Chemistry and aging of organosiloxane and fluorocarbon films grown from hyperthermal polyatomic ions

Abstract

Polyatomic ions can be used to deposit thin films, modify the phases of interfaces, dope trace elements into interface regions, impact specific chemical functionalities to a surface, and create micron- and nanometer-scale interface structures. This article demonstrates the broad flexibility over the modified surface properties allowed by variation of the incident ion chemical structure and kinetic energy. Organosiloxane (OS) films are deposited here on Al from mass-selected 15–100 eV Si2O(CH3)5+ ions. Monochromatic x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry are used to determine the OS film chemistry. The OS films vary from essentially organic (lightly cross-linked network) at 15 eV deposition to a more inorganic (highly cross-linked “silica like”) at 100 eV. XPS is also used to examine the aging of fluorocarbon films deposited on polystyrene by 25–100 eV CF3+ and C3F5+ ions. These films undergo only minor changes during aging, forming only a few percent oxygen on the surface. Surface restructuring and other processes are also observed in these fluorocarbon films during aging for up to 8 weeks.

On the Use of SIFT‐MS and PTR‐MS Experiments to Explore Reaction Mechanisms in Plasmas of Volatile Organics: Siloxanes

“…The role of ions in film formation is the subject of considerable debate. Studies using polyatomic hyperthermal ions show that polymer film growth is possible, albeit slow 12, 13. However, these studies use beams of a mass‐selected ion and these ions are much smaller than those detected in the plasma‐MS of VOCs.…”

“…This view is partially supported by ion beam studies: for example, the group of Hanley has demonstrated that polymeric coatings can be grown from beams of polyatomic hyperthermal ions using total ion fluences in the range of 2.5 × 10 15 –6 × 10 16 ions · cm −2 12, 13. In reference12 Hanley et al have grown thin film polymer coatings from beams of the polyatomic hyperthermal m / z 147 ion, derived from hexamethyldisiloxane (HMDSO), using total ion fluences and energies that we believe approximate to those in HMDSO plasma. By X‐ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) it was shown that there was very close agreement in the chemistry and molecular structure of these ion‐beam derived coatings to those deposited from plasmas of HMDSO.…”

“…Elsewhere we have postulated in plasmas of volatile functionalized organic compounds that yield functionalized coatings that the ion flux to collecting substrates could contribute to the overall mass of the growing plasma deposit 5–11. This view is partially supported by ion beam studies: for example, the group of Hanley has demonstrated that polymeric coatings can be grown from beams of polyatomic hyperthermal ions using total ion fluences in the range of 2.5 × 10 15 –6 × 10 16 ions · cm −2 12, 13. In reference12 Hanley et al have grown thin film polymer coatings from beams of the polyatomic hyperthermal m / z 147 ion, derived from hexamethyldisiloxane (HMDSO), using total ion fluences and energies that we believe approximate to those in HMDSO plasma.…”

Structure and Stability of C:H:O Plasma Polymer Films Co-Polymerized Using Dimethyl Carbonate

“…While the energy per monomer molecule in the plasma phase is pressure-invariant, the higher pressure enhances the residence time close to the surface and affects ion-assisted processes (due to more collisions). Additional effects related to the ion energy delivered to the surface are discussed in the literature including the contribution of hyperthermal intact molecular ions which becomes important at enhanced pressures [33,34]. Such ions (as formed in the gas phase at moderate energy input) arrive at low energies (several eV) at the surface resulting in their "soft landing".…”

Measurements of neutral plasma species in an argon/isopropyl alcohol plasma for the deposition of organic films

“…[21][22][23][24] Tra-ditionally, neutral chemistry was thought to dominate plasma polymer surface reactions, as in other plasma-enhanced chemical vapor deposition processes. This regards the relative importance of ions versus neutrals to the gas-surface dynamics.…”