Oxygen (<SUP>3</SUP>P) atom recombination on a Pyrex surface in an O<SUB>2</SUB> plasma

International audienceThe recombination of O (3P) atoms on the surface of a Pyrex tube containing a DC glow discharge in pure O2 was studied over a wide range of pressure (0.210 Torr) and discharge current (1040 mA) for two fixed surface temperatures ( 50 °C and 5 °C). The recombination probability, &#947;, was deduced from the observed atom loss rate (dominated by surface recombination) determined by time-resolved optical emission actinometry in partially-modulated (amplitude ~15%17%) discharges. The value of &#947; increased with discharge current at all pressures studied. As a function of pressure it passes through a minimum at ~0.75 Torr. At pressures above this minimum &#947; is well-correlated with the gas temperature, T g, (determined from the rotational structure of the O2 (b1&#931;g , v = 0) &#8594; O2(X3&#931;g &#8722;, v = 0) emission spectrum) which increases with pressure and current. The temperature of the atoms incident at the surface was deduced from a model, calibrated by measurements of the spatially-averaged gas temperature and validated by radial temperature profile measurements. The value of &#947; follows an Arrhenius law depending on the incident atom temperature, with an activation energy in the range 0.130.16 eV. At the higher surface temperature the activation energy is the same, but the pre-exponential factor is smaller. Under conditions where the O flux to the surface is low &#947; falls below this Arrhenius law. These results are well explained by an EleyRideal (ER) mechanism with incident O atoms recombining with both chemisorbed and more weakly bonded physisorbed atoms on the surface, with the kinetic energy of the incident atoms providing the energy to overcome the activation energy barrier. A phenomenological ER model is proposed that explains both the decrease in recombination probability with surface temperature as well as the deviations from the Arrhenius law when the O flux is low. At pressures below 0.75 Torr &#947; increases significantly, and also increases strongly with the discharge current. We attribute this effect to incident ions and fast neutrals arriving with sufficient energy to clean or chemically modify the surface, generating new adsorption sites. Discharge modeling confirms that at pressures below ~0.3 Torr a noticeable fraction of the ions arriving at the surface have adequate kinetic energy to break surface chemical bonds (>35 eV)

2D PIC modeling of the EUV induced hydrogen plasma and comparison to the observed carbon etching rate

The interaction between an EUV driven hydrogen plasma and a carbon covered surface was investigated using 2D PIC modeling and results were compared with experimental observations. The plasma is formed due to ionization of a low pressure hydrogen gas by the EUV photons and the photoelectrons from the surface. This results in ion fluxes to the surface, leading to the surface etching. We model the evolution of the plasma during and after the EUV pulse and obtain the energy resolved ion fluxes from the plasma to the surface. The carbon etching rates observed at various experimental conditions and estimated from computed ion fluxes for the same conditions agree under the assumption that the etching yield is close to one carbon atom per incoming hydrogen ion

Fluorine atoms interaction with the nanoporous materials: experiment and DFT simulation

Fluorine atoms interactions with organosilicate glass (OSG)-based low-κ dielectric films are experimentally and theoretically studied. One-dimensional 1-D Monte Carlo & gas-surface kinetics (MC&GSK) model and density functional theory (DFT) simulations used for the development of the multi-step mechanism of OSG films damage and etching are further verified on FTIR spectroscopy data. DFT method is applied to calculate vibrational mode frequencies and their shifts under F atoms flux. In the frame of 1-D model, evolutions of the SiCH3 and appeared SiCHxFy surface groups distributions inside the porous films are calculated as a function of F atoms dose. F atoms quasi-chemisorption on surface SiOx groups accompanied by fourth-coordinated Si atoms transition to pentavalent Si states is related with the experimentally observed fast fluorination stage and vibrational frequency shifts. In addition, quasi-chemisorbed F atoms induce the weakening of the adjacent Si–O bonds in OxSiFy surface complexes promoting breaks of these Si–O bonds under further F atoms attacks. Quasi-chemisorbed F atoms could be also responsible for F atoms recombination on SiOx surfaces

Experimental and DFT study of nitrogen atoms interactions with SiOCH low-

Damage of porous organosilicate glass (OSG) films with low dielectric constants (low-κ films) in plasma processing is a critical problem for modern microelectronics. For this problem, understanding and revealing of basic reaction steps for radicals etching and damage are of importance. Previously we have studied experimentally and theoretically the etching and damage of low-κ dielectric films under oxygen and fluorine atoms. Here the effects of N atoms on OSG films are studied experimentally by Fourier Transform InfraRed (FTIR) spectroscopy method and theoretically by density functional theory (DFT) method. Experimental FTIR spectra are compared with calculated vibrational spectra to reveal the relevant surface SiCHxNy groups which could be produced in multi-step reactive collisions of N atoms in ground and lower metastable states with OSG low-κ dielectric films

Data publication: Modification of Porous Ultralow‑k Film by Vacuum Ultraviolet Emission

Modification of spin-on-deposited porous PMO (periodic mesoporous organosilica) ultralow-k (ULK) SiCOH films (k = 2.33) containing both methyl terminal and methylene bridging groups by vacuum ultraviolet (VUV) emission from Xe plasma is studied. The temporal evolution of chemical composition, internal defects, and morphological properties (pore structure transformation) is studied by using Fourier transform infrared spectroscopy, in situ laser ellipsometry, spectroscopic ellipsometry, ellipsometric porosimetry (EP), positron-annihilation lifetime spectroscopy (PALS), and Doppler broadening positron-annihilation spectroscopy. Application of the different advanced diagnostics allows making conclusions on the dynamics of the chemical composition and pore structure. The time frame of the VUV exposure in the current investigation can be divided into two phases. During the first short phase, film loses almost all of its surface methyl and matrix bridging groups. An increase of material porosity due to removal of methyl groups with simultaneous matrix shrinkage is found by in situ ellipsometry. The removal of bridging bonds leads to an increase of matrix intrinsic porosity. Nevertheless, when the treated material is exposed to the ambient air, the sizes of micro- and mesopores and pores interconnectivity decrease with the VUV exposure time according to PAS and EP data. The last is the result of the additional film shrinkage caused by atmosphere exposure. During the second phase the increase of mesopore size is detected by both EP and PAS. The increase of mesopore size goes all the time as it is expected from in situ ellipsometry, but it is masked by the air exposure