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

Applications of Electron-Beam Generated Plasmas to Materials Processing

Nonequilibrium (Te≫Tion,gas) plasma processing often allows for greater process control with reduced environmental impact when compared to other materials processing methods, and therefore presents tremendous opportunities in the areas of thin film development and surface modification. The U.S. Naval Research Laboratory\u27s Large Area Plasma Processing System (LAPPS) has been developed based on the high-energy (2 keV) electron-beam ionization process, with the goal of maximizing the benefits of plasma processing over large areas (∼1 m2). This system has been shown to be: 1) efficient at producing plasma in any gas composition; 2) capable of producing low-temperature plasma electrons (orientation in TiN films, due to the increased atomic nitrogen ion flux. Polymer pretreatment studies were also initiated in these systems; polytetrafluoroethylene substrates pretreated with an oxygen LAPPS exposure demonstrated a significant increase in copper and aluminum film adhesion compared to untreated substrates, with the dominant factor believed to be the changed surface morphology. Similarly dramatic fluorination of polyethylene was demonstrated with plasmas generated in Ar/SF6 mixtures

Plasma Enhanced Surface Treatments using Electron Beam-Generated Plasmas

NRL has developed a ‘large area plasma processing system’ (LAPPS) utilizing a high energy (∼2 keV) modulated electron beam to drive the plasma ionization. This system has been shown to be (1) efficient at producing plasma in any gas composition, (2) capable of producing low temperature plasma electrons (9–1012 cm−3) and (3) scalable to large area (square meters). In this work, the progress of a number of applications using LAPPS is discussed. Nitride growth in stainless steel was investigated, which demonstrated high rates (up to 20 μm/h1/2) at low temperatures (≤462 °C). Complementary mass spectrometry showed that the nitriding results correlated to the flux of atomic ions delivered to the substrate. LAPPS was also combined with magnetron sputtering sources to form hybrid systems for surface pretreatments of polymers for metallization and thin film deposition of nitrides. In these systems, Teflon® substrates pretreated with an oxygen LAPPS exposure demonstrated a significant increase in copper and aluminum film adhesion compared to untreated substrates, with the dominant factor believed to be the changed surface morphology. The simultaneous operation of LAPPS with a titanium magnetron sputter source increased the growth of the 〈200〉 orientation in TiN films, due to the increased atomic nitrogen ion flux. Additional LAPPS systems are also discussed

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