Control of Plasma Flux Composition Incident on TiN Films during reactive Magnetron Sputtering and the Effect on Film Microstructure

A hybrid plasma enhanced physical vapor deposition (PEPVD) system consisting of an unbalanced dc magnetron and a pulsed electron beam-produced plasma was used to deposit reactively sputtered titanium nitride thin films. The system allowed for control of the magnitudes of the ion and neutral flux, in addition to the type of nitrogen ions (atomic or molecular) that comprised the flux. For all deposition experiments, the magnitude of the ion flux incident on the substrate was held constant, but the composition of the total flux was varied. X-ray diffraction and atomic force microscopy showed that crystallographic texture and surface morphology of the films were affected by the plasma flux composition during growth

Etching with Electron Beam Generated Plasmas

A modulated electron beam generated plasma has been used to dry etch standard photoresist materials and silicon. Oxygen–argon mixtures were used to etch organic resist material and sulfur hexafluoride mixed with argon or oxygen was used for the silicon etching. Etch rates and anisotropy were determined with respect to gas compositions, incident ion energy (from an applied rf bias) and plasma duty factor. For 1818 negative resist and i-line resists the removal rate increased nearly linearly with ion energy (up to 220 nm/min at 100 eV), with reasonable anisotropic pattern transfer above 50 eV. Little change in etch rate was seen as gas composition went from pure oxygen to 70% argon, implying the resist removal mechanism in this system required the additional energy supplied by the ions. With silicon substrates at room temperature, mixtures of argon and sulfur hexafluoride etched approximately seven times faster (1375 nm/min) than mixtures of oxygen and sulfur hexafluoride (,200 nm/min) with 200 eV ions, the difference is attributed to the passivation of the silicon by involatile silicon oxyfluoride sSiOxFyd compounds. At low incident ion energies, the Ar–SF6 mixtures showed a strong chemical (lateral) etch component before an ion-assisted regime, which started at ,75 eV. Etch rates were independent of the 0.5%–50% duty factors studied in this work

Etching with Electron Beam Generated Plasmas

A modulated electron beam generated plasma has been used to dry etch standard photoresist materials and silicon. Oxygen–argon mixtures were used to etch organic resist material and sulfur hexafluoride mixed with argon or oxygen was used for the silicon etching. Etch rates and anisotropy were determined with respect to gas compositions, incident ion energy (from an applied rf bias) and plasma duty factor. For 1818 negative resist and i-line resists the removal rate increased nearly linearly with ion energy (up to 220 nm/min at 100 eV), with reasonable anisotropic pattern transfer above 50 eV. Little change in etch rate was seen as gas composition went from pure oxygen to 70% argon, implying the resist removal mechanism in this system required the additional energy supplied by the ions. With silicon substrates at room temperature, mixtures of argon and sulfur hexafluoride etched approximately seven times faster (1375 nm/min) than mixtures of oxygen and sulfur hexafluoride (,200 nm/min) with 200 eV ions, the difference is attributed to the passivation of the silicon by involatile silicon oxyfluoride sSiOxFyd compounds. At low incident ion energies, the Ar–SF6 mixtures showed a strong chemical (lateral) etch component before an ion-assisted regime, which started at ,75 eV. Etch rates were independent of the 0.5%–50% duty factors studied in this work

Effect of Plasma Flux Composition on the Nitriding Rate of Stainless Steel

The total ion flux and nitriding rate for stainless steel specimens exposed to a modulated electron beam generated argon-nitrogen plasma were measured as a function of distance from the electron beam axis. The total ion flux decreased linearly with distance, but the nitriding rate increased under certain conditions, contrary to other ion flux/nitriding rate comparisons published in the literature. Variation in ion flux composition with distance was explored with a mass spectrometer and energy analyzer as a possible explanation for the anomalous nitriding rate response to ion flux magnitude. A transition in ion flux composition from mostly N2 1 to predominantly N1 ions with increasing distance was observed. Significant differences in molecular and atomic nitrogen ion energy distributions at a negatively biased electrode were also measured. An explanation for nitriding rate dependence based on flux composition and magnitude is proposed

Generation of Electron-Beam Produced Plasmas and Applications to Surface Modification

NRL has developed a number of hollow cathodes to generate sheets of electrons culminating in a ‘Large Area Plasma Processing System’ (LAPPS) based on the electron-beam ionization process. Beam ionization is fairly independent of gas composition and produces low temperature plasma electrons (9–1012 cm−3). The present system consists of a pulsed planar plasma distribution generated by a magnetically collimated sheet of 2 kV electrons (/cm2) injected into a neutral background of processing gases (oxygen, nitrogen, sulfur hexafluoride, argon). Operating pressures range from 2–13 Pa with 150–165 Gauss magnetic fields for a highly localized plasma density of ∼1011 cm−3. This plasma source demonstrated anisotropic removal rates of polymeric (photoresist) material and silicon with O2 and Ar/O2/SF6 mixtures, respectively. In pure nitrogen, this same source showed a surface nitriding rate of ∼1 μm/h of plasma exposure time on austenitic stainless steel at 400 °C. Time-resolved in situ plasma diagnostics (Langmuir probes and mass spectrometry) of these pulsed plasmas are also shown to illustrate the general plasma characteristics

Low-Temperature Nitriding of Stainless Steel in an Electron Beam Generated Plasma

An electron beam generated plasma processing system was characterized with in situ diagnostics and employed for a series of low energy (350 eV) stainless steel nitriding experiments in the temperature range of 325–462 °C. Plasma characterization yielded quantitative ion specie fluxes to the stainless steel workpiece in an argon–nitrogen plasma, with a significant fraction of the flux comprised of N+ ions. The nitriding rates were as high as 20 μm h−1/2 with surface layers exhibiting hardness values of approximately 15.5 GPa for specimens processed at all temperatures. X-ray diffraction analysis revealed nitrogen concentrations of approximately 30 at.% in all samples processed below 460 °C. The process activation energy was comparable to that in nitriding systems with higher ion fluxes, suggesting favorable plasma chemistry with respect to plasma nitriding applications

Electron-Beam-Generated Plasmas for Materials Processing

The results of investigations aimed at characterizing pulsed, electron-beam-produced plasmas for use in materials processing applications are discussed. In situ diagnostics of the bulk plasma and at the plasma/surface interface are reported for plasmas produced in Ar, N2, and mixtures thereof. Langmuir probes were employed to determine the local electron temperature, plasma density, and plasma potential within the plasma, while ion energy analysis and mass spectrometry were used to interrogate the ion flux at an electrode located adjacent to the plasma. The results illustrate the unique capabilities of electron-beam-produced plasmas and the various parameters available to optimize operating conditions for applications such as nitriding, etching, and thin film deposition