×10−3 mbar. Anisotropic etching of polysilicon over SiO2 was performed in the ring mode with pure Cl2 as feed gas and applying a radio-frequency (rf) extraction to the ECR plasma. Low damage etching was achieved due to the low direct-current (dc)-bias voltage of 150–200 V with very good anisotropy. The poly-Si etchrate was 85 nm/min with a selectivity of 18:1 to SiO2 and a uniformity of ±7.5% over 200 mm wafers.

Comportement à 700°C de métaux et alliages soumis à NbCl5 gazeux

The electrochemical reduction of NbCl5 performed at 700°C in a molten salt bath for obtaining niobium has shown that all metallic elements present in the cell are corroded. In such conditions the electrolysis produces only a Ni3 Nb alloy and never pure metallic niobium. To determine the effect of NbCl5 , we have studied the oxidation of metals (M = Ni, Cr, Nb, Fe, Ti) and alloys (NSMC-NS21C-NS22S-NS30-Inconel 600) put in vapors of niobium pentachloride. For the pure metal M this corrosion is limited by the formation of pure or mixed dichloride (M, Nb)Cl2 . Nickel and chromium are the most resistant in this atmosphere. The alloys with melai M as the main component show a much more important corrosion than pure metal. More ever the amount of corrosion is always too weak to explain the big production of NiCl2 that appears when a cell is continously feed with NbCl5 .We study now the same metals and alloys put in a molten salt bath having differents concentrations in NbCl5 .

Extremely high selective, highly anisotropic, and high rate electron cyclotron resonance plasma etching for n+ poly-Si at the electron cyclotron resonance position

Extremely high selective, highly anisotropic, and high rate electron cyclotron resonance (ECR) plasma etching for n+ poly-Si is achieved at the ECR position in a newly developed ECR plasma etching system. The selectivity ratio of the n+ poly-Si etching rate to the SiO2 etching rate is more than 100 at 5×10−4 Torr and 260 at 3×10−3 Torr in pure Cl2 gas at a substrate temperature of 30 °C. Furthermore, the selectivity ratio increases infinitely by using a Cl2/O2 gas mixture at 5×10−4 Torr. The n+ poly-Si etching rate is more than 3000 Å/min with no radio frequency (rf) bias under the above selectivity ratio conditions. The etching selectivity is generated by low ion energy at the ECR position. The high etching rate is achieved by high ion current density at the ECR position in the plasma chamber.

An investigation of the reactive ion etching of polysilicon in pure Cl2 plasmas by i n s i t u ellipsometry and quadrupole mass spectrometry

The simultaneous application of in situ ellipsometry and quadrupole mass spectrometry to the reactive ion etching of polysilicon/SiO2/Si(100) multilayers in pure Cl2 plasmas at 13.56 MHz is described. At 100 mTorr and 50 W the surface texture of the unetched polysilicon is retained, but significant roughening is induced when the power is raised to 100 W. Water vapor is shown to play a critical role in the roughening process and is probably due to micromasking by hydroxide groups at the polysilicon surface. Detailed models of the ellipsometric results for roughened surfaces are derived and correlated with their scanning electron microscopy images. When CClx (x=1–4) species are present in the plasma, due to the erosion of a carbon-containing resist, roughening of polysilicon is prevented at 100 W and the etch rate of the underlying SiO2 is increased. Accompanying this increase is a shift in the product distribution for SiO2 towards higher SiCl4 but lower O2. In contrast the etch rate and product distribution for polysilicon remain almost unaffected by the presence of resist.

A study of liquid molar volumes for some pure halogenated hydrocarbons and their binary mixtures

AbstractLiquid volume data have been measured at compressed liquid conditions for four pure refrigerants, CCl3 F, CCl2 F2, CHClF2 and C2 Cl2 F4, and three mixtures, CCl2 F2/CCl3 F, CCl2 F2/C2 Cl2 F4, and CHClF2/C2 Cl2 F4. A comparison of measured data and data reported in the literature with calculated data by three methods is presented. The three methods are the Thomson‐Brobst‐Hankinson correlation, and two equations of state according to Carnahan‐Starling‐de Santis and Lee‐Kesler‐Plöcker. In general the Thomson‐Brobst‐Hankinson correlation shows a smaller deviation from experimental data than the two equations of state examined.

Extremely high-selective electron cyclotron resonance plasma etching for phosphorus-doped polycrystalline silicon

Extremely high-selective etching for phosphorus-doped polycrystalline silicon is achieved at the electron cyclotron resonance (ECR) position in a newly developed ECR plasma etching system. The selectivity ratio (phosphorus-doped polycrystalline silicon etching rate/SiO2 etching rate) is around 100 at 5×10−4 Torr and 260 at 3×10−3 Torr. Furthermore, the polycrystalline silicon etching rate is more than 3000 Å/min in pure Cl2 etching gas with no rf bias under the above selectivity ratio conditions. The high etching selectivity ratio is generated by low ion energy due to no rf bias power and small magnetic field divergence. The high etching rate is achieved by high ion current density at the ECR position in the plasma chamber.